The centrifugal pump is one of the most important pieces of energy-consuming equipment in various hydraulic engineering applications. This paper takes a low specific speed centrifugal pump as the research object. Based on the research method combining numerical calculation and experimental verification, the influence of the gap drainage structure on the performance of the low specific speed centrifugal pump and its internal flow field distribution were investigated. The flow field inside the low specific speed centrifugal pump impeller under different gap widths was studied. The comparison between the numerical calculation results and the experimental results confirms that the numerical calculations in this paper have high accuracy. It was found that the gap drainage will reduce the head of the low specific speed centrifugal pump, but increase its hydraulic efficiency. Using a smaller gap width could greatly improve the performance of the low specific speed centrifugal pump on the basis of a slight reduction in the head. The high-pressure leakage flow at the gap flows from the blade pressure surface to the suction surface can effectively suppress the low-pressure area at the impeller inlet. The flow rate of the high-pressure leakage flow increases with the gap width. Excessive gap width may cause a low-pressure zone at the inlet of the previous flow passage. These results could serve as a reference for the subsequent gap design to further improve the operating stability of the low specific speed centrifugal pump.

The unsteady flow characteristics of pump as hydraulic turbine play a vital role in its safe and stable operation, while the ultra-low specific-speed centrifugal pump may face more stability problems due to the limitations of its flow conditions under the turbine working condition. Therefore, in this study, the unsteady characteristics of an ultra-low specific-speed centrifugal pump under turbine conditions are studied using a numerical simulation method, and the numerical simulation is verified using an experimental method. Based on the hydraulic losses of each flow passage component, the energy characteristics of pump as turbine (PAT) are established, and the distribution pattern of total pressure fluctuation in the turbine is studied. The results show that the rotor–stator interaction between the impeller and the tongue makes the hydraulic performance and the internal flow field change periodically. The pressure fluctuation intensities at the tongue, blade inlet edge, and balance hole are large, and the total pressure fluctuation in the three areas is intense in space and time. The internal flow characteristics at typical blade positions show that the secondary flow phenomena such as separation flow and wake flow near the tongue make the pressure gradient larger, which is an important influence mode of the rotor–stator interaction. This study provides a reference and guidance for the unsteady study of low specific-speed PAT.

Low specific speed centrifugal pumps are widely used in urban water supply, agricultural irrigation, petrochemical and other fields due to their small flow rate and high head. Therefore, the study of unsteady flow characteristics plays a vital role in its safe and stable operation. In this paper, numerical simulation and experimental methods are used to explore the unsteady performance of the pump. The results show that the fluctuations of the external characteristic such as head, shaft power and energy loss are due to the periodic disturbance of the flow field of pump. But the transient performance of shaft power and head shows different changing trends due to different influencing factors. In this paper, the transient process of hydraulic performance is divided into three stages according to the causes and characteristics of hydraulic fluctuations. Most of the hydraulic losses occur inside the impeller, so the impeller flow field determines the level of time average hydraulic performance. Although the hydraulic loss of the spiral case is small, it is greatly affected by the rotor-stator interaction, which affects the strength of the hydraulic fluctuation. This study is of great significance to the mechanism of rotor-stator interaction and the stable operation of low specific speed centrifugal pumps.

The characteristics of pressure pulsations in centrifugal pumps have attracted considerable attention. In this study, principal component analysis is used to discuss the pressure pulsations in a centrifugal pump with a low specific speed, and the primary causes for these pressure pulsations are analyzed in conjunction with experimental results. The results indicate that principal component analysis effectively separates the primary modes that influence the flow field characteristics. An excessive wrap angle results in the formation of a backflow vortex on the working face of the blade. Obvious stratification of the zero-order modal pressure indicates that the geometric structure of the impeller is rational and that the transient flow field is stable. The second- and third-order modes are conjugates, and their dominant frequency coincides with the dominant rotating frequency of the impeller, indicating that the pulsations of a single channel are the primary component of the pressure pulsations. The primary frequency (148.54 Hz) of the pressure pulsations at monitoring points distributed across the volute is three times the rotational frequency (49.51 Hz) of the impeller. The different positions and sub-frequencies of the monitoring points mean that the principal component analysis can effectively identify the impeller-induced sub-frequency difference.

Owing to the unique operating mechanism of the vortex pump, which differs from that of conventional vane pumps, inherent high-frequency flow fluctuations occur within the pump, leading to the natural imposition of radial forces on the impeller. The present work conducted a study on a vortex pump by numerical simulation. The numerical results are validated by comparing with experimental data. Based on the numerical calculation results, the frequency domains of pressure pulsations at several typical locations are presented. The annular interface between the rotor and the stator is developed, the characteristics of pressure and velocity pulsations including their intensity as well as the distributions of time-averaged pressure and velocity components across this interface are presented. Finally, the transient characters of the radial force acting on the impeller is studied. The results show that the numerical calculation results are in good agreement with the experimental data. The helical flow at the impeller outlet exerts a pronounced influence on the inlet-proximal regions flanking the outlet on both sides of the impeller, resulting in relatively large pressure and velocity pulsations. The induced effect of the fluid helix leads to a relatively high flow velocity on the side close to the wall surface, causing the radial velocity at the middle part of the impeller outlet to be much greater than that at other positions.

Due to the operational differences between vortex pumps and traditional vane pumps, complex vortex structures exist within vortex pumps. As the fluid gains mechanical energy repeatedly, the vortex also give rise to issues such as hydraulic losses, vibration, and noise. This study conducts a numerical simulation on vortex structures within a magnetic vortex pump with 56 short-straight blades on a single side and staggered blade arrangement on both sides. The numerical simulations are validated against experimental data. Based on numerical calculations, pressure pulsations and velocity pulsations within the impeller passages and casing were analyzed. Additionally, the distribution of pressure pulsation intensity, vorticity intensity, and turbulent kinetic energy dissipation at the rotor-stator interface was investigated. Finally, the vortex structures within the impeller and casing passages, along with their effects on the flow field, were analyzed in the axial, circumferential, and radial directions. Results show the numerical predictions agree well with experimental data. Influenced by the periodic evolution of vortices, velocity pulsations in the impeller and volute do not occur solely at the blade passing frequency. Circumferentially, two counter-rotating vortices exist on either side of the impeller, inducing a significantly higher velocity at the mid-section of the impeller outlet. Additionally, the vertical velocity near the blade root at the impeller inlet is bigger than that near the blade trailing edge. A radial flow separation vortex near the blade suction side creates a substantial pressure gradient from the pressure side to the suction side.