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yannossss January 12, 2011 11:45

Reduce Y+ values ?
Hi guys
I've got a little problem and I really hope someone could give me a clue

The assignment is about a centrifugal fan and the last question is "Compare the calculated wall shear stress with and without employing the boundary layer mesh on the wall of the volute. You are required to check the Y+ values to ensure the correct wall function implementation"

So, I've made the simulation for both fans (with and without boundary layer mesh).
Y+ values are perfect when the boundary layer mesh is applied and obviously they're not when boundary layer mesh is removed.

I asked my lecturer but his only answer was "there are many many ways to reduce the Y+" and it doesn't help at all

I've tried with the adapt tab and then Yplus/Ystar and then click on adapt but it doesnt really reduce the y+, it just adds more points and sometimes higher than the values I already got...

So I hope someone could help me on here.

Thank you

PS: I just read the 26th chapter of Fluent 6.3 user guide which is about the mesh adaptation. I've tried different things in Adapt - Y+/Y* and Adapt - Boundary, when I display the grid, I see that changes have been done but the Y+ doesn't go down.

Please help....

Rich1979 January 13, 2011 03:36

Try to use the fluent option Adjust boundary,which allows to increase the number of cells of the mesh near the wall.For example with a tri pave scheme from 1 triangle you get 4 smaller triangles.Increasing the cells near the wall you'll get a lesser value of y+ and so you could use for example Enhanced wall treatmente functions (if y+ is about 1).Hope to be helpful.

yannossss January 13, 2011 19:01

thanks a lot
thank you a lot lad
I finally realised my mistake thanks to "and so you could use for example Enhanced wall treatmente functions"

In fact, before I adaped the mesh and just right after checked Y+ values that didn't change

And 20 minutes ago I got the idea to initialize the problem again and run iterations and it worked ;)

Thank you very much...hope I'll get a good mark
Got to hand in it tomorrow. your answer was just on time


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