Aircraft icing in flight: Effects of impact of super cooled large droplets

In this study a computational method is presented which simulates the presence of a liquid layer on an airfoil and its effect on splashing of Supercooled Large Droplets (SLD). The thin liquid film is expected to have a significant influence on the impact behaviour of SLD. It will arise when the impacting droplets freeze only partially and leave behind a layer of runback water on top of the ice layer. The liquid film is modelled using the wall shear stress and by assuming a linear velocity profile within the water layer. The shear stress is calculated by coupling an integral boundary-layer method to a potential flow method. The SLD splashing model is extended with a deposition model that accounts for impact on a liquid film and includes the solidification time of the droplets. This solidification time is obtained using multiple approaches which are based on either planar solidification or dendritic solidification. Planar solidification is controlled by diffusion and based on the Stefan problem for heat conduction. Dendritic solidification is more rapid and mostly governed by kinetics. The comparison of the catching efficiency with experimental results for a NACA-23012 airfoil shows a significant improvement employing the new deposition model. Also, good agreement is found with the experimental results for the ice accretion on a NACA-0012 airfoil.