NUMERICAL STUDY ON OSCILLATING HYDROFOILS FOR ENERGY EXTRACTION

Nahian Masud

doi:10.7273/000007418

The global pursuit of clean and renewable energy has driven interest in unconventional technologies capable of operating efficiently in variable aquatic environments. Among these, flapping hydrofoils have emerged as a bioinspired solution for sustainable hydrokinetic energy harvesting. Using flapping hydrofoils is a promising approach to capturing hydrokinetic energy from river and tidal flows. Unlike traditional rotational mechanisms, flapping hydrokinetic devices offer several advantages, including simpler foil geometries, reduced structural demands, improved hydrodynamic performance, suitability for shallow waters, and lower impacts on aquatic ecosystems. While previous numerical studies have mainly focused on hydrofoils with fully prescribed motions, this study investigates the energy harvesting performance of an oscillating hydrofoil using a semi-passive model strategy. The pitching motion is prescribed while the heaving response is driven purely by unsteady hydrodynamic forces. A fully prescribed configuration is also simulated under matching flow and motion conditions to enable direct performance comparison. Simulations are performed using a 2-D unsteady Reynolds-Averaged Navier–Stokes (URANS) framework implemented via overset mesh around a NACA0012 hydrofoil in ANSYS Fluent. The numerical model is set at a Reynolds number of 3.6×105, representative of practical deployment in riverine environments. A series of simulations are first conducted to identify optimal operating parameters for the fully prescribed hydrofoil. A reduced frequency f ∗ = 0.1443, pitching amplitude of 70◦, and sinusoidal motion profiles were found to deliver the highest energy conversion efficiency. These parameters are subsequently applied to the semi-passive configuration, enabling the hydrofoil to respond freely in the vertical direction while maintaining a pitch input. Simulation results reveal that the fully prescribed system achieves a total efficiency of 38.6%, with heaving motion accounting for a heaving efficiency of 57.55% and a total average power output of 139.53 W. In contrast, the semi-passive model generates significant unsteady vertical motion—approximately three times larger in displacement—yet fails to convert this motion into usable power due to a lack of phase alignment between the hydrodynamic forces and the heaving response. This leads to negative net power generation (-446.61 W) and an overall efficiency of -31.87%. The unsteady heaving response exhibits irregularity across cycles, with sharp peaks in velocity and force magnitudes. These results indicate that while passive vertical motion in oscillating hydrofoils can induce large displacements, it does not inherently result in effective energy harvesting unless additional damping or synchronization mechanisms are introduced. The study highlights the need for further investigation into hybrid or semi-active strategies that can extract usable power from passive motion while preserving mechanical simplicity and adaptability to unsteady flow conditions.

NUMERICAL STUDY ON OSCILLATING HYDROFOILS FOR ENERGY EXTRACTION

Files and links (1)

Abstract

Metrics

Details