弧形公路隧道临界风速数值模拟研究

基于PyroSim软件,利用数值模拟的方法,建立弧度段圆心角分别为30°、60°、90°、120°、150°、180°的三维隧道模型,变换火源位置,分析弧度对于弧形隧道临界风速变化的影响。弧度段的直径为100 m,火源的热释放速率设置为20MW。在不同弧形的隧道中,当火源点在相同的弧度位置时,不同弧形隧道的临界风速变化不大;当火源位置在0°~90°位置变化时,临界风速随着弧度的增大而增大;当火源位置超过90°时,临界风速随着弧度的增大而减小。     

长直公路隧道火灾近火源区长度研究

为探究近火源区长度变化规律,以长直公路隧道为研究对象,利用量纲分析法推导近火源区长度关系式。采用FDS 6.2对42组工况进行数值模拟计算,分析火源功率、隧道断面形状两个因素对近火源区长度产生的影响。结果表明:隧道形状一定时,火源功率不断增大,烟气一维流动阶段起始点位置不断向后移动,近火源区长度不断增大。火源功率一定时,隧道断面高度不断增大,近火源区长度呈现逐渐减小的变化趋势;隧道断面宽度不断增大,近火源区呈现长度逐渐增大的变化趋势。根据模拟结果,明确了无量纲近火源区长度L*与无量纲火源功率Q*的1/3次方呈线性增长关系,建立了火源功率和隧道断面形状耦合作用下的近火源区长度预测模型。     

火源横向位置及面积对双车道公路隧道临界风速影响研究

为了探明火源横向位置对临界风速的影响规律,运用FDS研究马蹄形断面双车道公路隧道内火源位于隧道中心与侧壁两种场景下的临界风速,并改变火源面积,结合理论分析,与前人矩形断面隧道内的研究结果进行对比。结果表明：单位面积热释放速率一定时,临界风速随火源面积的增大而增大;壁面火的临界风速小于中心火的临界风速,与矩形断面隧道存在差异;且随着火源面积的扩大,壁面火与中心火的临界风速比值趋近于1;不能用“镜面效应”解释马蹄形隧道内壁面火与中心火临界风速差异的原因。     

堵塞效应下隧道火灾临界风速研究

为获取更为准确的隧道火灾临界风速算法,考虑火源阻塞比φ1、火源上游处阻塞比φ2均为0、0.23、0.41、0.64,选取了1.6,3.2,9.3 kW三种火源热释放率,通过正交数值试验计算了48种阻塞工况的临界风速值,推导了单纯火源阻塞、单纯火源上游阻塞、火源与上游同时阻塞时临界风速无量纲修正算法。研究结果表明：无论是增加火源处阻塞比还是加大火源上游阻塞比,临界风速值都会逐步减小,火源处阻塞对临界风速的影响更大。火源热释放率增加,临界风速也不断增大。仅火源处阻塞时,临界风速与(1-φ1)2/3成正比。仅火源上游阻塞时,临界风速与(1-φ2)1/3成正比。火源与上游同时阻塞时,临界风速与(1-φ1)2/3(1-φ2)1/3成正比。     

室外风对走廊温度分层和房间自然排烟的影响

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。     

断面宽度对纵向通风隧道火风压影响研究

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。     

地铁隧道火灾双点排烟的临界排烟量研究

基于1∶20的缩尺隧道模型进行一系列试验,研究地铁隧道火灾双点排烟系统下烟气温度分布特性及临界排烟量,并研究火源热释放率和风口长度对临界排烟量的影响。试验发现,临界排烟量随火源热释放率的增大而增大,随风口长度的增大呈现出先减小后增大的趋势,这说明存在一个临界风口长度。     

含渐缩段卜形分岔合流隧道火灾临界风速研究

为探究“卜”形分岔隧道这一特殊隧道结构对隧道火灾临界风速的影响,运用FDS构建了主路渐缩分岔隧道、主路等宽分岔隧道与直线隧道3种结构的缩尺寸隧道模型,通过数值模拟分析隧道渐缩结构与分岔角度对火灾临界风速的影响。研究表明,对于主路渐缩的分岔隧道,当火源所在位置的局部隧道宽度减小时,所需的临界风量变小。而火源位置确定时,隧道的渐缩结构、分岔角度和分岔结构对临界风速的影响不明显,并提出一种适用于隧道工程渐缩段任意火源位置临界风量的计算公式。对于主路位置的火灾,提出无量纲临界风速与无量纲热释放速率的关系式,与前人直线隧道的变化规律相似,而较高的隧道高度导致临界风速的转折点较大。     

