FR3140112A1 - Improvement of sealing in a turbomachine turbine - Google Patents

Abstract

The invention relates to a sealing assembly for a casing (4) of a low pressure turbine (1) of a turbomachine, the sealing assembly comprising: - an annular structure (5) extending around a longitudinal axis (X) and going from upstream to downstream, the annular structure (5) comprising an upstream end extending radially towards the interior of the structure (5) to define a first branch (53) from which extends axially upstream a second branch (54), - a ferrule (6) comprising a face (62) arranged opposite and at a distance from the first and second branches (53, 54) of the annular structure (5), sealing assembly comprising an annular thermal deflector (D) disposed between the annular structure (5) and ferrule (6), the thermal deflector (D) comprising a first axial wall (80) resting on an external surface (540) of the second branch (54), a second radial wall (81) extending from a downstream end of the first wall (80) along the first branch (53), a third radial wall (82) extending from a upstream end of the first wall (80) towards the inside so as to be opposite and at a distance from the face (62). Figure for abstract: Figure 4

Description

Improvement of sealing in a turbomachine turbine

GENERAL TECHNICAL AREA

The field of invention is that of turbomachines. More specifically, the invention relates to a sealing assembly for a turbomachine turbine, as well as a turbomachine comprising such an assembly.

STATE OF THE ART

A turbomachine, in particular a twin-body turbomachine, conventionally comprises, from upstream to downstream according to the direction of circulation of the flow in the turbomachine, a fan, a low pressure compressor, a high pressure compressor, a combustion chamber, a turbine high pressure and a low pressure turbine.

The low pressure turbine makes it possible to exploit and release the power generated in the combustion chamber.

As such, the sealing of the vein delimiting the flow passing through the low pressure turbine must be ensured in order to guarantee a high level of performance of the turbomachine. It is therefore necessary to avoid leaks from the vein towards the components making up the low pressure turbine casing.

There illustrates a turbine 1 for a turbomachine of known type.

Such a turbine comprises several successive stages each comprising a fixed blade 2 and a blade 3 rotating around an axis X of rotation (and longitudinal of the turbomachine).

By convention, in the present application, the terms "upstream" AM and "downstream" AV are defined in relation to the direction of air circulation in the turbine, that is to say from left to right on the . Likewise, by convention in the present application, the terms "interior" and "exterior", and "internal" and "external" are defined radially with respect to the axis X of the turbomachine. Finally, the term “circumferential” is used in relation to any annular part or sector of an annular part to designate an orientation, a direction or even a dimension considered with reference to the circumference of this part or this sector.

Each fixed blade 2 comprises a radially internal annular platform 21 and a radially external annular platform 22.

The fixed blade 2 is attached radially outwards to an external casing 4 of the turbine.

The blades 3 rotate inside an annular structure or sectored ring 5 attached to the external casing 4. This ring 5 is advantageously formed of several ring sectors 50 to overcome problems of expansion of the assembly. These ring sectors 50 which extend circumferentially in an arc of a circle are arranged circumferentially end to end.

The ring sectors 50 each internally carry a block of abradable material 51. These blocks of abradable material are capable of cooperating by friction with annular wipers 32 arranged at the radially outer periphery of each blade 3 of the rotor.

As visible in detail on the , the ring 5 comprises a main body 52 which extends radially inwards to define a first branch 53 which is substantially radial, the radially internal end of this first branch 53 extending axially upstream by a second branch 54.

At the level of the circumferential ends of the ring 5, housings 56 are provided in the form of slots into which tongues L are inserted. More precisely, the tongues L are partly mounted in housings 56 formed in the ring 5. In the case of several, such an assembly contributes to ensuring sealing between sectors.

In the connection zone of the body 52 to the first branch 53, the ring 5 comprises at least one appendage directed downstream which forms a hook 57, for its attachment to the casing 4 in which a reservation 40 is provided for this purpose .

Upstream of these two parts, there is an annular ferrule 6 which is used for positioning the casing and more generally for that of the high pressure turbine relative to the low pressure turbine, in order to ensure geometric continuity of the primary vein of the machine.

This shell 6 has a through opening 61 which has the function of directing air coming from the upstream compressor to cool the casing 4, mainly in the region of the hook 57.

A member 7 forming a seal is inserted between the ferrule 6 and the first branch 53 of the sector 50 and contributes to thermally protecting the region of the hook 57.

As shown in the , the ferrule 6 extends radially inwards well below the second branch 54 of sector 50.

