Feedback control of vortex shedding from a circular cylinder by rotationaloscillations

The present paper describes a new active method for controlling vortex shed ding from a circular cylinder in a uniform flow at medium Reynolds numbers. It uses rotary cylinder oscillations controlled by the feedback signal of a reference velocity in the cylinder wake. The effectiveness of this feedba ck control is evaluated by measuring the response of mean and fluctuating v elocities in the cylinder wake, the spanwise correlation, the power spectru m, and the fluid forces acting on the cylinder. It is found that the veloci ty fluctuations and the fluid forces are both reduced by the feedback contr ol with optimum values of the phase lag and feedback gain. The simultaneous flow visualization synchronized with the cylinder oscillation indicates th e attenuation as well as the mechanisms of vortex shedding under the feedba ck control, which is due to the dynamic effect of cylinder oscillation on t he vortex formation. (C) 2001 Academic Press.