Topological change of a hollow droplet impacting onto a cylindrical super-hydrophobic target: A numerical study

In this paper, we numerically investigate the dynamics of a hollow droplet impacting onto a small super-hydrophobic cylinder. Four distinct regimes are identified based on the topological changes experienced by the droplet during impact: direct bounce, break-retract, break-break, and rim break. The transitions between these regimes are discussed with respect to dimensionless parameters such as the Weber number and the droplet-to-target diameter ratio. Additionally, we propose theoretical predictions for these regime transitions, which show reasonable agreement with our numerical results. This study provides insights into the dynamics of hollow droplets impacting on rough surfaces and has potential applications in altering the topology of hollow and other compound droplets. • Performed direct numerical simulations of hollow droplet impacts on small targets. • Observed topological changes of hollow droplets during impact on small targets. • Identified four distinct impact regimes based on the droplet’s topological changes. • Developed theoretical models to describe the threshold of droplet breakup.