Compressible vortex loops in a shock tube with helium driver

An experimental study has been conducted on the generation and propagation of compressible vortex loops using helium as a driver gas. The study aimed at evaluating the flow characteristics of a compressible vortex loop generated using a lighter then air gas into air at ambient conditions. The advantage of such system when compared to a constant gas system based on ambient air is to effectively increase the Mach number while keeping the pressure ratio constant. Three driver pressures were used (4, 8, and 12bar) generating a theoretical Mach number value of 1.53, 1.89, and 2.12 respectively. Qualitative and quantitatve analysis were conducted. The generation of secondary vortex rings ahead of the main vortex ring were witnessed at all driver pressure. The structure of the trailing jet behind the vortex ring is shown to transition from a regular to a Mach reflection with increasing Mach disk size. The presence of the Mach disk results in the generation of vortical flow inside the main trailing jet with opposite circulation with respect to the outer jet boundary. Copyright © 2011 by Raffaello Mariani.