Active control of vortex shedding and fluid-dynamic forces on a square cylinder by micro-excitation of sidewall surfaces

The experimental studies on active control of vortex shedding frequency were conducted to suppress fluid-dynamic forces of a square cylinder. Each sidewall of the cylinder consists of four vibrating side-plates equipped with piezoelectric actuators. The vortex shedding frequency was controlled by means of a lock-in phenomenon that was caused by vibrating the side-plates transversely with amplitude less than 100 μm. The results are summarized as follows: (1) the spanwise synchronous excitation brings about reduction of the time-averaged drag coefficient C_d. It is reduced by approximately 20% of the natural condition. (2) When a half span of sidewall surface is vibrated with 180 degrees differential phase against the other half span, the vortices shed from each half span in the reversal phase mode. The fluctuating lift coefficient C_i' is reduced by approximately 70% of the natural condition with the reversal phase mode.