抄録
Previous studies have shown that a modification of the boundary layer of a bluff body can change the wake properties like the vortex shedding frequency and the base drag. In the present study the boundary layer has been modified by applying suction over the top and bottom surfaces of a bluff body. A level of suction above a certain threshold has been shown to give an asymptotic suction boundary layer. For the asymptotic suction boundary layer the boundary layer properties become independent of the free stream velocity and hence the boundary layer Reynolds number. The bluff body studied can be described as a rectangular forebody with a smooth leading edge and a blunt trailing edge. Hot-wire anemometry measurements have been carried out in the boundary layer of the forebody. For four different Reynolds numbers, all within the laminar regime, the suction coefficient has been varied in the range from the neutral case to the case for which the asymptotic suction boundary layer is reached. It is observed that as the suction coefficient approaches the asymptotic suction boundary layer threshold, the Strouhal number based on the shedding frequency approaches a constant value. The base pressure decreases as the boundary layer thickness decreases. Furthermore it is shown that the Strouhal number does not always decrease for an increase of the displacement thickness.
