Laboratory investigation on effects of flood intermittency on river delta dynamics

NASA Astrophysics Data System (ADS)

Miller, K. L.; Kim, W.

2015-12-01

In order to simplify the complex hydrological variability of flow conditions, experiments modeling delta evolution are often conducted using a representative "channel-forming" flood flow and then relate results to field settings using an intermittency factor, defined as the fraction of total time at flood conditions. Although this intermittency factor makes it easier to investigate how variables, such as relative base level and/or sediment supply, affect delta dynamics, little is known about how this generalization to a single flow condition affects delta processes. We conducted a set of laboratory experiments with periodic flow conditions to determine the effects of intermittent discharges on delta evolution. During the experiment, flood with a set water discharge and sediment supply, cycles between periods of normal flow where the water flux is halved and the sediment discharge is turned off. For each run, the magnitude of the flood is held constant, but the duration is assigned differently, thus varying the intermittency between 1 and 0.2. We find that as the intermittency factor decreases (duration of each flood period decreases), the delta topset has a larger, more elongated area with a shallower slope as a result of reworking on the delta topset during normal flow conditions. During periods of normal flow, the system adjusts towards a new equilibrium state that then in turn acts as the initial condition for the subsequent flood period. Furthermore, the natural delta avulsion cycle becomes obscured by the flood cycles as the flood duration becomes shorter than the autogenic behavior. These results suggest that the adjustment timescale for differing flow conditions is a factor in determining the overall shape of the delta and behavior of the fluviodeltaic channels. We conclude, periods of normal flow when topset sediment is reworked, may be just as important to delta dynamics as periods of flood when sediment is supplied to the system.

Experimental study on interfacial area transport in downward two-phase flow

NASA Astrophysics Data System (ADS)

Wang, Guanyi

In view of the importance of two group interfacial area transport equations and lack of corresponding accurate downward flow database that can reveal two group interfacial area transport, a systematic database for adiabatic, air-water, vertically downward two-phase flow in a round pipe with inner diameter of 25.4 mm was collected to gain an insight of interfacial structure and provide benchmarking data for two-group interfacial area transport models. A four-sensor conductivity probe was used to measure the local two phase flow parameters and data was collected with data sampling frequency much higher than conventional data sampling frequency to ensure the accuracy. Axial development of local flow parameter profiles including void fraction, interfacial area concentration, and Sauter mean diameter were presented. Drastic inter-group transfer of void fraction and interfacial area was observed at bubbly to slug transition flow. And the wall peaked interfacial area concentration profiles were observed in churn-turbulent flow. The importance of local data about these phenomenon on flow structure prediction and interfacial area transport equation benchmark was analyzed. Bedsides, in order to investigate the effect of inlet conditions, all experiments were repeated after installing the flow straightening facility, and the results were briefly analyzed. In order to check the accuracy of current data, the experiment results were cross-checked with rotameter measurement as well as drift-flux model prediction, the averaged error is less than 15%. Current models for two-group interfacial area transport equation were evaluated using these data. The results show that two-group interfacial area transport equations with current models can predict most flow conditions with error less than 20%, except some bubbly to slug transition flow conditions and some churn-turbulent flow conditions. The disagreement between models and experiments could result from underestimate of inter-group void transfer.

Review of blunt body wake flows at hypersonic low density conditions

NASA Technical Reports Server (NTRS)

Moss, J. N.; Price, J. M.

1996-01-01

Recent results of experimental and computational studies concerning hypersonic flows about blunted cones including their near wake are reviewed. Attention is focused on conditions where rarefaction effects are present, particularly in the wake. The experiments have been performed for a common model configuration (70 deg spherically-blunted cone) in five hypersonic facilities that encompass a significant range of rarefaction and nonequilibrium effects. Computational studies using direct simulation Monte Carlo (DSMC) and Navier-Stokes solvers have been applied to selected experiments performed in each of the facilities. In addition, computations have been made for typical flight conditions in both Earth and Mars atmospheres, hence more energetic flows than produced in the ground-based tests. Also, comparisons of DSMC calculations and forebody measurements made for the Japanese Orbital Reentry Experiment (OREX) vehicle (a 50 deg spherically-blunted cone) are presented to bridge the spectrum of ground to flight conditions.

Development flight tests of JetStar LFC leading-edge flight test experiment

NASA Technical Reports Server (NTRS)

Fisher, David F.; Fischer, Michael C.

1987-01-01

The overall objective of the flight tests on the JetStar aircraft was to demonstrate the effectiveness and reliability of laminar flow control under representative flight conditions. One specific objective was to obtain laminar flow on the JetStar leading-edge test articles for the design and off-design conditions. Another specific objective was to obtain operational experience on a Laminar Flow Control (LFC) leading-edge system in a simulated airline service. This included operational experience with cleaning requirements, the effect of clogging, possible foreign object damage, erosion, and the effects of ice particle and cloud encounters. Results are summarized.

Current Laminar Flow Control Experiments at NASA Dryden

NASA Technical Reports Server (NTRS)

Bowers, Al

2010-01-01

An experiment to demonstrate laminar flow over the swept wing of a subsonic transport is being developed. Discrete Roughness Elements are being used to maintain laminar flow over a substantial portion of a wing glove. This passive laminar flow technology has only come to be recognized as a significant player in airliner drag reduction in the last few years. NASA is implementing this experiment and is planning to demonstrate this technology at full-scale Bight cruise conditions of a small-to-medium airliner.

Bridge pressure flow scour for clear water conditions

DOT National Transportation Integrated Search

2009-10-01

The equilibrium scour at a bridge caused by pressure flow with critical approach velocity in clear-water simulation conditions was studied both analytically and experimentally. The flume experiments revealed that (1) the measured equilibrium scour pr...

Experimental investigation into the initiation and intensity of erosion in granular flows and its effect on flow dynamics with applications to pyroclastic density currents

NASA Astrophysics Data System (ADS)

Pollock, N. M.; Brand, B. D.; Roche, O.

2017-12-01

The macroscopic processes that control the behavior of pyroclastic density currents (PDCs) include the transportation and deposition of flow particles, entrainment of air, and interaction with topography. However, recent field studies demonstrate that substrate erosion by PDCs is also pervasive. Furthermore, analogue experiments suggest that erosion can increase flow runout distance up to 50%. We present the results from a series of analogue flume experiments on both non-fluidized and initially gas fluidized (i.e. high pore fluid pressure) granular flows. The experiments are designed to explore the controls on erosion initiation and intensity, and how erosion affects flow dynamics. A range of initial conditions allow us to explore how the angle of the bed (0°-20°) and diameter of substrate particles (40 to 700 μm) affect the onset of erosion. The experiments also explore how erosion, once initiated, affects the behavior of the flow in terms of velocity and runout distance. We observe that fluidized flows have increased runout distances of 50-300% relative to non-fluidized flows with the same initial conditions. Fluidized flows that travel over substrates composed of 40 μm particles consistently experience the largest increase in runout distance relative to non-fluidized flows, while flows over substrates of 80 μm particles experience the lowest increase. Erosion occurs for all experimental configurations in both non-fluidized and fluidized flows; however, the intensity of erosion varies widely, from small, millimeter-scale erosional features to decimeter sized wave-like features. Fluidized flows consistently show more intense erosion than non-fluidized flows, suggesting that the fluid-like behavior of these flows allows for efficient mixing between flow and substrate particles. These experiments demonstrate that erosion is a pervasive process for fluidized granular flows and that intense erosion is associated with increased flow runout distances. These results improve our understanding of the role of fluidization in erosion processes, what controls when PDCs become erosional, and how that erosion can alter flow behavior. To accurately model and predict hazards associated with PDCs, we must better understand erosional processes as they relate to these dangerous volcanic phenomena.

Virtual experiments: a new approach for improving process conceptualization in hillslope hydrology

NASA Astrophysics Data System (ADS)

Weiler, Markus; McDonnell, Jeff

2004-01-01

We present an approach for process conceptualization in hillslope hydrology. We develop and implement a series of virtual experiments, whereby the interaction between water flow pathways, source and mixing at the hillslope scale is examined within a virtual experiment framework. We define these virtual experiments as 'numerical experiments with a model driven by collective field intelligence'. The virtual experiments explore the first-order controls in hillslope hydrology, where the experimentalist and modeler work together to cooperatively develop and analyze the results. Our hillslope model for the virtual experiments (HillVi) in this paper is based on conceptualizing the water balance within the saturated and unsaturated zone in relation to soil physical properties in a spatially explicit manner at the hillslope scale. We argue that a virtual experiment model needs to be able to capture all major controls on subsurface flow processes that the experimentalist might deem important, while at the same time being simple with few 'tunable parameters'. This combination makes the approach, and the dialog between experimentalist and modeler, a useful hypothesis testing tool. HillVi simulates mass flux for different initial conditions under the same flow conditions. We analyze our results in terms of an artificial line source and isotopic hydrograph separation of water and subsurface flow. Our results for this first set of virtual experiments showed how drainable porosity and soil depth variability exert a first order control on flow and transport at the hillslope scale. We found that high drainable porosity soils resulted in a restricted water table rise, resulting in more pronounced channeling of lateral subsurface flow along the soil-bedrock interface. This in turn resulted in a more anastomosing network of tracer movement across the slope. The virtual isotope hydrograph separation showed higher proportions of event water with increasing drainable porosity. When combined with previous experimental findings and conceptualizations, virtual experiments can be an effective way to isolate certain controls and examine their influence over a range of rainfall and antecedent wetness conditions.

An approach to quantify sources, seasonal change, and biogeochemical processes affecting metal loading in streams: Facilitating decisions for remediation of mine drainage

USGS Publications Warehouse

Kimball, B.A.; Runkel, R.L.; Walton-Day, K.

2010-01-01

Historical mining has left complex problems in catchments throughout the world. Land managers are faced with making cost-effective plans to remediate mine influences. Remediation plans are facilitated by spatial mass-loading profiles that indicate the locations of metal mass-loading, seasonal changes, and the extent of biogeochemical processes. Field-scale experiments during both low- and high-flow conditions and time-series data over diel cycles illustrate how this can be accomplished. A low-flow experiment provided spatially detailed loading profiles to indicate where loading occurred. For example, SO42 - was principally derived from sources upstream from the study reach, but three principal locations also were important for SO42 - loading within the reach. During high-flow conditions, Lagrangian sampling provided data to interpret seasonal changes and indicated locations where snowmelt runoff flushed metals to the stream. Comparison of metal concentrations between the low- and high-flow experiments indicated substantial increases in metal loading at high flow, but little change in metal concentrations, showing that toxicity at the most downstream sampling site was not substantially greater during snowmelt runoff. During high-flow conditions, a detailed temporal sampling at fixed sites indicated that Zn concentration more than doubled during the diel cycle. Monitoring programs must account for diel variation to provide meaningful results. Mass-loading studies during different flow conditions and detailed time-series over diel cycles provide useful scientific support for stream management decisions.

Experimental and numerical investigation of centrifugal pumps with asymmetric inflow conditions

NASA Astrophysics Data System (ADS)

Mittag, Sten; Gabi, Martin

2015-11-01

Most of the times pumps operate off best point states. Reasons are changes of operating conditions, modifications, pollution and wearout or erosion. As consequences non-rotational symmetric flows, transient operational conditions, increased risk of cavitation, decrease of efficiency and unpredictable wearout can appear. Especially construction components of centrifugal pumps, in particular intake elbows, contribute to this matter. Intake elbows causes additional losses and secondary flows, hence non-rotational velocity distributions as intake profile to the centrifugal pump. As a result the impeller vanes experience permanent changes of the intake flow angle and with it transient flow conditions in the blade channels. This paper presents the first results of a project, experimentally and numerically investigating the consequences of non-rotational inflow to leading edge flow conditions of a centrifugal pump. Therefore two pumpintake- elbow systems are compared, by only altering the intake elbow geometry: a common single bended 90° elbow and a numerically optimized elbow (improved regarding rotational symmetric inflow conditions and friction coefficient). The experiments are carried out, using time resolved stereoscopic PIV on a full acrylic pump with refractions index matched (RIM) working fluid. This allows transient investigations of the flow field simultaneously for all blade leading edges. Additional CFD results are validated and used to further support the investigation i.e. for comparing an analog pump system with ideal inflow conditions.

Quasi-one-dimensional compressible flow across face seals and narrow slots. 1: Analysis

NASA Technical Reports Server (NTRS)

Zuk, J.; Ludwig, L. P.; Johnson, R. L.

1972-01-01

An analysis is presented for compressible fluid flow across shaft face seals and narrow slots. The analysis includes fluid inertia, viscous friction, and entrance losses. Subsonic and choked flow conditions can be predicted and analyzed. The model is valid for both laminar and turbulent flows. Results agree with experiment and with solutions which are more limited in applicability. Results show that a parallel film can have a positive film stiffness under choked flow conditions.

Computational Fluid Dynamics Modeling of Submerged Objects Under Unidirectional and Oscillatory Flows.

NASA Astrophysics Data System (ADS)

Fytanidis, D. K.; Wu, H.; Landry, B. J.; Garcia, M. H.

2017-12-01

Abandoned Unexploded Ordnances (UXOs) from wartime events, accidents, training or other military activities can be found in coastal environments. While the interest for these hazardous submerged objects is increased, there are still existing knowledge gaps regarding the mechanisms of incipient motion and flow behavior around UXOs lying on the seafloor. Numerical modeling of flow around near bed placed UXOs is conducted for unidirectional and oscillatory flow conditions using Computational Fluid Dynamics techniques. The Reynolds-Averaged Navier-Stokes (RANS) approach is used to simulate the complex turbulent flow field around UXOs. The numerical results are compared with two-dimensional Particle Image Velocimetry measurements from experiments conducted in unidirectional and oscillatory flow facilities within the Ven Te Chow Hydrosystems Laboratory to evaluate the accuracy of the applied RANS-based solver. Realistic boundary conditions are imposed in the numerical models to mimic the experimental conditions in the laboratory facilities. The comparison between the numerical results and the experimental data agrees well. In addition, the effect of the angle of attack on the forces that UXOs experience is examined. Numerical results suggest that the orientation of UXOs with respect to the mean flow is an important parameter for incipient motion under critical flow conditions which is in agreement with prior laboratory experimental results regarding the identification of critical flow conditions for the initiation of motion of UXOs. Finally, an extensive parametric analysis is conducted to evaluate the effect of the maximum current velocity and wave characteristics (maximum velocity and period) on the flow forces and the mean flow pattern around the objects.

Computation of viscous flows over airfoils, including separation, with a coupling approach

NASA Technical Reports Server (NTRS)

Leballeur, J. C.

1983-01-01

Viscous incompressible flows over single or multiple airfoils, with or without separation, were computed using an inviscid flow calculation, with modified boundary conditions, and by a method providing calculation and coupling for boundary layers and wakes, within conditions of strong viscous interaction. The inviscid flow is calculated with a method of singularities, the numerics of which were improved by using both source and vortex distributions over profiles, associated with regularity conditions for the fictitious flows inside of the airfoils. The viscous calculation estimates the difference between viscous flow and inviscid interacting flow, with a direct or inverse integral method, laminar or turbulent, with or without reverse flow. The numerical method for coupling determines iteratively the boundary conditions for the inviscid flow. For attached viscous layers regions, an underrelaxation is locally calculated to insure stability. For separated or separating regions, a special semi-inverse algorithm is used. Comparisons with experiments are presented.

Gas liquid flow at microgravity conditions - Flow patterns and their transitions

NASA Technical Reports Server (NTRS)

Dukler, A. E.; Fabre, J. A.; Mcquillen, J. B.; Vernon, R.

1987-01-01

The prediction of flow patterns during gas-liquid flow in conduits is central to the modern approach for modeling two phase flow and heat transfer. The mechanisms of transition are reasonably well understood for flow in pipes on earth where it has been shown that body forces largely control the behavior observed. This work explores the patterns which exist under conditions of microgravity when these body forces are suppressed. Data are presented which were obtained for air-water flow in tubes during drop tower experiments and Learjet trajectories. Preliminary models to explain the observed flow pattern map are evolved.

Onset of turbulence in accelerated high-Reynolds-number flow

NASA Astrophysics Data System (ADS)

Zhou, Ye; Robey, Harry F.; Buckingham, Alfred C.

2003-05-01

A new criterion, flow drive time, is identified here as a necessary condition for transition to turbulence in accelerated, unsteady flows. Compressible, high-Reynolds-number flows initiated, for example, in shock tubes, supersonic wind tunnels with practical limitations on dimensions or reservoir capacity, and high energy density pulsed laser target vaporization experimental facilities may not provide flow duration adequate for turbulence development. In addition, for critical periods of the overall flow development, the driving background flow is often unsteady in the experiments as well as in the physical flow situations they are designed to mimic. In these situations transition to fully developed turbulence may not be realized despite achievement of flow Reynolds numbers associated with or exceeding stationary flow transitional criteria. Basically our transitional criterion and prediction procedure extends to accelerated, unsteady background flow situations the remarkably universal mixing transition criterion proposed by Dimotakis [P. E. Dimotakis, J. Fluid Mech. 409, 69 (2000)] for stationary flows. This provides a basis for the requisite space and time scaling. The emphasis here is placed on variable density flow instabilities initiated by constant acceleration Rayleigh-Taylor instability (RTI) or impulsive (shock) acceleration Richtmyer-Meshkov instability (RMI) or combinations of both. The significant influences of compressibility on these developing transitional flows are discussed with their implications on the procedural model development. A fresh perspective for predictive modeling and design of experiments for the instability growth and turbulent mixing transitional interval is provided using an analogy between the well-established buoyancy-drag model with applications of a hierarchy of single point turbulent transport closure models. Experimental comparisons with the procedural results are presented where use is made of three distinctly different types of acceleration driven instability experiments: (1) classical, relatively low speed, constant acceleration RTI experiments; (2) shock tube, shockwave driven RMI flow mixing experiments; (3) laser target vaporization RTI and RMI mixing experiments driven at very high energy density. These last named experiments are of special interest as they provide scaleable flow conditions simulating those of astrophysical magnitude such as shock-driven hydrodynamic mixing in supernova evolution research.

Parallel-plate Flow Chamber and Continuous Flow Circuit to Evaluate Endothelial Progenitor Cells under Laminar Flow Shear Stress

PubMed Central

Lane, Whitney O.; Jantzen, Alexandra E.; Carlon, Tim A.; Jamiolkowski, Ryan M.; Grenet, Justin E.; Ley, Melissa M.; Haseltine, Justin M.; Galinat, Lauren J.; Lin, Fu-Hsiung; Allen, Jason D.; Truskey, George A.; Achneck, Hardean E.

2012-01-01

The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well quantifiable fluid shear stresses1. Our flow chamber design and flow circuit (Fig. 1) contains a transparent viewing region that enables testing of cell adhesion and imaging of cell morphology immediately before flow (Fig. 11A, B), at various time points during flow (Fig. 11C), and after flow (Fig. 11D). These experiments are illustrated with human umbilical cord blood-derived endothelial progenitor cells (EPCs) and porcine EPCs2,3. This method is also applicable to other adherent cell types, e.g. smooth muscle cells (SMCs) or fibroblasts. The chamber and all parts of the circuit are easily sterilized with steam autoclaving. In contrast to other chambers, e.g. microfluidic chambers, large numbers of cells (> 1 million depending on cell size) can be recovered after the flow experiment under sterile conditions for cell culture or other experiments, e.g. DNA or RNA extraction, or immunohistochemistry (Fig. 11E), or scanning electron microscopy5. The shear stress can be adjusted by varying the flow rate of the perfusate, the fluid viscosity, or the channel height and width. The latter can reduce fluid volume or cell needs while ensuring that one-dimensional flow is maintained. It is not necessary to measure chamber height between experiments, since the chamber height does not depend on the use of gaskets, which greatly increases the ease of multiple experiments. Furthermore, the circuit design easily enables the collection of perfusate samples for analysis and/or quantification of metabolites secreted by cells under fluid shear stress exposure, e.g. nitric oxide (Fig. 12)6. PMID:22297325

Aspects of turbulent-shear-layer dynamics and mixing

NASA Astrophysics Data System (ADS)

Slessor, Michael David

Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shearlayer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described. Chemically-reacting and non-reacting flows were investigated, the former relying on the (H2 + NO/F2) chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of "flip" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows. Both inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are "remembered" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, i. e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from all other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces laxge-scale entrainment and turbulent growth, but slightly enhances smallscale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.

Aspects of turbulent-shear-layer dynamics and mixing

NASA Astrophysics Data System (ADS)

Slessor, Michael David

Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shear-layer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described. Chemically-reacting and non-reacting flows were investigated, the former relying on the (Hsb2 + NO)/Fsb2 chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of "flip" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows. Both inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are "remembered" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, a.e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from ail other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces large-scale entrainment and turbulent growth, but slightly enhances small-scale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.

Boundary Condition Study for the Juncture Flow Experiment in the NASA Langley 14x22-Foot Subsonic Wind Tunnel

NASA Technical Reports Server (NTRS)

Rumsey, C. L.; Carlson, J.-R.; Hannon, J. A.; Jenkins, L. N.; Bartram, S. M.; Pulliam, T. H.; Lee, H. C.

2017-01-01

Because future wind tunnel tests associated with the NASA Juncture Flow project are being designed for the purpose of CFD validation, considerable effort is going into the characterization of the wind tunnel boundary conditions, particularly at inflow. This is important not only because wind tunnel flowfield nonuniformities can play a role in integrated testing uncertainties, but also because the better the boundary conditions are known, the better CFD can accurately represent the experiment. This paper describes recent investigative wind tunnel tests involving two methods to measure and characterize the oncoming flow in the NASA Langley 14- by 22-Foot Subsonic Tunnel. The features of each method, as well as some of their pros and cons, are highlighted. Boundary conditions and modeling tactics currently used by CFD for empty-tunnel simulations are also described, and some results using three different CFD codes are shown. Preliminary CFD parametric studies associated with the Juncture Flow model are summarized, to determine sensitivities of the flow near the wing-body juncture region of the model to a variety of modeling decisions.

Experiments in free shear flows: Status and needs for the future

NASA Technical Reports Server (NTRS)

Kline, S. J.; Coles, D. E.; Eggers, J. M.; Harsha, P. T.

1973-01-01

Experiments in free turbulent flows are recommended with the primary concern placed on classical flows in order to augment understanding and for model building. Five classes of experiments dealing with classical free turbulent flows are outlined and proposed as being of particular significance for the near future. These classes include the following: (1) Experiments clarifying the effect of density variation owing to use of different gases, with and without the additional effect of density variation due to high Mach number or other effects; (2) experiments clarifying the role and importance of various parameters which determine the behavior of the near field as well as the condictions under which any of these parameters can be neglected; (3) experiments determining the cumulative effect of initial conditions in terms of distance to fully established flow; (4) experiments for cases where two layers of distinctly different initial turbulence structure flow side by side at the same mean speed; and (5) experiment using contemporary experimental techniques to study structure in free turbulent shear flows in order to compliment and support contemporary work on boundary layers.

On discharge from poppet valves: effects of pressure and system dynamics

NASA Astrophysics Data System (ADS)

Winroth, P. M.; Ford, C. L.; Alfredsson, P. H.

2018-02-01

Simplified flow models are commonly used to design and optimize internal combustion engine systems. The exhaust valves and ports are modelled as straight pipe flows with a corresponding discharge coefficient. The discharge coefficient is usually determined from steady-flow experiments at low pressure ratios and at fixed valve lifts. The inherent assumptions are that the flow through the valve is insensitive to the pressure ratio and may be considered as quasi-steady. The present study challenges these two assumptions through experiments at varying pressure ratios and by comparing measurements of the discharge coefficient obtained under steady and dynamic conditions. Steady flow experiments were performed in a flow bench, whereas the dynamic measurements were performed on a pressurized, 2 l, fixed volume cylinder with one or two moving valves. In the latter experiments an initial pressure (in the range 300-500 kPa) was established whereafter the valve(s) was opened with a lift profile corresponding to different equivalent engine speeds (in the range 800-1350 rpm). The experiments were only concerned with the blowdown phase, i.e. the initial part of the exhaustion process since no piston was simulated. The results show that the process is neither pressure-ratio independent nor quasi-steady. A measure of the "steadiness" has been defined, relating the relative change in the open flow area of the valve to the relative change of flow conditions in the cylinder, a measure that indicates if the process can be regarded as quasi-steady or not.

Influence of gravity on transport and retention of representative engineered nanoparticles in quartz sand.

PubMed

Cai, Li; Zhu, Jinghan; Hou, Yanglong; Tong, Meiping; Kim, Hyunjung

2015-10-01

Four types of NPs: carbon nanotubes and graphene oxide (carbon-based NPs), titanium dioxide and zinc oxide metal-oxide NPs, were utilized to systematically determine the influence of gravity on the transport of NPs in porous media. Packed column experiments for two types of carbon-based NPs were performed under unfavorable conditions in both up-flow (gravity-negative) and down-flow (gravity-positive) orientations, while for two types of metal-oxide NPs, experiments were performed under both unfavorable and favorable conditions in both up-flow and down-flow orientations. Both breakthrough curves and retained profiles of two types of carbon-based NPs in up-flow orientation were equivalent to those in down-flow orientation, indicating that gravity had negligible effect on the transport and retention of carbon-based NPs under unfavorable conditions. In contrast, under both unfavorable and favorable conditions, the breakthrough curves for two types of metal-oxide NPs in down-flow orientation were lower relative to those in up-flow orientation, indicating that gravity could decrease the transport of metal-oxide NPs in porous media. The distinct effect of gravity on the transport and retention of carbon-based and metal-oxide NPs was mainly attributed to the contribution of gravity to the force balance on the NPs in quartz sand. The contribution of gravity was determined by the interplay of the density and sizes of NP aggregates under examined solution conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

"Batch" kinetics in flow: online IR analysis and continuous control.

PubMed

Moore, Jason S; Jensen, Klavs F

2014-01-07

Currently, kinetic data is either collected under steady-state conditions in flow or by generating time-series data in batch. Batch experiments are generally considered to be more suitable for the generation of kinetic data because of the ability to collect data from many time points in a single experiment. Now, a method that rapidly generates time-series reaction data from flow reactors by continuously manipulating the flow rate and reaction temperature has been developed. This approach makes use of inline IR analysis and an automated microreactor system, which allowed for rapid and tight control of the operating conditions. The conversion/residence time profiles at several temperatures were used to fit parameters to a kinetic model. This method requires significantly less time and a smaller amount of starting material compared to one-at-a-time flow experiments, and thus allows for the rapid generation of kinetic data. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of boundary conditions in helicoidal flow collimation: Consequences for the von Kármán sodium dynamo experiment.

PubMed

Varela, J; Brun, S; Dubrulle, B; Nore, C

2015-12-01

We present hydrodynamic and magnetohydrodynamic (MHD) simulations of liquid sodium flow with the PLUTO compressible MHD code to investigate influence of magnetic boundary conditions on the collimation of helicoidal motions. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multiblades impeller inspired by those used in the Von-Kármán-sodium (VKS) experiment. We show that the impinging of the large-scale flow upon the impeller generates a coherent helicoidal vortex inside the blades, located at a distance from the upstream blade piloted by the incident angle of the flow. This vortex collimates any existing magnetic field lines leading to an enhancement of the radial magnetic field that is stronger for ferromagnetic than for conducting blades. The induced magnetic field modifies locally the velocity fluctuations, resulting in an enhanced helicity. This process possibly explains why dynamo action is more easily triggered in the VKS experiment when using soft iron impellers.

Intermediate Scale Experimental Design to Validate a Subsurface Inverse Theory Applicable to Date-sparse Conditions

NASA Astrophysics Data System (ADS)

Jiao, J.; Trautz, A.; Zhang, Y.; Illangasekera, T.

2017-12-01

Subsurface flow and transport characterization under data-sparse condition is addressed by a new and computationally efficient inverse theory that simultaneously estimates parameters, state variables, and boundary conditions. Uncertainty in static data can be accounted for while parameter structure can be complex due to process uncertainty. The approach has been successfully extended to inverting transient and unsaturated flows as well as contaminant source identification under unknown initial and boundary conditions. In one example, by sampling numerical experiments simulating two-dimensional steady-state flow in which tracer migrates, a sequential inversion scheme first estimates the flow field and permeability structure before the evolution of tracer plume and dispersivities are jointly estimated. Compared to traditional inversion techniques, the theory does not use forward simulations to assess model-data misfits, thus the knowledge of the difficult-to-determine site boundary condition is not required. To test the general applicability of the theory, data generated during high-precision intermediate-scale experiments (i.e., a scale intermediary to the field and column scales) in large synthetic aquifers can be used. The design of such experiments is not trivial as laboratory conditions have to be selected to mimic natural systems in order to provide useful data, thus requiring a variety of sensors and data collection strategies. This paper presents the design of such an experiment in a synthetic, multi-layered aquifer with dimensions of 242.7 x 119.3 x 7.7 cm3. Different experimental scenarios that will generate data to validate the theory are presented.

DSMC Simulation of Separated Flows About Flared Bodies at Hypersonic Conditions

NASA Technical Reports Server (NTRS)

Moss, James N.

2000-01-01

This paper describes the results of a numerical study of interacting hypersonic flows at conditions that can be produced in ground-based test facilities. The computations are made with the direct simulation Monte Carlo (DSMC) method of Bird. The focus is on Mach 10 flows about flared axisymmetric configurations, both hollow cylinder flares and double cones. The flow conditions are those for which experiments have been or will be performed in the ONERA R5Ch low-density wind tunnel and the Calspan-University of Buffalo Research Center (CUBRC) Large Energy National Shock (LENS) tunnel. The range of flow conditions, model configurations, and model sizes provides a significant range of shock/shock and shock/boundary layer interactions at low Reynolds number conditions. Results presented will highlight the sensitivity of the calculations to grid resolution, contrast the differences in flow structure for hypersonic cold flows and those of more energetic but still low enthalpy flows, and compare the present results with experimental measurements for surface heating, pressure, and extent of separation.

The role of varying flow on channel morphology: a flume experiment

NASA Astrophysics Data System (ADS)

Hempel, L. A.; Grant, G.; Eaton, B. C.; Hassan, M. A.; Lewis, S.

2017-12-01

Numerous studies have explored how alluvial channels develop under different sediment and flow conditions, yet we still know very little about how channels adjust and respond to changing flow conditions. One reason for this oversight is the long-held idea that channels with complex flow regimes are adjusted to a single, channel-forming discharge. But growing evidence shows that channel form reflects time-dependent processes occuring over multiple flows. To better understand how stream channels adjust to a range of flows, and identify the timescales associated with those adjustments, we conducted a series of hydrograph experiments in a freely-adjustable flume that developed a self-formed, meander pattern with pool-riffle morphology. Hydrographs had different shapes, magnitudes, and durations, but the total sediment volume fed under equilibrium conditions was kept constant among experiments. We found that hydrograph shape controlled channel morphology, the rate of channel development, and degree of regularity in the pool-riffle pattern. Hydrographs with slowly rising rates of rise and fall produced channels that were equivalent in size to channels generated from constant flow experiments, and had regularly spaced pool-riffle and meander patterns, while hydrographs with fast rates of rise and fall produced undersized channels with a chaotic bed structure and pool-riffle pattern. The latter suggests that during quickly rising hydrographs, the flow rate increases faster than the channel capacity and planform pattern adjusts. We confirmed these observations by comparing the timescales associated with pool-riffle and planform curvature development, which were identified under simple, constant flow conditions, to the total duration of the hydrograph. Hydrographs with step durations equal to or longer than the channel adjustment time produced channels with a more regular pool-riffle patterns compared to channels with step durations shorter than the adjustment time. This work points to the importance of the hydrograph as a fundamental control on channel adjustment and offers the prospect of better understanding of how changes in the flow regime, either through climate, land use, or dams, translate into morphodynamic changes.

Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

NASA Astrophysics Data System (ADS)

Baar, Anne W.; de Smit, Jaco; Uijttewaal, Wim S. J.; Kleinhans, Maarten G.

2018-01-01

Large-scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near-bed flow conditions with varying secondary flow intensity, sediment sizes (0.17-4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modeling.

Collaborate and share: an experimental study of the effects of task and reward interdependencies in online games.

PubMed

Choi, Boreum; Lee, Inseong; Choi, Dongseong; Kim, Jinwoo

2007-08-01

Today millions of players interact with one another in online games, especially massively multiplayer online role-playing games (MMORPGs). These games promote interaction among players by offering interdependency features, but to date few studies have asked what interdependency design factors of MMORPGs make them fun for players, produce experiences of flow, or enhance player performance. In this study, we focused on two game design features: task and reward interdependency. We conducted a controlled experiment that compared the interaction effects of low and high task-interdependency conditions and low and high reward-interdependency conditions on three dependent variables: fun, flow, and performance. We found that in a low task-interdependency condition, players had more fun, experienced higher levels of flow, and perceived better performance when a low reward-interdependency condition also obtained. In contrast, in a high task-interdependency condition, all of these measures were higher when a high reward-interdependency condition also obtained.

Different Response of Sap Flow at Different Measurement Depths after Thinning in a Japanese Cypress Plantation

NASA Astrophysics Data System (ADS)

Chiu, C. W.; Gomi, T.; Onda, Y.; Kato, H.; Sakashita, W.; Sun, X.

2017-12-01

Thinning experiments in forests can alter light conditions and further affect growth rate and transpiration of the remained trees. Previous studies suggested transpiration was increased one year after thinning experiment due to improved canopy light condition. On the other hand, the anatomical and morphological responses to thinning are not react immediately because of the tree adaptation to the new surrounding conditions. It has been hypothesized that lower crown is connected to the inner part of sapwood and need more years to adapt new light conditions after thinning. However, our knowledge for the relationship between tree crown development and water movement inside the trunk after several years from thinning experiment was still limited due to lack of long-term field measurement after thinning. Therefore, in this study, we aim to examine the interannual variability of water movement inside the trunk accompanied the development of tree crown after thinning experiment. To do that, we applied sap flow measurement and terrestrial LiDAR survey from 2011 to 2017 in a Japanese cypress (Chamaecyparis obtusa) plantation in Japan, where 50% strip thinning experiment was conducted in the end of 2011. Consequently, we found sap flow densities at different measurement depths were not always increased year by year and those may relate to the crown development after thinning.

Neutron radiography experiments for verification of soluble boron mixing and transport modeling under natural circulation conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feltus, M.A.; Morlang, G.M.

1996-06-01

The use of neutron radiography for visualization of fluid flow through flow visualization modules has been very successful. Current experiments at the Penn State Breazeale Reactor serve to verify the mixing and transport of soluble boron under natural flow conditions as would be experienced in a pressurized water reactor. Different flow geometries have been modeled including holes, slots, and baffles. Flow modules are constructed of aluminum box material 1 1/2 inches by 4 inches in varying lengths. An experimental flow system was built which pumps fluid to a head tank and natural circulation flow occurs from the head tank throughmore » the flow visualization module to be radiographed. The entire flow system is mounted on a portable assembly to allow placement of the flow visualization module in front of the neutron beam port. A neutron-transparent fluorinert fluid is used to simulate water at different densities. Boron is modeled by gadolinium oxide powder as a tracer element, which is placed in a mixing assembly and injected into the system by remote operated electric valve, once the reactor is at power. The entire sequence is recorded on real-time video. Still photographs are made frame-by-frame from the video tape. Computers are used to digitally enhance the video and still photographs. The data obtained from the enhancement will be used for verification of simple geometry predictions using the TRAC and RELAP thermal-hydraulic codes. A detailed model of a reactor vessel inlet plenum, downcomer region, flow distribution area and core inlet is being constructed to model the AP600 plenum. Successive radiography experiments of each section of the model under identical conditions will provide a complete vessel/core model for comparison with the thermal-hydraulic codes.« less

Turbulent and Laminar Flow in Karst Conduits Under Unsteady Flow Conditions: Interpretation of Pumping Tests by Discrete Conduit-Continuum Modeling

NASA Astrophysics Data System (ADS)

Giese, M.; Reimann, T.; Bailly-Comte, V.; Maréchal, J.-C.; Sauter, M.; Geyer, T.

2018-03-01

Due to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several orders of magnitude from local (borehole) to regional (catchment) scale because of the large contrast in hydraulic parameters between matrix and conduit, their heterogeneity and anisotropy. One approach to deal with the scale effect problem in the estimation of hydraulic parameters of karst aquifers is the application of large-scale experiments such as long-term high-abstraction conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fractured matrix. The numerical discrete conduit-continuum modeling approach MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is employed to simulate laminar and nonlaminar conduit flow, induced by large-scale experiments, in combination with Darcian matrix flow. Effects of large-scale experiments were simulated for idealized settings. Subsequently, diagnostic plots and analyses of different fluxes are applied to interpret differences in the simulated conduit drawdown and general flow patterns. The main focus is set on the question to which extent different conduit flow regimes will affect the drawdown in conduit and matrix depending on the hydraulic properties of the conduit system, i.e., conduit diameter and relative roughness. In this context, CFPM1 is applied to investigate the importance of considering turbulent conditions for the simulation of karst conduit flow. This work quantifies the relative error that results from assuming laminar conduit flow for the interpretation of a synthetic large-scale pumping test in karst.

Influence of initial conditions on the flow patterns of a shock-accelerated thin fluid layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Budzinski, J.M.; Benjamin, R.F.; Jacobs, J.W.

1994-11-01

Previous observations of three flow patterns generated by shock acceleration of a thin perturbed, fluid layer are now correlated with asymmetries in the initial conditions. Using a different diagnostic (planar laser Rayleigh scattering) than the previous experiments, upstream mushrooms, downstream mushrooms, and sinuous patterns are still observed. For each experiment the initial perturbation amplitude on one side of the layer can either be larger, smaller, or the same as the amplitude on the other side, as observed with two images per experiment, and these differences lead to the formation of the different patterns.

3-D High-Lift Flow-Physics Experiment - Transition Measurements

NASA Technical Reports Server (NTRS)

McGinley, Catherine B.; Jenkins, Luther N.; Watson, Ralph D.; Bertelrud, Arild

2005-01-01

An analysis of the flow state on a trapezoidal wing model from the NASA 3-D High Lift Flow Physics Experiment is presented. The objective of the experiment was to characterize the flow over a non-proprietary semi-span three-element high-lift configuration to aid in assessing the state of the art in the computation of three-dimensional high-lift flows. Surface pressures and hot-film sensors are used to determine the flow conditions on the slat, main, and flap. The locations of the attachments lines and the values of the attachment line Reynolds number are estimated based on the model surface pressures. Data from the hot-films are used to determine if the flow is laminar, transitional, or turbulent by examining the hot-film time histories, statistics, and frequency spectra.

Chord length distributions interpretation using a polydispersed population: Modeling and experiments

NASA Astrophysics Data System (ADS)

Cameirao, A.; Le Ba, H.; Darbouret, M.; Herri, J.-M.; Peytavy, J.-L.; Glénat, P.

2012-03-01

Chord length distributions were measured during the crystallization of gas hydrates in a flow loop. The conditions on the flow loop were similar with the conditions in the marine pipelines. The flow loop was filled with water in oil emulsion and pressurized with methane (7 MPa) at low temperature (277 K). During crystallization water droplets crystallize and agglomerate. The CLD measures were interpreted in a preceding work [Le Ba et al., 2010] [1] by constructing random aggregates with known geometrical proprieties from a monodispersed population of droplets and calculating their CLD. Comparing calculated CLD with CLD from the experiment, the geometrical parameters: number of primary particles and fractal dimension of experimental aggregates are identified. However some differences remained between the experiment and the calculated CLD. In the present work the droplets population was considered polydispersed improving the comparison between the model and the experiment.

Importance of inlet boundary conditions for numerical simulation of combustor flows

NASA Technical Reports Server (NTRS)

Sturgess, G. J.; Syed, S. A.; Mcmanus, K. R.

1983-01-01

Fluid dynamic computer codes for the mathematical simulation of problems in gas turbine engine combustion systems are required as design and diagnostic tools. To eventually achieve a performance standard with these codes of more than qualitative accuracy it is desirable to use benchmark experiments for validation studies. Typical of the fluid dynamic computer codes being developed for combustor simulations is the TEACH (Teaching Elliptic Axisymmetric Characteristics Heuristically) solution procedure. It is difficult to find suitable experiments which satisfy the present definition of benchmark quality. For the majority of the available experiments there is a lack of information concerning the boundary conditions. A standard TEACH-type numerical technique is applied to a number of test-case experiments. It is found that numerical simulations of gas turbine combustor-relevant flows can be sensitive to the plane at which the calculations start and the spatial distributions of inlet quantities for swirling flows.

Dual-RiverSonde measurements of two-dimensional river flow patterns

USGS Publications Warehouse

Teague, C.C.; Barrick, D.E.; Lilleboe, P.M.; Cheng, R.T.; Stumpner, P.; Burau, J.R.

2008-01-01

Two-dimensional river flow patterns have been measured using a pair of RiverSondes in two experiments in the Sacramento-San Joaquin River Delta system of central California during April and October 2007. An experiment was conducted at Walnut Grove, California in order to explore the use of dual RiverSondes to measure flow patterns at a location which is important in the study of juvenile fish migration. The data available during the first experiment were limited by low wind, so a second experiment was conducted at Threemile Slough where wind conditions and surface turbulence historically have resulted in abundant data. Both experiments included ADCP near-surface velocity measurements from either manned or unmanned boats. Both experiments showed good comparisons between the RiverSonde and ADCP measurements. The flow conditions at both locations are dominated by tidal effects, with partial flow reversal at Walnut Grove and complete flow reversal at Threemile Slough. Both systems showed complex flow patterns during the flow reversals. Quantitative comparisons between the RiverSondes and an ADCP on a manned boat at Walnut Grove showed mean differences of 4.5 cm/s in the u (eastward) and 7.6 cm/s in the v (northward) components, and RMS differences of 14.7 cm/s in the u component and 21.0 cm/s in the v component. Quantitative comparisons between the RiverSondes and ADCPs on autonomous survey vessels at Threemile Slough showed mean differences of 0.007 cm/s in the u component and 0.5 cm/s in the v component, and RMS differences of 7.9 cm/s in the u component and 13.5 cm/s in the v component after obvious outliers were removed. ?? 2008 IEEE.

Kinetics of gibbsite dissolution under low ionic strength conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ganor, J.; Mogollon, J.L.; Lasaga, A.C.

1999-06-01

Experiments measuring synthetic gibbsite dissolution rates were carried out using both a stirred-flow-through reactor and a column reactor at 25 C, and pH range of 2.5--4.1. All experiments were conducted under far from equilibrium conditions ({Delta}G < {minus}1.1 kcal/mole). The experiments were performed with perchloric acid under relatively low (and variable) ionic strength conditions. An excellent agreement was found between the results of the well-mixed flow-through experiments and those of the (nonmixed) column experiments. This agreement shows that the gibbsite dissolution rate is independent of the stirring rate and therefore supports the conclusion of Bloom and Erich (1987) that gibbsitemore » dissolution reaction is surface controlled and not diffusion controlled. The Brunauer-Emmett-Teller (BET) surface area of the gibbsite increased during the flow-through experiments, while in the column experiments no significant change in surface area was observed. The significant differences in the BET surface area between the column experiments and the flow-through experiments, and the excellent agreement between the rates obtained by both methods, enable the authors to justify the substitution of the BET surface area for the reactive surface area. The dissolution rate of gibbsite varied as a function of the perchloric acid concentration. The authors interpret the gibbsite dissolution rate as a result of a combined effect of proton catalysis and perchlorate inhibition. Following the theoretical study of Ganor and Lasaga (1998) they propose specific reaction mechanisms for the gibbsite dissolution in the presence of perchloric acid. The mathematical predictions of two of these reaction mechanisms adequately describe the experimental data.« less

CFD Application to Flow-Accelerated Corrosion in Feeder Bends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietralik, John M.; Smith, Bruce A.W.

2006-07-01

Feeder piping in CANDU{sup R} plants experiences a thinning degradation mechanism called Flow-Accelerated Corrosion (FAC). The piping is made of carbon steel and has high water flow speeds. Although the water chemistry is highly alkaline with room-temperature pH in a range of 10.0-10.5, the piping has FAC rates exceeding 0.1 mm/year in some locations, e.g., in bends. One of the most important parameters affecting the FAC rate is the mass transfer coefficient for convective mass transport of ferrous ions. The ions are created at the pipe wall as a result of corrosion, diffuse through the oxide layer, and are transportedmore » from the oxide-layer/water interface to the bulk water by mass transport. Consequently, the local flow characteristics contribute to the highly turbulent convective mass transfer. Plant data and laboratory experiments indicate that the mass transfer step dominates FAC under feeder conditions. In this study, the flow and mass transfer in a feeder bend under operating conditions were simulated using the Fluent{sup TM} computer code. Because the flow speed is very high, with the Reynolds numbers in a range of several millions, and because the geometry is complex, experiments in a 1:1 scale were conducted with the main objective to validate flow simulations. The experiments measured pressure at several key locations and visualized the flow. The flow and mass transfer models were validated using available friction-factor and mass transfer correlations and literature experiments on mass transfer in a bend. The validation showed that the turbulence model that best predicts the experiments is the realizable k-{epsilon} model. Other two-equation turbulence models, as well as one-equation models and Reynolds stress models were tried. The near-wall treatment used the non-equilibrium wall functions. The wall functions were modified for surface roughness when necessary. A comparison of the local mass transfer coefficient with measured FAC rate in plant specimens shows very good agreement. Visualization experiments indicate secondary flows in the bends. No boundary layer separation was observed in experiments or in simulations. (authors)« less

Bubble Generation in a Continuous Liquid Flow Under Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Pais, Salvatore Cezar

1999-01-01

The present work reports a study of bubble generation under reduced gravity conditions for both co-flow and cross-flow configurations. Experiments were performed aboard the DC-9 Reduced Gravity Aircraft at NASA Glenn Research Center, using an air-water system. Three different flow tube diameters were used: 1.27, 1.9, and 2.54 cm. Two different ratios of air injection nozzle to tube diameters were considered: 0.1 and 0.2. Gas and liquid volumetric flow rates were varied from 10 to 200 ml/s. It was experimentally observed that with increasing superficial liquid velocity, the bubbles generated decreased in size. The bubble diameter was shown to increase with increasing air injection nozzle diameters. As the tube diameter was increased, the size of the detached bubbles increased. Likewise, as the superficial liquid velocity was increased, the frequency of bubble formation increased and thus the time to detach forming bubbles decreased. Independent of the flow configuration (for either single nozzle or multiple nozzle gas injection), void fraction and hence flow regime transition can be controlled in a somewhat precise manner by solely varying the gas and liquid volumetric flow rates. On the other hand, it is observed that uniformity of bubble size can be controlled more accurately by using single nozzle gas injection than by using multiple port injection, since this latter system gives rise to unpredictable coalescence of adjacent bubbles. A theoretical model, based on an overall force balance, is employed to study single bubble generation in the dynamic and bubbly flow regime. Under conditions of reduced gravity, the gas momentum flux enhances bubble detachment; however, the surface tension forces at the nozzle tip inhibits bubble detachment. Liquid drag and inertia can act either as attaching or detaching force, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with performed experiments. However, at higher superficial,liquid velocities, the bubble neck length begins to significantly deviate from the value of the air injection nozzle diameter and thus the theory no longer predicts the experiment behavior. Effects of fluid properties, injection geometry and flow conditions on generated bubble size are investigated using the theoretical model. It is shown that bubble diameter is larger in a reduced gravity environment than in a normal gravity environment at similar flow condition and flow geometry.

Possible effects of two-phase flow pattern on the mechanical behavior of mudstones

NASA Astrophysics Data System (ADS)

Goto, H.; Tokunaga, T.; Aichi, M.

2016-12-01

To investigate the influence of two-phase flow pattern on the mechanical behavior of mudstones, laboratory experiments were conducted. In the experiment, air was injected from the bottom of the water-saturated Quaternary Umegase mudstone sample under hydrostatic external stress condition. Both axial and circumferential strains at half the height of the sample and volumetric discharge of water at the outlet were monitored during the experiment. Numerical simulation of the experiment was tried by using a simulator which can solve coupled two-phase flow and poroelastic deformation assuming the extended-Darcian flow with relative permeability and capillary pressure as functions of the wetting-phase fluid saturation. In the numerical simulation, the volumetric discharge of water was reproduced well while both strains were not. Three dimensionless numbers, i.e., the viscosity ratio, the Capillary number, and the Bond number, which characterize the two-phase flow pattern (Lenormand et al., 1988; Ewing and Berkowitz, 1998) were calculated to be 2×10-2, 2×10-11, and 7×10-11, respectively, in the experiment. Because the Bond number was quite small, it was possible to apply Lenormand et al. (1988)'s diagram to evaluate the flow regime, and the flow regime was considered to be capillary fingering. While, in the numerical simulation, air moved uniformly upward with quite low non-wetting phase saturation conditions because the fluid flow obeyed the two-phase Darcy's law. These different displacement patterns developed in the experiment and assumed in the numerical simulation were considered to be the reason why the deformation behavior observed in the experiment could not be reproduced by numerical simulation, suggesting that the two-phase flow pattern could affect the changes of internal fluid pressure patterns during displacement processes. For further studies, quantitative analysis of the experimental results by using a numerical simulator which can solve the coupled processes of two-phase flow through preferential flow paths and deformation of porous media is needed. References: Ewing R. P., and B. Berkowitz (1998), Water Resour. Res., 34, 611-622. Lenormand, R., E. Touboul, and C. Zarcone (1988), J. Fluid Mech., 189, 165-187.

Controls on Lava Flow Morphology and Propagation: Using Laboratory Analogue Experiments

NASA Astrophysics Data System (ADS)

Peters, S.; Clarke, A. B.

2017-12-01

The morphology of lava flows is controlled by eruption rate, composition, cooling rate, and topography [Fink and Griffiths, 1990; Gregg and Fink, 2000, 2006]. Lava flows are used to understand how volcanoes, volcanic fields, and igneous provinces formed and evolved [Gregg and Fink., 1996; Sheth, 2006]. This is particularly important for other planets where compositional data is limited and historical context is nonexistent. Numerical modeling of lava flows remains challenging, but has been aided by laboratory analog experiments [Gregg and Keszrthelyi, 2004; Soule and Cashman, 2004]. Experiments using polyethylene glycol (PEG) 600 wax have been performed to understand lava flow emplacement [Fink and Griffiths, 1990, 1992; Gregg and Fink, 2000]. These experiments established psi (hereafter denoted by Ψ), a dimensionless parameter that relates crust formation and advection timescales of a viscous gravity current. Four primary flow morphologies corresponding to discreet Ψ ranges were observed. Gregg and Fink [2000] also investigated flows on slopes and found that steeper slopes increase the effective effusion rate producing predicted morphologies at lower Ψ values. Additional work is needed to constrain the Ψ parameter space, evaluate the predictive capability of Ψ, and determine if the preserved flow morphology can be used to indicate the initial flow conditions. We performed 514 experiments to address the following controls on lava flow morphology: slope (n = 282), unsteadiness/pulsations (n = 58), slope & unsteadiness/pulsations (n = 174), distal processes, and emplacement vs. post-emplacement morphologies. Our slope experiments reveal a similar trend to Gregg and Fink [2000] with the caveat that very high and very low local & source eruption rates can reduce the apparent predictive capability of Ψ. Predicted Ψ morphologies were often produced halfway through the eruption. Our pulse experiments are expected to produce morphologies unique to each eruption rate and promote tube formation and compound flows. Post-emplacement morphologies are modified by a variety of factors (e.g. solidification, deflation), which may not preserve the initial morphology produced during an eruption. Relating this morphology to the eruption conditions is pertinent to understanding the evolution of planetary surfaces.

The Study on Flow Velocity Measurement of Antarctic Krill Trawl Model Experiment in North Bay of South China Sea

NASA Astrophysics Data System (ADS)

Chen, Shuai; Wang, Lumin; Huang, Hongliang; Zhang, Xun

2017-10-01

From August 25 to 29, 2014, the project team carried out the experiment of Antarctic krill trawl in the Beihai Bay of the South China Sea. In order to understand the flow field of the network model in the course of the experiment, it is necessary to record the speed of the ship and to grasp the flow field of the ocean. Therefore, the ocean velocity is measured during the experiment. The flow rate in this experiment was measured using an acoustic Doppler flow meter (Vectoring Plus, Nortek, Norway). In order to compensate for the flow rate error caused by ship drift, the drift condition of the ship was also measured by the positioning device (Snapdragon MSM8274AB, Qualcomm, USA) used in the flow rate measurement. The results show that the actual velocity of the target sea area is in the range of 0.06-0.49 m / s and the direction is 216.17-351.70. And compared with the previous research, the influencing factors were analysed. This study proves that it is feasible to use point Doppler flow meter for velocity study in trawl model experiment.

Biodegradation of phenol, salicylic acid, benzenesulfonic acid, and iomeprol by Pseudomonas fluorescens in the capillary fringe

NASA Astrophysics Data System (ADS)

Hack, Norman; Reinwand, Christian; Abbt-Braun, Gudrun; Horn, Harald; Frimmel, Fritz H.

2015-12-01

Mass transfer and biological transformation phenomena in the capillary fringe were studied using phenol, salicylic acid, benzenesulfonic acid, and the iodinated X-ray contrast agent iomeprol as model organic compounds and the microorganism strain Pseudomonas fluorescens. Three experimental approaches were used: Batch experiments (uniform water saturation and transport by diffusion), in static columns (with a gradient of water saturation and advective transport in the capillaries) and in a flow-through cell (with a gradient of water saturation and transport by horizontal and vertical flow: 2-dimension flow-through microcosm). The reactors employed for the experiments were filled with quartz sand of defined particle size distribution (dp = 200…600 μm, porosity ε = 0.42). Batch experiments showed that phenol and salicylic acid have a high, whereas benzenesulfonic acid and iomeprol have a quite low potential for biodegradation under aerobic conditions and in a matrix nearly close to water saturation. Batch experiments under anoxic conditions with nitrate as electron acceptor revealed that the biodegradation of the model compounds was lower than under aerobic conditions. Nevertheless, the experiments showed that the moisture content was also responsible for an optimized transport in the liquid phase of a porous medium. Biodegradation in the capillary fringe was found to be influenced by both the moisture content and availability of the dissolved substrate, as seen in static column experiments. The gas-liquid mass transfer of oxygen also played an important role for the biological activity. In static column experiments under aerobic conditions, the highest biodegradation was found in the capillary fringe (e.g. βt/β0 (phenol) = 0 after t = 6 d) relative to the zone below the water table and unsaturated zone. The highest biodegradation occurred in the flow-through cell experiment where the height of the capillary fringe was largest.

Biodegradation of phenol, salicylic acid, benzenesulfonic acid, and iomeprol by Pseudomonas fluorescens in the capillary fringe.

PubMed

Hack, Norman; Reinwand, Christian; Abbt-Braun, Gudrun; Horn, Harald; Frimmel, Fritz H

2015-12-01

Mass transfer and biological transformation phenomena in the capillary fringe were studied using phenol, salicylic acid, benzenesulfonic acid, and the iodinated X-ray contrast agent iomeprol as model organic compounds and the microorganism strain Pseudomonas fluorescens. Three experimental approaches were used: Batch experiments (uniform water saturation and transport by diffusion), in static columns (with a gradient of water saturation and advective transport in the capillaries) and in a flow-through cell (with a gradient of water saturation and transport by horizontal and vertical flow: 2-dimension flow-through microcosm). The reactors employed for the experiments were filled with quartz sand of defined particle size distribution (dp=200...600 μm, porosity ε=0.42). Batch experiments showed that phenol and salicylic acid have a high, whereas benzenesulfonic acid and iomeprol have a quite low potential for biodegradation under aerobic conditions and in a matrix nearly close to water saturation. Batch experiments under anoxic conditions with nitrate as electron acceptor revealed that the biodegradation of the model compounds was lower than under aerobic conditions. Nevertheless, the experiments showed that the moisture content was also responsible for an optimized transport in the liquid phase of a porous medium. Biodegradation in the capillary fringe was found to be influenced by both the moisture content and availability of the dissolved substrate, as seen in static column experiments. The gas-liquid mass transfer of oxygen also played an important role for the biological activity. In static column experiments under aerobic conditions, the highest biodegradation was found in the capillary fringe (e.g. βt/β0 (phenol)=0 after t=6 d) relative to the zone below the water table and unsaturated zone. The highest biodegradation occurred in the flow-through cell experiment where the height of the capillary fringe was largest. Copyright © 2015 Elsevier B.V. All rights reserved.

A Computational Fluid Dynamics Study of Transitional Flows in Low-Pressure Turbines under a Wide Range of Operating Conditions

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.; Volino, R. J.; Corke, T. C.; Thomas, F. O.; Huang, J.; Lake, J. P.; King, P. I.

2007-01-01

A transport equation for the intermittency factor is employed to predict the transitional flows in low-pressure turbines. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mu(sub p) with the intermittency factor, gamma. Turbulent quantities are predicted using Menter's two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The model had been previously validated against low-pressure turbine experiments with success. In this paper, the model is applied to predictions of three sets of recent low-pressure turbine experiments on the Pack B blade to further validate its predicting capabilities under various flow conditions. Comparisons of computational results with experimental data are provided. Overall, good agreement between the experimental data and computational results is obtained. The new model has been shown to have the capability of accurately predicting transitional flows under a wide range of low-pressure turbine conditions.

Surfactant-induced flow compromises determination of air-water interfacial areas by surfactant miscible-displacement.

PubMed

Costanza-Robinson, Molly S; Henry, Eric J

2017-03-01

Surfactant miscible-displacement (SMD) column experiments are used to measure air-water interfacial area (A I ) in unsaturated porous media, a property that influences solute transport and phase-partitioning. The conventional SMD experiment results in surface tension gradients that can cause water redistribution and/or net drainage of water from the system ("surfactant-induced flow"), violating theoretical foundations of the method. Nevertheless, the SMD technique is still used, and some suggest that experimental observations of surfactant-induced flow represent an artifact of improper control of boundary conditions. In this work, we used numerical modeling, for which boundary conditions can be perfectly controlled, to evaluate this suggestion. We also examined the magnitude of surfactant-induced flow and its impact on A I measurement during multiple SMD flow scenarios. Simulations of the conventional SMD experiment showed substantial surfactant-induced flow and consequent drainage of water from the column (e.g., from 75% to 55% S W ) and increases in actual A I of up to 43%. Neither horizontal column orientation nor alternative boundary conditions resolved surfactant-induced flow issues. Even for simulated flow scenarios that avoided surfactant-induced drainage of the column, substantial surfactant-induced internal water redistribution occurred and was sufficient to alter surfactant transport, resulting in up to 23% overestimation of A I . Depending on the specific simulated flow scenario and data analysis assumptions used, estimated A I varied by nearly 40% and deviated up to 36% from the system's initial A I . We recommend methods for A I determination that avoid generation of surface-tension gradients and urge caution when relying on absolute A I values measured via SMD. Copyright © 2016 Elsevier Ltd. All rights reserved.

Computational Simulation of Acoustic Modes in Rocket Combustors

NASA Technical Reports Server (NTRS)

Harper, Brent (Technical Monitor); Merkle, C. L.; Sankaran, V.; Ellis, M.

2004-01-01

A combination of computational fluid dynamic analysis and analytical solutions is being used to characterize the dominant modes in liquid rocket engines in conjunction with laboratory experiments. The analytical solutions are based on simplified geometries and flow conditions and are used for careful validation of the numerical formulation. The validated computational model is then extended to realistic geometries and flow conditions to test the effects of various parameters on chamber modes, to guide and interpret companion laboratory experiments in simplified combustors, and to scale the measurements to engine operating conditions. In turn, the experiments are used to validate and improve the model. The present paper gives an overview of the numerical and analytical techniques along with comparisons illustrating the accuracy of the computations as a function of grid resolution. A representative parametric study of the effect of combustor mean flow Mach number and combustor aspect ratio on the chamber modes is then presented for both transverse and longitudinal modes. The results show that higher mean flow Mach numbers drive the modes to lower frequencies. Estimates of transverse wave mechanics in a high aspect ratio combustor are then contrasted with longitudinal modes in a long and narrow combustor to provide understanding of potential experimental simulations.

Simulation of turbulent shear flows at Stanford and NASA-Ames - What can we do and what have we learned?

NASA Technical Reports Server (NTRS)

Reynolds, W. C.

1983-01-01

The capabilities and limitations of large eddy simulation (LES) and full turbulence simulation (FTS) are outlined. It is pointed out that LES, although limited at the present time by the need for periodic boundary conditions, produces large-scale flow behavior in general agreement with experiments. What is more, FTS computations produce small-scale behavior that is consistent with available experiments. The importance of the development work being done on the National Aerodynamic Simulator is emphasized. Studies at present are limited to situations in which periodic boundary conditions can be applied on boundaries of the computational domain where the flow is turbulent.

Separation Control in a Centrifugal Bend Using Plasma Actuators

NASA Astrophysics Data System (ADS)

Arthur, Michael; Corke, Thomas

2011-11-01

An experiment and CFD simulation are presented to examine the use of plasma actuators to control flow separation in a 2-D channel with a 135° inside-bend that is intended to represent a centrifugal bend in a gas turbine engine. The design inlet conditions are P = 330 psia., T =1100° F, and M = 0 . 24 . For these conditions, the flow separates on the inside radius of the bend. A CFD simulation was used to determine the location of the flow separation, and the conditions (location and voltage) of a plasma actuator that was needed to keep the flow attached. The plasma actuator body force model used in the simulation was updated to include the effect of high-pressure operation. An experiment was used to validate the simulation and to further investigate the effect of inlet pressure and Mach number on the flow separation control. This involved a transient high-pressure blow-down facility. The flow field is documented using an array of static pressure taps in the channel outside-radius side wall, and a rake of total pressure probes at the exit of the bend. The results as well as the pressure effect on the plasma actuators are presented.

The high Reynolds number flow through an axial-flow pump

NASA Astrophysics Data System (ADS)

Zierke, W. C.; Straka, W. A.; Taylor, P. D.

1993-11-01

The high Reynolds number pump (HIREP) facility at ARL Penn State has been used to perform a low-speed, large-scale experiment of the incompressible flow of water through a two-blade-row turbomachine. HIREP can involve blade chord Reynolds numbers as high as 6,000,000 and can accommodate a variety of instrumentation in both a stationary and a rotating frame of reference. The objectives of this experiment were as follows: to provide a database for comparison with three-dimensional, viscous (turbulent) flow computations; to evaluate the engineering models; and to improve our physical understanding of many of the phenomena involved in this complex flow field. The experimental results include a large quantity of data acquired throughout HIREP. A five-hole probe survey of the inlet flow 37.0 percent chord upstream of the inlet guide vane (IGV) leading edge is sufficient to give information for the inflow boundary conditions, while some static-pressure information is available to help establish an outflow boundary condition.

Microgravity and bone cell mechanosensitivity: FLOW experiment during the DELTA mission

NASA Astrophysics Data System (ADS)

Bacabac, Rommel G.; Van Loon, Jack J. W. A.; de Blieck-Hogervorst, Jolanda M. A.; Semeins, Cor M.; Zandieh-Doulabi, Behrouz; Helder, Marco N.; Smit, Theo H.; Klein-Nulend, Jenneke

2007-09-01

The catabolic effects of microgravity on mineral metabolism in bone organ cultures might be explained as resulting from an exceptional form of disuse. It is possible that the mechanosensitivity of bone cells is altered under near weightlessness conditions, which likely contributes to disturbed bone metabolism observed in astronauts. In the experiment "FLOW", we tested whether the production of early signaling molecules that are involved in the mechanical load-induced osteogenic response by bone cells is changed under microgravity conditions. FLOW was one of the Biological experiment entries to the Dutch Soyuz Mission "DELTA" (Dutch Expedition for Life Science, Technology and Atmospheric Research). FLOW was flown by the Soyuz craft, launched on April 19, 2004, on its way to the International Space Station. Primary osteocytes, osteoblasts, and periosteal fibroblasts were incubated in plunger boxes, developed by Centre for Concepts in Mechatronics, using plunger activation events for single pulse fluid shear stress stimulations. Due to unforeseen hardware complications, results from in-flight cultures are considered lost. Ground control experiments showed an accumulative increase of NO in medium for osteocytes (as well as for osteoblasts and periosteal fibroblasts). Data from the online-NO sensor showed that the NO produced in medium by osteocytes increased sharply after pulse shear stress stimulations. COX-2 mRNA expression revealed high levels in osteoblasts compared to the other cell types tested. In conclusion, preparations for the FLOW experiment and preliminary ground results indicate that the FLOW setup is viable for a future flight opportunity.

Two-phase adiabatic pressure drop experiments and modeling under micro-gravity conditions

NASA Astrophysics Data System (ADS)

Longeot, Matthieu J.; Best, Frederick R.

1995-01-01

Thermal systems for space applications based on two phase flow have several advantages over single phase systems. Two phase thermal energy management and dynamic power conversion systems have the capability of achieving high specific power levels. However, before two phase systems for space applications can be designed effectively, knowledge of the flow behavior in a ``0-g'' acceleration environment is necessary. To meet this need, two phase flow experiments were conducted by the Interphase Transport Phenomena Laboratory Group (ITP) aboard the National Aeronautics and Space Administration's (NASA) KC-135, using R12 as the working fluid. The present work is concerned with modeling of two-phase pressure drop under 0-g conditions, for bubbly and slug flow regimes. The set of data from the ITP group includes 3 bubbly points, 9 bubbly/slug points and 6 slug points. These two phase pressure drop data were collected in 1991 and 1992. A methodology to correct and validate the data was developed to achieve high levels of confidence. A homogeneous model was developed to predict the pressure drop for particular flow conditions. This model, which uses the Blasius Correlation, was found to be accurate for bubbly and bubbly/slug flows, with errors not larger than 28%. For slug flows, however, the errors are greater, attaining values up to 66%.

Experiment of flow regime map and local condensing heat transfer coefficients inside three dimensional inner microfin tubes

NASA Astrophysics Data System (ADS)

Du, Yang; Xin, Ming Dao

1999-03-01

This paper developed a new type of three dimensional inner microfin tube. The experimental results of the flow patterns for the horizontal condensation inside these tubes are reported in the paper. The flow patterns for the horizontal condensation inside the new made tubes are divided into annular flow, stratified flow and intermittent flow within the test conditions. The experiments of the local heat transfer coefficients for the different flow patterns have been systematically carried out. The experiments of the local heat transfer coefficients changing with the vapor dryness fraction have also been carried out. As compared with the heat transfer coefficients of the two dimensional inner microfin tubes, those of the three dimensional inner microfin tubes increase 47-127% for the annular flow region, 38-183% for the stratified flow and 15-75% for the intermittent flow, respectively. The enhancement factor of the local heat transfer coefficients is from 1.8-6.9 for the vapor dryness fraction from 0.05 to 1.

Impact of Flight Enthalpy, Fuel Simulant, and Chemical Reactions on the Mixing Characteristics of Several Injectors at Hypervelocity Flow Conditions

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Baurle, Robert A.; Drummond, J. Philip

2016-01-01

The high total temperatures or total enthalpies required to duplicate the high-speed flight conditions in ground experiments often place stringent requirements on the material selection and cooling needs for the test articles and intrusive flow diagnostic equipment. Furthermore, for internal flows, these conditions often complicate the use of nonintrusive diagnostics that need optical access to the test section and interior portions of the flowpath. Because of the technical challenges and increased costs associated with experimentation at high values of total enthalpy, an attempt is often made to reduce it. This is the case for the Enhanced Injection and Mixing Project (EIMP) currently underway in the Arc-Heated Scramjet Test Facility at the NASA Langley Research Center. The EIMP aims to investigate supersonic combustion ramjet (scramjet) fuel injection and mixing physics, improve the understanding of underlying physical processes, and develop enhancement strategies and functional relationships between mixing performance and losses relevant to flight Mach numbers greater than 8. The experiments will consider a "direct-connect" approach and utilize a Mach 6 nozzle to simulate the combustor entrance flow of a scramjet engine. However, while the value of the Mach number is matched to that expected at the combustor entrance in flight, the maximum value of the total enthalpy for these experiments is limited by the thermal-structural limits of the uncooled experimental hardware. Furthermore, the fuel simulant is helium, not hydrogen. The use of "cold" flows and non-reacting mixtures of fuel simulants for mixing experiments is not new and has been extensively utilized as a screening technique for scramjet fuel injectors. In this study, Reynolds-averaged simulations are utilized (RAS) to systematically verify the implicit assumptions used by the EIMP. This is accomplished by first performing RAS of mixing for two injector configurations at planned nominal experimental conditions. The mixing parameters of interest, such as mixing efficiency and total pressure recovery, are then computed and compared to the values obtained from RAS under the true enthalpy conditions and using helium and hydrogen. Finally, the impact of combustion on mixing, often deemed small enough to neglect at hypervelocity conditions, is assessed by comparing the results obtained from the hydrogen-fueled reacting and non-reacting RAS. For reacting flows, in addition to mixing efficiency and total pressure recovery, the combustion efficiency and thrust potential are also considered. In all of the simulations, the incoming air Mach number and the fuel-to-air ratio are the same, while the total pressure, total enthalpy, and the fuel simulant vary depending on the case considered. It is found that under some conditions the "cold" flow experiments are a good approximation of the flight.

Technical note: Influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies

NASA Astrophysics Data System (ADS)

Li, Guo; Su, Hang; Kuhn, Uwe; Meusel, Hannah; Ammann, Markus; Shao, Min; Pöschl, Ulrich; Cheng, Yafang

2018-02-01

Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous or multiphase reaction kinetics under laminar flow conditions. Coating surface roughness may potentially distort the laminar flow pattern, induce turbulence and introduce uncertainties in the calculated uptake coefficient based on molecular diffusion assumptions (e.g., Brown/Cooney-Kim-Davis (CKD)/Knopf-Pöschl-Shiraiwa (KPS) methods), which has not been fully resolved in earlier studies. Here, we investigate the influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies. According to laminar boundary theory and considering the specific flow conditions in a coated-wall flow tube, we derive and propose a critical height δc to evaluate turbulence effects in the design and analysis of coated-wall flow tube experiments. If a geometric coating thickness δg is larger than δc, the roughness elements of the coating may cause local turbulence and result in overestimation of the real uptake coefficient (γ). We further develop modified CKD/KPS methods (i.e., CKD-LT/KPS-LT) to account for roughness-induced local turbulence effects. By combination of the original methods and their modified versions, the maximum error range of γCKD (derived with the CKD method) or γKPS (derived with the KPS method) can be quantified and finally γ can be constrained. When turbulence is generated, γCKD or γKPS can bear large difference compared to γ. Their difference becomes smaller for gas reactants with lower uptake (i.e., smaller γ) and/or for a smaller ratio of the geometric coating thickness to the flow tube radius (δg / R0). On the other hand, the critical height δc can also be adjusted by optimizing flow tube configurations and operating conditions (i.e., tube diameter, length, and flow velocity), to ensure not only unaffected laminar flow patterns but also other specific requirements for an individual flow tube experiment. We use coating thickness values from previous coated-wall flow tube studies to assess potential roughness effects using the δc criterion. In most studies, the coating thickness was sufficiently small to avoid complications, but some may have been influenced by surface roughness and local turbulence effects.

Experimental Investigation of the Behavior of Sub-Grid Scale Motions in Turbulent Shear Flow

NASA Technical Reports Server (NTRS)

Cantwell, Brian

1992-01-01

Experiments have been carried out on a vertical jet of helium issuing into a co-flow of air at a fixed exit velocity ratio of 2.0. At all the experimental conditions studied, the flow exhibits a strong self excited periodicity. The natural frequency behavior of the jet, the underlying fine-scale flow structure, and the transition to turbulence have been studied over a wide range of flow conditions. The experiments were conducted in a variable pressure facility which made it possible to vary the Reynolds number and Richardson number independently. A stroboscopic schlieren system was used for flow visualization and single-component Laser Doppler Anemometry was used to measure the axial component of velocity. The flow exhibits several interesting features. The presence of co-flow eliminates the random meandering typical of buoyant plumes in a quiescent environment and the periodicity of the helium jet under high Richardson number conditions is striking. Under these conditions transition to turbulence consists of a rapid but highly structured and repeatable breakdown and intermingling of jet and freestream fluid. At Ri = 1.6 the three-dimensional structure of the flow is seen to repeat from cycle to cycle. The point of transition moves closer to the jet exit as either the Reynolds number or the Richardson number increases. The wavelength of the longitudinal instability increases with Richardson number. At low Richardson numbers, the natural frequency scales on an inertial time scale. At high Richardson number the natural frequency scales on a buoyancy time scale. The transition from one flow regime to another occurs over a narrow range of Richardson numbers from 0.7 to 1. A buoyancy Strouhal number is used to correlate the high Richardson number frequency behavior.

Modeling fecal bacteria transport and retention in agricultural and urban soils under saturated and unsaturated flow conditions.

PubMed

Balkhair, Khaled S

2017-03-01

Pathogenic bacteria, that enter surface water bodies and groundwater systems through unmanaged wastewater land application, pose a great risk to human health. In this study, six soil column experiments were conducted to simulate the vulnerability of agricultural and urban field soils for fecal bacteria transport and retention under saturated and unsaturated flow conditions. HYDRUS-1D kinetic attachment and kinetic attachment-detachment models were used to simulate the breakthrough curves of the experimental data by fitting model parameters. Results indicated significant differences in the retention and drainage of bacteria between saturated and unsaturated flow condition in the two studied soils. Flow under unsaturated condition retained more bacteria than the saturated flow case. The high bacteria retention in the urban soil compared to agricultural soil is ascribed not only to the dynamic attachment and sorption mechanisms but also to the greater surface area of fine particles and low flow rate. All models simulated experimental data satisfactorily under saturated flow conditions; however, under variably saturated flow, the peak concentrations were overestimated by the attachment-detachment model and underestimated by the attachment model with blocking. The good match between observed data and simulated concentrations by the attachment model which was supported by the Akaike information criterion (AIC) for model selection indicates that the first-order attachment coefficient was sufficient to represent the quantitative and temporal distribution of bacteria in the soil column. On the other hand, the total mass balance of the drained and retained bacteria in all transport experiments was in the range of values commonly found in the literature. Regardless of flow conditions and soil texture, most of the bacteria were retained in the top 12 cm of the soil column. The approaches and the models used in this study have proven to be a good tool for simulating fecal bacteria transport under a variety of initial and boundary flow conditions, hence providing a better understanding of the transport mechanism of bacteria as well as soil removal efficiency. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ensemble urban flood simulation in comparison with laboratory-scale experiments: Impact of interaction models for manhole, sewer pipe, and surface flow

NASA Astrophysics Data System (ADS)

Noh, Seong Jin; Lee, Seungsoo; An, Hyunuk; Kawaike, Kenji; Nakagawa, Hajime

2016-11-01

An urban flood is an integrated phenomenon that is affected by various uncertainty sources such as input forcing, model parameters, complex geometry, and exchanges of flow among different domains in surfaces and subsurfaces. Despite considerable advances in urban flood modeling techniques, limited knowledge is currently available with regard to the impact of dynamic interaction among different flow domains on urban floods. In this paper, an ensemble method for urban flood modeling is presented to consider the parameter uncertainty of interaction models among a manhole, a sewer pipe, and surface flow. Laboratory-scale experiments on urban flood and inundation are performed under various flow conditions to investigate the parameter uncertainty of interaction models. The results show that ensemble simulation using interaction models based on weir and orifice formulas reproduces experimental data with high accuracy and detects the identifiability of model parameters. Among interaction-related parameters, the parameters of the sewer-manhole interaction show lower uncertainty than those of the sewer-surface interaction. Experimental data obtained under unsteady-state conditions are more informative than those obtained under steady-state conditions to assess the parameter uncertainty of interaction models. Although the optimal parameters vary according to the flow conditions, the difference is marginal. Simulation results also confirm the capability of the interaction models and the potential of the ensemble-based approaches to facilitate urban flood simulation.

