How to generate 2D meshes with pMesh

Since pMesh does not support 2D meshes, here is a workflow for 2D polyhedral meshes.

Step-by-step guide

  1. Start with a *.stl file of your domain

    1. Generated with external software

    2. Exported from OpenFOAM from a hexahedral blockMesh (useful for simple geometries, e.g. rectangular domains)
      Utility to export a surface *.stl file:

      ?> foamToSurface -tri surfaceMesh.stl

  2. Convert the *.stl to *.fms

    	?> surfaceToFMS surfaceMesh.stl

    and optionally edit the patch names in the *.fms file.

  3. Edit the system/meshDict file

    Adapt the maximum cell size in m to your domain size and generate boundary layers for the “empty” patches

    // mandatory settings
//  - relative or absolute
surfaceFile     "surfaceMesh.fms";
//  - maximum cell size
maxCellSize 0.014;

// optional global options
//  - refinement of cells at the boundaries
boundaryCellSize 0.014;
boundaryCellSizeRefinementThickness 0.014;
//  - performs refinement where cells are larger than feature size
minCellSize 0.014;

boundaryLayers
{
    // global options in dictionary (optional)
    //  - number of layers
    nLayers 2;
    //  - thicknes ratio
    thicknessRatio 1.1;
    //  - maximum thickness of first layer [m]
    maxFirstLayerThickness 0.014;

    // local settings
    patchBoundaryLayers
    {

        "front.*"
        {
            //  - number of layers (optional)
            nLayers 2;
            //  - thickness ratio (optional)
            thicknessRatio 1.1;
            //  - max thickness of first layer (optional) [m]
            maxFirstLayerThickness 0.1;
            //  - active of inactive
            allowDiscontinuity 0;
        }
        "back.*"
        {
            //  - number of layers (optional)
            nLayers 2;
            //  - thickness ratio (optional)
            thicknessRatio 1.1;
            //  - max thickness of first layer (optional) [m]
            maxFirstLayerThickness 0.1;
            //  - active of inactive
            allowDiscontinuity 0;
        }
    }

    optimiseLayer 1;

    optimisationParameters
    {
        featureSizeFactor 0.3;
        nSmoothNormals 20;
        maxNumIterations 20;
        reCalculateNormals  1;
        relThicknessTol 0.01;
    }
}

  4. Generate the mesh with pMesh

  5. Edit the system/extrudeMeshDict to extrude a 2D mesh from an empty patch

    constructFrom patch;

// If construct from patch/mesh:
sourceCase "../meshTrg";
sourcePatches (front);

// If construct from patch: patch to use for back (can be same as sourcePatch)
exposedPatchName front;

// If construct from surface:
//surface "movingWall.stl";

// Flip surface normals before usage. Valid only for extrude from surface or
// patch.
flipNormals false;

// Linear extrusion in point-normal direction
extrudeModel        linearNormal;

nLayers             1;

expansionRatio      1.0;

linearNormalCoeffs
{
    thickness       0.06;
}

// Do front and back need to be merged? Usually only makes sense for 360
// degree wedges.
mergeFaces false;

// Merge small edges. Fraction of bounding box.
mergeTol 0;

  6. Extrude the mesh

    ?> extrudeMesh

To obtain good polyhedral boundary faces it is sometimes useful to rotate the domain by 45° before pMesh is executed.
E.g. before exporting the surface file in step 1.b. execute

?> transformPoints -rotate-angle '((1 0 0) 45)'

and rotate the domain back before step 6.

?> transformPoints -rotate-angle '((1 0 0) -45)'

See also