ENH: snappyHexMesh: various improvements. See below or the default snappyHexMeshDict.

Refinement:
-----------
// Optionally avoid patch merging - keeps hexahedral cells
// (to be used with automatic refinement/unrefinement)
//mergePatchFaces off;

// Optional multiple locationsInMesh with corresponding optional cellZone
// (automatically generates faceZones inbetween)
locationsInMesh
(
    ((-0.09 -0.039 -0.049)  bottomAir)  // cellZone bottomAir
    ((-0.09 0.009 -0.049)   topAir)     // cellZone topAir
);

// Optional faceType and patchType specification for these faceZones
faceZoneControls
{
    bottomAir_to_topAir
    {
        faceType baffle;
    }
}

/ Optional checking of 'bleeding' of mesh through a specifying a locations
// outside the mesh
locationsOutsideMesh ((0 0 0)(12.3 101.17 3.98));

// Improved refinement: refine all cells with all (or all but one) sides refined

// Improved refinement: refine all cells with opposing faces with different
// refinement level. These cells can happen on multiply curved surfaces.
// Default on, can be switched off with
//interfaceRefine false;

Snapping
--------
// Optional smoothing of points at refinement interfaces. This will reduce
// the non-orthogonality at refinement interfaces.
//nSmoothInternal $nSmoothPatch;

Layering
--------

// Layers can be added to patches or to any side of a faceZone.
// (Any faceZone internally gets represented as two patches)

// The angle to merge patch faces can be set independently of the
// featureAngle. This is especially useful for large feature angles
// Default is the same as the featureAngle.
//mergePatchFacesAngle 45;

// Optional mesh shrinking type 'displacementMotionSolver'. It uses any
// displacementMotionSolver, e.g. displacementSBRStress
// (default is the medial-axis algorithm, 'displacementMedialAxis')
//meshShrinker displacementMotionSolver;