Three-Dimensional droplet splashing dynamics measurement with a stereoscopic shadowgraph system

In the current study, a novel three-dimensional (3D) measurement technique is established using a high-speed stereoscopic shadowgraph system, which is applied to investigate the 3D splashing dynamics of silicone oil dropping on liquid films quantitatively. Both crown-type splashing and crown wall bottom breakdown splashing morphologies are involved for measurement and comparison. Based on the shadowgraph images, the secondary droplets diameter, number and mass fraction are determined. The three-dimensional (3D) coordinates of the secondary droplets during the splashing processes are reconstructed and tracked, based on which the 3D trajectories, velocities, ejecting angles and kinetic energy are calculated and analysed. It is found that the secondary droplets in crown bottom breakdown cases have a larger mass fraction and kinetic energy than that in crown-type splashing cases. The measurement indicates that the radial velocity increases with the decreasing of film thickness, while the vertical velocity does not vary too much. Significant disparities between two-dimensional (2D) and three-dimensional (3D) velocity magnitudes as well as kinetic energy have been identified, which indicate that accurate time-resolved 3D measurements are of great importance for quantitative investigation of splashing phenomena and the high-speed stereoscopic shadowgraph system has been proved to be able to play a role.