Control of Flow Structure in Square Cross-Sectioned U Bend using Numerical Modeling

NASA Astrophysics Data System (ADS)

Yavuz, Mehmet Metin; Guden, Yigitcan

2014-11-01

Due to the curvature in U-bends, the flow development involves complex flow structures including Dean vortices and high levels of turbulence that are quite critical in considering noise problems and structural failure of the ducts. Computational fluid dynamic (CFD) models are developed using ANSYS Fluent to analyze and to control the flow structure in a square cross-sectioned U-bend with a radius of curvature Rc/D = 0.65. The predictions of velocity profiles on different angular positions of the U-bend are compared against the experimental results available in the literature and the previous numerical studies. The performances of different turbulence models are evaluated to propose the best numerical approach that has high accuracy with reduced computation time. The numerical results of the present study indicate improvements with respect to the previous numerical predictions and very good agreement with the available experimental results. In addition, a flow control technique is utilized to regulate the flow inside the bend. The elimination of Dean vortices along with significant reduction in turbulence levels in different cross flow planes are successfully achieved when the flow control technique is applied. The project is supported by Meteksan Defense Industries, Inc.

Dynamic analysis of pedestrian crossing behaviors on traffic flow at unsignalized mid-block crosswalks

NASA Astrophysics Data System (ADS)

Liu, Gang; He, Jing; Luo, Zhiyong; Yang, Wunian; Zhang, Xiping

2015-05-01

It is important to study the effects of pedestrian crossing behaviors on traffic flow for solving the urban traffic jam problem. Based on the Nagel-Schreckenberg (NaSch) traffic cellular automata (TCA) model, a new one-dimensional TCA model is proposed considering the uncertainty conflict behaviors between pedestrians and vehicles at unsignalized mid-block crosswalks and defining the parallel updating rules of motion states of pedestrians and vehicles. The traffic flow is simulated for different vehicle densities and behavior trigger probabilities. The fundamental diagrams show that no matter what the values of vehicle braking probability, pedestrian acceleration crossing probability, pedestrian backing probability and pedestrian generation probability, the system flow shows the "increasing-saturating-decreasing" trend with the increase of vehicle density; when the vehicle braking probability is lower, it is easy to cause an emergency brake of vehicle and result in great fluctuation of saturated flow; the saturated flow decreases slightly with the increase of the pedestrian acceleration crossing probability; when the pedestrian backing probability lies between 0.4 and 0.6, the saturated flow is unstable, which shows the hesitant behavior of pedestrians when making the decision of backing; the maximum flow is sensitive to the pedestrian generation probability and rapidly decreases with increasing the pedestrian generation probability, the maximum flow is approximately equal to zero when the probability is more than 0.5. The simulations prove that the influence of frequent crossing behavior upon vehicle flow is immense; the vehicle flow decreases and gets into serious congestion state rapidly with the increase of the pedestrian generation probability.

Reducing cross-sectional data using a genetic algorithm method and effects on cross-section geometry and steady-flow profiles

USGS Publications Warehouse

Berenbrock, Charles E.

2015-01-01

The effects of reduced cross-sectional data points on steady-flow profiles were also determined. Thirty-five cross sections of the original steady-flow model of the Kootenai River were used. These two methods were tested for all cross sections with each cross section resolution reduced to 10, 20 and 30 data points, that is, six tests were completed for each of the thirty-five cross sections. Generally, differences from the original water-surface elevation were smaller as the number of data points in reduced cross sections increased, but this was not always the case, especially in the braided reach. Differences were smaller for reduced cross sections developed by the genetic algorithm method than the standard algorithm method.

Hydraulic characteristics of the New River in the New River Gorge National River, West Virginia

USGS Publications Warehouse

Wiley, J.B.; Appel, David H.

1989-01-01

Traveltime, dispersion, water-surface and streambed profiles, and cross-section data were collected for use in application of flow and solute-transport models to the New River in the New River Gorge National River, West Virginia. Dye clouds subjected to increasing and decreasing flow rates (unsteady flow) showed that increasing flows shorten the cloud and decreasing flows lengthen the cloud. After the flow rate was changed and the flow was again steady, traveltime and dispersion characteristics were determined by the new rate of flow. Seven stage/streamflow relations identified the general changes of stream geometry throughout the study reach. Channel cross sections were estimated for model input. Low water and streambed profiles were developed from surveyed water surface elevations and water depths. (USGS)

Effects of fracture surface roughness and shear displacement on geometrical and hydraulic properties of three-dimensional crossed rock fracture models

NASA Astrophysics Data System (ADS)

Huang, Na; Liu, Richeng; Jiang, Yujing; Li, Bo; Yu, Liyuan

2018-03-01

While shear-flow behavior through fractured media has been so far studied at single fracture scale, a numerical analysis of the shear effect on the hydraulic response of 3D crossed fracture model is presented. The analysis was based on a series of crossed fracture models, in which the effects of fracture surface roughness and shear displacement were considered. The rough fracture surfaces were generated using the modified successive random additions (SRA) algorithm. The shear displacement was applied on one fracture, and at the same time another fracture shifted along with the upper and lower surfaces of the sheared fracture. The simulation results reveal the development and variation of preferential flow paths through the model during the shear, accompanied by the change of the flow rate ratios between two flow planes at the outlet boundary. The average contact area accounts for approximately 5-27% of the fracture planes during shear, but the actual calculated flow area is about 38-55% of the fracture planes, which is much smaller than the noncontact area. The equivalent permeability will either increase or decrease as shear displacement increases from 0 to 4 mm, depending on the aperture distribution of intersection part between two fractures. When the shear displacement continuously increases by up to 20 mm, the equivalent permeability increases sharply first, and then keeps increasing with a lower gradient. The equivalent permeability of rough fractured model is about 26-80% of that calculated from the parallel plate model, and the equivalent permeability in the direction perpendicular to shear direction is approximately 1.31-3.67 times larger than that in the direction parallel to shear direction. These results can provide a fundamental understanding of fluid flow through crossed fracture model under shear.

Moisture transfer through the membrane of a cross-flow energy recovery ventilator: Measurement and simple data-driven modeling

Treesearch

CR Boardman; Samuel V. Glass

2015-01-01

The moisture transfer effectiveness (or latent effectiveness) of a cross-flow, membrane based energy recovery ventilator is measured and modeled. Analysis of in situ measurements for a full year shows that energy recovery ventilator latent effectiveness increases with increasing average relative humidity and surprisingly increases with decreasing average temperature. A...

Calculation of flow about posts and powerhead model. [space shuttle main engine

NASA Technical Reports Server (NTRS)

Anderson, P. G.; Farmer, R. C.

1985-01-01

A three dimensional analysis of the non-uniform flow around the liquid oxygen (LOX) posts in the Space Shuttle Main Engine (SSME) powerhead was performed to determine possible factors contributing to the failure of the posts. Also performed was three dimensional numerical fluid flow analysis of the high pressure fuel turbopump (HPFTP) exhaust system, consisting of the turnaround duct (TAD), two-duct hot gas manifold (HGM), and the Version B transfer ducts. The analysis was conducted in the following manner: (1) modeling the flow around a single and small clusters (2 to 10) of posts; (2) modeling the velocity field in the cross plane; and (3) modeling the entire flow region with a three dimensional network type model. Shear stress functions which will permit viscous analysis without requiring excessive numbers of computational grid points were developed. These wall functions, laminar and turbulent, have been compared to standard Blasius solutions and are directly applicable to the cylinder in cross flow class of problems to which the LOX post problem belongs.

Analysis of the injection of a heated turbulent jet into a cross flow

NASA Technical Reports Server (NTRS)

Campbell, J. F.; Schetz, J. A.

1973-01-01

The development of a theoretical model is investigated of the incompressible jet injection process. The discharge of a turbulent jet into a cross flow was mathematically modeled by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The analytical results are supported by experimental data and demonstrate the usefulness of the theory for estimating the trajectory and flow properties of the jet for a variety of injection conditions. The capability of predicting jet flow properties, as well as two- and three-dimensional jet paths, was enhanced by obtaining the jet cross-sectional area during the solution of the conservation equations. Realistic estimates of temperature in the jet fluid were acquired by accounting for heat losses in the jet flow due to forced convection and to entrainment of free-stream fluid into the jet.

Experimental testing and modeling analysis of solute mixing at water distribution pipe junctions.

PubMed

Shao, Yu; Jeffrey Yang, Y; Jiang, Lijie; Yu, Tingchao; Shen, Cheng

2014-06-01

Flow dynamics at a pipe junction controls particle trajectories, solute mixing and concentrations in downstream pipes. The effect can lead to different outcomes of water quality modeling and, hence, drinking water management in a distribution network. Here we have investigated solute mixing behavior in pipe junctions of five hydraulic types, for which flow distribution factors and analytical equations for network modeling are proposed. First, based on experiments, the degree of mixing at a cross is found to be a function of flow momentum ratio that defines a junction flow distribution pattern and the degree of departure from complete mixing. Corresponding analytical solutions are also validated using computational-fluid-dynamics (CFD) simulations. Second, the analytical mixing model is further extended to double-Tee junctions. Correspondingly the flow distribution factor is modified to account for hydraulic departure from a cross configuration. For a double-Tee(A) junction, CFD simulations show that the solute mixing depends on flow momentum ratio and connection pipe length, whereas the mixing at double-Tee(B) is well represented by two independent single-Tee junctions with a potential water stagnation zone in between. Notably, double-Tee junctions differ significantly from a cross in solute mixing and transport. However, it is noted that these pipe connections are widely, but incorrectly, simplified as cross junctions of assumed complete solute mixing in network skeletonization and water quality modeling. For the studied pipe junction types, analytical solutions are proposed to characterize the incomplete mixing and hence may allow better water quality simulation in a distribution network. Published by Elsevier Ltd.

Accuracy of 1D microvascular flow models in the limit of low Reynolds numbers.

PubMed

Pindera, Maciej Z; Ding, Hui; Athavale, Mahesh M; Chen, Zhijian

2009-05-01

We describe results of numerical simulations of steady flows in tubes with branch bifurcations using fully 3D and reduced 1D geometries. The intent is to delineate the range of validity of reduced models used for simulations of flows in microcapillary networks, as a function of the flow Reynolds number Re. Results from model problems indicate that for Re less than 1 and possibly as high as 10, vasculatures may be represented by strictly 1D Poiseuille flow geometries with flow variation in the axial dimensions only. In that range flow rate predictions in the different branches generated by 1D and 3D models differ by a constant factor, independent of Re. When the cross-sectional areas of the branches are constant these differences are generally small and appear to stem from an uncertainty of how the individual branch lengths are defined. This uncertainty can be accounted for by a simple geometrical correction. For non-constant cross-sections the differences can be much more significant. If additional corrections for the presence of branch junctions and flow area variations are not taken into account in 1D models of complex vasculatures, the resultant flow predictions should be interpreted with caution.

Analysis of two-phase flow inter-subchannel mass and momentum exchanges by the two-fluid model approach

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

Ninokata, H.; Deguchi, A.; Kawahara, A.

1995-09-01

A new void drift model for the subchannel analysis method is presented for the thermohydraulics calculation of two-phase flows in rod bundles where the flow model uses a two-fluid formulation for the conservation of mass, momentum and energy. A void drift model is constructed based on the experimental data obtained in a geometrically simple inter-connected two circular channel test sections using air-water as working fluids. The void drift force is assumed to be an origin of void drift velocity components of the two-phase cross-flow in a gap area between two adjacent rods and to overcome the momentum exchanges at themore » phase interface and wall-fluid interface. This void drift force is implemented in the cross flow momentum equations. Computational results have been successfully compared to experimental data available including 3x3 rod bundle data.« less

Large Eddy Simulation and Reynolds-Averaged Navier-Stokes modeling of flow in a realistic pharyngeal airway model: an investigation of obstructive sleep apnea.

PubMed

Mihaescu, Mihai; Murugappan, Shanmugam; Kalra, Maninder; Khosla, Sid; Gutmark, Ephraim

2008-07-19

Computational fluid dynamics techniques employing primarily steady Reynolds-Averaged Navier-Stokes (RANS) methodology have been recently used to characterize the transitional/turbulent flow field in human airways. The use of RANS implies that flow phenomena are averaged over time, the flow dynamics not being captured. Further, RANS uses two-equation turbulence models that are not adequate for predicting anisotropic flows, flows with high streamline curvature, or flows where separation occurs. A more accurate approach for such flow situations that occur in the human airway is Large Eddy Simulation (LES). The paper considers flow modeling in a pharyngeal airway model reconstructed from cross-sectional magnetic resonance scans of a patient with obstructive sleep apnea. The airway model is characterized by a maximum narrowing at the site of retropalatal pharynx. Two flow-modeling strategies are employed: steady RANS and the LES approach. In the RANS modeling framework both k-epsilon and k-omega turbulence models are used. The paper discusses the differences between the airflow characteristics obtained from the RANS and LES calculations. The largest discrepancies were found in the axial velocity distributions downstream of the minimum cross-sectional area. This region is characterized by flow separation and large radial velocity gradients across the developed shear layers. The largest difference in static pressure distributions on the airway walls was found between the LES and the k-epsilon data at the site of maximum narrowing in the retropalatal pharynx.

Flow modeling and permeability estimation using borehole flow logs in heterogeneous fractured formations

USGS Publications Warehouse

Paillet, Frederick L.

1998-01-01

A numerical model of flow in the vicinity of a borehole is used to analyze flowmeter data obtained with high-resolution flowmeters. The model is designed to (1) precisely compute flow in a borehole, (2) approximate the effects of flow in surrounding aquifers on the measured borehole flow, (3) allow for an arbitrary number (N) of entry/exit points connected to M < N far-field aquifers, and (4) be consistent with the practical limitations of flowmeter measurements such as limits of resolution, typical measurement error, and finite measurement periods. The model is used in three modes: (1) a quasi-steady pumping mode where there is no ambient flow, (2) a steady flow mode where ambient differences in far-field water levels drive flow between fracture zones in the borehole, and (3) a cross-borehole test mode where pumping in an adjacent borehole drives flow in the observation borehole. The model gives estimates of transmissivity for any number of fractures in steady or quasi-steady flow experiments that agree with straddle-packer test data. Field examples show how these cross-borehole-type curves can be used to estimate the storage coefficient of fractures and bedding planes and to determine whether fractures intersecting a borehole at different locations are hydraulically connected in the surrounding rock mass.

An Experimental Study of Swirling Flows as Applied to Annular Combustors

NASA Technical Reports Server (NTRS)

Seal, Michael Damian, II

1997-01-01

This thesis presents an experimental study of swirling flows with direct applications to gas turbine combustors. Two separate flowfields were investigated: a round, swirling jet and a non-combusting annular combustor model. These studies were intended to allow both a further understanding of the behavior of general swirling flow characteristics, such as the recirculation zone, as well as to provide a base for the development of computational models. In order to determine the characteristics of swirling flows the concentration fields of a round, swirling jet were analyzed for varying amount of swirl. The experimental method used was a light scattering concentration measurement technique known as marker nephelometry. Results indicated the formation of a zone of recirculating fluid for swirl ratios (rotational speed x jet radius over mass average axial velocity) above a certain critical value. The size of this recirculation zone, as well as the spread angle of the jet, was found to increase with increase in the amount of applied swirl. The annular combustor model flowfield simulated the cold-flow characteristics of typical current annular combustors: swirl, recirculation, primary air cross jets and high levels of turbulence. The measurements in the combustor model made by the Laser Doppler Velocimetry technique, allowed the evaluation of the mean and rms velocities in the three coordinate directions, one Reynold's shear stress component and the turbulence kinetic energy: The primary cross jets were found to have a very strong effect on both the mean and turbulence flowfields. These cross jets, along with a large step change in area and wall jet inlet flow pattern, reduced the overall swirl in the test section to negligible levels. The formation of the strong recirculation zone is due mainly to the cross jets and the large step change in area. The cross jets were also found to drive a four-celled vortex-type motion (parallel to the combustor longitudinal axis) near the cross jet injection plane.

Three-dimensional vortex-induced vibrations of supported pipes conveying fluid based on wake oscillator models

NASA Astrophysics Data System (ADS)

Wang, L.; Jiang, T. L.; Dai, H. L.; Ni, Q.

2018-05-01

The present study develops a new three-dimensional nonlinear model for investigating vortex-induced vibrations (VIV) of flexible pipes conveying internal fluid flow. The unsteady hydrodynamic forces associated with the wake dynamics are modeled by two distributed van der Pol wake oscillators. In particular, the nonlinear partial differential equations of motion of the pipe and the wake are derived, taking into account the coupling between the structure and the fluid. The nonlinear equations of motion for the coupled system are then discretized by means of the Galerkin technique, resulting in a high-dimensional reduced-order model of the system. It is shown that the natural frequencies for in-plane and out-of-plane motions of the pipe may be different at high internal flow velocities beyond the threshold of buckling instability. The orientation angle of the postbuckling configuration is time-varying due to the disturbance of hydrodynamic forces, thus yielding sometimes unexpected results. For a buckled pipe with relatively low cross-flow velocity, interestingly, examining the nonlinear dynamics of the pipe indicates that the combined effects of the cross-flow-induced resonance of the in-plane first mode and the internal-flow-induced buckling on the IL and CF oscillation amplitudes may be significant. For higher cross-flow velocities, however, the effect of internal fluid flow on the nonlinear VIV responses of the pipe is not pronounced.

Computer simulation of Cerebral Arteriovenous Malformation-validation analysis of hemodynamics parameters.

PubMed

Kumar, Y Kiran; Mehta, Shashi Bhushan; Ramachandra, Manjunath

2017-01-01

The purpose of this work is to provide some validation methods for evaluating the hemodynamic assessment of Cerebral Arteriovenous Malformation (CAVM). This article emphasizes the importance of validating noninvasive measurements for CAVM patients, which are designed using lumped models for complex vessel structure. The validation of the hemodynamics assessment is based on invasive clinical measurements and cross-validation techniques with the Philips proprietary validated software's Qflow and 2D Perfursion. The modeling results are validated for 30 CAVM patients for 150 vessel locations. Mean flow, diameter, and pressure were compared between modeling results and with clinical/cross validation measurements, using an independent two-tailed Student t test. Exponential regression analysis was used to assess the relationship between blood flow, vessel diameter, and pressure between them. Univariate analysis is used to assess the relationship between vessel diameter, vessel cross-sectional area, AVM volume, AVM pressure, and AVM flow results were performed with linear or exponential regression. Modeling results were compared with clinical measurements from vessel locations of cerebral regions. Also, the model is cross validated with Philips proprietary validated software's Qflow and 2D Perfursion. Our results shows that modeling results and clinical results are nearly matching with a small deviation. In this article, we have validated our modeling results with clinical measurements. The new approach for cross-validation is proposed by demonstrating the accuracy of our results with a validated product in a clinical environment.

Prediction of vortex shedding from circular and noncircular bodies in supersonic flow

NASA Technical Reports Server (NTRS)

Mendenhall, M. R.; Perkins, S. C., Jr.

1984-01-01

An engineering prediction method and associated computer code NOZVTX to predict nose vortex shedding from circular and noncircular bodies in supersonic flow at angles of attack and roll are presented. The body is represented by either a supersonic panel method for noncircular cross sections or line sources and doublets for circular cross sections, and the lee side vortex wake is modeled by discrete vortices in crossflow planes. The three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted surface pressure distributions, flow field surveys, and aerodynamic characteristics is presented for bodies with circular and noncircular cross-sectional shapes.

Experimental Observation of Dispersion Phenomenon for Non-Newtonian flow in Porous Media

NASA Astrophysics Data System (ADS)

Bowers, C.; Schultz, P. B.; Fowler, C. P.; McClure, J. E.; Miller, C. T.

2017-12-01

The EPA has identified over 100 toxic species which are commonly found in hydraulic fracturing fluids, leading to concerns about their movement into endangered water supplies through spills and accelerated geological pathways. Before these concerns can be allayed, detailed study of the transport of dissolved species in non-Newtonian fluids is required. Up until now, most research into non-Newtonian flow has focused on two-parameter models, such as the Power law model; however, these models have been found to be insufficient when applied to hydraulic fracturing applications, due to high pressure flow through thin fractures and pore-throats. This work is focused on the Cross model, a four parameter model which has been found to accurately represent the flow of fracturing fluids. A series of one-dimensional flow through tracer tests have been conducted using a tritiated water tracer and an aqueous guar gum solution, a non-Newtonian fluid commonly used in the fracturing process, to investigate the effects of dispersion on species transport. These tests are compared to modeling results, and may be used to develop macroscale models for Cross model non-Newtonian fluids.

Kinetics of gravity-driven slug flow in partially wettable capillaries of varying cross section

NASA Astrophysics Data System (ADS)

Nissan, Alon; Wang, Qiuling; Wallach, Rony

2016-11-01

A mathematical model for slug (finite liquid volume) motion in not-fully-wettable capillary tubes with sinusoidally varying cross-sectional areas was developed. The model, based on the Navier-Stokes equation, accounts for the full viscous terms due to nonuniform geometry, the inertial term, the slug's front and rear meniscus hysteresis effect, and dependence of contact angle on flow velocity (dynamic contact angle). The model includes a velocity-dependent film that is left behind the advancing slug, reducing its mass. The model was successfully verified experimentally by recording slug movement in uniform and sinusoidal capillary tubes with a gray-scale high-speed camera. Simulation showed that tube nonuniformity has a substantial effect on slug flow pattern: in a uniform tube it is monotonic and depends mainly on the slug's momentary mass/length; an undulating tube radius results in nonmonotonic flow characteristics. The static nonzero contact angle varies locally in nonuniform tubes owing to the additional effect of wall slope. Moreover, the nonuniform cross-sectional area induces slug acceleration, deceleration, blockage, and metastable-equilibrium locations. Increasing contact angle further amplifies the geometry effect on slug propagation. The developed model provides a modified means of emulating slug flow in differently wettable porous media for intermittent inlet water supply (e.g., raindrops on the soil surface).

Analytic expressions for Atomic Layer Deposition: coverage, throughput, and materials utilization in cross-flow, particle coating, and spatial ALD

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

Yanguas-Gil, Angel; Elam, Jeffrey W.

2014-05-01

In this work, the authors present analytic models for atomic layer deposition (ALD) in three common experimental configurations: cross-flow, particle coating, and spatial ALD. These models, based on the plug-flow and well-mixed approximations, allow us to determine the minimum dose times and materials utilization for all three configurations. A comparison between the three models shows that throughput and precursor utilization can each be expressed by universal equations, in which the particularity of the experimental system is contained in a single parameter related to the residence time of the precursor in the reactor. For the case of cross-flow reactors, the authorsmore » show how simple analytic expressions for the reactor saturation profiles agree well with experimental results. Consequently, the analytic model can be used to extract information about the ALD surface chemistry (e. g., the reaction probability) by comparing the analytic and experimental saturation profiles, providing a useful tool for characterizing new and existing ALD processes. (C) 2014 American Vacuum Society« less

The flame structure and vorticity generated by a chemically reacting transverse jet

NASA Technical Reports Server (NTRS)

Karagozian, A. R.

1986-01-01

An analytical model describing the behavior of a turbulent fuel jet injected normally into a cross flow is developed. The model places particular emphasis on the contrarotating vortex pair associated with the jet, and predicts the flame length and shape based on entrainment of the oxidizer by the fuel jet. Effects of buoyancy and density variations in the flame are neglected in order to isolate the effects of large-scale mixing. The results are compared with a simulation of the transverse reacting jet in a liquid (acid-base) system. For a wide range of ratios of the cross flow to jet velocity, the model predicts flame length quite well. In particular, the observed transitional behavior in the flame length between cross-flow velocity to jet velocity of orifice ratios of 0.0 to 0.1, yielding an approximate minimum at the ratio 0.05, is reproduced very clearly by the present model. The transformation in flow structure that accounts for this minimum arises from the differing components of vorticity dominant in the near-field and far-field regions of the jet.

Vertical structure of mean cross-shore currents across a barred surf zone

USGS Publications Warehouse

Haines, John W.; Sallenger, Asbury H.

1994-01-01

Mean cross-shore currents observed across a barred surf zone are compared to model predictions. The model is based on a simplified momentum balance with a turbulent boundary layer at the bed. Turbulent exchange is parameterized by an eddy viscosity formulation, with the eddy viscosity Aυ independent of time and the vertical coordinate. Mean currents result from gradients due to wave breaking and shoaling, and the presence of a mean setup of the free surface. Descriptions of the wave field are provided by the wave transformation model of Thornton and Guza [1983]. The wave transformation model adequately reproduces the observed wave heights across the surf zone. The mean current model successfully reproduces the observed cross-shore flows. Both observations and predictions show predominantly offshore flow with onshore flow restricted to a relatively thin surface layer. Successful application of the mean flow model requires an eddy viscosity which varies horizontally across the surf zone. Attempts are made to parameterize this variation with some success. The data does not discriminate between alternative parameterizations proposed. The overall variability in eddy viscosity suggested by the model fitting should be resolvable by field measurements of the turbulent stresses. Consistent shortcomings of the parameterizations, and the overall modeling effort, suggest avenues for further development and data collection.

Resistance formulas in hydraulics-based models for routing debris flows

USGS Publications Warehouse

Chen, Cheng-lung; Ling, Chi-Hai

1997-01-01

The one-dimensional, cross-section-averaged flow equations formulated for routing debris flows down a narrow valley are identical to those for clear-water flow, except for the differences in the values of the flow parameters, such as the momentum (or energy) correction factor, resistance coefficient, and friction slope. Though these flow parameters for debris flow in channels with cross-sections of arbitrary geometric shape can only be determined empirically, the theoretical values of such parameters for debris flow in wide channels exist. This paper aims to derive the theoretical resistance coefficient and friction slope for debris flow in wide channels using a rheological model for highly-concentrated, rapidly-sheared granular flows, such as the generalized viscoplastic fluid (GVF) model. Formulating such resistance coefficient or friction slope is equivalent to developing a generally applicable resistance formula for routing debris flows. Inclusion of a nonuniform term in the expression of the resistance formula proves useful in removing the customary assumption that the spatially varied resistance at any section is equal to what would take place with the same rate of flow passing the same section under conditions of uniformity. This in effect implies an improvement in the accuracy of unsteady debris-flow computation.

Calculation of turbulence-driven secondary motion in ducts with arbitrary cross section

NASA Technical Reports Server (NTRS)

Demuren, A. O.

1989-01-01

Calculation methods for turbulent duct flows are generalized for ducts with arbitrary cross-sections. The irregular physical geometry is transformed into a regular one in computational space, and the flow equations are solved with a finite-volume numerical procedure. The turbulent stresses are calculated with an algebraic stress model derived by simplifying model transport equations for the individual Reynolds stresses. Two variants of such a model are considered. These procedures enable the prediction of both the turbulence-driven secondary flow and the anisotropy of the Reynolds stresses, in contrast to some of the earlier calculation methods. Model predictions are compared to experimental data for developed flow in triangular duct, trapezoidal duct and a rod-bundle geometry. The correct trends are predicted, and the quantitative agreement is mostly fair. The simpler variant of the algebraic stress model procured better agreement with the measured data.

Particle image and acoustic Doppler velocimetry analysis of a cross-flow turbine wake

NASA Astrophysics Data System (ADS)

Strom, Benjamin; Brunton, Steven; Polagye, Brian

2017-11-01

Cross-flow turbines have advantageous properties for converting kinetic energy in wind and water currents to rotational mechanical energy and subsequently electrical power. A thorough understanding of cross-flow turbine wakes aids understanding of rotor flow physics, assists geometric array design, and informs control strategies for individual turbines in arrays. In this work, the wake physics of a scale model cross-flow turbine are investigated experimentally. Three-component velocity measurements are taken downstream of a two-bladed turbine in a recirculating water channel. Time-resolved stereoscopic particle image and acoustic Doppler velocimetry are compared for planes normal to and distributed along the turbine rotational axis. Wake features are described using proper orthogonal decomposition, dynamic mode decomposition, and the finite-time Lyapunov exponent. Consequences for downstream turbine placement are discussed in conjunction with two-turbine array experiments.

A Model for the Vortex Pair Associated with a Jet in a Cross Flow

NASA Technical Reports Server (NTRS)

Sellers, William L.

1975-01-01

A model is presented for the contrarotating vortex pair that is formed by a round, turbulent, subsonic jet directed normally into a uniform, subsonic cross flow. The model consists of a set of algebraic equations that describe the properties of the vortex pair as a function of their location in the jet plume. The parameters of the model are physical characteristics of the vortices such as the vortex strength, spacing, and core size. These parameters are determined by velocity measurements at selective points in the jet plume.

Numerical study on turbulence modulation in gas-particle flows

NASA Astrophysics Data System (ADS)

Yan, F.; Lightstone, M. F.; Wood, P. E.

2007-01-01

A mathematical model is proposed based on the Eulerian/Lagrangian approach to account for both the particle crossing trajectory effect and the extra turbulence production due to particle wake effects. The resulting model, together with existing models from the literature, is applied to two different particle-laden flow configurations, namely a vertical pipe flow and axisymmetric downward jet flow. The results show that the proposed model is able to provide improved predictions of the experimental results.

Modeling flow and solute transport in irrigation furrows

USDA-ARS?s Scientific Manuscript database

This paper presents an internally coupled flow and solute transport model for free-draining irrigation furrows. Furrow hydraulics is simulated with a numerical zero-inertia model and solute transport is computed with a model based on a numerical solution of the cross-section averaged advection-dispe...

Flow in curved ducts of varying cross-section

NASA Astrophysics Data System (ADS)

Sotiropoulos, F.; Patel, V. C.

1992-07-01

Two numerical methods for solving the incompressible Navier-Stokes equations are compared with each other by applying them to calculate laminar and turbulent flows through curved ducts of regular cross-section. Detailed comparisons, between the computed solutions and experimental data, are carried out in order to validate the two methods and to identify their relative merits and disadvantages. Based on the conclusions of this comparative study a numerical method is developed for simulating viscous flows through curved ducts of varying cross-sections. The proposed method is capable of simulating the near-wall turbulence using fine computational meshes across the sublayer in conjunction with a two-layer k-epsilon model. Numerical solutions are obtained for: (1) a straight transition duct geometry, and (2) a hydroturbine draft-tube configuration at model scale Reynolds number for various inlet swirl intensities. The report also provides a detailed literature survey that summarizes all the experimental and computational work in the area of duct flows.

Synthesis of natural flows at selected sites in and near the Milk River basin, Montana, 1928-89

USGS Publications Warehouse

Cary, L.E.; Parrett, Charles

1995-01-01

Natural monthly streamflows were synthesized for the years 1928-89 at 2 sites in the St. Mary River Basin and 11 sites in the Milk River Basin in north- central Montana. The sites are represented as nodes in a streamflow accounting model being developed by the Bureau of Reclamation for the Milk River Basin. Recorded flows at most sites have been affected by human activities, including reservoir storage and irrigation diversions. The flows at the model nodes were corrected for the effects of these activities to obtain synthesized flows. The synthesized flows at nodes with seasonal and short-term records were extended using a statistical technique. The methods of synthesis varied, depending on upstream activities and information available. Flows at sites in the St. Mary River Basin and at the Milk River at Eastern Crossing of International Boundary pre- viously had been synthesized. The flows at mainstem sites downstream from the Milk River at Eastern Crossing were synthesized by adding synthesized natural runoff from intervening drainage areas to natural flows for Milk River at Eastern Crossing. Natural runoff from intervening drainage areas was estimated by multiplying recorded flows at selected index gaging stations on tributary streams by the ratio of the intervening drainage area to the combined drainage area of the index stations. The recorded flows for Milk River at Western Crossing of International Boundary and for Peoples Creek near Dodson, Montana, were assumed to be natural flows. The synthesized annual flows at the mouth of the Milk River compared favorably with the recorded flows near the mouth when the effects of upstream irrigation were considered.

Navier-Stokes analysis and experimental data comparison of compressible flow within ducts

NASA Technical Reports Server (NTRS)

Harloff, G. J.; Reichert, B. A.; Sirbaugh, J. R.; Wellborn, S. R.

1992-01-01

Many aircraft employ ducts with centerline curvature or changing cross-sectional shape to join the engine with inlet and exhaust components. S-ducts convey air to the engine compressor from the intake and often decelerate the flow to achieve an acceptable Mach number at the engine compressor by increasing the cross-sectional area downstream. Circular-to-rectangular transition ducts are used on aircraft with rectangular exhaust nozzles to connect the engine and nozzle. To achieve maximum engine performance, the ducts should minimize flow total pressure loss and total pressure distortion at the duct exit. Changes in the curvature of the duct centerline or the duct cross-sectional shape give rise to streamline curvature which causes cross stream pressure gradients. Secondary flows can be caused by deflection of the transverse vorticity component of the boundary layer. This vortex tilting results in counter-rotating vortices. Additionally, the adverse streamwise pressure gradient caused by increasing cross-sectional area can lead to flow separation. Vortex pairs have been observed in the exit planes of both duct types. These vortices are due to secondary flows induced by pressure gradients resulting from streamline curvature. Regions of low total pressure are produced when the vortices convect boundary layer fluid into the main flow. The purpose of the present study is to predict the measured flow field in a diffusing S-duct and a circular-to-rectangular transition duct with a full Navier-Stokes computer program, PARC3D, and to compare the numerical predictions with new detailed experimental measurements. The work was undertaken to extend previous studies and to provide additional CFD validation data needed to help model flows with strong secondary flow and boundary layer separation. The S-duct computation extends the study of Smith et al, and Harloff et al, which concluded that the computation might be improved by using a finer grid and more advanced turbulence models. The present study compares results for both the Baldwin-Lomas and k-epsilon turbulence models and is conducted with a refined grid. For the transition duct, two inlet conditions were considered, the first with straight flow and the second with swirling flow. The first case permits examination of the effects of the geometric transition on the flow field, while the second case includes the rotational flow effect characteristic of a gas turbine engine.

Gas-liquid-liquid three-phase flow pattern and pressure drop in a microfluidic chip: similarities with gas-liquid/liquid-liquid flows.

PubMed

Yue, Jun; Rebrov, Evgeny V; Schouten, Jaap C

2014-05-07

We report a three-phase slug flow and a parallel-slug flow as two major flow patterns found under the nitrogen-decane-water flow through a glass microfluidic chip which features a long microchannel with a hydraulic diameter of 98 μm connected to a cross-flow mixer. The three-phase slug flow pattern is characterized by a flow of decane droplets containing single elongated nitrogen bubbles, which are separated by water slugs. This flow pattern was observed at a superficial velocity of decane (in the range of about 0.6 to 10 mm s(-1)) typically lower than that of water for a given superficial gas velocity in the range of 30 to 91 mm s(-1). The parallel-slug flow pattern is characterized by a continuous water flow in one part of the channel cross section and a parallel flow of decane with dispersed nitrogen bubbles in the adjacent part of the channel cross section, which was observed at a superficial velocity of decane (in the range of about 2.5 to 40 mm s(-1)) typically higher than that of water for each given superficial gas velocity. The three-phase slug flow can be seen as a superimposition of both decane-water and nitrogen-decane slug flows observed in the chip when the flow of the third phase (viz. nitrogen or water, respectively) was set at zero. The parallel-slug flow can be seen as a superimposition of the decane-water parallel flow and the nitrogen-decane slug flow observed in the chip under the corresponding two-phase flow conditions. In case of small capillary numbers (Ca ≪ 0.1) and Weber numbers (We ≪ 1), the developed two-phase pressure drop model under a slug flow has been extended to obtain a three-phase slug flow model in which the 'nitrogen-in-decane' droplet is assumed as a pseudo-homogeneous droplet with an effective viscosity. The parallel flow and slug flow pressure drop models have been combined to obtain a parallel-slug flow model. The obtained models describe the experimental pressure drop with standard deviations of 8% and 12% for the three-phase slug flow and parallel-slug flow, respectively. An example is given to illustrate the model uses in designing bifurcated microchannels that split the three-phase slug flow for high-throughput processing.

On the cross-stream spectral method for the Orr-Sommerfeld equation

NASA Technical Reports Server (NTRS)

Zorumski, William E.; Hodge, Steven L.

1993-01-01

Cross-stream models are defined as solutions to the Orr-Sommerfeld equation which are propagating normal to the flow direction. These models are utilized as a basis for a Hilbert space to approximate the spectrum of the Orr-Sommerfeld equation with plane Poiseuille flow. The cross-stream basis leads to a standard eigenvalue problem for the frequencies of Poiseuille flow instability waves. The coefficient matrix in the eigenvalue problem is shown to be the sum of a real matrix and a negative-imaginary diagonal matrix which represents the frequencies of the cross-stream modes. The real coefficient matrix is shown to approach a Toeplitz matrix when the row and column indices are large. The Toeplitz matrix is diagonally dominant, and the diagonal elements vary inversely in magnitude with diagonal position. The Poiseuille flow eigenvalues are shown to lie within Gersgorin disks with radii bounded by the product of the average flow speed and the axial wavenumber. It is shown that the eigenvalues approach the Gersgorin disk centers when the mode index is large, so that the method may be used to compute spectra with an essentially unlimited number of elements. When the mode index is large, the real part of the eigenvalue is the product of the axial wavenumber and the average flow speed, and the imaginary part of the eigen value is identical to the corresponding cross-stream mode frequency. The cross-stream method is numerically well-conditioned in comparison to Chebyshev based methods, providing equivalent accuracy for small mode indices and superior accuracy for large indices.

Numerical modeling and analytical modeling of cryogenic carbon capture in a de-sublimating heat exchanger

NASA Astrophysics Data System (ADS)

Yu, Zhitao; Miller, Franklin; Pfotenhauer, John M.

2017-12-01

Both a numerical and analytical model of the heat and mass transfer processes in a CO2, N2 mixture gas de-sublimating cross-flow finned duct heat exchanger system is developed to predict the heat transferred from a mixture gas to liquid nitrogen and the de-sublimating rate of CO2 in the mixture gas. The mixture gas outlet temperature, liquid nitrogen outlet temperature, CO2 mole fraction, temperature distribution and de-sublimating rate of CO2 through the whole heat exchanger was computed using both the numerical and analytic model. The numerical model is built using EES [1] (engineering equation solver). According to the simulation, a cross-flow finned duct heat exchanger can be designed and fabricated to validate the models. The performance of the heat exchanger is evaluated as functions of dimensionless variables, such as the ratio of the mass flow rate of liquid nitrogen to the mass flow rate of inlet flue gas.

An ab initio chemical reaction model for the direct simulation Monte Carlo study of non-equilibrium nitrogen flows.

PubMed

Mankodi, T K; Bhandarkar, U V; Puranik, B P

2017-08-28

A new ab initio based chemical model for a Direct Simulation Monte Carlo (DSMC) study suitable for simulating rarefied flows with a high degree of non-equilibrium is presented. To this end, Collision Induced Dissociation (CID) cross sections for N 2 +N 2 →N 2 +2N are calculated and published using a global complete active space self-consistent field-complete active space second order perturbation theory N 4 potential energy surface and quasi-classical trajectory algorithm for high energy collisions (up to 30 eV). CID cross sections are calculated for only a selected set of ro-vibrational combinations of the two nitrogen molecules, and a fitting scheme based on spectroscopic weights is presented to interpolate the CID cross section for all possible ro-vibrational combinations. The new chemical model is validated by calculating equilibrium reaction rate coefficients that can be compared well with existing shock tube and computational results. High-enthalpy hypersonic nitrogen flows around a cylinder in the transition flow regime are simulated using DSMC to compare the predictions of the current ab initio based chemical model with the prevailing phenomenological model (the total collision energy model). The differences in the predictions are discussed.

Simulated interactions of pedestrian crossings and motorized vehicles in residential areas

NASA Astrophysics Data System (ADS)

Wang, Yan; Peng, Zhongyi; Chen, Qun

2018-01-01

To evaluate whether motorized vehicles can travel through a residential area, this paper develops a cellular automata (CA) model to simulate the interactions between pedestrian crossings and motorized vehicles in a residential area. In this paper, pedestrians determine their crossing speed according to their judgments of the position and velocity of the upcoming vehicles. The pedestrians may walk slowly or quickly or even run, and the pedestrian crossing time influences the vehicle movement. In addition, the proposed model considers the safety margin time needed for pedestrians to cross, and pedestrian-vehicle conflict is considered using the vehicle collision avoidance rule. Through simulations of interactions of pedestrian crossings with motorized vehicles' movement on a typical road in a residential area, the average wait time for pedestrians to cross and the average vehicle velocity under different pedestrian crossing volumes, different vehicle flows and different maximum vehicle velocities are obtained. To avoid an excessive waiting time for pedestrians to cross, the vehicle flow should be less than 180 veh/h, which allows an average of less than 10 s of waiting time; if the vehicle flow rate is less than 36 veh/h, then the waiting time is approximately 1 s. Field observations are conducted to validate the simulation results.

Evaluation of the discrete vortex wake cross flow model using vector computers. Part 2: User's manual for DIVORCE

NASA Technical Reports Server (NTRS)

Deffenbaugh, F. D.; Vitz, J. F.

1979-01-01

The users manual for the Discrete Vortex Cross flow Evaluator (DIVORCE) computer program is presented. DIVORCE was developed in FORTRAN 4 for the DCD 6600 and CDC 7600 machines. Optimal calls to a NASA vector subroutine package are provided for use with the CDC 7600.

Three-Dimensional Navier-Stokes Simulations with Two-Equation Turbulence Models of Intersecting Shock-Waves/Turbulent Boundary Layer at Mach 8.3

NASA Technical Reports Server (NTRS)

Bardina, J. E.; Coakley, T. J.

1994-01-01

An investigation of the numerical simulation with two-equation turbulence models of a three-dimensional hypersonic intersecting (SWTBL) shock-wave/turbulent boundary layer interaction flow is presented. The flows are solved with an efficient implicit upwind flux-difference split Reynolds-averaged Navier-Stokes code. Numerical results are compared with experimental data for a flow at Mach 8.28 and Reynolds number 5.3x10(exp 6) with crossing shock-waves and expansion fans generated by two lateral 15 fins located on top of a cold-wall plate. This experiment belongs to the hypersonic database for modeling validation. Simulations show the development of two primary counter-rotating cross-flow vortices and secondary turbulent structures under the main vortices and in each corner singularity inside the turbulent boundary layer. A significant loss of total pressure is produced by the complex interaction between the main vortices and the uplifted jet stream of the boundary layer. The overall agreement between computational and experimental data is generally good. The turbulence modeling corrections show improvements in the predictions of surface heat transfer distribution and an increase in the strength of the cross-flow vortices. Accurate predictions of the outflow flowfield is found to require accurate modeling of the laminar/turbulent boundary layers on the fin walls.

Modeling of molecular nitrogen collisions and dissociation processes for direct simulation Monte Carlo.

PubMed

Parsons, Neal; Levin, Deborah A; van Duin, Adri C T; Zhu, Tong

2014-12-21

The Direct Simulation Monte Carlo (DSMC) method typically used for simulating hypersonic Earth re-entry flows requires accurate total collision cross sections and reaction probabilities. However, total cross sections are often determined from extrapolations of relatively low-temperature viscosity data, so their reliability is unknown for the high temperatures observed in hypersonic flows. Existing DSMC reaction models accurately reproduce experimental equilibrium reaction rates, but the applicability of these rates to the strong thermal nonequilibrium observed in hypersonic shocks is unknown. For hypersonic flows, these modeling issues are particularly relevant for nitrogen, the dominant species of air. To rectify this deficiency, the Molecular Dynamics/Quasi-Classical Trajectories (MD/QCT) method is used to accurately compute collision and reaction cross sections for the N2(Σg+1)-N2(Σg+1) collision pair for conditions expected in hypersonic shocks using a new potential energy surface developed using a ReaxFF fit to recent advanced ab initio calculations. The MD/QCT-computed reaction probabilities were found to exhibit better physical behavior and predict less dissociation than the baseline total collision energy reaction model for strong nonequilibrium conditions expected in a shock. The MD/QCT reaction model compared well with computed equilibrium reaction rates and shock-tube data. In addition, the MD/QCT-computed total cross sections were found to agree well with established variable hard sphere total cross sections.

Nonlinear deformations of microcapsules in elongation flow

NASA Astrophysics Data System (ADS)

Deschamps, Julien; de Loubens, Clément; Boedec, Gwenn; Georgelin, Marc; Leonetti, Marc; Soft Matter; Biophysics Group Team

2014-11-01

Soft microcapsules are drops bounded by a thin elastic shell made of cross-linked proteins. They have numerous applications for drug delivery in bioengineering, pharmaceutics and medicine, where their mechanical stability and their dynamics under flow are crucial. They can also be used as red blood cells models. Here, we investigate the mechanical behaviour of microcapsules made of albumine in strong elongational flow, up to a stretching of 180% just before breaking. The set-up allows us to visualize the deformed shape in the two perpendicular main fields of view, to manage high capillary number and to manipulate soft microcapsules. The steady-state shape of a capsule in the planar elongational flow is non-axisymmetric. In each cross section, the shape is an ellipse but with different small axis which vary in opposite sense with the stretching. Whatever the degree of cross-linking and the size of the capsules, the deformations followed the same master-curve. Comparisons between numerical predictions and experimental results permit to conclude unambiguously that the more properly strain-energy model of membrane is the generalized Hooke model.

Preliminary study of the interactions caused by crossing shock waves and a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Ketchum, A. C.; Bogdonoff, S. M.; Fernando, E. M.; Batcho, P. F.

1989-01-01

The subject research, the first phase of an extended study of the interaction of crossing shock waves with a turbulent boundary layer, has revealed the complexity of the resulting flow. Detailed surface visualization and mean wall static pressure distributions show little resemblance to the inviscid flow approximation, and the exploratory high frequency measurements show that the flow downstream of the theoretical inviscid shock crossing position has a significant unsteady characteristic. Further developments of the (unsteady) high frequency measurements are required to fully characterize the unsteadiness and the requirements to include this component in flowfield modeling.

Filament turnover tunes both force generation and dissipation to control long-range flows in a model actomyosin cortex

PubMed Central

McCall, Patrick M.; Gardel, Margaret L.; Munro, Edwin M.

2017-01-01

Actomyosin-based cortical flow is a fundamental engine for cellular morphogenesis. Cortical flows are generated by cross-linked networks of actin filaments and myosin motors, in which active stress produced by motor activity is opposed by passive resistance to network deformation. Continuous flow requires local remodeling through crosslink unbinding and and/or filament disassembly. But how local remodeling tunes stress production and dissipation, and how this in turn shapes long range flow, remains poorly understood. Here, we study a computational model for a cross-linked network with active motors based on minimal requirements for production and dissipation of contractile stress: Asymmetric filament compliance, spatial heterogeneity of motor activity, reversible cross-links and filament turnover. We characterize how the production and dissipation of network stress depend, individually, on cross-link dynamics and filament turnover, and how these dependencies combine to determine overall rates of cortical flow. Our analysis predicts that filament turnover is required to maintain active stress against external resistance and steady state flow in response to external stress. Steady state stress increases with filament lifetime up to a characteristic time τm, then decreases with lifetime above τm. Effective viscosity increases with filament lifetime up to a characteristic time τc, and then becomes independent of filament lifetime and sharply dependent on crosslink dynamics. These individual dependencies of active stress and effective viscosity define multiple regimes of steady state flow. In particular our model predicts that when filament lifetimes are shorter than both τc and τm, the dependencies of effective viscosity and steady state stress on filament turnover cancel one another, such that flow speed is insensitive to filament turnover, and shows a simple dependence on motor activity and crosslink dynamics. These results provide a framework for understanding how animal cells tune cortical flow through local control of network remodeling. PMID:29253848

Study of flow structure in a four-vortex furnace model

NASA Astrophysics Data System (ADS)

Anufriev, I. S.; Sharypov, O. V.; Dekterev, A. A.; Shadrin, E. Yu.; Papulov, A. P.

2017-11-01

The flow pattern was studied for a four-vortex furnace of a coal-dust boiler. The paper presents results of experimental study of inner aerodynamics performed on a lab-scale isothermal model of the furnace device. The PIV method was used to receive the flow velocity fields for several cross sections. The analysis was performed for the spatial structure of the flow comprising four stable closed vortices with vertical axes of flow swirling.

Numerical Simulation of Multiphase Magnetohydrodynamic Flow and Deformation of Electrolyte-Metal Interface in Aluminum Electrolysis Cells

NASA Astrophysics Data System (ADS)

Hua, Jinsong; Rudshaug, Magne; Droste, Christian; Jorgensen, Robert; Giskeodegard, Nils-Haavard

2018-06-01

A computational fluid dynamics based multiphase magnetohydrodynamic (MHD) flow model for simulating the melt flow and bath-metal interface deformation in realistic aluminum reduction cells is presented. The model accounts for the complex physics of the MHD problem in aluminum reduction cells by coupling two immiscible fluids, electromagnetic field, Lorentz force, flow turbulence, and complex cell geometry with large length scale. Especially, the deformation of bath-metal interface is tracked directly in the simulation, and the condition of constant anode-cathode distance (ACD) is maintained by moving anode bottom dynamically with the deforming bath-metal interface. The metal pad deformation and melt flow predicted by the current model are compared to the predictions using a simplified model where the bath-metal interface is assumed flat. The effects of the induced electric current due to fluid flow and the magnetic field due to the interior cell current on the metal pad deformation and melt flow are investigated. The presented model extends the conventional simplified box model by including detailed cell geometry such as the ledge profile and all channels (side, central, and cross-channels). The simulations show the model sensitivity to different side ledge profiles and the cross-channel width by comparing the predicted melt flow and metal pad heaving. In addition, the model dependencies upon the reduction cell operation conditions such as ACD, current distribution on cathode surface and open/closed channel top, are discussed.

Drinking, driving, and crashing: a traffic-flow model of alcohol-related motor vehicle accidents.

PubMed

Gruenewald, Paul J; Johnson, Fred W

2010-03-01

This study examined the influence of on-premise alcohol-outlet densities and of drinking-driver densities on rates of alcohol-related motor vehicle crashes. A traffic-flow model is developed to represent geographic relationships between residential locations of drinking drivers, alcohol outlets, and alcohol-related motor vehicle crashes. Cross-sectional and time-series cross-sectional spatial analyses were performed using data collected from 144 geographic units over 4 years. Data were obtained from archival and survey sources in six communities. Archival data were obtained within community areas and measured activities of either the resident population or persons visiting these communities. These data included local and highway traffic flow, locations of alcohol outlets, population density, network density of the local roadway system, and single-vehicle nighttime (SVN) crashes. Telephone-survey data obtained from residents of the communities were used to estimate the size of the resident drinking and driving population. Cross-sectional analyses showed that effects relating on-premise densities to alcohol-related crashes were moderated by highway trafficflow. Depending on levels of highway traffic flow, 10% greater densities were related to 0% to 150% greater rates of SVN crashes. Time-series cross-sectional analyses showed that changes in the population pool of drinking drivers and on-premise densities interacted to increase SVN crash rates. A simple traffic-flow model can assess the effects of on-premise alcohol-outlet densities and of drinking-driver densities as they vary across communities to produce alcohol-related crashes. Analyses based on these models can usefully guide policy decisions on the sitting of on-premise alcohol outlets.

Dynamical systems characterization of inertial effects of fluid flow in a curved artery model under pulsatile flow forcing

NASA Astrophysics Data System (ADS)

Leggiero, Michael; Bulusu, Kartik V.; Plesniak, Michael W.

2013-11-01

The main objective of this study was to examine inertial effects in a 180-degree model of curved arteries under pulsatile inflow conditions. Two-component, two-dimensional particle image velocimetery (2C-2D PIV) data were acquired upstream of and at several cross-sectional locations in the curved artery model. A blood-analog fluid comprised of 71% saturated sodium iodide solution, 28% glycerol and 1% distilled water (by volume) was subjected to multi-harmonic pulsatile inflow functions. First, signal time-lag was quantified by cross-correlating the input (voltage-time) supplied to a programmable pump and the output PIV (flow rate-time) measurements. The experiment was then treated as a linear, time-invariant system, and frequency response was estimated for phase shifts across a certain spectrum. Input-output signal dissimilarities were attributable to intrinsic inertial effects of flow. By coupling pressure-time and upstream flow rate-time measurements, the experiment was modeled using system identification methods. Results elucidate the role of inertial effects in fluid flow velocity measurements and the effect of these delays on secondary flow structure detection in a curved artery model. Supported by the NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: A Realistic Cellular Automaton Model for Synchronized Traffic Flow

NASA Astrophysics Data System (ADS)

Zhao, Bo-Han; Hu, Mao-Bin; Jiang, Rui; Wu, Qing-Song

2009-11-01

A cellular automaton model is proposed to consider the anticipation effect in drivers' behavior. It is shown that the anticipation effect can be one of the origins of synchronized traffic flow. With anticipation effect, the congested traffic flow simulated by the model exhibits the features of synchronized flow. The spatiotemporal patterns induced by an on-ramp are also consistent with the three-phase traffic theory. Since the origin of synchronized flow is still controversial, our work can shed some light on the mechanism of synchronized flow.

Influence of strut cross-section of stents on local hemodynamics in stented arteries

NASA Astrophysics Data System (ADS)

Jiang, Yongfei; Zhang, Jun; Zhao, Wanhua

2016-05-01

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics (CFD) methods are performed to study how the shape and the aspect ratio (AR) of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress (WSS) in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.

Dissociation cross section for high energy O2-O2 collisions

NASA Astrophysics Data System (ADS)

Mankodi, T. K.; Bhandarkar, U. V.; Puranik, B. P.

2018-04-01

Collision-induced dissociation cross section database for high energy O2-O2 collisions (up to 30 eV) is generated and published using the quasiclassical trajectory method on the singlet, triplet, and quintet spin ground state O4 potential energy surfaces. At equilibrium conditions, these cross sections predict reaction rate coefficients that match those obtained experimentally. The main advantage of the cross section database based on ab initio computations is in the study of complex flows with high degree of non-equilibrium. Direct simulation Monte Carlo simulations using the reactive cross section databases are carried out for high enthalpy hypersonic oxygen flow over a cylinder at rarefied ambient conditions. A comparative study with the phenomenological total collision energy chemical model is also undertaken to point out the difference and advantage of the reported ab initio reaction model.

Cross-shore flow on the inner-shelf off southwest Portugal

NASA Astrophysics Data System (ADS)

Lamas, L.; Peliz, A.; Oliveira, P.; Dias, J.

2012-04-01

Velocity measurements from 4 bottom-mounted ADCP deployments (summers of 2006, 2007, 2008 and 2011) at a 12-m depth site off Sines, Portugal, complemented with time series of winds, waves and tides, are used to study the inner-shelf cross-shore flow dependence on wave, tidal and wind forcings. During these four summers, the dominating winds are from the north (upwelling-favorable), with strong diurnal sea breeze cycle throughout these periods. This quasi-steady wind circulation is sometimes interrupted by short event-like reversals. The observed records were split in different subsets according to tidal amplitude, wave height, cross- and along-shore wind magnitudes, and the vertical structure of the cross-shore flow was studied for each of these subsets. Despite different forcing conditions, the cross-shore velocity profiles usually show a vertical parabolic structure with maximum onshore flow at mid-depth, resembling the upwelling return flow for mid-shelf conditions, but atypical for the inner-shelf and in disagreement with other inner-shelf studies from other sites. We compare the observations with simplified 2D inner-shelf models and with results from other studies.

Numerical Study on Influence of Cross Flow on Rewetting of AHWR Fuel Bundle

PubMed Central

Kumar, Mithilesh; Mukhopadhyay, D.; Ghosh, A. K.; Kumar, Ravi

2014-01-01

Numerical study on AHWR fuel bundle has been carried out to assess influence of circumferential and cross flow rewetting on the conduction heat transfer. The AHWR fuel bundle quenching under accident condition is designed primarily with radial jets at several axial locations. A 3D (r, θ, z) transient conduction fuel pin model has been developed to carry out the study with a finite difference method (FDM) technique with alternating direction implicit (ADI) scheme. The single pin has been considered to study effect of circumferential conduction and multipins have been considered to study the influence of cross flow. Both analyses are carried out with the same fluid temperature and heat transfer coefficients as boundary conditions. It has been found from the analyses that, for radial jet, the circumferential conduction is significant and due to influence of overall cross flow the reductions in fuel temperature in the same quench plane in different rings are different with same initial surface temperature. Influence of cross flow on rewetting is found to be very significant. Outer fuel pins rewetting time is higher than inner. PMID:24672341

Secondary flow vortical structures in a 180∘ elastic curved vessel with torsion under steady and pulsatile inflow conditions

NASA Astrophysics Data System (ADS)

Najjari, Mohammad Reza; Plesniak, Michael W.

2018-01-01

Secondary flow structures in a 180∘ curved pipe model of an artery are studied using particle image velocimetry. Both steady and pulsatile inflow conditions are investigated. In planar curved pipes with steady flow, multiple (two, four, six) vortices are detected. For pulsatile flow, various pairs of vortices, i.e., Dean, deformed-Dean, Lyne-type, and split-Dean, are present in the cross section of the pipe at 90∘ into the bend. The effects of nonplanar curvature (torsion) and vessel dilatation on these vortical structures are studied. Torsion distorts the symmetric secondary flows (which exist in planar curvatures) and can result in formation of more complex vortical structures. For example, the split-Dean and Lyne-type vortices with same rotation direction originating from opposite sides of the cross section tend to merge together in pulsatile flow. The vortical structures in elastic vessels with dilatation (0.61%-3.23%) are also investigated and the results are compared with rigid model results. It was found that the secondary flow structures in rigid and elastic models are similar, and hence the local compliance of the vessel does not affect the morphology of secondary flow structures.

Coordinated Control of Cross-Flow Turbines

NASA Astrophysics Data System (ADS)

Strom, Benjamin; Brunton, Steven; Polagye, Brian

2016-11-01

Cross-flow turbines, also known as vertical-axis turbines, have several advantages over axial-flow turbines for a number of applications including urban wind power, high-density arrays, and marine or fluvial currents. By controlling the angular velocity applied to the turbine as a function of angular blade position, we have demonstrated a 79 percent increase in cross-flow turbine efficiency over constant-velocity control. This strategy uses the downhill simplex method to optimize control parameter profiles during operation of a model turbine in a recirculating water flume. This optimization method is extended to a set of two turbines, where the blade motions and position of the downstream turbine are optimized to beneficially interact with the coherent structures in the wake of the upstream turbine. This control scheme has the potential to enable high-density arrays of cross-flow turbines to operate at cost-effective efficiency. Turbine wake and force measurements are analyzed for insight into the effect of a coordinated control strategy.

Low-Frequency Oscillations and Transport Processes Induced by Multiscale Transverse Structures in the Polar Wind Outflow: A Three-Dimensional Simulation

NASA Technical Reports Server (NTRS)

Ganguli, Supriya B.; Gavrishchaka, Valeriy V.

1999-01-01

Multiscale transverse structures in the magnetic-field-aligned flows have been frequently observed in the auroral region by FAST and Freja satellites. A number of multiscale processes, such as broadband low-frequency oscillations and various cross-field transport effects are well correlated with these structures. To study these effects, we have used our three-dimensional multifluid model with multiscale transverse inhomogeneities in the initial velocity profile. Self-consistent-frequency mode driven by local transverse gradients in the generation of the low field-aligned ion flow and associated transport processes were simulated. Effects of particle interaction with the self-consistent time-dependent three-dimensional wave potential have been modeled using a distribution of test particles. For typical polar wind conditions it has been found that even large-scale (approximately 50 - 100 km) transverse inhomogeneities in the flow can generate low-frequency oscillations that lead to significant flow modifications, cross-field particle diffusion, and other transport effects. It has also been shown that even small-amplitude (approximately 10 - 20%) short-scale (approximately 10 km) modulations of the original large-scale flow profile significantly increases low-frequency mode generation and associated cross-field transport, not only at the local spatial scales imposed by the modulations but also on global scales. Note that this wave-induced cross-field transport is not included in any of the global numerical models of the ionosphere, ionosphere-thermosphere, or ionosphere-polar wind. The simulation results indicate that the wave-induced cross-field transport not only affects the ion outflow rates but also leads to a significant broadening of particle phase-space distribution and transverse particle diffusion.

The Effect of Backward-Facing Step Height on Instability Growth and Breakdown in Swept Wing Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Wlezien, Richard W.; King, Rudolph A.; Choudhari, Meelan

2015-01-01

A low-speed experiment was performed on a swept at plate model with an imposed pressure gradient to determine the effect of a backward-facing step on transition in a stationary-cross flow dominated flow. Detailed hot-wire boundary-layer measurements were performed for three backward-facing step heights of approximately 36, 45, and 49% of the boundary-layer thickness at the step. These step heights correspond to a subcritical, nearly-critical, and critical case. Three leading-edge roughness configurations were tested to determine the effect of stationary-cross flow amplitude on transition. The step caused a local increase in amplitude of the stationary cross flow for the two larger step height cases, but farther downstream the amplitude decreased and remained below the baseline amplitude. The smallest step caused a slight local decrease in amplitude of the primary stationary cross flow mode, but the amplitude collapsed back to the baseline case far downstream of the step. The effect of the step on the amplitude of the primary cross flow mode increased with step height, however, the stationary cross flow amplitudes remained low and thus, stationary cross flow was not solely responsible for transition. Unsteady disturbances were present downstream of the step for all three step heights, and the amplitudes increased with increasing step height. The only exception is that the lower frequency (traveling crossflow-like) disturbance was not present in the lowest step height case. Positive and negative spikes in instantaneous velocity began to occur for the two larger step height cases and then grew in number and amplitude downstream of reattachment, eventually leading to transition. The number and amplitude of spikes varied depending on the step height and cross flow amplitude. Despite the low amplitude of the disturbances in the intermediate step height case, breakdown began to occur intermittently and the flow underwent a long transition region.

Modelling the flooding capacity of a Polish Carpathian river: A comparison of constrained and free channel conditions

NASA Astrophysics Data System (ADS)

Czech, Wiktoria; Radecki-Pawlik, Artur; Wyżga, Bartłomiej; Hajdukiewicz, Hanna

2016-11-01

The gravel-bed Biała River, Polish Carpathians, was heavily affected by channelization and channel incision in the twentieth century. Not only were these impacts detrimental to the ecological state of the river, but they also adversely modified the conditions of floodwater retention and flood wave passage. Therefore, a few years ago an erodible corridor was delimited in two sections of the Biała to enable restoration of the river. In these sections, short, channelized reaches located in the vicinity of bridges alternate with longer, unmanaged channel reaches, which either avoided channelization or in which the channel has widened after the channelization scheme ceased to be maintained. Effects of these alternating channel morphologies on the conditions for flood flows were investigated in a study of 10 pairs of neighbouring river cross sections with constrained and freely developed morphology. Discharges of particular recurrence intervals were determined for each cross section using an empirical formula. The morphology of the cross sections together with data about channel slope and roughness of particular parts of the cross sections were used as input data to the hydraulic modelling performed with the one-dimensional steady-flow HEC-RAS software. The results indicated that freely developed cross sections, usually with multithread morphology, are typified by significantly lower water depth but larger width and cross-sectional flow area at particular discharges than single-thread, channelized cross sections. They also exhibit significantly lower average flow velocity, unit stream power, and bed shear stress. The pattern of differences in the hydraulic parameters of flood flows apparent between the two types of river cross sections varies with the discharges of different frequency, and the contrasts in hydraulic parameters between unmanaged and channelized cross sections are most pronounced at low-frequency, high-magnitude floods. However, because of the deep incision of the river, both cross section types are typified by a similar, low potential for the retention of floodwater in floodplain areas. The study indicated that even though river restoration has only begun here, it already brings beneficial effects for flood risk management, reducing flow energy and shear forces exerted on the bed and banks of the channel in unmanaged river reaches. Only within wide, unmanaged channel reaches can the flows of low-frequency, high-magnitude floods be conveyed with relatively low shear forces exerted on the channel boundary. In contrast, in channelized reaches, flow velocity and shear forces are substantially higher, inevitably causing bank erosion and channel incision.

A Martian global groundwater model

NASA Technical Reports Server (NTRS)

Howard, Alan D.

1991-01-01

A global groundwater flow model was constructed for Mars to study hydrologic response under a variety of scenarios, improving and extending earlier simple cross sectional models. The model is capable of treating both steady state and transient flow as well as permeability that is anisotropic in the horizontal dimensions. A single near surface confining layer may be included (representing in these simulations a coherent permafrost layer). Furthermore, in unconfined flow, locations of complete saturation and seepage are determined. The flow model assumes that groundwater gradients are sufficiently low that DuPuit conditions are satisfied and the flow component perpendicular to the ground surface is negligible. The flow equations were solved using a finite difference method employing 10 deg spacing of latitude and longitude.

Estimating monthly streamflow values by cokriging

USGS Publications Warehouse

Solow, A.R.; Gorelick, S.M.

1986-01-01

Cokriging is applied to estimation of missing monthly streamflow values in three records from gaging stations in west central Virginia. Missing values are estimated from optimal consideration of the pattern of auto- and cross-correlation among standardized residual log-flow records. Investigation of the sensitivity of estimation to data configuration showed that when observations are available within two months of a missing value, estimation is improved by accounting for correlation. Concurrent and lag-one observations tend to screen the influence of other available observations. Three models of covariance structure in residual log-flow records are compared using cross-validation. Models differ in how much monthly variation they allow in covariance. Precision of estimation, reflected in mean squared error (MSE), proved to be insensitive to this choice. Cross-validation is suggested as a tool for choosing an inverse transformation when an initial nonlinear transformation is applied to flow values. ?? 1986 Plenum Publishing Corporation.

Numerical analysis of flows of rarefied gases in long channels with octagonal cross section shapes

NASA Astrophysics Data System (ADS)

Szalmas, L.

2014-12-01

Isothermal, pressure driven rarefied gas flows through long channels with octagonal cross section shapes are analyzed computationally. The capillary is between inlet and outlet reservoirs. The cross section is constant along the axial direction. The boundary condition at the solid-gas interface is assumed to be diffuse reflection. Since the channel is long, the gaseous velocity is small compared to the average molecular speed. Consequently, a linearized description can be used. The flow is described by the linearized Bhatnagar-Gross-Krook kinetic model. The solution of the problem is divided into two stages. First, the local flow field is determined by assuming the local pressure gradient. Secondly, the global flow behavior is deduced by the consideration of the conservation of the mass along the axis of the capillary. The kinetic equation is solved by the discrete velocity method on the cross section. Both spatial and velocity spaces are discretized. A body fitted rectangular grid is used for the spatial space. Near the boundary, first-order, while in the interior part of the flow domain, second-order finite-differences are applied to approximate the spatial derivatives. This combination results into an efficient and straightforward numerical treatment. The velocity space is represented by a Gauss-Legendre quadrature. The kinetic equation is solved in an iterative manner. The local dimensionless flow rate is calculated and tabulated for a wide range of the gaseous rarefaction for octagonal cross sections with various geometrical parameters. It exhibits the Knudsen minimum phenomenon. The flow rates in the octagonal channel are compared to those through capillaries with circular and square cross sections. Typical velocity profiles are also shown. The mass flow rate and the distribution of the pressure are determined and presented for global pressure driven flows.

Baleen Hydrodynamics and Morphology of Cross-Flow Filtration in Balaenid Whale Suspension Feeding

PubMed Central

Werth, Alexander J.; Potvin, Jean

2016-01-01

The traditional view of mysticete feeding involves static baleen directly sieving particles from seawater using a simple, dead-end flow-through filtration mechanism. Flow tank experiments on bowhead (Balaena mysticetus) baleen indicate the long-standing model of dead-end filtration, at least in balaenid (bowhead and right) whales, is not merely simplistic but wrong. To recreate continuous intraoral flow, sections of baleen were tested in a flume through which water and buoyant particles circulated with variable flow velocity. Kinematic sequences were analyzed to investigate movement and capture of particles by baleen plates and fringes. Results indicate that very few particles flow directly through the baleen rack; instead much water flows anteroposteriorly along the interior (lingual) side of the rack, allowing items to be carried posteriorly and accumulate at the posterior of the mouth where they might readily be swallowed. Since water flows mainly parallel to rather than directly through the filter, the cross-flow mechanism significantly reduces entrapment and tangling of minute items in baleen fringes, obviating the need to clean the filter. The absence of copepods or other prey found trapped in the baleen of necropsied right and bowhead whales supports this hypothesis. Reduced through-baleen flow was observed with and without boundaries modeling the tongue and lips, indicating that baleen itself is the main if not sole agent of crossflow. Preliminary investigation of baleen from balaenopterid whales that use intermittent filter feeding suggests that although the biomechanics and hydrodynamics of oral flow differ, cross-flow filtration may occur to some degree in all mysticetes. PMID:26918630

Estimation of zeta potential of electroosmotic flow in a microchannel using a reduced-order model.

