LES approach to premixed methane/air flame propagating in the closed duct with a square-hole obstacle
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摘要: 为揭示置障管道内甲烷/空气预混火焰传播特性，运用高速摄影技术对甲烷/空气预混火焰的形状变化和火焰前锋的速度特性进行实验，并利用大涡模拟对管道内的流场结构进行数值分析。结果表明：置障管道内依次出现了球形火焰、指尖形火焰及“蘑菇”状火焰，且“蘑菇”状火焰出现之后，火焰开始反向传播；“蘑菇”状火焰是双涡旋结构与火焰前锋面相互作用的结果，而火焰的反向传播是由流场中出现逆流结构引起的；障碍物对火焰前锋有明显的加速作用；大涡模拟成功再现了实验中观察到的火焰形状、火焰前锋速度及流场结构，说明大涡模拟适用于置障管道内预混火焰传播特性的研究。Abstract: Aiming at revealing the characteristics of premixed methane/air flame propagating in an obstructed duct.A 4 mm thick obstacle with a square hole of 50 mm×50 mm was equipped at 210 mm from the ignition source. In the experiment, the high-speed video photography was used to study the flame shape changes and flame front speed. In the numerical simulation, the large eddy simulation (LES) was applied to investigating the flow structure. The results demonstrate that the flame-tip successively takes on a spherical, finger and mushroom-like shape, and the flame begins to propagate in the backward direction after the mushroom-like flame appears. The mushroom-like flame can be explained by the interaction of the flame with two vortexes, and the reverse flow emerged in the flow field leads to the backward motion of the premixed flame. The flame speed is accelerated significantly due to the obstacle and the flame tip speed reaches the maximum value of 17 m/s when the flame passes through the square hole of the obstacle. The flame shape changes and the flow structure observed in the experiments can be well reproduced in the numerical simulations using the LES model. It is indicated that the LES model can be used to predict the premixed flame propagating in an obstructed duct.
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图 2 置障管道内甲烷/空气预混火焰传播的高速摄影图像
Figure 2. Sequences of high-speed images of premixed methane/air flame propagating in an obstructed duct
图 3 甲烷/空气预混火焰传播的大涡模拟
Figure 3. Large eddy simulation of premixed methane/air flame propagating in obstructed duct
图 4 置障管道内甲烷/空气预混燃烧的流场结构
Figure 4. Flow field of premixed methane/air flame propagating in an obstructed duct
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