CFD Online Discussion Forums - [snappyHexMesh] bumpy on the surface of 3D wing in addlayer step with snappyHexMesh

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.

Code:

/*--------------------------------*- 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;