Determination of the heat release rate inside operational road tunnels by comparison with CFD calculations

Usually, during a fire inside a tunnel, the average heat release rate (HRR) is estimated according to the type of vehicle. Frequently, the overall HRR is considered, however it is also necessary to know its time evolution to design real time systems, particularly ventilation, which respond to fire events or signals as fast as possible. Nowadays, there is not a well established and generally accepted procedure to know the power liberated at each instant of time inside an operational tunnel. That procedure could help in taking the correct actions to adapt the tunnel ventilation in order to diminish the effects of the fire and the smoke. This work shows a method to calculate the heat release rate using sensors that can be installed inside an operational road tunnel. Besides, the location of the fire could also be calculated accurately and quickly. To achieve the previous purposes, a stationary database that depends on HRR, its location, and the ventilation speed is calculated with CFD programs; the data are compared with temperatures measured by the sensors located inside the tunnel. The program used to generate the database is the simplified model UPMTUNNEL. The predictions of the model are compared with the results of calculations carried out using the general purpose code FLUENT, and with measurements done in a tunnel with a real fire, produced with a fuel tray.     

Runehamar tunnel fire tests

Five large-scale fire tests, including one pool fire test and four HGV mock-up fire tests, were carried out in the Runehamar tunnel in Norway in year 2003. New data and new analyzes are presented in this paper, together with a short summary of previous work on these tests. Heat release rate (HRR), radiation, fire spread, gas production, backside wall temperature, visibility, backlayering, fire growth rate, gas temperature, flame length, ventilation and pulsation are investigated. Simple theoretical models are developed to estimate and predict these parameters. The correlations developed can be used by engineers working on fire safety in tunnels.     

隧道内火灾大小和火灾蔓延模拟研究

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。     

Development of a Methodology for Interface Boundary Selection in the Multiscale Road Tunnel Fire Simulations

The simulation of large complex dynamical systems such as a fire in road tunnels is necessary but costly. Therefore, there is a crucial need to design efficient models. Coupling of computational fluid dynamics (CFD) models and 1D network modeling simulations of a fire event, a multiscale method, can be a useful tool to increase the computational efficiency while the accuracy of simulations is maintained. The boundary between a CFD model (near field) and a 1D model (far field) plays a key role in the accuracy of simulations of large systems. The research presented in this paper develops a novel methodology to select the interface boundary between the 3D CFD model and a 1D model in the multiscale simulation of vehicle fire events in a tunnel. The development of the methodology is based on the physics of the fluid structure, turbulent kinetic energy of the dynamical system, and the vortex dynamics. The methodology was applied to a tunnel with 73.73 m² cross section and 960 m in length. Three different vehicle fire scenarios were investigated based on two different heat reslease rates (10 MW and 30 MW) and two different inlet velocities (1.5 m/s and 5 m/s). all parameters upstream and downstream of the fire source in all scenarios were investigated at t?=?900 s. The effect of changes in heat release rate (HRR) and air velocity on the selection of an interface boundary was investigated. The ratio between maximum longitudinal and transversal velocities was within a range of 10 to 20 in the quasi-1D region downstream of the fire source. The selected downstream interface boundary was 12D_h m downstream of the fire for the simulations. The upstream interface boundary was selected at 0.5 D_h m upstream the tip of the object when the velocity was greater than equal to the V_c. In the simulations with backlayering (V?<?V_c), the interface boundary was selected 10 m further from the tip of the backlayering (1.2 D_h). An indirect coupling strategy was utilized to couple CFD models to 1D models at the selected interface boundary; then, the coupled models results were compared to the full CFD model results. The calculated error between CFD and coupled models for mean temperature and velocity at different cross sections were calculated at less than 5%. The findings were used to recommend a modification to the selection of interface boundary in multiscale fire simulations in the road tunnels and more complex geometries such as mines.     

