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How are Wall Functions Practically Implemented!

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Old   June 1, 2016, 12:11
Default How are Wall Functions Practically Implemented!
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Hi,

I understand conceptually what wall functions are, why we need them, and to a good extent, their derivations and intuitions. However I feel that all my sources essentially only stop from there, and don't show the extra step on how they functions are practically implemented in code.

For example:

- As the wall functions are basically just "boundary conditions" are we only concerned at the values at the top of the wall functions, and how they meet with nodes?

- If this is the case, is the actual functional shape of these wall models of any concern? As in, can they look however they want (even if it doesn't fit experiment) so long as the value between top of the function, and the first node match in terms of BCs? OR is the entire functional shape important when you code up the wall function?

- Do the wall function implementations need to be specifically tailored in any way depending to the fluid solver scheme (turbulent solver)you are running?


I honestly can't get clear-cut questions on these issues from anywhere else I've looked. Textbooks and such only ever go over theory, derivations, and general discussions (which is great), but not down to an actual implementation stage (and I also find a lot of CFD courses never actually touch this issue as well )....

SO, any help on these questions would be fantastic . And I would appreciate links to any sources which could help me / any discussion on the issue.

Thanks!
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Old   June 1, 2016, 22:43
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https://www.sharcnet.ca/Software/Flu...ug/node512.htm

I never looked precisely at the wall equations code in Fluent, but I think that explains it pretty well.

If you speak OpenFOAM, you can look exactly how the wall functions are implemented here:

OpenFOAM-2.4.0/src/turbulenceModels/incompressible/RAS/derivedFvPatchFields/wallFunctions/

The details are different for different base turbulence models, of course, but you can probably look over kEpsilon under incompressible for simplicity.
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Old   June 2, 2016, 10:58
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Thanks for that! I also did some additional digging, and found some extra sources of information which I'll share here in case anyone runs into trouble in the future.

http://www.tfd.chalmers.se/~lada/pos..._report_WF.pdf

http://www.cfd-online.com/Forums/ope...mentation.html

http://www.cfd-online.com/Forums/mai...t-process.html

http://cerfacs.fr/~cfdbib/repository/TR_CFD_09_105.pdf

http://www.cfd-online.com/Forums/ope...lfunction.html

http://www.cfd-online.com/Wiki/Two_e...ls#cite_note-0

https://ceprofs.civil.tamu.edu/ssoco...s/Law_Wall.PDF

Versteeg pp. 275
.... and of course the suggestions by Michael Prinkey.

I think once you pointed me in the right direction initially I had a better understanding on which keywords to use in the search.

Last edited by pche8701; June 5, 2016 at 06:04.
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