X-ray densitometry of shock-excited Richtmyer-Meshkov instability at an air-xenon interface

Abstract

Experiments were performed in a vertical, square shock tube to study the development of the Richtmyer-Meshkov instability excited by the interaction of a shock wave with an air/xenon interface. The objective is to measure the mixing that occurs at the interface due to the instability. New flow visualization and densitometry techniques based on X-ray absorption by the xenon have been developed. Continuous interfaces between the gases are prepared by initially separating the gases with a metal plate which is retracted out of the tube prior to the release of the shock wave. Depending on the time elapsed between the end of plate retraction and shock arrival, the interface can be either quasisinusoidally or randomly perturbed. An X-ray 50 ns long flash is projected through the flow and a 20 x 25 cm X-ray negative is exposed at each run. The negatives are digitized and mean xenon-density profiles across the interfaces are generated by image processing methods developed specially for this purpose. The amplitude of the perturbations, the thickness of the diffuse interfaces and the growth rates of these two quantities are measured from the density profiles.

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