STUDY ON MULTI-STAGE SHEDDING CHARACTERISTICS OF CLOUD CAVITATION AROUND FLEXIBLE HYDROFOILS

The study investigates the cloud cavitation around a flexible hydrofoil using a combined approach of experimentation and numerical simulation. It focuses on analyzing the multi-stage shedding phenomenon of cloud cavitation and its induced hydrofoil vibration characteristics. Experimental observations of the evolution of cavity morphology are conducted using high-speed cameras. Numerical simulations of the flow field are performed using the standard PANS (partially-averaged Navier-Stokes) turbulence model and Zwart cavitation model, with a tight coupling algorithm for fluid-structure interaction analysis. Results indicate that within the range of cavitation numbers between 0.65 and 0.85, multi-stage shedding of cloud cavitation occurs around the flexible hydrofoil, with significant differences between primary and secondary shedding processes. Primary shedding exhibits larger scales and periods compared to secondary shedding; the mechanisms behind primary and secondary shedding differ, with the former attributed to mid-chord re-entrant jet and the latter to free-end re-entrant jet. The high-pressure area generated by primary shedding cavity is significantly larger but with relatively smaller pressure peaks compared to secondary shedding, exerting a stronger inhibitory effect on the growth of attached cavity, resulting in slower growth rates and smaller maximum lengths of secondary shedding cavity compared to primary ones. Primary shedding attached cavity surface rotational flow intensity is greater, the primary shedding cavity is mainly affected by shear effects, while the secondary shedding cavity mainly affected by rotational effects. The change of hydrodynamic loads on the elastic hydrofoil is mainly related to the primary shedding, and the effect of secondary shedding is weaker, while the main frequency of each order of structural vibration is consistent with the shedding frequency of cavity.