Fire Smoke Movement And Evolution Of Characteristic Parameters In The Double Long-Narrow And Confined Space Of Subway Tunnel/Train

In recent years,in order to relieve the increasingly urban road traffic jam caused by urbanization,subway systems have been widely constructed in maj or cities in China.However,the subway is a complex system,and the underground space is long-narrow and closed with high personnel density,which makes subway fires likely to develop into serious casualties.At present,most previous studies on subway fires are aimed at tunnel fires,but rarely involving the train carriage fire in the interval tunnel.In practice,the subway train may stop in the interval tunnel due to the power system failures caused by the train fire,and the passengers evacuate to the safe area through the door opened on one side and the longitudinal evacuation platform.At this time,the train with multiple openings on one side and the tunnel with openings at both ends together form a special double long-narrow space.The smoke movement behavior is quite different from the traditional tunnel fire,the existing theoretical models for smoke spread in tunnel fire dynamics may no longer applicable.Therefore,based on the fire scene of the double long-narrow and confined space of the subway tunnel and train,this thesis mainly carries out the following three aspects of research by using the method of modelscale experiment,numerical simulation and theoretical analysis:1.The smoke temperature distribution characteristics of the train fire under different fire sizes and fire locations in the natural ventilated tunnel were studied,and the empirical prediction relationship of the maximum temperature rise beneath the train ceiling was obtained.Firstly,based on the previous researches on tunnel fires,the effects of the lateral openings of the train with end-closed on the temperature distribution characteristics were compared and analyzed through modelscale experiments.Under the influence of the asymmetric flow field and the end wall of the train,the prediction model of the temperature beneath the ceiling in the traditional tunnel fire dynamics cannot be fully applied.Secondly,the effect of the longitudinal fire location were systematically analyzed by full-scale numerical simulations.Results showed that when the fire location deviates from the center to the end of the train,the temperature of the area on the offset side of the flame rises,and the flame tilts to the offset side.There is a critical fire source position.When the offset distance of the fire source is less than 0.67 times the half length of the train,the maximum temperature beneath the train ceiling is dominated by the entrainment pressure difference on both sides of the flame;otherwise,dominated by the effect of the heat feedback near the end wall.Based on dimensional analysis,with taking the train center and the critical fire location as the reference point,the segmental empirically predictive expression of the maximum temperature rise beneath the train ceiling was established.Finally,the longitudinal temperature decay beneath the train ceiling under different states of the fire plume impinging ceiling was validated following to the double exponential decay model.2.The smoke spread behavior of the train fire.under different longitudinal ventilation velocities,fire sizes and fire locations in a longitudinal ventilated tunnel was studied,and dimensionless prediction models for longitudinal temperature decay beneath the train ceiling upstream/downstream of the fire source were established.Under the blocking effect of the train itself,the maximum temperature rise beneath the train ceiling increases exponentially with the increase of the offset distance of the fire source,and has a power function relationship of-1/4 power with the longitudinal ventilation velocity.Based on the flame tilt characteristics,the method of equivalent wind velocity was proposed,a prediction model for the position of the maximum temperature on the longitudinal centerline was obtained when the weak plume impinges the train ceiling.Secondly,based on the single exponential decay model,the longitudinal temperature decay beneath the train ceiling was analyzed,in which the downstream temperature attenuation follows a uniform function.When the upstream smoke forward is close to the end wall of the train,the influence of the gradually enhanced heat feedback leads to the slower temperature decay.According to the effect of the heat feedback on the upstream smoke,the concept of critical backlayering length was proposed,and the upstream longitudinal temperature was then divided into three attenuation regions depending on the relationship between backlayering length,train length and fire location.Finally,the smoke layer height at different positions downstream of the train was analyzed by the integral ratio method,and it is found that the smoke layer height in the one-dimensional spreading state is consistent under different working condition and is much lower than the safe height of the smoke layer.3.The smoke overflow characteristics of the train fire and smoke temperature distribution in the tunnel were studied under natural/longitudinal ventilation conditions,and the complex evolution mode of the peak temperatures beneath the tunnel ceiling was revealed.By analyzing the smoke overflow characteristics at the lateral doors of the train,such as the mass flow rate,the height and temperature of the smoke layer,it is found that the smoke in the train under the conditions of natural ventilation and longitudinal ventilation mainly spills into the tunnel through the doors near the fire source and the train end,resulting in a variable number of peak temperatures in the area beneath the tunnel ceiling.In the natural ventilated tunnel,when the fire source gradually deviates from the center to the end of the train,the peak temperature increases exponentially,and the maximum temperature is distributed near the fire source.By considering the train fire as a fire scene between the tunnel fire and the enclosure fire,the concept of an equivalent virtual fire source was proposed,and the relationship between the maximum smoke temperature rise beneath the tunnel ceiling and the heat flux of the overflow smoke was further discussed.In the longitudinal ventilated tunnel,the distribution of the smoke temperature beneath the tunnel ceiling in space and time is related to the longitudinal ventilation velocity and the fire size.When the former is relatively small,the filling rate of the smoke layer beneath the tunnel ceiling is greater than the diffusion rate,the smoke temperature increases monotonically with showing multiple peaks,and the position of the maximum temperature gradually shifted from the downstream area near the fire source to the end of the train with the increasing longitudinal ventilation velocity.On the contrary,the smoke temperature nearly keeps constant with only a single peak temperature distributed at the downstream end of the train.Based on the dimensionless analysis and the experimental results,the linear relationship between the maximum temperature rise beneath the tunnel ceiling and the maximum temperature rise beneath the train ceiling was given.