Patent Application
20140356158
The application relates generally to gas turbine engines and, more particularly, to gas turbine engine vane assemblies.
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.
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 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.
Reference is now made to the accompanying figures, in which:
As best seen in
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
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
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
The specific configuration of the tip of the airfoil body 22 used in the illustrated embodiment is shown more clearly at
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.
