Shape oscillations in an initially nonspherical raindrop*

The dynamics of a nonspherical droplet falling in air is investigated via three-dimensional numer- ical simulations of the Navier-Stokes and continuity equations. The main focus of this work is to study the effects of the relative influence of surface tension force over the inertial force, and the orientation of the droplet. The range of parameters considered in this study is similar to a falling raindrops. A theoretical analysis is also conducted by neglecting gravity and in the limit of creep- ing flow. The expressions of the frequency and decay rate of the shape oscillations of a raindrop are derived, and compared against the the direct numerical simulation results. To the best of our knowledge, the influence of these physical parameters has not been considered so far in the context of raindrops.