Research On Internal Ballistic Flow Filed Characteristics Of Self-eject Launch

Self-eject launch utilizes only the engine energy as the missile thrust to leave the canister, with no requirement of additional power output devices. It is simply structured and highly efficient, which will increase the loading density and improve the battle responsiveness. Thus, it is of profound significance for self-eject launch design and optimization to research the interior ballistic flow field thoroughly including the changes of the flow field during the launch, the flow field characteristics and the influence factors. Taking the quick-response and high-speed missiles as background, the interior ballistic flow field of self-eject launch has been studied in details by means of CFD(Computational Fluid Dynamics) numerical calculation and experimental verification. The main work of the thesis is as follows.1. The interior ballistic flow field consisting of engine combustion chamber, nozzle and low pressure chamber is established systematically. The component equilibrium equations of the propellant combustion product are based on minimum Gibbs free energy, and these nonlinear equations are stably solved by homotopy algorithm. The combustion product is added into the flow control equations as sources. Dynamic mesh method is applied to simulate the combustion surface movement. Therefore, coupling calculation between solid propellant combustion and flow field changes is realized. C-H-O-N chemical reaction system which contains 12 constituents and 20 elementary reactions is established after researching the mechanism of RDX-CMDB combustion. The numerical model in the thesis is verified by conducting an engine free gas jet flow experiment. The temperature and the pressure between the numerical calculation and the experimental collecting data/high-speed photographs agree well, meaning that the numerical model established in this thesis is sufficiently qualified to simulate the chemical reaction process and the flow field state. The examination of the numerical iteration demonstrates that the solving procedure has iteration stability, high residual error convergence precision and small numerical dissipation, satisfying the computing requirements and the conservation law.2. After analyzing the typical process of the interior ballistic flow field of self-eject launch, the launch process is divided into three phases: the preliminary phase, the growing phase and the steady phase. In the preliminary phase, initial shock wave causes pressure oscillation in the low pressure chamber and the gas encounters air remnants leading to secondary combustion. In the growing phase, solid propellant keeps on burning, and the combustion chamber status tends to be equilibrium. The pressure and the temperature in the low pressure chamber go up to the maximum rapidly at first, then the pressure on the bottom of the missile descends fast as the missile moves forward and the volume of the low pressure chamber expands; the temperature descends comparatively slowly. Gradually the pressure in low pressure chamber takes a principal part in the missile thrust power as a result of high pressure outside of the engine impeding the engine thrust. At the same time, stationary shock wave in the nozzle divergent section moves slowly towards the nozzle throat; however, supersonic area still exists in the divergent section which indicates no influence on the combustion chamber. In the steady phase, the environment of the combustion chamber remains unchanged, the temperature and the pressure on the bottom of the missile keep on descending, and the missile still accelerates. Therefore, the velocity of the missile is quite large in this phase; the displacement of the missile is also the largest among these three phases.3. By adjusting the distance between the bottoms of the missile and the barrel, the influence on the interior ballistic flow fields of self-eject launch by the initial volume of the low pressure chamber is studied. It demonstrates that the initial volume affects the initial shock wave the most. Decreasing the initial volume will suppress the pressure oscillation on the bottom of the missile, improve the propellant’s energy exchange efficiency, increase the leaving velocity and reduce the leaving time; but the overload on the missile will be larger and the maximum temperature at the bottom of the missile will rise; and vice versa.4. The gas liquid solid multi-phase flow field which contains fused alumina droplets and solid alumina particles is established in the thesis based on the DPM(Deformable Parts Model), to analyze the effect of aluminum powder added into the propellant. The result shows that adding 15% aluminum powder induces a boost of the total temperature and total pressure in the combustion chamber, especially the total temperature rising by 619 K. As a consequence, the pressure and the temperature at the bottom of the missile become larger, the missile maximum overload also becomes larger, the leaving velocity increases and the leaving time shortens; while the propellant energy exchange efficiency is reduced by 49.3%. Taking into account of the fused alumina droplets fractures owing to the Rayleigh-Taylor instability, the diameter changes and the distribution of fused alumina droplets are obtained. The erosion and sediments formed by the solidification of the alumina particles in the walls and bottom of the barrel are studied as well. It demonstrates that the erosion and sediments occur in the early stage of the interior ballistic launch procedure in the self-eject launch; they will fade away as the low pressure chamber temperature rises up and the solid alumina particles start to melt again.5. To mitigate the large missile overload and the high temperature at the bottom of the missile, a cooling program, that is beforehand liquid water in the barrel, is proposed. The two-phase flow field containing gas and liquid water is established based on Mixture model, and the vaporization and the condensation process of the liquid water are represented by Lee model. It shows that when 2.545 kg liquid water is injected into the barrel, the propellant energy exchange efficiency falls down by 84.24% due to the vaporization; also there is vaporization eddy current which will lead to pressure fluctuation on the bottom of the missile and might cause vibration of the missile body. Nonetheless, the overall temperature of the barrel significantly descends, especially the maximum temperature at the bottom of the missile which is reduced by 76.02% sharply. In addition, the dispersed effect on the initial shock wave from the liquid water can suppress the preliminary pressure oscillation on the bottom of the missile.