AXIAL STAGE INJECTION DUAL FREQUENCY RESONATOR FOR A COMBUSTOR OF A GAS TURBINE ENGINE

A gas turbine engine (202) including a secondary fuel stage (218) which also functions as a dual frequency resonator. The engine includes a combustor (210) and a casing (205) enclosing the combustor to define a volume (214). The secondary fuel stage includes a nozzle (217) sized to be effective as a transverse resonator at a high frequency. The nozzle and the volume (214) of the casing are sized to be effective as a longitudinal resonator at an intermediate frequency.

FIELD OF THE INVENTION

The invention relates to gas turbine engines, and more particularly to a resonator used to dampen resonance frequencies in a combustor of a gas turbine engine.

BACKGROUND OF THE INVENTION

A conventional combustible gas turbine engine includes a compressor section, a combustion section including a plurality of can-annular combustor apparatuses, and a turbine section. Ambient air is compressed in the compressor section and directed to the combustor apparatuses in the combustion section.FIG. 1illustrates a conventional combustor10. As illustrated inFIG. 1, it is known that injecting fuel at two axially spaced apart fuel injection locations, i.e., via an upstream fuel stage16associated with a main combustion zone and a secondary fuel stage18downstream from the main combustion zone, reduces the production of NOxby the combustor10. For example, if a significant portion of fuel is injected at the secondary fuel stage18, the amount of time that secondary combustion products are at a high temperature is reduced as compared to first combustion products, created by the fuel injected by the upstream fuel stage16.

FIG. 2illustrates another conventional combustor110. During engine operation, acoustic pressure oscillations at undesirable frequencies can develop in the combustor110due to, for example, burning rate fluctuations inside the combustor110. Such pressure oscillations can damage components in the combustor110. To avoid such damage, one or more damping devices, such as a resonator124, can be formed by attaching a resonator box126to an outer peripheral surface128of the combustor liner122. As illustrated inFIG. 2, a plurality of resonators124can be aligned circumferentially about the liner122. The resonators124can be tuned to provide damping at a single transverse frequency.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized several limitations of the conventional resonator that is used to dampen pressure oscillations within a combustor of a gas turbine engine. For example, the inventors recognized that conventional resonators in a combustor take the form of additional components beyond those that are needed to direct and combust fluid in the combustion chamber. Based on this recognition, the present inventors developed a resonator using the existing components that direct and combust fluid in the combustion chamber, and thus eliminated the need for additional components.

The present inventors also recognized that conventional resonators in a combustor are limited to dampening one resonant frequency mode, per resonator design. Based on this recognition, the present inventors developed a resonator for a combustor, which simultaneously dampens a high frequency transverse mode and an intermediate frequency longitudinal mode, thereby reducing the number of required resonator designs to dampen multiple resonant frequency modes.

FIG. 3illustrates a gas turbine engine202including a compressor204that generates compressed air which is passed through a diffuser207and into a casing205with a volume214. The compressed air then enters a can-annular combustor210, where the compressed air is mixed with a fuel from a primary fuel stage and is ignited. As illustrated inFIG. 3, the casing volume214encloses the combustor210. A secondary fuel line234is directed to a secondary fuel stage218of the combustor210, to inject fuel into the air/fuel mixture within the combustor210at the secondary fuel stage218. Additionally, compressed air is injected into the combustor210at the secondary fuel stage218. The ignited air/fuel mixture is subsequently passed to a turbine206, to perform work, such as rotating a shaft208connecting the compressor204and the turbine206, for example. As illustrated inFIG. 3, the combustor210includes a resonator200at the secondary fuel stage218, to dampen multiple frequencies corresponding to resonant frequency modes of the combustor210, as described below.

FIG. 4illustrates the resonator200, which includes the combustor210and a flow sleeve212that encloses the combustor210. As further illustrated inFIG. 4, the combustor210includes the secondary fuel stage218located at a downstream secondary fuel injection location246. The secondary fuel line234is located at the secondary fuel stage218and includes an outlet236positioned to inject fuel into an inlet238of a nozzle217to deliver fuel to a combustion chamber240of the combustor210through the nozzle217.

