# Wall function's solving procedure.

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June 16, 2013, 23:50
Wall function's solving procedure.
#1
Senior Member

Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
Posts: 675
Rep Power: 8
Hi guys,

In this bounch of wall functions, we have this equation: see the image. just like it said: Provided U_p and Y_p is know, my problem arises,

How can I know U_p? Y_p is desided by the mesh, but U_p?

And I try to calculate this manually, via U_p, I can have tau, k, epsilon all of them, But all of them's value is up to U_p.

so anyideas?

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 June 18, 2013, 03:47 #2 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 531 Blog Entries: 14 Rep Power: 17 It is the value in the first cell near the wall, taken at the previous iteration.

 September 27, 2013, 08:33 wall function calculating procedure #3 New Member   saisai Join Date: Sep 2013 Posts: 4 Rep Power: 3 i am sorry to disturb. i have a question ,is it wall function only adopteded to the first cell layer ?i mean from the second layer ,begin to solve the k-e equation ,am i right ?i do really appreciate if you can give me some light .

 September 28, 2013, 09:09 #4 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 531 Blog Entries: 14 Rep Power: 17 The goal of wall functions is to provide approximate boundary conditions which would enable the resolution of viscous wall bounded flows without having to resolve the thin viscous layers at the wall. As such, this boundary conditions are obviously applied only to the first cell near the wall. This, at least, in general. There are specific models where a different set of equations is solved over an extended region over the wall. Hence, in a generic sense, the wall model is applied to more than one cell layer. But the philosophy, i think, is also different

 September 28, 2013, 22:22 #5 Senior Member   Dongyue Li Join Date: Jun 2012 Location: Torino, Italy Posts: 675 Rep Power: 8 At last, I think I know how it deal with the solving precedure. At first, you should solve Ueqn using the initial k,u,p. Then you get the velocity field. Solving the pressure equation, you can get the pressure field. Next, solving the k and epsilon equation. In this step, you have already the U_p; solve these equation and using the wall-funtions. You can get the k and epsilon. If I was wrong correct me. Thanks.

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