how to deal with bad quality cells?

phsieh2005 · July 18, 2011, 16:53

Dear OpenFOAMers,

I obtained a mesh with about 10% bad quality cells. There is nothing I can do to improve the cell quality. This mesh has already 8 million cells. So, I cannot add more cells to improve cell quality.

I am using simpleFoam solver. I have already use 1 iteration for non-orthogonality correction. Is there anything I can do to improve convergence? I am already using upwind for div in fvSchemes. Case is laminar.

Thanks!

Pei

sambo · July 18, 2011, 17:47

p { margin-bottom: 0.08in; } Did you try to visualize the bad elements by reading the sets with paraview and what kind of bad elements do you have (skewness , …)?

You can try to improve your convergence by reducing the under relaxation factors but a mesh with 10% of bad quality cells sounds really bad.

phsieh2005 · July 19, 2011, 09:53

Hi, Sambo,

Yes, I did plot the set in paraview. the issue is non-orthongonality.

I reduced under-relaxation coef of p to 0.2 and U to 0.5. Maybe I need to reduce them more? How about the schemes? I am already using upwind.

Pei

sambo · July 20, 2011, 10:35

Hi phsieh2005,
non-orthongonality:Try to increase the number of Non orthoganl correctors more („nNonOrthogonalCorrectors“ in the SIMPLE loop of fvSolutiom).
You also can try to increase your tolerance of p, U,k,epsilon (or omega).
But I am worry that this is not helping.

I would recommend to post your current result and to check which region or element(s) is the problem.
Maybe you have some recirculation at the outlet. In that case you can change your outlet boundary condition to InletOutlet.
For example: If you have a high k value at one element, you have to do a new mesh.

July 18, 2011, 16:53	how to deal with bad quality cells?	#1
phsieh2005 Senior Member Pei-Ying Hsieh Join Date: Mar 2009 Posts: 334 Rep Power: 18	Dear OpenFOAMers, I obtained a mesh with about 10% bad quality cells. There is nothing I can do to improve the cell quality. This mesh has already 8 million cells. So, I cannot add more cells to improve cell quality. I am using simpleFoam solver. I have already use 1 iteration for non-orthogonality correction. Is there anything I can do to improve convergence? I am already using upwind for div in fvSchemes. Case is laminar. Thanks! Pei

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July 18, 2011, 17:47		#2
sambo New Member SamboReal Join Date: Feb 2011 Posts: 9 Rep Power: 15	p { margin-bottom: 0.08in; } Did you try to visualize the bad elements by reading the sets with paraview and what kind of bad elements do you have (skewness , …)? You can try to improve your convergence by reducing the under relaxation factors but a mesh with 10% of bad quality cells sounds really bad.

July 19, 2011, 09:53		#3
phsieh2005 Senior Member Pei-Ying Hsieh Join Date: Mar 2009 Posts: 334 Rep Power: 18	Hi, Sambo, Yes, I did plot the set in paraview. the issue is non-orthongonality. I reduced under-relaxation coef of p to 0.2 and U to 0.5. Maybe I need to reduce them more? How about the schemes? I am already using upwind. Pei

July 20, 2011, 10:35		#4
sambo New Member SamboReal Join Date: Feb 2011 Posts: 9 Rep Power: 15	Hi phsieh2005, non-orthongonality:Try to increase the number of Non orthoganl correctors more („nNonOrthogonalCorrectors“ in the SIMPLE loop of fvSolutiom). You also can try to increase your tolerance of p, U,k,epsilon (or omega). But I am worry that this is not helping. I would recommend to post your current result and to check which region or element(s) is the problem. Maybe you have some recirculation at the outlet. In that case you can change your outlet boundary condition to InletOutlet. For example: If you have a high k value at one element, you have to do a new mesh.