[Commercial meshers] foamMeshToFluent - very high skewness after conversion!

kishpishar · January 18, 2015, 16:13

Dear FOAMers,

I am writing this post to get your expert opinion on the issue of skewness after mesh conversion that has been troubling for some time now.

I have meshed a relatively simple geometry with snappyHexMesh. CheckMesh reveals all quality parameters to be OK, with max. face skewness reported about 2. The case runs smoothly with first order schemes and I know that meshes with skewness up to 4 can be safely run with OpenFOAM.

When I convert the mesh using foamMeshToFluent and check the mesh in Fluent, it says there are many cells with equiangle skew more than 0.98. By this metric, the mesh is really bad. However, the case runs in Fluent as well.

I am aware that OpenFOAM and Fluent use different metrics for defining skewness - openfoam using a face based one which is a measure of the deviation of the vector connecting the cell centres from the face centroid and fluent, a cell based one for equiangle skew.

What I am confused is: After all it is the same mesh with the same points, nodes, faces and cells. By one defenition the mesh is perfectly OK while by the other, it is more or less useless. Can there be so much discordance between the two?

Any thoughts are most welcome. I would be happy to share the case if anyone needs.

-Kumar

wyldckat · January 18, 2015, 16:38

Quick answer - here's some reading material:

http://www.cfd-online.com/Forums/ope...tml#post524577 post #10

Quote:

Originally Posted by wyldckat

Meshing-wise, there have been some recent discoveries, which are somewhat documented on this thread: http://www.cfd-online.com/Forums/ope...mesh-pipe.html
Also, indirectly related to this: http://www.cfd-online.com/Forums/ope...e-changes.html

As for mesh diagnosis, here are some ideas:

[...]

As for tips for CFD newbies in general:

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January 18, 2015, 16:13	foamMeshToFluent - very high skewness after conversion!	#1
kishpishar Member Kumar Join Date: Jun 2013 Posts: 47 Rep Power: 13	Dear FOAMers, I am writing this post to get your expert opinion on the issue of skewness after mesh conversion that has been troubling for some time now. I have meshed a relatively simple geometry with snappyHexMesh. CheckMesh reveals all quality parameters to be OK, with max. face skewness reported about 2. The case runs smoothly with first order schemes and I know that meshes with skewness up to 4 can be safely run with OpenFOAM. When I convert the mesh using foamMeshToFluent and check the mesh in Fluent, it says there are many cells with equiangle skew more than 0.98. By this metric, the mesh is really bad. However, the case runs in Fluent as well. I am aware that OpenFOAM and Fluent use different metrics for defining skewness - openfoam using a face based one which is a measure of the deviation of the vector connecting the cell centres from the face centroid and fluent, a cell based one for equiangle skew. What I am confused is: After all it is the same mesh with the same points, nodes, faces and cells. By one defenition the mesh is perfectly OK while by the other, it is more or less useless. Can there be so much discordance between the two? Any thoughts are most welcome. I would be happy to share the case if anyone needs. -Kumar