An asymmetric bending-torsional piezoelectric energy harvester at low wind speed

This paper presents a detailed investigation on a novel asymmetric vortex-induced piezoelectric harvester for capturing wind energy at low wind speed. The asymmetric energy harvester undergoes both bending and torsional vibration caused by vortex-induced vibration. A comprehensive nonlinear distributed model of compound bending-torsion piezoelectric energy harvester is derived using the energy method based on the Euler-Bernoulli beam assumption. The theoretical results show that the asymmetric energy harvester has a lower natural frequency and a smaller electromechanical coefficient than the conventional vortex-induced piezoelectric energy harvester. The asymmetric configuration contributes to a lower corresponding optimal wind speed and is prone to vibrate compared with the symmetric configuration. Experiments were carried out and the experimental results were in good agreement with the numerical results. The asymmetric energy harvester has the advantage of generating more power at low wind speed compared with conventional energy harvester. The results show with the increasing of length of cylinder and eccentric distance, the natural frequency and optimal wind velocity drops, and there exists an optimal length of cylinder for maximum output power. This study provides a simple and feasible method to reduce the working wind speed for vortex-induced piezoelectric energy harvester.