Study On Aerodynamic Design And Flow Mechanism Of Super-Large Expansion Ratio Turbine With Water And Air Modes For A Cross-Media Engine

Transocean vehicle can meet both air and underwater navigation requirements,and transocean vehicle is also a very important weapon system,which can be used to attack submarines and ships.For a cross-media vehicle,the power output unit of the engine must adopt a single-stage super-large expansion ratio turbine because the engine must meet the limitations of power,efficiency and size in air and underwater modes,and the initial gas temperature and initial pressure of the underwater modal combustion system are very high.In order to meet the requirements of both air and underwater modes,the flow field inside the turbine is very complicated.Therefore,it is necessary to study the design method and internal flow mechanism of the single-stage super-expansion ratio turbine for the cross-medium engine,so as to obtain the main methods to improve key performance parameters such as power and efficiency.First of all,this paper studies the nozzle profile and the rotor blade profile of the turbine with super-large expansion ratio in the water-air mode of the transdielectric engine,and carries out the one-dimensional aerodynamic design research of the turbine with super-large expansion ratio in the water-air mode of the transdielectric engine based on the turturine theory,and carries out the numerical simulation calculation according to the designed nozzle and rotor blade.The results show that the gas velocity at the oblique cut outlet of the nozzle has reached supersonic under the water-air mode,and strong shock waves will form at the inlet position of the rotor blade corresponding to the nozzle outlet,causing boundary layer separation.Water turbine internal empty mode caused by local inlet circumferential parameters distribution will cause gas occur in the rotor flow passage of circumferential channeling flow is from the air inlet area to inlet area,gas is entered into the runner hub location inside,inside the flow channel will roll up from blade root to blade tip passage vortex,and then through the adjacent blade tip position into the flow passage of the blade clearance vortex formation,thus forming a smaller inlet area location entropy,the inlet position entropy is bigger,the phenomenon,especially in front of the nozzle trailing edge location entropy and total pressure loss coefficient is bigger,near flow loss is bigger.Secondly,considering the large increase in entropy near the front and back trailing edges of the oblique cut outlet of the air and underwater modal nozzle as well as the non-inlet position,as well as the strong shock wave in the main channel of the rotor blade,the influence law of the tilt Angle of the nozzle and the relative inlet Angle of the rotor blade on the turbine stage performance was deeply studied.,the results show that the water empty mode reduced when the tilt Angle of nozzle,the nozzle Angle cutting export ellipse area increases,moving blade inlet location of the nozzle exit Mach number can be reduced,and shock strength will reduce,boundary layer thickness decreases,and the separation of ease,inlet flow situation in the region is getting better,oblique nozzle exit before near the trailing edge position and the inlet location entropy becomes smaller,the flow loss decreases,turbine stage in the air and underwater mode under the condition of efficiency will be increased.At the same time,the inclination Angle of the nozzle will affect the ellipse area of the oblique outlet of the nozzle,which will also affect the number of blades and surface pressure affected by the main flow of the nozzle.Relative moving blade inlet Angle,small water nozzle exit empty mode of the rotor within the mainstream way high Mach number area will decrease obviously,the shock wave intensity drops,boundary layer separation will relieve,export moving blade trailing edge location Mach number is reduced,more speed loss,inlet flow situation in the region is getting better,nozzle Angle cutting export before near the trailing edge position and the inlet position entropy becomes smaller,the flow loss is reduced,the turbine stage efficiency are all in the ascension and the optimized efficiency increased by 6.6%,air mode underwater mode under increased by6.5%.Considering the influence of single change of nozzle or rotor inlet Angle on Mach number at rotor inlet,shock wave intensity,circumferential gas flow at turbine stage and turbine stage performance under water-air mode,the optimized performance of turbine stage and circumferential gas flow inside the turbine stage were studied in depth.The results show that the whole level optimized rotor passage internal strength of the shock wave was obviously lower than the single change nozzle or moving blade,turbine nozzle trailing edge location entropy decrease obviously,near the inlet area location entropy increase or decrease in small,turbine stage axial chord length each location flow loss coefficient decreased,flow loss is reduced,air mode under turbine stage efficiency is 7.02% higher than the original turbine stage,underwater mode under article after the whole level optimization,efficiency is 9.16% higher than the original turbine stage.Finally,the variable-condition characteristics of single-stage ultra-large expansion ratio turbine stage under air and underwater modes were studied,and then the flow field changes and flow loss distribution of single-stage ultra-large expansion ratio turbine stage were explored in the time and space when the inlet total pressure and rotating speed changed.The results show that under the air modal condition,with the increase of the total inlet pressure,the Mach number in the rotor flow passage will also increase,the shock wave intensity will increase,the entropy increase at the trailing edge before and after the nozzle oblique cut exit will increase significantly,the flow loss in the non-inlet region and inlet region in the flow passage will increase,and the efficiency of the turbine stage will decrease.When the rotating speed of the turbine stage increases,the high Mach number region in the main channel of the rotor blade will decrease,the shock wave intensity on the suction surface of the blade will decrease,the entropy increase and the total pressure loss coefficient of the chord length in different directions will decrease,and the efficiency of the turbine stage will increase.,underwater mode when inlet total pressure increase of blade not axial chord length position entropy and total pressure loss coefficient increase,the flow loss increases,resulting in decreased efficiency of turbine stage will be,when the turbine speed increase,the rotor import location shock wave intensity drops,entropy can reduce the inlet region,especially near the nozzle trailing edge location entropy fell the most obvious,no axial chord length location entropy and total pressure loss coefficient will decline,and the efficiency of turbine stage will rise.