This configuration exposes the radially internal part 60 of the ferrule 6, and more particularly its face 62 oriented downstream, to the hot air of vein V.

Furthermore, by construction, there is a significant space at the level of the first stage of the low pressure turbine and the first blade of the low pressure turbine, which makes the shroud 6 vulnerable to a potential reintroduction of vein air, symbolized by the arrow R, via the space E separating the ferrule 6 from the second branch 54.

In any case, unless a part forming a barrier against this reintroduction of vein air is introduced, the ferrule 6 is subjected to high temperatures and significant radiation, as is symbolized by the undulations S of the . We are then potentially exposed to the formation of cracks, which is not desirable.

A solution to resolve this problem consists of adding to the radially internal part 60 of the shell, a part (not shown here) forming a rampart.

In practice, this part is welded to the shell 6. But again, we are exposed to the formation of cracks, in particular due to the different nature of the materials of the shell and of the part forming the rampart, which causes coefficients of different expansion. It is therefore impossible to avoid the constraints leading to these cracks.

Another solution, as illustrated in , consists of extending the second branch 54 of sector 50 by a third radially internal branch 55 therefore forming a one-piece deflector which ensures the aforementioned function of rampart. However, due to the need to put in place a tab L, this branch necessarily has a negligible thickness, so that the spacing e between the ferrule 6 and the upstream face of this branch 55, taking into account the tolerances mounting, is relatively high.

However, a notorious phenomenon in this area of the turbine is that the blade 3 is subject to significant axial movement, so that the lip 32 risks coming into contact with the branch 55, which must absolutely be avoided.

PRESENTATION OF THE INVENTION

The aim of the invention is to propose a solution making it possible to thermally protect structural elements while avoiding the problems of crack formation explained above, and without risk of contact with moving elements.

To this end, the invention relates, according to a first aspect, to a sealing assembly for a low-pressure turbine casing of a turbomachine, the sealing assembly comprising:

- an annular structure extending around a longitudinal axis and going from upstream to downstream, the annular structure comprising an upstream end extending radially towards the interior of the structure to define a first branch from which 'extends axially upstream a second branch,

- a ferrule comprising a face arranged opposite and at a distance from the first and second branches of the annular structure,

the sealing assembly comprising an annular thermal deflector disposed between the annular structure and ferrule, the thermal deflector comprising a first axial wall resting on an external surface of the second branch, a second radial wall extending from a downstream end of the first wall along the first branch, a third radial wall extending from an upstream end of the first wall inwards so as to be opposite and at a distance from the face.

According to other advantageous and non-limiting characteristics of the invention, taken alone or according to a technically compatible combination of at least two of them:

- the thermal deflector comprises a fourth axial wall which extends upstream from the second wall, parallel to and opposite the first wall;

- the assembly comprises an elastic member disposed between the ferrule and the deflector, and extending from the face so as to press the thermal deflector against the first and second branches of the first structural element;

- the elastic member is a seal;

- the organ extends at least partly between the first and fourth walls;

- the annular structure comprises several annular sectors which extend circumferentially around the longitudinal axis, the sectors being adjacent;

- the annular thermal deflector is formed of several sectors arranged circumferentially around the longitudinal axis, the sectors of the deflector being adjacent;

- the circumferential dimension of a thermal deflector sector is equal to that of an annular sector, or is substantially equal to a multiple of that of an annular sector;

- one end of the third wall of each deflector sector comprises in the circumferential direction a tab forming a male member, while the opposite end comprises a tab forming a complementary female member;

- at least one sealing tab is mounted partly in a housing of a circumferential edge of an annular sector and for the other part, in a housing of a circumferential edge of an adjacent annular sector located opposite notice ;

- each annular sector has a hook adapted to be fixed to a casing;

- each deflector sector comprises a pair of tabs positioned on either side of said hook, to immobilize said deflector sector circumferentially;

- the annular structure is placed at the inlet of a low pressure turbine.

The invention relates, according to a second aspect, to a turbomachine assembly comprising a low pressure turbine, the low pressure turbine comprising a fixed external casing in connection with an upstream shroud, the turbomachine assembly comprising a sealing assembly according to the first aspect of the invention.

The invention relates, according to a third aspect, to a turbomachine comprising a turbomachine assembly according to the second aspect of the invention.

The invention relates, according to a fourth aspect, to an aircraft comprising a turbomachine according to the third aspect of the invention.