PubMed

Park, H M; Hong, S M; Lee, J S

2007-10-01

A reduced-order model is derived for electroosmotic flow in a microchannel of nonuniform cross section using the Karhunen-Loève Galerkin (KLG) procedure. The resulting reduced-order model is shown to predict electroosmotic flows accurately with minimal consumption of computer time for a wide range of zeta potential zeta and dielectric constant epsilon. Using the reduced-order model, a practical method is devised to estimate zeta from the velocity measurements of the electroosmotic flow in the microchannel. The proposed method is found to estimate zeta with reasonable accuracy even with noisy velocity measurements.

Curved-flow, rolling-flow, and oscillatory pure-yawing wind-tunnel test methods for determination of dynamic stability derivatives

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Grafton, S. B.; Lutze, F. H.

1981-01-01

Dynamic stability derivatives are evaluated on the basis of rolling-flow, curved-flow and snaking tests. Attention is given to the hardware associated with curved-flow, rolling-flow and oscillatory pure-yawing wind-tunnel tests. It is found that the snaking technique, when combined with linear- and forced-oscillation methods, yields an important method for evaluating beta derivatives for current configurations at high angles of attack. Since the rolling flow model is fixed during testing, forced oscillations may be imparted to the model, permitting the measurement of damping and cross-derivatives. These results, when coupled with basic rolling-flow or rotary-balance data, yield a highly accurate mathematical model for studies of incipient spin and spin entry.

Measurement of crossflow vortices, attachment-line flow, and transition using microthin hot films

NASA Technical Reports Server (NTRS)

Mangalam, S. M.; Agarwal, N. K.; Maddalon, D. V.; Saric, W. S.

1990-01-01

A flow diagnostic experiment was conducted on a 45-deg swept-wing model using surface-mounted, multielement, microthin, hot-film sensors. The cross-flow vortex spacing, the attachment-line flow characteristics, and the transition region were all determined using an advanced data acquisition and instrumentation system. In addition to the frequencies of traveling waves predicted by linear stability theory, amplified disturbances at much higher frequencies were observed. Simultaneous measurements from sensors located at a number of chord and span locations highlighted the strong three-dimensionality of the boundary-layer flow in the presence of cross-flow vortices. The state of the attachment-line boundary layer was determined using a multielement sensor wrapped around the wing leading edge. The transition region flow characteristics were also identified.

Cross-borehole flow analysis to characterize fracture connections in the Melechov Granite, Bohemian-Moravian Highland, Czech Republic

USGS Publications Warehouse

Paillet, Frederick L.; Williams, John H.; Urik, Joseph; Lukes, Joseph; Kobr, Miroslav; Mares, Stanislav

2012-01-01

Application of the cross-borehole flow method, in which short pumping cycles in one borehole are used to induce time-transient flow in another borehole, demonstrated that a simple hydraulic model can characterize the fracture connections in the bedrock mass between the two boreholes. The analysis determines the properties of fracture connections rather than those of individual fractures intersecting a single borehole; the model contains a limited number of adjustable parameters so that any correlation between measured and simulated flow test data is significant. The test was conducted in two 200-m deep boreholes spaced 21 m apart in the Melechov Granite in the Bohemian-Moravian Highland, Czech Republic. Transient flow was measured at depth stations between the identified transmissive fractures in one of the boreholes during short-term pumping and recovery periods in the other borehole. Simulated flows, based on simple model geometries, closely matched the measured flows. The relative transmissivity and storage of the inferred fracture connections were corroborated by tracer testing. The results demonstrate that it is possible to assess the properties of a fracture flow network despite being restricted to making measurements in boreholes in which a local population of discrete fractures regulates the hydraulic communication with the larger-scale aquifer system.

Inverse modeling of the hydraulic properties of fractured media : development of a flow tomography approach

NASA Astrophysics Data System (ADS)

Bour, O.; Klepikova, M.; Le Borgne, T.; De Dreuzy, J.

2013-12-01

Inverse modeling of hydraulic and geometrical properties of fractured media is a very challenging objective due to the spatial heterogeneity of the medium and the scarcity of data. Here we present a flow tomography approach that permits to characterize the location, the connectivity and the hydraulic properties of main flow paths in fractured media. The accurate characterization of the location, hydraulic properties and connectivity of major fracture zones is essential to model flow and solute transport in fractured media. Cross-borehole flowmeter tests, which consist of measuring changes in vertical borehole flows when pumping a neighboring borehole, were shown to be an efficient technique to provide information on the properties of the flow zones that connect borehole pairs [Paillet, 1998; Le Borgne et al., 2006]. The interpretation of such experiments may however be quite uncertain when multiple connections exist. In this study, we explore the potential of flow tomography (i.e., sequential cross-borehole flowmeter tests) for characterizing aquifer heterogeneity. We first propose a framework for inverting flow and drawdown data to infer fracture connectivity and transmissivities. Here we use a simplified discrete fracture network approach that highlights main connectivity structures. This conceptual model attempts to reproduce fracture network connectivity without taking fracture geometry (length, orientation, dip) into account. We then explore the potential of the method for simplified synthetic fracture network models and quantify the sensitivity of drawdown and borehole flow velocities to the transmissivity of the connecting flowpaths. Flow tomography is expected to be most effective if cross-borehole pumping induces large changes in vertical borehole velocities. The uncertainty of the transmissivity estimates increases for small borehole flow velocities. The uncertainty about the transmissivity of fractures that connect the main flowpath but not the boreholes is generally higher. We demonstrate that successively changing pumping and observation boreholes improves the quality of available information and reduces the indetermination of the problem. The inverse method is validated for different synthetic flow scenarios. It is shown to provide a good estimation of connectivity patterns and transmissivities of main flowpaths. Although the chosen fracture network geometry has been simplified, flow tomography appears to be a promising approach for characterizing connectivity patterns and transmissivities of fractured media.

Interrelationships of petiolar air canal architecture, water depth, and convective air flow in Nymphaea odorata (Nymphaeaceae).

PubMed

Richards, Jennifer H; Kuhn, David N; Bishop, Kristin

2012-12-01

Nymphaea odorata grows in water up to 2 m deep, producing fewer larger leaves in deeper water. This species has a convective flow system that moves gases from younger leaves through submerged parts to older leaves, aerating submerged parts. Petiolar air canals are the convective flow pathways. This study describes the structure of these canals, how this structure varies with water depth, and models how convective flow varies with depth. • Nymphaea odorata plants were grown at water depths from 30 to 90 cm. Lamina area, petiolar cross-sectional area, and number and area of air canals were measured. Field-collected leaves and leaves from juvenile plants were analyzed similarly. Using these data and data from the literature, we modeled how convective flow changes with water depth. • Petioles of N. odorata produce two central pairs of air canals; additional pairs are added peripherally, and succeeding pairs are smaller. The first three pairs account for 96% of air canal area. Air canals form 24% of petiolar cross-sectional area. Petiolar and air canal cross-sectional areas increase with water depth. Petiolar area scales with lamina area, but the slope of this relationship is lower in 90 cm water than at shallower depths. In our model, the rate of convective flow varied with depth and with the balance of influx to efflux leaves. • Air canals in N. odorata petioles increase in size and number in deeper water but at a decreasing amount in relation to lamina area. Convective flow also depends on the number of influx to efflux laminae.

Numerical simulation of a cross flow Marine Hydrokinetic turbine.

NASA Astrophysics Data System (ADS)

Hall, Taylor; Aliseda, Alberto

2011-11-01

In the search for alternative sources of energy, the kinetic energy of water currents in oceans, rivers and estuaries is being explored as predictable and environmentally benign. We are investigating the flow past a cross flow turbine in which a helical blade under hydrodynamic forces turns around a shaft perpendicular to the free stream. This type of turbine, while very different from the classical horizontal axis turbine commonly used in the wind energy field, presents advantages for stacking in very narrow constricted channels where the water currents are consistently high and therefore turbine installation may be economically feasible. We use a model of a helical four-bladed turbine in cross flow to investigate the efficiency of the energy capture and the dynamics of the turbulent wake. Scale model experiments in a flume are used to validate the numerical results on a stationary configuration as an initial step towards creating an accurate numerical model of the turbine. The simulation of the rotating turbine provides a full perspective on the effect of angular position on flow detachment and vortex shedding from the blade, as well as on the fluctuations of the shaft torque produced (a problematic feature of this type of turbine). The results are analyzed in terms of hydrodynamic optimization of the blade and its structural loading. Supported by DOE through the Northwest National Marine Renewable Energy Center.

A new model of arterial hemodynamics.

PubMed

Branzan, M; Sundri, G

1983-01-01

The determination of arterial blood flow parameters on the basis of ultrasound investigation requires a new hydrodynamic model of arterial circulation. Unlike previous research (Womersley, Bergel) considering the arterial pressure of its gradients to be known, the present model uses blood flow velocity and arterial radius magnitude easily obtained by ultrasound (Doppler effect). Processing these data requires the thorough analysis of rheological characteristics of blood flow and of arterial wall behaviour (elastic deformability). It has been assumed that: a) blood is a homogeneous and isotropic fluid; b) the artery has a cylindrical symmetry of a circular cross-section at any time moment; c) the pressure in the artery cross-section is constant. Because arterial dynamics has an undulatory character the Fourier analysis of the modified Navier-Stokes equations has been used. Finally, a simplified relation for blood pressure determination has been obtained.

Hemodynamics of 8 different configurations of stenting for bifurcation aneurysms.

PubMed

Kono, K; Terada, T

2013-10-01

SACE is performed for complex aneurysms. There are several configurations of stent placement for bifurcation aneurysms. We investigated hemodynamics among 8 different configurations of stent placement, which may relate to the recanalization rate. We created a silicone block model of a patient-specific asymmetric bifurcation aneurysm. Enterprise closed-cell stents were deployed in the model as various configurations. 3D images of these stents were obtained by micro-CT. We performed CFD simulations for a no-stent model and 8 stent models: a single stent from a proximal vessel to a right or left distal vessel, a horizontal stent, a kissing-Y stent with a uniformly narrowed structure, a nonoverlapping-Y stent, a virtual-Y stent with no narrowed structure (fusion of 2 single stents), and 2 different crossing-Y stents with a focally narrowed structure. Hemodynamic parameters were evaluated. Cycle-averaged velocity and WSS in the aneurysm were reduced because of stent placement in the following order: single stent (19% reduction in cycle-averaged velocity) < nonoverlapping-Y stent (29%) < virtual-Y stent (32%) < horizontal stent (39%) < kissing-Y stent (48%) < crossing-Y stent (54%). Kissing- and crossing-Y stents redirected impingement flow into the distal vessels because of lowered porosity of stents due to narrowed structures. Among 8 different configurations of stent placement, kissing- and crossing-Y stents showed the strongest reduction in flow velocity in the aneurysm because of lowered porosity of stents and redirection of impingement flow. This may be a desirable reconstruction of flow hemodynamics and may decrease recanalization rates in SACE.

Numerical Modeling of Three-Dimensional Confined Flows

NASA Technical Reports Server (NTRS)

Greywall, M. S.

1981-01-01

A three dimensional confined flow model is presented. The flow field is computed by calculating velocity and enthalpy along a set of streamlines. The finite difference equations are obtained by applying conservation principles to streamtubes constructed around the chosen streamlines. With appropriate substitutions for the body force terms, the approach computes three dimensional magnetohydrodynamic channel flows. A listing of a computer code, based on this approach is presented in FORTRAN IV language. The code computes three dimensional compressible viscous flow through a rectangular duct, with the duct cross section specified along the axis.

A Numerical Simulation of a Normal Sonic Jet into a Hypersonic Cross-Flow

NASA Technical Reports Server (NTRS)

Jeffries, Damon K.; Krishnamurthy, Ramesh; Chandra, Suresh

1997-01-01

This study involves numerical modeling of a normal sonic jet injection into a hypersonic cross-flow. The numerical code used for simulation is GASP (General Aerodynamic Simulation Program.) First the numerical predictions are compared with well established solutions for compressible laminar flow. Then comparisons are made with non-injection test case measurements of surface pressure distributions. Good agreement with the measurements is observed. Currently comparisons are underway with the injection case. All the experimental data were generated at the Southampton University Light Piston Isentropic Compression Tube.

User's Guide for Mixed-Size Sediment Transport Model for Networks of One-Dimensional Open Channels

USGS Publications Warehouse

Bennett, James P.

2001-01-01

This user's guide describes a mathematical model for predicting the transport of mixed sizes of sediment by flow in networks of one-dimensional open channels. The simulation package is useful for general sediment routing problems, prediction of erosion and deposition following dam removal, and scour in channels at road embankment crossings or other artificial structures. The model treats input hydrographs as stepwise steady-state, and the flow computation algorithm automatically switches between sub- and supercritical flow as dictated by channel geometry and discharge. A variety of boundary conditions including weirs and rating curves may be applied both external and internal to the flow network. The model may be used to compute flow around islands and through multiple openings in embankments, but the network must be 'simple' in the sense that the flow directions in all channels can be specified before simulation commences. The location and shape of channel banks are user specified, and all bedelevation changes take place between these banks and above a user-specified bedrock elevation. Computation of sediment-transport emphasizes the sand-size range (0.0625-2.0 millimeter) but the user may select any desired range of particle diameters including silt and finer (<0.0625 millimeter). As part of data input, the user may set the original bed-sediment composition of any number of layers of known thickness. The model computes the time evolution of total transport and the size composition of bed- and suspended-load sand through any cross section of interest. It also tracks bed -surface elevation and size composition. The model is written in the FORTRAN programming language for implementation on personal computers using the WINDOWS operating system and, along with certain graphical output display capability, is accessed from a graphical user interface (GUI). The GUI provides a framework for selecting input files and parameters of a number of components of the sediment-transport process. There are no restrictions in the use of the model as to numbers of channels, channel junctions, cross sections per channel, or points defining the cross sections. Following completion of the simulation computations, the GUI accommodates display of longitudinal plots of either bed elevation and size composition, or of transport rate and size composition of the various components, for individual channels and selected times during the simulation period. For individual cross sections, the GUI also allows display of time series of transport rate and size composition of the various components and of bed elevation and size composition.

Wind Effects on Flow Patterns and Net Fluxes in Density-Driven High-Latitude Channel Flow

NASA Astrophysics Data System (ADS)

Huntley, Helga S.; Ryan, Patricia

2018-01-01

A semianalytic two-dimensional model is used to analyze the interplay between the different forces acting on density-driven flow in high-latitude channels. In particular, the balance between wind stress, viscous forces, baroclinicity, and sea surface slope adjustments under specified flux conditions is examined. Weak winds are found not to change flow patterns appreciably, with minimal (<7%) adjustments to horizontal velocity maxima. In low-viscosity regimes, strong winds change the flow significantly, especially at the surface, by either strengthening the dual-jet pattern, established without wind, by a factor of 2-3 or initiating return flow at the surface. A nonzero flux does not result in the addition of a uniform velocity throughout the channel cross section, but modifies both along-channel and cross-channel velocities to become more symmetric, dominated by a down-channel jet centered in the domain and counter-clockwise lateral flow. We also consider formulations of the model that allow adjustments of the net flux in response to the wind. Flow patterns change, beyond uniform intensification or weakening, only for strong winds and high Ekman number. Comparisons of the model results to observational data collected in Nares Strait in the Canadian Archipelago in the summer of 2007 show rough agreement, but the model misses the upstream surface jet on the east side of the strait and propagates bathymetric effects too strongly in the vertical for this moderately high eddy viscosity. Nonetheless, the broad strokes of the observed high-latitude flow are reproduced.

IB-LBM simulation of the haemocyte dynamics in a stenotic capillary.

PubMed

Yuan-Qing, Xu; Xiao-Ying, Tang; Fang-Bao, Tian; Yu-Hua, Peng; Yong, Xu; Yan-Jun, Zeng

2014-01-01

To study the behaviour of a haemocyte when crossing a stenotic capillary, the immersed boundary-lattice Boltzmann method was used to establish a quantitative analysis model. The haemocyte was assumed to be spherical and to have an elastic cell membrane, which can be driven by blood flow to adopt a highly deformable character. In the stenotic capillary, the spherical blood cell was stressed both by the flow and the wall dimension, and the cell shape was forced to be stretched to cross the stenosis. Our simulation investigated the haemocyte crossing process in detail. The velocity and pressure were anatomised to obtain information on how blood flows through a capillary and to estimate the degree of cell damage caused by excessive pressure. Quantitative velocity analysis results demonstrated that a large haemocyte crossing a small stenosis would have a noticeable effect on blood flow, while quantitative pressure distribution analysis results indicated that the crossing process would produce a special pressure distribution in the cell interior and to some extent a sudden change between the cell interior and the surrounding plasma.

Hybrid LES/RANS Simulation of Transverse Sonic Injection into a Mach 2 Flow

NASA Technical Reports Server (NTRS)

Boles, John A.; Edwards, Jack R.; Baurle, Robert A.

2008-01-01

A computational study of transverse sonic injection of air and helium into a Mach 1.98 cross-flow is presented. A hybrid large-eddy simulation / Reynolds-averaged Navier-Stokes (LES/RANS) turbulence model is used, with the two-equation Menter baseline (Menter-BSL) closure for the RANS part of the flow and a Smagorinsky-type model for the LES part of the flow. A time-dependent blending function, dependent on modeled turbulence variables, is used to shift the closure from RANS to LES. Turbulent structures are initiated and sustained through the use of a recycling / rescaling technique. Two higher-order discretizations, the Piecewise Parabolic Method (PPM) of Colella and Woodward, and the SONIC-A ENO scheme of Suresh and Huyhn are used in the study. The results using the hybrid model show reasonably good agreement with time-averaged Mie scattering data and with experimental surface pressure distributions, even though the penetration of the jet into the cross-flow is slightly over-predicted. The LES/RANS results are used to examine the validity of commonly-used assumptions of constant Schmidt and Prandtl numbers in the intense mixing zone downstream of the injection location.

Shear thinning effects on blood flow in straight and curved tubes

NASA Astrophysics Data System (ADS)

Cherry, Erica M.; Eaton, John K.

2013-07-01

Simulations were performed to determine the magnitude and types of errors one can expect when approximating blood in large arteries as a Newtonian fluid, particularly in the presence of secondary flows. This was accomplished by running steady simulations of blood flow in straight and curved tubes using both Newtonian and shear-thinning viscosity models. In the shear-thinning simulations, the viscosity was modeled as a shear rate-dependent function fit to experimental data. Simulations in straight tubes were modeled after physiologically relevant arterial flows, and flow parameters for the curved tube simulations were chosen to examine a variety of secondary flow strengths. The diameters ranged from 1 mm to 10 mm and the Reynolds numbers from 24 to 1500. Pressure and velocity data are reported for all simulations. In the straight tube simulations, the shear-thinning flows had flattened velocity profiles and higher pressure gradients compared to the Newtonian simulations. In the curved tube flows, the shear-thinning simulations tended to have blunted axial velocity profiles, decreased secondary flow strengths, and decreased axial vorticity compared to the Newtonian simulations. The cross-sectionally averaged pressure drops in the curved tubes were higher in the shear-thinning flows at low Reynolds number but lower at high Reynolds number. The maximum deviation in secondary flow magnitude averaged over the cross sectional area was 19% of the maximum secondary flow and the maximum deviation in axial vorticity was 25% of the maximum vorticity.

Transient pressure analysis of a volume fracturing well in fractured tight oil reservoirs

NASA Astrophysics Data System (ADS)

Lu, Cheng; Wang, Jiahang; Zhang, Cong; Cheng, Minhua; Wang, Xiaodong; Dong, Wenxiu; Zhou, Yingfang

2017-12-01

This paper presents a semi-analytical model to simulate transient pressure curves for a vertical well with a reconstructed fracture network in fractured tight oil reservoirs. In the proposed model, the reservoir is a composite system and contains two regions. The inner region is described as a formation with a finite conductivity hydraulic fracture network and the flow in the fracture is assumed to be linear, while the outer region is modeled using the classical Warren-Root model where radial flow is applied. The transient pressure curves of a vertical well in the proposed reservoir model are calculated semi-analytically using the Laplace transform and Stehfest numerical inversion. As shown in the type curves, the flow is divided into several regimes: (a) linear flow in artificial main fractures; (b) coupled boundary flow; (c) early linear flow in a fractured formation; (d) mid radial flow in the semi-fractures of the formation; (e) mid radial flow or pseudo steady flow; (f) mid cross-flow; (g) closed boundary flow. Based on our newly proposed model, the effects of some sensitive parameters, such as elastic storativity ratio, cross-flow coefficient, fracture conductivity and skin factor, on the type curves were also analyzed extensively. The simulated type curves show that for a vertical fractured well in a tight reservoir, the elastic storativity ratios and crossflow coefficients affect the time and the degree of crossflow respectively. The pressure loss increases with an increase in the fracture conductivity. To a certain extent, the effect of the fracture conductivity is more obvious than that of the half length of the fracture on improving the production effect. With an increase in the wellbore storage coefficient, the fluid compressibility is so large that it might cover the early stage fracturing characteristics. Linear or bilinear flow may not be recognized, and the pressure and pressure derivative gradually shift to the right. With an increase in the skin effect, the pressure loss increases gradually.

Secondary flow structures in a 180∘ elastic curved vessel with torsion under steady and pulsatile inflow conditions

NASA Astrophysics Data System (ADS)

Najjari, Mohammad Reza; Plesniak, Michael W.

2017-11-01

Secondary flow vortical structures were investigated in an elastic 180° curved pipe with and without torsion under steady and pulsatile flow using particle image velocimetry (PIV). The elastic thin-walled curved pipes were constructed using Sylgard 184, and inserted into a bath of refractive index matched fluid to perform PIV. A vortex identification method was employed to identify various vortical structures in the flow. The secondary flow structures in the planar compliant model with dilatation of 0.61%-3.23% under pulsatile flow rate were compared with the rigid vessel model results, and it was found that local vessel compliance has a negligible effect on secondary flow morphology. The secondary flow structures were found to be more sensitive to out of plane curvature (torsion) than to vessel compliance. Torsion distorts the symmetry of secondary flow and results in more complex vortical structures in both steady and pulsatile flows. In high Re number steady flow with torsion, a single dominant vortical structure can be detected at the middle of the 90° cross section. In pulsatile flow with torsion, the split-Dean and Lyne-type vortices with same rotation direction originating from opposite sides of the cross section tend to merge together. supported by GW Center for Biomimetics and Bioinspired Engineering.

On the derivation of flow rating curves in data-scarce environments

NASA Astrophysics Data System (ADS)

Manfreda, Salvatore

2018-07-01

River monitoring is a critical issue for hydrological modelling that relies strongly on the use of flow rating curves (FRCs). In most cases, these functions are derived by least-squares fitting which usually leads to good performance indices, even when based on a limited range of data that especially lack high flow observations. In this context, cross-section geometry is a controlling factor which is not fully exploited in classical approaches. In fact, river discharge is obtained as the product of two factors: 1) the area of the wetted cross-section and 2) the cross-sectionally averaged velocity. Both factors can be expressed as a function of the river stage, defining a viable alternative in the derivation of FRCs. This makes it possible to exploit information about cross-section geometry limiting, at least partially, the uncertainty in the extrapolation of discharge at higher flow values. Numerical analyses and field data confirm the reliability of the proposed procedure for the derivation of FRCs.

An analysis of river bank slope and unsaturated flow effects on bank storage.

PubMed

Doble, Rebecca; Brunner, Philip; McCallum, James; Cook, Peter G

2012-01-01

Recognizing the underlying mechanisms of bank storage and return flow is important for understanding streamflow hydrographs. Analytical models have been widely used to estimate the impacts of bank storage, but are often based on assumptions of conditions that are rarely found in the field, such as vertical river banks and saturated flow. Numerical simulations of bank storage and return flow in river-aquifer cross sections with vertical and sloping banks were undertaken using a fully-coupled, surface-subsurface flow model. Sloping river banks were found to increase the bank infiltration rates by 98% and storage volume by 40% for a bank slope of 3.4° from horizontal, and for a slope of 8.5°, delay bank return flow by more than four times compared with vertical river banks and saturated flow. The results suggested that conventional analytical approximations cannot adequately be used to quantify bank storage when bank slope is less than 60° from horizontal. Additionally, in the unconfined aquifers modeled, the analytical solutions did not accurately model bank storage and return flow even in rivers with vertical banks due to a violation of the dupuit assumption. Bank storage and return flow were also modeled for more realistic cross sections and river hydrograph from the Fitzroy River, Western Australia, to indicate the importance of accurately modeling sloping river banks at a field scale. Following a single wet season flood event of 12 m, results showed that it may take over 3.5 years for 50% of the bank storage volume to return to the river. © 2011, The Author(s). Ground Water © 2011, National Ground Water Association.

The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets. M.S. Thesis

NASA Technical Reports Server (NTRS)

Cavage, William M.; Kuhlman, John M.

1993-01-01

An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

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

Sun Zhonghua, E-mail: z.sun@curtin.edu.a; Chaichana, Thanapong

The purpose of the study was to investigate the hemodynamic effect of stent struts (wires) on renal arteries in patients with abdominal aortic aneurysms (AAAs) treated with suprarenal stent-grafts. Two sample patients with AAA undergoing multislice CT angiography pre- and postsuprarenal fixation of stent-grafts were selected for inclusion in the study. Eight juxtarenal models focusing on the renal arteries were generated from the multislice CT datasets. Four types of configurations of stent wires crossing the renal artery ostium were simulated in the segmented aorta models: a single wire crossing centrally, a single wire crossing peripherally, a V-shaped wire crossing centrally,more » and multiple wires crossing peripherally. The blood flow pattern, flow velocity, wall pressure, and wall shear stress at the renal arteries pre- and post-stent-grafting were analyzed and compared using a two-way fluid structure interaction analysis. The stent wire thickness was simulated with a diameter of 0.4, 1.0, and 2.0 mm, and hemodynamic analysis was performed at different cardiac cycles. The interference of stent wires with renal blood flow was mainly determined by the thickness of stent wires and the type of configuration of stent wires crossing the renal ostium. The flow velocity was reduced by 20-30% in most of the situations when the stent wire thickness increased to 1.0 and 2.0 mm. Of the four types of configuration, the single wire crossing centrally resulted in the highest reduction of flow velocity, ranging from 21% to 28.9% among three different wire thicknesses. Wall shear stress was also dependent on the wire thickness, which decreased significantly when the wire thickness reached 1.0 and 2.0 mm. In conclusion, our preliminary study showed that the hemodynamic effect of suprarenal stent wires in patients with AAA treated with suprarenal stent-grafts was determined by the thickness of suprarenal stent wires. Research findings in our study are useful for follow-up of patients treated with suprarenal stent-grafts to ensure long-term safety of the suprarenal fixation.« less

Hydraulic conditions of flood flows in a Polish Carpathian river subjected to variable human impacts

NASA Astrophysics Data System (ADS)

Radecki-Pawlik, Artur; Czech, Wiktoria; Wyżga, Bartłomiej; Mikuś, Paweł; Zawiejska, Joanna; Ruiz-Villanueva, Virginia

2016-04-01

Channel morphology of the Czarny Dunajec River, Polish Carpathians, has been considerably modified as a result of channelization and gravel-mining induced channel incision, and now it varies from a single-thread, incised or regulated channel to an unmanaged, multi-thread channel. We investigated effects of these distinct channel morphologies on the conditions for flood flows in a study of 25 cross-sections from the middle river course where the Czarny Dunajec receives no significant tributaries and flood discharges increase little in the downstream direction. Cross-sectional morphology, channel slope and roughness of particular cross-section parts were used as input data for the hydraulic modelling performed with the 1D steady-flow HEC-RAS model for discharges with recurrence interval from 1.5 to 50 years. The model for each cross-section was calibrated with the water level of a 20-year flood from May 2014, determined shortly after the flood on the basis of high-water marks. Results indicated that incised and channelized river reaches are typified by similar flow widths and cross-sectional flow areas, which are substantially smaller than those in the multi-thread reach. However, because of steeper channel slope in the incised reach than in the channelized reach, the three river reaches differ in unit stream power and bed shear stress, which attain the highest values in the incised reach, intermediate values in the channelized reach, and the lowest ones in the multi-thread reach. These patterns of flow power and hydraulic forces are reflected in significant differences in river competence between the three river reaches. Since the introduction of the channelization scheme 30 years ago, sedimentation has reduced its initial flow conveyance by more than half and elevated water stages at given flood discharges by about 0.5-0.7 m. This partly reflects a progressive growth of natural levees along artificially stabilized channel banks. By contrast, sediments of natural levees deposited along the multi-thread channel and subsequently eroded in the course of lateral channel migration and floodplain reworking; as a result, they do not reduce the conveyance of floodplain flows in this reach. This study was performed within the scope of the Research Project DEC-2013/09/B/ST10/00056 financed by the National Science Centre of Poland.

Natural convection enhancement by a discrete vibrating plate and a cross-flow opening: a numerical investigation

NASA Astrophysics Data System (ADS)

Florio, L. A.; Harnoy, A.

2011-06-01

In this study, a unique combination of a vibrating plate and a cross-flow passage is proposed as a means of enhancing natural convection cooling. The enhancement potential was estimated based on numerical studies involving a representative model which includes a short, transversely oscillating plate, placed over a transverse cross-flow opening in a uniformly heated vertical channel wall dividing two adjacent vertical channels. The resulting velocity and temperature fields are analyzed, with the focus on the local thermal effects near the opening. The simulation indicates up to a 50% enhancement in the local heat transfer coefficient for vibrating plate amplitudes of at least 30% of the mean clearance space and frequencies of over 82 rad/s.

Wind-Tunnel Tests of a Portion of a PV-2 Helicopter Rotor Blade

NASA Technical Reports Server (NTRS)

Kemp, William B., Jr.

1945-01-01

A portion of a PV-2 helicopter rotor blade has been tested in the 6- by 6-foot test section of the Langley stability tunnel to determine if the aerodynamic characteristics were seriously affected by cross flow or fabric distortion. The outer portion of the blade was tested as a reflection plane model pivoted about the tunnel wall to obtain various angles of cross flow over the blade. Because the tunnel wall acts as a plane of sytry, the measured aerodynamic characteristics correspond to those of an airfoil having various angles of sweepforward and sweepback. Tests were made with the vents on the lower surface open and also with the vents sealed and the internal pressure held at -20 inches of water producing an internal pressure coefficient of -1.059. The change in contour resulting from the range of internal pressures used had very little effect on the aerodynamic characteristics of the blade. The test methods were considered to simulate inadequately the flow conditions over the rotor blade because the effects of cross flow were limited to conditions corresponding to sweep of the blade. The results indicated that this type of cross flow had only minor effects on the aerodynamic characteristics of the blade. It is believed, therefore, that future tests to determine the effects on the aerodynamic characteristics of cross flow should utilize complete rotors.

An Improved Model for a Once-through Counter-Cross-Flow Waste Heat Recovery Unit

DTIC Science & Technology

1983-09-01

RAnkine Cycle Energy Recovery (RACER) system. As conceived, the RACER system will be an unfired waste heat recovery system designed to convert waste... heater to arrive at the feedwater inlet. For the given geometry and flow conditions, the model will calcu- late the water inlet temperature consistent...when given feedwater inlet temperature, steam outlet tempera- ture, operating pressure, inlet and outlet gas conditions and gas flow rate. In this

A second-order accurate parabolized Navier-Stokes algorithm for internal flows

NASA Technical Reports Server (NTRS)

Chitsomboon, T.; Tiwari, S. N.

1984-01-01

A parabolized implicit Navier-Stokes algorithm which is of second-order accuracy in both the cross flow and marching directions is presented. The algorithm is used to analyze three model supersonic flow problems (the flow over a 10-degree edge). The results are found to be in good agreement with the results of other techniques available in the literature.

Particle Deposition in Human Lungs due to Varying Cross-Sectional Ellipticity of Left and Right Main Bronchi

NASA Astrophysics Data System (ADS)

Roth, Steven; Oakes, Jessica; Shadden, Shawn

2015-11-01

Particle deposition in the human lungs can occur with every breathe. Airbourne particles can range from toxic constituents (e.g. tobacco smoke and air pollution) to aerosolized particles designed for drug treatment (e.g. insulin to treat diabetes). The effect of various realistic airway geometries on complex flow structures, and thus particle deposition sites, has yet to be extensively investigated using computational fluid dynamics (CFD). In this work, we created an image-based geometric airway model of the human lung and performed CFD simulations by employing multi-domain methods. Following the flow simulations, Lagrangian particle tracking was used to study the effect of cross-sectional shape on deposition sites in the conducting airways. From a single human lung model, the cross-sectional ellipticity (the ratio of major and minor diameters) of the left and right main bronchi was varied systematically from 2:1 to 1:1. The influence of the airway ellipticity on the surrounding flow field and particle deposition was determined.

An entropy-based method for determining the flow depth distribution in natural channels

NASA Astrophysics Data System (ADS)

Moramarco, Tommaso; Corato, Giovanni; Melone, Florisa; Singh, Vijay P.

2013-08-01

A methodology for determining the bathymetry of river cross-sections during floods by the sampling of surface flow velocity and existing low flow hydraulic data is developed . Similar to Chiu (1988) who proposed an entropy-based velocity distribution, the flow depth distribution in a cross-section of a natural channel is derived by entropy maximization. The depth distribution depends on one parameter, whose estimate is straightforward, and on the maximum flow depth. Applying to a velocity data set of five river gage sites, the method modeled the flow area observed during flow measurements and accurately assessed the corresponding discharge by coupling the flow depth distribution and the entropic relation between mean velocity and maximum velocity. The methodology unfolds a new perspective for flow monitoring by remote sensing, considering that the two main quantities on which the methodology is based, i.e., surface flow velocity and flow depth, might be potentially sensed by new sensors operating aboard an aircraft or satellite.

Topological transitions in unidirectional flow of nematic liquid crystal

NASA Astrophysics Data System (ADS)

Cummings, Linda; Anderson, Thomas; Mema, Ensela; Kondic, Lou

2015-11-01

Recent experiments by Sengupta et al. (Phys. Rev. Lett. 2013) revealed interesting transitions that can occur in flow of nematic liquid crystal under carefully controlled conditions within a long microfluidic channel of rectangular cross-section, with homeotropic anchoring at the walls. At low flow rates the director field of the nematic adopts a configuration that is dominated by the surface anchoring, being nearly parallel to the channel height direction over most of the cross-section; but at high flow rates there is a transition to a flow-dominated state, where the director configuration at the channel centerline is aligned with the flow (perpendicular to the channel height direction). We analyze simple channel-flow solutions to the Leslie-Ericksen model for nematics. We demonstrate that two solutions exist, at all flow rates, but that there is a transition between the elastic free energies of these solutions: the anchoring-dominated solution has the lowest energy at low flow rates, and the flow-dominated solution has lowest energy at high flow rates. NSF DMS 1211713.

A visual investigation of turbulence in stagnation flow about a circular cylinder

NASA Technical Reports Server (NTRS)

Sadeh, W. Z.; Brauer, H. J.

1978-01-01

A visual investigation of turbulence in stagnation flow around a circular cylinder was carried out in order to gain a physical insight into the model advocated by the corticity-amplification theory. Motion pictures were taken from three different viewpoints, and a frame by frame examination of selected movie strips was conducted. Qualitative and quantitative analyses of the flow events focused on tracing the temporal and spatial evolution of a cross-vortex tube outlined by the entrained smoke filaments. The visualization supplied evidence verifying: (1) the selective stretching of cross-vortex tubes which is responsible for the amplification of cross vorticity and, hence, of streamwise turbulence; (2) the streamwise tilting of stretched cross-vortex tubes; (3) the existence of a coherent array of vortices near the stagnation zone; (4) the interaction of the amplified vorticity with the body laminar boundary layer; and, (5) the growth of a turbulent boundary layer.

Fluid-Structure Interaction Effects on Mass Flow Rates in Solid Rocket Motors

DTIC Science & Technology

2015-09-02

FEA ) is explored. A propellant flap in a cross flow is analyzed. Comparisons are made between an analytical solution, a solely CFD solution, a manual...finite element analysis ( FEA ) is explored.  A  propellant flap in a cross flow is analyzed.  Comparisons are made between an analytical  solution, a...Condition Zones ..................................................................... 11  Figure 6: Pressure Boundary Condition Applied to  FEA  model

Prediction of vortex shedding from circular and noncircular bodies in subsonic flow

NASA Technical Reports Server (NTRS)

Mendenhall, Michael R.; Lesieutre, Daniel J.

1987-01-01

An engineering prediction method and associated computer code VTXCLD are presented which predict nose vortex shedding from circular and noncircular bodies in subsonic flow at angles of attack and roll. The axisymmetric body is represented by point sources and doublets, and noncircular cross sections are transformed to a circle by either analytical or numerical conformal transformations. The leeward vortices are modeled by discrete vortices in crossflow planes along the body; thus, the three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted surface pressure distributions, flowfield surveys, and aerodynamic characteristics are presented for bodies with circular and noncircular cross sectional shapes.

Regional stochastic generation of streamflows using an ARIMA (1,0,1) process and disaggregation

USGS Publications Warehouse

Armbruster, Jeffrey T.

1979-01-01

An ARIMA (1,0,1) model was calibrated and used to generate long annual flow sequences at three sites in the Juniata River basin, Pennsylvania. The model preserves the mean, variance, and cross correlations of the observed station data. In addition, it has a desirable blend of both high and low frequency characteristics and therefore is capable of preserving the Hurst coefficient, h. The generated annual flows are disaggregated into monthly sequences using a modification of the Valencia-Schaake model. The low-flow frequency and flow duration characteristics of the generated monthly flows, with length equal to the historical data, compare favorably with the historical data. Once the models were verified, 100-year sequences were generated and analyzed for their low flow characteristics. One-, three- and six- month low-flow frequencies at recurrence intervals greater than 10 years are generally found to be lower than flow computed from the historical flows. A method is proposed for synthesizing flows at ungaged sites. (Kosco-USGS)

Hydroacoustic forcing function modeling using DNS database

NASA Technical Reports Server (NTRS)

Zawadzki, I.; Gershfield, J. L.; Na, Y.; Wang, M.

1996-01-01

A wall pressure frequency spectrum model (Blake 1971 ) has been evaluated using databases from Direct Numerical Simulations (DNS) of a turbulent boundary layer (Na & Moin 1996). Good agreement is found for moderate to strong adverse pressure gradient flows in the absence of separation. In the separated flow region, the model underpredicts the directly calculated spectra by an order of magnitude. The discrepancy is attributed to the violation of the model assumptions in that part of the flow domain. DNS computed coherence length scales and the normalized wall pressure cross-spectra are compared with experimental data. The DNS results are consistent with experimental observations.

Flow impedance in a uniform magnetically insulated transmission line

NASA Astrophysics Data System (ADS)

Mendel, C. W.; Seidel, D. B.

1999-12-01

In two recent publications [C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 2, 1332 (1995), C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 3, 4207 (1996)] relativistic electron flow in cylindrical magnetically insulated transmission lines was analyzed and modeled under the assumption of negligible electron pressure. The model allows power flow in these lines to be accurately calculated under most conditions. The model was developed for coaxial right circular cylindrical electrodes. It is shown here that the model applies equally well to arbitrary cylindrical systems, i.e., systems consisting of electrodes of arbitrary cross section.

Vertical gas injection into liquid cross-stream beneath horizontal surfaces

NASA Astrophysics Data System (ADS)

Lee, In-Ho; Makiharju, Simo; Lee, Inwon; Perlin, Marc; Ceccio, Steve

2013-11-01

Skin friction drag reduction on flat bottomed ships and barges can be achieved by creating an air layer immediately beneath the horizontal surface. The simplest way of introducing the gas is through circular orifices; however the dynamics of gas injection into liquid cross-streams under horizontal surfaces is not well understood. Experiments were conducted to investigate the development of the gas topology following its vertical injection through a horizontal surface. The liquid cross-flow, orifice diameter and gas flow rate were varied to investigate the effect of different ratios of momentum fluxes. The testing was performed on a 4.3 m long and 0.73 m wide barge model with air injection through a hole in the transparent bottom hull. The incoming boundary layer was measured via a pitot tube. Downstream distance based Reynolds number at the injection location was 5 × 105 through 4 × 106 . To observe the flow topology, still images and video were recorded from above the model (i.e. through the transparent hull), from beneath the bottom facing upward, and from the side at an oblique angle. The transition point of the flow topology was determined and analyzed.

A flow-simulation model of the tidal Potomac River

USGS Publications Warehouse

Schaffranek, Raymond W.

1987-01-01

A one-dimensional model capable of simulating flow in a network of interconnected channels has been applied to the tidal Potomac River including its major tributaries and embayments between Washington, D.C., and Indian Head, Md. The model can be used to compute water-surface elevations and flow discharges at any of 66 predetermined locations or at any alternative river cross sections definable within the network of channels. In addition, the model can be used to provide tidal-interchange flow volumes and to evaluate tidal excursions and the flushing properties of the riverine system. Comparisons of model-computed results with measured watersurface elevations and discharges demonstrate the validity and accuracy of the model. Tidal-cycle flow volumes computed by the calibrated model have been verified to be within an accuracy of ? 10 percent. Quantitative characteristics of the hydrodynamics of the tidal river are identified and discussed. The comprehensive flow data provided by the model can be used to better understand the geochemical, biological, and other processes affecting the river's water quality.

Aerodynamics of high aspect-ratio sails

NASA Astrophysics Data System (ADS)

Crook, Andrew; Gerritsen, Margot

2003-11-01

Experiments studying the aerodynamics of a 25circular-arc sail section (representative of an AC gennaker cross-section) have been undertaken in the 7x10 ft tunnels at NASA-Ames and Georgia Tech. The aims of the study are to gain a deeper physical understanding of the flow past downwind sails at various angles of incidence and Reynolds numbers, and to create a comprehensive database for validation of numerical models and turbulence models used by the yacht research community and competitive sailing industry. The reason for testing a rectangular planform sail with no spanwise variation in twist or cross-section is to first provide a detailed understanding of the flow topology around generic sail sections. Currently, data of sufficient accuracy to be used for CFD validation are not available. 3D experiments with realistic sail planforms and twisted onset flow are planned for the future. Two models have been tested, one with an AR of 15 and constructed from steel and the other with an AR of 10 and constructed from carbon-fiber and foam. The latter model has pressure tappings, whilst the former was coated with PSP. Pressure distributions, surface flow visualization and PIV reveal the details of the changing flow patterns and separation types with varying angle of incidence.

Film flow and heat transfer during condensation of steam on inclined and vertical nonround tubes

NASA Astrophysics Data System (ADS)

Nikitin, N. N.; Semenov, V. P.

2008-03-01

We describe a mathematical model for calculating heat transfer during film condensation of stagnant steam on inclined and vertical smooth tubes with cross sections of arbitrary shape that takes into account the action of surface tension forces. The heat-transfer coefficients are calculated, and the hydrodynamic pattern is presented in which a condensate film flows over the surface of nonround inclined and vertical tubes with cross-section of different shapes.

Cooling Panel Optimization for the Active Cooling System of a Hypersonic Aircraft

NASA Technical Reports Server (NTRS)

Youn, B.; Mills, A. F.

1995-01-01

Optimization of cooling panels for an active cooling system of a hypersonic aircraft is explored. The flow passages are of rectangular cross section with one wall heated. An analytical fin-type model for incompressible flow in smooth-wall rectangular ducts with coupled wall conduction is proposed. Based on this model, the a flow rate of coolant to each design minimum mass flow rate or coolant for a single cooling panel is obtained by satisfying hydrodynamic, thermal, and Mach number constraints. Also, the sensitivity of the optimal mass flow rate of coolant to each design variable is investigated. In addition, numerical solutions for constant property flow in rectangular ducts, with one side rib-roughened and coupled wall conduction, are obtained using a k-epsilon and wall function turbulence model, these results are compared with predictions of the analytical model.

Relative significance of microtopography and vegetation as controls on surface water flow on a low-gradient floodplain

USGS Publications Warehouse

Choi, Jungyill; Harvey, Judson W.

2014-01-01

Surface water flow controls water velocities, water depths, and residence times, and influences sediment and nutrient transport and other ecological processes in shallow aquatic systems. Flow through wetlands is substantially influenced by drag on vegetation stems but is also affected by microtopography. Our goal was to use microtopography data directly in a widely used wetland model while retaining the advantages of the model’s one-dimensional structure. The base simulation with no explicit treatment of microtopography only performed well for a period of high water when vegetation dominated flow resistance. Extended simulations using microtopography can improve the fit to low-water conditions substantially. The best fit simulation had a flow conductance parameter that decreased in value by 70 % during dry season such that mcrotopographic features blocked 40 % of the cross sectional width for flow. Modeled surface water became ponded and flow ceased when 85 % of the cross sectional width became blocked by microtopographic features. We conclude that vegetation drag dominates wetland flow resistance at higher water levels and microtopography dominates at low water levels with the threshold delineated by the top of microtopographic features. Our results support the practicality of predicting flow on floodplains using relatively easily measured physical and biological variables.

Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow.

PubMed

Song, Hongjun; Wang, Yi; Pant, Kapil

2013-01-01

This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space.

Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow

PubMed Central

Song, Hongjun; Wang, Yi; Pant, Kapil

2012-01-01

This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space. PMID:23554584

Analysis of an entrainment model of the jet in a crossflow

NASA Technical Reports Server (NTRS)

Chang, H. S.; Werner, J. E.

1972-01-01

A theoretical model has been proposed for the problem of a round jet in an incompressible cross-flow. The method of matched asymptotic expansions has been applied to this problem. For the solution to the flow problem in the inner region, the re-entrant wake flow model was used with the re-entrant flow representing the fluid entrained by the jet. Higher order corrections are obtained in terms of this basic solution. The perturbation terms in the outer region was found to be a line distribution of doublets and sources. The line distribution of sources represents the combined effect of the entrainment and the displacement.

Cross-stream diffusion under pressure-driven flow in microchannels with arbitrary aspect ratios: a phase diagram study using a three-dimensional analytical model

PubMed Central

Song, Hongjun; Wang, Yi; Pant, Kapil

2011-01-01

This article presents a three-dimensional analytical model to investigate cross-stream diffusion transport in rectangular microchannels with arbitrary aspect ratios under pressure-driven flow. The Fourier series solution to the three-dimensional convection–diffusion equation is obtained using a double integral transformation method and associated eigensystem calculation. A phase diagram derived from the dimensional analysis is presented to thoroughly interrogate the characteristics in various transport regimes and examine the validity of the model. The analytical model is verified against both experimental and numerical models in terms of the concentration profile, diffusion scaling law, and mixing efficiency with excellent agreement (with <0.5% relative error). Quantitative comparison against other prior analytical models in extensive parameter space is also performed, which demonstrates that the present model accommodates much broader transport regimes with significantly enhanced applicability. PMID:22247719

Cross-stream diffusion under pressure-driven flow in microchannels with arbitrary aspect ratios: a phase diagram study using a three-dimensional analytical model.

PubMed

Song, Hongjun; Wang, Yi; Pant, Kapil

2012-01-01

This article presents a three-dimensional analytical model to investigate cross-stream diffusion transport in rectangular microchannels with arbitrary aspect ratios under pressure-driven flow. The Fourier series solution to the three-dimensional convection-diffusion equation is obtained using a double integral transformation method and associated eigensystem calculation. A phase diagram derived from the dimensional analysis is presented to thoroughly interrogate the characteristics in various transport regimes and examine the validity of the model. The analytical model is verified against both experimental and numerical models in terms of the concentration profile, diffusion scaling law, and mixing efficiency with excellent agreement (with <0.5% relative error). Quantitative comparison against other prior analytical models in extensive parameter space is also performed, which demonstrates that the present model accommodates much broader transport regimes with significantly enhanced applicability.

Simulating wind and marine hydrokinetic turbines with actuator lines in RANS and LES

NASA Astrophysics Data System (ADS)

Bachant, Peter; Wosnik, Martin

2015-11-01

As wind and marine hydrokinetic (MHK) turbine designs mature, focus is shifting towards improving turbine array layouts for maximizing overall power output, i.e., minimizing wake interference for axial-flow or horizontal-axis turbines, or taking advantage of constructive wake interaction for cross-flow or vertical-axis turbines. Towards this goal, an actuator line model (ALM) was developed to provide a computationally feasible method for simulating full turbine arrays inside Navier-Stokes models. The ALM predicts turbine loading with the blade element method combined with sub-models for dynamic stall and flow curvature. The open-source software is written as an extension library for the OpenFOAM CFD package, which allows the ALM body force to be applied to their standard RANS and LES solvers. Turbine forcing is also applied to volume of fluid (VOF) models, e.g., for predicting free surface effects on submerged MHK devices. An additional sub-model is considered for injecting turbulence model scalar quantities based on actuator line element loading. Results are presented for the simulation of performance and wake dynamics of axial- and cross-flow turbines and compared with moderate Reynolds number experiments and body-fitted mesh, blade-resolving CFD. Work supported by NSF-CBET grant 1150797.

Effect of centrifugal forces on formation of secondary flow structures in a 180-degree curved artery model under pulsatile inflow conditions

NASA Astrophysics Data System (ADS)

Callahan, Shannon; Sajjad, Roshan; Bulusu, Kartik V.; Plesniak, Michael W.

2013-11-01

An experimental investigation of secondary flow structures within a 180-degree bent tube model of a curved artery was performed using phase-averaged, two-component, two-dimensional, particle image velocimetry (2C-2D PIV) under pulsatile inflow conditions. Pulsatile waveforms ranging from simple sinusoidal to physiological inflows were supplied. We developed a novel continuous wavelet transform algorithm (PIVlet 1.2) and applied it to vorticity fields for coherent secondary flow structure detection. Regime maps of secondary flow structures revealed new, deceleration-phase-dependent flow morphologies. The temporal instances where streamwise centrifugal forces dominated were associated with large-scale coherent structures, such as deformed Dean-, Lyne- and Wall-type (D-L-W) vortical structures. Magnitudes of streamwise and cross-stream centrifugal forces tend to balance during deceleration phases. Deceleration events were also associated with spatial reorganization and asymmetry in large-scale D-L-W secondary flow structures. Hence, the interaction between streamwise and cross-stream centrifugal forces that affects secondary flow morphologies is explained using a ``residual force'' parameter i.e., the difference in magnitudes of these forces. Supported by the NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.

Bridge-scour analysis using the water surface profile (WSPRO) model

USGS Publications Warehouse

Mueller, David S.; ,

1993-01-01

A program was developed to extract hydraulic information required for bridge-scour computations, from the Water-Surface Profile computation model (WSPRO). The program is written in compiled BASIC and is menu driven. Using only ground points, the program can compute average ground elevation, cross-sectional area below a specified datum, or create a Drawing Exchange Format (DXF) fie of cross section. Using both ground points ad hydraulic information form the equal-conveyance tubes computed by WSPRO, the program can compute hydraulic parameters at a user-specified station or in a user-specified subsection of the cross section. The program can identify the maximum velocity in a cross section and the velocity and depth at a user-specified station. The program also can identify the maximum velocity in the cross section and the average velocity, average depth, average ground elevation, width perpendicular to the flow, cross-sectional area of flow, and discharge in a subsection of the cross section. This program does not include any help or suggestions as to what data should be extracted; therefore, the used must understand the scour equations and associated variables to the able to extract the proper information from the WSPRO output.

Thermal response test data of five quadratic cross section precast pile heat exchangers.

PubMed

Alberdi-Pagola, Maria

2018-06-01

This data article comprises records from five Thermal Response Tests (TRT) of quadratic cross section pile heat exchangers. Pile heat exchangers, typically referred to as energy piles, consist of traditional foundation piles with embedded heat exchanger pipes. The data presented in this article are related to the research article entitled "Comparing heat flow models for interpretation of precast quadratic pile heat exchanger thermal response tests" (Alberdi-Pagola et al., 2018) [1]. The TRT data consists of measured inlet and outlet temperatures, fluid flow and injected heat rate recorded every 10 min. The field dataset is made available to enable model verification studies.

Cross-borehole slug test analysis in a fractured limestone aquifer

NASA Astrophysics Data System (ADS)

Audouin, Olivier; Bodin, Jacques

2008-01-01

SummaryThis work proposes new semi-analytical solutions for the interpretation of cross-borehole slug tests in fractured media. Our model is an extension of a previous work by Barker [Barker, J.A., 1988. A generalized radial flow model for hydraulic tests in fractured rock. Water Resources Research 24 (10), 1796-1804; Butler Jr., J.J., Zhan X., 2004. Hydraulic tests in highly permeable aquifers. Water Resources Research 40, W12402. doi:10.1029/2003/WR002998]. It includes inertial effects at both test and observation wells and a fractional flow dimension in the aquifer. The model has five fitting parameters: flow dimension n, hydraulic conductivity K, specific storage coefficient Ss, and effective lengths of test well Le and of observation well Leo. The results of a sensitivity analysis show that the most sensitive parameter is the flow dimension n. The model sensitivity to other parameters may be ranked as follows: K > Le ˜ Leo > Ss. The sensitivity to aquifer storage remains one or two orders of magnitude lower than that to other parameters. The model has been coupled to an automatic inversion algorithm for facilitating the interpretation of real field data. This inversion algorithm is based on a Gauss-Newton optimization procedure conditioned by re-scaled sensitivities. It has been used to interpret successfully cross-borehole slug test data from the Hydrogeological Experimental Site (HES) of Poitiers, France, consisting of fractured and karstic limestones. HES data provide flow dimension values ranging between 1.6 and 2.5, and hydraulic conductivity values ranging between 4.4 × 10 -5 and 7.7 × 10 -4 m s -1. These values are consistent with previous interpretations of single-well slug tests. The results of the sensitivity analysis are confirmed by calculations of relative errors on parameter estimates, which show that accuracy on n and K is below 20% and that on Ss is about one order of magnitude. The K-values interpreted from cross-borehole slug tests are one order of magnitude higher than those previously interpreted from interference pumping tests. These findings suggest that cross-borehole slug tests focus on preferential flowpath networks made by fractures and karstic channels, i.e. the head perturbation induced by a slug test propagates only through those flowpaths with the lowest hydraulic resistance. As a result, cross-borehole slug tests are expected to identify the hydrodynamic properties of karstic-channels and fracture flowpaths, and may be considered as complementary to pumping tests which more likely provide bulk properties of the whole fracture/karstic-channel/matrix system.

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

Gao, Zhiming; Abdelaziz, Omar; Qu, Ming

This paper introduces a first-order physics-based model that accounts for the fundamental heat and mass transfer between a humid-air vapor stream on feed side to another flow stream on permeate side. The model comprises a few optional submodels for membrane mass transport; and it adopts a segment-by-segment method for discretizing heat and mass transfer governing equations for flow streams on feed and permeate sides. The model is able to simulate both dehumidifiers and energy recovery ventilators in parallel-flow, cross-flow, and counter-flow configurations. The predicted tresults are compared reasonably well with the measurements. The open-source codes are written in C++. Themore » model and open-source codes are expected to become a fundament tool for the analysis of membrane-based dehumidification in the future.« less

Particle bed reactor modeling

NASA Technical Reports Server (NTRS)

Sapyta, Joe; Reid, Hank; Walton, Lew

1993-01-01

The topics are presented in viewgraph form and include the following: particle bed reactor (PBR) core cross section; PBR bleed cycle; fuel and moderator flow paths; PBR modeling requirements; characteristics of PBR and nuclear thermal propulsion (NTP) modeling; challenges for PBR and NTP modeling; thermal hydraulic computer codes; capabilities for PBR/reactor application; thermal/hydralic codes; limitations; physical correlations; comparison of predicted friction factor and experimental data; frit pressure drop testing; cold frit mask factor; decay heat flow rate; startup transient simulation; and philosophy of systems modeling.

Experiment measurement of Alford's force in axial-flow turbomachinery

NASA Technical Reports Server (NTRS)

Vance, J. M.; Laudadio, F. J.

1982-01-01

Results of experimental measurements made on a small high speed, axial flow test apparatus are presented to verify the existence of Alford's force (that circumferential variation of blade-tip clearances in axial-flow turbomachinery will produce cross-coupled (normal to the eccentricity) aerodynamic forces on the rotor) and to investigate the validity of his mathematical prediction model.

Calibration of the 7—Equation Transition Model for High Reynolds Flows at Low Mach

NASA Astrophysics Data System (ADS)

Colonia, S.; Leble, V.; Steijl, R.; Barakos, G.

2016-09-01

The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients that need tuning. In this paper, the γ—equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications. An aerofoil is used to evaluate the original model and calibrate it; while a large scale wind turbine blade is employed to show that the calibrated model can lead to reliable solutions for complex three-dimensional flows. The calibrated model shows promising results for both two-dimensional and three-dimensional flows, even if cross-flow instabilities are neglected.

Modelling gas dynamics in 1D ducts with abrupt area change

NASA Astrophysics Data System (ADS)

Menina, R.; Saurel, R.; Zereg, M.; Houas, L.

2011-09-01

Most gas dynamic computations in industrial ducts are done in one dimension with cross-section-averaged Euler equations. This poses a fundamental difficulty as soon as geometrical discontinuities are present. The momentum equation contains a non-conservative term involving a surface pressure integral, responsible for momentum loss. Definition of this integral is very difficult from a mathematical standpoint as the flow may contain other discontinuities (shocks, contact discontinuities). From a physical standpoint, geometrical discontinuities induce multidimensional vortices that modify the surface pressure integral. In the present paper, an improved 1D flow model is proposed. An extra energy (or entropy) equation is added to the Euler equations expressing the energy and turbulent pressure stored in the vortices generated by the abrupt area variation. The turbulent energy created by the flow-area change interaction is determined by a specific estimate of the surface pressure integral. Model's predictions are compared with 2D-averaged results from numerical solution of the Euler equations. Comparison with shock tube experiments is also presented. The new 1D-averaged model improves the conventional cross-section-averaged Euler equations and is able to reproduce the main flow features.

An efficient numerical model for multicomponent compressible flow in fractured porous media

NASA Astrophysics Data System (ADS)

Zidane, Ali; Firoozabadi, Abbas

2014-12-01

An efficient and accurate numerical model for multicomponent compressible single-phase flow in fractured media is presented. The discrete-fracture approach is used to model the fractures where the fracture entities are described explicitly in the computational domain. We use the concept of cross flow equilibrium in the fractures. This will allow large matrix elements in the neighborhood of the fractures and considerable speed up of the algorithm. We use an implicit finite volume (FV) scheme to solve the species mass balance equation in the fractures. This step avoids the use of Courant-Freidricks-Levy (CFL) condition and contributes to significant speed up of the code. The hybrid mixed finite element method (MFE) is used to solve for the velocity in both the matrix and the fractures coupled with the discontinuous Galerkin (DG) method to solve the species transport equations in the matrix. Four numerical examples are presented to demonstrate the robustness and efficiency of the proposed model. We show that the combination of the fracture cross-flow equilibrium and the implicit composition calculation in the fractures increase the computational speed 20-130 times in 2D. In 3D, one may expect even a higher computational efficiency.

Smoothed particle hydrodynamic modeling of volcanic debris flows: Application to Huiloac Gorge lahars (Popocatépetl volcano, Mexico)

NASA Astrophysics Data System (ADS)

Haddad, Bouchra; Palacios, David; Pastor, Manuel; Zamorano, José Juan

2016-09-01

Lahars are among the most catastrophic volcanic processes, and the ability to model them is central to mitigating their effects. Several lahars recently generated by the Popocatépetl volcano (Mexico) moved downstream through the Huiloac Gorge towards the village of Santiago Xalitzintla. The most dangerous was the 2001 lahar, in which the destructive power of the debris flow was maintained throughout the extent of the flow. Identifying the zone of hazard can be based either on numerical or empirical models, but a calibration and validation process is required to ensure hazard map quality. The Geoflow-SPH depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity-pressure version of the Biot-Zienkiewicz model, and was discretized using the smoothed particle hydrodynamics (SPH) method. The results of the calibrated SPH model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel. Moreover, the dependency of the results on topographic mesh resolution, initial lahar mass shape and dimensions is also investigated. The results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution, and an initial lahar mass shape that adopted the source area morphology. Field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths, the error being less than 20% for 11 of the 16 cross sections. This study demonstrates that the Geoflow-SPH model was able to accurately reproduce the lahar path and the extent of the flow, but also reproduced other parameters including flow velocity and deposit depth.

Interpreting the cross-sectional flow field in a river bank based on a genetic-algorithm two-dimensional heat-transport method (GA-VS2DH)

NASA Astrophysics Data System (ADS)

Su, Xiaoru; Shu, Longcang; Chen, Xunhong; Lu, Chengpeng; Wen, Zhonghui

2016-12-01

Interactions between surface waters and groundwater are of great significance for evaluating water resources and protecting ecosystem health. Heat as a tracer method is widely used in determination of the interactive exchange with high precision, low cost and great convenience. The flow in a river-bank cross-section occurs in vertical and lateral directions. In order to depict the flow path and its spatial distribution in bank areas, a genetic algorithm (GA) two-dimensional (2-D) heat-transport nested-loop method for variably saturated sediments, GA-VS2DH, was developed based on Microsoft Visual Basic 6.0. VS2DH was applied to model a 2-D bank-water flow field and GA was used to calibrate the model automatically by minimizing the difference between observed and simulated temperatures in bank areas. A hypothetical model was developed to assess the reliability of GA-VS2DH in inverse modeling in a river-bank system. Some benchmark tests were conducted to recognize the capability of GA-VS2DH. The results indicated that the simulated seepage velocity and parameters associated with GA-VS2DH were acceptable and reliable. Then GA-VS2DH was applied to two field sites in China with different sedimentary materials, to verify the reliability of the method. GA-VS2DH could be applied in interpreting the cross-sectional 2-D water flow field. The estimates of horizontal hydraulic conductivity at the Dawen River and Qinhuai River sites are 1.317 and 0.015 m/day, which correspond to sand and clay sediment in the two sites, respectively.

Modeling the evolution of channel shape: Balancing computational efficiency with hydraulic fidelity

USGS Publications Warehouse

Wobus, C.W.; Kean, J.W.; Tucker, G.E.; Anderson, R. Scott

2008-01-01

The cross-sectional shape of a natural river channel controls the capacity of the system to carry water off a landscape, to convey sediment derived from hillslopes, and to erode its bed and banks. Numerical models that describe the response of a landscape to changes in climate or tectonics therefore require formulations that can accommodate evolution of channel cross-sectional geometry. However, fully two-dimensional (2-D) flow models are too computationally expensive to implement in large-scale landscape evolution models, while available simple empirical relationships between width and discharge do not adequately capture the dynamics of channel adjustment. We have developed a simplified 2-D numerical model of channel evolution in a cohesive, detachment-limited substrate subject to steady, unidirectional flow. Erosion is assumed to be proportional to boundary shear stress, which is calculated using an approximation of the flow field in which log-velocity profiles are assumed to apply along vectors that are perpendicular to the local channel bed. Model predictions of the velocity structure, peak boundary shear stress, and equilibrium channel shape compare well with predictions of a more sophisticated but more computationally demanding ray-isovel model. For example, the mean velocities computed by the two models are consistent to within ???3%, and the predicted peak shear stress is consistent to within ???7%. Furthermore, the shear stress distributions predicted by our model compare favorably with available laboratory measurements for prescribed channel shapes. A modification to our simplified code in which the flow includes a high-velocity core allows the model to be extended to estimate shear stress distributions in channels with large width-to-depth ratios. Our model is efficient enough to incorporate into large-scale landscape evolution codes and can be used to examine how channels adjust both cross-sectional shape and slope in response to tectonic and climatic forcing. Copyright 2008 by the American Geophysical Union.

The effect of topography on pyroclastic flow mobility

NASA Astrophysics Data System (ADS)

Ogburn, S. E.; Calder, E. S.

2010-12-01

Pyroclastic flows are among the most destructive volcanic phenomena. Hazard mitigation depends upon accurate forecasting of possible flow paths, often using computational models. Two main metrics have been proposed to describe the mobility of pyroclastic flows. The Heim coefficient, height-dropped/run-out (H/L), exhibits an inverse relationship with flow volume. This coefficient corresponds to the coefficient of friction and informs computational models that use Coulomb friction laws. Another mobility measure states that with constant shear stress, planimetric area is proportional to the flow volume raised to the 2/3 power (A∝V^(2/3)). This relationship is incorporated in models using constant shear stress instead of constant friction, and used directly by some empirical models. Pyroclastic flows from Soufriere Hills Volcano, Montserrat; Unzen, Japan; Colima, Mexico; and Augustine, Alaska are well described by these metrics. However, flows in specific valleys exhibit differences in mobility. This study investigates the effect of topography on pyroclastic flow mobility, as measured by the above mentioned mobility metrics. Valley width, depth, and cross-sectional area all influence flow mobility. Investigating the appropriateness of these mobility measures, as well as the computational models they inform, indicates certain circumstances under which each model performs optimally. Knowing which conditions call for which models allows for better model selection or model weighting, and therefore, more realistic hazard predictions.

The development of an erosive burning model for solid rocket motors using direct numerical simulation

NASA Astrophysics Data System (ADS)

McDonald, Brian A.

A method for developing an erosive burning model for use in solid propellant design-and-analysis interior ballistics codes is described and evaluated. Using Direct Numerical Simulation, the primary mechanisms controlling erosive burning (turbulent heat transfer, and finite rate reactions) have been studied independently through the development of models using finite rate chemistry, and infinite rate chemistry. Both approaches are calibrated to strand burn rate data by modeling the propellant burning in an environment with no cross-flow, and adjusting thermophysical properties until the predicted regression rate matches test data. Subsequent runs are conducted where the cross-flow is increased from M = 0.0 up to M = 0.8. The resulting relationship of burn rate increase versus Mach Number is used in an interior ballistics analysis to compute the chamber pressure of an existing solid rocket motor. The resulting predictions are compared to static test data. Both the infinite rate model and the finite rate model show good agreement when compared to test data. The propellant considered is an AP/HTPB with an average AP particle size of 37 microns. The finite rate model shows that as the cross-flow increases, near wall vorticity increases due to the lifting of the boundary caused by the side injection of gases from the burning propellant surface. The point of maximum vorticity corresponds to the outer edge of the APd-binder flame. As the cross-flow increases, the APd-binder flame thickness becomes thinner; however, the point of highest reaction rate moves only slightly closer to the propellant surface. As such, the net increase of heat transfer to the propellant surface due to finite rate chemistry affects is small. This leads to the conclusion that augmentation of thermal transport properties and the resulting heat transfer increase due to turbulence dominates over combustion chemistry in the erosive burning problem. This conclusion is advantageous in the development of future models that can be calibrated to heat transfer conditions without the necessity for finite rate chemistry. These results are considered applicable for propellants with small, evenly distributed AP particles where the assumption of premixed APd-binder gases is reasonable.

Semi-analytical model of cross-borehole flow experiments for fractured medium characterization

NASA Astrophysics Data System (ADS)

Roubinet, D.; Irving, J.; Day-Lewis, F. D.

2014-12-01

The study of fractured rocks is extremely important in a wide variety of research fields where the fractures and faults can represent either rapid access to some resource of interest or potential pathways for the migration of contaminants in the subsurface. Identification of their presence and determination of their properties are critical and challenging tasks that have led to numerous fracture characterization methods. Among these methods, cross-borehole flowmeter analysis aims to evaluate fracture connections and hydraulic properties from vertical-flow-velocity measurements conducted in one or more observation boreholes under forced hydraulic conditions. Previous studies have demonstrated that analysis of these data can provide important information on fracture connectivity, transmissivity, and storativity. Estimating these properties requires the development of analytical and/or numerical modeling tools that are well adapted to the complexity of the problem. Quantitative analysis of cross-borehole flowmeter experiments, in particular, requires modeling formulations that: (i) can be adapted to a variety of fracture and experimental configurations; (ii) can take into account interactions between the boreholes because their radii of influence may overlap; and (iii) can be readily cast into an inversion framework that allows for not only the estimation of fracture hydraulic properties, but also an assessment of estimation error. To this end, we present a new semi-analytical formulation for cross-borehole flow in fractured media that links transient vertical-flow velocities measured in one or a series of observation wells during hydraulic forcing to the transmissivity and storativity of the fractures intersected by these wells. Our model addresses the above needs and provides a flexible and computationally efficient semi-analytical framework having strong potential for future adaptation to more complex configurations. The proposed modeling approach is demonstrated in the context of sensitivity analysis for a relatively simple two-fracture synthetic problem, as well as in the context of field-data analysis for fracture connectivity and estimation of corresponding hydraulic properties.

