A Numerical Study on the Aerodynamics of Freely Falling Planar Ice Crystals Journal of the Atmospheric Sciences

Fluid flow fields and fall patterns of falling planar ice crystals are studied by numerically solving the unsteady, incompressible Navier–Stokes equations using a commercially available computational fluid dynamics package. The ice crystal movement and orientation are explicitly simulated based on hydrodynamic forces and torques representing the 6 degrees of freedom. This study extends the current framework by investigating four planar-type ice crystals: crystals with sector-like branches, crystals with broad branches, stellar crystals, and ordinary dendritic crystals. The crystals range from 0.2 to 5 mm in maximum dimension, corresponding to Reynolds number ranges from 0.2 to 384. The results indicate that steady flow fields are generated for flows with Reynolds numbers less than 100; larger plates generate unsteady flow fields and exhibit horizontal translation, rotation, and oscillation. Empirical formulas for the drag coefficient, 900-hPa terminal velocity, and ventilation effect are given. Fall trajectory, pressure distribution, wake structure, vapor field, and vorticity field are examined.