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-   -   large y+ with enhanced wall treatment (https://www.cfd-online.com/Forums/fluent/89033-large-y-enhanced-wall-treatment.html)

 keryfluid June 1, 2011 22:00

large y+ with enhanced wall treatment

Hi everyone,
In fluent help it's said that though enhanced wall treatment requires y+~1, it should not be too bad if y+ is larger. I've been calculating heat transfer in a ribbed channel with the RNG k-e model and the enhance wall treatment. I found y+ on the edge of the rib sometimes can be higher than 5 but most of the wall has a yplus of the order of 1. I'm trying to figure out if this is ok, can you give me some advice?

 Amir June 2, 2011 02:28

Hi Kan,
you have to notice the average y+ over walls.(you can calculate it in FLUENT) it is said that in enhanced wall function, y+ should be lower than 5 but in many cases 10 is also acceptable, but not more than that.
the another important tip that you have to notice is that in such problems (heat transfer in turbulent flow) it's much more better to use node based gradients instead of cell based.

 Far June 2, 2011 05:15

basically enhanced wall treatment is made with the intension to lower the yplus effects on results (that is yplus sensitivity). So If you have the yplus ranging from 1 to 10 at different parts, your results will not change.

In other words if you have meshes with yplus less than 1 every where and second mesh with yplus varying fron 1 to 10, the results will always be same

 keryfluid June 2, 2011 10:05

Quote:
 Originally Posted by Amir (Post 310232) Hi Kan, you have to notice the average y+ over walls.(you can calculate it in FLUENT) it is said that in enhanced wall function, y+ should be lower than 5 but in many cases 10 is also acceptable, but not more than that. the another important tip that you have to notice is that in such problems (heat transfer in turbulent flow) it's much more better to use node based gradients instead of cell based.
thanks, I will have a try.

 A7A May 7, 2012 05:19

2 Attachment(s)
Hi,

I am also simulating a 2d ribbed channel heat transfer problem(to simplify the solution i simulate half of the channel), and i am using SST k-w model, but when i compare my Nusselt number with experimental Nusslet number i get wrong results:confused:.

I am using air temperature as temperature reference value, and the hydraulic diameter of the channel as a length reference value.

This a picture of mesh and geometry.

Any help will be totally appreciated.