Investigation On Acoustic Energy Amplitude Growth Rate Of Solid Rocket Motors With Different Geometries

As a propulsion system,solid rocket engine occupies an important position in the field of aviation,space and missile weapons.In the process of development and use of solid rocket engines,the unstable combustion phenomenon sometimes occurs,which causes the engine to not work properly.Nowadays,large aspect ratio engines are widely used,but such engines are more prone to unstable combustion at the end of operation.By calculating and comparing the sound amplitude growth rate of the engine model with different geometric parameters,the recognition of the linear prediction of the unstable combustion of the solid rocket motor will be improved.In this paper,a variety of theoretical calculation models of the pressure coupling response function are compared with the experimental data,and the best combustion model for NWR-11 composite propellants is obtained.At the same time,according to the linear theory of combustion instability,the stability prediction program is compiled.On this basis,the amplitude growth rate of linear acoustic energy for different geometries engine models is calculated.The main contents of this paper include the rational selection of the main influence factors of the gain term and damping term in the linear theory,simplifying the linear calculation method about the growth rate of the acoustic energy amplitude,and focusing on the comparison of the results of the 6 theoretical models of the pressure coupling response function.In the end,it is concluded that the combination of BDP model and homogeneous propellant theory is most consistent with the measured results.By establishing the engine calculation model,calculating the gain term,damping term and acoustic energy amplitude growth rate of different geometric structure models,and fitting the boundary between the linear stability and linear instability of the engine as a reference for the prediction of the stability of the engine.The results show that the growth rate of the acoustic energy amplitude of a large aspect ratio at the end of the work is from negative to positive at the end of the work,which explains why this type of engine is prone to combustion instability at the end of the work.With all calculation results,it can be seen that the acoustic energy amplitude growth rate increaseswith the increase of the aspect ratio of the engine and the diameter of the nozzle throat,that is,the stability of the engine is worse.In addition,this paper also points out that the current research often puts aside the effect of the nozzle throat size on the stability,and is only based on the "aspect ratio" to determine whether the engine has the possibility of unstable combustion,that is,the three parameters,engine length,combustion chamber diameter and nozzle throat diameter,should be similar to those of similar engines with similar stability.