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A. Gatherson. August 28, 2001 13:18

Wall functions.
Hi all,

I was wondering what the effect of say using a y* value of < 11.25 in fluent when employing standard wall functions would be. Also, what would the effect be if the y* value was too large...say >100. Large pressure gradienyts etc. may be present. Would the accuracy of the model be severly compromised? What would the likely error be?

thanks again.

John C. Chien August 28, 2001 13:32

Re: Wall functions.
(1). We don't know how the vendor implements the wall function treatment in the code, so the best place to get the information is from the vendor's support engineer. (2). It is a good idea to follow the guidelines listed for the particular code you are using. You may want to check into the user's guide, to see whether there are warning signs and the related consequences printed. (3). You could also test the code and check the results.

Herve August 30, 2001 11:49

Re: Wall functions.
If y+<11.25 your mesh encroaches with the laminar region.

y+ ~ 100 is still pretty good in a lot of problems using k-e or RSM. If you refer to Wilcox (1993) or Versteeg and Malalasekera (1995) 11.25<y+<500.

In most codes you can monitor this value. In CFX for example not the law of the wall is well detailed in the manual and you can easily implement your own using user fortran.

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