Visualization of compressible vortex rings using the background-oriented schlieren method

In this article, we attempt to validate flow visualization using the high-speed background-oriented schlieren (HiBOS) method, which is the BOS technique combined with a high-speed video camera as the recording device in the experiment. The method has been applied to shock-induced flow near the open end of a shock tube. Three incident shock Mach numbers were examined so that the BOS measurements could be compared with results given in the literature of particle-image velocimetry (PIV) measurements. Using the HiBOS technique, we were able to clearly view developing, compressible vortex rings and diffracted shock waves discharged from the open end of the shock tube. From the BOS images, we extracted the history of the propagation velocity, the diameter of the vortex ring, and the diameter of the vortex core, all of which agree with the corresponding PIV values reported in the literature.