CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM (http://www.cfd-online.com/Forums/openfoam/)
-   -   Turbulence dampening due to magnetic field in LES and RAS (http://www.cfd-online.com/Forums/openfoam/76920-turbulence-dampening-due-magnetic-field-les-ras.html)

eelcovv June 8, 2010 11:35

Turbulence dampening due to magnetic field in LES and RAS
 
Dear Foamers,

I have a question regarding the modification of turbulence due to a magnetic field. I want to dampen the eddy viscosity with a dampening term which depends on the B field.

For an LES I have already achieved this on the solver level by defining a new nuSgsDamped field and multiply it by the dampening factor

nuSgsDampend=nuSgs*exp(-(sigma/rho)*sqr(Cm*nuSgs->delta())*magSqr(B)/(nuSgs+nutSgs_small))

so that for large B fields the nuSgsDmp goes to zero.

My solver was set up in a LES context, but now I want to make it more generic in either a RAS or LES context, just as described for BuoyantBoussinesqPisoFoam:

http://openfoamwiki.net/index.php/Bu...LES_Capability

However, in the RAS context nuSgs->delta() does not excist and I need an alternative dampening based on for instance the eddy frequency

nuEffDampend=nuEff*exp(-(sigma/rho)*magSqr(B)/(omega+omega_small))

In order words, depending on either RAS or LES is used, an other dampening term is required. If I try to compile with the turbulence.H in stead of LESModel.H, the delta() function is not recognised anymore.

I am affraid I am running in some real advance OpenFOAM stuff. I am hoping on some advise how to approach this. Would it be best to create two different solvers? One based on LES, one on RAS ? I prefer not to. I want to swtich my run between RAS and LES just as is possible now for pimpleFoam (which also allows both LES and RAS).

Another way would to move the turbulent dampening due to the B field to the turbulenceModel level. Then I just need to define two turbulenceModels, one LES turbulence model called for instance SmagorinskyBdamped, and one for LES called kOmegaSTTBdamped. In that way I only have to change the turbulenceProperties dictionary when switching from LES to RAS.

Problem is that in the modification on turbulence level, I need to pass the values of the B field and also sigma (conductivity) etc to the turbulence model, and I would run into issues described by Thomas and Marc in this thread

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

This seems all a bit complicated to me. Again the question: is there somebody with an example of passing a field to a turbulence model ? Or is this very difficult, and should I better stick to the solver level instead of defining new turbulence models ? Hopefully somebody can give my some advice, or even a example (Thomas Baumann, do you happen to have an example of your T modified turbulence model).

Any hints appreciated

Kind regards,

Eelco


All times are GMT -4. The time now is 10:47.