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SELF-adaptive-grid METHOD WITH APPLICATION TO AIRFOIL FLOW

AIAA JOURNAL 1987年第4期25卷 513-520页

作者： NAKAHASHI, K DEIWERT, GS NASA AMES RES CTRMOFFETT FIELDCA 94035

A self-adaptive-grid method that is suitable for multidimensional steady and unsteady computations is described. Based on variational principles, a spring analogy is used to redistribute grid points in an optimal sense to reduce the overall solution error. User-specified parameters, denoting both maximum and minimum permissible grid spacings, are used to define the all-important constants, thereby minimizing the empiricism and making the method self-adaptive. Operator splitting and one-sided controls for orthogonality and smoothness are used to make the method practical, robust, and efficient. Examples are included for both steady and unsteady viscous flow computations about airfoils in two dimensions, as well as for a steady inviscid flow computation and a one-dimensional case. These examples illustrate the precise control the user has with the self-adaptive method and demonstrate a significant improvement in accuracy and quality of the solutions. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Freestream Mach Number Flow Conditions Boundary Layer Separation NACA 0012 Angle of Attack Computational Fluid Dynamics Boundary Value Problems Navier Stokes Equations adaptive grid algorithms Pressure Coefficient

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SOLUTION-adaptive grid PROCEDURE FOR HIGH-SPEED PARABOLIC FLOW SOLVERS

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AIAA JOURNAL 1991年第8期29卷 1232-1240页

作者： HARVEY, AD ACHARYA, S LAWRENCE, SL CHEUNG, S NASA AMES RES CTRMECH ENGNMOFFETT FIELDCA 94035 MARITIME CENT ANAL TEAM MOFFETT FIELDCA 94035

A solution-adaptive grid procedure based on an error equidistribution scheme is developed and applied to a parabolized Navier-Stokes solver. An improved method of selecting weighting functions is introduced that involves normalizing a combination of flowfield gradients and curvature of a number of dependent variables and then selecting the largest at each point. The scheme redistributes grid points line by line with grid point motion controlled by forces analogous to tensional and torsional spring forces with the spring constants set equal to the weighting functions. Torsional terms are functions of the grid point positions along neighboring grid lines and provide grid smoothness and stability. A grid-fitting scheme is introduced for external flows in which the number of grid points in the freestream are reduced to a minimum. Results for several problems are presented to demonstrate the improvements obtainable with the solution-adaptive grid procedure.

关键词： Freestream Mach Number Two Dimensional Flow Navier Stokes Solver Heat Transfer Coefficients Shock Wave Interaction Pressure Coefficient Navier Stokes Equations adaptive grid algorithms Poisson's Equation Aspect Ratio

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UNIFIED PARALLEL ALGORITHM FOR grid ADAPTATION ON A MULTIPLE-INSTRUCTION MULTIPLE-DATA ARCHITECTURE

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AIAA JOURNAL 1994年第9期32卷 1800-1807页

作者： VIDWANS, A KALLINDERIS, Y UNIV TEXAS DEPT AEROSP ENGN & ENGN MECHAUSTINTX 78712

A unified parallel algorithm for grid adaptation by local refinement/coarsening is presented. It is designed to be independent from the type of the grid. This is achieved by employing a generic data template that can be configured to capture the data structures for any computational grid regardless of structure and dimensionality. Furthermore, the algorithm itself is specified in terms of generic parallel primitives that are completely independent of the underlying parallel architecture. The unified parallel algorithm is employed for dynamic adaptation of three-dimensional unstructured tetrahedral grids on a partitioned memory multiple-instruction multiple-data architecture. Performance results are presented for the Intel iPSC/860.

关键词： Parallel Algorithm Unstructured grid Blast Wave Navier Stokes Algorithm Parallel Computers Parallel Computing Transonic Flow Interprocessor Communication adaptive grid algorithms Navier Stokes Equations

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SOLUTION-adaptive grid PROCEDURE FOR THE PARABOLIZED NAVIER-STOKES EQUATIONS

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AIAA JOURNAL 1992年第4期30卷 953-962页

作者： HARVEY, AD ACHARYA, S LAWRENCE, SL DOW CHEM CO USA RES & DEVMIDLANDMI NASA AMES RES CTRMOFFETT FIELDCA 94035

A solution-adaptive grid procedure based on an error equidistribution principle is developed and applied to a three-dimensional parabolized Navier-Stokes solver. The scheme redistributes grid points line by line in both crossflow directions, with grid point motion controlled by forces analogous to tensional and torsional spring forces. The tensional force is proportional to the error measure or a weighting function related to the error measure. The torsional force is used to control grid skewness relative to the upstream and cross-stream coordinate lines. Weighting functions are selected by first normalizing flowfield gradients and/or curvature of a number of dependent variables and then selecting the largest at each point. The hypersonic flow over a right-circular cone at three different yaw angles is studied to demonstrate the performance of the solution-adaptive grid procedure. Pitot pressure profiles and surface pressure computed using the solution-adaptive algorithm are compared with experimental results as well as with numerical results obtained using a fixed grid. Pitot pressure predictions using the adaptive grid algorithm show better agreement with experiment than those obtained using a fixed grid.

