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Hao February 17, 2009 01:00

hybrid RANS/LES in CFX?
Hi, does anybody know whether hybrid RANS/LES simulation is feasible in ANSYS CFX or not?

Glenn Horrocks February 17, 2009 17:57

Re: hybrid RANS/LES in CFX?

The SAS and DES turbulence models are hybrid RANS/LES models. I think you will find CFX is the best commercial code for hybrid RANS/LES models because of these options.

Glenn Horrocks

Hao February 20, 2009 01:31

Re: hybrid RANS/LES in CFX?
Thanks for the reply, Glenn. Is it possible to realize a zonal hrbrid RANS/LES simulation by using multiply domains in CFX?

Glenn Horrocks February 24, 2009 17:32

Re: hybrid RANS/LES in CFX?
Sorry, I don't know what you mean. Read the CFX documentation and/or talk to CFX support for further details of what is possible with SAS and DES.

Glenn Horrocks

Timon February 25, 2009 04:38

Re: hybrid RANS/LES in CFX?
I guess he means to ask if it's possible to assign different turbulence models for separated domains. If so: no this not possible, you need to use the same turbulence model everywhere.

The RANS/LES switch in DES is based on the local turbulence length scale and local grid scale, switching on LES when the grid is sufficiently fine to represent the local eddy size.

SAS is not a hybrid method, but basically an URANS method in which the resolved turbulence length is locally adaptive.

Note that there is a distinction between hybrid RANS-LES and DES. Hybrid RANS-LES is a zonal approach: SST in one domain and LES in the other domain. The SGS-model is then a typical LES-SGS model, e.g. Smagorinsky. DES is an adaptive approach, where all eddy sizes that cannot be represented by the grid are modeled with RANS. The SGS model used in LES-mode is RANS as well (as opposed to e.g. Smagorinsky in normal LES).

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