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arXiv 1609.06755physics.flu-dynnlin.PS
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连续燃烧前缘热扩散元胞不稳定性分析

Analysis of Thermo-Diffusive Cellular Instabilities in Continuum Combustion Fronts

Hossein Azizi, Sebastian Gurevich, Nikolas Provatas

摘要:

我们探索数值的形态图案的热扩散不稳定性燃烧前沿的连续燃料源,在一定范围内的路易斯数和点火温度,专注于细胞制度。为此,我们推广Brailovsky等人的模型,包括不同的过程动力学和反应物的异质性。广义模型推导出解析和验证与其他已建立的零级和一级动力学模型在无限路易斯数的限制。细胞和树枝状的不稳定性被发现在低路易斯数由于动态自适应网格细化技术,减少有限尺寸的影响,这可能会影响甚至排除这些模式的出现。该技术还允许实现非常大的计算域,从而能够研究系统尺寸效应。我们的数值线性稳定性分析与Brailovsky等人的分析结果是一致的。在临界Lewis数附近发现的不同类型的动力学,从稳态细胞到持续尖端分裂和细胞合并,在热扩散不稳定性的框架内得到了很好的描述,并与以前的数值研究一致。这些类型的动态被归类为“准线性”,其特征在于低振幅细胞,并可能遵循模式选择机制和线性理论规定的增长。低于此范围的路易斯数,高度非线性效应变得突出,大幅度,复杂的细胞和{ \it{seaweed} }树突形态出现。

英文摘要:

We explore numerically the morphological patterns of thermo-diffusive instabilities in combustion fronts with a continuum fuel source, within a range of Lewis numbers and ignition temperatures, focusing on the cellular regime. For this purpose, we generalize the model of Brailovsky et al. to include distinct process kinetics and reactant heterogeneity. The generalized model is derived analytically and validated with other established models in the limit of infinite Lewis number for zero-order and first-order kinetics. Cellular and dendritic instabilities are found at low Lewis numbers thanks to a dynamic adaptive mesh refinement technique that reduces finite size effects, which can affect or even preclude the emergence of these patterns. This technique also allows achieving very large computational domains, enabling the study of system-size effects. Our numerical linear stability analysis is consistent with the analytical results of Brailovsky et al. The distinct types of dynamics found in the vicinity of the critical Lewis number, ranging from steady-state cells to continued tip-splitting and cell-merging, are well described within the framework of thermo-diffusive instabilities and are consistent with previous numerical studies. These types of dynamics are classified as "quasi-linear" and characterized by low amplitude cells and may follow the mode selection mechanism and growth prescribed by the linear theory. Below this range of Lewis number, highly non-linear effects become prominent and large amplitude, complex cellular and {\it{seaweed}} dendritic morphologies emerge.

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