Experimental Investigation of the Velocity Field in a Controlled Wind-aided Propagating Fire Using Particle Image Velocimetry

Abstract

Experiments on wind-aided firespread across an array of small diameter discrete fuel elements using a Particle Image Velocimetry (PIV) and thermocouple system were carried out in a specially designed wind tunnel at Northrop Grumman Space Technology. The rate of spread is determined using data gathered from thermocouples that were uniformly spaced within the fuel elements along the primary fire spread direction. The fuel consisted of a two dimensional array of identical, evenly spaced, wooden elements, positioned vertically in holes in a ceramic substrate. Utilization of this fuel bed allowed for repeatability of experiments. The effect on firespread rate was investigated for two different fuel loadings. A PIV system was used to investigate the various fluid dynamic structures present within a propagating fire front, and how firespread was influenced. From analysis of the thermocouple and PIV data it was determined that in the high fuel loading situation (total dry fuel mass per unit fuel bed area, m = 3.12 kg/m 2 ) firespread was assisted by intense forced turbulent convection, which preheated the fuel elements downwind of the fire front. For the low fuel loading case (m = 0.78 kg/m 2 ) radiation played a more significant role in preheating of the unburned fuel elements.