Objective The axial and circumferential unsteady excitation forces generated by pump-jet rotors are important sources of hull vibration and shaft fatigue damage. Since pre-installed stators directly modify the inflow uniformity, it is essential to clarify the regulation law of stator structures on the amplitude-frequency characteristics of rotor excitation forces.
Method A pump-jet model incorporating a 5-blade pre-stator and a 4119 rotor installed on the Suboff stern is established. Unsteady CFD simulations are carried out based on RANS-SST k-ω turbulence model. The operating conditions with and without pre-stators are compared first. A single-factor analysis method is employed to investigate two key structural parameters: stator-rotor axial spacing and circumferential bending angle of the stator blades. The flow mechanisms are elucidated through pressure and velocity distributions on the rotor plane. Grid independence, time-step independence, and comparisons with published data are conducted to validate the numerical framework.
Results Pre-stators intensify inflow non-uniformity, introducing an additional high-frequency peak at 812 Hz in the axial excitation force spectrum, while the dominant frequency of circumferential excitation shifts to twice blade-passing frequency, accompanied by a significant increase in fluctuation amplitude. A moderate stator-rotor spacing of 0.2D–0.4D effectively suppresses excitation peaks over the entire frequency range. Increasing the stator bending angle shifts the dominant axial excitation frequency toward higher frequencies, while a bending angle of 5°–10° effectively reduces circumferential pulsation amplitudes. This reduction is primarily attributed to the redistribution of low-pressure regions near blade tips.
Conclusion Although pre-installed stators enhance pump-jet thrust performance, they also intensify vibration excitation. A combined configuration featuring a stator-rotor spacing of 0.2D–0.4D and a stator bending angle of 5°–10° can simultaneously mitigate axial and circumferential force pulsations while avoiding high/low-order structural resonance. This study provides numerical guidance for low-vibration optimization of pump-jet stator configurations.
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