Propagation and interaction of shock-generated vortices

This paper explores the propagation and interaction mechanisms demonstrated by compressible vortex rings. With spark shadowgraph and schlieren photography, we examine the vortical flow regimes produced by the impulse of a shock wave emerging from the open end of a shock tube. For shock-wave Mach numbers ranging from M_s = 1.0 to 2.0, three distinct flow regimes were identified. From M_s = 1.0 to 1.43, conventional-looking vortex rings are produced. These vortex rings are characterized by very thin cores and thus high circumferential instability wavenumbers. From M_s = 1.43 to 1.60, the axial flow velocity in the recirculating region of the vortex ring becomes supersonic, producing a rearward-facing shock wave embedded in this region. From M_s = 1.60 to 2.0, a secondary counter-rotating vortex ring forms ahead of the main vortex-ring. Finally, preliminary results on the interaction of two compressible vortex rings are presented.