Numerical Simulation on the Influence of Pipe Section Size on Hydrogen Flame Propagation Process in Closed Pipe

Zhou Ning; Mei Yuan; Li Xue; Chen Bing; Huang Wei-Qiu; Zhao Hui-Jun; Yuan Xiong-Jun

摘要

In order to reveal the influence of pipe section size effect on hydrogen detonation characteristics, Large Eddy Simulation (LES) model was used to numerically investigate the hydrogen/air detonation process in closed space of different size. The results show that in the process of flame propagation, the reflection frequency of the shear wave produced by the small cross-section pipeline is higher, which increases the probability of the tulip flame and flame structure distortion. For a 6-m-long square-closed pipe, the influence mechanism of the cross-section size on the flame propagation is different at different stages of flame propagation. In the early stage of flame propagation (that is, in the pipe segment 0-0.8 m away from the ignition end), the internal friction caused by the friction between the flame and the tube wall increases the turbulent intensity of the flammable cloud and accelerates the flame propagation. In a confined space with the cross-section edge length of 100 mm, the maximum flame propagation speed is 176.7 m/s, which is 48.5% faster than that in the confined space with the cross-section edge length of 250 mm. In the middle of the flame propagation (that is, in the pipe segment 0.8-5m away from the ignition end), the flame area increases sharply during combustion and releases more energy. Therefore, larger vortices are formed, and the flame propagation is accelerated by turbulence efficiency. The maximum flame propagation speed can reach 500 m/s when the cross-section edge length is 250 mm, which is 140.8% faster than that when the cross-section edge length is 100 mm. In the later stage of flame propagation (that is, in the pipe segment 0.8-5 m away from the ignition end), the pressure in the pipe increases sharply, and the reflected wave from the pipe end produces great resistance to the propagation of the flame front, and the flame propagation speed decreases sharply in the pipeline of various cross-sections.

机译：为了揭示管段尺寸效应对氢爆炸特性的影响，大型涡模拟（LES）模型用于数值研究不同尺寸的封闭空间中的氢气/空气爆轰过程。结果表明，在火焰传播的过程中，由小横截面管道产生的剪切波的反射频率较高，这增加了郁金香火焰和火焰结构变形的概率。对于6米长的方闭管，在火焰传播的不同阶段，火焰传播上的横截面尺寸的影响机理不同。在火焰传播的早期阶段（即，在管道区段0-0.8m远离点火端），火焰与管壁之间的摩擦引起的内部摩擦增加了易燃云的湍流强度并加速火焰传播。在横截面边长度为100mm的狭窄空间中，最大火焰传播速度为176.7米/秒，比限制空间中的速度快48.5％，横截面长度为250 mm。在火焰传播的中间（即，在离点火端0.8-5m的管区段中），火焰区域在燃烧期间急剧增加并且释放更多能量。因此，形成较大的涡流，并且火焰传播通过湍流效率加速。当横截面边长度为250mm时，最大火焰传播速度可以达到500米/秒，这比横截面边缘长度为100 mm的速度快140.8％。在火焰传播的后期阶段（即，在从点火端远离点火端部0.8-5段）中，管道中的压力急剧增加，并且来自管端的反射波产生了极大的阻力火焰前部，在各种横截面的管道中，火焰传播速度急剧下降。

Numerical Simulation on the Influence of Pipe Section Size on Hydrogen Flame Propagation Process in Closed Pipe

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