Modeling of Fuel Film Cooling on Chamber Hot Wall

DTIC Science & Technology

2013-12-01

flow at supercritical pressure. The fuel jet and the cross-flow interact. Some part of the jet is stripped off and entrained by the hot gas...modelers. The supercritical pressure makes information on equation of state and transport properties hard to come by. The large temperature range...the modeling of hydrocarbon fuel film cooling at supercritical pressures. A relevant recent simulation study by Yang and Sun [1] used a finite-rate

Rotor Aerodynamics in Ground Effect at Low Advance Ratios.

DTIC Science & Technology

1982-07-27

the rotor wake flows entirely downstream. At test conditions were the recirculating flow or ground vortex is present there are marked departures...ILLUSTRATIONS Figure Page 1 Cross Section of Test Facilty 12 2 Overall View of Test Facility and Rotor Model 13 3 Flow Pattern in Ground Vortex Regime, (v...entirely flowing downstream splits and a portion of the rotor wake flows forward (upstream) and then recirculates through the rotor or forms a vortex or

Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA

USGS Publications Warehouse

Oki, D.S.; Souza, W.R.; Bolke, E.L.; Bauer, G.R.

1998-01-01

The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Ground-water flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units.

Cross-formational flow of water into coalbed methane reservoirs: controls on relative permeability curve shape and production profile

PubMed Central

Karacan, C. Özgen

2017-01-01

Coalbed methane (CBM) wells tend to produce large volumes of water, especially when there is hydraulic connectivity between coalbed and nearby formations. Cross-formational flow between producing coal and adjacent formations can have significant production and environmental implications, affecting economic viability of production from these shallow reservoirs. Such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well. The aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis. A reservoir model is constructed to investigate the production performance of a CBM well when cross-formational flow is present between the coalbed and the overlying formation. Results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity. Due to hydraulic connectivity, water saturation within coalbed does not considerably change for a period of time, and hence, the peak of gas production is delayed. Upon depletion of the overlying formation, water saturation in coalbed quickly decreases. Rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production. As an important consequence, when cross-flow is present, gas and water relative permeability curves, derived from simulated production data, have distinctive features compared to the initial relative permeability curves. In the case of cross-flow, signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation, followed by rapid increase afterward for water and gas, respectively. The results and analyses presented in this work can help to assess the impact of cross-formational flow on reservoir variables derived from production data analysis and can also contribute to identifying hydraulic connectivity between coalbed and adjacent formations. PMID:28626492

Experimental investigation on in-plane/out-of-plane vortex-induced vibrations of curved cylinder in parallel and perpendicular flows

NASA Astrophysics Data System (ADS)

Srinil, Narakorn; Ma, Bowen; Zhang, Licong

2018-05-01

This study is motivated by an industrial need to better understand the vortex-induced vibration (VIV) of a curved structure subject to current flows with varying directions whose data for model calibration and validation are lacking. In this paper, new experimental investigations on the two-degree-of-freedom in-plane/out-of-plane VIV of a rigid curved circular cylinder immersed in steady and uniform free-stream flows are presented. The principal objective is to examine how the approaching flow direction versus the cylinder curvature plane affects cross-flow and in-line VIV and the associated hydrodynamic properties. This is achieved by testing the curved cylinder in 3 different flow orientations comprising the parallel flows aligned with the curvature vertical plane in convex and concave configurations, and the flows perpendicular to the curvature plane. The case of varying flow velocities in a subcritical flow range with a maximum Reynolds number of about 50,000 is considered for the curved cylinder with a low mass ratio and damping ratio. Experimental results are presented and discussed in terms of the cylinder response amplitudes, inclination angles, mean displacements, motion trajectories, oscillation frequencies, hydrodynamic forces, relative phases, fluid excitation and added inertia coefficients. Comparisons with other experimental results of curved and straight cylinder VIV are also presented. The experiments highlight the important effects of cylinder curvature versus flow orientation on the combined cross-flow/in-line VIV. The maximum (minimum) responses occur in the perpendicular (convex) flow case whereas the extended lower-branch responses occur in the concave flow case. For perpendicular flows, some meaningful features are observed, including the appearances of cross-flow mean displacements and asymmetric eight-shaped motion trajectories due to multiple 2:1:1 resonances where two out-of-plane and one in-plane dominant frequencies are simultaneously excited. Overall VIV phenomena caused by the system asymmetry should be recognised in a prediction model and design codes to capture the combined effects of curved configuration and approaching flow direction.

Implicit marching solution of compressible viscous subsonic flow in planar and axisymmetric ducts. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Towne, C. E.; Hoffman, J. D.

1982-01-01

A new streamwise marching procedure was developed and coded for compressible viscous subsonic flow in planar or axisymmetric ducts with or without centerbodies. The continuity, streamwise momentum, cross-flow momentum, and energy equations are written in generalized orthogonal curvilinear coordinates. To allow the use of a marching procedure, second derivatives in the streamwise momentum equation are written as the sum of a known two dimensional imposed pressure field and an unknown one dimensional viscous correction. For turbulent flow, the Reynolds stress and heat flux terms are modeled using two-layer eddy viscosity turbulence models.

Characterization of enzymatic micromachining for construction of variable cross-section microchannel topologies

PubMed Central

Ruggles, Molly E.; Jayaraman, Arul; Ugaz, Victor M.

2016-01-01

The ability to harness enzymatic activity as an etchant to precisely machine biodegradable substrates introduces new possibilities for microfabrication. This flow-based etching is straightforward to implement, enabling patterning of microchannels with topologies that incorporate variable depth along the cross-sectional dimension. Additionally, unlike conventional small-molecule formulations, the macromolecular nature of enzymatic etchants enables features to be precisely positioned. Here, we introduce a kinetic model to characterize the enzymatic machining process and its localization by co-injection of a macromolecular inhibitor species. Our model captures the interaction between enzyme, inhibitor, and substrate under laminar flow, enabling rational prediction of etched microchannel profiles so that cross-sectional topologies incorporating complex lateral variations in depth can be constructed. We also apply this approach to achieve simultaneous widening of an entire network of microchannels produced in the biodegradable polymeric substrate poly(lactic acid), laying a foundation to construct systems incorporating a broad range of internal cross-sectional dimensions by manipulating the process conditions. PMID:27190566

Characterization of Interactions between Surface Water and Near-Stream Groundwater along Fish Creek, Teton County, Wyoming, by Using Heat as a Tracer

USGS Publications Warehouse

Eddy-Miller, Cheryl A.; Wheeler, Jerrod D.; Essaid, Hedeff I.

2009-01-01

Fish Creek, a tributary of the Snake River, is about 25 river kilometers long and is located in Teton County in western Wyoming near the town of Wilson. Local residents began observing an increase in the growth of algae and aquatic plants in the stream during the last decade. Due to the known importance of groundwater to surface water in the area, the U.S. Geological Survey (USGS), in cooperation with the Teton Conservation District, conducted a study to characterize the interactions between surface water and near-stream groundwater along Fish Creek. The study has two main objectives: (1) develop an improved spatial and temporal understanding of water flow (fluxes) between surface water and groundwater, and (2) use a two-dimensional groundwater-flow and heat-transport model to interpret observed temperature and hydraulic-head distributions and to describe groundwater flow near Fish Creek. The study is intended to augment hydrologic information derived from previously published results of a seepage investigation on Fish Creek. Seepage measurements provide spatially averaged gains and losses over an entire reach for one point in time, whereas continuous temperature and water-level measurements provide continuous estimates of gain and loss at a specific location. Stage, water-level, and temperature data were collected from surface water and from piezometers completed in an alluvial aquifer at three cross sections on Fish Creek at Teton Village, Resor's Bridge, and Wilson from October 2004 to October 2006. The flow and energy (heat) transport model VS2DH was used to simulate flow through the streambed of Fish Creek at the Teton Village cross section from April 15 to October 14, 2006, (183 recharge periods) and at the Resor's Bridge and Wilson cross sections from June 6, 2005, to October 14, 2006 (496 recharge periods). A trial-and-error technique was used to determine the best match between simulated and measured data. These results were then used to calibrate the cross-sectional models and determine horizontal and vertical hydraulic conductivities. The fluxes of groundwater into the stream or fluxes of stream water into the alluvial aquifer were estimated by using the calibrated VS2DH model for each cross section. Results of the simulations indicated that surface water/groundwater interaction and hydraulic properties were different at the three cross sections. At the most upstream cross section, Teton Village, Fish Creek flowed intermittently and continually gained relatively large quantities of water from April through September. During other times of the year, the stream was dry near the cross section. Saturated hydraulic conductivity set at 1x10-4 m/s in both the horizontal and vertical directions resulted in the best match between simulated and measured temperatures. The Resor's Bridge cross section, about midway between the other two cross sections, was near the point where perennial flow begins. At this cross section, the stream gained water from groundwater during high flow in late spring and summer, was near equilibrium with groundwater during August and September, and lost water to groundwater during the remainder of the year. Horizontal hydraulic conductivity set at 5x10-5 m/s and vertical hydraulic conductivity set at 1x10-5 m/s resulted in the best match between simulated and measured temperatures. The Wilson cross section, the most downstream site, was at USGS streamflow-gaging station 13016450. This part of the stream is perennial and was almost always gaining a small volume of water from groundwater. Saturated hydraulic conductivity set at 1x10-4 m/s in the horizontal direction and at 5x10-6 m/s in the vertical direction resulted in the best match between simulated and measured temperatures. Quantitative values of the flux from groundwater into surface water were estimated by using VS2DH and ranged from 1.1 to 6.6 cubic meters per day (m3/d) at the Teton Village cross section, from -3.8 to 7.4 m3/d at t

Analytical modeling of circuit aerodynamics in the new NASA Lewis wind tunnel

NASA Technical Reports Server (NTRS)

Towne, C. E.; Povinelli, L. A.; Kunik, W. G.; Muramoto, K. K.; Hughes, C. E.; Levy, R.

1985-01-01

Rehabilitation and extention of the capability of the altitude wind tunnel (AWT) was analyzed. The analytical modeling program involves the use of advanced axisymmetric and three dimensional viscous analyses to compute the flow through the various AWT components. Results for the analytical modeling of the high speed leg aerodynamics are presented; these include: an evaluation of the flow quality at the entrance to the test section, an investigation of the effects of test section bleed for different model blockages, and an examination of three dimensional effects in the diffuser due to reentry flow and due to the change in cross sectional shape of the exhaust scoop.

Passive micromixers with dual helical channels

NASA Astrophysics Data System (ADS)

Liu, Keyin; Yang, Qing; Chen, Feng; Zhao, Yulong; Meng, Xiangwei; Shan, Chao; Li, Yanyang

2015-02-01

In this study, a three-dimensional (3D) micromixer with cross-linked double helical microchannels is studied to achieve rapid mixing of fluids at low Reynolds numbers (Re). The 3D micromixer takes full advantages of the chaotic advection model with helical microchannels; meanwhile, the proposed crossing structure of double helical microchannels enables two flow patterns of repelling flow and straight flow in the fluids to promote the agitation effect. The complex 3D micromixer is realized by an improved femtosecond laser wet etching (FLWE) technology embedded in fused silica. The mixing results show that cross-linked double helical microchannels can achieve excellent mixing within 3 cycles (300 μm) over a wide range of low Re (1.5×10-3~600), which compare well with the conventional passive micromixers. This highly-effective micromixer is hoped to contribute to the integration of microfluidic systems.

Microfluidic generation of aqueous two-phase system (ATPS) droplets by controlled pulsating inlet pressures.

PubMed

Moon, Byeong-Ui; Jones, Steven G; Hwang, Dae Kun; Tsai, Scott S H

2015-06-07

We present a technique that generates droplets using ultralow interfacial tension aqueous two-phase systems (ATPS). Our method combines a classical microfluidic flow focusing geometry with precisely controlled pulsating inlet pressure, to form monodisperse ATPS droplets. The dextran (DEX) disperse phase enters through the central inlet with variable on-off pressure cycles controlled by a pneumatic solenoid valve. The continuous phase polyethylene glycol (PEG) solution enters the flow focusing junction through the cross channels at a fixed flow rate. The on-off cycles of the applied pressure, combined with the fixed flow rate cross flow, make it possible for the ATPS jet to break up into droplets. We observe different droplet formation regimes with changes in the applied pressure magnitude and timing, and the continuous phase flow rate. We also develop a scaling model to predict the size of the generated droplets, and the experimental results show a good quantitative agreement with our scaling model. Additionally, we demonstrate the potential for scaling-up of the droplet production rate, with a simultaneous two-droplet generating geometry. We anticipate that this simple and precise approach to making ATPS droplets will find utility in biological applications where the all-biocompatibility of ATPS is desirable.

Finite volume solution for two-phase flow in a straight capillary

NASA Astrophysics Data System (ADS)

Yelkhovsky, Alexander; Pinczewski, W. Val

2018-04-01

The problem of two-phase flow in straight capillaries of polygonal cross section displays many of the dynamic characteristics of rapid interfacial motions associated with pore-scale displacements in porous media. Fluid inertia is known to be important in these displacements but is usually ignored in network models commonly used to predict macroscopic flow properties. This study presents a numerical model for two-phase flow which describes the spatial and temporal evolution of the interface between the fluids. The model is based on an averaged Navier-Stokes equation and is shown to be successful in predicting the complex dynamics of both capillary rise in round capillaries and imbibition along the corners of polygonal capillaries. The model can form the basis for more realistic network models which capture the effect of capillary, viscous, and inertial forces on pore-scale interfacial dynamics and consequent macroscopic flow properties.

On Theoretical Broadband Shock-Associated Noise Near-Field Cross-Spectra

NASA Technical Reports Server (NTRS)

Miller, Steven A. E.

2015-01-01

The cross-spectral acoustic analogy is used to predict auto-spectra and cross-spectra of broadband shock-associated noise in the near-field and far-field from a range of heated and unheated supersonic off-design jets. A single equivalent source model is proposed for the near-field, mid-field, and far-field terms, that contains flow-field statistics of the shock wave shear layer interactions. Flow-field statistics are modeled based upon experimental observation and computational fluid dynamics solutions. An axisymmetric assumption is used to reduce the model to a closed-form equation involving a double summation over the equivalent source at each shock wave shear layer interaction. Predictions are compared with a wide variety of measurements at numerous jet Mach numbers and temperature ratios from multiple facilities. Auto-spectral predictions of broadband shock-associated noise in the near-field and far-field capture trends observed in measurement and other prediction theories. Predictions of spatial coherence of broadband shock-associated noise accurately capture the peak coherent intensity, frequency, and spectral width.

Computational simulation of laboratory-scale volcanic jets

NASA Astrophysics Data System (ADS)

Solovitz, S.; Van Eaton, A. R.; Mastin, L. G.; Herzog, M.

2017-12-01

Volcanic eruptions produce ash clouds that may travel great distances, significantly impacting aviation and communities downwind. Atmospheric hazard forecasting relies partly on numerical models of the flow physics, which incorporate data from eruption observations and analogue laboratory tests. As numerical tools continue to increase in complexity, they must be validated to fine-tune their effectiveness. Since eruptions are relatively infrequent and challenging to observe in great detail, analogue experiments can provide important insights into expected behavior over a wide range of input conditions. Unfortunately, laboratory-scale jets cannot easily attain the high Reynolds numbers ( 109) of natural volcanic eruption columns. Comparisons between the computational models and analogue experiments can help bridge this gap. In this study, we investigate a 3-D volcanic plume model, the Active Tracer High-resolution Atmospheric Model (ATHAM), which has been used to simulate a variety of eruptions. However, it has not been previously validated using laboratory-scale data. We conducted numerical simulations of three flows that we have studied in the laboratory: a vertical jet in a quiescent environment, a vertical jet in horizontal cross flow, and a particle-laden jet. We considered Reynolds numbers from 10,000 to 50,000, jet-to-cross flow velocity ratios of 2 to 10, and particle mass loadings of up to 25% of the exit mass flow rate. Vertical jet simulations produce Gaussian velocity profiles in the near exit region by 3 diameters downstream, matching the mean experimental profiles. Simulations of air entrainment are of the correct order of magnitude, but they show decreasing entrainment with vertical distance from the vent. Cross flow simulations reproduce experimental trajectories for the jet centerline initially, although confinement appears to impact the response later. Particle-laden simulations display minimal variation in concentration profiles between cases with different mass loadings and size distributions, indicating that differences in particle behavior may not be evident at this laboratory scale.

Prediction of Bubble Diameter at Detachment from a Wall Orifice in Liquid Cross Flow Under Reduced and Normal Gravity Conditions

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Kamotani, Y.

2003-01-01

Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to theoretically investigate the effects of liquid cross-flow velocity, gas flow rate embodied in the momentum flux force, and orifice diameter on bubble formation in a wall-bubble injection configuration. A two-dimensional one-stage theoretical model based on a global force balance on the bubble evolving from a wall orifice in a cross liquid flow is presented in this work. In this model, relevant forces acting on the evolving bubble are expressed in terms of the bubble center of mass coordinates and solved simultaneously. Relevant forces in low gravity included the momentum flux, shear-lift, surface tension, drag and inertia forces. Under normal gravity conditions, the buoyancy force, which is dominant under such conditions, can be added to the force balance. Two detachment criteria were applicable depending on the gas to liquid momentum force ratio. For low ratios, the time when the bubble acceleration in the direction of the detachment angle is greater or equal to zero is calculated from the bubble x and y coordinates. This time is taken as the time at which all the detaching forces that are acting on the bubble are greater or equal to the attaching forces. For high gas to liquid momentum force ratios, the time at which the y coordinate less the bubble radius equals zero is calculated. The bubble diameter is evaluated at this time as the diameter at detachment from the fact that the bubble volume is simply given by the product of the gas flow rate and time elapsed. Comparison of the model s predictions was also made with predictions from a two-dimensional normal gravity model based on Kumar-Kuloor formulation and such a comparison is presented in this work.

Development of a hydrological model for simulation of runoff from catchments unbounded by ridge lines

NASA Astrophysics Data System (ADS)

Vema, Vamsikrishna; Sudheer, K. P.; Chaubey, I.

2017-08-01

Watershed hydrological models are effective tools for simulating the hydrological processes in the watershed. Although there are a plethora of hydrological models, none of them can be directly applied to make water conservation decisions in irregularly bounded areas that do not confirm to topographically defined ridge lines. This study proposes a novel hydrological model that can be directly applied to any catchment, with or without ridge line boundaries. The model is based on the water balance concept, and a linear function concept to approximate the cross-boundary flow from upstream areas to the administrative catchment under consideration. The developed model is tested in 2 watersheds - Riesel Experimental Watershed and a sub-basin of Cedar Creek Watershed in Texas, USA. Hypothetical administrative catchments that did not confirm to the location of ridge lines were considered for verifying the efficacy of the model for hydrologic simulations. The linear function concept used to account the cross boundary flow was based on the hypothesis that the flow coming from outside the boundary to administrative area was proportional to the flow generated in the boundary grid cell. The model performance was satisfactory with an NSE and r2 of ≥0.80 and a PBIAS of <25 in all the cases. The simulated hydrographs for the administrative catchments of the watersheds were in good agreement with the observed hydrographs, indicating a satisfactory performance of the model in the administratively bounded areas.

Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

USGS Publications Warehouse

Kumar, Nirnimesh; Voulgaris, George; Warner, John C.; Olabarrieta, Maitane

2012-01-01

Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK' 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from and . Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar/rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non-breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).

Exact Solutions for Wind-Driven Coastal Upwelling and Downwelling over Sloping Topography

NASA Astrophysics Data System (ADS)

Choboter, P.; Duke, D.; Horton, J.; Sinz, P.

2009-12-01

The dynamics of wind-driven coastal upwelling and downwelling are studied using a simplified dynamical model. Exact solutions are examined as a function of time and over a family of sloping topographies. Assumptions in the two-dimensional model include a frictionless ocean interior below the surface Ekman layer, and no alongshore dependence of the variables; however, dependence in the cross-shore and vertical directions is retained. Additionally, density and alongshore momentum are advected by the cross-shore velocity in order to maintain thermal wind. The time-dependent initial-value problem is solved with constant initial stratification and no initial alongshore flow. An alongshore pressure gradient is added to allow the cross-shore flow to be geostrophically balanced far from shore. Previously, this model has been used to study upwelling over flat-bottom and sloping topographies, but the novel feature in this work is the discovery of exact solutions for downwelling. These exact solutions are compared to numerical solutions from a primitive-equation ocean model, based on the Princeton Ocean Model, configured in a similar two-dimensional geometry. Many typical features of the evolution of density and velocity during downwelling are displayed by the analytical model.

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula

PubMed Central

Brooks, Hannah; Haines, Grant E.; Lin, M. Carly

2018-01-01

Vortical cross-step filtration in suspension-feeding fish has been reported recently as a novel mechanism, distinct from other biological and industrial filtration processes. Although crossflow passing over backward-facing steps generates vortices that can suspend, concentrate, and transport particles, the morphological factors affecting this vortical flow have not been identified previously. In our 3D-printed models of the oral cavity for ram suspension-feeding fish, the angle of the backward-facing step with respect to the model’s dorsal midline affected vortex parameters significantly, including rotational, tangential, and axial speed. These vortices were comparable to those quantified downstream of the backward-facing steps that were formed by the branchial arches of preserved American paddlefish in a recirculating flow tank. Our data indicate that vortices in cross-step filtration have the characteristics of forced vortices, as the flow of water inside the oral cavity provides the external torque required to sustain forced vortices. Additionally, we quantified a new variable for ram suspension feeding termed the fluid exit ratio. This is defined as the ratio of the total open pore area for water leaving the oral cavity via spaces between branchial arches that are not blocked by gill rakers, divided by the total area for water entering through the gape during ram suspension feeding. Our experiments demonstrated that the fluid exit ratio in preserved paddlefish was a significant predictor of the flow speeds that were quantified anterior of the rostrum, at the gape, directly dorsal of the first ceratobranchial, and in the forced vortex generated by the first ceratobranchial. Physical modeling of vortical cross-step filtration offers future opportunities to explore the complex interactions between structural features of the oral cavity, vortex parameters, motile particle behavior, and particle morphology that determine the suspension, concentration, and transport of particles within the oral cavity of ram suspension-feeding fish. PMID:29561890

On the stability of von Kármán rotating-disk boundary layers with radial anisotropic surface roughness

NASA Astrophysics Data System (ADS)

Garrett, S. J.; Cooper, A. J.; Harris, J. H.; Özkan, M.; Segalini, A.; Thomas, P. J.

2016-01-01

We summarise results of a theoretical study investigating the distinct convective instability properties of steady boundary-layer flow over rough rotating disks. A generic roughness pattern of concentric circles with sinusoidal surface undulations in the radial direction is considered. The goal is to compare predictions obtained by means of two alternative, and fundamentally different, modelling approaches for surface roughness for the first time. The motivating rationale is to identify commonalities and isolate results that might potentially represent artefacts associated with the particular methodologies underlying one of the two modelling approaches. The most significant result of practical relevance obtained is that both approaches predict overall stabilising effects on type I instability mode of rotating disk flow. This mode leads to transition of the rotating-disk boundary layer and, more generally, the transition of boundary-layers with a cross-flow profile. Stabilisation of the type 1 mode means that it may be possible to exploit surface roughness for laminar-flow control in boundary layers with a cross-flow component. However, we also find differences between the two sets of model predictions, some subtle and some substantial. These will represent criteria for establishing which of the two alternative approaches is more suitable to correctly describe experimental data when these become available.

Secondary flow structure in a model curved artery: 3D morphology and circulation budget analysis

NASA Astrophysics Data System (ADS)

Bulusu, Kartik V.; Plesniak, Michael W.

2015-11-01

In this study, we examined the rate of change of circulation within control regions encompassing the large-scale vortical structures associated with secondary flows, i.e. deformed Dean-, Lyne- and Wall-type (D-L-W) vortices at planar cross-sections in a 180° curved artery model (curvature ratio, 1/7). Magnetic resonance velocimetry (MRV) and particle image velocimetry (PIV) experiments were performed independently, under the same physiological inflow conditions (Womersley number, 4.2) and using Newtonian blood-analog fluids. The MRV-technique performed at Stanford University produced phase-averaged, three-dimensional velocity fields. Secondary flow field comparisons of MRV-data to PIV-data at various cross-sectional planes and inflow phases were made. A wavelet-decomposition-based approach was implemented to characterize various secondary flow morphologies. We hypothesize that the persistence and decay of arterial secondary flow vortices is intrinsically related to the influence of the out-of-plane flow, tilting, in-plane convection and diffusion-related factors within the control regions. Evaluation of these factors will elucidate secondary flow structures in arterial hemodynamics. Supported by the National Science Foundation under Grant Number CBET-0828903, and GW Center for Biomimetics and Bioinspired Engineering (COBRE). The MRV data were acquired at Stanford University in collaboration with Christopher Elkins and John Eaton.

Effects of the Canopy and Flux Tube Anchoring on Evaporation Flow of a Solar Flare

NASA Astrophysics Data System (ADS)

Unverferth, John; Longcope, Dana

2018-06-01

Spectroscopic observations of flare ribbons typically show chromospheric evaporation flows, which are subsonic for their high temperatures. This contrasts with many numerical simulations where evaporation is typically supersonic. These simulations typically assume flow along a flux tube with a uniform cross-sectional area. A simple model of the magnetic canopy, however, includes many regions of low magnetic field strength, where flux tubes achieve local maxima in their cross-sectional area. These are analgous to a chamber in a flow tube. We find that one-third of all field lines in a model have some form of chamber through which evaporation flow must pass. Using a one-dimensional isothermal hydrodynamic code, we simulated supersonic flow through an assortment of chambers and found that a subset of solutions exhibit a stationary standing shock within the chamber. These shocked solutions have slower and denser upflows than a flow through a uniform tube would. We use our solution to construct synthetic spectral lines and find that the shocked solutions show higher emission and lower Doppler shifts. When these synthetic lines are combined into an ensemble representing a single canopy cell, the composite line appears slower, even subsonic, than expected due to the outsized contribution from shocked solutions.

Investigation of Blade Angle of an Open Cross-Flow Runner

NASA Astrophysics Data System (ADS)

Katayama, Yusuke; Iio, Shouichiro; Veerapun, Salisa; Uchiyama, Tomomi

2015-04-01

The aim of this study was to develop a nano-hydraulic turbine utilizing drop structure in irrigation channels or industrial waterways. This study was focused on an open-type cross-flow turbine without any attached equipment for cost reduction and easy maintenance. In this study, the authors used an artificial indoor waterfall as lab model. Test runner which is a simple structure of 20 circular arc-shaped blades sandwiched by two circular plates was used The optimum inlet blade angle and the relationship between the power performance and the flow rate approaching theoretically and experimentally were investigated. As a result, the optimum inlet blade angle due to the flow rate was changed. Additionally, allocation rate of power output in 1st stage and 2nd stage is changed by the blade inlet angle.

Automated segmentation of blood-flow regions in large thoracic arteries using 3D-cine PC-MRI measurements.

PubMed

van Pelt, Roy; Nguyen, Huy; ter Haar Romeny, Bart; Vilanova, Anna

2012-03-01

Quantitative analysis of vascular blood flow, acquired by phase-contrast MRI, requires accurate segmentation of the vessel lumen. In clinical practice, 2D-cine velocity-encoded slices are inspected, and the lumen is segmented manually. However, segmentation of time-resolved volumetric blood-flow measurements is a tedious and time-consuming task requiring automation. Automated segmentation of large thoracic arteries, based solely on the 3D-cine phase-contrast MRI (PC-MRI) blood-flow data, was done. An active surface model, which is fast and topologically stable, was used. The active surface model requires an initial surface, approximating the desired segmentation. A method to generate this surface was developed based on a voxel-wise temporal maximum of blood-flow velocities. The active surface model balances forces, based on the surface structure and image features derived from the blood-flow data. The segmentation results were validated using volunteer studies, including time-resolved 3D and 2D blood-flow data. The segmented surface was intersected with a velocity-encoded PC-MRI slice, resulting in a cross-sectional contour of the lumen. These cross-sections were compared to reference contours that were manually delineated on high-resolution 2D-cine slices. The automated approach closely approximates the manual blood-flow segmentations, with error distances on the order of the voxel size. The initial surface provides a close approximation of the desired luminal geometry. This improves the convergence time of the active surface and facilitates parametrization. An active surface approach for vessel lumen segmentation was developed, suitable for quantitative analysis of 3D-cine PC-MRI blood-flow data. As opposed to prior thresholding and level-set approaches, the active surface model is topologically stable. A method to generate an initial approximate surface was developed, and various features that influence the segmentation model were evaluated. The active surface segmentation results were shown to closely approximate manual segmentations.

Computational Fluid Dynamics Modeling of the John Day Dam Tailrace

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

Rakowski, Cynthia L.; Perkins, William A.; Richmond, Marshall C.

US Army Corps of Engineers - Portland District required that a two-dimensional (2D) depth-averaged and a three-dimensional (3D) free-surface numerical models to be developed and validated for the John Day tailrace. These models were used to assess potential impact of a select group of structural and operational alternatives to tailrace flows aimed at improving fish survival at John Day Dam. The 2D model was used for the initial assessment of the alternatives in conjunction with a reduced-scale physical model of the John Day Project. A finer resolution 3D model was used to more accurately model the details of flow inmore » the stilling basin and near-project tailrace hydraulics. Three-dimensional model results were used as input to the Pacific Northwest National Laboratory particle tracking software, and particle paths and times to pass a downstream cross section were used to assess the relative differences in travel times resulting from project operations and structural scenarios for multiple total river flows. Streamlines and neutrally-buoyant particles were seeded in all turbine and spill bays with flows. For a Total River of 250 kcfs running with the Fish Passage Plan spill pattern and a spillwall, the mean residence times for all particles were little changed; however the tails of the distribution were truncated for both spillway and powerhouse release points, and, for the powerhouse releases, reduced the residence time for 75% of the particles to pass a downstream cross section from 45.5 minutes to 41.3 minutes. For a total river of 125 kcfs configured with the operations from the Fish Passage Plan for the temporary spillway weirs and for a proposed spillwall, the neutrally-buoyant particle tracking data showed that the river with a spillwall in place had the overall mean residence time increase; however, the residence time for 75% of the powerhouse-released particles to pass a downstream cross section was reduced from 102.4 min to 89 minutes.« less

Flow Structure and Channel Morphology at a Confluent-Meander Bend

NASA Astrophysics Data System (ADS)

Riley, J. D.; Rhoads, B. L.

2009-12-01

Flow structure and channel morphology in meander bends have been well documented. Channel curvature subjects flow through a bend to centrifugal acceleration, inducing a counterbalancing pressure-gradient force that initiates secondary circulation. Transverse variations in boundary shear stress and bedload transport parallel cross-stream movement of high velocity flow and determine spatial patterns of erosion along the outer bank and deposition along the inner bank. Laboratory experiments and numerical modeling of confluent-meander bends, a junction planform that develops when a tributary joins a meandering river along the outer bank of a bend, suggest that flow and channel morphology in such bends deviate from typical patterns. The purpose of this study is to examine three-dimensional (3-D) flow structure and channel morphology at a natural confluent-meander bend. Field data were collected in southeastern Illinois where Big Muddy Creek joins the Little Wabash River near a local maximum of curvature along an elongated meander loop. Measurements of 3-D velocity components were obtained with an acoustic Doppler current profiler (ADCP) for two flow events with differing momentum ratios. Channel bathymetry was also resolved from the four-beam depths of the ADCP. Analysis of velocity data reveals a distinct shear layer flanked by dual helical cells within the bend immediately downstream of the confluence. Flow from the tributary confines flow from the main channel along the inner part of the channel cross section, displacing the thalweg inward, limiting the downstream extent of the point bar, protecting the outer bank from erosion and enabling bar-building along this bank. Overall, this pattern of flow and channel morphology is quite different from typical patterns in meander bends, but is consistent with a conceptual model derived from laboratory experiments and numerical modeling.

EXPERIMENTS ON STABLY AND NEUTRALLY STRATIFIED FLOW OVER A MODEL THREE-DIMENSIONAL HILL

EPA Science Inventory

The flow structure over a bell shaped hill (reciprocal of a fourth order polynomial in cross section and height h) was studied in large and small stably stratified towing tanks (with uniform density gradients) and in an unstratified wind tunnel. Observations were made at Froude n...

Simulation of water-surface elevations for a hypothetical 100-year peak flow in Birch Creek at the Idaho National Engineering and Environmental Laboratory, Idaho

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

Berenbrock, C.; Kjelstrom, L.C.

1997-10-01

Delineation of areas at the Idaho National Engineering and Environmental Laboratory that would be inundated by a 100-year peak flow in Birch Creek is needed by the US Department of Energy to fulfill flood-plain regulatory requirements. Birch Creek flows southward about 40 miles through an alluvium-filled valley onto the northern part of the Idaho National Engineering and Environmental laboratory site on the eastern Snake River Plain. The lower 10-mile reach of Birch Creek that ends in Birch Creek Playa near several Idaho National Engineering and Environmental Laboratory facilities is of particular concern. Twenty-six channel cross sections were surveyed to developmore » and apply a hydraulic model to simulate water-surface elevations for a hypothetical 100-year peak flow in Birch Creek. Model simulation of the 100-year peak flow (700 cubic feet per second) in reaches upstream from State Highway 22 indicated that flow was confined within channels even when all flow was routed to one channel. Where the highway crosses Birch Creek, about 315 cubic feet per second of water was estimated to move downstream--115 cubic feet per second through a culvert and 200 cubic feet per second over the highway. Simulated water-surface elevation at this crossing was 0.8 foot higher than the elevation of the highway. The remaining 385 cubic feet per second flowed southwestward in a trench along the north side of the highway. Flow also was simulated with the culvert removed. The exact location of flood boundaries on Birch Creek could not be determined because of the highly braided channel and the many anthropogenic features (such as the trench, highway, and diversion channels) in the study area that affect flood hydraulics and flow. Because flood boundaries could not be located exactly, only a generalized flood-prone map was developed.« less

Poiseuille equation for steady flow of fractal fluid

NASA Astrophysics Data System (ADS)

Tarasov, Vasily E.

2016-07-01

Fractal fluid is considered in the framework of continuous models with noninteger dimensional spaces (NIDS). A recently proposed vector calculus in NIDS is used to get a description of fractal fluid flow in pipes with circular cross-sections. The Navier-Stokes equations of fractal incompressible viscous fluids are used to derive a generalization of the Poiseuille equation of steady flow of fractal media in pipe.

A comprehensive one-dimensional numerical model for solute transport in rivers

NASA Astrophysics Data System (ADS)

Barati Moghaddam, Maryam; Mazaheri, Mehdi; MohammadVali Samani, Jamal

2017-01-01

One of the mechanisms that greatly affect the pollutant transport in rivers, especially in mountain streams, is the effect of transient storage zones. The main effect of these zones is to retain pollutants temporarily and then release them gradually. Transient storage zones indirectly influence all phenomena related to mass transport in rivers. This paper presents the TOASTS (third-order accuracy simulation of transient storage) model to simulate 1-D pollutant transport in rivers with irregular cross-sections under unsteady flow and transient storage zones. The proposed model was verified versus some analytical solutions and a 2-D hydrodynamic model. In addition, in order to demonstrate the model applicability, two hypothetical examples were designed and four sets of well-established frequently cited tracer study data were used. These cases cover different processes governing transport, cross-section types and flow regimes. The results of the TOASTS model, in comparison with two common contaminant transport models, shows better accuracy and numerical stability.

Flow of variably fluidized granular masses across three-dimensional terrain 2. Numerical predictions and experimental tests

USGS Publications Warehouse

Denlinger, R.P.; Iverson, R.M.

2001-01-01

Numerical solutions of the equations describing flow of variably fluidized Coulomb mixtures predict key features of dry granular avalanches and water-saturated debris flows measured in physical experiments. These features include time-dependent speeds, depths, and widths of flows as well as the geometry of resulting deposits. Threedimensional (3-D) boundary surfaces strongly influence flow dynamics because transverse shearing and cross-stream momentum transport occur where topography obstructs or redirects motion. Consequent energy dissipation can cause local deceleration and deposition, even on steep slopes. Velocities of surge fronts and other discontinuities that develop as flows cross 3-D terrain are predicted accurately by using a Riemann solution algorithm. The algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization. Field observations and experiments indicate that flows in which fluid plays a significant role typically have high-friction margins with weaker interiors partly fluidized by pore pressure. Interaction of the strong perimeter and weak interior produces relatively steep-sided, flat-topped deposits. To simulate these effects, we compute pore pressure distributions using an advection-diffusion model with enhanced diffusivity near flow margins. Although challenges remain in evaluating pore pressure distributions in diverse geophysical flows, Riemann solutions of the depthaveraged 3-D Coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior. They provide a means of modeling debris flows, rock avalanches, pyroclastic flows, and related phenomena without invoking and calibrating Theological parameters that have questionable physical significance.

Interaction of a Gas Flow Carrying Nonspherical Microparticles with a Cross Cylinder

NASA Astrophysics Data System (ADS)

Amelyushkin, I. A.; Stasenko, A. L.

2018-05-01

A model of the dynamics of the particles-spheroids carried by a gas flow over a cross cylindrical body and rebounding from it has been developed. In this model, the gas flow around the particles is assumed to be viscous, and the reverse action of the particles on the gas and the collisions between them are not taken into account. The coefficients of recovery of the velocity components of the particles rebounded from the cylinder were determined on the basis of the heuristic theory in which the physical and mechanical properties of colliding bodies are considered. The influence of the ratio between the axes of particles-spheroids on the coefficient of wetting of the cylinder by them, the distributions of the mass-flow density of the particles and their velocity components over the cylinder surface, and the spatial distribution of the indicated quantities of the rotating particles rebounded from the cylinder was investigated numerically. The model proposed can be used for estimating the action of ice microcrystals and particles of volcanic ash emissions and dust storms on the structural elements of aircraft engines and small-size flying vehicles.

Interaction of a Gas Flow Carrying Nonspherical Microparticles with a Cross Cylinder

NASA Astrophysics Data System (ADS)

Amelyushkin, I. A.; Stasenko, A. L.

2018-03-01

A model of the dynamics of the particles-spheroids carried by a gas flow over a cross cylindrical body and rebounding from it has been developed. In this model, the gas flow around the particles is assumed to be viscous, and the reverse action of the particles on the gas and the collisions between them are not taken into account. The coefficients of recovery of the velocity components of the particles rebounded from the cylinder were determined on the basis of the heuristic theory in which the physical and mechanical properties of colliding bodies are considered. The influence of the ratio between the axes of particles-spheroids on the coefficient of wetting of the cylinder by them, the distributions of the mass-flow density of the particles and their velocity components over the cylinder surface, and the spatial distribution of the indicated quantities of the rotating particles rebounded from the cylinder was investigated numerically. The model proposed can be used for estimating the action of ice microcrystals and particles of volcanic ash emissions and dust storms on the structural elements of aircraft engines and small-size flying vehicles.

Development of a new semi-analytical model for cross-borehole flow experiments in fractured media

USGS Publications Warehouse

Roubinet, Delphine; Irving, James; Day-Lewis, Frederick D.

2015-01-01

Analysis of borehole flow logs is a valuable technique for identifying the presence of fractures in the subsurface and estimating properties such as fracture connectivity, transmissivity and storativity. However, such estimation requires the development of analytical and/or numerical modeling tools that are well adapted to the complexity of the problem. In this paper, we present a new semi-analytical formulation for cross-borehole flow in fractured media that links transient vertical-flow velocities measured in one or a series of observation wells during hydraulic forcing to the transmissivity and storativity of the fractures intersected by these wells. In comparison with existing models, our approach presents major improvements in terms of computational expense and potential adaptation to a variety of fracture and experimental configurations. After derivation of the formulation, we demonstrate its application in the context of sensitivity analysis for a relatively simple two-fracture synthetic problem, as well as for field-data analysis to investigate fracture connectivity and estimate fracture hydraulic properties. These applications provide important insights regarding (i) the strong sensitivity of fracture property estimates to the overall connectivity of the system; and (ii) the non-uniqueness of the corresponding inverse problem for realistic fracture configurations.

Hydrodynamics and sediment transport in a meandering channel with a model axial-flow hydrokinetic turbine

NASA Astrophysics Data System (ADS)

Hill, Craig; Kozarek, Jessica; Sotiropoulos, Fotis; Guala, Michele

2016-02-01

An investigation into the interactions between a model axial-flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field-scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine-induced scour and deposition patterns. In particular, it shows how the cross-section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.

Numerical simulation of ground-water flow in La Crosse County, Wisconsin, and into nearby pools of the Mississippi River

USGS Publications Warehouse

Hunt, Randall J.; Saad, David A.; Chapel, Dawn M.

2003-01-01

The models provide estimates of the locations and amount of ground-water flow into Pool 8 and the southern portion of Pool 7 of the Mississippi River. Ground-water discharges into all areas of the pools, except along the eastern shore in the vicinity of the city of La Crosse and immediately downgradient from lock and dam 7 and 8. Ground-water flow into the pools is generally greatest around the perimeter with decreasing amounts away from the perimeter. An area of relatively high ground-water discharge extends out towards the center of Pool 7 from the upper reaches of the pool and may

Cross-borehole flowmeter tests for transient heads in heterogeneous aquifers.

PubMed

Le Borgne, Tanguy; Paillet, Frederick; Bour, Olivier; Caudal, Jean-Pierre

2006-01-01

Cross-borehole flowmeter tests have been proposed as an efficient method to investigate preferential flowpaths in heterogeneous aquifers, which is a major task in the characterization of fractured aquifers. Cross-borehole flowmeter tests are based on the idea that changing the pumping conditions in a given aquifer will modify the hydraulic head distribution in large-scale flowpaths, producing measurable changes in the vertical flow profiles in observation boreholes. However, inversion of flow measurements to derive flowpath geometry and connectivity and to characterize their hydraulic properties is still a subject of research. In this study, we propose a framework for cross-borehole flowmeter test interpretation that is based on a two-scale conceptual model: discrete fractures at the borehole scale and zones of interconnected fractures at the aquifer scale. We propose that the two problems may be solved independently. The first inverse problem consists of estimating the hydraulic head variations that drive the transient borehole flow observed in the cross-borehole flowmeter experiments. The second inverse problem is related to estimating the geometry and hydraulic properties of large-scale flowpaths in the region between pumping and observation wells that are compatible with the head variations deduced from the first problem. To solve the borehole-scale problem, we treat the transient flow data as a series of quasi-steady flow conditions and solve for the hydraulic head changes in individual fractures required to produce these data. The consistency of the method is verified using field experiments performed in a fractured-rock aquifer.

The Importance of Parameter Variances, Correlations Lengths, and Cross-Correlations in Reactive Transport Models: Key Considerations for Assessing the Need for Microscale Information (Invited)

NASA Astrophysics Data System (ADS)

Reimus, P. W.

2010-12-01

A process-oriented modeling approach is implemented to examine the importance of parameter variances, correlation lengths, and especially cross-correlations in contaminant transport predictions over large scales. It is shown that the most important consideration is the correlation between flow rates and retardation processes (e.g., sorption, matrix diffusion) in the system. If flow rates are negatively correlated with retardation factors in systems containing multiple flow pathways, then characterizing these negative correlation(s) may have more impact on reactive transport modeling than microscale information. Such negative correlations are expected in porous-media systems where permeability is negatively correlated with clay content and rock alteration (which are usually associated with increased sorption). Likewise, negative correlations are expected in fractured rocks where permeability is positively correlated with fracture apertures, which in turn are negatively correlated with sorption and matrix diffusion. Parameter variances and correlation lengths are also shown to have important effects on reactive transport predictions, but they are less important than parameter cross-correlations. Microscale information pertaining to contaminant transport has become more readily available as characterization methods and spectroscopic instrumentation have achieved lower detection limits, greater resolution, and better precision. Obtaining detailed mechanistic insights into contaminant-rock-water interactions is becoming a routine practice in characterizing reactive transport processes in groundwater systems (almost necessary for high-profile publications). Unfortunately, a quantitative link between microscale information and flow and transport parameter distributions or cross-correlations has not yet been established. One reason for this is that quantitative microscale information is difficult to obtain in complex, heterogeneous systems, so simple systems that lack the complexity and heterogeneity of real aquifer materials are often studied. Another is that instrumentation used to obtain microscale information often probes only one variable or family of variables at a time, so linkages to other variables must be inferred by indirect means from other lines of evidence. Despite these limitations, microscale information can be useful in the development and validation of reactive transport models. For example, knowledge of mineral phases that have strong affinities for contaminants can help in the development of cross-correlations between flow and sorption parameters via characterization of permeability and mineral distributions in aquifers. Likewise, microscale information on pore structures in low-permeability zones and contaminant penetration distances into these zones from higher-permeability zones (e.g., fractures) can provide valuable constraints on the representation of diffusive mass transfer processes between flowing porosity and secondary porosity. The prioritization of obtaining microscale information in any groundwater system can be informed by modeling exercises such as those conducted for this study.

Concentration data and dimensionality in groundwater models: evaluation using inverse modelling

USGS Publications Warehouse

Barlebo, H.C.; Hill, M.C.; Rosbjerg, D.; Jensen, K.H.

1998-01-01

A three-dimensional inverse groundwater flow and transport model that fits hydraulic-head and concentration data simultaneously using nonlinear regression is presented and applied to a layered sand and silt groundwater system beneath the Grindsted Landfill in Denmark. The aquifer is composed of rather homogeneous hydrogeologic layers. Two issues common to groundwater flow and transport modelling are investigated: 1) The accuracy of simulated concentrations in the case of calibration with head data alone; and 2) The advantages and disadvantages of using a two-dimensional cross-sectional model instead of a three-dimensional model to simulate contaminant transport when the source is at the land surface. Results show that using only hydraulic heads in the nonlinear regression produces a simulated plume that is profoundly different from what is obtained in a calibration using both hydraulic-head and concentration data. The present study provides a well-documented example of the differences that can occur. Representing the system as a two-dimensional cross-section obviously omits some of the system dynamics. It was, however, possible to obtain a simulated plume cross-section that matched the actual plume cross-section well. The two-dimensional model execution times were about a seventh of those for the three-dimensional model, but some difficulties were encountered in representing the spatially variable source concentrations and less precise simulated concentrations were calculated by the two-dimensional model compared to the three-dimensional model. Summed up, the present study indicates that three dimensional modelling using both hydraulic heads and concentrations in the calibration should be preferred in the considered type of transport studies.

A study of thin liquid sheet flows

NASA Technical Reports Server (NTRS)

Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.

1993-01-01

This study was a theoretical and experimental investigation of thin liquid sheet flows in vacuum. A sheet flow created by a narrow slit of width, W, coalesces to a point at a distance, L, as a result of surface tension forces acting at the sheet edges. As the flow coalesces, the fluid accumulates in the sheet edges. The observed triangular shape of the sheet agrees with the calculated triangular result. Experimental results for L/W as a function of Weber number, We, agree with the calculated result, L/W = the sq. root of 8We. The edge cross sectional shape is found to oscillate from elliptic to 'cigar' like to 'peanut' like and then back to elliptic in the flow direction. A theoretical one-dimensional model was developed that yielded only elliptic solutions for the edge cross section. At the points where the elliptic shapes occur, there is agreement between theory and experiment.

A methodology for using borehole temperature-depth profiles under ambient, single and cross-borehole pumping conditions to estimate fracture hydraulic properties

NASA Astrophysics Data System (ADS)

Klepikova, Maria V.; Le Borgne, Tanguy; Bour, Olivier; Davy, Philippe

2011-09-01

SummaryTemperature profiles in the subsurface are known to be sensitive to groundwater flow. Here we show that they are also strongly related to vertical flow in the boreholes themselves. Based on a numerical model of flow and heat transfer at the borehole scale, we propose a method to invert temperature measurements to derive borehole flow velocities. This method is applied to an experimental site in fractured crystalline rocks. Vertical flow velocities deduced from the inversion of temperature measurements are compared with direct heat-pulse flowmeter measurements showing a good agreement over two orders of magnitudes. Applying this methodology under ambient, single and cross-borehole pumping conditions allows us to estimate fracture hydraulic head and local transmissivity, as well as inter-borehole fracture connectivity. Thus, these results provide new insights on how to include temperature profiles in inverse problems for estimating hydraulic fracture properties.

Study of transient behavior of finned coil heat exchangers

NASA Technical Reports Server (NTRS)

Rooke, S. P.; Elissa, M. G.

1993-01-01

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

NASA Technical Reports Server (NTRS)

Baker, D. N.; Mcpherron, R. L.

1990-01-01

A qualitative model of cross-tail current flow is considered. It is suggested that when magnetic reconnection begins, the current effectively flows across the plasma sheet both earthward and tailward of the disruption region near the neutral line. It is shown that an enhanced cross-tail current earthward of this region would thin the plasma sheet substantially due to the magnetic pinch effect. The results explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Flow of chemically reactive magneto Cross nanoliquid with temperature-dependent conductivity

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Ullah, Ikram; Waqas, Muhammad; Alsaedi, Ahmed

2018-05-01

Influence of temperature-dependent thermal conductivity on MHD flow of Cross nanoliquid bounded by a stretched sheet is explored. The combined feature of Brownian motion and thermophoresis in nanoliquid modeling is retained. In addition, the attributes of zero mass flux at sheet are imposed. First-order chemical reaction is retained. The resulting problems are numerically computed. Plots and tabulated values are presented and examined. It is figured out that larger thermophoretic diffusion and thermal conductivity significantly rise the thermal field, whereas opposite situation is seen for heat transfer rate.

On the Conservation of Cross Helicity and Wave Action in Solar-wind Models with Non-WKB Alfvén Wave Reflection

NASA Astrophysics Data System (ADS)

Chandran, Benjamin D. G.; Perez, Jean C.; Verscharen, Daniel; Klein, Kristopher G.; Mallet, Alfred

2015-09-01

The interaction between Alfvén-wave turbulence and the background solar wind affects the cross helicity (\\int {d}3x {\\boldsymbol{v}}\\cdot {\\boldsymbol{B}}) in two ways. Non-WKB reflection converts outward-propagating Alfvén waves into inward-propagating Alfvén waves and vice versa, and the turbulence transfers momentum to the background flow. When both effects are accounted for, the total cross helicity is conserved. In the special case that the background density and flow speed are independent of time, the equations of cross-helicity conservation and total-energy conservation can be combined to recover a well-known equation derived by Heinemann and Olbert that has been interpreted as a non-WKB generalization of wave-action conservation. This latter equation (in contrast to cross-helicity and energy conservation) does not hold when the background varies in time.

Numerical simulation of flow and melting characteristics of seawater-ice crystals two-phase flow in inlet straight pipe of shell and tube heat exchanger of polar ship

NASA Astrophysics Data System (ADS)

Xu, Li; Huang, Chang-Xu; Huang, Zhen-Fei; Sun, Qiang; Li, Jie

2018-05-01

The ice crystal particles are easy to enter into the seawater cooling system of polar ship together with seawater when it sails in the Arctic. They are easy to accumulate in the pipeline, causing serious blockage of the cooling pipe. In this study, the flow and melting characteristics of ice particles-seawater two-phase flow in inlet straight pipe of shell-and-tube heat exchanger were numerically simulated by using Eulerian-Eulerian two-fluid model coupled with the interphase heat and mass transfer model. The influences of inlet ice packing factor, ice crystal particle diameter, and inlet velocity on the distribution and melting characteristics of ice crystals were investigated. The degree of asymmetry of the distribution of ice crystals in the cross section decreases gradually when the IPF changes from 5 to 15%. The volume fractions of ice crystals near the top of the outlet cross section are 19.59, 19.51, and 22.24% respectively for ice packing factor of 5, 10 and 15%. When the particle diameter is 0.5 mm, the ice crystals are gradually stratified during the flow process. With particle diameters of 1.0 and 2.0 mm, the region with the highest volume fraction of ice crystals is a small circle and the contours in the cloud map are compact. The greater the inlet flow velocity, the less stratified the ice crystals and the more obvious the turbulence on the outlet cross section. The average volume fraction of ice crystals along the flow direction is firstly rapidly reduced and then stabilized after 300 mm.

Fluid mechanics of continuous flow electrophoresis

NASA Technical Reports Server (NTRS)

Saville, D. A.; Ostrach, S.

1978-01-01

The following aspects of continuous flow electrophoresis were studied: (1) flow and temperature fields; (2) hydrodynamic stability; (3) separation efficiency, and (4) characteristics of wide gap chambers (the SPAR apparatus). Simplified mathematical models were developed so as to furnish a basis for understanding the phenomena and comparison of different chambers and operating conditions. Studies of the hydrodynamic stability disclosed that a wide gap chamber may be particularly sensitive to axial temperature variations which could be due to uneven heating or cooling. The mathematical model of the separation process includes effects due to the axial velocity, electro-osmotic cross flow and electrophoretic migration, all including the effects of temperature dependent properties.

PHYSICAL MODELING OF CONTRACTED FLOW.

USGS Publications Warehouse

Lee, Jonathan K.

1987-01-01

Experiments on steady flow over uniform grass roughness through centered single-opening contractions were conducted in the Flood Plain Simulation Facility at the U. S. Geological Survey's Gulf Coast Hydroscience Center near Bay St. Louis, Miss. The experimental series was designed to provide data for calibrating and verifying two-dimensional, vertically averaged surface-water flow models used to simulate flow through openings in highway embankments across inundated flood plains. Water-surface elevations, point velocities, and vertical velocity profiles were obtained at selected locations for design discharges ranging from 50 to 210 cfs. Examples of observed water-surface elevations and velocity magnitudes at basin cross-sections are presented.

Project 0-1800 : NAFTA impacts on operations : executive summary

DOT National Transportation Integrated Search

2001-07-01

Project 0-1800 pioneered the use of modern micro-simulation models to analyze the complex procedures involved in international border crossing in Texas. Animated models simulate the entire southbound commercial traffic flow in two important internati...

ENHANCING HSPF MODEL CHANNEL HYDRAULIC REPRESENTATION

EPA Science Inventory

The Hydrological Simulation Program - FORTRAN (HSPF) is a comprehensive watershed model, which employs depth-area-volume-flow relationships known as hydraulic function table (FTABLE) to represent stream channel cross-sections and reservoirs. An accurate FTABLE determination for a...

Augment clinical measurement using a constraint-based esophageal model

NASA Astrophysics Data System (ADS)

Kou, Wenjun; Acharya, Shashank; Kahrilas, Peter; Patankar, Neelesh; Pandolfino, John

2017-11-01

Quantifying the mechanical properties of the esophageal wall is crucial to understanding impairments of trans-esophageal flow characteristic of several esophageal diseases. However, these data are unavailable owing to technological limitations of current clinical diagnostic instruments that instead display esophageal luminal cross sectional area based on intraluminal impedance change. In this work, we developed an esophageal model to predict bolus flow and the wall property based on clinical measurements. The model used the constraint-based immersed-boundary method developed previously by our group. Specifically, we first approximate the time-dependent wall geometry based on impedance planimetry data on luminal cross sectional area. We then fed these along with pressure data into the model and computed wall tension based on simulated pressure and flow fields, and the material property based on the strain-stress relationship. As examples, we applied this model to augment FLIP (Functional Luminal Imaging Probe) measurements in three clinical cases: a normal subject, achalasia, and eosinophilic esophagitis (EoE). Our findings suggest that the wall stiffness was greatest in the EoE case, followed by the achalasia case, and then the normal. This is supported by NIH Grant R01 DK56033 and R01 DK079902.

Numerical modeling of the near-field hydraulics of water wells.

PubMed

Houben, Georg J; Hauschild, Sarah

2011-01-01

Numerical flow models can be a useful tool for dimensioning water wells and to investigate the hydraulics in their near-field. Fully laminar flow can be assumed for all models calculated up to the screen. Therefore models can be used to predict--at least qualitatively, neglecting turbulent losses inside the well--the spatial distribution of inflow into the well and the overall hydraulic performance of different combinations of aquifer parameters and technical installations. Models for both horizontal (plan view) and vertical flow (cross section) to wells were calculated for a variety of setups. For the latter, this included variations of hydraulic conductivity of the screen, pump position, and aquifer heterogeneity. Models of suction flow control devices showed that they indeed can homogenize inflow, albeit at the cost of elevated entrance losses. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

Three-dimensional hydrogeologic framework model for use with a steady-state numerical ground-water flow model of the Death Valley regional flow system, Nevada and California

USGS Publications Warehouse

Belcher, Wayne R.; Faunt, Claudia C.; D'Agnese, Frank A.

2002-01-01

The U.S. Geological Survey, in cooperation with the Department of Energy and other Federal, State, and local agencies, is evaluating the hydrogeologic characteristics of the Death Valley regional ground-water flow system. The ground-water flow system covers an area of about 100,000 square kilometers from latitude 35? to 38?15' North to longitude 115? to 118? West, with the flow system proper comprising about 45,000 square kilometers. The Death Valley regional ground-water flow system is one of the larger flow systems within the Southwestern United States and includes in its boundaries the Nevada Test Site, Yucca Mountain, and much of Death Valley. Part of this study includes the construction of a three-dimensional hydrogeologic framework model to serve as the foundation for the development of a steady-state regional ground-water flow model. The digital framework model provides a computer-based description of the geometry and composition of the hydrogeologic units that control regional flow. The framework model of the region was constructed by merging two previous framework models constructed for the Yucca Mountain Project and the Environmental Restoration Program Underground Test Area studies at the Nevada Test Site. The hydrologic characteristics of the region result from a currently arid climate and complex geology. Interbasinal regional ground-water flow occurs through a thick carbonate-rock sequence of Paleozoic age, a locally thick volcanic-rock sequence of Tertiary age, and basin-fill alluvium of Tertiary and Quaternary age. Throughout the system, deep and shallow ground-water flow may be controlled by extensive and pervasive regional and local faults and fractures. The framework model was constructed using data from several sources to define the geometry of the regional hydrogeologic units. These data sources include (1) a 1:250,000-scale hydrogeologic-map compilation of the region; (2) regional-scale geologic cross sections; (3) borehole information, and (4) gridded surfaces from a previous three-dimensional geologic model. In addition, digital elevation model data were used in conjunction with these data to define ground-surface altitudes. These data, properly oriented in three dimensions by using geographic information systems, were combined and gridded to produce the upper surfaces of the hydrogeologic units used in the flow model. The final geometry of the framework model is constructed as a volumetric model by incorporating the intersections of these gridded surfaces and by applying fault truncation rules to structural features from the geologic map and cross sections. The cells defining the geometry of the hydrogeologic framework model can be assigned several attributes such as lithology, hydrogeologic unit, thickness, and top and bottom altitudes.

Flowmetering of drainage wells in Kuwait City, Kuwait

USGS Publications Warehouse

Paillet, Frederick L.; Senay, Y.; Mukhopadhyay, A.; Szekely, F.

2000-01-01

A heat-pulse flowmeter was used in six drainage wells in Kuwait City for flow profiling under both ambient and pumping conditions. The data collected were used in: (a) estimating the cross-flow among the screened intervals under ambient conditions; (b) estimating the relative transmissivity adjacent to the individual screen zones; and (c) determination of the hydraulic heads at the far boundaries of the large-scale aquifer zones. These inferences were cross-checked against known hydrogeology of the aquifer-aquitard system in the study area, and the calibration results of numerical flow modeling. The major conclusions derived from the flow measurements were: (a) the presence of natural downward cross-flow under ambient condition supported the hypothesis that the upper part of the Kuwait Group aquifer in the study area was divided into a series of permeable units (aquifers), separated by confining or semi-confining beds (aquitards); (b) the head differences between the different screened zones, derived through modeling of the flowmeter data of the wells, provided additional confirmation for the division of the upper part of the Kuwait Group aquifer into compartments in the study area; (c) flowmeter data indicated that the second and third aquifers were contributing most of the water to the well bores, compared with the uppermost (first) and the lowermost (fourth) aquifers; and (d) inflow to the wells during pumping was associated with discrete sub-intervals in the screened zones, controlled by local aquifer heterogeneity, and possibly clogging of screens and gravel pack.

Method and apparatus for affecting a recirculation zone in a cross flow

DOEpatents

Bathina, Mahesh [Andhra Pradesh, IN; Singh, Ramanand [Uttar Pradesh, IN

2012-07-17

Disclosed is a cross flow apparatus including a surface and at least one outlet located at the surface. The cross flow apparatus further includes at least one guide at the surface configured to direct an intersecting flow flowing across the surface and increase a velocity of a cross flow being expelled from the at least one outlet downstream from the at least one outlet.

Flow in water-intake pump bays: A guide for utility engineers. Final report

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

Ettema, R.

1998-09-01

This report is intended to serve as a guide for power-plant engineers facing problems with flow conditions in pump bays in water-intake structures, especially those located alongside rivers. The guide briefly introduces the typical prevailing flow field outside of a riverside water intake. That flow field often sets the inflow conditions for pump bays located within the water intake. The monograph then presents and discusses the main flow problems associated with pump bays. The problems usually revolve around the formation of troublesome vortices. A novel feature of this monograph is the use of numerical modeling to reveal diagnostically how themore » vortices form and their sensitivities to flow conditions, such as uniformity of approach flow entering the bay and water-surface elevation relative to pump-bell submergence. The modeling was carried out using a computer code developed specially for the present project. Pump-bay layouts are discussed next. The discussion begins with a summary of the main variables influencing bay flows. The numerical model is used to determine the sensitivities of the vortices to variations in the geometric parameters. The fixes include the use of flow-control vanes and suction scoops for ensuring satisfactory flow performance in severe flow conditions; notably flows with strong cross flow and shallow flows. The monograph ends with descriptions of modeling techniques. An extensive discussion is provided on the use of numerical model for illuminating bay flows. The model is used to show how fluid viscosity affects bay flow. The effect of fluid viscosity is an important consideration in hydraulic modeling of water intakes.« less

Artificial neural network analysis based on genetic algorithm to predict the performance characteristics of a cross flow cooling tower

NASA Astrophysics Data System (ADS)

Wu, Jiasheng; Cao, Lin; Zhang, Guoqiang

2018-02-01

Cooling tower of air conditioning has been widely used as cooling equipment, and there will be broad application prospect if it can be reversibly used as heat source under heat pump heating operation condition. In view of the complex non-linear relationship of each parameter in the process of heat and mass transfer inside tower, In this paper, the BP neural network model based on genetic algorithm optimization (GABP neural network model) is established for the reverse use of cross flow cooling tower. The model adopts the structure of 6 inputs, 13 hidden nodes and 8 outputs. With this model, the outlet air dry bulb temperature, wet bulb temperature, water temperature, heat, sensible heat ratio and heat absorbing efficiency, Lewis number, a total of 8 the proportion of main performance parameters were predicted. Furthermore, the established network model is used to predict the water temperature and heat absorption of the tower at different inlet temperatures. The mean relative error MRE between BP predicted value and experimental value are 4.47%, 3.63%, 2.38%, 3.71%, 6.35%,3.14%, 13.95% and 6.80% respectively; the mean relative error MRE between GABP predicted value and experimental value are 2.66%, 3.04%, 2.27%, 3.02%, 6.89%, 3.17%, 11.50% and 6.57% respectively. The results show that the prediction results of GABP network model are better than that of BP network model; the simulation results are basically consistent with the actual situation. The GABP network model can well predict the heat and mass transfer performance of the cross flow cooling tower.

ENHANCING HYDROLOGICAL SIMULATION PROGRAM - FORTRAN MODEL CHANNEL HYDRAULIC REPRESENTATION

EPA Science Inventory

The Hydrological Simulation Program– FORTRAN (HSPF) is a comprehensive watershed model that employs depth-area - volume - flow relationships known as the hydraulic function table (FTABLE) to represent the hydraulic characteristics of stream channel cross-sections and reservoirs. ...

Pulsatile spiral blood flow through arterial stenosis.

PubMed

Linge, Fabian; Hye, Md Abdul; Paul, Manosh C

2014-11-01

Pulsatile spiral blood flow in a modelled three-dimensional arterial stenosis, with a 75% cross-sectional area reduction, is investigated by using numerical fluid dynamics. Two-equation k-ω model is used for the simulation of the transitional flow with Reynolds numbers 500 and 1000. It is found that the spiral component increases the static pressure in the vessel during the deceleration phase of the flow pulse. In addition, the spiral component reduces the turbulence intensity and wall shear stress found in the post-stenosis region of the vessel in the early stages of the flow pulse. Hence, the findings agree with the results of Stonebridge et al. (2004). In addition, the results of the effects of a spiral component on time-varying flow are presented and discussed along with the relevant pathological issues.

Numerical investigation of thermal-hydraulic performance of channel with protrusions by turbulent cross flow jet

NASA Astrophysics Data System (ADS)

Sahu, M. K.; Pandey, K. M.; Chatterjee, S.

2018-05-01

In this two dimensional numerical investigation, small rectangular channel with right angled triangular protrusions in the bottom wall of test section is considered. A slot nozzle is placed at the middle of top wall of channel which impinges air normal to the protruded surface. A duct flow and nozzle flow combined to form cross flow which is investigated for heat transfer enhancement of protruded channel. The governing equations for continuity, momentum, energy along with SST k-ω turbulence model are solved with finite volume based Computational fluid dynamics code ANSYS FLUENT 14.0. The range of duct Reynolds number considered for this analysis is 8357 to 51760. The ratios of pitch of protrusion to height of duct considered are 0.5, 0.64 and 0.82. The ratios of height of protrusion to height of duct considered are 0.14, 0.23 and 0.29. The effect of duct Reynolds number, pitch and height of protrusion on thermal-hydraulic performance is studied under cross flow condition. It is found that heat transfer rate is more at relatively larger pitch and small pressure drop is found in case of low height of protrusion.

CFD simulations of the flow control performance applied for inlet of low drag high-bypass turbofan engine at cross flow regimes

NASA Astrophysics Data System (ADS)

Kursakov, I. A.; Kazhan, E. V.; Lysenkov, A. V.; Savelyev, A. A.

2016-10-01

Paper describes the optimization procedure for low cruise drag inlet of high-bypass ratio turbofan engine (HBRE). The critical cross-flow velocity when the flow separation on the lee side of the inlet channel occurs is determined. The effciency of different flow control devices used to improve the flow parameters at inlet section cross flow regime is analyzed. Boundary layer suction, bypass slot and vortex generators are considered. It is shown that flow control devices enlarge the stability range of inlet performance at cross flow regimes.

Regional Hydrogeochemistry of a Modern Coastal Mixing Zone

NASA Astrophysics Data System (ADS)

Wicks, Carol M.; Herman, Janet S.

1996-02-01

In west central Florida, groundwater samples were collected along flow paths in the unconfined upper Floridan aquifer that cross the inland, freshwater recharge area and the coastal discharge area. A groundwater flow and solute transport model was used to evaluate groundwater flow and mixing of fresh and saline groundwater along a cross section of the unconfined upper Floridan aquifer. Results show that between 8% and 15% of the fresh and 30-31% of the saline groundwater penetrates to the depth in the flow system where contact with and dissolution of gypsum is likely. The deeply circulating fresh and saline groundwater returns to the near-surface environment discharging CaSO4-rich water to the coastal area where it mixes with fresh CaHCO3 groundwater, resulting in a prediction of calcite precipitation in the modern mixing zone.

14C age reassessment of groundwater from the discharge zone due to cross-flow mixing in the deep confined aquifer

NASA Astrophysics Data System (ADS)

Mao, Xumei; Wang, Hua; Feng, Liang

2018-05-01

In a groundwater flow system, the age of groundwater should gradually increase from the recharge zone to the discharge zone within the same streamline. However, it is occasionally observed that the groundwater age becomes younger in the discharge zone in the piedmont alluvial plain, and the oldest age often appears in the middle of the plain. A new set of groundwater chemistry and isotopes was employed to reassess the groundwater 14C ages from the discharge zone in the North China Plain (NCP). Carbonate precipitation, organic matter oxidation and cross-flow mixing in the groundwater from the recharge zone to the discharge zone are recognized according to the corresponding changes of HCO3- (or DIC) and δ13C in the same streamline of the third aquifer of the NCP. The effects of carbonate precipitation and organic matter oxidation are calibrated with a 13C mixing model and DIC correction, but these corrected 14C ages seem unreasonable because they grow younger from the middle plain to the discharge zone in the NCP. The relationship of Cl- content and the recharge distance is used to estimate the expected Cl- content in the discharge zone, and ln(a14C)/Cl is proposed to correct the a14C in groundwater for the effect of cross-flow mixing. The 14C ages were reassessed with the corrected a14C due to the cross-flow mixing varying from 1.25 to 30.58 ka, and the groundwater becomes older gradually from the recharge zone to the discharge zone. The results suggest that the reassessed 14C ages are more reasonable for the groundwater from the discharge zone due to cross-flow mixing.

