共查询到19条相似文献,搜索用时 125 毫秒
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为了研究地铁区间隧道火灾临界风速和温度变化规律,建立了西安某地铁站区间隧道模型,采用FDS模拟软件对不同纵向通风条件下烟气流动和温度分布进行模拟。介绍模型的基本参数,根据Froude相似性原理建立了各个燃烧参数的相似性关系。利用FDS模拟不同火灾功率、不同通风速度时的温度和烟气速度分布。对比分析5、6、7、8、9、10 MW火灾功率下的临界风速变规律化并提出预测模型。结果表明:纵向通风风速设为3m/s时对防止9 MW以下的火源功率火灾烟气回流效果明显;热释放速率不大于10 MW时,隧道火灾中烟气温度不大于250℃,火源下风侧烟气流动速度不大于4 m/s。 相似文献
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ALAN BEARD RICHARD CARVEL PAUL JOWITT 《消防科学与技术》2007,26(2):125-131
隧道内火灾的热释放速率对火灾蔓延和烟气生成起着关键作用。影响热释放速率的关键参数包括:燃烧物特性、隧道形状、通风条件以及车辆流量。综述了几年来热释放速率对这些参数的依赖性所做的研究成果。设计了贝页斯概率模型来模拟火灾热释放速率受隧道形状以及纵向通风的影响,设计了定性模型来模拟火灾在类似海底隧道内从一个物体蔓延到另一个物体的情况,通风条件同样是纵向通风,并给出了此次研究的初步成果。 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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巷道火灾烟气控制模型是为了研究火灾烟气在巷道通风的条件下逆流运动行为而提出的。该模型提出了一个用于测定临界通风风速的分析公式,可以分析拦截火源近处的烟气,防止出现烟气逆流。实验证明,临界通风风速主要决定于火源的热释放速率。 相似文献
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临界风速可有效控制烟气蔓延,是隧道防灾通风重要参数。为分析隧道长度对临界风速的影响,采用量纲分析法构建临界风速与隧道长度关系公式,并分别在5 MW和30 MW火源热释放速率下,对不同长度隧道的火灾进行数值模拟以量化研究隧道长度对临界风速的影响。结果表明,隧道长度对临界风速具有影响,且不同火源释放速率时影响也有所不同:无量纲火源热释放速率小于0.15时,临界风速随隧道长度增大呈现1/41次方增长关系;无量纲火源热释放速率高于0.15时,临界风速随隧道长度增大呈现1/25次方增长关系。进而建立了考虑隧道长度的无量纲临界风速计算公式。 相似文献
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The “critical velocity” is the minimum air velocity required to suppress the smoke spreading against the longitudinal ventilation flow during tunnel fire situations. The current techniques for prediction of the values of the critical velocity for various tunnels were mainly based on semi-empirical equations obtained from the Froude number preservation combining with some experimental data. There are a few uncertainties in the current methods of prediction of the critical ventilation velocity. The first is the influence of the fire power on the critical ventilation velocity. The second is the effect of the tunnel geometry on the critical velocity. Both problems lead to the issues of the scaling techniques in tunnel fires. This study addressed these problems by carrying out a series of experimental tests in five model tunnels having the same height but different cross-sectional geometry. Detailed temperature and velocity distributions in the tunnels have been carried out. The experimental results showed that the critical velocity did vary with the tunnel cross-sectional geometry. It was also shown clearly that there are two regimes of variation of critical velocity against fire heat release rate. At low rates of heat release the critical velocity varies as the one-third power of the heat release rate, however at higher rates of heat release, the critical velocity becomes independent of fire heat release rate. Analysis of the distribution of temperature within the fire plumes showed that there were two fire plume distributions at the critical ventilation conditions. The change of the fire plume distribution coincided with the change of the regime in the curves of the critical velocity against fire heat release rate. The study used dimensionless velocity and dimensionless heat release rate with the tunnel hydraulic height (tunnel mean hydraulic diameter) as the characteristic length in the experimental data analysis. It was shown that the experimental data for the five tunnels can be correlated into simple formulae which can be used for scaling. The new scaling techniques are examined by applying the scaling techniques to the present experimental results and three large-scale experimental results available in the public literature. A good agreement has been obtained. This suggests that the scaling techniques can be used with confidence to predict the critical ventilation velocity for larger-scale tunnels in any cross-sectional geometry. Comprehensive CFD simulations have been carried out to examine the flow behaviour inside the tunnels. Validation against the experimental results showed that the CFD gave slightly lower but satisfactory prediction of the flow velocity. However the temperature prediction in the fire region was too high. The findings from the CFD simulations supported the ones from experimental tests. 相似文献
