建筑中庭及周围房间火灾烟气运动规律研究

运用FDS软件对中庭及周围房间发生火灾后烟气填充过程进行模拟,研究起火位置对烟气运动规律的影响。研究结果表明,中庭火源功率大,烟气温度最高。起火点位置越高,顶棚烟气层温度越大;受烟气控制系统及中庭蓄烟作用的影响,烟气层停留在起火层,不会影响下层人员疏散。分析结果对中庭及周围房间消防性能化设计提供参考。     

自然排烟有效性对扁平空间烟气层的影响

针对采用自然排烟方式的扁平空间建筑火灾,采用1∶20缩尺寸模型,研究不同排烟失效模式、火源功率和火源位置等因素对烟气层特性的影响。使用天平记录燃料质量变化并计算火源功率,采用热电偶采集顶棚下烟气层温度数据,研究扁平空间顶棚低温区和高温区的分布特性。试验表明:各工况下燃料质量损失速率变化不大;火源靠近壁面时,高温烟气区占比减少;排烟口和补风口的多种失效模式对扁平空间火灾的顶棚烟气层分布特征影响较小。     

热障效应对中庭自然排烟影响研究

采用数值模拟技术研究“热障效应”对中庭自然排烟效果的影响规律,分析不同火源功率在不同温度梯度下中庭顶部自然排烟口的排烟效果.结果显示,在高大空间内部,相同火源功率下,环境温度梯度越大,顶部烟气温度越低,通过顶棚开口向外的烟气质量流率越小.火源功率越小,环境温度梯度对顶部开口自然排烟效果的影响越明显,即热障效应的影响越突出.随着火源功率增大,环境温度梯度对自然排烟效果的影响逐渐减弱.     

水电站不同火源强度烟气运动模拟

应用FDS模拟水电站地下主厂房火灾烟气填充与流动动态过程,分析不同火源强度下烟气分层规律.重点分析火源强度为10 MW时的烟气填充过程、顶棚射流温度和横向烟气温度的变化特点.结果表明,烟气到达某一高度的时间随火源强度的变化服从一阶指数衰减;顶棚射流温度和烟气层横向温度变化具有很强的规律性;下层空气温度不高但浓度相对较高;同一水平面的烟气浓度分布很不均匀,距火源30 m以外处的浓度是距火源中心10 m以内处浓度的2～3倍.     

送排风对中庭烟气温度影响的实验研究

通过理论分析得出了无喷淋中庭火源的火焰气流各分区的高度范围及烟气温度随中庭高度的变化趋势.在模型中庭内进行了发烟实验,得到了在自然状态、上送风、下排烟和上送下排状态下烟气温度随模型中庭高度的变化曲线.实验结果与理论结果的对比表明,在湍流区二者偏差不大.     

综合管廊顶棚下方横向温度分布研究

通过FDS数值模拟研究不同火源功率、火源纵向位置对综合管廊横向温度分布的影响。研究表明:顶棚下方横向温度整体呈火源正上方温度高、两侧温度低的趋势，随着与火源中心距离增大，温度逐渐降低，趋于稳定。火源左侧温度高于右侧。当火源纵向位置一定时，火源功率越大，顶棚下方横向温度越高。相同火源功率下，火源距离管廊左封闭端越近，顶棚下方横向温度越高，这与综合管廊防火门等引起的烟气回流有关。综合考虑火源功率和火源纵向位置等因素，提出综合管廊顶棚下方横向温升预测模型，将模型计算值与数值模拟值进行对比，发现两者吻合度较好，相对误差在可接受范围内。     

酒店中庭自然排烟方式的数值模拟

分析青海某庭院式酒店中庭区域的烟气蔓延,通过模拟得到排烟口高度处烟气层内热流、质量流、体积流随时间变化的情况,分析建筑自然排烟系统的有效性,并对比排烟口布置位置对排烟效果的影响。通过计算得出排烟窗面积为内庭院面积的10%时能够保障建筑的消防安全。在4.0 MW的火源功率下,火源稳定之后150s左右烟气层稳定在30～32m高度处;自然排烟口位于庭院中心处的排烟效果优于排烟口位于四周。     

非规则大空间内烟气填充的研究

采用场模型和贴体坐标技术对某机场候机大厅的烟气填充情况进行了研究。研究结果表明,烟气下降到对人逃生有害的高度需要相当长的时间,随着火源强度的增加,顶棚射流速度和烟气温度增加,烟气层底面高度下降。     

不同季节高大中庭火灾烟气上升高度分析

采用理论计算和数值模拟方法,分析了不同季节、不同火灾功率下烟羽流上升高度,得出相应结论。火源功率越大,或室内温度梯度越小,则烟气上升高度越高。对于高大中庭,大部分火灾烟气无法上升至顶棚,应在不同高度上设置线型光束火灾探测器防止漏报,同时沿高度分层设置排烟设施,以排出无法上升至屋顶的烟气。     

