Turbine blade attachment rails for attachment fillet stress reduction

The present disclosure provides a fir tree coupling for gas turbine engine parts comprising a load beam having a longitudinal axis, a base, a first side, and a second side, a rail extending from the base of the load beam between the first side and the second side, a tooth running parallel to the longitudinal axis disposed on the first side of the load beam. The rail may comprise at least one of, a convex sidewall having a convex curvature, a concave sidewall having a concave curvature, or a vertical sidewall extending perpendicular to the base. The rail may comprise a sidewall comprising a sidewall step wherein the sidewall has a step cut into a portion of the rail. The rail may comprise a tapered sidewall wherein the tapered sidewall extends at an angle to the base.

FIELD

The present disclosure relates to gas turbine engines, and more specifically, to gas turbine blade to disk interface and attachment structures.

BACKGROUND

Low Cycle Fatigue (LCF) is a failure mechanism that may limit the in-service life of turbine airfoils, such as blades. Cracks may be initiated by LCF in turbine airfoils after a number of engine cycles. High stresses may arise due to the geometry of the turbine airfoil. In ‘fir tree’ type couplings between a turbine disk and a turbine blade, these stresses often arise in the attachment fillets adjacent to (radially outboard of) the blade-disk bearing surface.

SUMMARY

In various embodiments, the present disclosure provides a fir tree coupling comprising a load beam having a longitudinal axis, a base, a first side and a second side, a rail extending across the base of the load beam between the first side and the second side, a tooth running parallel to the longitudinal axis and disposed on the first side of the load beam.

In various embodiments, the rail comprises at least one of a convex sidewall having a convex curvature, a concave sidewall having a concave curvature, or a vertical sidewall extending perpendicular to the base. In various embodiments, the rail comprises a sidewall comprising a sidewall step wherein the sidewall has a step cut into a portion of the rail. In various embodiments, a rail comprises a tapered sidewall wherein the tapered sidewall extends at an angle to the base. In various embodiments, the rail is disposed at an angle to the longitudinal axis of the load beam. In various embodiments, the tooth includes a bearing surface. In various embodiments, the load beam comprises a top surface and a cooling passage passing through the load beam from the base to the top surface. In various embodiments, the rail is proximate an opening of the cooling passage. In various embodiments, the load beam comprises at least one of nickel, nickel alloy, titanium, or titanium alloy. In various embodiments, the load beam comprises a monocrystalline material.

In various embodiments, the present disclosure provides a blade assembly for a gas turbine engine comprising a platform having a dorsal surface and a ventral surface, an airfoil extending from the dorsal surface, a fir tree coupling extending from the ventral surface, the fir tree coupling comprising a load beam having a longitudinal axis, a base, a first side, and a second side, a rail extending across the base of the load beam between the first side and the second side, a tooth running parallel to the longitudinal axis and disposed on the first side of the load beam.

In various embodiments, the rail comprises at least one of a convex sidewall having a convex curvature, a concave sidewall having a concave curvature, or a vertical sidewall extending perpendicular to the base. In various embodiments, the rail comprises a sidewall comprising a sidewall step wherein the sidewall has a step cut into a portion of the rail. In various embodiments, the rail comprises a tapered sidewall wherein the tapered sidewall extends at an angle to the base. In various embodiments, the rail is disposed at an angle to the longitudinal axis of the load beam. In various embodiments, the fir tree coupling comprises a first cooling passage cooling passage in fluid communication with a second a cooling passage within at least one of the platform or the airfoil. In various embodiments, the rail is proximate the first cooling passage. In various embodiments, the fir tree coupling comprises at least one of nickel, nickel alloy, titanium, or titanium alloy. In various embodiments, the fir tree coupling comprises a monocrystalline material.

In various embodiments, the present disclosure provides a method of manufacturing a fir tree coupling comprising forming a load beam having a longitudinal axis, a base, a first side, a second side, and a tooth running parallel to the longitudinal axis and disposed on the first side of the load beam. In various embodiments, the method further comprises forming a rail extending across the base of the load beam between the first side and the second side.

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements.

DETAILED DESCRIPTION

All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural.

With reference toFIG. 1, an exemplary gas turbine engine2is provided. Gas turbine engine2is a two-spool turbofan that generally incorporates a fan section4, a compressor section6, a combustor section8and a turbine section10. Vanes51may be disposed throughout the gas turbine engine2. Alternative engines include, for example, an augmentor section among other systems or features. In operation, fan section4drives air along a bypass flow-path B while compressor section6drives air along a core flow-path C for compression and communication into combustor section8then expansion through turbine section10. Although depicted as a turbofan gas turbine engine2herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings is applicable to other types of turbine engines including three-spool architectures. A gas turbine engine may comprise an industrial gas turbine (IGT) or a geared aircraft engine, such as a geared turbofan, or non-geared aircraft engine, such as a turbofan, or may comprise any gas turbine engine as desired.

