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Required Y+ Range for k-Omega Standard and SST |
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#1 |
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Nian
Join Date: Jun 2019
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Hello,
This type of question might have appeared quite a lot in the forums, but I could not really find a definitive answer for it, so I would greatly appreciate it if anyone could help with the required y+ values for the turbulence models in Fluent: 1. Does k-omega Standard model use wall function at all? If so, does it mean that the y+ range should be between around 50 - 500? If not, what kind of range would the y+ value require? 2. As far as I am aware, k-omega SST does not use wall function and solves viscous layer directly, but some people have said it would require a y+ value of 1, some have said 5-10, so I was wondering if there might be a more certain answer for it? Thank you! |
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#2 |
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As far as Fluent is concerned, each
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#3 |
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Nian
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Quote:
Would the previous one (1-500) be applying for k-omega standard, and latter (1-10) for k-omega SST? Also, would you mind me asking what kind of range of Reynolds number would usually be considered as low Re simulation for external flow? Thank you very much! |
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#5 |
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Lucky
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Standard k-omega does have wall functions that kick in around wall y+ > 100. However, it is against the philosophy of the k-omega model to be using wall functions in the first place. The wall function is there just to make the k-omega model usable for coarse meshes. The wall function for omega is also quite garbage and not as robust compared to wall functions in epsilon models.
This wall function also exists in k-omega SST which blends a k-epsilon with a k-omega solution. But because the blending favors k-epsilon far from boundaries and k-omega near boundaries, the wall function that exists for the omega equation practically has no effect. In either case, the philosophy of using either the k-omega or k-omega SST model is to resolve viscous layers directly, so the recommendation is always going to be super low wall y+ when either of these models are involved. What's much more important than achieving the target y+ on only the first grid cell is resolution. You want to pack 10/30/100 cells across the boundary layer, etc. |
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Tags |
turbulence modelling, yplus |
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