University of Alberta
Edmonton, Alberta, Canada
This is a photograph taken 100ms after a 5.5mm fluorescein-dyed fluid drop impacts a pool of water. The drop is formed on a tip 38mm above the surface of the ppol. The photograph is taken from a shallow angle below the free-surface. This image shows the structure into which the vorticity created at the interface evolves. The structure consists of a primary vortex ring with three lobes -- or ``petals'' -- in the vortex ring's wake. These lobes are formed from a single vortex tube. Especially significant is a disconnection-reconnection process visible on the tips of the petals. Here, the lobes disconnect to form a series of smaller vortex rings which propel themselves under their self-induction away from the vertical axis of symmetry. The small vortex rings are positioned symmetrically about the vertical central axis preserving invariance of the structure's hydrodynamic impulse ${\bf I}=\frac{1}{2}\rho \int_v {\bf r}\times {\bf\omega} dv$ where $\rho$ is the fluid density, ${\bf r}$ is the position vector and ${\bf\omega}$ is the vorticity.