Multi-segment NACA0020 hydrofoil for flapping-foil energy harvesting in low-speed hydrokinetic flows

A multi-segment NACA0020 hydrofoil is proposed to improve flapping-foil energy harvesting in low-speed hydrokinetic flows by regulating the balance between heaving power generation and pitching power consumption. Two-dimensional unsteady CFD simulations were conducted to examine the effects of segment position, flat-plate thickness, trailing-segment type, and hybrid multi-segment configurations on hydrodynamic loads, power output, pressure distribution, and vortex evolution. A three-dimensional comparison was further performed to evaluate spanwise-flow and finite-span effects. The results show that the mid-chord flat-plate position P / c = 0.50 provides the best overall performance among the tested positions by enhancing heaving power while limiting pitching power loss. An intermediate flat-plate thickness T / c = 0.04 produces the most favorable thickness effect, whereas excessively thin or thick plates provide limited or even negative gains under some reduced frequencies. Among the trailing-segment cases, the NACA0020-NACA0005 hydrofoil achieves the maximum efficiency improvement of 13.6% at f * = 0.12. Three-dimensional simulations indicate that finite-span effects reduce the predicted efficiency, especially at high reduced frequency. The findings provide guidance for hydrofoil design in hydrokinetic energy-harvesting applications.