FR3136504A1 - Abradable element for a turbomachine turbine, comprising cells having different inclinations - Google Patents

Abstract

The present application relates to an abradable element (30) for a turbomachine turbine, extending longitudinally along an axis (A), in which the abradable element (30) comprises along the axis (A) an upstream part ( 33) and a downstream part (34) each comprising a plurality of cells, the upstream towards the downstream being defined in a direction of normal flow of the gas through the abradable element (30), all or part of the cells in the upstream part (33) having a greater dimension of longitudinal extension which extends along a first axis (X1) forming a first angle (α1) with the axis (A), all or part of the cells in the part downstream (34) having a greater dimension of longitudinal extension which extends along a second axis (X2) forming a second angle (α2) with the axis (A), in which the first angle (α1) is strictly positive and the second angle (α2) is negative or zero. Figure for abstract: Fig. 3a

Description

Abradable element for a turbomachine turbine, comprising cells having different inclinations

The present application concerns the field of aircraft turbomachines, more particularly concerns an abradable element for a turbomachine turbine as well as a turbine, a turbomachine and an aircraft comprising such an abradable element.

TECHNOLOGICAL BACKGROUND

An aircraft conventionally comprises at least one turbomachine to provide propulsion. The turbomachine can be a turbojet or a turboprop. The turbomachine extends substantially around a longitudinal axis. The turbomachine comprises, from upstream to downstream in the direction of flow of the gas flow through the turbomachine, a fan, at least one compressor, a combustion chamber, at least one turbine, and a gas exhaust nozzle .

The turbine comprises one or more stages, each stage comprising a fixed distributor and a movable wheel, the distributors and the movable wheels of the turbine being arranged alternately along the longitudinal axis. The turbine further comprises a fixed casing extending around the distributor and the movable wheel. An example of the design of a turbine is known from document FR 3 034 129 A1.

The distributor comprises fixed vanes distributed circumferentially around the longitudinal axis of the turbomachine and connected by their radially external ends to the fixed casing. The mobile wheel comprises an internal disk and movable blades circumferentially distributed around the disk and connected by their ends radially internal to the disk. The blades of the moving wheel are arranged at their external end facing the fixed casing. The disk of the moving wheel comprises a ferrule opposite which the internal ends of the fixed vanes of the distributor are located.

In such an arrangement, there is a first radial clearance between the external ends of the blades of the moving wheel and the fixed casing. In addition, there is a second radial clearance between the internal ends of the distributor vanes and the shroud. Taking into account in particular the differential expansions occurring when the turbomachine is in service, and which partly condition the radial clearances, these cannot be canceled. Consequently, part of the primary flow flowing at the level of the turbine, called leakage flow, passes between the moving wheel and the fixed casing, or between the distributor and the shell, in the spaces formed by the radial clearances.

In particular, as illustrated in , a leakage flow Ff' separates from the rest of the primary flow Fp' between the external ends of the blades 20' of the moving wheel and the casing 100' at the level of the first radial clearance. The first leak flow Ff' is then reinjected into the rest of the primary flow Fp' downstream of the moving street 20'. A second leak flow can pass between the internal ends of the vanes 10' of the distributor and the shroud of the movable wheel at the level of the second radial clearance. The second leak flow is then reinjected into the rest of the primary flow Fp' downstream of the distributor. The leakage flows each have a leakage rate which depends on the value of the respective radial clearance. The radial clearances therefore have a significant impact on the efficiency of the turbomachine, because the leakage flows bypass the blades of the turbine, and therefore lead to a reduction in the efficiency of the turbomachine.

Sealing wipers can be placed on the internal or external ends of the blades of the moving wheel and/or on the ferrule of the disc of the moving wheel. An abradable element is placed opposite the respective sealing lip, on an internal face of the fixed casing and/or on an internal end of the distributor vane. The abradable element makes it possible to reduce the value of the radial clearance between an element of the turbine which carries the abradable element and an element of the turbine which carries the sealing lip, and thus to limit the flow rate of the leak flow. The abradable element may have a cellular structure, for example a honeycomb structure. Document WO 2020/208224 A1 and document FR 3 073 890 A1 each describe an abradable element having a cellular structure with a variable density of cells. In operation, the movable sealing wiper may rub against the fixed abradable element, the abradable element wearing out before the sealing wiper. Radial clearances thus increase over time.

In addition, the reinjection of the leakage flows into the rest of the primary flow downstream of the abradable element disrupts the primary flow, due to a difference in orientation, in particular tangential, between the reinjected leakage flow and the rest of the primary flow, which also leads to a reduction in the efficiency of the turbomachine. The disturbance is accentuated due to the fact that a tangential speed of the leak flow at the level of the reinjection zone is kept low compared to a tangential speed of the leak flow at the level of the sampling zone, so as to reduce the static pressure in the sampling zone and to increase the static pressure in the reinjection zone to correspondingly reduce the flow rate of the leak flow. Thus, the leak flow presents in the reinjection zone a significant difference in tangential speed, or gyration, with the rest of the primary flow, which leads to significant mixing losses.

GENERAL PRESENTATION

An aim of the present application is to propose an abradable element for a turbomachine turbine making it possible to improve the efficiency of the turbomachine, in particular by limiting the impact of the leakage flow.

For this purpose, the application relates, according to a first aspect, to an abradable element for a turbomachine turbine, extending longitudinally along an axis around which the abradable element is intended to be mounted, in which the abradable element comprises along the axis an upstream part and a downstream part each comprising a plurality of cells, the upstream towards the downstream being defined according to a direction of normal flow of the gas through the abradable element when the turbomachine turbine is in operation, all or part of the cells in the upstream part having a greater dimension of longitudinal extension which extends along a first axis forming a first angle with the axis, all or part of the cells in the downstream part having a largest dimension of longitudinal extension which extends along a second axis forming a second angle with the axis, in which the first angle is strictly positive and the second angle is negative or zero, the first angle and the second angle each being taken in a plane transverse to the alveoli.

