纵向通风对隧道火灾烟气层结构及竖井排烟的影响机制研究

发布时间：2018-04-03 16:25

  本文选题：隧道火灾　切入点：烟气热分层　出处：《中国科学技术大学》2017年硕士论文

【摘要】：在我国经济飞速发展的大环境下,城市化进程正平稳有序地进行,为了降低区域人口增长带来的交通压力,地下空间的开发使用便成为城市发展的重要方向。近几年来,全国各城市修建大量城市公路隧道以及地铁隧道,为人们的交通出行带来极大便利。但随之而来的是,城市中各种隧道存在的火灾隐患以及已经出现的火灾事故给隧道消防工作的开展带来了巨大挑战。在火灾事故中,因吸入烟气窒息死亡的人数比例达到85%,对于隧道火灾,烟气运动规律研究以及高效排烟模式的选择对降低火灾事故损失、救援工作的开展具有重要意义。尽管前人已在此方面进行研究,但隧道中纵向风作为一重要边界条件,在其影响下的烟气运动规律,竖井区域流场、温度场结构,竖井排烟效率与无通风时有很大不同。因此本文通过进行理论分析,开展小尺寸实验以及全尺寸模拟实验,研究在纵向通风影响下的隧道火灾烟气热分层以及不同边界条件对竖井排烟的作用规律,主要内容为以下几个方面:1、烟气热分层及其判定方法对比。通过开展理论分析以及小尺寸实验,对隧道火灾中烟气在不同风速影响下的热分层现象及其变化规律、结构特点进行研究:对于5.73 kW火源,纵向通风风速达到0.0961m/s时烟气层稳定性开始被破坏,在风速超过0.226 m/s时完全紊乱。隧道火灾烟气层界面高度在纵向通风影响下为下降再升高,2.30 kW、5.74 kW、9.18 kW三种火源功率,其风速拐点分别为0.485 m/s、0.629 m/s、0.629 m/s。对不同热层判定方法结论进行对比分析:对于N系数法,建议N取值为30;低风速下可考虑无量纲温度法;浮力频率法判定结果偏低。2、对纵向通风影响下的竖井排烟烟气卷吸情况进行分析,采用小尺度实验研究纵向通风对隧道竖井区域烟气流场结构以及吸穿现象的影响规律。对于低高度竖井或纵向通风较大的工况,会出现外界冷空气自竖井顶部卷吸进入竖井内部的现象,影响烟气排出。在吸穿临界条件的判定中,无量纲数Fcritical=1.5在无风条件下尚可适用,但在纵向通风条件下不再适用,而Ricritical1.4则不受通风影响。3、通过开展数值模拟,对纵向通风、竖井高度、竖井排列方式影响下的竖井排烟效率、竖井内部流场及温度场分布情况进行研究:小于3m的竖井排烟量随着纵向通风的增加而降低;当竖井高度超过3m时,竖井排烟量随着纵向通风的增加先上升后降低,排烟量在风速为1.5～2 m/s时达到最大值。在无纵向通风条件下,新布置方式对吸穿现象的抑制作用明显,但当竖井在纵向风作用下达到最大排烟量时,布置方式对竖井的排烟量的提升有限。
[Abstract]:In order to reduce the traffic pressure brought by regional population growth, the development and use of underground space has become an important direction of urban development.In recent years, a large number of urban road tunnels and subway tunnels have been built in cities of China, which bring great convenience to people's transportation.However, fire hazards and fire accidents in various tunnels in cities have brought great challenges to the development of tunnel fire protection work.In the fire accident, the proportion of death caused by smoke inhalation asphyxiation reached 85. For tunnel fire, the study of smoke movement law and the choice of efficient smoke exhaust mode are of great significance to reduce the loss of fire accident and carry out rescue work.Although the previous researches have been carried out in this field, the vertical wind in tunnel is an important boundary condition, under its influence, the smoke movement law, the flow field in the shaft area, the structure of temperature field, the efficiency of exhaust smoke in the shaft are very different from those in the absence of ventilation.Therefore, through theoretical analysis, small scale experiments and full-scale simulation experiments, the thermal stratification of flue gas in tunnel fires under the influence of longitudinal ventilation and the effect of different boundary conditions on the exhaust smoke of vertical wells are studied in this paper.The main contents are as follows: 1, comparison of flue gas thermal stratification and its judging methods.Through theoretical analysis and small scale experiments, the thermal stratification phenomenon and its variation law of flue gas in tunnel fire under the influence of different wind speed are studied. The structural characteristics are as follows: for 5.73 kW fire source,The stability of the flue gas layer begins to be destroyed when the longitudinal ventilation wind speed reaches 0.0961m/s and is completely disturbed when the wind speed exceeds 0.226 m / s.Under the influence of longitudinal ventilation, the interface height of smoke layer of tunnel fire is decreased and then increased by 2.30 kW 5.74 kW / 9.18 kW, and the inflection point of wind velocity is 0.485 m / s ~ 0. 629 m / s / s ~ 0. 629 m / s respectively.The conclusions of different thermosphere determination methods are compared and analyzed: for the N coefficient method, the value of N is suggested to be 30, and the dimensionless temperature method can be considered at low wind speed.The method of buoyancy frequency is low. 2. The smoke entrainment of vertical shaft under the influence of longitudinal ventilation is analyzed. The influence of longitudinal ventilation on the structure of flue gas flow field and the phenomenon of suction in tunnel shaft is studied by small scale experiment.For low height shaft or large longitudinal ventilation conditions, the phenomenon of external cold air entrainment from the top of the shaft into the shaft interior will affect the flue gas discharge.In determining the critical condition of suction, the dimensionless Fcritical=1.5 can be applied under the condition of no wind, but not in the condition of longitudinal ventilation, while Ricritical1.4 is not affected by ventilation.The distribution of flow field and temperature field in the vertical shaft under the influence of the vertical well arrangement mode is studied: the smoke discharge quantity of the shaft with the increase of vertical ventilation decreases with the increase of vertical ventilation, and when the height of the shaft is more than 3m, the distribution of the flow field and the temperature field in the shaft is studied: when the height of the shaft is more than 3m,With the increase of vertical ventilation, the exhaust volume of the shaft first rises and then decreases, and the exhaust volume reaches the maximum when the wind speed is 1.5 ~ 2 m / s.Under the condition of no longitudinal ventilation, the new arrangement can restrain the phenomenon of suction obviously, but when the shaft reaches the maximum amount of exhaust smoke under the action of longitudinal wind, the way of layout has a limited effect on the increase of the exhaust volume of the shaft.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U453.5;U458

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