Effect of cross-wind on near-wall buoyant turbulent diffusion flame length and tilt

- Near-wall buoyant turbulent diffusion flame length elongation behavior due to cross air flow was revealed.
- A generalized correlation on the flame tilt angle of near-wall flame was developed.
- The relationship of dimensionless near wall flame length increasing with Froude number was revealed.

This paper investigates experimentally the effect of cross-wind on near-wall buoyant turbulent diffusion flame length and tilt, which has not been quantified in the literatures. Comprehensive experiments are conducted in a wind tunnel [66 m (Length) × 1.5 m (Width) × 1.3 m (Height)] employing a 5 cm square gaseous fuel sand box burner as fire source. Two different fire source positions are considered: at the middle of the two side wall (middle flame) or close to the side wall (near-wall burning) of the wind tunnel. The cross-wind speeds are ranged in 0-1.6 m/s. It was found that the mean flame length of near-wall burning is significantly higher than that of middle flame (free burning) for a given source heat release rate and cross-wind speed. However, for both burning conditions, the flame length firstly decrease, then increase and finally decrease again with increase in cross-wind speed. Non-dimensional correlations are proposed for the increasing regime of flame length against the Froude number (Fr), with two different coefficients suggested for these two burning conditions, respectively. The flame tilt angle is relatively smaller of near-wall burning than that of free burning for a given source heat release rate and cross-wind speed. The evolutions of the tangent values of the flame tilt angle are correlated non-dimensionally against a previously proposed global parameter including both heat release rate and cross-wind speed, accounting for the competition of the inertial force of the cross-wind with the buoyancy force of the fire source. The measured data are shown to be well correlated, with two different coefficients found for the two burning conditions, respectively.