Vortex-flutter internal resonance: A new mechanism for wind energy harvesting

Flow-induced vibrations (FIVs), traditionally regarded as structural hazards, offer significant untapped potential for ambient wind energy harvesting. Here, we report the first experimental implementation and theoretical investigation of internal resonance arising from the coupling between vortex-induced vibration (VIV) and flutter, which enables a new class of high-performance wind energy harvesters (WEHs). This coupling produces a synergistic interaction where the flutter-induced aerodynamic instability facilitates a 25-fold increase in power output at the critical onset, and the internal resonance mode outperforms VIV alone by a factor of 5. To explain this behavior, we develop an aero-electro-mechanical model that captures the emergence and characteristics of the internal resonance. Further experiments show that this internal resonance can be precisely tuned by adjusting the flag position and geometry, offering flexible and application-specific WEH design. Finally, we demonstrate the practical utility of the vortex-flutter coupled WEH by powering a wireless sensor node for real-time temperature monitoring. This work opens promising new pathways for aerodynamic WEHs by leveraging strong intermodal coupling between FIV mechanisms.