Assessment of zero-equation SGS models for simulating indoor environment

NASA Astrophysics Data System (ADS)

Taghinia, Javad; Rahman, Md Mizanur; Tse, Tim K. T.

2016-12-01

The understanding of air-flow in enclosed spaces plays a key role to designing ventilation systems and indoor environment. The computational fluid dynamics aspects dictate that the large eddy simulation (LES) offers a subtle means to analyze complex flows with recirculation and streamline curvature effects, providing more robust and accurate details than those of Reynolds-averaged Navier-Stokes simulations. This work assesses the performance of two zero-equation sub-grid scale models: the Rahman-Agarwal-Siikonen-Taghinia (RAST) model with a single grid-filter and the dynamic Smagorinsky model with grid-filter and test-filter scales. This in turn allows a cross-comparison of the effect of two different LES methods in simulating indoor air-flows with forced and mixed (natural + forced) convection. A better performance against experiments is indicated with the RAST model in wall-bounded non-equilibrium indoor air-flows; this is due to its sensitivity toward both the shear and vorticity parameters.

CFD Simulation and Experimental Validation of Fluid Flow and Particle Transport in a Model of Alveolated Airways

PubMed Central

Ma, Baoshun; Ruwet, Vincent; Corieri, Patricia; Theunissen, Raf; Riethmuller, Michel; Darquenne, Chantal

2009-01-01

Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a scaled-up model of alveolated airways. Steady flow (Re = 0.13) of silicone oil was captured by particle image velocimetry (PIV), and the trajectories of 0.5 mm and 1.2 mm spherical iron beads (representing 0.7 to 14.6 μm aerosol in vivo) were obtained by particle tracking velocimetry (PTV). At twelve selected cross sections, the velocity profiles obtained by CFD matched well with those by PIV (within 1.7% on average). The CFD predicted trajectories also matched well with PTV experiments. These results showed that air flow and aerosol transport in models of human alveolated airways can be simulated by CFD techniques with reasonable accuracy. PMID:20161301

CFD Simulation and Experimental Validation of Fluid Flow and Particle Transport in a Model of Alveolated Airways.

PubMed

Ma, Baoshun; Ruwet, Vincent; Corieri, Patricia; Theunissen, Raf; Riethmuller, Michel; Darquenne, Chantal

2009-05-01

Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a scaled-up model of alveolated airways. Steady flow (Re = 0.13) of silicone oil was captured by particle image velocimetry (PIV), and the trajectories of 0.5 mm and 1.2 mm spherical iron beads (representing 0.7 to 14.6 mum aerosol in vivo) were obtained by particle tracking velocimetry (PTV). At twelve selected cross sections, the velocity profiles obtained by CFD matched well with those by PIV (within 1.7% on average). The CFD predicted trajectories also matched well with PTV experiments. These results showed that air flow and aerosol transport in models of human alveolated airways can be simulated by CFD techniques with reasonable accuracy.

Peclet number analysis of cross-flow in porous gas diffusion layer of polymer electrolyte membrane fuel cell (PEMFC).

PubMed

Suresh, P V; Jayanti, Sreenivas

2016-10-01

Adoption of hydrogen economy by means of using hydrogen fuel cells is one possible solution for energy crisis and climate change issues. Polymer electrolyte membrane (PEM) fuel cell, which is an important type of fuel cells, suffers from the problem of water management. Cross-flow is induced in some flow field designs to enhance the water removal. The presence of cross-flow in the serpentine and interdigitated flow fields makes them more effective in proper distribution of the reactants on the reaction layer and evacuation of water from the reaction layer than diffusion-based conventional parallel flow fields. However, too much of cross-flow leads to flow maldistribution in the channels, higher pressure drop, and membrane dehydration. In this study, an attempt has been made to quantify the amount of cross-flow required for effective distribution of reactants and removal of water in the gas diffusion layer. Unit cells containing two adjacent channels with gas diffusion layer (GDL) and catalyst layer at the bottom have been considered for the parallel, interdigitated, and serpentine flow patterns. Computational fluid dynamics-based simulations are carried out to study the reactant transport in under-the-rib area with cross-flow in the GDL. A new criterion based on the Peclet number is presented as a quantitative measure of cross-flow in the GDL. The study shows that a cross-flow Peclet number of the order of 2 is required for effective removal of water from the GDL. Estimates show that this much of cross-flow is not usually produced in the U-bends of Serpentine flow fields, making these areas prone to flooding.

Determination of the nuclear incompressibility from the rapidity-dependent elliptic flow in heavy-ion collisions at beam energies 0.4A-1.0A GeV

NASA Astrophysics Data System (ADS)

Wang, Yongjia; Guo, Chenchen; Li, Qingfeng; Le Fèvre, Arnaud; Leifels, Yvonne; Trautmann, Wolfgang

2018-03-01

Background: The nuclear incompressibility (K0) plays a crucial role in understanding diverse phenomena in nuclear structure and reactions, as well as in astrophysics. Heavy-ion-collision measurements in combination with transport model simulations serve as important tools for extracting the nuclear incompressibility. However, uncertainties in transport models (or model dependence) partly affect the reliability of the extracted result. Purpose: In the present work, by using the recently measured data of rapidity-dependent flows, we constrain the incompressibility of nuclear matter and analyze the impact of model uncertainties on the obtained value. Method: The method is based on the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model in which the Skyrme potential energy-density functional is introduced. Three different Skyrme interactions which give different incompressibilities varying from K0 = 201 to 271 MeV are adopted. The incompressibility is deduced from the comparison of the UrQMD model simulations and the FOPI data for rapidity-dependent elliptic flow in Au + Au collisions at beam energies 0.4A-1.0A GeV. Results: The elliptic flow v2 as a function of rapidity y0 can be well described by a quadratic fit v2 =v20 +v22 ṡ y02 . It is found that the quantity v2n defined by v2n = |v20 | + |v22 | is quite sensitive to the incompressibility K0 and the in-medium nucleon-nucleon cross section, but not sensitive to the slope parameter L of the nuclear symmetry energy. Conclusions: With the FU3FP4 parametrization of the in-medium nucleon-nucleon cross section, an averaged K0 = 220 ± 40 MeV is extracted from the v2n of free protons and deuterons. However, remaining systematic uncertainties, partly related to the choice of in-medium nucleon-nucleon cross sections, are of the same magnitude (± 40 MeV). Overall, the rapidity dependent elliptic flow supports a soft symmetric-matter equation-of-state.

Preliminary hydraulic analysis and implications for restoration of Noyes Slough, Fairbanks, Alaska

USGS Publications Warehouse

Burrows, Robert L.; Langley, Dustin E.; Evetts, David M.

2000-01-01

The present-day channels of the Chena River and Noyes Slough in downtown Fairbanks, Alaska, were formed as sloughs of the Tanana River, and part of the flow of the Tanana River occupied these waterways. Flow in these channels was reduced after the completion of Moose Creek Dike in 1945, and flow in the Chena River was affected by regulation from the Chena River Lakes Flood Control Project, which was completed in 1980. In 1981, flow in the Chena River was regulated for the first time by Moose Creek Dam, located about 20 miles upstream from Fairbanks. Constructed as part of the Chena River Lakes Flood Control Project, the dam was designed to reduce maximum flows to 12,000 cubic feet per second in downtown Fairbanks. Cross-section measurements made near the entrance to Noyes Slough show that the channel bed of the Chena River has been downcutting, thereby reducing the magnitude and duration of flow in the slough. Consequently the slough slowly is drying up. The slough provides habitat for wildlife such as ducks, beaver, and muskrat and is a fishery for anadromous and other resident species. Beavers have built 10 dams in the slough. Declining flow in the slough may endanger the remaining habitat. Residents of the community wish to restore flow in Noyes Slough to create a clean, flowing waterway during normal summer flows. The desire is to enhance the slough as a fishery and habitat for other wildlife and for recreational boating. During this study, existing and new data were compiled to determine past and present hydraulic interaction between the Chena River and Noyes Slough. The U.S. Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HECRAS) computer program was used to construct a model to use in evaluating alternatives for increasing flow in the slough. Under present conditions, the Chena must flow at about 2,400 cubic feet per second or more for flow to enter Noyes Slough. In an average year, water flows in Noyes Slough for 106 days during the open-water season, and maximum flow is about 1,050 cubic feet per second. The model was used to test a single method of increasing flow in Noyes Slough. A modified channel 40 feet wide and about 2 feet deeper within the existing slough channel was simulated by changing the cross-section geometry in the HECRAS model. The resulting model showed that flow in such a modified slough channel would begin at a flow of about 830 cubic feet per second in the Chena River and would increase to a maximum flow of about 1,440 cubic feet per second. In an average year, flow would continue for 158 days during the open-water season. Theoretically, enlarging the slough channel by lowering its bed could increase flow, but other solutions are possible. Possible obstacles to excavating the channel, such as bridges and utility crossings, and the destruction of desirable features such as beaver dams were not considered in the study. Further engineering and economic analyses would be needed to assess the cost of excavation and future maintenance of the modified channel. A computer-modeling program such as HECRAS may provide a means for testing other solutions.

CRT--Cascade Routing Tool to define and visualize flow paths for grid-based watershed models

USGS Publications Warehouse

Henson, Wesley R.; Medina, Rose L.; Mayers, C. Justin; Niswonger, Richard G.; Regan, R.S.

2013-01-01

The U.S. Geological Survey Cascade Routing Tool (CRT) is a computer application for watershed models that include the coupled Groundwater and Surface-water FLOW model, GSFLOW, and the Precipitation-Runoff Modeling System (PRMS). CRT generates output to define cascading surface and shallow subsurface flow paths for grid-based model domains. CRT requires a land-surface elevation for each hydrologic response unit (HRU) of the model grid; these elevations can be derived from a Digital Elevation Model raster data set of the area containing the model domain. Additionally, a list is required of the HRUs containing streams, swales, lakes, and other cascade termination features along with indices that uniquely define these features. Cascade flow paths are determined from the altitudes of each HRU. Cascade paths can cross any of the four faces of an HRU to a stream or to a lake within or adjacent to an HRU. Cascades can terminate at a stream, lake, or HRU that has been designated as a watershed outflow location.

A new simple dynamo model for solar activity cycle

NASA Astrophysics Data System (ADS)

Yokoi, Nobumitsu; Schmitt, Dieter

2015-04-01

The solar magnetic activity cycle has been investigated in an elaborated manner with several types of dynamo models [1]. In most of the current mean-field approaches, the inhomogeneity of the large-scale flow is treated as an essential ingredient in the mean magnetic field equation whereas it is completely neglected in the turbulence equation. In this work, a new simple model for the solar activity cycle is proposed. The present model differs from the previous ones mainly in two points. First, in addition to the helicity coefficient α, we consider a term related to the cross helicity, which represents the effect of the inhomogeneous mean flow, in the turbulent electromotive force [2, 3]. Second, this transport coefficient (γ) is not treated as an adjustable parameter, but the evolution equation for γ is simultaneously solved. The basic scenario for the solar activity cycle in this approach is as follows: The toroidal field is induced by the toroidal rotation in mediation by the turbulent cross helicity. Then due to the α or helicity effect, the poloidal field is generated from the toroidal field. The poloidal field induced by the α effect produces a turbulent cross helicity whose sign is opposite to the original one (negative cross-helicity production). The cross helicity with this opposite sign induces a reversed toroidal field. Results of the eigenvalue analysis of the model equations are shown, which confirm the above scenario. References [1] Charbonneau, Living Rev. Solar Phys. 7, 3 (2010). [2] Yoshizawa, A. Phys. Fluids B 2, 1589 (1990). [3] Yokoi, N. Geophys. Astrophys. Fluid Dyn. 107, 114 (2013).

Size-Tuned Plastic Flow Localization in Irradiated Materials at the Submicron Scale

NASA Astrophysics Data System (ADS)

Cui, Yinan; Po, Giacomo; Ghoniem, Nasr

2018-05-01

Three-dimensional discrete dislocation dynamics (3D-DDD) simulations reveal that, with reduction of sample size in the submicron regime, the mechanism of plastic flow localization in irradiated materials transitions from irradiation-controlled to an intrinsic dislocation source controlled. Furthermore, the spatial correlation of plastic deformation decreases due to weaker dislocation interactions and less frequent cross slip as the system size decreases, thus manifesting itself in thinner dislocation channels. A simple model of discrete dislocation source activation coupled with cross slip channel widening is developed to reproduce and physically explain this transition. In order to quantify the phenomenon of plastic flow localization, we introduce a "deformation localization index," with implications to the design of radiation-resistant materials.

Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

NASA Astrophysics Data System (ADS)

Zhu, Lei; He, Qing; Shen, Jian

2018-02-01

A numerical modeling study of the influence of the lateral flow on the estuarine exchange flow was conducted in the north passage of the Changjiang estuary. The lateral flows show substantial variabilities within a flood-ebb tidal cycle. The strong lateral flow occurring during flood tide is caused primarily by the unique cross-shoal flow that induces a strong northward (looking upstream) barotropic force near the surface and advects saltier water toward the northern part of the channel, resulting in a southward baroclinic force caused by the lateral density gradient. Thus, a two-layer structure of lateral flows is produced during the flood tide. The lateral flows are vigorous near the flood slack and the magnitude can exceed that of the along-channel tidal flow during that period. The strong vertical shear of the lateral flows and the salinity gradient in lateral direction generate lateral tidal straining, which are out of phase with the along-channel tidal straining. Consequently, stratification is enhanced at the early stage of the ebb tide. In contrast, strong along-channel straining is apparent during the late ebb tide. The vertical mixing disrupts the vertical density gradient, thus suppressing stratification. The impact of lateral straining on stratification during spring tide is more pronounced than that of along-channel straining during late flood and early ebb tides. The momentum balance along the estuary suggests that lateral flow can augment the residual exchange flow. The advection of lateral flows brings low-energy water from the shoal to the deep channel during the flood tide, whereas the energetic water is moved to the shoal via lateral advection during the ebb tide. The impact of lateral flow on estuarine circulation of this multiple-channel estuary is different from single-channel estuary. A model simulation by blocking the cross-shoal flow shows that the magnitudes of lateral flows and tidal straining are reduced. Moreover, the reduced lateral tidal straining results in a decrease in vertical stratification from the late flood to early ebb tides during the spring tide. By contrast, the along-channel tidal straining becomes dominant. The model results illustrate the important dynamic linkage between lateral flows and estuarine dynamics in the Changjiang estuary.

A Model of Small Capacity Power Plant in Tateli Village, North Sulawesi

NASA Astrophysics Data System (ADS)

Sangari, F. J.; Rompas, P. T. D.

2017-03-01

The electricity supply in North Sulawesi is still very limited so ubiquitous electric current outage. It makes rural communities have problems in life because most uses electrical energy. One of the solutions is a model of power plants to supply electricity in Tateli village, Minahasa, North Sulawesi, Indonesia. The objective of this research is to get the model that generate electrical energy for household needs through power plant that using a model of Picohydro with cross flow turbine in Tateli village. The method used the study of literature, survey the construction site of the power plant and the characteristics of the location being a place of research, analysis of hydropower ability and analyzing costs of power plant. The result showed that the design model of cross flow turbines used in pico-hydro hydropower installations is connected to a generator to produce electrical energy maximum of 3.29 kW for household needs. This analyze will be propose to local government of Minahasa, North Sulawesi, Indonesia to be followed.

Integrated analysis of numerical weather prediction and computational fluid dynamics for estimating cross-ventilation effects on inhaled air quality inside a factory

NASA Astrophysics Data System (ADS)

Murga, Alicia; Sano, Yusuke; Kawamoto, Yoichi; Ito, Kazuhide

2017-10-01

Mechanical and passive ventilation strategies directly impact indoor air quality. Passive ventilation has recently become widespread owing to its ability to reduce energy demand in buildings, such as the case of natural or cross ventilation. To understand the effect of natural ventilation on indoor environmental quality, outdoor-indoor flow paths need to be analyzed as functions of urban atmospheric conditions, topology of the built environment, and indoor conditions. Wind-driven natural ventilation (e.g., cross ventilation) can be calculated through the wind pressure coefficient distributions of outdoor wall surfaces and openings of a building, allowing the study of indoor air parameters and airborne contaminant concentrations. Variations in outside parameters will directly impact indoor air quality and residents' health. Numerical modeling can contribute to comprehend these various parameters because it allows full control of boundary conditions and sampling points. In this study, numerical weather prediction modeling was used to calculate wind profiles/distributions at the atmospheric scale, and computational fluid dynamics was used to model detailed urban and indoor flows, which were then integrated into a dynamic downscaling analysis to predict specific urban wind parameters from the atmospheric to built-environment scale. Wind velocity and contaminant concentration distributions inside a factory building were analyzed to assess the quality of the human working environment by using a computer simulated person. The impact of cross ventilation flows and its variations on local average contaminant concentration around a factory worker, and inhaled contaminant dose, were then discussed.

Longitudinal variation in lateral trapping of fine sediment in tidal estuaries: observations and a 3D exploratory model

NASA Astrophysics Data System (ADS)

Chen, Wei; de Swart, Huib E.

2018-03-01

This study investigates the longitudinal variation of lateral entrapment of suspended sediment, as is observed in some tidal estuaries. In particular, field data from the Yangtze Estuary are analysed, which reveal that in one cross-section, two maxima of suspended sediment concentration (SSC) occur close to the south and north sides, while in a cross-section 2 km down-estuary, only one SSC maximum on the south side is present. This pattern is found during both spring tide and neap tide, which are characterised by different intensities of turbulence. To understand longitudinal variation in lateral trapping of sediment, results of a new three-dimensional exploratory model are analysed. The hydrodynamic part contains residual flow due to fresh water input, density gradients and Coriolis force and due to channel curvature-induced leakage. Moreover, the model includes a spatially varying eddy viscosity that accounts for variation of intensity of turbulence over the spring-neap cycle. By imposing morphodynamic equilibrium, the two-dimensional distribution of sediment in the domain is obtained analytically by a novel procedure. Results reveal that the occurrence of the SSC maxima near the south side of both cross-sections is due to sediment entrapment by lateral density gradients, while the second SSC maximum near the north side of the first cross-section is by sediment transport due to curvature-induced leakage. Coriolis deflection of longitudinal flow also contributes the trapping of sediment near the north side. This mechanism is important in the upper estuary, where the flow due to lateral density gradients is weak.

Laminar flow studies of a low-temperature space radiator model using D-shaped tubes

NASA Technical Reports Server (NTRS)

Cintula, T. C.; Prok, G. M.; Johnston, D. B.

1972-01-01

Test results of a low-temperature space radiator model are presented. Radiator performance is evaluated with a low-thermal-conductivity fluid in laminar flow in D-shaped cross-section tubes. The test covered a Reynolds number range from 50 to 4500 and a fluid temperature range from 294 to 414 K (70 to 286 F). For low-temperature radiators, the fluid-to-surface temperature differential was predominately influenced by fluid temperature in laminar flow. Heat transfer and pressure drop for the radiator tube could be predicted within engineering accuracy from existing correlations.

Flame deformation and entrainment associated with an isothermal transverse fuel jet

NASA Technical Reports Server (NTRS)

Jenkins, D. W.; Karagozian, A. R.

1992-01-01

This paper describes an analytical model of an incompressible, isothermal reacting jet in crossflow. The model represents the flow in the jet cross-section by a counter rotating vortex pair, a flow structure that has been observed to dominate the jet behavior. The reaction surface surrounding the fuel jet is represented as a composite of strained diffusion flames that are stretched and deformed by the vortex pair flow. The results shed new light on the interaction between the vortex pair circulation and flame structure evolution and their relation to the concept of entrainment.

Laser cross-flow gas system

DOEpatents

Duncan, David B.

1992-01-01

A method and laser apparatus are disclosed which provide for a cross-flow of gas near one end of a laser discharge tube. The cross-flow of gas causes a concentration gradient which affects diffusion of contaminants in the discharge tube towards the cross-flow of the gas, which contaminants are then withdrawn from the discharge tube.

Numerical investigation of airflow in an idealised human extra-thoracic airway: a comparison study

PubMed Central

Chen, Jie; Gutmark, Ephraim

2013-01-01

Large eddy simulation (LES) technique is employed to numerically investigate the airflow through an idealised human extra-thoracic airway under different breathing conditions, 10 l/min, 30 l/min, and 120 l/min. The computational results are compared with single and cross hot-wire measurements, and with time-averaged flow field computed by standard k-ω and k-ω-SST Reynolds averaged Navier-Stokes (RANS) models and the Lattice-Boltzmann method (LBM). The LES results are also compared to root-mean-square (RMS) flow field computed by the Reynolds stress model (RSM) and LBM. LES generally gives better prediction of the time-averaged flow field than RANS models and LBM. LES also provides better estimation of the RMS flow field than both the RSM and the LBM. PMID:23619907

Small Scale Mass Flow Plug Calibration

NASA Technical Reports Server (NTRS)

Sasson, Jonathan

2015-01-01

A simple control volume model has been developed to calculate the discharge coefficient through a mass flow plug (MFP) and validated with a calibration experiment. The maximum error of the model in the operating region of the MFP is 0.54%. The model uses the MFP geometry and operating pressure and temperature to couple continuity, momentum, energy, an equation of state, and wall shear. Effects of boundary layer growth and the reduction in cross-sectional flow area are calculated using an in- integral method. A CFD calibration is shown to be of lower accuracy with a maximum error of 1.35%, and slower by a factor of 100. Effects of total pressure distortion are taken into account in the experiment. Distortion creates a loss in flow rate and can be characterized by two different distortion descriptors.

Air flow and pollution in a real, heterogeneous urban street canyon: A field and laboratory study

NASA Astrophysics Data System (ADS)

Karra, Styliani; Malki-Epshtein, Liora; Neophytou, Marina K.-A.

2017-09-01

In this work we investigate the influence of real world conditions, including heterogeneity and natural variability of background wind, on the air flow and pollutant concentrations in a heterogeneous urban street canyon using both a series of field measurements and controlled laboratory experiments. Field measurements of wind velocities and Carbon Monoxide (CO) concentrations were taken under field conditions in a heterogeneous street in a city centre at several cross-sections along the length of the street (each cross-section being of different aspect ratio). The real field background wind was in fact observed to be highly variable and thus different Intensive Observation Periods (IOPs) represented by a different mean wind velocity and different wind variability were defined. Observed pollution concentrations reveal high sensitivity to local parameters: there is a bias towards the side closer to the traffic lane; higher concentrations are found in the centre of the street as compared to cross-sections closer to the junctions; higher concentrations are found at 1.5 height from the ground than at 2.5 m height, all of which are of concern regarding pedestrian exposure to traffic-related pollution. A physical model of the same street was produced for the purpose of laboratory experiments, making some geometrical simplifications of complex volumes and extrusions. The physical model was tested in an Atmospheric Boundary Layer water channel, using simultaneously Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF), for flow visualisation as well as for quantitative measurement of concentrations and flow velocities. The wind field conditions were represented by a steady mean approach velocity in the laboratory simulation (essentially representing periods of near-zero wind variability). The laboratory investigations showed a clear sensitivity of the resulting flow field to the local geometry and substantial three-dimensional flow patterns were observed throughout the modelled street. The real-field observations and the laboratory measurements were compared. Overall, we found that lower variability in the background wind does not necessarily ensure a better agreement between the airflow velocity measured in the field and in the lab. In fact, it was observed that in certain cross sections, the airflow was more affected by the particular complex architectural features such as building extrusions and balconies, which were not represented in the simplified physical model tested in the laboratory, than by the real wind field variability. For wind speed comparisons the most favourable agreement (36.6% of the compared values were within a factor of 2) was found in the case of lowest wind variability and in the section with the most simple geometry where the physical lab model was most similar to the real street. For wind direction comparisons the most favourable agreement (45.5% of the compared values was within ±45°) was found in the case with higher wind variability but in the cross-sections with more homogeneous geometrical features. Street canyons are often simplified in research and are often modelled as homogenous symmetrical canyons under steady flow, for practical purposes; our study as a whole demonstrates that natural variability and heterogeneity play a large role in how pollution disperses throughout the street, and therefore further detail in models is vital to understand real world conditions.

Numerical simulation of hydrothermal circulation in the Cascade Range, north-central Oregon

USGS Publications Warehouse

Ingebritsen, S.E.; Paulson, K.M.

1990-01-01

Alternate conceptual models to explain near-surface heat-flow observations in the central Oregon Cascade Range involve (1) an extensive mid-crustal magmatic heat source underlying both the Quaternary arc and adjacent older rocks or (2) a narrower deep heat source which is flanked by a relatively shallow conductive heat-flow anomaly caused by regional ground-water flow (the lateral-flow model). Relative to the mid-crustal heat source model, the lateral-flow model suggests a more limited geothermal resource base, but a better-defined exploration target. We simulated ground-water flow and heat transport through two cross sections trending west from the Cascade range crest in order to explore the implications of the two models. The thermal input for the alternate conceptual models was simulated by varying the width and intensity of a basal heat-flow anomaly and, in some cases, by introducing shallower heat sources beneath the Quaternary arc. Near-surface observations in the Breitenbush Hot Springs area are most readily explained in terms of lateral heat transport by regional ground-water flow; however, the deep thermal structure still cannot be uniquely inferred. The sparser thermal data set from the McKenzie River area can be explained either in terms of deep regional ground-water flow or in terms of a conduction-dominated system, with ground-water flow essentially confined to Quaternary rocks and fault zones.

Mapping the response of riparian vegetation to possible flow reductions in the Snake River, Idaho

USGS Publications Warehouse

Johnson, W. Carter; Dixon, Mark D.; Simons, Robert W.; Jenson, Susan; Larson, Kevin

1995-01-01

This study was initiated to determine the general effects of potential flow reductions in the middle Snake River (Swan Falls Dam downstream to the Idaho-Oregon border) on its riparian vegetation. Considerable water from the river is currently used to irrigate the adjacent Snake River Plain, and increased demand for water in the future is likely. The problem was subdivided into several research components including: field investigation of the existing riparian vegetation and river environment, hydrological modeling to calculate the effects of one flow scenario on hydrological regime, and integration of vegetation and hydrological modeling results with a Geographic Information System (GIs) to map the riverbed, island, and bank conditions under the scenario flow. Field work was conducted in summer 1990. Riparian vegetation along 40 U.S. Geological Survey cross-sections was sampled at approximately 1.25 mile intervals within the 50 mile long study area. Cross-section and flow data were provided by the U.S. Geological. Survey. GIs mapping of land/water cover using ARC/INFO was based on 1987 aerial photographs. Riverbed contour maps were produced by linking cross-section data, topographic contouring software (anudem), and GIs. The maps were used to spatially display shallow areas in the channel likely to become vegetated under reduced flow conditions. The scenario would reduce flow by approximately 20% (160 MAF) and lower the river an average of 0.5 ft. The scenario flow could cause a drop in the elevation of the riparian zone comparable to the drop in mean river level and expansion of the lower riparian zone into shallow areas of the channel. The GIs maps showed that the shallow areas of the channel more likely to become vegetated under the scenario flow are located in wide reaches near islands. Some possible ecological consequences of the scenario flow include a greater area of riparian habitat, reduced flow velocity and sedimentation in shallow channels leading to channel deactivation, increased island visitation and nest predation by predatory mammals due to loss of a water barrier between some islands and banks, and larger populations of alien plant species in the new riparian vegetation.

The study of the influence of the diameter ratio and blade number to the performance of the cross flow wind turbine by using 2D computational fluid dynamics modeling

NASA Astrophysics Data System (ADS)

Tjahjana, Dominicus Danardono Dwi Prija; Purbaningrum, Pradityasari; Hadi, Syamsul; Wicaksono, Yoga Arob; Adiputra, Dimas

2018-02-01

Cross flow turbine can be one of the alternative energies for regions with low wind speed. Collision between wind and the blades which happened two times caused the cross flow turbine to have high power coefficient. Some factors that influence the turbine power coefficient are diameter ratio and blade number. The objective of the research was to study the effect of the diameter ratio and the blade number to the cross flow wind turbine performance. The study was done in two dimensional (2D) computational fluid dynamics (CFD) simulation method using the ANSYS-Fluent software. The turbine diameter ratio were 0.58, 0.63, 0.68 and 0.73. The diameter ratio resulting in the highest power coefficient value was then simulated by varying the number of blades, namely 16, 20 and 24. Each variation was tested on the wind speed of 2 m/s and at the tip speed ratio (TSR) of 0.1 to 0.4 with the interval of 0.1. The wind turbine with the ratio diameter of 0.68 and the number of blades of 20 generated the highest power coefficient of 0.5 at the TSR of 0.3.

Robust control of drag and lateral dynamic response for road vehicles exposed to cross-wind gusts

NASA Astrophysics Data System (ADS)

Pfeiffer, Jens; King, Rudibert

2018-03-01

A robust closed-loop active flow control strategy for road vehicles under unsteady cross-wind conditions is presented. It is designed based on black-box models identified from experimental data for a 3D bluff body equipped with Coanda actuators along the rear edges. The controller adjusts the blowing rates of the actuators individually, achieving a drag reduction of about 15% while simultaneously improving cross-wind sensitivity. Hereby, the lateral vehicle dynamics and driver behavior are taken into account and replicated in the wind tunnel via a novel model support system. The effectiveness of the control strategy is demonstrated via cross-wind gust experiments.

An expert judgment model applied to estimating the safety effect of a bicycle facility.

PubMed

Leden, L; Gårder, P; Pulkkinen, U

2000-07-01

This paper presents a risk index model that can be used for assessing the safety effect of countermeasures. The model estimates risk in a multiplicative way, which makes it possible to analyze the impact of different factors separately. Expert judgments are incorporated through a Bayesian error model. The variance of the risk estimate is determined by Monte-Carlo simulation. The model was applied to assess the safety effect of a new design of a bicycle crossing. The intent was to gain safety by raising the crossings to reduce vehicle speeds and by making the crossings more visible by painting them in a bright color. Before the implementations, bicyclists were riding on bicycle crossings of conventional Swedish type, i.e. similar to crosswalks but delineated by white squares rather than solid lines or zebra markings. Automobile speeds were reduced as anticipated. However, it seems as if the positive effect of this was more or less canceled out by increased bicycle speeds. The safety per bicyclist was still improved by approximately 20%. This improvement was primarily caused by an increase in bicycle flow, since the data show that more bicyclists at a given location seem to benefit their safety. The increase in bicycle flow was probably caused by the new layout of the crossings since bicyclists perceived them as safer and causing less delay. Some future development work is suggested. Pros and cons with the used methodology are discussed. The most crucial parameter to be added is probably a model describing the interaction between motorists and bicyclists, for example, how risk is influenced by the lateral position of the bicyclist in relation to the motorist. It is concluded that the interaction seems to be optimal when both groups share the roadway.

Target Lagrangian kinematic simulation for particle-laden flows.

PubMed

Murray, S; Lightstone, M F; Tullis, S

2016-09-01

The target Lagrangian kinematic simulation method was motivated as a stochastic Lagrangian particle model that better synthesizes turbulence structure, relative to stochastic separated flow models. By this method, the trajectories of particles are constructed according to synthetic turbulent-like fields, which conform to a target Lagrangian integral timescale. In addition to recovering the expected Lagrangian properties of fluid tracers, this method is shown to reproduce the crossing trajectories and continuity effects, in agreement with an experimental benchmark.

Laser cross-flow gas system

DOEpatents

Duncan, D.B.

1992-11-24

A method and laser apparatus are disclosed which provide for a cross-flow of gas near one end of a laser discharge tube. The cross-flow of gas causes a concentration gradient which affects diffusion of contaminants in the discharge tube towards the cross-flow of the gas, which contaminants are then withdrawn from the discharge tube. 1 figure.

Cyanide removal from industrial wastewater by cross-flow nanofiltration: transport modeling and economic evaluation.

PubMed

Pal, Parimal; Bhakta, Pamela; Kumar, Ramesh

2014-08-01

A modeling and simulation study, along with an economic analysis, was carried out for the separation of cyanide from industrial wastewater using a flat sheet cross-flow nanofiltration membrane module. With the addition of a pre-microfiltration step, nanofiltration was carried out using real coke wastewater under different operating conditions. Under the optimum operating pressure of 13 bars and a pH of 10.0, a rate of more than 95% separation of cyanide was achieved. That model predictions agreed very well with the experimental findings, as is evident in the Willmott d-index value (> 0.95) and relative error (< 0.1). Studies were carried out with industrial wastewater instead of a synthetic solution, and an economic analysis was also done, considering the capacity of a running coking plant. The findings are likely to be very useful in the scale-up and design of industrial plants for the treatment of cyanide-bearing wastewater.

Effect of interactions between vehicles and pedestrians on fuel consumption and emissions

NASA Astrophysics Data System (ADS)

Li, Xiang; Sun, Jian-Qiao

2014-12-01

This paper presents a study of variations of fuel consumption and emissions of vehicles due to random street crossings of pedestrians. The pedestrian and vehicle movement models as well as the interaction model between the two entities are presented. Extensive numerical simulations of single and multiple cars are carried out to investigate the traffic flow rate, vehicle average speed, fuel consumption, CO, HC and NOx emissions. Generally more noncompliant road-crossings of pedestrians lead to higher level of fuel consumptions and emissions of vehicles, and the traffic situation can be improved by imposing higher vehicle speed limit to some extent. Different traffic characteristics in low and high vehicle density regions are studied. The traffic flow is more influenced by crossing pedestrians in the low vehicle density region, while in the high vehicle density region, the interactions among vehicles dominate. The main contribution of this paper lies in the qualitative analysis of the impact of the interactions between pedestrians and vehicles on the traffic, its energy economy and emissions.

Mathematical Model of Solidification During Electroslag Casting of Pilger Roll

NASA Astrophysics Data System (ADS)

Liu, Fubin; Li, Huabing; Jiang, Zhouhua; Dong, Yanwu; Chen, Xu; Geng, Xin; Zang, Ximin

A mathematical model for describing the interaction of multiple physical fields in slag bath and solidification process in ingot during pilger roll casting with variable cross-section which is produced by the electroslag casting (ESC) process was developed. The commercial software ANSYS was applied to calculate the electromagnetic field, magnetic driven fluid flow, buoyancy-driven flow and heat transfer. The transportation phenomenon in slag bath and solidification characteristic of ingots are analyzed for variable cross-section with variable input power under the conditions of 9Cr3NiMo steel and 70%CaF2 - 30%Al2O3 slag system. The calculated results show that characteristic of current density distribution, velocity patterns and temperature profiles in the slag bath and metal pool profiles in ingot have distinct difference at variable cross-sections due to difference of input power and cooling condition. The pool shape and the local solidification time (LST) during Pilger roll ESC process are analyzed.

Experimental research on crossing shock wave boundary layer interactions

NASA Astrophysics Data System (ADS)

Settles, G. S.; Garrison, T. J.

1994-10-01

An experimental research effort of the Penn State Gas Dynamics Laboratory on the subject of crossing shock wave boundary layer interactions is reported. This three year study was supported by AFOSR Grant 89-0315. A variety of experimental techniques were employed to study the above phenomena including planar laser scattering flowfield visualization, kerosene lampblack surface flow visualization, laser-interferometer skin friction surveys, wall static pressure measurements, and flowfield five-hole probe surveys. For a model configuration producing two intersecting shock waves, measurements were made for a range of oblique shock strengths at freestream Mach numbers of 3.0 and 3.85. Additionally, measurements were made at Mach 3.85 for a configuration producing three intersecting waves. The combined experimental dataset was used to formulate the first detailed flowfield models of the crossing-shock and triple-shock wave/boundary layer interactions. The structure of these interactions was found to be similar over a broad range of interaction strengths and is dominated by a large, separated, viscous flow region.

Circulation on the Inner-Shelf of Long Bay, South Carolina: Vertical Current Variability and Evidence for Cross-Shelf Variation in Near-Bed Currents

NASA Astrophysics Data System (ADS)

Gutierrez, B. T.; Voulgaris, G.; Work, P. A.; Seim, H.; Warner, J. C.

2004-12-01

Cross-shelf variations of near-bed currents and variations in vertical flow were investigated on the inner shelf of Long Bay, South Carolina during the spring and fall of 2001. Current meters sampled near-bed currents at six locations as well as vertical current profiles at three of the sites. The observations showed that the tides accounted for approximately 45-66% of the flow variability. The dominant tidal component, the semi-diurnal constituent M2, exhibited tidal ellipse orientations that are increasingly aligned with the coast closer to the shore. The largest M2 current magnitudes were identified closest to shore and over the top of a sand shoal located 5.5 km offshore of Myrtle Beach. The remaining flow variability was associated with sub-tidal flows which respond to the passage of low-pressure systems across the region. These weather systems were characterized by periods of southwesterly winds in advance of low-pressure centers followed by northeasterly winds as the systems passed over the study area. When strong southwesterly winds persisted, surface flow was oriented approximately in the direction of the wind. At the same time near-bottom flows were also directed to the northeast in the direction of the wind except during periods of stratification when vertical current profiles suggest near-bed onshore flow. The stratified flows were observed mainly during the spring deployment. For periods of strong northeasterly winds, currents were directed alongshore to the southwest and exhibited little variation throughout the water column. These observations are consistent with recent field and modeling studies for the inner-shelf. Comparison of the near-bed flow measurements during the fall deployment revealed a cross-shore gradient in alongshore flow during periods of strong northeasterly winds. During these episodes flows at the offshore measurement stations were oriented in the direction of the wind, while flows closest to shore occurred in the opposite direction. These observations reveal 1) conditions which contribute to cross-shore transport and 2) the presence of an alongshore flow gradient which may affect sediment transport patterns during certain meteorological conditions.

Applications of Quantum Theory of Atomic and Molecular Scattering to Problems in Hypersonic Flow

NASA Technical Reports Server (NTRS)

Malik, F. Bary

1995-01-01

The general status of a grant to investigate the applications of quantum theory in atomic and molecular scattering problems in hypersonic flow is summarized. Abstracts of five articles and eleven full-length articles published or submitted for publication are included as attachments. The following topics are addressed in these articles: fragmentation of heavy ions (HZE particles); parameterization of absorption cross sections; light ion transport; emission of light fragments as an indicator of equilibrated populations; quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen; evaluation of NUCFRG2, the semi-empirical nuclear fragmentation database; investigation of the single- and double-ionization of He by proton and anti-proton collisions; Bose-Einstein condensation of nuclei; and a liquid drop model in HZE particle fragmentation by hydrogen.

Evaluation of Liquid Fuel Spray Models for Hybrid RANS/LES and DLES Prediction of Turbulent Reactive Flows

NASA Astrophysics Data System (ADS)

Afshar, Ali

An evaluation of Lagrangian-based, discrete-phase models for multi-component liquid sprays encountered in the combustors of gas turbine engines is considered. In particular, the spray modeling capabilities of the commercial software, ANSYS Fluent, was evaluated. Spray modeling was performed for various cold flow validation cases. These validation cases include a liquid jet in a cross-flow, an airblast atomizer, and a high shear fuel nozzle. Droplet properties including velocity and diameter were investigated and compared with previous experimental and numerical results. Different primary and secondary breakup models were evaluated in this thesis. The secondary breakup models investigated include the Taylor analogy breakup (TAB) model, the wave model, the Kelvin-Helmholtz Rayleigh-Taylor model (KHRT), and the Stochastic secondary droplet (SSD) approach. The modeling of fuel sprays requires a proper treatment for the turbulence. Reynolds-averaged Navier-Stokes (RANS), large eddy simulation (LES), hybrid RANS/LES, and dynamic LES (DLES) were also considered for the turbulent flows involving sprays. The spray and turbulence models were evaluated using the available benchmark experimental data.

Simulated water-level and water-quality changes in the bolson-fill aquifer, Post Headquarters area, White Sands Missile Range, New Mexico

USGS Publications Warehouse

Risser, D.W.

1988-01-01

The quantity of freshwater available in the Post Headquarters well field, White Sand Missile Range, New Mexico, is limited and its quality is threatened by saltwater enroachment. A three-dimensional, finite-difference, groundwater flow model and a cross-sectional, density-dependent solute-transport model were constructed to simulate possible future water level declines and water quality changes in the Post Headquarters well field. A six-layer flow model was constructed using hydraulic-conductivity values in the upper 600 ft of saturated aquifer ranging from 0.1 to 10 ft/day, specific yield of 0.15, and average recharge of about 1,590 acre-ft/yr. Water levels simulated by the model closely matched measured water levels for 1948-82. Possible future water level changes for 1983-2017 were simulated using rates of groundwater withdrawal of 1,033 and 2 ,066 acre-ft/year and wastewater return flow of 0 or 30% of the groundwater withdrawal rate. The cross-sectional solute-transport model indicated that the freshwater zone is about 1,500 to 2,000 ft thick beneath the well field. Transient simulations show that solutes probably will move laterally toward the well field rather than from beneath the well field. (USGS)

Numerical Analysis of Ground-Water Flow and Salinity in the Ewa Area, Oahu, Hawaii

USGS Publications Warehouse

Oki, Delwyn S.; Souza, William R.; Bolke, Edward I.; Bauer, Glenn R.

1996-01-01

The coastal plain in the Ewa area of southwestern Oahu, Hawaii, is part of a larger, nearly continuous sedimentary coastal plain along Oahu's southern coast. The coastal sediments are collectively known as caprock because they impede the free discharge of ground water from the underlying volcanic aquifers. The caprock is a layered sedimentary system consisting of interbedded marine and terrestrial sediments of both high and low permeability. Before sugarcane cultivation ended in late 1994, shallow ground water from the upper limestone unit, which is about 60 to 200 feet thick, was used primarily for irrigation of sugarcane. A cross-sectional ground-water flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in the Ewa area. Controls considered were: (1) overall caprock hydraulic conductivity, (2) stratigraphic variations of hydraulic conductivity in the caprock, and (3) recharge. In addition, the effects of a marina excavation were evaluated. Within the caprock, variations in hydraulic conductivity, caused by caprock stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of ground-water flow and the distribution of water levels and salinity. Model results also show that a reduction of recharge will result in increased salinity throughout the caprock with the greatest change in the upper limestone layer. In addition, the model indicates that excavation of an ocean marina will lower water levels in the upper limestone layer. Results of cross-sectional modeling confirm the general ground-water flow pattern that would be expected in the layered sedimentary system in the Ewa caprock. Ground-water flow is: (1) predominantly upward in the low-permeability sedimentary units, and (2) predominantly horizontal in the high-permeability sedimentary units.

The Effect of Cross Flow on Slat Noise

NASA Technical Reports Server (NTRS)

Lockard, David P.; Choudhari, Meelan M.

2010-01-01

This paper continues the computational examination (AIAA Journal, Vol. 45, No. 9, 2007, pp. 2174-2186) of the unsteady flow within the slat cove region of a multi-element high-lift airfoil configuration. Two simulations have been performed to examine the effect of cross flow on the near-field fluctuations and far-field acoustics. The cross flow was imposed by changing the free-stream velocity vector and modifying the Reynolds number. The cross flow does appear to alter the dynamics in the cove region, but the impact on the noise seems to be more dependent on the flow conditions. However, separating out the true effects of the cross flow from those of the Mach and Reynolds number would require additional calculations to isolate those effects.

Sources of uncertainty in flood inundation maps

USGS Publications Warehouse

Bales, J.D.; Wagner, C.R.

2009-01-01

Flood inundation maps typically have been used to depict inundated areas for floods having specific exceedance levels. The uncertainty associated with the inundation boundaries is seldom quantified, in part, because all of the sources of uncertainty are not recognized and because data available to quantify uncertainty seldom are available. Sources of uncertainty discussed in this paper include hydrologic data used for hydraulic model development and validation, topographic data, and the hydraulic model. The assumption of steady flow, which typically is made to produce inundation maps, has less of an effect on predicted inundation at lower flows than for higher flows because more time typically is required to inundate areas at high flows than at low flows. Difficulties with establishing reasonable cross sections that do not intersect and that represent water-surface slopes in tributaries contribute additional uncertainties in the hydraulic modelling. As a result, uncertainty in the flood inundation polygons simulated with a one-dimensional model increases with distance from the main channel.

Exact solutions of the Navier-Stokes equations generalized for flow in porous media

NASA Astrophysics Data System (ADS)

Daly, Edoardo; Basser, Hossein; Rudman, Murray

2018-05-01

Flow of Newtonian fluids in porous media is often modelled using a generalized version of the full non-linear Navier-Stokes equations that include additional terms describing the resistance to flow due to the porous matrix. Because this formulation is becoming increasingly popular in numerical models, exact solutions are required as a benchmark of numerical codes. The contribution of this study is to provide a number of non-trivial exact solutions of the generalized form of the Navier-Stokes equations for parallel flow in porous media. Steady-state solutions are derived in the case of flows in a medium with constant permeability along the main direction of flow and a constant cross-stream velocity in the case of both linear and non-linear drag. Solutions are also presented for cases in which the permeability changes in the direction normal to the main flow. An unsteady solution for a flow with velocity driven by a time-periodic pressure gradient is also derived. These solutions form a basis for validating computational models across a wide range of Reynolds and Darcy numbers.

Flow behavior in the Wright Brothers Facility

NASA Technical Reports Server (NTRS)

Genn, S.

1984-01-01

It has become increasingly apparent that a reexamination of the flow characteristics in the low speed Wright Brothers Facility (WBF) is of some importance in view of recent improvements in the precision of the data acquisition system. In particular, the existence of local regions of separation, if any, in back portions of the circuit, and possible related unsteadiness, are of interest. Observations from that initial experiment did indicate some unsteady air flow problems in the cross leg, and thereafter the test region (Section A) was calibrated quantitatively. The intent was to learn something about the effect of upstream intermittent behavior flow on the test section flow, as well as to provide an extensive calibration as a standard for the effects induced by future alteration of the tunnel. Distributions of total pressure coefficients were measured first at one cross-section plane of the test section, namely the model station. Data were obtained for several tunnel speeds. The reduced data yielded an unexpected distribution involving larger pressures along the inside wall.

Modeling of Flow Transition Using an Intermittency Transport Equation

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.

1999-01-01

A new transport equation for intermittency factor is proposed to model transitional flows. The intermittent behavior of the transitional flows is incorporated into the computations by modifying the eddy viscosity, mu(sub t), obtainable from a turbulence model, with the intermittency factor, gamma: mu(sub t, sup *) = gamma.mu(sub t). In this paper, Menter's SST model (Menter, 1994) is employed to compute mu(sub t) and other turbulent quantities. The proposed intermittency transport equation can be considered as a blending of two models - Steelant and Dick (1996) and Cho and Chung (1992). The former was proposed for near-wall flows and was designed to reproduce the streamwise variation of the intermittency factor in the transition zone following Dhawan and Narasimha correlation (Dhawan and Narasimha, 1958) and the latter was proposed for free shear flows and was used to provide a realistic cross-stream variation of the intermittency profile. The new model was used to predict the T3 series experiments assembled by Savill (1993a, 1993b) including flows with different freestream turbulence intensities and two pressure-gradient cases. For all test cases good agreements between the computed results and the experimental data are observed.

Hydrogeology of well-field areas near Tampa, Florida; Phase I, development and documentation of a two-dimensional finite-difference model for simulation of steady-state ground-water flow

USGS Publications Warehouse

Hutchinson, C.B.; Johnson, Dale M.; Gerhart, James M.

1981-01-01

A two-dimensional finite-difference model was developed for simulation of steady-state ground-water flow in the Floridan aquifer throughout a 932-square-mile area, which contains nine municipal well fields. The overlying surficial aquifer contains a constant-head water table and is coupled to the Floridan aquifer by a leakage term that represents flow through a confining layer separating the two aquifers. Under the steady-state condition, all storage terms are set to zero. Utilization of the head-controlled flux condition allows head and flow to vary at the model-grid boundaries. Procedures are described to calibrate the model, test its sensitivity to input-parameter errors, and verify its accuracy for predictive purposes. Also included are attachments that describe setting up and running the model. An example model-interrogation run shows anticipated drawdowns that should result from pumping at the newly constructed Cross Bar Ranch and Morris Bridge well fields. (USGS)

Influence of omni-directional guide vane on the performance of cross-flow rotor for urban wind energy

NASA Astrophysics Data System (ADS)

Wicaksono, Yoga Arob; Tjahjana, Dominicus Danardono Dwi Prija; Hadi, Syamsul

2018-02-01

Vertical axis wind turbine like cross-flow rotor have some advantage there are, high self-starting torque, low noise, and high stability; so, it can be installed in the urban area to produce electricity. But, the urban area has poor wind condition, so the cross-flow rotor needs a guide vane to increase its performance. The aim of this study is to determine experimentally the effect of Omni-Directional Guide Vane (ODGV) on the performance of a cross-flow wind turbine. Wind tunnel experiment has been carried out for various configurations. The ODGV was placed around the cross-flow rotor in order to increase ambient wind environment of the wind turbine. The maximum power coefficient is obtained as Cpmax = 0.125 at 60° wind direction. It was 21.46% higher compared to cross-flow wind turbine without ODGV. This result showed that the ODGV able to increase the performance of the cross-flow wind turbine.

Measurement of flow separation in a human vocal folds model

NASA Astrophysics Data System (ADS)

Šidlof, Petr; Doaré, Olivier; Cadot, Olivier; Chaigne, Antoine

2011-07-01

The paper provides experimental data on flow separation from a model of the human vocal folds. Data were measured on a four times scaled physical model, where one vocal fold was fixed and the other oscillated due to fluid-structure interaction. The vocal folds were fabricated from silicone rubber and placed on elastic support in the wall of a transparent wind tunnel. A PIV system was used to visualize the flow fields immediately downstream of the glottis and to measure the velocity fields. From the visualizations, the position of the flow separation point was evaluated using a semiautomatic procedure and plotted for different airflow velocities. The separation point position was quantified relative to the orifice width separately for the left and right vocal folds to account for flow asymmetry. The results indicate that the flow separation point remains close to the narrowest cross-section during most of the vocal fold vibration cycle, but moves significantly further downstream shortly prior to and after glottal closure.

Water tunnel flow visualization using a laser

NASA Technical Reports Server (NTRS)

Beckner, C.; Curry, R. E.

1985-01-01

Laser systems for flow visualization in water tunnels (similar to the vapor screen technique used in wind tunnels) can provide two-dimensional cross-sectional views of complex flow fields. This parametric study documents the practical application of the laser-enhanced visualization (LEV) technique to water tunnel testing. Aspects of the study include laser power levels, flow seeding (using flourescent dyes and embedded particulates), model preparation, and photographic techniques. The results of this study are discussed to provide potential users with basic information to aid in the design and setup of an LEV system.

Development of Flow and Heat Transfer Models for the Carbon Fiber Rope in Nozzle Joints of the Space Shuttle Reusable Solid Rocket Motor

NASA Technical Reports Server (NTRS)

Wang, Q.; Ewing, M. E.; Mathias, E. C.; Heman, J.; Smith, C.; McCool, Alex (Technical Monitor)

2001-01-01

Methodologies have been developed for modeling both gas dynamics and heat transfer inside the carbon fiber rope (CFR) for applications in the space shuttle reusable solid rocket motor joints. Specifically, the CFR is modeled using an equivalent rectangular duct with a cross-section area, friction factor and heat transfer coefficient such that this duct has the same amount of mass flow rate, pressure drop, and heat transfer rate as the CFR. An equation for the friction factor is derived based on the Darcy-Forschheimer law and the heat transfer coefficient is obtained from pipe flow correlations. The pressure, temperature and velocity of the gas inside the CFR are calculated using the one-dimensional Navier-Stokes equations. Various subscale tests, both cold flow and hot flow, have been carried out to validate and refine this CFR model. In particular, the following three types of testing were used: (1) cold flow in a RSRM nozzle-to-case joint geometry, (2) cold flow in a RSRM nozzle joint No. 2 geometry, and (3) hot flow in a RSRM nozzle joint environment simulator. The predicted pressure and temperature history are compared with experimental measurements. The effects of various input parameters for the model are discussed in detail.

Measurements of Crossflow Instability Modes for HIFiRE 5 at Angle of Attack

DTIC Science & Technology

2017-11-15

temperature sensitive paint (TSP) did not show any vortices in noisy flow, and only revealed vortices in quiet flow for a subset of the Reynolds numbers for...evidence of traveling crossflow waves with a noisy freestream, even though the spectra of the surface pressure signals showed an expected progression...cone ray describing the minor axis, and retains a 2:1 elliptical cross-section to the tip. Figure 1: Photograph of model The model is made of solid 15

Identifying variably saturated water-flow patterns in a steep hillslope under intermittent heavy rainfall

USGS Publications Warehouse

El-Kadi, A. I.; Torikai, J.D.

2001-01-01

The objective of this paper is to identify water-flow patterns in part of an active landslide, through the use of numerical simulations and data obtained during a field study. The approaches adopted include measuring rainfall events and pore-pressure responses in both saturated and unsaturated soils at the site. To account for soil variability, the Richards equation is solved within deterministic and stochastic frameworks. The deterministic simulations considered average water-retention data, adjusted retention data to account for stones or cobbles, retention functions for a heterogeneous pore structure, and continuous retention functions for preferential flow. The stochastic simulations applied the Monte Carlo approach which considers statistical distribution and autocorrelation of the saturated conductivity and its cross correlation with the retention function. Although none of the models is capable of accurately predicting field measurements, appreciable improvement in accuracy was attained using stochastic, preferential flow, and heterogeneous pore-structure models. For the current study, continuum-flow models provide reasonable accuracy for practical purposes, although they are expected to be less accurate than multi-domain preferential flow models.

Modelling the effect of laminar axially directed blood flow on the dissolution of non-occlusive blood clots.

PubMed

Sersa, I; Vidmar, J; Grobelnik, B; Mikac, U; Tratar, G; Blinc, A

2007-06-07

Axially directed blood plasma flow can significantly accelerate thrombolysis of non-occlusive blood clots. Viscous forces caused by shearing of blood play an essential role in this process, in addition to biochemical fibrinolytic reactions. An analytical mathematical model based on the hypothesis that clot dissolution dynamics is proportional to the power of the flowing blood plasma dissipated along the clot is presented. The model assumes cylindrical non-occlusive blood clots with the flow channel in the centre, in which the flow is assumed to be laminar and flow rate constant at all times during dissolution. Effects of sudden constriction on the flow and its impact on the dissolution rate are also considered. The model was verified experimentally by dynamic magnetic resonance (MR) microscopy of artificial blood clots dissolving in an in vitro circulation system, containing plasma with a magnetic resonance imaging contrast agent and recombinant tissue-type plasminogen activator (rt-PA). Sequences of dynamically acquired 3D low resolution MR images of entire clots and 2D high resolution MR images of clots in the axial cross-section were used to evaluate the dissolution model by fitting it to the experimental data. The experimental data fitted well to the model and confirmed our hypothesis.

Paleomagnetic correlation of basalt flows in selected coreholes near the Advanced Test Reactor Complex, the Idaho Nuclear Technology and Engineering Center, and along the southern boundary, Idaho National Laboratory, Idaho

USGS Publications Warehouse

Hodges, Mary K.V.; Champion, Duane E.

2016-10-03

The U.S. Geological Survey, in cooperation with the U.S. Department of Energy, used paleomagnetic data from 18 coreholes to construct three cross sections of subsurface basalt flows in the southern part of the Idaho National Laboratory (INL). These cross sections, containing descriptions of the subsurface horizontal and vertical distribution of basalt flows and sediment layers, will be used in geological studies, and to construct numerical models of groundwater flow and contaminant transport.Subsurface cross sections were used to correlate surface vents to their subsurface flows intersected by coreholes, to correlate subsurface flows between coreholes, and to identify possible subsurface vent locations of subsurface flows. Correlations were identified by average paleomagnetic inclinations of flows, and depth from land surface in coreholes, normalized to the North American Datum of 1927. Paleomagnetic data were combined, in some cases, with other data, such as radiometric ages of flows. Possible vent locations of buried basalt flows were identified by determining the location of the maximum thickness of flows penetrated by more than one corehole.Flows from the surface volcanic vents Quaking Aspen Butte, Vent 5206, Mid Butte, Lavatoo Butte, Crater Butte, Pond Butte, Vent 5350, Vent 5252, Tin Cup Butte, Vent 4959, Vent 5119, and AEC Butte are found in coreholes, and were correlated to the surface vents by matching their paleomagnetic inclinations, and in some cases, their stratigraphic positions.Some subsurface basalt flows that do not correlate to surface vents, do correlate over several coreholes, and may correlate to buried vents. Subsurface flows which correlate across several coreholes, but not to a surface vent include the D3 flow, the Big Lost flow, the CFA buried vent flow, the Early, Middle, and Late Basal Brunhes flows, the South Late Matuyama flow, the Matuyama flow, and the Jaramillo flow. The location of vents buried in the subsurface by younger basalt flows can be inferred if their flows are penetrated by several coreholes, by tracing the flows in the subsurface, and determining where the greatest thickness occurs.

Cross Flow Parameter Calculation for Aerodynamic Analysis

NASA Technical Reports Server (NTRS)

Norman, David, Jr. (Inventor)

2014-01-01

A system and method for determining a cross flow angle for a feature on a structure. A processor unit receives location information identifying a location of the feature on the structure, determines an angle of the feature, identifies flow information for the location, determines a flow angle using the flow information, and determines the cross flow angle for the feature using the flow angle and the angle of the feature. The flow information describes a flow of fluid across the structure. The flow angle comprises an angle of the flow of fluid across the structure for the location of the feature.

Two-dimensional aerodynamic characteristics of several polygon-shaped cross-sectional models applicable to helicopter fuselages

NASA Technical Reports Server (NTRS)

Kelley, Henry L.; Crowell, Cynthia A.; Wilson, John C.

1992-01-01

A wind-tunnel investigation was conducted to determine 2-D aerodynamic characteristics of nine polygon-shaped models applicable to helicopter fuselages. The models varied from 1/2 to 1/5 scale and were nominally triangular, diamond, and rectangular in shape. Side force and normal force were obtained at increments of angle of flow incidence from -45 to 90 degrees. The data were compared with results from a baseline UH-60 tail-boom cross-section model. The results indicate that the overall shapes of the plots of normal force and side force were similar to the characteristic shape of the baseline data; however, there were important differences in magnitude. At a flow incidence of 0 degrees, larger values of normal force for the polygon models indicate an increase in fuselage down load of 1 to 2.5 percent of main-rotor thrust compared with the baseline value. Also, potential was indicated among some of the configurations to produce high fuselage side forces and yawing moments compared with the baseline model.

Laboratory Plasma Source as an MHD Model for Astrophysical Jets

NASA Technical Reports Server (NTRS)

Mayo, Robert M.

1997-01-01

The significance of the work described herein lies in the demonstration of Magnetized Coaxial Plasma Gun (MCG) devices like CPS-1 to produce energetic laboratory magneto-flows with embedded magnetic fields that can be used as a simulation tool to study flow interaction dynamic of jet flows, to demonstrate the magnetic acceleration and collimation of flows with primarily toroidal fields, and study cross field transport in turbulent accreting flows. Since plasma produced in MCG devices have magnetic topology and MHD flow regime similarity to stellar and extragalactic jets, we expect that careful investigation of these flows in the laboratory will reveal fundamental physical mechanisms influencing astrophysical flows. Discussion in the next section (sec.2) focuses on recent results describing collimation, leading flow surface interaction layers, and turbulent accretion. The primary objectives for a new three year effort would involve the development and deployment of novel electrostatic, magnetic, and visible plasma diagnostic techniques to measure plasma and flow parameters of the CPS-1 device in the flow chamber downstream of the plasma source to study, (1) mass ejection, morphology, and collimation and stability of energetic outflows, (2) the effects of external magnetization on collimation and stability, (3) the interaction of such flows with background neutral gas, the generation of visible emission in such interaction, and effect of neutral clouds on jet flow dynamics, and (4) the cross magnetic field transport of turbulent accreting flows. The applicability of existing laboratory plasma facilities to the study of stellar and extragalactic plasma should be exploited to elucidate underlying physical mechanisms that cannot be ascertained though astrophysical observation, and provide baseline to a wide variety of proposed models, MHD and otherwise. The work proposed herin represents a continued effort on a novel approach in relating laboratory experiments to astrophysical jet observation. There exists overwhelming similarity among these flows that has already produced some fascinating results and is expected to continue a high pay off in future flow similarity studies.

Illustration of cross flow of polystyrene melts through a coathanger die

NASA Astrophysics Data System (ADS)

Schöppner, V.; Henke, B.

2015-05-01

To design an optimal coathanger die with a uniform flow rate distribution and low pressure drop, it is essential to understand the flow conditions in the die. This is important because the quality of the product is influenced by the flow velocity and the flow rate distribution. In extrusion dies, cross flows also occur in addition to the main flow, which flow perpendicular to the main flow. This results in pressure gradients in the extrusion direction, which have an influence on flow distribution and pressure drop in the die. In recent decades, quantitative representation and analysis of physical flow processes have made considerable progress in predicting the weather, developing drive technologies and designing aircraft using simulation methods and lab trials. Using the flow-line method, the flow is analyzed in flat film extrusion dies with a rectangular cross-section, in particular cross flows. The simplest method to visualize the flow is based on the measurement of obstacle orientation in the flow field by adding individual particles. A near-surface flow field can be visualized by using wool or textile yarns. By sticking thin, frayed at the ends of strands of wool surface that is to be examined cross flows, near-wall profiles of the flow and vortex and separation regions can be visualized. A further possibility is to add glass fibers and analyze the fiber orientation by microscopy and x-ray analysis. In this paper the influence of process parameters (e.g. melt temperatures and throughput) on cross flow and fiber orientation is described.

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.

Separation Properties of Wastewater Containing O/W Emulsion Using Ceramic Microfiltration/Ultrafiltration (MF/UF) Membranes

PubMed Central

Nakamura, Kazuho; Matsumoto, Kanji

2013-01-01

Washing systems using water soluble detergent are used in electrical and mechanical industries and the wastewater containing O/W emulsion are discharged from these systems. Membrane filtration has large potential for the efficient separation of O/W emulsion for reuses of treated water and detergent. The separation properties of O/W emulsions by cross-flow microfiltration and ultrafiltration were studied with ceramic MF and UF membranes. The effects of pore size; applied pressure; cross-flow velocity; and detergent concentration on rejection of O/W emulsion and flux were systematically studied. At the condition achieving complete separation of O/W emulsion the pressure-independent flux was observed and this flux behavior was explained by gel-polarization model. The O/W emulsion tended to permeate through the membrane at the conditions of larger pore size; higher emulsion concentration; and higher pressure. The O/W emulsion could permeate the membrane pore structure by destruction or deformation. These results imply the stability of O/W emulsion in the gel-layer formed on membrane surface play an important role in the separation properties. The O/W emulsion was concentrated by batch cross-flow concentration filtration and the flux decline during the concentration filtration was explained by the gel- polarization model. PMID:24958621

Scale model performance test investigation of mixed flow exhaust systems for an energy efficient engine /E3/ propulsion system

NASA Technical Reports Server (NTRS)

Kuchar, A. P.; Chamberlin, R.

1983-01-01

As part of the NASA Energy Efficient Engine program, scale-model performance tests of a mixed flow exhaust system were conducted. The tests were used to evaluate the performance of exhaust system mixers for high-bypass, mixed-flow turbofan engines. The tests indicated that: (1) mixer penetration has the most significant affect on both mixing effectiveness and mixer pressure loss; (2) mixing/tailpipe length improves mixing effectiveness; (3) gap reduction between the mixer and centerbody increases high mixing effectiveness; (4) mixer cross-sectional shape influences mixing effectiveness; (5) lobe number affects mixing degree; and (6) mixer aerodynamic pressure losses are a function of secondary flows inherent to the lobed mixer concept.

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

The characteristics and dynamics of wave-driven flow across a platform coral reef in the Red Sea

NASA Astrophysics Data System (ADS)

Lentz, S. J.; Churchill, J. H.; Davis, K. A.; Farrar, J. T.; Pineda, J.; Starczak, V.

2016-02-01

Current dynamics across a platform reef in the Red Sea near Jeddah, Saudi Arabia, are examined using 18 months of current profile, pressure, surface wave, and wind observations. The platform reef is 700 m long, 200 m across with spatial and temporal variations in water depth over the reef ranging from 0.6 to 1.6 m. Surface waves breaking at the seaward edge of the reef cause a 2-10 cm setup of sea level that drives cross-reef currents of 5-20 cm s-1. Bottom stress is a significant component of the wave setup balance in the surf zone. Over the reef flat, where waves are not breaking, the cross-reef pressure gradient associated with wave setup is balanced by bottom stress. The quadratic drag coefficient for the depth-average flow decreases with increasing water depth from Cda = 0.17 in 0.4 m of water to Cda = 0.03 in 1.2 m of water. The observed dependence of the drag coefficient on water depth is consistent with open-channel flow theory and a hydrodynamic roughness of zo = 0.06 m. A simple one-dimensional model driven by incident surface waves and wind stress accurately reproduces the observed depth-averaged cross-reef currents and a portion of the weaker along-reef currents over the focus reef and two other Red Sea platform reefs. The model indicates the cross-reef current is wave forced and the along-reef current is partially wind forced.

Separation control in adverse pressure gradients using high-speed microjets

NASA Astrophysics Data System (ADS)

Kumar, Vikas

Inlets to aircraft propulsion systems must supply flow to the compressor with minimal pressure loss, flow distortion or unsteadiness. Flow separation in internal flows such as inlets and ducts in aircraft propulsion systems and external flows such as over aircraft wings, is undesirable as it reduces the overall system performance. The objective of present study is to understand the nature of separation and more importantly, to explore the applicability of high-speed microjets to actively control this flow separation. The geometry used for this experimental study was a generic backward facing "Stratford Ramp" equipped with arrays of high-speed microjets. The incoming flow was examined over a freestream velocity range of 10-65m/s and at ramp angle in range of 0-10°. It was observed that the flow separates at 30m/s and beyond for all angle of attack. The magnitude and extent of separation bubble increases with increasing adverse pressure gradients and/or increase in free-stream velocity. The separated flow for all the examined conditions was completely attached using suitable array of high-speed microjets. The most notable fact was that elimination of reverse velocity regions was accompanied by a reduction in flow unsteadiness and increased two-dimensionality in the flow. In particular, these gains were achieved with a minimal mass flux, less than 0.2% of the primary flow based on 30% Boundary Layer Ingesting duct. Detailed measurements were obtained to understand the flow control dynamics. The control effectiveness was found to be dependent on the actuation location with respect to separation, jet to cross-flow momentum ratio and the angle at which microjets supply the momentum. It was also determined that the control effect of the microjets, in part, is due to creation of strong stream-wise vortices which enhance the mixing between low-momentum fluid closer to the surface and high-momentum fluid further away from the surface. The penetration depth of microjets was found to be much higher than that of a jet exiting in to uniform cross-flow and correlations were developed to predict this. Subsequently, means for identification of the flow conditions were sought to develop a simple, robust, complete control strategy. It was observed that the flow conditions were very well represented in unsteady surface pressure measurements. The unsteady surface pressure and velocity field were correlated to develop a simple scheme to predict the peak unsteadiness location over the surface. The results from this model and knowledge of microjet in cross flow was used to provide guidelines for an active control strategy. A case study was then undertaken to validate the results obtained using the model. The results show that the model is a good first step towards developing a simple, robust, active-adaptive separation control strategy using microjets.

Studying flow close to an interface by total internal reflection fluorescence cross-correlation spectroscopy: Quantitative data analysis

NASA Astrophysics Data System (ADS)

Schmitz, R.; Yordanov, S.; Butt, H. J.; Koynov, K.; Dünweg, B.

