Exploring the impact of Hybrid Pitching on Foil-Based Energy Harvester Performance*

Oscillating hydrofoil-based energy harvesters are renowned for their high performance in converting hydrokinetic energy into usable power. By utilizing a combination of prescribed pitching and passive heaving motions, these systems can effectively capture the kinetic energy from water currents, maximizing energy output. However, the prescribed pitching motion can sometimes result in negative pitching power, which detracts from the overall efficiency of the system. Negative pitching power occurs when the energy required to maintain the prescribed motion exceeds the energy being harvested, leading to a net loss. Additionally, the positive pitching power cannot be harvested in the prescribed pitching motion. We propose hybrid pitching as a solution to these limitations. Ideally, hybrid pitching motion can effectively reduce the power consumed and let the energy be harvested when it is in the passive mode. However, the effectiveness of hybrid and the corresponding optimal switching strategies remain unexplored. In this study, we use a cyber-physical traverse to map the performance of various prescribed pitching profiles. We then explore a series of hybrid switching strategies based on diverse switching thresholds, such as pitching power sign, kinetic energy, or composite metrics, aiming to improve energy harvesting performance. Corresponding wake dynamics and passive heaving behaviors are also analyzed.