EP1965034B1 - Turbine stage in a turbomachine - Google Patents

Description

The present invention relates to a turbine stage in a turbomachine such as in particular an airplane turbojet or turboprop.

A turbomachine comprises a plurality of turbine stages each comprising a distributor formed of an annular row of stationary vanes and a rotor wheel rotatably mounted downstream of the distributor in a cylindrical or frustoconical envelope formed by ring sectors arranged circumferentially at the end. The first of these stages is a high-pressure stage and the other stages downstream are low-pressure stages.

It is important that the radial clearances between the paddle wheels and the corresponding ring sectors be optimized, to improve the efficiency of the turbomachine and to avoid any friction of the ends of the blades on the ring sectors, which would result in wear of these ends and degradation of the efficiency of the turbomachine at all operating speeds.

The ring sectors which surround the impeller of the high-pressure stage comprise at their upstream and downstream ends hooking means cooperating with corresponding means provided on an annular support disposed between the ring sectors and the casing. of turbine.

In operation, the hot gases leaving the combustion chamber of the turbomachine flow through the distributor of the high-pressure stage and exert on it an axial thrust downstream. This distributor tends to move downstream and come to bear by its outer periphery on the annular support of the ring sectors and to push downstream, resulting variations of the radial clearances between the blades. of the wheel and ring sectors.

One solution to this problem is to stiffen the annular support by forming it in one piece with a support housing located downstream of the ring sectors and for suspending the distributor of the first low-pressure stage to the turbine housing.

However, this solution has many disadvantages. The annular support and the ring sectors are fixedly connected to the support casing. It is therefore not possible to optimize the radial clearances between the blades and the ring sectors as a function of the speed of the turbomachine. In addition, the turbine casing is subjected in operation to non-uniform cooling air circulations on its periphery which show significant temperature gradients on the housing, resulting in deformations of the housing called "carcass distortions" and result in movements of the support housing and ring sectors hung on the annular support. The displacements of the ring sectors are random and uncontrolled and cause variations in the radial clearances between the blades and the ring sectors of the high-pressure stage which reduce the performance of the turbomachine.

Another solution to the problem mentioned above is to fix the support directly on the turbine casing. However, this solution is not satisfactory either because to ensure good axial rigidity of this support, its fastening means generally have a very large axial size. Moreover, this solution does not make it possible to solve the problems of displacement of the ring sectors related to carcass distortions of the turbine casing.

The requests FR-A1-2 887 939 , EP-A1-0487193 and EP-A1-0 059 420 describe turbomachines, comprising ferrules suspended from a housing by at least one U or V section element.

Requirement EP-A2-1 408 200 discloses a device for attaching a turbine ring sector to a housing, the ring sector having resiliently deformable fixing hooks on the housing.

The invention aims in particular to provide a simple, effective and economical solution to all the problems of the prior art.

It proposes for this purpose a turbine stage in a turbomachine, comprising ring sectors arranged around a turbine wheel and suspended from a turbine casing by an annular support, characterized in that the annular support comprises means for attaching the ring sectors and fastening means on the turbine casing, connected by two coaxial annular walls connected to one another and extending one to the inside of the other, this support section having a V-shaped or U-shaped and being elastically deformable in the radial direction to absorb at least part of the deformations of the turbine casing in operation.

According to the invention the ring sectors are suspended from the turbine casing by a radially deformable annular support so as to at least partially absorb the carcass distortions of the outer casing so that the casing formed by the ring sectors keeps a substantially constant diameter in operation. The invention makes it possible to maintain a substantially constant radial clearance between the wheel and the ring sectors of the high-pressure stage, as well as at the leading and trailing edges of the blades of this wheel. The annular support has moreover a good axial rigidity so that it can withstand without deformation in the axial support of the upstream side of the distributor of the high-pressure stage subjected to the thrust of the combustion gases.

The elastically deformable support comprises two coaxial annular walls connected to one another at one end and extending one inside the other, this support having a V-shaped or U-shaped section with a cross-section. oriented upstream or downstream.

