Abstract:This paper uses computational fluid dynamics (CFD) method to calculate three pump-jet thruster models with different fixed rotor spacing, and explores the influence of fixed rotor spacing on the propulsion performance and flow field characteristics of pump-jet thruster.The results show that the constant rotor spacing mainly affects the torque balance effect, and the greater the rotor spacing, the worse the torque balance effect.With the increase of the speed coefficient, the torque of the rear stator will exceed the torque of the rotor, making the pump-jet propeller in the state of "overbalance".The distribution characteristics of tangential and radial velocity fields between fixed rotors and the distribution characteristics of rotor surface pressure are analyzed.The pressure difference between the upper and lower surfaces of the rear stator is the main reason for its torque, and the pressure difference between the fixed rotor reaches the maximum in the middle part of the stator.The pressure difference between the upper and lower surfaces of the stator decreases with the increase of the spacing.PIV experiment was used to verify the accuracy of the numerical simulation method.The results of this paper can provide a basis for the design of pump-jet thrusters and the analysis of flow field characteristics.