Dynamic Behavior and Structure of Wind-Blown Flames

摘要: Time-dependent movements described as pulsing, puffing or swaying are among the most visible characteristics of open flames. In the fire safety field,“puffing” of pool fires has been well studied, with scaling of the frequency of flame pulsations with the size of the burner being well correlated with the diameter of the fire size [1]. For smaller fires, a “flickering” instability at a higher frequency than “puffing” is also formed at the top of small flames [2]. Despite many years of study, the dynamics of wind-driven fires, especially those resembling a line fire configuration have not been well documented, instead focusing on their steady or averaged characteristics [3]. This configuration has recently been found to be particularly relevant when attempting to understand propagating wildland fires, prompting this more detailed study of their time-dependent behavior.Recent studies of spreading fires in the 3× 3 m wind tunnel at the Missoula Fire Science Laboratory have shown coherent structures that form in the streamwise direction of the flow as well as spanwise fluctuations that propagate to the downstream edge of the flame zone contributing to fuel heating. The highly spatially-uniform fuel beds used in these experiments allowed for the observation of these structures with more repeatable results than previous efforts [4, 5]. The results suggest that flame spread in fine fuel beds is driven by non-steady convective heating and intermittent flame contact on fuel particles. These heating characteristics were measured using micro thermocouple arrays and high speed video. The travelling flaming region, however, made it difficult to carefully study these properties, such …