CFD Online Discussion Forums - [snappyHexMesh] snappyHexMesh: No layer at the outer surfaces of the mesh

Hi Foamers!

I have a -maybe simple- problem when generating a mesh of a prismatic body in snappyHexMesh. The layers are only produced in the inner part of the mesh while there are no layers on the outside boundaries of the mesh. This kind of mesh results in high values of yPlus close to the outer faces.

I created a very simple mesh of a cylinder to show that problem. I clipped the mesh twice to make the inner part visible (see attached pictures).

Here is the snappyHexMeshDict I used:

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  2.1.0                                 |

|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    object      snappyHexMeshDict;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



// Which of the steps to run

castellatedMesh true;

snap            true;

addLayers       true;



geometry

{

    circle.stl

    {

        type triSurfaceMesh;        name circle;

    }



};



// Settings for the castellatedMesh generation.

castellatedMeshControls

{



    // Refinement parameters



    maxLocalCells 15000000;



    maxGlobalCells 30000000;



    minRefinementCells 0;





    nCellsBetweenLevels 3;



    // Explicit feature edge refinement



    features

    (

    );



    // Surface based refinement



    refinementSurfaces

    {

        circle

        {

            level (1 1); // was (2 2) 

        }

    }



    resolveFeatureAngle 180;



    // Region-wise refinement



    refinementRegions

    {

    }



    // Mesh selection



    locationInMesh (0.45 0 0.0005);



    allowFreeStandingZoneFaces true;

}



// Settings for the snapping.

snapControls

{

    nSmoothPatch 3;



    tolerance 4.0;



    nSolveIter 30;



    nRelaxIter 5;

}







// Settings for the layer addition.

addLayersControls

{

    relativeSizes true;



    // Per final patch (so not geometry!) the layer information

    layers

    {

        "circle.*"

    {

        nSurfaceLayers 2;

    }

    }



    expansionRatio 1.25;



    finalLayerThickness 0.8;



    minThickness 0.25;



    nGrow 2;





    // Advanced settings



    featureAngle 180;

    nRelaxIter 5;

    nSmoothSurfaceNormals 1;

    nSmoothNormals 3;

    nSmoothThickness 10; 

    maxFaceThicknessRatio 0.5;

    maxThicknessToMedialRatio 0.3;

    minMedianAxisAngle 90;

    nBufferCellsNoExtrude 0;

    nLayerIter 50;

    nRelaxedIter 20;

}







// Generic mesh quality settings. At any undoable phase these determine

// where to undo.

meshQualityControls

{

    maxNonOrtho 65;

    maxBoundarySkewness 20;

    maxInternalSkewness 4;

    maxConcave 80;

    minVol 1e-13;

    minTetQuality 1e-30;

    minArea -1;

    minTwist 0.05;

    minDeterminant 0.001;

    minFaceWeight 0.05;

    minVolRatio 0.01;

    minTriangleTwist -1;

    // Advanced

    nSmoothScale 4;

    errorReduction 0.75;

    relaxed

    {

        maxNonOrtho 75; // war nicht hier

    }



}



debug 0;

mergeTolerance 1e-6;





// ************************************************************************* //

Anybody an idea to solve this?

Thanks in advance!