Normal droplet impact on horizontal moving films: an investigation of impact behaviour and regimes

Investigations of the impact regimes for a liquid droplet impacting onto horizontal moving liquid films are presented here for the first time. The aim of this study is to show the main impact outcomes and to highlight the effect the movement of films has upon these outcomes. The droplet diameters used in this experiment were 2.47 and 3.86 mm with impact Weber number of between 0.6 and 460. The Reynolds number of the moving film was between 351 and 1,818 depending on the flow rate (1-5.5 L/min) with changes in the film height of between 4.3 and 9.4 mm. The results showed that the impact outcomes exhibit the same regimes established for the impact on static liquids but with different transition boundaries. Moreover, the shape of the impact outcomes is unsymmetrical similar to the inclined impact on static liquids. The impact outcomes are shown to undergo a transition as the Reynolds number of the film increases, this occurs at a threshold value close to the expected transition between laminar and turbulent flow.