NOZZLE STAGE FOR A TURBINE ENGINE

Abstract

A nozzle stage for a turbine engine includes two substantially cylindrical rings, respectively an inner ring and an outer ring, with, extending between them: vanes carried by a first one of the rings; vanes carried by the second ring; and spacer-forming vanes interconnecting the two rings; the vanes of the first and second rings being arranged in alternation.

Description

The present invention relates to a nozzle stage for a compressor or a turbine of a turbine engine such as an airplane turboprop or turbojet.

A nozzle stage of this type comprises two substantially cylindrical rings extending one inside the other with substantially radial vanes extending between them.

A nozzle stage is generally a single piece and it may be made by casting or by machining (e.g. electrical discharge machining (EDM)), or by assembling and welding each vane to the rings.

Nevertheless, under such circumstances, the length of time required for fabricating a nozzle stage is relatively long. Furthermore, when the nozzle stage has a high density of vanes, i.e. when its vanes are close together in the circumferential direction, the above-mentioned fabrication techniques are difficult or even impossible to implement. When a tool is used for machining a nozzle vane or for welding said vane to the rings, the tool needs to be passed between two consecutive vanes of the stage, and that is not always possible when the circumferential pitch between two consecutive vanes is very small.

A particular object of the invention is to provide a solution to those problems that is simple, effective, and inexpensive.

The invention provides a nozzle stage, e.g. having a high density of vanes, that is easier to make than prior art nozzle stages, while using fabrication techniques that are simpler, faster, and less expensive.

To this end, the invention provides a nozzle stage for a turbine engine, the stage comprising two substantially cylindrical rings, respectively an inner ring and an outer ring, with substantially radial vanes extending between them, the stage being characterized in that it comprises a first series of vanes carried by a first one of the rings, a second series of vanes carried by the second ring, and connection means interconnecting the two rings, the vanes of the first and second rings being arranged in alternation.

Advantageously, the ring connection means comprise spacer vanes having their ends fastened to the first and second rings, respectively.

The nozzle stage of the invention thus essentially comprises two series of vanes together with connecting spacer vanes: a first series of vanes connected to the first ring and independent from the second ring; a second series of vanes connected to the second ring and independent of the first ring, with each vane of the second ring extending between two vanes of the first ring; and spacer vanes that are connected to both rings and that serve to hold together the parts of the nozzle stage.

Each ring thus carries approximately only half of the vanes of the stage, thereby doubling the inter-vane pitch and facilitating access to said vanes for the above-mentioned machining or welding tools, and thus making it easier to fabricate the nozzle stage.

The vanes of each series are preferably substantially regularly distributed around the longitudinal axis of the stage.

The circumferential pitch between two consecutive vanes of the first series is thus substantially equal to the circumferential pitch between two consecutive vanes of the second series and is substantially equal to twice the circumferential pitch of the vanes of a nozzle stage having the same density of vanes in the prior art. By way of example, the circumferential pitch between two consecutive vanes carried by one of the rings may be approximately 27 millimeters (mm) and the circumferential pitch between two consecutive vanes of the assembled stage may be approximately 13.5 mm.

According to another characteristic of the invention, the vanes of the first series have free ends that are flush with or at a short radial distance from the second ring, and the vanes of the second series have free ends that are flush with or at a short radial distance from the first ring. The radial distance between the free end of each vane of the second and third series and the corresponding ring is advantageously less than or equal to 0.05 mm, in such a manner as to avoid disturbing the flow of the stream of air between the rings of the stage.

Preferably, each ring is sectorized and comprises at least two annular sectors mounted end to end. Each annular sector of a ring may be formed as a single piece with the vanes that are carried by the ring sector, and may be made by casting or by machining, for example.

In a variant, the vanes carried by each annular sector of a ring are fitted thereto, being fastened to the ring sector, e.g. by brazing or welding.

According to another characteristic of the invention, the spacer vanes are connected to the rings in releasable manner. The radially outer end of each spacer vane may be threaded and may be engaged in a radial orifice of the outer ring and to receive a nut that bears against said outer ring.

The nozzle stage may also include an annular rail mounted on the inner ring and including an outer annular groove in which an inner annular rim of each sector of the inner ring and the radially inner end of each spacer vane are engaged by sliding in the circumferential direction.

Finally, the invention provides a turbine engine such as an airplane turboprop or turbojet, characterized in that it includes at least one nozzle stage as described above.

The invention can be better understood and other characteristics, details, and advantages thereof appear more clearly on reading the following description made by way of non-limiting example and with reference to the accompanying drawings, in which:

FIG. 1 is a fragmentary diagrammatic view in perspective of a nozzle stage of the invention;

FIG. 2 is a fragmentary diagrammatic view in perspective of the outer ring of the FIG. 1 nozzle stage;

FIG. 3 is a diagrammatic view in perspective and on a larger scale showing the fastening of a spacer vane to the outer ring of FIG. 2; and

FIGS. 4 and 5 are fragmentary diagrammatic views in perspective and on a larger scale of the nozzle stage of the invention.