Hyporheic hot moments: Dissolved oxygen dynamics in the hyporheic zone in response to surface flow perturbations

NASA Astrophysics Data System (ADS)

Kaufman, Matthew H.; Cardenas, M. Bayani; Buttles, Jim; Kessler, Adam J.; Cook, Perran L. M.

2017-08-01

Dissolved oxygen (DO) is a key environmental variable that drives and feeds back with numerous processes. In the aquatic sediment that makes up the hyporheic zone, DO may exhibit pronounced spatial gradients and complex patterns which control the distribution of a series of redox processes. Yet, little is known regarding the dynamics of hyporheic zone DO, especially under transitional flow regimes. Considering the natural tendency of rivers to be highly responsive to external forcing, these temporal dynamics are potentially just as important and pronounced as the spatial gradients. Here we use laboratory flume experiments and multiphysics flow and reactive transport modeling to investigate surface flow controls on the depth of oxygen penetration in the bed as well as the area of oxygenated sediment. We show that the hyporheic zone DO conditions respond over time scales of hours-to-days when subjected to practically instantaneous surface flow perturbations. Additionally, the flume experiments demonstrate that hyporheic zone DO conditions respond faster to surface flow acceleration than to deceleration. Finally, we found that the morphology of the dissolved oxygen plume front depends on surface flow acceleration or deceleration. This study thus shows that the highly dynamic nature of typical streams and rivers drives equally dynamic redox conditions in the hyporheic zone. Because the redox conditions and their distribution within the hyporheic zone are important from biological, ecological, and contaminant perspectives, this hyporheic redox dynamism has the potential to impact system scale aquatic chemical cycles.

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal, Ajay K.; Parthasarathy, Ramkumar

2004-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique suited for the microgravity environment. The flow structure was characterized by distributions of helium mole fraction obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. Experiments reveal that the global flow oscillations observed in Earth gravity are absent in microgravity. The report provides quantitative details of flow evolution as the experiment undergoes change in gravity in the drop tower.

Physical Limits on the Predictability of Erosion and Sediment Transport by Landslides and Debris Flows

NASA Astrophysics Data System (ADS)

Iverson, R. M.

2015-12-01

Episodic landslides and debris flows play a key role in sculpting many steep landscapes, and they also pose significant natural hazards. Field evidence, laboratory experiments, and theoretical analyses show that variations in the quantity, speed, and distance of sediment transport by landslides and debris flows can depend strongly on nuanced differences in initial conditions. Moreover, initial conditions themselves can be strongly dependent on the geological legacy of prior events. The scope of these dependencies is revealed by the results of landslide dynamics experiments [Iverson et al., Science, 2000], debris-flow erosion experiments [Iverson et al., Nature Geosci., 2011], and numerical simulations of the highly destructive 2014 Oso, Washington, landslide [Iverson et al., Earth Planet. Sci. Let., 2015]. In each of these cases, feedbacks between basal sediment deformation and pore-pressure generation cause the speed and distance of sediment transport to be very sensitive to subtle differences in the ambient sediment porosity and water content. On the other hand, the onset of most landslides and debris flows depends largely on pore-water pressure distributions and only indirectly on sediment porosity and water content. Thus, even if perfect predictions of the locations and timing of landslides and debris flows were available, the dynamics of the events - and their consequent hazards and sediment transport - would be difficult to predict. This difficulty is a manifestation of the nonlinear physics involved, rather than of poor understanding of those physics. Consequently, physically based models for assessing the hazards and sediment transport due to landslides and debris flows must take into account both evolving nonlinear dynamics and inherent uncertainties about initial conditions. By contrast, landscape evolution models that use prescribed algebraic formulas to represent sediment transport by landslides and debris flows lack a sound physical basis.

Real-Time Optical Monitoring of Flow Kinetics and Gas Phase Reactions Under High-Pressure OMCVD Conditions

NASA Technical Reports Server (NTRS)

Dietz, N.; McCall, S.; Bachmann, K. J.

2001-01-01

This contribution addresses the real-time optical characterization of gas flow and gas phase reactions as they play a crucial role for chemical vapor phase depositions utilizing elevated and high pressure chemical vapor deposition (HPCVD) conditions. The objectives of these experiments are to validate on the basis of results on real-time optical diagnostics process models simulation codes, and provide input parameter sets needed for analysis and control of chemical vapor deposition at elevated pressures. Access to microgravity is required to retain high pressure conditions of laminar flow, which is essential for successful acquisition and interpretation of the optical data. In this contribution, we describe the design and construction of the HPCVD system, which include access ports for various optical methods of real-time process monitoring and to analyze the initial stages of heteroepitaxy and steady-state growth in the different pressure ranges. To analyze the onset of turbulence, provisions are made for implementation of experimental methods for in-situ characterization of the nature of flow. This knowledge will be the basis for the design definition of experiments under microgravity, where gas flow conditions, gas phase and surface chemistry, might be analyzed by remote controlled real-time diagnostics tools, developed in this research project.

Rolling with the flow: bumblebees flying in unsteady wakes.

PubMed

Ravi, Sridhar; Crall, James D; Fisher, Alex; Combes, Stacey A

2013-11-15

Our understanding of how variable wind in natural environments affects flying insects is limited because most studies of insect flight are conducted in either smooth flow or still air conditions. Here, we investigate the effects of structured, unsteady flow (the von Karman vortex street behind a cylinder) on the flight performance of bumblebees (Bombus impatiens). Bumblebees are 'all-weather' foragers and thus frequently experience variable aerial conditions, ranging from fully mixed, turbulent flow to unsteady, structured vortices near objects such as branches and stems. We examined how bumblebee flight performance differs in unsteady versus smooth flow, as well as how the orientation of unsteady flow structures affects their flight performance, by filming bumblebees flying in a wind tunnel under various flow conditions. The three-dimensional flight trajectories and orientations of bumblebees were quantified in each of three flow conditions: (1) smooth flow, (2) the unsteady wake of a vertical cylinder (inducing strong lateral disturbances) and (3) the unsteady wake of a horizontal cylinder (inducing strong vertical disturbances). In both unsteady conditions, bumblebees attenuated the disturbances induced by the wind quite effectively, but still experienced significant translational and rotational fluctuations as compared with flight in smooth flow. Bees appeared to be most sensitive to disturbance along the lateral axis, displaying large lateral accelerations, translations and rolling motions in response to both unsteady flow conditions, regardless of orientation. Bees also displayed the greatest agility around the roll axis, initiating voluntary casting maneuvers and correcting for lateral disturbances mainly through roll in all flow conditions. Both unsteady flow conditions reduced the upstream flight speed of bees, suggesting an increased cost of flight in unsteady flow, with potential implications for foraging patterns and colony energetics in natural, variable wind environments.

Load-Flow in Multiphase Distribution Networks: Existence, Uniqueness, Non-Singularity, and Linear Models

DOE PAGES

Bernstein, Andrey; Wang, Cong; Dall'Anese, Emiliano; ...

2018-01-01

This paper considers unbalanced multiphase distribution systems with generic topology and different load models, and extends the Z-bus iterative load-flow algorithm based on a fixed-point interpretation of the AC load-flow equations. Explicit conditions for existence and uniqueness of load-flow solutions are presented. These conditions also guarantee convergence of the load-flow algorithm to the unique solution. The proposed methodology is applicable to generic systems featuring (i) wye connections; (ii) ungrounded delta connections; (iii) a combination of wye-connected and delta-connected sources/loads; and, (iv) a combination of line-to-line and line-to-grounded-neutral devices at the secondary of distribution transformers. Further, a sufficient condition for themore » non-singularity of the load-flow Jacobian is proposed. Finally, linear load-flow models are derived, and their approximation accuracy is analyzed. Theoretical results are corroborated through experiments on IEEE test feeders.« less

Load-Flow in Multiphase Distribution Networks: Existence, Uniqueness, Non-Singularity, and Linear Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernstein, Andrey; Wang, Cong; Dall'Anese, Emiliano

This paper considers unbalanced multiphase distribution systems with generic topology and different load models, and extends the Z-bus iterative load-flow algorithm based on a fixed-point interpretation of the AC load-flow equations. Explicit conditions for existence and uniqueness of load-flow solutions are presented. These conditions also guarantee convergence of the load-flow algorithm to the unique solution. The proposed methodology is applicable to generic systems featuring (i) wye connections; (ii) ungrounded delta connections; (iii) a combination of wye-connected and delta-connected sources/loads; and, (iv) a combination of line-to-line and line-to-grounded-neutral devices at the secondary of distribution transformers. Further, a sufficient condition for themore » non-singularity of the load-flow Jacobian is proposed. Finally, linear load-flow models are derived, and their approximation accuracy is analyzed. Theoretical results are corroborated through experiments on IEEE test feeders.« less

CFD validation experiments for hypersonic flows

NASA Technical Reports Server (NTRS)

Marvin, Joseph G.

1992-01-01

A roadmap for CFD code validation is introduced. The elements of the roadmap are consistent with air-breathing vehicle design requirements and related to the important flow path components: forebody, inlet, combustor, and nozzle. Building block and benchmark validation experiments are identified along with their test conditions and measurements. Based on an evaluation criteria, recommendations for an initial CFD validation data base are given and gaps identified where future experiments could provide new validation data.

Assessment of CFD Estimation of Aerodynamic Characteristics of Basic Reusable Rocket Configurations

NASA Astrophysics Data System (ADS)

Fujimoto, Keiichiro; Fujii, Kozo

Flow-fields around the basic SSTO-rocket configurations are numerically simulated by the Reynolds-averaged Navier-Stokes (RANS) computations. Simulations of the Apollo-like configuration is first carried out, where the results are compared with NASA experiments and the prediction ability of the RANS simulation is discussed. The angle of attack of the freestream ranges from 0° to 180° and the freestream Mach number ranges from 0.7 to 2.0. Computed aerodynamic coefficients for the Apollo-like configuration agree well with the experiments under a wide range of flow conditions. The flow simulations around the slender Apollo-type configuration are carried out next and the results are compared with the experiments. Computed aerodynamic coefficients also agree well with the experiments. Flow-fields are dominated by the three-dimensional massively separated flow, which should be captured for accurate aerodynamic prediction. Grid refinement effects on the computed aerodynamic coefficients are investigated comprehensively.

Multi-phase imaging of intermittency at steady state using differential imaging method by X-ray micro-tomography

NASA Astrophysics Data System (ADS)

Gao, Y.; Lin, Q.; Bijeljic, B.; Blunt, M. J.

2017-12-01

To observe intermittency in consolidated rock, we image a steady state flow of brine and decane in Bentheimer sandstone. We devise an experimental method based on X-ray differential imaging method to examine how changes in flow rate impact the pore-scale distribution of fluids during co-injection flow under dynamic flow conditions at steady state. This helps us elucidate the diverse flow regimes (connected, intermittent break-up, or continual break-up of the non-wetting phase pathways) for two capillary numbers. Also, relative permeability curves under both capillary and viscous limited conditions could be measured. We have performed imbibition sample floods using oil-brine and measured steady state relative permeability on a sandstone rock core in order to fully characterize the flow behaviour at low and high Ca. Two sets of experiments at high and low flow rates are provided to explore the time-evolution of the non-wetting phase clusters distribution under different flow conditions. The high flow rate is 0.5 mL/min, whose corresponding capillary number is 7.7×10-6. The low flow rate is 0.02 mL/min, whose capillary number is 3.1×10-7. A procedure based on using high-salinity brine as the contrast phase and applying differential imaging between the dry scan and that of the sample saturation with a 30 wt% Potassium iodide (KI) doped brine help to make sure there is no non-wetting phase in micro-pores. Then the intermittent phase in multiphase flow image at high Ca can be quantified by obtaining the differential image between the 30 wt% KI brine image and the scans that taken at each fixed fractional flow. By using the grey scale histogram distribution of the raw images at each condition, the oil proportion in the intermittent phase can be calculated. The pressure drops at each fractional flow at low and high Ca can be measured by high-precision pressure differential sensors and utilized to calculate to the relative permeability at pore scale. The relative permeability data and fw-Sw relationship obtained by our experiment at pore scale are compared with the data collected from experiments which were conducted at core scale, and they match well.

Continuous Flow Science in an Undergraduate Teaching Laboratory: Bleach-Mediated Oxidation in a Biphasic System

ERIC Educational Resources Information Center

Kairouz, Vanessa; Collins, Shawn K.

2018-01-01

An undergraduate teaching laboratory experiment involving a continuous flow, bleach-mediated oxidation of aldehydes under biphasic conditions was developed that allowed students to explore concepts of mixing or mass transport, solvent sustainability, biphasic reactions, phase transfer catalysis, and continuous flow chemistry.

Validation of Multi-Dimensional Stirling Engine Design Codes: Measurements in the 90-Degree Turn Test Section

NASA Technical Reports Server (NTRS)

Simon, Terrence W.; Adolfson, David

2006-01-01

The work to be presented herein was motivated largely by a desire to improve the understanding of oscillatory fluid mechanics inside a Stirling engine. To this end, a CFD project was undertaken at Cleveland State University with the goal of accurately predicting the fluid dynamics within an engine or engine component. Along with the CFD efforts, a code validation project was undertaken at the University of Minnesota. The material covered herein consists of four main parts. In section 1, an experimental investigation of a small aspect ratio impinging jet is discussed. Included in this discussion is a description of the test facilities and instrumentation. A presentation of the collected data is given and comments are made. Next, in section 2, a parallel experimental investigation is presented in which the same geometry as that of section 1 is used, but the flow conditions are changed from steady unidirectional flow to sinusoidally oscillating flow. In section Two, collected data are presented and comments are made. In section 3, a comparison is made between the results of sections 1 and 2, namely, sinusoidally oscillating flow results are compared to steady, unidirectional flow results from the same geometry. Finally, in section 4, a comparison is made between experimentally collected data (the main subject of this work) and CFD generated results. Furthermore, in appendix A, an introductory description of the primary measurement tool used in the experimental process the hot wire anemometer is given for the unfamiliar. The anemometer calibration procedure is described in appendix B. A portfolio of data reduction and data processing codes is provided in appendix C and lastly, a DVD and a roadmap of its contents is provided in an appendix D. 1.0 Unidirectional Flow Investigations 1.1 Introduction This unidirectional experimental program was undertaken to complement an oscillatory flow investigation conducted at the University of Minnesota. The oscillatory investigation is discussed thoroughly in section 2. We defer the description of the motivation behind these experiments until the introduction of section 2. The work that is discussed in this thesis began (chronologically) with oscillatory flow visualization experiments. It was decided that it would be valuable and important to investigate the flow under unidirectional conditions in the same geometry as that of the oscillatory experiments. The thought was that the unidirectional case would be less complicated to model with a CFD program (a moving boundary would be replaced with a steady state boundary condition). Thus, a series of unidirectional experiments were carried out to capture the important features of the flow within the test section. The purpose of these experiments was to provide a data set for comparison to CFD generated velocity fields. Hot-wire anemometry data were taken and flow visualization was conducted as a standard for code validation. The flow geometry was simple, such that it could be easily gridded in a CFD program. However, the geometry provided separation and transition zones, shear layers and recirculation zones. These characteristics made the flow complex and challenging for CFD computation. We comment that the order of experiments that produced this report is as follows: experimental flow visualization under oscillatory flow conditions was carried out; this was followed by unidirectional flow visualization and hot wire anemometry; finally, oscillatory hot wire anemometry was conducted. We present the results out of chronological order for the following reason: the unidirectional results are easier

Experimental Recreation of Large-Scale Coastal Bedforms and Hummocky Cross-Stratification in Sheet Flow Conditions

NASA Astrophysics Data System (ADS)

Vermaas, T.; Kleinhans, M. G.; Huisman, C.; Schretlen, J. L.; van der Werf, J. J.; Ribberink, J. S.; Ruessink, G.

2010-12-01

In shallow marine environments various types of large bed forms emerge under waves and currents. There is no consensus on whether and how these bedforms can be classified in a genetically meaningful sense. Hypotheses for their genesis vary from a large variety of causal mechanisms for a number of different ripples to a single growing instability mechanism, reflecting a limited understanding. Our objective is to understand the formative mechanism of a family of large bedforms referred to as Large Wave Ripples in coastal literature and Hummocks in sedimentological literature, which also describes the hummocky cross stratification (HCS) found in the sedimentary rock record. The formative conditions for hummocks have been debated extensively, particularly whether currents or specific particle sizes were required. We collected and compared existing field and laboratory data and we conducted a full scale experiment in the Hannover Grosse Welle wave flume (300 m long, 5 m wide and 7 m deep). Experiments were done for several conditions, including a storm sequence, with 0.7-1.7 m regular trochoidal waves or irregular waves with periods of 5-7.5 s over sand with mean particle sizes of 0.256 (in 2007) or 0.137 mm (in 2008). Bed profiles were collected mechanically and acoustically. A conductivity probe (CCM) was used to measure sheet flow thickness or absence and near-bed flow and suspended sand concentrations were measured in detail with acoustical profilers. From the data collection, we found that there is no distinction empirically between LWR and Hummocks. Both are found around the inception of sheet flow and have the same dimensions. In the experiments we produced short wave ripples superimposed on large wave ripples below and in the transition to sheet flow conditions. The SWR were well predicted by a recent particle-size dependent ripple length predictor. No available predictor matched the LWR dimensions. The LWR remained present in strong sheet flow conditions and migrated slowly in the direction of wave advance due to wave asymmetry. LWR height was less than 0.07 m whilst lengths were about 13 m. Despite the sheet flow conditions and fine sediment, the LWR scaled as orbital ripples though a factor of 2 longer (i.e. with the orbital diameter d = uT/pi with u the orbital velocity amplitude and T the wave period). Laquer peels of the 2007 experiment demonstrated that the LWR formed Hummocky Cross-Stratification. We conclude that hummocks were experimentally created in a full-scale facility during sheet flow conditions without currents. Furthermore, LWR and hummocks are the same features.

Application of Heterogeneous Copper Catalyst in a Continuous Flow Process: Dehydrogenation of Cyclohexanol

ERIC Educational Resources Information Center

Glin´ski, Marek; Ulkowska, Urszula; Iwanek, Ewa

2016-01-01

In this laboratory experiment, the synthesis of a supported solid catalyst (Cu/SiO2) and its application in the dehydrogenation of cyclohexanol performed under flow conditions was studied. The experiment was planned for a group of two or three students for two 6 h long sessions. The copper catalyst was synthesized using incipient wetness…

A comparative modeling study of a dual tracer experiment in a large lysimeter under atmospheric conditions

NASA Astrophysics Data System (ADS)

Stumpp, C.; Nützmann, G.; Maciejewski, S.; Maloszewski, P.

2009-09-01

SummaryIn this paper, five model approaches with different physical and mathematical concepts varying in their model complexity and requirements were applied to identify the transport processes in the unsaturated zone. The applicability of these model approaches were compared and evaluated investigating two tracer breakthrough curves (bromide, deuterium) in a cropped, free-draining lysimeter experiment under natural atmospheric boundary conditions. The data set consisted of time series of water balance, depth resolved water contents, pressure heads and resident concentrations measured during 800 days. The tracer transport parameters were determined using a simple stochastic (stream tube model), three lumped parameter (constant water content model, multi-flow dispersion model, variable flow dispersion model) and a transient model approach. All of them were able to fit the tracer breakthrough curves. The identified transport parameters of each model approach were compared. Despite the differing physical and mathematical concepts the resulting parameters (mean water contents, mean water flux, dispersivities) of the five model approaches were all in the same range. The results indicate that the flow processes are also describable assuming steady state conditions. Homogeneous matrix flow is dominant and a small pore volume with enhanced flow velocities near saturation was identified with variable saturation flow and transport approach. The multi-flow dispersion model also identified preferential flow and additionally suggested a third less mobile flow component. Due to high fitting accuracy and parameter similarity all model approaches indicated reliable results.

Online monitoring of a photocatalytic reaction by real-time high resolution FlowNMR spectroscopy.

PubMed

Hall, Andrew M R; Broomfield-Tagg, Rachael; Camilleri, Matthew; Carbery, David R; Codina, Anna; Whittaker, David T E; Coombes, Steven; Lowe, John P; Hintermair, Ulrich

2017-12-19

We demonstrate how FlowNMR spectroscopy can readily be applied to investigate photochemical reactions that require sustained input of light and air to yield mechanistic insight under realistic conditions. The Eosin Y mediated photo-oxidation of N-allylbenzylamine is shown to produce imines as primary reaction products from which undesired aldehydes form after longer reaction times. Facile variation of reaction conditions during the reaction in flow allows for probe experiments that give information about the mode of action of the photocatalyst.

The Flow of Energy

NASA Astrophysics Data System (ADS)

Znidarsic, F.; Robertson, G. A.

In this paper, the flow of energy in materials is presented as mechanical waves with a distinct velocity or speed of transition. This speed of transition came about through the observations of cold fusion experiments, i.e., Low Energy Nuclear Reactions (LENR) and superconductor gravity experiments, both assumed speculative by mainstream science. In consideration of superconductor junctions, the LENR experiments have a similar speed of transition, which seems to imply that the reactions in the LENR experiment are discrete quantized reactions (energy - burst vs. continuous). Here an attempt is made to quantify this new condition as it applies to electrons; toward the progression of quantized energy flows (discrete energy burst) as a new source of clean energy and force mechanisms (i.e, propulsion).

Biofilm growth in porous media: Experiments, computational modeling at the porescale, and upscaling

NASA Astrophysics Data System (ADS)

Peszynska, Malgorzata; Trykozko, Anna; Iltis, Gabriel; Schlueter, Steffen; Wildenschild, Dorthe

2016-09-01

Biofilm growth changes many physical properties of porous media such as porosity, permeability and mass transport parameters. The growth depends on various environmental conditions, and in particular, on flow rates. Modeling the evolution of such properties is difficult both at the porescale where the phase morphology can be distinguished, as well as during upscaling to the corescale effective properties. Experimental data on biofilm growth is also limited because its collection can interfere with the growth, while imaging itself presents challenges. In this paper we combine insight from imaging, experiments, and numerical simulations and visualization. The experimental dataset is based on glass beads domain inoculated by biomass which is subjected to various flow conditions promoting the growth of biomass and the appearance of a biofilm phase. The domain is imaged and the imaging data is used directly by a computational model for flow and transport. The results of the computational flow model are upscaled to produce conductivities which compare well with the experimentally obtained hydraulic properties of the medium. The flow model is also coupled to a newly developed biomass-nutrient growth model, and the model reproduces morphologies qualitatively similar to those observed in the experiment.

Impact of water flow conditions on the fate of ammonium and nitrate at the interface of the unsaturated and saturated zone

NASA Astrophysics Data System (ADS)

Glöckler, David; Gassen, Niklas; Stumpp, Christine

2017-04-01

Elevated nitrate concentrations in groundwater have caused severe environmental issues in the last decades. Mitigation strategies need to be developed to reduce the amount of nitrate without reducing crop yield though. Therefore, we need to understand nitrogen turnover processes and how they are influenced by hydrogeochemical conditions in the unsaturated and saturated zone. The objective of this study was to investigate the influence of flow conditions on transport processes and the fate of ammonium and nitrate released from slurry application. Experiments were conducted under controlled conditions in an aquifer model setup (1.1 x 0.6 x 0.2 m3). A diluted slurry mix was injected continuously. The inorganic nitrogen compounds were traced under different water regimes regarding recharge rates and water table position (steady-state, transient and stagnant flow conditions). Conservative tracers and mathematical modeling were used to identify water flow and transport. Spatiotemporal changes of dissolved oxygen, ammonium, nitrite, nitrate, dissolved organic carbon and matrix potential were identified through high resolution monitoring (0.05 m). The ecosystem immediately responded to the slurry application with enhanced microbial respiration and the first step of nitrification converting ammonium to nitrite. This process was dominating during the first ten days of the experiment. A complete nitrification was established after 20 days resulting in increasing nitrate concentrations. Less nitrate was measured below the water table during steady state flow conditions in contrast to transient conditions with a fluctuating water table which seemed to inhibit denitrification. Still denitrification was not the dominating process despite high concentration of dissolved organic carbon (4-20 mg/L). Even under stagnant flow conditions, nitrate stayed in the system and denitrification was limited. Anoxic conditions were not established due to the low bioavailability of the dissolved organic carbon. The results highlight the substantial impact of slurry application on groundwater quality for all tested hydrological scenarios.

Upward flow of supercritical CO2 with transition to gaseous conditions: Simulations for design of large-scale CO2 flow experiments at LUCI

NASA Astrophysics Data System (ADS)

Oldenburg, C. M.; Peters, C. A.; Dobson, P. F.; Doughty, C.

2010-12-01

Understanding the processes involved in large-scale upward flow of CO2 related to Geologic Carbon Sequestration (GCS) is critical to evaluating trapping mechanisms and potential impacts of CO2 leakage over long distances. The Laboratory for Underground CO2 Investigations (LUCI) is being planned to be built at DUSEL to host large-scale vertical CO2 and brine flow experiments. As conceived, LUCI would consist of a 500 m-long vertical raisebore approximately 3 m in diameter which will contain three suspended long-column pressure vessels. The long-column pressure vessels are planned to be 1 m in diameter with thermal control on the outer walls with a centralized inner fiberglass well for accommodating monitoring tools for determining phase saturation, porosity, temperature, and other properties of the flow region. The outer wall of the inner fiberglass well and the inner wall of the main vessel comprise the lateral boundaries of the long vertical annular regions that will be filled with porous media in which experiments investigating flow and transport, geochemical alterations of well cement, and biological processes involving injected CO2 will be performed. The large vertical extent of the column is needed to span the full range of CO2 conditions from supercritical (scCO2, P > 7.4 MPa, T > 31 °C) to gaseous CO2 that is believed to be significant as CO2 flows upwards. Here we consider the CO2-brine flow experiments in which the annular region will be pressurized at the top and bottom and contain brine-filled porous media through which scCO2 introduced at the bottom will flow upward. We are carrying out two-phase flow simulations of the buoyancy- and pressure-driven flow of CO2 and brine upward in the annular porous media region to further design the flow columns, e.g., to determine critical length and diameter requirements, as well as to plan the experiments to be performed. The simulations are carried out using TOUGH2/ECO2N, which models two-phase non-isothermal flow and transport of water, CO2, and NaCl in porous media. To treat important issues of drainage and imbibition at the leading and trailing edges of the CO2 slug, we employ hysteretic relative permeability functions. Simulation results will be presented showing flow rate, saturation, and temperature dependence on permeability, relative permeability parameters, size of initial CO2 slug, imposed upward flow rate, and different side boundary conditions (e.g., fully insulated and temperature equal to a constant geothermal gradient).

Thin-layer approximation and algebraic model for separated turbulent flows

NASA Technical Reports Server (NTRS)

Baldwin, B.; Lomax, H.

1978-01-01

An algebraic turbulence model for two- and three-dimensional separated flows is specified that avoids the necessity for finding the edge of the boundary layer. Properties of the model are determined and comparisons made with experiment for an incident shock on a flat plate, separated flow over a compression corner, and transonic flow over an airfoil. Separation and reattachment points from numerical Navier-Stokes solutions agree with experiment within one boundary-layer thickness. Use of law-of-the-wall boundary conditions does not alter the predictions significantly. Applications of the model to other cases are contained in companion papers.

Capillary Flow Experiment in Node 2

NASA Image and Video Library

2013-06-15

Astronaut Karen Nyberg,Expedition 36 flight engineer,works on the Capillary Flow Experiment (CFE) Vane Gap-1 (VG-1) setup in the Node 2/Harmony. The CFE-2 vessel is used to observe fluid interface and critical wetting behavior in a cylindrical chamber with elliptic cross-section and an adjustable central perforated vane. The primary objective of the Vane Gap experiments is to determine equilibrium interface configurations and critical wetting conditions for interfaces between interior corners separated by a gap.

Shear Wave Wavefront Mapping Using Ultrasound Color Flow Imaging.

PubMed

Yamakoshi, Yoshiki; Kasahara, Toshihiro; Iijima, Tomohiro; Yuminaka, Yasushi

2015-10-01

A wavefront reconstruction method for a continuous shear wave is proposed. The method uses ultrasound color flow imaging (CFI) to detect the shear wave's wavefront. When the shear wave vibration frequency satisfies the required frequency condition and the displacement amplitude satisfies the displacement amplitude condition, zero and maximum flow velocities appear at the shear wave vibration phases of zero and π rad, respectively. These specific flow velocities produce the shear wave's wavefront map in CFI. An important feature of this method is that the shear wave propagation is observed in real time without addition of extra functions to the ultrasound imaging system. The experiments are performed using a 6.5 MHz CFI system. The shear wave is excited by a multilayer piezoelectric actuator. In a phantom experiment, the shear wave velocities estimated using the proposed method and those estimated using a system based on displacement measurement show good agreement. © The Author(s) 2015.

Transient behavior of granular materials with symmetric conditions for tumbler shapes and fill fractions

NASA Astrophysics Data System (ADS)

Pohlman, Nicholas; Si, Yun

2014-11-01

The typical granular motion in circular tumblers is considered steady-state since there are no features to disrupt the top surface layer dimension. In polygon tumblers, however, the flowing layer is perpetually changing length, which creates unsteady conditions with corresponding change in the flow behavior. Prior work showed the minimization of free surface energy is independent of tumbler dimension, particle size, and rotation rate. This subsequent research reports on experiments where dimensional symmetry of the free surface in triangular and square tumblers with varying fill fractions do not necessarily produce the symmetric flow behaviors. Results of the quasi-2D tumbler experiment show that other dimensions aligned with gravity and the instantaneous free surface influence the phase when extrema for angle of repose and other flow features occur. The conclusion is that 50% fill fraction may produce geometric symmetry of dimensions, but the symmetry point of flow likely occurs at a lower fill fraction.

Skills-demands compatibility as a determinant of flow experience in an inductive reasoning task.

PubMed

Schiefele, Ulrich; Raabe, Andreas

2011-10-01

The skills-demands fit hypothesis of flow theory was examined. Based on the earlier finding that high demands in a game situation do not reduce the experience of flow, a cognitive task paradigm was used. The effect of skills-demands compatibility on the experience of flow but not of other, similar psychological states (i.e., concentration, negative and positive activation) was also investigated. Participants were 89 undergraduate students who worked on a number of inductive reasoning tasks in four successive trials with or without skills-demands compatibility. The results clearly supported the skills-demands fit hypothesis; concentration and activation were affected only by the tasks' difficulty. Inductive reasoning tasks are a useful tool for the experimental analysis of flow, and skills-demands compatibility is a significant and powerful condition of flow, but not of other, similar psychological states.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Y.; Huang, L. H.; Yang, F. P. Y.

The present study analytically reinvestigates the two-dimensional lift-up problem for a rigid porous bed that was studied by Mei, Yeung, and Liu [“Lifting of a large object from a porous seabed,” J. Fluid Mech. 152, 203 (1985)]. Mei, Yeung, and Liu proposed a model that treats the bed as a rigid porous medium and performed relevant experiments. In their model, they assumed the gap flow comes from the periphery of the gap, and there is a shear layer in the porous medium; the flow in the gap is described by adhesion approximation [D. J. Acheson, Elementary Fluid Dynamics (Clarendon, Oxford,more » 1990), pp. 243-245.] and the pore flow by Darcy’s law, and the slip-flow condition proposed by Beavers and Joseph [“Boundary conditions at a naturally permeable wall,” J. Fluid Mech. 30, 197 (1967)] is applied to the bed interface. In this problem, however, the gap flow initially mainly comes from the porous bed, and the shear layer may not exist. Although later the shear effect becomes important, the empirical slip-flow condition might not physically respond to the shear effect, and the existence of the vertical velocity affects the situation so greatly that the slip-flow condition might not be appropriate. In contrast, the present study proposes a more general model for the problem, applying Stokes flow to the gap, the Brinkman equation to the porous medium, and Song and Huang’s [“Laminar poroelastic media flow,” J. Eng. Mech. 126, 358 (2000)] complete interfacial conditions to the bed interface. The exact solution to the problem is found and fits Mei’s experiments well. The breakout phenomenon is examined for different soil beds, mechanics that cannot be illustrated by Mei’s model are revealed, and the theoretical breakout times obtained using Mei’s model and our model are compared. The results show that the proposed model is more compatible with physics and provides results that are more precise.« less

Two-dimensional lift-up problem for a rigid porous bed

NASA Astrophysics Data System (ADS)

Chang, Y.; Huang, L. H.; Yang, F. P. Y.

2015-05-01

The present study analytically reinvestigates the two-dimensional lift-up problem for a rigid porous bed that was studied by Mei, Yeung, and Liu ["Lifting of a large object from a porous seabed," J. Fluid Mech. 152, 203 (1985)]. Mei, Yeung, and Liu proposed a model that treats the bed as a rigid porous medium and performed relevant experiments. In their model, they assumed the gap flow comes from the periphery of the gap, and there is a shear layer in the porous medium; the flow in the gap is described by adhesion approximation [D. J. Acheson, Elementary Fluid Dynamics (Clarendon, Oxford, 1990), pp. 243-245.] and the pore flow by Darcy's law, and the slip-flow condition proposed by Beavers and Joseph ["Boundary conditions at a naturally permeable wall," J. Fluid Mech. 30, 197 (1967)] is applied to the bed interface. In this problem, however, the gap flow initially mainly comes from the porous bed, and the shear layer may not exist. Although later the shear effect becomes important, the empirical slip-flow condition might not physically respond to the shear effect, and the existence of the vertical velocity affects the situation so greatly that the slip-flow condition might not be appropriate. In contrast, the present study proposes a more general model for the problem, applying Stokes flow to the gap, the Brinkman equation to the porous medium, and Song and Huang's ["Laminar poroelastic media flow," J. Eng. Mech. 126, 358 (2000)] complete interfacial conditions to the bed interface. The exact solution to the problem is found and fits Mei's experiments well. The breakout phenomenon is examined for different soil beds, mechanics that cannot be illustrated by Mei's model are revealed, and the theoretical breakout times obtained using Mei's model and our model are compared. The results show that the proposed model is more compatible with physics and provides results that are more precise.

A High Performance Pulsatile Pump for Aortic Flow Experiments in 3-Dimensional Models.

PubMed

Chaudhury, Rafeed A; Atlasman, Victor; Pathangey, Girish; Pracht, Nicholas; Adrian, Ronald J; Frakes, David H

2016-06-01

Aortic pathologies such as coarctation, dissection, and aneurysm represent a particularly emergent class of cardiovascular diseases. Computational simulations of aortic flows are growing increasingly important as tools for gaining understanding of these pathologies, as well as for planning their surgical repair. In vitro experiments are required to validate the simulations against real world data, and the experiments require a pulsatile flow pump system that can provide physiologic flow conditions characteristic of the aorta. We designed a newly capable piston-based pulsatile flow pump system that can generate high volume flow rates (850 mL/s), replicate physiologic waveforms, and pump high viscosity fluids against large impedances. The system is also compatible with a broad range of fluid types, and is operable in magnetic resonance imaging environments. Performance of the system was validated using image processing-based analysis of piston motion as well as particle image velocimetry. The new system represents a more capable pumping solution for aortic flow experiments than other available designs, and can be manufactured at a relatively low cost.

A Novel True Triaxial Apparatus to Study the Geomechanical and Fluid Flow Aspects of Energy Exploitations in Geological Formations

NASA Astrophysics Data System (ADS)

Li, Minghui; Yin, Guangzhi; Xu, Jiang; Li, Wenpu; Song, Zhenlong; Jiang, Changbao

2016-12-01

Fluid-solid coupling investigations of the geological storage of CO2, efficient unconventional oil and natural gas exploitations are mostly conducted under conventional triaxial stress conditions ( σ 2 = σ 3), ignoring the effects of σ 2 on the geomechanical properties and permeability of rocks (shale, coal and sandstone). A novel multi-functional true triaxial geophysical (TTG) apparatus was designed, fabricated, calibrated and tested to simulate true triaxial stress ( σ 1 > σ 2 > σ 3) conditions and to reveal geomechanical properties and permeability evolutions of rocks. The apparatus was developed with the capacity to carry out geomechanical and fluid flow experiments at high three-dimensional loading forces and injection pressures under true triaxial stress conditions. The control and measurement of the fluid flow with effective sealing of rock specimen corners were achieved using a specially designed internally sealed fluid flow system. To validate that the apparatus works properly and to recognize the effects of each principal stress on rock deformation and permeability, stress-strain and permeability experiments and a hydraulic fracturing simulation experiment on shale specimens were conducted under true triaxial stress conditions using the TTG apparatus. Results show that the apparatus has advantages in recognizing the effects of σ 2 on the geomechanical properties and permeability of rocks. Results also demonstrate the effectiveness and reliability of the novel TTG apparatus. The apparatus provides a new method of studying the geomechanical properties and permeability evolutions of rocks under true triaxial stress conditions, promoting further investigations of the geological storage of CO2, efficient unconventional oil and gas exploitations.

Experimental studies of deposition at a debris-flow flume

USGS Publications Warehouse

Major, Jon J.

1995-01-01

Geologists commonly infer the flow conditions and the physical properties of debris flows from the sedimentologic, stratigraphic, and morphologic characteristics of their deposits. However, such inferences commonly lack corroboration by direct observation because the capricious nature of debris flows makes systematic observation and measurement of natural events both difficult and dangerous. Furthermore, in contrast to the numerous experimental studies of water flow and related fluvial deposition, few real-time observations and measurements of sediment deposition by large-scale mass flow of debris under controlled conditions have been made. Recent experiments at the U.S. Geological Survey debris-flow flume in the H. J. Andrews Experimental Forest, Oregon (Iverson and others, 1992) are shedding new insight on sediment deposition by debris flows and on the veracity of methods commonly used to reconstruct flow character from deposit characteristics.

Air flow in the boundary layer near a plate

NASA Technical Reports Server (NTRS)

Dryden, Hugh L

1937-01-01

The published data on the distribution of speed near a thin flat plate with sharp leading edge placed parallel to the flow (skin friction plate) are reviewed and the results of some additional measurements are described. The purpose of the experiments was to study the basic phenomena of boundary-layer flow under simple conditions.

Laminar Flow Breakdown due to Particle Interactions

DTIC Science & Technology

2012-08-01

theoretically predicted value of 200x106 in a heated pipe flow experiment – a fact which they attributed to naturally occurring particulates contained in the...the pipe wall, y, to boundary layer thickness, δ, reproduced from Hall [10...12 Figure 5 Estimated critical particle conditions on a heated laminar flow control body at three heating

On factors influencing air-water gas exchange in emergent wetlands

USGS Publications Warehouse

Ho, David T.; Engel, Victor C.; Ferron, Sara; Hickman, Benjamin; Choi, Jay; Harvey, Judson W.

2018-01-01

Knowledge of gas exchange in wetlands is important in order to determine fluxes of climatically and biogeochemically important trace gases and to conduct mass balances for metabolism studies. Very few studies have been conducted to quantify gas transfer velocities in wetlands, and many wind speed/gas exchange parameterizations used in oceanographic or limnological settings are inappropriate under conditions found in wetlands. Here six measurements of gas transfer velocities are made with SF6 tracer release experiments in three different years in the Everglades, a subtropical peatland with surface water flowing through emergent vegetation. The experiments were conducted under different flow conditions and with different amounts of emergent vegetation to determine the influence of wind, rain, water flow, waterside thermal convection, and vegetation on air-water gas exchange in wetlands. Measured gas transfer velocities under the different conditions ranged from 1.1 cm h−1 during baseline conditions to 3.2 cm h−1 when rain and water flow rates were high. Commonly used wind speed/gas exchange relationships would overestimate the gas transfer velocity by a factor of 1.2 to 6.8. Gas exchange due to thermal convection was relatively constant and accounted for 14 to 51% of the total measured gas exchange. Differences in rain and water flow among the different years were responsible for the variability in gas exchange, with flow accounting for 37 to 77% of the gas exchange, and rain responsible for up to 40%.

An in vitro experimental study of flow past aortic valve under varied pulsatile conditions

NASA Astrophysics Data System (ADS)

Zhang, Ruihang; Zhang, Yan

2017-11-01

Flow past aortic valve represents a complex fluid-structure interaction phenomenon that involves pulsatile, vortical, and turbulent conditions. The flow characteristics immediately downstream of the valve, such as the variation of pulsatile flow velocity, formation of vortices, distribution of shear stresses, are of particular interest to further elucidate the role of hemodynamics in various aortic diseases. However, the fluid dynamics of a realistic aortic valve is not fully understood. Particularly, it is unclear how the flow fields downstream of the aortic valve would change under varied pulsatile inlet boundary conditions. In this study, an in vitro experiment has been conducted to investigate the flow fields downstream of a silicone aortic valve model within a cardiovascular flow simulator. Phased-locked Particle Image Velocimetry measurements were performed to map the velocity fields and Reynolds normal and shear stresses at different phases in a cardiac cycle. Temporal variations of pressure across the valve model were measured using high frequency transducers. Results have been compared for different pulsatile inlet conditions, including varied frequencies (heart rates), magnitudes (stroke volumes), and cardiac contractile functions (shapes of waveforms).

High-lift flow-physics flight experiments on a subsonic civil transport aircraft (B737-100)

NASA Technical Reports Server (NTRS)

Vandam, Cornelis P.

1994-01-01

As part of the subsonic transport high-lift program, flight experiments are being conducted using NASA Langley's B737-100 to measure the flow characteristics of the multi-element high-lift system at full-scale high-Reynolds-number conditions. The instrumentation consists of hot-film anemometers to measure boundary-layer states, an infra-red camera to detect transition from laminar to turbulent flow, Preston tubes to measure wall shear stress, boundary-layer rakes to measure off-surface velocity profiles, and pressure orifices to measure surface pressure distributions. The initial phase of this research project was recently concluded with two flights on July 14. This phase consisted of a total of twenty flights over a period of about ten weeks. In the coming months the data obtained in this initial set of flight experiments will be analyzed and the results will be used to finalize the instrumentation layout for the next set of flight experiments scheduled for Winter and Spring of 1995. The main goal of these upcoming flights will be: (1) to measure more detailed surface pressure distributions across the wing for a range of flight conditions and flap settings; (2) to visualize the surface flows across the multi-element wing at high-lift conditions using fluorescent mini tufts; and (3) to measure in more detail the changes in boundary-layer state on the various flap elements as a result of changes in flight condition and flap deflection. These flight measured results are being correlated with experimental data measured in ground-based facilities as well as with computational data calculated with methods based on the Navier-Stokes equations or a reduced set of these equations. Also these results provide insight into the extent of laminar flow that exists on actual multi-element lifting surfaces at full-scale high-life conditions. Preliminary results indicate that depending on the deflection angle, the slat and flap elements have significant regions of laminar flow over a wide range of angles of attack. Boundary-layer transition mechanisms that were observed include attachment-line contamination on the slat and inflectional instability on the slat and fore flap. Also, the results agree fairly well with the predictions reported in a paper presented at last year's AIAA Fluid Dynamics Conference. The fact that extended regions of laminar flow are shown to exist on the various elements of the high-lift system raises the question what the effect is of loss of laminar flow as a result of insect contamiantion, rain or ice accumulation on high-life performance.

Recent experience in seeding transonic/supersonic flows at AEDC

NASA Astrophysics Data System (ADS)

Heltsley, F. L.

1985-10-01

The laser velocimeter has been utilized for several years at the Arnold Engineering and Development Center (AEDC) as a flow diagnostics tool. Most applications, following the initial proof-of-concept experiments, have involved relatively complex unknown flow fields in which the more conventional, intrusive techniques had either not been attempted or had yielded unsatisfactory results. A blunt-base nozzle-afterbody base flow study is discussed as a respresentative example of such applications. A wide variety of problems have been encountered during these tests, many of which have proven to be closely related to the size and/or size distribution of the seeding material within the fluid. Resulting measurement uncertainties could often not be conclusively resolved because of the unknown nature of the flow field. The other experiments listed were conducted to provide known aerodynamic conditions for comparison with the velocimeter results.

Recent experience in seeding transonic/supersonic flows at AEDC

NASA Technical Reports Server (NTRS)

Heltsley, F. L.

1985-01-01

The laser velocimeter has been utilized for several years at the Arnold Engineering and Development Center (AEDC) as a flow diagnostics tool. Most applications, following the initial proof-of-concept experiments, have involved relatively complex unknown flow fields in which the more conventional, intrusive techniques had either not been attempted or had yielded unsatisfactory results. A blunt-base nozzle-afterbody base flow study is discussed as a respresentative example of such applications. A wide variety of problems have been encountered during these tests, many of which have proven to be closely related to the size and/or size distribution of the seeding material within the fluid. Resulting measurement uncertainties could often not be conclusively resolved because of the unknown nature of the flow field. The other experiments listed were conducted to provide known aerodynamic conditions for comparison with the velocimeter results.

Virus transport during infiltration of a wetting front into initially unsaturated sand columns.

PubMed

Kenst, Andrew B; Perfect, Edmund; Wilhelm, Steven W; Zhuang, Jie; McCarthy, John F; McKay, Larry D

2008-02-15

We investigated the effect of different flow conditions on the transport of bacteriophage phiX174 in Memphis aquifer sand. Virus transport associated with a wetting front moving into an initially unsaturated horizontal sand column was experimentally compared with that observed under steady-state saturated vertical flow. Results obtained by sectioning the sand columns showthattotal (retained and free) resident virus concentrations decreased approximately exponentially with the travel distance. The rate of decline was similar under both transient unsaturated flow and steady-state saturated flow conditions. Total resident virus concentrations near the inlet were an order of magnitude greater than the virus concentration of the influent solution in both experiments, indicating continuous virus sorption during flow through this zone. Virus retardation was quantified using the ratio of the centroids of the relative saturation and virus concentration versus relative distance functions. The mean retardation factors were 6.43 (coefficient of variation, CV = 14.4%) and 8.22 (CV = 8.22%) for the transient unsaturated and steady-state saturated flow experiments, respectively. Attest indicated no significant difference between these values at P < 0.05. Air-water and air-water-solid interfaces are thought to enhance virus inactivation and sorption to solid particles. The similar retardation factors obtained may be attributable to the reduced presence of these interfaces in the two flow systems investigated as compared to steady-state unsaturated flow experiments in which these interfaces occur throughout the entire column.

Colloidal Asphaltene Deposition and Aggregation in Capillary Flow: Experiments and Mesoscopic Simulation

NASA Astrophysics Data System (ADS)

Boek, Edo S.; Ladva, Hemant K.; Crawshaw, John P.; Padding, Johan T.

2008-07-01

The aggregation and deposition of colloidal asphaltene in reservoir rock is a significant problem in the oil industry. To obtain a fundamental understanding of this phenomenon, we have studied the deposition and aggregation of colloidal asphaltene in capillary flow by experiment and simulation. For the simulation, we have used the stochastic rotation dynamics (SRD) method, in which the solvent hydrodynamic emerges from the collisions between the solvent particles, while the Brownian motion emerges naturally from the interactions between the colloidal asphaltene particles and the solvent. The asphaltene colloids interact through a screened Coulomb potential. We vary the well depth ɛ∝ and the flow rate v to obtain Peflow≫1 (hydrodynamic interactions dominate) and Re≪1 (Stokes flow). In the simulations, we impose a pressure drop over the capillary length and measure the corresponding solvent flow rate. We observe that the transient solvent flow rate decreases when the asphaltene particles become more "sticky". For a well depth ɛ∝ = 2kBT, a monolayer deposits on the capillary wall. With an increasing well depth, the capillary becomes totally blocked. The clogging is transient for ɛ∝ = 5kBT, but appears to be permanent for ɛ∝ = 10-20 kBT. We compare our simulation results with flow experiments in glass capillaries, where we use extracted asphaltenes in toluene, reprecipitated with n-heptane. In the experiments, the dynamics of asphaltene precipitation and deposition were monitored in a slot capillary using optical microscopy under flow conditions similar to those used in the simulation. Maintaining a constant flow rate of 5 μL min-1, we found that the pressure drop across the capillary first increased slowly, followed by a sharp increase, corresponding to a complete local blockage of the capillary. Doubling the flow rate to 10 μL min-1, we observe that the initial deposition occurs faster but the deposits are subsequently entrained by the flow. We calculate the change in the dimensionless permeability as a function of time for both experiment and simulation. By matching the experimental and simulation results, we obtain information about (1) the interaction potential well depth for the particular asphaltenes used in the experiments and (2) the flow conditions associated with the asphaltene deposition process.

Impact of Azimuthally Controlled Fluidic Chevrons on Jet Noise

NASA Technical Reports Server (NTRS)

Henderson, Brenda S.; Norum, Thomas D.

2008-01-01

The impact of azimuthally controlled air injection on broadband shock noise and mixing noise for single and dual stream jets was investigated. The single stream experiments focused on noise reduction for low supersonic jet exhausts. Dual stream experiments included high subsonic core and fan conditions and supersonic fan conditions with transonic core conditions. For the dual stream experiments, air was injected into the core stream. Significant reductions in broadband shock noise were achieved in a single jet with an injection mass flow equal to 1.2% of the core mass flow. Injection near the pylon produced greater broadband shock noise reductions than injection at other locations around the nozzle periphery. Air injection into the core stream did not result in broadband shock noise reduction in dual stream jets. Fluidic injection resulted in some mixing noise reductions for both the single and dual stream jets. For subsonic fan and core conditions, the lowest noise levels were obtained when injecting on the side of the nozzle closest to the microphone axis.

2-D Air-Breathing Lightcraft Engine Experiments in Hypersonic Conditions

NASA Astrophysics Data System (ADS)

Salvador, Israel I.; Myrabo, Leik N.; Minucci, Marco A. S.; de Oliveira, Antonio C.; Toro, Paulo G. P.; Chanes, José B.; Rego, Israel S.

2011-11-01

Experiments were performed with a 2-D, repetitively-pulsed (RP) laser Lightcraft model in hypersonic flow conditions. The main objective was the feasibility analysis for impulse generation with repetitively-pulsed air-breathing laser Lightcraft engines at hypersonic speeds. The future application of interest for this basic research endeavor is the laser launch of pico-, nano-, and micro-satellites (i.e., 0.1-100 kg payloads) into Low-Earth-Orbit, at low-cost and on-demand. The laser propulsion experiments employed a Hypersonic Shock Tunnel integrated with twin gigawatt pulsed Lumonics 620-TEA CO2 lasers (˜ 1 μs pulses), to produce the required test conditions. This hypersonic campaign was carried out at nominal Mach numbers ranging from 6 to 10. Time-dependent surface pressure distributions were recorded together with Schlieren movies of the flow field structure resulting from laser energy deposition. Results indicated laser-induced pressure increases of 0.7-0.9 bar with laser pulse energies of ˜ 170 J, on off-shroud induced breakdown condition, and Mach number of 7.

Research activity at the shock tube facility at NASA Ames

NASA Astrophysics Data System (ADS)

Sharma, Surendra P.

1992-03-01

The real gas phenomena dominate the relaxation process occurring in the flow around hypersonic vehicles. The air flow around these vehicles undergoes vibrational excitation, chemical dissociation, and ionization. These chemical and kinetic phenomena absorb energy, change compressibility, cause temperature to fall, and density to rise. In high-altitude, low density environments, the characteristic thicknesses of the shock layers can be smaller than the relaxation distances required for the gas to attain chemical and thermodynamic equilibrium. To determine the effects of chemical nonequilibrium over a realistic hypersonic vehicle, it would be desirable to conduct an experiment in which all aspects of fluid flow are simulated. Such an experiment is extremely difficult to setup. The only practical alternative is to develop a theoretical model of the phenomena and to compute the flow around the vehicle including the chemical nonequilibrium, and compare the results with the experiments conducted in the facilities under conditions where only a portion of the flow phenomena is simulated. Three types of experimental data are needed to assist the aerospace community in this model development process: (1) data which will enhance our phenomenological understanding of the relaxation process, (2) data on rate reactions for the relevant reactions, and (3) data on bulk properties, such as spectral radiation emitted by the gas, for a given set of aerodynamic conditions. NASA Ames is in a process of collecting such data by simulating the required aerothermochemical conditions in an electric arc driven shock tube.

Large-Scale Experiments in Microbially Induced Calcite Precipitation (MICP): Reactive Transport Model Development and Prediction

NASA Astrophysics Data System (ADS)

Nassar, Mohamed K.; Gurung, Deviyani; Bastani, Mehrdad; Ginn, Timothy R.; Shafei, Babak; Gomez, Michael G.; Graddy, Charles M. R.; Nelson, Doug C.; DeJong, Jason T.

2018-01-01

Design of in situ microbially induced calcite precipitation (MICP) strategies relies on a predictive capability. To date much of the mathematical modeling of MICP has focused on small-scale experiments and/or one-dimensional flow in porous media, and successful parameterizations of models in these settings may not pertain to larger scales or to nonuniform, transient flows. Our objective in this article is to report on modeling to test our ability to predict behavior of MICP under controlled conditions in a meter-scale tank experiment with transient nonuniform transport in a natural soil, using independently determined parameters. Flow in the tank was controlled by three wells, via a complex cycle of injection/withdrawals followed by no-flow intervals. Different injection solution recipes were used in sequence for transport characterization, biostimulation, cementation, and groundwater rinse phases of the 17 day experiment. Reaction kinetics were calibrated using separate column experiments designed with a similar sequence of phases. This allowed for a parsimonious modeling approach with zero fitting parameters for the tank experiment. These experiments and data were simulated using PHT3-D, involving transient nonuniform flow, alternating low and high Damköhler reactive transport, and combined equilibrium and kinetically controlled biogeochemical reactions. The assumption that microbes mediating the reaction were exclusively sessile, and with constant activity, in conjunction with the foregoing treatment of the reaction network, provided for efficient and accurate modeling of the entire process leading to nonuniform calcite precipitation. This analysis suggests that under the biostimulation conditions applied here the assumption of steady state sessile biocatalyst suffices to describe the microbially mediated calcite precipitation.

In situ flow cell for combined X-ray absorption spectroscopy, X-ray diffraction, and mass spectrometry at high photon energies under solar thermochemical looping conditions

NASA Astrophysics Data System (ADS)

Rothensteiner, Matthäus; Jenni, Joel; Emerich, Hermann; Bonk, Alexander; Vogt, Ulrich F.; van Bokhoven, Jeroen A.

2017-08-01

An in situ/operando flow cell for transmission mode X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and combined XAS/XRD measurements in a single experiment under the extreme conditions of two-step solar thermochemical looping for the dissociation of water and/or carbon dioxide was developed. The apparatus exposes materials to relevant conditions of both the auto-reduction and the oxidation sub-steps of the thermochemical cycle at ambient temperature up to 1773 K and enables determination of the composition of the effluent gases by online quadrupole mass spectrometry. The cell is based on a tube-in-tube design and is heated by means of a focusing infrared furnace. It was tested successfully for carbon dioxide splitting. In combined XAS/XRD experiments with an unfocused beam, XAS measurements were performed at the Ce K edge (40.4 keV) and XRD measurements at 64.8 keV and 55.9 keV. Furthermore, XRD measurements with a focused beam at 41.5 keV were carried out. Equimolar ceria-hafnia was auto-reduced in a flow of argon and chemically reduced in a flow of hydrogen/helium. Under reducing conditions, all cerium(iv) was converted to cerium(iii) and a cation-ordered pyrochlore-type structure was formed, which was not stable upon oxidation in a flow of carbon dioxide.

In situ flow cell for combined X-ray absorption spectroscopy, X-ray diffraction, and mass spectrometry at high photon energies under solar thermochemical looping conditions.

PubMed

Rothensteiner, Matthäus; Jenni, Joel; Emerich, Hermann; Bonk, Alexander; Vogt, Ulrich F; van Bokhoven, Jeroen A

2017-08-01

An in situ/operando flow cell for transmission mode X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and combined XAS/XRD measurements in a single experiment under the extreme conditions of two-step solar thermochemical looping for the dissociation of water and/or carbon dioxide was developed. The apparatus exposes materials to relevant conditions of both the auto-reduction and the oxidation sub-steps of the thermochemical cycle at ambient temperature up to 1773 K and enables determination of the composition of the effluent gases by online quadrupole mass spectrometry. The cell is based on a tube-in-tube design and is heated by means of a focusing infrared furnace. It was tested successfully for carbon dioxide splitting. In combined XAS/XRD experiments with an unfocused beam, XAS measurements were performed at the Ce K edge (40.4 keV) and XRD measurements at 64.8 keV and 55.9 keV. Furthermore, XRD measurements with a focused beam at 41.5 keV were carried out. Equimolar ceria-hafnia was auto-reduced in a flow of argon and chemically reduced in a flow of hydrogen/helium. Under reducing conditions, all cerium(iv) was converted to cerium(iii) and a cation-ordered pyrochlore-type structure was formed, which was not stable upon oxidation in a flow of carbon dioxide.

The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil: Suction coefficient analysis

NASA Technical Reports Server (NTRS)

Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.

1991-01-01

A swept supercritical wing incorporating laminar flow control at transonic flow conditions was designed and tested. The definition of an experimental suction coefficient and a derivation of the compressible and incompressible formulas for the computation of the coefficient from measurable quantities is presented. The suction flow coefficient in the highest velocity nozzles is shown to be overpredicted by as much as 12 percent through the use of an incompressible formula. However, the overprediction on the computed value of suction drag when some of the suction nozzles were operating in the compressible flow regime is evaluated and found to be at most 6 percent at design conditions.

Phase Distribution Phenomena for Simulated Microgravity Conditions: Experimental Work

NASA Technical Reports Server (NTRS)

Singhal, Maneesh; Bonetto, Fabian J.; Lahey, R. T., Jr.

1996-01-01

This report summarizes the work accomplished at Rensselaer to study phase distribution phenomenon under simulated microgravity conditions. Our group at Rensselaer has been able to develop sophisticated analytical models to predict phase distribution in two-phase flows under a variety of conditions. These models are based on physics and data obtained from carefully controlled experiments that are being conducted here. These experiments also serve to verify the models developed.

Phase Distribution Phenomena for Simulated Microgravity Conditions: Experimental Work

NASA Technical Reports Server (NTRS)

Singhal, Maneesh; Bonetto, Fabian J.; Lahey, R. T., Jr.

1996-01-01

This report summarizes the work accomplished at Rensselaer to study phase distribution phenomenon under simulated microgravity conditions. Our group at Rensselaer has been able to develop sophisticated analytical models to predict phase distribution in two-phase flows under variety of conditions. These models are based on physics and data obtained from carefully controlled experiments that are being conducted here. These experiments also serve to verify the models developed.

Experimentally Modeling Black and White Hole Event Horizons via Fluid Flow

NASA Astrophysics Data System (ADS)

Manheim, Marc E.; Lindner, John F.; Manz, Niklas

We will present a scaled down experiment that hydrodynamically models the interaction between electromagnetic waves and black/white holes. It has been mathematically proven that gravity waves in water can behave analogously to electromagnetic waves traveling through spacetime. In this experiment, gravity waves will be generated in a water tank and propagate in a direction opposed to a flow of varying rate. We observe a noticeable change in the wave's spreading behavior as it travels through the simulated horizon with decreased wave speeds up to standing waves, depending on the opposite flow rate. Such an experiment has already been performed in a 97.2 cubic meter tank. We reduced the size significantly to be able to perform the experiment under normal lab conditions.

Large-Scale Laboratory Experiments of Initiation of Motion and Burial of Objects under Currents and Waves

NASA Astrophysics Data System (ADS)

Landry, B. J.; Wu, H.; Wenzel, S. P.; Gates, S. J.; Fytanidis, D. K.; Garcia, M. H.

2017-12-01

Unexploded ordnances (UXOs) can be found at the bottom of coastal areas as the residue of military wartime activities, training or accidents. These underwater objects are hazards for humans and the coastal environment increasing the need for addressing the knowledge gaps regarding the initiation of motion, fate and transport of UXOs under currents and wave conditions. Extensive experimental analysis was conducted for the initiation of motion of UXOs under various rigid bed roughness conditions (smooth PVC, pitted steel, marbles, gravels and bed of spherical particles) for both unidirectional and oscillatory flows. Particle image velocimetry measurements were conducted under both flow conditions to resolve the flow structure estimate the critical flow conditions for initiation of motion of UXOs. Analysis of the experimental observations shows that the geometrical characteristics of the UXOs, their properties (i.e. volume, mass) and their orientation with respect to the mean flow play an important role on the reorientation and mobility of the examined objects. A novel unified initiation of motion diagram is proposed using an effective/unified hydrodynamic roughness and a new length scale which includes the effect of the projected area and the bed-UXO contact area. Both unidirectional and oscillatory critical flow conditions collapsed into a single dimensionless diagram highlighting the importance and practical applicability of the proposed work. In addition to the rigid bed experiments, the burial dynamics of proud UXOs on a mobile sand bed were also examined. The complex flow-bedform-UXOs interactions were evaluated which highlighted the effect of munition density on burial rate and final burial depth. Burial dynamics and mechanisms for motion were examined for various UXOs types, and results show that, for the case of the low density UXOs under energetic conditions, lateral transport coexists with burial. Prior to burial, UXO re-orientation was also observed depending on the geometric characteristics of the objects.

Benchmarking computational fluid dynamics models of lava flow simulation for hazard assessment, forecasting, and risk management

USGS Publications Warehouse

Dietterich, Hannah; Lev, Einat; Chen, Jiangzhi; Richardson, Jacob A.; Cashman, Katharine V.

2017-01-01

Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, designing flow mitigation measures, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics (CFD) models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, COMSOL, and MOLASSES. We model viscous, cooling, and solidifying flows over horizontal planes, sloping surfaces, and into topographic obstacles. We compare model results to physical observations made during well-controlled analogue and molten basalt experiments, and to analytical theory when available. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and OpenFOAM and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We assess the goodness-of-fit of the simulation results and the computational cost. Our results guide the selection of numerical simulation codes for different applications, including inferring emplacement conditions of past lava flows, modeling the temporal evolution of ongoing flows during eruption, and probabilistic assessment of lava flow hazard prior to eruption. Finally, we outline potential experiments and desired key observational data from future flows that would extend existing benchmarking data sets.

Definition of two-phase flow behaviors for spacecraft design

NASA Technical Reports Server (NTRS)

Reinarts, Thomas R.; Best, Frederick R.; Miller, Katherine M.; Hill, Wayne S.

1991-01-01

Data for complete models of two-phase flow in microgravity are taken from in-flight experiments and applied to an adiabatic flow-regime analysis to study the feasibility of two-phase systems for spacecraft. The data are taken from five in-flight experiments by Hill et al. (1990) in which a two-phase pump circulates a freon mixture and vapor and liquid flow streams are measured. Adiabatic flow regimes are analyzed based on the experimental superficial velocities of liquid and vapor, and comparisons are made with the results of two-phase flow regimes at 1 g. A motion analyzer records the flow characteristics at a rate of 1000 frames/sec, and stratified flow regimes are reported at 1 g. The flow regimes observed under microgravitational conditions are primarily annular and include slug and bubbly-slug regimes. The present data are of interest to the design and analysis of two-phase thermal-management systems for use in space missions.

Potential and viscous flow in VTOL, STOL or CTOL propulsion system inlets

NASA Technical Reports Server (NTRS)

Stockman, N. O.

1975-01-01

A method was developed for analyzing the flow in subsonic axisymmetric inlets at arbitrary conditions of freestream velocity, incidence angle, and inlet mass flow. An improved version of the method is discussed and comparisons of results obtained with the original and improved methods are given. Comparisons with experiments are also presented for several inlet configurations and for various conditions of the boundary layer from insignificant to separated. Applications of the method are discussed, with several examples given for specific cases involving inlets for VTOL lift fans and for STOL engine nacelles.

Effect of high strain rates on peak stress in a Zr-based bulk metallic glass

NASA Astrophysics Data System (ADS)

Sunny, George; Yuan, Fuping; Prakash, Vikas; Lewandowski, John

2008-11-01

The mechanical behavior of Zr41.25Ti13.75Cu12.5Ni10Be22.5 (LM-1) has been extensively characterized under quasistatic loading conditions; however, its mechanical behavior under dynamic loading conditions is currently not well understood. A Split-Hopkinson pressure bar (SHPB) and a single-stage gas gun are employed to characterize the mechanical behavior of LM-1 in the strain-rate regime of 102-105/s. The SHPB experiments are conducted with a tapered insert design to mitigate the effects of stress concentrations and preferential failure at the specimen-insert interface. The higher strain-rate plate-impact compression-and-shear experiments are conducted by impacting a thick tungsten carbide (WC) flyer plate with a sandwich sample comprising a thin bulk metallic glass specimen between two thicker WC target plates. Specimens employed in the SHPB experiments failed in the gage-section at a peak stress of approximately 1.8 GPa. Specimens in the high strain-rate plate-impact experiments exhibited a flow stress in shear of approximately 0.9 GPa, regardless of the shear strain-rate. The flow stress under the plate-impact conditions was converted to an equivalent flow stress under uniaxial compression by assuming a von Mises-like material behavior and accounting for the plane strain conditions. The results of these experiments, when compared to the previous work conducted at quasistatic loading rates, indicate that the peak stress of LM-1 is essentially strain rate independent over the strain-rate range up to 105/s.

Effect of varying experimental conditions on the viscosity of α-pinene derived secondary organic material

DOE PAGES

Grayson, James W.; Zhang, Yue; Mutzel, Anke; ...

2016-05-18

Knowledge of the viscosity of particles containing secondary organic material (SOM) is useful for predicting reaction rates and diffusion in SOM particles. In this study we investigate the viscosity of SOM particles as a function of relative humidity and SOM particle mass concentration, during SOM synthesis. The SOM was generated via the ozonolysis of α-pinene at < 5 % relative humidity (RH). Experiments were carried out using the poke-and-flow technique, which measures the experimental flow time ( τ exp, flow) of SOM after poking the material with a needle. In the first set of experiments, we show that τ exp,more » flow increased by a factor of 3600 as the RH increased from < 0.5 RH to 50 % RH, for SOM with a production mass concentration of 121 µg m -3. Based on simulations, the viscosities of the particles were between 6 × 10 5 and 5 × 10 7 Pa s at < 0.5 % RH and between 3 × 10 2 and 9 × 10 3 Pa s at 50 % RH. In the second set of experiments we show that under dry conditions τ exp, flow decreased by a factor of 45 as the production mass concentration increased from 121 to 14 000 µg m -3. From simulations of the poke-and-flow experiments, the viscosity of SOM with a production mass concentration of 14 000 µg m -3 was determined to be between 4 × 10 4 and 1.5 × 10 6 Pa s compared to between 6 × 10 5 and 5 × 10 7 Pa s for SOM with a production mass concentration of 121 µg m -3. The results can be rationalized by a dependence of the chemical composition of SOM on production conditions. Lastly, these results emphasize the shifting characteristics of SOM, not just with RH and precursor type, but also with the production conditions, and suggest that production mass concentration and the RH at which the viscosity was determined should be considered both when comparing laboratory results and when extrapolating these results to the atmosphere.« less

Large-Eddy Simulation of Propeller Crashback

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Mahesh, Krishnan

2013-11-01

Crashback is an operating condition to quickly stop a propelled vehicle, where the propeller is rotated in the reverse direction to yield negative thrust. The crashback condition is dominated by the interaction of free stream flow with strong reverse flow. Crashback causes highly unsteady loads and flow separation on blade surface. This study uses Large-Eddy Simulation to predict the highly unsteady flow field in propeller crashback. Results are shown for a stand-alone open propeller, hull-attached open propeller and a ducted propeller. The simulations are compared to experiment, and used to discuss the essential physics behind the unsteady loads. This work is supported by the Office of Naval Research.

Predicted and experimental steady and unsteady transonic flows about a biconvex airfoil

NASA Technical Reports Server (NTRS)

Levy, L. L., Jr.

1981-01-01

Results of computer code time dependent solutions of the two dimensional compressible Navier-Stokes equations and the results of independent experiments are compared to verify the Mach number range for instabilities in the transonic flow field about a 14 percent thick biconvex airfoil at an angle of attack of 0 deg and a Reynolds number of 7 million. The experiments were conducted in a transonic, slotted wall wind tunnel. The computer code included an algebraic eddy viscosity turbulence model developed for steady flows, and all computations were made using free flight boundary conditions. All of the features documented experimentally for both steady and unsteady flows were predicted qualitatively; even with the above simplifications, the predictions were, on the whole, in good quantitative agreement with experiment. In particular, predicted time histories of shock wave position, surface pressures, lift, and pitching moment were found to be in very good agreement with experiment for an unsteady flow. Depending upon the free stream Mach number for steady flows, the surface pressure downstream of the shock wave or the shock wave location was not well predicted.

Planform structure and heat transfer in turbulent free convection over horizontal surfaces

NASA Astrophysics Data System (ADS)

Theerthan, S. Ananda; Arakeri, Jaywant H.

2000-04-01

This paper deals with turbulent free convection in a horizontal fluid layer above a heated surface. Experiments have been carried out on a heated surface to obtain and analyze the planform structure and the heat transfer under different conditions. Water is the working fluid and the range of flux Rayleigh numbers (Ra) covered is 3×107-2×1010. The different conditions correspond to Rayleigh-Bénard convection, convection with either the top water surface open to atmosphere or covered with an insulating plate, and with an imposed external flow on the heated boundary. Without the external flow the planform is one of randomly oriented line plumes. At large Rayleigh number Ra and small aspect ratio (AR), these line plumes seem to align along the diagonal, presumably due to a large scale flow. The side views show inclined dyelines, again indicating a large scale flow. When the external flow is imposed, the line plumes clearly align in the direction of external flow. The nondimensional average plume spacing, Raλ1/3, varies between 40 and 90. The heat transfer rate, for all the experiments conducted, represented as RaδT-1/3, where δT is the conduction layer thickness, varies only between 0.1-0.2, showing that in turbulent convection the heat transfer rates are similar under the different conditions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jamieson-Hanes, Julia H.; Shrimpton, Heather K.; Veeramani, Harish

A flow-through cell experiment was conducted to evaluate Zn isotope fractionation during ZnS precipitation under microbially-mediated sulfate-reducing conditions. Synthetic groundwater containing 0.90 mM Zn was pumped through a cell containing creek sediment that was biostimulated to promote sulfate reducing conditions. Real-time, in situ X-ray absorption spectroscopy (XAS) was applied at the Zn K-edge to collect spectra via a Kapton® window in the front of the cell over the course of the experiment. Aqueous effluent samples were collected and analysed to determine concentrations of anions and cations, and Zn isotope ratios. The flow rate was increased step-wise during the experiment tomore » modify the residence time and produce changes in the extent of sulfate reduction, which in turn controlled the extent of ZnS precipitation. Greater enrichment in the heavier isotope in the aqueous phase relative to the input solution was associated with more extensive Zn removal. A Rayleigh curve was fit to the isotope data, where ε = -0.27 ± 0.06‰ (2σ). Evaluation of Zn isotope fractionation under controlled flow conditions is critical to improve the efficacy of this powerful analytical technique when applied to natural systems or remediation projects in the field.« less

Simulating flow around scaled model of a hypersonic vehicle in wind tunnel

NASA Astrophysics Data System (ADS)

Markova, T. V.; Aksenov, A. A.; Zhluktov, S. V.; Savitsky, D. V.; Gavrilov, A. D.; Son, E. E.; Prokhorov, A. N.

2016-11-01

A prospective hypersonic HEXAFLY aircraft is considered in the given paper. In order to obtain the aerodynamic characteristics of a new construction design of the aircraft, experiments with a scaled model have been carried out in a wind tunnel under different conditions. The runs have been performed at different angles of attack with and without hydrogen combustion in the scaled propulsion engine. However, the measured physical quantities do not provide all the information about the flowfield. Numerical simulation can complete the experimental data as well as to reduce the number of wind tunnel experiments. Besides that, reliable CFD software can be used for calculations of the aerodynamic characteristics for any possible design of the full-scale aircraft under different operation conditions. The reliability of the numerical predictions must be confirmed in verification study of the software. The given work is aimed at numerical investigation of the flowfield around and inside the scaled model of the HEXAFLY-CIAM module under wind tunnel conditions. A cold run (without combustion) was selected for this study. The calculations are performed in the FlowVision CFD software. The flow characteristics are compared against the available experimental data. The carried out verification study confirms the capability of the FlowVision CFD software to calculate the flows discussed.

Neural signatures of experimentally induced flow experiences identified in a typical fMRI block design with BOLD imaging

PubMed Central

Keller, Johannes; Grön, Georg

2016-01-01

Previously, experimentally induced flow experiences have been demonstrated with perfusion imaging during activation blocks of 3 min length to accommodate with the putatively slowly evolving “mood” characteristics of flow. Here, we used functional magnetic resonance imaging (fMRI) in a sample of 23 healthy, male participants to investigate flow in the context of a typical fMRI block design with block lengths as short as 30 s. To induce flow, demands of arithmetic tasks were automatically and continuously adjusted to the individual skill level. Compared against conditions of boredom and overload, experience of flow was evident from individuals’ reported subjective experiences and changes in electrodermal activity. Neural activation was relatively increased during flow, particularly in the anterior insula, inferior frontal gyri, basal ganglia and midbrain. Relative activation decreases during flow were observed in medial prefrontal and posterior cingulate cortex, and in the medial temporal lobe including the amygdala. Present findings suggest that even in the context of comparably short activation blocks flow can be reliably experienced and is associated with changes in neural activation of brain regions previously described. Possible mechanisms of interacting brain regions are outlined, awaiting further investigation which should now be possible given the greater temporal resolution compared with previous perfusion imaging. PMID:26508774

Experimental study on neptunium migration under in situ geochemical conditions

NASA Astrophysics Data System (ADS)

Kumata, M.; Vandergraaf, T. T.

