Temperature elevation and trajectory in the downwind region of rectangular fire sources in cross-winds

Abstract

The effect of cross-wind on the temperature elevation in the downwind region of rectangular diffusion burners was investigated in wind tunnel experiments. The experimental parameters were the geometry of the diffusion burner (the side length parallel and orthogonal to the cross-wind L1=0.2–0.8m and L2=0.4–2.0m, respectively, and the aspect ratio r=1–10), the heat release rate (Q˙=38.3–383.3 kW), and the inflow velocity of the cross-wind (U∞=0.59–1.49 m/s). Following the concept of the previously proposed point fire source model, the fractional contribution of the cross-wind velocity on the velocity along the trajectory N was introduced to close the system of governing equations, and a relevant line fire source model was derived. The line fire source model was correlated by the measurement results of the present experiment for the diffusion burner with the largest aspect ratio (r=10). Although the predicted temperature elevation along the trajectory by the present model was similar to that of the existing models, there was a substantial discrepancy in the predicted trajectory. For the unified analysis of temperature elevation and trajectories of the fire sources with various aspect ratios, the point fire source model was firstly tested to correlate the measurement results. As expected, the agreement was less successful for the results of the fire sources with large aspect ratios, especially in the region close to the fire source. Thus, the point fire source model was modified to consider the physical effects of the aspect ratio of the fire source and the attachment of the fire plume to the ground by invoking the correlations for the line fire source. With the modified model, the agreement between the predicted and measured results significantly improved. The proposed model is useful for assessing the hazards of wind-blown fire plumes in large outdoor fires on human activities such as firefighting or the evacuation of residents.