X-ray measurements of shock-induced mixing at an air/xenon interface

Citation

Bonazza, Riccardo (1992) X-ray measurements of shock-induced mixing at an air/xenon interface. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3h5j-yb71. https://resolver.caltech.edu/CaltechETD:etd-06232005-111112

Abstract

A new experimental technique to measure the density of a high atomic number gas at an interface has been developed and demonstrated. It is based on the absorption of X-rays by the high atomic number gas, and it was implemented in a vertical square shock tube for the study of shock-accelerated air/xenon interfaces. These were prepared by retracting a metal plate initially separating the two gases, prior to the release of the shock wave. Thus the interfaces were all of initial finite thickness. Interfaces of two types, quasi-sinusoidal and nominally flat, were examined. Object of study were the amplitude of large wavelength (25 - 100 mm) perturbations on the interface, and the thickness of the interface. An integral definition for the interface mean line (proposed in a previous numerical work at GALCIT) was adopted; a new integral definition for the interface thickness was proposed, making it feasible to study for the first time the thickness of quasi sinusoidal interfaces. Experiments were performed to image interfaces having interacted with the incident shock, the incident and the reflected shock, or a series of weak waves reverberating between the interface and the shock tube end wall. The results for the growth rates of the amplitudes were compared against a model based on the linear theory: The measured values are larger than the predicted ones in the case when the interface only interacts with the incident and the first reflected shocks. They are smaller than the theoretical ones in the case of multiple reverberations. The interface thickness exhibits essentially no growth upon interaction with the incident shock. The interaction of the reflected shock with the turbulent boundary layer behind the incident one generates random acoustical disturbances which reach the interface and cause the subsequent thickness growth. The thickness growth rates of nominally flat interfaces are larger than those previously found at GALCIT in a schlieren visualization experiment, in the case of two shock interactions. They are smaller in the case of multiple interactions. In the case of two shock interactions, wall vortices generated by the interaction of the reflected shock with the boundary layer behind the incident one severely affected the measurements. A correction was proposed to account for this effect in the measurements of the interface thickness. The need remains for a different experimental technique, capable of eliminating these adverse effects altogether.

Thesis Files