Numerical study of supercooled water droplets continuously impacting a superhydrophobic surface with different spacings

Supercooled water droplets impact the cold surface of an aircraft and form ice accumulations, which pose a threat to flight safety. Therefore, it is necessary to understand the dynamic behavior and phase transition process of these droplets. In this study, the dynamic process of double supercooled water droplets continuously impinging on a cold superhydrophobic surface (SHS) is numerically simulated using the Volume of Fluid (VOF) method in conjunction with the Solidification/Melting model. The study investigates the influences of droplet spacing and the Weber number (We) on droplet spreading and heat transfer characteristics. We observed three distinct mixing modes when double droplets impact at low Weber numbers: 'internal spreading', 'surface spreading', and 'shower spreading'. As the spacing between droplets increases, these modes appear in sequence. The maximum spreading factor transitions from a constant value to an increasing one, and the aggregation behavior of the double droplets intensifies. In the 'internal spreading' mixing mode, the vortices formed inside the double droplets impede the horizontal spreading, thus preventing an increase in the spreading area. Moreover, as the droplet spacing increases, the heat transfer between the droplets and the cold surface is enhanced. The contact area of the droplets with the cold surface is a decisive factor in heat transfer, outweighing the influence of the local heat transfer coefficient. This study enhances our understanding of the dynamics and heat transfer of double supercooled water droplets continuously impinging on a cold superhydrophobic surface (SHS) and contributes to the development of anti-icing and de-icing technologies.