Master's Thesis Defense

Leo Kastenberg

(Advisor: Prof. Suresh Menon)

"Combustion Noise Modeling Using Large Eddy Simulation

On

Monday, July 14 

2:00 p.m. 
Montgomery Knight Room 317

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 convected 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. Multiple conditions are simulated, including looking at the effect of fuel to air ratio. 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.

• Prof. Suresh Menon – School of Aerospace Engineering (advisor)
• Prof. Vigor Yang– School of Aerospace Engineering
• Dr. Vishal Acharya– School of Aerospace Engineering