Droplet impact dynamics on a rotating aluminum disk: Comparative study based on liquid properties

An experimental study has been conducted to explore the effect of liquid properties on the dynamics of a droplet impacting a rotating aluminum disk. The study focuses on water, ethanol, and a glycerol–water mixture to cover a wide range of Weber, Reynolds, and Ohnesorge numbers as well as contact angles. The investigation has identified four distinct regimes, including deposition, child droplet formation, asymmetric splash, and partial rebound, depending on the rotational speed, impact velocity, and liquid properties. The angular and radial spreading lengths of droplets at different operating conditions and times have been measured and different empirical correlations have been developed to link these lengths as well as the maximum radial and angular spreading lengths to the Reynolds (or Weber) number, the Ohnesorge number, dimensionless time, and contact angle hysteresis. It is revealed that the angular spreading length markedly increases with time and rotational speed. Conversely, an increase in the Ohnesorge number leads to a reduction in the angular spreading. The maximum radial spreading length diminishes with a decrease in impact velocity or an increase in the Ohnesorge number or the rotational speed. Additionally, it has been observed that within the deposition regime, as the Ohnesorge number increases or the contact angle decreases, the droplet does not retract radially. Upon droplet deposition on the rotating surface, it has been noted that a wave propagates across the droplet surface from its inner edge to the outer edge, leading to the formation of fingers. Remarkably, it has been determined that the velocity of this wave is unaffected by liquid properties and is solely determined by the rotational speed and impact velocity. Furthermore, a substantial increase in the number of fingers is observed with a decrease in the Ohnesorge number or an increase in the rotational speed.