Abstract To investigate the overpressure of methane-air explosions in straight large-scale tunnels, the computational fluid dynamics (CFD) code of Flame Accelerator Simulator (FLACS) was used and validated against experiments conducted at three different scales, and the effects of the volume concentration of methane in air, the blockage ratio (BR), the tunnel length, and the cross-section were studied. When analysed using the GaussAmp mathematical model, the maximum peak overpressure appears at a volume concentration of 10.30 % of methane in air. Blockage ratios (BR) of 0.15 and 0.3 resulted in the combustion of methane-air mixtures with the volume concentration of 6.5 % and 14.0 % of methane in air, producing a fatal overpressure of 21 kPa. When the BR increases up to 0.75, both the lean and rich mixtures cause a peak overpressure of over 60 kPa. Combustion of the same methane-air mixture produces the same overpressure, which decays approximately linearly at the same slope owing to a smooth wall roughness before travelling near the outlet, independent of the specific tunnel length. A method to characterise the cross-sections was proposed, and the maximum peak overpressure of different lengths of methane-air mixtures in different cross-sectional tunnels was found, presenting various regimes from a hump shape to a wave-like uplift and bowl shape. The cross-section parameters determine the degree of confinement and further control the maximum peak overpressure in the modelled tunnels. An exponential asymptotic model can be used to conveniently obtain the maximum peak overpressure. These phenomena indicate that approximately square-shaped cross-sections should be selected to avoid an extremely high overpressure in large-scale tunnels with the potentially significant accumulation of methane-air mixtures.

中文翻译：

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大型直隧道甲烷-空气混合气爆炸超压研究

摘要 为了研究大型直隧道中甲烷空气爆炸的超压，使用火焰加速器模拟器 (FLACS) 的计算流体动力学 (CFD) 代码，并针对在三个不同尺度上进行的实验以及体积的影响进行验证。研究了空气中甲烷的浓度、堵塞率 (BR)、隧道长度和横截面。当使用 GaussAmp 数学模型进行分析时，最大峰值超压出现在空气中甲烷体积浓度为 10.30% 时。0.15 和 0.3 的堵塞比 (BR) 导致空气中甲烷体积浓度为 6.5% 和 14.0% 的甲烷-空气混合物燃烧，产生 21 kPa 的致命超压。当 BR 增加到 0.75 时，稀混合物和浓混合物都会导致超过 60 kPa 的峰值超压。相同的甲烷-空气混合物的燃烧产生相同的超压，由于在出口附近行进前壁面光滑，与特定的隧道长度无关，超压以相同的斜率近似线性衰减。提出了一种表征横截面的方法，找到了不同横截面隧道中不同长度的甲烷-空气混合物的最大峰值超压，呈现出从驼峰状到波浪状隆起和碗状的各种状态。横截面参数确定限制程度并进一步控制模拟隧道中的最大峰值超压。可以使用指数渐近模型来方便地获得最大峰值超压。