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.

Inducer is often used to improve the cavitation performance of pump. In order to study the cavitation characteristics of inducer under low flow condition of high-speed pump, high-speed photography technology was employed in this paper to carry out visual experiments on the inducer of a high-speed centrifugal pump. In low flow rates, Cavitation distribution and evolution among the inducer were captured. The experimental results revealed that a band-shaped backflow vortex in the inlet pipe would occur when the flow rate was less than 0.3 Q_d. Moreover, the backflow vortex in the inlet pipe rotated with the inducer and the rotational speed of backflow vortex was approximately half of the inducer. The visualization test of 0.27 Q_d was carried out: when the NPSH was greater than 6.72 m, the bubbles in the inlet pipe were asymmetrical; When the NPSH dropped to 5.41 m, the cavitation was becoming less asymmetrical; When NPSH dropped to 3.81 m, cavitation evolved to the deteriorating stage, plenty of bubbles entered into the main impeller, resulting in a rapid decline of pump performance. Furthermore, the cavitation performance was worse at an extreme flow rate, and the NPSH value of 0.27 Q_d was 7.5% greater than that under design condition.

A semi-Y labyrinth seal (SYLS) is proposed to reduce leakage and enhance the stability of centrifugal pump. The calculation adopts a multifrequency circular whirling model with two-control user-defined functions (UDFs) and the numerical predictions align closely with experimental data for labyrinth seals. Furthermore, the influences of tilt angle, rotation speed, pressure difference, and internal clearance on the leakage performance, rotordynamic coefficients, and sealing stability are investigated. Compared to the traditional interlocking labyrinth seal (ILS) structure, the leakage of the counterflow semi-Y type labyrinth seal (CSYLS) and the downflow semi-Y type labyrinth seal (DSYLS) is reduced by approximately 19.2% and 29.8%, respectively. In addition, the effective damping of the CSYLS structure is approximately 50% greater than that of the conventional ILS structure.