# Patent

## Title
Foreign object damage resistant vane assembly

## Abstract

A vane including a root, a tip and an airfoil portion extending between the root and the tip, the vane also including a button portion interconnecting the airfoil portion and the root. The button portion protrudes beyond a profile of the airfoil a distance less than the root. The button portion includes leading and trailing ends free of sharp edges. The leading and trailing ends respectively protrude beyond leading and trailing edges of the airfoil portion.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation of U.S. patent application Ser. No. 11/223,129, filed on Sep. 12, 2005, the specification of which is incorporated herein by reference.


TECHNICAL FIELD
The invention relates generally to gas turbine engines, and particularly to improved vanes provided therein downstream of the engine fan or low pressure compressor.
BACKGROUND OF THE ART
Gas turbine engine vane assemblies are usually provided downstream of the engine fan and/or of a low pressure compressor to reduce the swirl in the air flow exiting the compressor. Such vane assemblies must be resistant to foreign object damage while having a minimum weight.
It is known to provide an inner shroud with slots receiving the vane tips in order to retain them. In such a configuration, a grommet is inserted in the slot such as to surround the vane tip thereby isolating the vane tip from the shroud. However, during a foreign object damage event a vane which is hit will move rearward as a result of the impact, and the vane edge, which tends to be sharp, can cause cutting of the grommet and damage to other surrounding components. Also, the airflow surrounding the grommets often produces a force which tends to lift and displace the grommets, thus requiring the use of adhesive or other similar measures to ensure that they stay in place. Such a use of adhesive complicates the installation and replacement of vanes. Moreover, the protruding grommets can disturb the airflow, which can alter the engine's performance.
Accordingly, there is a need to provide an improved vane assembly.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved vane assembly.
In one aspect, the present invention provides a vane assembly comprising: a shroud including an annular shroud ring and a shroud web radially extending from one side thereof, the shroud ring including a plurality of openings defined therethrough about a circumference thereof in alignment with said shroud web such that the shroud web extends across the openings; a grommet located in each of the plurality of openings having a cutout therein; and a plurality of vanes supported by and extending radially from the shroud ring opposite of the shroud web, each one of the plurality of vanes having a vane extremity located in the cutout one of the grommets, the vane extremity having a slot defined therein which receives a portion of the shroud for mating therewith.
In another aspect, the present invention provides a vane assembly for a gas turbine engine, the vane assembly comprising: a vane shroud having a shroud ring portion including a plurality of openings defined therethrough about a circumference thereof, a web portion extending radially from the shroud ring portion across the plurality of openings; a plurality of vanes extending radially from a side of the shroud ring portion opposite the web portion, each of said vanes having a vane tip received within one of the openings; means for isolating said vane tip from said shroud ring portion being disposed in each of the openings; and each of said vane tips being engaged with said vane shroud by retaining means for restricting movement of the vane tip in an axial direction relative to said vane shroud.
In another aspect, the present invention provides a method for attaching a vane tip in a vane assembly of a gas turbine engine, the method comprising the steps of: forming a shroud ring having a plurality of openings distributed about a circumference thereof and a web extending radially from the shroud ring across the plurality of openings; installing a grommet in each of the plurality of openings, such that a cutout extending therethrough is aligned with the openings; providing a plurality of vanes, each having a radially extending slot defined in a vane tip thereof; and inserting each vane tip into said cutouts of the grommets within said opening of the shroud ring so that the web is received within each radially extending slot.
There is also provided, in accordance with another aspect of the present invention, a vane for a vane assembly of a gas turbine engine, the vane assembly including a plurality of said vanes mounted to a supporting shroud via intermediate grommets, each said vane comprising an airfoil extending radially from a root portion to an opposed tip and defining a leading edge and a trailing edge corresponding to a flow direction of air passing through the vane assembly, the root portion being adapted to be mounted to the supporting shroud of the vane assembly, said tip having a slot defined therein between said leading and trailing edges of said airfoil, said slot being configured to receive a portion of the supporting shroud therein for mating therewith, thereby restricting movement of said vane tip relative to the supporting shroud in at least said flow direction.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.



DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
FIG. 1 is a side view of a gas turbine engine, in partial cross-section;
FIG. 2 is a side cross-sectional view of a vane assembly according to an embodiment of the present invention;
FIG. 3 is a perspective side view of a vane which is part of the assembly shown in FIG. 2;
FIG. 4 is a perspective underside view of a grommet which is part of the assembly shown in FIG. 2;
FIG. 5 is a perspective side view of a portion of an inner shroud which is part of the assembly shown in FIG. 2;
FIG. 6 is a perspective side view of a portion of the assembly shown in FIG. 2, showing a mating of the vane, grommet and inner shroud; and
FIG. 7 is a perspective side view of an inner shroud and grommet assembly according to the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a multistage compressor 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine 18 for extracting energy from the combustion gases.
Referring to the FIG. 2, the vane assembly 20 is located downstream of the fan 12. The vane assembly 20 includes an inner shroud 26 and a plurality of vanes 22 extending radially between the inner shroud 26 and an engine casing or an outer shroud 21. The inner shroud 26 includes a shroud ring 34 and a shroud web 36. Each of the vanes 22 has an airfoil portion 23 extending between the vane tip 24 and the vane root 25. The vane root 25 is attached to the outer shroud 21 and the vane tip 24 is retained in a grommet 28 inserted into an opening 54 (see FIG. 5) of the shroud ring 34. Throughout this description, the axial, radial and circumferential directions are defined respectively with respect to the central axis, radius and circumference of the shroud ring 34.
As seen in FIGS. 2 and 3, the airfoil portion 23 of each vane 22 defines a leading edge 27 and a trailing edge 29, such that an airflow passing through the vane assembly 20 will flow from the leading edge 27 to the trailing edge 29. The vane tip 24 includes a slot 38 defined therein and located between the leading and trailing edges 27, 29. The slot 38 has a generally rectangular shape and extends radially from the vane tip 24. At the opposite extremity of the vane 22 proximate the vane root 25 is disposed a button portion 31, which corresponds generally to the shape of the airfoil portion 23 however is slightly enlarged relative thereto, but nevertheless remains smaller than the adjacent vane root 25. The button portion 31 includes relatively blunt leading and trailing ends. As seen in FIG. 2, the button 31 is received within an outer grommet 33 disposed within the outer shroud 21 proximate the root end of the vane 22. The blunt vane button 31 accordingly helps to prevent the relatively sharp leading and trailing edges 27 and 29 of the vane airfoil 23 from tearing the outer grommet 33 during the assembly and/or disassembly process of the vane assembly or in the event of a bird strike.
Referring to FIG. 4, each grommet 28 includes a base portion 50 connected to a lip 46 by a recessed portion 48. The base portion 50 defines two opposite elongated lateral surfaces 49 extending generally along the axial direction. Two spaced apart tongues 40 extend perpendicularly from the lip 46 along the circumferential direction and define a slit 42 therebetween. A cutout 44 corresponding in shape to the vane tip 24 is defined within the grommet 28, extends through the base and recessed portions 50, 48, and is bordered by the lip 46. The grommet 28 also has a leading edge 30 and a trailing edge 32 connecting the lateral surfaces 49 and corresponding to the leading and trailing edges 27, 29 of the associated vane 22, as can be seen in FIG. 2. The grommets 28 are preferably made of a flexible material, such as rubber or the like, in order to be able to dampen vibrations of the assembly.
Referring to FIGS. 2 and 5, the shroud ring 34 has an inner surface 35 and an outer surface 37 defining a circumference of the shroud 26. The shroud web 36 is circular and extends generally radially from the inner surface 35 of the shroud ring 34 around the entire circumference thereof. The openings 54 are distributed along the circumference of the shroud ring 34. Each opening 54 corresponds in shape to the recessed portion 48 of one of the grommets 28 and is oriented according to a desired orientation of the vane 22 within the airflow. Thus, a grommet 28 is receivable within each opening 54, with the base portion 50 thereof abutting the outer surface 37 and the lip 46 abutting the inner surface 35. Adjacent to each opening 54, a mating slot 56 is defined within the shroud web 36.
Referring to FIGS. 2, 4 and 6, each of the openings 54 of the shroud ring 34 receives the recessed portion 48 of a grommet 28. The shroud web 36, at the mating slot 56, is received within the slit 42 of the grommet 28, with one of the tongues 40 abutting each side of the web 36. The vane tip 24 is inserted into the grommet cutout 44, the tongues 40 and shroud web 36 being received within the vane slot 38. Alternately, it is also possible to provide a deeper grommet slit 42 and vane slot 38 such as to eliminate the need for the mating slot 56.
Referring to FIGS. 4 and 7, the base portion 50 of each grommet 28 is shaped so that upon installation of the grommets 28, the lateral surfaces 49 of each grommet 28 will be in close contact with the lateral surfaces 49 of adjacent grommets 28, such that the base portions 50 together form a continuous gas path surface 52 along the entire circumference and at least an axial portion of the shroud 26. This configuration eliminates the need to use adhesives or similar measures to maintain the grommets in position, since the gas flows over the grommets, “pushing” them radially inward, instead of flowing between them and producing a lifting force thereon. The airflow is also smoother since it is not perturbed by an uneven surface which would be produced with conventional grommets having free spaces therebetween.
Alternatively, it is possible to provide an annulus portion or an entire annulus formed by the combined base portions 50 of the grommets 28, which are integrally connected to each other through the lateral surfaces 49 to form a single unit. In the case of an entire annulus, the grommets 28 would have to be made of a material sufficiently elastic to be able to stretch the annulus for insertion of the grommet lips 46 in into the shroud openings 54.
The vane assembly 20 thus efficiently retains the vane tip in the axial direction, providing additional stability to the vane position which reduces the risk of rearward movement of the vane tip 24 upon impact of a foreign object. This, in turn, reduces the risk of damage to the grommet 28 and adjacent components upon the impact of the foreign object. The vane slot 38 and mating slot 56 are easy to machine, and the grommet 28 with tongues 40 and slit 42 can be manufactured using the same process as other types of grommets.
The vane assembly 20 eliminates the need for adhesives or the like to maintain the grommets in place, which reduces costs and simplifies production and maintenance operations.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. For example, the vane assembly 20 can be used for other types of engine stators as well as in different fields, such as in ventilation systems. The grommets 28 can be used in outer shrouds as well as other types of vanes or rotor blades. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

