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September 20, 2010, 10:50 
Viscous terms in rhoCentralFoam

#1  
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Florian Ettner
Join Date: Mar 2009
Location: Munich, Germany
Posts: 41
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I have a few questions on the viscous terms in rhoCentralFoam. In the source code, the energy equation looks like this: Quote:
2. I think I understand the heat conduction in line 200. What kind of conduction of internal energy is in lines 198199 ? 3. What is the use of the repeated use of fvm and fvc discretisation of the same expressions in lines 197199? Why is it not applied to the heat conduction in line 200? I'd be glad if anybody could help me understanding this issue. It would be quite important to me, as I currently work on extending the solver to reactive flows. Thank you in advance! 

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March 14, 2012, 05:47 

#2 
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Alexander
Join Date: Mar 2009
Posts: 44
Rep Power: 10 
Good day to everyone!
I also use rhoCentralFoam and I am interesting in questions about viscous dissipation. And about your questions: 2. "I think I understand the heat conduction in line 200. What kind of conduction of internal energy is in lines 198199 ?" I want to know answer too =) Probably, it is turbulent heat transfer. In new version of rhoCentralFoam it is written as Code:
 fvm::laplacian(turbulence>alphaEff(), e) + fvc::laplacian(turbulence>alpha(), e) Answer is simple: there is solving of "corrector" step, because "fvm" means that for this term the matrix is prepared and the system wil be solved ("m" for "matrix"). Term with "fvc" means that term will be calculated in explicit way (the right part of matrix equation; "c" for "calculate"). So, lines 197200 is the corrector which include the influence of thermal conductivity part in energy equation. Why turbulence is there? I do not know. I hope, alpha is zero for laminar flow =) But the main question: is the dissipation correctly taken into account? Because in my laminar transsonic tests (with low Reynolds number about 100) heating due to dissipation is absent (although it should be meaningful) =( 

March 21, 2012, 04:05 

#3 
Member
Alexander
Join Date: Mar 2009
Posts: 44
Rep Power: 10 
I've just found that Prandtl number in rhoCentralFoam is always 1 (independent of what you have set in constant/thermophysicalProperties).
See bug http://www.openfoam.org/mantisbt/view.php?id=475 

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