Burning behavior of mixed-convection wind-driven flames under varying freestream conditions
2021
Singh, Abhinandan | Singh, Ajay V.
Wind-driven fires were experimentally-investigated to understand the influence of varying flow conditions on the local burning behavior of a condensed fuel surface. These flames imitate the fire dynamics of hazardous fires occurring in a forced-flow environment sharing the likes of wildland fires or ventilated compartment fires. The flame structure was probed using a digital camera. Small-scale wind-driven flames usually operate in a mixed-convection regime. Therefore, to decipher the competitive effect of buoyancy, momentum, and turbulence intensity, a non-dimensional parameter ξx=Grx1/ψx2n was evaluated at multiple streamwise locations within the pyrolysis zone. To quantify the dependence of each flame parameter, first, a comparison between the flame standoff and ξx was conducted, where a power-law trend was observed. Also, the convective heat transfer towards the fuel surface varied inversely with the flame standoff distance and ξx. Finally, the local mass burning rates were evaluated and plotted against the convective heat flux and ξx, where a positive linear scaling was observed for the former, and a negative power-law trend was shown by the latter. Based on the experimental measurements, a unified local mass burning rate correlation is proposed in the present work that performs exceptionally well for both laminar and turbulent boundary layer diffusion flames.
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