Droplet impact dynamics on shallow pools

High-speed droplet impact onto shallow pools can be seen throughout industry and nature: rain-induced icing, spray cooling, raindrops impinging onto puddles, and agricultural sprays coating plants – to name just a few examples. However, it is only in the last decade or so that the importance of a thin jet of fluid (ejecta sheet) during the first millisecond of impact on the subsequent dynamics has been appreciated. Using a combination of experiments and numerical simulations, we will explain the effect of pool depth, impact velocity, and the surrounding gas properties on ejecta sheet dynamics. These parameters will all be shown to have consequences for the satellite droplets generated. We will also discuss the 3D dynamics that result from breaking axisymmetry with pool base topology.