Numerical Simulation of Supercooled Droplets Deformation, Impingement and Freezing for In-Flight Icing

Water droplet deformation, impingement, and freezing are major processes in the study of in-flight icing. There are complex multi-physics phenomena involving interactions between gas, liquid, and solid. In this chapter, droplet deformation is first numerically investigated. Following this, its effects on airflow velocity, droplet diameter, and ambient temperature are systematically examined through coupling with the level-set method. Based on these studies, new droplet drag analytical models are proposed. Besides, for investigating the droplet impingement effect, especially the impingement on surfaces with different hydrophobicity, two numerical techniques (such as level-set and multi-phase Lattice Boltzmann) are employed and developed. The level-set method is used to simulate droplet impact on flat superhydrophobic surfaces; accordingly, a water droplet impingement model governed by Weber and Reynolds numbers is then proposed to predict the outcomes of droplet impingement. In addition, a three-dimensional pseudo-potential Lattice Boltzmann method is developed to investigate the droplet impingement on superhydrophobic surfaces with protrusions, with particular emphasis on the mechanism of contact time reduction. Finally, the droplet freezing phenomenon is numerically studied through the proposed method, in which the multiphase Lattice Boltzmann and the enthalpy porosity method are adopted to track the gas-liquid and solid-liquid interfaces, respectively. The evolution process of the interface during droplet freezing is visually illustrated, and the effect of droplet size, supercooling degree, and surface hydrophobicity on this process are systematically investigated and analyzed.