【作者】 朱杰；

【导师】 周允基；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2008， 博士

【摘要】 21世纪,世界经济和科学技术飞速发展,城市人口日趋密集,高层、超高层建筑不断增加,特别是在大城市、超大城市,超高层建筑已经成为一个城市现代化程度的的重要标志之一。超高层建筑中存在电梯井、楼梯井、管道井、电缆井等多种竖向通道,一旦发生火灾,在烟囱效应、热烟浮力以及近地风场的共同作用下,这些竖井将会极大地促进火势及烟气的蔓延,从而造成严重的危害。然而,目前世界上尚无完整系统的超高层建筑防火设计规范,尤其我国目前仅有《高层民用建筑防火设计规范》,也主要只是针对高层建筑制定的,超高层建筑火灾的一系列特有问题并没有包括进来。而关于火灾烟气运动的力源机理,国际上也没有开展过完善系统的研究,尤其针对超高层建筑竖井结构的研究更是空白。因此,开展对超高层建筑竖井内烟气驱动力及蔓延规律的研究具有重要的现实意义。本文在前人研究的基础上,依托香港裘挫基金和中国科技大学火灾科学国家重点实验室及西南交通大学的实验条件,并自主加工2.7m高的小尺寸竖井实验台,以现场实验和模拟实验相结合的研究方法开展了超高层建筑竖井内烟气驱动力、不同火源位置及不同侧向开口情况下烟气运动规律的研究,并在查阅大量文献资料基础上,运用相似理论和数值分析方法进行了相应的理论分析。利用小尺寸竖井实验台对单纯烟囱效应、单纯热烟浮力、室外风影响、综合作用等情况进行实验及数值模拟研究,研究所得结论如下:单纯烟囱效应随着竖井内外温差的增大而增大,在无外界热源维持竖井内外温差的情况下,烟囱效应将迅速消失,且当内外温差相差不大时,逆烟囱效应造成的气体流动较正烟囱效应的快;单纯热烟浮力仅在烟气蔓延前期起主导作用,随后温度升高后,竖井内外形成一定的温差,烟囱效应起主导作用;近地风场会对竖井内烟气蔓延产生极大的影响,但在开口位置与风向的不同组合条件下,对烟气蔓延作用的影响差别较大,风向对竖井内烟气蔓延的影响大小顺序为:迎风面＞侧面＞背风面;在各种驱动力共同作用下,能极大地促进竖井内烟气的蔓延,增加竖井内烟气量,改变烟气在竖井内的蔓延途径,且在整个实验过程中,三种作用均对火势及烟气的蔓延有较大的影响。对不同火源位置条件下竖井结构内的烟气运动规律进行实验和数值模拟研究,得出了火源位置因子与最高温度的分布关系及最高温度与所对应的位置高度的拟合函数,研究所得结论如下:随着火源位置的不断升高,中性面的位置也在上移;火源位置对烟气的蔓延有较大影响,其产生烟气均向上部区域蔓延,而其下部区域基本无烟;竖井内的最高温度与火源位置因子(h/H)呈反比例关系,火源位置越高,比例因子越大,竖井内的最高温度就越低。对不同侧向开口条件下竖井结构内的烟气运动规律进行实验和数值模拟研究,研究表明:竖井内烟气运动过程是随着竖井结构的不同而变化的,主要取决于进气口及侧向开口打开情况;仅有中性面以下侧向开口开放时,中性面以下侧向开口数与竖井烟气混合效果及呈正比关系;仅有中性面以上侧向开口开放及上下均有侧向开口开放时,下部烟气会以墙壁羽流形式沿开口墙面蔓延,除起火层外,在中性面以下的所有楼层中相对无烟,直到火灾的产烟量超过流动所能排放的烟量;封闭竖井内部烟气运动最为缓慢,顶部温升相对较慢;全开放竖井内,中性面以下侧向开口卷吸空气程度较大,烟气流动最快,竖井顶部温度最低,温度梯度比较一致,稳态情况下近似为一特定的值。本文研究所得出的这些结论,具有一定的可操作性和实用性,为超高层建筑火灾防治相关规范的制订提供了一定的理论依据。更多还原

