Piezoelectric energy harvesting by aeroelastic means

For the last few decades, piezoelectric (PZT) materials have been widely used in the field of micro/nano-electromechanical systems. One of the most important applications of the PZT material is energy harvesting by absorbing ambient energy from the operational conditions and converting it into electrical energy. This energy can be used to operate sensors and actuators. Moreover, it can be stored in batteries for later tasks. In this thesis, the harvester absorbs energy from the airflow, thanks fluid-structure interaction (FSI), and converts it into useful electrical energy. To analyze FSI, it is important to consider the whole dynamics of the system formed by the structure and the flow i.e., the aeroelastic system rather than considering them as two different systems. This coupling, from the mathematical point of view, occurs because the natural boundary condition of the structure is defined by the flow pressure which is mutually influenced by the structure. This leads to a very complex phenomenon that is intrinsically non-stationary and it is no longer possible to study it by considering the structure and the flow separately. The aeroelastic system remains stable up to a critical velocity of the flow known as flutter velocity which depends on the following media and the mechanical properties of the surrounding system. After this particular velocity, the aeroelastic system is no longer stable in its unperturbed condition. The system can no longer be considered as linear and stable oscillations arise, the so-called Limit Cycle. Indeed, the interaction of the fluid in the form of airflow with structure i.e., airfoil will transfer oscillations to the PZT which will result in energy harvesting. In the present work, the possibility of extracting energy by means of PZT transduction from an aeroelastic behavior, known as the Limit Cycle Oscillation (LCO), is investigated analytically, numerically and experimentally. A suitably designed aeroelastic device which is based on the use of PZT components is presented thanks to the flag-flutter phenomenon. The presented harvester is studied from the analytical, numerical and experimental points of view. A nonlinear piezoelectric aeroelastic energy harvester (PAEH) is modeled based on the FSI that represents an important area of research for the development of innovative energy harvesting solutions. This PAEH operates on LCOs that arise after the flutter velocity. The aim of this research is to study and design a nonlinear aeroelastic energy harvester. The PZT transduction from the Limit Cycle is investigated. Particular emphasis is placed on demonstrating a correct model of unsteadiness of aerodynamics. The unsteady aerodynamic model is a critical ingredient for a sound prediction of the nonlinear behavior of an aeroelastic system. Thus, it plays a vital role in the correct evaluation of the performance of an energy harvester based on the flutter phenomenon. Moreover, it is shown that if the unsteady nature of aerodynamics is not taken into account, the evaluation of the system stability margins is totally incorrect, even if a quasi-steady hypothesis is considered. Therefore, it is emphasized that the determination of the aerodynamic model is necessary for the correct prediction of PAEH performance. Indeed, harvesting performances, flutter boundaries, aeroelastic modes, and LCOs amplitude predicted by different models, are compared with the experimental data provided by wind tunnel tests. The present harvester has various applications in the field of aerospace engineering. As a result, it is shown that the overall system is suitable for energy harvesting and can be utilized to drive microelectronics i.e., wireless sensors in sub-orbital missions, launchers, space vehicles and in various aerospace applications.