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Old   February 26, 2009, 05:17
Default convergence
  #1
Tanveer ahmad Rubani
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is the meshing quality single most important factor for convergence of an CFD similation. How important is aspect ratio and volume expansion ratio in CFX mesh quality I am getting 4 elements of very high volume expansion ratio on surface of body in side my flow domain. how it is going to affect convergence.
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Old   February 26, 2009, 17:31
Default Re: convergence
  #2
Glenn Horrocks
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Hi,

Mesh quality is a key factor in convergence of a CFD simulation. Aspect ratio is important, but exactly what aspect ratio is the limit before it causes problems is problem dependent. For high accuracy surface tension flows aspect ratio >1.5 is bad news. For external aerodynamics flows in the boundary layer aspect ratio 100 is OK for the inflation layers.

Glenn Horrocks
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Old   February 27, 2009, 04:12
Default Re: convergence
  #3
radionline
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Very interesting!

At my last simulation I got a high Mesh expansion factor (appr. 100) In the Help I read it should be less than 20! How does it influence my results, or is it also depending from my problem? Remark: The solution converged...
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Old   March 1, 2009, 18:17
Default Re: convergence
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Glenn Horrocks
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Hi,

Its effect is problem dependent. As I previously said some simulations will handle it OK but some will not have a hope. The only way to be sure is to do a sensitivity analysis and find out on your case.

But as general guides the suggestions in the documentation are good for most simulations.

Glenn Horrocks
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Old   March 2, 2009, 02:33
Default Re: convergence
  #5
Zmur
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Hello. Sorry for interrupting. I had the same problem with those numbers (expansion factor and aspect ratio). The most annoying thing is that you get to know about the expansion factor only after the analysis have started. Is there a way to check the mesh for its expansion factor prior to running the analysis? What is a sensitivity analysis?
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Old   March 2, 2009, 04:23
Default Re: convergence
  #6
neewbie
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You can load your .def-file in the CFXPost and examine your meshquality.

A sensitvity analysis is a meshstudy on how an choosen value is changing with increasing/decreasing the meshresolution.

Regards, neewbie
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Old   March 4, 2009, 06:07
Default Re: convergence
  #7
radionline
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Exactly!

By the way, if you load your.def-file in CFX-Post you can't find the Mesh Expansion factor. In WB 12 (Preview) you can detect some Mesh-Parameters under Mesh Statistics directly after Meshing. But not all of them!

Regards radionline
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