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H.X. ChenN.A. Liu W.K. Chow 《Journal of Wind Engineering & Industrial Aerodynamics》2011,99(10):1025-1035
When a fire occurs in a room at ground level or a compartment located in the higher floors of a very tall building , the strong ambient wind will play an important role in fire spreading and smoke movement behavior. However, wind effect on compartment fire in cross ventilation condition has not been fully studied so far. In the present study, an effort has been made to study the wind effect on compartment fire in cross ventilation condition through experimental investigations. The experimental fire was generated by 250 ml n-heptane on the floor center of a cube enclosure with two opposite vents on the walls. The inside and outside gas temperature profiles at different vertical and horizontal locations were recorded by two thermocouple matrixes. The ambient wind velocity was set to 0, 1.5 and 3 m s−1. It is observed that the ambient wind would enhance the fire severity by increasing the compartment fire temperature and reducing the time to flashover. The spilled-out flame/plume would extend horizontally farther with the increase of wind speed. Simple theoretical analysis shows that there is a critical wind velocity, or a dimensional number, to differentiate whether the gas flow across the vents is bidirectional or unidirectional, which is believed to influence enclosure fire behavior greatly. 相似文献
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为研究室外风对走廊中火灾烟气分层特性和自然排烟的影响,在相似原理的基础上开展了1/3 缩尺寸实验。通过改变火源功率、室外风速和外窗尺寸,结合对走廊火灾烟气分层特性和自然排烟效果的判断,找出使分层失效的临界室外风速以及使自然排烟失效的临界室外风速,运用量纲分析和数据拟合的方法分析无量纲火源功率和无量纲临界失效风速之间的关系。研究发现,温度分层无量纲临界失效风速与无量纲火源功率呈现良好的线性关系,温度分层临界失效风速随窗口尺寸减小而增大;自然排烟无量纲临界失效风速与无量纲火源功率呈现显著的对数函数关系,窗口尺寸相同时,火源功率越大,自然排烟临界失效风速越大。 相似文献
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运用FDS模拟室内火灾烟气的运动规律,分析烟气层稳定性,以及门的尺寸、火源位置和火源面积对烟气温度及高度的影响。结果表明,具有稳定热释放速率的火源,燃烧一段时间后烟气层高度不会随时间发生变化;烟气层高度随门的高度和宽度增加而升高;火源处于房间中心时,烟气层高度随着门宽度增加迅速升高,与门高度的关系较小;随着火源面积增加,烟气层高度下降,温度升高。 相似文献
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An analysis of full-scale fire test experimental data is presented for a small compartment (3×3.6×2.3 m). A square steady fire source is placed in the center of the compartment. There is an open door and a horizontal opening in the roof, so that natural ventilation is established for the well-ventilated fire. A parameter study is performed, covering a range of total fire heat release rates (330, 440 and 550 kW), fire source areas (0.3×0.3 m and 0.6×0.6 m) and roof ventilation opening areas (1.45×1 m, 0.75×1 m and 0.5×1 m). The impact of the different parameters is examined on the smoke layer depth and the temperature variations in vertical direction in the compartment. Both mean temperatures and temperature fluctuations are reported. The total fire heat release rate value has the strongest influence on the hot smoke layer average temperature rise, while the influence of the fire source area and the roof opening is smaller. The hot smoke layer depth, determined from the measured temperature profiles, is primarily influenced by the fire source area, while the total fire heat release rate and the roof opening only have a small impact. Correlations are given for the hot smoke layer average temperature rise, the buoyancy reference velocity and the total smoke mass flow rate out of the compartment, as a function of the different parameters mentioned. Based on the experimental findings, it is discussed that different manual calculation methods, widely used for natural ventilation design of compartments in the case of fire, under-predict the hot layer thickness and total smoke mass flow rate, while the hot layer average temperature is over-estimated. 相似文献
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《Building and Environment》2005,40(2):183-194
