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The importance of a good mesh

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The importance of a good mesh

Posted July 3, 2022 at 04:22 by Vinzmann

Recently I've been running a simulation of a Ranque Hilsch Vortex Tube in OpenFOAM. This went well for a time but when I tried refining and implementing a new mesh, it all came crashing down, showing negative total temperatures with gradients of more than 600 K for neighbouring cells. Since my experience with OpenFOAM is still rather limited, I tried with refining every surface up to a ridiculously high degree. After that mishap I went into it with my head on straight and started looking at what snappyHexMesh was doing. I saw the truly abysmal layer generation, meaning that some places had no layers and the ones that had, were very badly layered. To fix this I stopped using relativeSizes and specified the absolute wall layer thickness, as I wanted to control this parameter anyways. At first I thought I could set nRelaxIter to 0 but this produced no layers at all so I set it back to 5. Next I increased the feature angle and slip feature angle so my relatively complex geometry would be meshed everywhere, especially at the sharp corners.

In conclusion:
look at your mesh and don't use relativeSizes for layer addition.
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