Cavitation evolution and radiation noise of a pre-swirl pump-jet propulsor in oblique flow

During the submarine's surfacing process, the rotor of the pump-jet propulsor (PJP) is subjected to nonuniform hydrodynamic loads and cavitation, inducing cavitation-induced noise. In this paper, the hybrid Reynolds Averaged Navier-Stokes/Large Eddy Simulation method, the Schnerr-Sauer model and Ffowcs Williams-Hawkings equations are adopted to explore the hydrodynamics, excitation force, radiation noise, cavitation evolution of the PJP with different cavitation numbers σ_n and oblique angles θ. The results show that when the σ_n decreases from 1.5 to 1.0, the rapid development of cavitation causes the hydrodynamic performance of the PJP to deteriorate rapidly, and the total thrust coefficient K_T decreases by 28.5%. The influence of σ_n on the excitation force is less than that of the θ. When θ equals 0 deg, its excitation force is approximately 1.5 times that when θ is 6 deg. As θ increases from 6 deg to 24 deg, the excitation force increases rapidly, and the excitation force of K_T increases by 4 times. The contribution of the excitation force to noise is reflected below 300 Hz, while the noise in the range of 300-5000 Hz is caused by cavitation. When θ is equal to 0 deg, the spatial distribution of cavitation is relatively uniform, the cavitation volume change rate is the fastest, and the collapse frequencies are almost the same. The cavitation-induced noises are superimposed on each other, and its total sound pressure level is nearly 7 dB higher than that when θ is 6 deg. This research provides a theoretical basis for the anticavitation and low-noise design of the PJPs.