Numerical Simulation Study On Ship Speed And Resistance Of Waterjet Propulsion Boat Based On Fully Structured Overset Mesh

Waterjet propulsion is a propulsion type that uses the reaction force of jet water to drive a ship forward.Because of its high efficiency at high speed,it is widely used in high-speed ships.However,due to the coupling of internal and external flow and ship attitude of waterjet propelled ship,the flow is more complex,which has aroused widespread interest of scholars all over the world.In this paper,the in-house viscous flow CFD software HUST-Ship(Hydrodynamic Unsteady Simulation Technology for Ship)is used to study the direct simulation of ship speed and resistance and "ship-waterjet" interaction of waterjet propulsion high-speed craft.The in-house software HUST-Ship adopts finite difference method to discretize SST k-ωturbulence model and URANS equations,fully structured overset mesh technique for spatial discretization of convective domain,PISO algorithm for pressure-velocity coupling solution,single-phase level-set method for free surface capture,and descriptive body force method based on PID control to match ship speed and rotating speed.The spatial flow field is coupled with the six-degree-of-freedom(6DOF)motion equations to predict the ship motions of the high-speed boat.The main research work of this paper is as follows:1)The direct simulation method of ship speed and resistance performance of waterjet propelled boat and the analysis method of ship-waterjet interaction based on fully structured overset mesh are established;2)Taking the standard model Delft372 waterjet propulsion catamaran as the research object,the uncertainty analysis of calm water resistance is carried out.By comparing the CFD results and EFD data of ship resistance and motions of Froude number Fr=0.15～0.7,the effectiveness and stability of the calculation method are verified;3)The momentum flux method is used to simulate the hydrodynamic performance of the waterjet propulsion system,including the open water performance of the waterjet and the calculation of the inlet duct efficiency of the waterjet propulsion;4)The free self-propulsion simulations of the waterjet propelled boat at different speeds are carried out.Through the PID control,the speeds of ship and propeller are automatically matched,the flow and torque characteristics of the waterjet are obtained,and the prediction method of ‘ship-waterjet’ interaction factor is established.The results show that the performance prediction method of waterjet based on momentum flux method can be used to predict the open water performance of waterjet,and the direct simulation method based on fully structured overset mesh and multi-degree of freedom motion coupling solution can accurately predict the ship speed and resistance of waterjet propulsion boat.The ‘ship-waterjet’ interaction is mainly manifested in the influence of the characteristics of the stern boundary layer on the inlet velocity of the waterjet and the influence of the waterjet on the stern pressure distribution.