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  • 1985-1989  (13)
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  • 1
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    An embedded mesh procedure for leading-edge vortex flows (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A cell-vertex scheme is outlined for solving the flow about a delta wing with M (sub infinity) is greater than 1. Embedded regions of mesh refinement allow solutions to be obtained which have much higher resolution than those achieved to date. Effects of mesh refinement and artificial viscosity on the solutions are studied, to determine at what point leading-edge vortex solutions are grid-converged. A macroscale and a microscale for the size of the vortex are defined, and it is shown that the macroscale (which includes the wing surface properties) is converged on a moderately refined grid, while the microscale is very sensitive to grid spacing. The level of numerical diffusion in the core of the vortex is found to be substantial. Comparisons with the experiment are made for two cases which have transonic cross-flow velocities.
    Keywords: AERODYNAMICS
    Type: NASA, Langley Research Center, Transonic Symposium: Theory, Application, and Experiment, Volume 1, Part 1; p 231-259
    Format: application/pdf
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  • 2
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    Applications of Euler equations to sharp edge delta wings with leading edge vortices (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Studies on the solution of discrete Euler equations past swept delta wing configurations with sharp leding edges are presented. Freestream Mach numbers range from zero to supersonic, although the Mach number normal to the leading edge is subsonic for all cases discussed. A few examples are given to show the application of the numerical methods to representative problems. The major dicussion is directed at the application of Computational Fluid Dynamics to the understanding of the fundamental fluid mechanic mechanisms of this class of flows.
    Keywords: AERODYNAMICS
    Type: AGARD Applications of Computational Fluid Dynamics in Aeronautics; 13 p
    Format: text
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  • 3
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    Visualization of three-dimensional CFD solutions (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The implementation is described of the FLOWVIS flow visualization package on a graphics supercomputer that provides real-time interactive investigation of three-dimensional CFD solutions on structured and unstructured meshes. The data structures are briefly described and the methods of visualizing flow fields are examined, including surface plots, particle paths, and planar displays in the flow field. Preliminary results using the package and work in progress are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 89-0138
    Format: text
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  • 4
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    Solutions for hypersonic viscous flow over delta wings (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A conical Navier-Stokes solver is developed to study hypersonic flow over delta wings. The differencing scheme used is van Leer flux vector splitting with MUSCL differencing. A flux limiter which involves a second difference in pressure was found to provide sharp, nonoscillatory shocks in windward and leeward flow regions. The governing equations are cast in finite-volume form and are solved using an explicit multistage method. A von Neumann stability analysis of a one-dimensional flux split model is used to predict the stability characteristics of the conical solver. The stability behavior of the scheme is found to strongly depend on the stage coefficients of the multistage scheme and on the order of accuracy of the upwind discretization.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-0126
    Format: text
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  • 5
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    Comparison of measured and computed pitot pressures in a leading edge vortex from a delta wing (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Calculations are presented for a 75-deg swept flat plate wing tested at a freestream Mach number of 1.95 and 10 degrees angle of attack. Good agreement is found between computational data and previous experimental pitot pressure measurements in the core of the vortex, suggesting that the total pressure losses predicted by the Euler equation solvers are not errors, but realistic predictions. Data suggest that the magnitude of the total pressure loss is related to the circumferential velocity field through the vortex, and that it increases with angle of attack and varies with Mach number and sweep angle.
    Keywords: AERODYNAMICS
    Format: text
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  • 6
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    Leading-edge vortex solutions with large total pressure losses (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Computations are presented for a Lambda = 75 deg delta wing in a supersonic freestream under two conditions which lead to leading-edge vortices. For one condition, analysis of the computed vortical flow reveals a closed streamline in the core. From varying computational parameters, it appears that this is due to truncation error of the convective derivatives. For the other condition, comparisons are made with wind-tunnel data, and good agreement is noted for pitot pressure distributions, flow angles on the symmetry plane, and the position of an embedded shock. Many of the aerodynamic parameters are shown to be insensitive to grid spacing.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-0039
    Format: text
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  • 7
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    Finite-volume method for the calculation of compressible chemically reacting flows (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 26; 1070-107
    Format: text
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  • 8
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    Prospects for Eulerian CFD analysis of helicopter vortex flows (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The applicability of current finite-volume CFD algorithms based on the Euler equations to the vortex flow over a helicopter in forward flight is investigated analytically. The general characteristics of the flow are reviewed; existing Euler, Navier-Stokes, perturbation, high-order, and adaptive methods are briefly characterized; and a novel Eulerian/Lagrangian approach with entropy and vorticity corrections is presented in detail. Numerical results for simple convection of a finite-core Lamb vortex moving downstream with its axis perpendicular to the flow are presented in graphs, and the possibility of extending the method to three-dimensional, viscous, and shock flows is discussed.
    Keywords: AERODYNAMICS
    Type: National Specialists'' Meeting on Aerodynamics and Aeroacoustics; Feb 25, 1987 - Feb 27, 1987; Arlington, TX; United States
    Format: text
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  • 9
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    Research in computational fluid dynamics (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The numerical integration of quasi-one-dimensional unsteady flow problems which involve finite rate chemistry are discussed, and are expressed in terms of conservative form Euler and species conservation equations. Hypersonic viscous calculations for delta wing geometries is also examined. The conical Navier-Stokes equations model was selected in order to investigate the effects of viscous-inviscid interations. The more complete three-dimensional model is beyond the available computing resources. The flux vector splitting method with van Leer's MUSCL differencing is being used. Preliminary results were computed for several conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-180542 , NAS 1.26:180542 , MIT-OSP-95315
    Format: application/pdf
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  • 10
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    Computational methods for vortex dominated compressible flows (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The principal objectives were to: understand the mechanisms by which Euler equation computations model leading edge vortex flows; understand the vortical and shock wave structures that may exist for different wing shapes, angles of incidence, and Mach numbers; and compare calculations with experiments in order to ascertain the limitations and advantages of Euler equation models. The initial approach utilized the cell centered finite volume Jameson scheme. The final calculation utilized a cell vertex finite volume method on an unstructured grid. Both methods used Runge-Kutta four stage schemes for integrating the equations. The principal findings are briefly summarized.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-181144 , NAS 1.26:181144 , MIT-OSP-93666
    Format: application/pdf
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