Effects of Strip Thickness and Damping on Flow-Induced Motions of a Circular Cylinder

Vortex-induced vibration (VIV) occurs as the flow around a bluff body, such as a cylinder, separates and causes the formation of vortices and a varied pressure distribution along the surface. Vortices are alternatingly shed, resulting in an alternating force on the body. VIV can have potentially destructive effects in structural applications, which prompted the majority of research to focus on mitigation and suppression efforts. Since the discovery of using vortex-induced vibration for energy harvesting by Bernitsas and group at the University of Michigan in 2005, researchers have begun to focus on augmentation mechanisms for VIV and galloping of circular cylinders for expanding energy harvesting capacity of the device. The current experimental work examines the effect of attaching smooth strips of varying thickness to a circular cylinder, as well as the effect of mass-damping for a given strip thickness, on its vibration response and power generation potential, and builds on previous work done by Vinod and Banerjee [1]. Five strip thicknesses ranging from 1.6% to 31% of the cylinder diameter were tested, along with three values of mass-damping. Each combination of thickness and damping experienced galloping at high flow velocities. Greater strip thickness resulted in a higher rate of increase of vibration amplitude with flow velocity, as well as a tendency to transition directly from VIV to galloping. Higher damping resulted in lower VIV amplitudes, a higher rate of increase in galloping amplitudes, lower vibration frequencies, and a lower Reynolds number range of synchronization. These observations show that higher strip thickness and lower damping lead to increased energy harvesting and power generation potential