Optimizing energy harvesting performance of a tandem hydrofoil turbine array with vortex-foil interactions

Tidal flow energy harvesting with oscillating hydrofoil turbines has become an important area of research as the need for more sustainable energy sources has increased in recent decades. As these turbines will be deployed in array configurations, it is essential to characterize optimal array kinematics and to understand how wake-foil interactions affect performance. Due to their structured wakes, it might be possible to improve the performance of hydrofoil arrays using constructive wake-foil interactions. In this study experiments were performed with prescribed-motion oscillating hydrofoils in a water flume where force and time-resolved PIV measurements were obtained in order to study array performance and wake-foil interactions. Three distinct types of interaction were observed: one where the trailing foil avoids the wake structures, another where interaction with wake vortices leads to worsened hydrofoil performance, and a case where vortex interactions lead to improved hydrofoil performance. From these observations it is apparent that in order to optimize the array performance the hydrofoils in the array do not share the same kinematics nor do they operate with the optimal kinematics of a single hydrofoil.