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-   -   turn off wall functions in Transition SST model? (http://www.cfd-online.com/Forums/fluent/102118-turn-off-wall-functions-transition-sst-model.html)

 johnp May 22, 2012 17:23

turn off wall functions in Transition SST model?

Hello,

I would like to turn off the wall functions in the new Transition SST turbulence model in FLUENT. Most of my experience has been with the SST k-omega model. When I turn off the wall functions, I use the command:

(rpsetvar 'kw-set-wall-w? #t)

Is there a similar command to turn off the wall functions for the transition model? I can't seem to track down the source for the command for the k-omega (but it works).

The flow problem I am looking at is the impingement of a submerged circular jet on a normal, flat plate (jet height/nozzle diameter = 15). The fluid is water and the jet Reynolds number is roughly 40,000. Since this problem should contain both laminar and turbulent flow, I am curious how the transition model will compare with the SST k-omega. The main quantity of interest is the wall shear stress in the impingement region. any suggestions are welcome. Thanks,

john

 Far May 23, 2012 01:20

Yes. Use y+ below 1 and wall function will be turned off!!!

PS. Transition model works only for Y+ < 1

 johnp May 23, 2012 12:05

Thanks for the reply. I'm glad to hear that the wall functions turn off automatically. I was surprised when I found that FLUENT will use wall functions with the SST k-omega regardless of y+.

 Far May 23, 2012 12:31

http://www.ansys.com/Products/Simula...lence+Modeling

Quote:
 4.13.6.*Enhanced Wall Treatment ω-Equation (EWT-ω) Unlike the standard epsilon-equation, the omega-equation can be integrated through the viscous sublayer without the need for a two-layer approach. This feature can be utilized for a y*-insensitive wall treatment by blending the viscous sublayer formulation and the logarithmic layer formulation based on y*. This formulation is the default for all omega-equation based models.

 Bionico May 24, 2012 09:28

Hello!
I'd want to try SST Transitional model, but my system has y+ 2.5 in some zones: does this situation hardly affect the results? or can I use this model anyway? (I think that's impossible to refine more the mesh because of memory limits...)

 Far May 24, 2012 09:47

No need to refine the mesh. Just put the first node below Y+< 1. This is mandatory. There are other restrictions are also there e.g. stream-wise refinement

 wanna88 November 13, 2014 05:40

Hi

May I know,

a) For transition SST 4 equations, in what conditions we should use the "Roughness correlation" as well as " Curvature Correction"?
b) Besides, how to calculate/specify for Geometry roughness height?

Thank you

Naima

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