Effect of wind speed on thermal behavior and airflow distribution within a firebrand pile: a numerical study

Firebrands are a major cause of spot ignition and fire spread in wildland–urban interface fires; however, their thermal behavior under varying airflow conditions remains not fully understood. This study employs numerical simulations to examine the influence of wind speed on the burning and thermal behavior of glowing firebrand piles. The analysis focuses on surface temperature, heat flux, and particle behavior under wind speeds ranging from 0.9 to 2.7 m/s. Results show that higher wind speeds (2.7 m/s) enhance surface oxidation and heat release, leading to increases in pile surface temperature and substrate incident heat flux by factors of approximately 1.2 and 1.6, respectively, compared with lower speeds (0.9 m/s). However, intensified convective cooling at higher airflow accelerates particle burnout, with a central particle consumed after about 100 s at 2.7 m/s, compared to more than 300 s at 0.9 m/s. For smoldering firebrand accumulations of 0.06 g/cm 2 , the simulated peak average total heat flux to the substrate ranged from 18 to 30 kW/m 2 under airflow speeds between 0.9 and 2.7 m/s. Notably, pronounced spatial variations were observed, with the windward region exhibiting substantially elevated localized heat fluxes. At an airflow speed of 2.7 m/s, localized values reached up to 76 kW/m 2 , while instantaneous peak fluxes exceeded 125 kW/m 2 . These findings improve understanding of heat transfer and combustion dynamics in firebrand piles.