Modeling concurrent flame spread over a thin solid in a low-speed flow tunnel

A three-dimensional model of concurrent flame spread over a thin solid in a low-speed flow tunnel in microgravity was formulated and numerically solved. In a parametric study varying the flow velocity, oxygen level, and tunnel and solid fuel widths, two distinctive types of flame behavior were noted. In high-oxygen-percentage and/or higher-speed flows, the flames were long and far away from the quenching limit. In such cases, three-dimensional effects were dominated by heat loss to the wall in the downstream portion of the flame. In low-oxygen and low-speed flows, the flames were short and in the region near the quenching limit. These near-limit flames were controlled by the oxygen supply rate. Oxygen-side diffusion in the crosswind direction became a dominant mechanism exhibiting large effects on the narrow three-dimensional flames. A number of trend reversals on spread rates and extinction limits were discovered for these near-limit flames. Aided by the detailed flame profiles obtained in the computations, an explanation for the reversal phenomena is offered in the paper.