As an underwater thruster, the pump-jet propulsor (PJP) exhibits low radiation noise but generates significant line spectral noise in the low-frequency band. In this paper, we equipped the PJP hub with two types of propeller boss cap fins (PBCF): one fixed and the other rotating with the rotor. The hybrid large eddy simulation and Reynolds-averaged Navier–Stokes method, along with the Ffowcs Williams-Hawkings (FW-H) equation, are employed to systematically analyze the hydrodynamics, exciting force, flow noise, and flow field of PJPs. The results indicate that the fixed PBCF improves the hydrodynamic performance and reduces the exiting force, raising the rotor's thrust coefficient by 9.22%–14.99%. The fixed PBCF also modifies the characteristics of line spectrum noise but causes an increase in the flow noise. The rotating PBCF increases the rotor's thrust coefficient by 2.03%–3.15%, decreasing both exciting force and line spectrum noise. For instance, at the advance coefficient of 0.8, its sound pressure level at the rotor frequency drops to 49.6%. Additionally, the rotating PBCF increases the pressure of the hub wake and effectively reduces the hub vortices' strengths. This paper provides a theoretical foundation for designing PJPs that enhance concealment and minimize vibrations and noise.

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 σn and oblique angles θ. The results show that when the σn 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 KT decreases by 28.5%. The influence of σn 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 KT 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.

Comprehensively grasping the wake dynamics of pump-jet propulsor (PJP) lies at the core of developing and fine-tuning future PJP design, particularly the exciting forces suppression and noise reduction. In this work, a pre-swirl stator PJP is considered to investigate its wake dynamics and evolution mechanics. The stress-blended eddy simulation (SBES) is implemented for obtaining turbulent flow, and dynamic mode decomposition (DMD) method is utilized to analyze the wake flow evolution. The numerical results align with the experimental data within an acceptable error and are employed to establish the dataset for DMD. With introducing the modal selection “DMD with criterion (DMDc),” the featured modes of the PJP wake are discussed in detail. Those dominant modes provide a multi-level perspective to analyze flow phenomena and enable the reconstruction of the original flow field within reasonable bounds, achieving the compression of flow information. Modal analysis reveals diverse flow patterns appearing at specific frequencies including the mean flow, tip leakage flow, rotor trailing vortices, as well as multiscale duct and hub wake flow. The turbulence instability in the PJP wake is primarily determined by the modes at the rotor blade passing frequency. The error between the wake flow reconstructed from the top six modes and obtained through SBES is less than 7%. This work broadens the cognition for the evolution mechanics of PJP wake flow field, showing excellent prospects in simplifying the analysis process and the flow simulation, as well as intelligently predicting the future evolution of the flow field.