In operation, the two coaxial walls of the support can move toward or away from one another to damp the carcass distortions of the turbine casing. The junction between the two walls is shaped to deform elastically and provide the support a spring function. This double wall structure also makes it possible to reinforce the axial rigidity of the support of the ring sectors.

According to a first embodiment of the invention, the annular support has a V-shaped cross-section and has two frustoconical walls respectively internal and external. The frustoconical wall For example, the internal portion may extend from hooking means of the ring sectors radially outwards and upstream to the outer frustoconical wall which extends radially outwards and downstream. In this case, the support defines an annular groove which opens axially downstream.

According to a second embodiment of the invention, the annular support has a U-shaped cross-section and comprises two substantially cylindrical walls, respectively internal and external. The inner cylindrical wall may be connected at its upstream end to hooking means of the ring sectors and at its downstream end to the downstream end of the outer cylindrical wall. The support here defines an annular groove oriented axially upstream.

Preferably, the outer wall comprises a radially outer annular flange for attachment to the turbine casing.

Advantageously, the inner wall is connected to an upstream end of the hooking means of the ring sectors so as to reinforce the axial rigidity of the support.

The junction between the inner and outer walls may have a C-shaped curved shape defining a concave annular surface and a convex annular surface. This junction advantageously comprises an annular rib extending substantially axially from its convex annular surface to stiffen the junction area of the two walls and distribute the stresses in this area. This annular rib has for example a cylindrical shape centered on the axis of revolution of the support.

The present invention also relates to a turbomachine turbine and a turbomachine, such as an airplane turbojet or turboprop, comprising at least one stage as described above.

The invention also relates to an annular support of ring sectors in a turbine stage of a turbomachine, characterized in that it has a U or V section and comprises at its inner periphery hooking means of the ring sectors, and at its outer periphery a radially outer annular flange.

• la figure 1 est une demi vue schématique partielle en coupe axiale d'un dispositif de fixation de secteurs d'anneau selon l'invention ;
• la figure 2 est une demi vue schématique partielle en coupe axiale d'une variante de réalisation du dispositif de fixation selon l'invention ;
• la figure 3 est une vue schématique partielle en perspective d'une autre variante de réalisation du dispositif de fixation selon l'invention ;

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of nonlimiting example and with reference to the accompanying drawings in which:

• the figure 1 is a partial schematic half-view in axial section of a ring sector fixing device according to the invention;
• the figure 2 is a partial schematic half view in axial section of an alternative embodiment of the fixing device according to the invention;
• the figure 3 is a partial schematic perspective view of another alternative embodiment of the fastening device according to the invention;

The figure 1 schematically represents a part of a turbomachine such as an airplane turbojet or turboprop comprising a turbine 10, 12 arranged downstream of a combustion chamber 14, this turbine comprising several stages: an upstream stage or high stage 10 and downstream stages or low-pressure stages 12.

The high-pressure stage 10 comprises a distributor 16 formed of an annular row of fixed vanes, and a vane wheel 18 mounted downstream of the distributor 16 and rotating in a substantially cylindrical casing formed by ring sectors. 20 arranged circumferentially end to end and suspended from a turbine casing 22.

Each low-pressure stage 12 also comprises a distributor and a paddle wheel of the aforementioned type, only the distributor 30 of the first low-pressure stage being visible in FIG. figure 1 . This distributor 30 is fixed to the turbine casing 22 by means of an annular support piece 32 arranged between the distributor 30 and the casing 22. The support piece 32 comprises at its radially inner end annular grooves which open towards the outside. downstream and in which are engaged circumferential edges 34 provided at the outer periphery of the distributor. The part 32 comprises a frustoconical wall 36 which extends radially outwards and upstream and is connected at its radially outer end to a radially outer annular flange 38 for attachment to a corresponding annular flange 24 provided at the end. upstream of the turbine casing 22.

