Experimental parametric study of a flap-NES passive absorber for post-flutter control

Aeroelastic instabilities present significant challenges in aircraft design, particularly for novel designs leveraging high aspect ratios and flexible wings to enhance aerodynamic efficiency. These advancements, seen in both high-altitude, high-endurance aircraft and commercial airliners, introduce complexities such as low resonant frequencies and increased susceptibility to aeroelastic instabilities, particularly flutter, which can lead to structural failure. The current certification process requires aircraft to be free from flutter within the operational flight envelope and beyond it, typically with a safety margin of 15% Various strategies have been explored to mitigate flutter and expand the flight envelope. In this work, passive vibration mitigation is applied to an experimental aeroelastic system exhibiting complex aeroelastic instabilities in a wind tunnel. The system consists of a rigid wing mounted on elastic supports with a flap that spans one-third of the wingspan and acts as an innovative nonlinear passive absorber. The setup includes pitch stiffness nonlinearity, which contributes to complex aeroelastic responses such as subcritical flutter and limit cycle oscillations. This solution benefits from aerodynamic damping and adds a very small amount of mass to the system. The main focus of this paper is to assess the influence of flap-NES parameters on aeroelastic behavior and to explore its potential impact on different wing configurations. Results show a delay in the onset of instability up to 34% in airspeed, a suppression of large amplitude vibrations due to stall flutter, and a removal of subcritical behavior.