Certain preferred but non-limiting characteristics of the abradable element according to the first aspect are the following, taken individually or in combination:

- the first angle is between 40° and 75°;

- the second angle is between 0° and -30°;

- the cells have at least one of the following shapes: a polygon, a parallelogram, a diamond, an ellipse;

- the plurality of cells of the upstream part and the plurality of cells of the downstream part each define a friction surface configured to extend opposite a sealing lip of the turbine, the friction surface of the plurality of cells of the upstream part extending along the axis along an axial dimension greater than the friction surface of the plurality of cells of the downstream part;

- the axial dimension of the friction surface of the plurality of cells of the upstream part is between 1 and 5 times greater than the axial dimension of the friction surface of the plurality of cells of the downstream part;

- the upstream part and the downstream part are arranged contiguously without overlapping along the axis;

- a junction between the upstream part and the downstream part forms a line oriented substantially perpendicular to the axis;

- the cells of the abradable element are obtained by additive manufacturing.

According to a second aspect, the application proposes a turbine for a turbomachine, comprising:
- a mobile wheel comprising a ferrule secured in rotation to a crown formed by a plurality of radial blades distributed around a disk centered on a turbine axis;
- a fixed distributor comprising a crown formed by a plurality of radial blades circumferentially distributed around a foot of the distributor centered on the turbine axis, the distributor extending around the shroud of the movable wheel;
- a fixed external casing which extends around the moving wheel and the distributor; And
- an abradable element according to the first aspect, the abradable element being mounted on the casing facing at least one blade of the moving wheel, and/or on the foot of the distributor facing the shroud of the moving wheel.

The turbine may be a low pressure turbine.

The upstream part and the downstream part of the abradable element can be arranged contiguously without overlapping along the axis, a junction between the upstream part and the downstream part forming a line oriented substantially perpendicular to the axis.

When the abradable element is mounted on the casing facing at least one blade of the movable wheel, the junction between the upstream part and the downstream part can extend closer to a trailing edge than to an edge. attack of the blade of the moving wheel.

When the abradable element is mounted on the foot of the distributor facing the shroud of the movable wheel, the junction between the upstream part and the downstream part can extend closer to a trailing edge than to a trailing edge. attack of the dawn of the distributor.

According to a third aspect, the application proposes a turbomachine comprising a turbine according to the second aspect.

The turbomachine can be a double-body turbomachine.

According to a fourth aspect, the application proposes an aircraft comprising at least one turbomachine according to the third aspect.

DESCRIPTION OF FIGURES

Other characteristics, purposes and advantages of the application will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read with reference to the appended drawings in which:

There , already commented on, is a schematic view in axial section illustrating a leak flow flowing between a moving wheel and a turbine casing of a turbomachine.

There is a schematic view in axial section illustrating a leak flow flowing in the cells of an abradable element, between a sealing lip of a moving wheel and a casing of the turbine.

There is a schematic perspective view of an abradable element according to a particular embodiment.

There is a schematic view from another perspective of the abradable element of the .

There is a schematic radial sectional view illustrating a primary flow flowing through a distributor and a moving wheel of a turbine.

There is a schematic radial sectional view illustrating a flow flowing through a distributor and a movable wheel of a turbine, an abradable element being disposed at the movable wheel.

There is a schematic perspective view of a distributor located between two movable wheels of a turbine, an abradable element according to one embodiment being mounted on the distributor facing a movable shroud of the turbine.

DETAILED DESCRIPTION General description of the turbomachine

An aircraft may comprise at least one turbomachine as described above. In the remainder of the application, the upstream and downstream are defined in relation to a normal flow direction of the gas through the abradable element when the turbomachine is in operation, which corresponds to a normal flow direction of the gas through the turbomachine in operation. Thus, a flow of air flows in the abradable element and in the turbomachine from upstream to downstream. The turbomachine extends around a longitudinal axis which corresponds to an axis of rotation of the turbomachine. A radial axis is an axis perpendicular to and passing through the longitudinal axis. A circumferential axis is an axis perpendicular to the longitudinal axis and not passing through it. A longitudinal direction, respectively radial or circumferential, corresponds to the direction of the longitudinal axis, respectively radial or circumferential. The longitudinal, radial and circumferential directions are orthogonal to each other.

The terms internal and external, or interior and exterior, respectively, are used with reference to a radial direction such that the internal, or interior, part or face of an element is closer to the longitudinal axis than the part or the external, or exterior, face of the same element.

The turbomachine can be a turbojet or a turboprop. The turbomachine may comprise a fan, at least one compressor, a combustion chamber, at least one turbine as described below and a gas exhaust nozzle. The turbine extends around a turbine axis which corresponds to an axis of rotation of the turbine and which may correspond to the longitudinal axis.

In a non-limiting embodiment, the turbomachine is a double-body, double-flow turbojet. The turbomachine comprises, from upstream to downstream, a fan, a low pressure compressor, a high pressure compressor, a combustion chamber, a high pressure turbine and a low pressure turbine. The high pressure turbine rotates the high pressure compressor via a high pressure shaft, and the low pressure turbine rotates the low pressure compressor via a low pressure shaft. The low pressure turbine can also rotate the fan either directly via the low pressure shaft, or via a reducer placed between the low pressure turbine and the fan, the reducer being driven in rotation by the low pressure shaft. During operation of the turbomachine, an air flow enters the turbomachine through an air inlet upstream of the nacelle, passes through the fan then is divided into a primary flow Fp and a secondary flow. The primary flow Fp flows in a primary flow vein and passes through the compressors, the combustion chamber and the turbines, and the secondary flow flows in a secondary flow vein which is concentric with the flow vein primary and is delimited radially outwards by the nacelle.