【Abstract】 With the rapid development of global economy, science and technology, many high-rise and even ultra high-rise buildings are built or to be built in dense urban areas in large cities or city groups over the world. Ultra high-rise buildings have already become one of the important symbols of urban modernization. There are stairwells, pipe and cable ducts, and other vertical channels in those ultra high-rise buildings. These shafts will facilitate the spread of fire and smoke in a fire by combining natural driving forces with stack effect, smoke buoyancy and wind action. However, there is still not yet a workable fire safety system for ultra high-rise buildings in the world. In China, only "Fire Protection Design Standard for High-Rise Civil Constructions" is formulated particularly for high-rise constructions. It does not include a list of specific fire safety provisions for protecting against ultra high-rise building fires. There are no complete systematic research on the mechanism of fire and smoke movement in the world, and very little research on vertical shafts in ultra high-rise buildings. Therefore, carrying out the study of smoke driving forces and the mechanism of smoke spread in the shafts of ultra high-rise buildings is very important.With the support of the Croucher Foundation in Hong Kong, the State Key Laboratory of Fire Science in the University of Science and Technology of China, The Hong Kong Polytechnic University and the Southwest Jiaotong University, experiments were carried out to study smoke movement and the associated driving forces in this thesis. Efforts were made on reviewing previous studies first. Scale model experiments on a 2.7 m tall vertical shaft were carried out. The natural smoke driving forces, the movement mechanism of smoke under the conditions of different fire positions and lateral openings in the shaft of an ultra high-rise building were investigated by combining scale model experiments and numerical models. Similarity theory and numerical analysis method were applied with reference to the literature.By using a small-scale shaft model, the effect of simple hot smoke buoyancy, outdoor air, their integrated effect and others were studied. From this part of study, it is found that the simple stack effect increases as the temperature difference between the inside and outside of the shaft becomes higher. Without the external heat source maintaining the temperature difference, stack effect will disappear quickly. When the temperature difference is not obvious, the gas flow under the reverse stack effect is faster than under the stack effect. The simple hot smoke buoyancy plays a leading role in the early stage of smoke spreading. As the temperature increases, there is a temperature difference between inside and outside of the shaft. Therefore, stack effect plays a leading role. The near-ground vent influences the smoke spreading inside the shaft significantly, but in the integrated condition of ventilating position and wind direction, the effect on smoke spreading is very different. The order of the impact of wind direction is as follows: wind surface > side surface > lee side. Under the integrated effect of various driving forces, it will facilitate smoke spreading greatly inside the shaft, increase the volume of gas inside the shaft, and change the spreading pattern of smoke. Throughout the course of the experiments, all of the three effects influence fire and smoke spreading significantly.In studying the movement of gas inside the shaft and from numerical simulations of gas under different heights of fire, the relationship between the fire location factor and the highest temperature was derived. A correlation relation of the maximum temperature with the location of fire was derived. From this part of study, it can be concluded that the height of the neutral plane increases with the location of the fire. The location of the fire affects smoke spreading significantly. Most of the smoke flows to the upper region of stack, and the bottom of the region is smoke-free. The maximum temperature in the stack is in inverse proportion to the fire location factor (h/H). The higher the position of the fire, the larger the fire location factor, and the lower the maximum temperature.By studying the movement of gas inside the shaft and from numerical simulations of gas under different opening conditions, other conclusions can be drawn. The movement of gas varies with the structure of the shaft, which mainly depends on the inlet vent and the opening. When only the vents below the neutral plane are open, the number of vents below the neutral plane have direct ratio with the effect of mixing with smoke. When only the vents above the neutral plane are open or some vents both above and below the neutral plane are open, the lower smoke extends in the form of a wall plume along the wall which has vents. Floors under the neutral plane are smoke-free until smoke produced is more than the smoke flowing out. When all the vents are closed, smoke moves slowly and the upper temperature increase slowly. When all the vents are open, there is large air entrainment through the vents below the neutral plane, the velocity of gas is fast. The temperature at the bottom of the stack is low with the same temperature gradient, in steady-state condition it is a constant.The results deduced from this thesis are practical and useful to the industry. Concepts are helpful to the government in drafting standards for fire protection in ultra high-rise buildings.更多还原