Abstract:
A vane assembly for a gas turbine engine including a shroud with openings defined therein about a circumference thereof and vanes extending radially from the shroud with a vane tip in each opening. Isolating means are disposed in each opening to isolate the vane tip from the shroud ring. Each vane tip is engaged with the shroud by retaining means for restricting movement of the vane tip in an axial direction relative to said shroud.

Description:
TECHNICAL FIELD  
       [0001]     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  
       [0002]     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.  
         [0003]     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&#39;s performance.  
         [0004]     Accordingly, there is a need to provide an improved vane assembly.  
       SUMMARY OF THE INVENTION  
       [0005]     It is therefore an object of this invention to provide an improved vane assembly.  
         [0006]     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.  
         [0007]     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.  
         [0008]     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.  
         [0009]     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.  
         [0010]     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  
       [0011]     Reference is now made to the accompanying figures depicting aspects of the present invention, in which:  
         [0012]      FIG. 1  is a side view of a gas turbine engine, in partial cross-section;  
         [0013]      FIG. 2  is a side cross-sectional view of a vane assembly according to an embodiment of the present invention;  
         [0014]      FIG. 3  is a perspective side, view of a vane which is part of the assembly shown in  FIG. 2 ;  
         [0015]      FIG. 4  is a perspective underside view of a grommet which is part of the assembly shown in  FIG. 2 ;  
         [0016]      FIG. 5  is a perspective side view of a portion of an inner shroud which is part of the assembly shown in  FIG. 2 ;  
         [0017]      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  
         [0018]      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  
       [0019]      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.  
         [0020]     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 .  
         [0021]     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.  
         [0022]     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.  
         [0023]     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 .  
         [0024]     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 .  
         [0025]     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.  
         [0026]     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 .  
         [0027]     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.  
         [0028]     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.  
         [0029]     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.