Bio-Inspired Flapping-Foil Energy Harvesters: Current Trends and Future Directions

Abstract

Flapping-foil energy harvesters offer a promising bio-inspired method for converting kinetic energy from wind, currents, and waves into usable power by mimicking the oscillatory motion of fish fins and bird wings. These systems rely on coupled pitching–heaving kinematics, unsteady vortex dynamics, and fluid–structure interaction to extract energy efficiently. This review synthesizes advances in flow physics, structural design, and power-take-off strategies, emphasizing leading-edge vortex formation, wake-foil interaction, reduced-frequency effects, and phase synchronization as key mechanisms governing energy capture. Developments in experiments, theoretical models, and computational fluid dynamics have enabled optimization of kinematics, passive and semi-passive control, structural flexibility, and non-sinusoidal motion profiles. Environmental factors such as turbulence, shear flow, free-surface effects, and wave interaction are evaluated to assess operational robustness. Recent innovations include tandem-foil configurations, adaptive deformation, hybrid piezo-electromagnetic systems, and machine-learning-assisted optimization. Remaining challenges include achieving stable performance under variable flow conditions, scaling for practical deployment, and integrating realistic power-take-off models. Future opportunities lie in morphing structures, intelligent control strategies, and large-scale experimental and field validation to advance flapping-foil systems toward reliable renewable-energy applications.