A Novel Multiscale Methodology for Simulating Tunnel Ventilation Flows During Fires

This paper applies a novel and fast modelling approach to simulate tunnel ventilation flows during fires. The complexity and high cost of full CFD models and the inaccuracies of simplistic zone or analytical models are avoided by efficiently combining mono-dimensional (1D) and CFD (3D) modelling techniques. A simple 1D network approach is used to model tunnel regions where the flow is fully developed (far field), and a detailed CFD representation is used where flow conditions require 3D resolution (near field). This multi-scale method has previously been applied to simulate tunnel ventilation systems including jet fans, vertical shafts and portals (Colella et al., Build Environ 44(12): 2357–2367, 2009) and it is applied here to include the effect of fire. Both direct and indirect coupling strategies are investigated and compared for steady state conditions. The methodology has been applied to a modern tunnel of 7 m diameter and 1.2 km in length. Different fire scenarios ranging from 10 MW to 100 MW are investigated with a variable number of operating jet fans. Comparison of cold flow cases with fire cases provides a quantification of the fire throttling effect, which is seen to be large and to reduce the flow by more than 30% for a 100 MW fire. Emphasis has been given to the discussion of the different coupling procedures and the control of the numerical error. Compared to the full CFD solution, the maximum flow field error can be reduced to less than few percents, but providing a reduction of two orders of magnitude in computational time. The much lower computational cost is of great engineering value, especially for parametric and sensitivity studies required in the design or assessment of ventilation and fire safety systems.     

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。     

An integrated approach for fire and explosion consequence modelling

Fire and explosion are accidents which potentially can occur in oil and gas processing facilities. While fire and explosion could occur as a consequence of each other, most published work has assessed fire and explosion separately, ignoring interactions between the two phenomena.The current study proposes a novel approach to model the entire sequences involved in a potential accident using liquid and gas release incidents as two test cases. The integrated scenario is modelled using Computational Fluid Dynamics (CFD) codes FLACS and FDS. An integrated approach is adopted to analyse and represent the effects (injuries/death) of the accident. The proposed approach can be used in designing safety measures to minimize the adverse impacts of such accidents. It can also serve as an important tool to develop safety training to improve emergency preparedness plans.     

Investigation of the effect of tunnel ventilation on crib fires through small-scale experiments

This paper adopts a series of 1:20 scale tunnel experiments based on a series of large-scale tunnel experiments to study the influence of forced ventilation on fires. The small-scale tunnel has dimensions of 0.365 m (W)×0.26 m (H)×11.9 m (L). Cribs using a wood-based material provide the fuel source and forced ventilation velocities from 0.23 to 1.90 m/s are used. From the study of the measured heat release rate (HRR) and mass loss rate data it is found that the forced air velocity affects the fire spread rate and burning efficiency and further affects peak HRR values at different air velocities. A simple model to describe these influences is proposed. This model is used to reproduce the enhancement of peak HRR for cribs with different porosity factors noted by Ingason [1] and to assess the effects of using different length of cribs on peak HRR. The results from these analyses suggest that different porosity fuels result different involvement of burning surface area and result different changes in peak HRR. However, no significant difference to the enhancement on fire size is found when the burning surface area is similar. It is also found that the trend in the enhancement on fire size by using sufficiently long crib and available ventilation conditions matches the predictions of Carvel and Beard [2] for two-lane tunnel heavy goods vehicle fires.     

Numerical simulation of fire in a tunnel: Comparative study of CFAST and CFX predictions

The mathematical modeling of fire growth and smoke movement in any enclosure is a formidable task. Two types of deterministic models are in vogue, zone models and field models (popularly known as CFD technique). CFAST is a popular zone model used for modeling of fires in enclosures. Likewise, CFX is a general purpose CFD code used for various purposes including modeling of fires. In the present paper, a tunnel of length 150 m having a rectangular cross-section of 80 m² has been considered for analyzing the temperature and velocity profiles generated by fire, placed at a distance of 20 m from one end of portal, by both CFAST and CFX. The simulation by CFAST has been carried out by dividing the tunnel into 1, 2, 5, 8, 10, 12 and 15 compartments of equal size, where these compartments are joined by openings or vents having same cross-section as that of the tunnel. In case of tunnel divided into 15 compartments the fire source position lies at the position of vent; CFAST predicted very high temperatures. The simulations have also been carried out by dividing tunnel into unequal sized compartments such that position of fire was at the center of the compartment. It was found that for accuracy of results, location of fire source inside compartment is an important factor. Computational difficulty was experienced when tunnel was divided into more than 15 compartments. In this paper, a comparative study of temperatures predicted by CFAST and CFX has been done. The CFX and CFAST predictions show that smoke temperature changes with a pattern roughly similar to that of heat release rate. The temperature profiles at selected positions cannot be predicted by CFAST unlike CFX. The detailed features like flame tilt, flow field can only be observed from CFX predictions.     

