Study on of Seepage Flow Velocity in Sand Layer Profile as Affected by Water Depth and Slope Gradience

NASA Astrophysics Data System (ADS)

Han, Z.; Chen, X.

2017-12-01

BACKGROUND: The subsurface water flow velocity is of great significance in understanding the hydrodynamic characteristics of soil seepage and the influence of interaction between seepage flow and surface runoff on the soil erosion and sediment transport process. OBJECTIVE: To propose a visualized method and equipment for determining the seepage flow velocity and measuring the actual flow velocity and Darcy velocity as well as the relationship between them.METHOD: A transparent organic glass tank is used as the test soil tank, the white river sand is used as the seepage test material and the fluorescent dye is used as the indicator for tracing water flow, so as to determine the thickness and velocity of water flow in a visualized way. Water is supplied at the same flow rate (0.84 L h-1) to the three parts with an interval of 1m at the bottom of the soil tank and the pore water velocity and the thickness of each water layer are determined under four gradient conditions. The Darcy velocity of each layer is calculated according to the water supply flow and the discharge section area. The effective discharge flow pore is estimated according to the moisture content and porosity and then the relationship between Darcy velocity and the measured velocity is calculated based on the water supply flow and the water layer thickness, and finally the correctness of the calculation results is verified. RESULTS: According to the velocity calculation results, Darcy velocity increases significantly with the increase of gradient; in the sand layer profile, the flow velocity of pore water at different depths increases with the increase of gradient; under the condition of the same gradient, the lower sand layer has the maximum flow velocity of pore water. The air-filled porosity of sand layer determines the proportional relationship between Darcy velocity and pore flow velocity. CONCLUSIONS: The actual flow velocity and Darcy velocity can be measured by a visualized method and the relationship between Darcy velocity and pore velocity can be expressed well by the air-filled porosity of sand layer. The flow velocity measurement and test method adopted in the research is effective and feasible. IMPLICATIONS: The visualized flow velocity measurement method can be applied to simulate and measure the characteristics of subsurface water flow in the soil.

Mach Number effects on turbulent superstructures in wall bounded flows

NASA Astrophysics Data System (ADS)

Kaehler, Christian J.; Bross, Matthew; Scharnowski, Sven

2017-11-01

Planer and three-dimensional flow field measurements along a flat plat boundary layer in the Trisonic Wind Tunnel Munich (TWM) are examined with the aim to characterize the scaling, spatial organization, and topology of large scale turbulent superstructures in compressible flow. This facility is ideal for this investigation as the ratio of boundary layer thickness to test section spanwise extent ratio is around 1/25, ensuring minimal sidewall and corner effects on turbulent structures in the center of the test section. A major difficulty in the experimental investigation of large scale features is the mutual size of the superstructures which can extend over many boundary layer thicknesses. Using multiple PIV systems, it was possible to capture the full spatial extent of large-scale structures over a range of Mach numbers from Ma = 0.3 - 3. To calculate the average large-scale structure length and spacing, the acquired vector fields were analyzed by statistical multi-point methods that show large scale structures with a correlation length of around 10 boundary layer thicknesses over the range of Mach numbers investigated. Furthermore, the average spacing between high and low momentum structures is on the order of a boundary layer thicknesses. This work is supported by the Priority Programme SPP 1881 Turbulent Superstructures of the Deutsche Forschungsgemeinschaft.

Locomotion of bacteria in liquid flow and the boundary layer effect on bacterial attachment

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

Zhang, Chao, E-mail: zhangchao@cqu.edu.cn; Institute of Engineering Thermophysics, Chongqing University, Chongqing 400030; Liao, Qiang, E-mail: lqzx@cqu.edu.cn

The formation of biofilm greatly affects the performance of biological reactors, which highly depends on bacterial swimming and attachment that usually takes place in liquid flow. Therefore, bacterial swimming and attachment on flat and circular surfaces with the consideration of flow was studied experimentally. Besides, a mathematical model comprehensively combining bacterial swimming and motion with flow is proposed for the simulation of bacterial locomotion and attachment in flow. Both experimental and theoretical results revealed that attached bacteria density increases with decreasing boundary layer thickness on both flat and circular surfaces, the consequence of which is inherently related to the competitionmore » between bacterial swimming and the non-slip motion with flow evaluated by the Péclet number. In the boundary layer, where the Péclet number is relatively higher, bacterial locomotion mainly depends on bacterial swimming. Thinner boundary layer promotes bacterial swimming towards the surface, leading to higher attachment density. To enhance the performance of biofilm reactors, it is effective to reduce the boundary layer thickness on desired surfaces. - Highlights: • Study of bacterial locomotion in flow as an early stage in biofilm formation. • Mathematical model combining bacterial swimming and the motion with flow. • Boundary layer plays a key role in bacterial attachment under flow condition. • The competition between bacterial swimming and the motion with flow is evaluated.« less

Effect of shock interactions on mixing layer between co-flowing supersonic flows in a confined duct

NASA Astrophysics Data System (ADS)

Rao, S. M. V.; Asano, S.; Imani, I.; Saito, T.

2018-03-01

Experiments are conducted to observe the effect of shock interactions on a mixing layer generated between two supersonic streams of Mach number M _{1} = 1.76 and M _{2} = 1.36 in a confined duct. The development of this mixing layer within the duct is observed using high-speed schlieren and static pressure measurements. Two-dimensional, compressible Reynolds averaged Navier-Stokes equations are solved using the k-ω SST turbulence model in Fluent. Further, adverse pressure gradients are imposed by placing inserts of small (<7% of duct height) but finite (> boundary layer thickness) thickness on the walls of the test section. The unmatched pressures cause the mixing layer to bend and lead to the formation of shock structures that interact with the mixing layer. The mixing layer growth rate is found to increase after the shock interaction (nearly doubles). The strongest shock is observed when a wedge insert is placed in the M _{2} flow. This shock interacts with the mixing layer exciting flow modes that produce sinusoidal flapping structures which enhance the mixing layer growth rate to the maximum (by 1.75 times). Shock fluctuations are characterized, and it is observed that the maximum amplitude occurs when a wedge insert is placed in the M _{2} flow.

Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body

NASA Astrophysics Data System (ADS)

Das, S. P.; Srinivasan, U.; Arakeri, J. H.

2013-07-01

Boundary layers are subject to favorable and adverse pressure gradients because of both the temporal and spatial components of the pressure gradient. The adverse pressure gradient may cause the flow to separate. In a closed loop unsteady tunnel we have studied the initiation of separation in unsteady flow past a constriction (bluff body) in a channel. We have proposed two important scalings for the time when boundary layer separates. One is based on the local pressure gradient and the other is a convective time scale based on boundary layer parameters. The flow visualization using a dye injection technique shows the flow structure past the body. Nondimensional shedding frequency (Strouhal number) is calculated based on boundary layer and momentum thicknesses. Strouhal number based on the momentum thickness shows a close agreement with that for flat plate and circular cylinder.

Numerical modeling of heat transfer during hydrogen absorption in thin double-layered annular ZrCo beds

NASA Astrophysics Data System (ADS)

Cui, Yehui; Zeng, Xiangguo; Kou, Huaqin; Ding, Jun; Wang, Fang

2018-06-01

In this work a three-dimensional (3D) hydrogen absorption model was proposed to study the heat transfer behavior in thin double-layered annular ZrCo beds. Numerical simulations were performed to investigate the effects of conversion layer thickness, thermal conductivity, cooling medium and its flow velocity on the efficiency of heat transfer. Results reveal that decreasing the layer thickness and improving the thermal conductivity enhance the ability of heat transfer. Compared with nitrogen and helium, water appears to be a better medium for cooling. In order to achieve the best efficiency of heat transfer, the flow velocity needs to be maximized.

30 CFR 77.215 - Refuse piles; construction requirements.

Code of Federal Regulations, 2010 CFR

2010-07-01

... on a pile shall be spread in layers and compacted in such a manner so as to minimize the flow of air... constructed in compacted layers not exceeding 2 feet in thickness and shall not have any slope exceeding 2... refuse pile in compacted layers exceeding 2 feet in thickness and with slopes exceeding 27° where...

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

NASA Technical Reports Server (NTRS)

Patrick, William P.

1987-01-01

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

Numerical studies of transverse curvature effects on transonic flow stability

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.; Daudpota, Q. I.

1992-01-01

A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.

Instability of fluid flow over saturated porous medium

NASA Astrophysics Data System (ADS)

Lyubimova, Tatyana; Kolchanova, Ekaterina; Lyubimov, Dmitry

2013-04-01

We investigate the stability of a fluid flow over a saturated porous medium. The problem is of importance due to the applications to washing out of contaminants from the bottom layer of vegetation, whose properties are similar to the properties of porous medium. In the case of porous medium with the relatively high permeability and porosity the flow involves a part of the fluid saturating the porous medium, with the tangential fluid velocity drop occurring because of the resistance of the solid matrix. The drop leads to the instability analogous to Kelvin-Helmholtz one accompanied by the formation of travelling waves. In the present paper we consider a two-layer system consisting of a pure fluid layer and a porous layer saturated by the fluid located underneath. The system is bounded by a rigid surface at the bottom and a non-deformable free surface at the top. It is under the gravity and inclined at a slight angle to the horizontal axis. The boundary conditions at the interface between the fluid and porous layers are the continuity of fluid velocities and the balance of normal and tangential stresses taking into account the resistance of the solid matrix with respect to the fluid flow near the interface [1-2]. The problem is solved in the framework of the Brinkman model applying the classical shooting algorithm with orthogonalization. The stability boundaries of the stationary fluid flow over the saturated porous medium with respect to the small oscillatory perturbations are obtained for the various values of the Darcy number and the ratio of the porous layer thickness to the full thickness of the system d. It was shown that at the d > 0.5 with increasing the porous layer thickness (or with decreasing of the fluid layer thickness) the stability threshold rises. This is because of the fact that the instability is primarily caused by perturbations located in the fluid layer. At the d < 0.5 the reduction of the porous layer thickness leads to the stability threshold growth. The numerical calculations were also conducted for nonlinear regimes of the flow applying the finite-element method. Flow characteristics are determined at supercritical values of parameters. The work was made under the financial support of Russian Foundation for Basic Research (Grant 12-01-00795). 1. Ochoa-Tapia J. A. and Whitaker S. Momentum transfer at the boundary between a porous medium and a homogeneous fluid-I. Theoretical development. Int. J. Heat Mass Transfer. 1995. N 38. P. 2635-2646. 2. Ochoa-Tapia J. A. and Whitaker S. Momentum transfer at the boundary between a porous medium and a homogeneous fluid-II. Comparison with experiment. Int. J. Heat Mass Transfer. 1995. N 38. P. 2647-2655.

Numerical simulations of the flow in the HYPULSE expansion tube

NASA Technical Reports Server (NTRS)

Wilson, Gregory J.; Sussman, Myles A.; Bakos, Robert J.

1995-01-01

Axisymmetric numerical simulations with finite-rate chemistry are presented for two operating conditions in the HYPULSE expansion tube. The operating gas for these two cases is nitrogen and the computations are compared to experimental data. One test condition is at a total enthalpy of 15.2 MJ/Kg and a relatively low static pressure of 2 kPa. This case is characterized by a laminar boundary layer and significant chemical nonequilibrium in the acceleration gas. The second test condition is at a total enthalpy of 10.2 MJ/Kg and a static pressure of 38 kPa and is characterized by a turbulent boundary layer. For both cases, the time-varying test gas pressure predicted by the simulations is in good agreement with experimental data. The computations are also found to be in good agreement with Mirels' correlations for shock tube flow. It is shown that the nonuniformity of the test gas observed in the HYPULSE expansion tube is strongly linked to the boundary layer thickness. The turbulent flow investigated has a larger boundary layer and greater test gas nonuniformity. In order to investigate possibilities of improving expansion tube flow quality by reducing the boundary layer thickness, parametric studies showing the effect of density and turbulent transition point on the test conditions are also presented. Although an increase in the expansion tube operating pressure level would reduce the boundary layer thickness, the simulations indicate that the reduction would be less than what is predicted by flat plate boundary layer correlations.

Boundary Layer Measurements in the Trisonic Gas-dynamics Facility Using Particle Image Velocimetery with CO2 Seeding

DTIC Science & Technology

2012-03-22

understanding of fluid mechanics and aircraft design. The fundamental theories, concepts and equations developed by men like Newton, Bernoulli ...resulting instantaneous flow field data from PIV, boundary layer effects, turbulence characteristics, vortex formation, and momentum thickness, for...divided by the momentum thickness, δ2, and displacement thickness, δ1, as seen in Equations (2.8) and (2.9

Leading-edge effects on boundary-layer receptivity

NASA Technical Reports Server (NTRS)

Gatski, Thomas B.; Kerschen, Edward J.

1990-01-01

Numerical calculations are presented for the incompressible flow over a parabolic cylinder. The computational domain extends from a region upstream of the body downstream to the region where the Blasius boundary-layer solution holds. A steady mean flow solution is computed and the results for the scaled surface vorticity, surface pressure and displacement thickness are compared to previous studies. The unsteady problem is then formulated as a perturbation solution starting with and evolving from the mean flow. The response to irrotational time harmonic pulsation of the free-stream is examined. Results for the initial development of the velocity profile and displacement thickness are presented. These calculations will be extended to later times to investigate the initiation of instability waves within the boundary-layer.

Mathematical Investigation of Fluid Flow, Mass Transfer, and Slag-steel Interfacial Behavior in Gas-stirred Ladles

NASA Astrophysics Data System (ADS)

Cao, Qing; Nastac, Laurentiu

2018-06-01

In this study, the Euler-Euler and Euler-Lagrange modeling approaches were applied to simulate the multiphase flow in the water model and gas-stirred ladle systems. Detailed comparisons of the computational and experimental results were performed to establish which approach is more accurate for predicting the gas-liquid multiphase flow phenomena. It was demonstrated that the Euler-Lagrange approach is more accurate than the Euler-Euler approach. The Euler-Lagrange approach was applied to study the effects of the free surface setup, injected bubble size, gas flow rate, and slag layer thickness on the slag-steel interaction and mass transfer behavior. Detailed discussions on the flat/non-flat free surface assumption were provided. Significant inaccuracies in the prediction of the surface fluid flow characteristics were found when the flat free surface was assumed. The variations in the main controlling parameters (bubble size, gas flow rate, and slag layer thickness) and their potential impact on the multiphase fluid flow and mass transfer characteristics (turbulent intensity, mass transfer rate, slag-steel interfacial area, flow patterns, etc.,) in gas-stirred ladles were quantitatively determined to ensure the proper increase in the ladle refining efficiency. It was revealed that by injecting finer bubbles as well as by properly increasing the gas flow rate and the slag layer thickness, the ladle refining efficiency can be enhanced significantly.

Method of forming a package for MEMS-based fuel cell

DOEpatents

Morse, Jeffrey D; Jankowski, Alan F

2013-05-21

A MEMS-based fuel cell package and method thereof is disclosed. The fuel cell package comprises seven layers: (1) a sub-package fuel reservoir interface layer, (2) an anode manifold support layer, (3) a fuel/anode manifold and resistive heater layer, (4) a Thick Film Microporous Flow Host Structure layer containing a fuel cell, (5) an air manifold layer, (6) a cathode manifold support structure layer, and (7) a cap. Fuel cell packages with more than one fuel cell are formed by positioning stacks of these layers in series and/or parallel. The fuel cell package materials such as a molded plastic or a ceramic green tape material can be patterned, aligned and stacked to form three dimensional microfluidic channels that provide electrical feedthroughs from various layers which are bonded together and mechanically support a MEMS-based miniature fuel cell. The package incorporates resistive heating elements to control the temperature of the fuel cell stack. The package is fired to form a bond between the layers and one or more microporous flow host structures containing fuel cells are inserted within the Thick Film Microporous Flow Host Structure layer of the package.

Method of forming a package for mems-based fuel cell

DOEpatents

Morse, Jeffrey D.; Jankowski, Alan F.

2004-11-23

A MEMS-based fuel cell package and method thereof is disclosed. The fuel cell package comprises seven layers: (1) a sub-package fuel reservoir interface layer, (2) an anode manifold support layer, (3) a fuel/anode manifold and resistive heater layer, (4) a Thick Film Microporous Flow Host Structure layer containing a fuel cell, (5) an air manifold layer, (6) a cathode manifold support structure layer, and (7) a cap. Fuel cell packages with more than one fuel cell are formed by positioning stacks of these layers in series and/or parallel. The fuel cell package materials such as a molded plastic or a ceramic green tape material can be patterned, aligned and stacked to form three dimensional microfluidic channels that provide electrical feedthroughs from various layers which are bonded together and mechanically support a MEMOS-based miniature fuel cell. The package incorporates resistive heating elements to control the temperature of the fuel cell stack. The package is fired to form a bond between the layers and one or more microporous flow host structures containing fuel cells are inserted within the Thick Film Microporous Flow Host Structure layer of the package.

Sheet flow and suspended sediment due to wave groups in a large wave flume

USGS Publications Warehouse

Dohmen-Janssen, C. M.; Hanes, D.M.

2005-01-01

A series of sand bed experiments was carried out in the Large Wave Flume in Hannover, Germany as a component of the SISTEX99 experiment. The experiments focussed on the dynamic sediment response due to wave group forcing over a flat sand bed in order to improve understanding of cross-shore sediment transport mechanisms and determine sediment concentrations, fluxes and net transport rates under these conditions. Sediment concentrations were measured within the sheet flow layer (thickness in the order of 10 grain diameters) and in the suspension region (thickness in the order of centimetres). Within the sheet flow layer, the concentrations are highly coherent with the instantaneous near-bed velocities due to each wave within the wave group. However, in the suspension layer concentrations respond much more slowly to changes in near-bed velocity. At several centimetres above the bed, the suspended sediment concentrations vary on the time scale of the wave group, with a time delay relative to the peak wave within the wave group. The thickness of the sheet flow changes with time. It is strongly coherent with the wave forcing, and is not influenced by the history or sequence of the waves within the group. The velocity of the sediment was also measured within the sheet flow layer some of the time (during the larger wave crests of the group), and the velocity of the fluid was measured at several cm above the sheet flow layer. The grain velocity and concentration estimates can be combined to estimate the sediment flux. The estimates were found to be consistent with previous measurements under monochromatic waves. Under these conditions, without any significant mean current, the sediment flux within the sheet flow layer was found to greatly exceed the sediment flux in the suspension layer. As a result, net transport rates under wave groups are similar to those under monochromatic waves. ?? 2004 Elsevier Ltd. All rights reserved.

Experimental Studies of Flow Separation of the NACA 2412 Airfoil at Low Speeds

NASA Technical Reports Server (NTRS)

Seetharam, H. C.; Rodgers, E. J.; Wentz, W. H., Jr.

1997-01-01

Wind tunnel tests have been conducted on an NACA 2412 airfoil section at Reynolds number of 2.2 x 10(exp 6) and Mach number of 0.13. Detailed measurements of flow fields associated with turbulent boundary layers have been obtained at angles of attack of 12.4 degrees, 14.4 degrees, and 16.4 degrees. Pre- and post-separated velocity and pressure survey results over the airfoil and in the associated wake are presented. Extensive force, pressure, tuft survey, hot-film survey, local skin friction, and boundary layer data are also included. Pressure distributions and separation point locations show good agreement with theory for the two layer angles of attack. Boundary layer displacement thickness, momentum thickness, and shape factor agree well with theory up to the point of separation. There is considerable disparity between extent of flow reversal in the wake as measured by pressure and hot-film probes. The difference is attributed to the intermittent nature of the flow reversal.

Progress and Observations of the Tjakastad Core- Barberton ICDP

NASA Astrophysics Data System (ADS)

Coetzee, Grace; Wilson, Allan; Arndt, Nicholas; Yobregat, Elsa

2013-04-01

The Barberton International Continental Drilling Program (ICDP) has drilled and recovered cores from four sites in the Barberton greenstone belt in South Africa. The BARB 1 (417 m) and BARB 2 (431 m) cores are drilled through a section of the Komati formation. These cores are drilled at a 45° angle, 50 m apart, and have a 140 m stratigraphic overlap. The BARB 1 and BARB 2 cores contain discernible komatiite and komatiitic basalt flow units along with unique volcanic textures such as spinifex, hyaloclastite and harrisite. A tumulus feature is present within the top 100 m of the BARB 1 core. The tumulus unit is 90 m thick and consists of a coarse-grained, basal olivine cumulate layer, a harrisite layer, a pyroxene spinifex layer and a hyaloclastite upper layer. Using major and trace element analyses together with petrological observations these layers are compared with komatiite flows (1-3 m thick) found in other parts of the core. The olivine cumulates from the tumulus layer are macrocrystic, ellipse shaped (2 cm in length) and contain a higher MgO content (45%) then the corresponding euhedral (0.5 mm) olivine cumulates of the komatiite flows which contain 34% MgO. Harrisitic texture forms by skeletal olivine megacrysts crystallizing upward from cumulate layers. The harrisite layer in the tumulus forms in the traditional fashion (above a cumulate layer) and is 14 m thick. It is similar in chemistry and texture to a unique harrisite layer (1.5 m thick) that has formed in a single komatiite flow. The harrisite in the tumulus has higher MgO content and larger skeletal olivines than the komatiite flow. The spinifex in the tumulus is predominantly pyroxene, whilst some flows contain olivine spinifex. The spinifex in the tumulus is commonly centimetres long and is light green grey in colour. The spinifex from the flows reaches a maximum of 5 cm in length; are green-grey to dark grey in colour and are often randomly oriented. The tumulus spinifex has 14-31% MgO whilst the spinifex in the flows has 25-32% MgO. The hyaloclastite, a quench fragmentation texture, in the tumulus section is analogous to the chill zones of the komatiite flows. It consists of fractured blocky fragments (30 cm in length) of lava, surrounded by a matrix of spherical particles of glass (0.5 mm to 1 cm) which have chill margins and inward cooling textures. It is important to determine which of these features is comparable to the chill margin of the flows and to establish if this glassy matrix material has been derived from a different source. The hyaloclastite comprises 24% volume of the tumulus, while chill margins comprise 15% volume. Comparing the chemistry and petrography of the tumulus to komatiite flows gives insight into processes occurring during tumulus formation.

High-frequency internal waves and thick bottom mixed layers observed by gliders in the Gulf Stream

NASA Astrophysics Data System (ADS)

Todd, Robert E.

2017-06-01

Autonomous underwater gliders are conducting high-resolution surveys within the Gulf Stream along the U.S. East Coast. Glider surveys reveal two mechanisms by which energy is extracted from the Gulf Stream as it flows over the Blake Plateau, a portion of the outer continental shelf between Florida and North Carolina where bottom depths are less than 1000 m. Internal waves with vertical velocities exceeding 0.1 m s-1 and frequencies just below the local buoyancy frequency are routinely found over the Blake Plateau, particularly near the Charleston Bump, a prominent topographic feature. These waves are likely internal lee waves generated by the subinertial Gulf Stream flow over the irregular bathymetry of the outer continental shelf. Bottom mixed layers with O(100) m thickness are also frequently encountered; these thick bottom mixed layers likely form in the lee of topography due to enhanced turbulence generated by O(1) m s-1 near-bottom flows.

Discussion of Boundary-Layer Characteristics Near the Wall of an Axial-Flow Compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mohoney, John J; Budinger, Ray E

1952-01-01

The boundary-layer velocity profiles in the tip region of an axial-flow compressor downstream of the guide vanes and downstream of the rotor were measured by use of total-pressure and claw-type yaw probes. These velocities were resolved into two components: one along the streamline of the flow outside the boundary layer, and the other perpendicular to it. The affinity among all profiles was thus demonstrated with the boundary-layer thickness and the deflection of the boundary layer at the wall as the generalizing parameters. By use of these results and the momentum-integral equations, boundary-layer characteristics on the walls of an axial-flow compressor were qualitatively evaluated.

Theoretical modeling of electroosmotic flow in soft microchannels: A variational approach applied to the rectangular geometry

NASA Astrophysics Data System (ADS)

Sadeghi, Arman

2018-03-01

Modeling of fluid flow in polyelectrolyte layer (PEL)-grafted microchannels is challenging due to their two-layer nature. Hence, the pertinent studies are limited only to circular and slit geometries for which matching the solutions for inside and outside the PEL is simple. In this paper, a simple variational-based approach is presented for the modeling of fully developed electroosmotic flow in PEL-grafted microchannels by which the whole fluidic area is considered as a single porous medium of variable properties. The model is capable of being applied to microchannels of a complex cross-sectional area. As an application of the method, it is applied to a rectangular microchannel of uniform PEL properties. It is shown that modeling a rectangular channel as a slit may lead to considerable overestimation of the mean velocity especially when both the PEL and electric double layer (EDL) are thick. It is also demonstrated that the mean velocity is an increasing function of the fixed charge density and PEL thickness and a decreasing function of the EDL thickness and PEL friction coefficient. The influence of the PEL thickness on the mean velocity, however, vanishes when both the PEL thickness and friction coefficient are sufficiently high.

Computation of the shock-wave boundary layer interaction with flow separation

NASA Technical Reports Server (NTRS)

Ardonceau, P.; Alziary, T.; Aymer, D.

1980-01-01

The boundary layer concept is used to describe the flow near the wall. The external flow is approximated by a pressure displacement relationship (tangent wedge in linearized supersonic flow). The boundary layer equations are solved in finite difference form and the question of the presence and unicity of the solution is considered for the direct problem (assumed pressure) or converse problem (assumed displacement thickness, friction ratio). The coupling algorithm presented implicitly processes the downstream boundary condition necessary to correctly define the interacting boundary layer problem. The algorithm uses a Newton linearization technique to provide a fast convergence.

Computer program for design of two-dimensional supersonic turbine rotor blades with boundary-layer correction

NASA Technical Reports Server (NTRS)

Goldman, L. J.; Scullin, V. J.

1971-01-01

A FORTRAN 4 computer program for the design of two-dimensional supersonic rotor blade sections corrected for boundary-layer displacement thickness is presented. The ideal rotor is designed by the method of characteristics to produce vortex flow within the blade passage. The boundary-layer parameters are calculated by Cohen and Reshotoko's method for laminar flow and Sasman and Cresci's method for turbulent flow. The program input consists essentially of the blade surface Mach number distribution and total flow conditions. The primary output is the corrected blade profile and the boundary-layer parameters.

Salt flow direction and velocity during subsalt normal faulting and syn-kinematic sedimentation—implications from analytical calculations

NASA Astrophysics Data System (ADS)

Warsitzka, M.; Kukowski, N.; Kley, J.

2018-04-01

Salt flow induced by subsalt normal faulting is mainly controlled by tilting of the salt layer, the amount of differential loading due to syn-kinematic deposition, and tectonic shearing at the top or the base of the salt layer. Our study addresses the first two mechanisms and aims to examine salt flow patterns above a continuously moving subsalt normal fault and beneath a syn-kinematic minibasin. In such a setting, salt either tends to flow down towards the basin centre driven by its own weight or is squeezed up towards the footwall side owing to loading differences between the minibasin and the region above the footwall block. Applying isostatic balancing in analytical models, we calculated the steady-state flow velocity in a salt layer. This procedure gives insights into (1) the minimum vertical offset required for upward flow to occur, (2) the magnitude of the flow velocity, and (3) the average density of the supra-salt cover layer at the point at which upward flow starts. In a sensitivity study, we examined how the point of flow reversal and the velocity patterns are influenced by changes of the salt and cover layer thickness, the geometry of the cover flexure, the dip of the subsalt fault, compaction parameters of the supra-salt cover, the salt viscosity and the salt density. Our model results reveal that in most geological scenarios, salt flow above a continuously displacing subsalt normal fault goes through an early phase of downward flow. At sufficiently high fault offset in the range of 700-2600 m, salt is later squeezed upward towards the footwall side. This flow reversal occurs at smaller vertical fault displacement, if the thickness of the pre-kinematic layer is larger, the sedimentation rate of the syn-kinematic cover is higher, the compaction coefficient of cover sediments (i.e. the density increase with depth) is larger or the average density of the salt is lower. Other geometrical parameters such as the width of the cover monocline, the dip of the basement fault or the thickness of the salt layer have no significant influence on the point of reversal, but modify the velocity of the salt flow.

Calibration of Axisymmetric and Quasi-1D Solvers for High Enthalpy Nozzles

NASA Technical Reports Server (NTRS)

Papadopoulos, P. E.; Gochberg, L. A.; Tokarcik-Polsky, S.; Venkatapathy, E.; Deiwert, G. S.; Edwards, Thomas A. (Technical Monitor)

1994-01-01

The proposed paper will present a numerical investigation of the flow characteristics and boundary layer development in the nozzles of high enthalpy shock tunnel facilities used for hypersonic propulsion testing. The computed flow will be validated against existing experimental data. Pitot pressure data obtained at the entrance of the test cabin will be used to validate the numerical simulations. It is necessary to accurately model the facility nozzles in order to characterize the test article flow conditions. Initially the axisymmetric nozzle flow will be computed using a Navier Stokes solver for a range of reservoir conditions. The calculated solutions will be compared and calibrated against available experimental data from the DLR HEG piston-driven shock tunnel and the 16-inch shock tunnel at NASA Ames Research Center. The Reynolds number is assumed to be high enough at the throat that the boundary layer flow is assumed turbulent at this point downstream. The real gas affects will be examined. In high Mach number facilities the boundary layer is thick. Attempts will be made to correlate the boundary layer displacement thickness. The displacement thickness correlation will be used to calibrate the quasi-1D codes NENZF and LSENS in order to provide fast and efficient tools of characterizing the facility nozzles. The calibrated quasi-1D codes will be implemented to study the effects of chemistry and the flow condition variations at the test section due to small variations in the driver gas conditions.

Enhancing cell-free layer thickness by bypass channels in a wall.

PubMed

Saadatmand, M; Shimogonya, Y; Yamaguchi, T; Ishikawa, T

2016-07-26

When blood flows near a wall, red blood cells (RBCs) drift away from the wall and a cell-free layer (CFL) is formed adjacent to the wall. Controlling the CFL thickness is important for preventing adhesion of cells in the design of biomedical devices. In this study, a novel wall configuration with stenoses and bypass channels is proposed to increase the CFL thickness. We found that the presence of bypass channels modified the spatial distribution of cells and substantially increased the CFL downstream of the stenosis. A single-bypass geometry with 5% hematocrit (Hct) blood flow showed a 1.7μm increase in CFL thickness compared to without the bypass. In the case of three bypass channels, a 3μm increase in CFL thickness was observed. The CFL enhancement was observed up to 10% Hct, but no significant enhancement of CFL was indicated for 20% Hct blood flow. The mechanism of the CFL enhancement was investigated using a numerical simulation of the flow field. The results showed that the distance between each streamline and the corner of the stenosis compared with size of RBC was important parameter in regulating CFL thickness. These results show the potential of the proposed mechanism to prevent adhesion of cells to biomedical devices. Copyright © 2015 Elsevier Ltd. All rights reserved.

Reynolds stress structures in a self-similar adverse pressure gradient turbulent boundary layer at the verge of separation.

NASA Astrophysics Data System (ADS)

Atkinson, C.; Sekimoto, A.; Jiménez, J.; Soria, J.

2018-04-01

Mean Reynolds stress profiles and instantaneous Reynolds stress structures are investigated in a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL) at the verge of separation using data from direct numerical simulations. The use of a self-similar APG-TBL provides a flow domain in which the flow gradually approaches a constant non-dimensional pressure gradient, resulting in a flow in which the relative contribution of each term in the governing equations is independent of streamwise position over a domain larger than two boundary layer thickness. This allows the flow structures to undergo a development that is less dependent on the upstream flow history when compared to more rapidly decelerated boundary layers. This APG-TBL maintains an almost constant shape factor of H = 2.3 to 2.35 over a momentum thickness based Reynolds number range of Re δ 2 = 8420 to 12400. In the APG-TBL the production of turbulent kinetic energy is still mostly due to the correlation of streamwise and wall-normal fluctuations, 〈uv〉, however the contribution form the other components of the Reynolds stress tensor are no longer negligible. Statistical properties associated with the scale and location of sweeps and ejections in this APG-TBL are compared with those of a zero pressure gradient turbulent boundary layer developing from the same inlet profile, resulting in momentum thickness based range of Re δ 2 = 3400 to 3770. In the APG-TBL the peak in both the mean Reynolds stress and the production of turbulent kinetic energy move from the near wall region out to a point consistent with the displacement thickness height. This is associated with a narrower distribution of the Reynolds stress and a 1.6 times higher relative number of wall-detached negative uv structures. These structures occupy 5 times less of the boundary layer volume and show a similar reduction in their streamwise extent with respect to the boundary layer thickness. A significantly lower percentage of wall-attached structures is observed in the present case when compared with a similar investigation of a rapidly decelerating APG-TBL, suggesting that these wall-attached features could be the remanent from the lower pressure gradient domain upstream.

Thin film instabilities: Rayleigh-Taylor with thermocapillarity and Kolmogorov flow in a soap film

NASA Astrophysics Data System (ADS)

Burgess, John Matthew

The Rayleigh-Taylor instability occurs when a more dense fluid layer is suspended above a less dense fluid layer in a gravitational field. The horizontal interface between the two fluids is unstable to infinitesimal deformations and the dense fluid falls. To counteract the destabilizing effects of gravity on the interface between two thin fluid layers, we apply a vertical temperature gradient, heating from below. The dependence of surface tension on temperature (``thermocapillarity'') can cause spatially-varying interfacial forces between two immiscible fluid layers if a variation in temperature along the interface is introduced. With an applied vertical temperature gradient, the deforming interface spontaneously develops temperature variations which locally adjust the surface tension to restore a flat interface. We find that these surface tension gradients can stabilize a more dense thin fluid layer (silicone oil, 0.015 cm thick) above a less dense thin fluid layer (air, 0.025 cm thick) in a gravitational field, in qualitative agreement with linear stability analysis. This is the first experimental observation of the stabilization of Rayleigh-Taylor instability by thermocapillary forces. We also examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). The film is in the x- y plane, where the forcing approximates a shape sin (y)x̂. Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number Rc~2 . In our soap film experiment, we find a critical value Rc~70 . This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. We conclude that flows in soap films cannot be decoupled from flows in the surrounding gas.

Mechanical stratification of autochthonous salt: Implications from basin-scale numerical models of rifted margin salt tectonics

NASA Astrophysics Data System (ADS)

Ings, Steven; Albertz, Markus

2014-05-01

Deformation of salt and sediments owing to the flow of weak evaporites is a common phenomenon in sedimentary basins worldwide, and the resulting structures and thermal regimes have a significant impact on hydrocarbon exploration. Evaporite sequences ('salt') of significant thickness (e.g., >1km) are typically deposited in many cycles of seawater inundation and evaporation in restricted basins resulting in layered autochthonous evaporite packages. However, analogue and numerical models of salt tectonics typically treat salt as a homogeneous viscous material, often with properties of halite, the weakest evaporite. In this study, we present results of two-dimensional plane-strain numerical experiments designed to illustrate the effects of variable evaporite viscosity and embedded frictional-plastic ('brittle') sediment layers on the style of salt flow and associated deformation of the sedimentary overburden. Evaporite viscosity is a first-order control on salt flow rate and the style of overburden deformation. Near-complete evacuation of low-viscosity salt occurs beneath expulsion basins, whereas significant salt is trapped when viscosity is high. Embedded frictional-plastic sediment layers (with finite yield strength) partition salt flow and develop transient contractional structures (folds, thrust faults, and folded faults) in a seaward salt-squeeze flow regime. Multiple internal sediment layers reduce the overall seaward salt flow during sediment aggradation, leaving more salt behind to be re-mobilized during subsequent progradation. This produces more seaward extensive allochthonous salt sheets. If there is a density difference between the embedded layers and the surrounding salt, then the embedded layers 'fractionate' during deformation and either float to the surface or sink to the bottom (depending on density), creating a thick zone of pure halite. Such a process of 'buoyancy fractionation' may partially explain the apparent paradox of layered salt in autochthonous salt basins and thick packages of pure halite in allochthonous salt sheets.

Analysis of turbulent free-convection boundary layer on flat plate

NASA Technical Reports Server (NTRS)

Eckert, E R G; Jackson, Thomas W

1950-01-01

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

Identification and assessment of groundwater flow and storage components of the relict Schöneben Rock Glacier, Niedere Tauern Range, Eastern Alps (Austria)

NASA Astrophysics Data System (ADS)

Winkler, Gerfried; Wagner, Thomas; Pauritsch, Marcus; Birk, Steffen; Kellerer-Pirklbauer, Andreas; Benischke, Ralf; Leis, Albrecht; Morawetz, Rainer; Schreilechner, Marcellus G.; Hergarten, Stefan

2016-06-01

More than 2,600 relict rock glaciers are known in the Austrian Alps but the knowledge of their hydraulic properties is severely limited. The relict Schöneben Rock Glacier (Niedere Tauern Range, Austria), with an extension of 0.17 km2, was investigated based on spring data (2006-2014) and seismic refraction survey. Spring-discharge hydrographs and natural and artificial tracer data suggest a heterogeneous aquifer with a layered internal structure for the relict rock glacier. The discharge behavior exhibits a fast and a delayed flow component. The spring discharge responds to recharge events within a few hours but a mean residence time of several months can also be observed. The internal structure of the rock glacier (up to several tens of meters thick) consists of: an upper blocky layer with a few meters of thickness, which lacks fine-grained sediments; a main middle layer with coarse and finer-grained sediments, allowing for fast flow; and an approximately 10-m-thick basal till layer as the main aquifer body responsible for the base flow. The base-flow component is controlled by (fine) sandy to silty sediments with low hydraulic conductivity and high storage capacity, exhibiting a difference in hydraulic conductivity to the upper layer of about three orders of magnitude. The high storage capacity of relict rock glaciers has an impact on water resources management in alpine catchments and potentially regulates the risk of natural hazards such as floods and related debris flows. Thus, the results highlight the importance of such aquifer systems in alpine catchments.

Streaming potential generated by a pressure-driven flow over a super-hydrophobic surface

NASA Astrophysics Data System (ADS)

Zhao, Hui

2010-11-01

The streaming potential generated by a pressured-driven flow over a weakly charged striped slip-stick surface (the zeta potential of the surface is smaller than the thermal potential (25 mV) with an arbitrary double layer thickness is theoretically studied by solving the Poisson-Boltzmann equation and Stokes equation. A series solution of the streaming potential is derived. Approximate expressions for the streaming potential in the limits of thin double layers and thick double layers are also presented, in excellent agreement with the full solution. The streaming potential is compared against that over a homogenously charged smooth surface. Our results indicate that the streaming potential over a super-hydrophobic surface only can be enhanced when the liquid-gas interface is charged. In addition, as the double layer thickness increases, the advantage of the super-hydrophobic surface diminishes. The impact of a slip-stick surface on the streaming potential might provide guidance for designing novel and efficient microfludic energy conversion devices using a super-hydrophobic surface.

Method and apparatus to produce and maintain a thick, flowing, liquid lithium first wall for toroidal magnetic confinement DT fusion reactors

DOEpatents

Woolley, Robert D.

2002-01-01

A system for forming a thick flowing liquid metal, in this case lithium, layer on the inside wall of a toroid containing the plasma of a deuterium-tritium fusion reactor. The presence of the liquid metal layer or first wall serves to prevent neutron damage to the walls of the toroid. A poloidal current in the liquid metal layer is oriented so that it flows in the same direction as the current in a series of external magnets used to confine the plasma. This current alignment results in the liquid metal being forced against the wall of the toroid. After the liquid metal exits the toroid it is pumped to a heat extraction and power conversion device prior to being reentering the toroid.

Absolute and convective instabilities in combined Couette-Poiseuille flow past a neo-Hookean solid

NASA Astrophysics Data System (ADS)

Patne, Ramkarn; Shankar, V.

2017-12-01

Temporal and spatio-temporal stability analyses are carried out to characterize the occurrence of convective and absolute instabilities in combined Couette-Poiseuille flow of a Newtonian fluid past a deformable, neo-Hookean solid layer in the creeping-flow limit. Plane Couette flow of a Newtonian fluid past a neo-Hookean solid becomes temporally unstable in the inertia-less limit when the parameter Γ = V η/(GR) exceeds a critical value. Here, V is the velocity of the top plate, η is the fluid viscosity, G is the shear modulus of the solid layer, and R is the fluid layer thickness. The Kupfer-Bers method is employed to demarcate regions of absolute and convective instabilities in the Γ-H parameter space, where H is the ratio of solid to fluid thickness in the system. For certain ranges of the thickness ratio H, we find that the flow could be absolutely unstable, and the critical Γ required for absolute instability is very close to that for temporal instability, thus making the flow absolutely unstable at the onset of temporal instability. In some cases, there is a gap in the parameter Γ between the temporal and absolute instability boundaries. The present study thus shows that absolute instabilities are possible, even at very low Reynolds numbers in flow past deformable solid surfaces. The presence of absolute instabilities could potentially be exploited in the enhancement of mixing at low Reynolds numbers in flow through channels with deformable solid walls.

Application of the Program Profile for the Design of Low-Speed, Low- Observable Configuration Airfoils

DTIC Science & Technology

1992-12-01

112 61 . Airfoil T503 - t/c = 3.79% .... ........... .. 113 62. Airfoil T503 Leading-Edge - t/c = 3.79% ..... ... 114 63. Pressure...points on C unit circle, 6 slope of airfoil surface near trailing edge 61 boundary-layer displacement thickness 62 boundary-layer momentum thickness 63...equivalent thickness NACA 4-digit airfoils . 4 II. Theory Potential-Flow Design Method This section will overview the basic theory used in PROFILE. Eppler

Interferometric data for a shock-wave/boundary-layer interaction

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Brown, James L.; Miles, John B.

1986-01-01

An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.

Quantitative, depth-resolved determination of particle motion using multi-exposure, spatial frequency domain laser speckle imaging.

PubMed

Rice, Tyler B; Kwan, Elliott; Hayakawa, Carole K; Durkin, Anthony J; Choi, Bernard; Tromberg, Bruce J

2013-01-01

Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer dynamics. To verify with experimental data, controlled phantom experiments with characteristic tissue optical properties were performed using a structured light speckle imaging system. Three main geometries were explored: 1) diffusive dynamic layer beneath a static layer, 2) static layer beneath a diffuse dynamic layer, and 3) directed flow (tube) submerged in a dynamic scattering layer. Data fits were performed using the Monte Carlo model, which accurately reconstructed the type of particle flow (diffusive or directed) in each layer, the layer thickness, and absolute flow speeds to within 15% or better.

Volcanic diapirs in the Orange Mountain flood basalt: New Jersey, USA

NASA Astrophysics Data System (ADS)

Puffer, John H.; Laskowich, Chris

2012-09-01

Diapir-shaped structures, 4-30 m high, consisting of vesicular basalt have intruded into the interior of a 50-70 m-thick subaerial Orange Mountain Basalt flow exposed at several rock quarries in northern New Jersey. The basalt flowed onto a travertine encrusted mudflat saturated with alkali salts. We propose that pressurized alkali vapors trapped under the lava created a vesicular and viscous flow bottom layer about 10 m thick. Vesicle coalescence within this layer increased its buoyancy where it locally accumulated into diapirs and displaced overlying lava. Large bubbles within the diapirs expanded upon intrusion into hot flow interiors where they explosively escaped leaving lenses of breccia. Some early diapirs reached the base of the upper lava crust. These diapirs document vapor driven convection of large blobs of contaminated lava into the lava core of the Orange Mountain flow.

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.

On radiative heat transfer in stagnation point flow of MHD Carreau fluid over a stretched surface

NASA Astrophysics Data System (ADS)

Khan, Masood; Sardar, Humara; Mudassar Gulzar, M.

2018-03-01

This paper investigates the behavior of MHD stagnation point flow of Carreau fluid in the presence of infinite shear rate viscosity. Additionally heat transfer analysis in the existence of non-linear radiation with convective boundary condition is performed. Moreover effects of Joule heating is observed and mathematical analysis is presented in the presence of viscous dissipation. The suitable transformations are employed to alter the leading partial differential equations to a set of ordinary differential equations. The subsequent non-straight common ordinary differential equations are solved numerically by an effective numerical approach specifically Runge-Kutta Fehlberg method alongside shooting technique. It is found that the higher values of Hartmann number (M) correspond to thickening of the thermal and thinning of momentum boundary layer thickness. The analysis further reveals that the fluid velocity is diminished by increasing the viscosity ratio parameter (β∗) and opposite trend is observed for temperature profile for both hydrodynamic and hydromagnetic flows. In addition the momentum boundary layer thickness is increased with velocity ratio parameter (α) and opposite is true for thermal boundary layer thickness.

Sub-Grid Modeling of Electrokinetic Effects in Micro Flows

NASA Technical Reports Server (NTRS)

Chen, C. P.

2005-01-01

Advances in micro-fabrication processes have generated tremendous interests in miniaturizing chemical and biomedical analyses into integrated microsystems (Lab-on-Chip devices). To successfully design and operate the micro fluidics system, it is essential to understand the fundamental fluid flow phenomena when channel sizes are shrink to micron or even nano dimensions. One important phenomenon is the electro kinetic effect in micro/nano channels due to the existence of the electrical double layer (EDL) near a solid-liquid interface. Not only EDL is responsible for electro-osmosis pumping when an electric field parallel to the surface is imposed, EDL also causes extra flow resistance (the electro-viscous effect) and flow anomaly (such as early transition from laminar to turbulent flow) observed in pressure-driven microchannel flows. Modeling and simulation of electro-kinetic effects on micro flows poses significant numerical challenge due to the fact that the sizes of the double layer (10 nm up to microns) are very thin compared to channel width (can be up to 100 s of m). Since the typical thickness of the double layer is extremely small compared to the channel width, it would be computationally very costly to capture the velocity profile inside the double layer by placing sufficient number of grid cells in the layer to resolve the velocity changes, especially in complex, 3-d geometries. Existing approaches using "slip" wall velocity and augmented double layer are difficult to use when the flow geometry is complicated, e.g. flow in a T-junction, X-junction, etc. In order to overcome the difficulties arising from those two approaches, we have developed a sub-grid integration method to properly account for the physics of the double layer. The integration approach can be used on simple or complicated flow geometries. Resolution of the double layer is not needed in this approach, and the effects of the double layer can be accounted for at the same time. With this approach, the numeric grid size can be much larger than the thickness of double layer. Presented in this report are a description of the approach, methodology for implementation and several validation simulations for micro flows.

Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

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

Mett, R. R.; Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202; Sidabras, J. W.

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approachesmore » the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.« less

Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

PubMed Central

Mett, R. R.; Hyde, J. S.

2016-01-01

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz. PMID:27587143

Micro-Ramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data

NASA Technical Reports Server (NTRS)

Hirt, Stefanie M.; Reich, David B.; O'Connor, Michael B.

2010-01-01

Computational fluid dynamics was used to study the effectiveness of micro-ramp vortex generators to control oblique shock boundary layer interactions. Simulations were based on experiments previously conducted in the 15 x 15 cm supersonic wind tunnel at NASA Glenn Research Center. Four micro-ramp geometries were tested at Mach 2.0 varying the height, chord length, and spanwise spacing between micro-ramps. The overall flow field was examined. Additionally, key parameters such as boundary-layer displacement thickness, momentum thickness and incompressible shape factor were also examined. The computational results predicted the effects of the micro-ramps well, including the trends for the impact that the devices had on the shock boundary layer interaction. However, computing the shock boundary layer interaction itself proved to be problematic since the calculations predicted more pronounced adverse effects on the boundary layer due to the shock than were seen in the experiment.

Micro-Ramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data

NASA Technical Reports Server (NTRS)

Hirt, Stephanie M.; Reich, David B.; O'Connor, Michael B.

2012-01-01

Computational fluid dynamics was used to study the effectiveness of micro-ramp vortex generators to control oblique shock boundary layer interactions. Simulations were based on experiments previously conducted in the 15- by 15-cm supersonic wind tunnel at the NASA Glenn Research Center. Four micro-ramp geometries were tested at Mach 2.0 varying the height, chord length, and spanwise spacing between micro-ramps. The overall flow field was examined. Additionally, key parameters such as boundary-layer displacement thickness, momentum thickness and incompressible shape factor were also examined. The computational results predicted the effects of the microramps well, including the trends for the impact that the devices had on the shock boundary layer interaction. However, computing the shock boundary layer interaction itself proved to be problematic since the calculations predicted more pronounced adverse effects on the boundary layer due to the shock than were seen in the experiment.

Effect of the Platinum Electroplated Layer Thickness on the Coatings' Microstructure

NASA Astrophysics Data System (ADS)

Zagula-Yavorska, Maryana; Gancarczyk, Kamil; Sieniawski, Jan

2017-03-01

CMSX 4 and Inconel 625 superalloys were coated by platinum layers (3 and 7 μm thick) in the electroplating process. The heat treatment of platinum layers (at 1,050 ˚C for 2 h) was performed to increase platinum adherence to the superalloys substrate. The diffusion zone obtained on CMSX 4 superalloy (3 and 7 μm platinum thick before heat treatment) consisted of two phases: γ-Ni(Al, Cr) and (Al0.25Pt0.75)Ni3. The diffusion zone obtained on Inconel 625 superalloy (3 μm platinum thick before heat treatment) consisted of the α-Pt(Ni, Cr, Al) phase. Moreover, γ-Ni(Cr, Al) phase was identified. The X-ray diffraction (XRD) results revealed the presence of platinum in the diffusion zone of the heat-treated coating (7 μm platinum thick) on Inconel 625 superalloy. The surface roughness parameter Ra of heat-treated coatings increased with the increase of platinum layers thickness. This was due to the unequal mass flow of platinum and nickel.

Thin-layer approximation and algebraic model for separated turbulent flows

NASA Technical Reports Server (NTRS)

Baldwin, B.; Lomax, H.

1978-01-01

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

Multiple sclerosis and optic nerve: an analysis of retinal nerve fiber layer thickness and color Doppler imaging parameters

PubMed Central

Akçam, H T; Capraz, I Y; Aktas, Z; Batur Caglayan, H Z; Ozhan Oktar, S; Hasanreisoglu, M; Irkec, C

2014-01-01

Purpose To compare both retinal nerve fiber layer thickness and orbital color Doppler ultrasonography parameters in patients with multiple sclerosis (MS) versus healthy controls. Methods This is an observational case–control study. Forty eyes from MS patients and twenty eyes from healthy volunteers were examined. Eyes were classified into three groups as group 1, eyes from MS patients with previous optic neuritis (n=20); group 2, eyes from MS patients without previous optic neuritis (n=20); and group 3, eyes from healthy controls (n=20). Following complete ophthalmologic examination and retinal nerve fiber layer thickness measurement for each group, blood flow velocities of posterior ciliary arteries, central retinal artery, ophthalmic artery, and superior ophthalmic vein were measured. Pourcelot index (resistive index), an indicator of peripheral vascular resistance, was also calculated. The statistical assessment was performed with the assistance of Pearson's Chi-square test, Mann–Whitney U-test, Kruskal–Wallis test, and Spearman's correlation test. Results The studied eyes exposed similar values in terms of intraocular pressure and central corneal thickness, implying no evidence in favor of glaucoma. All nerve fiber layer thickness values, except superior nasal quadrants, in group 1 were found to be significantly thinner than groups 2 and 3. Blood flow velocity and mean resistivity index parameters were similar in all the groups. Conclusions In MS patients, especially with previous optic neuritis, diminished retinal nerve fiber layer thickness was observed. Contrary to several studies in the current literature, no evidence supporting potential vascular origin of ocular involvement in MS was found. PMID:25081285

Transition of unsteady velocity profiles with reverse flow

NASA Astrophysics Data System (ADS)

Das, Debopam; Arakeri, Jaywant H.

1998-11-01

This paper deals with the stability and transition to turbulence of wall-bounded unsteady velocity profiles with reverse flow. Such flows occur, for example, during unsteady boundary layer separation and in oscillating pipe flow. The main focus is on results from experiments in time-developing flow in a long pipe, which is decelerated rapidly. The flow is generated by the controlled motion of a piston. We obtain analytical solutions for laminar flow in the pipe and in a two-dimensional channel for arbitrary piston motions. By changing the piston speed and the length of piston travel we cover a range of values of Reynolds number and boundary layer thickness. The velocity profiles during the decay of the flow are unsteady with reverse flow near the wall, and are highly unstable due to their inflectional nature. In the pipe, we observe from flow visualization that the flow becomes unstable with the formation of what appears to be a helical vortex. The wavelength of the instability [simeq R: similar, equals]3[delta] where [delta] is the average boundary layer thickness, the average being taken over the time the flow is unstable. The time of formation of the vortices scales with the average convective time scale and is [simeq R: similar, equals]39/([Delta]u/[delta]), where [Delta]u=(umax[minus sign]umin) and umax, umin and [delta] are the maximum velocity, minimum velocity and boundary layer thickness respectively at each instant of time. The time to transition to turbulence is [simeq R: similar, equals]33/([Delta]u/[delta]). Quasi-steady linear stability analysis of the velocity profiles brings out two important results. First that the stability characteristics of velocity profiles with reverse flow near the wall collapse when scaled with the above variables. Second that the wavenumber corresponding to maximum growth does not change much during the instability even though the velocity profile does change substantially. Using the results from the experiments and the stability analysis, we are able to explain many aspects of transition in oscillating pipe flow. We postulate that unsteady boundary layer separation at high Reynolds numbers is probably related to instability of the reverse flow region.

Inverse boundary-layer theory and comparison with experiment

NASA Technical Reports Server (NTRS)

Carter, J. E.

1978-01-01

Inverse boundary layer computational procedures, which permit nonsingular solutions at separation and reattachment, are presented. In the first technique, which is for incompressible flow, the displacement thickness is prescribed; in the second technique, for compressible flow, a perturbation mass flow is the prescribed condition. The pressure is deduced implicitly along with the solution in each of these techniques. Laminar and turbulent computations, which are typical of separated flow, are presented and comparisons are made with experimental data. In both inverse procedures, finite difference techniques are used along with Newton iteration. The resulting procedure is no more complicated than conventional boundary layer computations. These separated boundary layer techniques appear to be well suited for complete viscous-inviscid interaction computations.

Experimental investigation on the influence of boundary layer thickness on the base pressure and near-wake flow features of an axisymmetric blunt-based body

NASA Astrophysics Data System (ADS)

Mariotti, Alessandro; Buresti, Guido

2013-11-01

The influence of the thickness of the boundary layer developing over the surface of an axisymmetric bluff body upon its base pressure and near-wake flow is analyzed experimentally. The model, whose diameter-to-length ratio is d/ l = 0.175, has a forebody with an elliptical contour and a sharp-edged flat base; it is supported above a plate by means of a faired strut. The pressure distributions over the body lateral and base surfaces were obtained using numerous pressure taps, while the boundary layer profiles and the wake velocity field were measured through hot-wire anemometry. The tests were carried out at , at which the boundary layer over the lateral surface of the body becomes turbulent before reaching the base contour. Strips of emery cloth were wrapped in various positions around the body circumference in order to modify the thickness and the characteristics of the boundary layer. The results show that increasing the boundary layer thickness causes a decrease in the base suctions and a corresponding increase in the length of the mean recirculation region present behind the body. In the spectra of the velocity fluctuations measured within and aside the wake, a dominating peak becomes evident in the region downstream of the final part of the recirculation region. The relevant non-dimensional frequency decreases with increasing boundary layer thickness; however, a Strouhal number based on the wake width and the velocity defect at a suitable reference cross section downstream of the recirculation region is found to remain almost constant for the different cases.

An Innovative Flow-Measuring Device: Thermocouple Boundary Layer Rake

NASA Technical Reports Server (NTRS)

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Wrbanek, John D.; Blaha, Charles A.

2001-01-01

An innovative flow-measuring device, a thermocouple boundary layer rake, was developed. The sensor detects the flow by using a thin-film thermocouple (TC) array to measure the temperature difference across a heater strip. The heater and TC arrays are microfabricated on a constant-thickness quartz strut with low heat conductivity. The device can measure the velocity profile well into the boundary layer, about 65 gm from the surface, which is almost four times closer to the surface than has been possible with the previously used total pressure tube.

The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves

NASA Technical Reports Server (NTRS)

Duck, Peter W.

1989-01-01

The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.

Dynamic behavior of an unsteady trubulent boundary layer

NASA Technical Reports Server (NTRS)

Parikh, P. G.; Reynolds, W. C.; Jayaramen, R.; Carr, L. W.

1981-01-01

Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.

Control of a Normal Shock Boundary Layer Interaction with Ramped Vanes of Various Sizes

NASA Astrophysics Data System (ADS)

Lee, Sang; Loth, Eric

2017-11-01

A novel vortex generator design positioned upstream of a normal shock and a subsequent diffuser was investigated using large eddy simulations. In particular, ``ramped-vane'' flow control devices with three difference heights relative to the incoming boundary layer thickness (0.34 δ 0.52 δ and 0.75 δ were placed in a supersonic boundary layer with a freestream Mach number of 1.3 and a Reynolds number of 2,400 based on momentum thickness. These devices are similar to subsonic vanes but are designed to be more mechanically robust while having low wave drag. The devices generated strong streamwise vortices that entrained high momentum fluid to the near-wall region and increased turbulent mixing. The devices also decreased shock-induced flow separation, which resulted in a higher downstream skin friction in the diffuser. In general, the largest ramped-vane (0.75 δ) produced the largest reductions in flow separation, shape factor and overall unsteadiness. However, the medium-sized ramped vane (0.52 δ) was able to also reduce both the separation area and the diffuser displacement thickness. The smallest device (0.34 δ) had a weak impact of the flow in the diffuser, though a 10% reduction in the shape factor was achieved.

Enhanced interfacial deformation in a Marangoni flow: A measure of the dynamical surface tension

NASA Astrophysics Data System (ADS)

Leite Pinto, Rodrigo; Le Roux, Sébastien; Cantat, Isabelle; Saint-Jalmes, Arnaud

2018-02-01

We investigate the flows and deformations resulting from the deposition of a water soluble surfactant at a bare oil-water interface. Once the surfactant is deposited, we show that the oil-water interface is deformed with a water bump rising upward into the oil. For a given oil, the maximal deformation—located at the surfactant deposition point—decreases with the oil-layer thickness. We also observe a critical oil-layer thickness below which the deformation becomes as large as the oil layer, leading to the rupture of this layer and an oil-water dewetting. Experimentally, it is found that this critical thickness depends on the oil density and viscosity. We then provide an analytical modelization that explains quantitatively all these experimental features. In particular, our analysis allows us to derive an analytical relationship between the vertical profile of the oil-water interface and the in-plane surface tension profile. Therefore, we propose that the monitoring of the interface vertical shape can be used as a new spatially resolved tensiometry technique.

Observations of pockmark flow structure in Belfast Bay, Maine, Part 2: evidence for cavity flow

USGS Publications Warehouse

Fandel, Christina L.; Lippmann, Thomas C.; Foster, Diane L.; Brothers, Laura L.

2017-01-01

Pockmark flow circulation patterns were investigated through current measurements along the rim and center of two pockmarks in Belfast Bay, Maine. Observed time-varying current profiles have a complex vertical and directional structure that rotates significantly with depth and is strongly dependent on the phase of the tide. Observations of the vertical profiles of horizontal velocities in relation to relative geometric parameters of the pockmark are consistent with circulation patterns described qualitatively by cavity flow models (Ashcroft and Zhang 2005). The time-mean behavior of the shear layer is typically used to characterize cavity flow, and was estimated using vorticity thickness to quantify the growth rate of the shear layer horizontally across the pockmark. Estimated positive vorticity thickness spreading rates are consistent with cavity flow predictions, and occur at largely different rates between the two pockmarks. Previously modeled flow (Brothers et al. 2011) and laboratory measurements (Pau et al. 2014) over pockmarks of similar geometry to those examined herein are also qualitatively consistent with cavity flow circulation, suggesting that cavity flow may be a good first-order flow model for pockmarks in general.

An analysis of the crossover between local and massive separation on airfoils

NASA Technical Reports Server (NTRS)

Barnett, M.; Carter, J. E.

1987-01-01

Massive separation on airfoils operating at high Reynolds number is an important problem to the aerodynamicist, since its onset generally determines the limiting performance of an airfoil, and it can lead to serious problems related to aircraft control as well as turbomachinery operation. The phenomenon of crossover between local separation and massive separation on realistic airfoil geometries induced by airfoil thickness is investigated for low speed (incompressible) flow. The problem is studied both for the asymptotic limit of infinite Reynolds number using triple-deck theory, and for finite Reynolds number using interacting boundary-layer theory. Numerical results are presented which follow the evolution of the flow as it develops from a mildly separated state to one dominated by the massively separated flow structure as the thickness of the airfoil geometry is systematically increased. The effect of turbulence upon the evolution of the flow is considered, and the impact is significant, with the principal effect being the suppression of the onset of separation. Finally, the effect of surface suction and injection for boundary-layer control is considered. The approach which was developed provides a valuable tool for the analysis of boundary-layer separation up to and beyond stall. Another important conclusion is that interacting boundary-layer theory provides an efficient tool for the analysis of the effect of turbulence and boundary-layer control upon separated vicsous flow.

Boundary layer effects on liners for aircraft engines

NASA Astrophysics Data System (ADS)

Gabard, Gwénaël

2016-10-01

The performance of acoustic treatments installed on aircraft engines is strongly influenced by the boundary layer of the grazing flow on the surface of the liner. The parametric study presented in this paper illustrates the extent of this effect and identifies when it is significant. The acoustic modes of a circular duct with flow are calculated using a finite difference method. The parameters are representative of the flow conditions, liners and sound fields found in current turbofan engines. Both the intake and bypass ducts are considered. Results show that there is a complex interplay between the boundary layer thickness, the direction of propagation and the liner impedance and that the boundary layer can have a strong impact on liner performance for typical configurations (including changes of the order of 30 dB on the attenuation of modes associated with tonal fan noise). A modified impedance condition including the effect of a small but finite boundary layer thickness is considered and compared to the standard Myers condition based on an infinitely thin boundary layer. We show how this impedance condition can be implemented in a mode calculation method by introducing auxiliary variables. This condition is able to capture the trends associated with the boundary layer effects and in most cases provides improved predictions of liner performance.

Flow Separation

DTIC Science & Technology

1975-11-01

PLENUM CHAMBER 4 DIFFUSER 2 FIXEn NOZZLE BLOCK 5 MODEL i MOVABLE NOZZLE BLOCK 6 SUPPORT Fig. 3. Trl-Color Filter ...boun- dary layer ( Model 2) to examine scaling effects. Special attention was paid to the phenomenon of flow separation in three dimensions...consequence. Special attention should be paid to the difference in scale of an average boundary layer thickness between Model 1 and 2. Because

Direct Numerical Simulation of Automobile Cavity Tones

NASA Technical Reports Server (NTRS)

Kurbatskii, Konstantin; Tam, Christopher K. W.

2000-01-01

The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.

Impact of thickness on the structural properties of high tin content GeSn layers

NASA Astrophysics Data System (ADS)

Aubin, J.; Hartmann, J. M.; Gassenq, A.; Milord, L.; Pauc, N.; Reboud, V.; Calvo, V.

2017-09-01

We have grown various thicknesses of GeSn layers in a 200 mm industrial Reduced Pressure - Chemical Vapor Deposition cluster tool using digermane (Ge2H6) and tin tetrachloride (SnCl4). The growth pressure (100 Torr) and the F(Ge2H6)/F(SnCl4) mass-flow ratio were kept constant, and incorporation of tin in the range of 10-15% was achieved with a reduction in temperature: 325 °C for 10% to 301 °C for 15% of Sn. The layers were grown on 2.5 μm thick Ge Strain Relaxed Buffers, themselves on Si(0 0 1) substrates. We used X-ray Diffraction, Atomic Force Microscopy, Raman spectroscopy and Scanning Electron Microscopy to measure the Sn concentration, the strain state, the surface roughness and thickness as a function of growth duration. A dramatic degradation of the film was seen when the Sn concentration and layer thickness were too high resulting in rough/milky surfaces and significant Sn segregation.

Modeling of the processes of natural and waste water purification in the reactor-clarifier

NASA Astrophysics Data System (ADS)

Primak, O. D.; Skolubovich, Yu. L.; Fedorova, N. N.; Voitov, E. L.

2018-03-01

The results of the filtration process simulation in a reactor-clarifier installation using a suspended loading layer are presented. Calculations were carried out in ANSYS Fluent on the basis of the Navier-Stokes equations supplemented by the equations of the Eulerian model of multiphase taking into account granularity of the particle phase. The unsteady picture of the formation of a fluidized («boiling») layer of particles is obtained. The results of parametric calculations allowing to estimate the effect of the flow velocity, the loading layer thickness, the thickness of sand and other parameters on the fluidized bed structure are presented. The liquid flow rate at which the loading grains are not washed out is determined. The diameter of particles and the height of the loading layer, at which the filter material is suspended and thus normal operation of the plant is ensured, are defined.

A Method to Predict the Thickness of Poorly-Bonded Material Along Spray and Spray-Layer Boundaries in Cold Spray Deposition

NASA Astrophysics Data System (ADS)

Li, Yangfan; Hamada, Yukitaka; Otobe, Katsunori; Ando, Teiichi

2017-02-01

Multi-traverse CS provides a unique means for the production of thick coatings and bulk materials from powders. However, the material along spray and spray-layer boundaries is often poorly bonded as it is laid by the leading and trailing peripheries of the spray that carry powder particles with insufficient kinetic energy. For the same reason, the splats in the very first layer deposited on the substrate may not be bonded well either. A mathematical spray model was developed based on an axisymmetric Gaussian mass flow rate distribution and a stepped deposition yield to predict the thickness of such poorly-bonded layers in multi-traverse CS deposition. The predicted thickness of poorly-bonded layers in a multi-traverse Cu coating falls in the range of experimental values. The model also predicts that the material that contains poorly bonded splats could exceed 20% of the total volume of the coating.

