Experimental Study And Umerical Simunation Of Subway Tunnel Fire With Nature Ventilation

With the process of rapid development of subway construction, energy conservation and disaster prevention become the focus of our attention. Natural ventilation that made use of piston wind induced by metro operation at the top opening of metro tunnel is a possible means of ventilation technology. When the train fire occur inside the tunnel with natural ventilation, how to control smoke spreading in order to ensure the safety of evacuation, is a worth deeply research project. In this paper, the subway fire model tests with natural ventilation carried out and the natural ventilation tunnel fire with the top opening of the metro tunnel was simulated and analyzed by use of FDS software and large-eddy simulation under the different conditions of opening.Using 1/15 reduced scale model and the Froude simulation method, the natural ventilation subway fire model tests carried out. While the test of the vent of a certain width at different spacing, length and height carried out in different fire heat release rate, the tunnel smoke temperature distribution and the flue gas temperature, flow rate of the vent were measured. The results showed that:the smoke concentration and temperature in the area between the two vent that fire source located are high. Flue gas mainly discharges through the first vent, followed that the concentration and temperature are sharply reduced; with the increasing of spacing between the vent, the temperature and flow rate of the smoke discharged through the vent reduced; the temperature and smoke flow is less affected by different vent length, height and whether there is a model train inside the tunnel.The numerical simulation results that obtained by using fire simulation software FDS (Fire Dynamics Simulation) and large-eddy model (LES) were compared with the experimental results. The results show that natural ventilation subway fire model test results and numerical simulation results agree well, indicating that the FDS software can be used for subway fire simulation analysis of natural ventilation. Through the analysis of the tunnel fire environmental control standards and the fire heat release rate, obtained four parameters of the fire environment control:the tunnel roof wall smoke temperature, the smoke temperature, CO concentration and visibility at human height in the tunnel; fire heat release rate take the peak 10MW in simulated time. The main control standard of the tunnel fire environment is the visibility at human height. When the visibility was more than 8.4m, the remaining three parameters meet the demands of human escape.After great numbers of simulation at different conditions of the vent by using FDS, we carried out a detailed calculation and analysis on the flue gas flow through the vent and the human security, and finally obtained reasonable conditions of the vent that meet the requirements of disaster prevention. Research also indicated that when the vent spacing is less than 80m, the least length of the vent to meet the requirements of human security has decreased drastically. As a result, the length of the vent can be designed very small when the vent spacing is small, but it causes too many vents. When the vent spacing is greater than 160m, in particular, after 180m, the least length of the vent to meet the requirements of human security has increased drastically. It is considered that the reasonable vent spacing is between 80m-160m.