[luca]

maybe I'm not right, but in LaunderSharma compressible model Epsilon equation, we have that :

... + fvm::SuSp((C3 - 2.0/3.0*C1)*rho_*divU, epsilon_)

and in the default turbulenceProperties file we have:

C3 = -0.33

I think that we have to change the default value of C3 as:

C3 = 0.33

or we have to change the formulation of Epsilon eq. as:

... + fvm::SuSp((- C3 - 2.0/3.0*C1)*rho_*divU, epsilon_) or

... - fvm::SuSp(( C3 + 2.0/3.0*C1)*rho_*divU, epsilon_)

because the term C3*rho_*divU has to be positive in RHS of Epsilon equation.

I'm right ?!?

Luca

[mattijs]

Please post a bug report (in OpenFOAM-bugs) if you think it is incorrect.

[hjasak]

Nope - this is to do with the C3 term in engines simulations, where it turns out that a "small positive constant" C3 actually needs to be negative to get the right behaviour. Find an old-ish engines modelling Thesis from Imperial College and you will find the details.

Hrv

[luca]

so why we have different formulation in epsilon Eqn. between LaunderSharmaKE and kEpsilon turbulence model, (except f2() term)

kEpsilon

C1*G*epsilon_/k_
- fvm::SuSp(((2.0/3.0)*C1 + C3)*rho_*divU, epsilon_)
- fvm::Sp(C2*rho_*epsilon_/k_, epsilon_)


LaunderSharmaKE

C1*G*epsilon_/k_
+ fvm::SuSp((C3 - 2.0/3.0*C1)*rho_*divU, epsilon_)
- fvm::Sp(C2*f2()*rho_*epsilon_/k_, epsilon_)


Luca

[hjasak]

In that case: hmm. What does the original paper say?

Hrv