Abstract: Multistage centrifugal mixed-flow pumps are commonly used to transport high-pressure gas-liquid two-phase fluids. However, gas pockets often develop in the impeller section of such pumps due to gas-phase compressibility and the inter-phase slip velocity, and cause uneven flow distribution with inconsistent pressure-boosting capabilities across pump stages. This study presents experimental tests on two systems of 3-stage and 25-stage centrifugal pumps, and examines the influence of inlet gas volume fraction (IGVF) on the inter-stage characteristics. We apply an Euler-Euler inhomogeneous flow model to simulate the 3-stage system for conditions of different gas compressibilities. The results show that at single water phase conditions, pressure rises nearly the same across different impellers. For gas-liquid conditions, the overall pressure-boosting capacity decreases significantly with the increasing IGVF, with the secondary and final-stage impellers outperforming the first stage. Gas accumulation intensifies in the impeller passages, spreading along the suction sides of the blades up to the outlet. Velocity threshold analysis reveals that velocity-area ratio decreases stage by stage at the low thresholds, while increases progressively at the medium thresholds, indicating an enhanced impeller pressurization. For gas-liquid conditions, pulsating entropy generation losses are primarily concentrated near the impeller inlet and diffuser inlet. This study lays a basis for optimizing the design of multistage mixed-flow pumps.

Key words: multistage centrifugal pump, inter-stage characteristics, numerical simulation, gas volume fraction, flow pattern