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how to get the right y+ value.

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Old   May 29, 2010, 02:07
Question how to get the right y+ value.
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danardono
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Does anybody know how to get the right y+ value in Ansys CFX?

As long as I know, there are 2 ways to get the result, but they give different values for the same CFD calculation results.

#1. On "tools", the function calculator. Choose function: areave Location: "walls" variable: yplus (not solver yplus).
This option will give a certain y+ value.

#2. Under "outline" apply the following settings to default domain:
-mode : variable
-variable : Yplus
This option will give a range of y+ on entire surface (walls) of the model.

In my case, the y+ gotten from #1 is not in the range of y+ gotten from #2.

Thanks a lot..
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Old   May 29, 2010, 07:08
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Glenn Horrocks
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But you are comparing an area averaged y+ to a y+ range, so you are not comparing the same thing. Can you explain what you mean better?
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Old   May 29, 2010, 09:08
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danardono
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Thanks a lot for responding.
I know that I compare different things. But in my opinion (please tell me if I'm wrong), the y+ area averaged value should be in the y+ range value. In my case, for example the area averaged value is around 22, but the range is from 0 to 11.

Actually what I need is to check the y+ value, in order to check the accuracy of the 3D problems. Would you please tell me which way is the best to check th y+?

regards
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Old   May 29, 2010, 17:59
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Glenn Horrocks
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Generally there are only a few surfaces where the y+ matters. So you look at those surfaces and do plots of y+ or max/min functions on the surfaces of interest to check they are OK. There is no point doing averages over the entire domain if it includes walls of no interest.
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Old   May 30, 2010, 04:38
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OK, I understand..
Thank you very much for your help..

best regards..
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