2011-12-01

Total internal reflection fluorescence cross-correlation spectroscopy (TIR-FCCS) has recently [S. Yordanov , Optics ExpressOPEXFF1094-408710.1364/OE.17.021149 17, 21149 (2009)] been established as an experimental method to probe hydrodynamic flows near surfaces, on length scales of tens of nanometers. Its main advantage is that fluorescence occurs only for tracer particles close to the surface, thus resulting in high sensitivity. However, the measured correlation functions provide only rather indirect information about the flow parameters of interest, such as the shear rate and the slip length. In the present paper, we show how to combine detailed and fairly realistic theoretical modeling of the phenomena by Brownian dynamics simulations with accurate measurements of the correlation functions, in order to establish a quantitative method to retrieve the flow properties from the experiments. First, Brownian dynamics is used to sample highly accurate correlation functions for a fixed set of model parameters. Second, these parameters are varied systematically by means of an importance-sampling Monte Carlo procedure in order to fit the experiments. This provides the optimum parameter values together with their statistical error bars. The approach is well suited for massively parallel computers, which allows us to do the data analysis within moderate computing times. The method is applied to flow near a hydrophilic surface, where the slip length is observed to be smaller than 10nm, and, within the limitations of the experiments and the model, indistinguishable from zero.

Advancements in engineering turbulence modeling

NASA Technical Reports Server (NTRS)

Shih, T.-H.

1991-01-01

Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence.

Simulating nitrate response functions in watersheds: Case studies in the United States and New Zealand

NASA Astrophysics Data System (ADS)

Gusyev, Maksym; Abrams, Daniel; Morgenstern, Uwe; Stewart, Michael

2016-04-01

Non-point sources of nitrate contamination are a common concern in different parts of the world and are difficult to characterize. Due to the solubility of nitrate, it easily enters groundwater and may take years or decades to completely flush to a stream. During this time, it may undergo denitrification, in particular if dissolved oxygen levels are low, requiring a representation of spatially distributed nitrate input as well as detailed hydrogeology. In this presentation, nitrate response functions are generated with four different methodologies that are listed in the order of decreasing degrees of freedom: groundwater flow and chemical transport (MODFLOW/MT3D), groundwater flow with solute particle tracing (MODFLOW/MODPATH), cross-sectional groundwater flow model (MODFLOW), and lumped parameter models (LPMs). We tested these approaches in selected watersheds in the Eastern and Midwestern United States as well as New Zealand and found similar nitrate results in all cases despite different model complexities. It is noted that only the fully three dimensional MODFLOW models with MT3D or MODPATH could account for detailed patterns of land use and nitrate applications; the cross-sectional models and lumped parameter models could only do so approximately. Denitrification at depth could also be explicitly accounted for in all four approaches, although this was not a major factor in any of the watersheds investigated.

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.

Simulated peak flows and water-surface profiles for Scott Creek near Sylva, North Carolina

USGS Publications Warehouse

Pope, B.F.

1996-01-01

Peak flows were simulated for Scott Creek, just upstream from Sylva, in Jackson County, North Carolina, in order to provide Jackson County officials with information that can be used to improve preparation for and response to flash floods along the reach of Scott Creek that flows through Sylva. A U.S. Geological Survey rainfall-runoff model was calibrated using observed rainfall and streamflow data collected from March 1994 through September 1995. Standard errors for calibration were 34 percent for runoff volumes and 21 percent for peak flows. The calibrated model was used to simulate peak flows resulting from syn- thetic rainfall amounts of 1.0, 2.5, 5.0, and 7.5 inches in 24-hour periods. For each rainfall amount, peak flows were simulated under low-, moderate-, and high-antecedent soil-moisture conditions, represented by selected 3-month periods of daily rainfall and evaporation record from nearby climatic-data measuring stations. Simulated peak flows ranged from 89 to 10,100 cubic feet per second. Profiles of water-surface elevations for selected observed and simu- lated peak flows were computed for the reach of Scott Creek that flows through Sylva, North Carolina. The profiles were computed using the U.S. Army Corps of Engineers HEC-2 Water Surface Profiles computer program and channel cross-section data collected by the Tennessee Valley Authority. The stage-discharge relation for Scott Creek at the simulation site has changed since the collection of the cross-section data. These changes, however, are such that the water-surface profiles presented in this report likely overestimate the true water-surface elevations at the simulation site for a given peak flow

Fabrication, measurement, and modeling of electro-osmotic flow in micromachined polymer microchannels

NASA Astrophysics Data System (ADS)

Suriyage, Nihal U.; Ghantasala, Muralidhar K.; Iovenitti, Pio; Harvey, Erol C.

2004-03-01

Electroosmotic pumping in the microchannels fabricated in polycarbonate (PC), polyethyleneterephthalate (PET) and SU-8 polymer substrates was investigated and species transportation was modeled, in an attempt to show the suitability of low cost polymer materials for the development of disposable microfluidic devices. Microchannels and the fluid reservoirs were fabricated using excimer laser ablation and hot embossing techniques. Typical dimensions of the microchannels were 60μm (width) x 50μm (depth) x 45mm (length). Species transportation in the microchannels under electroosmosis was modeled by finite element method (FEM) with the help of NetFlow module of the CoventorWareTM computational fluid dynamics (CFD) package. In particular, electroosmosis and electrophoresis in a crossed microfluidic channel was modeled to calculate the percentage species mass transportation when the concentration shape of the Gaussian input species plug and the location of the injection point are varied. Change in the concentration shape of the initial species plug while it is electroosmotically transported along the crossed fluidic channel was visualized. Results indicated that Excimer laser ablated PC and PET devices have electroosmotic mobility in the range 2 to 5 x10-4 cm2/V.s, zeta potential 30 to 70 mV and flow rates of the order of 1 to 3 nL/s under an electric field of 200 V/cm. With the electroosmotic mobility value of PC the simulation results show that a crossed fluidic channel is electroosmotically pumping about 91% of the species mass injected along one of its straight channels.

Modeling Groundwater Flow and Infiltration at Potential Low-Level Radioactive Waste Disposal Sites in Taiwan

NASA Astrophysics Data System (ADS)

Arnold, B. W.; Lee, C.; Ma, C.; Knowlton, R. G.

2006-12-01

Taiwan is evaluating representative sites for the potential disposal of low-level radioactive waste (LLW), including consideration of shallow land burial and cavern disposal concepts. A representative site for shallow land burial is on a small island in the Taiwan Strait with basalt bedrock. The shallow land burial concept includes an engineered cover to limit infiltration into the waste disposal cell. A representative site for cavern disposal is located on the southeast coast of Taiwan. The tunnel system for this disposal concept would be several hundred meters below the mountainous land surface in argillite bedrock. The LLW will consist of about 966,000 drums, primarily from the operation and decommissioning of four nuclear power plants. Sandia National Laboratories and the Institute of Nuclear Energy Research have collaborated to develop performance assessment models to evaluate the long-term safety of LLW disposal at these representative sites. Important components of the system models are sub-models of groundwater flow in the natural system and infiltration through the engineered cover for the shallow land burial concept. The FEHM software code was used to simulate groundwater flow in three-dimensional models at both sites. In addition, a higher-resolution two-dimensional model was developed to simulate flow through the engineered tunnel system at the cavern site. The HELP software was used to simulate infiltration through the cover at the island site. The primary objective of these preliminary models is to provide a modeling framework, given the lack of site-specific data and detailed engineering design specifications. The steady-state groundwater flow model at the island site uses a specified recharge boundary at the land surface and specified head at the island shoreline. Simulated groundwater flow vectors are extracted from the FEHM model along a cross section through one of the LLW disposal cells for utilization in radionuclide transport simulations in the performance assessment model with the BLT-MS software. Infiltration through the engineered cover is simulated to be about 3 mm/yr and 49 mm/yr, with and without a geomembrane layer, respectively. For the cavern LLW disposal site, the FEHM basin-scale flow model uses specified recharge flux, constant head at the ocean shoreline, and head-dependent flux boundaries along flowing streams. Groundwater flow vectors are extracted along a cross section for use in radionuclide transport simulations. Transport simulations indicate that a significant fraction of contaminants may ultimately discharge to nearby streams. FEHM flow simulations with the drift-scale model indicate that the flow rates within the backfilled tunnels may be more than two orders of magnitude lower than in the host rock. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Cross-flow electrochemical reactor cells, cross-flow reactors, and use of cross-flow reactors for oxidation reactions

DOEpatents

Balachandran, Uthamalingam; Poeppel, Roger B.; Kleefisch, Mark S.; Kobylinski, Thaddeus P.; Udovich, Carl A.

1994-01-01

This invention discloses cross-flow electrochemical reactor cells containing oxygen permeable materials which have both electron conductivity and oxygen ion conductivity, cross-flow reactors, and electrochemical processes using cross-flow reactor cells having oxygen permeable monolithic cores to control and facilitate transport of oxygen from an oxygen-containing gas stream to oxidation reactions of organic compounds in another gas stream. These cross-flow electrochemical reactors comprise a hollow ceramic blade positioned across a gas stream flow or a stack of crossed hollow ceramic blades containing a channel or channels for flow of gas streams. Each channel has at least one channel wall disposed between a channel and a portion of an outer surface of the ceramic blade, or a common wall with adjacent blades in a stack comprising a gas-impervious mixed metal oxide material of a perovskite structure having electron conductivity and oxygen ion conductivity. The invention includes reactors comprising first and second zones seprated by gas-impervious mixed metal oxide material material having electron conductivity and oxygen ion conductivity. Prefered gas-impervious materials comprise at least one mixed metal oxide having a perovskite structure or perovskite-like structure. The invention includes, also, oxidation processes controlled by using these electrochemical reactors, and these reactions do not require an external source of electrical potential or any external electric circuit for oxidation to proceed.

Cross-flow vortex structure and transition measurements using multi-element hot films

NASA Technical Reports Server (NTRS)

Agarwal, Naval K.; Mangalam, Siva M.; Maddalon, Dal V.; Collier, Fayette S., Jr.

1991-01-01

An experiment on a 45-degree swept wing was conducted to study three-dimensional boundary-layer characteristics using surface-mounted, micro-thin, multi-element hot-film sensors. Cross-flow vortex structure and boundary-layer transition were measured from the simultaneously acquired signals of the hot films. Spanwise variation of the root-mean-square (RMS) hot-film signal show a local minima and maxima. The distance between two minima corresponds to the stationary cross-flow vortex wavelength and agrees with naphthalene flow-visualization results. The chordwise and spanwise variation of amplified traveling (nonstationary) cross-flow disturbance characteristics were measured as Reynolds number was varied. The frequency of the most amplified cross-flow disturbances agrees with linear stability theory.

The effect of bathymetric filtering on nearshore process model results

USGS Publications Warehouse

Plant, N.G.; Edwards, K.L.; Kaihatu, J.M.; Veeramony, J.; Hsu, L.; Holland, K.T.

2009-01-01

Nearshore wave and flow model results are shown to exhibit a strong sensitivity to the resolution of the input bathymetry. In this analysis, bathymetric resolution was varied by applying smoothing filters to high-resolution survey data to produce a number of bathymetric grid surfaces. We demonstrate that the sensitivity of model-predicted wave height and flow to variations in bathymetric resolution had different characteristics. Wave height predictions were most sensitive to resolution of cross-shore variability associated with the structure of nearshore sandbars. Flow predictions were most sensitive to the resolution of intermediate scale alongshore variability associated with the prominent sandbar rhythmicity. Flow sensitivity increased in cases where a sandbar was closer to shore and shallower. Perhaps the most surprising implication of these results is that the interpolation and smoothing of bathymetric data could be optimized differently for the wave and flow models. We show that errors between observed and modeled flow and wave heights are well predicted by comparing model simulation results using progressively filtered bathymetry to results from the highest resolution simulation. The damage done by over smoothing or inadequate sampling can therefore be estimated using model simulations. We conclude that the ability to quantify prediction errors will be useful for supporting future data assimilation efforts that require this information.

Supercritical flow characteristics at abrupt expansion structure

NASA Astrophysics Data System (ADS)

Lim, Jia Jun; Puay, How Tion; Zakaria, Nor Azazi

2017-10-01

When dealing with the design of a hydraulic structure, lateral expansion is often necessary for flow emerging at high velocity served as a cross-sectional transition. If the abrupt expansion structure is made to diverge rapidly, it will cause the major part of the flow fail to follow the boundaries. If the transition is too gradual, it will result in a waste of structural material. A preliminary study on the flow structure near the expansion and its relationship with flow parameter is carried out in this study. A two-dimensional depth-averaged model is developed to simulate the supercritical flow at the abrupt expansion structure. Constrained Interpolation Profile (CIP) scheme (which is of third order accuracy) is adopted in the numerical model. Results show that the flow structure and flow characteristics at the abrupt expansion can be reproduced numerically. The validation of numerical result is done against analytical studies. The result from numerical simulation showed good agreement with the analytical solution.

Riverbank erosion induced by gravel bar accretion

NASA Astrophysics Data System (ADS)

Klösch, Mario; Habersack, Helmut

2010-05-01

Riverbank erosion is known to be strongly fluvially controlled and determination of shear stresses at the bank surface and at the bank toe is a crucial point in bank erosion modeling. In many modeling attempts hydraulics are simulated separately in a hydrodynamic-numerical model and the simulated shear stresses are further applied onto the bank surface in a bank erosion model. Hydrodynamics are usually simulated at a constant geometry. However, in some cases bed geometry may vary strongly during the event, changing the conditions for hydrodynamics along the bank. This research seeks to investigate the effect of gravel bar accretion during high discharges on final bank retreat. At a restored section of the Drava River bed widenings have been implemented to counter bed degradation. There, in an initiated side-arm, self-dynamic widening strongly affects bed development and long-term connectivity to the main channel. Understanding the riverbank erosion processes there would help to improve planning of future restoration measures. At one riverbank section in the side-arm large bank retreat was measured repeatedly after several flow events. This section is situated between two groins with a distance of 60 m, which act as lateral boundaries to the self-widening channel. In front of this bank section a gravel bar developed. During low flow condition most discharge of the side-arm flows beside the gravel bar along the bank, but shear stresses are too low for triggering bank erosion. For higher discharges results from a two-dimensional hydrodynamic-numerical model suggested shear stresses there to be generally low during the entire events. At some discharges the modeled flow velocities even showed to be recirculating along the bank. These results didn't explain the observed bank retreat. Based on the modeled shear stresses, bank erosion models would have greatly underestimated the bank retreat induced by the investigated events. Repeated surveys after events applying terrestrial photogrammetry, continuous observation of the bank section with a time-lapse camera and continuous measurement of soil hydrological variables showed that around the flow peaks steeper banks collapsed, when matric suction and hence soil shear strength decreased below critical values. But much larger bank erosion with continuous transport of failed blocks from the bank toe was observed to occur during the falling limbs of the hydrographs, when discharge went back to mean flow condition. The flow velocities along the bank then were much larger than at the same discharges during the rising limbs of the hydrographs. Surveys of the riverbed demonstrated a temporary decreased cross section for the flow along the bank because of aggradation and resulting gravel bar accretion during the event. The decreased cross section led to the high flow velocities and shear stresses observed at the end of the events. After every bar accretion, the cross section was re-established by bed degradation along the bank and by massive bank erosion. Monitoring results of the gravel bar accretion and bank retreat are presented. Shear stresses modeled at a constant geometry are compared to the shear stresses modeled when bar accretion was considered. The results highlight the importance of non-equilibrium sediment transport processes during flood events for bank erosion and the need for its consideration in bank erosion modeling. Demonstrated here at a riverbank between groins, bar accretion may play a general role at gravel-bed rivers for bank erosion, particularly near lateral constraints.

Evolution of supersonic corner vortex in a hypersonic inlet/isolator model

NASA Astrophysics Data System (ADS)

Huang, He-Xia; Tan, Hui-Jun; Sun, Shu; Ling, Yu

2016-12-01

There are complex corner vortex flows in a rectangular hypersonic inlet/isolator. The corner vortex propagates downstream and interacts with the shocks and expansion waves in the isolator repeatedly. The supersonic corner vortex in a generic hypersonic inlet/isolator model is theoretically and numerically analyzed at a freestream Mach number of 4.92. The cross-flow topology of the corner vortex flow is found to obey Zhang's theory ["Analytical analysis of subsonic and supersonic vortex formation," Acta Aerodyn. Sin. 13, 259-264 (1995)] strictly, except for the short process with the vortex core situated in a subsonic flow which is surrounded by a supersonic flow. In general, the evolution history of the corner vortex under the influence of the background waves in the hypersonic inlet/isolator model can be classified into two types, namely, from the adverse pressure gradient region to the favorable pressure gradient region and the reversed one. For type 1, the corner vortex is a one-celled vortex with the cross-sectional streamlines spiraling inwards at first. Then the Hopf bifurcation occurs and the streamlines in the outer part of the limit cycle switch to spiraling outwards, yielding a two-celled vortex. The limit cycle shrinks gradually and finally vanishes with the streamlines of the entire corner vortex spiraling outwards. For type 2, the cross-sectional streamlines of the corner vortex spiral outwards first. Then a stable limit cycle is formed, yielding a two-celled vortex. The short-lived limit cycle forces the streamlines in the corner vortex to change the spiraling trends rapidly. Although it is found in this paper that there are some defects on the theoretical proof of the limit cycle, Zhang's theory is proven useful for the prediction and qualitative analysis of the complex corner vortex in a hypersonic inlet/isolator. In addition, three conservation laws inside the limit cycle are obtained.

Numerical solution of a multi-ion one-potential model for electroosmotic flow in two-dimensional rectangular microchannels.

PubMed

Van Theemsche, Achim; Deconinck, Johan; Van den Bossche, Bart; Bortels, Leslie

2002-10-01

A new more general numerical model for the simulation of electrokinetic flow in rectangular microchannels is presented. The model is based on the dilute solution model and the Navier-Stokes equations and has been implemented in a finite-element-based C++ code. The model includes the ion distribution in the Helmholtz double layer and considers only one single electrical' potential field variable throughout the domain. On a charged surface(s) the surface charge density, which is proportional to the local electrical field, is imposed. The zeta potential results, then, from this boundary condition and depends on concentrations, temperature, ion valence, molecular diffusion coefficients, and geometric conditions. Validation cases show that the model predicts accurately known analytical results, also for geometries having dimensions comparable to the Debye length. As a final study, the electro-osmotic flow in a controlled cross channel is investigated.

Injection dynamics of gelled propellants

NASA Astrophysics Data System (ADS)

Yoon, Changjin

Gel propellants have been recognized as attractive candidates for future propulsion systems due to the reduced tendency to spill and the energy advantages over solid propellants. One of strong benefits emphasized in gel propellant applications is a throttling capability, but the accurate flow control is more complicated and difficult than with conventional Newtonian propellants because of the unique rheological behaviors of gels. This study is a computational effort directed to enhance understanding of the injector internal flow characteristics for gel propellants under rocket injection conditions. In simulations, the emphasized rheology is a shear-thinning which represents a viscosity decrease with increasing a shear rate. It is described by a generalized Newtonian fluid constitutive equation and Carreau-Yasuda model. Using this rheological model, two injection schemes are considered in the present study: axially-fed and cross-fed injection for single-element and multi-element impinging injectors, respectively. An axisymmetric model is developed to describe the axially-fed injector flows and fully three-dimensional model is utilized to simulate cross-fed injector flows. Under axially-fed injection conditions investigated, three distinct modes, an unsteady, steady, and hydraulic flip mode, are observed and mapped in terms of Reynolds number and orifice design. In an unsteady mode, quasi-periodic oscillations occur near the inlet lip leading mass pulsations and viscosity fluctuations at the orifice exit. This dynamic behavior is characterized using a time-averaged discharge coefficient, oscillation magnitude and frequency by a parametric study with respect to an orifice design, Reynolds number and rheology. As a result, orifice exit flows for gel propellants appear to be significantly influenced by a viscous damping and flow resistance due to a shear thinning behavior and these are observed in each factors considered. Under conditions driven by a manifold crossflow, unsteady and asymmetric flow structures are revealed as a series of vortices generated from the unstable vena contracta. Here, flows are characterized by an orifice design, manifold/core injection velocity ratio, Reynolds number and rheology. A significant decrease of discharge coefficients is noted with increasing the manifold flow. As the manifold crossflow increases, stronger friction losses are exerted on the leeward, and lead to larger hydraulic losses across the injector. In addition, calculations show that discharge coefficients decrease and the unsteadiness is mitigated as the viscosity increases by fluid rheology variations. A larger and more distinct horseshoe vortex is observed, and pulsation magnitude and viscosity fluctuations are mitigated with increasing viscosity. The oscillation frequency, however, remains unchanged even though the viscosity curves at the high shear rate are modified. All these observations confirm the conclusion that the role of viscous damping and flow resistance is more critical in cross-fed injection conditions than in axially-fed one.

Consistent initial conditions for the Saint-Venant equations in river network modeling

NASA Astrophysics Data System (ADS)

Yu, Cheng-Wei; Liu, Frank; Hodges, Ben R.

2017-09-01

Initial conditions for flows and depths (cross-sectional areas) throughout a river network are required for any time-marching (unsteady) solution of the one-dimensional (1-D) hydrodynamic Saint-Venant equations. For a river network modeled with several Strahler orders of tributaries, comprehensive and consistent synoptic data are typically lacking and synthetic starting conditions are needed. Because of underlying nonlinearity, poorly defined or inconsistent initial conditions can lead to convergence problems and long spin-up times in an unsteady solver. Two new approaches are defined and demonstrated herein for computing flows and cross-sectional areas (or depths). These methods can produce an initial condition data set that is consistent with modeled landscape runoff and river geometry boundary conditions at the initial time. These new methods are (1) the pseudo time-marching method (PTM) that iterates toward a steady-state initial condition using an unsteady Saint-Venant solver and (2) the steady-solution method (SSM) that makes use of graph theory for initial flow rates and solution of a steady-state 1-D momentum equation for the channel cross-sectional areas. The PTM is shown to be adequate for short river reaches but is significantly slower and has occasional non-convergent behavior for large river networks. The SSM approach is shown to provide a rapid solution of consistent initial conditions for both small and large networks, albeit with the requirement that additional code must be written rather than applying an existing unsteady Saint-Venant solver.

Jetting of a shear banding fluid in rectangular ducts

PubMed Central

Salipante, Paul F.; Little, Charles A. E.; Hudson, Steven D.

2017-01-01

Non-Newtonian fluids are susceptible to flow instabilities such as shear banding, in which the fluid may exhibit a markedly discontinuous viscosity at a critical stress. Here we report the characteristics and causes of a jetting flow instability of shear banding wormlike micelle solutions in microfluidic channels with rectangular cross sections over an intermediate volumetric flow regime. Particle-tracking methods are used to measure the three-dimensional flow field in channels of differing aspect ratios, sizes, and wall materials. When jetting occurs, it is self-contained within a portion of the channel where the flow velocity is greater than the surroundings. We observe that the instability forms in channels with aspect ratio greater than 5, and that the location of the high-velocity jet appears to be sensitive to stress localizations. Jetting is not observed in a lower concentration solution without shear banding. Simulations using the Johnson-Segalman viscoelastic model show a qualitatively similar behavior to the experimental observations and indicate that compressive normal stresses in the cross-stream directions support the development of the jetting flow. Our results show that nonuniform flow of shear thinning fluids can develop across the wide dimension in rectangular microfluidic channels, with implications for microfluidic rheometry. PMID:28691108

Propagating mass accretion rate fluctuations in black hole X-ray binaries: quantitative tests

NASA Astrophysics Data System (ADS)

Rapisarda, S.; Ingram, A.; van der Klis, M.

2017-10-01

Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of Black Hole X-ray Binaries (BHBs). However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and QPO. Because of propagation, the emission from different regions of the disc/hot flow geometry is correlated. In our study we applied the model PROPFLUC on different BHBs (including XTE J1550-564 and Cygnus X-1) in different spectral states, fitting jointly the power spectra in two energy bands and the cross-spectrum between these two bands. This represents the first study to utilize quantitive fitting of a physical model simultaneously to observed power and cross-spectra. For the case of XTE J1550-564, which displays a strong QPO, we found quantitative and qualitative discrepancies between model predictions and data, whereas we find a good fit for the Cygnus X-1 data, which does not display a QPO. We conclude that the discrepancies are generic to the propagating fluctuations paradigm, and may be related to the mechanism originating the QPO.

A semi-automated tool for reducing the creation of false closed depressions from a filled LIDAR-derived digital elevation model

USGS Publications Warehouse

Waller, John S.; Doctor, Daniel H.; Terziotti, Silvia

2015-01-01

Closed depressions on the land surface can be identified by ‘filling’ a digital elevation model (DEM) and subtracting the filled model from the original DEM. However, automated methods suffer from artificial ‘dams’ where surface streams cross under bridges and through culverts. Removal of these false depressions from an elevation model is difficult due to the lack of bridge and culvert inventories; thus, another method is needed to breach these artificial dams. Here, we present a semi-automated workflow and toolbox to remove falsely detected closed depressions created by artificial dams in a DEM. The approach finds the intersections between transportation routes (e.g., roads) and streams, and then lowers the elevation surface across the roads to stream level allowing flow to be routed under the road. Once the surface is corrected to match the approximate location of the National Hydrologic Dataset stream lines, the procedure is repeated with sequentially smaller flow accumulation thresholds in order to generate stream lines with less contributing area within the watershed. Through multiple iterations, artificial depressions that may arise due to ephemeral flow paths can also be removed. Preliminary results reveal that this new technique provides significant improvements for flow routing across a DEM and minimizes artifacts within the elevation surface. Slight changes in the stream flow lines generally improve the quality of flow routes; however some artificial dams may persist. Problematic areas include extensive road ditches, particularly along divided highways, and where surface flow crosses beneath road intersections. Limitations do exist, and the results partially depend on the quality of data being input. Of 166 manually identified culverts from a previous study by Doctor and Young in 2013, 125 are within 25 m of culverts identified by this tool. After three iterations, 1,735 culverts were identified and cataloged. The result is a reconditioned elevation dataset, which retains the karst topography for further analysis, and a culvert catalog.

Modeling Water-Surface Elevations and Virtual Shorelines for the Colorado River in Grand Canyon, Arizona

USGS Publications Warehouse

Magirl, Christopher S.; Breedlove, Michael J.; Webb, Robert H.; Griffiths, Peter G.

2008-01-01

Using widely-available software intended for modeling rivers, a new one-dimensional hydraulic model was developed for the Colorado River through Grand Canyon from Lees Ferry to Diamond Creek. Solving one-dimensional equations of energy and continuity, the model predicts stage for a known steady-state discharge at specific locations, or cross sections, along the river corridor. This model uses 2,680 cross sections built with high-resolution digital topography of ground locations away from the river flowing at a discharge of 227 m3/s; synthetic bathymetry was created for topography submerged below the 227 m3/s water surface. The synthetic bathymetry was created by adjusting the water depth at each cross section up or down until the model?s predicted water-surface elevation closely matched a known water surface. This approach is unorthodox and offers a technique to construct one-dimensional hydraulic models of bedrock-controlled rivers where bathymetric data have not been collected. An analysis of this modeling approach shows that while effective in enabling a useful model, the synthetic bathymetry can differ from the actual bathymetry. The known water-surface profile was measured using elevation data collected in 2000 and 2002, and the model can simulate discharges up to 5,900 m3/s. In addition to the hydraulic model, GIS-based techniques were used to estimate virtual shorelines and construct inundation maps. The error of the hydraulic model in predicting stage is within 0.4 m for discharges less than 1,300 m3/s. Between 1,300-2,500 m3/s, the model accuracy is about 1.0 m, and for discharges between 2,500-5,900 m3/s, the model accuracy is on the order of 1.5 m. In the absence of large floods on the flow-regulated Colorado River in Grand Canyon, the new hydraulic model and the accompanying inundation maps are a useful resource for researchers interested in water depths, shorelines, and stage-discharge curves for flows within the river corridor with 2002 topographic conditions.

Electron-Impact Excitation Cross Sections for Modeling Non-Equilibrium Gas

NASA Technical Reports Server (NTRS)

Huo, Winifred M.; Liu, Yen; Panesi, Marco; Munafo, Alessandro; Wray, Alan; Carbon, Duane F.

2015-01-01

In order to provide a database for modeling hypersonic entry in a partially ionized gas under non-equilibrium, the electron-impact excitation cross sections of atoms have been calculated using perturbation theory. The energy levels covered in the calculation are retrieved from the level list in the HyperRad code. The downstream flow-field is determined by solving a set of continuity equations for each component. The individual structure of each energy level is included. These equations are then complemented by the Euler system of equations. Finally, the radiation field is modeled by solving the radiative transfer equation.

Effect of energy equation in one control-volume bulk-flow model for the prediction of labyrinth seal dynamic coefficients

NASA Astrophysics Data System (ADS)

Cangioli, Filippo; Pennacchi, Paolo; Vannini, Giuseppe; Ciuchicchi, Lorenzo

2018-01-01

The influence of sealing components on the rotordynamic stability of turbomachinery has become a key topic because the oil and gas market is increasingly demanding high rotational speeds and high efficiency. This leads the turbomachinery manufacturers to design higher flexibility ratios and to reduce the clearance of the seals. Accurate prediction of the effective damping of seals is critical to avoid instability problems; in recent years, "negative-swirl" swirl brakes have been used to reverse the circumferential direction of the inlet flow, which changes the sign of the cross-coupled stiffness coefficients and generates stabilizing forces. Experimental tests for a teeth-on-stator labyrinth seal were performed by manufacturers with positive and negative pre-swirl values to investigate the pre-swirl effect on the cross-coupled stiffness coefficient. Those results are used as a benchmark in this paper. To analyse the rotor-fluid interaction in the seals, the bulk-flow numeric approach is more time efficient than computational fluid dynamics (CFD). Although the accuracy of the coefficients prediction in bulk-flow models is satisfactory for liquid phase application, the accuracy of the results strongly depends on the operating conditions in the case of the gas phase. In this paper, the authors propose an improvement in the state-of-the-art bulk-flow model by introducing the effect of the energy equation in the zeroth-order solution to better characterize real gas properties due to the enthalpy variation along the seal cavities. The consideration of the energy equation allows for a better estimation of the coefficients in the case of a negative pre-swirl ratio, therefore, it extend the prediction fidelity over a wide range of operating conditions. The numeric results are also compared to the state-of-the-art bulk-flow model, which highlights the improvement in the model.

Investigation of spiral blood flow in a model of arterial stenosis.

PubMed

Paul, Manosh C; Larman, Arkaitz

2009-11-01

The spiral component of blood flow has both beneficial and detrimental effects in human circulatory system [Stonebridge PA, Brophy CM. Spiral laminar flow in arteries? Lancet 1991; 338: 1360-1]. We investigate the effects of the spiral blood flow in a model of three-dimensional arterial stenosis with a 75% cross-sectional area reduction at the centre by means of computational fluid dynamics (CFD) techniques. The standard k-omega model is employed for simulation of the blood flow for the Reynolds number of 500 and 1000. We find that for Re=500 the spiral component of the blood flow increases both the total pressure and velocity of the blood, and some significant differences are found between the wall shear stresses of the spiral and non-spiral induced flow downstream of the stenosis. The turbulent kinetic energy is reduced by the spiral flow as it induces the rotational stabilities in the forward flow. For Re=1000 the tangential component of the blood velocity is most influenced by the spiral speed, but the effect of the spiral flow on the centreline turbulent kinetic energy and shear stress is mild. The results of the effects of the spiral flow are discussed in the paper along with the relevant pathological issues.

Spatially dependent diffusion coefficient as a model for pH sensitive microgel particles in microchannels

PubMed Central

Pieprzyk, S.; Heyes, D. M.; Brańka, A. C.

2016-01-01

Solute transport and intermixing in microfluidic devices is strongly dependent on diffusional processes. Brownian Dynamics simulations of pressure-driven flow of model microgel particles in microchannels have been carried out to explore these processes and the factors that influence them. The effects of a pH-field that induces a spatial dependence of particle size and consequently the self-diffusion coefficient and system thermodynamic state were focused on. Simulations were carried out in 1D to represent some of the cross flow dependencies, and in 2D and 3D to include the effects of flow and particle concentration, with typical stripe-like diffusion coefficient spatial variations. In 1D, the mean square displacement and particle displacement probability distribution function agreed well with an analytically solvable model consisting of infinitely repulsive walls and a discontinuous pH-profile in the middle of the channel. Skew category Brownian motion and non-Gaussian dynamics were observed, which follows from correlations of step lengths in the system, and can be considered to be an example of so-called “diffusing diffusivity.” In Poiseuille flow simulations, the particles accumulated in regions of larger diffusivity and the largest particle concentration throughput was found when this region was in the middle of the channel. The trends in the calculated cross-channel diffusional behavior were found to be very similar in 2D and 3D. PMID:27795750

A computational study on the influence of insect wing geometry on bee flight mechanics

PubMed Central

Feaster, Jeffrey; Bayandor, Javid

2017-01-01

ABSTRACT Two-dimensional computational fluid dynamics (CFD) is applied to better understand the effects of wing cross-sectional morphology on flow field and force production. This study investigates the influence of wing cross-section on insect scale flapping flight performance, for the first time, using a morphologically representative model of a bee (Bombus pensylvanicus) wing. The bee wing cross-section was determined using a micro-computed tomography scanner. The results of the bee wing are compared with flat and elliptical cross-sections, representative of those used in modern literature, to determine the impact of profile variation on aerodynamic performance. The flow field surrounding each cross-section and the resulting forces are resolved using CFD for a flight speed range of 1 to 5 m/s. A significant variation in vortex formation is found when comparing the ellipse and flat plate with the true bee wing. During the upstroke, the bee and approximate wing cross-sections have a much shorter wake structure than the flat plate or ellipse. During the downstroke, the flat plate and elliptical cross-sections generate a single leading edge vortex, while the approximate and bee wings generate numerous, smaller structures that are shed throughout the stroke. Comparing the instantaneous aerodynamic forces on the wing, the ellipse and flat plate sections deviate progressively with velocity from the true bee wing. Based on the present findings, a simplified cross-section of an insect wing can misrepresent the flow field and force production. We present the first aerodynamic study using a true insect wing cross-section and show that the wing corrugation increases the leading edge vortex formation frequency for a given set of kinematics. PMID:29061734

A computational study on the influence of insect wing geometry on bee flight mechanics.

PubMed

Feaster, Jeffrey; Battaglia, Francine; Bayandor, Javid

2017-12-15

Two-dimensional computational fluid dynamics (CFD) is applied to better understand the effects of wing cross-sectional morphology on flow field and force production. This study investigates the influence of wing cross-section on insect scale flapping flight performance, for the first time, using a morphologically representative model of a bee ( Bombus pensylvanicus ) wing. The bee wing cross-section was determined using a micro-computed tomography scanner. The results of the bee wing are compared with flat and elliptical cross-sections, representative of those used in modern literature, to determine the impact of profile variation on aerodynamic performance. The flow field surrounding each cross-section and the resulting forces are resolved using CFD for a flight speed range of 1 to 5 m/s. A significant variation in vortex formation is found when comparing the ellipse and flat plate with the true bee wing. During the upstroke, the bee and approximate wing cross-sections have a much shorter wake structure than the flat plate or ellipse. During the downstroke, the flat plate and elliptical cross-sections generate a single leading edge vortex, while the approximate and bee wings generate numerous, smaller structures that are shed throughout the stroke. Comparing the instantaneous aerodynamic forces on the wing, the ellipse and flat plate sections deviate progressively with velocity from the true bee wing. Based on the present findings, a simplified cross-section of an insect wing can misrepresent the flow field and force production. We present the first aerodynamic study using a true insect wing cross-section and show that the wing corrugation increases the leading edge vortex formation frequency for a given set of kinematics. © 2017. Published by The Company of Biologists Ltd.

Numerical Simulation of Blood Flow in Human Artery Using (A, Q) and (A, u) Systems

NASA Astrophysics Data System (ADS)

Mungkasi, Sudi; Wijayanti Budiawan, Inge

2018-03-01

In this paper, we model blood flow in human artery in the form of (𝐴, 𝑄) and (𝐴, 𝑢) systems, then we use the Lax-Friedrichs finite volume method to find the numerical solution of each model. Here 𝐴 represents the cross sectional area of the artery, 𝑄 denotes the discharge of the blood flow, and 𝑢 is the velocity of the blood flow. We simulate the numerical scheme of each model and investigate how the blood pressure pulse propagates in human artery. Particularly, we use the residual of 𝐴 to determine which system is better numerically. We obtain that the (𝐴, 𝑄) system is better numerically than the (𝐴, 𝑢) system, because the absolute of the residual of 𝐴 using the (𝐴, 𝑄) system is smaller than the absolute of the residual of 𝐴 using the (𝐴, 𝑢) system.

Empirical flow parameters : a tool for hydraulic model validity

USGS Publications Warehouse

Asquith, William H.; Burley, Thomas E.; Cleveland, Theodore G.

2013-01-01

The objectives of this project were (1) To determine and present from existing data in Texas, relations between observed stream flow, topographic slope, mean section velocity, and other hydraulic factors, to produce charts such as Figure 1 and to produce empirical distributions of the various flow parameters to provide a methodology to "check if model results are way off!"; (2) To produce a statistical regional tool to estimate mean velocity or other selected parameters for storm flows or other conditional discharges at ungauged locations (most bridge crossings) in Texas to provide a secondary way to compare such values to a conventional hydraulic modeling approach. (3.) To present ancillary values such as Froude number, stream power, Rosgen channel classification, sinuosity, and other selected characteristics (readily determinable from existing data) to provide additional information to engineers concerned with the hydraulic-soil-foundation component of transportation infrastructure.

Experimental investigation and CFD analysis on cross flow in the core of PMR200

DOE PAGES

Lee, Jeong -Hun; Yoon, Su -Jong; Cho, Hyoung -Kyu; ...

2015-04-16

The Prismatic Modular Reactor (PMR) is one of the major Very High Temperature Reactor (VHTR) concepts, which consists of hexagonal prismatic fuel blocks and reflector blocks made of nuclear gradegraphite. However, the shape of the graphite blocks could be easily changed by neutron damage duringthe reactor operation and the shape change can create gaps between the blocks inducing the bypass flow.In the VHTR core, two types of gaps, a vertical gap and a horizontal gap which are called bypass gap and cross gap, respectively, can be formed. The cross gap complicates the flow field in the reactor core by connectingmore » the coolant channel to the bypass gap and it could lead to a loss of effective coolant flow in the fuel blocks. Thus, a cross flow experimental facility was constructed to investigate the cross flow phenomena in the core of the VHTR and a series of experiments were carried out under varying flow rates and gap sizes. The results of the experiments were compared with CFD (Computational Fluid Dynamics) analysis results in order to verify its prediction capability for the cross flow phenomena. Fairly good agreement was seen between experimental results and CFD predictions and the local characteristics of the cross flow was discussed in detail. Based on the calculation results, pressure loss coefficient across the cross gap was evaluated, which is necessary for the thermo-fluid analysis of the VHTR core using a lumped parameter code.« less

Boundary effects on forced drainage through aqueous foam

NASA Astrophysics Data System (ADS)

Brannigan, G.; de Alcantara Bonfim, O. F.

2001-03-01

The flow of liquid through foam confined in vertical tubes was investigated by measuring the velocity vf of the liquid front forced down by gravity for various flow rates Q. The power law relating the velocity to flow rate of the incoming liquid (v_f ~ Q^α) was observed for tubes of various cross-sectional areas, A. The exponent α was found to vary linearly with the reciprocal of the area: α= 0.325 + 13.7 mm^2/A . This further supports the node-dominated foam drainage model, which predicts α= 1/3 in the limit of infinite cross-sectional area. This relation appears to be independent of bubble size, suggesting that using smaller foam bubbles may not alleviate boundary effects. The results of these experiments also partially explain the discrepancies in measurements of α reported in previous works.

Simulation of unsteady flow and solute transport in a tidal river network

USGS Publications Warehouse

Zhan, X.

2003-01-01

A mathematical model and numerical method for water flow and solute transport in a tidal river network is presented. The tidal river network is defined as a system of open channels of rivers with junctions and cross sections. As an example, the Pearl River in China is represented by a network of 104 channels, 62 nodes, and a total of 330 cross sections with 11 boundary section for one of the applications. The simulations are performed with a supercomputer for seven scenarios of water flow and/or solute transport in the Pearl River, China, with different hydrological and weather conditions. Comparisons with available data are shown. The intention of this study is to summarize previous works and to provide a useful tool for water environmental management in a tidal river network, particularly for the Pearl River, China.

Comprehensive Validation of an Intermittency Transport Model for Transitional Low-Pressure Turbine Flows

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.

2005-01-01

A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment. and unsteady wake-blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, Mu(sub t), with the intermittency factor, gamma. Turbulent quantities are predicted by using Menter's two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, acceleration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake-blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.

Three-Dimensional Modeling of Flow and Thermochemical Behavior in a Blast Furnace

NASA Astrophysics Data System (ADS)

Shen, Yansong; Guo, Baoyu; Chew, Sheng; Austin, Peter; Yu, Aibing

2015-02-01

An ironmaking blast furnace (BF) is a complex high-temperature moving bed reactor involving counter-, co- and cross-current flows of gas, liquid and solid, coupled with heat and mass exchange and chemical reactions. Two-dimensional (2D) models were widely used for understanding its internal state in the past. In this paper, a three-dimensional (3D) CFX-based mathematical model is developed for describing the internal state of a BF in terms of multiphase flow and the related thermochemical behavior, as well as process indicators. This model considers the intense interactions between gas, solid and liquid phases, and also their competition for the space. The model is applied to a BF covering from the burden surface at the top to the liquid surface in the hearth, where the raceway cavity is considered explicitly. The results show that the key in-furnace phenomena such as flow/temperature patterns and component distributions of solid, gas and liquid phases can be described and characterized in different regions inside the BF, including the gas and liquids flow circumferentially over the 3D raceway surface. The in-furnace distributions of key performance indicators such as reduction degree and gas utilization can also be predicted. This model offers a cost-effective tool to understand and control the complex BF flow and performance.

Modelling heat transfer during flow through a random packed bed of spheres

NASA Astrophysics Data System (ADS)

Burström, Per E. C.; Frishfelds, Vilnis; Ljung, Anna-Lena; Lundström, T. Staffan; Marjavaara, B. Daniel

2018-04-01

Heat transfer in a random packed bed of monosized iron ore pellets is modelled with both a discrete three-dimensional system of spheres and a continuous Computational Fluid Dynamics (CFD) model. Results show a good agreement between the two models for average values over a cross section of the bed for an even temperature profiles at the inlet. The advantage with the discrete model is that it captures local effects such as decreased heat transfer in sections with low speed. The disadvantage is that it is computationally heavy for larger systems of pellets. If averaged values are sufficient, the CFD model is an attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also on non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.

Quasi One-Dimensional Unsteady Modeling of External Compression Supersonic Inlets

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Kratz, Jonathan

2012-01-01

The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of an axisymmetric external compression supersonic inlet is being developed. The model utilizes compressible flow computational fluid dynamics to model the internal inlet segment as well as the external inlet portion between the cowl lip and normal shock, and compressible flow relations with flow propagation delay to model the oblique shocks upstream of the normal shock. The external compression portion between the cowl-lip and the normal shock is also modeled with leaking fluxes crossing the sonic boundary, with a moving CFD domain at the normal shock boundary. This model has been verified in steady state against tunnel inlet test data and it s a first attempt towards developing a more comprehensive model for inlet dynamics.

On the Bayesian Treed Multivariate Gaussian Process with Linear Model of Coregionalization

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

Konomi, Bledar A.; Karagiannis, Georgios; Lin, Guang

2015-02-01

The Bayesian treed Gaussian process (BTGP) has gained popularity in recent years because it provides a straightforward mechanism for modeling non-stationary data and can alleviate computational demands by fitting models to less data. The extension of BTGP to the multivariate setting requires us to model the cross-covariance and to propose efficient algorithms that can deal with trans-dimensional MCMC moves. In this paper we extend the cross-covariance of the Bayesian treed multivariate Gaussian process (BTMGP) to that of linear model of Coregionalization (LMC) cross-covariances. Different strategies have been developed to improve the MCMC mixing and invert smaller matrices in the Bayesianmore » inference. Moreover, we compare the proposed BTMGP with existing multiple BTGP and BTMGP in test cases and multiphase flow computer experiment in a full scale regenerator of a carbon capture unit. The use of the BTMGP with LMC cross-covariance helped to predict the computer experiments relatively better than existing competitors. The proposed model has a wide variety of applications, such as computer experiments and environmental data. In the case of computer experiments we also develop an adaptive sampling strategy for the BTMGP with LMC cross-covariance function.« less

Adaptive estimation of state of charge and capacity with online identified battery model for vanadium redox flow battery

NASA Astrophysics Data System (ADS)

Wei, Zhongbao; Tseng, King Jet; Wai, Nyunt; Lim, Tuti Mariana; Skyllas-Kazacos, Maria

2016-11-01

Reliable state estimate depends largely on an accurate battery model. However, the parameters of battery model are time varying with operating condition variation and battery aging. The existing co-estimation methods address the model uncertainty by integrating the online model identification with state estimate and have shown improved accuracy. However, the cross interference may arise from the integrated framework to compromise numerical stability and accuracy. Thus this paper proposes the decoupling of model identification and state estimate to eliminate the possibility of cross interference. The model parameters are online adapted with the recursive least squares (RLS) method, based on which a novel joint estimator based on extended Kalman Filter (EKF) is formulated to estimate the state of charge (SOC) and capacity concurrently. The proposed joint estimator effectively compresses the filter order which leads to substantial improvement in the computational efficiency and numerical stability. Lab scale experiment on vanadium redox flow battery shows that the proposed method is highly authentic with good robustness to varying operating conditions and battery aging. The proposed method is further compared with some existing methods and shown to be superior in terms of accuracy, convergence speed, and computational cost.

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.

Study on performance and flow field of an undershot cross-flow water turbine comprising different number of blades

NASA Astrophysics Data System (ADS)

Nishi, Yasuyuki; Hatano, Kentaro; Inagaki, Terumi

2017-10-01

Recently, small hydroelectric generators have gained attention as a further development in water turbine technology for ultra low head drops in open channels. The authors have evaluated the application of cross-flow water turbines in open channels as an undershot type after removing the casings and guide vanes to substantially simplify these water turbines. However, because undershot cross-flow water turbines are designed on the basis of cross-flow water turbine runners used in typical pipelines, it remains unclear whether the number of blades has an effect on the performance or flow fields. Thus, in this research, experiments and numerical analyses are employed to study the performance and flow fields of undershot cross-flow water turbines with varying number of blades. The findings show that the turbine output and torque are lower, the fluctuation is significantly higher, and the turbine efficiency is higher for runners with 8 blades as opposed to those with 24 blades.

Beach groundwater dynamics

NASA Astrophysics Data System (ADS)

Horn, Diane P.

2002-11-01

An understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution. Coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level (SWL), but the exact nature of the relationship between swash flows, beach watertable flow and cross-shore sediment transport is not fully understood. This paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled. After defining the principal terms relating to beach groundwater, the behavior, measurement and modelling of beach groundwater dynamics is described. Research questions related to the mechanisms of surface-subsurface flow interaction are reviewed, particularly infiltration, exfiltration and fluidisation. The implications of these mechanisms for sediment transport are discussed.

Secondary flow in a curved artery model with Newtonian and non-Newtonian blood-analog fluids

NASA Astrophysics Data System (ADS)

Najjari, Mohammad Reza; Plesniak, Michael W.

2016-11-01

Steady and pulsatile flows of Newtonian and non-Newtonian fluids through a 180°-curved pipe were investigated using particle image velocimetry (PIV). The experiment was inspired by physiological pulsatile flow through large curved arteries, with a carotid artery flow rate imposed. Sodium iodide (NaI) and sodium thiocyanate (NaSCN) were added to the working fluids to match the refractive index (RI) of the test section to eliminate optical distortion. Rheological measurements revealed that adding NaI or NaSCN changes the viscoelastic properties of non-Newtonian solutions and reduces their shear-thinning property. Measured centerline velocity profiles in the upstream straight pipe agreed well with an analytical solution. In the pulsatile case, secondary flow structures, i.e. deformed-Dean, Dean, Wall and Lyne vortices, were observed in various cross sections along the curved pipe. Vortical structures at each cross section were detected using the d2 vortex identification method. Circulation analysis was performed on each vortex separately during the systolic deceleration phase, and showed that vortices split and rejoin. Secondary flow structures in steady flows were found to be morphologically similar to those in pulsatile flows for sufficiently high Dean number. supported by the George Washington University Center for Biomimetics and Bioinspired Engineering.

Modeling and design of optimal flow perfusion bioreactors for tissue engineering applications.

PubMed

Hidalgo-Bastida, L Araida; Thirunavukkarasu, Sundaramoorthy; Griffiths, Sarah; Cartmell, Sarah H; Naire, Shailesh

2012-04-01

Perfusion bioreactors have been used in different tissue engineering applications because of their consistent distribution of nutrients and flow-induced shear stress within the tissue-engineering scaffold. A widely used configuration uses a scaffold with a circular cross-section enclosed within a cylindrical chamber and inlet and outlet pipes which are connected to the chamber on either side through which media is continuously circulated. However, fluid-flow experiments and simulations have shown that the majority of the flow perfuses through the center. This pattern creates stagnant zones in the peripheral regions as well as in those of high flow rate near the inlet and outlet. This non-uniformity of flow and shear stress, owing to a circular design, results in limited cell proliferation and differentiation in these areas. The focus of this communication is to design an optimized perfusion system using computational fluid dynamics as a mathematical tool to overcome the time-consuming trial and error experimental method. We compared the flow within a circular and a rectangular bioreactor system. Flow simulations within the rectangular bioreactor are shown to overcome the limitations in the circular design. This communication challenges the circular cross-section bioreactor configuration paradigm and provides proof of the advantages of the new design over the existing one. Copyright © 2011 Wiley Periodicals, Inc.

Integrated reservoir characterization and flow simulation for well targeting and reservoir management, Iagifu-Hedinia field, Southern Highlands Province, Papua New Guinea

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

Franklin, S.P.; Livingston, J.E.; Fitzmorris, R.E.

Infill drilling based on integrated reservoir characterization and flow simulation is increasing recoverable reserves by 20 MMBO, in lagifu-Hedinia Field (IHF). Stratigraphically-zoned models are input to window and full-field flow simulations, and results of the flow simulations target deviated and horizontal wells. Logging and pressure surveys facilitate detailed reservoir management. Flooding surfaces are the dominant control on differential depletion within and between reservoirs. The primary reservoir is the basal Cretaceous Toro Sandstone. Within the IHF, Toro is a 100 m quartz sandstone composed of stacked, coarsening-upward parasequences within a wave-dominated deltaic complex. Flooding surfaces are used to form a hydraulicmore » zonation. The zonation is refined using discontinuities in RIFT pressure gradients and logs from development wells. For flow simulation, models use 3D geostatistical techniques. First, variograms defining spatial correlation are developed. The variograms are used to construct 3D porosity and permeability models which reflect the stratigraphic facies models. Structure models are built using dipmeter, biostratigraphic, and surface data. Deviated wells often cross axial surfaces and geometry is predicted from dip domain and SCAT. Faults are identified using pressure transient data and dipmeter. The Toro reservoir is subnormally pressured and fluid contacts are hydrodynamically tilted. The hydrodynamic flow and tilted contacts are modeled by flow simulation and constrained by maps of the potentiometric surface.« less

Hydraulic survey and scour assessment of Bridge 524, Tanana River at Big Delta, Alaska

USGS Publications Warehouse

Heinrichs, Thomas A.; Langley, Dustin E.; Burrows, Robert L.; Conaway, Jeffrey S.

2007-01-01

Bathymetric and hydraulic data were collected August 26–28, 1996, on the Tanana River at Big Delta, Alaska, at the Richardson Highway bridge and Trans-Alaska Pipeline crossing. Erosion along the right (north) bank of the river between the bridge and the pipeline crossing prompted the data collection. A water-surface profile hydraulic model for the 100- and 500-year recurrence-interval floods was developed using surveyed information. The Delta River enters the Tanana immediately downstream of the highway bridge, causing backwater that extends upstream of the bridge. Four scenarios were considered to simulate the influence of the backwater on flow through the bridge. Contraction and pier scour were computed from model results. Computed values of pier scour were large, but the scour during a flood may actually be less because of mitigating factors. No bank erosion was observed at the time of the survey, a low-flow period. Erosion is likely to occur during intermediate or high flows, but the actual erosion processes are unknown at this time.

Control of vortical separation on conical bodies

NASA Technical Reports Server (NTRS)

Mourtos, Nikos J.; Roberts, Leonard

1987-01-01

In a variety of aeronautical applications, the flow around conical bodies at incidence is of interest. Such applications include, but are not limited to, highly maneuverable aircraft with delta wings, the aerospace plane and nose portions of spike inlets. The theoretical model used has three parts. First, the single line vortex model is used within the framework of slender body theory, to compute the outer inviscid field for specified separation lines. Next, the three dimensional boundary layer is represented by a momentum equation for the cross flow, analogous to that for a plane boundary layer; a von Karman Pohlhausen approximation is applied to solve this equation. The cross flow separation for both laminar and turbulent layers is determined by matching the pressure at the upper and lower separation points. This iterative procedure yields a unique solution for the separation lines and consequently for the position of the vortices and the vortex lift on the body. Lastly, control of separation is achieved by blowing tangentially from a slot located along a cone generator. It is found that for very small blowing coefficients, the separation can be postponed or suppressedy completely.

Data for calibrating unsteady-flow sediment-transport models, East Fork River, Wyoming, 1975

USGS Publications Warehouse

Mahoney, Holly A.; Andrews, Edmund D.; Emmett, William W.; Leopold, Luna Bergere; Meade, Robert H.; Myrick, Robert M.; Nordin, Carl F.

1976-01-01

In 1975, data to calibrate a one-dimensional unsteady-flow and sediment-transport routing model were collected on a reach of the East Fork River of western Wyoming. The reach, 3.1 miles (5 kilometers) in length, wan immediately upstream from a previously established bedload sampling station. Nineteen channel cross sections were sounded at regular intervals during the spring-runoff period. Four stage recorders provided continuous records of water-surface elevations. Samples of bed material at most of the cross sections were obtained prior to high water. Streamflow and sediment-discharge measurements were collected at four of the sections.The physiography and hydrology of the contributing watershed, the study reach, and the equipment and techniques used in data collection are described briefly. The bulk of the report is a presentation of data for the several-week period of late May to early June 1975, for which concurrent water discharge data, bedload transport and size data, and cross-section depth measurements were collected. In addition, some data collected in 1973 and 1974 and before and after the calibration period in 1975 are included for completeness.

An impact of environmental changes on flows in the reach scale under a range of climatic conditions

NASA Astrophysics Data System (ADS)

Karamuz, Emilia; Romanowicz, Renata J.

2016-04-01

The present paper combines detection and adequate identification of causes of changes in flow regime at cross-sections along the Middle River Vistula reach using different methods. Two main experimental set ups (designs) have been applied to study the changes, a moving three-year window and low- and high-flow event based approach. In the first experiment, a Stochastic Transfer Function (STF) model and a quantile-based statistical analysis of flow patterns were compared. These two methods are based on the analysis of changes of the STF model parameters and standardised differences of flow quantile values. In the second experiment, in addition to the STF-based also a 1-D distributed model, MIKE11 was applied. The first step of the procedure used in the study is to define the river reaches that have recorded information on land use and water management changes. The second task is to perform the moving window analysis of standardised differences of flow quantiles and moving window optimisation of the STF model for flow routing. The third step consists of an optimisation of the STF and MIKE11 models for high- and low-flow events. The final step is to analyse the results and relate the standardised quantile changes and model parameter changes to historical land use changes and water management practices. Results indicate that both models give consistent assessment of changes in the channel for medium and high flows. ACKNOWLEDGEMENTS This research was supported by the Institute of Geophysics Polish Academy of Sciences through the Young Scientist Grant no. 3b/IGF PAN/2015.

Determination of biologically significant hydrologic condition metrics in urbanizing watersheds: an empirical analysis over a range of environmental settings

USGS Publications Warehouse

Steuer, Jeffrey J.; Stensvold, Krista A.; Gregory, Mark B.

2010-01-01

We investigated the relations among 83 hydrologic condition metrics (HCMs) and changes in algal, invertebrate, and fish communities in five metropolitan areas across the continental United States. We used a statistical approach that employed Spearman correlation and regression tree analysis to identify five HCMs that are strongly associated with observed biological variation along a gradient of urbanization. The HCMs related to average flow magnitude, high-flow magnitude, high-flow event frequency, high-flow duration, and rate of change of stream cross-sectional area were most consistently associated with changes in aquatic communities. Although our investigation used an urban gradient design with short hydrologic periods of record (≤1 year) of hourly cross-sectional area time series, these five HCMs were consistent with previous investigations using long-term daily-flow records. The ecological sampling day often was included in the hydrologic period. Regression tree models explained up to 73, 92, and 79% of variance for specific algal, invertebrate, and fish community metrics, respectively. National models generally were not as statistically significant as models for individual metropolitan areas. High-flow event frequency, a hydrologic metric found to be transferable across stream type and useful for classifying habitat by previous research, was found to be the most ecologically relevant HCM; transformation by precipitation increased national-scale applicability. We also investigated the relation between measures of stream flashiness and land-cover indicators of urbanization and found that land-cover characteristic and pattern variables, such as road density, percent wetland, and proximity of developed land, were strongly related to HCMs at both a metropolitan and national scale and, therefore, may be effective land-use management options in addition to wholesale impervious-area reduction.

Opened end-to-side technique for end-to-side anastomosis and analyses by an elastic true-to-scale silicone rubber model.

PubMed

Mücke, Thomas; Ritschl, Lucas M; Balasso, Andrea; Wolff, Klaus-Dietrich; Mitchell, David A; Liepsch, Dieter

2014-01-01

The end-to-side anastomosis is frequently used in microvascular free flap transfer, but detailed rheological analyses are not available. The purpose of this study was to introduce a new modified end-to-side (Opened End-to-Side, OES-) technique and compare the resulting flow pattern to a conventional technique. The new technique was based on a bi-triangulated preparation of the branching-vessel end, resulting in a "fish-mouthed" opening. We performed two different types of end-to-side anastomoses in forty pig coronary arteries and produced one elastic, true-to-scale silicone rubber model of each anastomosis. Then we installed the transparent models in a circulatory experimental setup that simulated the physiological human blood flow. Flow velocity was measured with the one-component Laser-Doppler-Anemometer system, recording flow axial and perpendicular to the model at four defined cross-sections for seven heart cycles in each model. Maximal and minimal axial velocities ranged in the conventional model between 0.269 and -0.122 m/s and in the experimental model between 0.313 and -0.153 m/s. A less disturbed flow velocity distribution was seen in the experimental model distal to the anastomosis. The OES-technique showed superior flow profiles distal to the anastomosis with minor tendencies of flow separation and represents a new alternative for end-to-side anastomosis. Copyright © 2013 Wiley Periodicals, Inc.

Predator-prey model for the self-organization of stochastic oscillators in dual populations

NASA Astrophysics Data System (ADS)

Moradi, Sara; Anderson, Johan; Gürcan, Ozgür D.

2015-12-01

A predator-prey model of dual populations with stochastic oscillators is presented. A linear cross-coupling between the two populations is introduced following the coupling between the motions of a Wilberforce pendulum in two dimensions: one in the longitudinal and the other in torsional plain. Within each population a Kuramoto-type competition between the phases is assumed. Thus, the synchronization state of the whole system is controlled by these two types of competitions. The results of the numerical simulations show that by adding the linear cross-coupling interactions predator-prey oscillations between the two populations appear, which results in self-regulation of the system by a transfer of synchrony between the two populations. The model represents several important features of the dynamical interplay between the drift wave and zonal flow turbulence in magnetically confined plasmas, and a novel interpretation of the coupled dynamics of drift wave-zonal flow turbulence using synchronization of stochastic oscillator is discussed.

Space shuttle orbiter rear mounted reaction control system jet interaction study. [hypersonic wind tunnel tests

NASA Technical Reports Server (NTRS)

Rausch, J. R.

1977-01-01

The effect of interaction between the reaction control system (RCS) jets and the flow over the space shuttle orbiter in the atmosphere was investigated in the NASA Langley 31-inch continuous flow hypersonic tunnel at a nominal Mach number of 10.3 and in the AEDC continuous flow hypersonic tunnel B at a nominal Mach number of 6, using 0.01 and .0125 scale force models with aft RCS nozzles mounted both on the model and on the sting of the force model balance. The data show that RCS nozzle exit momentum ratio is the primary correlating parameter for effects where the plume impinges on an adjacent surface and mass flow ratio is the parameter when the plume interaction is primarily with the external stream. An analytic model of aft mounted RCS units was developed in which the total reaction control moments are the sum of thrust, impingement, interaction, and cross-coupling terms.

Cattaneo-Christov heat flux effect on hydromagnetic radiative Oldroyd-B liquid flow across a cone/wedge in the presence of cross-diffusion

NASA Astrophysics Data System (ADS)

Gnaneswara Reddy, M.

2018-01-01

The present article scrutinizes the prominent characteristics of the Cattaneo-Christov heat flux on magnetohydrodynamic Oldroyd-B radiative liquid flow over two different geometries. The effects of cross-diffusion are considered in the modeling of species and energy equations. Similarity transformations are employed to transmute the governing flow, species and energy equations into a set of nonlinear ordinary differential equations (ODEs) with the appropriate boundary conditions. The final system of dimensionless equations is resolved numerically by utilizing the R-K-Fehlberg numerical approach. The behaviors of all physical pertinent flow controlling variables on the three flow distributions are analyzed through plots. The obtained numerical results have been compared with earlier published work and reveal good agreement. The Deborah numbers γ1 and γ2 have quite opposite effects on velocity and energy fields. The increase in thermal relaxation parameter β corresponds to a decrease in the fluid temperature. This study has salient applications in heat and mass transfer manufacturing system processing for energy conversion.

Optimal Sparse Upstream Sensor Placement for Hydrokinetic Turbines

NASA Astrophysics Data System (ADS)

Cavagnaro, Robert; Strom, Benjamin; Ross, Hannah; Hill, Craig; Polagye, Brian

2016-11-01

Accurate measurement of the flow field incident upon a hydrokinetic turbine is critical for performance evaluation during testing and setting boundary conditions in simulation. Additionally, turbine controllers may leverage real-time flow measurements. Particle image velocimetry (PIV) is capable of rendering a flow field over a wide spatial domain in a controlled, laboratory environment. However, PIV's lack of suitability for natural marine environments, high cost, and intensive post-processing diminish its potential for control applications. Conversely, sensors such as acoustic Doppler velocimeters (ADVs), are designed for field deployment and real-time measurement, but over a small spatial domain. Sparsity-promoting regression analysis such as LASSO is utilized to improve the efficacy of point measurements for real-time applications by determining optimal spatial placement for a small number of ADVs using a training set of PIV velocity fields and turbine data. The study is conducted in a flume (0.8 m2 cross-sectional area, 1 m/s flow) with laboratory-scale axial and cross-flow turbines. Predicted turbine performance utilizing the optimal sparse sensor network and associated regression model is compared to actual performance with corresponding PIV measurements.

Active Flow Control in an Aggressive Transonic Diffuser

NASA Astrophysics Data System (ADS)

Skinner, Ryan W.; Jansen, Kenneth E.

2017-11-01

A diffuser exchanges upstream kinetic energy for higher downstream static pressure by increasing duct cross-sectional area. The resulting stream-wise and span-wise pressure gradients promote extensive separation in many diffuser configurations. The present computational work evaluates active flow control strategies for separation control in an asymmetric, aggressive diffuser of rectangular cross-section at inlet Mach 0.7 and Re 2.19M. Corner suction is used to suppress secondary flows, and steady/unsteady tangential blowing controls separation on both the single ramped face and the opposite flat face. We explore results from both Spalart-Allmaras RANS and DDES turbulence modeling frameworks; the former is found to miss key physics of the flow control mechanisms. Simulated baseline, steady, and unsteady blowing performance is validated against experimental data. Funding was provided by Northrop Grumman Corporation, and this research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357.

Flow structure and heat exchange analysis in internal cooling channel of gas turbine blade

NASA Astrophysics Data System (ADS)

Szwaba, Ryszard; Kaczynski, Piotr; Doerffer, Piotr; Telega, Janusz

2016-08-01

This paper presents the study of the flow structure and heat transfer, and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade. The investigations focus on heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include corner fillet, ribs with fillet radii and special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.

Mixing in the shear superposition micromixer: three-dimensional analysis.

PubMed

Bottausci, Frederic; Mezić, Igor; Meinhart, Carl D; Cardonne, Caroline

2004-05-15

In this paper, we analyse mixing in an active chaotic advection micromixer. The micromixer consists of a main rectangular channel and three cross-stream secondary channels that provide ability for time-dependent actuation of the flow stream in the direction orthogonal to the main stream. Three-dimensional motion in the mixer is studied. Numerical simulations and modelling of the flow are pursued in order to understand the experiments. It is shown that for some values of parameters a simple model can be derived that clearly represents the flow nature. Particle image velocimetry measurements of the flow are compared with numerical simulations and the analytical model. A measure for mixing, the mixing variance coefficient (MVC), is analysed. It is shown that mixing is substantially improved with multiple side channels with oscillatory flows, whose frequencies are increasing downstream. The optimization of MVC results for single side-channel mixing is presented. It is shown that dependence of MVC on frequency is not monotone, and a local minimum is found. Residence time distributions derived from the analytical model are analysed. It is shown that, while the average Lagrangian velocity profile is flattened over the steady flow, Taylor-dispersion effects are still present for the current micromixer configuration.

Geologic cross sections and preliminary geologic map of the Questa Area, Taos County, New Mexico

USGS Publications Warehouse

Bauer, Paul W.; Grauch, V.J.S.; Johnson, Peggy S.; Thompson, Ren A.; Drenth, Benjamin J.; Kelson, Keith I.

2015-01-01

In 2011, the senior authors were contacted by Ron Gardiner of Questa, and Village of Questa Mayor Esther Garcia, to discuss the existing and future groundwater supply for the Village of Questa. This meeting led to the development of a plan in 2013 to perform an integrated geologic, geophysical, and hydrogeologic investigation of the Questa area by the New Mexico Bureau of Geology & Mineral Resources (NMBG), the U.S. Geological Survey (USGS), and New Mexico Tech (NMT). The NMBG was responsible for the geologic map and geologic cross sections. The USGS was responsible for a detailed geophysical model to be incorporated into the NMBG products. NMT was responsible for providing a graduate student to develop a geochemical and groundwater flow model. This report represents the final products of the geologic and geophysical investigations conducted by the NMBG and USGS. The USGS final products have been incorporated directly into the geologic cross sections. The objective of the study was to characterize and interpret the shallow (to a depth of approximately 5,000 ft) three-dimensional geology and preliminary hydrogeology of the Questa area. The focus of this report is to compile existing geologic and geophysical data, integrate new geophysical data, and interpret these data to construct three, detailed geologic cross sections across the Questa area. These cross sections can be used by the Village of Questa to make decisions about municipal water-well development, and can be used in the future to help in the development of a conceptual model of groundwater flow for the Questa area. Attached to this report are a location map, a preliminary geologic map and unit descriptions, tables of water wells and springs used in the study, and three detailed hydrogeologic cross sections shown at two different vertical scales. The locations of the cross sections are shown on the index map of the cross section sheet.

A novel simulation theory and model system for multi-field coupling pipe-flow system

NASA Astrophysics Data System (ADS)

Chen, Yang; Jiang, Fan; Cai, Guobiao; Xu, Xu

2017-09-01

Due to the lack of a theoretical basis for multi-field coupling in many system-level models, a novel set of system-level basic equations for flow/heat transfer/combustion coupling is put forward. Then a finite volume model of quasi-1D transient flow field for multi-species compressible variable-cross-section pipe flow is established by discretising the basic equations on spatially staggered grids. Combining with the 2D axisymmetric model for pipe-wall temperature field and specific chemical reaction mechanisms, a finite volume model system is established; a set of specific calculation methods suitable for multi-field coupling system-level research is structured for various parameters in this model; specific modularisation simulation models can be further derived in accordance with specific structures of various typical components in a liquid propulsion system. This novel system can also be used to derive two sub-systems: a flow/heat transfer two-field coupling pipe-flow model system without chemical reaction and species diffusion; and a chemical equilibrium thermodynamic calculation-based multi-field coupling system. The applicability and accuracy of two sub-systems have been verified through a series of dynamic modelling and simulations in earlier studies. The validity of this system is verified in an air-hydrogen combustion sample system. The basic equations and the model system provide a unified universal theory and numerical system for modelling and simulation and even virtual testing of various pipeline systems.

Inducer analysis/pump model development

NASA Astrophysics Data System (ADS)

Cheng, Gary C.

