SimScale CAE Forum

Resolving the boundary layer kOmegaSST

Hi,

I am happy with the choice of boundary conditions for the field variables when it comes to resolving the boundary layer at wall patches.

My question is how strict is the y+ condition? Should the mesh be fine enough to ensure a y+ < 1, or is it acceptable to have a y+ < 5?

In addition, should the y+ condition be satisfied by all cells? Or is it enough to have the patch average below 1 or 5? I have extracted this data using the yPlus post-processing function.

This is with respect to an ABL flow around a building.

Thanks,
Lloyd

Hi Lloyd!

The kOmegaSST is known to give accurate results for yPlus being well below ~ 30. However for most implementations of the model it is good practice to go for y+ ~ 1!

@CFD-SQUAD, please add your two cents if necessary!

Edit: If you use wall functions you can go higher by the way (50-200 imho!) - would have to reassure myself here and look it up :wink:

Best,

Jousef

Hi @LloydE, just a reminder, you can reach out to me if you need technical support, typically our application engineers don’t monitor the forums, but can be reached in the chat function or by email during your professional trial.

Firstly, we should say that the k-omega SST implementation for LBM and PWC is a little different from the usual solver. The regular OpenFOAM based implementation we recommend to operate in log law region (k-epsilon mode, 30<Y+<200 ish) or in k-omega SST approaching 1. The LBM/PWC implementation is a bit more of a brute and can be used across the board but recommended not exceeding Y+ > 2000 or for the buildings of interest, not exceeding Y+>200. For curved geometries where separation position is likely to affect results (think round buildings, not curved corners) a smaller Y+ might be needed, usually, I describe it to be approaching 1.

Hope this helps,
Darren

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