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  • Life and Medical Sciences  (1,516)
  • FLUID MECHANICS AND HEAT TRANSFER  (725)
  • 1990-1994  (2,241)
  • 1975-1979
  • 1915-1919
  • 1991  (2,241)
Collection
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  • 1990-1994  (2,241)
  • 1975-1979
  • 1915-1919
Year
  • 1
    Publication Date: 2019-08-28
    Description: Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. A boiling and condensing experiment was built in which R-12 was used as the working fluid. A two-phase pump was used to circulate a freon mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown five times aboard the NASA KC-135 aircraft which simulates zero-g conditions by its parabolic flight trajectory. Test conditions included stratified and annual flow regimes in 1-g which became bubbly, slug, or annular flow regimes on 0-g. A portion of this work is the analysis of adiabatic flow regimes. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 3 (A93-13751 03-20); p. 1230-1235.
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  • 2
    Publication Date: 2019-08-28
    Description: Several aspects of the kinetic models used in the collision phase of Monte Carlo direct simulations have been studied. Accurate molecular velocity distribution function predictions require a significantly increased number of computational cells in one maximum slope shock thickness, compared to predictions of macroscopic properties. The shape of the highly repulsive portion of the interatomic potential for argon is not well modeled by conventional interatomic potentials; this portion of the potential controls high Mach number shock thickness predictions, indicating that the specification of the energetic repulsive portion of interatomic or intermolecular potentials must be chosen with care for correct modeling of nonequilibrium flows at high temperatures. It has been shown for inverse power potentials that the assumption of variable hard sphere scattering provides accurate predictions of the macroscopic properties in shock waves, by comparison with simulations in which differential scattering is employed in the collision phase. On the other hand, velocity distribution functions are not well predicted by the variable hard sphere scattering model for softer potentials at higher Mach numbers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Symposium on Rarefied Gas Dynamics; Jul 08, 1990 - Jul 14, 1990; Aachen; Germany
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  • 3
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    In:  Other Sources
    Publication Date: 2019-08-28
    Description: The equations for superfluid helium flowing through a straight tube with heated walls are integrated. The model equations are based on those of Landau as modified for superfluid turbulence by Gorter and Mellink (1949). The model is implemented by the program SUPERFLOW which runs on a personal computer. The effect of the heating level on the mass flux, the energy flux, and the pressure and temperature profiles is investigated. The four types of profiles which occur without sidewall heating are also found with heated walls. The progression through these four types is shown to depend primarily on the dimensionless parameter, defined previously to characterize the unheated profiles, and a dimensionless ratio of heat fluxes. The pressure and temperature maxima which rise well above the boundary values increase significantly with sidewall heating. Approximate design equations for estimating the mass flux and the profiles are presented. The physical basis of the results is discussed. These results are useful in the design of optimal cooling loops and other superfluid flow systems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Advances in cryogenic engineering. Vol. 37A - Proceedings of the 1991 Cryogenic Engineering Conference, Univ. of Alabama, Huntsville, June 11-14, 1991 (A93-48578 20-37); p. 81-88.