1994-03-01

Current design of high performance turbopumps for rocket engines requires effective and robust analytical tools to provide design information in a productive manner. The main goal of this study was to develop a robust and effective computational fluid dynamics (CFD) pump model for general turbopump design and analysis applications. A finite difference Navier-Stokes flow solver, FDNS, which includes an extended k-epsilon turbulence model and appropriate moving zonal interface boundary conditions, was developed to analyze turbulent flows in turbomachinery devices. In the present study, three key components of the turbopump, the inducer, impeller, and diffuser, were investigated by the proposed pump model, and the numerical results were benchmarked by the experimental data provided by Rocketdyne. For the numerical calculation of inducer flows with tip clearance, the turbulence model and grid spacing are very important. Meanwhile, the development of the cross-stream secondary flow, generated by curved blade passage and the flow through tip leakage, has a strong effect on the inducer flow. Hence, the prediction of the inducer performance critically depends on whether the numerical scheme of the pump model can simulate the secondary flow pattern accurately or not. The impeller and diffuser, however, are dominated by pressure-driven flows such that the effects of turbulence model and grid spacing (except near leading and trailing edges of blades) are less sensitive. The present CFD pump model has been proved to be an efficient and robust analytical tool for pump design due to its very compact numerical structure (requiring small memory), fast turnaround computing time, and versatility for different geometries.

Inducer analysis/pump model development

NASA Technical Reports Server (NTRS)

Cheng, Gary C.

1994-01-01

Current design of high performance turbopumps for rocket engines requires effective and robust analytical tools to provide design information in a productive manner. The main goal of this study was to develop a robust and effective computational fluid dynamics (CFD) pump model for general turbopump design and analysis applications. A finite difference Navier-Stokes flow solver, FDNS, which includes an extended k-epsilon turbulence model and appropriate moving zonal interface boundary conditions, was developed to analyze turbulent flows in turbomachinery devices. In the present study, three key components of the turbopump, the inducer, impeller, and diffuser, were investigated by the proposed pump model, and the numerical results were benchmarked by the experimental data provided by Rocketdyne. For the numerical calculation of inducer flows with tip clearance, the turbulence model and grid spacing are very important. Meanwhile, the development of the cross-stream secondary flow, generated by curved blade passage and the flow through tip leakage, has a strong effect on the inducer flow. Hence, the prediction of the inducer performance critically depends on whether the numerical scheme of the pump model can simulate the secondary flow pattern accurately or not. The impeller and diffuser, however, are dominated by pressure-driven flows such that the effects of turbulence model and grid spacing (except near leading and trailing edges of blades) are less sensitive. The present CFD pump model has been proved to be an efficient and robust analytical tool for pump design due to its very compact numerical structure (requiring small memory), fast turnaround computing time, and versatility for different geometries.

Pressure and heating-rate distributions on a corrugated surface in a supersonic turbulent boundary layer

NASA Technical Reports Server (NTRS)

Sawyer, J. W.

1977-01-01

Drag and heating rates on wavy surfaces typical of current corrugated plate designs for thermal protection systems were determined experimentally. Pressure-distribution, heating-rate, and oil-flow tests were conducted in the Langley Unitary Plan wind tunnel at Mach numbers of 2.4 and 4.5 with the corrugated surface exposed to both thick and thin turbulent boundary layers. Tests were conducted with the corrugations at cross-flow angles from 0 deg to 90 deg to the flow. Results show that for cross-flow angles of 30 deg or less, the pressure drag coefficients are less than the local flat-plate skin-friction coefficients and are not significantly affected by Mach number, Reynolds number, or boundary-layer thickness over the ranges investigated. For cross-flow angles greater than 30 deg, the drag coefficients increase significantly with cross-flow angle and moderately with Reynolds number. Increasing the Mach number causes a significant reduction in the pressure drag. The average and peak heating penalties due to the corrugated surface are small for cross-flow angles of 10 deg or less but are significantly higher for the larger cross-flow angles.

Annular-Cross-Section CFE Chamber

NASA Technical Reports Server (NTRS)

Sharnez, Rizwan; Sammons, David W.

1994-01-01

Proposed continuous-flow-electrophoresis (CFE) chamber of annular cross section offers advantages over conventional CFE chamber, and wedge-cross-section chamber described in "Increasing Sensitivity in Continuous-Flow Electrophoresis" (MFS-26176). In comparison with wedge-shaped chamber, chamber of annular cross section virtually eliminates such wall effects as electro-osmosis and transverse gradients of velocity. Sensitivity enhanced by incorporating gradient maker and radial (collateral) flow.

Simulation technique for modeling flow on floodplains and in coastal wetlands

USGS Publications Warehouse

Schaffranek, Raymond W.; Baltzer, Robert A.

1988-01-01

The system design is premised on a proven, areal two-dimensional, finite-difference flow/transport model which is supported by an operational set of computer programs for input data management and model output interpretation. The purposes of the project are (1) to demonstrate the utility of the model for providing useful highway design information, (2) to develop guidelines and procedures for using the simulation system for evaluation, analysis, and optimal design of highway crossings of floodplain and coastal wetland areas, and (3) to identify improvements which can be effected in the simulation system to better serve the needs of highway design engineers. Two case study model implementations, being conducted to demonstrate the simulation system and modeling procedure, are presented and discussed briefly.

Genetic connectivity for two bear species at wildlife crossing structures in Banff National Park.

PubMed

Sawaya, Michael A; Kalinowski, Steven T; Clevenger, Anthony P

2014-04-07

Roads can fragment and isolate wildlife populations, which will eventually decrease genetic diversity within populations. Wildlife crossing structures may counteract these impacts, but most crossings are relatively new, and there is little evidence that they facilitate gene flow. We conducted a three-year research project in Banff National Park, Alberta, to evaluate the effectiveness of wildlife crossings to provide genetic connectivity. Our main objective was to determine how the Trans-Canada Highway and crossing structures along it affect gene flow in grizzly (Ursus arctos) and black bears (Ursus americanus). We compared genetic data generated from wildlife crossings with data collected from greater bear populations. We detected a genetic discontinuity at the highway in grizzly bears but not in black bears. We assigned grizzly bears that used crossings to populations north and south of the highway, providing evidence of bidirectional gene flow and genetic admixture. Parentage tests showed that 47% of black bears and 27% of grizzly bears that used crossings successfully bred, including multiple males and females of both species. Differentiating between dispersal and gene flow is difficult, but we documented gene flow by showing migration, reproduction and genetic admixture. We conclude that wildlife crossings allow sufficient gene flow to prevent genetic isolation.

Genetic connectivity for two bear species at wildlife crossing structures in Banff National Park

PubMed Central

Sawaya, Michael A.; Kalinowski, Steven T.; Clevenger, Anthony P.

2014-01-01

Roads can fragment and isolate wildlife populations, which will eventually decrease genetic diversity within populations. Wildlife crossing structures may counteract these impacts, but most crossings are relatively new, and there is little evidence that they facilitate gene flow. We conducted a three-year research project in Banff National Park, Alberta, to evaluate the effectiveness of wildlife crossings to provide genetic connectivity. Our main objective was to determine how the Trans-Canada Highway and crossing structures along it affect gene flow in grizzly (Ursus arctos) and black bears (Ursus americanus). We compared genetic data generated from wildlife crossings with data collected from greater bear populations. We detected a genetic discontinuity at the highway in grizzly bears but not in black bears. We assigned grizzly bears that used crossings to populations north and south of the highway, providing evidence of bidirectional gene flow and genetic admixture. Parentage tests showed that 47% of black bears and 27% of grizzly bears that used crossings successfully bred, including multiple males and females of both species. Differentiating between dispersal and gene flow is difficult, but we documented gene flow by showing migration, reproduction and genetic admixture. We conclude that wildlife crossings allow sufficient gene flow to prevent genetic isolation. PMID:24552834

Groundwater-flow model for the Wood River Valley aquifer system, south-central Idaho

USGS Publications Warehouse

Fisher, Jason C.; Bartolino, James R.; Wylie, Allan H.; Sukow, Jennifer; McVay, Michael

2016-06-27

Subsurface outflow beneath the Big Wood River near Stanton Crossing. Temporal changes in aquifer storage are most affected by areal recharge and groundwater pumping, and also contribute to changes in streamflow gains.

Rational design of capillary-driven flows for paper-based microfluidics.

PubMed

Elizalde, Emanuel; Urteaga, Raúl; Berli, Claudio L A

2015-05-21

The design of paper-based assays that integrate passive pumping requires a precise programming of the fluid transport, which has to be encoded in the geometrical shape of the substrate. This requirement becomes critical in multiple-step processes, where fluid handling must be accurate and reproducible for each operation. The present work theoretically investigates the capillary imbibition in paper-like substrates to better understand fluid transport in terms of the macroscopic geometry of the flow domain. A fluid dynamic model was derived for homogeneous porous substrates with arbitrary cross-sectional shapes, which allows one to determine the cross-sectional profile required for a prescribed fluid velocity or mass transport rate. An extension of the model to slit microchannels is also demonstrated. Calculations were validated by experiments with prototypes fabricated in our lab. The proposed method constitutes a valuable tool for the rational design of paper-based assays.

Cross-axis synchronous flow-through coil planet centrifuge for large-scale preparative counter-current chromatography. III. Performance of large-bore coils in slow planetary motion.

PubMed

Ito, Y; Zhang, T Y

1988-11-25

A preparative capability of the present cross-axis synchronous flow-through coil planet centrifuge was demonstrated with 0.5 cm I.D. multilayer coils. Results of the model studies with short coils indicated that the optimal separations are obtained at low revolutional speeds of 100-200 rpm in both central and lateral coil positions. Preparative separations were successfully performed on 2.5-10 g quantities of test samples in a pair of multilayer coils connected in series with a total capacity of 2.5 l. The sample loading capacity will be scaled up in several folds by increasing the column width.

Effects of uncertain topographic input data on two-dimensional flow modeling in a gravel-bed river

USGS Publications Warehouse

Legleiter, C.J.; Kyriakidis, P.C.; McDonald, R.R.; Nelson, J.M.

2011-01-01

Many applications in river research and management rely upon two-dimensional (2D) numerical models to characterize flow fields, assess habitat conditions, and evaluate channel stability. Predictions from such models are potentially highly uncertain due to the uncertainty associated with the topographic data provided as input. This study used a spatial stochastic simulation strategy to examine the effects of topographic uncertainty on flow modeling. Many, equally likely bed elevation realizations for a simple meander bend were generated and propagated through a typical 2D model to produce distributions of water-surface elevation, depth, velocity, and boundary shear stress at each node of the model's computational grid. Ensemble summary statistics were used to characterize the uncertainty associated with these predictions and to examine the spatial structure of this uncertainty in relation to channel morphology. Simulations conditioned to different data configurations indicated that model predictions became increasingly uncertain as the spacing between surveyed cross sections increased. Model sensitivity to topographic uncertainty was greater for base flow conditions than for a higher, subbankfull flow (75% of bankfull discharge). The degree of sensitivity also varied spatially throughout the bend, with the greatest uncertainty occurring over the point bar where the flow field was influenced by topographic steering effects. Uncertain topography can therefore introduce significant uncertainty to analyses of habitat suitability and bed mobility based on flow model output. In the presence of such uncertainty, the results of these studies are most appropriately represented in probabilistic terms using distributions of model predictions derived from a series of topographic realizations. Copyright 2011 by the American Geophysical Union.

Electron cyclotron thruster new modeling results preparation for initial experiments

NASA Technical Reports Server (NTRS)

Hooper, E. Bickford

1993-01-01

The following topics are discussed: a whistler-based electron cyclotron resonance heating (ECRH) thruster; cross-field coupling in the helicon approximation; wave propagation; wave structure; plasma density; wave absorption; the electron distribution function; isothermal and adiabatic plasma flow; ECRH thruster modeling; a PIC code model; electron temperature; electron energy; and initial experimental tests. The discussion is presented in vugraph form.

Analysis of the cross flow in a radial inflow turbine scroll

NASA Technical Reports Server (NTRS)

Hamed, A.; Abdallah, S.; Tabakoff, W.

1977-01-01

Equations of motion were derived, and a computational procedure is presented, for determining the nonviscous flow characteristics in the cross-sectional planes of a curved channel due to continuous mass discharge or mass addition. An analysis was applied to the radial inflow turbine scroll to study the effects of scroll geometry and the through flow velocity profile on the flow behavior. The computed flow velocity component in the scroll cross-sectional plane, together with the through flow velocity profile which can be determined in a separate analysis, provide a complete description of the three dimensional flow in the scroll.

STUDENT-TEACHER POPULATION GROWTH MODEL--DYNAMOD II.

ERIC Educational Resources Information Center

ZABROWSKI, EDWARD K.; AND OTHERS

DYNAMOD II IS A COMPUTERIZED MARKOVIAN-TYPE FLOW MODEL DEVELOPED TO PROVIDE ESTIMATES OF THE EDUCATIONAL POPULATION OF STUDENTS AND TEACHERS OVER SELECTED INTERVALS OF TIME. THE POPULATION IS CROSS-CLASSIFIED INTO 108 GROUPS BY SEX, RACE, AGE, AND EDUCATIONAL CATEGORY. THIS NOTE DESCRIBES THE METHODOLOGY USED IN DYNAMOD II, COMPARES DYNAMOD II…

Synthetic Jets in Cross-flow. Part 1; Round Jet

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Milanovic, Ivana M.

2003-01-01

Results of an experimental investigation on synthetic jets from round orifices with and without cross-flow are presented. Jet Reynolds number up to 46,000 with a fully turbulent approach boundary layer, and Stokes number up to 400. are covered. The threshold of stroke length for synthetic jet formation. in the absence of the cross-flow, is found to be Lo /D approximately 0.5. Above Lo /D is approximately 10, the profiles of normalized centerline mean velocity appear to become invariant. It is reasoned that the latter threshold may be related to the phenomenon of saturation of impulsively generated vortices. In the presence of the cross-flow, the penetration height of a synthetic jet is found to depend on the momentum- flux ratio . When this ratio is defined in terms of the maximum jet velocity and the cross-flow velocity. not only all data collapse but also the jet trajectory is predicted well by correlation equation available for steady jets-in-cross-flow. Distributions of mean velocity, streamwise vorticity as well as turbulence intensity for a synthetic jet in cross-flow are found to be similar to those of a steady jet-in-cross-flow. A pair of counter-rotating streamwise vortices, corresponding to the bound vortex pair of the steady case, is clearly observed. Mean velocity distribution exhibits a dome of low momentum fluid pulled up from the boundary layer, and the entire domain is characterized by high turbulence.

Glaciation and regional groundwater flow in the Fennoscandian shield

USGS Publications Warehouse

Provost, A.M.; Voss, C.I.; Neuzil, C.E.

2012-01-01

Regional-scale groundwater flow modeling of the Fennoscandian shield suggests that groundwater flow can be strongly affected by future climate change and glaciation. We considered variable-density groundwater flow in a 1500-km-long and approximately 10-km-deep cross-section through southern Sweden. Groundwater flow and shield brine transport in the cross-sectional model were analyzed under projected surface conditions for the next 140 ka. Simulations suggest that blockage of recharge and discharge by low-permeability permafrost or cold-based ice causes sinking of brine and consequent freshening of near-surface water in areas of natural discharge. Although recharge of basal meltwater is limited by the requirement that water pressure at the base of the ice sheet not exceed the pressure exerted by the weight of the ice, warm-based ice with basal melting creates a potential for groundwater recharge rates much larger than those of present, ice-free conditions. In the simulations, regional-scale redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (approximately 10 ka). During glacial retreat, significant upward flow of groundwater may occur below the ice sheet owing to pressure release. If the mechanical loading efficiency of the rocks is high, both subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are reduced because of loading-induced pressure changes. The maximum rate of groundwater discharge in the simulations occurs at the receding ice margin, and some discharge occurs below incursive postglacial seas. Recharge of basal meltwater could decrease the concentration of dissolved solids significantly below present-day levels at depths of up to several kilometers and may bring oxygenated conditions to an otherwise reducing chemical environment for periods exceeding 10 ka.

Virtual and Experimental Visualization of Flows in Packed Beds of Spheres Simulating Porous Media Flows

NASA Technical Reports Server (NTRS)

Hendricks, R. C.; Athavale, M. M.; Lattime, S. B.; Braun, M. J.

1998-01-01

A videotape presentation of flow in a packed bed of spheres is provided. The flow experiment consisted of three principal elements: (1) an oil tunnel 76.2 mm by 76.2 mm in cross section, (2) a packed bed of spheres in regular and irregular arrays, and (3) a flow characterization methodology, either (a) full flow field tracking (FFFT) or (b) computational fluid dynamic (CFD) simulation. The refraction indices of the oil and the test array of spheres were closely matched, and the flow was seeded with aluminum oxide particles. Planar laser light provided a two-dimensional projection of the flow field, and a traverse simulated a three-dimensional image of the entire flow field. Light focusing and reflection rendered the spheres black, permitting visualization of the planar circular interfaces in both the axial and transverse directions. Flows were observed near the wall-sphere interface and within the set of spheres. The CFD model required that a representative section of a packed bed be formed and gridded, enclosing and cutting six spheres so that symmetry conditions could be imposed at all cross-boundaries. Simulations had to be made with the flow direction at right angles to that used in the experiments, however, to take advantage of flow symmetry. Careful attention to detail was required for proper gridding. The flow field was three-dimensional and complex to describe, yet the most prominent finding was flow threads, as computed in the representative 'cube' of spheres with face symmetry and conclusively demonstrated experimentally herein. Random packing and bed voids tended to disrupt the laminar flow, creating vortices.

Particle dispersion in homogeneous turbulence using the one-dimensional turbulence model

DOE PAGES

Sun, Guangyuan; Lignell, David O.; Hewson, John C.; ...

2014-10-09

Lagrangian particle dispersion is studied using the one-dimensional turbulence (ODT) model in homogeneous decaying turbulence configurations. The ODT model has been widely and successfully applied to a number of reacting and nonreacting flow configurations, but only limited application has been made to multiphase flows. We present a version of the particle implementation and interaction with the stochastic and instantaneous ODT eddy events. The model is characterized by comparison to experimental data of particle dispersion for a range of intrinsic particle time scales and body forces. Particle dispersion, velocity, and integral time scale results are presented. Moreover, the particle implementation introducesmore » a single model parameter β p , and sensitivity to this parameter and behavior of the model are discussed. Good agreement is found with experimental data and the ODT model is able to capture the particle inertial and trajectory crossing effects. Our results serve as a validation case of the multiphase implementations of ODT for extensions to other flow configurations.« less

Modeling two-phase flow in PEM fuel cell channels

NASA Astrophysics Data System (ADS)

Wang, Yun; Basu, Suman; Wang, Chao-Yang

2008-05-01

This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-channels of a proton exchange membrane (PEM) fuel cell. Envisaging the mini-channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy's law and the M2 formalism, which allow estimate of the parameters key to fuel cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel cells are fully discussed: liquid water buildup towards the fuel cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-channels.

Buoyant Outflows in the Presence of Ccomplex Topography

DTIC Science & Technology

2010-09-30

of the flow exchange through the Dardanelles Strait on the Aegean Sea coastal flows, cross-shelf exchanges and basin -wide eddy field; e) examine...enhance the predictive capability of operational Navy models, by developing and testing a methodology to link the Mediterranean and Black Sea basins ...in the Aegean Sea through the Dardanelles Strait was shown to have a significant impact on the basin -wide circulation, with implications on the

Direct Numerical Simulations of a Full Stationary Wind-Turbine Blade

NASA Astrophysics Data System (ADS)

Qamar, Adnan; Zhang, Wei; Gao, Wei; Samtaney, Ravi

2014-11-01

Direct numerical simulation of flow past a full stationary wind-turbine blade is carried out at Reynolds number, Re = 10,000 placed at 0 and 5 (degree) angle of attack. The study is targeted to create a DNS database for verification of solvers and turbulent models that are utilized in wind-turbine modeling applications. The full blade comprises of a circular cylinder base that is attached to a spanwise varying airfoil cross-section profile (without twist). An overlapping composite grid technique is utilized to perform these DNS computations, which permits block structure in the mapped computational space. Different flow shedding regimes are observed along the blade length. Von-Karman shedding is observed in the cylinder shaft region of the turbine blade. Along the airfoil cross-section of the blade, near body shear layer breakdown is observed. A long tip vortex originates from the blade tip region, which exits the computational plane without being perturbed. Laminar to turbulent flow transition is observed along the blade length. The turbulent fluctuations amplitude decreases along the blade length and the flow remains laminar regime in the vicinity of the blade tip. The Strouhal number is found to decrease monotonously along the blade length. Average lift and drag coefficients are also reported for the cases investigated. Supported by funding under a KAUST OCRF-CRG grant.

Stability Analysis for Rotating Stall Dynamics in Axial Flow Compressors

DTIC Science & Technology

1999-01-01

modes determines collectively local stability of the compressor model. Explicit conditions are obtained for local stability of rotating stall which...critical modes determines the stability for rotating stall collectively . We point out that although in a special case our stability condition for...strict crossing assumption implies that the zero solution changes its stability as ~, crosses ~’c. For instance, odk (yc ) > 0 implies that the zero

A study of internal energy relaxation in shocks using molecular dynamics based models

NASA Astrophysics Data System (ADS)

Li, Zheng; Parsons, Neal; Levin, Deborah A.

2015-10-01

Recent potential energy surfaces (PESs) for the N2 + N and N2 + N2 systems are used in molecular dynamics (MD) to simulate rates of vibrational and rotational relaxations for conditions that occur in hypersonic flows. For both chemical systems, it is found that the rotational relaxation number increases with the translational temperature and decreases as the rotational temperature approaches the translational temperature. The vibrational relaxation number is observed to decrease with translational temperature and approaches the rotational relaxation number in the high temperature region. The rotational and vibrational relaxation numbers are generally larger in the N2 + N2 system. MD-quasi-classical trajectory (QCT) with the PESs is also used to calculate the V-T transition cross sections, the collision cross section, and the dissociation cross section for each collision pair. Direct simulation Monte Carlo (DSMC) results for hypersonic flow over a blunt body with the total collision cross section from MD/QCT simulations, Larsen-Borgnakke with new relaxation numbers, and the N2 dissociation rate from MD/QCT show a profile with a decreased translational temperature and a rotational temperature close to vibrational temperature. The results demonstrate that many of the physical models employed in DSMC should be revised as fundamental potential energy surfaces suitable for high temperature conditions become available.

An operational GLS model for hydrologic regression

USGS Publications Warehouse

Tasker, Gary D.; Stedinger, J.R.

1989-01-01

Recent Monte Carlo studies have documented the value of generalized least squares (GLS) procedures to estimate empirical relationships between streamflow statistics and physiographic basin characteristics. This paper presents a number of extensions of the GLS method that deal with realities and complexities of regional hydrologic data sets that were not addressed in the simulation studies. These extensions include: (1) a more realistic model of the underlying model errors; (2) smoothed estimates of cross correlation of flows; (3) procedures for including historical flow data; (4) diagnostic statistics describing leverage and influence for GLS regression; and (5) the formulation of a mathematical program for evaluating future gaging activities. ?? 1989.

Simple model of foam drainage

NASA Astrophysics Data System (ADS)

Fortes, M. A.; Coughlan, S.

1994-10-01

A simple model of foam drainage is introduced in which the Plateau borders and quadruple junctions are identified with pools that discharge through channels to pools underneath. The flow is driven by gravity and there are friction losses in the exhausting channels. The equation of Bernoulli combined with the Hagen-Poiseuille equation is applied to describe the flow. The area of the cross section of the exhausting channels can be taken as a constant or may vary during drainage. The predictions of the model are compared with standard drainage curves and with the results of a recently reported experiment in which additional liquid is supplied at the top of the froth.

Modeling Turbulent Combustion for Variable Prandtl and Schmidt Number

NASA Technical Reports Server (NTRS)

Hassan, H. A.

2004-01-01

This report consists of two abstracts submitted for possible presentation at the AIAA Aerospace Science Meeting to be held in January 2005. Since the submittal of these abstracts we are continuing refinement of the model coefficients derived for the case of a variable Turbulent Prandtl number. The test cases being investigated are a Mach 9.2 flow over a degree ramp and a Mach 8.2 3-D calculation of crossing shocks. We have developed an axisymmetric code for treating axisymmetric flows. In addition the variable Schmidt number formulation was incorporated in the code and we are in the process of determining the model constants.

3D Coupled Thermal-Hydraulic Model of the Lower Yarmouk Gorge, Jordan Rift Valley

NASA Astrophysics Data System (ADS)

Walther, M.; Magri, F.; Inbar, N.; Möller, P.; Raggad, M.; Rödiger, T.; Rosenthal, E.; Shentsis, I.; Siebert, C.; Volpi, G.

2017-12-01

It is supposed that the Lower Yarmouk Gorge (LYG), in the Jordan Rift Valley acts as the mixing zone of two crossing flow pathways: N-S from the Hermon Mountains and from the Ajlun Dome, and E-W from Jebel al Arab Mountain in Syria (also known as Huran Plateau or Yarmouk drainage basin). As a result, several springs can be found within the gorge. These are characterized by widespread temperatures (20 - 60 °C) which indicate that, beside the complex regional flow, also ascending thermal waters control the hydrologic behavior of the LYG. Previous simulations based on a conceptual simplified 3D model (Magri et al., 2016) showed that crossing flow paths result from the coexistence of convection, that can develop for example along NE-SW oriented faults within the gorge or in permeable aquifers below Maastrichtian aquiclude, and additional flow fields that are induced by the N-S topographic gradients. Here we present the first 3D hydrogeological model of the entire LYG that includes structural features based on actual logs and interpreted seismic lines from both Israeli and Jordanian territories. The model distinguishes seven units from upper Eocene to the Lower Triassic, accounting for major aquifers, aquicludes and deep-cutting faults. Recharges are implemented based on the numerical representation developed by Shentsis (1990) that considers relationships between mean annual rain and topographic elevation. The model reveals that topography-driven N-S and E-W flows strongly control the location of discharge areas while the anomalous spring temperature is not necessarily linked to the presence of fault convection. Local permeability anisotropy due to aquifers folding or facies changes are features sufficient for the rising of hot fluids. Shentsis, I., 1990. Mathematical models for long-term prediction of mountainous river runoff: methods, information and results, Hydrological Sciences Journal, 35:5, 487-500 Magri, F., Möller, S., Inbar, N., Möller, P., Raggad, M., Rödiger, T., Rosenthal, E., Siebert, C., 2016. 2D and 3D coexisting modes of thermal convection in fractured hydrothermal systems - Implications for transboundary flow in the Lower Yarmouk Gorge. Marine and Petroleum Geology 78, 750-758.

Predicting membrane flux decline from complex mixtures using flow-field flow fractionation measurements and semi-empirical theory.

PubMed

Pellegrino, J; Wright, S; Ranvill, J; Amy, G

2005-01-01

Flow-Field Flow Fractionation (FI-FFF) is an idealization of the cross flow membrane filtration process in that, (1) the filtration flux and crossflow velocity are constant from beginning to end of the device, (2) the process is a relatively well-defined laminar-flow hydrodynamic condition, and (3) the solutes are introduced as a pulse-input that spreads due to interactions with each other and the membrane in the dilute-solution limit. We have investigated the potential for relating FI-FFF measurements to membrane fouling. An advection-dispersion transport model was used to provide 'ideal' (defined as spherical, non-interacting solutes) solute residence time distributions (RTDs) for comparison with 'real' RTDs obtained experimentally at different cross-field velocities and solution ionic strength. An RTD moment analysis based on a particle diameter probability density function was used to extract "effective" characteristic properties, rather than uniquely defined characteristics, of the standard solute mixture. A semi-empirical unsteady-state, flux decline model was developed that uses solute property parameters. Three modes of flux decline are included: (1) concentration polarization, (2) cake buildup, and (3) adsorption on/in pores, We have used this model to test the hypothesis-that an analysis of a residence time distribution using FI-FFF can describe 'effective' solute properties or indices that can be related to membrane flux decline in crossflow membrane filtration. Constant flux filtration studies included the changes of transport hydrodynamics (solvent flux to solute back diffusion (J/k) ratios), solution ionic strength, and feed water composition for filtration using a regenerated cellulose ultrafiltration membrane. Tests of the modeling hypothesis were compared with experimental results from the filtration measurements using several correction parameters based on the mean and variance of the solute RTDs. The corrections used to modify the boundary layer mass transfer coefficient and the specific resistance of cake or adsorption layers demonstrated that RTD analysis is potentially useful technique to describe colloid properties but requires improvements.

Modes of cross-shore sediment transport on the shoreface of the Middle Atlantic Bight

USGS Publications Warehouse

Wright, L.D.; Boon, John D.; Kim, S.C.; List, J.H.

1991-01-01

The mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3-year field study. The study was conducted in the southern part of the Middle Atlantic Bight in the depth region 7–17 m using instrumented tripods supporting electromagnetic current meters, pressure sensors, suspended sediment concentration sensors, and sonar altimeters. The observations embraced fairweather, moderate energy, swell-dominated, and storm conditions. Cross-shore mean flows ranged from near zero during fairweather to > 20 cm s−1 during the storm; oscillatory flows were on the order of 10 cm s−1 during fairweather and 100 cm s−1 during the storm. Suspended sediment concentrations at about 10 cm above the bed were < 0.1 kg m−3 under fairweather conditions, 1–2 kg m−3 under moderate swell conditions, and > 5 kg m−3 during the storm.Three methods were applied to evaluate the relative importance of incident waves, long-period oscillations, mean flows and gravity in effecting shoreward or seaward sediment flux: (1) an energetics transport model was applied to instantaneous near-bottom velocity data, (2) higher moments of near-bottom flows were estimated and compared, and (3) suspended sediment fluxes were estimated directly from the instantaneous products of cross-shore velocity and suspended sediment concentration. The results show that measurable contributions were made by all four of the processes. Most significantly, mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy. Incident waves were, in all cases, the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection. Low-frequency effects involving wave groups and long-period waves made secondary contributions to cross-shore sediment flux. Contrary to expectations, low-frequency fluxes were just as often shoreward as seaward. Whereas cross-correlations between suspended sediment concentration and the instantaneous near-bottom current speed were high and in phase under storm conditions, they were weak and out of phase during fairweather conditions. This suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment.

Numerical study of turbulent secondary flows in curved ducts

NASA Technical Reports Server (NTRS)

Hur, N.; Thangam, S.; Speziale, C. G.

1989-01-01

The pressure driven, fully-developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear Kappa - Iota model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully-developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

Trend of heat flow in france: relation with deep structures

NASA Astrophysics Data System (ADS)

Vasseur, Guy; Nouri, Yamina; Groupe Fluxchaf

1980-06-01

The trend of heat flow over France is discussed using both direct measurements at equilibrium in boreholes and file data. The two types of data are found to be in agreement. They exhibit high heat flow values over the Massif Central and the Vosges. An E-W cross section across the Massif Central allows us to observe the relationship between the high heat flow values, the thinning of the crust and the uprising of the asthenosphere deduced from seismic and gravity measurements. High heat flow values could be explained using a cinematic model where upward convection occurs in the upper mantle for a period of 40 m.y. with a vertical velocity reaching 5 mm/y.

Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity

NASA Technical Reports Server (NTRS)

Pais, S. C.; Kamotani, Y.; Bhunia, A.; Ostrach, S.

1999-01-01

The present investigation reports a study of bubble generation under reduced gravity conditions, using both a co-flow and a cross-flow configuration. This study may be used in the conceptual design of a space-based thermal management system. Ensuing two-phase flow void fraction can be accurately monitored using a single nozzle gas injection system within a continuous liquid flow conduit, as utilized in the present investigation. Accurate monitoring of void fraction leads to precise control of heat and mass transfer coefficients related to a thermal management system; hence providing an efficient and highly effective means of removing heat aboard spacecraft or space stations. Our experiments are performed in parabolic flight aboard the modified DC-9 Reduced Gravity Research Aircraft at NASA Lewis Research Center, using an air-water system. For the purpose of bubble dispersion in a flowing liquid, we use both a co-flow and a cross-flow configuration. In the co-flow geometry, air is introduced through a nozzle in the same direction with the liquid flow. On the other hand, in the cross-flow configuration, air is injected perpendicular to the direction of water flow, via a nozzle protruding inside the two-phase flow conduit. Three different flow conduit (pipe) diameters are used, namely, 1.27 cm, 1.9 cm and 2.54 cm. Two different ratios of nozzle to pipe diameter (D(sub N))sup * are considered, namely (D(sub N))sup * = 0.1 and 0.2, while superficial liquid velocities are varied from 8 to 70 cm/s depending on flow conduit diameter. It is experimentally observed that by holding all other flow conditions and geometry constant, generated bubbles decrease in size with increase in superficial liquid velocity. Detached bubble diameter is shown to increase with air injection nozzle diameter. Likewise, generated bubbles grow in size with increasing pipe diameter. Along the same lines, it is shown that bubble frequency of formation increases and hence the time to detachment of a forming bubble decreases, as the superficial liquid velocity is in-creased. Furthermore, it is shown that the void fraction of the resulting two-phase flow increases with volumetric gas flow rate Q(sub d), pipe diameter and gas injection nozzle diameter, while they decrease with surrounding liquid flow. The important role played by flowing liquid in detaching bubbles in a reduced gravity environment is thus emphasized. We observe that the void fraction can be accurately controlled by using single nozzle gas injection, rather than by employing multiple port injection, since the later system gives rise to unpredictable coalescence of adjacent bubbles. It is of interest to note that empirical bubble size and corresponding void fraction are somewhat smaller for the co-flow geometry than the cross-flow configuration at similar flow conditions with similar pipe and nozzle diameters. In order to supplement the empirical data, a theoretical model is employed to study single bubble generation in the dynamic (Q(sub d) = 1 - 1000 cu cm/s) and bubbly flow regime within the framework of the co-flow configuration. This theoretical model is based on an overall force balance acting on the bubble during the two stages of generation, namely the expansion and the detachment stage. Two sets of forces, one aiding and the other inhibiting bubble detachment are identified. Under conditions of reduced gravity, gas momentum flux enhances, while the surface tension force at the air injection nozzle tip inhibits bubble detachment. In parallel, liquid drag and inertia can act as both attaching and detaching forces, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with our experimental results. However, at higher superficial liquid velocities, as the bubble loses its spherical form, empirical bubble size no longer matches the theoretical predictions. In summary, we have developed a combined experimental and theoretical work, which describes the complex process of bubble generation and resulting two-phase flow in a microgravity environment. Results of the present study can be used in a wide range of space-based applications, such as thermal energy and power generation, propulsion, cryogenic storage and long duration life support systems, necessary for programs such as NASA's Human Exploration for the Development of Space (HEDS).

Sand deposition in the Colorado River in the Grand Canyon from flooding of the Little Colorado River

USGS Publications Warehouse

Wiele, S.M.; Graf, J.B.; Smith, J.D.

1996-01-01

Methods for computing the volume of sand deposited in the Colorado River in Grand Canyon National Park by floods in major tributaries and for determining redistribution of that sand by main-channel flows are required for successful management of sand-dependent riparian resources. We have derived flow, sediment transport, and bed evolution models based on a gridded topography developed from measured channel topography and used these models to compute deposition in a short reach of the river just downstream from the Little Colorado River, the largest tributary in the park. Model computations of deposition from a Little Colorado River flood in January 1993 were compared to bed changes measured at 15 cross sections. The total difference between changes in cross-sectional area due to deposition computed by the model and the measured changes was 6%. A wide reach with large areas of recirculating flow and large depressions in the main channel accumulated the most sand, whereas a reach with similar planimetric area but a long, narrow shape and relatively small areas of recirculating flow and small depressions in the main channel accumulated only about a seventh as much sand. About 32% of the total deposition was in recirculation zones, 65% was in the main channel, and 3% was deposited along the channel margin away from the recirculation zone. Overall, about 15% of the total input of sand from this Little Colorado River flood was deposited in the first 3 km below the confluence, suggesting that deposition of the flood-derived material extended for only several tens of kilometers downstream from the confluence.

Analysis of penetration and mixing of gas jets in supersonic cross flow

NASA Technical Reports Server (NTRS)

Billig, F. S.; Schetz, J. A.

1992-01-01

The JETPEN analysis for gas jets in a supersonic cross flow developed earlier at APL/JHU has been extended in several important ways. First, the treatment of cases with injection at angles other than 90 deg has been redone. Next, the second of the three regions formerly treated has been eliminated. Third, the region downstream of the Mach disk for underexpanded cases has been reformulated such that turbulent entrainment of main stream fluid into the plume is modeled, and the equations of motion are solved marching downstream. These changes now permit prediction of the variation in composition, mixing area growth and all other flow variables along the plume. The analysis has been verified by comparison of predictions and experiment over a wide range of conditions. The result is an analysis capable of reliable predictions of the major flowfield variables that can be run on a PC.

Turbulent flow computation in a circular U-Bend

NASA Astrophysics Data System (ADS)

Miloud, Abdelkrim; Aounallah, Mohammed; Belkadi, Mustapha; Adjlout, Lahouari; Imine, Omar; Imine, Bachir

2014-03-01

Turbulent flows through a circular 180° curved bend with a curvature ratio of 3.375, defined as the the bend mean radius to pipe diameter is investigated numerically for a Reynolds number of 4.45×104. The computation is performed for a U-Bend with full long pipes at the entrance and at the exit. The commercial ANSYS FLUENT is used to solve the steady Reynolds-Averaged Navier-Stokes (RANS) equations. The performances of standard k-ɛ and the second moment closure RSM models are evaluated by comparing their numerical results against experimental data and testing their capabilities to capture the formation and extend this turbulence driven vortex. It is found that the secondary flows occur in the cross-stream half-plane of such configurations and primarily induced by high anisotropy of the cross-stream turbulent normal stresses near the outer bend.

Wall Y+ approach for dealing with turbulent flow through a constant area duct

NASA Astrophysics Data System (ADS)

Shukla, Isha; Tupkari, Swapnil S.; Raman, Ashok K.; Mullick, A. N.

2012-06-01

The study of flow development in curved ducts has been carried out since the last century. It is of fundamental interest because of its numerous applications in fluid engineering, such as flow through pipeline, in heat exchangers, ventilators, gas turbines, aircraft intakes, gas turbines and centrifugal pumps. The flow development through this type of curved ducts depends on its geometrical and dynamical parameters. In the present paper an approach has been made for dealing with turbulent flows within a curved duct with a rectangular cross-section and the result obtained from the experimental work has been compared and validated through numerical simulation by using Fluent CFD codes. The experiment is carried out at mass average velocity based on the inlet cross section as 40m/s. In the present study using the wall y+ as guidance in selecting the appropriate grid configuration and corresponding turbulence models are investigated. The standard k-ɛ, standard k-ω, Reynolds Stress Model (RSM) and Spalart-Almaras (SA) turbulence models are used to solve the closure problem. Their behaviours together with the accompanying near-wall treatments are investigated for wall Y+ value less than 5 covering the viscous sub layer and Y+ value ranging 5 to 30 in the buffer region. Notably, adopting a wall Y+ in the log-law region, where Y+ value is greater than 30, has also been taken care during the study. After various trials the optimum results were obtained for the K-ω model with a mesh count of 0.54 millions. In this, the value of Y+ was almost within the required range, i.e. 5

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels.

PubMed

Choi, Woo June; Qin, Wan; Chen, Chieh-Li; Wang, Jingang; Zhang, Qinqin; Yang, Xiaoqi; Gao, Bruce Z; Wang, Ruikang K

2016-07-01

Optical microangiography (OMAG) is a powerful optical angio-graphic tool to visualize micro-vascular flow in vivo. Despite numerous demonstrations for the past several years of the qualitative relationship between OMAG and flow, no convincing quantitative relationship has been proven. In this paper, we attempt to quantitatively correlate the OMAG signal with flow. Specifically, we develop a simplified analytical model of the complex OMAG, suggesting that the OMAG signal is a product of the number of particles in an imaging voxel and the decorrelation of OCT (optical coherence tomography) signal, determined by flow velocity, inter-frame time interval, and wavelength of the light source. Numerical simulation with the proposed model reveals that if the OCT amplitudes are correlated, the OMAG signal is related to a total number of particles across the imaging voxel cross-section per unit time (flux); otherwise it would be saturated but its strength is proportional to the number of particles in the imaging voxel (concentration). The relationship is validated using microfluidic flow phantoms with various preset flow metrics. This work suggests OMAG is a promising quantitative tool for the assessment of vascular flow.

Conceptual Model Evaluation using Advanced Parameter Estimation Techniques with Heat as a Tracer

NASA Astrophysics Data System (ADS)

Naranjo, R. C.; Morway, E. D.; Healy, R. W.

2016-12-01

Temperature measurements made at multiple depths beneath the sediment-water interface has proven useful for estimating seepage rates from surface-water channels and corresponding subsurface flow direction. Commonly, parsimonious zonal representations of the subsurface structure are defined a priori by interpretation of temperature envelopes, slug tests or analysis of soil cores. However, combining multiple observations into a single zone may limit the inverse model solution and does not take full advantage of the information content within the measured data. Further, simulating the correct thermal gradient, flow paths, and transient behavior of solutes may be biased by inadequacies in the spatial description of subsurface hydraulic properties. The use of pilot points in PEST offers a more sophisticated approach to estimate the structure of subsurface heterogeneity. This presentation evaluates seepage estimation in a cross-sectional model of a trapezoidal canal with intermittent flow representing four typical sedimentary environments. The recent improvements in heat as a tracer measurement techniques (i.e. multi-depth temperature probe) along with use of modern calibration techniques (i.e., pilot points) provides opportunities for improved calibration of flow models, and, subsequently, improved model predictions.

Rheological properties of simulated debris flows in the laboratory environment

USGS Publications Warehouse

Ling, Chi-Hai; Chen, Cheng-lung; Jan, Chyan-Deng; ,

1990-01-01

Steady debris flows with or without a snout are simulated in a 'conveyor-belt' flume using dry glass spheres of a uniform size, 5 or 14 mm in diameter, and their rheological properties described quantitatively in constants in a generalized viscoplastic fluid (GVF) model. Close agreement of the measured velocity profiles with the theoretical ones obtained from the GVF model strongly supports the validity of a GVF model based on the continuum-mechanics approach. Further comparisons of the measured and theoretical velocity profiles along with empirical relations among the shear stress, the normal stress, and the shear rate developed from the 'ring-shear' apparatus determine the values of the rheological parameters in the GVF model, namely the flow-behavior index, the consistency index, and the cross-consistency index. Critical issues in the evaluation of such rheological parameters using the conveyor-belt flume and the ring-shear apparatus are thus addressed in this study.

Sonic environment of aircraft structure immersed in a supersonic jet flow stream

NASA Technical Reports Server (NTRS)

Guinn, W. A.; Balena, F. J.; Soovere, J.

1976-01-01

Test methods for determining the sonic environment of aircraft structure that is immersed in the flow stream of a high velocity jet or that is subjected to the noise field surrounding the jet, were investigated. Sonic environment test data measured on a SCAT 15-F model in the flow field of Mach 1.5 and 2.5 jets were processed. Narrow band, lateral cross correlation and noise contour plots are presented. Data acquisition and reduction methods are depicted. A computer program for scaling the model data is given that accounts for model size, jet velocity, transducer size, and jet density. Comparisons of scaled model data and full size aircraft data are made for the L-1011, S-3A, and a V/STOL lower surface blowing concept. Sonic environment predictions are made for an engine-over-the-wing SST configuration.

Adaptive particle-based pore-level modeling of incompressible fluid flow in porous media: a direct and parallel approach

NASA Astrophysics Data System (ADS)

Ovaysi, S.; Piri, M.

2009-12-01

We present a three-dimensional fully dynamic parallel particle-based model for direct pore-level simulation of incompressible viscous fluid flow in disordered porous media. The model was developed from scratch and is capable of simulating flow directly in three-dimensional high-resolution microtomography images of naturally occurring or man-made porous systems. It reads the images as input where the position of the solid walls are given. The entire medium, i.e., solid and fluid, is then discretized using particles. The model is based on Moving Particle Semi-implicit (MPS) technique. We modify this technique in order to improve its stability. The model handles highly irregular fluid-solid boundaries effectively. It takes into account viscous pressure drop in addition to the gravity forces. It conserves mass and can automatically detect any false connectivity with fluid particles in the neighboring pores and throats. It includes a sophisticated algorithm to automatically split and merge particles to maintain hydraulic connectivity of extremely narrow conduits. Furthermore, it uses novel methods to handle particle inconsistencies and open boundaries. To handle the computational load, we present a fully parallel version of the model that runs on distributed memory computer clusters and exhibits excellent scalability. The model is used to simulate unsteady-state flow problems under different conditions starting from straight noncircular capillary tubes with different cross-sectional shapes, i.e., circular/elliptical, square/rectangular and triangular cross-sections. We compare the predicted dimensionless hydraulic conductances with the data available in the literature and observe an excellent agreement. We then test the scalability of our parallel model with two samples of an artificial sandstone, samples A and B, with different volumes and different distributions (non-uniform and uniform) of solid particles among the processors. An excellent linear scalability is obtained for sample B that has more uniform distribution of solid particles leading to a superior load balancing. The model is then used to simulate fluid flow directly in REV size three-dimensional x-ray images of a naturally occurring sandstone. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability, which compares well with the available network modeling and Lattice-Boltzmann permeabilities available in the literature for the same sandstone. We show that the model conserves mass very well and is stable computationally even at very narrow fluid conduits. The transient- and the steady-state fluid flow patterns are presented as well as the steady-state flow rates to compute absolute permeability. Furthermore, we discuss the vital role of our adaptive particle resolution scheme in preserving the original pore connectivity of the samples and their narrow channels through splitting and merging of fluid particles.

Flow quality of NAL two-dimensional transonic wind tunnel. Part 1: Mach number distributions, flow angularities and preliminary study of side wall boundary layer suction

NASA Technical Reports Server (NTRS)

Sakakibara, Seizo; Takashima, Kazuaki; Miwa, Hitoshi; Oguni, Yasuo; Sato, Mamoru; Kanda, Hiroshi

1988-01-01

Experimental data on the flow quality of the National Aerospace Laboratory two-dimensional transonic wind tunnel are presented. Mach number distributions on the test section axis show good uniformity which is characterized by the two sigma (standard deviation) values of 0.0003 to 0.001 for a range of Mach numbers from 0.4 to 1.0. Flow angularities, which were measured by using a wing model with a symmetrical cross section, remained within 0.04 deg for Mach numbers from 0.2 to 0.8. Side wall boundary layer suction was applied through a pair of porous plates. The variation of aerodynamic properties of the model due to the suction mass flow rate change is presented with a brief discussion. Two dimensionality of the flow over the wing span is expected to be improved by applying the appropriate suction rate, which depends on the Mach number, Reynolds number, and lift coefficient.

Suppression of the sonic heat transfer limit in high-temperature heat pipes

NASA Astrophysics Data System (ADS)

Dobran, Flavio

1989-08-01

The design of high-performance heat pipes requires optimization of heat transfer surfaces and liquid and vapor flow channels to suppress the heat transfer operating limits. In the paper an analytical model of the vapor flow in high-temperature heat pipes is presented, showing that the axial heat transport capacity limited by the sonic heat transfer limit depends on the working fluid, vapor flow area, manner of liquid evaporation into the vapor core of the evaporator, and lengths of the evaporator and adiabatic regions. Limited comparisons of the model predictions with data of the sonic heat transfer limits are shown to be very reasonable, giving credibility to the proposed analytical approach to determine the effect of various parameters on the axial heat transport capacity. Large axial heat transfer rates can be achieved with large vapor flow cross-sectional areas, small lengths of evaporator and adiabatic regions or a vapor flow area increase in these regions, and liquid evaporation in the evaporator normal to the main flow.

Evaporating Spray in Supersonic Streams Including Turbulence Effects

NASA Technical Reports Server (NTRS)

Balasubramanyam, M. S.; Chen, C. P.

2006-01-01

Evaporating spray plays an important role in spray combustion processes. This paper describes the development of a new finite-conductivity evaporation model, based on the two-temperature film theory, for two-phase numerical simulation using Eulerian-Lagrangian method. The model is a natural extension of the T-blob/T-TAB atomization/spray model which supplies the turbulence characteristics for estimating effective thermal diffusivity within the droplet phase. Both one-way and two-way coupled calculations were performed to investigate the performance of this model. Validation results indicate the superiority of the finite-conductivity model in low speed parallel flow evaporating sprays. High speed cross flow spray results indicate the effectiveness of the T-blob/T-TAB model and point to the needed improvements in high speed evaporating spray modeling.

Quantitative assessment of paravalvular leakage after transcatheter aortic valve replacement using a patient-specific pulsatile flow model.

PubMed

Tanaka, Yutaka; Saito, Shigeru; Sasuga, Saeko; Takahashi, Azuma; Aoyama, Yusuke; Obama, Kazuto; Umezu, Mitsuo; Iwasaki, Kiyotaka

2018-05-01

Quantitative assessment of post-transcatheter aortic valve replacement (TAVR) aortic regurgitation (AR) remains challenging. We developed patient-specific anatomical models with pulsatile flow circuit and investigated factors associated with AR after TAVR. Based on pre-procedural computed tomography (CT) data of the six patients who underwent transfemoral TAVR using a 23-mm SAPIEN XT, anatomically and mechanically equivalent aortic valve models were developed. Forward flow and heart rate of each patient in two days after TAVR were duplicated under mean aortic pressure of 80mmHg. Paravalvular leakage (PVL) volume in basal and additional conditions was measured for each model using an electromagnetic flow sensor. Incompletely apposed tract between the transcatheter and aortic valves was examined using a micro-CT. PVL volume in each patient-specific model was consistent with each patient's PVL grade, and was affected by hemodynamic conditions. PVL and total regurgitation volume increased with the mean aortic pressure, whereas closing volume did not change. In contrast, closing volume increased proportionately with heart rate, but PVL did not change. The minimal cross-sectional gap had a positive correlation with the PVL volumes (r=0.89, P=0.02). The gap areas typically occurred in the vicinity of the bulky calcified nodules under the native commissure. PVL volume, which could be affected by hemodynamic conditions, was significantly associated with the minimal cross-sectional gap area between the aortic annulus and the stent frame. These data may improve our understanding of the mechanism of the occurrence of post-TAVR PVL. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Isopycnal deepening of an under-ice river plume in coastal waters: Field observations and modeling

NASA Astrophysics Data System (ADS)

Li, S. Samuel; Ingram, R. Grant

2007-07-01

The Great Whale River, located on the southeast coast of Hudson Bay in Canada, forms a large river plume under complete landfast ice during early spring. Short-term fluctuations of plume depth have motivated the present numerical study of an under-ice river plume subject to tidal motion and friction. We introduce a simple two-layer model for predicting the vertical penetration of the under-ice river plume as it propagates over a deepening topography. The topography is idealized but representative. Friction on the bottom surface of the ice cover, on the seabed, and at the plume interface is parameterized using the quadratic friction law. The extent of the vertical penetration is controlled by dimensionless parameters related to tidal motion and river outflow. Model predictions are shown to compare favorably with under-ice plume measurements from the river mouth. This study illustrates that isopycnal deepening occurs when the ice-cover vertical motion creates a reduced flow cross-section during the ebbing tide. This results in supercritical flow and triggers the downward plume penetration in the offshore. For a given river discharge, the freshwater source over a tidal cycle is unsteady in terms of discharge velocity because of the variation in the effective cross-sectional area at the river mouth, through which freshwater flows.

Investigation of surface fluctuating pressures on a 1/4 scale YC-14 upper surface blown flap model

NASA Technical Reports Server (NTRS)

Pappa, R. S.

1979-01-01

Fluctuating pressures were measured at 30 positions on the surface of a 1/4-scale YC-14 wing and fuselage model during an outdoor static testing program. These data were obtained as part of a NASA program to study the fluctuating loads imposed on STOL aircraft configurations and to further the understanding of the scaling laws of unsteady surface pressure fields. Fluctuating pressure data were recorded at several discrete engine thrust settings for each of 16 configurations of the model. These data were reduced using the technique of random data analysis to obtain auto-and cross-spectral density functions and coherence functions for frequencies from 0 to 10 kHz, and cross-correlation functions for time delays from 0 to 10.24 ms. Results of this program provide the following items of particular interest: (1) Good collapse of normalized PSD functions on the USB flap was found using a technique applied by Lilley and Hodgson to data from a laboratory wall-jet apparatus. (2) Results indicate that the fluctuating pressure loading on surfaces washed by the jet exhaust flow was dominated by hydrodynamic pressure variations, loading on surface well outside the flow region dominated by acoustic pressure variations, and loading near the flow boundaries from a mixture of the two.

Flow control of an elongated jet in cross-flow: Film cooling effectiveness enhancement using surface dielectric barrier discharge plasma actuator

NASA Astrophysics Data System (ADS)

Audier, P.; Fénot, M.; Bénard, N.; Moreau, E.

2016-02-01

The case presented here deals with plasma flow control applied to a cross-flow configuration, more specifically to a film cooling system. The ability of a plasma dielectric barrier discharge actuator for film cooling effectiveness enhancement is investigated through an experimental set-up, including a film injection from an elongated slot into a thermally uniform cross-flow. Two-dimensional particle image velocimetry and infrared-thermography measurements are performed for three different blowing ratios of M = 0.4, 0.5, and 1. Results show that the effectiveness can be increased when the discharge is switched on, as predicted by the numerical results available in literature. Whatever the blowing ratio, the actuator induces a deflection of the jet flow towards the wall, increases its momentum, and delays its diffusion in the cross-flow.

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.

A refined and dynamic cellular automaton model for pedestrian-vehicle mixed traffic flow

NASA Astrophysics Data System (ADS)

Liu, Mianfang; Xiong, Shengwu

2016-12-01

Mixed traffic flow sharing the “same lane” and having no discipline on road is a common phenomenon in the developing countries. For example, motorized vehicles (m-vehicles) and nonmotorized vehicles (nm-vehicles) may share the m-vehicle lane or nm-vehicle lane and pedestrians may share the nm-vehicle lane. Simulating pedestrian-vehicle mixed traffic flow consisting of three kinds of traffic objects: m-vehicles, nm-vehicles and pedestrians, can be a challenge because there are some erratic drivers or pedestrians who fail to follow the lane disciplines. In the paper, we investigate various moving and interactive behavior associated with mixed traffic flow, such as lateral drift including illegal lane-changing and transverse crossing different lanes, overtaking and forward movement, and propose some new moving and interactive rules for pedestrian-vehicle mixed traffic flow based on a refined and dynamic cellular automaton (CA) model. Simulation results indicate that the proposed model can be used to investigate the traffic flow characteristic in a mixed traffic flow system and corresponding complicated traffic problems, such as, the moving characteristics of different traffic objects, interaction phenomenon between different traffic objects, traffic jam, traffic conflict, etc., which are consistent with the actual mixed traffic system. Therefore, the proposed model provides a solid foundation for the management, planning and evacuation of the mixed traffic flow.

Fractionating power and outlet stream polydispersity in asymmetrical flow field-flow fractionation. Part II: programmed operation.

PubMed

Williams, P Stephen

2017-01-01

Asymmetrical flow field-flow fractionation (As-FlFFF) is a widely used technique for analyzing polydisperse nanoparticle and macromolecular samples. The programmed decay of cross flow rate is often employed. The interdependence of the cross flow rate through the membrane and the fluid flow along the channel length complicates the prediction of elution time and fractionating power. The theory for their calculation is presented. It is also confirmed for examples of exponential decay of cross flow rate with constant channel outlet flow rate that the residual sample polydispersity at the channel outlet is quite well approximated by the reciprocal of four times the fractionating power. Residual polydispersity is of importance when online MALS or DLS detection are used to extract quantitative information on particle size or molecular weight. The theory presented here provides a firm basis for the optimization of programmed flow conditions in As-FlFFF. Graphical abstract Channel outlet polydispersity remains significant following fractionation by As-FlFFF under conditions of programmed decay of cross flow rate.

The Prediction of Noise Due to Jet Turbulence Convecting Past Flight Vehicle Trailing Edges

NASA Technical Reports Server (NTRS)

Miller, Steven A. E.

2014-01-01

High intensity acoustic radiation occurs when turbulence convects past airframe trailing edges. A mathematical model is developed to predict this acoustic radiation. The model is dependent on the local flow and turbulent statistics above the trailing edge of the flight vehicle airframe. These quantities are dependent on the jet and flight vehicle Mach numbers and jet temperature. A term in the model approximates the turbulent statistics of single-stream heated jet flows and is developed based upon measurement. The developed model is valid for a wide range of jet Mach numbers, jet temperature ratios, and flight vehicle Mach numbers. The model predicts traditional trailing edge noise if the jet is not interacting with the airframe. Predictions of mean-flow quantities and the cross-spectrum of static pressure near the airframe trailing edge are compared with measurement. Finally, predictions of acoustic intensity are compared with measurement and the model is shown to accurately capture the phenomenon.

Two-phase flow pressure drop and heat transfer during condensation in microchannels with uniform and converging cross-sections

NASA Astrophysics Data System (ADS)

Kuo, Ching Yi; Pan, Chin

2010-09-01

This study experimentally investigates steam condensation in rectangular microchannels with uniform and converging cross-sections and a mean hydraulic diameter of 135 µm. The steam flow in the microchannels was cooled by water cross-flowing along its bottom surface, which is different from other methods reported in the literature. The flow patterns, two-phase flow pressure drop and condensation heat transfer coefficient are determined. The microchannels with the uniform cross-section design have a higher heat transfer coefficient than those with the converging cross-section under condensation in the mist/annular flow regimes, although the latter work best for draining two-phase fluids composed of uncondensed steam and liquid water, which is consistent with the result of our previous study. From the experimental results, dimensionless correlations of condensation heat transfer for the mist and annular flow regions and a two-phase frictional multiplier are developed for the microchannels with both types of cross-section designs. The experimental data agree well with the obtained correlations, with the maximum mean absolute errors of 6.4% for the two-phase frictional multiplier and 6.0% for the condensation heat transfer.

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

Jablonská, Jana, E-mail: jana.jablonska@vsb.cz; Kozubková, Milada, E-mail: milada.kozubkova@vsb.cz

Cavitation today is a very important problem that is solved by means of experimental and mathematical methods. The article deals with the generation of cavitation in convergent divergent nozzle of rectangular cross section. Measurement of pressure, flow rate, temperature, amount of dissolved air in the liquid and visualization of cavitation area using high-speed camera was performed for different flow rates. The measurement results were generalized by dimensionless analysis, which allows easy detection of cavitation in the nozzle. For numerical simulation the multiphase mathematical model of cavitation consisting of water and vapor was created. During verification the disagreement with the measurementsmore » for higher flow rates was proved, therefore the model was extended to multiphase mathematical model (water, vapor and air), due to release of dissolved air. For the mathematical modeling the multiphase turbulence RNG k-ε model for low Reynolds number flow with vapor and air cavitation was used. Subsequently the sizes of the cavitation area were verified. In article the inlet pressure and loss coefficient depending on the amount of air added to the mathematical model are evaluated. On the basis of the approach it may be create a methodology to estimate the amount of released air added at the inlet to the modeled area.« less

Elastic electron scattering from formamide

NASA Astrophysics Data System (ADS)

Buk, M. V.; Bardela, F. P.; da Silva, L. A.; Iga, I.; Homem, M. G. P.

2018-05-01

Differential cross sections for elastic electron scattering by formamide (NH2CHO) were measured in the 30–800 eV and 10°–120° ranges. The angular distribution of scattered electrons was obtained using a crossed electron beam-molecular beam geometry. The relative flow technique was applied to normalize our data. Integral and momentum-transfer cross sections were derived from the measured differential cross sections. Theoretical results in the framework of the independent-atom model at the static-exchange-polarization plus absorption level of approximation are also given. The present measured and calculated results are compared with those available in the literature showing a generally good agreement.

Experimental Research on the Dense CFB's Riser and the Simulation Based on the EMMS Model

NASA Astrophysics Data System (ADS)

Wang, X. Y.; Wang, S. D.; Fan, B. G.; Liao, L. L.; Jiang, F.; Xu, X.; Wu, X. Z.; Xiao, Y. H.

2010-03-01

The flow structure in the CFB (circulating fluidized bed) riser has been investigated. Experimental studies were performed in a cold square section unit with 270 mm×270 mm×10 m. Since the drag force model based on homogeneous two-phase flow such as the Gidaspow drag model could not depict the heterogeneous structures of the gas-solid flow, the structure-dependent energy-minimization multi-scale (EMMS) model based on the heterogenerity was applied in the paper and a revised drag force model based on the EMMS model was proposed. A 2D two-fluid model was used to simulate a bench-scale square cross-section riser of a cold CFB. The typical core-annulus structure and the back-mixing near the wall of the riser were observed and the assembly and fragmentation processes of clusters were captured. By comparing with the Gidaspow drag model, the results obtained by the revised drag model based on EMMS shows better consistency with the experimental data. The model can also depict the difference from the two exit configurations. This study once again proves the key role of drag force in CFD (Computational Fluid Dynamics) simulation and also shows the availability of the revised drag model to describe the gas-solid flow in CFB risers.

A NEW SIMPLE DYNAMO MODEL FOR STELLAR ACTIVITY CYCLE

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

Yokoi, N.; Hamba, F.; Schmitt, D.

2016-06-20

A new simple dynamo model for stellar activity cycle is proposed. By considering an inhomogeneous flow effect on turbulence, it is shown that turbulent cross helicity (velocity–magnetic-field correlation) enters the expression of turbulent electromotive force as the coupling coefficient for the mean absolute vorticity. This makes the present model different from the current α –Ω-type models in two main ways. First, in addition to the usual helicity ( α ) and turbulent magnetic diffusivity ( β ) effects, we consider the cross-helicity effect as a key ingredient of the dynamo process. Second, the spatiotemporal evolution of cross helicity is solvedmore » simultaneously with the mean magnetic fields. The basic scenario is as follows. In the presence of turbulent cross helicity, the toroidal field is induced by the toroidal rotation. Then, as in usual models, the α effect generates the poloidal field from the toroidal one. This induced poloidal field produces a turbulent cross helicity whose sign is opposite to the original one (negative production). With this cross helicity of the reversed sign, a reversal in field configuration starts. Eigenvalue analyses of the simplest possible model give a butterfly diagram, which confirms the above scenario and the equatorward migrations, the phase relationship between the cross helicity and magnetic fields. These results suggest that the oscillation of the turbulent cross helicity is a key for the activity cycle. The reversal of the cross helicity is not the result of the magnetic-field reversal, but the cause of the latter. This new model is expected to open up the possibility of the mean-field or turbulence closure dynamo approaches.« less

Spacer geometry and particle deposition in spiral wound membrane feed channels.

PubMed

Radu, A I; van Steen, M S H; Vrouwenvelder, J S; van Loosdrecht, M C M; Picioreanu, C

2014-11-01

Deposition of microspheres mimicking bacterial cells was studied experimentally and with a numerical model in feed spacer membrane channels, as used in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane systems. In-situ microscopic observations in membrane fouling simulators revealed formation of specific particle deposition patterns for different diamond and ladder feed spacer orientations. A three-dimensional numerical model combining fluid flow with a Lagrangian approach for particle trajectory calculations could describe very well the in-situ observations on particle deposition in flow cells. Feed spacer geometry, positioning and cross-flow velocity sensitively influenced the particle transport and deposition patterns. The deposition patterns were not influenced by permeate production. This combined experimental-modeling approach could be used for feed spacer geometry optimization studies for reduced (bio)fouling. Copyright © 2014 Elsevier Ltd. All rights reserved.

A small-scale turbulence model

NASA Technical Reports Server (NTRS)

Lundgren, T. S.

1992-01-01

A model for the small-scale structure of turbulence is reformulated in such a way that it may be conveniently computed. The model is an ensemble of randomly oriented structured two dimensional vortices stretched by an axially symmetric strain flow. The energy spectrum of the resulting flow may be expressed as a time integral involving only the enstrophy spectrum of the time evolving two-dimensional cross section flow, which may be obtained numerically. Examples are given in which a k(exp -5/3) spectrum is obtained by this method without using large wave number asymptotic analysis. The k(exp -5/3) inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the two-dimensional enstrophy spectrum. The results are insensitive to time dependence of the strain-rate, including even intermittent on-or-off strains.

Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model

USGS Publications Warehouse

Laenen, Antonius; Hansen, R.P.

1988-01-01

A one-dimensional, unsteady-state, open-channel model was used to analytically reproduce three lahar events. Factors contributing to the success of the modeling were: (1) the lahars were confined to a channel, (2) channel roughness was defined by field information, and (3) the volume of the flow remained relatively unchanged for the duration of the peak. Manning 's 'n ' values used in computing conveyance in the model were subject to the changing rheology of the debris flow and were calculated from field cross-section information (velocities used in these calculations were derived from super-elevation or run-up formulas). For the events modeled in this exercise, Manning 's 'n ' calculations ranged from 0.020 to 0.099. In all lahar simulations, the rheology of the flow changed in a downstream direction during the course of the event. Chen 's 'U ', the mudflow consistency index, changed approximately an order of magnitude for each event. The ' u ' values ranged from 5-2,260 kg/m for three events modeled. The empirical approach adopted in this paper is useful as a tool to help predict debris-flow behavior, but does not lead to understanding the physical processes of debris flows. (Author 's abstract)

a Marker-Based Eulerian-Lagrangian Method for Multiphase Flow with Supersonic Combustion Applications

NASA Astrophysics Data System (ADS)

Fan, Xiaofeng; Wang, Jiangfeng

2016-06-01

The atomization of liquid fuel is a kind of intricate dynamic process from continuous phase to discrete phase. Procedures of fuel spray in supersonic flow are modeled with an Eulerian-Lagrangian computational fluid dynamics methodology. The method combines two distinct techniques and develops an integrated numerical simulation method to simulate the atomization processes. The traditional finite volume method based on stationary (Eulerian) Cartesian grid is used to resolve the flow field, and multi-component Navier-Stokes equations are adopted in present work, with accounting for the mass exchange and heat transfer occupied by vaporization process. The marker-based moving (Lagrangian) grid is utilized to depict the behavior of atomized liquid sprays injected into a gaseous environment, and discrete droplet model 13 is adopted. To verify the current approach, the proposed method is applied to simulate processes of liquid atomization in supersonic cross flow. Three classic breakup models, TAB model, wave model and K-H/R-T hybrid model, are discussed. The numerical results are compared with multiple perspectives quantitatively, including spray penetration height and droplet size distribution. In addition, the complex flow field structures induced by the presence of liquid spray are illustrated and discussed. It is validated that the maker-based Eulerian-Lagrangian method is effective and reliable.

Modelling catchment areas for secondary care providers: a case study.

PubMed

Jones, Simon; Wardlaw, Jessica; Crouch, Susan; Carolan, Michelle

2011-09-01

Hospitals need to understand patient flows in an increasingly competitive health economy. New initiatives like Patient Choice and the Darzi Review further increase this demand. Essential to understanding patient flows are demographic and geographic profiles of health care service providers, known as 'catchment areas' and 'catchment populations'. This information helps Primary Care Trusts (PCTs) to review how their populations are accessing services, measure inequalities and commission services; likewise it assists Secondary Care Providers (SCPs) to measure and assess potential gains in market share, redesign services, evaluate admission thresholds and plan financial budgets. Unlike PCTs, SCPs do not operate within fixed geographic boundaries. Traditionally, SCPs have used administrative boundaries or arbitrary drive times to model catchment areas. Neither approach satisfactorily represents current patient flows. Furthermore, these techniques are time-consuming and can be challenging for healthcare managers to exploit. This paper presents three different approaches to define catchment areas, each more detailed than the previous method. The first approach 'First Past the Post' defines catchment areas by allocating a dominant SCP to each Census Output Area (OA). The SCP with the highest proportion of activity within each OA is considered the dominant SCP. The second approach 'Proportional Flow' allocates activity proportionally to each OA. This approach allows for cross-boundary flows to be captured in a catchment area. The third and final approach uses a gravity model to define a catchment area, which incorporates drive or travel time into the analysis. Comparing approaches helps healthcare providers to understand whether using more traditional and simplistic approaches to define catchment areas and populations achieves the same or similar results as complex mathematical modelling. This paper has demonstrated, using a case study of Manchester, that when estimating the catchment area of a planned new hospital, the extra level of detail provided by the gravity model may prove necessary. However, in virtually all other applications, the Proportional Flow method produced the optimal model for catchment populations in Manchester, based on several criteria: it produced the smallest RMS error; it addressed cross-boundary flows; the data used to create the catchment was readily available to SCPs; and it was simpler to reproduce than the gravity model method. Further work is needed to address how the Proportional Flow method can be used to reflect service redesign and handle OAs with zero or low activity. A next step should be the rolling out of the method across England and looking at further drill downs of data such as catchment by Healthcare Resource Group (HRG) rather than specialty level.