Streakline flow visualization of discrete hole film cooling with holes inclined 30 deg to surface

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.; Lane, J. M.

1976-01-01

Film injection from three rows of discrete holes angled 30 deg to the surface in line with mainstream flow and spaced 5 diameters apart in a staggered array was visualized by using helium bubbles as tracer particles. Both the main stream and the film injectant were ambient air. Detailed streaklines showing the turbulent motion of the film mixing with the main stream were obtained by photographing small, neutrally buoyant helium-filled soap bubbles which followed the flow field. The ratio of boundary layer thickness to hole diameter and the Reynolds number were typical of gas turbine film cooling applications. The results showed the behavior of the film and its interaction with the main stream for a range of blowing rates and two initial boundary layer thicknesses.

MODFLOW Ground-Water Model - User Guide to the Subsidence and Aquifer-System Compaction Package (SUB-WT) for Water-Table Aquifers

USGS Publications Warehouse

Leake, S.A.; Galloway, D.L.

2007-01-01

A new computer program was developed to simulate vertical compaction in models of regional ground-water flow. The program simulates ground-water storage changes and compaction in discontinuous interbeds or in extensive confining units, accounting for stress-dependent changes in storage properties. The new program is a package for MODFLOW, the U.S. Geological Survey modular finite-difference ground-water flow model. Several features of the program make it useful for application in shallow, unconfined flow systems. Geostatic stress can be treated as a function of water-table elevation, and compaction is a function of computed changes in effective stress at the bottom of a model layer. Thickness of compressible sediments in an unconfined model layer can vary in proportion to saturated thickness.

Geometrical control of dissipation during the spreading of liquids on soft solids

NASA Astrophysics Data System (ADS)

Zhao, Menghua; Dervaux, Julien; Narita, Tetsuharu; Lequeux, François; Limat, Laurent; Roché, Matthieu

2018-02-01

Gel layers bound to a rigid substrate are used in cell culture to control differentiation and migration and to lower the friction and tailor the wetting of solids. Their thickness, often considered a negligible parameter, affects cell mechanosensing or the shape of sessile droplets. Here, we show that the adjustment of coating thickness provides control over energy dissipation during the spreading of flowing matter on a gel layer. We combine experiments and theory to provide an analytical description of both the statics and the dynamics of the contact line between the gel, the liquid, and the surrounding atmosphere. We extract from this analysis a hitherto-unknown scaling law that predicts the dynamic contact angle between the three phases as a function of the properties of the coating and the velocity of the contact line. Finally, we show that droplets moving on vertical substrates coated with gel layers having linear thickness gradients drift toward regions of higher energy dissipation. Thus, thickness control opens the opportunity to design a priori the path followed by large droplets moving on gel-coated substrates. Our study shows that thickness is another parameter, besides surface energy and substrate mechanics, to tune the dynamics of liquid spreading and wetting on a compliant coating, with potential applications in dew collection and free-surface flow control.

High Reynolds number rough wall turbulent boundary layer experiments using Braille surfaces

NASA Astrophysics Data System (ADS)

Harris, Michael; Monty, Jason; Nova, Todd; Allen, James; Chong, Min

2007-11-01

This paper details smooth, transitional and fully rough turbulent boundary layer experiments in the New Mexico State high Reynolds number rough wall wind tunnel. The initial surface tested was generated with a Braille printer and consisted of an uniform array of Braille points. The average point height being 0.5mm, the spacing between the points in the span was 0.5mm and the surface consisted of span wise rows separated by 4mm. The wavelength to peak ratio was 8:1. The boundary layer thickness at the measurement location was 190mm giving a large separation of roughness height to layer thickness. The maximum friction velocity was uτ=1.5m/s at Rex=3.8 x10^7. Results for the skin friction co-efficient show that this surface follows a Nikuradse type inflectional curve and that Townsends outer layer similarity hypothesis is valid for rough wall flows with a large separation of scales. Mean flow and turbulence statistics will be presented.

A theoretical method for the analysis and design of axisymmetric bodies. [flow distribution and incompressible fluids

NASA Technical Reports Server (NTRS)

Beatty, T. D.

1975-01-01

A theoretical method is presented for the computation of the flow field about an axisymmetric body operating in a viscous, incompressible fluid. A potential flow method was used to determine the inviscid flow field and to yield the boundary conditions for the boundary layer solutions. Boundary layer effects in the forces of displacement thickness and empirically modeled separation streamlines are accounted for in subsequent potential flow solutions. This procedure is repeated until the solutions converge. An empirical method was used to determine base drag allowing configuration drag to be computed.

Viscous flow in and around a cavity surrounded by a concentric permeable patch

NASA Astrophysics Data System (ADS)

Palaniappan, D.

2017-11-01

Steady viscous incompressible fluid flow in and around a spherical fluid cavity of radius a surrounded by a permeable patch with thickness b - a is investigated in the limit of low-Reynolds number. Our model uses the Stokes equations in the pure fluid regions and the Darcy law in the concentric permeable patch. Analytic solutions for the velocity and pressure fields are derived in singularity form involving the key parameters such as the Darcy permeability coefficient k and the thickness of the permeable layer. The Faxen law for the hydrodynamical drag acting on the concentric spherical geometry due to an arbitrary incident flow is extracted from our singularity solutions. It is found that the thickness of the permeable layer and the permeability play a crucial role in controlling the drag. An expression for the mass of the fluid that enters the outer sphere is calculated by integrating the exterior radial velocity field. The hydrodynamic force on the concentric spherical shell due to the flow induced by a Stokeslet is also derived from our general expressions. Several special cases of interest are deduced from our exact analysis. The results are of some interest in the prediction of forces exerted on the walls in certain biological models with permeable layers. I request you to place my presentation on the 19th (Sunday) as I have to give final exams on Monday. Thank you.

On the design of airfoils in which the transition of the boundary layer is delayed

NASA Technical Reports Server (NTRS)

Tani, Itiro

1952-01-01

A method is presented for designing suitable thickness distributions and mean camber lines for airfoils permitting extensive chordwise laminar flow. Wind tunnel and flight tests confirming the existence of laminar flow; possible maintenance of laminar flow by area suction; and the effects of wind tunnel turbulence and surface roughness on the promotion of premature boundary layer transition are discussed. In addition, estimates of profile drag and scale effect on maximum lift of the derived airfoils are made.

Mantle flow tectonics - The influence of a ductile lower crust and implications for the formation of topographic uplands on Venus

NASA Technical Reports Server (NTRS)

Bindschadler, Duane L.; Parmentier, E. Marc

1990-01-01

The crust and mantle of Venus can be represented by a model of a layered structure stratified in both density and viscosity. This structure consists of a brittle-elastic upper crustal layer; a ductile weaker crustal layer; a strong upper mantle layer, about 10 percent denser than the crust; and a weaker substrate, representing the portion of the mantle in which convective flow occurs which is a primary source of large-scale topographic and tectonic features. This paper examines the interactions between these four layers and the mantle flow driven by thermal or compositional variations. Solutions are found for a flow driven by a buoyancy-force distribution within the mantle and by relief at the surface and crust-mantle boundary. It is shown that changes in crustal thickness are driven by vertical normal stresses due to mantle flow and by shear coupling of horizontal mantle flow into the crust.

Behavior of turbulent boundary layers on curved convex walls

NASA Technical Reports Server (NTRS)

Schmidbauer, Hans

1936-01-01

The system of linear differential equations which indicated the approach of separation and the so-called "boundary-layer thickness" by Gruschwitz is extended in this report to include the case where the friction layer is subject to centrifugal forces. Evaluation of the data yields a strong functional dependence of the momentum change and wall drag on the boundary-layer thickness radius of curvature ratio for the wall. It is further shown that the transition from laminar to turbulent flow occurs at somewhat higher Reynolds Numbers at the convex wall than at the flat plate, due to the stabilizing effect of the centrifugal forces.

Characteristics of secondary flows in rough-wall turbulent boundary layers

NASA Astrophysics Data System (ADS)

Vanderwel, Christina; Ganapathisubramani, Bharathram

2015-11-01

Large-scale secondary motions consisting of counter-rotating vortices and low- and high-momentum pathways can form in boundary layers that develop over rough surfaces. We experimentally investigated the sensitivity of these secondary motions to spanwise arrangement of the roughness by studying the flow over streamwise-aligned rows of elevated roughness with systematically-varied spacing. The roughness is created with LEGO blocks mounted along the floor of the wind tunnel and Stereo-PIV is used to measure the velocity field in a cross-plane. Results show that the secondary flows are strongest when the spanwise spacing of the surface topology is comparable with the boundary layer thickness. We discuss how these results are relevant to flows over arbitrary topologies and how these secondary motions influence the Reynolds stress distribution in the boundary layer.

Hypersonic Boundary Layer Stability over a Flared Cone in a Quiet Tunnel

NASA Technical Reports Server (NTRS)

Lachowicz, Jason T.; Chokani, Ndaona; Wilkinson, Stephen P.

1996-01-01

Hypersonic boundary layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82x106/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the model in a low-disturbance environment. Point measurements with a single hot wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode disturbances were the most unstable and scaled with the boundary layer thickness. The integrated growth rates of the second mode compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with high free stream disturbance levels.

Pressure-sensing performance of upright cylinders in a Mach 10 boundary-layer

NASA Technical Reports Server (NTRS)

Johnson, Steven; Murphy, Kelly

1994-01-01

An experimental research program to provide basic knowledge of the pressure-sensing performance of upright, flushported cylinders in a hypersonic boundary layer is described. Three upright cylinders of 0.25-, 0.5- and l.0-in. diameters and a conventional rake were placed in the test section sidewall boundary layer of the 31 Inch Mach 10 Wind Tunnel at NASA Langley Research Center, Hampton, Virginia. Boundary-layer pressures from these cylinders were compared to those measured with a conventional rake. A boundary-layer thickness-to-cylinder-diameter ratio of 8 proved sufficient to accurately measure an overall pressure profile and ascertain the boundary-layer thickness. Effects of Reynolds number, flow angularity, and shock wave impingement on pressure measurement were also investigated. Although Reynolds number effects were negligible at the conditions studied, flow angularity above 10 deg significantly affects the measured pressures. Shock wave impingement was used to investigate orifice-to-orifice pressure crosstalk. No crosstalk was measured. The lower pressure measured above the oblique shock wave impingement showed no influence of the higher pressure generated at the lower port locations.

Turbidity Currents With Equilibrium Basal Driving Layers: A Mechanism for Long Runout

NASA Astrophysics Data System (ADS)

Luchi, R.; Balachandar, S.; Seminara, G.; Parker, G.

2018-02-01

Turbidity currents run out over 100 km in lakes and reservoirs, and over 1,000 km in the ocean. They do so without dissipating themselves via excess entrainment of ambient water. Existing layer-averaged formulations cannot capture this. We use a numerical model to describe the temporal evolution of a turbidity current toward steady state under condition of zero net sediment flux at the bed. The flow self-partitions itself into two layers. The lower "driving layer" approaches an invariant flow thickness, velocity profile, and suspended sediment concentration profile that sequesters nearly all of the suspended sediment. This layer can continue indefinitely at steady state over a constant bed slope. The upper "driven layer" contains a small fraction of the suspended sediment. The devolution of the flow into these two layers likely allows the driving layer to run out long distances.

Differential analysis for the turbulent boundary layer on a compressor blade element (including boundary-layer separation)

NASA Technical Reports Server (NTRS)

Schmidt, J. F.; Todd, C. A.

1974-01-01

A two-dimensional differential analysis is developed to approximate the turbulent boundary layer on a compressor blade element with strong adverse pressure gradients, including the separated region with reverse flow. The predicted turbulent boundary layer thicknesses and velocity profiles are in good agreement with experimental data for a cascade blade, even in the separated region.

Flow Fields of the 3.5 Ga Komati Formation, South Africa: Geochemical, Stratigraphic, and Temporal relationships between Massive, Vesicular, and Spinifex flows

NASA Astrophysics Data System (ADS)

Dann, J. C.

2007-12-01

A challenge of Archean volcanology is to reconstruct submarine flow fields by mapping and analyzing vertically dipping sequences of lavas. Some flow fields are bound by sediments and/or seafloor alteration that mark clear gaps in volcanism. Flow fields in the Lower Komati Fm are defined by alternating layers of komatiite (26% MgO) and komatiitic basalt (15% MgO). Five komatiite flow fields (100-200m thick) repeat the same stratigraphic zoning of spinifex overlying massive komatiite, and each flow field has a distinct Al2O3/CaO, a ratio unaffected by olivine fractionation, consistent with the contention that each komatiite flow field represents a distinct batch of mantle melting. Although massive and spinifex komatiite form distinct stratigraphic units on a map scale, detailed outcrop mapping reveals that the change in flow type represents a transition within a single flow field. In one type of transition, thin massive flows alternate with spinifex flow lobes of a compound flow unit. In another, a vesicular flow along the boundary links the underlying massive komatiite and overlying spinifex flows in time. The vesicular flow has alternating spinifex and vesicular layers that form a distinctive crust above a thick massive interior. Locally, this crust is tilted, intruded by massive komatiite from the interior, and overlain by a thick breccia including a spinifex flow broken into blocks and rotated like dominoes by the tilting. These outcrop relations indicate that spinifex flow lobes were starting to flow over the vesicular flow before it had undergone differential inflation, a temporal link between the lower massive and upper spinifex komatiites consistent with their belonging to the same flow field. The transition in flow type may reflect 1) an overlap of proximal and distal facies of komatiite flows as eruption rates waned and/or 2) thermal maturation prior to eruption. Early, cooler, crystal-rich, massive lava, flowing out as thick sheet flows, was replaced by hotter, crystal-poor, less degassed lava, flowing out as spinifex flows.

Flow visualization of discrete hole film cooling for gas turbine applications

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.

1975-01-01

Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing neutrally buoyant helium filled soap bubbles which follow the flow field. The bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included.

Effect of Thickness-to-Chord Ratio on Flow Structure of Low Swept Delta Wing

NASA Astrophysics Data System (ADS)

Gulsacan, Burak; Sencan, Gizem; Yavuz, Mehmet Metin

2017-11-01

The effect of thickness-to-chord (t/C) ratio on flow structure of a delta wing with sweep angle of 35 degree is characterized in a low speed wind tunnel using laser illuminated smoke visualization, particle image velocimetry, and surface pressure measurements. Four different t/C ratio varying from 4.75% to 19% are tested at angles of attack 4, 6, 8, and 10 degrees for Reynolds numbers Re =10,000 and 35,000. The results indicate that the effect of thickness-to-chord ratio on flow structure is quite substantial, such that, as the wing thickness increases, the flow structure transforms from leading edge vortex to three-dimensional separated flow regime. The wing with low t/C ratio of 4.75% experiences pronounced surface separation at significantly higher angle of attack compared to the wing with high t/C ratio. The results might explain some of the discrepancies reported in previously conducted studies related to delta wings. In addition, it is observed that the thickness of the shear layer separated from windward side of the wing is directly correlated with the thickness of the wing. To conclude, the flow structure on low swept delta wing is highly affected by t/C ratio, which in turn might indicate the potential usage of wing thickness as an effective flow control parameter.

Category 5: Sound Generation In Viscous Problems. Problem 2: Sound Generation By Flow Over a Cavity

NASA Technical Reports Server (NTRS)

Henderson, Brenda S.

2004-01-01

The discrete frequency sound produced by the flow of air at low subsonic speeds over a deep cavity was investigated. A long aspect ratio rectangular cavity with a leading edge overhang that cut off of the cavity opening was placed flush with the top surface of a wind tunnel. The approach flow velocity was maintained at 50 m/s for the benchmark problem although results are also presented for other conditions. Boundary layer measurements conducted with a single element hotwire anemometer indicated that the boundary layer thickness just upstream of the cavity was equal to 17 mm. Sound pressure level measurements were made at three locations in the cavity: the center of the leading edge wall, the center of the cavity floor, and the center of the trailing edge wall. Three discrete tones were measured at all three locations with corresponding Strouhal numbers (based on cavity opening length and approach flow velocity) equal to 0.24, 0.26, and 0.41. The amplitudes of each tone were approximately equal at each measurement location in the cavity. Measurements made at other approach flow conditions indicated that the approach flow velocity and the boundary layer thickness affected the frequency characteristics of the discrete tones.

Competitive separation of di- vs. mono-valent cations in electrodialysis: effects of the boundary layer properties.

PubMed

Kim, Younggy; Walker, W Shane; Lawler, Desmond F

2012-05-01

In electrodialysis desalination, the boundary layer near ion-exchange membranes is the limiting region for the overall rate of ionic separation due to concentration polarization over tens of micrometers in that layer. Under high current conditions, this sharp concentration gradient, creating substantial ionic diffusion, can drive a preferential separation for certain ions depending on their concentration and diffusivity in the solution. Thus, this study tested a hypothesis that the boundary layer affects the competitive transport between di- and mono-valent cations, which is known to be governed primarily by the partitioning with cation-exchange membranes. A laboratory-scale electrodialyzer was operated at steady state with a mixture of 10mM KCl and 10mM CaCl(2) at various flow rates. Increased flows increased the relative calcium transport. A two-dimensional model was built with analytical solutions of the Nernst-Planck equation. In the model, the boundary layer thickness was considered as a random variable defined with three statistical parameters: mean, standard deviation, and correlation coefficient between the thicknesses of the two boundary layers facing across a spacer. Model simulations with the Monte Carlo method found that a greater calcium separation was achieved with a smaller mean, greater standard deviation, or more negative correlation coefficient. The model and experimental results were compared for the cationic transport number as well as the current and potential relationship. The mean boundary layer thickness was found to decrease from 40 to less than 10 μm as the superficial water velocity increased from 1.06 to 4.24 cm/s. The standard deviation was greater than the mean thickness at slower water velocities and smaller at faster water velocities. Copyright © 2012 Elsevier Ltd. All rights reserved.

The effects of forcing on a single stream shear layer and its parent boundary layer

NASA Technical Reports Server (NTRS)

Haw, Richard C.; Foss, John F.

1990-01-01

Forcing and its effect on fluid flows has become an accepted tool in the study and control of flow systems. It has been used both as a diagnostic tool, to explore the development and interaction of coherent structures, and as a method of controlling the behavior of the flow. A number of forcing methods have been used in order to provide a perturbation to the flow; among these are the use of an oscillating trailing edge, acoustically driven slots, external acoustic forcing, and mechanical piston methods. The effect of a planar mechanical piston forcing on a single stream shear layer is presented; it can be noted that this is one of the lesser studied free shear layers. The single stream shear layer can be characterized by its primary flow velocity scale and the thickness of the separating boundary layer. The velocity scale is constant over the length of the flow field; theta (x) can be used as a width scale to characterize the unforced shear layer. In the case of the forced shear layer the velocity field is a function of phase time and definition of a width measure becomes somewhat problematic.

Relating Vorticity Confinement to the Menter Shear Stress Transport Turbulence Model

DTIC Science & Technology

2008-01-01

uses a bent nose to effect aerodynamic control. The baseline geometry was constructed with CFDGEN using wind tunnel model blueprints and it...For the problem at hand, Reference 23 was used to find the boundary layer thickness at the separation point of a cylinder in cross flow and relate it...to the cylinder radius. Although it was only possible to find the thickness of a laminar boundary layer, the ratio of measured turbulent and laminar

Diffusion or advection? Mass transfer and complex boundary layer landscapes of the brown alga Fucus vesiculosus.

PubMed

Lichtenberg, Mads; Nørregaard, Rasmus Dyrmose; Kühl, Michael

2017-03-01

The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O 2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O 2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O 2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O 2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant-microbe interactions. © 2017 The Author(s).

Diffusion or advection? Mass transfer and complex boundary layer landscapes of the brown alga Fucus vesiculosus

PubMed Central

Nørregaard, Rasmus Dyrmose

2017-01-01

The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant–microbe interactions. PMID:28330986

Effect of aspect ratio on sidewall boundary-layer influence in two-dimensional airfoil testing

NASA Technical Reports Server (NTRS)

Murthy, A. V.

1986-01-01

The effect of sidewall boundary layers in airfoil testing in two-dimensional wind tunnels is investigated. The non-linear crossflow velocity variation induced because of the changes in the sidewall boundary-layer thickness is represented by the flow between a wavy wall and a straight wall. Using this flow model, a correction for the sidewall boundary-layer effects is derived in terms of the undisturbed sidewall boundary-layer properties, the test Mach number and the airfoil aspect ratio. Application of the proposed correction to available experimental data showed good correlation for the shock location and pressure distribution on airfoils.

Evaluation of a technique to generate artificially thickened boundary layers in supersonic and hypersonic flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Hingst, W. R.; Davis, D. O.; Blair, A. B., Jr.

1991-01-01

The feasibility of using a contoured honeycomb model to generate a thick boundary layer in high-speed, compressible flow was investigated. The contour of the honeycomb was tailored to selectively remove momentum in a minimum of streamwise distance to create an artificially thickened turbulent boundary layer. Three wind tunnel experiments were conducted to verify the concept. Results indicate that this technique is a viable concept, especially for high-speed inlet testing applications. In addition, the compactness of the honeycomb boundary layer simulator allows relatively easy integration into existing wind tunnel model hardware.

Forward-facing steps induced transition in a subsonic boundary layer

NASA Astrophysics Data System (ADS)

Zh, Hui; Fu, Song

2017-10-01

A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.

Turbulent boundary layer in high Rayleigh number convection in air.

PubMed

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.

The effect of inlet boundary layer thickness on the flow within an annular S-shaped duct

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

Sonoda, T.; Arima, T.; Oana, M.

1999-07-01

Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the effect of the inlet boundary layer (IBL) on the flow. A duct with six struts and the geometry as that used to connect compressor spools on the experimental small two-spool turbofan engine was investigated. A curved downstream annular passage with similar meridional flow path geometry to that of the centrifugal compressor has been fitted at the exit of S-shaped duct. Two types of the IBL (i.e., thin and thick IBL) were used. Results showed that large differencesmore » of flow patterns were observed at the S-shaped duct exit between two types of IBL, though the value of net total pressure loss has not been remarkably changed. According to overall total pressure loss, which includes the IBL loss, the total pressure loss was greatly increased near the hub as compared to that for a thin one. For the thick IBL, a vortex pair related to the hub-side horseshoe vortex and the separated flow found at the strut trailing edge has been clearly captured in the form of the total pressure loss contours and secondary flow vectors, experimentally and numerically. The high-pressure loss regions on either side of the strut wake near the hub may act on a downstream compressor performance. There is a much-distorted three-dimensional flow patterns at the exit of S-shaped duct. This means that the aerodynamic sensitivity of S-shaped duct to the IBL thickness is very high. Therefore, sufficient care is needed to design not only downstream aerodynamic components (for example, centrifugal impeller) but also upstream aerodynamic components (LPC OGV).« less

Dependencies of surface plasmon coupling effects on the p-GaN thickness of a thin-p-type light-emitting diode.

PubMed

Su, Chia-Ying; Lin, Chun-Han; Yao, Yu-Feng; Liu, Wei-Heng; Su, Ming-Yen; Chiang, Hsin-Chun; Tsai, Meng-Che; Tu, Charng-Gan; Chen, Hao-Tsung; Kiang, Yean-Woei; Yang, C C

2017-09-04

The high performance of a light-emitting diode (LED) with the total p-type thickness as small as 38 nm is demonstrated. By increasing the Mg doping concentration in the p-AlGaN electron blocking layer through an Mg pre-flow process, the hole injection efficiency can be significantly enhanced. Based on this technique, the high LED performance can be maintained when the p-type layer thickness is significantly reduced. Then, the surface plasmon coupling effects, including the enhancement of internal quantum efficiency, increase in output intensity, reduction of efficiency droop, and increase of modulation bandwidth, among the thin p-type LED samples of different p-type thicknesses that are compared. These advantageous effects are stronger as the p-type layer becomes thinner. However, the dependencies of these effects on p-type layer thickness are different. With a circular mesa size of 10 μm in radius, through surface plasmon coupling, we achieve the record-high modulation bandwidth of 625.6 MHz among c-plane GaN-based LEDs.

Flight-measured pressure characteristics of aft-facing steps in high Reynolds number flow at Mach numbers of 2.20, 2.50, and 2.80 and comparison with other data

NASA Technical Reports Server (NTRS)

Powers, S. G.

1978-01-01

The YF-12 airplane was studied to determine the pressure characteristics associated with an aft-facing step in high Reynolds number flow for nominal Mach numbers of 2.20, 2.50, and 2.80. Base pressure coefficients were obtained for three step heights. The surface static pressures ahead of and behind the step were measured for the no-step condition and for each of the step heights. A boundary layer rake was used to determine the local boundary layer conditions. The Reynolds number based on the length of flow ahead of the step was approximately 10 to the 8th power and the ratios of momentum thickness to step height ranged from 0.2 to 1.0. Base pressure coefficients were compared with other available data at similar Mach numbers and at ratios of momentum thickness to step height near 1.0. In addition, the data were compared with base pressure coefficients calculated by a semiempirical prediction method. The base pressure ratios are shown to be a function of Reynolds number based on momentum thickness. Profiles of the surface pressures ahead of and behind the step and the local boundary layer conditions are also presented.

Stability analysis of the onset of vortex shedding for wakes behind flat plates

NASA Astrophysics Data System (ADS)

Wang, Shuai; Liu, Li; Zhang, Shi-Bo; Wen, Feng-Bo; Zhou, Xun

2018-04-01

Above a critical Reynolds number, wake flows behind flat plates become globally unstable, the leading modal instability in this case is known as Kelvin-Helmholtz mechanism. In this article, both local and BiGlobal linear instability analyses are performed numerically to study the onset of the shedding process. Flat plates with different base shapes are considered to assess geometry effects, and the relation between the critical shedding Reynolds number, Re_cr , and the boundary layer thickness is studied. Three types of base shapes are used: square, triangular and elliptic. It is found that the base shape has a great impact on the growth rate of least stable disturbance mode, thus would influence Re_cr greatly, but it has little effect on the vortex shedding frequency. The shedding frequency is determined mainly by boundary layer thickness and has little dependence on the Reynolds number and base shape. We find that for a fixed Reynolds number, increasing boundary layer thickness acted in two ways to modify the global stability characteristics: It increases the length of the absolute unstable region and it makes the flow less locally absolutely unstable in the near-wake region, and these two effects work against each other to destabilize or stabilize the flow.

A steadying effect of acoustic excitation on transitory stall

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1991-01-01

The effect of acoustic excitation on a class of separated flows with a transitional boundary layer at the point of separation is considered. Experimental results on the flow over airfoils, a two-dimensional backward-facing step, and through large angle conical diffusers are presented. In all cases, the separated flow undergoes large amplitude fluctuations, much of the energy being concentrated at unusually low frequencies. In each case, an appropriate high frequency acoustic excitation is found to be effective in reducing the fluctuations substantially. The effective excitation frequency scales on the initial boundary layer thickness and the effect is apparently achieved through acoustic tripping of the separating boundary layer.

Effects of mass transfer on MHD three dimensional flow of a Prandtl liquid over a flat plate in the presence of chemical reaction

NASA Astrophysics Data System (ADS)

Ganesh Kumar, K.; Rizwan-ul-Haq; Rudraswamy, N. G.; Gireesha, B. J.

The present study addresses the three-dimensional flow of a Prandtl fluid over a Riga plate in the presence of chemical reaction and convective condition. The converted set of boundary layer equations are solved numerically by RKF four-fifth method. Obtained numerical results for flow and mass transfer characteristics are discussed for various physical parameters. Additionally, the skin friction coefficient and Sherwood number are also presented. It is found that, the momentum boundary layer thickness is dominant for higher values of α and solutal boundary layer is low for higher Schmidt number and chemical reaction parameter.

Hydraulic permeability of multilayered collagen gel scaffolds under plastic compression-induced unidirectional fluid flow.

PubMed

Serpooshan, Vahid; Quinn, Thomas M; Muja, Naser; Nazhat, Showan N

2013-01-01

Under conditions of free fluid flow, highly hydrated fibrillar collagen gels expel fluid and undergo gravity driven consolidation (self-compression; SC). This process can be accelerated by the application of a compressive stress (plastic compression; PC) in order to generate dense collagen scaffolds for tissue engineering. To define the microstructural evolution of collagen gels under PC, this study applied a two-layer micromechanical model that was previously developed to measure hydraulic permeability (k) under SC. Radially confined PC resulted in unidirectional fluid flow through the gel and the formation of a dense lamella at the fluid expulsion boundary which was confirmed by confocal microscopy of collagen immunoreactivity. Gel mass loss due to PC and subsequent SC were measured and applied to Darcy's law to calculate the thickness of the lamella and hydrated layer, as well as their relative permeabilities. Increasing PC level resulted in a significant increase in mass loss fraction and lamellar thickness, while the thickness of the hydrated layer dramatically decreased. Permeability of lamella also decreased from 1.8×10(-15) to 1.0×10(-15) m(2) in response to an increase in PC level. Ongoing SC, following PC, resulted in a uniform decrease in mass loss and k with increasing PC level and as a function SC time. Experimental k data were in close agreement with those estimated by the Happel model. Calculation of average k values for various two-layer microstructures indicated that they each approached 10(-15)-10(-14) m(2) at equilibrium. In summary, the two-layer micromechanical model can be used to define the microstructure and permeability of multi-layered biomimetic scaffolds generated by PC. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Modeling of Multiphase Flow through Thin Porous Layers: Application to a Polymer Electrolyte Fuel Cell (PEFC)

NASA Astrophysics Data System (ADS)

Qin, C.; Hassanizadeh, S.

2013-12-01

Multiphase flow and species transport though thin porous layers are encountered in a number of industrial applications, such as fuel cells, filters, and hygiene products. Based on some macroscale models like the Darcy's law, to date, the modeling of flow and transport through such thin layers has been mostly performed in 3D discretized domains with many computational cells. But, there are a number of problems with this approach. First, a proper representative elementary volume (REV) is not defined. Second, one needs to discretize a thin porous medium into computational cells whose size may be comparable to the pore sizes. This suggests that the traditional models are not applicable to such thin domains. Third, the interfacial conditions between neighboring layers are usually not well defined. Last, 3D modeling of a number of interacting thin porous layers often requires heavy computational efforts. So, to eliminate the drawbacks mentioned above, we propose a new approach to modeling multilayers of thin porous media as 2D interacting continua (see Fig. 1). Macroscale 2D governing equations are formulated in terms of thickness-averaged material properties. Also, the exchange of thermodynamic properties between neighboring layers is described by thickness-averaged quantities. In Comparison to previous macroscale models, our model has the distinctive advantages of: (1) it is rigorous thermodynamics-based model; (2) it is formulated in terms of thickness-averaged material properties which are easily measureable; and (3) it reduces 3D modeling to 2D leading to a very significant reduction of computation efforts. As an application, we employ the new approach in the study of liquid water flooding in the cathode of a polymer electrolyte fuel cell (PEFC). To highlight the advantages of the present model, we compare the results of water distribution with those obtained from the traditional 3D Darcy-based modeling. Finally, it is worth noting that, for specific case studies, a number of material properties in the model need to be determined experimentally, such as mass and heat exchange coefficients between neighboring layers. Fig. 1: Schematic representation of three thin porous layers, which may exchange mass, momentum, and energy. Also, a typical averaging domain (REV) is shown. Note that the layer thickness and thus the REV height can be spatially variable. Also, in reality, the layers are tightly stacked and there is no gap between them.

Size segregation in a granular bore

NASA Astrophysics Data System (ADS)

Edwards, A. N.; Vriend, N. M.

2016-10-01

We investigate the effect of particle-size segregation in an upslope propagating granular bore. A bidisperse mixture of particles, initially normally graded, flows down an inclined chute and impacts with a closed end. This impact causes the formation of a shock in flow thickness, known as a granular bore, to travel upslope, leaving behind a thick deposit. This deposit imprints the local segregated state featuring both pure and mixed regions of particles as a function of downstream position. The particle-size distribution through the depth is characterized by a thin purely small-particle layer at the base, a significant linear transition region, and a thick constant mixed-particle layer below the surface, in contrast to previously observed S-shaped steady-state concentration profiles. The experimental observations agree with recent progress that upward and downward segregation of large and small particles respectively is asymmetric. We incorporate the three-layer, experimentally observed, size-distribution profile into a depth-averaged segregation model to modify it accordingly. Numerical solutions of this model are able to match our experimental results and therefore motivate the use of a more general particle-size distribution profile.

Laminar Flow Breakdown due to Particle Interactions

DTIC Science & Technology

2012-08-01

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

Kinematics and dynamics of salt movement driven by sub-salt normal faulting and supra-salt sediment accumulation - combined analogue experiments and analytical calculations

NASA Astrophysics Data System (ADS)

Warsitzka, Michael; Kukowski, Nina; Kley, Jonas

2017-04-01

In extensional sedimentary basins, the movement of ductile salt is mainly controlled by the vertical displacement of the salt layer, differential loading due to syn-kinematic deposition, and tectonic shearing at the top and the base of the salt layer. During basement normal faulting, salt either tends to flow downward to the basin centre driven by its own weight or it is squeezed upward due to differential loading. In analogue experiments and analytical models, we address the interplay between normal faulting of the sub-salt basement, compaction and density inversion of the supra-salt cover and the kinematic response of the ductile salt layer. The analogue experiments consist of a ductile substratum (silicone putty) beneath a denser cover layer (sand mixture). Both layers are displaced by normal faults mimicked through a downward moving block within the rigid base of the experimental apparatus and the resulting flow patterns in the ductile layer are monitored and analysed. In the computational models using an analytical approximative solution of the Navier-Stokes equation, the steady-state flow velocity in an idealized natural salt layer is calculated in order to evaluate how flow patterns observed in the analogue experiments can be translated to nature. The analytical calculations provide estimations of the prevailing direction and velocity of salt flow above a sub-salt normal fault. The results of both modelling approaches show that under most geological conditions salt moves downwards to the hanging wall side as long as vertical offset and compaction of the cover layer are small. As soon as an effective average density of the cover is exceeded, the direction of the flow velocity reverses and the viscous material is squeezed towards the elevated footwall side. The analytical models reveal that upward flow occurs even if the average density of the overburden does not exceed the density of salt. By testing various scenarios with different layer thicknesses, displacement rate or lithological parameters of the cover, our models suggest that the reversal of material flow usually requires vertical displacements between 700 and 2000 m. The transition from downward to upward flow occurs at smaller fault displacements, if the initial overburden thickness and the overburden density are high and if sedimentation rate keeps pace with the displacement rate of the sub-salt normal fault.

Laminar-Turbulent Transition Behind Discrete Roughness Elements in a High-Speed Boundary Layer

NASA Technical Reports Server (NTRS)

Choudhari, Meelan M.; Li, Fei; Wu, Minwei; Chang, Chau-Lyan; Edwards, Jack R., Jr.; Kegerise, Michael; King, Rudolph

2010-01-01

Computations are performed to study the flow past an isolated roughness element in a Mach 3.5, laminar, flat plate boundary layer. To determine the effects of the roughness element on the location of laminar-turbulent transition inside the boundary layer, the instability characteristics of the stationary wake behind the roughness element are investigated over a range of roughness heights. The wake flow adjacent to the spanwise plane of symmetry is characterized by a narrow region of increased boundary layer thickness. Beyond the near wake region, the centerline streak is surrounded by a pair of high-speed streaks with reduced boundary layer thickness and a secondary, outer pair of lower-speed streaks. Similar to the spanwise periodic pattern of streaks behind an array of regularly spaced roughness elements, the above wake structure persists over large distances and can sustain strong enough convective instabilities to cause an earlier onset of transition when the roughness height is sufficiently large. Time accurate computations are performed to clarify additional issues such as the role of the nearfield of the roughness element during the generation of streak instabilities, as well as to reveal selected details of their nonlinear evolution. Effects of roughness element shape on the streak amplitudes and the interactions between multiple roughness elements aligned along the flow direction are also investigated.

The effect of viscoelasticity on the stability of a pulmonary airway liquid layer

NASA Astrophysics Data System (ADS)

Halpern, David; Fujioka, Hideki; Grotberg, James B.

2010-01-01

The lungs consist of a network of bifurcating airways that are lined with a thin liquid film. This film is a bilayer consisting of a mucus layer on top of a periciliary fluid layer. Mucus is a non-Newtonian fluid possessing viscoelastic characteristics. Surface tension induces flows within the layer, which may cause the lung's airways to close due to liquid plug formation if the liquid film is sufficiently thick. The stability of the liquid layer is also influenced by the viscoelastic nature of the liquid, which is modeled using the Oldroyd-B constitutive equation or as a Jeffreys fluid. To examine the role of mucus alone, a single layer of a viscoelastic fluid is considered. A system of nonlinear evolution equations is derived using lubrication theory for the film thickness and the film flow rate. A uniform film is initially perturbed and a normal mode analysis is carried out that shows that the growth rate g for a viscoelastic layer is larger than for a Newtonian fluid with the same viscosity. Closure occurs if the minimum core radius, Rmin(t), reaches zero within one breath. Solutions of the nonlinear evolution equations reveal that Rmin normally decreases to zero faster with increasing relaxation time parameter, the Weissenberg number We. For small values of the dimensionless film thickness parameter ɛ, the closure time, tc, increases slightly with We, while for moderate values of ɛ, ranging from 14% to 18% of the tube radius, tc decreases rapidly with We provided the solvent viscosity is sufficiently small. Viscoelasticity was found to have little effect for ɛ >0.18, indicating the strong influence of surface tension. The film thickness parameter ɛ and the Weissenberg number We also have a significant effect on the maximum shear stress on tube wall, max(τw), and thus, potentially, an impact on cell damage. Max(τw) increases with ɛ for fixed We, and it decreases with increasing We for small We provided the solvent viscosity parameter is sufficiently small. For large ɛ ≈0.2, there is no significant difference between the Newtonian flow case and the large We cases.

Stability of spatially developing boundary layers

NASA Astrophysics Data System (ADS)

Govindarajan, Rama

1993-07-01

A new formulation of the stability of boundary-layer flows in pressure gradients is presented, taking into account the spatial development of the flow. The formulation assumes that disturbance wavelength and eigenfunction vary downstream no more rapidly than the boundary-layer thickness, and includes all terms of O(1) and O(R(exp -1)) in the boundary-layer Reynolds number R. Although containing the Orr-Sommerfeld operator, the present approach does not yield the Orr-Sommerfeld equation in any rational limit. In Blasius flow, the present stability equation is consistent with that of Bertolotti et al. (1992) to terms of O(R(exp -1)). For the Falkner-Skan similarity solutions neutral boundaries are computed without the necessity of having to march in space. Results show that the effects of spatial growth are striking in flows subjected to adverse pressure gradients.

Micro-Scale Regenerative Heat Exchanger

NASA Technical Reports Server (NTRS)

Moran, Matthew E.; Stelter, Stephan; Stelter, Manfred

2004-01-01

A micro-scale regenerative heat exchanger has been designed, optimized and fabricated for use in a micro-Stirling device. Novel design and fabrication techniques enabled the minimization of axial heat conduction losses and pressure drop, while maximizing thermal regenerative performance. The fabricated prototype is comprised of ten separate assembled layers of alternating metal-dielectric composite. Each layer is offset to minimize conduction losses and maximize heat transfer by boundary layer disruption. A grating pattern of 100 micron square non-contiguous flow passages were formed with a nominal 20 micron wall thickness, and an overall assembled ten-layer thickness of 900 microns. Application of the micro heat exchanger is envisioned in the areas of micro-refrigerators/coolers, micropower devices, and micro-fluidic devices.

A Water Model Study on Mixing Behavior of the Two-Layered Bath in Bottom Blown Copper Smelting Furnace

NASA Astrophysics Data System (ADS)

Shui, Lang; Cui, Zhixiang; Ma, Xiaodong; Jiang, Xu; Chen, Mao; Xiang, Yong; Zhao, Baojun

2018-05-01

The bottom-blown copper smelting furnace is a novel copper smelter developed in recent years. Many advantages of this furnace have been found, related to bath mixing behavior under its specific gas injection scheme. This study aims to use an oil-water double-phased laboratory-scale model to investigate the impact of industry-adjustable variables on bath mixing time, including lower layer thickness, gas flow rate, upper layer thickness and upper layer viscosity. Based on experimental results, an overall empirical relationship of mixing time in terms of these variables has been correlated, which provides the methodology for industry to optimize mass transfer in the furnace.

Modeling of Ice Flow and Internal Layers Along a Flow Line Through Swiss Camp in West Greenland

NASA Technical Reports Server (NTRS)

Wang, W. L.; Zwally, H. Jay; Abdalati, W.; Luo, S.; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

An anisotropic ice flow line model is applied to a flow line through Swiss Camp (69.57 N, 49.28 W) in West Greenland to estimate the dates of internal layers detected by Radio-Echo Sounding measurements. The effect of an anisotropic ice fabric on ice flow is incorporated into the steady state flow line model. The stress-strain rate relationship for anisotropic ice is characterized by an enhancement factor based on the laboratory observations of ice deformation under combined compression and shear stresses. By using present-day data of accumulation rate, surface temperature, surface elevation and ice thickness along the flow line as model inputs, a very close agreement is found between the isochrones generated from the model and the observed internal layers with confirmed dates. The results indicate that this part of Greenland ice sheet is primarily in steady state.

Separation behavior of boundary layers on three-dimensional wings

NASA Technical Reports Server (NTRS)

Stock, H. W.

1981-01-01

An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.

Rarefaction and Non-equilibrium Effects in Hypersonic Flows about Leading Edges of Small Bluntness

NASA Astrophysics Data System (ADS)

Ivanov, Mikhail; Khotyanovsky, Dmitry; Kudryavtsev, Alexey; Shershnev, Anton; Bondar, Yevgeniy; Yonemura, Shigeru

2011-05-01

A hypersonic flow about a cylindrically blunted thick plate at a zero angle of attack is numerically studied with the kinetic (DSMC) and continuum (Navier-Stokes equations) approaches. The Navier-Stokes equations with velocity slip and temperature jump boundary conditions correctly predict the flow fields and surface parameters for values of the Knudsen number (based on the radius of leading edge curvature) smaller than 0.1. The results of computations demonstrate significant effects of the entropy layer on the boundary layer characteristics.

Why is there evidence for flowing ice at mid-latitudes on Mars but not at the poles?

NASA Astrophysics Data System (ADS)

Smith, I. B.

2017-12-01

Ice has been detected on Mars in many places, from the polar caps, to mid-latitudes. In many locations there exists evidence for glacial flow. This raises the possibility of flow for the polar layered deposits (PLD). Since the >2000 m thick ice deposits were first observed, speculation about their flow status have persisted. Several stratigraphic predictions regarding flow have been made (Figure 1), but these predictions are not supported with observational data (Smith and Holt 2015) The disagreement between model and observations has led to a general consensus that the polar ice flows more slowly than other processes acting on the PLD, but the reasoning is not understood. Here I posit that the polar layered deposits do not act as a single, generic ice sheet. Instead, they act as a stack of thin ice sheets, where each layer is separated by a boundary of dust, and all layers flow individually. The layers act as barriers to vertical flow, so the viscosity of the cold ice can only be expressed through lateral expansion. I plan to present a simple experiment demonstrating the multi-layer, stacked flow hypothesis. I will demonstrate that the layers themselves flow but do not deform the entire ice sheet, as previously predicted. This allows for the PLD to retain their steep slopes and prevents many of the predicted flow features to form. The major component of this hypothesis is that the dust layers hinder flow. Thus, constraining the friction coefficient, viscosity, tensile strength and compressibility of the dust layers becomes an important next step for testing the stacked, multi-layer flow scenario. Acknowledgements: Thanks to Eric Larour and David Goldsby for helpful comments.

NO PLIF Study of Hypersonic Transition Over a Discrete Hemispherical Roughness Element

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Bathel, Brett F.; Ivey, Christopher; Inman, Jennifer A.; Jones, Stephen B.

2009-01-01

Nitric oxide (NO) planar laser-induced fluorescence (PLIF) has been use to investigate the hypersonic flow over a flat plate with and without a 2-mm (0.08-in) radius hemispherical trip. In the absence of the trip, for all angles of attack and two different Reynolds numbers, the flow was observed to be laminar and mostly steady. Boundary layer thicknesses based on the observed PLIF intensity were measured and compared with a CFD computation, showing agreement. The PLIF boundary layer thickness remained constant while the NO flowrate was varied by a factor of 3, indicating non-perturbative seeding of NO. With the hemispherical trip in place, the flow was observed to be laminar but unsteady at the shallowest angle of attack and lowest Reynolds number and appeared vigorously turbulent at the steepest angle of attack and highest Reynolds number. Laminar corkscrew-shaped vortices oriented in the streamwise direction were frequently observed to transition the flow to more turbulent structures.

Capillary trapping of particles in thin-film flows

NASA Astrophysics Data System (ADS)

Dressaire, Emilie; Gomez, Michael; Colnet, Benedicte; Sauret, Alban

2017-11-01

When a thin layer of suspension flows over a substrate, some particles remain trapped on the solid surface. When the thickness of the liquid layer is comparable to the particle size, the particles deform the liquid interface, which leads to local interactions. These effects modify the transport of particles and the dynamics of the liquid films. Here, we characterize how capillary interactions affect the transport and deposition of non-Brownian particles moving in thin liquid films and the resulting loss of transported material. We focus on gravitational drainage flows, in which the film thickness becomes comparable to the particle size. Depending on the concentration of particles, we find that the drainage dynamics exhibits behavior that cannot be captured with a continuum model, due to the deposition of particles on the substrate. ANR-16-CE30-0009 & CNRS-PICS-07242 & ACS-PRF 55845-ND9.

Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

NASA Technical Reports Server (NTRS)

Nagamatsu, H. T.; Brower, W. B., Jr.; Bahi, L.; Ross, J.

1982-01-01

The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO 2/Si with oxide films deposited

NASA Astrophysics Data System (ADS)

Chen, Changhong; Huang, Dexiu; Zhu, Weiguang; Feng, Yi; Wu, Xigang

2006-08-01

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO 2/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600 °C, PtTi 3+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650 °C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO 2, the first two layers spaced by 65 nm encapsulate the Pt surface by the first layer with 60 nm thick forming at its surface and by the next layer with 35 nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO 2- x formed by the residual Ti oxidizing.

Gasdynamic simulations of the solar wind interaction with Venus - Boundary layer formation

NASA Astrophysics Data System (ADS)

McGary, J. E.

1993-05-01

A 2D gasdynamic simulation of the mass-loaded solar wind flow around the dayside of Venus is presented. For average ionopause conditions near 300 km, the simulations show that mass loading from the pickup of oxygen ions produces a boundary layer of finite thickness along the ionopause. Within this layer and toward the ionopause, the temperature decreases and the total mass density increases significantly. Furthermore, there is a shear in the bulk flow velocity across the boundary layer, such that the tangential flow decreases in speed as the ionopause is approached and remains low along the ionopause which is consistent with Pioneer Venus observations. Numerical simulations are carried out for various mass addition rates and demonstrate that the boundary layer develops when oxygen ion production exceeds approximately 2 x 10 exp 5/cu m per s.

Highly conductive, multi-layer composite precursor composition to fuel cell flow field plate or bipolar plate

DOEpatents

Jang, Bor Z [Centerville, OH; Zhamu, Aruna [Centerville, OH; Guo, Jiusheng [Centerville, OH

2011-02-15

This invention provides a moldable, multiple-layer composite composition, which is a precursor to an electrically conductive composite flow field plate or bipolar plate. In one preferred embodiment, the composition comprises a plurality of conductive sheets and a plurality of mixture layers of a curable resin and conductive fillers, wherein (A) each conductive sheet is attached to at least one resin-filler mixture layer; (B) at least one of the conductive sheets comprises flexible graphite; and (C) at least one resin-filler mixture layer comprises a thermosetting resin and conductive fillers with the fillers being present in a sufficient quantity to render the resulting flow field plate or bipolar plate electrically conductive with a conductivity no less than 100 S/cm and thickness-direction areal conductivity no less than 200 S/cm.sup.2.

Development of a Flow Field for Testing a Boundary-Layer-Ingesting Propulsor

NASA Technical Reports Server (NTRS)

Hirt, Stefanie M.; Arend, David J.; Wolter, John D.

2017-01-01

The test section of the 8- by 6-Foot Supersonic Wind Tunnel at NASA Glenn Research Center was modified to produce the test conditions for a boundary-layer-ingesting propulsor. A test was conducted to measure the flow properties in the modified test section before the propulsor was installed. Measured boundary layer and freestream conditions were compared to results from computational fluid dynamics simulations of the external surface for the reference vehicle. Testing showed that the desired freestream conditions and boundary layer thickness could be achieved; however, some non-uniformity of the freestream conditions, particularly the total temperature, were observed.

Simulation of Vortex Structure in Supersonic Free Shear Layer Using Pse Method

NASA Astrophysics Data System (ADS)

Guo, Xin; Wang, Qiang

The method of parabolized stability equations (PSE) are applied in the analysis of nonlinear stability and the simulation of flow structure in supersonic free shear layer. High accuracy numerical techniques including self-similar basic flow, high order differential method, appropriate transformation and decomposition of nonlinear terms are adopted and developed to solve the PSE effectively for free shear layer. The spatial evolving unstable waves which dominate the flow structure are investigated through nonlinear coupling spatial marching methods. The nonlinear interactions between harmonic waves are further analyzed and instantaneous flow field are obtained by adding the harmonic waves into basic flow. Relevant data agree well with that of DNS. The results demonstrate that T-S wave does not keeping growing exponential as the linear evolution, the energy transfer to high order harmonic modes and finally all harmonic modes get saturation due to the nonlinear interaction; Mean flow distortion is produced by the nonlinear interaction between the harmonic and its conjugate harmonic, makes great change to the average flow and increases the thickness of shear layer; PSE methods can well capture the large scale nonlinear flow structure in the supersonic free shear layer such as vortex roll-up, vortex pairing and nonlinear saturation.

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

NASA Technical Reports Server (NTRS)

Corke, T. C.; Guezennec, Y.; Nagib, H. M.

1981-01-01

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Passive Flap Actuation by Reversing Flow in Laminar Boundary Layer Separation

NASA Astrophysics Data System (ADS)

Parsons, Chase; Lang, Amy; Santos, Leo; Bonacci, Andrew

2017-11-01

Reducing the flow separation is of great interest in the field of fluid mechanics in order to reduce drag and improve the overall efficiency of aircraft. This project seeks to investigate passive flow control using shark inspired microflaps in laminar boundary layer separation. This study aims to show that whether a flow is laminar or turbulent, laminar and 2D or turbulent and 3D, microflaps actuated by reversing flow is a robust means of controlling flow separation. In order to generate a controlled adverse pressure gradient, a rotating cylinder induces separation at a chosen location on a flat plate boundary layer with Re above 10000. Within this thick boundary layer, digital particle image velocimetry is used to map the flow. This research can be used in the future to better understand the nature of the bristling shark scales and its ability to passively control separation. Results show that microflaps successfully actuated due to backflow and that this altered the formation of flow separation. I would like to thank the NSF for REU Grant EEC 1659710 and the Army Research Office for funding this project.

Heat transfer and fluid mechanics measurements in transitional boundary layer flows

NASA Technical Reports Server (NTRS)

Wang, T.; Simon, T. W.; Buddhavarapu, J.

1985-01-01

Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.

Observations of the Effect of Wing Appendages and Flaps on the Spread of Separation of Flow over the Wing

NASA Technical Reports Server (NTRS)

Hartwig, G

1941-01-01

The spread of the separation of flow on three tapered wings insymmetrical and unsymmetrical flow was observed with silk tufts. By equal thickness and chord distribution the wings manifested a different form of lifting line. The principal result of the study was that the wings alone first disclosed complete breakdown of the flow at the tips, even the one with twist, but that after adding fuselage and engine nacelles, the twisted wing broke down completely first in the wing center. The observed boundary layer motions transverse to the main flow direction were briefly explored as to their possible influence on the spread of the separation. On top of that certain disclosures were afforded in which the transverse motions observed in the boundary layer became perceptible even above the boundary layer.

Factors Influencing Pitot Probe Centerline Displacement in a Turbulent Supersonic Boundary Layer

NASA Technical Reports Server (NTRS)

Grosser, Wendy I.

1997-01-01

When a total pressure probe is used for measuring flows with transverse total pressure gradients, a displacement of the effective center of the probe is observed (designated Delta). While this phenomenon is well documented in incompressible flow and supersonic laminar flow, there is insufficient information concerning supersonic turbulent flow. In this study, three NASA Lewis Research Center Supersonic Wind Tunnels (SWT's) were used to investigate pitot probe centerline displacement in supersonic turbulent boundary layers. The relationship between test conditions and pitot probe centerline displacement error was to be determined. For this investigation, ten circular probes with diameter-to-boundary layer ratios (D/delta) ranging from 0.015 to 0.256 were tested in the 10 ft x 10 ft SWT, the 15 cm x 15 cm SWT, and the 1 ft x 1 ft SWT. Reynolds numbers of 4.27 x 10(exp 6)/m, 6.00 x 10(exp 6)/in, 10.33 x 10(exp 6)/in, and 16.9 x 10(exp 6)/m were tested at nominal Mach numbers of 2.0 and 2.5. Boundary layer thicknesses for the three tunnels were approximately 200 mm, 13 mm, and 30 mm, respectively. Initial results indicate that boundary layer thickness, delta, and probe diameter, D/delta play a minimal role in pitot probe centerline offset error, Delta/D. It appears that the Mach gradient, dM/dy, is an important factor, though the exact relationship has not yet been determined. More data is needed to fill the map before a conclusion can be drawn with any certainty. This research provides valuable supersonic, turbulent boundary layer data from three supersonic wind tunnels with three very different boundary layers. It will prove a valuable stepping stone for future research into the factors influencing pitot probe centerline offset error.

The behavior of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient. Ph.D. Thesis - Washington Univ., Seattle, Aug. 1972

NASA Technical Reports Server (NTRS)

Rose, W. C.

1973-01-01

The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.

Generalization of Boundary-Layer Momentum-Integral Equations to Three-Dimensional Flows Including Those of Rotating System

NASA Technical Reports Server (NTRS)

Mager, Arthur

1952-01-01

The Navier-Stokes equations of motion and the equation of continuity are transformed so as to apply to an orthogonal curvilinear coordinate system rotating with a uniform angular velocity about an arbitrary axis in space. A usual simplification of these equations as consistent with the accepted boundary-layer theory and an integration of these equations through the boundary layer result in boundary-layer momentum-integral equations for three-dimensional flows that are applicable to either rotating or nonrotating fluid boundaries. These equations are simplified and an approximate solution in closed integral form is obtained for a generalized boundary-layer momentum-loss thickness and flow deflection at the wall in the turbulent case. A numerical evaluation of this solution carried out for data obtained in a curving nonrotating duct shows a fair quantitative agreement with the measures values. The form in which the equations are presented is readily adaptable to cases of steady, three-dimensional, incompressible boundary-layer flow like that over curved ducts or yawed wings; and it also may be used to describe the boundary-layer flow over various rotating surfaces, thus applying to turbomachinery, propellers, and helicopter blades.

Diffusion boundary layers ameliorate the negative effects of ocean acidification on the temperate coralline macroalga Arthrocardia corymbosa.

PubMed

Cornwall, Christopher E; Boyd, Philip W; McGraw, Christina M; Hepburn, Christopher D; Pilditch, Conrad A; Morris, Jaz N; Smith, Abigail M; Hurd, Catriona L

2014-01-01

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 'ambient' and 7.65 a worst case 'ocean acidification' scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO3) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.

Preliminary observations and logs of BARB 1 and BARB 2: komatiites from the Tjakastad site

NASA Astrophysics Data System (ADS)

Coetzee, Grace; Arndt, Nicholas; Wilson, Allan

2013-04-01

The BARB 1 and BARB 2 cores intersect a suite of komatiite flows and komatiitic basalts as well as fragmental rocks of the Komati Formation of the Onverwacht Group, Barberton Greenstone Belt. The cores give important and previously unattainable information on the structures, textures and contact relationships between individual komatiite flows and different lithological units within the flows. BARB 1 was drilled at -48° on a 5° azimuth to a depth of 419.9 m. This core contains a unique volcanic tumulus succession in the stratigraphically lower 100 m and the rest of the core consists of about 59 flows of spinifex-textured komatiite (1-3 m thick), massive komatiite (0.5-10 m thick), komatiitic basalt (1-9 m thick) and a single basalt layer (10 m thick), intruded by gabbro (0.5-2 m thick) and a single dolerite dyke (18 m thick). BARB 2, approximately 50 m from BARB 1 and parallel to it, was drilled at -45°on an 8° azimuth to a depth of 431.5 m. This core contains approximately 39 flows of komatiite (0.5-10 m thick) and komatiitic basalt (2-23 m thick) which contain possible selvages of pillows. Basalt flows are more numerous (0.3-4 m thick) in BARB 2 whilst gabbro (0.6-7 m thick) is less prevalent. The dolerite dyke observed in BARB 1 does not occur in BARB 2. As the Barberton strata young towards the east, the cores intersected the stratigraphy in a reverse sequence. The cores were drilled such that there exists a 141 m overlap in stratigraphy between them. The section 141 m from the base of BARB 1 should theoretically correlate with the top 141 m of BARB 2. However, this overlap is not evident in the core or in the core logs. A single gabbro layer appears to be lithologically correlatable between both holes. There is no apparent correlation between the pattern of the komatiite flows leading to an initial conclusion that the komatiite flows were not laterally extensive or changed laterally in form over short distances. In both cores the proportion of komatiitic basalt appears to increase with depth. However, chemical analyses indicate that some of the units originally logged as komatiitic basalt are actually komatiite. The rocks have all undergone alteration to serpentine, and in extreme cases are carbonated together with carbonate veins. Despite the alteration, the original spinifex and olivine cumulate textures, as a well as primary volcanic structures, including spectacular hyaloclastite in the cumulus unit, are well preserved. To date 140 samples have been analysed for major and trace elements and controls by olivine and possibly orthopyroxene have been demonstrated.

Interaction Between Downwelling Flow and the Laterally-Varying Thickness of the North American Lithosphere Inferred from Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Behn, M. D.; Conrad, C. P.; Silver, P. G.

2005-12-01

Shear flow in the asthenosphere tends to align olivine crystals in the direction of shear, producing a seismically anisotropic asthenosphere that can be detected using a number of seismic techniques (e.g., shear-wave splitting (SWS) and surface waves). In the ocean basins, where the asthenosphere has a relatively uniform thickness and lithospheric anisotropy appears to be small, observed azimuthal anisotropy is well fit by asthenospheric shear flow in global flow models driven by a combination of plate motions and mantle density heterogeneity. In contrast, beneath the continents both the lithospheric ceiling and asthenospheric thickness may vary considerably across cratonic regions and ocean-continent boundaries. To examine the influence of a continental lithosphere with variable thickness on predictions of continental seismic anisotropy, we impose lateral variations in lithospheric viscosity in global models of mantle flow driven by plate motions and mantle density heterogeneity. For the North American continent, the Farallon slab descends beneath a deep cratonic root, producing downwelling flow in the upper mantle and convergent flow beneath the cratonic lithosphere. We evaluate both the orientation of the predicted azimuthal anisotropy and the depth dependence of radial anisotropy for this downwelling flow and find that the inclusion of a strong continental root provides an improved fit to observed SWS observations beneath the North American craton. Thus, we hypothesize that at least some continental anisotropy is associated with sub-lithospheric viscous shear, although fossil anisotropy in the lithospheric layer may also contribute significantly. Although we do not observe significant variations in the direction of predicted anisotropy with depth, we do find that the inclusion of deep continental roots pushes the depth of the anisotropy layer deeper into the upper mantle. We test several different models of laterally-varying lithosphere and asthenosphere viscosity. These models can be used to separate the contributions of asthenospheric flow and lithospheric fossil fabric in observations of continental anisotropy.

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

NASA Astrophysics Data System (ADS)

Nimmo, John R.; Creasey, Kaitlyn M.; Perkins, Kim S.; Mirus, Benjamin B.

2017-03-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

Preferential flow, diffuse flow, and perching in an interbedded fractured-rock unsaturated zone

USGS Publications Warehouse

Nimmo, John R.; Creasey, Kaitlyn M; Perkins, Kimberlie; Mirus, Benjamin B.

2017-01-01

Layers of strong geologic contrast within the unsaturated zone can control recharge and contaminant transport to underlying aquifers. Slow diffuse flow in certain geologic layers, and rapid preferential flow in others, complicates the prediction of vertical and lateral fluxes. A simple model is presented, designed to use limited geological site information to predict these critical subsurface processes in response to a sustained infiltration source. The model is developed and tested using site-specific information from the Idaho National Laboratory in the Eastern Snake River Plain (ESRP), USA, where there are natural and anthropogenic sources of high-volume infiltration from floods, spills, leaks, wastewater disposal, retention ponds, and hydrologic field experiments. The thick unsaturated zone overlying the ESRP aquifer is a good example of a sharply stratified unsaturated zone. Sedimentary interbeds are interspersed between massive and fractured basalt units. The combination of surficial sediments, basalts, and interbeds determines the water fluxes through the variably saturated subsurface. Interbeds are generally less conductive, sometimes causing perched water to collect above them. The model successfully predicts the volume and extent of perching and approximates vertical travel times during events that generate high fluxes from the land surface. These developments are applicable to sites having a thick, geologically complex unsaturated zone of substantial thickness in which preferential and diffuse flow, and perching of percolated water, are important to contaminant transport or aquifer recharge.

Suspended-Bed Reactor preliminary design, /sup 233/U--/sup 232/Th cycle. Final report (revised)

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

Karam, R.A.; Alapour, A.; Lee, C.C.

1977-11-01

The preliminary design Suspended-Bed Reactor is described. Coated particles about 2 mm in diameter are used as the fuel. The coatings consist of three layers: (1) low density pyrolytic graphite, 70 ..mu.. thick, (2) silicon carbide pressure vessel, 30 ..mu.. thick, and (3) ZrC layer, 50 ..mu.. thick, to protect the pressure vessel from moisture and oxygen. The fuel kernel can be either uranium-thorium dicarbide or metal. The coated particles are suspended by helium gas (coolant) in a cluster of pressurized tubes. The upward flow of helium fluidizes the coated particles. As the flow rate increases, the bed of particlesmore » is lifted upward to the core section. The particles are restrained at the upper end of the core by a suitable screen. The overall particle density in the core is just enough for criticality condition. Should the helium flow cease, the bed in the core section will collapse, and the particles will flow downward into the section where the increased physical spacings among the tubes brings about a safe shutdown. By immersing this section of the tubes in a large graphite block to serve as a heat sink, dissipation of decay heat becomes manageable. This eliminates the need for emergency core cooling systems.« less

Diagnosis at a glance of biological non-Newtonian fluids with Film Interference Flow Imaging (FIFI)

NASA Astrophysics Data System (ADS)

Hidema, R.; Yamada, N.; Furukawa, H.

2012-04-01

In the human body, full of biological non-Newtonian fluids exist. For example, synovial fluids exist in our joints, which contain full of biopolymers, such as hyaluronan and mucin. It is thought that these polymers play critical roles on the smooth motion of the joint. Indeed, luck of biopolymers in synovial fluid cause joint pain. Here we study the effects of polymer in thin liquid layer by using an original experimental method called Film Interference Flow Imaging (FIFI). A vertically flowing soap film containing polymers is made as two-dimensional flow to observe turbulence. The thickness of water layer is about 4 μm sandwiched between surfactant mono-layers. The interference pattern of the soap film is linearly related to the flow velocity in the water layer through the change in the thickness of the film. Thus the flow velocity is possibly analyzed by the single image analysis of the interference pattern, that is, FIFI. The grid turbulence was made in the flowing soap films containing the long flexible polymer polyethyleneoxide (PEO, Mw=3.5x106), and rigid polymer hydroxypropyl cellulose (HPC, Mw > 1.0 x106). The decaying process of the turbulence is affected by PEO and HPC at several concentrations. The effects of PEO are sharply seen even at low concentrations, while the effects of HPC are gradually occurred at much higher concentration compared to the PEO. It is assumed that such a difference between PEO and HPC is due to the polymer stretching or polymer orientation under turbulence, which is observed and analyzed by FIFI. We believe the FIFI will be applied in the future to examine biological fluids such as synovial fluids quickly and quantitatively.

Impact of mechanical heterogeneity on joint density in a welded ignimbrite

NASA Astrophysics Data System (ADS)

Soden, A. M.; Lunn, R. J.; Shipton, Z. K.

2016-08-01

Joints are conduits for groundwater, hydrocarbons and hydrothermal fluids. Robust fluid flow models rely on accurate characterisation of joint networks, in particular joint density. It is generally assumed that the predominant factor controlling joint density in layered stratigraphy is the thickness of the mechanical layer where the joints occur. Mechanical heterogeneity within the layer is considered a lesser influence on joint formation. We analysed the frequency and distribution of joints within a single 12-m thick ignimbrite layer to identify the controls on joint geometry and distribution. The observed joint distribution is not related to the thickness of the ignimbrite layer. Rather, joint initiation, propagation and termination are controlled by the shape, spatial distribution and mechanical properties of fiamme, which are present within the ignimbrite. The observations and analysis presented here demonstrate that models of joint distribution, particularly in thicker layers, that do not fully account for mechanical heterogeneity are likely to underestimate joint density, the spatial variability of joint distribution and the complex joint geometries that result. Consequently, we recommend that characterisation of a layer's compositional and material properties improves predictions of subsurface joint density in rock layers that are mechanically heterogeneous.

Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO.

