Flange joint assembly for use in a gas turbine engine

A flange joint assembly includes a first structure including a first flange and a second structure including a second flange coupled to the first flange to form a joint therebetween. The second flange includes a radially outer surface. The flange joint assembly also includes a compression ring coupled to at least the radially outer surface and configured to apply a compressive force to the radially outer surface to reduce an amount of tension stress within said second flange.

BACKGROUND

The application described herein relates generally to gas turbine engines, and more specifically to a flange joint assembly for use in a gas turbine engine.

Gas turbine engines typically include an inlet, a fan, low and high pressure compressors, a combustor, and low and high pressure turbines. The compressors compress air which is channeled to the combustor where it is mixed with fuel. The mixture is then ignited for generating hot combustion gases. The combustion gases are channeled to the turbine(s) which extracts energy from the combustion gases for powering the compressor(s), as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator. Each of the compressors, combustor, and turbines include casing that are coupled to adjacent casings a flange joints.

During engine operation, significant heat is produced which raises the temperature of the casings and their respective flanges. However, in at least some known turbine engines, the inner surface of each casing is exposed to different temperatures than the outer surface of the casing such that any joint comprising multiple flanges experiences high thermal gradients within each flange. Such thermal gradients introduce significant tension stresses onto the flanges which in turn decrease the service lifetime of the flanges and, therefore, the casings. Shorter service life (durability) of turbine engine components increases maintenance frequency and associated costs.

BRIEF DESCRIPTION

In one aspect, a flange joint assembly is provided.

The flange joint assembly includes a first structure including a first flange and a second structure including a second flange coupled to the first flange to form a joint therebetween. The second flange includes a radially outer surface. The flange joint assembly also includes a compression ring coupled to at least the radially outer surface and configured to apply a compressive force to the radially outer surface to reduce an amount of tension stress within said second flange.

In another aspect, a method assembling a gas turbine engine is provided. The method includes forming a compression ring and coupling the compression ring to a radially outer surface of a first flange of a first structure. The compression ring is coupled to apply a compressive force to the radially outer surface to reduce an amount of tension stress within the first flange. The method also includes coupling the first flange to a second flange of a second structure to form a flange joint assembly.

DETAILED DESCRIPTION

The exemplary assemblies and methods described herein overcome at least some disadvantages of known systems and methods for reducing tension stress in a flange joint on a gas turbine engine. Moreover, the assemblies and methods described herein include a first structure having a first flange and a second structure having a second flange coupled to the first flange to form a joint therebetween. The second flange includes a lip portion that at least partially overlaps the first flange. The flange joint assembly also includes a compression ring coupled to a radially outer surface of the lip portion and configured to apply a compressive force to the lip portion to introduce an amount of pre-stress into the joint. Such a compression pre-stress decreases the operational tension stresses in the flange caused by the thermal gradients therein from the different inner and outer surface temperatures and also facilitates increasing the service lifetime of the flange and the casing overall.

Advantages of the flange joint assembly described herein include introducing a compression pre-stress that allows for a decrease weight of the engine when compared to a flange lip portion thickness increase required to decreases operation stresses to a similar level. The comparative reduction in weight for the same benefit results in a more fuel efficient engine having reduced operational costs. Furthermore, the compression pre-stress increases the service lifetime of the components and, therefore, reduces the costs of engine maintenance and ownership.

As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The term “low coefficient of thermal expansion material” refers to a material which grows relatively less as the temperature increases.

As used herein, the terms “axial” and “axially” refer to directions and orientations that extends substantially parallel to a centerline of the turbine engine. The term “forward” used in conjunction with “axial” or “axially” refers to moving in a direction toward the engine inlet, or a component being relatively closer to the engine inlet as compared to another component. The term “aft” used in conjunction with “axial” or “axially” refers to moving in a direction toward the engine outlet, or a component being relatively closer to the engine outlet as compared to another component. Moreover, the terms “radial” and “radially” refer to directions and orientations that extends substantially perpendicular to the centerline of the turbine engine.

