【作者】 吴珂；

【导师】 孙志林； 黄志义；

【作者基本信息】 浙江大学 ， 防灾减灾工程及防护工程， 2008， 博士

【摘要】 长隧道火灾造成的灾难性后果已引起各国学者的广泛关注。随着我国经济持续高速增长及隧道长大化发展,隧道火灾事故的发生几率将呈上升趋势。隧道火灾释放出大量的高温有毒烟气,不仅对人员造成巨大伤害,且会使隧道结构受损而降低隧道的整体稳定性。因此,研究长隧道火灾烟气的运动规律及结构防火安全性无疑具有重要的意义。本文在总结国内外隧道火灾研究成果和经验的基础上,应用多相湍流反应流体动力学、热分析动力学等学科交叉手段,通过理论分析、数值模拟、比尺模型试验、热重试验、红外光谱分析试验等方法对长隧道火灾过程及结构防火等问题进行深入地研究。取得主要成果如下:（1）本文基于湍流燃烧理论构建的隧道火灾三维数学模型弥补了传统体积热源模型未考虑火源燃烧过程、只能模拟低风速隧道火灾之不足。利用该模型首次揭示燃烧对隧道火灾流场结构的塑造作用,并定量分析烟气的脉动效应。LES能捕捉到受迫火焰的三个分区——连续火焰区、间歇火焰区和浮力羽流区,刻画出火源上方温度的大幅波动和烟气的脉动细节。对于复杂的湍流问题,LES优于k-ε模型。（2）通过数值模拟系统分析隧道火灾烟气的三维运动规律,在纵向排烟模式下,烟气羽流运动受浮力和强制对流的共同作用,可分为三维螺旋涡流区、二维均匀分层区和一维纵向蔓延区3个特征阶段:而集中排烟模式存在双向不对称、双向对称和单向3种排烟方式。（3）首次进行沥青材料燃烧的热重和红外光谱分析试验,揭示沥青及其胶浆的燃烧机理、特征,并对其燃烧气态产物成分、释放规律进行分析,发现:1)沥青胶浆的燃烧过程可分为稳定阶段、活泼挥发分燃烧、二次挥发分燃烧、残炭燃烧4个阶段;沥青的燃烧过程可分为稳定阶段、活泼挥发分燃烧、二次挥发分及残炭燃烧3个阶段:2)沥青及其胶浆燃烧的主要气态产物为CO₂、CO、NO、NO₂及SO₂。其中,CO主要在活泼挥发分析出燃烧阶段产生;SO₂的排放量主要取决于样品的含硫量;活泼挥发分含量和空气流量对沥青及其胶浆燃烧气态产物的释放规律有较大影响,增加空气流量虽能减少CO的产生,但会增加碳黑的排放量。热动力学分析表明,对于沥青胶浆燃烧的第二至四阶段,三维扩散模型的Z-L-T方程、Jander方程、一维相边界反应模型的Mampel Power法则分别是最概然的机理函数;而沥青燃烧的第二、三阶段的最概然机理函数则为三级反应级数模型和满足Mampel Power法则的一维相边界反应模型;（4）采用数值模拟与物理试验相结合的方法对隧道火灾过程中的结构安全性进行分析:1)热分析试验测得室温固化植筋胶的玻璃化转变温度为106.2℃,据此通过数值计算获得,当植筋位置与受火面之间的混凝土厚度超过22cm时,植筋胶用于隧道工程是安全的;2)低于10MW规模的隧道火灾基本不会引燃沥青混凝土路面,对20和50MW规模的隧道火灾,只要分别保持2和4m·s^-1的通风,也基本能确保沥青路面不被引燃。沥青混凝土路面发生燃烧对隧道火灾的影响是有限的,其最大释热率不超过火灾规模的1.7%;3)在集中排烟模式下,顶隔板上表面可能发生爆裂的区域要远大于其下表面,二者间差距随火灾规模的增大而增大。受混凝土不良导热性影响,顶隔板上下表面始终存在着较大温差,由此产生的巨大温度应力可能导致顶隔板在隧道火灾过程中发生破坏。更多还原

