Structure and control of thermoacoustic instabilities in a gas-turbine combustor

Abstract

Thermoacoustic instability was investigated and controlled in an experimental low-emission swirl stabilized combustor, in which the acoustic boundary conditions were modified to obtain combustion instability. Several axisymmetric and helical unstable modes were identified for fully premixed and partially premixed/diffusion combustion. These unstable modes were associated with flow instabilities related to the recirculation region on the combustor axis and shear layer instabilities at the sudden expansion (dump plane). The spatial locations of the intense combustion regions associated with the different unstable modes were visualized by phase locked images of OH chemiluminescence. The axisymmetric mode showed large variation of the heat release during one cycle, while the helical modes showed variations in the radial location of maximal heat release. A closed loop active control system was employed to suppress the thermoacoustic pressure oscillations and to reduce NO x emissions. Microphone and OH emission...