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October 15, 2012, 15:18 |
BCs for k and epsilon at walls with y+=1
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#1 |
Senior Member
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 287
Rep Power: 21 |
Hello everybody,
I would like to know the following for OpenFOAM 2.1.1: when setting up a turbulent flow case with a mesh that leads to y+ values of 1 I do not need to use wall functions. What is the correct BC for k and epsilon in such a case Are they fixedValue=0 or zeroGradient? Similar question for k-omega models also. I have found this post http://www.cfd-online.com/Forums/ope...m-1-5-dev.html but it refers to previous OF releases Thanks! Last edited by vangelis; October 15, 2012 at 16:44. |
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October 16, 2012, 03:22 |
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#2 |
Member
Roland
Join Date: Mar 2009
Location: Netherlands
Posts: 92
Rep Power: 17 |
Hi Vangelis,
To my understanding you would (theoretically) set both at fixedValue = 0, as there is no turbulence possible in the viscous sublayer. And as there is no turbulence, you also can't have dissipation of turbulence. I say theoretical because actually setting the BC's to 0 would result in a division by zero in the OpenFOAM implementation. In practice you would therefore set them to a very small value, for example fixedValue = 1e-12. Best regards, Sylvester |
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October 16, 2012, 03:51 |
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#3 |
Senior Member
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 287
Rep Power: 21 |
Hi Sylvester!
Thank you very much for your reply. Best regards Vangelis |
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October 16, 2012, 08:57 |
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#4 |
Senior Member
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 287
Rep Power: 21 |
Hi Sylvester
I forgot to also specify that nut should also be set to fixedValue=0 like k, right? Vangelis |
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October 16, 2012, 09:14 |
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#5 | |
Member
Roland
Join Date: Mar 2009
Location: Netherlands
Posts: 92
Rep Power: 17 |
Hi Vangelis,
Or use nutLowReWallFunction, which makes the patch accessible from yPlusRAS. From nutLowReWallFunctionFvPatchScalarField.H: Quote:
Sylvester ps. Can we perhaps expect improved OpenFOAM pre-processing in ANSA v13.3? |
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October 16, 2012, 10:25 |
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#6 |
Senior Member
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 287
Rep Power: 21 |
We are trying to do this.
And in this sense thank you for your help! so you mean that it is better to use nutLowReWallFunction so that afterwards I can get values for y+? Otherwise it would be the same as setting fixedValue=0 for nut at walls? |
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October 16, 2012, 10:52 |
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#7 |
Member
Roland
Join Date: Mar 2009
Location: Netherlands
Posts: 92
Rep Power: 17 |
Hi Vangelis,
Yes, from what I can gather it is better to use the nutLowReWallFunction. But I haven't done much work with low Re turbulence models, so I may be wrong here. Best regards, Sylvester |
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October 16, 2012, 11:45 |
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#8 |
Senior Member
Vangelis Skaperdas
Join Date: Mar 2009
Location: Thessaloniki, Greece
Posts: 287
Rep Power: 21 |
Thanks again Sylvester!
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