EP1586743B1 - Turbine shroud - Google Patents

Description

The invention relates to a turbine ring forming the outer casing of the rotor of this turbine. The invention is particularly applicable to a high pressure turbine located immediately downstream of the combustion chamber of an aircraft turbojet engine. It relates more particularly to the connection and cooling of the sectors constituting said turbine ring.

In a turbine of the type indicated above, driven by very hot gases, the rotor rotates inside a fixed turbine ring formed by a plurality of curved sectors joined end to end, circumferentially, to form the envelope. rotor. The temperature of the gases driving the impeller is such that the thermomechanical stresses that are created in and between the sectors can cause deterioration reducing the life of the rings. Typically, the formation of small cracks and / or spalling of the inner (so-called hot surface) side of the sectors is often observed, mainly in the vicinity of the connections between adjacent sectors.

To ensure a good seal of the ring gear, reducing non-working air leaks and to prevent reintroductions of hot gases, sealing systems are provided between these adjacent sectors, comprising tabs extending between these sectors. and housed in slots made vis-à-vis in the adjacent radial faces of said sectors.

For example, a known sector 1 represented in figure 1 , comprises a sealing system comprising four tongues 2-5, housed in slots 6, 7, 8. The tongue 3 is folded and extends between two slots 6, 7 opening into one another and welcoming d Other straight tabs 2, 4. The slots are difficult to machine accurately, especially because of the difference in thickness required to insert the folded tab. The positioning of the latter is delicate. In addition, the tongue 2 is entirely housed in a slot 6 parallel to the hot face 9 of the sector and at a short distance therefrom. However, the practice of the slots, creates areas of stress concentration which, when they are close to the surface hot, weaken the room and accelerate its deterioration. On the other hand, US 5,997,247 discloses a stator sector (and not a rotor casing) having sealing tabs inserted into slots communicating with each other, which require stripping at their junctions. In addition, cross-sector leakage sections can not be perfectly controlled.

The invention makes it possible to eliminate these disadvantages.

In the first place, the invention relates to a turbine ring forming a rotor casing, of the type constituted by a plurality of sectors, joined end to end with the interposition of sealing systems comprising tabs extending between adjacent sectors, said tabs being accommodated. in slots made opposite each other in adjacent radial faces of said sectors, characterized in that each sealing system is constituted by straight tabs engaged in respective rectilinear slots of said radial faces and that the slots made on each radial face are independent, that is to say that said slots do not communicate with each other.

The fact of making the sealing system from straight tabs simplifies the realization of the slots and facilitates the mounting of the tabs therein. In addition, the control of the positioning of the tongues is improved because of support surfaces better controlled because strictly linear. Overall, the leakage sections are reduced. A configuration with only three tabs will be described later.

More particularly, the turbine ring defined above is also advantageously characterized in that each sealing system comprises a first and a second tongues extending chevron on the inside of said radial faces, said tabs being engaged in slots rectilinear of said radial faces defining their relative positions with precision. In this way, the air leak between two consecutive sectors can be precisely calibrated. This leak can therefore be identical in all inter-sector spaces. Overall, it is estimated that the leak rate can be reduced by 10 to 20% compared to the configuration of the prior art described above.

Another advantage of the invention lies in the fact that the arrangement of the chevron tongues on the side of the hot face makes it possible both to move the stress concentration zones away from said hot face (since the slits deviate from the latter) and also to provide sufficient space between the tabs and the hot face to open air ejection channels cooling supplied from a cavity in the sector itself.

More specifically, the invention also relates to a turbine ring according to the preceding definition in which each sector comprises a cooling air circulation cavity, characterized in that it further comprises air ejection channels s extending between said cavity and at least one radial face of the sector, these channels opening on said radial face between an inner edge thereof and said first and second tongues.

• la figure 1 représente une face radiale d'un secteur entrant dans la constitution d'un anneau de turbine conforme à l'état de la technique ;
• la figure 2 représente une face radiale d'un secteur entrant dans la constitution d'un anneau de turbine conforme à l'invention ;
• la figure 3 est une vue schématique de deux secteurs consécutifs représentés selon la flèche 3 de la figure 2 ;
• la figure 4 est une vue schématique du carter associé à de tels secteurs d'anneau ;
• la figure 5 est une vue schématique illustrant diverses orientations possibles desdites première et deuxième languettes ; et
• les figures 6 à 8 sont des vues partielles de variantes d'un secteur de la figure 3.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given solely by way of example and with reference to the appended drawings in which:

• the figure 1 represents a radial face of a sector entering the constitution of a turbine ring according to the state of the art;
• the figure 2 represents a radial face of a sector used in the constitution of a turbine ring according to the invention;
• the figure 3 is a schematic view of two consecutive sectors represented along arrow 3 of the figure 2 ;
• the figure 4 is a schematic view of the casing associated with such ring sectors;
• the figure 5 is a schematic view illustrating various possible orientations of said first and second tongues; and
• the Figures 6 to 8 are partial views of variants of a sector of the figure 3 .

