[jakethejake]

Dear Foamers,

I'm facing a (at least for me) strange behaviour of the layering part of snappyHexMesh (OF used is the Foundation version v6).

Case setup:
- I have a wall with a refinement region downstream. Therefore I set the relativesSizes to false to have a uniform boundary layer in every region (transition non-refinement to the refinement area). In the base case I used five layers with firstLayerThickness and expansionRatio specified.
- Now I have a case with an increased boundary layer thickness and want to resolve that by modifying the mesh in the region next to the wall. Options: I could either increase the number of layers or increase the first cell height respectively expansion ratio.
- With both options I see there is some kind of a "critical height" of the layer pack where the meshing breaks down the uniform boundary layer and kind of ignores the flag "relativesSizes = false"
--> Result for each option case is that I get a non uniform layer pack between the refinement and non-refinement regions.


Does anyone know how to deal with kind of "critical height" or getting rid of that behaviour? Or is it related to some strange parameters in the advanced settings section?

Find attached the pictures of the castellated mesh and the operations.
1. Castellated Mesh
2. Added five layers (expansionRatio 1.2; firstLayerThickness 0.00015)
3. Added six layers (expansionRatio 1.2; firstLayerThickness 0.00015)
4. Added five layers (expansionRatio 1.25; firstLayerThickness 0.00015)
5. Added five layers (expansionRatio 1.2; firstLayerThickness 0.00017)


Can anyone help?


Cheers,
jakethejake

addLayersControls
{
    // Global parameters
    relativeSizes             false; // false, usually with firstLayerThickness
    expansionRatio          1.2;
    //thickness               0.0015;
    //finalLayerThickness  0.00044;
    minThickness             0.00015;
    firstLayerThickness     0.00015;
    

    // Per final patch (so not geometry!) the layer information
    layers
    {
        tubeWall
        {
            nSurfaceLayers 5;
            // Local parameters
            //expansionRatio             1.2;
        }
    }

    // Advanced settings
    featureAngle                 30;    
    slipFeatureAngle             30;

    nGrow                         0;

    nLayerIter                     50;
    nRelaxedIter                 20;
    nRelaxIter                     5;

    nSmoothSurfaceNormals         1;
    nSmoothNormals                 3;
    nSmoothThickness             10;
    maxFaceThicknessRatio         0.5;
    maxThicknessToMedialRatio     0.3;

    minMedialAxisAngle             90;
    minMedianAxisAngle             90;
    nMedialAxisIter               10;

    nBufferCellsNoExtrude         0;
    additionalReporting         false;
 }

[Fedegenti]

Try toggling off decompose polyhedra and triangulate the slice