Non-simultaneous impact of droplets on a hydrophobic cylinder

•The non-simultaneous impact of double droplets on the hydrophobic cylindrical wall is investigated.•Effects of impact velocity, horizontal spacing and vertical spacing on droplet dynamics are analyzed.•The MSD, COM, and β of double droplets impacting the wall are reported.•The effect of horizontal spacing on droplet spreading performance is more significant. The interaction between droplets and walls is ubiquitous, with the impact of multiple droplets on solid surfaces being the most common scenario. In this study, the spreading and flow characteristics of a pair of droplets impacting a curved wall at the mesoscale at different times are simulated using the Many-Body Dissipative Particle Dynamics (MDPD) method. The effects of the impact velocity, horizontal spacing, and vertical spacing of the droplets on the interfacial evolution process are discussed. The coalescence spreading modes, mean square displacement (MSD), center of mass (COM), and spreading coefficient (SC) of the double droplets as they change over time under various parameters are analyzed. The results indicate that when the droplets impact simultaneously, they spread uniformly, forming a liquid film with a central protrusion. In contrast, when impacting non-simultaneously, the second droplet’s impact on the already spread film causes further spreading or retraction, leading to a deviation in the central raised area of the merged droplets. The horizontal spacing significantly affects the merging and disturbance of the liquid film during non-simultaneous impacts. At lower impact velocities, the horizontal spacing notably influences the axial MSD of the droplets, whereas at higher impact velocities, the spreading capability of the droplets on the wall is enhanced, showing a different trend in MSD with changes in horizontal spacing. The vertical spacing also significantly affects the merging and disturbance of the liquid film, especially at lower impact velocities, where the vertical spacing determines whether the double droplets coalesce. Both impact velocity and droplet spacing jointly influence the dynamic behavior of the droplets, particularly in non-simultaneous impacts. The spacing has a minor impact on the trend of the SC but significantly affects the peak spreading coefficient (PSC) and its timing. An increase in horizontal spacing leads to an increased PSC, while an increase in vertical spacing results in a decreased PSC, accompanied by a delay in the spreading time. Compared to vertic