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Tubrulence model diffusion term ???

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Old   June 5, 2012, 05:37
Default Tubrulence model diffusion term ???
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Tobias Holzmann
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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
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File Type: pdf Turbulenzmodell_Diffusionterm.pdf (72.2 KB, 11 views)
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Old   June 5, 2012, 06:22
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Eysteinn Helgason
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Quote:
Originally Posted by Tobi View Post
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..
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Old   June 5, 2012, 07:21
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Tobias Holzmann
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Quote:
Originally Posted by eysteinn View Post
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 "
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