Droplets splashing upon films of the same fluid of various depths

We explore the effects of fluid films of variable depths on droplets impacting into them. Corresponding to a range of fluid "film'' depths, a non-dimensional parameter-H*, defined as the ratio of the film thickness to the droplet diameter-is varied in the range 0.1 <= H* <= 10. In general, the effect of the fluid film imposes a dramatic difference on the dynamics of the droplet-surface interaction when compared to a similar impact on a dry surface. This is illustrated by the size distribution and number of the splash products. While thin fluid films (H*approximate to 0.1) promote splashing, thicker films (1 <= H* <= 10) act to inhibit it. The relative roles of surface tension and viscosity are investigated by comparison of a matrix of fluids with low and high values of these properties. Impingement conditions, as characterized by Reynolds and Weber numbers, are varied by velocity over a range from 1.34 to 4.22 m/s, maintaining a constant droplet diameter of 2.0 mm. The dependence of splashing dynamics, characterized by splash product size and number, on the fluid surface tension and viscosity and film thickness are discussed.