Rebound dynamics and directional migration of a droplet impacting on a macro-structured superhydrophobic surface

Directional migration of droplets is important for anti-icing, self-cleaning, and water collection technologies. In this paper, the rebound dynamics and directional migration of a droplet impacting a macro-structured surface are explored via numerical simulations. Two Weber number (We) regimes are considered: a low We regime and a high We regime. The influence of the vertex angle (α) on the horizontal transport of a droplet impacting an isosceles triangular ridge textured on a superhydrophobic surface is investigated. In both the low and high We regimes, as α increases, there is a noticeable rise in momentum loss in the vertical direction and a significant conversion of momentum to the horizontal direction across the ridge. In the low We regime, droplet splitting occurs during the retraction phase, while in the high We regime, the droplet splitting occurs during the spreading-retraction transition phase. In the low We regime, the transportation distance in the horizontal direction across the ridge of the droplet is minimum at α = 20° and maximum at α = 80°, while in the high We regime, such distance is minimum at α = 100° and maximum at α = 60°. By adjusting α and We, a transport distance of 6–17 times the droplet's diameter is achievable for We < 20, and 14–31 times for We ≥ 20. These findings offer a theoretical foundation for the precise control of droplets through impact on the macroscopic ridge. The obtained results contribute to the fundamental understanding of droplet directional migration and are valuable for related engineering applications.