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May 9, 2006, 07:16 
Hello,
Im creating a case w

#1 
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Hello,
Im creating a case whera a fluid of incompressible fluid is beeing heated from a constant heat flux from one of the walls. As temperature B.C for that wall I have put upp the condition fixed gradien (uniform) which works fine. Th problem is which value to use for the konstant temperature gradient. Im using the formula deltaT=q''/kEff. The problem is to find a value for the constant kEff=kTurb+k (where kTurb is the problem) Deos anyone know how I can find this value out? Thanks /Erik 

November 25, 2011, 04:47 

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Anne Gerdes
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As far as I know k_eff = v/Pr + nu_t/Prt
where nu is the kinematic viscosity, nu_t the turbulent viscosity and Pr and Pr_t Prandtlnumber, laminar and turbulent, respectively. 

August 29, 2012, 18:47 

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Anonymous
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Hi Anne and Erik,
I'm new to OpenFOAM and CFD. I'm trying to determine the heat transfer from a problem I setup. It is a heated concentric cylinder problem that I solved with the kepsilon model with buoyantBoussinesqPimpleFoam. It appears to solve for kappat (kinematic turbulent thermal conductivity), k (turbulent kinetic energy), nut (turbulent viscosity), alphat (thermal diffusivity), epsilon (kinetic energy dissipation rate), and a few others. I'm a little lost as to what equation to use to get the effective thermal conductivity though. If I can get k_eff, I have a formula for my particular setup to get the heat transfer. But I'm stuck on how to get k_eff. Any suggestions? 

September 10, 2012, 06:05 

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Anne Gerdes
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Hey Tiffany,
kappa_eff is the sum of kappa_t and kappa. The ladder is computed from nu/Pr which are defined in constant/transportProperties. Kind Regards Anne 

December 29, 2013, 09:25 

#5 
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Peter
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Hi, Tiffany!
Have you solve your problem yet? I have a similar question. As mentioned by Anne, k_eff = v/Pr + nu_t/Prt, then I guess k_eff is not a constant because nu_t is not. Am I right? If it is so, then how to set up the temperature boundary condition for a give heat flux? Regards Peter 

January 8, 2014, 09:08 

#6  
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Anne Gerdes
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Hey Peter,
there are wall functions for kappat, namely Quote:
On the other boundaries you can set kappat to "calculated" as it is computed from nut, which is computed from the turbulent properties (omega, k, epsilon,...). You can also use "symmetryPlane" or "empty", depending on the case that you would like to simulate. Kind Regards Anne 

January 8, 2014, 21:10 

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Peter
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Quote:
Quote:


January 12, 2014, 21:07 

#8  
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Peter
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Hi, Anne!
Thank you for reply. Here is my kappt boundary: Quote:
By the way, my simulation seems to blow up after thousands of time steps and I have no idea what causes that. Could it be the fvSchemes? Regards Peter 

January 13, 2014, 04:32 

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Anne Gerdes
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Dear Peter,
I think if your mesh is fine enough you can set kappat like that. What kind of boundary is boundary "Top" in your case? In which sense does the simulation blow up? Residuals? Continuity error? 

January 13, 2014, 06:46 

#10  
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Peter
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Dear Anne,
"Top" is an open boundary which I treated the same way as the "outlet" boundary. This is U at "top" boundary: Quote:
Perhaps I should use the QUICK scheme for the discretization of the energy equation, the same way as a simulation work in literature. Thanks again for your reply. Best, Peter 

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