allow overset hole to be further away from the wall patch

Functionality to add/problem to solve

The code I am attaching here allows to grow the hole and thus push back the interpolation interface from background to component mesh. Some issues in terms of stability still remain, but combined with pimple pressure under-relaxation on the final iteration I was able to obtain satisfactory results. I did not run the cases in an isolated manner so I cannot calculate the speedup that should come from the fewer calculated cells.

Target audience

Users running CFD with fully resolved boundary layers and overset

Proposal

That's my implementation, based on tips from @Mattijs cellVolumeWeightPushFront.7z

What does success look like, and how can we measure that?

The influence of the "push" parameter can be seen in the following comparison of a two-blade cycloidal rotor simulation. Here the captions refer to

• pushAndRelax: pushed a the inner interpolation interface (the hole) by 24 steps and relaxed the interpolation interface to make it approximately 4 cells thick on interfaces (hole and overset) using the nPushFront 24; and layerRelax 0.25; lines in fvSchemes oversetInterpolation dictionary
• pushNoRelax: WARNING: RAN WITHOUT PUSH pushed but not relaxation, thus layerRelax 1; <-- I'll update this post when I rerun the case with proper push
• noPush: layer relaxation but no push
• noPushNoRelax: no layer relaxation and no push

All other parameters for these 4 examples are maintained identical. The most flagrant differences are for vorticity (the wave at the interface) and for turbulent viscosity nut (the better preserved field through the interface)

And the following show how the calculated (blue), interpolated (white) and hole (red) cells are distributed. Both left and right airfoils have the same distribution, but I've removed the calculated cells on the right airfoil (component) mesh to show the background mesh.

Links / references

I think most overset codes do keep the interpolation far from the wall and also in a zone where the cell sizes roughly match.

Funding

Not necessary