CA2832772A1

CA2832772A1 - Stator blades of an axial turbocompressor and manufacturing process

Info

Publication number: CA2832772A1
Application number: CA2832772A
Authority: CA
Inventors: Xavier Charles
Original assignee: Techspace Aero SA
Current assignee: Safran Aero Boosters SA
Priority date: 2012-11-21
Filing date: 2013-11-13
Publication date: 2014-05-21
Anticipated expiration: 2033-11-13
Also published as: RU2013151836A; CN103836002A; RU2568353C2; US20140294574A1; EP2735706A1; EP2735706B1; EP2735706B8; CA2832772C

Abstract

A stator of an axial turbomachine compressor comprising an external shell with a row of openings and an internal annular groove designed to hold an annular layer of abradable material forming a strip is described. The stator further includes a row of stator blades adjacent to the row of openings. The stator blades comprise platforms with surfaces matching the openings, the said platforms being fitted in the openings so as to mask them. Weld beads fix the platforms at their junctions with the openings. On one side of the row of stator blades a portion of the weld bead is situated axially in the internal annular groove. Methods of manufacturing the stator are also described.

Description

STATOR BLADES OF AN AXIAL TURBOCOMPRESSOR AND MANUFACTURING
PROCESS
Field [0001] The invention relates to the stator of an axial turbomachine. An axial turbomachine comprising a compressor and a turbine fitted with stators is disclosed, as well as a manufacturing process of an axial turbomachine stator.
Prior art [0002] In order to achieve a high compression ratio, an axial turbomachine compressor commonly has several stages. A stage essentially consists of a row of rotor blades followed by a row of stator blades. The cumulative lengths of these stages dictate the length of the compressor.

[0003] Patent FR 2404102 Al discloses a fixed ring of blades of an axial turbomachine. The ring has an external shell having openings arranged in an annular row. The blades include external platforms which are welded in the openings of the external shell. The external shell comprises an annular cavity filled with abradable material, the said cavity being located close to the apertures and platforms. The cross section of the shell thus has a section of variable thickness close to the welded section between the shell and the platforms. The variable thickness of material in the vicinity of the weld bead generates an inhomogeneity which can cause problems in carrying out the welding.

[0004] Patent FR2958323 A discloses a low pressure compressor of a turbomachine comprising several bladed stator stages. A stator stage has an external shell in which aligned openings are formed. The blades have platforms which mate with the contours of the internal edges of the openings in the external shell. A weld at their junction is used to fix the blades through their platforms to the external shell. The size of the platforms ensures the bodies of the blades are not exposed during the welding operation.

[0005] However, to achieve optimum fixing by the welds, spatial and geometric constraints must be observed. Among other things, the weld must be arranged to be in a homogeneous medium. This may result in the welding having to be carried out away from bends and preferably through parts having constant thicknesses. To overcome these constraints, the curved region must be distanced from the blades, which leads to a lengthening of the blade platforms, and thus of the compressor.

[0006] In the context of a turbomachine, the low-pressure compressor occupies much of the space. Extending it has an impact on the size and design of the turbomachine housing. The weight of the latter is increased. When such a turbomachine is used as a means of propelling an aeroplane, the onboard weight is increased, as is that of the equipment needed for its support. The primary energy requirements and the wing surface area must be modified.

[0007] Patent EP2202388 Al discloses a turbomachine stator assembled with overlap. Two cylindrical portions of the stator flanges overlap at the stator blades. This method of assembly is based on fixing using blind bolts.
Although reducing the axial length, this solution increases the radial diameter. Moreover, this solution is not suitable for welding as visual inspection of both sides of the weld is not possible. This configuration does not lend itself to electron beam welding due to the presence of the blade in the weld.
Summary The technical problem [0008] The invention aims to solve at least one of the problems presented by the prior art. In an aspect, the invention aims to lighten the turbomachine. In another aspect, the invention aims to make the turbomachine more compact.

The invention can also improve the performance of the engine and more particularly its compressor.
Technical solution [0009] The disclosure relates to a stator of an axial turbomachine comprising an external shell with an annular array of openings and at least one internal annular groove designed to hold an annular layer of abradable material, a row of stator blades with platforms located in the openings and fixed by one or more weld beads between the platforms and the openings, wherein the row of openings and the internal groove partially overlap so that part of the weld bead(s) is/are positioned axially in the internal groove.

