Research On Mechanism Of The Effect Of Ignition Pressurization On A Solid Propellant Grain Crack

For the operation process of SRM is extremely complicated, experimental and theoretical investigations on the process have been conducted for several decades. And some significative math models and criterions have been established for a normal operation process of SRM. Defects in propellant grains can originate during manufacture, transportation, storage, handle, ignition, combustion, procedures, which make the internal ballistic parameters deviate from the design, a catastrophic accident such as deflagration and detonation may happened to the SRM. So it is necessary to investigate the operation process of SRM with defect propellant grain.The study of the dynamics of abnormal operation process of SRM has reported little until now. The department, which in charge of designing new type missile, expects researchers to establish a set of judge criterion and system determination of SRM failure and to provide a guidance of prolonging SRM life.The requirements compose a background of this research. The interaction mechanism of the ignition pressunzation process in the propellant grain crack is studied by numerical simulation of ignition dynamics process of SRM. The main work of this thesis can be summarized as follows:1. Based upon literature survey of investigations conducted to study the SRM with defect propellant grain, an important viewpoint is provided, that is, during the ignition pressurization, making the phenomena of non-linearity and unsteady flow in solid propellant cracks clear are greatly helpful to understanding physical mechanism of solid propellant grains failure and to establishing a criterion determination of SRM failure. Analyzing the limitations of investigations using experimental and numerical methods and analogizing the above phenomena, an innovative project is put forward, it unites macro-field and micro-field numerical methods to simulate the above phenomena. The project is not only a method used to investigate the mechanism of solid propellant grains failure but also an implement of criterion determination of SRM failure.2. The flow field in SRM with defect propellant grain is studied by simulated method, and a set of simulation software is established and implemented. Based on Navier-Stokes equation; a uniformed dispersed method is adopted, which is suitable for dealing with turbulent flow, two-phase flow, and non-equilibrium flow; especially, an uncoupled non-equilibrium method is put forward to resolve the rigidity in non-equilibrium flow, and this method have two main advantages: simple on deducing formulas and advantageous onmodulating reaction dynamic models. With the particle simulation method employed to trace the trajectory of solid particles, the two-phase flow is numerically simulated. And two-equation k -e turbulent model is used to solve the turbulent flow fields. Base upon N-S equation and the above theoretical models, a set of simulation software is established and validated credible, and the software can efficaciously simulated complex flow field, such as two-phase flow, and non-equilibrium flow. This software is an important implement of investigating propagation process in solid propellant cracks under ignition rapid pressurization, and also a significative assistant of establishing a set of judge criterion determination of SRM failure.3. The effect of portfire to SMR is reviewed, and most researches are qualitative analysis, but it is lack of quantitative analysis. Large numbers of ignition engine are employed in bulky SRM with inner aperture combustion. By proceeding from all-gaseous state N-S equation and ENO difference scheme, a jet hypothesis is adopted, the flow jets produced by ignitions are numerical simulated in a certain type SRM with latent nozzle, and the effect of shock wave to the inner surface of grain is studied. It shows that a shock structure appears and an excess pressure builds up during the operation process of ignition engine.4. The pressure accepted from macro-field simulation on an observation point is used in micro-field simulation, and an approximate model zooming in on the local observation point is introduced. Based on all-gaseous state N-S equation and above theoretical models, detailed numerical investigations of symmetric and 3-D unsteady flow field of shock wave diffracting over cracks with different scales have been performed. And several important conclusions from the simulation investigation are summarized as follows. Firstly, it is a non-linearity relation between the crack depth and the excess pressure in the crack, and as the crack depth increased, the excess pressure in the crack tip increased. Secondly, as the crack depth increased, a shrewd oscillation of excess pressure in the crack is induced and attenuates slowly, and destroys the integrality of the propellant grains. These conclusions are helpful to understand the phenomena of non-linearity and unsteady flow in solid propellant cracks and also advantageous to realize the characteristics of combustion in SRM with defect propellant grains. For example, the above conclusions are agree with the experimental results and can be used to understand the four models of grain failure provided by Professor K. K. Kou.5. A computing model without ignition delaying and the above approximate mode are adopted. Based on non-equilibrium flow dynamics equations and above computing models, detailed numerical investigations of unsteady flow field with of shock wave diffracting over cracks have been performed, and the combustion is considered to closely simulate the actual rocket condition. Compared with the above results in all-gaseous state condition, the effect of shock wave to the crack in a real combustion condition is qualitative analysis. It shows thatthe ignition shack waves can spread into a crack contacted with air, even without ignition delaying, for the effect of shack waves kinetic load on the grains, a destroy on the integrality of the propellant grains may be induced. These conclusions can be used to understand the experimental phenomena in experiments, it is different in essence of the inducing the pressure abnormal in chamber of two kinds of defect gains: defect gains cracks contacted with air and inner grains with closed air bubbles, the pressure on the latter gains can be forecasted using a theory of increasing burning surface, but the abnormal pressure value on the former gains is higher than the value using the theory forecasting.6. Introduced different "virtual" jets at different location on grains to represent the grains defects, and equivalent simulations considering the two-phase flow model are conducted. It shows the structure of flow field is influenced by the interaction of particles and gas. The computing conclusions of two-phase flow have a more practical application and have a help to develop a more accurate combustion model of SRM with defects.