An outer casing 28 surrounding the combustion chamber 14 is also provided at its downstream end with a radially outer annular flange 26 which is held axially tight on the flanges 38 and 24 of the support piece 32 and the turbine casing 22 by the intermediate means 40 of the screw-nut type. The combustion chamber 14 is fixed to the outer casing 28 via an annular wall 29 extending from the downstream end of the chamber radially outwardly and downstream and comprising at its radially outer end fastening means to the outer casing 28.

The ring sectors 20 are suspended from the turbine casing 22 by means of an annular support 50 which is housed in an annular enclosure 52 delimited upstream by the annular wall 29 of the combustion chamber 14 and at the same time. downstream by the frustoconical wall 36 of the support piece 32. This annular support comprises at its inner periphery means 54 for hooking the ring sectors 20 and at its outer periphery means 72 for fixing on the turbine casing 22 .

According to the invention, this annular support 50 is elastically deformable in the radial direction to at least partially damp the carcass distortions to which the turbine casing 22 is subjected in operation of the turbomachine, so that the cylindrical envelope formed by the sectors of ring 20 retains a substantially constant diameter.

The annular support 50 comprises at its inner periphery two radial annular walls 57, 58, respectively upstream and downstream, which are connected to one another by a cylindrical wall 60. The radial walls 57, 58 comprise at their radially internal ends downstream cylindrical flanges 62 which cooperate with hooks circumferential members 63, 64 provided at the upstream and downstream ends of the ring sectors 20. An annular locking member 66 with a C-section is engaged axially downstream on the downstream cylindrical rim 62 of the support and on the downstream hooks 64 of the sectors. ring to ensure the locking of the assembly.

In figure 1 , the median portion of the annular support 50 is elastically deformable in the radial direction and has a U-shaped section whose base is oriented downstream, this part comprising two coaxial cylindrical walls 68, 70 extending from one to the other. inside each other and connected to each other at their downstream end.

The internal cylindrical wall 68 extends around the cylindrical wall 60 of the attachment means, at a distance from the latter, and is connected at its upstream end to the radially outer end of the upstream radial wall 57 of the locking means. hanging. The downstream end of the inner wall 68 is connected to the downstream end of the outer cylindrical wall 70 which has a smaller axial dimension than that of the inner wall 68 and which extends around a downstream part of the wall internal 68, away from it. The junction 74 between the inner 68 and outer 70 walls has a curved shape C. The upstream end of the outer wall 70 is connected to a radially outer annular flange 72 which is clamped between the flange 26 of the outer casing 28 and the flanges 38, 24 of the support piece 32 and the turbine casing 22.

In operation of the turbomachine, the housings 28 and 22 are not uniformly ventilated and cooled on their periphery, which generates large temperature gradients on these housings and results in carcass distortions. The annular support 50 for fixing the ring sectors 20 makes it possible to dampen these distortions by elastic deformation of its medial portion in the radial direction. This deformation results in the approximation or removal of the walls 68, 70 in the radial direction. This support is sufficiently rigid in the axial direction to be able to resist without deformation to the axial thrust exerted on the upstream side by the distributor 16 of the high-pressure stage, this distributor being supported at 76 by its outer periphery on the upstream face of the upstream radial wall 57 of the support. The radial clearances 78 between the vanes of the wheel 18 and the ring sectors 20 can thus be adjusted precisely, in particular according to the different operating speeds of the turbomachine.

We have shown in figure 2 an alternative embodiment of the invention in which the elastically deformable middle portion of the annular support 50 has a biconical shape and has a V-shaped section whose tip is oriented upstream. This part comprises two coaxial frustoconical walls 80, 82 extending one inside the other and connected to each other at their upstream ends.

The internal frustoconical wall 80 extends from the radially outer end of the upstream radial wall 57 'of the attachment means 54', radially outwardly and upstream, that is to say upstream of the hooking means 54 '.

The radially outer end of the inner wall 80 is connected to the radially inner end of the outer frustoconical wall 82 which extends radially outwards and downstream around the inner wall 80. The outer wall 82 is connected at its downstream end to a radially outer annular flange 84 which is clamped axially between the flange 26 of the outer casing 28 and the flanges 38, 24 of the support piece 32 and the turbine casing 22. The junction 86 between the inner walls 80 and outer 82 has a curved shape at C and defines upstream a convex annular surface and downstream a concave annular surface.

