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

#1 
Guest
Posts: n/a

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 

#2 
Senior Member
Anne Gerdes
Join Date: Aug 2010
Location: Hamburg
Posts: 168
Rep Power: 9 
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 

#3 
New Member
Anonymous
Join Date: Aug 2012
Posts: 8
Rep Power: 7 
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 

#4 
Senior Member
Anne Gerdes
Join Date: Aug 2010
Location: Hamburg
Posts: 168
Rep Power: 9 
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 
Member
Peter
Join Date: Nov 2011
Posts: 46
Rep Power: 8 
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  
Senior Member
Anne Gerdes
Join Date: Aug 2010
Location: Hamburg
Posts: 168
Rep Power: 9 
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 

#7  
Member
Peter
Join Date: Nov 2011
Posts: 46
Rep Power: 8 
Quote:
Quote:


January 12, 2014, 21:07 

#8  
Member
Peter
Join Date: Nov 2011
Posts: 46
Rep Power: 8 
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 

#9 
Senior Member
Anne Gerdes
Join Date: Aug 2010
Location: Hamburg
Posts: 168
Rep Power: 9 
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  
Member
Peter
Join Date: Nov 2011
Posts: 46
Rep Power: 8 
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 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Effective Thermal Conductivity  Merlin  CFX  2  July 23, 2015 07:10 
thermal conductivity  Cirilo  Siemens  3  April 23, 2012 12:08 
Anisotropic thermal conductivity  Helger Dooley  CFX  2  September 1, 2005 08:52 
walls thermal conductivity  ana  Main CFD Forum  1  July 14, 2005 18:16 
thermal conductivity  Magnus Rohde  Phoenics  2  May 22, 2003 07:36 