Mode coupling and flow energy harvesting by a flapping foil

TLDR

Flapping foils can harvest kinetic energy from wind or current, and this capability is amplified by coupling between multiple motion modes where one mode is externally activated and energy is extracted from the others. The study develops a Navier–Stokes–based numerical model to assess the performance of such a mode‑coupled flapping‑foil system at low Reynolds numbers. The model examines how mechanical design choices and operational parameters influence the system’s behavior. The results demonstrate that vortex‑body interactions enable partial recovery of leading‑edge vortex energy, thereby enhancing energy‑harvesting performance.

Abstract

As demonstrated in recent studies, the bioinspired flapping foils are capable of harvesting kinetic energy from incoming wind or current. A practical measure to achieve this is via the coupling between different modes in a system with multiple degrees of freedom. A typical scenario includes external activation of one motion mode and extracting the mechanical energy from other modes that follow. In this study we create a numerical model based upon the Navier–Stokes equations to investigate the performance of such a system in low Reynolds numbers. The effects of both the mechanical design and the operational parameters are examined. Specifically, we concentrate on the vorticity control mechanisms involved in the process, and demonstrate that through vortex-body interactions energy of the leading-edge vortices can be partially recovered to enhance the energy harvesting capacity.