Abstract Variation in flow characteristics triggered through the fire-wind interface can potentially damage the buildings during bushfires. Fire-wind enhancement which is referred to as the increase of wind velocity, caused by the fire-wind interaction, is one of the destructive phenomena in this regard. In spite of the significance, the underlying mechanism contributing to this phenomenon is still not well understood. This study employs computational fluid dynamic (CFD) simulation to fundamentally investigate the effects of free-stream wind velocity on fire-wind enhancement through analyzing the momentum and buoyancy of fluid. Fire-wind interaction is shown to cause the generation of fire-induced longitudinal negative pressure gradient which results in fire-induced pressure and viscous forces in longitudinal direction. These forces are further found as the prime reason for the distortion of the wind velocity profile. A module is implemented to the FireFOAM solver to calculate and extract these forces quantitatively. The results reveal that under a constant fire intensity, the level of distortion and/or enhancement in the wind velocity profile comparatively reduces with the increase of free-stream wind velocity. A new non-dimensional group (modified Euler number) is introduced to take into account dominant fire-induced forces causing fire-wind enhancement. Richardson number and the modified Euler number are employed to determine the influence of free-stream wind velocity and longitudinal distance from the fire source on wind velocity enhancement. Large-eddy simulation (LES) results indicate that while the level of enhancement generally depends on both Richardson and the modified Euler number, the location of the maximum level of enhancement along the plume centreline coincides with the maximum value of modified Euler number under a constant free-stream wind velocity scenario.

中文翻译：

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风速对火风增强效应的数值分析

摘要 通过火-风界面触发的流动特性变化可能会在丛林大火期间损坏建筑物。由火风相互作用引起的火风增强，即风速的增加，是这方面的破坏性现象之一。尽管意义重大，但导致这种现象的潜在机制仍未得到很好的理解。本研究采用计算流体动力学 (CFD) 模拟，通过分析流体的动量和浮力，从根本上研究自由流风速对火风增强的影响。研究表明，火风相互作用会导致火灾引起的纵向负压梯度的产生，从而导致火灾引起的纵向压力和粘性力。进一步发现这些力是风速剖面失真的主要原因。FireFOAM 求解器实现了一个模块，以定量计算和提取这些力。结果表明，在一定的火力强度下，随着自由流风速的增加，风速剖面的畸变和/或增强程度相对降低。引入了一个新的无量纲群（修改的欧拉数）以考虑导致火风增强的主要火力。采用理查森数和修正欧拉数确定自由流风速和距火源纵向距离对风速增强的影响。