Wind-tunnel tests on the post-critical response of classical-flutter-based generators

Harvesting energy from two-degree-of-freedom flutter requires large-amplitude steady-state oscillations. Nevertheless, the post critical behaviour of this aeroelasic instability is still an open issue. The present study attempts to improve its scientific understanding and to supply information for the design of more unstable solutions for energy-harvesting applications. In this framework, the energy extraction was simulated through additional damping in the transverse motion component. Then, the influence of some governing parameters was explored through wind-tunnel tests and parametric linear analyses. It was found that a small mass unbalance downstream of the elastic centre is fundamental to anticipate the instability and to obtain unstable systems also in the presence of high damping levels. Moreover, the still-air frequency ratio is the main responsible for the magnitude of the pitching-to-heaving amplitude ratio. An increment of the heaving damping significantly affects the motion amplitude and conditions the optimal position of the elastic axis. Finally, the post-critical response seems to be little affected by the flow turbulence, suggesting the high potentiality of flutter-based generators for applications in real-flow environments. (C) 2017 The Authors. Published by Elsevier Ltd.