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-   -   closure coefficients in 2-eq. turb. models (http://www.cfd-online.com/Forums/main/6894-closure-coefficients-2-eq-turb-models.html)

Michael December 4, 2003 11:59

closure coefficients in 2-eq. turb. models
 
I am interested in varying the closure coefficients of a two-equation turbulence model for a given CFD simulation in order to see the effect (or lack of effect) from the corresponding coefficients. Is there a standard way to do this? Most coefficients are rather small ~0.01 to ~10, so randomly varying them, which would result in very large numbers as coefficient inputs, would necessitate the collection of a huge amount of data in order to see the effects on the flow field. Any help on this topic would be greatly appreciated.

Thanks in advance.

Jarmo Monttinen December 6, 2003 12:41

Re: closure coefficients in 2-eq. turb. models
 
I would suggest something along the lines that was done with the Spalart-Allmaras model (AIAA-92-0439). Apply this approach to whatever you wish to do with the model in the end and built from the simplest case up.

-- Jarmo

sylvain December 8, 2003 13:15

Re: closure coefficients in 2-eq. turb. models
 
First of all, you may try to solve your two equtaions models manually in very simple case :

Decay of homogeneous turbulence (U=0; k(t=0)>0; Eps(t=0)>0)

Growing of homogeneous turbulence under constant shear stress (dU/Dy >0; k(t=0)>0; Eps(t=0)>0)

Asymptotic boundary layer between two flat plane in the log low region (Production(k)=Eps), Du/Dy is known, uv is known...

Then you may see what is the effect of each constant and try to guess what should be their best variation domain.

As an example, forn the k-eps model :

Decay -> Ceps_2 (k propto t^(x), x depends on Ceps_2)

Homogeneus shear stress -> Ceps2-Ceps1; C_nu (uv/k(t->infinity) is known ...)

Boundary Layer : C_nu, Sigma_eps (see Patel for Sigma_eps)



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