Propagation of corrugated flames in the flamelet regime

研究湍流环境中的预混火焰在许多工业应用中具有重要意义。同时，湍流燃烧是一项艰巨的挑战，因为它的复杂性，主要是由于化学和湍流之间的强烈耦合。在过去的半个世纪里，研究的重点是确定预混火焰在湍流中传播的通用模型，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，实验数据表现出很大的离散性，建模和仿真工作总是依赖于特别的闭合假设和经验确定的系数。直接数值模拟忠实地表示所有尺度上的物理化学过程，无论大小，而不调用任何湍流和/或其他还原模型，由于计算成本高得令人望而却步，目前是无懈可击的。智力优势：拟议的工作将使用系统地从质量、动量和能量的完全守恒定律导出的简化流体动力学模型来处理火焰与湍流相互作用所产生的复杂动力学。在流体力学理论的背景下，火焰由一个表面表示，该表面将燃烧的气体与未燃烧的气体分开，根据一条定律传播到新鲜的混合物中，该定律连同火焰前沿的条件，模拟了在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的自由边界问题，这是一个相当具有挑战性的问题，但用现有的计算方法更容易处理。将制定一种适当的方法，在两个和三个空间维度实施流体力学模型。由于火焰表面是明确确定的，所有与其传播相关的信息将直接包含在火焰拓扑和同一位置的流场中。这使得可以独立或同时分析湍流火焰速度与湍流强度和湍流尺度的相关性，以及其他局部火焰和流动特性，如火焰前锋曲率、流体动力应变、化学反应放热和气体热膨胀。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也将被研究，这些在以前的湍流研究中总是被忽略。抑制发动机内的燃烧不稳定性在燃烧室设计中具有重要意义。拟议研究的变革性本质是通过可获得的方法解决多维火焰的复杂动力学及其与潜在湍流的相互作用，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。广泛影响：拟议的工作属于湍流燃烧的小火焰区域，包括许多实际应用，包括火花点火发动机和冲压发动机。更深入地了解火焰在这种状态下的传播将导致更好的设计能力，并反过来对改进燃烧技术产生影响。拟议工作的更广泛影响将通过技术和科学界的出版物和专题介绍以及教育和培训学生和青年科学家来实现。这将有助于扩大国家科技人力资源基础。拟议活动的成果将被纳入教学，主要是在研究生一级，并用于发展课堂和教学模式。

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.