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nutRoughWallFunction v1.6 - Values for Ks and Cs |
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#1 |
New Member
Join Date: Mar 2010
Posts: 6
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Hello everyone
There are already some posts about nutRoughWallFunction, e.g. "nutRoughWallFunction and Surface Roughness Documented". But still I have a problem. The following piece of code { type nutRoughWallFunction::Ks; value uniform 0.001; type nutRoughWallFunction::Cs; value uniform 0.5; } seems to be correct. If I leave the values for Ks or Cs I get an error message. Nevertheless, I always get the same result no matter which values are chosen. I have also used different meshes but the result is always the same. Does anyone know a solution to this problem? I think I am not the only one who is interested in this topic. Thanks in advance. Kind regards, Irina |
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#2 |
Senior Member
Richard Smith
Join Date: Mar 2009
Location: Enfield, NH, USA
Posts: 138
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nutRoughWallFunction in OpenFOAM 1.6 doesn't work correctly due to a bug. Try the latest 1.6.x from the git repository for the corrected version.
For more details on using nutRoughWallFunction try: http://www.cfd-online.com/Forums/ope...ocumented.html Hope this helps.
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#3 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
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Hello everybody,
I still have problems using nutRoughWallFunction with 1.6.x. More in detail, I have the same problems as posted above: whenever I change Ks (from extremely low to extremely high values), the results I get are always the same. I am studying the flow around an airfoil at Re 1.5 millions and modeling turbulence with the KOmegaSST model. I defined the airfoil surface as: Code:
airfoil { type nutRoughWallFunction::Ks; value uniform 0.00048; } I tried different angles of attack and let the simulations converge till 1000 time steps. However, no changes on the aerodynamic coefficients while changing Ks. I tried different Ks, including 0 (smooth surface) and 1 meters, and also different turbulence models (kEpsilon). No changes. I am wandering if there is still some bug on the nutRoughWallFunction. Any experience on that? Suggestions? Is there any incompatibility between schemes or parameter definition that let the simulation do not take into account the Ks? Any help is appreciated. Cheers, mad Last edited by maddalena; June 17, 2010 at 10:12. Reason: mispelled nutRoughWallFunction with nutWallFunction, observations apply without changes |
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#4 |
Senior Member
Stefan Herbert
Join Date: Dec 2009
Location: Darmstadt, Germany
Posts: 129
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Hi,
I've already worked with rough wall function in 1.6.x in my results are fine. Changing Ks had a big influence in my case. But I'm not sure if your BC is defined correctly, because you give no value for Ks but just for nut, which is in my opinion completely ignored. I used something like Code:
airfoil { type nutRoughWallFunction; Ks uniform 1e-5; Cs uniform 0.5; value uniform 0.0; } Stefan |
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#5 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 ![]() |
Hi Stefan and thanks for your answer.
I followed what posted by Irina above... However, using: Code:
airfoil { type nutRoughWallFunction; value uniform 0.0; Ks uniform 0.00048; Cs uniform 0.5; } Maybe I installed the new OF 1.6.x version not properly. Do you know how can I switch on some debug to check whether the nutRoughWallFunction references are correct? In order to check if is a problem with my openFoam, I could also run a case that is working for sure for someone else... Maybe you have a really simple case I can test... May I try it? Thank you. mad |
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#6 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 ![]() |
Ok, switched on the debug flag (see Userguide!)
If I change the Ks, I can see that:
Thus, probably there is something wrong with my installation... What do you think? mad |
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#7 |
New Member
Join Date: Mar 2010
Posts: 6
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Hi Maddalena
I installed OpenFOAM 1.7.x and used lowerWall { type nutRoughWallFunction; Ks uniform 0.24; Cs uniform 0.5; value uniform 0.0; } as was suggested by Stefan. When changing Ks values my results changed as well. Finally, everything works fine. Maybe you should also install the latest version. Cheers, Irina |
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#8 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
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Hi Irina and thanks for your interest. My problem was something different, see http://www.cfd-online.com/Forums/ope...tml#post264132. Everything worked when I changed mesh resolution.
Regards, maddalena |
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#9 | |
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Getnet
Join Date: Aug 2011
Location: LSU
Posts: 20
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Quote:
Thanks |
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#10 |
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Join Date: Jul 2012
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#11 |
Member
David GISEN
Join Date: Jul 2009
Location: Germany
Posts: 68
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Hi hfs,
my only idea is to use fixedValue for nuSgs and e.g. nuTilda or every other LES parameter. Maybe it's possible to calibrate this value to behave like a normal roughness parameter. What do you think? Cheers |
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#12 |
Member
Join Date: Jul 2012
Posts: 66
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Thanks for the idea ... am not sure ... will get back to you!
Thanks! |
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nutroughwallfunction |
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