Mesoscopic solidification mechanism of supercooled droplets under strong convective cooling

During aircraft takeoff or landing, it often has to pass through clouds containing supercooled droplets. In such conditions, high-speed droplet impacts on the wing or fuselage surfaces can easily trigger icing, posing a serious threat to flight safety. To address this issue, this study numerically investigates the freezing behavior of microscale supercooled droplets impacting cold surfaces under low-temperature and strong convection conditions, using a mesoscopic approach to reveal the underlying dynamics. Results show that when a micron-scale droplet impacts a cold surface, it rapidly freezes to form an ice shell, which significantly suppresses rebound. Even at scales where surface tension dominates, the droplet cannot recover its original dynamic characteristics. When cold airflow is considered, both the freezing rate and ice shell thickness further increase, with the frozen region gradually expanding outward from the droplet center, imposing stronger restrictions on the rebound process. For inclined impacts, in addition to the strong suppression of rebound similar to normal impacts, the leading edge in the velocity direction is more prone to ice shell formation, which not only hinders forward spreading but also interacts with tail-end freezing to ultimately form irregular ice structures. Com-prehensive analysis indicates that heat conduction through the cold surface remains the dominant mechanism governing the freezing rate, but the influence of cold airflow on the freezing morphology is critical and cannot be neglected. This study provides new mesoscopic numerical evidence for understanding the freezing mechanism of microscale droplet impacts on aircraft surfaces, offering valuable reference for the optimization of anti-icing and de-icing designs.