# Question about using turbulence model to laminar flow

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 November 3, 2012, 21:09 Question about using turbulence model to laminar flow #1 Senior Member     Meimei Wang Join Date: Jul 2012 Posts: 494 Rep Power: 8 Hi, Would using turbulent flow model(like K-Omega or Reynolds stress model) to laminar flow bring large inaccuracy? Thanks. __________________ Best regards, Meimei

 November 4, 2012, 10:01 #2 Member     Pedram Mojtabavi Join Date: Apr 2011 Location: Iran Posts: 66 Rep Power: 7 Hi Anna, You mean what happens if we use a turbulent model in a laminar flow? Turbulent flows have different physics, so we use different turbulent equations because the Navier-Stokes equations do not give a correct answer when the flow enters into the turbulent territory (for example Newton laws cannot be applied in quantum physics). On the other hand, solving a laminar flow with a turbulent model does not give a correct answer either and we have to be sure about the flow regime, and then choose the models. Best regards.

 November 7, 2012, 17:41 #3 New Member   James Join Date: Oct 2012 Posts: 18 Rep Power: 5 Hi, what about domain with different flow regimes? For instance in some part of domain you can consider a laminar flow (Re < 2100) but in other flow is turbulent or transient What turbulence model should be applied in this case? Best regards

 November 7, 2012, 18:03 #4 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 13 Pure laminar flow: In A perfect turb model, eddy viscosity should return to zero in the framework of EVM, however this is not always true. So, Most turb models are dissipative by nature, and if your flow does not have turbulent dissipation, and extracting energy from it would surely cause deviation. Transitional flow, Be aware that the models you listed are supposed to run in FT mode, they are not working well in transitional flow. Huge error would occur. There are models can handle this, but of cause not to predict natural transition. Turbulent flow, Pay special attention, that in lots of industrial flow, regions of laminar exist, turb models you listed are still having great difficulties in these flows. 想起北大的一位老师讲到，湍流存在大家都知道，但具体是啥却极难描绘。 __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

January 25, 2013, 20:11
#5
Senior Member

Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8
Quote:
 Originally Posted by James_ Hi, what about domain with different flow regimes? For instance in some part of domain you can consider a laminar flow (Re < 2100) but in other flow is turbulent or transient What turbulence model should be applied in this case? Best regards

Thanks for your answer. I have to use Reynolds stress model to fluid transforming from turbulent to laminar.(turbulent flow go into a channel with complex wall geometry) So I have to use LRR model to turbulent, transitional, laminar fluid at the same time. The Re is about 1000.

So I'm interested to know: How inaccurate would Reynolds stress model be for transitional and laminar flow?
__________________
Best regards,
Meimei

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