Free Impact Loading Solid Rocket Motor Propellant Ignition Characteristics Research

With the development of remote and miniaturization of rocket weapons, free filling grain with large length-diameter ratio and high loading density is widely used in solid rocket motors. The ignition process of solid rocket motor is typical transient excitation process. The impact load characteristics and the mechanical properties of the solid propellant grains during the ignition process of free filling grain SRM is very complicated, the structural integrity of the grain is easy to damage, meanwhile, growth of the internal microscopic defects may lead to structural damage. Research on the impact properties of grain during the process of free filling solid rocket motors is contained in this article.The two-dimensional axisymmetric model of free filling SRM was established, the heat transfer of grain and process of the propellant combustion plus quality was programmed with user-defined functions, the fluid-structure interaction interface software MpCCI, FLUENT and ABAQUS software was taken in numerical simulation, pressure loads distribution law in the flow field of motor and mechanical impact properties of propellant during ignition process was analyzed. This article contents the following aspects:(1) According to the flow field of motor and pressure loads on grain during ignition process in free filling SRM, the mechanical structure of propellant grain was analyzed. The study indicated that the ignition shock wave during the early stages of ignition cause the stress concentration of propellant grain and the stress concentration dynamically spread with shock wave in channel; while the main reason of impact on grain during propellant combustion stage is the spread process of high-pressure gas, maximum Mise stress and displacement of deformation occurs after the pressure wave before nozzle cover is open. After the cover is open, transient impact properties of grain disappear and pressure loads become stabilized.(2) The effect on ignition impact characteristics of grain under different igniter mass flow rate, igniter vents diameter, the distance between igniter and grain and jet angle were studied with fluid-structure interaction method, research obtained flow field characteristics in SRM, distribution law of pressure difference, and mechanical properties of grain. The results show that the effect of mass flow rate on mechanical shocks during ignition is much more complicated. There is an optimal value of diameter, distance between igniter and grain and jet angle to reduce the mechanical shock during ignition.(3) The effect of propellant characteristic parameters on ignition impact characteristics was studied with fluid-structure interaction method. The results show that propellant burning rate and Poisson’s ratio have a greater impact on ignition impact characteristics after propellant ignited. Mise stress and displacement deformation significantly increase with increase of propellant burning rate. The stress and deformation of grain increase while Poisson’s ratio increase when Poisson’s ratio is close to0.5. While Poisson’s ratio reduces significantly, there is a greater influence on the mechanical structure of the grain after the blocking cover is open.The research on ignition impact characteristics and the influencing factors in free filling SRM can provide a theoretical basis for this class of solid rocket motor design.