Fire Dynamics Simulator (Version 4.0) Simulation for Tunnel Fire Scenarios with Forced,Transient, Longitudinal Ventilation Flows

In this study, a series of sensitivity analyses were conducted to evaluate a computational fluid dynamic (CFD) model, Fire Dynamics Simulator (FDS) version 4.0, for tunnel fire simulations. A tunnel fire test with a fire size on the order of a 100 MW with forced, time-varying longitudinal ventilation was chosen from the Memorial Tunnel Ventilation Test Program (MTVTP) after considering recent tunnel fire accidents and the use of CFD models in practice. A careful study of grid size and parameters used in the Large Eddy Simulation (LES) turbulence model—turbulent Prandtl number, turbulent Schmidt number, and Smagorinsky constant—was conducted. More detailed analyses were performed to refine the smoke layer prediction of FDS, especially on backflow (i.e., a reversed smoke flow near the ceiling). Also, energy conservation was checked for this scenario in FDS. A simple guideline is given for smoke layer simulations using FDS for similar tunnel fire scenarios.     

Fire safety aspects of PCM-enhanced gypsum plasterboards: An experimental and numerical investigation

New trends in building energy efficiency include thermal storage in building elements that can be achieved via the incorporation of Phase Change Materials (PCM). Gypsum plasterboards enhanced with micro-encapsulated paraffin-based PCM have recently become commercially available. This work aims to shed light on the fire safety aspects of using such innovative building materials, by means of an extensive experimental and numerical simulation study. The main thermo-physical properties and the fire behaviour of PCM-enhanced plasterboards are investigated, using a variety of methods (i.e. thermo-gravimetric analysis, differential scanning calorimetry, cone calorimeter, scanning electron microscopy). It is demonstrated that in the high temperature environment developing during a fire, the PCM paraffins evaporate and escape through the failed encapsulation shells and the gypsum plasterboard's porous structure, emerging in the fire region, where they ignite increasing the effective fire load. The experimental data are used to develop a numerical model that accurately describes the fire behaviour of PCM-enhanced gypsum plasterboards. The model is implemented in a Computational Fluid Dynamics (CFD) code and is validated against cone calorimeter test results. CFD simulations are used to demonstrate that the use of paraffin-based PCM-enhanced construction materials may, in case the micro-encapsulation shells fail, adversely affect the fire safety characteristics of a building.     

公铁合建越江隧道列车运动压力波数值模拟

本文采用CFD方法对地铁通过公铁合建越江隧道产生的压力波进行了数值模拟分析。基于国内某公铁合建越江隧道相关尺寸建立其下部地铁隧道三维几何模型,采用动网格方法模拟列车从驶入到驶出隧道的全过程。利用国外模型实验数据验证了本文数值模拟方法的可靠性,根据隧道内压力变化曲线,分析了由于列车通过隧道引起的压力变化规律。计算得到进入疏散通道防火门处的压力峰值,最大值1910Pa,最小值-1060Pa,与疏散通道内30~50Pa的正压有较大的压力差。     

An Experimental Study of Smoke Movement in Multi-Storey Buildings

This paper presents the results of an experimental study of smoke movement in a 10-storey building. Eight full-scale experiments including four real fuel fires and four propane fires were conducted in the National Research Council Canada (NRCC)’s 10-storey experimental tower to generate smoke movement data that can be used for the validation of computer models. The heat release rate (HRR) of fire cannot be measured in this tower, so to estimate the HRR of fuel-package fires in this study, an approach using propane as a fuel was developed to reproduce the temperature distribution of various fuel-package tests.     

Innovative experimental reduced scale model of road tunnel equipped with realistic longitudinal ventilation system

Road tunnels require ventilation system for different reasons in order to provide a good level of safety and effectiveness in ordinary service and, in case of fire, to prevent the upstream smoke flow (back-layering phenomena). To evaluate the ventilation system, full scale experiments are more expensive both in terms of the costs and time, and the CFD model has high uncertainty without experimental validation. In this paper the authors have made and characterized experimentally a reduced scale impulsive jet fan in order to carry out a scaled longitudinal road tunnel subsection equipped with a realistic ventilation system. This innovative reduced scale model of road tunnel could give more relevant information such as phenomenology and performance of full-scale tunnel using suitable similarity rules. It could be useful to do parametrical studies or to focus on particular physical aspects (i.e. smoke pattern of thermal plume behavior with respect to usual experimental sections reported in literature). The innovative reduced scale model presented in this paper can provide a useful alternative method with respect to the full-scale experiments.Moreover, the authors have simulated numerically, by means the CFD commercial software FLUENT®, the scaled road tunnel and have compared experimental and numerical results in terms of axial velocity.     

