Droplet Impact Modeling with Displaced Airflow Effects

This study presents preliminary work on predicting aircraft surface icing of large, supercooled droplets. The framework is based on a computational model of three-dimensional multiphase droplet impact on solid surfaces under standard temperature and pressure conditions. Rutkowski et al. (2003) demonstrated that neglecting initial spreading dynamics leads to significant disparities in the freezing mechanisms, so the impact dynamics (i.e., general behavior, spread diameter, height) obtained from the simulations are compared with experimental data across a wide range of Weber numbers. The model uses dynamic contact angles as boundary conditions, utilizing empirical equations to characterize surface properties to allow various fluid-surface combinations. Preliminary calculations showed significant deviations in spreading characteristics for water. Fu et al. (2021) reported that the low-viscosity fluids are susceptible to displaced airflow effects when droplet velocity is high. This phenomenon increases the apparent contact angle, and the surface behaves more hydrophobically. The viscosity of water increases as it is cooled, but it remains well below the threshold at which it would no longer be considered a low-viscosity fluid. This effect is thus incorporated into a proposed adjusted model for the advancing contact angle (ACA) and applied during the first milliseconds of the droplet's advancing phase. This adjusted model will be applied in future simulations of droplet icing predictions.