The effect of the (a) grid resolution and (b) Reynolds number on the mean velocity profile for lx = ly = 0.005δ. (a) 102×32×52 (red squares), 128×40×64 (blue circles), 152×48×76 (yellow triangles). (b) Reτ = 950 (red squares), Reτ = 2000 (blue circles), Reτ = 4200, (yellow triangles). DNS (black dashed lines).