Large-amplitude flow-induced vibration of cylindrical pendulums

We experimentally investigated the self-excited vibration of a cylindrical pendulum in a uniform flow as a fundamental step in evaluating its feasibility for energy harvesting. In the pendulum configuration, a cylinder is fixed to rigid 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 cylinder. In contrast to past studies of vortex-induced vibration, which mainly used reduced velocity to characterize the pendulum dynamics, our study introduced non-dimensional free-stream velocity, which is the relative magnitude of the restoring bending moment of the sheet to the hydrodynamic moment acting on the cylinder. We confirmed that all pendulums converted to an oscillatory mode at similar non-dimensional velocity and had almost identical amplitude and frequency responses at given non-dimensional velocity. The pendulum was able to oscillate with the amplitude much larger than its diameter in the limited range of the non-dimensional velocity. Mutual interactions between the two cylindrical pendulums closely arranged in tandem were also investigated, and the dependence of the amplitude response on center-to-center distance and the transition from vortex-induced vibration to wake galloping were observed.