Research On The Flow Process Of Solid Rocket Motor At The Initial Stage Of Ignition

With the development of rocket weapons and the appearance of modified double-base propellants,free loading grains with large aspect ratios are widely used in solid rocket motors.The ignition process of a free loading grain motor is very complicated and affected by many factors.In this paper,numerical simulation of the ignition transient process of solid rocket motor with tubular-grain and star-grain is carried out,and the ignition test of the star-grain solid rocket motor is completed.Then the fluid-structural coupling method is used to analyze the impact of the free loading grain during the ignition process.The specific work is as follows:A two-dimensional axisymmetric numerical analysis of the ignition transient process of a solid rocket motor with tubular charge is carried out.The change of the flow field in the combustion chamber during the ignition transient process is given,and the influence of different factors during the ignition transient process is also studied.Studies have shown that the ignition lag period takes 1.8ms,the charge completely ignites time is about 5.2ms,and the head pressure can reach 11.5MPa at equilibrium;Besides,the larger the ignition mass-flow,the shorter the time to reach the ignition lag period,and the faster the propellant charge surface is ignited in the early stage of the flame propagation period;the higher the opening pressure of the nozzle closure,the higher the pressure peaks at the head and back of the combustion chamber when opening,and the higher the pressure rise rate in the combustion chamber during the gas filling period.Numerical analysis of the ignition transient process of a solid rocket motor with a star-hole charge is carried out,and the flow field changes and flame propagation laws of the ignition transient process are obtained,as well as the influence of the initial temperature of the propellant on the ignition process.On this basis,an solid rocket motor ignition test was also carried out.The results show that the higher the temperature,the faster the rate of pressure rise,the shorter the nozzle closure opening time and the complete ignition time of the propellant,and the greater the equilibrium pressure.The simulation and experimental results have similar trends,with an error between 16.5% and 21.2%.The fluid-structural coupling simulation analysis of the ignition process of a solid rocket motor with free loading grain is carried out,and the pressure difference between the inner and outer surfaces of the grains during the ignition process is obtained,and the influence of the charge structure is obtained.The results show that the pressure difference between the inside and outside of the propellant charge suddenly changes from-0.7MPa to0.9MPa within 6-8ms after ignition,the maximum pressure difference that appears at the end of the charge is about 2.5MPa.The pressure difference changes cause the stress concentration position to shift from the outer wall surface of the end of the grain to the inner wall surface.The maximum equivalent stress during the ignition process can reach4.1MPa,and the stress concentration position appears at the end of the charge.