Study On Air Velocity Distribution Characteristics And Monitoring Method In Subway Interval Tunnel

The air velocity in the subway tunnel affects the exclusion of the heat and moisture and the convection heat transfer between the airflow and the wall, determines the distribution of dust and harmful gas in the subway tunnel. In addition, the piston wind will also cause changes in the pressure, thus reduce staff comfort, and it may endanger the safety of facilities, so the size and distribution of air velocity determines whether there is a good environment in the subway tunnel. In order to ensure the reasonable wind environment in the tunnel, it is necessary to carry out long-term monitoring of the air velocity in the subway tunnel. This paper adopted numerical simulation method to conduct research and analysis on the circular subway from the following aspects:Firstly, one-dimensional simulation is carried out for the distribution of the air velocity in the subway tunnel. The air velocity distribution in the whole tunnel and the variation law of the piston speed during the passage of the train in the interval tunnel is analyzed. The simulation results show that the range of air velocity caused by the train is usually between 2m / s and 10m / s. There is a gas disturbance section of the longitudinal airflow near the train in the tunnel, but after a distance from the train, the longitudinal air velocity in the tunnel will form a uniform and stable air flow.Secondly, according to the range of air velocity in the interval tunnel, the selection of the location of the wind speed monitoring points is analyzed based on the two selection routes for the circular subway tunnel with different diameters. The results show that the method of the air velocity monitoring point of the subway tunnel is arranged at the position of the average air velocity point of the section so that directly measuring the average air velocity of the tunnel is not feasible. Put air velocity monitoring point is arranged in the tunnel near the wall, It is feasible to monitor the average air velocity in the tunnel by modifying the average air velocity in the tunnel by modifying the air velocity of the monitoring point, and the relationship between the air velocity of the monitoring point and the average air velocity of the tunnel is linear.Finally, taking into account that when the train is running through the air velocity monitoring point , the sensor collected air velocity data will no longer be corrected to accurately reflect the average air velocity within the tunnel due to the impact of air flow around the train. To provide a basis for the removal of invalid data, for different speed and different blocking conditions when the train through the monitoring point, the length range of the invalid data of the air velocity sensor is analyzed and studied. The results show that, when the train is runing in the tunnel, the length of the airflow disturbance caused by the rear is much longer than the airflow disturbance in the front, and the change is more complicated. When running in the same diameter tunnel, the greater the train speed, the longer the length of the airflow disturbance section behind the train, and the shorter the length of the front airflow interference section. When the train running speed is same, the larger the piston ratio of the tunnel, the shorter the length of the airflow disturbance section in the rear of the train, and the length of the front airflow disturbance section is basically same.