In the rest of the application, a movable element of the turbine corresponds to an element adapted to be driven in rotation around the axis of the turbine, in particular around the longitudinal axis, as opposed to a fixed element of the turbine.

The turbine has one or more stages each consisting of a distributor and a moving wheel. The distributors and the moving wheels are arranged alternately along the turbine axis. Thus, the turbine includes:
- a movable wheel comprising a shroud 26 integral in rotation with a crown formed by a plurality of radial blades 20 distributed around a disk 25 centered on a turbine axis;
- a fixed distributor comprising a crown formed by a plurality of radial blades 10 circumferentially distributed around a foot of the distributor centered on the turbine axis, the distributor extending around the shroud 26 of the movable wheel;
- a fixed external casing 100 which extends around the moving wheel and the distributor; And
- an abradable element 30 according to any one of the modes, examples and variant embodiments described below, the abradable element 30 being mounted on the casing 100 facing at least one blade 20 of the movable wheel, and/ or on the foot of the distributor opposite the ferrule 26 of the moving wheel.

The casing 100 and the distributor, which includes the vanes 10 of the distributor, are fixed elements. The moving wheel, which includes the blades 20 of the moving wheel, the disc 25 and the ferrule 26, is a moving element.

The turbine may be a low pressure turbine. Alternatively, the turbine may be a high pressure turbine.

The turbine axis may correspond to the longitudinal axis. A blade, for example a blade 10 of the distributor or a blade 20 of the movable wheel, extends radially with respect to the longitudinal axis and has an aerodynamic profile delimited axially upstream by a leading edge and in downstream by a trailing edge. The blade 10, 20 comprises an outer end, or head, and an inner end, or root, radially opposite the outer end.

The movable wheel is adapted to extend inside the casing 100. The blades 20 of the movable wheel can be connected to the disc 25 at their internal ends. The external ends of the blades 20 of the moving wheel are arranged facing the turbine casing 100. The ferrule 26 of the movable wheel can form an axial flange mechanically connecting the parts of the disc 25 located opposite two successive movable turbine wheels.

The distributor is adapted to extend inside the casing 100, around the ferrule 26 of the moving wheel. The distributor thus extends between the ferrule 26 and the casing 100. The vanes 10 of the distributor can be connected to the casing 100 at their external ends. The internal ends of the blades 10 of the distributor are arranged facing the shroud 26 of the moving wheel of the turbine.

The distributor of one stage of the turbine is configured so that a flow of fluid entering this stage, typically comprising gases coming from the combustion chamber, is accelerated and deflected by the vanes 10 of the distributor towards the vanes. 20 of the movable wheel of this stage so as to drive them in rotation around the turbine axis. Thus, the turbine is driven in rotation by expansion of a gas passing through the blades 20 of the moving wheel.

A first radial clearance is present between the external ends of the blades 20 of the moving wheel and the fixed casing 100. A second radial clearance is present between the internal ends of the fixed vanes 10 of the distributor and the movable shroud 26.

Consequently, part of the primary flow Fp flowing in the primary stream at the level of the turbine passes between a movable element 20, 26 and a fixed element 10, 100 of the turbine, in the spaces formed respectively by the first radial clearance and by the second radial clearance. This part of the primary flow Fp constitutes a leakage flow Ff1, Ff2. In particular, a first leakage flow Ff1 separates from the rest of the primary flow Fp to bypass the moving wheel from the outside. The first leak flow Ff1 thus passes between the external ends of the blades 20 of the moving wheel and the fixed casing 100 at the level of the first radial clearance. The first leak flow Ff1 is then reinjected into the rest of the primary flow Fp downstream of the mobile street, upstream and/or at the distributor. A second leak flow Ff2 separates from the rest of the primary flow Fp to bypass the distributor from the inside. The second leak flow Ff2 thus passes between the internal ends of the vanes 10 of the distributor and the shroud 26 at the level of the second radial clearance. The second leak flow Ff2 is then reinjected into the rest of the primary flow Fp downstream of the distributor, where appropriate upstream and/or at a moving wheel of a following stage of the turbine.

General description of the abradable element

There and the illustrate by non-limiting example an abradable element 30 for a turbomachine turbine conforming to a particular embodiment.

The abradable element 30 extends longitudinally along an axis A around which the abradable element 30 is intended to be mounted. The abradable element 30 comprises along the axis A an upstream part 33 and a downstream part 34 each comprising a plurality of cells, the upstream towards the downstream being defined according to a normal flow direction of the gas through the abradable element 30 when the turbomachine turbine is in operation.

All or part of the cells in the upstream part 33 have a greater dimension of longitudinal extension which extends along a first axis X1 forming a first angle α1 with the axis A. All or part of the cells in the downstream part 34 present a larger dimension of longitudinal extension which extends along a second axis X2 forming a second angle α2 with the axis A. The first angle α1 is strictly positive and the second angle α2 is negative or zero, the first angle α1 and the second angle α2 each being taken in a plane transverse to the cells.

Axis A is adapted to be oriented from upstream to downstream in a normal flow direction of the gas through the turbomachine in operation. Thus, the axis A can be substantially parallel to the turbine axis, or have an inclination strictly between 0° and 90° relative to the turbine axis. When the axis A is inclined relative to the turbine axis, the abradable element 30 can have a frustoconical shape, a generatrix of which corresponds to the turbine axis, where appropriate to the longitudinal axis, the abradable element 30 widening downstream.