The upstream radial walls 57 'and downstream 58' of the attachment means 54 'are here interconnected by a frustoconical wall 60' which is aligned with the internal frustoconical wall 80 of the support to increase its axial rigidity.

The figure 3 represents another variant embodiment of the device according to the invention which differs from that of the figure 2 in that it includes a cylindrical rib 88 which extends axially upstream from the radial annular surface of the junction 86 of the inner and outer walls of the support. This rib 88 makes it possible to stiffen the junction zone of the two walls and to distribute the stresses in this zone.

Claims (12)

1. A turbine stage for a turbomachine, comprising ring sectors (20) arranged about a turbine impeller (18) and suspended from a turbine casing (22) by an annular support (50), characterized in that the annular support comprises means (54,54') for coupling the ring sectors and means (72) for attachment to the turbine casing (22), connected by two coaxial annular walls (68,70,80,82) connected to one another and extending one inside the other, said support having:

   - a V-shaped section comprising two respectively inner and outer frustoconical walls (80,82) defining said two coaxial annular walls, the inner frustoconical wall (80), the inner frustoconical wall (80) being aligned with a frustoconical wall (60') connecting the upstream radial wall (57') and the downstream radial wall (58') of the coupling means (54'), or

   - a U-shaped section comprising two respectively inner and outer substantially cylindrical walls (68,70) defining said two coaxial annular walls,

   said support being able to be elastically deformed in a radial direction to absorb at least a portion of the deformations of the turbine casing in operation.
2. The turbine stage as claimed in claim 1, characterized in that the inner frustoconical wall (80) extends from means (54') for coupling the ring sectors radially outward and in the upstream direction up to the outer frustoconical wall (82) which extends radially outward and in the downstream direction.
3. The turbine stage as claimed in claim 1, characterized in that the inner cylindrical wall (68) is connected at its upstream end to means (54) for coupling the ring sectors and at its downstream end to the downstream end of the outer cylindrical wall (70).
4. The turbine stage as claimed in one of the preceding claims, characterized in that the outer wall (70,82) comprises a radially outer annular flange (72,84) for attachment to the turbine casing (22).
5. The turbine stage as claimed in one of the preceding claims, characterized in that the inner wall (68,80) is connected to an upstream end of means for coupling (54,54') the ring sectors.
6. The turbine stage as claimed in one of the preceding claims, characterized in that the junction (74,86) between the inner and outer walls has a curved C shape defining a concave annular surface and a convex annular surface.
7. The turbine stage as claimed in claim 6, characterized in that the junction (86) comprises an annular rib (88) extending substantially axially from its convex annular surface.
8. The turbine stage as claimed in claim 7, characterized in that the annular rib (88) is of cylindrical shape centered on the axis of revolution of the annular support (50).
9. The turbine stage as claimed in anyone of the preceding claims, characterized in that the annular support (50) is formed in a single piece.
10. A turbomachine turbine, which comprises at least one stage as claimed in one of the preceding claims.
11. A turbomachine, such as an aircraft turbojet or turboprop, which comprises at least one turbine stage as claimed in one of claims 1 to 8.
12. An annular support for ring sectors (20) for a turbine stage comprising a turbine casing, characterized in that said annular support comprises, at its inner periphery, means (54,54') for coupling the ring sectors, and, at its outer periphery, a radially outer annular flange (72,84), and has:

    - a V-shaped section comprising two respectively inner and outer frustoconical walls (80,82) defining said two coaxial annular walls, the inner frustoconical wall (80), the inner frustoconical wall (80) being aligned with a frustoconical wall (60') connecting the upstream radial wall (57') and the downstream radial wall (58') of the coupling means, or

    - a U-shaped section comprising two respectively inner and outer substantially cylindrical walls (68,70) defining said two coaxial annular walls,

    said support being able to be elastically deformed in a radial direction to absorb at least a portion of the deformations of the turbine casing in operation.

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