The advantages of the invention are multiple.

There is no need to attach the heat baffle to the first structural member, so potential problems with cracking due to different expansion coefficients are completely avoided.

In addition, ease of assembly is improved.

In addition, the thickness of this profile-shaped deflector can be greatly reduced, in any case compared to the solution illustrated in , so that any potential contact between the defector and other elements is ruled out.

PRESENTATION OF FIGURES

Other characteristics and advantages of the invention will appear from the description which will now be made, with reference to the appended drawings, which represent, by way of indication but not limitation, different possible embodiments.

In these drawings:

- there is a sectional view of a low pressure turbine according to the state of the art;

- there is a detailed view of part of the turbine of the ;

- there is a view analogous to the , according to a different embodiment;

- there is another view similar to the two previous figures, integrating the sealing assembly according to the invention;

- there is detail of the , aiming to show more particularly the particular shape of a deflector of the sealing assembly;

- there is a detailed view representing more particularly one end of the aforementioned deflector;

- there is a perspective view of a sealing ring sector according to one embodiment of the invention;

- there is a detailed view intended to show how a hook secured to a ring sector cooperates with the aforementioned deflector;

- there is a perspective view of two adjacent ring sectors, which cooperate with a single deflector.

In all the figures, identical elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION

Figures 4 to 9 illustrate a sealing assembly according to one embodiment. Note that the elements which are identical to those of the low pressure turbine previously described in relation to Figures 1 and 2 will not be described again.

The sealing assembly according to the invention is essentially distinguished from that which has been described with reference to the or 3 by the fact that it comprises an annular thermal deflector D of sheet metal type.

As is visible in particular in the , the thermal deflector D comprises a first wall 80 directed axially.

This first wall 80 is extended at its downstream end by a second wall 81 directed radially outwards, and at its upstream end by a third wall 82 directed radially inwards.

As is visible in particular in the , a ring 5 extends around a longitudinal axis and extends upstream in a radial manner towards the interior to define a first branch 53 substantially radial and the radially internal end of this first branch 53 extending axially towards the upstream by a second branch 54. The second branch 54 having an external circumferential face 540.

Furthermore, an annular ferrule 6 comprises a part 60 which extends radially inwards well below the second branch 54 of the ring 5 comprising a face 62 arranged opposite and at a distance from the first and second branches 53, 54 of the first structural element 5. This configuration exposes the radially internal part 60, and more particularly the part of its face 62 oriented downstream which extends inwards well below the second branch 54, at the hot air from vein V.

And as shown more particularly by , the first and second walls 80 and 81 of the annular thermal deflector D are dimensioned to support and cover on the one hand the face 540 of the second branch 54 of the ring 5 and, on the other hand, the first branch 53 .

And the third wall 82 extends, for its part, opposite the face 62 of the shell 6, in order to materialize a thermal protection rampart for this face.

Advantageously, the installation of the annular thermal deflector D does not require any welding or other means of connection to the first structural element 5. In fact, it rests by its wall 80 against the second branch 54.

According to one embodiment, the annular thermal deflector D is blocked axially by a member 7 which, as presented in the introduction, preferably consists of a seal, this elastic member pressing the wall 80 against the first branch 53 of the first structural element 5. The member 7 can optionally be an Omega type seal. As can be seen in the figures, the annular thermal deflector D comprises a fourth wall 83, which extends in the extension of the second wall 81, parallel to and opposite the first wall 80. This fourth wall 83 contributes to centering the organ 7 and to protect it thermally.

According to a possible embodiment, the ring 5 is formed of several ring sectors 50 in order to resolve the expansion problems of the assembly. These ring sectors 50 extend circumferentially in an arc of a circle, and are arranged circumferentially end to end.

According to one embodiment, at the circumferential ends of the ring sectors 50 are provided housings 56 in the form of slots into which tongues L can be introduced. More precisely, the tongues would be mounted partly in the housings 56 of a sector 50 and partly in the housing of an adjacent sector. This assembly helps to ensure sealing between sectors.

In the same way as for the ring 5, the deflector D can be made up of several identical sectors 8 arranged adjacently in the circumferential direction.

According to one embodiment, the length, that is to say the circumferential dimension of a sector 8 is substantially equal to that of a sector 50 of a ring.

Alternatively, this length is substantially equal to a multiple of that of a sector 50 of a ring. Thus, as illustrated in , sector 8 has a length such that it covers two adjacent sectors 50.

