CAREER: Impact of Turbulence on Mechanisms of Combustion Instability

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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.