The impact of droplets on an inclined falling liquid film is studied experimentally using high-speed imaging.
The falling film is created on a flat substrate with controllable thicknesses and flow rates. Droplets with different
sizes and speeds are used to study the impact process under various Ohnesorge and Weber numbers, and film
Reynolds numbers. A number of phenomena associated with droplet impact are identified and analyzed, such
as bouncing, partial coalescence, total coalescence, and splashing. The effects of droplet size, speed, as well the
film flow rate are studied culminating in the generation of an impact regime map. The analysis of the lubrication
force acted on the droplet via the gas layer shows that a higher flow rate in the liquid film produces a larger
lubrication force, slows down the drainage process, and increases the probability of droplet bouncing. Our results
demonstrate that the flowing film has a profound effect on the droplet impact process and associated phenomena,
which are markedly more complex than those accompanying impact on initially quiescent films.