US2873947A - Blade mounting for compressors, turbines and like fluid flow machines - Google Patents

Description

1959 s. w. H. PERRY 2,873,947

BLADE MOUNTING FOR COMPRESSORS, TURBINES AND LIKE FLUID FLOW MACHINES Filed Nov. 8. 1954 2 Sheets-Sheet 1 /4 v /8 7 v T\ Feb. 17, 1959 s. w. H. PERRY 2,873,947

- BLADE MOUNTING FOR COMPRESSORS, TURBINEZS AND LIKE FLUID FLOW MACHINES Flled Nov 8 1954 2 Sheets-Sheet 2 Fig. 2

United States Patent BLADE MOUNTING FOR COMPRESSORS, TUR- BINES AND LIKE FLUID FLOW MACHINES Sydney William, Henry Perry, Farnborough, England, asslgnor to Power Jets (Research. and Development) Limited, London, England,a British company Application November 8, 1954, Serial No. 467,561

Claims priority, application Great Britain November 26, 1953 7 Claims. Cl. 253-77 1 This invention relates to the mounting of rotor blades for turbines, compressors, and like bladed fluid flow machines.

. Such blades usually comprise a working portion of aerofoil'or other profiled cross-section and a root part which is shaped to engage in a corresponding seating in the, rotor. tree-root is one of .the most suitable root formations from the point of view of load carrying capacity. Such a formation, however, is not suitable for blades made of materials which'are highly notch-sensitive, that is, materials which are brittle and readily liable to fracture under stress concentrations resulting from sharp corners, indentations and the like. Such materials include refractory ceramics consisting, for example, of sintered oxides, silicides, carbides or borides of metals such as beryllium,:aluminium or titanium, and sintered metalcerarnic mixtures (known as ceramels or cermets) consisting, for example, of one or more of the above ceramic materials and a metal such as nickel. For materials such as those mentioned above, a dovetail root formation with well rounded corners or a bulb or other root formation without any sharp corners is to be preferred so that stress concentrations are minimised. This sort of root formation, however, has a lower load-carrying capacity than a fir-tree root and so under some circumstances may be unsuitable for direct attachment to a rotor in which there is only a limited bearing area between the blade and the rotor, e. g. a rotor made up of axially spaced thin discs. Even with metal blades, the formation of a fir-tree or indeed any other form of root involves complicated machining operations, in addition to the operations re- -:quired to form the aerofoil part of the blade.

According to the inventioma rotor for a turbine, compressor or like bladed fluid flow machine comprises a rotor disc and a row of radially extending blades, each blade having an enlarged foot at its radially inner end and being secured to the rotor disc by means of aretaining piece engaging with said foot and itself secured to the rotor disc.

The retaining piece may itself have a root formation engaging in a corresponding seating in the rotor disc. In a preferred form of the invention, each blade is secured to the rotor disc by a pair of retaining pieces, one engaging with each side ofthe blade foot. The retaining pieces may be disposed around the periphery of the rotor circumferentially alternating with the blades so that each retaining piece engages with the feet of the blades on each side thereof.

The present invention islprimarily' concerned with blades made of a notch sensitive material. Such blades the side faces of the dovetail and the apex of the'wedge having a root formation engaging in a corresponding seat- It has been found that the well known'fir- Ice ing in the rotor disc. Inparticular, the apex of the wedge may have a fir-tree root formation.

One embodiment of the invention will now be described with reference to the accompanying drawings of which:

Fig. 1 is an axial half section of the turbine of an aircraft gas turbine jet propulsion power plant, the section being taken on the line-i-I in Figure 2.

Fig. 2 is a fragmentary end view of the turbine rotor taken on the line II-II in Fig. 1.

Referring to Fig. 1, the turbine rotor disc is made up of five thin discs 1a, 1b, 1c, 1d and 1e of sheet metal, axially spaced apart and held between two massive end discs 2, 3. The discs are held together by a ring of bolts 4 symmetrically disposed round the turbine axis, the spacing of the sheet metal discs being maintained by spacing washers 5 threaded onto the bolts. The rotor carries on its periphery a row of turbine blades 6 made of a notchsensitive material such as a refractory ceramic or a sintered metal-ceramic mixture, e. g., those referred to above.

The turbine rotor is mounted on the end of a driving shaft 7, the other end of which is connected to the compressor of the gas turbine plant (not shown). The shaft is supported by a hearing it carried in a housing 21 supported by a spider 9 from a main structural member 10 constituting the backbone of the plant.

The turbine rotor blades 6 are enclosed by a stationary cylindrical outer wall 11. Immediately upstream of the rotor blades is a row of turbine inlet nozzle vanes 12, supported between inner and outer cylindrical members 13, 14, defining a nozzle inlet passage to the turbine rotor blades. The outer member 14 abuts axially with and is connected to the wall 11 enclosing the rotor blades, while the adjacent edges of the inner member 13 and the rotor" end disc 2 are formed with cooperating surfaces aifording a seal 15 to prevent hot gases leaking from the working fluid passage through the turbine into the interior of the plant. The upstream ends of the members 13, 14 are'connected to walls 16, 17 constituting the air casing ofthe combustion chamber of the gas turbine plant, and the downstream end of wall 11 is connected to a tubular member 18 forming with a conical fairing 19 downstream of the turbine rotor an exhaust duct through which the exhaust gases from the turbine are discharged asa propulsive jet stream.