As is particularly visible in the , and according to a possible embodiment, one end of the third wall 82 of the sector 8 of the annular thermal deflector D comprises, in the circumferential direction, a tab 820 which forms a male member, while the opposite end of this wall ( not visible in the figure), includes a leg forming a complementary female organ. In this way, when two sectors are positioned in continuity with each other, the male organs of one and the female organs of the other overlap.

As mentioned previously, each sector 50 comprises at least one appendage 57 in the form of a hook adapted for its attachment to the casing 4.

According to an advantageous embodiment of the present invention, a single appendix 57 is provided on each sector. This helps to eliminate its hyperstatism, while improving its assembly and manufacturability.

Furthermore, sector 8 is provided with blocking means which allow it to be blocked circumferentially in relation to ring sector 50 via appendix 57.

These blocking means are particularly visible at the . These are two tangential stop tabs 810 which are in one piece with the wall 81 and whose spacing is equal, to the nearest clearance, to the length, that is to say the circumferential dimension of the appendix 57.

In the embodiment presented in which the sector comprises a fourth wall 83 ( ), this is interrupted locally to allow the passage of said tabs 810.

Claims (15)

Sealing assembly of a casing (4) of a low pressure turbine (1) of a turbomachine,
the sealing assembly comprising:
- an annular structure (5) extending around a longitudinal axis (X) and going from upstream to downstream, the annular structure (5) comprising an upstream end extending radially towards the inside of the structure (5) to define a first branch (53) from which a second branch (54) extends axially upstream,
- a ferrule (6) comprising a face (62) arranged opposite and at a distance from the first and second branches (53, 54) of the annular structure (5),
the sealing assembly comprising an annular thermal deflector (D) disposed between the annular structure (5) and ferrule (6), the thermal deflector (D) comprising a first axial wall (80) resting on an external surface (540) of the second branch (54), a second radial wall (81) extending from a downstream end of the first wall (80) along the first branch (53), a third radial wall (82) extending from an upstream end of the first wall (80) towards the inside so as to be facing and at a distance from the face (62). Sealing assembly according to claim 1, in which the thermal deflector (D) comprises a fourth axial wall (83) which extends upstream from the second wall (81), parallel and opposite the first wall ( 80). Sealing assembly according to any one of claims 1 to 2, comprising an elastic member (7) disposed between the ferrule (6) and the deflector, and extending from the face (62) so as to press the thermal deflector (D) against the first and second branches of the first structural element (5). Assembly according to claim 3, in which the elastic member (7) is a seal. Sealing assembly according to claim 4 in combination with claim 2, in which the member (7) extends at least partly between the first (80) and fourth walls (83). Sealing assembly according to one of claims 1 to 5, in which the annular structure (5) comprises several annular sectors (50) which extend circumferentially around the longitudinal axis, the sectors (50) being adjacent. Sealing assembly according to one of claims 1 to 6, in which the annular thermal deflector (D) is formed of several sectors (8) arranged circumferentially around the longitudinal axis, the sectors (8) of the deflector being adjacent. Sealing assembly according to claim 7, in which the circumferential dimension of a sector (8) of thermal deflector (D) is equal to that of an annular sector (50), or is substantially equal to a multiple of that of an annular sector (50). Sealing assembly according to one of claims 7 to 8, in which one end of the third wall (82) of each sector (8) of deflector (D) comprises in the circumferential direction a tab (820) forming a male member , while the opposite end has a tab forming a complementary female organ. Sealing assembly according to one of claims 6 to 9, in which at least one sealing tab (L) is mounted partly in a housing (56) of a circumferential edge of an annular sector (50) and for the other part, in a housing of a circumferential edge of an adjacent annular sector (50) located opposite. Sealing assembly according to one of claims 6 to 10, in which each annular sector (50) comprises a hook (57) adapted to be fixed to a casing (4). Sealing assembly according to one of claims 7 to 11, in which each sector (8) of deflector (D) comprises a pair of tabs (810) positioned on either side of said hook (57), to immobilize said deflector sector (8) circumferentially. Turbomachine assembly comprising a low pressure turbine, the low pressure turbine comprising a fixed external casing (4) in connection with an upstream shroud (6), the turbomachine assembly comprising a sealing assembly according to one of claims 1 to 12 arranged downstream of the ferrule (6). Assembly according to claim 13, in which the annular structure is arranged at the inlet of the low pressure turbine. Turbomachine comprising a turbomachine assembly according to one of claims 13 to 14.