Effects of particle volume concentration on the leakage vortex and erosion characteristics of semi-open centrifugal pumps

Interactions often occur between particle impact, leakage vortex production, and particle trajectory in a semi-open centrifugal pump. These interactions can aggravate the complexity of erosion under solid-liquid two-phase flow condition. In this research, the two-way coupling Euler-Lagrange and Finnie erosion model was proposed to determine the solid-liquid two-phase flow field under different particle volume concentrations in semi-open centrifugal pump. A systematic investigation was conducted to clarify the influence of particle volume concentration on the structure characteristics of leakage vortex, particle migration trajectory, and erosion. The correlation analysis was utilized to reveal the specific mechanism between particle volume concentration, tip clearance leakage vortex, and the erosion of flow passage components. The results show that the pressure gradually increased from the impeller inlet to the outlet under the solid-liquid two-phase condition. Compared with the clear water condition, there was the increase in the pressure for the accumulation of particles in the flow passage, where the maximum pressure increased by 4%. Once the particle volume concentration was less than 1%, there was the similar structure and characteristics of tip leakage vortex, tip separation vortex, and passage vortex in the impeller passages. A few particles inhibited the flow separation at the boundary layer. Correspondingly, the low-pressure area was reduced near the blade leading edge, which was conducive to the improvement of pump hydraulic performance. Particles with a diameter of 0.5 mm were belonged to the large size and mass particles, indicating the low fluid ability to carry them. As a result, most particles were remained the original direction of axial movement after entering the impeller. The obstruction effect was found to combine with the tip clearance leakage vortex. Particles were easy to impact the leading edge near the blade bottom and the suction surface near the blade tip, which were in the severe erosion and more outstanding spot erosion. The particles were frequently impacted on the surface of flow passage components, as the particle volume concentration increased, leading to the serious erosion of the hub and inlet edge of blade pressure surface. Meanwhile, the serious crowding among particles in the flow passage caused some particles to deviate from the running track, and then impact the blade suction surface with the fluid. Therefore, the linear erosion appeared near the blade bottom at the outlet edge of suction surface, and then the erosion range was gradually extended to the inlet. Once the particle volume concentration was greater than 3%, the average erosion rate of the hub increased faster and eventually greater than the blades. The number of particles increased to flow into the tip clearance layer with the increase of particle volume concentration. The frequent impact of particles on the tip leakage vortex led to their breakdown, separation, and refusion, which was aggravated the flow unsteadiness. In addition, more collision and friction between particles caused the increase of the energy consumption and hydraulic loss of fluid transport particles, indicating the significantly reduced pump head and efficiency. This finding can provide the theoretical references for the optimal design and safe operation of semi-open centrifugal pump under solid-liquid two-phase conditions.