复杂结构隧道火灾烟气逆流与温度分布的数值模拟
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摘要
隧道结构对火灾具有一定的影响,为了得到大曲率、变坡度复杂结构隧道火灾的烟气特性,依托深圳市某长大公路隧道建设工程,建立隧道模型,利用Star-CD/CCM~+数值模拟软件的烟火向导模块,对不同通风速度下的重型货车火灾进行了模拟研究,分析了不同通风速度下隧道内的纵向温度分布规律。结果表明:火灾热释放速率为30 MW时,无通风条件下,火灾烟气的最高温度位于隧道顶棚下方20 cm处,火源正上方的温度最大达到1 190℃,隧道坡度的存在使得火源上游烟气逐渐向下游扩散,下游烟气温度在300 s后保持在500℃以上,该高温会对隧道结构造成一定的损伤;控制烟气逆流的临界风速为4. 0 m/s,大于由Wu&Baker经验公式得到的值,表明隧道曲率对流场运动有一定的抑制作用;在该临界风速的作用下,烟气向火源下游扩散,扩散速度为6 m/s,烟气的最高温度降低至550℃,且位置向火源下游偏移6 m。建议火源下游行驶车辆的疏散逃生速度大于6m/s。
This paper is aimed at making a numerical simulation for the tunnel fire by using the software known as the Star-CD/CCM~+ of fire and smoke wizard module. The goal of the paper is to simulate the fires that take place with the heavy goods vehicles moving up at the different longitudinal ventilation velocities in the closed tunnel. Since in most cases,tunnel structure is characteristic with the complicated curvature structures and variable slopes,they may have obvious impact on the fire prevention and salvation. Therefore,we have established a tunnel model so as to identify and determine the smoke-fire characteristic features based on a highway tunnel construction project in Shenzhen with long-range tunnels. To achieve the purpose,we have made first of all an exploration of the longitudinal temperature distribution regularity with the tunnel at different ventilation velocity rates.Comparing the smoke movement conditions at the different longitudinal ventilation structures,we have gained the critical ventilation velocity rates under 30 MW fire conditions,and then worked out the safety and in-time evacuation possibilities of the emergency evacuation of the downstream vehicles under the operation of the critical ventilation. The results of our study show that,if the critical heat release rate of the fire are supposed to be 30 MW,the highest temperature on the spot of the fire should at least take place at the 20 cm below the tunnel top in a state of full block with no ventilation at all,and the highest temperature ought to go up instantly and quickly reach 1 190 ℃ in the central part of the fire source. In such a situation,due to the presence of the tunnel slope,the smoke from the upstream of the fire source may gradually get diffused in a downward way,with the temperature of the smoke from there may stay at about 500 ℃ for 300 s since the fire broke out,which is likely to lead to the damage to the tunnel structure. In front of the danger risk,the critical ventilation range for preventing the back layer fire-smoke should be 4 m/s,which is greater than the ventilation rate obtained by Wu &Baker's empirical formula. This may imply that it is possible for the tunnel winding to have a certain inhibition effect on the fire spreading. And,it is also under the condition of the critical ventilation that the smoke may diffuse in a downward way from the fire source at a diffusion velocity of 6 m/s at the highest temperature of the smoke-fire spreading and then lower down to 550 ℃,with the position being lowered to 6 m downstream of the fire source. This may suggest that the evacuation speed of the vehicles traveling downwardly from the fire source should be greater than 6 m/s.
This paper is aimed at making a numerical simulation for the tunnel fire by using the software known as the Star-CD/CCM~+ of fire and smoke wizard module. The goal of the paper is to simulate the fires that take place with the heavy goods vehicles moving up at the different longitudinal ventilation velocities in the closed tunnel. Since in most cases,tunnel structure is characteristic with the complicated curvature structures and variable slopes,they may have obvious impact on the fire prevention and salvation. Therefore,we have established a tunnel model so as to identify and determine the smoke-fire characteristic features based on a highway tunnel construction project in Shenzhen with long-range tunnels. To achieve the purpose,we have made first of all an exploration of the longitudinal temperature distribution regularity with the tunnel at different ventilation velocity rates.Comparing the smoke movement conditions at the different longitudinal ventilation structures,we have gained the critical ventilation velocity rates under 30 MW fire conditions,and then worked out the safety and in-time evacuation possibilities of the emergency evacuation of the downstream vehicles under the operation of the critical ventilation. The results of our study show that,if the critical heat release rate of the fire are supposed to be 30 MW,the highest temperature on the spot of the fire should at least take place at the 20 cm below the tunnel top in a state of full block with no ventilation at all,and the highest temperature ought to go up instantly and quickly reach 1 190 ℃ in the central part of the fire source. In such a situation,due to the presence of the tunnel slope,the smoke from the upstream of the fire source may gradually get diffused in a downward way,with the temperature of the smoke from there may stay at about 500 ℃ for 300 s since the fire broke out,which is likely to lead to the damage to the tunnel structure. In front of the danger risk,the critical ventilation range for preventing the back layer fire-smoke should be 4 m/s,which is greater than the ventilation rate obtained by Wu &Baker's empirical formula. This may imply that it is possible for the tunnel winding to have a certain inhibition effect on the fire spreading. And,it is also under the condition of the critical ventilation that the smoke may diffuse in a downward way from the fire source at a diffusion velocity of 6 m/s at the highest temperature of the smoke-fire spreading and then lower down to 550 ℃,with the position being lowered to 6 m downstream of the fire source. This may suggest that the evacuation speed of the vehicles traveling downwardly from the fire source should be greater than 6 m/s.
