Numerical analysis on plume temperature properties formed above a harmonically oscillating fire source

Large eddy simulation (LES) of turbulent buoyant plumes formed above an oscillating fire source has been carried out so as to clarify their temperature properties in the offshore environment. For the sake of simplicity, we are concerned here only with a rolling environment among six-degree-of-freedom system of complex ship motion. Furthermore, under the assumption of a small rolling angle, unsteady fire source movement associated with the rolling motion can be approximated by simple harmonic oscillation in the horizontal direction. Numerical results obtained under several sets of oscillation conditions, especially under different amplitude conditions, are compared with temperature variations of conventional axisymmetric and two-dimensional fire plumes above stationary sources. Consequently, it has been clarified that in the case where the amplitude is four times longer than the side length of a square source, the present buoyant plumes exhibit almost the same feature as the two-dimensional fire plume in the lower part of the buoyant plume region. On the other hand, it has been found that for any value of amplitude, the temperature properties are close to those of axisymmetric plumes in the upper part of the buoyant plume region. Based on these findings, a simple theoretical model to estimate the variation in mean excess temperature as a function of elevation has been developed by the use of a well-recognized, semi-analytical solution of the axisymmetric plume formed above a virtual point source. It has been confirmed that this simple model can reasonably reproduce the same plume features as obtained by the LES simulations.     

隧道火灾中火羽流特性的数值模拟

利用F luen t软件对隧道火灾中火羽流特性进行了模拟分析,研究了隧道坡度对火羽流的影响,与前人所进行的数值模拟进行了比较,为隧道火灾的研究提供了一种有效的研究手段,为进一步研究隧道火灾临界通风速度奠定了基础。     

竖井内羽流上升驱动力实验分析

为得到竖井内烟囱效应与浮力对羽流上升造成的影响,搭建了小尺寸竖井火灾实验平台,测量了不同燃料、不同油池尺寸条件下两端开放及底部封闭竖井内温度分布,对各驱动力进行了理论分析.结果表明:两端开放竖井内火灾热烟气上升受到烟囱效应与自身浮力的共同作用,且烟囱效应驱动力占主导;底部封闭竖井内热烟气上升仅靠自身浮力作用;两端开放竖井内烟气受到向上的驱动力更大.在相同火源及竖井尺寸条件下,两端开放竖井内向上驱动力与底部封闭竖井内向上驱动力的比值随油池直径的变大而增大,平均斜率为0.32.     

三维单室火灾温度及速度场的数值模拟

利用 FL UENT CFD软件平台对单室火灾中烟气流动、传热及燃烧过程进行数值模拟 ,计算结果与实验数据吻合较好。     

One-dimensional analysis of the global chimney effect in the case of fire in an inclined tunnel

A one-dimensional computational analysis is presented of the global chimney effect due to a fire source in an inclined tunnel. Fire-induced flows are not accounted for in the present study: the computed velocity, due to global heating, is to be superposed as an initial and/or boundary condition in detailed computational fluid dynamics (CFD) simulations in a region of interest. The results must not be used as a replacement for such detailed simulations in e.g. network problems. Two calculation options are explained for the global chimney effect. The first method is based on the global heating of the entire tunnel part between the fire source and the higher positioned tunnel outlet. In the other method, the initial fire-influenced region is restricted to a certain distance and, as soon as a prescribed temperature rise is met, the fire-influenced region length increases until the tunnel outlet is reached. The treatment of the enthalpy flow rate through the fire-influenced region boundaries is discussed. In order to identify the most important parameters and to quantify their influence on the global chimney effect, a sensitivity study is presented with respect to the different model ingredients. The following quantities are examined: fire source heat release rate, tunnel inclination angle, tunnel length, tunnel wall roughness, ambient temperature, ambient pressure conditions, tunnel cross-section area, and fire source position. Attention is focused onto the fire-influenced region mean temperature and the air velocity at the tunnel inlet. The inlet air velocity is quantified by means of a correlation, taking into account the parameters mentioned.     

Computer program for an uninhibited smoke plume and associated computer software

A Program Plume has been created to compute the air entrainment for a given fire size and a specified hot layer height. The solution is based on integration of conservation law equations. The empirical assumptions are related to the flame height and to the coefficient of entrainment and are based on the experimental data of California's Institute of Technology. Calculations are compared with the experimental results obtained in the field tests. The program seems to describe the experimental data better than other known methods. A software package called Firecalc includes seven modules, based on the plume model, which describe hot layer properties in confined compartments relevant to practical situations. The computational results of these modules are also in good agreement with available results of field and laboratory tests.     

