Patent Publication Number: US-9840929-B2

Title: Gas turbine engine vane assembly and method of mounting same

Description:
TECHNICAL FIELD 
     The application relates generally to gas turbine engines and, more particularly, to gas turbine engine vane assemblies. 
     BACKGROUND 
     During assembly, gas turbine engine vanes are typically inserted into position in their casing via a corresponding slot in an outer case and then slid radially-inwardly into place, such that the vane extends radially between the inner and outer cases. A wider portion at the end or root of the vane acts as a stop, which abuts against the outer case and holds the vane in the radially-inward direction. The vane may be held in the radially-outward direction using a belt surrounding the outer case and vanes. 
     Especially at the fan outer case, it may be desirable to provide a seal between the root of the vane and the casing slot, to reduce pressure loss. It is therefore known to use a grommet made of a resilient material around the vane root to provide such a seal. The fore and aft edges of the vanes are relatively sharp, and thus vanes having enlarged step or flange portions having a blunter shape have been used for receipt within the grommet. Improvements of these solutions remain sought, to further reduce weight and improve ease of manufacture. 
     SUMMARY 
     There is provided a vane assembly mountable within a slot in an case of a gas turbine engine, the vane assembly comprising: a vane having an elongated airfoil body extending to a tip, and a grommet disposed around the tip, the grommet being of a material more resilient than a material of the airfoil body, the grommet having an outer surface surrounding the tip, a radially-inner surface and a radially-outer surface; and an insert having a closed loop shape with a radially-outer edge and a radially-inner edge, the closed loop shape having an inner surface matingly shaped to receive the outer surface of the grommet, and an outer surface matingly shaped to be snugly received in the slot, wherein one of the radially-outer edge and the radially-inner edge has an outwardly protruding lip shaped to abuttingly and sealingly engage a corresponding surface of the case around the slot, and the other one of the radially-inner edge and the radially-outer edge having hooks being resilient and inwardly flexible to engage the insert into one end of the slot, the hooks biased outwardly for engaging with a corresponding feature of the case, the insert being thereby trapped in the slot in position to snugly receive the grommet therein in a sealed engagement. 
     There is also provided a method of mounting a vane to a slot provided in a fan case of a turbofan gas turbine engine, the method comprising: inserting an insert into one end of the slot, flexing hooks of the insert and sliding the hooks out an other end of the slot, the hooks then engaging onto one face of the fan case with an outwardly protruding lip of the insert abutting against an opposite face of the fan case, the insert having an inner opening extending across the fan case and having an inner surface; and inserting an airfoil body of a vane through the inner opening of the insert and sliding the vane body radially inwardly until a grommet provided integral to a tip of the vane comes snugly into sealed engagement with the inner surface of the insert. 
     There is further provided a gas turbine engine having at least one compressor vane assembly having a plurality of vanes extending radially between an outer case and an inner case of the compressor and protruding into corresponding slots in the case, each vane assembly comprising: a vane having an elongated airfoil body extending to a tip, and a grommet disposed at the tip, the grommet being of a material more resilient than a material of the airfoil body, the grommet having an outer surface surrounding the tip, a radially-inner surface and a radially-outer surface; and an insert having a closed loop shape with a radially-outer edge and a radially-inner edge, the closed loop shape having an inner surface matingly shaped to receive the outer surface of the grommet, and an outer surface matingly shaped to be snugly received in the slot, wherein one of the radially-outer edge and the radially-inner edge has an outwardly protruding lip shaped to abuttingly and sealingly engage a corresponding surface of the case around the slot, and the other one of the radially-inner edge and the radially-outer edge having hooks being resilient and inwardly flexible for engaging the insert into one end of the slot, the hooks being biased outwardly for snapping onto a corresponding feature of the case, the insert being thereby trapped in the slot in position to snugly receive the grommet therein in a sealed engagement. 
