浅谈大空间火灾烟气运动规律的计算机模拟

分析并讨论了当前大尺度空间火灾烟气运动规律的计算机模拟研究现状。结果表明,采用大涡模拟方法结合多单元区域模拟是研究火灾烟气运动规律的发展趋势。     

Turbulence statistics in a fire room model by large eddy simulation

Fire and smoke movement in a room is influenced by the turbulence characteristics (such as Reynolds stress, turbulent heat flux, etc.) of the flow and temperature fields. In order to accurately predict fire and smoke movement by computational fluid dynamics (CFD), it is necessary to verify these turbulence quantities. The purpose of this study is to predict the turbulence structure of the flow and temperature fields due to a fire in the compartment by large eddy simulation (LES) using detailed experimental data to verify the simulation results. The results show reasonably good agreement with experimental data for both the mean flow properties and the turbulence quantities with the exception of the region near ceiling. This study provides useful information for verifying LES technique when applied to compartment fires.     

Effects of buoyancy induced roof ventilation systems for smoke removal in tunnel fires

The present article highlights the performance of natural roof ventilation systems and its effects on tunnel fire flow characteristics. Numerical analysis is performed using Large Eddy Simulations (LES) to predict fire growth rate and smoke movement in tunnel with single and multiple roof openings. The smoke venting performance of ceiling vents are investigated by varying the vent size and fire source locations. The critical parameters such as mass flow rate through ceiling openings, smoke traveling time and fire growth patterns are presented. The ceiling openings are effective in transferring hot gases and reduces the longitudinal smoke velocity. The heat source and ceiling vent locations significantly affects the vent performance and smoke behavior in tunnel. The present results are in good agreement with the experimental results available in literature.     

A smoke detector activation algorithm for large eddy simulation fire modeling

This study chronicles the development and integration of a smoke detector activation algorithm (known as the SDAA) that describes the response time of a smoke detector into a large eddy simulation (LES) fire model [Roby RJ, Olenick SM, Zhang W, Carpenter DJ, Klassen MS, Torero JL. Smoke detector activation algorithm version 1 technical reference guide. NISTIR Report; 2006, in press]. Although the SDAA could be used with any CFD smoke movement model, the results here address specifically its application to the fire dynamics simulator (FDS). The fire model predicts the smoke concentration and velocity adjacent to the detector while an algorithm based on characteristic velocity-based lag times describes the transport of smoke into the sensing chamber of the smoke detector. The experimental data from a multi-room compartment fire were used for comparison and a series of benchmark studies provide a mechanism to establish the sensitivity of the model to the different input parameters. The SDAA was found to be very accurate in determining detector activation times for both high- and low-velocity smoke flows.     

气溶胶特性引起的感烟探测器灵敏性的数值预测

本研究结合时滞动力学灵敏度算法，描述了感烟探测器的反应时间，与时滞动力学灵敏度算法同时，大涡模拟火灾模型预测了与探测器相接近的烟浓度值，并描述了烟进入传感小室的输送情景。基于初始粒子的大小和分布，计算传感小室内的烟粒子浓度。由标准试验方法得出了实验数据。比较预测值和实验值，得出了合理一致的结果。     

Effect of Ventilation System on Smoke and Fire Spread in a Public Transport Interchange

In this report, a large eddy simulation (LES) model is used to investigate the conventional types of ventilation system design in the context of a public transport interchange. Various airflow patterns based on two of the most popular ventilation designs (mixing and displacement) are simulated to determine their effect on the fire. The simulation program chosen is the fire dynamics simulator (FDS) published by National Institute of Standards and Technology (NIST). It is found that increased airflow causes the fire temperature to increase by as much as 500 K. Extraction of smoke mixture by fans (exhaust only system) significantly decreases the spread of smoke and fire. Ventilation inlets located at the ground level help to increase the smoke and fire intensity in the occupied zone. Displacement ventilation increases fire intensity and current.     

Numerical simulation of fire-induced flow through a stairwell

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.     

