Simulations and experiments of boundary layer flow over a fully rough wall*

We investigate the effects of three-dimensional roughness on turbulence in the logarithmic layer using direct numerical simulation (DNS) and wind tunnel experiments.  The DNS apply an immersed boundary method to model flow over an arbitrarily complicated rough wall boundary. As the simulations progress, an adaptive mesh refinement (AMR) scheme updates the mesh dynamically to resolve small details of the flow along the wall and in areas of high vorticity. We use the simulations to identify coherent structures in the logarithmic layer. Size, size distribution and spatial organization of vortices are studied, as well as the presence of zones of uniform momentum (UMZs) and the associated internal shear layers.  The simulations are complemented by wind tunnel experiments at a matched roughness geometry and friction Reynolds number Reτ. We compare the numerical and experimental results as a means to validate the numerical methods.