     In another aspect, there is further still provided a vane assembly mountable to a slot in an fan case of a turbofan gas turbine engine, the vane assembly comprising: a vane having an elongated airfoil body extending to a tip, and a grommet made integral to the tip, the grommet being of a material more resilient than a material of the airfoil body, the grommet having an outer surface surrounding the tip and being snugly engageable with the slot. 
     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, in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIG. 2  is a schematic oblique view showing vane tips extending into slots in a fan outer case; 
         FIG. 3  is a schematic cross-sectional view of a first example of a portion of a vane assembly; 
         FIG. 4  is a schematic oblique view of an insert of the vane assembly of  FIG. 3 ; 
         FIG. 5  is a schematic cross-sectional view showing the insert of  FIG. 4  mounted to a slot; 
         FIG. 6  is a side elevation view of a portion of the insert; 
         FIG. 7  is a side elevation view of a vane tip of the assembly of  FIG. 3 ; 
         FIG. 8  is a schematic cross-sectional view of the vane tip and grommet of  FIG. 3 ; 
         FIG. 9  is a schematic elevation view of an alternate embodiment of a vane tip; 
         FIG. 10  is a schematic cross-sectional view of an alternate embodiment of an insert and slot assembly; 
         FIG. 11  is a schematic cross-sectional view of an alternate embodiment of a slot; 
         FIG. 12  is an alternate example of a fastener; 
         FIG. 13  is an alternate example of a fastener; 
         FIG. 14  is a schematic cross-sectional view of an alternate example of a vane tip and grommet assembly; 
         FIG. 15  is a schematic elevation view of the vane tip of  FIG. 14  without the grommet. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a turbofan 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 section  18  for extracting energy from the combustion gases. 
     As best seen in  FIG. 2 , a plurality of vanes  20  are provided downstream of the fan  12  and are circumferentially interspaced from one another. The vanes  20  have an airfoil body  22  which extends radially between an inner case  24  and an outer case  26 . A radially-outer tip  28  of the vane protrudes into the outer case  26  as best seen in  FIG. 3 . 
     A grommet  30  is made integral to the radially-outer vane tip  28 . For instance, if the airfoil body  22  is made of injection moulded plastic such as PEEK (Polyether ether ketone) as is more and more common nowadays, this relatively brittle material can also be coated with a metal coating to enhance its structural properties. Alternately still, the grommet  30  can be co-moulded with the airfoil body  22  or the grommet can be potted (e.g. formed by dipping the vane tip into a grommet mould). The airfoil body  22  can alternately be made of aluminum or any other suitable material, for instance. 
     The grommet is characterized by being substantially more resilient than the material of the airfoil body  22 , which is useful to form a satisfactory seal which will impede pressure loss in the radially-outward direction. The grommet  30  can be made of natural or synthetic rubber, or of polyurethane, to name a couple of examples. Since the grommet  30  is of a more resilient material than the airfoil body  22 , and that the airfoil body  22  extends in a continuous manner to the tip  28 , the presence of the does not cause high stress concentration areas at the interface  32  such as could be the case with a vane head made of a same material than the body. 
     The vane tip  28  is held in the slot  34  via the grommet  30 . The grommet  30  can be said to have a radially-outer surface  36 , a radially-inner surface  38 , an inner surface  40  in contact with the airfoil body  22 , and an outer surface  42  surrounding the airfoil body  22 . To resist the loads which can be expected during normal engine operation and in the event of a bird strike, the vane tip  28  should be held in the slot  34  not only in the plane of the fan case  26 , but also in both the radially outward  33  and the radially inward  35  directions. The outer surface  42  can be made to snugly adapt directly to the inner surface  44  of the slot  34  which would allow the vane tip  28  to be held in the plane of the slot. Moreover, with the vanes typically being inserted into the duct externally, across the fan case  26  in the radially inner direction  35 , the assembly could be made to support the grommet  30  in the radially-inward direction such as by using a radially-inward tapering shape in the slot  34  shown in  FIG. 11  for instance, and an external device such as a fastener or belt be used to hold the vane tip  28  in the radially-outward direction and maintain the seal with the slot. 
