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large y+ with enhanced wall treatment

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Old   June 1, 2011, 22:00
Exclamation large y+ with enhanced wall treatment
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Kan Rui
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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?
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Old   June 2, 2011, 02:28
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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.
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Old   June 2, 2011, 05:15
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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
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Old   June 2, 2011, 10:05
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Kan Rui
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Quote:
Originally Posted by Amir View Post
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.
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Old   May 7, 2012, 05:19
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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.

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.
Thank you in advance.
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