Quantification of VIV-driven energy transfer for a circular cylinder with a pair of bumps at Reynolds number 150

Vortex-induced vibration (VIV) based energy conversion is a promising methodology to generate electricity by utilizing the flow energy neglected and eventually dissipated in nature, as the power generation process is sustainable and free from emission of pollutants. In this vein, micro-scale energy convertors driven in low-Reynolds-number flows have caught the attention for engineering applications. As the performance of the convertors highly depends on the acting forces or VIV responses, VIV amplifications are necessary to elevate the power output or energy conversion efficiency toward a level of engineering practicability. The attachment of a pair of bumps on an elastically mounted circular cylinder was demonstrated as an effective way to elevate the energy output for VIV-based energy convertors. However, most of relevant studies were conducted for turbulent flows as high-capacity energy convertors are of significant interest for direct engineering applications. On the other hand, the effects of the bumps on the energy transfer have rarely been studied for low Reynolds number flows. This paper then aims to quantify the effects of the circumferential locations of a pair of bumps on the energy transfer ratio in a single circular cylinder VIV configuration for Reynolds number 150. The circumferential location of the bumps is optimized under the synchronization condition, and this is compared with the plain cylinder VIV configuration; the energy transfer ratio is appreciably elevated when the bumps are placed at θ = 60 or 75-degree.