Shock accelerated cylindrical gas inhomogeneities. Part 2 - A heavy gas cylinder

Experiments have been carried out in which a cylindrical volume of a heavy gas is impulsively accelerated by a weak shock wave. A laminar jet of sulphur hexafluoride (SF_6) is used to produce the heavy gas cylinder. Planar laser induced fluorescence (PLIF) is used to visualize the flow. In viewing the PLIF images it is discovered that the vorticity that early on resides on the boundary between the two gasses, separates from the cylinder to form a pair of vortices. Subsequently these vortices wrap the heavy gas around them. This process is quite different from what is observed when the cylinder is lighter than its surroundings. Similar experiments with helium (part 1 of this series) showed that a small amount light gas stays with the vorticity, eventually becoming part of the vortex cores. A simple model capable of explaining these differences is presented. In addition, the displacement of the jet cross section is measured and agrees reasonably well with previous experimental and computational results.