Effect of pre-swirl on gas–liquid two-phase flow characteristics in a helical axial-flow pump

In helical axial-flow pumps for gas–liquid multiphase transport, unsteady flow induced by the interaction between the trailing edge of the guide vanes and the impeller inlet often deteriorates the hydraulic performance. In this study, pre-swirl regulation is implemented by adjusting the outlet angle of the front guide vanes. Using the Eulerian multiphase model and the SST k-ω turbulence model, the influence of pre-swirl on internal flow characteristics and hydraulic performance under various gas volume fractions (GVFs) is investigated. The results show that negative pre-swirl increases the inlet incidence angle, intensifies impingement at the impeller leading edge, and leads to a decrease in both head and efficiency. Conversely, positive pre-swirl alleviates inlet flow separation, enhances flow uniformity, and improves pump performance. At a GVF of 0.3, a pre-swirl angle of 80° increases the head by 36.0% compared to the non-swirl case, while the efficiency improves by 1.06% in the 30°–50° range. Furthermore, appropriate pre-swirl angles reduce recirculation zones and suppress gas accumulation near the impeller tip, resulting in improved two-phase flow stability. These findings provide theoretical guidance for hydraulic optimization of gas–liquid multiphase axial-flow pumps.