Influences of duct parameters on the propulsion features and radiated noise of a pre-swirl stator pump-jet propulsor

The duct is crucial for a pump-jet propulsor (PJP), deciding the flow channel, rotor design, hull matching, and dimensions, profoundly impacting the flow characteristics, propulsion, and noise. This paper utilizes the improved delayed detached eddy simulation for obtaining the high-fidelity flow and couples with the Ffowcs Williams-Hawkings equations for quantifying the radiated noise to discuss the influences of duct parameters on the performances and flow in the equivalent thrust condition. The results indicate that the duct parameters significantly affect the duct flow, such as the forward stagnation point and flow separation, ulteriorly the whole flow field and performance of the PJP. The gap size, inclination angle, inlet diameter, and outlet diameter of the duct show significant impacts, whereas the duct length and maximum thickness exert modest influences. When the inappropriate duct parameter causes the flow separation outside the duct passage, the propulsion drops, and noise notably increases. When the flow separation occurs inside the duct passage, though the propulsion performance slightly changes, the noise and thrust fluctuation increase significantly, even the magnitude order changes. When the flow separation does not occur around the duct, such as a large inclination angle or inlet diameter, which presents the high jet-speed ratio, the PJP achieves a higher propulsion performance but not low noise because the rotor generates a higher load and consistently high-intensity tip and wake vortices. The duct parameters that perform optimal propulsion do not coincide with the ones that generate minimal noise performance. These insights provide theoretical support for refining PJP configurations, aiming to enhance efficiency, reduce noise, or achieve a balance.