Effects of different blade deflection angles on internal flow-induced noise in a shaftless pump-jet propulsor

Abstract

Shaftless pump-jet propulsors offer high propulsion efficiency but also generate significant flow-induced noise due to complex internal rotating flows. This study investigates blade deflection angles of ‒2°, 0°, and +2° through unsteady simulations with the RNG k–ε turbulence model, supported by experimental validation. Dominant noise frequencies are extracted using Fast Fourier Transform, and a hybrid CFD-acoustic method based on Lighthill’s acoustic analogy is applied. Results show that as the deflection angle increases from ‒2° to +2°, thrust and efficiency decrease slightly but remain acceptable. The +2° configuration yields more concentrated and continuous wake vortex bands, suppresses large-scale vortices in impeller passages, and enhances rotating flow coherence. Noise energy is primarily concentrated below 1000 Hz, with dominant peaks at the shaft frequency and its harmonics. At +2°, both the dominant-frequency sound pressure level and the overall sound pressure level decrease at most monitoring points, achieving a maximum reduction of approximately 1.69 dB without significant performance loss.