The uneven heating of tree stems in wildland surface fires is a pervasive phenomenon that leads to uneven charring and fire scars and is caused by the interaction between flames, ambient wind, and the cylindrical stem. The Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology has been used to numerically model the results of an experimental study on the charring of tree stems in a wind tunnel [1]. The wind tunnel was modeled as a 42 x 42 x 200 cm rectangular chamber having a fire-brick base with a variable diameter stem section in the center. The ends were open, allowing a constant velocity wind flow through the chamber. The fire was modeled as a constant speed heading fire with a heat release rate of 260 W/m2. The charring pattern was inferred from data on temperature and heat flux at the boundary on both the windward and leeward sides of the tree.
Results/Conclusions
Charring patterns were generated for tree diameters of 4, 6, and 8 cm with wind speeds of 1.0, 2.5, and 4.0 m/s with a constant rate of fire spread and compared with the experimental results of Inoue. The effect of varying the rate of the fire spread from 0.05 to 0.25 m/s was also investigated for a tree diameter of 6 cm and 1 m/s wind speed.
[1] Shoji Inoue, A Fundamental Study on Fire-scar of Stem in a Forest Fire - Estimation of Wind Velocity from Stem-bark Char by Examination using Wind Tunnel, Translation of Japanese Journal of Forest Environment, 41(1), 19-24 (1999).
