Search NASA⌕ Search

SEARCH · Search NASA

Results for “normalizing flows”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Benchmark Data for Evaluation of NASA Impedance Eduction Methods

Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type, source level, and mean flow Mach number on the impedances educed with these liners are explored. Existing models are used to predict the impedance for each test condition and are compared with educed impedance spectra to determine their validity. The results suggest that educed impedances are similar for either a stepped sine or swept sine source. The predicted models are acceptable for the perforate liner and are quite good for the calibration and wire mesh liners.

acoustic↗
NASA NTRSDate not supplied

Benchmark Data for Evaluation of NASA Impedance Eduction Methods

Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type, source level, and mean flow Mach number on the impedances educed with these liners are explored. Existing models are used to predict the impedance for each test condition, and are compared with educed impedance spectra to determine their validity. The results suggest that educed impedances are similar for either a stepped sine or swept sine source. The predicted models are acceptable for the perforate liner, and are quite good for the calibration and wire mesh liners.

acoustic↗
NASA NTRSDate not supplied

Comparisons of Impedance Prediction Models for Perforate-over-Honeycomb Liners

A large dataset is used to evaluate the efficacy of multiple impedance prediction models for perforate-over-honeycomb liners. Two-factorial analysis is used to explore the relative importance of the key parameters used in these models. Tests are conducted in the NASALangley Normal Incidence Tube and Grazing Flow Impedance Tube with over eighty perforate facesheets at multiple source sound pressure levels, Mach numbers and frequencies. Each prediction model is then compared with this dataset to determine how well each method predicts the measured data. Finally, an optimizer is used to further improve the ability of one of these models to reproduce the measured results.

acoustic↗
NASA NTRSDate not supplied

Comparisons of Impedance Prediction Models for Perforate-over-Honeycomb Liners

A large dataset is used to evaluate the efficacy of multiple impedance prediction models for perforate-over-honeycomb liners. Two-factorial analysis is used to explore the relative importance of the key parameters used in these models. Tests are conducted in the NASALangley Normal Incidence Tube and Grazing Flow Impedance Tube with over eighty perforate facesheets at multiple source sound pressure levels, Mach numbers and frequencies. Each prediction model is then compared with this dataset to determine how well each method predicts the measured data. Finally, an optimizer is used to further improve the ability of one of these models to reproduce the measured results.

acoustic↗
NASA NTRS2016

Comparison of Cross Correlation and Optical Flow Methods for Processing Retroreflective and Natural Background BOS Data

Background oriented schlieren images have historically been generated by calculating the observed pixel displacement between an image pair using normalized cross-correlation methods. This work uses optical flow data reduction methods to solve the displacement fields. A well established method used in the computer vision community, optical flow is the apparent brightness motion in an image sequence. The regularization method of Horn and Schunck is used to create schlieren images using two data sets: a supersonic shockjet plume interaction at the NASA Ames Unitary Plan Wind Tunnel, and a transonic flight test of a T-38 using a naturally occurring background performed in conjunction with NASA Ames and Armstrong research centers. Results are presented and contrasted with those using normalized cross-correlation methods. The optical flow images are found to provided significantly more detail at a decreased computational time.

schlieren↗
NASA NTRS2001

Near-Horizontal, Two-Phase Flow Patterns of Nitrogen and Hydrogen at Low Mass Heat and Flux (on CD-ROM)

One reason for NASA's interest in cryogenic two-phase flow with low mass and heat flux is the need to design spacecraft heat exchangers used for vaporizing cryogenic propellants. The CD-ROM provides digitized movies of particular flow patterns observed in experimental work. The movies have been provided in (QuickTime9Trademark) format, encoded at 320w x 240h pixels, 15 fps, using the Sorenson(Trademark) Video Codec for compression. Experiments were conducted to obtain data on the two-phase (liquid and vapor) flow behavior of cryogenic nitrogen and hydrogen under low mass and heat flux conditions. Tests were performed in normal gravity with a 1.5 degree up flow configuration. View ports in the apparatus permitted visual observation of the two-phase flow patterns. Computer codes to predict flow patterns were developed from theoretical/empirical models reported in the literature. Predictions from the computer codes were compared with experimental flow pattern observations. Results are presented employing the traditional two-dimensional flow pattern map format using the liquid and gas superficial velocities as coordinates. In general, the agreement between the experimental results and the analytical predictive methods is reasonably good. Small regions of the flow pattern maps are identified where the models are deficient as a result of neglecting phase change phenomena. Certain regions of the maps were beyond the range of the experiments and could not be completely validated. Areas that could benefit from further work include modeling of the transition from separated flow, collection of additional data in the bubble and annular flow regimes, and collection of experimental data at other inclination angles, tube diameters and high heat flux.

