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April 22, 2010, 10:31 |
RANS vs LES
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#1 |
New Member
Remy Cavecchia
Join Date: Apr 2010
Posts: 4
Rep Power: 16 |
Hi everybody,
I'm studying CFD and I want to learn a bit more about turbulences. I want to compare a simulation done with a RANS model with Data I have for the same simulation but realised with a LES. The idea is to see what can be do with RANS to achieve pretty good results. I'd just like to know as a start point what kind of Mesh I need, to get acceptable results. I mean what kind of value for Yplus? My problem is about an turbulent pipe flow : D=140mm Re=80000. Thanks for helping me. |
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April 22, 2010, 16:15 |
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#2 |
Senior Member
Join Date: Feb 2010
Posts: 148
Rep Power: 17 |
There are many difference RANS models. Which one do you want to use?
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April 23, 2010, 02:30 |
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#3 |
New Member
Remy Cavecchia
Join Date: Apr 2010
Posts: 4
Rep Power: 16 |
I'm gonna use the k-epsilon model.
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April 23, 2010, 09:45 |
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#4 |
Senior Member
Join Date: Feb 2010
Posts: 148
Rep Power: 17 |
The following is quoted directly from ANSYS online support:
For the k-e model, y+ should be less than 300. If y+ is below about 11 for the k-e model then it still works fine, but the model does not make use of the fine near wall mesh, so the mesh is wasted. Essentially the k-e model always uses the Scalable Wall Functions. The Scalable Wall Function approach is not valid below y+~=11, so the mesh is ignored below y+~= 11.There is no low-Re implementation of the k-e model in CFX. If there were, the low-Re k-e model would require y+<0.2 and has other problems too. k-e always uses Scalable Wall Functions, hence y+<300 is the requirement. There's some additional information at http://www.cfd-online.com/Forums/cfx...value-sst.html I hope this helps. |
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April 24, 2010, 07:41 |
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#5 |
New Member
Remy Cavecchia
Join Date: Apr 2010
Posts: 4
Rep Power: 16 |
Ok, thank you for your help!!
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