Gas turbines are widely used in industrial, marine, aircraft and power generation operations. A gas turbine includes a compressor section, a combustion section disposed downstream from the compressor section and a turbine section positioned downstream from the combustion section. The combustion section generally includes multiple combustor cans annularly arranged around an outer casing such as a compressor discharge casing. In particular configurations, each combustor can includes multiple bundled tube or micro-mixer type fuel nozzles annularly arranged around a center fuel nozzle.
Combustion instability/dynamics is a phenomenon which occurs in gas turbines that utilize lean pre-mixed combustion such as those having bundled tube or micro-mixer type fuel nozzles. Depending on the nature or mechanism of excitation of combustion chamber modes, combustion instability can be low/high frequency. A low or lower frequency (i.e. 200-400 Hz) combustion dynamics field is caused by excitation of axial modes, whereas a high or higher frequency (i.e. greater than about 1.0 kHz) dynamic field is generally caused by the excitation of radial and azimuthal modes of the combustion chambers and is commonly referred to as screech.
The overall dynamic field created includes a combustion field component and an acoustic component that pass along the combustor during combustion. Under certain operating conditions, the combustion component and the acoustic component couple to create a high and/or low frequency dynamic field which may have a negative impact on various gas turbine components such as combustion liners, transition pieces. In addition, the high frequency dynamic field may excite modes of downstream gas turbine components such as turbine blades, thus potentially contributing to high cycle fatigue.
In-phase combustion dynamics are particularly of concern when instabilities between the adjacent cans are coherent (i.e., there is a strong relationship in the frequency and the amplitude of the instability from one can to the next can). Such coherent in-phase combustion dynamics can also excite the turbine blades and lead to durability issues, thereby limiting the operability of the gas turbine.
Current systems and/or methodologies for mitigating combustion dynamics include damping systems which are designed to mitigate one particular frequency and/or a limited frequency range. For example, either the high frequency tones or the low frequency tones. Accordingly, a system for mitigating both low and high frequency in-phase combustion dynamics within combustors, particularly those which include bundled tube fuel nozzles, would be useful.
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