Investigation into the stall inception of low specific-speed centrifugal pumps

Stall in centrifugal pumps can induce adverse effects on unit operation, such as operational instability and low–frequency pressure pulsations. In deep stall, a substantial increase in energy demand is required to restore the impeller's internal flow to a stable condition. However, the onset and evolution mechanisms of stall remain poorly understood. Clarifying the characteristics and mechanisms of stall inception is therefore of significant importance. In this study, high–fidelity numerical simulations were conducted to investigate the topological evolution of three–dimensional flow structures within the impeller during stall inception, with the objective of elucidating its formation mechanism. Through combined qualitative and quantitative analyses, internal flow–field characteristics and circumferential flow–rate distributions were systematically compared under stall and non–stall conditions. The results indicate that the circumferential coefficient of variation (CV) of the single–passage flow–rate coefficient is highly sensitive to variations in operating conditions. During the dynamic transition from non–stall to stall conditions, the evolution of internal flow patterns within the impeller closely follows the trend of the CV curve. This correlation enables precise identification of stall inception and reveals its spatiotemporal characteristics. Moreover, transient analysis of the slip–angle distribution reveals that alternate stall in centrifugal impellers is driven by the combined action of a separation vortex and a corner vortex. The corner vortex, generated at the junction between the shroud and the blade suction surface, plays a dominant role during stall inception. These findings provide valuable guidance for preventing centrifugal pumps from entering stall conditions and for extending their range of stable, efficient performance.