Modal Analysis of Direct Core Noise in a Model Combustor

Abstract

Combustion noise is a growing concern for gas turbine designers, especially the presence of prominent tonal structures or thermoacoustic instabilities. High fidelity simulations such as compressible large eddy simulation (LES) have demonstrated great potential in predicting the behavior of these reacting flows, but these methods generate massive amounts of data and efficient techniques are required to isolate the behavior and underlying physics of acoustic structures. Multiple modaldecomposition techniques have gained prominence across a variety of fields for identifying the underlying dynamics of complex systems, including the fast Fourier Transform (FFT), proper orthogonal decomposition (POD), and dynamic mode decomposition (DMD). Here, these three techniques are applied to the pressure field taken from a compressible LES of a gas turbine model combustor (GTMC). Comparisons are made between the structures identified by each algorithm as well as the capacity of each technique to identify mode amplitude and assign cardinality to the modes. Lastly, comments are offered about the advantages and disadvantages, including robustness, of the methods studied.