Student Name: Reid Fly

Advisor: Dr. Timothy Lieuwen

Milestone: PhD Thesis Proposal

Degree Program: Aerospace Engineering

Title: Characterization and Modeling of Nonlinearly Interacting Thermoacoustic Modes in a High Pressure Gas Turbine Combustor

Abstract: Thermoacoustic instability is a widely-recognized performance limitation found in a variety of combustion systems, and pushing operations towards higher power and reduced emissions has created conditions where these instabilities are more prevalent. Because of their importance in determining operability limits and structural loads, the effort to understand, model, and predict these pressure and heat release oscillations has garnered much attention. Decades of experimental analysis and modeling work has resulted in a very robust understanding of the linear behavior and stability of thermoacoustic modes. However, numerous experiments have noted the presence of limit cycles, intermittency, and chaos which cannot be understood through linear analyses. Further complicating these systems is the presence of multiple linearly-unstable modes whose coupling can cause yet more complex behaviors. This work proposes to contribute to the understanding of the nonlinear dynamics of coupled thermoacoustic modes through both experimental characterization and model building. A novel experimental facility will explore both the steady-state and transient behavior of a system with multiple interacting modes. By using a hydraulically-actuated variable-length exhaust, this test setup can precisely control acoustic mode shapes without altering operating conditions. A data campaign will characterize the dynamics of global and spatially-resolved heat release and acoustic pressure in this rig at high speed across gas-turbine relevant operating conditions. To extract more generalizable information about the underlying physics in the system, a reduced order model will be constructed to reproduce the observed behaviors. By connecting model terms to physical phenomena, the model will help uncover the mechanisms underpinning the system dynamics. In turn, this model and the associated learnings will aid in the modeling of thermoacoustics in pursuit of better design and more predictable operation of gas turbine combustors.

Date and time: 2026-04-28, 9:30 am - 11:30 am

Location: Food Processing Technology Building - Auditorium 102

Committee:
Dr. Timothy Lieuwen (advisor), School of Aerospace Engineering
Dr. Timothy Lieuwen, School of Aerospace Engineering
Dr. Benjamin Emerson, School of Aerospace Engineering
Dr. Keegan Moore, School of Aerospace Engineering
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