The following disclosure relates generally to gas turbine engines and, more particularly, to turbine nozzles and other gas turbine engine components having stress relief slots filled with high temperature sealing material, as well as to methods for fabricating gas turbine engine components having sealed stress relief slots.
Gas turbine engines are commonly produced to include turbine nozzles, which accelerate and turn combustive gas flow toward the blades of a turbine rotor downstream of the nozzle. The turbine nozzle may have a generally annular or ring-shaped body including an inner endwall, an outer endwall circumscribing the inner endwall, and a series of circumferentially-spaced vanes extending between the inner and outer endwalls. The inner endwall, the outer endwall, and the vanes define a number of combustive gas flow paths through the turbine nozzle, which conduct hot combustive gas flow during operation of the gas turbine engine. While portions of the nozzle are exposed to combustive gas flow during engine operation, other portions of the turbine nozzle body and its associated mounting features are bathed in relatively cool airflow bled from a cold section of the engine and directed along an outer cooling flow path. In certain cases, undesired leakage can occur across the turbine nozzle interface between the outer cooling flow path and the core gas flow path. Such leakage can negatively affect the efficiency of the gas turbine engine, especially when smaller in size, and may increase the volume of airflow required for cooling purposes.
Leakage across the turbine nozzle mounting interfaces can be reduced through the usage of annular compression seals, such as flexible, pressure-activated metal seals. Such seals may be compressed between the mounting features of the turbine nozzle (e.g., rails extending radially from the opposing ends of the nozzle) and neighboring static structures within the engine. Temperature limitations may require that such compression seals are radially offset from the core gas flow path by a certain distance to reduce the operational temperatures to which the seals are exposed. The turbine nozzle rails may thus be elongated in a radial direction to allow such a radial offset between the compression seals and the core gas flow path. Unfortunately, this also has the effect of increasing temperature differentials that develop across the radially-elongated rails during engine operation, which may result in excessively high hoop stresses within the rails thereby hastening Thermomechanical Fatigue (TMF) and reducing the service lifespan of the turbine nozzle. TMF within the turbine nozzle rails may be alleviated through the formation of stress relief slots at strategic locations in the nozzle rail. The inclusion of stress relief slots in the nozzle rail may, however, permit an undesirably large amount of leakage across the turbine nozzle mounting interfaces thereby defeating the purpose of the compression seals or at least diminishing the effectiveness thereof.
It is thus desirable to provide embodiments of a turbine nozzle having stress relief slots formed at one or more circumferential locations in the radially-elongated rails or similar mounting features, which reduce TMF within the turbine nozzle while also minimizing leakage across the turbine nozzle mounting interfaces. More generally, it would be desirable to produce embodiments of a gas turbine engine component, such as a turbine nozzle or a combustor liner, including stress relief slots providing the above-noted benefits. Finally, it would be desirable to provide embodiments of a gas turbine engine employing such a gas turbine engine component, as well as methods for fabricating such a gas turbine engine component. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.
Embodiments of a gas turbine engine are provided including a core gas flow path, a secondary cooling flow path, and a gas turbine engine component. The gas turbine engine component includes a component body through which the core gas flow path extends, a radially-extending wall projecting from the component body and into the secondary cooling flow path, and one or more stress relief slots formed in the radially-extending wall. The stress relief slots are filled with a high temperature sealing material, which impedes leakage between the secondary cooling and core gas flow paths and which cracks or fractures to alleviate thermomechanical stress within the radially-extending wall during operation of the gas turbine engine.
Further provided are embodiments of a gas turbine engine component, such as a turbine nozzle or combustor liner. In one embodiment, the gas turbine engine component includes a component body having a radially-extending wall projecting therefrom. The component body and the radially-extending wall are exposed to a core gas flow path and to a secondary cooling flow path, respectively, when the gas turbine engine component is installed within the gas turbine engine. A plurality of stress relief slots extends axially through the radially-extending wall. A high temperature sealing material plugs or fills the plurality of stress relief slots and impedes leakage across the radially-extending wall. The high temperature sealing material cracks or factures to alleviate thermomechanical stress when a temperature differential develops across the radially-extending wall during usage of the component.
