Ideas for modelling effect of roughness on drag?

andy2O

Hi All,

I'm looking at computing the drag on a body within a confined turbulent flow. Normally, in order to resolve drag on a body I would use a low-Reynolds number turbulence model such as SST, with low values of y+ to resolve the boundary layers well. However, in this case I would also like to model the effect of surface roughness of the body on the drag coefficient to get a qualitative understanding of how roughness will alter the drag coefficients.

How could this be done in CFX? Can it be done?!

My understanding of the surface roughness model in CFX is that it only works with wall functions where y+ >> 1, and that it would therefore not be valid to use it with low y+ values. However if I do use larger y+ values I would not normally trust the drag values from CFD anyway. So what can I do?

Any thoughts or advice would be very welcome.

Best regards, andy2o