Patent Application
20100166545
This invention relates generally to gas turbine engines and more particularly to stationary aerodynamic members of such engines.
Gas turbine engines include one or more rows of stationary airfoils referred to as stators or vanes, which are as used to turn airflow to a downstream stage of rotating airfoils referred to as blades or buckets. Stators must withstand significant aerodynamic loads, and also provide significant damping to endure potential vibrations.
Particularly in small scale stator assemblies, the airfoils plus their surrounding support members are typically manufactured as an integral machined casting or a machined forging. Stators have also been fabricated by welding or brazing. Neither of these configurations are conducive to ease of individual airfoil replacement or repair.
Other stator configurations (e.g. mechanical assemblies) are known which allow easy disassembly. However, these configurations lack features that enhance the rigidity of the assembly while maintaining significant damping.
These and other shortcomings of the prior art are addressed by the present invention, which provides a stator assembly that is rigid and well-damped in operation which can be readily disassembled to facilitate repair or replacement of individual components.
According to one aspect, a stator assembly for a gas turbine engine includes: (a) an outer shroud having a circumferential array of outer slots; (b) an inner shroud having a circumferential array of inner slots; (c) a plurality of airfoil-shaped vanes extending between the inner and outer shrouds, each vane having inner and outer ends which are received in the inner and outer slots; and (d) an annular, resilient retention ring spring which engages the inner ends of the vanes and urges them in a radially inward direction.
According to another aspect of the invention, a method of assembling a stator assembly for a gas turbine engine includes: (a) providing an outer shroud having a circumferential array of outer slots; (b) providing an inner shroud having a circumferential array of inner slots; (c) inserting a plurality of airfoil-shaped vanes through the inner and outer slots; and (d) engaging the inner ends of the vanes with a resilient retention ring which urges them in a radially inward direction.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
In the illustrated example, the engine is a turbofan engine. However, the principles described herein are equally applicable to turboprop, turbojet, and turbofan engines, as well as turbine engines used for other vehicles or in stationary applications.
As shown in
The outer shroud 38 is a rigid metallic member and has an outer face 48 which is bounded by spaced-apart, radially-outwardly-extending forward and aft flanges 50 and 52. One or both of these flanges 50 and 52 include bolt holes or other features for mechanical attachment to the casing 12. A circumferential array of airfoil-shaped outer slots 54 which are sized to receive the vanes 42 pass through the outer shroud 38. in the particular example shown, the outer shroud 38 includes a forward overhang 56 which serves as a shroud for the first stage 30 of booster blades.
The inner shroud 40 is a rigid member which may be formed from, e.g., metal or plastic, and has an inner face 58 which is bounded by spaced-apart, radially-inwardly-extending forward and aft flanges 60 and 62. Cooperatively, the forward and aft flanges 60 and 62 and the inner face 58 define an annular inner cavity 64. A circumferential array of airfoil-shaped inner slots 66 which are sized to receive the vanes 42 pass through the inner shroud 40.
Each of the vanes 42 is airfoil-shaped and has inner and outer ends 68 and 70, a leading edge 72, and a trailing edge 74. An overhanging platform 76 (see
An axially-elongated outer grommet 84 is disposed between the platform 76 and the outer shroud 38. It has a central, generally airfoil-shaped opening which receives the outer end 70 of the vane 42. The outer grommet 84 is manufactured from a dense, resilient material which will hold the vane 42 and outer shroud 38 in a desired relative position while providing vibration dampening. Nonlimiting examples of suitable materials include fluorocarbon or fluorosilicone elastomers. Optionally, an inner grommet (not shown) of construction similar to the outer grommet 84 may be installed between the inner end 68 of the vane 42 and the inner shroud 40.
The retention ring 44 is a generally annular resilient member which engages the hooks 82 and preloads them in a radially-inward direction. The retention ring 44 may be constructed of spring steel, high strength alloys (e.g. nickel-based alloys such as INCONEL), or a similar material. The retention ring 44 incorporates features to ensure secure connection to the hooks 82. In the illustrated example the retention ring 44 has a “wave” or “corrugated” form and generally describes a flattened sinusoidal shape in a plane perpendicular to the axis A (see
The filler block 46 (see
The stator assembly 32 is assembled as follows, with reference to
In the event disassembly or repair is required, all or part of the filler block 46 is removed, for example by being cut, ground, or chemically dissolved. The retention ring 44 may then be disengaged from one or more of the vanes 42 and any vane 42 that requires service or replacement may be removed. Alternatively the retention ring 44 may be cut to disengage it. Any or all of the filler block 46, the inner shroud 40, the outer grommets 84 and the inner grommets (if used) may be considered expendable for repair purposes. Upon reinstallation the inner shroud 40 and/or grommets would be replaced (if necessary) and the a new filler block 46 (or portions thereof) would be re-formed as described above for initial installation. The re-use of the vanes 42 and the outer ring 38 provides for an economically viable repair.
The stator assembly described above has multiple advantages over prior art designs. It is weight effective because of the use of separate airfoils and fabrication with non-metallic components. Efficient outer flowpath sealing is provided by the retention ring radial preload force. It provides easy and flexible assembly repair or airfoil replacement compared with machined, welded, or brazed configurations. It has rigidity advantages over prior art fabricated small scale stator assemblies. It provided reduced vane static stresses, offering flexibility to employ different vane airfoil material choices without compromising the assembly concept Finally, increased assembly vibration damping is provided through the use of non-metallic grommets and the resilient filler block 46.
The foregoing has described a stator assembly for a gas turbine engine. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.
