Direct Numerical Simulation of the Aerodynamically Rough Atmospheric Boundary Layer – Scaling Analysis of Rough Periodic Surfaces

Virtually all atmospheric flows in nature are, to some extend, flows over rough surfaces with roughness sizes from the sub-millimeter to meter scale. Roughness as an inherent feature of the atmospheric boundary layer (ABL) enhances drag, mixing and transport properties of the flow (w.r.t. pollutants, moisture, temperature ...). To study the effect of roughness on the ABL, we perform direct numerical simulations (DNS) of the turbulent neutral Ekman flow over rough surfaces. The lower boundary of the simulation domain is covered with fully resolved three-dimensional cubical roughness elements of varying mean heights (small compared to the boundary layer thickness). The parameters of our simulations correspond to the transitionally and fully rough regime. The spatially fully resolved data allow precise estimation of the roughness parameters: friction velocity, z-nought for scalar and momentum as well as the displacement height. Those parameters are used to present a universal scaling of velocities and scalar profiles in the logarithmic layer for rough flows, which is studied in depth.