CFD Online Discussion Forums - Tubrulence model diffusion term ???

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Tubrulence model diffusion term ???

hi all together,

i have a question to the RNG-kEpsilon equation respectively to the diffusion term.

Well in the code there is the following equation:

Code:

// Dissipation equation

    tmp<fvScalarMatrix> epsEqn

    (

        fvm::ddt(rho_, epsilon_)

      + fvm::div(phi_, epsilon_)

      - fvm::laplacian(DepsilonEff(), epsilon_)

      ==

        (C1_ - R)*G*epsilon_/k_

      - fvm::SuSp(((2.0/3.0)*C1_ + C3_)*rho_*divU, epsilon_)

      - fvm::Sp(C2_*rho_*epsilon_/k_, epsilon_)

    );

especially to that code!!!

Code:

- fvm::laplacian(DepsilonEff(), epsilon_)

the diffusivity is calculated in the header file like:

Code:

mut_/sigmaEps_ + mu()

Thats all clear but I have that equation in my literature (pdf)
and (please correct me) if I set the diffusion term to the left and transform it I get:

Code:

mu() - mut_/sigmaEps

Hope I asked clearly.
Thx in advance,
tobi

Quote:

Originally Posted by Tobi (Post 364790)

hi all together,

i have a question to the RNG-kEpsilon equation respectively to the diffusion term.

Well in the code there is the following equation:

Code:

// Dissipation equation

    tmp<fvScalarMatrix> epsEqn

    (

        fvm::ddt(rho_, epsilon_)

      + fvm::div(phi_, epsilon_)

      - fvm::laplacian(DepsilonEff(), epsilon_)

      ==

        (C1_ - R)*G*epsilon_/k_

      - fvm::SuSp(((2.0/3.0)*C1_ + C3_)*rho_*divU, epsilon_)

      - fvm::Sp(C2_*rho_*epsilon_/k_, epsilon_)

    );

especially to that code!!!

Code:

- fvm::laplacian(DepsilonEff(), epsilon_)

the diffusivity is calculated in the header file like:

Code:

mut_/sigmaEps_ + mu()

Thats all clear but I have that equation in my literature (pdf)
and (please correct me) if I set the diffusion term to the left and transform it I get:

Code:

mu() - mut_/sigmaEps

Hope I asked clearly.
Thx in advance,
tobi

Hmm . . . my literature says nu+nu_t/sigma_epsilon not nu - nu_t/sigma_epsilon for the diffusion term in the epsilon eq..

Quote:

Originally Posted by eysteinn (Post 364797)

Hmm . . . my literature says nu+nu_t/sigma_epsilon not nu - nu_t/sigma_epsilon for the diffusion term in the epsilon eq..

Well thx for your replay!
I see that in the diffusion term for k its like " nu + nu_t/sigma_k"

I ll have a look at my bible "Ferziger" :)
"May be its just a mistake while copying things :D"