Study On The Suppression Of Unstable Combustion By Typical Structure Of Solid Rocket Motor

With the development of aerospace industry,the requirements for the performance of solid rocket motors are increasing,and the unstable combustion problem has re-emerged,causing many serious consequences,resulting in longer development cycles and increased research expenses.Suppressing or eliminating the pressure oscillations inside the engine is the ultimate goal of unstable combustion research in solid rocket engines.In this paper,the typical structure inside a solid rocket motor is studied numerically from the viewpoint of reducing the gain and increasing the damping to obtain its suppression effect on the unstable combustion.Firstly,based on the 1/12 model of VKI engine,the research on the influence of the length,thickness,tilt angle and serrated insulation plate on the pressure oscillation characteristics of the combustion chamber was carried out in depth through the three-dimensional large eddy simulation calculation method,and the suppression effect of the insulation plate structure on the unstable combustion was analyzed.The research shows that when the length of the insulation plate varies between 1～11 mm,the smaller the length of the insulation plate,the smaller the amplitude of pressure oscillation in the combustion chamber,and the better the suppression effect on unstable combustion;The thickness of the insulation plate between 1～4mm,with the increase in the thickness of the insulation plate,the amplitude of the main frequency of pressure oscillation first decreases and then increases,through the reasonable design of the thickness of the insulation plate,to avoid the emergence of large pressure amplitude,can achieve the inhibition of unstable combustion;The pressure oscillation frequency in the combustion chamber is dispersed and the pressure amplitude is reduced by50.8% after the tilt angle of the insulation plate is reduced from 90° to 45°,which can achieve the suppression of unstable combustion;The sawtooth shaped insulation plate shifts the main frequency of pressure oscillation to the second natural acoustic frequency,and reduces the amplitude of pressure oscillation by about 62.8%.Therefore,forming a notch or groove on the insulation plate has an important suppression effect on unstable combustion.Then,the damping characteristics of the nozzle were studied by the pulse decay method,and the suppression effect of the nozzle on unstable combustion was analyzed and obtained.It is shown that reducing the nozzle convergence half-angle,adopting convex convergence section profile,and reducing the submerged cavity volume will increase the nozzle damping,enhance the stability of the engine,and achieve the suppression of unstable combustion.Finally,the effect of charge cavity on engine stability was studied in depth.The study showed that: the head charge cavity increased the engine damping by about 43% compared with the tail charge cavity,and the engine stability was better and the suppression of unstable combustion was stronger;at the same time,the engine damping increased by about 28% when the cavity width was increased from 60 mm to 120 mm while the cavity volume remained unchanged,which indicated that the larger the cavity width,the better the engine stability and the suppression of unstable combustion was stronger.This paper provides some reference for solving the unstable combustion problem of solid rocket engines by studying the suppression effect of typical structures in engines on unstable combustion.