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Tip clearance loss is a limitation of the improvement of turbomachinery performance. Previous studies show the tip clearance loss is generated by the leakage flow through the tip clearance, and is roughly in close relation with the gap size. In this study, a pumpjet propulsor with different size of tip clearance(  =0.2mm、 0.5mm、 1mm、 2mm、 3mm) has been presented to investigate the influence of the tip clearance on a pumpjet propulsor. This analysis was carried out by solving Reynolds Averaged Navier-Stokes (RANS) method with the commercial Computational Fluid Dynamic (CFD) code CFX14.5, and the SST k  turbulence model is applied. In order to verify the accuracy of numerical simulation method, calculations were carried out with a worldwide employed propeller (the E779A propeller). Simulation results show that the open water efficiency decreases gradually in the same advance coefficient (J) with the increasing of tip clearance. However, the open water efficiency is basically unchanged after the tip clearance is bigger than 2mm. The effects of tip clearance on the tip-separation vortex and the tip-leakage vortex are discussed. the area affected by the tip-separation vortex and the tip-leakage vortex is becoming bigger and bigger as the tip clearance increases. And as the tip clearance increases, the core of tipseparation vortex and tip-leakage vortex are "contact", they transfer to each other. The position of the contact is moved to following edge in the axial direction, and the position is 1/3 of the blade tip away from leading edge in the case =3mm . The main effected area of different tip clearance, which is the low pressure area, is mainly focus at the area above 0.9 spanwise of the suction side of rotor blade.

Pumpjet Propulsor; Tip clearance; Computational fluid dynamic (CFD). The tip vortex structure.