Vortex pumps play a crucial role in industrial and municipal settings by transferring high-viscosity and particle-laden fluids. However, their performance and reliability are significantly compromised by cavitation. Identifying and diagnosing cavitation promptly is essential for maintaining the proper operation of vortex pumps. The use of current signals as a non-invasive monitoring method has shown great promise in detecting multi-cavitation states. The proposed method integrates dual-tree complex wavelet transform with variational mode decomposition to decompose current signals into multiple modes. Subsequently, the Bayesian optimized locally weighted K-nearest neighbor algorithm is employed to accurately identify multi-cavitation states. High-speed photography is also utilized to observe the incipient, developing, and collapsing phases of cavitation. The results indicate that the proposed method achieves a detection accuracy of 96.67% at a flow rate of 40 m³/h, outperforming other flow conditions. The recognition accuracy reaches 98.33% under stable flow conditions, while accuracies of 92.33% and 93.67% are observed for flow rates of 35 m³/h and 45 m³/h, respectively. The overall average recognition rate across all tested flow conditions is 94.22%. This methodology not only demonstrates high effectiveness in identifying cavitation states but also offers a reliable and practical solution for fault diagnosis in fluid mechanical systems. It significantly contributes to the improvement of operational efficiency, reliability, and maintenance strategies in industrial and municipal pumping systems.

Purpose: Rotating stall is an unsteady flow phenomenon that causes instabilities and low efficiency in pumps. The purpose of this paper is to investigate the rotating stall characteristics and unsteady behavior of stall cells in a centrifugal pump impeller at low flow rates. Design/methodology/approach: A developed large eddy simulation with dynamic mixed nonlinear model is performed to evaluate the unsteady flow in a centrifugal pump impeller. The rotating stall flow field through the centrifugal pump impeller is analyzed under three typical flow rates. Frequency spectrum analysis are carried out on the series of pressure fluctuation to get the rotating stall characteristics. The size and intensity of stall cells are also analyzed using time-averaged vorticity and static pressure. Findings: The rotating stall cell first occurs in the suction side of the blade and exhibits an obvious life cycle including decay mergence, shedding, growing and development with a low frequency. With the decrease of flow rate, the amplitude of pressure fluctuations in the impeller tends to be larger, the propagated speed of stall cells and rotating stall frequency tends to be smaller, but the number of cells remains unchanged. The size of stall cells increases as the flow rate decreases, but intensity changes is very little. Originality/value: The rotating stall characteristics in a centrifugal pump impeller under low flow rates are presented first using a developed large eddy simulation approach.

Francis turbines are most widely used in hydropower due to their characteristics which include a fast response and wide time-scale operation. The vortex rope inside Francis turbines is a common flow phenomenon, which always causes strong vibration, pressure pulsations, fatigue load, and even serious failure of the components. Vortex suppression methods can effectively change the velocity and pressure distribution of the flow field in the draft tube, reduce the volume of vortex rope and the amplitude of pressure pulsation, inhibit the development of cavitation erosion, and improve the operation stability of the hydro turbine. However, the vortex suppression method is not suitable for all working conditions, and the vortex suppression effect is also different. There are still many problems with how to analyze the vortex suppression effect and practicability of the turbine from multi-dimensions. It is of great significance to analyze the vortex suppression techniques and their practicability in hydraulic turbines from various aspects. The primary focus of the present study is to analyze the hazards of vortex rope in draft tubes and summarize the methods of suppressing vortex rope and pressure pulsation. This review article provides a basis for controlling the vortex rope in the draft tube, which can help the designers choose the suitable control method to mitigate it. Future research directions are also briefly discussed.

It is of great significance to predict the energy performance of centrifugal pumps for the improvement of the pump design. However, the complex internal flow always affects the performance prediction of centrifugal pumps, particularly under low-flow operating conditions. Relying on the data-fitting method, a multi-condition performance prediction method for centrifugal pumps is proposed, where the performance relationship is incorporated into the particle swarm optimization algorithm, and the prediction model is optimized by automatically meeting the performance constraints. Compared with the experimental results, the performance under multiple operating conditions is well predicted by introducing performance constraints with the mean absolute relative error (MARE) for the head, power and efficiency of 0.85%, 1.53%,1.15%, respectively. By comparing the extreme gradient boosting and support vector regression models, the support vector regression is more suitable for the prediction of performance curves. Finally, by introducing performance constraints, the proposed model demonstrates a dramatic decrease in the head, power and efficiency of MARE by 98.64%, 82.06%, and 85.33%, respectively, when compared with the BP neural network.

Cavitation-induced flow instabilities in vortex pumps critically degrade hydraulic performance and operational lifespan. This study investigates the evolution of the vapor cavities within vortex pumps across various cavitation states using both numerical simulations and experimental analysis. The unsteady flow dynamics within the impeller channel are examined, and the relationships among pressure pulsations, vortex volume, and vapor volume fraction are analyzed. As cavitation intensifies, the vapor volume expands progressively. Notably, the time required for the vapor to expand during critical cavitation is twice as long as that for severe cavitation, whereas the contraction time is one-fourth. The variation in vortex volume inside the impeller follows a distinct pattern, initially increasing and then decreasing, with the peak occurring during critical cavitation. The interactions between pressure pulsations, vapor volume fraction, and vortex volume become increasingly complex, especially during severe cavitation, where the amplitude of pressure pulsations significantly decreases, the vapor volume fraction increases, and vortex volume fluctuations are suppressed. Wavelet coherence analysis reveals the coupling dynamics of these three variables across different temporal scales and frequency bands, with enhanced coherence observed in the low-frequency range (0–50 Hz). These findings provide valuable insights for the optimization and development of vortex pumps in municipal and industrial fluid transport applications.