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[snappyHexMesh] unsymmetric boundary layer extrusion on simple symmetric geometry

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Old   March 28, 2017, 08:23
Default unsymmetric boundary layer extrusion on simple symmetric geometry
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Attesz
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Hello all,

I am preparing a simple pipe simulation using snappy. Even though the geometry is a simple open pipe, snappy can not extrude boundary layers on the walls near the inlet. If I choose different refinement levels and boundary layer final thickness, it gets either better, or worse.

Is this normal? If not, what am I doing wrong?
mesh.jpg

Code:
/*--------------------------------*- C++ -*----------------------------------*\
|       o          |                                                          |
|    o     o       | HELYX-OS                                                  |
|   o   O   o      | Version: v2.4.0                                           |
|    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
    {
        inner_wrap.stl
        {
            type triSurfaceMesh;
            name inner_wrap;
            appendRegionName false;
        }

        external_walls.stl
        {
            type triSurfaceMesh;
            name external_walls;
            appendRegionName false;
        }

        edge_wall.stl
        {
            type triSurfaceMesh;
            name edge_wall;
            appendRegionName false;
        }

        internal_walls.stl
        {
            type triSurfaceMesh;
            name internal_walls;
            appendRegionName false;
        }

        INLET.stl
        {
            type triSurfaceMesh;
            name INLET;
            appendRegionName false;
        }

        cylinder_vr5
        {
            type searchableCylinder;
            point1 ( 0.0 -0.5 0.28 );
            point2 ( 0.0 0.55 0.28 );
            radius 0.2;
        }

        cylinder_vr6
        {
            type searchableCylinder;
            point1 ( 0.0 -0.3 0.28 );
            point2 ( 0.0 0.5 0.28 );
            radius 0.08;
        }

        cylinder_vr4
        {
            type searchableCylinder;
            point1 ( 0.0 -1.0 0.28 );
            point2 ( 0.0 0.6 0.28 );
            radius 0.5;
        }

        cylinder_vr3
        {
            type searchableCylinder;
            point1 ( 0.0 -2.0 0.28 );
            point2 ( 0.0 0.8 0.28 );
            radius 1.0;
        }

        cylinder_vr2
        {
            type searchableCylinder;
            point1 ( 0.0 -3.0 0.28 );
            point2 ( 0.0 1.0 0.28 );
            radius 2.0;
        }

        cylinder_vr1
        {
            type searchableCylinder;
            point1 ( 0.0 -5.0 0.28 );
            point2 ( 0.0 1.5 0.28 );
            radius 3.0;
        }

    }

    castellatedMeshControls
    {
        features
        (
        
        {
            file "external_walls_line.eMesh";
            levels ((0.0 6));
            refineFeatureEdgesOnly false;
        }

        
        {
            file "edge_wall_line.eMesh";
            levels ((0.0 9));
            refineFeatureEdgesOnly false;
        }

        
        {
            file "internal_walls_line.eMesh";
            levels ((0.0 7));
            refineFeatureEdgesOnly false;
        }

        
        {
            file "INLET_line.eMesh";
            levels ((0.0 7));
            refineFeatureEdgesOnly false;
        }

        );
        refinementSurfaces
        {
            external_walls
            {
                level ( 0 0 );
            }

            edge_wall
            {
                level ( 8 8 );
            }

            internal_walls
            {
                level (7 7 );
            }

            INLET
            {
                level ( 7 7 );
            }

        }

        refinementRegions
        {
            inner_wrap
            {
                mode inside;
                levels (( 1E5 7 ));
            }

            edge_wall
            {
                mode distance;
                levels (( 0.01 8 ) ( 0.05 7 ) ( 0.1 6 ) );
            }

            cylinder_vr5
            {
                mode inside;
                levels (( 1E5 5 ));
            }

            cylinder_vr6
            {
                mode inside;
                levels (( 1E5 6 ));
            }

            cylinder_vr4
            {
                mode inside;
                levels (( 1E5 4 ));
            }

            cylinder_vr3
            {
                mode inside;
                levels (( 1E5 3 ));
            }

            cylinder_vr2
            {
                mode inside;
                levels (( 1E5 2 ));
            }

            cylinder_vr1
            {
                mode inside;
                levels (( 1E5 1 ));
            }

        }

        locationInMesh ( 0.0 0.0 1.0 );
        maxLocalCells 1000000;
        maxGlobalCells 20000000;
        minRefinementCells 0;
        nCellsBetweenLevels 5;
        resolveFeatureAngle 30.0;
        allowFreeStandingZoneFaces true;
        planarAngle 30.0;
        maxLoadUnbalance 0.1;
    }

    snapControls
    {
        nSolveIter 300;
        nSmoothPatch 5;
        tolerance 5.0;
        nRelaxIter 8;
        nFeatureSnapIter 80;
        implicitFeatureSnap true;
        explicitFeatureSnap true;
        multiRegionFeatureSnap true;
    }

    addLayersControls
    {
        layers
        {
            external_walls
            {
                nSurfaceLayers 5;
                expansionRatio 1.25;
                finalLayerThickness 0.8;
            }

            edge_wall
            {
                 nSurfaceLayers 5;
                expansionRatio 1.25;
                finalLayerThickness 0.8;
            }

            internal_walls
            {
                nSurfaceLayers 5;
                expansionRatio 1.25;
                finalLayerThickness 0.8;
            }

        }

        relativeSizes true;
        expansionRatio 1.2;
        finalLayerThickness 0.6;
        minThickness 0.0001;
        nGrow 0;
        featureAngle 240.0;
        slipFeatureAngle 80.0;
        nRelaxIter 5;
        nSmoothSurfaceNormals 1;
        nSmoothNormals 3;
        nSmoothThickness 10;
        maxFaceThicknessRatio 0.5;
        maxThicknessToMedialRatio 0.3;
        minMedialAxisAngle 90;
        nBufferCellsNoExtrude 0;
        nLayerIter 50;
        nRelaxedIter 20;
        writeVTK false;
        noErrors false;
        layerRecovery 1;
        growZoneLayers false;
        projectGrownUp 0.0;
    }

    meshQualityControls
    {
        maxNonOrtho 65.0;
        maxBoundarySkewness 20;
        maxInternalSkewness 4;
        maxConcave 80.0;
        minFlatness 0.5;
        minVol 1.0E-13;
        minTetQuality 1.0E-15;
        minArea -1.0;
        minTwist 0.02;
        minDeterminant 0.001;
        minFaceWeight 0.05;
        minVolRatio 0.01;
        minTriangleTwist -1.0;
        nSmoothScale 4;
        errorReduction 0.75;
        relaxed
        {
            maxNonOrtho 75;
        }

    }

    debug 0;
    mergeTolerance 1.0E-6;
    autoBlockMesh false;
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Old   April 25, 2017, 07:13
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I think that is quite common problem.

Snappy is not very competent for making boundary layers in corners or in complex geometry.
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