Drop ejection from vibrating damped, dampened wings

Abstract

The task of moisture removal from small, delicate surfaces such as sensors and flight surfaces on micro-flyers can be challenging due to remote location and small scale. Robustness is enhanced when such surfaces, of comparable scale to deposited drops, can remove deposition without external influence. At this scale, the dynamics of a solid surface responding to a mechanical input is highly-coupled to the fluid resting above. In this study, we explore highly-coupled fluid–solid mechanics using singular liquid drops of water and a glycerin solution resting on millimetric, forced cantilevers. These wing-inspired cantilevers are sinusoidally displaced at their base across 85–115 Hz, producing surface accelerations up to 45 gravities at drop release. We observe three principal drop release modes: sliding, normal-to-cantilever ejection, and drop pinch-off. Release modes are dependent on drop and cantilever properties, and cantilever motion. Predictions of ejection modes are accomplished by application of Euler elastica theory and drop adhesion forces. Lastly, we determine damping of cantilever motion imposed by sloshing drops.