Deformation and fragmentation of a water drop in collision with a thin cylinder

We experimentally study the collision of a falling water drop with a thin horizontal cylinder, focusing on phenomena that play a crucial role in the hydrodynamics of the collision but have not been studied previously. We address two different collision scenarios. In the first case, the drop is split into two separate parts connected by a liquid sheet oriented transversely to the cylinder. The surface tension of the sheet causes the parts to approach and merge, or the sheet breaks up and each part continues to move independently. The second scenario is realized at low collision velocities. In this case, the sheet is not formed, and the separation or merging of the drop parts is controlled by their surface tension driven deformations. We analyze the factors (drop velocity, cylinder diameter, and cylinder wettability) that govern the realizability of these scenarios. We also propose a simple criterion that predicts the transition from one scenario to the other.