Each nozzle217, by itself, is sized to be effective as a transverse resonator, to dampen a transverse frequency corresponding to a resonant transverse mode combustion-induced vibrations of the combustor210. In an exemplary embodiment, as illustrated inFIG. 4, a length220of the nozzle217is sized such that the nozzle is effective as the transverse resonator. In an exemplary embodiment, a ratio of the nozzle length to nozzle diameter may be in a range of 0.5-5.0, for example. However, the ratio of nozzle length to nozzle diameter is not limited to any specific range. In an exemplary embodiment, the nozzle217acts as a half-wave resonator in a transverse dimension, such that the length220is sized in order for an integral number of half-wavelengths of a transverse frequency to fit along the length220, where the transverse frequency corresponds to a resonant transverse mode of the combustor210. In another exemplary embodiment, as illustrated inFIG. 4, the nozzle217defines an opening222, and a cross-sectional width221of the opening222is sized such that the nozzle is effective as the transverse resonator. In an exemplary embodiment, a ratio of the nozzle diameter to combustor diameter may be in a range of 0.01-0.1, for example. However, the ratio of the nozzle diameter to combustor diameter is not limited to any specific range. In another exemplary embodiment, the cross-sectional width221, in addition to the nozzle length220and a volume within the nozzle217are sized such that the nozzle is effective as the transverse resonator.FIG. 5illustrates an alternate resonator200′ with a nozzle217′ that is located at the downstream secondary fuel injection location246of the combustor210. As illustrated inFIG. 5, the nozzle217′ defines a conical opening222′ with a reduced cross-sectional width221′ toward an outlet226′ of the nozzle217′. In an exemplary embodiment, the conical opening may be angled within a range of 75-90 degrees, for example. However, the angle of the conical opening is not limited to any specific range. AlthoughFIGS. 4-5illustrate nozzles with cylindrical (FIG. 4) and conical (FIG. 5) shaped cross-sectional areas, the embodiments of the present invention is not limited to these arrangements and the nozzles may have any cross-sectional area arrangement, provided that the cross-sectional area is such that the nozzle is effective as the transverse resonator. In an exemplary embodiment, the nozzle217is sized to dampen a transverse frequency in a range of 2900-2950 Hz, for example, which corresponds to a resonant transverse mode of the combustor210. However, this transverse frequency range is merely exemplary and the resonator of the present invention is not limited to dampening any specific transverse frequency range, since the design parameters (i.e. length, cross-sectional area, shape, volume, number of nozzles, etc) of the resonator nozzle can be adjusted such that the resonator dampens any desired transverse frequency range. In an exemplary embodiment, the number of nozzles217at the secondary fuel stage218may be within a range of 8-12 nozzles, for example. However, this range is merely exemplary and any number of nozzles may be used at the secondary fuel stage218, provided that the resonator is effective as a transverse resonator.

The combination of the nozzle217and the casing volume214(FIG. 3) are effective as a longitudinal resonator, and the nozzle217and the volume214are sized in order for the longitudinal resonator to dampen a longitudinal frequency corresponding to a resonant longitudinal mode of the combustor210. In an exemplary embodiment, the longitudinal frequency dampened by the longitudinal resonator may depend on the casing volume and/or on a longitudinal dimension within the casing volume, depending on the geometry of the casing and the target resonant longitudinal mode to be dampened. In an exemplary embodiment, the longitudinal frequency dampened by the longitudinal resonator may depend on a combination of the casing volume and the sum of all of nozzles within each combustor. In an exemplary embodiment, the casing volume214acts as a cavity and the nozzles217act as a neck of a Helmholtz resonator, for example. In order to be effective as the longitudinal resonator, the quantity of the nozzles217may be adjusted. In an exemplary embodiment, the number of nozzles217at the secondary fuel stage218may be within a range of 8-12 nozzles, for example. However, this range is merely exemplary and any number of nozzles may be used at the secondary fuel stage218, provided that the resonator is effective as a longitudinal resonator. In an exemplary embodiment, the nozzle217and the casing volume214are sized to dampen a longitudinal frequency in a range of 50-150 Hz, for example, which corresponds to a resonant longitudinal mode of the combustor210. However, this longitudinal frequency range is merely exemplary and the resonator of the present invention is not limited to dampening any specific longitudinal frequency range, since the parameter (i.e. number of nozzles) of the resonator nozzle and the volume of the casing can be adjusted during a design phase such that the resonator dampens any desired longitudinal frequency range.

FIG. 6illustrates an alternate combustor200″ including the nozzle217positioned at the secondary fuel stage218, as with the combustor200ofFIG. 4discussed above. As with the combustor200ofFIG. 4, the nozzle217of the combustor200″ is sized to be effective as a transverse resonator at a first frequency that corresponds to a first resonant transverse mode of the combustor210. However, the combustor200″ further includes a third fuel stage254at a downstream third fuel injection location252that is downstream of the second fuel stage218at the downstream secondary fuel injection location246. The combustor200″ includes a second nozzle219″ at the third fuel stage254that is sized to be effective as a transverse resonator at a second frequency that corresponds to a second resonant transverse mode of the combustor210, where the second frequency is different than the first frequency and the second resonant transverse mode is different than the first resonant transverse mode. The second nozzle219″ does not extend beyond an inner diameter of the combustion liner wall230of the combustor210. In contrast, the nozzle217extends beyond the inner diameter of the combustion liner wall230. AlthoughFIG. 6depicts the first nozzle217positioned at the secondary fuel stage218and extending beyond the inner diameter of the combustion liner wall230, and the second nozzle219″ positioned at the third fuel stage254and not extending beyond the inner diameter of the combustion liner wall230, this arrangement is merely exemplary, and the nozzles at each of the second and third stages may all extend beyond the inner diameter of the combustion liner wall or may all not extend beyond the inner diameter of the combustion liner wall, or some combination thereof, for example. Additionally, althoughFIG. 6depicts that one nozzle may be arranged at a secondary fuel stage and one nozzle may be arranged at a third fuel stage downstream of the secondary fuel stage, this is merely exemplary, as more than one nozzle may be arranged at each of the secondary or third fuel stages, and one or more nozzle(s) may be arranged at additional fuel stages downstream of the third fuel stage, for example. In an exemplary embodiment, the number of nozzles that are arranged at each of the second and third fuel stages may be within the range of 8-12 nozzles, for example. However, this range is merely exemplary and any number of nozzles may be used at each of the second and third stages, provided that the resonator is effective as a transverse resonator.

