Hi all. I am doing a simple CFD simulation flow past over spherical body to understand the concept of y+ and boundary layer.
I have a simple question related to log-law layer. I read that for this region the value should be in between the range of 30 to 300. Now, how I should know that for my simulation y+ value 35 is good enough or 60 or some high value?
The wall functions rely on the universal law of the wall, which basically states that the velocity distribution very near to a wall is similar for almost all turbulent flows. One of the most prominent parameters when judging the applicability of wall functions is the so-called dimensionless wall distance y+.
One can interpret y+ as a local Reynolds number, which means that its magnitude can be expected to determine the relative importance of viscous and turbulent processes. For the sake of completeness, let’s briefly introduce the friction velocity uτ. It should be evident that the viscosity ν and wall shear stress τw are important parameters. From these quantities and ρ we define the viscous scales being appropriate viscous scales and length scales in the near-wall region.
The value of y+ depends on your turbulence model. if you use structure mesh with SST model than the range of y+ is from 1 to 5. For K epsilon model it is up to 30. for unstructured mesh the value of y+ should be below 1.
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