A STOCHASTIC MODEL OF ATMOSPHERIC RIME ICING

ABSTRACT. The accumulation of rime ice on structures, due to the impact and freezing of small water droplets, has been modelled as a stochastic process. Individual droplets are introduced into the flow field about the structure at a random position. Their trajectories are then calculated to determine the position of impact on the structure, or on previously impacted droplets. By assuming that the droplets maintain their shape on impact, the modelled accretion is gradually built up, one droplet at a time. In the present paper, attention has been limited to a circular cylinder as the collecting structure, and it has been assumed that the flow field and the ice accumulation are strictly two-dimensional. With these assumptions, the influence of the droplet / cylinder diameter ratio and of the air speed upon the resulting predictions has been investigated. The main feature of interest in the model prediction is the development, near the edges of the accumulation, of discrete structures called "rime feathers". The mechanism for the growth of these rime feathers is described, and a comparison is made between the characteristics of the predicted structures and of some natural rime feathers grown in an icing wind tunnel