Abstract The study focuses on the fire-induced smoke flow in a naturally ventilated tunnel with large cross-sectional vertical shafts. For the shaft with large cross-section, the smoke is exhausted along four sides of the shaft, in which condition, the complete plug-holing occurs and the fresh air is entrained into the shaft strongly. In this work, studies on the longitudinal smoke temperature rise, smoke mass and heat exhausted as well as air entrainment from the shaft with large cross-section are performed theoretically. A method to predict the maximum smoke temperature rise downstream the shaft and the smoke back-layering length in naturally ventilated tunnel fires is proposed. Meanwhile, a series of small-scale fire tests was carried out by considering heat release rates (HRR) of the fires, shaft heights and adjacent shaft intervals. Experimental results indicate that the smoke back-layering length decreases with the increasing shaft heights, but it seems to be independent of the HRRs that are greater than 25.8 kW employed in the present work. Lastly, the validation of the proposed models is conducted by comparing with experimental results, which indicates that the models predict well the maximum smoke temperature rise on the downstream side of the shaft and the smoke back-layering length for small fires. The present study contributes to a guidance for smoke control in naturally ventilated tunnel fires with vertical shafts.

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大断面竖井自然通风隧道火灾致烟流的理论与实验研究

摘要 研究了大横截面竖井自然通风隧道内火灾引起的烟气流动。对于大断面的竖井，烟气沿竖井的四个侧面排出，在这种情况下，发生完全堵孔，新鲜空气被强烈吸入竖井。本文从理论上对大截面竖井的纵向烟温升、烟质量和排热以及空气夹带进行了研究。提出了一种预测自然通风隧道火灾中竖井下游烟气最大温升和烟气背层长度的方法。同时，考虑火灾的热释放率（HRR）、竖井高度和相邻竖井间距，进行了一系列小规模火灾试验。实验结果表明，烟气背层长度随着竖井高度的增加而减小，但它似乎与当前工作中采用的大于 25.8 kW 的 HRR 无关。最后，通过与实验结果的对比对所提出的模型进行了验证，表明该模型能够很好地预测竖井下游侧的最大烟温升和小火时烟气背层长度。本研究有助于指导具有垂直竖井的自然通风隧道火灾中的烟雾控制。通过与实验结果的对比对所提模型进行了验证，表明该模型较好地预测了竖井下游侧烟气最大温升和小火时烟气回层长度。本研究有助于指导具有垂直竖井的自然通风隧道火灾中的烟雾控制。通过与实验结果的对比对所提模型进行了验证，表明该模型较好地预测了竖井下游侧烟气最大温升和小火时烟气回层长度。本研究有助于指导具有垂直竖井的自然通风隧道火灾中的烟雾控制。