纵向风作用下竖井自然排烟对隧道内烟气逆流长度的影响

Effect of smoke exhaust from shaft on smoke back-layering length in tunnel under longitudinal ventilation

为了研究纵向风作用下隧道内竖井自然排烟对烟气逆流长度的影响,采用数值模拟的方法,建立了不同竖井高度的全尺寸隧道模型。并选取无竖井排烟的工况作为对照组,模拟不同火源功率下,改变竖井与火源纵向距离时竖井自然排烟对烟气逆流长度的影响和竖井排烟失效临界风速的变化。结果表明:当纵向风风速较小时,竖井对烟气逆流起抑制作用;随着风速增大,烟气逆流被控制在竖井近域范围内,竖井对烟气逆流的抑制作用减弱;当风速足够大时,烟气逆流将被完全限制在竖井下游,此时竖井排烟作用失效,且对纵向通风气流起到分流作用,烟气逆流长度反而变长。在此基础上,提出了竖井排烟失效临界风速的概念,竖井排烟失效临界风速随竖井高度增加而增大。

This paper focuses on the smoke back-layering length in a tunnel with a vertical shaft upstream of fire under longitudinal ventilation.Numerical simulations were carried out in a full-scale tunnel with different shaft heights,and the conditions without shaft were selected as the control group to quantify the changes of smoke back-layering length caused by natural ventilation at different fire source-vertical shaft distances and fire sources.The results show that when the longitudinal ventilation velocity is small,the smoke backflow spreads upstream of the shaft,and the shaft can inhibit the back-layering distance.The higher the shaft is,the shorter the smoke back-layering length.With the increase of longitudinal velocity,the smoke back-layering can be controlled near the shaft.When the ventilation velocity is large enough,the smoke backflow will be restricted entirely downstream of the shaft.In this situation,the shaft is no longer valid to exhaust smoke and can only exhaust the upstream longitudinal ventilation.That is,a part of longitudinal wind is directly exhausted through the shaft,thus undermining the strength of longitudinal ventilation to some extent.On this basis,we propose the concept of critical velocity at which smoke exhaust of shaft is invalid,and the critical velocity increases with the elevation of shaft height.