Abstract This paper has analyzed the ambient pressure on the effect of the efficiency of the mechanical smoke extraction system in tunnel fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). The simulation results indicate that it is not the instance that the higher the exhaust rate, the better the smoke exhaust efficiency of the exhaust vent. There is a critical exhaust rate at which excessive fresh air entrainment, such as plug-holing of the smoke layer, can be avoided. The mechanical smoke exhausting process is affected by two competitive forces: horizontal inertial force and vertical suction force. The thickness and horizontal velocity of the thermal smoke layer in the tunnel increase as the ambient pressure decreases. At this time, the vertical suction force required for the occurrence of the plug-holing phenomenon increases, and thus the critical exhaust rate increases. A linear relationship between the dimensionless critical exhaust rate V c r i ∗ and the modified heat release rate Q ˙ ∗ was proposed to characterize the influence of ambient pressure on the mechanical smoke exhaust efficiency. When the exhaust rate is 0.5 times the critical exhaust rate, the smoke mass fraction exhausted from the exhaust vent (E) reaches the maximum value.

中文翻译：

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环境压力对隧道火灾机械排烟效率影响的数值研究

摘要 本文分析了环境压力对隧道火灾机械排烟系统效率的影响。这些是通过大涡模拟 (LES) 和火灾动力学模拟器 (FDS) 进行模拟的。仿真结果表明，并非排气率越高，排气口的排烟效率越好。存在一个临界排气率，在该排放率下可以避免过多的新鲜空气夹带，例如烟层堵塞。机械排烟过程受到两种竞争力的影响：水平惯性力和垂直吸力。隧道内热烟层的厚度和水平速度随着环境压力的降低而增加。此时，发生堵孔现象所需的垂直吸力增加，从而临界排气率增加。提出了无量纲临界排气率 V cri * 和修正的热释放率 Q ˙ * 之间的线性关系来表征环境压力对机械排烟效率的影响。当排气速率为临界排气速率的 0.5 倍时，从排气口（E）排出的烟气质量分数达到最大值。