Still further provided are embodiments of a method for fabricating a gas turbine engine component, such as a turbine nozzle or combustor liner. In one embodiment, the method includes obtaining a component body having a radially-extending wall projecting therefrom, cutting or otherwise forming a plurality of stress relief slots in the radially-extending wall, and infiltrating or filling the plurality of stress relief slots with a high temperature sealing material to impede leakage across the radially-extending wall between the secondary cooling and core gas flow paths. The high temperature sealing material is selected to have a mechanical strength less than the parent material of the radially-extending wall such that the sealing material preferentially fractures to relieve thermomechanical stress when a temperature gradient develops across the radially-extending wall during usage of the turbine nozzle.
At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and:
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawings figures are not necessarily drawn to scale. For example, the dimensions of some of the elements or regions in the figures may be exaggerated relative to other elements or regions to help improve understanding of embodiments of the invention.
The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following Detailed Description. Terms such as “comprise,” “include,” “have,” and variations thereof are utilized herein to denote non-exclusive inclusions. Such terms may thus be utilized in describing processes, articles, apparatuses, and the like that include one or more named steps or elements, but may further include additional unnamed steps or elements.
As illustrated in
During operation of GTE 20, air is drawn into intake section 22 and accelerated by intake fan 32. A portion of the accelerated air is directed through a bypass flow passage 56, which is provided between nacelle assembly 34 and engine case 38 and conducts relatively cool airflow over and around engine case 38. The remaining portion of air exhausted from intake fan 32 is directed into compressor section 36 and compressed by compressor 36 to raise the temperature and pressure of the core airflow. The hot, compressed airflow is supplied to combustion section 26 wherein the air is mixed with fuel and combusted utilizing one or more combustors 58 included within section 26. The combustive gasses expand rapidly and flow through turbine section 28 to rotate the turbine rotors of HP turbine rotor 40 and LP turbine rotor 42. HP turbine nozzle 43 further accelerates the combustive gas flow and helps to impart the gas flow with a desired tangential component prior to reaching HP turbine rotor 40. Similarly, LP turbine nozzle 45 receives the gas flow discharged from HP turbine rotor 40, accelerates and turns the gas flow toward the blades of LP turbine rotor 42. The rotation of turbine rotors 40 and 42 drives the rotation of shafts 44 and 46, respectively, which, in turn, drives the rotation of compressor 36 and intake fan 32. The rotation of shafts 44 and 46 also provides significant power output, which may be utilized in a variety of different manners, depending upon whether GTE 20 assumes the form of a turbofan, turboprop, turboshaft, turbojet engine, or an auxiliary power unit, to list but a few examples. After flowing through turbine section 28, the combustive gas flow is then directed into exhaust section 30 wherein mixer 54 mixes the combustive gas flow with the cooler bypass air received from bypass flow passages 56. Finally, the combustive gas flow is exhausted from GTE 20 through propulsion nozzle 50.
Turbine nozzle 60 is fabricated to further include mounting features facilitating installation of nozzle 60 within a gas turbine engine. For example, as indicated in
Nozzle rails 70 and 72 may be integrally formed with outer endwall 62 as, for example, as a single cast piece. More generally, turbine nozzle 60 may itself be produced as a single cast and machined piece or, perhaps, produced utilizing multiple cast pieces. In this latter regard, turbine nozzle 60 may be fabricated as a brazed turbine nozzle wherein endwall 62, endwall 64, and vanes 66 are cast as separate pieces, which are subsequently assembled and bonded to yield the finished nozzle 60. In further embodiments, turbine nozzle 60 can be produced as a bi-cast turbine nozzle wherein vanes 66 are first cast, arranged in their desired positions, and endwalls 62 and 64 are then cast thereover using an investment casting process. In further embodiments, multiple wedge-shaped or arc-shaped pieces are cast and subsequently bolted together or otherwise assembled to produce the completed turbine nozzle (commonly referred to as a “segmented turbine nozzle”). Each arc-shaped piece may include a segment of the outer endwall, a segment of the inner endwall, and a number of vanes (typically two to three vanes) extending therebetween. Thus, when assembled, the arc-shaped pieces collectively form an annular turbine nozzle similar to that shown in
