Numerical Simulation for Prediction of Secondary Droplets by Water Droplet Impingement on Thin Water Film Using E-MPS Method

Ice accretion is a phenomenon in which super-cooled water droplets or ice particles in the atmosphere impinge on a solid surface, and an ice layer is formed there. The ice accretion on an aircraft threatens navigation safety because it causes deformation of the wing shapes and reduces the aerodynamic performance. Hence, it is a significant technical issue to predict icing during the design phase of an aircraft. When the droplet diameter is over 40 μm, it is called a super-cooled large droplet (i.e. SLD). It is well known that splash and rebound occur when a SLD impinges on a wall. Especially, as splash generates secondary droplets, it forms very complex ice shapes due to the secondary droplets. Furthermore, liquid film on a wall significantly affects the impact behavior. Therefore, it is necessary to consider the secondary droplet generation and the existence of liquid film on the impact behavior of an SLD in aircraft icing. Considering these backgrounds, we simulated the droplet impact behavior on a thin water film by using the Explicit-Moving Particle Simulation (E-MPS) method. Through the present study, the following insights are obtained; (1) In the case of vertical impact, each dimension of the crown shows a similar tendency to change with time as in the experiment. (2) In the case of oblique impact, secondary droplets are generated at the impact angle between 75 to 31 degrees, and the total mass of secondary droplets reaches a maximum of around 39 degrees.