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-   -   about Subgrid-scale model (http://www.cfd-online.com/Forums/openfoam-solving/79924-about-subgrid-scale-model.html)

impecca September 8, 2010 11:57

about Subgrid-scale model
 
Hi, foamers.

Is there anyone who can recommend me a SGS model for the airfoil case?
(of course LES, Reynolds number is less than 100,000)
Based on some literature reviews, some works are done with 'Dynamic smagorinsky' model and some works are done with 'Mixed-sclae model' ( Sagaut, P. 1996 : Numerical simulations of separated flows with subgrid models) or 'Mixed-time model' (Inagaki et al. 2005 : A Mixed-time-scale SGS model with fixed model - parameters for practical LES).


I've checked 'dynamic Smagorinsky model' in openfoam but one line (below) is ambiguous in the dynSmagorinsky.C file.


00060 dimensionedScalar MMMM = average(magSqr(MM));


here I don't understand what 'average' means. Does it mean averaging in whole domain? if it means averaging whole domain, this model doesn't seem so attractive since original model averaged only in homogeneous directions.

So I tried to look for 'Mixed-scale model' or 'Mixed-time model' in openfoam but these two models are not implemented yet. I am also wondering is there anyone who implemented these two models into openfoam.


To sum,
which sgs model do you recommend for the airfoil case ?
what is the 'average' mean in the 'dynamic Smagorinsky model' ?
Is there anyone who implement 'Mixed -scale model' or 'Mixed-time model' into the openfoam ?

Thanks in advance

Yusik

alberto September 9, 2010 10:26

Quote:

Originally Posted by impecca (Post 274477)
I've checked 'dynamic Smagorinsky model' in openfoam but one line (below) is ambiguous in the dynSmagorinsky.C file.


00060 dimensionedScalar MMMM = average(magSqr(MM));


here I don't understand what 'average' means. Does it mean averaging in whole domain? if it means averaging whole domain, this model doesn't seem so attractive since original model averaged only in homogeneous directions.

The homogeneous direction does not exist in general cases. As a consequence who implemented the model decided to average on the domain. You can easily replace the average with a local average, as done by many authors in the literature. It means changing only a few lines of the code.

Similarly, the mixed-time model simply redefines the SGS viscosity as a function of a certain time-scale, with some theoretical advantage. You could implement it by starting from an existing model (like the dynamic one) in OF.

Best,

impecca September 12, 2010 13:47

wrong questions sorry

zxj160 December 20, 2013 07:54

Quote:

Originally Posted by alberto (Post 274612)

Similarly, the mixed-time model simply redefines the SGS viscosity as a function of a certain time-scale, with some theoretical advantage. You could implement it by starting from an existing model (like the dynamic one) in OF.

Best,

Hi Alberto,
Could you suggest a related tutorial case? I am tring to using the dynamic Smagorinsky model, but without success.

My best regards,
Jian

zxj160 December 20, 2013 11:36

Quote:

Originally Posted by alberto (Post 274612)

Similarly, the mixed-time model simply redefines the SGS viscosity as a function of a certain time-scale, with some theoretical advantage. You could implement it by starting from an existing model (like the dynamic one) in OF.

Best,

Hi Alberto,
Could you suggest a related tutorial case? I am tring to using the dynamic Smagorinsky model, but without success.

My best regards,
Jian


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