底部排气装置快速降压过程中燃烧流动特性数值分析

为研究底部排气（简称底排）装置出炮口时发射药燃气流动特性和点火具瞬态燃烧特性，采用半密闭爆发器模拟底排弹出炮口时的快速降压过程，借助高速录像系统观测了近喷口喷焰羽流的发展行为，并以此验证数值模型的有效性。在试验基础上，采用高分辨率迎风格式AUSM⁺、两方程Realizable k-ε湍流模型和有限速率化学模型，建立了降压过程中发射药燃气与点火具燃烧射流相互作用的二维轴对称模型，并以基于内节点的有限体积法进行数值模拟，分析了底排装置降压过程中两股高温燃气射流的耦合特性。结果表明：底排装置降压过程中，喷焰羽流由超音速强欠膨胀射流逐渐转变为亚音速流动，波系结构经历马赫反射到规则反射的转变，形成周期性钻石型激波和菱形火焰串，最终变成连续火焰；喷焰羽流变成亚音速流动后，底排装置内点火具火焰下游处径向热对流和热扩散比上游更强烈，底排药柱下端温度最高，首先复燃。

Numerical Investigation of Combustion and Flow Characteristics of Combustion Gas in Rapid Depressurization Process of Base Bleed Unit

The combustion gas flow characteristics of propellant and the transient combustion characteristics of igniter during the ejection of base bleed unit (BBU) from the muzzle are studied. A semi-closed bomb is used to simulate the rapid depressurization process during the ejection of base bleed projectile from the muzzle, and the development behavior of near-nozzle exhaust plume is recorded by using a high-speed camera, hereby verifying the validity of the numerical model. Based on the experiment, a two-dimensional axisymmetric model for interaction between propellant combustion gas and igniter jet during depressurization is set up by using high-resolution upwind scheme AUSM⁺, two-equation Realizable k-ε turbulence model and finite-rate chemical model. The coupling characteristics of two high temperature gas jets are simulated and analyzed by using the cell-centered finite volume method. The results show that, during depressurization of BBU, the exhaust plume changes from highly underexpanded supersonic jet to subsonic flow, and the wave structure undergoes the transformation from Mach reflection to regular reflection, resulting in the formation of periodic shock diamond and rhombus flame string, eventually the exhaust plume becomes a continuous flame. While the exhaust plume becomes a subsonic flow, the radial heat convection and thermal diffuse downstream the combustion flame of igniter are more intense than those upstream in BBU. Therefore the temperature at the backward position of base bleed propellant is the highest, and gives rise to fire firstly.