Characteristics Analysis Of Pressure Oscillation In A Dual Pulse Solid Rocket Motor

In recent years, with the development of space technology and the advancement of missile,a higher performance of solid rocket motor is required,such as higher propellant capacity factor,complicated grain,higher energy composite propellant. Howerver, these kinds of solid rocket motors are prone to combustion instability during the working process. At present,acoustic combustion instability was found in several motors during the design process. Combustion instability is one of the difficult problems in the design and development of solid rocket motor. The pressure oscillation causes the thrust oscillation, which deviates from the design requirements of the engine and have a strong influence on the mechanical structure and control system of the aircraft. It leads to poor performance of the flight, in serious conditions can result in the failure of the missile mission.Based on dual pulse Solid Rocket Motor combustion instability phenomenon, the key driving and damping characteristics of combustion instability in solid rocket motors are numerically and experimentally studied in this paper. The main research work and conclusions are as follows:Based on dual pulse solid rocket motor with complicated grain, the acoustic changing characthersitcs are analyzed by FEA(Finite Element Analysis) method. Typical acoustic pressure distribution and the frequency characthersitcs during the motor working process are obtained by numerical simulation. Results indicate that the first and second axial acoustic frequencies of first stage firstly decrease and then increase with the burning time and decrease in second stage. The typical dual pulse solid rocket combustion chamber cavity is simplified into T type cavity. The effects of some critical geometrical parameters on the acoustic frequency are studied by finite element method, especially axial length ratio of first to second stage.For dual pulse solid rocket motor, the corner vortex-shedding-driven pressure oscillations are numerically studied via the LES(Large Eddy Simulation) method. The fluid structure and pressure oscillation characteristics are obtained by numerical simulation.A backward facing step,which is formed by complicated grain,would give birth to corner vortex shedding. Backward step reduces during the motor working process and the vortex shedding dissipates during the transport process,so coupling- vortex-acoustic eliminates and motor tends to be stable.The particles damping characteristics were studied by pulse attenuation method, and the numerical results satisfy well with the theory value. Results indicate that the combustion chamber pressure has little influence on the particles damping; the optimum particle size was obtained via comparing different particle sizes under certain condition. The particle content has great influence on the particle damping, and the damping is linear with the content. In the actual motor, it can effectively restrain the occurrence of combustion instability of the motor by modifying the formulation of the propellant and appropriate increasing content of the inert particles.