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  • Life and Medical Sciences  (1,790)
  • Engineering  (748)
  • FLUID MECHANICS AND HEAT TRANSFER  (385)
  • 1990-1994  (2,923)
  • 1994  (2,923)
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  • 1990-1994  (2,923)
Year
  • 1
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    International Symposium on Microgravity Science and Application (ISMSA), Beijing, China, May 10-13, 1993 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Papers at this conference on Microgravity Science and Technology concerned fluid science and biotechnology. Some representative titles include the following: Hydrodynamic Instabilities in Thermocapillary Flow; Marangoni Convection in Immiscible Double Liquid Layers; Note on the Instability of Capillary Jet with Thermocapillarity; Residual Gravity Jitter Effects on Fluid Processes; Responsive Motion of Bubbles to Periodic g-jitter; and Protein Crystallization in Space.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Microgravity Science and Technology (ISSN 0938-0108); 7; 2; 139 p.
    Format: text
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  • 2
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    Unique determination of solutions to the Burnett equations (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Recent success in applying the Burnett equations to the one-dimensional shock-structure problem has raised the issue of whether the full Burnett equations can be used replace the Navier-Stokes equations for solving boundary-value problems in rarefied gasdynamics. As is familiar from the classical rarefied gasdynamics literature, the Burnett equations, if not solved as a successive approximation to the Navier-Stokes equations for a small Knudsen number, would require more boundary conditions than those in the Navier-Stokes system, owing to the presence of the higher-order derivatives. In this paper, this issue is examined with concrete solution examples for the steady Couette flows, addressing specifically whether solutions to the full Burnett equations can be uniquely determined without adding more boundary conditions than those in the Navier-Stokes system. The analysis, supported by detailed numerical solutions, confirms that additional boundary conditions are needed as long as the Knudsen number is not identically zero, lest the solution to the Burnett equations is not unique.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 32; 5; p. 985-990
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  • 3
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    Three-dimensional fully spectral numerical method for mantle convection with depth-dependent properties (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A semi-implicit fully spectral collocation method for the simulation of three-dimensional mantle convection with depth-dependent thermo-dynamic and transport properties is presented. The variable property Navier-Stokes equation expressed in terms of the primitive variable velocity and pressure is solved with the mass continuity and temperature equations. The periodic horizontal boundary conditions allow a Fourier expansion for the two horizontal directions. The stress-free, impermeable isothermal boundary conditions along with the depth dependent coefficients are handled with a Chebyshev expansion in the vertical direction. In the limit of an infinite Prandtl number appropriate to mantle convection, the inertial terms in the momentum equation are unimportant. In this case an explicit solution of a Poisson equation for pressure can be avoided; instead a fourth-order equation for vertical velocity can be solved. Simultaneous imposition of both impermeable and continuity boundary conditions during the vertical velocity evaluation is discussed. The pressure distributions on the top and bottom bounding planes were determined by means of an influence matrix technique. The numerical method employed here avoids time-splitting errors and enforces velocity boundary conditions and continuity over the entire domain, including the boundaries, to machine accuracy. Strongly time-dependent three-dimensional solutions up to a surface Rayleigh number of 1 x 10(exp 7) have been obtained. Strong upwellings, pulsating chaotically, are formed by the collective merging of cylindrical plumes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 113; 1; p. 62-74
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  • 4
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    Effect of grid aspect ratio on convergence (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The effects of high-aspect-ratio grids on algorithm convergence are considered by means of vector stability theory and computational experiments. The results indicate that approximately factored implicit schemes experience convergence deterioration because of nonoptimum local time-stepping procedures and increased need for viscous preconditioning. Based on this insight, an enhanced algorithm is devised using improved selection of the local time step, appropriate definition of the viscous preconditioning matrix, and proper implementation of the boundary conditions. The new algorithm provides uniformly efficient convergence at all aspect ratios for both Euler and Navier-Stokes computations for a variety of test problems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 32; 12; p. 2401-2408
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  • 5
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    Computation of oscillating airfoil flows with one- and two-equation turbulence models (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: The ability of one- and two-equation turbulence models to predict unsteady separated flows over airfoils is evaluated. An implicit, factorized, upwind-biased numerical scheme is used for the integration of the compressible, Reynolds-averaged Navier-Stokes equations. The turbulent eddy viscosity is obtained from the computed mean flowfield by integration of the turbulent field equations. One- and two-equation turbulence models are first tested for a separated airfoil flow at fixed angle of incidence. The same models are then applied to compute the unsteady flowfields about airfoils undergoing oscillatory motion at low subsonic Mach numbers. Experimental cases where the flow has been tripped at the leading-edge and where natural transition was allowed to occur naturally are considered. The more recently developed turbulence models capture the physics of unsteady separated flow significantly better than the standard kappa-epsilon and kappa-omega models. However, certain differences in the hysteresis effects are observed. For an untripped high-Reynolds-number flow, it was found necessary to take into account the leading-edge transitional flow region to capture the correct physical mechanism that leads to dynamic stall.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 32; 12; p. 2359-2365