Referring initially toFIG. 1, a schematic side section view of a gas turbine engine10is shown. The function of the gas turbine engine is to extract energy from high pressure and temperature combustion gases and convert the energy into mechanical energy for work. The gas turbine engine10has an engine inlet end12wherein air enters a core engine13after passing through a fan section18. Core engine13is defined generally by a compressor14, a combustor16, a multistage high pressure turbine (HPT)20, and a separate low pressure turbine (LPT)21. Collectively, the core engine13provides thrust or power during operation. The gas turbine engine10may be used for aviation, power generation, industrial, marine or the like.

In operation, air enters through the air inlet end12of the engine10and moves through at least one stage of compression where the air pressure is increased and directed to the combustor16. The compressed air is mixed with fuel and burned providing the hot combustion gas which exits the combustor16toward the high pressure turbine20. At the high pressure turbine20, energy is extracted from the hot combustion gas causing rotation of turbine blades which in turn cause rotation of the shaft24about engine axis26. The shaft24passes toward the front of the engine to continue rotation of the one or more compressor stages14, a turbofan18or inlet fan blades, depending on the turbine design. The turbofan18is connected by the shaft28to LPT21and creates thrust for the turbine engine10. LPT21may also be utilized to extract further energy and power additional compressor stages.

FIG. 2is a schematic illustration of a portion of core engine13illustrating an exemplary flange joint assembly100and an alternative flange joint assembly300. More specifically,FIG. 2illustrates the interface between compressor14, combustor16, high pressure turbine20, and low pressure turbine21. In the exemplary embodiment, combustor16includes a combustor case30and diffuser31that combine to partially define a plenum32for housing a fuel injector34and combustion chamber36therein. Combustor case30includes a forward flange38coupled to a casing15of compressor14, an intermediate flange40coupled to another combustor component, and an aft flange42coupled to high pressure turbine20and low pressure turbine21. In the exemplary embodiment, core engine13includes flange joint assembly100at aft flange42of combustor casing30. Alternatively, flange joint assembly300is located forward flange38and include forward flange38, diffuser31, and compressor casing15. Generally, as described in further detail below, flange joint assemblies100and300are positioned at any location having a joint formed between two components coupled together at respective flanges. In the exemplary embodiment, flange joint assemblies100and300apply a compressive force that generates a radial compression pre-stress on aft flange42or forward flange38to facilitate increasing the service lifetime of aft flange42or forward flange38and combustor casing30. Alternatively, flange joint assemblies100and300increase the service lifetime of any component, and is not limited to use with flanges38and/or42of combustor casing30.

FIG. 3is an enlarged perspective view of flange joint assembly100andFIG. 4is an enlarged side view of flange joint assembly100shown inFIG. 2. In the exemplary embodiment, flange joint assembly100includes a LPT case44having a first flange46, combustor case30having aft or second flange42, a HPT case50having a third flange52, a support shroud54having a fourth flange56, and a compression ring102. HPT case50and support shroud are positioned radially inward of combustor case30and LPT case44. In the exemplary embodiment, flanges46,42,52, and56and ring102are coupled together with a plurality of circumferentially-spaced fasteners104to form a joint106. More specifically, each of flanges46,42,52, and56include an aligned opening through which fastener106is inserted to coupled flanges46,42,52, and56together. First flange46is positioned most aft and second flange42positioned most forward such that third and fourth flanges52and56are coupled therebetween.

In the exemplary embodiment, second flange42includes a radial portion108and an axial lip portion110extending from a distal end of radial portion108. Radial portion108is substantially parallel with flanges46,52, and56, while lip portion110extends in an axial direction to at least partially overlap each of flanges46,52, and56. Lip portion110facilitates concentrically aligning flanges46,52, and56to control gaps between casings30,44,50, and54and rotating blades (not shown) positioned radially inward thereof. However, as described above, joint106is subject to high thermal gradients because of the temperature differences between the radially inner and outer portions of flanges46,42,52, and56. Such thermal gradients induce undesired tension stresses on joint106, and more specifically, on flanges46,42,52, and56where fasteners104are located.

