Numerical Simulation Of Smoke Management For A Curved Road Tunnel

With socio-economic development and the improvement of people's living standards,China's road transportation developed rapidly,bringing about a gradually increasing road transportation networks density.Meanwhile,as an important part of road transportation,the number and length of road tunnels increase correspondingly.Although road tunnels facilitate people's trip,the following would be the incidence of tunnel fires as well as the expandable hazards increases greatly.Although a road tunnel fire is an accident of small possibility,its disastrous consequence cannot be neglected.On the basis of analyzing the category of road tunnels and smoke propagation of road tunnel fires,a road tunnel with a semitransverse ventilation system was selected to investigate smoke management in curved tunnels due to the fact that studies conducted before were aimed at straight tunnels.Numerical studies were performed to study smoke movement,and operating strategies for the emergency ventilation system were optimized,and the feasibility of using jet fans to control smoke backlayering was analyzed.The main works of this paper are as follows:(1)Characteristics,developing trends,and applicability of different road tunnel ventilation systems were introduced,and smoke propagation and measures to prevent smoke backlayering were analyzed,and the control strategies for emergency ventilation systems were discussed.(2)Road tunnel fires with a heat release rate of 30 MW were simulated numerically using fire dynamics simulation software FDS.Velocity fields,temperature fields,concentration fields of CO,and visibility were analyzed.For a fire located in the curved region,smoke backlayering was much more severe than that in the straight region,smoke propagated slower and the temperature rise in the downstream of fires were much higher than that for a fire in the straight region.(3)According to the numerical simulation results,two improved operating strategies and one improved operating strategy for the emergency ventilation system were put forward for fires located in the curved region and for fires located in the straight region,respectively.Numerical simulation were conducted correspondingly.Simulation results showed that smoke backlayering was 20 m shorter for fires located in the straight region and 50 m shorter for fires located in the curved region.(4)On the basis of the optimizing analyses of the operating strategies for theexisting semitransverse emergency ventilation system,numerical simulations were conducted for the strategy of installing ceiling jet fans along the curved region of the tunnel to increase longitudinal velocity and reduce backlayering length,the feasibility of using jet fans to improve smoke management in the curved region of a road tunnel was studied preliminarily.Simulation results showed that the range of influence and the harmfulness for fires located in the curved region of the tunnel were more severe than that for fires located in the straight region.For fires located in curved regions of road tunnels,special measures must be implemented instead of using operating strategies for emergency ventilation system for fires located in the straight regions of road tunnels mechanically.