| The numerical study on ignition transient of Solid Rocket Motor (SRM) has great engineering background and actual meaning, for the reason that the ignition failures and even explosive accidents occur easily in the ignition process of SRM which is extremely complicated. Two aspects of ignition transient problems presented in this paper were simulated by the CFD software FLUENT.Firstly, axisymmetric numerical simulation of long passage SRM with internal and external combustion cylindrical-grain during ignition transient was carried out using the source item method and UDF (user define function) technique of CFD software FLUENT. The flow field of the ignition transient was analysed and the pressure-time curve at motor head was obtained. The ignition plan was also optimized through ignition control technique. The study results show that simulation pressure-time curve is good accordance with test curve. The optimized ignition plan can decrease ignition delay time obviously. This method can provide reference for next ignition improvement design and test.Secondly, nonlinear unsteady ignition pressurization process of SRM with submerged nozzle was simulated numerically before the opening of nozzle closure. The formation mechanism of ignition shock wave and pressure oscillation at grain surface were analyzed, and the effect of the cavity volume induced by submerged nozzle and the exit pressure of igniter on pressure oscillation were studied numerically. Then the numerical simulation of shock wave diffraction on propellant crack was presented in this paper, using the flow parameter of ignition pressurization process as the boundary condition of crack inlet. And the propagation law of shock wave in the crack and the effect of geometry on overpressure were studied. The simulation results show that the pressure at the motor head and in the cavity oscillate most intense, and the pressure gradient is much larger than normal condition. The results indicate that the pressure peak and pressure gradient peak decrease with increasing the volume of cavity, and increase with increasing the exit pressure of igniter. The crack propagation occur easily at the top of the crack where is the stress concentration field. The crack geometry has great importance on overpressure, and the stress concentration formation in triangle crack is more easily than rectangle crack, which makes crack propagation possible. |
