Investigation of the effect of top clearance on cavitation characteristics and stability of axial flow pump

To investigate the influence of top clearance on the cavitation characteristics of axial pumps and their safety and stability after cavitation, this paper carries out numerical simulations of axial pumps with different lobe top clearances based on the SST(Shear-Stress-Transport) $\kappa-\omega$ turbulence model and the Rayleigh-Plesset homogeneous flow cavitation model. Comparative analyses of blade surface pressure distribution, vacuole volume fraction distribution, turbulent kinetic energy distribution, blade deformation and equivalent stresses are carried out through fluid-structure interaction calculations. The results show that the head and efficiency of the pump decrease with the increase of the gap, but the increase of the gap does not change the primary part of cavitation, which occurs at the inlet edge of the blade, and expands along the chord direction of the blade, and finally covers the whole blade. With the increase of clearance, the area of low-pressure area and cavity volume on the blade surface decreases, and the distribution area of high turbulent kinetic energy increases first and then decreases. The maximum deformation and maximum equivalent stress under cavitation show a trend of increasing first and then decreasing. The maximum deformation area occurs at the tip of the blade, and the stress distribution at the root of the blade is the most concentrated, which is prone to fatigue damage. Appropriate increase of the gap is beneficial to improve the anti-cavitation performance and stability of the pump. When the gap is 2 mm, the operation condition of the pump is the best.