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-   -   y+ for k-omega = 30 ??? (http://www.cfd-online.com/Forums/fluent/40971-y-k-omega-30-a.html)

 Ralf Schmidt May 15, 2006 05:59

y+ for k-omega = 30 ???

Hi,

the Fluent Manual suggests to have the y+ for k-w within the log layer 30 < y+ < 300 - a value close to the lower bound is most desirable.

I do not know, if thats a good idea. I have bad results compared to the same msh with k-e and wall functions.

The other point is, that for y+ = 30, the first cell is ab. 10% of the charactersitic lenght (diamater of a cylinder in axial flow).

Any Ideas?

Ralf

 fanzhong Meng May 15, 2006 11:03

Re: y+ for k-omega = 30 ???

hi In Fluent user's manual,it is y* should be in the region between 30 to 300. not y+! If you want to use k-w model with enhanced wall treatment, you should alway keep your y+ close to 1. In this way, you can probably solve the boundary layer better!

fanzhong Meng

 Ralf Schmidt May 16, 2006 02:05

Re: y+ for k-omega = 30 ???

Hi!

Thanks for your reply. But: the Fluent Manual (FLUENT 6.2 Documentation) is very clear at this point:

node466, section 11.10.4

"Near-Wall Mesh Guidelines for the k- omega Models

...if [Transitional Flows] option is not active, then the mesh guidelines should be the same as for the wall functions"

and further on:

node463, section 11.10.1

"Near-Wall Mesh Guidelines for Wall Functions

For standard or non-equilibrium wall functions, each wall-adjacent cell's centroid should be located within the log-law layer, 30 < y+ < 300. A y+ value close to the lower bound y+ = 30 is most desirable."

Now, the question might be, if it is importand to have the "Transitional Flows option" not active for a cylinder in axial flow at Re = 20000 (based on cylinder Diameter)?

Any Idea???

Ralf

 Donald May 20, 2006 17:28

Re: y+ for k-omega = 30 ???

Fluent's k-omega model is not good, look at the formula from standford university. Use rsm instead.

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