Supporting Structure For The Blades Of Turbomachines

Abstract

In and for a fluid handling turbomachine having a relatively rotatable bld stator and rotor, a blade supporting structure comprising at least one corrugated annular element coaxial with the axis of the machine and perforated with openings in each of which a blade is fitted or embedded at one of its ends in order that the blade body is disposed obliquely in relation to the general direction of the corrugations in said corrugated element.

Description

This invention relates to a supporting structure for blades, for example, stator blades, in a fluid handling machine having a relatively rotatable stator and rotor, hereinafter referred to as a turbomachine, such as a compressor, a turbine or a pump.

A structure of this kind is often designed to withstand the key stresses, in particular bending, to which the machine is subjected and must, consequently, have a high stiffness.

Known structures employed for this purpose generally comprise an external structure made up, for example, of a set of cylindrical or frusto-conical casings assembled together axially, or again two half-shells joined to one another along an axial plane. The stator blades are fixed, at one of their ends, to said external structure, in order to form one or more successive blade rows. It is often advantageous, where the attainment of rigidity in the assembly is concerned, to make this a rigid attachment, for example by effecting the same by brazing or welding, so that it consequently represents an embedded or restrained attachment. Equally, it is possible to provide an internal structure to which the blades are fixed by their other ends.

Because of their stiffness, the supporting structures thus far known exhibit the drawback, in particular in the case where the blades are fixed to them in embedded fashion, that they do not provide adequate damping of the vibrations to which the blades are subjected in operation and this makes for increased risk of fatigue failure on the part of the blades. These structures are, furthermore, relatively heavy and this is a particular drawback where the turbomachine is designed for part of a gas-turbine power plant for aviation applications.

The object of the invention is simultaneously to overcome these two drawbacks.

In accordance with the invention, therefore, a blade-supporting structure is designed to comprise at least one corrugated or undulating annular element disposed coaxially relative to the axis of the machine, said element being formed with openings in which each of the blades is fitted at one of its ends, each of said openings extending in a direction oblique to the general directions of the folds or corrugations in said corrugated element and passing through at least two successive corrugations. Preferably, said corrugated element will be located between two skins or liners, so as to form the core of a sandwich structure.

This structure, in the application with which the invention is concerned, has the essential advantage of combining two apparently contradictory qualities, namely a high structural rigidity, thus enabling the supporting structure which it forms to withstand at least some of the main stresses to which the machine is subjected, and, on the other hand, a local flexibility which makes it possible to damp the vibrations developing in the blades which are fixed to said structure. This structure is, furthermore, much lighter than the conventional supporting structures whilst having the same or even better stiffness.

The corrugated element doing duty as the core of the structure can be assembled so that the general direction of its folds or corrugations is substantially parallel to the axis of the turbomachine, this, in particular, making for high transverse stiffness. Equally, however, it can be assembled in such a manner, and in particular in the case where the supporting structure does not have to withstand any substantial bending stresses, that the general direction of its folds or corrugations is substantially circumferential.

In accordance with one advantageous embodiment, the core of the sandwich structure may comprise at least two generally concentric corrugated elements, whose folds or corrugations extend either in the same direction (advantageously with different or with a certain difference in phase), or in two mutually perpendicular directions. In this manner, simultaneously both the stiffness of the supporting structure and its capacity to damp blade vibrations, are improved.

In accordance with another arrangement of the invention, applicable in particular to situations where considerations of weight are of relatively minor importance, the supporting sandwich structure can be fixed to the interior of a conventional rigid external housing casing.

The description which now follows in relation to the accompanying drawing will indicate how the invention may be carried into practice.

IN THE DRAWINGS:

FIG. 1 is a schematic view, in section on an axial plane, of a part of the stator of a turbomachine comprising a stator blade supporting structure in accordance with the invention;

FIGS. 2 to 11 are schematic views relating to different embodiments of said supporting structure or to its assembly;

FIGS. 1a, 2a and 5a are sectional views on the lines Ia-Ia, IIa-IIa and Va-Va respectively, of the structures respectively illustrated in FIGS. 1, 2 and 5;

FIGS. 12, 13 and 14 are explanatory diagrams relating to the vibratory phenomena occurring in the turbomachine during operation.

In FIGS. 1 and 1a, part of the stator of a turbomachine, such as an axial-flow compressor for a turbojet engine, has been shown, and indeed, more specifically, a supporting structure for a row of stator blades 1. This structure comprises an external casing section 2 and a internal casing section 3 each constituted, in part at least, by a body of sandwich structure. Each of these sections comprises an annular corrugated element 2a or 3a forming the core, between two "skins" 3b, 3c or 3b, 3c. In this example, the general direction of the folds or corrugations in the elements 2a and 3a is substantially circumferential.

In order to enable an external casing section 2 to be assembled to the next adjacent casing (not shown), there is fixed to each end of the casing section, for example by welding and after previous local pinching of the sandwich structure, a ring 4 formed with a groove 4a or with a tongue so that sealed attachment to an adjacent complementary ring, belonging to the next casing section, can be effected.

