Scaling analysis of downstream heating and flow dynamics of fires over an inclined surface

Fire spread is known to accelerate uphill over inclined surfaces due to an intrinsic coupling between geometry and fire-induced flows, especially when the slope exceeds a critical angle. The fundamental relationships which govern this close coupling, however, are not yet fully understood. To investigate these relationships, propane-fueled fires were produced over a tilt table at the Missoula Fire Sciences Lab. Large-scale fire tests with heat-release rates ranging from 81 kW to 2.25 MW were conducted. The angle of inclination, θ, was varied between 0∘ and 30∘. A micro-thermocouple array along the centerline of the table was used to measure downstream gas temperatures. Flames were seen to start attaching to the inclined surface at θ = 18∘, independent of the fireline intensity. The centerline temperatures under attached flame conditions are consistent with McCaffrey's buoyant flame temperature correlation, suggesting the buoyancy-driven nature of the inclined fires. The local gas velocity was measured using temperature-correlation velocimetry through the streamwise temperature signals. Results show that the local flow was accelerated in the attached flame region driven by buoyancy before reaching a peak. Velocity of the flow slowed down after the peak due to weaker buoyancy within the intermittent and plume regions. The mean surface velocity of the attached flame scales directly with the angle of inclination (sinθ) and the fireline intensity (I2/3), providing a promising method to evaluate convective heat transfer using the geometry of the inclined fire.