Temperature profile of ceiling jet flow along an inclined unconfined ceiling

Many theoretically and/or experimentally derived correlations have been proposed for predicting the response time of a fixed-temperature heat detector and/or a heat sensitive device of a sprinkler in a given fire scenario. These correlations have been developed on the basis of the property of the ceiling jet flow below a flat and smooth ceiling. Some previous studies have reported on the ceiling jet flow generated by a steady fire below an inclined smooth ceiling. However, the exact dependence of the ceiling jet flow on the inclination angle has not yet been clarified.     

Calculating fire plume characteristics in a two-layer environment

Methods are developed to determine axial gas flow conditions within a weakly buoyant plume that passes from an ambient quiescent environment, in which the plume originates, to an upper layer at elevated temperatures. The methods are appropriate for inclusion in two-layer analysis of enclosure fire. In particular, they are first steps in developing a prediction of actuation time for thermally activated automatic sprinklers exposed to an enclosure fire. Results obtained with various methods are compared with measurements in a 1.22 m diameter cylindrical enclosure. National Bureau of Standards Reference: David D. Evans, “Calculating Fire Plume Characteristics in a Two Layer Environment”, Fire Technology, Vol. 20, No. 3, August 1984, p. 39. Note: This paper is a contribution of the National Bureau of Standards and is not subject to copyright.     

Heat flux profile upon building facade with side walls due to window ejected fire plume: An experimental investigation and global correlation

This paper investigates the heat flux profile upon building facade with side wall constraints due to ejected fire plumes from a window of an under-ventilated compartment fire. A reduced-scale model (1:8), consisting of a cubic fire compartment with a facade wall attached and two side walls located symmetrically at both sides of the window is developed. The window dimensions and the side wall distances are changed in experiments, representing different ventilations and constraints on fire plume entrainment. Five heat flux gauges are employed in measurement of vertical heat flux profile upon the facade wall. Results show that with the decrease in separation distance of side walls, the heat flux increases for small windows where dimensionless excess heat release rate ${\dot{Q}}_{ex}^{⁎}\ge 1.3$ (“(half) axisymmetric fire” regime), meanwhile shows weak dependency on side wall separation distance for large windows where ${\dot{Q}}_{ex}^{⁎}<1.3$ (“wall fire” regime). A new global formula is proposed to characterize the vertical profile of heat flux based on Lee’s model without side walls as further modified by a parameter K in relation to the separation distance of side walls and characteristic length scales of the window. Experimental data for different windows and side wall separation distances are well collapsed by the proposed formula.     

建筑火灾中烟气生成量的计算方法

介绍了不同条件下几种典型烟气生成量的计算方法，为建筑火灾中防排烟系统设计与建筑内烟气流动规律预测提供参考。     

高层建筑的火灾自动报警与消防联动控制设计

根据高层建筑的特点,结合具体工程实例,详细介绍了高层建筑的火灾自动报警与消防联动控制系统的设计情况,以完善高层建筑消防控制系统,确保高层建筑消防安全。     

隧道火灾温度测试方法、升温曲线的分析应用

介绍了隧道火灾实验中测量不同车辆燃烧时车内和隧道温度的方法及不同车辆燃烧时车内外隧道代表性测点温度随时间变化的情况;并介绍了国外在隧道混凝土结构耐火灾性能评价中常用的温度一时间升温曲线.同时,应用IS0834标准升温曲线,对20个混凝土立方体试件进行的抗压强度实验,并通过扫描电子显微镜(SEM),对实验后的混凝土试件进行的微观分析.     

