Research On Gas Flow Field Structure And Thrust Characteristics Of Rocket Motor With Scarfed Nozzle

The scarfed nozzle technology plays an important role in the separation of missile stages,thrust termination and thrust vector control technology.As a special-shaped nozzle structure,the scarfed nozzle has a certain angle between the engine nozzle axis and the combustion chamber axis.At the same time,the nozzle outlet will also adopt an asymmetric inclined structure design,which will cause the great difference between the internal and external gas flow field structure of the engine scarfed nozzle and the conventional nozzle.In addition,due to the asymmetric geometry of the scarfed nozzle,the design of the scarfed nozzle is more complex than the conventional nozzle.Based on the structural design and engineering application of scarfed nozzle,based on the commonly used double-base propellant,this paper systematically studies the internal gas flow field characteristics,external tail flame flow field characteristics and thrust characteristics of the solid rocket motor(SRM)scarfed nozzle by means of theoretical analysis,experimental demonstration and numerical simulation.On this basis,the effects of characteristic parameters such as scarfed nozzle structure and external inflow condition on the flow field and thrust characteristics of engine nozzle are explored.At the same time,theoretical research has been carried out on the AP/HTPB composite propellant that is currently being widely used,which provides a reference for the further application of small scarfed nozzle rocket motor.The main research work of this paper is as follows:(1)According to the characteristic parameter requirements of the overall initial plan of the scarfed nozzle solid rocket motor in the engineering background project,the nozzle structure and double-base propellant charge structure design of a small scarfed nozzle motor was completed.Established a test platform for the pressure and thrust characteristics of the combustion chamber of scarfed nozzle motor,as well as a test platform of the flow field of the motor nozzle gas plume,and carried out related experimental research work.In addition,the change rules of the combustion chamber pressure and thrust,as well as the structural characteristics of nozzle gas tail flame flow field obtained from the experiment are analyzed in detail.The test results show that the thrust with a certain angle can be obtained by using the scarfed nozzle motor,indicating that this type of motor has thrust deflection.At the same time,during the engine working process,the pressure curve of combustion chamber is smooth,the flame structure of the gas plume flow field is clear,and the state is stable,indicating that the scarfed nozzle motor is stable and reliable.It lays a foundation for the follow-up theoretical research and numerical simulation in this paper.(2)Using the method of combining the unsteady compressible N-S equation and the Realizable k-? turbulence model,the numerical simulation of the flow field characteristics and thrust characteristics of the scarfed nozzle test motor is carried out,and the numerical results are compared with the experimental data to verify the numerical method.On this basis,numerical simulation methods are also used to study the influence of changes in structural parameters such as nozzle scarfed angle and inlet installation angle on the flow field and thrust characteristics of the motor nozzle.Research indicates that,when the rocket motor nozzle adopts a chamfered structure design,this kind of scarfed nozzle rocket motor will have thrust deflection.On one hand,when the nozzle inlet installation angle of rocket motor is the same but the nozzle outlet scarfed angle is different,for different angles of scarfed nozzle,with the increase of the nozzle canted angle,the gas mass flow rate and thrust of rocket motor nozzle change little,but the nozzle axial thrust Fx linearly increases,the lateral thrust Fy linearly decreases,and the thrust deflection angle decreases continuously.On the other hand,when the installation angle of scarfed nozzle inlet changes,the nozzle inlet velocity,nozzle mass flow rate and flow coefficient and the nozzle total thrust are mainly affected by the nozzle inlet installation angle.With the increase of the installation angle of nozzle inlet,the inlet velocity,mass flow rate,flow coefficient and total thrust of scarfed nozzle continue to decrease,but the decreasing trend continues to slow down.(3)Based on the test of the gas plume flow field of scarfed nozzle,the N-S governing equations containing the component transport terms and the chemical reaction terms are established,and the numerical simulation method is used to study the gas plume flow field characteristics of rocket motor scarfed nozzle.Then,and the influences of the characteristic parameters of atmospheric environmental conditions and nozzle canted angle on the gas composition and flow field distribution of rocket motor nozzle plume are explored.The results show that: when considering the re-burning reaction of gas plume,the temperature of nozzle gas flow field is much higher than the flow field temperature without considering the re-burning phenomenon.And,the re-burning phenomenon of gas plume flow field mainly occurs in the gas-air turbulence mixing area and the fully developed area of gas jet;but in the core area of the initial section of gas jet,the re-burning phenomenon is not obvious.For different atmospheric incoming flow conditions,as the altitude increases,the influence area and deflection angle of gas jet gradually increase;however,as the incoming flow Mach number increases,the interactions between compression wave and expansion wave in the core area of flow field gradually weaken,the number of wave nodes in the flow field decreases,and the influence area of gas jet also gradually decreases.At the same time,when the altitude is 0km,the re-burning phenomenon of nozzle gas plume is more intense;as the altitude increases,the intensity of gas re-burning reaction weakens;and when the altitude increases to10 km,the temperature of gas flow field no longer rises significantly,so the re-burning reaction is relatively weak.(4)Aiming at the gas-solid two-phase flow problem in the scarfed nozzle of the AP/HTPB composite propellant charge,the gas-particle two-phase fluid model and the multi-region hybrid grid technology are used to study the interaction law between gas phase and particle phase in the canted nozzle of rocket moter.The results show that the particles have little influence on the flow field structure at the boundary of scarfed nozzle,but have a great influence on the flow field structure in the core area near the nozzle axis.Due to the existence of particle phase,there is a flow field region with low gas flow velocity and high temperature near the nozzle axis,and the range of this region gradually expands along the nozzle axis.The change of the particle phase mass fraction will cause the change of the particle concentration in the nozzle,and then affects the performance of the scarfed nozzle motor.The larger the particle phase mass fraction,the smaller the nozzle thrust,and the greater the nozzle two-phase flow loss.For a small scarfed nozzle motor,it is more reasonable to select a double-base propellant as the main engine charge under the premise of the overall design plan and the combustion chamber pressure is limited.