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danar May 29, 2010 02:07

how to get the right y+ value.
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..

ghorrocks May 29, 2010 07:08

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?

danar May 29, 2010 09:08

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+?


ghorrocks May 29, 2010 17:59

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.

danar May 30, 2010 04:38

OK, I understand..
Thank you very much for your help..

best regards..

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