That’s another fine mesh…
Dr. Mesh, CD-adapco

If, like me, you come from the “blood, sweat and tears” school of CFD meshing, the recent developments in automatic meshing technology might have left you feeling a little disorientated. The problem is that many of us learnt our trade at a time when the only true measure of mesh quality was the number of hours that you spent building it by hand. Back then the automatic in “automatic meshing” was really just a byword for “quick but dirty.”

Not anymore. CD-adapco’s investment in polyhedral meshing technology has resulted in a meshing technique that is as automatic as tetrahedral meshing but with an accuracy comparable to that of a hexahedral grid.

The most striking thing about polyhedral meshes is that they are so easy to create. If you haven’t joined the polyhedral revolution already, I suggest that after finishing this article, you sit down and try to make a polyhedral mesh for yourself. My guess is that whether you are a closet hand-mesher or not, you will be pleasantly surprised by the result.

The easiest way to generate a polyhedral mesh is using either STAR-Design or the STAR-CAD Series. Designed to be used by non- CFD specialists, these products allow you to generate quality polyhedral meshes directly from your solid CAD model with no more than a couple of clicks of the mouse. Meshes are created from within the CAD environment and linked directly to the CAD solid model. Upon any change in the design, the mesh can be regenerated with a single button click, respecting the boundary conditions and resolution prescribed for the previous design iteration.

For those of you that prefer vertex-by-vertex control, polyhedral meshes can now also be generated through the Automatic Meshing panel in pro-STAR (for the recently released STAR-CD V4). In common with all of the polyhedral meshing approaches described here, extrusion layers are created automatically as part of the process.

The most powerful method of generating polyhedral meshes, however, is using STAR-CCM+ V2, in which the mesher is linked to the surface wrapper and surface remesher in a so called “meshing pipeline”. This provides a fully automatic path from surface import to mesh generation (and then beyond to solution and post-processing). Once set up, the meshing pipeline defines all of the steps necessary to create a directly comparable mesh from a different starting surface. Upon generating a new mesh, STAR-CCM+ automatically maps the solution from the old mesh onto the new one, providing the best possible initial condition for the new simulation.

STAR-CCM+ V2 also includes a brand new trimmer that takes advantage of the fact that the new solvers don’t distinguish between trimmed cells and any other type of n-faced polyhedra. Because the trimmer is no longer restricted to just a few trimmed-cell topologies it has far more latitude in its trimming. This means that “unresolved cells” and “couples errors” are a thing of the past (in fact there are no more couples at all – all meshes are now fully conformal).

This also opens the door to new trimming opportunities, users are able to trim from templates of tetrahedral and regular polyhedra as well as the traditional hexahedra.

Of course, you aren’t just limited to one approach. Meshes can be transferred between STAR-CD V4 and STAR-CCM+ using the .ccm file, which includes not only the mesh, but also the boundary region definitions. STAR-Design Gateway and STAR-CAD Gateways can also be used to make meshes for either solver.

All of which leaves me with another problem: What to do with all the time that I used to spend creating meshes. Things have become so bad recently that I have even been considering a return to medicine...

Now where did I put those rubber gloves?

Dr. Mesh

Dr. Mesh surgery is open. Please send comments and suggestions to dr.mesh@cd-adapco.com