The sandwich structure of the internal casings 3 is likewise pinched at its edges and bent in order to enable the attachment, for example by welding or brazing, of sealing rings 5. These latter operate in a manner known per se with labyrinth arrangements carried by the rotor of the machine and shown in FIG. 11.

The external casing section 2 and the internal casing section 3 are punched to fit the shape and setting angle of the blades 1. Thus, elongated openings are formed each of which extends lengthwise in a direction oblique to the general direction of the corrugations in the corrugated elements 2a and 3a and passes through or across at least two successive corrugations. In these elongated openings the respective ends of the blades are fitted either by simply press-fitting them in position, or by securing them by some other method such as welding, brazing, diffusion or bonding. FIGs. 2 and 2a relate to a variant embodiment in accordance with which the general direction of the folds or corrugations in the corrugated elements 2a, 3a, is substantially parallel to the axis of the turbomachine. In addition, the rings 4 of FIG. 1 are replaced by flanges 6 attached, for example by welding, to the two previously pinched ends of the casing section 2. The adjacent flanges of two successive casing sections are advantageously assembled together by bolts.

FIG. 3 relates to a variant embodiment in accordance with which the external supporting structure comprises a plurality of casing sections 2, cylindrical or frusto-conical in form, assembled together axially. At least at one of its ends, the structure terminates in an attached flange 7 similar (with the exception of a shoulder 7a ) to the flanges 6 described in respect of FIG. 2. The fixing together of the casing sections 2, on the other hand, is effected by flanges 8 which are produced by pinching and folding the sandwich structure itself, said flanges being bolted together at 9.

FIG. 4 illustrates a variant embodiment which differs from the arrangement shown in FIG. 1 simply by the fact that the tongued and grooved rings 4 are replaced by rings 10 with interlocking teeth 11 so that the casing sections are centered and prevented from rotating in relation to one another.

FIGS. 5 and 5a relate to a variant embodiment of the arrangement shown in FIGS. 2 and 2a, in accordance with which the folds or corrugations in the corrugated elements 2a and 3a extend respectively in circumferential and axial directions. FIG. 5 likewise illustrates the fixing together of the successive flanges, by bolts 12.

FIGS. 6 and 7 relate to variant embodiments of the invention in which the core of the sandwich structure is made up of at least two concentric corrugated annular elements 12a, 22a, separated from one another by an intermediate "skin" 2d. In accordance with the embodiment shown in FIG. 6, the folds or corrugations in said elements extend in two mutually perpendicular directions, namely circumferentially in the case of the element 12a and axially in the case of the element 22a. In the embodiment shown in FIG. 7, these folds extend in the same direction, for example circumferentially. In this case, the spacing or the phase of the corrugations 12a will advantageously be made different to that of the corrugations 22a, this increasing the transverse rigidity of the supporting structure assembly.

FIG. 8 illustrates a variant embodiment of the invention in accordance with which the core of the sandwich structure comprises three concentric corrugated annular elements 102a 112a, 122a, separated from one another by intermediate skins 2e, 2f. As in the case of FIG. 7, the spacing of the corrugations 112a differs from that of those 102a and 122a, and these latter can themselves be so arranged in relation to one another as to give a certain difference in phase which is beneficial in increasing the stiffness of the supporting structure assembly.

FIG. 9 relates to a variant embodiment of the invention in accordance with which the corrugations of the element 2a, instead of being simple as in the preceding cases, have a complex periodic profile.

FIGS. 10 and 11 relate to two variant embodiments of the invention in accordance with which the supporting structures 2 (sandwich structures), for the stator blades, are fixed to the interior of a conventional rigid housing constituted, for example, by a stack of rings such as those marked 20.

In accordance with FIG. 10, the supporting structures 2 present flanges 21, 22 fixed by bolts 23 to the housing rings 20.

In accordance with FIG. 11, the supporting structures 2 are fixed to the housing on the one hand in the circumferential direction by a system of splines 24, and on the other hand, in the axial direction, by the axial stacking of said structures and the fitting of retainer rings 25. This figure also shows the relative arrangement of two rows of stator blades 1 and a row of rotor blades 26 carried by a disc 27. Assembled on the latter there are labyrinth arrangements 28 cooperating with the sealing rings 5.

FIGS. 12, 13 and 14 provide a highly schematic illustration of the vibratory phenomena to which reference has been made hereinbefore.

As those skilled in the art will realize, the stator blades 1, exposed to vibrations of aerodynamic nature in the fluid flowing through the turbomachine, themselves experience mechanical vibrations for example in the fundamental mode 1a or at a harmonic, for example the second harmonic 1b. The amplitudes of these vibrations, illustrated in FIG. 12, have been exaggerated simply in order to clarify the drawing. As FIGS. 13 and 14 show, the elongations e are along the large axis B--B of the blade profile.

