Meshing with foamyHexMesh

foamyHexMesh is a new mesh generator added in OpenFOAM 2.3.0.

In this post, I tried foamyHexMesh for simple shapes (a box and a sphere).

Thinking of foamyHexMesh as a meshing tool for air-flow simulations about a car, I created the box as the computational domain which has inlet and outlet, and the sphere as a substitute of a car.

Box

Sphere

I exported these shapes as STL files. Box.stl is separated into 4 parts (inlet, outlet, side, and ground).

The diagonal points of the box is (-1, -1, 0) and (1, 1, 1). And the center of the sphere is (0, 0, 0) and the radius of the sphere is 0.5.

Box.stl

Sphere.stl

Here are the steps of using foamyHexMesh.

1. Modify orientations of the faces of STL files at first

$ surfaceOrient constant/triSurface/Sphere.stl -inside '(-0.9 0 0.1)' constant/triSurface/Sphere.stl
$ surfaceOrient constant/triSurface/Box.stl -inside '(-0.9 0 0.1)' constant/triSurface/Box.stl

2. Create intersections of the 2 shapes

$ surfaceBooleanFeatures intersection constant/triSurface/Sphere.stl constant/triSurface/Box.stl

3. Run foamyHexMesh

$ foamyHexMesh

4. Run collapseEdges

$ surfaceBooleanFeatures intersection constant/triSurface/Sphere.stl constant/triSurface/Box.stl
$ collapseEdges -latestTime -collapseFaces

The resulting mesh is as follows.

If there are 2 or more parts in STL files, they turn into different mesh regions.

In this case, faces on the Box.stl are separated into 4 mesh regions ('box_inlet', 'box_outlet', 'box_side', 'box_ground').

Mesh surfaces

Mesh surfaces

Mesh surfaces and edges

Mesh surfaces and edges

I copied foamyHexMeshDict from the simpleShapes tutorial case, and editted it for the case of this post.

surfaceCellSizeCoeff seems to be the relative size of the cell against the defaultCellSize.

In this case, defaultCellSize = 0.05 and surfaceCellSizeCoeff = 1 (box), 0.5 (sphere).

Therefore the cell size on the surface = 0.05 (box), 0.025(sphere).

I changed some other parameters but I just found very few differences.

========
foamyHexMeshDict:

// Include defaults parameters from master dictionary
#include "$WM_PROJECT_DIR/etc/caseDicts/foamyHexMeshDict"
geometry
{
    Sphere.stl
    {
        name sphere;
        type triSurfaceMesh;
    }
    Box.stl
    {
        name box;
        type triSurfaceMesh;
    }
}

surfaceConformation
{
    locationInMesh (-0.9 0 0.1);
    featurePointControls
    {
        specialiseFeaturePoints off;
        edgeAiming              off;
        guardFeaturePoints      off;
        snapFeaturePoints       off;
        circulateEdges          off;
    }
    // Geometry to mesh to
    geometryToConformTo
    {
        sphere
        {
            featureMethod   none;
            patchInfo
            {
                type        wall;
                inGroups    (groupSphere);
            }
        }
        box
        {
            featureMethod   extractFeatures;
            includedAngle   140;
            mode            outside;
            patchInfo
            {
                type        wall;
                inGroups    (groupBox);
            }
        }
    }
    additionalFeatures
    {
        boxSphereIntersection
        {
            featureMethod           extendedFeatureEdgeMesh;
            extendedFeatureEdgeMesh "Sphere_Box_intersection.extendedFeatureEdgeMesh";
        }
    }
}

initialPoints
{
    initialPointsMethod         autoDensity;
    autoDensityCoeffs
    {
        minCellSizeLimit        0.01;
        minLevels               0;
        maxSizeRatio            2;
        sampleResolution        1;
        surfaceSampleResolution 1;
    }
}

motionControl
{
    defaultCellSize         0.05;
    minimumCellSizeCoeff    0;
    // For background cell size and alignment grid
    maxSmoothingIterations  100;
    maxRefinementIterations 0;
    shapeControlFunctions
    {
        sphere
        {
            type                        searchableSurfaceControl;
            priority                    2;
            mode                        outside;
            surfaceCellSizeFunction     uniformValue;
            uniformValueCoeffs
            {
                surfaceCellSizeCoeff    0.5;
            }
            cellSizeFunction            linearDistance;
            linearDistanceCoeffs
            {
                distanceCellSizeCoeff   1;
                distanceCoeff           1;
            }
        }
        box
        {
            type                searchableSurfaceControl;
            priority            1;
            mode                bothSides;
            surfaceCellSizeFunction uniformValue;
            uniformValueCoeffs
            {
                surfaceCellSizeCoeff 1.0;
            }
            cellSizeFunction        uniform;
            uniformCoeffs
            {}
        }
    }
    // Output lots and lots of .obj files
    objOutput                   no;
    // Timing and memory usage.
    timeChecks                  no;
}

// After simulation, when converting to polyMesh, filter out small faces/edges.
// Do not change. See cvControls.H
polyMeshFiltering
{
    filterEdges                 on;
    filterFaces                 on;
    writeTetDualMesh            false;
}

meshQualityControls
{
    #include "meshQualityDict"
}