Experimental and numerical study of the post-impact behavior of a water droplet impacting on a hydrophilic surface with a cylindrical cavity

In this study, we couple a laboratory experiment with numerical simulations to investigate the post-impact behavior of a water droplet impacting a hydrophilic surface with a cylindrical cavity. In the experiment, we observe that either an increase in the depth of the cavity or a decrease in its diameter will promote crown formation, and the crown will be higher but narrower on a deeper or narrower cavity. Moreover, a higher impact speed leads to a larger crown. The numerical simulations of post-impact droplet behavior are in good agreement with the experimental results. More importantly, they shed light on the physics underlying the formation and development of the crown by computing the forces induced on the bottom, vertical wall, and surrounding wall of the cavity as the droplet impacts there. The simulations suggest that the cavity size and the impact speed play significant roles in determining the force profiles and thus whether a crown forms and, if so, how large it is. On the basis of the experimental and numerical results, we construct regime diagrams for the crown formation by considering the critical values of cavity size and impact speed.