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-   -   YPlus value -- CFX 5.7 (http://www.cfd-online.com/Forums/cfx/20842-yplus-value-cfx-5-7-a.html)

NeedHelp December 5, 2004 16:49

YPlus value -- CFX 5.7
 
I am doing flow through wall problems, I choose SST model for it, but SST model is good for Yplus value less than 2, the Yplus value I got is always bigger than 2, min I got is around 3, can I still use SST model?

Also sometimes I use more elements for mesh, but Yplus value got bigger, can somebody give some suggestions on Yplus value vs. mesh? and how it affect model selection and results?

Thanks.

Glenn Horrocks December 5, 2004 17:39

Re: YPlus value -- CFX 5.7
 
Hi,

The SST model with automatic wall functions is fine for y+ up to several hundred. Of course it will be in wall function mode rather than integrate to the wall mode for these large y+ and that may or may not be appropriate for you simulation depending on what you are doing.

Glenn Horrocks

James Date December 6, 2004 07:25

Re: YPlus value -- CFX 5.7
 
Yep,

Like Glenn said, the SST will just run using the standard wall function approach in the Y+ > 1 range. Your best bet is to go back and reduce your first cell size and re-run the simulation and check the Y+. I usually do one or two Y+ scoping runs (solving for 10 or so iterations) to get a feel for the Y+, subsequently modifying the mesh density near the wall to get the correct Y+.

Regards

James

Susn December 7, 2004 21:46

Re: YPlus value -- CFX 5.7
 
Hi, I am puzzled in y+, Could you tell me the rang of y+ when using different models? Susn


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