CA2724800A1

CA2724800A1 - Two-part shroud or shroud section for a stator stage with vanes of an axial compressor

Info

Publication number: CA2724800A1
Application number: CA2724800A
Authority: CA
Inventors: Andre Lhoest; Christophe Remy
Original assignee: Techspace Aero SA
Current assignee: Safran Aero Boosters SA
Priority date: 2009-12-14
Filing date: 2010-12-10
Publication date: 2011-06-14
Anticipated expiration: 2030-12-10
Also published as: US20110142651A1; CA2724800C; EP2336572A1; EP2336572B1

Abstract

The invention relates to a shroud or shroud section (8) for a stator stage with vanes of an axial compressor. The shroud or shroud section (8) is made of composite material and is built in two parts (12, 14), each comprising a series of notches (16, 18) corresponding to a half of the profile of the vanes (4), so as to form apertures that follow the shape of the vanes when the two parts are assembled. The two parts also comprise mutual fastening means (20, 21) adapted to ensure their assembly.

Description

TWO-PART SHROUD OR SHROUD SECTION FOR A STATOR STAGE WITH
VANES OF AN AXIAL COMPRESSOR

Technical field [0001] The invention relates to a shroud for a stator with vanes of an axial compressor, more particularly to an internal shroud of a stator, more particularly still, to an internal shroud made of composite material. Such compressors are typically present in turbojet engines, jet prop engines, and gas generators.

Prior art

[0002] An axial compressor typically comprises a series of compression stages, each being constituted of a circumferential arrangement of vanes mounted on their bases on a rotor. A stator serving as a casing surrounds the rotor and the blades. The ends of the rotor blades move in the vicinity of the internal surface of the stator. The fluid, typically air, is thus displaced and compressed according to an annular jet, concentric to the rotation axis of the rotor. The rotor thus comprises several rows of circumferential blades, spaced apart from one another. Rows of stationary vanes are mounted on the stator between the rows of rotor blades for the purpose of rectifying the airflow between two stages of the compressor. These stator vanes conventionally comprise an internal shroud at their ends for the purpose of delimiting the internal envelope of the fluid stream. This shroud conventionally has an annular shape with an outer surface that is shaped specifically for the defining of the flow. The outer surface comprises a series of apertures or holes adapted to receive the inner ends of the vanes which are fixed at their outer ends or bases to the stator. This shroud also ensures that the vanes are affixed to one another in the area of their inner ends. The internal surface of the shroud is lined with a friable material or else more conventionally called "abradable" from the English term. This layer of abradable material is adapted to cooperate by friction with one or several circumferential ribs on the rotor in order to make it somewhat leak-proof. These ribs are more conventionally called knife edges.

[0003] The patent document EP 1 213 484 Al of the same applicant as this application discloses an internal shroud and an external shroud of a compressor stator stage, these shrouds being conventionally made of metal. This document relates to a device for connecting the vanes to the shrouds by means of a band which is inserted in apertures made at each end of the vanes passing through the holes of the shrouds, the band serving as a locking key with respect to the outer and inner surfaces of the external and internal shrouds, respectively.

[0004] As a function of the dimensions and materials used and also to facilitate the assembly, it can be interesting to segment the shroud into several sections. Indeed, in the case of a shroud made of composite material, for example, it can be difficult to inject the resin of the composite material over lengthy pieces, which means that it is interesting to segment the shroud so as to reduce the length of the sections. Segmenting the shroud can also prove to be interesting to compensate for the differential expansions in the area of the vanes themselves and of parts of the stator supporting the vanes. The aerodynamic performance of a segmented composite shroud is diminished for the following reasons:

[0005] The method of manufacture by plastic or resin injection requires the use of a mold to give the final shape. The general shape of a section is an arc of circle whereas the unmolding direction on a surface of the section is axial and not radial. The shroud holes have main axes which correspond to radii starting from the rotation axis of the rotor; these axes are therefore inclined with respect to the unmolding direction. Consequently, the holes have an unnecessarily flared section toward the unmolding direction. The adjustment between the holes of the shroud and the vanes is unnecessarily large and unfavorable from an aerodynamic standpoint. It is indeed desirable for the shroud surface in contact with the fluid stream, particularly in the area of the junction with the vanes, to be as continuous as possible.