PubMed

Kim, Junyeon; Sinha, Jaivardhan; Hayashi, Masamitsu; Yamanouchi, Michihiko; Fukami, Shunsuke; Suzuki, Tetsuhiro; Mitani, Seiji; Ohno, Hideo

2013-03-01

Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

General Solutions for Hydromagnetic Free Convection Flow over an Infinite Plate with Newtonian Heating, Mass Diffusion and Chemical Reaction

NASA Astrophysics Data System (ADS)

Fetecau, Constatin; Shah, Nehad Ali; Vieru, Dumitru

2017-12-01

The problem of hydromagnetic free convection flow over a moving infinite vertical plate with Newtonian heating, mass diffusion and chemical reaction in the presence of a heat source is completely solved. Radiative and porous effects are not taken into consideration but they can be immediately included by a simple rescaling of Prandtl number and magnetic parameter. Exact general solutions for the dimensionless velocity and concentration fields and the corresponding Sherwood number and skin friction coefficient are determined under integral form in terms of error function or complementary error function of Gauss. They satisfy all imposed initial and boundary conditions and can generate exact solutions for any problem with technical relevance of this type. As an interesting completion, uncommon in the literature, the differential equations which describe the thermal, concentration and momentum boundary layer, as well as the exact expressions for the thicknesses of thermal, concentration or velocity boundary layers were determined. Numerical results have shown that the thermal boundary layer thickness decreases for increasing values of Prandtl number and the concentration boundary layer thickness is decreasing with Schmidt number. Finally, for illustration, three special cases are considered and the influence of physical parameters on some fundamental motions is graphically underlined and discussed. The required time to reach the flow according with post-transient solution (the steady-state), for cosine/sine oscillating concentrations on the boundary is graphically determined. It is found that, the presence of destructive chemical reaction improves this time for increasing values of chemical reaction parameter.

Are annual layers preserved in NorthGRIP Eemian ice?

NASA Astrophysics Data System (ADS)

Kettner, E.; Bigler, M.; Nielsen, M. E.; Steffensen, J. P.; Svensson, A.

2009-04-01

A newly developed setup for continuous flow analysis (CFA) of ice cores in Copenhagen is optimized for high resolution analysis of four components: Soluble sodium (mainly deriving from sea salt), soluble ammonium (related to biological processes and biomass burning events), insoluble dust particles (basically transported from Asian deserts to Greenland), and the electrolytic melt water conductivity (which is a bulk signal for all ionic constituents). Furthermore, we are for the first time implementing a flow cytometer to obtain high quality dust concentration and size distribution profiles based on individual dust particle measurements. Preliminary measurements show that the setup is able to resolve annual layers of 1 cm thickness. Ice flow models predict that annual layers in the Eemian section of the Greenland NorthGRIP ice core (130-115 ka BP) have a thickness of around 1 cm. However, the visual stratigraphy of the ice core indicates that the annual layering in the Eemian section may be disturbed by micro folds and rapid crystal growth. In this case study we will measure the impurity content of an Eemian segment of the NorthGRIP ice core with the new CFA setup. This will allow for a comparison to well-known impurity levels of the Holocene in both Greenland and Antarctic ice and we will attempt to determine if annual layers are still present in the ice.

Heat addition to a subsonic boundary layer: A preliminary analytical study

NASA Technical Reports Server (NTRS)

Macha, J. M.; Norton, D. J.

1971-01-01

A preliminary analytical study of the effects of heat addition to the subsonic boundary layer flow over a typical airfoil shape is presented. This phenomenon becomes of interest in the space shuttle mission since heat absorbed by the wing structure during re-entry will be rejected to the boundary layer during the subsequent low speed maneuvering and landing phase. A survey of existing literature and analytical solutions for both laminar and turbulent flow indicate that a heated surface generally destabilizes the boundary layer. Specifically, the boundary layer thickness is increased, the skin friction at the surface is decreased and the point of flow separation is moved forward. In addition, limited analytical results predict that the angle of attack at which a heated airfoil will stall is significantly less than the stall angle of an unheated wing. These effects could adversely affect the lift and drag, and thus the maneuvering capabilities of booster and orbiter shuttle vehicles.

The Pioneer Ultramafic Complex of the Barberton Greenstone Belt, South Africa

NASA Astrophysics Data System (ADS)

Cooper, M. R.; Byerly, G. R.; Lowe, D. R.; Thompson, M. E.

2005-12-01

The 3.55-3.22 Ga Barberton Greenstone Belt is an approximately 100km x 30km northeast trending, isoclinally folded, volcanic and sedimentary succession surrounded by intrusive granitic rocks. It is perhaps Earth's best preserved mid-Archean supracrustal sequence and also among the most magnesian, making it an ideal location for studying compositionally distinct rocks of the Archean, such as komatiites. The Pioneer Ultramafic Complex has been interpreted as a komatiitic intrusion but we argue that it is a sequence of layered komatiitic flows and interbedded tuffs correlative with other komatiitic extrusive units of the 3.29 Ga Weltevreden Formation, the uppermost formation of the Onverwacht Group. The Pioneer Ultramafic Complex contains at least 900m of section in the study area, including at least 5 flow sets, with individual flows up to 100 m thick, sections of tuff up to 100m thick and additional thinner tuff units. The base of the sequence is in fault contact with the Sawmill Ultramafic Complex, which is similar to and perhaps correlative with the Pioneer. The top of the sequence is bounded by the Moodies Fault and slightly younger sedimentary rocks of the Fig Tree and Moodies Groups. Typical flows of the Pioneer have highly serpentinized olivine-rich cumulate bases, fresh olivine bearing peridotitic lithologies in central portions, and increasing pyroxene content, pyroxene size, and elongation of grains toward the flow tops. Three of the five flows are capped with random and/or oriented spinifex layers. The tuffs within this and other layered ultramafic complexes of the Barberton Greenstone Belt are mostly fine grained, slaty serpentinites that were previously interpreted as bedding horizontal zones of shearing. However, rare preservation of angular and vesicular lapilli, and more commonly cross-stratification in finer grained layers, provide strong evidence that these layers represent tuffs. High chromium and other trace element contents suggest they are komatiitic tuffs likely co-magmatic with the interbedded komatiitic lava flows. Compositions of fresh olivines range between 91 to 93 percent forsterite, indicating a komatiitic melt composition. In addition to olivine phenocrysts, fresh chromite, orthopyroxene, pigeonite, and augite are all present as smaller intercumulus crystals or microphenocrysts. The pyroxenes have Mg numbers up to 89 and Al/Ti ratios approximately 10-15. The latter are consistent with the Al/Ti ratios of 20-30 found within the komatiites and tuffs analyzed thus far. These ratios indicate the flows belong to the aluminium undepleted group of komatiites. The rock and mineral chemistry of these flows allow us to determine melt compositions and explore correlations and relationships with other komatiitic flows and layered ultramafic complexes of the Barberton Greenstone Belt. Field studies of these flows help characterize an Archean igneous complex believed to represent shallow marine deposition of komatiitic tuffs and coeval emplacement of thick vertically differentiated komatiitic flows.

Anatomy and dynamics of a floodplain, Powder River, Montana, U.S.A.

USGS Publications Warehouse

Pizzuto, J.E.; Moody, J.A.; Meade, R.H.

2008-01-01

Centimeter-scale measurements on several Powder River floodplains provide insights into the nature of overbank depositional processes that created the floodplains; during a 20-year period after a major flood in 1978. Rising stages initially entered across a sill at the downriver end of the floodplains. Later, as stages continued to rise, water entered the floodplains through distinct low saddles along natural levees. The annual maximum depth of water over the levee crest averaged 0.19 in from 1983 through 1996, and the estimated flow velocities were approximately 0.15 m s-1. Water ponded in the floodplain trough, a topographic low between the natural levee and the pre-flood riverbank, and mud settled as thin layers of nearly constant thickness. Mud layers alternated with sand layers, which were relatively thick near the channel. Together, these beds created a distinctive natural levee. In some locations, individual flood deposits began as a thin mud layer that gradually coarsened upwards to medium-grained sand. Coarsening-upwards sequences form initially as mud because only the uppermost layers of water in the channel supply the first overbank flows, which are rich in mud but starved of sand. At successively higher stages, fine sands and then medium sands increase in concentration in the floodwater and are deposited as fine- and medium-sand layers overlying the initial mud layer. Theoretical predictions from mathematical models of sediment transport by advection and diffusion indicate that these processes acting alone are unlikely to create the observed sand layers of nearly uniform thickness that extend across much of the floodplain. We infer that other transport processes, notably bedload transport, must be important along Powder River. Even with the centimeter-scale measurements of floodplain deposits, daily hydraulic data, and precise annual surface topographic surveys, we were unable to determine any clear correspondence between the gauged flow record of overbank floods and the depositional layers mapped in the floodplain. These results provide a detailed example of floodplain deposits and depositional processes that should prove useful for interpreting natural levee deposits in a variety of geologic settings. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980

USGS Publications Warehouse

Kieffer, S.W.; Sturtevant, B.

1988-01-01

Nearly horizontal, quasi-periodic erosional features of 7-m average transverse wavelength and of order 100-m length occur in scattered locations from 3.5 to 9 km from the crater at Mount St. Helens under deposits of the lateral blast of May 18, 1980. We attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography, namely, by streamline curvature in regions of reattachment downstream of sheltered regions, and by the cross-flow component of flow subparallel to ridge crests. The diameter of the vortices and their transverse spacing, inferred from the distance between furrows, are taken to be of the order of the boundary layer thickness. The inferred boundary layer thickness (???14 m at 9 km from the source of the blast) is consistent with the running length from the mountain to the furrow locations. The orientation of furrows induced by the cross-flow instability can be used to measure the upwash angle and estimate the flow Mach number: at the central ridge of Spirit Lake the Mach number is inferred to have been about 2.5, and the flow velocity approximately 235 m/s. -from Authors

Mean velocity and turbulence measurements in a 90 deg curved duct with thin inlet boundary layer

NASA Technical Reports Server (NTRS)

Crawford, R. A.; Peters, C. E.; Steinhoff, J.; Hornkohl, J. O.; Nourinejad, J.; Ramachandran, K.

1985-01-01

The experimental database established by this investigation of the flow in a large rectangular turning duct is of benchmark quality. The experimental Reynolds numbers, Deans numbers and boundary layer characteristics are significantly different from previous benchmark curved-duct experimental parameters. This investigation extends the experimental database to higher Reynolds number and thinner entrance boundary layers. The 5% to 10% thick boundary layers, based on duct half-width, results in a large region of near-potential flow in the duct core surrounded by developing boundary layers with large crossflows. The turbulent entrance boundary layer case at R sub ed = 328,000 provides an incompressible flowfield which approaches real turbine blade cascade characteristics. The results of this investigation provide a challenging benchmark database for computational fluid dynamics code development.

Conductive sub-layer of twisted-tape-induced swirl-flow heat transfer in vertical circular tubes with various twisted-tape inserts

NASA Astrophysics Data System (ADS)

Hata, K.; Fukuda, K.; Masuzaki, S.

2018-04-01

Twisted-tape-induced swirl-flow heat transfer due to exponentially increasing heat inputs with various exponential periods ( Q = Q 0 exp(t/τ), τ = 6.04 to 23.07 s) and twisted-tape-induced pressure drop was systematically measured for various mass velocities ( G = 4115 to 13,656 kg/m2 s), inlet liquid temperatures ( T in = 285.88 to 299.09 K), and inlet pressures ( P in = 847.45 to 943.29 kPa) using an experimental water loop flow. Measurements were made over a 59.2-mm effective length and three sections (upper, middle, and lower positions), within which four potential taps were spot-welded onto the outer surface of a 6-mm-inner-diameter, 69.6-mm-heated length, 0.4-mm-thickness platinum circular test tube. Type SUS304 twisted tapes with a width w = 5.6 mm, a thickness δ T = 0.6 mm, a total length l = 372 mm, and twist ratios y = 2.39 and 4.45 were employed in this study. The RANS equations (Reynolds Averaged Navier-Stokes Simulation) with a k-ɛ turbulence model for a circular tube 6 mm in diameter and 636 mm in length were numerically solved for heating of water with a heated section 6 mm in diameter and 70 mm in length using the CFD code, under the same conditions as the experimental ones and considering the temperature dependence of the thermo-physical properties concerned. The theoretical values of surface heat flux q on the circular tubes with twisted tapes with twist ratios y of 2.39 and 4.45 were found to be almost in agreement with the corresponding experimental values of heat flux q, with deviations of less than 30% for the range of temperature difference between the average heater inner surface temperature and the liquid bulk mean temperature ΔT L [ = T s,av - T L , T L = ( T in + T out )/2] considered in this study. The theoretical values of the local surface temperature T s , local average liquid temperature T f,av , and local liquid pressure drop ΔP x were found to be within almost 15% of the corresponding experimental ones. The thickness of the conductive sub-layer δ CSL and the nondimensional thickness of the conductive sub-layer y + CSL on the circular tubes with various twisted-tape inserts were determined on the basis of numerical solutions for the swirl velocities u sw ranging from 5.23 to 21.18 m/s. Correlations between the conductive sub-layer thickness δ CSL and the nondimensional thickness of the conductive sub-layer y + CSL for twisted-tape-induced swirl-flow heat transfer in a vertical circular tube were derived.

Exact solutions of laminar-boundary-layer equations with constant property values for porous wall with variable temperature

NASA Technical Reports Server (NTRS)

Donoughe, Patrick L; Livingood, John N B

1955-01-01

Exact solution of the laminar-boundary-layer equations for wedge-type flow with constant property values are presented for transpiration-cooled surfaces with variable wall temperatures. The difference between wall and stream temperature is assumed proportional to a power of the distance from the leading edge. Solutions are given for a Prandtl number of 0.7 and ranges of pressure-gradient, cooling-air-flow, and wall-temperature-gradient parameters. Boundary-layer profiles, dimensionless boundary-layer thicknesses, and convective heat-transfer coefficients are given in both tabular and graphical form. Corresponding results for constant wall temperature and for impermeable surfaces are included for comparison purposes.

Refractive Index Effects on Radiation in an Absorbing, Emitting, and Scattering Laminated Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting temperature radiative energy flow in a two-region semitransparent laminated layer in the limit of zero heat conduction. The composite is heated on its two sides by unequal amounts of incident radiation. The two layers of the composite have different refractive indices, and each material absorbs, emits, and isotropically scatters radiation. The interfaces are diffuse, and all interface reflections are included. To illustrate the thermal behavior that is readily calculated from the equations, typical results an given for various optical thicknesses and refractive indices of the layers. Internal reflections have a substantial effect on the temperature distribution and radiative heat flow.

Field Verification of Stable Perched Groundwater in Layered Bedrock Uplands

USGS Publications Warehouse

Carter, J.T.; Gotkowitz, M.B.; Anderson, M.P.

2011-01-01

Data substantiating perched conditions in layered bedrock uplands are rare and have not been widely reported. Field observations in layered sedimentary bedrock in southwestern Wisconsin, USA, provide evidence of a stable, laterally extensive perched aquifer. Data from a densely instrumented field site show a perched aquifer in shallow dolomite, underlain by a shale-and-dolomite aquitard approximately 25 m thick, which is in turn underlain by sandstone containing a 30-m-thick unsaturated zone above a regional aquifer. Heads in water supply wells indicate that perched conditions extend at least several kilometers into hillsides, which is consistent with published modeling studies. Observations of unsaturated conditions in the sandstone over a 4-year period, historical development of the perched aquifer, and perennial flow from upland springs emanating from the shallow dolomite suggest that perched groundwater is a stable hydrogeologic feature under current climate conditions. Water-table hydrographs exhibit apparent differences in the amount and timing of recharge to the perched and regional flow systems; steep hydraulic gradients and tritium and chloride concentrations suggest there is limited hydraulic connection between the two. Recognition and characterization of perched flow systems have practical importance because their groundwater flow and transport pathways may differ significantly from those in underlying flow systems. Construction of multi-aquifer wells and groundwater withdrawal in perched systems can further alter such pathways. ?? 2010 The Author(s). Journal compilation ?? 2010 National Ground Water Association.

Re-Innovating Recycling for Turbulent Boundary Layer Simulations

NASA Astrophysics Data System (ADS)

Ruan, Joseph; Blanquart, Guillaume

2017-11-01

Historically, turbulent boundary layers along a flat plate have been expensive to simulate numerically, in part due to the difficulty of initializing the inflow with ``realistic'' turbulence, but also due to boundary layer growth. The former has been resolved in several ways, primarily dedicating a region of at least 10 boundary layer thicknesses in width to rescale and recycle flow or by extending the region far enough downstream to allow a laminar flow to develop into turbulence. Both of these methods are relatively costly. We propose a new method to remove the need for an inflow region, thus reducing computational costs significantly. Leveraging the scale similarity of the mean flow profiles, we introduce a coordinate transformation so that the boundary layer problem can be solved as a parallel flow problem with additional source terms. The solutions in the new coordinate system are statistically homogeneous in the downstream direction and so the problem can be solved with periodic boundary conditions. The present study shows the stability of this method, its implementation and its validation for a few laminar and turbulent boundary layer cases.

Dynamics of Active Separation Control at High Reynolds Numbers

NASA Technical Reports Server (NTRS)

Pack, LaTunia G.; Seifert, Avi

2000-01-01

A series of active flow control experiments were recently conducted at high Reynolds numbers on a generic separated configuration. The model simulates the upper surface of a 20% thick Glauert-Goldschmied type airfoil at zero angle of attack. The flow is fully turbulent since the tunnel sidewall boundary layer flows over the model. The main motivation for the experiments is to generate a comprehensive data base for validation of unsteady numerical simulation as a first step in the development of a CFD design tool, without which it would not be possible to effectively utilize the great potential of unsteady flow control. This paper focuses on the dynamics of several key features of the baseline as well as the controlled flow. It was found that the thickness of the upstream boundary layer has a negligible effect on the flow dynamics. It is speculated that separation is caused mainly by the highly convex surface while viscous effects are less important. The two-dimensional separated flow contains unsteady waves centered on a reduced frequency of 0.9, while in the three dimensional separated flow, frequencies around a reduced frequency of 0.3 and 1 are active. Several scenarios of resonant wave interaction take place at the separated shear-layer and in the pressure recovery region. The unstable reduced frequency bands for periodic excitation are centered on 1.5 and 5, but these reduced frequencies are based on the length of the baseline bubble that shortens due to the excitation. The conventional works well for the coherent wave features. Reproduction of these dynamic effects by a numerical simulation would provide benchmark validation.

Improved Small-Particle Powders for Plasma Spraying

NASA Technical Reports Server (NTRS)

Nguyen, QuynhGiao, N.; Miller, Robert A.; Leissler, George W.

2005-01-01

Improved small-particle powders and powder-processing conditions have been developed for use in plasma spray deposition of thermal-barrier and environmental barrier coatings. Heretofore, plasma-sprayed coatings have typically ranged in thickness from 125 to 1,800 micrometers. As explained below, the improved powders make it possible to ensure complete coverage of substrates at unprecedently small thicknesses of the order of 25 micrometers. Plasma spraying involves feeding a powder into a hot, high-velocity plasma jet. The individual powder particles melt in the plasma jet as they are propelled towards a substrate, upon which they splat to build up a coating. In some cases, multiple coating layers are required. The size range of the powder particles necessarily dictates the minimum thickness of a coating layer needed to obtain uniform or complete coverage. Heretofore, powder particle sizes have typically ranged from 40 to 70 micrometers; as a result, the minimum thickness of a coating layer for complete coverage has been about 75 micrometers. In some applications, thinner coatings or thinner coating layers are desirable. In principle, one can reduce the minimum complete-coverage thickness of a layer by using smaller powder particles. However, until now, when powder particle sizes have been reduced, the powders have exhibited a tendency to cake, clogging powder feeder mechanisms and feed lines. Hence, the main problem is one of synthesizing smaller-particle powders having desirable flow properties. The problem is solved by use of a process that begins with a spray-drying subprocess to produce spherical powder particles having diameters of less than 30 micrometers. (Spherical-particle powders have the best flow properties.) The powder is then passed several times through a commercial sifter with a mesh to separate particles having diameters less than 15 micrometers. The resulting fine, flowable powder is passed through a commercial fluidized bed powder feeder into a plasma spray jet.

Modulation of solid electrolyte interphase of lithium-ion batteries by LiDFOB and LiBOB electrolyte additives

NASA Astrophysics Data System (ADS)

Huang, Shiqiang; Wang, Shuwei; Hu, Guohong; Cheong, Ling-Zhi; Shen, Cai

2018-05-01

Solid-electrolyte interphase (SEI) layer is an organic-inorganic composite layer that allows Li+ transport across but blocks electron flow across and prevents solvent diffusing to electrode surface. Morphology, thickness, mechanical and chemical properties of SEI are important for safety and cycling performance of lithium-ion batteries. Herein, we employ a combination of in-situ AFM and XPS to investigate the effects of two electrolyte additives namely lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) on SEI layer. LiDFOB is found to result in a thin but hard SEI layer containing more inorganic species (LiF and LiCO3); meanwhile LiBOB promotes formation of a thick but soft SEI layer containing more organic species such as ROCO2Li. Findings from present study will help development of electrolyte additives that promote formation of good SEI layer.

Can a novel silver nano coating reduce infections and maintain cell viability in vitro?

PubMed

Qureshi, Ammar T; Landry, Jace P; Dasa, Vinod; Janes, Marlene; Hayes, Daniel J

2014-03-01

Herein we report a facile layer-by-layer method for creating an antimicrobial coating composed of silver nanoparticles on medical grade titanium test discs. Nanoscale silver nanoparticle layers are attached to the titanium orthopedic implant material via aminopropyltriethoxy silane crosslinker that reacts with neighboring silane moieties to create an interconnected network. A monolayer of silane, followed by a monolayer of silver nanoparticles would form one self-assembled layer and this process can be repeated serially, resulting in increased silver nanoparticles deposition. The release rate of silver ion increases predictably with increasing numbers of layers and at appropriate thicknesses these coatings demonstrate 3-4 log reduction of viable Escherichia coli and Staphylococcus aureus bacteria. Increasing the thickness of the coatings resulted in reduced bacterial colonization as determined by fluorescent staining and image analysis. Interestingly, the cytotoxicity of murine 3T3 cells as quantified by fluorescent staining and flow cytometry, was minimal and did not vary significantly with the coating thickness. Additionally, these coatings are mechanically stable and resist delamination by orthogonal stress test. This simple layer-by-layer coating technique may provide a cost-effective and biocompatible method for reducing microbial colonization of implantable orthopedic devices.

Structure of the screening layer near a plane isolated body in the deep vacuum. Part 2. Monoenergetic isotropic flow

NASA Astrophysics Data System (ADS)

Gunko, Yuri F.; Gunko, Natalia A.

2018-05-01

In this paper we consider the problem of determining the structure of the electric field near the surface of a flat insulated body under conditions of a deep vacuum. It is assumed that the emitted particles are electrons leaving the body surface under the influence of ionizing radiation whose velocities distribution near the surface is isotropic. It is estimated the thickness of the screening layer under conditions of stationary emission from a flat surface. The solutio of the problem of determining a stationary self-consistent electric field near the surface is found in a simple analytical form. The thickness of the screening layer is calculated from this formula.

Vertical Structural Variation and Their Development of the Sanukayama Rhyolite Lava in Kozushima Island, Japan

NASA Astrophysics Data System (ADS)

Furukawa, K.; Uno, K.; Kanamaru, T.; Nakai, K.

2017-12-01

We revealed structural development of the Pleistocene Sanukayama rhyolite lava of Kozushima Island, Japan. The good exposure, with about 130 m thick, provides valuable opportunity to understand the vertical structural variation. This exposure corresponds to the upper half of the lava. The paleomagnetic results show that the lava emplaced in subaerial condition at least in the exposed part. The vertical lithofacies are divided into the pumiceous (25-40 m thick), obsidian (40-60 m), spherulitic (30-50 m) layers from top to base. The pumiceous layer is characterized by massive foliated pumice. The foliation dips are gradually changed from gentle (10-30°) in lower part to steep (around 90°) in upper part. This shows the balloon-like morphology. The massive pumiceous layer would be generated from late stage diapiric inflation of the lava (Fink and Manley, 1987). The obsidian layer is composed of massive and welded-brecciated parts. The ductile-deformed light-colored veins, with a few mm thick, are frequently developed. In the microscopic observation, the veins are composed of broken crystals and obsidian clasts indicating fracturing of the lava followed by ductile deformation such as the RFH process (Tuffen et al., 2003). In this layer, extensive vesiculation and microlite development must have been prevented by higher load pressure and faster cooling, respectively. Consequently, they resulted in formation of the obsidian. The spherulitic layer is characterized by development of the ductile-deformed flow banding. The microscopic observation shows that the bands are formed by the spherulite trail. Furthermore, the microlites are aligned within the spherulites. In the heat-retained inner part of the lava, microlites would be developed around the healed fractures. The microlites acted as nucleation site of spherulite. In transition layer between obsidian and spherulitic layers (<10 m thick), the fragments of spherulitic rhyolite are entrained within the obsidian layer. This would be caused by high flow-induced shear arising from their rheological contrast. We showed the complicated structure of the Sanukayama rhyolite lava, especially for varied crystal occurrences. The variation is considered to be caused by specific phenomena of high-viscous magma such as sluggish atomic mobility and lava fracturing.

An experimental and computational investigation of the flow field about a transonic airfoil in supercritical flow with turbulent boundary-layer separation

NASA Technical Reports Server (NTRS)

Rubesin, M. W.; Okuno, A. F.; Levy, L. L., Jr.; Mcdevitt, J. B.; Seegmiller, H. L.

1976-01-01

A combined experimental and computational research program is described for testing and guiding turbulence modeling within regions of separation induced by shock waves incident in turbulent boundary layers. Specifically, studies are made of the separated flow the rear portion of an 18%-thick circular-arc airfoil at zero angle of attack in high Reynolds number supercritical flow. The measurements include distributions of surface static pressure and local skin friction. The instruments employed include highfrequency response pressure cells and a large array of surface hot-wire skin-friction gages. Computations at the experimental flow conditions are made using time-dependent solutions of ensemble-averaged Navier-Stokes equations, plus additional equations for the turbulence modeling.

Generation of net sediment transport by velocity skewness in oscillatory sheet flow

NASA Astrophysics Data System (ADS)

Chen, Xin; Li, Yong; Chen, Genfa; Wang, Fujun; Tang, Xuelin

2018-01-01

This study utilizes a qualitative approach and a two-phase numerical model to investigate net sediment transport caused by velocity skewness beneath oscillatory sheet flow and current. The qualitative approach is derived based on the pseudo-laminar approximation of boundary layer velocity and exponential approximation of concentration. The two-phase model can obtain well the instantaneous erosion depth, sediment flux, boundary layer thickness, and sediment transport rate. It can especially illustrate the difference between positive and negative flow stages caused by velocity skewness, which is considerably important in determining the net boundary layer flow and sediment transport direction. The two-phase model also explains the effect of sediment diameter and phase-lag to sediment transport by comparing the instantaneous-type formulas to better illustrate velocity skewness effect. In previous studies about sheet flow transport in pure velocity-skewed flows, net sediment transport is only attributed to the phase-lag effect. In the present study with the qualitative approach and two-phase model, phase-lag effect is shown important but not sufficient for the net sediment transport beneath pure velocity-skewed flow and current, while the asymmetric wave boundary layer development between positive and negative flow stages also contributes to the sediment transport.

Investigation of mucus transport in an idealized lung airway model using multiphase CFD analysis

NASA Astrophysics Data System (ADS)

Rajendran, Rahul; Banerjee, Arindam

2015-11-01

Mucus, a Bingham fluid is transported in the pulmonary airways by consistent beating of the cilia and exhibits a wide range of physical properties in response to the core air flow and various pathological conditions. A better understanding of the interfacial instability is required as it plays a crucial role in gas transport, mixing, mucus clearance and drug delivery. In the current study, mucus is modelled as a Newtonian fluid and the two phase gas-liquid flow in the airways is investigated using an inhomogeneous Eulerian-Eulerian approach. The complex interface between the phases is tracked using the conventional VOF (Volume of Fluid) method. Results from our CFD simulations which are performed in idealized single and double bifurcation geometries will be presented and the influence of airflow rate, mucus layer thickness, mucus viscosity, airway geometry (branching & diameter) and surface tension on mucus flow behavior will be discussed. Mean mucus layer thickness, pressure drop due to momentum transfer & increased airway resistance, mucus transport speed and the flow morphology will be compared to existing experimental and theoretical data.

Analysis of crossover between local and massive separation on airfoils

NASA Technical Reports Server (NTRS)

Barnett, Mark

1987-01-01

The occurrence of massive separation on airfoils operating at high Reynolds number poses an important problem to the aerodynamicist. In the present study, the phenomenon of crossover, induced by airfoil thickness, between local separation and massive separation is investigated for low speed (incompressible), symmetric flow past realistic airfoil geometries. This problem is studied both for the infinite Reynolds number asymptotic limit using triple-deck theory and for finite Reynolds number using interacting boundary-layer theory. Numerical results are presented which illustrate how the flow evolves from local to massive separation as the airfoil thickness is increased. The results of the triple-deck and the interacting boundary-layer analyses are found to be in qualitative agreement for the NACA four digit series and an uncambered supercritical airfoil. The effect of turbulence on the evolution of the flow is also considered. Solutions are presented for turbulent flows past a NACA 0014 airfoil and a circular cylinder. For the latter case, the calculated surface pressure distribution is found to agree well with experimental data if the proper eddy pressure level is specified.

Influence of thickness and permeability of endothelial surface layer on transmission of shear stress in capillaries

NASA Astrophysics Data System (ADS)

Zhang, SongPeng; Zhang, XiangJun; Tian, Yu; Meng, YongGang; Lipowsky, Herbert

2015-07-01

The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous domain within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the permeability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interfacial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stresses between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.

Improving Long-term Post-wildfire hydrologic simulations using ParFlow

NASA Astrophysics Data System (ADS)

Lopez, S. R.; Kinoshita, A. M.

2015-12-01

Wildfires alter the natural hydrologic processes within a watershed. After vegetation is burned, the combustion of organic material and debris settles into the soil creating a hydrophobic layer beneath the soil surface with varying degree of thickness and depth. Vegetation regrowth rates vary as a function of radiative exposure, burn severity, and precipitation patterns. Hydrologic models used by the Burned Area Emergency Response (BAER) teams use input data and model calibration constraints that are generally either one-dimensional, empirically-based models, or two-dimensional, conceptually-based models with lumped parameter distributions. These models estimate runoff measurements at the watershed outlet; however, do not provide a distributed hydrologic simulation at each point within the watershed. This work uses ParFlow, a three-dimensional, distributed hydrologic model to (1) correlate burn severity with hydrophobicity, (2) evaluate vegetation recovery rate on water components, and (3) improve flood prediction for managers to help with resource allocation and management operations in burned watersheds. ParFlow is applied to Devil Canyon (43 km2) in San Bernardino, California, which was 97% burned in the 2003 Old Fire. The model set-up uses a 30m-cell size resolution over a 6.7 km by 6.4 km lateral extent. The subsurface reaches 30 m and is assigned a variable cell thickness. Variable subsurface thickness allows users to explicitly consider the degree of recovery throughout the stages of regrowth. Burn severity maps from remotely sensed imagery are used to assign initial hydrophobic layer parameters and thickness. Vegetation regrowth is represented with satellite an Enhanced Vegetation Index. Pre and post-fire hydrologic response is evaluated using runoff measurements at the watershed outlet, and using water component (overland flow, lateral flow, baseflow) measurements.

A thickness-weighted average perspective of force balance in an idealized circumpolar current

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

Ringler, Todd Darwin; Saenz, Juan Antonio; Wolfram, Jr., Phillip Justin

The exact, three-dimensional thickness-weighted averaged (TWA) Boussinesq equations are used to diagnose eddy-mean flow interaction in an idealized circumpolar current (ICC). The force exerted by mesoscale eddies on the TWA velocity is expressed as the divergence of the Eliassen-Palm flux tensor. Consistent with previous findings, the analysis indicates that the dynamically relevant definition of the ocean surface layer is comprised of the set of buoyancy coordinates that ever reside at the ocean surface at a given horizontal position. The surface layer is found to be a physically distinct object with a diabatic- and force-balance that is largely isolated from themore » underlying adiabatic region in the interior. Within the ICC surface layer, the TWA meridional velocity is southward/northward in the top/bottom half, and has a value near zero at the bottom. In the top half of the surface layer, the zonal forces due to wind stress and meridional advection of potential vorticity act to accelerate the TWA zonal velocity; equilibrium is obtained by eddies decelerating the zonal flow via a downward flux of eastward momentum that increases with depth. In the bottom half of the surface layer, the accelerating force of the wind stress is balanced by the eddy force and meridional advection of potential vorticity. The bottom of the surface layer coincides with the location where the zonal eddy force, meridional advection of potential vorticity and zonal wind stress force are all zero. The net meridional transport, S f, within the surface layer is a small residual of its southward and northward TWA meridional flows. Furthermore, the mean meridional gradient of surface-layer buoyancy is advected by S f to balance the surface buoyancy fluxs.« less

A thickness-weighted average perspective of force balance in an idealized circumpolar current

DOE PAGES

Ringler, Todd Darwin; Saenz, Juan Antonio; Wolfram, Jr., Phillip Justin; ...

2016-11-22

The exact, three-dimensional thickness-weighted averaged (TWA) Boussinesq equations are used to diagnose eddy-mean flow interaction in an idealized circumpolar current (ICC). The force exerted by mesoscale eddies on the TWA velocity is expressed as the divergence of the Eliassen-Palm flux tensor. Consistent with previous findings, the analysis indicates that the dynamically relevant definition of the ocean surface layer is comprised of the set of buoyancy coordinates that ever reside at the ocean surface at a given horizontal position. The surface layer is found to be a physically distinct object with a diabatic- and force-balance that is largely isolated from themore » underlying adiabatic region in the interior. Within the ICC surface layer, the TWA meridional velocity is southward/northward in the top/bottom half, and has a value near zero at the bottom. In the top half of the surface layer, the zonal forces due to wind stress and meridional advection of potential vorticity act to accelerate the TWA zonal velocity; equilibrium is obtained by eddies decelerating the zonal flow via a downward flux of eastward momentum that increases with depth. In the bottom half of the surface layer, the accelerating force of the wind stress is balanced by the eddy force and meridional advection of potential vorticity. The bottom of the surface layer coincides with the location where the zonal eddy force, meridional advection of potential vorticity and zonal wind stress force are all zero. The net meridional transport, S f, within the surface layer is a small residual of its southward and northward TWA meridional flows. Furthermore, the mean meridional gradient of surface-layer buoyancy is advected by S f to balance the surface buoyancy fluxs.« less

Looking Into and Through the Ross Ice Shelf - ROSETTA-ICE

NASA Astrophysics Data System (ADS)

Bell, R. E.

2015-12-01

Our current understanding of the structure and stability of the Ross Ice Shelf is based on satellite studies of the ice surface and the 1970's RIGGS program. The study of the flowlines evident in the MODIS imagery combined with surface geophysics has revealed a complex history with ice streams Mercer, Whillans and Kamb changing velocity over the past 1000 years. Here, we present preliminary IcePod and IceBridge radar data acquired in December 2014 and November 2013 across the Ross Ice Shelf that show clearly, for the first time, the structure of the ice shelf and provide insights into ice-ocean interaction. The three major layers of the ice shelf are (1) the continental meteoric ice layer), ice formed on the grounded ice sheet that entered the ice shelf where ice streams and outlet glaciers crossed the grounding line (2) the locally accumulating meteoric ice layer, ice and snow that forms from snowfall on the floating ice shelf and (3) a basal marine ice layer. The locally accumulating meteoric ice layer contains well-defined internal layers that are generally parallel to the ice surface and thickens away from the grounding line and reaches a maximum thickness of 220m along the line crossing Roosevelt Island. The continental meteoric layer is located below a broad irregular internal reflector, and is characterized by irregular internal layers. These internal layers are often folded, likely a result of deformation as the ice flowed across the grounding line. The basal marine ice layer, up to 50m thick, is best resolved in locations where basal crevasses are present, and appears to thicken along the flow at rates of decimeters per year. Each individual flowband of the ice shelf contains layers that are distinct in their structure. For example, the thickness of the locally accumulated layer is a function of both the time since crossing the grounding line and the thickness of the incoming ice. Features in the meteoric ice, such as distinct folds, can be traced between the two IceBridge lines located 47 km apart. The ROSETTA-ICE program will begin a systematic mapping of the Ross Ice Shelf and sub-ice topography using the IcePod system beginning in 2015. Together the new gravity-derived bathymetry and the mapping of the ice shelf structure will provide key insights into the stability of the ice shelf.

Characterisation of the wall-slip during extrusion of heavy-clay products

NASA Astrophysics Data System (ADS)

Kocserha, I.; Gömze, A. L.; Kulkov, S.; Kalatur, E.; Buyakova, S. P.; Géber, R.; Buzimov, A. Y.

2017-01-01

During extrusion through the extrusion die, heavy-clay compounds are usually show plug flow with extensive slip at the wall of the die. In this study, the viscosity and the thickness of the slip layer were investigated. For the examination a brick-clay from Malyi (Hungary) deposit was applied as a raw material. The clay was characterised by XRPD, BET, SEM and granulometry. As the slip layer consists of suspension of the fine clay fraction so the clay minerals content of the clay (d<2µm) was separated by the help of sedimentation. The viscosity of suspension with different water content was measured by means of rotational viscosimeter. The thickness of the slip layer was calculated from the measured viscosity and other data obtained from an earlier study with capillary rheometer. The calculated thickness value showed a tendency to reach a limit value by increasing the extrusion speed.

Plasma-based actuators for turbulent boundary layer control in transonic flow

NASA Astrophysics Data System (ADS)

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

2017-10-01

The study is devoted to development of methods for active control of flow structure typical for the aircraft wings in transonic flow with turbulent boundary layer. The control strategy accepted in the study was based on using of the effects of plasma discharges interaction with miniature geometrical obstacles of various shapes. The conceptions were studied computationally using 3D RANS, URANS approaches. The results of the computations have shown that energy deposition can significantly change the flow pattern over the obstacles increasing their influence on the flow in boundary layer region. Namely, one of the most interesting and promising data were obtained for actuators basing on combination of vertical wedge with asymmetrical plasma discharge. The wedge considered is aligned with the local streamlines and protruding in the flow by 0.4-0.8 of local boundary layer thickness. The actuator produces negligible distortion of the flow at the absence of energy deposition. Energy deposition along the one side of the wedge results in longitudinal vortex formation in the wake of the actuator providing momentum exchange in the boundary layer. The actuator was manufactured and tested in wind tunnel experiments at Mach number 1.5 using the model of flat plate. The experimental data obtained by PIV proved the availability of the actuator.

Effect of Sub-Boundary Layer Vortex Generations on Incident Turbulence

NASA Technical Reports Server (NTRS)

Casper, J.; Lin, J. C.; Yao, C. S.

2003-01-01

Sub-boundary layer vortex generators were tested in a wind tunnel to assess their effect on the velocity field within the wake region of a turbulent boundary layer. Both mean flow quantities and turbulence statistics were measured. Although very small relative to the boundary layer thickness, these so-called micro vortex generators were found to have a measurable effect on the power spectra and integral length scales of the turbulence at a distance many times the height of the devices themselves. In addition, the potential acoustic impact of these devices is also discussed. Measured turbulence spectra are used as input to an acoustic formulation in a manner that compares predicted sound pressure levels that result from the incident boundary-layer turbulence, with and without the vortex generators in the flow.

Design and Fabrication of High-Efficiency CMOS/CCD Imagers

NASA Technical Reports Server (NTRS)

Pain, Bedabrata

2007-01-01

An architecture for back-illuminated complementary metal oxide/semiconductor (CMOS) and charge-coupled-device (CCD) ultraviolet/visible/near infrared- light image sensors, and a method of fabrication to implement the architecture, are undergoing development. The architecture and method are expected to enable realization of the full potential of back-illuminated CMOS/CCD imagers to perform with high efficiency, high sensitivity, excellent angular response, and in-pixel signal processing. The architecture and method are compatible with next-generation CMOS dielectric-forming and metallization techniques, and the process flow of the method is compatible with process flows typical of the manufacture of very-large-scale integrated (VLSI) circuits. The architecture and method overcome all obstacles that have hitherto prevented high-yield, low-cost fabrication of back-illuminated CMOS/CCD imagers by use of standard VLSI fabrication tools and techniques. It is not possible to discuss the obstacles in detail within the space available for this article. Briefly, the obstacles are posed by the problems of generating light-absorbing layers having desired uniform and accurate thicknesses, passivation of surfaces, forming structures for efficient collection of charge carriers, and wafer-scale thinning (in contradistinction to diescale thinning). A basic element of the present architecture and method - the element that, more than any other, makes it possible to overcome the obstacles - is the use of an alternative starting material: Instead of starting with a conventional bulk-CMOS wafer that consists of a p-doped epitaxial silicon layer grown on a heavily-p-doped silicon substrate, one starts with a special silicon-on-insulator (SOI) wafer that consists of a thermal oxide buried between a lightly p- or n-doped, thick silicon layer and a device silicon layer of appropriate thickness and doping. The thick silicon layer is used as a handle: that is, as a mechanical support for the device silicon layer during micro-fabrication.

Retinal nerve fiber layer thickness map and blood flow pulsation measured with SDOCT

NASA Astrophysics Data System (ADS)

Mujat, Mircea; Chan, Raymond C.; Cense, Barry; Pierce, Mark; Park, Hyle; Joo, Chulmin; Chen, Teresa C.; de Boer, Johannes F.

2006-02-01

Spectral-Domain Optical Coherence Tomography (SDOCT) allows for in-vivo video-rate investigation of biomedical tissue depth structure intended for non-invasive optical diagnostics. It has been suggested that OCT can be used for di-agnosis of glaucoma by measuring the thickness of the Retinal Nerve Fiber Layer (RNLF). We present an automated method for determining the RNFL thickness from a 3-D dataset based on edge detection using a deformable spline algo-rithm. The RNFL thickness map is combined with an integrated reflectance map and retinal cross-sectional images to provide the ophthalmologist with a familiar image for interpreting the OCT data. The video-rate capabilities of our SDOCT system allow for mapping the true retinal topography since motion artifacts are significantly reduced as com-pared to slower time-domain systems. Combined with Doppler Velocimetry, SDOCT also provides information on retinal blood flow dynamics. We analyzed the pulsatile nature of the bidirectional flow dynamics in an artery-vein pair for a healthy volunteer at different locations and for different blood vessel diameters. The Doppler phase shift is determined as the phase difference at the same point of adjacent depth profiles, and is integrated over the area delimited by two circles corresponding to the blood vessels location. Its temporal evolution clearly shows the blood flow pulsatile nature, the cardiac cycle, in both artery and vein. The artery is identified as having a stronger variation of the integrated phase shift. We observe that artery pulsation is always easily detectable, while vein pulsation seems to depend on the veins diameter.

LLE review. Quarterly report, January 1994--March 1994, Volume 58

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

Simon, A.

1994-07-01

This volume of the LLE Review, covering the period Jan - Mar 1994, contains articles on backlighting diagnostics; the effect of electron collisions on ion-acoustic waves and heat flow; using PIC code simulations for analysis of ultrashort laser pulses interacting with solid targets; creating a new instrument for characterizing thick cryogenic layers; and a description of a large-aperture ring amplifier for laser-fusion drivers. Three of these articles - backlighting diagnostics; characterizing thick cryogenic layers; and large-aperture ring amplifier - are directly related to the OMEGA Upgrade, now under construction. Separate abstracts have been prepared for articles from this report.

Marangoni flow on an inkjet nozzle plate

NASA Astrophysics Data System (ADS)

de Jong, Jos; Reinten, Hans; Wijshoff, Herman; van den Berg, Marc; Delescen, Koos; van Dongen, Rini; Mugele, Frieder; Versluis, Michel; Lohse, Detlef

2007-11-01

In piezo inkjet printing, nozzle failures are often caused by an ink layer on the nozzle plate. It is experimentally shown that the ink layer at the nozzle is formed through streamers of ink, emanating from a central ink band on the nozzle plate. The streamers propagate over a wetting nanofilm of 13nm thickness, directed toward the actuated nozzles. The motion of the front end of the streamers follows a power law in time with an exponent 1/2 . The observations are consistent with a surface tension gradient driven flow. The origin of the Marangoni flow is an effective lower surfactant concentration of the ink around the nozzle.

Electro-osmotic flow in a rotating rectangular microchannel

PubMed Central

Ng, Chiu-On; Qi, Cheng

2015-01-01

An analytical model is presented for low-Rossby-number electro-osmotic flow in a rectangular channel rotating about an axis perpendicular to its own. The flow is driven under the combined action of Coriolis, pressure, viscous and electric forces. Analytical solutions in the form of eigenfunction expansions are developed for the problem, which is controlled by the rotation parameter (or the inverse Ekman number), the Debye parameter, the aspect ratio of the channel and the distribution of zeta potentials on the channel walls. Under the conditions of fast rotation and a thin electric double layer (EDL), an Ekman–EDL develops on the horizontal walls. This is essentially an Ekman layer subjected to electrokinetic effects. The flow structure of this boundary layer as a function of the Ekman layer thickness normalized by the Debye length is investigated in detail in this study. It is also shown that the channel rotation may have qualitatively different effects on the flow rate, depending on the channel width and the zeta potential distributions. Axial and secondary flows are examined in detail to reveal how the development of a geostrophic core may lead to a rise or fall of the mean flow. PMID:26345088

The actuation of microflaps inspired by shark scales deeply embedded in a boundary layer

NASA Astrophysics Data System (ADS)

Morris, Jackson; Lang, Amy; Hubner, Paul

2016-11-01

Thanks to millions of years of natural selection, sharks have evolved to become quick apex predators. Shark skin is made up of microscopic scales on the order of 0.2 mm in size. This array of scales is hypothesized to be a flow control mechanism where individual scales are capable of being passively actuated by reversed flow in water due to their preferential orientation to attached flow. Previous research has proven shark skin to reduce flow separation in water, which would result in lower pressure drag. We believe shark scales are strategically sized to interact with the lower 5 percent of the boundary layer, where reversed flow occurs close to the wall. To test the capability of micro-flaps to be actuated in air various sets of flaps, inspired by shark scale geometry, were rapidly prototyped. These microflaps were tested in a low-speed wind tunnel at various flow speeds and boundary layer thicknesses. Boundary layer flow conditions were measured using a hot-wire probe and microflap actuation was observed. Microflap actuation in airflow would mean that this bio-inspired separation control mechanism found on shark skin has potential application for aircraft. Boeing.

Structure of a reattaching supersonic shear flow

NASA Technical Reports Server (NTRS)

Samimy, M.; Abu-Hijleh, B. A. K.

1988-01-01

A Mach 1.83 fully developed turbulent boundary layer with boundary layer thickness, free stream velocity, and Reynolds number of 7.5 mm, 476 m/s, and 6.2 x 10 to the 7th/m, respectively, was separated at a 25.4-mm backward step and formed a shear layer. Fast-response pressure transducers, schlieren photography, and LDV were used to study the structure of this reattaching shear flow. The preliminary results show that large-scale relatively organized structures with limited spanwise extent form in the free shear layer. Some of these structures appear to survive the recompression and reattachment processes, while others break down into smaller scales and the flow becomes increasingly three-dimensional. The survived large-scale structures lose their organization through recompression/reattachment, but regain it after reattachment. The structures after reattachment form a 40-45-degree angle relative to the free stream and deteriorate gradually as they move downstream.

Seismic wave propagation through an extrusive basalt sequence

NASA Astrophysics Data System (ADS)

Sanford, Oliver; Hobbs, Richard; Brown, Richard; Schofield, Nick

2016-04-01

Layers of basalt flows within sedimentary successions (e.g. in the Faeroe-Shetland Basin) cause complex scattering and attenuation of seismic waves during seismic exploration surveys. Extrusive basaltic sequences are highly heterogeneous and contain strong impedance contrasts between higher velocity crystalline flow cores (˜6 km s-1) and the lower velocity fragmented and weathered flow crusts (3-4 km s-1). Typically, the refracted wave from the basaltic layer is used to build a velocity model by tomography. This velocity model is then used to aid processing of the reflection data where direct determination of velocity is ambiguous, or as a starting point for full waveform inversion, for example. The model may also be used as part of assessing drilling risk of potential wells, as it is believed to constrain the total thickness of the sequence. In heterogeneous media, where the scatter size is of the order of the seismic wavelength or larger, scattering preferentially traps the seismic energy in the low velocity regions. This causes a build-up of energy that is guided along the low velocity layers. This has implications for the interpretation of the observed first arrival of the seismic wave, which may be a biased towards the low velocity regions. This will then lead to an underestimate of the velocity structure and hence the thickness of the basalt, with implications for the drilling of wells hoping to penetrate through the base of the basalts in search of hydrocarbons. Using 2-D acoustic finite difference modelling of the guided wave through a simple layered basalt sequence, we consider the relative importance of different parameters of the basalt on the seismic energy propagating through the layers. These include the proportion of high to low velocity material, the number of layers, their thickness and the roughness of the interfaces between the layers. We observe a non-linear relationship between the ratio of high to low velocity layers and the apparent velocity of the first arrival suggesting that such a sequence may cause a reduction of the apparent velocity by as much as 1 km s-1. We also find that the rate of amplitude decay in the higher velocity layer is related to the interface roughness between the basalt layers.

The numerical study of the influence of rheological parameters stratified flows characteristics in cable dies

NASA Astrophysics Data System (ADS)

Kozitsyna, M. V.; Trufanova, N. M.

2017-01-01

Today the process of coextrusion is the most technological in the cable production with cross-linked polyethylene, composed of two or more layers of polymeric insulation. Since the covering technology is a simultaneous imposition of all necessary layers (two semiconducting shields on the insulation and conductor and one - on insulation), the main focus of this study is the analysis of significance of various factors influence on stratified flows characteristics. This paper has considered the flow of two abnormally viscous liquids in the cable head. The problem has been solved through a three-dimensional statement by applying the finite element method in the Ansys software package. The influence has been estimated by varying the rheological properties of materials to create all necessary layers thickness.

The influence of flow parameters on the transition to turbulence in supersonic boundary layer on swept wing

NASA Astrophysics Data System (ADS)

Semionov, N. V.; Yermolaev, Yu. G.; Kosinov, A. D.; Dryasov, A. D.; Semenov, A. N.; Yatskikh, A. A.

2016-10-01

The paper is devoted to an experimental study of laminar-turbulent transition in a three-dimensional supersonic boundary layer. The experiments were conducted at the low nose supersonic wind tunnel T-325 of ITAM at Mach numbers M=2 - 4. Model is a symmetrical wing with a 45° sweep angle, a 3 percent-thick circular-arc airfoil. The influence of flow parameters, such as the Mach number, unit Reynolds number, angle of attack, level of perturbations on the transitions to turbulence are on the consideration. Transition Reynolds numbers are obtained. Analysis of all obtained data allow to determine reliable value of Retr of swept wing supersonic boundary layer, that especially important at consideration of experiments fulfilled at different flow conditions in different wind tunnels.

Condensing Heat Exchanger with Hydrophilic Antimicrobial Coating

NASA Technical Reports Server (NTRS)

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor)

2014-01-01

A multi-layer antimicrobial hydrophilic coating is applied to a substrate of anodized aluminum, although other materials may form the substrate. A silver layer is sputtered onto a thoroughly clean anodized surface of the aluminum to about 400 nm thickness. A layer of crosslinked, silicon-based macromolecular structure about 10 nm thickness overlies the silver layer, and the outermost surface of the layer of crosslinked, silicon-based macromolecular structure is hydroxide terminated to produce a hydrophilic surface with a water drop contact angle of less than 10.degree.. The coated substrate may be one of multiple fins in a condensing heat exchanger for use in the microgravity of space, which has narrow channels defined between angled fins such that the surface tension of condensed water moves water by capillary flow to a central location where it is pumped to storage. The antimicrobial coating prevents obstruction of the capillary passages.

Pervasive Layering in the Lunar Highland Crust: Evidence from Apollos 15, 16,and 17

NASA Technical Reports Server (NTRS)

Lowman, Paul D., Jr.; Yang, Tiffany

2005-01-01

This paper presents results of a photogeologic reconnaissance of 70 mm photographs taken on the lunar surface during the Apollo 15, 16, and 17 missions, whose primary objective was to investigate the lunar highland crust. Photographs at all three sites, notably the Apennine Front, show pervasive layered structure. These layers are easily distinguished from lighting artifacts, and are considered genuine crustal structures. Their number, thickness, and extent implies that they are lava flows, not ejecta blankets or intrusive features. They appear to be the upper part of the earliest lunar crust, possibly forming a layer tens of kilometers thick. Remote sensing studies (X-ray fluorescence and reflectance spectroscopy), indicate that the highland crust is dominantly a feldspathic basalt. It is concluded that the highland layers represent a global crust formed by eruptions of high-alumina basalt in the first few hundred million years of the Moon's history.

Turbulent flow around a wing-fuselage type juncture

NASA Technical Reports Server (NTRS)

Kubendran, L. R.; Mcmahon, H. M.; Hubbartt, J. E.

1985-01-01

The flow over a 58-mm-thick uniform-thickness winglike body having a 1.5:1 elliptical leading edge and joined to a large flat plate (representing an aircraft fuselage) is characterized experimentally at freestream velocity 15 m/s, corresponding to Reynolds number 940,000/m, using hot-wire anemometry. The results are presented graphically, and it is found that the horseshoe vortex formed by the separation of the fuselage boundary layer ahead of the wing leading edge is effective in transporting turbulence and modifying the mean-flow characteristics and the turbulent-stress distribution. It is suggested that the slenderness ratio of the leading edge is the dominant factor affecting the strength and location of the vortex.

Viscous-inviscid calculations of jet entrainment effects on the subsonic flow over nozzle afterbodies

NASA Technical Reports Server (NTRS)

Wilmoth, R. G.

1980-01-01

A viscous-inviscid interaction model was developed to account for jet entrainment effects in the prediction of the subsonic flow over nozzle afterbodies. The model is based on the concept of a weakly interacting shear layer in which the local streamline deflections due to entrainment are accounted for by a displacement-thickness type of correction to the inviscid plume boundary. The entire flow field is solved in an iterative manner to account for the effects on the inviscid external flow of the turbulent boundary layer, turbulent mixing and chemical reactions in the shear layer, and the inviscid jet exhaust flow. The components of the computational model are described, and numerical results are presented to illustrate the interactive effects of entrainment on the overall flow structure. The validity of the model is assessed by comparisons with data obtained form flow-field measurements on cold-air jet exhausts. Numerical results and experimental data are also given to show the entrainment effects on nozzle boattail drag under various jet exhaust and free-stream flow conditions.

Investigation at supersonic and subsonic Mach numbers of auxiliary inlets supplying secondary air flow to ejector exhaust nozzles

NASA Technical Reports Server (NTRS)

Hearth, Donald P; Cubbison, Robert W

1956-01-01

The results indicated increases in auxiliary-inlet pressure recovery with increases in scoop height relative to the boundary-layer thickness. The pressure recovery increased at about the same rate as theoretically predicted for an inlet in a boundary layer having a one-seventh power profile, but was only about 0.68 to 0.75 of the theoretically obtainable values. Under some operating conditions, flow from the primary jet was exhausted through the auxiliary inlet. This phenomenon could be predicted from the ejector pumping characteristics.

Thermal boundary layer due to sudden heating of fluid

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

Kurkal, K.R.; Munukutla, S.

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers. 6 refs.

Thermal boundary layer due to sudden heating of fluid

NASA Astrophysics Data System (ADS)

Kurkal, K. R.; Munukutla, S.

1989-10-01

This paper proposes to solve computationally the heat-transfer problems (introduced by Munukutla and Venkataraman, 1988) related to a closed-cycle pulsed high-power laser flow loop. The continuity and the momentum equations as well as the unsteady energy equation are solved using the Keller-Box method. The solutions were compared with the steady-state solutions at large times, and the comparison was found to be excellent. Empirical formulas are proposed for calculating the time-dependent boundary-layer thickness and mass-heat transfer, that can be used by laser flow loop designers.

On the three-dimensional instability of laminar boundary layers on concave walls

NASA Technical Reports Server (NTRS)

Gortler, Henry

1954-01-01

A study is made of the stability of laminar boundary-layer profiles on slightly curved walls relative to small disturbances that result from vortices whose axes are parallel to the principal direction of flow. The result is an eigenvalue problem by which, for a given undisturbed flow at a prescribed wall, the amplification or decay is computed for each Reynolds number and each vortex thickness. For neutral disturbances (zero amplification) a critical Reynolds number is determined for each vortex distribution. The numerical calculation produces amplified disturbances on concave walls only.

Patterns of brittle deformation under extension on Venus

NASA Technical Reports Server (NTRS)

Neumann, G. A.; Zuber, M. T.

1994-01-01

The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

Pressures in Tumuli: A Study of Tumuli Formation

NASA Technical Reports Server (NTRS)

Hansen, James E.

2005-01-01

Tumuli form via localized inflation in surface lava flows. These domed features have widths of 10-20 m, lengths of 10-150 m, and heights of 1-9 m. The axial fracture exposes a brittle crust overlying a ductilely deformed layer. The total crustal thickness is typically less than lm. Tumuli are observed on both terrestrial and martian lava flow surfaces, and provide insight on the flow formation processes and rates. Past studies have estimated the inflation pressure using a bending model for a circular, thin elastic plate, assuming small deflection (Rossi and Gudmundson, 1996). This formulation results in unrealistic pressures for some tumuli. We thus examine alternative models, including those with different shapes, bending of the ductile crust, large deflection, plastic deformation, and thick plate bending. Using the thickness of the ductile crust in the equations for thin, circular plates reduces most pressures to reasonable values. Alternative plate shapes do not cause a significant reduction in inflation pressure. Although the large deflection equations should be applicable based on the plate thickness to tumuli height ratios, they give even less realistic pressures. Tumuli with unrealistic pressures appear to have exceeded the critical bending moment, and have relatively thick crusts, requiring thick plate bending models.

Laminar flow drag reduction on soft porous media.

PubMed

Mirbod, Parisa; Wu, Zhenxing; Ahmadi, Goodarz

2017-12-08

While researches have focused on drag reduction of various coated surfaces such as superhydrophobic structures and polymer brushes, the insights tso understand the fundamental physics of the laminar skin friction coefficient and the related drag reduction due to the formation of finite velocity at porous surfaces is still relatively unknown. Herein, we quantitatively investigated the flow over a porous medium by developing a framework to model flow of a Newtonian fluid in a channel where the lower surface was replaced by various porous media. We showed that the flow drag reduction induced by the presence of the porous media depends on the values of the permeability parameter α = L/(MK) 1/2 and the height ratio δ = H/L, where L is the half thickness of the free flow region, H is the thickness and K is the permeability of the fiber layer, and M is the ratio of the fluid effective dynamic viscosity μ e in porous media to its dynamic viscosity μ. We also examined the velocity and shear stress profiles for flow over the permeable layer for the limiting cases of α → 0 and α → ∞. The model predictions were compared with the experimental data for specific porous media and good agreement was found.

Breakdown of Burton Prim Slichter approach and lateral solute segregation in radially converging flows

NASA Astrophysics Data System (ADS)

Priede, J.; Gerbeth, G.

2005-11-01

A theoretical study is presented of the effect of a radially converging melt flow, which is directed away from the solidification front, on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) solution describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for the flows converging along the solidification front. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. Although such a divergence can formally be avoided by restricting the axial extension of the melt to a layer of finite height, radially uniform solute distributions are possible only for weak melt flows with an axial velocity away from the solidification front comparable to the growth rate. There is a critical melt velocity for each growth rate at which the solution passes through a singularity and becomes physically inconsistent for stronger melt flows. To resolve these inconsistencies we consider a solidification front presented by a disk of finite radius R0 subject to a strong converging melt flow and obtain an analytic solution showing that the radial solute concentration depends on the radius r as ˜ln(R0/r) and ˜ln(R0/r) close to the rim and at large distances from it. The logarithmic increase of concentration is limited in the vicinity of the symmetry axis by the diffusion becoming effective at a distance comparable to the characteristic thickness of the solute boundary layer. The converging flow causes a solute pile-up forming a logarithmic concentration peak at the symmetry axis which might be an undesirable feature for crystal growth processes.

Dynamics of Active Separation Control at High Reynolds Numbers

NASA Technical Reports Server (NTRS)

Pack, LaTunia G.; Seifert, Avi

2000-01-01

A series of active flow control experiments were recently conducted at high Reynolds numbers on a generic separated configuration. The model simulates the upper surface of a 20% thick Glauert-Goldschmied type airfoil at zero angle of attack. The flow is fully turbulent since the tunnel sidewall boundary layer flows over the model. The main motivation for the experiments is to generate a comprehensive data base for validation of unsteady numerical simulation as a first step in the development of a CFD design tool, without which it would not be possible to effectively utilize the great potential of unsteady flow control. This paper focuses on the dynamics of several key features of the baseline as well as the controlled flow. It was found that the thickness of the upstream boundary layer has a negligible effect on the flow dynamics. It is speculated that separation is caused mainly by the highly convex surface while viscous effects are less important. The two-dimensional separated flow contains unsteady waves centered on a reduced frequency of 0.8, while in the three dimensional separated flow, frequencies around a reduced frequency of 0.3 and 1 are active. Several scenarios of resonant wave interaction take place at the separated shear-layer and in the pressure recovery region. The unstable reduced frequency bands for periodic excitation are centered on 1.5 and 5, but these reduced frequencies are based on the length of the baseline bubble that shortens due to the excitation. The conventional swept wing-scaling works well for the coherent wave features. Reproduction of these dynamic effects by a numerical simulation would provide benchmark validation.

Hot foil transducer skin friction sensor

NASA Technical Reports Server (NTRS)

Vranas, T. (Inventor)

1982-01-01

The device utilizes foil transducers with only one edge exposed to the fluid flow. The surfaces are polished producing a foil transducer that does not generate turbulence while sufficiently thick to carry the required electrical current for high temperature fluid flow. The assembly utilizes a precut layered metal sandwich with attached electrodes eliminating a need for welding and individual sensor calibration.

Self-sustained oscillations of a shock wave interacting with a boundary layer on a supercritical airfoil

NASA Technical Reports Server (NTRS)

Ventres, C. S.; Howe, M. S.

1984-01-01

A theory is proposed of the self-sustaining oscillations of a weak shock on an airfoi in steady, transonic flow. The interaction of the shock with the boundary layer on the airfoil produces displacement thickness fluctuations which convect downstream and generate sound by interaction with the trailing edge. A feedback loop is established when this sound impinges on the shock wave, resulting in the production of further fluctuations in the displacement thickness. The details are worked out for an idealized mean boundary layer velocity profile, but strong support for the basic hypotheses of the theory is provided by a comparison with recent experiments involving the generation of acoustic 'tone bursts' by a supercritical airfoil section.

Self-sustained oscillations of a shock wave interacting with a boundary layer on a supercritical airfoil

NASA Technical Reports Server (NTRS)

Ventres, C. S.; Howe, M. S.

1983-01-01

A theory is proposed of the self-sustaining oscillations of a weak shock on an airfoil in steady, transonic flow. The interaction of the shock with the boundary layer on the airfoil produces displacement thickness fluctuations which convect downstream and generate sound by interaction with the trailing edge. A feedback loop is established when this sound impinges on the shock wave, resulting in the production of further fluctuations in the displacement thickness. The details are worked out for an idealized mean boundary layer velocity profile, but strong support for the basic hypotheses of the theory is provided by a comparison with recent experiments involving the generation of acoustic "tone bursts' by a supercritical airfoil section.

Magnetic property zonation in a thick lava flow

NASA Astrophysics Data System (ADS)

Audunsson, Haraldur; Levi, Shaul; Hodges, Floyd

1992-04-01

Intraflow structures and magmatic evolution in an extensive and thick (30-60 m) basaltic lava flow are examined on the basis of grain size and composition-dependent magnetic properties of titanomagnetite materials. Microprobe data indicate that the intraflow oxidation state Fe(3+)/Fe(2+) of the initially precipitated primary titanomagnetites increases with falling equilibrium temperature from the flow margins to a maximum near the center, the position of lowest equilibrium temperature. In contrast, Curie temperature measurements indicate that titanomagnetite oxidation increases with height in the flow. Modification of the initially symmetric equilibrium titanomagnetite compositions was caused by subsolidus high-temperature oxidation possibly due to hydrogen loss produced by dissociation of magmatic water, as well as unknown contributions of circulating air and percolating water from above. The titanomagnetites of the basal layer of the flow remain essentially unaltered.

Predicting the flow & noise of a rotor in a turbulent boundary layer using an actuator disk -- RANS approach

NASA Astrophysics Data System (ADS)

Buono, Armand C.

The numerical method presented in this study attempts to predict the mean, non-uniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent boundary layer (Configuration 3), were analyzed for a variety of advance ratios ranging from J = 0.48 to J =1.44. CFD results are shown to be in agreement with previous works and validated with experimental data of reverse flow occurring within the boundary layer above the flat plate upstream of a rotor in the Virginia Tech's Stability Wind Tunnel facility. Results from Configuration 3 will be used in future aero-acoustic computations.

Transonic flow about a thick circular-arc airfoil

NASA Technical Reports Server (NTRS)

Mcdevitt, J. B.; Levy, L. L., Jr.; Deiwert, G. S.

