Study on flow characteristics of tip clearance leakage flow in spiral axial-flow multiphase pump

This paper, based on the Q-criterion vortex identification method and the theory of vortex transport equations, systematically investigates the impact mechanism of the top clearance of spiral axial multiphase flow pump blades on the leakage flow characteristics. By constructing a vortex dynamics analysis framework, the paper focuses on revealing the evolution law of the vortex structure of the top leakage vortex and quantitatively clarifies the influence mechanism of gap size on the spatial evolution of leakage vortices. The research results show that there is a critical phenomenon of forward–reverse conversion in the top leakage flow. When the gap size increases from 0.5 mm to 1.1 mm, the critical point relative arc length advances from 0.94 to 0.73, showing significant gap sensitivity; the maximum axial velocity in the gap channel shows a non-monotonic variation characteristic, with the maximum axial velocity at a 0.8 mm gap (5.39 m/s), followed by 0.5 mm (3.85 m/s), and the minimum at 1.1 mm (1.22 m/s); there are three typical vortex structures in the blade passage: separation vortex, gap leakage vortex, and blade passage vortex. Among them, the evolution of the separation vortex is dominated by the rotation effect (Coriolis force contribution >66%), the gap leakage vortex is jointly controlled by inertial stretching and the rotation effect, and the dynamic characteristics of the blade passage vortex show significant time-varying features. Under the 0.8 mm gap condition, the interaction between the separation vortex and the leakage vortex enhances the turbulent kinetic energy in the blade passage vortex area, and through vortex-turbulence synergy, it strengthens the rotation effect. The vortex evolution mechanism and gap effect quantitative rules proposed in this study provide a theoretical basis and innovative ideas for the refined design of impellers and active control of leakage flow in spiral axial multiphase flow pumps.