Thermoacoustic stability analysis of an annular combustion chamber with acoustic low order modeling and validation against experiment

A low order acoustic network model is used to examine the stability of an annular combustor for different operating points. The results obtained by this approach are compared against experimental data from a full annular combustor. This annular combustor, in contrast to commonly used single burners or sector rigs, was used to include also 2-dimensional effects like the influence of circumferential modes, which can occur in practical gas turbine applications. The influence of the flame enters the network model simulation through an experimentally measured flame transfer function in terms of the response of heat release to acoustic velocity fluctuations. This flame transfer function, which has been measured at a stable operating point, is then used as a basis for the determination of flame transfer functions at other operating points by means of scaling methods. The transition to instability is thereby simulated by determination of the complex eigen modes, applying methods from control theory. The analytically determined stability behavior is compared to the experimentally measured one, with the aim to enhance and validate the network model approach as a means of predicting combustion instabilities in early design stages.