On the drawings and more particularly on the Figures 2 to 4 there is shown turbine ring sectors 11 constituting the fixed casing of a rotor, not shown. This is the high-pressure turbine of a turbojet engine. This turbine is placed downstream of the combustion chamber. In this case, such a ring consists of 32 ring 11 sectors curves such as those shown end to end to form a slightly conical envelope surrounding said rotor. Each sector 11 is constituted a thick, slightly curved plate to reconstitute the ring. There is an inner face 12 substantially rectangular, slightly concave, so-called "hot face", in contact with the vein and an outer face 14 substantially rectangular, called "cold face". With respect to the flow of hot gas through the rotor, there is also an inlet edge 16 facing the nozzle of the combustion chamber and an opposite outlet edge 18. Each sector 11 further comprises two radial faces 20, 21 through which it connects circumferentially to neighboring sectors, by sealing systems 26 (see FIG. figure 2 ) mentioned above. Each sealing system 26 consists of a set of tabs engaged in corresponding slots defined in said radial faces 20, 21 facing each other. Each tongue is engaged in two slots belonging to two ring sectors circumferentially adjacent.

The ends of the blades of the rotor move opposite the inner surface of the ring thus formed. The direction of rotation is indicated by the arrow F, on the figure 2 . The hot gases expelled from the combustion chamber thus flow close to the inner surface of the ring which must withstand very high temperatures. It is therefore necessary both to minimize as much as possible the thermal gradients in the structure of the ring (and therefore minimize in particular the gas leaks between the sectors) and effectively cool said ring. For this purpose, a portion of the air delivered by the compressor which supplies the combustion chamber is used. To do this, each sector 11 is hollow and comprises a cooling air circulation cavity 35 fed from the outside.

The figure 4 illustrates very schematically the position of the ring formed by all of the sectors 11. A turbine casing 15 defines with this ring an annular cavity 17. The assembly extends radially outside the impeller with high pressure 19 itself axially interposed between the high pressure distributor 21 and the low pressure distributor 23. Air from the compressor is taken upstream of the combustion chamber and enters (via holes) into the annular cavity 17. This cavity fed so all ring sectors. Each ring sector ( figure 3 ) comprises two distinct cavities 39 and 40 in the shape of a paper clip, separated by a partition 42 and respectively fed by orifices 37 and 38. The air flowing in the cavity 39 escapes through a series of channels of objection 44 opening on the inlet edge 16 of the ring sector while the air flowing in the cavity 40 escapes through a series of ejection channels 46 opening on the output edge 18 of the ring sector.

With the exception of the sealing systems between the sectors, the arrangement described so far is known per se. The invention relates in particular to an advantageous development of said inter-sector sealing systems.

More particularly ( Figures 2 to 4 ), each sealing system 26 here consists of three straight tabs engaged in respective straight slots of the radial faces of the two adjacent sectors. In particular, each sealing system ( figure 2 ) has a first tongue 27 and a second tongue 28, located on the inside of said radial faces, that is to say on the hot faces side of the sectors. The tongues 27, 28 are arranged in chevron, that is to say engaged in slots 31, 32 of said radial faces which extend obliquely with respect to the inner faces 12 and outer 14 of the sectors. These slots define the relative positions of the two tabs.

In addition, each sealing system comprises a third tongue 29 extending substantially from one end to the other of the adjacent sectors, parallel to the axis of the ring, on the outer side of said radial faces. The tongue 29 is engaged in rectilinear slots 33 of adjacent sectors. As we see on the figure 2 , the first tongue 27 extends between a point A located near the inlet edge of the two sectors, towards the inside (near the hot faces) and a point B located near the third tongue 29. The second tongue 28 is positioned so that it extends between a point C located near the outlet edge 18 of each of the two sectors, inwardly and a point D located near the first tongue, substantially between the middle and two-thirds of it from point A.

The pressures that are established in the inter-sector spaces inside and outside and between said first and second tabs on the one hand and the third tab on the other hand, are such that said first and third tabs 27 , 29 are pressed against the inner faces of the slots 31, 33 in which they are lodged while said second tongue 28 is pressed against the outer faces of the slot 32 in which it is housed, as can be seen in FIG. figure 2 .

The length of the first tongue 27 depends on the angle it makes with the third tongue 29. Once this angle is determined (several possibilities are represented on the figure 5 ) the position and the length of the second tab derive from it.

The angle defined by the first and third tab can be between 15 and 70 °, approximately.

