FR3102207A1 - Turbine distributor comprising an annular sealing element with isostatic retention - Google Patents

Abstract

The invention relates to a turbine distributor (16), comprising bladed sectors (17) assembled in an arrangement having a shape of revolution about a longitudinal axis (AX), each bladed sector (17) comprising a head and a foot (21) connected to each other by at least one blade (22-25). The distributor comprises an annular sealing element (18) surrounded by the feet (21) of the bladed sectors (17), which has a radially inner face covered with an abradable material (19). At least three annular linear connections (32) oriented radially with respect to the longitudinal axis (AX), connect the annular sealing element (18) to a root (21) of the bladed sector (17). Figure for the abstract: Figure 4.

Description

Turbine distributor comprising an isostatically maintained annular sealing element

The invention relates to a turbojet engine and more generally to a turbomachine comprising a distributor having a radially inner face carrying an annular sealing element of a labyrinth-type seal, this annular sealing element being made of an abradable material to cooperate with wipers carried by a rotor opposite this annular sealing element.

PRIOR ART

A turbofan engine has an inlet duct through which air is drawn into a low pressure compressor or fan before being split into a central primary stream and a secondary stream surrounding the primary stream.

The primary flow circulates in a space called the primary stream, and it passes through rotating elements comprising bladed wheels carried by the rotor of the turbomachine and fixed elements of the rectifier and distributor type carried by the stator of the turbomachine.

The stator comprises various casings including in particular a high pressure compressor casing, a primary stream casing, a high pressure turbine casing, and an exhaust casing.

The secondary flow circulates in a space called secondary stream which extends radially between the inner stream and an external structure called hull or nacelle of the turbojet engine, which surrounds the turbomachine.

After being set in motion by the fan and having passed through fixed outlet blades called OGVs (outlet guide vanes in English), this secondary flow is propelled backwards to generate thrust. The primary flow, which also comes from the flow set in motion by the fan, for its part successively passes through a high pressure compressor, a combustion chamber then high pressure and low pressure turbines, and makes it possible to drive the fan before being propelled out of of the turbomachine. The high pressure turbine is rotationally linked with the high pressure compressor, and the low pressure turbine is rotationally linked with the low pressure compressor.

Such a low-pressure turbine, marked 1 in the partial view of FIG. 1, is thus surrounded by a casing portion 2 and comprises stages, including a distributor 3 formed by a series of fixed blades 4 rigidly fixed to the portion housing 2 surrounding a rotor. This rotor has a flange 6 which carries a disk 7 carrying blades 8 immediately downstream of the distributor 3. Another disk 9 carrying blades 11 is located upstream of the distributor 3, also being carried by the flange 6.

Sealing between the rotating disk 7 and a radially internal cylindrical face of the distributor is ensured by means of a labyrinth seal comprising an abradable material 12 carried by the radially internal cylindrical face of the distributor and by wipers 13 carried by the disc 7. These wipers cooperate with a radially inner surface of the abradable material to provide a seal.

More particularly, the distributor 3 is formed of several bladed sectors arranged circumferentially around the stator, each bladed sector comprising a root and a head connected to each other by several blades. The feet of the different bladed sectors jointly delimit the radially inner face of the distributor covered with abradable material.

The coating of abradable material covering the radially inner face of the distributor thus comprises a discontinuity at the junction of each pair of adjacent bladed sectors. These discontinuities constitute the seat of gas leaks which penalize the efficiency of the turbine.

As such, it has been envisaged to provide an annular sealing element formed in one piece to present a continuous radially internal face, which can in fact be covered with abradable material without discontinuity.

Nevertheless, in operation, the low pressure distributor undergoes high thermal stresses, which leads in the prior art the annular sealing element comprising abradable element fixed to the distributor to undergo high thermal stresses and therefore to expand according to the expansions of the distributor which may be significant. This leads in particular to large clearances between the abradable material and the wipers due to the fact that the diameter of the annular sealing element varies significantly depending on the operating mode.

The object of the invention is to provide a solution for limiting the variations in diameter of the annular sealing element as a function of the operating speed of the engine, so as in particular to reduce leaks through the labyrinth seal.

