Cavitation can cause noise in the water-jet pump. If cavitation occurs in the water-jet pump, the hydraulic components in the pump are prone to erosion. The surface erosion reduces energy delivery efficiency and increases maintenance costs. The decline in pump performance will lead to the instability of the entire energy system. In this paper, the cavitation flow structure of the water-jet pump is studied by the method of numerical simulation and experiment, which provides a reference for the prediction and improvement of cavitation. Based on the closed test platform, in order to reveal the physical process of cavitation evolution, high-speed photography is used to capture the complex cavitation flow phenomenon in the pump. After that, the cavitation vortex structure was further explored by numerical simulation. Through the simulation of the impeller blade tip leakage flow and the Tip Leakage Vortex Cavitation (TLVC) characteristics under different cavitation conditions, the flow mechanism of the impeller blade tip leakage flow and the separation vortex induced by the cavitation region under different cavitation conditions were revealed. The main factors affecting the development of the cavitation wake vortex structures were summarized.

To investigate the impact of tip clearance variation on the cavitation performance of a high-speed pump-jet propeller, Fluent software was employed for simulation calculations. The study utilized the RNG k-ε turbulence model and ZGB cavitation, conducting three-dimensional numerical simulations under both steady and transient conditions. A pump-jet propeller with a rated speed of 20,000 r/min was used to set three kinds of clearance for simulation, and the simulation proved to be reliable by comparison with the experiment. Initially, the analysis examined the effect of tip clearance on cavitation characteristics and cavitation volume under steady-state conditions, while also studying the distribution patterns of cavitation. Subsequently, the radial force and pressure pulsation of the jet propeller are analyzed by FFT processing, aiming at the influence of tip clearance on the structural strength of the pump-jet propeller. Under the design conditions, the smaller tip clearance shows better performance, while the larger tip clearance shows stronger anti-cavitation ability than the smaller clearance. In addition, the greater the tip clearance, the greater the radial force and pressure pulsation, which will adversely affect the pump-jet structure. The research results provide some references for further research on the effect of high-speed pump-jet propeller structures on performance.

To diagnose common failures in vertical Essential Service Water Pumps (SEC), a method combining the wavelet packet transform (WPT) and the support vector machine (SVM) was adopted. This allowed us to construct a diagnostic model capable of classifying multiple states, including the six types of faults and normal conditions in SEC pumps. The diagnostic model utilized the wavelet packet coefficients to capture sub-bands with a higher energy share and reconstruct the signals. The model inputs the 12 frequency features into the support vector machine to analyze the vibration signals gathered from the SEC pump benchmark. The study illustrates that the proposed method can accurately differentiate between various fault conditions when compared to the WPT method, combined with the artificial neural network (ANN) approach. It attains a superior overall precision of up to 94%, and it displays excellent generalization and strong adaptability.

This paper proposes a data-driven prediction scheme for the remaining life of centrifugal pump bearings based on the KPCA–LSTM network. A centrifugal pump bearing fault experiment bench is built to collect data, and the performance of time domain, frequency domain, and time-frequency domain characteristics under different working conditions is analyzed. Time domain characteristics, frequency domain characteristics, wavelet packet decomposition energy characteristics, and CEEMDAN energy features are found to be able to capture fault information under different working conditions. Therefore, 43 sensitive features are determined from the time domain, frequency domain, and time-frequency domain. Through the analysis of XJTU-SY bearing life cycle data and based on the weighted scores of monotonicity, robustness, and trend indicators, twelve outstanding characteristics of the bearing in the whole life cycle are selected, and a one-dimensional feature quantity that can characterize the life-degradation process of the centrifugal pump bearing is constructed after KPCA dimension reduction processing. The LSTM network, sensitive to time series, is selected to predict and analyze the constructed one-dimensional feature trend, and the prediction effects of the BP network and the CNN network are compared. The results show that this method has advantages in prediction accuracy and model training time.

Due to the operation conditions and system characteristics of the essential service water system of nuclear power plants, water hammer pressure fluctuates in each transient process. In order to further analyze the characteristics of the water hammer and the harm this can cause to system equipment, this paper uses one-dimensional transient computing software to simulate the water hammer characteristics of the system under different operating conditions and at different water levels. The instantaneous pressure data of water hammer in the essential service water system were used as input conditions for fatigue analysis of components, and the fatigue damage of at-risk parts was calculated. The results show that the pressure fluctuation due to single pump outage is greater than that due to single pump start-up and the start-up of double pumps. The maximum pressure of the system under the design flood level is greater than that of other water levels, and the maximum pressure of the system under each working condition is 3.87 MPa. The most at-risk part of the system pressure fluctuation is the return valve, followed by the valve after a bend in a pipe and the tee pipe fitting. In the whole system, the joint of the main branch of a tee pipe experiences the greatest fatigue damage, and the theoretical fatigue life is 127.55 years.

Pump-jet propellers are currently the mainstream propulsion method for underwater vehicles, and cavitation is an important factor limiting the high speed and miniaturization of pump-jet propellers. In order to explore the cavitation performance of high-speed pump-jet propellers, based on the modified SST turbulence model and the Zwart cavitation model, a three-dimensional numerical simulation of unsteady internal cavitation flow was carried out by comparing the impeller with specific speed n_s = 1920 using FLUENT 2020R2 software. At the same time, the occurrence and development process of cavitation under 0.95 Q, 1.0 Q, and 1.05 Q conditions were analyzed (Q is the mass flow), the changes in gas volume fraction in the impeller channel were captured, the distribution characteristics of cavitation under different NPSH values were explored, and the change law of cavitation with time was determined. The results show that, when NPSH dropped to 95 m, the impeller cavitation first occurred under the 1.05 Q operating condition, and the impeller cavitation volume fraction was 0.0379525. When NPSH dropped to 85 m, the impeller cavitation occurred under the 1.0 Q operating condition, and the impeller cavitation volume fraction was 0.0185164. When NPSH dropped to 80 m, the impeller cavitation occurred under the condition of 0.95 Q, and the volume fraction of the impeller cavitation was 0.013541. The high-speed pump-jet propeller had better anti-cavitation ability with a small flow rate. The cavitation distribution law under the three operating conditions was similar; cavitation was first generated on the impeller inlet edge and near the shroud, and the vacuoles with large volumes were mostly concentrated on the impeller inlet side. As the NPSH gradually decreased, the entire flow channel was gradually occupied by vacuoles. As the flow decreased, the corresponding NPSH also decreased. When NPSH dropped to 50 m, the volume fraction of the impeller under all three operating conditions reached around 0.4. As the cavitation only occurred on the suction surface, the volume fraction of the cavitation on the suction surface exceeded 0.8, at which time the impeller had already undergone severe cavitation. Within a complete cycle, bubbles first appeared at the inlet edge of the impeller (measured near the shroud) and gradually spread toward the middle and rear of the impeller, ultimately covering the suction surface of the impeller. Under the design condition, the experimental results of the model pump were consistent with the numerical simulation results, and the error was only 2.68%, thus verifying the reliability of the numerical simulation. The research results provide a reference for the in-depth study of the cavitation performance of high-speed pump-jet propellers and provide a good theoretical basis and practical significance in the engineering field for the high-speed and miniaturization process of high-speed pump-jet propellers.