Effect of obstacles on flame acceleration of propane-air explosion
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摘要: 研究了障碍物阻塞率、障碍物间距、障碍物空间位置对丙烷-空气爆炸过程及火焰加速效应的影响。采用雷诺平均（RANS）方程和湍流火焰封闭燃烧模型计算非稳态燃烧过程，主要分析障碍物周围复杂流场特性以及湍流涡与火焰面作用的详细机理。结果表明：阻塞率在0.5~0.7时，障碍物间距对火焰加速效果的影响较大，其中障碍物间距为一倍管径时火焰加速效应最大；而障碍物的空间位置对火焰传播的影响更为显著，当障碍物位于管道单侧时，湍流涡强度最大，火焰褶皱最明显，火焰传播速度最快。Abstract: The effects of blockage ratio, obstacles spacing and obstacles spatial position on the flame acceleration and explosion process of propane-air were studied in this paper.The unsteady combustion process was calculated by using the Reynolds averaged (RANS) equation and turbulent flame closure combustion model. The complex flow field around obstacles and the detailed mechanism of the interaction between the turbulent vortex and the flame surface were analyzed. The results showed that if the vortex zone is short compared to obstacles spacing, one portion of the flame would get in touch with the tube wall and some flame area would be reduced. For the higher blockage ratio, the flame area is the most important factor affecting the flame acceleration and the optimum flame acceleration can be achieved at the obstacles spacing of roughly one tube diameter. In contrast, the obstacles spacing shows little effect on the flame acceleration at lower value of blockage ratio. The flame interacted with vortex steadily during the process of flame propagation result in flame area enhancement that was counteracted by flame area extinction resulting from flame-wall interactions. However, as the blockage ratio increases to a critical value, the vorticity concentration area occupied most of the space between obstacles, therefore, the probability of contact between the flame and the tube wall became very small. In addition, the influence of the spatial position of the obstacles on the flame propagation was more significant. When the obstacles located on both sides of the pipe or in the middle of the pipe, the initial vortex intensity was too small to consume easily and there was no obvious flame folding. The most rapid flame propagation was observed when the obstacles was located on the unilateral side of the pipe, the turbulence vortex intensity in the flow field was the largest, the flame folding was also the most obvious with the process of chemical reaction.
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图 2 火焰速度的实验值与计算值的对比
Figure 2. Comparison of experimentaland calculated flame velocities
图 4 障碍物空间位置-管道截面图
Figure 4. Schematic diagram of cross section of pipeline and obstacles spatial positions
图 5 不同障碍物间距下的火焰平均加速度
Figure 5. Average flame accelerationunder different obstacles spacing
图 6 阻塞率为0.5时障碍物空间位置对火焰传播的影响
Figure 6. Influence of obstacles spatial position on flame propagation when blocking rate is 0.5
图 9 障碍物不同间距下火焰翻越障碍物时的流场
Figure 9. Flow field when flame crosses obstacles at different obstacle spacings
图 10 火焰翻越不同空间位置障碍物时的流场
Figure 10. Vector velocity field when flame crosses over obstacles at different spatial positions
表 1 湍流模型的计算结果与实验结果的对比
Table 1. Comparison between calculated results of turbulence models and experimental results
方法 pm/MPa δpm/% vm/(m·s-1) δvm/% 实验 0.508 - 194.8 - 可实现k-ε 0.565 0 11.22 182.75 6.59 RNG k-ε 0.412 7 23.09 145.00 34.3 SST k-ω 0.363 7 39.68 150.40 29.52 
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