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A CFD model of the 4th Beijing subway line was used to study the effect of longitudinal ventilation on heat and smoke plume movement in the tunnel. The critical ventilation velocity is correlated with the heat release rate for both a simplified heat fire source model and a complete combustion fire source model with methane gas as fuel. The influences of the heat source length and the fuel gas inlet geometry on the critical velocity are investigated for both fire source models. The results show that the influences of the combustion process and fire source area variation are not included in models based on Froude number preservation theory. Thus, Ri is no longer suitable as a dimensionless number for the critical ventilation velocity when the fire geometry or combustion conditions influence the results. The back-layering air temperature above the front of the fire source can be used to explain the different critical velocity variation regimes for all the simulation conditions. 相似文献
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Jae Seong Roh Hong Sun Ryou Dong Hyeon Kim Woo Sung Jung Yong Jun Jang 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2007,22(3):262-271
Since the prediction of ‘critical velocity’ is important to control the smoke in tunnel fires, many researches have been carried out to predict critical velocity with various fire sizes, tunnel shape, tunnel slope, and so forth. But few researches have been conducted to estimate critical ventilation velocity for varied burning rate by longitudinal ventilation, although burning rate of fuel is influenced by ventilation conditions. Therefore, there is a need to investigate the difference of upstream smoke layer (e.g., backlayering) between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation.In this study, the 1/20 reduced-scale experiments using Froude scaling are conducted to examine the difference of backlayering between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation. And the experimental results obtained are compared with numerical ones. Three-dimensional simulations of smoke flow in the tunnel fire with the measured burning rates have been carried out using Fire Dynamics Simulator; Ver. 406 code, which is developed by National Institute of Standards and Technology. They show a good degree of agreement, even if some deviation in temperature downstream of the fire is evident. Since ventilation velocity had a greater enhancing effect on the burning rate of fuel due to oxygen supply effect, the critical ventilation velocity should be calculated on the basis of varied HRR by ventilation velocity. 相似文献
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Theoretical analyses and model-scale experiments have been conducted to investigate the critical velocity in a tunnel cross-passage which is defined as the minimum ventilation velocity through the fireproof door to prevent smoke from flowing into a cross-passage. The effect of the fireproof door geometry, heat release rate, ventilation velocity and fire source location were taken into account. The critical velocity in a tunnel cross-passage varies approximately as 3/2 power of the fireproof door height, as one-third power of the heat release rate and as exponential law of the ventilation velocity, almost independent of the fireproof door width. The critical Froude Number mainly ranges from 5 to 10 and consequently as it is not a constant value it is not very suitable to predict the critical velocity in a tunnel cross-passage. A dimensionless correlation that can correlate well with the experimental data was proposed. 相似文献