1998-12-01

Results are reported for migration experiments performed with Np under in situ geochemical conditions over a range of groundwater flow rates in columns of crushed rock in a specially designed facility at the 240-level of the Underground Research Laboratory (URL) near Pinawa, Manitoba, Canada. This laboratory is situated in an intrusive granitic rock formation, the Lac du Bonnet batholith. Highly altered granitic rock and groundwater were obtained from a major subhorizontal fracture zone at a depth of 250 m in the URL. The granite was wet-crushed and wet-sieved with groundwater from this fracture zone. The 180-850-μm size fraction was selected and packed in 20-cm long, 2.54-cm in diameter Teflon™-lined stainless steel columns. Approximately 30-ml vols of groundwater containing 3HHO and 237Np were injected into the columns at flow rates of 0.3, 1, and 3 ml/h, followed by elution with groundwater, obtained from the subhorizontal fracture, at the same flow rates, for a period of 95 days. Elution profiles for 3HHO were obtained, but no 237Np was detected in the eluted groundwater. After terminating the migration experiments, the columns were frozen, the column material was removed and cut into twenty 1-cm thick sections and each section was analyzed by gamma spectrometry. Profiles of 237Np were obtained for the three columns. A one-dimensional transport model was fitted to the 3HHO breakthrough curves to obtain flow parameters for this experiment. These flow parameters were in turn applied to the 237Np concentration profiles in the columns to produce sorption and dispersion coefficients for Np. The results show a strong dependence of retardation factors ( Rf) on flow rate. The decrease in the retarded velocity of the neptunium ( Vn) varied over one order of magnitude under the geochemical conditions for these experiments.

Evaluation of the tropospheric flows to a major Southern Hemisphere stratospheric warming event using NCEP/NCAR Reanalysis data with a PSU/NCAR nudging MM5V3 model

NASA Astrophysics Data System (ADS)

Wang, K.

2008-04-01

Previous studies of the exceptional 2002 Southern Hemisphere (SH) stratospheric warming event lead to some uncertainty, namely the question of whether excessive heat fluxes in the upper troposphere and lower stratosphere are a symptom or cause of the 2002 SH warming event. In this work, we use a hemispheric version of the MM5 model with nudging capability and we devised a novel approach to separately test the significance of the stratosphere and troposphere for this year. We paired the flow conditions from 2002 in the stratosphere and troposphere, respectively, against the conditions in 1998 (a year with displaced polar vortex) and in 1948 (a year with strong polar vortex that coincided with the geographical South Pole). Our experiments show that the flow conditions from below determine the stratospheric flow features over the polar region. Regardless of the initial stratospheric conditions in 1998 or 1948, when we simulated these past stratospheres with the troposphere/lower stratosphere conditions constrained to 2002 levels, the simulated middle stratospheres resemble those observed in 2002 stratosphere over the polar region. On the other hand, when the 2002 stratosphere was integrated with the troposphere/lower stratosphere conductions constrained to 1948 and 1998, respectively, the simulated middle stratospheric conditions over the polar region shift toward those of 1948 and 1998. Thus, our experiments further support the wave-forcing theory as the cause of the 2002 SH warming event.

Dynamics of Rarefied Gas and Molecular Gas Dynamics.

DTIC Science & Technology

1983-08-25

results of experiment and calculations according to the theory of the first intermolecular collisions and according to the theory of the viscous flows of...connection with this arises the question about the procedure of the recalculation of the results of tube experiment for the actual conditions with the...conditions of experiments did not exceed 4%. For the cones with the smaller aperture angles it was less. For measuring of the aerodynamic forces and

Coupled Fracture and Flow in Shale in Hydraulic Fracturing

NASA Astrophysics Data System (ADS)

Carey, J. W.; Mori, H.; Viswanathan, H.

2014-12-01

Production of hydrocarbon from shale requires creation and maintenance of fracture permeability in an otherwise impermeable shale matrix. In this study, we use a combination of triaxial coreflood experiments and x-ray tomography characterization to investigate the fracture-permeability behavior of Utica shale at in situ reservoir conditions (25-50 oC and 35-120 bars). Initially impermeable shale core was placed between flat anvils (compression) or between split anvils (pure shear) and loaded until failure in the triaxial device. Permeability was monitored continuously during this process. Significant deformation (>1%) was required to generate a transmissive fracture system. Permeability generally peaked at the point of a distinct failure event and then dropped by a factor of 2-6 when the system returned to hydrostatic failure. Permeability was very small in compression experiments (< 1 mD), possibly because of limited fracture connectivity through the anvils. In pure share experiments, shale with bedding planes perpendicular to shear loading developed complex fracture networks with narrow apertures and peak permeability of 30 mD. Shale with bedding planes parallel to shear loading developed simple fractures with large apertures and a peak permeability as high as 1 D. Fracture systems held at static conditions for periods of several hours showed little change in effective permeability at hydrostatic conditions as high as 140 bars. However, permeability of fractured systems was a function of hydrostatic pressure, declining in a pseudo-linear, exponential fashion as pressure increased. We also observed that permeability decreased with increasing fluid flow rate indicating that flow did not follow Darcy's Law, possibly due to non-laminar flow conditions, and conformed to Forscheimer's law. The coupled deformation and flow behavior of Utica shale, particularly the large deformation required to initiate flow, indicates the probable importance of activation of existing fractures in hydraulic fracturing and that these fractures can have adequate permeability for the production of hydrocarbon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stephen Seong Lee

Fuel flow to individual burners is complicated and difficult to determine on coal fired boilers, since coal solids were transported in a gas suspension that is governed by the complex physics of two-phase flow. The objectives of the project were the measurements of suspended coal solids-flows in the simulated test conditions. Various extractive methods were performed manually and can give only a snapshot result of fuel distribution. In order to measure particle diameter & velocity, laser based phase-Doppler particle analyzer (PDPA) and particle image velocimetry (PIV) were carefully applied. Statistical methods were used to analyze particle characteristics to see whichmore » factors have significant effect. The transparent duct model was carefully designed and fabricated for the laser-based-instrumentation of solids-flow monitoring (LISM). The experiments were conducted with two different kinds of particles with four different particle diameters. The particle types were organic particles and saw dust particles with the diameter range of 75-150 micron, 150-250 micron, 250-355 micron and 355-425 micron. The densities of the particles were measured to see how the densities affected the test results. Also the experiment was conducted with humid particles and fog particles. To generate humid particles, the humidifier was used. A pipe was connected to the humidifier to lead the particle flow to the intersection of the laser beam. The test results of the particle diameter indicated that, the mean diameter of humid particles was between 6.1703 microns and 6.6947 microns when the humid particle flow was low. When the humid particle flow was high, the mean diameter was between 6.6728 microns and 7.1872 microns. The test results of the particle mean velocity indicated that the mean velocity was between 1.3394 m/sec and 1.4556 m/sec at low humid particle flow. When the humid particle flow was high, the mean velocity was between 1.5694 m/sec and 1.7856 m/sec. The Air Flow Module, TQ AF 17 and shell ondina oil were used to generate fog particles. After the oil was heated inside the fog generator, the blower was used to generate the fog. The fog flew along the pipe to the intersection of the laser beam. The mean diameter of the fog particles was 5.765 microns. Compared with the humid particle diameter, we observed that the mean diameter of the fog particles was smaller than the humid particles. The test results of particle mean velocity was about 3.76 m/sec. Compared with the mean velocity of the humid particles, we can observed the mean velocity of fog particles were greater than humid particles. The experiments were conducted with four different kinds of particles with five different particle diameters. The particle types were organic particles, coal particles, potato particles and wheat particles with the diameter range of 63-75 micron, less than 150 micron, 150-250 micron, 250-355 micron and 355-425 micron. To control the flow rate, the control gate of the particle dispensing hopper was adjusted to 1/16 open rate, 1/8 open rate and 1/4 open rate. The captured image range was 0 cm to 5 cm from the control gate, 5 cm to 10 cm from the control gate and 10 cm to 15 cm from the control gate. Some of these experiments were conducted under both open environment conditions and closed environment conditions. Thus these experiments had a total of five parameters which were type of particles, diameter of particles, flow rate, observation range, and environment conditions. The coal particles (diameter between 63 and 75 microns) tested under the closed environment condition had three factors that were considered as the affecting factors. They were open rate, observation range, and environment conditions. In this experiment, the interaction of open rate and observation range had a significant effect on the lower limit. On the upper limit, the open rate and environment conditions had a significant effect. In addition, the interaction of open rate and environment conditions had a significant effect. The coal particles tested (diameter between 63 and 75 microns) under open environment, two factors were that considered as the affecting factors. They were the open rate and observation ranges. In this experiment, there was no significant effect on the lower limit. On the upper limit, the observation range had a significant effect. In addition, the interaction of open rate and observation range had a significant effect for the source of variation with 95% of confidence based on analysis of variance (ANOVA) results.« less

Effects of intermittent flow and irradiance level on back reef Porites corals at elevated seawater temperatures

USGS Publications Warehouse

Smith, L.W.; Birkeland, C.

2007-01-01

Corals inhabiting shallow back reef habitats are often simultaneously exposed to elevated seawater temperatures and high irradiance levels, conditions known to cause coral bleaching. Water flow in many tropical back reef systems is tidally influenced, resulting in semi-diurnal or diurnal flow patterns. Controlled experiments were conducted to test effects of semi-diurnally intermittent water flow on photoinhibition and bleaching of the corals Porites lobata and P. cylindrica kept at elevated seawater temperatures and different irradiance levels. All coral colonies were collected from a shallow back reef pool on Ofu Island, American Samoa. In the high irradiance experiments, photoinhibition and bleaching were less for both species in the intermittent high-low flow treatment than in the constant low flow treatment. In the low irradiance experiments, there were no differences in photoinhibition or bleaching for either species between the flow treatments, despite continuously elevated seawater temperatures. These results suggest that intermittent flow associated with semi-diurnal tides, and low irradiances caused by turbidity or shading, may reduce photoinhibition and bleaching of back reef corals during warming events. ?? 2006 Elsevier B.V. All rights reserved.

A Study on Water Surface Profiles of Rivers with Constriction

NASA Astrophysics Data System (ADS)

Qian, Chaochao; Yamada, Tadashi

2013-04-01

Water surface profile of rivers with constrictions is precious in both classic hydraulics and river management practice. This study was conducted to clarify the essences of the water surface profiles. 3 cases of experiments and 1D numerical calculations with different discharges were made in the study and analysis solutions of the non-linear basic equation of surface profile in varied flow without considering friction were derived. The manning's number was kept in the same in each case by using crosspiece roughness. We found a new type of water surface profile of varied flow from the results of 1D numerical calculation and that of experiments and named it as Mc curve because of its mild condition with constriction segment. This kind of curves appears as a nature phenomenon ubiquitously. The process of water surface forming is dynamic and bore occurs at the upper side of constriction during increasing discharge before the surface profile formed. As a theoretical work, 3 analysis solutions were derived included 2 physical-meaning solutions in the study by using Man-Machine system. One of the derived physical-meaning solutions was confirmed that it is validity by comparing to the results of 1D numerical calculation and that of experiments. The solution represents a flow profile from under critical condition at the upper side to super critical condition at the down side of constriction segment. The other derived physical-meaning solution represents a flow profile from super critical condition at the upper side to under critical condition at the down side of constriction segment. These two kinds of flow profiles exist in the nature but no theoretical solution can express the phenomenon. We find the depth distribution only concerned with unit width discharge distribution and critical depth under a constant discharge from the derived solutions. Therefor, the profile can be gained simply and precisely by using the theoretical solutions instead of numerical calculation even in practice.

The role of heater thermal response in reactor thermal limits during oscillartory two-phase flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruggles, A.E.; Brown, N.W.; Vasil`ev, A.D.

1995-09-01

Analytical and numerical investigations of critical heat flux (CHF) and reactor thermal limits are conducted for oscillatory two-phase flows often associated with natural circulation conditions. It is shown that the CHF and associated thermal limits depend on the amplitude of the flow oscillations, the period of the flow oscillations, and the thermal properties and dimensions of the heater. The value of the thermal limit can be much lower in unsteady flow situations than would be expected using time average flow conditions. It is also shown that the properties of the heater strongly influence the thermal limit value in unsteady flowmore » situations, which is very important to the design of experiments to evaluate thermal limits for reactor fuel systems.« less

Dependence of energy characteristics of ascending swirling air flow on velocity of vertical blowing

NASA Astrophysics Data System (ADS)

Volkov, R. E.; Obukhov, A. G.; Kutrunov, V. N.

2018-05-01

In the model of a compressible continuous medium, for the complete Navier-Stokes system of equations, an initial boundary problem is proposed that corresponds to the conducted and planned experiments and describes complex three-dimensional flows of a viscous compressible heat-conducting gas in ascending swirling flows that are initiated by a vertical cold blowing. Using parallelization methods, three-dimensional nonstationary flows of a polytropic viscous compressible heat-conducting gas are constructed numerically in different scaled ascending swirling flows under the condition when gravity and Coriolis forces act. With the help of explicit difference schemes and the proposed initial boundary conditions, approximate solutions of the complete system of Navier-Stokes equations are constructed as well as the velocity and energy characteristics of three-dimensional nonstationary gas flows in ascending swirling flows are determined.

The effect of venting on cookoff of a melt-castable explosive (Comp-B)

DOE PAGES

Hobbs, Michael L.; Kaneshige, Michael J.

2015-03-01

Occasionally, our well-controlled cookoff experiments with Comp-B give anomalous results when venting conditions are changed. For example, a vented experiment may take longer to ignite than a sealed experiment. In the current work, we show the effect of venting on thermal ignition of Comp-B. We use Sandia’s Instrumented Thermal Ignition (SITI) experiment with various headspace volumes in both vented and sealed geometries to study ignition of Comp-B. In some of these experiments, we have used a boroscope to observe Comp-B as it melts and reacts. We propose that the mechanism for ignition involves TNT melting, dissolution of RDX, and complexmore » bubbly liquid flow. High pressure inhibits bubble formation and flow is significantly reduced. At low pressure, a vigorous dispersed bubble flow was observed.« less

Flow dynamics and salt transport in a coastal aquifer driven by a stratified saltwater body: Lab experiment and numerical modeling

NASA Astrophysics Data System (ADS)

Oz, Imri; Shalev, Eyal; Yechieli, Yoseph; Gavrieli, Ittai; Gvirtzman, Haim

2014-04-01

This paper examines the transient development and the steady-state configuration of groundwater within a coastal aquifer adjacent to a stratified saltwater body. Such systems consist of three different water types: the regional fresh groundwater, and low and high salinity brines forming the upper and lower water layers of the stratified water body, respectively. The dynamics, location and the geometry of the interfaces and the density-driven circulation flows that develop in the aquifer are examined using laboratory experiments and numerical modeling at the same scale. The results show that the transient intrusion of the different water bodies into the aquifer takes place at different rates, and that the locations of the interfaces between them change with time, before reaching steady-state. Under steady-state conditions both the model and the experiments show the existence of three interfaces between the three water types. The numerical model, which is calibrated against the salinity distribution and groundwater discharge rate in the laboratory experiments, allows the quantification of the flow rates and flow patterns within the aquifer. These flow patterns, which cannot be derived from laboratory experiments, show the transient development of three circulation cells which are confined between the three interfaces. These results confirm the hypothesis that has been previously suggested based solely on a steady-state numerical modeling defined by a conceptual understanding. Parametric analysis shows that the creation of three circulation cells and three interfaces is limited to certain conditions and defines the ranges for the creation of this unique system.

Hillslope-scale experiment demonstrates role of convergence during two-step saturation

USGS Publications Warehouse

Gevaert, A. I.; Teuling, A. J.; Uijlenhoet, R.; DeLong, Stephen B.; Huxman, T. E.; Pangle, L. A.; Breshears, David D.; Chorover, J.; Pelletier, John D.; Saleska, S. R.; Zeng, X.; Troch, Peter A.

2014-01-01

Subsurface flow and storage dynamics at hillslope scale are difficult to ascertain, often in part due to a lack of sufficient high-resolution measurements and an incomplete understanding of boundary conditions, soil properties, and other environmental aspects. A continuous and extreme rainfall experiment on an artificial hillslope at Biosphere 2's Landscape Evolution Observatory (LEO) resulted in saturation excess overland flow and gully erosion in the convergent hillslope area. An array of 496 soil moisture sensors revealed a two-step saturation process. First, the downward movement of the wetting front brought soils to a relatively constant but still unsaturated moisture content. Second, soils were brought to saturated conditions from below in response to rising water tables. Convergent areas responded faster than upslope areas, due to contributions from lateral subsurface flow driven by the topography of the bottom boundary, which is comparable to impermeable bedrock in natural environments. This led to the formation of a groundwater ridge in the convergent area, triggering saturation excess runoff generation. This unique experiment demonstrates, at very high spatial and temporal resolution, the role of convergence on subsurface storage and flow dynamics. The results bring into question the representation of saturation excess overland flow in conceptual rainfall-runoff models and land-surface models, since flow is gravity-driven in many of these models and upper layers cannot become saturated from below. The results also provide a baseline to study the role of the co-evolution of ecological and hydrological processes in determining landscape water dynamics during future experiments in LEO.

Numerical study of Tallinn storm-water system flooding conditions using CFD simulations of multi-phase flow in a large-scale inverted siphon

NASA Astrophysics Data System (ADS)

Kaur, K.; Laanearu, J.; Annus, I.

2017-10-01

The numerical experiments are carried out for qualitative and quantitative interpretation of a multi-phase flow processes associated with malfunctioning of the Tallinn storm-water system during rain storms. The investigations are focused on the single-line inverted siphon, which is used as under-road connection of pipes of the storm-water system under interest. A multi-phase flow solver of Computational Fluid Dynamics software OpenFOAM is used for simulating the three-phase flow dynamics in the hydraulic system. The CFD simulations are performed with different inflow rates under same initial conditions. The computational results are compared essentially in two cases 1) design flow rate and 2) larger flow rate, for emptying the initially filled inverted siphon from a slurry-fluid. The larger flow-rate situations are under particular interest to detected possible flooding. In this regard, it is anticipated that the CFD solutions provide an important insight to functioning of inverted siphon under a restricted water-flow conditions at simultaneous presence of air and slurry-fluid.

Visualization of Flow in Pressurizer Spray Line Piping and Estimation of Thermal Stress Fluctuation Caused by Swaying of Water Surface

NASA Astrophysics Data System (ADS)

Oumaya, Toru; Nakamura, Akira; Onojima, Daisuke; Takenaka, Nobuyuki

The pressurizer spray line of PWR plants cools reactor coolant by injecting water into pressurizer. Since the continuous spray flow rate during commercial operation of the plant is considered insufficient to fill the pipe completely, there is a concern that a water surface exists in the pipe and may periodically sway. In order to identify the flow regimes in spray line piping and assess their impact on pipe structure, a flow visualization experiment was conducted. In the experiment, air was used substituted for steam to simulate the gas phase of the pressurizer, and the flow instability causing swaying without condensation was investigated. With a full-scale mock-up made of acrylic, flow under room temperature and atmospheric pressure conditions was visualized, and possible flow regimes were identified based on the results of the experiment. Three representative patterns of swaying of water surface were assumed, and the range of thermal stress fluctuation, when the surface swayed instantaneously, was calculated. With the three patterns of swaying assumed based on the visualization experiment, it was confirmed that the thermal stress amplitude would not exceed the fatigue endurance limit prescribed in the Japanese Design and Construction Code.

Wavelength selection and symmetry breaking in orbital wave ripples

NASA Astrophysics Data System (ADS)

Nienhuis, Jaap H.; Perron, J. Taylor; Kao, Justin C. T.; Myrow, Paul M.

2014-10-01

Sand ripples formed by waves have a uniform wavelength while at equilibrium and develop defects while adjusting to changes in the flow. These patterns arise from the interaction of the flow with the bed topography, but the specific mechanisms have not been fully explained. We use numerical flow models and laboratory wave tank experiments to explore the origins of these patterns. The wavelength of "orbital" wave ripples (λ) is directly proportional to the oscillating flow's orbital diameter (d), with many experimental and field studies finding λ/d ≈ 0.65. We demonstrate a coupling that selects this ratio: the maximum length of the flow separation zone downstream of a ripple crest equals λ when λ/d ≈ 0.65. We show that this condition maximizes the growth rate of ripples. Ripples adjusting to changed flow conditions develop defects that break the bed's symmetry. When d is shortened sufficiently, two new incipient crests appear in every trough, but only one grows into a full-sized crest. Experiments have shown that the same side (right or left) wins in every trough. We find that this occurs because incipient secondary crests slow the flow and encourage the growth of crests on the next flank. Experiments have also shown that when d is lengthened, ripple crests become increasingly sinuous and eventually break up. We find that this occurs because crests migrate preferentially toward the nearest adjacent crest, amplifying any initial sinuosity. Our results reveal the mechanisms that form common wave ripple patterns and highlight interactions among unsteady flows, sediment transport, and bed topography.

CFD study on the effects of boundary conditions on air flow through an air-cooled condenser

NASA Astrophysics Data System (ADS)

Sumara, Zdeněk; Šochman, Michal

2018-06-01

This study focuses on the effects of boundary conditions on effectiveness of an air-cooled condenser (ACC). Heat duty of ACC is very often calculated for ideal uniform velocity field which does not correspond to reality. Therefore, this study studies the effect of wind and different landscapes on air flow through ACC. For this study software OpenFOAM was used and the flow was simulated with the use of RANS equations. For verification of numerical setup a model of one ACC cell with dimensions of platform 1.5×1.5 [m] was used. In this experiment static pressures behind fan and air flows through a model of surface of condenser for different rpm of fan were measured. In OpenFOAM software a virtual clone of this experiment was built and different meshes, turbulent models and numerical schemes were tested. After tuning up numerical setup virtual model of real ACC system was built. Influence of wind, landscape and height of ACC on air flow through ACC has been investigated.

Internal Flow of Contra-Rotating Small Hydroturbine at Off- Design Flow Rates

NASA Astrophysics Data System (ADS)

SHIGEMITSU, Toru; TAKESHIMA, Yasutoshi; OGAWA, Yuya; FUKUTOMI, Junichiro

2016-11-01

Small hydropower generation is one of important alternative energy, and enormous potential lie in the small hydropower. However, efficiency of small hydroturbines is lower than that of large one. Then, there are demands for small hydroturbines to keep high performance in wide flow rate range. Therefore, we adopted contra-rotating rotors, which can be expected to achieve high performance. In this research, performance of the contra-rotating small hydroturbine with 60mm casing diameter was investigated by an experiment and numerical analysis. Efficiency of the contra-rotating small hydroturbine was high in pico-hydroturbine and high efficiency could be kept in wide flow rate range, however the performance of a rear rotor decreased significantly in partial flow rates. Then, internal flow condition, which was difficult to measure experimentally, was investigated by the numerical flow analysis. Then, a relation between the performance and internal flow condition was considered by the numerical analysis result.

A numerical study of the complex flow structure in a compound meandering channel

NASA Astrophysics Data System (ADS)

Moncho-Esteve, Ignacio J.; García-Villalba, Manuel; Muto, Yasu; Shiono, Koji; Palau-Salvador, Guillermo

2018-06-01

In this study, we report large eddy simulations of turbulent flow in a periodic compound meandering channel for three different depth conditions: one in-bank and two overbank conditions. The flow configuration corresponds to the experiments of Shiono and Muto (1998). The predicted mean streamwise velocities, mean secondary motions, velocity fluctuations, turbulent kinetic energy as well as mean flood flow angle to meandering channel are in good agreement with the experimental measurements. We have analyzed the flow structure as a function of the inundation level, with particular emphasis on the development of the secondary motions due to the interaction between the main channel and the floodplain flow. Bed shear stresses have been also estimated in the simulations. Floodplain flow has a significant impact on the flow structure leading to significantly different bed shear stress patterns within the main meandering channel. The implications of these results for natural compound meandering channels are also discussed.

Burst Speed of Wild Fishes under High-Velocity Flow Conditions Using Stamina Tunnel with Natural Guidance System in River

NASA Astrophysics Data System (ADS)

Izumi, Mattashi; Yamamoto, Yasuyuki; Yataya, Kenichi; Kamiyama, Kohhei

Swimming experiments were conducted on wild fishes in a natural guidance system stamina tunnel (cylindrical pipe) installed in a fishway of a local river under high-velocity flow conditions (tunnel flow velocity : 211 to 279 cm·s-1). In this study, the swimming characteristics of fishes were observed. The results show that (1) the swimming speeds of Tribolodon hakonensis (Japanese dace), Phoxinus lagowshi steindachneri (Japanese fat-minnow), Plecoglossus altivelis (Ayu), and Zacco platypus (Pale chub) were in proportion to their body length under identical water flow velocity conditions; (2) the maximum burst speed of Japanese dace and Japanese fat-minnow (measuring 4 to 6 cm in length) was 262 to 319 cm·s-1 under high flow velocity conditions (225 to 230 cm·s-1), while the maximum burst speed of Ayu and Pale chub (measuring 5 cm to 12 cm in length) was 308 to 355 cm·s-1 under high flow velocity conditions (264 to 273 cm·s-1) ; (3) the 50cm-maximum swimming speed of swimming fishes was 1.07 times faster than the pipe-swimming speed; (4) the faster the flow velocity, the shorter the swimming distance became.

Effect of gravity on colloid transport through water-saturated columns packed with glass beads: modeling and experiments.

PubMed

Chrysikopoulos, Constantinos V; Syngouna, Vasiliki I

2014-06-17

The role of gravitational force on colloid transport in water-saturated columns packed with glass beads was investigated. Transport experiments were performed with colloids (clays: kaolinite KGa-1b, montmorillonite STx-1b). The packed columns were placed in various orientations (horizontal, vertical, and diagonal) and a steady flow rate of Q = 1.5 mL/min was applied in both up-flow and down-flow modes. All experiments were conducted under electrostatically unfavorable conditions. The experimental data were fitted with a newly developed, analytical, one-dimensional, colloid transport model. The effect of gravity is incorporated in the mathematical model by combining the interstitial velocity (advection) with the settling velocity (gravity effect). The results revealed that flow direction influences colloid transport in porous media. The rate of particle deposition was shown to be greater for up-flow than for down-flow direction, suggesting that gravity was a significant driving force for colloid deposition.

Ecosystem Consequences of Contrasting Flow Regimes in an Urban Effects Stream Mesocosm Study

EPA Science Inventory

A stream mesocosm experiment was conducted to study the ecosystem-wide effects of two replicated flow hydrograph treatments programmed in an attempt to compare a simulated predevelopment condition to the theoretical changes that new development brings, while accounting for engine...

Generation of dense plume fingers in saturated-unsaturated homogeneous porous media

NASA Astrophysics Data System (ADS)

Cremer, Clemens J. M.; Graf, Thomas

2015-02-01

Flow under variable-density conditions is widespread, occurring in geothermal reservoirs, at waste disposal sites or due to saltwater intrusion. The migration of dense plumes typically results in the formation of vertical plume fingers which are known to be triggered by material heterogeneity or by variations in source concentration that causes the density variation. Using a numerical groundwater model, six perturbation methods are tested under saturated and unsaturated flow conditions to mimic heterogeneity and concentration variations on the pore scale in order to realistically generate dense fingers. A laboratory-scale sand tank experiment is numerically simulated, and the perturbation methods are evaluated by comparing plume fingers obtained from the laboratory experiment with numerically simulated fingers. Dense plume fingering for saturated flow can best be reproduced with a spatially random, time-constant perturbation of the solute source. For unsaturated flow, a spatially and temporally random noise of solute concentration or a random conductivity field adequately simulate plume fingering.

Image-based Lagrangian Particle Tracking in Bed-load Experiments.

PubMed

Radice, Alessio; Sarkar, Sankar; Ballio, Francesco

2017-07-20

Image analysis has been increasingly used for the measurement of river flows due to its capabilities to furnish detailed quantitative depictions at a relatively low cost. This manuscript describes an application of particle tracking velocimetry (PTV) to a bed-load experiment with lightweight sediment. The key characteristics of the investigated sediment transport conditions were the presence of a covered flow and of a fixed rough bed above which particles were released in limited number at the flume inlet. Under the applied flow conditions, the motion of the individual bed-load particles was intermittent, with alternating movement and stillness terms. The flow pattern was preliminarily characterized by acoustic measurements of vertical profiles of the stream-wise velocity. During process visualization, a large field of view was obtained using two action-cameras placed at different locations along the flume. The experimental protocol is described in terms of channel calibration, experiment realization, image pre-processing, automatic particle tracking, and post-processing of particle track data from the two cameras. The presented proof-of-concept results include probability distributions of the particle hop length and duration. The achievements of this work are compared to those of existing literature to demonstrate the validity of the protocol.

Single element injector cold flow testing for STME swirl coaxial injector element design

NASA Technical Reports Server (NTRS)

Hulka, J.; Schneider, J. A.

1993-01-01

An oxidizer-swirled coaxial element injector is being investigated for application in the Space Transportation Main Engine (STME). Single element cold flow experiments were conducted to provide characterization of the STME injector element for future analysis, design, and optimization. All tests were conducted to quiescent, ambient backpressure conditions. Spray angle, circumferential spray uniformity, dropsize, and dropsize distribution were measured in water-only and water/nitrogen flows. Rupe mixing efficiency was measured using water/sucrose solution flows with a large grid patternator for simple comparative evaluation of mixing. Factorial designs of experiment were used for statistical evaluation of injector geometrical design features and propellant flow conditions on mixing and atomization. Increasing the free swirl angle of the liquid oxidizer had the greatest influence on increasing the mixing efficiency. The addition of gas assistance had the most significant effect on reducing oxidizer droplet size parameters and increasing droplet size distribution. Increasing the oxidizer injection velocity had the greatest influence for reducing oxidizer droplet size parameters and increasing size distribution for non-gas assisted flows. Single element and multi-element subscale hot fire testing are recommended to verify optimized designs before committing to the STME design.

Effects of Gravity on Supercritical Water Oxidation (SCWO) Processes

NASA Technical Reports Server (NTRS)

Hegde, Uday; Hicks, Michael

2013-01-01

The effects of gravity on the fluid mechanics of supercritical water jets are being studied at NASA to develop a better understanding of flow behaviors for purposes of advancing supercritical water oxidation (SCWO) technologies for applications in reduced gravity environments. These studies provide guidance for the development of future SCWO experiments in new experimental platforms that will extend the current operational range of the DECLIC (Device for the Study of Critical Liquids and Crystallization) Facility on board the International Space Station (ISS). The hydrodynamics of supercritical fluid jets is one of the basic unit processes of a SCWO reactor. These hydrodynamics are often complicated by significant changes in the thermo-physical properties that govern flow behavior (e.g., viscosity, thermal conductivity, specific heat, compressibility, etc), particularly when fluids transition from sub-critical to supercritical conditions. Experiments were conducted in a 150 ml reactor cell under constant pressure with water injections at various flow rates. Flow configurations included supercritical jets injected into either sub-critical or supercritical water. Profound gravitational influences were observed, particularly in the transition to turbulence, for the flow conditions under study. These results will be presented and the parameters of the flow that control jet behavior will be examined and discussed.

Comparative study on aerodynamic heating under perfect and nonequilibrium hypersonic flows

NASA Astrophysics Data System (ADS)

Wang, Qiu; Li, JinPing; Zhao, Wei; Jiang, ZongLin

2016-02-01

In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics (LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.

Rapid determination of tartaric acid in wines.

PubMed

Bastos, Sandra S T; Tafulo, Paula A R; Queirós, Raquel B; Matos, Cristina D; Sales, M Goreti F

2009-08-01

A flow-spectrophotometric method is proposed for the routine determination of tartaric acid in wines. The reaction between tartaric acid and vanadate in acetic media is carried out in flowing conditions and the subsequent colored complex is monitored at 475 nm. The stability of the complex and the corresponding formation constant are presented. The effect of wavelength and pH was evaluated by batch experiments. The selected conditions were transposed to a flow-injection analytical system. Optimization of several flow parameters such as reactor lengths, flow-rate and injection volume was carried out. Using optimized conditions, a linear behavior was observed up to 1000 microg mL(-1) tartaric acid, with a molar extinction coefficient of 450 L mg(-1) cm(-1) and +/- 1 % repeatability. Sample throughput was 25 samples per hour. The flow-spectrophotometric method was satisfactorily applied to the quantification of TA in wines from different sources. Its accuracy was confirmed by statistical comparison to the conventional Rebelein procedure and to a certified analytical method carried out in a routine laboratory.

Friction-term response to boundary-condition type in flow models

USGS Publications Warehouse

Schaffranek, R.W.; Lai, C.

1996-01-01

The friction-slope term in the unsteady open-channel flow equations is examined using two numerical models based on different formulations of the governing equations and employing different solution methods. The purposes of the study are to analyze, evaluate, and demonstrate the behavior of the term in a set of controlled numerical experiments using varied types and combinations of boundary conditions. Results of numerical experiments illustrate that a given model can respond inconsistently for the identical resistance-coefficient value under different types and combinations of boundary conditions. Findings also demonstrate that two models employing different dependent variables and solution methods can respond similarly for the identical resistance-coefficient value under similar types and combinations of boundary conditions. Discussion of qualitative considerations and quantitative experimental results provides insight into the proper treatment, evaluation, and significance of the friction-slope term, thereby offering practical guidelines for model implementation and calibration.

Bedload fluctuations in a steep macro-rough channel

NASA Astrophysics Data System (ADS)

Ghilardi, Tamara; Franca, Mário J.; Schleiss, Anton J.

2014-05-01

It is known that bedload fluctuates over time in steep rivers with wide grain size distributions, even when conditions of constant sediment feed and water discharge are met. Bedload fluctuations are periodic and related to fluctuations in the flow velocity and channel bed morphology. In cascade morphologies, the presence of large relatively immobile boulders has a strong impact on flow conditions and sediment transport; their influence on bedload fluctuations is considered in this research. Sediment transport fluctuations were investigated in a set of 38 laboratory experiments carried out on a steep tilting flume, under several conditions of constant sediment and water discharge, for three different slopes (S=6.7%, 9.9%, and 13%). The impact of the diameter and spatial density of randomly placed boulders was studied for several flow conditions. Along with the sediment transport and bulk mean flow velocity, the boulder protrusion, boulder surface, and number of hydraulic jumps, which are indicators of the channel morphology, were measured regularly during the experiments. Periodic bedload pulses are clearly visible in the data collected during the experiments, along with well correlated fluctuations in the flow velocity and bed morphology parameters. Well-behaved cyclic oscillations in the auto-correlation and cross-correlation functions confirm the periodicity of the observed fluctuations and show that the durations of these cycles are similar, although not necessarily in phase. A detailed analysis of data time series and image acquired during the tests show a link between bedload pulses and different bed states, boulder protrusion, and surface grain size distributions. A feedback system exists among channel morphology, flow kinematics and sediment transport. A phase analysis for the observed variables, based on the identification of bedload cycles in the instantaneous signal, is performed. The link between the phases of bedload and each of the morphological parameters show a hysteretic path. The relation between the phase-averaged bedload and the phase-averaged flow velocity show a considerable lesser degree of hysteresis. Comparing the phase averaged bedload of the experiments, it is observed that the shape of bedload cycles is the same for all tested hydraulic conditions. The cycles present a long duration low sediment transport event and a shorter peak transport event. This indicates that long periods of sediment aggradations alternate with short erosion periods, even under constant hydraulic conditions. The bedload pulses may be characterized by their amplitude and period as a function of various boulder spatial densities and diameters. We show that for higher stream power, the fluctuations decrease, both in cycle duration and in amplitude. The presence of boulders increases the stream power needed to transport a given amount of sediment, thus decreasing fluctuations. KEY WORDS: Bedload fluctuations; Morphological changes; Sediment transport; Boulders; Steep channel.

Experimental study on the signs of particulate structures formation in annular geometry of rapid granular shear flows

NASA Astrophysics Data System (ADS)

Ritvanen, J.; Jalali, P.

2009-06-01

Rapid granular shear flow is a classical example in granular materials which exhibits both fluid-like and solid-like behaviors. Another interesting feature of rapid granular shear flows is the formation of ordered structures upon shearing. Certain amount of granular material, with uniform size distribution, is required to be loaded in the container in order to shear it under stable conditions. This work concerns the experimental study of rapid granular shear flows in annular Couette geometry. The flow is induced by continuous rotation of the plate over the top of the granular bed in an annulus. The compressive pressure, driving torque, instantaneous bed height from three symmetric locations and rotational speed of the shearing plate are measured. The annulus has a capacity of up to 15 kg of spherical steel balls of 3 mm in diameter. Rapid shear flow experiments are performed in one compressive force and rotation rate. The sensitivity of fluctuations is then investigated by different means through monodisperse packing. In this work, we present the results of the experiments showing how the flow properties depend on the amount of loaded granular material which is varied by small amounts between different experiments. The flow can exist in stable (fixed behavior) and unstable (time-dependent behavior) regimes as a function of the loaded material. We present the characteristics of flow to detect the formation of any additional structured layer in the annulus. As a result, an evolution graph for the bed height has been obtained as material is gradually added. This graph shows how the bed height grows when material increases. Using these results, the structure inside the medium can be estimated at extreme stable and unstable conditions.

Pore Scale Dynamics of Microemulsion Formation.

PubMed

Unsal, Evren; Broens, Marc; Armstrong, Ryan T

2016-07-19

Experiments in various porous media have shown that multiple parameters come into play when an oleic phase is displaced by an aqueous solution of surfactant. In general, the displacement efficiency is improved when the fluids become quasi-miscible. Understanding the phase behavior oil/water/surfactant systems is important because microemulsion has the ability to generate ultralow interfacial tension (<10(-2) mN m(-1)) that is required for miscibility to occur. Many studies focus on microemulsion formation and the resulting properties under equilibrium conditions. However, the majority of applications where microemulsion is present also involve flow, which has received relatively less attention. It is commonly assumed that the characteristics of an oil/water/surfactant system under flowing conditions are identical to the one under equilibrium conditions. Here, we show that this is not necessarily the case. We studied the equilibrium phase behavior of a model system consisting of n-decane and an aqueous solution of olefin sulfonate surfactant, which has practical applications for enhanced oil recovery. The salt content of the aqueous solution was varied to provide a range of different microemulsion compositions and oil-water interfacial tensions. We then performed microfluidic flow experiments to study the dynamic in situ formation of microemulsion by coinjecting bulk fluids of n-decane and surfactant solution into a T-junction capillary geometry. A solvatochromatic fluorescent dye was used to obtain spatially resolved compositional information. In this way, we visualized the microemulsion formation and the flow of it along with the excess phases. A complex interaction between the flow patterns and the microemulsion properties was observed. The formation of microemulsion influenced the flow regimes, and the flow regimes affected the characteristics of the microemulsion formation. In particular, at low flow rates, slug flow was observed, which had profound consequences on the pore scale mixing behavior and resulting microemulsion properties.

Capillary channel flow experiments aboard the International Space Station

NASA Astrophysics Data System (ADS)

Conrath, M.; Canfield, P. J.; Bronowicki, P. M.; Dreyer, M. E.; Weislogel, M. M.; Grah, A.

2013-12-01

In the near-weightless environment of orbiting spacecraft capillary forces dominate interfacial flow phenomena over unearthly large length scales. In current experiments aboard the International Space Station, partially open channels are being investigated to determine critical flow rate-limiting conditions above which the free surface collapses ingesting bubbles. Without the natural passive phase separating qualities of buoyancy, such ingested bubbles can in turn wreak havoc on the fluid transport systems of spacecraft. The flow channels under investigation represent geometric families of conduits with applications to liquid propellant acquisition, thermal fluids circulation, and water processing for life support. Present and near future experiments focus on transient phenomena and conduit asymmetries allowing capillary forces to replace the role of gravity to perform passive phase separations. Terrestrial applications are noted where enhanced transport via direct liquid-gas contact is desired.

Identifiability of sorption parameters in stirred flow-through reactor experiments and their identification with a Bayesian approach.

PubMed

Nicoulaud-Gouin, V; Garcia-Sanchez, L; Giacalone, M; Attard, J C; Martin-Garin, A; Bois, F Y

2016-10-01

This paper addresses the methodological conditions -particularly experimental design and statistical inference- ensuring the identifiability of sorption parameters from breakthrough curves measured during stirred flow-through reactor experiments also known as continuous flow stirred-tank reactor (CSTR) experiments. The equilibrium-kinetic (EK) sorption model was selected as nonequilibrium parameterization embedding the K d approach. Parameter identifiability was studied formally on the equations governing outlet concentrations. It was also studied numerically on 6 simulated CSTR experiments on a soil with known equilibrium-kinetic sorption parameters. EK sorption parameters can not be identified from a single breakthrough curve of a CSTR experiment, because K d,1 and k - were diagnosed collinear. For pairs of CSTR experiments, Bayesian inference allowed to select the correct models of sorption and error among sorption alternatives. Bayesian inference was conducted with SAMCAT software (Sensitivity Analysis and Markov Chain simulations Applied to Transfer models) which launched the simulations through the embedded simulation engine GNU-MCSim, and automated their configuration and post-processing. Experimental designs consisting in varying flow rates between experiments reaching equilibrium at contamination stage were found optimal, because they simultaneously gave accurate sorption parameters and predictions. Bayesian results were comparable to maximum likehood method but they avoided convergence problems, the marginal likelihood allowed to compare all models, and credible interval gave directly the uncertainty of sorption parameters θ. Although these findings are limited to the specific conditions studied here, in particular the considered sorption model, the chosen parameter values and error structure, they help in the conception and analysis of future CSTR experiments with radionuclides whose kinetic behaviour is suspected. Copyright © 2016 Elsevier Ltd. All rights reserved.

Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Dobson, Patrick F.; Kneafsey, Timothy J.; Sonnenthal, Eric L.; Spycher, Nicolas; Apps, John A.

2003-05-01

Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 °C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 °C at the top and 130 °C at the bottom. The fracture began to seal with amorphous silica within 5 days. A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment. These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However, differences in fluid flow rates and thermal gradients between the experimental setup and anticipated conditions at Yucca Mountain need to be factored into scaling the results of the dissolution/precipitation experiments and associated simulations to THC models for the potential Yucca Mountain repository.

Study of Natural Fiber Breakage during Composite Processing

NASA Astrophysics Data System (ADS)

Quijano-Solis, Carlos Jafet

Biofiber-thermoplastic composites have gained considerable importance in the last century. To provide mechanical reinforcement to the polymer, fibers must be larger than a critical aspect ratio (length-to-width ratio). However, biofibers undergo breakage in length or width during processing, affecting their final aspect ratio in the composites. In this study, influence on biofiber breakage by factors related to processing conditions, fiber morphology and the flow type was investigated through: a) experiments using an internal mixer, a twin-screw extruder (TSE) or a capillary rheometer; and b) a Monte Carlo computer simulation. Composites of thermomechanical fibers of aspen or wheat straw mixed with polypropylene were studied. Internal mixer experiments analyzed wheat straw and two batches of aspen fibers, named AL and AS. AL fibers had longer average length. Processing variables included the temperature, rotors speed and fiber concentration. TSE experiments studied AL and AS fiber composites under various screws speeds, temperatures and feeding rates of the polymer and fibers. Capillary rheometers experiments determined AL fiber breakage in shear and elongational flows for composites processed at different concentrations, temperatures, and strain rates. Finally, the internal mixer experimental results where compared to Monte Carlo simulation predictions. The simulation focused on fiber length breakage due to fiber-polymer interactions. Internal mixer results showed that final fiber average length depended almost solely on processing conditions while final fiber average width depended on both processing conditions and initial fiber morphology. In the TSE, processing conditions as well as initial fiber length influenced final average length. TSE results showed that the fiber concentration regime seems to influence the effect of processing variables on fiber breakage. Capillary rheometer experiments demonstrated that biofiber breakage happens in both elongational and shear flows. In some cases, percentage of biofiber breakage in elongational flow is higher. In general, simulation predictions of final average lengths were in good agreement with experiments, indicating the importance of fiber-polymer interactions on fiber breakage. The largest discrepancies were obtained at higher fiber concentration composites; these differences might be resolved, in future simulations, by including the effect of fiber-fiber interactions.

Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars

NASA Astrophysics Data System (ADS)

Dixon, Emily M.; Elwood Madden, Andrew S.; Hausrath, Elisabeth M.; Elwood Madden, Megan E.

2015-04-01

Jarosite flow-through dissolution experiments were conducted in ultrapure water (UPW), pH 2 sulfuric acid, and saturated NaCl and CaCl2 brines at 295-298 K to investigate how hydrologic variables may affect jarosite preservation and reaction products on Mars. K+-based dissolution rates in flowing UPW did not vary significantly with flow rate, indicating that mineral surface reactions control dissolution rates over the range of flow rates investigated. In all of the solutions tested, hydrologic variables do not significantly affect extent of jarosite alteration; therefore, jarosite is equally likely to be preserved in flowing or stagnant waters on Mars. However, increasing flow rate did affect the mineralogy and accumulation of secondary reaction products. Iron release rates in dilute solutions increased as the flow rate increased, likely due to nanoscale iron (hydr)oxide transport in flowing water. Anhydrite formed in CaCl2 brine flow-through experiments despite low temperatures, while metastable gypsum and bassanite were observed in batch experiments. Therefore, observations of the hydration state of calcium sulfate minerals on Mars may provide clues to unravel past salinity and hydrologic conditions as well as temperatures and vapor pressures.

Numerical prediction of a draft tube flow taking into account uncertain inlet conditions

NASA Astrophysics Data System (ADS)

Brugiere, O.; Balarac, G.; Corre, C.; Metais, O.; Flores, E.; Pleroy

2012-11-01

The swirling turbulent flow in a hydroturbine draft tube is computed with a non-intrusive uncertainty quantification (UQ) method coupled to Reynolds-Averaged Navier-Stokes (RANS) modelling in order to take into account in the numerical prediction the physical uncertainties existing on the inlet flow conditions. The proposed approach yields not only mean velocity fields to be compared with measured profiles, as is customary in Computational Fluid Dynamics (CFD) practice, but also variance of these quantities from which error bars can be deduced on the computed profiles, thus making more significant the comparison between experiment and computation.

Mass transfers induced by flow of CO2 rich-brine through fractured cement: experiment and modeling

NASA Astrophysics Data System (ADS)

Habdoulghafour, H.; Luquot, L.; Gouze, P.

2011-12-01

Long-term confinement failure is a key issue in the assessment of the confidence levels of CO2 storage. Evaluating the potential for CO2 leakage through wells (casing, cements and interfaces with the cap-rock) is of primary importance for the analysis of latent and short-range risks of confinement failure. Some controversy remains regarding the risk of conventional cements. While some researchers argue that they may fail, EOR oil industry experience suggests the opposite. The issue is non-trivial. Experimental investigations on cement alteration mechanism triggered by CO2-rich brine show that both carbonation and de-carbonation mechanisms may occur and are the dominant mass exchange processes. It is tempting to conclude from the results of batch experiments that cement carbonation tends to decrease porosity and permeability, whereas de-carbonation increases both, but these assumptions must be tested using realistic flow-through experiments. Here we investigated the effect of CO2 rich-brine flowing through fractured portlandite-rich cement plugs. Experiments were carried out under realistic in situ conditions (T=80°C and P=10 MPa). Monitoring the fluid composition at the outlet allows us to measure the rate at which portlandite and CSH are dissolved and Ca-carbonate (calcite) precipitated. The precipitation of carbonate limits the fluid access to the inner part of cement (by diffusion) but, in the condition of forced flow-through CO2-rich brine in the fracture, this carbonate layer is subsequently dissolved as showed by the X-ray micro tomography performed post-mortem. Despite these coupled dissolution-precipitation mechanisms (and the on-going reaction front displacement), the permeability of the fracture remains almost constant during the experiment because the effective aperture controlled by the undissolved fraction of the cement (i.e. silica-rich minerals) is preserved. For the studied conditions, it can be concluded that the flow properties of the fractured cements are conserved, while the chemical and probably the mechanical properties of the cement are deeply modified.

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

NASA Technical Reports Server (NTRS)

Griffin, D. W.; Yep, T. W.; Agrawal, A. K.

2005-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2- second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes change in gravity in the drop tower.

Characteristic Analysis and Experiment of a Dynamic Flow Balance Valve

NASA Astrophysics Data System (ADS)

Bin, Li; Song, Guo; Xuyao, Mao; Chao, Wu; Deman, Zhang; Jin, Shang; Yinshui, Liu

2017-12-01

Comprehensive characteristics of a dynamic flow balance valve of water system were analysed. The flow balance valve can change the drag efficient automatically according to the condition of system, and the effective control flowrate is constant in the range of job pressure. The structure of the flow balance valve was introduced, and the theoretical calculation formula for the variable opening of the valve core was derived. A rated pressure of 20kPa to 200kPa and a rated flowrate of 10m3/h were offered in the numerical work. Static and fluent CFX analyses show good behaviours: through the valve core structure optimization and improve design of the compressive spring, the dynamic flow balance valve can stabilize the flowrate of system evidently. And experiments show that the flow control accuracy is within 5%.

Can we use only Grain Size Data for Paleo-Flow Reconstructions?

NASA Astrophysics Data System (ADS)

Perillo, M. M.; Pohl, F.; Eggenhuisen, J. T.; Fedele, J.; Hoyal, D. C. J. D.; Mohrig, D. C.

2015-12-01

Paleo-flow and paleo-environmental reconstruction from ancient deposits is a critical task for earth surface scientists interested in the sedimentary record. Forming processes are commonly interpreted from the architectural characteristics of sedimentary deposits using quantitative relationships derived from experiments or geomorphic studies. However, very little attention has been paid to the equivalent problem at the scale of micro-facies: can we interpret the conditions at the time of sediment accumulation from grain size information in a small sample? Here we investigate the use of grain size distributions alone to reconstruct the flow conditions based on a set of experiments conducted in a 2D flume tank in the Eurotank facilities at Utrecht University. The experiments are designed for the examination of grain size distributions within sediments which were deposited by flows with known conditions (e.g. velocity, turbulence, shear velocity, concentration). By changing the slope of the flume tank we were able to create a range of flows from strongly depositional (depletive) to bypassing. Inspired by Eastwood et al (2012), we propose a working methodology to link the grain size distribution of the deposit to flow conditions. Our method utilizes the following empiric relations: i) the finer fraction of the deposit was deposited while most of that range surpass the Bagnold (1966)'s suspension threshold (shear velocity υ* approx. 3 times the settling velocity ωs); ii) the mean fraction was at incipient suspension stage (υ* ~ ωs); iii) the finer portion of the coarser grains were at bedload/saltation stage, where u* is approx. υ*c (critical shear velocity for initiation of motion); and iv) the coarser portion of the coarser grains were at creep-bedload stage, where υ* is approx. 0.7υ*c . We test whether this set of rules can be applied to the probability distribution function of deposit grainsize in an inversion that converges on a single value for the shear velocity, and whether this inverted shear velocity is in accordance with the experimental flow conditions. Preliminary application of this method to outcrop work will be given. Bagnold, R. (1966), U. S. Geol. Surv. Prof. Pap., 422-I, 37 pp. Eastwood, E. N., G. Kocurek, D. Mohrig, and T. Swanson (2012), J. Geophys. Res., 117, F03035, doi:10.1029/2012JF002368.

Zonal Acoustic Velocimetry in 30-cm, 60-cm, and 3-m Laboratory Models of the Outer Core

NASA Astrophysics Data System (ADS)

Rojas, R.; Doan, M. N.; Adams, M. M.; Mautino, A. R.; Stone, D.; Lekic, V.; Lathrop, D. P.

2016-12-01

A knowledge of zonal flows and shear is key in understanding magnetic field dynamics in the Earth and laboratory experiments with Earth-like geometries. Traditional techniques for measuring fluid flow using visualization and particle tracking are not well-suited to liquid metal flows. This has led us to develop a flow measurement technique based on acoustic mode velocimetry adapted from helioseismology. As a first step prior to measurements in the liquid sodium experiments, we implement this technique in our 60-cm diameter spherical Couette experiment in air. To account for a more realistic experimental geometry, including deviations from spherical symmetry, we compute predicted frequencies of acoustic normal modes using the finite element method. The higher accuracy of the predicted frequencies allows the identification of over a dozen acoustic modes, and mode identification is further aided by the use of multiple microphones and by analyzing spectra together with those obtained at a variety of nearby Rossby numbers. Differences between the predicted and observed mode frequencies are caused by differences in flow patterns present in the experiment. We compare acoustic mode frequency splittings with theoretical predictions for stationary fluid and solid body flow condition with excellent agreement. We also use this technique to estimate the zonal shear in those experiments across a range of Rossby numbers. Finally, we report on initial attempts to use this in liquid sodium in the 3-meter diameter experiment and parallel experiments performed in water in the 30-cm diameter experiment.

Experimental constraints on the outgassing dynamics of basaltic magmas

NASA Astrophysics Data System (ADS)

Pioli, L.; Bonadonna, C.; Azzopardi, B. J.; Phillips, J. C.; Ripepe, M.

2012-03-01

The dynamics of separated two-phase flow of basaltic magmas in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10-2-102 m/s), conduit diameters (100-2 m), and magma viscosities (3-300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as Co (distribution parameter) and Froude number, which control the maximum vesicularity of the magma in the column, and the gas rise speed of gas slugs. It predicts that magma vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 103-104 m3/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by magma vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in magma viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring magma homogeneity and stable conditions.

[Testing the efficacy of disinfectants during drinking water treatment. A new experimental set-up at the German EPA (Umweltbundesamt - UBA)].

PubMed

Grützmacher, G; Bartel, H; Althoff, H W; Clemen, S

2007-03-01

A set-up for experiments in the flow-through mode was constructed in order to test the efficacy of substances used for disinfecting water during drinking water treatment. A flow-through mode - in contrast to experiments under stationary conditions (so-called batch experiments) - was chosen, because this experimental design allows experiments to be carried out under constant conditions for an extended time (up to one week) and because efficacy testing is possible repeatedly, simultaneously and under exactly the same conditions for short (about 0.5 min) and also longer (about 47 min) contact times. With this experimental design the effect of biofilms along the inner pipe surfaces can be included in the observations. The construction of the experimental set-up is based on experience with laboratory flow-through systems that were installed by the UBA's drinking water department (formerly Institute for Water-, Soil- and Air Hygiene (WaBoLu) Institute) for testing disinfection with chlorine. In the first step, a test pipe for the simulation of a water works situation was installed. Water of different qualities can be mixed in large volumes beforehand so that the experimental procedure can be run with constant water quality for a minimum of one week. The kinetics of the disinfection reaction can be observed by extracting samples from eight sampling ports situated along the test pipe. In order to assign exact residence times to each of the sampling ports, tracer experiments were performed prior to testing disinfectant efficacy. This paper gives the technical details of the experimental set-up and presents the results of the tracer experiments to provide an introduction with respect to its potential.

Strategy Plan A Methodology to Predict the Uniformity of Double-Shell Tank Waste Slurries Based on Mixing Pump Operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

J.A. Bamberger; L.M. Liljegren; P.S. Lowery

This document presents an analysis of the mechanisms influencing mixing within double-shell slurry tanks. A research program to characterize mixing of slurries within tanks has been proposed. The research program presents a combined experimental and computational approach to produce correlations describing the tank slurry concentration profile (and therefore uniformity) as a function of mixer pump operating conditions. The TEMPEST computer code was used to simulate both a full-scale (prototype) and scaled (model) double-shell waste tank to predict flow patterns resulting from a stationary jet centered in the tank. The simulation results were used to evaluate flow patterns in the tankmore » and to determine whether flow patterns are similar between the full-scale prototype and an existing 1/12-scale model tank. The flow patterns were sufficiently similar to recommend conducting scoping experiments at 1/12-scale. Also, TEMPEST modeled velocity profiles of the near-floor jet were compared to experimental measurements of the near-floor jet with good agreement. Reported values of physical properties of double-shell tank slurries were analyzed to evaluate the range of properties appropriate for conducting scaled experiments. One-twelfth scale scoping experiments are recommended to confirm the prioritization of the dimensionless groups (gravitational settling, Froude, and Reynolds numbers) that affect slurry suspension in the tank. Two of the proposed 1/12-scale test conditions were modeled using the TEMPEST computer code to observe the anticipated flow fields. This information will be used to guide selection of sampling probe locations. Additional computer modeling is being conducted to model a particulate laden, rotating jet centered in the tank. The results of this modeling effort will be compared to the scaled experimental data to quantify the agreement between the code and the 1/12-scale experiment. The scoping experiment results will guide selection of parameters to be varied in the follow-on experiments. Data from the follow-on experiments will be used to develop correlations to describe slurry concentration profile as a function of mixing pump operating conditions. This data will also be used to further evaluate the computer model applications. If the agreement between the experimental data and the code predictions is good, the computer code will be recommended for use to predict slurry uniformity in the tanks under various operating conditions. If the agreement between the code predictions and experimental results is not good, the experimental data correlations will be used to predict slurry uniformity in the tanks within the range of correlation applicability.« less

Sheet-like and plume-like thermal flow in a spherical convection experiment performed under microgravity

NASA Astrophysics Data System (ADS)

Breuer, D.; Futterer, B.; Plesa, A.; Krebs, A.; Zaussinger, F.; Egbers, C.

2013-12-01

In mantle dynamics research, experiments, usually performed in rectangular geometries in Earth-based laboratories, have the character of ';exploring new physics and testing theories' [1]. In this work, we introduce our spherical geometry experiments on electro-hydrodynamical driven Rayleigh-Benard convection that have been performed for both temperature-independent (`GeoFlow I'), and temperature-dependent fluid viscosity properties (`GeoFlow II') with a measured viscosity contrast up to 1.5. To set up a self-gravitating force field, we use a high voltage potential between the inner and outer boundaries and a dielectric insulating liquid and perform the experiment under microgravity conditions at the ISS [2, 3]. Further, numerical simulations in 3D spherical geometry have been used to reproduce the results obtained in the `GeoFlow' experiments. For flow visualisation, we use Wollaston prism shearing interferometry which is an optical method producing fringe pattern images. Flow pattern differ between our two experiments (Fig. 1). In `GeoFlow I', we see a sheet-like thermal flow. In this case convection patterns have been successfully reproduced by 3D numerical simulations using two different and independently developed codes. In contrast, in `GeoFlow II' we obtain plume-like structures. Interestingly, numerical simulations do not yield this type of solution for the low viscosity contrast realised in the experiment. However, using a viscosity contrast of two orders of magnitude or higher, we can reproduce the patterns obtained in the `GeoFlow II' experiment, from which we conclude that non-linear effects shift the effective viscosity ratio [4]. References [1] A. Davaille and A. Limare (2009). In: Schubert, G., Bercovici, D. (Eds.), Treatise on Geophysics - Mantle Dynamics. [2] B. Futterer, C. Egbers, N. Dahley, S. Koch, L. Jehring (2010). Acta Astronautica 66, 193-100. [3] B. Futterer, N. Dahley, S. Koch, N. Scurtu, C. Egbers (2012). Acta Astronautica 71, 11-19. [4] B. Futterer, A. Krebs, A.-C. Plesa, F. Zaussinger, D.Breuer, C. Egbers (2013). submitted to Journal of Fluid Mechanics. Fig. 1: a) Sheet-like thermal flow in the GeoFlow I spherical experiment with silicone oil of temperature-stable properties (RaE=1.17e6); b) Plume-like dominated flow in the GeoFlow II experiment using a fluid with temperature dependent viscosity and volume expansion (RaE=1.87e6).

The effects of boundary conditions on the steady-state response of three hypothetical ground-water systems; results and implications of numerical experiments

USGS Publications Warehouse

Franke, O. Lehn; Reilly, Thomas E.

1987-01-01

The most critical and difficult aspect of defining a groundwater system or problem for conceptual analysis or numerical simulation is the selection of boundary conditions . This report demonstrates the effects of different boundary conditions on the steady-state response of otherwise similar ground-water systems to a pumping stress. Three series of numerical experiments illustrate the behavior of three hypothetical groundwater systems that are rectangular sand prisms with the same dimensions but with different combinations of constant-head, specified-head, no-flow, and constant-flux boundary conditions. In the first series of numerical experiments, the heads and flows in all three systems are identical, as are the hydraulic conductivity and system geometry . However, when the systems are subjected to an equal stress by a pumping well in the third series, each differs significantly in its response . The highest heads (smallest drawdowns) and flows occur in the systems most constrained by constant- or specified-head boundaries. These and other observations described herein are important in steady-state calibration, which is an integral part of simulating many ground-water systems. Because the effects of boundary conditions on model response often become evident only when the system is stressed, a close match between the potential distribution in the model and that in the unstressed natural system does not guarantee that the model boundary conditions correctly represent those in the natural system . In conclusion, the boundary conditions that are selected for simulation of a ground-water system are fundamentally important to groundwater systems analysis and warrant continual reevaluation and modification as investigation proceeds and new information and understanding are acquired.

Adaptive-Wall Wind-Tunnel Investigations

DTIC Science & Technology

1981-02-01

boundary condition for unconfined flow. In this way, theory and experiment are combined to minimize wall interference. The concept of an adaptive wall...should be noted that although shock waves extend to the walls, the exterior-flow calculation was based on subcritical-flow theory . Goodyer’s configuration...and v by aerodynamic probes. Both subsonic and transonic small- disturbance theory were used, as appropriate, to evaluate the functional rela

Flow Visualization Techniques in Wind Tunnel Tests of a Full-Scale F/A-18 Aircraft

NASA Technical Reports Server (NTRS)

Lanser, Wendy R.; Botha, Gavin J.; James, Kevin D.; Bennett, Mark; Crowder, James P.; Cooper, Don; Olson, Lawrence (Technical Monitor)

1994-01-01

The proposed paper presents flow visualization performed during experiments conducted on a full-scale F/A-18 aircraft in the 80- by 120-Foot Wind-Tunnel at NASA Ames Research Center. The purpose of the flow-visualization experiments was to document the forebody and leading edge extension (LEX) vortex interaction along with the wing flow patterns at high angles of attack and low speed high Reynolds number conditions. This investigation used surface pressures in addition to both surface and off-surface flow visualization techniques to examine the flow field on the forebody, canopy, LEXS, and wings. The various techniques used to visualize the flow field were fluorescent tufts, flow cones treated with reflective material, smoke in combination with a laser light sheet, and a video imaging system for three-dimension vortex tracking. The flow visualization experiments were conducted over an angle of attack range from 20 deg to 45 deg and over a sideslip range from -10 deg to 10 deg. The various visualization techniques as well as the pressure distributions were used to understand the flow field structure. The results show regions of attached and separated flow on the forebody, canopy, and wings as well as the vortical flow over the leading-edge extensions. This paper will also present flow visualization comparisons with the F-18 HARV flight vehicle and small-scale oil flows on the F-18.

A CFD validation roadmap for hypersonic flows

NASA Technical Reports Server (NTRS)

Marvin, Joseph G.

1992-01-01

A roadmap for computational fluid dynamics (CFD) code validation is developed. The elements of the roadmap are consistent with air-breathing vehicle design requirements and related to the important flow path components: forebody, inlet, combustor, and nozzle. Building block and benchmark validation experiments are identified along with their test conditions and measurements. Based on an evaluation criteria, recommendations for an initial CFD validation data base are given and gaps identified where future experiments would provide the needed validation data.

A CFD validation roadmap for hypersonic flows

NASA Technical Reports Server (NTRS)

Marvin, Joseph G.

1993-01-01

A roadmap for computational fluid dynamics (CFD) code validation is developed. The elements of the roadmap are consistent with air-breathing vehicle design requirements and related to the important flow path components: forebody, inlet, combustor, and nozzle. Building block and benchmark validation experiments are identified along with their test conditions and measurements. Based on an evaluation criteria, recommendations for an initial CFD validation data base are given and gaps identified where future experiments would provide the needed validation data.

The role of the hyporheic flow on sediment transport processes : an experimental approach using particle image velocimetry

NASA Astrophysics Data System (ADS)

Rousseau, Gauthier; Sklivaniti, Angeliki; Vito Papa, Daniel; Ancey, Christophe

2017-04-01

The study of river dynamics usually considers a turbulent stream on an impervious bed. However, it is known that part of the total discharge takes place through the erodible bed, especially for mountain rivers. This hyporheic flow (or subsurface flow) is likely to play an active role in the stability of the erodible bed. The question then arises: How does the hyporheic flow affect bed stability and thereby bed load transport? Monitoring hyporheic flow under natural conditions remains a key challenge. Laboratory experiments and new measurement techniques shed new light on this problem. Using PIV-LIF method (Particle Image Velocimetry - Laser Induced Fluorescence) we investigate hyporheic flows through erodible beds. The experiment is conducted in a 2-m-long and 6-cm-width flume with 2-mm-diameter glass beads and 4-mm-diameter natural pebbles under turbulent stream conditions. In parallel, we develop a simple analytical model that accounts for the interaction between the surface and subsurface flows at the bed interface. As the Reynolds number of the hyporheic flow is fairly high (10 to 100), inertia cannot be neglected. This leads us to use the Darcy-Forchheimer law instead of Darcy's law to model hyporheic flows. We show that this model is consistent with the PIV-LIF experimental results. Moreover, the PIV-LIF data show that hyporheic flows modify the velocity profile and turbulence. Our measurements and empirical model emphasize the exchange processes in coarse-grained river for incipient sediment motion.

Discharge stabilization studies of CO laser gas mixtures in quasi-steady supersonic flow

NASA Technical Reports Server (NTRS)

Srinivasan, G.; Smith, J. A.

1976-01-01

Experiments were conducted to study the applicability of a double discharge stabilization scheme in conditions appropriate for high energy CO lasers in supersonic flows. A Ludwieg tube impulse flow facility and a ballasted capacitor bank provided essentially steady flow and discharge conditions (d.c.) for times longer than ten electrode length-flow transit times. Steady, arc-free, volume discharges were produced in a Mach 3 test cavity using an auxiliary discharge to stabilize the main discharge in N2 and He/CO mixture. A signigicant result is the lack of observed plasma E/N changes in response to auxiliary discharge current changes. Also, where glow discharges were obtained, the energy loading achieved was very much less than the threshold level required for laser operation.

Numerical study of the effects of Planetary Boundary Layer structure on the pollutant dispersion within built-up areas.

PubMed

Miao, Yucong; Liu, Shuhua; Zheng, Yijia; Wang, Shu; Liu, Zhenxin; Zhang, Bihui

2015-06-01

The effects of different Planetary Boundary Layer (PBL) structures on pollutant dispersion processes within two idealized street canyon configurations and a realistic urban area were numerically examined by a Computational Fluid Dynamics (CFD) model. The boundary conditions of different PBL structures/conditions were provided by simulations of the Weather Researching and Forecasting model. The simulated results of the idealized 2D and 3D street canyon experiments showed that the increment of PBL instability favored the downward transport of momentum from the upper flow above the roof to the pedestrian level within the street canyon. As a result, the flow and turbulent fields within the street canyon under the more unstable PBL condition are stronger. Therefore, more pollutants within the street canyon would be removed by the stronger advection and turbulent diffusion processes under the unstable PBL condition. On the contrary, more pollutants would be concentrated in the street canyon under the stable PBL condition. In addition, the simulations of the realistic building cluster experiments showed that the density of buildings was a crucial factor determining the dynamic effects of the PBL structure on the flow patterns. The momentum field within a denser building configuration was mostly transported from the upper flow, and was more sensitive to the PBL structures than that of the sparser building configuration. Finally, it was recommended to use the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme, which can explicitly output the needed turbulent variables, to provide the boundary conditions to the CFD simulation. Copyright © 2015. Published by Elsevier B.V.

CFD Validation Studies for Hypersonic Flow Prediction

NASA Technical Reports Server (NTRS)

Gnoffo, Peter A.

2001-01-01

A series of experiments to measure pressure and heating for code validation involving hypersonic, laminar, separated flows was conducted at the Calspan-University at Buffalo Research Center (CUBRC) in the Large Energy National Shock (LENS) tunnel. The experimental data serves as a focus for a code validation session but are not available to the authors until the conclusion of this session. The first set of experiments considered here involve Mach 9.5 and Mach 11.3 N2 flow over a hollow cylinder-flare with 30 degree flare angle at several Reynolds numbers sustaining laminar, separated flow. Truncated and extended flare configurations are considered. The second set of experiments, at similar conditions, involves flow over a sharp, double cone with fore-cone angle of 25 degrees and aft-cone angle of 55 degrees. Both sets of experiments involve 30 degree compressions. Location of the separation point in the numerical simulation is extremely sensitive to the level of grid refinement in the numerical predictions. The numerical simulations also show a significant influence of Reynolds number on extent of separation. Flow unsteadiness was easily introduced into the double cone simulations using aggressive relaxation parameters that normally promote convergence.

CFD Validation Studies for Hypersonic Flow Prediction

NASA Technical Reports Server (NTRS)

Gnoffo, Peter A.

2001-01-01

A series of experiments to measure pressure and heating for code validation involving hypersonic, laminar, separated flows was conducted at the Calspan-University at Buffalo Research Center (CUBRC) in the Large Energy National Shock (LENS) tunnel. The experimental data serves as a focus for a code validation session but are not available to the authors until the conclusion of this session. The first set of experiments considered here involve Mach 9.5 and Mach 11.3 N, flow over a hollow cylinder-flare with 30 deg flare angle at several Reynolds numbers sustaining laminar, separated flow. Truncated and extended flare configurations are considered. The second set of experiments, at similar conditions, involves flow over a sharp, double cone with fore-cone angle of 25 deg and aft-cone angle of 55 deg. Both sets of experiments involve 30 deg compressions. Location of the separation point in the numerical simulation is extremely sensitive to the level of grid refinement in the numerical predictions. The numerical simulations also show a significant influence of Reynolds number on extent of separation. Flow unsteadiness was easily introduced into the double cone simulations using aggressive relaxation parameters that normally promote convergence.

Vapor-screen flow-visualization experiments in the NASA Langley 0.3-m transonic cryogenic tunnel

NASA Technical Reports Server (NTRS)

Selby, G. V.

1986-01-01

The vortical flow on the leeward side of a delta-wing model has been visualized at several different tunnel conditions in the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel using a vapor-screen flow-visualization technique. Vapor-screen photographs of the subject flow field are presented and interpreted relative to phenomenological implications. Results indicate that the use of nitrogen fog in conjunction with the vapor-screen technique is feasibile.

Particle size reduction in debris flows: Laboratory experiments compared with field data from Inyo Creek, California

NASA Astrophysics Data System (ADS)

Arabnia, O.; Sklar, L. S.; Mclaughlin, M. K.

2014-12-01

Rock particles in debris flows are reduced in size through abrasion and fracture. Wear of coarse sediments results in production of finer particles, which alter the bulk material rheology and influence flow dynamics and runout distance. Particle wear also affects the size distribution of coarse particles, transforming the initial sediment size distribution produced on hillslopes into that delivered to the fluvial channel network. A better understanding of the controls on particle wear in debris flows would aid in the inferring flow conditions from debris flow deposits, in estimating the initial size of sediments entrained in the flow, and in modeling debris flow dynamics and mapping hazards. The rate of particle size reduction with distance traveled should depend on the intensity of particle interactions with other particles and the flow boundary, and on rock resistance to wear. We seek a geomorphic transport law to predict rate of particle wear with debris flow travel distance as a function of particle size distribution, flow depth, channel slope, fluid composition and rock strength. Here we use four rotating drums to create laboratory debris flows across a range of scales. Drum diameters range from 0.2 to 4.0 m, with the largest drum able to accommodate up to 2 Mg of material, including boulders. Each drum has vanes along the boundary to prevent sliding. Initial experiments use angular clasts of durable granodiorite; later experiments will use less resistant rock types. Shear rate is varied by changing drum rotational velocity. We begin experiments with well-sorted coarse particle size distributions, which are allowed to evolve through particle wear. The fluid is initially clear water, which rapidly acquires fine-grained wear products. After each travel increment all coarse particles (mass > 0.4 g) are weighed individually. We quantify particle wear rates using statistics of size and mass distributions, and by fitting various comminution functions to the data. Laboratory data are compared with longitudinal evolution of grain size and angularity of particles deposited by debris flows along Inyo Creek, Sierra Nevada, California. Preliminary results suggest wear rates can be scaled across drum sizes and to field conditions using non-dimensional metrics of flow dynamics including Savage, Bagnold, and Froude numbers.

Modeling variability in porescale multiphase flow experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ling, Bowen; Bao, Jie; Oostrom, Mart

Microfluidic devices and porescale numerical models are commonly used to study multiphase flow in biological, geological, and engineered porous materials. In this work, we perform a set of drainage and imbibition experiments in six identical microfluidic cells to study the reproducibility of multiphase flow experiments. We observe significant variations in the experimental results, which are smaller during the drainage stage and larger during the imbibition stage. We demonstrate that these variations are due to sub-porescale geometry differences in microcells (because of manufacturing defects) and variations in the boundary condition (i.e.,fluctuations in the injection rate inherent to syringe pumps). Computational simulationsmore » are conducted using commercial software STAR-CCM+, both with constant and randomly varying injection rate. Stochastic simulations are able to capture variability in the experiments associated with the varying pump injection rate.« less

The Herschel-Quincke tube: the attenuation conditions and their sensitivity to mean flow.

PubMed

Karlsson, Mikael; Glav, Ragnar; Abom, Mats

2008-08-01

The classic Herschel-Quincke tube is a parallel connection of two ducts yielding multiple noise attenuation maxima via destructive interference. This problem has been discussed to different degrees by a number of authors over the years. This study returns to the basics of the system for the purpose of furthering the understanding of the conditions necessary for noise attenuation and especially their sensitivity to mean flow. First, the transmission loss for an N-duct system with mean flow and arbitrary conditions of state in the different ducts is derived. Next, the two types of conditions yielding the attenuation maxima are studied. In addition to a discussion of the underlying physics, generic expressions for frequencies at which maximum attenuation occur are presented. Experiments without mean flow generally show good agreement with theory based on straight duct elements. However, more detailed models may be required for accurate simulations in the presence of mean flow. A simple model compensating for the losses associated with bends is shown to improve the results significantly for the geometry studied.

CFD Analysis of Mixing Characteristics of Several Fuel Injectors at Hypervelocity Flow Conditions

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Drummond, J. Philip; Baurle, Robert A.

