Parallel pump systems are widely used in industries. However, pumps are often operating under off-design conditions due to many reasons, which reduces the efficiency and reliability of the pumps. This paper aims at reducing the power consumption of parallel pump systems and improving the reliability of pumps by improving the operation points of pumps. To achieve this goal, a combination of selecting the proper number of pumps to put into operation and their speed is needed. Also, a control valve is adopted to further improve the operation points. The optimization model is built for a parallel pump system. Particle swarm optimization algorithm is used to solve the problem. Experimental verification shows that the proposed method improves the reliability and can also reduce power consumption for some cases compared to conventional PID speed regulation method. But for cases with large flow, extra power might be needed because the control valve introduces extra flow resistance in order to improve the operation point. The proposed method can be easily extended to applications based on their requirements on reliability.

Centrifugal pump rotor system is a complex vibration system due to the unsteady multi-scale fluid–solid interactions (FSIs). In order to explore the coupling vibration of the rotor system between the multi-scale fluid domain and different flow conditions, the bidirectional fluid–solid interaction (BFSI) was carried out, and the numerical and experimental results of the centrifugal pump performance were compared. The transient forces of the impeller and vibration characteristics of rotor system considering BFSI for different flow rates, wear-ring clearances, and axial movements were also studied in detail. The results show that the maximum errors of head and efficiency between the simulation and experiment are only 5.41% and 2.33%, respectively. The radial force of impeller is smallest at 1.0Qd and the axial force decreases with the increase in flow rate. The average deformation and stress of the rotor system reaches to 0.35 mm and 70.7 MPa, respectively, when the axial movement increases to +1.5 mm. The vibration acceleration on the blades increases gradually from the root to the top, and the vibration acceleration on the shaft is greater than that at the impeller.

Cavitation erosion can seriously affect the performance of hydraulic machinery. To assess its risk, the cavitation erosion that covered a NACA0015 hydrofoil was investigated using experiment and simulation. In particular, the material strength threshold was considered in the experiment, and soft specimens were employed instead of common painting surfaces. High-speed cameras were utilized to capture cavity morphology, while pressure sensors simultaneously measured the impact intensity of cavitation collapse. Additionally, an erosion assessment method based on pressure impact was used in the numerical simulation. The results indicate that the cavitation erosion risk can be indicated by the intensity of pressure impact, which is caused by the collapse of cavity. The high erosion risk appears near 60% of chord length where shedding cloud collapses. Due to the influence of middle-entrant jet and side-entrant jets, the erosion risks are different at various span-wise locations. Additionally, the response differs for different materials exposed to cavitation. When the material strength threshold is low, the chord-wise difference of cavitation erosion is not significant, because the slight impact can also generate erosion pits. When the threshold is high, the chord-wise difference of erosion becomes larger, and erosion pits are more centralized.

In order to study the correlation mechanism between the flow characteristics and the fluid-induced force under the compound whirl motion in the centrifugal pump, the RNG k-ε model is selected in this paper to simulate a low specific speed centrifugal pump with impeller eccentricity based on the N-S equation. The changes of fluid-induced force with impeller eccentricity and the unsteady flow characteristics of the internal flow field of centrifugal pump under different flow conditions and rotation speeds are investigated, and the relationship between the fluid-induced force of the impeller and the internal flow field characteristics is discussed. The results show that the trend of fluid-induced force and the pressure coefficient is similar. When the rotation speed changes and when the flow is similar, the pressure coefficient under different rotation speeds almost coincides. With the increase of impeller speed and impeller eccentricity, the dynamic and static interferences between the impeller and the volute tongue are more significant, the uneven distribution of the pressure around the impeller makes the internal flow of centrifugal pump more disordered and increases the fluid-induced force near the volute tongue. The research results can provide important reference value for accurately grasping the internal flow excitation principle of the centrifugal pump.

Solving the static equilibrium position is one of the most important parts of dynamic coefficients calculation and further coupled calculation of rotor system. The main contribution of this study is testing the superlinear iteration convergence method—twofold secant method, for the determination of the static equilibrium position of journal bearing with finite length. Essentially, the Reynolds equation for stable motion is solved by the finite difference method and the inner pressure is obtained by the successive over-relaxation iterative method reinforced by the compound Simpson quadrature formula. The accuracy and efficiency of the twofold secant method are higher in comparison with the secant method and dichotomy. The total number of iterative steps required for the twofold secant method are about one-third of the secant method and less than one-eighth of dichotomy for the same equilibrium position. The calculations for equilibrium position and pressure distribution for different bearing length, clearance and rotating speed were done. In the results, the eccentricity presents linear inverse proportional relationship to the attitude angle. The influence of the bearing length, clearance and bearing radius on the load-carrying capacity was also investigated. The results illustrate that larger bearing length, larger radius and smaller clearance are good for the load-carrying capacity of journal bearing. The application of the twofold secant method can greatly reduce the computational time for calculation of the dynamic coefficients and dynamic characteristics of rotor-bearing system with a journal bearing of finite length.