Effects of microvortex generators on cavitation erosion by changing periodic shedding into new structures

Abstract

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.