The abradable element 30 has low resistance to friction and wear, so that when the abradable element 30 comes into contact, during the operation of the turbomachine, with another element of the turbine, the abradable element 30 is started without damaging the other element.

The abradable element 30 can be arranged so as to cover a face, for example an internal face, of a fixed element 10, 100 of the turbine. Thus, the abradable element 30 is carried by the fixed element, such as a blade 10 of the distributor or the casing 100, and is located opposite a corresponding movable element 20, 26 of the turbine. As illustrated by way of non-limiting example in , the leakage flow Ff1, Ff2 passes into the cells of the abradable element 30, between the fixed element 10, 100 which carries the abradable element 30 and the movable element 20, 26, in particular between the fixed element 10, 100 and a sealing wiper 40 which is carried by the movable element 20, 26. Thus, the leak flow Ff1, Ff2 is directed by the cells, the abradable element 30 imparting a direction to the flow.

The abradable element 30 comprises a plurality of cells. In particular, the abradable element 30 may comprise a base 31, or plate, and a cellular structure 32 formed by the plurality of cells and comprising the upstream part 33 and the downstream part 34 of the abradable element 30.

The base 31 is adapted to be fixed to a face, for example an internal face, of a fixed element 10, 100 of the turbine. The base 31 carries the cellular structure 32, serving as a support for the cellular structure 32.

The cellular structure 32 may correspond to a layer of a material with a honeycomb-type cellular structure (commonly called “Nida”). Thus, the cellular structure 32 forms wells extending radially from the base 31 towards the movable element 20, 26 facing which the abradable element 30 is arranged. The alveolar structure 23 can be formed by a plurality of cells juxtaposed in a continuous network according to a pattern of the abradable element 30. The alveolar structure 32 is adapted to be in contact with the leak flow Ff1, Ff2 circulating in the primary vein . The cellular structure 32 can be arranged in a radially internal position relative to the base 31, outside and facing a movable element 20, 26. The cellular structure 32 is adapted to come into contact with the element mobile 20, 26 facing which the abradable element 30 is arranged during operation of the turbomachine. More particularly, each cell of the cellular structure 32 may comprise a first end, which may be an external end, adapted to be in contact with the base 31, and a second end, which may be an internal end, opposite the first end and adapted to come into contact with the movable element 20, 26 opposite which the abradable element 30 is arranged during operation of the turbomachine. The second ends of the cells are intended to wear before the mobile element 20, 26 during contact with the mobile element 20, 26.

In a first variant embodiment, all the cells in the upstream part 33 have a greater dimension of longitudinal extension which extends along the first axis X1. All the cells of the upstream part 33 are thus aligned with each other and inclined according to the first angle α1.

In a second alternative embodiment, only part of the cells in the upstream part 33 has a greater dimension of longitudinal extension which extends along the first axis X1. Only part of the cells of the upstream part 33 are thus aligned with each other and inclined according to the first angle α1. The other cells of the upstream part 33 have larger dimensions extending along one or more axes different from the first axis X1 and forming one or more angle(s) different from the first angle α1 with the axis A. A majority of the cells in the upstream part 33 may have a greater dimension of longitudinal extension which extends along the first axis X1.

In a third alternative embodiment, all the cells in the downstream part 34 have a greater dimension of longitudinal extension which extends along the second axis X2. All the cells of the downstream part 34 are thus aligned with each other and inclined according to the second angle α2.

In a fourth alternative embodiment, only part of the cells in the downstream part 34 has a greater dimension of longitudinal extension which extends along the second axis X2. Only part of the cells of the downstream part 34 are thus aligned with each other and inclined according to the second angle α2. The other cells of the downstream part 34 have larger dimensions extending along one or more axes different from the second axis X2 and forming one or more angle(s) different from the second angle α2 with the axis A. A majority of the cells in the downstream part 34 may have a greater dimension of longitudinal extension which extends along the second axis X2.

The first alternative embodiment is compatible with the third alternative embodiment and the fourth alternative embodiment. The second alternative embodiment is compatible with the third alternative embodiment and the fourth alternative embodiment.

The first angle α1 formed between the first axis X1 of the cells of the upstream part 33 and the axis A is different and may have a sign opposite the second angle α2 formed between the second axis axis A. In other words, the cells of the abradable element 30 are arranged in an irregular abradable element 30 pattern, the pattern of the abradable element 30 exhibiting an axial evolution. The leak flow Ff1, Ff2 which passes into the cells of the abradable element 30 is therefore first directed by the cells of the upstream part 33 in a first direction, then directed by the cells of the downstream part 34 in a second direction, as illustrated by way of non-limiting example in , in , and in . Thus, the leakage flow Ff1, Ff2 can be deflected by the abradable element 30 so as in particular to reduce the reinjection of the leakage flow Ff1, Ff2 into the primary flow Fp downstream of the abradable element 30, therefore to improve the efficiency of the turbomachine. The leakage flow Ff1, Ff2 can thus be straightened by the abradable element 30 in the downstream part 34 so as to reduce its gyration to a value close to that of the rest of the primary flow Fp, in order to facilitate its reintroduction into the rest of the primary flow Fp downstream of the abradable element 30. In other words, an abradable element 30 having cells oriented according to several different angles α1, α2 makes it possible to control the gyration of the leak flow Ff1, Ff2 at the level of the abradable element 30, in order to reduce a difference in orientation between the leak flow Ff1, Ff2 and the rest of the primary flow Fp flowing along the blades 10, 20 of the moving wheel and the turbine distributor, this primary flow Fp being illustrated by way of non-limiting example in . The abradable element 30 thus makes it possible to reduce the losses generated by the presence of the first and second radial clearances between the mobile elements 20, 26 and the fixed elements 10, 100 of the turbine. The efficiency of the turbomachine is thus improved.