[0010] According to an embodiment disclosed herein, the blade platforms form a lip defining the internal groove.

[0011] According to another embodiment, the platforms extend over a portion of the bottom of the internal groove.

[0012] According to yet another embodiment, the openings pass through the shell and the groove.

[0013] According to yet another embodiment, the platforms have the general shape of a parallelogram, preferably rectangular, with an upstream side and a downstream side, that part of the weld bead(s) positioned axially in the internal groove extending along one of the upstream and downstream sides of the parallelogram.

[0014] According to yet another embodiment, the openings extend along a main direction predominantly oriented along the stator axis, the said main direction preferentially forming an angle less than 450, more preferably less than 30 even more preferably less than 15 with the said axis.

[0015] According to yet another embodiment, the external shell preferably comprises a single-piece circular wall with a first section comprising the internal groove and a second section comprising the row of openings and blades, the said wall forming a shoulder between the said sections.

[0016] According to yet another embodiment, the platforms have surfaces additional to the openings.

[0017] According to yet another embodiment, the external shell and/or the stator blade platforms have a generally constant thickness.

[0018] According to yet another embodiment, the blade platforms are essentially embedded in the openings of the external shell.

[0019] According to yet another embodiment, the section of the internal groove extends along a main direction substantially corresponding to the stator axis, and has a substantially constant depth greater than 1.00 mm, preferably greater than 2.00 mm, even more preferably greater than 3.00 mm.

[0020] According to yet another embodiment, the internal annular groove has two shoulders, with at least one of the two shoulders inclined with respect to the perpendicular to the bottom of the internal annular groove.

[0021] According to yet another embodiment, the stator has blades attached to the external shell by means other than welding.

[0022] According to yet another embodiment, the stator is a compressor stator, preferably a low-pressure compressor.

[0023] By low-pressure compressor is meant a compressor arranged downstream of the turbofan. Its inlet pressure is similar to the atmospheric pressure at altitudes encountered during aircraft manoeuvres.

[0024] According to yet another embodiment, the internal annular groove has a length greater than 5.00 mm, preferably greater than 10.00 mm, preferably greater than 20.00 mm. This length is measured along the stator axis.

[0025] According to yet another embodiment, the materials of at least one platform and of the shell are grades of alloy substantially similar or compatible for being welded to each other.

[0026] According to yet another embodiment, the shell has two internal annular grooves, one being located upstream and the other downstream of the openings, the first part of the weld bead(s) being located in the upstream groove and a second part of the weld bead(s) being located in the downstream groove.

[0027] According to yet another embodiment, the platforms have a thickness greater than that of the external shell at the openings.

[0028] According to yet another embodiment, the weld has a break in the weld on the edges of the annular groove in the external shell [0029] According to yet another embodiment, the platform has a portion extending along the outer surface of the external shell and which is welded to the said face axially in the internal groove.

[0030] The invention also relates to a turbomachine comprising at least one compressor with at least one stator and at least a turbine with at least one stator, wherein the or at least one of the compressor and/or turbine stators is in accordance with the invention.

[0031] The invention also relates to a method of manufacturing a stator in accordance with the invention, comprising the following steps: (a) provision of the external shell and blades, (b) locating and welding the platforms in the openings of the external shell, (c) fixing the layer of abradable material in the internal groove.

[0032] According to an embodiment, the method comprises the following stage between steps (b) and (c): machining the internal surface of the shell to form the internal groove.

[0033] The invention can shorten a turbomachine acting as a compressor. Each stator stage combined with a strip of abradable material saves a few millimetres. One centimetre can be saved across the whole of a low-pressure compressor.

[0034] The invention can also provide an aerodynamic advantage since the welds on the stream side are covered by the abradable material. Indeed, some of the irregularities that the welds have in the stream are now covered by the abradable material. This is achieved by means of an extension of the weld, as well as constructing a platform and an external shell with a step.

[0035] The invention can facilitate the design of a turbomachine and does not require there to be unused spaces between the fixed and moving blade rows. If necessary, these rows can be moved closer to each other in order to improve flow management and thus optimize engine performance.

[0036] The manufacture of such a stator can also be facilitated. Accessibility to the welds is improved because in places they are distanced from the blades, and located in an open throat. The dimensions of the groove enable welds to be made which cause some rise in temperature.
Short description of the diagrams [0037] Figure 1 shows a section through an axial turbomachine in accordance with an aspect of the invention.

