  The interaction of a shock wave with a spherical density inhomogeneity leads
to the development of a vortex ring through the impulsive deposition of
baroclinic vorticity. The present fluid dynamics videos display this phenomenon
and were experimentally investigated at the Wisconsin Shock Tube Laboratory's
(WiSTL) 9.2 m, downward firing shock tube. The tube has a square internal
cross-section (0.25 m x 0.25 m) with multiple fused silica windows for optical
access. The spherical soap bubble is generated by means of a pneumatically
retracted injector and released into free-fall 200 ms prior to initial shock
acceleration. The downward moving, M = 2.07 shock wave impulsively accelerates
the bubble and reflects off the tube end wall. The reflected shock wave
re-accelerates the bubble (reshock), which has now developed into a vortex
ring, depositing additional vorticity. In the absence of any flow disturbances,
the flow behind the reflected shock wave is stationary. As a result, any
observed motion of the vortex ring is due to circulation. The shocked vortex
ring is imaged at 12,500 fps with planar Mie scattering.
