Study On The Smoke Spreading Rule Of Fire In Moving Train In Subway Tunnel

Due to its large passenger capacity,relatively closed environment and difficulty in heat and smoke extraction,subway fire is very easy to cause serious damage.In the existing research on subway tunnel fire,the main considerations include the scene of equipment and facilities ignition,train fire detention,train movement after fire,and set up train as a whole fire source for smoke analysis.However,few studies had been done on the internal fire of train carriages in tunnels.For this reason,this paper took the scene of fire source moving with the train as the research object.Through theoretical analysis and numerical simulation,the smoke spread rule in the train carriage was discussed,and the influence of train running speed,the parameters of ventilation and smoke exhaust system and the length of the carriage on the smoke spreading were analyzed.The specific research contents include:1)The piston wind effect of train motion in tunnel and the influence of the top opening of the carriage on the air exchange and air distribution inside the carriage were analyzed,and the correctness of the numerical simulation was verified;2)The fire of luggage inside the carriage was analyzed.The influence of train running speed and ventilation and smoke exhaust modes on the smoke flow process inside the carriage was analyzed.The variation of velocity field,temperature field and smoke concentration with time and the relationship between temperature,smoke concentration and train running speed were given,and the relative optimized ventilation mode was determined.3)By comparing the monitoring point temperature and smoke concentration in three carriages and single carriage under the same condition of fire source,the influence of train length on the fire smoke spread inside the carriage was analyzed.It should be pointed out that in above calculation,the train motion includes four stages,which are acceleration,uniform speed,deceleration,and rest.The sliding grid method and UDF code written by C language were adopted in simulation.The volume heat source model was used to simulate the luggage fire.Considering the worst condition,it is assumed that the fire will occur and increase rapidly at the completion of the acceleration stage of the train,and its heat release rate will reach the maximum when the train runs to the middle of the tunnel.The results show that the piston wind has obvious influence on the airflow inside the train through the opening of the roof.After the fire broke out inside the moving car,the temperature inside the car increased with time and presented an asymmetric distribution.The temperature at the rear of the car was much higher than that at the front;The temperature and smoke concentration of monitoring points in the carriage decrease quadratically with the increase of run speed;When the side fan is closed,the rear fan is up,and the front fan is down,the smoke can be discharged more timely;Compared with the single compartment,the temperature and smoke concentration of the same monitoring points relative to the fire source in the three compartments were greatly reduced.The research of this subject has certain reference value and guiding significance for the evacuation strategy and the design of the ventilation and smoke exhaust system of the train after a fire broke out in the carriage.