纵向风对隧道柴油池火影响的试验研究

在全尺寸隧道模型中开展了试验研究,采用柴油池火设计了2.8~12.2 MW共8组工况,考查了油盘面积2~5 m~2、纵向风速0.2~2.0 m/s条件下隧道火灾烟气层形态、热释放速率和火源燃烧速率的变化规律。研究发现,各工况在该区域附近的烟气分层效果较好,纵向风速对各工况中火源区烟气分层影响不明显。热释放速率经验计算值比测量值普遍高7%~30%,但当火源面积较大、纵向风速较高时经验计算值显著低于测量值。火源平均燃烧速率表现出与热释放速率一致的变化规律,随隧道纵向风速增大而增大。在纵向风作用下,3 m~2和5 m~2柴油池火的燃烧速率比无风环境下分别高出18.4%和25.1%。     

城市V形坡隧道火灾最高温度数值模拟

采用FDS 数值模拟方法,对V 形坡隧道火灾时烟气运动特性及隧道纵向中心线上温度分布情况进行研究,并提出不同火灾位置时顶板最大温升参数经验预测模型。结果表明,火源位于变坡点右侧120 m 时,隧道纵向中心线峰值温度点向下游偏移,偏移距离随坡度的增加而增加,隧道顶板最高温度随坡度的增加而减小。通过推导无量纲火源位置与变坡点距离不同时的最大温升参数预测模型得出,无量纲最大温升参数随无量纲火源位置的增大而增大、与无量纲热释放速率的0.8 次幂成正比,且与隧道坡度呈非线性非单调关系。     

考虑人员逃生公路隧道火灾控制风速研究

公路隧道火灾人员逃生与控制风速关系密切。本研究基于PHOENICS软件,建立了矩形、圆形及马蹄形断面下二、三及四车道9种计算模型,选取了大客车(20 MW)及无载重货车(30 MW)2种火源释放率, 选取了2.0 m/s、2.5 m/s、3.0 m/s、3.5 m/s及4.0 m/s的入口风速共计40种主要常见火灾工况,考虑了纵向通风对人体极限温度承受值的影响,采用了杨涛修正的动态火源释放率曲线及周勇狄修正的克拉尼公式,选用了适当的人员逃生条件,给出了每种工况8个特征时刻的10个特征点的温度值及曲线图,给出了燃烧5 min、12 min、30 min后火源处的纵横断面温度云图及中轴面烟气云图,给出了对应于火源燃烧位置上下游8个特征位置下人员逃生的忍受时间与逃离时间。研究得出:在基于人员逃生条件下矩形断面隧道在火源释放率为20 MW时二车道控制风速为3.0 m/s,三、四车道均为2.5 m/s;30 MW时二、三、四车道控制风速均为3.5 m/s,圆形与马蹄形断面隧道在火源释放率为20 MW时二、三、四车道控制风速均为3.5 m/s,30 MW时二车道控制风速均为4.0 m/s,三、四车道均为3.5 m/s。在火灾发生1 min后,人员以1 m/s从火源上下游进行疏散均可安全逃生。     

超大断面水平隧道纵向通风临界风速CFD分析

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.     