1975-01-01

An experimental and theoretical study of transonic flow over a thick airfoil, prompted by a need for adequately documented experiments that could provide rigorous verification of viscous flow simulation computer codes, is reported. Special attention is given to the shock-induced separation phenomenon in the turbulent regime. Measurements presented include surface pressures, streamline and flow separation patterns, and shadowgraphs. For a limited range of free-stream Mach numbers the airfoil flow field is found to be unsteady. Dynamic pressure measurements and high-speed shadowgraph movies were taken to investigate this phenomenon. Comparisons of experimentally determined and numerically simulated steady flows using a new viscous-turbulent code are also included. The comparisons show the importance of including an accurate turbulence model. When the shock-boundary layer interaction is weak the turbulence model employed appears adequate, but when the interaction is strong, and extensive regions of separation are present, the model is inadequate and needs further development.

Estimating reservoir permeability from gravity current modeling of CO2 flow at Sleipner storage project, North Sea

NASA Astrophysics Data System (ADS)

Cowton, L. R.; Neufeld, J. A.; Bickle, M.; White, N.; White, J.; Chadwick, A.

2017-12-01

Vertically-integrated gravity current models enable computationally efficient simulations of CO2 flow in sub-surface reservoirs. These simulations can be used to investigate the properties of reservoirs by minimizing differences between observed and modeled CO2 distributions. At the Sleipner project, about 1 Mt yr-1 of supercritical CO2 is injected at a depth of 1 km into a pristine saline aquifer with a thick shale caprock. Analysis of time-lapse seismic reflection surveys shows that CO2 is distributed within 9 discrete layers. The trapping mechanism comprises a stacked series of 1 m thick, impermeable shale horizons that are spaced at 30 m intervals through the reservoir. Within the stratigraphically highest reservoir layer, Layer 9, a submarine channel deposit has been mapped on the pre-injection seismic survey. Detailed measurements of the three-dimensional CO2 distribution within Layer 9 have been made using seven time-lapse surveys, providing a useful benchmark against which numerical flow simulations can be tested. Previous simulations have, in general, been largely unsuccessful in matching the migration rate of CO2 in this layer. Here, CO2 flow within Layer 9 is modeled as a vertically-integrated gravity current that spreads beneath a structurally complex caprock using a two-dimensional grid, considerably increasing computational efficiency compared to conventional three-dimensional simulators. This flow model is inverted to find the optimal reservoir permeability in Layer 9 by minimizing the difference between observed and predicted distributions of CO2 as a function of space and time. A three parameter inverse model, comprising reservoir permeability, channel permeability and channel width, is investigated by grid search. The best-fitting reservoir permeability is 3 Darcys, which is consistent with measurements made on core material from the reservoir. Best-fitting channel permeability is 26 Darcys. Finally, the ability of this simplified numerical model to forecast CO2 flow within Layer 9 is tested. Permeability recovered by modeling a suite of early seismic surveys is used to predict the CO2 distribution for a suite of later seismic surveys with a considerable degree of success. Forecasts have also been carried out that can be tested using future seismic surveys.

Hydrogeologic unit flow characterization using transition probability geostatistics.

PubMed

Jones, Norman L; Walker, Justin R; Carle, Steven F

2005-01-01

This paper describes a technique for applying the transition probability geostatistics method for stochastic simulation to a MODFLOW model. Transition probability geostatistics has some advantages over traditional indicator kriging methods including a simpler and more intuitive framework for interpreting geologic relationships and the ability to simulate juxtapositional tendencies such as fining upward sequences. The indicator arrays generated by the transition probability simulation are converted to layer elevation and thickness arrays for use with the new Hydrogeologic Unit Flow package in MODFLOW 2000. This makes it possible to preserve complex heterogeneity while using reasonably sized grids and/or grids with nonuniform cell thicknesses.

Representation of turbulent shear stress by a product of mean velocity differences

NASA Technical Reports Server (NTRS)

Braun, W. H.

1977-01-01

A quadratic form in the mean velocity for the turbulent shear stress is presented. It is expressed as the product of two velocity differences whose roots are the maximum velocity in the flow and a cutoff velocity below which the turbulent shear stress vanishes. Application to pipe and channel flows yields the centerline velocity as a function of pressure gradient, as well as the velocity profile. The flat plate, boundary-layer problem is solved by a system of integral equations to obtain friction coefficient, displacement thickness, and momentum-loss thickness. Comparisons are made with experiment.

Layered Crustal Anisotropy in the NE Tibetan Plateau Inferred from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Jiang, C.; Yang, Y.; Zheng, Y.

2016-12-01

The Tibetan Plateau is the highest and largest plateau in the world with an average elevation of 4-5 km and 60-70 km thick crust, about twice of the thickness of average continental crust. Two end-member models have bene invoked to explain the crustal thickening and the growth of the plateau: (1) continuous and uniform thickening of the whole crust and (2) mid/lower crustal channel flow. However, which mechanism dominates the crustal thickening and the growth of the plateau is still under hot debate. Seismic anisotropy can provide observational constraints on deformation mode, which would have distinguished pattern resulting from the two different thickening models. Thus, by studying seismic anisotropy, we can distinguish different models of crustal thickening and plateau growth. In this study, we employ an eikonal tomography method of ambient noise to investigate azimuthal anisotropy of Rayleigh waves in the NE Tibetan Plateau. Our tomography reveals significant anisotropy in the crust. In particular, stratification of crustal azimuthal anisotropy is observed: an upper crustal anisotropic layer characterized by a NE-SW fast direction and a mid/lower crustal anisotropic layer with a NNE-SSW fast direction. The dominantly NE-SW oriented anisotropy in the upper crust is likely caused by shape-preferred orientation (SPO) of faults and fractures in the shallow depths. The anisotropy in the mid/lower crust, however, is nearly orthogonal to that in the shallow crust, suggesting a different mechanism. The NNE-SSW fast direction coincides with the proposed flow direction by the crustal flow model in NE Tibetan Plateau, suggesting anisotropy in the mid/lower crust may be related to the crustal flow. The two-layered crustal stratigraphy observed in the NE Tibetan Plateau is contrary to the continuous thickening model, but favours the crustal flow model.

A novel low profile wireless flow sensor to monitor hemodynamic changes in cerebral aneurysm

NASA Astrophysics Data System (ADS)

Chen, Yanfei; Jankowitz, Brian T.; Cho, Sung Kwon; Chun, Youngjae

2015-03-01

A proof of concept of low-profile flow sensor has been designed, fabricated, and subsequently tested to demonstrate its feasibility for monitoring hemodynamic changes in cerebral aneurysm. The prototype sensor contains three layers, i.e., a thin polyurethane layer was sandwiched between two sputter-deposited thin film nitinol layers (6μm thick). A novel superhydrophilic surface treatment was used to create hemocompatible surface of thin nitinol electrode layers. A finite element model was conducted using ANSYS Workbench 15.0 Static Structural to optimize the dimensions of flow sensor. A computational fluid dynamics calculations were performed using ANSYS Workbench Fluent to assess the flow velocity patterns within the aneurysm sac. We built a test platform with a z-axis translation stage and an S-beam load cell to compare the capacitance changes of the sensors with different parameters during deformation. Both LCR meter and oscilloscope were used to measure the capacitance and the resonant frequency shifts, respectively. The experimental compression tests demonstrated the linear relationship between the capacitance and applied compression force and decreasing the length, width and increasing the thickness improved the sensor sensitivity. The experimentally measured resonant frequency dropped from 12.7MHz to 12.48MHz, indicating a 0.22MHz shift with 200g ( 2N) compression force while the theoretical resonant frequency shifted 0.35MHz with 50g ( 0.5N). Our recent results demonstrated a feasibility of the low-profile flow sensor for monitoring haemodynamics in cerebral aneurysm region, as well as the efficacy of the use of the surface treated thin film nitinol for the low-profile sensor materials.

Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition

NASA Technical Reports Server (NTRS)

Grosch, C. E.

1980-01-01

A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.

Mechanical properties of metal-ceramic nanolaminates: Effect of constraint and temperature

DOE PAGES

Yang, Ling Wei; Mayer, Carl; Li, Nan; ...

2017-09-21

Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanicalmore » response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). Here, these mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.« less

Investigation of viscous/inviscid interaction in transonic flow over airfoils with suction

NASA Technical Reports Server (NTRS)

Vemuru, C. S.; Tiwari, S. N.

1988-01-01

The viscous/inviscid interaction over transonic airfoils with and without suction is studied. The streamline angle at the edge of the boundary layer is used to couple the viscous and inviscid flows. The potential flow equations are solved for the inviscid flow field. In the shock region, the Euler equations are solved using the method of integral relations. For this, the potential flow solution is used as the initial and boundary conditions. An integral method is used to solve the laminar boundary-layer equations. Since both methods are integral methods, a continuous interaction is allowed between the outer inviscid flow region and the inner viscous flow region. To avoid the Goldstein singularity near the separation point the laminar boundary-layer equations are derived in an inverse form to obtain solution for the flows with small separations. The displacement thickness distribution is specified instead of the usual pressure distribution to solve the boundry-layer equations. The Euler equations are solved for the inviscid flow using the finite volume technique and the coupling is achieved by a surface transpiration model. A method is developed to apply a minimum amount of suction that is required to have an attached flow on the airfoil. The turbulent boundary layer equations are derived using the bi-logarithmic wall law for mass transfer. The results are found to be in good agreement with available experimental data and with the results of other computational methods.

Anomalous spin Hall magnetoresistance in Pt/Co bilayers

NASA Astrophysics Data System (ADS)

Kawaguchi, Masashi; Towa, Daiki; Lau, Yong-Chang; Takahashi, Saburo; Hayashi, Masamitsu

2018-05-01

We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance within the plane transverse to the current flow, of Pt/Co bilayers. We find that the SMR increases with increasing Co thickness: the effective spin Hall angle for bilayers with thick Co exceeds the reported values of Pt when a conventional drift-diffusion model is used. An extended model including spin transport within the Co layer cannot account for the large SMR. To identify its origin, contributions from other sources are studied. For most bilayers, the SMR increases with decreasing temperature and increasing magnetic field, indicating that magnon-related effects in the Co layer play little role. Without the Pt layer, we do not observe the large SMR found for the Pt/Co bilayers with thick Co. Implementing the effect of the so-called interface magnetoresistance and the textured induced anisotropic scattering cannot account for the Co thickness dependent SMR. Since the large SMR is present for W/Co but its magnitude reduces in W/CoFeB, we infer that its origin is associated with a particular property of Co.

Towards an entropy-based detached-eddy simulation

NASA Astrophysics Data System (ADS)

Zhao, Rui; Yan, Chao; Li, XinLiang; Kong, WeiXuan

2013-10-01

A concept of entropy increment ratio ( s¯) is introduced for compressible turbulence simulation through a series of direct numerical simulations (DNS). s¯ represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f s to describe the boundary layer region and propose an entropy-based detached-eddy simulation method (SDES). This approach follows the spirit of delayed detached-eddy simulation (DDES) proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performances are compared in the following flows, namely, pure attached flow with thick boundary layer (a supersonic flat-plate flow with high Reynolds number), fully separated flow (the supersonic base flow), and separated-reattached flow (the supersonic cavity-ramp flow). The Reynolds-averaged Navier-Stokes (RANS) resolved region is reliably preserved and the modeled stress depletion (MSD) phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.

Drag of two-dimensional small-amplitude symmetric and asymmetric wavy walls in turbulent boundary layers

NASA Technical Reports Server (NTRS)

Lin, J. C.; Walsh, M. J.; Balasubramanian, R.

1984-01-01

Included are results of an experimental investigation of low-speed turbulent flow over multiple two-dimensional transverse rigid wavy surfaces having a wavelength on the order of the boundary-layer thickness. Data include surface pressure and total drag measurements on symmetric and asymmetric wall waves under a low-speed turbulent boundary-layer flow. Several asymmetric wave configurations exhibited drag levels below the equivalent symmetric (sine) wave. The experimental results compare favorably with numerical predictions from a Reynolds-averaged Navier-Stokes spectral code. The reported results are of particular interest for the estimation of drag, the minimization of fabrication waviness effects, and the study of wind-wave interactions.

On an Asymptotically Consistent Unsteady Interacting Boundary Layer

NASA Technical Reports Server (NTRS)

Bartels, Robert E.

2007-01-01

This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.

Boundary layer relaminarization device

NASA Technical Reports Server (NTRS)

Creel, Theodore R. (Inventor)

1992-01-01

Relamination of a boundary layer formed in supersonic flow over the leading edge of a swept airfoil is accomplished by means of at least one band, especially a quadrangular band, and most preferably a square band. Each band conforms to the leading edge and the upper and lower surfaces of the airfoil as an integral part thereof and extends perpendicularly from the leading edge. Each band has a height of about two times the thickness of the maximum expected boundary layer.

Noninvasive Imaging of Retinal Morphology and Microvasculature in Obese Mice Using Optical Coherence Tomography and Optical Microangiography

PubMed Central

Zhi, Zhongwei; Chao, Jennifer R.; Wietecha, Tomasz; Hudkins, Kelly L.; Alpers, Charles E.; Wang, Ruikang K.

2014-01-01

Purpose. To evaluate early diabetes-induced changes in retinal thickness and microvasculature in a type 2 diabetic mouse model by using optical coherence tomography (OCT)/optical microangiography (OMAG). Methods. Twenty-two-week-old obese (OB) BTBR mice (n = 10) and wild-type (WT) control mice (n = 10) were imaged. Three-dimensional (3D) data volumes were captured with spectral domain OCT using an ultrahigh-sensitive OMAG scanning protocol for 3D volumetric angiography of the retina and dense A-scan protocol for measurement of the total retinal blood flow (RBF) rate. The thicknesses of the nerve fiber layer (NFL) and that of the NFL to the inner plexiform layer (IPL) were measured and compared between OB and WT mice. The linear capillary densities within intermediate and deep capillary layers were determined by the number of capillaries crossing a 500-μm line. The RBF rate was evaluated using an en face Doppler approach. These quantitative measurements were compared between OB and WT mice. Results. The retinal thickness of the NFL to IPL was significantly reduced in OB mice (P < 0.01) compared to that in WT mice, whereas the NFL thickness between the two was unchanged. 3D depth-resolved OMAG angiography revealed the first in vivo 3D model of mouse retinal microcirculation. Although no obvious differences in capillary vessel densities of the intermediate and deep capillary layers were detected between normal and OB mice, the total RBF rate was significantly lower (P < 0.05) in OB mice than in WT mice. Conclusions. We conclude that OB BTBR mice have significantly reduced NFL–IPL thicknesses and total RBF rates compared with those of WT mice, as imaged by OCT/OMAG. OMAG provides an unprecedented capability for high-resolution depth-resolved imaging of mouse retinal vessels and blood flow that may play a pivotal role in providing a noninvasive method for detecting early microvascular changes in patients with diabetic retinopathy. PMID:24458155

Forced-folding by laccolith and saucer-shaped sill intrusions on the Earth, planets and icy satellites

NASA Astrophysics Data System (ADS)

Michaut, Chloé

2017-04-01

Horizontal intrusions probably initially start as cracks, with negligible surface deformation. Once their horizontal extents become large enough compared to their depths, they make room for themselves by lifting up their overlying roofs, creating characteristic surface deformations that can be observed at the surface of planets. We present a model where magma flows below a thin elastic overlying layer characterized by a flexural wavelength Λ and study the dynamics and morphology of such a magmatic intrusion. Our results show that, depending on its size, the intrusion present different shapes and thickness-to-radius relationships. During a first phase, elastic bending of the overlying layer is the main source of driving pressure in the flow; the pressure decreases as the flow radius increases, the intrusion is bell-shaped and its thickness is close to being proportional to its radius. When the intrusion radius becomes larger than 4 times Λ, the flow enters a gravity current regime and progressively develops a pancake shape with a flat top. We study the effect of topography on flow spreading in particular in the case where the flow is constrained by a lithostatic barrier within a depression, such as an impact crater on planets or a caldera on Earth. We show that the resulting shape for the flow depends on the ratio between the flexural wavelength of the layer overlying the intrusion and the depression radius. The model is tested against terrestrial data and is shown to well explain the size and morphology of laccoliths and saucer-shaped sills on Earth. We use our results to detect and characterize shallow solidified magma reservoirs in the crust of terrestrial planets and potential shallow water reservoirs in the ice shell of icy satellites.

An experimental investigation of heat transfer to reusable surface insulation tile array gaps in a turbulent boundary layer with pressure gradient. M.S. Thesis

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1975-01-01

An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer to space shuttle reusable surface insulation (RSI) tile array gaps under thick, turbulent boundary layer conditions. Heat transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel wall boundary layer at a nominal freestream Mach number of 10.3 and freestream unit Reynolds numbers of 1.6, 3.3, and and 6.1 million per meter. Transverse pressure gradients were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel wall boundary layer flow was obtained by measurement of boundary layer pitot pressure profiles, and flat plate wall pressure and heat transfer. Flat plate wall heat transfer data were correlated and a method was derived for prediction of smooth, curved array heat transfer in the highly three-dimensional tunnel wall boundary layer flow and simulation of full-scale space shuttle vehicle pressure gradient levels was assessed.

Simulations of laminar boundary-layer flow encountering large-scale surface indentions

NASA Astrophysics Data System (ADS)

Beratlis, N.; Balaras, E.; Squires, K.; Vizard, A.

2016-03-01

The transition from laminar to turbulent flow over dimples and grooves has been investigated through a series of direct numerical simulations. Emphasis has been given to the mechanism of transition and the momentum transport in the post-dimple boundary layer. It has been found that the dimple geometry plays an important role in the evolution of the turbulent boundary layer downstream. The mechanism of transition in all cases is that of the reorientation of the spanwise vorticity into streamwise oriented structures resembling hairpin vortices commonly encountered in wall bounded turbulent flows. Although qualitatively the transition mechanism amongst the three different cases is similar, important quantitative differences exist. It was shown that two-dimensional geometries like a groove are more stable than three-dimensional geometries like a dimple. In addition, it was found that the cavity geometry controls the initial thickness of the boundary layer and practically results in a shift of the virtual origin of the turbulent boundary layer. Important differences in the momentum transport downstream of the dimples exist but in all cases the boundary layer grows in a self-similar manner.

An experimental study of low Re cavity vortex formation embedded in a laminar boundary layer

NASA Astrophysics Data System (ADS)

Gautam, Sashank; Lang, Amy; Wilroy, Jacob

2016-11-01

Laminar boundary layer flow across a grooved surface leads to the formation of vortices inside rectangular cavities. The nature and stability of the vortex inside any single cavity is determined by the Re and cavity geometry. According to the hypothesis, under low Re and stable vortex conditions a single cavity vortex leads to a roller-bearing effect which results in a decrease in drag as quantified by velocity profiles measured within the boundary layer. At higher Re once the vortex becomes unstable, drag should increase due to the mixing of low-momentum fluid within the cavity and the outer boundary layer flow. The primary objective of this experiment is to document the phenomenon using DPIV in a tow tank facility. This study focuses on the transition of the cavity flow from a steady to an unsteady state as the Re is increased above a critical value. The change in boundary layer momentum and cavity vortex characteristics are documented as a function of Re and boundary layer thickness. Funding from NSF CBET fluid dynamics Grant 1335848 is gratefully acknowledged.

The dependence of the strength and thickness of field-aligned currents on solar wind and ionospheric parameters

PubMed Central

Johnson, Jay R.; Wing, Simon

2017-01-01

Sheared plasma flows at the low-latitude boundary layer (LLBL) correlate well with early afternoon auroral arcs and upward field-aligned currents. We present a simple analytic model that relates solar wind and ionospheric parameters to the strength and thickness of field-aligned currents (Λ) in a region of sheared velocity, such as the LLBL. We compare the predictions of the model with DMSP observations and find remarkably good scaling of the upward region 1 currents with solar wind and ionospheric parameters in region located at the boundary layer or open field lines at 1100–1700 magnetic local time. We demonstrate that Λ~nsw−0.5 and Λ ~ L when Λ/L < 5 where L is the auroral electrostatic scale length. The sheared boundary layer thickness (Δm) is inferred to be around 3000 km, which appears to have weak dependence on Vsw. J‖ has dependencies on Δm, Σp, nsw, and Vsw. The analytic model provides a simple way to organize data and to infer boundary layer structures from ionospheric data. PMID:29057194

Conceptual and numerical models of the glacial aquifer system north of Aberdeen, South Dakota

USGS Publications Warehouse

Marini, Katrina A.; Hoogestraat, Galen K.; Aurand, Katherine R.; Putnam, Larry D.

2012-01-01

This U.S. Geological Survey report documents a conceptual and numerical model of the glacial aquifer system north of Aberdeen, South Dakota, that can be used to evaluate and manage the city of Aberdeen's water resources. The glacial aquifer system in the model area includes the Elm, Middle James, and Deep James aquifers, with intervening confining units composed of glacial till. The Elm aquifer ranged in thickness from less than 1 to about 95 feet (ft), with an average thickness of about 24 ft; the Middle James aquifer ranged in thickness from less than 1 to 91 ft, with an average thickness of 13 ft; and the Deep James aquifer ranged in thickness from less than 1 to 165 ft, with an average thickness of 23 ft. The confining units between the aquifers consisted of glacial till and ranged in thickness from 0 to 280 ft. The general direction of groundwater flow in the Elm aquifer in the model area was from northwest to southeast following the topography. Groundwater flow in the Middle James aquifer was to the southeast. Sparse data indicated a fairly flat potentiometric surface for the Deep James aquifer. Horizontal hydraulic conductivity for the Elm aquifer determined from aquifer tests ranged from 97 to 418 feet per day (ft/d), and a confined storage coefficient was determined to be 2.4x10-5. Estimates of the vertical hydraulic conductivity of the sediments separating the Elm River from the Elm aquifer, determined from the analysis of temperature gradients, ranged from 0.14 to 2.48 ft/d. Average annual precipitation in the model area was 19.6 inches per year (in/yr), and agriculture was the primary land use. Recharge to the Elm aquifer was by infiltration of precipitation through overlying outwash, lake sediments, and glacial till. The annual recharge for the model area, calculated by using a soil-water-balance method for water year (WY) 1975-2009, ranged from 0.028 inch in WY 1980 to 4.52 inches in WY 1986, with a mean of 1.56 inches. The annual potential evapotranspiration, calculated in soil-water-balance analysis, ranged from 21.8 inches in WY 1983 to 27.0 inches in WY 1985, with a mean of 24.6 inches. Water use from the glacial aquifer system primarily was from the Elm aquifer for irrigation, municipal, and suburban water supplies, and the annual rate ranged from 1.0 to 2.4 cubic feet per second (ft3/s). The MODFLOW-2005 numerical model represented the Elm aquifer, the Middle James aquifer, and the Deep James aquifer with model layers 1-3 respectively separated by confining layers 1-2 respectively. Groundwater flow was simulated with 75 stress periods beginning October 1, 1974, and ending September 30, 2009. Model grid spacing was 200 by 200 ft and boundaries were represented by specified-head boundaries and no-flow boundaries. The model used parameter estimation that focused on minimizing the difference between 954 observed and simulated hydraulic heads for 135 wells. Calibrated mean horizontal hydraulic conductivity values for model layers 1-3 were 94, 41, and 30 ft/d respectively. Vertical hydraulic conductivity values for confining layers 1 and 2 were 0.0002 and 0.0003 ft/d, respectively. Calibrated specific yield for model layer 1was 0.1 and specific storage ranged from 0.0003 to 0.0005 per foot. Calibrated mean recharge rates ranged from 2.5 in/yr where glacial till thickness was less than 10 ft to 0.8 in/yr where glacial till thickness was greater than 30 ft. Calibrated mean annual evapotranspiration rate was 8.8 in/yr. Simulated net streamflow gain from model layer 1 was 3.1 ft3/s.

Unsteady boundary layer flow and heat transfer of a Casson fluid past an oscillating vertical plate with Newtonian heating.

PubMed

Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

2014-01-01

In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.

Experimental study of the laminar-turbulent transition of a concave wall in a parallel flow

NASA Technical Reports Server (NTRS)

Bippes, H.

1978-01-01

The instability of the laminar boundary layer flow along a concave wall was studied. Observations of these three-dimensional boundary layer phenomena were made using the hydrogen-bubble visualization technique. With the application of stereo-photogrammetric methods in the air-water system it was possible to investigate the flow processes qualitatively and quantitatively. In the case of a concave wall of sufficient curvature, a primary instability occurs first in the form of Goertler vortices with wave lengths depending upon the boundary layer thickness and the wall curvature. At the onset the amplification rate is in agreement with the linear theory. Later, during the non-linear amplification stage, periodic spanwise vorticity concentrations develop in the low velocity region between the longitudinal vortices. Then a meandering motion of the longitudinal vortex streets subsequently ensues, leading to turbulence.

The Influence of Subglacial Hydrology on Ice Stream Velocity in a Physical Model

NASA Astrophysics Data System (ADS)

Wagman, B. M.; Catania, G.; Buttles, J. L.

2011-12-01

We use a physical model to investigate how changes in subglacial hydrology affect ice motion in ice streams found in the West Antarctic Ice Sheet. Ice streams are modeled using silicone polymer placed over a thin water layer to simulate ice flow dominated by basal sliding. Dynamic similarity between modeled and natural ice streams is achieved through direct comparison of the glacier force balance using the conditions on Whillans Ice Stream (WIS) as our goal.This ice stream has a force balance that has evolved through time due to increased basal resistance. Currently, between 50-90% of the driving stress is supported by the ice stream shear margins [Stearns et al., JGlac 2005]. A similar force balance can be achieved in our model with a surface slope of 0.025. We test two hypotheses; 1) the distribution and thickness of the subglacial water layer influences the ice flow speed and thus the force balance and can reproduce the observed slowdown of WIS and; 2) shear margins are locations where transitions in water layer thickness occur.

The Fluorescent-Oil Film Method and Other Techniques for Boundary-Layer Flow Visualization

NASA Technical Reports Server (NTRS)

Loving, Donald L.; Katzoff, S.

1959-01-01

A flow-visualization technique, known as the fluorescent-oil film method, has been developed which appears to be generally simpler and to require less experience and development of technique than previously published methods. The method is especially adapted to use in the large high-powered wind tunnels which require considerable time to reach the desired test conditions. The method consists of smearing a film of fluorescent oil over a surface and observing where the thickness is affected by the shearing action of the boundary layer. These films are detected and identified, and their relative thicknesses are determined by use of ultraviolet light. Examples are given of the use of this technique. Other methods that show promise in the study of boundary-layer conditions are described. These methods include the use of a temperature-sensitive fluorescent paint and the use of a radiometer that is sensitive to the heat radiation from a surface. Some attention is also given to methods that can be used with a spray apparatus in front of the test model.

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

Hammond, Glenn Edward; Bao, J; Huang, M

Hyporheic exchange is a critical mechanism shaping hydrological and biogeochemical processes along a river corridor. Recent studies on quantifying the hyporheic exchange were mostly limited to local scales due to field inaccessibility, computational demand, and complexity of geomorphology and subsurface geology. Surface flow conditions and subsurface physical properties are well known factors on modulating the hyporheic exchange, but quantitative understanding of their impacts on the strength and direction of hyporheic exchanges at reach scales is absent. In this study, a high resolution computational fluid dynamics (CFD) model that couples surface and subsurface flow and transport is employed to simulate hyporheicmore » exchanges in a 7-km long reach along the main-stem of the Columbia River. Assuming that the hyporheic exchange does not affect surface water flow conditions due to its negligible magnitude compared to the volume and velocity of river water, we developed a one-way coupled surface and subsurface water flow model using the commercial CFD software STAR-CCM+. The model integrates the Reynolds-averaged Navier-Stokes (RANS) equation solver with a realizable κ-ε two-layer turbulence model, a two-layer all y + wall treatment, and the volume of fluid (VOF) method, and is used to simulate hyporheic exchanges by tracking the free water-air interface as well as flow in the river and the subsurface porous media. The model is validated against measurements from acoustic Doppler current profiler (ADCP) in the stream water and hyporheic fluxes derived from a set of temperature profilers installed across the riverbed. The validated model is then employed to systematically investigate how hyporheic exchanges are influenced by surface water fluid dynamics strongly regulated by upstream dam operations, as well as subsurface structures (e.g. thickness of riverbed and subsurface formation layers) and hydrogeological properties (e.g. permeability). The results suggest that the thickness of riverbed alluvium layer is the dominant factor for reach-scale hyporheic exchanges, followed by the alluvium permeability, the depth of the underlying impermeable layer, and the assumption of hydrostatic pressure.« less

Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet

NASA Astrophysics Data System (ADS)

Yu, Taejong; Moon, Hojoon; You, Donghyun; Kim, Dokyun; Ovsyannikov, Andrey

2014-11-01

Jet wiping, which is a hydrodynamic method for controlling the liquid film thickness in coating processes, is constrained by a rather violent film instability called splashing. The instability is characterized by the ejection of droplets from the runback flow and results in an explosion of the film. The splashing phenomenon degrades the final coating quality. In the present research, a volume-of-fluid (VOF)-based method, which is developed at Cascade Technologies, is employed to simulate the air-liquid multiphase flow dynamics. The present numerical method is based on an unstructured-grid unsplit geometric VOF scheme and guarantees strict conservation of mass of two-phase flow, The simulation results are compared with experimental measurements such as the liquid-film thickness before and after the jet wiping, wall pressure and shear stress distributions. The trajectories of liquid droplets due to the fluid motion entrained by the gas-jet operation, are also qualitatively compared with experimental visualization. Physical phenomena observed during the liquid-layer breakup due to an impinging jet is characterized in order to develop ideas for controlling the liquid-layer instability and resulting splash generation and propagation. Supported by the Grant NRF-2012R1A1A2003699, the Brain Korea 21+ program, POSCO, and 2014 CTR Summer Program.

Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators

NASA Astrophysics Data System (ADS)

Singh, Ashish; Little, Jesse

2016-11-01

A low speed turbulent mixing layer (Reθo =1282, U1 /U2 = 0 . 28 and U2 = 11 . 8 m / s) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number (St) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. Air Force Office of Scientific Research (FA9550-12-1-0044).

A Classification of Subaqueous Density Flows Based on Transformations From Proximal to Distal Regions

NASA Astrophysics Data System (ADS)

Hermidas, Navid; Eggenhuisen, Joris; Luthi, Stefan; Silva Jacinto, Ricardo; Toth, Ferenc; Pohl, Florian

2017-04-01

Transformations of a subaqueous density flow from proximal to distal regions are investigated. A classification of these transformations based on the state of the free shear and boundary layers and existence of a plug layer during transition from a debris flow to a turbidity current is presented. A connection between the emplaced deposit by the flow and the relevant flow type is drawn through the results obtained from a series of laboratory flume experiments. These were performed using 9%, 15%, and 21% sediment mixture concentrations composed of sand, silt, clay, and tap water, on varying bed slopes of 6°, 8°, and 9.5°, and with discharge rates of 10[m3/h] and 15[m3/h]. Stress-controlled rheometry experiments were performed on the mixtures to obtain apparent viscosity data. A classification was developed based on the imposed flow conditions, where a cohesive flow may fall within one of five distinct flow types: 1) a cohesive plug flow (PF) with a laminar free shear and boundary layers, 2) a top transitional plug flow (TTPF) containing a turbulent free shear layer, a plug layer, and a laminar boundary layer, 3) a complete transitional plug flow (CTPF) consisting of a turbulent free shear and boundary layers and a plug, 4) a transitional turbidity current (TTC) with a turbulent free shear layer and a laminar boundary layer, and, 5) a completely turbulent turbidity current (TC). During the experiments, flow type PF resulted in en masse deposition of a thick uniform ungraded muddy sand mixture, which was emplaced once the yield stress overcame the gravitational forces within the tail region of the flow. Flow type TTPF resulted in deposition of a thin ungraded basal clean sand layer during the run. This layer was covered by a muddy sand deposit from the tail. Flow type TTC did not deposit any sediment during the run. A uniform muddy sand mixture was emplaced by the tail of the flow. Flow type TC resulted in deposition of poorly sorted massive bottom sand layer. This layer was overlain by either a muddy sand mixture or a sand and silt planar lamination. Flow type CTPF was not observed during the experiments. Furthermore, it was observed that flows which are in transition from a TTC to a TTPF result in a thin bottom clean sand layer covered by a banded transitional interval. This was overlain by a muddy sand layer and a very thin clean sand layer, resulting from traction by dilute turbulent wake. In all cases a mud cap was emplaced on top of the deposit after the runs were terminated.

Integrated optical silicon IC compatible nanodevices for biosensing applications

NASA Astrophysics Data System (ADS)

Lechuga, Laura M.; Sepulveda, Borja; Llobera, Andreu; Calle, Ana; Dominguez, Carlos M.

2003-04-01

Biological and chemical sensing is one of the application fields where integrated optical nanodevices can play an important role [1]. We present a Silicon Integrated Mach-Zehnder Interferometer Nanodevice using a Total Internal Refraction waveguide configuration. The induced changes due to a biomolecular interactions in the effective refractive index of the waveguide,is monitored by the measurement of the change in the properties of the propagating light. For using this device as a biosensor, the waveguides of the structure must verify two conditions: work in the monomode regime and to have a Surface Sensivity as high as possible in the sensing arm. The MZI device structure is: (i) a Si wafer with a 500 mm thickness (ii) a 2 mm thick thermal Silicon-Oxide layer with a refractive index of 1.46 (iii) a LPCVD Silicon Nitride layer of 100 nm thickness and a refractive index of 2.00, which is used as the guiding layer. To achieve monomode behavior is needed to define a rib structure, with a depth of only 3 nm, on the Silicon Nitride layer by a lithographic step. This rib structure is performed by RIE and is the most critical step in the microfabrication of the device. Over the structure a protective layer of LPCVD SiO2 is deposited, with a 2 mm thickness and a refractive index of 1.46, which is patterned (photolithography) and etched (RIE) to define the sensing arm. The high sensivity of these devices makes them quite suitable for biosensing applications. For that, without loosing their activity the receptors biomolecules are covanlently immobilized, at nanometer scale , on the sensor area surface. Biospecific molecular recognition takes places when the complementary analyte to the receptor is flowed over the receptor using a flow system. Several biosensing applications have been performed with this device as enviromental pollutant control, immunosensing or genetic detection.

Symposium on Turbulent Shear Flows (3rd), University of California, Davis, California, 9-11 September 1981.

DTIC Science & Technology

1981-09-01

1970, p. 417. 16 Wieghardt, K., Tillmann, W., "On the Turbulent Friction Layer for Rising Pressure", NACA, TM 1374, 1957. 17 Andersen, P.S., Kays, W.M...thickness is 5000. derived from the "Strong Reynolds Analogy" (S.R.A.) A 12 eeg . deflection of the wall around a sharp edge may be us d o ep es nt p~-- o Tu...which yields (3) / / 02 /S - t 02 S = Se-t boundayI y,0in flame I with so as the initial shear layer thickness. zonemod 2S 10 / tms 2. Initial

Fire and Thermal Effects of HD 1.3 Accidents: History, Research, and Analysis

DTIC Science & Technology

2010-07-01

consisted of a 1.3 cm thick steel plate (representing the external case), two layers of NBR rubber (representing case lining and ablative...1.3 cm steel plate, 2 layers of NBR rubber , 2.5 cm PMMA • Nitrogen co-flow to prevent ignition of NBR layers • 1D HEATING for prediction 0 200 400...and 100 kW/m 2 . The NBR layers will pyrolyze at elevated temperatures. In a real motor, those gases would be contained by the pressure tight case

Large-scale experimental observations of sheet flow on a sandbar under skewed-asymmetric waves

NASA Astrophysics Data System (ADS)

Mieras, Ryan S.; Puleo, Jack A.; Anderson, Dylan; Cox, Daniel T.; Hsu, Tian-Jian

2017-06-01

A novel large wave flume experiment was conducted on a fixed, barred beach with a sediment pit on the sandbar, allowing for the isolation of small-scale bed response to large-scale forcing. Concurrent measurements of instantaneous sheet layer sediment concentration profiles and near-bed velocity profiles were obtained on a sandbar for the first time. Two sediment distributions were used with median grain diameters, d50, of 0.17 and 0.27 mm. Sheet flow occurred primarily under wave crests, where sheet thickness increased with increasing wave height. A proportionality constant, Λ, was used to relate maximum Shields parameter to maximum sheet thickness (normalized by d50), with bed shear stress computed using the quadratic drag law. An enhanced sheet layer thickness was apparent for the smaller sediment experiments (Λ = 18.7), when directly compared to closed-conduit oscillatory flow tunnel data (Λ = 10.6). However, Λ varied significantly (5 < Λ < 31) depending on the procedure used to estimate grain roughness, ks, and wave friction factor, fw. Three models for ks were compared (keeping the model for fw fixed): constant ks = 2.5d50, and two expressions dependent on flow intensity, derived from steady and oscillatory sheet flow experiments. Values of ks/d50 varied by two orders of magnitude and exhibited an inverse relationship with Λ, where Λ ˜ 30 for ks/d50 of O(1) while Λ ˜ 5 for ks/d50 of O(100). Two expressions for fw were also tested (with the steady flow-based model for ks), yielding a difference of 69% (Λ ˜ 13 versus Λ ˜ 22).

Influence of boundary on the effect of double-layer polarization and the electrophoretic behavior of soft biocolloids.

PubMed

Yeh, Li-Hsien; Fang, Kuo-Ying; Hsu, Jyh-Ping; Tseng, Shiojenn

2011-12-01

The electrophoresis of a soft particle comprising a rigid core and a charged porous membrane layer in a narrow space is modeled. This simulates, for example, the capillary electrophoresis of biocolloids such as cells and microorganisms, and biosensor types of device. We show that, in addition to the boundary effect, the effects of double-layer polarization (DLP) and the electroosmotic retardation flow can be significant, yielding interesting electrophoretic behaviors. For example, if the friction coefficient of the membrane layer and/or the boundary is large, then the DLP effect can be offset by the electroosmotic retardation flow, making the particle mobility to decrease with increasing double layer thickness, which is qualitatively consistent with many experimental observations in the literature, but has not been explained clearly in previous analyses. In addition, depending upon the thickness of double layer, the friction of the membrane layer of a particle can either retard or accelerate its movement, an interesting result which has not been reported previously. This work is the first attempt to show solid evidence for the influence of a boundary on the effect of DLP and the electrophoretic behavior of soft particles. The model proposed is verified by the experimental data in the literature. The results of numerical simulation provide valuable information for the design of bio-analytical apparatus such as nanopore-based sensing applications and for the interpretation of relevant experimental data. Copyright © 2011 Elsevier B.V. All rights reserved.

Field and numerical descriptions of fracture geometries and terminations in chalk containing chert layers and inclusions; implications for groundwater flow in Danish chalk aquifers

NASA Astrophysics Data System (ADS)

Seyum, S.

2017-12-01

This study is a description of the fracture distribution in laterally discontinuous chalk and chert layers, with an investigation on how fracture lengths and apertures vary as a function of applied stresses, material properties, and interface properties. Natural fractures intersect laterally extensive, discontinuous, chalk-chert material interfaces in 62 million-year old to 72 million-year old Chalk Group formations exposed at Stevns Klint, Denmark. Approximately one-third of Denmark's fresh water use is from chalk and limestone regional aquifers of the Chalk Group formations, where rock permeability is dominantly a function of open fracture connectivities. Fractured, centimeter- to decimeter-thick chert layers and inclusions (101 GPa elastic stiffness) are interlayered with fractured, meter-thick chalk layers (100 GPa elastic stiffness). Fractures are observed to terminate against and cross chalk-chert interfaces, affecting the vertical flow of water and pollutants between aquifers. The discontinuous and variably thin nature of chert layers at Stevns Klint effectively merges adjacent fracture-confining layers of chalk along discrete position intervals, resulting in lateral variability of fracture spacing. Finite element numerical models are designed to describe fracture interactions with stiff, chert inclusions of various shapes, thicknesses, widths, orientations, and interface friction and fracture toughness values. The models are two-dimensional with isotropic, continuous material in plane strain and uniformly applied remote principal stresses. These characteristics are chosen based on interpretations of the petrophysics of chalk and chert, the burial history of the rock, and the scale of investigation near fracture tips relative to grain sizes. The result are value ranges for relative stiffness contrasts, applied stresses, and material interface conditions that would cause fractures to cross, terminate at, or form along chalk-chert interfaces, with emphasis on conditions that reproduce measured fracture geometries. The results of this study provide predictive, field-supported fracture geometries for flow models and, with appropriate changes to the parameters, the methodology is applicable to describing fracture geometries in chalk hydrocarbon systems.

Turbulent boundary layer on the surface of a sea geophysical antenna

NASA Astrophysics Data System (ADS)

Smol'Yakov, A. V.

2010-11-01

A theory is constructed that makes it possible to calculate the initial parameters necessary for calculating the hydrodynamic (turbulent) noise, which is a handicap to the operation of sea geophysical antennas. Algorithms are created for calculating the profile and defect of the average speed, displacement thickness, momentum thickness, and friction resistance in a turbulent boundary layer on a cylinder in its axial flow. Results of calculations using the developed theory are compared to experimental data. As the diameter of the cylinder tends to infinity, all relations of the theory pass to known relations for the boundary layer on a flat plate. The developed theory represents the initial stage of creating a method to calculate hydrodynamic noise, which is handicap to the operation of sea geophysical antennas.

Static Buckling Model Tests and Elasto-plastic Finite Element Analysis of a Pile in Layers with Various Thicknesses

NASA Astrophysics Data System (ADS)

Okajima, Kenji; Imai, Junichi; Tanaka, Tadatsugu; Iida, Toshiaki

Damage to piles in the liquefied ground is frequently reported. Buckling by the excess vertical load could be one of the causes of the pile damage, as well as the lateral flow of the ground and the lateral load at the pile head. The buckling mechanism is described as a complicated interaction between the pile deformation by the vertical load and the earth pressure change cased by the pile deformation. In this study, series of static buckling model tests of a pile were carried out in dried sand ground with various thickness of the layer. Finite element analysis was applied to the test results to verify the effectiveness of the elasto-plastic finite element analysis combining the implicit-explicit mixed type dynamic relaxation method with the return mapping method to the pile buckling problems. The test results and the analysis indicated the possibility that the buckling load of a pile decreases greatly where the thickness of the layer increases.

In Vitro Engineering of Vascularized Tissue Surrogates

PubMed Central

Sakaguchi, Katsuhisa; Shimizu, Tatsuya; Horaguchi, Shigeto; Sekine, Hidekazu; Yamato, Masayuki; Umezu, Mitsuo; Okano, Teruo

2013-01-01

In vitro scaling up of bioengineered tissues is known to be limited by diffusion issues, specifically a lack of vasculature. Here, we report a new strategy for preserving cell viability in three-dimensional tissues using cell sheet technology and a perfusion bioreactor having collagen-based microchannels. When triple-layer cardiac cell sheets are incubated within this bioreactor, endothelial cells in the cell sheets migrate to vascularize in the collagen gel, and finally connect with the microchannels. Medium readily flows into the cell sheets through the microchannels and the newly developed capillaries, while the cardiac construct shows simultaneous beating. When additional triple-layer cell sheets are repeatedly layered, new multi-layer construct spontaneously integrates and the resulting construct becomes a vascularized thick tissue. These results confirmed our method to fabricate in vitro vascularized tissue surrogates that overcomes engineered-tissue thickness limitations. The surrogates promise new therapies for damaged organs as well as new in vitro tissue models. PMID:23419835

Serially connected solid oxide fuel cells having monolithic cores

DOEpatents

Herceg, Joseph E.

1987-01-01

A solid oxide fuel cell for electrochemically combining fuel and oxidant for generating galvanic output, wherein the cell core has an array of cell segments electrically serially connected in the flow direction, each segment consisting of electrolyte walls and interconnect that are substantially devoid of any composite inert materials for support. Instead, the core is monolithic, where each electrolyte wall consists of thin layers of cathode and anode materials sandwiching a thin layer of electrolyte material therebetween. Means direct the fuel to the anode-exposed core passageways and means direct the oxidant to the cathode-exposed core passageways; and means also direct the galvanic output to an exterior circuit. Each layer of the electrolyte composite materials is of the order of 0.002-0.01 cm thick; and each layer of the cathode and anode materials is of the order of 0.002-0.05 cm thick. Between 2 and 50 cell segments may be connected in series.

Determination of Boundary-Layer Transition on Three Symmetrical Airfoils in the NACA Full-Scale Wind Tunnel

NASA Technical Reports Server (NTRS)

Silverstein, Abe; Becker, John V

1938-01-01

For the purpose of studying the transition from laminar to turbulent flow, boundary-layer measurements were made in the NACA full-scale wind tunnel on three symmetrical airfoils of NACA 0009, 0012, and 0018 sections. The effects of variations in lift coefficient, Reynolds number, and airfoil thickness on transition were investigated. Air speed in the boundary layer was measured by total-head tubes and by hot wires; a comparison of transition as indicated by the two techniques was obtained. The results indicate no unique value of Reynolds number for the transition, whether the Reynolds number is based upon the distance along the chord or upon the thickness of the boundary layer at the transition point. In general, the transition is not abrupt and occurs in a region that varies in length as a function of the test conditions.

Analysis of the separated boundary layer flow on the surface and in the wake of blunt trailing edge airfoils

NASA Technical Reports Server (NTRS)

Goradia, S. H.; Mehta, J. M.; Shrewsbury, G. S.

1977-01-01

The viscous flow phenomena associated with sharp and blunt trailing edge airfoils were investigated. Experimental measurements were obtained for a 17 percent thick, high performance GAW-1 airfoil. Experimental measurements consist of velocity and static pressure profiles which were obtained by the use of forward and reverse total pressure probes and disc type static pressure probes over the surface and in the wake of sharp and blunt trailing edge airfoils. Measurements of the upper surface boundary layer were obtained in both the attached and separated flow regions. In addition, static pressure data were acquired, and skin friction on the airfoil upper surface was measured with a specially constructed device. Comparison of the viscous flow data with data previously obtained elsewhere indicates reasonable agreement in the attached flow region. In the separated flow region, considerable differences exist between these two sets of measurements.

Chemical reaction and heat generation/absorption aspects in MHD nonlinear convective flow of third grade nanofluid over a nonlinear stretching sheet with variable thickness

NASA Astrophysics Data System (ADS)

Qayyum, Sajid; Hayat, Tasawar; Alsaedi, Ahmed

Nonlinear thermal radiation and chemical reaction in magnetohydrodynamic (MHD) flow of third grade nanofluid over a stretching sheet with variable thickness are addressed. Heat generation/absorption and nonlinear convection are considered. The sheet moves with nonlinear velocity. Sheet is convectively heated. In addition zero mass flux condition for nanoparticle concentration is imposed. Results for velocity, temperature, concentration, skin friction and local Nusselt number are presented and examined. It is found that velocity and boundary layer thickness are increasing for Reynolds number. Temperature is a increasing function of the heat generation/absorption parameter while it causes a decrease in the heat transfer rate. Moreover effect of Brownian motion and chemical reaction on the concentration are quite reverse.

Complex large-scale convection of a viscous incompressible fluid with heat exchange according to Newton's law

NASA Astrophysics Data System (ADS)

Gorshkov, A. V.; Prosviryakov, E. Yu.

2017-12-01

The paper considers the construction of analytical solutions to the Oberbeck-Boussinesq system. This system describes layered Bénard-Marangoni convective flows of an incompressible viscous fluid. The third-kind boundary condition, i. e. Newton's heat transfer law, is used on the boundaries of a fluid layer. The obtained solution is analyzed. It is demonstrated that there is a fluid layer thickness with tangential stresses vanishing simultaneously, this being equivalent to the existence of tensile and compressive stresses.

Subcutaneous Fascial Bands—A Qualitative and Morphometric Analysis

PubMed Central

Li, Weihui; Ahn, Andrew C.

2011-01-01

Background Although fascial bands within the subcutaneous (SQ) layer are commonly seen in ultrasound images, little is known about their functional role, much less their structural characteristics. This study's objective is to describe the morphological features of SQ fascial bands and to systematically evaluate the bands using image analyses tools and morphometric measures. Methods In 28 healthy volunteers, ultrasound images were obtained at three body locations: the lateral aspect of the upper arm, medial aspect of the thigh and posterior aspect of lower leg. Using image analytical techniques, the total SQ band area, fascial band number, fascial band thickness, and SQ zone (layer) thickness were determined. In addition, the SQ spatial coherence was calculated based on the eigenvalues associated with the largest and smallest eigenvectors of the images. Results Fascial bands at these sites were contiguous with the dermis and the epimysium forming an interconnected network within the subcutaneous tissue. Subcutaneous blood vessels were also frequently encased by these fascial bands. The total SQ fascial band area was greater at the thigh and calf compared to the arm and was unrelated to SQ layer (zone) thickness. The thigh was associated with highest average number of fascial bands while calf was associated with the greatest average fascial band thickness. Across body regions, greater SQ zone thickness was associated with thinner fascial bands. SQ coherence was significantly associated with SQ zone thickness and body location (calf with statistically greater coherence compared to arm). Conclusion Fascial bands are structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. This cohesive network also encases subcutaneous vessels and may indirectly mediate blood flow. The quantity and morphological characteristics of the SQ fascial band may reflect the composite mechanical forces experienced by the body part. PMID:21931632

Flow field survey near the rotational plane of an advanced design propeller on a JetStar airplane

NASA Technical Reports Server (NTRS)

Walsh, K. R.

1985-01-01

An investigation was conducted to obtain upper fuselage surface static pressures and boundary layer velocity profiles below the centerline of an advanced design propeller. This investigation documents the upper fuselage velocity flow field in support of the in-flight acoustic tests conducted on a JetStar airplane. Initial results of the boundary layer survey show evidence of an unusual flow disturbance, which is attributed to the two windshield wiper assemblies on the aircraft. The assemblies were removed, eliminating the disturbances from the flow field. This report presents boundary layer velocity profiles at altitudes of 6096 and 9144 m (20,000 and 30,000 ft) and Mach numbers from 0.6 to 0.8, and it investigated the effects of windshield wiper assemblies on these profiles. Because of the unconventional velocity profiles that were obtained with the assemblies mounted, classical boundary layer parameters, such as momentum and displacement thicknesses, are not presented. The effects of flight test variables (Mach number and angles of attack and sideslip) and an advanced design propeller on boundary layer profiles - with the wiper assemblies mounted and removed - are presented.

Prediction of mean flow data for adiabatic 2-D compressible turbulent boundary layers

NASA Astrophysics Data System (ADS)

Motallebi, Fariborz

1995-02-01

This report presents a method for the prediction of mean flow data (i.e. , skin friction, velocity profile, and shape parameter) for adiabatic two-dimensional compressible turbulent boundary layers at zero pressure gradient. The transformed law of the wall, law of the wake, the van Driest model for the complete inner region, and a correlation between the Reynolds number based on the boundary layer integral length scale (Re(sub Delta*)) and the Reynolds number based on the boundary layer momentum thickness (Re(sub theta)) were used to predict the mean flow quantities. The results for skin friction coefficient show good agreement with a number of existing theories including those of van Driest and Huang et al. Comparison with a large number of experimental data suggests that at least for transonic and supersonic flows, the velocity profile as described by van Driest and Coles is Reynolds number dependent and should not be presumed universal. Extra information or perhaps a better physical approach to the formulation of the mean structure of compressible turbulent boundary layers, even in zero pressure gradient and adiabatic condition, is required in order to achieve complete (physical and mathematical) convergence when it is applied in any prediction methods.

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

Gavignet, A.A.; Sobey, I.J.

At present, drilling of highly deviated wells is complicated by the possibility of the formation of a thick bed of cuttings at low flow rates. The bed of cuttings can cause large torque loads on drill pipe and can fall back around the bit resulting in a stuck bit. Previous investigators have made experimental observations which show that bed formation is characterized by a relatively rapid increase in bed thickness as either the flow rate is lowered past some critical value, or as the deviation from the vertical increases. The authors present a simple model which explains these observations. Themore » model shows that the bed thickness is controlled by the interfacial stress caused by the different velocities of the mud and the cuttings layer. The results confirm previous observations that bed formation is relatively insensitive to mud rheology. Eccentricity of the drill pipe in the hole is an important factor. The model is used to determine critical flow rate needed to prevent the formation of a thick bed of cuttings and the inclination, hole size and rate of penetration are varied.« less

Aero-Hydroacoustics for Ships. Volume 2

DTIC Science & Technology

1984-06-01

Willmarth and Yang and Afzal and Narasimha. The subject of laminat turbulent transitional flows has beea examined by Yasuhara. 2 2 6 Currently there is no... composite structure of N ppanels of dimensions Li, L3 d thickness h subjected to boundary-layer flow. If we are interested in a hydro- oustic application...Reynolds number, in which case the wake vorticity will very likely be disordered. Laminat -flow airfoils’ (or, say, for 6"Reynolds numbers less than 1

Flow of ultra-hot Precambrian orogens and the making of crustal layering in Phanerozoic orogenic plateaux

NASA Astrophysics Data System (ADS)

Chardon, Dominique; Gapais, Denis; Cagnard, Florence; Jayananda, Mudlappa; Peucat, Jean-Jacques

2010-05-01

Reassessment of structural / metamorphic properties of ultra-hot Precambrian orogens and shortening of model weak lithospheres support a syn-convergence flow mode on an orogen scale, with a large component of horizontal finite elongation parallel to the orogen. This orogen-scale flow mode combines distributed shortening, gravity-driven flow, lateral escape, and three-dimensional mass redistribution of buried supracrustal rocks, magmas and migmatites in a thick fluid lower crust. This combination preserves a nearly flat surface and Moho. The upper crust maintains a nearly constant thickness by real-time erosion and near-field clastic sedimentation and by ablation at its base by burial of pop-downs into the lower crust. Steady state regime of these orogens is allowed by activation of an attachment layer that maintains kinematic compatibility between the thin and dominantly plastic upper crust and a thick "water bed" of lower crust. Because very thin lithospheres of orogenic plateaux and Precambrian hot orogens have similar thermomechanical structures, bulk orogenic flow comparable to that governing Precambrian hot orogens should actually operate through today's orogenic plateaux as well. Thus, syn-convergence flow fabrics documented on exposed crustal sections of ancient hot orogens that have not undergone collapse may be used to infer the nature of flow fabrics that are imaged by geophysical techniques beneath orogenic plateaux. We provide a detailed geological perspective on syn-convergence crustal flow in relation to magma emplacement and partial melting on a wide oblique crustal transition of the Neoarchean ultra-hot orogen of Southern India. We document sub-horizontal bulk longitudinal flow of the partially molten lower crust over a protracted period of 60 Ma. Bulk flow results from the interplay of (1) pervasive longitudinal transtensional flow of the partially molten crust, (2) longitudinal coaxial flow on flat fabrics in early plutons, (3) distributed, orogen-normal shortening, (4) emplacement of late prolate shape plutons in the direction of flow, and (5) late, conjugate strike-slip shearing. The macroscopic- to regional scale tectonoplutonic pattern produced by longitudinal flow forms a flat composite anisotropy throughout the lower crust. In the light of GPS data, these results suggest that bulk longitudinal flow accounts for observed deformation of the Tibetan plateau as well as for its seismic structure. This flow mode may be preferred to lateral, east-directed channel flow because it combines both lateral gravity-driven thinning and distributed, orogen-normal shortening of the crust. These results further suggest that lower crustal seismic reflectivity in orogenic belts may not necessarily images fabrics produced by extensional tectonics, as commonly thought, but crustal layering produced by syn-convergence lateral flow.

Aero-Heating of Shallow Cavities in Hypersonic Freestream Flow

NASA Technical Reports Server (NTRS)

Everhart, Joel L.; Berger, Karen T.; Merski, N. R., Jr.; Woods, William A.; Hollingsworth, Kevin E.; Hyatt, Andrew; Prabhu, Ramadas K.

2010-01-01

The purpose of these experiments and analysis was to augment the heating database and tools used for assessment of impact-induced shallow-cavity damage to the thermal protection system of the Space Shuttle Orbiter. The effect of length and depth on the local heating disturbance of rectangular cavities tested at hypersonic freestream conditions has been globally assessed using the two-color phosphor thermography method. These rapid-response experiments were conducted in the Langley 31-Inch Mach 10 Tunnel and were initiated immediately prior to the launch of STS-114, the initial flight in the Space Shuttle Return-To-Flight Program, and continued during the first week of the mission. Previously-designed and numerically-characterized blunted-nose baseline flat plates were used as the test surfaces. Three-dimensional computational predictions of the entire model geometry were used as a check on the design process and the two-dimensional flow assumptions used for the data analysis. The experimental boundary layer state conditions were inferred using the measured heating distributions on a no-cavity test article. Two test plates were developed, each containing 4 equally-spaced spanwise-distributed cavities. The first test plate contained cavities with a constant length-to-depth ratio of 8 with design point depth-to-boundary-layer-thickness ratios of 0.1, 0.2, 0.35, and 0.5. The second test plate contained cavities with a constant design point depth-to-boundary-layer-thickness ratio of 0.35 with length-to-depth ratios of 8, 12, 16, and 20. Cavity design parameters and the test condition matrix were established using the computational predictions. Preliminary results indicate that the floor-averaged Bump Factor (local heating rate nondimensionalized by upstream reference) at the tested conditions is approximately 0.3 with a standard deviation of 0.04 for laminar-in/laminar-out conditions when the cavity length-to-boundary-layer thickness is between 2.5 and 10 and for cavities in the depth-to-boundary-layer-thickness range of 0.3 to 0.8. Over this same range of conditions and parameters, preliminary results also indicate that the maximum Bump Factor on the cavity centerline falls between 2.0 and 2.75, as long as the cavity-exit conditions remain laminar. Cavities with length-to-boundary-layer-thickness ratio less than 2.5 can not be easily classified with this approach and require further analysis.

Characteristics of a-IGZO/ITO hybrid layer deposited by magnetron sputtering.

PubMed

Bang, Joon-Ho; Park, Hee-Woo; Cho, Sang-Hyun; Song, Pung-Keun

2012-04-01

Transparent a-IGZO (In-Ga-Zn-O) films have been actively studied for use in the fabrication of high-quality TFTs. In this study, a-IGZO films and a-IGZO/ITO double layers were deposited by DC magnetron sputtering under various oxygen flow rates. The a-IGZO films showed an amorphous structure up to 500 degrees C. The deposition rate of these films decreased with an increase in the amount of oxygen gas. The amount of indium atoms in the film was confirmed to be 11.4% higher than the target. The resistivity of double layer follows the rules for parallel DC circuits The maximum Hall mobility of the a-IGZO/ITO double layers was found to be 37.42 cm2/V x N s. The electrical properties of the double layers were strongly dependent on their thickness ratio. The IGZO/ITO double layer was subjected to compressive stress, while the ITO/IGZO double layer was subjected to tensile stress. The bending tolerance was found to depend on the a-IGZO thickness.

Ac electroosmotic flows above coplanar electrodes

NASA Astrophysics Data System (ADS)

Kweon Suh, Yong

2009-03-01

Interactive numerical method has been proposed to calculate the ac electroosmotic flows above a pair of coplanar electrodes. The thin electrical triple layer (ETL) has been modeled by an asymptotic theory developed by the authors. The model corresponds to a simple dynamic equation for the surface charge density representing the integrated charge over the inner layer. Interactive calculation of the dynamic equation and the Laplace equation for several periods of ac frequency then yielded steady-state distribution of potential and the potential drop across the Stern and inner layers. The Smoluchowski's slip velocity was then determined from those two set of data and used as the boundary condition for the calculation of the Stokes' flow above the electrodes. We have shown that our solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness and the adsorption coefficients.

Crystal accumulation in the Hanford Waste Treatment Plant high level waste melter: Summary of FY2016 experiements

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

Fox, K.; Fowley, M.; Miller, D.

2016-12-01

Five experiments were completed with the full-scale, room temperature Hanford Waste Treatment and Immobilization Plant (WTP) high-level waste (HLW) melter riser test system to observe particle flow and settling in support of a crystal tolerant approach to melter operation. A prototypic pour rate was maintained based on the volumetric flow rate. Accumulation of particles was observed at the bottom of the riser and along the bottom of the throat after each experiment. Measurements of the accumulated layer thicknesses showed that the settled particles at the bottom of the riser did not vary in thickness during pouring cycles or idle periods.more » Some of the settled particles at the bottom of the throat were re-suspended during subsequent pouring cycles, and settled back to approximately the same thickness after each idle period. The cause of the consistency of the accumulated layer thicknesses is not year clear, but was hypothesized to be related to particle flow back to the feed tank. Additional experiments reinforced the observation of particle flow along a considerable portion of the throat during idle periods. Limitations of the system are noted in this report and may be addressed via future modifications. Follow-on experiments will be designed to evaluate the impact of pouring rate on particle re-suspension, the influence of feed tank agitation on particle accumulation, and the effect of changes in air lance positioning on the accumulation and re-suspension of particles at the bottom of the riser. A method for sampling the accumulated particles will be developed to support particle size distribution analyses. Thicker accumulated layers will be intentionally formed via direct addition of particles to select areas of the system to better understand the ability to continue pouring and re-suspend particles. Results from the room temperature system will be correlated with observations and data from the Research Scale Melter (RSM) at Pacific Northwest National Laboratory, and coordinated with modeling efforts underway at Idaho National Laboratory.« less

Planar fuel cell utilizing nail current collectors for increased active surface area

DOEpatents

George, Thomas J.; Meacham, G. B. Kirby

2002-03-26

A plurality of nail current collector members are useful in the gas flow passages of an electrochemical device to optimize the active surfaces of the device and to provide structural support. In addition, the thicknesses of cathode and anode layers within the electrochemical device are varied according to current flow through the device to reduce resistance and increase operating efficiency.

Planar fuel cell utilizing nail current collectors for increased active surface area

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

George, Thomas J.; Meacham, G.B. Kirby

1999-11-26

A plurality of nail current collector members are useful in the gas flow passages of an electrochemical device to optimize the active surfaces of the device and to provide structural support. In addition, the thicknesses of cathode and anode layers within the electrochemical device are varied according to current flow through the device to reduce resistance and increase operating efficiency.

Influence of the angle between the wind and the isothermal surfaces on the boundary layer structures in turbulent thermal convection.

PubMed

Shishkina, Olga; Wagner, Sebastian; Horn, Susanne

2014-03-01

We derive the asymptotes for the ratio of the thermal to viscous boundary layer thicknesses for infinite and infinitesimal Prandtl numbers Pr as functions of the angle β between the large-scale circulation and an isothermal heated or cooled surface for the case of turbulent thermal convection with laminar-like boundary layers. For this purpose, we apply the Falkner-Skan ansatz, which is a generalization of the Prandtl-Blasius one to a nonhorizontal free-stream flow above the viscous boundary layer. Based on our direct numerical simulations (DNS) of turbulent Rayleigh-Bénard convection for Pr=0.1, 1, and 10 and moderate Rayleigh numbers up to 108 we evaluate the value of β that is found to be around 0.7π for all investigated cases. Our theoretical predictions for the boundary layer thicknesses for this β and the considered Pr are in good agreement with the DNS results.

Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 2. [computer programs

NASA Technical Reports Server (NTRS)

Omori, S.

1973-01-01

As described in Vol. 1, the eddy viscosity is calculated through the turbulent kinetic energy, in order to include the history of the flow and the effect of chemical reaction on boundary layer characteristics. Calculations can be performed for two different cooling concepts; that is, transpiration and regeneratively cooled wall cases. For the regenerative cooling option, coolant and gas side wall temperature and coolant bulk temperature in a rocket engine can be computed along the nozzle axis. Thus, this computer program is useful in designing coolant flow rate and cooling tube geometry, including the tube wall thickness as well as in predicting the effects of boundary layers along the gas side wall on thrust performances.

Ductile crustal flow in Europe's lithosphere

NASA Astrophysics Data System (ADS)

Tesauro, Magdala; Burov, Evgene B.; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

2011-12-01

Potential gravity theory (PGT) predicts the presence of significant gravity-induced horizontal stresses in the lithosphere associated with lateral variations in plate thickness and composition. New high resolution crustal thickness and density data provided by the EuCRUST-07 model are used to compute the associated lateral pressure gradients (LPG), which can drive horizontal ductile flow in the crust. Incorporation of these data in channel flow models allows us to use potential gravity theory to assess horizontal mass transfer and stress transmission within the European crust. We explore implications of the channel flow concept for a possible range of crustal strength, using end-member 'hard' and 'soft' crustal rheologies to estimate strain rates at the bottom of the ductile crustal layers. The models show that the effects of channel flow superimposed on the direct effects of plate tectonic forces might result in additional significant horizontal and vertical movements associated with zones of compression or extension. To investigate relationships between crustal and mantle lithospheric movements, we compare these results with the observed directions of mantle lithospheric anisotropy and GPS velocity vectors. We identify areas whose evolution could have been significantly affected by gravity-driven ductile crustal flow. Large values of the LPG are predicted perpendicular to the axes of European mountain belts, such as the Alps, Pyrenees-Cantabrian Mountains, Dinarides-Hellenic arc and Carpathians. In general, the crustal flow is directed away from orogens towards adjacent weaker areas. Gravitational forces directed from areas of high gravitational potential energy to subsiding basin areas can strongly reduce lithospheric extension in the latter, leading to a gradual late stage inversion of the entire system. Predicted pressure and strain rate gradients suggest that gravity driven flow may play an essential role in European intraplate tectonics. In particular, in a number of regions the predicted strain rates are comparable to tectonically induced strain rates. These results are also important for quantifying the thickness of the low viscosity zones in the lowermost part of the crustal layers.

Two-layer Crustal Structure of the Contiguous United States from Joint Inversion of USArray Receiver Functions and Gravity

NASA Astrophysics Data System (ADS)

Ma, X.; Lowry, A. R.

