Support Structure For Rotor Blades Of Turbo-machines

Abstract

A support structure for rotor blades of a turbo-machine comprises a substially cylindrical or conical hollow drum of fibrous material and a plurality of blade-carrier bars of metal attached side by side on the outer surface of the blades.

Description

The present invention relates to support structures for the rotor blades of turbo-machines and relates more particularly, but not exclusively, to the compressor rotors of turbo-jet engines.

An essential problem which arises in the design of turbo-jet engines is that of reducing to the maximum extent, the weights of their various component parts, without at the same time impairing their mechanical strength. It has already been proposed, for this reason, that recourse should be had to composite materials made of an assembly of fibres such as silica fibres, boron fibres or carbon fibres, embedded in an appropriate binder such as a synthetic resin or a metal deposited, in particular, by electrolysis or by atomising. The materials can, for example, be obtained by winding a fibre or bunch of fibres in a continuous fashion onto a mandrel and covering the resultant winding with a binder. Experience has shown that these composite or fibrous materials, for an equivalent mechanical strength, have a much lower weight than conventional metallic materials so that they are particularly desirable for use in the construction of elements such as rotors for turbo-machines, which, in operation, are subjected to high mechanical stresses.

In this latter application, however, one comes up against certain difficulties as far as the blade support facility is concerned.

It should be noted, in this context, that in a correctly designed support system, several requirements have to be satisfied simultaneously: The blades must be capable of being assembled accurately, they must be capable of easy assembly and dismantling, and finally the support system must be capable of resisting very high tear-out stresses due to the action of the centrifugal force on the blades.

In rotors comprising a drum made of a conventional material, frequently a rabbet type attachment technique is resorted to to satisfy these requirements. For this purpose, the drum is provided with a series of grooves, of dove-tail section for example, used to receive the blade roots which latter are profiled in a corresponding manner.

However, it appears that the transfer, purely and simply, of this kind of technique to rotors of fibrous material, is not always desirable or indeed possible. These materials, in other words, are quite difficult to machine especially where it is necessary to give them a relatively complex profile such as a dove-tail. In addition, this kind of machining, bearing in mind the heterogeneous nature of the materials in question, gives rise to the risk that the mechanical strength of the components will be impaired in the zones where they are subjected to tear-out stresses due to the centrifugal force.

The object of the present invention is to resolve the aforestated difficulties in order to make it possible, under satisfactory technical and economic conditions, to use fibrous materials to produce a rotor blade support structure for use in turbo-machines.

A support structure in accordance with the invention accordingly comprises, in combination, a hollow drum of fibrous material, a plurality of blade-carrier bars of metal arranged side by side on the external surface of the drum of fibrous material and extending each in the axial direction thereof, and at least one ring of fibrous material circumferentially arranged in hoop fashion around the metal bars to retain the bars on the drum.

In accordance with a preferred embodiment, each metal bar, viewed in section in a plane containing the drum axis, exhibits a crenellated configuration comprising one or more projections alternating with one or more depressions which latter open in the radially outer direction of the drum and each extend in the circumferential direction thereof, the homologous depressions formed in the successive bars being disposed in circumferential extension of one another in order to constitute one or more annular grooves in which said ring or rings can be received.

Advantageously, each metal bar is formed on its external face, with at least one profiled axial groove (for example of dovetail section) shallower than said depression or depressions and constituting, in at least one of the projections of said crenellated configuration, a location for a correspondingly profiled blade root.

Advantageously, the radial thickness of a ring of fibrous material, measured from the bottom of the depression in which said ring is located, is at most equal to the radial height of the contiguous projection, measured between the base thereof and the bottom of the groove formed therein.

In accordance with an arrangement of the invention, which is applicable in this latter case, the length, measured in a direction parallel with the axis of the drum, of a projection is greater than that of the blade root fitted in the groove formed in said projection.

The rotor can thus be equipped with a plurality of spacers each of which has a root whose profile is identical with that of the blade roots, said spacer root having two axially spaced end portions which respectively penetrate into the grooves in two successive projections in one and the same bar and abut against the roots of the blades respectively fitted in said grooves, in such a fashion that said spacer, in the region of a ring of fibrous material, straddles the depression defined between said projections.

Advantageously, the aforesaid spacers will be provided, on their radially outer face, with labyrinth partitions designed to cooperate, in a sealing relationship, with a structure fixed to the stator of the turbo-machine.

In accordance with another feature of the invention, the projections in the aforesaid metal bars are partially recessed in order to lighten the bars.

