Research On The Influence Of Urban Intersection Shape And Subway Entrance And Exit On The Natural Ventilation Of Subway Station Halls

With the acceleration of the urbanization process in China,the demand for people’s transportation is increasing,and urban rail transit,such as the subway,is in a rapid development stage as an efficient and convenient transportation mode.The quality of the air environment in subway stations has also received increasing attention.The effective use of natural ventilation plays a role in energy saving and sustainability in improving the indoor air environment.In the transition season,introducing natural wind into the subway station from outside is of great significance for changing its air quality and energy saving.At present,most researches on natural ventilation of subway stations focus on the heat pressure in the station and the effect of piston wind when the train stops.There is little research on how outdoor air enters the subway station hall floor and how outdoor traffic pollutants diffuse into the station hall floor under the effect of outdoor wind pressure.This article will focus on the study of the natural ventilation of the subway station floor under the effect of outdoor wind pressure,and analyze the influence of the shape of urban intersections and the form of subway import and export.Based on this,this article will focus on the following work:In this paper,the environmental parameters of the outdoor and station hall floor of a subway station in Nanjing are first tested.The main content of the test is the temperature and humidity,CO₂concentration and PM2.5 concentration of outdoor and subway station hall floor with time.Experimental data shows:The change of CO₂concentration in the subway station hall floor is the same as the change of passenger flow;The PM2.5 concentration at the station hall floor is higher than the PM2.5concentration outside the subway station;The change trend of indoor and outdoor PM2.5 concentration levels with time is similar,and the indoor PM2.5 concentration changes greatly.The indoor and outdoor PM2.5 concentrations have a strong correlation（R²=0.993）.Recorded and analyzed the CO concentration data published by the outdoor environmental monitoring station,and found that the outdoor CO concentration gradually increased during peak hours,causing serious traffic pollution.Then this article rationalizes the intersections of urban streets,entrances and exits of subway stations,hall floors of subway stations and surrounding buildings,and establishes ideal physical models of subway stations.Then this paper rationally simplified the intersections of urban streets,subway entrances,subway halls and their surrounding buildings,established an ideal physical model of the subway station,and conducted a coupled simulation of the air flow between the city intersection and the subway hall floor.The characteristics of the diffusion of traffic pollutants from the city intersection to the subway station hall floor are studied.Use indicators such as the average wind speed at the station hall floor,the average concentration of pollutants at the station hall floor,and the number of air changes.The influence of the shape of street intersections（"T"and"十"）and the form of subway import and export（flat entry and shed entry）on the natural ventilation capacity and air quality of the subway station hall floor were analyzed.Research indicates:1.Under the two types of intersections and the two types of subway entrance and exit,the air flow pattern is similar in the same wind direction in the station hall floor,and the average wind speed is different;Under the wind direction of 45°and 90°,the effective hall-crossing effect can be formed in the station hall floor;Regardless of whether it is a"T"or"十"intersection,a shed entry or a flat entry and exit,when the wind direction is 45°,the average wind speed of the pedestrian height in the station hall floor is the largest,all exceeding 0.6m/s;However,at 0°wind direction and 180°,the airflow entering the station hall floor failed to effectively pass through the station hall floor to the other side,and the highest average wind speed was only 0.32m/s.2.Regardless of whether it is a"T"or"十"intersection,a shed entry or a flat entry and exit,the average concentration of pollutants at the pedestrian height of the subway station hall floor is higher when the wind direction is 90°.The average concentration of the flat entrance and exit at the"T"intersection reaches 17.1 mg/m³,and the shed entrance is 13.7 mg/m³;The average concentration at the entrance and exit of the shed at the"十"type intersection reached 26.13 mg/m³,and the flat entrance was 20.22 mg/m³.3.The ventilation volume of the subway station hall floor of the"T"type intersection reaches the maximum at the wind direction of 135°,and the ACH value increases from 20.9h^-1（flat entry type）to 24.5h^-1（shed entry type）;At 45°wind direction,the shed entry and exit can also increase the ventilation of the station hall floor,and the ACH value is increased from 16.3h^-1（flat entry type）to 17.8h^-1（shed entry type）;In the 90°and 180°wind directions,compared with the flat entry and exit,the ventilation of the station hall floor inside the shed entry and exit is significantly reduced,and the ACH value is reduced from 13.2h^-1 and 8.3h^-1to 8.8h^-1 and 4.2h^-1respectively;When the wind direction is 0°,the ACH value is reduced from 14.3h^-1（flat-entry type）to 13.9h^-1（shed-entered type）.At this time,the decrease in the ventilation volume of the station hall floor is relatively small.On the whole,the change of wind direction has a greater impact on the ventilation of the station hall floor under the shed-entry entrance and exit.Only when the wind direction is 45°and 135°,the ventilation of the station hall floor is promoted.4.The ventilation volume of the subway station hall floor of the"十"intersection reaches its maximum when the wind direction is 45°（135°）,and the ACH value increases from 17.5h^-1（flat entry type）to 18.8h^-1（shed entry type）.At this time,the shed-type entrance and exit plays a role in promoting the ventilation of the station hall floor;At 0°（180°）and 90°wind directions,the shed-type entrance and exit seriously affects the natural ventilation performance of the subway station hall floor.At this time,the ACH value decreased from 13.4h-1 and 10.3h-1 to 4.2h^-1 and 5.51h^-1,respectively.On the whole,in the"十"intersection,the ventilation effect of the station hall floor in the flat entrance and exit is relatively stable.