2015-12-01

The composition and thickness of crustal layering is fundamental to understanding the evolution and dynamics of continental lithosphere. Lowry and Pérez-Gussinyé (2011) found that the western Cordillera of the United States, characterized by active deformation and high heat flow, is strongly correlated with low bulk crustal seismic velocity ratio. They interpreted this observation as evidence that quartz controls continental tectonism and deformation. We will present new imaging of two-layer crustal composition and structure from cross-correlation of observed receiver functions and model synthetics. The cross-correlation coefficient of the two-layer model increases significantly relative to an assumed one-layer model, and the lower crustal thickness map from raw two-layer modeling (prior to Bayesian filtering with gravity models and Optimal Interpolation) clearly shows Colorado plateau and Appalachian boundaries, which are not apparent in upper crustal models, and also the high vP/vS fill the most of middle continental region while low vP/vS are on the west and east continental edge. In the presentation, we will show results of a new algorithm for joint Bayesian inversion of thickness and vP/vS of two-layer continental crustal structure. Recent thermodynamical modeling of geophysical models based on lab experiment data (Guerri et al., 2015) found that a large impedance contrast can be expected in the midcrust due to a phase transition that decreases plagioclase and increases clinopyroxene, without invoking any change in crustal chemistry. The depth of the transition depends on pressure, temperature and hydration, and in this presentation we will compare predictions of layer thicknesses and vP/vS predicted by mineral thermodynamics to those we observe in the USArray footprint.

Phase-Field Simulation of Concentration and Temperature Distribution During Dendritic Growth in a Forced Liquid Metal Flow

NASA Astrophysics Data System (ADS)

Du, Lifei; Zhang, Rong

2014-12-01

A phase-field model with convection is employed to investigate the effect of liquid flow on the dendritic structure formation of a Ni-Cu alloy during rapid solidification. Temperature and solute diffusion are significantly changed with induced liquid metal flow, and distribution changes of concentration and temperature are also analyzed and discussed. The solute segregation is affected due to the concentration diffusion layer thickness change caused by the liquid flow. The flow reduces the solute segregation in the upstream and leads to a fast dendrite growing, while solidifying in the downstream gets constrained with the large solute diffusion layer. Increasing flow velocity increases the asymmetry of dendrite morphology with much more suppressed growth in the downstream. The temperature distribution is also asymmetrical due to the non-uniform latent heat released during solidification coupling with heat diffusion changed by the liquid flow. Therefore, the forced liquid flow significantly affects the dendrite morphology, concentration, and temperature distributions in the solidifying microstructure.

Keeping Enceladus Warm

NASA Astrophysics Data System (ADS)

Travis, B. J.; Schubert, G.

2012-12-01

Despite its small size, Enceladus emits considerable heat, especially at its south pole, even long after simple thermal models predict it should be frozen. A number of energy mechanisms have been proposed as responsible for this heating, such as TDH (tidal dissipative heating), and convection and shearing in the ice shell, but why energy outflow is primarily at the south pole is still debated. It is not known if TDH has operated continuously at Enceladus. Crater relaxation simulations suggest considerable heat flow has occurred over long stretches of its history. One process missing from previous models is fluid flow, both in an ocean layer and in the silicate core. The simulations described here are part of a study to estimate the impact of hydrothermal flow and to explore under what conditions, and for how long, an ocean layer could persist on Enceladus, with or without TDH. Our model geometry is 2-D spherical (radius and latitude) for most simulations, with one 3-D spherical simulation. We assume a silicate core of about 160 km radius, overlain by an H2O layer out to 250 km radius. Ice shell thickness is initially 15 km. Flow in an ocean layer is represented by a simplified Navier-Stokes model, and porous flow occurs in the core. Surface temperature distribution follows observed values. Radiogenic heating produces about 0.3 GW in the model. A simple TDH model is active in some simulations. Salts and/or NH3 may be present in the interior of Enceladus, and would strongly depress freezing; our model uses a low eutectic salt as an analog. The ice shell's thickness is not required to remain fixed, but can change dynamically, in response to local thermodynamics. Initial core temperature and permeability are unknowns. Initial core temperature is varied over several hundred oC, and permeability is varied over 1-100 millidarcies. In our simulations, typically, a flow field develops characterized by sinking flow at the equator and rising plumes at the poles. A broad thickening of ice in the equatorial region occurs, so much so that flow is gradually restricted to the polar regions, with the south pole flow stronger than at the northern pole. A feedback develops; cooler, sinking flow at the equator results in thickening of the ice there which in turn tends to isolate flow to the deeper ocean plus core region at the poles. The rate at which this pattern develops depends on the presence or absence of TDH. Except at the surface, a nearly cylindrical region from north to south through the model remains fluid. The presence of salt and/or NH3 allows liquid conditions and flow even as the ocean temperature falls well below 0 oC. At higher initial core temperatures, boiling occurs deep in the core because of the low overburden pressure. An approximately 70 km thick difference in ice thickness can develop between equator and poles. However, due to the low gravity of Enceladus, this would give rise to a buoyant pressure difference of only about 5 bars, which is less than shear strength measurements in ice. The core slowly cools, and eventually the ocean may freeze completely without TDH, but that can take on the order of several hundred million years or more. If episodes of strong TDH occurred on that time scale or shorter, a polar ocean might then persist indefinitely.

Acoustic Receptivity of Mach 4.5 Boundary Layer with Leading- Edge Bluntness

NASA Technical Reports Server (NTRS)

Malik, Mujeeb R.; Balakumar, Ponnampalam

2007-01-01

Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows where second mode instability is dominant. Computations are performed to investigate the effect of leading-edge thickness and it is found that bluntness tends to stabilize the boundary layer. Furthermore, the relative significance of fast acoustic waves is enhanced in the presence of bluntness. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle.

Analytical study of Cattaneo-Christov heat flux model for a boundary layer flow of Oldroyd-B fluid

NASA Astrophysics Data System (ADS)

F, M. Abbasi; M, Mustafa; S, A. Shehzad; M, S. Alhuthali; T, Hayat

2016-01-01

We investigate the Cattaneo-Christov heat flux model for a two-dimensional laminar boundary layer flow of an incompressible Oldroyd-B fluid over a linearly stretching sheet. Mathematical formulation of the boundary layer problems is given. The nonlinear partial differential equations are converted into the ordinary differential equations using similarity transformations. The dimensionless velocity and temperature profiles are obtained through optimal homotopy analysis method (OHAM). The influences of the physical parameters on the velocity and the temperature are pointed out. The results show that the temperature and the thermal boundary layer thickness are smaller in the Cattaneo-Christov heat flux model than those in the Fourier’s law of heat conduction. Project supported by the Deanship of Scientific Research (DSR) King Abdulaziz University, Jeddah, Saudi Arabia (Grant No. 32-130-36-HiCi).

Effect of thermal radiation and chemical reaction on non-Newtonian fluid through a vertically stretching porous plate with uniform suction

NASA Astrophysics Data System (ADS)

Khan, Zeeshan; Khan, Ilyas; Ullah, Murad; Tlili, I.

2018-06-01

In this work, we discuss the unsteady flow of non-Newtonian fluid with the properties of heat source/sink in the presence of thermal radiation moving through a binary mixture embedded in a porous medium. The basic equations of motion including continuity, momentum, energy and concentration are simplified and solved analytically by using Homotopy Analysis Method (HAM). The energy and concentration fields are coupled with Dankohler and Schmidt numbers. By applying suitable transformation, the coupled nonlinear partial differential equations are converted to couple ordinary differential equations. The effect of physical parameters involved in the solutions of velocity, temperature and concentration profiles are discussed by assign numerical values and results obtained shows that the velocity, temperature and concentration profiles are influenced appreciably by the radiation parameter, Prandtl number, suction/injection parameter, reaction order index, solutal Grashof number and the thermal Grashof. It is observed that the non-Newtonian parameter H leads to an increase in the boundary layer thickness. It was established that the Prandtl number decreases thee thermal boundary layer thickness which helps in maintaining system temperature of the fluid flow. It is observed that the temperature profiles higher for heat source parameter and lower for heat sink parameter throughout the boundary layer. Fromm this simulation it is analyzed that an increase in the Schmidt number decreases the concentration boundary layer thickness. Additionally, for the sake of comparison numerical method (ND-Solve) and Adomian Decomposition Method are also applied and good agreement is found.

Microgravity Effects on Plant Boundary Layers

NASA Technical Reports Server (NTRS)

Stutte, Gary; Monje, Oscar

2005-01-01

The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

The effects of thick sediment upon continental breakup: seismic imaging and thermal modeling of the Salton Trough, southern California

NASA Astrophysics Data System (ADS)

Han, L.; Hole, J. A.; Lowell, R. P.; Stock, J. M.; Fuis, G. S.; Driscoll, N. W.; Kell, A. M.; Kent, G. M.; Harding, A. J.; Gonzalez-Fernandez, A.; Lázaro-Mancilla, O.

2015-12-01

Continental rifting ultimately creates a deep accommodation space for sediment. When a major river flows into a late-stage rift, thick deltaic sediment can change the thermal regime and alter the mechanisms of extension and continental breakup. The Salton Trough, the northernmost rift segment of the Gulf of California plate boundary, has experienced the same extension as the rest of the Gulf, but is filled to sea level by sediment from the Colorado River. Unlike the southern Gulf, seafloor spreading has not initiated. Instead, seismicity, high heat flow, and minor volcanoes attest to ongoing rifting of thin, transitional crust. Recently acquired controlled-source seismic refraction and wide-angle reflection data in the Salton Trough provide constraints upon crustal architecture and active rift processes. The crust in the central Salton Trough is only 17-18 km thick, with a strongly layered but relatively one-dimensional structure for ~100 km in the direction of plate motion. The upper crust includes 2-4 km of Colorado River sediment. Crystalline rock below the sediment is interpreted to be similar sediment metamorphosed by the high heat flow and geothermal activity. Meta-sediment extends to at least 9 km depth. A 4-5 km thick layer in the middle crust is either additional meta-sediment or stretched pre-existing continental crust. The lowermost 4-5 km of the crust is rift-related mafic magmatic intrusion or underplating from partial melting in the hot upper mantle. North American lithosphere in the Salton Trough has been almost or completely rifted apart. The gap has been filled by ~100 km of new transitional crust created by magmatism from below and sedimentation from above. These processes create strong lithologic, thermal, and rheologic layering. While heat flow in the rift is very high, rapid sedimentation cools the upper crust as compared to a linear geotherm. Brittle extension occurs within new meta-sedimentary rock. The lower crust, in comparison, is maintained hot and weak by the overlying sedimentary thermal blanket. The lower crust stretches by ductile flow and magmatism is not localized. In this passive rift driven by distant plate motions, rapid sedimentation and its thermal effects delay final breakup of the crust and the onset of seafloor spreading.

Investigation of MHD flow structure and fluctuations by potassium lineshape fitting

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

Bauman, L.E.

1993-12-31

Multiple Potassium D-line emission absorption spectra from a high temperature, coal-fired flow have been fit to a radiative transfer, boundary layer flow model. The results of fitting spectra from the aerodynamic duct of the Department of Energy Coal-Fired Flow Facility provide information about the thickness and shape of the thermal boundary layer and the bulk potassium seed atom density in a simulated magnetohydrodynamic channel flow. Probability distribution functions for the entire set of more than six thousand spectra clearly indicate the typical values and magnitude of fluctuations for the flow: core temperature of 2538 {plus_minus} 20 K, near wall temperaturemore » of 1945 {plus_minus} 135 K, boundary layer width of about 1 cm, and potassium seed atom density of (5.1 {plus_minus} 0.8)x 10{sup 22}/m{sup 3}. Probability distribution functions for selected times during the eight hours of measurements indicate occasional periods of unstable combustion. In addition, broadband particle parameters during the unstable start of the test may be related to differing particle and gas temperatures. The results clearly demonstrate the ability of lineshape fitting to provide valuable data for diagnosing the high speed turbulent flow.« less

Fluid dynamic mechanisms and interactions within separated flows

NASA Astrophysics Data System (ADS)

Dutton, J. C.; Addy, A. L.

1990-02-01

The significant results of a joint research effort investigating the fundamental fluid dynamic mechanisms and interactions within high-speed separated flows are presented in detail. The results have obtained through analytical and numerical approaches, but with primary emphasis on experimental investigations of missile and projectile base flow-related configurations. The objectives of the research program focus on understanding the component mechanisms and interactions which establish and maintain high-speed separated flow regions. The analytical and numerical efforts have centered on unsteady plume-wall interactions in rocket launch tubes and on predictions of the effects of base bleed on transonic and supersonic base flowfields. The experimental efforts have considered the development and use of a state-of-the-art two component laser Doppler velocimeter (LDV) system for experiments with planar, two-dimensional, small-scale models in supersonic flows. The LDV experiments have yielded high quality, well documented mean and turbulence velocity data for a variety of high-speed separated flows including initial shear layer development, recompression/reattachment processes for two supersonic shear layers, oblique shock wave/turbulent boundary layer interactions in a compression corner, and two-stream, supersonic, near-wake flow behind a finite-thickness base.

A Reynolds stress model for near-wall turbulence

NASA Technical Reports Server (NTRS)

Durbin, P. A.

1993-01-01

The paper formulates a tensorially consistent near-wall second-order closure model. Redistributive terms in the Reynolds stress equations are modeled by an elliptic relaxation equation in order to represent strongly nonhomogeneous effects produced by the presence of walls; this replaces the quasi-homogeneous algebraic models that are usually employed, and avoids the need for ad hoc damping functions. The model is solved for channel flow and boundary layers with zero and adverse pressure gradients. Good predictions of Reynolds stress components, mean flow, skin friction, and displacement thickness are obtained in various comparisons to experimental and direct numerical simulation data. The model is also applied to a boundary layer flowing along a wall with a 90-deg, constant-radius, convex bend.

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

NASA Astrophysics Data System (ADS)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

Simulation of Flow Fluid in the BOF Steelmaking Process

NASA Astrophysics Data System (ADS)

Lv, Ming; Zhu, Rong; Guo, Ya-Guang; Wang, Yong-Wei

2013-12-01

The basic oxygen furnace (BOF) smelting process consists of different chemical reactions among oxygen, slag, and molten steel, which engenders a vigorous stirring process to promote slagging, dephosphorization, decarbonization, heating of molten steel, and homogenization of steel composition and temperature. Therefore, the oxygen flow rate, lance height, and slag thickness vary during the smelting process. This simulation demonstrated a three-dimensional mathematical model for a 100 t converter applying four-hole supersonic oxygen lance and simulated the effect of oxygen flow rate, lance height, and slag thickness on the flow of molten bath. It is found that as the oxygen flow rate increases, the impact area and depth increases, which increases the flow speed in the molten bath and decreases the area of dead zone. Low oxygen lance height benefits the increase of impact depth and accelerates the flow speed of liquid steel on the surface of the bath, while high oxygen lance height benefits the increase of impact area, thereafter enhances the uniform distribution of radial velocity in the molten steel and increases the flow velocity of molten steel at the bottom of furnace hearth. As the slag thickness increases, the diameter of impinging cavity on the slag and steel surface decreases. The radial velocity of liquid steel in the molten bath is well distributed when the jet flow impact on the slag layer increases.

Characterization of a multilayer aquifer using open well dilution tests.

PubMed

West, L Jared; Odling, Noelle E

2007-01-01

An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evolution allows discrete permeable layers within the aquifer to be identified. Dilution profiles for well sections between permeable layers are then converted into vertical borehole flow velocities and their evolution, using an analytic solution to the advection-dispersion equation applied to borehole flow. The dilution approach is potentially able to measure much smaller flow velocities that would be detectable using flowmeters. Vertical flow velocity data from the observation wells are then matched to those generated using a hydraulic model of the aquifer system, "shorted" by the observation wells, to yield the hydraulic properties of the constituent layers. Observation well flow monitoring of pumping tests represents a cost-effective alternative or preliminary approach to pump testing each layer of a multilayer aquifer system separately using straddle packers or screened wells and requires no prior knowledge of permeable layer depths and thicknesses. The modification described here, of using tracer dilution rather than flowmeter logging to obtain well flow velocities, allows the approach to be extended to greater well separations, thus characterizing a larger volume of the aquifer. An example of the application of this approach to a multilayer Chalk Aquifer in Yorkshire, Northeast England, is presented.

Stratigraphy of the 1902 and 1929 nuée-ardente deposits, Mt. Pelée, Martinique

NASA Astrophysics Data System (ADS)

Bourdier, J. L.; Boudon, G.; Gourgaud, A.

1989-08-01

Mild nuée ardentes in 1902-1903 and 1929-1930 at Mt. Pelée formed high-aspect ratio (H.A.R.) deposits (i.e. deposits with a high thickness/extent ratio) in the Rivière Blanche channel. Several violent nuées ardentes from May to August, 1902, yielded low aspect ratio (L.A.R.) deposits unevenly blanketing an area of 58 km 2 on the southwestern flank of the volcano. Three closely spaced nuées ardentes on August 30 additionally affected 56 km 2 on the southeastern flank. The L.A.R. deposits are divided into eight stratigraphic units (U1-U8), either compound or consisting of a single flow unit. The deposits of the largest nuées ardentes, on May 8, 20 and August 30, 1902 are identified as U1, U3 and U8, respectively, and can be traced over most of the area. Individual L.A.R. flow units are lenticular and show large, erratic lateral variations of thickness and grain-size. Most flow units consist of three distinct beds: Bed 1 is a few centimeters thick, lenticular, fines-depleted layer. Bed 2 is the thickest layer and contains more silt-sized ash than bed 1. It is normally graded as a whole, though reverse grading may occur in the lower part. Bed 2 generally consists of two parts: bed 2a, nonbedded, and bed 2b, finer-grained and laminated with cross-bedding and duned structures. Bed 3 is a thin, silty, capping layer which contains accretionary lapilli. The distribution of the L.A.R. flow units, especially of the coarse-grained facies, suggests that they were formed from overpressured blast-flows expanding radially from the vent at a high rate, in the same manner as the laterally directed blast of Mount St. Helens on May 18, 1980. The transport system of the major 1902 nuées ardentes was an inflated, relatively low-concentration, turbulent cloud as suggested by several lines of evidence: (1) the transported material was able to cross ridges up to 300 m high; (2) many scour-and-fill and other erosional features can be observed in the deposits at any distance from the vent; (3) survivors within the devastated area on May 8 did not experience a dense, low-profile cloud but instead a choking, hot ash-laden cloud; (4) many human corpses in St. Pierre remained where they fell instead of having floated away. If the current flow-surge terminology were to be used, the 1902 blast-flows would be better considered as pyroclastic surges. The normally graded, multi-layered structure of the flow units is also consistent with deposits primarily formed from relatively low-concentration flows.

Predicting active-layer soil thickness using topographic variables at a small watershed scale

PubMed Central

Li, Aidi; Tan, Xing; Wu, Wei; Liu, Hongbin; Zhu, Jie

2017-01-01

Knowledge about the spatial distribution of active-layer (AL) soil thickness is indispensable for ecological modeling, precision agriculture, and land resource management. However, it is difficult to obtain the details on AL soil thickness by using conventional soil survey method. In this research, the objective is to investigate the possibility and accuracy of mapping the spatial distribution of AL soil thickness through random forest (RF) model by using terrain variables at a small watershed scale. A total of 1113 soil samples collected from the slope fields were randomly divided into calibration (770 soil samples) and validation (343 soil samples) sets. Seven terrain variables including elevation, aspect, relative slope position, valley depth, flow path length, slope height, and topographic wetness index were derived from a digital elevation map (30 m). The RF model was compared with multiple linear regression (MLR), geographically weighted regression (GWR) and support vector machines (SVM) approaches based on the validation set. Model performance was evaluated by precision criteria of mean error (ME), mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2). Comparative results showed that RF outperformed MLR, GWR and SVM models. The RF gave better values of ME (0.39 cm), MAE (7.09 cm), and RMSE (10.85 cm) and higher R2 (62%). The sensitivity analysis demonstrated that the DEM had less uncertainty than the AL soil thickness. The outcome of the RF model indicated that elevation, flow path length and valley depth were the most important factors affecting the AL soil thickness variability across the watershed. These results demonstrated the RF model is a promising method for predicting spatial distribution of AL soil thickness using terrain parameters. PMID:28877196

Investigation of flow fields within large scale hypersonic inlet models

NASA Technical Reports Server (NTRS)

Gnos, A. V.; Watson, E. C.; Seebaugh, W. R.; Sanator, R. J.; Decarlo, J. P.

1973-01-01

Analytical and experimental investigations were conducted to determine the internal flow characteristics in model passages representative of hypersonic inlets for use at Mach numbers to about 12. The passages were large enough to permit measurements to be made in both the core flow and boundary layers. The analytical techniques for designing the internal contours and predicting the internal flow-field development accounted for coupling between the boundary layers and inviscid flow fields by means of a displacement-thickness correction. Three large-scale inlet models, each having a different internal compression ratio, were designed to provide high internal performance with an approximately uniform static-pressure distribution at the throat station. The models were tested in the Ames 3.5-Foot Hypersonic Wind Tunnel at a nominal free-stream Mach number of 7.4 and a unit free-stream Reynolds number of 8.86 X one million per meter.

A viscous-inviscid interactive compressor calculations

NASA Technical Reports Server (NTRS)

Johnston, W.; Sockol, P. M.

1978-01-01

A viscous-inviscid interactive procedure for subsonic flow is developed and applied to an axial compressor stage. Calculations are carried out on a two-dimensional blade-to-blade region of constant radius assumed to occupy a mid-span location. Hub and tip effects are neglected. The Euler equations are solved by MacCormack's method, a viscous marching procedure is used in the boundary layers and wake, and an iterative interaction scheme is constructed that matches them in a way that incorporates information related to momentum and enthalpy thicknesses as well as the displacement thickness. The calculations are quasi-three-dimensional in the sense that the boundary layer and wake solutions allow for the presence of spanwise (radial) velocities.

Modern aspects of nonlinear convection and magnetic field in flow of thixotropic nanofluid over a nonlinear stretching sheet with variable thickness

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Qayyum, Sajid; Alsaedi, Ahmed; Ahmad, Bashir

2018-05-01

Main objective of present analysis is to study the magnetohydrodynamic (MHD) nonlinear convective flow of thixotropic nanofluid. Flow is due to nonlinear stretching surface with variable thickness. Nonlinear thermal radiation and heat generation/absorption are utilized in the energy expression. Convective conditions and zero mass flux at sheet are considered. Intention in present analysis is to develop a model for nanomaterial comprising Brownian motion and thermophoresis phenomena. Appropriate transformations are implemented for the conversion of partial differential systems into a sets of ordinary differential equations. The transformed expressions have been scrutinized through homotopic algorithm. Behavior of various sundry variables on velocity, temperature, nanoparticle concentration, skin friction coefficient and local Nusselt number are displayed through graphs. It is concluded that qualitative behaviors of temperature and thermal layer thickness are similar for radiation and temperature ratio variables. Moreover an enhancement in heat generation/absorption show rise to thermal field.

Hydraulic transport across hydrophilic and hydrophobic nanopores: Flow experiments with water and n-hexane.

PubMed

Gruener, Simon; Wallacher, Dirk; Greulich, Stefanie; Busch, Mark; Huber, Patrick

2016-01-01

We experimentally explore pressure-driven flow of water and n-hexane across nanoporous silica (Vycor glass monoliths with 7- or 10-nm pore diameters, respectively) as a function of temperature and surface functionalization (native and silanized glass surfaces). Hydraulic flow rates are measured by applying hydrostatic pressures via inert gases (argon and helium, pressurized up to 70 bar) on the upstream side in a capacitor-based membrane permeability setup. For the native, hydrophilic silica walls, the measured hydraulic permeabilities can be quantitatively accounted for by bulk fluidity provided we assume a sticking boundary layer, i.e., a negative velocity slip length of molecular dimensions. The thickness of this boundary layer is discussed with regard to previous capillarity-driven flow experiments (spontaneous imbibition) and with regard to velocity slippage at the pore walls resulting from dissolved gas. Water flow across the silanized, hydrophobic nanopores is blocked up to a hydrostatic pressure of at least 70 bar. The absence of a sticking boundary layer quantitatively accounts for an enhanced n-hexane permeability in the hydrophobic compared to the hydrophilic nanopores.

Numerical investigation of an internal layer in turbulent flow over a curved hill

NASA Technical Reports Server (NTRS)

Kim, S-W.

1989-01-01

The development of an internal layer in a turbulent boundary layer flow over a curved hill is investigated numerically. The turbulence field of the boundary layer flow over the curved hill is compared with that of a turbulent flow over a symmetric airfoil (which has the same geometry as the curved hill except that the leading and trailing edge plates were removed) to study the influence of the strongly curved surface on the turbulence field. The turbulent flow equations are solved by a control-volume based finite difference method. The turbulence is described by a multiple-time-scale turbulence model supplemented with a near-wall turbulence model. Computational results for the mean flow field (pressure distributions on the walls, wall shearing stresses and mean velocity profiles), the turbulence structure (Reynolds stress and turbulent kinetic energy profiles), and the integral parameters (displacement and momentum thicknesses) compared favorably with the measured data. Computational results show that the internal layer is a strong turbulence field which is developed beneath the external boundary layer and is located very close to the wall. Development of the internal layer was more obviously observed in the Reynolds stress profiles and in the turbulent kinetic energy profiles than in the mean velocity profiles. In this regard, the internal layers is significantly different from wall-bounded simple shear layers in which the mean velocity profile characterizes the boundary layer most distinguishably. Development of such an internal layer, characterized by an intense turbulence field, is attributed to the enormous mean flow strain rate caused by the streamline curvature and the strong pressure gradient. In the turbulent flow over the curved hill, the internal layer begin to form near the forward corner of the hill, merges with the external boundary layer, and develops into a new fully turbulent boundary layer as the fluid flows in the downstream direction. For the flow over the symmetric airfoil, the boundary layer began to form from almost the same location as that of the curved hill, grew in its strength, and formed a fully turbulent boundary layer from mid-part of the airfoil and in the downstream region. Computational results also show that the detailed turbulence structure in the region very close to the wall of the curved hill is almost the same as that of the airfoil in most of the curved regions except near the leading edge. Thus the internal layer of the curved hill and the boundary layer of the airfoil were also almost the same. Development of the wall shearing stress and separation of the boundary layer at the rear end of the curved hill mostly depends on the internal layer and is only slightly influenced by the external boundary layer flow.

Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites

NASA Astrophysics Data System (ADS)

Blancon, J.-C.; Tsai, H.; Nie, W.; Stoumpos, C. C.; Pedesseau, L.; Katan, C.; Kepenekian, M.; Soe, C. M. M.; Appavoo, K.; Sfeir, M. Y.; Tretiak, S.; Ajayan, P. M.; Kanatzidis, M. G.; Even, J.; Crochet, J. J.; Mohite, A. D.

2017-03-01

Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum wells has enabled high-efficiency optoelectronic devices. Two-dimensional (2D) Ruddlesden-Popper perovskites are solution-processed quantum wells wherein the band gap can be tuned by varying the perovskite-layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite-crystal units (>1.3 nanometers) is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers. These states provide a direct pathway for dissociating excitons into longer-lived free carriers that substantially improve the performance of optoelectronic devices.

The electrical resistance of gold-capped chromium thin films

NASA Astrophysics Data System (ADS)

Ohashi, Masashi; Sawabu, Masaki; Ohashi, Kohei; Miyagawa, Masahiro; Maeta, Kae; Kubota, Takahide; Takanashi, Koki

2018-03-01

We studied the electrical resistance of polycrystalline chromium films capped by a gold layer. No anomaly was detected by resistance measurements of 10 nm thick film around room temperature, indicating that the antiferromagnetic interaction may be suppressed as decreasing the thickness of the chromium film. The sheet resistance Rs (T) curves differ from polycrystalline chromium films in previous studies because of the electrical current flows through a gold capping layer. On the other hand, the resistance drop is observed at T C = 1.15±0.05 K as that of polycrystalline chromium films in the previous report. It means that such resistance drop is not related to the chromium oxide layer on a polycrystalline chromium films. However, it is difficult to conclude that superconducting transition occurs because of the large residual resistance below the temperature where the resistance drop is observed.

An experimental study of the wall-pressure fluctuations beneath low Reynolds number turbulent boundary layers.

PubMed

Van Blitterswyk, Jared; Rocha, Joana

2017-02-01

A more complete understanding of the physical relationships, between wall-pressure and turbulence, is required for modeling flow-induced noise and developing noise reduction strategies. In this study, the wall-pressure fluctuations, induced by low Reynolds number turbulent boundary layers, are experimentally studied using a high-resolution microphone array. Statistical characteristics obtained using traditional cross-correlation and cross-spectra analyses are complimented with wall-pressure-velocity cross-spectra and wavelet cross-correlations. Wall-pressure-velocity correlations revealed that turbulent activity in the buffer layer contributes at least 40% of the energy to the wall-pressure spectrum at all measured frequencies. As Reynolds number increases, the low-frequency energy shifts from the buffer layer to the logarithmic layer, as expected for regions of uniform streamwise momentum formed by hairpin packets. Conditional cross-spectra suggests that the majority of broadband wall-pressure energy is concentrated within the packets, with the pressure signatures of individual hairpin vortices estimated to decay on average within traveling ten displacement thicknesses, and the packet signature is retained for up to seven boundary layer thicknesses on average.

A Real-Time Method for Estimating Viscous Forebody Drag Coefficients

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Hurtado, Marco; Rivera, Jose; Naughton, Jonathan W.

2000-01-01

This paper develops a real-time method based on the law of the wake for estimating forebody skin-friction coefficients. The incompressible law-of-the-wake equations are numerically integrated across the boundary layer depth to develop an engineering model that relates longitudinally averaged skin-friction coefficients to local boundary layer thickness. Solutions applicable to smooth surfaces with pressure gradients and rough surfaces with negligible pressure gradients are presented. Model accuracy is evaluated by comparing model predictions with previously measured flight data. This integral law procedure is beneficial in that skin-friction coefficients can be indirectly evaluated in real-time using a single boundary layer height measurement. In this concept a reference pitot probe is inserted into the flow, well above the anticipated maximum thickness of the local boundary layer. Another probe is servomechanism-driven and floats within the boundary layer. A controller regulates the position of the floating probe. The measured servomechanism position of this second probe provides an indirect measurement of both local and longitudinally averaged skin friction. Simulation results showing the performance of the control law for a noisy boundary layer are then presented.

Membrane catalyst layer for fuel cells

DOEpatents

Wilson, Mahlon S.

1993-01-01

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors

NASA Technical Reports Server (NTRS)

Grimes, C. A.; Kouzoudis, D.

2000-01-01

Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al2O3 that reversibly changes mass in response to humidity. c2000 Elsevier Science S.A. All rights reserved.

Evidence of unfrozen liquids and seismic anisotropy at the base of the polar ice sheets

NASA Astrophysics Data System (ADS)

Wittlinger, Gérard; Farra, Véronique

2015-03-01

We analyze seismic data from broadband stations located on the Antarctic and Greenland ice sheets to determine polar ice seismic velocities. P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P-receiver functions) are used to estimate in-situ P-wave velocity (Vp) and P-to-S velocity ratio (Vp/Vs) of polar ice. We find that the polar ice sheets have a two-layer structure; an upper layer of variable thickness (about 2/3 of the total thickness) with seismic velocities close to the standard ice values, and a lower layer of approximately constant thickness with standard Vp but ∼25% smaller Vs. The lower layer ceiling corresponds approximately to the -30 °C isotherm. Synthetic modeling of P-receiver functions shows that strong seismic anisotropy and low vertical S velocity are needed in the lower layer. The seismic anisotropy results from the preferred orientation of ice crystal c-axes toward the vertical. The low vertical S velocity may be due to the presence of unfrozen liquids resulting from premelting at grain joints and/or melting of chemical solutions buried in the ice. The strongly preferred ice crystal orientation fabric and the unfrozen fluids may facilitate polar ice sheet basal flow.

Modeling of flow-induced shear stress applied on 3D cellular scaffolds: Implications for vascular tissue engineering.

PubMed

Lesman, Ayelet; Blinder, Yaron; Levenberg, Shulamit

2010-02-15

Novel tissue-culture bioreactors employ flow-induced shear stress as a means of mechanical stimulation of cells. We developed a computational fluid dynamics model of the complex three-dimensional (3D) microstructure of a porous scaffold incubated in a direct perfusion bioreactor. Our model was designed to predict high shear-stress values within the physiological range of those naturally sensed by vascular cells (1-10 dyne/cm(2)), and will thereby provide suitable conditions for vascular tissue-engineering experiments. The model also accounts for cellular growth, which was designed as an added cell layer grown on all scaffold walls. Five model variants were designed, with geometric differences corresponding to cell-layer thicknesses of 0, 50, 75, 100, and 125 microm. Four inlet velocities (0.5, 1, 1.5, and 2 cm/s) were applied to each model. Wall shear-stress distribution and overall pressure drop calculations were then used to characterize the relation between flow rate, shear stress, cell-layer thickness, and pressure drop. The simulations showed that cellular growth within 3D scaffolds exposes cells to elevated shear stress, with considerably increasing average values in correlation to cell growth and inflow velocity. Our results provide in-depth analysis of the microdynamic environment of cells cultured within 3D environments, and thus provide advanced control over tissue development in vitro. 2009 Wiley Periodicals, Inc.

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

Seo, Jooyeok; Lee, Chulyeon; Han, Hyemi

We report a tactile touch sensor based on a planar liquid crystal-gated-organic field-effect transistor (LC-g-OFET) structure. The LC-g-OFET touch sensors were fabricated by forming the 10 μm thick LC layer (4-cyano-4{sup ′}-pentylbiphenyl - 5CB) on top of the 50 nm thick channel layer (poly(3-hexylthiophene) - P3HT) that is coated on the in-plane aligned drain/source/gate electrodes (indium-tin oxide - ITO). As an external physical stimulation to examine the tactile touch performance, a weak nitrogen flow (83.3 μl/s) was employed to stimulate the LC layer of the touch device. The LC-g-OFET device exhibited p-type transistor characteristics with a hole mobility of 1.5more » cm{sup 2}/Vs, but no sensing current by the nitrogen flow touch was measured at sufficiently high drain (V{sub D}) and gate (V{sub G}) voltages. However, a clear sensing current signal was detected at lower voltages, which was quite sensitive to the combination of V{sub D} and V{sub G}. The best voltage combination was V{sub D} = −0.2 V and V{sub G} = −1 V for the highest ratio of signal currents to base currents (i.e., signal-to-noise ratio). The change in the LC alignment upon the nitrogen flow touch was assigned as the mechanism for the present LC-g-OFET touch sensors.« less

Stratigraphy and Geochemistry of a Fond St. Jean Cinder Cone, Dominica

NASA Astrophysics Data System (ADS)

Isenburg, T.; Frey, H. M.; Waters, L. E.; Dunn, S.; Manon, M. R. F.

2017-12-01

Current geologic maps of Dominica generally classify the south-eastern portion of the island surrounding the Foundland stratovolcano as "mafic breccias and thin lava flows of Foundland center" (Smith et al. 2013). A detailed survey of the stratigraphy of a road cut at Fond St. Jean provides evidence for a mafic cinder cone on the flanks of Foundland. The 39 m thick stratigraphic sequence, dipping 60˚ north, includes a basal unit of scoria overlain by a meter of basaltic breccia and repeating layers of massive and rubbly flows, which range from 1 to 10 m in thickness. These flows transition into an additional, 2 m thick scoria deposit capped by a meter of massive basalt, which sits beneath another 3-4 m scoria deposit. Another layer of massive flow then transitions to three units of alternating air fall and ash lenses. Air fall units are 0.5 m in thickness but pinch and swell regularly, and ash lenses are roughly 10 cm thick. All units contain plagioclase + olivine + clinopyroxene + orthopyroxene + titanomagnetite. Though the phase assemblage is consistent between basaltic units, different crystal morphologies serve to define individual massive flows. Variations in the texture of materials deposited by the cinder cone provides evidence for cyclic explosive and effusive episodes. Massive samples at the bottom of the stratigraphic section contain abundant, large olivine and tabular, elongate plagioclase. Plagioclase compositions between individual stratigraphic units span a similar range in composition. Massive flows throughout the column contain similar, weakly zoned plagioclase cores (An84-94) with 10-30 µm sodic rims (An58-78; most rims are 68). Plagioclase microlites (long axes ≤100µm) span a wide range of compositions (An50-90). Three different air fall units contain plagioclase rims ranging in composition from An58-86 and cores ranging from An84-92, with the exception of a single core that has a composition of An61. Olivine in most units ranges in composition from Fo55-70. Spinels are ubiquitous throughout each of the units in the section and are consistently titanomagnetites. The potential genetic relationship between the cinder cone and Foundland is unclear, as the Foundland basalts are olivine-poor and contain amphibole, suggesting a wetter source magma for Foundland.

Downstream influence of swept slot injection in hypersonic turbulent flow

NASA Technical Reports Server (NTRS)

Hefner, J. N.; Cary, A. M., Jr.; Bushnell, D. B.

1977-01-01

Results of an experimental and numerical investigation of tangential swept slot injection into a thick turbulent boundary layer at Mach 6 are presented. Film cooling effectiveness, skin friction, and flow structure downstream of the swept slot injection were investigated. The data were compared with that for unswept slots, and it was found that cooling effectiveness and skin friction reductions are not significantly affected by sweeping the slot.

Control of unsteadiness of a shock wave/turbulent boundary layer interaction by using a pulsed-plasma-jet actuator

NASA Astrophysics Data System (ADS)

Narayanaswamy, Venkateswaran; Raja, Laxminarayan L.; Clemens, Noel T.

2012-07-01

A pulsed-plasma jet actuator is used to control the unsteady motion of the separation shock of a shock wave/boundary layer interaction formed by a compression ramp in a Mach 3 flow. The actuator is based on a plasma-generated synthetic jet and is configured as an array of three jets that can be injected normal to the cross-flow, pitched, or pitched and skewed. The typical peak jet exit velocity of the actuators is about 300 m/s and the pulsing frequencies are a few kilohertz. A study of the interaction between the pulsed-plasma jets and the shock/boundary layer interaction was performed in a time-resolved manner using 10 kHz schlieren imaging. When the actuator, pulsed at StL ≈ 0.04 (f = 2 kHz), was injected into the upstream boundary layer, the separation shock responded to the plasma jet by executing a rapid upstream motion followed by a gradual downstream recovery motion. Schlieren movies of the interaction showed that the separation shock unsteadiness was locked to the pulsing frequency of the actuator, with amplitude of about one boundary layer thickness. Wall-pressure measurements made under the intermittent region showed about a 30% decrease in the overall magnitude of the pressure fluctuations in the low-frequency band associated with unsteady large-scale motion of the separated flow. Furthermore, by increasing the pulsing frequency to 3.3 kHz, the amplitude of the separation shock oscillation was reduced to less than half the boundary layer thickness. Investigation into the effect of the actuator location on the shock wave/boundary layer interaction (SWBLI) showed qualitatively and quantitatively that the actuator placed upstream of the separation shock caused significant modification to the SWBLI unsteadiness, whereas injection from inside the separation bubble did not cause a noticeable effect.

Numerical investigation of internal high-speed viscous flows using a parabolic technique

NASA Technical Reports Server (NTRS)

Anderson, O. L.; Power, G. D.

1985-01-01

A feasibility study has been conducted to assess the applicability of an existing parabolic analysis (ADD-Axisymmetric Diffuser Duct), developed previously for subsonic viscous internal flows, to mixed supersonic/subsonic flows with heat addition simulating a SCRAMJET combustor. A study was conducted with the ADD code modified to include additional convection effects in the normal momentum equation when supersonic expansion and compression waves are present. A set of test problems with weak shock and expansion waves have been analyzed with this modified ADD method and stable and accurate solutions were demonstrated provided the streamwise step size was maintained at levels larger than the boundary layer displacement thickness. Calculations made with further reductions in step size encountered departure solutions consistent with strong interaction theory. Calculations were also performed for a flow field with a flame front in which a specific heat release was imposed to simulate a SCRAMJET combustor. In this case the flame front generated relatively thick shear layers which aggravated the departure solution problem. Qualitatively correct results were obtained for these cases using a marching technique with the convective terms in the normal momentum equation suppressed. It is concluded from the present study that for the class of problems where strong viscous/inviscid interactions are present a global iteration procedure is required.

Analysis of an anisotropic coastal aquifer system using variable-density flow and solute transport simulation

USGS Publications Warehouse

Souza, W.R.; Voss, C.I.

1987-01-01

The groundwater system in southern Oahu, Hawaii consists of a thick, areally extensive freshwater lens overlying a zone of transition to a thick saltwater body. This system is analyzed in cross section with a variable-density groundwater flow and solute transport model on a regional scale. The simulation is difficult, because the coastal aquifer system has a saltwater transition zone that is broadly dispersed near the discharge area, but is very sharply defined inland. Steady-state simulation analysis of the transition zone in the layered basalt aquifer of southern Oahu indicates that a small transverse dispersivity is characteristic of horizontal regional flow. Further, in this system flow is generally parallel to isochlors and steady-state behavior is insensitive to the longitudinal dispersivity. Parameter analysis identifies that only six parameters control the complex hydraulics of the system: horizontal and vertical hydraulic conductivity of the basalt aquifer; hydraulic conductivity of the confining "caprock" layer; leakance below the caprock; specific yield; and aquifer matrix compressibility. The best-fitting models indicate the horizontal hydraulic conductivity is significantly greater than the vertical hydraulic conductivity. These models give values for specific yield and aquifer compressibility which imply a considerable degree of compressive storage in the water table aquifer. ?? 1987.

Linear flow dynamics near a T/NT interface

NASA Astrophysics Data System (ADS)

Teixeira, Miguel; Silva, Carlos

2011-11-01

The characteristics of a suddenly-inserted T/NT interface separating a homogeneous and isotropic shear-free turbulence region from a non-turbulent flow region are investigated using rapid distortion theory (RDT), taking full account of viscous effects. Profiles of the velocity variances, TKE, viscous dissipation rate, turbulence length scales, and pressure statistics are derived, showing very good agreement with DNS. The normalized inviscid flow statistics at the T/NT interface do not depend on the form of the assumed TKE spectrum. In the non-turbulent region, where the flow is irrotational (except within a thin viscous boundary layer), the dissipation rate decays as z-6, where z is distance from the T/NT interface. The mean pressure exhibits a decrease towards the turbulence due to the associated velocity fluctuations, consistent with the generation of a mean entrainment velocity. The vorticity variance and dissipation rate display large maxima at the T/NT interface due to the existing inviscid discontinuities of the tangential velocity, and these maxima are quantitatively related to the thickness of the viscous boundary layer (VBL). At equilibrium, RDT suggests that the thickness of the T/NT interface scales on the Kolmogorov microscale. We acknowledge the financial support of FCT under Project PTDC/EME-MFE/099636/2008.

A model for capillary rise in micro-tube restrained by a sticky layer

NASA Astrophysics Data System (ADS)

Shen, Anqi; Xu, Yun; Liu, Yikun; Cai, Bo; Liang, Shuang; Wang, Fengjiao

2018-06-01

Fluid transport in a microscopic capillary under the effects of a sticky layer was theoretically investigated. A model based on the classical Lucas-Washburn (LW) model is proposed for the meniscus rise with the sticky layer present. The sticky layer consists of two parts: a fixed (located at the wall) and a movable part (located on the inside of the capillary), affecting the micro-capillary flow in different ways. Within our model, the movable layer is defined by the capillary radius and pressure gradient. From the model it follows that the fixed sticky layer leads to a decrease of capillary radius, while the movable sticky layer increases flow resistance. The movable layer thickness varies with the pressure gradient, which in turn varies with the rising of the meniscus. The results of our theoretical calculation also prove that the capillary radius has a greater effect on the meniscus height, rather than the additional resistance caused by the movable layer. Moreover, the fixed sticky layer, which affects the capillary radius, has a greater influence than the movable sticky layer. We conclude that the sticky layer causes a lower imbibition height than the LW model predicts.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, expressions provide the temperature distribution and heat flow for a diffusing medium with a continually varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Flow visualization of discrete hole film cooling for gas turbine applications

NASA Technical Reports Server (NTRS)

Colladay, R. S.; Russell, L. M.

1975-01-01

Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied for three different hole angles: (1) normal, (2) slanted 30 deg to the surface in the direction of the mainstream, and (3) slanted 30 deg to the surface and 45 deg laterally to the mainstream. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing very small neutrally buoyant helium filled 'soap' bubbles which follow the flow field. Unlike smoke, which diffuses rapidly in the high turbulent mixing region associated with discrete hole blowing, the bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, the analytical expressions provide the temperature distribution and heat flow for a diffusing medium with a continuously varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Travelling waves above the canopy of aquatic vegetation

NASA Astrophysics Data System (ADS)

Lyubimov, D.; Lyubimova, T.; Baidina, D.

2012-04-01

When fluid moves over a saturated porous medium with high permeability and porosity, the flow partially involves the fluid in porous medium, however, because of the great resistance force there arises sharp drop of tangential velocity. This leads to the development of instability similar to the Kelvin-Helmholtz instability on discontinuity surface of the tangential velocities of homogeneous fluids. Analogy becomes even more complete if we take into account the deformability of porous medium under the influence of pressure changes. Intensive vortices above the canopy of aquatic vegetation can lead to the coherent oscillations of vegetation, such traveling waves are called monami [1]. In the present paper we investigate stability of steady flow over a saturated porous medium. The importance of this problem is related to the applications to the dynamics of pollutants in the bottom layer of vegetation: the accumulation at low flow and salvo emissions with increasing velocity. We consider a two-layer system consisting of a layer of a viscous incompressible fluid and porous layer saturated with the same fluid located underneath. The lower boundary of the system is assumed to be rigid, the upper boundary - free and non-deformable. Weak slope of the river is taken into account. The problem is solved within the framework of single approach in which a two-layer system is described by a single system of equations for saturated porous medium and the presence of two layers is modeled by introducing variable permeability and porosity, depending on vertical coordinate. The flow in a saturated porous medium is described by the Brinkman model. Solution of the problem for steady flow shows that the velocity profile has two inflection points, which leads to the instability. The neutral curves are obtained for different values of the ratio d of porous layer thickness to full thickness. It is found that the dependence of critical Reynolds number on d is non-monotonic and the wave number of most dangerous perturbations increases monotonically with d. The effect of the deformability of porous medium on linear stability conditions is also investigated. Non-linear flow regimes are studied numerically by finite difference method. The calculations are performed for the rectangular domains whose length is taken to be equal to the wavelength of most dangerous perturbations according to linear stability theory. The calculations show that for low values of Reynolds number the stationary uni-directional flow is realized. Starting from a certain Reynolds number, the stationary oscillations are established with amplitude and frequency depending on the parameters. Analysis of the velocity fields corresponding to different phases of the oscillation period, shows that the observed waves travel in the direction of the basic flow. The work was made under financial support of Russian Foundation for Basic Research. 1. Ghisalberti, M., Nepf, H.M., 2002, Mixing layers and coherent structures in vegetated aquatic flows, J. of Geophysical Research. 107, C2.

Impact experiments in viscous fluid media

NASA Technical Reports Server (NTRS)

Greeley, R.

1984-01-01

Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. The resulting models, for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-veocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studied. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SHSV in the vicinity of the low-velocity zone. Near the East Pacific Rise, however, SVSH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of about 50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures A new model for Average Earth is obtained which includes a thin LID. This model extends the fit of a P.R.E.M. type model to shorter period surface waves.

Uniform Deposition of Protein Incorporated Mineral Layer on Three-Dimensional Porous Polymer Scaffolds

PubMed Central

Segvich, Sharon; Smith, Hayes C.; Luong, Linh N.; Kohn, David H.

2009-01-01

Inorganic–organic hybrid materials designed to facilitate bone tissue regeneration use a calcium phosphate mineral layer to encourage cell adhesion, proliferation, and osteogenic differentiation. Mineral formed on porous materials is often discontinuous through the thickness of the scaffold. This study aimed to uniformly coat the pores of three-dimensional (3D) porous, polymer scaffolds with a bone-like mineral layer in addition to uniformly incorporating a model protein within this mineral layer. A filtration system designed to induce simulated body fluid flow through the interstices of 3D polylactic-co-glycolic acid scaffolds (10-mm diameter × 2-mm thickness) illustrated that a uniform, continuous mineral layer can be precipitated on the pore surfaces of a 3D porous structure within 5 days. MicroCT analysis showed increased mineral volume percent (MV%) (7.86 ± 3.25 MV%, p = 0.029) and continuous mineralization of filtered scaffolds compared with two static control groups (floating, 0.16 ± 0.26 MV% and submerged, 0.20 ± 0.01 MV%). Furthermore, the system was effective in coprecipitating a model protein, bone sialoprotein (BSA), within the mineral layer. A 10-fold increase in BSA incorporation was seen when coprecipitated filtered scaffolds (1308 ± 464 μg) were compared to a submerged static control group (139 ± 45 μg), p < 0.001. Confocal microscopy visually confirmed uniform coprecipitation of BSA throughout the thickness of the filtration scaffolds. The designed system enables 3D mineralization through the thickness of porous materials, and provides the option of including coprecipitated biomolecular cues within the mineral layer. This approach of providing a 3D conductive and osteoinductive environment could be conducive to bone tissue regeneration. PMID:17618505

Large eddy simulation of trailing edge noise

NASA Astrophysics Data System (ADS)

Keller, Jacob; Nitzkorski, Zane; Mahesh, Krishnan

2015-11-01

Noise generation is an important engineering constraint to many marine vehicles. A significant portion of the noise comes from propellers and rotors, specifically due to flow interactions at the trailing edge. Large eddy simulation is used to investigate the noise produced by a turbulent 45 degree beveled trailing edge and a NACA 0012 airfoil. A porous surface Ffowcs-Williams and Hawkings acoustic analogy is combined with a dynamic endcapping method to compute the sound. This methodology allows for the impact of incident flow noise versus the total noise to be assessed. LES results for the 45 degree beveled trailing edge are compared to experiment at M = 0 . 1 and Rec = 1 . 9 e 6 . The effect of boundary layer thickness on sound production is investigated by computing using both the experimental boundary layer thickness and a thinner boundary layer. Direct numerical simulation results of the NACA 0012 are compared to available data at M = 0 . 4 and Rec = 5 . 0 e 4 for both the hydrodynamic field and the acoustic field. Sound intensities and directivities are investigated and compared. Finally, some of the physical mechanisms of far-field noise generation, common to the two configurations, are discussed. Supported by Office of Naval research.

Mechanical characterization and durability of sintered porous transport layers for polymer electrolyte membrane electrolysis

NASA Astrophysics Data System (ADS)

Borgardt, Elena; Panchenko, Olha; Hackemüller, Franz Josef; Giffin, Jürgen; Bram, Martin; Müller, Martin; Lehnert, Werner; Stolten, Detlef

2018-01-01

Differential pressure electrolysis offers the potential for more efficient hydrogen compression. Due to the differential pressures acting within the electrolytic cell, the porous transport layer (PTL) is subjected to high stress. For safety reasons, the PTL's mechanical stability must be ensured. However, the requirements for high porosity and low thickness stand in contrast to that for mechanical stability. Porous transport layers for polymer electrolyte membrane (PEM) electrolysis are typically prepared by means of the thermal sintering of titanium powder. Thus far, the factors that influence the mechanical strength of the sintered bodies and how all requirements can be simultaneously fulfilled have not been investigated. Here, the static and dynamic mechanical properties of thin sintered titanium sheets are investigated ex-situ via tensile tests and periodic loading in a test cell, respectively. In order for a sintered PTL with a thickness of 500 μm and porosities above 25% to be able to withstand 50 bar differential pressure in the cell, the maximum flow field width should be limited to 3 mm. Thus, a method was developed to test the suitability of PTL materials for use in electrolysis for various differential pressures and flow field widths.

Layer-specific blood-flow MRI of retinitis pigmentosa in RCS rats☆

PubMed Central

Li, Guang; Garza, Bryan De La; Shih, Yen-Yu I.; Muir, Eric R.; Duong, Timothy Q.

2013-01-01

The Royal College of Surgeons (RCS) rat is an established animal model of retinitis pigmentosa, a family of inherited retinal diseases which starts with loss of peripheral vision and progresses to eventual blindness. Blood flow (BF), an important physiological parameter, is intricately coupled to metabolic function under normal physiological conditions and is perturbed in many neurological and retinal diseases. This study reports non-invasive high-resolution MRI (44 × 44 × 600 μm) to image quantitative retinal and choroidal BF and layer-specific retinal thicknesses in RCS rat retinas at different stages of retinal degeneration compared with age-matched controls. The unique ability to separate retinal and choroidal BF was made possible by the depth-resolved MRI technique. RBF decreased with progressive retinal degeneration, but ChBF did not change in RCS rats up to post-natal day 90. We concluded that choroidal and retinal circulations have different susceptibility to progressive retinal degeneration in RCS rats. Layer-specific retinal thickness became progressively thinner and was corroborated by histological analysis in the same animals. MRI can detect progressive anatomical and BF changes during retinal degeneration with laminar resolution. PMID:22721720

Layer-specific blood-flow MRI of retinitis pigmentosa in RCS rats.

PubMed

Li, Guang; De La Garza, Bryan; Shih, Yen-Yu I; Muir, Eric R; Duong, Timothy Q

2012-08-01

The Royal College of Surgeons (RCS) rat is an established animal model of retinitis pigmentosa, a family of inherited retinal diseases which starts with loss of peripheral vision and progresses to eventual blindness. Blood flow (BF), an important physiological parameter, is intricately coupled to metabolic function under normal physiological conditions and is perturbed in many neurological and retinal diseases. This study reports non-invasive high-resolution MRI (44 × 44 × 600 μm) to image quantitative retinal and choroidal BF and layer-specific retinal thicknesses in RCS rat retinas at different stages of retinal degeneration compared with age-matched controls. The unique ability to separate retinal and choroidal BF was made possible by the depth-resolved MRI technique. RBF decreased with progressive retinal degeneration, but ChBF did not change in RCS rats up to post-natal day 90. We concluded that choroidal and retinal circulations have different susceptibility to progressive retinal degeneration in RCS rats. Layer-specific retinal thickness became progressively thinner and was corroborated by histological analysis in the same animals. MRI can detect progressive anatomical and BF changes during retinal degeneration with laminar resolution. Copyright © 2012 Elsevier Ltd. All rights reserved.

Amazonian mid- to high-latitude glaciation on Mars: Supply-limited ice sources, ice accumulation patterns, and concentric crater fill glacial flow and ice sequestration

NASA Astrophysics Data System (ADS)

Fastook, James L.; Head, James W.

2014-02-01

Concentric crater fill (CCF) occurs in the interior of impact craters in mid- to high latitudes on Mars and is interpreted to have formed by glacial ice flow and debris covering. We use the characteristics and orientation of deposits comprising CCF, the thickness of pedestal deposits in mid- to high-latitude pedestal craters (Pd), the volumes of the current polar caps, and information about regional slopes and ice rheology to address questions about (1) the maximum thickness of regional ice deposits during the Late Amazonian, (2) the likelihood that these deposits flowed regionally, (3) the geological regions and features most likely to induce ice-flow, and (4) the locations and environments in which ice is likely to have been sequestered up to the present. We find that regional ice flow under Late Amazonian climate conditions requires ice thicknesses exceeding many hundreds of meters for slopes typical of the vast majority of the surface of Mars, a thickness for the mid-latitudes that is well in excess of the total volume available from polar ice reservoirs. This indicates that although conditions for mid- to high-latitude glaciation may have persisted for tens to hundreds of millions of years, the process is “supply limited”, with a steady state reached when the polar ice cap water ice supply becomes exhausted. Impact craters are by far the most abundant landform with associated slopes (interior wall and exterior rim) sufficiently high to induce glacial ice flow under Late Amazonian climate conditions, and topographic slope data show that Amazonian impact craters have been clearly modified, undergoing crater interior slope reduction and floor shallowing. We show that these trends are the predictable response of ice deposition and preferential accumulation and retention in mid- to high-latitude crater interiors during episodes of enhanced spin-axis obliquity. We demonstrate that flow from a single episode of an inter-crater terrain layer comparable to Pedestal Crater deposit thicknesses (~50 m) cannot fill the craters in a time period compatible with the interpreted formation times of the Pedestal Crater mantled ice layers. We use a representative obliquity solution to drive an ice flow model and show that a cyclical pattern of multiply recurring layers can both fill the craters with a significant volume of ice, as well as transport debris from the crater walls out into the central regions of the craters. The cyclical pattern of waxing and waning mantling layers results in a rippled pattern of surface debris extending out into the crater interiors that would manifest itself as an observable concentric pattern, comparable in appearance to concentric crater fill. In this scenario, the formation of mantling sublimation till layers seals the accumulating ice and sequesters it from significant temperature variations at diurnal, annual and spin-axis/orbital cycle time scales, to produce ancient ice records preserved today below CCF crater floors. Lack of meltwater features associated with concentric crater fill provides evidence that the Late Amazonian climate did not exceed the melting temperature in the mid- to high-latitudes for any significant period of time. Continued sequestration of ice with time in CCF and related deposits (lobate debris aprons and lineated valley fill) further reduces the already supply-limited polar ice sources, suggesting that there has been a declining reservoir of available ice with each ensuing glacial period. Together, these deposits represent a candidate library of climate chemistry and global change dating from the Late Amazonian, and a non-polar water resource for future exploration.

Structure development in melt processing isotactic polypropylene, polypropylene blends/compounds and dynamically vulcanized polyolefin TPEs

NASA Astrophysics Data System (ADS)

Yu, Yishan

The influence of various fillers, nucleating agents and ethylene propylene diene terpolymer (EPDM) additive on crystalline modification (alpha-, beta- and smectic forms) and crystalline orientation of polypropylene in die extrudates, melt spun filaments, thick rods, blow molded bottles and injection molded parts of isotactic polypropylene (PP), its blends/compounds and dynamically vulcanized polypropylene thermoplastic elastomers (TPEs) were experimentally studied under a range of cooling and processing conditions. The phenomena of crystallization, polymorphism and orientation in processing of both thin and thick samples (filaments, rods, bottles and injection molded parts) were simulated through transport laws incorporating polymer crystallization kinetics. Continuous cooling transformation (CCT) curves for the various material systems investigated were developed under quiescent and uniaxial stress conditions. We applied experimental data on polymorphism of thin sections to predict crystalline structure variation in thick parts. The predictions were consistent with experiments. For filaments, the polypropylene crystalline orientation-spinline stress relationship is generally similar for the neat PP, blends/compounds and TPEs. However, the blends and TPEs have much lower birefringence apparently due to a lack of orientation in the rubber phase. It was shown that the polypropylene contribution to the birefringence for the neat PP and its blends is the same at the same spinline stress. For bottles, the inflation pressures used have little effect on orientation of either polypropylene crystals or disc-shaped talc filler. The talc discs are highly oriented parallel to the bottle surface. For the bottles without talc, the orientation of polypropylene crystallographic axes are low. The polypropylene crystallographic b-axes in the talc filled bottles are more highly oriented. For injection molded parts, it was found that a low orientation layer exists between the part surface and an intermediate highly oriented layer in the parts of neat PP and its blends/compounds. The thickness of this layer increases as the injection pressure decreases. This layer was not formed in the TPE parts. This would seem to be associated with the TPEs exhibiting a yield stress in shear flow and not exhibiting fountain flow in mold filling. For all parts studied, the orientation characteristics of polypropylene crystallographic axes in the highly oriented layer are similar from sample to sample. The strong orientation of the c-axis parallel to the machine direction and the b-axis perpendicular to the machine direction are observed in the highly oriented layer. The talc discs in both the highly oriented layer and the intermediate position are highly oriented parallel to the part face due to melt flow. At intermediate position in the talc-filled parts, the polypropylene crystallographic (040) planes prefer to align themselves parallel to the part surface but are not so well oriented when the talc is absent.

A Composite Medium Approximation for Moisture Tension-Dependent Anisotropy in Unsaturated Layered Sediments

NASA Astrophysics Data System (ADS)

Pruess, K.

2001-12-01

Sedimentary formations often have a layered structure in which hydrogeologic properties have substantially larger correlation length in the bedding plane than perpendicular to it. Laboratory and field experiments and observations have shown that even small-scale layering, down to millimeter-size laminations, can substantially alter and impede the downward migration of infiltrating liquids, while enhancing lateral flow. The fundamental mechanism is that of a capillary barrier: at increasingly negative moisture tension (capillary suction pressure), coarse-grained layers with large pores desaturate more quickly than finer-grained media. This strongly reduces the hydraulic conductivity of the coarser (higher saturated hydraulic conductivity) layers, which then act as barriers to downward flow, forcing water to accumulate and spread near the bottom of the overlying finer-grained material. We present a "composite medium approximation" (COMA) for anisotropic flow behavior on a typical grid block scale (0.1 - 1 m or larger) in finite-difference models. On this scale the medium is conceptualized as consisting of homogeneous horizontal layers with uniform thickness, and capillary equilibrium is assumed to prevail locally. Directionally-dependent relative permeabilities are obtained by considering horizontal flow to proceed via "conductors in parallel," while vertical flow involves "resistors in series." The model is formulated for the general case of N layers, and implementation of a simplified two-layer (fine-coarse) approximation in the multiphase flow simulator TOUGH2 is described. The accuracy of COMA is evaluated by comparing numerical simulations of plume migration in 1-D and 2-D unsaturated flow with results of fine-grid simulations in which all layers are discretized explicitly. Applications to water seepage and solute transport at the Hanford site are also described. This work was supported by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098 through Memorandum Purchase Order 248861-A-B2 between Pacific Northwest National Laboratory and Lawrence Berkeley National Laboratory.

Normal stress effects on Knudsen flow

NASA Astrophysics Data System (ADS)

Eu, Byung Chan

2018-01-01

Normal stress effects are investigated on tube flow of a single-component non-Newtonian fluid under a constant pressure gradient in a constant temperature field. The generalized hydrodynamic equations are employed, which are consistent with the laws of thermodynamics. In the cylindrical tube flow configuration, the solutions of generalized hydrodynamic equations are exactly solvable and the flow velocity is obtained in a simple one-dimensional integral quadrature. Unlike the case of flow in the absence of normal stresses, the flow develops an anomaly in that the flow in the boundary layer becomes stagnant and the thickness of such a stagnant velocity boundary layer depends on the pressure gradient, the aspect ratio of the radius to the length of the tube, and the pressure (or density and temperature) at the entrance of the tube. The volume flow rate formula through the tube is derived for the flow. It generalizes the Knudsen flow rate formula to the case of a non-Newtonian stress tensor in the presence of normal stress differences. It also reduces to the Navier-Stokes theory formula in the low shear rate limit near equilibrium.

Fracture Networks from a deterministic physical model as 'forerunners' of Maze Caves

NASA Astrophysics Data System (ADS)

Ferer, M. V.; Smith, D. H.; Lace, M. J.

2013-12-01

'Fractures are the chief forerunners of caves because they transmit water much more rapidly than intergranular pores.[1] Thus, the cave networks can follow the fracture networks from which the Karst caves formed by a variety of processes. Traditional models of continental Karst define water flow through subsurface geologic formations, slowly dissolving the rock along the pathways (e.g. water saturated with respect to carbon dioxide flowing through fractured carbonate formations). We have developed a deterministic, physical model of fracturing in a model geologic layer of a given thickness, when that layer is strained in one direction and subsequently in a perpendicular direction. It was observed that the connected fracture networks from our model visually resemble maps of maze caves. Since these detailed cave maps offer critical tools in modeling cave development patterns and conduit flow in Karst systems, we were able to test the qualitative resemblance by using statistical analyses to compare our model networks in geologic layers of four different thicknesses with the corresponding statistical analyses of four different maze caves, formed in a variety of geologic settings. The statistical studies performed are: i) standard box-counting to determine if either the caves or the model networks are fractal. We found that both are fractal with a fractal dimension Df ≈ 1.75 . ii) for each section inside a closed path, we determined the area and perimeter-length, enabling a study of the tortuosity of the networks. From the dependence of the section's area upon its perimeter-length, we have found a power-law behavior (for sufficiently large sections) characterized by a 'tortuosity' exponent. These exponents have similar values for both the model networks and the maze caves. The best agreement is between our thickest model layer and the maze-like part of Wind Cave in South Dakota where the data from the model and the cave overlie each other. For the present networks from the physical model, we assumed that the geologic layer was of uniform thickness and that the strain in both directions were the same. The latter may not be the case for the Brazilian, Toca de Boa Cave. These assumptions can be easily modified in our computer code to reflect different geologic histories. Even so the quantitative agreement suggests that our model networks are statistically realistic both for the 'forerunners' of caves and for general fracture networks in geologic layers, which should assist the study of underground fluid flow in many applications for which fracture patterns and fluid flow are difficult to determine (e.g., hydrology, watershed management, oil recovery, carbon dioxide sequestration, etc.). Keywords - Fracture Networks, Karst, Caves, Structurally Variable Pathways, hydrogeological modeling 1 Arthur N. Palmer, CAVE GEOLOGY, pub. Cave Books, Dayton OH, (2007).

Calculations of electric currents in Europa

NASA Technical Reports Server (NTRS)

Colburn, D. S.; Reynolds, R. T.

