Research On Power Loss And Influences Of Gap Flow On The Performance Of Rim-driven Thruster Under Different Effects

Rim-driven thruster(RDT),which highly integrates the driven motor and propeller blades,is a new type electric propulsion device.The advantages of high power density,low vibration and noise and being green and eco-friendly have significantly contributed to its great popularity all over the world.The driven motor in RDT is immersed in water,which is different from ordinary motor,Heat would generate when motor stator,rotor and water lubricating bearings work and be partly taken away by water in flow channel,and the other critical function of gap is to provide water as lubrication for bearings.Therefore,the design of the channel is one of the technical difficulties with RDT because of the fact that on one hand,multi-dimensional flows emerge in the channel and mutual influences of different flows arise,which affects motor cooling,density of magnetic field and performance of bearings;and on the other hand,as the flow channel consists of radial gap and axial gaps at both rim ends,torque which results in extra power loss is produced when rotor rotates at a high speed,and is closely related to gap structure and sizes.This thesis investigated the friction power loss,motor cooling and their influences on RDT performance with CFD method by establishing numerical models and imposing different boundary conditions.The main research work and conclusions are as follows.(1)Each component in RDT was introduced,as well as how they affect each other when working.Flow passage component of the 5.5 kW RDT were designed,and then the characteristics of multiple fields in gap domain and multiple dimensions between gap domain and blades domain were revealed.(2)The numerical method for friction power loss of gap domain in RDT was brought up and validated by comparing the numerical results and empirical results.The effects of gap sizes in radial and axial direction and different boundary conditions on friction power loss of gap domain were studied.The results showed that the radial gap contributes more friction power loss than that of axial gaps,and the friction power loss increased when rotation speed,inlet velocity and gap sizes increased.Another interesting discovery is that friction power loss in gap domain is insensitive to whether the axial gaps were symmetrical or not but is more related to overall size in axial direction.(3)The complete numerical model for RDT was established to study the mutual influences between gap doamin and the performance of propeller blades.Another numerical model based on 1.5 MW RDT was built to study the heat dissipation in the gap The results showed that blades motion had little effects on pressure and velocity distribution in the gap.On the other hand,the gap flow affected the thrust and torque of blades and rim significantly.And the performance of rim degraded when gap sizes increased.A great deal of heat would generate in megawatt-level RDT,and given that the heat was mainly carried out with water flow in the gap,the highest temperature rose to 93?C in gap domain.(4)The effects of bearings with different structures and parameters on the performance of RDT and friction power loss in gap domain were studied.The results showed that the L type bearing created more power loss than that of conical bearing due to its more complicated structure.When the number of grooves on L type bearing increased,the thrusts of propeller blades and thruster increased while rim thrusts decreased.On the contrary,when the number of grooves on conical bearing increased,the thrusts of propeller blades and thruster decreased while rim thrusts increased.