Thermoacoustic Modeling of a Gas Turbine Using Transfer Functions Measured at Full Engine Pressure Available to Purchase

Thermoacoustic transfer functions have been measured of a full-scale gas turbine burner operating at full engine pressure. Excitation of the high-pressure test facility was done using a siren that modulated part of the combustion airflow. Pulsation probes have been used to record the acoustic response of the system to this excitation. In addition, the flame’s luminescence response was measured by multiple photomultiplier tubes and a light spectrometer. Three techniques to obtain the thermoacoustic transfer function are proposed and employed: two combined acoustical-optical technique and a purely acoustic technique. The first acoustical-optical technique uses one single optical signal capturing the chemiluminescence intensity of the flame as a measure for the heat release in the flame. It only works, if heat release fluctuations in the flame have only one contribution, e.g. equivalence ratio or mass flow fluctuations. The second acoustic-optical acoustic-optical technique makes use of the different response of the flame’s luminescence at different optical wavelengths bands to acoustic excitation. It also works, if the heat release fluctuations have two contributions, e.g. equivalence ratio and mass flow fluctuation. For the purely acoustic technique, a new method was developed in order to obtain the flame transfer function, burner transfer function and flame source term from only three pressure transducer signals. The purely acoustic method could be validated by the results obtained from the acoustic-optical techniques. The acoustic and acoustic-optical methods have been compared and a discussion on the benefits and limitations of the methods is given. The measured transfer functions have been implemented into a non-linear, three-dimensional, time domain network model of a gas turbine with an annular combustion chamber. The predicted pulsation behavior shows a good agreement with pulsation measurements on a field gas turbine.