Fuel nozzle assembly that exhibits a frequency different from a natural operating frequency of a gas turbine engine and method of assembling the same

A method of assembling a fuel nozzle assembly for a gas turbine engine having a natural operating frequency includes providing a flange and providing a premix tube. The flange is fabricated from a first alloy such that the flange is configured to exhibit a first frequency that is different than the natural operating frequency of the gas turbine engine. The premix tube is fabricated from a second alloy such that the premix tube is configured to exhibit a second frequency that is different from the natural operating frequency of the gas turbine engine. The premix tube is coupled to the flange.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to gas turbine engines and, more particularly, to center fuel nozzles used within gas turbine engines.

At least some known gas turbine engines ignite a fuel-air mixture in a combustor to generate a combustion gas stream that is channeled to a turbine via a hot gas path. Compressed air is channeled to the combustor by a compressor. Combustor assemblies typically use fuel nozzles that facilitate fuel and air delivery to a combustion region of the combustor. The turbine converts the thermal energy of the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, for example, an electric generator or a pump.

Known fuel nozzle assemblies include a flange that extends from an end cover that serves as the structural base of the fuel nozzle. A premix tube extends from the flange and is coupled to a swirler. The natural frequency of the fuel nozzle assemblies are generally a function of both the shape and length of the flange and premix tube combination. Moreover, in known fuel nozzle assemblies, the operating frequency of the gas turbine engine may produce low cycle and/or high cycle fatigue in fuel nozzle components and joints, such as for example, the flange, the premix tube, and/or the swirler, and/or joints defined between the components. Moreover, in known fuel nozzle assemblies, stress concentrations around the fuel nozzle assembly and/or an increase in structural break-out into the fuel holes as a result of the fuel nozzle assembly may develop if the natural frequency is similar to, or substantially the same as, the operating rotor frequency (including first through fourth multiple of rotor frequency), combustion tones and siren tones of the gas turbine engine.

Many known fuel nozzle assemblies use a variety of components that are manufactured from a variety of materials and that are coupled together with welded and brazed joints, such as along the joints defined between the flange, the premix tube and/or the swirler. Because of the different material properties, the different components may have different thermal growth rates and/or magnitudes of thermal expansion and contraction. Additionally, over time, the welded and brazed joints may be prone to fatigue, cracking, or premature failure during operation when exposed to the operating frequencies produced by the gas turbine engine.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method is provided for assembling a fuel nozzle assembly for a gas turbine engine having a natural operating frequency. The method includes providing a flange and a premix tube. The flange is fabricated from a first alloy such that the flange is configured to exhibit a first frequency that is different than the natural operating frequency of the gas turbine engine. The premix tube is fabricated from a second alloy such that the premix tube is configured to exhibit a second frequency that is different from the natural operating frequency of the gas turbine engine. The premix tube is coupled to the flange.

In another aspect, a fuel nozzle assembly is provided for a gas turbine engine including a combustor. The gas turbine engine has a natural operating frequency. The fuel nozzle assembly includes a flange and a premix tube. The flange includes a first end and a second end. The flange first end is coupled to the combustor. The flange is fabricated from a first alloy such that the flange is configured to exhibit a first frequency that is different than the natural operating frequency of the gas turbine engine. The premix tube includes a first end coupled to the flange second end. The premix tube is fabricated from a second alloy such that the premix tube is configured to exhibit a second frequency that is different than the natural operating frequency of the gas turbine engine.

In yet another aspect, a gas turbine engine is provided. The gas turbine engine has a natural operating frequency. The gas turbine engine includes a combustor and a fuel nozzle assembly. The fuel nozzle assembly includes a flange and a premix tube. The flange includes a first end and a second end. The flange is fabricated from a first alloy such that the flange is configured to exhibit a first frequency that is different than the natural operating frequency of the gas turbine engine. The flange is coupled to the combustor at the flange first end. The premix tube includes a first end coupled to the flange second end. The premix tube is fabricated from a second alloy such that the premix tube is configured to exhibit a second frequency that is different than the natural operating frequency of the gas turbine engine.

Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Additional features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration of an exemplary gas turbine engine100. In the exemplary embodiment, engine100includes a compressor102and a combustor104. Combustor104includes a combustion region105and a fuel nozzle assembly106. Engine100also includes a turbine108and a common compressor/turbine shaft110(sometimes referred to as rotor110). Compressor102also is rotatably coupled to rotor110. In the exemplary embodiment, there is a plurality of combustors104and fuel nozzle assemblies106. In the following discussion, unless otherwise indicated, only one of each component will be discussed. In one embodiment, gas turbine engine100is a PG9371 9FBA Heavy Duty Gas Turbine Engine commercially available from General Electric Company, Schenectady, N.Y. Notably, the present invention is not limited to any one particular engine and may be used in connection with other gas turbine engines, for example, such as the MS7001FA (7FA), MS9001FA (9FA), MS7001FB (7FB) and MS9001FB (9FB) engine models commercially available from General Electric Company, Schenectady, N.Y.

During operation, air flows through compressor102and compressed air is supplied to combustor104. Specifically, a substantial amount of the compressed air is supplied to fuel nozzle assembly106that is integral to combustor104. Some combustors have at least a portion of air flow from compressor104distributed to a dilution air sub-system (not shown inFIG. 1) and most combustors have at least some seal leakage. Fuel nozzle assembly106is in flow communication with combustion region105. Fuel nozzle assembly106is also in flow communication with a fuel source (not shown inFIG. 1) and channels fuel and air to combustion region105. Combustor104ignites and combusts fuel, for example, natural gas and/or fuel oil, to generate a high temperature combustion gas stream. Combustor104is coupled in flow communication with turbine108and turbine108converts thermal energy from the combustion gases discharged by Combustor104to mechanical rotational energy. Turbine108is rotatably coupled to rotor110.

FIG. 2is a fragmentary illustration of an exemplary fuel delivery assembly200that may be used with turbine engine100(shown inFIG. 1) as a component of combustor104(shown inFIG. 1). In the exemplary embodiment, fuel delivery assembly200includes at least one fuel supply feed202and an atomized air cartridge sub-assembly203. Sub-assembly203includes a plurality of air supply tubes204that are coupled to a plurality of inner atomized air tubes205. Fuel nozzle assembly200also includes a combustor end cover sub-assembly206. Cover sub-assembly206includes a plurality of premix fuel supply passages218for channeling air and fuel (discussed further below), an end cover plate body208, and a plurality of end cover-to-combustor casing fasteners210. In the exemplary embodiment, body208is formed via a machining process wherein a plurality of channels211are formed within body208that are sized to receive, but are not limited to only receiving, premix fuel supply passages218, a diffusion fuel supply passage220, a plurality of atomized air supply tubes204, a fuel nozzle insert sub-assembly212, a plurality of end cover-to-combustor casing fasteners210, a plurality of insert-to-end cover fasteners214, and a plurality of cap-to-end cover fasteners217. Alternatively, an existing body208may be retrofitted in accordance with the teachings described here. In the exemplary embodiment, cover sub-assembly206is coupled to combustor104(shown inFIG. 1) casings via fasteners210, and atomizing air cartridge sub-assemblies203are coupled to end cover plate body208.

Fuel delivery assembly200also includes a plurality of fuel nozzle insert sub-assemblies212and a fuel nozzle sub-assembly225. Fuel nozzle sub-assembly225includes a plurality of nozzle radially outer tubes216, a plurality of intermediate tubes223, a cap mounting flange222, and a plurality of radially inner tubes221, an annular diffusion fuel passage219and a fuel nozzle cap224. In the exemplary embodiment, fuel nozzle insert sub-assembly212is coupled to end cover plate body208via fasteners214, and a cap224is coupled to end cover plate body208via fasteners217and cap mounting flange222.

