Gas turbine engine variable vane assembly

A method facilitates assembling a variable vane assembly for a gas turbine engine including a casing and an inner shroud. The method comprises providing at least one variable vane including a radially inner spindle that includes a groove defined therein that has at least one machined face, and coupling the variable vane radially between the casing and the inner shroud such that at least a portion of the radially inner spindle is inserted at least partially through an opening extending radially through the inner shroud. The method also comprises securing the variable vane to the inner shroud by engaging the spindle machined face with a retainer coupled to the inner shroud.

BACKGROUND OF THE INVENTION

This invention relates generally to gas turbine engines, and more specifically to variable stator vane assemblies used with gas turbine engines.

At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine, a combustor which burns a mixture of fuel and air, and low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. At least some known rotor assemblies, such as a high pressure compressors', include a plurality of rows of circumferentially spaced rotor blades, wherein adjacent rows of rotor blades are separated by rows of variable stator vane (VSV) assemblies. More specifically, a plurality of variable stator vane assemblies are secured to casing extending around the rotor assembly and wherein each row of VSV assemblies includes a plurality of circumferentially spaced variable vanes. The orientation of each row of vanes relative to the rotor blades is variable to control airflow through the rotor assembly.

At least one known variable stator vane assembly includes a trunnion bushing that is partially positioned around a portion of a variable vane so that the variable vane extends through the trunnion bushing. Each variable vane is coupled radially between the casing and the inner shroud such that the trunnion bushing extends between the casing and a radially outer spindle extending from the vane, and such that an inner bushing extends between the inner shroud and a radially inner spindle extending from the vane. More specifically, and with respect to the radially inner side of the variable vane, the inner shroud is retained to the VSV's by a plurality of cylindrical pins extending through a respective hole formed in the inner shroud and into a matching cylindrical groove formed along the radial inner spindle and the inner bushing. Accordingly, only line-to-line contact is established between each pin and each vane, and as such, to prevent the inner shroud from rotating with respect to the variable vanes coupled thereto, two pins must be used per shroud.

Over time, because only line-to-line sealing is defined between each pin and each variable vane, wear between the pins and variable vanes may cause possible gas leakage paths to develop within the VSV assembly. Such leakage may result in failure of the bushing due to oxidation and erosion caused by high velocity high temperature air. Furthermore, once the bushing fails, an increase in leakage past the variable vane occurs, which results in a corresponding rotor performance loss. In addition, the loss of the bushing allows contact between the vane and the casing and/or inner shroud which may cause wear and increase the engine overhaul costs.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a method for assembling a variable vane assembly for a gas turbine engine including a casing and an inner shroud is provided. The method comprises providing at least one variable vane including a radially inner spindle that includes a groove defined therein that has at least one machined face, and coupling the variable vane radially between the casing and the inner shroud such that at least a portion of the radially inner spindle is inserted at least partially through an opening extending radially through the inner shroud. The method also comprises securing the variable vane to the inner shroud by engaging the spindle machined face with a retainer coupled to the inner shroud.

In another aspect, a variable vane assembly for a gas turbine engine including a casing is provided. The variable vane assembly includes a variable vane and a retainer. The variable vane includes a radially inner spindle and a radially outer spindle. The radially inner and outer spindles are configured to rotatably couple the vane within the gas turbine engine. At least one of the radially inner and radially outer spindles includes at least one groove defined therein that includes at least one machined face. The retainer engages the groove at least one machined face to securely couple the variable vane within the gas turbine engine. The retainer is configured to facilitate reducing wear of the variable vane.

In a further aspect, a gas turbine engine is provided. The engine includes a rotor comprising a rotor shaft and a plurality of rows of rotor blades, a casing surrounding the rotor blades, and a variable vane assembly. The variable vane assembly includes at least one row of circumferentially spaced variable vanes and a retainer assembly. The at least one row of variable vanes is rotatably coupled to the casing and extends between an adjacent pair of the plurality of rows of rotor blades. Each of the variable vanes includes a radially inner spindle configured to rotatably couple the vane within the gas turbine engine. Each of the radially inner spindles includes at least one groove defined therein and having at least one machined face, the retainer assembly includes at least one retainer for engaging each spindle groove at least one machined face to securely couple each variable vane within the gas turbine engine. Each retainer is configured to facilitate reducing wear of each of the variable vanes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration of a gas turbine engine10including a low pressure compressor12, a high pressure compressor14, and a combustor16. Engine10also includes a high pressure turbine18and a low pressure turbine20. Compressor12and turbine20are coupled by a first shaft24, and compressor14and turbine18are coupled by a second shaft26. In one embodiment, the gas turbine engine is a CF6 available from General Electric Company, Cincinnati, Ohio.

In operation, air flows through low pressure compressor12and compressed air is supplied from low pressure compressor12to high pressure compressor14. The highly compressed air is delivered to combustor16. Airflow from combustor16drives turbines18and20before exiting gas turbine engine10.

