Ferrofluid seals are considered a next-generation sealing technology for hydraulic machinery due to their outstanding performance. However, experiments and engineering applications have revealed issues with seal failure, the mechanisms of which remain poorly understood. This study focuses on centrifugal pumps, employing numerical simulations to analyze the hydrodynamic characteristics and pressure pulsations in the sealing clearance. A coupling interface between the three-dimensional fluid machinery numerical results and two-dimensional ferrofluid seal numerical results was established to investigate the effects of mean and pulsating pressures on the ferrofluid interface morphology and the mechanisms of seal failure. The results indicate that the rotation of the centrifugal pump shaft induces forced vortices in the sealing clearance. Influenced by the clearance structure, these forced vortices generate free vortices with similar flow patterns. The vortex motion is identified as the primary factor causing pressure pulsations in the sealing clearance, with an amplitude of approximately 0.18 MPa due to scale limitations. Compared to the morphology of ferrofluid seals under mean pressure, pulsating flow does not cause partial detachment of the ferrofluid but accelerates the rupture process of the ferrofluid sealing ring. Under the critical pressure of the ferrofluid sealing ring, pulsating pressure causes significant damage within 0.8 s. This study concludes that the stability and failure of ferrofluid seals in centrifugal pumps are strongly governed by vortex-induced pressure fluctuations and the interaction between magnetic field distribution and flow dynamics. The designed four-level ferrofluid sealing device can effectively withstand peak pressure pulsations, demonstrating reliable sealing performance. These findings provide critical insights for optimizing ferrofluid seal designs and can guide the development of more reliable sealing technologies in high-speed hydraulic machinery, improving operational safety and efficiency.

This paper studies the flow characteristics of the pump turbine of a pump under operating conditions during the outlet pressure variation process, aiming to improve its operational stability in pumping and compressing air energy storage systems. Through numerical simulations of the flow process, the pressure distribution and pressure pulsation characteristics in key areas such as the volute, double-row impeller, runner, and tailpipe are analyzed in depth. The study reveals that during the outlet pressure variation process under operating conditions, the pressure distribution is directly influenced by the outlet pressure variation, while pressure pulsation is mainly affected by the dynamic and static interference within the unit, with the pressure pulsation amplitude influenced by the rate of pressure variation. The results indicate that during the outlet pressure variation process, it is important to prevent the outlet pressure from staying in unstable working ranges to reduce the intensity of pressure pulsation. A smoother rate of pressure variation should be adopted before stopping the outlet pressure variation to reduce the “pressure variation inertia” and enhance the overall operational stability of the water turbine unit.

Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units. Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines. In this study, ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube. The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation. The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone, which formed a counterclockwise-clockwise-counterclockwise distribution pattern. Simultaneously, there were many secondary flows in the draft tube. Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity. When the cross-sectional shape of the draft tube was changed, the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube, with extreme values at the center and at the walls. The vortex stretching and dilatation terms played a major role in the change in vorticity, with the baroclinic torque having an effect at the center of the vortex rope, this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application.