关键词： Navier Stokes Equations Yaw adaptive grid algorithms Roe Approximate Riemann Solver Hypersonic Flows Boundary Layer Thickness Mach Number Bow Shock Aspect Ratio Riemann Problem

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FINITE-ELEMENT METHOD FOR INCOMPRESSIBLE VISCOUS FLOWS WITH adaptive HYBRID gridS

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AIAA JOURNAL 1994年第8期32卷 1617-1625页

作者： KALLINDERIS, Y NAKAJIMA, K University of Texas at Austin Austin Texas 78712

A new adaptive finite element numerical method has been developed for the unsteady Navier-Stokes equations of incompressible flow in two dimensions. The momentum equations combined with a pressure correction equation are solved employing a nonstaggered grid. The solution is advanced in time with an explicit/implicit marching scheme. An adaptive algorithm has been implemented, which refines the grid locally to resolve detected flow features. A combination of quadrilateral as well as triangular cells provides a stable and accurate numerical treatment of grid interfaces that are located within regions of high gradients. Applications of the developed adaptive algorithm include both steady and unsteady flows, with low and high Reynolds numbers. Comparisons with analytical as well as experimental data evaluate accuracy and robustness of the method.

关键词： Incompressible Viscous Flow Galerkin Finite Element Approach Freestream Velocity adaptive grid algorithms Navier Stokes Equations Strouhal Number Blasius Boundary Layer Poisson's Equation Bilinear Quadrilateral Element Skin Friction

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New approach for radiative-transfer computations in axisymmetric scattering hot media

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2001年第3期15卷 317-325页

作者： Baudoux, PE Roblin, A Chervet, P ONERA Dept Opt Theor & Appl F-91761 Palaiseau France

An atmospheric three-dimensional discrete ordinate method, called the Spherical Harmonics Discrete Ordinate Method (SHDOM), is extended to nonequilibrium and axisymmetric media such as rocket plumes, which contain hot reactive gases and metallic oxide particles like alumina. A spherical harmonics base is used to improve the source function evaluation while solving the radiative-transfer equation. The source function includes the chemiluminescence radiation produced by gas reactions, the particles thermal radiation, and the in-scattering term, During the iteration process, the in-scattering term is evaluated with a spherical harmonics base using the radiance field calculated along discrete ordinates until the source function converges. Test cases in simple geometries, like plane parallel media or square enclosures, show the accuracy of SHDOM results according to others calculated by reference models. An extended Arrhenius law is used to model the middle-ultraviolet chemiluminescent radiation produced by the CO + O recombination. Finally, SHDOM is applied to the radiance field emitted by realistic rocket plume sections represented by infinite cylinders or finite cylindrical media shadowed by a mask representing the rocket body.

关键词： Chemiluminescence Radiative Transfer Spherical Harmonics Rocket Motor Rockets Single Scattering Albedo Atmospheric Radiative Transfer adaptive grid algorithms Radiation Absorption Thermal Radiation

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Neural network detection of shockwaves

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AIAA JOURNAL 2002年第3期40卷 531-536页

作者： Berdahl, C USAF Res Lab Computat Sci Branch Wright Patterson AFB OH 45433 USA

Contemporary neural networks simulate the operation of brain subsystems with substantially higher fidelity than was possible a few years ago. These improvements offer new opportunities to use the cognitive competence of neural networks in fluid mechanics. One such opportunity is developed by taking concepts from their origin in neuroscience through a neural network to the fluid mechanics. The discussion focuses on one brain subsystem (the "What" pathway of the visual system), adapts an existing neural network model of the visual system (the boundary contour system/feature contour system), and shows how a flowfield scalar can excite a pattern of simulated neural activity. The neural network uses three types of shunting neurons found in the retina, lateral geniculate nucleus, and cortical area V1. When shown the density field of a supersonic channel flow, certain neurons in the neural network become active when a shock passes nearby. These active neurons provide a pattern of neural activity that could feed into higher-level What pathway neural networks to make more sophisticated inferences about structures present in a flow. The challenges posed by embedding the current neural network in these higher-level brain structures suggest a promising research agenda.

