Effects of an immiscible liquid film on an impacting droplet

We combine a laboratory experiment with numerical simulation to investigate the impact of a water droplet on a silicone oil film. The experimental observation presents that the existence of the immiscible liquid film promotes the occurrence of splashing, but continuously increasing the dimensionless thickness of the film from 0.027 to 0.11 limits the splashing. The numerical simulation accurately captures the flow dynamics around the water-oil interface and the individual post-impact behaviors of the water and oil components. It not only successfully reproduces the laboratory observation, but also provides the underlying physics of the flow behaviors of the immiscible impacting process. The simulation suggests that the higher pressure formed at the root of the crown leads to a wider crown on the thinner film, whereas the steeper streamlines create higher crown on the thicker film, due to the transferred momentum between water and oil components. More importantly, the numerical simulation sheds light on the processes that control the splashing behavior of both the water and oil components of the crown. On the thinner film, the difference between the mean velocities of the advancing nose and the root of the water and oil coronas is higher, whereas the neck thickness of the coronas is lower. As a result, the coronas, within the scope of this study, are prone to splash on the thinner film. In addition, the higher difference in mean velocities and the thinner neck arise in the oil corona, than in the water corona, leading the oil corona to break up more easily.