2016-01-01

CFD analysis is presented of the mixing characteristics and performance of three fuel injectors at hypervelocity flow conditions. The calculations were carried out using the VULCAN-CFD solver and Reynolds-Averaged Simulations (RAS). The high Mach number flow conditions match those proposed for the planned experiments conducted as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The EIMP aims to investigate scramjet fuel injection and mixing physics, improve the understanding of underlying physical processes, and develop enhancement strategies and functional relationships relevant to flight Mach numbers greater than eight. Because of the high Mach number flow considered, the injectors consist of a fuel placement device, a strut; and a fluidic vortical mixer, a ramp. These devices accomplish the necessary task of distributing and mixing fuel into the supersonic cross-flow albeit via different strategies. Both of these devices were previously studied at lower flight Mach numbers where they exhibited promising performance in terms of mixing efficiency and total pressure recovery. For comparison, a flush-wall injector is also included. This type of injector generally represents the simplest method of introducing fuel into a scramjet combustor, however, at high flight Mach number conditions, the dynamic pressure needed to induce sufficient fuel penetration may be difficult to achieve along with other requirements such as achieving desired levels of fuel-to-air mixing at the required equivalence ratio. The three injectors represent the baseline configurations planned for the experiments. The current work discusses the mixing flow field behavior and differences among the three fuel injectors, mixing performance as described by the mixing efficiency and the total pressure recovery, and performance considerations based on the thrust potential.

The perfect debris flow? Aggregated results from 28 large-scale experiments

USGS Publications Warehouse

Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Berti, Matteo

2010-01-01

Aggregation of data collected in 28 controlled experiments reveals reproducible debris-flow behavior that provides a clear target for model tests. In each experiment ∼10 m3 of unsorted, water-saturated sediment composed mostly of sand and gravel discharged from behind a gate, descended a steep, 95-m flume, and formed a deposit on a nearly horizontal runout surface. Experiment subsets were distinguished by differing basal boundary conditions (1 versus 16 mm roughness heights) and sediment mud contents (1 versus 7 percent dry weight). Sensor measurements of evolving flow thicknesses, basal normal stresses, and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated, coarse-grained, high-friction snouts, followed by bodies of nearly liquefied, finer-grained debris. Mud enhanced flow mobility by maintaining high pore pressures in flow bodies, and bed roughness reduced flow speeds but not distances of flow runout. Roughness had these effects because it promoted debris agitation and grain-size segregation, and thereby aided growth of lateral levees that channelized flow. Grain-size segregation also contributed to development of ubiquitous roll waves, which had diverse amplitudes exhibiting fractal number-size distributions. Despite the influence of these waves and other sources of dispersion, the aggregated data have well-defined patterns that help constrain individual terms in a depth-averaged debris-flow model. The patterns imply that local flow resistance evolved together with global flow dynamics, contradicting the hypothesis that any consistent rheology applied. We infer that new evolution equations, not new rheologies, are needed to explain how characteristic debris-flow behavior emerges from the interactions of debris constituents.

Flow rate and temperature characteristics in steady state condition on FASSIP-01 loop during commissioning

NASA Astrophysics Data System (ADS)

Juarsa, M.; Giarno; Rohman, A. N.; Heru K., G. B.; Witoko, J. P.; Sony Tjahyani, D. T.

2018-02-01

The need for large-scale experimental facilities to investigate the phenomenon of natural circulation flow rate becomes a necessity in the development of nuclear reactor safety management. The FASSIP-01 loop has been built to determine the natural circulation flow rate performance in the large-scale media and aimed to reduce errors in the results for its application in the design of new generation reactors. The commissioning needs to be done to define the capability of the FASSIP-01 loop and to prescribe the experiment limitations. On this commissioning, two scenarios experimental method has been used. The first scenario is a static condition test which was conducted to verify measurement system response during 24 hours without electrical load in heater and cooler, there is water and no water inside the rectangular loop. Second scenario is a dynamics condition that aims to understand the flow rate, a dynamic test was conducted using heater power of 5627 watts and coolant flow rate in the HSS loop of 9.35 LPM. The result of this test shows that the temperature characterization on static test provide a recommendation, that the experiments should be done at night because has a better environmental temperature stability compared to afternoon, with stable temperature around 1°C - 3°C. While on the dynamic test, the water temperature difference between the inlet-outlets in the heater area is quite large, about 7 times the temperature difference in the cooler area. The magnitude of the natural circulation flow rate calculated is much larger at about 300 times compared to the measured flow rate with different flow rate profiles.

Environmental Factors that Influence Physiological Functioning of Eight Bottomland Hardwood Species

NASA Astrophysics Data System (ADS)

Kassahun, Z.; Renninger, H. J.

2017-12-01

With increases in extreme precipitation, flooding, and prolonged drought events in the southeastern United States, bottomland hardwood forests are expected to experience a drastic shift in their productivity and composition. As environmental conditions shift, certain tree species may experience an increase in productivity or could be more negatively affected over more resilient species, leading to a shift in species composition, water use, and carbon uptake. The goals of this research were to use sap flow measurements, leaf phenology, and photosynthetic rates to study species-specific responses to environmental drivers. Sap flow of eight co-occurring hardwood species as well as soil moisture and vapor pressure deficit were measured continuously over the course of a calendar year that included drought conditions and extended saturated soil conditions. We found that cherrybark oak used the most water during the growing season, about 20% more water than the next highest consumer, swamp chestnut oak. Given low, ample or saturated soil moisture conditions, we found that sap flow of winged elm, American elm, cherrybark oak, and shagbark hickory exhibited varying relationships with vapor pressure deficit under the different soil moisture conditions. While the relationship between sap flow and vapor pressure deficit did not differ depending on soil moisture in willow oak, swamp chestnut oak, and green ash. This suggests that winged elm, American elm, cherrybark oak, and shagbark hickory may be more negatively affected by drought conditions while willow oak, swamp chestnut oak, and green ash are more drought tolerant. Regarding leaf phenology, willow oak, cherrybark oak, and shagbark hickory were the first to experience leaf abscission at the end of the growing season when extended drought conditions occurred. In terms of leaf gas exchange, green ash exhibited the highest photosynthesis and transpiration rates, resulting in the lowest water-use efficiency compared with other study species. Taken together, these responses can be used to estimate forest water budgets given stand species composition or to predict individual species resilience or adaptation to a changing climate, which can improve land surface models and identify species in this forest type that will be most successful under future climate conditions.

Gas transport and vesicularity in low-viscosity liquids

NASA Astrophysics Data System (ADS)

Pioli, Laura; Bonadonna, Costanza; Abdulkareem, Lokman; Azzopardi, Barry; Phillips, Jeremy

2010-05-01

Vesicle textures of basaltic scoria preserve information on magma bubble content at fragmentation and are commonly used to constrain degassing, vesiculation and magma permeability. These studies are based on the assumption that microscale textures are representative of the conduit-scale structures and processes. However, the conditions for which this assumption is valid have not been investigated in detail. We have investigated conduit-scale structures by performing a series of experiments of separate two-phase flows in a 6.5-m high cylindrical bubble column using a combination of air with pure glucose syrup, water-syrup mixtures and pure water to reproduce open-system degassing and strombolian activity conditions in the upper volcanic conduit (i.e. at very low or zero liquid fluxes). We have varied gas fluxes, initial liquid height, gas inlet configuration and liquid viscosity and analyzed flow regimes and properties. Temperature and pressure were measured at several heights along the pipe and vesicularity was calculated using pressure data, liquid level measurements and an Electrical Capacitance tomography (ECT) system, which measures instantaneous vesicularity and phase distribution from capacitance measurements between pairs of electrodes placed uniformly around the pipe circumference. The aim of the experiments was to identify the effect of gas-flow rates on the flow regimes (i.e. bubbly, slug, churn and annular), the main degassing structures and the total gas content of the column. The effect of increasing and decreasing gas flow rates was also studied to check hysteresis effects. Results indicate that the vesicularity of the liquid column depends primarily on gas flux, whereas flow regimes exert a minor control. In fact, vesicularity increases with gas flux following a power-law trend whose exponent depends on the viscosity of the liquid. In addition, distributions of instantaneous gas fraction in the column cross section during syrup experiments have shown that gas is mainly transported by large, conduit-size bubbles rising in a microvesicular liquid. Coalescence processes occur throughout the whole column, and are strongly affected by bubble size, shearing and flow dynamics. Increasing gas fluxes increases frequency and length of the large bubbles but does not affect the concentration of small bubbles in the liquid matrix. Scaling of these experiments suggest that these conditions could be met in low viscosity, crystal-poor magmas and we therefore suggest that this dynamics could also characterize two-phase flow in open conduit mafic systems.

Implications of surfactant-induced flow for miscible-displacement estimation of air-water interfacial areas in unsaturated porous media.

PubMed

Costanza-Robinson, Molly S; Zheng, Zheng; Henry, Eric J; Estabrook, Benjamin D; Littlefield, Malcolm H

2012-10-16

Surfactant miscible-displacement experiments represent a conventional means of estimating air-water interfacial area (A(I)) in unsaturated porous media. However, changes in surface tension during the experiment can potentially induce unsaturated flow, thereby altering interfacial areas and violating several fundamental method assumptions, including that of steady-state flow. In this work, the magnitude of surfactant-induced flow was quantified by monitoring moisture content and perturbations to effluent flow rate during miscible-displacement experiments conducted using a range of surfactant concentrations. For systems initially at 83% moisture saturation (S(W)), decreases of 18-43% S(W) occurred following surfactant introduction, with the magnitude and rate of drainage inversely related to the surface tension of the surfactant solution. Drainage induced by 0.1 mM sodium dodecyl benzene sulfonate, commonly used for A(I) estimation, resulted in effluent flow rate increases of up to 27% above steady-state conditions and is estimated to more than double the interfacial area over the course of the experiment. Depending on the surfactant concentration and the moisture content used to describe the system, A(I) estimates varied more than 3-fold. The magnitude of surfactant-induced flow is considerably larger than previously recognized and casts doubt on the reliability of A(I) estimation by surfactant miscible-displacement.

Macropore system characteristics controls on non-reactive solute transport at different flow rates

NASA Astrophysics Data System (ADS)

Larsbo, Mats; Koestel, John

2014-05-01

Preferential flow and transport in macroporous soils are important pathways for the leaching of agrochemicals through soils. Preferential solute transport in soil is to a large extent determined by the macropore system characteristics and the water flow conditions. The importance of different characteristics of the macropore system is likely to vary with the flow conditions. The objective of this study was to determine which properties of the macropore system that control the shape of non-reactive tracer solute breakthrough curves at different steady-state flow rates. We sampled five undisturbed columns (20 cm high, 20 cm diameter) from the soil surface of four soils with clay contents between 21 and 50 %. Solute transport experiments were carried out under unsaturated conditions at 2, 4, 6, 8 and 12 mm h-1 flow rates. For each flow rate a pulse of potassium bromide solution was applied at the soil surface and the electrical conductivity was measured with high temporal resolution in the column effluent. We used the 5 % arrival time and the holdback factor to estimate the degree of preferential transport from the resulting breakthrough curves. Unsaturated hydraulic conductivities were measured at the soil surface of the columns using a tension disc infiltrometer. The macropore system was imaged by industrial X-ray computed tomography at a resolution of 125 μm in all directions. Measures of the macropore system characteristics including measures of pore continuity were calculated from these images using the ImageJ software. Results show that the degree of preferential transport is generally increasing with flow rate when larger pores become active in the transport. The degree of preferential flow was correlated to measures of macropore topology. This study show that conclusions drawn from experiments carried out at one flow rate should generally not be extrapolated to other flow rates.

Navier-Stokes structure of merged layer flow on the spherical nose of a space vehicle

NASA Technical Reports Server (NTRS)

Jain, A. C.; Woods, G. H.

1988-01-01

Hypersonic merged layer flow on the forepart of a spherical surface of a space vehicle has been investigated on the basis of the full steady-state Navier-Stokes equations using slip and temperature jump boundary conditions at the surface and free-stream conditions far from the surface. The shockwave-like structure was determined as part of the computations. Using an equivalent body concept, computations were carried out under conditions that the Aeroassist Flight Experiment (AFE) Vehicle would encounter at 15 and 20 seconds in its flight path. Emphasis was placed on understanding the basic nature of the flow structure under low density conditions. Particular attention was paid to the understanding of the structure of the outer shockwave-like region as the fluid expands around the sphere. Plots were drawn for flow profiles and surface characteristics to understand the role of dissipation processes in the merged layer of the spherical nose of the vehicle.

Liquid jet breakup regimes at supercritical pressures

DOE PAGES

Oefelein, Joseph C.; Dahms, Rainer Norbert Uwe

2015-07-23

Previously, a theory has been presented that explains how discrete vapor–liquid interfaces become diminished at certain high-pressure conditions in a manner that leads to well known qualitative trends observed from imaging in a variety of experiments. Rather than surface tension forces, transport processes can dominate over relevant ranges of conditions. In this paper, this framework is now generalized to treat a wide range of fuel-oxidizer combinations in a manner consistent with theories of capillary flows and extended corresponding states theory. Different flow conditions and species-specific molecular properties are shown to produce distinct variations of interfacial structures and local free molecularmore » paths. These variations are shown to occur over the operating ranges in a variety of propulsion and power systems. Despite these variations, the generalized analysis reveals that the envelope of flow conditions at which the transition from classical sprays to diffusion-dominated mixing occurs exhibits a characteristic shape for all liquid–gas combinations. As a result, for alkane-oxidizer mixtures, it explains that these conditions shift to higher pressure flow conditions with increasing carbon number and demonstrates that, instead of widely assumed classical spray atomization, diffusion-dominated mixing may occur under relevant high-pressure conditions in many modern devices.« less

Probing quantum and classical turbulence analogy in von Kármán liquid helium, nitrogen, and water experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saint-Michel, B.; Aix Marseille Université, CNRS, Centrale Marseille, IRPHE UMR 7342, 13384 Marseille; Herbert, E.

2014-12-15

We report measurements of the dissipation in the Superfluid helium high REynold number von Kármán flow experiment for different forcing conditions. Statistically steady flows are reached; they display a hysteretic behavior similar to what has been observed in a 1:4 scale water experiment. Our macroscopical measurements indicate no noticeable difference between classical and superfluid flows, thereby providing evidence of the same dissipation scaling laws in the two phases. A detailed study of the evolution of the hysteresis cycle with the Reynolds number supports the idea that the stability of the steady states of classical turbulence in this closed flow ismore » partly governed by the dissipative scales. It also supports the idea that the normal and the superfluid components at these temperatures (1.6 K) are locked down to the dissipative length scale.« less

Design of a microfluidic system for red blood cell aggregation investigation.

PubMed

Mehri, R; Mavriplis, C; Fenech, M

2014-06-01

The purpose of this paper is to design a microfluidic apparatus capable of providing controlled flow conditions suitable for red blood cell (RBC) aggregation analysis. The linear velocity engendered from the controlled flow provides constant shear rates used to qualitatively analyze RBC aggregates. The design of the apparatus is based on numerical and experimental work. The numerical work consists of 3D numerical simulations performed using a research computational fluid dynamics (CFD) solver, Nek5000, while the experiments are conducted using a microparticle image velocimetry system. A Newtonian model is tested numerically and experimentally, then blood is tested experimentally under several conditions (hematocrit, shear rate, and fluid suspension) to be compared to the simulation results. We find that using a velocity ratio of 4 between the two Newtonian fluids, the layer corresponding to blood expands to fill 35% of the channel thickness where the constant shear rate is achieved. For blood experiments, the velocity profile in the blood layer is approximately linear, resulting in the desired controlled conditions for the study of RBC aggregation under several flow scenarios.

An experimental study of geyser-like flows induced by a pressurized air pocket

NASA Astrophysics Data System (ADS)

Elayeb, I. S.; Leon, A.; Choi, Y.; Alnahit, A. O.

2015-12-01

Previous studies argues that the entrapment of pressurized air pockets within combined sewer systems can produce geyser flows, which is an oscillating jetting of a mixture of gas-liquid flows. To verify that pressurized air pockets can effectively produce geysers, laboratory experiments were conducted. However, past experiments were conducted in relatively small-scale apparatus (i.e. maximum φ2" vertical shaft). This study conducted a set of experiments in a larger apparatus. The experimental setup consists of an upstream head tank, a downstream head tank, a horizontal pipe (46.5ft long, φ6") and a vertical pipe (10ft long, φ6"). The initial condition for the experiments is constant flow discharge through the horizontal pipe. The experiments are initiated by injecting an air pocket with pre-determined volume and pressure at the upstream end of the horizontal pipe. The air pocket propagates through the horizontal pipe until it arrives to the vertical shaft, where it is released producing a geyser-like flow. Three flow rates in the horizontal pipe and three injected air pressures were tested. The variables measured were pressure at two locations in the horizontal pipe and two locations in the vertical pipe. High resolution videos at two regions in the vertical shaft were also recorded. To gain further insights in the physics of air-water interaction, the laboratory experiments were complemented with numerical simulations conducted using a commercial 3D CFD model, previously validated with experiments.

Laboratory outreach: student assessment of flow cytometer fluidics in zero gravity.

PubMed

Crucian, B; Norman, J; Brentz, J; Pietrzyk, R; Sams, C

2000-10-01

Due to the the clinical utility of the flow cytometer, the National Aeronautics and Space Administration (NASA) is interested in the design of a space flight-compatible cytometer for use on long-duration space missions. Because fluid behavior is altered dramatically during space flight, it was deemed necessary to validate the principles of hydrodynamic focusing and laminar flow (cytometer fluidics) in a true microgravity environment. An experiment to validate these properties was conducted by 12 students from Sweetwater High School (Sweetwater, TX) participating in the NASA Reduced Gravity Student Flight Opportunity, Class of 2000. This program allows high school students to gain scientific experience by conducting an experiment on the NASA KC-135 zero gravity laboratory aircraft. The KC-135 creates actual zero-gravity conditions in 30-second intervals by flying a highly inclined parabolic flight path. The experiment was designed by their mentor in the program, the Johnson Space Center's flow cytometrist Brian Crucian, PhD, MT(ASCP). The students performed the experiment, with the mentor, onboard the NASA zero-gravity research aircraft in April 2000.

Experimental and numerical investigations of high temperature gas heat transfer and flow in a VHTR reactor core

NASA Astrophysics Data System (ADS)

Valentin Rodriguez, Francisco Ivan

High pressure/high temperature forced and natural convection experiments have been conducted in support of the development of a Very High Temperature Reactor (VHTR) with a prismatic core. VHTRs are designed with the capability to withstand accidents by preventing nuclear fuel meltdown, using passive safety mechanisms; a product of advanced reactor designs including the implementation of inert gases like helium as coolants. The present experiments utilize a high temperature/high pressure gas flow test facility constructed for forced and natural circulation experiments. This work examines fundamental aspects of high temperature gas heat transfer applied to VHTR operational and accident scenarios. Two different types of experiments, forced convection and natural circulation, were conducted under high pressure and high temperature conditions using three different gases: air, nitrogen and helium. The experimental data were analyzed to obtain heat transfer coefficient data in the form of Nusselt numbers as a function of Reynolds, Grashof and Prandtl numbers. This work also examines the flow laminarization phenomenon (turbulent flows displaying much lower heat transfer parameters than expected due to intense heating conditions) in detail for a full range of Reynolds numbers including: laminar, transition and turbulent flows under forced convection and its impact on heat transfer. This phenomenon could give rise to deterioration in convection heat transfer and occurrence of hot spots in the reactor core. Forced and mixed convection data analyzed indicated the occurrence of flow laminarization phenomenon due to the buoyancy and acceleration effects induced by strong heating. Turbulence parameters were also measured using a hot wire anemometer in forced convection experiments to confirm the existence of the flow laminarization phenomenon. In particular, these results demonstrated the influence of pressure on delayed transition between laminar and turbulent flow. The heat dissipating capabilities of helium flow, due to natural circulation in the system at both high and low pressure, were also examined. These experimental results are useful for the development and validation of VHTR design and safety analysis codes. Numerical simulations were performed using a Multiphysics computer code, COMSOL, displaying less than 5% error between the measured graphite temperatures in both the heated and cooled channels. Finally, new correlations have been proposed describing the thermal-hydraulic phenomena in buoyancy driven flows in both heated and cooled channels.

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

DOE PAGES

Varela, J.; Oak Ridge National Lab.; Brun, S.; ...

2017-05-01

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varela, J.; Oak Ridge National Lab.; Brun, S.

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

NASA Astrophysics Data System (ADS)

Varela, J.; Brun, S.; Dubrulle, B.; Nore, C.

2017-05-01

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Kármán-Sodium dynamo experiment. The aim of the study is to analyze the influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified Cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Kármán-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbers between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically, the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and the impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and the impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller compared to a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.

Buoyancy Driven Shear Flows of Bubble Suspensions

NASA Technical Reports Server (NTRS)

Koch, D. L.; Hill, R. J.; Chellppannair, T.; Zenit, R.; Zenit, R.; Spelt, P. D. M.

1999-01-01

In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1a nd Re >> 1, for which comparisons are made with kinetic theory and numerical simulations. Here Re = gamma(a(exp 2)/nu is the Reynolds number and We = rho(gamma(exp 2))a(exp 3)/sigma is the Weber number; gamma is the shear rate, a is the bubble radius, nu is the kinematic viscosity of the liquid, rho is the density of the liquid, and sigma is the surface tension of the gas/liquid interface. Kang et al. calculated the bubble phase pressure and velocity variance of sheared bubble suspensions under conditions where the bubbles are spherical and the liquid phase velocity field can be approximated using potential flow theory, i.e. We= 0 and Re >> 1. Such conditions can be achieved in an experiment using gas bubbles, with a radius of O(0.5mm), in water. The theory requires that there be no average relative motion of the gas and liquid phases, hence the motivation for an experimental program in microgravity. The necessity of performing preliminary, Earth based experiments, however, requires performing experiments where the gas phase rises in the liquid, which significantly complicates the comparison of experiments with theory. Rather than comparing experimental results with theory for a uniform, homogeneous shear flow, experiments can be compared directly with solutions of the averaged equations of motion for bubble suspensions. This requires accounting for the significant lift force acting on the gas phase when the bubbles rise parallel to the average velocity of the sheared suspension. Shear flows can be produced in which the bubble phase pressure gradient, arising from shear induced collisions amongst the bubbles, balances a body force (centrifugal or gravitational) on the gas phase. A steady, non-uniform gas volume fraction can be measured, from which the bubble phase pressure gradient can be obtained and compared to theory and numerical simulations. The presence of bounding walls further complicates the experiments, since the detailed interactions of the bubbles with bounding walls is not well understood, especially in the presence of gravity, where the momentum and energy exchange depends on the inclination of the wall.

Flow rate impacts on capillary pressure and interface curvature of connected and disconnected fluid phases during multiphase flow in sandstone

NASA Astrophysics Data System (ADS)

Herring, Anna L.; Middleton, Jill; Walsh, Rick; Kingston, Andrew; Sheppard, Adrian

2017-09-01

We investigate capillary pressure-saturation (PC-S) relationships for drainage-imbibition experiments conducted with air (nonwetting phase) and brine (wetting phase) in Bentheimer sandstone cores. Three different flow rate conditions, ranging over three orders of magnitude, are investigated. X-ray micro-computed tomographic imaging is used to characterize the distribution and amount of fluids and their interfacial characteristics. Capillary pressure is measured via (1) bulk-phase pressure transducer measurements, and (2) image-based curvature measurements, calculated using a novel 3D curvature algorithm. We distinguish between connected (percolating) and disconnected air clusters: curvatures measured on the connected phase interfaces are used to validate the curvature algorithm and provide an indication of the equilibrium condition of the data; curvature and volume distributions of disconnected clusters provide insight to the snap-off processes occurring during drainage and imbibition under different flow rate conditions.

Using the Richtmyer-Meshkov flow to infer the strength of LY-12 aluminum at extreme conditions

NASA Astrophysics Data System (ADS)

Yin, Jianwei; Pan, Hao; Peng, Jiangxiang; Wu, Zihui; Yu, Yuying; Hu, Xiaomian

2017-06-01

An improved analytical model of the Richtmyer-Meshkov (RM) flow in the elastoplastic materials is presented in this paper. This model describes the stabilization by yield strength (Y) effect on the RM flow in solids and linear relationships between initial configurations of perturbation and the growth. Then we make use of the model to analysis the explosion driven RM flow experiments with solid LY12 and test our model by comparing the predicted Y of existing strength models. Finally, we perform a plate impact experiment with solid LY12 aluminium alloy to validate our model and infer Y is about 1.23 GPa for a 28 GPa shock and a strain rate of 7.5 ×106 .

Zero-G experiments in two-phase fluids flow regimes

NASA Technical Reports Server (NTRS)

Heppner, D. B.; King, C. D.; Littles, J. W.

1975-01-01

The two-phase flows studied were liquid and gas mixtures in a straight flow channel of circular cross-section. Boundaries between flow regimes have been defined for normogravity on coordinates of gas quality and total mass velocity; and, when combined with boundary expressions having a Froude number term, an analytical model was derived predicting boundary shifts with changes in gravity level. Experiments with air and water were performed, first in the normogravity environment of a ground laboratory and then in 'zero gravity' aboard a KC-135 aircraft flying parabolic trajectories. Data reduction confirmed regime boundary shifts in the direction predicted, although the magnitude was a little less than predicted. Pressure drop measurements showed significant increases for the low gravity condition.

Numerical simulation of transient hypervelocity flow in an expansion tube

NASA Technical Reports Server (NTRS)

Jacobs, P. A.

1992-01-01

Several numerical simulations of the transient flow of helium in an expansion tube are presented in an effort to identify some of the basic mechanisms which cause the noisy test flows seen in experiments. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in experiments. In particular, the discontinuity in tube diameter of the primary diaphragm station introduced a transverse perturbation to the expanding driver gas and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either small amplitude, low frequency noise possibly introduced during shock compression or large amplitude, high frequency noise associated with the passage of the reflected head of the unsteady expansion.

Lonely GPFUTV-the movement of water under the action of unknown vacuum

NASA Astrophysics Data System (ADS)

Lin, Weiyi

2013-11-01

In this paper, firstly, the experiment on the flow resistance of the aerated pipe flow is introduced. The experimental research on comparison between different volumes of air entrained is presented. Secondly, the characteristics of gravity pipe flow under the action of Torricelli's vacuum, shortly called as GPFUTV are dissertated, including creative and functional design, fundamental principle, etc. Under the joint action of an unknown vacuum energy and the formation of non-aerated flow the water flow is full-pipe and continuous, high-speed and non-rotational as distinguished from turbulent flow. Thirdly, an appeal in relation to the experimental research, the applied studies and basic theory research is given. For instance, experimental study of Torricelli's experiment phenomenon in the vacuum environment, applied study of the potential for GPFUTV to be developed for deep seawater suction technology and lifting technology for deep ocean mining, theoretical study of flow stability and flow resistance under GPFUTV condition, etc. At last, the famous GPFUTV project is illustrated. 12 years of rigorous and independent survey research.

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

NASA Technical Reports Server (NTRS)

Yep, Tze-Wing; Agrawal, Ajay K.; Griffin, DeVon; Salzman, Jack (Technical Monitor)

2001-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet flow was significantly influenced by the gravity. The jet in microgravity was up to 70 percent wider than that in Earth gravity. The jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes a change in gravity in the drop tower.

An atmospheric pressure high-temperature laminar flow reactor for investigation of combustion and related gas phase reaction systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oßwald, Patrick; Köhler, Markus

A new high-temperature flow reactor experiment utilizing the powerful molecular beam mass spectrometry (MBMS) technique for detailed observation of gas phase kinetics in reacting flows is presented. The reactor design provides a consequent extension of the experimental portfolio of validation experiments for combustion reaction kinetics. Temperatures up to 1800 K are applicable by three individually controlled temperature zones with this atmospheric pressure flow reactor. Detailed speciation data are obtained using the sensitive MBMS technique, providing in situ access to almost all chemical species involved in the combustion process, including highly reactive species such as radicals. Strategies for quantifying the experimentalmore » data are presented alongside a careful analysis of the characterization of the experimental boundary conditions to enable precise numeric reproduction of the experimental results. The general capabilities of this new analytical tool for the investigation of reacting flows are demonstrated for a selected range of conditions, fuels, and applications. A detailed dataset for the well-known gaseous fuels, methane and ethylene, is provided and used to verify the experimental approach. Furthermore, application for liquid fuels and fuel components important for technical combustors like gas turbines and engines is demonstrated. Besides the detailed investigation of novel fuels and fuel components, the wide range of operation conditions gives access to extended combustion topics, such as super rich conditions at high temperature important for gasification processes, or the peroxy chemistry governing the low temperature oxidation regime. These demonstrations are accompanied by a first kinetic modeling approach, examining the opportunities for model validation purposes.« less

Zero Boil-Off Tank (ZBOT) Experiment

NASA Technical Reports Server (NTRS)

Mcquillen, John

2016-01-01

The Zero-Boil-Off Tank (ZBOT) experiment has been developed as a small scale ISS experiment aimed at delineating important fluid flow, heat and mass transport, and phase change phenomena that affect cryogenic storage tank pressurization and pressure control in microgravity. The experiments use a simulant transparent low boiling point fluid (PnP) in a sealed transparent Dewar to study and quantify: (a) fluid flow and thermal stratification during pressurization; (b) mixing, thermal destratification, depressurization, and jet-ullage penetration during pressure control by jet mixing. The experiment will provide valuable microgravity empirical two-phase data associated with the above-mentioned physical phenomena through highly accurate local wall and fluid temperature and pressure measurements, full-field phase-distribution and flow visualization. Moreover, the experiments are performed under tightly controlled and definable heat transfer boundary conditions to provide reliable high-fidelity data and precise input as required for validation verification of state-of-the-art two-phase CFD models developed as part of this research and by other groups in the international scientific and cryogenic fluid management communities.

Centrifuge impact cratering experiment 5

NASA Technical Reports Server (NTRS)

1984-01-01

Transient crates motions, cratering flow fields, crates dynamics, determining impact conditions from total crater welt, centrifuge quarter-space cratering, and impact cratering mechanics research is documented.

Multiphase groundwater flow near cooling plutons

USGS Publications Warehouse

Hayba, D.O.; Ingebritsen, S.E.

1997-01-01

We investigate groundwater flow near cooling plutons with a computer program that can model multiphase flow, temperatures up to 1200??C, thermal pressurization, and temperature-dependent rock properties. A series of experiments examines the effects of host-rock permeability, size and depth of pluton emplacement, single versus multiple intrusions, the influence of a caprock, and the impact of topographically driven groundwater flow. We also reproduce and evaluate some of the pioneering numerical experiments on flow around plutons. Host-rock permeability is the principal factor influencing fluid circulation and heat transfer in hydrothermal systems. The hottest and most steam-rich systems develop where permeability is of the order of 10-15 m2. Temperatures and life spans of systems decrease with increasing permeability. Conduction-dominated systems, in which permeabilities are ???10-16m2, persist longer but exhibit relatively modest increases in near-surface temperatures relative to ambient conditions. Pluton size, emplacement depth, and initial thermal conditions have less influence on hydrothermal circulation patterns but affect the extent of boiling and duration of hydrothermal systems. Topographically driven groundwater flow can significantly alter hydrothermal circulation; however, a low-permeability caprock effectively decouples the topographically and density-driven systems and stabilizes the mixing interface between them thereby defining a likely ore-forming environment.

A wind tunnel study on the effects of complex topography on wind turbine performance

NASA Astrophysics Data System (ADS)

Howard, Kevin; Hu, Stephen; Chamorro, Leonardo; Guala, Michele

2012-11-01

A set of wind tunnel experiments were conducted to study the response of a wind turbine under flow conditions typically observed at the wind farm scale, in complex terrain. A scale model wind turbine was placed in a fully developed turbulent boundary layer flow obtained in the SAFL Wind Tunnel. Experiments focused on the performance of a turbine model, under the effects induced by a second upwind turbine or a by three-dimensional, sinusoidal hill, peaking at the turbine hub height. High frequency measurements of fluctuating streamwise and wall normal velocities were obtained with a X-wire anemometer simultaneously with the rotor angular velocity and the turbine(s) voltage output. Velocity measurements in the wake of the first turbine and of the hill were used to determine the inflow conditions for the downwind test turbine. Turbine performance was inferred by the mean and fluctuating voltage statistics. Specific experiments were devoted to relate the mean voltage to the mean hub velocity, and the fluctuating voltage to the unsteadiness in the rotor kinematics induced by the perturbed (hill or turbine) or unperturbed (boundary layer) large scales of the incoming turbulent flow. Results show that the voltage signal can be used to assess turbine performance in complex flows.

Massive units deposited by bedload transport in sheet flow mode

NASA Astrophysics Data System (ADS)

Viparelli, E.; Hernandez Moreira, R. R.; Jafarinik, S.; Sanders, S.; Huffman, B.; Parker, G.; Kendall, C.

2017-12-01

A sandy massive (structureless) unit overlying a basal erosional surface and underlying a parallel or cross-laminated unit often characterizes turbidity current and coastal storm deposits. The basal massive units are thought to be the result of relatively rapid deposition of suspended sediment. However, suspension-based models fail to explain how basal massive units can be emplaced for long distances, far away from the source and can contain gravel particles as floating clasts. Here we present experimental results that can significantly change the understanding of the processes forming turbidity current and coastal storm deposits. The experiments were performed in open channel flow mode in the Hydraulics Laboratory at the University of South Carolina. The sediment was a mixture of sand size particles with a geometric mean diameter of 0.95 mm and a geometric standard deviation of 1.65. Five experiments were performed with a flow rate of 30 l/s and sediment feed rates varying between 1.5 kg/min and 20 kg/min. Each experiment was characterized by two phases, 1) the equilibration phase, in which we waited for the system to reach equilibrium condition, and 2) the aggradation phase, in which we slowly raised the water surface base level to induce channel bed aggradation under the same transport conditions observed over the equilibrium bed. Our experiments show that sandy massive units can be the result of deposition from a thick bedload layer of colliding grains, the sheet flow layer. The presence of this sheet flow layer explains how a strong, sustained current can emplace extensive massive units containing gravel clasts. Although our experiments were conducted in open-channel mode, observations of bedload driven by density underflows suggest that our results are directly applicable to sheet flows driven by deep-sea turbidity currents. More specifically, we believe that this mechanism offers an explanation for massive turbidites that heretofore have been identified as the deposits of "high density" turbidity currents.

Evolution of a Planar Wake in Adverse Pressure Gradient

NASA Technical Reports Server (NTRS)

Driver, David M.; Mateer, George G.

2016-01-01

In the interest of improving the predictability of high-lift systems at maximum lift conditions, a series of fundamental experiments were conducted to study the effects of adverse pressure gradient on a wake flow. Mean and fluctuating velocities were measured with a two-component laser-Doppler velocimeter. Data were obtained for several cases of adverse pressure gradient, producing flows ranging from no reversed flow to massively reversed flow. While the turbulent Reynolds stresses increase with increasing size of the reversed flow region, the gradient of Reynolds stress does not. Computations using various turbulence models were unable to reproduce the reversed flow.

Flow Field Characterization of an Angled Supersonic Jet Near a Bluff Body

NASA Technical Reports Server (NTRS)

Wolter, John D.; Childs, Robert; Wernet, Mark P.; Shestopalov, Andrea; Melton, John E.

2011-01-01

An experiment was performed to acquire data from a hot supersonic jet in cross flow for the purpose of validating computational fluid dynamics (CFD) turbulence modeling relevant to the Orion Launch Abort System. Hot jet conditions were at the highest temperature and pressure that could be acquired in the test facility. The nozzle pressure ratio was 28.5, and the nozzle temperature ratio was 3. These conditions are different from those of the flight vehicle, but sufficiently high to model the observed turbulence features. Stereo Particle Image Velocimetry (SPIV) data and capsule pressure data are presented. Features of the flow field are presented and discussed

Excitation condition analysis of guided wave on PFA tubes for ultrasonic flow meter.

PubMed

Li, Xuan; Xiao, Xufeng; Cao, Li

2016-12-01

Impurity accumulation, which decreases the accuracy of flow measurement, is a critical problem when applying Z-shaped or U-shaped ultrasonic flow meters on straight PFA tubes. It can be expected that the guided wave can be used to implement flow measurement on straight PFA tubes. In this paper, the propagation of guided wave is explained by finite element simulations for the flow meter design. Conditions of guided wave generation, including the excitation frequency and the wedge structure, are studied in the simulations. The wedge is designed as a cone which is friendly to be manufactured and installed. The cone angle, the piezoelectric wafer's resonant frequency and the vibration directions are studied in the simulations. The simulations shows that the propagation of guided wave in thin PFA tubes is influenced by the piezoelectric wafers' resonant frequency and the vibration direction when the mode is on the 'water line'. Based on the results of the simulations, an experiment is conducted to verify the principles of excitation conditions, which performs flow measurement on a straight PFA tube well. Copyright © 2016 Elsevier B.V. All rights reserved.

Performance Characteristics of a Cross-Flow Hydrokinetic Turbine under Unsteady Conditions

NASA Astrophysics Data System (ADS)

Flack, Karen; Lust, Ethan; Bailin, Ben

2017-11-01

Performance characteristics are presented for a cross-flow hydrokinetic turbine designed for use in a riverine environment. The test turbine is a 1:6 scale model of a three-bladed device (9.5 m span, 6.5 m diameter) that has been proposed by the Department of Energy. Experiments are conducted in the large towing tank (116 m long, 7.9 m wide, 5 m deep) at the United States Naval Academy. The turbine is towed beneath a moving carriage at a constant speed in combination with a shaft motor to achieve the desired tip speed ratio (TSR) range. The measured quantities of turbine thrust, torque and RPM result in power and thrust coefficients for a range of TSR. Results will be presented for cases with quiescent flow at a range of Reynolds numbers and flow with mild surface waves, representative of riverine environments. The impact of unsteady flow conditions on the average turbine performance was not significant. Unsteady flow conditions did have an impact on instantaneous turbine performance which operationally would result in unsteady blade loading and instantaneous power quality.

Flow splitting in numerical simulations of oceanic dense-water outflows

NASA Astrophysics Data System (ADS)

Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Özgökmen, Tamay M.

2017-05-01

Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0 =Q0N3 /g‧2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g‧ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions

ERIC Educational Resources Information Center

Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio

2010-01-01

This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, and…

Flow Experience and Educational Effectiveness of Teaching Informatics Using AR

ERIC Educational Resources Information Center

Giasiranis, Stefanos; Sofos, Loizos

2017-01-01

The purpose of this study was the investigation of the added value of technology of augmented reality (AR) in education and, particularly, whether this contributes to both student performance improvement, as well as the appearance of the psychological condition of Flow, which according to research, has had a positive effect on their performance…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grayson, James W.; Zhang, Yue; Mutzel, Anke

Knowledge of the viscosity of particles containing secondary organic material (SOM) is useful for predicting reaction rates and diffusion in SOM particles. In this study we investigate the viscosity of SOM particles as a function of relative humidity and SOM particle mass concentration, during SOM synthesis. The SOM was generated via the ozonolysis of α-pinene at < 5 % relative humidity (RH). Experiments were carried out using the poke-and-flow technique, which measures the experimental flow time ( τ exp, flow) of SOM after poking the material with a needle. In the first set of experiments, we show that τ exp,more » flow increased by a factor of 3600 as the RH increased from < 0.5 RH to 50 % RH, for SOM with a production mass concentration of 121 µg m -3. Based on simulations, the viscosities of the particles were between 6 × 10 5 and 5 × 10 7 Pa s at < 0.5 % RH and between 3 × 10 2 and 9 × 10 3 Pa s at 50 % RH. In the second set of experiments we show that under dry conditions τ exp, flow decreased by a factor of 45 as the production mass concentration increased from 121 to 14 000 µg m -3. From simulations of the poke-and-flow experiments, the viscosity of SOM with a production mass concentration of 14 000 µg m -3 was determined to be between 4 × 10 4 and 1.5 × 10 6 Pa s compared to between 6 × 10 5 and 5 × 10 7 Pa s for SOM with a production mass concentration of 121 µg m -3. The results can be rationalized by a dependence of the chemical composition of SOM on production conditions. Lastly, these results emphasize the shifting characteristics of SOM, not just with RH and precursor type, but also with the production conditions, and suggest that production mass concentration and the RH at which the viscosity was determined should be considered both when comparing laboratory results and when extrapolating these results to the atmosphere.« less

Mass transfer from a circular cylinder: Effects of flow unsteadiness and slight nonuniformities

NASA Technical Reports Server (NTRS)

Marziale, M. L.; Mayle, R. E.

1984-01-01

Experiments were performed to determine the effect of periodic variations in the angle of the flow incident to a turbine blade on its leading edge heat load. To model this situation, measurements were made on a circular cylinder oscillating rotationally in a uniform steady flow. A naphthalene mass transfer technique was developed and used in the experiments and heat transfer rates are inferred from the results. The investigation consisted of two parts. In the first, a stationary cylinder was used and the transfer rate was measured for Re = 75,000 to 110,000 and turbulence levels from .34 percent to 4.9 percent. Comparisons with both theory and the results of others demonstrate that the accuracy and repeatability of the developed mass transfer technique is about + or - 2 percent, a large improvement over similar methods. In the second part identical flow conditions were used but the cylinder was oscillated. A Strouhal number range from .0071 to .1406 was covered. Comparisons of the unsteady and steady results indicate that the magnitude of the effect of oscillation is small and dependent on the incident turbulence conditions.

Preparation of Geophysical Fluid Flow Experiments With The Rotating Spherical Gap Flow Model In Space

NASA Astrophysics Data System (ADS)

Egbers, C.

The'GeoFlow' is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluid Mechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field simi- lar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment re- quires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth`s liquid core the experiment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heat- ing the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number.

Traffic Vehicle Counting in Jam Flow Conditions Using Low-Cost and Energy-Efficient Wireless Magnetic Sensors.

PubMed

Bao, Xu; Li, Haijian; Xu, Dongwei; Jia, Limin; Ran, Bin; Rong, Jian

2016-11-06

The jam flow condition is one of the main traffic states in traffic flow theory and the most difficult state for sectional traffic information acquisition. Since traffic information acquisition is the basis for the application of an intelligent transportation system, research on traffic vehicle counting methods for the jam flow conditions has been worthwhile. A low-cost and energy-efficient type of multi-function wireless traffic magnetic sensor was designed and developed. Several advantages of the traffic magnetic sensor are that it is suitable for large-scale deployment and time-sustainable detection for traffic information acquisition. Based on the traffic magnetic sensor, a basic vehicle detection algorithm (DWVDA) with less computational complexity was introduced for vehicle counting in low traffic volume conditions. To improve the detection performance in jam flow conditions with a "tailgating effect" between front vehicles and rear vehicles, an improved vehicle detection algorithm (SA-DWVDA) was proposed and applied in field traffic environments. By deploying traffic magnetic sensor nodes in field traffic scenarios, two field experiments were conducted to test and verify the DWVDA and the SA-DWVDA algorithms. The experimental results have shown that both DWVDA and the SA-DWVDA algorithms yield a satisfactory performance in low traffic volume conditions (scenario I) and both of their mean absolute percent errors are less than 1% in this scenario. However, for jam flow conditions with heavy traffic volumes (scenario II), the SA-DWVDA was proven to achieve better results, and the mean absolute percent error of the SA-DWVDA is 2.54% with corresponding results of the DWVDA 7.07%. The results conclude that the proposed SA-DWVDA can implement efficient and accurate vehicle detection in jam flow conditions and can be employed in field traffic environments.

The neurochemistry and social flow of singing: bonding and oxytocin

PubMed Central

Keeler, Jason R.; Roth, Edward A.; Neuser, Brittany L.; Spitsbergen, John M.; Waters, Daniel J. M.; Vianney, John-Mary

2015-01-01

Music is used in healthcare to promote physical and psychological well-being. As clinical applications of music continue to expand, there is a growing need to understand the biological mechanisms by which music influences health. Here we explore the neurochemistry and social flow of group singing. Four participants from a vocal jazz ensemble were conveniently sampled to sing together in two separate performances: pre-composed and improvised. Concentrations of plasma oxytocin and adrenocorticotropic hormone (ACTH) were measured before and after each singing condition to assess levels of social affiliation, engagement and arousal. A validated assessment of flow state was administered after each singing condition to assess participants' absorption in the task. The feasibility of the research methods were assessed and initial neurochemical data was generated on group singing. Mean scores of the flow state scale indicated that participants experienced flow in both the pre-composed (M = 37.06) and improvised singing conditions (M = 34.25), with no significant difference between conditions. ACTH concentrations decreased in both conditions, significantly so in the pre-composed singing condition, which may have contributed to the social flow experience. Mean plasma oxytocin levels increased only in response to improvised singing, with no significant difference between improvised and pre-composed singing conditions observed. The results indicate that group singing reduces stress and arousal, as measured by ACTH, and induces social flow in participants. The effects of pre-composed and improvised group singing on oxytocin are less clear. Higher levels of plasma oxytocin in the improvised condition may perhaps be attributed to the social effects of improvising musically with others. Further research with a larger sample size is warranted. PMID:26441614

Traffic Vehicle Counting in Jam Flow Conditions Using Low-Cost and Energy-Efficient Wireless Magnetic Sensors

PubMed Central

Bao, Xu; Li, Haijian; Xu, Dongwei; Jia, Limin; Ran, Bin; Rong, Jian

2016-01-01

The jam flow condition is one of the main traffic states in traffic flow theory and the most difficult state for sectional traffic information acquisition. Since traffic information acquisition is the basis for the application of an intelligent transportation system, research on traffic vehicle counting methods for the jam flow conditions has been worthwhile. A low-cost and energy-efficient type of multi-function wireless traffic magnetic sensor was designed and developed. Several advantages of the traffic magnetic sensor are that it is suitable for large-scale deployment and time-sustainable detection for traffic information acquisition. Based on the traffic magnetic sensor, a basic vehicle detection algorithm (DWVDA) with less computational complexity was introduced for vehicle counting in low traffic volume conditions. To improve the detection performance in jam flow conditions with a “tailgating effect” between front vehicles and rear vehicles, an improved vehicle detection algorithm (SA-DWVDA) was proposed and applied in field traffic environments. By deploying traffic magnetic sensor nodes in field traffic scenarios, two field experiments were conducted to test and verify the DWVDA and the SA-DWVDA algorithms. The experimental results have shown that both DWVDA and the SA-DWVDA algorithms yield a satisfactory performance in low traffic volume conditions (scenario I) and both of their mean absolute percent errors are less than 1% in this scenario. However, for jam flow conditions with heavy traffic volumes (scenario II), the SA-DWVDA was proven to achieve better results, and the mean absolute percent error of the SA-DWVDA is 2.54% with corresponding results of the DWVDA 7.07%. The results conclude that the proposed SA-DWVDA can implement efficient and accurate vehicle detection in jam flow conditions and can be employed in field traffic environments. PMID:27827974

Vortex breakdown in simple pipe bends

NASA Astrophysics Data System (ADS)

Ault, Jesse; Shin, Sangwoo; Stone, Howard

2016-11-01

Pipe bends and elbows are one of the most common fluid mechanics elements that exists. However, despite their ubiquity and the extensive amount of research related to these common, simple geometries, unexpected complexities still remain. We show that for a range of geometries and flow conditions, these simple flows experience unexpected fluid dynamical bifurcations resembling the bubble-type vortex breakdown phenomenon. Specifically, we show with simulations and experiments that recirculation zones develop within the bends under certain conditions. As a consequence, fluid and particles can remain trapped within these structures for unexpectedly-long time scales. We also present simple techniques to mitigate this recirculation effect which can potentially have impact across industries ranging from biomedical and chemical processing to food and health sciences.

Hydrodynamics of the Semi-Immersed Cylinder by Forced Oscillation Model Testing

NASA Astrophysics Data System (ADS)

Song, Chun-hui; Fu, Shi-xiao; Tang, Xiao-ying; Hu, Ke; Ma, Lei-xin; Ren, Tong-xin

2018-03-01

In this paper, the hydrodynamic coefficients of a horizontal semi-immersed cylinder in steady current and oscillatory flow combining with constant current are obtained via forced oscillation experiments in a towing tank. Three nondimensional parameters ( Re, KC and Fr) are introduced to investigate their effects on the hydrodynamic coefficients. The experimental results show that overtopping is evident and dominates when the Reynolds number exceeds 5×105 in the experiment. Under steady current condition, overtopping increases the drag coefficient significantly at high Reynolds numbers. Under oscillatory flow with constant current condition, the added mass coefficient can even reach a maximum value about 3.5 due to overtopping while the influence of overtopping on the drag coefficient is minor.

Graphical User Interface Development for Representing Air Flow Patterns

NASA Technical Reports Server (NTRS)

Chaudhary, Nilika

2004-01-01

In the Turbine Branch, scientists carry out experimental and computational work to advance the efficiency and diminish the noise production of jet engine turbines. One way to do this is by decreasing the heat that the turbine blades receive. Most of the experimental work is carried out by taking a single turbine blade and analyzing the air flow patterns around it, because this data indicates the sections of the turbine blade that are getting too hot. Since the cost of doing turbine blade air flow experiments is very high, researchers try to do computational work that fits the experimental data. The goal of computational fluid dynamics is for scientists to find a numerical way to predict the complex flow patterns around different turbine blades without physically having to perform tests or costly experiments. When visualizing flow patterns, scientists need a way to represent the flow conditions around a turbine blade. A researcher will assign specific zones that surround the turbine blade. In a two-dimensional view, the zones are usually quadrilaterals. The next step is to assign boundary conditions which define how the flow enters or exits one side of a zone. way of setting up computational zones and grids, visualizing flow patterns, and storing all the flow conditions in a file on the computer for future computation. Such a program is necessary because the only method for creating flow pattern graphs is by hand, which is tedious and time-consuming. By using a computer program to create the zones and grids, the graph would be faster to make and easier to edit. Basically, the user would run a program that is an editable graph. The user could click and drag with the mouse to form various zones and grids, then edit the locations of these grids, add flow and boundary conditions, and finally save the graph for future use and analysis. My goal this summer is to create a graphical user interface (GUI) that incorporates all of these elements. I am writing the program in Java, a language that is portable among platforms, because it can run on different operating systems such as Windows and Unix without having to be rewritten. I had no prior experience of programming in Java at the start of my internship; I am continuously learning as I create the program. I have written the part of the program that enables a user to draw several zones, edit them, and store their locations. The next phase of my project is to allow the user to click on the side of a zone and create a boundary condition for it. A previous intern wrote a program that allows the user to input boundary conditions. I can integrate the two programs to create a larger, more usable program. After that, I will develop a way for the user to save the graph for future reference. Another eventual goal is to make the GUI capable of creating three-dimensional zones as well. Researchers such as my mentor, Dr. David Ashpis, need a quick, user-friendly

A high precision gas flow cell for performing in situ neutron studies of local atomic structure in catalytic materials

DOE PAGES

Olds, Daniel; Page, Katharine; Paecklar, Arnold A.; ...

2017-03-17

Gas-solid interfaces enable a multitude of industrial processes, including heterogeneous catalysis; however, there are few methods available for studying the structure of this interface under operating conditions. Here, we present a new sample environment for interrogating materials under gas-flow conditions using time-of-flight neutron scattering under both constant and pulse probe gas flow. Outlined are descriptions of the gas flow cell and a commissioning example using the adsorption of N 2 by Ca-exchanged zeolite-X (Na 78–2xCa xAl 78Si 144O 384,x ≈ 38). We demonstrate sensitivities to lattice contraction and N 2 adsorption sites in the structure, with both static gas loadingmore » and gas flow. A steady-state isotope transient kinetic analysis of N 2 adsorption measured simultaneously with mass spectrometry is also demonstrated. In the experiment, the gas flow through a plugged-flow gas-solid contactor is switched between 15N 2 and 14N 2 isotopes at a temperature of 300 K and a constant pressure of 1 atm; the gas flow and mass spectrum are correlated with the structure factor determined from event-based neutron total scattering. As a result, available flow conditions, sample considerations, and future applications are discussed.« less

Feasibility analysis of large length-scale thermocapillary flow experiment for the International Space Station

NASA Astrophysics Data System (ADS)

Alberts, Samantha J.

The investigation of microgravity fluid dynamics emerged out of necessity with the advent of space exploration. In particular, capillary research took a leap forward in the 1960s with regards to liquid settling and interfacial dynamics. Due to inherent temperature variations in large spacecraft liquid systems, such as fuel tanks, forces develop on gas-liquid interfaces which induce thermocapillary flows. To date, thermocapillary flows have been studied in small, idealized research geometries usually under terrestrial conditions. The 1 to 3m lengths in current and future large tanks and hardware are designed based on hardware rather than research, which leaves spaceflight systems designers without the technological tools to effectively create safe and efficient designs. This thesis focused on the design and feasibility of a large length-scale thermocapillary flow experiment, which utilizes temperature variations to drive a flow. The design of a helical channel geometry ranging from 1 to 2.5m in length permits a large length-scale thermocapillary flow experiment to fit in a seemingly small International Space Station (ISS) facility such as the Fluids Integrated Rack (FIR). An initial investigation determined the proposed experiment produced measurable data while adhering to the FIR facility limitations. The computational portion of this thesis focused on the investigation of functional geometries of fuel tanks and depots using Surface Evolver. This work outlines the design of a large length-scale thermocapillary flow experiment for the ISS FIR. The results from this work improve the understanding thermocapillary flows and thus improve technological tools for predicting heat and mass transfer in large length-scale thermocapillary flows. Without the tools to understand the thermocapillary flows in these systems, engineers are forced to design larger, heavier vehicles to assure safety and mission success.

Effects of nonlocal hydromechanics in a flow in thin channels

NASA Astrophysics Data System (ADS)

Aydagulov, R. R.; Ganiev, O. R.

2017-04-01

An approach to viscous friction is described as nonlocal momentum exchange between different layers of a fluid. The Navier-Stokes equations are replaced by pseudo-differential equations hyperbolic in time. In this case, instead of zero velocity on the boundary, a nonlocal nonlinear boundary condition is set in the form of the velocity dependence of the coefficient before the intensity of the momentum exchange with the boundary. The non-newtonian character of the viscosity of water is shown in experiments with thin insulin needles and explained by the nonlinear character of the momentum exchange of water with the boundary. The calculations agree very well both with our experiments and with the experiments of other authors. Calculations show that the flow decreases more than one-and-a-half times in comparison with the Poiseuille flow for channels with a diameter of 360-390 μm, which is confirmed in experiments.

Using Magnetic Field Gradients to Simulate Variable Gravity in Fluids and Materials Experiments

NASA Technical Reports Server (NTRS)

Ramachandran, Narayanan

2006-01-01

Fluid flow due to a gravitational field is caused by sedimentation, thermal buoyancy, or solutal buoyancy induced convection. During crystal growth, for example, these flows are undesirable and can lead to crystal imperfections. While crystallization in microgravity can approach diffusion limited growth conditions (no convection), terrestrially strong magnetic fields can be used to control fluid flow and sedimentation effects. In this work, a theory is presented on the stability of solutal convection of a magnetized fluid(weak1y paramagnetic) in the presence of a magnetic field. The requirements for stability are developed and compared to experiments performed within the bore of a superconducting magnet. The theoretical predictions are in good agreement with the experiments. Extension of the technique can also be applied to study artificial gravity requirements for long duration exploration missions. Discussion of this application with preliminary experiments and application of the technique to crystal growth will be provided.

Experiments in a flighted conveyor comparing shear rates in compressed versus free surface flows

NASA Astrophysics Data System (ADS)

Pohlman, Nicholas; Higgins, Hannah; Krupiarz, Kamila; O'Connor, Ryan

2017-11-01

Uniformity of granular flow rate is critical in industry. Experiments in a flighted conveyor system aim to fill a gap in knowledge of achieving steady mass flow rate by correlating velocity profile data with mass flow rate measurements. High speed images were collected for uniformly-shaped particles in a bottom-driven flow conveyor belt system from which the velocity profiles can be generated. The correlation of mass flow rates from the velocity profiles to the time-dependent mass measurements will determine energy dissipation rates as a function of operating conditions. The velocity profiles as a function of the size of the particles, speed of the belt, and outlet size, will be compared to shear rate relationships found in past experiments that focused on gravity-driven systems. The dimension of the linear shear and type of decaying transition to the stationary bed may appear different due to the compression versus dilation space in open flows. The application of this research can serve to validate simulations in discrete element modeling and physically demonstrate a process that can be further developed and customized for industry applications, such as feeding a biomass conversion reactor. Sponsored by NIU's Office of Student Engagement and Experiential Learning.

Heading perception in patients with advanced retinitis pigmentosa

NASA Technical Reports Server (NTRS)

Li, Li; Peli, Eli; Warren, William H.

2002-01-01

PURPOSE: We investigated whether retinis pigmentosa (RP) patients with residual visual field of < 100 degrees could perceive heading from optic flow. METHODS: Four RP patients and four age-matched normally sighted control subjects viewed displays simulating an observer walking over a ground. In experiment 1, subjects viewed either the entire display with free fixation (full-field condition) or through an aperture with a fixation point at the center (aperture condition). In experiment 2, patients viewed displays of different durations. RESULTS: RP patients' performance was comparable to that of the age-matched control subjects: heading judgment was better in the full-field condition than in the aperture condition. Increasing display duration from 0.5 s to 1 s improved patients' heading performance, but giving them more time (3 s) to gather more visual information did not consistently further improve their performance. CONCLUSIONS: RP patients use active scanning eye movements to compensate for their visual field loss in heading perception; they might be able to gather sufficient optic flow information for heading perception in about 1 s.

Heading perception in patients with advanced retinitis pigmentosa.

PubMed

Li, Li; Peli, Eli; Warren, William H

2002-09-01

We investigated whether retinis pigmentosa (RP) patients with residual visual field of < 100 degrees could perceive heading from optic flow. Four RP patients and four age-matched normally sighted control subjects viewed displays simulating an observer walking over a ground. In experiment 1, subjects viewed either the entire display with free fixation (full-field condition) or through an aperture with a fixation point at the center (aperture condition). In experiment 2, patients viewed displays of different durations. RP patients' performance was comparable to that of the age-matched control subjects: heading judgment was better in the full-field condition than in the aperture condition. Increasing display duration from 0.5 s to 1 s improved patients' heading performance, but giving them more time (3 s) to gather more visual information did not consistently further improve their performance. RP patients use active scanning eye movements to compensate for their visual field loss in heading perception; they might be able to gather sufficient optic flow information for heading perception in about 1 s.

An Improved Treatment of External Boundary for Three-Dimensional Flow Computations

NASA Technical Reports Server (NTRS)

Tsynkov, Semyon V.; Vatsa, Veer N.

1997-01-01

We present an innovative numerical approach for setting highly accurate nonlocal boundary conditions at the external computational boundaries when calculating three-dimensional compressible viscous flows over finite bodies. The approach is based on application of the difference potentials method by V. S. Ryaben'kii and extends our previous technique developed for the two-dimensional case. The new boundary conditions methodology has been successfully combined with the NASA-developed code TLNS3D and used for the analysis of wing-shaped configurations in subsonic and transonic flow regimes. As demonstrated by the computational experiments, the improved external boundary conditions allow one to greatly reduce the size of the computational domain while still maintaining high accuracy of the numerical solution. Moreover, they may provide for a noticeable speedup of convergence of the multigrid iterations.

The significance of GW-SW interactions for biogeochemical processes in sandy streambeds

NASA Astrophysics Data System (ADS)

Arnon, Shai; De Falco, Natalie; Fox, Aryeh; Laube, Gerrit; Schmidt, Christian; Fleckenstein, Jan; Boano, Fulvio

2015-04-01

Stream-groundwater interactions have a major impact on hyporheic exchange fluxes in sandy streambeds. However, the physical complexity of natural streams has limited our ability to study these types of interactions systematically, and to evaluate their importance to biogeochemical processes and nutrient cycling. In this work we were able to quantify the effect of losing and gaining fluxes on hyporheic exchange and nutrient cycling in homogeneous and heterogeneous streambeds by combining experiments in laboratory flumes and modeling. Tracer experiments for measuring hyporheic exchange were done using dyes and NaCl under various combinations of overlying water velocity and losing or gaining fluxes. Nutrient cycling experiments were conducted after growing a benthic biofilm by spiking with Sodium Benzoate (as a source of labile dissolved organic carbon, DOC) and measuring DOC and oxygen dynamics. The combination of experimental observations and modeling revealed that interfacial transport increases with the streambed hydraulic conductivity and proportional to the square of the overlying water velocity. Hyporheic exchange fluxes under losing and gaining flow conditions were similar, and became smaller when the losing or gaining flux increases. Increasing in streambed hydraulic conductivity led to higher hyporheic fluxes and reduction in the effects of losing and gaining flow conditions to constrain exchange. Despite the evident effect of flow conditions on hyporheic exchange, labile DOC uptake was positively linked to increasing overlying water velocity but was not affected by losing and gaining fluxes. This is because microbial aerobic activity was taking place at the upper few millimeters of the streambed as shown by local oxygen consumption rates, which was measured using microelectrodes. Based on modeling work, it is expected that GW-SW interaction will be more significant for less labile DOC and anaerobic processes. Our results enable us to study systematically the coupling between flow conditions and biogeochemical processes under highly controlled physical and chemical conditions and are expected to improve our understanding of nutrient cycling in streams.

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer.

PubMed

Köhler, Markus; Oßwald, Patrick; Krueger, Dominik; Whitside, Ryan

2018-02-19

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

Regional-scale analysis of karst underground flow deduced from tracing experiments: examples from carbonate aquifers in Malaga province, southern Spain

NASA Astrophysics Data System (ADS)

Barberá, J. A.; Mudarra, M.; Andreo, B.; De la Torre, B.

2018-02-01

Tracer concentration data from field experiments conducted in several carbonate aquifers (Malaga province, southern Spain) were analyzed following a dual approach based on the graphical evaluation method (GEM) and solute transport modeling to decipher flow mechanisms in karst systems at regional scale. The results show that conduit system geometry and flow conditions are the principal factors influencing tracer migration through the examined karst flow routes. Solute transport is mainly controlled by longitudinal advection and dispersion throughout the conduit length, but also by flow partitioning between mobile and immobile fluid phases, while the matrix diffusion process appears to be less relevant. The simulation of tracer breakthrough curves (BTCs) suggests that diffuse and concentrated flow through the unsaturated zone can have equivalent transport properties under extreme recharge, with high flow velocities and efficient mixing due to the high hydraulic gradients generated. Tracer mobilization within the saturated zone under low flow conditions mainly depends on the hydrodynamics (rather than on the karst conduit development), which promote a lower longitudinal advection and retardation in the tracer migration, resulting in a marked tailing effect of BTCs. The analytical advection-dispersion equation better approximates the effective flow velocity and longitudinal dispersion estimations provided by the GEM, while the non-equilibrium transport model achieves a better adjustment of most asymmetric and long-tailed BTCs. The assessment of karst underground flow properties from tracing tests at regional scale can aid design of groundwater management and protection strategies, particularly in large hydrogeological systems (i.e. transboundary carbonate aquifers) and/or in poorly investigated ones.

Which key properties controls the preferential transport in the vadose zone under transient hydrological conditions

NASA Astrophysics Data System (ADS)

Groh, J.; Vanderborght, J.; Puetz, T.; Gerke, H. H.; Rupp, H.; Wollschlaeger, U.; Stumpp, C.; Priesack, E.; Vereecken, H.

2015-12-01

Understanding water flow and solute transport in the unsaturated zone is of great importance for an appropriate land use management strategy. The quantification and prediction of water and solute fluxes through the vadose zone can help to improve management practices in order to limit potential risk on our fresh water resources. Water related solute transport and residence time is strongly affected by preferential flow paths in the soil. Water flow in soils depends on soil properties and site factors (climate or experiment conditions, land use) and are therefore important factors to understand preferential solute transport in the unsaturated zone. However our understanding and knowledge of which on-site properties or conditions define and enhance preferential flow and transport is still poor and mostly limited onto laboratory experimental conditions (small column length and steady state boundary conditions). Within the TERENO SOILCan lysimeter network, which was designed to study the effects of climate change on soil functions, a bromide tracer was applied on 62 lysimeter at eight different test sites between Dec. 2013 and Jan. 2014. The TERENO SOILCan infrastructure offers the unique possibility to study the occurrence of preferential flow and transport of various soil types under different natural transient hydrological conditions and land use (crop, bare and grassland) at eight TERENO SOILCan observatories. Working with lysimeter replicates at each observatory allows defining the spatial variability of preferential transport and flow. Additionally lysimeters in the network were transferred within and between observatories in order to subject them to different rainfall and temperature regimes and enable us to relate the soil type susceptibility of preferential flow and transport not only to site specific physical and land use properties, but also to different transient boundary conditions. Comparison and statistical analysis between preferential flow indicators 5% arrival time and potential key soil properties, site factors and boundary conditions will be presented in order to identify key properties which control the preferential transport in the vadose zone under transient hydrological conditions.

Two-phase gas-liquid flow characteristics inside a plate heat exchanger

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nilpueng, Kitti; Wongwises, Somchai

In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-watermore » mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)« less

Zonal Rate Model for Axial and Radial Flow Membrane Chromatography. Part I: Knowledge Transfer Across Operating Conditions and Scales

PubMed Central

Ghosh, Pranay; Vahedipour, Kaveh; Lin, Min; Vogel, Jens H; Haynes, Charles A; von Lieres, Eric

2013-01-01

The zonal rate model (ZRM) has previously been applied for analyzing the performance of axial flow membrane chromatography capsules by independently determining the impacts of flow and binding related non-idealities on measured breakthrough curves. In the present study, the ZRM is extended to radial flow configurations, which are commonly used at larger scales. The axial flow XT5 capsule and the radial flow XT140 capsule from Pall are rigorously analyzed under binding and non-binding conditions with bovine serum albumin (BSA) as test molecule. The binding data of this molecule is much better reproduced by the spreading model, which hypothesizes different binding orientations, than by the well-known Langmuir model. Moreover, a revised cleaning protocol with NaCl instead of NaOH and minimizing the storage time has been identified as most critical for quantitatively reproducing the measured breakthrough curves. The internal geometry of both capsules is visualized by magnetic resonance imaging (MRI). The flow in the external hold-up volumes of the XT140 capsule was found to be more homogeneous as in the previously studied XT5 capsule. An attempt for model-based scale-up was apparently impeded by irregular pleat structures in the used XT140 capsule, which might lead to local variations in the linear velocity through the membrane stack. However, the presented approach is universal and can be applied to different capsules. The ZRM is shown to potentially help save valuable material and time, as the experiments required for model calibration are much cheaper than the predicted large-scale experiment at binding conditions. Biotechnol. Bioeng. 2013; 110: 1129–1141. © 2012 Wiley Periodicals, Inc. PMID:23097218

Design and numerical simulation on an auto-cumulative flowmeter in horizontal oil-water two-phase flow

NASA Astrophysics Data System (ADS)

Xie, Beibei; Kong, Lingfu; Kong, Deming; Kong, Weihang; Li, Lei; Liu, Xingbin; Chen, Jiliang

2017-11-01

In order to accurately measure the flow rate under the low yield horizontal well conditions, an auto-cumulative flowmeter (ACF) was proposed. Using the proposed flowmeter, the oil flow rate in horizontal oil-water two-phase segregated flow can be finely extracted. The computational fluid dynamics software Fluent was used to simulate the fluid of the ACF in oil-water two-phase flow. In order to calibrate the simulation measurement of the ACF, a novel oil flow rate measurement method was further proposed. The models of the ACF were simulated to obtain and calibrate the oil flow rate under different total flow rates and oil cuts. Using the finite-element method, the structure of the seven conductance probes in the ACF was simulated. The response values for the probes of the ACF under the conditions of oil-water segregated flow were obtained. The experiments for oil-water segregated flow under different heights of the oil accumulation in horizontal oil-water two-phase flow were carried out to calibrate the ACF. The validity of the oil flow rate measurement in horizontal oil-water two-phase flow was verified by simulation and experimental results.

Design and numerical simulation on an auto-cumulative flowmeter in horizontal oil-water two-phase flow.

PubMed

Xie, Beibei; Kong, Lingfu; Kong, Deming; Kong, Weihang; Li, Lei; Liu, Xingbin; Chen, Jiliang

2017-11-01

In order to accurately measure the flow rate under the low yield horizontal well conditions, an auto-cumulative flowmeter (ACF) was proposed. Using the proposed flowmeter, the oil flow rate in horizontal oil-water two-phase segregated flow can be finely extracted. The computational fluid dynamics software Fluent was used to simulate the fluid of the ACF in oil-water two-phase flow. In order to calibrate the simulation measurement of the ACF, a novel oil flow rate measurement method was further proposed. The models of the ACF were simulated to obtain and calibrate the oil flow rate under different total flow rates and oil cuts. Using the finite-element method, the structure of the seven conductance probes in the ACF was simulated. The response values for the probes of the ACF under the conditions of oil-water segregated flow were obtained. The experiments for oil-water segregated flow under different heights of the oil accumulation in horizontal oil-water two-phase flow were carried out to calibrate the ACF. The validity of the oil flow rate measurement in horizontal oil-water two-phase flow was verified by simulation and experimental results.

Numerical Leak Detection in a Pipeline Network of Complex Structure with Unsteady Flow

NASA Astrophysics Data System (ADS)

Aida-zade, K. R.; Ashrafova, E. R.

2017-12-01

An inverse problem for a pipeline network of complex loopback structure is solved numerically. The problem is to determine the locations and amounts of leaks from unsteady flow characteristics measured at some pipeline points. The features of the problem include impulse functions involved in a system of hyperbolic differential equations, the absence of classical initial conditions, and boundary conditions specified as nonseparated relations between the states at the endpoints of adjacent pipeline segments. The problem is reduced to a parametric optimal control problem without initial conditions, but with nonseparated boundary conditions. The latter problem is solved by applying first-order optimization methods. Results of numerical experiments are presented.

Flight Test Results from the Rake Airflow Gage Experiment on the F-15B Airplane

NASA Technical Reports Server (NTRS)

Frederick, Michael A.; Ratnayake, Nalin A.

2011-01-01

The Rake Airflow Gage Experiment involves a flow-field survey rake that was flown on the Propulsion Flight Test Fixture at the NASA Dryden Flight Research Center using the Dryden F-15B research test bed airplane. The objective of this flight test was to ascertain the flow-field angularity, local Mach number profile, total pressure distortion, and dynamic pressure at the aerodynamic interface plane of the Channeled Centerbody Inlet Experiment. This new mixed-compression, supersonic inlet is planned for flight test in the near term. Knowledge of the flow-field characteristics at this location underneath the airplane is essential to flight test planning and computational modeling of the new inlet, an< it is also applicable for future propulsion systems research that may use the Propulsion Flight Test Fixture. This report describes the flight test preparation and execution, and the local flow-field properties calculated from pressure measurements of the rake. Data from the two Rake Airflow Gage Experiment research flights demonstrate that the F-15B airplane, flying at a free-stream Mach number of 1.65 and a pressure altitude of 40,000 ft, would achieve the desired local Mach number for the future inlet flight test. Interface plane distortion levels of 2 percent and a local angle of attack of -2 deg were observed at this condition. Alternative flight conditions for future testing and an exploration of certain anomalous data also are provided.

Understanding Transition to Turbulence in Shear Layers.

DTIC Science & Technology

1983-05-01

Imperfect bifurcations ; circular Couette flow 24 0.02.06 Interpretations of experiments on Poiseuille flow 26 ( a ) Absence of turbulence far Re > Re 27 (b...instability of the shear layer. This is a very effective com- bination, which fuels most flow-conditioned acoustic resonances, includ- ing organ pipes and...variable density as encountered in aeronautics are *confined to Appendix A , Sections A .07, A .08, A .10- A .15, and Chapter 10. Effects of stratification as

A Lagrangian Analysis of a Developing and Non-Developing Disturbance Observed During the PREDICT Experiment

DTIC Science & Technology

2012-12-03

paper provides an introduction of Lagrangian techniques for locating flow boundaries that encompass regions of recirculation in time- dependent flows...the low- to mid- level embryonic vortex from adverse conditions, while the 1The glossary on NOAA’s Hurricane Research Division’s web - site uses...wave or disturbance. This paper provides an introduction of Lagrangian techniques for locating flow boundaries that encompass regions of recirculation

Are large-scale manipulations of streamflow for ecological outcomes effective either as experiments or management actions? (Invited)

NASA Astrophysics Data System (ADS)

Konrad, C. P.; Olden, J.

2013-12-01

Dams impose a host of impacts on freshwater and estuary ecosystems. In recent decades, dam releases for ecological outcomes have been increasingly implemented to mitigate for these impacts and are gaining global scope. Many are designed and conducted using an experimental framework. A recent review of large-scale flow experiments (FE) evaluates their effectiveness and identifies ways to enhance their scientific and management value. At least 113 large-scale flow experiments affecting 98 river systems globally have been documented over the last 50 years. These experiments span a range of flow manipulations from single pulse events to comprehensive changes in flow regime across all seasons and different water year types. Clear articulation of experimental objectives, while not universally practiced, was crucial for achieving management outcomes and changing dam operating policies. We found a strong disparity between the recognized ecological importance of a multi faceted flow regimes and discrete flow events that characterized 80% of FEs. Over three quarters of FEs documented both abiotic and biotic outcomes, but only one third examined multiple trophic groups, thus limiting how this information informs future dam management. Large-scale flow experiments represent a unique opportunity for integrated biophysical investigations for advancing ecosystem science. Nonetheless, they must remain responsive to site-specific issues regarding water management, evolving societal values and changing environmental conditions and, in particular, can characterize the incremental benefits from and necessary conditions for changing dam operations to improve ecological outcomes. This type of information is essential for understanding the full context of value based trade-offs in benefits and costs from different dam operations that can serve as an empirical basis for societal decisions regarding water and ecosystem management. FE may be the best approach available to managers for resolving critical uncertainties that impede decision making in adaptive settings, for example, when we lack sufficient understanding to model biophysical responses to alternative operations. Integrated long term monitoring of biotic abiotic responses and defining clear management based objectives highlight ways for improving the efficiency and value of FEs.

Turbofan Acoustic Propagation and Radiation

NASA Technical Reports Server (NTRS)

Eversman, Walter

2000-01-01

This document describes progress in the development of finite element codes for the prediction of near and far field acoustic radiation from the inlet and aft fan ducts of turbofan engines. The report consists of nine papers which have appeared in archival journals and conference proceedings, or are presently in review for publication. Topics included are: 1. Aft Fan Duct Acoustic Radiation; 2. Mapped Infinite Wave Envelope Elements for Acoustic Radiation in a Uniformly Moving Medium; 3. A Reflection Free Boundary Condition for Propagation in Uniform Flow Using Mapped Infinite Wave Envelope Elements; 4. A Numerical Comparison Between Multiple-Scales and FEM Solution for Sound Propagation in Lined Flow Ducts; 5. Acoustic Propagation at High Frequencies in Ducts; 6. The Boundary Condition at an Impedance Wall in a Nonuniform Duct with Potential Flow; 7. A Reverse Flow Theorem and Acoustic Reciprocity in Compressible Potential Flows; 8. Reciprocity and Acoustics Power in One Dimensional Compressible Potential Flows; and 9. Numerical Experiments on Acoustic Reciprocity in Compressible Potential Flows.