Landscape genetics as a tool for conservation planning: predicting the effects of landscape change on gene flow.

PubMed

van Strien, Maarten J; Keller, Daniela; Holderegger, Rolf; Ghazoul, Jaboury; Kienast, Felix; Bolliger, Janine

2014-03-01

For conservation managers, it is important to know whether landscape changes lead to increasing or decreasing gene flow. Although the discipline of landscape genetics assesses the influence of landscape elements on gene flow, no studies have yet used landscape-genetic models to predict gene flow resulting from landscape change. A species that has already been severely affected by landscape change is the large marsh grasshopper (Stethophyma grossum), which inhabits moist areas in fragmented agricultural landscapes in Switzerland. From transects drawn between all population pairs within maximum dispersal distance (< 3 km), we calculated several measures of landscape composition as well as some measures of habitat configuration. Additionally, a complete sampling of all populations in our study area allowed incorporating measures of population topology. These measures together with the landscape metrics formed the predictor variables in linear models with gene flow as response variable (F(ST) and mean pairwise assignment probability). With a modified leave-one-out cross-validation approach, we selected the model with the highest predictive accuracy. With this model, we predicted gene flow under several landscape-change scenarios, which simulated construction, rezoning or restoration projects, and the establishment of a new population. For some landscape-change scenarios, significant increase or decrease in gene flow was predicted, while for others little change was forecast. Furthermore, we found that the measures of population topology strongly increase model fit in landscape genetic analysis. This study demonstrates the use of predictive landscape-genetic models in conservation and landscape planning.

Simulating effects of highway embankments on estuarine circulation

USGS Publications Warehouse

Lee, Jonathan K.; Schaffranek, Raymond W.; Baltzer, Robert A.

1994-01-01

A two-dimensional depth-averaged, finite-difference, numerical model was used to simulate tidal circulation and mass transport in the Port Royal Sound. South Carolina, estuarine system. The purpose of the study was to demonstrate the utility of the Surface-Water. Integrated. Flow and Transport model (SWIFT2D) for evaluating changes in circulation patterns and mass transport caused by highway-crossing embankments. A model of subregion of Port Royal Sound including the highway crossings and having a grid size of 61 m (200ft) was derived from a 183-m (600-ft) model of the entire Port Royal Sound estuarine system. The 183-m model was used to compute boundary-value data for the 61-m submodel, which was then used to simulate flow conditions with and without the highway embankments in place. The numerical simulations show that, with the highway embankment in place, mass transport between the Broad River and Battery Creek is reduced and mass transport between the Beaufort River and Battery Creek is increased. The net result is that mass transport into and out of upper Battery Creek is reduced. The presence of the embankments also alters circulation patterns within Battery Creek.

Modeling pedestrian gap crossing index under mixed traffic condition.

PubMed

Naser, Mohamed M; Zulkiple, Adnan; Al Bargi, Walid A; Khalifa, Nasradeen A; Daniel, Basil David

2017-12-01

There are a variety of challenges faced by pedestrians when they walk along and attempt to cross a road, as the most recorded accidents occur during this time. Pedestrians of all types, including both sexes with numerous aging groups, are always subjected to risk and are characterized as the most exposed road users. The increased demand for better traffic management strategies to reduce the risks at intersections, improve quality traffic management, traffic volume, and longer cycle time has further increased concerns over the past decade. This paper aims to develop a sustainable pedestrian gap crossing index model based on traffic flow density. It focusses on the gaps accepted by pedestrians and their decision for street crossing, where (Log-Gap) logarithm of accepted gaps was used to optimize the result of a model for gap crossing behavior. Through a review of extant literature, 15 influential variables were extracted for further empirical analysis. Subsequently, data from the observation at an uncontrolled mid-block in Jalan Ampang in Kuala Lumpur, Malaysia was gathered and Multiple Linear Regression (MLR) and Binary Logit Model (BLM) techniques were employed to analyze the results. From the results, different pedestrian behavioral characteristics were considered for a minimum gap size model, out of which only a few (four) variables could explain the pedestrian road crossing behavior while the remaining variables have an insignificant effect. Among the different variables, age, rolling gap, vehicle type, and crossing were the most influential variables. The study concludes that pedestrians' decision to cross the street depends on the pedestrian age, rolling gap, vehicle type, and size of traffic gap before crossing. The inferences from these models will be useful to increase pedestrian safety and performance evaluation of uncontrolled midblock road crossings in developing countries. Copyright © 2017 National Safety Council and Elsevier Ltd. All rights reserved.

Development of a cross-section based stream package for MODFLOW

NASA Astrophysics Data System (ADS)

Ou, G.; Chen, X.; Irmak, A.

2012-12-01

Accurate simulation of stream-aquifer interactions for wide rivers using the streamflow routing package in MODFLOW is very challenging. To better represent a wide river spanning over multiple model grid cells, a Cross-Section based streamflow Routing (CSR) package is developed and incorporated into MODFLOW to simulate the interaction between streams and aquifers. In the CSR package, a stream segment is represented as a four-point polygon instead of a polyline which is traditionally used in streamflow routing simulation. Each stream segment is composed of upstream and downstream cross-sections. A cross-section consists of a number of streambed points possessing coordinates, streambed thicknesses and streambed hydraulic conductivities to describe the streambed geometry and hydraulic properties. The left and right end points are used to determine the locations of the stream segments. According to the cross-section geometry and hydraulic properties, CSR calculates the new stream stage at the cross-section using the Brent's method to solve the Manning's Equation. A module is developed to automatically compute the area of the stream segment polygon on each intersected MODFLOW grid cell as the upstream and downstream stages change. The stream stage and streambed hydraulic properties of model grids are interpolated based on the streambed points. Streambed leakage is computed as a function of streambed conductance and difference between the groundwater level and stream stage. The Muskingum-Cunge flow routing scheme with variable parameters is used to simulate the streamflow as the groundwater (discharge or recharge) contributes as lateral flows. An example is used to illustrate the capabilities of the CSR package. The result shows that the CSR is applicable to describing the spatial and temporal variation in the interaction between streams and aquifers. The input data become simple due to that the internal program automatically interpolates the cross-section data to each model grid cell.

Classifying low flow hydrological regimes at a regional scale

NASA Astrophysics Data System (ADS)

Kirkby, M. J.; Gallart, F.; Kjeldsen, T. R.; Irvine, B. J.; Froebrich, J.; Lo Porto, A.; de Girolamo, A.; Mirage Team

2011-12-01

The paper uses a simple water balance model that partitions the precipitation between actual evapotranspiration, quick flow and delayed flow, and has sufficient complexity to capture the essence of climate and vegetation controls on this partitioning. Using this model, monthly flow duration curves have been constructed from climate data across Europe to address the relative frequency of ecologically critical low flow stages in semi-arid rivers, when flow commonly persists only in disconnected pools in the river bed. The hydrological model is based on a dynamic partitioning of precipitation to estimate water available for evapotranspiration and plant growth and for residual runoff. The duration curve for monthly flows has then been analysed to give an estimate of bankfull flow based on recurrence interval. Arguing from observed ratios of cross-sectional areas at flood and low flows, hydraulic geometry suggests that disconnected flow under "pool" conditions is approximately 0.1% of bankfull flow. Flow duration curves define a measure of bankfull discharge on the basis of frequency. The corresponding frequency for pools is then read from the duration curve, using this (0.1%) ratio to estimate pool discharge from bank full discharge. The flow duration curve then provides an estimate of the frequency of poorly connected pool conditions, corresponding to this discharge, that constrain survival of river-dwelling arthropods and fish. The methodology has here been applied across Europe at 15 km resolution, and the potential is demonstrated for applying the methodology under alternative climatic scenarios.

Sele coastal plain flood risk due to wave storm and river flow interaction

NASA Astrophysics Data System (ADS)

Benassai, Guido; Aucelli, Pietro; Di Paola, Gianluigi; Della Morte, Renata; Cozzolino, Luca; Rizzo, Angela

2016-04-01

Wind waves, elevated water levels and river discharge can cause flooding in low-lying coastal areas, where the water level is the interaction between wave storm elevated water levels and river flow interaction. The factors driving the potential flood risk include weather conditions, river water stage and storm surge. These data are required to obtain inputs to run the hydrological model used to evaluate the water surface level during ordinary and extreme events regarding both the fluvial overflow and storm surge at the river mouth. In this paper we studied the interaction between the sea level variation and the river hydraulics in order to assess the location of the river floods in the Sele coastal plain. The wave data were acquired from the wave buoy of Ponza, while the water level data needed to assess the sea level variation were recorded by the tide gauge of Salerno. The water stages, river discharges and rating curves for Sele river were provided by Italian Hydrographic Service (Servizio Idrografico e Mareografico Nazionale, SIMN).We used the dataset of Albanella station (40°29'34.30"N, 15°00'44.30"E), located around 7 km from the river mouth. The extreme river discharges were evaluated through the Weibull equation, which were associated with their return period (TR). The steady state river water levels were evaluated through HEC-RAS 4.0 model, developed by Hydrologic Engineering Center (HEC) of the United States Army Corps of Engineers Hydrologic Engineering Center (USACE,2006). It is a well-known 1D model that computes water surface elevation (WSE) and velocity at discrete cross-sections by solving continuity, energy and flow resistance (e.g., Manning) equation. Data requirements for HEC-RAS include topographic information in the form of a series of cross-sections, friction parameter in the form of Manning's n values across each cross-section, and flow data including flow rates, flow change locations, and boundary conditions. For a steady state sub-critical simulation, the boundary condition is a known downstream WSE, in this case the elevated water level due to wave setup, wind setup and inverted barometer, while the upstream boundary condition consisted in WSE corresponding to river discharges associated to different return periods. The results of the simulations evidence, for the last 10 kilometers of the river, the burst of critical inundation scenarios even with moderate flow discharge, if associated with concurrent storm surge which increase the water level at the river mouth, obstructing normal flow discharge.

Cross-flow shearing effects on the trajectory of highly buoyant bent-over plumes

NASA Astrophysics Data System (ADS)

Tohidi, Ali; Kaye, Nigel Berkeley; Gollner, Michael J.

2017-11-01

The dynamics of highly buoyant plumes in cross-flow is ubiquitous throughout both industrial and environmental phenomena. The rise of smoke from a chimney, wastewater discharge into river currents, and dispersion of wildfire plumes are only a few instances. There have been many previous studies investigating the behavior of jets and highly buoyant plumes in cross-flow. So far, however, very little attention has been paid to the role of shearing effects in the boundary layer on the plume trajectory, particularly on the rise height. Numerical simulations and dimensional analysis are conducted to characterize the near- and far-field behavior of a highly buoyant plume in a boundary layer cross-flow. The results show that shear in the cross-flow leads to large differences in the rise height of the plume in relation to a uniform cross-flow, especially at far-field. This material is based upon work supported by the National Science Foundation under Grant No.1200560. Any opinions, findings, and conclusions or recommendations expressed in the material are of the authors and do not necessarily reflect the views of NSF.

Porosity development in coastal carbonate aquifers

USGS Publications Warehouse

Sanford, W.E.; Konikow, Leonard F.

1989-01-01

Combines geochemical mixing theory with the hydrodynamics of fresh-water-salt-water mixing zones in a coupled reaction-transport model. Results from the reaction-path model PHREEQE are used with a variable-density groundwater flow and solute-transport model to simulate an idealized cross section of a coastal carbonate aquifer. The dissolution process is sensitive to fresh-water chemistry, groundwater velocities, and sea-level movement. -from Authors

The interaction of moderately strong shock waves with thick perforated walls of low porosity

NASA Technical Reports Server (NTRS)

Grant, D. J.

1972-01-01

A theoretical prediction is given of the flow through thick perforated walls of low porosity resulting from the impingement of a moderately strong traveling shock wave. The model was a flat plate positioned normal to the direction of the flow. Holes bored in the plate parallel to the direction of the flow provided nominal hole length-to-diameter ratios of 10:1 and an axial porosity of 25 percent of the flow channel cross section. The flow field behind the reflected shock wave was assumed to behave as a reservoir producing a quasi-steady duct flow through the model. Rayleigh and Fanno duct flow theoretical computations for each of three possible auxiliary wave patterns that can be associated with the transmitted shock (to satisfy contact surface compatibility) were used to provide bounding solutions as an alternative to the more complex influence coefficients method. Qualitative and quantitative behavior was verified in a 1.5- by 2.0-in. helium shock tube. High speed Schlieren photography, piezoelectric pressure-time histories, and electronic-counter wave speed measurements were used to assess the extent of correlation with the theoretical flow models. Reduced data indicated the adequacy of the bounding theory approach to predict wave phenomena and quantitative response.

Cross-Shelf Exchange.

PubMed

Brink, K H

2016-01-01

Cross-shelf exchange dominates the pathways and rates by which nutrients, biota, and materials on the continental shelf are delivered and removed. This follows because cross-shelf gradients of most properties are usually far greater than those in the alongshore direction. The resulting transports are limited by Earth's rotation, which inhibits flow from crossing isobaths. Thus, cross-shelf flows are generally weak compared with alongshore flows, and this leads to interesting observational issues. Cross-shelf flows are enabled by turbulent mixing processes, nonlinear processes (such as momentum advection), and time dependence. Thus, there is a wide range of possible effects that can allow these critical transports, and different natural settings are often governed by different combinations of processes. This review discusses examples of representative transport mechanisms and explores possible observational and theoretical paths to future progress.

Engagement, Flow, Self-Efficacy, and Eustress of University Students: A Cross-National Comparison Between the Philippines and Argentina.

PubMed

Mesurado, Belén; Richaud, María Cristina; Mateo, Niño José

2016-01-01

This study examined how self-efficacy, eustress, and flow interact with academic engagement. First, it aimed to test a theoretical model that proposes that self-efficacy and eustress promote both flow and engagement and that, in turn, the state of flow promotes academic engagement in undergraduate student. We hypothesized that the theoretical model would be invariant for two countries: the Philippines and Argentina. Secondly, this research aimed to compare the levels of self-efficacy, eustress, study-flow and academic engagement experiences in students from both countries. One hundred seventy-six Filipinos and 171 Argentinean students participated in the study by completing inventories using the Utrecht Student Engagement Scale (Schaufeli, Martínez, et al., 2002), Optimal Experience Survey (Mesurado, 2008), Self-efficacy Scale (O'Sullivan, 2011), and Eustress Scale (O'Sullivan, 2011). Results show that the theoretical model fits the data well in both countries and is invariant across the Philippines and Argentina. Self-efficacy has a positive effect on flow and engagement, whereas eustress has a significant positive relationship with flow but is not directly associated with engagement. However, eustress has an indirect effect, through flow, on student engagement. On the other hand, there are different levels of engagement, flow, self-efficacy, and eustress. Argentinean students scored higher on absorption, dedication, self-efficacy, and flow. Filipino students, meanwhile, scored higher on eustress.

Machine Learning Interface for Medical Image Analysis.

PubMed

Zhang, Yi C; Kagen, Alexander C

2017-10-01

TensorFlow is a second-generation open-source machine learning software library with a built-in framework for implementing neural networks in wide variety of perceptual tasks. Although TensorFlow usage is well established with computer vision datasets, the TensorFlow interface with DICOM formats for medical imaging remains to be established. Our goal is to extend the TensorFlow API to accept raw DICOM images as input; 1513 DaTscan DICOM images were obtained from the Parkinson's Progression Markers Initiative (PPMI) database. DICOM pixel intensities were extracted and shaped into tensors, or n-dimensional arrays, to populate the training, validation, and test input datasets for machine learning. A simple neural network was constructed in TensorFlow to classify images into normal or Parkinson's disease groups. Training was executed over 1000 iterations for each cross-validation set. The gradient descent optimization and Adagrad optimization algorithms were used to minimize cross-entropy between the predicted and ground-truth labels. Cross-validation was performed ten times to produce a mean accuracy of 0.938 ± 0.047 (95 % CI 0.908-0.967). The mean sensitivity was 0.974 ± 0.043 (95 % CI 0.947-1.00) and mean specificity was 0.822 ± 0.207 (95 % CI 0.694-0.950). We extended the TensorFlow API to enable DICOM compatibility in the context of DaTscan image analysis. We implemented a neural network classifier that produces diagnostic accuracies on par with excellent results from previous machine learning models. These results indicate the potential role of TensorFlow as a useful adjunct diagnostic tool in the clinical setting.

Numerical investigation on nonlinear effect and vortex formation of oscillatory flow throughout a short tube in a thermoacoustic Stirling engine

NASA Astrophysics Data System (ADS)

Yang, Peng; Chen, Hui; Liu, Yingwen

2017-06-01

In this paper, a two-dimensional axisymmetric model of a thermoacoustic Stirling engine with a short tube where the cross section narrows has been developed. The transient streamlines and vortex formation through short tubes with different diameters in oscillatory flow have been investigated visually by computational fluid dynamics. Three dimensionless parameters, Reynolds number (Re), Keulegan-Carpenter number (KC), and Womersley number (Wo), are used to describe the flow regime and vortex characteristic throughout the short tube. High Re and Wo numbers indicate that the oscillatory flow develops into the turbulent flow through the short tube. The KC number has a direct effect on the transition of streamlines and the development of the vortex. For a small cross section where KC ≈ 1, streamlines rotate and the vortex forms at both sides of the short tube. The vortex stays in the main flow region, and intensity varies as streamlines are convected downstream. The velocity along the radius presents a Poiseuille profile within the influence of the vortex. For a large cross section where KC < 1, streamlines pass the short tube with little rotation and the vortex disappears in the main flow region and confines near the short tube. The velocity profile tends to be flat. The nonlinear effects including instantaneous pressure drop and power dissipation throughout the short tube are also discussed. It shows that the time averaged pressure drop is generated at the cost of power dissipation. Finally, the "effectiveness" is applied to evaluate the performance of the short tube. The results suggest that increasing the diameter of the short tube is in favor of reducing power dissipation, which is beneficial to improve "effectiveness."

On the effects of improved cross-section representation in one dimensional flow routing models applied to ephemeral rivers

USDA-ARS?s Scientific Manuscript database

Flash floods are an important component of the semi-arid hydrological cycle, and provide the potential for groundwater recharge as well as posing a dangerous natural hazard. A number of catchment models have been applied to flash flood prediction; however, in general they perform poorly. This study ...

Higher-order compositional modeling of three-phase flow in 3D fractured porous media based on cross-flow equilibrium

NASA Astrophysics Data System (ADS)

Moortgat, Joachim; Firoozabadi, Abbas

2013-10-01

Numerical simulation of multiphase compositional flow in fractured porous media, when all the species can transfer between the phases, is a real challenge. Despite the broad applications in hydrocarbon reservoir engineering and hydrology, a compositional numerical simulator for three-phase flow in fractured media has not appeared in the literature, to the best of our knowledge. In this work, we present a three-phase fully compositional simulator for fractured media, based on higher-order finite element methods. To achieve computational efficiency, we invoke the cross-flow equilibrium (CFE) concept between discrete fractures and a small neighborhood in the matrix blocks. We adopt the mixed hybrid finite element (MHFE) method to approximate convective Darcy fluxes and the pressure equation. This approach is the most natural choice for flow in fractured media. The mass balance equations are discretized by the discontinuous Galerkin (DG) method, which is perhaps the most efficient approach to capture physical discontinuities in phase properties at the matrix-fracture interfaces and at phase boundaries. In this work, we account for gravity and Fickian diffusion. The modeling of capillary effects is discussed in a separate paper. We present the mathematical framework, using the implicit-pressure-explicit-composition (IMPEC) scheme, which facilitates rigorous thermodynamic stability analyses and the computation of phase behavior effects to account for transfer of species between the phases. A deceptively simple CFL condition is implemented to improve numerical stability and accuracy. We provide six numerical examples at both small and larger scales and in two and three dimensions, to demonstrate powerful features of the formulation.

Macrosegregation Due to Convection in Al-19Cu Alloy Directionally Solidified Through an Abrupt Expansion in Cross-Section: A Comparison with Al-7Si

NASA Astrophysics Data System (ADS)

Ghods, M.; Lauer, M.; Grugel, R. N.; Tewari, S. N.; Poirier, D. R.

2017-10-01

Hypoeutectic Al-19 wt.% Cu alloys were directionally solidified at two different growth speeds in cylindrical molds that featured an abrupt increase in cross-section, from 3.2 to 9.5 mm in diameter. The effects of thermosolutal convection and shrinkage flow induced by the cross-section change on macrosegregation were investigated. Dendrite clustering and extensive radial macrosegregation were seen, particularly in the larger cross-section after expansion. Negative longitudinal macrosegregation right after the cross-section increase was observed; the extent of macrosegregation, however, decreases with increasing growth speed. Both thermal and flow effects due to cross-section change were seen to influence the radial macrosegregation immediately before, and after the expansion. Radial macrosegregation pattern was found to be changing as the mushy zone enters the larger cross-section region above the cross-section change where the solidification is in its unsteady state. The effect of the solutal expansion coefficient on macrosegregation was studied by comparing the degree of thermosolutal convection in Al-19 wt.% Cu with a previous study in which we investigated Al-7 wt.% Si. A two-dimensional model accounting for both shrinkage and thermosolutal convection was used to simulate the resulting steepling, as well as the axial and radial macrosegregation. The experimentally observed macrosegregation associated with the expansion during directional solidification is well predicted by the numerical simulations.

Dispersion mechanisms of a tidal river junction in the Sacramento–San Joaquin Delta, California

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

Gleichauf, Karla T.; Wolfram, Philip J.; Monsen, Nancy E.

In branching channel networks, such as in the Sacramento–San Joaquin River Delta, junction flow dynamics contribute to dispersion of ecologically important entities such as fish, pollutants, nutrients, salt, sediment, and phytoplankton. Flow transport through a junction largely arises from velocity phasing in the form of divergent flow between junction channels for a portion of the tidal cycle. Field observations in the Georgiana Slough junction, which is composed of the North and South Mokelumne rivers, Georgiana Slough, and the Mokelumne River, show that flow phasing differences between these rivers arise from operational, riverine, and tidal forcing. A combination of Acoustic Dopplermore » Current Profile (ADCP) boat transecting and moored ADCPs over a spring–neap tidal cycle (May to June 2012) monitored the variability of spatial and temporal velocity, respectively. Two complementary drifter studies enabled assessment of local transport through the junction to identify small-scale intrajunction dynamics. We supplemented field results with numerical simulations using the SUNTANS model to demonstrate the importance of phasing offsets for junction transport and dispersion. Different phasing of inflows to the junction resulted in scalar patchiness that is characteristic of MacVean and Stacey’s (2011) advective tidal trapping. Furthermore, we observed small-scale junction flow features including a recirculation zone and shear layer, which play an important role in intra-junction mixing over time scales shorter than the tidal cycle (i.e., super-tidal time scales). Thus, the study period spanned open- and closed-gate operations at the Delta Cross Channel. Synthesis of field observations and modeling efforts suggest that management operations related to the Delta Cross Channel can strongly affect transport in the Delta by modifying the relative contributions of tidal and riverine flows, thereby changing the junction flow phasing.« less

Dispersion mechanisms of a tidal river junction in the Sacramento–San Joaquin Delta, California

DOE PAGES

Gleichauf, Karla T.; Wolfram, Philip J.; Monsen, Nancy E.; ...

2014-12-17

In branching channel networks, such as in the Sacramento–San Joaquin River Delta, junction flow dynamics contribute to dispersion of ecologically important entities such as fish, pollutants, nutrients, salt, sediment, and phytoplankton. Flow transport through a junction largely arises from velocity phasing in the form of divergent flow between junction channels for a portion of the tidal cycle. Field observations in the Georgiana Slough junction, which is composed of the North and South Mokelumne rivers, Georgiana Slough, and the Mokelumne River, show that flow phasing differences between these rivers arise from operational, riverine, and tidal forcing. A combination of Acoustic Dopplermore » Current Profile (ADCP) boat transecting and moored ADCPs over a spring–neap tidal cycle (May to June 2012) monitored the variability of spatial and temporal velocity, respectively. Two complementary drifter studies enabled assessment of local transport through the junction to identify small-scale intrajunction dynamics. We supplemented field results with numerical simulations using the SUNTANS model to demonstrate the importance of phasing offsets for junction transport and dispersion. Different phasing of inflows to the junction resulted in scalar patchiness that is characteristic of MacVean and Stacey’s (2011) advective tidal trapping. Furthermore, we observed small-scale junction flow features including a recirculation zone and shear layer, which play an important role in intra-junction mixing over time scales shorter than the tidal cycle (i.e., super-tidal time scales). Thus, the study period spanned open- and closed-gate operations at the Delta Cross Channel. Synthesis of field observations and modeling efforts suggest that management operations related to the Delta Cross Channel can strongly affect transport in the Delta by modifying the relative contributions of tidal and riverine flows, thereby changing the junction flow phasing.« less

A two-dimensional hydrodynamic model of the St. Clair-Detroit River waterway in the Great Lakes basin

USGS Publications Warehouse

Holtschlag, David J.; Koschik, John A.

2002-01-01

The St. Clair–Detroit River Waterway connects Lake Huron with Lake Erie in the Great Lakes basin to form part of the international boundary between the United States and Canada. A two-dimensional hydrodynamic model is developed to compute flow velocities and water levels as part of a source-water assessment of public water intakes. The model, which uses the generalized finite-element code RMA2, discretizes the waterway into a mesh formed by 13,783 quadratic elements defined by 42,936 nodes. Seven steadystate scenarios are used to calibrate the model by adjusting parameters associated with channel roughness in 25 material zones in sub-areas of the waterway. An inverse modeling code is used to systematically adjust model parameters and to determine their associated uncertainty by use of nonlinear regression. Calibration results show close agreement between simulated and expected flows in major channels and water levels at gaging stations. Sensitivity analyses describe the amount of information available to estimate individual model parameters, and quantify the utility of flow measurements at selected cross sections and water-level measurements at gaging stations. Further data collection, model calibration analysis, and grid refinements are planned to assess and enhance two-dimensional flow simulation capabilities describing the horizontal flow distributions in St. Clair and Detroit Rivers and circulation patterns in Lake St. Clair.

Refraction of Sound Emitted Near Solid Boundaries from a Sheared Jet

NASA Technical Reports Server (NTRS)

Dill, Loren H.; Oyedrian, Ayo A.; Krejsa, Eugene A.

1998-01-01

A mathematical model is developed to describe the sound emitted from an arbitrary point within a turbulent flow near solid boundaries. A unidirectional, transversely sheared mean flow is assumed, and the cross-section of the cold jet is of arbitrary shape. The analysis begins with Lilley's formulation of aerodynamic noise and, depending upon the specific model of turbulence used, leads via Fourier analysis to an expression for the spectral density of the intensity of the far-field sound emitted from a unit volume of turbulence. The expressions require solution of a reduced Green's function of Lilley's equation as well as certain moving axis velocity correlations of the turbulence. Integration over the entire flow field is required in order to predict the sound emitted by the complete flow. Calculations are presented for sound emitted from a plugflow jet exiting a semi-infinite flat duct. Polar plots of the far-field directivity show the dependence upon frequency and source position within the duct. Certain model problems are suggested to investigate the effect of duct termination, duct geometry, and mean flow shear upon the far-field sound.

Single event time series analysis in a binary karst catchment evaluated using a groundwater model (Lurbach system, Austria).

PubMed

Mayaud, C; Wagner, T; Benischke, R; Birk, S

2014-04-16

The Lurbach karst system (Styria, Austria) is drained by two major springs and replenished by both autogenic recharge from the karst massif itself and a sinking stream that originates in low permeable schists (allogenic recharge). Detailed data from two events recorded during a tracer experiment in 2008 demonstrate that an overflow from one of the sub-catchments to the other is activated if the discharge of the main spring exceeds a certain threshold. Time series analysis (autocorrelation and cross-correlation) was applied to examine to what extent the various available methods support the identification of the transient inter-catchment flow observed in this binary karst system. As inter-catchment flow is found to be intermittent, the evaluation was focused on single events. In order to support the interpretation of the results from the time series analysis a simplified groundwater flow model was built using MODFLOW. The groundwater model is based on the current conceptual understanding of the karst system and represents a synthetic karst aquifer for which the same methods were applied. Using the wetting capability package of MODFLOW, the model simulated an overflow similar to what has been observed during the tracer experiment. Various intensities of allogenic recharge were employed to generate synthetic discharge data for the time series analysis. In addition, geometric and hydraulic properties of the karst system were varied in several model scenarios. This approach helps to identify effects of allogenic recharge and aquifer properties in the results from the time series analysis. Comparing the results from the time series analysis of the observed data with those of the synthetic data a good agreement was found. For instance, the cross-correlograms show similar patterns with respect to time lags and maximum cross-correlation coefficients if appropriate hydraulic parameters are assigned to the groundwater model. The comparable behaviors of the real and the synthetic system allow to deduce that similar aquifer properties are relevant in both systems. In particular, the heterogeneity of aquifer parameters appears to be a controlling factor. Moreover, the location of the overflow connecting the sub-catchments of the two springs is found to be of primary importance, regarding the occurrence of inter-catchment flow. This further supports our current understanding of an overflow zone located in the upper part of the Lurbach karst aquifer. Thus, time series analysis of single events can potentially be used to characterize transient inter-catchment flow behavior of karst systems.

Single event time series analysis in a binary karst catchment evaluated using a groundwater model (Lurbach system, Austria)

PubMed Central

Mayaud, C.; Wagner, T.; Benischke, R.; Birk, S.

2014-01-01

Summary The Lurbach karst system (Styria, Austria) is drained by two major springs and replenished by both autogenic recharge from the karst massif itself and a sinking stream that originates in low permeable schists (allogenic recharge). Detailed data from two events recorded during a tracer experiment in 2008 demonstrate that an overflow from one of the sub-catchments to the other is activated if the discharge of the main spring exceeds a certain threshold. Time series analysis (autocorrelation and cross-correlation) was applied to examine to what extent the various available methods support the identification of the transient inter-catchment flow observed in this binary karst system. As inter-catchment flow is found to be intermittent, the evaluation was focused on single events. In order to support the interpretation of the results from the time series analysis a simplified groundwater flow model was built using MODFLOW. The groundwater model is based on the current conceptual understanding of the karst system and represents a synthetic karst aquifer for which the same methods were applied. Using the wetting capability package of MODFLOW, the model simulated an overflow similar to what has been observed during the tracer experiment. Various intensities of allogenic recharge were employed to generate synthetic discharge data for the time series analysis. In addition, geometric and hydraulic properties of the karst system were varied in several model scenarios. This approach helps to identify effects of allogenic recharge and aquifer properties in the results from the time series analysis. Comparing the results from the time series analysis of the observed data with those of the synthetic data a good agreement was found. For instance, the cross-correlograms show similar patterns with respect to time lags and maximum cross-correlation coefficients if appropriate hydraulic parameters are assigned to the groundwater model. The comparable behaviors of the real and the synthetic system allow to deduce that similar aquifer properties are relevant in both systems. In particular, the heterogeneity of aquifer parameters appears to be a controlling factor. Moreover, the location of the overflow connecting the sub-catchments of the two springs is found to be of primary importance, regarding the occurrence of inter-catchment flow. This further supports our current understanding of an overflow zone located in the upper part of the Lurbach karst aquifer. Thus, time series analysis of single events can potentially be used to characterize transient inter-catchment flow behavior of karst systems. PMID:24748687

Comparative Study of Three Reconnection X-Line Models at the Earth's Dayside Magnetopause Using In Situ Observations

NASA Astrophysics Data System (ADS)

Souza, V. M. C. E. S.; Gonzalez, W.; Sibeck, D. G.; Koga, D.; Walsh, B.; Mendes, O., Jr.

2017-12-01

This work examines the large-scale aspects of magnetic field reconnection at the Earth's dayside magnetopause. We use two sets of reconnection events, which are identified mostly by the in situ detection of accelerated and Alfvénic plasma flows. We intercompare three analytical models that predict the reconnection X-line location and orientation, namely the Trattner et al., (2007) and Swisdak and Drake (2007) models, and also a modified version of the component merging model (Gonzalez and Mozer 1974, Sonnerup 1974). In the first set of reconnection observations, we show three fortuitous, quasi-simultaneous dayside magnetopause crossing events where two widely separated spacecraft detect reconnection signatures, and the X-line location and orientation can be inferred from the observations. We compare X-line model predictions to those inferred from observations. These three reconnection events indicate the presence of an extended (>7 Earth radii in length), component-type reconnection X-line on Earth's dayside magnetopause connecting and structuring the reconnection signatures at locations far apart. In the second set of reconnection events, we analyze the X-line models' performance in predicting the observed reconnection outflow direction, i.e., its north-south and/or east-west senses, in a total of 75 single, rather than multiple and quasi-simultaneous, magnetopause crossing events, where reconnection-associated plasma flows were clearly present. We found that the Swisdak and Drake's (2007) X-line model performs slightly better, albeit not statistically significant, when predicting both accelerated plasma flow north-south and east-west components in 73% and 53% of the cases, respectively, as compared to the Trattner et al., (2007) model (70% north-south, 42% east-west), and the modified component merging model (66% north-south, 50% east-west).

NIST/ISAC standardization study: variability in assignment of intensity values to fluorescence standard beads and in cross calibration of standard beads to hard dyed beads.

PubMed

Hoffman, Robert A; Wang, Lili; Bigos, Martin; Nolan, John P

2012-09-01

Results from a standardization study cosponsored by the International Society for Advancement of Cytometry (ISAC) and the US National Institute of Standards and Technology (NIST) are reported. The study evaluated the variability of assigning intensity values to fluorophore standard beads by bead manufacturers and the variability of cross calibrating the standard beads to stained polymer beads (hard-dyed beads) using different flow cytometers. Hard dyed beads are generally not spectrally matched to the fluorophores used to stain cells, and spectral response varies among flow cytometers. Thus if hard dyed beads are used as fluorescence calibrators, one expects calibration for specific fluorophores (e.g., FITC or PE) to vary among different instruments. Using standard beads surface-stained with specific fluorophores (FITC, PE, APC, and Pacific Blue™), the study compared the measured intensity of fluorophore standard beads to that of hard dyed beads through cross calibration on 133 different flow cytometers. Using robust CV as a measure of variability, the variation of cross calibrated values was typically 20% or more for a particular hard dyed bead in a specific detection channel. The variation across different instrument models was often greater than the variation within a particular instrument model. As a separate part of the study, NIST and four bead manufacturers used a NIST supplied protocol and calibrated fluorophore solution standards to assign intensity values to the fluorophore beads. Values assigned to the reference beads by different groups varied by orders of magnitude in most cases, reflecting differences in instrumentation used to perform the calibration. The study concluded that the use of any spectrally unmatched hard dyed bead as a general fluorescence calibrator must be verified and characterized for every particular instrument model. Close interaction between bead manufacturers and NIST is recommended to have reliable and uniformly assigned fluorescence standard beads. Copyright © 2012 International Society for Advancement of Cytometry.

Tomographic sensing and localization of fluorescently labeled circulating cells in mice in vivo

NASA Astrophysics Data System (ADS)

Zettergren, Eric; Swamy, Tushar; Runnels, Judith; Lin, Charles P.; Niedre, Mark

2012-07-01

Sensing and enumeration of specific types of circulating cells in small animals is an important problem in many areas of biomedical research. Microscopy-based fluorescence in vivo flow cytometry methods have been developed previously, but these are typically limited to sampling of very small blood volumes, so that very rare circulating cells may escape detection. Recently, we described the development of a ‘diffuse fluorescence flow cytometer’ (DFFC) that allows sampling of much larger blood vessels and therefore circulating blood volumes in the hindlimb, forelimb or tail of a mouse. In this work, we extend this concept by developing and validating a method to tomographically localize circulating fluorescently labeled cells in the cross section of a tissue simulating optical flow phantom and mouse limb. This was achieved using two modulated light sources and an array of six fiber-coupled detectors that allowed rapid, high-sensitivity acquisition of full tomographic data sets at 10 Hz. These were reconstructed into two-dimensional cross-sectional images using Monte Carlo models of light propagation and the randomized algebraic reconstruction technique. We were able to obtain continuous images of moving cells in the sample cross section with 0.5 mm accuracy or better. We first demonstrated this concept in limb-mimicking optical flow photons with up to four flow channels, and then in the tails of mice with fluorescently labeled multiple myeloma cells. This approach increases the overall diagnostic utility of our DFFC instrument.

Flow rate limitation in open wedge channel under microgravity

NASA Astrophysics Data System (ADS)

Wei, YueXing; Chen, XiaoQian; Huang, YiYong

2013-08-01

A study of flow rate limitation in an open wedge channel is reported in this paper. Under microgravity condition, the flow is controlled by the convection and the viscosity in the channel as well as the curvature of the liquid free surface. A maximum flow rate is achieved when the curvature cannot balance the pressure difference leading to a collapse of the free surface. A 1-dimensional theoretical model is used to predict the critical flow rate and calculate the shape of the free surface. Computational Fluid Dynamics tool is also used to simulate the phenomenon. Results show that the 1-dimensional model overestimates the critical flow rate because extra pressure loss is not included in the governing equation. Good agreement is found in 3-dimensional simulation results. Parametric study with different wedge angles and channel lengths show that the critical flow rate increases with increasing the cross section area; and decreases with increasing the channel length. The work in this paper can help understand the surface collapsing without gravity and for the design in propellant management devices in satellite tanks.

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.

Effects of lung disease on the three-dimensional structure and air flow pattern in the human airway tree

NASA Astrophysics Data System (ADS)

van de Moortele, Tristan; Nemes, Andras; Wendt, Christine; Coletti, Filippo

2016-11-01

The morphological features of the airway tree directly affect the air flow features during breathing, which determines the gas exchange and inhaled particle transport. Lung disease, Chronic Obstructive Pulmonary Disease (COPD) in this study, affects the structural features of the lungs, which in turn negatively affects the air flow through the airways. Here bronchial tree air volume geometries are segmented from Computed Tomography (CT) scans of healthy and diseased subjects. Geometrical analysis of the airway centerlines and corresponding cross-sectional areas provide insight into the specific effects of COPD on the airway structure. These geometries are also used to 3D print anatomically accurate, patient specific flow models. Three-component, three-dimensional velocity fields within these models are acquired using Magnetic Resonance Imaging (MRI). The three-dimensional flow fields provide insight into the change in flow patterns and features. Additionally, particle trajectories are determined using the velocity fields, to identify the fate of therapeutic and harmful inhaled aerosols. Correlation between disease-specific and patient-specific anatomical features with dysfunctional airflow patterns can be achieved by combining geometrical and flow analysis.

Modeling the Effects of Cu Content and Deformation Variables on the High-Temperature Flow Behavior of Dilute Al-Fe-Si Alloys Using an Artificial Neural Network.

PubMed

Shakiba, Mohammad; Parson, Nick; Chen, X-Grant

2016-06-30

The hot deformation behavior of Al-0.12Fe-0.1Si alloys with varied amounts of Cu (0.002-0.31 wt %) was investigated by uniaxial compression tests conducted at different temperatures (400 °C-550 °C) and strain rates (0.01-10 s -1 ). The results demonstrated that flow stress decreased with increasing deformation temperature and decreasing strain rate, while flow stress increased with increasing Cu content for all deformation conditions studied due to the solute drag effect. Based on the experimental data, an artificial neural network (ANN) model was developed to study the relationship between chemical composition, deformation variables and high-temperature flow behavior. A three-layer feed-forward back-propagation artificial neural network with 20 neurons in a hidden layer was established in this study. The input parameters were Cu content, temperature, strain rate and strain, while the flow stress was the output. The performance of the proposed model was evaluated using the K-fold cross-validation method. The results showed excellent generalization capability of the developed model. Sensitivity analysis indicated that the strain rate is the most important parameter, while the Cu content exhibited a modest but significant influence on the flow stress.

Numerical Estimation of the Outer Bank Resistance Characteristics in AN Evolving Meandering River

NASA Astrophysics Data System (ADS)

Wang, D.; Konsoer, K. M.; Rhoads, B. L.; Garcia, M. H.; Best, J.

2017-12-01

Few studies have examined the three-dimensional flow structure and its interaction with bed morphology within elongate loops of large meandering rivers. The present study uses a numerical model to simulate the flow pattern and sediment transport, especially the flow close to the outer-bank, at two elongate meandering loops in Wabash River, USA. The numerical grid for the model is based on a combination of airborne LIDAR data on floodplains and the multibeam data within the river channel. A Finite Element Method (FEM) is used to solve the non-hydrostatic RANS equation using a K-epsilon turbulence closure scheme. High-resolution topographic data allows detailed numerical simulation of flow patterns along the outer bank and model calibration involves comparing simulated velocities to ADCP measurements at 41 cross sections near this bank. Results indicate that flow along the outer bank is strongly influenced by large resistance elements, including woody debris, large erosional scallops within the bank face, and outcropping bedrock. In general, patterns of bank migration conform with zones of high near-bank velocity and shear stress. Using the existing model, different virtual events can be simulated to explore the impacts of different resistance characteristics on patterns of flow, sediment transport, and bank erosion.

Modeling the Effects of Cu Content and Deformation Variables on the High-Temperature Flow Behavior of Dilute Al-Fe-Si Alloys Using an Artificial Neural Network

PubMed Central

Shakiba, Mohammad; Parson, Nick; Chen, X.-Grant

2016-01-01

The hot deformation behavior of Al-0.12Fe-0.1Si alloys with varied amounts of Cu (0.002–0.31 wt %) was investigated by uniaxial compression tests conducted at different temperatures (400 °C–550 °C) and strain rates (0.01–10 s−1). The results demonstrated that flow stress decreased with increasing deformation temperature and decreasing strain rate, while flow stress increased with increasing Cu content for all deformation conditions studied due to the solute drag effect. Based on the experimental data, an artificial neural network (ANN) model was developed to study the relationship between chemical composition, deformation variables and high-temperature flow behavior. A three-layer feed-forward back-propagation artificial neural network with 20 neurons in a hidden layer was established in this study. The input parameters were Cu content, temperature, strain rate and strain, while the flow stress was the output. The performance of the proposed model was evaluated using the K-fold cross-validation method. The results showed excellent generalization capability of the developed model. Sensitivity analysis indicated that the strain rate is the most important parameter, while the Cu content exhibited a modest but significant influence on the flow stress. PMID:28773658

Nonrelativistic grey S n -transport radiative-shock solutions

DOE PAGES

Ferguson, J. M.; Morel, J. E.; Lowrie, R. B.

2017-06-01

We present semi-analytic radiative-shock solutions in which grey Sn-transport is used to model the radiation, and we include both constant cross sections and cross sections that depend on temperature and density. These new solutions solve for a variable Eddington factor (VEF) across the shock domain, which allows for interesting physics not seen before in radiative-shock solutions. Comparisons are made with the grey nonequilibrium-diffusion radiative-shock solutions of Lowrie and Edwards [1], which assumed that the Eddington factor is constant across the shock domain. It is our experience that the local Mach number is monotonic when producing nonequilibrium-diffusion solutions, but that thismore » monotonicity may disappear while integrating the precursor region to produce Sn-transport solutions. For temperature- and density-dependent cross sections we show evidence of a spike in the VEF in the far upstream portion of the radiative-shock precursor. We show evidence of an adaptation zone in the precursor region, adjacent to the embedded hydrodynamic shock, as conjectured by Drake [2, 3], and also confirm his expectation that the precursor temperatures adjacent to the Zel’dovich spike take values that are greater than the downstream post-shock equilibrium temperature. We also show evidence that the radiation energy density can be nonmonotonic under the Zel’dovich spike, which is indicative of anti-diffusive radiation flow as predicted by McClarren and Drake [4]. We compare the angle dependence of the radiation flow for the Sn-transport and nonequilibriumdiffusion radiation solutions, and show that there are considerable differences in the radiation flow between these models across the shock structure. Lastly, we analyze the radiation flow to understand the cause of the adaptation zone, as well as the structure of the Sn-transport radiation-intensity solutions across the shock structure.« less

Nonrelativistic grey S n -transport radiative-shock solutions

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

Ferguson, J. M.; Morel, J. E.; Lowrie, R. B.

We present semi-analytic radiative-shock solutions in which grey Sn-transport is used to model the radiation, and we include both constant cross sections and cross sections that depend on temperature and density. These new solutions solve for a variable Eddington factor (VEF) across the shock domain, which allows for interesting physics not seen before in radiative-shock solutions. Comparisons are made with the grey nonequilibrium-diffusion radiative-shock solutions of Lowrie and Edwards [1], which assumed that the Eddington factor is constant across the shock domain. It is our experience that the local Mach number is monotonic when producing nonequilibrium-diffusion solutions, but that thismore » monotonicity may disappear while integrating the precursor region to produce Sn-transport solutions. For temperature- and density-dependent cross sections we show evidence of a spike in the VEF in the far upstream portion of the radiative-shock precursor. We show evidence of an adaptation zone in the precursor region, adjacent to the embedded hydrodynamic shock, as conjectured by Drake [2, 3], and also confirm his expectation that the precursor temperatures adjacent to the Zel’dovich spike take values that are greater than the downstream post-shock equilibrium temperature. We also show evidence that the radiation energy density can be nonmonotonic under the Zel’dovich spike, which is indicative of anti-diffusive radiation flow as predicted by McClarren and Drake [4]. We compare the angle dependence of the radiation flow for the Sn-transport and nonequilibriumdiffusion radiation solutions, and show that there are considerable differences in the radiation flow between these models across the shock structure. Lastly, we analyze the radiation flow to understand the cause of the adaptation zone, as well as the structure of the Sn-transport radiation-intensity solutions across the shock structure.« less

Tunable two-dimensional acoustic meta-structure composed of funnel-shaped unit cells with multi-band negative acoustic property

NASA Astrophysics Data System (ADS)

Cho, Sungjin; Kim, Boseung; Min, Dongki; Park, Junhong

2015-10-01

This paper presents a two-dimensional heat-exhaust and sound-proof acoustic meta-structure exhibiting tunable multi-band negative effective mass density. The meta-structure was composed of periodic funnel-shaped units in a square lattice. Each unit cell operates simultaneously as a Helmholtz resonator (HR) and an extended pipe chamber resonator (EPCR), leading to a negative effective mass density creating bandgaps for incident sound energy dissipation without transmission. This structure allowed large heat-flow through the cross-sectional area of the extended pipe since the resonance was generated by acoustic elements without using solid membranes. The pipes were horizontally directed to a flow source to enable small flow resistance for cooling. Measurements of the sound transmission were performed using a two-load, four-microphone method for a unit cell and small reverberation chamber for two-dimensional panel to characterize the acoustic performance. The effective mass density showed significant frequency dependent variation exhibiting negative values at the specific bandgaps, while the effective bulk modulus was not affected by the resonator. Theoretical models incorporating local resonances in the multiple resonator units were proposed to analyze the noise reduction mechanism. The acoustic meta-structure parameters to create broader frequency bandgaps were investigated using the theoretical model. The negative effective mass density was calculated to investigate the creation of the bandgaps. The effects of design parameters such as length, cross-sectional area, and volume of the HR; length and cross-sectional area of the EPCR were analyzed. To maximize the frequency band gap, the suggested acoustic meta-structure panel, small neck length, and cross-sectional area of the HR, large EPCR length was advantageous. The bandgaps became broader when the two resonant frequencies were similar.

The NCOREL computer program for 3D nonlinear supersonic potential flow computations

NASA Technical Reports Server (NTRS)

Siclari, M. J.

1983-01-01

An innovative computational technique (NCOREL) was established for the treatment of three dimensional supersonic flows. The method is nonlinear in that it solves the nonconservative finite difference analog of the full potential equation and can predict the formation of supercritical cross flow regions, embedded and bow shocks. The method implicitly computes a conical flow at the apex (R = 0) of a spherical coordinate system and uses a fully implicit marching technique to obtain three dimensional cross flow solutions. This implies that the radial Mach number must remain supersonic. The cross flow solutions are obtained by using type dependent transonic relaxation techniques with the type dependency linked to the character of the cross flow velocity (i.e., subsonic/supersonic). The spherical coordinate system and marching on spherical surfaces is ideally suited to the computation of wing flows at low supersonic Mach numbers due to the elimination of the subsonic axial Mach number problems that exist in other marching codes that utilize Cartesian transverse marching planes.

The flows structure in unsteady gas flow in pipes with different cross-sections

NASA Astrophysics Data System (ADS)

Plotnikov, Leonid; Nevolin, Alexandr; Nikolaev, Dmitrij

2017-10-01

The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle) in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.

Numerical modeling of heat transfer in molten silicon during directional solidification process

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

Srinivasan, M.; Ramasamy, P., E-mail: ramasamyp@ssn.edu.in

2015-06-24

Numerical investigation is performed for some of the thermal and fluid flow properties of silicon melt during directional solidification by numerical modeling. Dimensionless numbers are extremely useful to understand the heat and mass transfer of fluid flow on Si melt and control the flow patterns during crystal growth processes. The average grain size of whole crystal would increase when the melt flow is laminar. In the silicon growth process, the melt flow is mainly driven by the buoyancy force resulting from the horizontal temperature gradient. The thermal and flow pattern influences the quality of the crystal through the convective heatmore » and mass transport. The computations are carried out in a 2D axisymmetric model using the finite-element technique. The buoyancy effect is observed in the melt domain for a constant Rayleigh number and for different Prandtl numbers. The convective heat flux and Reynolds numbers are studied in the five parallel horizontal cross section of melt silicon region. And also, velocity field is simulated for whole melt domain with limited thermal boundaries. The results indicate that buoyancy forces have a dramatic effect on the most of melt region except central part.« less

The effects of non-Newtonian blood flow on curved stenotic coronary artery

NASA Astrophysics Data System (ADS)

Li, Shuang; Chin, Cheng; Monty, Jason; Barlis, Peter; Ooi, Andrew

2017-11-01

Direct numerical simulations (DNS) are carried out using both Newtonian and non-Newtonian viscosity models under a pulsatile physiological flow condition to study the influences of the non-Newtonian blood property on the flow fields in the idealised curved stenotic artery model. Quemada model is adopted to simulate the non-Newtonian blood in the simulations. Both time-averaged and selected instantaneous velocity, vorticity and pressure data are examined and the differences between the Newtonian and non-Newtonian flows are examined. The non-Newtonian simulations tend to have blunted axial velocity profile compared to the Newtonian cases. In the proximal of post-stenotic region, smaller recirculation bubbles are observed because of the non-Newtonian effects. Decreased secondary flow strengths are observed upstream of stenosis while higher magnitudes of secondary flows are found out downstream of stenosis. The deviation of mean cross-sectionally axial vorticity is minimal except at the peak systole, where an additional vortice appears near the centre of the 90 degrees plane that is more pronounced in the Newtonian case. The influence of blood-analog viscosity increases the mean pressure drops. However, lower instantaneous pressure losses at peak systole are observed in contrast to the Newtonian blood analog fluid.

Effects of drop acceleration and deceleration on particle capture in a cross-flow gravity tower at intermediate drop Reynolds numbers.

PubMed

Kumar, Anoop; Gupta, S K; Kale, S R

2007-04-01

Cross-flow gravity towers are particle scrubbing devices in which water is sprayed from the top into particle-laden flow moving horizontally. Models for predicting particle capture assume drops traveling at terminal velocity and potential flow (ReD > 1000) around it, however, Reynolds numbers in the intermediate range of 1 to 1000 are common in gravity towers. Drops are usually injected at velocities greater than their terminal velocities (as in nozzles) or from near rest (perforated tray) and they accelerate/decelerate to their terminal velocity in the tower. Also, the effects of intermediate drop Reynolds number on capture efficiency have been simulated for (a) drops at their terminal velocity and (b) drops accelerating/decelerating to their terminal velocity. Tower efficiency based on potential flow about the drop is 40%-50% greater than for 200 mm drops traveling at their terminal velocity. The corresponding values for 500 mm drops are about 10%-20%. The drop injection velocity is important operating parameter. Increase in tower efficiency by about 40% for particles smaller than 5 mm is observed for increase in injection velocity from 0 to 20 m/s for 200 and 500mm drops.

Predicting Turbulent Convective Heat Transfer in Three-Dimensional Duct Flows

NASA Technical Reports Server (NTRS)

Rokni, M.; Gatski, T. B.

1999-01-01

The performance of an explicit algebraic stress model is assessed in predicting the turbulent flow and forced heat transfer in straight ducts, with square, rectangular, trapezoidal and triangular cross-sections, under fully developed conditions over a range of Reynolds numbers. Iso-thermal conditions are imposed on the duct walls and the turbulent heat fluxes are modeled by gradient-diffusion type models. At high Reynolds numbers (>/= 10(exp 5)), wall functions are used for the velocity and temperature fields; while at low Reynolds numbers damping functions are introduced into the models. Hydraulic parameters such as friction factor and Nusselt number are well predicted even when damping functions are used, and the present formulation imposes minimal demand on the number of grid points without any convergence or stability problems. Comparison between the models is presented in terms of the hydraulic parameters, friction factor and Nusselt number, as well as in terms of the secondary flow patterns occurring within the ducts.

Evaluation of flood inundation in Crystal Springs Creek, Portland, Oregon

USGS Publications Warehouse

Stonewall, Adam; Hess, Glen

2016-05-25

Efforts to improve fish passage have resulted in the replacement of six culverts in Crystal Springs Creek in Portland, Oregon. Two more culverts are scheduled to be replaced at Glenwood Street and Bybee Boulevard (Glenwood/Bybee project) in 2016. Recently acquired data have allowed for a more comprehensive understanding of the hydrology of the creek and the topography of the watershed. To evaluate the impact of the culvert replacements and recent hydrologic data, a Hydrologic Engineering Center-River Analysis System hydraulic model was developed to estimate water-surface elevations during high-flow events. Longitudinal surface-water profiles were modeled to evaluate current conditions and future conditions using the design plans for the culverts to be installed in 2016. Additional profiles were created to compare with the results from the most recent flood model approved by the Federal Emergency Management Agency for Crystal Springs Creek and to evaluate model sensitivity.Model simulation results show that water-surface elevations during high-flow events will be lower than estimates from previous models, primarily due to lower estimates of streamflow associated with the 0.01 and 0.002 annual exceedance probability (AEP) events. Additionally, recent culvert replacements have resulted in less ponding behind crossings. Similarly, model simulation results show that the proposed replacement culverts at Glenwood Street and Bybee Boulevard will result in lower water-surface elevations during high-flow events upstream of the proposed project. Wider culverts will allow more water to pass through crossings, resulting in slightly higher water-surface elevations downstream of the project during high-flows than water-surface elevations that would occur under current conditions. For the 0.01 AEP event, the water-surface elevations downstream of the Glenwood/Bybee project will be an average of 0.05 ft and a maximum of 0.07 ft higher than current conditions. Similarly, for the 0.002 AEP event, the water-surface elevations will be an average of 0.04 ft and a maximum of 0.19 ft higher than current conditions.

Modeling of static and flowing-gas diode pumped alkali lasers

NASA Astrophysics Data System (ADS)

Barmashenko, Boris D.; Auslender, Ilya; Yacoby, Eyal; Waichman, Karol; Sadot, Oren; Rosenwaks, Salman

2016-03-01

Modeling of static and flowing-gas subsonic, transonic and supersonic Cs and K Ti:Sapphire and diode pumped alkali lasers (DPALs) is reported. A simple optical model applied to the static K and Cs lasers shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. The model reproduces the observed threshold pump power in K DPAL which is much higher than that predicted by standard models of the DPAL. Scaling up flowing-gas DPALs to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. The performance of subsonic and, in particular, supersonic DPALs is compared with that of transonic, where supersonic nozzle and diffuser are spared and high power mechanical pump (needed for recovery of the gas total pressure which strongly drops in the diffuser), is not required for continuous closed cycle operation. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry, however, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.

SPH numerical investigation of the characteristics of an oscillating hydraulic jump at an abrupt drop

NASA Astrophysics Data System (ADS)

De Padova, Diana; Mossa, Michele; Sibilla, Stefano

2018-02-01

This paper shows the results of the smooth particle hydrodynamics (SPH) modelling of the hydraulic jump at an abrupt drop, where the transition from supercritical to subcritical flow is characterised by several flow patterns depending upon the inflow and tailwater conditions. SPH simulations are obtained by a pseudo-compressible XSPH scheme with pressure smoothing; turbulent stresses are represented either by an algebraic mixing-length model, or by a two-equation k- ɛ model. The numerical model is applied to analyse the occurrence of oscillatory flow conditions between two different jump types characterised by quasi-periodic oscillation, and the results are compared with experiments performed at the hydraulics laboratory of Bari Technical University. The purpose of this paper is to obtain a deeper understanding of the physical features of a flow which is in general difficult to be reproduced numerically, owing to its unstable character: in particular, vorticity and turbulent kinetic energy fields, velocity, water depth and pressure spectra downstream of the jump, and velocity and pressure cross-correlations can be computed and analysed.

Investigation of a supersonic cruise fighter model flow field

NASA Technical Reports Server (NTRS)

Reubush, D. E.; Bare, E. A.

1985-01-01

An investigation was conducted in the Langley 16-Foot Transonic Tunnel to survey the flow field around a model of a supersonic cruise fighter configuration. Local values of angle of attack, side flow, Mach number, and total pressure ratio were measured with a single multi-holed probe in three survey areas on a model previously used for nacelle/nozzle integration investigations. The investigation was conducted at Mach numbers of 0.6, 0.9, and 1.2, and at angles of attack from 0 deg to 10 deg. The purpose of the investigation was to provide a base of experimental data with which theoretically determined data can be compared. To that end the data are presented in tables as well as graphically, and a complete description of the model geometry is included as fuselage cross sections and wing span stations. Measured local angles of attack were generally greater than free stream angle of attack above the wing and generally smaller below. There were large spanwise local angle-of-attack and side flow gradients above the wing at the higher free stream angles of attack.

HYDROGEN ELECTROLYZER FLOW DISTRIBUTOR MODEL

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

Shadday, M

2006-09-28

The hybrid sulfur process (HyS) hydrogen electrolyzer consists of a proton exchange membrane (PEM) sandwiched between two porous graphite layers. An aqueous solution of sulfuric acid with dissolved SO{sub 2} gas flows parallel to the PEM through the porous graphite layer on the anode side of the electrolyzer. A flow distributor, consisting of a number of parallel channels acting as headers, promotes uniform flow of the anolyte fluid through the porous graphite layer. A numerical model of the hydraulic behavior of the flow distributor is herein described. This model was developed to be a tool to aid the design ofmore » flow distributors. The primary design objective is to minimize spatial variations in the flow through the porous graphite layer. The hydraulic data from electrolyzer tests consists of overall flowrate and pressure drop. Internal pressure and flow distributions are not measured, but these details are provided by the model. The model has been benchmarked against data from tests of the current electrolyzer. The model reasonably predicts the viscosity effect of changing the fluid from water to an aqueous solution of 30 % sulfuric acid. The permeability of the graphite layer was the independent variable used to fit the model to the test data, and the required permeability for a good fit is within the range literature values for carbon paper. The model predicts that reducing the number of parallel channels by 50 % will substantially improve the uniformity of the flow in the porous graphite layer, while maintaining an acceptable pressure drop across the electrolyzer. When the size of the electrolyzer is doubled from 2.75 inches square to 5.5 inches square, the same number of channels as in the current design will be adequate, but it is advisable to increase the channel cross-sectional flow area. This is due to the increased length of the channels.« less

Two-phase flow characterization based on advanced instrumentation, neural networks, and mathematical modeling

NASA Astrophysics Data System (ADS)

Mi, Ye

1998-12-01

The major objective of this thesis is focused on theoretical and experimental investigations of identifying and characterizing vertical and horizontal flow regimes in two-phase flows. A methodology of flow regime identification with impedance-based neural network systems and a comprehensive model of vertical slug flow have been developed. Vertical slug flow has been extensively investigated and characterized with geometric, kinematic and hydrodynamic parameters. A multi-sensor impedance void-meter and a multi-sensor magnetic flowmeter were developed. The impedance void-meter was cross-calibrated with other reliable techniques for void fraction measurements. The performance of the impedance void-meter to measure the void propagation velocity was evaluated by the drift flux model. It was proved that the magnetic flowmeter was applicable to vertical slug flow measurements. Separable signals from these instruments allow us to unearth most characteristics of vertical slug flow. A methodology of vertical flow regime identification was developed. Supervised neural network and self-organizing neural network systems were employed. First, they were trained with results from an idealized simulation of impedance in a two-phase mixture. The simulation was mainly based on Mishima and Ishii's flow regime map, the drift flux model, and the newly developed model of slug flow. Then, these trained systems were tested with impedance signals. The results showed that the neural network systems were appropriate classifiers of vertical flow regimes. The theoretical models and experimental databases used in the simulation were reliable. Furthermore, this approach was applied successfully to horizontal flow identification. A comprehensive model was developed to predict important characteristics of vertical slug flow. It was realized that the void fraction of the liquid slug is determined by the relative liquid motion between the Taylor bubble tail and the Taylor bubble wake. Relying on this understanding and experimental results, a special relationship was built for the void fraction of the liquid slug. The prediction of the void fraction of the liquid slug was considerably improved. Experimental characterization of vertical slug flows was performed extensively with the impedance void-meter and the magnetic flowmeter. The theoretical predictions were compared with the experimental results. The agreements between them are very satisfactory.

Flow regions of granules in Dorfan Impingo filter for gas cleanup

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

Kuo, J.T.; Smid, J.; Hsiau, S.S.

1999-07-01

Inside a two-dimensional model of the louvered Dorfan Impingo panel with transparent front and rear walls the flow region of filter granules without gas cross flow were observed. The white PE beads were used as filter granules. Colored PE beads served as tracers. Filter granules were discharged and circulated to the bed. The flow rate of filter medium was controlled by the belt conveyor. The image processing system including a Frame Grabber and JVC videocamera was used to record the granular flow. Every image of motion was digitized and stored in a file. The flow patterns and the quasi-stagnant zonesmore » history in the moving granular bed were evaluated. The experiment showed fast central moving region (flowing core) of filter granules and quasi-stagnant zones close to louver walls.« less

The dynamics of bedrock channel adjustment: Modeling the influence of sediment supply, weathering, and lithology on channel cross-sectional and longitudinal shape

NASA Astrophysics Data System (ADS)

Wobus, C.; Tucker, G.; Anderson, R.; Kean, J.; Small, E.; Hancock, G.

2007-12-01

The cross-sectional form of a natural river channel controls the capacity of the system to carry water off a landscape, to convey sediment derived from hillslopes, and to erode its bed and banks. Numerical models that describe the response of a landscape to changes in climate or tectonics therefore require formulations that can accommodate changes in channel cross-sectional geometry through time. We have developed a 2D numerical model that computes the formation of a channel in a cohesive, detachment-limited substrate subject to steady, unidirectional flow. Boundary shear stress is calculated using a simple approximation of the flow field in which log-velocity profiles are assumed to apply along vectors that are perpendicular to the local boundary surface. The resulting model predictions for the velocity structure, peak boundary shear stress, and equilibrium channel shape compare well with the predictions of a more sophisticated but more computationally demanding ray-isovel model. For example, the mean velocities computed by the two models are consistent to within ~3%, and the predicted peak shear stress is consistent to within ~7%. The efficiency of our model makes it suitable for calculations of long-term morphologic change both in single cross-sections and in series of cross-sections arrayed downstream. For a uniform substrate, the model predicts a strong tendency toward a fixed width-to-depth ratio, regardless of gradient or discharge. The model predicts power-law relationships between width and discharge with an exponent near 2/5, and between width and gradient with an exponent near -1/5. Recent enhancements to the model include the addition of sediment, which increases the width-to-depth ratio at steady state by favoring erosion of the channel walls relative to the channel bed (the "cover effect"). Inclusion of a probability density function of discharges with a simple parameterization of weathering along channel banks leads to the formation of model strath terraces. Downstream changes in substrate erodibility or tectonic uplift rate lead to step-function changes in channel width, consistent with empirical observations. Finally, explicit inclusion of bedload transport allows channel width, gradient, and the pattern of sediment flux to evolve dynamically, allowing us to explore the response of bedrock channels to both spatial patterns of rock uplift, and temporal variations in sediment input.

Stereo Particle Image Velocimetry Measurements of Transition Downstream of a Backward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Yao, Chung-Sheng

2017-01-01

Stereo particle image velocimetry measurements were performed downstream of a backward-facing step in a stationary-cross flow dominated flow. The PIV measurements exhibit excellent quantitative and qualitative agreement with the previously acquired hotwire data. Instantaneous PIV snapshots reveal new information about the nature and cause of the \\spikes" that occurred prior to breakdown in both the hotwire and PIV data. The PIV snapshots show that the events occur simultaneously across multiple stationary cross flow wavelengths, indicating that this is not simply a local event, but is likely caused by the 2D Tollmien-Schlichting instability that is introduced by the step. While the TS instability is a 2D instability, it is also modulated in the spanwise direction due to interactions with the stationary cross flow, as are the other unsteady disturbances present. Because of this modulation, the "spike" events cause an instantaneous increase of the spanwise modulation of the streamwise and spanwise velocity initially caused by the stationary cross flow. Breakdown appears to be caused by this instantaneous modulation, possibly due to a high-frequency secondary instability similar to a traveling-cross flow breakdown scenario. These results further illuminate the respective roles of the stationary cross flow and unsteady disturbances in transition downstream of a backward-facing step.

Direct simulation of heat transfer in a turbulent swept flow over a wire in a channel

NASA Astrophysics Data System (ADS)

Ranjan, Reetesh; Pantano, Carlos; Fischer, Paul; Siegel, Andrew

2009-11-01

We present results from direct numerical simulations of heat transfer (considered as a passive scalar) in a turbulent swept flow across a thin, cylindrical wire in a channel. This model mimics the flow through the wire-wrapped fuel pins typical of fast neutron reactor designs. Mean flow develops both along the wire and across the wire, leading to the formation of a turbulent cross-flow regime in the channel. This leads to improvement in heat transfer properties of the channel surface due to enhancement in mixing. The friction Reynolds number in the axial direction is approximately 305. Cross-flow friction Reynolds numbers ranging from 0 to 115 are examined. Two passive scalars at Prandtl number of 1.0 and 0.01 respectively, are simulated in this study. Constant flux boundary conditions are used along the walls of the channel and adiabatic conditions are used along the surface of the wire. The numerical method uses spectral elements in the plane perpendicular to the wire axis and Fourier decomposition in the direction of the axis of the wire. The simulations use up to 107 million collocation points and were performed at the Argonne Leadership BG/P supercomputer. The passive scalar field statistics are investigated, including mean scalar field, turbulence statistics and instantaneous surface scalar distribution.

The liquid fuel jet in subsonic crossflow

NASA Technical Reports Server (NTRS)

Nguyen, T. T.; Karagozian, A. R.

1990-01-01

An analytical/numerical model is described which predicts the behavior of nonreacting and reacting liquid jets injected transversely into subsonic cross flow. The compressible flowfield about the elliptical jet cross section is solved at various locations along the jet trajectory by analytical means for free-stream local Mach number perpendicular to jet cross section smaller than 0.3 and by numerical means for free-stream local Mach number perpendicular to jet cross section in the range 0.3-1.0. External and internal boundary layers along the jet cross section are solved by integral and numerical methods, and the mass losses due to boundary layer shedding, evaporation, and combustion are calculated and incorporated into the trajectory calculation. Comparison of predicted trajectories is made with limited experimental observations.

Analysis of capacity and traffic operations impacts of the World Trade Bridge in Laredo

DOT National Transportation Integrated Search

2001-07-01

Project 0-1800 pioneered the use of modern micro-simulation software to analyze the complex procedures involved in international border crossings. The animated models simulate the entire southbound commercial traffic flow, starting with U.S. Customs ...

Evaluation of the performance of the cross-flow air classifier in manufactured sand processing via CFD-DEM simulations

NASA Astrophysics Data System (ADS)

Petit, H. A.; Irassar, E. F.; Barbosa, M. R.

