【作者】 李林杰；

【导师】 孙金华； 纪杰；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2014， 博士

【摘要】 近年来,我国兴建了越来越多的高层建筑,且伴随着高层建筑火灾事故频发,造成了大量的人员伤亡和财产损失,统计结果表明,火灾中有超过百分之八十的人员死亡是由于有毒烟气造成的。高层建筑由于建筑高,扑救和控制火势难度大,人员疏散困难。建筑内部的竖向通道(电梯井,楼梯井,管道井)容易成为火势迅速蔓延的重要途径。火灾烟气在高层建筑的竖向通道内运动主要驱动力有烟囱效应,湍流混合运动,热浮力,另外还容易受到外界风的影响。因此研究这几种驱动力作用下高层建筑火灾烟气的运动特性以及这几种作用力作用下房间内火源的燃烧,对于高层建筑火灾防治有着重要意义。本文围绕烟囱效应,湍流混合作用,热浮力,外界风等作用力,采用实验研究与理论分析相结合的方式,利用大空间的1：3楼梯井实验台以及1：3火溢流实验台,开展了相应的研究。具体工作包括：研究烟气前锋在顶部开放和顶部封闭的楼梯井内的上升时间,结合理论分析,得到烟气前锋上升无量纲时间与楼梯井无量纲高度的定量关系式,结果表明,开放楼梯井和封闭楼梯井内的烟气前锋上升时间分别与火源功率的三分之一次方成反比,与无量纲上升高度的1.227次方和2.135次方成正比,与烟气在竖井中的上升时间进行对比,发现烟气在楼梯井中上升比竖井中慢。开放楼梯井内的烟气温度在经历一段时间之后,会进入一个稳定的阶段,即楼梯井内的温度不随时间变化,分析稳定阶段楼梯井内温度的无量纲温升与无量纲高度的关系,发现无量纲温升随着无量纲高度的增加而指数衰减,衰减的系数近似与楼梯井内的烟气的质量流量成反比,并通过实验数据验证了这一点。分析楼梯井温度稳定分布情况下内外的压强差和楼梯井开口处空气和烟气的流速,得到了楼梯井内烟气流动的流动系数,流动系数的值表明,楼梯井的结构对楼梯井内烟气流动的阻力非常大。研究了烟气在顶部封闭的竖向通道内湍流混合作用下的运动,前人研究封闭竖向通道内流体湍流混合运动时未考虑壁面传热,本文通过理论分析建立了考虑壁面传热的竖向通道内流体湍流混合运动方程。在1：3尺寸的楼梯井实验台中,开展了一系列火源产生的热浮力羽流在顶部封闭的楼梯井中湍流混合运动实验,并将实验数据与前人及本文推导的湍流混合运动方程的数值求解结果进行对比。对比结果表明,本文提出的湍流混合运动方程可以较好地模拟强热浮力羽流在顶部封闭的竖向楼梯井内的湍流混合运动,前人的模型计算的结果比实验值偏高。研究了多个开口的楼梯井在火灾情况下中性面的位置,通过实验中测得的温度数据,风速数据以及拍摄的视频,判定了多开口楼梯井中性面的位置。结合楼梯井内的温度分布,利用流体静力学方程,伯努利方程和质量守恒方程,计算火灾情况下多个开口楼梯井的中性面位置,计算结果和实验得到的结果对比,发现两者符合得较好。结果表明在相同开口状况下,不同火源功率对楼梯井中性面位置的影响较小,火源功率较小时,楼梯井中性面高度会偏低。在三个开口的楼梯井中,楼梯井的中性面位置主要由楼梯井的开口状况决定。利用1：3尺寸的火溢流实验台,研究了在着火房间热浮力作用下,着火房间外的溢流火焰形态,分析了溢流火焰在水平和竖直方向上的长度,建立了火焰尺寸与火源功率以及着火房间开口状况之间的耦合关系式,并分析了溢流火焰震动频率与房间开口状况之间的关系。研究了在外界风和着火房间热浮力共同作用下,着火房间内的通风状况,以及通风状态对着火房间内燃烧的影响。更多还原