Bubble and Slug Flow at Microgravity Conditions: State of Knowledge and Open Questions

NASA Technical Reports Server (NTRS)

Colin, C.; Fabre, J.; McQuillen, J.

1996-01-01

Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.

Experimental quantification of solute transport through the vadose zone under dynamic boundary conditions with dye tracers and optical methods.

NASA Astrophysics Data System (ADS)

Cremer, Clemens; Neuweiler, Insa

2017-04-01

Knowledge of subsurface solute transport processes is vital to investigate e.g. groundwater contamination, nutrient uptake by plant roots and to implement remediation strategies. Beside field measurements and numerical simulations, physical laboratory experiments represent a way to establish process understanding and furthermore validate numerical schemes. Atmospheric forcings, such as erratically varying infiltration and evaporation cycles, subject the shallow subsurface to local and temporal variations in water content and associated hydraulic conductivity of the prevailing porous media. Those variations in material properties can cause flow paths to differ between upward and downward flow periods. Thereby, the unsaturated subsurface presents a highly complicated, dynamic system. Following an extensive systematical numerical investigation of flow and transport through bimodal, unsaturated porous media under dynamic boundary conditions (Cremer et al., 2016), we conduct physical laboratory experiments in a 22 cm x 8 cm x 1 cm flow cell where we introduce structural heterogeneity in the form sharp material interfaces between different porous media. In all experiments, a constant pressure head is implemented at the lower boundary, while cyclic infiltration-evaporation phases are applied at the soil surface. As a reference case a stationary infiltration with a rate corresponding to the cycle-averaged infiltration rate is applied. By initial application of dye tracers, solute transport within the domain is visualized such that transport paths and redistribution processes can be observed in a qualitative manner. Solute leaching is quantified at the bottom outlet, where breakthrough curves are obtained via spectroscopy. Liquid and vapor flow in and out of the domain is obtained from multiple balances. Thereby, the interplay of material structural heterogeneity and alternating flow (transport) directions and flow (transport) paths is investigated. Results show lateral transport through the material interface which differs between the stationary (unilateral) and dynamic cases (bilateral). This qualitative observation is confirmed by breakthrough curves for dynamic experiments which generally show the trend of faster initial breakthrough and increased tailing when compared to stationary infiltration results. Literature Cremer, C.J.M., I. Neuweiler, M. Bechtold, J. Vanderborght (2016): Solute Transport in Heterogeneous Soil with Time-Dependent Boundary Conditions, Vadose Zone Journal 15 (6) DOI: 10.2136/vzj2015.11.0144

Experimental Investigation and Analysis of HEC-6 River Morphological Model

NASA Astrophysics Data System (ADS)

Tingsanchali, Tawatchai; Supharatid, Seree

1996-05-01

Only comparatively few experimental studies have been carried out to investigate the performance of the HEC-6 river morphological model. The model was developed by the Hydrologic Engineering Center of the US Army Corps of Engineers. In this study, experiments were carried out in a 20 m long concrete flume 0.6 m wide with varying rectangular cross-sections. The channel bed is paved with uniform sand of D50 = 0.9 mm and D90 = 1.2 mm within the test reach of 12 m. Two types of experiments were carried out with sediment transport, one under steady uniform flow and another under steady non-uniform flow conditions. Nine steady uniform flow experiments were carried out to compare the measured equilibrium relationship of flow and sediment transport rate with two bedload formulae, namely, Du Boys and Meyer-Peter and Muller, and with three total load formulae, namely, Toffaleti, Laursen and Yang. It was found that even though the sediment transport consists of a certain portion of bedload, the total load formulae give satisfactory results and better agreement than the two bedload formulae. Five steady non-uniform flow experiments were carried out under various conditions of varying bed profile and channel width and also with sediment addition and withdrawal. The measured transient water surface and bed profiles are compared with the computed results from the HEC-6 model. It was found that the Toffaleti and Yang total load formulae used in the HEC-6 model give the most satisfactory prediction of actual bed profiles under various conditions of non-uniform flow and sediment transport. The effects of Manning's n, variations of sediment inflow, various sediment transport formulae, sediment grain size and the model numerical parameters, i.e. distance interval x and numerical weighting factor, on the computed water surface and bed profiles were determined. It was found that the selection of the sediment transport formulae has the most significant effect on the computed results. It can be concluded that the HEC-6 model can predict satisfactorily a long-term average pattern of local scour and deposition along a channel with either a small abrupt change in geometry or gradually varying cross-sections. However, the accuracy of the model prediction is reduced in the regions where highly non-uniform flow occurs.

Decoupling flood and interflood deposits for delta island formation and channel bifurcation

NASA Astrophysics Data System (ADS)

Daniller-Varghese, M. S.; Kim, W.

2016-12-01

Channel islands' size and organization dictate delta networks' morphology. To understand their complex network organization, a single channel island node within that network should be investigated first as the fundamental building block. When a sediment-laden flow enters slack water, it loses momentum and carrying capacity, depositing its sediment. As sediment accumulates, flow moves around it and a mouth bar island develops. We present an experimental investigation of island formation and channel bifurcation using the Sediment Transport and Earth-surface Processes (STEP) basin. We made mouth bar deposits and flow bifurcations in transport-limited turbulent conditions. Time-lapse images, elevation scans on the deltaic surface, and a low-cost particle imaging velocimetry system allow us to characterize the flow and depositional evolution of our experimental islands. Using two flow discharges (0.355 l/s, 6 l/s) and uniform sediment, our experiments have two characteristic advection lengths and corresponding deposit types. One, associated with interflood bedload transport, and the other with flood-suspended transport: proximal low-angle deposits and distal steep deposits, respectively. By varying the frequency of floods (one every 20s-20 mins) while keeping sediment and water mass constant across experiments, we are able to control the time and spatial organization of these two deposit types and examine the effect on bifurcation length and bifurcation incidence time. As the interflood flow deposit and flood deposit accumulate sediment over time, the interflood deposit encroaches onto the flood deposit. Flow is routed from the interflood deposit to the flood deposit but does not have the momentum to uniformly cover it. The flow becomes unsteady, and bifurcates around an island. After the bifurcation, the island's vertical aggradation rate also increases. The experiments suggest that the interaction between deposits stemming from different particle advection lengths is a sufficient condition for island formation and flow bifurcation.

Validation of the actuator line and disc techniques using the New MEXICO measurements

NASA Astrophysics Data System (ADS)

Sarmast, S.; Shen, W. Z.; Zhu, W. J.; Mikkelsen, R. F.; Breton, S. P.; Ivanell, S.

2016-09-01

Actuator line and disc techniques are employed to analyse the wake obtained in the New MEXICO wind turbine experiment. The New MEXICO measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.

Experimental and Computational Study of the Hydrodynamics of Trickle Bed Flow Reactor Operating Under Different Pressure Conditions

NASA Astrophysics Data System (ADS)

Rabbani, S.; Ben Salem, I.; Nadeem, H.; Kurnia, J. C.; Shamim, T.; Sassi, M.

2014-12-01

Pressure drop estimation and prediction of liquid holdup play a crucial role in design and operation of trickle bed reactors. Experiments are performed for Light Gas Oil (LGO)-nitrogen system in ambient temperature conditions in an industrial pilot plant with reactor height 0.79 m and diameter of 0.0183 m and pressure ranging from atmospheric to 10 bars. It was found that pressure drop increased with increase in system pressure, superficial gas velocity and superficial liquid velocity. It was demonstrated in the experiments that liquid holdup of the system increases with the increase in superficial liquid velocity and tends to decrease with increase in superficial gas velocity which is in good agreement with existing literature. Similar conditions were also simulated using CFD-software FLUENT. The Volume of Fluid (VoF) technique was employed in combination with "discrete particle approach" and results were compared with that of experiments. The overall pressure drop results were compared with the different available models and a new comprehensive model was proposed to predict the pressure drop in Trickle Bed Flow Reactor.

Definition of two-phase flow behaviors for spacecraft design

NASA Technical Reports Server (NTRS)

Reinarts, Thomas R.; Best, Frederick R.; Miller, Katherine M.; Hill, Wayne S.

1991-01-01

Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. A boiling and condensing experiment was built in which R-12 was used as the working fluid. A two-phase pump was used to circulate a freon mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown five times aboard the NASA KC-135 aircraft which simulates zero-g conditions by its parabolic flight trajectory. Test conditions included stratified and annual flow regimes in 1-g which became bubbly, slug, or annular flow regimes on 0-g. A portion of this work is the analysis of adiabatic flow regimes. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes.

Analog and numerical experiments investigating force chain influences on bed conditions in granular flows

NASA Astrophysics Data System (ADS)

Estep, J.; Dufek, J.

2013-12-01

Granular flows are fundamental processes in several terrestrial and planetary natural events; including surficial flows on volcanic edifices, debris flows, landslides, dune formation, rock falls, sector collapses, and avalanches. Often granular flows can be two-phase, whereby interstitial fluids occupy void space within the particulates. The mobility of granular flows has received significant attention, however the physics that govern their internal behavior remain poorly understood. Here we extend upon previous research showing that force chains can transmit extreme localized forces to the substrates of free surface granular flows, and we combine experimental and computational approaches to further investigate the forces at the bed of simplified granular flows. Analog experiments resolve discrete bed forces via a photoelastic technique, while numerical experiments validate laboratory tests using discrete element model (DEM) simulations. The current work investigates (1) the role of distributed grain sizes on force transmission via force chains, and (2) how the inclusion of interstitial fluids effects force chain development. We also include 3D numerical simulations to apply observed 2D characteristics into real world perspective, and ascertain if the added dimension alters force chain behavior. Previous research showed that bed forces generated by force chain structures can transiently greatly exceed (by several 100%) the bed forces predicted from continuum approaches, and that natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses. This work suggests that force chain activity may play an important role in the bed physics of dense granular flows by influencing substrate entrainment. Photoelastic experiment image showing force chains in gravity driven granular flow.

DSMC Computations for Regions of Shock/Shock and Shock/Boundary Layer Interaction

NASA Technical Reports Server (NTRS)

Moss, James N.

2001-01-01

This paper presents the results of a numerical study of hypersonic interacting flows at flow conditions that include those for which experiments have been conducted in the Calspan-University of Buffalo Research Center (CUBRC) Large Energy National Shock (LENS) tunnel and the ONERA R5Ch low-density wind tunnel. The computations are made with the direct simulation Monte Carlo (DSMC) method of Bird. The focus is on Mach 9.3 to 11.4 flows about flared axisymmetric configurations, both hollow cylinder flares and double cones. The results presented highlight the sensitivity of the calculations to grid resolution, provide results concerning the conditions for incipient separation, and provide information concerning the flow structure and surface results for the extent of separation, heating, pressure, and skin friction.

Effect of flow rate on environmental variables and phytoplankton dynamics: results from field enclosures

NASA Astrophysics Data System (ADS)

Zhang, Haiping; Chen, Ruihong; Li, Feipeng; Chen, Ling

2015-03-01

To investigate the effects of flow rate on phytoplankton dynamics and related environment variables, a set of enclosure experiments with different flow rates were conducted in an artificial lake. We monitored nutrients, temperature, dissolved oxygen, pH, conductivity, turbidity, chlorophyll- a and phytoplankton levels. The lower biomass in all flowing enclosures showed that flow rate significantly inhibited the growth of phytoplankton. A critical flow rate occurred near 0.06 m/s, which was the lowest relative inhibitory rate. Changes in flow conditions affected algal competition for light, resulting in a dramatic shift in phytoplankton composition, from blue-green algae in still waters to green algae in flowing conditions. These findings indicate that critical flow rate can be useful in developing methods to reduce algal bloom occurrence. However, flow rate significantly enhanced the inter-relationships among environmental variables, in particular by inducing higher water turbidity and vegetative reproduction of periphyton ( Spirogyra). These changes were accompanied by a decrease in underwater light intensity, which consequently inhibited the photosynthetic intensity of phytoplankton. These results warn that a universal critical flow rate might not exist, because the effect of flow rate on phytoplankton is interlinked with many other environmental variables.

Coupled fluid and solid evolution in analogue volcanic vents

NASA Astrophysics Data System (ADS)

Solovitz, Stephen A.; Ogden, Darcy E.; Kim, Dave (Dae-Wook); Kim, Sang Young

2014-07-01

Volcanic eruptions emit rock particulates and gases at high speed and pressure, which change the shape of the surrounding rock. Simplified analytical solutions, field studies, and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions. Here we present results from a newly developed laboratory-scale apparatus designed to study this coupled process. The experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material, which evolves through time during the experiment. The compressed air was injected at approximately 2.5 times atmospheric pressure. We fabricated rock analogues from sand and steel powder samples with a three-dimensional printing process. We studied the fluid development using phase-locked particle image velocimetry, while simultaneously observing the solid development via a video camera. We found that the fluid response was much more rapid than that of the solid, permitting a quasi-steady approximation. In most cases, the solid vent flared out rapidly, increasing its diameter by 20 to 100%. After the initial expansion, the vent and flow field achieved a near-steady condition for a long duration. The new expanded vent shapes permitted lower vent exit pressures and larger jet radii. In one experiment, after an initial vent shape development and establishment of steady flow behavior, rock failure occurred a second time, resulting in a new exit diameter and new steady state. This second failure was not precipitated by changes in the nozzle flow condition, and it radically changed the downstream flow dynamics. This experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow.

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

PubMed

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

Dynamics of polymers in elongational flow studied by the neutron spin-echo technique

NASA Astrophysics Data System (ADS)

Rheinstädter, Maikel C.; Sattler, Rainer; Häußler, Wolfgang; Wagner, Christian

2010-09-01

The nanoscale fluctuation dynamics of semidilute high molecular weight polymer solutions of polyethylenoxide (PEO) in D 2O under non-equilibrium flow conditions were studied by the neutron spin-echo technique. The sample cell was in contraction flow geometry and provided a pressure driven flow with a high elongational component that stretched the polymers most efficiently. Neutron scattering experiments in dilute polymer solutions are challenging because of the low polymer concentration and corresponding small quasi-elastic signals. A relaxation process with relaxation times of about 10 ps was observed, which shows anisotropic dynamics with applied flow.

Study of two-phase flows in reduced gravity

NASA Astrophysics Data System (ADS)

Roy, Tirthankar

Study of gas-liquid two-phase flows under reduced gravity conditions is extremely important. One of the major applications of gas-liquid two-phase flows under reduced gravity conditions is in the design of active thermal control systems for future space applications. Previous space crafts were characterized by low heat generation within the spacecraft which needed to be redistributed within the craft or rejected to space. This task could easily have been accomplished by pumped single-phase loops or passive systems such as heat pipes and so on. However with increase in heat generation within the space craft as predicted for future missions, pumped boiling two-phase flows are being considered. This is because of higher heat transfer co-efficients associated with boiling heat transfer among other advantages. Two-phase flows under reduced gravity conditions also find important applications in space propulsion as in space nuclear power reactors as well as in many other life support systems of space crafts. Two-fluid model along with Interfacial Area Transport Equation (IATE) is a useful tool available to predict the behavior of gas-liquid two-phase flows under reduced gravity conditions. It should be noted that considerable differences exist between two-phase flows under reduced and normal gravity conditions especially for low inertia flows. This is because due to suppression of the gravity field the gas-liquid two-phase flows take a considerable time to develop under reduced gravity conditions as compared to normal gravity conditions. Hence other common methods of analysis applicable for fully developed gas-liquid two-phase flows under normal gravity conditions, like flow regimes and flow regime transition criteria, will not be applicable to gas-liquid two-phase flows under reduced gravity conditions. However the two-fluid model and the IATE need to be evaluated first against detailed experimental data obtained under reduced gravity conditions. Although lot of studies have been done in the past to understand the global structure of gas-liquid two-phase flows under reduced gravity conditions, using experimental setups aboard drop towers or aircrafts flying parabolic flights, detailed data on local structure of such two-phase flows are extremely rare. Hence experiments were carried out in a 304 mm inner diameter (ID) test facility on earth. Keeping in mind the detailed experimental data base that needs to be generated to evaluate two-fluid model along with IATE, ground based simulations provide the only economic path. Here the reduced gravity condition is simulated using two-liquids of similar densities (water and Therminol 59 RTM in the present case). Only adiabatic two-phase flows were concentrated on at this initial stage. Such a large diameter test section was chosen to study the development of drops to their full extent (it is to be noted that under reduced gravity conditions the stable bubble size in gas-liquid two-phase flows is much larger than that at normal gravity conditions). Twelve flow conditions were chosen around predicted bubbly flow to cap-bubbly flow transition region. Detailed local data was obtained at ten radial locations for each of three axial locations using state-of-the art multi-sensor conductivity probes. The results are presented and discussed. Also one-group as well as two-group, steady state, one-dimensional IATE was evaluated against data obtained here and by other researchers, and the results presented and discussed.

Unsteady features of the flow on a bump in transonic environment

NASA Astrophysics Data System (ADS)

Budovsky, A. D.; Sidorenko, A. A.; Polivanov, P. A.; Vishnyakov, O. I.; Maslov, A. A.

2016-10-01

The study deals with experimental investigation of unsteady features of separated flow on a profiled bump in transonic environment. The experiments were conducted in T-325 wind tunnel of ITAM for the following flow conditions: P0 = 1 bar, T0 = 291 K. The base flow around the model was studied by schlieren visualization, steady and unsteady wall pressure measurements and PIV. The experimentally data obtained using PIV are analyzed by Proper Orthogonal Decomposition (POD) technique to investigate the underlying unsteady flow organization, as revealed by the POD eigenmodes. The data obtained show that flow pulsations revealed upstream and downstream of shock wave are correlated and interconnected.

Analytical skin friction and heat transfer formula for compressible internal flows

NASA Technical Reports Server (NTRS)

Dechant, Lawrence J.; Tattar, Marc J.

1994-01-01

An analytic, closed-form friction formula for turbulent, internal, compressible, fully developed flow was derived by extending the incompressible law-of-the-wall relation to compressible cases. The model is capable of analyzing heat transfer as a function of constant surface temperatures and surface roughness as well as analyzing adiabatic conditions. The formula reduces to Prandtl's law of friction for adiabatic, smooth, axisymmetric flow. In addition, the formula reduces to the Colebrook equation for incompressible, adiabatic, axisymmetric flow with various roughnesses. Comparisons with available experiments show that the model averages roughly 12.5 percent error for adiabatic flow and 18.5 percent error for flow involving heat transfer.

Investigation of Natural Circulation Instability and Transients in Passively Safe Small Modular Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishii, Mamoru

The NEUP funded project, NEUP-3496, aims to experimentally investigate two-phase natural circulation flow instability that could occur in Small Modular Reactors (SMRs), especially for natural circulation SMRs. The objective has been achieved by systematically performing tests to study the general natural circulation instability characteristics and the natural circulation behavior under start-up or design basis accident conditions. Experimental data sets highlighting the effect of void reactivity feedback as well as the effect of power ramp-up rate and system pressure have been used to develop a comprehensive stability map. The safety analysis code, RELAP5, has been used to evaluate experimental results andmore » models. Improvements to the constitutive relations for flashing have been made in order to develop a reliable analysis tool. This research has been focusing on two generic SMR designs, i.e. a small modular Simplified Boiling Water Reactor (SBWR) like design and a small integral Pressurized Water Reactor (PWR) like design. A BWR-type natural circulation test facility was firstly built based on the three-level scaling analysis of the Purdue Novel Modular Reactor (NMR) with an electric output of 50 MWe, namely NMR-50, which represents a BWR-type SMR with a significantly reduced reactor pressure vessel (RPV) height. The experimental facility was installed with various equipment to measure thermalhydraulic parameters such as pressure, temperature, mass flow rate and void fraction. Characterization tests were performed before the startup transient tests and quasi-steady tests to determine the loop flow resistance. The control system and data acquisition system were programmed with LabVIEW to realize the realtime control and data storage. The thermal-hydraulic and nuclear coupled startup transients were performed to investigate the flow instabilities at low pressure and low power conditions for NMR-50. Two different power ramps were chosen to study the effect of startup power density on the flow instability. The experimental startup transient results showed the existence of three different flow instability mechanisms, i.e., flashing instability, condensation induced flow instability, and density wave oscillations. In addition, the void-reactivity feedback did not have significant effects on the flow instability during the startup transients for NMR-50. ii Several initial startup procedures with different power ramp rates were experimentally investigated to eliminate the flow instabilities observed from the startup transients. Particularly, the very slow startup transient and pressurized startup transient tests were performed and compared. It was found that the very slow startup transients by applying very small power density can eliminate the flashing oscillations in the single-phase natural circulation and stabilize the flow oscillations in the phase of net vapor generation. The initially pressurized startup procedure was tested to eliminate the flashing instability during the startup transients as well. The pressurized startup procedure included the initial pressurization, heat-up, and venting process. The startup transient tests showed that the pressurized startup procedure could eliminate the flow instability during the transition from single-phase flow to two-phase flow at low pressure conditions. The experimental results indicated that both startup procedures were applicable to the initial startup of NMR. However, the pressurized startup procedures might be preferred due to short operating hours required. In order to have a deeper understanding of natural circulation flow instability, the quasi-steady tests were performed using the test facility installed with preheater and subcooler. The effect of system pressure, core inlet subcooling, core power density, inlet flow resistance coefficient, and void reactivity feedback were investigated in the quasi-steady state tests. The experimental stability boundaries were determined between unstable and stable flow conditions in the dimensionless stability plane of inlet subcooling number and Zuber number. To predict the stability boundary theoretically, linear stability analysis in the frequency domain was performed at four sections of the natural circulation test loop. The flashing phenomena in the chimney section was considered as an axially uniform heat source. And the dimensionless characteristic equation of the pressure drop perturbation was obtained by considering the void fraction effect and outlet flow resistance in the core section. The theoretical flashing boundary showed some discrepancies with previous experimental data from the quasi-steady state tests. In the future, thermal non-equilibrium was recommended to improve the accuracy of flashing instability boundary. As another part of the funded research, flow instabilities of a PWR-type SMR under low pressure and low power conditions were investigated experimentally as well. The NuScale reactor design was selected as the prototype for the PWR-type SMR. In order to experimentally study the natural circulation behavior of NuScale iii reactor during accidental scenarios, detailed scaling analyses are necessary to ensure that the scaled phenomena could be obtained in a laboratory test facility. The three-level scaling method is used as well to obtain the scaling ratios derived from various non-dimensional numbers. The design of the ideally scaled facility (ISF) was initially accomplished based on these scaling ratios. Then the engineering scaled facility (ESF) was designed and constructed based on the ISF by considering engineering limitations including laboratory space, pipe size, and pipe connections etc. PWR-type SMR experiments were performed in this well-scaled test facility to investigate the potential thermal hydraulic flow instability during the blowdown events, which might occur during the loss of coolant accident (LOCA) and loss of heat sink accident (LOHS) of the prototype PWR-type SMR. Two kinds of experiments, normal blowdown event and cold blowdown event, were experimentally investigated and compared with code predictions. The normal blowdown event was experimentally simulated since an initial condition where the pressure was lower than the designed pressure of the experiment facility, while the code prediction of blowdown started from the normal operation condition. Important thermal hydraulic parameters including reactor pressure vessel (RPV) pressure, containment pressure, local void fraction and temperature, pressure drop and natural circulation flow rate were measured and analyzed during the blowdown event. The pressure and water level transients are similar to the experimental results published by NuScale [51], which proves the capability of current loop in simulating the thermal hydraulic transient of real PWR-type SMR. During the 20000s blowdown experiment, water level in the core was always above the active fuel assemble during the experiment and proved the safety of natural circulation cooling and water recycling design of PWR-type SMR. Besides, pressure, temperature, and water level transient can be accurately predicted by RELAP5 code. However, the oscillations of natural circulation flow rate, water level and pressure drops were observed during the blowdown transients. This kind of flow oscillations are related to the water level and the location upper plenum, which is a path for coolant flow from chimney to steam generator and down comer. In order to investigate the transients start from the opening of ADS valve in both experimental and numerical way, the cold blow-down experiment is conducted. For the cold blowdown event, different from setting both reactor iv pressure vessel (RPV) and containment at high temperature and pressure, only RPV was heated close to the highest designed pressure and then open the ADS valve, same process was predicted using RELAP5 code. By doing cold blowdown experiment, the entire transients from the opening of ADS can be investigated by code and benchmarked with experimental data. Similar flow instability observed in the cold blowdown experiment. The comparison between code prediction and experiment data showed that the RELAP5 code can successfully predict the pressure void fraction and temperature transient during the cold blowdown event with limited error, but numerical instability exists in predicting natural circulation flow rate. Besides, the code is lack of capability in predicting the water level related flow instability observed in experiments.« less

Flow Induced Spring Coefficients of Labyrinth Seals for Application in Rotor Dynamics

NASA Technical Reports Server (NTRS)

Benckert, H.; Wachter, J.

1980-01-01

Flow induced aerodynamic spring coefficients of labyrinth seals are discussed and the restoring force in the deflection plane of the rotor and the lateral force acting perpendicularly to it are also considered. The effects of operational conditions on the spring characteristics of these components are examined, such as differential pressure, speed, inlet flow conditions, and the geometry of the labyrinth seals. Estimation formulas for the lateral forces due to shaft rotation and inlet swirl, which are developed through experiments, are presented. The utilization of the investigations is explained and results of stability calculations, especially for high pressure centrifugal compressors, are added. Suggestions are made concerning the avoidance of exciting forces in labyrinths.

Modeling and simulation of high-speed wake flows

NASA Astrophysics Data System (ADS)

Barnhardt, Michael Daniel

High-speed, unsteady flows represent a unique challenge in computational hypersonics research. They are found in nearly all applications of interest, including the wakes of reentry vehicles, RCS jet interactions, and scramjet combustors. In each of these examples, accurate modeling of the flow dynamics plays a critical role in design performance. Nevertheless, literature surveys reveal that very little modern research effort has been made toward understanding these problems. The objective of this work is to synthesize current computational methods for high-speed flows with ideas commonly used to model low-speed, turbulent flows in order to create a framework by which we may reliably predict unsteady, hypersonic flows. In particular, we wish to validate the new methodology for the case of a turbulent wake flow at reentry conditions. Currently, heat shield designs incur significant mass penalties due to the large margins applied to vehicle afterbodies in lieu of a thorough understanding of the wake aerothermodynamics. Comprehensive validation studies are required to accurately quantify these modeling uncertainties. To this end, we select three candidate experiments against which we evaluate the accuracy of our methodology. The first set of experiments concern the Mars Science Laboratory (MSL) parachute system and serve to demonstrate that our implementation produces results consistent with prior studies at supersonic conditions. Second, we use the Reentry-F flight test to expand the application envelope to realistic flight conditions. Finally, in the last set of experiments, we examine a spherical capsule wind tunnel configuration in order to perform a more detailed analysis of a realistic flight geometry. In each case, we find that current 1st order in time, 2nd order in space upwind numerical methods are sufficiently accurate to predict statistical measurements: mean, RMS, standard deviation, and so forth. Further potential gains in numerical accuracy are demonstrated using a new class of flux evaluation schemes in combination with 2nd order dual-time stepping. For cases with transitional or turbulent Reynolds numbers, we show that the detached eddy simulation (DES) method holds clear advantage over heritage RANS methods. From this, we conclude that the current methodology is sufficient to predict heating of external, reentry-type applications within experimental uncertainty.

Kr-PLIF for scalar imaging in supersonic flows.

PubMed

Narayanaswamy, V; Burns, R; Clemens, N T

2011-11-01

Experiments were performed to explore the use of two-photon planar laser-induced fluorescence (PLIF) of krypton gas for applications of scalar imaging in supersonic flows. Experiments were performed in an underexpanded jet of krypton, which exhibited a wide range of conditions, from subsonic to hypersonic. Excellent signal-to-noise ratios were obtained, showing the technique is suitable for single-shot imaging. The data were used to infer the distribution of gas density and temperature by correcting the fluorescence signal for quenching effects and using isentropic relations. The centerline variation of the density and temperature from the experiments agree very well with those predicted with an empirical correlation and a CFD simulation (FLUENT). Overall, the high signal levels and quantifiable measurements indicate that Kr-PLIF could be an effective scalar marker for use in supersonic and hypersonic flow applications.

Numerical simulation study on the distribution law of smoke flow velocity in horizontal tunnel fire

NASA Astrophysics Data System (ADS)

Liu, Yejiao; Tian, Zhichao; Xue, Junhua; Wang, Wencai

2018-02-01

According to the fluid similarity theory, the simulation experiment system of mining tunnel fire is established. The grid division of experimental model roadway is carried on by GAMBIT software. By setting the boundary and initial conditions of smoke flow during fire period in FLUENT software, using RNG k-Ɛ two-equation turbulence model, energy equation and SIMPLE algorithm, the steady state numerical simulation of smoke flow velocity in mining tunnel is done to obtain the distribution law of smoke flow velocity in tunnel during fire period.

Remote Infrared Thermography for In-Flight Flow Diagnostics

NASA Technical Reports Server (NTRS)

Shiu, H. J.; vanDam, C. P.

1999-01-01

The feasibility of remote in-flight boundary layer visualization via infrared in incompressible flow was established in earlier flight experiments. The past year's efforts focused on refining and determining the extent and accuracy of this technique of remote in-flight flow visualization via infrared. Investigations were made into flow separation visualization, visualization at transonic conditions, shock visualization, post-processing to mitigate banding noise in the NITE Hawk's thermograms, and a numeric model to predict surface temperature distributions. Although further flight tests are recommended, this technique continues to be promising.

Seeding for laser velocimetry in confined supersonic flows with shocks

NASA Technical Reports Server (NTRS)

Lepicovsky, J.; Bruckner, R. J.

1996-01-01

There is a lack of firm conclusions or recommendations in the open literature to guide laser velocimeter (LV) users in minimizing the uncertainty of LV data acquired in confined supersonic flows with steep velocity gradients. This fact led the NASA Lewis Research Center (LeRC) in Cleveland (Ohio, USA), and the Institute of Propulsion Technology of DLR in Cologne (Germany) to a joint research effort to improve reliability of LV measurements in supersonic flows. Over the years, NASA and DLR have developed different expertise in laser velocimetry, using different LV systems: Doppler and two-spot (L2F). The goal of the joint program is to improve the reliability of LV measurements by comparing results from experiments in confined supersonic flows performed under identical test conditions but using two different LV systems and several seed particle generators. Initial experiments conducted at the NASA LERC are reported in this paper. The experiments were performed in a narrow channel with Mach number 2.5 flow containing an oblique shock wave generated by an immersed 25-dg wedge.

Visualization experiments on steam injection in Hele-Shaw cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kong, Xianli; Haghighi, M.; Yortsos, Y.C.

1992-03-01

Flow visualization experiments have been successfully employed in reservoir engineering research for many years. They involve 2-D geometries in transparent Hele-Shaw cells and glass micromodels. Although much work has been done on immiscible flows (drainage or imbibition), visualization of steamfloods, which constitute a major part of current EOR methods, has not been attempted to data. In this paper, we present experimental results on steam injection in a transparent, pyrex glass Hele-Shaw cell. Both synthetic (Dutrex 739) and natural heavy oils were used under a variety of conditions, including effects of gravity.

A numerical study of diurnally varying surface temperature on flow patterns and pollutant dispersion in street canyons

NASA Astrophysics Data System (ADS)

Tan, Zijing; Dong, Jingliang; Xiao, Yimin; Tu, Jiyuan

2015-03-01

The impacts of the diurnal variation of surface temperature on street canyon flow pattern and pollutant dispersion are investigated based on a two-dimensional street canyon model under different thermal stratifications. Uneven distributed street temperature conditions and a user-defined wall function representing the heat transfer between the air and the street canyon are integrated into the current numerical model. The prediction accuracy of this model is successfully validated against a published wind tunnel experiment. Then, a series of numerical simulations representing four time scenarios (Morning, Afternoon, Noon and Night) are performed at different Bulk Richardson number (Rb). The results demonstrate that uneven distributed street temperature conditions significantly alters street canyon flow structure and pollutant dispersion characteristics compared with conventional uniform street temperature assumption, especially for the morning event. Moreover, air flow patterns and pollutant dispersion are greatly influenced by diurnal variation of surface temperature under unstable stratification conditions. Furthermore, the residual pollutant in near-ground-zone decreases as Rb increases in noon, afternoon and night events under all studied stability conditions.

Accelerated Weathering of Fluidized Bed Steam Reformation Material Under Hydraulically Unsaturated Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pierce, Eric M.

2007-09-16

To predict the long-term fate of low- and high-level waste forms in the subsurface over geologic time scales, it is important to understand the behavior of the corroding waste forms under conditions the mimic to the open flow and transport properties of a subsurface repository. Fluidized bed steam reformation (FBSR), a supplemental treatment technology option, is being considered as a waste form for the immobilization of low-activity tank waste. To obtain the fundamental information needed to evaluate the behavior of the FBSR waste form under repository relevant conditions and to monitor the long-term behavior of this material, an accelerated weatheringmore » experiment is being conducted with the pressurized unsaturated flow (PUF) apparatus. Unlike other accelerated weathering test methods (product consistency test, vapor hydration test, and drip test), PUF experiments are conducted under hydraulically unsaturated conditions. These experiments are unique because they mimic the vadose zone environment and allow the corroding waste form to achieve its final reaction state. Results from this on-going experiment suggest the volumetric water content varied as a function of time and reached steady state after 160 days of testing. Unlike the volumetric water content, periodic excursions in the solution pH and electrical conductivity have been occurring consistently during the test. Release of elements from the column illustrates a general trend of decreasing concentration with increasing reaction time. Normalized concentrations of K, Na, P, Re (a chemical analogue for 99Tc), and S are as much as 1 × 104 times greater than Al, Cr, Si, and Ti. After more than 600 days of testing, the solution chemistry data collected to-date illustrate the importance of understanding the long-term behavior of the FBSR product under conditions that mimic the open flow and transport properties of a subsurface repository.« less

Bedforms formed by experimental supercritical density flows

NASA Astrophysics Data System (ADS)

Naruse, Hajime; Izumi, Norihiro; Yokokawa, Miwa; Muto, Tetsuji

2014-05-01

This study reveals characteristics and formative conditions of bedforms produced by saline density flows in supercritical flow conditions, especially focusing on the mechanism of the formation of plane bed. The motion of sediment particles forming bedforms was resolved by high-speed cameras (1/1000 frame/seconds). Experimental density flows were produced by mixtures of salt water (1.01-1.04 in density) and plastic particles (1.5 in specific density, 140 or 240 mm in diameter). Salt water and plastic particles are analogue materials of muddy water and sand particles in turbidity currents respectively. Acrylic flume (4.0 m long, 2.0 cm wide and 0.5 m deep) was submerged in an experimental tank (6.0 m long, 1.8 m wide and 1.2 m deep) that was filled by clear water. Features of bedforms were observed when the bed state in the flume reached equilibrium condition. The experimental conditions range 1.5-4.2 in densimetric Froude number and 0.2-0.8 in Shields dimensionless stress. We report the two major discoveries as a result of the flume experiments: (1) Plane bed under Froude-supercritical flows and (2) Geometrical characteristics of cyclic steps formed by density flows. (1) Plane bed was formed under the condition of supercritical flow regime. In previous studies, plane bed has been known to be formed by subcritical unidirectional flows (ca. 0.8 in Froude number). However, this study implies that plane bed can also be formed by supercritical conditions with high Shields dimensionless stress (>0.4) and very high Froude number (> 4.0). This discovery may suggest that previous estimations of paleo-hydraulic conditions of parallel lamination in turbidites should be reconsidered. The previous experimental studies and data from high-speed camera suggest that the region of plane bed formation coincides with the region of the sheet flow developments. The particle transport in sheet flow (thick bedload layer) induces transform of profile of flow shear stress, which may be related with the formation of the plane bed. (2) This study also revealed geometrical characteristics of cyclic steps. Cyclic step is a type of bedform that is frequently observed in flanks of submarine levees. This study proved that cyclic steps of density flows show different geometry to those formed by open channel flows. Cyclic steps formed by open channel flows have generally asymmetrical geometry in which lee side is short, whereas cyclic steps formed by density flows are relatively symmetrical and varies their morphology remarkably depending on flow conditions.

A numerical experiment that provides new results regarding the inception of separation in the flow around a circular cylinder

NASA Astrophysics Data System (ADS)

Malamataris, Nikolaos; Liakos, Anastasios

2015-11-01

The exact value of the Reynolds number regarding the inception of separation in the flow around a circular cylinder is still a matter of research. This work connects the inception of separation with the calculation of a positive pressure gradient around the circumference of the cylinder. The hypothesis is that inception of separation occurs when the pressure gradient becomes positive around the circumference. From the most cited laboratory experiments that have dealt with that subject of inception of separation only Thom has measured the pressure gradient there at very low Reynolds numbers (up to Re=3.5). For this reason, the experimental conditions of his tunnel are simulated in a new numerical experiment. The full Navier Stokes equations in both two and three dimensions are solved with a home made code that utilizes Galerkin finite elements. In the two dimensional numerical experiment, inception of separation is observed at Re=4.3, which is the lowest Reynolds number where inception has been reported computationally. Currently, the three dimensional experiment is under way, in order to compare if there are effects of three dimensional theory of separation in the conditions of Thom's experiments.

Partially to fully saturated flow through smooth, clean, open fractures: qualitative experimental studies

NASA Astrophysics Data System (ADS)

Jones, Brendon R.; Brouwers, Luke B.; Dippenaar, Matthys A.

2018-05-01

Fractures are both rough and irregular but can be expressed by a simple model concept of two smooth parallel plates and the associated cubic law governing discharge through saturated fractures. However, in natural conditions and in the intermediate vadose zone, these assumptions are likely violated. This paper presents a qualitative experimental study investigating the cubic law under variable saturation in initially dry free-draining discrete fractures. The study comprised flow visualisation experiments conducted on transparent replicas of smooth parallel plates with inlet conditions of constant pressure and differing flow rates over both vertical and horizontal inclination. Flow conditions were altered to investigate the influence of intermittent and continuous influx scenarios. Findings from this research proved, for instance, that saturated laminar flow is not likely achieved, especially in nonhorizontal fractures. In vertical fractures, preferential flow occupies the minority of cross-sectional area despite the water supply. Movement of water through the fractured vadose zone therefore becomes a matter of the continuity principle, whereby water should theoretically be transported downward at significantly higher flow rates given the very low degree of water saturation. Current techniques that aim to quantify discrete fracture flow, notably at partial saturation, are questionable. Inspired by the results of this study, it is therefore hypothetically improbable to achieve saturation in vertical fractures under free-draining wetting conditions. It does become possible under extremely excessive water inflows or when not free-draining; however, the converse is not true, as a wet vertical fracture can be drained.

DSMC simulations of shock interactions about sharp double cones

NASA Astrophysics Data System (ADS)

Moss, James N.

2001-08-01

This paper presents the results of a numerical study of shock interactions resulting from Mach 10 flow about sharp double cones. Computations are made by using the direct simulation Monte Carlo (DSMC) method of Bird. The sensitivity and characteristics of the interactions are examined by varying flow conditions, model size, and configuration. The range of conditions investigated includes those for which experiments have been or will be performed in the ONERA R5Ch low-density wind tunnel and the Calspan-University of Buffalo Research Center (CUBRC) Large Energy National Shock (LENS) tunnel.

DSMC Simulations of Shock Interactions About Sharp Double Cones

NASA Technical Reports Server (NTRS)

Moss, James N.

2000-01-01

This paper presents the results of a numerical study of shock interactions resulting from Mach 10 flow about sharp double cones. Computations are made by using the direct simulation Monte Carlo (DSMC) method of Bird. The sensitivity and characteristics of the interactions are examined by varying flow conditions, model size, and configuration. The range of conditions investigated includes those for which experiments have been or will be performed in the ONERA R5Ch low-density wind tunnel and the Calspan-University of Buffalo Research Center (CUBRC) Large Energy National Shock (LENS) tunnel.

A comparative flow visualization study of thermocapillary flow in drops in liquid-liquid systems

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Rashidnia, N.

1991-01-01

Experiments are performed to visualize thermocapillary flow in drops in an immiscible host liquid. The host liquid used is silicone oil. Drops of three different liquids are used, viz, vegetable oil, water-methanol mixture anad pure methanol. Clear evidence of thermocapillary flow is seen in vegetable oil drops. For a mixture of water and methanol (approximately 50-50 by weight), natural convection is seen to dominate the flow outside the drop. Pure methanol drops exhibit thermocapillary flow, but dissolve in silicone oil. A small amount of water added to pure methanol significantly reduces the dissolution. Flow oscillations occur in this system for both isothermal and non-isothermal conditions.

Blockade of Tumor Cell TGF-Betas: A Strategy to Reverse Antiestrogen Resistance in Human Breast Cancer

DTIC Science & Technology

2002-01-01

the TM- FKHRL1 construct exhibited exclusive nuclear localization Cell Cycle Analysis by Flow Cytometry of the HA-tagged mutant under any experimental...distribution as measured by flow cytometry (Figure 8A). ALS AND METHODS. Consistent with its antiapoptotic effect, these results, addi- tion of TGFI3... flow cytometry . Under these conditions more than 95% of selected cells expressed GFP at the time of experiments. Immunoblot Analysis. Cells were

Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine

NASA Astrophysics Data System (ADS)

Panov, L. V.; Chirkov, D. V.; Cherny, S. G.; Pylev, I. M.; Sotnikov, A. A.

2012-09-01

Numerical technique was developed for simulation of cavitating flows through the flow passage of a hydraulic turbine. The technique is based on solution of steady 3D Navier—Stokes equations with a liquid phase transfer equation. The approch for setting boundary conditions meeting the requirements of cavitation testing standard was suggested. Four different models of evaporation and condensation were compared. Numerical simulations for turbines of different specific speed were compared with experiment.

Electrophoretic separation of cells and particles from rat pituitary and rat spleen

NASA Technical Reports Server (NTRS)

Hymer, Wesley C.

1993-01-01

There are 3 parts to the IML-2 TX-101 experiment. Part 1 is a pituitary cell culture experiment. Part 2 is a pituitary cell separation experiment using the Japanese free flow electrophoresis unit (FFEU). Part 3 is a pituitary secretory granule separation experiment using the FFEU. The objectives of this three part experiment are: (1) to determine the kinetics of production of biologically active growth hormone (GH) and prolactin (PRL) in rat pituitary GH and PRL cells in microgravity (micro-g); (2) to investigate three mechanisms by which a micro-g-induced lesion in hormone production may occur; and (3) to determine the quality of separations of pituitary cells and organelles by continuous flow electrophoresis (CFE) in micro-g under conditions where buoyancy-induced convection is eliminated.

Thermocapillary convection in two immiscible liquid layers with free surface

NASA Technical Reports Server (NTRS)

Doi, Takao; Koster, Jean N.

1993-01-01

Thermocapillary convection is studied in two immiscible liquid layers with one free surface, one liquid/liquid interface, and differential heating applied parallel to the interfaces. An analytical solution is introduced for infinite horizontal layers. The defining parameter for the flow pattern is lambda, the ratio of the temperature coefficient of the interfacial tension to that of the surface tension. Four different flow patterns exist under zero gravity conditions. 'Halt' conditions which halt the fluid motion in the lower encapsulated liquid layer have been found. A numerical experiment is carried out to study effects of vertical end walls on the double layer convection in a 2D cavity. The halt condition obtained from the analytical study is found to be valid in the limit of small Reynolds numbers. The flow in the encapsulated liquid layer can be suppressed substantially.

Interaction of a Rectangular Jet with a Flat-Plate Placed Parallel to the Flow

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Brown, C. A.; Bridges, J. A.

2013-01-01

An experimental study is carried out addressing the flowfield and radiated noise from the interaction of a large aspect ratio rectangular jet with a flat plate placed parallel to but away from the direct path of the jet. Sound pressure level spectra exhibit an increase in the noise levels for both the 'reflected' and 'shielded' sides of the plate relative to the free-jet case. Detailed cross-sectional distributions of flowfield properties obtained by hot-wire anemometry are documented for a low subsonic condition. Corresponding mean Mach number distributions obtained by Pitot-probe surveys are presented for high subsonic conditions. In the latter flow regime and for certain relative locations of the plate, a flow resonance accompanied by audible tones is encountered. Under the resonant condition the jet cross-section experiences an 'axis-switching' and flow visualization indicates the presence of an organized 'vortex street'. The trends of the resonant frequency variation with flow parameters exhibit some similarities to, but also marked differences with, corresponding trends of the well-known edgetone phenomenon.

Numerical and Experimental Studies of the Natural Convection Flow Within a Horizontal Cylinder Subjected to a Uniformly Cold Wall Boundary Condition. Ph.D. Thesis - Va. Poly. Inst. and State Univ.

NASA Technical Reports Server (NTRS)

Stewart, R. B.

1972-01-01

Numberical solutions are obtained for the quasi-compressible Navier-Stokes equations governing the time dependent natural convection flow within a horizontal cylinder. The early time flow development and wall heat transfer is obtained after imposing a uniformly cold wall boundary condition on the cylinder. Solutions are also obtained for the case of a time varying cold wall boundary condition. Windware explicit differ-encing is used for the numerical solutions. The viscous truncation error associated with this scheme is controlled so that first order accuracy is maintained in time and space. The results encompass a range of Grashof numbers from 8.34 times 10,000 to 7 times 10 to the 7th power which is within the laminar flow regime for gravitationally driven fluid flows. Experiments within a small scale instrumented horizontal cylinder revealed the time development of the temperature distribution across the boundary layer and also the decay of wall heat transfer with time.

Dancing to "groovy" music enhances the experience of flow.

PubMed

Bernardi, Nicolò F; Bellemare-Pepin, Antoine; Peretz, Isabelle

2018-05-06

We investigated whether dancing influences the emotional response to music, compared to when music is listened to in the absence of movement. Forty participants without previous dance training listened to "groovy" and "nongroovy" music excerpts while either dancing or refraining from movement. Participants were also tested while imitating their own dance movements, but in the absence of music as a control condition. Emotion ratings and ratings of flow were collected following each condition. Dance movements were recorded using motion capture. We found that the state of flow was increased specifically during spontaneous dance to groovy excerpts, compared with both still listening and motor imitation. Emotions in the realms of vitality (such as joy and power) and sublimity (such as wonder and nostalgia) were evoked by music in general, whether participants moved or not. Significant correlations were found between the emotional and flow responses to music and whole-body acceleration profiles. Thus, the results highlight a distinct state of flow when dancing, which may be of use to promote well-being and to address certain clinical conditions. © 2018 New York Academy of Sciences.

A mean curvature model for capillary flows in asymmetric containers and conduits

NASA Astrophysics Data System (ADS)

Chen, Yongkang; Tavan, Noël; Weislogel, Mark M.

2012-08-01

Capillarity-driven flows resulting from critical geometric wetting criterion are observed to yield significant shifts of the bulk fluid from one side of the container to the other during "zero gravity" experiments. For wetting fluids, such bulk shift flows consist of advancing and receding menisci sometimes separated by secondary capillary flows such as rivulet-like flows along gaps. Here we study the mean curvature of an advancing meniscus in hopes of approximating a critical boundary condition for fluid dynamics solutions. It is found that the bulk shift flows behave as if the bulk menisci are either "connected" or "disconnected." For the connected case, an analytic method is developed to calculate the mean curvature of the advancing meniscus in an asymptotic sense. In contrast, for the disconnected case the method to calculate the mean curvature of the advancing and receding menisci uses a well-established procedure. Both disconnected and connected bulk shifts can occur as the first tier flow of more complex compound capillary flows. Preliminary comparisons between the analytic method and the results of drop tower experiments are encouraging.

Effects of Wing Sweep on Boundary-layer Transition for a Smooth F-14A Wing at Mach Numbers from 0.700 to 0.825

NASA Technical Reports Server (NTRS)

Anderson, Bianca Trujillo; Meyer, Robert R., Jr.

1990-01-01

The results are discussed of the variable sweep transition flight experiment (VSTFE). The VSTFE was a natural laminar flow experiment flown on the swing wing F-14A aircraft. The main objective of the VSTFE was to determine the effects of wing sweep on boundary layer transition at conditions representative of transport aircraft. The experiment included the flight testing of two laminar flow wing gloves. Glove 1 was a cleanup of the existing F-14A wing. Glove 2, not discussed herein, was designed to provide favorable pressure distributions for natural laminar flow at Mach number (M) 0.700. The transition locations presented for glove 1 were determined primarily by using hot film sensors. Boundary layer rake data was provided as a supplement. Transition data were obtained for leading edge wing sweeps of 15, 20, 25, 30, and 35 degs, with Mach numbers ranging from 0.700 to 0.825, and altitudes ranging from 10,000 to 35,000 ft. Results show that a substantial amount of laminar flow was maintained at all the wing sweeps evaluated. The maximum transition Reynolds number of 13.7 x 10(exp 6) was obtained for the condition of 15 deg of sweep, M = 0.800, and an altitude of 20,000 ft.

Flow Effects on the Flammability Diagrams of Solid Fuels: Microgravity Influence on Ignition Delay

NASA Technical Reports Server (NTRS)

Cordova, J. L.; Walther, D. C.; Fernandez-Pello, A. C.; Steinhaus, T.; Torero, J. L.; Quintere, J. G.; Ross, H. D.

1999-01-01

The possibility of an accidental fire in space-based facilities is a primary concern of space exploration programs. Spacecraft environments generally present low velocity air currents produced by ventilation and heating systems (of the order of 0.1 m/s), and fluctuating oxygen concentrations around that of air due to CO2 removal systems. Recent experiments of flame spread in microgravity show the spread rate to be faster and the limiting oxygen concentration lower than in normal-gravity. To date, there is not a material flammability-testing protocol that specifically addresses issues related to microgravity conditions. The present project (FIST) aims to establish a testing methodology that is suitable for the specific conditions of reduced gravity. The concepts underlying the operation of the LIFT apparatus, ASTM-E 1321-93, have been used to develop the Forced-flow Ignition and flame-Spread Test (FIST). As in the LIFT, the FIST is used to obtain the flammability diagrams of the material, i.e., graphs of ignition delay time and flame spread rate as a function of the externally applied radiant flux, but under forced flow rather than natural convection conditions, and for different oxygen concentrations. Although the flammability diagrams are similar, the flammability properties obtained with the FIST are found to depend on the flow characteristics. A research program is currently underway with the purpose of implementing the FIST as a protocol to characterize the flammability performance of solid materials to be used in microgravity facilities. To this point, tests have been performed with the FIST apparatus in both normal-gravity and microgravity conditions to determine the effects of oxidizer flow characteristics on the flammability diagrams of polymethylmethacrylate (PMMA) fuel samples. The experiments are conducted at reduced gravity in a KC- 135 aircraft following a parabolic flight trajectory that provides up to 25 seconds of low gravity. The objective of the experiments is to obtain data of ignition delay and flame spread rate at low flow velocities (0.1 to 0.2 m/s), which cannot be obtained under normal gravity because of the natural convection induced flows (approx. 0.5 m/s). Due to the limited reduced gravity time, the data can only be obtained for high radiant fluxes, and are consequently limited in scope. These tests do, however, provide insight into the flammability diagram characteristics at low velocity and reduced gravity, and also into the implications of the flow-dependence of the flammability properties under environments similar to those encountered in space facilities.

Dynamics of flow control in an emulated boundary layer-ingesting offset diffuser

NASA Astrophysics Data System (ADS)

Gissen, A. N.; Vukasinovic, B.; Glezer, A.

2014-08-01

Dynamics of flow control comprised of arrays of active (synthetic jets) and passive (vanes) control elements , and its effectiveness for suppression of total-pressure distortion is investigated experimentally in an offset diffuser, in the absence of internal flow separation. The experiments are conducted in a wind tunnel inlet model at speeds up to M = 0.55 using approach flow conditioning that mimics boundary layer ingestion on a Blended-Wing-Body platform. Time-dependent distortion of the dynamic total-pressure field at the `engine face' is measured using an array of forty total-pressure probes, and the control-induced distortion changes are analyzed using triple decomposition and proper orthogonal decomposition (POD). These data indicate that an array of the flow control small-scale synthetic jet vortices merge into two large-scale, counter-rotating streamwise vortices that exert significant changes in the flow distortion. The two most energetic POD modes appear to govern the distortion dynamics in either active or hybrid flow control approaches. Finally, it is shown that the present control approach is sufficiently robust to reduce distortion with different inlet conditions of the baseline flow.

Analytical investigation of critical phenomena in MHD power generators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1980-07-31

Critical phenomena in the Arnold Engineering Development Center (AEDC) High Performance Demonstration Experiment (HPDE) and the US U-25 Experiment, are analyzed. Also analyzed are the performance of a NASA-specified 500 MW(th) flow train and computations concerning critica issues for the scale-up of MHD Generators. The HPDE is characterized by computational simulations of both the nominal conditions and the conditions during the experimental runs. The steady-state performance is discussed along with the Hall voltage overshoots during the start-up and shutdown transients. The results of simulations of the HPDE runs with codes from the Q3D and TRANSIENT code families are compared tomore » the experimental results. The results of the simulations are in good agreement with the experimental data. Additional critica phenomena analyzed in the AEDC/HPDE are the optimal load schedules, parametric variations, the parametric dependence of the electrode voltage drops, the boundary layer behavior, near electrode phenomena with finite electrode segmentation, and current distribution in the end regions. The US U-25 experiment is characterized by computational simulations of the nominal operating conditions. The steady-state performance for the nominal design of the US U-25 experiment is analyzed, as is the dependence of performance on the mass flow rate. A NASA-specified 500 MW(th) MHD flow train is characterized for computer simulation and the electrical, transport, and thermodynamic properties at the inlet plane are analyzed. Issues for the scale-up of MHD power trains are discussed. The AEDC/HPDE performance is analyzed to compare these experimental results to scale-up rules.« less

Convection Effects During Bulk Transparent Alloy Solidification in DECLIC-DSI and Phase-Field Simulations in Diffusive Conditions

NASA Astrophysics Data System (ADS)

Mota, F. L.; Song, Y.; Pereda, J.; Billia, B.; Tourret, D.; Debierre, J.-M.; Trivedi, R.; Karma, A.; Bergeon, N.

2017-08-01

To study the dynamical formation and evolution of cellular and dendritic arrays under diffusive growth conditions, three-dimensional (3D) directional solidification experiments were conducted in microgravity on a model transparent alloy onboard the International Space Station using the Directional Solidification Insert in the DEvice for the study of Critical LIquids and Crystallization. Selected experiments were repeated on Earth under gravity-driven fluid flow to evidence convection effects. Both radial and axial macrosegregation resulting from convection are observed in ground experiments, and primary spacings measured on Earth and microgravity experiments are noticeably different. The microgravity experiments provide unique benchmark data for numerical simulations of spatially extended pattern formation under diffusive growth conditions. The results of 3D phase-field simulations highlight the importance of accurately modeling thermal conditions that strongly influence the front recoil of the interface and the selection of the primary spacing. The modeling predictions are in good quantitative agreements with the microgravity experiments.

Statistical learning of action: the role of conditional probability.

PubMed

Meyer, Meredith; Baldwin, Dare

2011-12-01

Identification of distinct units within a continuous flow of human action is fundamental to action processing. Such segmentation may rest in part on statistical learning. In a series of four experiments, we examined what types of statistics people can use to segment a continuous stream involving many brief, goal-directed action elements. The results of Experiment 1 showed no evidence for sensitivity to conditional probability, whereas Experiment 2 displayed learning based on joint probability. In Experiment 3, we demonstrated that additional exposure to the input failed to engender sensitivity to conditional probability. However, the results of Experiment 4 showed that a subset of adults-namely, those more successful at identifying actions that had been seen more frequently than comparison sequences-were also successful at learning conditional-probability statistics. These experiments help to clarify the mechanisms subserving processing of intentional action, and they highlight important differences from, as well as similarities to, prior studies of statistical learning in other domains, including language.

Application of a simple power law for transport ratio with bimodal distributions of spherical grains under oscillatory forcing

NASA Astrophysics Data System (ADS)

Holway, Kevin; Thaxton, Christopher S.; Calantoni, Joseph

2012-11-01

Morphodynamic models of coastal evolution require relatively simple parameterizations of sediment transport for application over larger scales. Calantoni and Thaxton (2008) [6] presented a transport parameterization for bimodal distributions of coarse quartz grains derived from detailed boundary layer simulations for sheet flow and near sheet flow conditions. The simulation results, valid over a range of wave forcing conditions and large- to small-grain diameter ratios, were successfully parameterized with a simple power law that allows for the prediction of the transport rates of each size fraction. Here, we have applied the simple power law to a two-dimensional cellular automaton to simulate sheet flow transport. Model results are validated with experiments performed in the small oscillating flow tunnel (S-OFT) at the Naval Research Laboratory at Stennis Space Center, MS, in which sheet flow transport was generated with a bed composed of a bimodal distribution of non-cohesive grains. The work presented suggests that, under the conditions specified, algorithms that incorporate the power law may correctly reproduce laboratory bed surface measurements of bimodal sheet flow transport while inherently incorporating vertical mixing by size.

From catastrophic acceleration to deceleration of liquid plugs in prewetted capillary tubes

NASA Astrophysics Data System (ADS)

Magniez, Juan; Baudoin, Michael; Zoueshtiagh, Farzam; Lemac/Lics Team

2016-11-01

Liquid/gas flows in capillaries are involved in a multitude of systems including flow in porous media, petroleum extraction, imbibition of paper or flows in pulmonary airways in pathological conditions. Liquid plugs, witch compose the biphasic flows, can have a dramatic impact on patients with pulmonary obstructive diseases, since they considerably alter the circulation of air in the airways and thus can lead to severe breathing difficulties. Here, the dynamics of liquid plugs in prewetted capillary tube is investigated experimentally and theoretically, with a particular emphasis on the role of the prewetting films and of the driving condition (constant flow rate, constant pressure). For both driving conditions, the plugs can either experience a continuous increase or decrease of their size. While this phenomenon is regular in the case of imposed flow rate, a constant pressure head can lead to a catastrophic acceleration of the plug and eventually its rupture or a dramatic increase of the plug size. A theoretical model is proposed to explain the transition between theses two regimes. These results give a new insight on the critical pressure required for airways obstruction and reopening. IEMN, International Laboratory LEMAC/LICS, UMR CNRS 8520, University of Lille.

An Experimental Investigation of Wall-Cooling Effects on Hypersonic Boundary-Layer Stability in a Quiet Wind Tunnel

NASA Technical Reports Server (NTRS)

Blanchard, Alan E.; Selby, Gregory V.

1996-01-01

One of the primary reasons for developing quiet tunnels is for the investigation of high-speed boundary-layer stability and transition phenomena without the transition-promoting effects of acoustic radiation from tunnel walls. In this experiment, a flared-cone model under adiabatic- and cooled-wall conditions was placed in a calibrated, 'quiet' Mach 6 flow and the stability of the boundary layer was investigated using a prototype constant-voltage anemometer. The results were compared with linear-stability theory predictions and good agreement was found in the prediction of second-mode frequencies and growth. In addition, the same 'N=10' criterion used to predict boundary-layer transition in subsonic, transonic, and supersonic flows was found to be applicable for the hypersonic flow regime as well. Under cooled-wall conditions, a unique set of continuous spectra data was acquired that documents the linear, nonlinear, and breakdown regions associated with the transition of hypersonic flow under low-noise conditions.

Carbon black retention in saturated natural soils: Effects of flow conditions, soil surface roughness and soil organic matter.

PubMed

Lohwacharin, J; Takizawa, S; Punyapalakul, P

2015-10-01

We evaluated factors affecting the transport, retention, and re-entrainment of carbon black nanoparticles (nCBs) in two saturated natural soils under different flow conditions and input concentrations using the two-site transport model and Kelvin probe force microscopy (KPFM). Soil organic matter (SOM) was found to create unfavorable conditions for the retention. Despite an increased flow velocity, the relative stability of the estimated maximum retention capacity in soils may suggest that flow-induced shear stress forces were insufficient to detach nCB. The KPFM observation revealed that nCBs were retained at the grain boundary and on surface roughness, which brought about substantial discrepancy between theoretically-derived attachment efficiency factors and the ones obtained by the experiments using the two-site transport model. Thus, decreasing ionic strength and increasing solution pH caused re-entrainment of only a small fraction of retained nCB in the soil columns. Copyright © 2015 Elsevier Ltd. All rights reserved.

Modelling morphology evolution during solidification of IPP in processing conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pantani, R., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it; De Santis, F., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it; Speranza, V., E-mail: rpantani@unisa.it, E-mail: fedesantis@unisa.it, E-mail: vsperanza@unisa.it, E-mail: gtitomanlio@unisa.it

During polymer processing, crystallization takes place during or soon after flow. In most of cases, the flow field dramatically influences both the crystallization kinetics and the crystal morphology. On their turn, crystallinity and morphology affect product properties. Consequently, in the last decade, researchers tried to identify the main parameters determining crystallinity and morphology evolution during solidification In processing conditions. In this work, we present an approach to model flow-induced crystallization with the aim of predicting the morphology after processing. The approach is based on: interpretation of the FIC as the effect of molecular stretch on the thermodynamic crystallization temperature; modelingmore » the molecular stretch evolution by means of a model simple and easy to be implemented in polymer processing simulation codes; identification of the effect of flow on nucleation density and spherulites growth rate by means of simple experiments; determination of the condition under which fibers form instead of spherulites. Model predictions reproduce most of the features of final morphology observed in the samples after solidification.« less

Numerical analysis of rotating stall instabilities of a pump- turbine in pump mode

NASA Astrophysics Data System (ADS)

Xia, L. S.; Cheng, Y. G.; Zhang, X. X.; Yang, J. D.

2014-03-01

Rotating stall may occur at part load flow of a pump-turbine in pump mode. Unstable flow structures developing under stall condition can lead to a sudden drop of efficiency, high dynamic load and even cavitation. CFD simulations on a pump-turbine model in pump mode were carried out to reveal the onset and developed mechanisms of these unstable flow phenomena at part load. The simulation results of energy-discharge and efficiency characteristics are in good agreement with those obtained by experiments. The more deviate from design conditions with decreasing flow rate, the more flow separations within the vanes. Under specific conditions, four stationary separation zones begin to progress on the circumference, rotating at a fraction of the impeller rotation rate. Rotating stalls lead to the flow in the vane diffuser channels alternating between outward jet flow and blockage. Strong jets impact the spiral casing wall causing high pressure pulsations. Severe separations of the stall cells disturb the flow inducing periodical large amplitude pressure fluctuations, of which the intensity at different span wise of the guide vanes is different. The enforced rotating nonuniform pressure distributions on the circumference lead to dynamic uniform forces on the impeller and guide vanes. The results show that the CFD simulations are capable to gain the complicated flow structure information for analysing the unstable characteristics of the pump mode at part load.

Modeling Submarine Lava Flow with ASPECT

NASA Astrophysics Data System (ADS)

Storvick, E. R.; Lu, H.; Choi, E.

2017-12-01

Submarine lava flow is not easily observed and experimented on due to limited accessibility and challenges posed by the fast solidification of lava and the associated drastic changes in rheology. However, recent advances in numerical modeling techniques might address some of these challenges and provide unprecedented insight into the mechanics of submarine lava flow and conditions determining its wide-ranging morphologies. In this study, we explore the applicability ASPECT, Advanced Solver for Problems in Earth's ConvecTion, to submarine lava flow. ASPECT is a parallel finite element code that solves problems of thermal convection in the Earth's mantle. We will assess ASPECT's capability to model submarine lava flow by observing models of lava flow morphology simulated with GALE, a long-term tectonics finite element analysis code, with models created using comparable settings and parameters in ASPECT. From these observations we will contrast the differing models in order to identify the benefits of each code. While doing so, we anticipate we will learn about the conditions required for end-members of lava flow morphology, for example, pillows and sheet flows. With ASPECT specifically we focus on 1) whether the lava rheology can be implemented; 2) how effective the AMR is in resolving morphologies of the solidified crust; 3) whether and under what conditions the end-members of the lava flow morphologies, pillows and sheets, can be reproduced.

The Dynamics of Flow and Three-dimensional Motion Around a Morphologically Complex Aquatic Plant

NASA Astrophysics Data System (ADS)

Boothroyd, R.; Hardy, R. J.; Warburton, J.; Marjoribanks, T.

2016-12-01

Aquatic vegetation has a significant impact on the hydraulic functioning of river systems. The morphology of an individual plant can influence the mean and turbulent properties of the flow, and the plant posture reconfigures to minimise drag. We report findings from a flume and numerical experiment investigating the dynamics of motion and three-dimensional flow around an isolated Hebe odora plant over a range of flow conditions. In the flume experiment, a high definition video camera recorded plant motion dynamics and three-dimensional velocity profiles were measured using an acoustic Doppler velocimeter. By producing a binary image of the plant in each frame, the plant dynamics can be quantified. Zones of greatest plant motion are on the upper and leeward sides of the plant. With increasing flow the plant is compressed and deflected downwards by up to 18% of the unstressed height. Plant tip motions are tracked and shown to lengthen with increasing flow, transitioning from horizontally dominated to vertically dominated motion. The plant acts as a porous blockage to flow, producing spatially heterogeneous downstream velocity fields with the measured wake length decreasing by 20% with increasing flow. These measurements are then used as boundary conditions and to validate a computational fluid dynamics (CFD) model. By explicitly accounting for the time-averaged plant posture, good agreement is found between flume measurements and model predictions. The flow structures demonstrate characteristics of a junction vortex system, with plant shear layer turbulence dominated by Kelvin-Helmholtz and Görtler-type vortices generated through shear instability. With increasing flow, drag coefficients decrease by up to 8%, from 1.45 to 1.34. This is equivalent to a change in the Manning's n term from 0.086 to 0.078.

iCFD: Interpreted Computational Fluid Dynamics - Degeneration of CFD to one-dimensional advection-dispersion models using statistical experimental design - The secondary clarifier.

PubMed

Guyonvarch, Estelle; Ramin, Elham; Kulahci, Murat; Plósz, Benedek Gy

2015-10-15

The present study aims at using statistically designed computational fluid dynamics (CFD) simulations as numerical experiments for the identification of one-dimensional (1-D) advection-dispersion models - computationally light tools, used e.g., as sub-models in systems analysis. The objective is to develop a new 1-D framework, referred to as interpreted CFD (iCFD) models, in which statistical meta-models are used to calculate the pseudo-dispersion coefficient (D) as a function of design and flow boundary conditions. The method - presented in a straightforward and transparent way - is illustrated using the example of a circular secondary settling tank (SST). First, the significant design and flow factors are screened out by applying the statistical method of two-level fractional factorial design of experiments. Second, based on the number of significant factors identified through the factor screening study and system understanding, 50 different sets of design and flow conditions are selected using Latin Hypercube Sampling (LHS). The boundary condition sets are imposed on a 2-D axi-symmetrical CFD simulation model of the SST. In the framework, to degenerate the 2-D model structure, CFD model outputs are approximated by the 1-D model through the calibration of three different model structures for D. Correlation equations for the D parameter then are identified as a function of the selected design and flow boundary conditions (meta-models), and their accuracy is evaluated against D values estimated in each numerical experiment. The evaluation and validation of the iCFD model structure is carried out using scenario simulation results obtained with parameters sampled from the corners of the LHS experimental region. For the studied SST, additional iCFD model development was carried out in terms of (i) assessing different density current sub-models; (ii) implementation of a combined flocculation, hindered, transient and compression settling velocity function; and (iii) assessment of modelling the onset of transient and compression settling. Furthermore, the optimal level of model discretization both in 2-D and 1-D was undertaken. Results suggest that the iCFD model developed for the SST through the proposed methodology is able to predict solid distribution with high accuracy - taking a reasonable computational effort - when compared to multi-dimensional numerical experiments, under a wide range of flow and design conditions. iCFD tools could play a crucial role in reliably predicting systems' performance under normal and shock events. Copyright © 2015 Elsevier Ltd. All rights reserved.

Hydrodynamic resistance parameters for ErPr rare-earth regenerator material under steady and periodic flow conditions

NASA Astrophysics Data System (ADS)

Pathak, M. G.; Helvensteijn, B. P.; Patel, V. C.; Ghiaasiaan, S. M.; Mulcahey, T. I.; Kashani, A.; Feller, J. R.

2014-01-01

The regenerator, typically a microporous structure that is subject to periodic flow of a cryogenic fluid, is a critical component of pulse tube or Stirling cryocoolers, which are widely used for high-demand aerospace and defense applications. In this investigation, experiments were conducted in which steady and oscillatory flows of helium were imposed on ErPr rare-Earth regenerator filler material and mass flow and pressure drop data were recorded under ambient temperature conditions. A computational fluid dynamics (CFD)-assisted method was applied for the analysis and interpretation of the experimental data. The permeability and inertial coefficients that lead to agreement between the experimental data and computational simulations were iteratively obtained. The Darcy permeability and Forchheimer inertial coefficients were obtained and were found to be functions of the system charge pressure, operating frequency, and compressor piston stroke within the studied range of interest. The results also exhibit that the periodic flow hydrodynamic resistance parameters are in general different than steady flow parameters.

Extension of sonic anemometry to high subsonic Mach number flows

NASA Astrophysics Data System (ADS)

Otero, R.; Lowe, K. T.; Ng, W. F.

2017-03-01

In the literature, the application of sonic anemometry has been limited to low subsonic Mach number, near-incompressible flow conditions. To the best of the authors’ knowledge, this paper represents the first time a sonic anemometry approach has been used to characterize flow velocity beyond Mach 0.3. Using a high speed jet, flow velocity was measured using a modified sonic anemometry technique in flow conditions up to Mach 0.83. A numerical study was conducted to identify the effects of microphone placement on the accuracy of the measured velocity. Based on estimated error strictly due to uncertainty in time-of-acoustic flight, a random error of +/- 4 m s-1 was identified for the configuration used in this experiment. Comparison with measurements from a Pitot probe indicated a velocity RMS error of +/- 9 m s-1. The discrepancy in error is attributed to a systematic error which may be calibrated out in future work. Overall, the experimental results from this preliminary study support the use of acoustics for high subsonic flow characterization.

Flow control of a centrifugal fan in a commercial air conditioner

NASA Astrophysics Data System (ADS)

Kim, Jiyu; Bang, Kyeongtae; Choi, Haecheon; Seo, Eung Ryeol; Kang, Yonghun

2015-11-01

Air-conditioning fans require a low noise level to provide user comfort and quietness. The aerodynamic noise sources are generated by highly unsteady, turbulent structures near the fan blade. In this study, we investigate the flow characteristics of a centrifugal fan in an air-conditioner indoor unit and suggest control ideas to develop a low noise fan. The experiment is conducted at the operation condition where the Reynolds number is 163000 based on the blade tip velocity and chord length. Intermittent separation occurs at the blade leading edge and thus flow significantly fluctuates there, whereas vortex shedding occurs at the blade trailing edge. Furthermore, the discharge flow observed in the axial plane near the shroud shows low-frequency intermittent behaviors, resulting in high Reynolds stresses. To control these flow structures, we modify the shapes of the blade leading edge and shroud of the centrifugal fan and obtain noise reduction. The flow characteristics of the base and modified fans will be discussed. Supported by 0420-20130051.

Laboratory Experiments of Sand Ripples with Bimodal Size Distributions Under Asymmetric Oscillatory Flows

NASA Astrophysics Data System (ADS)

Calantoni, J.; Landry, B. J.

2010-12-01

The dynamics of sand ripples are vital to understanding numerous coastal processes such as sediment transport, wave attenuation, boundary layer development, and seafloor acoustic properties. Though significant laboratory research has been conducted to elucidate oscillatory flow morphodynamics under various constant and transient forcing conditions, the majority of the previous experiments were conducted only for beds with unimodal size distributions of sediment. Recent oscillatory flow experiments as well as past laboratory observations in uniform flows suggest that the presence of heterogeneous size sand compositions may significantly impact ripple morphology, resulting in a variety of observable effects (e.g., sediment sorting, bed armoring, and altered transport rates). Experimental work was conducted in a small oscillatory flow tunnel at the Sediment Dynamics Laboratory at the Naval Research Laboratory, Stennis Space Center. Three different monochromatic oscillatory forcings having velocity asymmetry were used to study sand ripple dynamics over five bimodal and two unimodal sediment beds. The seven different mixtures were composed using two unimodal sands of different colors (blue/white) and median grain diameters (d=0.31 mm / d=0.65 mm) combined into various mixtures by mass (i.e., 0/100; 10/90; 25/75; 50/50; 75/25; 90/10; and 100/0 which denotes mass percentage of blue/white sand, respectively, within each mixture). High-definition video of the sediment bed profile was acquired in conjunction with sediment trap measurements to resolve differences in ripple geometries, migration and evolution rates due to the different sediment mixtures and flow conditions. Observational findings clearly illustrate sediment stratification within ripple crests and the depth of the active mixing layer in addition to supporting sediment sorting in previous research on symmetric oscillatory flows in which the larger grains collect on top of ripple crests and smaller grains in the troughs. Preliminary quantitative results illuminate variations in equilibrium ripple geometry, ripple migration rates, and transition time scales between equilibrium states, all as functions of the sediment size mixture and flow forcing.

The effect of small temperature gradients on flow in a continuous flow electrophoresis chamber

NASA Technical Reports Server (NTRS)

Rhodes, P. H.; Snyder, R. S.

1982-01-01

Continuous flow electrophoresis employs an electric field to separate biological cells suspended in a flowing liquid buffer solution. Good separations based on differences in electrophoretic mobility are obtained only when a unidirectional flow is maintained. The desired flow has a parabolic structure in the narrow dimension of the chamber and is uniform acros the width, except near the edges where the no-slip condition prevails. However, because of buoyancy, very small laterall or axial temperature gradients deform the flow significantly. The results of experiments conducted with a specially instrumented chamber show the origin and structure of the buoyancy-driven perturbations. It is found that very small temperature gradients can disturb the flow significantly, as was predicted by earlier theoretical work.

How humans use visual optic flow to regulate stepping during walking.