[0006] Furthermore, independent of this requirement related to the unmolding, the holes of a segmented composite shroud must be provided to be slightly larger than the section of the vanes which go through them because of the assembly process. Indeed, once a first section is in place, it needs to be pulled up along the vanes in order to leave minimum room for the adjacent end of the section to be set in place next, so the first section can then be pulled down toward its final position. The clearance increase between the holes and the vanes, in particular in the area of the outer surface, is detrimental to the aerodynamics of the stator stage.
The object of the invention is to provide a shroud that overcomes at least one of the aforementioned drawbacks, more particularly to provide a shroud that is easy to mount and has good aerodynamic characteristics.

Summary of the invention

[0007] The invention consists of a shroud or shroud section made of composite material for a stator stage with vanes of an axial compressor, the shroud or shroud section being adapted to receive an end of the vanes, comprising: at least one first curved element with at least one first notch corresponding to a first portion of the contour of the end of the vanes;
at least one second curved element having a generally similar shape as the first curved element with at least a second notch corresponding to a second portion of the contour of the end of the vanes, the first and second notch or notches forming one or several pair(s) of notches; the first and second curved elements being adapted to be arranged axially against one another so as to confine the profile of the end of the vanes in each pair of first and second notches. The second portion of the contour of the end of the vanes preferably corresponds to the rest of the contour which is not concerned with the first portion, so that the first and second notches surround the entirety of the contour of the vanes.

[0008] Such a construction has numerous advantages, mostly from the standpoint of an ease of assembly on the vanes and from the standpoint of aerodynamics of the flow of the fluid stream into the stator.

[0009] Indeed, this modular construction with the pairs of notches forming the apertures of the shroud enables a substantially easier assembly in comparison with a conventional segmented shroud, each section of which being required to be carefully placed in front of the series of vanes to which it must be mounted and must then be pulled up along the vanes in the area of one lateral end in order to leave enough room for the adjacent end of the next section.

[0010] Furthermore, this modular construction makes it possible to use another way of unmolding the segments made of composite material by getting rid of the unavoidable requirement with the segments of a conventional shroud of having to unmold in a direction forming an angle with the main directions of some apertures thus formed. The apertures of each segment of a conventional shroud are indeed different from one another in order to take into account the projection of the vane according to the direction of assembly.
These differences lead to assembly adjustments which are too great, having a detrimental effect on the aerodynamics of the flow.

[0011] Each curved element forming the shroud comprises at least two, preferably three, even more preferably at least four, notches.

[0012] According to an advantageous embodiment of the invention, each of the first and second curved elements comprises an assembly edge in a plane, perpendicular to the main axis of the compressor, the assembly edges being adapted to come into contact with one another during the assembly of the two curved elements, preferably, by becoming closer together in a direction corresponding approximately to the flow direction.

[0013] According to another advantageous embodiment of the invention, the first and/or second portion of the contour of the end of the vanes correspond(s) to approximately half of the profile in the direction of the flow. This measure allows the apertures to take on the shape of the barrel-shaped vanes.

[0014] According to yet another advantageous embodiment of the invention, the first curved element comprises an assembly edge adapted to cooperate by insertion with an assembly edge of the second segment during the assembly of the two curved elements, preferably by becoming closer in a direction corresponding approximately to the direction of the flow.

[0015] According to yet another advantageous embodiment of the invention, the assembly edge of one of the first and second curved elements comprises a groove according to the curved direction and the assembly edge of the other of the first and second curved elements comprises a projecting portion, the groove and the projecting portion being interrupted by the respective notch or notches of the first and second curved elements.

[0016] According to yet another advantageous embodiment of the invention, the shroud is an internal shroud with a U-shaped section with the opening of the U being directed toward the center of the shroud so as to form a recess adapted to receive some abradable material and where the limit between the first and second curved elements is located approximately toward the center of the U.

