Controlled vortex-induced vibration on a fix-supported flexible cylinder in cross-flow

This paper presents an experimental study on the closed-loop control of the vortex-induced vibration of a flexible square cylinder, fixed at both ends, in a cross-flow. Curved piezoceramic actuators were embedded underneath one cylinder surface to generate a controllable motion to perturb the interaction between flow and structure. Five control schemes were investigated based on the feedback from either individual or combined responses of structural vibration and fluctuating flow. Experiments were conducted in the first-mode resonance of the cylinder, when the vortex-shedding frequency coincided with the first-mode natural frequency of the fluid-structure system. The control effect on the structural vibration and the flow was simultaneously monitored using laser vibrometer, optical fiber Bragg grating (FBG) sensor, hot wires, particle image velocimetry, laser-induced fluorescence flow visualization and laser Doppler anemometer. The performances of the different schemes were assessed and compared. The best performance was achieved using the scheme whose feedback signal was a combination of flow and structural vibration. Vortex shedding was almost completely destroyed, resulting in a reduction by 85% in the vortex strength, by 71% in the structural vibration amplitude, and by 30% in the drag coefficient. It was found that the control effect altered the nature of the fluid-structure interactions, changing the in-phased fluid-structure synchronization into anti-phased interactions, thus significantly enhancing the damping of the fluid-structure system and contributing to greatly attenuated vortex shedding and the structural vibration.