Effective energy harvesting in weak- and limited-airflow environments via butterfly-inspired rotary aerodynamic mechanism

초록

Supplying energy to building safety equipment autonomously and reliably from weak and spatially confined airflow—such as that encountered in heating, ventilation, and air-conditioning systems—is challenging due to the lack of excitation mechanisms capable of sustaining stable energy conversion at low wind speeds. Conventional wind energy harvesters, based on linear resonance or classical galloping, typically exhibit narrow operating bandwidths and insufficient robustness under such conditions. Hence, this study introduces a nonlinear energy-harvesting pathway based on rotational galloping inspired by the dynamics of slowly flapping butterfly wings. The proposed mechanism enables stable energy extraction through moment-driven self-excited rotation rather than transverse force instability. Based on this principle, a rotational galloping electromagnetic energy harvester is designed and experimentally investigated in a wind tunnel, with its rotational response and electrical output characterized under varying geometric configurations. To elucidate the underlying dynamics, a coupled electromechanical model is developed based on the extended Hamilton principle, which represents unsteady aerodynamic torque with a multiple-time-delay formulation. High-fidelity numerical simulations combined with finite-time Lyapunov exponent analysis reveal the role of 3D coherent vortices in sustaining rotational oscillations. A Morlet wavelet analysis further captures the system’s nonlinear dynamic characteristics. Finally, the proposed harvester is integrated with an ultra-low-voltage energy management scheme to enable power conditioning and low-power device operation under weak-airflow conditions.

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