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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Numerical solutions of the complete Navier-Stokes equations

Using ideas from the kinetic theory, the Navier-Stokes equations are modified in such a way that they can be cast as a set of first order hyperbolic equations. This is achieved by incorporating time dependent terms into the definition of the stress tensor and the heat flux vectors. The boundary conditions are then determined from the theory of characteristics. Because the resulting equations reduce to the traditional Navier-Stokes equations when the steady state is reached, the present approach provides a straightforward scheme for the determination of inflow and outflow boundary conditions. The method is validated by comparing its predictions with known exact solutions of the steady Navier-Stokes equations.

Hassan, H. A.↗
NASA NTRS1987

Investigation of low-speed turbulent separated flow around airfoils

Described is a low-speed wind tunnel experiment to measure the flowfield around a two-dimensional airfoil operating close to maximum lift. Boundary layer separation occurs on the upper surface at x/c=0.85. A three-component laser velocimeter, coupled with a computer-controlled data acquisition system, was used to obtain three orthogonal mean velocity components and three components of the Reynolds stress tensor in both the boundary layer and wake of the airfoil. Pressure distributions on the airfoil, skin friction distribution on the upper surface of the airfoil, and integral properties of the airfoil boudary layer are also documented. In addition to these near-field flow properties, static pressure distributions, both upstream and downstream from the airfoil and on the walls of the wind tunnel, are also presented.

Wadcock, Alan J.↗
NASA NTRS1987

Resonance absorption of magnetohydrodynamic surface waves - Viscous effects

The effects of viscosity on the resonance absorption of incompressible MHD surface waves, which occurs when the waves are supported by a thin 'transition layer' rather than by a discontinuous surface, are considered. The behavior of the plasma and fields inside the transition layer is considered, allowing for classical viscosity. An inhomogeneous Airy equation for the velocity component along the propagative direction is obtained in the vicinity of the resonant field line. The viscous stress tensor for a magnetized plasma is considered, and a simple algebraic steady state equation is obtained for the velocity component along the background magnetic field. The net heating rate is evaluated and found to be independent of the viscosity coefficient, and to correspond to the surface wave 'decay rate' obtained from ideal MHD equations.

Hollweg, Joseph V.↗
NASA NTRS1987

Rectangular subsonic jet flowfield study

The flowfield of a rectangular jet with 2:1 aspect ratio was studied at an axial Reynolds number of 127,000, using a three-dimensional laser anemometer. The flowfield surveys resulted in mean velocity vector field plots and contour plots of the Reynolds stress tensor components for the major and minor axes. These data contribute substantially to currently available data of jet flowfields.

Morrison, Gerald L.↗
NASA NTRS1987

Computer simulation of ledge formation and ledge interaction for the silicon (111) free surface

Both strip and triangular clusters, composed of 2 -1 -1 line ledges, have been simulated on the Si (111) surface. The long-range ledge-ledge interaction and the surface stress tensor distribution have been evaluated for these two pill-box geometries using a semiempirical potential-energy function that incorporates both two-body and three-body contributions. The consequences of the ledge-ledge interaction on two-dimensional nucleation for Si (111) has been evaluated as a function of Si adatom supersaturation and shown to differ significantly from conventional theory, where such interaction is neglected.

Balamane, H.↗
NASA NTRS1988

3-D LDA study of a rectangular jet

The flow field of a rectangular jet with a 2:1 aspect ratio was studied at an axial Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry. The flow field survey resulted in mean velocity vector field plots and contour plots of the Reynolds stress tensor components. This paper presents contour plots in the planes of the jet minor and major axes at different axial locations. These data contribute substantially to currently available data of jet flow fields and will provide a valuable database for three-dimensional modeling.

Morrison, Gerald L.↗
NASA NTRS1987

Boundary conditions for the Navier-Stokes equations

Using ideas from kinetic theory, the Navier-Stokes equations are modified in such a way that they can be cast as a set of first order hyperbolic equations. This is achieved by incorporating time dependent terms into the definition of the stress tensor and the heat flux vectors. The boundary conditions are then determined from the theory of characteristics. Because the resulting equations reduce to the traditional Navier-Stokes equations when the steady state is reached, the present approach provides a straightforward scheme for the determination of inflow and outflow boundary conditions. The method is validated by comparing its predictions with exact and numerical solutions of the steady Navier-Stokes equations.

Rudisill, Edgar N., Jr.↗
NASA NTRS1988

Experimental verification of a secondary recirculation zone in a labyrinth seal

The existence of a secondary recirculation zone inside the cavities of a labyrinth seal operating at a Reynolds number of 15,000 and a Taylor number of 10,300 has been experimentally verified. A three-dimensional laser Doppler anemometer system was used to measure the complete mean velocity and Reynolds stress tensor distributions in the first, third, fifth and seventh cavities of a seven cavity labyrinth seal which had a clearance of 1.27 mm.

Morrison, G. L.↗
NASA NTRS1988

3-D laser anemometer measurements in an annular seal

The flow field inside an annular seal with a 0.00127 m clearance was measured using a 3-D laser Doppler anemometer system. Through the use of this system, the mean velocity vector and the entire Reynolds stress tensor distributions were measured for the entire length of the seal (0.0373 m). The seal was operated at a Reynolds number of 27,000 and a Taylor number of 6,600.