## Claims

1. A vane comprising a root, a tip and an airfoil portion extending between the root and the tip, the vane including a button portion interconnecting the airfoil portion and the root, the button portion protruding beyond a profile of the airfoil a distance less than the root, the button portion having leading and trailing ends free of sharp edges, the leading and trailing ends respectively protruding beyond leading and trailing edges of the airfoil portion.

2. The vane as defined in claim 1, wherein the button portion has a profile corresponding to that of the airfoil portion.

3. The vane as defined in claim 1, wherein the button portion protrudes from the airfoil portion around an entire perimeter thereof.

4. The vane as defined in claim 3, wherein the root protrudes outwardly from the button portion about an entire perimeter thereof.

5. A vane assembly for a gas turbine engine, the assembly comprising an inner shroud located inwardly of and concentric with an outer shroud such as to define a flowpath therebetween, and a plurality of circumferentially spaced apart vanes extending between the inner and outer shrouds across the flowpath, each vane including a root, a button portion connected to the root, an airfoil portion extending from the button portion opposite of the root, and a tip engaged to the inner shroud, the button portion being free of sharp edges and at least part of the button portion protruding beyond the airfoil portion a distance less than the root, each button portion being received in a grommet engaged in a corresponding one of a series of openings defined through the outer shroud.

6. The vane assembly as defined in claim 5, wherein each grommet includes a portion extending around the opening and located between the outer casing and the root.

7. The vane assembly as defined in claim 5, wherein the button portion has a profile corresponding to that of the airfoil portion.

8. The vane assembly as defined in claim 5, wherein the button portion protrudes from the airfoil portion around an entire perimeter thereof.

9. The vane assembly as defined in claim 8, wherein the root protrudes from the button portion around an entire perimeter thereof.

10. A rotor assembly for a gas turbine engine, the rotor assembly comprising rotating blades, an outer casing surrounding the rotating blades and having a series of circumferentially and regularly spaced apart openings defined therethrough downstream of the blades, an inner shroud located inwardly of and concentric with the outer casing such as to define a flowpath therebetween, and a plurality of circumferentially spaced apart vanes extending between the inner shroud and outer casing across the flowpath, each vane including a tip engaged to the inner shroud, an airfoil portion extending from the tip and across the flowpath, a button portion connected to the airfoil portion opposite of the tip, and a root connected to the button portion opposite of the airfoil portion, each button portion being free of sharp edges and being received in a grommet engaged in a corresponding one the openings defined through the outer casing, at least part of the button portion protruding from the airfoil portion a distance less than the root.

11. The rotor assembly as defined in claim 10, wherein each grommet includes a portion extending around the corresponding one of the openings and located between the outer casing and the root.

12. The rotor assembly as defined in claim 10, wherein the button portion has a profile corresponding to that of the airfoil portion.

13. The rotor assembly as defined in claim 10, wherein the button portion protrudes from the airfoil portion around an entire perimeter thereof.

14. The rotor assembly as defined in claim 13, wherein the root protrudes from the button portion around an entire perimeter thereof.