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燃气火灾蔓延过程中的火焰传播机理
The Mechanism of Flame Propagation of the Gas Fire Spreading

导  师: 吴晋湘

学科专业: 080702

授予学位: 硕士

作  者: ;

机构地区: 河北工业大学

摘  要: 火灾科学作为一门新兴的学科受到了世界各国的极大关注和广泛研究,特别是火灾研究中的湍流问题一直是困扰火灾科学研究的难题。湍流火焰的火焰结构以及蔓延机理一直是各国学者研究的重点。 本文通过对湍流火焰前锋结构分析,发现随着管径减小,预热区与反应区的厚度均增大,且火焰位移速度增加。通过对时间步长与空间步长的分析发现,最适时间步长=网格尺寸//特征速度。计算网格尺寸越小,计算所得火焰面褶皱程度越强,火焰前锋厚度越小,位移速度越大。当数值模拟采用的时间步长未达到最适时间步长时,减小时间步长与减小计算网格尺寸对数值计算结果的影响相同。 通过对自适应网格计算结果的分析发现,自适应网格能够减小火焰面处网格尺寸,随着网格尺寸的减小,计算所得的火焰位移速度增加,火焰面厚度变薄,温度梯度增加,计算结果更接近真实火焰蔓延结果。数值模拟过程采用自适应网格可以节省计算机资源,提高计算效率。 通过对箱体内的燃烧实验结果分析发现,窗口开度越小,最佳浓度位置越接近箱体顶部,初始燃烧涡团越靠近箱体顶部,箱体内燃烧持续时间越长。燃气发生泄露后,燃烧均经历点火期、发展期、剧烈燃烧、燃烧减弱、回燃、熄火六个阶段。随着燃气泄露速度的增大,箱体内的燃气总量增加,气流扰动加强,燃烧剧烈程度加大,火焰回燃现象越明显。 通过对箱体内燃气泄露并引发火灾的数值模拟分析发现,箱体内数值模拟过程计算时间步长采用1ms进行数值计算最合适。分析发现:箱体窗口开度、箱体空间大小与燃气泄露速度对火焰面形状没有影响;燃烧涡团左侧火焰锋面厚度要大于右侧火焰锋面厚度;箱体窗口开度越小,火焰蔓延速度越大;燃气泄露速度越小, As a new discipline, fire science has attracted great attention in recent years. Turbulence is a difficult problem of fire science research. The turbulent flame structure and spread has been the focus of the research of scholars from various countries. In this paper, with the turbulent flame front structure analysis, we found the preheat zone and reaction zone thickness increases, and the flame spread rate increases as the diameter decreases. The optimal time step is equal to grid size divided by characteristic velocity. The flame folds strengthen and thickness of the flame front reduced with the reduction in size of the grid. The effect of reducing the time step and grid size almost the same when the numerical calculation has not reached the optimum time step. The application of adaptive grid could save computing resources. And the results of adaptive grid are much better than large-size grid. The local gas velocity increases with the reduction in the size of the grid. Thus it making the flame displacement velocity increased by flame speed. With the reduction in size of the grid, the thickness of the flame surface reduced, the temperature gradient increases. And that lead to increase of flame speed. According to the combustion experiments analysis, we found that the initial combustion eddy and the position of optimum concentration are closer to the top of box when the window opening is smaller, and the duration of combustion increase. The flame experienced six stages, ignition, flame development, intense burning, burning weakened, flame back draft and flameout. As gas leakage rate increases, the airflow disturbance and the flame intensity increases. The phenomenon of flame back draft is more obvious when the gas leak speed increase. According to the numerical calculation, we found the most appropriate time step size is lms. The window opening, combustion chamber size and leak rate have no effect on the shape of flame. The thickness of left side of the flame front is greater than the right side of

关 键 词: 火焰前锋 蔓延 时间步长 网格自适应 湍流燃烧

领  域: [建筑科学]

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