Experimental Technology and Management

[Objective] Effective control of ventilation parameters is critical in metro tunnel safety research. Since cross-passage wind is driven by inter-tunnel pressure differentials, investigating the impact of tunnel air supply on wind speed is therefore vital. Furthermore, train-induced piston wind can damage cross-passage fire doors, compromising operational safety and highlighting the need to assess the feasibility of eliminating fire doors through an optimized air supply design. Thus, this study clarifies the influence of air supply parameters on cross-passage airflow, compares cross-passage wind speeds derived from full-scale cold smoke experiments and thermal simulations of real fire scenarios, evaluates the feasibility of eliminating fire doors, and supports the optimization of metro fire ventilation systems and fire prevention research. [Methods] Here, full-scale experiments were combined with numerical simulation to explore the study objectives. Specifically, multi-condition ventilation and smoke tests were conducted in a Zhengzhou metro tunnel, utilizing a portable large-section anemometer to ensure the accuracy of the experimental data. The test setup comprised the tunnel structure, cold smoke device, and corresponding measuring systems. As cold smoke could not replicate the thermal buoyancy of real fires, full-scale thermal smoke simulations were performed using a fire dynamics simulator(FDS) and computational fluid dynamics software developed by NIST, which was validated for fire dynamics studies through multi-scale tests. Building on this, the smoke flow was analyzed under various air supply and exhaust conditions, with cross-passage wind speeds compared between the cold smoke experiments and FDS-simulated real fire scenarios. [Results] First, the simulation data obtained under fire-free conditions were consistent with the results of cold smoke tests, verifying the feasibility of the numerical simulation method. Second, real fires generate significant heat, causing hot smoke to rise owing to thermal buoyancy. This enhances vertical airflow in the tunnel and results in higher cross-passage wind speeds compared with cold smoke tests, though the velocity increase was limited by wall friction. Third, the distance(spacing) between air supply and exhaust ports, along with the status of platform screen doors, alters the inter-tunnel pressure differential; furthermore, the presence of a train can obstruct pressure-driven airflow, slightly reducing cross-passage wind speed. Fourth, cold smoke tests confirmed that a rational ventilation design can achieve the cross-passage wind speeds exceeding 2 m/s. Fifth, the ventilation modes corresponding to Conditions 1-3, 2-3, and 3-3 effectively increased wind speeds in both tunnels and cross-passages across different train positions and fire locations. [Conclusions] Based on the study results, the following conclusions are drawn: first, cold smoke experiments demonstrated that optimized ventilation can maintain a cross-passage wind speed exceeding 2 m/s during emergencies. This indicates the feasibility of eliminating fire doors, which could reduce construction and maintenance costs and enhance cross-passage evacuation efficiency. Second, ventilation Conditions 1-3, 2-3, and 3-3 optimize the emergency ventilation effect of metro tunnels, providing practical references for engineering applications. Third, the validity of the effective model is confirmed by the consistency between the fire-free simulation results and experimental data. In fire scenarios, cross-passage wind speed is influenced by thermal buoyancy, smoke viscosity, and smoke density. Among them, thermal buoyancy increases the speed, whereas wall friction suppresses it.