Paper reports on diffraction and focusing of toroidal shock waves when discharged from the open end of a compact vertical co-axial annular shock tube. The toroidal shock wave focusing and its reflection from center has been studied numerically by Jiang and Takayama (1998) but it has not been yet verified experimentally. In the present study, for producing annular shock waves a compact vertical co-axial diaphragmless shock tube is designed and constructed. This shock tube is capable of producing ring-shaped shock waves with minimum initial disturbances, suitable for investigating shock wave focusing problems. Three dimensional diffusive holographic interferometry method is successfully applied to visualize three-dimensional shock wave motion. The propagation and focusing process of toroidal shock waves and its reflection from center of convergence are quantitatively observed.
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