An Experimental Investigation on Splashing Characteristics of Supercooled Large Droplets Impinging onto Inclined Surfaces

This study investigates the impact dynamics and reaction forces generated by single water droplets impacting hydrophilic and superhydrophobic (SHS) surfaces under a variety of Weber numbers (We = 300-1000), surface temperatures (25.0ºand -10.0ºC), and oblique impact angles (0º-60º). High-speed imaging was used to observe the morphology of the droplets at all the different conditions, displaying the lamella evolution, spreading, breakup, and splash formation, while a quartz force sensor measured the transient normal reaction force, which was nondimensionalized to compare across the several conditions. Results show that increasing the impact angle reduces the peak normalized force by about 50%-70% between 0º and 60º as the normal momentum component decreases and the lamella becomes increasingly asymmetric and directed downstream. Comparisons across the Weber numbers reveal that lower Weber numbers result in larger peak forces, as higher Weber number droplets redistribute their momentum into radial spreading and thin-sheet expansion rather than normal surface loading. Wettability also affects droplet morphology, as hydrophilic surfaces promote smoother, axisymmetric spreading, whereas SHS coatings introduce early rim breakup, fragmentation, splashing, and significantly reduced contact time. However, the peak magnitudes remain relatively similar between the two coatings for a given Weber number and angle. Subzero conditions increase fluid viscosity and partially freeze the droplets, suppressing radial expansion and leading to larger peak forces than in room temperature conditions. These findings demonstrate how inertia, wettability, temperature, and impact geometry redistribute momentum during droplet impact, dictating the force dynamics relevant to icing, erosion, and anti-icing surface design.