Droplet breakup and rebound during impact on small cylindrical superhydrophobic targets

The impact behavior of a water droplet on small cylindrical superhydrophobic targets is studied numerically and theoretically. A numerical model using the volume of fluid method is developed to simulate the droplet impact process on small cylindrical superhydrophobic targets. The model is verified by comparing the calculated results with the experimental observations in our previous work and reference. The influences of the Weber number and the target-to-droplet diameter ratio (less than one) on the droplet impact behaviors, including the droplet profile and the deformation factor, are investigated. The results indicate that a larger Weber number accelerates the spreading and falling of the droplet and promotes the droplet breakup. An increase in the diameter ratio delays the spreading and falling of the droplet on the side of the target, thus enhancing the deformation and rebound of the droplet. Both the increases in the Weber number and the diameter ratio contribute to a larger maximum deformation factor. Furthermore, the droplet breakup criterion is analyzed theoretically based on the energy conservation. A formula describing the relationship between the critical Weber number and the diameter ratio for the droplet breakup is proposed, which shows high prediction accuracy compared with the numerical values. The critical Weber number for the droplet breakup becomes larger with the increase in the diameter ratio. The findings in this research deepen our understanding of the mechanism of droplet impact on small targets.