Impact dynamics of successive droplets impinging on a superhydrophobic surface

The impact behavior of multiple droplets is frequently encountered in practical applications such as anti-icing and spray cooling. In this study, the lattice Boltzmann method is employed to study the successive impact of two droplets on a superhydrophobic surface. The effects of horizontal distance between droplet centers (l*), the impact time interval (Δt*), and the Weber number (We) on impact dynamics are systematically investigated. During the spreading phase, inertial forces dominate, rendering the process largely independent of l*, Δt*, and We. In contrast, the receding dynamics exhibit significant sensitivity to these parameters. A small l* leads to asymmetric impact, resulting in three distinct spreading stages and a notable increase in contact time. The parameter Δt* governs the timing at which the trailing droplet interacts with the liquid film generated by the leading droplet, thereby influencing the duration of the second spreading event. Increasing We enhances both the spreading diameter and rate, while higher We values reduce contact time by accelerating the receding process. Based on the interaction patterns between the leading and trailing droplets, four distinct impact regimes (I–IV) are identified, and corresponding three-dimensional phase diagrams of We–l*–Δt* are constructed. Contact time is strongly dependent on the impact regime: it is significantly prolonged in regime IV and stabilizes in regime III, while elevated We values contribute to the reduction of contact time. This work advances the fundamental understanding of sequential droplet impact dynamics and provides a theoretical foundation for the effective control of contact time in engineering applications.