The non-uniformity of the propeller wake field will lead to noise deterioration and structural strength problems of the underwater vehicles. Therefore, the study of jet flow technology is of great significance for improving the uniformity of the wake field and reducing vibration and noise. In this study, the Reynolds-averaged Navier–Stokes method and Ffowcs Williams and Hawkings acoustic model are used together to ascertain the influence of jet flow on the hydrodynamic and noise performance of the propeller. The accuracy of the numerical simulation method is verified through the convergence analysis of the calculation results. The hydrodynamic performance of the submarine and propeller with jet flows on different parameters is studied. The results show that the triangular jet can significantly improve the non-uniformity of the circumferential distribution of the wake field at the propeller plane and reduce the dynamic bearing force of the propeller blade. Simultaneously, the spectrum analysis of the numerical simulation results of the propeller noise shows that, compared with the no jet condition, the total sound pressure level at the propeller plane in the low-frequency range can be reduced by more than 3 dB using jet flow in front of the propeller. Hence, the low-frequency discrete spectrum noise of the submarine propeller can be better controlled.

Contra-rotating propellers (CRPs) are widely used in different kinds of underwater vessels, owing to their excellent stability, propulsive efficiency, and balanced torque distribution characteristics. However, the cavitation that occurs due to their high rotational speeds also generates high levels of cavitation noise. In this study, CRP noise radiations were predicted via detached-eddy simulations with the shear stress transfer k-ω turbulence model, the Ffowcs Williams–Hawkings (FW–H) acoustics model, and the Schnerr–Sauer cavitation model. The cavitation noise of the CRP was predicted using sound radiation theory for spherical bubbles and compared to non-cavitation noise levels from the FW–H equation. It was found that the non-cavitation noise of the CRP is significantly louder in the axial direction than in the radial direction. Furthermore, the noise sound-pressure levels (SPLs) of the flow field generally decrease with increasing frequency. When the effects of cavitation on the flow are taken into account, the SPLs of the CRP noise become significantly higher at all equidistant positions from the center of the propeller. The anisotropy in sound pressure also becomes insignificant when cavitation is present.

This paper presents a numerical modeling procedure for the idealization of vortex shedding effects in the wake flow field of a NACA0009 hydrofoil. During the simulation, the lift and drag acting on the hydrofoil were monitored, and the vortex-shedding frequency of the hydrofoil was analyzed. The effects of inflow velocity, trailing-edge thickness, angle of attack, and maximum hydrofoil thickness on vortex shedding were investigated. The results indicate that an increase in the inflow velocity led to an increase in the vortex-shedding frequency and a negligible change in the Strouhal number. Furthermore, as the thickness of the trailing edge increased, the vortex-shedding frequency decreased gradually, whereas the Strouhal number first increased and then decreased. Vortex shedding and lift curve oscillations ceased altogether after the angle of attack of the hydrofoil increased beyond a certain threshold. When the maximum hydrofoil thickness was increased while keeping the thickness and chord length of the trailing edge constant, the vortex-shedding frequency decreased.

Vortex shedding of freely rotating hydrofoils and the fluctuations in hydrodynamic loads are typical problems in marine engineering. Hence, the hydrodynamic mechanism should be investigated in detail. In this study, the Reynolds-averaged Navier–Stokes method is used to analyze the unsteady flow characteristics of a two-dimensional freely rotating hydrofoil in uniform flow at different Reynolds numbers. The accuracy of the numerical simulation method is verified through convergence analysis of the simulation results. According to the mechanical characteristics and flow field distributions, the effects of three Reynolds numbers from 5 × 10⁴ to 1.2 × 10⁶ and five rotation centers from 0.2c to 0.4c on the dynamic stall of the hydrofoil are analyzed. The results show that the rotation center considerably influences the dynamic stall characteristics of the hydrofoil. As the rotation center approaches 0.4c, the amplitudes of the drag and lift coefficients and the rotation angle of the hydrofoil clearly increase by at least 206%, 10.5%, and 185%, respectively, along with the vortex shedding frequency, which also leads to the increase in the Strouhal number by at least 17.3%. Furthermore, the recovery of the drag and lift coefficients is delayed, resulting in an evident hysteresis effect. Simultaneously, this dynamic stall results in the decrease in the velocity distribution amplitude in the wake field and the increase in the pressure difference between the upper and lower surfaces. The continuous shedding of strong vortices from the trailing edge also leads to more complicated flow field characteristics.

The propeller wake can cause vibrations on the rudder surface, which worsen the noise and reliability. The vibration monitoring of the rudder operating in the propeller wake with fluid-structure interaction (FSI) method is still challenging. In the present study, the structural response during propeller-rudder interaction is investigated using detached eddy simulation. Three-dimensional distributions of loads, stresses, and deformations are discussed. The leading and trailing edges exhibit the strongest deformations in opposite directions, which are S-shaped. The strongest lateral deformation occurs between the tip vortex and hub vortex regions. In the tip vortex region, the dominant lateral vibrations fluctuate at the blade passing frequency (BPF) and shaft frequency (SF). However, the 75 Hz-fluctuation becomes significant at the trailing edge of the rudder. In the hub vortex region, the lateral deformation fluctuates mainly at 75 Hz except the area near the leading edge. There are weak vibrations occurring at the natural frequencies of the rudder when the natural frequencies of the rudder are much higher than the SF and BPF. However, the plate in the propeller suffers intense vibrations at the frequencies near the natural frequencies, where the natural frequencies of the plate are close to SF and BPF.