Fig. 1. “Z” configuration schlieren system

Fig. 2. Images of three-dimensional perturbation with schlieren system. (a) Theoretical result; (b) experimental result

Fig. 3. Focusing schlieren visualization system. (a) Schematic; (b) source grid and cutoff grid

Fig. 4. Image of three-dimensional perturbation with parallel line grid

Fig. 5. Annulus grid. (a) Source grid; (b) cutoff grid

Fig. 6. Three-dimensional perturbation imaging by modified focusing schlieren system. (a) Image of ultrasonic perturbation on the plane at the center of cavity; (b) images of ultrasonic perturbation with different excited powers