Simulation Analysis On Smoke Flowing Characteristics In Road Tunnel

With the growing number and increasing length of road tunnels,the probability of fire accidents in the tunnels has risen as well and road tunnel safety issues seems to be more important.Road tunnel fire has caused social attention as it has the characteristics of fire spreading fast,poor condition of control smoke,heat and smoke concentration,difficulty in evacuation and rescue work,resulting in serious consequences and leading to worse influence.Because smoke is the greatest threat to human life security,therefore,carring out the studies on spread rule of fire smoke in road tunnel is of great significance.Based on the system analysis of research status at home and on abroad,the paper applies the method of numerical simulation to study the spread rule of fire smoke in road tunnel.Targeted analysis is conducted on some fields such as the maximum smoke temperature of the tunnel roof,changes of temperature along the length,the critical wind speed and smoke control,to provide the appropriate basis for the deep study on spread rule of fire smoke in road tunnel and smoke control in engineering tunnel.The main conclusions can be listed as follows:(1)Using the fire dynamics simulation software-FDS to establish the three-dimensional numerical model of road tunnel,the paper analyses smoke temperature,visibility changes on different conditions.Carrying out the analysis combining with the tunnel ceiling maximum flue gas temperature Kurioka model,the paper verifys the validity of the Kurioka model and obtains the proper conditions.Studies show that the model has a higher prediction accuracy when ventilation velocity is greater than or equal to 2m/s,when the ventilation velocity is less than 2m/s,the case of model has certain prediction error.On the basis,using the numerical analysis method to amend the model accordingly,the maximum flue gas temperature correction model in road tunnel under the conditions of the lower ventilation velocity is put forward;(2)Through the numerical simulation and analysis of the road tunnel temperature variation along the length,the twice attenuation model of the average temperature change along the tunnel is put forward,including a linear fast decay model near the middle of the fire and a natural exponential decay mode;(3)On the 15MW and 30MW fire heat release rate conditions,through analysing of the smoke spread process under the different wind speed obtain the critical longitudinal ventilation velocity interval.Combined with Wu and Baker's empirical formula,the results show that the critical wind speed forecasting precision is higher under 15MW fire heat release rate,and the critical wind speed forecasting result is less deviation under 30MW fire heat release rate.It verifys the correctness of the formula of critical longitudinal ventilation velocity.By observing the smoke spread process and analysing correlatively,it shows the validity of the tunnel ventilation velocity in inhibiting the spread of the upstream smoke and reducing smoke concentration;...