Abstract
In this study, we numerically simulated the behavior of droplets supplied from the front part of an object as well as their paths on the surface of it. This object models the windshield and the side door glass of an automobile running in the rain. Some characteristic behaviors of a droplet on the body surface are already known, although it is still difficult to numerically reproduce them. The main purpose of this study is, therefore, to simulate one of such behaviors, i.e., droplets near the leading edge on the side glass tend to be lifted upwards. In the simulation, the Lagrangian method is employed, where four forces act on a droplet, i.e., aerodynamic drag, adhesion, viscous friction, and gravity. A numerical simulation of one droplet showed that the droplet's behavior strongly depends on its diameter: Specifically, the effects of aerodynamic force and viscous friction are dominant in the case of a large diameter. From this observation, we assumed that there is a "PATH" created by a droplet on the surface, meaning a wet region, on which the viscous friction is reduced once the droplet passed. We incorpolated this PATH effect into the simulation code, and obtained better agreement with the corresponding experiment.
