Effect of Trimmed Rear Shroud on Performance and Axial Thrust of Multi-Stage Centrifugal Pump With Emphasis on Visualizing Flow Losses

Multi-stage centrifugal pumps are frequently used in high-lift applications and consume considerable energy, but suffer from poor performance and large axial force. The rear shroud of impeller is trimmed for reducing axial thrust, but this degrades performance. This study analyzes performance degradation and optimizes performance and axial force. Experiments and simulations are conducted on different ratios of rear shroud to front shroud (lambda). Total pressure losses are calculated, and flow losses are visualized using the entropy generation method. Both measured and simulated performances decrease as the rear shroud is trimmed. Designs with different lambda meet the head coefficient requirement of 1.1. However, lambda of 0.86 has the best efficiency of 42.7%, lambda of 0.83 reaches 42.5%, lambda of 0.8 shows the lowest efficiency of 39.9%. Efficiency in the middle channel improves as the rear shroud is trimmed, but this cannot offset increased losses in the impeller and rear side chamber. Entropy production is exacerbated in the axial passage between impeller and rear side chamber due to the collision between impeller-driven flow and pressure-driven backflow. When lambda is reduced by 0.03, axial thrust drops by 7%. To compromise between performance and axial thrust, lambda should be designed at 0.83.