Stochastic models of ice accretion

New stochastic models have been developed to simulate atmospheric ice accretions at low values of impaction parameters. In 2-dimensional models of ice accretion on cylindrical objects (disks impinging on a larger size disk) the restriction of rectilinear trajectories is removed and some flow dynamics is introduced by analytically calculating the droplet impact direction, in relationship to the aerodynamic conditions. Moreover, polydisperse droplets are considered instead of monodisperse ones. The numerical experiments indicate that the growth direction of the rime feathers can be theoretically predicted by a simple relationship involving three characteristic growth angles. Comparisons with experimental and theoretical results are presented. Model simulations in 3-dimensions (monodispersed spheres impinging on a particle embryo or a cylinder) have been obtained with a purely ballistic approach (rectilinear trajectories). The 3-D density has also been computed, by integrating along the axis of the cylinder circular sectors of 1 degree in width. Comparison with a 2-D density profile confirms the angle β=20° as the main growth characteristic for 3-D aggregates