Gas turbine engine2generally comprises a low speed spool12and a high speed spool14mounted for rotation about an engine central longitudinal axis X-X′ relative to an engine static structure16via several bearing systems18-1,18-2, and18-3. It should be understood that bearing systems is alternatively or additionally provided at locations, including for example, bearing system18-1, bearing system18-2, and bearing system18-3.

Low speed spool12generally comprises an inner shaft20that interconnects a fan22, a low pressure compressor section24, e.g., a first compressor section, and a low pressure turbine section26, e.g., a second turbine section. Inner shaft20is connected to fan22through a geared architecture28that drives the fan22at a lower speed than low speed spool12. Geared architecture28comprises a gear assembly42enclosed within a gear housing44. Gear assembly42couples the inner shaft20to a rotating fan structure. High speed spool14comprises an outer shaft80that interconnects a high pressure compressor section32, e.g., second compressor section, and high pressure turbine section34, e.g., first turbine section. A combustor36is located between high pressure compressor section32and high pressure turbine section34. A mid-turbine frame38of engine static structure16is located generally between high pressure turbine section34and low pressure turbine section26. Mid-turbine frame38supports one or more bearing systems18, such as18-3, in turbine section10. Inner shaft20and outer shaft80are concentric and rotate via bearing systems18about the engine central longitudinal axis X-X′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine.

The core airflow C is compressed by low pressure compressor section24then high pressure compressor section32, mixed and burned with fuel in combustor36, then expanded over high pressure turbine section34and low pressure turbine section26. Mid-turbine frame38includes surface structures40, which are in the core airflow path. Turbines26,34rotationally drive the respective low speed spool12and high speed spool14in response to the expansion.

Gas turbine engine2is, for example, a high-bypass geared aircraft engine. The bypass ratio of gas turbine engine2is optionally greater than about six (6). The bypass ratio of gas turbine engine2is optionally greater than ten (10). Geared architecture28is an epicyclic gear train, such as a star gear system, e.g., sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear, or other gear system. Geared architecture28has a gear reduction ratio of greater than about 2.3 and low pressure turbine section26has a pressure ratio that is greater than about five (5). The bypass ratio of gas turbine engine2is greater than about ten (10:1). The diameter of fan22is significantly larger than that of the low pressure compressor section24, and the low pressure turbine section26has a pressure ratio that is greater than about 5:1. Low pressure turbine section26pressure ratio is measured prior to inlet of low pressure turbine section26as related to the pressure at the outlet of low pressure turbine section26prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of a suitable geared architecture engine and that the present disclosure contemplates other turbine engines including direct drive turbofans.

An engine2may comprise a rotor blade68or a stator vane51. Stator vanes51may be arranged circumferentially about the engine central longitudinal axis X-X′. Stator vanes51may be variable, meaning the angle of attack of the airfoil of the stator vane may be variable relative to the airflow proximate to the stator vanes51. The angle of attack of the variable stator vane51may be variable during operation, or may be fixable for operation, for instance, being variable during maintenance or construction and fixable for operation. In various embodiments, it may be desirable to affix a variable vane51in fixed position (e.g., constant angle of attack).

In various embodiments, a fir tree coupling is disclosed for interfacing an airfoil (e.g., a blade) with a turbine disk of a gas turbine engine. A fir tree coupling, according to various embodiments, may comprise a load beam having a longitudinal axis, a base, a first side, and a second side. The fir tree coupling may comprise a plurality of teeth running parallel or substantially parallel the load beam longitudinal axis and disposed on the first side and the second side of the load beam. In various embodiments, the teeth have bearing surfaces which transmit loads at the blade-disk interface. The blade-disk interface load may be concentrated as a high stress in an attachment fillet disposed between the teeth of the fir tree coupling. The base of the fir tree coupling may comprise rails extending from the base between the first side and the second side which may reduce attachment fillet stress and tend to mitigate LCF.

In various embodiments, a blade assembly may comprise a fir tree coupling, an airfoil, and a platform having a dorsal and a ventral surface. The airfoil extends from the dorsal surface of the platform and the fir tree coupling extends from the ventral surface of the platform. The blade assembly is coupled to a turbine disk by the fir tree coupling which transmits the centrifugal force acting on the airfoil resulting from the airfoil's rotation about the gas turbine engine shaft to the turbine disk through the bearing surfaces of the fir tree coupling teeth. The centrifugal force induces bending in the teeth which tends to concentrate stresses at the lower most attachment fillet between the teeth. The aforesaid stress concentrations may propagate cracking which tends to drive LCF. In various embodiments, rails extending from the base of the fir tree coupling resist tooth bending by compression of the rails, reducing attachment fillet stresses, and thereby tending to mitigating LCF.