Accordingly, in the exemplary embodiment, flange joint assembly100includes compression ring102coupled to a radially outer surface112of lip portion110. As described in further detail below, compression ring102applies a radial compressive force, represented by arrow114, on radially outer surface112that introduces a compression pre-stress onto joint106. Such a compression pre-stress decreases the operational tension stresses in flanges46,42,52, and56caused by the thermal gradients therein from the differing temperatures of the inner and outer portions of each flange46,42,52, and56and also facilitates increasing the service lifetime of flanges46,42,52, and56and casings30,44,50, and54overall. Alternatively, compression ring102increases the service lifetime of any component within engine10about which it is coupled and is not limited to use with aft flange42of combustor casing30.

In the exemplary embodiment, compression ring102is of a unitary or one piece circumferential structure and may have various cross-sectional shapes. For example, according to the illustrated embodiment, the cross-section of compression ring102is generally rectangular and may have curved or sharp corners. Alternatively, compression ring102includes any cross-sectional shape that facilitates operation of flange joint assembly as described herein.

In the exemplary embodiment, compression ring is formed from a first material having a predetermined coefficient of thermal expansion (CTE). For example, compression ring102is manufactured from stainless steel, a nickel-based super alloy, or ceramic matrix composite material. Alternatively, compression ring102comprises any high-strength material that resists high temperatures and severe mechanical stress while exhibiting high surface stability. Flange42, and therefore lip portion110, is formed from a different material having a predetermined CTE that is greater than the CTE of compression ring102. During operation, lip portion110reaches its CTE temperature before compression ring102and attempts to expand into compression ring102. However, compression ring102limits radial thermal expansion of lip portion110and facilitates applying compressive force114on radially outer surface114to introduce a pre-stress and reduce tension stresses in flanges46,42,52, and56caused by thermal gradients. Alternatively, lip portion110and compression ring102are formed from the same material and are coupled together by an interference fit that applies force114to lip portion110, as described in further detail below.

Furthermore, in the exemplary embodiment, compression ring102is coupled to lip portion110via an interference fit to facilitate applying compressive force114on radially out surface112. More specifically, compression ring102includes a radially inner surface116that defines a first inner diameter when compression ring102is at a non-operational temperature and a second inner diameter when compression ring102is at an operational temperature. Further, radially outer surface112of lip portion110defines a radially outer diameter that is between the first and second diameters of compression ring. The interference fit between lip portion110and compression ring102occurs due the different CTEs. More specifically, compression ring102may be heated to expand its diameter to the second, larger diameter and positioned on lip portion110. As compression ring102cools, the diameter of compression ring decreases towards the first diameter, which is smaller than the radially outer diameter of lip portion110. According, as compression ring102cools, compressive force114is applied to radially outer surface112by radially inner surface116. In the exemplary embodiment, the interference fit, that is, the difference between the first diameter of compression ring102and the radially outer diameter of lip portion110, is approximately within a range of 0.001 inch (in.) to 0.015 in. More specifically, the difference between the first diameter of compression ring102and the radially outer diameter of lip portion110is approximately within a range of 0.005 in. to 0.008 in. Alternatively, the interference fit is any distance that facilitates operation of flange joint assembly100as described herein.

As shown inFIG. 4, flange joint assembly100also includes a plurality of brackets118coupled to first flange46and/or to second flange42. Brackets118are coupled to flanges42and46to prevent axial movement of compression ring102during operation. In one embodiment, brackets118are separate components attached to either or both of flanges42and46.

