Effects of Impeller Trimming on Performance in a Double-suction Centrifugal Pump

Abstract

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 1.4Q_d 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.