Analytic study on combustion instability with a thermoacoustic network model

The acoustic characteristics of the combustion system, as well as the response of the flame to the fluctuations of incoming fluid, exert a fundamental influence on the conditions in which the instability may occur. Data from low-order thermoacoustic model were used to identify the frequencies, mode shape and nonlinear behavior of thermoacoustic instabilities. Low-order models described the acoustic characteristics of combustor system as a series of subsystems. In the flame model, heat release rate oscillation was written as the linear and nonlinear function of incoming velocity fluctuation. Nonlinearities were introduced into the linear flame model to predict triggering instabilities and limit cycle amplitudes. Several test cases compared with the experiments of laboratory combustor were analyzed in order to invest the effect of nonlinear terms in the flame model. The results agree well with the experiments, showing that the code can be used to describe the characteristics of the combustion instability and predict directly the limit cycle amplitudes from nonlinear flame model.