FIG. 1 shows a portion of a nozzle stage 10 of the invention, comprising two coaxial rings 12 and 14, respectively an inner ring and outer ring, with substantially radial vanes 16, 18, and 20 extending between them, the rings 12 and 14 and the vanes 16, 18, and 20 being described in greater detail below with reference to FIGS. 2 to 5.

This nozzle stage 10 forms part of a turbine or a compressor in a turbine engine. It forms a stator element of the turbine or the compressor and it is arranged between two rotor stages of the turbine or the compressor, each of which is formed by a rotor wheel having an annular row of blades.

In the example shown, the nozzle stage 10 comprises two annular portions each occupying about 180° (only one of which is shown), these two portions being arranged end to end circumferentially and fastened together by appropriate means, e.g. of the nut-and-bolt type.

The portion of the nozzle stage 10 that is shown comprises an annular sector 15 of the outer ring 14 (extending over about 180°) and three annular sectors 13 of the inner ring 12 (each extending over about 55° to 60°, which sectors are arranged circumferentially end to end. FIG. 2 is a diagrammatic perspective view of the sector 15 of the outer ring 14.

This sector 15 carries a first series of vanes 16 that are connected via their radially outer ends to a cylindrical wall 22 of the sector.

These vanes 16 are regularly distributed around the longitudinal axis of the nozzle stage and they are spaced apart from one another at a circumferential pitch K. The vanes 16 carried by the sector 15 may be thirty in number, for example.

The vanes 16 may be formed integrally with the sector 15 or they may be fittings that are fastened via their radially outer ends to the cylindrical wall 22 of the sector 15.

The ring sector 15 also includes an annular wall 24 extending radially outwards for mounting the nozzle stage 10 in the turbine or the compressor of the turbine engine.

The cylindrical wall 22 of the ring sector 15 includes substantially radial orifices 28 in which the radially outer ends of spacer-forming vanes 20 are engaged, which vanes serve to connect the two rings 12 and 14 securely together.

In the example shown in FIG. 1, these spacer vanes 20 are four in number and they are regularly distributed around the longitudinal axis of the stage. Amongst these four spacer vanes 20, two are situated at the circumferential ends of the ring sector 15. The other two vanes 20 of the ring sector 15 are situated at a distance from the circumferential ends of the sector, each being arranged between two consecutive vanes 16 carried by the sector.

The fastening of a vane 20 is shown on a larger scale in FIG. 3.

At its radially outer end, the vane 20 has a cylindrical stud 26 that is engaged in an orifice 28 in the cylindrical wall 22 of the ring sector 15 and that has its radially outer portion threaded so as to receive from the outside a nut 30 that is to bear against the outside surface of the wall 22 of the ring sector 15, either directly or via a washer 32.

At its radially inner end, the vane 20 includes a platform 34 that is connected to a root 36 that is substantially I-shaped in section (in a plane containing the longitudinal axis of the stage).

Each vane 20 is mounted on the ring sector 15 by being moved radially in translation from the inside towards the outside until its stud 26 is engaged in one of the orifices 28 of the ring sector 15. The nut 30 is then screwed onto the threaded portion of the stud and is tightened against the ring sector so as to hold the vane 20 stationary in a radial direction on the ring sector 15.

FIGS. 4 and 5 show another step in mounting the nozzle stage 10 of the invention, in which each sector 13 of the inner ring 12 is arranged between two platforms 34 of spacer vanes 20.

Each sector 13 of the inner ring carries a series of vanes 18 that extend radially outwards from an outer cylindrical surface of the sector. Each sector 13 carries nine vanes 18 in the example shown. Each of these vanes 18 is arranged between two consecutive vanes 16 of the sector 15 of the outer ring, or between one of those vanes 16 and a spacer vane 20.

The vanes 18 may be formed integrally with the corresponding ring sector 13 or they may be fitted thereto, being fastened to said sector via their radially inner ends.

Each inner ring sector 13 is mounted on the outer ring as follows. The sector 13 is aligned with the outer ring 15 and is placed at an axial distance therefrom, and it is then moved in axial translation towards the sector 15, until the vanes 18 of the sector 13 are between the vanes 16 of the sector 15.

In this position, the circumferential pitch between a vane 18 of the sector 13 and a vane 16 of the sector 15 is equal to K/2.

The free ends of the vanes 18 are flush with or at a short radial distance from the ring sector 15, and the free ends of the vanes 16 are flush with or at a short radial distance from the ring sector 13. These distances are preferably less than or equal to 0.05 mm. Each inner ring sector 13 is aligned in a circumferential direction with the platforms 34 of the adjacent spacer vanes 20 and presents a section in a plane containing the longitudinal axis of the stage that is of a shape that is identical to the shape of the platforms 34 and of the roots 36 of the spacer vanes 20.

An annular rail 40 (shown in FIGS. 1, 4, and 5) extending over about 180° serves to fasten the sectors 13 of the inner ring 12 securely to the spacer vanes 20.

