Single Drop Splash on Thin Film: Measurements of Crown Characteristics

The impact of a single drop on a liquid film was studied by photographic techniques. A drop generator capable to produce single liquid (water) drops of millimetric size (with a good repeatability) was positioned at different distances from the horizontal wall onto which drops impacted by gravity. The wall was covered by a liquid layer whose thickness could be varied. The fluid motion was studied by means of a CCD camera (1 ?s exposure time) from different positions. In particular, the use of a transparent (glass) wall allowed to study the impact phenomenon from below by a proper optical set-up. Quantitative analysis of the crown evolution was then possible, crown diameter (internal and external), crown elevation and thickness were measured, with different degree of accuracy, as a function of impact Weber number and nondimensional film thickness. Number of jets protruding from the upper rim was also recorded as well as their average size and growth rate. The gathered quantitative data allowed a thorough analysis of the process, and some interesting features of crown evolution are reported together with comparison with existing models.