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January 24, 2012, 21:32 
Turbulent heat flux through the wall

#1 
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Yuri Feldman
Join Date: Mar 2011
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Dear forum,
I am really confused about how I should compute heat flux through the static boundary in the presence of turbulent incompressible flow if I use the basic ke model. According to the heat transfer theory Q''=(k_lam+k_turb)(dT/dn), where k_lam is a some constant value of a certain fluid and k_turb=cp*miu_t/Pr_t. It looks like everything is clear : cp is known, the commonly used value of Pr_t is 0.85, miu_t is calculated from ke model. The twist is that the boundary value of miu_t (niu_t for incompressible flow) is set to zero (I am talking about buouantBoussinesqPimpleFoam tutorial for hotRoom). The same is done for the boundary value of miu_t in Fluent. Then it is completely unclear what is the difference between calculating of heat flux for laminar and turbulent flows. I will be very grateful if somebody clarifies this issue, many thanks, Yuri 

January 25, 2012, 14:34 

#2 
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Yuri Feldman
Join Date: Mar 2011
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please anybody can say his opinion,
I really need your help Last edited by feldy77; January 25, 2012 at 18:59. 

January 25, 2012, 18:50 

#3  
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Kai
Join Date: May 2010
Location: Stockholm
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k_turb
Quote:
And the temperature relies on the turbulent model you included although you will have the same gradient at the wall. I am sure temperature in the bulk is totally different between laminar and turbulent flows due to the different heat transfer coeff in the bulk.
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Kai 

January 25, 2012, 19:04 

#4 
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Yuri Feldman
Join Date: Mar 2011
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Kai,
Thank you for your reply. Maybe you can explain me then, why the openFoam utility wallHeatTransfer utilizes alafaeff whcich consists of turbulent amd laminar components and not jus uses the laminar component only Many thanks, yuri 

January 25, 2012, 19:21 

#5 
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Kai
Join Date: May 2010
Location: Stockholm
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It is all dependent on the expectation you have. The wall viscosity should be modelled actually. I can only say that the treatment of zero wall viscosity is rather crude. If you would like to model wall viscosity, plz refer to the file "wallViscosity.H" in the solver of bubbleFoam.
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Kai 

March 6, 2012, 08:33 

#6  
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Goutam Saha
Join Date: Dec 2011
Location: UK
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Quote:
Looking forward to see your reply. 

March 6, 2012, 14:33 

#7 
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A_R
Join Date: Jun 2009
Posts: 118
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Dear Foamers
for kepsilon model, you must use wallfunction for nut. and without it, the solution is not acceptable. 

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