FIG. 2is partial enlarged schematic view of a gas turbine engine rotor assembly30, such as compressor14.FIG. 3is an enlarged exploded view of a variable stator vane assembly44that may be coupled within rotor assembly30.FIG. 4is a cross-sectional view of a portion of variable stator vane assembly44and taken along line4—4. Rotor assembly14includes a plurality of stages, and each stage includes a row of rotor blades40and a row of variable stator vane (VSV) assemblies44. In the exemplary embodiment, rotor blades40are supported by rotor disks46and are coupled to rotor shaft26. Rotor shaft26is surrounded by a casing50that extends circumferentially around compressor14and supports variable stator vane assemblies44.

Each variable stator vane assembly44is a low-boss vane assembly that includes a variable vane52that includes a radially outer vane stem or spindle54that extends substantially perpendicularly from a vane platform56. More specifically, vane platform56extends between variable vane52and spindle54. Each spindle54extends through a respective opening58defined in casing50to enable variable vane52to be coupled to casing50. Casing50includes a plurality of openings58. A lever arm60extends from each variable vane52and is utilized to selectively rotate variable vanes52for changing an orientation of vanes52relative to the flowpath through compressor14to facilitate increased control of airflow through compressor14.

Each variable stator vane52also includes a radially inner vane stem or spindle70that extends substantially perpendicularly from a radially inward vane platform72. More specifically, vane platform72extends between variable vane52and spindle70, and has an outer diameter D1that is larger than an outer diameter D2of spindle70. As described in more detail below, each spindle70extends through a respective opening94defined in an inner shroud assembly78.

A groove80is formed within spindle70between platform72and a radially inner end84of spindle70. Groove80extends substantially circumferentially around spindle70and includes at least one machined face86that is substantially planar. More specifically, in the exemplary embodiment, groove80is formed with a pair of machined faces86that are opposed and are substantially parallel. Accordingly, groove80divides spindle70into an intermediate portion87that extends between groove80and platform72, and a radially inner portion88that extends from groove80to radially inner end84. In the exemplary embodiment, faces86are separated by a distance D3defined by groove80which has a diameter D4that is smaller than spindle outer diameter D2.

In the exemplary embodiment, shroud assembly78is formed from a plurality of arcuate shroud segments90that abut together such that shroud assembly78extends substantially circumferentially within engine10. In an alternative embodiment, shroud assembly78is formed from an annular shroud member. Each shroud segment90includes a plurality of circumferentially spaced stem openings94that extend radially through shroud segment90between a radially outer surface96of shroud segment90and a radially inner surface98of shroud segment90. Each shroud segment90also includes a plurality of circumferentially spaced retainer openings100that extend generally axially at least partially through shroud segment90from a downstream upstream side102of shroud segment90towards an upstream side104of shroud segment90.

In the exemplary embodiment, each shroud segment stem opening94includes a recessed portion110, a base portion112, and a body portion114extending therebetween. Recessed portion110is sized to receive spindle70therethrough such that when platform72is received therein, a radial outer surface116of platform72is substantially flush with shroud radial outer surface96when vane52is secured to inner shroud assembly78. Accordingly, recessed portion110has a cross-sectional profile that is substantially similar to that of platform72. In the exemplary embodiment, recessed portion110is substantially circular.

Opening body portion114extends from recessed portion110and is sized to receive spindle70therethrough. More specifically, when variable vane52is secured to inner shroud assembly78, at least a portion of an inner bushing120, described in more detail below, circumscribes spindle portion70and more specifically, spindle portion87. Accordingly, stem opening body portion114is sized to receive spindle70and a body portion122of inner bushing120therein. Moreover, stem opening body portion114has a cross-sectional profile that is substantially similar to that defined by an external surface124of inner bushing body portion122. In the exemplary embodiment, stem opening body portion114has a substantially circular cross-sectional profile.

Opening base portion112extends from body portion114and is sized to receive at least a portion of spindle70therein. More specifically, when variable vane52is secured to inner shroud assembly78at least a portion of inner bushing120circumscribes spindle portion88. Accordingly, stem opening base portion112is sized to receive spindle70and a base portion130of inner bushing120therein. Moreover, stem opening base portion112has a cross-sectional profile that is substantially similar to that defined by that of inner bushing base portion130. In the exemplary embodiment, stem opening base portion112has a substantially rectangular cross-sectional profile, and as such, base portion112facilitates orienting inner bushing120with respect to shroud assembly78and variable vane assembly44.

