# Viscous terms in rhoCentralFoam

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

September 20, 2010, 10:50
Viscous terms in rhoCentralFoam
#1
Member

Florian Ettner
Join Date: Mar 2009
Location: Munich, Germany
Posts: 41
Rep Power: 9
Dear Foamers,
I have a few questions on the viscous terms in rhoCentralFoam. In the source code, the energy equation looks like this:

Quote:
 00176 solve 00177 ( 00178 fvm::ddt(rhoE) 00179 + fvc::div(phiEp) 00180 - fvc::div(sigmaDotU) 00181 ); 00182 00183 e = rhoE/rho - 0.5*magSqr(U); 00184 e.correctBoundaryConditions(); 00185 thermo.correct(); 00186 rhoE.boundaryField() = 00187 rho.boundaryField()* 00188 ( 00189 e.boundaryField() + 0.5*magSqr(U.boundaryField()) 00190 ); 00191 00192 if (!inviscid) 00193 { 00194 volScalarField k("k", thermo.Cp()*mu/Pr); 00195 solve 00196 ( 00197 fvm::ddt(rho, e) - fvc::ddt(rho, e) 00198 - fvm::laplacian(thermo.alpha(), e) 00199 + fvc::laplacian(thermo.alpha(), e) 00200 - fvc::laplacian(k, T) 00201 ); 00202 thermo.correct(); 00203 rhoE = rho*(e + 0.5*magSqr(U)); 00204 }
1. Why is the viscous term "sigmaDotU" included in the inviscid equation?
2. I think I understand the heat conduction in line 200. What kind of conduction of internal energy is in lines 198-199 ?
3. What is the use of the repeated use of fvm and fvc discretisation of the same expressions in lines 197-199? 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!

 March 14, 2012, 05:47 #2 Member   Alexander Join Date: Mar 2009 Posts: 41 Rep Power: 9 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 198-199 ?" 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)``` 3. "What is the use of the repeated use of fvm and fvc discretisation of the same expressions in lines 197-199?" 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 197-200 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 trans-sonic 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: 41 Rep Power: 9 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

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post nikosb Main CFD Forum 0 January 17, 2010 17:07 titio OpenFOAM Running, Solving & CFD 0 March 19, 2009 17:02 andy Main CFD Forum 7 June 16, 2006 11:38 Michael Halls-Moore Main CFD Forum 0 April 3, 2006 07:52 Brindaban Ghosh Main CFD Forum 2 June 24, 2000 04:22

All times are GMT -4. The time now is 00:00.

 Contact Us - CFD Online - Top