Mechanism of Urban Fire Spread by Firebrands using Fire Wind Tunnel Experiments and CFD Analysis

1.研究目的本研究旨在进行火灾风洞实验，以阐明在风荷载下燃烧房屋产生的火焰的性质和行为，并将实验结果与计算流体动力学(CFD)技术相结合，开发基于火焰的火灾蔓延模拟模型。2.研究成果(1)关于火焰的产生日本建筑研究所的火灾风洞设施内建造了一座防火房屋。对火灾期间产生的火焰的数量、形状、大小和其他方面进行了时间序列测量，系统地改变了流入风速和其他参数。在此基础上，对火灾房屋在风荷载等因素作用下产生的火焰量进行了概括。(2)针对火焰的散布问题，通过对火灾动力学模拟器(FD-…)的改进，建立了一个数值模拟模型更多来自美国国家标准与技术研究院的S(音译)预测了火焰的散布区域。它的设计是为了处理火灾中的快速热量和密度变化，以及考虑作用在散射颗粒上的阻力和升力。该模型基于对和歌山县白滨温泉发生的火灾中火种散布区域的实况调查结果进行了全面验证。锥形量热计还使用类似火焰的木屑进行了测试，以从产热率和质量变化方面阐明散落的火焰的热行为。(3)关于坠落的火焰的热损害潜力在地震后屋顶瓦片通常从结构上脱落的情况下，由于用于屋顶结构的木质材料暴露，现场火灾风险变得很高。鉴于此，根据航拍照片和在阪神-旭日大地震后对神户市进行的实地调查，统计了屋顶瓦片倒塌的木结构建筑物的数量，对结构破坏程度进行了分类。此外，还提出了预测地震后屋面瓦片瞬间脱落的一般表达式。为了弄清屋面现场火灾行为，以屋面瓦片脱落状态和风速为参数，进行了火灾风洞实验。(4)火灾蔓延模拟模型的开发结合上述(1)、(2)、(3)的研究成果，建立了基于火标的火灾蔓延模拟模型。还进行了实际建成区的案例研究。较少

1.Purpose of the ResearchThis study was intended to perform fire wind tunnel experiments to elucidate the properties and behavior of firebrands produced from burning houses under a wind load and to develop a firebrand-based fire-spreading simulation model by combining the experiment results with the Computational Fluid Dynamics(CFD) technique.2.Findings of the Research(1)With regard to firebrand generationA fire resistant house was constructed inside the fire wind tunnel facility at the Building Research Institute, Japan. Time-series measurements were conducted for quantity, shape, size, and other aspects of firebrands generated during a fire, systematically varying the speed of inflow wind and other parameters. Based on those results, the quantity of firebrands generated from a burning house under a wind load and other factors were generalized.(2)With regard to the scattering of firebrandsA numerical simulation model was developed through modification of the Fire Dynamics Simulator(FD … More S) of the National Institute of Standards and Technologies(NIST) to predict the firebrand scattering area. It was designed to deal with rapid thermal and density changes in a fire, as well as to take into account the drag and lift forces working on scattering particles. The model was subjected to full validation based on the results of a fact-finding survey of the firebrand scattering area in a fire that broke out at the Shirahama Spa, Wakayama prefecture. Cone calorimeter tests were also conducted using wood chips resembling firebrands to clarify the thermal behavior of scattering firebrands in terms of the heat generation rate and mass changes.(3)With regard to the thermal damage potential of falling firebrandsIn a post-earthquake situation in which roof tiles have usually fallen off of a structure, the spot fire risks become high because of the exposure of wooden materials used for roof structures. Given that, based on aerial photographs and field surveys performed of the city of Kobe after the Great Hanshin-Awaji Earthquake, the number of wooden buildings with fallen roof tiles was counted, classifying the level of structural damage. In addition, a general expression was proposed for predicting the shedding of roof tiles immediately after an earthquake. To clarify the spot fire behavior of roofs, fire wind tunnel experiments were performed using the shedding status of roof tiles and wind speed as parameters.(4)Development of firebrand fire spread simulation modelA firebrand-based fire-spreading simulation model was developed by integrating the findings described in (1),(2) and (3) above. Case studies of actual built-up areas were also conducted. Less