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fvSchenes: laplacianSchemes

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Old   August 24, 2018, 13:24
Default fvSchenes: laplacianSchemes
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gu1
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Hello,

I have a doubt related to the surface-normal gradient schemes, below is described the log.checkMesh of my mesh.

Quote:
$ checkMesh -allTopology -allGeometry

Checking geometry...
Overall domain bounding box (-0.0999998 -0.0999998 0) (0.0999998 0.0999998 2)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (-1.90394189e-15 -1.90716853e-15 -8.55469839e-18) OK.
Max cell openness = 2.97460393e-16 OK.
Max aspect ratio = 13.6105489 OK.
Minimum face area = 1.11120589e-05. Maximum face area = 0.000163558947. Face area magnitudes OK.
Min volume = 1.85200908e-07. Max volume = 1.02892303e-06. Total volume = 0.0627309696. Cell volumes OK.
Mesh non-orthogonality Max: 9.6835347 average: 2.63548259
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.4318385 OK.
Coupled point location match (average 6.66133815e-16) OK.
Face tets OK.
Min/max edge length = 0.00113645172 0.01666667 OK.
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : min = 1 average = 1
All face flatness OK.
Cell determinant (wellposedness) : minimum: 0.153833429 average: 2.57817791
Cell determinant check OK.
Concave cell check OK.
Face interpolation weight : minimum: 0.428623081 average: 0.488083617
Face interpolation weight check OK.
Face volume ratio : minimum: 0.634366657 average: 0.951150797
Face volume ratio check OK.

Mesh OK.

End
My non-orthogonality is low, and I think this is really good.
However I'm not sure which scheme to use for laplacianSchene. Should I use corrected? orthogonal? limited 1.0?
I'm using 'limited 1.0', but I do not know if it's the best for my case ...
What would be the difference between them in the results that I will get?
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Old   October 4, 2018, 08:05
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Could anyone help me?
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Old   October 4, 2018, 08:52
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Hi,
personally, an average non-orthogonality of 2.xy is almost zero. I would use the orthogonal scheme or the uncorrected one (limited with limiter zero -> similar to orthogonal but with some under relaxation; somehow like matrix relaxation with factor 1) or the corrected. The limited scheme with a limiter factor > 0 is generally used for higher non-orthogonal meshes because the correction term can cause problems if the angle increases too much > 70. Thus, it is more for high non-orthogonality). All schemes can be used, but the accuracy might change from second order to first order.

A better summary (more or less the same):
Surface Normal Gradient Schemes

The differences are related to accuracy and stability. The surface-normal gradient calculation is an important quantity.
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Old   October 6, 2018, 16:44
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Quote:
Originally Posted by Tobi View Post
Hi Tobi, it's nice to talk to you.

Thanks for the clarification. I recently completed some of the preliminary tests I was doing, and this topic was meant to ''cover'' the lack of knowledge that still existed in my setup.

I used the ''limited 1.0'' scheme which is ''similar'' to ''corrected'', but I believe it is not similar due to the clarification you mentioned, in relation to the relaxation coefficients... anyway, I believe that I did not make a bad choice. Now I am thinking of using ''uncorrected'' and later ''orthogonal''.

I will post the test results to your knowledge.
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Old   October 7, 2018, 06:41
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Quote:
Originally Posted by gu1 View Post
I... was meant to ''cover'' the lack of knowledge that still existed in my setup.
I have lack of knowledge too. There are so many things to consider always. I feel very impressed by those people, who know (more or less) anything.
Good luck with your work.
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