1986-01-01

Electrical currents should flow in the Galilean satellite, Europa, because it is located in Jupiter's corotating magnetosphere. The possible magnitudes of these currents are calculated by assuming that Europa is a differentiated body consisting of an outer H2O layer and a silicate core. Two types of models are considered here: one in which the water is completely frozen and a second in which there is an intermediate liquid layer. For the transverse electric mode (eddy currents), the calculated current density in a liquid layer is approximately 10 to the -5/Am. For the transverse magnetic mode (unipolar generator), the calculated current density in the liquid is severely constrained by the ice layer to a range of only 10 to the -10 to -11th power/ Am, for a total H2O thickness of 100 km, provided that neither layer is less than 4 km thick. The current density is less for a completely frozen H2O layer. If transient cracks were to appear in the ice layer, thereby exposing liquid, the calculated current density could rise to a range of 10 to the -6 to 10 to the -5/Am, depending on layer thicknesses, which would require an exposed area of 10 to the -9 to 10 to the -8 of the Europa surface. The corresponding total current of 2.3x10 to the 5th power A could in 1 yr. electrolyze 7x10 to the 5th power kg of water (and more if the cells were in series), and thereby store up to 10 the 8th power J of energy, but it is not clear how electrolysis can take place in the absence of suitable electrodes. Electrical heating would be significant only if the ice-layer thickness were on the order of 1 m, such as might occur if an exposed liquid surface were to freeze over; the heating under this condition could hinder the thickening of the ice layer.

Electroosmosis over charge-modulated surfaces with finite electrical double layer thicknesses: Asymptotic and numerical investigations

NASA Astrophysics Data System (ADS)

Ghosh, Uddipta; Mandal, Shubhadeep; Chakraborty, Suman

2017-06-01

Here we attempt to solve the fully coupled Poisson-Nernst-Planck-Navier-Stokes equations, to ascertain the influence of finite electric double layer (EDL) thickness on coupled charge and fluid dynamics over patterned charged surfaces. We go beyond the well-studied "weak-field" limit and obtain numerical solutions for a wide range of EDL thicknesses, applied electric field strengths, and the surface potentials. Asymptotic solutions to the coupled system are also derived using a combination of singular and regular perturbation, for thin EDLs and low surface potential, and good agreement between the two solutions is observed. Counterintuitively to common arguments, our analysis reveals that finite EDL thickness may either increase or decrease the "free-stream velocity" (equivalent to net throughput), depending on the strength of the applied electric field. We also unveil a critical EDL thickness for which the effect of finite EDL thickness on the free-stream velocity is the most prominent. Finally, we demonstrate that increasing the surface potential and the applied field tends to influence the overall flow patterns in the contrasting manners. These results may be of profound importance in developing a comprehensive theoretical basis for designing electro-osmotically actuated microfluidic mixtures.

Extreme Events on a Low-Gradient River and Delta: Evidence for Sediment Mass Movements on the Subaqueous Delta and a Mechanism for Creating Hyperpycnal Flow onto the Shelf

NASA Astrophysics Data System (ADS)

Dellapenna, T. M.; Carlin, J. A.; Williams, J. R.

2016-02-01

The Brazos River empties into the Gulf of Mexico (GOM) forming a wave-influenced, muddy, subaqueous delta (SAD). Recent research in the estuarine reach of the river and on the SAD, however, found evidence for significant mass wasting of the delta-front and potential evidence of hyperpycnal flow, a processes typically associated with higher gradient and higher sediment yield rivers. The study used high-resolution geophysics on the SAD and water-column profiling in the lower river to investigate the transfer to and fate of fluvial sediment on the shelf. The SAD side scan mosaic combined with core data reveal that the eastern portion was dominated by exposed relict, consolidated sediment; an erosional scarp along the upper shoreface; and a thinning of the Holocene strata immediately downslope of the scarp. Holocene strata thickness increases into deeper water. These features suggest sediment mass wasting on the delta front. After rapidly prograding during the early and mid 20th century, reductions in sediment load due anthropogenic influences, and a shift in the primary depocenter lead to erosion on these abandoned portions of the delta. During an elevated fluvial discharge event, a >1 m thick fluid mud layer was found along a 6 km span of the river 2 km upstream from the mouth. The river's salt wedge was shown to inhibit sediment export from the river to the GOM, and facilitate deposition of mud in the lower river. We believe that the mud layer in the lower river builds during moderate and low discharge periods and remobilized during increased discharge, potentially resulting in hyperpyncnal flow to the shelf. We observed suspended sediment concentrations up to 100 g/l in the fluid mud layer during this event. While our observations did not capture the transition from fluid mud to hyperpycnal flow, we believe that with persistent increased discharge the fluid mud layer could transition to hyperpycnal flow.

Environmental Assessment of Installation Development at Fairchild Air Force Base, Washington

DTIC Science & Technology

2007-05-01

attributed to natural topography and AT/FP setback requirements. • Natural Topography. There are a number of basalt rock outcroppings within the JPRA...facility. A setback of 50 feet is required around each basalt rock outcropping. These outcroppings and setbacks limit 38.1 acres from potential...extent of the Miocene-aged Columbia Plateau lava flows. Layers of basalt might be as much as 500 feet thick with interbeds between layers of gravels

More-reliable SOS ion implantations

NASA Technical Reports Server (NTRS)

Woo, D. S.

1980-01-01

Conducting layer prevents static charges from accumulating during implantation of silicon-on-sapphire MOS structures. Either thick conducting film or thinner film transparent to ions is deposited prior to implantation, and gaps are etched in regions to be doped. Grounding path eliminates charge flow that damages film or cracks sapphire wafer. Prevention of charge buildup by simultaneously exposing structure to opposite charges requires equipment modifications less practical and more expensive than deposition of conducting layer.

Microstructural Evolution during Mid-Crustal Shear Zone Thickening and Thinning, Mount Irene Detachment Zone, Fiordland, New Zealand

NASA Astrophysics Data System (ADS)

Negrini, M.; Smith, S. A. F.; Scott, J.; Rooney, J. S.; Demurtas, M.

2016-12-01

Recent work has shown that ductile shear zones experience cyclic variations in stress and strain rate due to, for example, elastic loading from earthquake slip on brittle faults or the presence of rigid particles and asperities within the shear zone. Such non-steady state flow conditions can promote microstructural changes including a decrease in grain sizes followed by a switch in the main deformation mechanisms. Understanding the microstructural changes that occur during non steady-state deformation is therefore critical in evaluating shear zone rheology. The Mount Irene shear zone formed during Cretaceous extension in the middle crust and was active at temperatures of 600°C and pressures of 6 kbar. The shear zone localized in a basal calcite marble layer typically 3-5 m thick containing hundreds of thin (mm-cm) calc-silicate bands that are now parallel to the shear zone boundaries. The lower boundary of the shear zone preserves meter-scale undulations that cause the shear zone to be squeezed in to regions that are <1.5 m thick. The calc-silicate bands act as "flow markers" and allow individual shear zone layers to be traced continuously through thick and thin regions, implying that the mylonites experienced cyclic variations in stress and strain rate. Calc-mylonite samples collected from the same layer close to the base of the shear zone reveal that layer thinning was accompanied by progressive microstructural changes including intense twinning, stretching and flattening of large calcite porphyroclasts as well as the development of interconnected networks of recrystallized calcite aggregates. EBSD analysis shows that the recrystallized aggregates contain polygonal calcite grains with microstructures (e.g. grain quadruple junctions) similar to those reported for neighbor-switching processes associated with grain boundary sliding and superplasticity. Ongoing and future work will utilize samples from across the full thickness of the shear zone to determine key microstructural changes and deformation mechanisms that accommodated shear zone thinning and thickening during non-steady state deformation.

Applicability of preparative overpressured layer chromatography and direct bioautography in search of antibacterial chamomile compounds.

PubMed

Móricz, Agnes M; Ott, Péter G; Alberti, Agnes; Böszörményi, Andrea; Lemberkovics, Eva; Szoke, Eva; Kéry, Agnes; Mincsovics, Emil

2013-01-01

In situ sample preparation and preparative overpressured layer chromatography (OPLC) fractionation on a 0.5 mm thick adsorbent layer of chamomile flower methanol extract prepurified by conventional gravitation accelerated column chromatography were applied in searching for bioactive components. Sample cleanup in situ on the adsorbent layer subsequent to sample application was performed using mobile phase flow in the opposite direction (the input and output of the eluent was exchanged). The antibacterial effect of the fractions obtained from the stepwise gradient OPLC separation with the flow in the normal direction was evaluated by direct bioautography against two Gram-negative bacteria: the luminescence gene tagged plant pathogenic Pseudomonas syringae pv. maculicola, and the naturally luminescent marine bacterium Vibrio fischeri. The fractions having strong activity were analyzed by SPME-GC/MS and HPLC/MS/MS. Mainly essential oil components, coumarins, flavonoids, phenolic acids, and fatty acids were tentatively identified in the fractions.

An experimental study of the turbulent boundary layer on a transport wing in subsonic and transonic flow

NASA Technical Reports Server (NTRS)

Spaid, Frank W.; Roos, Frederick W.; Hicks, Raymond M.

1990-01-01

The upper surface boundary layer on a transport wing model was extensively surveyed with miniature yaw probes at a subsonic and a transonic cruise condition. Additional data were obtained at a second transonic test condition, for which a separated region was present at mid-semispan, aft of mid-chord. Significant variation in flow direction with distance from the surface was observed near the trailing edge except at the wing root and tip. The data collected at the transonic cruise condition show boundary layer growth associated with shock wave/boundary layer interaction, followed by recovery of the boundary layer downstream of the shock. Measurements of fluctuating surface pressure and wingtip acceleration were also obtained. The influence of flow field unsteadiness on the boundary layer data is discussed. Comparisons among the data and predictions from a variety of computational methods are presented. The computed predictions are in reasonable agreement with the experimental data in the outboard regions where 3-D effects are moderate and adverse pressure gradients are mild. In the more highly loaded mid-span region near the trailing edge, displacement thickness growth was significantly underpredicted, except when unrealistically severe adverse pressure gradients associated with inviscid calculations were used to perform boundary layer calculations.

Experimental evaluation of heat transfer on a 1030:1 area ratio rocket nozzle

NASA Technical Reports Server (NTRS)

Kacynski, Kenneth J.; Pavli, Albert J.; Smith, Tamara A.

1987-01-01

A 1030:1 carbon steel, heat-sink nozzle was tested. The test conditions included a nominal chamber pressure of 2413 kN/sq m and a mixture ratio range of 2.78 to 5.49. The propellants were gaseous oxygen and gaseous hydrogen. Outer wall temperature measurements were used to calculate the inner wall temperature and the heat flux and heat rate to the nozzle at specified axial locations. The experimental heat fluxes were compared to those predicted by the Two-Dimensional Kinetics (TDK) computer model analysis program. When laminar boundary layer flow was assumed in the analysis, the predicted values were within 15 percent of the experimental values for the area ratios of 20 to 975. However, when turbulent boundary layer conditions were assumed, the predicted values were approximately 120 percent higher than the experimental values. A study was performed to determine if the conditions within the nozzle could sustain a laminar boundary layer. Using the flow properties predicted by TDK, the momentum-thickness Reynolds number was calculated, and the point of transition to turbulent flow was predicted. The predicted transition point was within 0.5 inches of the nozzle throat. Calculations of the acceleration parameter were then made to determine if the flow conditions could produce relaminarization of the boundary layer. It was determined that if the boundary layer flow was inclined to transition to turbulent, the acceleration conditions within the nozzle would tend to suppress turbulence and keep the flow laminar-like.

Experimental evaluation of heat transfer on a 1030:1 area ratio rocket nozzle

NASA Technical Reports Server (NTRS)

Kacynski, Kenneth J.; Pavli, Albert J.; Smith, Tamara A.

1987-01-01

A 1030:1 carbon steel, heat-sink nozzle was tested. The test conditions included a nominal chamber pressure of 2413 kN/sq m and a mixture ratio range of 2.78 to 5.49. The propellants were gaseous oxygen and gaseous hydrogen. Outer wall temperature measurements were used to calculate the inner wall temperature and the heat flux and heat rate to the nozzle at specified axial locations. The experimental heat fluxes were compared to those predicted by the Two-Dimensional Kinetics (TDK) computer model analysis program. When laminar boundary layer flow was assumed in the analysis, the predicted values were within 15% of the experimental values for the area ratios of 20 to 975. However, when turbulent boundary layer conditions were assumed, the predicted values were approximately 120% higher than the experimental values. A study was performed to determine if the conditions within the nozzle could sustain a laminar boundary layer. Using the flow properties predicted by TDK, the momentum-thickness Reynolds number was calculated, and the point of transition to turbulent flow was predicted. The predicted transition point was within 0.5 inches of the nozzle throat. Calculations of the acceleration parameter were then made to determine if the flow conditions could produce relaminarization of the boundary layer. It was determined that if the boundary layer flow was inclined to transition to turbulent, the acceleration conditions within the nozzle would tend to suppress turbulence and keep the flow laminar-like.

Experimental Investigation of Vortex Structures in Wake of Hyperboloid-Shaped Model by Means of 2D Particle Image Velocimetry Measurement

NASA Astrophysics Data System (ADS)

Barraclough, V.; Novotný, J.; Šafařík, P.

2018-06-01

This paper deals with flow around a bluff body of hyperboloid shape. It consists of results gathered in the course of research by means of Particle Image Velocimetry (PIV). The experiments were carried out by means of low-frequency 2D PIV in a range of Reynolds numbers from 40000 to 50000. A hyperboloid-shaped model was measured in a wind tunnel with a modelled atmospheric boundary layer (and additionally, in a low-speed wind tunnel with low turbulence). The model was tested in a subcritical range of Reynolds numbers and various planes in a wake of the model were captured with the intention of getting an estimation of 3D flow structures. The tunnel with the modelled atmospheric boundary layer has a high rate of turbulence, so the influence of the turbulence of incoming flow on the wake could be outlined. The ratio of the height of the model to a thickness of the modelled boundary layer in the tunnel was 1/3, meaning the turbulence in the boundary layer strongly influenced the flow around the model; it suppresses the wake which leads to a lot shorter area of recirculation than low turbulence incoming flow would cause.

Steady flow and heat transfer analysis of Phan-Thein-Tanner fluid in double-layer optical fiber coating analysis with Slip Conditions

NASA Astrophysics Data System (ADS)

Khan, Zeeshan; Shah, Rehan Ali; Islam, Saeed; Jan, Bilal; Imran, Muhammad; Tahir, Farisa

2016-10-01

Modern optical fibers require double-layer coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride (PVC) and low-high density polyethylene (LDPE/HDPE), nylon and Polysulfone. In this paper, double-layer optical fiber coating is performed using melt polymer satisfying PTT fluid model in a pressure type die using wet-on-wet coating process. The assumption of fully developed flow of Phan-Thien-Tanner (PTT) fluid model, two-layer liquid flows of an immiscible fluid is modeled in an annular die, where the fiber is dragged at a higher speed. The equations characterizing the flow and heat transfer phenomena are solved exactly and the effects of emerging parameters (Deborah and slip parameters, characteristic velocity, radii ratio and Brinkman numbers on the axial velocity, flow rate, thickness of coated fiber optics, and temperature distribution) are reported in graphs. It is shown that an increase in the non-Newtonian parameters increase the velocity in the absence or presence of slip parameters which coincides with related work. The comparison is done with experimental work by taking λ → 0 (non-Newtonian parameter).

Steady flow and heat transfer analysis of Phan-Thein-Tanner fluid in double-layer optical fiber coating analysis with Slip Conditions

PubMed Central

Khan, Zeeshan; Shah, Rehan Ali; Islam, Saeed; Jan, Bilal; Imran, Muhammad; Tahir, Farisa

2016-01-01

Modern optical fibers require double-layer coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride (PVC) and low-high density polyethylene (LDPE/HDPE), nylon and Polysulfone. In this paper, double-layer optical fiber coating is performed using melt polymer satisfying PTT fluid model in a pressure type die using wet-on-wet coating process. The assumption of fully developed flow of Phan-Thien-Tanner (PTT) fluid model, two-layer liquid flows of an immiscible fluid is modeled in an annular die, where the fiber is dragged at a higher speed. The equations characterizing the flow and heat transfer phenomena are solved exactly and the effects of emerging parameters (Deborah and slip parameters, characteristic velocity, radii ratio and Brinkman numbers on the axial velocity, flow rate, thickness of coated fiber optics, and temperature distribution) are reported in graphs. It is shown that an increase in the non-Newtonian parameters increase the velocity in the absence or presence of slip parameters which coincides with related work. The comparison is done with experimental work by taking λ → 0 (non-Newtonian parameter). PMID:27708412

Steady flow and heat transfer analysis of Phan-Thein-Tanner fluid in double-layer optical fiber coating analysis with Slip Conditions.

PubMed

Khan, Zeeshan; Shah, Rehan Ali; Islam, Saeed; Jan, Bilal; Imran, Muhammad; Tahir, Farisa

2016-10-06

Modern optical fibers require double-layer coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride (PVC) and low-high density polyethylene (LDPE/HDPE), nylon and Polysulfone. In this paper, double-layer optical fiber coating is performed using melt polymer satisfying PTT fluid model in a pressure type die using wet-on-wet coating process. The assumption of fully developed flow of Phan-Thien-Tanner (PTT) fluid model, two-layer liquid flows of an immiscible fluid is modeled in an annular die, where the fiber is dragged at a higher speed. The equations characterizing the flow and heat transfer phenomena are solved exactly and the effects of emerging parameters (Deborah and slip parameters, characteristic velocity, radii ratio and Brinkman numbers on the axial velocity, flow rate, thickness of coated fiber optics, and temperature distribution) are reported in graphs. It is shown that an increase in the non-Newtonian parameters increase the velocity in the absence or presence of slip parameters which coincides with related work. The comparison is done with experimental work by taking λ → 0 (non-Newtonian parameter).

Seismic Velocities and Thicknesses of Alluvial Deposits along Baker Creek in the Great Basin National Park, East-Central Nevada

USGS Publications Warehouse

Allander, Kip K.; Berger, David L.

2009-01-01

To better understand how proposed large-scale water withdrawals in Snake Valley may affect the water resources and hydrologic processes in the Great Basin National Park, the National Park Service needs to have a better understanding of the relations between streamflow and groundwater flow through alluvium and karst topography of the Pole Canyon Limestone. Information that is critical to understanding these relations is the thickness of alluvial deposits that overlay the Pole Canyon Limestone. In mid-April 2009, the U.S. Geological Survey and National Park Service used seismic refraction along three profiles adjacent to Baker Creek to further refine understanding of the local geology. Two refractors and three distinct velocity layers were detected along two of the profiles and a single refractor and two distinct velocity layers were detected along a third profile. In the unsaturated alluvium, average velocity was 2,000 feet per second, thickness ranged from about 7 to 20 feet along two profiles downstream of the Narrows, and thickness was at least 100 feet along a single profile upstream of the Narrows. Saturated alluvium was only present downstream of the Narrows - average velocity was 4,400 feet per second, and thickness ranged from about 40 to 110 feet. The third layer probably represented Pole Canyon Limestone or Tertiary granitic rock units with an average velocity of 12,500 feet per second. Along the upstream and middle profiles (profiles 3 and 1, respectively), the depth to top of the third layer ranged from at least 60 to 110 feet below land surface and is most likely the Pole Canyon Limestone. The third layer at the farthest downstream profile (profile 2) may be a Tertiary granitic rock unit. Baker Creek is disconnected from the groundwater system along the upstream profile (profile 3) and streamflow losses infiltrate vertically downward to the Pole Canyon Limestone. Along the downstream and middle profiles (profiles 2 and 1, respectively), the presence of a shallow water table indicates that low permeability Tertiary granitic rock may extend across the Baker Creek Drainage intersecting the Pole Canyon Limestone. The Tertiary granitic rock may be acting as a barrier to groundwater flow within the Pole Canyon Limestone.

Evidence for water-mediated mechanisms in coral–algal interactions

PubMed Central

Jorissen, Hendrikje; Skinner, Christina; Osinga, Ronald; de Beer, Dirk

2016-01-01

Although many coral reefs have shifted from coral-to-algal dominance, the consequence of such a transition for coral–algal interactions and their underlying mechanisms remain poorly understood. At the microscale, it is unclear how diffusive boundary layers (DBLs) and surface oxygen concentrations at the coral–algal interface vary with algal competitors and competitiveness. Using field observations and microsensor measurements in a flow chamber, we show that coral (massive Porites) interfaces with thick turf algae, macroalgae, and cyanobacteria, which are successful competitors against coral in the field, are characterized by a thick DBL and hypoxia at night. In contrast, coral interfaces with crustose coralline algae, conspecifics, and thin turf algae, which are poorer competitors, have a thin DBL and low hypoxia at night. Furthermore, DBL thickness and hypoxia at the interface with turf decreased with increasing flow speed, but not when thick turf was upstream. Our results support the importance of water-mediated transport mechanisms in coral–algal interactions. Shifts towards algal dominance, particularly dense assemblages, may lead to thicker DBLs, higher hypoxia, and higher concentrations of harmful metabolites and pathogens along coral borders, which in turn may facilitate algal overgrowth of live corals. These effects may be mediated by flow speed and orientation. PMID:27512146

Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

NASA Astrophysics Data System (ADS)

Raayai-Ardakani, Shabnam; McKinley, Gareth H.

2017-09-01

Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4%-8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source Computational Fluid Dynamics solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios ( λ / L ), aspect ratios ( 2 A / λ ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the high-speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.

Serially connected solid oxide fuel cells having monolithic cores

DOEpatents

Herceg, J.E.

1985-05-20

Disclosed is a solid oxide fuel cell for electrochemically combining fuel and oxidant for generating galvanic output. The cell core has an array of cell segments electrically serially connected in the flow direction, each segment consisting of electrolyte walls and interconnect that are substantially devoid of any composite inert materials for support. Instead, the core is monolithic, where each electrolyte wall consists of thin layers of cathode and anode materials sandwiching a thin layer of electrolyte material therebetween. Means direct the fuel to the anode-exposed core passageways and means direct the oxidant to the cathode-exposed core passageways; and means also direct the galvanic output to an exterior circuit. Each layer of the electrolyte composite materials is of the order of 0.002 to 0.01 cm thick; and each layer of the cathode and anode materials is of the order of 0.002 to 0.05 cm thick. Between 2 and 50 cell segments may be connected in series.

Thermocouple Boundary Layer Rake

NASA Technical Reports Server (NTRS)

Hwang, Danny P. (Inventor); Will, Herbert A. (Inventor); Fralick, Gustave C. (Inventor)

2002-01-01

Apparatus and method for providing a velocity flow profile near a reference surface. A measuring device utilizes a plurality of thermojunction pairs to provide the velocity flow profile in accordance with behavior of a gas relative to a constant thickness strut which stands vertically from the reference surface such that the span is normal to the surface, and the chord is parallel to the surface along the initial flow direction. Each thermojunction is carried on either side of a heater formed on a measuring surface in a constant thickness portion of a strut. Additionally, each thermojunction of a given pair is located at a predetermined height from the reference surface. Gas velocity data obtained from temperature differentials from one side of the heater to the other at each successive height is utilized to generate the velocity and turbulence level profiles.

Rheology of surface granular flows

NASA Astrophysics Data System (ADS)

Orpe, Ashish V.; Khakhar, D. V.

Surface granular flow, comprising granular material flowing on the surface of a heap of the same material, occurs in several industrial and natural systems. The rheology of such a flow was investigated by means of measurements of velocity and number-density profiles in a quasi-two-dimensional rotating cylinder, half-filled with a model granular material monosize spherical stainless-steel particles. The measurements were made at the centre of the cylinder, where the flow is fully developed, using streakline photography and image analysis. The stress profile was computed from the number-density profile using a force balance which takes into account wall friction. Mean-velocity and root-mean-square (r.m.s.)-velocity profiles are reported for different particle sizes and cylinder rotation speeds. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter d and velocity by a characteristic shear rate dot{gamma}_C = [gsin(beta_m-beta_s)/dcosbeta_s](1/2) and the particle diameter, where beta_m is the maximum dynamic angle of repose and beta_s is the static angle of repose. The maximum dynamic angle of repose is found to vary with the local flow rate. The scaling is also found to work for the r.m.s. velocity profiles. The mean velocity is found to decay exponentially with depth in the bed, with decay length lambda=1.1d. The r.m.s. velocity shows similar behaviour but with lambda=1.7d. The r.m.s. velocity profile shows two regimes: near the free surface the r.m.s. velocity is nearly constant and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, is not constant anywhere in the layer and has a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. Above the transition point the velocity distributions are Gaussian and below the transition point the velocity distributions gradually approach a Poisson distribution. The shear stress increases roughly linearly with depth. The variation in the apparent viscosity eta with r.m.s. velocity u shows a relatively sharp transition at the shear-rate maximum, and in the region below this point the apparent viscosity eta˜ u(-1.5) . The measurements indicate that the flow comprises two layers: an upper low-viscosity layer with a nearly constant r.m.s. velocity and a lower layer of increasing viscosity with a decreasing r.m.s. velocity. The thickness of the upper layer depends on the local flow rate and is independent of particle diameter while the reverse is found to hold for the lower-layer thickness. The experimental data is compared with the predictions of three models for granular flow.

Linear growth rates of resistive tearing modes with sub-Alfvénic streaming flow

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

Wu, L. N.; College of Sciences, China Jiliang University, Hangzhou 310018; Ma, Z. W., E-mail: zwma@zju.edu.cn

2014-07-15

The tearing instability with sub-Alfvénic streaming flow along the external magnetic field is investigated using resistive MHD simulation. It is found that the growth rate of the tearing mode instability is larger than that without the streaming flow. With the streaming flow, there exist two Alfvén resonance layers near the central current sheet. The larger perturbation of the magnetic field in two closer Alfvén resonance layers could lead to formation of the observed cone structure and can largely enhance the development of the tearing mode for a narrower streaming flow. For a broader streaming flow, a larger separation of Alfvénmore » resonance layers reduces the magnetic reconnection. The linear growth rate decreases with increase of the streaming flow thickness. The growth rate of the tearing instability also depends on the plasma beta (β). When the streaming flow is embedded in the current sheet, the growth rate increases with β if β < β{sub s}, but decreases if β > β{sub s}. The existence of the specific value β{sub s} can be attributed to competition between the suppressing effect of β and the enhancing effect of the streaming flow on the magnetic reconnection. The critical value β{sub s} increases with increase of the streaming flow strength.« less

Linear and weakly nonlinear aspects of free shear layer instability, roll-up, subharmonic interaction and wall influence

NASA Technical Reports Server (NTRS)

Cain, A. B.; Thompson, M. W.

1986-01-01

The growth of the momentum thickness and the modal disturbance energies are examined to study the nature and onset of nonlinearity in a temporally growing free shear layer. A shooting technique is used to find solutions to the linearized eigenvalue problem, and pseudospectral weakly nonlinear simulations of this flow are obtained for comparison. The roll-up of a fundamental disturbance follows linear theory predictions even with a 20 percent disturbance amplitude. A weak nonlinear interaction of the disturbance creates a finite-amplitude mean shear stress which dominates the growth of the layer momentum thickness, and the disturbance growth rate changes until the fundamental disturbance dominates. The fundamental then becomes an energy source for the harmonic, resulting in an increase in the growth rate of the subharmonic over the linear prediction even when the fundamental has no energy to give. Also considered are phase relations and the wall influence.

Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites

DOE PAGES

Blancon, Jean -Christophe Robert; Tsai, Hsinhan; Nie, Wanyi; ...

2017-03-09

Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum wells has enabled high-efficiency optoelectronic devices. Two-dimensional (2D) Ruddlesden-Popper perovskites are solution-processed quantum wells wherein the band gap can be tuned by varying the perovskite-layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite-crystal units (>1.3 nanometers) is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovskitemore » layers. Furthermore, these states provide a direct pathway for dissociating excitons into longer-lived free carriers that substantially improve the performance of optoelectronic devices.« less

Strength and Elastic thickness of the lithosphere and implication on ductile crustal flow in Europe

NASA Astrophysics Data System (ADS)

Tesauro, M.; Kaban, M. K.; Cloetingh, S. A. P. L.

2012-04-01

The strength and effective elastic thickness (Te) of the lithosphere control its response to tectonic and surface processes. We present the first global strength and effective elastic thickness maps, which are determined using physical properties from recent crustal and lithospheric models. We estimated the lithospheric temperature from inversion of a tomography model and we extrapolated the results to the surface using crustal isotherms for different tectonic provinces based on characteristic values of radiogenic heat production. We assumed different rheologies of the upper and lower crust for continental areas, on the base of the geological features distribution. The results obtained allow us to compare for the first time the lithospheric characteristics of the different tectonic areas. The Te estimated from the strength is compared with the Te obtained by flexural loading and spectral studies. Lithospheric strength is primarily controlled by the crust in young (Phanerozoic) geological provinces characterized by low Te (~25 km), high topography (>1000 m) and active seismicity. In contrast, the old (Achaean and Proterozoic) cratons of the continental plates show strength primarily in the lithospheric mantle, high Te (over 100 km), low topography (<1000 m) and very low seismicity. Using high resolution crustal thickness and density data provided by the EuCRUST-07 model we compute for the European continent the associated lateral pressure gradients (LPG), which can drive horizontal ductile flow in the crust. Incorporation of these data in channel flow models allows us to use potential gravity theory to assess horizontal mass transfer and stress transmission within the European crust. We explore implications of the channel flow concept for a possible range of crustal strength, using end-member 'hard' and 'soft' crustal rheologies to estimate strain rates at the bottom of the ductile crustal layers. The models show that the effects of channel flow superimposed on the direct effects of plate tectonic forces might result in additional significant horizontal and vertical movements associated with zones of compression or extension. Large values of the LPG are predicted perpendicular to the axes of European mountain belts, such as the Alps, Pyrenees-Cantabrian Mountains, Dinarides-Hellenic arc and Carpathians. In general, the crustal flow is directed away from orogens towards adjacent weaker areas. Predicted pressure and strain rate gradients suggest that gravity driven flow may play an essential role in European intraplate tectonics. These results are also important for quantifying the thickness of the low viscosity zones in the lowermost part of the crustal layers.

Closed-loop separation control over a sharp edge ramp using genetic programming

NASA Astrophysics Data System (ADS)

Debien, Antoine; von Krbek, Kai A. F. F.; Mazellier, Nicolas; Duriez, Thomas; Cordier, Laurent; Noack, Bernd R.; Abel, Markus W.; Kourta, Azeddine

2016-03-01

We experimentally perform open and closed-loop control of a separating turbulent boundary layer downstream from a sharp edge ramp. The turbulent boundary layer just above the separation point has a Reynolds number Re_{θ }≈ 3500 based on momentum thickness. The goal of the control is to mitigate separation and early re-attachment. The forcing employs a spanwise array of active vortex generators. The flow state is monitored with skin-friction sensors downstream of the actuators. The feedback control law is obtained using model-free genetic programming control (GPC) (Gautier et al. in J Fluid Mech 770:442-457, 2015). The resulting flow is assessed using the momentum coefficient, pressure distribution and skin friction over the ramp and stereo PIV. The PIV yields vector field statistics, e.g. shear layer growth, the back-flow area and vortex region. GPC is benchmarked against the best periodic forcing. While open-loop control achieves separation reduction by locking-on the shedding mode, GPC gives rise to similar benefits by accelerating the shear layer growth. Moreover, GPC uses less actuation energy.

The numerical study of the coextrusion process of polymer melts in the cable head

NASA Astrophysics Data System (ADS)

Kozitsyna, M. V.; Trufanova, N. M.

2017-06-01

The process of coextrusion consists in a simultaneous creation of all necessary insulating layers of different polymers in the channel of a special forming tool. The main focus of this study is the analysis of technological, geometrical and rheological characteristics on the values of the layer’s thickness. In this paper are considered three geometries of cable head on the three-dimensional and two-dimensional representation. The mathematical models of separate and joint flow of polymer melts have been implemented by the finite element method in Ansys software package. The velocity fields, temperature, pressure in the cross-sections of the channel and by the length have been obtained. The influence of some thickness characteristics of insulation layers has been identified.

Marangoni convection in Casson liquid flow due to an infinite disk with exponential space dependent heat source and cross-diffusion effects

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.; Shashikumar, N. S.; Hayat, T.; Alsaedi, A.

2018-06-01

Present work aims to investigate the features of the exponential space dependent heat source (ESHS) and cross-diffusion effects in Marangoni convective heat mass transfer flow due to an infinite disk. Flow analysis is comprised with magnetohydrodynamics (MHD). The effects of Joule heating, viscous dissipation and solar radiation are also utilized. The thermal and solute field on the disk surface varies in a quadratic manner. The ordinary differential equations have been obtained by utilizing Von Kármán transformations. The resulting problem under consideration is solved numerically via Runge-Kutta-Fehlberg based shooting scheme. The effects of involved pertinent flow parameters are explored by graphical illustrations. Results point out that the ESHS effect dominates thermal dependent heat source effect on thermal boundary layer growth. The concentration and temperature distributions and their associated layer thicknesses are enhanced by Marangoni effect.

Burgers approximation for two-dimensional flow past an ellipse

NASA Technical Reports Server (NTRS)

Dorrepaal, J. M.

1982-01-01

A linearization of the Navier-Stokes equation due to Burgers in which vorticity is transported by the velocity field corresponding to continuous potential flow is examined. The governing equations are solved exactly for the two dimensional steady flow past an ellipse of arbitrary aspect ratio. The requirement of no slip along the surface of the ellipse results in an infinite algebraic system of linear equations for coefficients appearing in the solution. The system is truncated at a point which gives reliable results for Reynolds numbers R in the range 0 R 5. Predictions of the Burgers approximation regarding separation, drag and boundary layer behavior are investigated. In particular, Burgers linearization gives drag coefficients which are closer to observed experimental values than those obtained from Oseen's approximation. In the special case of flow past a circular cylinder, Burgers approximation predicts a boundary layer whose thickness is roughly proportional to R-1/2.

Prediction of High-Lift Flows using Turbulent Closure Models

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; Gatski, Thomas B.; Ying, Susan X.; Bertelrud, Arild

1997-01-01

The flow over two different multi-element airfoil configurations is computed using linear eddy viscosity turbulence models and a nonlinear explicit algebraic stress model. A subset of recently-measured transition locations using hot film on a McDonnell Douglas configuration is presented, and the effect of transition location on the computed solutions is explored. Deficiencies in wake profile computations are found to be attributable in large part to poor boundary layer prediction on the generating element, and not necessarily inadequate turbulence modeling in the wake. Using measured transition locations for the main element improves the prediction of its boundary layer thickness, skin friction, and wake profile shape. However, using measured transition locations on the slat still yields poor slat wake predictions. The computation of the slat flow field represents a key roadblock to successful predictions of multi-element flows. In general, the nonlinear explicit algebraic stress turbulence model gives very similar results to the linear eddy viscosity models.

Effective Elastic Thickness of the Lithosphere in Continental China from Heat Flow: Implications for the Lithospheric Rheology

NASA Astrophysics Data System (ADS)

Liu, S.; Wang, L.

2006-12-01

The effective elastic thickness (Te) of lithosphere is one parameter describing the responses of the lithosphere to long term forces, and is still controversial in estimation by different methods. Here we present the effective elastic thickness of the lithosphere in continental China from heat flow data by the method proposed by Burov et al, J.G.R., 1995,100(B3):3905-3927. Our results show that Te varies much in different sub-areas in continental China due to different geological evolution and associated thermal regimes. Te is much greater than the crustal thickness in the area where the heat flow is really low and the lithosphere is really thick, indicating much more contribution from the lithospheric mantle and the dominative control of the mantle with olivine on the rheology of the lithosphere, and the major basins (Tarim, Junggar, Ordos and Sichuan basins) in central-western China share this characteristic. For instance, the Te of the Tarim basin is 66km with crustal thickness of 45km. Te is less than the crustal thickness in the region where the heat flow is relatively high, and approximates to the crustal brittle-ductile transition depth, suggesting more contribution from the crust and the dominative control of the felsic crust on the rheology of the lithosphere, and this phenomenon is obvious in the SE coastal China, eastern North China and the orogenic belts. Compared the estimated Te with the seismogenic layer thickness (Ts) available in China, it is also found that the Te is much greater than Ts in the major basins with low heat flow, and is similar to Ts in the active zones with high heat flow, which is inconsistent with that Te is usually smaller than Ts proposed by Maggi et al., Geology,2000,28(6):495-498. Generally, two end elements rheological modes for continental lithosphere of the strong crust-weak mantle and the weak crust-strong mantle are all available in continental China considering different thermal regime, composition and geological evolution.

Lear jet boundary layer/shear layer laser propagation experiments

NASA Technical Reports Server (NTRS)

Gilbert, K.

1980-01-01

Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

Thermocouple Rakes for Measuring Boundary Layer Flows Extremely Close to Surface

NASA Technical Reports Server (NTRS)

Hwang, Danny P.; Fralick, Gustave C.; Martin, Lisa C.; Blaha, Charles A.

2001-01-01

Of vital interest to aerodynamic researchers is precise knowledge of the flow velocity profile next to the surface. This information is needed for turbulence model development and the calculation of viscous shear force. Though many instruments can determine the flow velocity profile near the surface, none of them can make measurements closer than approximately 0.01 in. from the surface. The thermocouple boundary-layer rake can measure much closer to the surface than conventional instruments can, such as a total pressure boundary layer rake, hot wire, or hot film. By embedding the sensors (thermocouples) in the region where the velocity is equivalent to the velocity ahead of a constant thickness strut, the boundary-layer flow profile can be obtained. The present device fabricated at the NASA Glenn Research Center microsystem clean room has a heater made of platinum and thermocouples made of platinum and gold. Equal numbers of thermocouples are placed both upstream and downstream of the heater, so that the voltage generated by each pair at the same distance from the surface is indicative of the difference in temperature between the upstream and downstream thermocouple locations. This voltage differential is a function of the flow velocity, and like the conventional total pressure rake, it can provide the velocity profile. In order to measure flow extremely close to the surface, the strut is made of fused quartz with extremely low heat conductivity. A large size thermocouple boundary layer rake is shown in the following photo. The latest medium size sensors already provide smooth velocity profiles well into the boundary layer, as close as 0.0025 in. from the surface. This is about 4 times closer to the surface than the previously used total pressure rakes. This device also has the advantage of providing the flow profile of separated flow and also it is possible to measure simultaneous turbulence levels within the boundary layer.

Feather roughness reduces flow separation during low Reynolds number glides of swifts.

PubMed

van Bokhorst, Evelien; de Kat, Roeland; Elsinga, Gerrit E; Lentink, David

2015-10-01

Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with an evolutionary window to high glide performance. © 2015. Published by The Company of Biologists Ltd.

Laboratory-based observations of capillary barriers and preferential flow in layered snow

NASA Astrophysics Data System (ADS)

Avanzi, F.; Hirashima, H.; Yamaguchi, S.; Katsushima, T.; De Michele, C.

2015-12-01

Several evidences are nowadays available that show how the effects of capillary gradients and preferential flow on water transmission in snow may play a more important role than expected. To observe these processes and to contribute in their characterization, we performed observations on the development of capillary barriers and preferential flow patterns in layered snow during cold laboratory experiments. We considered three different layering (all characterized by a finer-over-coarser texture in grain size) and three different water input rates. Nine samples of layered snow were sieved in a cold laboratory, and subjected to a constant supply of dyed tracer. By means of visual inspection, horizontal sectioning and liquid water content measurements, the processes of ponding and preferential flow were characterized as a function of texture and water input rate. The dynamics of each sample were replicated using the multi-layer physically-based SNOWPACK model. Results show that capillary barriers and preferential flow are relevant processes ruling the speed of liquid water in stratified snow. Ponding is associated with peaks in LWC at the boundary between the two layers equal to ~ 33-36 vol. % when the upper layer is composed by fine snow (grain size smaller than 0.5 mm). The thickness of the ponding layer at the textural boundary is between 0 and 3 cm, depending on sample stratigraphy. Heterogeneity in water transmission increases with grain size, while we do not observe any clear dependency on water input rate. The extensive comparison between observed and simulated LWC profiles by SNOWPACK (using an approximation of Richards Equation) shows high performances by the model in estimating the LWC peak over the boundary, while water speed in snow is underestimated by the chosen water transport scheme.

Active flow control insight gained from a modified integral boundary layer equation

NASA Astrophysics Data System (ADS)

Seifert, Avraham

2016-11-01

Active Flow Control (AFC) can alter the development of boundary layers with applications (e.g., reducing drag by separation delay or separating the boundary layers and enhancing vortex shedding to increase drag). Historically, significant effects of steady AFC methods were observed. Unsteady actuation is significantly more efficient than steady. Full-scale AFC tests were conducted with varying levels of success. While clearly relevant to industry, AFC implementation relies on expert knowledge with proven intuition and or costly and lengthy computational efforts. This situation hinders the use of AFC while simple, quick and reliable design method is absent. An updated form of the unsteady integral boundary layer (UIBL) equations, that include AFC terms (unsteady wall transpiration and body forces) can be used to assist in AFC analysis and design. With these equations and given a family of suitable velocity profiles, the momentum thickness can be calculated and matched with an outer, potential flow solution in 2D and 3D manner to create an AFC design tool, parallel to proven tools for airfoil design. Limiting cases of the UIBL equation can be used to analyze candidate AFC concepts in terms of their capability to modify the boundary layers development and system performance.

Theoretical face pressure and drag characteristics of forward-facing steps in supersonic turbulent boundary layers

NASA Technical Reports Server (NTRS)

Patel, D. K.; Czarnecki, K. R.

1975-01-01

A theoretical investigation of the pressure distributions and drag characteristics was made for forward facing steps in turbulent flow at supersonic speeds. An approximate solution technique proposed by Uebelhack has been modified and extended to obtain a more consistent numerical procedure. A comparison of theoretical calculations with experimental data generally indicated good agreement over the experimentally available range of ratios of step height to boundary layer thickness from 7 to 0.05.

Boundary layer simulator improvement

NASA Technical Reports Server (NTRS)

Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

1984-01-01

High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

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

Peterson, Kenneth A.; Knudson, Richard T.; Smith, Frank R.

Generally annular full tape thickness conductors are formed in single or multiple tape layers, and then stacked to produce an annular solid conductive wall for enclosing an electromagnetic isolation cavity. The conductors may be formed using punch and fill operations, or by flowing conductor-containing material onto the tape edge surfaces that define the interior sidewalls of the cavity.

Geothermal Heating, Convective Flow and Ice Thickness on Mars

NASA Technical Reports Server (NTRS)

Rosenberg, N. D.; Travis, B. J.; Cuzzi, J.

2001-01-01

Our 3D calculations suggest that hydrothermal circulation may occur in the martian regolith and may significantly thin the surface ice layer on Mars at some locations due to the upwelling of warm convecting fluids driven solely by background geothermal heating. Additional information is contained in the original extended abstract.

Changes in the turbulent boundary layer structure associated with net drag reduction by outer layer manipulators

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Falco, R. E.

1987-01-01

A specially designed wind tunnel was used to examine the effects of tandemly arranged parallel plate manipulators (TAPPMs) on a turbulent boundary-layer structure and the associated drag. Momentum balances, as well as measurements of the local shear stress from the velocity gradient near the wall, were used to obtain the net drag and local skin friction changes. Two TAPPMs, identical except for the thickness of their plates, were used in the study. Results with .003 inch plates were a maximum net drag reduction of 10 percent at 58 beta sub o (using a momentum balance). At 20 beta sub o, simultaneous laser sheet flow visualization and hot-wire anemometry data showed that the Reynolds stress in the large eddies was significantly reduced, as were the streamwise and normal velocity components. Using space-time correlations the reductions were again identified. Furthermore, quantitative flow visualization showed that the outward normal velocity of the inner region was also significantly decreased in the region around 20 beta sub o. However, throughout the first 130 beta sub o, the measured sublayer thickness with the TAPPMs in place was 15 to 20 percent greater. The data showed that the skin friction, as well as the structure of the turbulence, was strongly modified in the first 35 beta sub o, but that they both significantly relaxed toward unmanipulated boundary layer values by 50 beta sub o.

Advanced Space Propulsion System Flowfield Modeling

NASA Technical Reports Server (NTRS)

Smith, Sheldon

1998-01-01

Solar thermal upper stage propulsion systems currently under development utilize small low chamber pressure/high area ratio nozzles. Consequently, the resulting flow in the nozzle is highly viscous, with the boundary layer flow comprising a significant fraction of the total nozzle flow area. Conventional uncoupled flow methods which treat the nozzle boundary layer and inviscid flowfield separately by combining the two calculations via the influence of the boundary layer displacement thickness on the inviscid flowfield are not accurate enough to adequately treat highly viscous nozzles. Navier Stokes models such as VNAP2 can treat these flowfields but cannot perform a vacuum plume expansion for applications where the exhaust plume produces induced environments on adjacent structures. This study is built upon recently developed artificial intelligence methods and user interface methodologies to couple the VNAP2 model for treating viscous nozzle flowfields with a vacuum plume flowfield model (RAMP2) that is currently a part of the Plume Environment Prediction (PEP) Model. This study integrated the VNAP2 code into the PEP model to produce an accurate, practical and user friendly tool for calculating highly viscous nozzle and exhaust plume flowfields.

Effects of Cavities and Protuberances on Transition over Hypersonic Vehicles

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei; Venkatachari, Balaji

2011-01-01

Surface protuberances and cavities on a hypersonic vehicle are known to cause several aerodynamic or aerothermodynamic issues. Most important of all, premature transition due to these surface irregularities can lead to a significant rise in surface heating. To help understand laminar-turbulent transition induced by protuberances or cavities on a Crew Exploration Vehicle (CEV) surface, high-fidelity numerical simulations are carried out for both types of trips on a CEV wind tunnel model. Due to the large bluntness, these surface irregularities reside in an accelerating subsonic boundary layer. For the Mach 6 wind tunnel conditions with a roughness Reynolds number Re(sub kk) of 800, it was found that a protuberance with a height to boundary layer thickness ratio of 0.73 leads to strong wake instability and spontaneous vortex shedding, while a cavity with identical geometry only causes a rather weak flow unsteadiness. The same cavity with a larger Reynolds number also leads to similar spontaneous vortex shedding and wake instability. The wake development and the formation of hairpin vortices for both protuberance and cavity were found to be qualitatively similar to that observed for an isolated hemisphere submerged in a subsonic, low speed flat-plate boundary layer. However, the shed vortices and their accompanying instability waves were found to be slightly stabilized downstream by the accelerating boundary layer along the CEV surface. Despite this stabilizing influence, it was found that the wake instability spreads substantially in both wall-normal and azimuthal directions as the flow is evolving towards a transitional state. Similarities and differences between the wake instability behind a protuberance and a cavity are investigated. Computations for the Mach 6 boundary layer over a slender cylindrical roughness element with a height to the boundary layer thickness of about 1.1 also shows spontaneous vortex shedding and strong wake instability. Comparisons of detailed flow structures associated with protuberances at subsonic and supersonic edge Mach numbers indicate distinctively different instability mechanisms.

Turbidity currents with equilibrium basal driving layers: a mechanism for long-runout turbidity currents

NASA Astrophysics Data System (ADS)

Luchi, R.; Balachandar, S.; Seminara, G.; Parker, G.

2017-12-01

Turbidity currents in lakes and oceans involve leveed channels that document coherent runouts of 100's and up to 1000's of km. They do so without dissipating themselves via excess entrainment of ambient water. It is generally known that currents associated with stable stratification, such as thermohaline underflows, undergo dissipation as they entrain ambient water. Here we ask why some continuous turbidity currents do not follow this tendency, as they can run out extremely long distances while maintaining their coherency. A current that becomes ever thicker downstream due to ambient water entrainment cannot select the scales necessary to maintain a coherent, slowly-varying channel depth and width over 1000 km. It has been assumed that a turbidity current may tend to a state with a densimetric Froude so low that ambient water entrainment is largely suppressed. Here, we show that such an argument is a case of special pleading. Instead, suspended sediment 'fights back' against upward mixing through its fall velocity; the water may be entrained, but the sediment need not follow. We use a formulation capturing the flow vertical structure to show the conditions under which a turbidity current can asymptotically partition itself into two layers. The lower 'driving layer' approaches an asymptotic state with invariant flow thickness, velocity profile and suspended sediment concentration profile when traversing a constant bed slope under bypass conditions. This thickness provides a scale for channel characteristics. The upper 'driven layer' continues to entrain ambient water, but the concentration there becomes ever more dilute, and the layer ultimately has no interaction with near-bed processes (and by implication bed morphology). This partition is a likely candidate for the mechanism by which the driving layer is able to run out long distances, maintaining coherence and keeping confined, over repeated flow events, within a leveed subaqueous channel of its own creation.

Effects of deposition temperature and ammonia flow on metal-organic chemical vapor deposition of hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Rice, Anthony; Allerman, Andrew; Crawford, Mary; Beechem, Thomas; Ohta, Taisuke; Spataru, Catalin; Figiel, Jeffrey; Smith, Michael

2018-03-01

The use of metal-organic chemical vapor deposition at high temperature is investigated as a means to produce epitaxial hexagonal boron nitride (hBN) at the wafer scale. Several categories of hBN films were found to exist based upon precursor flows and deposition temperature. Low, intermediate, and high NH3 flow regimes were found to lead to fundamentally different deposition behaviors. The low NH3 flow regimes yielded discolored films of boron sub-nitride. The intermediate NH3 flow regime yielded stoichiometric films that could be deposited as thick films. The high NH3 flow regime yielded self-limited deposition with thicknesses limited to a few mono-layers. A Langmuir-Hinshelwood mechanism is proposed to explain the onset of self-limited behavior for the high NH3 flow regime. Photoluminescence characterization determined that the intermediate and high NH3 flow regimes could be further divided into low and high temperature behaviors with a boundary at 1500 °C. Films deposited with both high NH3 flow and high temperature exhibited room temperature free exciton emission at 210 nm and 215.9 nm.

Near Field Trailing Edge Tone Noise Computation

NASA Technical Reports Server (NTRS)

Loh, Ching Y.

2002-01-01

Blunt trailing edges in a flow often generate tone noise due to wall-jet shear layer and vortex shedding. In this paper, the space-time conservation element (CE/SE) method is employed to numerically study the near-field noise of blunt trailing edges. Two typical cases, namely, flow past a circular cylinder (aeolian noise problem) and flow past a flat plate of finite thickness are considered. The computed frequencies compare well with experimental data. For the aeolian noise problem, comparisons with the results of other numerical approaches are also presented.

Intermittent Turbulence in the Attachment Line Flow Formed on an Infinite Swept Wing

NASA Technical Reports Server (NTRS)

Poll, Ian

2007-01-01

The transition process which takes place in the attachment-line boundary layer in the presence of gross contamination is an issue of considerable interest to wing designers. It is well known that this flow is very sensitive to the presence of isolated roughness and that transition can be initiated at a very low value of the local medium thickness Reynolds number.Moreover, once the attachment line is turbulent, the flow over the whole wing chords, top and bottom surface, will be turbulent and this has major implications for wind drag.

Numerical study of large-eddy breakup and its effect on the drag characteristics of boundary layers

NASA Technical Reports Server (NTRS)

Kinney, R. B.; Taslim, M. E.; Hung, S. C.

1985-01-01

The break-up of a field of eddies by a flat-plate obstacle embedded in a boundary layer is studied using numerical solutions to the two-dimensional Navier-Stokes equations. The flow is taken to be incompressible and unsteady. The flow field is initiated from rest. A train of eddies of predetermined size and strength are swept into the computational domain upstream of the plate. The undisturbed velocity profile is given by the Blasius solution. The disturbance vorticity generated at the plate and wall, plus that introduced with the eddies, mix with the background vorticity and is transported throughout the entire flow. All quantities are scaled by the plate length, the unidsturbed free-stream velocity, and the fluid kinematic viscosity. The Reynolds number is 1000, the Blasius boundary layer thickness is 2.0, and the plate is positioned a distance of 1.0 above the wall. The computational domain is four units high and sixteen units long.

An evaluation of four single element airfoil analytic methods

NASA Technical Reports Server (NTRS)

Freuler, R. J.; Gregorek, G. M.

1979-01-01

A comparison of four computer codes for the analysis of two-dimensional single element airfoil sections is presented for three classes of section geometries. Two of the computer codes utilize vortex singularities methods to obtain the potential flow solution. The other two codes solve the full inviscid potential flow equation using finite differencing techniques, allowing results to be obtained for transonic flow about an airfoil including weak shocks. Each program incorporates boundary layer routines for computing the boundary layer displacement thickness and boundary layer effects on aerodynamic coefficients. Computational results are given for a symmetrical section represented by an NACA 0012 profile, a conventional section illustrated by an NACA 65A413 profile, and a supercritical type section for general aviation applications typified by a NASA LS(1)-0413 section. The four codes are compared and contrasted in the areas of method of approach, range of applicability, agreement among each other and with experiment, individual advantages and disadvantages, computer run times and memory requirements, and operational idiosyncrasies.

Instability of two-layer film flows due to the interacting effects of surfactants, inertia, and gravity

NASA Astrophysics Data System (ADS)

Kalogirou, Anna

2018-03-01

We consider a two-fluid shear flow where the interface between the two fluids is coated with an insoluble surfactant. An asymptotic model is derived in the thin-layer approximation, consisting of a set of nonlinear partial differential equations describing the evolution of the film and surfactant disturbances at the interface. The model includes important physical effects such as Marangoni forces (caused by the presence of surfactant), inertial forces arising in the thick fluid layer, as well as gravitational forces. The aim of this study is to investigate the effect of density stratification or gravity—represented through the Bond number Bo—on the flow stability and the interplay between the different (de)stabilisation mechanisms. It is found that gravity can either stabilise or destabilise the interface (depending on fluid properties) but not always as intuitively anticipated. Different traveling-wave branches are presented for varying Bo, and the destabilising mechanism associated with the Marangoni forces is discussed.

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study

PubMed Central

Wang, Juan; Jang, Yongseok; Wan, Guojiang; Giridharan, Venkataraman; Song, Guang-Ling; Xu, Zhigang; Koo, Youngmi; Qi, Pengkai; Sankar, Jagannathan; Huang, Nan; Yun, Yeoheung

2016-01-01

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography. PMID:28626241

Structural and optical properties of Ga auto-incorporated InAlN epilayers

NASA Astrophysics Data System (ADS)

Taylor, E.; Smith, M. D.; Sadler, T. C.; Lorenz, K.; Li, H. N.; Alves, E.; Parbrook, P. J.; Martin, R. W.

2014-12-01

InAlN epilayers deposited on thick GaN buffer layers grown by metalorganic chemical vapour deposition (MOCVD) revealed an auto-incorporation of Ga when analysed by wavelength dispersive x-ray (WDX) spectroscopy and Rutherford backscattering spectrometry (RBS). Samples were grown under similar conditions with the change in reactor flow rate resulting in varying Ga contents of 12-24%. The increase in flow rate from 8000 to 24 000 sccm suppressed the Ga auto-incorporation which suggests that the likely cause is from residual Ga left behind from previous growth runs. The luminescence properties of the resultant InAlGaN layers were investigated using cathodoluminescence (CL) measurements.

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study.

PubMed

Wang, Juan; Jang, Yongseok; Wan, Guojiang; Giridharan, Venkataraman; Song, Guang-Ling; Xu, Zhigang; Koo, Youngmi; Qi, Pengkai; Sankar, Jagannathan; Huang, Nan; Yun, Yeoheung

2016-03-01

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography.

Nonlinear Radiation Heat Transfer Effects in the Natural Convective Boundary Layer Flow of Nanofluid Past a Vertical Plate: A Numerical Study

PubMed Central

Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

2014-01-01

The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge–Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter. PMID:25251242

Vacuum-bag-only processing of composites

NASA Astrophysics Data System (ADS)

Thomas, Shad

Ultrasonic imaging in the C-scan mode in conjunction with the amplitude of the reflected signal was used to measure flow rates of an epoxy resin film penetrating through the thickness of single layers of woven carbon fabric. Assemblies, comprised of a single layer of fabric and film, were vacuum-bagged and ultrasonically scanned in a water tank during impregnation at 50°C, 60°C, 70°C, and 80°C. Measured flow rates were plotted versus inverse viscosity to determine the permeability in the thin film, non-saturated system. The results demonstrated that ultrasonic imaging in the C-scan mode is an effective method of measuring z-direction resin flow through a single layer of fabric. The permeability values determined in this work were consistent with permeability values reported in the literature. Capillary flow was not observed at the temperatures and times required for pressurized flow to occur. The flow rate at 65°C was predicted from the linear plot of flow rate versus inverse viscosity. The effects of fabric architecture on through-thickness flow rates during impregnation of an epoxy resin film were measured by ultrasonic imaging. Multilayered laminates comprised of woven carbon fabrics and epoxy films (prepregs) were fabricated by vacuum-bagging. Ultrasonic imaging was performed in a heated water tank (65°C) during impregnation. Impregnation rates showed a strong dependence on fabric architecture, despite similar areal densities. Impregnation rates are directly affected by inter-tow spacing and tow nesting, which depend on fabric architecture, and are indirectly affected by areal densities. A new method of predicting resin infusion rates in prepreg and resin film infusion processes was proposed. The Stokes equation was used to derive an equation to predict the impregnation rate of laminates as a function of fabric architecture. Flow rate data previously measured by ultrasound was analyzed with the new equation and the Kozeny-Carman equation. A fiber interaction parameter was determined as a function of fabric architecture. The derived equation is straight-forward to use, unlike the Kozeny-Carman equation. The results demonstrated that the newly derived equation can be used to predict the resin infusion rate of multilayer laminates.

Alveolar Thin Layer Flows and Surfactant Dynamics

NASA Astrophysics Data System (ADS)

Roumie, Ahmad; Jbaily, Abdulrahman; Szeri, Andrew J.

2017-11-01

Pulmonary surfactants play a vital role in everyday respiration. They regulate surface tension in the lungs by diffusing through the hypophase, a liquid layer that lines the interior surface of the alveoli, and adsorbing to the existing air-fluid interface. This decreases the equilibrium surface tension value by as much as a factor of 3, minimizing breathing effort and preventing lung collapse at the end of exhalation. Given that the hypophase thickness h lies within the range 0.1 μm < h <0.5 μm , and that the average alveolar radius R is 100 μm , for some purposes the hypophase may usefully be modeled as a fluid layer on a flat sheet representing the alveolar wall. Moreover, because of the large aspect ratio, the lubrication approximation can be applied. The aim of the present work is to study the interaction between the straining of the alveolar wall and the fluid flow in the hypophase. The analysis is governed by the relative magnitudes of the time scales of surfactant diffusion, adsorption, desorption, viscous dissipation and sheet straining. Cases of particular interest include non-uniform surfactant concentration at the interface, leading to Marangoni flows and a non-uniform hypophase thickness profile. The analytical formulation and numerical simulations are presented. This work is motivated by a need to understand alveolar deformation during breathing, and to do so in a way that derives from improved understanding of the fluid mechanics of the problem.

The Presence of Dense Material in the Deep Mantle: Implications for Plate Motion

NASA Astrophysics Data System (ADS)

Stein, C.; Hansen, U.

2017-12-01

The dense material in the deep mantle strongly interacts with the convective flow in the mantle. On the one hand, it has a restoring effect on rising plumes. On the other hand, the dense material is swept about by the flow forming dense piles. Consequently this affects the plate motion and, in particular, the onset time and the style of plate tectonics varies considerably for different model scenarios. In this study we apply a thermochemical mantle convection model combined with a rheological model (temperature- and stress-dependent viscosity) that allows for plate formation according to the convective flow. The model's starting condition is the post-magma ocean period. We analyse a large number of model scenarios ranging from variations in thickness, density and depth of a layer of dense material to different initial temperatures.Furthermore, we present a mechanism in which the dense layer at the core-mantle boundary forms without prescribing the thickness or the density contrast. Due to advection-assisted diffusion, long-lived piles can be established that act on the style of convection and therefore on plate motion. We distinguish between the subduction-triggered regime with early plate tectonics and the plume-triggered regime with a late onset of plate tectonics. The formation of piles by advection-assisted diffusion is a typical phenomenon that appears not only at the lower boundary, but also at internal boundaries that form in the layering phase during the evolution of the system.

Macular Choroidal Small-Vessel Layer, Sattler's Layer and Haller's Layer Thicknesses: The Beijing Eye Study.

PubMed

Zhao, Jing; Wang, Ya Xing; Zhang, Qi; Wei, Wen Bin; Xu, Liang; Jonas, Jost B

2018-03-13

To study macular choroidal layer thickness, 3187 study participants from the population-based Beijing Eye Study underwent spectral-domain optical coherence tomography with enhanced depth imaging for thickness measurements of the macular small-vessel layer, including the choriocapillaris, medium-sized choroidal vessel layer (Sattler's layer) and large choroidal vessel layer (Haller's layer). In multivariate analysis, greater thickness of all three choroidal layers was associated (all P < 0.05) with higher prevalence of age-related macular degeneration (AMD) (except for geographic atrophy), while it was not significantly (all P > 0.05) associated with the prevalence of open-angle glaucoma or diabetic retinopathy. There was a tendency (0.07 > P > 0.02) toward thinner choroidal layers in chronic angle-closure glaucoma. The ratio of small-vessel layer thickness to total choroidal thickness increased (P < 0.001; multivariate analysis) with older age and longer axial length, while the ratios of Sattler's layer and Haller's layer thickness to total choroidal thickness decreased. A higher ratio of small-vessel layer thickness to total choroidal thickness was significantly associated with a lower prevalence of AMD (early type, intermediate type, late geographic type). Axial elongation-associated and aging-associated choroidal thinning affected Haller's and Sattler's layers more markedly than the small-vessel layer. Non-exudative and exudative AMD, except for geographic atrophy, was associated with slightly increased choroidal thickness.

Effect of viscosity of a thermoplastic prepreg and matrix upon winding of rings

NASA Astrophysics Data System (ADS)

Stavrov, V. P.; Markov, A. V.; Zhernovskii, A. V.; Friedrich, K. F.

2000-05-01

The problem of compression of a unidirectional layer and shear of a polymer interlayer during winding of rings is considered. The equations determining the dependence of the layer thickness and stresses on the parameters entering into the power flow law for a prepreg and polymer matrix and on the basic parameters of the winding process—the initial tension of the prepreg, its placement rate, and the radius of a mandrel—are derived. The ring thickness measurements obtained at various temperatures and initial tension forces of plies confirm the adequacy of the model offered. It is found that the viscous properties of the prepreg and matrix upon winding affect the relative change in the layer thickness to a greater extent than the stresses in these layers. With increase in temperature and tension force upon winding, the effect of viscous deformations of the prepreg and matrix increases. A decrease in viscosity and an increase in the tension force of the tape lead to a higher strength of the ring in tension and interlaminar shear; however, the growing percolation of the polymer melt leads to a greater inhomogeneity of the structure of the composite in the ring and to a lower reinforcing effect of the factors mentioned.

Electrical resistivity tomography determines the spatial distribution of clay layer thickness and aquifer vulnerability, Kandal Province, Cambodia

NASA Astrophysics Data System (ADS)

Uhlemann, Sebastian; Kuras, Oliver; Richards, Laura A.; Naden, Emma; Polya, David A.

2017-10-01

Despite being rich in water resources, many areas of South East Asia face difficulties in securing clean water supply. This is particularly problematic in regions with a rapidly growing population. In this study, the spatial variability of the thickness of a clay layer, controlling surface - groundwater interactions that affect aquifer vulnerability, was investigated using electrical resistivity tomography (ERT). Data were acquired along two transects, showing significant differences in the imaged resistivities. Borehole samples were analyzed regarding particle density and composition, and linked to their resistivity. The obtained relationships were used to translate the field electrical resistivities into lithologies. Those revealed considerable variations in the thickness of the clay layer, ranging from 0 m up to 25 m. Geochemical data, highlighting zones of increased ingress of surface water into the groundwater, confirmed areas of discontinuities in the clay layer, which act as preferential flow paths. The results may guide urban planning of the Phnom Penh city expansion, in order to supply the growing population with safe water. The presented approach of using geophysics to estimate groundwater availability, accessibility, and vulnerability is not only applicable to Kandal Province, Cambodia, but also to many other areas of fast urbanization in South East Asia and beyond.

Surface-properties relationship in sputtered Ag thin films: Influence of the thickness and the annealing temperature in nitrogen

NASA Astrophysics Data System (ADS)

Guillén, C.; Herrero, J.

2015-01-01

Metal layers with high roughness and electrical conductivity are required as back-reflector electrodes in several optoelectronic devices. The metal layer thickness and the process temperature should be adjusted to reduce the material and energetic costs for the electrode preparation. Here, Ag thin films with thickness ranging from 30 to 200 nm have been deposited by sputtering at room temperature on glass substrates. The structure, morphology, optical and electrical properties of the films have been analyzed in the as-grown conditions and after thermal treatment in flowing nitrogen at various temperatures in the 150-550 °C range. The surface texture has been characterized by the root-mean-square roughness and the correlation length coefficients, which are directly related to the electrical resistivity and the light-scattering parameter (reflectance haze) for the various samples. The increment in the reflectance haze has been used to detect surface agglomeration processes that are found dependent on both the film thickness and the annealing temperature. A good compromise between light-scattering and electrical conductivity has been achieved with 70 nm-thick Ag films after 350 °C heating.

Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects

NASA Technical Reports Server (NTRS)

Lachowicz, Jason T.; Chokani, Ndaona

1996-01-01

Hypersonic boundary layer measurements over a flared cone were conducted in a Mach 6 quiet wind tunnel at a freestream unit Reynolds number of 2.82 million/ft. This Reynolds number provided laminar-to-transitional flow over the cone model in a low-disturbance environment. Four interchangeable nose-tips, including a sharp-tip, were tested. Point measurements with a single hot-wire using a novel constant voltage anemometer were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the transitional state of the boundary layer and to identify instability modes. Results suggest that second mode disturbances were the most unstable and scaled with the boundary layer thickness. The second mode integrated growth rates compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode subharmonic. The subharmonic disturbance wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that nonlinear disturbances are not associated with 'high' free stream disturbance levels. Nose-tip radii greater than 2.7% of the base radius completely stabilized the second mode.