纵向通风与竖井自然排烟下隧道火灾烟气特性实验研究

中国逐渐发展成为世界上隧道和地下工程最多的国 家,其长隧道数量和长度跻身世界前列。据统计,火灾中85%的 人员死亡是由热烟气造成的,目前隧道中采用较为广泛的排烟系 统有纵向排烟系统、集中排烟系统和横向排烟系统,而针对长隧道 来说,我国广泛采用的是竖井式纵向通风,因此,研究纵向通风与 竖井排烟综合效应下隧道火灾烟气流动特性及温度分布规律具有 重要意义。本文建立了1：10 缩尺寸竖井隧道模型,主隧道长度 16.5 m,宽度1.3 m,高度0.65 m;竖井通过排烟横通道与主隧道 连接,排烟横通道设置在主隧道侧面中部,尺寸为1.2 m 长、0.6 m 宽、0.4 m 高;竖井横截面为半径0.6 m 的1/4 圆,高4.6 m。在 竖井隧道模型中开展了一系列油池火实验,选取2 种方形燃烧池 （20 cm×20 cm、23 cm×23 cm）作为火源,设置2 个纵向火源位置 （位置A：火源中心线与排烟横通道中心线距离0.375 m;位置B： 火源中心线与排烟横通道中心线距离1.375 m）,7 种纵向通风风 速（0,0.18,0.27,0.35,0.44,0.52,0.69 m/s）,定量分析不同工 况下温度分布及烟气逆流长度。研究结果表明：当无纵向通风时, 火焰与隧道地板垂直,且呈轴对称形态;当有纵向通风时,火焰向 下游偏移,且纵向通风风速越大,火焰向下游偏移越明显;当纵向 通风风速为0 m/s 时,由于竖井的存在,火源上、下游两侧烟气温 度分布并非对称,火源下游（竖井侧）烟气温度下降速度较快,与单 洞隧道烟气温度分布明显不同;随纵向通风风速增加,烟气逆流长 度和烟气温度减小,而最大温度偏移距离整体呈增加趋势;当无量 纲纵向通风风速v′＜0.19 时,主隧道最大温升△Tmax 与Q2/3/ Hef 5/3 呈正比,而当无量纲纵向通风风速v′＞0.19 时,主隧道最大 温升△Tmax 与Q? /(vb1/3Hef 5/3)呈正比,但常数系数均小于Li 等预 测模型中的常数系数;竖井隧道内无量纲纵向烟气温度分布符合 Fan 和Ji 等建立的纵向温度衰减模型,衰减系数k′在1.36~1.63 范围内变化,但其值明显大于单洞隧道纵向温度衰减系数k′;另 外,当火源位于位置A 时,最大烟气温度低于火源位于位置B 时 的最大烟气温度,无量纲纵向烟气温度衰减速度慢于火源位于位 置B 时衰减速度。     

Effect of cross section and ventilation on heat release rates in tunnel fires

Model scale fire tests were performed in tunnels with varying tunnel widths and heights in order to study the effect of tunnel cross-section and ventilation velocity on the heat release rate (HRR) for both liquid pool fires and solid fuel fires. The results showed that for well ventilated heptane pool fires, the tunnel width nearly has no influence on the HRR whilst a lower tunnel height clearly increases the HRR. For well ventilated solid fuel fires, the HRR increases by approximately 25% relative to a free burn test but the HRR is not sensitive to either tunnel width, tunnel height or ventilation velocity. For solid fuel fires that were not well ventilated, the HRRs could be less than those in free burn laboratory tests. In the case of ventilation controlled fires the HRRs approximately lie at the same level as for cases with natural ventilation.     

Numerical Investigation of Back-Layering Length and Critical Velocity in Curved Subway Tunnels with Different Turning Radius

Curved tunnels are inevitable subjected to the city underground geological conditions. Due to the catastrophic consequence of tunnel fires with high population density, the related researches on fire safety of curved tunnel are full of significance. Therefore, a series of curved subway tunnels with turning radius of 300–1000 m were investigated numerically by FDS 5.5.3 in terms of the smoke back-layering length and critical ventilation velocity under the heat release rate of 5–10 MW. Theoretical analysis shows that the curved tunnel with the local resistance has an advantage of preventing smoke spreading compared with straight tunnel. The simulation results also indicated that both the smoke back-layering length and the critical ventilation velocity increased with the rising turning radius, and the straight tunnel has the largest values. In fact, the local resistance impact factor for the smoke back-layering length in the curved tunnel, \( k_{f} \), was controlled by turning radius \( R \) and ventilation velocity \( V \). The dimensionless critical velocity increased slightly from \( 0.638Q^{*1/3} \) to \( 0.669Q^{*1/3} \) when the turning radius increased from 300 m to 1000 m. Without considering the influence of turning radius (local resistance), previous models cannot be applied to the curved tunnel. The improved prediction models about smoke back-layering length and critical velocity with the factor of turning radius could provide a technical guideline for the tunnel ventilation designs.     

