Piezoaeroelastic energy harvesting based on an airfoil with double plunge degrees of freedom: modeling and numerical analysis

In this paper, a piezoaeroelastic energy harvester based on an airfoil with double plunge degrees of freedom is proposed to additionally take advantage of the vibrational energy of the airfoil pitch motion. The analytical model of the proposed harvester is built, and an equivalent model using the well-explored pitch–plunge configuration is presented. The nonlinear aerodynamics is calculated based on the dynamic stall model. The dynamic response, average power output, energy harvesting efficiency, and cut-in speed (flutter speed) of the proposed harvester are numerically studied. It is demonstrated that the harvester with double-plunge configuration outperforms its equivalent pitch–plunge counterpart in terms of both the power output and energy harvesting efficiency beyond the flutter boundary. In addition, case studies are performed to reduce the cut-in speed and to enhance the energy harvesting efficiency of the proposed harvester, including the airfoil mass characteristics, the configuration, mass, damping, and stiffness characteristics of the two plunge supporting devices, and the load resistances in the external circuits. It is shown that the cut-in speed is greatly reduced by increasing the airfoil mass while tuning the mass eccentricity. The mass of the first (windward) supporting device should be a bit smaller than that of the second one for an applicable cut-in speed and a high-energy harvesting efficiency. Besides, the decrease of airfoil mass moment of inertia or the damping of the supporting devices is shown to be beneficial for the energy harvesting performance. In addition, the optimal location of the first supporting device is found to be at the airfoil leading edge. Decreasing the distance between the two supporting devices reduces the cut-in speed. The load resistances affect the cut-in speed slightly, and optimal values are found to maximize the energy harvesting efficiency