An experimental study of nonstationary instabilities of planar shock waves in ionizing argon

A multipulse laser-Schlieren technique was used to study the time behavior of instabilities in the translational front of planar shock waves in ionizing argon in the 10 x 18 cm hypervelocity shock tube at UTIAS. Using a ruby laser in a combined normal-lasing/giant-pulse mode, at least two monochromatic light pulses were obtained about 7 microns apart. A Schlieren system compatible with the 23 cm dia Mach-Zehnder interferometer was created with maximum sensitivity for some low-density conditions. The almost-sinusoidal perturbations were found to change with time; some like a standing wave, and others like a travelling wave. It was not, however, possible to associate the observed perturbations with either form of wave motion in nearly half of the cases. A simple graph provides a way to predict the shape of the perturbations from the shock-wave parameters.