Study of Interacting Turbulent Flames Using Direct Numerical Simulation and Laser Diagnostics

排放法规正变得越来越严格，传统的燃烧技术无法满足新法规规定的低ppm水平。因此，需要寻找替代技术，使稀薄燃烧概念能够满足标准，但需要清楚地了解稀薄预混料的可燃性和火焰稳定性。然而，稀薄的预混火焰容易出现热声不稳定性，因为它们对混合物的流体动力学和热化学状态的小尺度变化高度敏感。越来越清楚的是，相互作用的火焰是在稀薄预混燃烧中产生热声振荡的主要机制。预混燃烧通常比非预混燃烧更难模拟，因为预混料中反应表面的传播，结果是湍流预混燃烧的工程模型明显不如非预混燃烧的工程模型发达。一个尚未解决的主要问题是对火焰刷内反应表面之间的小规模相互作用提供令人满意的描述，这是限制反应表面积增长的主要机制。由于这一基本限制，现有的模型不能很好地适应描述引起燃烧室压力变化和热声不稳定的大规模火焰-火焰相互作用。在目前的工作中，我们建议在基础水平上使用直接数值模拟和激光诊断来研究火焰之间的相互作用。在本文所考虑的双“V”型火焰构型中，相互作用过程受上游湍流的控制，并产生足够长的相互作用时间，以便在实验中进行统计抽样。这种几何形状类似于燃气涡轮发动机环形燃烧室中的燃烧器-燃烧器相互作用过程，所模拟的相互作用过程被认为是湍流火焰行为的有效表示。这项工作的预期结果是对火焰之间相互作用过程的密切理解，导致预混合湍流燃烧的修订模型的发展，包含限制火焰表面积增长过程的物理有效描述，并具有模拟大规模火焰-火焰相互作用的能力。

Emissions legislation is becoming ever more stringent and the conventional combustion technologies are incapable of meeting the low ppm levels set by the new legislation. Thus, alternative technologies need to be found and the lean burn concepts have the ability to meet the standards but the ignitability and flame stability of lean premixtures need to be understood clearly. However, lean premixed flames are prone to thermo--acoustic instabilities, because of their high sensitivity to even small scale variations in the fluid dynamic and thermo--chemical state of the mixture. It is becoming clear that interacting flames are a dominant mechanism for creating thermo--acoustic oscillations in lean premixed combustion. Premixed combustion is often more difficult to simulate than nonpremixed combustion, because of the propagation of reacting surfaces in premixtures, with the consequence that engineering models for turbulent premixed combustion are significantly less well developed than those for nonpremixed combustion. A major unsolved problem is to provide a satisfactory description of the small scale interactions between reacting surfaces, within a flame brush, which form the major mechanism for limiting the growth of reacting surface area. Because of this fundamental limitation, existing models are not well adapted to describe the large scale flame-flame interactions that give rise to pressure variations and thermo-acoustic instabilities in combustion chambers.In the present work, we propose to investigate the mutual interaction between flames at a fundamental level using direct numerical simulation and laser diagnostics. In the configuration of twin ``V'' flames considered here the interaction process is controlled by the upstream turbulence and yields a sufficiently long interaction time for statistical sampling in experiments. This geometry is akin to burner--to--burner interaction process inthe annular combustor of a gas turbine engine, and the interaction process to be simulated is considered to be a valid representation of behaviour in turbulent flames. The expected outcome from this work is a close understanding of processes occurring during interaction between flames, leading to development of a revised model for premixed turbulent combustion, containing a physically valid description of processes limiting growth of flame surface area, and with a capability to simulate large scale flame-flame interactions.