Wave propagation on splat induced by liquid drop impingement

Abstract

This study investigates the interaction between an impacting liquid drop and a static, axisymmetric splat generated on a solid prior to impact, focusing mainly on the wave production and propagation on the splat with low impact velocity. Using high-speed video, the wave generation is observed and analyzed, including a first wave caused by drop kinetic energy, and secondary and tertiary capillary waves subjected to surface tension. Also, the wave propagation magnitude is discussed concerning the effects of Weber number and fluid viscosity, the purpose of which is to provide a suitable method for predicting the wave diameter. Results show that increasing Weber number decreases the wave propagation slightly, but this effect becomes less significant at higher Weber number. In particular to the fluid of butanol with high viscosity, the wave propagation is very insensitive to Weber number. The formula based on the kinematic discontinuity theory can be modified to predict the wave propagation magnitude with a fairly good agreement, for both the kinematic wave and the capillary wave. In addition, the dynamic wavelength situated between the first and secondary waves, and the propagation speed of the wave during the drop–splat interaction are also analyzed. This study advances the fundamental understanding of the spray evaporative cooling with low volumetric flux.