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-   -   Minimum Y+? (http://www.cfd-online.com/Forums/fluent/48046-minimum-y.html)

Tom April 25, 2008 07:04

Minimum Y+?
 
Hi,

Im trying to model flow about a protrution where couette flow is present and was looking at near wall meshing.

From what I've read a Y+ of around 30-100 is optimum in most cases. My meshing currently has a Y+ ranging from around 1-10. Is this a problem? Does it matter that my boundary layers are over refined? Will it mess up the solver's near wall treatment? From what Ive read Y+ is used to approximate a boundary layer profile from minimal points, will fluent use only my first couple of points to approximate the boundary layer instead of the many that are in fact placed in there? If so would it work to simply use adaptive meshing to coarsen the grid to a minimum Y+ of 30?

Any help would be greatly appreciated.

Cheers,

Tom

AAA April 25, 2008 18:38

Re: Minimum Y+?
 
Hi

according to the manual, y+ must be in the 30-300 range if you are using the standard wall function, and in the 1-5 range ir you are using the enhanced wall treatment. I suggest you shift to the enhanced wall treatment and start y+ adaption till you get a value in the 1-5 range, otherwise, you probabely have to go back to Gambit and re-mesh. Unfortunately, you can only coarsen your mesh if you have previously refined it in the same case.

Regards

AAA

Tom April 25, 2008 19:21

Re: Minimum Y+?
 
Thanks for your help! I did wonder why it wasn't adapting any cells when I tried to coarsen the grid! And switching to enhanced wall treatment certainly seems like a better option than going back to gambit!

AAA April 25, 2008 19:40

Re: Minimum Y+?
 
Hi again

This site might be of help to you too

http://geolab.larc.nasa.gov/APPS/YPlus/

Regards

AAA


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