Comparison of Two and Three Dimensional Simulations of Fires at Wildland Urban Interface

Abstract

Three dimensional simulations of forest fire and wind induced flows are very time consuming because the size of the computational problem becomes very large. From the economical viewpoint, the use of twodimensional simulations is an attractive alternative as means to reduce the computational cost by one or two orders of magnitude. However, the real fires and turbulent flows are never really two-dimensional, and making such simplification may introduce errors whose magnitude is not well known in advance. In this work, the effect of the 2D assumption is studied by performing a series of simulations in both two and three dimensions, and reporting the difference in the effects on structures. The results show that 2D simulations can be used for order-of-magnitude type of analysis, for which purpose they are well suited due to the small computing times. However, the differences seem to be too large for accurate predictions of the building and human response. Therefore, the critical simulations of the future analysis should be made in three dimensions. KEYWORDS

Numerical Investigation of Bushfire-Wind Interaction and its Impact on Building Structure

“…In 2009, Hostikka et al [26] reported a numerical investigation of fires at wildland urban interface using domain size in the order of tens of meters and grid size down to 6.25 cm. The aim of their study was to compare 2-D and 3-D simulations and the scope was limited to the investigation of the thermal impact of bushfire on a building.…”

“…Cunningham et al [22] used a hyperbolic tangential function, whereas Hostikka et al [26] used a power function. In the current study the power function of the form…”

Forest fire impacts on buildings

“…However, the differences seem to be too large for accurate predictions of the building response. Therefore, the critical simulations of the impacts to target should be made in three dimensions [11]. Figure 2 below describes a simplified case where a forest fire front has reached a building and has caused ignition of a combustible facade of the building.…”

“…Recently the effect of 2D assumption in calculations has been studied by performing a series of simulations in both two and three dimensions [11]. The simulations were performed using the Fire Dynamics Simulator (FDS) software [12], which is commonly used to simulate the fire phenomena both inside and outside buildings.…”

Study of wildfire in-draft flows for counter fire operations

“…The two-dimensional representation allows for a reduction in the computational cost by two orders of magnitude. A recent VTT study [4] compares the results of two and three dimensional models of wildfires. The conclusions validate the application of two-dimensional analysis to this study since the entrainment flow that is being analyzed here is more concerned with flow patterns and range of values rather than finely accurate velocities fields.…”