EAGER: Experimental investigation of physical-space scalar structure and unresolved mixing to improve large-eddy simulation of turbulent combustion

本计画研究燃烧中的关键过程-紊流混合。湍流燃烧在许多工程应用中发生并起着重要作用，例如喷气发动机、燃气涡轮机发电机、内燃机和化学加工厂。这种器件的现代设计过程需要采用数值建模来评估设计选择并优化设计参数。然而，目前最先进的建模方法，大涡模拟（LES），尽管几十年的研究工作，仍然没有先进的工程设计所需的准确性，主要是因为未解决的混合过程没有很好地预测。以前的努力，以了解混合已部分阻碍了占主导地位的LES方法。本研究将使用S. B。以Pope为框架，克服了传统方法的局限性.然而，新方法也在实验技术和数据分析方法方面提出了挑战。研究人员将采用新的激光诊断技术和新的统计分析方法。该研究将大大推进对湍流燃烧基本物理学的理解，这将有可能开发具有足够精度的燃烧模型，用于设计高性能和低排放的工程设备，这将对社会和环境产生积极影响。对所获得的物理学的理解也将有利于涉及湍流和强非线性现象之间相互作用的其他研究领域，如化学工程过程，大气物理，大气化学，本项目利用最近发展起来的自调节场大涡模拟方法研究物理空间结构和未解决的混合以及它们与化学的相互作用（Pope 2010）作为框架，其克服了过滤LES方法的局限性。研究人员将在湍流非反应同轴射流和射流火焰中进行实验。二维图像将在同轴射流中获得。将采用新的基于光解离的诊断技术和新的统计分析方法。悉尼火焰的直接数值模拟（Thorsten et al. 2019），其中包含3D图像，将补充实验。研究人员将分析物理空间标量结构及其在自适应联合PDF中的表示及其输运方程中的非封闭混合项。研究结果为进一步研究预混火焰中混合物组分和温度的混合规律提供了基础。研究人员将分析物理空间标量结构对自适应标量JEFFECT和非封闭混合项的影响。该项目是第一个使用新的自适应LES方法作为框架。这也是第一次真正的二维图像的混合物分数和温度与解决耗散尺度获得湍流碳氢化合物火焰没有重大的妥协的假设。该研究结果预计将大大推进对未解决的物理学的理解，这对于开发能够准确预测多标量混合和毒性-化学相互作用的改进混合模型至关重要。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

This project investigates a key process, turbulent mixing, in combustion. Turbulent combustion occurs and plays an important role in many engineering applications, such as jet engines, gas turbine generators, internal combustion engines, and chemical processing plants. The modern design process of such devices needs to employ numerical modeling to evaluate design choices and to optimize design parameters. However, the current state-of-the art modeling approach, large-eddy simulation (LES), despite decades of research efforts, still does not have the accuracy needed for advanced engineering design, primarily because the unresolved mixing process is not well predicted. Previous efforts to understand mixing had been partially hampered by the predominant LES approach. This research will investigate mixing using the novel LES approach developed by S. B. Pope as the framework, which overcomes the limitations of the traditional approach. The new approach, however, also poses challenges in experimental techniques and data analysis methods. The researchers will employ a new laser diagnostic technique and new statistical analysis method. The research will significantly advance the understanding of the fundamental physics in turbulent combustion, which will potentially enable development of combustion models with sufficient accuracy for designing high-performance and low emission engineering devices, which will have a positive impact on society and the environment. The understanding of the physics gained will also benefit other research areas involving interactions between turbulence and strongly nonlinear phenomena, such as chemical engineering processes, atmospheric physics, atmospheric chemistry, and environment systems.This project investigates the physical-space structure and the unresolved mixing as well as their interaction with chemistry using the recently developed self-conditioned fields LES approach (Pope 2010) as the framework, which overcomes the limitations of the filtering LES approach. The researchers will conduct experiments in turbulent non-reactive coaxial jets and in jet flames. Two-dimensional images will be obtained in coaxial jets. A new photo-dissociation-based diagnostic technique and new statistical analysis method will be used. Direct numerical simulation of a Sydney flame (Thorsten et al. 2019), which contains 3D images, will complement the experiments. Researchers will analyze the physical-space scalar structure and its representation in the self-conditioned joint PDF and the unclosed mixing terms in its transport equation. The results provide a basis for investigating the mixing of mixture fraction and temperature in piloted turbulent partially premixed (Sandia) flames. The researchers will analyze the effects of the physical-space scalar structure on the self-conditioned scalar JMDF and the unclosed mixing terms. The project is the first to use the novel self-conditioned LES approach as the framework. It is also the first time true two-dimensional images of mixture fraction and temperature with resolved dissipation scales are obtained in turbulent hydrocarbon flames without major compromising assumptions. The results are expected to significantly advance the understanding of the unresolved physics essential for developing improved mixing models capable of accurately predicting multiscalar mixing and turbulence-chemistry interaction.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.