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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2024)

Modern gas turbine combustors are prone to combustion instabilities characterized by large pressure fluctuations, which can compromise safe and efficient operation and potentially cause severe hardware damage. This phenomenon, known as thermoacoustic instability, results from the interaction between the acoustic field and unsteady heat release. In recent decades, the widespread adoption of LPP (lean premixed pre-vaporized) combustors in gas turbines has significantly reduced greenhouse gas emissions. However, the increased susceptibility of these lean premixed flames to perturbations also heightens the risk of thermoacoustic instability, spurring extensive research in this field.

Given the critical role of combustion instability in gas turbines, this study provides a comprehensive analysis from multiple perspectives. In the first part, we conducted multiple experimental investigations to explore the unsteady flame dynamics resulting from various perturbations, including turbulence, unequal mass and thermal diffusion, and the nonlinear coupling of multi-flame configurations with acoustic interactions.

In the second part, we shifted our focus to investigating the complex dynamics of thermoacoustic instability from a dynamical system perspective. We developed a phenomenological framework based on synchronization theory to model thermoacoustic instability, which effectively captured the dynamical behavior in both laminar and turbulent thermoacoustic systems. Additionally, we introduced a data-driven modal analysis for thermoacoustic instability, enabling the identification of early warning signals for the onset of instability.

In the second part, we shifted our focus to investigating the complex dynamics of thermoacoustic instability from a dynamical system perspective. We developed a phenomenological framework based on synchronization theory to model thermoacoustic instability, which effectively captured the dynamic behavior in both laminar and turbulent thermoacoustic systems. Additionally, we introduced a data-driven modal analysis for thermoacoustic instability, enabling the identification of early warning signals for the onset of instability.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2020)
    We, herein, present a new model based on the framework of synchronization to describe a thermoacoustic system and capture the multiple bifurcations that such a system undergoes. Instead of applying flame describing function to depict the unsteady heat release rate as the flame's response to acoustic perturbation, the new model considers the acoustic field and the unsteady heat release rate as a pair of nonlinearly coupled damped oscillators. By varying the coupling strength, multiple dynamical behaviors, including limit cycle oscillation, quasi-periodic oscillation, strange nonchaos, and chaos can be captured. Furthermore, the model was able to qualitatively replicate the different behaviors of a laminar thermoacoustic system observed in experiments by Kabiraj et al.~[Chaos 22, 023129 (2012)]. By analyzing the temporal variation of the phase difference between heat release rate oscillations and pressure oscillations under different dynamical states, we show that the characteristics of the dynamical states depend on the nature of synchronization between the two signals, which is consistent with previous experimental findings.
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