Vibration-induced droplet ejection is a novel way to create a spray. In this method,
a liquid drop is placed on a vertically vibrating solid surface. The vibration leads to
the formation of waves on the free surface. Secondary droplets break off from the
wave crests when the forcing amplitude is above a critical value. When the forcing
frequency is small, only low-order axisymmetric wave modes are excited, and a single
secondary droplet is ejected from the tip of the primary drop. When the forcing
frequency is high, many high-order non-axisymmetric modes are excited, the motion
is chaotic, and numerous small secondary droplets are ejected simultaneously from
across the surface of the primary drop. In both frequency regimes a crater may
form that collapses to create a liquid spike from which droplet ejection occurs. An
axisymmetric, incompressible, Navier–Stokes solver was developed to simulate the
low-frequency ejection process. A volume-of-fluid method was used to track the free
surface, with surface tension incorporated using the continuum-surface-force method.
A time sequence of the simulated interface shape compared favourably with an
experimental sequence. The dynamics of the droplet ejection process was investigated,
and the conditions under which ejection occurs and the effect of the system parameters
on the process were determined.