Study On The Influence Of Longitudinal Wind And Shaft On The Development Of Tunnel Fire

The construction and development of the tunnel has greatly eased the pressure on the city’s traffic.However,because of the tunnel is a semi-enclosed and narrow space,once a fire accident occurs,a large amount of toxic and harmful fumes and heat generated is difficult to discharge in a timely and effective manner.Mechanical ventilation and natural ventilation settings effectively reduce the risk of tunnel fires.When the vehicle in a tunnel fires,the combustion characteristics of the fire and the smoke layer in the tunnel change with the vertical wind in the tunnel.If the smoke exhaust installation cannot be set up properly,a large number of toxic and harmful high-temperature smoke will accumulate in the tunnel.This has intensified the destructive nature of the fire and hindered the rescue work in the later period.Therefore,it has great significance to study the combustion characteristics of fires in tunnels under the double action of longitudinal winds and vertical shafts.In this paper,the 1:10 small-scale experimental test was constructed based on the similarity criterion.The fire plume characteristics and shaft smoke emission characteristics in tunnel fires were studied.In the study of the combustion characteristics of the fire source,the fire source power,the maximum temperature under the ceiling,and the longitudinal temperature distribution of the flue gas were studied,and the fitting equations of dimensionless fire source power and dimensionless maximum temperature were established.The results of the study indicate that in the case of a tunnel fire with a vertical shaft under vertical wind conditions.The heat release rate of the fire source and the increase of the dimensionless shaft height of the shaft show a linear growth relationship;the heat release rate of the fire source and the increase of the vertical wind speed in the tunnel show a exponential growth trend;with the dimensionless longitudinal wind speed increasing The non-dimensional maximum temperature in the tunnel is also increasing,and the growth trend is roughly in line with exponential growth.In this paper,the relationship between flame and longitudinal wind has been modified to obtain a new relationship between flame tilt angle and vertical wind speed.By studying the characteristics of shaft exhaust smoke under different longitudinal wind conditions,the study shows that the vertical shaft exhaust smoke process is affected by many factors.With the increase of shaft height,the smoke exhaust effect is not always increasing.When the shaft height is too high,it will cause the bottom of the shaft to have the plug-holing,reduce the efficiency of shaft exhaust,and there will be a critical value for shaft height.When the shaft height exceeds the critical value,the effect of smoke will decrease.In this paper,the critical Froude number when the phenomenon of suction and puncture occurs is verified,and the critical Froude number suitable for the longitudinal effect of vertical wind and shaft is obtained.The shaft obtained in this experiment the dimensionless height at optimum exhaust efficiency is 1.When the height of the shaft remains unchanged,with the increase of the vertical wind speed in the tunnel,the thickness of the smoke layer in the tunnel will gradually increase,which is favorable to the smoke extraction process.However,when the longitudinal wind speed exceeds the critical value,the flue gas separation will be destruction reduces the temperature of the flue gas,causing the stack effect of the shaft to decrease.According to the study in this paper,when the dimensionless longitudinal wind speed is 0.2,the tunnel can achieve the best smoke exhaust effect.