A network-based smoke control program with consideration of energy transfer in ultra-high-rise buildings, CAU_ESCAP

Ultra-high-rise buildings allow for the efficient use of land, but they are vulnerable to disasters such as fires. Therefore, the development of network models for analyzing the characteristics of smoke movement in ultra-high-rise buildings is necessary for cost-effective design of smoke control systems and operation decisions. A new network-based smoke control program, CAU_ESCAP, is developed in this study, which is a program that can consider the energy transfer. CAU_ESCAP is validated with existing programs, ASCOS and COSMO, by analyzing the smoke movement. After that, fire in an ultra-high-rise building of 55 stories is applied with CAU_ESCAP for analyzing the smoke movement and the mass flow rate of the smoke control system due to the variation of heat release rate and door conditions of the fire floor. The pressure difference between the fire room and the protecting area does not vary in the closed-door case in the fire room, but vary significantly in the opened-door case. Therefore, the smoke from fire would be spread to other spaces if there is no instantaneous increase in the mass flow rate of pressurization when the door is opened by occupants for evacuation.     

Large eddy simulation of compartment fire with solid combustibles

For properly describing practical building fire processes with solid combustibles, the pyrolysis kinetics model of solid combustibles and the large eddy simulation (LES) approach are applied to the simulation of the thermal decomposition of the polyurethane foam (PUF) slab and the space fire spread in a compartment. The instantaneous variations of the heat release rate of the PUF slab, the smoke temperature, and the smoke interface height with time are obtained under different ventilation conditions. They are in agreement with the measured data. The ventilation conditions have distinct effects on the interactions between the pyrolysis of the PUF slab and the space fire spread. Influenced by the space fire spread, the heat flux on the top plane of the PUF slab exhibits a non-uniform distribution. The PUF slab is consumed in an asymmetric manner.     

基于大型场所的FDS数值模拟分析

使用FDS软件模拟了大型娱乐场所中发生火灾时烟气流动的三种情况,分别讨论了有无水喷淋作用。排烟措施及防烟分隔情况下的烟气蔓延情况,结果表明大涡模拟FDS可以用来预测大尺度较复杂结构中的烟气流动,能够清楚地显示流动情况。     

中庭火灾烟气流动的大涡模拟

采用大涡模拟的方法,对中庭火灾烟气的流动过程进行了模拟,了解了中庭烟气的蔓延过程,得到了烟气的速度场和温度场、顶棚射流的速度和温度的详细结果。模拟结果表明,大涡模拟能比较准确地预测中庭内烟气的流动状态,可用于指导中庭建筑的防火设计。     

Numerical simulation of the spread of smoke in an atrium under fire scenario

The Fire Dynamics Simulator code is used to investigate the smoke movement in an atrium under fire scenario. At first, by comparing with experimental data of the atrium fire under low and high heat release rates, reasonable model constants of C_s and Pr_t and appropriate grid system are determined for simulating smoke movement in the atrium, the simulation results are in good agreement with those experimental data. Then, the performance of different smoke exhaust methods in the atrium is studied. Smoke filling processes are investigated under different natural and enhanced smoke exhaust methods. Simulated results show that natural smoke exhaust method is preferred when the smoke exhaust vents are located at the ceiling of the atrium. On the other hand, when the smoke exhaust vents are located on the walls of the atrium, the higher positions of the smoke exhaust vents are preferred. In addition, the influence of the fire source locations on the smoke spreading process is presented in this paper, three kinds of fire source locations are studied, they are central fire, side wall fire and corner fire. Results indicate that the descending process of the smoke layer is the slowest when the fire source is at the corner of the atrium.     

移动式排烟装备在地铁火灾中的应用研究

讨论了地铁中常用的几种移动式排烟装备的性能和特点，通过中山北一路地铁试验，测试了地铁中的烟气流动态势，分析了地铁烟气流动特点。系统的阐述了地铁中移动式排烟装备的应用战术——正压送风，负压排风，并通过试验分析了消防水枪水力排烟在地铁火场中的应用。     

居民自建房楼梯-走道组合结构火灾烟气运动

采用大涡模拟技术对居民自建房楼梯-走道组合结构中的火灾烟气运动规律进行数值模拟。通过对烟气及速度矢量场的分析发现,火灾烟气在建筑内的流动可以分为5个不同的阶段。通过对FDS源程序进行改进,提取烟气粒子的位置随时间变化的信息,得到烟气粒子的拉格朗日运动轨迹,展示烟气的几种典型运动形式。烟气在进入走道后最初的环形运动多是贴近壁面的,而后环形轨道路径越来越远离壁面靠近中心部位,环形轨迹的路径也越来越小。     

Numerical simulations on fire spread and smoke movement in an underground car park