During operation, fuel is channeled to fuel nozzle assembly200via at least one supply feed202from a fuel source (not shown inFIG. 2). Premix fuel is channeled to tube216via passage218and fuel nozzle insert sub-assembly212as illustrated by arrows. Diffusion fuel is channeled to passage219via tube220as illustrated by arrows. Combustion air is channeled from compressor102(shown inFIG. 1) to air supply tubes204prior to being channeled to tube205as illustrated by arrows. Generally, a plurality of fuel nozzle assemblies200are spaced circumferentially about rotor110(shown inFIG. 1) to ensure a circumferential stream of combustion gases, with a substantially uniform temperature is generated within combustor104and channeled to turbine108(shown inFIG. 1). A portion of fuel nozzle assembly200, including insert sub-assembly212, as illustrated within the dotted lines, is illustrated inFIG. 3and described in more detail below.

FIG. 3is an enlarged cross-sectional schematic view of an exemplary fuel nozzle assembly300. In the exemplary embodiment, fuel nozzle assembly300has a centerline axis302and is coupled to an end cover304via a fuel nozzle flange306. A premix tube308coupled to flange306at a first joint310includes a radially outer surface312. In the exemplary embodiment, premix tube308is coupled to flange306via a weld such as, but not limited to, an electron beam weld. Alternatively, premix tube308may be coupled to flange306using any coupling device, such as, for example, a braze, screws, bolts, and/or any fastener that enables fuel nozzle assembly300to function as described herein. Premix tube308extends a variable length L1from joint310towards a combustion chamber311. In the exemplary embodiment, length L1is manipulated to properly tune the natural frequency of fuel nozzle assembly300, wherein flange306and the premix tube assembly operate at a natural frequency that is different than an operating rotor frequency (including first through fourth multiple of rotor frequency), combustion tones and siren tones of the gas turbine engine100(shown inFIG. 1).

Fuel nozzle assembly300includes a radially inner tube314that is coupled to flange306along a second joint315. Tubes308and314define a substantially annular first premixed fuel supply passage316. Additionally, inner tube314defines a diffusion fuel passage318. In the exemplary embodiment, passages316and318are coupled in flow communication to a plurality of fuel sources (not shown inFIG. 3).

Fuel nozzle assembly300includes a substantially annular inlet flow conditioner (IFC)320. In the exemplary embodiment, IFC320includes a radially outer wall322that includes a plurality of perforations324, and an end wall326that is positioned on an aft end of IFC320and extends between wall322and surface312. Walls322and326, and surface312define a substantially annular IFC chamber328therebetween. Chamber328is in flow communication with a cooling passage (not shown inFIG. 3) via perforations324. Fuel nozzle assembly300also includes a tubular transition member330that is coupled to wall322. Transition member330defines a substantially annular transition chamber332that is substantially concentrically aligned with respect to first premixed fuel supply passage316and that is positioned such that an IFC outlet passage334extends between chambers328and332.

In the exemplary embodiment, fuel nozzle assembly300also includes an air swirler assembly or swozzle assembly340for use with gaseous fuel injection. Swozzle340includes a substantially tubular shroud342that is coupled to transition member330, and a substantially tubular hub344that is coupled to tube308along a joint346. In the exemplary embodiment, hub344is coupled to tube308via an electron beam weld. Alternatively, hub344may be coupled to tube308using any coupling device, such as for example, a braze, screws, bolts, and/or any fastener that enables fuel nozzle assembly300to function as described herein. Shroud342and hub344define an annular chamber348therebetween, wherein a plurality of hollow turning vanes350extend between shroud342and hub344. Chamber348is coupled in flow communication with chamber332, and hub344includes a plurality of turning vane passages (not shown inFIG. 3) that are in flow communication with premixed fuel supply passage316. A plurality of premixed gas injection ports (not shown inFIG. 3) are defined within hollow turning vanes350.

Fuel nozzle assembly300includes a substantially annular fuel-air mixing passage354that is defined by a tubular shroud extension356and by a tubular hub extension358. Passage354is coupled in flow communication with chamber352, and extensions356and358are each coupled to shroud342and to hub344, respectively.