The blades 1 are embedded at their respective ends in the supporting structures 2, 3, namely the sandwich structures described hereinbefore. FIG. 13 corresponds to the case in which the corrugations in the material are axially disposed; this material then has a high radial rigidity and, by contrast, a certain degree of circumferential flexibility. FIG. 14 relates to the case in which the corrugations in the material extend circumferentially; its rigidity and flexibility are then respectively circumferential and axial. In both cases and by virtue of the substantially oblique disposition of the blades 1 in relation to the axis of the turbomachine, there is at least one component x or y, of the vibratory movement, in respect of which the restrained end of the blade cooperates with an elastic structure constituted by corrugated element 2a. GIven appropriate dimensioning and assembly of said element, it can be arranged that its resonance frequency is at all times far below that of the blade with the result that, as those skilled in the art will appreciate, the vibrations of the latter damped.

In the case where the sandwich structure utilized has two mutually perpendicular corrugation directions as shown for example in FIG. 6, or again in the case where the directions of the corrugations in external and internal supporting structures 2 and 3 respectively, are at right-angles to one another (as shown for example in FIG. 5), the vibration-damping effect just referred to is still more pronounced.

The main stresses to which the turbomachine is subjected being generally axial and radial, it may be a useful feature to use for the external supporting structure a sandwich material incorporating at least one element with axial corrugations, as shown in FIGS. 2 and 6, at any rate in the case where it is necessary to take into account the internal arrangement of the corrugations in order to achieve a stiff stator assembly. On the other hand, where said stiffness is provided anyway by a conventional external casing, as shown in FIGS. 10 and 11, the choice of the type of corrugations depends essentially upon its anti-vibration properties.

It will be apparent that the embodiments described are open to modification in various ways without departing from the scope of the invention as defined in the appended claims. Thus, in particular, the stator blades supporting structures which have been illustrated in the form of casing sections designed for axial assembly, could be replaced by half-shells or shell segments assembled together along axial lines.

Claims

We claim:

1. A turbomachine comprising at least one corrugated annular support element which extends coaxially with the axis of the machine, said corrugated element being perforated with a plurality of elongated openings each of which extends lengthwise in a direction oblique to the general direction of the corrugations in said corrugated element and passes through at least two successive corrugations, and a plurality of blades each having one of its ends shaped to and fixedly fitted in a corresponding elongated opening and secured to a plurality of said corrugations.

2. A turbomachine according to claim 1 wherein the general direction of the corrugations in the corrugated element is substantially parallel to the axis of the machine.

3. A turbomachine according to claim 1 wherein the general direction of the corrugations in the corrugated element is substantially circumferential.

4. A turbomachine according to claim 1 further comprising two skins between which said corrugated element is located, whereby to form a sandwich structure.

5. A turbomachine according to claim 1 comprising two corrugated annular elements arranged in radially spaced concentric coaxial relation to the axis of the machine, each such element being perforated with a plurality of elongated openings, each opening in a corrugated element extending lengthwise in a direction oblique to the general direction of the corrugations in said corrugated element and passing through at least two corrugations in said element, each opening in one of said corrugated elements being in radial registration with an opening in the other corrugated element; and a plurality of blades each having its opposite ends fitting in a corresponding pair of radially spaced registering openings.

6. A turbomachine according to claim 5 wherein the corrugations in the two concentric corrugated elements extend in the same general direction.

7. A turbomachine according to claim 6 wherein the peaks of said corrugations in each of said elements are generally uniformly spaced apart and the spacing of the corrugations of the two elements is different.

8. A turbomachine according to claim 6 wherein the corrugations in the two respective corrugated elements are each generally of the shape of a regular sinuous curve and the curves of the two elements are out of phase.

9. A turbomachine according to claim 5 wherein the corrections in the two corrugated elements respectively extend at right angles to one another.

10. A turbomachine according to claim 1 wherein said annular corrugated element comprises at least two annular sections arranged in axial succeeding relation.

11. A turbomachine according to claim 1 further comprising a rigid external housing, and means fixing said annular corrugated element to the interior of said external housing.

12. A turbomachine according to claim 1 comprising at least two corrugated annular elements arranged in radially adjacent concentric coaxial relation to the axis of the machine, each such element being perforated with a plurality of elongated openings, each opening in a corrugated element extending lengthwise in a direction oblique to the general direction of the corrugations in said corrugated element and passing through at least two corrugations in said element, each opening in one of said corrugated elements being in radial registration with an opening in at least one other corrugated element; and a plurality of blades each having one of its ends fitting into at least two corresponding registering openings in such radially adjacent corrugated elements.

13. A turbomachine according to claim 12 wherein the corrugations in the two concentric corrugated elements extend in the same general direction.

14. A turbomachine according to claim 13 wherein the peaks of said corrugations in each of said elements are generally uniformly spaced apart and the spacing of the corrugations in the two elements is different.

15. A turbomachine according to claim 13 wherein the corrugations in the two respective corrugated elements are each generally of the shape of a regular sinuous curve and the curves of the two elements are out of phase.

16. A turbomachine according to claim 12 wherein the corrugations in the two corrugated elements respectively extend at right angles to one another.