free-slip wall boundary

[garcfd]

I finally got the free-slip wall boundary condition to work properly.

(It was much simpler than previous attempts, using wall reflection matrices and ‘reaching’ into the flow field)

This is what I posted on LinkedIn and Twitter/X

#UFOLBM sports car model with free-slip wall boundary condition (https://www.thingiverse.com/thing:6884252). This case was 125 million cells, and ran on runpod A40 GPU, 3 hours runtime, 100k iterations. Saving slices of data for post-processing every 1000 iterations, all done in Paraview. The settings are Re=600,000 giving 10m/sec simulated speed for a reference length of 1 metre.

I have created a free-slip (tangential flow) wall boundary condition as an alternative to the ‘bounce-back’ method. The approach is to calculate the tangential component of velocity at the ‘cut-cells’ and then recompute “fin” (the incoming populations) from the new tangential velocity. No bounce-back is needed, and it only uses the wall cut-cells not the interior dead cells. The only slight issue I had was with conflicting surface normals in the STL geometry, so I had to fix the STL to make it suitable.

https://drive.google.com/file/d/1bAgDmYRPGOZhoNFcYn78lkeqM299ly6y

https://drive.google.com/file/d/1fC2H64ng13AmfhurBWx0-WmfuBtzaFaX

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