Reflection and focusing of toroidal shock waves from coaxial annular shock tubes

Focusing of a toroidal shock wave emitted from a coaxial annular shock tube and the resulting shack wave reflection were studied numerically with a dispersion-controlled scheme. The numerical code was first applied to prediction of a shock wave discharged from the open-end of a circular shock tube into ambient air. The numerical interferogram was constructed from the numerical result, taking three-dimensional density distribution into account, to directly compare with an experimental interferogram. Obtaining good agreement between these results, the numerical method was applied to shock waves discharged from a coaxial annular shock tube with various initial shock Mach numbers and in different configurations. It was found that intense shock focusing appears when the toroidal shock waves merge at the axis of symmetry. A somewhat unusual shock wave reflection was also observed in the case of higher shock Mach numbers. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.