An Experimental Study on the Droplet Impinging Dynamics and Icing Process on Cold Surfaces with Different Wettabilities

Supercooled large droplet (SLD) impingement remains a significant concern for aircraft and Unmanned Aerial Vehicle (UAV) surfaces operating in cold and moist environments, where traditional anti-icing methods may be insufficient or power demanding. This experimental study investigates the impact dynamics and freezing behavior of millimeter-scale supercooled large water droplets on hydrophilic and superhydrophobic surfaces (SHS) under high-inertia conditions. Experiments were conducted at surface temperatures of −5°C, −10°C, and −15°C using simultaneous high-speed imaging and infrared thermography to capture both the morphological evolution and unsteady heat transfer process during droplet impingement and phase change. The droplets, impacting at a Weber number (We) of approximately 1200 and Reynolds number (Re) of 11,500, exhibit rapid spreading and recoil upon contact. On hydrophilic surfaces, freezing initiates within a few seconds after impact, with the thermal core dissipating quickly and solidification progressing radially. In contrast, droplets on SHS surfaces display significant freezing delays—up to 120 seconds at −5°C—along with persistent thermal hotspots, indicating localized latent heat retention and suppressed ice nucleation. These results demonstrate that surface wettability plays a key role in modulating not only the early impact behavior but also the longer-term freezing process. The combined use of thermal and visual techniques assists in attaining a detailed comparison of energy dissipation, freezing onset, and post-impact morphology. Findings support the potential of SHS coatings as passive anti-icing strategies for systems where weight, power, and maintenance constraints limit the use of active thermal protection.