Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain

The wind and slope are deemed to be the determinant factors driving the extreme or erratic spread behaviour of wildfire, which however has not been fully investigated, especially to elaborate the mechanism of fire spread associated with heat transfer and fluid dynamics. A systematic study is therefore carried out based on a physical-based simulation and Proper Orthogonal Decomposition (POD) analysis. Results show that compared to the wind, the slope plays a more profound effect on the fire structure; with the increase of slope, the fireline undergoes a transition from a W-shape to the U- and pointed V-shape, accompanied by the stripe burning zones, indicating a faster spread but incomplete combustion. The wind effect is distinguished to mainly induce the turbulent backflow ahead of the fire front, while the slope effect promotes the convective heating by the enhanced slant fire plume. Different mechanisms are also identified for the heat transfer ahead of fireline, i.e., the radiative heat is affected by the combined effects of flame length and view angle, and in contrast, the convective part of heating flux is dominated by the action of flame attachment, which is demonstrated to play a crucial role for the fire spread acceleration at higher slopes (>20∘). The POD analysis shows the distinct pattern of flame pulsating for the respective wind and slope effects, which sheds light on modeling the unsteady features of fire spreading and reconfirms the necessity of considering the different effects of these two environmental factors.