Analysis of the effect of a venting structure on slow cookoff of Comp-B based on a universal cookoff model
摘要: 为了探究热刺激作用下泄压结构对熔铸炸药点火时间及点火前内部物理场变化的影响，设计了有/无泄压结构烤燃弹的内部多点测温慢烤对比试验。基于炸药通用烤燃模型（universal cookoff model, UCM），建立了炸药熔化后受浮升力驱动流动，反应速率随压力、反应进程等变化的B炸药烤燃计算模型，对有/无泄压结构烤燃弹的炸药在升温过程中的温度场及内部压力变化等情况进行了数值模拟，并与试验结果进行比较。结果表明：慢烤条件下，烤燃弹内部压力呈先缓后急上升趋势；有泄压结构烤燃弹在结构作用前的压力变化趋势与无泄压结构的一致，泄压结构的作用会使炸药自热反应速率骤然降低，炸药内部温度下降，自热反应速率降低和产物气泡驱动的对流共同导致了点火时间的延后；由于对流的作用，炸药点火点都在弹体顶部区域。Abstract: In order to study the influence of the venting structure on the ignition time and the internal physical field changes before thermal ignition of melt cast explosives, slow cookoff tests with multi-point temperature measurements were designed for two groups of ammunitions with or without a venting structure. The area of the venting hole was designed to meet the requirements of the pressure balance method for the critical cross-sectional area. The temperature-time curves of the two ammunitions heated at a rate of 3.3 ℃/h were obtained through the tests. The opening time of the venting hole was determined. It was found that venting led to a decrease in the internal temperature of the explosive and delayed the ignition time. A universal cookoff model (UCM), including the buoyancy-driven flow after the explosive melt and the variation of the decomposition rate with pressure and reaction process, was applied to the cookoff simulation of Comp-B. In the simulation, the ammunition without a venting structure was considered to be sealed during the cookoff process. The opening time of the venting hole for the ammunition with a venting structure was determined based on the test. After the venting hole was opened, the ammunition was considered to be fully ventilated, and the decomposition rate of the explosive reduced. The variations of the temperature field and internal pressure of the ammunitions with or without a venting structure during the cookoff process were simulated. The results show that under the slow cookoff condition, the internal pressure of the ammunition increases slowly at first and then sharply. The pressure change trend of the ammunition with a venting structure is the same as that without a venting structure. The action of the venting structure will suddenly reduce the decomposition rate of the explosive, and then the internal temperature decreases. The decrease in the decomposition rate and the product bubbles-driven convection lead to a delay in the ignition time. Due to the convection, the ignition points of the explosives are all in the top area.
表 1 不同尺寸的网格及计算结果
Table 1. Calculation results with meshes of different sizes
1 0.6 116 144 173.26 5.01 2 0.5 163 800 173.24 4.96 3 0.4 221 680 173.22 4.84
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