PubMed

Salinas, Mandy M; Wilken, Jason M; Dingwell, Jonathan B

2017-09-01

Humans use visual optic flow to regulate average walking speed. Among many possible strategies available, healthy humans walking on motorized treadmills allow fluctuations in stride length (L n ) and stride time (T n ) to persist across multiple consecutive strides, but rapidly correct deviations in stride speed (S n =L n /T n ) at each successive stride, n. Several experiments verified this stepping strategy when participants walked with no optic flow. This study determined how removing or systematically altering optic flow influenced peoples' stride-to-stride stepping control strategies. Participants walked on a treadmill with a virtual reality (VR) scene projected onto a 3m tall, 180° semi-cylindrical screen in front of the treadmill. Five conditions were tested: blank screen ("BLANK"), static scene ("STATIC"), or moving scene with optic flow speed slower than ("SLOW"), matched to ("MATCH"), or faster than ("FAST") walking speed. Participants took shorter and faster strides and demonstrated increased stepping variability during the BLANK condition compared to the other conditions. Thus, when visual information was removed, individuals appeared to walk more cautiously. Optic flow influenced both how quickly humans corrected stride speed deviations and how successful they were at enacting this strategy to try to maintain approximately constant speed at each stride. These results were consistent with Weber's law: healthy adults more-rapidly corrected stride speed deviations in a no optic flow condition (the lower intensity stimuli) compared to contexts with non-zero optic flow. These results demonstrate how the temporal characteristics of optic flow influence ability to correct speed fluctuations during walking. Copyright © 2017 Elsevier B.V. All rights reserved.

Characterization of the NASA Langley Arc Heated Scramjet Test Facility Using NO PLIF

NASA Technical Reports Server (NTRS)

Kidd, F. Gray, III; Narayanaswamy, Venkateswaran; Danehy, Paul M.; Inman, Jennifer A.; Bathel, Brett F.; Cabell, Karen F.; Hass, Neal E.; Capriotti, Diego P.; Drozda, Tomasz G.; Johansen, Criag T.

2014-01-01

The nitric oxide planar laser-induced fluorescence (NO PLIF) imaging was used to characterize the air flow of the NASA Langley Arc Heated Scramjet Test Facility (AHSTF) configured with a Mach 6 nozzle. The arc raises the enthalpy of the test gas in AHSTF, producing nitric oxide. Nitric oxide persists as the temperature drops through the nozzle into the test section. NO PLIF was used to qualitatively visualize the flowfield at different experimental conditions, measure the temperature of the gas flow exiting the facility nozzle, and visualize the wave structure downstream of the nozzle at different operating conditions. Uniformity and repeatability of the nozzle flow were assessed. Expansion and compression waves on the free-jet shear layer as the nozzle flow expands into the test section were visualized. The main purpose of these experiments was to assess the uniformity of the NO in the freestream gas for planned experiments, in which NO PLIF will be used for qualitative fuel-mole-fraction sensitive imaging. The shot-to-shot fluctuations in the PLIF signal, caused by variations in the overall laser intensity as well as NO concentration and temperature variations in the flow was 20-25% of the mean signal, as determined by taking the standard deviation of a set of images obtained at constant conditions and dividing by the mean. The fluctuations within individual images, caused by laser sheet spatial variations as well as NO concentration and temperature variations in the flow, were about 28% of the mean in images, determined by taking standard deviation within individual images, dividing by the mean in the same image and averaged over the set of images. Applying an averaged laser sheet intensity correction reduced the within-image intensity fluctuations to about 10% suggesting that the NO concentration is uniform to within 10%. There was no significant difference in flow uniformity between the low and high enthalpy settings. While not strictly quantitative, the temperature maps show qualitative agreement with the computations of the flow.

Experimental investigation of turbine disk cavity aerodynamics and heat transfer

NASA Technical Reports Server (NTRS)

Daniels, W. A.; Johnson, B. V.

1993-01-01

An experimental investigation of turbine disk cavity aerodynamics and heat transfer was conducted to provide an experimental data base that can guide the aerodynamic and thermal design of turbine disks and blade attachments for flow conditions and geometries simulating those of the space shuttle main engine (SSME) turbopump drive turbines. Experiments were conducted to define the nature of the aerodynamics and heat transfer of the flow within the disk cavities and blade attachments of a large scale model simulating the SSME turbopump drive turbines. These experiments include flow between the main gas path and the disk cavities, flow within the disk cavities, and leakage flows through the blade attachments and labyrinth seals. Air was used to simulate the combustion products in the gas path. Air and carbon dioxide were used to simulate the coolants injected at three locations in the disk cavities. Trace amounts of carbon dioxide were used to determine the source of the gas at selected locations on the rotors, the cavity walls, and the interstage seal. The measurements on the rotor and stationary walls in the forward and aft cavities showed that the coolant effectiveness was 90 percent or greater when the coolant flow rate was greater than the local free disk entrainment flow rate and when room temperature air was used as both coolant and gas path fluid. When a coolant-to-gas-path density ratio of 1.51 was used in the aft cavity, the coolant effectiveness on the rotor was also 90 percent or greater at the aforementioned condition. However, the coolant concentration on the stationary wall was 60 to 80 percent at the aforementioned condition indicating a more rapid mixing of the coolant and flow through the rotor shank passages. This increased mixing rate was attributed to the destabilizing effects of the adverse density gradients.

Scalar Measurements and Analysis of Helium Jets in Earth Gravity and Microgravity using Rainbow Schlieren Deflectometry

NASA Technical Reports Server (NTRS)

Yep, Tze Wing

2001-01-01

Recent experiments have shown that low-density gas jets injected into a high-density gas undergo an instability mode leading to highly periodic oscillations in the flow field. The transition from laminar to turbulent flow in these jets is abrupt, without a gradual change in scales. Although this type of instability at high Richardson numbers has been attributed to buoyancy, direct physical evidence was not acquired through experiments. In this study, several experiments were conducted in Earth gravity and microgravity to acquire qualitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The operating parameters of this study included the tube inside diameter, the jet Reynolds number, and the jet Richardson number. Tubes with inside diameters of 19.05 mm and 31.75 mm were used in the experiments conducted in the drop tower. The jet flow was analyzed using quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and the resulting helium mole fraction obtained from color schlieren images taken at 60 Hz. Three sets of experimental data with respect to three schlieren fields of view were acquired for each tube. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low-density jet was buoyancy-induced. This study provides quantitative details of temporal flow evolution as the experiments undergo change in gravity in the drop tower.

Visual flow scene effects on the somatogravic illusion in non-pilots.

PubMed

Eriksson, Lars; von Hofsten, Claes; Tribukait, Arne; Eiken, Ola; Andersson, Peter; Hedström, Johan

2008-09-01

The somatogravic illusion (SGI) is easily broken when the pilot looks out the aircraft window during daylight flight, but it has proven difficult to break or even reduce the SGI in non-pilots in simulators using synthetic visual scenes. Could visual-flow scenes that accommodate compensatory head movement reduce the SGI in naive subjects? We investigated the effects of visual cues on the SGI induced by a human centrifuge. The subject was equipped with a head-tracked, head-mounted display (HMD) and was seated in a fixed gondola facing the center of rotation. The angular velocity of the centrifuge increased from near zero until a 0.57-G centripetal acceleration was attained, resulting in a tilt of the gravitoinertial force vector, corresponding to a pitch-up of 30 degrees. The subject indicated perceived horizontal continuously by means of a manual adjustable-plate system. We performed two experiments with within-subjects designs. In Experiment 1, the subjects (N = 13) viewed a darkened HMD and a presentation of simple visual flow beneath a horizon. In Experiment 2, the subjects (N = 12) viewed a darkened HMD, a scene including symbology superimposed on simple visual flow and horizon, and this scene without visual flow (static). In Experiment 1, visual flow reduced the SGI from 12.4 +/- 1.4 degrees (mean +/- SE) to 8.7 +/- 1.5 degrees. In Experiment 2, the SGI was smaller in the visual flow condition (9.3 +/- 1.8 degrees) than with the static scene (13.3 +/- 1.7 degrees) and without HMD presentation (14.5 +/- 2.3 degrees), respectively. It is possible to reduce the SGI in non-pilots by means of a synthetic horizon and simple visual flow conveyed by a head-tracked HMD. This may reflect the power of a more intuitive display for reducing the SGI.

Dynamic stability analysis for capillary channel flow: One-dimensional and three-dimensional computations and the equivalent steady state technique

NASA Astrophysics Data System (ADS)

Grah, Aleksander; Dreyer, Michael E.

2010-01-01

Spacecraft technology provides a series of applications for capillary channel flow. It can serve as a reliable means for positioning and transport of liquids under low gravity conditions. Basically, capillary channels provide liquid paths with one or more free surfaces. A problem may be flow instabilities leading to a collapse of the liquid surfaces. A result is undesired gas ingestion and a two phase flow which can in consequence cause several technical problems. The presented capillary channel consists of parallel plates with two free liquid surfaces. The flow rate is established by a pump at the channel outlet, creating a lower pressure within the channel. Owing to the pressure difference between the liquid phase and the ambient gas phase the free surfaces bend inwards and remain stable as long as they are able to resist the steady and unsteady pressure effects. For the numerical prediction of the flow stability two very different models are used. The one-dimensional unsteady model is mainly based on the Bernoulli equation, the continuity equation, and the Gauss-Laplace equation. For three-dimensional evaluations an open source computational fluid dynamics (CFD) tool is applied. For verifications the numerical results are compared with quasisteady and unsteady data of a sounding rocket experiment. Contrary to previous experiments this one results in a significantly longer observation sequence. Furthermore, the critical point of the steady flow instability could be approached by a quasisteady technique. As in previous experiments the comparison to the numerical model evaluation shows a very good agreement for the movement of the liquid surfaces and for the predicted flow instability. The theoretical prediction of the flow instability is related to the speed index, based on characteristic velocities of the capillary channel flow. Stable flow regimes are defined by stability criteria for steady and unsteady flow. The one-dimensional computation of the speed index is based on the technique of the equivalent steady system, which is published for the first time in the present paper. This approach assumes that for every unsteady state an equivalent steady state with a special boundary condition can be formulated. The equivalent steady state technique enables a reformulation of the equation system and an efficient and reliable speed index computation. Furthermore, the existence of the numerical singularity at the critical point of the steady flow instability, postulated in previous publication, is demonstrated in detail. The numerical singularity is related to the stability criterion for steady flow and represents the numerical consequence of the liquid surface collapse. The evaluation and generation of the pressure diagram is demonstrated in detail with a series of numerical dynamic flow studies. The stability diagram, based on one-dimensional computation, gives a detailed overview of the stable and instable flow regimes. This prediction is in good agreement with the experimentally observed critical flow conditions and results of three-dimensional CFD computations.

Influence of shear stress and size on viability of endothelial cells exposed to gold nanoparticles

NASA Astrophysics Data System (ADS)

Fede, C.; Albertin, Giovanna; Petrelli, L.; De Caro, R.; Fortunati, I.; Weber, V.; Ferrante, Camilla

2017-09-01

Screening nanoparticle toxicity directly on cell culture can be a fast and cheap technique. Nevertheless, to obtain results in accordance with those observed in live animals, the conditions in which cells are cultivated should resemble the one encountered in live systems. Microfluidic devices offer the possibility to satisfy this requirement, in particular with endothelial cell lines, because they are capable to reproduce the flowing media and shear stress experienced by these cell lines in vivo. In this work, we exploit a microfluidic device to observe how human umbilical vein endothelial cells (HUVEC) viability changes when subject to a continuous flow of culture medium, in which spherical citrate-stabilized gold nanoparticles of different sizes and at varying doses are investigated. For comparison, the same experiments are also run in multiwells where the cells do not experience the shear stress induced by the flowing medium. We discuss the results considering the influence of mode of exposure and nanoparticle size (24 and 13 nm). We observed that gold nanoparticles show a lower toxicity under flow conditions with respect to static and the HUVEC viability decreases as the nanoparticle surface area per unit volume increases, regardless of size.

Three-dimensional structure of dominant instabilities in turbulent flow over smooth and rough boundaries

NASA Astrophysics Data System (ADS)

Grass, A. J.; Stuart, R. J.; Mansour-Tehrani, M.

1991-01-01

The current status of knowledge regarding coherent vortical structures in turbulent boundary layers and their role in turbulence generation are reviewed. The investigations reported in the study concentrate attention on rough-wall flows prevailing in the geophysical environment and include an experiment determining the three-dimensional form of the turbulence structures linked to the ejection and inrush events observed over rough walls and an experiment concerned with measuring the actual spanwise scale of the near-wall structures for boundary conditions ranging from hydrodynamically smooth to fully rough. It is demonstrated that horseshoe vortical structures are present and play an important role in rough-wall flows and they increase in scale with increasing wall distance, while a dominant spanwise wavelength occurs in the instantaneous cross-flow distribution of streamwise velocity close to the rough wall.

Polystyrene latex separations by continuous flow electrophoresis on the Space Shuttle

NASA Technical Reports Server (NTRS)

Snyder, R. S.; Rhodes, P. H.; Miller, T. Y.; Micale, F. J.; Mann, R. V.

1986-01-01

The seventh mission of the Space Shuttle carried two NASA experiments in the McDonnell Douglas Astronautics Corporation continuous flow electrophoresis system. The objectives were to test the operation of continuous flow electrophoresis in a reduced gravity environment using stable particles with established electrokinetic properties and specifically to evaluate the influence of the electrical properties of the sample constituents on the resolution of the continuous flow electrophoretic device. Polystrene latex microspheres dispersed in a solution with three times the electrical conductivity of the curtain buffer separated with a significantly larger band spread compared to the second experiment under matched conductivity conditions. It is proposed that the sample of higher electrical conductivity distorted the electric field near the sample stream so that the polystyrene latex particles migrated toward the chamber walls where electroosmosis retarded and spread the sample.

Flow field and friction factor of slush nitrogen in a horizontal circular pipe

NASA Astrophysics Data System (ADS)

Jin, Tao; Li, Yijian; Wu, Shuqin; Wei, Jianjian

2018-04-01

Slush nitrogen is the low-temperature two-phase fluid with solid nitrogen particle suspended in the liquid nitrogen. The flow characteristics of slush nitrogen in a horizontal pipe with the diameter of 16 mm have been experimentally and numerically investigated, under the operating conditions with the inlet flow velocity of 0-4 m/s and the solid volume fraction of 0-23%. The numerical results for pressure drop agree well with those of the experiments, with the relative errors of ±5%. The experimental and numerical results both show that the pressure drop of slush nitrogen is greater than that of subcooled liquid nitrogen and rises with the increasing particle concentration, under the working conditions in present work. Based on the simulation result, the flow pattern evolution of slush nitrogen with the increasing slush Reynolds number has been discussed, which can be classified into homogenous flow, heterogeneous flow and moving bed. The slush effective viscosity and the slush Reynolds number are calculated with Cheng & Law formula, which includes the effects of particle shape, size and type and has a high accuracy for high concentration slurries. Based on the slush Reynolds number, an experimental empirical correlation considering particle conditions for the friction factor of slush nitrogen flow is obtained.

Mechanisms influencing older adolescents' bedtimes during videogaming: the roles of game difficulty and flow.

PubMed

Smith, Lisa J; King, Daniel L; Richardson, Cele; Roane, Brandy M; Gradisar, Michael

2017-11-01

A relationship between evening technology use and sleep has been established, and models suggest various mechanisms to explain this relationship. Recent updates to these models also suggest the influence of individual difference factors, such that the relationship between technology and sleep varies between young people. Flow is an experience of immersion and time distortion that could vary between adolescents when using technology. The aim of the present study was to investigate the effects of flow on the self-selected bedtimes of adolescents when videogaming. Seventeen older adolescent, experienced videogamers (age = 15.9 ± 0.83 years), played a new videogame on two school-night evenings in a sleep laboratory. Game difficulty was set to "hard" one evening (flow condition) and "easy" on the other evening (disrupted flow). Trait and state flow were measured, along with heart rate during videogaming, and bedtime measured objectively with real-time cameras. An interaction effect for heart rate indicated an elevated heart rate in the easy condition after 150 min of gaming (p < 0.02). No significant differences were found in bedtimes between the easy and hard conditions (p = 0.77). Adolescents high on trait flow played for longer and selected significantly later bedtimes than their low trait flow peers but only for the hard (flow) condition (12:22 AM vs. 10:53 PM, p = 0.004). Similarly, adolescents with high state flow went to bed significantly later than those low on state flow (12:24 PM vs. 10:52 PM, p = 0.001), again only in the hard condition. These findings suggest that individual and situational characteristics may amplify the effects of technology use on the "sleep" of adolescents and provides support for the displacement of bedtime hypothesis. Copyright © 2017 Elsevier B.V. All rights reserved.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

PubMed

Lee, Sang Joon; Park, Han Wook; Jung, Sung Yong

2014-09-01

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Modeling steady-state dynamics of macromolecules in exponential-stretching flow using multiscale molecular-dynamics-multiparticle-collision simulations.

PubMed

Ghatage, Dhairyasheel; Chatterji, Apratim

2013-10-01

We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensional flow) in the incompressible limit, which enables us to study the response of suspended macromolecules to the flow by computer simulations. The flow field in this flow is defined by v(x) = εx, where v(x) is the velocity of the fluid and ε is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow in a channel of uniform square cross section with periodic boundary conditions in directions perpendicular to the flow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfect elongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretching rheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry by exponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in our simulations. The fluid particles added along the length of the tube are the same fluid particles which exit the channel due to the flow; thus mass conservation is maintained in our model by default. We also suggest a scheme for possible realization of exponential-stretching flow in experiments. To establish our method as a useful tool to study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volume interactions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers in the fluid to study their responses to the exponential-stretched flow and show that the responses of macromolecules in the two flows are very similar. We demonstrate that the variation of number density of the suspended colloids along the direction of flow is in tune with our expectations. We also conclude from our study of the deformation of star polymers with different numbers of arms f that the critical flow gradient ε(c) at which the star undergoes the coil-to-stretch transition is independent of f for f = 2,5,10, and 20.

Adaptive Conditioning of Multiple-Point Geostatistical Facies Simulation to Flow Data with Facies Probability Maps

NASA Astrophysics Data System (ADS)

Khodabakhshi, M.; Jafarpour, B.

2013-12-01

Characterization of complex geologic patterns that create preferential flow paths in certain reservoir systems requires higher-order geostatistical modeling techniques. Multipoint statistics (MPS) provides a flexible grid-based approach for simulating such complex geologic patterns from a conceptual prior model known as a training image (TI). In this approach, a stationary TI that encodes the higher-order spatial statistics of the expected geologic patterns is used to represent the shape and connectivity of the underlying lithofacies. While MPS is quite powerful for describing complex geologic facies connectivity, the nonlinear and complex relation between the flow data and facies distribution makes flow data conditioning quite challenging. We propose an adaptive technique for conditioning facies simulation from a prior TI to nonlinear flow data. Non-adaptive strategies for conditioning facies simulation to flow data can involves many forward flow model solutions that can be computationally very demanding. To improve the conditioning efficiency, we develop an adaptive sampling approach through a data feedback mechanism based on the sampling history. In this approach, after a short period of sampling burn-in time where unconditional samples are generated and passed through an acceptance/rejection test, an ensemble of accepted samples is identified and used to generate a facies probability map. This facies probability map contains the common features of the accepted samples and provides conditioning information about facies occurrence in each grid block, which is used to guide the conditional facies simulation process. As the sampling progresses, the initial probability map is updated according to the collective information about the facies distribution in the chain of accepted samples to increase the acceptance rate and efficiency of the conditioning. This conditioning process can be viewed as an optimization approach where each new sample is proposed based on the sampling history to improve the data mismatch objective function. We extend the application of this adaptive conditioning approach to the case where multiple training images are proposed to describe the geologic scenario in a given formation. We discuss the advantages and limitations of the proposed adaptive conditioning scheme and use numerical experiments from fluvial channel formations to demonstrate its applicability and performance compared to non-adaptive conditioning techniques.

Transient states of air parameters after a stoppage and re-start of the main fan / Stany przejściowe parametrów powietrza po postoju i załączeniu wentylatora głównego

NASA Astrophysics Data System (ADS)

Wasilewski, Stanisław

2012-12-01

A stoppage of the main ventilation fan constitutes a disturbance of ventilation conditions of a deepmine and its effects can cause serious hazards by generating transient states of air and gas flow. Main ventilation fans are the basic deep-mine facilities; therefore, under mining regulations it is only allowed to stop them with the consent and under the conditions specified by the mine maintenance manager. The stoppage of the main ventilation fan may be accompanied by transient air parameters, including the air pressure and flow patterns. There is even the likelihood of reversing the direction of air flow, which, in case of methane mines, can pose a major hazard, particularly in sections of the mine with fire fields or large goaf areas. At the same time, stoppages of deep-mine main ventilation fans create interesting research conditions, which if conducted under the supervision of the monitoring systems, can provide much information about the transient processes of pressure, air and gas flow in underground workings. This article is a discussion of air parameter observations in mine workings made as part of such experiments. It also presents the procedure of the experiments, conducted in three mines. They involved the observation of transient processes of mine air parameters, and most interestingly, the recording of pressure and air and gas flow in the workings of the mine ventilation networks by mine monitoring systems and using specialist recording instruments. In mining practice, both in Poland and elsewhere, software tools and computer modelling methods are used to try and reproduce the conditions prior to and during disasters based on the existing network model and monitoring system data. The use of these tools to simulate the alternatives of combating and liquidation of the gas-fire hazard after its occurrence is an important issue. Measurement data collected during the experiments provides interesting research material for the verification and validation of the software tools used for the simulation of processes occurring in deep-mine ventilation systems.

Rock fragment movement in shallow rill flow - A laboratory study

NASA Astrophysics Data System (ADS)

Becker, Kerstin; Wirtz, Stefan; Seeger, Manuel; Gronz, Oliver; Remke, Alexander; Iserloh, Thomas; Brings, Christine; Casper, Markus; Ries, Johannes B.

2014-05-01

Studies concerning rill erosion mainly deal with the erosion and transport of fine material. The transport of rock fragments is examined mostly for mountain rivers. But there are important differences between the conditions and processes in rivers and in rills: (1) In most cases, the river cuts into a coarse substrate, where fine material is sparse, whereas rill erosion occurs on arable land. So the main part of the substrate is fine material and only single rock fragments influence the processes. (2) In rivers, the water depth is relatively high. There are a lot of studies about hydraulic parameters in such flows, but there is almost nothing known about hydraulic conditions in surface runoff events of a few centimeters. Additionally, little information exists about the rock fragment movement as a part of rill erosion processes on arable land. This knowledge should be increased because rock fragments cause non-stationary water turbulences in rills, which enhance the erosive force of flowing water. Field experiments can only show the fact that a certain rock fragment has moved: The starting point and the final position can be estimated. But the moving path and especially the initiation of the movement is not detectable under field conditions. Hence, we developed a laboratory setup to analyze the movement of rock fragments depending on rock fragment properties (size, form), slope gradient, flow velocity and surface roughness. By observing the rock fragments with cameras from two different angles we are able (1) to measure the rotation angles of a rock fragment during the experiment and (2) to deduce different rock fragment movement patterns. On this poster we want to present the experimental setup, developed within the scope of a master thesis, and the results of these experiments.

Transition from Forward Smoldering to Flaming in Small Polyurethane Foam Samples

NASA Technical Reports Server (NTRS)

Bar-Ilan, A.; Putzeys, O.; Rein, G.; Fernandez-Pello, A. C.

2004-01-01

Experimental observations are presented of the effect of the flow velocity and oxygen concentration, and of a thermal radiant flux, on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. The experiments are part of a project studying the transition from smolder to flaming under conditions encountered in spacecraft facilities, i.e., microgravity, low velocity variable oxygen concentration flows. Because the microgravity experiments are planned for the International Space Station, the foam samples had to be limited in size for safety and launch mass reasons. The feasible sample size is too small for smolder to self propagate because of heat losses to the surrounding environment. Thus, the smolder propagation and the transition to flaming had to be assisted by reducing the heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed in a wind tunnel. Three of the sample lateral-sides are maintained at elevated temperature and the fourth side is exposed to an upward flow and to a radiant flux. It is found that decreasing the flow velocity and increasing its oxygen concentration, and/or increasing the radiant flux enhances the transition to flaming, and reduces the delay time to transition. Limiting external ambient conditions for the transition to flaming are reported for the present experimental set-up. The results show that smolder propagation and the transition to flaming can occur in relatively small fuel samples if the external conditions are appropriate. The results also indicate that transition to flaming occurs in the char left behind by the smolder reaction, and it has the characteristics of a gas-phase ignition induced by the smolder reaction, which acts as the source of both gaseous fuel and heat.

Algicidal activity of an actinomycete strain, Streptomyces rameus, against Microcystis aeruginosa.

PubMed

Phankhajon, Kanchariya; Somdee, Anchana; Somdee, Theerasak

2016-09-01

An actinomycete strain (KKU-A3) with algicidal activity against Microcystis aeruginosa was isolated from soil in Khon Kaen Province, Thailand. Based on its phenotypic characteristics and 16S rDNA sequence, strain KKU-A3 was identified as Streptomyces rameus. Strain KKU-A3 also exhibited algicidal activity against the cyanobacteria Synechococcus elongatus, Cylindrospermum sp. and Oscillatoria sp. A mathematical and statistical technique was used to optimize the culture conditions and maximize its anti-Microcystis activity. The single factor experiments indicated that glucose and casein were the most effective carbon and nitrogen sources, respectively, and produced the highest anti-Microcystis activity. Response surface methodology indicated that the optimum culture conditions were 19.81 g/L glucose and 2.0 g/L casein at an initial pH of 7.8 and an incubation temperature of 30 °C. The anti-Microcystis activity increased from 82% to 95% under optimum conditions. In an internal airlift loop bioreactor, the removal of M. aeruginosa KKU-13 by the bacterium was investigated in batch and continuous flow experiments. In the batch experiment, KKU-A3 displayed maximum anti-Microcystis activity of 95% at day 7, whereas in the continuous flow experiment, KKU-A3 displayed maximum anti-Microcystis activity of 95% at day 10.

Using Nonlinearity and Contact Lines to Control Fluid Flow in Microgravity

NASA Technical Reports Server (NTRS)

Perlin, M.; Schultz, W. W.; Bian, X.; Agarwal, M.

2002-01-01

Slug flows in a tube are affected by surface tension and contact lines, especially under microgravity. Numerical analyses and experiments are conducted of slug flows in small-diameter tubes with horizontal, inclined and vertical orientations. A PID-controlled, meter-long platform capable of following specified motions is used. An improved understanding of the contact line boundary condition for steady and unsteady contact-line motion is expected. Lastly, a direct fluid-handling method using nonlinear oscillatory motion of a tube is presented.

Robust vehicle detection under various environmental conditions using an infrared thermal camera and its application to road traffic flow monitoring.

PubMed

Iwasaki, Yoichiro; Misumi, Masato; Nakamiya, Toshiyuki

2013-06-17

We have already proposed a method for detecting vehicle positions and their movements (henceforth referred to as "our previous method") using thermal images taken with an infrared thermal camera. Our experiments have shown that our previous method detects vehicles robustly under four different environmental conditions which involve poor visibility conditions in snow and thick fog. Our previous method uses the windshield and its surroundings as the target of the Viola-Jones detector. Some experiments in winter show that the vehicle detection accuracy decreases because the temperatures of many windshields approximate those of the exterior of the windshields. In this paper, we propose a new vehicle detection method (henceforth referred to as "our new method"). Our new method detects vehicles based on tires' thermal energy reflection. We have done experiments using three series of thermal images for which the vehicle detection accuracies of our previous method are low. Our new method detects 1,417 vehicles (92.8%) out of 1,527 vehicles, and the number of false detection is 52 in total. Therefore, by combining our two methods, high vehicle detection accuracies are maintained under various environmental conditions. Finally, we apply the traffic information obtained by our two methods to traffic flow automatic monitoring, and show the effectiveness of our proposal.

Experimental investigation into the impact of vegetation on fan morphology and flow

NASA Astrophysics Data System (ADS)

Clarke, Lucy; McLelland, Stuart; Coulthard, Tom

2013-04-01

Riparian vegetation can significantly influence the geomorphology of fluvial systems, affecting channel geometry and flow dynamics. However, there is still limited understanding of the role vegetation plays in the development of alluvial fans, despite the large number of vegetated fans located in temperate and humid climates. An understanding of the feedback loops between water flow, sediment dynamics and vegetation is key to understanding the geomorphological response of alluvial fans. But it is difficult to investigate these relationships in the natural world due to the complexity of the geomorphic and biological processes and timescales involved. To examine the effects of vegetation on channel form, flow dynamics and morphology during fan evolution, a series of experiments were conducted using the Total Environment Simulator at the Deep, an experimental facility operated by the University of Hull. The experiments followed a 'similarity of processes' approach and so were not scaled to a specific field prototype. Live vegetation (alfalfa) was used to simulate the influence of vegetation on the fan development. A range of experiments were conducted on fan plots 2x2m in size, the same initial conditions and constant water discharge and sediment feed rates were used, but the vegetation density and amount of geomorphic time (when the sediment and water were running and there was active fan development) between seeding / vegetation growth varied between runs. The fan morphology was recorded at regular intervals using a laser scanner (at 1mm resolution) and high resolution video recording and overhead photography was also used to gain near-continuous data quantifying fan topography, flow patterns, channel migration and avulsion frequency. Image analysis also monitored the spatial extent of vegetation establishment. The use of these techniques allowed collection of high resolution spatial and temporal data on fan development with minimal disruption to the experiments. The results of the preliminary experiments showed that vegetation did influence the morphology and flow conditions during fan evolution. Vegetation reduced the number of active channels, and increasing the vegetation density also led to lower lateral migration rates, the formation of narrower and deeper channels and an increase in fan slope.

Experimental study on the performance of the vapor injection refrigeration system with an economizer for intermediate pressures

NASA Astrophysics Data System (ADS)

Moon, Chang-Uk; Choi, Kwang-Hwan; Yoon, Jung-In; Kim, Young-Bok; Son, Chang-Hyo; Ha, Soo-Jung; Jeon, Min-Ju; An, Sang-Young; Lee, Joon-Hyuk

2018-04-01

In this study, to investigate the performance characteristics of vapor injection refrigeration system with an economizer at an intermediate pressure, the vapor injection refrigeration system was analyzed under various experiment conditions. As a result, the optimum design data of the vapor injection refrigeration system with an economizer were obtained. The findings from this study can be summarized as follows. The mass flow rate through the compressor increases with intermediate pressure. The compression power input showed an increasing trend under all the test conditions. The evaporation capacity increased and then decreased at the intermediate pressure, and as such, it became maximum at the given intermediate pressure. The increased mass flow rate of the by-passed refrigerant enhanced the evaporation capacity at the low medium pressure range, but the increased saturation temperature limited the subcooling degree of the liquid refrigerant after the application of the economizer when the intermediate pressure kept rising, and degenerated the evaporation capacity. The coefficient of performance (COP) increased and then decreased with respect to the intermediate pressures under all the experiment conditions. Nevertheless, there was an optimum intermediate pressure for the maximum COP under each experiment condition. Therefore, the optimum intermediate pressure in this study was found at -99.08 kPa, which is the theoretical standard medium pressure under all the test conditions.

Preparation of Geophysical Fluid Flow Experiments ( GeoFlow ) in the Fluid Science Laboratory on ISS

NASA Astrophysics Data System (ADS)

Egbers, C.

The ,,GeoFlow" is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluidmechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field similar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment requires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth's liquid core the exp eriment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heating the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number. Results of preparatory experiments and numerical simulation of the space experiment will be presented. Funding from DLR under grant 50 WM 0122 is greatfully ackwnoledged.

Influence of liquid temperature and flow rate on enamel erosion and surface softening.

PubMed

Eisenburger, M; Addy, M

2003-11-01

Enamel erosion and softening are based on chemical processes which could be influenced by many factors including temperature and acid flow rate. Knowledge of the influence of these variables could have relevance to research experiments and clinical outcomes. Both parameters were investigated using an ultrasonication and profilometry method to assess erosion depth and surface softening of enamel. The influence of temperature was studied by eroding polished human enamel samples at 4, 20, 35 or 50 degrees C for 2 h. Secondly, different liquid flow conditions were established by varying acid agitation. Additionally, a slow laminar flow and a jet of citric acid, to simulate drinking through a straw, were applied to specimens. Erosion depth increased significantly with acid temperature from 11.0 microm at 4 degrees C to 35.8 microm at 50 degrees C. Surface softening increased much more slowly and plateaued at 2.9 microm to 3.5 microm after 35 degrees C. A strong dependence of erosion on liquid flow was revealed. In unstirred conditions only 8.6 microm erosion occurred, which increased to 22.2 microm with slow stirring and 40.9 microm with fast stirring. Surface softening did not increase correspondingly with its largest extent at slow stirring at 3.4 microm.The implication of these data are: first, the conditions for erosion experiments in vitro or in situ need to be specified for reliable comparisons between studies. Secondly, erosion of teeth by soft drinks are likely to be influenced both by the temperature of the drink and individual drinking habits.

Experiment for validation of fluid-structure interaction models and algorithms.

PubMed

Hessenthaler, A; Gaddum, N R; Holub, O; Sinkus, R; Röhrle, O; Nordsletten, D

2017-09-01

In this paper a fluid-structure interaction (FSI) experiment is presented. The aim of this experiment is to provide a challenging yet easy-to-setup FSI test case that addresses the need for rigorous testing of FSI algorithms and modeling frameworks. Steady-state and periodic steady-state test cases with constant and periodic inflow were established. Focus of the experiment is on biomedical engineering applications with flow being in the laminar regime with Reynolds numbers 1283 and 651. Flow and solid domains were defined using computer-aided design (CAD) tools. The experimental design aimed at providing a straightforward boundary condition definition. Material parameters and mechanical response of a moderately viscous Newtonian fluid and a nonlinear incompressible solid were experimentally determined. A comprehensive data set was acquired by using magnetic resonance imaging to record the interaction between the fluid and the solid, quantifying flow and solid motion. Copyright © 2016 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.

Postural control and perceptive configuration: influence of expertise in gymnastics.

PubMed

Gautier, Geoffroy; Thouvarecq, Régis; Vuillerme, Nicolas

2008-07-01

The purpose of the present experiment was to investigate how postural adaptations to the perceptive configuration are modified by specific gymnastics experience. Two groups, one expert in gymnastics and the other non-expert, had to maintain the erected posture while optical flow was imposed as follows: 20s motionless, 30s approaching motion, and 20s motionless. The centre of pressure and head displacements were analysed. The postural adaptations were characterised by the variability of movements for the flow conditions and by the postural latencies for the flow transitions. The results showed that the gymnasts tended to minimise their body movements and were more stationary (head) but not more stable (COP) than the non-gymnasts. These results suggest that gymnastics experience develops a specific postural adaptability relative to the perceptive configuration. We conclude that a specific postural experience could be considered as an intrinsic constraint, which leads to modification in the patterns of functional adaptation in the perceptive motor space.

Wind-tunnel experiments of turbulent flow over a surface-mounted 2-D block in a thermally-stratified boundary layer

NASA Astrophysics Data System (ADS)

Zhang, Wei; Markfort, Corey; Porté-Agel, Fernando

2014-11-01

Turbulent flows over complex surface topography have been of great interest in the atmospheric science and wind engineering communities. The geometry of the topography, surface roughness and temperature characteristics as well as the atmospheric thermal stability play important roles in determining momentum and scalar flux distribution. Studies of turbulent flow over simplified topography models, under neutrally stratified boundary-layer conditions, have provided insights into fluid dynamics. However, atmospheric thermal stability has rarely been considered in laboratory experiments, e.g., wind-tunnel experiments. Series of wind-tunnel experiments of thermally-stratified boundary-layer flow over a surface-mounted 2-D block, in a well-controlled boundary-layer wind tunnel, will be presented. Measurements using high-resolution PIV, x-wire/cold-wire anemometry and surface heat flux sensors were conducted to quantify the turbulent flow properties, including the size of the recirculation zone, coherent vortex structures and the subsequent boundary layer recovery. Results will be shown to address thermal stability effects on momentum and scalar flux distribution in the wake, as well as dominant mechanism of turbulent kinetic energy generation and consumption. The authors gratefully acknowledge funding from the Swiss National Foundation (Grant 200021-132122), the National Science Foundation (Grant ATM-0854766) and NASA (Grant NNG06GE256).

A Experimental Investigation of Hydrodynamic Forces on Circular Cylinders in Sinusoidal and Random Oscillating Flow

NASA Astrophysics Data System (ADS)

Longoria, Raul Gilberto

An experimental apparatus has been developed which can be used to generate a general time-dependent planar flow across a cylinder. A mass of water enclosed with no free surface within a square cross-section tank and two spring pre-loaded pistons is oscillated using a hydraulic actuator. A circular cylinder is suspended horizontally in the tank by two X-Y force transducers used to simultaneously measure the total in-line and transverse forces. Fluid motion is measured using a differential pressure transducer for instantaneous acceleration and an LVDT for displacement. This investigation provides measurement of forces on cylinders subjected to planar fluid flow velocity with a time (and frequency) dependence which more accurately represent the random conditions encountered in a natural ocean environment. The use of the same apparatus for both sinusoidal and random experiments provides a quantified assessment of the applicability of sinusoidal planar oscillatory flow data in offshore structure design methods. The drag and inertia coefficients for a Morison equation representation of the inline force are presented for both sinusoidal and random flow. Comparison of the sinusoidal results is favorable with those of previous investigations. The results from random experiments illustrates the difference in the force mechanism by contrasting the force transfer coefficients for the inline and transverse forces. It is found that application of sinusoidal results to random hydrodynamic inline force prediction using the Morison equation wrongly weighs the drag and inertia components, and the transverse force is overpredicted. The use of random planar oscillatory flow in the laboratory, contrasted with sinusoidal planar oscillatory flow, quantifies the accepted belief that the force transfer coefficients from sinusoidal flow experiments are conservative for prediction of forces on cylindrical structures subjected to random sea waves and the ensuing forces. Further analysis of data is conducted in the frequency domain to illustrate models used for predicting the power spectral density of the inline force including a nonlinear describing function method. It is postulated that the large-scale vortex activity prominent in sinusoidal oscillatory flow is subdued in random flow conditions.

Laboratory experiments on solute transport in bimodal porous media under cyclic precipitation-evaporation boundary conditions

NASA Astrophysics Data System (ADS)

Cremer, Clemens; Neuweiler, Insa

2016-04-01

Flow and solute transport in the shallow subsurface is strongly governed by atmospheric boundary conditions. Erratically varying infiltration and evaporation cycles lead to alternating upward and downward flow, as well as spatially and temporally varying water contents and associated hydraulic conductivity of the prevailing materials. Thus presenting a highly complicated, dynamic system. Knowledge of subsurface solute transport processes is vital to assess e.g. the entry of, potentially hazardous, solutes to the groundwater and nutrient uptake by plant roots and can be gained in many ways. Besides field measurements and numerical simulations, physical laboratory experiments represent a way to establish process understanding and furthermore validate numerical schemes. With the aim to gain a better understanding and to quantify solute transport in the unsaturated shallow subsurface under natural precipitation conditions in heterogeneous media, we conduct physical laboratory experiments in a 22 cm x 8 cm x 1 cm flow cell that is filled with two types of sand and apply cyclic infiltration-evaporation phases at the soil surface. Pressure at the bottom of the domain is kept constant. Following recent studies (Lehmann and Or, 2009; Bechtold et al., 2011a), heterogeneity is introduced by a sharp vertical interface between coarse and fine sand. Fluorescent tracers are used to i) qualitatively visualize transport paths within the domain and ii) quantify solute leaching at the bottom of the domain. Temporal and spatial variations in water content during the experiment are derived from x-ray radiographic images. Monitored water contents between infiltration and evaporation considerably changed in the coarse sand while the fine sand remained saturated throughout the experiments. Lateral solute transport through the interface in both directions at different depths of the investigated soil columns were observed. This depended on the flow rate applied at the soil surface and significantly influenced solute leaching. Dynamic boundary conditions generally resulted in faster initial breakthrough and stronger tailing. References: Bechtold, M., S. Haber-Pohlmeier, J. Vanderborght, A. Pohlmeier, T.P.A. Ferré and H. Veerecken. 2011a. Near-surface solute redistribution during evaporation. Geophys. Res. Lett., 38, L17404, doi:10.1029/2011GL048147. Lehmann, P. and D. Or. 2009. Evaporation and capillary coupling across vertical textural contrasts in porous media. Phys. Rev. E, 80, 046318, doi:10.1103/PhysRevE.80.046318.

Neutron imaging of diabatic two-phase flows relevant to air conditioning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geoghegan, Patrick J; Sharma, Vishaldeep

The design of the evaporator of an air conditioning system relies heavily on heat transfer coefficients and pressure drop correlations that predominantly involve an estimate of the changing void fraction and the underlying two-phase flow regime. These correlations dictate whether the resulting heat exchanger is oversized or not and the amount of refrigerant charge necessary to operate. The latter is particularly important when dealing with flammable or high GWP refrigerants. Traditional techniques to measure the void fraction and visualize the flow are either invasive to the flow or occur downstream of the evaporator, where some of the flow distribution willmore » have changed. Neutron imaging has the potential to visualize two-phase flow in-situ where an aluminium heat exchanger structure becomes essentially transparent to the penetrating neutrons. The subatomic particles are attenuated by the passing refrigerant flow. The resulting image may be directly related to the void fraction and the overall picture provides a clear insight into the flow regime present. This work presents neutron images of the refrigerant Isopentane as it passes through the flow channels of an aluminium evaporator at flowrates relevant to air conditioning. The flow in a 4mm square macro channel is compared to that in a 250 m by 750 m rectangular microchannel in terms of void fraction and regime. All neutron imaging experiments were conducted at the High Flux Isotope Reactor, an Oak Ridge National Laboratory facility« less

Very high pressure liquid chromatography using core-shell particles: quantitative analysis of fast gradient separations without post-run times.

PubMed

Stankovich, Joseph J; Gritti, Fabrice; Stevenson, Paul G; Beaver, Lois A; Guiochon, Georges

2014-01-17

Five methods for controlling the mobile phase flow rate for gradient elution analyses using very high pressure liquid chromatography (VHPLC) were tested to determine thermal stability of the column during rapid gradient separations. To obtain rapid separations, instruments are operated at high flow rates and high inlet pressure leading to uneven thermal effects across columns and additional time needed to restore thermal equilibrium between successive analyses. The purpose of this study is to investigate means to minimize thermal instability and obtain reliable results by measuring the reproducibility of the results of six replicate gradient separations of a nine component RPLC standard mixture under various experimental conditions with no post-run times. Gradient separations under different conditions were performed: constant flow rates, two sets of constant pressure operation, programmed flow constant pressure operation, and conditions which theoretically should yield a constant net heat loss at the column's wall. The results show that using constant flow rates, programmed flow constant pressures, and constant heat loss at the column's wall all provide reproducible separations. However, performing separations using a high constant pressure with programmed flow reduces the analysis time by 16% compared to constant flow rate methods. For the constant flow rate, programmed flow constant pressure, and constant wall heat experiments no equilibration time (post-run time) was required to obtain highly reproducible data. Copyright © 2013 Elsevier B.V. All rights reserved.

The effect of bedload transport on mean and turbulent flow properties

NASA Astrophysics Data System (ADS)

Carbonneau, Patrice E.; Bergeron, Normand E.

2000-11-01

This paper reports the results of a flume experiment that was designed to investigate the effect of bedload transport on mean and turbulent properties of the flow. The experiment consisted of varying the bedload transport rate for a given hydraulic condition, and of measuring the flow velocity profiles using an Acoustic Doppler Velocimeter (ADV) for each transport rate in order to allow for comparison. Bedload transport was produced by injecting gravel-size particles ( D50=7.4 mm) with a conveyer belt mounted at the upstream end of the flume. The results indicate that the effect of bedload on flow characteristics is complex. It is shown that bedload transport causes opposite effects on flow velocity depending on the roughness of the bed and the relative magnitude of flow and sediment transport variables. A better understanding of these conflicting results is obtained from the application of an energy budget approach to the analysis of velocity data. This approach demonstrates that bedload affects flow velocity by modifying the rate of dissipation of turbulent kinetic energy. However, the mechanisms responsible for the modification of turbulent dissipation are still unknown.

Static response of deformable microchannels

NASA Astrophysics Data System (ADS)

Christov, Ivan C.; Sidhore, Tanmay C.

2017-11-01

Microfluidic channels manufactured from PDMS are a key component of lab-on-a-chip devices. Experimentally, rectangular microchannels are found to deform into a non-rectangular cross-section due to fluid-structure interactions. Deformation affects the flow profile, which results in a nonlinear relationship between the volumetric flow rate and the pressure drop. We develop a framework, within the lubrication approximation (l >> w >> h), to self-consistently derive flow rate-pressure drop relations. Emphasis is placed on handling different types of elastic response: from pure plate-bending, to half-space deformation, to membrane stretching. The ``simplest'' model (Stokes flow in a 3D rectangular channel capped with a linearly elastic Kirchhoff-Love plate) agrees well with recent experiments. We also simulate the static response of such microfluidic channels under laminar flow conditions using ANSYSWorkbench. Simulations are calibrated using experimental flow rate-pressure drop data from the literature. The simulations provide highly resolved deformation profiles, which are difficult to measure experimentally. By comparing simulations, experiments and our theoretical models, we show good agreement in many flow/deformation regimes, without any fitting parameters.

Review of Research into the Concept of the Microblowing Technique for Turbulent Skin Friction Reduction

NASA Technical Reports Server (NTRS)

2004-01-01

A new technology for reducing turbulent skin friction, called the Microblowing Technique (MBT), is presented. Results from proof-of-concept experiments show that this technology could potentially reduce turbulent skin friction by more than 50% of the skin friction of a solid flat plate for subsonic and supersonic flow conditions. The primary purpose of this review paper is to provide readers with information on the turbulent skin friction reduction obtained from many experiments using the MBT. Although the MBT has a penalty for obtaining the microblowing air associated with it, some combinations of the MBT with suction boundary layer control methods are an attractive alternative for a real application. Several computational simulations to understand the flow physics of the MBT are also included. More experiments and computational fluid dynamics (CFD) computations are needed for the understanding of the unsteady flow nature of the MBT and the optimization of this new technology.

Influence of Geometry and Flow Variation on Jet Mixing and NO Formation in a Model Staged Combustor Mixer with Eight Orifices

NASA Technical Reports Server (NTRS)

Samuelsen, G. S.; Sowa, W. A.; Hatch, M. S.

1996-01-01

A series of non-reacting parametric experiments was conducted to investigate the effect of geometric and flow variations on mixing of cold jets in an axis-symmetric, heated cross flow. The confined, cylindrical geometries tested represent the quick mix region of a Rich-Burn/Quick-Mix/Lean-Burn (RQL) combustor. The experiments show that orifice geometry and jet to mainstream momentum-flux ratio significantly impact the mixing characteristic of jets in a cylindrical cross stream. A computational code was used to extrapolate the results of the non-reacting experiments to reacting conditions in order to examine the nitric oxide (NO) formation potential of the configurations examined. The results show that the rate of NO formation is highest immediately downstream of the injection plane. For a given momentum-flux ratio, the orifice geometry that mixes effectively in both the immediate vicinity of the injection plane, and in the wall regions at downstream locations, has the potential to produce the lowest NO emissions. The results suggest that further study may not necessarily lead to a universal guideline for designing a low NO mixer. Instead, an assessment of each application may be required to determine the optimum combination of momentum-flux ratio and orifice geometry to minimize NO formation. Experiments at reacting conditions are needed to verify the present results.

Preferential Flow and Transport of Cryptosporidium Parvum Oocysts Through Vadose Zone: Experiments and Modeling

NASA Astrophysics Data System (ADS)

Darnault, C. J.; Darnault, C. J.; Garnier, P.; Kim, Y.; Oveson, K.; Jenkins, M.; Ghiorse, W.; Baveye, P.; Parlange, J.; Steenhuis, T.

2001-12-01

Oocysts of the protozoan Cryptosporidium parvum, when they contaminate drinking water supplies, can cause outbreaks of Cryptosporidiosis, a common waterborne disease. Of the different pathways by which oocysts can wind up in drinking water, one has received very little attention to date; because soils are often considered to be perfect filters, the transport of oocysts through the subsoil to groundwater by preferential flow is generally ignored. To evaluate its significance, three set of laboratory experiments investigated transport of oocysts through vadose zone. Experiment set I was carried out in a vertical 50 cm-long column filled with silica sand, under conditions known to foster fingered flow. Experiment set II investigates the effect of gas-water interfaces by modifying the hydrodynamical conditions in the sand columns with water-repellent sand barriers. Experiment III involved undisturbed soil columns subjected to macropores flow. The sand and soil columns were subjected to artificial rainfall and were allowed to reach steady-state. At that point, feces of contaminated calves were applied at the surface, along with a known amount of KCl to serve as tracer, and rainfall was continued at the same rate. The breakthrough of oocysts and Cl-, monitored in the effluent, demonstrate the importance of preferential flow - fingered flow and macropore flow - on the transport of oocysts through vadose zone. Peak oocyst concentrations were not appreciably delayed, compared to Cl-, and in some cases, occurred even before the Cl- peak. However, the numbers of oocysts present in the effluents were still orders of magnitude higher than the 5 to 10 oocysts per liter that are considerable sufficient to cause cryptosporidiosis in healthy adults. The transport of oocysts was simulated based on a partitioning the soil profile in both a distribution zone and a preferential zone, In particular, the model simulates accurately the markedly asymmetric breakthrough patterns, and the long exponential tailing. The spatial distribution of oocysts suggest a close relationship between oocyst retention and the extent of gas-water interfaces; sharp increases in oocyst numbers are consistently observed in regions of the sand where the water content has steep gradients, and therefore where one expects capillary meniscii to have maximal extent. These observations imply that oocyst transport in the vadose zone is likely to be very limited in the absence of preferential flow. However, experimental results suggest that the transport of oocysts in the subsurface via preferential flow may create a significant risk of groundwater contamination in some situations.

Smoke Point in Co-flow Experiment

NASA Technical Reports Server (NTRS)

Urban, David L.; Sunderland, Peter B.; Yuan, Zeng-Guang

2009-01-01

The Smoke Point In Co-flow Experiment (SPICE) determines the point at which gas-jet flames (similar to a butane-lighter flame) begin to emit soot (dark carbonaceous particulate formed inside the flame) in microgravity. Studying a soot emitting flame is important in understanding the ability of fires to spread and in control of soot in practical combustion systems space. Previous experiments show that soot dominates the heat emitted from flames in normal gravity and microgravity fires. Control of this heat emission is critical for prevention of the spread of fires on Earth and in space for the design of efficient combustion systems (jet engines and power generation boilers). The onset of soot emission from small gas jet flames (similar to a butane-lighter flame) will be studied to provide a database that can be used to assess the interaction between fuel chemistry and flow conditions on soot formation. These results will be used to support combustion theories and to assess fire behavior in microgravity. The Smoke Point In Co-flow Experiment (SPICE) will lead to a o improved design of practical combustors through improved control of soot formation; o improved understanding of and ability to predict heat release, soot production and emission in microgravity fires; o improved flammability criteria for selection of materials for use in the next generation of spacecraft. The Smoke Point In Co-flow Experiment (SPICE) will continue the study of fundamental phenomena related to understanding the mechanisms controlling the stability and extinction of jet diffusion flames begun with the Laminar Soot Processes (LSP) on STS-94. SPICE will stabilize an enclosed laminar flame in a co-flowing oxidizer, measure the overall flame shape to validate the theoretical and numerical predictions, measure the flame stabilization heights, and measure the temperature field to verify flame structure predictions. SPICE will determine the laminar smoke point properties of non-buoyant jet diffusion flames (i.e., the properties of the largest laminar jet diffusion flames that do not emit soot) for several fuels under different nozzle diameter/co-flow velocity configurations. Luminous flame shape measurements would also be made to verify models of the flame shapes under co-flow conditions. The smoke point is a simple measurement that has been found useful to study the influence of flow and fuel properties on the sooting propensity of flames. This information would help support current understanding of soot processes in laminar flames and by analogy in turbulent flames of practical interest.

Dielectrophoretic particle-particle interaction under AC electrohydrodynamic flow conditions.

PubMed

Lee, Doh-Hyoung; Yu, Chengjie; Papazoglou, Elisabeth; Farouk, Bakhtier; Noh, Hongseok M

2011-09-01

We used the Maxwell stress tensor method to understand dielectrophoretic particle-particle interactions and applied the results to the interpretation of particle behaviors under alternating current (AC) electrohydrodynamic conditions such as AC electroosmosis (ACEO) and electrothermal flow (ETF). Distinct particle behaviors were observed under ACEO and ETF. Diverse particle-particle interactions observed in experiments such as particle clustering, particles keeping a certain distance from each other, chain and disc formation and their rotation, are explained based on the numerical simulation data. The improved understanding of particle behaviors in AC electrohydrodynamic flows presented here will enable researchers to design better particle manipulation strategies for lab-on-a-chip applications. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of azimuthal diversion rail on an ATON-type Hall thruster

NASA Astrophysics Data System (ADS)

Xu, Zhang; Liqiu, Wei; Liang, Han; Yongjie, Ding; Daren, Yu

2017-03-01

A newly designed azimuthal diversion rail (ADR) is studied and used to enhance the ionization process in an ATON-type Hall thruster. The diversion rail efficiently reduces the neutral flow axial velocity, and hence, increases the resistance time of atoms in the discharge channel of the Hall thruster. Thrust performances, in terms of thrust, anode efficiency and ion beam divergence, are found to be improved because of the application of the diversion rail, especially at low mass flow rate conditions. Experiment results reveal that the ADR increases the mass utilization under insufficient mass flow rate operating conditions. The design of the ADR broadens the efficient operating range of Hall thrusters and has significant contribution to multi-mode Hall thruster development.

Breakdown characteristics of atmospheric dielectric barrier discharge in gas flow condition

NASA Astrophysics Data System (ADS)

Fan, Zhihui; Yan, Huijie; Wang, Yuying; Liu, Yidi; Guo, Hongfei; Ren, Chunsheng

2018-05-01

Experimental investigations of the breakdown characteristics of plate-to-plate dielectric barrier discharge excited by an AC source at different gas flow conditions are carried out. The ignition voltage for the appearance of the very first discharge filament and the breakdown voltage in each discharge half cycle in continuous operation are examined. As revealed by the results of the indoor air experiment, the ignition voltage manifests a monotonous increase with the increase in the gas flow rate, while the breakdown voltage has a marked decline at the low gas flow rate and increases slightly as the gas flow rate is higher than 10 m/s. As regards the obvious decreases in the ignition voltage and breakdown voltage, the decrease in the humidity with the increase in the gas flow rate plays a dominant role. As regards the increase in breakdown voltage, the memory effect from the preceding discharge is considered. The losses of metastable particles, together with particles having high translational energy in the gas flow, are considered to be the most critical factors.

An investigation into the stability of commercial versus MG63-derived hepatocyte growth factor under flow cultivation conditions.

PubMed

Meneghello, Giulia; Storm, Michael P; Chaudhuri, Julian B; De Bank, Paul A; Ellis, Marianne J

2015-03-01

The scale-up of tissue engineering cell culture must ensure that conditions are maintained while also being cost effective. Here we analyse the stability of hepatocyte growth factor (HGF) to investigate whether concentrations change under dynamic conditions, and compare commercial recombinant human HGF as an additive in 'standard medium', to HGF secreted by the osteosarcoma cell line MG63 as a 'preconditioned medium'. After 3 h under flow conditions, HGF in the standard medium degraded to 40% of its original concentration but HGF in the preconditioned medium remained at 100%. The concentration of secreted HGF was 10 times greater than the working concentration of commercially-available HGF. Thus HGF within this medium has increased stability; MG63-derived HGF should therefore be investigated as a cost-effective alternative to current lyophilised powders for use in in vitro models. Furthermore, we recommend that those intending to use HGF (or other growth factors) should consider similar stability testing before embarking on experiments with media flow.

Studies on sodium boiling phenomena in out of pile rod bundles for various accidental situations in Liquid Metal Fast Breeder Reactors (LMFBR) experiments and interpretations

NASA Astrophysics Data System (ADS)

Seiler, J. M.; Rameau, B.

Bundle sodium boiling in nominal geometry for different accident conditions is reviewed. Voiding of a subassembly is controlled by not only hydrodynamic effects but mainly by thermal effects. There is a strong influence of the thermal inertia of the bundle material compared to the sodium thermal inertia. Flow instability, during a slow transient, can be analyzed with numerical tools and estimated using simplified approximations. Stable boiling operational conditions under bundle mixed convection (natural convection in the reactor) can be predicted. Voiding during a fast transient can be approximated from single channel calculations. The phenomenology of boiling behavior for a subassembly with inlet completely blocked, submitted to decay heat and lateral cooling; two-phase sodium flow pressure drop in a tube of large hydraulic diameter under adiabatic conditions; critical flow phenomena and voiding rate under high power, slow transient conditions; and onset of dry out under local boiling remains problematical.

Are atmospheric surface layer flows ergodic?

NASA Astrophysics Data System (ADS)

Higgins, Chad W.; Katul, Gabriel G.; Froidevaux, Martin; Simeonov, Valentin; Parlange, Marc B.

2013-06-01

The transposition of atmospheric turbulence statistics from the time domain, as conventionally sampled in field experiments, is explained by the so-called ergodic hypothesis. In micrometeorology, this hypothesis assumes that the time average of a measured flow variable represents an ensemble of independent realizations from similar meteorological states and boundary conditions. That is, the averaging duration must be sufficiently long to include a large number of independent realizations of the sampled flow variable so as to represent the ensemble. While the validity of the ergodic hypothesis for turbulence has been confirmed in laboratory experiments, and numerical simulations for idealized conditions, evidence for its validity in the atmospheric surface layer (ASL), especially for nonideal conditions, continues to defy experimental efforts. There is some urgency to make progress on this problem given the proliferation of tall tower scalar concentration networks aimed at constraining climate models yet are impacted by nonideal conditions at the land surface. Recent advancements in water vapor concentration lidar measurements that simultaneously sample spatial and temporal series in the ASL are used to investigate the validity of the ergodic hypothesis for the first time. It is shown that ergodicity is valid in a strict sense above uniform surfaces away from abrupt surface transitions. Surprisingly, ergodicity may be used to infer the ensemble concentration statistics of a composite grass-lake system using only water vapor concentration measurements collected above the sharp transition delineating the lake from the grass surface.

Variability of 4D flow parameters when subjected to changes in MRI acquisition parameters using a realistic thoracic aortic phantom.

PubMed

Montalba, Cristian; Urbina, Jesus; Sotelo, Julio; Andia, Marcelo E; Tejos, Cristian; Irarrazaval, Pablo; Hurtado, Daniel E; Valverde, Israel; Uribe, Sergio

2018-04-01

To assess the variability of peak flow, mean velocity, stroke volume, and wall shear stress measurements derived from 3D cine phase contrast (4D flow) sequences under different conditions of spatial and temporal resolutions. We performed controlled experiments using a thoracic aortic phantom. The phantom was connected to a pulsatile flow pump, which simulated nine physiological conditions. For each condition, 4D flow data were acquired with different spatial and temporal resolutions. The 2D cine phase contrast and 4D flow data with the highest available spatio-temporal resolution were considered as a reference for comparison purposes. When comparing 4D flow acquisitions (spatial and temporal resolution of 2.0 × 2.0 × 2.0 mm 3 and 40 ms, respectively) with 2D phase-contrast flow acquisitions, the underestimation of peak flow, mean velocity, and stroke volume were 10.5, 10 and 5%, respectively. However, the calculated wall shear stress showed an underestimation larger than 70% for the former acquisition, with respect to 4D flow, with spatial and temporal resolution of 1.0 × 1.0 × 1.0 mm 3 and 20 ms, respectively. Peak flow, mean velocity, and stroke volume from 4D flow data are more sensitive to changes of temporal than spatial resolution, as opposed to wall shear stress, which is more sensitive to changes in spatial resolution. Magn Reson Med 79:1882-1892, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Laboratory Experiments to Investigate Breakout and Bifurcation of Lava Flows on Mars

NASA Astrophysics Data System (ADS)

Miyamoto, H.; Zimbelman, J. R.; Tokunaga, T.; Tosaka, H.

2001-05-01

Mars Orbiter Camera (MOC) images show that many lava flows on Mars have morphologies quite similar to aa lava flows. Such flows often have many lobes and branches that overlap each other, making a compound flow unit. These features cannot be explained by any simple flow model because longer effusion duration will simply make the flow longer, although actual lavas often will bifurcate to make additonal flow units. Similarly, formation of a lava tube is difficult to predict by a model that does not contain preset conditions for their formation. Treatment of the surface crust is very important to the flow morphology, especially for effusion over a long duration. To understand the effect of a crust on flow morphology, paraffin wax is especially useful in laboratory experiments. In our experiments, a flow on a constant slope typically progresses with a constant width at first. Then, the flow front cools to form a crust, which inhibits the progress of the flow. At that time, the flow sometimes becomes sinuous or ceases its movement. With a sufficient flux after that, uplift of thickness (inflation) can occur. Uplift sometimes attains a sufficient thickening to produce a breakout at the side of the flow, bifurcating to form a new cooling unit. Bifurcated flows do not always follow the main flow (some branches moved several cm away from the initial flow). The bifurcations continue to develop into a complicated flow field, given a sufficiently long duration of effusion. Although the movement of the flow with a surface crust is difficult to predict, our simple analysis suggests that the maximum thickness attained by the inflation (by fluid continuing to enter a stopped flow) before a breakout can occur is roughly estimated by a balance between the overpressure and the crust tensile strength. The maximum extent of a bifurcated flow after a breakout can probably be constrained, which will be a significant goal for future modeling of compound flows.

Keeping the secret: Insights from repeated catchment-scale tracer experiments under transient conditions

NASA Astrophysics Data System (ADS)

Bogner, Christina; Hauhs, Michael; Lange, Holger

2016-04-01

Catchment-level tracer experiments are generally performed to identify site-specific hydrological response functions of the catchment. The existence and uniqueness of these response functions are hardly ever questioned. Here, we report on a series of replicated tracer experiments in two small first-order catchments, G1 (0.6 ha, roofed) and F4 (2.3 ha, without roof) at Gårdsjön in SW Sweden. The soils in both catchments are shallow (< 50 cm) with the bedrock partly visible at the surface. In G1 (irrigated area approximately 1000 m2), tracer experiments were conducted under a roof between 1993 and 2003 during steady state flow conditions. In contrast, in F4 (irrigated area approximately 500 m2) the experiments were done without a roof mostly at transient conditions. The catchment F4 was equipped with a sprinkler system with a watering capacity of around 38-45 m3 day-1. Natural rainfall comes in addition. A bromide tracer solution was injected to groundwater at a single location about 40 m upstream the weir over a period of less than an hour, and was monitored using a set of groundwater tubes and the weir at the outlet over the following 4 days. In addition, discharge was measured. The experiments were repeated each summer from 2007 to 2015. While steady state conditions were guaranteed in G1, steady runoff has been achieved only four times in F4. We investigated tracer recovery rates against cumulated runoff since tracer application. Substantially different transit times and qualitatively different behaviour of the breakthrough curves were observed, even under steady state conditions. In G1, no single system response function could be identified in 5 replicates. Similarly, the catchment response functions in F4 under steady state differed between experiments. However, they remained in a similar range as in G1. Based on these results, we question the identifiability of flow paths and system properties, such as saturated water content or hydrologic transmissivity, at the catchment scale using tracer experiments. Rather, the series demonstrate the utter importance of the initial and boundary conditions which largely determine the response of the system to inert tracer pulses.

The COSIMA experiments and their verification, a data base for the validation of two phase flow computer codes

NASA Astrophysics Data System (ADS)

Class, G.; Meyder, R.; Stratmanns, E.

1985-12-01

The large data base for validation and development of computer codes for two-phase flow, generated at the COSIMA facility, is reviewed. The aim of COSIMA is to simulate the hydraulic, thermal, and mechanical conditions in the subchannel and the cladding of fuel rods in pressurized water reactors during the blowout phase of a loss of coolant accident. In terms of fuel rod behavior, it is found that during blowout under realistic conditions only small strains are reached. For cladding rupture extremely high rod internal pressures are necessary. The behavior of fuel rod simulators and the effect of thermocouples attached to the cladding outer surface are clarified. Calculations performed with the codes RELAP and DRUFAN show satisfactory agreement with experiments. This can be improved by updating the phase separation models in the codes.

Removal of Cr(VI) from Aqueous Environments Using Micelle-Clay Adsorption

PubMed Central

Qurie, Mohannad; Khamis, Mustafa; Manassra, Adnan; Ayyad, Ibrahim; Nir, Shlomo; Scrano, Laura; Bufo, Sabino A.; Karaman, Rafik

2013-01-01

Removal of Cr(VI) from aqueous solutions under different conditions was investigated using either clay (montmorillonite) or micelle-clay complex, the last obtained by adsorbing critical micelle concentration of octadecyltrimethylammonium ions onto montmorillonite. Batch experiments showed the effects of contact time, adsorbent dosage, and pH on the removal efficiency of Cr(VI) from aqueous solutions. Langmuir adsorption isotherm fitted the experimental data giving significant results. Filtration experiments using columns filled with micelle-clay complex mixed with sand were performed to assess Cr(VI) removal efficiency under continuous flow at different pH values. The micelle-clay complex used in this study was capable of removing Cr(VI) from aqueous solutions without any prior acidification of the sample. Results demonstrated that the removal effectiveness reached nearly 100% when using optimal conditions for both batch and continuous flow techniques. PMID:24222757

Experimental investigation of bubbling in particle beds with high solid holdup

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Songbai; Hirahara, Daisuke; Tanaka, Youhei

2011-02-15

A series of experiments on bubbling behavior in particle beds was performed to clarify three-phase flow dynamics in debris beds formed after core-disruptive accident (CDA) in sodium-cooled fast breeder reactors (FBRs). Although in the past, several experiments have been performed in packed beds to investigate flow patterns, most of these were under comparatively higher gas flow rate, which may be not expected during an early sodium boiling period in debris beds. The current experiments were conducted under two dimensional (2D) and three dimensional (3D) conditions separately, in which water was used as liquid phase, and bubbles were generated by injectingmore » nitrogen gas from the bottom of the viewing tank. Various particle-bed parameters were varied, including particle-bed height (from 30 mm to 200 mm), particle diameter (from 0.4 mm to 6 mm) and particle type (beads made of acrylic, glass, alumina and zirconia). Under these experimental conditions, three kinds of bubbling behavior were observed for the first time using digital image analysis methods that were further verified by quantitative detailed analysis of bubbling properties including surface bubbling frequency and surface bubble size under both 2D and 3D conditions. This investigation, which hopefully provides fundamental data for a better understanding and an improved estimation of CDAs in FBRs, is expected to benefit future analysis and verification of computer models developed in advanced fast reactor safety analysis codes. (author)« less

The development of kilohertz planar laser diagnostics for applications in high power turbulent flames

NASA Astrophysics Data System (ADS)

Slabaugh, Carson Daniel

In modern gas-turbine combustors, flame stabilization is achieved by inducing exhaust gas circulation within the flame zone through swirl-induced vortex breakdown. Swirling flows exhibit strong shear regions resulting in high turbulence and effective mixing. In combustion, these flows are characterized by complex unsteady interactions between turbulent flow structures and chemical reactions. Developments in high-resolution, quantitative, experimental measurement techniques must continue to improve fundamental understanding and support modeling efforts. This work describes the development of a gas turbine combustion experiment to support the application of advanced optical measurement techniques in flames operating at realistic engine conditions. Facility requirements are addressed, including instrumentation and control needs for remote operation when working with high energy flows. The methodology employed in the design of the optically-accessible combustion chamber is elucidated, including window considerations and thermal management of the experimental hardware under extremely high heat loads. Experimental uncertainties are also quantified. The stable operation of the experiment is validated using multiple techniques and the boundary conditions are verified. The successful prediction of operating conditions by the design analysis is documented and preliminary data is shown to demonstrate the capability of the experiment to produce high-fidelity datasets for advanced combustion research. Building on this experimental infrastructure, simultaneous measurements of velocity and scalar fields were performed in turbulent nonpremixed flames at gas turbine engine operating conditions using 5 kHz Particle-Image Velocimetry (PIV) and OH Planar Laser Induced Fluorescence (OH-PLIF). The experimental systems and the challenges associated with acquiring useful data at high pressures and high thermal powers are discussed. The quality of the particle scattering images used in the two-dimensional, two-component velocity field measurements is discussed. The effects of high flame luminosity and particle defocusing on the signal-to-noise ratio are discussed. Laser sheet absorption effects, which have been reported to be severe in many previous high pressure OH-PLIF attempts, were not observed to be significant in this work. The time-averaged peak and (spatial) mean signal to noise ratios were 12.7 and 6.3, respectively, at the flame B operating condition; 550 kW total thermal power and 1.0 MPa combustion chamber pressure. Simultaneous 5 kHz PIV and OH-PLIF measurements showed good agreement between single-shot flow-flame interactions, but unresolved, out-of-plane velocity components restricted the interpretation of the temporal context. At a 5 kHz interrogation frequency, the temporal resolution of the measurements was found to be sufficient for only the largest scales within the turbulent flame. The development of an analysis library for the extraction of physical data from highly-resolved planar measurements is also described. The resolution of the measurements, in space and time, is described with respect to the integral scales of the flow. The mean flow structure and its resultant effect on flame behavior is discussed. A method to perform mass-weighted averaging of flow variables was developed for direct comparison of turbulent flow properties between experimental measurements and computations. Conditional statistical sampling and length-scale filtering were used to elucidate details of flow-flame interactions as they pertain to sub-grid modeling in large-eddy simulations.

Event-shape fluctuations and flow correlations in ultra-relativistic heavy-ion collisions

DOE PAGES

Jia, Jiangyong

2014-12-01

I review recent measurements of a large set of flow observables associated with event-shape fluctuations and collective expansion in heavy ion collisions. First, these flow observables are classified and experiment methods are introduced. The experimental results for each type of observables are then presented and compared to theoretical calculations. A coherent picture of initial condition and collective flow based on linear and non-linear hydrodynamic responses is derived, which qualitatively describe most experimental results. I discuss new types of fluctuation measurements that can further our understanding of the event-shape fluctuations and collective expansion dynamics.

Oscillatory/chaotic thermocapillary flow induced by radiant heating

NASA Technical Reports Server (NTRS)

Hsieh, Kwang-Chung; Thompson, Robert L.; Vanzandt, David; Dewitt, Kenneth; Nash, Jon

1994-01-01

The objective of this paper is to conduct ground-based experiments to measure the onset conditions of oscillatory Marangoni flow in laser-heated silicone oil in a cylindrical container. For a single fluid, experimental data are presented using the aspect ratio and the dynamic Bond number. It is found that for a fixed aspect ratio, there seems to be an asymptotic limit of the dynamic Bond number beyond which no onset of flow oscillation could occur. Experimental results also suggested that there could be a lower limit of the aspect ratio below which there is no onset of oscillatory flow.

Experimental investigation of recirculating cells in laminar coaxial jets.

NASA Technical Reports Server (NTRS)

Warpinski, N. R.; Nagib, H. M.; Lavan, Z.

1972-01-01

Utilizing several unique means of introducing smoke into the flow field for careful visualization in addition to hot-wire techniques, experiments are performed in a specially designed facility producing laminar flows up to considerably high Reynolds numbers. Characteristics of the cells and the flow conditions that bring them about are documented by smoke photographs in the Reynolds number velocity ratio plane and the results are compared to previous analytical predictions. The cells are found to fall into three categories with different flow characteristics involving unsteadiness in position, and shear layer instabilities which result in higher mixing with the outer streams.-

The effect of low ventilation rate with elevated bioeffluent concentration on work performance, perceived indoor air quality, and health symptoms.

PubMed

Maula, H; Hongisto, V; Naatula, V; Haapakangas, A; Koskela, H

2017-11-01

The aim of this laboratory experiment was to study the effects of ventilation rate, and related changes in air quality, predominantly bioeffluents, on work performance, perceived indoor air quality, and health symptoms in a typical conditions of modern open-plan office with low material and equipment emissions. In Condition A, outdoor air flow rate of 28.2 l/s person (CO 2 level 540 ppm) was applied and in Condition B, outdoor air flow rate was 2.3 l/s person (CO 2 level 2260 ppm). CO 2 concentration level was used as an indicator of bioeffluents. Performance was measured with seven different tasks which measure different cognitive processes. Thirty-six subjects participated in the experiment. The exposure time was 4 hours. Condition B had a weak negative effect on performance only in the information retrieval tasks. Condition B increased slightly subjective workload and perceived fatigue. No effects on health symptoms were found. The intensity of symptoms was low in both conditions. The experimental condition had an effect on perceived air quality and observed odor intensity only in the beginning of the session. Although the room temperature was controlled in both conditions, the heat was perceived to impair the performance more in Condition B. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Development of Flow Boiling and Condensation Experiment on the International Space Station- Normal and Low Gravity Flow Boiling Experiment Development and Test Results

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Hall, Nancy R.; Hasan, Mohammad M.; Wagner, James D.; May, Rochelle L.; Mackey, Jeffrey R.; Kolacz, John S.; Butcher, Robert L.; Frankenfield, Bruce J.; Mudawar, Issam;

Transient Point Infiltration In The Unsaturated Zone

NASA Astrophysics Data System (ADS)

Buecker-Gittel, M.; Mohrlok, U.

The risk assessment of leaking sewer pipes gets more and more important due to urban groundwater management and environmental as well as health safety. This requires the quantification and balancing of transport and transformation processes based on the water flow in the unsaturated zone. The water flow from a single sewer leakage could be described as a point infiltration with time varying hydraulic conditions externally and internally. External variations are caused by the discharge in the sewer pipe as well as the state of the leakage itself. Internal variations are the results of microbiological clogging effects associated with the transformation processes. Technical as well as small scale laboratory experiments were conducted in order to investigate the water transport from an transient point infiltration. From the technical scale experiment there was evidence that the water flow takes place under transient conditions when sewage infiltrates into an unsaturated soil. Whereas the small scale experiments investigated the hydraulics of the water transport and the associated so- lute and particle transport in unsaturated soils in detail. The small scale experiment was a two-dimensional representation of such a point infiltration source where the distributed water transport could be measured by several tensiometers in the soil as well as by a selective measurement of the discharge at the bottom of the experimental setup. Several series of experiments were conducted varying the boundary and initial con- ditions in order to derive the important parameters controlling the infiltration of pure water from the point source. The results showed that there is a significant difference between the infiltration rate in the point source and the discharge rate at the bottom, that could be explained by storage processes due to an outflow resistance at the bottom. This effect is overlayn by a decreasing water content decreases over time correlated with a decreasing infiltration rate. As expected the initial conditions mainly affects the time scale for the water transport. Additionally, the influence of preferential flow paths on the discharge distribution could be found due to the heterogenieties caused by the filling and compaction process of the sandy soil.

