Marine centrifugal pumps are mostly used on board ship, for transferring liquid from one point to another. Based on the combination of orthogonal testing and numerical simulation, this paper optimizes the structure of a drainage trough for a typical low-specific speed centrifugal pump, determines the priority of the various geometric factors of the drainage trough on the pump performance, and obtains the optimal impeller drainage trough scheme. The influence of drainage tank structure on the internal flow of a low-specific speed centrifugal pump is also analyzed. First, based on the experimental validation of the initial model, it is determined that the numerical simulation method used in this paper is highly accurate in predicting the performance of low-specific speed centrifugal pumps. Secondly, based on the three factors and four levels of the impeller drainage trough in the orthogonal test, the orthogonal test plan is determined and the orthogonal test results are analyzed. This work found that slit diameter and slit width have a large impact on the performance of low-specific speed centrifugal pumps, while long and short vane lap lengths have less impact. Finally, we compared the internal flow distribution between the initial model and the optimized model, and found that the slit structure could effectively reduce the pressure difference between the suction side and the pressure side of the blade. By weakening the large-scale vortex in the flow path and reducing the hydraulic losses, the drainage trough impellers obtained based on orthogonal tests can significantly improve the hydraulic efficiency of low-specific speed centrifugal pumps.

Sewage pumps are one of the most popular types of fluid machinery in municipal, industrial, and environmental engineering and many other fields. The influence of tip clearance size on the pump performance and internal flow field distribution within a sewage pump was investigated in this study based on numerical calculation and test verification. Three models with different tip clearances were obtained by adjusting the assembly structure and simulated by the computational fluid dynamics software to solve the Navier-Stokes equations for three-dimensional steady flow. The accuracy of numerical methods was verified by comparison with the experimental results. The sewage pump performance under different tip clearances was then compared and analyzed. The structure and propagation of the vortices inside the impeller caused by the leakage flow with different tip gaps were also analyzed. The leakage flow in the impeller couples with the cover reflection and secondary flows, forming different vortex structures in various locations of the impeller channel. These vortex structures cause large hydraulic losses near the blade suction surfaces. This finding could provide useful insights for the improvement of the hydraulic performance and operational stability of semi-open sewage pumps.

Electrical Submersible Pumps (ESP) are one of the most reliable and efficient ways to lift oil or water from the ground or deep-sea to the surface. How to reduce the pressure pulsation and increase reliability is a challenging issue in the ESP design processes. In this study, a typical three-stage ESP model was selected as the research object. Based on numerical calculations and validation tests, the flow-field distribution mechanism within the dynamic and static interference zones of multi-stage ESP was investigated. Meanwhile, the inter-stage variability of pressure pulsation characteristics within the main hydraulic components was explored by Morlet continuous wavelet transform. The results showed that the numerical predicted performance has an excellent agreement with the experimental results, which confirms the accuracy of the numerical calculations. The time-domain characteristics of pressure pulsation at each monitoring location within the ESP showed high disorder due to the inter-stage propagation and coupling of the pressure pulsations. The low-frequency signal in the pressure pulsation signal had not only a cascading superposition of intensity, but also a significant phase difference. It was found that the main form of propagation between pulsating signal levels is the low-frequency signal. This work may facilitate the reduction or control of the pressure pulsations and thus improve the operation stability of ESP.

The unstable operation of a centrifugal pump under the gas-liquid two-phase condition seriously affects its performance and reliability. In order to study the gas phase distribution and the unsteady force in an impeller, based on the Euler-Euler heterogeneous flow model, the steady and unsteady numerical calculations of the gas-liquid two-phase full flow field in a centrifugal pump was carried out, and the simulation results were compared with the test data. The results show that the test results are in good agreement with the simulation data, which proves the accuracy of the numerical calculation method. The energy performance curve of the model pump decreases with the increase of the gas content, which illustrates a serious impact on the performance under the part-load operating condition. The results reveal that the high-efficiency-operating range become narrow, as the gas content increases. The gas phase is mainly distributed on the suction surface of the impeller blades. When the gas content reaches a certain value, the gas phase separation occurs. As the inlet gas content increases, the radial force on the impeller blades decreases. The pattern of the pressure pulsation is similar to that under pure water and low gas content conditions, and the number of peaks during the pulsation is equal to the number of the impeller blades. After the gas content reaches a certain value, the pressure fluctuates disorderly and the magnitude and the direction of radial force change frequently, which are detrimental to the operation stability of the pump. The intensity of the pressure pulsations in the impeller flow channel continues to increase in the direction of the flow under pure water conditions. The pressure pulsation intensities at the blade inlet and the volute tongue become more severe with the increase of the gas content.

No abstract

No abstract

No abstract

The complex multiscale characteristics of particle flow are notoriously difficult to predict. In this study, the evolution process of bubbles and the variation of bed height were investigated by conducting high-speed photographic experiments to verify the reliability of numerical simulations. The gas–solid flow characteristics of bubbling fluidized beds with different particle diameters and inlet flow rates were systematically investigated by coupling computational fluid dynamics (CFD) and discrete element method (DEM). The results show that the fluidization in the fluidized bed will change from bubbling fluidization to turbulent fluidization and finally to slugging fluidization, and the conversion process is related to the particle diameter and inlet flow rate. The characteristic peak is positively correlated with the inlet flow rate, but the frequency corresponding to the characteristic peak is constant. The time required for the Lacey mixing index (LMI) to reach 0.75 decreases with increasing inlet flow rate; at the same diameter, the inlet flow rate is positively correlated with the peak of the average transient velocity; and as the diameter increases, the distribution of the average transient velocity curve changes from “M” to linear. The results of the study can provide theoretical guidance for particle flow characteristics in biomass fluidized beds.