topic Re: how do I view y+ when using IWF with k epsilon model in CFD Forum

how do I view y+ when using IWF with k epsilon model

Anonymous — Thu, 20 Aug 2020 18:38:37 GMT

How do I view y+ when using IWF with k-epsilon model?

I ran a model using k-epsilon turbulence model and intelligent wall formulation. When I tried to display y+, it showed 0 for all surfaces. How can I assess whether or not the boundary layer was modeled correctly?

Thanks!

MArk

Re: how do I view y+ when using IWF with k epsilon model

frederic.gaillard.7 — Thu, 20 Aug 2020 19:49:02 GMT

Hello Mark,

You can enable Y+ visualisation under the result quantities in the solver tab

How many iteration did you give to your scenario ?
Thx

Fred

Re: how do I view y+ when using IWF with k epsilon model

frederic.gaillard.7 — Thu, 20 Aug 2020 19:57:19 GMT

for k-epsilon your Y+ should lie between 35 and 350

for SST komega your Y+ should be lower than 1

hope it helps

Re: how do I view y+ when using IWF with k epsilon model

Anonymous — Thu, 20 Aug 2020 20:25:09 GMT

I'm able to visualize it now - not sure why it showed as all zero before.

Nonetheless, most of the surface of the model shows with a very low y+ (below 11). I have 5 wall layers, a layer factor of 0.62 and a layer gradation of 1.2. I would have thought I would have had better y+ values.

What is the benefit of the Intelligent wall formulation for the ke turbulence model? Does it allow for y+ values to be between 0 and 350, vs between 35 and 350?

BTW, I ran 804 iterations

Thanks!

Mark

Re: how do I view y+ when using IWF with k epsilon model

Anonymous — Thu, 20 Aug 2020 20:25:10 GMT

Thanks! Does that hold for when intelligent wall formulation is being used?

Re: how do I view y+ when using IWF with k epsilon model

frederic.gaillard.7 — Thu, 20 Aug 2020 22:12:23 GMT

Hello Mark,

The desired values of Y+ is directly link with the turbulence used. If you use k-epsilon model, Y+ must be in that interval otherwise the pressure drop will be under estimated (Y+<35) or over estimated (Y+>350)

this is what Autodesk had to say about the Intellignet Wall Formulation

''The Intelligent Wall Formulation reduces the sensitivity of results to the level of mesh refinement along the wall. It is enabled by default for SST k-omega.''

Hope it helps

Fred

Re: how do I view y+ when using IWF with k epsilon model

Anonymous — Fri, 21 Aug 2020 11:09:09 GMT

I understand, basically using IWF doesn't absolve me from the 35-350 y+ requirement.

My y+ values are unacceptably low. My understanding is that using the ke turbulence model, I should increase the layer factor to get my y+ values up to the acceptable range. Are there any rules of thumb / methodologies as to how to adjust the layer factor, or do I just bump it up via trial and error, completely rerun the model and see what the new y+ values are?

Thanks again!

Mark

Re: how do I view y+ when using IWF with k epsilon model

frederic.gaillard.7 — Fri, 21 Aug 2020 14:22:56 GMT

Hello Mark,

Try the basic and intermediate level and let me know how it goes.

For more information check out this video : Understanding Turbulence Model

Hope It Helps
Fred