Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches

This study assesses and compares two alternative approaches to determine the acoustic scattering matrix of a pre-mixed turbulent swirl combustor: 1) The acoustic scattering matrix coefficients are obtained directly from a compressible Large Eddy Simulation (LES). Specifically, the incoming and outgoing characteristic waves f and g extracted from the LES are used to determine the respective transmission and reflection coefficients via System Identification techniques. 2) The flame transfer function (FTF) is identified from LES time series data of upstream velocity and heat release rate. The transfer matrix of the reactive combustor is then derived by combining the FTF with the Rankine-Hugoniot relations across a compact heat source and a transfer matrix of the cold combustor, which is deduced from a linear network model. Linear algebraic transformation of the transfer matrix consequently yields the combustor scattering matrix. A cross-comparison study that includes comprehensive experimental data shows that both approaches successfully predict the scattering matrix of the reactive turbulent swirl combustor.