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Running high non orthogonality mesh

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Old   May 1, 2023, 05:08
Default Running high non orthogonality mesh
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Marco Carbotta
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Hello everyone, I'm trying to run a polyheadral mesh from a commercial mesher in OpenFOAM with chtMultiRegionSimpleFoam, but given the nature of the mesh it's very unstable and the simulation diverges, the max non orthogonality of the mesh is 98 and there are 16627 faces with orthogonality over 70, am I just wasting my time trying to run this?

I tried running simpleFoam and then switching to chtMultiRegionSimpleFoam but as soon as I run a few steps with cht the k and epsilon values explode and so does the temperature (I think it's a problem with the solving of p).
I tried lots of different schemes and I'm using the following relaxation factors:
p_rgh and p= 0.3
k and epsilon= 0.5
h=0.9
U=0.5

I know I'd need a better mesh but it's really hard to get one, does it make sense to even try or will it never give me results that make sense? I'll attach the checkMesh for reference

Thanks in advance for any response, it will sure ease my day
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File Type: txt log_checkMesh.txt (9.5 KB, 18 views)
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Old   May 1, 2023, 08:31
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Kuzey Can Derman
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You can use nNonOrthogonalCorrectors in fvSolution if you haven't already. It helps to solve meshes with high orthogonality. In your case you should run a high number of loops but you will find the exact number by experimenting yourself, start with 3 and increment it.

But this is not a definite solution, you have a very high orthogonality mesh, it may not work.

Btw it looks like you have other mesh problems like open cells, they may cause problem too, can you use "checkMesh -latestTime -meshQuality -allTopology -allGeometry" and post the output?
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Old   May 1, 2023, 15:27
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Marco Carbotta
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Hey, thanks for the answer

I've been using a nonorthogonal corrector value of 3 but I've read that after that it doesn't matter too much so I left it there, I tried running with 4 and 5 but still no luck, I'll test with higher values, thanks for the suggestion.

Here is my full checkmesh file, as you said I do have some open cells, but I've also checked an older version of the mesh before trying to "repair" it and that one doesn't have open cells but has an even higher non-ortho.

I'm also uploading my fvSchemes in case I could be doing something better there, I'm trying to run with first order schemes at first for more stability and change to second order later.
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File Type: txt fvSchemes.txt (1.7 KB, 12 views)
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Old   May 2, 2023, 14:41
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Paulin FERRO
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Give up if you have max non-ortho > 90 and remesh.

By the way nNonOrthogonalCorrectors is from my experience not the best way for dealing with high non ortho cells (1 or 2 iterations is fine).

The good way is to limit the non orthogonal correction for laplacian schemes.

Still from my experience, it would be preferable to have your max non ortho < 85.
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