Numerical study on the hydrodynamic performance of a semi-passive oscillating hydrofoil

Abstract The bio-inspired oscillating hydrofoils are capable of harvesting energy from tidal currents. In this study, the effects of mechanical (spring and damping coefficients) and kinematic (pitching amplitude and oscillation frequency) parameters on the performance of the semi-passive oscillating hydrofoil (NACA 0015) system were numerically studied at a high Reynolds number of 106. It is found that the spring (k *) is necessary to obtain a stable heaving response. The initial pitching angle has a significant effect on the heaving response, while it has a little impact on the power output. The balance position of the heaving response deviates notably from the initial position, especially when the initial pitching angle is zero. A larger damping coefficient (c *) results in poor energy harvesting performance due to a smaller oscillation amplitude. The heaving amplitude increases firstly and decreases afterward with the increase of the pitching amplitude ( θ 0 ), while it decreases monotonically with increasing oscillation frequency (f *). When f *>0.15, the heaving and pitching power coefficients increase and decrease with increasing f *, respectively. The net power coefficient decreases at high oscillation frequencies because the increase in the heaving power coefficient is smaller than the decrease in the pitching power coefficient. When k* = 0.5 and c* = 0.8π, an optimal energy harvesting efficiency of 40.84% is achieved at θ 0 = 85 ° and f * = 0.125.