Control of the aerodynamic forces of a finite-length square cylinder with steady slot suction at its free end.

A steady slot suction near the free-end leading edge of a finite-length square cylinder was used to control its aerodynamic forces. The aspect ratio ( H / d , where H and d are the height and width of the cylinder, respectively) of the tested cylinder was 5. The tested suction ratio Q , which was defined as the ratio of the suction velocity at the slot ( U s ) to U ∞ , ranged from 0 to 4. It was found that the overall aerodynamic forces reduce quickly with the increase of Q from 0 to 1, then recovers slightly with Q from 1 to 2, and keep approximately constant with Q  ≥ 2. The maximum reduction of the overall mean drag, fluctuating drag and fluctuating lift occurs at Q  = 1, which reaches 3.6%, 17.8% and 45.5%, respectively. The steady slot suction reduces the aerodynamic forces not only near the free end, but also over the entire cylinder span. At Q  = 1, the shear flow emanating from the free-end leading edge reattaches on the free end forming a recirculation bubble. The enhanced momentum transport between the free-end shear flow and the wake suppresses the spanwise vortex shedding and aerodynamic forces the most effectively. [ABSTRACT FROM AUTHOR]