The Linear Acoustic Instability Assessment Of Large Aspect Ratio Solid Rocket Motor

The large aspect ratio solid rocket motor plays an important role in China’s aerospace field because of its large thrust,large charge and strong endurance,which can meet the military requirements of many missiles.However the large aspect ratio solid rocket motor will have poor combustion stability in the engine as the working time increases,especially in the end of the engine operation,some abnormal combustion phenomenon causes the engine to violently oscillate and even damage the engine.The acoustic instability of solid rocket motors with large aspect ratio can be better understood by comparing the pressure attenuation oscillations at different charge positions of the wing columns,the gain and damping of different propellants and non-geometrical structures,and the increase of acoustic energy amplitude.Based on the linear theory of combustion instability,this paper has written a software for the prediction of combustion instability,which can be associated with CFD software and CATIA software for relevant calculation and model establishment.The software mainly includes flow field model building module,chemical calculation module,acoustic modal calculation module,acoustic damping calculation module,pressure coupling response calculation module,instability prediction module,grid generation module,flow field calculation module.The flow field model building module,grid generation module and flow field calculation module in the software are used to simulate the pulse pressure attenuation oscillation process in the combustion chamber of the front wing column-type charge structure engine and the rear wing column-type charge structure engine in five different working hours.Ｉt is concluded that the performance of the combustion chamber of the engine with front wing charge structure is better than that of the engine with rear wing charge structure at these five different working hours.It is concluded that the stability of the engine with front wing column charge structure is better than that of the engine with rear wing column charge structure in these five working hours.The flow field model of the engine is used to establish the module,the chemical calculation module,the acoustic modal calculation module,the acoustic damping calculation module,the pressure coupling response calculation module and the instability prediction module for calculation.By changing the pressure index of the propellant and the burning rate of the propellant,the length of the combustion chamber of the engine,the radius of the combustion chamber,and the radius of the nozzle throat of the engine,the gain and various damping and the growth rate of the amplitude of sound energy at different working hours of the engine were calculated,and then the curve was plotted as the change with time.The results show that the growth rate of acoustic energy amplitude increases with the increase of engine pressure index.When the combustion rate of propellant increases,the combustion surface amplification coefficient of the engine decreases,the absolute value of damping decreases,and the growth rate of the amplitude of sound energy decreases.When the length of the engine increases,the combustion surface amplification coefficient decreases,the absolute value of damping decreases,and the growth rate of the amplitude of sound energy increases.When the radius of the combustion chamber is reduced or the throat radius of the engine nozzle is increased,the amplitude of the acoustic energy amplitude of the engine will become smaller.And radius of the combustion chamber and nozzle throat radius for the set value,the same proportion increase of radius and spray combustion chamber throat radius,it is concluded that the vibration amplitude of the sound energy growth engine will be smaller,launch a chance more stable,so it is concluded that the stability assessment of the engine was not only by means of length to diameter ratio or the size of the throat diameter ratio to determine whether stable,should the engine’s combustion chamber length,radius of the combustion chamber and the relations between and among spray throat radius more overall consideration.