Energy Harvesting from a Flapping Hydrofoil with Prescribed Pitch Profile

Document Type : Article

Authors

1 1Aerospace Engineering Department, Sharif University of Technology

2 College of Interdisciplinary Science and Technology, University of Tehran

3 Aerospace Engineering Department, Sharif University of Technology

Abstract

This work investigates a semi-active mechanism for harvesting energy from water flow using a flapping hydrofoil with a prescribed pitch profile and passively induced heave motion. The hydrofoil is connected via a hinged arm to an electrical generator, constraining the foil’s vertical motion to an arc centered at the generator (Fig. 1). A pitch profile is imposed by an actuator and controller, while the hydrodynamic forces generate the plunging response; the arm transmits torque to the generator. A coupled multiphysics model is developed that integrates (i) the dynamics of the power take-off, actuator, and controller (Eqs. (1)–(7)), and (ii) unsteady two-dimensional Reynolds-Averaged Navier–Stokes simulations with the k–ω SST model for the surrounding flow (Eq. (10)). The coupling is performed in Fluent using user-defined functions with sliding meshes that represent the arm and pitching block (Figs. 3–6). To validate the model, we compare its predictions against oscillating NACA0012 data and a published flapping-hydrofoil harvester case (Figs. 7–10). We employ a greedy search (Eq. (14)) to identify the dominant non-dimensional parameters the dominant non-dimensional parameters and their optima: the natural frequency and damping ratios (actuator-to-generator), the target effective angle of attack, and the critical arm angle. Under the tested conditions (Table 1), the optimized configuration delivers a net electrical power of 770 W, with dominant contributions near the reversals of the heave motion (Fig. 15).

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