Enhancing wind energy–harvesting performance using Apollonian fractal bluff body

초록

This study introduces an efficient galloping-based piezoelectric wind energy harvester (PWEH) featuring an Apollonian gasket–inspired self-similar fractal bluff body to enhance energy-harvesting performance under low-wind-speed conditions. By introducing hierarchical fractal geometry, the vibration mechanism of a conventional circular bluff body is transformed from vortex-induced vibration to galloping-dominated oscillations, which enables stable and broadband energy harvesting. A systematic multi-stage fractal optimization strategy is implemented, which involves progressively refining the bluff-body geometry through first-order, second-order, and third-order fractal configurations by jointly tuning the fractal diameter ratios and tangency angles. Under the optimal third-order fractal configuration, the system achieves a maximum interval-averaged output power of 7.89 mW, which represents a substantial improvement over both the non-fractal and lower-order fractal variants. A finite-time Lyapunov exponent analysis reveals that the optimized fractal geometries promote persistent flow asymmetry and coherent vortex interactions, which underpin the enhanced galloping response. A reduced-order mathematical model is developed and validated experimentally, with prediction errors below 5%. The practical utility of the PWEH is demonstrated by using it to power an emergency exit light through supercapacitor charging, switching, and discharging steps.

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