[0017] According to another advantageous embodiment of the invention, each of the first and second curved elements comprises means for mutual fastening, these means being preferably of the clip-type.

[0018] According to another advantageous embodiment of the invention, the mutual fastening means are such that they cooperate by elastic engagement of surfaces with positive contact when the first and second curved elements move closer together in a direction corresponding approximately to the flow direction.

[0019] According to another advantageous embodiment of the invention, the mutual fastening means comprise several elements projecting over one of the first and second curved elements in a direction corresponding approximately to the direction for moving the first and second curved elements closer together.

[0020] According to another advantageous embodiment of the invention, the mutual fastening means are arranged on the respective assembly edges of the first and second curved elements.

[0021] According to another advantageous embodiment of the invention, each end of the shroud section comprises a section whose shape corresponds to that of the end of the vanes so that the junction between two adjacent sections corresponds to the shape of the vane.

[0022] According to another advantageous embodiment of the invention, each end of the shroud section comprises means for connecting to an adjacent section, these connection means having a positive contact, preferably on both sides of the junction on each of the first and second curved elements.

[0023] According to another advantageous embodiment of the invention, the first and second curved elements are each ring-shaped, preferably closed.

[0024] According to another advantageous embodiment of the invention, one of the first and second curved elements is ring-shaped, preferably closed, and comprises several second curved elements corresponding to sections of the ring and adapted to be arranged successively against the ring-shaped curved element so as to confine, over the entire perimeter of the ring, the shape of the vane roots in each pair of first and second notches.

[0025] The invention also comprises a shroud for a stator stage with vanes of an axial compressor comprising several shroud sections such as described hereinabove.

Brief description of the drawings

[0026] Figure 1 is a partial, cross-sectional view of an axial compressor with, among other things, a shroud according to the invention.

[0027] Figure 2 is a perspective view of a shroud section according to the invention.

[0028] Figure 3 is a perspective view according to another angle of the shroud section according to figure 1 mounted on a row of vanes.

[0029] Figure 4 is a bottom, perspective view of the shroud section of figure 3.
Description of the embodiments

[0030] Figure 1 shows a cross-sectional view of part of an axial compressor, typically of a jet engine or turbine engine. The compressor comprises a rotor 5 rotating about the axis 2. The rotor comprises a series of blades 6 fixed onto its circumference, corresponding to a stator stage.
The flow direction of the fluid to be compressed is shown by the arrow. The casing 3, or the stator, of the compressor comprises a series of vanes 4 fixed at their bases.
This series of vanes constitutes a stator of the fluid stream located between two blade rows of the mobile wheel, the upstream row not being represented. A row of blades of the mobile wheel and the guide vane downstream constitute a stage of the compressor. The inner ends of the vanes 4 are connected to a shroud 8. The shroud has the general shape of a circular ring following the shape of the rotor 5. The shroud 8 thus delimits the lower or internal part of the annular fluid stream passing through the stator. It is kept in place by the vanes and makes the rotor 5 leak-proof. The shroud comprises on its inner surface a layer of abradable material 10. The rotor 5 comprises two circumferential ribs, more commonly called knife edges 9, cooperating with the layer of friable material 10. The abradable material 10 is applied and then machined so as to present a sealing surface 11 cooperating with the knife edges. This material has friction properties with the metal of the knife edges and the ability to disintegrate into fine dust in case of contact with the knife edges when the rotor is in rotation. The knife edges 9 and the surface 11 made of friable material thus constitute a labyrinth seal.
[0031 ] The shroud 8 is constituted of a series of sections shaped in an arc-of-circle such as shown in figure 2. The section shown in figure 2 is constituted of two elements in an arc-of-circle 12 and 14, each forming about a half, in a direction corresponding to that of the axis of the machine, of the shroud section along to a median arc-of-circle.
[0032] The curved element 12 comprises a series of notches 16 adapted to follow the shape of the corresponding end of the vanes. The notches 16 are, in principle, identical, taking into account the fact that all the vanes of a stator stage are generally identical and uniformly distributed on the circumference of the shroud. The notches 16 are such that they correspond to about half of the profile of the vanes, the half being in a general direction corresponding to the flow direction of the fluid, or to the longitudinal direction of the section of a vane. The curved element 12 comprises an outer surface 22 of revolution, corresponding generally to a segment or piece of a cylinder, that is, a surface directed toward the outside of the circle or ring which forms the complete shroud. This surface is the surface delimiting the inner envelope of the fluid stream passing through the stator. It is delimited on one side by a rounded edge 26 and on the other side by an edge 27 crossing through the notches 16 and adapted to come into contact with a corresponding edge 29 of the other curved element 14. This contact edge 27 comprises a groove 28 extending in parallel to the outer surface 22 and below this surface. The groove 28, as the edge 27, is interrupted by the notches 16.

