A numerical study on the effects of naturally ventilated shaft and fire locations in urban tunnels

In more and more tunnels, natural ventilation mode with vertical shafts has been gradually employed. However, there are few studies investigating the influences of fire and shaft positions on natural ventilation performance currently. Therefore, this study investigated the effects of the transverse distance from fire source to tunnel sidewall, the longitudinal distance from fire source to shaft, and the transverse distance from shaft to sidewall on natural ventilation effectiveness in a tunnel fire by using Fire Dynamics Simulator. The typical characteristic parameters of smoke, such as mass flow rate, temperature distribution, and velocity vector were analyzed; besides, the phenomenon of plug‐holing was discussed. The results have shown that the mass flow rate of gas exhausted by the shaft decreases slightly with the increase of longitudinal distance from fire source to shaft. When the longitudinal distance from fire source to shaft is constant, changing the transverse distance from shaft to sidewall will have a more obvious effect on the effectiveness of exhausting smoke than changing the transverse distance from fire source to sidewall; in addition, the phenomenon of plug‐holing is more serious when the shaft is close to the sidewall.     

Study on the influence of air supply and smoke exhaust on full transverse exhaust of long highway tunnel

This study investigated the efficacy of the full transverse exhaust method for smoke extraction in tunnel fires. It examines factors such as the number and layout of air supply and exhaust outlets, analyzing their impact on smoke spread, tunnel temperature, visibility, and airflow. The results demonstrate that the full transverse exhaust method effectively controls smoke emissions in raised highway tunnels. It limits smoke spread, reduces tunnel temperature, and effectively controls the fire-affected area. The number and layout of outlets significantly influence smoke dispersion, with fewer exhaust outlets providing better smoke control and optimizing the tunnel environment. However, insufficient outlets disrupt gas flow stability. The position of exhaust outlets affects smoke distribution, and caution is advised to prevent directing fresh air flow toward the fire. Opening an equal number of exhaust outlets on one side of the fire source yields superior smoke extraction results, reducing tunnel ceiling temperatures and minimizing risks to personnel and structures. Though stabilization may take longer, this configuration proves advantageous. The study offers valuable insights and practical guidelines for implementing the full transverse smoke control method in real-world scenarios.     

Study of smoke movement characteristics in tunnel fires in high-altitude areas

Understanding smoke temperature distributions and transport characteristics is of great importance to control and exhaust thermal-driven smoke. However, previous studies have focused on this problem in plain areas, whereas ambient pressure decreases as elevation increases. This study investigates the influence of ambient pressure on the hot gas temperature distribution and movement characteristics in a tunnel fire. A series of numerical simulations are carried out in a vehicle tunnel with various heat release rates (HRRs) and ambient pressures. The results show that the maximum temperature and longitudinal temperature distribution under the tunnel ceiling increase with decreasing ambient pressure due to less heat loss caused by lower air density. In addition, the vertical temperatures of the smoke are slightly higher under lower ambient pressure, and this phenomenon makes the smoke spread slightly faster while the smoke layer thickness remains nearly the same under different ambient pressures. The results can provide a reference for tunnel lining design and ventilation arrangements in high-altitude areas.     

Numerical analysis of smoke flow under the effect of longitudinal airflow in a tunnel fire

This study investigated the influence of the longitudinal airflow on the smoke propagation in a tunnel by large-eddy simulation, which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with varying the longitudinal airflow in the tunnel. Six fire scenarios have been simulated with Fire Dynamics Simulator (FDS) and the results of the longitudinal distribution of CO concentration, temperature distribution, interface height, stratification, and the efficiency of smoke extraction in the tunnel have been analyzed to evaluate the different fire cases. FDS predicted a CO concentration distribution compared to calculated values using the Hu model. Furthermore, the predicted maximum smoke temperatures are compared to those given by the Kurioka model. A reasonably good agreement has been obtained for both models. The obtained results showed that the increase of the forced airflow velocity has for results a loss of stratification and significant decrease in the efficiency of extraction.     

New approaches to determine the interface height of fire smoke based on a three-layer zone model and its verification in large confined space

Large confined space has high incidence of fires, which seriously threatens the safety of people working there. Understanding the distribution of smoke in such large space is critical to fire development prediction and smoke control. Three improved methods for the stratification interface prediction of fire smoke are developed, including of improved intra-variance, integral ratio and N-percentage methods. In these methods, the interface height is determined by the vertical temperature distribution based on a three-layer smoke zone model, which is an improvement of a two-layer zone model. Thereafter, the three improved methods are applied to several typical fire cases simulated CFD to predict the smoke interface, and their applicability and reliability are verified by comparison of the smoke stratification results with the filed simulation results. Results show that the three improved methods can effectively determine the location of the three-layer zone model's interface, and they have the ability to predict smoke interface for fires with different fire source types and ventilation conditions.     