To this end, the subject of the invention is a turbine nozzle, comprising bladed sectors arranged to form a crown around a longitudinal axis, each bladed sector comprising a head and a foot connected to each other by at least one vane, one the annular sealing element surrounded and carried by the roots of bladed sectors which has a radially internal face covered with an abradable material, and at least three annular linear connections oriented radially with respect to the longitudinal axis , each annular linear link connecting the annular sealing element to a bladed sector foot.

With this solution, there are no discontinuities in the abradable material liable to cause leaks, the annular sealing element is maintained without constraint, whatever the thermal state of the turbojet engine.

Thus, the expansion of the distributor and that of the sealing ring are decoupled. In addition, it is thus possible to control the position of the sealing element in operation, for example by controlling the temperature of the air circulating in a cavity located for example radially under the distributor, that is to say closer of the longitudinal axis than the distributor.

Thus, the performance is improved because the clearances between the abradable material and the wipers are controlled since the radial position of the radially inner surface of the sealing ring is better controlled in operation. In the design, it is also possible to provide for smaller clearances between the wiper and the abradable material because the abradable element is subject to fewer thermal stresses in operation. This improves performance by being able to design weaker games.

The invention also relates to a distributor thus defined, in which each bladed sector comprises an annular linear connection, the annular sealing element being connected to each bladed sector by a corresponding annular linear connection.

The invention also relates to a distributor thus defined, in which each annular linear connection comprises a finger comprising a body oriented radially and carrying a bulb, and a corresponding hole oriented radially and having a diameter corresponding to that of the bulb, the bulb being sliding in the hole.

The invention also relates to a defined distributor, in which at least one hole has a flared mouth.

The invention also relates to a distributor thus defined, in which the finger of each annular linear connection is carried by the annular sealing element and in which the corresponding hole is formed in a root of the bladed sector.

The invention also relates to a distributor thus defined, comprising at least one bladed sector foot provided with a radial wall, in which is formed a hole of an annular linear connection, this hole extending radially.

The invention also relates to a distributor thus defined, in which each bulb is located at the free end of a corresponding finger body.

The invention also relates to a distributor thus defined, comprising at least one helical spring engaged in a hole of an annular linear connection and arranged between a corresponding finger end and the bottom of the hole.

The invention also relates to a turbomachine turbine comprising a distributor thus defined.

The invention also relates to a turbomachine comprising a turbine thus defined.

is a view in partial longitudinal section of a low pressure turbine according to the state of the art;

is a local view in longitudinal section of a seal according to the state of the art;

is a perspective view of a low pressure turbine nozzle according to the invention;

is a perspective view of a distributor portion with its connection to the annular internal sealing element in the distributor according to the invention;

is a perspective view showing the radial annular linear connection connecting a dispenser foot with the annular internal sealing element according to the invention;

is a side sectional view at the beginning of the assembly of a distributor according to the invention in a turbine;

is a side sectional view at the end of assembly of a distributor according to the invention in a turbine.

EXPOS E DETAIL E PARTICULAR EMBODIMENTS

The distributor marked with 16 in FIG. 3 is made up of several bladed sectors marked with 17 joined together to jointly form an assembly having a shape of revolution, which is secured by its outer periphery to the casing of the turbojet engine in order to be held thereto.

Each bladed sector 17 comprises a radially outer head, and a radially inner foot, each having the shape of an arcuate upright, connected to one another by fixed blades which here are four in number.

All of the heads of the bladed sectors define an external annular structure of the distributor 16 while all of the feet define an internal annular structure of this distributor 16.

Additionally, this distributor 16 carries an annular inner sealing element 18 formed and which is provided on its radially inner face with a ring of abradable material 19 cooperating with wipers such as the wipers 13 of FIG. 2, to form with those this is a watertight barrier.

According to the invention, the annular sealing element 18 is secured to the bladed sectors by annular linear connections oriented radially to ensure that it remains centered on the axis AX including when it expands and contracts under the effect of thermal variations.