服装类商场中庭建筑的火灾相似模型实验研究

通过相似模型实验，得到了服装类中庭建筑火灾的火源燃烧发展规律和火源释热率变化规律；分析得到了该类中庭建筑的火灾烟气填充运动规律。     

The impact of atrium shape on natural smoke ventilation

The performance efficiency of natural smoke ventilation in atria spaces are influenced greatly by several design decisions such as atrium shape, height, size and openings location. This paper investigates the impact of atrium shape (horizontal profile) on smoke ventilation performance in naturally ventilated atria. Three different configurations (square, rectangular and triangular prism) with the same area, height, and hence, volume were tested. The smoke ventilation performance is being assessed in terms of smoke filling time using a computational fire dynamic simulator (FDS). FDS is used to simulate the natural smoke filling resulting from atrium fire in the three configurations. The smoke layer interface height as a function of time and soot mass fraction and temperature as a function of height have been registered during the simulation. The predicted transport lag time for initial formation of the smoke layer beneath the ceiling (ceiling jet) was compared for the three tests. In order to test sensitivity of the shapes, all other parameters were designed to be similar in the three tests, and the same fire scenario was applied including inlet and outlet area, and fire size and location. The results showed that the rectangular configuration contributes better to smoke ventilation, and that the triangular configuration is the most critical in terms of smoke filling time, followed by the square configuration.     

火源高度对隧道烟气温度及质量流量影响研究

由于隧道发生火灾后实际的燃烧面要高于隧道地面,距离隧道拱顶也越近,因此对隧道的危害也越大。通过CFD数值模拟软件进行了一系列不同火源功率的全尺寸数值计算,研究了火源高度对隧道内温度分布及烟气质量流量的影响。研究发现:火源高度对拱顶温度分布有着明显的影响,火源高度越高,火源附近温度衰减越慢;在远离火源的地方,不同火源高度的拱顶温度衰减相差不大,考虑火源高度后拱顶温度衰减略慢于没有考虑火源高度。火源高度及火源功率对一维蔓延阶段的烟气质量流量有影响,考虑火源高度后烟气质量流量要明显小于火源位于隧道地面的情形,但随着火源功率增大,它们之间的区别越来越小。考虑火源高度后相同火源功率下烟气分层高度显著提高,而人体耐受温度位置变化不大。     

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.     

A numerical study of atrium fires using deterministic models

The smoke filling process for the three types of atrium space containing a fire source are simulated using the two types of deterministic fire model; zone model and field model. The zone model used in this simulation is CFAST (Version 3.1) developed at the Building and Fire Research Laboratories, NIST in the USA. The field model is a self-developed CFD model based on full consideration of the compressibility and k–ε modeling for the turbulence. This article is focused on finding out the smoke movement and temperature distribution in atrium spaces. A computational procedure for predicting velocity and temperature distribution in fire-induced flow is based on the solution of three-dimensional Navier–Stokes conservation equations for mass, momentum, energy, species etc. using a finite volume method and non-staggered grid system. Since air is entrained from the bottom of the plume, total mass flow in the plume continuously increases. Also, the ceiling jet continuously decreases in temperature, smoke concentration and velocity; and increase in thickness with increasing radius. The fire models, i.e. zone models and field models, predicted similar results for the smoke layer temperature and the smoke layer interface heights. This is important in fire safety, and it can be considered that the required safe egress time in three types of atrium used, in this paper is about 5 min.     

A Simplified Mathematical Model for Predicting the Vertical Temperature Profiles in Enclosure Fires Without Vertical Opening

This paper presents a mathematical model to predict the instantaneous temperature profiles in sealed or ceiling vented compartment fires. It has been observed in the existing research that in compartments without vertical opening, smoke fills the volume very soon indicating that the so-called one-zone type distribution forms quickly, and the gas temperature inclines linearly with height above the fire source. These characteristics are different from the smoke filling properties in enclosure fires with vertical openings. An assumption of linear distribution for temperature was introduced and a modified one-zone model was subsequently proposed in order to predict the transient smoke temperature profiles after the smoke fills the enclosure. With the knowledge of the heat release rate, the prediction model was established based on unsteady energy conservation by changing the heat loss factor using the semi-empirical models for fire plume and ceiling jet. Experiments including sealed and ceiling vented conditions were conducted to validate the model and the comparisons between measurements and predictions suggested the model can give fairly satisfactory estimations for the transient temperature profiles for both tests.     

中庭空间烟气蔓延对火灾探测的影响研究

针对建筑中庭不同顶棚高度下火灾烟气蔓延及感烟探测过程,基于火灾动力学模拟软件(FDS) 开展了数值模拟试验。研究了顶棚处温度及能见度云图的变化情况,并分析了不同高度条件下线型光束感烟探测、消光系数及温度值的参数曲线特征。结果显示,顶棚处减光率到达50%/m 的时间和顶棚高度存在较好的函数关系y=26.58 × 1.06x,对应的R 值为0.996;顶棚高度≥30 m 时,竖直布置线型光束火灾探测器也是一种较好的选择。该研究能够为中庭内消防工程设计及火灾探测报警系统的布置及设计提供技术支撑,提高建筑消防安全水平。