Performance Study And Experimental Verification Of Ejector Nozzles In Wide Range Tandem TBCC Exhaust System

TBCC propulsion system has the characteristics of high specific impulse and repeatability,so it has become a hot research topic in the world.TBCC exhaust system is an important thrust generating part in the whole propulsion system,its significance can be imagined.In this paper,various research methods,including theoretical analysis,numerical simulation and experimental verification,are used to conduct a comprehensive study of the tandem TBCC nozzle.First of all,through extensive research on the research literature of tandem TBCC at home and abroad,the thesis understands the overall working mode of tandem TBCC engine,and understands the significance of tandem TBCC nozzle for propulsion system.On the basis of investigation,the influence of the structure of auxiliary doors on the performance and flow filed structure of the exhaust system is studied under the condition of low nozzle pressure ratio.Then the influence of the design parameters of the auxiliary doors on the flow field structure and performance of the combined nozzle is studied,too.The results show that the auxiliary door structure can reduce the flow separation area on the outer wall of the main nozzle and effectively improve the thrust in the nozzle.The combined nozzle with auxiliary door can also inject the ambient air flow,reduce the backflow area and bottom resistance of the nozzle,thus reducing the thrust loss and improving the overall performance of the combined nozzle.When the secondary nozzle pressure ratio is increased or the main nozzle pressure ratio is decreased,the degree of under expansion at the outlet of the main flow nozzle is reduced,the sonic line moves to the downstream direction,and the main mass flow rate is reduced.Increasing the ratio of main nozzle pressure and secondary nozzle pressure can increase the air mass flow rate ejected by the auxiliary doors.In the study of the intake channel distance of different auxiliary doors,it is found that when the intake channel distance of the auxiliary doors is short,the injected environmental fluid is blocked by the secondary flow at the throat of the ejector nozzle,which is not conducive to the injection of environmental fluid by the auxiliary doors;when the distance is long,the distance between the secondary flow jet and the ejector nozzle is far,which is also not conducive to the injection of environmental fluid.Secondly,the three-dimensional numerical simulation of the tandem TBCC exhaust system in each typical state of the flight envelope is carried out,and the flow field structure and aerodynamic performance of the tandem combined nozzle in different states are obtained.Then,by changing the design parameters of the ejector nozzle,the influence of the design parameters on the aerodynamic performance of the combined nozzle is studied.The results show that at high Mach number,the main flow leaves the main flow nozzle to form an expanding aerodynamic profile,in which the main flow continues to expand and accelerate,providing thrust for the nozzle.The closer the nozzle throat is to the downstream,the lower the secondary mass flow rate and the lower the thrust coefficient.The larger the throat diameter is,the higher the secondary mass flow rate is,but the lower the momentum is,the lower the thrust coefficient is.With the increase of the trailing edge angle of the nozzle,the total mass flow rate at the exit of the nozzle decreases,but the main flow at the exit expands more fully.The larger the momentum thrust provided,the higher the thrust coefficient.At low Mach number,the auxiliary doors injects the ambient air flow,which improves the overall performance of the nozzle.When the diameter of the nozzle is increased,the ambient air mass flow rate and the thrust coefficient of the combined nozzle increase.At last,the cold flow experiment of the tandem nozzle was carried out in the wind tunnel,and the pressure distribution data,outlet flow field structure and thrust measurement value of the model wall were obtained.The experimental results show that the wall pressure of the ejector nozzle is in good agreement with the numerical simulation results,and there is a certain deviation between the measured value of the experimental thrust and the calculated value,but it is within the full range accuracy of the balance.The width and height of the Mach disk in the low Mach number state obtained by numerical simulation are consistent with those in the experiment,but the width of the Mach disk in the high Mach number state is slightly smaller than that in the experiment.In general,the numerical simulation results are more reliable and accurate.