[0033] The curved element 14 opposite the curved element 12 is generally similar. It comprises a series of notches 18 corresponding to the notches 16 of the opposite curved element 12 and adapted to form, when the two curved elements are arranged in an adjacent and corresponding manner, a series of apertures or openings which follow the shape of the vanes.
The shape of the notches 18 thus corresponds to the rest of the section of the vanes, that is, to the portion of the contour of the vane which is not covered by the notch 16 of the opposite curved element 12. As a result, the notches 18 can have a slightly or even substantially different profile than those of the opposite notches 16, as a function of the section of the end of the vane to be surrounded. Similar to the opposite curved element 12, the curved element 14 comprises an outer surface 22, generally cylindrical or ring-shaped, that is, a surface directed toward the outside of the circle or ring which forms the complete shroud. This surface is the surface delimiting the inner envelope of the fluid stream passing through the stator. It is delimited on one side by a rounded edge 24 and on the other side by an edge 29 passing through the notches 18 and adapted to come into contact with the corresponding edge 27 of the opposite curved element 12. This contact edge 29 comprises a tongue 30 or lug extending in parallel to the outer surface 22 and at a lower level of this surface. The tongue 30, as the edge 29, is interrupted by the notches 18.
[0034] The curved element 14 also comprises in the area of its contact edge 29, at a level that is lower than that of the outer surface 22, a series of elastic hooks generally directed toward the opposite curved element 12 during the assembly and adapted to cooperate by flexion followed by a movement for returning to a position close to the initial position with corresponding housings provided in the area of the contact edge 27 of the opposite curved element 12.
These hooks are arranged by pairs with a generally U-shaped profile directed toward the outside and where the ends of the U-shaped legs each comprise a boss forming the hook as such with a surface inclined with respect to the direction for inserting the hooks in their housings 21 of the opposite curved elements and with a surface that is generally perpendicular to this direction and being able to come into positive contact with a corresponding surface of the housings. The bosses in question are arranged at each end of the two U-shaped legs and so as to be laterally directed toward the outside of the U.
[0035] The shroud section is provided to be mounted by assembling the two elements about the vanes. In practice, the two elements 12 and 14 are arranged in front of one another, similar to the drawing of figure 2, by first engaging each of the elements with the row of vanes which is adapted to be fixed to this shroud section. Once each element is engaged with the row of vanes, that is when the notches of each element cooperate, at least partially, with the vanes, moving the two elements closer together is very easy since it is guided, at least in a plane generally at a tangent to the outer surface 22 of the shroud, by the vanes. Putting the respective contact edges 27 and 29 in correspondence can require one or more movements in a direction that is perpendicular to the plane at a tangent to the outer surface 22 of the shroud.
The tongue 30 of the element 14 is arranged facing the groove 28 of the opposite element 12 so as to ensure an efficient guiding during the assembly. The mutual fastening of the two elements is carried out by applying a force for moving the contact edges closer together so as to make the resilient hooks penetrate in the respective housings up to the point where the parts with the positive contact surfaces override the corresponding surfaces of the housings. The legs can then return to a position close to that before insertion and where the positive contact surfaces of the hooks mesh with the corresponding surfaces of the housings.
[0036] Alternatively, the shroud section can be assembled before the vanes are mounted. The elements 12 and 14 are thus assembled by a similar movement to that described hereinabove, but without the presence of the vanes. The section is then mounted pre-assembled on the vanes.
