Research On Underwater Pumpjet Design Method And Numerical Optimization

As a less-developed propulsion type,pumpjet propulsion has been paid more and more attention by researchers because of its concealment and excellent hydrodynamic performance.Since in early days it was used in the military field,there are few documents available due to the confidentiality.However,with the increasing demand for ocean resources in recent years,the focus of research has gradually transformed to the civil field.Nowadays,the pumpjet has been gradually used in civil marine equipment.The research on the design and hydrodynamic performance of the pumpjet plays a positive role in the development of small and medium-sized underwater vehicles.This paper pays attention on the design theory and performance of the pumpjet for the small and medium-sized underwater vehicles.The main contents and achievements of the paper are described as follows:Firstly,this paper represents the background and significance of the research,then summarizes the relevant design theory and the research status of hydrodynamic performance at home and abroad according to the literature research.The design theory research is conducted from direct method and the three-dimensional inverse method.Secondly,from the view of direct method,two different design methods of lifting design method(based on the design theory of axial flow pump)and lifting line method(based on the design theory of propeller)are theoretically studied,and the relevant calculation equations are derived.Finally,the design of pumpjet according to the relevant parameters and the target requirements is accomplished including the hydraulic models.Then,the three-dimensional flow field numerical model of the pumpjet is established by using the relevant basic control equation and turbulence model.By comparing and analyzing the pressure distribution characteristics and velocity distribution characteristics between these two methods,and the following conclusions are obtained:(1)Compared with the lifting line method,the efficiency of the pump jet propeller designed by the lifting design method is higher at low and medium speed,and the range of the two high efficiency zones is almost the same.(2)From the view of the pressure distribution characteristics,the whole blade passage designed by the lifting design method is basically a high-pressure area,with a higher degree of fluid movement magnitude with more uniform and efficient outcomes.(3)From the view of the speed distribution characteristics,it can be found that the energy loss of the pumpjet designed by the lifting design method is smaller and the speed is more stable.Although the speed of the streamline is lower,the jet flow from the outlet is relatively uniform.The speed of the pumpjet designed by the lifting line method is higher and the thrust produced will be greater.Then the model designed by the lifting method is chosen for optimization research,and the script files are used to integrate the 3D modeling,mesh generation,numerical simulation and post-processing software in Isight platform,and the Particle Swarm Optimization(PSO)algorithm is selected to automatically optimize the selected optimization variables,and the following results are obtained:(1)In terms of structure,it can be concluded from the comparison of the structure before and after optimization that the hub ratio of the rotor changes from 0.4to 0.45,the placement Angle of rotor changes to 69.66~o,the tip clearance changes to1.9mm,the gap of rotor and stator increases to 33.49mm,and the stator placement angle increases to 82~o.(2)From hydrodynamic performance,two kinds of working conditions after by optimizing the efficiency of the weighted average increased by 5.03%,the highest efficiency increased by 5.14%,the optimal thrust weighted average increased by5991.6 N,increased about 224.8N.After optimization,the thrust coefficient and efficiency curves are shifted to large speed as a whole,and the optimal operating point is also slightly shifted.At high speed,the efficiency decreases slightly slowly,and the high efficiency area is widened to a certain extent.(3)In the flow field,the condition of blade channel is basically unchanged,and work is done more evenly.On the other hand,the velocity produced is more stable and faster,and the thrust generated become larger.Lastly,the increase of axial velocity is not obvious,and the tangential and radial velocity remains unchanged.Then,the three-dimensional inverse design method is used to design the pumpjet.The design theory is described firstly,and the relevant solution equations are derived.Secondly,in order to facilitate comparative analysis,the hydraulic model design is completed according to the parameters and design objectives in the before models.After that,the Turbo grid software is used to divide the grid and solve the numerical simulation.The results are compared with the results of the direct method,as follows:(1)The thrust coefficient is larger under different working conditions,and the working point of the negative thrust produced by the stator moves to the right,reflecting the better and more stable matching of the rotor stator.From the efficiency point of view,the model designed by 3D inverse design method is more efficient,the highest efficiency is x%higher,the efficiency area is wider and the efficiency value is more stable at medium speed.(2)The blade pressure obtained by inverse method is more likely to generate cavitation at the inlet edge,but the area is also smaller,and the pressure distribution in most other areas is more uniform.The rotor has a greater work on the main stream and higher efficiency.The stator has obvious rectification effect,but it has weaker inhibition effect on the main stream.The velocity is higher and more stable.(3)The pumpjet designed by this method has higher outlet velocity and becomes more stable,but the energy loss is also higher.(4)The pumpjet designed by this method has good cavitation resistance,especially at medium and high speed.In conclusion,for the pumpjet used by small and medium-sized underwater vehicles,if the emphasis is on large thrust and high efficiency,the inverse design method is suitab to adopt;If the emphasis is on anti-cavitation performance,the direct method will be adopted.