Vortex ring formation at the open end of a shock tube: A particle image velocimetry study

• Published in: Physics of fluids (1994) 2004-04, Vol.16 (4), p.1008-1019
• Main Authors: Arakeri, J. H., Das, D., Krothapalli, A., Lourenco, L.
• Format: Article
• Language: English
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/1.1649339

The vortex ring generated subsequent to the diffraction of a shock wave from the open end of a shock tube is studied using particle image velocimetry. We examine the early evolution of the compressible vortex ring for three-exit shock Mach numbers, 1.1, 1.2, and 1.3. For the three cases studied, the ring formation is complete at about tU b /D=2, where t is time, U b is fluid velocity behind shock as it exits the tube and D is tube diameter. Unlike in the case of piston generated incompressible vortex rings where the piston velocity variation with time is usually trapezoidal, in the shock-generated vortex ring case the exit fluid velocity doubles from its initial value U b before it slowly decays to zero. At the end of the ring formation, its translation speed is observed to be about 0.7 U b . During initial formation and propagation, a jet-like flow exists behind the vortex ring. The vortex ring detachment from the tailing jet, commonly referred to as pinch-off, is briefly discussed.