TWO PHASE FLOW↗
NASA NTRS1991

A laser velocimeter investigation of the normal shock-wave boundary layer interaction

Nonintrusive 3-D measurements were made of a normal shock wave/turbulent boundary layer interaction. The measurements were made through a quadrant of a square test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made near the corner in the vicinity of the shock where 3-D flow effects were expected to be significant. Laser Doppler velocimetry, surface static pressure measurements, and flow visualization techniques were used for two freestream nominal Mach number test cases: 1.6 and 1.3. No turbulence information was obtained. The mean velocity measurements were converted to Mach number by recording the wind tunnel total temperature. Some shock oscillation was present during both of the test cases. After startup of the wind tunnel, the shock oscillated with an amplitude of approx. + or - 1 cm, however, after reaching steady condition, the shock oscillation amplitude was greatly reduced, as evidenced by the laser velocimeter results. The Mach 1.3 test case resulted in a nearly uniform flow without secondary shock waves and with no or very isolated corner separation.

Chriss, Randall M.↗
NASA NTRS1992

Numerical simulation of spacecraft propellant tank draining characteristics

Liquid residual at the incipience of suction dip, and slosh wave excitation under normal and various reduced gravity environments and different flow rates of liquid have been investigated during the liquid hydrogen draining. It shows that the liquid residual at the incipience of suction dip increases as the values of gravity environment decrease from normal gravity ot lower reduced gravity. Flow fields with lower flow rates of liquid draining are responsible for the excitation higher wave amplitude slosh waves.

Hung, R. J.↗
NASA NTRS1988

Dynamical criterion for a marginally unstable, quasi-linear behavior in a two-layer model

A two-layer quasi-geostrophic flow forced by meridional variations in heating can be in regimes ranging from radiative equilibrium to forced geostrophic turbulence. Between these extremes is a regime where the time-mean (zonal) flow is marginally unstable. Using scaling arguments, it is concluded that such a marginally unstable state should occur when a certain parameter, measuring the strength of wave-wave interactions relative to the beta effect and advection by the thermal wind, is small. Numerical simulations support this proposal. A transition from the marginally unstable regime to a more nonlinear regime is then examined through numerical simulations with different radiative forcings. It is found that transition is not caused by secondary instability of waves in the marginally unstable regime. Instead, the time-mean flow can support a number of marginally unstable normal modes. These normal modes interact with each other, and if they are of sufficient amplitude, the flow enters a more nonlinear regime.

Ebisuzaki, W.↗
NASA NTRS1982

Comparison of three-dimensional turbulent boundary-layer calculations with experiment

A numerical simulation is carried out of the incompressible three-dimensional turbulent boundary-layer experiments of van den Berg and Elsenaar (1972), Dechow (1977), and Muller (1982). The simulation is effected by integrating the boundary-layer equations together with an algebraic eddy-viscosity turbulence model. With this computational method, the downstream portion of the flow treated by van den Berg and Elsenaar, where the crossflow is large, cannot be predicted. It is believed that this flow is significantly influenced by elliptic flow-field effects. Even though Dechow's experiment also indicated departures from the boundary-layer concept, the calculations made here agree reasonably well with the mean-flow development up to separation. The normal pressure gradients in Muller's experiment are found to be negligible in regions with large skewing, making it possible to test turbulence models using the boundary-layer equations. The simulation of this flow compares favorably with the experimental data throughout the flow field.

Muller, U. R.↗
NASA NTRS1976

Table and charts of equilibrium normal-shock properties for hydrogen-helium mixtures with velocities to 70 km/sec. Volume 1: 0.95 H2-0.05 He (by volume)

Equilibrium thermodynamic and flow properties are presented in tabulated and graphical form for moving, standing, and reflected normal shock waves into hydrogen-helium mixtures representative of postulated outer planet atmospheres. These results are presented in four volumes and the volmetric compositions of the mixtures are 0.95H2-0.05He in Volume 1, 0.90H2-0.10He in Volume 2, 0.85H2-0.15He in Volume 3, and 0.75H2-0.25He in Volume 4. Properties include pressure, temperature, density, enthalpy, speed of sound, entropy, molecular-weight ratio, isentropic exponent, velocity, and species mole fractions. Incident (moving) shock velocities are varied from 4 to 70 km/sec for a range of initial pressure of 5 N/sq m to 100 kN/sq m. Results are applicable to shock-tube flows and for determining flow conditions behind the normal portion of the bow shock about a blunt body at high velocities in postulated outer planet atmospheres. The document is a revised version of the original edition of NASA SP-3085 published in 1974.