2018-01-01

Manufactured sands are particulate materials obtained as by product of rock crushing. Particle sizes in the sand can be as high as 6 mm and as low as a few microns. The concrete industry has been increasingly using these sands as fine aggregates to replace natural sands. The main shortcoming is the excess of particles smaller than <0.075 mm (Dust). This problem has been traditionally solved by a washing process. Air classification is being studied to replace the washing process and avoid the use of water. The complex classification process can only been understood with the aid of CFD-DEM simulations. This paper evaluates the applicability of a cross-flow air classifier to reduce the amount of dust in manufactured sands. Computational fluid dynamics (CFD) and discrete element modelling (DEM) were used for the assessment. Results show that the correct classification set up improves the size distribution of the raw materials. The cross-flow air classification is found to be influenced by the particle size distribution and the turbulence inside the chamber. The classifier can be re-designed to work at low inlet velocities to produce manufactured sand for the concrete industry.

DSMC simulations of shock tube experiments for the dissociation rate of nitrogen

NASA Astrophysics Data System (ADS)

Bird, G. A.

2012-11-01

The DSMC method has been used to simulate the flow associated with several experiments that led to predictions of the dissociation rate in nitrogen. One involved optical interferometry to determine the density behind strong shock wave and the other involved the measurement of the shock tube end-wall pressure after the reflection of a similar shock wave. DSMC calculations for the un-reflected shock wave were made with the older TCE model that converts rate coefficients to reaction cross-sections, with the newer Q-K model that predicts the rates and with a set of reaction cross-sections for nitrogen dissociation from QCT calculations. A comparison of the resulting density profiles with the measured profile provides a test of the validity of the DSMC chemistry models. The DSMC reaction rates were sampled directly in the DSMC calculation, both far downstream where the flow is in equilibrium and in the non-equilibrium region immediately behind the shock. This permits a critical evaluation of data reduction procedures that were employed to deduce the dissociation rate from the measured quantities.

Experimental investigations of aeration efficiency in high-head gated circular conduits.

PubMed

Cihat Tuna, M; Ozkan, Fahri; Baylar, Ahmet

2014-01-01

The primary purpose of water aeration is to increase the oxygen saturation of the water. This can be achieved by using hydraulic structures because of substantial air bubble entrainment at these structures. Closed conduit aeration is a particular instance of this. While there has been a great deal of research on air-demand ratio within closed conduit, very little research has specifically addressed aeration efficiency of closed conduit. In the present work an experimental study was conducted to investigate the aeration efficiency of high-head gated circular conduits. Results showed that high-head gated circular conduits were effective for oxygen transfer. The effects of Froude number and ratio of the water cross-sectional flow area to the conduit cross-sectional area on aeration efficiency were particularly significant, whereas the effect of conduit length was only moderate. Further, a design formula for the aeration efficiency was presented relating the aeration efficiency to ratio of water cross-sectional flow area to conduit cross-sectional area and Froude number. The obtained results will be useful in future modeling processes and aid the practicing engineer in predicting aeration efficiency for design purposes.

Flow in out-of-plane double S-bonds

NASA Technical Reports Server (NTRS)

Schmidt, M. C.; Whitelaw, J. H.; Yianneskis, M.

1986-01-01

Developing flows in two out-of-plane double S-bend configurations have been measured by laser-Doppler anemometry. The first duct had a rectangular cross-section 40mmx40mm at the inlet and consisted of a uniform area 22.5 deg. - 22.5 deg. S-duct upstream with a 22.5 deg.- 22.5 deg. S- diffuser downstream. The second duct had a circular cross-section and consisted of a 45 deg. - 45 deg. uniform area S-duct upstream with a 22.5 deg. -22.5 deg. S-diffuser downstream. In both configurations the ratio of the mean radius of curvature to the inlet hydraulic diameter was 7.0, the exit-to-inlet area ratio of the diffusers was 1.5 and the ducts were connected so that the centerline of the S-duct lay in a plane normal to that of the S-diffuser. Streamwise and cross-stream velocity components were measured in laminar flow for the rectangular duct and in turbulent flow for both configurations; measurements of the turbulence levels, cross-correlations and wall static pressures were also made in the turbulent flow cases. Secondary flows of the first kind are present in the first S-duct and they are complemented or counteracted by the secondary flows generated by the area expansion and by the curvature of the S-diffusers downstream. Cross-stream velocities with magnitudes up to 0.19 and 0.11 of the bulk velocity were measured in the laminar and turbulent flows respectively in the rectangular duct and six cross-flow vortices were evident at the exit of the duct in both flow cases. The turbulent flow in the circular duct was qualitatively similar to that in the rectangular configuration, but the cross-stream velocities measured at the exit plane were smaller in the circular geometry. The results are presented in sufficient detail and accuracy for the assessment of numerical calculation methods and are listed in tabular form for this purpose.

Experimental and simulation flow rate analysis of the 3/2 directional pneumatic valve

NASA Astrophysics Data System (ADS)

Blasiak, Slawomir; Takosoglu, Jakub E.; Laski, Pawel A.; Pietrala, Dawid S.; Zwierzchowski, Jaroslaw; Bracha, Gabriel; Nowakowski, Lukasz; Blasiak, Malgorzata

The work includes a study on the comparative analysis of two test methods. The first method - numerical method, consists in determining the flow characteristics with the use of ANSYS CFX. A modeled poppet directional valve 3/2 3D CAD software - SolidWorks was used for this purpose. Based on the solid model that was developed, simulation studies of the air flow through the way valve in the software for computational fluid dynamics Ansys CFX were conducted. The second method - experimental, entailed conducting tests on a specially constructed test stand. The comparison of the test results obtained on the basis of both methods made it possible to determine the cross-correlation. High compatibility of the results confirms the usefulness of the numerical procedures. Thus, they might serve to determine the flow characteristics of directional valves as an alternative to a costly and time-consuming test stand.

Effect of load transients on SOFC operation—current reversal on loss of load

NASA Astrophysics Data System (ADS)

Gemmen, Randall S.; Johnson, Christopher D.

The dynamics of solid oxide fuel cell (SOFC) operation have been considered previously, but mainly through the use of one-dimensional codes applied to co-flow fuel cell systems. In this paper several geometries are considered, including cross-flow, co-flow, and counter-flow. The details of the model are provided, and the model is compared with some initial experimental data. For parameters typical of SOFC operation, a variety of transient cases are investigated, including representative load increase and decrease and system shutdown. Of particular note for large load decrease conditions (e.g., shutdown) is the occurrence of reverse current over significant portions of the cell, starting from the moment of load loss up to the point where equilibrated conditions again provide positive current. Consideration is given as to when such reverse current conditions might most significantly impact the reliability of the cell.

Effects of channel constriction on upstream steering of flow around Locke Island, Columbia River, Washington

NASA Astrophysics Data System (ADS)

Loy, G. E.; Furbish, D. J.; Covey, A.

2010-12-01

Landsliding of the White Bluffs along the Columbia River in Washington State has constricted the width of the river on one side of Locke Island, a two-kilometer long island positioned in the middle of the channel. Associated changes in flow are thought to be causing relatively rapid erosion of Locke Island on the constricted side. This island is of cultural significance to Native American tribes of south-central Washington, so there are social as well as scientific reasons to understand how the alteration of stream channel processes resulting from the landsliding might be influencing observed erosion rates. Simple hydrodynamic calculations suggest that the constriction on one side of the island creates an upstream backwater effect. As a consequence a cross-stream pressure gradient upstream of the island results in steering of flow around the island into the unobstructed thread. This diversion of water decreases the discharge through the constriction. Therefore, flow velocities within the constriction are not necessarily expected to be higher than those in the unobstructed thread, contrary to initial reports suggesting that higher velocities within the constriction are the main cause of erosion. We set up streamtable experiments with lapse rate imaging to illustrate the backwater effects of the channel constriction and the associated cross-stream steering of flow around a model island. Our experiments are scaled by channel roughness and slope rather than geometrically, as the main focus is to understand the mechanical behavior of flow in this type of island-landslide system. In addition, we studied the stream velocities and flow steering as well as the magnitude of the backwater effect in both the constricted and unobstructed channels using tracer particles in the time-lapse images. These experimental data are compared with calculated upstream backwater distances determined from the known water-surface slope, flow depth, total discharge, and bed roughness. Furthermore, this experimental work will inform subsequent numerical modeling of flow and field-based measurements at Locke Island.

Rapid and efficient mixing in a slip-driven three-dimensional flow in a rectangular channel

NASA Astrophysics Data System (ADS)

Pacheco, J. Rafael; Ping Chen, Kang; Hayes, Mark A.

2006-08-01

A method for generating mixing in an electroosmotic flow of an electrolytic solution in a three-dimensional channel is proposed. When the width-to-height aspect ratio of the channel cross-section is large, mixing of a blob of a solute in a slip-driven three-dimensional flow in a rectangular channel can be used to model and assess the effectiveness of this method. It is demonstrated through numerical simulations that under certain operating conditions, rapid and efficient mixing can be achieved. Future investigation will include the solution of the exact equations and experimentation.

Interpretive geologic cross sections for the Death Valley regional flow system and surrounding areas, Nevada and California

USGS Publications Warehouse

Sweetkind, D.S.; Dickerson, R.P.; Blakely, R.J.; Denning, Paul

2001-01-01

This report presents a network of 28 geologic cross sections that portray subsurface geologic relations within the Death Valley regional ground-water system, a ground-water basin that encompasses a 3? x 3? area (approximately 70,000 km2) in southern Nevada and eastern California. The cross sections transect that part of the southern Great Basin that includes Death Valley, the Nevada Test Site, and the potential high-level nuclear waste underground repository at Yucca Mountain. The specific geometric relationships portrayed on the cross sections are discussed in the context of four general sub-regions that have stratigraphic similarities and general consistency of structural style: (1) the Nevada Test Site vicinity; (2) the Spring Mountains, Pahrump Valley and Amargosa Desert region; (3) the Death Valley region; and (4) the area east of the Nevada Test Site. The subsurface geologic interpretations portrayed on the cross sections are based on an integration of existing geologic maps, measured stratigraphic sections, published cross sections, well data, and geophysical data and interpretations. The estimated top of pre-Cenozoic rocks in the cross sections is based on inversion of gravity data, but the deeper parts of the sections are based on geologic conceptual models and are more speculative. The region transected by the cross sections includes part of the southern Basin and Range Province, the northwest-trending Walker Lane belt, the Death Valley region, and the northern Mojave Desert. The region is structurally complex, where a locally thick Tertiary volcanic and sedimentary section unconformably overlies previously deformed Proterozoic through Paleozoic rocks. All of these rocks have been deformed by complex Neogene ex-tensional normal and strike-slip faults. These cross sections form a three-dimensional network that portrays the interpreted stratigraphic and structural relations in the region; the sections form part of the geologic framework that will be incorporated in a complex numerical model of ground-water flow in the Death Valley region.

Two-dimensional fluid dynamics in a sharply bent channel: Laminar flow, separation bubble, and vortex dynamics

NASA Astrophysics Data System (ADS)

Matsumoto, Daichi; Fukudome, Koji; Wada, Hirofumi

2016-10-01

Understanding the hydrodynamic properties of fluid flow in a curving pipe and channel is important for controlling the flow behavior in technologies and biomechanics. The nature of the resulting flow in a bent pipe is extremely complicated because of the presence of a cross-stream secondary flow. In an attempt to disentangle this complexity, we investigate the fluid dynamics in a bent channel via the direct numerical simulation of the Navier-Stokes equation in two spatial dimensions. We exploit the absence of secondary flow from our model and systematically investigate the flow structure along the channel as a function of both the bend angle and Reynolds number of the laminar-to-turbulent regime. We numerically suggest a scaling relation between the shape of the separation bubble and the flow conductance, and construct an integrated phase diagram.

A design method for entrance sections of transonic wind tunnels with rectangular cross sections

NASA Technical Reports Server (NTRS)

Lionel, L.; Mcdevitt, J. B.

1975-01-01

A mathematical technique developed to design entrance sections for transonic or high-speed subsonic wind tunnels with rectangular cross sections is discribed. The transition from a circular cross-section setting chamber to a rectangular test section is accomplished smoothly so as not to introduce secondary flows (vortices or boundary-layer separation) into a uniform test stream. The results of static-pressure measurements in the transition region and of static and total-pressure surveys in the test section of a pilot model for a new facility at the Ames Research Center are presented.

Preliminary evaluation of ground-water flow in Bear Creek Valley, the Oak Ridge Reservation, Tennessee

USGS Publications Warehouse

Bailey, Z.C.

1988-01-01

Bear Creek Valley, Tennessee contains hazardous waste disposal sites where contaminants leach into ground and surface water. Groundwater flow and the potential migration of contaminants is poorly understood. The Valley is underlain by calcareous shale that contains limestone units. Ridges to the north and south are underlain by interbedded sandstones, siltstone and shale, and by massive, siliceous dolomite, respectively. The bedrock, which dips about 45 degrees southeast, is overlain by regolith to a maximum thickness of 80 ft. Observed hydraulic conductivities for the regolith range from 0.01 to 13 ft/day, and for the bedrock, from 0.001 to 11 ft/day. Groundwater flow is probably toward streams and is preferential along strike because of an areal anisotropy in hydraulic conductivity. A cross sectional groundwater flow model was used to test the conceptualized flow system and to help identify areas where additional data are needed. The preliminary model shows a pattern of recharge at both ridges, flow toward the valley, and upward flow that discharges into Bear Creek. Final model values of hydraulic conductivity in the bedrock range from 0.01 to 0.1 ft/day and reflect an areal anisotropy ratio of 1:5. Simulated recharge was 10 inches/year. (USGS)

Modeling of convection, temperature distribution and dendritic growth in glass-fluxed nickel melts

NASA Astrophysics Data System (ADS)

Gao, Jianrong; Kao, Andrew; Bojarevics, Valdis; Pericleous, Koulis; Galenko, Peter K.; Alexandrov, Dmitri V.

2017-08-01

Melt flow is often quoted as the reason for a discrepancy between experiment and theory on dendritic growth kinetics at low undercoolings. But this flow effect is not justified for glass-fluxed melts where the flow field is weaker. In the present work, we modeled the thermal history, flow pattern and dendritic structure of a glass-fluxed nickel sample by magnetohydrodynamics calculations. First, the temperature distribution and flow structure in the molten and undercooled melt were simulated by reproducing the observed thermal history of the sample prior to solidification. Then the dendritic structure and surface temperature of the recalescing sample were simulated. These simulations revealed a large thermal gradient crossing the sample, which led to an underestimation of the real undercooling for dendritic growth in the bulk volume of the sample. By accounting for this underestimation, we recalculated the dendritic tip velocities in the glass-fluxed nickel melt using a theory of three-dimensional dendritic growth with convection and concluded an improved agreement between experiment and theory.

Three-Dimensional Geologic Framework Model for a Karst Aquifer System, Hasty and Western Grove Quadrangles, Northern Arkansas

USGS Publications Warehouse

Turner, Kenzie J.; Hudson, Mark R.; Murray, Kyle E.; Mott, David N.

2007-01-01

Understanding ground-water flow in a karst aquifer benefits from a detailed conception of the three-dimensional (3D) geologic framework. Traditional two-dimensional products, such as geologic maps, cross-sections, and structure contour maps, convey a mental picture of the area but a stronger conceptualization can be achieved by constructing a digital 3D representation of the stratigraphic and structural geologic features. In this study, a 3D geologic model was created to better understand a karst aquifer system in the Buffalo National River watershed in northern Arkansas. The model was constructed based on data obtained from recent, detailed geologic mapping for the Hasty and Western Grove 7.5-minute quadrangles. The resulting model represents 11 stratigraphic zones of Ordovician, Mississippian, and Pennsylvanian age. As a result of the highly dissected topography, stratigraphic and structural control from geologic contacts and interpreted structure contours were sufficient for effectively modeling the faults and folds in the model area. Combined with recent dye-tracing studies, the 3D framework model is useful for visualizing the various geologic features and for analyzing the potential control they exert on the ground-water flow regime. Evaluation of the model, by comparison to published maps and cross-sections, indicates that the model accurately reproduces both the surface geology and subsurface geologic features of the area.

Experimental & Numerical Modeling of Non-combusting Model Firebrands' Transport

NASA Astrophysics Data System (ADS)

Tohidi, Ali; Kaye, Nigel

2016-11-01

Fire spotting is one of the major mechanisms of wildfire spread. Three phases of this phenomenon are firebrand formation and break-off from burning vegetation, lofting and downwind transport of firebrands through the velocity field of the wildfire, and spot fire ignition upon landing. The lofting and downwind transport phase is modeled by conducting large-scale wind tunnel experiments. Non-combusting rod-like model firebrands with different aspect ratios are released within the velocity field of a jet in a boundary layer cross-flow that approximates the wildfire velocity field. Characteristics of the firebrand dispersion are quantified by capturing the full trajectory of the model firebrands using the developed image processing algorithm. The results show that the lofting height has a direct impact on the maximum travel distance of the model firebrands. Also, the experimental results are utilized for validation of a highly scalable coupled stochastic & parametric firebrand flight model that, couples the LES-resolved velocity field of a jet-in-nonuniform-cross-flow (JINCF) with a 3D fully deterministic 6-degrees-of-freedom debris transport model. The validation results show that the developed numerical model is capable of estimating average statistics of the firebrands' flight. Authors would like to thank support of the National Science Foundation under Grant No. 1200560. Also, the presenter (Ali Tohid) would like to thank Dr. Michael Gollner from the University of Maryland College Park for the conference participation support.

Method and apparatus for controlling cross contamination of microfluid channels

DOEpatents

Hasselbrink, Jr., Ernest F.; Rehm, Jason E [Alameda, CA; Paul, Phillip H [Livermore, CA; Arnold, Don W [Livermore, CA

2006-02-07

A method for controlling fluid flow at junctions in microchannel systems. Control of fluid flow is accomplished generally by providing increased resistance to electric-field and pressure-driven flow in the form of regions of reduced effective cross-sectional area within the microchannels and proximate a channel junction. By controlling these flows in the region of a microchannel junction it is possible to eliminate sample dispersion and cross contamination and inject well-defined volumes of fluid from one channel to another.

Multi-scale modelling of non-uniform consolidation of uncured toughened unidirectional prepregs

NASA Astrophysics Data System (ADS)

Sorba, G.; Binetruy, C.; Syerko, E.; Leygue, A.; Comas-Cardona, S.; Belnoue, J. P.-H.; Nixon-Pearson, O. J.; Ivanov, D. S.; Hallett, S. R.; Advani, S. G.

2018-05-01

Consolidation is a crucial step in manufacturing of composite parts with prepregs because its role is to eliminate inter- and intra-ply gaps and porosity. Some thermoset prepreg systems are toughened with thermoplastic particles. Depending on their size, thermoplastic particles can be either located in between plies or distributed within the inter-fibre regions. When subjected to transverse compaction, resin will bleed out of low-viscosity unidirectional prepregs along the fibre direction, whereas one would expect transverse squeeze flow to dominate for higher viscosity prepregs. Recent experimental work showed that the consolidation of uncured toughened prepregs involves complex flow and deformation mechanisms where both bleeding and squeeze flow patterns are observed [1]. Micrographs of compacted and cured samples confirm these features as shown in Fig.1. A phenomenological model was proposed [2] where bleeding flow and squeeze flow are combined. A criterion for the transition from shear flow to resin bleeding was also proposed. However, the micrographs also reveal a resin rich layer between plies which may be contributing to the complex flow mechanisms during the consolidation process. In an effort to provide additional insight into these complex mechanisms, this work focuses on the 3D numerical modelling of the compaction of uncured toughened prepregs in the cross-ply configuration described in [1]. A transversely isotropic fluid model is used to describe the flow behaviour of the plies coupled with interplay resin flow of an isotropic fluid. The multi-scale flow model used is based on [3, 4]. A numerical parametric study is carried out where the resin viscosity, permeability and inter-ply thickness are varied to identify the role of important variables. The squeezing flow and the bleeding flow are compared for a range of process parameters to investigate the coupling and competition between the two flow mechanisms. Figure 4 shows the predicted displacement of the sample edge with the multi-scale compaction model after one time step [3]. The ply distortion and resin flow observed in Fig.1 is qualitatively retrieved by the computational model.

Influence of internal channel geometry of gas turbine blade on flow structure and heat transfer

NASA Astrophysics Data System (ADS)

Szwaba, Ryszard; Kaczynski, Piotr; Telega, Janusz; Doerffer, Piotr

2017-12-01

This paper presents the study of the influence of channel geometry on the flow structure and heat transfer, and also their correlations on all the walls of a radial cooling passage model of a gas turbine blade. The investigations focus on the heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of internal cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include a corner fillets, ribs with fillet radii and a special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which has very realistic features.

Variable speed limit strategies analysis with mesoscopic traffic flow model based on complex networks

NASA Astrophysics Data System (ADS)

Li, Shu-Bin; Cao, Dan-Ni; Dang, Wen-Xiu; Zhang, Lin

As a new cross-discipline, the complexity science has penetrated into every field of economy and society. With the arrival of big data, the research of the complexity science has reached its summit again. In recent years, it offers a new perspective for traffic control by using complex networks theory. The interaction course of various kinds of information in traffic system forms a huge complex system. A new mesoscopic traffic flow model is improved with variable speed limit (VSL), and the simulation process is designed, which is based on the complex networks theory combined with the proposed model. This paper studies effect of VSL on the dynamic traffic flow, and then analyzes the optimal control strategy of VSL in different network topologies. The conclusion of this research is meaningful to put forward some reasonable transportation plan and develop effective traffic management and control measures to help the department of traffic management.

An efficient semi-implicit method for three-dimensional non-hydrostatic flows in compliant arterial vessels.

PubMed

Fambri, Francesco; Dumbser, Michael; Casulli, Vincenzo

2014-11-01

Blood flow in arterial systems can be described by the three-dimensional Navier-Stokes equations within a time-dependent spatial domain that accounts for the elasticity of the arterial walls. In this article, blood is treated as an incompressible Newtonian fluid that flows through compliant vessels of general cross section. A three-dimensional semi-implicit finite difference and finite volume model is derived so that numerical stability is obtained at a low computational cost on a staggered grid. The key idea of the method consists in a splitting of the pressure into a hydrostatic and a non-hydrostatic part, where first a small quasi-one-dimensional nonlinear system is solved for the hydrostatic pressure and only in a second step the fully three-dimensional non-hydrostatic pressure is computed from a three-dimensional nonlinear system as a correction to the hydrostatic one. The resulting algorithm is robust, efficient, locally and globally mass conservative, and applies to hydrostatic and non-hydrostatic flows in one, two and three space dimensions. These features are illustrated on nontrivial test cases for flows in tubes with circular or elliptical cross section where the exact analytical solution is known. Test cases of steady and pulsatile flows in uniformly curved rigid and elastic tubes are presented. Wherever possible, axial velocity development and secondary flows are shown and compared with previously published results. Copyright © 2014 John Wiley & Sons, Ltd.

Viability of Cross-Flow Fan with Helical Blades for Vertical Take-off and Landing Aircraft

DTIC Science & Technology

2012-09-01

fluid dynamics (CFD) software, ANSYS - CFX , a three-dimensional (3-D) straight-bladed model was validated against previous study’s experimental results...computational fluid dynamics software (CFD), ANSYS - CFX , a three-dimensional (3-D) straight-bladed model was validated against previous study’s experimental...37 B. SIZING PARAMETERS AND ILLUSTRATION ................................. 37 APPENDIX B. ANSYS CFX PARAMETERS

Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

NASA Astrophysics Data System (ADS)

Kumar, Nirnimesh; Voulgaris, George; Warner, John C.; Olabarrieta, Maitane

The coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST) enables simulations that integrate oceanic, atmospheric, wave and morphological processes in the coastal ocean. Within the modeling system, the three-dimensional ocean circulation module (ROMS) is coupled with the wave generation and propagation model (SWAN) to allow full integration of the effect of waves on circulation and vice versa. The existing wave-current coupling component utilizes a depth dependent radiation stress approach. In here we present a new approach that uses the vortex force formalism. The formulation adopted and the various parameterizations used in the model as well as their numerical implementation are presented in detail. The performance of the new system is examined through the presentation of four test cases. These include obliquely incident waves on a synthetic planar beach and a natural barred beach (DUCK' 94); normal incident waves on a nearshore barred morphology with rip channels; and wave-induced mean flows outside the surf zone at the Martha's Vineyard Coastal Observatory (MVCO). Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK' 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from Garcez Faria et al. (1998, 2000). Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar/rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non-breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).

Laser interferometer skin-friction measurements of crossing-shock-wave/turbulent-boundary-layer interactions

NASA Technical Reports Server (NTRS)

Garrison, T. J.; Settles, G. S.; Narayanswami, N.; Knight, D. D.

1994-01-01

Wall shear stress measurements beneath crossing-shock-wave/turbulent boundary-layer interactions have been made for three interactions of different strengths. The interactions are generated by two sharp fins at symetric angles of attack mounted on a flat plate. The shear stress measurements were made for fin angles of 7 and 11 deg at Mach 3 and 15 deg at Mach 3.85. The measurements were made using a laser interferometer skin-friction meter, a device that determines the wall shear by optically measuring the time rate of thinning of an oil film placed on the test model surface. Results of the measurements reveal high skin-friction coefficients in the vicinity of the fin/plate junction and the presence of quasi-two-dimensional flow separation on the interaction center line. Additionally, two Navier-Stokes computations, one using a Baldwin-Lomax turbulence model and one using a k-epsilon model, are compared with the experimental results for the Mach 3.85, 15-deg interaction case. Although the k-epsilon model did a reasonable job of predicting the overall trend in portions of the skin-friction distribution, neither computation fully captured the physics of the near-surface flow in this complex interaction.

Electric fluid pump

DOEpatents

Van Dam, Jeremy Daniel; Turnquist, Norman Arnold; Raminosoa, Tsarafidy; Shah, Manoj Ramprasad; Shen, Xiaochun

2015-09-29

An electric machine is presented. The electric machine includes a hollow rotor; and a stator disposed within the hollow rotor, the stator defining a flow channel. The hollow rotor includes a first end portion defining a fluid inlet, a second end portion defining a fluid outlet; the fluid inlet, the fluid outlet, and the flow channel of the stator being configured to allow passage of a fluid from the fluid inlet to the fluid outlet via the flow channel; and wherein the hollow rotor is characterized by a largest cross-sectional area of hollow rotor, and wherein the flow channel is characterized by a smallest cross-sectional area of the flow channel, wherein the smallest cross-sectional area of the flow channel is at least about 25% of the largest cross-sectional area of the hollow rotor. An electric fluid pump and a power generation system are also presented.

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels

PubMed Central

Choi, Woo June; Qin, Wan; Chen, Chieh-Li; Wang, Jingang; Zhang, Qinqin; Yang, Xiaoqi; Gao, Bruce Z.; Wang, Ruikang K.

2016-01-01

Optical microangiography (OMAG) is a powerful optical angio-graphic tool to visualize micro-vascular flow in vivo. Despite numerous demonstrations for the past several years of the qualitative relationship between OMAG and flow, no convincing quantitative relationship has been proven. In this paper, we attempt to quantitatively correlate the OMAG signal with flow. Specifically, we develop a simplified analytical model of the complex OMAG, suggesting that the OMAG signal is a product of the number of particles in an imaging voxel and the decorrelation of OCT (optical coherence tomography) signal, determined by flow velocity, inter-frame time interval, and wavelength of the light source. Numerical simulation with the proposed model reveals that if the OCT amplitudes are correlated, the OMAG signal is related to a total number of particles across the imaging voxel cross-section per unit time (flux); otherwise it would be saturated but its strength is proportional to the number of particles in the imaging voxel (concentration). The relationship is validated using microfluidic flow phantoms with various preset flow metrics. This work suggests OMAG is a promising quantitative tool for the assessment of vascular flow. PMID:27446700

Nurses' exhaustion: the role of flow at work between job demands and job resources.

PubMed

Zito, Margherita; Cortese, Claudio G; Colombo, Lara

2016-01-01

In the light of the job demands-resources model, this study aimed to detect the mediating role of flow at work between job demands and job resources on one side, and exhaustion on the other. In a historical period where it is necessary to reduce the abandonment of nursing profession, flow is a useful tool to investigate the factors that can promote work motivation and prevent psychological distress. A cross-sectional study was conducted in a hospital, and 279 nurses completed a questionnaire. Analyses conducted are descriptive statistics, alphas, correlations and a structural equations model that considers the mediating role of flow at work. Findings show both the central role of job resources in determining flow at work, and the mediating role of flow at work in decreasing exhaustion, starting from job resources, and in decreasing the effect of job demands on exhaustion. Moreover, flow at work directly decreases exhaustion. Results show the relevance of containing job demands and provide job resources to promote positive experiences at work. To promote flow at work, organizations should offer specific resources, such as supervisors' support, job autonomy, and psychological support to manage the emotional charge. © 2015 John Wiley & Sons Ltd.

Extension and application of the Preissmann slot model to 2D transient mixed flows

NASA Astrophysics Data System (ADS)

Maranzoni, Andrea; Dazzi, Susanna; Aureli, Francesca; Mignosa, Paolo

2015-08-01

This paper presents an extension of the Preissmann slot concept for the modeling of highly transient two-dimensional (2D) mixed flows. The classic conservative formulation of the 2D shallow water equations for free surface flows is adapted by assuming that two fictitious vertical slots, aligned along the two Cartesian plane directions and normally intersecting, are added on the ceiling of each integration element. Accordingly, transitions between free surface and pressurized flow can be handled in a natural and straightforward way by using the same set of governing equations. The opportunity of coupling free surface and pressurized flows is actually useful not only in one-dimensional (1D) problems concerning sewer systems but also for modeling 2D flooding phenomena in which the pressurization of bridges, culverts, or other crossing hydraulic structures can be expected. Numerical simulations are performed by using a shock-capturing MUSCL-Hancock finite volume scheme combined with the FORCE (First-Order Centred) solver for the evaluation of the numerical fluxes. The validation of the mathematical model is accomplished on the basis of both exact solutions of 1D discontinuous initial value problems and reference radial solutions of idealized test cases with cylindrical symmetry. Furthermore, the capability of the model to deal with practical field-scale applications is assessed by simulating the transit of a bore under an arch bridge. Numerical results show that the proposed model is suitable for the prediction of highly transient 2D mixed flows.

Assessment of Flood Mitigation Solutions Using a Hydrological Model and Refined 2D Hydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Khuat Duy, B.; Archambeau, P.; Dewals, B. J.; Erpicum, S.; Pirotton, M.

2009-04-01

Following recurrent inundation problems on the Berwinne catchment, in Belgium, a combined hydrologic and hydrodynamic study has been carried out in order to find adequate solutions for the floods mitigation. Thanks to detailed 2D simulations, the effectiveness of the solutions can be assessed not only in terms of discharge and height reductions in the river, but also with other aspects such as the inundated surfaces reduction and the decrease of inundated buildings and roads. The study is carried out in successive phases. First, the hydrological runoffs are generated using a physically based and spatially distributed multi-layer model solving depth-integrated equations for overland flow, subsurface flow and baseflow. Real floods events are simulated using rainfall series collected at 8 stations (over 20 years of available data). The hydrological inputs are routed through the river network (and through the sewage network if relevant) with the 1D component of the modelling system, which solves the Saint-Venant equations for both free-surface and pressurized flows in a unified way. On the main part of the river, the measured river cross-sections are included in the modelling, and existing structures along the river (such as bridges, sluices or pipes) are modelled explicitely with specific cross sections. Two gauging stations with over 15 years of continuous measurements allow the calibration of both the hydrologic and hydrodynamic models. Second, the flood mitigation solutions are tested in the simulations in the case of an extreme flooding event, and their effects are assessed using detailed 2D simulations on a few selected sensitive areas. The digital elevation model comes from an airborne laser survey with a spatial resolution of 1 point per square metre and is completed in the river bed with a bathymetry interpolated from cross-section data. The upstream discharge is extracted from the 1D simulation for the selected rainfall event. The study carried out with this methodology allowed to assess the suggested solutions with multiple effectiveness criteria and therefore constitutes a very useful support for decision makers.

Flow Duct Data for Validation of Acoustic Liner Codes for Impedance Eduction

NASA Technical Reports Server (NTRS)

Ahuja, K. K.; Munro, Scott; Gaeta, R. J., Jr.

2000-01-01

The objective of the study reported here was to acquire acoustic and flow data with hard and lined duct wall duct sections for validation of a liner prediction code being developed at NASA LaRC. Both the mean flowfield and acoustic flowfields were determined in a cross-plane of the rectangular duct. A flow duct facility with acoustic drivers connected to a rectangular (4.7 x 2.0 inch) source section and a linear acoustic liner mounted downstream of the source section was used in this study. The liner section was designed to allow liner materials to be placed on all 4 walls of the duct. The test liner was of the locally-reacting type and was made from a ceramic material. The material, consisting of a tubular structure, was provided by NASA LaRC. The liner was approximately 8.89 cm (3.5 inches) thick. For the current study, only the two "short" sides of the duct were lined with liner material. The other two sides were hard walls. Two especially built instrumentation sections were attached on either sides of the liner section to allow acoustic and flow measurements to be made upstream and downstream of the liner. The two instrumentation duct sections were built to allow measurement of acoustic and flow properties at planes perpendicular to flow upstream and downstream of the liner section. The instrumentation section was also designed to provide a streamwise gradient in acoustic (complex) pressure from which the acoustic particle velocity, needed for the model validation, can be computed. Flow measurements included pressure, temperature, and velocity profiles upstream of the liner section. The in-flow sound pressure levels and phases were obtained with a microphone probe equipped with a nose cone in two cross planes upstream of the liner and two cross plane downstream of the liner. In addition to the acoustic measurements at the cross planes. axial centerline acoustic data was acquired using an axially traversing microphone probe which was traversed from a location upstream of the liner to some distance downstream of the liner. All probes used here had to be calibrated with respect to a standard microphone equipped with a nose cone to allow for the effects of flow.

Pressure data for four analytically defined arrow wings in supersonic flow. [Langley Unitary Plan Wind Tunnel tests

NASA Technical Reports Server (NTRS)

Townsend, J. C.

1980-01-01

In order to provide experimental data for comparison with newly developed finite difference methods for computing supersonic flows over aircraft configurations, wind tunnel tests were conducted on four arrow wing models. The models were machined under numeric control to precisely duplicate analytically defined shapes. They were heavily instrumented with pressure orifices at several cross sections ahead of and in the region where there is a gap between the body and the wing trailing edge. The test Mach numbers were 2.36, 2.96, and 4.63. Tabulated pressure data for the complete test series are presented along with selected oil flow photographs. Comparisons of some preliminary numerical results at zero angle of attack show good to excellent agreement with the experimental pressure distributions.

Load-based approaches for modelling visual clarity in streams at regional scale.

PubMed

Elliott, A H; Davies-Colley, R J; Parshotam, A; Ballantine, D

2013-01-01

Reduction of visual clarity in streams by diffuse sources of fine sediment is a cause of water quality impairment in New Zealand and internationally. In this paper we introduce the concept of a load of optical cross section (LOCS), which can be used for load-based management of light-attenuating substances and for water quality models that are based on mass accounting. In this approach, the beam attenuation coefficient (units of m(-1)) is estimated from the inverse of the visual clarity (units of m) measured with a black disc. This beam attenuation coefficient can also be considered as an optical cross section (OCS) per volume of water, analogous to a concentration. The instantaneous 'flux' of cross section is obtained from the attenuation coefficient multiplied by the water discharge, and this can be accumulated over time to give an accumulated 'load' of cross section (LOCS). Moreover, OCS is a conservative quantity, in the sense that the OCS of two combined water volumes is the sum of the OCS of the individual water volumes (barring effects such as coagulation, settling, or sorption). The LOCS can be calculated for a water quality station using rating curve methods applied to measured time series of visual clarity and flow. This approach was applied to the sites in New Zealand's National Rivers Water Quality Network (NRWQN). Although the attenuation coefficient follows roughly a power relation with flow at some sites, more flexible loess rating curves are required at other sites. The hybrid mechanistic-statistical catchment model SPARROW (SPAtially Referenced Regressions On Watershed attributes), which is based on a mass balance for mean annual load, was then applied to the NRWQN dataset. Preliminary results from this model are presented, highlighting the importance of factors related to erosion, such as rainfall, slope, hardness of catchment rock types, and the influence of pastoral development on the load of optical cross section.

Specific features of the flow structure in a reactive type turbine stage

NASA Astrophysics Data System (ADS)

Chernikov, V. A.; Semakina, E. Yu.

2017-04-01

The results of experimental studies of the gas dynamics for a reactive type turbine stage are presented. The objective of the studies is the measurement of the 3D flow fields in reference cross sections, experimental determination of the stage characteristics, and analysis of the flow structure for detecting the sources of kinetic energy losses. The integral characteristics of the studied stage are obtained by averaging the results of traversing the 3D flow over the area of the reference cross sections before and behind the stage. The averaging is performed using the conservation equations for mass, total energy flux, angular momentum with respect to the axis z of the turbine, entropy flow, and the radial projection of the momentum flux equation. The flow parameter distributions along the channel height behind the stage are obtained in the same way. More thorough analysis of the flow structure is performed after interpolation of the experimentally measured point parameter values and 3D flow velocities behind the stage. The obtained continuous velocity distributions in the absolute and relative coordinate systems are presented in the form of vector fields. The coordinates of the centers and the vectors of secondary vortices are determined using the results of point measurements of velocity vectors in the cross section behind the turbine stage and their subsequent interpolation. The approach to analysis of experimental data on aerodynamics of the turbine stage applied in this study allows one to find the detailed space structure of the working medium flow, including secondary coherent vortices at the root and peripheral regions of the air-gas part of the stage. The measured 3D flow parameter fields and their interpolation, on the one hand, point to possible sources of increased power losses, and, on the other hand, may serve as the basis for detailed testing of CFD models of the flow using both integral and local characteristics. The comparison of the numerical and experimental results, as regards local characteristics, using statistical methods yields the quantitative estimate of their agreement.

The effect of varying Mach number on crossing, glancing shocks/turbulent boundary-layer interactions

NASA Technical Reports Server (NTRS)

Hingst, W. R.; Williams, K. E.

1991-01-01

Two crossing side-wall shocks interacting with a supersonic tunnel wall boundary layer have been investigated over a Mach number range of 2.5 to 4.0. The investigation included a range of equal shock strengths produced by shock generators at angles from 4.0 to 12.0 degrees. Results of flow visualization show that the interaction is unseparated at the low shock generator angles. With increasing shock strength, the flow begins to form a separated region that grows in size and moves forward and eventually the model unstarts. The wall static pressures show a symmetrical compression that merges on the centerline upstream of the inviscid shock locations and becomes more 1D downstream. The region of the 1D pressure gradient moves upstream with increasing shock strengths until it coincides with the leading edge of the shock generators at the limit before model unstart. At the limiting conditions the wall pressure gradients are primarily in the axial direction throughout.

The Effect of Acoustic Forcing on Instabilities and Breakdown in Swept-Wing Flow over a Backward-Facing Step

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Shishkov, Olga; Wlezien, Richard W.; King, Rudolph A.; Choudhari, Meelan

2016-01-01

Instability interaction and breakdown were experimentally investigated in the flow over a swept backward-facing step. Acoustic forcing was used to excite the Tollmien-Schlichting (TS) instability and to acquire phase-locked results. The phase-averaged results illustrate the complex nature of the interaction between the TS and stationary cross flow instabilities. The weak stationary cross flow disturbance causes a distortion of the TS wavefront. The breakdown process is characterized by large positive and negative spikes in velocity. The positive spikes occur near the same time and location as the positive part of the TS wave. Higher-order spectral analysis was used to further investigate the nonlinear interactions between the TS instability and the traveling cross flow disturbances. The results reveal that a likely cause for the generation of the spikes corresponds to nonlinear interactions between the TS, traveling cross flow, and stationary cross flow disturbances. The spikes begin at low amplitudes of the unsteady and steady disturbances (2-4% U (sub e) (i.e. boundary layer edge velocity)) but can achieve very large amplitudes (20-30 percent U (sub e) (i.e. boundary layer edge velocity)) that initiate an early, though highly intermittent, breakdown to turbulence.

A tool to estimate bar patterns and flow conditions in estuaries when limited data is available

NASA Astrophysics Data System (ADS)

Leuven, J.; Verhoeve, S.; Bruijns, A. J.; Selakovic, S.; van Dijk, W. M.; Kleinhans, M. G.

2017-12-01

The effects of human interventions, natural evolution of estuaries and rising sea-level on food security and flood safety are largely unknown. In addition, ecologists require quantified habitat area to study future evolution of estuaries, but they lack predictive capability of bathymetry and hydrodynamics. For example, crucial input required for ecological models are values of intertidal area, inundation time, peak flow velocities and salinity. While numerical models can reproduce these spatial patterns, their computational times are long and for each case a new model must be developed. Therefore, we developed a comprehensive set of relations that accurately predict the hydrodynamics and the patterns of channels and bars, using a combination of the empirical relations derived from approximately 50 estuaries and theory for bars and estuaries. The first step is to predict local tidal prisms, which is the tidal prism that flows through a given cross-section. Second, the channel geometry is predicted from tidal prism and hydraulic geometry relations. Subsequently, typical flow velocities can be estimated from the channel geometry and tidal prism. Then, an ideal estuary shape is fitted to the measured planform: the deviation from the ideal shape, which is defined as the excess width, gives a measure of the locations where tidal bars form and their summed width (Leuven et al., 2017). From excess width, typical hypsometries can be predicted per cross-section. In the last step, flow velocities are calculated for the full range of occurring depths and salinity is calculated based on the estuary shape. Here, we will present a prototype tool that predicts equilibrium bar patterns and typical flow conditions. The tool is easy to use because the only input required is the estuary outline and tidal amplitude. Therefore it can be used by policy makers and researchers from multiple disciplines, such as ecologists, geologists and hydrologists, for example for paleogeographic reconstructions.

Efficient and robust compositional two-phase reservoir simulation in fractured media

NASA Astrophysics Data System (ADS)

Zidane, A.; Firoozabadi, A.

2015-12-01

Compositional and compressible two-phase flow in fractured media has wide applications including CO2 injection. Accurate simulations are currently based on the discrete fracture approach using the cross-flow equilibrium model. In this approach the fractures and a small part of the matrix blocks are combined to form a grid cell. The major drawback is low computational efficiency. In this work we use the discrete-fracture approach to model the fractures where the fracture entities are described explicitly in the computational domain. We use the concept of cross-flow equilibrium in the fractures (FCFE). This allows using large matrix elements in the neighborhood of the fractures. We solve the fracture transport equations implicitly to overcome the Courant-Freidricks-Levy (CFL) condition in the small fracture elements. Our implicit approach is based on calculation of the derivative of the molar concentration of component i in phase (cαi ) with respect to the total molar concentration (ci ) at constant volume V and temperature T. This contributes to significant speed up of the code. The hybrid mixed finite element method (MFE) is used to solve for the velocity in both the matrix and the fractures coupled with the discontinuous Galerkin (DG) method to solve the species transport equations in the matrix, and a finite volume (FV) discretization in the fractures. In large scale problems the proposed approach is orders of magnitude faster than the existing models.

Viability of Cross-Flow Fan for Vertical Take-Off and Landing Aircraft

DTIC Science & Technology

2012-06-01

NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS Approved for public release; distribution is unlimited VIABILITY OF CROSS...FLOW FAN FOR VERTICAL TAKE-OFF AND LANDING AIRCRAFT by Christopher T. Delagrange June 2012 Thesis Advisor: Garth V. Hobson Second...AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE Viability of Cross-Flow Fan for Vertical Take-Off and Landing Aircraft 5. FUNDING

Fundamental Physics and Model Assumptions in Turbulent Combustion Models for Aerospace Propulsion

DTIC Science & Technology

2014-06-01

of the equation of state is enabling to this variables split since a constant pressure implies that density can be obtained ... of models, the Reynolds stress term is first expressed as the sum of the deviatoric and isotropic stress parts. The deviatoric part is given by: τD...interpretation with regard to turbulent flow. It may be more appropriate to look at the modeling of the cross- stress terms in the LES equations

Time Resolved Stereo Particle Image Velocimetry Measurements of the Instabilities Downstream of a Backward-Facing Step in a Swept-Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Yao, Chung-Sheng

2017-01-01

Time-resolved particle image velocimetry (TRPIV) measurements are performed down-stream of a swept backward-facing step, with a height of 49% of the boundary-layer thickness. The results agree well qualitatively with previously reported hotwire measurements, though the amplitudes of the fluctuating components measured using TRPIV are higher. Nonetheless, the low-amplitude instabilities in the flow are fairly well resolved using TR- PIV. Proper orthogonal decomposition is used to study the development of the traveling cross flow and Tollmien-Schlichting (TS) instabilities downstream of the step and to study how they interact to form the large velocity spikes that ultimately lead to transition. A secondary mode within the traveling cross flow frequency band develops with a wavelength close to that of the stationary cross flow instability, so that at a certain point in the phase, it causes an increase in the spanwise modulation initially caused by the stationary cross flow mode. This increased modulation leads to an increase in the amplitude of the TS mode, which, itself, is highly modulated through interactions with the stationary cross flow. When the traveling cross flow and TS modes align in time and space, the large velocity spikes occur. Thus, these three instabilities, which are individually of low amplitude when the spikes start to occur (U'rms/Ue <0.03), interact and combine to cause a large flow disturbance that eventually leads to transition.

Preferential Flow Paths In A Karstified Spring Catchment: A Study Of Fault Zones As Conduits To Rapid Groundwater Flow

NASA Astrophysics Data System (ADS)

Kordilla, J.; Terrell, A. N.; Veltri, M.; Sauter, M.; Schmidt, S.

2017-12-01

In this study we model saturated and unsaturated flow in the karstified Weendespring catchment, located within the Leinetal graben in Goettingen, Germany. We employ the finite element COMSOL Multiphysics modeling software to model variably saturated flow using the Richards equation with a van Genuchten type parameterization. As part of the graben structure, the Weende spring catchment is intersected by seven fault zones along the main flow path of the 7400 m cross section of the catchment. As the Weende spring is part of the drinking water supply in Goettingen, it is particularly important to understand the vulnerability of the catchment and effect of fault zones on rapid transport of contaminants. Nitrate signals have been observed at the spring only a few days after the application of fertilizers within the catchment at a distance of approximately 2km. As the underlying layers are known to be highly impermeable, fault zones within the area are likely to create rapid flow paths to the water table and the spring. The model conceptualizes the catchment as containing three hydrogeological limestone units with varying degrees of karstification: the lower Muschelkalk limestone as a highly conductive layer, the middle Muschelkalk as an aquitard, and the upper Muschelkalk as another conductive layer. The fault zones are parameterized based on a combination of field data from quarries, remote sensing and literary data. The fault zone is modeled considering the fracture core as well as the surrounding damage zone with separate, specific hydraulic properties. The 2D conceptual model was implemented in COMSOL to study unsaturated flow at the catchment scale using van Genuchten parameters. The study demonstrates the importance of fault zones for preferential flow within the catchment and its effect on the spatial distribution of vulnerability.

Study on an undershot cross-flow water turbine

NASA Astrophysics Data System (ADS)

Nishi, Yasuyuki; Inagaki, Terumi; Li, Yanrong; Omiya, Ryota; Fukutomi, Junichiro

2014-06-01

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water turbines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after attaching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effective head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine efficiency. Also, the runner with no bottom plate differed from runners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full rotational speed range compared with that found in runners that had a bottom plate.

On modeling pressure diffusion in non-homogeneous shear flows

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Rogers, M. M.; Durbin, P.; Lele, S. K.

1996-01-01

New models are proposed for the 'slow and 'rapid' parts of the pressure diffusive transport based on the examination of DNS databases for plane mixing layers and wakes. The model for the 'slow' part is non-local, but requires the distribution of the triple-velocity correlation as a local source. The latter can be computed accurately for the normal component from standard gradient diffusion models, but such models are inadequate for the cross component. More work is required to remedy this situation.

Flow field and dissolved oxygen distributions in the outer channel of the Orbal oxidation ditch by monitor and CFD simulation.

PubMed

Guo, Xuesong; Zhou, Xin; Chen, Qiuwen; Liu, Junxin

2013-04-01

In the Orbal oxidation ditch, denitrification is primarily accomplished in the outer channel. However, the detailed characteristics of the flow field and dissolved oxygen (DO) distribution in the outer channel are not well understood. Therefore, in this study, the flow velocity and DO concentration in the outer channel of an Orbal oxidation ditch system in a wastewater treatment plant in Beijing (China) were monitored under actual operation conditions. The flow field and DO concentration distributions were analyzed by computed fluid dynamic modeling. In situ monitoring and modeling both showed that the flow velocity was heterogeneous in the outer channel. As a result, the DO was also heterogeneously distributed in the outer channel, with concentration gradients occurring along the flow direction as well as in the cross-section. This heterogeneous DO distribution created many anoxic and aerobic zones, which may have facilitated simultaneous nitrification-denitrification in the channel. These findings may provide supporting information for rational optimization of the performance of the Orbal oxidation ditch.

Cross-stream migration of active particles

NASA Astrophysics Data System (ADS)

Uspal, William; Katuri, Jaideep; Simmchen, Juliane; Miguel-Lopez, Albert; Sanchez, Samuel

For natural microswimmers, the interplay of swimming activity and external flow can promote robust directed motion, e.g. propulsion against (upstream rheotaxis) or perpendicular to the direction of flow. These effects are generally attributed to their complex body shapes and flagellar beat patterns. Here, using catalytic Janus particles as a model system, we report on a strong directional response that naturally emerges for spherical active particles in a channel flow. The particles align their propulsion axis to be perpendicular to both the direction of flow and the normal vector of a nearby bounding surface. We develop a deterministic theoretical model that captures this spontaneous transverse orientational order. We show how the directional response emerges from the interplay of external shear flow and swimmer/surface interactions (e.g., hydrodynamic interactions) that originate in swimming activity. Finally, adding the effect of thermal noise, we obtain probability distributions for the swimmer orientation that show good agreement with the experimental probability distributions. Our findings show that the qualitative response of microswimmers to flow is sensitive to the detailed interaction between individual microswimmers and bounding surfaces.

Development and verification of methods for predicting flow rates through leaks in valves and couplings

NASA Technical Reports Server (NTRS)

Russell, John M.

1993-01-01

This is the final report of a research effort which addresses the title problem. The report discusses two broad models of flows, which represent the following extreme cases: (1) inertia-dominated flow, where friction is relatively insignificant; and (2) friction-dominated flow where inertia is insignificant. In class (2), the leak channel might consist of the gap between a scratch in a plastic seal and a polished metal plate against which the seal is pressed. Here, the cross section of the leak channel is modeled as a flat bottomed crescent. A publication generated under the present grant period presents an exact solution of the equations of fully-developed laminar pipe flow of a liquid in the case of a crescent beneath a hyperbolic arc. A Master's thesis project supported by the present grant presents the corresponding solution beneath a circular arc. A second publication reviews the flow of a gas through the same channel, which may be analyzed by a standard one-dimensional model (Fanno flow) for an engineering approximation. Finally, the report discusses the design and progress in the fabrication of a leak-test cell, in which one may measure the flow of fluid through a controlled flaw in a seal. The aim of such measurements is to furnish data for comparison with the predictions of the theory.

Traffic of leukocytes in microfluidic channels with rectangular and rounded cross-sections.

PubMed

Yang, Xiaoxi; Forouzan, Omid; Burns, Jennie M; Shevkoplyas, Sergey S

2011-10-07

Traffic of leukocytes in microvascular networks (particularly through arteriolar bifurcations and venular convergences) affects the dynamics of capillary blood flow, initiation of leukocyte adhesion during inflammation, and localization and development of atherosclerotic plaques in vivo. Recently, a growing research effort has been focused on fabricating microvascular networks comprising artificial vessels with more realistic, rounded cross-sections. This paper investigated the impact of the cross-sectional geometry of microchannels on the traffic of leukocytes flowing with human whole blood through a non-symmetrical bifurcation that consisted of a 50 μm mother channel bifurcating into 30 μm and 50 μm daughter branches. Two versions of the same bifurcation comprising microchannels with rectangular and rounded cross-sections were fabricated using conventional multi-layer photolithography to produce rectangular microchannles that were then rounded in situ using a recently developed method of liquid PDMS/air bubble injection. For microchannels with rounded cross-sections, about two-thirds of marginated leukocytes traveling along a path in the top plane of the bifurcation entered the smallest 30 μm daughter branch. This distribution was reversed in microchannels with rectangular cross-sections--the majority of leukocytes traveling along a similar path continued to follow the 50 μm microchannels after the bifurcation. This dramatic difference in the distribution of leukocyte traffic among the branches of the bifurcation can be explained by preferential margination of leukocytes towards the corners of the 50 μm mother microchannels with rectangular cross-sections, and by the additional hindrance to leukocyte entry created by the sharp transition from the 50 μm mother microchannel to the 30 μm daughter branch at the intersection. The results of this study suggest that the trajectories of marginated leukocytes passing through non-symmetrical bifurcations are significantly affected by the cross-sectional geometry of microchannels and emphasize the importance of using microfludic systems with geometrical configurations closely matching physiological configurations when modeling the dynamics of whole blood flow in the microcirculation.

Regeneratively cooled transition duct with transversely buffered impingement nozzles

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

Morrison, Jay A; Lee, Ching-Pang; Crawford, Michael E

2015-04-21

A cooling arrangement (56) having: a duct (30) configured to receive hot gases (16) from a combustor; and a flow sleeve (50) surrounding the duct and defining a cooling plenum (52) there between, wherein the flow sleeve is configured to form impingement cooling jets (70) emanating from dimples (82) in the flow sleeve effective to predominately cool the duct in an impingement cooling zone (60), and wherein the flow sleeve defines a convection cooling zone (64) effective to cool the duct solely via a cross-flow (76), the cross-flow comprising cooling fluid (72) exhausting from the impingement cooling zone. In themore » impingement cooling zone an undimpled portion (84) of the flow sleeve tapers away from the duct as the undimpled portion nears the convection cooling zone. The flow sleeve is configured to effect a greater velocity of the cross-flow in the convection cooling zone than in the impingement cooling zone.« less

Three-dimensional flow structures past a bio-prosthetic valve in an in-vitro model of the aortic root.

PubMed

Hasler, David; Obrist, Dominik

2018-01-01

The flow field past a prosthetic aortic valve comprises many details that indicate whether the prosthesis is functioning well or not. It is, however, not yet fully understood how an optimal flow scenario would look, i.e. which subtleties of the fluid dynamics in place are essential regarding the durability and compatibility of a prosthetic valve. In this study, we measured and analyzed the 3D flow field in the vicinity of a bio-prosthetic heart valve in function of the aortic root size. The measurements were conducted within aortic root phantoms of different size, mounted in a custom-built hydraulic setup, which mimicked physiological flow conditions in the aorta. Tomographic particle image velocimetry was used to measure the 3D instantaneous velocity field at various instances. Several 3D fields (e.g. instantaneous and mean velocity, 3D shear rate) were analyzed and compared focusing on the impact of the aortic root size, but also in order to gain general insight in the 3D flow structure past the bio-prosthetic valve. We found that the diameter of the aortic jet relative to the diameter of the ascending aorta is the most important parameter in determining the characteristics of the flow. A large aortic cross-section, relative to the cross-section of the aortic jet, was associated with higher levels of turbulence intensity and higher retrograde flow in the ascending aorta.

Determination of secondary flow morphologies by wavelet analysis in a curved artery model with physiological inflow

NASA Astrophysics Data System (ADS)

Bulusu, Kartik V.; Hussain, Shadman; Plesniak, Michael W.

2014-11-01

Secondary flow vortical patterns in arterial curvatures have the potential to affect several cardiovascular phenomena, e.g., progression of atherosclerosis by altering wall shear stresses, carotid atheromatous disease, thoracic aortic aneurysms and Marfan's syndrome. Temporal characteristics of secondary flow structures vis-à-vis physiological (pulsatile) inflow waveform were explored by continuous wavelet transform (CWT) analysis of phase-locked, two-component, two-dimensional particle image velocimeter data. Measurements were made in a 180° curved artery test section upstream of the curvature and at the 90° cross-sectional plane. Streamwise, upstream flow rate measurements were analyzed using a one-dimensional antisymmetric wavelet. Cross-stream measurements at the 90° location of the curved artery revealed interesting multi-scale, multi-strength coherent secondary flow structures. An automated process for coherent structure detection and vortical feature quantification was applied to large ensembles of PIV data. Metrics such as the number of secondary flow structures, their sizes and strengths were generated at every discrete time instance of the physiological inflow waveform. An autonomous data post-processing method incorporating two-dimensional CWT for coherent structure detection was implemented. Loss of coherence in secondary flow structures during the systolic deceleration phase is observed in accordance with previous research. The algorithmic approach presented herein further elucidated the sensitivity and dependence of morphological changes in secondary flow structures on quasiperiodicity and magnitude of temporal gradients in physiological inflow conditions.

Performance characterization of complex fuel port geometries for hybrid rocket fuel grains

NASA Astrophysics Data System (ADS)

Bath, Andrew

This research investigated the 3D printing and burning of fuel grains with complex geometry and the development of software capable of modeling and predicting the regression of a cross-section of these complex fuel grains. The software developed did predict the geometry to a fair degree of accuracy, especially when enhanced corner rounding was turned on. The model does have some drawbacks, notably being relatively slow, and does not perfectly predict the regression. If corner rounding is turned off, however, the model does become much faster; although less accurate, this method does still predict a relatively accurate resulting burn geometry, and is fast enough to be used for performance-tuning or genetic algorithms. In addition to the modeling method, preliminary investigations into the burning behavior of fuel grains with a helical flow path were performed. The helix fuel grains have a regression rate of nearly 3 times that of any other fuel grain geometry, primarily due to the enhancement of the friction coefficient between the flow and flow path.

Modeling the pharyngeal pressure during adult nasal high flow therapy.

PubMed

Kumar, Haribalan; Spence, Callum J T; Tawhai, Merryn H

2015-12-01

Subjects receiving nasal high flow (NHF) via wide-bore nasal cannula may experience different levels of positive pressure depending on the individual response to NHF. In this study, airflow in the nasal airway during NHF-assisted breathing is simulated and nasopharyngeal airway pressure numerically computed, to determine whether the relationship between NHF and pressure can be described by a simple equation. Two geometric models are used for analysis. In the first, 3D airway geometry is reconstructed from computed tomography images of an adult nasal airway. For the second, a simplified geometric model is derived that has the same cross-sectional area as the complex model, but is more readily amenable to analysis. Peak airway pressure is correlated as a function of nasal valve area, nostril area and cannula flow rate, for NHF rates of 20, 40 and 60 L/min. Results show that airway pressure is related by a power law to NHF rate, valve area, and nostril area. Copyright © 2015 Elsevier B.V. All rights reserved.

Modeling and measurements of dispersion in a multi-generational model of the human airways

NASA Astrophysics Data System (ADS)

Fresconi, Frank

2005-11-01

A detailed knowledge of the flow and dispersion within the human respiratory tract is desirable for numerous reasons. Both risk assessments of exposure to toxic particles in the environment, and the design of medical delivery systems targeting both lung-specific conditions (asthma, cystic fibrosis, and chronic obstructive pulmonary disease) and system-wide ailments (diabetes, cancer, hormone replacement) would profit from such an understanding. The present work features both theoretical and experimental efforts aimed at elucidating the fluid mechanics of the lung. Steady streaming due to dissimilar velocity profiles between inspiration and expiration is addressed theoretically. This model employs a parameterized velocity profile to determine the effect on mass transport in the limit of no mixing and full mixing in the cross-section. Particle image velocimetry and laser induced fluorescence measurements of oscillatory flows in anatomically accurate models (single and multi-generational) of the conductive region of the lung illustrate pertinent flow features. Results are interpreted in the light of physiological applications.

Modeling flow around bluff bodies and predicting urban dispersion using large eddy simulation.

PubMed

Tseng, Yu-Heng; Meneveau, Charles; Parlange, Marc B

2006-04-15

Modeling air pollutant transport and dispersion in urban environments is especially challenging due to complex ground topography. In this study, we describe a large eddy simulation (LES) tool including a new dynamic subgrid closure and boundary treatment to model urban dispersion problems. The numerical model is developed, validated, and extended to a realistic urban layout. In such applications fairly coarse grids must be used in which each building can be represented using relatively few grid-points only. By carrying out LES of flow around a square cylinder and of flow over surface-mounted cubes, the coarsest resolution required to resolve the bluff body's cross section while still producing meaningful results is established. Specifically, we perform grid refinement studies showing that at least 6-8 grid points across the bluff body are required for reasonable results. The performance of several subgrid models is also compared. Although effects of the subgrid models on the mean flow are found to be small, dynamic Lagrangian models give a physically more realistic subgrid-scale (SGS) viscosity field. When scale-dependence is taken into consideration, these models lead to more realistic resolved fluctuating velocities and spectra. These results set the minimum grid resolution and subgrid model requirements needed to apply LES in simulations of neutral atmospheric boundary layer flow and scalar transport over a realistic urban geometry. The results also illustrate the advantages of LES over traditional modeling approaches, particularly its ability to take into account the complex boundary details and the unsteady nature of atmospheric boundary layer flow. Thus LES can be used to evaluate probabilities of extreme events (such as probabilities of exceeding threshold pollutant concentrations). Some comments about computer resources required for LES are also included.

Cross diffusion effect on MHD mixed convection flow of nonlinear radiative heat and mass transfer of Casson fluid over a vertical plate

NASA Astrophysics Data System (ADS)

Ganesh Kumar, K.; Archana, M.; Gireesha, B. J.; Krishanamurthy, M. R.; Rudraswamy, N. G.

2018-03-01

A study on magnetohydrodynamic mixed convection flow of Casson fluid over a vertical plate has been modelled in the presence of Cross diffusion effect and nonlinear thermal radiation. The governing partial differential equations are remodelled into ordinary differential equations by using similarity transformation. The accompanied differential equations are resolved numerically by using Runge-Kutta-Fehlberg forth-fifth order along with shooting method (RKF45 Method). The results of various physical parameters on velocity and temperature profiles are given diagrammatically. The numerical values of the local skin friction coefficient, local Nusselt number and local Sherwood number also are shown in a tabular form. It is found that, effect of Dufour and Soret parameter increases the temperature and concentration component correspondingly.

Calculation of linearized supersonic flow over slender cones of arbitrary cross section

NASA Technical Reports Server (NTRS)

Mascitti, V. R.

1972-01-01

Supersonic linearized conical-flow theory is used to determine the flow over slender pointed cones having horizontal and vertical planes of symmetry. The geometry of the cone cross sections and surface velocities are expanded in Fourier series. The symmetry condition permits the uncoupling of lifting and nonlifting solutions. The present method reduces to Ward's theory for flow over a cone of elliptic cross section. Results are also presented for other shapes. Results by this method diverge for cross-sectional shapes where the maximum thickness is large compared with the minimum thickness. However, even for these slender-body shapes, lower order solutions are good approximations to the complete solution.

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

USGS Publications Warehouse

Saffer, D.M.; Bekins, B.A.; Hickman, S.

2003-01-01

Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

NASA Technical Reports Server (NTRS)

Crawford, R. A.

1988-01-01

The influence of bulk turbulence and boundary layer thickness on the secondary flow development in a square, 90 degree turning duct was investigated. A three-dimensional laser velocimetry system was utilized to measure the mean and fluctuating components of velocity at six cross-planes in the duct. The results from this investigation, with entrance boundary layer thickness of 20 percent, were compared with the thin boundary layer results documented in NASA CR-174811. The axial velocity profiles, cross-flow velocities, and turbulence intensities were compared and evaluated with regard to the influence of bulk turbulence intensity and boundary layer thickness, and the influence was significant. The results of this investigation expand the 90 degree curved duct experimental data base to higher turbulence levels and thicker entrance boundary layers. The experimental results provide a challenging benchmark data base for computational fluid dynamics code development and validation. The variation of inlet bulk turbulence intensity provides additional information to aid in turbulence model evaluation.

Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks and the Effects on Thermal, Electrical, and Mechanical Performance

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

Recknagle, Kurtis P.; Koeppel, Brian J.; Sun, Xin

2007-04-30

Numerical simulations were performed to determine the effect that varying the percent on-cell steam-methane reformation would have on the thermal, electrical, and mechanical performance of generic, planar solid oxide fuel cell stacks. The study was performed using three-dimensional model geometries for cross-, co-, and counter-flow configuration stacks of 10x10- and 20x20-cm cell sizes. The analysis predicted the stress and temperature difference would be minimized for the 10x10-cm counter- and cross-flow stacks when 40 to 50% of the reformation reaction occurred on the anode. Gross electrical power density was virtually unaffected by the reforming. The co-flow stack benefited most from themore » on-cell reforming and had the lowest anode stresses of the 20x20-cm stacks. The analyses also suggest that airflows associated with 15% air utilization may be required for cooling the larger (20x20-cm) stacks.« less

Numerical and experimental research on pentagonal cross-section of the averaging Pitot tube

NASA Astrophysics Data System (ADS)

Zhang, Jili; Li, Wei; Liang, Ruobing; Zhao, Tianyi; Liu, Yacheng; Liu, Mingsheng

2017-07-01

Averaging Pitot tubes have been widely used in many fields because of their simple structure and stable performance. This paper introduces a new shape of the cross-section of an averaging Pitot tube. Firstly, the structure of the averaging Pitot tube and the distribution of pressure taps are given. Then, a mathematical model of the airflow around it is formulated. After that, a series of numerical simulations are carried out to optimize the geometry of the tube. The distribution of the streamline and pressures around the tube are given. To test its performance, a test platform was constructed in accordance with the relevant national standards and is described in this paper. Curves are provided, linking the values of flow coefficient with the values of Reynolds number. With a maximum deviation of only  ±3%, the results of the flow coefficient obtained from the numerical simulations were in agreement with those obtained from experimental methods. The proposed tube has a stable flow coefficient and favorable metrological characteristics.

Intermittent strong transport of the quasi-adiabatic plasma state.

PubMed

Kim, Chang-Bae; An, Chan-Yong; Min, Byunghoon

2018-06-05

The dynamics of the fluctuating electrostatic potential and the plasma density couched in the resistive-drift model at nearly adiabatic state are simulated. The linear modes are unstable if the phase difference between the potential and the density are positive. Exponential growth of the random small perturbations slows down due to the nonlinear E × B flows that work in two ways. They regulate the strength of the fluctuations by transferring the energy from the energy-producing scale to neighboring scales and reduce the cross phase at the same time. During quasi-steady relaxation sporadic appearance of very strong turbulent particle flux is observed that is characterized by the flat energy spectrum and the broad secondary peak in the mesoscale of the order of the gyro-radius. Such boost of the transport is found to be caused by presence of relatively large cross phase as the E × B flows are not effective in cancelling out the cross phase.

Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers

NASA Astrophysics Data System (ADS)

Kalpakli, Athanasia; Örlü, Ramis; Tillmark, Nils; Alfredsson, P. Henrik

2011-12-01

Turbulent pulsatile flows through pipe bends are prevalent in internal combustion engine components which consist of bent pipe sections and branching conduits. Nonetheless, most of the studies related to pulsatile flows in pipe bends focus on incompressible, low Womersley and low Dean number flows, primarily because they aim in modeling blood flow, while internal combustion engine related flows have mainly been addressed in terms of integral quantities and consist of single point measurements. The present study aims at bridging the gap between these two fields by means of time-resolved stereoscopic particle image velocimetry measurements in a pipe bend with conditions that are close to those encountered in exhaust manifolds. The time/phase-resolved three-dimensional cross-sectional flow-field 3 pipe diameters downstream the pipe bend is captured and the interplay between different secondary motions throughout a pulse cycle is discussed.

Sample stream distortion modeled in continuous-flow electrophoresis

NASA Technical Reports Server (NTRS)

Rhodes, P. H.

1979-01-01

Buoyancy-induced disturbances in an electrophoresis-type chamber were investigated. Five tracer streams (latex) were used to visualize the flows while a nine-thermistor array sensed the temperature field. The internal heating to the chamber was provided by a 400 Hz electrical field. Cooling to the chamber was provided on the front and back faces and, in addition, on both chamber side walls. Disturbances to the symmetric base flow in the chamber occurred in the broad plane of the chamber and resulted from the formation of lateral and axial temperature gradients. The effect of these gradients was to retard or increase local flow velocities at different positions in the chamber cross section, which resulted in lateral secondary flows being induced in the broad plane of the chamber. As the adverse temperature gradients increased in magnitude, the critical Rayleigh number was approached and reverse (separated) flow became apparent, which, subsequently, led to the onset of time variant secondary flows.