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-   -   Germano dynamic LES model (http://www.cfd-online.com/Forums/main/4379-germano-dynamic-les-model.html)

Tim February 5, 2002 12:43

Germano dynamic LES model
 
Hi,

I am having some problems with The Germano dynamic Smagorinsky model and wonder if anyone out there has any experience with it. I am not sure how to obatin test scale strains and velocities from the grid scale information I have. I would be grateful if anyone can offer any advice.

Tim.

Jongdae Kim February 5, 2002 17:15

Re: Germano dynamic LES model
 
I'm using only Standard Smagorinsky model. I just know a little bit on the dynamic model. I'll describe what I know step by step. I hope this would be help.

1. Along the homogeneous directions, double your cell size. Consider these enlarged control volume as your test grid. Here, homogeneous directions mean that cell sizes are equal in these direction.

2. And then do filtering : if you use top-hat filter, just do the averaging along the homogeneous direction. In the enlarged control volume, you'll have at three velocities. So you can get test filtered velocity from those three. Now you can get test filtered velocities.

3. Now you can calulate Cs(x,y,z,t) based on Germano identity.

If you don't have homogeneous directions, I'm not sure how to calculate exactly. Time could be a kind of homogeneous direction.

Some cases (including my problems. I mentioned a few days ago on this topic), LES using just Standard Smagorinsky model is reasonable tool. I'm not sure what is your topic. But at first why don't you try simple model and if the results are not satisfactory, please try advanced model.

Jongdae Kim.


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