[0038] Figure 2 shows an axial turbomachine compressor in accordance with an aspect of the invention.

[0039] Figure 3 shows a simplified view of a compressor stator section according to an aspect of the invention.

[0040] Figure 4 shows a stator manufacturing step in a first implementation process aspect of the invention.

[0041] Figure 5 shows a first stator manufacturing step in a second implementation process aspect of the invention.

[0042] Figure 6 shows a second stator manufacturing step in a second implementation process aspect of the invention.
Description of the embodiments [0043] In the following description, the terms interior and exterior refer to a position relative to the axis of rotation of an axial turbomachine. The same applies to the terms internal and external. Lengths are measured along the axis of rotation of the turbomachine, heights radially and widths at right angles to the heights.

[0044] Figure 1 shows an axial turbomachine. In this case it is a double-flow turbojet. The turbojet 2 comprises a first compression stage, a so-called low-pressure compressor 8, a second compression stage, a so-called high-pressure compressor 10, a combustion chamber 12 and one or more turbine stages 14. In operation, the mechanical power of the turbine 14 is transmitted through the central shaft to the rotor 4 and drives the two compressors 8 and 10. Reduction mechanisms may increase the speed of rotation transmitted to the compressors. Further, different, turbine stages can be connected to the compressor stages through concentric shafts. These latter comprise several rotor blade rows associated with stator blade rows.
The rotation of the rotor thus generates a flow of air and progressively compresses it up to the inlet of the combustion chamber 12. An inlet fan commonly called a turbofan 6 is coupled to the rotor 4 and generates an airflow which is divided into a primary flow 16 passing through the different stages of the turbomachine mentioned above and a secondary flow 18 passing through an annular passage (shown in part) running the length of the machine which then rejoins the main flow at the turbine outlet.

[0045] Figure 2 is a sectional view of a low-pressure compressor of an axial turbomachine such as that in Figure 1. The diagram shows a portion of the inlet fan or turbofan 6 and the flow splitter nose 20 separating the primary flow 16 and the secondary flow 18. The rotor 4 includes several rows of rotor blades 22. The housing comprises several stators 24 associated with rotor blade rows 22. Each stator comprises a row of stator blades 26. Each pair of rotor and associated stator blade rows forms one compressor stage of the compressor 8.

[0046] Figure 3 illustrates part of the stator 24 of the turbomachine. The stator 24 forms a ring having as its axis the axis of symmetry of rotation of the turbomachine. It comprises an external shell 28 in which a stator blade 26 is fixed. The external shell 28 has an internal surface to channel the primary flow. Its internal surface is a surface of revolution. It is substantially cylindrical and shows a variation in diameter, for example a reduction in diameter in the direction of flow. The shell has a body of revolution developed from a profile of revolution. The profile of revolution has a first part 30 and a second part 32 connected by a curved region 34. The first part 30 and the second part 32 can be interleaved at the curved region 34.

[0047] The first part 30 may be an upstream portion. It has an internal annular groove in which there is an annular layer 36 of abradable material. This material is able to be eroded by friction when a rotor blade tip 22 comes into contact with it. The layer of abradable material 36 may form an annular band of substantially constant thickness, in order to streamline and simplify its implementation. The internal surface of the layer of abradable material 36 is flush with the internal surface of the platform of the stator blade 26. This configuration optimises the flow and creates no surface discontinuity to disrupt the flow.

[0048] The length of the layer of abradable material 36 is dictated by the length of the tip of the rotor blade 22 opposite it. Upstream and downstream borders can be added to this length to take turbomachine service variations into account. These lengths are measured along the axis of rotation of the turbomachine. The length of the layer of abradable material 36 may be considered as a fixed datum of the turbomachine's geometry.

[0049] The second part 32 may be a downstream portion. It has an external annular groove forming an annular recess. This recess will lighten the external shell.

[0050] The second part 32 has an opening through the external shell 28. The stator blade has a platform 38 with a surface matching the opening so as to mask the latter. The platform 38 is fixed at its junction with the opening, preferably at its edges, preferably along its entire margin.

