Cavitation is one of the most important aspects of the stable and safe operation of a centrifugal pump. To examine the dynamics of cavitation vortex in a centrifugal pump, the cavitating flow is investigated by using the modified shear stress transport (SST) k-ω turbulence model with the Zwart cavitation model. The numerical results are confirmed by comparing them with those obtained from experimental tests. The results show that there is a critical cavitation number of σ_c at each flow rate condition. As the cavitation number σ exceeds σ_c, the pump head remains stable. Conversely, the head rapidly decreases when the σ falls below σ_c. As the σ decreases, the pump experiences successively incipient cavitation, slight cavitation, and severe cavitation. At the stage of severe cavitation conditions, the vortex structures are generated at the tail of cavitation in the flow passage. The vorticity transport method is employed to analyze the vortex dynamics, and it is found that the vortex area contains high vorticity. The dominant contribution to the generation of vorticity comes from the vortex stretching and dilation terms acting in different directions. The contribution of the baroclinic torque to vorticity generation at the vapor-liquid interface is significant. The Coriolis force has a negligible impact on vorticity transport.

Tip leakage flow and induced unstable cavitation can significantly damage the performance of axial waterjet pumps. This study investigated the impact of blade numbers on cavitating conditions in an axial waterjet pump by conducting tests of performance characteristics and high-speed photography experiments on three-blade and four-blade impellers. The results showed that the critical cavitation number σ_c of the three-blade impeller was larger, while the four-blade impeller flow pattern deteriorated more rapidly after σ_c. Various cavitation structures in the tip region were observed under different conditions, including clearance cavitation, shear layer cavitation, tip leakage vortex cavitation, and suction-side-perpendicular cavitating vortices (SSPCVs). Tip cavitation maps of the test impellers were drawn based on the flow rate coefficient and cavitation number variation. The three-blade impeller exhibited a wider range of severe cavitation, particularly with an increased occurrence of SSPCVs. With the cavitation number and flow rate coefficient decreased, the SSPCV generated from triangular cavitation cloud shedding presented an increased trend in scale and quantity. Conversely, in the case of the four-blade impeller, SSPCVs were often disrupted by the adjacent blade during migration and interfered with the tip cavitation in the neighboring flow passage.

The stability of axial flow pumps is significantly affected by the tip leakage vortex (TLV), which is generated through the entrainment of the main flow. This study explores the effects of circumferential grooving in the rotor chamber on the tip leakage vortex of an axial flow pump by using the SST k-ω turbulence model. Numerical results were validated with prototype pump experiments. At the design condition, circumferential grooves positioned near the blade leading edge enhance both the pump’s efficiency and head. Grooves implemented at the mid-chord to trailing-edge regions are relatively close to those of the prototype pump. The implementation of grooves at both leading and trailing regions resulted in significantly degraded performance compared to the other two cases. However, at reduced flow rates, grooving in the rotor chamber leads to a decline in performance. Grooves positioned near the blade’s leading edge interfere with the ingress of the TLV into the suction side, suppressing vortex formation. Vortex structures and low-pressure regions are closer to the blade, reducing flow instability. In contrast, grooving in the middle and rear rotor chamber induces instability in the tip region. These findings offer theoretical guidance for suppressing the TLV and enhancing the stability of axial flow pumps.

To study instability in the unsteady cavitating flow in a liquid rocket engine inducer, visualization experiments of non-cavitating and cavitating flows inside a model inducer were carried out at different flow conditions. Visual experiments were carried out to capture the evolution of non-cavitating and cavitating flows in a three-bladed inducer by using a high-speed camera. The external characteristic performance, cavitation performance, and pressure pulsation were analyzed based on the observation of non-cavitation and cavitation development and their instabilities. Under non-cavitation conditions, the change of flow rate has a significant impact on the pressure pulsation characteristics in the inducer. The occurrence of cavitation aggravated the instability of the flow and caused the intensity of pressure pulsation at each measuring point to increase. This cavitation structure has strong instability, and the tail region is often accompanied by shedding cavitation clouds perpendicular to the blade surface.

This paper investigates the pressure fluctuation characteristics induced by cavitation in the blade-tip region of an axial flow pump through experimental and numerical methods. Compared with previous studies, this research not only analyzes the development of cavitation bubbles under varying flow rates but also explores the transient pressure fluctuation features caused by cavitation. It is found that partial-loading conditions tend to exacerbate cavitation, leading to more pronounced transient flow characteristics. The primary frequency of pressure fluctuations consistently corresponds to the impeller’s rotational frequency and its harmonics, with the magnitude inversely related to flow rate. At the same cavitation stage, lower flow rates exhibit larger amplitudes and more significant fluctuations in high-frequency components. This indicates stronger entrainment disturbance between the cavitation morphology and the mainstream in the blade-tip region at lower flow rates, resulting in more complex flow structures. This study provides a theoretical basis for understanding the mechanisms of pressure fluctuations induced by cavitation in the blade-tip region of axial flow pumps.

A novel pumped storage system using centrifugal pumps to transfer water between reservoirs in coastal hydropower plants has significantly mitigated grid instability. However, frequent start–stop operations of large vertical centrifugal pumps, which serve as the core equipment, severely affect the operational stability of these systems. In this study, the intrinsic connection between the cavitating flow field and irreversible losses during the process was analyzed using the entropy production theory. The time–frequency characteristics of pressure pulsation in pump were analyzed by using the continuous wavelet transform. The results indicate that with the reduction in the flow rate and rotational speed, the sheet cavitation at the impeller inlet rapidly weakens until it vanishes. The cavity cavitation within the draft tube commences to emerge in the turbine mode. Separation vortices are formed due to the mismatch in the flow angle at the impeller outlet. These vortices induce local cavitation, causing both a rapid energy loss increase and high-amplitude, low-frequency pressure pulsations. During transient processes, flow instabilities induce high-amplitude, low-frequency pressure pulsations within the stay vane region, with maximum amplitude attained during runaway condition. The research results provide a theoretical foundation for the stable operation of centrifugal pumps.