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Results from a series of fire tests carried out in a horizontal model tunnel (1:10) with longitudinal ventilation are presented. Pool fire with methanol as the fuel was used to simulate the fire source. Temperature and velocity distribution in the model tunnel were measured. The heat release rate, maximum gas temperature under the ceiling, back-layering length and critical velocity were investigated and compared with models proposed previously. Predicted maximum gas temperature under tunnel ceiling by Kurioka’s model agreed well with the experimental data with maximum discrepancy less than 20%. Dimensionless back-layering length was found decreased with the increase of the dimensionless ventilation velocity nearly linearly. Due to the difference between the experimental conditions and validating conditions of models proposed previously, diversities were found between the experimental results and predicted values base on Froude modeling. Maximum discrepancy on critical velocity might be about 40%. Models considering the effect of boundaries and heat loss of smoke more detailedly remain to be further developed. 相似文献
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为了研究分岔隧道在采取纵向通风排烟系统时各匝道所需临界风速,设计合流型和分流型两种Y 字型分岔隧道。数值模拟设定30 MW 火灾规模,对比Y 字型隧道各匝道的临界风速与单坡坡度隧道临界风速的理论值,并分别对匝道内2 m 和6.2 m 处的纵向温度进行分析。结果表明,对于非着火匝道,当匝道内的临界通风风速与单坡度隧道的理论值相当时,能保证烟气不通过岔口蔓延到该匝道;对于合流型隧道的着火匝道,其临界风速小于单坡度隧道的临界风速理论值;分流型隧道的着火匝道所需临界风速大于同等单坡度隧道的临界风速理论值。 相似文献
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为解决高黎贡山大瑞铁路高地温深埋特长隧道高温热害问题,常采取通风降温与机械制冷降温相结合的措施。针对某一施工段,当通风降温能力到达限值仍无法使得隧道内空气温度满足规范时,需开启机械制冷设备。本文首先联立围岩与空气稳态传热方程和空气换热方程,利用隧道内壁面与空气换热第三类边界条件,求解出隧道内空气温度解析解。随后,以某一施工段出渣工序为例,迭代求解出隧道内不同回风速度和地下涌出热水散热功率下,施工隧道开挖面附近最高气温为28 ℃时的洞口临界大气温度。经计算发现,洞口临界大气温度与地下涌出热水散热功率负相关,与回风速度正相关;结合当地气象参数,量化单独采用通风就能使工作面附近气温满足规范要求的洞口大气温度变化区间,为进一步制定制冷设备运行计划提供理论依据。 相似文献
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超大断面水平隧道纵向通风临界风速CFD分析 总被引:4,自引:1,他引:3
首先介绍了临界风速研究的基本思路及国内外主要研究成果.结合国内某长大公路隧道设计,建立一长300m、水力高度10.64m的水平隧道模型,通过CFD模拟确定超大断面隧道临界风速的影响因子及相应的准则关联式.模拟表明:与火灾热释放速率相比,环境温度的影响可以忽略不计;与Atkinson(模型试验)及Buxton(大尺度试验)相似,临界风速随热释放速率的变化分为两个区域,与低热释放速率时不同,一旦热释放速率超过40MW,临界风速的变化明显趋于缓慢. 相似文献
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Jae Seong Roh Seung Shin Yang Hong Sun Ryou Myong O Yoon Youn Tae Jeong 《Building and Environment》2008,43(7):1225-1231
The 1/20 reduced-scale experiments using Froude scaling are conducted to investigate the effect of longitudinal ventilation velocity on the burning rate in tunnel fires. The n-heptane pool fires with heat release rate ranging from 3.71 to 15.6 kW are used in this study. A load cell is used to measure the mass loss rate of burning fuel and the temperature distributions are measured by K-type thermocouples in order to investigate smoke movement. The ventilation velocity in the reduced-scale tunnel is controlled by the wind tunnel through an inverter. The increases in ventilation velocity lead to enhance burning rate of n-heptane fuel. The reason is that the oxygen supply effect prevails rather than the cooling effect as the ventilation velocity increases. As a result, the heat release rates in experiment are larger than constant heat release rates by 4.45–11.3 times in the n-heptane pool fires. Also, it is found that non-dimensional critical ventilation velocity is proportional to one-third power of non-dimensional heat release rate. 相似文献