[0051] Fixing is carried out by welding, preferably by seam welding, preferably continuously. The weld bead is formed over the entire periphery of the opening so as to create a seal. Welding forms a weld bead with an upstream part 40 and a downstream part 42, and side parts (not shown). This weld can be achieved by electron beam welding.

[0052] Advantageously, the second part 32 comprises a row of openings holding a row of stator blade platforms. Preferably, the external edges of the platform 38 extend the length of the internal edges of the openings. Preferably, the openings are similarly shaped to the platforms 38.

[0053] The upstream part of the weld 40 is located under the layer of abradable material 36. At this location, the shape of the body of the external shell 28 is substantially straight. The upstream part of the weld 40 is positioned so as to overcome any geometric constraints. The position of the weld can no longer be located between the curved region 34 and the body of the stator blade.
Thus the constraints imposed to extend the platform between the curved region 34 and the blade body no longer exist. In addition, the length of the upstream portion of the weld 40 is less than the length of the layer of abradable material 36 and the presence of the upstream part 40 of the weld no longer affects the length of the external shell 28.

[0054] Thus, compared to a stator known by prior art, that part of the platform between the stator blade body and the curved region 34 can be shortened.
This reduction in axial length affects the external shell 28. For this, all the welded stator blades on one stage must have their upstream part 40 of their welds arranged in the same groove. A substantial reduction in length can be achieved at each upstream or downstream weld located under a layer of abradable material 28. This reduction can be greater than 2.00 mm, preferably greater than 3.00 mm. Over a compressor comprising several stages of compression, for example, three stages of compression, the invention might yield a reduction of more than 10.00 mm. The engine housing can also be shortened. These reductions enable the turbomachine to be both lightened and made stronger.

[0055] The teachings of the invention can also be applied to a turbomachine turbine stator. A weld on a stator blade platform can be shifted axially so as to remove it from a region having constraints. Thus, a significant reduction in length can be attained by applying the teachings of the invention to both the turbomachine's compressor(s) and turbine(s). In this case, the abradable material may be a material with a honeycomb structure.

[0056] Various processes enable the stator 24 to be implemented.

[0057] Figure 4 shows an intermediate stator 24 implementation step in a first fabrication process. The stator 24 is formed from an external shell with openings in which the platforms are housed. The shell 28 and the platforms 38 show their finished dimensions.

[0058] A weld bead is made at the junction between the platforms and the openings of the external shell. The weld bead is basically thin, its thickness being close to that of the external shell 28. It is cheap to produce due to its small cross section. A thickened portion 44 can be added at the platform in the curved region 34. After welding, the thickened portion 44 is machined, for example by turning.

[0059] The first method for fabricating the stator comprises the following steps:
a. manufacture the external shell 28 and the blades 26 to their finished dimensions;
b. locate and weld the platforms 38 in the openings of the external shell 28 so that they are flush with the internal surfaces;
c. weld the platforms 38 to the openings in the external shell.

[0060] Figure 5 shows a first intermediate step in the manufacture of the stator 24 shown in Figure 3. Figure 5 has the same numbering scheme as in previous figures for the same or similar elements, but the numbering is incremented by 100. Specific numbers are used for items specific to this embodiment.

[0061] In this process, the stator is made from rough-finish platforms 138 and a rough-finish blade 126 with a rough-finish external shell 128 having radially thickened portions. They may have equal thicknesses where they join. The rough-finish platforms 138 and the rough-finish blades 126 are fitted into the openings of the rough-finish external shell 128 and are then welded at their junctions. Figure 5 illustrates a rough-finish upstream part 140 and a rough-finish downstream part 142 of the weld bead. The assembly thus obtained is a rough-finish stator 124.

[0062] Figure 6 shows a second intermediate stage of the second stator manufacturing process. The second intermediate step includes machining operations on the rough-finish stator shown in Figure 5. The machining operations may include rough and/or final machining.

[0063] An internal machining pass 102 is carried out on the internal surface of the rough-finish stator 124. It creates an annular groove into which a layer of abradable material may be deposited. Several annular grooves arranged axially can be made to accommodate several annular layers of abradable material. The internal machining 102 extends axially on the rough-finish external shell 128 and on part of the rough-finish platforms 138. It also removes material from the upstream portion 102 of the weld bead.

