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 June 9, 2011, 06:38 About rhoPorousSimpleFoam #1 New Member   Manoj L Das Join Date: Mar 2011 Location: Calcutta, India Posts: 25 Rep Power: 6 Hi, I have a small question. If 'rhoPorousSimpleFoam' is a steady state solver then why it asks for 'deltaT'? If it is a pseudo time step then What will be the difference in solution if we run the case with different deltaT, say the same case is run once with dt=1sec and once with say dt= 0.001 sec?? Further, as in the governing equation the porosity comes only in time derivative (ddt) term, then how it considers the porosity if it is a steady state solver? Regards, MLD

 June 9, 2011, 09:53 #2 New Member   Dima Risch Join Date: Jun 2011 Location: Cologne Posts: 22 Rep Power: 6 Hi, MLD i think deltaT is set to calculate the total amount of iterations startTime 0; endTime 50; deltaT 1; should be the same like startTime 0; endTime 5; deltaT 0.1; (but not sure) therefore writeInterval had to be >= 1 in what governing equation do you find the porosity comes only in time derivative (ddt) term like i understand you can set the porousZone/porosity Explizit or Implizit if(pressureImplicitPorosity){...} else(...){...} in the UEqn and pEqn pressureImplicitPorosity is defined in createFields and is set ON with the nUCorrectors entry in the fvSolution the porosity is considered in the UEqn by pZones.addResistance(UEqn()); but i am new to OpenFoam and to fluiddynamics and this is what i understand, please correct me, if i am wrong. regards, Dima

 June 10, 2011, 11:12 #3 New Member   Dima Risch Join Date: Jun 2011 Location: Cologne Posts: 22 Rep Power: 6 Hi, MLD, its me again now i found the governing equation you talked about, and i understand why you ask this so i take a look at the porousZone files in /OpenFOAM/OpenFOAM-1.7.1/src/finiteVolume/cfdTools/general/porousMedia/ and in the porousZone.H i found Code: ``` //- porosity of the zone (0 < porosity <= 1) // Placeholder for treatment of temporal terms. // Currently unused. scalar porosity_;``` so in a steadystate solver the time derivative doesn't matter and therefore only the source term which is represented in the Darcy-Forchheimer law is important regards, Dima

 June 13, 2011, 00:49 #4 New Member   Manoj L Das Join Date: Mar 2011 Location: Calcutta, India Posts: 25 Rep Power: 6 Hi Dima, Thanks for your quick replies. And you are right, I was also studying the codes of 'rhoPorousSimleFoam' and found that it does not consider the porosity 'phi' explicitly, but it considers the superficial velocity instead. Check also the following link... RhoExplicitPorousSimpleFoam. In my case considering only the porous drag is not enough and at some point of time I would have to use another solver named 'rhoPorousMRFSimpleFoam' which seems to be a transient solver for porosity. We can share our experiences. In fact my projects requirements are beyond the existing solver capabilities in OF and after getting the results from the existing solvers I would like to modify the existing solvers for my project needs, which would consider the transient porosity from DEM (discrete element modeling). Regards, -MLD

 June 13, 2011, 05:38 #5 New Member   Manoj L Das Join Date: Mar 2011 Location: Calcutta, India Posts: 25 Rep Power: 6 Hi, What form of Energy euation is solved in rhoPorousSimpleFoam. I mean, does it takes the heat transfer between fluid and solid parts. And if yes then where it asks for the thermal conductivities of fluid and solid. See the part of the code in file hEqn.H : 00001 { 00002 fvScalarMatrix hEqn 00003 ( 00004 fvm::div(phi, h) 00005 - fvm::Sp(fvc::div(phi), h) 00006 - fvm::laplacian(turbulence->alphaEff(), h) 00007 == 00008 fvc::div(phi/fvc::interpolate(rho)*fvc::interpolate(p, "div(U,p)")) 00009 - p*fvc::div(phi/fvc::interpolate(rho)) 00010 ); Here, what it refer to 'alphaEff()', is it thermal diffusivity?? The question may be stupid as I ma new user of this kind of code. Regards, MLD

June 14, 2011, 05:07
#6
New Member

Dima Risch
Join Date: Jun 2011
Location: Cologne
Posts: 22
Rep Power: 6
Hi,

i think you are right with the 'alphaEff()' is the thermal diffusivity.

EDIT: in e.g. src/turbulenceModels/compressible/RAS/kEpsilon/kEpsilon.H
Quote:
 //- Return the effective turbulent thermal diffusivity virtual tmp alphaEff() const { return tmp ( new volScalarField("alphaEff", alphat_ + alpha()) ); }
what form of Energy equation is solved i am not sure too, but i think it treats with just one "region" (fluid).

maybe chtMultiRegionFoam takes both fluid and solid in its Energy/Temperature Eqn.

would be nice, if someone who is familiar with that could reply

regards, Dima

Last edited by dima; June 14, 2011 at 06:13.

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