A thermoacoustic instability observed within a lean swirl-stabilized burner is analyzed by means of numerical calculations. As extension to previously reported numerical data for the considered test case, the numerical domain is extended to include the fuel plenum and the acoustic outlet impedance is modeled by time domain impedance boundary conditions.
The predicted thermoacoustic frequency is in excellent agreement with experimental findings. Furthermore, the thermoacoustic feedback loop is discussed by means of phase resolved data which show that a variation of the equivalence ratio within the swirler is the driving mechanism of the instability. Finally, the Rayleigh criterion is shown to be satisfied within the combustion chamber. Hence, a closed thermoacoustic feedback loop is observed.