A numerical investigation of the impact of surface topology on laminar boundary layers

NASA Astrophysics Data System (ADS)

Beratlis, Nikolaos; Squires, Kyle; Balaras, Elias

2015-11-01

Surface topology, such as dimples or trip wires, has been utilized in the past for passive separation control over bluff bodies. The majority of the work, however, has focused on the indirect effects on the drag and lift forces, while the details of the impact on the boundary layer evolution are not well understood. Here we report a series of DNS of flow over a single row of spherical and hexagonal dimples, as well as, circular grooves. The Reynolds number and the thickness of the incoming laminar boundary layer is carefully controlled. In all cases transition to turbulence downstream of the elements comes with reorientation of the spanwise vorticity into hairpin like vortices. Although qualitatively the transition mechanism amongst different dimples and grooves is similar, important quantitative differences exist: two-dimensional geometries such as the groove, are more stable than three-dimensional geometries. In addition, it was found that the cavity geometry controls the initial thickness of the boundary layer and practically results in a shift of the virtual origin of the turbulent boundary layer. Important differences in the momentum transport downstream of the dimples exist, but in all cases the boundary layer evolves in a self-similar manner.

Testing and Performance Verification of a High Bypass Ratio Turbofan Rotor in an Internal Flow Component Test Facility

NASA Technical Reports Server (NTRS)

VanZante, Dale E.; Podboy, Gary G.; Miller, Christopher J.; Thorp, Scott A.

2009-01-01

A 1/5 scale model rotor representative of a current technology, high bypass ratio, turbofan engine was installed and tested in the W8 single-stage, high-speed, compressor test facility at NASA Glenn Research Center (GRC). The same fan rotor was tested previously in the GRC 9x15 Low Speed Wind Tunnel as a fan module consisting of the rotor and outlet guide vanes mounted in a flight-like nacelle. The W8 test verified that the aerodynamic performance and detailed flow field of the rotor as installed in W8 were representative of the wind tunnel fan module installation. Modifications to W8 were necessary to ensure that this internal flow facility would have a flow field at the test package that is representative of flow conditions in the wind tunnel installation. Inlet flow conditioning was designed and installed in W8 to lower the fan face turbulence intensity to less than 1.0 percent in order to better match the wind tunnel operating environment. Also, inlet bleed was added to thin the casing boundary layer to be more representative of a flight nacelle boundary layer. On the 100 percent speed operating line the fan pressure rise and mass flow rate agreed with the wind tunnel data to within 1 percent. Detailed hot film surveys of the inlet flow, inlet boundary layer and fan exit flow were compared to results from the wind tunnel. The effect of inlet casing boundary layer thickness on fan performance was quantified. Challenges and lessons learned from testing this high flow, low static pressure rise fan in an internal flow facility are discussed.

Groundwater flow in a coastal peatland and its influence on submarine groundwater discharge

NASA Astrophysics Data System (ADS)

Ptak, T.; Ibenthal, M.; Janssen, M.; Massmann, G.; Lenartz, B.

2017-12-01

Coastal peatlands are characterized by intense interactions between land and sea, comprising both a submarine discharge of fresh groundwater and inundations of the peatland with seawater. Nutrients and salts can influence the biogeochemical processes both in the shallow marine sediments and in the peatland. The determination of flow direction and quantity of groundwater flow are therefore elementary. Submarine groundwater discharge (SGD) has been reported from several locations in the Baltic. The objective of this study is to quantify the exchange of fresh and brackish water across the shoreline in a coastal peatland in Northeastern Germany, and to assess the influence of a peat layer extending into the Baltic Sea. Below the peatland, a shallow fine sand aquifer differs in depth and is limited downwards by glacial till. Water level and electrical conductivity (EC) are permanently measured in different depths at eight locations in the peatland. First results indicate a general groundwater flow direction towards the sea. Electrical conductivity measurements suggest different permeabilities within the peat layer, depending on its thickness and degradation. Near the beach, EC fluctuates partially during storm events due to seawater intrusion and reverse discharge afterwards. The groundwater flow will be verified with a 3D model considering varying thicknesses of the aquifer. Permanent water level and electrical conductivity readings, meteorological data and hydraulic conductivity from slug tests and grain size analysis are the base for the calibration of the numerical model.

Chemical Reactions in Turbulent Mixing Flows

DTIC Science & Technology

1989-10-15

response, following the program control actuation. 3 in 2 vs. roughly the 8in2 required for the M1 = 1.5 (high speed stream Mach number) flow planned for...Papamoschou & Roshko (1988) as the compressibility-effect parameter, on the growth rate of the mixing layers was studied. In a finite thickness...attained is at present controversial; an issue that will have to be resolved both theoretically as well as with the planned for experiments. A sample plot

Wall-pressure fluctuations beneath a spatially evolving turbulent boundary layer

NASA Astrophysics Data System (ADS)

Mahesh, Krishnan; Kumar, Praveen

2016-11-01

Wall-pressure fluctuations beneath a turbulent boundary layer are important in applications dealing with structural deformation and acoustics. Simulations are performed for flat plate and axisymmetric, spatially evolving zero-pressure-gradient turbulent boundary layers at inflow Reynolds number of 1400 and 2200 based on momentum thickness. The simulations generate their own inflow using the recycle-rescale method. The results for mean velocity and second-order statistics show excellent agreement with the data available in literature. The spectral characteristics of wall-pressure fluctuations and their relation to flow structure will be discussed. This work is supported by ONR.

Features of sound propagation through and stability of a finite shear layer

NASA Technical Reports Server (NTRS)

Koutsoyannis, S. P.

1976-01-01

The plane wave propagation, the stability and the rectangular duct mode problems of a compressible inviscid linearly sheared parallel, but otherwise homogeneous flow, are shown to be governed by Whittaker's equation. The exact solutions for the perturbation quantities are essentially Whittaker M-functions. A number of known results are obtained as limiting cases of exact solutions. For the compressible finite thickness shear layer it is shown that no resonances and no critical angles exist for all Mach numbers, frequencies and shear layer velocity profile slopes except in the singular case of the vortex sheet.

[Influence of Vallisneria spiralis on the physicochemical properties of black-odor sediment in urban sluggish river].

PubMed

Xu, Kuan; Liu, Bo; Wang, Guo-Xiang; Ma, Jiu-Yuan; Cao, Xun; Zhou, Feng

2013-07-01

Using Indoor simulation method, the effect of Vallisneria spiralis on the physicochemical propertise of black and stink sediment was investigated. The surface sediment of urban sluggish river which had been heavily polluted was used as material in the study. The results showed that the redox environment of the sediment was significantly improved by Vallisneria spiralis. During the experiment, the Eh of surface sediment rose from -70 mV to 90 mV. The ferrous content was reduced by 25% in the experiment group while increased by 38% in the control group; the organic matter was decomposed effectively, prevented from natural decomposition to the smelly substances. There was a 3 mm thick greyish yellow oxide layer after 7 days in the experimental group, and the oxide layer gradually thickened over time. The thickness of the oxide layer reached 11 mm at the end of the experiment, and no significant odor was detected. On the contrary, the oxide layer in the control group was only 1 mm thick and the thickness remained unchanged. Meanwhile, an obnoxious odor existed during the whole experiment. The roots of Vallisneria spiralis had significant influence on the porosity of sediment. On one hand, the densification of sediment could be improved by Vallisneria spiralis. On the other hand, Vallisneria spiralis was able to change the state of the surface sediment flows, reduce the erosion of river sediment and inhibit the transfer of black-odor substances, which has a positive ecological meaning.

Assessment of fluctuating pressure gradient using acceleration spectra in near wall flows

NASA Astrophysics Data System (ADS)

Cadel, Daniel; Lowe, K. Todd

2015-11-01

Separation of contributions to the fluctuating acceleration from pressure gradient fluctuations and viscous shear fluctuations in the frequency domain is examined in a turbulent boundary layer. Past work leveraging turbulent accelerations for pressure gradient measurements has neglected the viscous shear term from the momentum equation--an invalid assumption in the case of near wall flows. The present study seeks to account for the influence of the viscous shear term and spectrally reject its contribution, which is thought to be concentrated at higher frequencies. Spectra of velocity and acceleration fluctuations in a flat plate, zero pressure gradient turbulent boundary layer at a momentum thickness Reynolds number of 7500 are measured using a spatially resolving three-component laser Doppler velocimeter. This canonical case data is applied for validation of the spectral approach for future application in more complex aerodynamic flows.

Improvement of Subsonic Basic Research Tunnel Flow Quality as Applied to Wall Mounted Testing

NASA Technical Reports Server (NTRS)

Howerton, Brian M.

1995-01-01

A survey to determine the characteristics of a boundary layer that forms on the wall of the Subsonic Basic Research Tunnel has been performed. Early results showed significant differences in the velocity profiles as measured spanwise across the wall. An investigation of the flow in the upstream contraction revealed the presence of a separation bubble at the beginning of the contraction which caused much of the observed unsteadiness. Vortex generators were successfully applied to the contraction inlet to alleviate the separation. A final survey of the wall boundary layer revealed variations in the displacement and momentum thicknesses to be less than +/- 5% for all but the most upper portion of the wall. The flow quality was deemed adequate to continue the planned follow-on tests to help develop the semi-span test technique.

A Microfabricated Segmented-Involute-Foil Regenerator for Enhancing Reliability and Performance of Stirling Engines

NASA Technical Reports Server (NTRS)

Ibrahim, Mounir; Danila, Daniel; Simon, Terrence; Mantell, Susan; Sun, Liyong; Gadeon, David; Qiu, Songgang; Wood, Gary; Kelly, Kevin; McLean, Jeffrey

2007-01-01

An actual-size microfabricated regenerator comprised of a stack of 42 disks, 19 mm diameter and 0.25 mm thick, with layers of microscopic, segmented, involute-shaped flow channels was fabricated and tested. The geometry resembles layers of uniformly-spaced segmented-parallel-plates, except the plates are curved. Each disk was made from electro-plated nickel using the LiGA process. This regenerator had feature sizes close to those required for an actual Stirling engine but the overall regenerator dimensions were sized for the NASA/Sunpower oscillating-flow regenerator test rig. Testing in the oscillating-flow test rig showed the regenerator performed extremely well, significantly better than currently used random-fiber material, producing the highest figures of merit ever recorded for any regenerator tested in that rig over its approximately 20 years of use.

A Comparative Study for Flow of Viscoelastic Fluids with Cattaneo-Christov Heat Flux.

PubMed

Hayat, Tasawar; Muhammad, Taseer; Alsaedi, Ahmed; Mustafa, Meraj

2016-01-01

This article examines the impact of Cattaneo-Christov heat flux in flows of viscoelastic fluids. Flow is generated by a linear stretching sheet. Influence of thermal relaxation time in the considered heat flux is seen. Mathematical formulation is presented for the boundary layer approach. Suitable transformations lead to a nonlinear differential system. Convergent series solutions of velocity and temperature are achieved. Impacts of various influential parameters on the velocity and temperature are sketched and discussed. Numerical computations are also performed for the skin friction coefficient and heat transfer rate. Our findings reveal that the temperature profile has an inverse relationship with the thermal relaxation parameter and the Prandtl number. Further the temperature profile and thermal boundary layer thickness are lower for Cattaneo-Christov heat flux model in comparison to the classical Fourier's law of heat conduction.

Three dimensional rotating flow of Powell-Eyring nanofluid with non-Fourier's heat flux and non-Fick's mass flux theory

NASA Astrophysics Data System (ADS)

Ibrahim, Wubshet

2018-03-01

This article numerically examines three dimensional boundary layer flow of a rotating Powell-Eyring nanofluid. In modeling heat transfer processes, non-Fourier heat flux theory and for mass transfer non-Fick's mass flux theory are employed. This theory is recently re-initiated and it becomes the active research area to resolves some drawback associated with the famous Fourier heat flux and mass flux theory. The mathematical model of the flow problem is a system of non-linear partial differential equations which are obtained using the boundary layer analysis. The non-linear partial differential equations have been transformed into non-linear high order ordinary differential equations using similarity transformation. Employing bvp4c algorithm from matlab software routine, the numerical solution of the transformed ordinary differential equations is obtained. The governing equations are constrained by parameters such as rotation parameter λ , the non-Newtonian parameter N, dimensionless thermal relaxation and concentration relaxation parameters δt and δc . The impacts of these parameters have been discussed thoroughly and illustrated using graphs and tables. The findings show that thermal relaxation time δt reduces the thermal and concentration boundary layer thickness. Further, the results reveal that the rotational parameter λ has the effect of decreasing the velocity boundary layer thickness in both x and y directions. Further examination pinpoints that the skin friction coefficient along x-axis is an increasing and skin friction coefficient along y-axis is a decreasing function of rotation parameter λ . Furthermore, the non-Newtonian fluid parameter N has the characteristic of reducing the amount of local Nusselt numbers -f″ (0) and -g″ (0) both in x and y -directions.

Unsteady turbulent boundary layers in swimming rainbow trout.

PubMed

Yanase, Kazutaka; Saarenrinne, Pentti

2015-05-01

The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided. © 2015. Published by The Company of Biologists Ltd.

The dynamics and control of fluctuating pressure loads in the reattachment region of a supersonic free shear layer

NASA Technical Reports Server (NTRS)

Smits, A. J.

1990-01-01

The primary aim is to investigate the mechanisms which cause the unsteady wall-pressure fluctuations in shock wave turbulent shear layer interactions. The secondary aim is to find means to reduce the magnitude of the fluctuating pressure loads by controlling the unsteady shock motion. The particular flow proposed for study is the unsteady shock wave interaction formed in the reattachment zone of a separated supersonic flow. Similar flows are encountered in many practical situations, and they are associated with high levels of fluctuating wall pressure. Wall pressure fluctuations were measured in the reattachment region of the supersonic free shear layer. The free shear layer was formed by the separation of a Mach 2.9 turbulent boundary layer from a backward facing step. Reattachment occurred on a 20 deg ramp. By adjusting the position of the ramp, the base pressure was set equal to the freestream pressure, and the free shear layer formed in the absence of a separation shock. An array of flush-mounted, miniature, high-frequency pressure transducers was used to make multichannel measurements of the fluctuating wall pressure in the vicinity of the reattachment region. Contrary to previous observations of this flow, the reattachment region was found to be highly unsteady, and the pressure fluctuations were found to be significant. The overall behavior of the wall pressure loading is similar in scale and magnitude to the unsteadiness of the wall pressure field in compression ramp flows at the same Mach number. Rayleigh scattering was used to visualize the instantaneous shock structure in the streamwise and spanwise direction. Spanwise wrinkles on the order of half the boundary layer thickness were observed.

Capillary trapping in thin-film flows of particles

NASA Astrophysics Data System (ADS)

Sauret, Alban; Gomez, Michael; Dressaire, Emilie

Flows of suspensions have been modeled on a continuum level by using constitutive relations to capture how the viscosity varies with the particle concentration. However, in thin liquid films, where the thickness of the liquid layer is comparable to the particle size, the particles deform the liquid interface, which leads to local interactions. These effects modify the transport of particles and could result in the contamination of the surface and the loss of transported material. Here, we characterize how capillary interactions affect the transport and deposition of non-Brownian particles moving in thin liquid films. We focus on gravitational drainage flows, in which the film thickness becomes comparable to the particle size. Depending on the concentration of particles, we find that the dynamics of the drainage exhibits behavior that cannot be captured with a Newtonian model, due to the deposition of particles on the substrate. ANR-16-CE30-0009 and CNRS-PICS-07242.

Time resolved flow-field measurements of a turbulent mixing layer over a rectangular cavity

NASA Astrophysics Data System (ADS)

Bian, Shiyao; Driscoll, James F.; Elbing, Brian R.; Ceccio, Steven L.

2011-07-01

High Reynolds number, low Mach number, turbulent shear flow past a rectangular, shallow cavity has been experimentally investigated with the use of dual-camera cinematographic particle image velocimetry (CPIV). The CPIV had a 3 kHz sampling rate, which was sufficient to monitor the time evolution of large-scale vortices as they formed, evolved downstream and impinged on the downstream cavity wall. The time-averaged flow properties (velocity and vorticity fields, streamwise velocity profiles and momentum and vorticity thickness) were in agreement with previous cavity flow studies under similar operating conditions. The time-resolved results show that the separated shear layer quickly rolled-up and formed eddies immediately downstream of the separation point. The vortices convect downstream at approximately half the free-stream speed. Vorticity strength intermittency as the structures approach the downstream edge suggests an increase in the three-dimensionality of the flow. Time-resolved correlations reveal that the in-plane coherence of the vortices decays within 2-3 structure diameters, and quasi-periodic flow features are present with a vortex passage frequency of ~1 kHz. The power spectra of the vertical velocity fluctuations within the shear layer revealed a peak at a non-dimensional frequency corresponding to that predicted using linear, inviscid instability theory.

Effect of Boundary-Layer Bleed Hole Inclination Angle and Scaling on Flow Coefficient Behavior

NASA Technical Reports Server (NTRS)

Eichorn, Michael B.; Barnhart, Paul J.; Davis, David O.; Vyas, Manan A.; Slater, John W.

2013-01-01

Phase II data results of the Fundamental Inlet Bleed Experiments study at NASA Glenn Research Center are presented which include flow coefficient behavior for 21 bleed hole configurations. The bleed configurations are all round holes with hole diameters ranging from 0.795 to 6.35 mm, hole inclination angles from 20deg to 90deg, and thickness-to-diameter ratios from 0.25 to 2.0. All configurations were tested at a unit Reynolds number of 2.46 10(exp 7)/m and at discrete local Mach numbers of 1.33, 1.62, 1.98, 2.46, and 2.92. Interactions between the design parameters of hole diameter, hole inclination angle, and thickness-to-diameter as well as the interactions between the flow parameters of pressure ratio and Mach number upon the flow coefficient are examined, and a preliminary statistical model is proposed. An existing correlation is also examined with respect to this data.

Analysis of permafrost depths on Mars

NASA Technical Reports Server (NTRS)

Crescenti, G. H.

1984-01-01

The Martian surface thermal characteristics as they effect the thickness and distribution of the permafrost are discussed. Parameters such as temperature mean, maximum, and minimum, heat flow values, and damping depths are derived and applied to a model of the Martian cryosphere. A comparison is made between the permafrost layers of Earth and Mars.

Effects of model layer simplification using composite hydraulic properties

USGS Publications Warehouse

Sepúlveda, Nicasio; Kuniansky, Eve L.

2010-01-01

The effects of simplifying hydraulic property layering within an unconfined aquifer and the underlying confining unit were assessed. The hydraulic properties of lithologic units within the unconfined aquifer and confining unit were computed by analyzing the aquifer-test data using radial, axisymmetric two-dimensional (2D) flow. Time-varying recharge to the unconfined aquifer and pumping from the confined Upper Floridan aquifer (USA) were simulated using 3D flow. Conceptual flow models were developed by gradually reducing the number of lithologic units in the unconfined aquifer and confining unit by calculating composite hydraulic properties for the simplified lithologic units. Composite hydraulic properties were calculated using either thickness-weighted averages or inverse modeling using regression-based parameter estimation. No significant residuals were simulated when all lithologic units comprising the unconfined aquifer were simulated as one layer. The largest residuals occurred when the unconfined aquifer and confining unit were aggregated into a single layer (quasi-3D), with residuals over 100% for the leakage rates to the confined aquifer and the heads in the confining unit. Residuals increased with contrasts in vertical hydraulic conductivity between the unconfined aquifer and confining unit. Residuals increased when the constant-head boundary at the bottom of the Upper Floridan aquifer was replaced with a no-flow boundary.

Flow and heat transfer of nanofluid over a stretching sheet with non-linear velocity in the presence of thermal radiation and chemical reaction

NASA Astrophysics Data System (ADS)

Madaki, A. G.; Roslan, R.; Kandasamy, R.; Chowdhury, M. S. H.

2017-04-01

In this paper, the effects of Brownian motion, thermophoresis, chemical reaction, heat generation, magnetohydrodynamic and thermal radiation has been included in the model of nanofluid flow and heat transfer over a moving surface with variable thickness. The similarity transformation is used to transform the governing boundary layer equations into ordinary differential equations (ODE). Both optimal homotopy asymptotic method (OHAM) and Runge-Kutta fourth order method with shooting technique are employed to solve the resulting ODEs. For different values of the pertinent parameters on the velocity, temperature and concentration profiles have been studied and details are given in tables and graphs respectively. A comparison with the previous study is made, where an excellent agreement is achieved. The results demonstrate that the radiation parameter N increases, with the increase in both the temperature and the thermal boundary layer thickness respectively. While the nanoparticles concentration profiles increase with the influence of generative chemical reaction γ < 0, while it decreases with destructive chemical reaction γ > 0.

Simulations of the kinematic dynamo onset of spherical Couette flows with smooth and rough boundaries.

PubMed

Finke, K; Tilgner, A

2012-07-01

We study numerically the dynamo transition of an incompressible electrically conducting fluid filling the gap between two concentric spheres. In a first series of simulations, the fluid is driven by the rotation of a smooth inner sphere through no-slip boundary conditions, whereas the outer sphere is stationary. In a second series a volume force intended to simulate a rough surface drives the fluid next to the inner sphere within a layer of thickness one-tenth of the gap width. We investigate the effect of the boundary layer thickness on the dynamo threshold in the turbulent regime. The simulations show that the boundary forcing simulating the rough surface lowers the necessary rotation rate, which may help to improve spherical dynamo experiments.

Experimental studies of shock-wave/wall-jet interaction in hypersonic flow

NASA Technical Reports Server (NTRS)

Holden, Michael S.; Rodriguez, Kathleen

1994-01-01

Experimental studies have been conducted to examine slot film cooling effectiveness and the interaction between the cooling film and an incident planar shock wave in turbulent hypersonic flow. The experimental studies were conducted in the 48-inch shock tunnel at Calspan at a freestream Mach number of close to 6.4 and at a Reynolds number of 35 x 10(exp 6) based on the length of the model at the injection point. The Mach 2.3 planar wall jet was generated from 40 transverse nozzles (with heights of both 0.080 inch and 0.120 inch), producing a film that extended the full width of the model. The nozzles were operated at pressures and velocities close to matching the freestream, as well as at conditions where the nozzle flows were over- and under-expanded. A two-dimensional shock generator was used to generate oblique shocks that deflected the flow through total turnings of 11, 16, and 21 degrees; the flows impinged downstream of the nozzle exits. Detailed measurements of heat transfer and pressure were made both ahead and downstream of the injection station, with the greatest concentration of measurements in the regions of shock-wave/boundary layer interaction. The major objectives of these experimental studies were to explore the effectiveness of film cooling in the presence of regions of shock-wave/boundary layer interaction and, more specifically, to determine how boundary layer separation and the large recompression heating rates were modified by film cooling. Detailed distributions of heat transfer and pressure were obtained in the incident shock/wall-jet interaction region for a series of shock strengths and impingement positions for each of the two nozzle heights. Measurements were also made to examine the effects of nozzle lip thickness on cooling effectiveness. The major conclusion from these studies was that the effect of the cooling film could be readily dispersed by relatively weak incident shocks, so the peak heating in the recompression region was not significantly reduced by even the largest levels of film cooling. For the case studies in the absence of film cooling, the interaction regions were unseparated. However, adding film cooling resulted in regions of boundary layer separation induced in the film cooling layer -- the size of which regions first increased and then decreased with increased film cooling. Surprisingly, the size of the separated regions and the magnitude of the recompression heating were not strongly influenced by the thickness of the cooling film, nor by the point of shock impingement relative to the exit plane of the nozzles. The lip thickness was found to have little effect on cooling effectiveness. Measurements with and in the absence of shock interaction were compared with the results of earlier experimental studies and correlated in terms of the major parameters controlling these flows.

Experimental studies of shock-wave/wall-jet interaction in hypersonic flow, part A

NASA Technical Reports Server (NTRS)

Holden, Michael S.; Rodriguez, Kathleen

1994-01-01

Experimental studies have been conducted to examine slot film cooling effectiveness and the interaction between the cooling film and an incident planar shock wave in turbulent hypersonic flow. The experimental studies were conducted in the 48-inch shock tunnel at Calspan at a freestream Mach number of close to 6.4 and at a Reynolds number of 35 x 10(exp 6) based on the length of the model at the injection point. The Mach 2.3 planar wall jet was generated from 40 transverse nozzles (with heights of both 0.080 inch and 0.120 inch), producing a film that extended the full width of the model. The nozzles were operated at pressures and velocities close to matching the freestream, as well as at conditions where the nozzle flows were over- and under-expanded. A two-dimensional shock generator was used to generate oblique shocks that deflected the flow through total turnings of 11, 16, and 21 degrees; the flows impinged downstream of the nozzle exits. Detailed measurements of heat transfer and pressure were made both ahead and downstream of the injection station, with the greatest concentration of measurements in the regions of shock-wave/boundary layer interaction. The major objectives of these experimental studies were to explore the effectiveness of film cooling in the presence of regions of shock-wave/boundary layer interaction and, more specifically, to determine how boundary layer separation and the large recompression heating rates were modified by film cooling. Detailed distributions of heat transfer and pressure were obtained in the incident-shock/wall-jet interaction region for a series of shock strengths and impingement positions for each of the two nozzle heights. Measurements were also made to examine the effects of nozzle lip thickness on cooling effectiveness. The major conclusion from these studies was that the effect of the cooling film could be readily dispersed by relatively weak incident shocks, so the peak heating in the recompression region was not significantly reduced by even the largest levels of film cooling. For the case studies in the absence of film cooling, the interaction regions were unseparated. However, adding film cooling resulted in regions of boundary layer separation induced in the film cooling layer, the size of which regions first increased and then decreased with increased film cooling. Surprisingly, the size of the separated regions and the magnitude of the recompression heating were not strongly influenced by the thickness of the cooling film, nor by the point of shock impingement relative to the exit plane of the nozzles. The lip thickness was found to have little effect on cooling effectiveness. Measurements with and in the absence of shock interaction were compared with the results of earlier experimental studies and correlated in terms of the major parameters controlling these flows.

Navier-Stokes analysis of radial turbine rotor performance

NASA Technical Reports Server (NTRS)

Larosiliere, L. M.

1993-01-01

An analysis of flow through a radial turbine rotor using the three-dimensional, thin-layer Navier-Stokes code RVC3D is described. The rotor is a solid version of an air-cooled metallic radial turbine having thick trailing edges, shroud clearance, and scalloped-backface clearance. Results are presented at the nominal operating condition using both a zero-clearance model and a model simulating the effects of the shroud and scalloped-backface clearance flows. A comparison with the available test data is made and details of the internal flow physics are discussed, allowing a better understanding of the complex flow distribution within the rotor.

An analysis method for multi-component airfoils in separated flow

NASA Technical Reports Server (NTRS)

Rao, B. M.; Duorak, F. A.; Maskew, B.

1980-01-01

The multi-component airfoil program (Langley-MCARF) for attached flow is modified to accept the free vortex sheet separation-flow model program (Analytical Methods, Inc.-CLMAX). The viscous effects are incorporated into the calculation by representing the boundary layer displacement thickness with an appropriate source distribution. The separation flow model incorporated into MCARF was applied to single component airfoils. Calculated pressure distributions for angles of attack up to the stall are in close agreement with experimental measurements. Even at higher angles of attack beyond the stall, correct trends of separation, decrease in lift coefficients, and increase in pitching moment coefficients are predicted.

A new flow model for highly separated airfoil flows at low speeds

NASA Technical Reports Server (NTRS)

Zumwalt, G. W.; Naik, S. N.

1979-01-01

An analytical model for separated airfoil flows is presented which is based on experimentally observed physical phenomena. These include a free stagnation point aft of the airfoil and a standing vortex in the separated region. A computer program is described which iteratively matches the outer potential flow, the airfoil turbulent boundary layer, the separated jet entrainment, mass conservation in the separated bubble, and the rear stagnation pressure. Separation location and pressure are not specified a priori. Results are presented for surface pressure coefficient and compared with experiment for three angles of attack for a GA(W)-1, 17% thick airfoil.

Experimental study of the flow over a backward-facing rounded ramp

NASA Astrophysics Data System (ADS)

Duriez, Thomas; Aider, Jean-Luc; Wesfreid, Jose Eduardo

2010-11-01

The backward-facing rounded ramp (BFR) is a very simple geometry leading to boundary layer separation, close to the backward facing step (BFS) flow. The main difference with the BFS flow is that the separation location depends on the incoming flow while it is fixed to the step edge for the BFS flow. Despite the simplicity of the geometry, the flow is complex and the transition process still has to be investigated. In this study we investigate the BFR flow using time-resolved PIV. For Reynolds number ranging between 300 and 12 000 we first study the time averaged properties such as the positions of the separation and reattachment, the recirculation length and the shear layer thickness. The time resolution also gives access to the characteristic frequencies of the time-dependant flow. An appropriate Fourier filtering of the flow field, around each frequency peak in the global spectrum, allows an investigation of each mode in order to extract its wavelength, phase velocity, and spatial distribution. We then sort the spectral content and relate the main frequencies to the most amplified Kelvin-Helmholtz instability mode and its harmonics, the vortex pairing, the low frequency recirculation bubble oscillation and the interactions between all these phenomena.

Evidence for water-mediated mechanisms in coral-algal interactions.

PubMed

Jorissen, Hendrikje; Skinner, Christina; Osinga, Ronald; de Beer, Dirk; Nugues, Maggy M

2016-08-17

Although many coral reefs have shifted from coral-to-algal dominance, the consequence of such a transition for coral-algal interactions and their underlying mechanisms remain poorly understood. At the microscale, it is unclear how diffusive boundary layers (DBLs) and surface oxygen concentrations at the coral-algal interface vary with algal competitors and competitiveness. Using field observations and microsensor measurements in a flow chamber, we show that coral (massive Porites) interfaces with thick turf algae, macroalgae, and cyanobacteria, which are successful competitors against coral in the field, are characterized by a thick DBL and hypoxia at night. In contrast, coral interfaces with crustose coralline algae, conspecifics, and thin turf algae, which are poorer competitors, have a thin DBL and low hypoxia at night. Furthermore, DBL thickness and hypoxia at the interface with turf decreased with increasing flow speed, but not when thick turf was upstream. Our results support the importance of water-mediated transport mechanisms in coral-algal interactions. Shifts towards algal dominance, particularly dense assemblages, may lead to thicker DBLs, higher hypoxia, and higher concentrations of harmful metabolites and pathogens along coral borders, which in turn may facilitate algal overgrowth of live corals. These effects may be mediated by flow speed and orientation. © 2016 The Author(s).

Shear Stress induced Stretching of Red Blood Cells by Oscillating Bubbles within a Narrow Gap

NASA Astrophysics Data System (ADS)

Li, Fenfang; Mohammadzadeh, Milad; Ohl, Claus-Dieter; Claus-Dieter Ohl Team

2013-11-01

The flow pattern, especially the boundary layer caused by the expanding/contracting bubble in a narrow gap (15 μm) and the resultant stretching of red blood cells is investigated in this work. High speed recordings show that a red blood cell (biconcave shape, thickness of 1-2 μm) can be elongated to five times its original length by a laser-induced cavitation bubble within the narrow gap. However, flexible cancer cells in suspension (RKO, spherical shape, diameter of 10-15 μm) are hardly elongated under the same experimental condition. We hypothesize that the shear stress at the boundary layer is crucial for this elongation to occur. Therefore, in order to resolve the related fluid dynamics, we conducted numerical simulations using the finite element method (Fluent). The rapidly expanding/contracting vapor bubble is successfully modeled by employing viscosity and surface tension. The transient pressure inside the bubble and the velocity profile of the flow is obtained. We observe strong shear near the upper and lower boundary during the bubble oscillation. The flow fields are compared with analytical solutions to transient and pulsating flows in 2D. In the experiment the red blood cells sit within the lower boundary layer, thus are probably elongated by this strong shear flow. In contrast, the spherical cancer cells are of comparable size to the gap height so that they are lesser affected by this boundary layer flow.

Earth Observations taken by the Expedition 22 Crew

NASA Image and Video Library

2009-12-09

ISS022-E-008285 (9 Dec. 2009) --- Llullaillaco volcano on the Argentina-Chile border is featured in this image photographed by an Expedition 22 crew member on the International Space Station. The summit of Llullaillaco volcano has an elevation of 6,739 meters above sea level, making it the highest historically active volcano in the world. The current Llullaillaco stratovolcano ? a typically high, cone-shaped volcano built from successive layers of thick lava flows and eruption products like ash and rock fragments ? is built on top of an older stratovolcano. The last explosive eruption of the volcano occurred in 1877 based on historical records. This detailed photograph of Llullaillaco illustrates an interesting volcanic feature known as a coulee (top left). Coulees are formed from highly viscous, thick lavas that flow onto a steep surface; as they flow slowly downwards, the top of the flow cools and forms a series of parallel ridges oriented at 90 degrees to the direction of flow (somewhat similar in appearance to the pleats of an accordion). The sides of the flow can also cool faster than the center, leading to the formation of wall-like structures known as flow levees (center).

Finite volume solution of the compressible boundary-layer equations

NASA Technical Reports Server (NTRS)

Loyd, B.; Murman, E. M.

1986-01-01

A box-type finite volume discretization is applied to the integral form of the compressible boundary layer equations. Boundary layer scaling is introduced through the grid construction: streamwise grid lines follow eta = y/h = const., where y is the normal coordinate and h(x) is a scale factor proportional to the boundary layer thickness. With this grid, similarity can be applied explicity to calculate initial conditions. The finite volume method preserves the physical transparency of the integral equations in the discrete approximation. The resulting scheme is accurate, efficient, and conceptually simple. Computations for similar and non-similar flows show excellent agreement with tabulated results, solutions computed with Keller's Box scheme, and experimental data.

Ice sublimation and rheology - Implications for the Martian polar layered deposits

NASA Astrophysics Data System (ADS)

Hofstadter, M. D.; Murray, B. C.

1990-04-01

If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

Ice sublimation and rheology - Implications for the Martian polar layered deposits

NASA Technical Reports Server (NTRS)

Hofstadter, Mark D.; Murray, Bruce C.

1990-01-01

If the sublimation and creep of water ice are important processes in the Martian polar layered deposits, ice-rich scenario formation and evolution schemes must invoke a mechanism for the inhibition of sublimation, such as a dust layer derived from the residue of the sublimating deposits. This layer could be of the order of 1 m in thickness. If the deposits are ice-rich, flows of more than 1 km should have occurred. It is noted that the dust particles in question may be cemented by such ice that may be present, but that impurities may also have served to cement dust particles together even in the absence of ice.

Constraints on the Lithospheric Strength at Volcanic Rifted Margins from the Geometry of Seaward Dipping Reflectors Using Analytic and Numerical Models

NASA Astrophysics Data System (ADS)

Tian, X.; Buck, W. R.

2017-12-01

Seaward dipping reflectors (SDRs) are found at many rifted margins. Drilling indicates SDRs are interbedded layers of basalts and sediments. Multi-channel seismic reflection data show SDRs with various width (2 100 km), thickness (1 15 km) and dip angles (0 30). Recent studies use analytic thin plate models (AtPM) to describe plate deflections under volcanic loads. They reproduce a wide range of SDRs structures without detachment faulting. These models assume that the solidified dikes provide downward loads at the rifting center. Meanwhile, erupted lava flows and sediments fill in the flexural depression and further load the lithosphere. Because the strength of the lithosphere controls the amount and wavelength of bending, the geometries of SDRs provide a window into the strength of the lithosphere during continental rifting. We attempt to provide a quantitative mapping between the SDR geometry and the lithospheric strength and thickness during rifting. To do this, we first derive analytic solutions to two observables that are functions of effective elastic thickness (Te). One observable (Xf) is the horizontal distance for SDRs to evolve from flat layers to the maximum bent layers. Another observable is the ratio between the thickness and the tangent of the maximum slope of SDRs at Xf. We then extend the AtPM to numerical thin plate models (NtPM) with spatially restricted lava flows. AtPM and NtPM show a stable and small relative difference in terms of the two observables with different values of Te. This provides a mapping of Te between NtPM and AtPM models. We also employ a fully two-dimensional thermal-mechanical treatment with elasto-visco-plastic rheology to simulate SDRs formation. These models show that brittle yielding due to bending can reduce the Te of the lithosphere by as much as 50% of the actual brittle lithospheric thickness. Quantification of effects of plastic deformation on bending allow us to use Te to link SDRs geometries to brittle lithospheric thickness. From published seismic reflection data, we obtain a global map of Te at volcanic rifted margins that ranges from 2 12 km using the AtPM and NtPM mapping. The corresponding brittle lithospheric thickness ranges from 6 20 km. In addition, preliminary results show Te increases along a given margin with distance away from a Large Igneous Province.

Atmospheric pressure spatial atomic layer deposition web coating with in situ monitoring of film thickness

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

Yersak, Alexander S.; Lee, Yung C.; Spencer, Joseph A.

Spectral reflectometry was implemented as a method for in situ thickness monitoring in a spatial atomic layer deposition (ALD) system. Al{sub 2}O{sub 3} films were grown on a moving polymer web substrate at 100 °C using an atmospheric pressure ALD web coating system, with film growth of 0.11–0.13 nm/cycle. The modular coating head design and the in situ monitoring allowed for the characterization and optimization of the trimethylaluminum and water precursor exposures, purge flows, and web speed. A thickness uniformity of ±2% was achieved across the web. ALD cycle times as low as 76 ms were demonstrated with a web speed of 1 m/smore » and a vertical gap height of 0.5 mm. This atmospheric pressure ALD system with in situ process control demonstrates the feasibility of low-cost, high throughput roll-to-roll ALD.« less

T-COMP—A suite of programs for extracting transmissivity from MODFLOW models

USGS Publications Warehouse

Halford, Keith J.

2016-02-12

Simulated transmissivities are constrained poorly by assigning permissible ranges of hydraulic conductivities from aquifer-test results to hydrogeologic units in groundwater-flow models. These wide ranges are derived from interpretations of many aquifer tests that are categorized by hydrogeologic unit. Uncertainty is added where contributing thicknesses differ between field estimates and numerical models. Wide ranges of hydraulic conductivities and discordant thicknesses result in simulated transmissivities that frequently are much greater than aquifer-test results. Multiple orders of magnitude differences frequently occur between simulated and observed transmissivities where observed transmissivities are less than 1,000 feet squared per day.Transmissivity observations from individual aquifer tests can constrain model calibration as head and flow observations do. This approach is superior to diluting aquifer-test results into generalized ranges of hydraulic conductivities. Observed and simulated transmissivities can be compared directly with T-COMP, a suite of three FORTRAN programs. Transmissivity observations require that simulated hydraulic conductivities and thicknesses in the volume investigated by an aquifer test be extracted and integrated into a simulated transmissivity. Transmissivities of MODFLOW model cells are sampled within the volume affected by an aquifer test as defined by a well-specific, radial-flow model of each aquifer test. Sampled transmissivities of model cells are averaged within a layer and summed across layers. Accuracy of the approach was tested with hypothetical, multiple-aquifer models where specified transmissivities ranged between 250 and 20,000 feet squared per day. More than 90 percent of simulated transmissivities were within a factor of 2 of specified transmissivities.

Mechanical modeling and characteristic study for the adhesive contact of elastic layered media

NASA Astrophysics Data System (ADS)

Zhang, Yuyan; Wang, Xiaoli; Tu, Qiaoan; Sun, Jianjun; Ma, Chenbo

2017-11-01

This paper investigates the adhesive contact between a smooth rigid sphere and a smooth elastic layered medium with different layer thicknesses, layer-to-substrate elastic modulus ratios and adhesion energy ratios. A numerical model is established by combining elastic responses of the contact system and an equation of equivalent adhesive contact pressure which is derived based on the Hamaker summation method and the Lennard-Jones intermolecular potential law. Simulation results for hard layer cases demonstrate that variation trends of the pull-off force with the layer thickness and elastic modulus ratio are complex. On one hand, when the elastic modulus ratio increases, the pull-off force decreases at smaller layer thicknesses, decreases at first and then increases at middle layer thicknesses, while increases monotonously at larger layer thicknesses. On the other hand, the pull-off force decreases at first and then increases with the increase in the layer thickness. Furthermore, a critical layer thickness above which the introduction of hard layer cannot reduce adhesion and an optimum layer thickness under which the pull-off force reaches a minimum are found. Both the critical and optimum layer thicknesses become larger with an increase in the Tabor parameter, while they tend to decrease with the increase in the elastic modulus ratio. In addition, the pull-off force increases sublinearly with the adhesion energy ratio if the layer thickness and elastic modulus ratio are fixed.

Improvement of crystalline quality of N-polar AlN layers on c-plane sapphire by low-pressure flow-modulated MOCVD

NASA Astrophysics Data System (ADS)

Takeuchi, M.; Shimizu, H.; Kajitani, R.; Kawasaki, K.; Kumagai, Y.; Koukitu, A.; Aoyagi, Y.

2007-01-01

The growth of N-polar AlN layers on c-plane sapphire is reported. Low-temperature AlN (LT-AlN) layers were used as seeding buffer layers with pre-nitridation for sapphire. To avoid strong vapor-phase reaction between trimethylaluminum (TMA) and ammonia (NH 3) and to improve the crystalline quality, low-pressure flow-modulated (FM) metal-organic chemical vapor deposition (MOCVD) technique was introduced with careful optimization of the FM sequence. The surface morphologies and the crystalline quality defined by the X-ray diffraction (XRD) (0 0 2) and (1 0 0) rocking curve measurements strongly depended on the LT-AlN thickness and on the TMA coverage per cycle of the FM growth. The sample showing the best XRD data with a good morphology was almost completely etched in aqueous KOH solution owing to N-polarity. From the plan-view transmission electron microscopy (TEM) observation, the dislocation density was counted to be about 3×10 10 cm -2.

Compositional depth profile of a native oxide LPCVD MNOS structure using X-ray photoelectron spectroscopy and chemical etching

NASA Technical Reports Server (NTRS)

Wurzbach, J. A.; Grunthaner, F. J.

1983-01-01

It is pointed out that there is no report of an unambiguous analysis of the composition and interfacial structure of MNOS (metal-nitride oxide semiconductor) systems, despite the technological importance of these systems. The present investigation is concerned with a study of an MNOS structure on the basis of a technique involving the use of X-ray photoelectron spectroscopy (XPS) with a controlled stopped-flow chemical-etching procedure. XPS is sensitive to the structure of surface layers, while stopped-flow etching permits the controlled removal of overlying material on a scale of atomic layers, to expose new surface layers as a function of thickness. Therefore, with careful analysis of observed intensities at measured depths, this combination of techniques provides depth resolution between 5 and 10 A. According to the obtained data there is intact SiO2 at the substrate interface. There appears to be a thin layer containing excess bonds to silicon on top of the SiO2.

STC-SAB program users manual for the turbulent boundary layer and turbulent separation prediction methods employed in the NASA Langley streamtube curvature computer program

NASA Technical Reports Server (NTRS)

Ferguson, D. R.

1972-01-01

The streamtube curvature program (STC) has been developed to predict the inviscid flow field and the pressure distribution about nacelles at transonic speeds. The effects of boundary layer are to displace the inviscid flow and effectively change the body shape. Thus, the body shape must be corrected by the displacement thickness in order to calculate the correct pressure distribution. This report describes the coupling of the Stratford and Beavers boundary layer solution with the inviscid STC analysis so that all nacelle pressure forces, friction drag, and incipient separation may be predicted. The usage of the coupled STC-SAB computer program is outlined and the program input and output are defined. Included in this manual are descriptions of the principal boundary layer tables and other revisions to the STC program. The use of the viscous option is controlled by the engineer during program input definition.

Optimal Control of Shock Wave Turbulent Boundary Layer Interactions Using Micro-Array Actuation

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Tinapple, Jon; Surber, Lewis

2006-01-01

The intent of this study on micro-array flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to determine optimal designs of micro-array actuation for controlling the shock wave turbulent boundary layer interactions within supersonic inlets and compare these concepts to conventional bleed performance. The term micro-array refers to micro-actuator arrays which have heights of 25 to 40 percent of the undisturbed supersonic boundary layer thickness. This study covers optimal control of shock wave turbulent boundary layer interactions using standard micro-vane, tapered micro-vane, and standard micro-ramp arrays at a free stream Mach number of 2.0. The effectiveness of the three micro-array devices was tested using a shock pressure rise induced by the 10 shock generator, which was sufficiently strong as to separate the turbulent supersonic boundary layer. The overall design purpose of the micro-arrays was to alter the properties of the supersonic boundary layer by introducing a cascade of counter-rotating micro-vortices in the near wall region. In this manner, the impact of the shock wave boundary layer (SWBL) interaction on the main flow field was minimized without boundary bleed.

Designing the Color of Hot-Dip Galvanized Steel Sheet Through Destructive Light Interference Using a Zn-Ti Liquid Metallic Bath

NASA Astrophysics Data System (ADS)

Levai, Gabor; Godzsák, Melinda; Török, Tamas I.; Hakl, Jozsef; Takáts, Viktor; Csik, Attila; Vad, Kalman; Kaptay, George

2016-07-01

The color of hot-dip galvanized steel sheet was adjusted in a reproducible way using a liquid Zn-Ti metallic bath, air atmosphere, and controlling the bath temperature as the only experimental parameter. Coloring was found only for samples cooled in air and dipped into Ti-containing liquid Zn. For samples dipped into a 0.15 wt pct Ti-containing Zn bath, the color remained metallic (gray) below a 792 K (519 °C) bath temperature; it was yellow at 814 K ± 22 K (541 °C ± 22 °C), violet at 847 K ± 10 K (574 °C ± 10 °C), and blue at 873 K ± 15 K (600 °C ± 15 °C). With the increasing bath temperature, the thickness of the adhered Zn-Ti layer gradually decreased from 52 to 32 micrometers, while the thickness of the outer TiO2 layer gradually increased from 24 to 69 nm. Due to small Al contamination of the Zn bath, a thin (around 2 nm) alumina-rich layer is found between the outer TiO2 layer and the inner macroscopic Zn layer. It is proven that the color change was governed by the formation of thin outer TiO2 layer; different colors appear depending on the thickness of this layer, mostly due to the destructive interference of visible light on this transparent nano-layer. A complex model was built to explain the results using known relationships of chemical thermodynamics, adhesion, heat flow, kinetics of chemical reactions, diffusion, and optics. The complex model was able to reproduce the observations and allowed making predictions on the color of the hot-dip galvanized steel sample, as a function of the following experimental parameters: temperature and Ti content of the Zn bath, oxygen content, pressure, temperature and flow rate of the cooling gas, dimensions of the steel sheet, velocity of dipping the steel sheet into the Zn-Ti bath, residence time of the steel sheet within the bath, and the velocity of its removal from the bath. These relationships will be valuable for planning further experiments and technologies on color hot-dip galvanization of steel by Zn-Ti alloys.

Deciphering Depositional Signals in the Bed-Scale Stratigraphic Record of Submarine Channels

NASA Astrophysics Data System (ADS)

Sylvester, Z.; Covault, J. A.

2017-12-01

Submarine channels are important conduits of sediment transfer from rivers and shallow-marine settings into the deep sea. As such, the stratigraphic record of submarine-channel systems can store signals of past climate- and other environmental changes in their upstream sediment-source areas. This record is highly fragmented as channels are primarily locations of sediment bypass; channelized turbidity currents are likely to leave a more complete record in areas away from and above the thalweg. However, the link between the thick-bedded axial channel deposits that record a small number of flows and the much larger number of thin-bedded turbidites forming terrace- and levee deposits is poorly understood. We have developed a relatively simple two-dimensional model that, given a number of input flow parameters (mean velocity, grain size, duration of deposition, flow thickness), predicts the thickness and composition of the turbidite that is left behind in the channel and in the overbank areas. The model is based on a Rouse-type suspended sediment concentration profile and the Garcia-Parker entrainment function. In the vertical direction, turbidites tend to rapidly become thinner and finer-grained with height above thalweg, due to decreasing concentration. High near-thalweg concentrations result in thick axial beds. However, an increase in flow velocity can result in high entrainment and no deposition at the bottom of the channel, yet a thin layer of sand and mud is still deposited higher up on the channel bank. If channel thalwegs are largely in a bypass condition, relatively minor velocity fluctuations result in a few occasionally preserved thick beds in the axis, and numerous thin turbidites - and a more complete record - on the channel banks. We use near-seafloor data from the Niger Delta slope and an optimization algorithm to show how our model can be used to invert for likely flow parameters and match the bed thickness and grain size of 100 turbidites observed in a core taken from a slope channel terrace.

Effects of Reynolds number on orifice induced pressure error

NASA Technical Reports Server (NTRS)

Plentovich, E. B.; Gloss, B. B.

1982-01-01

Data previously reported for orifice induced pressure errors are extended to the case of higher Reynolds number flows, and a remedy is presented in the form of a porous metal plug for the orifice. Test orifices with apertures 0.330, 0.660, and 1.321 cm in diam. were fabricated on a flat plate for trials in the NASA Langley wind tunnel at Mach numbers 0.40-0.72. A boundary layer survey rake was also mounted on the flat plate to allow measurement of the total boundary layer pressures at the orifices. At the high Reynolds number flows studied, the orifice induced pressure error was found to be a function of the ratio of the orifice diameter to the boundary layer thickness. The error was effectively eliminated by the insertion of a porous metal disc set flush with the orifice outside surface.

Experimental study of flow reattachment in a single-sided sudden expansion

NASA Technical Reports Server (NTRS)

Westphal, R. V.; Johnston, J. P.; Eaton, J. K.

1984-01-01

The reattachment of a fully turbulent, two dimensional, separated shear layer downstream of a single-sided sudden expansion in a planar duct flow was examined experimentally. The importance of changing the structure of the separated shear layer on the reattachment process itself was examined. For all cases, the Reynolds number based on step height was greater than 20,000, the expansion ratio was 5/3, and the inlet boundary layer was less than one-half step height in thickness. A crucially important phase was the development of a pulsed wall probe for measurement of skin friction in the reattachment region, thus providing an unambiguous definition of the reattachment length. Quantitative features of reattachment - including streamwise development of the mean and fluctuating velocity field, pressure rise, and skin friction - were found to be similar for all cases studied when scaled by the reattachment length. A definition of the reattachment zone is proposed.

Microwave reflection, transmission, and absorption by human brain tissue

NASA Astrophysics Data System (ADS)

Ansari, M. A.; Akhlaghipour, N.; Zarei, M.; Niknam, A. R.

2018-04-01

These days, the biological effects of electromagnetic (EM) radiations on the brain, especially in the frequency range of mobile communications, have caught the attention of many scientists. Therefore, in this paper, the propagation of mobile phone electromagnetic waves in the brain tissues is investigated analytically and numerically. The brain is modeled by three layers consisting of skull, grey and white matter. First, we have analytically calculated the microwave reflection, transmission, and absorption coefficients using signal flow graph technique. The effect of microwave frequency and variations in the thickness of layers on the propagation of microwave through brain are studied. Then, the penetration of microwave in the layers is numerically investigated by Monte Carlo method. It is shown that the analytical results are in good agreement with those obtained by Monte Carlo method. Our results indicate the absorbed microwave energy depends on microwave frequency and thickness of brain layers, and the absorption coefficient is optimized at a number of frequencies. These findings can be used for comparing the microwave absorbed energy in a child's and adult's brain.

Preparation of nanocrystalline TiN coated cubic boron nitride powders by a sol-gel process.

PubMed

Park, Hee S; Umer, M Adeel; Ryu, Ho J; Hong, Soon H

2011-01-01

Cubic boron nitride (cBN) particles coated with 20 wt% nanocrystalline TiN were prepared by coating the surface of cBN particles with TiO2, followed by nitridation with NH3 gas at 900 degrees C. Coating of TiO2 on cBN powders was accomplished by a sol-gel process from a solution of titanium (IV) isopropoxide and anhydrous ethanol. An amorphous TiO(x) layer of 50 nm thickness was homogenously formed on the surface of the cBN particles by the sol-gel process. The amorphous layer was then crystallized to an anatase TiO2 phase through calcination in air at 400 degrees C. The crystallized TiO2 layer was 50 nm in thickness, and the size of TiO2 particles comprising the layer was nearly 10 nm. The TiO2 on cBN surfaces was completely converted into nanocrystalline TiN of uniform particles 20 nm in size on cBN particles by nitridation under flowing NH3 gas.

Convection in superposed fluid and porous layers

NASA Technical Reports Server (NTRS)

Chen, Falin; Chen, C. F.

1992-01-01

Thermal convection due to heating from below in a porous layer underlying a fluid layer has been analyzed using the Navier-Stokes equations for the fluid layers and the extended Darcy equation (including Brinkman and Forchheimer terms) for the porous layer. The flow is assumed to be two-dimensional and periodic in the horizontal direction. The numerical scheme used is a combined Galerkin and finite-difference method, and appropriate boundary conditions are applied at the interface. Results have been obtained for depth ratios of 0, 0.1, 0.2, 0.5, and 1.0, where this ratio is defined as the ratio of the thickness of the fluid layer to that of the porous layer. For the depth ratio of 0.1, the convection is dominated by the porous layer, similar to the situation at onset, even though the Rayleigh number for the fluid layer is well into the supercritical regime.

Method for fabrication of electrodes

DOEpatents

Jankowski, Alan F.; Morse, Jeffrey D.; Barksdale, Randy

2004-06-22

Described herein is a method to fabricate porous thin-film electrodes for fuel cells and fuel cell stacks. Furthermore, the method can be used for all fuel cell electrolyte materials which utilize a continuous electrolyte layer. An electrode layer is deposited on a porous host structure by flowing gas (for example, Argon) from the bottomside of the host structure while simultaneously depositing a conductive material onto the topside of the host structure. By controlling the gas flow rate through the pores, along with the process conditions and deposition rate of the thin-film electrode material, a film of a pre-determined thickness can be formed. Once the porous electrode is formed, a continuous electrolyte thin-film is deposited, followed by a second porous electrode to complete the fuel cell structure.

The effects of streamwise concave curvature on turbulent boundary layer structure

NASA Astrophysics Data System (ADS)

Jeans, A. H.; Johnston, J. P.

1982-06-01

Concave curvature has a relatively large, unpredictable effect on turbulent boundary layers. Some, but not all previous studies suggest that a large-scale, stationary array of counter-rotating vortices exists within the turbulent boundary layer on a concave wall. The objective of the present study was to obtain a qualitative model of the flow field in order to increase our understanding of the underlying physics. A large free-surface water channel was constructed in order to perform a visual study of the flow. Streamwise components of mean velocity and turbulence intensity were measured using a hot film anemometer. The upstream boundary was spanwise uniform with a momentum thickness to radius of curvature of 0.05. Compared to flat wall flow, large-scale, randomly distributed sweeps and ejections were seen in the boundary layer on the concave wall. The sweeps appear to suppress the normal mechanism for turbulence production near the wall by inhibiting the bursting process. The ejections appear to enhance turbulence production in the outer layers as the low speed fluid convected from regions near the wall interacts with the higher speed fluid farther out. The large-scale structures did not occur at fixed spanwise locations, and could not be called roll cells or vortices.

Pressure gradient effects on heat transfer to reusable surface insulation tile-array gaps

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1975-01-01

An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer within space shuttle reusable surface insulation (RSI) tile-array gaps under thick, turbulent boundary-layer conditions. Heat-transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel-wall boundary layer at a nominal free-stream Mach number and free-stream Reynolds numbers. Transverse pressure gradients of varying degree were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel-wall boundary-layer flow was obtained by measurement of boundary-layer pitot pressure profiles, wall pressure, and heat transfer. Flat-plate heat-transfer data were correlated and a method was derived for prediction of heat transfer to a smooth curved surface in the highly three-dimensional tunnel-wall boundary-layer flow. Pressure on the floor of the RSI tile-array gap followed the trends of the external surface pressure. Heat transfer to the surface immediately downstream of a transverse gap is higher than that for a smooth surface at the same location. Heating to the wall of a transverse gap, and immediately downstream of it, at its intersection with a longitudinal gap is significantly greater than that for the simple transverse gap.

The Edge Detectors Suitable for Retinal OCT Image Segmentation

PubMed Central

Yang, Jing; Gao, Qian; Zhou, Sheng

2017-01-01

Retinal layer thickness measurement offers important information for reliable diagnosis of retinal diseases and for the evaluation of disease development and medical treatment responses. This task critically depends on the accurate edge detection of the retinal layers in OCT images. Here, we intended to search for the most suitable edge detectors for the retinal OCT image segmentation task. The three most promising edge detection algorithms were identified in the related literature: Canny edge detector, the two-pass method, and the EdgeFlow technique. The quantitative evaluation results show that the two-pass method outperforms consistently the Canny detector and the EdgeFlow technique in delineating the retinal layer boundaries in the OCT images. In addition, the mean localization deviation metrics show that the two-pass method caused the smallest edge shifting problem. These findings suggest that the two-pass method is the best among the three algorithms for detecting retinal layer boundaries. The overall better performance of Canny and two-pass methods over EdgeFlow technique implies that the OCT images contain more intensity gradient information than texture changes along the retinal layer boundaries. The results will guide our future efforts in the quantitative analysis of retinal OCT images for the effective use of OCT technologies in the field of ophthalmology. PMID:29065594

Complementary velocity and heat transfer measurements in a rotating turbine cooling passage

NASA Astrophysics Data System (ADS)

Bons, Jeffrey Peter

An experimental investigation was conducted on the internal flowfield of a simulated turbine blade cooling passage. The passage is of a square cross-section and was manufactured from quartz for optical accessibility. Velocity measurements were taken using Particle Image Velocimetry for both heated and non-heated cases. Thin film resistive heaters on the four passage walls allow heat to be added to the coolant flow without obstructing laser access. Under the same conditions, an infrared detector with associated optics collected wall temperature data for use in calculating local Nusselt number. The test section was operated with radial outward flow and at values of Reynolds number, Rotation number, and density ratio typical of applications. Velocity data for the non-heated case document the evolution of the Coriolis-induced double vortex. The vortex has the effect of increasing the leading side boundary layer thickness while decreasing the trailing side boundary layer thickness. Also, the streamwise component of the Coriolis acceleration creates a thinned side wall boundary layer. These data reveal an unsteady, turbulent flowfield in the cooling passage. Velocity data for the heated case show a strongly distorted streamwise profile indicative of a buoyancy effect on the leading side. The Coriolis vortex is the mechanism for the accumulation of stagnant flow on the leading side of the passage. Heat transfer data show a maximum factor of two difference in the Nusselt number from trailing side to leading side. An estimate of this heat transfer disparity based on the measured boundary layer edge velocity yields approximately the same factor of two. A momentum integral model was developed for data interpretation which accounts for Coriolis and buoyancy effects. Calculated streamwise profiles and secondary flows match the experimental data well. The model, the velocity data, and the heat transfer data combine to suggest the presence of separated flow on the leading wall starting at about five passage widths for the conditions studied. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

An experimental investigation of a two and a three-dimensional low speed turbulent boundary layer

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.; Melnik, W. L.

1976-01-01

Experimental studies of a two and a three-dimensional low speed turbulent boundary layer were conducted on the side wall of a boundary layer wind tunnel. The 20 ft. long test section, with a rectangular cross section measuring 17.5 in. x 46 in., produced a 3.5 in. thick turbulent boundary layer at a free stream Reynolds number. The three-dimensional turbulent boundary layer was produced by a 30 deg swept wing-like model faired into the side wall of the test section. Preliminary studies in the two-dimensional boundary layer indicated that the flow was nonuniform on the 46 in. wide test wall. The nonuniform boundary layer is characterized by transverse variations in the wall shear stress and is primarily caused by nonuniformities in the inlet damping screens.

The Steady Flow Resistance of Perforated Sheet Materials in High Speed Grazing Flows

NASA Technical Reports Server (NTRS)

Syed, Asif A.; Yu, Jia; Kwan, H. W.; Chien, E.; Jones, Michael G. (Technical Monitor)

2002-01-01

A study was conducted to determine the effects of high speed grazing air flow on the acoustic resistance of perforated sheet materials used in the construction of acoustically absorptive liners placed in commercial aircraft engine nacelles. Since DC flow resistance of porous sheet materials is known to be a major component of the acoustic resistance of sound suppression liners, the DC flow resistance of a set of perforated face-sheets and linear 'wiremesh' face-sheets was measured in a flow duct apparatus (up to Mach 0.8). Samples were fabricated to cover typical variations in perforated face-sheet parameters, such as hole diameter, porosity and sheet thickness, as well as those due to different manufacturing processes. The DC flow resistance data from perforated sheets were found to correlate strongly with the grazing flow Mach number and the face-sheet porosity. The data also show correlation against the boundary layer displacement thickness to hole-diameter ratio. The increase in resistance with grazing flow for punched aluminum sheets is in good agreement with published results up to Mach 0.4, but is significantly larger than expected above Mach 0.4. Finally, the tests demonstrated that there is a significant increase in the resistance of linear 'wiremesh' type face-sheet materials.

Sedimentary characteristics of the 2004 Indian Ocean tsunami in Ban Talae Nok, southwestern Ranong province, Thailand

NASA Astrophysics Data System (ADS)

Monecke, K.; Beitel, J.; Moran, K.; Moore, A.

2006-12-01

Ban Talae Nok, a village on the Andaman shoreline of Thailand, was hit by the December 26, 2004, tsunami with wave heights up to ~13 meters. Eyewitnesses reported the passage of four to five waves with the second being the largest, followed by the third and fourth waves. The tsunami flooded an area with open grassy fields, small cashew nut plantations and a wetland within a local swale. The wave stopped against hills ~500 m from the shoreline, where watermarks still indicate a flow depth of approximately 1 m. Erosion at the beach is marked by a ~30 cm high scarp cutting a former gravelly beach trail ~60 m inshore of the present shoreline. Deposition of tsunami sand started behind the former beach trail at 80 m inshore. The tsunami deposit changes significantly in thickness and composition along a flow parallel transect that was measured and sampled within this study. The most seaward deposit is about 10 cm thick and consists of three distinct layers that show internal as well as overall normal grading from coarse sand into fine sand. The coarse base contains gravels from the old beach trail and shell fragments. Locally, cross stratification is visible at the top. Farther landward the deposit thins and only one normally graded layer is visible. Behind a small ridge where the wetland begins, the tsunami sediments again reveal three normally graded layers with shell- rich, medium-coarse sand grading into brown-gray mud, probably eroded from the wetland. This deposit thins farther inland from ~30 cm to 8 cm and consists of only one layer. The thickest deposit along the transect is 125 cm thick and can be found in a low at the landward end of the wetland. It consists of normally graded coarse to fine sand with rip-up clasts at the base and climbing ripples in the middle of the deposit section. In the adjacent grassy field the deposit is up to 40 cm thick and consists of medium to coarse sand with shell fragments grading into fine to medium sands, which continue to the foot of the hills.

Design of a High-Reynolds Number Recirculating Water Tunnel

NASA Astrophysics Data System (ADS)

Daniel, Libin; Elbing, Brian

2014-11-01

An experimental fluid mechanics laboratory focused on turbulent boundary layers, drag reduction techniques, multiphase flows and fluid-structure interactions has recently been established at Oklahoma State University. This laboratory has three primary components; (1) a recirculating water tunnel, (2) a multiphase pipe flow loop, and (3) a multi-scale flow visualization system. The design of the water tunnel is the focus of this talk. The criteria used for the water tunnel design was that it had to produce a momentum-thickness based Reynolds number in excess of 104, negligible flow acceleration due to boundary layer growth, maximize optical access for use of the flow visualization system, and minimize inlet flow non-uniformity. This Reynolds number was targeted to bridge the gap between typical university/commercial water tunnels (103) and the world's largest water tunnel facilities (105) . These objectives were achieved with a 152 mm (6-inch) square test section that is 1 m long and has a maximum flow speed of 10 m/s. The flow non-uniformity was mitigated with the use of a tandem honeycomb configuration, a settling chamber and an 8.5:1 contraction. The design process that produced this final design will be presented along with its current status.

Progression of soot cake layer properties during the systematic regeneration of diesel particulate filters measured with neutron tomography

DOE PAGES

Toops, Todd J.; Pihl, Josh A.; Finney, Charles E. A.; ...

2015-01-16

Although particulate filters (PFs) have been a key component of the emission control system for modern diesel engines, there remain significant questions about the basic regeneration behavior of the filters and how it changes with accumulation of increasing soot layers. This effort describes a systematic deposition and regeneration of particulate matter in 25-mm diameter × 76-mm long wall-flow PFs composed of silicon carbide (SiC) material. The initial soot distributions were analyzed for soot cake thickness using a nondestructive neutron imaging technique. With the PFs intact, it was then possible to sequentially regenerate the samples and reanalyze them, which was performedmore » after nominal 20, 50, and 70 % regenerations. The loaded samples show a relatively uniform distribution of particulate with an increasing soot cake thickness and nearly identical initial density of 70 mg/cm 3. Throughout regeneration, the soot cake thickness initially decreases significantly while the density increases to 80–90 mg/cm 3. After ~50 % regeneration, the soot cake thickness stays relatively constant, but instead, the density decreases as pores open up in the layer (~35 mg/cm 3 at 70 % regeneration). Here, complete regeneration initially occurs at the rear of the PF channels. With this information, a conceptual model of the regeneration is proposed.« less

Progression of soot cake layer properties during the systematic regeneration of diesel particulate filters measured with neutron tomography

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

Toops, Todd J.; Pihl, Josh A.; Finney, Charles E. A.

