[Kim sung hwan]

Dear cfd-users,

i have tried making external mesh by running snappyHexMesh for simulating a OneraM6 wing. but i meet a problem the addlayer processing in snappyHexMesh. Until snapping, i got reasonable snapping results on the wing surface.

however, after addlayer step, i found some bumps between upper and lower level of refinement level. when i got uniform cells near a surface using distance refinement, i could
resolve this problem. but it makes too many total cells so, it's not efficient.

I have tried many parametric study, but i can't find the solution about this issue.


I attached four screenshots and below there's my snappyHexMeshDict.

I would appreciate any help for solve this problem.

/*--------------------------------*- C++ -*----------------------------------*\
|       o          |                                                          |
|    o     o       | HelyxOS                                                  |
|   o   O   o      | Version: v1.0.3                                           |
|    o     o       | Web:     http://www.engys.com                            |
|       o          |                                                          |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object snappyHexMeshDict;
}

    castellatedMesh true;
    snap true;
    addLayers true;
    geometry
    {
        M6.stl
        {
            type triSurfaceMesh;
            name M6;
        }

        box1
        {
            type searchableBox;
            min (-0.5 0.0 -0.5 );
            max (2.0 1.5 0.5 );
        }

    }

    castellatedMeshControls
    {
        features
        (
        
        {
            file "M6.eMesh";
            level 8;
        }

        );
        refinementSurfaces
        {
            M6
            {
                regions
                {
                }

                level (7 8 );
            }

        }

        refinementRegions
        {
            box1
            {
                mode inside;
                levels (( 1E5 3 ));
            }

        }

        locationInMesh (3.0 3.0 1.0 );
        maxLocalCells 1000000;
        maxGlobalCells 2000000;
        minRefinementCells 0;
        nCellsBetweenLevels 5;
        resolveFeatureAngle 5;
        allowFreeStandingZoneFaces false;
    }

    snapControls
    {
        nSolveIter 300;
        nSmoothPatch 3;
        tolerance 1.0;
        nRelaxIter 5;
        nFeatureSnapIter 10;
        implicitFeatureSnap false;
        explicitFeatureSnap true;
        multiRegionFeatureSnap false;
    }

    addLayersControls
    {
        layers
        {
            M6_ascii_io_exported_from_Pointwise
            {
                nSurfaceLayers 2;
            }

        }

        relativeSizes false;
        expansionRatio 1.1;
        finalLayerThickness 2.0E-4;
        minThickness 1.0E-5;
        nGrow 0;
        featureAngle 60;
        slipFeatureAngle 30;
        nRelaxIter 3;
        nSmoothSurfaceNormals 1;
        nSmoothNormals 3;
        nSmoothThickness 10;
        maxFaceThicknessRatio 0.8;
        maxThicknessToMedialRatio 0.3;
        minMedianAxisAngle 90;
        nBufferCellsNoExtrude 0;
        nLayerIter 50;
        nRelaxedIter 20;
    }

    meshQualityControls
    {
        maxNonOrtho 65;
        maxBoundarySkewness 20;
        maxInternalSkewness 4;
        maxConcave 80;
        minFlatness 0.5;
        minVol 1.00E-13;
        minTetQuality -1e30;
        minArea -1;
        minTwist 0.02;
        minDeterminant 0.001;
        minFaceWeight 0.02;
        minVolRatio 0.01;
        minTriangleTwist -1;
        nSmoothScale 4;
        errorReduction 0.75;
    }

    debug 0;
    mergeTolerance 1E-6;

[lav]

Hi,

Has this problem been resolved? I have done 2 things to remove the protruded surfaces.

1. Make the "allowfreestandingZonefaces" as true in snappyHexMesh Dict
2. On moving to higher number of cells, I could still see the bumpy surfaces , so I went to increase the "minTetQuality " in the meshQualitycontrols .

I am not sure if this the right point of looking at the problem. Is there any another better way of doing this ?

[Artur]

Hi,

Have you tried playing around with the snapping distance tolerance parameter? I've found it to be quite crucial for getting good mesh on and very near the body surface. Sadly I've had problems in getting the quality I want with different refinement levels as was the case in the original post...

Can you comment on the effect of the changes you've made?

All the best,

A