Experimental and Numerical Visualization of Droplet-Induced Crown Splashing Dynamics

Abstract

The objective of this study was to visualize the droplet-induced crown splashing dynamics at high spatial and temporal resolutions. In this work, the effects of droplet train impingement on crown splashing dynamics were investigated experimentally and numerically. Experimentally, a HFE-7100 droplet train was produced using a piezo-electric droplet generator at a frequency ( f ) of 7500 Hz resulting in a droplet Weber number (We) of 489. Droplet-induced crown splashing dynamics was captured using a high-speed imaging system. It was observed that the free rim of the droplet-induced crown was smooth and axisymmetric during the early crown propagation phases (t*< 5, where t* = 2πft). However, development of cusps was observed on the free rim during the intermediate phases (5< t* <8.5). It was found that the sites of the spikes distributed almost uniformly along the periphery of the free rim. At late phases (t* > 8.5), fingering, detachment and secondary droplets (i.e. splashing) were observed on the free rim. Results show that the number of cusps (finally becoming fingers and spikes) based on experiments (ncups,exp) agrees well with the prediction (ncups,th) given by the Plateau-Rayleigh instability theory. Numerical simulations were carried out using a 3D transient coupled level set-volume of fluid (CLSVOF) solver with Courant number less than 1. A grid independence study was performed to ensure the results were independent of grid size. Reasonable agreement was reached between the numerical and experimental data in terms of crown morphology at different phases. This study should lead to a better understanding of the evolution of droplet-induced crown morphology at splashing conditions.