【Abstract】 In the last decades, many skyscrapers have been constructed all over the world, with the fire occurred frequently which is responsible for a number of casualties and property losses. When high-rise buildings catch fire, it is difficult to put out the fire and evacuate the people. There are many vertical shafts in high-rise buildings, such as elevator wells and stairwells. These shafts may be paths for smoke spread in case of fires. Stack effect and turbulent mixing are the two physical mechanisms which are primarily responsible for vertical motion of buoyant gas within a vertical shaft. In addition, the external wind can also affect the buoyant gas move in the buildings. Statistics showed that more than80percent deaths in fire were caused by toxic gases, such as carbon monoxide. Therefore, it is important to study the motion of buoyant gas driving by these mechanisms and the motion of buoyant gas influence on the fire burning for the fire prevention and control.In this dissertation, Experimental researches, theoretical analysises were carried out to investigate the motion of buoyant gas driving by stack effect, turbulent mixing and external wind. The experiments were carried out in a1:3scale stairwell model and a1:3scale room model. Specific work includes:A set of burning experiments were conducted in a1/3scale stairwell to investigate the rise time of fire-induced buoyant plumes and the discharge coefficient of the stairwell. Results show that the time for the front of a buoyant plume to reach a given height from a fire source is inversely proportional to the1/3power of the heat release rate and proportional to the1.203, and2.129power of the height in the stairwell with top vent open and closed, respectively. The experimental results were correlated by the non-dimensional time and non-dimensional height. Results are proposed to predict rise time of fire plume fronts. Discharge coefficient of the stairwell was calculated based on the velocity at the openings of the stairwell and the temperature distribution in the stairwell. A value of0.23was proposed to be the discharge coefficient of the stairwell.Previous studies on the turbulent mixing process in closed shafts did not take into account the heat transfer from the hot buoyant plume to the boundaries such as walls. In this paper, a modified theoretical model predicting the one-dimensional turbulent mixing process in vertical shafts is proposed with the heat transfer from the hot buoyant plume to the boundaries involved. A set of small scale experiments were conducted to validate this model. A propane gas burner was used as the heat source to provide steady heat release rate. The comparison between the model predicted and experimental results show that the Cooper’s turbulent mixing model which didn’t consider the heat transfer from boundary gives higher predictions compared to the temperature data measured in experiment whereas the current modified model leads to more comparable results. Therefore the heat transfer process between the plume and the boundaries should be included in any modeling for the case of buoyant plume rising in closed shafts.A set of burning experiments were conducted in a1/3scale stairwell to investigate the characteristics of fire induced buoyant plume movement in a12-storey stairwell with three vents. Results show that the temperature of fire plume generally decreases with height in the stairwell on the steady state, and the distribution of smoke temperature in stairwell is mainly determined by the heat release rate (HRR) of fire source. The variation trends of temperature and velocity profiles measured at the middle opening were used to determine the location of neutral plane, and the determined results were confirmed by the pictures of flow field (lightened by the laser sheet). Based on the temperature distribution in stairwell and theoretical analysis, the location of neutral plane in the stairwell was calculated and the results were in good agreements with experimental results. The location of the neutral plane was mainly affected by the height of the middle opening. For cases with the same middle opening, the heat release rate of fire source weakly affected the location of neutral plane.The ejecting fire behavior from compartment with two openings under thermal forces and external wind was revealed. The experiments were carried out in a1:3scale compartment room to study the flame ejected from opening of a building compartment on the effect of thermal forces. Based on two character length of the compartment room, the ejected flame length and height are correlated by the non-dimensional heat release rate. When the flame ejected from opening of the compartment, the relationship between the shape of the opening and ejected flame oscillation frequency was revealed. Tthe impact of external wind couple with the thermal forces on the ventilation of the compartment which influence the mass loss rate of the oil pool were also revealed.更多还原