圆筒形地下立体停车库火灾火源位置与火势蔓延规律研究

选取一个典型的圆筒形地下立体停车库作为研究对象，运用star-ccm+软件，采用数值模拟的方法对车库内自然通风条件下的火灾场景进行模拟计算。分别选择负一层、负六层以及负十层作为起火点，计算得出：火源位置越深入地下，着火车位顶棚中心温度越高，最高可达942℃，与起火点同层的车位顶棚中心温度均高于200℃。当某车辆发生火灾后，其相邻车辆、上方车辆、相对车辆将分别在起火后的240、312、322 s左右被引燃；火源位置越往下，引燃附近车辆的时间越短。同时，通过计算值与理论值的对比，讨论了计算火源附近车辆被引燃时间理论公式的适用性。     

Influence of longitudinal fire location on smoke characteristics under the tunnel ceiling

The critical ventilation velocity is almost the most well‐investigated fire phenomenon in the tunnel fire research field whereas previous studies have always investigated it when the fire source is distant from the downstream tunnel exit. Fortunately, a recent study provided a set of data on the critical ventilation velocity for tunnel fires occurring near tunnel exits by small‐scaled experiments, nevertheless, with a lack of further analysis. To demonstrate the relationship of the critical ventilation velocity and the distance between the fire and tunnel exit more explicitly and detailedly, a quantitative and graphical study was carried out and a correlation was presented in this paper. Inspired by this, a set of small‐scaled experiments were carried out to investigate the influence of different longitudinal fire locations on maximum smoke temperature under the tunnel ceiling. Results show that unlike the critical ventilation velocity, the maximum smoke temperature was not obviously affected by longitudinal fire location. Copyright © 2014 John Wiley & Sons, Ltd.     

隧道内液化天然气管道泄漏火灾温度场的数值模拟

以某实际液化天然气（LNG）输运工程为例,采用计算流体动力学方法,建立隧道内LNG管道泄漏火灾的数学模型,分别以3种不同的泄漏情况对LNG泄漏火灾流场进行了数值模拟计算,得到了3种不同泄漏强度的LNG火灾温度场的实时分布情况,并分别对其火灾温度场随时间的变化及危险性进行了分析。结果表明：泄漏强度最小的情况下,火灾发生后隧道温度升幅不大,温度变化幅度平缓,危险性相对较小;泄漏强度居中的情况下,火灾发生后隧道内温度变化幅度较大,变化趋势较为剧烈,危险性显著增加;泄漏强度最大的情况下,火灾发生后隧道内温度是3种情况中最高的,且隧道内会出现烟气堆积的情况,十分危险,应着力避免此类事故的发生。     

Effect of altitude on vertical temperature distribution and longitudinal smoke layer thickness in long tunnel fires

Based on large eddy simulation, a series of long tunnel fire experiments with different heat release rates (HRRs) and altitudes were carried out. The vertical temperature and thickness of fire smoke are studied. The simulation results show that the higher the altitude, the lower the flame temperature rise, while the change of smoke plume temperature rise is opposite. The movement of smoke in the tunnel can be divided into four regions, and the smoke layer thickness in the longitudinal direction of the tunnel corresponds to the latter three regions. The thickness in Region II increases along the longitudinal direction, the thickness in Region III is a constant value, and the thickness in Region IV increases along the longitudinal direction. Besides, the change of altitude only has an effect on the smoke layer thickness in Region IV. Then, by considering the altitude, HRR, and smoke layer thickness, and using dimensional analysis, an empirical formula for predicting the smoke layer thickness under the influence of altitude in Region IV was established.     

两池火耦合作用下柴油拱顶罐热响应的数值模拟

化工园区多池火事故是典型的高后果低概率事件。鉴于目前两池火辐射模型存在一定局限性,本文采用数值模拟方法,以3个直线排布的5000m³柴油拱顶罐为研究场景,从热释放速率、火焰形态、热辐射强度三方面分析两池火燃烧特性,并与单池火场景对比,考虑储罐间距这一影响因素,进一步研究目标储罐热响应。结果表明：采用GB 50160—2008（2018年版）规定的防火间距,两燃烧罐产生的池火会发生耦合作用,并得出目标储罐受到的热辐射强度分布,最高热辐射达17.04kW/m²;两池火作用下目标储罐的温度、Mises应力与失效时间分别为644℃、356MPa、936s,单池火为488℃、280MPa、2880s,目标储罐在两池火作用下的变形也比单池火更为严重;随着储罐间距增加,目标储罐的温度与Mises应力逐渐减小,失效时间逐渐增加,当储罐间距为标准防火间距的2.5倍（20m）时,失效时间为2800s,与单池火作用产生的失效时间2880s较为接近。本研究可为优化储罐防火间距及区域韧性提升提供理论指导。     

