Flow-induced vibration of cylindrical pendulums

Abstract

We experimentally investigated self-excited vibration of a cylindrical pendulum in a uniform flow as a fundamental step to evaluate its feasibility to energy harvesting. In the pendulum configuration, a cylinder is fixed to rigid upper plates via a thin elastic sheet so that it can swing perpendicularly to the free stream and cause periodic deformation of the elastic sheet. The dynamics of the pendulum were examined by varying free-stream speed and several geometric parameters of the pendulum. Whereas the past studies on vortex-induced vibration have mainly used reduced velocity, our study introduced non-dimensional free-stream velocity, the relative magnitude of the restoring bending moment of the sheet to the hydrodynamic moment acting on the cylinder, to characterize the pendulum dynamics. We confirmed that all pendulums showed similar amplitude and frequency responses at a given non-dimensional velocity and an oscillatory mode started to occur at a similar non-dimensional velocity. Mutual interaction of two cylindrical pendulums closely arranged in tandem was investigated as well, which discloses the dependence of amplitude response on center-to-center distance and the transition from vortex-induced vibration to wake galloping. General flow patterns of both single and dual pendulums were also identified by flow visualization.