Experimental Study On Smoke Temperature And Flow Characteristics Of Tunnel Fire During Sealing

With the rapid development of transportation and society,the number of tunnels built at home and abroad is increasin.However,the tunnel is a restricted space with a narrow and long structure.Once a fire occurs in the tunnel,it is not effectively controlled and may cause mass deaths and injuries accidents.At present,domestic and foreign scholars have matured their research systems on tunnel fire dynamics and control measures in terms of tunnel slope,location of fire sources,and suppression of longitudinal ventilation.Different fire suppression methods will change the change of temperature and smoke in the tunnel Sealing fire prevention is an effective method to control tunnel fire.However,it is rare to study the characteristics of tunnel fire during the closure process.Therefore,this paper aims to reveal tne changes in temperature characteristics and smoke characteristics of tunnel fire during the sealing process,and conducts the following research by means of scale test and FDS numerical simulation:The similarity criterion was used to build a 1/10 scale test bench.The change pattern of flame shape under different sealing ratios and different fire source power conditions was studied.The results show that the inclination angle between the flame and the ground ncreased with the increase of the sealing ratio.When the tunnel was completely sealed,theflame burnt vertically and was accompanied by the ceiling jet.The larger the power of the source,the larger the area of the flame in the same sealing ration.Based on the results of scale test,the temperature variation and distribution in the process of sealing were studied.The analyses show that with the increase of the sealing ratio increases to 75%,a sudden temperature increase occurred in the tunnel,and the center temperature of the tunnel ceiling entered the attenuation stage in advance.25%and 50%sealing ratio will caused the high temperature area dominated by the thermal radiation of the plume to shift to the down side of the tunnel.The models of tunnel fire ceiling temperature attenuation under different sealing ratio conditions were established,and the temperature decreased of the downwind side exhibited an exponentially decreasing relationship.FDS numerical simulation software was used to simulate the smoke characteristics under different sealing ratio,longitudinal ventilation velocity and different fire power.The results show that with the increase of the sealing ratio,the length and thickness of the backflow of smoke increased,and greater the longitudinal ventilation speed,the smoke backflow and the sinking of the smoke could be effectively controlled.Longitudinal ventilation produced shear flow field and destroyed the thermal stability of smoke layer.The appearance of the sealing caused a new airflow vortex zone in the tunnel.Combined with the numerical simulation results,the prediction and correction model of smoke backflow length and critical wind speed in the sealing process was established.The accuracy of this model and several typical models was analyzed.The results show that the length of the smoke backflow with the sealing factor is in good agreement with the previous models.The error between the critical wind speed prediction model and the previous models is no more than 8.7%.The prediction model provides a certain theoretical reference for the study of tunnel fire.