The effect of pyrolysis and combustion temperatures on smoke density

The small-scale smoke testing apparatus now proposed as a standard in France under the designation NF–T51–073 measures the total obscuration from a stream of smoke generated from a small sample. Although like other small-scale fire tests, it is not claimed to be of relevance to real fire situations, it is possible by varying the temperature over a wide range (200–900°C) to obtain a plot of specific optical density for various materials which broadly corresponds with general experience and certain other smoke tests. The plots show that nearly all flammable substances give a rapid rise in smoke opacity in the 350–500°C region above which there is always a steep drop sometimes to smoke densities of virtually zero. Apart from one or two synthetic materials which show a very low smoke density through-out, there is no general trend as between natural and synthetic substances. Oxygen depletion which often occurs in a real fire situation has some effect on the smoke density but it is not a major one. On the other hand, in some cases reheating the smoke can have quite a dramatic effect, due very probably to further pyrolysis and combustion.     

Overall stability analysis of oversized steel‐framed buildings in a fire

Our present paper summarizes the shortcomings in the current fire‐resistant design of oversized steel structures and proposes a method for overall stability analysis of steel structures in the event of fire. The Fire Dynamics Simulator (FDS) software platform–based large‐eddy simulation technology can accurately reflect the environment in a fire scenario and correctly predict the spatial–temporal change in the smoke temperature field within an oversized space. Adopting the FDS software and finite element structural analysis (ANSYS) coupling can fundamentally overcome the natural defect of adopting the International Organization for Standardization (ISO) standard curve (or other indoor homogeneous temperature increase curves) that substitutes a point for the overview of a field. They reflect the structural additional internal force and internal force redistribution incurred by the gradient temperature difference of the spatial–temporal changing nonhomogeneous temperature field and both theoretically and technically realize the analysis of structural heat transfer and mechanical properties in a natural fire. Furthermore, a modified model to predict the steel temperature curve in localized fire is also proposed. The localized fire in large spaces can be treated as a point fire source to evaluate the flame thermal radiation to steel members in the modified model. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires

This paper investigates the effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires. A series of numerical simulations were conducted in a 1/5 small-scale tunnel with the different heat release rates (50-100 kW), longitudinal ventilation velocities (0.5-1 m/s), passenger blockage lengths (2-6 m), and ratios (0.17-0.267). The typical smoke flow properties in different tunnel fire scenarios are analyzed, and the results show that under the same heat release rate and longitudinal ventilation velocity, the smoke back-layering length, maximum smoke temperature, and downstream smoke layer height decrease with increasing passenger blockage length or ratio. The Li correlations can well predict the smoke back-layering length and maximum smoke temperature in tunnel fire scenarios without the passenger blockage. When the passenger blockage exists, the modified local ventilation velocity that takes the blockage length and ratio into account has been proposed to correct the Li correlations. The smoke back-layering length and maximum smoke temperature with the different blockage lengths and ratios can be predicted by the modified correlations, which are shown to well reproduce the simulation results.     

竖直射流火撞击障碍管道数值模拟分析

当前对于竖直向上屏障射流火的研究大多集中于顶棚射流,对于竖直向上射流火羽流撞击管道的研究相对较少。为研究竖直向上射流火羽流撞击管道的特征演化行为,基于燃烧学及流体力学基本原理,运用Fluent数值模拟软件,通过控制变量法对不同热释放速率、障碍管道直径及管壁-火源间距因素进行探究。研究表明障碍管道直径和管壁-火源间距对火焰高度和宽度均有一定程度的影响,且得到了基于Froude数的无量纲火焰高度表征模型。     

竖直射流火撞击障碍管道数值模拟分析

当前对于竖直向上屏障射流火的研究大多集中于顶棚射流,对于竖直向上射流火羽流撞击管道的研究相对较少。为研究竖直向上射流火羽流撞击管道的特征演化行为,基于燃烧学及流体力学基本原理,运用Fluent数值模拟软件,通过控制变量法对不同热释放速率、障碍管道直径及管壁-火源间距因素进行探究。研究表明障碍管道直径和管壁-火源间距对火焰高度和宽度均有一定程度的影响,且得到了基于Froude数的无量纲火焰高度表征模型。     

Use of zone models on simulating compartmental fires with forced ventilation

Performance of three fire zone models BR12, CCFM.VENTS and CFAST in simulating forced ventilation fires with low heat release and high ventilation rates were studied experimentally. A fire chamber of length 4.0 m, width 3.0 m height 2.8 m with adjustable ventilation rates was used. Burning tests were carried out with wood cribs and methanol to study the preflashover stage of a compartmental fire and the effect of ventilation. The mass loss rate of fuel, temperature distribution of the compartment and the air intake rate were measured. The heat release rates of the fuel were calculated from the measured mass loss rate. The smoke temperature was used as the validation parameter. A scoring system is proposed to compare the results predicted by the three models. An empirical expression for calculating the smoke temperature is assessed. Lastly, the Computational Fluid Dynamics technique is also used for comparing the simulated fire environment.     

