Effects of wall suction on a 2D rough wall turbulent boundary layer

Hot-wire measurements carried out in a 2D rough wall turbulent boundary layer subjected to a wall suction through a porous strip show that the outer part of the boundary layer is deflected inward (toward the wall), thus impacting on the roughness elements close to the suction strip. This leads to an increased drag coefficient associated with an increased energy input, arguably, resulting from an intensified shedding of vortical structures from the roughness elements. Conversely to the smooth wall case, suction does not lead to relaminarization of the boundary layer. It also seems that suction does not alter significantly the turbulence structure of the boundary layer.