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Yplus value too low for my simulations

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Old   February 20, 2021, 04:57
Question Yplus value too low for my simulations
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I have been simulating a flow over turbine blade us K-omega automatic wall functions. I ended up choosing a very small value of the first element offset. Now, I am getting a Yplus <0.25 over the entire blade.

I read in the CFX manual that the automatic wall functions takes care if the mesh nodes are created inside the viscous sub-layer during mesh refinement.

My all subsequent simulations are based on this. I wanted to know if my results will be reliable? Could there be any justification for having Yplus <0.25?
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Old   February 20, 2021, 05:14
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You are correct in theory that the automatic wall functions can handle any reasonable value of y+. But in practice if your y+ gets too small then round off errors cause problems, so it is possible to go too small. In my experience the threshold of round off error problems is not much below y+=1. Round off errors will cause convergence difficulties.

If you can remesh using y+=1.0 and rerun it this will tell you whether you need a mesh as fine as y+<0.25. Many simulations don't need a mesh that fine.
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
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automatic wall treatment, k-omega model, y plus ranges, y plus selection

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