Research On Temperature Distribution Characteristics Of Tunnel Fire Based On Distributed Optical Fiber Monitoring

Highway tunnels are an important part of my country’s transportation network.With the continuous construction of mountain-crossing sea tunnels,the safety issues of highway tunnels need to be solved urgently.Highway tunnels are semi-closed,long and narrow,and have low visibility.Once a fire occurs,it is difficult to detect and extinguish the fire,which is extremely dangerous and destructive.The use of advanced fire detection technology to timely monitor the location of the fire source and predict the scale of the fire is of great significance to the prevention and control of highway tunnel fires.Aiming at the problem of tunnel fire safety,this paper adopts two research methods of scaled physical model test and numerical simulation,analyzes in detail the temperature distribution law of tunnel fire under natural ventilation,and uses a distributed optical fiber temperature sensing fire detection system to realize the Rapid location of fire source and prediction of fire scale.In order to study the application of distributed optical fiber sensing technology in tunnel fire monitoring,using similar theories,a 1:20 scaled tunnel model was established to obtain the distribution law of tunnel fire temperature,and the distributed optical fiber temperature measurement,fire scale and fire source location were discussed.Correspondence between and its similarities and differences with traditional thermocouple test results.The results show that the distributed optical fiber monitoring system is similar to the temperature measured by the thermocouple,and the distributed optical fiber temperature measurement is more comprehensive and accurate,and it is worthy of being promoted and applied to tunnel fire monitoring.At the same time,the pyrosim dynamic simulation software was used to establish the same tunnel model as the physical model test.The tunnel fire temperature distribution under different fire source powers was analyzed and compared with the model test results.The results show that the trend of the temperature curve obtained by the model test and the numerical simulation is basically the same.Under natural ventilation conditions,as the scale of the fire increases,the temperature of the tunnel rises as a whole,and the vault reaches the highest temperature.As the distance from the fire source increases,The vault temperature decays exponentially and remains stable after a certain distance.In the direction of the cross section of the tunnel,with the heat radiation and the flow of smoke,the temperature of the dome rises rapidly,which is significantly higher than the arch shoulder and the arch waist.The temperature of the section above the arch waist transitions according to a linear law,and the temperature of the arch waist and the arch bottom changes.It is not obvious,and the transition is basically uniform.By summarizing the temperature empirical formulas of domestic and foreign scholars and discussing the influence of different fire source powers on the maximum temperature of the vault,the formula for the maximum temperature rise of the vault in the event of a fire in the tunnel under natural ventilation is obtained.Analyze the longitudinal and circumferential temperature distribution laws of the tunnel space when the temperature reaches a steady state.Under all test conditions,the changes of the dimensionless temperature and the distance of the fire source are analyzed,and the power exponential function is fitted to it,and the correlation coefficient is higher,and the longitudinal temperature distribution formula of the tunnel is obtained.Through distributed optical fiber to carry out long-distance and blind-zone full coverage monitoring along the tunnel,it can be visually analyzed that the fire source is located at the location with the largest Brillouin frequency shift,so as to achieve rapid fire location and remind evacuees to pay attention to avoidance.Combining the formula for the maximum temperature rise of the vault and the formula for the longitudinal temperature distribution can realize the prediction of the fire scale.