Leakage between the secondary cooling flow path and the core gas flow path may occur at the interfaces between the turbine nozzle 60, mounting feature 88, and mounting feature 90 if not adequately sealed. In the case of larger gas turbine engines, such leakage may have relatively little impact on engine performance. However, in the case of smaller gas turbine engine platforms, leakage between the secondary cooling and core gas flow paths can have an appreciable impact on overall engine performance. Additionally, leakage between the secondary cooling and core gas flow paths can increase the volume of airflow bled from the cold section and directed along secondary cooling flow path 94 for cooling purposes. Annular compression seals can be utilized to significantly reduce such leakage. For example, as shown in
While effective at impeding gas flow leakage, annular compression seals 96 and 98 may be associated with temperature limitations requiring compression seal 96 and/or seal 98 to be radially offset from the core gas flow path 92. For example, and with continued reference to the exemplary embodiment shown in
As the radial height (HFR) of forward nozzle rail 70 increases, so too does the temperature differential that develops across rail 70 during engine operation. Undesirably rapid TMF may consequently occur within nozzle rail 70 and the neighboring regions of turbine nozzle 60 if the resultant thermomechanical stress is not addressed. For this reason, a plurality of stress relief slots 74 may be formed through an outer annular region of nozzle rail 70. Stress relief slots 74 may be angularly spaced about the centerline of nozzle 60 at substantially regular intervals; however, this need not always be the case.
With continued reference to
During fabrication of turbine nozzle 60, stress relief slots 74 may be cut into forward nozzle rail 70 utilizing, for example, an Electrical Discharge Machining (EDM) wire technique. Advantageously, such a technique may allow the respective widths of slots 74 to be minimized. For example, as indicated in
As a temperature gradient develops across forward nozzle rail 70, hairline cracks or factures may develop within the high temperature sealing material 104 contained within stress relief slots 74. Such fractures are advantageous in the sense that they allow stress relief slots 74 to provide their primary function of alleviating thermomechanical stress within forward rail 70 and turbine nozzle 60 during engine operation. It may be noted that a certain amount of leakage may occur across the fractures within sealed stress relief slots 74. However, any such leakage will be a small fraction of that which would otherwise occur if stress relief slots 74 were not filled with the high temperature sealing material. This may be more fully appreciated by referring once again to
The foregoing has thus provided embodiments of a gas turbine engine component including sealed stress relief slots, which reduce thermomechanical stress while also minimizing leakage between core gas flow and secondary cooling flow paths. In certain embodiments, the stress relief slots may be formed in the forward and/or aft rail of a turbine nozzle and filled with a braze material, such as a nickel-based braze material. The high temperature sealing material is preferably selected to have a mechanical strength less than the parent material of the nozzle rail such that the sealing material preferentially fractures to alleviate thermomechanical stress within the rail during operation of the gas turbine engine; the term “fracture” encompassing separations occurring along the bond interface between the high temperature sealing material and the surfaces of the stress relief slots. While primarily described in the context of a turbine nozzle having one or more radially-elongated rails, it is emphasized that the sealed stress relief slots can also be formed in other gas turbine engine component having at least one radially-extending wall projecting from the component body and into a secondary cooling flow path. For example, in further embodiment, the sealed stress relief slots may be formed in a radially-extending flange provided around the aft outlet end of a combustor liner.
While primarily described above in the context of a turbine engine component and, specifically, a turbine nozzle. The foregoing description also provided embodiments of a method for fabricating such a gas turbine engine component. In one embodiment, the method includes independently fabricating, purchasing from a supplier, or otherwise obtaining a component body having a radially-extending wall projecting therefrom. A plurality of stress relief slots is cut into or otherwise formed in the radially-extending wall. The plurality of stress relief slots are then filled or infiltrated with a high temperature sealing material, which impedes leakage across the radially-extending wall between the core gas flow path and the secondary cooling flow path. The high temperature sealing material is selected or formulated to have a mechanical strength less than the material from which the radially-extending wall is produced such that the high temperature sealing material preferentially fractures to relieve thermomechanical stress when a temperature gradient develops across the radially-extending wall.
While multiple exemplary embodiments have been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set-forth in the appended Claims.
This invention was made with Government support under W911W6-08-2-0001 awarded the U.S. Army (AATE Program). The Government has certain rights in the invention.
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