A tubular diffusion flame nozzle assembly360is coupled to hub344such that an annular diffusion fuel passage318is at least partially defined. Assembly360also defines an annular air passage362in cooperation with hub extension358. Fuel nozzle assembly300also includes a slotted gas tip363that is coupled to hub extension358and to assembly360. Tip363includes a plurality of gas injectors364and air injectors366, and coupled in flow communication with, and facilitates fuel and air mixing in, combustion chamber311.

During operation, fuel nozzle assembly300receives compressed air from air supply tube204(shown inFIG. 2) via a plenum (not shown inFIG. 3) surrounding fuel nozzle assembly300. Most of the air used for combustion enters assembly300via IFC320and is channeled to premixing components. Specifically, air enters IFC320via perforations324and mixes within chamber328, and air exits IFC320via passage334and enters swozzle inlet chamber348via transition piece chamber332. A portion of high pressure air entering air supply tube204is also channeled into an air-atomized liquid fuel cartridge (not shown inFIG. 3) inserted within diffusion fuel passage318.

Fuel nozzle assembly300receives fuel from a fuel source (not shown inFIG. 3) via premixed fuel supply passage316. Fuel is channeled from premixed fuel supply passage316to the plurality of primary gas injection ports defined within turning vanes350.

Air channeled into swozzle inlet chamber348from transition piece chamber332is swirled via turning vanes350prior to being mixed with fuel, and the fuel/air mixture is then channeled into swozzle outlet chamber352for additional mixing. The fuel and air mixture is then channeled to mixing passage354prior to being discharged from assembly300into combustion chamber311. In addition, diffusion fuel channeled through diffusion fuel passage318is discharged through gas injectors364into combustion chamber311wherein the diffusion fuel is mixed with, and combusts with, air discharged from air injectors366.

FIG. 4is a cross-sectional schematic view of flange306used with fuel nozzle assembly300. In the exemplary embodiment, flange306is fabricated to operate between a whole number frequency multiple of the operating frequency of gas turbine engine100. More specifically, and in the exemplary embodiment, gas turbine engine100operates at a frequency of approximately 50 Hz. Flange306is fabricated to operate at a natural frequency that will substantially avoid 50 Hz or multiples thereof, such as for example 100 hertz, 150 hertz, 200 hertz, etc. More specifically, in the exemplary embodiment, flange306is fabricated to operate at a natural frequency of about 175 Hz to about 180 Hz. The exemplary embodiment applies to a Class 9 Gas Turbine but can be applied to multiple engine classes such as Class 7 with a 60 Hz rotor tone with multiple rotor tones of 120 Hz, 180 Hz and 240 Hz.

To ensure fuel nozzle assembly300operates with a desired natural frequency, flange306is fabricated with a centerline axis302and includes a mounting portion380and a substantially frusto-conical shaped body382that together define an outside length L2for controlling the desired natural frequency. In the exemplary embodiment, body382is converged and is fabricated with an angle A1of approximately 10° to enable fuel nozzle assembly300to operate at a frequency of between about 175 Hz to about 180 Hz. In the exemplary embodiment, length L2is approximately 3.75 in. (95.25 mm) and enables fuel nozzle assembly300to operate at a frequency of between about 175 Hz to about 180 Hz. Alternatively, body382may be fabricated with any angle A1, and length L2may be any length that enables fuel nozzle assembly300to function as described herein.

FIG. 5is a cross-sectional schematic view of premix tube308. In the exemplary embodiment, premix tube308has a centerline axis302and is fabricated to operate at a frequency that is different than an operating frequency of gas turbine engine100. More specifically, in the exemplary embodiment, premix tube308has a length L1of approximately 14 inches (in.) (357 millimeters (mm)), wherein premix tube308operates at a frequency that is different than an operating frequency of gas turbine engine100(shown inFIG. 1) i.e., 50 hertz or multiples thereof). Alternatively, L1may be any length that enables fuel nozzle assembly300to function as described herein.

