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. © 2019, Editorial Board of Acta Armamentarii. All right reserved.