Numerical Investigation of an Intake Duct for a Waterjet Propulsion System Using Modified Partially Averaged Navier-Stokes Method

When the marine vessels exceed the speed of 30 knots, it is preferred to adopt the waterjet propulsion method due to its high propulsive efficiency, good maneuverability, less vibration and good anti-cavitation performance. The efficiency of the waterjet pump is up to 90% with advanced modern design methods while 7∼9% of total power is lost in the intake duct. In this paper, the flow simulation in an intake duct has been conducted using the modified partially averaged Navier-Stokes method for better understanding of flow features inside the intake duct and instructing how to reduce the power loss at various ship speeds and inlet velocity ratio (IVR) with considering the hull boundary layer. The nonuniformity and perpendicularity at the impeller plane is applied to analyze the flow quality at the outlet plane of intake duct. The results indicate that the nonuniformity decreases while the perpendicularity increases with increasing IVR. Thus a large IVR together with a high ship speed would cause better outflows. Further analyses of the pressure along the ramp and cutwater depict that cavitation easily occurs at the upper side of the cutwater with a larger IVR. The hydraulic efficiency is seen to firstly increase and then decrease with an increase in IVR. The hydraulic efficiency of the intake duct is over 80% during IVR = 0.4∼1.2 with the maximum value of 92.19% at IVR = 0.6.