Enhancing energy harvesting efficiency by utilizing twisting kinematics in flutter-driven wind energy harvester

Vibration-driven wind energy harvesters (WEHs) are much eco-friendly than wind turbines because of their quiet and safe operation for surrounding humans and animals. However, the low energy harvesting efficiency limits the wide application of vibration-driven WEHs. The present study designs a flutter-driven WEH based on the decoupling structure between bending and twisting stiffnesses, which produces predictable violent oscillation in the wind. The WEH electromechanical coupling model considering the aeroelastic effects is established based on the Hamiltonian principle. The effects of bending and twisting stiffnesses on the flutter on-set speed, flutter frequency, and electric output are analyzed numerically. The wind energy harvesting performance is evaluated in a low-speed wind tunnel. The electric outputs bending and twisting kinematics are compared by sticking two lead zirconate titanate patches on corresponding positions of the decoupling structure. The test results show that the electric output power densities of present WEH in 9 m s⁻¹ wind from bending and twisting kinematics are 1497.33 μW cm⁻³ and 200.22 μW cm⁻³, respectively. The bending and twisting energy conversion efficiencies are 0.31% and 29.6%, respectively. The effective enhancement of wind energy harvesting efficiency is achieved by adding twisting kinematics into the WEH. Up to 13.4% additional output power is obtained in the present WEH compared against the WEH with only bending kinematics. With the additional twisting kinematic energy, the present flutter-driven energy harvester is capable of lighting one 10 μW light-emitting diode at a wind speed of 6 m s⁻¹. This demonstration gives a potential way of enhancing the WEH’s energy harvesting efficiency. Future work would focus on the structural design and optimization with detailed applications.