火源尺寸对地铁隧道火灾临界风速的影响

以地铁区间隧道为研究对象,考虑有无列车两种情况,采用火灾动力学模拟软件FDS 5.5.3对不同火源尺寸条件下控制地铁隧道火灾烟气不向上游蔓延的临界风速进行数值模拟。结果表明:火源功率一定时,有无列车情况下火源高度、长度及宽度均对临界风速产生影响。无列车时,临界风速随着火源高度、长度、宽度的增加逐渐减小;有列车时,临界风速随着火源高度、宽度的增加先增大后减小,随着火源长度的增大而递减。     

Temperature and velocity distributions from numerical simulations of ceiling jets under unconfined,inclined ceilings

Numerical simulations of ceiling jets under unconfined, inclined ceilings were conducted with the open-source code FireFOAM. A range of ceiling inclinations, 0–30° was considered with a 14 kW convective heat release rate (HRR) heptane fire used as the plume source, and the ceiling mid-point clearance from the top of the 0.228 m diameter burner kept fixed at 0.89 m. The predicted temperature and velocity in the developing ceiling jets were compared against the experimental data and empirical correlations. Temperature and velocity predictions on the elevated side of the ceiling are in general agreement with experimental data. Flow reversal in the lower side of the ceiling was predicted with good confidence, and comparison with experimental data was found to be reasonable. Following existing convention in the literature, the predicted results were non-dimensionalized using the convective HRR, ceiling height and radial distance from the ceiling mid-point. Comparison of the non-dimensional data on the elevated ceiling side showed better agreement for temperature against the correlation, whereas predicted velocity data showed a wider spread around the correlation values.     

高层建筑消防监督管理工作探析

近年来,我国的高层建筑数量和规模不断扩大,不仅缓解了城市人口的居住问题,同时也为广大人民群众提供了娱乐、工作的场所.与传统的多层建筑不同的是高层建筑的高度较高、层数较多,人口高度集中,火灾安全隐患广泛存在.为保障城市消防安全,需要进一步加强高层建筑消防监督管理工作.文章结合消防监督管理工作的现状,简要介绍了消防监督管理的重要性和高层建筑的火灾特点,并着重分析了消防监督管理工作的现存问题和相关建议,以期为广大消防工作者带来一定的工作参考.     

水平喷射火撞击垂直障碍物的温度特性研究

为了研究喷射火撞击邻近建筑物后火羽流的温度场特性,采用数值模拟软件建立喷射火模型,模拟不同长宽比的矩形泄漏孔甲烷水平喷射火撞击障碍物场景,分析喷射火温度在水平方向和障碍物壁面垂直方向的分布特征。结果表明：障碍物壁面温度场受燃气喷射速率和泄漏孔形状特征影响显著;泄漏速率越大,温升区宽度更宽,泄漏孔长宽比越大,温升区域的宽度弱化越显著;泄漏速率增加,使温升区在垂直方向上和水平面上的影响范围更宽,且泄漏孔长宽比增大使温升区厚度增加,水平面的影响宽度发生变化。     

Experimental study of the effects of a thermal plume entrainment mode on the flow structure: Application to fire

The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free thermal plume was examined by generating a plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the plume. We then determined the structure of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume.     

A study on ceiling jet characteristics in an inclined tunnel

The characteristics of a ceiling jet of an inclined tunnel in a fire will be studied and reported in this paper. Scale modeling experiments on a ceiling jet in a model tunnel of length 3.0 m, width 0.8 m and height 1.0 m inclined at different angles of 0°, 10°, 20° and 30° were carried out. Numerical studies by large eddy simulation were then performed. Both experimental observation and numerical simulation indicated that the characteristics of the temperature and velocity fields near the upper tunnel are different from those obtained using the empirical equations reported in the literature. Another set of empirical equations for gas temperature and flow velocity along the tunnel were fitted by experimental data. These derived empirical equations are useful for estimating the temperature and flow velocity patterns for the ceiling jet in an inclined tunnel with an angle within the range 0–30°.     

管廊内火源高度与防火封堵耦合作用下温度分布

为研究管廊内火源高度与防火封堵耦合作用下的温度分布,搭建了1:3的缩尺寸马蹄形管廊模型,通过改变火源的高度和管廊一端的开闭情况,分析管廊内的温度分布.结果表明,高度为10 cm的火源较其他高度的火源在管廊一端封闭的情况下最高温度值最大.在垂直方向上,管廊内的烟气层厚度与火源高度和一端是否封闭关系不大,始终为17 cm左...     

火灾后钢筋混凝土结构火灾温度的判断方法

对火灾后钢筋混凝土结构火灾温度的现行判断方法进行了论述,并说明了各种方法的具体使用,以准确判断火灾后钢筋混凝土结构火灾温度,从而为判断火灾后混凝土结构损伤程度和进行结构修复提供依据。