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Old   April 17, 2007, 00:03
Default help me with grid independent investigation
  #1
kang
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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!
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Old   April 17, 2007, 06:42
Default Re: help me with grid independent investigation
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Johnny
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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.

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Old   April 17, 2007, 08:18
Default Re: help me with grid independent investigation
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kang
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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.
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Old   April 17, 2007, 10:54
Default Re: help me with grid independent investigation
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Omer
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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.
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Old   April 17, 2007, 18:26
Default Re: help me with grid independent investigation
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kang
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Hi,Omer, you are right.I have been silly.I got it now. Thanks.
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