Impact dynamics of droplets on inclined superhydrophobic cylindrical surfaces: Maximum spreading in axial and azimuthal directions

Droplet impact on surfaces is a fundamental phenomenon in many engineering applications. The asymmetry induced by surface curvature during impact has garnered significant attention due to its relevance in anti-icing strategies for cables and other curved interfaces. While previous studies have extensively examined droplet dynamics on superhydrophobic cylinders oriented horizontally under low Weber number (We) impacts, real-world scenarios often involve high Weber number impacts (We>100) and varying obliqueness, leading to complex post-impact behavior. This study systematically investigates the effect of inclination on both axial and azimuthal orientations of the asymmetric post-impact lamella. It is observed that the typical elliptical lamella formed on horizontal cylinders becomes increasingly distorted as the inclination angle, α, increases. Both axial and azimuthal spreading lengths exhibit a decreasing trend with an increase in α. Furthermore, the low hysteresis characteristic of the surface results in reduced adhesion forces, promoting a sliding motion of the lamella along the cylinder's axis. Various post-impact phenomena, including asymmetric bouncing, receding breakup, nucleation-induced film rupture, and fluid lamella splashing, were documented. A modified scaling relation incorporating the inclination angle is proposed to predict the azimuthal spreading length at maximum extension, while axial elongation is modeled using mass and energy balance considerations. The predictive models exhibit strong agreement with experimental results, offering valuable insight into the complex droplet impact dynamics on inclined superhydrophobic cylindrical surfaces.