Referring now to Fig. 2 each blade 6 comprises a working portion 6a of aerofoil cross-section which is integral with .a circumferentially extending root platform .617 and a foot 6c which in axial section is of substantially dovetail cross-section with the corners rounded off. The blades are disposed around the periphery of the rotor with the under surfaces of the dovetail feet resting on projections 31 of the peripheries of the sheet metal discs 10:, 11), etc. and the side faces 6d of the dovetails extending in an axial or generally axial direction. Between each adjacent pair of blade feet 60 there is a retaining piece 20 which is substantially Wedge-shaped in cross-section with the apex pointing radially inwardly and with its sides extending in an axial or generally axial direction. The radially outer part of each retaining piece has side faces 20a which bear against the side faces 6d of the dovetail feet of the blades on each side thereon, while the radially inner or apex part 26b of the retaining piece has a fir-tree root formation and engages in corresponding axially aligned recessed seatings 32 in the sheet metal discs 1a, 1b, etc. The centrifugal loads on the blades are thus transmitted through the retaining pieces to the sheet metal discs. As can be seen from Fig. 1, the blade feet 60 and. the retaining pieces 20 extend axially to spanthe sheet metal discs 1a, 1b etc.

The blades and retaining pieces are retained against axial displacement by the end discs 2, 3 which extend radially outwardly of the peripheries of the sheet metal discs.

The faces 6d on the blade feet engage with the faces 2% of the retaining pieces over the Whole of their axial extent so that there is the maxirnum bearing area available to transmit the centrifugal loads. Since there is an extended bearing area available, local concentrations of bearing load are minimised. Moreover the dovetail shape of afoot with rounded corners is inherently suitable for the avoidance of internal stress concentrations.

Since the rotor is laminar, the bearing area between the retaining pieces 2% and the discs 1a, 11'), etc. is reduced as compared with the bearing area that would be available in a corresponding solid rotor, but this is compensated for by the inherently greater load carrying capacity of the fir-tree root as compared with the dovetail feet of the blades. Also'there will be local stress concentrations in the retaining pieces at their points of contact with the discs, but the retaining pieces are made of a heat resisting steel or the like which is capable of withstanding such stress concentrations. The retaining pieces may con veniently be cut from rolled strip material of the appropriate cross-section.

It is found that, for optimum stress conditions, the angle at at which the faces Zita of the retaining pieces 2b are inclined to the radial direction should not be less than 30.

It is to be noted that the above described construction obviates the necessity for making a blade of ceramic or like material with a fir-tree root. Further if the ceramic blades were in direct engagement with the laminar rotor, it would be necessary for the laminations to be very close together to avoid undue stress concentrations on the blade root. By the use of retaining pieces made of a material in which stress concentrations are not so important this difficulty is overcome, at least to some extent, and more widely spaced laminations can be used. The main limitin}; factor is the necessity to provide a bearing area between the retaining pieces and the sheet metal discs having a load carrying capacity equivalent to that of the bearing 7 area between the blades and the retaining pieces.

In order to cool the rotor and the blades, cooling air may be led into the spaces between the sheet metal discs 1a, 1b, etc. The end disc 2, and the first four sheet metal discs are provided with holes 22a, 22b, 22c, 22d, 22a decreasing in size from the inlet side of the rotor to effect the desired distribution of air among the spaces between the discs. The cooling air is tapped oil from the compressor and is led to the rotor through the space inside the main structural member 10. This member has an extension 23 carrying seals Mengaging with a flange Zn on the face of the end disc 2 to prevent leakage of cooling air into the gas flow path through the turbine. The bearing housing 21 has an extension 2111 around the shaft 7 also carrying seals 25 to prevent the cooling air reaching the bearing.

The air from the spaces between the rotor discs 1a, 1b, etc. escapes through holes 290 in the retaining pieces into the spaces 26 under the blade platforms ab where it constitutes a heat insulating layer. it finally passes into the gas stream through gaps between adjacent blade platforms 6b.

In addition some of the air may pass into holes 6e in the blades themselves, extending from their under surfaces to their tips.

