Combustor Flow Field Characterization with Acoustic Forcing and Swirl Fluctuations
Open Access
- Author:
- Mathews, Benjamin Francis
- Area of Honors:
- Mechanical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Dr. Jacqueline Antonia O'Connor, Thesis Supervisor
Dr. Hosam Kadry Fathy, Thesis Honors Advisor - Keywords:
- swirl
vorticity
combustion instabilities
gas turbines
acoustic forcing
precessing vortex core
combustor - Abstract:
- Gas turbine combustion systems, such as those used for aircraft propulsion and power generation, are susceptible to a phenomenon known as combustion instabilities. Combustion instabilities can result in reduced engine operability, structural fatigue, and in extreme circumstances, catastrophic engine failure. Due to increased regulations on pollutant emissions, systems such as gas turbines are forced to run at fuel lean conditions with premixing. These operating conditions, while effective at reducing emissions, make the system more susceptible to combustion instabilities and therefore research into the combustion instability phenomena is as important as ever. Prior research has identified vorticity fluctuations as an important coupling mechanism present during velocity-coupled combustion instabilities in swirl-stabilized flames, which is a common stabilization method used in gas turbines. These vorticity fluctuations can be induced by longitudinal acoustic pressure oscillations that are convected across the swirler and dump plane upstream of the flame. While these vorticity fluctuations have been identified in a number of configurations using both experimental and simulation techniques, the sensitivity of this mechanism to flow configuration and boundary conditions has not been studied parametrically. In this study, we investigate the impact of time-averaged swirl level, forcing frequency and amplitude on vorticity fluctuation dynamics in the azimuthal direction of a non-reacting swirling jet with and without confinement. The goal of this work is to better understand the dependence of vorticity fluctuations on these various parameters as well as the vorticity conversion processes that occur in the flow. We have shown that vorticity fluctuation levels vary with time-averaged swirl number, particularly in the presence of a self-excited precessing vortex core, which reduces the flow receptivity to the acoustically forced fluctuations. Additionally, variations in forcing frequency and amplitude excite flow response in different portions of the flow, particularly for different swirl numbers with and without confinement. The implications of these results are discussed and future work is proposed.