Effects of mass unbalance and high levels of external damping on the post-critical flutter of a flat plate

The post-critical flutter regime is still an open issue, despite the interest for its applications in the field of energy harvesting, where the knowledge of the self-sustained motion at large amplitudes is of crucial importance. In the paper, the experimental approach has been followed to investigate this issue. The role of some governing parameters, mainly the mass centre position and the damping level in the translational degree of freedom, were investigated through wind tunnel tests, evaluating their effects on the critical condition and subsequent oscillatory regime. Linear analyses supported the identification of the instability threshold. Downstream mass eccentricity of about 0.05 times the section chord significantly anticipated the critical onset velocity and modified the motion characteristics, in terms of ratio between translational and rotation amplitudes and their phase difference. External damping was introduced, up to a ratio-to-critical value of 18%, and the consequent reduction of the motion amplitudes was clearly shown. In particular, even if the amplitude-velocity diagrams always maintained the same qualitative features, a non-linear dependence on the damping level of its slopes was apparent. In addition, a theoretically stable configuration with large damping was found to perform self-sustained motion if triggered by large initial conditions.