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How to exploit SGS kinetic energy with Smagorinsky model in LES

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Old   November 3, 2014, 14:06
Default How to exploit SGS kinetic energy with Smagorinsky model in LES
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Bobi
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Greetings Foamers

I have performed a LES simulation in a cylindrical grid employing Smagorinsky model. I want to find out the quantity of the SGS kinetic energy. By searching a bit in this location:
$Foamsrc/ turbulenceModels/compressible/LES/Smagorinsky/Smagorinsky.H file in O.F-2.1.x, we can see that

Code:
\verbatim

        B = 2/3*k*I - 2*nuSgs*dev(D)

    where

        D = symm(grad(U));
        k from rho*D:B + ce*rho*k^3/2/delta = 0
        muSgs = ck*rho*sqrt(k)*delta
    \endverbatim
and also

Code:
    //- Return SGS kinetic energy
        //  calculated from the given velocity gradient
        tmp<volScalarField> k(const tmp<volTensorField>& gradU) const
        {
            volSymmTensorField D(symm(gradU));

            volScalarField a(ce_/delta());
            volScalarField b((2.0/3.0)*tr(D));
            volScalarField c(2*ck_*delta()*(dev(D) && D));

            return sqr((-b + sqrt(sqr(b) + 4*a*c))/(2*a));
        }

        //- Return SGS kinetic energy
The above lines point out that the SGS kinetic energy is computed in Smagorinsky approach. However, this variable is not written down during simulation. I have finished my simulation and I want to find a way to exploit this variable out of my results.

I think the k file in 0 folder at the start of solution was SGS kinetic energy as well.

Would somebody hint me that how can I exploit it out of my solution? Since the k file is no longer saved in time steps after starting solution.

Best,

Bobi
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Old   November 10, 2014, 17:18
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Hi Bobi,

I can't think of a straight forward way of computing this, without coding. Therefore, I moved your thread to the programming sub-forum.

You'll need look at least 2 utilities for ideas:
The idea is that you need to call the method "k()", instead of "R()".
But the detail is that the "R" utility is meant for RAS, which is why I mentioned "yPlusLESWCompressible".

Best regards,
Bruno
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Old   November 11, 2014, 01:16
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Dear Bruno

Many Thanks.

I am going to look into your hints.

Best Regards
Bobi
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Old   December 14, 2014, 07:58
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Dear Bruno

I have been through your written utility:"yPlusLESWCompressible"

I tried to do sth similar for the k_Sgs in Smagorinsky-based LES. However, it was a bit confusing for me . According to the formula :
k_Sgs=\left(\frac{\mu_Sgs}{\rho \, C_s \, \Delta}\right)^{2}

\rho comes from combustion (flameletFoam), \mu_Sgs comes from LES simulation (compressible flow solver). C_S is a constant parameter and \Delta is lesmodel::delta.

Is it possible for you to write a similar utility as "yPlusLESWCompressible" for k_Sgs in Smagorinsky approach which would be very useful for students working with Smagorinsky-based LES approach?

Just one point: Due to variations of thermodynamic formats between O.F 2.1.x and O.F. 2.3.x , Is it possible that the coming utility works with O.F. 2.1.x as well. Since lots of Foamers (like me) are still working with 2.1.x format.

Best Regards,

Bobi

Last edited by babakflame; December 14, 2014 at 09:08.
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