Study On Ventilation Organization Optimization Of Subway Tunnel

In today’s society,subway has become a rapidly developing mode of transportation because of its high speed,high comfort and large transportation capacity.It is estimated that by the end of 2050,the total length of light rail and subway in China will reach 2000 km,and the urban rail transit system will be able to accommodate about 50%～80% of the total urban passenger traffic.However,the subway tunnel also has some problems,such as the temperature rising year by year and the huge energy consumption of the ventilation system.The maximum use of piston wind has become a hot topic in the subway tunnel ventilation.Taking a station of Lanzhou Metro Line 1 and the interval tunnels on both sides as the research object,this paper studies the setting mode and structural type of the piston air shaft of the metro tunnel by using the methods of theoretical calculation,numerical simulation and theoretical analysis.Firstly,this paper introduces the formation mechanism of piston wind in metro tunnel,and expounds the calculation formula of longitudinal average piston wind speed in metro tunnel.At the same time,the measured data of Shenzhen Metro Line 1 in the published literature are used for comparison and verification.It is found that the relative difference between the theoretical calculation result of piston wind speed and the measured data is10.7%,which verifies the rationality of the theoretical formula.Then the ventilation grid model is established by using the engineering parameters of Shenzhen Metro Line 1 for numerical simulation.The relative difference between the simulated value and the measured value is only 2.24%,which ensures the reliability of the simulation method in this paper.Based on the above,the grid model is established according to the actual engineering parameters of Lanzhou Metro Line 1,the working conditions are set by using the method of control variables,and the two-dimensional and three-dimensional models are comprehensively used to study the influence of the opening mode of the piston air shaft,the distance between the piston air shaft and the station,the vehicle speed,the area of the piston air shaft and the structural form of the piston air shaft on the tunnel ventilation organization.It is found that:(1)If the subway station is to be equipped with double air shafts,the mutual influence between adjacent piston air shafts should be taken into account.The ventilation performance of the piston air shaft at the incoming end is suppressed,while the ventilation performance of the air shaft at the outgoing end is slightly promoted;(2)Under the condition of larger air shaft area,the ventilation volume will also be larger,but the growth rate of air volume is slightly less than that of air shaft area.When the air shaft area ratio is 2:5,the corresponding air volume ratio is about 3:4.Therefore,other factors such as pressure wave,temperature field and local climatic conditions should be considered comprehensively in the study of piston air shaft area;(3)The inclined angle of the horizontal section of the piston air shaft has a significant impact on the ventilation effect,and changing the air duct angle has a greater impact on the piston ventilation effect than changing the air duct length.(4)The piston wind speed increases gradually with the increase of subway speed per hour,and the maximum piston wind speed is approximately linearly proportional to the train speed per hour.Finally,from the perspective of wind speed and ventilation volume,the relevant numerical simulation results of the piston air shaft are analyzed,and a more reasonable optimization and improvement scheme is put forward: the effect of using the double air shaft system for natural ventilation in the subway station is better than the single air shaft system,but if the subway station considers using the single air shaft system for natural ventilation,the effect of setting the air shaft at the exit end is better than that at the entrance end,and the air shafts at the entry and exit ends are set as 10 ° air shafts It is more ideal to be located 150 m away from the platform.At this time,the vehicle speed is higher,the piston wind is more fully utilized,and the ventilation volume is greater,which is more conducive to the ventilation of the tunnel.