Numerical simulation of swept-wing flows

NASA Technical Reports Server (NTRS)

Reed, Helen L.

1991-01-01

Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.

Nuclear magnetic resonance characterization of the stationary dynamics of partially saturated media during steady-state infiltration flow

NASA Astrophysics Data System (ADS)

Rassi, Erik M.; Codd, Sarah L.; Seymour, Joseph D.

2011-01-01

Flow in porous media and the resultant hydrodynamics are important in fields including but not limited to the hydrology, chemical, medical and petroleum industries. The observation and understanding of the hydrodynamics in porous media are critical to the design and optimal utilization of porous media, such as those seen in trickle-bed reactors, medical filters, subsurface flows and carbon sequestration. Magnetic resonance (MR) provides for a non-invasive technique that can probe the hydrodynamics on pore and bulk scale lengths; many previous works have characterized fully saturated porous media, while rapid MR imaging (MRI) methods in particular have previously been applied to partially saturated flows. We present time- and ensemble-averaged MR measurements to observe the effects on a bead pack partially saturated with air under flowing water conditions. The 10 mm internal diameter bead pack was filled with 100 μm borosilicate glass beads. Air was injected into the bead pack as water flowed simultaneously through the sample at 25 ml h-1. The initial partially saturated state was characterized with MRI density maps, free induction decay (FID) experiments, propagators and velocity maps before the water flow rate was increased incrementally from 25 to 500 ml h-1. After the maximum flow rate of 500 ml h-1, the MRI density maps, FID experiments, propagators and velocity maps were repeated and compared to the data taken before the maximum flow rate. This work shows that a partially saturated single-phase flow has global flow dynamics that return to characteristic flow statistics once a steady-state high flow rate has been reached. This high flow rate pushed out a significant amount of the air in the bead pack and caused the return of a preferential flow pattern. Velocity maps indicated that local flow statistics were not the same for the before and after blow out conditions. It has been suggested and shown previously that a flow pattern can return to similar statistics if the preceding flow history is similar.

Water velocity tolerance in tadpoles of the foothill yellow-legged frog (Rana boylii): Swimming performance, growth, and survival

Treesearch

S. Kupferberg; A. Lind; V. Thill; S. Yarnell

2011-01-01

We explored the effects of large magnitude flow fluctuations in rivers with dams, commonly referred to as pulsed flows, on tadpoles of the lotic-breeding Foothill Yellow-legged Frog, Rana boylii. We quantified the velocity conditions in habitats occupied by tadpoles and then conducted experiments to assess the tolerance to values at the upper limit...

Testing of a "smart-pebble" for measuring particle transport statistics

NASA Astrophysics Data System (ADS)

Kitsikoudis, Vasileios; Avgeris, Loukas; Valyrakis, Manousos

2017-04-01

This paper presents preliminary results from novel experiments aiming to assess coarse sediment transport statistics for a range of transport conditions, via the use of an innovative "smart-pebble" device. This device is a waterproof sphere, which has 7 cm diameter and is equipped with a number of sensors that provide information about the velocity, acceleration and positioning of the "smart-pebble" within the flow field. A series of specifically designed experiments are carried out to monitor the entrainment of a "smart-pebble" for fully developed, uniform, turbulent flow conditions over a hydraulically rough bed. Specifically, the bed surface is configured to three sections, each of them consisting of well packed glass beads of slightly increasing size at the downstream direction. The first section has a streamwise length of L1=150 cm and beads size of D1=15 mm, the second section has a length of L2=85 cm and beads size of D2=22 mm, and the third bed section has a length of L3=55 cm and beads size of D3=25.4 mm. Two cameras monitor the area of interest to provide additional information regarding the "smart-pebble" movement. Three-dimensional flow measurements are obtained with the aid of an acoustic Doppler velocimeter along a measurement grid to assess the flow forcing field. A wide range of flow rates near and above the threshold of entrainment is tested, while using four distinct densities for the "smart-pebble", which can affect its transport speed and total momentum. The acquired data are analyzed to derive Lagrangian transport statistics and the implications of such an important experiment for the transport of particles by rolling are discussed. The flow conditions for the initiation of motion, particle accelerations and equilibrium particle velocities (translating into transport rates), statistics of particle impact and its motion, can be extracted from the acquired data, which can be further compared to develop meaningful insights for sediment transport mechanics from a Lagrangian perspective and at unprecedented temporal detail and accuracy.

Wire Insulation Flammability Experiment: USML-1 One Year Post Mission Summary

NASA Technical Reports Server (NTRS)

Greenberg, Paul S.; Sacksteder, Kurt R.; Kashiwagi, Takashi

1994-01-01

Herein we report the results from the Wire Insulation Flammability (WIF) Experiment performed in the Glovebox Facility on the USML-1 mission. This experiment explored various aspects of electrically induced fire scenarios in a reduced gravity environment. Under quiescent microgravity conditions, heat and mass transfer are dominated by diffusive and radiative transport; while in normal-gravity buoyancy induced convection often dominates. Of considerable scientific and practical interest is the intermediate situation of combustion occurring in the presence of imposed gas flows, with lower characteristic velocities than those induced by buoyancy in noma1 gravity. Two distinct cases naturally arise: flow direction opposed to, or concurrent with, the flame spread direction. Two tests of each kind were conducted in the WIF experiment, providing the first controlled demonstration of flame spreading in forced convection ever conducted in space. Four test modules were flown. The wire insulation, 1.5 mm in diameter, was polyethylene, extruded onto nichrome wire. Temperatures of the wh3 cores and insulation heated in quiescent and flowing environments were measured. Video and still-camera images of the samples, burning in air flowing at approximately 10 cm/sec, were recorded to obtain flame characteristics including spread rate, structure and temperature. Flame spread rates in concurrent flow were approximately twice those in opposed flow. In concurrent and opposed flow regimes, the spreading flames stabilized around a bead of molten insulation material, within which bubble nucleation was observed. An ignition attempt without flow mated a quiescent cloud of vaporized fuel which ignited dramatically yet failed to sustain normal flame spread. Finally, all tests produced substantial soot agglomerates, particularly the concurrent flow tests; and the collected soot has a morphology very distinct from soot formed in normal gravity flames. Several unexpected and unique microgravity combustion phenomena were observed.

Computer aided approximation of flow rate through systemic-pulmonary arterial shunts (SPAS).

PubMed

Vennemann, Peter; Montag, Michael; Peters, Franz; Merzkirch, Wolfgang

2012-02-22

The discrimination of flow rates through bronchial arteries that are affected by pathological SPAS today still happens solely qualitatively. A reproducible quantification of flow rates, however, would enable the comprehension of phenomena like the intensified shunt perfusion seen in cases of chronic inflammations or the characterization of SPAS that may cause cardiovascular problems. A computational program is developed, that allows the modeling of individual bronchial arteries on the basis of the information provided by angiography. Angiographic images are available from the standard clinical assessment of SPAS. The flow through continuous and geometrically measurable vessel segments and SPAS is given by the law of Hagen-Poiseuille. The discharge through healthy branches is calculated by means of allometric scaling laws. The simulation results are verified by flow experiments in artificial vessel networks made of glass and PE tubing. The experimental set-up mimics realistic, pulsating pressure and flow conditions. When applied to the artificial vessel networks, the model described herein provides results for the volumetric flow rate that differ from values measured in laboratory experiments by <6%. The computer model is also applied to real angiographic images. Due to inaccuracies during the deduction of the geometry and due to necessary simplifications of the model, we expect significant deviations between calculated and real flow rates in bronchial systems. Nevertheless, the presented method enables the physician to objectively estimate the order of magnitude of volumetric flow through individual SPAS fairly independently from his experience and without the need of measurements additional to the mandatory angiography.

Influence of neighboring adherent cells on laminar flow induced shear stress in vitro—A systematic study

PubMed Central

Djukelic, Mario; Westerhausen, Christoph

2017-01-01

Cells experience forces if subjected to laminar flow. These forces, mostly of shear force character, are strongly dependent not only on the applied flow field itself but also on hydrodynamic effects originating from neighboring cells. This particularly becomes important for the interpretation of data from in vitro experiments in flow chambers without confluent cell layers. By employing numerical Finite Element Method simulations of such assemblies of deformable objects under shear flow, we investigate the occurring stress within elastic adherent cells and the influence of neighboring cells on these quantities. For this, we simulate single and multiple adherent cells of different shapes fixed on a solid substrate under laminar flow parallel to the substrate for different velocities. We determine the local stress within the cells close to the cell-substrate-interface and the overall stress of the cells by surface integration over the cell surface. Comparing each measurand in the case of a multiple cell situation with the corresponding one of single cells under identical conditions, we introduce a dimensionless influence factor. The systematic variation of the distance and angle between cells, where the latter is with respect to the flow direction, flow velocity, Young's modulus, cell shape, and cell number, enables us to describe the actual influence on a cell. Overall, we here demonstrate that the cell density is a crucial parameter for all studies on flow induced experiments on adherent cells in vitro. PMID:28798851

[Research about effect of spray drying conditions on hygroscopicity of spray dry powder of gubi compound's water extract and its mechanism].

PubMed

Zong, Jie; Shao, Qi; Zhang, Hong-Qing; Pan, Yong-Lan; Zhu, Hua-Xu; Guo, Li-Wei

2014-02-01

To investigate moisture content and hygroscopicity of spray dry powder of Gubi compound's water extract obtained at different spray drying conditions and laying a foundation for spray drying process of Chinese herbal compound preparation. In the paper, on the basis of single-factor experiments, the author choose inlet temperature, liquid density, feed rate, air flow rate as investigated factors. The experimental absorption rate-time curve and scanning electron microscopy results showed that under different spray drying conditions the spray-dried powders have different morphology and different adsorption process. At different spray-dried conditions, the morphology and water content of the powder is different, these differences lead to differences in the adsorption process, at the appropriate inlet temperature and feed rate with a higher sample density and lower air flow rate, in the experimental system the optimum conditions is inlet temperature of 150 degrees C, feed density of 1.05 g x mL(-1), feed rate of 20 mL x min(-1) air flow rate of 30 m3 x h(-1).

Application of chemical oxidation to remediate HCH-contaminated soil under batch and flow through conditions.

PubMed

Usman, Muhammad; Tascone, Oriane; Rybnikova, Victoria; Faure, Pierre; Hanna, Khalil

2017-06-01

This is the first study describing the chemical oxidation of hexachlorocyclohexanes (HCHs) in contaminated soil under water saturated and unsaturated flow through conditions. Soil contaminated with β-HCH (45 mg kg -1 ) and γ-HCH (lindane, 25 mg kg -1 ) was sampled from former lindane waste storage site. Efficiency of following treatments was tested at circumneutral pH: H 2 O 2 alone, H 2 O 2 /Fe II , Na 2 S 2 O 8 alone, Na 2 S 2 O 8 /Fe II , and KMnO 4 . Experimental conditions (oxidant dose, liquid/solid ratio, and soil granulometry) were first optimized in batch experiments. Obtained results revealed that increasing dose of H 2 O 2 improved the oxidation efficiency while in Na 2 S 2 O 8 system, maximum HCHs were removed at 300 mM. However, oxidation efficiency was slightly improved by Fe II -activation. Increasing the solid/liquid ratio decreased HCH removal in soil samples crushed to 500 μm while an opposite trend was observed for 2-mm samples. Dynamic column experiments showed that oxidation efficiency followed the order KMnO 4  > Na 2 S 2 O 8 /Fe II  > Na 2 S 2 O 8 whatever the flow condition, whereas the removal extent declined at higher flow rate (e.g., ~50% by KMnO 4 at 0.5 mL/min as compared to ~30% at 2 mL/min). Both HCH removal and oxidant decomposition extents were found higher in saturated columns than the unsaturated ones. While no significant change in relative abundance of soil mineral constituents was observed before and after chemical oxidation, more than 60% of extractable organic matter was lost after chemical oxidation, thereby underscoring the non-selective behavior of chemical oxidation in soil. Due to the complexity of soil system, chemical oxidation has rarely been reported under flow through conditions, and therefore our findings will have promising implications in developing remediation techniques under dynamic conditions closer to field applications.

Medication and volume delivery by gravity-driven micro-drip intravenous infusion: potential variations during "wide-open" flow.

PubMed

Pierce, Eric T; Kumar, Vikram; Zheng, Hui; Peterfreund, Robert A

2013-03-01

Gravity-driven micro-drip infusion sets allow control of medication dose delivery by adjusting drops per minute. When the roller clamp is fully open, flow in the drip chamber can be a continuous fluid column rather than discrete, countable, drops. We hypothesized that during this "wide-open" state, drug delivery becomes dependent on factors extrinsic to the micro-drip set and is therefore difficult to predict. We conducted laboratory experiments to characterize volume delivery under various clinically relevant conditions of wide-open flow in an in vitro laboratory model. A micro-drip infusion set, plugged into a bag of normal saline, was connected to a high-flow stopcock at the distal end. Vertically oriented IV catheters (gauges 14-22) were connected to the stopcock. The fluid meniscus height in the bag was fixed (60-120 cm) above the outflow point. The roller clamp on the infusion set was in fully open position for all experiments resulting in a continuous column of fluid in the drip chamber. Fluid volume delivered in 1 minute was measured 4 times with each condition. To model resistive effects of carrier flow, volumetric infusion pumps were used to deliver various flow rates of normal saline through a carrier IV set into which a micro-drip infusion was "piggybacked." We also compared delivery by micro-drip infusion sets from 3 manufacturers. The volume of fluid delivered by gravity-driven infusion under wide-open conditions (continuous fluid column in drip chamber) varied 2.9-fold (95% confidence interval, 2.84-2.96) depending on catheter size and fluid column height. Total model resistance of the micro-drip with stopcock and catheter varied with flow rate. Volume delivered by the piggybacked micro-drip decreased up to 29.7% ± 0.8% (mean ± SE) as the carrier flow increased from 0 to 1998 mL/min. Delivery characteristics of the micro-drip infusion sets from 3 different manufacturers were similar. Laboratory simulation of clinical situations with gravity-driven micro-drip infusion sets under wide-open flow conditions revealed that infusion rate (drug and/or volume delivery) can vary widely depending on extrinsic factors including catheter size, fluid column height, and carrier flow. The variable resistance implies nonlaminar flow in the micro-drip model that cannot be easily predicted mathematically. These findings support the use of mechanical pumps instead of gravity-driven micro-drips to enhance the precision and safety of IV infusions, especially for vasoactive drugs.

Predictions of Critical Heat Flux in Annular Pipes with TRACEv4.160 code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jasiulevicius, Audrius; Macian-Juan, Rafael

2006-07-01

This paper presents the assessment of TRACE (version v4.160) against the Critical Heat Flux (CHF) experiments in annular tubes performed at the Royal Institute of Technology (KTH) in Stockholm, Sweden. The experimental database includes data for coolant mass fluxes between 250 and 2500 kg/m{sup 2}s and inlet subcooling of 10 and 40 K at a pressure of 70 bar. The work presented in this paper supplements the calculations of single round tube experiments carried out earlier and provides a broader scope of validated geometries. In addition to the Biasi and CISE-GE CHF correlations available in the code, a number ofmore » experimental points at low flow conditions are available for the annular geometry experiments, which also permitted the assessment of the Biasi/Zuber CHF correlation used in TRACE v4.160 for low flow conditions. Experiments with different axial power distribution were simulated and the effects of the axial power profile and the coolant inlet subcooling on the TRACE predictions were investigated. The results of this work show that the Biasi/Zuber correlation provides good estimation of the CHF at 70 bar, and, for the same conditions, the simulation of the annular experiments resulted in the calculation of lower CHF values compared to single-tube experiments. The analysis of the performance of the standard TRACE CHF correlations shows that the CISE-GE correlation yields critical qualities (quality at CHF) closer to the experimental values at 70 bar than the Biasi correlation for annular flow conditions. Regarding the power profile, the results of the TRACE calculations seem to be very sensitive to its shape, since, depending on the profile, different accuracies in the predictions were noted while other system conditions remained constant. The inlet coolant subcooling was also an important factor in the accuracy of TRACE CHF predictions. Thus, an increase in the inlet subcooling led to a clear improvement in the estimation of the critical quality with both Biasi and CISE-GE correlations. To complement the work, three additional CHF correlations were implemented in TRACE v4.160, namely the Bowring, Tong W-3 and Levitan-Lantsman CHF models, in order to assess the applicability of these correlations to simulate the CHF in annular tubes. The improvement of CHF predictions for low coolant mass flows (up to 1500 kg/m{sup 2}s) is noted when applying Bowring CHF correlation. However, the increase in the inlet subcooling increases the error in predicted critical quality with the Bowring correlation. The Levitan-Lantsman and Tong-W-3 correlations provide results similar to the Biasi model. Therefore, the most correct CHF predictions among the investigated correlations were obtained using CISE-GE model in the standard TRAC v4.160 code. (authors)« less

Reactor transient control in support of PFR/TREAT TUCOP experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrows, D.R.; Larsen, G.R.; Harrison, L.J.

1984-01-01

Unique energy deposition and experiment control requirements posed bythe PFR/TREAT series of transient undercooling/overpower (TUCOP) experiments resulted in equally unique TREAT reactor operations. New reactor control computer algorithms were written and used with the TREAT reactor control computer system to perform such functions as early power burst generation (based on test train flow conditions), burst generation produced by a step insertion of reactivity following a controlled power ramp, and shutdown (SCRAM) initiators based on both test train conditions and energy deposition. Specialized hardware was constructed to simulate test train inputs to the control computer system so that computer algorithms couldmore » be tested in real time without irradiating the experiment.« less

Fluid flow analysis and vertical gradient freeze crystal growth in a travelling magnetic field

NASA Astrophysics Data System (ADS)

Lantzsch, R.; Grants, I.; Galindo, V.; Patzold, O.; Gerbeth, G.; Stelter, M.; Croll, A.

2006-12-01

In bulk crystal growth of semiconductors the concept of remote flow control by means of alternating magnetic fields has attracted considerable interest (see, e.g., te{1,2,3,4,5,6}). In this way the melt flow can be tailored for growth under optimised conditions to improve the crystal properties and/or the growth yield. A promising option is to apply an axially travelling magnetic wave to the melt (Travelling Magnetic Field - TMF). It introduces a mainly axial Lorentz force, which leads to meridional flow patterns. In recent numerical studies te{3}, te{6} the TMF has been recognised to be a versatile and efficient tool to control the heat and mass transport in the melt. For the Vertical Bridgman/Vertical Gradient Freeze (VB/VGF) growth, the beneficial effect of an adequately adjusted TMF-induced flow was clearly demonstrated in te{6} in terms of the reduction of thermal shear stress at the solid-liquid interface. In this paper, we present experimental and numerical results on the TMF driven convection in an isothermal model fluid as well as first VGF-TMF crystal growth experiments. The model investigations are focused on the transition from laminar to instationary flow conditions that should be avoided in crystal growth applications. The VGF experiments were aimed at growing Ga doped germanium single crystals under the influence of the travelling field in a newly developed VGF-TMF equipment. Figs 4, Refs 10.

Sheet flow and suspended sediment due to wave groups in a large wave flume

USGS Publications Warehouse

Dohmen-Janssen, C. M.; Hanes, D.M.

2005-01-01

A series of sand bed experiments was carried out in the Large Wave Flume in Hannover, Germany as a component of the SISTEX99 experiment. The experiments focussed on the dynamic sediment response due to wave group forcing over a flat sand bed in order to improve understanding of cross-shore sediment transport mechanisms and determine sediment concentrations, fluxes and net transport rates under these conditions. Sediment concentrations were measured within the sheet flow layer (thickness in the order of 10 grain diameters) and in the suspension region (thickness in the order of centimetres). Within the sheet flow layer, the concentrations are highly coherent with the instantaneous near-bed velocities due to each wave within the wave group. However, in the suspension layer concentrations respond much more slowly to changes in near-bed velocity. At several centimetres above the bed, the suspended sediment concentrations vary on the time scale of the wave group, with a time delay relative to the peak wave within the wave group. The thickness of the sheet flow changes with time. It is strongly coherent with the wave forcing, and is not influenced by the history or sequence of the waves within the group. The velocity of the sediment was also measured within the sheet flow layer some of the time (during the larger wave crests of the group), and the velocity of the fluid was measured at several cm above the sheet flow layer. The grain velocity and concentration estimates can be combined to estimate the sediment flux. The estimates were found to be consistent with previous measurements under monochromatic waves. Under these conditions, without any significant mean current, the sediment flux within the sheet flow layer was found to greatly exceed the sediment flux in the suspension layer. As a result, net transport rates under wave groups are similar to those under monochromatic waves. ?? 2004 Elsevier Ltd. All rights reserved.

Scattering matrix elements of biological particles measured in a flow through system: theory and practice.

PubMed

Sloot, P M; Hoekstra, A G; van der Liet, H; Figdor, C G

1989-05-15

Light scattering techniques (including depolarization experiments) applied to biological cells provide a fast nondestructive probe that is very sensitive to small morphological differences. Until now quantitative measurement of these scatter phenomena were only described for particles in suspension. In this paper we discuss the symmetry conditions applicable to the scattering matrices of monodisperse biological cells in a flow cytometer and provide evidence that quantitative measurement of the elements of these scattering matrices is possible in flow through systems. Two fundamental extensions to the theoretical description of conventional scattering experiments are introduced: large cone integration of scattering signals and simultaneous implementation of the localization principle to account for scattering by a sharply focused laser beam. In addition, a specific calibration technique is proposed to account for depolarization effects of the highly specialized optics applied in flow through equipment.

Erosion in radial inflow turbines. Volume 2: Balance of centrifugal and radial drag forces on erosive particles

NASA Technical Reports Server (NTRS)

Clevenger, W. B., Jr.; Tabakoff, W.

1974-01-01

The particle motion in two-dimensional free and forced inward flowing vortices is considered. A particle in such a flow field experiences a balance between the aerodynamic drag forces that tend to drive erosive particles toward the axis, and centrifugal forces that prevent these particles from traveling toward the axis. Results predict that certain sizes of particles will achieve a stable orbit about the turbine axis in the inward flowing free vortex. In this condition, the radial drag force is equal to the centrifugal force. The sizes of particles that will achieve a stable orbit is shown to be related to the gas flow velocity diagram at a particular radius. A second analysis yields a description of particle sizes that will experience a centrifugal force that is greater than the radial component of the aerodynamic drag force for a more general type of particle motion.

Feasibility study of hidden flow imaging based on laser speckle technique using multiperspectives contrast images

NASA Astrophysics Data System (ADS)

Abookasis, David; Moshe, Tomer

2014-11-01

This paper demonstrates the insertion of lens array in the front of a CCD camera in a laser speckle imaging (LSI) like-technique to acquire multiple speckle reflectance projections for imaging blood flow in an intact biological tissue. In some of LSI applications, flow imaging is obtained by thinning or removing of the upper tissue layers to access blood vessels. In contrast, with the proposed approach flow imaging can be achieved while the tissue is intact. In the system, each lens from an hexagonal lens array observed the sample from slightly different perspectives and captured with a CCD camera. In the computer, these multiview raw images are converted to speckled contrast maps. Then, a self-deconvolution shift-and-add algorithm is employed for processing yields high contrast flow information. The method is experimentally validated first with a plastic tube filled with scattering liquid running at different controlled flow rates hidden in a biological tissue and then extensively tested for imaging of cerebral blood flow in an intact rodent head experience different conditions. A total of fifteen mice were used in the experiments divided randomly into three groups as follows: Group 1 (n=5) consisted of injured mice experience hypoxic ischemic brain injury monitored for ~40 min. Group 2 (n=5) injured mice experience anoxic brain injury monitored up to 20 min. Group 3 (n=5) experience functional activation monitored up to ~35 min. To increase tissue transparency and the penetration depth of photons through head tissue layers, an optical clearing method was employed. To our knowledge, this work presents for the first time the use of lens array in LSI scheme.

Remedial Amendment Delivery near the Water Table Using Shear Thinning Fluids: Experiments and Numerical Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oostrom, Martinus; Truex, Michael J.; Vermeul, Vincent R.

2014-08-19

The use of shear thinning fluids (STFs) containing xanthan is a potential enhancement for emplacing a solute amendment near the water table and within the capillary fringe. Most research to date related to STF behavior has involved saturated and confined conditions. A series of flow cell experiments were conducted to investigate STF emplacement in variable saturated homogeneous and layered heterogeneous systems. Besides flow visualization using dyes, amendment concentrations and pressure data were obtained at several locations. The experiments showed that injection of STFs considerably improved the subsurface distribution near the water table by mitigating preferential flow through higher permeability zonesmore » compared to no-polymer injections. The phosphate amendment migrated with the xanthan SFT without retardation. Despite the high viscosity of the STF, no excessive mounding or preferential flow were observed in the unsaturated zone. The STOMP simulator was able to predict the experimentally observed fluid displacement and amendment concentrations reasonably well. Cross flow between layers could be interpreted as the main mechanism to transport STFs into lower permeability layers based on the observed pressure gradient and concentration data in layers of differing hydraulic conductivity.« less

Feasibility study: Atmospheric general circulation experiment, volume 1

NASA Technical Reports Server (NTRS)

Homsey, R. J. (Editor)

1981-01-01

The atmospheric general circulation experiment (AGCE) uses a rotating fluid flow cell assembly. The key technical areas affecting the feasibility of the design and operation of the AGCE are investigated. The areas investigated include materials for the flow cell assembly, thermal design, high voltage power supply design, effective retrieval and handling of experiment data and apparatus configuration. Several materials, DMSO and m-tolunitrile, were selected as candidate fluids for the flow cell principally for their high dielectric constant which permits the high voltage power supply design to be held to 15 kV and still simulate terrestrial gravity. Achievement of a low dissipation factor in the fluid to minimize internal heating from the applied electrical field depends strongly on purification and handling procedures. The use of sapphire as the outer hemisphere for the flow cell provides excellent viewing conditions without a significant impact on attaining the desired thermal gradients. Birefringent effects from sapphire can be held to acceptably low limits. Visualization of flow fluid is achieved through the motion of a dot matrix formed by photochromic dyes. Two dyes found compatible with the candidate fluids are spiropyran and triarylmethane. The observation of the dot motion is accomplished using a flying spot scanner.

Effects of confinement, geometry, inlet velocity profile, and Reynolds number on the asymmetry of opposed-jet flows

NASA Astrophysics Data System (ADS)

Ansari, Abtin; Chen, Kevin K.; Burrell, Robert R.; Egolfopoulos, Fokion N.

2018-04-01

The opposed-jet counterflow configuration is widely used to measure fundamental flame properties that are essential targets for validating chemical kinetic models. The main and key assumption of the counterflow configuration in laminar flame experiments is that the flow field is steady and quasi-one-dimensional. In this study, experiments and numerical simulations were carried out to investigate the behavior and controlling parameters of counterflowing isothermal air jets for various nozzle designs, Reynolds numbers, and surrounding geometries. The flow field in the jets' impingement region was analyzed in search of instabilities, asymmetries, and two-dimensional effects that can introduce errors when the data are compared with results of quasi-one-dimensional simulations. The modeling involved transient axisymmetric numerical simulations along with bifurcation analysis, which revealed that when the flow field is confined between walls, local bifurcation occurs, which in turn results in asymmetry, deviation from the one-dimensional assumption, and sensitivity of the flow field structure to boundary conditions and surrounding geometry. Particle image velocimetry was utilized and results revealed that for jets of equal momenta at low Reynolds numbers of the order of 300, the flow field is asymmetric with respect to the middle plane between the nozzles even in the absence of confining walls. The asymmetry was traced to the asymmetric nozzle exit velocity profiles caused by unavoidable imperfections in the nozzle assembly. The asymmetry was not detectable at high Reynolds numbers of the order of 1000 due to the reduced sensitivity of the flow field to boundary conditions. The cases investigated computationally covered a wide range of Reynolds numbers to identify designs that are minimally affected by errors in the experimental procedures or manufacturing imperfections, and the simulations results were used to identify conditions that best conform to the assumptions of quasi-one-dimensional modeling.

Experiments on Pool-riffle Sequences with Multi-fractional Sediment Bed During Floods

NASA Astrophysics Data System (ADS)

Rodriguez, J. F.; Vahidi, E.; Bayat, E.; de Almeida, G. A. M.; Saco, P. M.

2017-12-01

The morphodynamics of pools and riffles has been the subject of research for over a century and has more recently attracted intense attention for their central role in providing habitat diversity conditions, both in terms of flow and substrate. Initial efforts to explain the long-term stability of the pool-riffle (PR) sequences (often referred to as self-maintenance) focused almost exclusively on cross sectional flow characteristics (either average or near bed velocity or shear stress), using episodic shifts in higher shear stress or velocities from riffles to pools during floods (i.e. reversal conditions) as an indication of the long-term self-maintenance of the structures.. However, less attention has been paid to the interactions of flow unsteadiness, sediment supply and sedimentological contrasts as the drivers for maintaining PR sequences. Here we investigate these effects through laboratory experiments on a scaled-down PR sequence of an existing gravel bed river. Froude similitude and equality of Shields' number were applied to scale one- to four-year recurrence flood events and sediment size distributions, respectively. We conducted experiments with different hydrographs and different sedimentological conditions. In each experiment we continuously measured velocities and shear stresses (using acoustic velocity profilers) bed levels (using a bed profiler) and bed grain size distribution (using an automatic digital technique on the painted bed sediments) during the hydrographs. Our results show that the most important factors for self-maintenance were the sediment bed composition, the level of infilling of the pool and the sediment supply grainsize distribution. These results highlight the need to consider the time varying sedimentological characteristics of a PR sequence to assess its capacity for self-maintenance.

Computation of Turbulent Recirculating Flow in Channels, and for Impingement Cooling

NASA Technical Reports Server (NTRS)

Chang, Byong Hoon

1992-01-01

Fully elliptic forms of the transport equations have been solved numerically for two flow configurations. The first is turbulent flow in a channel with transverse rectangular ribs, and the second is impingement cooling of a plane surface. Both flows are relevant to proposed designs for active cooling of hypersonic vehicles using supercritical hydrogen as the coolant. Flow downstream of an abrupt pipe expansion and of a backward-facing step were also solved with various near-wall turbulence models as benchmark problems. A simple form of periodicity boundary condition was used for the channel flow with transverse rectangular ribs. The effects of various parameters on heat transfer in channel flow with transverse ribs and in impingement cooling were investigated using the Yap modified Jones and Launder low Reynolds number k-epsilon turbulence model. For the channel flow, predictions were in adequate agreement with experiment for constant property flow, with the results for friction superior to those for heat transfer. For impingement cooling, the agreement with experiment was generally good, but the results suggest that improved modelling of the dissipation rate of turbulence kinetic energy is required in order to obtain improved heat transfer prediction, especially near the stagnation point. The k-epsilon turbulence model was used to predict the mean flow and heat transfer for constant and variable property flows. The effect of variable properties for channel flow was investigated using the same turbulence model, but comparison with experiment yielded no clear conclusions. Also, the wall function method was modified for use in the variable properties flow with a non-adiabatic surface, and an empirical model is suggested to correctly account for the behavior of the viscous sublayer with heating.

Flow-induced phase separation of active particles is controlled by boundary conditions.

PubMed

Thutupalli, Shashi; Geyer, Delphine; Singh, Rajesh; Adhikari, Ronojoy; Stone, Howard A

2018-05-22

Active particles, including swimming microorganisms, autophoretic colloids, and droplets, are known to self-organize into ordered structures at fluid-solid boundaries. The entrainment of particles in the attractive parts of their spontaneous flows has been postulated as a possible mechanism underlying this phenomenon. Here, combining experiments, theory, and numerical simulations, we demonstrate the validity of this flow-induced ordering mechanism in a suspension of active emulsion droplets. We show that the mechanism can be controlled, with a variety of resultant ordered structures, by simply altering hydrodynamic boundary conditions. Thus, for flow in Hele-Shaw cells, metastable lines or stable traveling bands can be obtained by varying the cell height. Similarly, for flow bounded by a plane, dynamic crystallites are formed. At a no-slip wall, the crystallites are characterized by a continuous out-of-plane flux of particles that circulate and re-enter at the crystallite edges, thereby stabilizing them. At an interface where the tangential stress vanishes, the crystallites are strictly 2D, with no out-of-plane flux. We rationalize these experimental results by calculating, in each case, the slow viscous flow produced by the droplets and the long-ranged, many-body active forces and torques between them. The results of numerical simulations of motion under the action of the active forces and torques are in excellent agreement with experiments. Our work elucidates the mechanism of flow-induced phase separation in active fluids, particularly active colloidal suspensions, and demonstrates its control by boundaries, suggesting routes to geometric and topological phenomena in an active matter.

Comparison of Mixing Characteristics for Several Fuel Injectors on an Open Plate and in a Ducted Flowpath Configuration at Hypervelocity Flow Conditions

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Shenoy, Rajiv R.; Passe, Bradley J.; Baurle, Robert A.; Drummond, J. Philip

2017-01-01

In order to reduce the cost and complexity associated with fuel injection and mixing experiments for high-speed flows, and to further enable optical access to the test section for nonintrusive diagnostics, the Enhanced Injection and Mixing Project (EIMP) utilizes an open flat plate configuration to characterize inert mixing properties of various fuel injectors for hypervelocity applications. The experiments also utilize reduced total temperature conditions to alleviate the need for hardware cooling. The use of "cold" flows and non-reacting mixtures for mixing experiments is not new, and has been extensively utilized as a screening technique for scramjet fuel injectors. The impact of reduced facility-air total temperature, and the use of inert fuel simulants, such as helium, on the mixing character of the flow has been assessed in previous numerical studies by the authors. Mixing performance was characterized for three different injectors: a strut, a ramp, and a flushwall. The present study focuses on the impact of using an open plate to approximate mixing in the duct. Toward this end, Reynolds-averaged simulations (RAS) were performed for the three fuel injectors in an open plate configuration and in a duct. The mixing parameters of interest, such as mixing efficiency and total pressure recovery, are then computed and compared for the two configurations. In addition to mixing efficiency and total pressure recovery, the combustion efficiency and thrust potential are also computed for the reacting simulations.

Estimated flows of gases and carbon within CEEF ecosystem composed of human, crops and goats

NASA Astrophysics Data System (ADS)

Tako, Y.; Komatsubara, O.; Honda, G.; Arai, R.; Nitta, K.

The Closed Ecology Experiment Facilities (CEEF) can be used as a test bed for Controlled Ecological Life Support Systems (CELSS), because technologies developed for the CEEF system facilitate self-sufficient material circulation necessary for long term missions such as Lunar and Mars exploration. In the experiment conducted under closed condition in FY2003, rice and soybeans were cultivated sequentially in two chambers and a chamber, each having a cultivation area of 30 m2 and floor area of 43 m2, inside the Plantation Module with artificial lighting of the CEEF. In the chamber having a cultivation area of 60 m2 and floor area of 65 m2, inside the Plantation Module with natural and artificial lighting, peanuts and safflowers were also cultivated. Stable transplant (or seeding) and harvest of each crop were maintained during a month. Flows of CO2, O2 and carbon to and from the crops were analyzed during the stable cultivation period. Simulated works and stay in the CEEF lasting five days were conducted two times under ventilating condition in FY2003. Gas exchange of human was estimated using heart rate data collected during the experiments and correlation between gas exchange rate and heart rate. Gas exchange rate and carbon balance of female goats were determined using an open-flow measurement system with a gastight chamber. From these results, flows of gases and carbon in the CEEF were discussed.

Development of Electrical Capacitance Sensors for Accident Tolerant Fuel (ATF) Testing at the Transient Reactor Test (TREAT) Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Maolong; Ryals, Matthew; Ali, Amir

2016-08-01

A variety of instruments are being developed and qualified to support the Accident Tolerant Fuels (ATF) program and future transient irradiations at the Transient Reactor Test (TREAT) facility at Idaho National Laboratory (INL). The University of New Mexico (UNM) is working with INL to develop capacitance-based void sensors for determining the timing of critical boiling phenomena in static capsule fuel testing and the volume-averaged void fraction in flow-boiling in-pile water loop fuel testing. The static capsule sensor developed at INL is a plate-type configuration, while UNM is utilizing a ring-type capacitance sensor. Each sensor design has been theoretically and experimentallymore » investigated at INL and UNM. Experiments are being performed at INL in an autoclave to investigate the performance of these sensors under representative Pressurized Water Reactor (PWR) conditions in a static capsule. Experiments have been performed at UNM using air-water two-phase flow to determine the sensitivity and time response of the capacitance sensor under a flow boiling configuration. Initial measurements from the capacitance sensor have demonstrated the validity of the concept to enable real-time measurement of void fraction. The next steps include designing the cabling interface with the flow loop at UNM for Reactivity Initiated Accident (RIA) ATF testing at TREAT and further characterization of the measurement response for each sensor under varying conditions by experiments and modeling.« less

Experimental feasibility of investigating acoustic waves in Couette flow with entropy and pressure gradients

NASA Technical Reports Server (NTRS)

Parrott, Tony L.; Zorumski, William E.; Rawls, John W., Jr.

1990-01-01

The feasibility is discussed for an experimental program for studying the behavior of acoustic wave propagation in the presence of strong gradients of pressure, temperature, and flow. Theory suggests that gradients effects can be experimentally observed as resonant frequency shifts and mode shape changes in a waveguide. A convenient experimental geometry for such experiments is the annular region between two co-rotating cylinders. Radial temperature gradients in a spinning annulus can be generated by differentially heating the two cylinders via electromagnetic induction. Radial pressure gradients can be controlled by varying the cylinder spin rates. Present technology appears adequate to construct an apparatus to allow independent control of temperature and pressure gradients. A complicating feature of a more advanced experiment, involving flow gradients, is the requirement for independently controlled cylinder spin rates. Also, the boundary condition at annulus terminations must be such that flow gradients are minimally disturbed. The design and construction of an advanced apparatus to include flow gradients will require additional technology development.

Facilitated strontium transport by remobilization of strontium-containing secondary precipitates in Hanford Site subsurface.

PubMed

Wang, Guohui; Um, Wooyong

2013-03-15

Significantly enhanced immobilization of radionuclides (such as (90)Sr and (137)Cs) due to adsorption and coprecipitation with neo-formed colloid-sized secondary precipitates has been reported at the U.S. Department of Energy's Hanford Site. However, the stability of these secondary precipitates containing radionuclides in the subsurface under changeable field conditions is not clear. Here, the authors tested the remobilization possibility of Sr-containing secondary precipitates (nitrate-cancrinite) in the subsurface using saturated column experiments under different geochemical and flow conditions. The columns were packed with quartz sand that contained secondary precipitates (nitrate-cancrinite containing Sr), and leached using colloid-free solutions under different flow rates, varying pH, and ionic strength conditions. The results indicate remobilization of the neo-formed secondary precipitates could be possible given a change of pH of ionic strength and flow rate conditions. The remobility of the neo-formed precipitates increased with the rise in the leaching solution flow rate and pH (in a range of pH 4-11), as well as with decreasing solution ionic strength. The increased mobility of Sr-containing secondary precipitates with changing background conditions can be a potential source for additional radionuclide transport in Hanford Site subsurface environments. Published by Elsevier B.V.

Oscillatory Excitation of Unsteady Compressible Flows over Airfoils at Flight Reynolds Numbers

NASA Technical Reports Server (NTRS)

Seifert, Avi; Pack, LaTunia G.

1999-01-01

An experimental investigation, aimed at delaying flow separation due to the occurrence of a shock-wave-boundary-layer interaction, is reported. The experiment was performed using a NACA 0012 airfoil and a NACA 0015 airfoil at high Reynolds number incompressible and compressible flow conditions. The effects of Mach and Reynolds numbers were identified, using the capabilities of the cryogenic-pressurized facility to maintain one parameter fixed and change the other. Significant Reynolds number effects were identified in the baseline compressible flow conditions even at Reynolds number of 10 and 20 million. The main objectives of the experiment were to study the effects of periodic excitation on airfoil drag-divergence and to alleviate the severe unsteadiness associated with shock-induced separation (known as "buffeting"). Zero-mass-flux oscillatory blowing was introduced through a downstream directed slot located at 10% chord on the upper surface of the NACA 0015 airfoil. The effective frequencies generated 2-4 vortices over the separated region, regardless of the Mach number. Even though the excitation was introduced upstream of the shock-wave, due to experimental limitations, it had pronounced effects downstream of it. Wake deficit (associated with drag) and unsteadiness (associated with buffeting) were significantly reduced. The spectral content of the wake pressure fluctuations indicates of steadier flow throughout the frequency range when excitation was applied. This is especially important at low frequencies which are more likely to interact with the airframe.

Comparison of Three Model Concepts for Streaming Potential in Unsaturated Porous Media

NASA Astrophysics Data System (ADS)

Huisman, J. A.; Satenahalli, P.; Zimmermann, E.; Vereecken, H.

2017-12-01

Streaming potential is the electric potential generated by fluid flow in a charged porous medium. Although streaming potential in saturated conditions is well understood, there still is considerable debate about the adequate modelling of streaming potential signals in unsaturated soil because different concepts are available to estimate the effective excess charge in unsaturated conditions. In particular, some studies have relied on the volumetric excess charge, whereas others proposed to use the flux-averaged excess charge derived from the water retention or relative permeability function. The aim of this study is to compare measured and modelled streaming potential signals for two different flow experiments with sand. The first experiment is a primary gravity drainage of a long column equipped with non-polarizing electrodes and tensiometers, as presented in several previous studies. Expected differences between the three concepts for the effective excess charge are only moderate for this set-up. The second experiment is a primary drainage of a short soil column equipped with non-polarizing electrodes and tensiometers using applied pressure, where differences between the three concepts are expected to be larger. A comparison of the experimental results with a coupled model of streaming potential for 1D flow problems will provide insights in the ability of the three model concepts for effective excess charge to describe observed streaming potentials.

Agency and Gender Influence Older Adults' Presence-Related Experiences in an Interactive Virtual Environment.

PubMed

Kothgassner, Oswald D; Goreis, Andreas; Kafka, Johanna X; Hlavacs, Helmut; Beutl, Leon; Kryspin-Exner, Ilse; Felnhofer, Anna

2018-05-01

While virtual humans are increasingly used to benefit the elderly, considerably little is still known about older adults' virtual experiences. However, due to age-related changes, older adults' perceptions of virtual environments (VEs) may be unique. Hence, our objective was to examine possible gender differences in immersion, flow, and emotional states as well as physical and social presence in elderly males and females interacting either with a computer-controlled agent or a human-controlled avatar. Seventy-eight German-speaking older adults were randomly assigned to an avatar or an agent condition and were exposed to a brief social encounter in a virtual café. Results indicate no overall gender differences, but a significant effect of agency on social presence, physical presence, immersion, and flow. Participants in the avatar condition reported higher levels in all measures, except for involvement. Furthermore, significant gender × agency interactions were found, with females showing more social presence, spatial presence, and flow when interacting with a human-controlled avatar and more realism when conversing with an agent. Also, all participants showed significant changes in their affect post exposure. In sum, older adults' virtual experiences seem to follow unique patterns, yet, they do not preclude the elderly from successfully participating in VEs.

Investigations of flowfields found in typical combustor geometries

NASA Technical Reports Server (NTRS)

Lilley, D. G.

1984-01-01

Studies are concerned with experimental and theoretical research on 2-D axisymmetric geometries under low speed, nonreacting, turbulent, swirling flow conditions. The flow enters the test section and proceeds into a larger chamber (the linear expansion ratio D/d = 2, 1.5 and 1) via a sudden or gradual expansion (side wall angle alpha = 90 and 45 degrees). A weak or strong nozzle (of area ratio A/a = 2 and 4) may be positioned downstream at x/D = 2 to form a contraction exit to the test section. Inlet swirl vanes are adjustable to a variety of vane angles with values of theta = 0, 38, 45, 60 and 70 degrees being emphasized. The objective is to determine the effect of these parameters on isothermal flow field patterns, time mean velocities and turbulence quantities, and to establish an improved simulation in the form of a computer prediction code equipped with a suitable turbulence model. The goal of the on going research is to perform experiments and complementary computations with the idea of doing the necessary type of research that will yield improved calculation capability. This involves performing experiments where time mean turbulence quantities are measured and taking input conditions and running an existing prediction code for a variety of test cases so as to compare predictions against experiment.

ADVANCED CUTTINGS TRANSPORT STUDY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stefan Miska; Troy Reed; Ergun Kuru

2004-09-30

The Advanced Cuttings Transport Study (ACTS) was a 5-year JIP project undertaken at the University of Tulsa (TU). The project was sponsored by the U.S. Department of Energy (DOE) and JIP member companies. The objectives of the project were: (1) to develop and construct a new research facility that would allow three-phase (gas, liquid and cuttings) flow experiments under ambient and EPET (elevated pressure and temperature) conditions, and at different angle of inclinations and drill pipe rotation speeds; (2) to conduct experiments and develop a data base for the industry and academia; and (3) to develop mechanistic models for optimizationmore » of drilling hydraulics and cuttings transport. This project consisted of research studies, flow loop construction and instrumentation development. Following a one-year period for basic flow loop construction, a proposal was submitted by TU to the DOE for a five-year project that was organized in such a manner as to provide a logical progression of research experiments as well as additions to the basic flow loop. The flow loop additions and improvements included: (1) elevated temperature capability; (2) two-phase (gas and liquid, foam etc.) capability; (3) cuttings injection and removal system; (4) drill pipe rotation system; and (5) drilling section elevation system. In parallel with the flow loop construction, hydraulics and cuttings transport studies were preformed using drilling foams and aerated muds. In addition, hydraulics and rheology of synthetic drilling fluids were investigated. The studies were performed under ambient and EPET conditions. The effects of temperature and pressure on the hydraulics and cuttings transport were investigated. Mechanistic models were developed to predict frictional pressure loss and cuttings transport in horizontal and near-horizontal configurations. Model predictions were compared with the measured data. Predominantly, model predictions show satisfactory agreements with the measured data. As a part of this project, instrumentation was developed to monitor cuttings beds and characterize foams in the flow loop. An ultrasonic-based monitoring system was developed to measure cuttings bed thickness in the flow loop. Data acquisition software controls the system and processes the data. Two foam generating devices were designed and developed to produce foams with specified quality and texture. The devices are equipped with a bubble recognition system and an in-line viscometer to measure bubble size distribution and foam rheology, respectively. The 5-year project is completed. Future research activities will be under the umbrella of Tulsa University Drilling Research Projects. Currently the flow loop is being used for testing cuttings transport capacity of aqueous and polymer-based foams under elevated pressure and temperature conditions. Subsequently, the effect of viscous sweeps on cuttings transport under elevated pressure and temperature conditions will be investigated using the flow loop. Other projects will follow now that the ''steady state'' phase of the project has been achieved.« less

Experiments and numerical modeling of fast flowing liquid metal thin films under spatially varying magnetic field conditions

NASA Astrophysics Data System (ADS)

Narula, Manmeet Singh

Innovative concepts using fast flowing thin films of liquid metals (like lithium) have been proposed for the protection of the divertor surface in magnetic fusion devices. However, concerns exist about the possibility of establishing the required flow of liquid metal thin films because of the presence of strong magnetic fields which can cause flow disrupting MHD effects. A plan is underway to design liquid lithium based divertor protection concepts for NSTX, a small spherical torus experiment at Princeton. Of these, a promising concept is the use of modularized fast flowing liquid lithium film zones, as the divertor (called the NSTX liquid surface module concept or NSTX LSM). The dynamic response of the liquid metal film flow in a spatially varying magnetic field configuration is still unknown and it is suspected that some unpredicted effects might be lurking. The primary goal of the research work being reported in this dissertation is to provide qualitative and quantitative information on the liquid metal film flow dynamics under spatially varying magnetic field conditions, typical of the divertor region of a magnetic fusion device. The liquid metal film flow dynamics have been studied through a synergic experimental and numerical modeling effort. The Magneto Thermofluid Omnibus Research (MTOR) facility at UCLA has been used to design several experiments to study the MHD interaction of liquid gallium films under a scaled NSTX outboard divertor magnetic field environment. A 3D multi-material, free surface MHD modeling capability is under development in collaboration with HyPerComp Inc., an SBIR vendor. This numerical code called HIMAG provides a unique capability to model the equations of incompressible MHD with a free surface. Some parts of this modeling capability have been developed in this research work, in the form of subroutines for HIMAG. Extensive code debugging and benchmarking exercise has also been carried out. Finally, HIMAG has been used to study the MHD interaction of fast flowing liquid metal films under various divertor relevant magnetic field configurations through numerical modeling exercises.

From antidunes to step-pools

NASA Astrophysics Data System (ADS)

Recking, Alain; Leduc, Pauline

2014-05-01

Step-pools are bed morphologies that are typical in high-gradient streams , recognizable by a staircase-like longitudinal profile resulting from accumulation of cobbles and boulders that are transverse to the channel and alternating with pools containing finer sediments. Within the last two decades step-pools have been the subject of increased efforts to characterize their nature; however their origin is still in debate. Researchers have very soon suspected step-pools to be the residual form of antidunes produced during flooding, but this hypothesis was continuously contested. Other theories has been proposed, considering, that step-pool profile develops a maximum flow resistance, or that pools geometry is controlled by the energy of a falling jet, or that steps form by boulders accumulation in a channel-spanning manner. All these theories gave very satisfying results when compared with experimental data, but does it mean that the antidune theory should we abandoned? We performed new flume experiments on steep slopes to investigate the antidune origin for step-pools. Our experiments showed that step-pools can have several origins, depending on the flow conditions and sediment mixture used. In some circumstances antidunes were well observed but did not produce stable step-pools morphology. In many occasions, step-pools obtained in the flume were isolated step-pools, with no real apparent periodicity. Only a few flow and sediment conditions allowed us to reproduce trains of antidunes which stabilized at the flow recession to produce stable periodical step-pools. These conditions are presented and discussed.

An Experimental Investigation On The Antidune Origin of Step-pools

NASA Astrophysics Data System (ADS)

Recking, A.; Leduc, P.

2013-12-01

Step-pools are bed morphologies that are typical in high-gradient streams , recognizable by a staircase-like longitudinal profile resulting from accumulation of cobbles and boulders that are transverse to the channel and alternating with pools containing finer sediments. Within the last two decades step-pools have been the subject of increased efforts to characterize their nature; however their origin is still in debate. Researchers have very soon suspected step-pools to be the residual form of antidunes produced during flooding, but this hypothesis was continuously contested. Other theories has been proposed, considering, that step-pool profile develops a maximum flow resistance, or that pools geometry is controlled by the energy of a falling jet, or that steps form by boulders accumulation in a channel-spanning manner. All these theories gave very satisfying results when compared with experimental data, but does it mean that the antidune theory should we abandoned? We performed new flume experiments on steep slopes to investigate the antidune origin for step-pools. Our experiments showed that step-pools can have several origins, depending on the flow conditions and sediment mixture used. In some circumstances antidunes were well observed but did not produce stable step-pools morphology. In many occasions, step-pools obtained in the flume were isolated step-pools, with no real apparent periodicity. Only a few flow and sediment conditions allowed us to reproduce trains of antidunes which stabilized at the flow recession to produce stable periodical step-pools. These conditions are presented and discussed.

Characteristic of Secondary Flow Caused by Local Density Change in Standing Acoustic Fields

NASA Astrophysics Data System (ADS)

Tonsho, Kazuyuki; Hirosawa, Takuya; Kusakawa, Hiroshi; Kuwahara, Takuo; Tanabe, Mitsuaki

Secondary flow is a flow which is caused by the interference between standing acoustic fields and local density change. The behavior of the secondary flow depends on the location of the given local density change in the standing acoustic fields. When the density change is given at the middle of a velocity node and the neighboring velocity anti-node (middle point) or when it is given at the velocity anti-node in standing acoustic fields, the secondary flow shows particular behavior. Characteristic of the secondary flow at the two positions was predicted by numerical simulations. It was examined from these simulations whether the driving mechanism of the flow can be explained by the kind of acoustic radiation force that has been proposed so far. The predicted secondary flow was verified by experiments. For both the simulations and experiments, the standing acoustic fields generated in a cylinder are employed. In the experiments, the acoustic fields are generated by two loud speakers that are vibrated in same phase in a chamber. The employed resonance frequency is about 1000 Hz. The chamber is filled with air of room temperature and atmospheric pressure. In the numerical simulations and experiments, the local density change is given by heating or cooling. Because the secondary flow is influenced by buoyancy, the numerical simulations were done without taking gravity force into account and a part of the experiments were done by the microgravity condition using a drop tower. As a result of the simulations, at the middle point, the heated air was blown toward the node and the cooled air was blown toward the anti-node. It is clarified that the secondary flow is driven by the expected kind of acoustic radiation force. At the anti-node, both the heated and cooled air expands perpendicular to the traveling direction of the sound wave. The driving mechanism of the secondary flow can not be explained by the acoustic radiation force, and a detailed analysis is done. Through the comparison between experimental and numerical results, it was verified that the secondary flow is qualitatively predictable by the numerical simulations.

Channel Extension in Deep-Water Distributive Systems

NASA Astrophysics Data System (ADS)

Hoyal, D. C.; Sheets, B. A.

2007-12-01

The cyclic nature of channel and lobe formation in submarine fans is the result of the unstable and ephemeral nature of newly formed distributary channels. Avulsion cycles are initiated as unconfined sheet flow immediately following avulsion followed by stages of channel incision and extension, deposition of channel mouth deposits, and often channel backfilling. In contrast with those in alluvial and deltaic environments, avulsion cycles in submarine fans are relatively poorly understood due to the difficulty of observing deep ocean processes, either over short timescales needed to measure the hydrodynamics of active turbidity currents, or over longer timescales needed for the morphodynamic evolution of individual distributary channels and avulsion events. Here we report the results of over 80 experiments in a 5m x 3m x1m deep tank using saline (NaCl) density flows carrying low-density plastic sediment (SG 1.5) flowing down an inclined ramp. These experiments were designed to investigate trends observed in earlier self-organized experimental submarine fans with well-developed avulsion cycles, in which distributive lobes were observed to form on relatively high slopes. In particular, we were interested in investigating the relationship between channel extension length (distance from the inlet to the point where the flow becomes de-channelized, transitioning into a mouth-bar/lobe) and slope. The results of the experiments are clear but counter-intuitive. Channels appear to extend in discrete segments and channel extension length is inversely related to slope over a wide range of slopes (5-17 degrees). In addition, channel extension seems largely independent of inlet flow density (salt concentration) over the experimental range (10-24 g/cc). Measurements of densimetric Froude number (Fr') indicate Fr' increases downstream to near critical conditions at the channel lobe transition. Our preliminary interpretation is that distributary channels become unstable due to acceleration to Fr'-critical conditions and the formation of a depositional hydraulic jump, which perturbs sediment transport and ends channel extension. Similar morphodynamic length scale controls are observed in shallow water fan-delta experiments (e.g., SAFL DB-03) and in 2-D depositional cyclic steps. The experiments seem to explain two interesting observations from the earlier self-organized fan experiments and from real submarine fans. Firstly, the observation of 'perched' fills at the steep entrances to salt withdrawal minibasins (e.g., in the Gulf of Mexico) suggesting higher sedimentation rates (or inefficient sediment transport) on higher slopes (initially higher than at the slope break downstream). Secondly, strong progradation as the fan evolves and slope decreases in 'perched' fans suggests increasing flow efficiency on lower slopes, at least over a certain window of parameter space. Apparently deep water systems have a tendency to self-regulate even when flows differ significantly in initial density. The observed modulation to Fr'-critical flow appears to be an important control on length scales in deep- water distributive channel systems, potentially explaining strong deepwater progradation or 'delta-like' patterns that have remained paradoxical. Near critical conditions have been inferred from observations of many active submarine fans but the extent to which these results from conservative density currents apply to non-conservative and potentially 'ignitive' turbidity currents is the subject of ongoing investigation.

How rivers remember: The impacts of prior stress history on grain scale topography and bedload transport

NASA Astrophysics Data System (ADS)

Masteller, C.; Finnegan, N. J.

2016-12-01

Memory is preserved in rivers through the sorting and arrangement of grains on their beds, which reflect previous flow conditions. Manifestations of this phenomenon include observed hysteresis in bedload rating curves (e.g., Moog and Whiting, 1998; Reid et al., 1985) and correlations between the stage at the start of a transport event and the stage at the end of transport during a previous event (Turowski et al., 2011). This observed history dependence represents a key difficulty in the accurate prediction of bedload transport rates. To begin to systematically explore these memory effects on fluvial bedload transport, we experimentally examined how a gravel bed river responds to variations in prior stress history. Specifically, we compare the response of the grain-scale topography of a gravel riverbed to both below and above threshold flow conditions. We find that under low flow, when no sediment transport occurs, the bed compacts as the highest protruding grains pivot into low elevation pockets. This reorganization appears to occur logarithmically with low flow duration, making it analogous to compaction observed in dry granular flows subjected to agitation. The amount of prior compaction affects bedload transport rates at the onset of above threshold flow, with more compact beds yielding less bedload flux. In contrast, we find that under sediment-transporting flows, the bed dilates because grains are re-deposited in relatively precarious positions. During the same applied transport flow, we observe that the most pronounced dilation occurs when the initial bed is the most compact, suggesting that the potential for dilation is related to the degree of previous compaction. These observations highlight that a gravel bed experiences two different behaviors, compaction under low shear stresses, and dilation under high, sediment transporting, shear stresses. This observation is consistent with previous studies on the compaction and dilation of granular media, as well as flume experiments conducted using glass beads. Further, this study highlights the varying response of grain-scale topography and bedload transport rates to prior flow and bed conditions, demonstrating history dependence in fluvial systems.

Constrains on the Rheology of the Lithosphere Inferred from Nano-Forsterite Deformation Experiments

NASA Astrophysics Data System (ADS)

Gasc, J.; Demouchy, S. A.; Barou, F.; Koizumi, S.

2017-12-01

The rheology of the lithospheric mantle is usually inferred from experiments performed at temperatures and strain rates greater than in the Earth. In these conditions, deformation occurs via dislocation creep and the flow laws obtained experimentally are then extrapolated to natural conditions. Despite the difficulty of achieving steady-state flow at low temperatures (<1200°C), recent studies have shown that low-temperature deformation of olivine implies different deformation mechanisms and that rotational defects, i.e. disclinations, might be involved in the low-temperature rheology of the mantle. To help constrain the rheology of the upper mantle and address the role of the various defects at play at the microscopic scale, we used a high-pressure high-temperature gas medium deformation apparatus (aka. Paterson press) to deform pre-sintered nano-forsterite aggregates. The fine-grained nature of the samples allows us to probe the deformation mechanisms at play when dislocation creep is limited. Experiments were performed at 300 MPa, 900-1200°C, and constant displacement yielding strain rates around 10-5 s-1. The samples were analyzed using state-of-the-art microscopy techniques. EBSD analysis did not reveal crystal preferred orientation. However, grain plasticity was evidenced and takes place almost exclusively via subgrain formation with rotation around the c-axis, a condition that does not allow sustainable plastic flow. Further investigations are ongoing to identify if other defects, such as disclinations are present. Grain rotation was also evidenced by a shape preferred orientation. Regardless of the mechanisms involved, rheology data show that the samples are stronger (from 0.5-2 GPa) than their iron-bearing olivine counterparts, due to a combined effect of grain size and composition (Fe has a softening effect on olivine). The temperature dependence is weaker than predicted by high temperature data in the dislocation creep regime, but remains greater than reported from experiments and models in the same conditions for olivine, which has important implications regarding the strength of the lithospheric mantle.

Mode decomposition and Lagrangian structures of the flow dynamics in orbitally shaken bioreactors

NASA Astrophysics Data System (ADS)

Weheliye, Weheliye Hashi; Cagney, Neil; Rodriguez, Gregorio; Micheletti, Martina; Ducci, Andrea

2018-03-01

In this study, two mode decomposition techniques were applied and compared to assess the flow dynamics in an orbital shaken bioreactor (OSB) of cylindrical geometry and flat bottom: proper orthogonal decomposition and dynamic mode decomposition. Particle Image Velocimetry (PIV) experiments were carried out for different operating conditions including fluid height, h, and shaker rotational speed, N. A detailed flow analysis is provided for conditions when the fluid and vessel motions are in-phase (Fr = 0.23) and out-of-phase (Fr = 0.47). PIV measurements in vertical and horizontal planes were combined to reconstruct low order models of the full 3D flow and to determine its Finite-Time Lyapunov Exponent (FTLE) within OSBs. The combined results from the mode decomposition and the FTLE fields provide a useful insight into the flow dynamics and Lagrangian coherent structures in OSBs and offer a valuable tool to optimise bioprocess design in terms of mixing and cell suspension.

The thermodynamics of dense granular flow and jamming

NASA Astrophysics Data System (ADS)

Lu, Shih Yu

The scope of the thesis is to propose, based on experimental evidence and theoretical validation, a quantifiable connection between systems that exhibit the jamming phenomenon. When jammed, some materials that flow are able to resist deformation so that they appear solid-like on the laboratory scale. But unlike ordinary fusion, which has a critically defined criterion in pressure and temperature, jamming occurs under a wide range of conditions. These condition have been rigorously investigated but at the moment, no self-consistent framework can apply to grains, foam and colloids that may have suddenly ceased to flow. To quantify the jamming behavior, a constitutive model of dense granular flows is deduced from shear-flow experiments. The empirical equations are then generalized, via a thermodynamic approach, into an equation-of-state for jamming. Notably, the unifying theory also predicts the experimental data on the behavior of molecular glassy liquids. This analogy paves a crucial road map for a unifying theoretical framework in condensed matter, for example, ranging from sand to fire retardants to toothpaste.

The structure of dilute combusting sprays

NASA Technical Reports Server (NTRS)

Shuen, J. S.; Solomon, A. S. P.; Faeth, F. M.

1985-01-01

An experimental and theoretical study of drop processes in a turbulent flame is described. The experiments involved a monodisperse (105 and 180 micro m initial diameter) stream of methanol drops injected at the base of a turbulent methane-fueled diffusion flame burning in still air. The following measurements were made: mean and fluctuating phase velocities, mean drop number flux, drop-size distributions and mean gas-phase temperatures. Measurements were compared with predictions of two separated flow models: (1) deterministic separated flow, where drop-turbulence interactions are ignored; and (2) stochastic separated flow, where drop-turbulence interactions are considered using random-walk computations. The stochastic separated flow analysis yielded best agreement with measurements, since it provides for turbulent dispersion of drops which was important for present test conditions (and probably for most combusting sprays as well). Distinguishing the presence or absence of envelope flames around the drops, however, was relatively unimportant for present test conditions, since the drops spent most of their lifetime in fuel-rich regions of the flow where this distinction is irrelevant.

Error estimation for CFD aeroheating prediction under rarefied flow condition

NASA Astrophysics Data System (ADS)

Jiang, Yazhong; Gao, Zhenxun; Jiang, Chongwen; Lee, Chunhian

2014-12-01

Both direct simulation Monte Carlo (DSMC) and Computational Fluid Dynamics (CFD) methods have become widely used for aerodynamic prediction when reentry vehicles experience different flow regimes during flight. The implementation of slip boundary conditions in the traditional CFD method under Navier-Stokes-Fourier (NSF) framework can extend the validity of this approach further into transitional regime, with the benefit that much less computational cost is demanded compared to DSMC simulation. Correspondingly, an increasing error arises in aeroheating calculation as the flow becomes more rarefied. To estimate the relative error of heat flux when applying this method for a rarefied flow in transitional regime, theoretical derivation is conducted and a dimensionless parameter ɛ is proposed by approximately analyzing the ratio of the second order term to first order term in the heat flux expression in Burnett equation. DSMC simulation for hypersonic flow over a cylinder in transitional regime is performed to test the performance of parameter ɛ, compared with two other parameters, Knρ and MaṡKnρ.

Verification of the karst flow model under laboratory controlled conditions

NASA Astrophysics Data System (ADS)

Gotovac, Hrvoje; Andric, Ivo; Malenica, Luka; Srzic, Veljko

2016-04-01

Karst aquifers are very important groundwater resources around the world as well as in coastal part of Croatia. They consist of extremely complex structure defining by slow and laminar porous medium and small fissures and usually fast turbulent conduits/karst channels. Except simple lumped hydrological models that ignore high karst heterogeneity, full hydraulic (distributive) models have been developed exclusively by conventional finite element and finite volume elements considering complete karst heterogeneity structure that improves our understanding of complex processes in karst. Groundwater flow modeling in complex karst aquifers are faced by many difficulties such as a lack of heterogeneity knowledge (especially conduits), resolution of different spatial/temporal scales, connectivity between matrix and conduits, setting of appropriate boundary conditions and many others. Particular problem of karst flow modeling is verification of distributive models under real aquifer conditions due to lack of above-mentioned information. Therefore, we will show here possibility to verify karst flow models under the laboratory controlled conditions. Special 3-D karst flow model (5.6*2.6*2 m) consists of concrete construction, rainfall platform, 74 piezometers, 2 reservoirs and other supply equipment. Model is filled by fine sand (3-D porous matrix) and drainage plastic pipes (1-D conduits). This model enables knowledge of full heterogeneity structure including position of different sand layers as well as conduits location and geometry. Moreover, we know geometry of conduits perforation that enable analysis of interaction between matrix and conduits. In addition, pressure and precipitation distribution and discharge flow rates from both phases can be measured very accurately. These possibilities are not present in real sites what this model makes much more useful for karst flow modeling. Many experiments were performed under different controlled conditions such as different levels in left and right end of reservoirs (boundary conditions), different flow regimes in conduits, flow with and without precipitation, free and pressurized discharge from conduits or influence of epikarst (top layer) on recession period. Experimental results are verified by conventional karst flow model (such as MODFLOW-CFP) showing that hydraulic (distributive) models can describe complex behavior of karst flow processes if substantial amount of input data are known from site investigations and monitoring. These results enable us to develop more advanced karst flow models that will improve understanding and analysis of complex flow processes in the real karst aquifers.

Computing nonhydrostatic shallow-water flow over steep terrain

USGS Publications Warehouse

Denlinger, R.P.; O'Connell, D. R. H.

2008-01-01

Flood and dambreak hazards are not limited to moderate terrain, yet most shallow-water models assume that flow occurs over gentle slopes. Shallow-water flow over rugged or steep terrain often generates significant nonhydrostatic pressures, violating the assumption of hydrostatic pressure made in most shallow-water codes. In this paper, we adapt a previously published nonhydrostatic granular flow model to simulate shallow-water flow, and we solve conservation equations using a finite volume approach and an Harten, Lax, Van Leer, and Einfeldt approximate Riemann solver that is modified for a sloping bed and transient wetting and drying conditions. To simulate bed friction, we use the law of the wall. We test the model by comparison with an analytical solution and with results of experiments in flumes that have steep (31??) or shallow (0.3??) slopes. The law of the wall provides an accurate prediction of the effect of bed roughness on mean flow velocity over two orders of magnitude of bed roughness. Our nonhydrostatic, law-of-the-wall flow simulation accurately reproduces flume measurements of front propagation speed, flow depth, and bed-shear stress for conditions of large bed roughness. ?? 2008 ASCE.

Swirl-Stabilized Injector Flow and Combustion Dynamics for Liquid Propellants at Supercritical Conditions

DTIC Science & Technology

2007-02-08

was employed to study the vapor cavitation during liquid carbon dioxide expansion through a sharp-orifice nozzle. Numerical experiments demonstrated...Combustion Dynamics for 6b. GRANT NUMBER Liquid Propellants at Supercritical Conditions FA9550-04-1-0014 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT...fundamental knowledge of supercritical combustion of liquid propellants under conditions representative of contemporary rocket engines. Both shear and

Optimization of Synthesis Conditions of Carbon Nanotubes via Ultrasonic-Assisted Floating Catalyst Deposition Using Response Surface Methodology

PubMed Central

Mohammadian, Narges; Ghoreishi, Seyyed M.; Hafeziyeh, Samira; Saeidi, Samrand; Dionysiou, Dionysios D.

2018-01-01

The growing use of carbon nanotubes (CNTs) in a plethora of applications has provided to us a motivation to investigate CNT synthesis by new methods. In this study, ultrasonic-assisted chemical vapor deposition (CVD) method was employed to synthesize CNTs. The difficulty of controlling the size of clusters and achieving uniform distribution—the major problem in previous methods—was solved by using ultrasonic bath and dissolving ferrocene in xylene outside the reactor. The operating conditions were optimized using a rotatable central composite design (CCD), which helped optimize the operating conditions of the method. Response surface methodology (RSM) was used to analyze these experiments. Using statistical software was very effective, considering that it decreased the number of experiments needed to achieve the optimum conditions. Synthesis of CNTs was studied as a function of three independent parameters viz. hydrogen flow rate (120–280 cm3/min), catalyst concentration (2–6 wt %), and synthesis temperature (800–1200 °C). Optimum conditions for the synthesis of CNTs were found to be 3.78 wt %, 184 cm3/min, and 976 °C for catalyst concentration, hydrogen flow rate, and synthesis temperature, respectively. Under these conditions, Raman spectrum indicates high values of (IG/ID), which means high-quality CNTs. PMID:29747451

Burnout in the horizontal tubes of a furnace waterwall panel

NASA Astrophysics Data System (ADS)

Kamenetskii, B. Ya.

2009-08-01

An experimental study of heat transfer that occurs in tubes nonuniformly heated over the perimeter at low velocities of subcooled water flowing in them is presented. Experiments with unsteady supply of heat made it possible to determine heat fluxes under burnout conditions. Unusually low values of critical heat fluxes were obtained under such conditions.

Oxygen consumption along bed forms under losing and gaining streamflow conditions

NASA Astrophysics Data System (ADS)

De Falco, Natalie; Arnon, Shai; Boano, Fulvio

2016-04-01

Recent studies have demonstrated that bed forms are the most significant geomorphological structure that drives hyporheic exchange and biogeochemical processes in stream networks. Other studies also demonstrated that due to the hyporheic flow patterns within bed form, biogeochemical processes do not occur uniformly along and within the bed forms. The objective of this work was to systematically evaluate how losing or gaining flow conditions affect oxygen consumption by biofilm along sandy bed forms. We measured the effects of losing and gaining flow conditions on oxygen consumption by combining modeling and experiments in a novel laboratory flume system that enable the control of losing and gaining fluxes. Oxygen consumption was measured after growing a benthic biofilm fed with Sodium Benzoate (as a carbon source) and measuring the distribution of oxygen in the streambed with microelectrodes. The experimental results were analyzed using a novel code that calculates vertical profiles of reaction rates in the presence of hyporheic water fluxes. These experimental observations and modeling revealed that oxygen distribution varied along the bed forms. The zone of oxygen consumption (i.e. depth of penetration) was the largest at the upstream side of the bed form and the smallest in the lee side (at the lowest part of the bed form), regardless of the flow conditions. Also, the zone of oxygen consumption was the largest under losing conditions, the smallest under gaining conditions, and in-between under neutral conditions. The distribution of oxygen consumption rates determined with our new model will be also discussed. Our preliminary results enable us to show the importance of the coupling between flow conditions and oxygen consumption along bed forms and are expected to improve our understanding of nutrient cycling in streams.

Effects of chronic pollution and water flow intermittency on stream biofilms biodegradation capacity.

PubMed

Rožman, Marko; Acuña, Vicenç; Petrović, Mira

2018-02-01

A mesocosm case study was conducted to gain understanding and practical knowledge on biofilm emerging contaminants biodegradation capacity under stressor and multiple stressor conditions. Two real life scenarios: I) biodegradation in a pristine intermittent stream experiencing acute pollution and II) biodegradation in a chronically polluted intermittent stream, were examined via a multifactorial experiment using an artificial stream facility. Stream biofilms were exposed to different water flow conditions i.e. permanent and intermittent water flow. Venlafaxine, a readily biodegradable pharmaceutical was used as a measure of biodegradation capacity while pollution was simulated by a mixture of four emerging contaminants (erythromycin, sulfisoxazole, diclofenac and imidacloprid in addition to venlafaxine) in environmentally relevant concentrations. Biodegradation kinetics monitored via LC-MS/MS was established, statistically evaluated, and used to link biodegradation with stress events. The results suggest that the effects of intermittent flow do not hinder and may even stimulate pristine biofilm biodegradation capacity. Chronic pollution completely reduced biodegradation in permanent water flow experimental treatments while no change in intermittent streams was observed. A combined effect of water flow conditions and emerging contaminants exposure on biodegradation was found. The decrease in biodegradation due to exposure to emerging contaminants is significantly greater in streams with permanent water flow suggesting that the short and medium term biodegradation capacity in intermittent systems may be preserved or even greater than in perennial streams. Copyright © 2017 Elsevier Ltd. All rights reserved.

Biofilm development of an opportunistic model bacterium analysed at high spatiotemporal resolution in the framework of a precise flow cell

PubMed Central

Lim, Chun Ping; Mai, Phuong Nguyen Quoc; Roizman Sade, Dan; Lam, Yee Cheong; Cohen, Yehuda

2016-01-01

Life of bacteria is governed by the physical dimensions of life in microscales, which is dominated by fast diffusion and flow at low Reynolds numbers. Microbial biofilms are structurally and functionally heterogeneous and their development is suggested to be interactively related to their microenvironments. In this study, we were guided by the challenging requirements of precise tools and engineered procedures to achieve reproducible experiments at high spatial and temporal resolutions. Here, we developed a robust precise engineering approach allowing for the quantification of real-time, high-content imaging of biofilm behaviour under well-controlled flow conditions. Through the merging of engineering and microbial ecology, we present a rigorous methodology to quantify biofilm development at resolutions of single micrometre and single minute, using a newly developed flow cell. We designed and fabricated a high-precision flow cell to create defined and reproducible flow conditions. We applied high-content confocal laser scanning microscopy and developed image quantification using a model biofilm of a defined opportunistic strain, Pseudomonas putida OUS82. We observed complex patterns in the early events of biofilm formation, which were followed by total dispersal. These patterns were closely related to the flow conditions. These biofilm behavioural phenomena were found to be highly reproducible, despite the heterogeneous nature of biofilm. PMID:28721252

The NASA Ames Hypersonic Combustor-Model Inlet CFD Simulations and Experimental Comparisons

NASA Technical Reports Server (NTRS)

Venkatapathy, E.; Tokarcik-Polsky, S.; Deiwert, G. S.; Edwards, Thomas A. (Technical Monitor)

1995-01-01

Computations have been performed on a three-dimensional inlet associated with the NASA Ames combustor model for the hypersonic propulsion experiment in the 16-inch shock tunnel. The 3-dimensional inlet was designed to have the combustor inlet flow nearly two-dimensional and of sufficient mass flow necessary for combustion. The 16-inch shock tunnel experiment is a short duration test with test time of the order of milliseconds. The flow through the inlet is in chemical non-equilibrium. Two test entries have been completed and limited experimental results for the inlet region of the combustor-model are available. A number of CFD simulations, with various levels of simplifications such as 2-D simulations, 3-D simulations with and without chemical reactions, simulations with and without turbulent conditions, etc., have been performed. These simulations have helped determine the model inlet flow characteristics and the important factors that affect the combustor inlet flow and the sensitivity of the flow field to these simplifications. In the proposed paper, CFD modeling of the hypersonic inlet, results from the simulations and comparison with available experimental results will be presented.

