Feature runtime selection geometry

Summary

Have user selectable scheme for calculating the geometry factors (centres, volumes, correctionvectors etc)

Resolved bugs (If applicable)

Better handling of high-aspect ratio cells. See e.g. #1519 (closed)

More flexibility in specialised handling of mesh types.

Details of new models (If applicable)

system/fvSchemes has a new optional entry geometry which selects the geometry scheme:

geometry
{
    type            highAspectRatio;
    minAspect       10;
    maxAspect       100;
}

The default (called basic) is the normal, primitiveMesh functionality. The additional set of geometry schemes are:

• highAspectRatio : for high-aspect ratio cells reverts to face-area weighted face-centre average. This avoids large truncation errors for extreme aspect ratio cells (at the cost of loosing 2nd order centroid calculation). It is useful for running e.g. tet-meshes with low-Re extrusion layers.
• averageNeighbour : version of highAspectRatio that assumes extruded cells and tries to align cell centres on either side of a face.
• stabilised : this is the Foundation's alternative method of calculating the face centre/area (area contributions weighted with the normal). Note that it only affects the mesh faces calculation, not that of the individual faces

Apart from the basic scheme the various alternatives are still under development.

Risks

Default is identical behaviour. The run-time selection is performed at the fvSchemes level so e.g. application working on the polyMesh instead of fvMesh level (e.g. blockMesh) will not use the new structure.