Effect of wind speed on wildfire interaction with multiple structures in the wildland�urban interface

Abstract

: Structure loss in wildland fires has substantially escalated during the last few decades, affected by expanded development in the countryside region, variation in fuel treatment strategies, and climate change. Wildland-urban interface (WUI) fires are a complex multi-physics problem, especially with wind direction and speed varying along natural environments. Comprehending the influence of wind speed on the behaviour of wildland fires and the resulting thermal effects is vital for accurately predicting the damage that structures may incur when exposed to such fires. This paper presents a numerical modeling approach to investigate the effect of wind speed variation on the thermal heat flux and temperature profiles of an array of structures in a typical WUI area. To simulate the effects of a wind-driven wildfire on a suburban area, nine cubic structures, each measuring 6 × 6 × 6 m, were arranged in a grid of three rows of three. The size and shape of these structures were modeled after those used in the full-scale Silsoe cube experiment (Richards and Hoxey 2012). The numerical modelling was performed using FireFOAM, a coupled fire-atmosphere model supported by a large eddy simulation (LES) solver in an open-source CFD tool called OpenFOAM. A set of two wind velocities was modelled to simulate fires burning with an intensity of 10 MW/m. The accuracy of the numerical results was confirmed by comparing them with the aerodynamic measurements of a full-scale building model under normal conditions, without the presence of fire. This analysis revealed the key physical factors that influenced the spread of the fire and its thermal effects on the buildings. The results show that at a constant fire intensity of 10 MW/m 2 , an increase in wind speed from 6 m/s to 12 m/s causes an increase in the surface temperature of all buildings, however, the temperature rise is higher on the first row of buildings compared to the second and the third row. A comparison of the temperature contours at wind speeds of 6 m/s and 12 m/s also revealed that both the average and local temperatures increased with higher wind speeds, reaching a maximum value. However, further increases in wind speed up to 12 m/s resulted in a decrease in the temperature downstream of the fire source due to convective cooling. Furthermore, the analysis of the surface temperature profile ahead of the fire front revealed that the presence of buildings has a significant impact on the development and formation of buoyant instabilities, which directly influence the behaviour of the advancing fire line. This integrated approach of fire-atmosphere modeling represents a crucial advancement in comprehending the dynamics and potential consequences of large wind-driven wildfires in the WUI region. Despite the limitations posed by experimental results in studying the effects of wind-driven wildfires on structures, the current research aims to contribute to the understanding of fire behaviour prediction in WUI. This article serves as an initial report on the application of CFD modeling to examine how variations in wind speed affect wind-fire interaction with multiple buildings in the WUI area.