Dynamics of a liquid lamella resulting from the impact of a water drop on a small target

The dynamics of a circular liquid lamella resulting from the collision of a water drop with a small disc–like target was studied experimentally and theoretically. Such a type of collision also acts as a model of drop impacts on plane surfaces in the absence of liquid friction, and therefore for more widespread collisions of drops of inviscid liquid with solid surfaces. We propose a simple model to describe the dynamics of the lamella resulting from the drop impact and also predict the structure of the liquid flow in the lamella. It is based on the observations that during the drop collision with the target, the liquid is ejected at an approximately constant flow rate with a velocity that significantly decreases in time. The resulting distributions of velocities, local flow rates and film thickness in the lamella are calculated. Besides, we have measured the distribution of the local Weber numbers by generating Mach–like rupture waves (we have called them Mach–Taylor waves) in the lamella, which follows the Taylor theory of disintegration of fluid sheets. Unknown parameters of the model are obtained from the comparison between the theoretical expression for local Weber number and the experimental data. The time evolution of the lamella diameter was obtained by numerical integration of the model. It was found that during the lamella life, zones of metastability could be formed in the lamella. In these zones a propagating rupture hole cannot be transported away by the flow and it yields to destabilization. One metastability zone expands from the target towards the external rim, and it is the opposite for the other one.