On the effects of cavitation and free surface for hydrokinetic H-Darrieus cross-flow turbine

Choosing the appropriate design of hydrokinetic turbine for a given resource and projected deployment is crucial for energy extraction. Cavitation plays a major role in such design choices. Previous experimental studies have suggested that cavitation might explain the low performance of H-Darrieus cross-flow turbines in high-speed inflows. To better understand the effects of cavitation and free surface on these turbines, 2D URANS numerical simulations at high Reynolds number are conducted at different inflow velocities, tip-speed ratios and immersion depths. The results show that cavitation is greatly susceptible to appear for high velocities and low immersion depths. This cavitation is detrimental to the performances since it deteriorates the effective shape of the blades as well as promoting vortex shedding. The impact is even more pronounced at low tip-speed ratios because, for higher tip-speed ratios, the effective angles of attack are smaller, thus reducing the suction peak on the blades. The present results provide insight to help better choose the turbine solidity depending on deployment site characteristics.