Computational investigation of thermo-diffusive instabilities in flames: from laminar cellular structures to turbulent flows

不稳定火焰的传播是众多自然现象和工程应用的中心。了解和模拟这些不稳定的火焰以及它们如何与湍流相互作用，对于设计高效和清洁的能源转换设备、降低意外爆炸的风险和理解天体物理现象至关重要。这项工作是为了进行计算研究，以揭示接近极限的预混火焰锋面的完整几何图形。虽然主要的焦点是热扩散不稳定的火焰，但预计结果将揭示许多其他的科学问题。这项工作将导致高保真计算模型的发展，用于设计和优化推进应用的高性能燃烧系统。实验观测和理论研究很早就指出了层流稳定火焰和热扩散不稳定火焰之间的区别。遗憾的是，目前用于模拟大规模湍流火焰的最新技术无法充分预测本质上不稳定的反应混合物的流场。这项工作是为了量化使不稳定火焰与稳定火焰不同的基本特征：蜂窝结构的大小和火焰锋面传播的加速度。这两个特征构成了建立任何大型涡流模拟(LES)模型的基础：它们决定了LES过滤器的大小，并控制了化学源项的关闭。该提议的力度依赖于考虑从一维球形火焰到二维静止管状火焰，再到三维不稳定层流和湍流火焰的广泛范围。在整个分析过程中，不会采取准确性的捷径，以前被忽视的影响(如索雷特/杜福尔)将被重新考虑并包括在内(如果必要)。结果将是反应区几何结构的完整图景，拟议的工作将对许多自然现象和工程应用产生重要影响：从能源产生到安全到天体物理。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The propagation of unstable flames is at the center of numerous natural phenomena and engineering applications. Understanding and modeling these unstable flames and how they interact with turbulent flows are of critical importance to designing efficient and clean energy conversion devices, mitigating the risks of accidental explosions, and understanding astrophysical phenomena. This work is to conduct a computational study to reveal a complete picture of the geometry of the near-limit premixed flame front. While the primary focus is on thermo-diffusively unstable flames, the results are expected to shed light onto numerous additional scientific problems. This work will lead to the development of high-fidelity computational models, which will be used for designing and optimizing high-performance combustion systems for propulsion application.Experimental observations and theoretical studies have long pointed out the differences between laminar stable flames and thermo-diffusively unstable flames. Unfortunately, state-of-the-art techniques currently used to simulate large-scale turbulent flames fail to adequately predict the flow field of reacting mixtures that are intrinsically unstable. This work is to quantify the fundamental characteristics that make unstable flames different from their stable counterparts: the size of the cellular structure and the acceleration of the flame front propagation. These two features form the foundation onto which any Large Eddy Simulation (LES) models will be built: they determine the size of the LES filter and control the closure of the chemical source terms. The strength of the proposal relies on considering an extensive range of conditions from 1D spherical flames, to 2D stationary tubular flames, to 3D unstable laminar and turbulent flames. Throughout the analysis, no shortcut of accuracy will be taken, and previously neglected effects (such as Soret/Dufour) will be revisited and included (if necessary). The outcome will be a complete picture of the geometry of the reaction zone, and the proposed work will have important impacts on many natural phenomena and engineering applications: from energy generation to safety to astrophysics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.