Cavitation erosion is a common phenomenon and continues to be a primary concern in the fields of hydraulic machinery. It is important to develop effective methods to avoid adverse effects. In the previous studies, the microvortex generators (VGs) were arranged parallel to the leading edge on the surface of the NACA0015 hydrofoil and, thus, changed the feature of the attached cavity. However, the effect on cavitation erosion has not been studied. The current work aims at understanding the aggressiveness of cavitation structures and the intensity of impact changed by microvortex generators. This study presents findings of experimental investigation of impulsive loading on the hydrofoil surface from collapsing cavities. Attempts to predict the cavitation erosion aggressiveness and the relationship with cavitation structures were based on visual observations. Under certain cavitation conditions, the periodic shedding disappears after the micro-VGs are installed. By dispersing the collapse in time and space, the maximum pressure fluctuation is reduced by 32% and the acoustic power is reduced by 10.8 dB at about 20 kHz. The maximum impact energy appears to be concentrated around the cavity closure. The maximum impact energy of a hydrofoil with VGs is 48% of that of a smooth hydrofoil. When the attack angle is lower, the erosion at the leading edge is more obvious on the smooth hydrofoil. Thus, the effect of VGs on alleviating the erosion at the leading edge is more prominent. The characteristic feature of vortex generators is their strong swirling motion that allows them to promote large-scale mixing of fluids with different momentum and energy. The unsteadiness is alleviated by VGs because of the interaction with the reverse flow.

Attached cavitation is a type of common cavitation phenomenon in fluid machinery. It is important to develop methods to control its generation. From the view of cavitation inception, the generation of attached cavitation is greatly influenced by the separated boundary layer upstream of cavitation detachment. In this research, a row of microscopic delta-shaped counter-rotating vortex generators (VGs) was applied on the leading edge of the NACA0015 hydrofoil in order to suppress the boundary layer separation and then suppress the generation of attached cavitation. The application of VGs fixed the position of cavitation inception on hydrofoil thus the sheet cavitation became more stable and the cloud cavity shed from hydrofoil with trim trailing edge more regularly. It was found that cavitation inception always appeared adjacent to VGs due to the low pressure in the corner of streamwise vortices induced by VGs. Hydrofoil with VGs showed an entirely different cavitation morphology on the leading edge. A row of separate microscopic vortex cavitation was induced by the counter-rotating vortices firstly. With the lower the height of VGs, the longer the length of these vortex cavitation due to the weaker interaction between vortices and main flow. Following the vortex cavitation, the attached cavitation was developing, but without typical “finger” structure anymore.

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Transitional cavity shedding is known as the stage of attached cavitation with high instability and distinct periodicity. In this study, we experimentally investigated the dynamic characteristics of transitional cavity (0.8≤L/c<1) shedding on NACA0015 hydrofoil with high-speed video observation and synchronous pressure measurement. In the partial cavity (0.4<L/c<0.8) oscillation, the sheet cavitation grew along the chord with good spanwise uniformity, and the middle-entrant jet played a dominant role in cavity shedding. Meanwhile, in the transitional cavity oscillation, the previous shedding cavity exhibited a prohibitive effect on the growth of sheet cavitation on the hydrofoil, resulting in concave cavity closure line. Moreover, two symmetrical side-entrant jets originated at the near-wall ends and induced the two-stage shedding phenomenon. The aft and fore parts of the sheet cavitation shed separated as different forms and eventually merged into the large-scale cloud cavity.