Direct numerical simulation of an oscillatory boundary layer close to a rough wall

In the present contribution, the boundary layer generated close to a rough wall by an oscillatory, uniform pressure gradient is studied. The flow simulates the boundary layer generated at the sea bottom by a monochromatic propagating wave. The problem is tackled by numerical means and detailed information on flow dynamics is obtained. In particular, the evolution of vorticity is considered and the coherent vortex structures which are formed within the boundary layer are identified. The force exerted by the fluid on the bed and on the roughness elements is computed along with its pressure and viscous components.