Stigma as two degrees of freedom energy sink for flutter suppression

Abstract

This paper presents a novel explanation on the aerodynamic function of the dragonfly stigma, which is a pigmented spot with heavier masses near the tip of a dragonfly’s wing. Dynamic modeling based on the micro-structures shows that the stigma can be simplified as two lumped masses connected by a massless beam, and installed on the primary structure by two tow springs. This model works as a two degrees of freedom (2DoF) energy sink. Theoretical modeling and numerical simulations prove that the stigma is capable to suppress flutter — a self-excited vibration. The flutter velocity of a system with the stigma is increased by 15.8% comparing to the case without the stigma, while this increase is only 3.7% if the stigma is merely considered as a counterweight. The limit cycle oscillations (LCOs) of wing’s pitch motion are also significantly reduced. A comparison in the discussion further reveals that this energy sink structure of the stigma has advantages over conventional energy sinks, which is worthy of follow-up bionic research.