A supercooled water drop impact and solidification: effect of substrate roughness and air flow

Ice accretion is often caused by the nucleation and freezing of a supercooled water drop after its impact on working surfaces, such as aircraft wings, transmission lines or fan blades, it threatens the safe operation of the equipment and even leads to catastrophic failures. Therefore, it is crucial to better understand the physics of supercooled drop impact. The main subject of this study is the observation of a supercooled drop impact and measurements of a freezing time. The experiments are performed in a vertical wind tunnel, installed in a cold room. The phenomenon is observed with a high-speed video system. In the experiments, the air velocity has been varied from 0 to 22.5 m/s. Additionally, three substrates of different roughness have been investigated. It has been found that higher roughness of the substrate leads to a higher probability of nucleation after impact. Additionally, the higher air velocity also prompts earlier nucleation inception. Furthermore, intriguing cavities and voids formed from the drop breakup upon impact on rough substrates have been observed, which have an effect on the nucleation as well.