深圳前海地下道路人员逃生疏散研究

深圳市前海地下道路,具有地下立交、多点进出、变截面、长度特长等突出的结构特点,其火灾特性、疏散救援组织等更为复杂,因此需对地下道路逃生疏散结构设计的合理性进行研究。首先对地下道路疏散通道逃生出口通行能力、大型车辆人员疏散时间关键参数进行了现场实验研究,其次采用CFD软件模拟地下道路火灾烟气发展规律并确定可用安全疏散时间ASET,最后采用STEPS软件模拟地下道路人员疏散逃生所需安全疏散时间RSET。结果显示地下道路发生火灾时,人员基本8 min内可以疏散到无火灾隧道,但为保证人员均能在危险到来前安全疏散,应及时开启通风系统,以保证温度、CO浓度及可见度均在忍耐范围内。     

Numerical studies on atrium smoke movement and control with validation by field tests

Many computer fire models were developed in the literature with the rapid advancement of information technology. With the possibility of implementing engineering performance-based fire codes, fire models are used frequently in hazard assessment. Among the different approaches, fire field models using the technique of computational fluid dynamics (CFD) are widely used. The approach takes the advantage of predicting the fire environment in a ‘microscopic’ picture. Air flow pattern, pressure and temperature contours can be predicted. However, it is not easy to validate the CFD predicted results. Most of the field models are only validated by some experiments not specially designed for such purpose. There are very few studies on comparison with field measurements in actual sites. Whether those models are suitable for use are queried, leading to challenges. In this paper, the CFD tool fire dynamics simulator developed at the National Institute of Standards and Technology in USA will be applied to study atrium fires. Smoke layer interface height and air temperatures inside the atrium are simulated. The experimental data on atrium hot smoke tests carried out recently was used. CFD results predicted can be validated by comparing with the experimental results.     

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.     

Findings of the International Road Tunnel Fire Detection Research Project

Fire detection systems are essential fire protection elements for road tunnels to detect fires, activate safety systems and direct evacuation and firefighting. However, information on the performance of these systems is limited and guidelines for application of tunnel fire detection systems are not fully developed. The National Research Council of Canada and the Fire Protection Research Foundation, with support of government organizations, industries and private sector organizations, have completed a research project to investigate current fire detection technologies for road tunnel protection. The project included studies on the detection performance of current fire detection technologies with both laboratory and field fire tests combined with computer modelling studies. This paper provides an overview of the findings of the project. Fire detectors, fire scenarios and test protocols used in the test program are described. A summary of the research results of the series of full-scale fire tests conducted in a laboratory tunnel facility and in an operating road tunnel as well as of the computer modelling activities will be reported.     

秦岭特长公路隧道火灾温度场的数值模拟

近年来世界各国的隧道火灾事故引发人们对隧道安全问题进行了广泛的探讨,尤其是对长大公路隧道的安全问题越发关注。由于隧道结构的特殊性,使得隧道内发生火灾时的状况格外复杂,其中烟流和温度扩散对隧道安全构成严重威胁,因此对隧道火灾温度场的深入研究将有利于隧道火灾预防及救援工作的展开。为了向秦岭特长公路隧道的防灾预案提供可靠依据,采用计算流体力学方法,利用商业CFD软件STAR-CD对秦岭特长公路隧道火灾温度场进行数值模拟,研究其纵、横断面的温度分布情况,数值模拟提供了较详细的数据和变化特征,为秦岭特长公路隧道的防灾救援提供了技术依据,也对认识其他长大公路隧道火灾灾变机理也有一定的参考作用。     

Study of smoke backlayering during suppression in tunnels

Full-scale suppression tests and Computational Fluid Dynamics (CFD) simulations were carried out to investigate the effect of Water-based Fixed Fire Fighting Systems (WFFFS) on the effectiveness of longitudinal ventilation systems in resisting smoke backlayering in tunnels. Test results show that WFFFS enables longitudinal ventilation systems to resist smoke backlayering with a lower velocity than the critical velocity for the same size of tunnel fire. Based on data obtained from the test program and the simulation program, a design method is proposed to estimate the velocity required to resist smoke backlayering in tunnels when WFFFS is active.