Numerical studies on evaluation of smoke control system of underground metro rail transport system in India having jet injection system: A case study

The rail based urban transport system is being developed for national capital of India, New Delhi. The smoke control using ventilation in case of fire inside the tunnel, similar to Delhi Metro corridor has been investigated using computational fluid dynamics technique. A section of tunnel having dimensions 400 m long, 5.5 m wide and 6 m high is considered for simulation. The analysis has been carried out by assuming a variable fire source with a peak heat release rate (HRR) of 16 MW, located at the center of the tunnel. Ventilation ducts are located in the ceiling near the tunnel portals and are inclined at 10 degrees to the plane of the ceiling through which fans discharge air. The influence of the fire HRR curve slope on the smoke flow dynamics in a realistic tunnel model fitted with jet injection type longitudinal ventilation system has been investigated. In case of fire two cases are studied: (1) fans activated immediately after detection, (2) fans activated at delayed times to take into account the response time for the fans to achieve its maximum speed. The velocity of supply and exhaust fans necessary to remove smoke in 30 s from the upstream direction is determined. The velocities of fan required to produce desired critical velocity in the longitudinal direction for different HRR of fire is predicted.     

A Study of the Critical Velocity of Smoke Bifurcation Flow in Tunnel with Longitudinal Ventilation

Small longitudinal velocity cannot prevent backlayering in tunnel fire, while excessive longitudinal velocity will destroy stratification of smoke layer and lead to bifurcation flow. As smoke bifurcation flow proceeds, the longitudinal flow is divided into two streams and flow along both sidewalls of the tunnel ceiling. The critical velocity of bifurcation flow is the minimum value at which bifurcation flow starts to occur. To investigate the critical velocity of bifurcation flow, experiments and CFD simulations were conducted. Experiment was carried out in a reduced-scale tunnel, which is 8 m long, 1 m wide and 0.5 m high. The numerical research was performed using FDS. In simulation, the computational region of a tunnel is 200 m long, 10 m wide. The heat release rate (1 MW to 6 MW) and the height (4 m to 8 m) is changed in the 30 simulation scenarios. Theoretical analysis showed that the dimensionless critical velocity of bifurcation flow only depends on the dimensionless heat release rates, and a mathematical equation is proposed. The reduced-scale experiments indicated that the critical velocity of bifurcation flow is 1.48 times that of critical velocity for preventing backlayering, and the coefficient is in agreement with CFD simulation.     

区间隧道列车火灾通风临界时间研究

计算地铁区间列车火灾人员所需安全疏散时间,与模拟所得可用安全疏散时间对比,确定区间人员疏散策略及通风临界时间。研究表明：地铁列车外部中间位置着火停靠在区间,火源功率分别为5、7.5、10 MW,需启动纵向通风排烟系统,组织人员向上风向疏散。火源功率为5 MW,纵向通风风速为2.0 m/s时,150~180 s 开始通风可保证人员安全疏散;火源功率为7.5、10 MW,纵向通风风速分别为2.4、2.6 m/s 时,120~180 s 开始通风可保证人员安全疏散。风机由静止转换为事故工况的通风临界时间为120 s,由运转转换为事故工况的通风临界时间为90 s。     

The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

In order to detect a fire and provide adequate fire protection to a tunnel structure, the maximum gas temperature beneath the ceiling to which the structure is exposed needs to be estimated. Theoretical analysis of maximum gas temperature beneath a tunnel ceiling based on a plume theory is given. The heat release rate, longitudinal ventilation velocity and tunnel geometry are taken into account. Two series of model-scale experimental tests were also carried out. The results of both analysis and experiments show that the maximum excess gas temperature beneath the ceiling can be divided into two regions. When the dimensionless ventilation velocity is greater than 0.19, the maximum excess gas temperature beneath the tunnel ceiling increases linearly with the heat release rate and decreases linearly with the longitudinal ventilation velocity. When the dimensionless ventilation velocity is less than 0.19, the maximum excess gas temperature beneath the ceiling varies as the two-thirds power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity. In both regions, the maximum excess gas temperature varies as the −5/3 power of the vertical distance between the fire source bottom and tunnel ceiling. The investigation presented here considers only the cases when the continuous flame region is lower than the ceiling height.