FIG. 5is an enlarged side view of an alternative flange joint assembly200including an alternative compression ring202. Like components in flange joint assemblies100and200are labeled with identical reference numbers inFIGS. 4 and 5. In one embodiment, compression ring202includes a plurality of cooling channels204defined therethrough to facilitate cooling compression ring202. AlthoughFIG. 5illustrates cooling channels204as being radially oriented, cooling channels204may also be axially oriented. Cooling channels204are exposed to a cooling airflow (not shown) that facilitate reducing the temperature of compression ring202. When the temperature of compression ring202decreases, the radially inner diameter of compression ring202decreases proportionally such that compression ring202exert additional force114on lip portion110. That is, cooling channels204facilitate increasing the amount of compressive force114on lip portion110by reducing the temperature and diameter of compression ring202.

Additionally, compression ring202includes a plurality of fins205extending from a radially outer surface of ring202. Fins205increase the surface area of the outer portion of ring202to facilitate cooling compression ring202. In one embodiment, ring202includes both cooling channels204and fins205. In another embodiment, ring202includes only one of cooling channels204and fins205.

In flange joint assembly200, lip portion110includes a groove206defined in radially outer surface112. Compression ring202includes a complementary-shaped projection208that is sized for insertion into groove206in lip portion. Groove206and projection208serve to orient compression ring202and to aid in assembly and in preventing axial movement of compression ring202. Groove206and projection208may be used in combination with or in place of plurality of brackets118.

FIG. 6is an enlarged side view of alternative flange joint assembly300shown inFIG. 2. Flange joint assembly300includes compressor case15having a first flange17, combustor case30having forward or second flange38, diffuser31having a third flange35, and a compression ring302. In one embodiment, flanges17,35, and38and ring302are coupled together with a plurality of circumferentially-spaced fasteners304to form a joint306. More specifically, each of flanges17,35, and38include an aligned opening308through which fastener304is inserted to couple flanges17,35, and38together. First flange17is positioned most forward and second flange38positioned most aft such that third flange35is coupled therebetween.

As shown inFIG. 6, diffuser31includes a first lip portion310coupled to an inner surface314of compressor case15and a second lip portion312coupled to an inner surface316of combustor casing30. Lip portions310and312facilitate concentrically aligning flanges17,35, and38to control gaps between casings15,31, and30and rotating blades (not shown) positioned radially inward thereof. However, as described above, joint306is subject to high thermal gradients because of the temperature differences between the radially inner and outer portions of flanges17,35, and38. Such thermal gradients induce undesired tension stresses on joint306, and more specifically, on flanges17,35, and38where fasteners304are located.

Accordingly, in the exemplary embodiment, flange joint assembly300includes compression ring302coupled to a radially outer surface318of second flange38. As described in further detail herein, compression ring302applies a radial compressive force, represented by arrow320, on radially outer surface318that decreases the operational tension stresses in flange38caused by the thermal gradients therein from the differing temperatures of the inner and outer portions of flange38and also facilitates increasing the service lifetime of flange38and casing30overall. Alternatively, compression ring302increases the service lifetime of any component within engine10about which it is coupled and is not limited to use with forward flange38of combustor casing30. Optionally, flange joint assembly300also includes a second compression ring322coupled about a radially outer surface324of first flange17. Compression rings302and322are substantially similar in function. In one embodiment, flange joint assembly300includes a single compression ring302that extends axially over each flange38,35, and17or multiple compression rings302and322that are coupled about any of flanges38,35, and17. Compression rings302and322are formed from the same materials and in the same manner as compression ring102and flange joint assembly300is assembled using substantially similar methods as flange assembly100, so such materials and methods are not repeated herein with respect to flange joint assembly300for clarity.

