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-   -   LES required y+ (http://www.cfd-online.com/Forums/main/77041-les-required-y.html)

zoozoozoo June 11, 2010 01:54

LES required y+
 
Hi everyone,

I'm using LES Smagorinsky. This turbulence model solves only the large eddies explicitly, and model the effect of the smaller and more universal eddies on the larger ones.

I was wondering, how good is this model for solving the viscous sub-layer? AND what is an appropriate y+ value. Do I need a y+ < 2 like for SST?

Every answer is appreciated.

cheers
zzz

siw June 11, 2010 06:36

To quote the paragraph "Boundary Layers" in the "Setting up an LES Simulation" section on page 108 of the ANSYS CFX-Solver Modeling Guide Release 12.1, ANSYS Inc., Canonsburg, PA.

"If the boundary layer structure is important, you should resolve it with at least 15 points across the boundary layer and with the first grid point at a position of approximately y+ = 1. Note however, that large aspect rations [sic] in the mesh are not suitable for LES. This often results in excessive resolution requirements for boundary layer flows".

zoozoozoo June 12, 2010 04:38

Thanks siw.
I couldn't find the ANSYS CFX-Solver Modeling Guide Release 12.1 on my system or in the internet. Where did you get that?
regards
zzz

siw June 12, 2010 05:23

I'm a CFX customer so it came with the software.

zoozoozoo June 12, 2010 06:08

I'm using Ansys CFX in the UNI computer lab. Probably have to ask my lecturer...
Thanks although
zzz

siw June 12, 2010 07:11

Go to Help in the CFX Launcher (I tend to use it standalone rather than in Workbench) and search using LES and you'll find it there.

zoozoozoo June 12, 2010 07:25

cheers siw,
that's it. I just tried to find it in the common ansys help. CFX Launcher - great.

Thanks a lot.
zzz


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