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Effect of unsteady stretching on the flame local dynamics

机译：不稳定拉伸对火焰局部动力学的影响

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摘要

Numerical simulations employing detailed reaction kinetics and transport have been applied to calculate steady-state and harmonically excited laminar hydrogen-air flames with equivalence ratios ranging from fuel-lean to fuel-rich mixtures. The objective is to gain a basic understanding of the influence of unsteady flow stretching on the flame's response. The flame displacement speed and consumption speed have been evaluated, together with stretch, curvature and strain. In the steady-state simulations, a quasi-linear correlation has been obtained for the flame speeds with stretch for a moderate range, which confirms the applicability of the asymptotic relation for small stretch. In the case of unsteady flow conditions, a phase shift is observed between the oscillations of the fluid flow and the flame surface position, indicating a delayed response of the flame to changing flow conditions. The corresponding delay time or relaxation time is found to be depending on the turnover time of the flow oscillations. The flame response in terms of displacement from its steady state location is shown to be dampened at higher excitation frequencies and for flames with large flame transit times tau(L0). Due to the delayed response, the local consumption speeds at different phase angles show different dependences on flame stretch. This discrepancy is large for flames in flows excited with lower frequencies as well as equivalence ratios with smaller flame transit times. Also, a larger variation of consumption speeds from different phase angles over flame stretch has been observed for regions with positive stretch, because the internal structure of the flame is altered, leading locally to smaller flame transit times. This explains the large scattering of flame propagation statistics in turbulent combustion, where the flow is characterized by a cascade of interacting vortices with different turnover frequencies. The unsteady effect is quantitatively analysed by comparing the characteristic times of the flame and the flow. In this way, an extension of the Markstein regression has been provided based on the simulation results, giving Ma as a function of the Damkohler number defined by Da = tau(flow)/tau(L0) = S-L0/delta(L0)/f. Evaluating the consumption speed for different phases during a turnover period of the oscillations and averaging over the period results in a correlation of the averaged Markstein number with the Damkohler number. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：应用详细的反应动力学和输运的数值模拟已用于计算稳态比和谐波激发的层流氢空气火焰，当量比范围从贫燃料到富燃料混合物。目的是对不稳定流动对火焰响应的影响有一个基本的了解。评估了火焰的位移速度和消耗速度，以及拉伸，曲率和应变。在稳态模拟中，在中等范围内具有拉伸的火焰速度已获得准线性相关性，这证实了渐近关系在小拉伸中的适用性。在不稳定的流动条件下，在流体流动的振动与火焰表面位置之间会观察到相移，表明火焰对变化的流动条件有延迟的响应。发现相应的延迟时间或弛豫时间取决于流动振荡的周转时间。在较高的激发频率下，对于火焰传递时间为tau（L0）较大的火焰，火焰从稳态位置位移的响应被抑制。由于响应延迟，不同相角的局部消耗速度对火焰拉伸的依赖性不同。对于以较低频率激发的气流中的火焰以及具有较短火焰传递时间的当量比，此差异很大。同样，对于正拉伸区域，由于火焰内部结构的改变，局部地导致更短的火焰传播时间，因此在具有正拉伸的区域中观察到了在火焰拉伸期间不同相位角的消耗速度的较大变化。这解释了湍流燃烧中火焰传播统计数据的大量散布，其中流动的特征是具有不同转换频率的相互作用涡流的级联。通过比较火焰和流动的特征时间来定量分析非稳态效应。这样，基于仿真结果提供了Markstein回归的扩展，使Ma成为Da = tau（flow）/ tau（L0）= S-L0 / delta（L0）定义的Damkohler数的函数。 /F。在振荡的周转周期内评估不同相位的消耗速度并对该周期进行平均，可以得出平均马克斯坦数与达姆霍勒数的相关性。 （C）2016年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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  • 来源
    《Combustion and Flame》 |2017年第1期|170-179|共10页
  • 作者

    Zhang F.; Zirwes T.; Habisreuther P.; Bockhorn H.;

  • 作者单位

    Karlsruhe Inst Technol, Div Combust Technol, Engler Bunte Inst, Engler Bunte Ring 1, D-76I3I Karlsruhe, Germany;

    Karlsruhe Inst Technol, Div Combust Technol, Engler Bunte Inst, Engler Bunte Ring 1, D-76I3I Karlsruhe, Germany;

    Karlsruhe Inst Technol, Div Combust Technol, Engler Bunte Inst, Engler Bunte Ring 1, D-76I3I Karlsruhe, Germany;

    Karlsruhe Inst Technol, Div Combust Technol, Engler Bunte Inst, Engler Bunte Ring 1, D-76I3I Karlsruhe, Germany;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Detailed numerical simulation; Turbulent combustion; Flame stretch; Markstein number; OpenFOAM;

    机译：详细的数值模拟;湍流燃烧;火焰拉伸;马克斯坦数;OpenFOAM;

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