Patent Application
20180112542
The application relates generally to rotors for a gas turbine engine, and more particularly to such rotors having blades removably mounted thereto.
Gas turbine engine rotors, such as those used in compressors or turbine sections of the gas turbine engine, generally include a disc to which a plurality of blades is removably mounted. These blades typically have shaped roots that are received within correspondingly shaped slots in the periphery of the disc. The slots are typically open on each axial end of the disc. Accordingly, when a blade is received within the slot of the disc, it is axially slid into the slot from either the upstream or downstream side of the disc. Once in position, a fastener on each side of the disc is required in order to axially align the blades in the correct position and trap the blade roots within the slots of the disc.
In one aspect, there is provided a rotor for a gas turbine engine comprising a disc having opposite first and second end surfaces axially spaced apart by a peripheral surface circumferentially extending about the rotor, a plurality of slots defined in the peripheral surface and each having a length in an axial direction extending between a first slot opening in the first end surface and a second slot opening in the second end surface, each of the plurality of slots having a tapered shape with at least one dimension of a cross-sectional shape of the slot reducing along at least a portion of the length of the slot, wherein the at least one dimension at the first slot opening is greater than the at least one dimension at the second slot opening to define said tapered shape; and a plurality of blades each having a root received in a respective one of said slots, the root having a complimentary shape and size to said respective one of said slots.
In another aspect, there is provided a blade for a rotor of a gas turbine engine, the blade comprising an airfoil portion extending between a radially inward base and a radially outward tip; and a root attached to the radially inward base of the airfoil portion and extending along a generally axial length, the root having a cross-sectional size varying along the length of the root between a first root end and a second root end, wherein the root has a tapered shape with at least one dimension of a cross-sectional shape of the root decreasing along at least a portion of the length of the root, wherein the at least one dimension at the first root end is greater than the at least one dimension at the second root end.
In a further aspect, there is provided a method of forming a blade of a rotor of a gas turbine engine, the method comprising forming a tapered root of the blade with at least one dimension of a cross-sectional shape of the root progressively reducing along at least a portion of an axial length of the root, wherein the at least one dimension at a first root end is greater than the at least one dimension at a second root end.
Reference is now made to the accompanying figures in which:
Referring to
The disc 22 has two opposite end surfaces 30, 32 which are axially spaced apart by a peripheral surface 34. The peripheral surface 34 circumferentially extends around the rotor 20. In a particular embodiment, the end surfaces 30, 32 are substantially parallel relative to each other and substantially perpendicular relative to the axis 28 of the engine 10. In a particular embodiment, the front end surface 30 is an upstream surface of the rotor 20 relative to a direction of the combustion gases in the turbine section 18. In an alternate embodiment, the rear end surface 32 is the upstream surface of the rotor 20 in the compressor section 14. Thus, in the compressor section 14, a differential pressure of the air across the compressor rotor acts on the front surface 30 of the rotor 20 and in the turbine section 18, a differential pressure of the combustion gases across the turbine rotor acts on the front surface 30 of the rotor 20. In other words, a force derived from the differential pressure across the rotor 20 acts on the front end surface 30 during the normal operation of the gas turbine engine 10.
The disc 22 includes a plurality of slots 36 defined in a peripheral portion such as a rim 38 thereof through the peripheral surface 34, each of the slots 36 extending between the end surfaces 30, 32 of the disc. In a particular embodiment, the slots 36 extend generally axially. In another particular embodiment, the slots can be slightly skewed relative to the axis 28 of the rotor 20. The slots 36 can be any suitable groove, opening and/or recess formed in the disc to receive a generally complementary portion of one of the blades 24 in order to thereby connect, secure and/or attach the blade 24 onto the disc 22. Each slot 36 defines a circumferential inlet 40 having a width W extending circumferentially between two opposite edges 42 of the inlet 40 in the peripheral surface 34, and extends radially inward from the inlet 40 to a depth D defined by a distance between the inlet 40 to a point 44 of the slot furthest from the inlet 40. Each slot 36 also extends through the rim 38 of the disc 22 between a front slot opening 46 defined in the front end surface 30 and a rear slot opening 48 defined in the rear end surface 32. The slots 36 can extends generally axially or slightly skewed relative to the axis 28 of the rotor 20. A length L of the slot is defined between the front and rear slot openings 46, 48. In a particular embodiment, the slots 36 are equally circumferentially spaced apart about the outer periphery of the disc 22.
Generally, the slots 36 have the same, substantially the same and/or similar cross-sectional shape. The shape of the slot 36 is tapered along the length L. In a particular embodiment, the cross-sectional shape varies in cross-sectional size along the length L thereof. Alternatively, the cross-sectional size can be maintained while tapering the slot 36. In the embodiment shown, the slots 36 have a tapered shape reducing in one dimension of the cross-sectional shape along the length L. Consequently, each of the slots 36, and thus each of the corresponding blade root received therein, have a cross-sectional shape that tapers from the front slot opening 46 to the rear slot opening 48, and therefore the front slot opening 46 defines a cross-sectional size that is larger than that of the opposed rear slot opening 48. Although in the embodiments shown the slot 36 is continuously tapered, in an alternate embodiment, the slot 36 can be discontinuously tapered. Thus the term “tapered” is not limited to progressive and uniform tapered shape. Alternately expressed, the term “taper” can also include a discrete reduction in cross-sectional size in which one or more portions of the slot 36 can be tapered along its length L while other portions maintain generally constant cross-sectional dimensions. The tapering of the slots 36 and of the blade roots accordingly means that the blade roots can only be inserted into the slots 36 from one of the two axial sides 30, 32 of the rotor disc 22.
To taper the shape of the slot 36, at least one dimension of the cross-sectional shape of the slot 36 is reduced at one side of the rotor relative to the other side of the rotor. Additional dimensions can also be reduced. In the embodiment shown, the width W of the slots 36 continuously decreases from one side of the slot to the other. In an alternate embodiment, the depth D of the slots continuously decreases. In yet another embodiment, the width W and the depth D are continuously decreased from one side of the slot to the other. In yet another alternate embodiment, one dimension can be reduced while another dimension is increased, for example, to maintain a substantially constant cross-sectional area over the length of the slot, even if one or more dimensions decrease over the length. In all cases, a tapered and/or wedged shape slot (and thus complimentary blade root) is thus provided, such that the blade root can be inserted and removed from only one side (i.e. that with the largest dimension(s)) of the slot.
Referring to
The cross-sectional shape of each of the slots 36 in the rotor disc 33 can be any suitable geometrical profile. In the embodiment shown, the cross-sectional shape of the slots 36 and the complementary blade roots is a firtree profile. In an alternate embodiment, the cross-sectional shape may have a dovetail profile.
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The slots 36 and the correspondingly conforming roots 52 are formed by varying the cross-sectional size along the axial length of the rotor 20. In a particular embodiment, the slots 36 and the roots 52 are shaped by electrical discharge machining (EDM), given the accuracy of the EDM machining process. Alternate machining processes can however alternately be used.
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 appended claims.
