| The use of mechanical ventilation combined with purification technology is a way to solve the problem of pollution of urban road tunnels.However,Researches on such kind of ventilation and purification system are limited,the coupled effect of ventilation and purification is ambiguous and the control effect of contaminants is unclear.To deepen the understanding of such systems and propose specific suggestions for designing,this paper conducts the following research:1.Experimental study of scale model.According to the basic characteristics of tunnel ventilation and ventilation system,the local tunnel model with bypass air duct is set up.The velocity distribution of local tunnels and the concentration of pollutants under different flow conditions are tested.The regular pattern of air flow and pollutant treatment is analyzed.2.The numerical simulation of airflow in typical air purification station of tunnel is carried out,and the effect of pollutant treatment is analyzed.It shows that “air back flow” phenomenon will occur with the unreasonable purification system operation,resulting in different cleaning load between the two purification tunnels.In addition,the air volume of the purification station is not related to the upstream tunnel environment and when the ratio of bypass air volume to the main tunnel is 100%,the pollutant concentration at the portal is the lowest.3.The influence of geometrical structure on the ventilation performance of typical purification station is studied by numerical simulation method.A new type of structure is proposed,which can avoid the “air back flow” phenomenon.It is found that the inlet angle and length of the bypass tunnel have little effect on the ventilation performance of the purification station(the air volume of bypass tunnel and the main tunnel is basically unchanged).The outlet angle of the bypass tunnel and the length of the main tunnel have a certain role(the air volume of bypass tunnel is unchanged,the air volume of main tunnel changed).After analyzing characteristics of the flow field in the purification station,it is found that the formation of "air barrier" is the main reason of poor performance of the purification station.Accordingly,a new type of purification station structure is proposed and it can avoid “air back flow” phenomenon.4.In order to consider the influence of jet fans and vehicle movement on the purification effect,a three-dimensional numerical model of full-length tunnel which can consider various factors is established and verified.It can be used to simulate and analyze the flow field and pollutant concentration field under different traffic scenarios and different ventilation and purification operation.5.The Guimiao Road tunnel in ShenZhen was simulated by using the established three-dimensional numerical model.The distribution of pollutants in tunnels was analyzed under different traffic condition and different operation condition of purifition and ventilation system.And the operation strategy of the purification station is given when the traffic volume and speed changed.This study can provide guidance for the design and operation of highway tunnel purification and ventilation system. |
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