Velocity wall function

Tibo99 · January 14, 2021, 15:59

Hi everyone!

Hope you going well.

I was trying to implement a BC as a wall function for U like one shown in the picture.

I'm was trying to find something similar but I found nothing so far. Is someone here able to guide me with something, tutorial, BC template for U.

Or, is maybe better to implement a shear/gradient at the wall?

Thanks and best Regards,

mAlletto · January 16, 2021, 09:13

https://www.openfoam.com/documentati...lFunction.html

This is quite close to what you look for I think.

I've never seen a wall function for U which implements the velocity at the wall directly. You usually compute the wall shear stress which is consistent with your assumed velocity profile. In this case a logarithmic velocity distribution over the cell adjacent to the wall

Best

Michael

HPE · January 16, 2021, 17:00

Also, have a look at https://www.openfoam.com/documentati...lFunction.html , particularly the citations where

Eqs. 6-7 in
PJ Richards and RP Hoxey. Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model. In Computational Wind Engineering 1, pages 145–153. Elsevier, 1993.

were mentioned for the implementation.

Hope it helps.

Tibo99 · January 18, 2021, 09:56

I use 'nutkAtmRoughWallFunction'' from openfoam v1906 and the results on U isn't what it should compare to the analytics solution close to the wall. Also, I noticed that the one suggested in openfoam v2006 doesn't seams exactly the same.

So, I assume that I still need to set U at the wall U = (0 0 0)?

Do you have an idea or rational explanation why the author in this case present this that way (Uw) instead of presenting it with 'nutw' or it's probably based on the authors preferences?

Thank you for replying!

Tibo99 · January 18, 2021, 10:51

It's work! I got the right results on the velocity.

Thank you again!

January 16, 2021, 09:13		#2
mAlletto Senior Member Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 616 Rep Power: 16	https://www.openfoam.com/documentati...lFunction.html This is quite close to what you look for I think. I've never seen a wall function for U which implements the velocity at the wall directly. You usually compute the wall shear stress which is consistent with your assumed velocity profile. In this case a logarithmic velocity distribution over the cell adjacent to the wall Best Michael Tibo99 likes this.

January 16, 2021, 17:00		#3
HPE Senior Member Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 931 Rep Power: 13	Also, have a look at https://www.openfoam.com/documentati...lFunction.html , particularly the citations where Eqs. 6-7 in PJ Richards and RP Hoxey. Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model. In Computational Wind Engineering 1, pages 145–153. Elsevier, 1993. were mentioned for the implementation. Hope it helps. Tibo99 likes this. __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

January 18, 2021, 10:51		#5
Tibo99 Senior Member René Thibault Join Date: Dec 2019 Location: Canada Posts: 114 Rep Power: 6	It's work! I got the right results on the velocity. Thank you again! Last edited by Tibo99; January 26, 2021 at 15:30.

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January 18, 2021, 09:56		#4
Tibo99 Senior Member René Thibault Join Date: Dec 2019 Location: Canada Posts: 114 Rep Power: 6	I use 'nutkAtmRoughWallFunction'' from openfoam v1906 and the results on U isn't what it should compare to the analytics solution close to the wall. Also, I noticed that the one suggested in openfoam v2006 doesn't seams exactly the same. So, I assume that I still need to set U at the wall U = (0 0 0)? Do you have an idea or rational explanation why the author in this case present this that way (Uw) instead of presenting it with 'nutw' or it's probably based on the authors preferences? Thank you for replying!