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kang April 17, 2007 00:03

help me with grid independent investigation
 
I am doing simulation of turbulent flow in a long pipe. in order to get grid independence. I increase elements from 478982 to 510873, but the result became worse. why it happened? and sometimes the solver complaint my mesh " maximum expansion factor = 20.6>20!" when it happens, can I trust the result? cheers!

Johnny April 17, 2007 06:42

Re: help me with grid independent investigation
 
Typically a mesh independence study involves refining a mesh by a factor of 2, not by 10% as you have done. Also, you should ensure that you are modifying the mesh uniformly - you probably didn't do this which resulted in an increased expansion factor.


kang April 17, 2007 08:18

Re: help me with grid independent investigation
 
Thanks a lot for your answering.I just started to do cfx and I am not sure about my mesh refinement. The pipe has the length of 2m and the diameter of 0.05m. I set the inflation layers as 15 and the first prism thickness as 0.03cm. when I do refining, I double the default body spacing and the default face spacing, while leave the others unchanged. Am I right? Could you explain 'modifying the mesh uniformly' to me? Thanks again.

Omer April 17, 2007 10:54

Re: help me with grid independent investigation
 
By doubling the body spacing , you get a finer mesh? I have no idea, how you are able to do that.....!

You can also use the "global Mesh scaling" under options in the Mesh tree in CFX, to refine your mesh. Set lower than 1 to get finer, set higher than 1 to get courser mesh.

kang April 17, 2007 18:26

Re: help me with grid independent investigation
 
Hi,Omer, you are right.I have been silly.I got it now. Thanks.


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