Morrison, G. L.↗
NASA NTRS1987

A nonlinear viscoelastic constitutive equation - Yield predictions in multiaxial deformations

Yield stress predictions of a nonlinear viscoelastic constitutive equation for amorphous polymer solids have been obtained and are compared with the phenomenological von Mises yield criterion. Linear viscoelasticity theory has been extended to include finite strains and a material timescale that depends on the instantaneous temperature, volume, and pressure. Results are presented for yield and the correct temperature and strain-rate dependence in a variety of multiaxial deformations. The present nonlinear viscoelastic constitutive equation can be formulated in terms of either a Cauchy or second Piola-Kirchhoff stress tensor, and in terms of either atmospheric or hydrostatic pressure.

Shay, R. M., Jr.↗
NASA NTRS1989

A preliminary compressible second-order closure model for high speed flows

A preliminary version of a compressible second-order closure model that was developed in connection with the National Aero-Space Plane Project is presented. The model requires the solution of transport equations for the Favre-averaged Reynolds stress tensor and dissipation rate. Gradient transport hypotheses are used for the Reynolds heat flux, mass flux, and turbulent diffusion terms. Some brief remarks are made about the direction of future research to generalize the model.

Speziale, Charles G.↗
NASA NTRS1988

Eddy viscosity measurements in a rectangular jet

The flow field of a rectangular jet with a 2:1 aspect ratio was studied at a Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry (LDV). Velocity gradients, Reynolds stress tensor components, and scalar eddy viscosities are presented for the major and minor axis planes of the jet. The eddy viscosity model was found to be applicable only in the direction of maximum mean velocity gradient.

Swan, David H.↗
NASA NTRS1988

Equilibrium shape and location of a liquid drop acoustically positioned in a resonant rectangular chamber

The effect of a standing wave field in a rectangular chamber on the shape and location of an acoustically positioned drop or bubble is calculated. The sample deformation and equilibrium position are obtained from an analysis of the spherical harmonic projections of the total surface stress tensor. The method of calculation relies on the assumed condition that the sample is only slightly distorted from a spherical form. The equilibrium location of a levitated drop is combined with a formula introduced by Hasegawa (1979) to calcualte the ka dependence of the radiation force function. The present theory is valid for large as well as small ka values. Calculations in the small ka limit agree with previous theories and experimental results. Examples are presented for nonplane-wave modes as well as plane-wave rectangular modes.

Jackson, H. W.↗
NASA NTRS1989

Rectangular subsonic jet flow field measurements

Flow field measurements are presented of 3 subsonic rectangular cold air jets. The 3 cases presented had aspect ratios of 1 x 2, 1 x 4 at a Mach number of 0.09 and an aspect ratio of 1 x 2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemoneter system. The presented data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data is presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made. All tabular data are available in ASCII format on MS-DOS compatible disks.

Morrison, Gerald L.↗
NASA NTRS1990

Rectangular subsonic jet flow field measurements

Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made.

Morrison, Gerald L.↗
NASA NTRS1990

A turbulent two-phase flow model for nebula flows

A new and very efficient turbulent two-phase flow numericaly model is described to analyze the environment of a protoplanetary nebula at a stage prior to the formation of planets. Focus is on settling processes of dust particles in flattened gaseous nebulae. The model employs a perturbation technique to improve the accuracy of the numerical simulations of such flows where small variations of physical quantities occur over large distance ranges. The particles are allowed to be diffused by gas turbulence in addition to settling under gravity. Their diffusion coefficients is related to the gas turbulent viscosity by the non-dimensional Schmidt number. The gas turbulent viscosity is determined by the means of the eddy viscosity hypothesis that assumes the Reynolds stress tensor proportional to the mean strain rate tensor. Zero- and two-equation turbulence models are employed. Modeling assumptions are detailed and discussed. The numerical model is shown to reproduce an existing analytical solution for the settling process of particles in an inviscid nebula. Results of nebula flows are presented taking into account turbulence effects of nebula flows. Diffusion processes are found to control the settling of particles.

Champney, Joelle M.↗
NASA NTRS1990

Vorticity, turbulence production, and turbulence induced accelerations in a rectangular jet as measured using 3-D LDA

The flow field of a rectangular jet with a 4:1 aspect ratio (50.4 x 12.7 mm) was studied at a Reynolds number of 100,000 (Mach number 0.09) using a 3-D laser Doppler anemometer system. Measurements were performed along the major and minor axis planes and at various downstream cross-sections of the jet. The mean velocity vector and entire Reynolds stress tensor were measured and presented in a previous publication. The present work presents the vorticity vector, turbulence production, and turbulence induced acceleration vector distributions which were calculated from the previously presented data.

Morrison, Gerald L.↗
NASA NTRS1990

Toward the large-eddy simulation of compressible turbulent flows

New subgrid-scale models for the large-eddy simulation of compressible turbulent flows are developed and tested based on the Favre-filtered equations of motion for an ideal gas. A compressible generalization of the linear combination of the Smagorinsky model and scale-similarity model, in terms of Favre-filtered fields, is obtained for the subgrid-scale stress tensor. An analogous thermal linear combination model is also developed for the subgrid-scale heat flux vector. The two dimensionless constants associated with these subgrid-scale models are obtained by correlating with the results of direct numerical simulations of compressible isotropic turbulence performed on a 96(exp 3) grid using Fourier collocation methods. Extensive comparisons between the direct and modeled subgrid-scale fields are provided in order to validate the models. A large-eddy simulation of the decay of compressible isotropic turbulence (conducted on a coarse 32(exp 3) grid) is shown to yield results that are in excellent agreement with the fine grid direct simulation. Future applications of these compressible subgrid-scale models to the large-eddy simulation of more complex supersonic flows are discussed briefly.

Erlebacher, G.↗