Enhanced aeroelastic energy harvesting by exploiting combined nonlinearities: theory andexperiment

Abstract

Converting aeroelastic vibrations into electricity for low power generation has receivedgrowing attention over the past few years. In addition to potential applications foraerospace structures, the goal is to develop alternative and scalable configurations for windenergy harvesting to use in wireless electronic systems. This paper presents modeling andexperiments of aeroelastic energy harvesting using piezoelectric transduction with a focuson exploiting combined nonlinearities. An airfoil with plunge and pitch degrees of freedom(DOF) is investigated. Piezoelectric coupling is introduced to the plunge DOF whilenonlinearities are introduced through the pitch DOF. A state-space model is presented andemployed for the simulations of the piezoaeroelastic generator. A two-state approximationto Theodorsen aerodynamics is used in order to determine the unsteady aerodynamic loads.Three case studies are presented. First the interaction between piezoelectric powergeneration and linear aeroelastic behavior of a typical section is investigated for a set ofresistive loads. Model predictions are compared to experimental data obtainedfrom the wind tunnel tests at the flutter boundary. In the second case study,free play nonlinearity is added to the pitch DOF and it is shown that nonlinearlimit-cycle oscillations can be obtained not only above but also below the linearflutter speed. The experimental results are successfully predicted by the modelsimulations. Finally, the combination of cubic hardening stiffness and free playnonlinearities is considered in the pitch DOF. The nonlinear piezoaeroelastic response isinvestigated for different values of the nonlinear-to-linear stiffness ratio. The free playnonlinearity reduces the cut-in speed while the hardening stiffness helps in obtainingpersistent oscillations of acceptable amplitude over a wider range of airflow speeds.Such nonlinearities can be introduced to aeroelastic energy harvesters (exploitingpiezoelectric or other transduction mechanisms) for performance enhancement.