Numerical investigation of cavitation-vortex interaction with special emphasis on the multistage shedding process

The objective of this paper is to investigate the physical interaction of the cavitation-vortex dynamics around a 3D Delft hydrofoil by large eddy simulations combined with the Zwart–Gerber–Belamri cavitation model. Transient sheet/cloud cavitating flows around the twisted hydrofoil involves the primary and secondary cavity shedding characterized by a U-shape structure, which is consistent with previous experimental data. Different vortex identification methods, namely, the ω criterion, Q criterion, Ω method and Liutex method, are applied to identify and analyze the vortex structure. The Liutex method is further utilized to visualize the detail of vortex structure in the primary and secondary cavity shedding process, especially for formation and development of the U- shape structure. For the primary cavity shedding process, the U- shape structure is the main feature of the shedding process. The primary U- shape vortex structure experiences distortion, and breaks into two parts at the vortex neck. Then, the front part develops into a O-shape structure, whereas the rear part still maintains a U- shape structure. Finally, both parts are dissipative completely in the form of U-shape structures. The shear plays a major role in the primary cavity shedding. For the secondary cavity shedding, U-shape, Ω-shape, O-shape, and hairpin vortexes are observed. The secondary U-shape vortex structure twists and deforms to form a hairpin vortex when the secondary cavity sheds completely, and finally dissipates with a smaller magnitude hairpin vortex. Rotation plays a major role in the secondary cavity shedding.