Characteristic patterns of thermodiffusively unstable premixed lean hydrogen flames
Characteristic patterns of thermodiffusively unstable premixed lean hydrogen flames
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DOI：
10.1016/j.proci.2018.06.072
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发表时间：
2019-01-01
影响因子：
3.4
通讯作者：
Pitsch, Heinz
中科院分区：
文献类型：
--
作者：
Berger, Lukas;Kleinheinz, Konstantin;Pitsch, Heinz
大规模的二维数值模拟热扩散不稳定，贫油，预混氢火焰已进行了详细的有限速率化学分析火焰的内在尺度。该模拟具有较长的积分时间和较大的域尺寸，以排除约束对火焰前锋动态的影响。对于足够大的域的大小，火焰的总消耗速度被发现成为独立的域的大小。的火焰前锋的特征尺度的评估揭示了存在一个最小和最大的火焰固有长度尺度。最小的长度表现为局部尖点，这导致形成特征细胞沿着火焰前锋。它们的大小是非常接近的最不稳定的波长预测的线性稳定性分析的火焰前锋的演变在线性制度。独立的域的大小，一个特定的最大的火焰固有结构，这里被称为火焰指，出现从多个小规模的尖点的相互作用。热扩散不稳定的火焰被发现定期形成和破坏这些火焰手指，但一个全球性的尖点，这是已知的纯流体动力学不稳定的火焰出现的形成被抑制。最大刻度指的有限尺寸是由其运动的不稳定性解释的。当它们向未燃烧的混合物前进时，它们倾向于倾斜并横向移动，从而最终再次被火焰的其余部分合并。这种现象是由于火焰指和它们前面的发散速度场的相互作用引起的。最后，当量比和未燃气体温度的影响进行了研究，发现只有在热扩散不稳定的火焰的情况下，火焰手指的发展。(C)2018燃烧研究所爱思唯尔公司出版All rights reserved.
Large-scale two-dimensional numerical simulations of thermodiffusively unstable, lean, premixed hydrogen flames have been performed using detailed finite rate chemistry to analyze flame intrinsic scales. The simulations feature a long integration time and large domain sizes to rule out effects of confinement on the dynamics of the flame front. For sufficiently large domain sizes, the total consumption speed of the flame is found to become independent of the domain size. An assessment of the characteristic scales of the flame front corrugation reveals the existence of a smallest and a largest flame intrinsic length scale. The smallest length manifests itself by local cusps, which lead to the formation of characteristic cells along the flame front. Their size is remarkably close to the most unstable wavelength predicted by a linear stability analysis of the flame front evolution in the linear regime. Independently of the domain size, a specific largest flame intrinsic structure, here referred to as flame finger, emerges from the interaction of multiple small-scale cusps. Thermodiffusively unstable flames are found to periodically form and destroy these flame fingers, but the formation of a global cusp that is known to emerge for purely hydrodynamically unstable flames is suppressed. The finite size of the largest scale fingers is explained by an instability in their movement. As they proceed towards the unburnt mixture, they tend to tilt and move laterally, thereby eventually being incorporated again by the rest of the flame. This behavior arises from the interaction of the flame fingers and the diverging velocity field ahead of them. Finally, the effect of equivalence ratio and unburnt gas temperature is investigated showing that flame fingers are found to develop only in case of a thermodiffusively unstable flame. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.