A DNS study on the stabilization mechanism of a turbulent lifted ethylene jet flame in highly-heated coflow
A DNS study on the stabilization mechanism of a turbulent lifted ethylene jet flame in highly-heated coflow
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DOI：
10.1016/j.proci.2010.06.147
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
C. Yoo;E. Richardson;R. Sankaran;Jacqueline H. Chen
中科院分区：
文献类型：
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作者：
C. Yoo;E. Richardson;R. Sankaran;Jacqueline H. Chen
采用直接数值模拟（DNS）方法，对高温并流中三维空间发展的乙烯湍流射流火焰近场进行了简化，确定了稳定化机理。DNS是在射流雷诺数为10，000时进行的，网格点超过12.9亿。结果表明，火焰底部贫燃料混合气的自燃是提升射流火焰稳定的主要原因。Damköhler数和化学爆炸模式（CEM）分析也证实了自燃发生在火焰底部。除了自燃之外，火焰底部的拉格朗日跟踪揭示了大规模流动结构的通过及其与火焰底部波动的相关性，类似于先前的研究（Yoo等人，J. Fluid Mech.640（2009）453-481）中描述的方法。还观察到，本发明的离焰基座呈现出以快速向上游移动和较慢向下游移动为特征的周期性“锯齿”形移动。这是一个结果的火焰被稳定的热贫燃料混合物中的连续自燃事件和对流引起的高速射流和同向流速度之间的平衡。这是证实了拉格朗日跟踪的关键变量，包括火焰法向速度，位移速度，标量耗散率，并在稳定点的混合分数。
Direct numerical simulation (DNS) of the near-field of a three-dimensional spatially-developing turbulent ethylene jet flame in highly-heated coflow is performed with a reduced mechanism to determine the stabilization mechanism. The DNS was performed at a jet Reynolds number of 10,000 with over 1.29 billion grid points. The results show that auto-ignition in a fuel-lean mixture at the flame base is the main source of stabilization of the lifted jet flame. The Damköhler number and chemical explosive mode (CEM) analysis also verify that auto-ignition occurs at the flame base. In addition to auto-ignition, Lagrangian tracking of the flame base reveals the passage of large-scale flow structures and their correlation with the fluctuations of the flame base similar to a previous study (Yoo et al., J. Fluid Mech. 640 (2009) 453–481) with hydrogen/air jet flames. It is also observed that the present lifted flame base exhibits a cyclic ‘saw-tooth’ shaped movement marked by rapid movement upstream and slower movement downstream. This is a consequence of the lifted flame being stabilized by a balance between consecutive auto-ignition events in hot fuel-lean mixtures and convection induced by the high-speed jet and coflow velocities. This is confirmed by Lagrangian tracking of key variables including the flame-normal velocity, displacement speed, scalar dissipation rate, and mixture fraction at the stabilization point.