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  • 4
    Publication Date: 2019-08-28
    Description: Data for complete models of two-phase flow in microgravity are taken from in-flight experiments and applied to an adiabatic flow-regime analysis to study the feasibility of two-phase systems for spacecraft. The data are taken from five in-flight experiments by Hill et al. (1990) in which a two-phase pump circulates a freon mixture and vapor and liquid flow streams are measured. Adiabatic flow regimes are analyzed based on the experimental superficial velocities of liquid and vapor, and comparisons are made with the results of two-phase flow regimes at 1 g. A motion analyzer records the flow characteristics at a rate of 1000 frames/sec, and stratified flow regimes are reported at 1 g. The flow regimes observed under microgravitational conditions are primarily annular and include slug and bubbly-slug regimes. The present data are of interest to the design and analysis of two-phase thermal-management systems for use in space missions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Space Nuclear Power Systems Symposium; Jan 06, 1991 - Jan 10, 1991; Albuquerque, NM; United States
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  • 5
    Publication Date: 2019-08-14
    Description: The long history of research into the internal structure of turbulent boundary layers has not provided a unified picture of the physics responsible for turbulence production and dissipation. The goals of the present research are to: (1) define the current state of boundary layer structure knowledge; and (2) utilize direct numerical simulation results to help close the unresolved issues identified in part A and to unify the fragmented knowledge of various coherent motions into a consistent kinematic model of boundary layer structure. The results of the current study show that all classes of coherent motion in the low Reynolds number turbulent boundary layer may be related to vortical structures, but that no single form of vortex is representative of the wide variety of vortical structures observed. In particular, ejection and sweep motions, as well as entrainment from the free-streem are shown to have strong spatial and temporal relationships with vortical structures. Disturbances of vortex size, location, and intensity show that quasi-streamwise vortices dominate the buffer region, while transverse vortices and vortical arches dominate the wake region. Both types of vortical structure are common in the log region. The interrelationships between the various structures and the population distributions of vortices are combined into a conceptual kinematic model for the boundary layer. Aspects of vortical structure dynamics are also postulated, based on time-sequence animations of the numerically simulated flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-103859 , A-91123 , NAS 1.15:103859
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  • 6
    Publication Date: 2019-08-13
    Description: A summary, viewgraphs, and a transcript of discussions of a workshop on computational fluid dynamics code validation/calibration are presented. The workshop focused on inlet/forebody interactions in high-speed ramjets.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: CPIA-PUBL-551 , AD-A236878 , Computational Fluid Dynamics Code Validation/Calibration: JANNAF Airbreathing Propulsion Subcommittee Workshop: High-Speed Inlet Forebody Interactions; Jan 10, 1991 - Jan 11, 1991; Reno, NV; United States
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  • 7
    Publication Date: 2019-08-13
    Description: An overview is given of compressible Navier Stokes codes and up-wind solvers. Code validation efforts, inlet analysis requirements, and computational fluid dynamics modeling uncertainties are covered. Information is given in viewgraph form.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computational Fluid Dynamics Code Validation(Calibration. JANNAF Airbreathing Propulsion Subcommittee Workshop: High-Speed Inlet Forebody Interactios; 179-195|JANNAF CFD Code Validation/Calbration Workshop Series: High-Speed Inlet Forebody Interactions; Jan 10, 1991 - Jan 11, 1991; Reno, NV; United States
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  • 8
    Publication Date: 2019-08-13
    Description: High Mach helium tests are described in the form of the view-graphs. The following topics are included: high-speed inlet-forebody interaction tests; helium tunnel; boundary layer approaching inlet; ramp surface pressure distribution; static pressure on ramp; and pressure variation across wedge and ramp.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: JANNAF Airbreathing Propulsion Subcommittee Workshop: 1st Workshop on High-Speed Inlet-Forebodt Interactions; Jan 10, 1991 - Jan 11, 1991; Reno, NV; United States|Computational Fluid Dynamics Code Validation(Calibration. JANNAF Airbreathing Propulsion Subcommittee Workshop: High-Speed Inlet Forebody Internactions; 31-48
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  • 9
    Publication Date: 2019-07-27
    Description: A general multiblock method for the solution of the three-dimensional, unsteady, compressible, thin-layer Navier-Stokes equations has been developed. The convective and pressure terms are spatially discretized using Roe's flux differencing technique while the viscous terms are centrally differenced. An explicit Runge-Kutta method is used to advance the solution in time. Local time stepping, adaptive implicit residual smoothing, and the Full Approximation Storage (FAS) multigrid scheme are added to the explicit time stepping scheme to accelerate convergence to steady state. Results for three-dimensional test cases are presented and discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Gesellschaft fuer Angewandte Mathematik und Mechanik, Conference on Numerical Methods in Fluid Mechanics; Sept. 25-27, 1991; Lausanne; Switzerland|; 10 p.
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  • 10
    Publication Date: 2019-07-27
    Description: The heat flux and Reynolds stress budgets are presented for a buoyant plume. The terms involving pressure correlations are obtained as the closing terms in these budgets. Despite certain measurement errors, these budgets provide useful information about how various phenomena contribute to the transport of second moments. These experimental results are used to assess the local equilibrium assumption and to investigate why the mechanical to thermal time scale ratio for a buoyant plume is different than the commonly recommended value. Analysis show that this departure is a consequence of the local equilibrium assumption being not satisfied in the present experiment.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Symposium on Turbulent Shear Flows; Sept. 9-11, 1991; Munich; Germany
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