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Grid Resolution Study of a Drag Prediction Workshop Configuration using the NSU3D Unstructured Mesh Solver

Motivation. Both AIAA Drag Prediction Workshops have shown large scatter in CFD resultsGrid convergence not achievedBoth AIAA Drag Prediction Workshops have shown generally poor agreement of CFD with experimental resultsCL vs. incidenceMoment predictionsNotable exceptions in both workshopsNot

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Grid Resolution Study of a Drag Prediction Workshop Configuration using the NSU3D Unstructured Mesh Solver

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    1. Grid Resolution Study of a Drag Prediction Workshop Configuration using the NSU3D Unstructured Mesh Solver Dimitri J. Mavriplis Department of Mechanical Engineering University of Wyoming

    2. Motivation Both AIAA Drag Prediction Workshops have shown large scatter in CFD results Grid convergence not achieved Both AIAA Drag Prediction Workshops have shown generally poor agreement of CFD with experimental results CL vs. incidence Moment predictions Notable exceptions in both workshops Not well understood

    3. Intricacies of DPW Cases Generic/Simple Wing Body (Nacelle) configurations Substantial amounts of flow separation Appears in sensitive areas (trailing edge) Indicative of off-design conditions Particularly challenging for CFD codes DPW is good test case for sensitivity studies in CFD solvers More benign attached flow cases should be piece of cake for current RANS solvers

    4. Motivation Follow on Studies: E.M. Lee-Rausch et. al.: AIAA 2003-3400 E.M. Lee-Rausch et. al.: AIAA 2004-0554 General lack of grid convergence In many cases, agreement between codes gets worse with increased grid refinement Issues Raised (running different codes on same grids with same turbulence model): Modeling vs. discretization error Effects due to: Structured vs. unstructured Cell centered vs. vertex based discretizations Use of prisms or tetrahedra in boundary layer regions Upwind versus Artificial Dissipation Thin layer vs. Full Navier-Stokes terms Distance function calculation

    5. Motivation Follow up on DPW and previous studies to better understand sources of error Determine dominant sources of error through sensitivity studies Modeling error: Distance function evaluation methods Thin Layer vs. Full Navier Stokes Dissipation Levels (re: upwind flux functions) Grid Resolution Goal is not to match experimental data but to better understand importance of various sources of error and establish requirements for grid convergence Leave turbulence and transition models unchanged SA model/fully turbulent

    6. Families of Grids Grid Convergence studies require families of grids derived by globally coarsening or refining an initial grid to maintain similar relative variations in grid resolution Family of 4 grids: 1.1 million points 3.0 million points Original DPW2 grids (VGRIDns) 9.1 million points 72 million points Generated by uniform refinement of 9.1 million pt grid Single grid of different family 65 million points Generated c/o S. Pirzadeh, NASA Langley, VGRIDns 64bit version on NASA Columbia Supercomputer

    7. Baseline (3M pt) DPW 2 Grid 4 cells across blunt TE 7.e-06 chords spacing at wall y+ ~ 1, 26 cells/layers in boundary layer

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