Although particulate filters (PFs) have been a key component of the emission control system for modern diesel engines, there remain significant questions about the basic regeneration behavior of the filters and how it changes with accumulation of increasing soot layers. This effort describes a systematic deposition and regeneration of particulate matter in 25-mm diameter × 76-mm long wall-flow PFs composed of silicon carbide (SiC) material. The initial soot distributions were analyzed for soot cake thickness using a nondestructive neutron imaging technique. With the PFs intact, it was then possible to sequentially regenerate the samples and reanalyze them, which was performedmore » after nominal 20, 50, and 70 % regenerations. The loaded samples show a relatively uniform distribution of particulate with an increasing soot cake thickness and nearly identical initial density of 70 mg/cm 3. Throughout regeneration, the soot cake thickness initially decreases significantly while the density increases to 80–90 mg/cm 3. After ~50 % regeneration, the soot cake thickness stays relatively constant, but instead, the density decreases as pores open up in the layer (~35 mg/cm 3 at 70 % regeneration). Here, complete regeneration initially occurs at the rear of the PF channels. With this information, a conceptual model of the regeneration is proposed.« less

Wafer-scale synthesis of monolayer and few-layer MoS2 via thermal vapor sulfurization

NASA Astrophysics Data System (ADS)

Robertson, John; Liu, Xue; Yue, Chunlei; Escarra, Matthew; Wei, Jiang

2017-12-01

Monolayer molybdenum disulfide (MoS2) is an atomically thin, direct bandgap semiconductor crystal potentially capable of miniaturizing optoelectronic devices to an atomic scale. However, the development of 2D MoS2-based optoelectronic devices depends upon the existence of a high optical quality and large-area monolayer MoS2 synthesis technique. To address this need, we present a thermal vapor sulfurization (TVS) technique that uses powder MoS2 as a sulfur vapor source. The technique reduces and stabilizes the flow of sulfur vapor, enabling monolayer wafer-scale MoS2 growth. MoS2 thickness is also controlled with great precision; we demonstrate the ability to synthesize MoS2 sheets between 1 and 4 layers thick, while also showing the ability to create films with average thickness intermediate between integer layer numbers. The films exhibit wafer-scale coverage and uniformity, with electrical quality varying depending on the final thickness of the grown MoS2. The direct bandgap of grown monolayer MoS2 is analyzed using internal and external photoluminescence quantum efficiency. The photoluminescence quantum efficiency is shown to be competitive with untreated exfoliated MoS2 monolayer crystals. The ability to consistently grow wafer-scale monolayer MoS2 with high optical quality makes this technique a valuable tool for the development of 2D optoelectronic devices such as photovoltaics, detectors, and light emitters.

Porous and Microporous Honeycomb Composites as Potential Boundary-Layer Bleed Materials

NASA Technical Reports Server (NTRS)

Davis, D. O.; Willis, B. P.; Schoenenberger, M.

1997-01-01

Results of an experimental investigation are presented in which the use of porous and microporous honeycomb composite materials is evaluated as an alternate to perforated solid plates for boundary-layer bleed in supersonic aircraft inlets. The terms "porous" and "microporous," respectively, refer to bleed orifice diameters roughly equal to and much less than the displacement thickness of the approach boundary-layer. A Baseline porous solid plate, two porous honeycomb, and three microporous honeycomb configurations are evaluated. The performance of the plates is characterized by the flow coefficient and relative change in boundary-layer profile parameters across the bleed region. The tests were conducted at Mach numbers of 1.27 and 1.98. The results show the porous honeycomb is not as efficient at removing mass compared to the baseline. The microporous plates were about equal to the baseline with one plate demonstrating a significantly higher efficiency. The microporous plates produced significantly fuller boundary-layer profiles downstream of the bleed region for a given mass flow removal rate than either the baseline or the porous honeycomb plates.

Simulating Lahars Using A Rotating Drum

NASA Astrophysics Data System (ADS)

Neather, Adam; Lube, Gert; Jones, Jim; Cronin, Shane

2014-05-01

A large (0.5 m in diameter, 0.15 m wide) rotating drum is used to investigate the erosion and deposition mechanics of lahars. To systematically simulate the conditions occurring in natural mass flows our experimental setup differs from the common rotating drum employed in industrial/engineering studies. Natural materials with their typical friction properties are used, as opposed to the frequently employed spherical glass beads; the drum is completely water-proof, so solid/air and solid/liquid mixtures can be investigated; the drum velocity and acceleration can be precisely controlled using a software interface to a micro-controller, allowing for the study of steady, unsteady and intermediate flow regimes. The drum has a toughened glass door, allowing high-resolution, high-speed video recording of the material inside. Vector maps of the velocities involved in the flows are obtained using particle image velocimetry (PIV). The changes in velocity direction and/or magnitude are used to locate the primary internal boundaries between layers of opposite flow direction, as well as secondary interfaces between shear layers. A range of variables can be measured: thickness and number of layers; the curvature of the free surface; frequency of avalanching; position of the centre of mass of the material; and the velocity profiles of the flowing material. Experiments to date have focussed on dry materials, and have had a fill factor of approximately 0.3. Combining these measured variables allows us to derive additional data of interest, such as mass and momentum flux. It is these fluxes that we propose will allow insight into the erosion/deposition mechanics of a lahar. A number of conclusions can be drawn to date. A primary interface separates flowing and passive region (this interface has been identified in previous studies). As well as the primary interface, the flowing layer separates into individual shear layers, with individual erosion/deposition and flow histories. This complex flow geometry and process of erosion and deposition seen in our high speed videos is more complicated than previously reported in the literature. We identify two layers only in the slowest flows (< 0.5 rad s-1), while faster ones (< 4 rad s-1) include between three and five. As the rotational velocity of the drum increases, the curvature of the free surface increases. In the central part of the drum, the primary interfaces occasionally merges into an elliptical zone rather than a linear shear boundary. Inside this zone is a complete circulation of material. These zones' size and number appears to be a function of the rotational velocity of the drum. These "Neather cells" (as we tentatively name these phenomena) can reach as large as 20 mm in thickness. The centre of mass' deflection from vertical is linearly dependent on rotational velocity, whilst the typical flow regimes as identified by Mellmann [2001] show no influence. The frequency of avalanches increases with velocity up to a critical velocity (approximately 1.1 rad s-1), after which the avalanche frequency remains constant. 1 References J Mellmann. The transverse motion of solids in rotating cylinders-forms of motion and transition behavior. Powder Technology, 118(3):251-270, 2001.

Flow and transport within a coastal aquifer adjacent to a stratified water body

NASA Astrophysics Data System (ADS)

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

2016-04-01

The existence of a freshwater-saltwater interface and the circulation flow of saltwater beneath the interface is a well-known phenomenon found at coastal aquifers. This flow is a natural phenomenon that occurs due to density differences between fresh groundwater and the saltwater body. The goals of this research are to use analytical, numerical, and physical models in order to examine the configuration of the freshwater-saltwater interface and the density-driven flow patterns within a coastal aquifer adjacent to long-term stratified saltwater bodies (e.g. meromictic lake). Such hydrological systems are unique, as they consist of three different water types: the regional fresh groundwater, and low and high salinity brines forming the upper and lower water layers of the stratified water body, respectively. This research also aims to examine the influence of such stratification on hydrogeological processes within the coastal aquifer. The coastal aquifer adjacent to the Dead Sea, under its possible future meromictic conditions, serves as an ideal example to examine these processes. The results show that adjacent to a stratified saltwater body three interfaces between three different water bodies are formed, and that a complex flow system, controlled by the density differences, is created, where three circulation cells are developed. These results are significantly different from the classic circulation cell that is found adjacent to non-stratified water bodies (lakes or oceans). In order to obtain a more generalized insight into the groundwater behavior adjacent to a stratified water body, we used the numerical model to perform sensitivity analysis. The hydrological system was found be sensitive to three dimensionless parameters: dimensionless density (i.e. the relative density of the three water bodies'); dimensionless thickness (i.e. the ratio between the relative thickness of the upper layer and the whole thickness of the lake); and dimensionless flux. The results also show that this configuration of three interfaces and three circulation cells, which is expected to develop adjacent to the stratified Dead Sea, is expected to decrease the dissolution rates of salt layer that is located within the adjacent aquifer, by one order of magnitude in comparison to the dissolution rates today. Therefore, the processes of salt dissolution and sinkhole formation adjacent to the Dead Sea will be relatively restrained.

Chemical differentiation of a convecting planetary interior: Consequences for a one-plate planet such as Venus

NASA Technical Reports Server (NTRS)

Parmentier, E. M.; Hess, P. C.

1992-01-01

Chemically depleted mantle forming a buoyant, refractory layer at the top of the mantle can have important implications for the evolution of the interior and surface. On Venus, the large apparent depths of compensation for surface topographic features might be explained if surface topography were supported by variations in the thickness of a 100-200 km thick chemically buoyant mantle layer or by partial melting in the mantle at the base of such a layer. Long volcanic flows seen on the surface may be explained by deep melting that generates low-viscosity MgO-rich magmas. The presence of a shallow refractory mantle layer may also explain the lack of volcanism associated with rifting. As the depleted layer thickens and cools, it becomes denser than the convecting interior and the portion of it that is hot enough to flow can mix with the convecting mantle. Time dependence of the thickness of a depleted layer may create episodic resurfacing events as needed to explain the observed distribution of impact craters on the venusian surface. We consider a planetary structure consisting of a crust, depleted mantle layer, and a thermally and chemically well-mixed convecting mantle. The thermal evolution of the convecting spherical planetary interior is calculated using energy conservation: the time rate of change of thermal energy in the interior is equated to the difference in the rate of radioactive heat production and the rate of heat transfer across the thermal boundary layer. Heat transfer across the thermal boundary layer is parameterized using a standard Nusselt number-Rayleigh number relationship. The radioactive heat production decreases with time corresponding to decay times for the U, Th, and K. The planetary interior cools by the advection of hot mantle at temperature T interior into the thermal boundary layer where it cools conductively. The crust and depleted mantle layers do not convect in our model so that a linear conductive equilibrium temperature distribution is assumed. The rate of melt production is calculated as the product of the volume flux of mantle into the thermal boundary layer and the degree of melting that this mantle undergoes. The volume flux of mantle into the thermal boundary layer is simply the heat flux divided by amount of heat lost in cooling mantle to the average temperature in the thermal boundary layer. The degree of melting is calculated as the temperature difference above the solidus, divided by the latent heat of melting. A maximum degree of melting is prescribed corresponding to the maximum amount of basaltic melt that the mantle can initially generate. As the crust thickens, the pressure at the base of the crust becomes high enough and the temperature remains low enough for basalt to transform to dense eclogite.

Influence of ammonia flow rate for improving properties of polycrystalline GaN

NASA Astrophysics Data System (ADS)

Ariff, A.; Ahmad, M. A.; Hassan, Z.; Zainal, N.

2018-06-01

Post-annealing treatment in ammonia ambient is widely accepted for GaN material, but less works have been done to investigate the influence of the ammonia (NH3) flow rate for reducing the N-deficiency as well as improving the quality of the material. In this work, we investigated the influence of NH3 flow rate at 1, 2, 3, and 4 slm in improving properties of a ∼1 μm thick polycrystalline GaN layer. Our simulation work suggested that the uniformity of temperature and pressure gradient of the NH3 gas did not lead to the reduction of N-deficiency of the polycrystalline GaN layer. Instead, it was found that the mitigation of the N-deficiency was strongly influenced by the fluid velocity of the NH3 gas, which had passed over the layer. Either at lower or higher fluid velocity, the chance for the active N atoms to incorporate into the GaN lattice structure was low. Therefore, the N-deficiency on the polycrystalline GaN layer could not be minimized under these conditions. As measured by EDX, the N atoms incorporation was the most effective when the NH3 flow rate at 3 slm, suggesting the flow rate significantly improved the N-deficiency of the polycrystalline GaN layer. Furthermore, it favored the formation of larger hexagonal faceted grains, with the smallest FWHM of XRD peaks from the GaN diffractions in (10 1 bar 0), (0002) and (10 1 bar 1) orientations, while allowing the polycrystalline GaN layer to show sharp and intense emissions peak of NBE in a PL spectrum.

Computation of the turbulent boundary layer downstream of vortex generators

NASA Astrophysics Data System (ADS)

Chang, Paul K.

1987-12-01

The approximate analysis of three-dimensional incompressible turbulent boundary layer downstream of vortex generators is presented. Extensive numerical computations are carried out to assess the effectiveness of single-row, counter-rotating vane-type vortex generators to alleviate flow separation lines. Flow separation downstream of the vortex generators on a thick airfoil are determined in terms of size, location, and arrangement of the vortex generators. These lines are compared with the separation line without the vortex generators. High efficiency is obtained with the moderately slender rectangular blade of the generator. The results indicate that separations is alleviated more effectively in the region closer to the symmetry axis of the generator than in the outer region of the symmetry axis. No optimum conditions for the alleviation of flow separation are established in this investigation, and no comparisons are made with other analytical results and experimental data.

Numerical Investigation of PLIF Gas Seeding for Hypersonic Boundary Layer Flows

NASA Technical Reports Server (NTRS)

Johanson, Craig T.; Danehy, Paul M.

2012-01-01

Numerical simulations of gas-seeding strategies required for planar laser-induced fluorescence (PLIF) in a Mach 10 air flow were performed. The work was performed to understand and quantify adverse effects associated with gas seeding and to compare different flow rates and different types of seed gas. The gas was injected through a slot near the leading edge of a flat plate wedge model used in NASA Langley Research Center's 31- Inch Mach 10 Air Tunnel facility. Nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulation results showing the deflection of the velocity field for each of the cases are presented. Streamwise distributions of velocity and concentration boundary layer thicknesses as well as vertical distributions of velocity, temperature, and mass distributions are presented for each of the cases. Relative merits of the different seeding strategies are discussed.

Depletion of solar wind plasma near a planetary boundary

NASA Technical Reports Server (NTRS)

Zwan, B. J.; Wolf, R. A.

1976-01-01

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a 'depletion layer', a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth, the theory predicts that the density should be reduced by a factor exceeding 2 in a layer about 700-1300 km thick if the Alfven Mach number in the solar wind, is equal to 8. Scaling of the model calculations to Venus and Mars suggests layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospheric effects.

Coherent substructure of turbulence near the stagnation zone of a bluff body

NASA Technical Reports Server (NTRS)

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

1980-01-01

The evolution of freestream turbulence in crossflow about a circular cylinder was studied in order to identify the existence of a coherent substructure which is the outcome of the amplification of freesteam turbulence by the stretching mechanism in diverging flow about a bluff body. Visualization of the flow events revealed the selective stretching of cross-vortex tubes and the emergence of an organized turbulent flow pattern near the cylinder stagnation zone. Significant amplification of the total turbulent energy of the streamwise fluctuating velocity was consistently monitored. Realization of selective amplification at scales larger than the neutral scale of the stagnation flow was indicated by the variation of the discrete streamwise turbulent energy. A most amplified scale, characteristic of the energy containing eddies within the coherent substructure and commensurate with the boundary-layer thickness, was detected. Penetration of the amplified turbulence into the cylinder boundary layer led to the retardation of separation and to a concurrent decrease in the drag coefficient at subcritical cylinder-diameter Reynolds numbers.

The diffusive boundary layer of sediments: oxygen microgradients over a microbial mat

NASA Technical Reports Server (NTRS)

Jorgensen, B. B.; Des Marais, D. J.

1990-01-01

Oxygen microelectrodes were used to analyze the distribution of the diffusive boundary layer (DBL) at the sediment-water interface in relation to surface topography and flow velocity. The sediment, collected from saline ponds, was covered by a microbial mat that had high oxygen consumption rate and well-defined surface structure. Diffusion through the DBL constituted an important rate limitation to the oxygen uptake of the sediment. The mean effective DBL thickness decreased from 0.59 to 0.16 mm as the flow velocity of the overlying water was increased from 0.3 to 7.7 cm s-1 (measured 1 cm above the mat). The oxygen uptake rate concurrently increased from 3.9 to 9.4 nmol cm-2 min-1. The effects of surface roughness and topography on the thickness and distribution of the DBL were studied by three-dimensional mapping of the sediment-water interface and the upper DBL boundary at 0.1-mm spatial resolution. The DBL boundary followed mat structures that had characteristic dimensions > 1/2 DBL thickness but the DBL had a dampened relief relative to the mat. The effective surface area of the sediment-water interface and of the upper DBL boundary were 31 and 14% larger, respectively, than a flat plane. Surface topography thereby increased the oxygen flux across the sediment-water interface by 49% relative to a one-dimensional diffusion flux calculated from the vertical oxygen microgradients.

Critical pressure and multiphase flow in Blake Ridge gas hydrates

USGS Publications Warehouse

Flemings, P.B.; Liu, Xiuying; Winters, W.J.

2003-01-01

We use core porosity, consolidation experiments, pressure core sampler data, and capillary pressure measurements to predict water pressures that are 70% of the lithostatic stress, and gas pressures that equal the lithostatic stress beneath the methane hydrate layer at Ocean Drilling Program Site 997, Blake Ridge, offshore North Carolina. A 29-m-thick interconnected free-gas column is trapped beneath the low-permeability hydrate layer. We propose that lithostatic gas pressure is dilating fractures and gas is migrating through the methane hydrate layer. Overpressured gas and water within methane hydrate reservoirs limit the amount of free gas trapped and may rapidly export methane to the seafloor.

Features of sound propagation through and stability of a finite shear layer

NASA Technical Reports Server (NTRS)

Koutsoyannis, S. P.

1977-01-01

The plane wave propagation, the stability, and the rectangular duct mode problems of a compressible, inviscid, linearly sheared, parallel, homogeneous flow are shown to be governed by Whittaker's equation. The exact solutions for the perturbation quantities are essentially the Whittaker M-functions where the nondimensional quantities have precise physical meanings. A number of known results are obtained as limiting cases of the exact solutions. For the compressible finite thickness shear layer it is shown that no resonances and no critical angles exist for all Mach numbers, frequencies, and shear layer velocity profile slopes except in the singular case of the vortex sheet.

Process for the deposition of high temperature stress and oxidation resistant coatings on silicon-based substrates

DOEpatents

Sarin, V.K.

1991-07-30

A process is disclosed for depositing a high temperature stress and oxidation resistant coating on a silicon nitride- or silicon carbide-based substrate body. A gas mixture is passed over the substrate at about 900--1500 C and about 1 torr to about ambient pressure. The gas mixture includes one or more halide vapors with other suitable reactant gases. The partial pressure ratios, flow rates, and process times are sufficient to deposit a continuous, fully dense, adherent coating. The halide and other reactant gases are gradually varied during deposition so that the coating is a graded coating of at least two layers. Each layer is a graded layer changing in composition from the material over which it is deposited to the material of the layer and further to the material, if any, deposited thereon, so that no clearly defined compositional interfaces exist. The gases and their partial pressures are varied according to a predetermined time schedule and the halide and other reactant gases are selected so that the layers include (a) an adherent, continuous intermediate layer about 0.5-20 microns thick of an aluminum nitride or an aluminum oxynitride material, over and chemically bonded to the substrate body, and (b) an adherent, continuous first outer layer about 0.5-900 microns thick including an oxide of aluminum or zirconium over and chemically bonded to the intermediate layer.

Process for the deposition of high temperature stress and oxidation resistant coatings on silicon-based substrates

DOEpatents

Sarin, Vinod K.

1991-01-01

A process for depositing a high temperature stress and oxidation resistant coating on a silicon nitride- or silicon carbide-based substrate body. A gas mixture is passed over the substrate at about 900.degree.-1500.degree. C. and about 1 torr to about ambient pressure. The gas mixture includes one or more halide vapors with other suitable reactant gases. The partial pressure ratios, flow rates, and process times are sufficient to deposit a continuous, fully dense, adherent coating. The halide and other reactant gases are gradually varied during deposition so that the coating is a graded coating of at least two layers. Each layer is a graded layer changing in composition from the material over which it is deposited to the material of the layer and further to the material, if any, deposited thereon, so that no clearly defined compositional interfaces exist. The gases and their partial pressures are varied according to a predetermined time schedule and the halide and other reactant gases are selected so that the layers include (a) an adherent, continuous intermediate layer about 0.5-20 microns thick of an aluminum nitride or an aluminum oxynitride material, over and chemically bonded to the substrate body, and (b) an adherent, continuous first outer layer about 0.5-900 microns thick including an oxide of aluminum or zirconium over and chemically bonded to the intermediate layer.

Protection from high-velocity impact particles for quartz glass by coatings on the basis of Al-Si-N

NASA Astrophysics Data System (ADS)

Bozhko, I. A.; Rybalko, E. V.; Fedorischeva, M. V.; Solntsev, V. L.; Cherniavsky, A. G.; Kaleri, A. Yu.; Psakhie, S. G.; Sergeev, V. P.

2016-11-01

The paper presents the results of the research of the phase composition and the mechanical properties of the coatings on the basis of Al-Si-N system produced by pulsed magnetron sputtering on the KV glass substrates. By the X-ray diffraction method, it has been discovered that the coatings contain AlN phase (hcp) with different thickness. The deposition of Al-Si-N coating system allows both increasing the microhardness of the surface layer of the quartz glass up to 29 GPa, and maintaining high elastic properties (We > 0.70). The laboratory tests have been carried out involving the impact of high-speed flows of iron particles on the Al-Si-N protective coating with different thicknesses produced by pulsed magnetron sputtering. The increase of Al-Si-N coating thickness from 1µm to 10µm decreases 4-fold the surface density of the craters on the samples caused by a high-speed flow of iron particles.

Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films

NASA Astrophysics Data System (ADS)

Cao, Zhiqiang; Zhang, Xin

2004-10-01

The structural relaxation of plasma-enhanced chemical-vapor-deposited (PECVD) silane-based silicon oxide films during thermal cycling and annealing has been studied using wafer curvature measurements. These measurements, which determine stress in the amorphous silicon oxide films, are sensitive to both plastic deformation and density changes. A quantitative case study of such changes has been done based upon the experimental results. A microstructure-based mechanism elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then used to explain a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD silicon oxide films with a thickness varying from 1to40μm were studied, as certain demanding applications in microelectromechanical systems require such thick films serving as heat/electrical insulation layers.

A rational approach to the use of Prandtl's mixing length model in free turbulent shear flow calculations

NASA Technical Reports Server (NTRS)

Rudy, D. H.; Bushnell, D. M.

1973-01-01

Prandtl's basic mixing length model was used to compute 22 test cases on free turbulent shear flows. The calculations employed appropriate algebraic length scale equations and single values of mixing length constant for planar and axisymmetric flows, respectively. Good agreement with data was obtained except for flows, such as supersonic free shear layers, where large sustained sensitivity changes occur. The inability to predict the more gradual mixing in these flows is tentatively ascribed to the presence of a significant turbulence-induced transverse static pressure gradient which is neglected in conventional solution procedures. Some type of an equation for length scale development was found to be necessary for successful computation of highly nonsimilar flow regions such as jet or wake development from thick wall flows.

Impact of beaver ponds on river discharge and sediment deposition along the Chevral River, Ardennes, Belgium

NASA Astrophysics Data System (ADS)

Nyssen, Jan; Frankl, Amaury; Pontzeele, Jolien; De Visscher, Maarten; Billi, Paolo

2013-04-01

With the recovery of the European beaver (Castor fiber) and their capacity to engineer fluvial landscapes, questions arise as to how they influence river discharge and sediment transport. The Chevral river (Ardennes, Belgium) contains two beaver dam sequences which appeared in 2004 and count now about 30 dams. Flow discharges and sediment fluxes were measured at the in- and outflow of each dam sequence. Volumes of sediment deposited behind the dams were measured. Between 2004 and 2011, peak flows were topped off, and the magnitude of extreme events decreased. 1710 m³ of sediment were deposited behind the beaver dams, with an average sediment thickness of 25 cm. The thickness of the sediment layer is related to the area of the beaver ponds. Along the stream, beaver pond sediment thickness displayed a sinusoidal deposition pattern, in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers. A downstream textural coarsening in the dam sequences was also observed, probably due to dam failures subsequent to surges. Differences in sediment flux between the in- and outflow at the beaver pond sequence were related to the river hydrograph, with deposition taking place during the rising limbs and slight erosion during the falling limbs. The seven-year-old sequences have filtered 190 tons of sediment out of the Chevral river, which is of the same order of magnitude as the 374 tons measured in pond deposits, with the difference between the values corresponding to beaver excavations (60 tons), inflow from small tributaries, and runoff from the valley flanks. Hydrogeomorphic effects of C. fiber and C. canadensis activity are similar in magnitude. The detailed analysis of changes to hydrology in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration and catchment management.

Infrared Images of Boundary Layer Transition on the D8 Transport Configuration in the LaRC 14- by 22-Foot Subsonic Tunnel

NASA Technical Reports Server (NTRS)

Mason, Michelle L.; Gatlin, Gregory M.

2015-01-01

Grit, trip tape, or trip dots are routinely applied on the leading-edge regions of the fuselage, wings, tails or nacelles of wind tunnel models to trip the flow from laminar to turbulent. The thickness of the model's boundary layer is calculated for nominal conditions in the wind tunnel test to determine the effective size of the trip dots, but the flow over the model may not transition as intended for runs with different flow conditions. Temperature gradients measured with an infrared camera can be used to detect laminar to turbulent boundary layer transition on a wind tunnel model. This non-intrusive technique was used in the NASA Langley 14- by 22-Foot Subsonic Tunnel to visualize the behavior of the flow over a D8 transport configuration model. As the flow through the wind tunnel either increased to or decreased from the run conditions, a sufficient temperature difference existed between the air and the model to visualize the transition location (due to different heat transfer rates through the laminar and the turbulent boundary layers) for several runs in this test. Transition phenomena were visible without active temperature control in the atmospheric wind tunnel, whether the air was cooler than the model or vice-versa. However, when the temperature of the model relative to the air was purposely changed, the ability to detect transition in the infrared images was enhanced. Flow characteristics such as a wing root horseshoe vortex or the presence of fore-body vortical flows also were observed in the infrared images. The images of flow features obtained for this study demonstrate the usefulness of current infrared technology in subsonic wind tunnel tests.

Supersonic flow visualization of a nacelle in close proximity to a simulated wing

NASA Technical Reports Server (NTRS)

Biber, Kasim; Ellis, David R.

1993-01-01

A flow visualization study was made in the 9 x 9 inch supersonic wind tunnel at Wichita State University to examine shock and boundary layer flow interaction for a nacelle in close proximity to the lower surface of a simulated wing. The test matrix included variations of angle of attack from -2 degrees to +4 degrees, nacelle-wing gap from 0.5 to 3-nacelle inlet diameter (0.12 inch), and Reynolds number based on nacelle length (1.164 inch) from 1.16 x 10(exp 6) to 1.45 x 10(exp 6) at a nominal Mach number of 2. Schlieren pictures of wing and nacelle flowfield were recorded by a video camera during each tunnel run. Results show that the nacelle inlet shock wave remains attached to the inlet lip and its impingement does not significantly affect the wing boundary layer. At the nacelle trailing edge location, the wing boundary layer thickness is approximately one nacelle inlet diameter at alpha = 0 degrees and it decreases with increase of angle of attack.

Effect of free-stream turbulence on boundary layer transition.

PubMed

Goldstein, M E

2014-07-28

This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number Rλ based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity ε is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number εRλ and the plate thickness and are held fixed (at O(1) and O(λ), respectively) in the limit as [Formula: see text] and ε→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry

NASA Astrophysics Data System (ADS)

Squire, D. T.; Morrill-Winter, C.; Hutchins, N.; Marusic, I.; Schultz, M. P.; Klewicki, J. C.

2016-10-01

Two particle image velocimetry arrangements are used to make true spatial comparisons between smooth- and rough-wall boundary layers at high Reynolds numbers across a very wide range of streamwise scales. Together, the arrangements resolve scales ranging from motions on the order of the Kolmogorov microscale to those longer than twice the boundary layer thickness. The rough-wall experiments were obtained above a continuous sandpaper sheet, identical to that used by Squire et al. [J. Fluid Mech. 795, 210 (2016), 10.1017/jfm.2016.196], and cover a range of friction and equivalent sand-grain roughness Reynolds numbers (12 000 ≲δ+≲ 18000, 62 ≲ks+≲104 ). The smooth-wall experiments comprise new and previously published data spanning 6500 ≲δ+≲17 000 . Flow statistics from all experiments show similar Reynolds number trends and behaviors to recent, well-resolved hot-wire anemometry measurements above the same rough surface. Comparisons, at matched δ+, between smooth- and rough-wall two-point correlation maps and two-point magnitude-squared coherence maps demonstrate that spatially the outer region of the boundary layer is the same between the two flows. This is apparently true even at wall-normal locations where the total (inner-normalized) energy differs between the smooth and rough wall. Generally, the present results provide strong support for Townsend's [The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, 1956), Vol. 1] wall-similarity hypothesis in high Reynolds number fully rough boundary layer flows.

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

Genet, Helene; McGuire, A. David; Barrett, K.

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and testedmore » a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layercaused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness of 1.1 m on average by 2100. The combination of warming and fire led to a simulated cumulative loss of 9.6 kgC m 2 on average by 2100. Our analysis suggests that ecosystem carbon storage in boreal forests in interior Alaska is particularly vulnerable, primarily due to the combustion of organic layer thickness in fire and the related increase in active layer thickness that exposes previously protected permafrost soil carbon to decomposition.« less

Impacts of age and sex on retinal layer thicknesses measured by spectral domain optical coherence tomography with Spectralis.

PubMed

Nieves-Moreno, María; Martínez-de-la-Casa, José M; Morales-Fernández, Laura; Sánchez-Jean, Rubén; Sáenz-Francés, Federico; García-Feijoó, Julián

2018-01-01

To examine differences in individual retinal layer thicknesses measured by spectral domain optical coherence tomography (SD-OCT) (Spectralis®) produced with age and according to sex. Cross-sectional, observational study. The study was conducted in 297 eyes of 297 healthy subjects aged 18 to 87 years. In one randomly selected eye of each participant the volume and mean thicknesses of the different macular layers were measured by SD-OCT using the instrument's macular segmentation software. Volume and mean thickness of macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), retinal pigmentary epithelium (RPE) and photoreceptor layer (PR). Retinal thickness was reduced by 0.24 μm for every one year of age. Age adjusted linear regression analysis revealed mean GCL, IPL, ONL and PR thickness reductions and a mean OPL thickness increase with age. Women had significantly lower mean GCL, IPL, INL, ONL and PR thicknesses and volumes and a significantly greater mRNFL volume than men. The thickness of most retinal layers varies both with age and according to sex. Longitudinal studies are needed to determine the rate of layer thinning produced with age.

Skewness and flatness factors of the longitudinal velocity derivative in wall-bounded flows

NASA Astrophysics Data System (ADS)

Djenidi, Lyazid; Antonia, Robert A.; Talluru, Murali K.; Abe, Hiroyuki

2017-06-01

Hot-wire measurements are carried out in turbulent boundary layers over smooth and rough walls in order the assess the behavior of the skewness (S ) and flatness (F ) factors of the longitudinal velocity derivative as y , the distance from the wall, increases. The measurements are complemented by direct numerical simulations of a smooth wall turbulent channel flow. It is observed that, as the distance to the wall increases, S and F vary significantly before approaching a constant in the outer layer of the boundary layer. Further, S and F exhibit a nontrivial dependence on the Taylor microscale Reynolds number (Reλ). For example, in the region below about 0.2 δ (δ is the boundary layer thickness) where Reλ varies significantly, S and F strongly vary with Reλ and can be multivalued at a given Reλ. In the outer region, between 0.3 δ and 0.6 δ , S , F , and Reλ remain approximately constant. The channel flow direct numerical simulation data for S and F exhibit a similar behavior. These results point to the ambiguity that can arise when assessing the Reλ dependence of S and F in wall shear flows. In particular, the multivaluedness of S and F can lead to erroneous conclusions if y /δ is known only poorly, as is the case for the atmospheric shear layer (ASL). If the laboratory turbulent boundary layer is considered an adequate surrogate to the neutral ASL, then the behavior of S and F in the ASL is expected to be similar to that reported here.

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

Blancon, Jean -Christophe Robert; Tsai, Hsinhan; Nie, Wanyi

Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum wells has enabled high-efficiency optoelectronic devices. Two-dimensional (2D) Ruddlesden-Popper perovskites are solution-processed quantum wells wherein the band gap can be tuned by varying the perovskite-layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photogenerated electrons and holes are strongly bound by Coulomb interactions or excitons, the photophysics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite-crystal units (>1.3 nanometers) is dominated by lower-energy states associated with the local intrinsic electronic structure of the edges of the perovskitemore » layers. Furthermore, these states provide a direct pathway for dissociating excitons into longer-lived free carriers that substantially improve the performance of optoelectronic devices.« less

Non-destructive prediction of enteric coating layer thickness and drug dissolution rate by near-infrared spectroscopy and X-ray computed tomography.

PubMed

Ariyasu, Aoi; Hattori, Yusuke; Otsuka, Makoto

2017-06-15

The coating layer thickness of enteric-coated tablets is a key factor that determines the drug dissolution rate from the tablet. Near-infrared spectroscopy (NIRS) enables non-destructive and quick measurement of the coating layer thickness, and thus allows the investigation of the relation between enteric coating layer thickness and drug dissolution rate. Two marketed products of aspirin enteric-coated tablets were used in this study, and the correlation between the predicted coating layer thickness and the obtained drug dissolution rate was investigated. Our results showed correlation for one product; the drug dissolution rate decreased with the increase in enteric coating layer thickness, whereas, there was no correlation for the other product. Additional examination of the distribution of coating layer thickness by X-ray computed tomography (CT) showed homogenous distribution of coating layer thickness for the former product, whereas the latter product exhibited heterogeneous distribution within the tablet, as well as inconsistent trend in the thickness distribution between the tablets. It was suggested that this heterogeneity and inconsistent trend in layer thickness distribution contributed to the absence of correlation between the layer thickness of the face and side regions of the tablets, which resulted in the loss of correlation between the coating layer thickness and drug dissolution rate. Therefore, the predictability of drug dissolution rate from enteric-coated tablets depended on the homogeneity of the coating layer thickness. In addition, the importance of micro analysis, X-ray CT in this study, was suggested even if the macro analysis, NIRS in this study, are finally applied for the measurement. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of Flush-Mounted, S-Duct Inlets with Large Amounts of Boundary Layer Ingestion

NASA Technical Reports Server (NTRS)

Berrier, Bobby L.; Morehouse, Melissa B.

2003-01-01

A new high Reynolds number test capability for boundary layer ingesting inlets has been developed for the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. Using this new capability, an experimental investigation of four S-duct inlet configurations with large amounts of boundary layer ingestion (nominal boundary layer thickness of about 40% of inlet height) was conducted at realistic operating conditions (high subsonic Mach numbers and full-scale Reynolds numbers). The objectives of this investigation were to 1) provide a database for CFD tool validation on boundary layer ingesting inlets operating at realistic conditions and 2) provide a baseline inlet for future inlet flow-control studies. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on duct exit diameter) from 5.1 million to a full-scale value of 13.9 million, and inlet mass-flow ratios from 0.39 to 1.58 depending on Mach number. Results of this investigation indicate that inlet pressure recovery generally decreased and inlet distortion generally increased with increasing Mach number. Except at low Mach numbers, increasing inlet mass-flow increased pressure recovery and increased distortion. Increasing the amount of boundary layer ingestion (by decreasing inlet throat height) or ingesting a boundary layer with a distorted (adverse) profile decreased pressure recovery and increased distortion. Finally, increasing Reynolds number had almost no effect on inlet distortion but increased inlet recovery by about one-half percent at a Mach number near cruise.

Design, fabrication and testing of an air-breathing micro direct methanol fuel cell with compound anode flow field

NASA Astrophysics Data System (ADS)

Wang, Luwen; Zhang, Yufeng; Zhao, Youran; An, Zijiang; Zhou, Zhiping; Liu, Xiaowei

2011-10-01

An air-breathing micro direct methanol fuel cell (μDMFC) with a compound anode flow field structure (composed of the parallel flow field and the perforated flow field) is designed, fabricated and tested. To better analyze the effect of the compound anode flow field on the mass transfer of methanol, the compound flow field with different open ratios (ratio of exposure area to total area) and thicknesses of current collectors is modeled and simulated. Micro process technologies are employed to fabricate the end plates and current collectors. The performances of the μDMFC with a compound anode flow field are measured under various operating parameters. Both the modeled and the experimental results show that, comparing the conventional parallel flow field, the compound one can enhance the mass transfer resistance of methanol from the flow field to the anode diffusion layer. The results also indicate that the μDMFC with an anode open ratio of 40% and a thickness of 300 µm has the optimal performance under the 7 M methanol which is three to four times higher than conventional flow fields. Finally, a 2 h stability test of the μDMFC is performed with a methanol concentration of 7 M and a flow velocity of 0.1 ml min-1. The results indicate that the μDMFC can work steadily with high methanol concentration.

Boundary-layer effects in droplet splashing

NASA Astrophysics Data System (ADS)

Riboux, Guillaume; Gordillo, Jose Manuel

2017-11-01

A drop falling onto a solid substrate will disintegrate into smaller parts when its impact velocity exceeds the so called critical velocity for splashing. Under these circumstances, the very thin liquid sheet ejected tangentially to the solid after the drop touches the substrate, lifts off as a consequence of the aerodynamic forces exerted on it and finally breaks into smaller droplets, violently ejected radially outwards, provoking the splash. Here, the tangential deceleration experienced by the fluid entering the thin liquid sheet is investigated making use of boundary layer theory. The velocity component tangent to the solid, computed using potential flow theory provides the far field boundary condition as well as the pressure gradient for the boundary layer equations. The structure of the flow permits to find a self similar solution of the boundary layer equations. This solution is then used to calculate the boundary layer thickness at the root of the lamella as well as the shear stress at the wall. The splash model presented in, which is slightly modified to account for the results obtained from the boundary layer analysis, provides a very good agreement between the measurements and the predicted values of the critical velocity for the splash.

On the role of infiltration and exfiltration in swash zone boundary layer dynamics

NASA Astrophysics Data System (ADS)

Pintado-Patiño, José Carlos; Torres-Freyermuth, Alec; Puleo, Jack A.; Pokrajac, Dubravka

2015-09-01

Boundary layer dynamics are investigated using a 2-D numerical model that solves the Volume-Averaged Reynolds-Averaged Navier-Stokes equations, with a VOF-tracking scheme and a k - ɛ turbulence closure. The model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds. The spatial gradients of the velocity, bed shear stress, and turbulence intensity terms are investigated with reference to bottom boundary layer (BL) dynamics. Numerical results show that the mean vorticity responds to flow divergence/convergence at the surface that result from accelerating/decelerating portions of the flow, bed shear stress, and sinking/injection of turbulence due to infiltration/exfiltration. Hence, the zero up-crossing of the vorticity is employed as a proxy of the BL thickness inside the shallow swash zone flows. During the uprush phase, the BL develops almost instantaneously with bore arrival and fluctuates below the surface due to flow instabilities and related horizontal straining. In contrast, during the backwash phase, the BL grows quasi-linearly with less influence of surface-induced forces. However, the infiltration produces a reduction of the maximum excursion and duration of the swash event. These effects have important implications for the BL development. The numerical results suggest that the BL growth rate deviates rapidly from a quasi-linear trend if the infiltration is dominant during the initial backwash phase and the flat plate boundary layer theory may no longer be applicable under these conditions.

Wake Instabilities Behind Discrete Roughness Elements in High Speed Boundary Layers

NASA Technical Reports Server (NTRS)

Choudhari, Meelan; Li, Fei; Chang, Chau-Lyan; Norris, Andrew; Edwards, Jack

2013-01-01

Computations are performed to study the flow past an isolated, spanwise symmetric roughness element in zero pressure gradient boundary layers at Mach 3.5 and 5.9, with an emphasis on roughness heights of less than 55 percent of the local boundary layer thickness. The Mach 5.9 cases include flow conditions that are relevant to both ground facility experiments and high altitude flight ("cold wall" case). Regardless of the Mach number, the mean flow distortion due to the roughness element is characterized by long-lived streamwise streaks in the roughness wake, which can support instability modes that did not exist in the absence of the roughness element. The higher Mach number cases reveal a variety of instability mode shapes with velocity fluctuations concentrated in different localized regions of high base flow shear. The high shear regions vary from the top of a mushroom shaped structure characterizing the centerline streak to regions that are concentrated on the sides of the mushroom. Unlike the Mach 3.5 case with nearly same values of scaled roughness height k/delta and roughness height Reynolds number Re(sub kk), the odd wake modes in both Mach 5.9 cases are significantly more unstable than the even modes of instability. Additional computations for a Mach 3.5 boundary layer indicate that the presence of a roughness element can also enhance the amplification of first mode instabilities incident from upstream. Interactions between multiple roughness elements aligned along the flow direction are also explored.

A comparative parametric study of a catalytic plate methane reformer coated with segmented and continuous layers of combustion catalyst for hydrogen production

NASA Astrophysics Data System (ADS)

Mundhwa, Mayur; Parmar, Rajesh D.; Thurgood, Christopher P.

2017-03-01

A parametric comparison study is carried out between segmented and conventional continuous layer configurations of the coated combustion-catalyst to investigate their influence on the performance of methane steam reforming (MSR) for hydrogen production in a catalytic plate reactor (CPR). MSR is simulated on one side of a thin plate over a continuous layer of nickel-alumina catalyst by implementing an experimentally validated surface microkinetic model. Required thermal energy for the MSR reaction is supplied by simulating catalytic methane combustion (CMC) on the opposite side of the plate over segmented and continuous layer of a platinum-alumina catalyst by implementing power law rate model. The simulation results of both coating configurations of the combustion-catalyst are compared using the following parameters: (1) co-flow and counter-flow modes between CMC and MSR, (2) gas hourly space velocity and (3) reforming-catalyst thickness. The study explains why CPR designed with the segmented combustion-catalyst and co-flow mode shows superior performance not only in terms of high hydrogen production but also in terms of minimizing the maximum reactor plate temperature and thermal hot-spots. The study shows that the segmented coating requires 7% to 8% less combustion-side feed flow and 70% less combustion-catalyst to produce the required flow of hydrogen (29.80 mol/h) on the reforming-side to feed a 1 kW fuel-cell compared to the conventional continuous coating of the combustion-catalyst.

DNA Molecules in Microfluidic Oscillatory Flow

PubMed Central

Chen, Y.-L.; Graham, M.D.; de Pablo, J.J.; Jo, K.; Schwartz, D.C.

2008-01-01

The conformation and dynamics of a single DNA molecule undergoing oscillatory pressure-driven flow in microfluidic channels is studied using Brownian dynamics simulations, accounting for hydrodynamic interactions between segments in the bulk and between the chain and the walls. Oscillatory flow provides a scenario under which the polymers may remain in the channel for an indefinite amount of time as they are stretched and migrate away from the channel walls. We show that by controlling the chain length, flow rate and oscillatory flow frequency, we are able to manipulate the chain extension and the chain migration from the channel walls. The chain stretch and the chain depletion layer thickness near the wall are found to increase as the Weissenberg number increases and as the oscillatory frequency decreases. PMID:19057656

Fluid dynamic modeling and numerical simulation of low-density hypersonic flow

NASA Astrophysics Data System (ADS)

Cheng, H. K.; Wong, Eric Y.

1988-06-01

The concept of a viscous shock-layer and several related versions of continuum theories/methods are examined for their adequacy as a viable framework to study flow physics and aerothermodynamics of relevance to sustained hypersonic flights. Considering the flat plate at angle of attack, or the wedge, as a generic example for the major aerodynamic component of a hypersonic vehicle, the relative importance of the molecular-transport effects behind the shock (in the form of the 'shock slip') and the wall-slip effects are studied. In the flow regime where the shock-transition-zone thickness remains small compared to the shock radius of curvature, a quasi-one-dimensional shock structure under the Burnett/thirteen-moment approximation, as well as particulate/collisional models, can be consistently developed. The fully viscous version of the shock-layer model is shown to provide the crucial boundary condition downstream the shock in this case. The gas-kinetic basis of the continuum description for the flow behind the bow shock, and certain features affecting the non-equilibrium flow chemistry, are also discussed.

Fluid dynamic modeling and numerical simulation of low-density hypersonic flow

NASA Technical Reports Server (NTRS)

Cheng, H. K.; Wong, Eric Y.

1988-01-01

The concept of a viscous shock-layer and several related versions of continuum theories/methods are examined for their adequacy as a viable framework to study flow physics and aerothermodynamics of relevance to sustained hypersonic flights. Considering the flat plate at angle of attack, or the wedge, as a generic example for the major aerodynamic component of a hypersonic vehicle, the relative importance of the molecular-transport effects behind the shock (in the form of the 'shock slip') and the wall-slip effects are studied. In the flow regime where the shock-transition-zone thickness remains small compared to the shock radius of curvature, a quasi-one-dimensional shock structure under the Burnett/thirteen-moment approximation, as well as particulate/collisional models, can be consistently developed. The fully viscous version of the shock-layer model is shown to provide the crucial boundary condition downstream the shock in this case. The gas-kinetic basis of the continuum description for the flow behind the bow shock, and certain features affecting the non-equilibrium flow chemistry, are also discussed.

Computational Study of Surface Tension and Wall Adhesion Effects on an Oil Film Flow Underneath an Air Boundary Layer

NASA Technical Reports Server (NTRS)

Celic, Alan; Zilliac, Gregory G.

1998-01-01

The fringe-imaging skin friction (FISF) technique, which was originally developed by D. J. Monson and G. G. Mateer at Ames Research Center and recently extended to 3-D flows, is the most accurate skin friction measurement technique currently available. The principle of this technique is that the skin friction at a point on an aerodynamic surface can be determined by measuring the time-rate-of-change of the thickness of an oil drop placed on the surface under the influence of the external air boundary layer. Lubrication theory is used to relate the oil-patch thickness variation to shear stress. The uncertainty of FISF measurements is estimated to be as low as 4 percent, yet little is known about the effects of surface tension and wall adhesion forces on the measured results. A modified version of the free-surface Navier-Stokes solver RIPPLE, developed at Los Alamos National Laboratories, was used to compute the time development of an oil drop on a surface under a simulated air boundary layer. RIPPLE uses the volume of fluid method to track the surface and the continuum surface force approach to model surface tension and wall adhesion effects. The development of an oil drop, over a time period of approximately 4 seconds, was studied. Under the influence of shear imposed by an air boundary layer, the computed profile of the drop rapidly changes from its initial circular-arc shape to a wedge-like shape. Comparison of the time-varying oil-thickness distributions computed using RIPPLE and also computed using a greatly simplified numerical model of an oil drop equation which does not include surface tension and wall adhesion effects) was used to evaluate the effects of surface tension on FISF measurement results. The effects of surface tension were found to be small but not necessarily negligible in some cases.

Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

PubMed

Sharma, N; Periasamy, C; Chaturvedi, N

2018-07-01

In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

Nonuniform concentration - A mechanism for drag reduction.

NASA Technical Reports Server (NTRS)

Rivard, W. C.; Kulinski, E. S.

1972-01-01

A large reduction in drag coefficient has been observed in certain external flows of aqueous solutions with high molecular weight polymer additives. A change in the near wake configuration is phenomenologically responsible for the drag reduction, but the underlying mechanism is presently unknown. An analogy to known phenomena in particulate suspensions is drawn which suggests nonuniform concentration of the polymer additive as an explanation. An analysis of the boundary layer on a sphere with varying viscosity was made to investigate the effect. The results indicate early transition to turbulence for concentration variations whose length scale is small compared with the momentum boundary layer thickness. Stabilization and delayed transition are indicated for thicker concentration layers. Observations are suggested for the thin concentration layers.

An investigation of turbulence structure in a low-Reynolds-number incompressible turbulent boundary

NASA Technical Reports Server (NTRS)

White, B. R.; Strataridakis, C. J.

1987-01-01

An existing high turbulence intensity level (5%) atmospheric boundary-layer wind tunnel has been successfully converted to a relatively low level turbulence (0.3%) wind tunnel through extensive modification, testing, and calibration. A splitter plate was designed, built, and installed into the wind-tunnel facility to create thick, mature, two-dimensional turbulent boundary layer flow at zero pressure gradient. Single and cross hot-wire measurements show turbulent boundary layer characteristics of good quality with unusually large physical size, i.e., viscous sublayer of the order of 1 mm high. These confirm the potential ability of the tunnel to be utilized for future high-quality near-wall turbulent boundary layer measurements. It compares very favorably with many low turbulence research tunnels.

Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition

NASA Astrophysics Data System (ADS)

Carcione, José M.; Poletto, Flavio

2013-12-01

It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.

Modeling the effects of fire severity and climate warming on active layer and soil carbon dynamics of black spruce forests across the landscape in interior Alaska

USGS Publications Warehouse

Genet, H.; McGuire, Anthony David; Barrett, K.; Breen, A.; Euskirchen, E.S.; Johnstone, J.F.; Kasischke, E.S.; Melvin, A.M.; Bennett, A.; Mack, M.C.; Rupp, T.S.; Schuur, A.E.G.; Turetsky, M.R.; Yuan, F.

2013-01-01

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layer caused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness of 1.1 m on average by 2100. The combination of warming and fire led to a simulated cumulative loss of 9.6 kgC m−2 on average by 2100. Our analysis suggests that ecosystem carbon storage in boreal forests in interior Alaska is particularly vulnerable, primarily due to the combustion of organic layer thickness in fire and the related increase in active layer thickness that exposes previously protected permafrost soil carbon to decomposition.

Influence of process fluids properties on component surface convective heat emission

NASA Astrophysics Data System (ADS)

Ivanova, T. N.; Korshunov, A. I.; Zavialov, P. M.

2018-03-01

When grinding with metal-working process fluid, a thin layer of inhibited liquid is formed between the component and the grinding wheel under the action of viscous forces. This can be defined as a hydrodynamic boundary layer or a thermal boundary layer. In this work, the thickness of the layers is studied depending on the viscosity of the fluid, inertia forces, velocity and pressure of the flow; also the causes of their occurrence are identified. It is established that under turbulent flow, the viscosity of the flow and the diffusion rate are much higher than in laminar flow, which also affects heat emission. Calculation of heat transfer in a single-phase chemically homogeneous medium of process liquids has shown that their properties, such as viscosity, thermal conductivity, density and heat capacity are of primary importance. The results of experimental studies of these characteristics are presented. When determining the heat transfer coefficient, functional correlations between the physical variables of the process fluid and the change in time and space have been established. As a result of the studies carried out to determine the heat transfer coefficient of a plate immersed in the process fluid, it is established that the intensification of the cooling process of the treated surface immersed in the coolant is more intense than with other methods of coolant supplying. An increase in the pulsation rate of the process liquid flow and the length of the flow displacement path leads to an increase in the heat transfer coefficient of the treated surface and a decrease in the temperature that arises during grinding.

On the nonlinear development of the most unstable Goertler vortex mode

NASA Technical Reports Server (NTRS)

Denier, James P.; Hall, Philip

1991-01-01

The nonlinear development of the most unstable Gortler vortex mode in boundary layer flows over curved walls is investigated. The most unstable Gortler mode is confined to a viscous wall layer of thickness O(G -1/5) and has spanwise wavelength O(G 11/5); it is, of course, most relevant to flow situations where the Gortler number G is much greater than 1. The nonlinear equations covering the evolution of this mode over an O(G -3/5) streamwise lengthscale are derived and are found to be of a fully nonparallel nature. The solution of these equations is achieved by making use of the numerical scheme used by Hall (1988) for the numerical solution of the nonlinear Gortler equations valid for O(1) Gortler numbers. Thus, the spanwise dependence of the flow is described by a Fourier expansion, whereas the streamwise and normal variations of the flow are dealt with by employing a suitable finite difference discretization of the governing equations. Our calculations demonstrate that, given a suitable initial disturbance, after a brief interval of decay, the energy in all the higher harmonics grows until a singularity is encountered at some downstream position. The structure of the flowfield as this singularity is approached suggests that the singularity is responsible for the vortices, which are initially confined to the thin viscous wall layer, moving away from the wall and into the core of the boundary layer.

Geometrical and Structural Asperities on Fault Surfaces

NASA Astrophysics Data System (ADS)

Sagy, A.; Brodsky, E. E.; van der Elst, N.; Agosta, F.; di Toro, G.; Collettini, C.

2007-12-01

Earthquake dynamics are strongly affected by fault zone structure and geometry. Fault surface irregularities and the nearby structure control the rupture nucleation and propagation, the fault strength, the near-field stress orientations and the hydraulic properties. New field observations demonstrate the existence of asperities in faults as displayed by topographical bumps on the fault surface and hardening of the internal structure near them. Ground-based LIDAR measurements on more than 30 normal and strike slip faults in different lithologies demonstrate that faults are not planar surfaces and roughness is strongly dependent on fault displacement. In addition to the well-understood roughness exemplified by abrasive striations and fracture segmentation, we found semi-elliptical topographical bumps with wavelengths of a few meters. In many faults the bumps are not spread equally on the surface and zones can be bumpier than others. The bumps are most easily identified on faults with total displacement of dozens to hundreds of meters. Smaller scale roughness on these faults is smoothed by abrasive processes. A key site in southern Oregon shows that the topographic bumps are closely tied to the internal structure of the fault zone. At this location, we combine LiDAR data with detailed structural analysis of the fault zone embedded in volcanic rocks. Here the bumps correlate with an abrupt change in the width of the cohesive cataclasite layer that is exposed under a thin ultracataclasite zone. In most of the exposures the cohesive layer thickness is 10-20 cm. However, under protruding bumps the layer is always thickened and the width can locally exceed one meter. Field and microscopic analyses show that the layer contains grains with dimensions ranging from less than 10 μ up to a few centimeters. There is clear evidence of internal flow, rotation and fracturing of the grains in the layer. X-Ray diffraction measurements of samples from the layer show that the bulk mineralogy is identical to that of the host rock, although thin section analysis suggests that some alteration and secondary mineralization of the grains also occurs. We infer that the cohesiveness of the layer is a consequence of repacking and cementation similar to deformation bands in granular material. By comparing the thickness of the cohesive layer on several secondary faults in this fault area we found that the average thickness of the layer increases with total slip. The correlation is nonlinear and the thickening rate decreases with increasing slip. We conclude that granular flow decreasing with increasing slip and thus the deformation is continually localized.

On the Opening of Thick Walled Elastic Tubes: A Fluid-Structure Model for Acid Reflux

NASA Astrophysics Data System (ADS)

Ghosh, Sudip; Kahrilas, Peter

2005-11-01

A coupled fluid-structure mathematical model was developed to quantify rapid opening of thick-walled elastic tubes, a phenomenon underlying biological flows such as gastroesophageal reflux disease (GERD). The wall was modeled using non-linear finite deformation theory to predict space-time radial distention of an axisymmetric tube with luminal fluid flow. Anisotropic azimuthal and longitudinal muscle-induced stresses were incorporated, and interstitial material properties were assumed isotropic and linearly elastic. Fluid flow was modeled using lubrication theory with inertial correction. Opening and flow were driven by a specified inflow pressure and zero pressure gradient was specified at outflow. No-slip and surface force balance were applied at the fluid-wall interface. Viscoelasticity was modeled with ad hoc damping and the evolution of the tube geometry was predicted at mid-layer. A potentially important discovery was made when applied to studies of initiation of opening with GERD: while material stiffness is of minor consequence, small changes in resting lumen distension (˜2 mm diameter) may be a sensitive distinguishing feature of the disease.

Effects of Mg pre-flow, memory, and diffusion on the growth of p-GaN with MOCVD (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tu, Charng-Gan; Chen, Hao-Tsung; Chen, Sheng-Hung; Chao, Chen-Yao; Kiang, Yean-Woei; Yang, Chih-Chung

2017-02-01

In MOCVD growth, two key factors for growing a p-type structure, when the modulation growth or delta-doping technique is used, include Mg memory and diffusion. With high-temperature growth (>900 degree C), doped Mg can diffuse into the under-layer. Also, due to the high-pressure growth and growth chamber coating in MOCVD, plenty Mg atoms exist in the growth chamber for a duration after Mg supply is ended. In this situation, Mg doping continues in the following designated un-doped layers. In this paper, we demonstrate the study results of Mg preflow, memory, and diffusion. The results show that pre-flow of Mg into the growth chamber can lead to a significantly higher Mg doping concentration in growing a p-GaN layer. In other words, a duration for Mg buildup is required for high Mg incorporation. Based on SIMS study, we find that with the pre-flow growth, a high- and a low-doping p-GaN layer are formed. The doping concentration difference between the two layers is about 10 times. The thickness of the high- (low-) doping layer is about 40 (65) nm. The growth of the high-doping layer starts 10-15 min after Mg supply starts (Mg buildup time). The diffusion length of Mg into the AlGaN layer beneath (Mg content reduced to <5%) is about 10 nm. The memory time of Mg in the growth chamber is about 60 min, after which the Mg doping concentration is reduced to <1%.

Evaluation of Flush-Mounted, S-Duct Inlets With Large Amounts of Boundary Layer Ingestion

NASA Technical Reports Server (NTRS)

Berrier, Bobby L.; Morehouse, Melissa B.

2003-01-01

A new high Reynolds number test capability for boundary layer ingesting inlets has been developed for the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. Using this new capability, an experimental investigation of four S-duct inlet configurations with large amounts of boundary layer ingestion (nominal boundary layer thickness of about 40% of inlet height) was conducted at realistic operating conditions (high subsonic Mach numbers and full-scale Reynolds numbers). The objectives of this investigation were to 1) develop a new high Reynolds number, boundary-layer ingesting inlet test capability, 2) evaluate the performance of several boundary layer ingesting S-duct inlets, 3) provide a database for CFD tool validation, and 4) provide a baseline inlet for future inlet flow-control studies. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on duct exit diameter) from 5.1 million to a fullscale value of 13.9 million, and inlet mass-flow ratios from 0.39 to 1.58 depending on Mach number. Results of this investigation indicate that inlet pressure recovery generally decreased and inlet distortion generally increased with increasing Mach number. Except at low Mach numbers, increasing inlet mass-flow increased pressure recovery and increased distortion. Increasing the amount of boundary layer ingestion (by decreasing inlet throat height and increasing inlet throat width) or ingesting a boundary layer with a distorted profile decreased pressure recovery and increased distortion. Finally, increasing Reynolds number had almost no effect on inlet distortion but increased inlet recovery by about one-half percent at a Mach number near cruise.

Recycling inflow method for simulations of spatially evolving turbulent boundary layers over rough surfaces

NASA Astrophysics Data System (ADS)

Yang, Xiang I. A.; Meneveau, Charles

2016-01-01

The technique by Lund et al. to generate turbulent inflow for simulations of developing boundary layers over smooth flat plates is extended to the case of surfaces with roughness elements. In the Lund et al. method, turbulent velocities on a sampling plane are rescaled and recycled back to the inlet as inflow boundary condition. To rescale mean and fluctuating velocities, appropriate length scales need be identified and for smooth surfaces, the viscous scale lν = ν/uτ (where ν is the kinematic viscosity and uτ is the friction velocity) is employed for the inner layer. Different from smooth surfaces, in rough wall boundary layers the length scale of the inner layer, i.e. the roughness sub-layer scale ld, must be determined by the geometric details of the surface roughness elements and the flow around them. In the proposed approach, it is determined by diagnosing dispersive stresses that quantify the spatial inhomogeneity caused by the roughness elements in the flow. The scale ld is used for rescaling in the inner layer, and the boundary layer thickness δ is used in the outer region. Both parts are then combined for recycling using a blending function. Unlike the blending function proposed by Lund et al. which transitions from the inner layer to the outer layer at approximately 0.2δ, here the location of blending is shifted upwards to enable simulations of very rough surfaces in which the roughness length may exceed the height of 0.2δ assumed in the traditional method. The extended rescaling-recycling method is tested in large eddy simulation of flow over surfaces with various types of roughness element shapes.

Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using laser Doppler anemometry

NASA Astrophysics Data System (ADS)

Herpin, Sophie; Perret, Laurent; Mathis, Romain; Tanguy, Christian; Lasserre, Jean-Jacques

2018-05-01

Laser Doppler anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of δ ^+=32{,}300. The boundary layer thickness to cube height ratio (δ /h=22.7) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy (z=h/4, h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy.

Osmosis in Cortical Collecting Tubules

PubMed Central

Schafer, James A.; Patlak, Clifford S.; Andreoli, Thomas E.

1974-01-01

This paper reports a theoretical analysis of osmotic transients and an experimental evaluation both of rapid time resolution of lumen to bath osmosis and of bidirectional steady-state osmosis in isolated rabbit cortical collecting tubules exposed to antidiuretic hormone (ADH). For the case of a membrane in series with unstirred layers, there may be considerable differences between initial and steady-state osmotic flows (i.e., the osmotic transient phenomenon), because the solute concentrations at the interfaces between membrane and unstirred layers may vary with time. A numerical solution of the equation of continuity provided a means for computing these time-dependent values, and, accordingly, the variation of osmotic flow with time for a given set of parameters including: Pf (cm s–1), the osmotic water permeability coefficient, the bulk phase solute concentrations, the unstirred layer thickness on either side of the membrane, and the fractional areas available for volume flow in the unstirred layers. The analyses provide a quantitative frame of reference for evaluating osmotic transients observed in epithelia in series with asymmetrical unstirred layers and indicate that, for such epithelia, Pf determinations from steady-state osmotic flows may result in gross underestimates of osmotic water permeability. In earlier studies, we suggested that the discrepancy between the ADH-dependent values of Pf and PDDw (cm s–1, diffusional water permeability coefficient) was the consequence of cellular constraints to diffusion. In the present experiments, no transients were detectable 20–30 s after initiating ADH-dependent lumen to bath osmosis; and steady-state ADH-dependent osmotic flows from bath to lumen and lumen to bath were linear and symmetrical. An evaluation of these data in terms of the analytical model indicates: First, cellular constraints to diffusion in cortical collecting tubules could be rationalized in terms of a 25-fold reduction in the area of the cell layer available for water transport, possibly due in part to transcellular shunting of osmotic flow; and second, such cellular constraints resulted in relatively small, approximately 15%, underestimates of Pf. PMID:4846767

Linear stability analysis of particle-laden hypopycnal plumes

NASA Astrophysics Data System (ADS)

Farenzena, Bruno Avila; Silvestrini, Jorge Hugo

2017-12-01

Gravity-driven riverine outflows are responsible for carrying sediments to the coastal waters. The turbulent mixing in these flows is associated with shear and gravitational instabilities such as Kelvin-Helmholtz, Holmboe, and Rayleigh-Taylor. Results from temporal linear stability analysis of a two-layer stratified flow are presented, investigating the behavior of settling particles and mixing region thickness on the flow stability in the presence of ambient shear. The particles are considered suspended in the transport fluid, and its sedimentation is modeled with a constant valued settling velocity. Three scenarios, regarding the mixing region thickness, were identified: the poorly mixed environment, the strong mixed environment, and intermediate scenario. It was observed that Kelvin-Helmholtz and settling convection modes are the two fastest growing modes depending on the particles settling velocity and the total Richardson number. The second scenario presents a modified Rayleigh-Taylor instability, which is the dominant mode. The third case can have Kelvin-Helmholtz, settling convection, and modified Rayleigh-Taylor modes as the fastest growing mode depending on the combination of parameters.

Analysis of viscous transonic flow over airfoil sections

NASA Technical Reports Server (NTRS)

Huff, Dennis L.; Wu, Jiunn-Chi; Sankar, L. N.

1987-01-01

A full Navier-Stokes solver has been used to model transonic flow over three airfoil sections. The method uses a two-dimensional, implicit, conservative finite difference scheme for solving the compressible Navier-Stokes equations. Results are presented as prescribed for the Viscous Transonic Airfoil Workshop to be held at the AIAA 25th Aerospace Sciences Meeting. The NACA 0012, RAE 2822 and Jones airfoils have been investigated for both attached and separated transonic flows. Predictions for pressure distributions, loads, skin friction coefficients, boundary layer displacement thickness and velocity profiles are included and compared with experimental data when possible. Overall, the results are in good agreement with experimental data.

Thermal radiation influence on MHD flow of a rotating fluid with heat transfer through EFGM solutions

NASA Astrophysics Data System (ADS)

Prasad, D. V. V. Krishna; Chaitanya, G. S. Krishna; Raju, R. Srinivasa

2018-05-01

The aim of this research work is to find the EFGM solutions of the unsteady magnetohydromagnetic natural convection heat transfer flow of a rotating, incompressible, viscous, Boussinesq fluid is presented in this study in the presence of radiative heat transfer. The Rosseland approximation for an optically thick fluid is invoked to describe the radiative flux. Numerical results obtained show that a decrease in the temperature boundary layer occurs when the Prandtl number and the radiation parameter are increased and the flow velocity approaches steady state as the time parameter t is increased. These findings are in quantitative agreement with earlier reported studies.

Computational study of the vortex path variation with the VG height

NASA Astrophysics Data System (ADS)

Fernández-Gámiz, U.; Zamorano, G.; Zulueta, E.

2014-06-01

An extensive range of conventional, vane-type, passive vortex generators (VGs) are in use for successful applications of flow separation control. In most cases, the VG height is designed with the same thickness as the local boundary layer at the VG position. However, in some applications, these conventional VGs may produce excess residual drag. The so-called low-profile VGs can reduce the parasitic drag associated to this kind of passive control devices. As suggested by many authors, low-profile VGs can provide enough momentum transfer over a region several times their own height for effective flow-separation control with much lower drag. The main objective of this work is to study the variation of the path and the development of the primary vortex generated by a rectangular VG mounted on a flat plate with five different device heights h = δ, h1 = 0.8δ, h2 = 0.6δ, h3 = 0.4δ and h4 = 0.25m, where 5 is the local boundary layer thickness. For this purpose, computational simulations have been carried out at Reynolds number Re = 1350 based on the height of the conventional VG h = 0.25m with the angle of attack of the vane to the oncoming flow β = 18.5°. The results show that the VG scaling significantly affects the vortex trajectory and the peak vorticity generated by the primary vortex.