Numerical Investigation of Different Tip Clearances Effect on the Hydrodynamic Performance of Pumpjet Propulsor

Previous studies show that the tip clearance loss limits the improvement of turbomachinery performance, and it is roughly in close relation with the gap size. In this study, a pumpjet propulsor (PJP) with different sizes of tip clearances (delta = 0.2, 0.5, 1, 2, 3 mm) has been presented to investigate the influence of tip clearances on PJP. This analysis is based on computational fluid dynamic (CFD) method, and the SST k-omega turbulence model is applied. Calculations are carried out with a worldwide employed ducted propeller (the Ka4-70 propeller in 19A duct) to verify the numerical simulation. And the grid independence validation is discussed. The numerical simulation of PJP flow with different tip clearances is carried out. Results show that the open water efficiency decreases gradually with the increase of tip clearance. The efficiency decreasing is caused by the tip flow loss. The shape of tip vortex of PJP which consisted of tip-separation vortex and tip-leakage vortex is presented. Furthermore, the formation and spread process of tip vortex at different tip clearances are discussed. Then, the effect of different tip clearances on the pressure field of rotor blade is investigated. The main pressure area affected by different tip clearances is mainly concentrated in the area above 0.9 spanwise of the suction side of rotor blade. Beyond that, the effects of different tip clearances on the velocity field of PJP has been studied.