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What wall function for y+ below 30?

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Old   November 1, 2006, 11:50
Default What wall function for y+ below 30?
Ralf Schmidt
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I have a grid, where the yplus values are close to 30 (20-50). Now, the question is, what wall function will be appropiate? the standard wall function is good for 30 < yplus < 300 and for the other wall functions, yplus has to be below 5.

So what is the right choice? I don't want to modell the whole geometry again, because of 3 reasons:

- first: it was a hell lot of work to generate that geometry,

- second: to increase yplus, the gab between two walls is to small and

- third: to lower yplus, to many cells will result.

Any idea?

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Old   November 2, 2006, 03:50
Default Re: What wall function for y+ below 30?
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Standard wall functions are not the only ones working with 30 < y+ < 300. Non-equilibrium wall functions are a derivative of standard wall functions, sensitized to adverse pressure gradient. They are absolutely OK to use when APG is medium (for high APG they are no longer appropriate, you will need y+=1 mesh and low-Re model). I used these non-equilibrium functions on airfoils like Onera M6 and on transonic compressor blades like NASA Rotor 37 with y+(medium)=33-40, and the results were excellent.

y+ values between 20 and 50 are quite OK, if the 20 values are only on small portion of the wall or in not so important areas.

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