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 run_cfd June 9, 2011 06:38

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

 dima June 9, 2011 09:53

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

 dima June 10, 2011 11:12

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

 run_cfd June 13, 2011 00:49

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... http://www.cfd-online.com/Forums/ope...implefoam.html.

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

 run_cfd June 13, 2011 05:38

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

 dima June 14, 2011 05:07

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

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