Scattering and generation of acoustic energy by a premix swirl burner

The scattering and generation of acoustic energy by a premix swirl burner is scrutinized, The analysis is formulated in terms of the scattering matrix of the burner, determined by a combination of computational fluid dynamics and system identification as well as experiment supplemented with simple analytical models for flame frequency response and burner transfer matrix. Remarkably, it is found that in a narrow range of frequencies, incoming acoustic waves are amplified strongly by the unsteady heat release, i.e. acoustic energy is generated. Although the computational and experimental data were obtained for one specific swirl burner design, further analysis suggests that such behavior should be common for many burner designs. Consequences for thermo-acoustic stability as well as burner and combustor design strategies are discussed.