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Viscosity ratio in gammatheta transition model based on kw sst turb model 

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June 6, 2012, 06:24 
Viscosity ratio in gammatheta transition model based on kw sst turb model

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In Langtry's parer on gammatheta transition model,viscosity ratio is defined as rho*k/(w*mu),where mu is laminar viscosity and rho is density.however, in kw sst turb model,turbulence viscosity is not defined as rho*k/w but max( rho*k/w,something else). why viscosity ratio in gammatheta transition model is not calculated from turbMu/laminarMu ?
supplement:usually,turb model equations and transition model equations are solved alternately,so,i don't understand why not use turb viscosity directly that already given by turb model. Last edited by Qiaol618; June 6, 2012 at 23:36. Reason: additional explanation 

June 6, 2012, 21:51 

#2 
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Mehdi
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because Mut is the property that we want to obtain it, and we use turbulence model to do it. I think what you mention about viscosity ratio is used for initial and boundary conditions.
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June 6, 2012, 23:30 

#3 
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Maybe i didn't say my question clear.Transition model calculates viscosity ratio in the mentioned manner at every grid cell and time step.usually,turb model equations and transition model equations are solved alternately,so,i don't understand why not use turb viscosity directly that already given by turb model.


June 7, 2012, 00:36 

#4 
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I encourge you to ask this question directly Dr. Florain Menter florian.menter@ansys.com; martin.kuntz@ansys.com, robin.langtry@ansys.com and let us know as well.
http://www.ansys.com/staticassets/AN...Turbulence.pdf 

June 7, 2012, 02:48 

#5  
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Quote:
according what I understood from your question and what I have studied about gamma Retheta, transition model finally calculates effective gamma and this value is used in K equation in turbulence model for finding trigger of transition (this value shows if specific point is in turbulence region or not.) and Mut is abtained. so transition model doesn't calculate Mut. if you read it, please introduce me in which papre and which section.
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Best Regards; Mehdi Email: mb.pejvak[at]Gmail[dot]com 

June 7, 2012, 12:10 

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June 7, 2012, 13:53 

#7 
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Mehdi
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I think Mut=min(a1*k/w,a1*k/F2/S) is used only for preventing overprediction of shear stress in turbulence model in strong adverse pressure gradient (As menter mentioned in his paper) and used second term of this formula for this purpose. so I think it is not necessary to use it in Fonset in transition modeling.
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Best Regards; Mehdi Email: mb.pejvak[at]Gmail[dot]com 

June 9, 2012, 06:43 

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