This rail 40 has an outer annular groove 42 of section that is of a shape that is substantially complementary to the shape of the roots 36 of the vanes 20 and of the ring sectors 13. The roots of the vanes 20 co-operate with the side walls of the grooves 42 in the rail to prevent the vanes turning about their axes, and they are held radially by annular rims 44 that extend towards each other from the side walls of the groove 42.

The roots 36 of the vanes 20 and each sector 13 are engaged by sliding in the circumferential direction into the annular groove 42 of the rail, by moving the rail 40 in the circumferential direction over the sectors 13 of the inner ring 12 and over the root 36 of the vanes 20.

For this purpose, the root 36 of a vane 20 that is located at one of the circumferential ends of the ring sector 15 is engaged in a circumferential end of the groove 42 of the rail 40, and then the rail is moved in sliding in the circumferential direction over the sectors 13 of the inner ring until the circumferential ends of the rail are substantially in radial alignment with the circumferential ends of the ring sector 15.

At its inner periphery, the rail 40 may carry an annular element 46 of abradable material that is to co-operate in friction with annular wipers carried by the rotor of the turbine or the compressor so as to form a labyrinth type seal.

The first and second portions of the nozzle stage are identical and assembled in the same manner. These two portions are then placed end to end and fastened securely to each other in order to form the nozzle stage.

In the example shown in the drawings, the portion shown of the nozzle stage 10 comprises thirty vanes 16 of the first series, twenty-seven (=3×9) vanes 18 of the second series, and four spacer vanes 20. The second portion (not shown) of this stage 10 is identical.

It is possible advantageously to interpose an undulating spring-forming blade 48 between the bottom of the root 36 of the vane 20, the base of the sector 13, and the bottom 50 of the groove 42 in the rail 40 (FIG. 5) in order to ensure continuous contact between the root 36 of the vane 20 and the corresponding portion of each sector 13 with the rims 44 of the groove 42 in the rail 40.

The radial heights of the rims 44 of the groove 42 in the rail are determined relative to the radial dimensions of the connections between the roots 36 of the vanes 20 and their platforms 34 so as to obtain a snug fit of the roots of the vanes 20 in the groove 42 in the rail, and likewise for the corresponding portions of the sectors 13. As a result, the outside faces of the platforms 34 of the vanes 20 and the corresponding portions of the sectors 13 are at exactly the same level, thereby ensuring continuity of the inside surface defining the passage for fluid flow through the nozzle stage.

Claims

1-13. (canceled)

14. A nozzle stage for a turbine engine, the stage comprising:

two substantially cylindrical rings, of respectively an inner ring and an outer ring, with substantially radial vanes extending between them;

a first series of vanes carried by a first one of the rings;

a second series of vanes carried by the second ring; and

connection means interconnecting the two rings, the vanes of the first ring alternating with the vanes of the second ring.

15. A nozzle stage according to claim 14, wherein the vanes of each series are substantially regularly distributed around the longitudinal axis of the stage.

16. A nozzle stage according to claim 14, wherein the ring connection means comprises spacer vanes having their ends fastened to the first ring and to the second ring, respectively.

17. A nozzle stage according to claim 14, wherein each ring is sectorized and comprises at least two annular sectors mounted end to end.

18. A nozzle stage according to claim 16, wherein each ring is sectorized and comprises at least two annular sectors mounted end to end, and further comprising an annular rail mounted on the inner ring and including an outer annular groove in which an inner annular rim of each sector of the inner ring and the radially inner end of each spacer vane are engaged by sliding in the circumferential direction.

19. A nozzle stage according to claim 18, further comprising undulating spring-forming blades interposed between a bottom of the annular groove in the rail and both the sectors of the inner ring and roots of the spacer vanes.

20. A nozzle stage according to claim 14, wherein the vanes of the first series have free ends that are flush with or at a short radial distance from the second ring, and the vanes of the second series have free ends that are flush with or at a short radial distance from the first ring.

21. A nozzle stage according to claim 20, wherein the radial distance between the free end of each vane of the first and second series and the corresponding ring is less than or equal to 0.05 mm.

22. A nozzle stage according to claim 17, wherein each annular sector of a ring is formed integrally with the vanes carried by the ring sector.

23. A nozzle stage according to claim 17, wherein the vanes carried by each annular sector of a ring are fitted thereto, being fastened to the ring sector.

24. A nozzle stage according to claim 16, wherein the spacer vanes are connected to the rings in a releasable manner.

25. A nozzle stage according to claim 16, wherein the radially outer end of each spacer vane is threaded and is engaged in a radial orifice of the outer ring and receives a nut that bears against the outer ring.

26. A nozzle stage according to claim 22, wherein each annular sector of a ring is formed by casting or by machining with the vanes carried by the ring sector.

27. A nozzle stage according to claim 23, wherein the vanes carried by each annular sector of a ring are fastened thereto by brazing or welding.

28. A turbine engine, comprising:

at least one nozzle stage according to claim 14.