Comparative Numerical Investigation on Flow Characteristics of Pump-Jets with Accelerating Duct and Decelerating Duct

The mutual interaction between the duct and components of pump-jet can induce significant effects on the overall flow properties and inner flow field. In order to compare the properties of pumpjets with accelerating and decelerating ducts and investigate the effects of duct profiles parameters of two different ducts on the flow characteristics, a detailed numerical analysis is implemented on the flow characteristics and interaction of the pump-jet with different duct profile parameters. Beforehand, the comparison of experiment and simulation of propeller VP1304 and the pump-jet under mooring conditions are adopted to validate numerical methodology. In this paper, five cambers f (f=0.5t, 0.25t, 0, -0.25t, -0.5t) and three angles of attack α (α= 4°, 0°, -4°) of duct profile, employed to distinguish accelerating and decelerating ducts, are considered carefully, focusing on the flow field information and propulsion performance. The results, including the comparison of single ducts with different f and α, and comparison of pump-jet with 2 types of ducts distinguished by different f and α, are exhibited. It shows that the flow velocity at the outlet of the accelerating ducts is significantly higher compared to the inlet velocity, as opposed to the phenomenon produced by decelerating ducts. Compared with the change of α, the variation of f makes the internal evolution of the flow field more intuitive. Further results indicate that the maximum efficiency of pump-jet drops after the modest growth as the cambers decrease, whose location shift towards the lower advance coefficient J. The alteration of α leads to making the trend more direct and apparent for the decelerating and accelerating ducts. It is advantageous for the high f to the cavitation resistance of inside components, like rotor blades and stator blades. The impacts of changing α on the distribution of pressure in pump-jets with accelerating and decelerating ducts are more prominent than changing f. Moreover, the effects of both variations of f and α on the circumferential distributions of the velocity components are prominent, while there are still significant differences between these changes. Additionally, the velocity distribution at the inlet of pump-jets with decelerating ducts is higher than that at the outlet, and the velocity distribution of pump-jets with accelerating ducts presents the opposite pattern.