Research On Dynamic Characteristics Of Fluidic Nozzle Throat In Solid Rocket Motor

The fluidic nozzle throat(FNT)adjustment technology has lots of advantages.For example,it has no moving parts,high reliability,small thrust loss.The exhaust of secondary flow can provide additional thrust.The expansion ratio of primary flow can be adjusted so that the nozzle can always work in the optimum design state.And FNT can combine the shock vector control(SVC)technology in the same system to achieve thrust magnitude and direction control.However,the engineering application of FNT in solid rocket motor is still in the primary stage.Many previous studies mainly focused on steady-state characteristics,and for the dynamic characteristics there is still no clear understanding due to the lack of research.Meanwhile,there is still much room for improvement in the regulation of steadystate/dynamic performance optimization and integration with other control systems.Therefore,in this thesis,theoretical derivation,numerical simulation and cold/heat experiments are combined to carry out a depth research on its dynamic characteristics on the basis of summarizing steady-state characteristics of FNT and SVC.The process of secondary flow injecting into nozzle was analyzed theoretically.Some relevant physical variables were defined and a formula for the effective throat area ratio and the modified mass flow ratio was derived and verified by numerical calculations and others' experimental data.The influence parameters of FNT,such as effective throat area ratio,thrust adjustment ratio and nozzle expansion ratio were studied by a steady-state algorithm.The modified mass flow ratio was redefined and extend it to the conditions,which the primary,secondary flow have different temperatures and molar mass.The research results show that after jet injection,vortexes are formed at the upstream and downstream of injection port and the primary flow is squeezed.Increasing the mass flow ratio of secondary and primary flow,can increase the throat choke performance and thrust adjustment ratio,but its effect will gradually weaken.At the same time,the increase of mass flow ratio will reduce the expansion ratio of nozzle,making it unable to fully expand.At the same mass flow ratio,increasing the temperature of secondary flow,reducing the average molar mass,and changing to a working medium that can react with primary flow can also increase the steady-state performance of the FNT.Meanwhile,the smaller injection area has a slight improvement in the adjustment performance,and there is an optimal injection angle to make the optimal adjustment performance.The secondary flow injection process was researched by numerical simulation.The changes of the flow field in the nozzle were studied after secondary flow turn on/off,as well as the influence of injection structure,flow parameters and secondary combustion on the nozzle thrust.It is found that the whole adjustment process has no overshoot and smooth transition to a new equilibrium state,which can be roughly divided into the stage of pressure transfer,gas blocking and balance stabilization,and the balance stability phase is the longest.At the same mass flow ratio,the increase of the secondary flow temperature,the decrease of the molar mass,the decrease of the injection port area,the decrease of the injection angle,and the secondary combustion of the primary flow,can increase the rise rate of the combustion chamber pressure and final balance pressure,but cannot reduce the nozzle response delay due to the increase in final balance pressure.The nozzle damping decreases slightly with the increase of the mass flow ratio of the nozzle throat injection.When the mass flow ratio is less than 0.5,the reduction is less than8%,which is not conducive to suppressing unstable combustion,but compared with mechanically adjusting plan of throat area,FNT has a smaller damping reduction.In order to adjust the thrust magnitude and vector of engine,the SVC is combined with the FNT and the steady-state/dynamic characteristics are analyzed.The results show that the thrust vector angle reached a maximum when the oblique shock,formed by secondary flow injection at divergent section,just enters the nozzle completely.Secondary flow injection at throat and the increase in mass flow ratio will reduce shock angle,weaken shock intensity,and increase mass flow ratio at divergent section for maximum thrust vector angle.At the same mass flow ratio of divergent section injection,the higher the secondary flow temperature,the greater the thrust adjustment ratio,and the smaller the mass flow ratio required to reach the maximum thrust vector angle.The closer the injection port of divergent section is to the exit,the greater the maximum value of the thrust vector angle.For a fluidic nozzle at the maximum value of the thrust vector angle,Keeping the same mass flow ratio,moving injection port toward the outlet of the nozzle,the thrust adjustment ratio and the vector angle change little,but the maximum value of the thrust vector angle increases.Moving injection port toward throat,the thrust adjustment ratio increases,the thrust vector angle decreases,but it is still at the thrust vector angle maximum state at that time.In dynamic adjustment,the dynamic response delay of the throat jet injection is one order of magnitude larger than that of the divergent jet.There is an overshoot adjustment injecting at divergent section,but there is not at throat.When injecting secondary flow at throat before divergent section,the response of the thrust vector angle is faster,but there is almost no effect on the response of the thrust adjustment ratio.So injecting secondary flow at diverging section first is beneficial to increase the response rate.A thrust vector test system was established to verify the new concept of modified mass flow ratio,which is used to generalize cold flow conclusions to different jet temperatures and molar mass conditions.A theoretical formula of thrust adjustment ratio was derived and verified.For combinations of FNT and SVC,the phase difference between the FNT and SVC injectors exerts the biggest influence on the vector control performance.SVC can still achieve an acceptable performance by opening the FNT and SVC injectors at the opposite quadrants,and with different phase shifts in their displacement,to avoid strong jet interface development.Liquid secondary flow or secondary flow incorporating copper powder can effectively improve the dynamic performance of FNT.