The Fire Dynamic Simulator code is used to investigate fire spread and smoke movement in a large underground car park under different fire scenarios. Initially, by comparing with experimental results of heat release rate of a single car fire, the development of car fire is designed by letting surface densities of the fuel over the car. Fire spread and movement of smoke are then investigated under different ventilation conditions. Simulated results show that the development of car fire in the underground car park can be classified into four stages; namely an initial stage, a developed stage, an extinction and re-burning stage and another fast-developed stage. Affected by ventilation systems, fire develops rapidly resulting in consuming most oxygen quickly followed by early extinction of the fire. After extinction of the fire, with more ambient air drawn into the car park due to ventilation, re-ignition takes place with accelerated development. In addition, detailed field distributions of temperature and velocity vectors are given. It is found that the smoke layer decent to the top of the car after 15 min and the hot smoke flows in a disorderly manner resulting in the spread of fire more rapidly.     

Development of a hybrid field and zone model for fire smoke propagation simulation in buildings

A novel hybrid fire model combining the traditional field and zone modeling approaches to simulate the fire smoke propagation in a multi-storey building is presented in this paper. In the hybrid model, the field model is used to model the fire smoke movement in rooms with complex fire-induced airflow where the two-layer zone assumption of the zone model is not valid, e.g. in the room of fire origin. The zone model is used to model the fire smoke propagation in the rooms/corridors where the hot smoke layer is well stratified and the smoke movement can be reasonably simulated based on the two-zone concept. The fundamentals of the hybrid fire model are presented and discussed in this paper. The interface treatment between the field model and the zone model is presented in detail. In addition, some examples highlighting the application of the new hybrid model to simulate the smoke propagation in a multi-storey building are also presented. The hybrid model provides a more accurate prediction of fire smoke propagation and consumes less computational resources in comparison to the full zone and full field models, respectively.     

Wind effects on smoke motion and temperature of ventilation-controlled fire in a two-vent compartment

High-rise building fire is often influenced by the ambient wind. Study concerning fire behavior in the compartment of high-rise buildings in wind environment is needed for exploring some effective methods used for evaluation of compartment fire smoke movement and control. In this paper, smoke flowing direction and temperature of ventilation-controlled fire in a two-vent compartment are studied when ambient wind blows to the vent at higher altitude. It is found that there is a critical wind speed, above which the direction of smoke movement is dominated by wind rather than by buoyancy. It is also found that ambient wind has a complex influence on smoke temperature in the compartment. When wind speed exceeds another critical value, only one steady state appears in the smoke temperature rising curve. Otherwise three steady states appear. Heat transfer through the compartment walls has great influence on the second critical wind speed.     

模型车厢内火灾烟气层运动模拟分析

旅客列车车厢内发生火灾时，火灾烟气的运动状况直接影响旅客的人身安全，往往造成重大的人员伤亡和巨大的财产损失。采用模型实验、数值模拟的方法对运行的旅客列车经过隧道发生火灾时车厢内烟气层高度的特征进行了研究，将旅客列车卧铺车厢处理为多个受限空间的组合，研究了车厢内烟气层高度在开口不同状况下的变化规律。模型实验与数值模拟相结合为列车车厢火灾研究提供了理论分析模型和实验研究方法，研究成果为车厢防火设计提供了重要的技术依据。     

火灾烟气毒性评价新的"RRC"动态模型及工程应用

就火灾中的死亡人数而言，最主要的威胁来自于火灾中的烟气。目前已经有很多种模型来描述火灾中的烟气毒性危害，如CO随机模型、FED、FEC和N气体模型。所有这些模型都不能反应真实火灾中烟气浓度的时空变化。根据真实火灾中的烟气危害度，选取人员的呼吸率、人员在火灾中的逃生路径、特定建筑中的烟气浓度场分布等三个对于人员致死具有决定性的因素，初步建立一个新的“RRC”动态模型来描述火灾中的烟气毒性危害，并通过算例展示了模型的工程应用。     

室外风对高层建筑竖井内烟气运动影响的数值模拟

采用火灾模拟专业软件FDS对不同火源位置、不同风向条件下火灾烟气的运动进行模拟,测定典型位置处温度、速度、CO及CO2体积分数变化情况。实验结果表明:在近地风场中,风向对竖井内烟气蔓延的影响大小顺序为迎风>背风>侧风,竖井开口位于迎风面时,外界风对竖井内烟气运动影响最大:火源位于中性面以上时,烟气通过竖井与前室的开口向竖井内蔓延,并向下运动;而火源位于中性面以下时,前室内烟气向外部运动,竖井内无烟气流入。