Influence of sweep angle on performance of a fully-passive oscillating-plate hydrokinetic turbine prototype

Power extraction performance of a fully-passive oscillating-plate hydrokinetic turbine prototype was investigated experimentally using measurements of the kinematics of the flat plate and the estimated power extraction. Two configurations were considered: a flat plate with a 6${}^{\circ }$ sweep angle and an unswept plate (control configuration), which were undergoing fully-passive pitching and heaving motions in uniform inflow at Reynolds numbers ranging from 15,000 to 30,000. The resulting kinematic parameters and the power extraction performance were evaluated for both plates. The influence of the bottom endplate was also studied to investigate the extent of the spanwise flow and its effects at the tip of the plate. The swept plate experienced significant flow-induced forces acting in the direction of the heaving motion over a larger portion of the oscillation cycle, compared to the unswept plate. Consequently, the swept plate reached comparatively larger heaving amplitudes at high values of the inflow velocity, which resulted in higher power coefficient values but comparable efficiency values, relative to the unswept plate. Moreover, the energy-harvesting performance of the swept plate was consistent over a wider range of inflow velocities, compared to the unswept plate. The presence of the bottom endplate significantly impacted the kinematics of the swept plate, suggesting a dominant role of the spanwise convection of vorticity, which induced substantial tip losses.