Behavior of a water droplet impacting a thin water film

The splash morphology and central jet characteristics of a water droplet impacting a thin water film were investigated for carefully controlled liquid film thicknesses of 120-700 mu m using a chromatic confocal displacement sensor. The investigations studied the influences of liquid film thickness, impact velocity and surface characteristics. The coalescence and prompt splash morphologies that included three secondary types were presented in a scatter map based on parameter K and dimensionless film thickness delta. A critical threshold was found between a prompt splash with a delayed splash and a prompt splash without a delayed splash. The results show that the splash morphology is sensitive to the film thickness in this range. The surface characteristics affect the expanding of the crown base by changing the flow drag. Observations of the central jet show that the active central jet breakup depends on the film thickness and the impact velocity. [GRAPHICS]