The interaction between fuel inclination and horizontal wind: Experimental study using thin wire

Abstract

Forward flame spread behavior changes significantly with both the fuel inclination and the wind velocity, but interactions between the inclination and horizontal wind is still not well understood. In this work, a controlled laboratory experiment is conducted in a wind tunnel providing a horizontal wind ranged from 0 (quiescent) to 2.5 m/s, and a thin electrical wire as fuel that can be inclined from a horizontal (0°) to a vertical (90°). An electrical wire of 0.8-mm diameter with copper core and polyethylene insulation was used as the characteristic thin fuel. The flame-spread rate, as well as the flame geometrical characteristics, was quantified as a function of the wind velocity and wire inclination. Results show that as the horizontal wind velocity is increased, the flame-spread rate over the wire for all inclination angles first increased to a maximum, and then, slightly decreased until blow-off. The critical inclination for flame acceleration decreases from 45° to 15° as the wind velocity increases. The fastest flame spread along the inclined wire occurs when the wind pushes the flame parallel to the fuel. The interaction between the fuel inclination and wind velocity are quantified using the Froude number. Moreover, the blown-off wind velocity decreases as the fuel inclination is increased, which can be explained by a critical strain rate (536 s−1). This work provides valuable information for fire behaviors under wind not only on the inclined wires and roofs in structure fires, but also on inclined branches in wildland fires.