Smoke movement and ambient airflow in a stairwell under fire scenarios are studied numerically using large eddy simulation. Numerical investigation is performed on a typical two-storey confined stairwell, with an open door on the top floor and a fire source on the ground floor. Results show the existence of fairly distinct layers of hot smoke and ambient air under different fire scenarios. It is found that heat release rate has a remarkable effect on distributions of smoke temperature, velocity and oxygen concentration. This paper indicates that detailed patterns of velocity, temperature and species concentration and their evolutions can be predicted by numerical simulation of a stairwell during a fire. 相似文献
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采用试验与数值模拟研究隧道双火源火灾临界风速变化,重点研究双火源功率和火源间距对临界风速的影响。结果表明:随着火源间距增加,临界风速逐渐降低,当两火源间距达到极限距离时,临界风速不再变化;当进风口侧火源功率确定时,在极限间距内出风口侧火源功率增大时,临界风速增大,说明出风口侧的火源对进风口侧的烟气回流有促进作用;在极限间距内,临界风速随火源间距增加呈二次方递减到一个稳定值;两火源总功率越大,临界风速随着间距增加降低的幅度越明显。并得到了临界风速的预测公式。 相似文献
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针对不同断面宽度隧道中发生火灾时的火风压变化问题,利用Fluent软件模拟隧道内发生火灾的情况,分析隧道宽度对临界风速的影响以及隧道宽度、火源功率和通风速度对火风压的影响。研究表明,火源功率较小时,宽度越小的隧道,临界风速越大;随着火源功率的增大,临界风速之间的差距减小。火风压中火区绕流阻力和热烟摩阻增量会随着风速的增大而相互作用。导致火风压会先随风速的增大而增大,到达一个峰值后会随着风速增大而减小,最后当通风速度增大到临界风速后趋于稳定的数值。随着隧道宽度的增大,通风速率对火风压的影响逐渐减弱。建立不同宽度隧道在不同通风速率和火源功率下的隧道火风压计算公式,为隧道火灾通风设计提供参考。 相似文献
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现有的公路隧道火灾通风计算方法,是按正常运营通风设计的风机配置,考虑火灾发生后一定数量风机的损坏,计算火灾情况下能够提供的隧道内风速,用该风速和阻止烟流逆流的临界风速比较来验算火灾时期通风的安全性。但在公路隧道的火灾过程中,火灾烟流阻力确实存在,且对隧道火灾时的烟气流动影响较大。本文将烟流阻力引进传统的公路隧道通风计算中,给出了公路隧道火灾通风时的改进计算公式。通过算例,证明了改进的计算方法更符合隧道火灾时实际概况,为隧道火灾时的通风控制提供了科学依据。 相似文献
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通过数值模拟建立了7种不同横截面形状的全尺寸跨座式单轨隧道模型,研究隧道横截面形状和坡度对隧道火灾烟气蔓延的影响.研究发现长方形隧道顶部温度普遍较高,其次为带有拱顶的隧道,正方形隧道顶部温度普遍较低,圆形隧道底部温度最低.在大火源功率条件下,坡度对临界风速的影响较小.离火源较远的位置,坡度对排烟效果的影响更加明显:随着... 相似文献
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为探究相对风速对高速列车车厢火灾烟流及温度分布的影响,利用PyroSim建立我国复兴号某型二等座车厢火灾数值计算模型。在着火后3 min关闭外端门条件下,研究车窗破裂状态及不同的相对风速对车厢火灾烟流及温度分布的影响,评估火灾作用下高架桥列车运行的安全性。结果表明:对于人为砸碎应急逃生窗的情况,无论是形成单侧开口还是对流开口,对客室内部整体温度没有明显影响,火灾初期车厢火势主要向逃生窗破裂一侧蔓延;随着相对风速的增加,车厢走道温度降低,烟气抵达两侧客室端门的时间延长;在火灾初期,相对风速的增加对两侧通过台的冷却和排烟作用较为明显,缩小了危险区的范围;50 s前火源点附近很小范围为轻危险区,大致在(-2,2) m,车厢走道大多处在安全区,是人员逃生的最佳时段,综合考虑人员疏散及火势的蔓延情况,提出列车车厢发生火灾后安全运行速度为40 km/h。 相似文献
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为探究环境风速对聚氨酯泡沫水平顺流火蔓延的影响,开展多组工况对比实验,分析不同侧向风速对火蔓延典型特征参数(火焰形态、质量损失和近域场温度及辐射)影响。实验结果表明:侧向风速会缩短热解前锋预热角形成时间,且预热角度大小与风速呈负相关,预热角减小会增大火焰前锋对预热区热反馈面积,使火蔓延速度增加;火焰前锋受侧向风速拉伸效应主导下的空气卷吸作用,火蔓延过程中熔融滴落频率增大,加大次生火灾危险性;同时火蔓延过程中材料的质量损失率随风速增加而增加;风速的冷却效应在火蔓延前期占主导地位,但仍会促进火蔓延速度,且水平板材上下两侧辐射峰值差逐渐增大。 相似文献
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采用实体火灾试验与 FDS 数值模拟相结合的方式,研究不同环境风场条件下,面积为 6 m 2 的前室中两个相对开启外窗的自然排烟效果,分析温度和烟密度分布。结果表明,影响排烟效果的主导因素是开窗面积,风速对前室下部温度的影响幅度大于上部温度。随着环境风速的增大,上部温度呈现缓慢线性下降的趋势,而下部温度由于烟气的沉降反而上升。根据模拟结果,提出当风速增大时,关闭迎风面窗户能改善烟气沉降现象,降低下层烟气温度,有利于人员安全疏散。 相似文献
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We consider two horizontally connected compartments with four openings and one compartment on fire; the height of one compartment is fixed, while that of the other varies. A simple small-scale experimental study using air was performed to demonstrate the existence of two stable flow solutions at the same height ratio. Moreover, a macroscopic zonal model is used to theoretically analyze smoke flow direction and smoke mass flow rate. Under different ranges of height ratio, four patterns of smoke flow are identified and studied. One of the solutions is unstable, while the other three solutions are stable, as shown by nonlinear dynamic analysis. Therefore, two stable solutions of smoke flow exist at the same height ratio and ambient conditions when the height ratio is larger than a critical value, and the critical value is shown to be a transcritical bifurcation point. The implications of smoke flow bifurcation on smoke control in an atrium or building with a stairwell are also discussed. 相似文献