Comparison of the experimentally observed and simulated evolution of
the shocked column's density. Because these images are negatives, regions
of high gas density are darker than regions of low gas density. The initial
conditions of the column are shown at the far left; its initial diameter
is about 6 millimeters. The shock wave moves from left to right. Time
also proceeds from left to right, with 140 microseconds between frames.
Time is measured from the moment the shock wave has left the downstream
edge of the column. The entire experiment is over in less than a thousandth
of a second. Good agreement is seen in the larger-scale structure of the
density snapshots. Differences in the smaller-scale structure are the
subject of continuing research. Note the pair of large vortices on the
downstream side of the shock-wave/column interaction. The core of one
of these vortices is used as a reference point for comparing the experimentally
observed and simulated velocities late in the instability's evolution.