Miller, C. G., III↗
NASA NTRS1990

Interaction of a streamwise vortex with a turbulent mixing layer

The interaction of a single streamwise vortex with a plane turbulent mixing layer is experimentally studied. Initially, near the mixing layer origin, the vortex rides just below the layer and only affects the mixing layer properties near the bottom side of the mixing layer. Once the vortex starts to become embedded within the mixing layer and active interaction has begun, the effect of the vortex is to grossly distort the mean velocity and turbulence contours over the whole width of the mixing layer. The induced cross-flow velocities in the mixing layer result in the production of additional normal Reynolds stresses which in turn act with mean flow gradients to generate extra shear stresses. In particular, the secondary shear stress (SSS) achieves an absolute peak value equivalent to about 40 percent of the maximum primary shear stress. The position and decay of the SSS peak are then found to be strongly correlated with those of the streamwise vortex.

Bell, James H.↗
NASA NTRS2001

Restraint of Liquid Jets by Surface Tension in Microgravity Modeled

Tension in Microgravity Modeled Microgravity poses many challenges to the designer of spacecraft tanks. Chief among these are the lack of phase separation and the need to supply vapor-free liquid or liquidfree vapor to the spacecraft processes that require fluid. One of the principal problems of phase separation is the creation of liquid jets. A jet can be created by liquid filling, settling of the fluid to one end of the tank, or even closing a valve to stop the liquid flow. Anyone who has seen a fountain knows that jets occur in normal gravity also. However, in normal gravity, the gravity controls and restricts the jet flow. In microgravity, with gravity largely absent, jets must be contained by surface tension forces. Recent NASA experiments in microgravity (Tank Pressure Control Experiment, TPCE, and Vented Tank Pressure Experiment, VTRE) resulted in a wealth of data about jet behavior in microgravity. VTRE was surprising in that, although it contained a complex geometry of baffles and vanes, the limit on liquid inflow was the emergence of a liquid jet from the top of the vane structure. Clearly understanding the restraint of liquid jets by surface tension is key to managing fluids in low gravity. To model this phenomenon, we need a numerical method that can track the fluid motion and the surface tension forces. The fluid motion is modeled with the Navier-Stokes equation formulated for low-speed incompressible flows. The quantities of velocity and pressure are placed on a staggered grid, with velocity being tracked at cell faces and pressure at cell centers. The free surface is tracked via the introduction of a color function that tracks liquid as 1/2 and gas as -1/2. A phase model developed by Jacqmin is used. This model converts the discrete surface tension force into a barrier function that peaks at the free surface and decays rapidly. Previous attempts at this formulation have been criticized for smearing the interface. However, by sharpening the phase function, double gridding the fluid function, and using a higher order solution for the fluid function, interface smearing is avoided. These equations can be rewritten as two coupled Poisson equations that also include the velocity. The method of solution is as follows: first, the phase equations are solved from this solution, a velocity field is generated, then a successive overrelaxation scheme is used to solve for a pressure field consistent with the velocity solution. After the code was implemented in axisymmetric form and verified by several test cases, the drop tower runs of Aydelott were modeled. The model handed the free-surface deformation quite nicely, even to the point of modeling geyser growth in the regime where the free surface was no longer restrained. A representative run is shown.

Chato, David J.↗
NASA NTRS2002

Influence of Turbulence on the Restraint of Liquid Jets by Surface Tension in Microgravity Investigated

Microgravity poses many challenges to the designer of spacecraft tanks. Chief among these are the lack of phase separation and the need to supply vapor-free liquid or liquidfree vapor to the spacecraft processes that require fluid. One of the principal problems of phase separation is the creation of liquid jets. A jet can be created by liquid filling, settling of the fluid to one end of the tank, or even closing a valve to stop the liquid flow. Anyone who has seen a fountain knows that jets occur in normal gravity also. However, in normal gravity, the gravity controls and restricts the jet flow. In microgravity, with gravity largely absent, surface tension forces must contain jets. To model this phenomenon, a numerical method that tracks the fluid motion and the surface tension forces is required. Jacqmin has developed a phase model that converts the discrete surface tension force into a barrier function that peaks at the free surface and decays rapidly away. Previous attempts at this formulation were criticized for smearing the interface. This can be overcome by sharpening the phase function, double gridding the fluid function, and using a higher order solution for the fluid function. The solution of this equation can be rewritten as two coupled Poisson equations that also include the velocity. After the code was implemented in axisymmetric form and verified by several test cases at the NASA Glenn Research Center, the drop tower runs of Aydelott were modeled. Work last year with a laminar model was found to overpredict Aydelott's results, except at the lowest Reynolds number conditions of 400. This year, a simple turbulence model was implemented by adding a turbulent viscosity based on the mixing-length hypothesis and empirical measurements of previous works. Predictions made after this change was implemented have been much closer to experimentally observed flow patterns and geyser heights. Two model runs is shown. The first, without any turbulence correction, breaks through the free surface and strikes the far end of the tank. In the second, the turbulence spreads the jet momentum over more of the free surface, enabling the surface tension forces to turn the jet back into the bulk liquid. The model geyser height with the second model is 1.1 cm. This is quite close to the 1.5-cm geyser height measured by Aydelott.

