Experimental investigation of a drag assisted vortex-induced vibration energy converter

Abstract

In this study, the Vortex-Induced Vibration (VIV) of a pivoted cylinder is experimentally investigated as a potential source of energy harvesting. The design of a physical model and a theoretical analysis presented and experimental measurements on the laboratory prototype are reported. In particular, we investigate the effect of the pivot point placement, arm length ratio (L*=l/D) and natural frequency (fN) on the VIV performance over a Reynolds number range, 2880≤Re≤22300.Classical studies show that the synchronization phenomenon (lock-in) occurs when the vortex formation frequency (fv) is close enough to the body's natural frequency (fN). Due to the configuration of the cylinder in this research, fN is also a function of flow velocity as well as the physical specifications of the system.The tests were conducted for the arm length ratio between 0.47 and 3.16 and three different spring stiffnesses were used to change the natural frequency. Results show that maximum output power is principally influenced by the arm length ration L* when the pivot point is located at the downstream, but reduced velocity is the controlling parameter when the pivot point is at the upstream. However, there is an optimum value of L* in both cases depending on the location of the pivot point and the stiffness of the spring. Based on observations, the optimum arm length ratio is relatively lower when the pivot point is at the downstream.The maximum efficiency of 31.4% has been observed for downstream placement of the pivot point by taking advantage of drag force and 2% for the upstream placement. Although the range of Reynolds numbers with high efficiency is wider when the pivot is located at the downstream, the performance of the system doesn't necessarily improve with increasing the Reynolds number in both cases.