Experimental investigation on unsteady force suppression of a pump-jet rotor by oscillating stator trailing edge flaps

Objectives The unsteady forces generated by the pump-jet rotor directly affect the coupled vibration and noise levels of the submarine. Methods This study aims to mitigate the rotor excitation force through active flow control. Actively actuated flaps are integrated into the stator to regulate rotor-stator interaction by coupling the secondary flow induced by flap actuation with the internal pump-jet flow. A pump-jet propulsor with oscillating stator trailing edge flaps is designed. Control experiments in a large cavitation water tunnel laboratory are conducted on the SUBOFF’s rear pump-jet propulsor, equipped with front stator flaps. Results Test results indicate that under self-propulsion conditions at different speeds, flap actuation reduces the rotor's unsteady force by at least 15 dB at the blade passing frequency (BPF). Flap actuation reduces unsteady forces at the shaft rotating frequency and twice the blade passing frequency by no less than 7 dB. Conclusions These findings demonstrate that stator flap actuation can significantly suppress the characteristic spectral lines of the rotor excitation force, providing a novel approach for controlling the line spectrum of pump-jet unsteady forces.