Surface Flow Characterization of Fires Under the Combined Effect of Slope and Wind

Abstract During wildland fire spread both slope and wind act together to modify fire dynamics, commonly accelerating the rate of fire spread. To investigate this coupling effect, flow field measurements were conducted on stationary gaseous fires produced over a tilt table in a wind tunnel, with fireline intensities ranging from 41 to 123 kW/m. The angle of inclination ( θ ) and the wind speed ( V ) were varied from 0 to 30° and 0.30 to 1.27 m/s, respectively. The surface gas velocity of the fire at various downstream locations was measured using temperature-correlation velocimetry (TCV), which was enabled using streamwise temperature signals from an array of micro-thermocouples. The effect of the slope was converted to an equivalent surface velocity, $$\:{U}_{slope}$$ , following the concept of fire-induced flow over an inclined surface. A momentum analysis was conducted to isolate the coupling effect of slope and wind based on $$\:{U}_{slope}$$ , V , and the mean measured surface gas velocity within the attached flame region, $$\:{U}_{attach}$$ . Finally, a relationship was proposed to predict the mean velocity of the downstream flow using the upstream wind velocity, flame geometry, and the angle of inclination. The proposed relationship enables estimation of downstream heat transfer from a flame to unburnt fuel ahead of the fire, providing a generalized method to evaluate the combined slope and wind effect on heating which drives forward fire spread.