Abstract: Addressing the icing problem on aircraft surfaces and internal engine structures in aviation, alongside the practical need for developing passive anti-icing technologies, the study systematically investigated the dynamic processes of droplet impact on low-temperature horizontal and inclined micro-nano structured surfaces. The study was achieved through a combined approach of experimental research and theoretical derivation. Based on the energy conservation equation, the influence mechanisms of micro-nano structures, surface temperature, and impact velocity on droplet impact patterns, spreading coefficient, and freezing time were elucidated. A predictive model for the maximum droplet spreading coefficient has been established. Research findings indicate that low-temperature surfaces inhibit droplet rebound. As temperature decreases, droplet impact pattern sequentially exhibits complete rebound, partial rebound, and deposition. When surface temperature exceeds -5°C, droplets first spread before retracting, with micro- nano structures significantly reducing the spreading coefficient. Below -5°C, droplets enter the freezing stage after reaching maximum spreading and the spreading coefficient increases initially before stabilizing. During the freezing stage, the spreading coefficient increases as the surface temperature decreases. The maximum spreading coefficient of droplets on low-temperature surfaces follows a one-half power law with Weber number. Micro-nano composite structures exhibit stronger delaying capabilities against droplet freezing compared to micro surfaces. Increasing the surface inclination angle, raising surface temperature, and reducing the droplet Weber number can effectively prolong the droplet freezing time.

Key words: Droplet impact, micro-nano structure, impact pattern, spreading coefficient, freezing time