In Figure 4, a bladed sector 17 has a foot 21 connected by four blades 22, 23, 24, 25 to its head which is not shown in this figure. This foot 21 has the shape of an annular arc having, in a plane passing through the longitudinal axis AX, a section whose shape corresponds to the letter T. It comprises more particularly a platform 27 in the form of a portion of a truncated cylinder, or of truncated cone, extended towards the axis AX by a stiffening radial wall 28 in the form of a flat crown portion extending along a plane normal to the axis AX. In other words, the foot 21 has the shape of a T-section, which extends over an angular portion corresponding to the circumferential extent of the bladed sector 17, around the axis AX.

The annular sealing element 18 which extends around the axis AX, here comprises an annular upright 29 extending over 360° around the axis AX, and which has a radially internal face covered with a material abradable 19 extending substantially continuously over this entire surface.

The annular upright 29 comprises a cylindrical portion 30 coaxial with the axis AX, provided with an outer central rim 31 in the form of a flat crown oriented normal to the axis AX, the cylindrical portion 30 carrying the abradable material 19 and the outer central flange 31 being in connection with the radial wall 28.

As illustrated in Figure 4, when the assembly is in place, the rim 31 extends in line with the radial wall 28.

More precisely, the outer central flange 31 of the annular sealing element 18 is linked to the radial wall 28 of the foot 21 by an annular linear link 32 which is formed by a radial finger 33 extending the flange 31, which is engaged in a corresponding hole 34 to slide therein. This hole 34 also extends radially with respect to the axis AX, being formed in the thickness of the radial wall 28.

More particularly, and as seen in Figure 5, the finger 33 comprises a generally cylindrical body 36 having a diameter significantly smaller than that of the hole 34, and which is terminated by a bulb 37 having an external diameter corresponding to that of the hole 34.

The cooperation of the finger 33 with the hole 34 thus constitutes an annular linear connection, that is to say having four degrees of freedom. As shown in Figure 5, the finger 33 and the hole 34 extend in a radial direction marked AR.

More concretely, the finger 33 engaged in the hole 34 is thus free to:

– translate along the radial axis AR;

– rotate in a plane containing the AR and AX axes;

– rotate in a plane normal to the AX axis and containing the AR axis;

– turn on itself around the rear axis.

The invention takes advantage of the degree of freedom in translation, which allows the annular sealing element 18 to expand and contract without being offset with respect to the axis AX. When the temperature of the annular sealing element decreases with respect to that of the bladed sectors, it can retract while remaining centered on the axis AX, while then establishing a radial play between its external face and the feet of the bladed sectors. . When the temperature of the annular sealing element increases in relation to that of the bladed sectors, it can expand by reducing the radial play separating its radially outer face and the feet of the bladed sectors. Thus, the radial position of the annular sealing element 18 is less affected by the temperature variations that may occur in the gas flow path, thus ensuring better control of the clearances in operation.

The invention also takes advantage of the degree of freedom in rotation in a plane passing through the axes AX and AR, which allows an inclination of the bladed sector 17 with respect to a plane normal to the axis AX, this inclination being called tilting.

In order to increase the maximum possible tilting for a bladed sector 17, the hole 34 has a mouth, marked 38 in Figure 5, which is flared so as to increase the maximum possible inclination of the finger 33 with respect to the hole 34.

Furthermore, the maximum possible inclination of the finger 33 is also conditioned by the difference in diameter between the body 36 of the finger and the diameter of the hole 34: the maximum inclination is all the higher as this difference in diameters is important. .

In the example of the figures, the bulb 37 has an olive shape, but other curved shapes are possible, such as in particular a spherical shape, or even a disc shape, the determining element with regard to this bulb being its diameter. external which corresponds to the nominal diameter of the hole 34.

Additionally, a helical spring can be engaged in the hole 34 to be interposed between the end of the finger 33 and the bottom of the hole 34, so as to be continuously stressed in compression, in order to limit the vibrations of the bladed sector and of the annular sealing element 18 when the assembly is in service.

The number of annular linear connections is at least three, advantageously distributed evenly around the axis AX, to ensure centered maintenance of the annular sealing element 18 including when its diameter fluctuates with thermal variations.

