泄爆过程中二次爆炸的动力学机理研究

DYNAMICS IN EXTERNAL SECONDARY EXPLOSION DURING VENTING

在容积为0.00814m3的柱形泄爆容器中,对泄爆现象进行实验研究.容器内充满当量比为1的甲烷-空气预混气,采用底端中心点火,泄爆压力为230±15kPa.基于κ-ε湍流模型和EBU燃烧模型,利用同位网格的SIMPLE算法,对该现象进行了数值模拟.实验和计算获得的外轴线上4个测压点的压力曲线和外流场的阴影和数值照片,形象地描述了高压泄爆时外部流场的变化.数值结果与实验结果基本一致.根据实验和数值结果,详细地讨论了泄爆过程中二次爆炸产生的动力学机理.泄爆的初始阶段,在破膜激波的引导下,泄出的未燃气体因欠膨胀在外流场形成稀疏波低压区和悬激波高压区.高压区可燃气体密度和温度上升,成为高密度的预热区域.随后,火焰以射流形式从泄爆口泄出,点燃可燃气云.受湍流等因素的影响,特别在高密度的预热区域,燃烧速率可能迅速增大,从而导致二次爆炸.

Vented explosion tests in a 0.008 14m^3 steel cylindrical vessel connected to a duct, filled with stoichiometric ratio of CH4-Air, have been performed with central ignition in the end plane and the failure pressure 230±15 kPa. Moreover it was simulated by using colocated grids SIMPLE schemes, based on the k-ε turbulent model and EBU combustion model. The pressure-time profiles at the four measurement points along the outside axis and the sequential shadowgraphs of the external flowfield both in test and simulation were clear to show the generation and development of the rupture shock and secondary explosion wave. The calculated results were in good agreement with the measured results in trend. In this paper, based on the experimental and numerical results, the dynamics mechanism of the occurrence of secondary explosions was elucidate systematically. At the early stage of venting, there existed rupture shock wave, low pressure area and suspended shock （high pressure area） about the axis in the external flowfield, which were formed due to the under-expansion of the released gas. At the same time, the high density pre-heating area was formed due to the density and temperature increase of the combustible gas in the high pressure area. When the jet flame came out and ignited the external flammable gas, the secondary explosion occurred for the violent combustion （especially in the pre-heating area） with the interaction of the turbulence, barocline effect etc.