Shaft-type natural ventilation offer a sustainable and cost-effective alternative to mechanical systems for the mitigation of smoke hazards. This study investigated the behavior of smoke with the application of unpowered ventilation caps in 1/15 scale shallow-buried urban road tunnels with shafts, and analyzed parameters such as the shaft axis wheelbase, shaft width, shaft width-to-height ratio, and heat release rate (HRR). The results show that the dimensionless HRR as an independent relationship with the dimensionless ceiling temperature rise in both the presence and absence of the unpowered ventilation cap. According to the experimental results, dimensionless length of smoke backlayering increases significantly with the increase of the HRR. In addition, the smoke backlayering length is positively correlated with the shaft width, and the backlayering length decreases and then increases with increases of the axis wheelbase. Moreover, the chimney effect is facilitated with the shaft height increase, which enhances exhaust effect, and the backlayering length decreases with the increase in the shaft height when the aspect ratio is greater than 0.5. Once the critical shaft width-to-height ratio is reached, the change in the shaft height no longer has an effect on the backlayering length. Finally, a dimensionless backlayering length calculation model based on the shaft parameters with different shaft exhaust effects is developed by combining the discriminant factors. The findings have crucial implications for fire prevention and safety management, and provide a valuable reference for future studies and engineering applications.

中文翻译：

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无动力通风帽及竖井参数对竖井自然通风隧道火灾烟气蔓延的影响

竖井式自然通风为机械系统提供了一种可持续且经济高效的替代方案，可减轻烟雾危害。本研究以1/15比例浅埋城市公路竖井隧道为例，研究了无动力通风帽的烟气行为，并对竖井轴距、竖井宽度、竖井宽高比、竖井宽高比等参数进行了分析。热释放率（HRR）。结果表明，无论有无动力通风帽，无因次 HRR 与无因次天花板温升均存在独立关系。根据实验结果，随着HRR的增加，烟气背层的无量纲长度显着增加。此外，烟气背层长度与轴宽呈正相关，且随着轴轴距的增大，背层长度先减小后增大。而且，随着井道高度的增加，有利于烟囱效应，从而增强排气效果，并且当长径比大于0.5时，背层长度随着井道高度的增加而减小。一旦达到临界竖井宽高比，竖井高度的变化就不再对背层长度产生影响。最后，结合判别因素，建立了基于不同竖井排气效应的竖井参数的无量纲背层长度计算模型。研究结果对消防和安全管理具有重要意义，为未来的研究和工程应用提供了宝贵的参考。