引文
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[7] WANG Feng(王峰). Research on key parameters of operating ventilation in curved road tunnels(曲线公路隧道营运通风关键参数研究)[D]. Chengdu:Southwest Jiaotong University,2008.
[8] XI Y H,MAO J,BAI G,et al. Safe velocity of on-fire train running in the tunnel[J]. Tunnelling&Underground Space Technology Incorporating Trenchless Technology Research,2016,60:210-223.
[9] XI Y H,CHOW W K,MAO J. Aerodynamics simulation on density jump in a long corridor fire[J]. Tunnelling&Underground Space Technology Incorporating Trenchless Technology Research,2015,50:23-31.
[10] XI Yanhong(郗艳红),MAO Jun(毛军). Effects of moving speed of on-fire subway train on heat release rate[J]. Journal of South China University of Technology:Natural Science Edition(华南理工大学学报:自然科学版),2016,44(4):123-129.
[11] JUSEOG K,CHANHOON Y,SUNGWOOK Y,et al.Determination of the applicable exhaust airflow rate through a ventilation shaft in the case of road tunnel fires[J]. Safety Science,2010,48(6):722-728.
[12] WU Y,BAKER M Z A. Control of smoke flow in tunnel fires using longitudinal ventilation systems—a study of the critical velocity[J]. Fire Safety Journal,2000,35(4):363-390.
[13] ATKINSON G T,WU Y. Smoke control in sloping tunnels[J]. Fire Safety Journal,1996,27(4):335-341.
[14] LI Kaiyuan(李开源),HUO Ran(霍然),LIU Yang(刘洋). Study on the temperature change of the plume tipping zone under longitudinal ventilation of tunnel fire[J]. Journal of Safety and Environment(安全与环境学报),2006,6(3):38-41.
[2] LI Junmei(李俊梅),XU Peng(许鹏),LI Yanfeng(李炎峰),et al. Numerical and experimental study of the critical velocity in titled tunnel[J]. Journal of Beijing University of Technology(北京工业大学学报),2017,43(11):1706-1712.
[3] HU L H,HUO R,PENG W,et al. On the maximum smoke temperature under the ceiling in tunnel fires[J].Tunnelling&Underground Space Technology Incorporating Trenchless Technology Research,2006,21(6):650-655.
[4] YI Liang(易亮),YANG Yang(杨洋),XU Zhisheng(徐志胜),et al. Experimental study on maximum temperature of vault smoke in longitudinally ventilated highway tunnel fire[J]. Journal of Combustion Science and Technology(燃烧科学与技术),2011,17(2):109-114.
[5] YAN Zhiguo(闫志国),YANG Qixin(杨其新),ZHU Hehua(朱合华),et al. An experimental study of fire hazard at the Qinling highway tunnel[J]. China Civil Engineering Journal(土木工程学报),2005,38(11):96-101.
[6] ATKINSON G T,WU Y. Smoke control in sloping tunnels[J]. Fire Safety Journal,1996,27(4):335-341.
[7] WANG Feng(王峰). Research on key parameters of operating ventilation in curved road tunnels(曲线公路隧道营运通风关键参数研究)[D]. Chengdu:Southwest Jiaotong University,2008.
[8] XI Y H,MAO J,BAI G,et al. Safe velocity of on-fire train running in the tunnel[J]. Tunnelling&Underground Space Technology Incorporating Trenchless Technology Research,2016,60:210-223.
[9] XI Y H,CHOW W K,MAO J. Aerodynamics simulation on density jump in a long corridor fire[J]. Tunnelling&Underground Space Technology Incorporating Trenchless Technology Research,2015,50:23-31.
[10] XI Yanhong(郗艳红),MAO Jun(毛军). Effects of moving speed of on-fire subway train on heat release rate[J]. Journal of South China University of Technology:Natural Science Edition(华南理工大学学报:自然科学版),2016,44(4):123-129.
[11] JUSEOG K,CHANHOON Y,SUNGWOOK Y,et al.Determination of the applicable exhaust airflow rate through a ventilation shaft in the case of road tunnel fires[J]. Safety Science,2010,48(6):722-728.
[12] WU Y,BAKER M Z A. Control of smoke flow in tunnel fires using longitudinal ventilation systems—a study of the critical velocity[J]. Fire Safety Journal,2000,35(4):363-390.
[13] ATKINSON G T,WU Y. Smoke control in sloping tunnels[J]. Fire Safety Journal,1996,27(4):335-341.
[14] LI Kaiyuan(李开源),HUO Ran(霍然),LIU Yang(刘洋). Study on the temperature change of the plume tipping zone under longitudinal ventilation of tunnel fire[J]. Journal of Safety and Environment(安全与环境学报),2006,6(3):38-41.