Finally, the first strictly positive angle α1 makes it possible to maximize the tangential speed of the leak flow Ff1, Ff2 upstream of the abradable element, and the second negative or zero angle α2 makes it possible to maximize the tangential speed of the leak flow Ff1, Ff2 downstream of the abradable element 30. Thus, the shear losses of the leak flow Ff1, Ff2 with the rest of the primary flow Fp flowing into the turbine are reduced. Indeed, in particular when the turbine axis corresponds to the longitudinal axis, the first axis X1 of the cells of the upstream part 33 is directed according to a first strictly positive inclination with respect to the axis A and the circumferential direction. It is understood that a “positive” or “negative” sign of an angle corresponds to its sign in the trigonometric direction. The first angle α1, which corresponds to the first inclination, is configured to reduce a difference in tangential speed between the leakage flow Ff1, Ff2 at the level of its sampling in the primary flow Fp upstream of the abradable element 30, and the remainder of the primary flow Fp. The first strictly positive angle α1 thus makes it possible to limit the pressure losses at the level of the separation between the leakage flow Ff1, Ff2 and the rest of the primary flow Fp upstream of the abradable element 30 and the mobile element 20, 26. The efficiency of the turbomachine is thus improved. The second axis In particular, when the second angle α2 is zero, the second axis X2 is parallel to the axis A and to the circumferential direction. The second angle α2, which corresponds to the second inclination, is configured to reduce a difference in tangential speed between the leakage flow Ff1, Ff2 at the level of its reinjection into the primary flow Fp, and the rest of the primary flow Fp. The second negative or zero angle α1 thus makes it possible, by straightening the leakage flow Ff1, Ff2 before its reinjection into the rest of the primary flow Fp, to limit the disturbance of the flow in the primary vein due to the reintroduction of the flow of leak Ff1, Ff2, and therefore to limit the pressure losses at the level of the reintroduction of the leak flow Ff1, Ff2 into the rest of the primary flow Fp downstream of the abradable element 30 and the mobile element 20, 26. In particular , a flow shearing effect, particularly in the tangential direction, is thus avoided. The efficiency of the turbomachine is thus improved.

In a first embodiment, illustrated by way of non-limiting example in and in , the abradable element 30 is arranged so as to partially cover an internal face of the casing 100, the abradable element 30 being arranged facing a blade 20 of the movable wheel, more particularly facing the head of a blade 20 of the moving wheel. The abradable element 30 thus makes it possible to limit a flow rate of the first leak flow Ff1 by reducing the value of the first clearance.

The turbine may comprise a single abradable element 30 according to the first embodiment. The single abradable element 30 can extend substantially over an entire circumference of the internal face of the casing 100, so as to be arranged facing all of the blades 20 of the moving wheel, or alternatively can cover only a part of the circumference of the internal face of the casing 100, so as to be arranged facing a single blade 20 or a selection of several blades 20 of the moving wheel. Alternatively, the turbine may comprise several abradable elements 30 according to the first embodiment. For example, an abradable element 30 can be associated with a corresponding blade 20 of the mobile wheel, and be placed opposite said corresponding blade 20. The number of abradable elements 30 may be less than or equal to the number of blades 20 of the moving wheel.

In a second embodiment, illustrated by way of non-limiting example in , the abradable element 30 is arranged so as to cover the internal end of the foot of the distributor facing the ferrule 26 of the movable wheel and facing a vane 10 of the distributor, the abradable element 30 being mounted on the foot of the distributor. The abradable element 30 thus makes it possible to limit a flow rate of the second leak flow Ff2 by reducing the value of the second clearance.

The turbine may comprise a single abradable element 30 according to the second embodiment. The single abradable element 30 is mounted on the foot of the distributor at the level of a single vane 10 of the distributor and facing the shroud 26. Alternatively, the turbine may comprise several abradable elements 30 according to the second embodiment. For example, an abradable element 30 can be associated with a corresponding vane 10 of the distributor, several abradable elements 30 being arranged on the foot of the distributor at the level of several vanes 10 of the distributor. The number of abradable elements 30 may be less than or equal to the number of vanes 10 of the distributor.

The first embodiment is compatible with the second embodiment, that is to say that at least one abradable element 30 can be arranged so as to cover the casing 100 facing at least one blade 20 of the wheel. mobile, and/or at least one abradable element 30 can be arranged so as to cover the internal end of the foot of the distributor facing the ferrule 26.

First angle and second angle

The first angle α1 can be between 40° and 75°, for example can be equal to 50°, 60° or 70°. Such a first angle α1 makes it possible to further reduce the difference in orientation and tangential speed between the leakage flow Ff1, Ff2 and the rest of the primary flow Fp at the level of taking the leakage flow Ff1, Ff2 out of the primary flow Fp . Thus, the pressure losses at the level of the separation of the leak flow Ff1, Ff2 relative to the rest of the primary flow Fp are still limited, which makes it possible to further improve the efficiency of the turbomachine.

The second angle α2 can be between 0° and -30°, for example can be equal to -10° or -20°, and/or can be strictly negative. Such a second angle α2 makes it possible to further reduce the difference in orientation and tangential speed between the leakage flow Ff1, Ff2 and the rest of the primary flow Fp at the level of the reinjection of the leakage flow Ff1, Ff2 into the primary flow Fp. Thus, the pressure losses at the level of the reinjection of the leak flow Ff1, Ff2 into the rest of the primary flow Fp are still limited, which makes it possible to further improve the efficiency of the turbomachine.

