Fast Droplet Shedding via Aerodynamic Ratchet on a Moving Surface

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.