Time-resolved visualization of shock---vortex systems emitted from an open shock tube

AbstractWhen a shock wave leaves an open-ended shock tube, it generates a vortex ring that subsequently detaches from the shock tube and follows the expanding shock front. This classical problem of shock-vortex interaction has been visualized in unprecedented detail and temporal resolution by means of time-resolved shadow, schlieren and shearing interferometry sequences obtained with a newly developed ultrahigh-speed color video camera. This device is capable of taking 144 frames with full-frame resolution of 720 × 410 pixels at rates of up to one million frames per second. Apart from shadowgraphy, the visualization techniques used in this study were direction- and magnitude-indicating color schlieren and polychrome shearing interferometry. The process was observed both with the standard normal view of the flow field and with an oblique view, which facilitated the identification of some three-dimensional flow features. The obtained results clearly show the development of individual flow elements, including some that so far have eluded a proper description. One example is the secondary, counter-rotating vortex ring, which at a later time wraps around the main vortex ring before disintegrating upon merging with the shear layer that surrounds the gas exiting from the tube.Graphical abstract[IMAGE]