Numerical investigation of tip clearance effects on propulsion performance and pressure fluctuation of a pump-jet propulsor

摘要

Rotor-stator interaction and tip clearance between rotor blade tip and shroud of a pump jet propulsor can induce strong pressure fluctuations and vibrations, which may cause damage of the propulsion system at some severe working conditions. This paper investigates numerically the effects of tip clearance on propulsion performance and pressure fluctuations in a pump jet propulsor. The shear-stress transport (SST) k-omega turbulence model together with the sliding mesh technique are adopted to simulate the three-dimensional unsteady flow. The accuracy of the computation results is verified through available experimental data of propulsion performance with a tip clearance of 1 mm. The comparison of hydrodynamic performance for pump jet propulsor with tip clearance of 0, 1 mm, 2 mm and 4 mm shows that the thrust and propulsion efficiency can be reduced significantly due to the increase of tip clearance sizes. Further results indicate that the decrease of thrust and torque of the pump-jet propulsor with tip clearance is mainly caused by the change of time-averaged pressure distributions on the rotor blade in the range of 0.8R-1.OR (where R is the rotor diameter). In addition, a method based on Statistics is applied to reveal the characteristics of pressure fluctuations at all grid nodes on the whole blade surface, and the result shows that the amplitudes of pressure fluctuations increase significantly on the blade surface when the tip clearance size is enlarged, especially on the blade tip, blade root and the leading edge. Moreover, it is found that the tip clearance effects do not change the main frequency of thrust and torque fluctuations, while it has a significant impact on the amplitudes of fluctuations, especially in the higher frequency band.