COMBUSTION DRIVEN OSCILLATIONS: NUMERICAL PREDICTION OF DYNAMIC BEHAVIOR OF GAS TURBINE FLAMES

Strong acoustical pulsations in gas turbines caused by interaction of the combustion supply system, cavity acoustics and dynamic flame behavior could result in engine failure or increased wear and tear. Knowledge of the thermoacoustic characteristics of new combustion systems during the design phase helps to avoid or minimize the occurence of these oscillations. Consequently, prediction of the behavior of these complex acoustical systems is necessary. One key issue in the feedback loop describing these systems is the dynamic behavior of the flame due to acoustic excitation. Here, a method to determine dynamic characteristics of a flame will be described and applied to a real gas turbine flame. Special focus will be placed on the three-dimensional behavior of this turbulent swirled flame. Therefore, a steady-state simulation of the turbulent flow-field and the combustion process will be performed. A subsequent transient simulation with a sudden change in inlet mass flow at the beginning will lead to a transient response of the flame. From this, the important characteristic times in the interesting directions, axial and circumferential direction of the gas turbine combustion chamber. are deduced.