In order to research the relationship between impeller trimming and performance in a double-suction centrifugal pump, impellers were trimmed 11mm and 22mm respectively. Numerical methods were applied combined with the original one, and experimental validation was also carried out on original and 11mm model. The performance and difference of total pressure between volute inlet and outlet was calculated, meanwhile, distributions of velocity and turbulence eddy dissipation on volute middle section were analyzed. The results indicate that the head drops with the trimming process and discontinuity appears when trimmed 22mm. The impeller trimmed 11mm is the most efficient under part-load and design conditions, while the original model has the lowest efficiency. Efficiency in trimmed cases decreases dramatically under over-load condition, especially when trimmed 22mm. Duo to rotor-stator interaction between impeller and volute receded by the enlarged clearance, the head losses inside the volute decrease with impeller trimming but increase significantly under 1.4Qd when trimmed 22mm. The extremely high shock losses resulting from exaggerated impeller outlet flow angle and dissipation near volute tongue account for it. Moreover, the losses in volute diffuser channel increase due to the vortexes generated by flow separation and backflow. The losses in volute will be improved by impeller trimming within reasonable limits in a double-suction pump. This research provides theoretical foundation for impeller trimming in double-suction centrifugal pumps.
© 2021 Institute of Physics Publishing. All rights reserved.

To improve the efficiency of a multistage centrifugal pump at design point, the response surface methodology was applied to construct an approximation function between the design-point efficiency of the first stage in multistage centrifugal pump and the design variables of the impeller. First, important geometric parameters are selected as factors of a one-factor experimental design. Four parameters that had greater influence on the hydraulic efficiency were screened out from the simulation results using parameter sensitivity analysis. The optimal design points for each level of the parameters were then determined by central composite design and the response surface analysis method. The efficiencies of the impeller schemes generated in the Design-Expert software was executed with CFD. The effects of the single parameters were analysed, and the approximation model solved to find the optimal parameter combination that improve the efficiency by 3.62% at design point. And the inner flow was improved in high flow rate condition.
© 2021 Institute of Physics Publishing. All rights reserved.

Numerical results obtained by calculations using URANS k-epsilon turbulence model combined with the Euler-Euler inhomogeneous two-phase model are presented including different inlet void fraction values in the inlet section of a centrifugal pump. Local information inside the impeller are extracted from CFD results to get more deep understanding on gas and water flow structures. Results explain the reason why pump performance degradation is more pronounced for low flow rates compared to high flow rates and the importance of inlet void fraction evolution with inlet gas fraction. They also confirm what has been already measured for overall performance modification and more locally visualized in existing open literature in such research field.
© 2018 American Society of Mechanical Engineers (ASME). All right reserved.

The volute casing used in centrifugal pumps is efficient for the transformation of kinetic energy into pressure energy, however, its asymmetric hydraulic design makes the flow in diffuser-discharge-channel (DDC) inhomogeneous, resulting in unsatisfactory flow patterns. In this study, the unsteady numerical simulations are carried out to investigate the transient flow characteristics in DDC. The accuracy of numerical results is found to agree well with experimental performance and pressure fluctuations. It is observed that the flow in DDC is significantly uneven. At the elbow of DDC, the static pressure on the volute left side (VL) is larger than the volute right side (VR) due to the flow impact and flow separation respectively. Thereby, this high-pressure gradient induces the secondary flow on the cross sections of DDC. Further, there is an obvious dependency of pressure fluctuations in the discharge pipe on the strong interaction between the impeller and tongue, in which four small peaks and four large peaks can be observed. At each moment, the pressure on VL gradually decreases from the inlet of discharge pipe to the pump outlet, while it increases on VR, finally, two sides tend to be the same. The pressure fluctuation intensity gradually becomes equivalent-distributed. In particular, it should be noticed that the energy loss in the diffuser part is larger than the discharge pipe, which requires a redesign concerning hydraulic performance. This study can help to better understand the transient flow characteristics and provide guidance for reducing flow loss in the volute casing.
© 2018 American Society of Mechanical Engineers (ASME). All right reserved.