Flammability hazards of typical fuels used in wind turbine nacelle

This study aims to develop a complete methodology for assessing flammability hazards of typical fuels (ie, transformer oil, hydraulic oil, gear oil, and lubricating grease) used in a wind turbine nacelle by combining different experimental techniques such as thermogravimetric analysis and cone calorimetry. Pyrolysis properties (onset temperature, temperature of maximum mass loss rate, and mass residue) and reaction‐to‐fire properties (ignition time, heat release rate, mass loss rate, and smoke release rate) were determined and used for a preliminary assessment of thermal stability and flammability hazards. Additional indices, for ignition and thermal behavior (effective heat of combustion, average smoke yield, and smoke point height, heat release capacity, fire hazard parameter, and smoke parameter, were calculated to provide a more advanced assessment of the hazards in a wind turbine. Results show that pyrolysis of transformer oil, lubricating grease, hydraulic oil, and gear oil occur in the range of 150°C to 550°C. Lubricating grease and transformer oil show the higher and lower thermal stabilities with maximum pyrolysis rate temperatures of 471°C and 282°C, respectively. The measured relation between ignition time and radiant heat flux agrees well with Janssens method (a power of 0.55). The aforementioned indices appear to provide a reasonable prediction of performance under real fire conditions according to a full‐scale fire test documented by Declercq and Van Schevensteen. The results of the study indicate that transformer oil is the easiest to ignite while lubricating grease is the most difficult to ignite but also has the highest smoke production rate; that transformer oil has the highest heat release rate while gear oil has the lowest; and that the fire hazard parameter is the highest for transformer oil and the smoke parameter is the highest for lubricating grease. The potential of this type of work to design safer wind turbines under performance‐based approaches is clearly clarified.     

固体推进剂燃烧诱发热烟气运动的大涡模拟

利用空间火蔓延与烟气运动的大涡模拟方法,探讨了固体推进剂燃烧时在舱室内形成的火蔓延和烟气的运动,计算出室内烟气温度、墙壁温度与地面热流密度随时间的变化,与试验结果相符合.计算结果表明,固体推进剂火灾初期室内的气体受到热烟气的挤压像受到活塞的推挤一样流出门口;顶棚温度出现位于靠近火源和通风口连接通道所处的垂直截面附近的局...     

Study on the heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires

The heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires were studied in this paper. Through the dimensional analysis, the dimensionless relationship between the heat exhaust coefficient, heat release rate, exhaust vent size, and exhaust velocity was obtained. In addition, this paper also studied the effect of the lateral exhaust vent on the smoke flow field. Results showed that the lateral smoke exhaust caused strong air entrainment on the downstream of the exhaust vent and boundary layer separation on the upstream of the exhaust vent. As the exhaust velocity increased, the degree of air entrainment gradually increased, and the smoke layer near the exhaust vent gradually became thinning and plug‐holing phenomenon occurred; meanwhile, the boundary layer separation would be suppressed or disappear, but the increase of the heat release rate would enhance the boundary layer separation. As the exhaust vent got narrower, the air entrainment downstream of the exhaust vent was reduced, and the boundary layer separation also got weaker.     

Experimental study on the effect of lateral concentrated smoke extraction on smoke stratification in the longitudinal ventilated tunnel

Smoke is the main cause of death in tunnel fires. It is one of the important measures to maintain smoke stratification in the early stage of tunnel fire. This article focused on experimentally studying the combined effect of lateral concentrated smoke extraction and longitudinal ventilation on the smoke stratification, which never be revealed before. The velocity of the smoke layer and air layer, vertical temperature distribution, and the flow patterns of the smoke were measured. It was found that the longitudinal ventilation and lateral concentrated smoke extraction would affect the flow of the smoke and change the shear velocity between the smoke layer and air layer, then, the patterns of the smoke layer will be affected. And the flow patterns with Froude (Fr) number can be classified into three categories: (a)Fr < 0.6 , with stable smoke stratification; (b) 0.6 < Fr < 0.85 , with a stable smoke stratification but the blurring interface; and (c) Fr > 0.85 , the smoke layer is completely unstable. The result can provide a reference for ventilation design of immersed tube tunnels.