Fast Droplet Shedding via Aerodynamic Ratchet on a Moving Surface

Abstract

The rapid detachment of liquid from engineered surfaces is significant to applications ranging from self-cleaning and energy harvesting to anti-icing. While droplet repellency on stationary surfaces has been extensively achieved through surface chemistry and micro/nanotexture, the impact dynamics of droplets on rapidly moving surfaces remains poorly understood. Here, we systematically investigated the interaction between droplets and a moving surface with a horizontal velocity up to 50 m/s, identifying two distinct bouncing regimes. At low surface velocities, droplets undergo asymmetric bouncing, leading to a modest contact time reduction of approximately 25%. Above a critical surface velocity, however, droplets detach in the pancake configuration, reducing the contact time by approximately 65%. This transition arises from the lubrication pressure generated by an entrained air layer between the droplet and the rapidly moving surface, which suppresses conventional retraction and promotes early lift-off. We develop a scaling law that predicts the critical velocity separating these two regimes, providing a quantitative framework for controlling droplet contact time on moving surfaces. These findings not only advance fundamental understanding of liquid–solid interactions on moving surfaces but also offer practical strategies for minimizing liquid–surface contact in high-speed systems, including ice prevention in aircraft engines and erosion mitigation in turbine blades.