The slots can be machined precisely and are perfectly localized. The tabs can be inserted into these slots and their relative positions can be perfectly controlled. It follows that the leakage section between said first and second tongues (S ₁ ) and the leakage section between the first and third tongues (S ₂ ) are perfectly controlled.

With particular regard to Figures 2 and 3 Another interesting feature of the invention, which concerns the cooling of the radial faces 20, 21 from the cooling air circulation cavity 35, shows that each sector comprises air ejection channels. 50, extending between the cavity 40 and at least one radial face of the sector. These channels open on the radial face 20 between the inner edge thereof (hot face) and said first and second tongues 27, 28. The chevron arrangement of the two tongues makes it possible to practice these air ejection channels. The channels are arranged in a row parallel to the axis of the ring. In the example of the figure 3 they all extend perpendicularly at the radial face. In the example of the figure 6 some channels 50 extend perpendicular to the radial face but others at the ends of said row or at least one of them are made at an angle and diverging with respect to the first, here in a direction from the cavity towards the radial face. The angle between the diverging channels may be between 10 and 120 ° One could also in some cases provide channels made at an angle and converging in the other direction. According to the variant of the figure 7 the parallel channels are at an angle to a direction perpendicular to the radial face. The angle is such that the air is ejected obliquely towards the rear of the ring. In the variant of the figure 8 the parallel channels are at an angle to a direction perpendicular to the radial face. The angle is such that the air is ejected obliquely towards the front of the ring.

According to the example, the channels 50 open on the radial face 20 which is that the blades first reach given the direction of rotation indicated by the arrow F. This is favorable to avoid or limit reintroductions of hot gas in the spaces inter-segment. One could also practice similar channels in the opposite wall, opening on the radial face 21. The air escaping channels 50 cools the wall in which they are practiced by convection (thermal pumping) while the opposite wall (face 21) is cooled by the impact of the air jets. In addition, the air jets escaping from the ducts 50 establish a kind of fluidic system preventing the ingestion of hot gases.

Note further that, preferably, the slots 31, 32, 33 are independent, that is to say they do not communicate with each other. This avoids having to make remains at the junction of two slots. Inter-sector leakage sections are also reduced.

The invention also relates to any ring sector or ring sector assembly having the characteristics described above.

Claims (12)

1. A turbine ring forming a rotor shroud, the ring being of the type constituted by a plurality of sectors (11) interconnected end to end with interposed sealing systems comprising tongues (27, 28, 29) extending between adjacent sectors, said tongues being housed in slots formed facing each other in adjacent radial faces of said sectors, each sealing system being constituted by rectilinear tongues engaged in respective rectilinear slots (31, 32, 33) in said radial faces, characterized in that the slots formed in each radial face are independent, i.e. said slots (31, 32, 33) do not communicate with one another.
2. A turbine ring according to claim 1, characterized in that each sealing system between two sectors comprises first and second tongues (27, 28) extending in a chevron configuration from the insides of said radial faces, said tongues being engaged in slots (31, 32) in said radial faces defining their relative positions.
3. A turbine ring according to claim 2, characterized in that each sealing system includes a third tongue (29) extending substantially from one end to the other of the adjacent sectors, parallel to the axis of the ring, and on the outside of said radial faces.
4. A turbine ring according to claim 3, characterized in that said first tongue (27) extends between a point (A) situated close to an inlet edge of each sector, towards the inside, and a point (B) situated close to said third tongue.
5. A turbine ring according to claim 4, characterized in that the angle defined by the directions of said first and third tongues lies in the range 15° to 70°.
6. A turbine ring according to claim 4 or claim 5, characterized in that said second tongue (28) extends between a point (C) situated close to an outlet edge of each sector, towards the inside, and a point (D) situated close to said first tongue, substantially between its middle and a point two-thirds of the way therealong.
7. A turbine ring according to claim 4 or claim 5, in which each sector includes a cooling air flow cavity (40), characterized in that each sector includes air ejection channels (50) extending between said cavity and at least one radial face (20) of said sector, these channels opening out in said radial face between an inside edge thereof and said first and second tongues.
8. A turbine ring according to claim 7, characterized in that at least some of the channels extend substantially perpendicularly to said radial face.
9. A turbine ring according to claim 7, characterized in that the orifices of said channels are disposed in a row extending parallel to the axis of the ring.
10. A turbine ring according to claim 9, characterized in that channels situated at the ends of said row are formed at an angle and diverge relative to the other channels on going from the cavity towards the radial face.
11. A turbine ring according to any preceding claim, characterized in that the facing slots of two adjacent radial faces of said sectors house a single tongue (27, 28, 29).
12. A turbine, characterized in that it includes a ring according to any preceding claim.

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