With reference now toFIG. 2, in accordance with various embodiments, a blade assembly100comprises an airfoil102, a platform104, and a fir tree coupling200. Airfoil102extends from dorsal surface106of platform104. Fir tree coupling200includes teeth202and base210and extends from ventral surface108of platform104. Xyz axes are shown for convenience, with z extending perpendicular to the xy plane. In that regard, a measurement point displaced in the positive z-axis direction from a given reference point may be considered “above” or on “top” of the given reference point. In contrast, a measurement point displaced in the negative z-axis direction from the given reference point may be considered “below” or on “bottom” of the given reference point. In that regard, the terms “top” and “bottom” may refer to relative positions along the z-axis. For example, airfoil102is on top of platform104and fir tree coupling200is below airfoil102. Rails204extend across the y axis below (with reference to the z-axis) the base210of fir tree coupling200.

With reference now toFIG. 3, a blade-disk attachment region, in accordance with various embodiments, is shown. Blade assembly100is inserted into turbine disk301and coupled by fir tree coupling200. As disk301rotates at high speed, centrifugal force300is generated, which is transmitted into disk301at bearing surfaces203of teeth202, tending to induce bending302, which tends to concentrate stress at attachment fillets304. The compressive force303is resisted by rails204and tends to reduce stress at attachment fillets304.

In various embodiments and with reference now toFIGS. 4A and 4B, a fir tree coupling200is shown to comprise a load beam206having a first side212and a second side214, a base210, and a longitudinal axis207. In various embodiments, the load beam may further comprise a top surface208. In various embodiments, a plurality of teeth202disposed on the first side212and second side214extend laterally (along the y-axis) and run parallel to the longitudinal axis207(along the x-axis). Rails204extend below (along the z-axis) base210and run between the first side212and second side214of the load beam.

In various embodiments, a fir tree coupling may be made of metal, an alloy, nickel, nickel alloy, titanium, or titanium alloy. In various embodiments, a fir tree coupling may be surface treated or may be heat treated by precipitation hardening or age hardening. In various embodiments, a fir tree coupling may be a precipitation-hardening austenite nickel-chromium superalloy such as that sold commercially as Inconel®. In various embodiments, a fir tree coupling may be a single crystal or monocrystalline solid.

In various embodiments and with reference now toFIGS. 2, 4A, 5A, and 5B, cooling passages216in the base of a fir tree coupling, such as base210, may be disposed between rails such as rails204and extend upward (along the z-axis) from the base through the load beam to a top surface such as top surface208of a fir tree coupling. Cooling passages216may extend radially outward through the airfoil. Cooling passages216may have an opening in a base such as base210and may form part of a cooling system for a blade assembly such as blade assembly100and be in fluid communication with a second cooling passage disposed within a platform such as platform104or an airfoil such as airfoil102.

In various embodiments and with reference now toFIG. 5A and 5C, rails such as rails204may be perpendicular to the longitudinal axis of a load beam such as longitudinal axis207. In various embodiments, rails such as rails217and218may be disposed at an angle to the longitudinal axis of a load beam such as longitudinal axis207. In various embodiments, rails such as rails204may be disposed proximate cooling passages such as cooling passages216. In various embodiments, cooling passages may be skewed relative to the longitudinal axis.

In various embodiments and with reference now toFIGS. 6Athru6E, rails such as rails204may comprise at least one of a tapered sidewall600wherein the tapered sidewall extends below the base at an angle, a convex sidewall602wherein the rail extension below the base is bounded by a convex curvature of the convex sidewall, a vertical sidewall604wherein the rail sidewall extends perpendicular below the base, a sidewall comprising a sidewall step608wherein the sidewall has a step609cut into a portion of the rail thickness, or a concave sidewall610wherein the rail sidewall extension below the base is bounded by a concave curvature of the sidewall.

In various embodiments and with reference now toFIG. 7, a method700of manufacturing a fir tree coupling may comprise forming a load beam702having a longitudinal axis, a base, a first side, a second side, a tooth running parallel to the longitudinal axis and disposed on the first side of the load beam, and forming a rail704extending across the base of the load beam between the first side and the second side. Forming may comprise subtractive manufacturing such as casting, forging, milling, grinding, machining, and the like. Forming may also comprise additive manufacturing, such as electron-beam melting, selective laser sintering, electron-beam freeform fabrication, and the like. Forming may also comprises joining such as welding, brazing and/or other suitable methods.