Study On Characteristics Of Smoke Movement And Smoke Exhaust In The Subway Tunnel With Metro Train

Along with the acceleration of China’s urbanization process and the rapid growth of urban population,urban road traffic pressure is more and more big,and various cities to give priority to the development of subway transportation system as public transport system,due to its small ground space occupation,larger passenger carrying capacity,faster running speed,and environmental protection and energy saving.However,the fire safety problem has been one of the problems that people pay attention to in the subway system.The influence of subway train on the fire smoke and the smoke gas transport properties in the situation where the subway train docked in the subway tunnel because of fire,including the distribution of smoke gas temperature under the tunnel ceiling,smoke gas back-layering length and the thermal environment in the fire downstream space,were presented and studied in this paper.In addition,the influence of subway train on the smoke movement was also investigated,as well as the comparison of smoke exhaust effect of several kinds of common tunnel ventilation and smoke exhaust,to explore its application in subway tunnel ventilation.The main results obtained are as follows:1.Through numerical simulation,when the subway train stops in the tunnel because of fire,the subway train has an important influence on the ceiling temperature distribution,under the longitudinal ventilation conditions:the temperature distribution under the roof no longer mutually symmetrical,subway trains makes the smoke gas temperature decreases to the room temperature rapidly,blocking heat transferred to the upstream and inhibiting the fire spread to the upstream effectively.Fire downstream under the roof of the temperature distribution is an exponential decay distribution and attenuation index increased with the increase of longitudinal ventilation velocity,the length of the subway train effect on temperature distribution is relatively small.2.For the thermal environment of the downstream of the fire,metro train is help to strengthen longitudinal ventilation and fire plume interactions and mixing,and the longitudinal ventilation velocity is greater,simulative effect is more obvious,makes the smoke concentration increases in the fire downstream space as well as the visible distance away from declined.In the condition of the same longitudinal ventilation rates,subway trains also largely increases the temperature of the lower space,but the the concentration distribution value of poisonous gases CO compared to no presence of subway train is small,due to the fully diluted.3.The influence of the length of the subway train on the countercurrent length of the hot flue gas is studied by placing different lengths of the subway train model in the subway tunnel model.It is found that the hot flue gas countercurrent length is larger than the subway train length The length will decrease as the length of the train increases,but when the hot air countercurrent length is less than the subway train length,the hot flue gas upstream length will not vary with the length of the train.Through the data fitting analysis,we can see that when the subway train contains the subway train,the non-dimensional flue gas countercurrent length of the hot flue gas can be expressed by the following formula:4.Through comparative analysis the effect of six different forms of ventilation and smoke exhaust methods by numerical simulation,pure longitudinal ventilation effect is the worst,because it doesn’t actually exhaust the fire smoke outside,but blew them to the fire downstream tunnel,which has quite adverse influence on personnel evacuation,fire fighting and rescue.Fully transverse ventilation,semi transverse ventilation style of combining specific point type smoke and longitudinal ventilation and-point type smoke exhaust,smoke control effect is very good.For the combination of longitudinal ventilation and smoke extraction in single point,due to the smoke window is few,the smoke control effect is not better than the above several ways,but still better than the pure longitudinal ventilation.5.In different smoke exhaust situations,the effect of subway trains basically the same as reducing the tunnel of the effective ventilation area to increase the tunnel longitudinal airflow rate,but the effect of smoke control and control of smoke spread is not the same.In the pure longitudinal ventilation and vertical ventilation and single point type smoke combined,the subway train is not conducive to the flue gas control,and in the transverse and semi transverse and specific point in flue gas to heat flue gas control in the longitudinal ventilation and smoke exhaust,the impact of subway train has an close relationship with the position of the exhaust window.Under the fixed-movable combined pattern,the addition of the movable fan further produces a cooling effect on the downstream of the fire source.On the basis of increasing the air volume of the movable fan,the difference in the smoke exhaust effect between the different inclined angles gradually appears,and the smoke exhaust effect is gradually becoming ideal.When applying the arrangement pattern of movable fans in series,compared with increasing the number of movable fan of the same specification,increasing the ventilation volume of movable fan has a more significant effect on reducing the temperature in the tunnel.