# Physical model: MRF RANS

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 January 31, 2014, 17:11 Physical model: MRF RANS #1 Member   Julian Langowski Join Date: May 2011 Location: Bremen, Germany Posts: 91 Rep Power: 15 Dear Foamers, again I have a question. I am simulating a wind turbine, using SIMPLE, the MRF approach with a 120° wedge and cyclic boundaries and RANS (kOmegaSST) turbulence modelling. Currently I am trying to figure out the exact physical equations I am actually using. I do know and understand: - the Navier Stokes equation and its RANS formulation - the formulation of the Navier Stokes equation in its MRF formuation (from here: http://openfoamwiki.net/index.php/Se...RF_development) What I don't understand: - How do both formulations look like in combination? - Does MRFSource in fvOptions only add the Coriolis term? - Would the MRF approach work for unsteady flows? As I understand, for unsteady flow there have to be considered further time-dependent terms. If somebody knows a helpful reference or already has figured it out, I would be greatful for any help. I am not very experienced in reading the source code, but I am also thankful for hints, where in the code to look. Best regards Julian __________________ πάντα ῥεῖ - Heraclitus

 February 5, 2014, 10:22 #2 Member   Julian Langowski Join Date: May 2011 Location: Bremen, Germany Posts: 91 Rep Power: 15 Hi, my current thoughts: The formula looks like the one described in the link above, but instead of kinematic viscosity (nu) I simply have (nu + nut). Does that sound right? Best regards Julian __________________ πάντα ῥεῖ - Heraclitus

 February 5, 2014, 10:25 #3 New Member   Farhad N. Join Date: Apr 2010 Posts: 6 Rep Power: 16 as far as I know you can use pimpleFoam (an unsteady solver) with fvOption where you'll be able to add MRF zones. I believe you can use any turbulence model available with pimple. best

 February 15, 2014, 08:21 #4 Member   Julian Langowski Join Date: May 2011 Location: Bremen, Germany Posts: 91 Rep Power: 15 Dear farhad, thanks for your reply. Good to know, that fvOptions does work with pimple, too. Any other suggestions, how the Navier Stokes equation looks in the combined MRF + RANS formulation? Best regards Julian __________________ πάντα ῥεῖ - Heraclitus

February 17, 2014, 06:14
#5
Senior Member

Gerhard Holzinger
Join Date: Feb 2012
Location: Austria
Posts: 339
Rep Power: 28
Quote:
 Originally Posted by Ruli Dear Foamers, What I don't understand: - Does MRFSource in fvOptions only add the Coriolis term? Best regards Julian
Hi,

the file MRFZone.C contains a method called correctBoundaryVelocity(). There the velocity at all boundaries within the MRFZone are corrected, i.e. the solid body rotation is applied.

Code:
```void Foam::MRFZone::correctBoundaryVelocity(volVectorField& U) const
{
const vector Omega = this->Omega();

// Included patches
forAll(includedFaces_, patchi)
{
const vectorField& patchC = mesh_.Cf().boundaryField()[patchi];

vectorField pfld(U.boundaryField()[patchi]);

forAll(includedFaces_[patchi], i)
{
label patchFacei = includedFaces_[patchi][i];

pfld[patchFacei] = (Omega ^ (patchC[patchFacei] - origin_));
}

U.boundaryField()[patchi] == pfld;
}
}```

 Tags cyclic, mrf, rans, simple, wind turbine