An investigation of bi-directional flame-acoustic interactions during thermoacoustic instabilities

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Gas turbines used for power generation and propulsion can experience large pressure fluctuations as a result of thermoacoustic instabilities. These instabilities arise from the interaction of sound and heat release within the engine combustion chamber and represent a major challenge for safe and reliable operation of the engine. The frequent occurrence of thermoacoustic instabilities can limit the performance and the lifetime of gas turbine combustors, particularly when running under conditions designed to reduce emissions and fuel consumption. However, due to complex processes including chemical reactions, turbulent flow, heat release, and acoustic, a detailed simulation of thermoacoustic instabilities remains challenging and computationally expensive. The proposed project aims to develop a simpler mathematical model that can predict and capture the transition from stable to unstable behavior in combustors. Experiments will be carried out to assess the model's performance and to provide benchmark data for validating models developed by other researchers. The outcome of the study will enable engine designers to predict and mitigate thermoacoustic instabilities and improve reliability and performance. As a broader impact of the work, undergraduate and graduate students, particularly from underrepresented minority groups, will gain experience in using advanced experimental and modeling tools.The program proposes to develop a synchronization-based framework to design low order models capable of capturing the dynamic transitional behaviors in turbulent combustors during thermoacoustic instabilities. The study, which synergistically includes modeling and experimental components, will facilitate the development of improved predictive tools to provide better control strategies in mitigating prevalent thermoacoustic instabilities. In modeling, the primary objective is to introduce a system of two mutually coupled oscillators, representing the flame and acoustics, to capture the bi-directional nature of the feedback in thermoacoustic instability. Such a model will capture three dynamical states, periodic, intermittent, and chaotic, observed in practical systems, hence overcome the shortcoming of unidirectionally coupled models, such as FTFs and FDFs. Furthermore, the program will develop experimental strategies, where the two-way coupled systems can be simulated by perturbing a flame with acoustic forcing whose frequency and amplitude are modulated based on the ensuing flame dynamics. The experiments will enable us to observe the differences in local and global flame dynamics when perturbed with coupled or de-coupled acoustic forcing and to gather data for model validation.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.