CAREER: Impact of Turbulence on Mechanisms of Combustion Instability

燃烧不稳定性是一个影响许多关键动力和推进技术的问题，包括喷气发动机、发电燃气轮机、火箭、锅炉和工艺炉。在不稳定状态下，湍流如何改变火焰的行为仍然是一个重要的问题。特别是，在高性能发动机中，湍流/火焰相互作用是否改变了不稳定性反馈机制？目前的数值模型是否包括正确的物理？提出的工作解决了这些问题，使用系统的实验方法来检查燃烧不稳定性的各个关键方面。先进的激光诊断将用于成像流场和火焰，解锁湍流和不稳定反馈回路之间的耦合。PI还将与许多其他早期职业教师合作，有效地传播这项研究的成果，并提高学生的教育经验。特别是，PI将促进早期职业研究人员的在线网络，以共享研究和教学材料。这将有利于向教师职业的过渡，并促进美国各地大学的高质量热流体教育。所提出的工作的技术目标是了解湍流对热声反馈回路的三个关键组成部分的影响：决定流动对外部扰动敏感性的流场的流体动力学不稳定性；驱动热释放率振荡的耦合机制；以及这些干扰在非小火焰状态下产生热释放率振荡的机制。这种系统的方法采用基于理论的实验设计来探索湍流在燃烧不稳定性框架内影响流动稳定性、耦合机制物理和火焰行为的方式。总体的智力贡献将在燃烧不稳定状态图的制定中做出，该图表描述了在一系列操作条件下热声不稳定期间火焰的行为。在此框架下，这项工作将对湍流火焰和燃烧不稳定性的基本理解，预测工业相关设备中燃烧不稳定性的能力以及pi的职业发展产生重大影响。这项工作的结果也将用于发展、实施和传播面向本科生和研究生的案例研究。案例研究将侧重于与燃烧相关的问题，使一系列学生了解燃烧在社会中的重要性；案例研究将通过一个在线门户网站，通过早期职业教师网络进行传播。案例研究的发展根植于基于理论的教育设计，包括形成在线内容的最佳实践，以研究为基础的技术，以改善招聘和保留服务不足的学生群体，以及为早期职业教师建立一个以将燃烧科学融入课堂为中心的实践社区。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Combustion instability is an issue that affects many critical power and propulsion technologies, including jet engines, power-generation gas turbines, rockets, boilers, and process furnaces. Significant questions remain about how turbulence alters flame behavior during instability. In particular, in high-performance engines, does the turbulence/flame interaction change the instability feedback mechanisms and do the present numerical models include the correct physics? The proposed work addresses these questions using a systematic experimental approach to examine various key aspects of combustion instability. Advanced laser diagnostics will be used to image the flowfield and the flame, unlocking the coupling between turbulence and the instability feedback loop. The PI will also work with many other early-career faculty to effectively disseminate the results of this research and enhance the educational experience of students. In particular, the PI will facilitate an online network of early-career researchers to share research and teaching materials. This will ease the transition into faculty careers and promote high-quality thermofluids education at universities across the United States.The technical goal of the proposed work is to understand the impact of turbulence on three critical components of the thermoacoustic feedback loop: the hydrodynamic instability of the flowfield that determines the susceptibility of the flow to external disturbances; the coupling mechanisms that drive heat release rate oscillations; and the mechanism by which these disturbances create heat release rate oscillations in non-flamelet regimes. This systematic approach uses theory-based experimental design to probe the ways in which turbulence impacts flow stability, coupling-mechanism physics, and flame behavior within the framework of combustion instability. The overarching intellectual merit contribution will be made in the formulation of the combustion instability regime diagram that describes the behavior of flames during thermoacoustic instability over a range of operating conditions. In following this framework, this work will have significant impacts on fundamental understanding of turbulent flames and combustion instability, the ability to predict combustion instability in industry-relevant devices, and the PIs career development. The results of this work will also feed into the development, implementation, and dissemination of case studies for undergraduate and graduate audiences. The case studies will focus on combustion-related issues, exposing a range of students to the importance of combustion in society; case studies will be disseminated through a network of early-career faculty through an online portal. The development of the case studies is rooted in theory-based educational design, including best-practices for the formation of online content, research-based techniques for improving recruitment and retention of under-served student populations, and the robust development of a community of practice for early-career faculty centered on incorporating combustion science into the classroom.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.