This principle of assembly, just like the previous assembly principle described in detail in the previous paragraph, provides the advantage of allowing a shroud with apertures and a profile that is very adjusted to the profile of the vanes to be made, while doing away with the requirements caused by the unmolding of a conventional shroud section at the apertures. The unmolding of a conventional shroud section is generally done by moving away part of the mold corresponding to the outer surface and to the apertures over at least part of the thickness of the shroud from the outer surface. The curved nature of the shroud section causes the axes of the apertures to correspond to radii of the shroud and can thus form an angle with the unmolding direction. This requirement calls for a section of the apertures that flares more than what is required for the assembly. However, the previous principle of assembly described in detail in the previous paragraph has the added advantage to make it easier to assemble the shroud and mount it on the vanes.
[0037] Figure 3 shows the shroud section of figure 2 once assembled and mounted on a row of vanes 4. One can see that the outer surface 22 of the shroud 8 remains continuous and regular in the junction area. The mutual fastening is ensured by a pair of elastic hooks 20 between each pair of neighboring vanes. The vanes 4 can be fixed to the shroud by applying glue or an elastomer serving as glue ensuring a dual function, namely, that of ensuring a mechanical connection and a tight sealing. To do so, the ends of the vanes slightly project under the apertures so as to receive the glue or the elastomer.
[0038] It must be noted that other methods for mechanically connecting the vanes and the shroud can be provided. Indeed, it is absolutely conceivable to provide for a band to be placed through the holes made in the ends of the vanes so as to ensure a mechanical connection preventing the vanes from exiting the shroud, such as disclosed in the document EP 1 213 484 Al discussed in the "Prior art" section. In this case, it would be more practical to provide for a band to be placed before the shroud is mounted on the vanes.
[0039] Figure 3 also shows the U-shaped section with the open portion directed toward the center of the shroud, forming a recess adapted to receive the abradable material in the form of a paste by projection or by any other equivalent or similar method.
[0040] Figure 4 is an enlarged view of a part of the bottom of the shroud section mounted on the vanes shown in figure 3. It shows well the precision of the adjustment between the apertures formed by the pairs of notches 16 and 18 and the vanes 4. The fact that each notch of a pair of notches 16 and 18 forming an aperture surrounds the blade over approximately half of its length (according to the flow direction) makes it possible to precisely adjust the apertures on tunnel-section vanes, that is, vanes whose section is substantially thicker in the middle than on the edges (leading or trailing).
[0041] The shroud sections such as shown in figures 2, 3, and 4 can have ends with a profile corresponding to that of the end of the vanes, so that the junction between two adjacent sections corresponds to the profile of the blade (not shown). Preferably, each shroud section end comprises means for connecting to an adjacent section, these connection means being of the positive contact type, preferably on both sides of the junction on each of the curved elements forming a section. This positive contact ideally cooperates with a relative sliding movement along vanes between two adjacent sections.
[0042] It must be noted that the shape, number, and position of the elastic hooks as mutual fastening means for curved elements are given only by way of non-limiting example. Indeed, various alternatives which are similar and/or equivalent to these fastening means are possible, as a function of diverse parameters such as the choice of materials, manufacturing requirements (molding/unmolding for non-metallic materials), ease of assembly and disassembly, desired resistance to disassembly.
[0043] It must also be noted that the shroud can be made of two elements of the type previously described, namely the curved elements 12 and 14, each forming a complete ring.
These elements will preferably form a closed ring. Alternatively, the shroud can be composed of a first element forming a complete ring and preferably closed, and a series of curved elements adapted to be arranged against the first element and adjacent to one another along the circumference of the first element.
[0044] It must also be noted that it is, of course, conceivable to apply the shroud according to the invention to a stator stage whose vanes are not necessarily identical and/or uniformly distributed over the entire circumference. In this case, the apertures formed by the pairs of notches will not be uniformly distributed but rather according to the vanes of the stator.
[0045] It must also be noted that, although the embodiment of the invention was described in relation to an internal shroud, the invention is similarly applicable to an external shroud.

