小尺度火旋风临界环量数值模拟与特性分析

Numerical simulation and characteristic analysis of small scale fire whirl's critical circulation

为奠定中大尺度火旋风成型临界环量理论及实验基础,规避火旋风的生成和威胁,基于6壁面强制诱导火旋风发生装置,采用大涡模拟技术,开展小尺度火旋风成型临界环量数值模拟研究。通过数值模拟计算小尺度火旋风的临界环量,采用线性拟合提出小尺度火源火旋风的临界环量与火源尺寸的关系式,得到特定单位面积热释放速率条件下,小尺度火旋风的临界环量Γ与火源尺寸l成Γ=0.465 8+0.081 29l的线性关系。通过旋风速度参量分析,得到火旋风切向速度沿径向方向从涡核中心到涡核半径处近似线性增加到最大值并沿涡核半径外缓慢下降,切向速度沿高度方向先增大后减小等变化规律,发现火旋风切向速度与Rankine涡模型相符。

To lay a foundation for large scale fire whirl＇s critical circulation theory and experiment research, and avoid threaten of fire whirl, six-wall-surfaces forced induction generator of fire whirl and large eddy simulation was used to research the small scale fire whirl＇s critical circulation. Based on simulation and revised numerical processing method, the relationship between critical value and fire scale was obtained by linear fitting. If the heat release rate per area is a constant, the critical values Γ and fire scale l are in accord with Γ=0.465 8＋0.081 29 l. After measurement and analysis of the fire whirl＇s velocities, it was found that the tangential velocity increases to the maximum value along the radial direction from vortex core to edge, then reduces slowly along radial direction, and increases first then decreases along vertical direction. The fire whirl＇s tangential velocity is coincident with Rankine vortex.