FIG. 7is a schematic diagram of a method400of assembling the gas turbine engine shown inFIG. 1. Method400includes forming402_compression ring102. Forming402compression ring102includes forming compression ring from a material such as, but not limited to, stainless steel, nickel-based super alloy, and CMC such that compression ring102has a CTE lower than the CTE of the material from which second flange42and lip portion110are formed. In one embodiment, forming402compression ring102includes fabricating compression ring as a solid, unitary or one-piece, continuous or seamless member forged or machined in a closed loop shape from a solid material ingot. In another embodiment, forming402compression ring102includes bonding together, such as by welding, opposing ends of a strip of material to form a closed loop shape. Alternatively, compression ring102is formed by any method, such as but not limited to sheet metal stamping and forming, that facilitates operation of method300as described herein. Furthermore, forming402compression ring202includes forming402at least one of cooling channels204therethrough and/or forming304protrusion208extending from radially inner surface116of compression ring202such that protrusion208is configured for insertion into groove206defined in radially outer surface112of lip portion110.

In the exemplary embodiment, method400also includes coupling404compression ring102to radially outer surface112of lip portion110such that compression ring102applies compressive force114to radially outer surface112. Coupling404includes coupling404compression ring102to lip portion110via an interference fit. In one embodiment, coupling404includes heating compression ring102such that the first inner diameter of compression ring102, which is smaller than an outer diameter of lip portion110, increases to a second inner diameter that is larger than the outer diameter of lip portion110. Coupling404further includes positioning compression ring102about lip portion110and cooling compression ring102to cause compression ring102to decrease in size from the second inner diameter to an operational diameter substantially similar to the outer diameter of lip portion110. As compression ring102cools, it shrinks in diameter and seats itself circumferentially onto lip portion110. At ambient temperature, due to the smaller diameter of inner surface116of compression ring102compared to the outer diameter of outer surface112of lip portion110, an interference fit is formed. The interference fit results in radial compressive circumferential force114being applied to lip portion110by compression ring102.

In another embodiment, coupling404includes cooling combustor case30with liquid nitrogen or other means, to a predetermined temperature such that a first outer diameter of lip portion110, which is larger than an inner diameter of compression ring102, decreases to a second outer diameter that is smaller than the inner diameter of compression ring102. Coupling404further includes positioning compression ring102about lip portion110and heating combustor case30to cause lip portion110to increase in size from the second outer diameter to an operational diameter substantially similar to the inner diameter of compression ring110. As combustor case30expands, compression ring110limits the amount of combustor case30expansion such that compression ring102applies compressive force114to radially outer surface112of lip portion110. Furthermore, method400includes any combination of heating and cooling compression ring102and combustor case30that enables operation of flange joint assembly100as described herein. Additionally, method400includes coupling406the first flange to the second flange42to form flange joint assembly100

In another embodiment, as described above, the interference fit may be introduced through using force to press fit compression ring102onto lip portion110or wrap fit compression ring102around lip portion110before bonding the compression ring102ends without applying heating or cooling to change size.

The exemplary assemblies and methods described herein overcome at least some disadvantages of known systems and methods for reducing tension stress in a flange joint on a gas turbine engine. Moreover, the assemblies and methods described herein include a first structure having a first flange and a second structure having a second flange coupled to the first flange to form a joint therebetween. The second flange includes a lip portion that at least partially overlaps the first flange. The flange joint assembly also includes a compression ring coupled to a radially outer surface of the lip portion and configured to apply a compressive force to the lip portion to introduce an amount of pre-stress into the joint. Such a compression pre-stress decreases the operational tension stresses in the flanges caused by the thermal gradients therein from the differing temperatures of the inner and outer portions of each flange and also facilitates increasing the service lifetime of the flanges and the casings overall.

A technical effect of the above described flange joint assembly is that introducing compression pre-stress allows for a decrease weight of the engine when compared to a flange lip portion thickness increase required to decreases operation stresses to a similar level. The comparative reduction in weight for the same benefit results in a more fuel efficient engine having reduced operational costs. Furthermore, the compression pre-stress increases the service lifetime of the components and, therefore, reduces the costs of engine maintenance and ownership.

Exemplary embodiments of flange joint assemblies are described above in detail. The flange joint assemblies, and methods of assembling such assemblies and devices are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the assemblies may also be used in combination with other systems having flange joints, and are not limited to practice with only the turbine engines as described herein.