Concurrent energy harvesting from vibratory base excitations and aerodynamic flows

This paper presents theoretical and experimental investigations into the potential of utilizing a piezoaeroelastic micropower generator to harvest energy from the combination of an external base excitation and an aerodynamic load. In particular, a harvester consisting of a rigid airfoil supported by a flexural piezoelectric beam and a torsional spring is placed in an incompressible air flow and subjected to an external harmonic base excitation in the plunge direction. Electromechanical equations describing the nonlinear system are given along with theoretical simulations. The performance of the piezoaeroelastic generator is studied experimentally below and above the flutter speed and found to exhibit qualitative agreement with the theory. Below the flutter speed, the response of the harvester is observed to be always periodic with the air flow serving to amplify the influence of the base excitation on the response by reducing the effective stiffness of the system, and hence, increasing the RMS output power. Beyond the flutter speed, the harvester's response and its performance were observed to depend on the nearness of the excitation frequency to the frequency of the self-sustained oscillations induced by the flutter instability and the magnitude of the base excitation. When the base excitation is small and/or the excitation frequency is not close to the frequency of the self-sustained oscillations, the response of the harvester is two-period quasiperiodic with amplitude modulation due to the presence of two incommensurate frequencies. This amplitude modulation reduces the RMS output power. On the other hand, when the frequency of excitation is close to the frequency of the self-sustained oscillations and/or the amplitude of excitation is large enough to quench the quasiperiodic behavior, the response becomes periodic and the output power increases exhibiting little dependence on the base excitation.