Bio-inspired Hydrokinetic Turbine Based on a Flapping Foil: An Experimental Study of Two Design Variations

Given the current energy transition conjuncture, the part of renewable in the electricity production grid are to be drastically increased. Besides, the hydraulic potential of low-current sites is relevant and remains under-exploited. A novel bio-inspired hydrokinetic turbine based on a flapping foil could efficiently harvest such hydraulic energy while minimizing environmental impact. In the present work, an experimental study of a reduced-scale fully passive flapping foil hydrokinetic turbine has been conducted. Two design variations for the foil have been considered. In design #1, the foil is mounted without winglets and interacts with the free surface. In design #2, the foil is completely immersed and is equipped with winglets. Thanks to an original dynamic tuning of the structural parameters, experiments have been conducted in a wide range of configurations for both design variations. Results show that comparable performances can be achieved with both designs provided that the structural parameters are set accordingly. Design #2 works optimally when the pitching axis located at one-third of the chord-length from the leading edge, while design #1 achieves better efficiencies with the pitching axis further downstream towards the trailing edge. The experiments conducted allowed for identifying the optimised configurations for each design. They may both be employed under different environmental conditions to efficiently harvest the hydrokinetic energy of a low-current flow.