Splashing Model for Impact of Supercooled Large Droplets on a Thin Liquid Film

Abstract

Compared to conventional icing additional droplet phenomena have to be accounted for in icing caused by supercooled large droplets (SLD) such as splashing, rebound, breakup and deformation. In this study the effect of the presence of a thin liquid film of water on the surface has been investigated. This liquid layer can arise when SLD droplets freeze only partially following impact on the airfoil. The effect of the liquid film is simulated by using the wall shear stress and by assuming a linear velocity profile in the liquid layer. The shear stress is calculated by coupling an integral boundary-layer method to a potential ow method. An improved splashing model has been implemented in the existing com-putational method. This splashing model consists of a deposition model that accounts for splashing during impact of droplets on a liquid layer. In an extension to this model different solidification models have been investigated to estimate the time of solidification of a liquid splat produced on the surface after impact. One is a planar solidification model which is described by the Stefan problem for heat conduction and which is mostly controlled by diffusion. The second model is based on dendritic solidification, which is rapid and gov-erned by kinetics. The results of the deposition model on SLD ice accretion are compared with data from experiments on a NACA-23012 airfoil and on a NACA-0012 airfoil. Good agreement is found.