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Old   February 24, 2004, 15:36
Default LES
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I am trying to set up a large Eddy similation in CFX5.6 and I could not get any write up on it. Is there any tutorial on using it in CFX5.6 ? or any one with experience setting one up who can give me some guidance ?
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Old   February 24, 2004, 17:03
Default Re: LES
Glenn Horrocks
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Hi Meri,

I have no experience with it, however you may be interested to know that there is a DES model (detached eddy simulation) coming in the next release, 5.7. It uses a RANS formulation in attached boundary layers, and goes to LES for the large eddy turbulent structures. I think there was a paper put on the CFX community web site about it a few weeks ago.

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Old   March 14, 2004, 07:07
Default Re: LES
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Hi Glenn / Meri, there is a paper on the DES setup and I believe there is also the CCL file on the CFX comunity web site telling you how to setup the DES model in CFX5.6 - its very simple, however there are lots of meshing issues. Unlike LES where the mesh is generally fine all over with DES you have to be more careful as a fine mesh can cause a trip in the equations, changing them from RANS to LES just due to the mesh resolution. Dr Menter has papers on this and has also implamented a means of limiting this effect. I'd suggest reading the presentations on the FLOWMANIA web site (see useful sites on the cfd-online website).

As for setting up an LES model, again that is fairly easy. Attnetion should ba placed on mesh and inlet boundary conditions. The model obviously has to be transient so time stepping is an issue. Check out the main forum to answer lots of these types of questions. But the basic setup in CFX56 is just a case of choosing transient simulation and then the right turbulence model. There are also functions in place to extract RMS values from results etc and a whole lot of other statistical data which you will probably need.

I hope this helps, I'm no expert, just have read the documentation, tried a few runs and read a whole load of LES / DES stuff.

Good luck

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