In other words, thanks to the radial annular linear connections, the mounting of the annular sealing element is substantially isostatic. When the nominal diameter of the annular sealing element 18 increases with respect to the internal diameter delimited by the feet of the bladed sectors, the various fingers of the connections slide radially in their respective holes over substantially the same strokes, so that the centering of the annular sealing element 18 on the axis AX is retained.

In general, the number of annular linear connections to be implemented is conditioned by the mechanical strength required for the annular internal sealing element. This number of connections, which is at least three, can be increased to provide, for example, an annular linear connection of the annular sealing element with each bladed sector making up the distributor.

By authorizing a tilting of the bladed sectors with respect to the annular sealing element, the annular linear connections simplify the assembly of the distributor by allowing its so-called tilting assembly, as illustrated schematically in Figures 6 and 7.

The assembly of the distributor 16 thus consists in bringing it as a whole closer to the adjacent bladed disc, identified by 39 in FIGS. 6 and 7, by moving it along the axis AX, the assembly consisting of the bladed sectors 17 and the annular sealing element 18 then forming a whole. This approximation is carried out until the heads 41 of the bladed sectors 17 are engaged in the corresponding attachments of a casing 42 surrounding the assembly.

As schematically illustrated in FIG. 7, once the heads 41 are secured to the casing 42, the tilting of the sectors 17 authorized by the links 32 makes it possible to adjust the position of the annular sealing element 18 longitudinally, in order to place it to the right of corresponding wipers 43 carried by the bladed disc 39.

Throughout the assembly phase, the annular sealing element remains centered on the axis AX, regardless of the greater or lesser tilting of the bladed sectors. Thanks to the conservation of the centering of the annular sealing element during assembly, it remains concentric with the wipers, which allows it to be easily translated along the axis AX around these wipers.

Furthermore, the differential thermal expansions also tend to cause a tilting of the bladed sectors, so that the presence of the annular linear connections which allow this tilting makes it possible to reduce the mechanical stresses undergone by the whole of the distributor in all the thermal states of the turbojet. .

Claims (10)

Turbine distributor (16), comprising bladed sectors (17) arranged to form a ring around a longitudinal axis (AX), each bladed sector (17) comprising a head and a foot (21) connected to each other the other by at least one vane (22-25), an annular sealing element (18) surrounded and carried by roots (21) of bladed sectors (17) and which has a radially inner face covered with an abradable material (19), and at least three annular linear connections (32) oriented radially with respect to the longitudinal axis (AX), each annular linear connection (32) connecting the annular sealing element (18) to a foot (21 ) of bladed sector (17). 2. Distributor according to claim 1, wherein each bladed sector (17) comprises an annular linear connection (32), the annular sealing element (18) being connected to each bladed sector (17) by an annular linear connection ( 32) corresponding. 3. Dispenser according to claim 1 or 2, wherein each annular linear connection (32) comprises a finger (33) comprising a body (36) carrying a bulb (37), and a corresponding hole (34) having a diameter corresponding to that of the bulb (37), the bulb (37) being sliding in the hole (34). 4. Dispenser according to claim 3, wherein at least one hole (34) has a mouth (38) flared. 5. Dispenser according to claim 3 or 4, wherein the finger (33) of each annular connection (32) is carried by the annular sealing element (18) and wherein the corresponding hole (34) is formed in a foot (21) of bladed sector (17). 6. Distributor according to one of claims 4 to 5, comprising at least one foot (21) of bladed sector (17) provided with a radial wall (28) in which is formed a hole (34) of a linear connection annular (32), this hole (34) extending radially. 7. Dispenser according to one of claims 3 to 6, wherein each bulb (37) is located at the free end of a body (36) of corresponding finger (33). 8. Distributor according to one of claims 3 to 7, comprising at least one helical spring engaged in a hole (34) of an annular linear connection (32) and disposed between a corresponding finger end (33) and the bottom of the hole (34). 9. Turbomachine turbine comprising a distributor according to one of claims 1 to 8. 10. Turbomachine comprising a turbine according to claim 9.