【Abstract】 The disaster caused by long tunnel fires has aroused extensive attention. With the rapid growth of economy and the build of longer and longer tunnels, the risk of tunnel fires will increase consequentially. A mass of high-temperature toxic gas released by tunnel fires not only causes great harm to persons, but also damages the tunnel’s structure which will reduce the overall stability of tunnel. Therefore, studies on the movement characteristics of smoke and the structure fire-resistant security of long tunnels are of great significance.Based on conclusion of tunnel fires researches, applying multi-discipline integration analysis, such as multiphase turbulent reacting fluid dynamics and thermal analysis kinetics, the processes of long tunnel fires and the structure fireproofing were studied through theoretical analysis, numerical simulation, scale model test, thermogravimetric experiment and infrared-spectrum analysis. A series of valuable achievements were got.（1） The three-dimensional mathematical model of tunnel fires based on the theory of turbulent combustion can make up for the traditional VHS model which ignores combustion effect and only simulate tunnel fires under low ventilation velocity. Based on the current model, the effect of combustion on the flow structure in tunnel fires was revealed for the first time, and the pulsation of smoke was quantitatively analyzed. LES can capture three zones of forced flames - continuous flame, intermittent flame and plume zone, and portray the large fluctuations of temperature and the detail pulse of the smoke flow at the top of the fire source. Therefore, LES has many advantages than k -εmodel for complex turbulent problem.（2） Three-dimensional movement characteristics of smoke were analyzed by numerical simulations. Under the longitudinal exhaust, the movement of smoke plume influenced by both buoyancy and forced convection can be divided into three special sections: 3D spiral vortex flow section, 2D stratified flow section and 1D longitudinal spreading section. While under the central exhaust, two-way asymmetric, two-way symmetric and one-way manner are existed. （3） It was the first time that the thermogravimetric experiment and infrared-spectrum analysis on combustion of asphalt and its cement were carried out, in order to reveal the mechanism and characteristics of samples combustion, and analyze the component and releasing law of its gaseous products, which showed as following:1) The combustion process of asphalt cement has four phases including heating, oxidation of primary volatiles, oxidation of secondary volatiles, and oxidation of residual carbon. The combustion process of asphalt typically has three phases, including heating, oxidation of primary volatiles, and oxidation of secondary volatiles and residual carbon.2) Main gaseous products of asphalt and its cement combustion are CO₂, CO, NO, NO₂ and SO₂. Among these species, CO is mainly produced during the oxidation of volatiles, and the emission of SO₂ is mostly related with the sulfur content in the sample. The active volatile content and the air flux have significant impacts on the releasing law of gaseous products. Increasing air flux could reduce CO emission, otherwise it would increase soot.Kinetic analysis shows that the most probable kinetic function describing the last three phases of asphalt cement combustion are Z-L-T equation, Jander equation of 3D diffusion model and Mampel Power law based on 1D surface reaction model respectively, and the model F3 and R1 are considered as the most suitable kinetic mechanisms respectively for the second and the third phases of asphalt combustion.（4） The security of structure in tunnel fires was analyzed through numerical simulations and experiments: 1) Thermal analysis tests found that the glass transition temperature of adhesive was 106.2℃. based on this the numerical calculations showed that applying adhesive to tunnel engineering was safe when the thickness of concrete between planting-bar and concrete surface facing fire was over 22 cm. 2) when the fire load is lower than 10 MW Asphalt pavement will almost not to be ignited which can also be basically insured when the fire load is 20 or 50 MW, as long as ventilation velocity is kept at 2 or 4 m·s^-1 respectively. The influence of asphalt concrete pavement combustion is limited on tunnel fires and its heat release rate won’t exceed 1.7 percent of fire load. 3) Under the central exhaust mode, the areas where could burst on the top surface of head clapboard are much larger than which on the bottom surface, consequently the difference between them would increase along with the increasing fire loads. Affected by weak conduction of concrete, the large temperature difference would be always existed between the top and bottom surface of head clapboard, thus the head clipboard may be destroyed in tunnel fires by the resulting huge temperature stress.更多还原