[0064] One or more external machining passes 104 may be carried out on the outer surface of the rough-finish stator 124. These machining passes enable the stator to be lightened by removing material. Such machining passes can be performed on the rough-finish stator blade platforms 138 as well as in the downstream part 142 of the weld bead.

[0065] The internal and/or external machining passes are advantageously carried out by turning to improve their circularity and cylindricity.

[0066] The second method for fabricating the stator comprises the following steps:
a. manufacture the rough-finish external shell 128 and the rough-finish blades 126 and the rough-finish platforms 138;
b. locate and weld the rough-finish platforms 138 in the openings of the external rough-finish shell 128;
c. carry out internal machining 102 on the internal face of the rough-finish external shell 128, carry out external machining 104 of the external face of the rough-finish external shell 128;
d. fit the layer of abradable material in the internal groove.

[0067] The second manufacturing process has the advantage of welding on a flat surface. This weld will be more homogeneous and therefore more durable.
In addition, welding can change the crystal structure of materials and make them more brittle. This embrittlement, combined with a curved region, can shorten the life of the piece so formed. Thermal and vibratory stress may precipitate mechanical failure. By locating a weld under the strip of abradable material, away from the curved region, the shell becomes more durable.

Claims

1 . Axial turbomachine stator, comprising:
- an external shell with an annular array of openings and at least one internal annular groove designed to hold an annular layer of abradable material, - a row of stator blades with platforms located in the openings and secured by one or more weld beads between the platforms and the openings, wherein the row of openings and the internal groove partially overlap so that a part of the weld bead(s) is/are positioned axially in the internal groove.

2. Stator according to Claim 1, wherein the platforms of the blades form a lip defining the internal groove.

3. Stator according to Claim 1 or 2, wherein the platforms extend over a portion of the bottom of the internal groove.

4. Stator according to any one of Claims 1 to 3, wherein the openings pass through the shell and the internal groove.

5. Stator according to any one of Claims 1 to 4, wherein the platforms have the general shape of a parallelogram with an upstream side and a downstream side, the part of the weld bead(s) positioned axially in the internal groove extend along one of the upstream and downstream sides of the parallelogram.

6. Stator according to any one of Claims 1 to 5, wherein the platforms are rectangular.

7. Stator according to any one of Claims 1 to 5, wherein the openings extend along a main direction predominantly oriented along the axis of the stator.

8. Stator according to Claim 7, wherein the said main direction forms an angle less than 45° with the said axis of the stator.

9. Stator according to Claim 8, wherein the said main direction forms an angle less than 30° with the said axis of the stator.

10. Stator according to Claim 9, wherein the said main direction forms an angle less than 15° with the said axis of the stator.

11. Stator according to any one of Claims 1 to 10, wherein the external shell comprises a single-piece circular wall with a first section comprising the internal groove and a second section comprising the row of openings and blades, the said wall forming a shoulder between the said sections.

12. Stator according to any one of Claims 1 to 11, wherein the platforms the have surfaces additional to the openings.

13. Stator according to any one of Claims 1 to 12, wherein the external shell and/or the platforms of the stator blades are generally of constant thickness.

14. Stator according to any one of Claims 1 to 13, wherein the platforms of the blades are substantially embedded in the openings of the external shell.

15. Stator according to any one of Claims 1 to 14, wherein the internal section of the groove extends in a main direction corresponding substantially to the axis of the stator, and has a substantially constant depth greater than 1.00 mm.

16. Stator according to Claim 15, wherein the internal section of the groove has a substantially constant depth greater than 2.00 mm.

17. Stator according to Claim 16, wherein the internal section of the groove has a substantially constant depth greater than 3.00 mm.

18. Stator according to any one of Claims 1 to 17, wherein the internal annular groove comprises two shoulders, at least one of the two shoulders is inclined relative to the perpendicular to the bottom of the internal annular groove.

19. Turbomachine comprising at least a compressor with at least one stator and at least one turbine with at least one stator, wherein the or at least one of the compressor and/or turbine stators is in accordance with one any one of Claims to 18.

20. A method of manufacturing a stator according to any one of Claims 1 to 18, comprising the following steps:
(a) make the external shell and the blades;
(b) locate and weld the platforms in the openings of the external shell;
(c) fit the layer of abradable material in the internal groove.

21. A method of manufacturing a stator according to Claim 20, wherein the method includes the following step between steps (b) and (c):
machine the inner surface of the shell to form the inner groove.