An absolute value of the first angle α1 can be strictly greater than an absolute value of the second angle α2. In other words, the first angle is stronger than the second angle, the cells of the upstream part 33 being more inclined relative to axis A than the cells of the downstream part 34. The cells of the upstream part 33 thus impart a higher tangential speed to the leak flow Ff1, Ff2 than the cells of the downstream part 34. The tangential speed of the leak flow Ff1, Ff2 circulating in the cells of the abradable element 30 is thus further increased, which allows less bypass of the mobile element 20, 26 by the leakage flow Ff1, Ff2. The shear losses of the leak flow Ff1, Ff2 with the rest of the primary flow Fp flowing into the turbine are thus further reduced, which makes it possible to further improve the efficiency of the turbomachine.

Geometry of the cells and the upstream and downstream parts

Each cell of the abradable element 30 may comprise a hollow cell delimited by at least one wall forming a closed contour and extending perpendicular to the base 31 of the abradable element 30. The cells may be arranged adjacent to each other. relative to the others, so as to form a continuous abradable element 30.

One or more wall(s) of the cell can extend in the direction of greatest dimension of longitudinal extension of the cell. Thus, one or more walls of the cells in the upstream part 33 are oriented along the first angle α1 with the axis A. Likewise, one or more walls of the cells in the downstream part 34 are oriented along the second angle α2 with the A axis.

The cells in the upstream part 33 may have a geometry and/or dimensions substantially equivalent, or alternatively different, to those of the cells in the downstream part 34.

The cells may have any appropriate shape to form the cellular structure 32 of the abradable element 30. For example, the cells may have at least one of the following shapes: a polygon, a parallelogram, a rectangle, a diamond, a hexagon , an ellipse.

If necessary, the shape of the cell can be flattened, or elongated, to give the cell a direction of greater dimension of longitudinal extension, for example oriented along the first axis X1 or the second axis X2. For example, the cell may have the shape of an irregular hexagon comprising two sides of greater longitudinal extension oriented along the first axis X1 or the second axis X2.

When the cell has a diamond shape, the first angle α1 of a cell of the upstream part 33, respectively the second angle α2 of a cell of the downstream part 34, can correspond to an angle formed by a diagonal of the diamond of the cell which is oriented from upstream to downstream. All the diamonds of the cells of the upstream part 33 can be identical to each other, and all the diamonds of the cells of the downstream part 34 can be identical to each other and be different from the diamonds of the cells of the upstream part 33 at least because the second angle α2 is different from the first angle α1.

Each cell has a cell surface area which corresponds to a surface of the hollow cell delimited by the wall of the cell. The plurality of cells of the upstream part 33 and the plurality of cells of the downstream part 34 can each define a friction surface configured to extend in front of a movable element 20, 26 of the turbine, in particular in face of a sealing lip 40 of the turbine, said sealing lip 40 being for example arranged on the movable element 20, 26 facing the abradable element 30. The abradable element 30 thus extends over a friction surface which corresponds to the sum of the friction surface of the plurality of cells of the upstream part 33 and the friction surface of the plurality of cells of the downstream part 34. The friction surface of the abradable element 30 can correspond substantially to the sum of the surfaces of each cell of the abradable element 30, the friction surface of the plurality of cells of the upstream part 33 corresponding to the sum of the surfaces of each cell of the upstream part 33 and the friction surface of the plurality of cells of the downstream part 34 corresponding to the sum of the surfaces of each cell of the downstream part 34.

The friction surface of the plurality of cells of the upstream part 33 can extend along the axis A along an axial dimension greater, or even strictly greater, than the friction surface of the plurality of cells of the part downstream 34. More particularly, the axial dimension of the friction surface of the plurality of cells of the upstream part 33 can be between 1 and 5 times greater than the axial dimension of the friction surface of the plurality of cells of the downstream part 34, for example can be between 2 and 3 times greater than the axial dimension of the friction surface of the plurality of cells of the downstream part 34. These friction surface values make it possible to further reduce the differences in tangential speed between the leak flow Ff1, Ff2 and the rest of the primary flow Fp at the level of sampling and reintroduction of the leak flow Ff1, Ff2, and thus to further improve the efficiency of the turbomachine.

The abradable element 30 may have the shape of a parallelepiped, or even a plate, having a length, a width and a depth. The length corresponds to a dimension in the direction of the axis A. The depth corresponds to a dimension in a direction of the walls of the cells and can be small compared to the length and the width of the abradable element 30. The width corresponds to a dimension in a direction substantially perpendicular to the direction of length and the direction of depth. The cellular structure 32 of the abradable element 30 may have a length and/or a width less than or equal to a length and a width of the base 31. When the axis A is substantially parallel to the turbine axis and that the turbine axis corresponds to the longitudinal axis, the length direction of the abradable element 30 corresponds to the longitudinal direction, the width direction corresponds to the circumferential direction, and the depth direction corresponds to the direction radial.

When the abradable element has a substantially parallelepiped shape, the friction surface of the abradable element 30 is obtained by multiplying the length and the width of the abradable element 30. The width of the upstream part 33 of the abradable element 30 can be substantially equal to the width of the downstream part 34 of the abradable element 30. Thus, the difference between the friction surface of the plurality of cells of the upstream part 33 and the friction surface of the plurality of cells of the downstream part 34 correspond to a difference in length between the upstream part 33 and the downstream part 34. Thus, the upstream part 33 can have a length greater, or even strictly greater, than a length of the downstream part 34, for example between 1 and 5 times greater than the length of the downstream part 34, for example between 2 and 3 times greater than the length of the downstream part 34. and the illustrate a non-limiting example in which the friction surface of the plurality of cells of the upstream part 33 is approximately 2 times greater than the friction surface of the plurality of cells of the downstream part 34 of the abradable element 30, the length of the upstream part 33 being approximately 2 times greater than the length of the downstream part 34 and the width of the upstream part 33 being substantially equal to the width of the downstream part 34.

