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，以阐明风荷载下燃烧房屋产生的火焰的特性和行为，并通过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。在日本建筑研究所的火灾风洞设施内建造了一座耐火房屋。时间序列测量进行了火灾过程中产生的火把的数量，形状，大小和其他方面，系统地改变流入风的速度和其他参数。在此基础上，归纳了风荷载等因素作用下房屋燃烧产生的火源量。（2）对火灾动力学模拟器（FD）进行了改进，建立了火灾目标散布的数值模拟模型 关于我们 S）来预测燃烧物的散射面积。它的设计是为了处理火灾中快速的热量和密度变化，以及考虑到对散射颗粒的阻力和升力。根据和歌山县白滨温泉发生的火灾中燃烧物散布区域的实况调查结果，对该模型进行了全面验证。锥形量热仪测试也进行了使用木屑类似的火把，澄清的热行为散射火把的发热速率和质量变化。（3）关于防火板坠落的热损伤可能性在地震后，屋顶瓦片通常从建筑物上脱落的情况下，由于用于屋顶结构的木制材料暴露在外，现场火灾的风险变得很高。鉴于此，根据坂神淡路大地震后对科比市进行的航空摄影和实地调查，统计了屋顶瓦片脱落的木结构建筑物的数量，并对结构受损程度进行了分类。此外，还提出了一个预测地震后屋面瓦脱落的一般表达式。为研究屋面的火灾特性，以屋面瓦片脱落情况和风速为参数，进行了屋面火灾风洞试验。（4）火标火灾蔓延模拟模型的开发综合上述（1）、（2）和（3）的研究结果，开发了基于火标的火灾蔓延模拟模型。还对实际建成区进行了个案研究。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