Novel duct configurations for flapping foil energy harvester: Design and performance evaluation

This study examines the power generation performance of flapping foil energy harvesters confined within various duct configurations, including three novel designs: straight–divergent, divergent–flange, and straight–divergent–flange. These configurations were compared against a conventional divergent duct and without-duct configuration to evaluate their impact on aerodynamic performance and energy extraction. Numerical simulations using computational fluid dynamics showed that the proposed duct geometries significantly influence flow stability, vortex formation, and energy transfer. Among the tested designs, the straight–divergent–flange duct demonstrated the highest performance, characterized by well-organized vortex structures, large high-velocity regions, and intense pressure gradients that enhance aerodynamic forces and maximize power generation. To optimize this configuration, we systematically varied the duct wall spacing (3–7 chord lengths) and the divergent angle (20°–50°). The results indicate that power output is sensitive to these parameters, with an optimal configuration identified at a duct wall spacing of approximately five chord lengths and divergent angles between 35° and 40°. Under these conditions, the power output increased by 87.6% compared to the case without a duct, surpassing the conventional divergent duct, which achieved only a 36.5% improvement. These findings underscore the importance of a tailored duct geometry for optimizing energy harvesting efficiency and demonstrate the potential of innovative duct designs to enhance flapping foil energy conversion.