Junction between the upstream part and the downstream part

In a first embodiment, the upstream part 33 and the downstream part 34 are arranged contiguously without overlapping along the axis A. The upstream part 33 and the downstream part 34 of the abradable element 30 are thus axially contiguous , a downstream cell of the upstream part 33 being in contact with an upstream cell of the downstream part 34.

The junction 35 between the upstream part 33 and the downstream part 34 can form a line oriented substantially perpendicular to the axis A. Thus, the junction 35 between the upstream part 33 and the downstream part 34 is a straight line arranged in a predetermined position of the axis A. When the axis A is parallel to the turbine axis and the turbine axis corresponds to the longitudinal axis, the junction 35 between the upstream part 33 and the downstream part 34 is thus directed substantially along the radial axis. Alternatively, the junction 35 between the upstream part 33 and the downstream part 34 may have any other suitable geometry, for example a line presenting an inclination strictly between 0° and 90° to the axis A, a curved line, etc.

The junction 35 between the upstream part 33 and the downstream part 34 can be located closer to the trailing edge than to the leading edge of the blade 10, 20 of the movable element 20, 26 facing which the abradable element 30. More particularly, as illustrated by way of non-limiting examples in and in , the junction 35 between the upstream part 33 and the downstream part 34 can be located substantially at the level of the trailing edge of said blade 10, 20, that is to say in a substantially identical position along the axis of turbine, the junction 35 being external with respect to the blade 10, 20.

When the abradable element 30 is mounted on the casing 100 facing at least one blade 20 of the movable wheel, the junction 35 between the upstream part 33 and the downstream part 34 can extend closer to the trailing edge than of the leading edge of the blade 20 of the moving wheel, for example substantially at the level of said trailing edge of the blade 20 of the moving wheel facing which the abradable element 30 extends.

When the abradable element 30 is mounted on the foot of the distributor facing the shroud 26 of the movable wheel and facing at least one blade 10 of the distributor, the junction 35 between the upstream part 33 and the downstream part 34 can extend closer to the trailing edge than to the leading edge of the blade 10 of the distributor, for example substantially at the level of said trailing edge of the blade 10 of the distributor opposite which the abradable element extends 30.

In a second exemplary embodiment, the upstream part 33 and the downstream part 34 are separated by at least one intermediate part having cells whose direction of greatest longitudinal extension dimension is oriented along one or more axes different from the first axis X1 and the second axis X2.

For example, an intermediate part located, for example arranged contiguously, between the upstream part 33 and the downstream part 34 may comprise a plurality of cells. All or part of the cells in the intermediate part have a greater dimension of longitudinal extension which extends along a third axis forming a third angle with the axis A, the third angle being strictly included between the first angle α1 and the second angle α2. Such an intermediate part allows a more gradual evolution of the tangential speed of the leak flow Ff1, Ff2 circulating through the cells of the abradable element 30. Several intermediate parts can be present, each having a respective intermediate part axis, the angles formed between each of the axes of each intermediate part and the axis A being different and each being strictly included between the first angle α1 and the second angle α2. The intermediate parts are arranged from the upstream part 33 to the downstream part 34 in descending order of the angles of the intermediate part axes, so that the angles formed between the cells and the axis A gradually decrease from the upstream towards the downstream of the abradable element 30. Such several intermediate parts allow an even more gradual evolution of the tangential speed of the leak flow Ff1, Ff2 circulating through the cells of the abradable element 30.

Alternatively, the cells of the intermediate part of the abradable element 30 may have a greater dimension of longitudinal extension which extends along different axes, said different axes forming different angles with the axis A, said different angles gradually decreasing between an upstream end and a downstream end of the intermediate part of the abradable element 30, in particular from the first angle α1 at the upstream end to the second angle α2 at the downstream end. Such an intermediate part comprising cells having a progressive change of angle allows an even more gradual evolution of the tangential speed of the leak flow Ff1, Ff2 circulating through the cells of the abradable element 30.

Seal (lip + abradable)

The turbine may further comprise a sealing lip 40 placed on a movable element 20, 26 facing an abradable element 30 mounted on a fixed element 10, 100 of the turbine. The sealing lip 40 and the abradable element 30 together form a seal. The seal ensures a seal between the movable element 20, 26 in rotation and the fixed element 10, 100 located opposite the seal. During operation of the turbomachine, the sealing lip 40 has a speed of rotation around the turbine axis corresponding to that of the movable element 20, 26. The seal makes it possible to reduce the flow rate of the flow of leak Ff1, Ff2 bypassing the mobile element 20, 26, and thus further improve the efficiency of the turbomachine. The sealing lip 40 can be formed in one piece with the movable element 20, 26, or be attached and fixed on the movable element 20, 26. During operation of the turbomachine, in particular when thermal expansions or differential mechanical forces due to heating or centrifugal forces and occurring in circumstances such as transient regimes temporarily bring the abradable element 30 and the sealing lip 40 into contact, the sealing lip 40 cuts into the abradable element 30 without being itself worn by contact. For example, a sealing wiper 40 can be placed on the head of a blade 20 of the movable wheel facing the casing 100. Alternatively or in addition, a sealing wiper 40 can be placed on the ferrule 26 of the movable wheel, facing at least one vane 10 of the distributor.

The seal formed by the pair of sealing lip 40 and abradable element 30 can be a labyrinth seal. The seal may comprise one or more sealing lips 40 spaced from each other along the turbine axis. Each sealing lip 40 extends from the movable element 20, 26 towards the abradable element 30 mounted on the fixed element 10, 100, that is to say from the inside towards the outside of the turbomachine. The abradable element 30 is arranged opposite the sealing lips 40 of the seal.

