The utility tunnels have been applied extensively to run the various pipelines in the urban areas such as the gas pipeline, electrical power cables, and the likes. Contradicting with the rapid development of the utility tunnels is the ambiguity of the fire protection code to which one critical point is whether to ventilate in the fire accident, which is hampered by the effect of wind on the combustion gain. Therefore, this paper combines the plume function with the backlayering length and critical backflow velocity to explore the plume shape, optimize the ventilation environment, and decrease its combustion gain in which shows three key features that include the concavity and convexity characteristics, instability of plume, and the balance feature. Moreover, through their derived five plume shape constraints, we acquire the optimal wind environment. Furthermore, we found that the expected length is 0.12 in optimal condition when the original critical velocity is larger than 0.43, and the other cases are 0.05 for expected length. Meanwhile, the ventilation velocity needs to be increased three to seven times. The study provides new insight into the plume flow under the wind environment and would accelerate the formalization of fire protection design for utility tunnel.

中文翻译：

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最佳风环境下防止烟气回流和燃烧收益的烟羽形状研究

公用事业隧道已被广泛应用于市区中的各种管道，例如天然气管道，电力电缆等。与公用事业隧道的快速发展相反的是，消防法规的含糊不清之处在于，在火灾事故中是否要进行通风是一个关键点，这一点受风对燃烧增益的影响而受到阻碍。因此，本文将羽状流功能与背层长度和临界回流速度相结合，以探索羽状体形状，优化通风环境并降低其燃烧增益，其中显示出三个关键特征，包括凹度和凸度特性，羽状不稳定性，和平衡功能。此外，通过推导的五个羽状形状约束，我们获得了最佳的风环境。此外，我们发现在最佳条件下，当原始临界速度大于0.43时，预期长度为0.12，而在其他情况下，预期长度为0.05。同时，通风速度需要提高三到七倍。该研究为风环境下的烟流提供了新的见解，并将加快公用事业隧道消防设计的形式化。