In the exemplary embodiment, premix tube308includes a tapered portion390that enables a greater air flow through fuel nozzle assembly300, and more specifically through swozzle assembly340(shown inFIG. 3). In the exemplary embodiment, tapered portion390is formed with at an angle A2of about 5°. Alternatively, tapered portion390may converge at any angle A2that enables fuel nozzle assembly300to function as described herein. Moreover, in the exemplary embodiment, premix tube308includes an outer wall392that has a thickness T of approximately 0.19 (in.) (4.76 (mm)). Alternatively, outer wall392may be formed with any thickness T that enables fuel nozzle assembly300to function as described herein.

FIG. 6is a flow diagram of an exemplary method400for use in fabricating fuel nozzle assembly300(shown inFIG. 3). In the exemplary embodiment, method400includes fabricating402flange306from stainless steel410, fabricating404premix tube308from stainless steel410and coupling406premix tube308to flange306using an electron beam weld at joint310. Flange306is then coupled408to end cover304using a plurality of fasteners (not shown). Using stainless steel410enables flange306and premix tube308to operate at a frequency that is different than a natural operating frequency of gas turbine engine100, as described in more detail herein. Additionally, using stainless steel410increases the number of compression and expansion cycles that each component may undergo as compared the materials used in known fuel nozzle assemblies. As a result the life of each component is facilitated to be increased. Alternatively, flange306and premix tube308may be fabricated from any other material that enables fuel nozzle assembly300to function as described herein. Coupling flange306to premix tube308with an electron beam welded joint facilitates increasing a structural strength and a resilience of the fuel nozzle assembly and facilitates increasing the durability and life expectancy of the fuel nozzle assembly during engine operations.

Method400includes fabricating410swozzle assembly340from stainless steel347and coupling412swozzle assembly340to a downstream end394of premix tube308using an electron beam weld at joint346. Using stainless steel347enables swozzle assembly340, when coupled to premix tube308as described herein, to operate at a frequency that is different than the operating frequency of gas turbine engine100, as described herein. Additionally, using stainless steel347facilitates increasing the number of compression and expansion cycles that swozzle assembly340may undergo as compared to known fuel nozzle assemblies, and as such facilitates increasing a useful life of the component. Alternatively, swozzle assembly340may be fabricated from any material that enables fuel nozzle assembly300to function as described herein. Coupling swozzle assembly340to premix tube308with an electron beam welded joint facilitates increasing a structural strength and a resilience of the fuel nozzle assembly and facilitates increasing the durability and life expectancy of the fuel nozzle assembly during engine operations.

Exemplary embodiments of fuel nozzle assemblies are described in detail above. The above-described systems are used to deliver a mixture of fuel and air to the engine's combustion chamber, and are fabricated to substantially balance the frequency margin within the engine while providing a more robust and resilient design immediately upstream from the combustion chamber. More specifically, the flange and premix tube within each fuel nozzle assembly integrates both a structural design and natural frequency tuning to facilitate optimizing the design to balance the frequency margin, low cycle fatigue (LCF), high cycle fatigue (HCF) capability and aerodynamic impact. Such fuel nozzle assemblies reduce stress concentrations, minimized break-out into fuel holes, and tune natural frequencies to provide adequate frequency margin with rotor speeds and combustion tones with minimized aerodynamic interference.

Moreover, the systems and method described herein eliminate the braze joint between the flange and premix tube by utilizing an electron beam welded joint to provide a stiffer, or resilient fuel nozzle assembly and increase the durability of the fuel nozzle assembly during engine operation. The contour of the flange and premix tube shape and wall thickness are manipulated to control and improve the natural frequency margin, LCF and HCF are optimized to provide a robust durable design to improve product life.

Additionally, the choice of materials used to fabricate the fuel nozzle assembly described herein significantly reduces costs associated with the production of such fuel nozzles. The materials used also increase the number of cycles that each component may undergo, thereby significantly increasing the life of each component.

Although the apparatus and methods described herein are described in the context of fuel nozzle assemblies for gas turbine engines, it is understood that the apparatus and methods are not limited to such applications. Likewise, the system components illustrated are not limited to the specific embodiments described herein, but rather, system components can be utilized independently and separately from other components described herein.