Investigation Of Nature Ventilation In Subway Tunnel With Upper Vents

The problem of energy conservation and environment protection in the design of environment control system of metro, which occurs in the rapid development process of metro in our country, is one of new problems and difficult problems to be solved urgently. In the design environment control design of the section subway tunnel, the ventilation type of natural ventilation that made use of piston wind induced by metro operation at the top opening of metro tunnel, is economical and safety and environment protection, and will be an worth deeply research project. Based on the scientific research development plan project of China Railway Second Survey and Design Institute Group Ltd, which is Research of natural ventilation with the top opening of the metro tunnel, natural ventilation with the top opening of the metro tunnel was simulated and analyzed by one dimension environment control simulation software of metro and three dimension computational fluid dynamics software.The typical cases of natural ventilation with the top opening of the metro tunnel which used dynamic mesh are simulated, compared to the one dimension simulation results in the same case. The three dimension results and one dimension results have better consistency by mean of comparison and analysis. That the ventilation rate of one dimension numerical calculation has a little less than that of three dimensions numerical calculation shows the result by one dimension numerical calculation is believable and safer.The ventilation rate under the cases of different section tunnel length and different opening modes in a double-tracked horseshoe-shaped tunnel by one dimension environment control simulation software is simulated. This paper analyzes ventilation rate and air change of the section tunnel from the following two aspects, to meet standard of air change and to meet standard of exhaust of waste heat, and analyzes corresponding train pairs calculated according to above standard and the worst conditions when the trains located at the position of trains passing. It can concluded by analyzing results in detail in terms of ventilation and air change that when the central spacing between adjacent ventilation openings is greater than 200m, with an increasing number of opening, the increase of ventilation rate is more obvious. When the central spacing between adjacent ventilation openings is less than 200m, the increase of opening has little influence on ventilation rate. The fitting formula between total area of opening and section tunnel length to meet the standard of air change and exhaust of waste heat is obtained when the central spacing between adjacent ventilation openings is less than 200m.We come to the preliminary conclusion that the opening at the top of tunnel meets the demand of ventilation and air change of section tunnel by natural ventilation mode and provides theoretical basis and technical basis for rational natural ventilation program in engineering practice.