城市地下排水管道中燃气爆炸及气-液两相耦合作用规律

The law of gas explosion and gas-liquid coupling in urban underground drainage pipelines

为研究城市地下排水管道中燃气爆炸传播特性和气-液两相耦合作用规律,基于气-液两相流理论和计算流体力学方法,对不同水深率下的天然气/空气混合物的爆炸-加速-衰减过程进行了数值模拟。研究结果表明:当水深率小于0.7时,随着水深率的增加,气相空间的长径比增大,燃料燃烧加剧,火焰的加速现象逐渐显著,导致峰值超压逐渐增大,超压峰值显现时间逐渐缩短,且峰值超压沿轴向的提升效果更加显著;当水深率达到0.7时,火焰在管道内的传播明显受阻,水震荡产生的波动及细水柱迅速占据了有限的气相空间,阻断了火焰的自维持传播,使得爆炸超压仅在点火源附近显现。不同水深率条件下,管道中相同区域内,同一时刻水面被扬起的高度和气相区域的速度场不同,被卷扬起的低温液体对其相邻区域的高温火焰形成降温和阻断,之后由于气体的宏观流动,与液面相邻的低温气体流动至管道内高温区域,进而造成管道内火焰温度降低,同时,水的震荡和细水柱的飞扬大大降低了爆炸超压风险。

There are frequent gas explosion accidents in urban rain and sewage drainage pipes,which pose a serious threat to people’s lives and property safety.To study the propagation characteristics of gas explosion and the law of gas-liquid twophase coupling in urban underground drainage pipes,based on the gas-liquid two-phase flow theory and computational fluid dynamics method,a numerical simulation study of the explosion-acceleration-decay process of gas/air mixture under different water depth ratio was conducted.The results show that when the water depth ratio is less than 0.7,as the water depth ratio increases,the long-diameter ratio of the gas phase space increases,the fuel combustion intensifies,and the flame acceleration phenomenon gradually becomes significant,which leads to a gradual increase in peak overpressure,a gradual reduction in peak overpressure time,and a more significant effect of peak overpressure along the axial direction.When the water depth ratio reaches 0.7,the propagation of the flame in the pipeline is blocked,and the fluctuation caused by the water shock and the fine water column quickly occupy a small gas phase space,blocking the continuous propagation of the flame,which makes the explosion overpressure appear only near the ignition source.Under different water depth ratios,in the same zone of the pipeline and at the same moment,the height of the water being rolled up and the velocity field of the gas phase region is different,and the cryogenic liquid is rolled up to cool and block the high-temperature flame in the adjacent zone.Then,due to the macroscopic flow of the gas,the cryogenic gas adjacent to the liquid surface flows to the high-temperature region in the pipeline,resulting in a decrease in the flame temperature in the pipeline.The shock of water and the flying of fine water columns greatly reduce the risk of explosion overpressure.The research results provide a scientific basis for the explosion protection of urban gas lifelines.