Research on the Performance of Shaftiess Water-jet Propulsion

This paper presents the results of an investigation on the feasibility and superiority of the shaftless water-jet propulsion. Resulting from the elimination of the upstream driving shaft, the shaftless model is a rim driven propulsion where shaftless water-jet pump and intake duct are the major parts. The computational fluid dynamics (CFD) methodology was used to calculate the performance and visualise the flow of the shaftless water-jet installation, and the numerical model was validated with available experimental data. AS the result of reducing the velocity circulation at the inlet of the rotor, there was nearly 2% increment in the performance prediction of the shaftless water-jet pump than the traditional. Based on the theoretical formula, it infers that the increasing flow rate and head of the shaftless pump would deliver more thrust to the vessel on the design condition (vs=30knot), and the variation of jet velocity ratio would contribute to extending of propulsion efficiency. Flow field analysis has proved that the removal shaft could minimise the velocity non-uniformity and eliminate the flow separation around the shaft, so there would be less energy losses in the intake duct. With the improvement of intake duct, it also reduces the backflow and blocking at the shroud. Furthermore it produces a more uniform inflow for the rotor to ensure better efficiency and reliability of the propulsion. Performance analysis shows that the shaftless model delivers more thrust (3%) than the traditional on the design speed. In order to match the resistance, the shaftless water-jet propulsion has to decrease the rotation speed of the engine to compensate for the increment of thrust, it means that the shaftless model could possess more efficiency (4%) and save more energy for operating. On the off-design condition, the shaftless model is proved to extend the working range and broaden the high efficiency region resulting from the increment of output volume.