Flame morphology of pool fire in cross airflows: A theoretical analysis and generalized relations for comprehensive data of fire sizes, fuels and flow speeds

This paper provides a comprehensive parameter study into the flame morphologic characteristics (flame base drag length l(dr), flame trajectory length l(tr), horizontal flame length l(hori) and vertical flame height l(vert)) of pool fires under cross airflows. A scaling analysis was performed on the basis of physically the balance of the momentum flux of the cross airflow to the buoyancy flux of the flame and its determination on the flow development, which controls the air entrainment for stoichiometric combustion hence the flame morphologic characteristics. With the increasing of cross airflow speed, the flame flow could be plume type (buoyancy flux is important) or boundary layer type (cross airflow momentum flux dominant), and the evolution behaviors of flame morphologic parameters were revealed. Based on the analysis, a generalized function was developed with a new dimensionless heat release rate Q(center dot)* defined, in which U-w(2)/g (a term representing the competition of cross airflow momentum to buoyancy of the fire) was found as the appropriate characteristic length. Experimental results obtained in the present study with a square gaseous burner for various cross airflow speeds (U-w) and heat release rates, as well as those reported extensively in the literatures for comprehensive ranges of fuels (15 types of fuel), pool sizes (diameter or square burner side length: 0.05 m to 52 m) and cross airflow speeds (0.43 m s(-1) to 13.5 m s(-1)), were gathered to validate the developed model. The experimental data of comprehensive ranges showed to be well represented by the proposed function and practical generalized correlations for the above flame parameters were obtained for characterizing the flame morphologic characteristics in cross airflows.