One-dimensional acoustic modeling of thermoacoustic instabilities (on cd)

In this paper the acoustic stability of a premixed turbulent natural gas flame confined in a combustor is investigated. Specifically when the flame is operated in a lean premixed mode, the thermoacoustic system is known to exhibit instabilities. These arise from a feedback mechanism between the oscillatory flow and heat release rate perturbations in the flame and often lead to large amplitude pressure and velocity perturbations in the combustor. The acoustics of the combustor are described with a one-dimensional transfer matrix method. The feedback mechanisms that can cause instabilities are included in this method. The (complex) frequency for which the determinant of the transfer matrix goes to zero indicates an instability. An important factor in the one-dimensional acoustic model is the transfer function between the oscillatory flow and heat release rate perturbations. This transfer function is obtained from a well-stirred reactor dynamic combustion model. Results show that the one-dimensional acoustic model in combination with a well-stirred reactor model is able to describe realistic gas turbine stability behaviour.