Rough wall turbulent boundary layers at high packing densities

We study rough wall turbulent boundary layers at high surface coverage densities (SCD). We conduct wall-modeled large eddy simulations (WMLES) of flow over aligned cube arrays at surface SCD from 0.4 to 0.9, where the cubes are resolved using an immerse boundary method. The mean flow shows a small velocity deficit at high SCDs, and the flow “slip” over the roughness elements. In addition, two peaks are found in the uu profile at SCD=0.6, where u is the streamwise velocity fluctuation. We show this two-peak behavior is the result of a competition between the Reynolds stress above the roughness-occupied layer and the dispersive stress within the roughness-occupied layer. We will also present evidence from direct numerical simulation (DNS) for the reduced velocity deficit in the mean flow and the two peaks in the turbulent stress profile.