关键词： Neural Networks CFD Oblique Shock Feature Detection Feedforward adaptive grid algorithms Stress Concentration Unstructured grid Fluid Density Freestream

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SPACE-MARCHING CALCULATIONS ABOUT HYPERSONIC CONFIGURATIONS USING A SOLUTION-adaptive MESH ALGORITHM

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AIAA JOURNAL 1993年第10期31卷 1809-1818页

作者： HARVEY, AD ACHARYA, S LAWRENCE, SL LOUISIANA STATE UNIV DEPT MECH ENGNBATON ROUGELA 70803 NASA AMES RES CTRAPPL COMPUTAT FLUIDS BRANCHMOFFETT FIELDCA 94035

A solution-adaptive marching algorithm is developed and applied to a three-dimensional parabolized Navier-Stokes equation solver. The resulting algorithm obtains accurate solutions by using a spatial-marching/adaptive-grid procedure. The adaptation step redistributes grid points line by line in both crossflow directions, with grid point motion controlled by forces analogous to tensional and torsional spring forces with the tensional force proportional to the error measure or weighting functions. The solution-adaptive marching procedure is applied to the hypersonic flow about two generic aircraft configurations. The first of these is an all-body-type geometry with elliptical cross sections and is studied at angles of attack of 0, 5, and 15 deg. The second geometry is a generic blended-wing-body design. Results are presented that demonstrate the improvements in flowfield resolution obtainable with the solution-adaptive marching procedure over conventional fixed grid techniques. Computed pitot pressure profiles obtained using the solution-adaptive algorithm show improved agreement with experimental data compared to predictions obtained using a fixed grid.

关键词： adaptive grid algorithms Hypersonic Flows Navier Stokes Equations Angle of Attack Aircraft Configurations Freestream Mach Number Bow Shock Aspect Ratio Roe Approximate Riemann Solver Stagnation Point

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PARALLEL DYNAMIC LOAD-BALANCING ALGORITHM FOR 3-DIMENSIONAL adaptive UNSTRUCTURED gridS

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AIAA JOURNAL 1994年第3期32卷 497-505页

作者： VIDWANS, A KALLINDERIS, Y VENKATAKRISHNAN, V UNIV TEXAS DEPT AEROSP ENGN & ENGN MECHAUSTINTX 78712 INST COMP APPLICAT SCI & ENGN HAMPTONVA 23681

adaptive local grid refinement/coarsening results in unequal distribution of work load among the processors of a parallel system. A novel method for balancing the load in cases of dynamically changing tetrahedral grids is developed. The approach employs local exchange of cells among processors to redistribute the load equally. An important part of the load-balancing algorithm is the method employed by a processor to determine which cells within its subdomain are to be exchanged. Two such methods are presented and compared. The strategy for load balancing is based on the divide-and-conquer approach that leads to an efficient parallel algorithm. This method is implemented on a distributed-memory multiple instruction multiple data system.

关键词： Unstructured grid Parallel Algorithm Parallel Computers Transonic Flow Annealing adaptive grid algorithms Vector Supercomputers Numerical Simulation Tetrahedral Element Parallel Computing

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adaptive REFINEMENT-COARSENING SCHEME FOR 3-DIMENSIONAL UNSTRUCTURED MESHES

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AIAA JOURNAL 1993年第8期31卷 1440-1447页

作者： KALLINDERIS, Y VIJAYAN, P University of Texas at Austin Austin Texas 78712

The paper describes the development and application of an adaptive algorithm for tetrahedral grids. An initial unstructured grid is adapted by employing local division, as well as deletion of the tetrahedral cells. The process is dynamic, and the adapted grid changes follow evolution of the solution. Adaptation of the cells consists of normal division of a tetrahedron into eight subcells, as well as directional division into two or four subcells. A major issue of such adaptive grid algorithms is elimination of hanging nodes that appear on the edges in the interface between the embedded and unembedded zones. A novel technique has been developed for treatment of such interface cells that can be applied to eliminate any possible hanging node configuration in a simple way. A special data structure based on octrees has been developed, which is flexible to handle all different types of cell division/deletion. Application cases include a moving source, as well as transonic flow around the ONERA M6 wing.

关键词： adaptive grid algorithms Data Structures Transonic Flow Unstructured grid Aspect Ratio Computational Fluid Dynamics Angle of Attack Mach Number Pressure Coefficient Finite Volume Scheme

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