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

1.研究目的本研究通过火灾风洞实验，研究了房屋燃烧产生的火种在风荷载作用下的特性和行为，并将实验结果与计算流体力学（CFD）技术相结合，建立了基于火种的火灾蔓延模拟模型。研究结果(1)关于火种的产生在日本建筑研究所的防火风洞设施内建造了一座防火房屋。对火灾中产生的火种的数量、形状、大小等方面进行了时间序列测量，系统地改变了入流风速和其他参数。在此基础上，总结了在风荷载和其他因素作用下房屋燃烧产生的火种数量。(2)针对火种的散射问题，通过对美国国家标准与技术研究院（NIST）的火焰动力学模拟器（FD…More S）进行改进，建立了火种散射区域的数值模拟模型。它的设计是为了处理火灾中快速的热量和密度变化，以及考虑对散射粒子起作用的阻力和升力。在和歌山县白滨温泉发生的火灾中，对火焰扩散区域进行了实况调查，并对该模型进行了全面验证。还利用类似于燃炭的木屑进行了锥形量热计测试，以阐明散射燃炭在产热率和质量变化方面的热行为。(3)关于掉落火种的热损伤潜力在地震后，屋顶瓦片通常从建筑物上脱落，由于屋顶结构使用的木质材料暴露在外，现场火灾的风险很高。因此，根据阪神-淡路大地震发生后对神户市进行的航空照片和实地调查，统计了屋顶瓦片倒塌的木制建筑的数量，并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立即脱落的一般表达式。为明确屋面的现场火灾行为，以屋面瓦脱落情况和风速为参数进行了火灾风洞试验。综合上述(1)、(2)、(3)的研究结果，建立了基于火种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