Combustion Noise Modeling Using Large Eddy Simulation

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KASTENBERG-THESIS-2025.pdf (3.49 MB)
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Kastenberg, Leo M.
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Daniel Guggenheim School of Aerospace Engineering
The Daniel Guggenheim School of Aeronautics was established in 1931, with a name change in 1962 to the School of Aerospace Engineering
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https://hdl.handle.net/1853/78724
Abstract
Aircraft noise pollution is detrimental to human well-being in the vicinity of airports. Historically, the main sources of combustion noise have been fan, compressor, combustor, turbine, and jet noise. Advances such as improvements in blade geometry, acoustic liners, and the advent of high-bypass turbofans have reduced noise from non-combustion sources. Now, combustion noise is one of the major contributors to engine noise, and it will need to be addressed in order to significantly reduce aircraft noise pollution. Combustion noise can be divided into two types: direct and indirect noise. Direct noise is produced when unsteady heat release rate in the flame creates fluctuations in pressure which are then propagated downstream. Indirect noise is produced when fluctuations in entropy, vorticity, and composition are convected downstream and accelerated through either a nozzle or turbine. Although vortical and compositional inhomogeneities have been shown to produce indirect noise, entropy fluctuations are the main source. This thesis uses Large Eddy Simulation (LES) to analyze the production of direct and indirect noise in a Rich-Quench-Lean (RQL) combustor. Two conditions are simulated at different fuel to air ratios. The simulation results are validated against data from a Georgia Tech experiment. Several techniques are used to analyze the results of the LES to determine the mechanisms of generation of combustion noise. A technique combining LES results with a Helmholtz equation solution to the combustor geometry is used to separate out the effects of direct and indirect noise in the LES noise spectrum. This is done in conjunction with numerical signal processing techniques to examine the complex interactions of entropy and acoustic waves in the system. These techniques are then applied to examine differences in noise generation when operating at low and high fuel-air-ratios.
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2025-07-30
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