Steady-state simulation of Ahmed body Part 1 of 3 (Meshing)

In this series of articles, a steady-state simulation of Ahmed body is presented. For the simulation, simpleFoam with realizableKE turbulence model was used.

You can see the definition of Ahmed body in CFD-Wiki.

The slant angle and wind speed were set to 30 degrees and 60 m/s. The drag coefficient of this case was measured in the wind tunnel tests by Ahmed et al. [1].

For the comparison of the drag coefficients with the wind tunnel tests, I separated the model into 7 regions.

The slice of the mesh on the y=0 plane is shown in the following images.

The number of the cells is approximately 2.9 million.

References
1. S.R. Ahmed, G. Ramm, Some Salient Features of the Time-Averaged Ground Vehicle Wake, SAE-Paper 840300, 1984


BlockMeshDict:

    convertToMeters 1;

    vertices        
    (
        (-3.4 -1.76 -0.05)
        (6.52 -1.76 -0.05)
        (6.52  1.76 -0.05)
        (-3.4  1.76 -0.05)
        (-3.4 -1.76  1.87)
        (6.52 -1.76  1.87)
        (6.52  1.76  1.87)
        (-3.4  1.76  1.87)
    );

    blocks          
    (
        hex (0 1 2 3 4 5 6 7) (124 88 48) simpleGrading (1 1 1)
    );

    edges           
    (
    );

    patches         
    (
        patch inlet
        (
            (4 0 3 7)
        )
        patch side 
        (
            (3 2 6 7)
            (7 4 5 6)
            (4 0 1 5)
        )
        wall ground 
        (
            (0 1 2 3)
        )
        patch outlet 
        (
            (5 1 2 6)
        )
    );

    mergePatchPairs 
    (
    );

snappyHexMeshDict:

    castellatedMesh true;

    snap            true;

    addLayers       true;

    geometry

    {

        AhmedBody_30deg.stl

        {

            type triSurfaceMesh;

            name ahmed;

        }

    };

    castellatedMeshControls

    {

        maxLocalCells 100000000;

        maxGlobalCells 100000000;

        minRefinementCells 0;

        maxLoadUnbalance 0;

        nCellsBetweenLevels 8;

        features

        (

            {

                file "AhmedBody_30deg.eMesh";

                level 4;

            }

        );

        refinementSurfaces

        {

            "ahmed"

            {

                level (4 4);

                

                patchInfo

                {

                    type wall;

                    inGroups (ahmed);

                }

            }

        }

        resolveFeatureAngle 30;

        refinementRegions

        {

        }

        locationInMesh (-1.1 0.1 0.1);

        allowFreeStandingZoneFaces true;

    }

    snapControls

    {

        nSmoothPatch 10;

        tolerance 2.0;

        nSolveIter 300;

        nRelaxIter 10;

        // Feature snapping

            nFeatureSnapIter 30;

            implicitFeatureSnap false;

            explicitFeatureSnap true;

            multiRegionFeatureSnap false;

    }

    addLayersControls

    {

        relativeSizes true;

        layers

        {

            "ahmed_*"

            {

                nSurfaceLayers 6;

            }

            ground

            {

                nSurfaceLayers 6;

            }

        }

        expansionRatio 1.308;

        finalLayerThickness 0.79762265822016;

        minThickness 0.0001;

        nGrow 0;

        // Advanced settings

        featureAngle 60;

        slipFeatureAngle 30;

        nRelaxIter 10;

        nSmoothSurfaceNormals 50;

        nSmoothNormals 50;

        nSmoothThickness 100;

        maxFaceThicknessRatio 1.0;

        maxThicknessToMedialRatio 1.0;

        minMedianAxisAngle 130;

        nBufferCellsNoExtrude 0;

        nLayerIter 50;

    }

    meshQualityControls

    {

        maxNonOrtho 65;

        maxBoundarySkewness 4;

        maxInternalSkewness 4;

        maxConcave 80;

        minVol 1e-13;

        minTetQuality 1e-9;

        minArea -1;

        minTwist 0.02;

        minDeterminant 0.001;

        minFaceWeight 0.02;

        minVolRatio 0.01;

        minTriangleTwist -1;

        // Advanced

        nSmoothScale 4;

        errorReduction 0.75;

    }

    // Advanced

    debug 0;

    mergeTolerance 1E-6;