Optimal energy harvesting kinematics for compliant membrane hydrofoils

Oscillating hydrofoils are increasingly being studied as an alternative to rotary turbines for extracting energy from tidal and fluvial flows due to their lower tip speed, smaller interturbine spacing and better applicability to shallow flows. Compliant membrane hydrofoils have been proposed to improve the low cycle efficiency of oscillating turbines, increasing lift and power coefficients dramatically due to their dynamic cambering. While the performance of oscillating hydrofoils has been shown to be highly dependent on their kinematics, the six dimensional parameter space of the membrane hydrofoil (heaving amplitude, pitching amplitude, pitch-heave phase, frequency, Young's modulus, and triangular to trapezoidal profile parameter) has never been comprehensively studied. In this work, the Nalder Mead optimization method is used to find the kinematic parameters which yield the optimal power coefficient of a heaving and pitching membrane hydrofoil by autonomously performing exhaustive and extensive water flume experiments. The routine illuminates trends in performance across the parameter space while avoiding time intensive mapping. Extension of this approach to the kinematics and material properties for arrays of turbines for large scale deployment is also investigated.