In accordance with yet another feature of the invention, the metal bars are attached to the drum of fibrous material, by gluing.

As will be understood, the design of a blade support structure in accordance with the invention, does not require any machining of the drum of fibrous material. The attachment of the blades is effected without any particular difficulty and by a conventional method, the profiled blade roots being fitted in profiled grooves formed in the metal bars. Finally, the strength of these latter vis-a-vis the tear-out stresses produced by the centrifugal force, is ensured by the provision of the rings of fibrous material which act as hoops.

Although they are metal, the aforesaid bars do not produce more than a limited increase in the weight of the structure. It can be pointed out in this context that these bars are drastically lightened by the depressions, grooves and recesses formed in them. Their mechanical strength is nevertheless considerable bearing in mind the way in which they are hooped by the rings of fibrous material. In the support structure in accordance with the invention, the assembly constituted by the drum, the bars and the rings is, ultimately, lighter than a metal drum of the same strength as used in the building of the rotor in a conventional turbo machine.

The description which now follows in relation to the attached drawing, given purely by way of non-limitative example, will indicate how the invention may be put into effect.

In the drawings:

FIG. 1 is an axial half-section along the line I--I of FIG. 2, through part of a turbo machine equipped with a support structure in accordance with the invention; and

FIGS. 2 and 3 are partial transverse sectional views respectively on the lines II--II and III--III of FIG. 1, of said turbo machine.

In FIGS. 1 to 3, the rotor blade support structure of a turbo machine such as a low-pressure compressor designed for fitting to a turbo-jet engine is indicated generally at 1.

The structure comprises a hollow drum 2, with its axis X'-X, and a plurality of bars 3 extending in each case in the axial direction of said drum and attached side by side in a contiguous manner (see FIG. 2) to the external surface thereof.

The drum 2 is made of a fibrous material and can be produced by winding a fibre, for example a glass fibre or carbon fibre, onto a cylindrical or slightly conical mandrel which functions as a mould. The operation is carried out in the conventional way by rotating the mandrel about its own axis and simultaneously causing the fibre to execute an alternating rectilinear motion parallel to the mandrel axis. In this fashion, a crossed helical winding is obtained which ensures that the drum is flexionally and torsionally rigid. The fibres are covered, during the winding operation, with an appropriate binder such as synthetic resin material. After the binder has hardened, the mandrel is withdrawn from the thus-formed drum.

The bars 3 are made of metal, advantageously titanium. Each of them has a smooth internal face by which it is attached, advantageously by gluing (for example by means of a resin-based adhesive), to the external surface of the drum, and an external face shaped in the manner shown.

As shown in FIG. 1, each of the metal bars 3, viewed in section in a plane containing the axis of the drum, exhibits a crenellated configuration comprising projections 4a, 4b . . . 4p . . . alternating with depressions 5a, 5b . . . 5p . . . . In order to lighten the structure, each of said projections is partially recessed as indicated at 16. Each of the depressions 5a, 5b . . . 5p . . . opens in the radially outer direction of the drum and extends in the circumferential direction thereof.

As shown in FIG. 3, the homologous depressions such as those 5p formed in successive bars are disposed in circumferential extension of one another, in order to constitute annular grooves 6a, 6b . . . 6p.

As shown in FIG. 2, each metal bar 3 further presents on its external face at least one axial profiled groove such as those 7a, 7b, 7c shallower than the depressions 5a, 5b . . . 5p. The groove 7a will advantageously have a dove-tail section whilst the grooves 7b and 7c each form a half dove-tail section. Two half dove-tail sections belonging to two adjacent bars together form a complete dove-tail. This arrangement, however, is by no means mandatory and the connection between two adjacent bars could equally well be effected in a joint plane located between two grooves such as 7a, 7b.

The grooves 7a, 7b, 7c each extend over the axial length of the projections 4a, 4b . . . 4p between two axially consecutive depressions such as 5a, 5b.

The dove-tails formed by the grooves 7a and the grooves 7b-7c, each constitute suitable locations adapted to receive, opposite the projections 4a, 4b . . . 4p . . . . a correspondingly profiled blade root. In FIGS. 1 and 2, reference numerals 8 and 9 have been used to indicate a rotor blade and its root, respectively, and reference numeral 15 to indicate a stator blade. These blades are advantageously made of titanium.

In each of the annular grooves 6a, 6b . . . 6p . . . there is located a ring 10a, 10b . . . 10p . . . of fibrous material wound circumferentially, ater the manner of a hoop, around the metal bars 3. The radial thickness e of a ring such as that 10p, measured from the bottom of the groove 5p, will advantageously be less than or equal to the radial height h of the contiguous projections 4p measured between the base of said projection and the base of a groove such as that 7a formed therein.

