| Summary: | FireFOAM solver is used to simulate downward flame spread on the surface of a single-wall corrugated board with different inclination angles (0° ∼ −30°), and to study countercurrent fire spread behavior and heat transfer control mechanism on solid surfaces under different inclination angles. The simulation results show that when the inclination angle is less than −20° the fire spread rate and mass loss rate will first decrease and then stabilize. Combining the flow field and temperature field, it can be found that the cold air entrained by the flame will have a cooling effect occurs on the distal end of the downstream surface during the fire spread process. By analyzing the two heat transfer modes of convection and radiation in the preheating zone, it is found that the heat flux received by the solid surface is dominated by convection, while the radiation heat flux is the main reason for the deceleration stage and the speed difference of quasi-steady-state spreading under different inclination angles. In the process of inclined downward fire spreading, the behavior of deceleration followed by uniformity appears because the heat transfer mechanism changes from ignition energy control to flame spread control.
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