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

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 portion (33) and a downstream portion (34) each comprising a plurality of cells, the upstream to downstream being defined according to a normal flow direction of the gas through the abradable element (30), all or part of the cells in the upstream portion (33) having a greater longitudinal extension dimension 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 portion (34) having a greater longitudinal extension dimension 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

Title of the invention: Abradable element for a turbomachine turbine, comprising cells having different inclinations Technical field

[0001] The present application relates to the field of aircraft turbomachines, more particularly relates to an abradable element for a turbomachine turbine as well as a turbine, a turbomachine and an aircraft comprising such an abradable element. TECHNOLOGICAL BACKGROUND

[0002] An aircraft conventionally comprises at least one turbomachine to provide propulsion. The turbomachine may 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 stream through the turbomachine, a fan, at least one compressor, a combustion chamber, at least one turbine, and a gas exhaust nozzle.

[0003] 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 a design of a turbine is known from document FR 3 034 129 AL

[0004] The distributor comprises fixed blades distributed circumferentially around the longitudinal axis of the turbomachine and connected by their radially external ends to the fixed casing. The movable wheel comprises an internal disc and movable blades circumferentially distributed around the disc and connected by their radially internal ends to the disc. The blades of the movable wheel are arranged at their external end facing the fixed casing. The disc of the movable wheel comprises a ferrule facing which are located the internal ends of the fixed blades of the distributor.

[0005] In such an arrangement, there is a first radial clearance between the outer ends of the blades of the moving wheel and the fixed casing. In addition, there is a second radial clearance between the inner ends of the blades of the distributor and the shroud. Taking into account in particular the differential expansions occurring when the turbomachine is in operation, and which partly condition the radial clearances, these cannot be cancelled. Consequently, a part of the primary flow flowing at the turbine, called leakage flow, passes between the moving wheel and the fixed casing, or between the distributor and the shroud, in the spaces formed by the radial clearances.

[0006] In particular, as illustrated in [Fig. 1], a leakage flow Ff' separates from the remainder of the primary flow Fp' between the outer ends of the blades 20' of the moving wheel and the casing 100' at the first radial clearance. The first leakage flow Ff' is then reinjected into the remainder of the primary flow Fp' downstream of the moving wheel 20'. A second leakage flow can pass between the inner ends of the blades 10' of the nozzle and the shroud of the moving wheel at the second radial clearance. The second leakage flow is then reinjected into the remainder of the primary flow Fp' downstream of the nozzle. The leakage flows each have a leakage flow rate that 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 cause a reduction in the efficiency of the turbomachine.

[0007] Sealing lips may be arranged on the inner or outer ends of the blades of the moving wheel and / or on the shell of the disk of the moving wheel. An abradable element is arranged opposite the respective sealing lip, on an inner face of the fixed casing and / or on an inner end of the vane of the distributor. 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 leakage flow. The abradable element may have a honeycomb 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 honeycomb structure with a variable density of cells.In operation, the movable sealing lip may rub against the fixed abradable element, the abradable element wearing out before the sealing lip. Radial clearances thus increase over time.

[0008] Furthermore, the reinjection of the leakage flows into the remainder of the primary flow downstream of the abradable element disturbs the primary flow, due to a difference in orientation, in particular tangential, between the reinjected leakage flow and the remainder of the primary flow, which also results in a reduction in the efficiency of the turbomachine. The disturbance is accentuated by the fact that a tangential speed of the leakage flow at the reinjection zone is kept low compared to a tangential speed of the leakage flow at 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 consequently reduce the flow rate of the leakage flow. Thus, the leakage flow has in the reinjection zone a significant difference in tangential speed, or gyration, with the remainder of the primary flow, which leads to significant mixing losses. GENERAL STATEMENT

[0009] An aim of the present application is to propose an abradable element for a turbomachine turbine enabling the efficiency of the turbomachine to be improved, in particular by limiting the impact of the leakage flow.

[0010] For this purpose, the subject of the application, according to a first aspect, is 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 portion and a downstream portion each comprising a plurality of cells, the upstream to downstream portion being defined according to a normal flow direction of the gas through the abradable element when the turbomachine turbine is in operation, all or part of the cells in the upstream portion having a greater longitudinal extension dimension which extends along a first axis forming a first angle with the axis, all or part of the cells in the downstream portion having a greater longitudinal extension dimension 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.