Chato, David J.↗
NASA NTRS2004

Contact Angle Influence on Geysering Jets in Microgravity Investigated

Microgravity poses many challenges to the designer of spacecraft tanks. Chief among these are the lack of phase separation and the need to supply vapor-free liquid or liquid-free vapor to the spacecraft processes that require fluid. One of the principal problems of phase separation is the creation of liquid jets. A jet can be created by liquid filling, settling of the fluid to one end of the tank, or even closing a valve to stop the liquid flow. Anyone who has seen a fountain knows that jets occur in normal gravity also. However, in normal gravity, the gravity controls and restricts the jet flow. In microgravity, with gravity largely absent, surface tension forces must be used to contain jets. To model this phenomenon, a numerical method that tracks the fluid motion and the surface tension forces is required. Jacqmin has developed a phase model that converts the discrete surface tension force into a barrier function that peaks at the free surface and decays rapidly away. Previous attempts at this formulation were criticized for smearing the interface. This can be overcome by sharpening the phase function, double gridding the fluid function, and using a higher-order solution for the fluid function. The solution of this equation can be rewritten as two coupled Poisson equations that also include the velocity.

Chato, David J.↗
NASA NTRSDate not supplied

Designing the Imaging and Breadboard System for FBCE-TL Project

This presentation outlines the support work done on designing the imaging and breadboard system of the Transfer Line (TL) project, which is the third module for the Flow Boiling and Condensation Experiment (FBCE) operating in the Fluids Integrated Rack on-board the International Space Station (ISS). The goal of the FBCE is to serve as a facility for flow boiling and condensation investigating two-phase flow and heat transfer data in microgravity. The TL module aims use existing FBCE hardware to study cryogenic chilldown, a large component of cryogenic propellant tank transfer research. The TL test module will perform chilldown studies with normal-perfluorohexane (nPFH), a cryogenic simulant, flowing through a super-heated line, which is heated through the process of Joule-heating. SolidWorks and Creo were used to create electrically conductive pipe junctions that connect and seal several Indium Tin Oxide (ITO) coated sapphire tube sections together to allow for low leak probability fluid flow and circumferentially uniform electrical current density. It is necessary to understand and calculate the thermal expansion of the tubing sections such that the junctions would not leak at anticipated operating temperatures and pressures, would maintain electrical contact, and not crack the crystalline tubes. Optical imaging techniques were used to build an experimentally validated image remapping process for flight-like setups of cylindrical tubes. Then MATLAB was used to create an algorithm that distorts an image based on the refraction of light passing through the mediums we were imaging through to accurately visualize the cryogenic chilldown that is of scientific interest. This research will assist NASA to move forward with long-duration spaceflight missions where knowledge of efficient heat transfer processes becomes more critical.

imaging system↗
NASA NTRS2000

Selected contribution: redistribution of pulmonary perfusion during weightlessness and increased gravity

To compare the relative contributions of gravity and vascular structure to the distribution of pulmonary blood flow, we flew with pigs on the National Aeronautics and Space Administration KC-135 aircraft. A series of parabolas created alternating weightlessness and 1.8-G conditions. Fluorescent microspheres of varying colors were injected into the pulmonary circulation to mark regional blood flow during different postural and gravitational conditions. The lungs were subsequently removed, air dried, and sectioned into approximately 2 cm(3) pieces. Flow to each piece was determined for the different conditions. Perfusion heterogeneity did not change significantly during weightlessness compared with normal and increased gravitational forces. Regional blood flow to each lung piece changed little despite alterations in posture and gravitational forces. With the use of multiple stepwise linear regression, the contributions of gravity and vascular structure to regional perfusion were separated. We conclude that both gravity and the geometry of the pulmonary vascular tree influence regional pulmonary blood flow. However, the structure of the vascular tree is the primary determinant of regional perfusion in these animals.

short duration↗