y+ with k-w SST model and high surface roughness
I have a school project where I have to model the flow over a cold cylinder with a diameter of several meters and try to figure out the influence of surface roughness on the heat flux that the wall of the cylinder receives from the surrounding hot and moist air in transverse flow. I use k-w SST model for turbulence
For this, I have to make my roughness vary between 2 micrometers to 1 mm, but for the higher values of roughness (tipically 1 mm) my y+ is exploding from about 1 without roughness to about 40.
I know that to model heat transfer I have to keep a y+ under 5 to have at least one node in my viscous sublayer but I can't figure out how to reduce me value of y+ now.
I tried to lower my fist cell height (which is already at 1 micrometer) but when I do it, it doesn't change the value of y+ !!
I noticed that I can lower a bit the value of y+ by changing the growth rate of my inflation but when I make it near 1, the y+ increases again...
My question is : Do I need to keep a y+ of about 1 (and under 5) when I deal with surface roughness or is that impossible ? And if I need to, which parameters can I change to achieve that ?
Thank you for reading me and have a nice day !