Freezing behaviors of impacting water droplets on cold inclined surfaces

•Strong coupling between drop-scale fluid dynamics and solidification are achieved.•Effects of inclined impact angles on the freezing morphologies are explored.•The rivulet length shows a non-monotonic dependence with impact velocity.•Effects of subcooling degree on the issue and geometry of rivulets are examined. Freezing of impacting water droplets on cold inclined surfaces is ubiquitous in nature and many engineering applications. Most of previous studies are limited to the regime where the interaction between the solidification and drop-scale fluid dynamics are weak. In this work, we explore the freezing behaviors of water droplets upon impacting an inclined super-hydrophilic surface at a sufficiently low temperature, so as to improve the coupling effect between the solidification and drop-scale fluid dynamics. Different from an almost identical ice shape when the surface inclination angle α = 30°, the ice at its leading edge becomes steeper with the subcooling degree ΔT when α = 45°. Intriguingly, when α = 60°, the interactions between rivulet dynamics and solidification result in the non-monotonic variations of the rivulet length with impact velocity. Besides, the increasing ΔT has negative (positive) effects on the rivulet length at the low (high) impact velocity regime. Furthermore, the slenderness of rivulet increases with ΔT, indicating the coupling degree between the solidification and rivulet dynamics.