FIG. 7illustrates an end view of the resonator200ofFIG. 4at the downstream secondary fuel injection location246and a plurality of nozzles217,219arranged at the secondary fuel stage218. The nozzles217,219are arranged at the downstream second fuel injection location246with an angle228between adjacent nozzles217,219in a plane transverse to the combustor longitudinal axis. In an exemplary embodiment, the angle228is selected such that the nozzles217,219are effective as transverse and longitudinal resonators. In an exemplary embodiment, the angle may be within a range of 15-90 degrees, for example. However, the angle is not limited to any specific range. In an exemplary embodiment, the angle may be determined based on the specific transverse mode that needs to be dampened, for example. AlthoughFIG. 7illustrates two nozzles217,219arranged at the secondary fuel stage218, the embodiment of the present invention is not limited to this number of nozzles and any plurality of nozzles may be arranged at the secondary fuel stage, provided that the angle between adjacent nozzles is sized such that the nozzles are effective transverse and longitudinal resonators.

In an exemplary embodiment, the nozzles217,219at the secondary fuel stage218may be individually sized (i.e. length, cross-sectional area, etc.) such that a first nozzle217is effective as a transverse resonator at a first frequency and a second nozzle219is effective as a transverse resonator at a second frequency that is different than the first frequency. For example, the nozzles217,219may have different lengths and/or different cross-sectional areas, such that the nozzle217and the nozzle219are sized to be effective as transverse resonators at a respective first and second frequency. Although the above example discusses that two nozzles at the secondary fuel stage may be sized differently to be effective transverse resonators at two distinct frequencies, the embodiment of the present invention is not limited to this arrangement, and includes any plurality of nozzles at the secondary fuel stage being sized differently, to be effective transverse resonators at a plurality of distinct frequencies, for example. Additionally, the length and cross-sectional areas of the nozzles217,219may be sized, in addition to the casing volume214, to ensure that the desired longitudinal frequency is dampened.

FIG. 8depicts a plot of the frequency response function (FRF) of the resonator200for a range of frequencies during operation of the combustor210. As illustrated inFIG. 8, the resonator200is effective to simultaneously dampen a transverse frequency242corresponding to a resonant transverse mode of the combustor210and to dampen a longitudinal frequency244corresponding to a resonant longitudinal mode of the combustor210. The transverse frequency242dampened by the nozzle217corresponds to a high frequency mode with a range of approximately 2900-2950 Hz, and is based on the sizing characteristics (i.e. length, opening, cross-sectional area, etc) of the nozzle217. The FRF248of the resonator200at the transverse frequency242is based on the combination of the individual dampening effects of each nozzle217at the secondary fuel stage218. Although the transverse frequency242discussed above lies within a sample range of 2900-2950 Hz, this range is merely exemplary, may include a wider range of 1200-4500 Hz and the embodiments of the present invention is not limited to these ranges and may include any resonant transverse mode of the combustor, provided that the nozzles can be sized to dampen the transverse frequency corresponding to the resonant transverse mode.

As further illustrated inFIG. 8, the longitudinal frequency244is an intermediate frequency mode with a range of approximately 50-150 Hz. The FRF250of the resonator200at the longitudinal frequency244, and the range of the longitudinal frequency mode244, are based on the volume214of the casing205in combination with the characteristics of the nozzles217,219in each combustor210of the engine202. The number of nozzles217at the secondary fuel stage218may affect the longitudinal frequency244, such as the center frequency within the range of the longitudinal frequency244, for example. Although the longitudinal frequency mode244discussed above lies within a sample range of 50-150 Hz, this range is merely exemplary, may include a wider range of 50-400 Hz and the embodiments of the present invention is not limited to these ranges and may include any resonant longitudinal mode of the combustor, provided that the casing volume and the nozzles are sized to dampen the longitudinal frequency corresponding to the resonant longitudinal mode.

In the above embodiment, the resonator200dampens a wider range of the longitudinal frequency244(100 Hz) than the range of the transverse frequency242(50 Hz). Since the range of the dampened transverse frequency242for each nozzle design is relatively narrow, more than one nozzle design may be employed in the resonator, to increase the total range of dampened transverse frequencies. As previously discussed, multiple nozzle designs may be provided, where each nozzle design is configured to dampen a respective transverse frequency range.