[0011] Some preferred but non-limiting features of the abradable element according to the first aspect are the following, taken individually or in combination:

[0012] - the first angle is between 40° and 75°;

[0013] - the second angle is between 0° and -30°;

[0014] - the cells have at least one of the following shapes: a polygon, a parallel the elogram, a rhombus, an ellipse;

[0015] - 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 portion extending along the axis along an axial dimension greater than the friction surface of the plurality of cells of the downstream portion;

[0016] - the axial dimension of the friction surface of the plurality of cells of the part upstream is between 1 and 5 times greater than the axial dimension of the friction surface of the plurality of cells of the downstream part;

[0017] - the upstream part and the downstream part are arranged contiguously without along the axis;

[0018] - a junction between the upstream part and the downstream part forms a line oriented sen possibly perpendicular to the axis;

[0019] - the cells of the abradable element are obtained by additive manufacturing.

[0020] According to a second aspect, the application proposes a turbine for a turbomachine, comprising: - a mobile wheel comprising a ferrule integral in rotation with a crown formed by a plurality of radial blades distributed around a disc centered on an axis of turbine; - 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 shell of the moving wheel; - a fixed external casing which extends around the movable wheel and the distributor; and - an abradable element according to the first aspect, the abradable element being mounted on the casing opposite at least one blade of the movable wheel, and / or on the foot of the distributor opposite the shell of the movable wheel.

[0021] The turbine may be a low pressure turbine.

[0022] The upstream portion and the downstream portion of the abradable element may be arranged contiguously without overlapping along the axis, a junction between the upstream portion and the downstream portion forming a line oriented substantially perpendicular to the axis.

[0023] When the abradable element is mounted on the casing opposite at least one blade of the moving wheel, the junction between the upstream part and the downstream part may extend closer to a trailing edge than to a leading edge of the blade of the moving wheel.

[0024] When the abradable element is mounted on the foot of the distributor opposite the shroud of the moving wheel, the junction between the upstream part and the downstream part can extend closer to a trailing edge than to a leading edge of the distributor blade.

[0025] According to a third aspect, the application proposes a turbomachine comprising a turbine according to the second aspect.

[0026] The turbomachine may be a double-spool turbomachine.

[0027] According to a fourth aspect, the application proposes an aircraft comprising at least one turbomachine according to the third aspect. DESCRIPTION OF FIGURES

[0028] Other characteristics, aims and advantages of the application will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

[0029] [Fig.l], already commented on, is a schematic axial sectional view illustrating a leakage flow flowing between a moving wheel and a turbine casing of a turbomachine.

[0030] [Fig.2] is a schematic axial sectional view illustrating a leakage flow flowing in the cells of an abradable element, between a sealing lip of a moving wheel and a casing of the turbine.

[0031] [Fig.3a] is a schematic perspective view of an abradable element according to a particular embodiment.

[0032] [Fig.3b] is a schematic view from another perspective of the element abradable of [Fig.3a].

[0033] [Fig.4a] is a schematic radial sectional view illustrating a primary flow flowing through a distributor and a moving wheel of a turbine.

[0034] [Fig.4b] is a schematic radial sectional view illustrating a flow flowing through a distributor and a moving wheel of a turbine, an abradable element being disposed at the moving wheel.

[0035] [Fig. 5] is a schematic perspective view of a distributor located between two moving wheels of a turbine, an abradable element according to one embodiment being mounted on the distributor opposite a moving shell of the turbine. DETAILED DESCRIPTION General description of the turbomachine

[0036] An aircraft may comprise at least one turbomachine as described above. In the remainder of the application, upstream and downstream are defined relative 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, an air flow 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 the longitudinal axis and passing through it. 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.

[0037] The terms internal and external, or inner and outer, respectively, are used with reference to a radial direction such that the internal, or inner, portion or face of an element is closer to the longitudinal axis than the external, or outer, portion or face of the same element.

[0038] The turbomachine may 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.

[0039] In a non-limiting exemplary embodiment, the turbomachine is a twin-spool, twin-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 by 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 reduction gear arranged between the low-pressure turbine and the fan, the reduction gear being rotated 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 and then divides 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 primary flow vein and is delimited radially outwards by the nacelle.