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  • 6
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    Application of a distributed network in computational fluid dynamic simulations (1994)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: A general-purpose 3-D, incompressible Navier-Stokes algorithm is implemented on a network of concurrently operating workstations using parallel virtual machine (PVM) and compared with its performance on a CRAY Y-MP and on an Intel iPSC/860. The problem is relatively computationally intensive, and has a communication structure based primarily on nearest-neighbor communication, making it ideally suited to message passing. Such problems are frequently encountered in computational fluid dynamics (CDF), and their solution is increasingly in demand. The communication structure is explicitly coded in the implementation to fully exploit the regularity in message passing in order to produce a near-optimal solution. Results are presented for various grid sizes using up to eight processors.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Supercomputer Applications (ISSN 0890-2720); 8; 1; p. 64-67
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  • 7
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    Boundary Conditions for Unsteady Compressible Flows (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: This paper explores solutions to the spherically symmetric Euler equations. Motivated by the work of Hagstrom and Hariharan and Geer and Pope, we modeled the effect of a pulsating sphere in a compressible medium. The literature available on this suggests that an accurate numerical solution requires artificial boundary conditions which simulate the propagation of nonlinear waves in open domains. Until recently, the boundary conditions available were in general linear and based on nonreflection. Exceptions to this are the nonlinear nonreflective conditions of Thompson, and the nonlinear reflective conditions of Hagstrom and Hariharan. The former are based on the rate of change of the incoming characteristics; the latter rely on asymptotic analysis and the method of characteristics and account for the coupling of incoming and outgoing characteristics. Furthermore, Hagstrom and Hariharan have shown that, in a test situation in which the flow would reach a steady state over a long time, Thompson's method could lead to an incorrect steady state. The current study considers periodic flows and includes all possible types and techniques of boundary conditions. The technique recommended by Hagstrom and Hariharan proved superior to all others considered and matched the results of asymptotic methods that are valid for low subsonic Mach numbers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106737 , ICOMP-94-22 , E-9138 , NAS 1.15:106737
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  • 8
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    The Flow Induced by the Coalescence of Two Initially Stationary Drops (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: The coalescence of two initially stationary drops of different size is investigated by solving the unsteady, axisymmetric Navier-Stokes equations numerically, using a Front-Tracking/Finite Difference method. Initially, the drops are put next to each other and the film between them ruptured. Due to surface tension forces, the drops coalesce rapidly and the fluid from the small drop is injected into the larger one. For low nondimensional viscosity, or Ohnesorge number, little mixing takes place and the small drop fluid forms a blob near the point where the drops touched initially. For low Ohnesorge number, on the other hand, the small drop forms a jet that penetrates far into the large drop. The penetration depth also depends on the size of the drops and shows that for a given fluid of sufficiently low viscosity, there is a maximum penetration depth for intermediate size ratios.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106752 , ICOMP-94-24 , E-9168 , NAS 1.15:106752
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  • 9
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    Experimental Investigation of Jet-Induced Mixing of a Large Liquid Hydrogen Storage Tank (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: Experiments have been conducted to investigate the effect of fluid mixing on the depressurization of a large liquid hydrogen storage tank. The test tank is approximately ellipsoidal, having a volume of 4.89 m(exp 3) and an average wall heat flux of 4.2 W/m(exp 2) due to external heat input. A mixer unit was installed near the bottom of the tank to generate an upward directed axial jet flow normal to the liquid-vapor interface. Mixing tests were initiated after achieving thermally stratified conditions in the tank either by the introduction of hydrogen gas into the tank or by self-pressurization due to ambient heat leak through the tank wall. The subcooled liquid jet directed towards the liquid-vapor interface by the mixer induced vapor condensation and caused a reduction in tank pressure. Tests were conducted at two jet submergence depths for jet Reynolds numbers from 80,000 to 495,000 and Richardson numbers from 0.014 to 0.52. Results show that the rate of tank pressure change is controlled by the competing effects of subcooled jet flow and the free convection boundary layer flow due to external tank wall heating. It is shown that existing correlations for mixing time and vapor condensation rate based on small scale tanks may not be applicable to large scale liquid hydrogen systems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106629 , E-8926 , NAS 1.15:106629 , AIAA PAPER 94-2079 , Joint Thermophysics and Heat Transfer Conference; Jun 20, 1994 - Jun 23, 1994; Colorado Springs, CO; United States
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  • 10
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    Update to the NASA Lewis Ice Accretion Code LEWICE (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: This report is intended as an update to NASA CR-185129 'User's Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE).' It describes modifications and improvements made to this code as well as changes to the input and output files, interactive input, and graphics output. The comparison of this code to experimental data is shown to have improved as a result of these modifications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-195387 , E-9150 , NAS 1.26:195387
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