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[ANSYS Meshing] y* and surface roughness

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Old   December 13, 2019, 11:40
Default y* and surface roughness
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Hi everyone!

I have a couple of questions regarding y*/y+ and best practices for meshing and wall functions:

1. If we assume the same free stream velocity, what is the relation between y*/y+ and surface roughness? I assume a bigger surface roughness would yield higher shear stress, so y+ would be higher for higher surface roughness. Is this correct? Does this also maintain for y* (based on kinetic energy) ? In the case of using wall functions, shall we still aim for the guideline of y* in the range of 30 to 300?

2. If I use Fluent's Poly mesh with prism cells on walls, How can I allow for an adequate boundary layer cell size and adequate y* while still having a reasonable cell count and avoid huge growth factors and changes between the prism and poly cells?

Thanks in advance guys!
Sapere aude!
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