In the exemplary embodiment, inner bushing120is substantially symmetrical about a centerline axis of symmetry138, and bushing120is fabricated from a wear-resistant material that has relatively low wear and frictional properties. In one embodiment, bushing120is fabricated from a polyimide material such as, but not limited to, Vespel. In another embodiment, bushing120is fabricated from a metallic material. Bushing body portion122extends radially outwardly from bushing base portion130and includes a pair of substantially parallel slots140extending chordwise through body portion122and separated by a distance141. Distance141is approximately equal to the diameter D4defined by groove80. More specifically, in the exemplary embodiment, body portion122has a toroidal cross-section and includes an inner surface142and a substantially parallel outer surface144. Inner surface142defines a cavity146therein and slots140extend across body portion122and through cavity146. In the exemplary embodiment, each slot142is identical and is defined by a substantially rectangular cross-sectional profile within body portion surfaces142and144.

Bushing base portion130extends from bushing body portion122and includes an inner surface150and an outer surface152. In the exemplary embodiment, inner surface150is substantially circular and has a diameter (not shown) that is slightly larger than spindle radially outer portion diameter D2. Moreover, in the exemplary embodiment, outer surface152is substantially rectangular and defines an outer perimeter that is slightly smaller than that defined by stem opening base portion112. Accordingly, stem opening base portion114facilitates orienting bushing base portion130, and inner bushing120with respect to shroud assembly78and vane assembly44.

Shroud retainer openings100extend generally axially into shroud segment90from shroud segment downstream side104towards shroud segment upstream side102. In the exemplary embodiment, openings100are defined by substantially rectangular cross-sectional profiles that are sized approximately equal to the cross-sectional profiles defined by bushing slots140. Accordingly, shroud retainer openings100are spaced a distance160that is approximately equal to slot distance141. When variable vane52is fully coupled to each shroud segment90, openings100and slots140are substantially concentrically aligned with respect to each other.

Shroud retainer openings100extend inwardly from a recessed portion162of shroud segment90. Shroud segment recessed portion162is sized to receive a portion of a retainer180, described in more detail below, therein, such that when retainer180is coupled to shroud segment90, an outer surface182of retainer180is substantially flush with an outer surface184of shroud downstream side104.

Retainer180includes a pair of retaining arms188that are substantially parallel and that extend substantially perpendicularly outward from a retainer base190. In the exemplary embodiment, each arm188is substantially rectangular shaped and includes substantially planar surfaces194that are configured to engage spindle machined faces86.

During assembly of vane assembly44, initially variable vane radially inner spindle70is inserted through a respective shroud segment stem opening94from a radially outer side200of shroud segment90towards a radially inner side202of shroud segment90. When seated within opening94, vane platform72is received within opening recessed portion110such that platform radial outer surface116is substantially flush with shroud radial outer surface96. Moreover, when fully seated within opening94, spindle groove80is concentrically aligned with respect to shroud-retainer openings100.

Inner bushing120is then inserted from shroud segment radially inner side192into the same segment opening94such that bushing120extends around vane spindle70and between spindle70and shroud segment90. More specifically, when bushing120is fully inserted within opening94, bushing body portion122circumscribes spindle intermediate portion87, and bushing base portion130circumscribes spindle outer portion88. Moreover, when fully seated within opening94, bushing slots140are concentrically aligned with respect to shroud retainer openings100.

Retainer180is then slidably coupled within shroud segment retainer openings100to secure bushing120and shroud segment90to vane52. More specifically, when fully seated within openings100, retainer arms188each extend through bushing slots140and engage groove machined faces86on both sides of spindle70. Accordingly, contact is created between a pair of substantially planar surfaces along each side of vane spindle70which facilitates reducing rotation of shroud segment90with respect to vane52. As such, vane52is essentially captured within retainer arms188such that lateral motion of vane52is facilitated to be reduced during engine operation. Moreover, the forked retainer design results in a radially shorter shroud that has a smaller area for pressure loads to act on, and therefore facilitates reducing a bending moment induced to outer spindle54. As such, wear between retainer180and vane52is facilitated to be reduced, thus extending a useful life of vane assembly44.

During operation, retainer180facilitates securing bushing120in position to reduce air leakage between vane spindle70and shroud assembly78, and such that variable vane52and shroud segment90are separated with a low friction surface. Radial clamping between retainer180and spindle machined faces86facilitates reducing relative rotation of inner shroud segments90with respect to variable vanes52. As a result, engine overhaul costs will be facilitated to be reduced.

The above-described variable vane assemblies are cost-effective and highly reliable. The VSV assembly includes a variable vane that includes a spindle having substantially planar machined faces defined thereon. The VSV assembly also includes a retainer that couples through the inner shroud segments in such a manner that retaining contact is created along the pair of machined faces and along opposite sides of the spindle, rather than being created only with line-to-line contact. Accordingly, wear generated between the retainer and the vane is reduced. As a result, the retainer design facilitates extending a useful life of the VSV assembly in a cost-effective and reliable manner.

Exemplary embodiments of VSV assemblies are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. Each retainer component can also be used in combination with other VSV components and with other configurations of VSV assemblies.