【作者】 纪杰；

【导师】 霍然；

【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】 目前,地铁已成为解决大中型城市交通拥挤的重要工具,在推动城市发展的同时,也为消防安全带来了新的问题和挑战。近年来,群死群伤的重特大地铁火灾事故频繁出现,充分暴露出现有地铁站消防控制措施的不足,因此,研究地铁站火灾中烟气的流动特点与通风控制模式具有重要意义。国内外地铁火灾统计结果表明,人员伤亡主要源于烟气中毒和窒息。要有效地控制火灾产生的烟气,就必须了解烟气在地铁站内的蔓延规律和沿程质量卷吸特性。传统的双层区域模拟仅通过羽流卷吸模型考虑烟气层的质量增加,而忽略其他位置的卷吸对烟气层质量的贡献,地铁站的长度尺度较大,应用双层区域模拟思想显然是不合适的。根掘卷吸机理不同,可将地铁站内的烟气蔓延过程分为4个阶段,即羽流上升阶段、撞击顶棚后的径向蔓延阶段、向一维水平蔓延的过渡阶段和一维水平蔓延阶段。本文通过理论分析建立了后3个阶段的烟气质量卷吸速率模型,并通过小尺寸地铁模型实验确定了模型中的常系数。将后3个阶段的子模型与Zukoski羽流模型相结合,建立了可预测地铁站内距火源任意距离处的烟气层质量流率的理论模型。本文通过小尺寸地铁模型实验和数值模拟,对地铁站台端部和中部起火时,开启不同位置的排烟口所造成的烟气层界面湍流动力学卷吸效应的差异对机械排烟效果的影响进行了分析。结果表明,火灾时不宜启动位于一维蔓延阶段的机械排烟口,即距火源距离不宜大于站台宽度的1.33倍,以尽量降低由于排烟口启动所施加的外力对烟气分层流动的扰动,从而有效地减少由此引起的烟气层卷吸加剧所导致的烟气层质量增加。站台端部起火时,并非排烟口越多、分布越均匀排烟效果越好,宜单独启动靠近站台端壁的排烟口或同时启动火源两侧的排烟口,而对于站台中部起火时,则直同时启动火源两侧的排烟口。地铁火灾时,两层间的楼梯既是人员逃生路径又是烟气蔓延通道,防止烟气侵入该区域对人员安全疏散有重要意义。本文分析了地铁站内楼梯口处空气幕挡烟的可行性,根据楼梯口处空气幕与烟气来流相互作用下流场所呈现的动力学特征,将流场划分为三段,即撞击掺混段、温差射流段和与地面撞击段。分析了撞击掺混段内由于烟气来流撞击导致的空气幕射流轴线角度改变,并基于完全掺混假设分析了空气幕与烟流能量交换导致的空气幕射流温度升高。在温差射流段内,基于温差射流假设并结合经验公式,建立了空气幕射流竖向速度衰减预测模型。在与地面撞击段内,将不发生撞击作为完全挡住烟气来流的临界条件,结合前两个子模型,得到了烟气完全不进入受保护侧的临界条件理论预测模型。将求解模型得到的空气幕出口速度区间作为边界和初始条件,采用FLUENT求解器,对两层间中庭式楼梯口处风幕挡烟效果进行了数值模拟分析,结果表明将空气幕流场分为三段进行分析的思想是合理的,模拟结果较好地验证了理论预测模型的合理性。随着地铁交通的飞速发展,多层地铁站越来越多。本文针对多层地铁站中间层起火的情况,采用场模拟软件FDS,分析了起火层下层送风系统运行对起火层排烟的影响,提出上下层应同时开启送风系统的通风控制模式,采用该模式,有助于提高起火层的排烟效果。更多还原

【Abstract】 Presently,subway has become a important measure to improve the public transportation situation in large and medium sized cities.While promoting city development,many new problems and challenges to fire safety are presented.In recent years,several disastrous subway fires occurred continuously,with a large number of casualties and the insufficiency of current fire control measures is fully uncovered.Therefore,it is of much significance to study the smoke movement characteristics and ventilation control modes in subway station fires.Statistics showed that the smoke was the most fatal factor in subway fires.To effectively control the fire-induced smoke.it is necessary to get acquainted with the smoke movement and entrainment characteristics along the subway station.In the conventional two-layer zone model,the mass addition of smoke layer is calculated only by a plume entrainment model and the contribution caused by entrainment at other positions are neglected.The length dimension of a subway station is far larger than the width dimension,and evidently the two-layer zone model is not applicable. Based on the different entrainment mechanisms,the smoke movement in a subway station can be divided into 4 stages,i.e.the plume rising stage,the radial spread stage after impinging onto the ceiling,the transitional stage to be one-dimensional horizontal spread and the one-dimensional horizontal spread stage.With theoretical analysis,the models of mass entrainment rate across the smoke layer interface were built for the 2～4th stage.The empirical constants in the models were determinated by the small-scale experimental results.With a series of small-scale mechanical smoke exhaust experiments and numerical simulations,the influence of turbulent entrainment intensity at smoke layer interface,due to different relative locations of exhaust opening to fire source,on mechanical smoke exhaust efficiency were studied.Results showed that when the exhaust openings were operated in the stage of one-dimensional horizontal spread,the turbulent entrainment effect at smoke layer interface would be evidently intensive, leading to poor smoke control effect.It is recommended to operate the exhaust openings in the range of the longitudinal distance to fire source less than 1.33 times of station width.For the fire between one staircase and the end wall of station,the traditional concept that distributing the smoke exhaust openings more evenly and with more openings will lead to better smoke contorl effect is not applicable.It is recommended to operate separately the openings near the end wall,or the openings on both sides of the fire source.And for the fire between two staircases,the openings on both sides of the fire source should be operated symmetrically.During subway fires,the staircase linking two floors is not only the passage of human evacuation,but also smoke spread.Therefore,for the personal safety,it is important to protect this area from smoke.The flow filed of smokeproof air curtain at staircase were divided into 3 sections,i.e.the section of impinging mixture,nonisothermal jet section and impinging floor.In the section of impinging mixture,the angle change of air curtain jet axis by smoke-flow impinging,and based on the hypothesis of uniform mixture,the temperature increment in air curtain jet by energy exchange were analyzed,In the section of non-isothermal jet,combining empirical formula,a model was built for predicting the vertical velocity attenuation of jet axis.In the section of impinging floor,no impinging was taken as the critical condition for complete confinement of fire-induced smoke.Combining two previous submodels,the critical formulas for absolutely preventing smoke from intruding the protected side were obtained.With the numerical solutions of the formulas as the initial and boundary conditions and Fluent,the smoke confinement effect of air curtain at a staircase with a atrium was numerically analyzed.Results showed that the three-section analysis method is reasonable and the simulated results verified the rationality of the theoretical prediction model.With the rapid progress of subway transport,complicated multi-floor subway stations are being built more and more.Aiming at the fire in middle floor of multi-floor station and with the aid of FDS,the influence of the operation mode of air supply system in the lower floor on mechanical smoke exhaust effect in the fire floor was analysed,and a ventilation control mode that the air supply systems in both lower and upper floors should be operated was proposed.更多还原