Paradigm Change: Alternate Approaches to Constitutive and Necking Models for Sheet Metal Forming

NASA Astrophysics Data System (ADS)

Stoughton, Thomas B.; Yoon, Jeong Whan

2011-08-01

This paper reviews recent work proposing paradigm changes for the currently popular approach to constitutive and failure modeling, focusing on the use of non-associated flow rules to enable greater flexibility to capture the anisotropic yield and flow behavior of metals using less complex functions than those needed under associated flow to achieve that same level of fidelity to experiment, and on the use of stress-based metrics to more reliably predict necking limits under complex conditions of non-linear forming. The paper discusses motivating factors and benefits in favor of both associated and non-associated flow models for metal forming, including experimental, theoretical, and practical aspects. This review is followed by a discussion of the topic of the forming limits, the limitations of strain analysis, the evidence in favor of stress analysis, the effects of curvature, bending/unbending cycles, triaxial stress conditions, and the motivation for the development of a new type of forming limit diagram based on the effective plastic strain or equivalent plastic work in combination with a directional parameter that accounts for the current stress condition.

Volumetric Lattice Boltzmann Simulation for Fluid dynamics and Turbulence in Practical Syringes

NASA Astrophysics Data System (ADS)

Lima, Everton; Deep, Debanjan; Yu, Huidan (Whitney)

2012-11-01

We conduct numerical experiments to study fluid dynamics and turbulence in syringes using volumetric lattice Boltzmann method (VLBM) that is developed for dealing with arbitrary moving boundaries. Several common used medical syringes are used to predict the efficiency and safety of syringes experiencing low flow infusion rates. It is found that smaller size syringes reach a steady flow rate much sooner than larger ones, which are in quantitative agreement with experimental results. The relation between the syringe size and its steady flow rate is revealed. At low flow rates, corner vortices are observed. We explore conditions that lead to turbulent flow aiming to aid safer syringe application in nursing practices.

The effect of deformation on two-phase flow through proppant-packed fractured shale samples: A micro-scale experimental investigation

NASA Astrophysics Data System (ADS)

Arshadi, Maziar; Zolfaghari, Arsalan; Piri, Mohammad; Al-Muntasheri, Ghaithan A.; Sayed, Mohammed

2017-07-01

We present the results of an extensive micro-scale experimental investigation of two-phase flow through miniature, fractured reservoir shale samples that contained different packings of proppant grains. We investigated permeability reduction in the samples by conducting experiments under a wide range of net confining pressures. Three different proppant grain distributions in three individual fractured shale samples were studied: i) multi-layer, ii) uniform mono-layer, and iii) non-uniform mono-layer. We performed oil-displacing-brine (drainage) and brine-displacing-oil (imbibition) flow experiments in the proppant packs under net confining pressures ranging from 200 to 6000 psi. The flow experiments were performed using a state-of-the-art miniature core-flooding apparatus integrated with a high-resolution, X-ray microtomography system. We visualized fluid occupancies, proppant embedment, and shale deformation under different flow and stress conditions. We examined deformation of pore space within the proppant packs and its impact on permeability and residual trapping, proppant embedment due to changes in net confining stress, shale surface deformation, and disintegration of proppant grains at high stress conditions. In particular, geometrical deformation and two-phase flow effects within the proppant pack impacting hydraulic conductivity of the medium were probed. A significant reduction in effective oil permeability at irreducible water saturation was observed due to increase in confining pressure. We propose different mechanisms responsible for the observed permeability reduction in different fracture packings. Samples with dissimilar proppant grain distributions showed significantly different proppant embedment behavior. Thinner proppant layer increased embedment significantly and lowered the onset confining pressure of embedment. As confining stress was increased, small embedments caused the surface of the shale to fracture. The produced shale fragments were then entrained by the flow and partially blocked pore-throat connections within the proppant pack. Deformation of proppant packs resulted in significant changes in waterflood residual oil saturation. In-situ contact angles measured using micro-CT images showed that proppant grains had experienced a drastic alteration of wettability (from strong water-wet to weakly oil-wet) after the medium had been subjected to flow of oil and brine for multiple weeks. Nanometer resolution SEM images captured nano-fractures induced in the shale surfaces during the experiments with mono-layer proppant packing. These fractures improved the effective permeability of the medium and shale/fracture interactions.

Magnetic bucket for rotating unmagnetized plasma.

PubMed

Katz, Noam; Collins, Cami; Wallace, John; Clark, Mike; Weisberg, David; Jara-Almonte, Jon; Reese, Ingrid; Wahl, Carl; Forest, Cary

2012-06-01

A new experiment is described which generates flow in unmagnetized plasma. Confinement is provided by a cage of permanent magnets, arranged to form an axisymmetric, high-order, multipolar magnetic field. This field configuration-sometimes called a "magnetic bucket"-has a vanishingly small field in the core of the experiment. Toroidal rotation is driven by J × B forces applied in the magnetized edge. The cross-field current that is required for this forcing flows from anodes to thermionic cathodes, which are inserted between the magnet rings. The rotation at the edge reaches 3 km/s and is viscously coupled to the unmagnetized core plasma. We describe the conditions necessary for rotation, as well as a 0-dimensional power balance used to understand plasma confinement in the experiment.

Pilot Study for UVA-LED Disinfection of Escherichia coli in Water for Space and Earth Applications

NASA Technical Reports Server (NTRS)

Ragolta, Carolina

2010-01-01

To test the efficacy of UVA-LED disinfection, a solution of Escherichia coli was pumped through a modified drip flow reactor at a flow rate of 1 ml/min. The experiment was conducted in a controlled environment chamber to ensure that temperature did not cause disinfection. The reactor featured three wells with different treatments: UVA-LED irradiation, UVA-LEDs with Ti02, and UVA-LEDs with nanosilver. Samples from each well were taken throughout a 340 hour period, inactivated, assayed, and analyzed for E. coli disinfection. Results of the duplicate experiments indicated longer exposure times are needed for UVA-LED disinfection of E. coli in water. Further research would consider a longer sampling period and different test conditions, such as increased contact area and various flow rates.

Forced response unsteady aerodynamics in a multistage compressor

NASA Astrophysics Data System (ADS)

Capece, Vincent Ralph

The fundamental flow physics of the unsteady aerodynamics associated with forced vibrations in turbomachinery are investigated. Unique data are obtained through a series of experiments in a three stage axial flow research compressor which quantify the unsteady harmonic gust interaction phenomena over a range of operating and geometric conditions at high values of reduced frequency. In these experiments the effects of the following on the stator vane unsteady aerodynamics were quantified: (1) the steady aerodynamic loading, (2) the detailed waveform of the aerodynamic forcing function, including the chordwise and transverse gust components, (3) multistage blade row interactions, and (4) the solidity, ranging from a design value of 1.09 to an isolated airfoil. In addition, the effect of flow separation on the unsteady aerodynamics of an isolated airfoil was also investigated.

The influence of flow parameters on the transition to turbulence in supersonic boundary layer on swept wing

NASA Astrophysics Data System (ADS)

Semionov, N. V.; Yermolaev, Yu. G.; Kosinov, A. D.; Dryasov, A. D.; Semenov, A. N.; Yatskikh, A. A.

2016-10-01

The paper is devoted to an experimental study of laminar-turbulent transition in a three-dimensional supersonic boundary layer. The experiments were conducted at the low nose supersonic wind tunnel T-325 of ITAM at Mach numbers M=2 - 4. Model is a symmetrical wing with a 45° sweep angle, a 3 percent-thick circular-arc airfoil. The influence of flow parameters, such as the Mach number, unit Reynolds number, angle of attack, level of perturbations on the transitions to turbulence are on the consideration. Transition Reynolds numbers are obtained. Analysis of all obtained data allow to determine reliable value of Retr of swept wing supersonic boundary layer, that especially important at consideration of experiments fulfilled at different flow conditions in different wind tunnels.

Six-flow operations for catalyst development in Fischer-Tropsch synthesis: Bridging the gap between high-throughput experimentation and extensive product evaluation

NASA Astrophysics Data System (ADS)

Sartipi, Sina; Jansma, Harrie; Bosma, Duco; Boshuizen, Bart; Makkee, Michiel; Gascon, Jorge; Kapteijn, Freek

2013-12-01

Design and operation of a "six-flow fixed-bed microreactor" setup for Fischer-Tropsch synthesis (FTS) is described. The unit consists of feed and mixing, flow division, reaction, separation, and analysis sections. The reactor system is made of five heating blocks with individual temperature controllers, assuring an identical isothermal zone of at least 10 cm along six fixed-bed microreactor inserts (4 mm inner diameter). Such a lab-scale setup allows running six experiments in parallel, under equal feed composition, reaction temperature, and conditions of separation and analysis equipment. It permits separate collection of wax and liquid samples (from each flow line), allowing operation with high productivities of C5+ hydrocarbons. The latter is crucial for a complete understanding of FTS product compositions and will represent an advantage over high-throughput setups with more than ten flows where such instrumental considerations lead to elevated equipment volume, cost, and operation complexity. The identical performance (of the six flows) under similar reaction conditions was assured by testing a same catalyst batch, loaded in all microreactors.

Navier-Stokes simulations of slender axisymmetric shapes in supersonic, turbulent flow

NASA Astrophysics Data System (ADS)

Moran, Kenneth J.; Beran, Philip S.

1994-07-01

Computational fluid dynamics is used to study flows about slender, axisymmetric bodies at very high speeds. Numerical experiments are conducted to simulate a broad range of flight conditions. Mach number is varied from 1.5 to 8 and Reynolds number is varied from 1 X 10(exp 6)/m to 10(exp 8)/m. The primary objective is to develop and validate a computational and methodology for the accurate simulation of a wide variety of flow structures. Accurate results are obtained for detached bow shocks, recompression shocks, corner-point expansions, base-flow recirculations, and turbulent boundary layers. Accuracy is assessed through comparison with theory and experimental data; computed surface pressure, shock structure, base-flow structure, and velocity profiles are within measurement accuracy throughout the range of conditions tested. The methodology is both practical and general: general in its applicability, and practicaal in its performance. To achieve high accuracy, modifications to previously reported techniques are implemented in the scheme. These modifications improve computed results in the vicinity of symmetry lines and in the base flow region, including the turbulent wake.

Deuterium used as artificial tracer in column studies under saturated water flow conditions

NASA Astrophysics Data System (ADS)

Koeniger, P.; Geiges, M.; Leibundgut, Ch.

2003-04-01

In contrast to numerous investigations using deuterium as an environmental tracer, hydrological investigations with deuterium-labelled water are rather rare. Currently applications in groundwater studies are restricted due to increasing costs of spiking large water quantities but an application as intelligent tracer might be of advantage especially in combination with other tracers and under distinct environmental conditions. Therefore deuterium was applied as artificial tracer in column experiments that are well proved as a tool to characterise tracer behaviour in recent studies. Deuterium was tested in comparison to the more familiar conservative tracer fluorescein. Varying experimental conditions, e.g. column length (0.5, 1.0, 1.5 m), initial tracer concentration (0.01, 0.02, 0.2 mg) and flow velocity (1.5 to 6.0 m/d) were used to investigate tracer behaviour under saturated water flow conditions. Deuterium was analysed using an H/Device with chrome reduction connected to an isotope ratio mass spectrometer and expressed in relative concentrations [per mill V-SMOW]. Theoretical tracer breakthrough curves were calculated using a one dimensional dispersion model. The results indicate higher mean transport velocities and smaller dispersion for deuterium in all experiments. Due to different molecule properties that also determine the interaction of soil substrate and tracer, deuterium indicates a more conservative transport behaviour. Deuterium is non-toxic, completely soluble, chemically and biologically stable and not subject to light-influenced decay. Furthermore, it shows promise for investigations of water flow in the unsaturated zone, and of interactions of water in soil-plant-atmosphere systems. A further discussion of problems, together with possibilities for applying deuterium as an artificial tracer, will be presented.

KENNEDY SPACE CENTER, FLA. - Dr. Paul Hintze (left) explains to Center Director Jim Kennedy a project he is working at the KSC Beach Corrosion Test Site. Hitze is doing post-graduate work for the National Research Council. The test facility site was established in the 1960s and has provided more than 30 years of historical information on the long-term performance of many materials in use at KSC and other locations around the world. Located 100 feet from the Atlantic Ocean approximately 1 mile south of the Space Shuttle launch sites, the test facility includes an atmospheric exposure site, a flowing seawater exposure site, and an on-site electrochemistry laboratory and monitoring station. The beach laboratory is used to conduct real-time corrosion experiments and provides for the remote monitoring of surrounding weather conditions. The newly added flowing seawater immersion facility provides for the immersion testing of materials and devices under controlled conditions.

NASA Image and Video Library

2003-08-21

KENNEDY SPACE CENTER, FLA. - Dr. Paul Hintze (left) explains to Center Director Jim Kennedy a project he is working at the KSC Beach Corrosion Test Site. Hitze is doing post-graduate work for the National Research Council. The test facility site was established in the 1960s and has provided more than 30 years of historical information on the long-term performance of many materials in use at KSC and other locations around the world. Located 100 feet from the Atlantic Ocean approximately 1 mile south of the Space Shuttle launch sites, the test facility includes an atmospheric exposure site, a flowing seawater exposure site, and an on-site electrochemistry laboratory and monitoring station. The beach laboratory is used to conduct real-time corrosion experiments and provides for the remote monitoring of surrounding weather conditions. The newly added flowing seawater immersion facility provides for the immersion testing of materials and devices under controlled conditions.

KENNEDY SPACE CENTER, FLA. - Louis MacDowell (right), Testbed manager, explains to Center Director Jim Kennedy the use of astmospheric calibration specimens. Placed at various locations, they can rank the corrosivity of the given environment. The KSC Beach Corrosion Test Site was established in the 1960s and has provided more than 30 years of historical information on the long-term performance of many materials in use at KSC and other locations around the world. Located 100 feet from the Atlantic Ocean approximately 1 mile south of the Space Shuttle launch sites, the test facility includes an atmospheric exposure site, a flowing seawater exposure site, and an on-site electrochemistry laboratory and monitoring station. The beach laboratory is used to conduct real-time corrosion experiments and provides for the remote monitoring of surrounding weather conditions. The newly added flowing seawater immersion facility provides for the immersion testing of materials and devices under controlled conditions.

NASA Image and Video Library

2003-08-21

KENNEDY SPACE CENTER, FLA. - Louis MacDowell (right), Testbed manager, explains to Center Director Jim Kennedy the use of astmospheric calibration specimens. Placed at various locations, they can rank the corrosivity of the given environment. The KSC Beach Corrosion Test Site was established in the 1960s and has provided more than 30 years of historical information on the long-term performance of many materials in use at KSC and other locations around the world. Located 100 feet from the Atlantic Ocean approximately 1 mile south of the Space Shuttle launch sites, the test facility includes an atmospheric exposure site, a flowing seawater exposure site, and an on-site electrochemistry laboratory and monitoring station. The beach laboratory is used to conduct real-time corrosion experiments and provides for the remote monitoring of surrounding weather conditions. The newly added flowing seawater immersion facility provides for the immersion testing of materials and devices under controlled conditions.

Ground-water flow in low permeability environments

USGS Publications Warehouse

Neuzil, Christopher E.

1986-01-01

Certain geologic media are known to have small permeability; subsurface environments composed of these media and lacking well developed secondary permeability have groundwater flow sytems with many distinctive characteristics. Moreover, groundwater flow in these environments appears to influence the evolution of certain hydrologic, geologic, and geochemical systems, may affect the accumulation of pertroleum and ores, and probably has a role in the structural evolution of parts of the crust. Such environments are also important in the context of waste disposal. This review attempts to synthesize the diverse contributions of various disciplines to the problem of flow in low-permeability environments. Problems hindering analysis are enumerated together with suggested approaches to overcoming them. A common thread running through the discussion is the significance of size- and time-scale limitations of the ability to directly observe flow behavior and make measurements of parameters. These limitations have resulted in rather distinct small- and large-scale approaches to the problem. The first part of the review considers experimental investigations of low-permeability flow, including in situ testing; these are generally conducted on temporal and spatial scales which are relatively small compared with those of interest. Results from this work have provided increasingly detailed information about many aspects of the flow but leave certain questions unanswered. Recent advances in laboratory and in situ testing techniques have permitted measurements of permeability and storage properties in progressively “tighter” media and investigation of transient flow under these conditions. However, very large hydraulic gradients are still required for the tests; an observational gap exists for typical in situ gradients. The applicability of Darcy's law in this range is therefore untested, although claims of observed non-Darcian behavior appear flawed. Two important nonhydraulic flow phenomena, osmosis and ultrafiltration, are experimentally well established in prepared clays but have been incompletely investigated, particularly in undisturbed geologic media. Small-scale experimental results form much of the basis for analyses of flow in low-permeability environments which occurs on scales of time and size too large to permit direct observation. Such large-scale flow behavior is the focus of the second part of the review. Extrapolation of small-scale experimental experience becomes an important and sometimes controversial problem in this context. In large flow systems under steady state conditions the regional permeability can sometimes be determined, but systems with transient flow are more difficult to analyze. The complexity of the problem is enhanced by the sensitivity of large-scale flow to the effects of slow geologic processes. One-dimensional studies have begun to elucidate how simple burial or exhumation can generate transient flow conditions by changing the state of stress and temperature and by burial metamorphism. Investigation of the more complex problem of the interaction of geologic processes and flow in two and three dimensions is just beginning. Because these transient flow analyses have largely been based on flow in experimental scale systems or in relatively permeable systems, deformation in response to effective stress changes is generally treated as linearly elastic; however, this treatment creates difficulties for the long periods of interest because viscoelastic deformation is probably significant. Also, large-scale flow simulations in argillaceous environments generally have neglected osmosis and ultrafiltration, in part because extrapolation of laboratory experience with coupled flow to large scales under in situ conditions is controversial. Nevertheless, the effects are potentially quite important because the coupled flow might cause ultra long lived transient conditions. The difficulties associated with analysis are matched by those of characterizing hydrologic conditions in tight environments; measurements of hydraulic head and sampling of pore fluids have been done only rarely because of the practical difficulties involved. These problems are also discussed in the second part of this paper.

Flow-Driven Waves and Phase-Locked Self-Organization in Quasi-One-Dimensional Colonies of Dictyostelium discoideum

NASA Astrophysics Data System (ADS)

Gholami, A.; Steinbock, O.; Zykov, V.; Bodenschatz, E.

2015-01-01

We report experiments on flow-driven waves in a microfluidic channel containing the signaling slime mold Dictyostelium discoideum. The observed cyclic adenosine monophosphate (cAMP) wave trains developed spontaneously in the presence of flow and propagated with the velocity proportional to the imposed flow velocity. The period of the wave trains was independent of the flow velocity. Perturbations of flow-driven waves via external periodic pulses of the signaling agent cAMP induced 1 ∶1 , 2 ∶1 , 3 ∶1 , and 1 ∶2 frequency responses, reminiscent of Arnold tongues in forced oscillatory systems. We expect our observations to be generic to active media governed by reaction-diffusion-advection dynamics, where spatially bound autocatalytic processes occur under flow conditions.

Assessing the thermal dissipation sap flux density method for monitoring cold season water transport in seasonally snow-covered forests

DOE PAGES

Chan, Allison M.; Bowling, David R.

2017-05-26

Productivity of conifers in seasonally snow-covered forests is high before and during snowmelt when environmental conditions are optimal for photosynthesis. Climate change is altering the timing of spring in many locations, and changes in the date of transition from winter dormancy can have large impacts on annual productivity. Sap flow methods provide a promising approach to monitor tree activity during the cold season and the winter–spring and fall–winter transitions. Although sap flow techniques have been widely used, cold season results are generally not reported. Here we examine the feasibility of using the Granier thermal dissipation (TD) sap flux density methodmore » to monitor transpiration and dormancy of evergreen conifers during the cold season. We conducted a laboratory experiment which demonstrated that the TD method reliably detects xylem water transport (when it occurs) both at near freezing temperature and at low flow rate, and that the sensors can withstand repeated freeze–thaw events. However, the dependence between sensor output and water transport rate in these experiments differed from the established TD relation. In field experiments, sensors installed in two Abies forests lasted through two winters and a summer with low failure. The baseline (no-flow) sensor output varied considerably with temperature during the cold season, and a new baseline algorithm was developed to accommodate this variation. The Abies forests differed in elevation (2070 and 2620 m), and there was a clear difference in timing of initiation and cessation of transpiration between them. We conclude that the TD method can be reliably used to examine water transport during cold periods with associated low flow conditions« less

Assessing the thermal dissipation sap flux density method for monitoring cold season water transport in seasonally snow-covered forests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chan, Allison M.; Bowling, David R.

Productivity of conifers in seasonally snow-covered forests is high before and during snowmelt when environmental conditions are optimal for photosynthesis. Climate change is altering the timing of spring in many locations, and changes in the date of transition from winter dormancy can have large impacts on annual productivity. Sap flow methods provide a promising approach to monitor tree activity during the cold season and the winter–spring and fall–winter transitions. Although sap flow techniques have been widely used, cold season results are generally not reported. Here we examine the feasibility of using the Granier thermal dissipation (TD) sap flux density methodmore » to monitor transpiration and dormancy of evergreen conifers during the cold season. We conducted a laboratory experiment which demonstrated that the TD method reliably detects xylem water transport (when it occurs) both at near freezing temperature and at low flow rate, and that the sensors can withstand repeated freeze–thaw events. However, the dependence between sensor output and water transport rate in these experiments differed from the established TD relation. In field experiments, sensors installed in two Abies forests lasted through two winters and a summer with low failure. The baseline (no-flow) sensor output varied considerably with temperature during the cold season, and a new baseline algorithm was developed to accommodate this variation. The Abies forests differed in elevation (2070 and 2620 m), and there was a clear difference in timing of initiation and cessation of transpiration between them. We conclude that the TD method can be reliably used to examine water transport during cold periods with associated low flow conditions« less

Evaluation of acoustic Doppler velocimetry (ADV) performance under various probe configurations

NASA Astrophysics Data System (ADS)

Liu, Da; Valyrakis, Manousos

2017-04-01

Acoustic Doppler velocimetry (ADV) is widely used as one of the most versatile and robust flow diagnostics tools for both laboratory and field studies across a range of research and applied themes spanning engineering eco-hydraulics and geomorphology. A range of specific ADV probes with varying specifications, are readily available for use by professionals and researchers. However, in practice using certain ADV equipment under certain default configurations can easily result in obtaining flow diagnostics that are non-representative of the real flow conditions. This appears to be true for most probes but even more those with which higher temporal resolution can be achieved - which many times is desired for assessing turbulence levels, amongst others. A preliminary examination revealed that there is a varying level of dependency on a number of the probes' configuration parameters, which even though detailed in the user manual, a definite guide for the user is lacking. Subsequently users of this equipment may end up underutilizing or using it in a manner that returns inaccurate results. There are little, if any, resources in obtaining a better understanding on how to use the probe effectively. To this goal a series of laboratory experiments are conducted, under the same open channel flow conditions, using a profiler (ADCP VectrinoII from Nortek®) aiming to cover the full range of probe configuration combinations that can be used in practice. For each experiment, single or multiple point measurements are taken to reconstruct velocity and turbulence intensity profiles. These are conducted at the same location (mid-channel) under the same flow conditions (referring to steady uniform flow and fully developed turbulence) for all probe configurations. In particular, the effect of tested parameters (including Range length, Range to fist cell, Sampling rate, Ping algorithm, Transmit pulse size and Cell size) on the sensitivity and accuracy of the obtained results is assessed. The signal to noise ratio (SNR) and the correlation of the measurement are used in evaluating the data quality, while a qualitative comparison of the resulting profiles for flow diagnostics is enabled using reference profiles obtained via a VectrinoI ADV (from Nortek®) and MicroADV (from Sontek®) respectively under the exactly same flow condition at the same location. These observations are important to identify its best configuration for a given probe towards improving the data quality and accuracy.

In Situ Steam Fracture Experiments.

DTIC Science & Technology

1984-12-31

pressure and tempera- ture data for use in validation of multi-phase flow models describing - condensation/vaporization, heat-transfer, and fluid/vapor...provide an excellent base for development and/or verification of steam-fracture models for low- permeability materials where heat transfer is significant...representative of post-shot cavity conditions. Steam flow tests have been performed at S-CUBED in a 3-meter long by 20-centimeter diameter sand column. In

Engagement with Novel Virtual Environments: The Role of Perceived Novelty and Flow in the Development of the Deficient Self-Regulation of Internet Use and Media Habits

ERIC Educational Resources Information Center

Tokunaga, Robert Shota

2013-01-01

This article extends theory on the deficient self-regulation (DSR) of Internet use and media habits by integrating predictors relevant to technology use. It introduces novelty perceptions of a technology and flow as conditions that increase the likelihood of experiencing DSR and media habits. An experiment, with between- and within-subjects…

Vortex dipolar structures in a rigid model of the larynx at flow onset

NASA Astrophysics Data System (ADS)

Chisari, N. E.; Artana, G.; Sciamarella, D.

2011-02-01

Starting jet airflow is investigated in a channel with a pair of consecutive slitted constrictions approximating the true and false vocal folds in the human larynx. The flow is visualized using the Schlieren optical technique and simulated by solving the Navier-Stokes equations for an incompressible two-dimensional viscous flow. Laboratory and numerical experiments show the spontaneous formation of three different classes of vortex dipolar structures in several regions of the laryngeal profile under conditions that may be assimilated to those of voice onset.

Numerical simulation of a hovering rotor using embedded grids

NASA Technical Reports Server (NTRS)

Duque, Earl-Peter N.; Srinivasan, Ganapathi R.

1992-01-01

The flow field for a rotor blade in hover was computed by numerically solving the compressible thin-layer Navier-Stokes equations on embedded grids. In this work, three embedded grids were used to discretize the flow field - one for the rotor blade and two to convect the rotor wake. The computations were performed at two hovering test conditions, for a two-bladed rectangular rotor of aspect ratio six. The results compare fairly with experiment and illustrates the use of embedded grids in solving helicopter type flow fields.

On the computation of steady Hopper flows. II: von Mises materials in various geometries

NASA Astrophysics Data System (ADS)

Gremaud, Pierre A.; Matthews, John V.; O'Malley, Meghan

2004-11-01

Similarity solutions are constructed for the flow of granular materials through hoppers. Unlike previous work, the present approach applies to nonaxisymmetric containers. The model involves ten unknowns (stresses, velocity, and plasticity function) determined by nine nonlinear first order partial differential equations together with a quadratic algebraic constraint (yield condition). A pseudospectral discretization is applied; the resulting problem is solved with a trust region method. The important role of the hopper geometry on the flow is illustrated by several numerical experiments of industrial relevance.

The growth of homogeneous semiconductor crystals in a centrifuge by the stabilizing influence of the Coriolis force

NASA Astrophysics Data System (ADS)

Müller, G.; Neumann, G.; Weber, W.

1992-04-01

Both experimental and numerical results on crystal growth and fluid flow studies carried out in a centrifuge are reported. It is shown that the formation of doping striations can be avoided in the vertical Bridgman and the horizontal zone melting growth of Te-doped InSb if the centrifugal acceleration is increased beyond a critical value depending on the thermal boundary conditions. Furthermore, the maximum rate for the growth of inclusion free GaSb crystals grown by the travelling heater method (THM) is increased by a factor of 10 if this method is carried out at an acceleration of 20 times earth gravity. Model experiments in the Bridgman configuration using a test cell with liquid Ga and a larger series of thermocouples are conducted by varying the thermal boundary conditions and the rotation rate of the centrifuge. A three-dimensional time dependent numerical simulation of the fluid flow under the experimental conditions was carried out using a finite difference numerical scheme. It follows clearly that the Coriolis force acting on the melt in the rotating centrifuge system significantly influences the buoyancy-driven convection with respect to the flow patterns as well as the stability. The Coriolis force causes two very different flow states (I and II), depending on whether the rotation sense of the flow is in the same or in the opposite direction to that of the centrifuge. Type I is very similar to that normally observed on earth. Type II is only observed on the centrifuge and has a very large stability range of steady convection which can be used to grow striation-free crystals. All results give excellent agreement between model experiments and numerical calculations, which finally leads to a fully satisfying explanation of the crystal growth results on our centrifuge.

Fluid dynamics and low gravity effects of chemical vapor deposition

NASA Technical Reports Server (NTRS)

Nyce, Thomas A.; Rosenberger, Franz

1990-01-01

Based on the comparison between experimental data and numerical results for the growth of GaAs from TMGa, it was shown that 3D simulations are necessary to simulate rectangular CVD reactors even when operated under subcritical (Ra) conditions. The important points found are summarized in the three attached reprints. The experimental studies of mixed convection in horizontal channels have shown three regimes of high Ra (22,220) number flows. At Re = 18.5, the rolls develop very quickly, significantly modulating the axial velocity even before it reaches the beginning of the hot plate. A few centimeters downstream, the velocities become asymmetric about the vertical centerplane and at x = 12 cm, become unsteady. These asymmetries were predicted theoretically, but experimental evidence has not been published prior to this work. At Re = 36, the axial velocity is only slightly modified at x = 0. Although the flow remains steady and symmetric about the vertical centerplane, there is a small spatial oscillation in the velocities over the length of the channel. The period of this oscillation was around 5 cm. At Re = 54, the longitudinal rolls developed smoothly over a length of 30 cm, with no asymmetries, unsteadiness, or spatial oscillations. Comparison of numerical simulations of these flows to experiments has revealed the importance and difficulty of setting proper thermal boundary conditions on the sidewalls. Calculated flows and experimentally measured flows showed very similar profiles, but at different axial locations, with the rolls developing more rapidly in the experiments. This is directly attributable to partially conducting sidewalls of the apparatus being hotter in the entrance section than the adiabatic walls of the simulations. A thorough comparison of the experimental data and numerical results for a variety of sidewall boundary conditions is in preparation.

The Subsurface Flow and Transport Laboratory: A New Department of Energy User's Facility for Intermediate-Scale Experimentation

NASA Astrophysics Data System (ADS)

Wietsma, T. W.; Oostrom, M.; Foster, N. S.

2003-12-01

Intermediate-scale experiments (ISEs) for flow and transport are a valuable tool for simulating subsurface features and conditions encountered in the field at government and private sites. ISEs offer the ability to study, under controlled laboratory conditions, complicated processes characteristic of mixed wastes and heterogeneous subsurface environments, in multiple dimensions and at different scales. ISEs may, therefore, result in major cost savings if employed prior to field studies. A distinct advantage of ISEs is that researchers can design physical and/or chemical heterogeneities in the porous media matrix that better approximate natural field conditions and therefore address research questions that contain the additional complexity of processes often encountered in the natural environment. A new Subsurface Flow and Transport Laboratory (SFTL) has been developed for ISE users in the Environmental Spectroscopy & Biogeochemistry Facility in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The SFTL offers a variety of columns and flow cells, a new state-of-the-art dual-energy gamma system, a fully automated saturation-pressure apparatus, and analytical equipment for sample processing. The new facility, including qualified staff, is available for scientists interested in collaboration on conducting high-quality flow and transport experiments, including contaminant remediation. Close linkages exist between the SFTL and numerical modelers to aid in experimental design and interpretation. This presentation will discuss the facility and outline the procedures required to submit a proposal to use this unique facility for research purposes. The W. R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility, is sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

Supersonic/Hypersonic Laminar Heating Correlations for Rectangular and Impact-Induced Open and Closed Cavities

NASA Technical Reports Server (NTRS)

Everhart, Joel L.

2008-01-01

Impact and debris damage to the Space Shuttle Orbiter Thermal Protection System tiles is a random phenomenon, occurring at random locations on the vehicle surface, resulting in random geometrical shapes that are exposed to a definable range of surface flow conditions. In response to the 2003 Final Report of the Columbia Accident Investigation Board, wind tunnel aeroheating experiments approximating a wide range of possible damage scenarios covering both open and closed cavity flow conditions were systematically tested in hypersonic ground based facilities. These data were analyzed and engineering assessment tools for damage-induced fully-laminar heating were developed and exercised on orbit. These tools provide bounding approximations for the damaged-surface heating environment. This paper presents a further analysis of the baseline, zero-pressure-gradient, idealized, rectangular-geometry cavity heating data, yielding new laminar correlations for the floor-averaged heating, peak cavity endwall heating, and the downstream decay rate. Correlation parameters are derived in terms of cavity geometry and local flow conditions. Prediction Limit Uncertainty values are provided at the 95%, 99% and 99.9% levels of significance. Non-baseline conditions, including non-rectangular geometries and flows with known pressure gradients, are used to assess the range of applicability of the new correlations. All data variations fall within the 99% Prediction Limit Uncertainty bounds. Importantly, both open-flow and closed-flow cavity heating are combined into a single-curve parameterization of the heating predictions, and provide a concise mathematical model of the laminar cavity heating flow field with known uncertainty.

Fluid Pocket Generation in Response to Heterogeneous Reactivity of a Rock Fracture Under Hydrothermal Conditions

NASA Astrophysics Data System (ADS)

Okamoto, A.; Tanaka, H.; Watanabe, N.; Saishu, H.; Tsuchiya, N.

2017-10-01

Fractures are the location of various water-rock interactions within the Earth's crust; however, the impact of the chemical heterogeneity of fractures on hydraulic properties is poorly understood. We conducted flow-through experiments on the dissolution of granite with a tensile fracture at 350°C and fluid pressure of 20 MPa with confining pressure of 40 MPa. The aperture structures were evaluated by X-ray computed tomography before and after the experiments. Under the experimental conditions, quartz grains dissolve rapidly to produce grain-scale pockets on the fracture surface, whereas altered feldspar grains act as asperities to sustain the open cavities. The fracture contained gouge with large surface area. The feedback between fluid flow and the rapid dissolution of gouge material produced large fluid pockets, whereas permeability did not always increase significantly. Such intense hydrological-chemical interactions could strongly influence the porosity-permeability relationship of fractured reservoirs in the crust.

Estimating pesticide sampling rates by the polar organic chemical integrative sampler (POCIS) in the presence of natural organic matter and varying hydrodynamic conditions

USGS Publications Warehouse

Charlestra, Lucner; Amirbahman, Aria; Courtemanch, David L.; Alvarez, David A.; Patterson, Howard

2012-01-01

The polar organic chemical integrative sampler (POCIS) was calibrated to monitor pesticides in water under controlled laboratory conditions. The effect of natural organic matter (NOM) on the sampling rates (Rs) was evaluated in microcosms containing -1 of total organic carbon (TOC). The effect of hydrodynamics was studied by comparing Rs values measured in stirred (SBE) and quiescent (QBE) batch experiments and a flow-through system (FTS). The level of NOM in the water used in these experiments had no effect on the magnitude of the pesticide sampling rates (p > 0.05). However, flow velocity and turbulence significantly increased the sampling rates of the pesticides in the FTS and SBE compared to the QBE (p < 0.001). The calibration data generated can be used to derive pesticide concentrations in water from POCIS deployed in stagnant and turbulent environmental systems without correction for NOM.

Rheological measurements in reduced gravity

NASA Astrophysics Data System (ADS)

Bakhtiyarov, Sayavur I.; Overfelt, Ruel A.

1999-01-01

Rheology of fluidized beds and settling suspensions were studied experimentally in a series of reduced gravity parabolic flights aboard NASA's KC-135 aircraft. Silica sands of two different size distributions were fluidized by air. The slurries were made using silica sand and Glycerol solution. The experimental set up incorporated instrumentation to measure the air flow rate, the pressure drop and the apparent viscosity of the fluidized sand and sand suspensions at a wide range of the shear rates. The fluidization chamber and container had transparent walls to allow visualization of the structure changes involved in fluidization and in Couette flow in reduced gravity. Experiments were performed over a broad range of gravitational accelerations including microgravity and double gravity conditions. The results of the flight and ground experiments reveal significant differences in overall void fraction and hence in the apparent viscosity of fluidized sand and sand suspensions under microgravity as compared to one-g conditions.

Pilot points method for conditioning multiple-point statistical facies simulation on flow data

NASA Astrophysics Data System (ADS)

Ma, Wei; Jafarpour, Behnam

2018-05-01

We propose a new pilot points method for conditioning discrete multiple-point statistical (MPS) facies simulation on dynamic flow data. While conditioning MPS simulation on static hard data is straightforward, their calibration against nonlinear flow data is nontrivial. The proposed method generates conditional models from a conceptual model of geologic connectivity, known as a training image (TI), by strategically placing and estimating pilot points. To place pilot points, a score map is generated based on three sources of information: (i) the uncertainty in facies distribution, (ii) the model response sensitivity information, and (iii) the observed flow data. Once the pilot points are placed, the facies values at these points are inferred from production data and then are used, along with available hard data at well locations, to simulate a new set of conditional facies realizations. While facies estimation at the pilot points can be performed using different inversion algorithms, in this study the ensemble smoother (ES) is adopted to update permeability maps from production data, which are then used to statistically infer facies types at the pilot point locations. The developed method combines the information in the flow data and the TI by using the former to infer facies values at selected locations away from the wells and the latter to ensure consistent facies structure and connectivity where away from measurement locations. Several numerical experiments are used to evaluate the performance of the developed method and to discuss its important properties.

Stably stratified canopy flow in complex terrain

NASA Astrophysics Data System (ADS)

Xu, X.; Yi, C.; Kutter, E.

2015-07-01

Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem-atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k-ϵ turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this two-dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional Navier-Stokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.

Flow regime alterations under changing climate in two river basins: Implications for freshwater ecosystems

USGS Publications Warehouse

Gibson, C.A.; Meyer, J.L.; Poff, N.L.; Hay, L.E.; Georgakakos, A.

2005-01-01

We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee-Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river-floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee-Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee-Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability of the river to assimilate wastewater treatment plant effluent. Our study illustrates the types of changes that river ecosystems might experience under future climates. Copyright ?? 2005 John Wiley & Sons, Ltd.

Robust Vehicle Detection under Various Environmental Conditions Using an Infrared Thermal Camera and Its Application to Road Traffic Flow Monitoring

PubMed Central

Iwasaki, Yoichiro; Misumi, Masato; Nakamiya, Toshiyuki

2013-01-01

We have already proposed a method for detecting vehicle positions and their movements (henceforth referred to as “our previous method”) using thermal images taken with an infrared thermal camera. Our experiments have shown that our previous method detects vehicles robustly under four different environmental conditions which involve poor visibility conditions in snow and thick fog. Our previous method uses the windshield and its surroundings as the target of the Viola-Jones detector. Some experiments in winter show that the vehicle detection accuracy decreases because the temperatures of many windshields approximate those of the exterior of the windshields. In this paper, we propose a new vehicle detection method (henceforth referred to as “our new method”). Our new method detects vehicles based on tires' thermal energy reflection. We have done experiments using three series of thermal images for which the vehicle detection accuracies of our previous method are low. Our new method detects 1,417 vehicles (92.8%) out of 1,527 vehicles, and the number of false detection is 52 in total. Therefore, by combining our two methods, high vehicle detection accuracies are maintained under various environmental conditions. Finally, we apply the traffic information obtained by our two methods to traffic flow automatic monitoring, and show the effectiveness of our proposal. PMID:23774988

Turbulent Transition in Electromagnetically Levitated Drops

NASA Technical Reports Server (NTRS)

Hyers, Robert W.; Trapaga, G.; Abedian, B.; Matson, D. M.; Rose, M. Franklin (Technical Monitor)

2000-01-01

Electromagnetic levitation (EML) is an important tool in materials research. Because a sample can be processed without contact with a container, experiments may be performed on high temperature, highly reactive, and undercooled liquid metals. Many of these experiments are affected by fluid flow in the sample, driven by the electromagnetic positioning force. Despite the importance of convection in these experiments, the transition to turbulence is not well understood in this system. However, we have observed a transition from laminar to turbulent flow in EML droplets in the course of microgravity experiments in TEMPUS on the Space Shuttle (STS-94). The transition occurs repeatably and over a narrow range of conditions. These experimental observations are compared with two competing theories about the transition to turbulence. Also, the results of a particle tracking study of the instabilities leading up to the transition to turbulence are presented.

An investigation of two phase flow pressure drops in a reduced acceleration environment

NASA Astrophysics Data System (ADS)

Wheeler, Montgomery W.; Best, Frederick R.; Reinarts, Thomas R.

1993-01-01

Thermal systems for space applications based on two phase flow have several advantages over single phase systems. Two phase thermal energy management and dynamic power conversion system advantages include the capability of achieving high specific power levels. Before two phase systems for space applications can be designed effectively, knowledge of the flow behavior in a reduced acceleration environment is necessary. To meet these needs, two phase flow experiments were conducted aboard the National Aeronautic and Space Administration's KC-135 using R12 as the working fluid. Annular flow two phase pressure drops were measured through 10.41-mm ID 1.251-m long glass tubing during periods with acceleration levels in the range ±0.05 G. The experiments were conducted with emphasis on achieving data with a high level of accuracy. The reduced acceleration annular flow pressure drops were compred with pressure drops measured in a 1-G environment for similar flow conditions. The reduced acceleration pressure drops were found to be 45% greater than the 1-G pressure drops. In addition, the reduced acceleration annular flow interfacial friction factors were compared with models for vertical up-flow in a 1-G environment. The reduced acceleration interfacial friction factor data was not predicted by the 1-G models.

Internal-liquid-film-cooling Experiments with Air-stream Temperatures to 2000 Degrees F. in 2- and 4-inch-diameter Horizontal Tubes

NASA Technical Reports Server (NTRS)

Kinney, George R; Abramson, Andrew E; Sloop, John L

1952-01-01

Report presents the results of an investigation conducted to determine the effectiveness of liquid-cooling films on the inner surfaces of tubes containing flowing hot air. Experiments were made in 2- and 4-inch-diameter straight metal tubes with air flows at temperatures from 600 degrees to 2000 degrees F. and diameter Reynolds numbers from 2.2 to 14 x 10(5). The film coolant, water, was injected around the circumference at a single axial position on the tubes at flow rates from 0.02 to .24 pound per second per foot of tube circumference (0.8 to 12 percent of the air flow). Liquid-coolant films were established and maintained around and along the tube wall in concurrent flow with the hot air. The results indicated that, in order to film cool a given surface area with as little coolant flow as possible, it may be necessary to limit the flow of coolant introduced at a single axial position and to introduce it at several axial positions. The flow rate of inert coolant required to maintain liquid-film cooling over a given area of tube surface can be estimated when the gas-flow conditions are known by means of a generalized plot of the film-cooling data.

On the flow structure of cloud cavitating flow around an axisymmetric body near the free surface

NASA Astrophysics Data System (ADS)

Wang, Yiwei; Wu, Xiaocui; Huang, Chenguang; Yu, XianXian

2015-12-01

The influence of the free surface on the cavitating flow is an important issue involved in the design of high speed surface vehicles. In the present paper, unsteady cavitating turbulent flow around an axisymmetric body near the free surface was investigated by both launching experiment and LES simulation. The vortex motion induced by cavity shedding under the effect of the free surface is emphatically analyzed by comparing with the submerged condition. The vortex shedding process around the projectile is not synchronized, while the asymmetric characteristic in collapse process is more remarkable, with the generation of multiple vortex ring structures.

Flight Test Results from the Rake Airflow Gage Experiment on the F-15B Airplane

NASA Technical Reports Server (NTRS)

Frederick, Michael A.; Ratnayake, Nalin A.

2010-01-01

The Rake Airflow Gage Experiment involves a flow-field survey rake that was flown on the Propulsion Flight Test Fixture at the NASA Dryden Flight Research Center using the Dryden F-15B research test bed airplane. The objective of this flight test was to ascertain the flow-field angularity, local Mach number profile, total pressure distortion, and dynamic pressure at the aerodynamic interface plane of the Channeled Centerbody Inlet Experiment. This new mixed-compression, supersonic inlet is planned for flight test in the near term. Knowledge of the flow-field characteristics at this location underneath the airplane is essential to flight test planning and computational modeling of the new inlet, and it is also applicable for future propulsion systems research that may use the Propulsion Flight Test Fixture. This report describes the flight test preparation and execution, and the local flowfield properties calculated from pressure measurements of the rake. Data from the two Rake Airflow Gage Experiment research flights demonstrate that the F-15B airplane, flying at a free-stream Mach number of 1.65 and a pressure altitude of 40,000 ft, would achieve the desired local Mach number for the future inlet flight test. Interface plane distortion levels of 2 percent and a local angle of attack of 2 were observed at this condition. Alternative flight conditions for future testing and an exploration of certain anomalous data also are provided.

Lanthanide-labeled clay: A new method for tracing sediment transport in Karst

USGS Publications Warehouse

Mahler, B.J.; Bennett, P.C.; Zimmerman, M.

1998-01-01

Mobile sediment is a fundamental yet poorly characterized aspect of mass transport through karst aquifers. Here the development and field testing of an extremely sensitive particle tracer that may be used to characterize sediment transport in karst aquifers is described. The tracer consists of micron-size montmorillonite particles homoionized to the lanthanide form; after injection and retrieval from a ground water system, the lanthanide ions are chemically stripped from the clay and quantified by high performance liquid chromatography. The tracer meets the following desired criteria: low detection limit; a number of differentiable signatures; inexpensive production and quantification using standard methods; no environmental risks; and hydrodynamic properties similar to the in situ sediment it is designed to trace. The tracer was tested in laboratory batch experiments and field tested in both surface water and ground water systems. In surface water, arrival times of the tracer were similar to those of a conservative water tracer, although a significant amount of material was lost due to settling. Two tracer tests were undertaken in a karst aquifer under different flow conditions. Under normal flow conditions, the time of arrival and peak concentration of the tracer were similar to or preceded that of a conservative water tracer. Under low flow conditions, the particle tracer was not detected, suggesting that in low flow the sediment settles out of suspension and goes into storage.Mobile sediment is a fundamental yet poorly characterized aspect of mass transport through karst aquifers. Here the development and field testing of an extremely sensitive particle tracer that may be used to characterize sediment transport in karst aquifers is described. The tracer consists of micron-size montmorillonite particles homoionized to the lanthanide form; after injection and retrieval from a ground water system, the lanthanide ions are chemically stripped from the clay and quantified by high performance liquid chromatography. The tracer meets the following desired criteria: low detection limit; a number of differentiable signatures; inexpensive production and quantification using standard methods; no environmental risks; and hydrodynamic properties similar to the in situ sediment it is designed to trace. The tracer was tested in laboratory batch experiments and field tested in both surface water and ground water systems. In surface water, arrival times of the tracer were similar to those of a conservative water tracer, although a significant amount of material was lost due to settling. Two tracer tests were undertaken in a karst aquifer under different flow conditions. Under normal flow conditions, the time of arrival and peak concentration of the tracer were similar to or preceded that of a conservative water tracer. Under low flow conditions, the particle tracer was not detected, suggesting that in low flow the sediment settles out of suspension and goes into storage.

Observations from borehole dilution logging experiments in fractured crystalline rock under variable hydraulic conditions

USGS Publications Warehouse

Harte, Philip T.; Anderson, Alton; Williams, John H.

2014-01-01

Identifying hydraulically active fractures in low permeability, crystalline-bedrock aquifers requires a variety of geophysical and hydrogeophysical borehole tools and approaches. One such approach is Single Borehole Dilution Tests (SBDT), which in some low flow cases have been shown to provide greater resolution of borehole flow than other logging procedures, such as vertical differential Heat Pulse Flowmeter (HPFM) logging. Because the tools used in SBDT collect continuous profiles of water quality or dye changes, they can identify horizontal flow zones and vertical flow. We used SBDT with a food grade blue dye as a tracer and dual photometer-nephelometer measurements to identify low flow zones.SBDT were conducted at seven wells with open boreholes (exceeding 300 ft). At most of the wells HPFM logs were also collected. The seven wells are set in low-permeability, fractured granite and gneiss rocks underlying a former tetrachloroeythylene (PCE) source area at the Savage Municipal Well Superfund site in Milford, NH. Time series SBDT logs were collected at each of the seven wells under three distinct hydraulic conditions: (1) ambient conditions prior to a pump test at an adjacent well, (2) mid test, after 2-3 days of the start of the pump test, and (3) at the end of the test, after 8-9 days of the pump test. None of the SBDT were conducted under pumping conditions in the logged well. For each condition, wells were initially passively spiked with blue dye once and subsequent time series measurements were made.Measurement accuracy and precision of the photometer tool is important in SBDT when attempting to detect low rates of borehole flow. Tests indicate that under ambient conditions, none of the wells had detectable flow as measured with HPFM logging. With SBDT, 4 of the 7 showed the presence of some very low flow. None of 5 (2 of the 7 wells initially logged with HPFM under ambient conditions were not re-logged) wells logged with the HPFM during the pump test had detectable flow. However, 3 of the 5 wells showed the patterns of very low flow with SBDT during the pump test including pumping induced changes of inflow and outflow patterns at one well.

Vascular functioning and the water balance of ripening kiwifruit (Actinidia chinensis) berries

PubMed Central

Clearwater, Michael J.; Luo, Zhiwei; Ong, Sam Eng Chye; Blattmann, Peter; Thorp, T. Grant

2012-01-01

Indirect evidence suggests that water supply to fleshy fruits during the final stages of development occurs through the phloem, with the xylem providing little water, or acting as a pathway for water loss back to the plant. This inference was tested by examining the water balance and vascular functioning of ripening kiwifruit berries (Actinidia chinensis var. chinensis ‘Hort16A’) exhibiting a pre-harvest ‘shrivel’ disorder in California, and normal development in New Zealand. Dye labelling and mass balance experiments indicated that the xylem and phloem were both functional and contributed approximately equally to the fruit water supply during this stage of development. The modelled fruit water balance was dominated by transpiration, with net water loss under high vapour pressure deficit (Da) conditions in California, but a net gain under cooler New Zealand conditions. Direct measurement of pedicel sap flow under controlled conditions confirmed inward flows in both the phloem and xylem under conditions of both low and high Da. Phloem flows were required for growth, with gradual recovery after a step increase in Da. Xylem flows alone were unable to support growth, but did supply transpiration and were responsive to Da-induced pressure fluctuations. The results suggest that the shrivel disorder was a consequence of a high fruit transpiration rate, and that the perception of complete loss or reversal of inward xylem flows in ripening fruits should be re-examined. PMID:22155631

An experimental flow-through assessment of acidic Fe/Mg smectite formation on early Mars

NASA Astrophysics Data System (ADS)

Sutter, B.; Peretyazhko, T.; Garcia, A. H.; Ming, D. W.

2017-12-01

Orbital observations have detected the phyllosilicate smectite in layered material hundreds of meters thick, intracrater depositional fans, and plains sediments on Mars; however, the detection of carbonate deposits is limited. Instead of neutral/alkaline conditions during the Noachian, early Mars may have experienced mildly acidic conditions derived from volcanic acid-sulfate solutions that allowed Fe/Mg smectite formation but prevented widespread carbonate formation. The detection of acid sulfates (e.g., jarosite) associated with smectite in Mawrth Vallis supports this hypothesis. Previous work demonstrated smectite (saponite) formation in closed hydrologic systems (batch reactor) from basaltic glass at pH 4 and 200°C (Peretyazhko et al., 2016 GCA). This work presents results from alteration of basaltic glass from alkaline to acidic conditions in open hydrologic systems (flow-through reactor). Preliminary experiments exposed basaltic glass to deionized water at 190°C at 0.25 ml/min where solution pH equilibrated to 9.5. These initial high pH experiments were conducted to evaluate the flow-through reactor system before working with lower pHs. Smectite at this pH was not produced and instead X-ray diffraction results consistent with serpentine was detected. Experiments are in progress exposing basaltic glass from pH 8 down to pH 3 to determine what range of pHs could allow for smectite formation in this experimental open-system. The production of smectite under an experimental open-system at low pHs if successful, would support a significant paradigm shift regarding the geochemical evolution of early Mars: Early Mars geochemical solutions were mildly acidic, not neutral/alkaline. This could have profound implications regarding early martain microbiology where acid conditions instead of neutral/alkaline conditions will require further research in terrestrial analogs to address the potential for biosignature preservation on Mars (Johnson et al., 2016, LPSC).

A steady-state continuous flow chamber for the study of daytime and nighttime chemistry under atmospherically relevant NO levels

NASA Astrophysics Data System (ADS)

Zhang, Xuan; Ortega, John; Huang, Yuanlong; Shertz, Stephen; Tyndall, Geoffrey S.; Orlando, John J.

2018-05-01

Experiments performed in laboratory chambers have contributed significantly to the understanding of the fundamental kinetics and mechanisms of the chemical reactions occurring in the atmosphere. Two chemical regimes, classified as high-NO vs. zero-NO conditions, have been extensively studied in previous chamber experiments. Results derived from these two chemical scenarios are widely parameterized in chemical transport models to represent key atmospheric processes in urban and pristine environments. As the anthropogenic NOx emissions in the United States have decreased remarkably in the past few decades, the classic high-NO and zero-NO conditions are no longer applicable to many regions that are constantly impacted by both polluted and background air masses. We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady-state continuous flow mode for the study of atmospheric chemistry under intermediate NO conditions. This particular chemical regime is characterized by constant sub-ppb levels of NO and can be created in the chamber by precise control of the inflow NO concentration and the ratio of chamber mixing to residence timescales. Over the range of conditions achievable in the chamber, the lifetime of peroxy radicals (RO2), a key intermediate from the atmospheric degradation of volatile organic compounds (VOCs), can be extended to several minutes, and a diverse array of reaction pathways, including unimolecular pathways and bimolecular reactions with NO and HO2, can thus be explored. Characterization experiments under photolytic and dark conditions were performed and, in conjunction with model predictions, provide a basis for interpretation of prevailing atmospheric processes in environments with intertwined biogenic and anthropogenic activities. We demonstrate the proof of concept of the steady-state continuous flow chamber operation through measurements of major first-generation products, methacrolein (MACR) and methyl vinyl ketone (MVK), from OH- and NO3-initiated oxidation of isoprene.

Identification of Instability Modes of Transition in Underexpanded Jets

NASA Technical Reports Server (NTRS)

Inman, Jennifer A.; Danehy, Paul M.; Nowak, Robert J.; Alderfer, David W.

2008-01-01

A series of experiments into the behavior of underexpanded jet flows has been conducted at NASA Langley Research Center. Two nozzles supplied with high-pressure gas were used to generate axisymmetric underexpanded jets exhausting into a low-pressure chamber. These nozzles had exit Mach numbers of 1 and 2.6, though this paper will present cases involving only the supersonic nozzle. Reynolds numbers based on nozzle exit conditions ranged from about 300 to 22,000, and nozzle exit-to-ambient jet pressure ratios ranged from about 1 to 25. For the majority of cases, the jet fluid was a mixture of 99.5% nitrogen seeded with 0.5% nitric oxide (NO). Planar laser-induced fluorescence (PLIF) of NO is used to visualize the flow, visualizing planar slices of the flow rather than path integrated measurements. In addition to revealing the size and location of flow structures, PLIF images were also used to identify unsteady jet behavior in order to quantify the conditions governing the transition to turbulent flow. Flow structures that contribute to the growth of flow instabilities have been identified, and relationships between Reynolds number and transition location are presented. By highlighting deviations from mean flow properties, PLIF images are shown to aide in the identification and characterization of flow instabilities and the resulting process of transition to turbulence.

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

NASA Astrophysics Data System (ADS)

Kwon, Jae-Min; Ku, S.; Choi, M. J.; Chang, C. S.; Hager, R.; Yoon, E. S.; Lee, H. H.; Kim, H. S.

2018-05-01

We perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E × B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Te -driven trapped electron modes. This implies that the enhanced E × B flow can sustain a quasi-internal transport barrier for Te in an inner region neighboring the magnetic island. The enhanced E × B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.

A full-scale STOVL ejector experiment

NASA Technical Reports Server (NTRS)

Barankiewicz, Wendy S.

1993-01-01

The design and development of thrust augmenting short take-off and vertical landing (STOVL) ejectors has typically been an iterative process. In this investigation, static performance tests of a full-scale vertical lift ejector were performed at primary flow temperatures up to 1560 R (1100 F). Flow visualization (smoke generators, yarn tufts and paint dots) was used to assess inlet flowfield characteristics, especially around the primary nozzle and end plates. Performance calculations are presented for ambient temperatures close to 480 R (20 F) and 535 R (75 F) which simulate 'seasonal' aircraft operating conditions. Resulting thrust augmentation ratios are presented as functions of nozzle pressure ratio and temperature. Full-scale experimental tests such as this are expensive, and difficult to implement at engine exhaust temperatures. For this reason the utility of using similarity principles -- in particular, the Munk and Prim similarity principle for isentropic flow -- was explored. At different primary temperatures, exit pressure contours are compared for similarity. A nondimensional flow parameter is then shown to eliminate primary nozzle temperature dependence and verify similarity between the hot and cold flow experiments. Under the assumption that an appropriate similarity principle can be established, then properly chosen performance parameters should be similar for both hot flow and cold flow model tests.

Βiocolloid and colloid transport through water-saturated columns packed with glass beads: Effect of gravity

NASA Astrophysics Data System (ADS)

Chrysikopoulos, C. V.; Syngouna, V. I.

2013-12-01

The role of gravitational force on biocolloid and colloid transport in water-saturated columns packed with glass beads was investigated. Transport experiments were performed with biocolloids (bacteriophages: ΦΧ174, MS2) and colloids (clays: kaolinite KGa-1b, montmorillonite STx-1b). The packed columns were placed in various orientations (horizontal, vertical, and diagonal) and a steady flow rate of Q=1.5 mL/min was applied in both up-flow and down-flow modes. All experiments were conducted under electrostatically unfavorable conditions. The experimental data were fitted with a newly developed, analytical, one dimensional, colloid transport model, accounting for gravity effects. The results revealed that flow direction has a significant influence on particle deposition. The rate of particle deposition was shown to be greater for up-flow than for down-flow direction, suggesting that gravity was a significant driving force for biocolloid and colloid deposition. Schematic illustration of a packed column with up-flow velocity having orientation (-i) with respect to gravity. The gravity vector components are: g(i)= g(-z) sinβ i, and g(-j)= -g(-z) cosβ j. Experimental setup showing the various column arrangements: (a) horizontal, (b) diagonal, and (c) vertical.

Effect of seabed roughness on tidal current turbines

NASA Astrophysics Data System (ADS)

Gupta, Vikrant; Wan, Minping

2017-11-01

Tidal current turbines are shown to have potential to generate clean energy for a negligible environmental impact. These devices, however, operate in high to moderate current regions where the flow is highly turbulent. It has been shown in flume tank experiments at IFREMER in Boulogne-Sur-Mer (France) and NAFL in the University of Minnesota (US) that the level of turbulence and boundary layer profile affect a turbine's power output and wake characteristics. A major factor that determines these marine flow characteristics is the seabed roughness. Experiments, however, cannot simulate the high Reynolds number conditions of real marine flows. For that, we rely on numerical simulations. High accuracy numerical methods, such as DNS, of wall-bounded flows are very expensive, where the number of grid-points needed to resolve the flow varies as (Re) 9 / 4 (where Re is the flow Reynolds number). While numerically affordable RANS methods compromise on accuracy. Wall-modelled LES methods, which provide both accuracy and affordability, have been improved tremendously in the recent years. We discuss the application of such numerical methods for studying the effect of seabed roughness on marine flow features and their impact on turbine power output and wake characteristics. NSFC, Project Number 11672123.

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, Jae-Min; Ku, S.; Choi, M. J.

Here, we perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E x B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Tmore » e-driven trapped electron modes. This implies that the enhanced E x B flow can sustain a quasi-internal transport barrier for T e in an inner region neighboring the magnetic island. The enhanced E x B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.« less

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

DOE PAGES

Kwon, Jae-Min; Ku, S.; Choi, M. J.; ...

2018-05-01

Here, we perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E x B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Tmore » e-driven trapped electron modes. This implies that the enhanced E x B flow can sustain a quasi-internal transport barrier for T e in an inner region neighboring the magnetic island. The enhanced E x B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.« less

Simulation of fluid flows during growth of organic crystals in microgravity

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Sutter, James K.; Balasubramaniam, R.; Fowlis, William K.; Radcliffe, M. D.; Drake, M. C.

1987-01-01

Several counter diffusion type crystal growth experiments were conducted in space. Improvements in crystal size and quality are attributed to reduced natural convection in the microgravity environment. One series of experiments called DMOS (Diffusive Mixing of Organic Solutions) was designed and conducted by researchers at the 3M Corporation and flown by NASA on the space shuttle. Since only limited information about the mixing process is available from the space experiments, a series of ground based experiments was conducted to further investigate the fluid dynamics within the DMOS crystal growth cell. Solutions with density differences in the range of 10 to the -7 to 10 to the -4 power g/cc were used to simulate microgravity conditions. The small density differences were obtained by mixing D2O and H2O. Methylene blue dye was used to enhance flow visualization. The extent of mixing was measured photometrically using the 662 nm absorbance peak of the dye. Results indicate that extensive mixing by natural convection can occur even under microgravity conditions. This is qualitatively consistent with results of a simple scaling analysis. Quantitave results are in close agreement with ongoing computational modeling analysis.

Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device

DOE PAGES

Silva, Bruno F. B.; Zepeda-Rosales, Miguel; Venkateswaran, Neeraja; ...

2014-10-30

In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ~±11° in themore » velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen–Leslie–Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (~90 and 0°). Lastly, the technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays.« less

Enhancement of Condensation Heat Transfer by Counter-Corrent Wavy Flow in a Vertical Tube

NASA Astrophysics Data System (ADS)

Teranishi, Tsunenobu; Ozawa, Takanori; Takimoto, Akira

As a basic research for the development of a high-performance and environment-friendly thermal energy recovery system, detailed experiments have been conducted to investigate the mechanism of the enhancement of condensation heat transfer by the counter-current moist air flow in a vertical tube. From the results of visual observation of the phenomena by using a high-speed video recorder and the measurement of condensate rate respectively from an upper and a bottom end of a cooled tube, in which various humidity vapor of air and water flowed upward or downward, the dynamic behavior of liquid film condensed on cooled surface and moist air flow was classified into four distinctive patterns in quality and quantity. Further, the effect of the scale and the operating condition such as the diameter and the length of tube, the vapor concentration and the moist air temperature, on the condensation rate of counter-current wavy flow was clarified in relation to the pattern and condition of occurrence of the wavy flow of liquid film and flooding due to the shear forces between the interface of liquid and moist air flow.

The Role of Fine Sediment Content on Soil Consolidation and Debris Flows Development after Earthquake

NASA Astrophysics Data System (ADS)

Lyu, L.; Xu, M., III; Wang, Z.

2017-12-01

Fine sediment has been identified as an important factor determining the critical runoff that initiates debris flows because its contribution to shear strength through consolidation. Especially, owing to the 2008 Wenchuan earthquake in China enormous of loose sediment with different fractions of fine particles was eroded and supplied as materials for debris flows. The loose materials are gradually consolidated along with time, and therefore stronger rainfall is required to overcome the shear strength and to initiate debris flows. In this study, flume experiments were performed to explore soil consolidation and shear strength on mass failure and debris flow initiation under the conditions that different fractions of fine sediment were contained in the materials. Under the low content of fine sediment conditions (mass percentages: 0-10%), the debris flows formed with large pores and low shear strength and thus fine particles were too few to fill up the pores among the coarse particles. The consolidation rate was mostly influenced by the content of the fine particles. Consolidation of fine particles caused an increase of the shear strength and decrease of the rainfall infiltration, and therefore, debris flow initiation required stronger rainfall as the consolidation of the fine particles developed.

DNS study of speed of sound in two-phase flows with phase change

NASA Astrophysics Data System (ADS)

Fu, Kai; Deng, Xiaolong

2017-11-01

Heat transfer through pipe flow is important for the safety of thermal power plants. Normally it is considered incompressible. However, in some conditions compressibility effects could deteriorate the heat transfer efficiency and even result in pipe rupture, especially when there is obvious phase change, due to the much lower sound speed in liquid-gas mixture flows. Based on the stratified multiphase flow model (Chang and Liou, JCP 2007), we present a new approach to simulate the sound speed in 3-D compressible two-phase dispersed flows, in which each face is divided into gas-gas, gas-liquid, and liquid-liquid parts via reconstruction by volume fraction, and fluxes are calculated correspondingly. Applying it to well-distributed air-water bubbly flows, comparing with the experiment measurements in air water mixture (Karplus, JASA 1957), the effects of adiabaticity, viscosity, and isothermality are examined. Under viscous and isothermal condition, the simulation results match the experimental ones very well, showing the DNS study with current method is an effective way for the sound speed of complex two-phase dispersed flows. Including the two-phase Riemann solver with phase change (Fechter et al., JCP 2017), more complex problems can be numerically studied.

Flight evaluation of an insect contamination protection system for laminar flow wings

NASA Technical Reports Server (NTRS)

Croom, C. C.; Holmes, B. J.

1985-01-01

The maintenance of minimum wing leading edge contamination is critical to the preservation of drag-reducing laminar flow; previous methods for the prevention of leading edge contamination by insects have, however, been rendered impractical by their excessive weight, cost, or inconvenience. Attention is presently given to the results of a NASA flight experiment which evaluated the performance of a porous leading edge fluid-discharge ice protection system in the novel role of insect contamination removal; high insect contamination conditions were also noted in the experiment. Very small amounts of the fluid are found to be sufficient for insect contamination protection.

How does sediment affect the hydraulics of bedrock-alluvial rivers?

NASA Astrophysics Data System (ADS)

Hodge, Rebecca; Hoey, Trevor; Maniatis, George; Leprêtre, Emilie

2016-04-01

Relationships between flow, sediment transport and channel morphology are relatively well established in coarse-grained alluvial channels. Developing equivalent relationships for bedrock-alluvial channels is complicated by the two different components that comprise the channel morphology: bedrock and sediment. These two components usually have very different response times to hydraulic forcing, meaning that the bedrock morphology may be inherited from previous conditions. The influence of changing sediment cover on channel morphology and roughness will depend on the relative magnitudes of the sediment size and the spatial variations in bedrock elevation. We report results from experiments in a 0.9m wide flume designed to quantify the interactions between flow and sediment patch morphology using two contrasting bedrock topographies. The first topography is a plane bed with sand-scale roughness, and the second is a 1:10 scale, 3D printed, model of a bedrock channel with spatially variable roughness (standard deviation of elevations = 12 mm in the flume). In all experiments, a sediment pulse was added to the flume (D50 between 7 and 15 mm) and sediment patches were allowed to stabilise under constant flow conditions. The flow was then incrementally increased in order to identify the discharges at which sediment patches and isolated grains were eroded. In the plane bed experiments ˜20% sediment cover is sufficient to alter the channel hydraulics through the increased roughness of the bed; this impact is expressed as the increased discharge at which isolated grains are entrained. In the scaled bed experiments, partial sediment cover decreased local flow velocities on a relatively smooth area of the bed. At the scale of the entire channel, the bed morphology, and the hydraulics induced by it, was a primary control on sediment cover stability at lower sediment inputs. At higher inputs, where sediment infilled the local bed topography, patches were relatively more stable, suggesting an increased impact on the hydraulics and the role of grain-grain interactions. We draw together these experiments using a theoretical framework to express the impact of sediment cover on channel roughness and hence hydraulics.

Experimental and numerical characterization of the water flow in spacer-filled channels of spiral-wound membranes.

PubMed

Bucs, Szilard S; Linares, Rodrigo Valladares; Marston, Jeremy O; Radu, Andrea I; Vrouwenvelder, Johannes S; Picioreanu, Cristian

2015-12-15

Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels. Two-dimensional water velocity fields were measured in a flow cell (representing the feed spacer-filled flow channel of a spiral wound reverse osmosis membrane module without permeate production) at several planes throughout the channel height. At linear flow velocities (volumetric flow rate per cross-section of the flow channel considering the channel porosity, also described as crossflow velocities) used in practice (0.074 and 0.163 m·s(-1)) the recorded flow was laminar with only slight unsteadiness in the upper velocity limit. At higher linear flow velocity (0.3 m·s(-1)) the flow was observed to be unsteady and with recirculation zones. Measurements made at different locations in the flow cell exhibited very similar flow patterns within all feed spacer mesh elements, thus revealing the same hydrodynamic conditions along the length of the flow channel. Three-dimensional (3-D) computational fluid dynamics simulations were performed using the same geometries and flow parameters as the experiments, based on steady laminar flow assumption. The numerical results were in good agreement (0.85-0.95 Bray-Curtis similarity) with the measured flow fields at linear velocities of 0.074 and 0.163 m·s(-1), thus supporting the use of model-based studies in the optimization of feed spacer geometries and operational conditions of spiral wound membrane systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

Two-Phase Flow in Packed Columns and Generation of Bubbly Suspensions for Chemical Processing in Space

NASA Technical Reports Server (NTRS)

Motil, Brian J.; Green, R. D.; Nahra, H. K.; Sridhar, K. R.

2000-01-01

For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow, packed column operated in two ground-based low gravity facilities (two-second drop tower and KC- 135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity. For bubbly suspensions, the experimental hardware for generation of uniformly sized bubbles in Couette flow in microgravity conditions is described. Experimental work was performed on a number of bubbler designs, and the capillary bubble tube was found to produce the most consistent size bubbles. Low air flow rates and low Couette flow produce consistent 2-3 mm bubbles, the size of interest for the "Behavior of Rapidly Sheared Bubbly Suspension" flight experiment. Finally the mass transfer implications of these two-phase flows is qualitatively discussed.

Microgravity

NASA Image and Video Library

1985-05-04

A 16mm film frame shows convective regions inside silicone oil playing the part of a stellar atmosphere in the Geophysical Fluid Flow Cell (GFFC). An electrostatic field pulled the oil inward to mimic gravity's effects during the experiments. The GFFC thus produced flow patterns that simulated conditions inside the atmospheres of Jupiter and the Sun and other stars. Numbers of the frame indicate temperatures and other conditions. This image is from the Spacelab-3 flight in 1985. GFFC was reflown on U.S. Microgravity Laboratory-2 in 1995. The principal investigator was John Hart of the University of Colorado at Boulder. It was managed by NASA's Marshall Space Flight Center. (Credit: NASA/Marshall Space Flight Center)

The influences of tip clearance on the performance of nozzle blades of radial turbines - Experiment and performance prediction at three nozzle angles

NASA Astrophysics Data System (ADS)

Hyun, Yong-Ik; Yamaguchi, Michiteru; Hayami, Hiroshi; Senoo, Yasutoshi

1988-05-01

In order to study the influence of tip clearance on the turning angle and pressure loss of turbine nozzles, experimental results were obtained for nozzle angles at which the throat area was 0.8 and 1.4 times the rated condition. Contour maps of the total pressure loss and of the spanwise distributions of the mean exit-flow angle have been obtained. Although the two-layer flow model of Senoo et al., (1987) is shown to accurately predict the effects of tip clearance, it underestimates the clearance effect for a lightly loaded condition.

Aerodynamic and torque characteristics of enclosed Co/counter rotating disks

NASA Astrophysics Data System (ADS)

Daniels, W. A.; Johnson, B. V.; Graber, D. J.

1989-06-01

Experiments were conducted to determine the aerodynamic and torque characteristics of adjacent rotating disks enclosed in a shroud, in order to obtain an extended data base for advanced turbine designs such as the counterrotating turbine. Torque measurements were obtained on both disks in the rotating frame of reference for corotating, counterrotating and one-rotating/one-static disk conditions. The disk models used in the experiments included disks with typical smooth turbine geometry, disks with bolts, disks with bolts and partial bolt covers, and flat disks. A windage diaphragm was installed at mid-cavity for some experiments. The experiments were conducted with various amounts of coolant throughflow injected into the disk cavity from the disk hub or from the disk OD with swirl. The experiments were conducted at disk tangential Reynolds number up to 1.6 x 10 to the 7th with air as the working fluid. The results of this investigation indicated that the static shroud contributes a significant amount to the total friction within the disk system; the torque on counterrotating disks is essentially independent of coolant flow total rate, flow direction, and tangential Reynolds number over the range of conditions tested; and a static windage diaphragm reduces disk friction in counterrotating disk systems.

Gene flow in genetically modified wheat.

PubMed

Rieben, Silvan; Kalinina, Olena; Schmid, Bernhard; Zeller, Simon L

2011-01-01

Understanding gene flow in genetically modified (GM) crops is critical to answering questions regarding risk-assessment and the coexistence of GM and non-GM crops. In two field experiments, we tested whether rates of cross-pollination differed between GM and non-GM lines of the predominantly self-pollinating wheat Triticum aestivum. In the first experiment, outcrossing was studied within the field by planting "phytometers" of one line into stands of another line. In the second experiment, outcrossing was studied over distances of 0.5-2.5 m from a central patch of pollen donors to adjacent patches of pollen recipients. Cross-pollination and outcrossing was detected when offspring of a pollen recipient without a particular transgene contained this transgene in heterozygous condition. The GM lines had been produced from the varieties Bobwhite or Frisal and contained Pm3b or chitinase/glucanase transgenes, respectively, in homozygous condition. These transgenes increase plant resistance against pathogenic fungi. Although the overall outcrossing rate in the first experiment was only 3.4%, Bobwhite GM lines containing the Pm3b transgene were six times more likely than non-GM control lines to produce outcrossed offspring. There was additional variation in outcrossing rate among the four GM-lines, presumably due to the different transgene insertion events. Among the pollen donors, the Frisal GM line expressing a chitinase transgene caused more outcrossing than the GM line expressing both a chitinase and a glucanase transgene. In the second experiment, outcrossing after cross-pollination declined from 0.7-0.03% over the test distances of 0.5-2.5 m. Our results suggest that pollen-mediated gene flow between GM and non-GM wheat might only be a concern if it occurs within fields, e.g. due to seed contamination. Methodologically our study demonstrates that outcrossing rates between transgenic and other lines within crops can be assessed using a phytometer approach and that gene-flow distances can be efficiently estimated with population-level PCR analyses. © 2011 Rieben et al.