As shown in FIG. 1, the length, measured in a direction parallel with the axis of the drum 2, of each of the projections 4a, 4b . . . 4p . . . is greater than that of the blade root 9 fitted in the groove (such as 7a) formed in said projection. This particular feature, associated with the earlier one, makes it possible to fit spacers 11 each of which has a root 12 with an identical profile with that of the roots 9 of the blade 8. Each spacer root 12 has two axially spaced end portions which can be fitted in the grooves (for example the grooves 7a) of two successive projections (such as those 4a, 4b) in one and the same bar and abut against the roots 9 of the blades 8 respectively fitted in said grooves. Thus, each spacer 11, in the region of a ring such as that 10b, of fibrous material, straddles the depression comprised between said projections.

Each spacer 11, at its radially outer face, exhibits labyrinth partitions 13 designed to co-operate in sealing fashion with a stator ring 14 which, at their internal radius, links together the stator blades 15.

The turbo machine is assembled in a conventional manner. If the stator is made up of a series of one-piece rings which already carry a ring of stator blades 15, then the assembly operation is carried out in sections. For example, one starts by fitting the rotor blades 8 of a stage, then the spacers 11 separating this stage from the next, then a ring of stator blades 15, then the rotor blades 8 of the next stage, and so on. In the case where the stator is split into two parts or half-shells, at an axial split plane, the rotor can be completely equipped with all its blades 8 before assembling in the stator.

In operation, the adhesion of the bars 3 to the drum 2 is sufficient to produce entrainment of these latter into rotational motion along with the drum. The tear-out forces acting upon the metal bars due to the centrifugal force, are withstood by the rings 10a, 10b . . . 10p . . . which act as hoops.

It will be observed that the most important part of the support structure 1 (drum 2 and rings 10a, 10b, 10p . . . ) is made of high-strength, low-weight fibrous material. The design of the blade root and its location, however, remains conventional and is facilitated by the use of metal bars 3 which make it possible to overcome the drawbacks inherent in the use of fibrous materials. It will be observed, too, that the relative increase in weight of the structure due to the presence of the metal bars, is very much restricted by reason of the multiple depressions, grooves and recesses which are formed in said bars.

It goes without saying that the embodiment described is purely an example and is open to modification, in particular by the substitution of equivalent techniques, without in so doing departing from the scope of the invention.

Claims

We claim:

1. A support structure for turbo-machine rotor blades comprising, in combination, a hollow drum of fibrous material, a plurality of blade-carrier bars of metal arranged side by side on the external surface of said drum of fibrous material and extending each in the axial direction thereof, and at least one ring of fibrous material circumferentially arranged in hoop fashion around said metal bars to retain said bars on said drum.

2. A structure according to claim 1 in which said metal bar, in longitudinal cross-section, exhibits a crenellated configuration comprising at least one projection alternating with at least one radially outwardly opening depression extending in the circumferential direction, the corresponding depressions formed in said successive bars being disposed in circumferential registering relation to constitute at least one annular groove used to receive one such ring.

3. A structure according to claim 2 in which each metal bar is formed, on its external face, with at least one axially profiled groove shallower than said depression and constituting, in at least one of the projections of said crenellated configuration, a location designed to receive a blade root profiled in a corresponding manner.

4. A structure according to claim 3 in which the radial thickness of said ring of fibrous material, measured from the bottom of said depression, is at most equal to the radial height of the contiguous projection, measured between the base of said projection and the bottom of the groove formed therein.

5. A structure according to claim 4 in which the length of a projection, measured in a direction parallel with the drum axis, is greater than that of the blade root fitted in the groove formed in said projection; and in which said structure further comprises a plurality of spacers each with a root having a profile identical with said blade roots, said spacer root presenting two axially spaced end portions which respectively penetrate into the grooves in two successive projections in one and the same bar and abut against the roots of the blades respectively fitted in said grooves, in such a fashion that said spacer, in the region of said ring of fibrous material, straddles the depression defined between said projections.

6. A structure according to claim 5 in which said spacers, on their radially outer face carry labyrinth partitions designed to cooperate, in sealing relationship, with a structure fixed to the stator of the turbo-machine.

7. A structure according to claim 2 in which said projections of the metal bars are partially recessed.

8. A structure according to claim 1 in which said metal bars are glued to said drum of fibrous material.