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-   -   Strange boundaries for k and epsilon (http://www.cfd-online.com/Forums/openfoam-solving/58151-strange-boundaries-k-epsilon.html)

henning December 16, 2008 09:55

Hi, I have a pipe looking l
 
Hi,

I have a pipe looking like this:

http://www.cfd-online.com/OpenFOAM_D...es/1/10355.jpg

and its extruded along the flow direction (z-axis).

When I run simpleFoam (3000 Steps) I get unrealistic values for k(at least 184 though u = 3.725 m/s). Also near the boundaries they look strange. k should go back to 0 and epsilon should rise constantly.

http://www.cfd-online.com/OpenFOAM_D...es/1/10351.png http://www.cfd-online.com/OpenFOAM_D...es/1/10352.png

I made a simpler case with a 2D channel and a similar mesh. Here the results look quite good.

http://www.cfd-online.com/OpenFOAM_D...es/1/10353.png http://www.cfd-online.com/OpenFOAM_D...es/1/10354.png

Any idea what i am doing wrong?

B.c.s for k and epsilon are zeroGradient (similar to the tutorial cases in simpleFoam / turbFoam) and just for the internal field I gave values. I also tried values on inlet but then I get an error message saying I need zeroGradient at inlet patch.

Thanks for your help

Henning

pierre December 16, 2008 11:24

what turbulence model do you u
 
what turbulence model do you use?

Have you had a look at boundaryFoam and its tutorial? Even channelOodles. That might help.


Pierre

juanduque December 16, 2008 15:10

Why don't you try a different
 
Why don't you try a different mesh configuration, check O-Grid configuration, that might help.

henning December 17, 2008 06:07

I am using the classical k-eps
 
I am using the classical k-epsilon model.

I took a look on boundaryFoam. It uses zeroGradient b.c. for both, k and epsilon as well. channelOodles didn't help me that much since it is LES and i am not so familar with LES.

And changing the mesh ... well, I don't like to use O-Grid for this solution since I would prefer a mesh that can be made finer at the boundaries easyly.

Maybe any other ideas?

Anyhow, thank you very very much for your help so far.

Henning

henning January 7, 2009 03:54

Well, found my problem. Did pa
 
Well, found my problem. Did patch instead of wall in blockMeshDict. It's always the simple things that make life so interesting ;)


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