Shock accelerated vortex ring

TL;DR

This study experimentally investigates how shock waves interact with spherical density inhomogeneities, creating vortex rings through baroclinic vorticity deposition, using high-speed imaging in a shock tube setup.

Contribution

It provides detailed experimental visualization of vortex ring formation and evolution due to shock interaction with inhomogeneities, including re-shock effects.

Findings

Vortex rings form from shock-accelerated bubbles.

Re-shock enhances vortex ring circulation.

Flow behind reflected shock remains stationary without disturbances.

Abstract

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.