Active control of vortex-induced off-resonance vibration of a flexible structure in crossflow

Closed-loop control of vortex-induced non-resonant flexible cylinder vibration is experimentally investigated in this paper. Piezo-ceramic actuators were embedded inside the cylinder to cause an oscillation of the cylinder surface, which subsequently altered the fluid-structure interaction. Experiments were conducted in a wind tunnel at Reynolds number of 2800 and 8000. Two typical control schemes, i.e. Y-control and u + Y-control, were deployed using feedback signals from structural vibration Y and combined Y and fluctuating flow velocity u, respectively. The control effects on Y and flow were assessed using laser vibrometer, optical fiber Bragg grating (FBG) sensor, hot wires and particle image velocimetry (PIV), respectively. Experimental results show that both vortex shedding from the cylinder and the vortex-induced non-resonant vibration were effectively suppressed. The best control effects were observed with u + Y-control in use; the root mean square values of Y, structural strain rate ε_y along the lift direction and u, i.e. Y_ms, ε_{y rms} and u_rms, and circulation Γ dropped by 58%, 52%, 53% and 88% at Re = 8000, respectively. It was found that the control effectively modified the nature of the fluid-structure interaction by changing the in-phased fluid-structure synchronization at all dominant frequencies into anti-phased interaction, accounting for the suppression in both vortex shedding and structural vibration.