Experimental study on a plane shock wave accelerating a gas bubble

Abstract

A detailed experimental study of the interaction between a planar shock wave and an isolated spherical gas inhomogeneity is presented here. Different configurations have been considered: a shock wave moving from one gas into another, of similar density, lower density and one of higher density. Sequences of shadowgraph pictures obtained during the same run provided useful insights into several mechanisms such as shock wave reflection, refraction and focusing, distortion of the bubble interface, and vortex formation. Based on these sequences, the changes with time in the characteristic bubble sizes were plotted and the results showed that the influence of the shock wave Mach number is significantly greater in the case of light gas bubbles. The displacement of the inhomogeneity relative to the surrounding gas was determined and compared to Rudinger and Somers’ model. In all the cases studied, although the measurements were found to agree well with the theoretical predictions, in the initial acceleration phase, the final translational motions of the vortex ring were not accurately predicted by the model. The database obtained was used to estimate the resulting pattern of circulation, which was compared to other existing models. The circulation was found to increase with both the Mach number and the density ratio across the interface and was always overestimated by the models. These differences are probably caused by the presence of pulverized soap film trapped in the vortices, which reduces the motion and the strength of the resulting flow. A large number of tests are performed over a significant range of shock wave Mach numbers and density differences, with the use of high-speed imaging methods to track the vortex evolution during a single test shot. The database obtained should provide a useful tool for checking the validity of many codes and models describing the dynamics of shock/bubble interactions.