     Henceforth, in this example, it was preferred to provide the vane tip assembly  29  with two additional components: an insert  48  and a fastener  50 . More specifically, the insert  48  in this embodiment can be made of a somewhat resilient material, such as a plastic for instance, and provided generally in a closed loop shape with a base or outwardly protruding lip  53  at one edge  56  and hooks  51  at the opposite edge  58 , and be engineered to be firmly pressed across the slot  34  from one side thereof (e.g. the radially inner side  52 ) with the hooks  51  resiliently yielding until the hooks  51  protrude out the other side (e.g. the radially-outer side  54 ) to snap into position against a corresponding feature of the case  26  such as a portion of an opposite face of the case  26  adjacent the slot  34 , at which point the lip  53  provides a firm abutment against the other face of the case (e.g. side  52 ) with the slot trapped between the hooks  51  and the base  53 , or, otherwise said, with the insert  48  engaging with the slot  34  such as to lock together. 
     The function of the snap hooks  51  are both to hold the insert  48  in place during the assembly of remainder of the parts and to prevent the vane and grommet  30  being ingested inwards during the impact due to foreign object damage. 
     The exact shape of the insert  48  which was selected in this specific example is shown more clearly in  FIG. 4 . The closed-loop shape of the insert  48  can also be seen to include an outer surface  60  which is shaped to snugly engage the inner surface  44  of the slot  34 , and an inner surface  62  which is shaped to snugly and sealingly receive an outer surface  64  of the grommet  30 . 
     Moreover, the shape of the insert  48  can be freely designed, and it can be designed with fastener apertures  66 ,  68 , for instance, the exact shape, number, position, and configuration of which can be freely adapted to the specifics of alternate embodiments. 
     In the illustrated embodiment, the insert  48  has two fastener apertures  66 ,  68 , both provided on the radially outer edge  58  of the insert  48 , with one on each side of the grommet  30  when the grommet is in its working position, and aligned along a fastener axis  71 . A fastener  50  can be inserted through both fastener apertures, and press radially-inwardly upon the radially-outward surface of the grommet or vane tip  28  to exert the retention of the vane tip  28  in the radially-outward direction. In the illustrated embodiment, the fastener is a simple tie-wrap attachment. In alternate embodiments, it can be a split pin or wave spring such as illustrated in  FIG. 12 or 13 , to name two alternate examples. 
     The specific configuration of the tip of the airfoil body  22  used in the illustrated embodiment is shown more clearly at  FIG. 7 , where it can be seen that the radially-outer end of the airfoil body  22  is also provided with a fastener slot  70  in this example, which can cooperate with the fastener  50  and the fastener slots  66 ,  68 , and the tapered shape of the grommet and insert  48  to maintain the vane tip  28  in its working position even in the event of a bird strike or the like. More specifically, the fastener slot  70  is aligned with fastener slots  66  and  68  when the grommet is sealingly received in the insert  48 . Moreover, in this specific embodiment, the radially-outer end of the airfoil body  22  is provided with apertures  72  through which the material of the grommet extends, which allows the grommet  30  to be firmly held against the airfoil body  22 . 
       FIG. 5  shows an embodiment where the inner surface of the slot extends radially (non-tapered) but where the inner surface of the insert nevertheless extends tapered in the radially-inner direction. 
       FIG. 9  shows an embodiment where an elongated slot  80  is provided through the airfoil body  22  and across which the material of the grommet can extend. Furthermore, in the embodiment of  FIG. 9 , the fastener slots are of a number of two, showing that various alternate configurations are possible. 
       FIG. 10  shows an alternate embodiment where both the outer surface of the insert and the inner surface of the insert extend radially (i.e. non-tapered). 
       FIGS. 14 and 15  show an alternate embodiment where the vane body  122  is provided with laterally-extending wings  190  and where the grommet  130  is firmly secured to the vane body by way of the wings  190 . 
     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 departing from the scope of the invention disclosed. 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 scope of the appended claims.