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Wall Functions & Turbulence Models Query [y plus ranges]

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Old   August 14, 2018, 15:37
Question Wall Functions & Turbulence Models Query [y plus ranges]
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Hi I'm trying to understand the wall functions and turbulence models and the requirements to satisfy each mathematical model via the mesh.

Please correct me if I'm wrong below.
  • Standard wall functions y+ range 30 < 300
  • Enhanced wall treatment, Fluent manual doesn't appear to be clear on this issue, some say < 1 others say <10.
  • For k-w models y+ < 1 for all.
Thanks.
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Old   August 14, 2018, 15:54
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Standard wall functions can certainly be used in the y+<10 range. Standard wall functions have a low reynolds number treatment. What's special about enhanced wall functions, is the enhanced part.

Omega models are designed for low y+, but they can tolerate (they use wall functions) for high y+ meshes. Note that k-w SST model is a blended k-e and k-w model that tolerates high and low y+ meshes.

y+ < 10 or y+ < 1 is a matter of a lot of personal preference and experience. The point is to be low. The demarcation between viscous sublayer <5 versus linear region <10 only confounds the issue even more. If it matters to you, then do a grid sensitivity study.

What's more important than the wall y+ is the total # of grid points you have across the boundary layer and this is not captured by simply plotting y+.
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Old   August 14, 2018, 16:02
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So I should forget about y+ and do mesh sensitivity study?
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Old   August 15, 2018, 03:57
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You should always do a mesh sensitivity study. Especially if you ever plan on publishing anything.
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Old   August 18, 2018, 02:48
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I understand you are talking about the greater mesh region but there must be some kind of rule book regarding wall functions/turbulence model and y+ right?
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