I claim:

1. A rotor for a turbine, compressor or like bladed fluid flow machine comprising a rotor disc made up of a plurality of coaxial thin discs axially spaced apart from one another at least at their peripheries; at least one radially extending rotor blade made of a notch-sensitive material mounted externally of the peripheries of the thin discs, the blade having at its root end an enlarged foot formed on each side with a face extending in a generally axial direction; means securing said blade to the thin discs, said means comprising a pair ofseparately 4 formed retaining pieces, one on each side of the blade foot and axially spanning all the thin discs, each piece being made of a material capable; of withstanding stress concentrations and being formed with a generally axially extending side face engaging with and radially overlapping the adjacent side face on the blade foot, and means securing each of said pieces to all of said thin discs; and means retaining said blade against axial displacement. Y

2. A rotor for a turbine, compressor or like bladed fluid flow machine comprising a rotor disc made up of a plurality of coaxial thin discs axially spaced apart from one another at least at their peripheries; a row of radially extendingrotor blades made of a notch-sensitive material disposed around and externally of the peripheries of the thin discs, each blade having at its root end an enlarged foot formed on each side with a face extending in a generally axial direction; means securing said blades to the thin discs, said means comprising a plurality of separately formed retaining pieces disposed around the peripheries of the thin discs, circumferentially alternating with the blades and axially spanning all the thin discs, each re taining piece being made of a material capable of with standing stress concentrations and being formed on each side with a generally axially extending face engaging with and radially overlapping the face on the side of the blade foot adjacent thereto, and means securing each said retaining piece to all the thin discs; and means retaining said blades against axial displacement.

3. A rotor for a turbine, compressor or like bladed fluid flow machine comprising a'rotor disc made up of a plurality of coaxial thin discs axially spaced apart from one another at least at their peripheries and each formed with at least two recessed root seatings in its periphery; at least one radially ext ending rotor blade made of a notch-sensitive material mourned externally of the peripheries of the thin discs, each blade having at its root end an enlarged foot formed on each side with a continuous face extending in a generally axial direction and spanning the thin discs; means securing said blade to the thin discs, said means comprising a pair of separately formed retaining pieces one on each side of the blade foot and axially spanning all the thin discs, each piece being made of a material capable of withstanding stress concentrations and being formed with a generally axially extending continuous side face spanning the thin discs and engaging with and radially overlapping the adjacent side face on the blade foot and including a part having a root formation engaging in one of said seatings in each of said thin discs; and means retaining said blade against axial displacement.

4. A rotor for a turbine, compressor or like bladed fluid flow machine comprising a rotor disc made up of a plurality of coaxial thin discs axially spaced apart from one another at least at their peripheries, and each formed with aplurality of recessed root seatings in its periphery; a row of radially extending rotor blades made of a notchsensitive material disposed around and externally of the peripheries of the thin discs, each blade having at its root end an enlarged foot formed on each side with a continuous face extending in a generally axial direction and spanning the thin discs; means securing said blades to the thin discs, said means comprising a plurality of separately formed retaining pieces disposed around the periphcries of the thin discs, circumferentially alternating with the blades and axially spanning all the thin discs, each retaining piece being made of a material capable of Withstanding stress concentrations and being formed. on each side with a generally: axially extending contiuous face spanning the thin discs and engaging with and radially plurality of coaxial thin discs axially spaced apart from one another at least at their peripheries and each formed with a plurality of recessed root seatings in its periphery; a row of radially extending rotor blades made of a notchsensitive material disposed around and externally of the peripheries of the thin discs, each blade having at its root end an enlarged foot of dove-tail cross-section having continuous side faces extending in a generally axial direction and spanning the thin discs; means securing said blades to the thin discs, said means comprising a plurality of separately formed retaining pieces made of a material capable of withstanding stress concentrations circumferentially alternating with the blades and axially spanning all the thin discs, each retaining piece being substantially wedge shaped in cross-section with the apex pointing radially inwardly, the wedge having continuous side faces extending in a generally axial direction and axially spanning the thin discs and each engaging with and radially overlapping the side face of the dovetail blade foot adjacent thereto, and the apex of the wedge having a root formation and engaging in one of said seatings in each of said thin discs; and means retaining said blades against axial displacement.

6. A rotor according to claim 5 wherein said seatings in the thin discs and said root formations on the wedgeshaped retaining pieces are of fir-tree root form.

7. A rotor for a turbine, compressor or the like bladed fluid flow machine comprising a rotor disc made up of two co-axial end discs and a plurality of thin discs coaxial with, lying between and of smaller diameter than radially extending rotor blades made of a notch-sensitive material disposed around and externally of the peripheries of the thin discs, each blade having at its root end an enlarged foot lying between the end discs and formed on each side with a continuous face extending in a generally axial direction and axially spanning the thin discs and at each end with a face abutting with the side face of one of the end discs; a plurality of separately formed retaining pieces made of a material capable of withstanding stress concentrations disposed around the peripheries of the thin discs and lying between the end discs circumferentially alternating wtih the blades and axially spanning all the thin discs, each retaining piece being formed on each side with a generally axially extending continuous face axially spanning the thin discs and engaging with and radially overlapping the face on the side of the blade adjacent thereto and at each end with a face abutting with the side face of one of the end discs, said piece including a part having a root formation engaging in one of said seatings in each of the thin discs.

References Cited in the file of this patent UNITED STATES PATENTS 1,585,713 Herr May 25, 1926 2,657,008 Atkinson Oct. 27, 1953 2,665,880 Schorner Jan. 12, 1954 2,751,189 Ledwith June 19, 1956 FOREIGN PATENTS 131,574 Australia Mar. 1, 1949 674,543 Great Britain June 25, 1952 823,672 Germany Dec. 6, 1951

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