Study On Pollutants Crossflow At The Portals Of Closely-spaced Tunnel

With the rapid development of China’s economy,highway construction is also booming.As an indispensable and important part of highway in mountainous areas,the number and length of tunnels are also growing rapidly.The ventilation system of mountain tunnel not only consumes enormous energy,but also has some problems,such as unreasonable design,low utilization rate of equipment and serious waste of energy.These problems bring greater energy burden to the ventilation system.With the popularization of automobiles,the traffic flow in tunnels also increases.Automobile exhaust is one of the main sources of air pollutants in tunnels.It contains harmful substances such as CO,NOx,smoke and so on.If not handled effectively,it will seriously affect the health and driving safety of the people in tunnels.Therefore,ventilation system must be set up in tunnels to discharge harmful gases and send fresh air into tunnel,and ensure the safety and comfort of the tunnel environment.Therefore,the study on pollutant crossflow at the portals of closely-spaced tunnel is in line with the basic national policy of energy conservation,and is of great significance for the sustained and benign development of highway construction,especially tunnel construction in China.Most of the existing studies on pollutant crossflow at tunnel portals in China are limited to the dispersion of pollutants at single tunnel portals and the dispersion of pollutants between two portals of double highway tunnels.At present,there are few studies on pollutant dispersion at the multi-portals of closely-spaced tunnel,and related studies do not take into account the effects of valley wind speed,distance between two lines and distance between upstream and downstream at the same time,but these three factors must exist at the same time in practical projects.At present,no scholar has studied the problem of pollutant crossflow at the portals of closely-spaced tunnel with four tunnels with considering the three factors of valley wind speed,distance between two lines and distance between upstream and downstream at the same time,and has not given the relevant calculation formula.Firstly,this paper summarizes the research status of tunnel ventilation and pollutant crossflow at the portals of tunnel,and introduces the research theory of ventilation aerodynamics in highway tunnel.In this paper,FLUENT software is used to analyze the influence of air dispersion at the portals of closely-spaced tunnel with four tunnels in a valley.Including:(1)the problem that pollutants discharged from upstream tunnels are absorbed into downstream tunnels because they can not diffuse in time;(2)the problem of pollutant crossflow of adjacent tunnels.Based on k-? two-equation turbulence model and component transfer equations,the effects of valley wind speed,distance between two lines and distance between upstream and downstream on pollutant crossflow in closely-spaced tunnel are simulated and analyzed by CFD software FLUENT.The calculation formulas of transverse crossflow and longitudinal crossflow are fitted according to the simulated data.Finally,the physical model experiment of pollutant crossflow at the portals of closely-spaced tunnel is carried out,and the model demonstration and experimental analysis of pollutant crossflow phenomena at the portals of closely-spaced tunnel are carried out combined with numerical simulation.