Study on the thrust fluctuation and vortices of a pump-jet propulsor under different duct parameters

Improving underwater propulsor performance is endlessly pursued, not only the propulsion but the vibration and radiated noise. The latter is highly related to the unsteady characteristics of forces and flow. This paper investigates the effects of duct parameters on the thrust fluctuation and flow features of a pre-swirl stator pump-jet propulsor (PJP) via embedded large eddy simulation (ELES). The duct parameters include inclination angle, tip clearance, axial length, maximum thickness, and diameters of duct inlet and duct outlet. The numerical approach is verified with experiments, showing good precision. The performance is first discussed, followed by the thrust fluctuation analysis to reveal the varying law of the thrust fluctuation level with duct parameters. Then, the velocity and pressure around the duct are presented to inspect the causes of differences in performance and thrust fluctuation. Finally, the vortices in the flow field are identified and considered the vortex evolution of the tip clearance vortex for inspecting the instability mechanism under different ducts. Results show that the duct parameters significantly affect the performance and thrust fluctuation. The instability mechanism of the tip clearance vortex also presents notable differences. Overall, the study should be helpful in the duct design and reduce thrust fluctuation, and will eventually benefit low-noise pump-jet design.