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May 4, 2005, 21:35 
Turbulence models

#1 
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Hi, I am new to CFD. May I know under what situation should I use BaldwinLomax model over kepsilon models? This is the first time I actually came across this model as most textbooks mentioned only kepsilon or komega models.
Any advice will be very much appreciated. 

May 5, 2005, 06:41 
Re: Turbulence models

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The BaldwinLomax model is a very robust and simple model which can produce surpricingly good results for turbomachinery blading simulations. It is suitable to use for quick design iterations. If you want to predict stall, complex 3D flows or separations it is probably not that suitable.


May 5, 2005, 21:21 
Re: Turbulence models

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I read it somewhere that the BaldwinLomax model is more suitable than kepsilon in the case of transonic flow, but no explanation was given. Is this true?


May 6, 2005, 07:43 
Re: Turbulence models

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The BaldwinLomax model is a much simpler algebraic turbulence model which does not include any transported turbulent quantities. That makes it very robust and it seldom behaves very badly.
Kepsilon on the other hand is a twoequation model which transports two turbulent properties (turbulent energy and dissipation). This makes it possible for kepsilon models and other twoequation models to account for history effects in a way which BaldwinLomax can never do. Hence, kepsilon is a more advanced model with the potential of predicting more complex phenomena. However, kepsilon models often produce completely unphysicial results with unrealisticly viscous regions. This often happens in regions with strong normal strain, ie in regions with strong acceleration or decelleration. In transonic flows where you have shocks the shocks can often make your standard kepsilon model produce this kind of problematic viscous regions. To handle this you need special versions of the kepsilon models that, for example, have some extra realizability constraint applied to them. Hence, there is no simple answer to your question. Which model is best depends on your case (weather or not history effects are important), your own experience in identifying problems with kepslion models and which kepsilon model you are using. 

May 28, 2005, 09:50 
Re: Turbulence models

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What about the SpallarsAlmarlas? in case of incompressible simulation like water pumps. i found that in some cases the SA model behaves better than the BL, while some case not.


May 28, 2005, 17:19 
Re: Turbulence models

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The SpalartAlmares model is a oneequation model that it something in between an algebraic model like the BaldwinLomax model and a twoequation model like the kepsilon model. Since it includes one transported turbulent quantity it has the potential to include at least some history effects (transportation of turbulent energy). It is a more modern model than the BL model, but that is of course not a guarantee that it always produces better results.
Tha SA model is very robust and is easy to use. For attached flows it often produces good results. It is popular in aerospace applications and for quick designiteration simulations in the turbomachinery field. The SA model rarely produces the completely unphysical results that a kepsilon model can produce sometimes. This has made the SA model quite popular in the last 5 years. Spalart has also developed a nice DES variant of the SA model, where the large eddies are resolved and the smaller edies are modeled using the SA model. This type of hybrid RANS/LES models have produced very good results for massively separated flows in aerospace applications  there is a very nice example of a SA DES simulation of a stalling F18 which you can probably find on the net if you google a bit. For heat transfer applications I'd not recommend SA. It often underpredicts heattransfer. 

August 12, 2005, 06:33 
Re: Turbulence models

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What are the better turbulence models to predict the flow pattern and heat transfer in a stator rotor cavity like in turbomachinery secondary flow regions where many strong recirculating zones are present.
Thanks, Kali 

October 10, 2005, 06:42 
Re: Turbulence models

#8 
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hi, can u please send me basic materials for reynolds stress modeling and its latest trend in cfd.
thank you bye, sathish kumar 

October 14, 2005, 04:55 
Re: Turbulence models

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respected sir i am working on a small ducted propellor, duct diameter is 180 mm and its lenght is .1 m in which the propellor is installed. this whole geometry is moving with speed 10m/sec. and rpm of motor used to rotate the propellor is 10000. now please tell me which model is better to use. baldwin_lomax , SpallarsAlmarlas or ke model. flow is nearly steady and this ducted propellor is used for uav. u r kindly requested to reply as soon as possible. sohail muhammad amjad


November 8, 2005, 23:31 
Re: Turbulence models

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respected sir , kindly suggest the suitable model for external aerodynamics of car. thanks vivek


June 10, 2010, 15:51 

#11 
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Quentin
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Hi,
I was wondering if the SpalartAllmaras model implemented in Fine/turbo has been implemented to use wall functions when the mesh resolution is not sufficiently fine (like in Fluent). Because in my case I have 100<y+<250 and I'm wondering if results obtained with a so high y+ have any value? Best regards Quentin 

August 5, 2010, 16:07 

#12 
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Bedotto, I would recommend refining your grid to determine whether your y+ value is sufficient. Essentally, demonstrate grid independence.


August 6, 2010, 08:19 
cfd

#13 
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balan
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how to calculate the lift drag by using cfd?


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