Propagation of corrugated flames in the flamelet regime

小火焰状态下波纹火焰的传播

• 批准号: 1067259
• 负责人: Moshe Matalon
• 金额: $ 30万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2015-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1067259&HistoricalAwards=false
• 关键词: Propagation; corrugated; flames; flamelet; regime

1067259Matalon The study of premixed flames in a turbulent environment is of great interest in many industrial applications. At the same time turbulent combustion is a formidable challenge due to its complexity, mainly arising from the strong coupling between chemistry and turbulence. Research in the last half century has focused on the determination of a universal model for the propagation of a premixed flame in a turbulent flow and, in particular, a model for the turbulent flame speed. Experimental data exhibit a wide scatter due to accuracy of the methods and operating conditions, and modeling and simulation efforts have invariably relied on ad-hoc closure assumptions and empirically determined coefficients. Direct numerical simulations that faithfully represent the physico-chemical processes on all scales, small and large, without invoking any turbulence and/or other reduction models are currently unassailable due to the prohibitively high computational cost.Intellectual merit: The proposed work will address the complex dynamics that result from flame interaction with turbulence using a simplified hydrodynamic model derived systematically from the full conservation laws of mass, momentum and energy. In the context of the hydrodynamic theory the flame is represented by a surface separating burned from unburned gas which propagates into the fresh mixture according to a law that, together with the conditions across the flame front, mimic the influences of diffusion and chemical reaction occurring within the flame zone. The mathematical formulation involves a nonlinear, free-boundary problem that is quite challenging, but is more easily tractable by existing computational means. An appropriate methodology will be developed for the implementation of the hydrodynamic model in two and three-spatial dimensions. Since the flame surface is determined unambiguously, all pertinent information to its propagation will be directly contained in the flame topology and in the flow field at the same location. This permits the independent or concurrent analysis of the dependence of the turbulent flame speed on turbulence intensity and turbulence scale, as well as on other local flame and flow properties, such as flame front curvature, hydrodynamic strain, heat release by chemical reactions and gas thermal expansion. The effect of instabilities on flame propagation and their role on the overall burning process, which have been invariably neglected in previous studies involving turbulent flows, will also be studied. Suppression of combustion instabilities within engines is of major importance in the design of combustor chambers. The transformational nature of the proposed research is in addressing the complex dynamics of multi-dimensional flames and their interaction with the underlying turbulence by accessible means, and in extending fundamental understanding of combustion phenomena with predictive capabilities that are based on physical first principles.Broader impact: The proposed work falls within the flamelet regime of turbulent combustion, which encompasses many practical applications, including spark-ignition engines and ramjets. Deeper understanding of flame propagation in this regime will lead to better design capabilities and, in turn, will have an effect on improving combustion technologies. The broader impact of the proposed work will occur through publications and presentations in the technical and scientific community and by educating and training students and young scientists. This will serve extending the national human-resources base for science and technology. Results from the proposed activity will be integrated into teaching, primarily at the graduate level, and in developing models used in the classroom and for pedagogy.

小行星1067259 湍流环境中预混火焰的研究在许多工业应用中具有重要意义。同时，湍流燃烧由于其复杂性是一个巨大的挑战，主要是由于化学和湍流之间的强耦合。在过去的半个世纪的研究集中在确定一个通用的模型，在湍流中的预混火焰的传播，特别是，湍流火焰速度的模型。由于方法和操作条件的准确性，实验数据表现出广泛的分散，建模和模拟工作总是依赖于特设封闭假设和经验确定的系数。直接数值模拟忠实地代表了所有尺度上的物理化学过程，无论大小，而无需调用任何湍流和/或其他简化模型，由于计算成本过高，目前是无懈可击的。拟议的工作将解决复杂的动力学，从火焰与湍流相互作用的结果，使用简化的流体动力学模型系统地从完整的质量守恒定律，动量和能量。在流体动力学理论的背景下，火焰由将已燃烧的气体与未燃烧的气体分离的表面表示，该表面根据一个定律传播到新鲜混合物中，该定律与穿过火焰前缘的条件一起模拟火焰区内发生的扩散和化学反应的影响。数学公式涉及一个非线性、自由边界问题，该问题相当具有挑战性，但通过现有的计算方法更容易处理。将为二维和三维空间流体动力学模型的实施制定适当的方法。由于火焰表面是明确确定的，所有相关的信息，其传播将直接包含在火焰拓扑结构和流场在同一位置。这允许独立或并发的分析湍流火焰速度的依赖湍流强度和湍流尺度，以及其他局部火焰和流动特性，如火焰前曲率，流体动力学应变，热释放的化学反应和气体热膨胀。不稳定性对火焰传播的影响及其在整个燃烧过程中的作用，这在以前的研究中总是被忽略，涉及湍流，也将进行研究。抑制发动机内的燃烧不稳定性在燃烧室的设计中是非常重要的。拟议研究的变革性质是通过可获得的手段解决多维火焰的复杂动力学及其与底层湍流的相互作用，并通过基于物理第一原理的预测能力扩展对燃烧现象的基本理解。拟议的工作福尔斯湍流燃烧的小火焰制度，其中包括许多实际应用，包括火花点火发动机和冲压发动机。深入了解这一领域的火焰传播将提高设计能力，进而对改进燃烧技术产生影响。拟议工作的更广泛影响将通过出版物和在技术和科学界的介绍以及教育和培训学生和青年科学家产生。这将有助于扩大国家科技人力资源基础。拟议活动的结果将纳入教学，主要是研究生一级的教学，并纳入制定课堂和教学法使用的模式。