【作者】 孙晓乾；

【导师】 霍然； 周允基；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2009， 博士

【摘要】 随着城市的发展和建设步伐的建快,越来越多的高层建筑在大城市中林立起来,且高度越建越高。高层建筑在给人们带来便利、满足人们的功能要求的美观需求的同时,也给火灾防治带来了很多新问题。同时,近年来发生的几次高层建筑火灾表明,火灾中楼梯井等竖向通道既是人员疏散的重要通道,也有可能像封闭不严的电梯井和管道一样,成为火灾烟气竖向蔓延的途径,严重威胁人员的安全疏散。因此,研究高层建筑竖井、楼梯井等竖向通道的烟气流动特性及其合理的控制策略具有重要意义。火灾烟气流动本身就是一种复杂的浮力驱动流,同时,由于竖井、楼梯井自身竖直狭长结构和楼梯井内踏步结构等的限制以及可能存在的烟囱效应影响,使得竖向通道内的烟气流动比一般建筑火灾烟气流动更为特殊,本论文就针对这些问题开展研究。论文的具体工作包括:建立了考虑壁面传热和竖井内空气温度变化的顶部侧向开口竖井的烟气充填模型和一维稳态运动模型。传统的模型中未考虑火灾烟气温度沿着竖井竖向衰减这一重要特征,本论文通过去除Boussinesq近似假设在模型中清晰研究了烟气温度在竖井内的时空分布,并通过小尺寸实验较好地验证了模型预测结果。在羽流上升充填阶段,竖井内温升随时间变化大致符合指数规律,无量纲温升变化大致随无量纲时间呈线性变化,羽流前锋大致随时间呈现指数关系上升,且其无量纲关系式大致满足线性关系;在稳定燃烧阶段,竖井内竖向烟气温度分布及其无量纲形式均呈指数规律衰减。在高度为27m的实际楼梯井内系统地开展了一系列的全尺寸现场实验,并结合数值模拟研究了封闭楼梯井内的烟气充填和运动规律。测量了烟气在封闭楼梯井内的温度分布和烟气在楼梯井内的特殊流动形式,研究表明,在两层踏步之间上部和下部的涡流加剧了烟气与空气的热对流,这种涡流是由踏步间上下部分的温差决定的;并进一步验证了Qin在高度较低的楼梯井中发现的烟气分层现象。全尺寸现场实验为高层建筑楼梯井烟气运动研究积累了宝贵的实验数据。通过1/3尺度的小尺寸实验研宄了顶部楼层开门的楼梯井内烟气流动特性和烟囱效应对相邻着火房间燃烧状况的影响。研究表明,随着火源产生的热量和烟气进入到楼梯井,使得楼梯井内温度升高,加大了烟囱效应,使烟气在楼梯井内以更快的速度上升;稳定时楼梯井内温度沿竖向高度大致呈指数衰减分布。楼梯井内烟囱效应形成的强补风也加快了燃料的燃烧速度,单侧强补风使得火焰向前室侧近乎呈水平倾斜,火焰被外部进入的空气从中间分开,出现“分岔”现象。论文通过数值模拟研究,对火灾情况下楼梯井加压送风系统的不同风机安装位置、风机风量大小、火源位置、开门楼层以及一、二道门的门缝宽度对楼梯井加压送风效果的影响进行了较为全面的探讨,提出了影响楼梯间加压送风的临界门缝宽度和优化风机布置位置,这些研究成果可为完善相关的实际高层建筑防排烟设计提供技术支撑。更多还原

【Abstract】 Many high-rise buildings had been constructed in trecent years with rapid development of cities.High-rise buildings makes people’s life more convenient, satisfies the architectural artistic and meets the function requirements.However,it also brings about many new fire safety problems for us.High-rise building fire has attached more and more research attention due to the fire disasters occurred in recent years.A stairwell connecting different floors of a building used for occupant transportation maybe becomes a path for smoke spread in case of fire,which would endanger the occupants’ lives.Smoke control in stairwell is very important for saving lives in case of high-rise fire.However,in order to provide appropriate fire safety,the dynamics of smoke spreading in shafts and stairwells should be well understood first.Interaction of three factors would make the smoke movement induced by fire in shafts and stairwells much more complex than in normal compartment.The three factors are fire induced buoyancy,the confinement of vertical long-narrow configuration of shafts and stairwells and the flow resistance of the stairwell.In this thesis,the above issues will be focused on.A model was developed for predicting the transient plume rise in the vertical direction in a shaft and its steady upward movement in high-rise building fires as Boussinesq approximation was not suitable when the smoke temperature was high under larger fires.Heat transfer from hot gases to side walls and the density variations due to temperature rise were considered,The traditional models by former researchers usually take considerations of the above both issues for simplification.The temperature rise curves in the growing period roughly fit exponential increase with time,and their non-dimensional curves to be linear increase tendency.The transient front of smoke plume in shaft can be rationally simplified to be an exponential form versus time,and their non-dimensional expressions to be linear functions.An exponential decay model with an equation to predict the vertical temperature distribution in steady stage in shafts was also found by theoretical consideration.The above theoretical models and curves were all further verified by 1/8 scaled experiments.Full-scale fire experiments were conducted in a 27 m tall stairwell,along with CFD numerical simulation,to study the smoke filling and movement induced by fire in stairwell.Dynamic and thermal physics characteristics,including smoke temperature field,upward traveling velocity of smoke,pressure distribution and the flow pattern,were measured.Vortices were found both in the upper and lower zone of each floor and the convection between heat and cool gases was enhanced in the vortices.This was attributed to the greater turbulences in these regions.The size of hot gas vortices increases with higher temperature difference between the upper and lower zones.The smoke stratification found by Qin in lower stairwells was also verified by the experiments and simulations in higher stairwells.These experiments systematically provided important full scale data for high-rise building fire research.Experiments were conducted in a 1/3 scaled 12-level stairwell configuration with the top floor opening to outside to study the smoke movement in stairwell and the effect of stack effect to the adjacent compartment combustion.With the development of fire,more and more smoke and heat was transferred to the stairwell by fire,which promote the inner temperature in stairwell and accelerate the stack effect and the stack effect would further accelerate the traveling speed of smoke.The temperature was found exponentially decay with height in the stairwell in steady stage.The burning rate was also accelerated by the stack effect in the stairwell,because air convection was enhanced by the stack effect and strong air supply was only through the compartment door to outside.An air flow induced by stack effect also made the flame nearly inclined to horizontal.The make-up air separated the flame into two branches.Finally,the function of the stairwelll pressurization system was numerically studied by considering various factors,such as the position of fire and pressurization fan,the stairwell door crack,and ventilation conditions.Some considerations were taken for the optimization of the stairwelll pressurization design in aid of human evacuation.These had provided technical support for the improvement of the design for pressurized smoke control system in high-rise buildings.更多还原