Understanding energy transfer in aeroelastic flutter and exploiting free-play induced flutter for energy harvesting

Abstract

<p>Aeroelasticity is well established research area involving undesirable coupling between elasticity, inertia and aerodynamics. Flutter is characterized as an unstable self excited aeroelastic system response, which leads to catastrophic structural failure. It is widely studied how various nonlinearities in fluid flow, structural stiffness, damping, and free-play in the joints affect the phenomenon in different ways. While most of the work in the literature is focused on how to avoid potentially catastrophic onset of flutter, this work unravels the mechanism of energy exchange that takes place between coupled fluid and structure system. The focus of this work is to investigate how to harness the energy in otherwise undesirable phenomenon. The flutter state of interest is the limit cycle oscillations(LCO) which represents marginally stable structural response. More fundamental study aimed at energy aspect of the interaction is done using a simple 2D airfoil (NACA 0012) system with two degrees of freedom and hyperbolic free-play nonlinearity. Variation of kinetic, potential, total energy and balanced energy interaction are established and analyzed in details. The representative experimental results are discussed from energy perspective which motivated the development of high fidelity fully coupled computational model discussed in this thesis. The work presents energy transfer dynamics for this 3D model. The energy analysis from 2D and 3D configuration suggests that there is a potential for harnessing energy that is transferred from flow field to the structure during aeroelastic flutter. The magnetostrictive materials like Galfenol can be used to efficiently convert the energy transferred to the structure by flow field into electrical energy. The dynamics of magnetostriction for Galfenol is presented using published properties of Galfenol by its manufacturer Etrema. For an example, 3D airfoil system simulation results are presented for open circuit voltage that will be generated using the proposed concept. This research gives a deeper understanding of energy exchange between structure and flow field during different phases of dynamic response of aeroelastic system.</p>