69. Analysis of High Energy Impact of a Raindrop on Water

The present paper is devoted to the analysis of the impact of a raindrop on water. The studied configuration is focused on the effects of high energy splash regimes, caused by the impact of large droplets at high velocity. Such cases, which mimic raindrops falling on the surface of the ocean at their terminal speed, are characterized by short time scales and complex mechanisms, and they have received little attention until now. The GERRIS opensource solver is used to perform three-dimensional simulations of the impact. The capabilities of octree adaptive mesh refinement enable to capture the small-scale features of the flow, while the Volume Of Fluid (VOF) approach combined with a balanced force surface tension calculation is applied to advect the volume fraction of liquid and reconstruct the interfaces. A post-processing of the results has been developed to identify each object resulting from the splash and characterize their evolution in time. Specifically, the contour of the liquid/gas structure created at the impact is reconstructed as well as the size and position of the ligaments and droplets aerosolized in the atmosphere. The results are compared to experimental data obtained previously by Murphy et al. (J Fluid Mech 780:536–577): both the crown formation above the cavity created by the impact, the ligaments emanating from the rim at the top of the crown, and the downward liquid jet that pierces through the bottom of the cavity, are correctly reproduced by the model. A very good quantitative agreement is also obtained regarding the time evolution of the crown dimensions, including its closure after the initial phase of expansion.