Evolution of shock-accelerated double-layer gas cylinder

Abstract

Developments of the shock-accelerated concentric double-layer gas cylinder with an air cylinder embedded into an SF6 cylinder have been experimentally investigated for the first time. The double-layer gas cylinder is created by the soap film technique. Effects of the inner cylinder on the evolution of the outer one are highlighted by changing the radius ratio, i.e., a ratio of the inner radius to the outer one. The flow features show that the two cylinders evolve independently at the early stage, whereas they couple together at the late stage. The presence of the inner cylinder changes the behavior of shock movements, and a vortex pair instead of an outward jet is generated at the downstream interface. The scale of the vortex pair is proportional to the initial radius ratio. The rarefaction waves generated from the upstream interface of the inner cylinder accelerate the upstream interface of the outer cylinder earlier than the single-layer SF6 cylinder. Depending on the radius ratio, the acceleration induced by the rarefaction wave impact either prolongs or shortens the linear phase of the upstream interface movement. The waves' effect results in the failure of the nonlinear model in predicting the upstream interface movement. For the outer cylinder, its movements in both the streamwise and spanwise directions are promoted by the inner one. For the inner cylinder, its movements in the streamwise and spanwise directions are, respectively, inhibited and promoted by the outer one. As the radius ratio increases, the effect of promotion or prohibition is stronger.