[MikeWorth]

I'm trying to mesh a surface where at one particular end of the surface the layers need to extend further away from the wall. I think I'm almost there - I have 3 patches that represent the 'thin' and 'thick' regions plus a 'transition' region that avoids too abrupt a change. SHM can apply different thickness layers to these three bits, but the transitions are not smooth - the layers all get 'pinched' in towards the surface as shown in this image:


The definitions are calculated to have the same number of layers each (thinking that it would make for a nice one-to-one transition...) but with different start sizes and growth rates as follows:

addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes false;

    // Per final patch (so not geometry!) the layer information
    layers
    {
        thin
        {
            //Calculated using https://openfoamwiki.net/index.php/Scripts/blockMesh_grading_calculation
            nSurfaceLayers 14;
            firstLayerThickness 5e-6;
            expansionRatio 1.258498951;
        }

        transition
        {
            //Calculated using https://openfoamwiki.net/index.php/Scripts/blockMesh_grading_calculation
            nSurfaceLayers 14;
            firstLayerThickness 29e-6;
            expansionRatio 1.109512254;
        }
        
        thick
        {
            //Calculated using https://openfoamwiki.net/index.php/Scripts/blockMesh_grading_calculation
            nSurfaceLayers 14;
            firstLayerThickness 78e-6;
            expansionRatio 1.033918581;
        }
    }



    // Expansion factor for layer mesh
    expansionRatio 1.258498951;

    // Wanted thickness of final added cell layer. If multiple layers
    // is the
    // thickness of the layer furthest away from the wall.
    // Relative to undistorted size of cell outside layer.
    // is the thickness of the layer furthest away from the wall.
    // See relativeSizes parameter.
    //finalLayerThickness 1;

    firstLayerThickness 5e-6;

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // Relative to undistorted size of cell outside layer.
    minThickness 4e-6;

    // If points get not extruded do nGrow layers of connected faces that are
    // also not grown. This helps convergence of the layer addition process
    // close to features.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 0;

    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 170;

    // At non-patched sides allow mesh to slip if extrusion direction makes
    // angle larger than slipFeatureAngle.
    slipFeatureAngle 30;

    // Maximum number of snapping relaxation iterations. Should stop
    // before upon reaching a correct mesh.
    nRelaxIter 3;

    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 1;

    // Number of smoothing iterations of interior mesh movement direction
    nSmoothNormals 3;

    // Smooth layer thickness over surface patches
    nSmoothThickness 10;

    // Stop layer growth on highly warped cells
    maxFaceThicknessRatio 0.5;

    // Reduce layer growth where ratio thickness to medial
    // distance is large
    maxThicknessToMedialRatio 0.3;

    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x.
    minMedialAxisAngle 90;


    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;
}

Can anyone help me understand why this pinching exists, and how to get rid of it?

Many thanks,
Mike