@article {bnh-8366, title = {Physics-based modelling of junction fires: Parametric study}, journal = {International Journal of Wildland Fire}, year = {2023}, month = {02/2023}, abstract = {

Background; Junction fires occur when two fire fronts merge. The ROS and HRR of the junction quickly increase more than that of each fire front; this effect is exacerbated by slopes. Aims; Numerical modelling of junction fires and an interpretation of their behaviour is given by examining the key factors that influence the fires. Methods; Physics-based simulations of laboratory-scale junction fires were performed for shrub fuel bed using FIRESTAR3D. Twenty cases were simulated to quantify the effect of slope (0{\textdegree} to 40{\textdegree}) and junction angles (15{\textdegree} to 90{\textdegree}). Key results; Accelerative and decelerative behaviours were observed for junction angles lower than 45{\textdegree}, but above this, deceleration was absent. The behaviour was firmly related to junction angle evolution which controlled the flame and the interactions between fire fronts. HRR followed similar trends; maximum HRR increased with increasing junction angle. Convection was found to be the primary heat transfer mode in the initial propagation phase. In non-slope cases, radiation was the dominant method of heat transfer, but convection dominated fires on slopes. Conclusions; The physics-based model provided great insight into junction fire behaviour. The junction angle was critical for determining ROS and fire behaviour. Implications; The research helped to assess the effects of some topographical parameters in extreme fires. Situational awareness, operational predictions, and firefighter safety will consequently improve.

}, keywords = {fire behavior, physics-based model}, url = {https://www.publish.csiro.au/WF/justaccepted/WF22121}, author = {Ahmed Hassan and Gilbert Accary and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-7359, title = {Physics-Based Simulations of Flow and Fire Development Downstream of a Canopy}, journal = {Atmosphere}, volume = {11}, year = {2020}, month = {06/2020}, abstract = {

The behavior of a grassland fire propagating downstream of a forest canopy has been simulated numerically using the fully physics-based wildfire model FIRESTAR3D. This configuration reproduces quite accurately the situation encountered when a wildfire spreads from a forest to an open grassland, as can be the case in a fuel break or a clearing, or during a prescribed burning operation. One of the objectives of this study was to evaluate the impact of the presence of a canopy upstream of a grassfire, especially the modifications of the local wind conditions before and inside a clearing or a fuel break. The knowledge of this kind of information constitutes a major element in improving the safety conditions of forest managers and firefighters in charge of firefighting or prescribed burning operations in such configurations. Another objective was to study the behavior of the fire under realistic turbulent flow conditions, i.e., flow resulting from the interaction between an atmospheric boundary layer (ABL) with a surrounding canopy. Therefore, the study was divided into two phases. The first phase consisted of generating an ABL/canopy turbulent flow above a pine forest (10 m high, 200 m long) using periodic boundary conditions along the streamwise direction. Large Eddy Simulations (LES) were carried out for a sufficiently long time to achieve a quasi-fully developed turbulence. The second phase consisted of simulating the propagation of a surface fire through a grassland, bordered upstream by a forest section (having the same characteristics used for the first step), while imposing the turbulent flow obtained from the first step as a dynamic inlet condition to the domain. The simulations were carried out for a wind speed that ranged between 1 and 12 m/s; these values have allowed the simulations to cover the two regimes of propagation of surfaces fires, namely plume-dominated and wind-driven fires

}, keywords = {canopy, fire spread, grassland fire, Large Eddy Simulation, physics-based model}, doi = {https://doi.org/10.3390/atmos11070683}, url = {https://www.mdpi.com/2073-4433/11/7/683}, author = {Gilbert Accary and Duncan Sutherland and Nicolas Frangieh and Khalid Moinuddin and Ibrahim Shamseddine and Sofiane Merdji and Dominique Morvan} }