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  • FLUID MECHANICS AND HEAT TRANSFER
  • 1995-1999  (244)
  • 1
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    The coefficient of restitution of ice particles in glancing collisions: Experimental results for unfrosted surfaces (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Both Saturn's rings and planetesimal disks are made up of particles in Keplerian orbits. Inelastic collisions between these particles regulate their dynamical evolution and possible aggregation. We present an experiment to simulate glancing collisions in Saturn's rings and in planetesimal disks and thus measure contributions to the energy loss for both normal and tangential velocity components. In this experiment, a spherical iceball mounted on a long-period, two dimensional pendulum is made to impact a flat ice surface in a low-temperature environment. This paper describes the experimental apparatus in detail and presents results for smooth unfrosted surfaces. The energy loss for tangential motion is suprisingly low, indicating that very little friction is present at low impact speeds for relatively smooth ice surfaces and temperatures near 100 K. We have also investigated room-temperature collisions of a rubber ball on a rough surface to understand the energy loss in situations where the tangential friction force is not small. In this analogous case, the energy loss is maximum for impact angles in the range 45 deg-60 deg.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 188-199
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  • 2
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    Implementation of a 3D mixing layer code on parallel computers (1995)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper summarizes our progress and experience in the development of a Computational-Fluid-Dynamics code on parallel computers to simulate three-dimensional spatially-developing mixing layers. In this initial study, the three-dimensional time-dependent Euler equations are solved using a finite-volume explicit time-marching algorithm. The code was first programmed in Fortran 77 for sequential computers. The code was then converted for use on parallel computers using the conventional message-passing technique, while we have not been able to compile the code with the present version of HPF compilers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 95-6111 , ; 9 p.|AIAA, Aerospace Planes and Hypersonics Technologies Conference; Apr 03, 1995 - Apr 07, 1995; Chattanooga, TN; United States
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  • 3
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    Convergence properties of finite-difference hydrodynamics schemes in the presence of shocks (1995)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We investigate the asymptotic convergence of finite-difference schemes for the Euler equations when the limiting solution contains shocks. The Lax-Wendroff theorem guarantees that certain conservative schemes converge to correct, physically valid solutions. We focus on two one-dimensional operator-split schemes with explicit artificial-viscosity terms. One, an internal-energy scheme, does not satisfy the assumptions of Lax-Wendroff; the other, a conservative total-energy scheme, does. With viscous lengths chosen proportional to the grid size, we find that both schemes converge to their zero-grid-size limits at the theoretically expected rate, but only the conversative scheme converges toward correct solutions of the inviscid fluid equations. We show that the difference in their behaviors results directly from the presence of shocks in the limiting solution. Empirically, we find that when the viscous lenghts tend toward zero more slowly than the grid size, however the nonconservative scheme also converges toward correct solutions. We characterize the asymptotic behavior of the total-energy scheme in a particular problem in which a shock forms. As the grid is refined, a Cauchy error approaches the expected rate of change slowly. We show that the changes in the artificial viscosity alter the diffusion of small-amplitude waves. The differences associated with such waves make the dominant contribution to the Cauchy error. We formulate an analytic model to relate the rate of approach to the effect of varying diffusion in waves and find quantitative agreement with our numerical results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: The Astrophysical Journal Supplement Series (ISSN 0067-0049); 96; 2; p. 627-641
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  • 4
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    Computations of Viscous Flows in Complex Geometries Using Multiblock Grid Systems (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: Generating high quality, structured, continuous, body-fitted grid systems (multiblock grid systems) for complicated geometries has long been a most labor-intensive and frustrating part of simulating flows in complicated geometries. Recently, new methodologies and software have emerged that greatly reduce the human effort required to generate high quality multiblock grid systems for complicated geometries. These methods and software require minimal input form the user-typically, only information about the topology of the block structure and number of grid points. This paper demonstrates the use of the new breed of multiblock grid systems in simulations of internal flows in complicated geometries. The geometry used in this study is a duct with a sudden expansion, a partition, and an array of cylindrical pins. This geometry has many of the features typical of internal coolant passages in turbine blades. The grid system used in this study was generated using a commercially available grid generator. The simulations were done using a recently developed flow solver, TRAF3D.MB, that was specially designed to use multiblock grid systems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-198419 , NAS 1.26:198419 , ICOMP-95-23 , AIAA PAPER 95-0177 , E-9992 , NIPS-95-06251 , Aerospace Sciences Meeting and Exhibit; Jan 09, 1995 - Jan 12, 1995; Reno, NV; United States
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  • 5
