Objectives The unsteady force of the rotor is the main excitation source of pump-jet shafting vibration, and rotor-stator interaction has an important impact on the characteristics of the unsteady force. Therefore, the suppression method of pump-jet unsteady force should be studied.

Methods Oscillating flaps are introduced onto the trailing edge of the stator. The secondary flow generated by the flaps is used to affect the rotor inflow conditions so as to suppress the unsteady force of the rotor. A numerical model is established on the basis of the unsteady Reynolds-averaged Navier–Stokes equation (URANS) method of the shear stress transport (SST k–ω) turbulence model, and a SUBOFF with full appendages and a pump-jet with stator trailing edge flaps is taken as the research object. Aiming at suppressing the unsteady force amplitude at the rotor blade passing frequency, the oscillating law of the stator flaps is given.

Results The results show that under the optimal control of the flaps, the hydrodynamic performance of the pump-jet varies by less than 1%, the axial unsteady force of the rotor decreases by 83.35% at the rotor blade pass frequency (BPF) and that of a single rotor blade decreases by 81.8% at the rotor BPF. Further analysis shows that the oscillating flaps can manipulate the stator wake and velocity on the rotor inlet plane.

Conclusions The results show that stator trailing edge flaps can significantly suppress the characteristic line spectrum of rotor unsteady force while maintaining hydrodynamic performance, which will shed some light on controlling the BPF line spectra of pump-jets.