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vijeshjoshi23 July 27, 2009 05:27

What is "mesh quality" in ICEM-CFD
Hi friends,
What are all the things we have to check to confirm that the mesh generated does not contain bad elements. Even if some bad elements are unavoidable what is the limiting number for bad elements? At present, I m checking skewness only. Plz reply...

Thank you...

brissyben July 27, 2009 07:23

Need to ensure volumes are greater than 0, and determinats are greater than 0. your mesh will not run if you have -ve volumes or determinants.

Look at angles as well, should be above 18 but i think most solvers can handle above 9 - look in the help manual it tells you all about these

PSYMN July 28, 2009 09:40

Depends on your solver...
This is definitely a solver based question… Look at your solver manual (or ask on that portion of the CFD-Online site) and find out what the requirements are. Some solvers are fine with 179 degree internal angles, others are very sensitive to angle quality. Some solvers are sensitive to pyramids but don’t mind really skewed prisms instead…

One thing to keep in mind is that most solvers are going to sneak in a factor of safety, so you may read that they need an internal angle of at least 18 degrees. In reality, 9 degrees would probably be fine and you may even be able to get away with >0 degrees. By publishing higher requirements, the solver tech support can blame any convergence issues on the mesh ;^).

I check a few usual suspects. ICEM CFD “Quality” (circumsphere ratio) should usually be above 0.1 for tetras and hexas, and above 0.01 for prisms. Determinant (1/jacobian) should be greater than 0.1. Angle should be greater than 9 or 18 degrees. Often I will have a few cells of lower quality. As long as they are above zero and not in a critical region, I may still try to run the model and see if it will converge.

PSYMN July 28, 2009 09:42

2 quick notes.
oh yea, two more quick thoughts about ICEM CFD quality...

First, prism quality in ICEM CFD is calculated harshly. They divide the prism into 3 tetras and report the quality of the worst one (circumsphere ratio) as the prism quality. This makes the ICEM CFD prisms look much worse than they are, so keep that in mind when comparing qualities between softwares.

Second, at 12.0, ICEM CFD added a TGrid Skew metric to make it easier for Fluent users to check their quality against the Fluent manual. At 12.1, ICEM CFD added an Expansion rate metric for CFX users. (12.1 is not due out until the end of 2009, but the check is already in the Beta version.)

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