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

由于热声不稳定性，用于发电和推进的燃气轮机可能会经历巨大的压力波动。这些不稳定性是由发动机燃烧室内的声和热释放相互作用引起的，对发动机的安全可靠运行构成了重大挑战。热声不稳定性的频繁发生可能会限制燃气轮机燃烧室的性能和寿命，特别是在旨在减少排放和燃料消耗的条件下运行时。然而，由于包括化学反应、湍流、热释放和声学在内的复杂过程，对热声不稳定性的详细模拟仍然具有挑战性和计算代价。该项目旨在开发一种更简单的数学模型，能够预测和捕捉燃烧室中从稳定行为到不稳定行为的转变。将进行实验，以评估模型的性能，并为验证其他研究人员开发的模型提供基准数据。研究结果将使发动机设计者能够预测和缓解热声不稳定性，并提高可靠性和性能。作为这项工作的更广泛的影响，本科生和研究生，特别是来自代表性不足的少数群体，将获得使用先进的实验和建模工具的经验。该计划建议开发一个基于同步的框架来设计能够捕获热声不稳定期间湍流燃烧室中动态过渡行为的低阶模型。这项研究协同包括建模和实验部分，将促进改进的预测工具的开发，以提供更好的控制策略来缓解普遍存在的热声不稳定性。在建模中，主要目标是引入一个由两个相互耦合的振子组成的系统，代表火焰和声学，以捕捉热声不稳定性中反馈的双向性质。该模型可以捕捉实际系统中观察到的周期、间歇和混沌三种动态状态，从而克服了单向耦合模型的缺点。此外，该计划将开发实验策略，其中双向耦合系统可以通过利用声力扰动火焰来模拟，声力的频率和幅度根据随后的火焰动力学进行调制。这些实验将使我们能够观察在耦合或非耦合声强迫扰动下局部和全球火焰动力学的差异，并收集用于模型验证的数据。这一奖项反映了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。

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.