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  • 1
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    A semi-Lagrangian approach to the shallow water equation (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We present a formulation of the shallow water equations that emphasizes the conservation of potential vorticity. A locally conservative semi-Lagrangian time-stepping scheme is developed, which leads to a system of three coupled PDE's to be solved at each time level. We describe a smoothing analysis of these equations, on which an effective multigrid solver is constructed. Some results from applying this solver to the static version of these equations are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, The Sixth Copper Mountain Conference on Multigrid Methods, Part 2; p 593-604
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  • 2
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    Determination of optimum fin profile for a zero-G capillary drained condenser (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents the analytical formulation and numerical results for heat transfer in a high heat flux condenser that relies on capillary flow along shaped fins (Gregorig surfaces) and a drainage network embedded in the condenser walls. Results are shown for a variety of fin profile shapes in order to show the geometric trade-offs involved in seeking a maximum effective heat transfer coefficient for the fin. Predictions of the model show excellent agreement with previously reported measurements for steam. Based on this work, a profile has been selected for a 2 kW ammonia condenser currently under development for use in space. In that design the fin half width is 0.5 mm and the model predicts a heat transfer coefficient referred to the base of the fin of 9 W/sq cm deg C for a heat flux of 10/W sq cm at the base.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-1686
    Format: text
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  • 3
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    Multigrid methods for flow transition in three-dimensional boundary layers with surface roughness (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The efficient multilevel adaptive method has been successfully applied to perform direct numerical simulations (DNS) of flow transition in 3-D channels and 3-D boundary layers with 2-D and 3-D isolated and distributed roughness in a curvilinear coordinate system. A fourth-order finite difference technique on stretched and staggered grids, a fully-implicit time marching scheme, a semi-coarsening multigrid method associated with line distributive relaxation scheme, and an improved outflow boundary-condition treatment, which needs only a very short buffer domain to damp all order-one wave reflections, are developed. These approaches make the multigrid DNS code very accurate and efficient. This allows us not only to be able to do spatial DNS for the 3-D channel and flat plate at low computational costs, but also to do spatial DNS for transition in the 3-D boundary layer with 3-D single and multiple roughness elements, which would have extremely high computational costs with conventional methods. Numerical results show good agreement with the linear stability theory, the secondary instability theory, and a number of laboratory experiments. The contribution of isolated and distributed roughness to transition is analyzed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-4540 , NAS 1.26:4540
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  • 4
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    Onset of hexagons in surface-tension-driven Benard convection (1994)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: High resolution laboratory experiments with large aspect ratio are being conducted for thin fluid layers heated from below and bounded from above by a free surface. The fluid depths are chosen sufficiently small (less than 0.06 cm) so that surface tension is the dominant driving mechanisms; the Rayleigh number is less than 5 for the results reported here. Shadowgraph visualization reveals that the primary instability leading to hexagons is slightly hysteretic (approximately 1 percent). Preliminary measurements of the convection amplitude using infrared imaging are also presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Second Microgravity Fluid Physics Conference; p 33-38
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  • 5
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    Flow transition with 2-D roughness elements in a 3-D channel (1993)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: We develop a new numerical approach to study the spatially evolving instability of the streamwise dominant flow in the presence of roughness elements. The difficulty in handling the flow over the boundary surface with general geometry is removed by using a new conservative form of the governing equations and an analytical mapping. The numerical scheme uses second-order backward Euler in time, fourth-order central differences in all three spatial directions, and boundary-fitted staggered grids. A three-dimensional channel with multiple two-dimensional-type roughness elements is employed as the test case. Fourier analysis is used to decompose different Fourier modes of the disturbance. The results show that surface roughness leads to transition at lower Reynolds number than for smooth channels.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, The Sixth Copper Mountain Conference on Multigrid Methods, Part 2; p 377-391
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  • 6
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    Laser velocimeter and total pressure measurements in circular-to-rectangular transition ducts (1988)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A comprehensive set of total pressure and three-component laser velocimetry (LV) data were obtained within two circular-to-rectangular transition ducts at low subsonic speeds. This set of reference data was acquired for use in identifying secondary flow mechanisms and for assessing the accuracy of computational procedures for calculating such flows. Data were obtained at the inlet and exit planes of an aspect ratio three duct having a length-to-diameter ratio of one (AR310) and an aspect ratio six duct having a length-to-diameter ratio of three (AR630). Each duct was unseparated throughout its transition section. It is therefore concluded that secondary flows can play an important part in the fluid dynamics of transition ducts and needs to be addressed in computational analysis. The strength of the secondary flows depends on both the aspect ratio and relative axial duct length.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-182286 , NAS 1.26:182286 , UTRC-87-41
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  • 7
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    Boundary layer energization by means of optimized vortex generators (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A three-dimensional, multi-block, multi-zone, Euler analysis has been developed and applied to analyze the flow processes induced by a lateral array of low profile vortex generators (VG). These vortex generators have been shown to alleviate boundary layer separation through the generation of streamwise vorticity. The analysis has been applied to help develop improved VG configurations in an efficient manner. Special attention has been paid to determining the accuracy requirements of the solver for calculations in which vortical mechanisms are dominant. The analysis has been used to assess the effectiveness or boundary layer energization capacity of different VG's, including the effect of scale and shape variation. Finally, the analysis has been validated through comparisons with experimental data obtained in a large-scale low-speed wind tunnel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-0445 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 11 p.
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  • 8
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    Parallel multilevel adaptive methods (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The progress of a project for the design and analysis of a multilevel adaptive algorithm (AFAC/HM/) targeted for the Navier Stokes Computer is discussed. The results of initial timing tests of AFAC, coupled with multigrid and an efficient load balancer, on a 16-node Intel iPSC/2 hypercube are included. The results of timing tests are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Conference on Numerical Methods in Fluid Dynamics; Jun 27, 1988 - Jul 01, 1988; Williamsburg, VA; United States
    Format: text
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