When the sealing lip 40 is placed on the head of a blade 20 of the movable wheel, the sealing lip 40 can be placed on a platform 50 attached and fixed on the head of the blade 20 of the movable wheel . More particularly, the sealing lip(s) 40 may correspond to radial projections oriented towards the outside of the platform 50 of the blade 20 of the moving wheel.

The junction 35 between the upstream part 33 and the downstream part 34 of the abradable element 30 can extend between two sealing wipers 40, in particular between an upstream wiper and a downstream wiper arranged downstream of the upstream wiper. Thus, the tangential speed of the leak flow Ff1, Ff2 at the level of the sealing lips 40 is maximized, which makes it possible to further reduce the shear losses of the leak flow Ff1, Ff2 with the rest of the primary flow Fp flowing through the turbine. More particularly, the leakage flow Ff1, Ff2 is deflected by the upstream lip, so that it has a strong gyratory component after passing the upstream lip. The abradable element 30 then straightens the leak flow Ff1, Ff2 to reduce its gyration, or even change its direction to facilitate its reintroduction into the rest of the primary flow Fp once the leak flow Ff1, Ff2 has passed the downstream lip .

Manufacturing of cells

The cells, in particular the cell structure 32, of the abradable element 30, can be obtained by additive manufacturing. Thus, the cellular structure 32 can be formed from a single material, and the upstream part 33 and the downstream part 34 having the first and second different angles α1, α2 can be easily manufactured, including at the level of the junction 35 between the upstream part 33 and the downstream part 34.

Additive manufacturing can be ensured by successive deposition of layers of metal powders fused by laser beam to form the network of cells forming the layer of material with cellular structure 32.

The abradable element 30 can be coated with a particular surface treatment, for example NiCrAlY or ceramic (for example ZrO2 type).

The solution described above is not limited to the embodiments described, and can be used in other locations of the turbomachine comprising a mobile element rotating around the longitudinal axis and a fixed element.

Other embodiments can be envisaged and a person skilled in the art can easily modify the modes or examples of embodiment set out above or consider others while remaining within the scope of the application.

Claims (10)

Abradable element (30) for a turbomachine turbine extending longitudinally along an axis (A) around which the abradable element (30) is intended to be mounted, in which the abradable element (30) comprises along the axis (A), an upstream part (33) and a downstream part (34) each comprising a plurality of cells, the upstream towards the downstream being defined according to a normal flow direction of the gas through the abradable element (30) when the turbomachine turbine is in operation, all or part of the cells in the upstream part (33) having a greater dimension of longitudinal extension which extends along a first axis (X1) forming a first angle (α1 ) with the axis (A), all or part of the cells in the downstream part (34) having a greater dimension of longitudinal extension which extends along a second axis (X2) forming a second angle (α2) with the axis (A), in which the first angle (α1) is strictly positive and the second angle (α2) is negative or zero, the first angle (α1) and the second angle (α2) each being taken in a plane transverse to the alveoli. Abradable element (30) according to claim 1, in which the first angle (α1) is between 40° and 75°. Abradable element (30) according to claim 1 or 2, in which the second angle (α2) is between 0° and -30° Abradable element (30) according to any one of claims 1 to 3, in which the cells have at least one of the following shapes: a polygon, a parallelogram, a diamond, an ellipse. Abradable element (30) according to any one of claims 1 to 4, in which the plurality of cells of the upstream part (33) and the plurality of cells of the downstream part (34) each define a configured friction surface to extend opposite a sealing lip (40) of the turbine, and in which the friction surface of the plurality of cells of the upstream part (33) extends along the axis ( A) along an axial dimension greater than the friction surface of the plurality of cells of the downstream part (34). Abradable element (30) according to claim 5, in which the axial dimension of the friction surface of the plurality of cells of the upstream part (33) is between 1 and 5 times greater than the axial dimension of the friction surface of the plurality of cells of the downstream part (34). Abradable element (30) according to any one of claims 1 to 6, in which the upstream part (33) and the downstream part (34) are arranged contiguously without overlapping along the axis (A), and in which a junction (35) between the upstream part (33) and the downstream part (34) forms a line oriented substantially perpendicular to the axis (A). Turbine, in particular a low pressure turbine, for a turbomachine, comprising:
- a mobile wheel comprising a ferrule (26) integral in rotation with a crown formed by a plurality of radial vanes (20) distributed around a disc (25) centered on a turbine axis;
- a fixed distributor comprising a crown formed by a plurality of radial vanes (10) circumferentially distributed around a foot of the distributor centered on the turbine axis, the distributor extending around the shroud (26) of the wheel mobile ;
- a fixed external casing (100) which extends around the moving wheel and the distributor; And
- an abradable element (30) according to any one of claims 1 to 7, the abradable element (30) being mounted on the casing (100) facing at least one blade (20) of the movable wheel, and /or on the foot of the distributor opposite the ferrule (26) of the moving wheel. Turbine according to claim 8, in which the upstream part (33) and the downstream part (34) of the abradable element (30) are arranged contiguously without overlapping along the axis (A), a junction (35 ) between the upstream part (33) and the downstream part (34) forming a line oriented substantially perpendicular to the axis (A), in which when the abradable element (30) is mounted on the casing (100) facing d a blade (20) of the movable wheel, the junction (35) between the upstream part (33) and the downstream part (34) extends closer to a trailing edge than to a leading edge of the blade (20) of the moving wheel, and in which when the abradable element (30) is mounted on a blade (10) of the distributor facing the shroud (26) of the disc (25) of the moving wheel, the junction (35) between the upstream part (33) and the downstream part (34) extends closer to a trailing edge than to a leading edge of the vane (10) of the distributor. Turbomachine comprising a turbine according to claim 9.