Boundary Layer Separation Under Strong Adverse Pressure Gradient Over Smooth and Rough Walls

Separation of the turbulent boundary layer, is among the most critical phenomena that determine the efficiency of flow devices, ranging from airplane wings to turbine and compressor blades, to curved ducts. In many of these cases roughness is present, and increases the wall friction, due to the contribution of pressure drag. In this study Large-eddy Simulations are carried out on flat-plate boundary layer over smooth and rough surfaces in the presence of an adverse pressure gradient, strong enough to induce separation. Roughness causes early flow separation due to increased momentum deficit and decrease of turbulent kinetic energy production