Wall Roughness bigger than smallest cell size
 

Hi Guys,

I'm dealing with the following issue: Simulating a rotating wheel with different roughness values on the tire surface. 1, 2, 4 and 8 mm. My smallest cell size is 1.25.

When simulating with 2, 4 and 8mm my results get unreal. I understand that when penetrating the smallest cell size, my boundary layer model change. My question is how does it change? What is the physical description for this? Y+ values are around 140, so I'm already in the log law layer.

Thanks.
Yuriy