| Nowadays,the modern underwater vehicles and ships increasingly require the propulsion systems with high speed and superior acoustic performances.Ordinarily,with the increase of advance speed,the propulsion system would be confronted with various types of problem.The typical propulsion device,propeller often suffers with excessive noise,cavitation and deterioration of propulsion efficiency when applied to high-speed propulsion.While water-jet pumps,as a form of propulsion with high propulsion efficiency,good cavitation performance and low noise,have been widely used in various types of high-performance underwater vehicles and ships,especially for high speed ones.However,when the advance speed is further increased,the blade loading and related performances of water-jet pump deteriorate as well,which also results in cavitation,unstable flow,intense noise and vibration.In order to solve these problems,the contra-rotating rotors technology is applied to the design of water-jet pump.As a result,the energy density and acoustic performance of water-jet pump improves significantly.Although the contra-rotating water-jet pump has great advantages in high-speed propulsion,its related technologies such as hydraulic design and structural design are still not well developed.In order to further understand the contra-rotating technique and promote the application of contra-rotating water jet pump,this paper is concerned with the study of the hydraulic design and rotor interaction characteristics of contra-rotating rotors.Firstly,a hydraulic model of contra-rotating water-jet pump is designed,and the internal flow field and loss mechanism are analyzed.Furthermore,the relationship between the key airfoil parameters and the characteristics of pressure pulsation and radial forces are investigated.Finally,the experimental system of the contra-rotating water-jet pump is designed to provide theoretical and technical support for the performances validation.The main work of this paper is shown as follows:(1)The steady and unsteady CFD numerical simulation methods of contra-rotating pump are verified.For the study of the hydraulic performance,pressure pulsation characteristics and internal flow field structure of the contra-rotating water-jet pump,the mesh of boundary layer,turbulence model,sampling time length and time step,boundary conditions are studied.And the reliability of the numerical simulation scheme is verified by the relevant experimental data.(2)Based on the major performances of a vehicle and the experimental system capacity,the main design parameters of contra-rotating waterjet pump are determined and the hydraulic design is carried out.The relationship among the camber line geometry,blade loading distribution and cavitation performance is studied.Maintaining the same total blade loading,the lowest pressure on suction surface of the blade is increased through the optimization of the loading distribution,so that the cavitation performance is significantly improved.And the demand of high hydraulic performance and cavitation performance is simultaneously met.(3)The suppression method of rotor-rotor interaction is studied based on the thickness distribution of airfoil and the geometry of camber line.Specifically,the flow field structure,pressure fluctuation,and radial excitation forces of contra-rotating water-jet pump with different airfoil thickness distribution and camber line geometry are analyzed.The results show that the pressure fluctuation of the contra-rotating water-jet pump is mainly caused by the non-uniformity of flow field distribution,and the radial forces are mainly generated by the interaction between front and rear rotors.Besides,moving the airfoil maximum thickness position appropriately can improve the uniformity of the interaction flow field,reduce the pressure fluctuation strength,and decrease the radial excitation forces.While,reducing the beta angle near the trailing edge of front rotor can properly improve the outflow uniformity of the front rotor,so that the pressure pulsation and radial forces of the rear rotor are significantly decreased.(4)In order to further verify the technology of contra-rotating water-jet pump,the design of its mechanical structure and experimental system is carried out.The detailed mechanical structures and related measurement system are all concluded.The whole system is still under manufacturing,and it will be beneficial to further support the performances validation of contra-rotating propulsion technology. |
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