Numerical Study On The Hydrodynamic Performance Of Steering And Reversing Unit Of Waterjet Propulsion System

In the last decades,waterjet propulsion system has found considerable application on a wide range of high-performance vessels due to its outstanding advantages of high efficiency,good manoeuvrability,less vibration and noise.As the control device of waterjet propulsion system,the hydrodynamic performance of steering and reversing unit is closely related to the waterjet efficiency,and its improper design may even result in the loss of ship power performance and manoeuvrability.Therefore,prediction study on the hydrodynamic performance of the steering and reversing unit is of great significance for the design of waterjet propulsion system with excellent performance as well as the improvement and development of waterjet propulsion technology.In this thesis,numerical simulation of the hydrodynamic performance of steering and reversing unit is carried out.Classic types of steering and reversing unit at home and abroad are summarized,together with their advantages,disadvantages and application.The basic theories and methods of Computational Fluid Dynamics applied in the numerical simulations are introduced.Hydrodynamic analysis of steering and reversing unit is performed with momentum theorem,and the formulae for computing the reversal thrust of two widely-used types of reversing buckets are presented.Numerical model of a flush type of waterjet intake duct is set up,and three-dimensional viscous flow within the waterjet duct under forward,backward and oblique moving conditions is simulated by commercial CFD software Fluent to analyze the effect of steering and reversing unit on the hydrodynamic performance of waterjet.The computed results under forward conditions are in good agreements with the available experimental data,demonstrating the validity of the adopted numerical method.On this basis,the effects of different ship motions on the flow characteristics are compared and analyzed in terms of pressure distribution,velocity profile,with and without shaft.The numerical results show that under backward and oblique moving conditions,the flow is less uniform,the pressure is lower,and cavitation and flow separation are more likely to occur within the intake duct.This study is of some reference value for the design and improvement of waterjet propulsion system.