Claims

1. Shroud or shroud section made of composite material for a stator stage with vanes of an axial compressor, the shroud or shroud section being adapted to receive an end of the vanes;
characterized in that it comprises:
at least one first curved element with at least one first notch corresponding to a first portion of the contour of the end of the vanes;
at least one second curved element having a generally similar shape to that of the first curved element with at least one second notch corresponding to a second portion of the contour of the ends of the vanes, the first and second notch or notches forming one or several pairs of notches;
the first and second curved elements being adapted to be arranged axially against one another, so as to confine the profile of the end of the vanes in each pair of first and second notches.

2 Shroud or shroud section according to claim 1, characterized in that each of the first and second curved elements comprises an assembly edge in a plane that is perpendicular to the main axis of the compressor adapted to come into mutual contact during the assembly of the two curved elements, preferably by becoming closer in a direction corresponding approximately to the flow direction.

3. Shroud or shroud section according to claim 1 or 2, characterized in that the first and/or second portion of the contour of the end of the vanes corresponds approximately to half of the profile of the end of the vanes in the flow direction.

4. Shroud or shroud section according to any one of claims 1 to 3, characterized in that the first curved element comprises an assembly edge adapted to cooperate by insertion with an assembly edge of the second segment during the assembly of the two curved elements, preferably by becoming closer in a direction corresponding approximately to the flow direction.

5. Shroud or shroud section according to claim 4, characterized in that the assembly edge of one of the first end second curved elements comprises a groove along the curved direction and the assembly edge of the other of the first and second curved elements comprises a projecting part, the groove and the projecting part being interrupted by the respective notch or notches of the first and second curved elements.

6. Shroud or shroud section according to any one of claims 1 to 5, characterized in that the shroud is an internal shroud with a U-shaped section with the opening of the U
directed toward the center of the shroud so as to form a recess adapted to received the abradable material and where the limit between the first and second curved elements is located approximately toward the center of the U.

7. Shroud or shroud section according to any one of claims 1 to 6, characterized in that each of the first and second curved elements comprises mutual fastening means, these means being preferably of the clip-type.

8. Shroud or shroud section according to claim 7, characterized in that the mutual fastening means are such that they cooperate by elastic engagement of positive contact surfaces when the first and second curved elements become closer together along a direction corresponding approximately to the flow direction.

9. Shroud or shroud section according to claim 8, characterized in that the mutual fastening means comprise several elements projecting over one of the first and second curved elements along a direction corresponding approximately to the direction for moving the first and second curved elements closer together

10. Shroud or shroud section according to any one of claims 4, 5, and 7 to 9, characterized in that the mutual fastening means are arranged under the respective assembly edges of the first and second curved elements.

11. Shroud section according to any one of claims 1 to 10, characterized in that each end of the shroud section comprises a section whose profile corresponds to that of the end of the vanes so that the junction between two adjacent sections corresponds to the vane profile.

12 Shroud section according to claim 11, characterized in that each end of the shroud section comprises means for connecting to an adjacent section, these connection means having a positive contact, preferably on both sides of the junction on each of the first and second curved elements.

13. Shroud according to any one of claims 1 to 12, characterized in that each of the first and second curved elements is ring-shaped, preferably closed.

14. Shroud according to any one of claims 1 to 13, characterized in that one of the first and second curved elements is ring-shaped, preferably closed, and in that it comprises several second curved elements corresponding to sections of the ring and adapted to be successively arranged against the ring-shaped curved element so as to confine, over the entire perimeter of the ring, the shape of the vane roots in each pair of first and second notches.

15. Shroud for a stator stage with vanes of an axial compressor comprising several shroud sections according to any one of claims 1 to 14.