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    Evaluation of Boundary Conditions for Computational Aeroacoustics (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: The performance of three boundary conditions for aeroacoustics were investigated, namely, (1) Giles-1990; (2) Tam and Webb-1993, and (3) Thompson-1987. For each boundary condition, various implementations were tested to study the sensitivity of their performance to the implementation procedure. Details of all implementations are given. Results are shown for the acoustic field of a monopole in a uniform freestream.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106645 , NAS 1.15:106645 , AIAA PAPER 95-0160 , E-8950 , Aerospace Sciences Meeting; Jan 05, 1995 - Jan 12, 1995; Reno, NV; United States
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  • 6
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    Adaptive Mesh Refinement in Curvilinear Body-Fitted Grid Systems (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: To be truly compatible with structured grids, an AMR algorithm should employ a block structure for the refined grids to allow flow solvers to take advantage of the strengths of unstructured grid systems, such as efficient solution algorithms for implicit discretizations and multigrid schemes. One such algorithm, the AMR algorithm of Berger and Colella, has been applied to and adapted for use with body-fitted structured grid systems. Results are presented for a transonic flow over a NACA0012 airfoil (AGARD-03 test case) and a reflection of a shock over a double wedge.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: E-9990 , NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; 233-240
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  • 7
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    Numerical Prediction of Turbulent Oscillating Flow and Heat Transfer in Pipes with Various End Geometries (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: Unsteady flow is present in man, machine and nature. The flow of blood in arteries and capillaries in the human body is pulsatile-composed of a mean flow superposed with an oscillating component. The tides that wash in and out of rivers, harbors and estuaries are unsteady flows with very long periods of oscillation. Many engineering devices employ pulsatile and oscillating flow. Pulsating flow is defined here as a periodic flow with a net displacement of fluid over each flow cycle. Oscillating flow is defined as a period flow with a zero mean over each cycle. The subject of this thesis is oscillating flow and heat transfer in pipes which make up the heater and cooler sections of the NASA Space Power Research Engine (SPRE) currently under development. This engine uses the Stirling cycle as the thermal energy converter in a power plant for future space applications. The information presented in this thesis will of course be applicable to the design of many types of machinery which employ oscillating flow and heat transfer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-198416 , NAS 1.26:198416 , E-9983 , NIPS-96-07710
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  • 8
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    Calculations of Diffuser Flows with an Anisotropic K-Epsilon Model (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: A newly developed anisotropic K-epsilon model is applied to calculate three axisymmetric diffuser flows with or without separation. The new model uses a quadratic stress-strain relation and satisfies the realizability conditions, i.e., it ensures both the positivity of the turbulent normal stresses and the Schwarz' inequality between any fluctuating velocities. Calculations are carried out with a finite-element method. A second-order accurate, bounded convection scheme and sufficiently fine grids are used to ensure numerical credibility of the solutions. The standard K-epsilon model is also used in order to highlight the performance of the new model. Comparison with the experimental data shows that the anisotropic K-epsilon model performs consistently better than does the standard K-epsilon model in all of the three test cases.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-198418 , NAS 1.26:198418 , E-9988 , ICOMP-95-21 , CMOTT-95-4 , NIPS-96-07528 , International Symposium on Engineering Turbulence Modeling and Measurements; May 27, 1996 - May 29, 1996; Crete; Greece
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  • 9
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    An Adaptive Semi-Implicit Scheme for Simulations of Unsteady Viscous Compressible Flows (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: A numerical scheme for simulation of unsteady, viscous, compressible flows is considered. The scheme employs an explicit discretization of the inviscid terms of the Navier-Stokes equations and an implicit discretization of the viscous terms. The discretization is second order accurate in both space and time. Under appropriate assumptions, the implicit system of equations can be decoupled into two linear systems of reduced rank. These are solved efficiently using a Gauss-Seidel method with multigrid convergence acceleration. When coupled with a solution-adaptive mesh refinement technique, the hybrid explicit-implicit scheme provides an effective methodology for accurate simulations of unsteady viscous flows. The methodology is demonstrated for both body-fitted structured grids and for rectangular (Cartesian) grids.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-198420 , NAS 1.26:198420 , ICOMP-95-24 , AIAA PAPER 95-1727 , E-9993 , NIPS-95-06483
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  • 10
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    Convective Heat Transfer from Castings of Ice Roughened Surfaces in Horizontal Flight (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Eight different types of ice growths, characterizing different types of roughness, were obtained from these plates, from which aluminum castings were made. Test strips taken from these castings were outfitted with heat flux gages, such that when placed in a dry wind tunnel, they could be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for parallel flow, which simulates horizontal flight, were studied. The results of this investigation can be used to help size heaters for wings, helicopter rotor blades, jet engine intakes, etc., or de-icing for anti-icing applications where the flow is parallel to the iced surface.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-107109 , NAS 1.15:107109 , E-10010 , NIPS-95-06275 , International Icing Symposium 1995; Sep 18, 1995 - Sep 21, 1995; Montreal; Canada
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