[0040] In the remainder of the application, a movable element of the turbine corresponds to an element adapted to be driven in rotation around the turbine axis, in particular around the longitudinal axis, as opposed to a fixed element of the turbine.

[0041] The turbine comprises one or more stages each consisting of a distributor and a movable wheel. The distributors and the movable wheels are arranged alternately along the turbine axis. Thus, the turbine comprises: - a mobile wheel comprising a ferrule 26 integral in rotation with a crown formed by a plurality of radial blades 20 distributed around a disc 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 shell 26 of the moving wheel; - a fixed external casing 100 which extends around the movable wheel and the distributor; and - an abradable element 30 according to any one of the embodiments, examples and variants described below, the abradable element 30 being mounted on the casing 100 opposite at least one blade 20 of the movable wheel, and / or on the foot of the distributor opposite the ferrule 26 of the movable wheel.

[0042] The casing 100 and the distributor, which includes the vanes 10 of the distributor, are fixed elements. The movable wheel, which includes the vanes 20 of the movable wheel, the disc 25 and the ferrule 26, is a movable element.

[0043] The turbine may be a low pressure turbine. Alternatively, the turbine may be a high pressure turbine.

[0044] 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 moving wheel, extends radially with respect to the longitudinal axis and has an aerodynamic profile delimited axially upstream by a leading edge and downstream by a trailing edge. The blade 10, 20 comprises an outer end, or head, and an inner end, or foot, radially opposite the outer end.

[0045] The movable wheel is adapted to extend inside the casing 100. The blades 20 of the movable wheel may be connected to the disc 25 at their inner ends. The outer ends of the blades 20 of the movable wheel are arranged opposite the turbine casing 100. The shroud 26 of the movable wheel may form an axial flange mechanically connecting the parts of the disc 25 located opposite two successive turbine movable wheels.

[0046] The distributor is adapted to extend inside the casing 100, around the shell 26 of the moving wheel. The distributor thus extends between the shell 26 and the casing 100. The vanes 10 of the distributor can be connected to the casing 100 at their outer ends. The inner ends of the vanes 10 of the distributor are arranged opposite the shell 26 of the moving wheel of the turbine.

[0047] The distributor of a 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 the latter in rotation around the turbine axis. Thus, the turbine is driven in rotation by expansion of a gas passing through the vanes 20 of the movable wheel.

[0048] A first radial clearance is present between the outer ends of the blades 20 of the moving wheel and the fixed casing 100. A second radial clearance is present between the inner ends of the fixed blades 10 of the distributor and the moving ferrule 26.

[0049] Consequently, a portion of the primary flow Fp flowing in the primary vein at 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 portion of the primary flow Fp constitutes a leakage flow Ffl, Ff2. In particular, a first leakage flow Ffl separates from the remainder of the primary flow Fp to bypass the movable wheel from the outside. The first leakage flow Ffl thus passes between the outer ends of the blades 20 of the movable wheel and the casing 100 fixed at the first radial clearance. The first leakage flow Ffl is then reinjected into the remainder of the primary flow Fp downstream of the movable street, upstream and / or at the distributor. A second leakage flow Ff2 separates from the remainder of the primary flow Fp to bypass the distributor from the inside.The second leakage flow Ff2 thus passes between the internal ends of the blades 10 of the distributor and the shroud 26 at the level of the second radial clearance. The second leakage flow Ff2 is then reinjected into the rest of the primary flow Fp downstream of the distributor, if necessary upstream and / or at the level of a moving wheel of a following stage of the turbine. General description of the abradable element

[0050] [Fig.3a] and [Fig.3b] illustrate by way of non-limiting example an abradable element 30 for a turbomachine turbine according to a particular embodiment.

[0051] 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 portion 33 and a downstream portion 34 each comprising a plurality of cells, the upstream to downstream portion being defined according to a normal flow direction of the gas through the abradable element 30 when the turbomachine turbine is in operation.

[0052] All or part of the cells in the upstream part 33 has a greater longitudinal extension dimension which extends along a first axis X1 forming a first angle a1 with the axis A. All or part of the cells in the downstream part 34 has a greater longitudinal extension dimension which extends along a second axis X2 forming a second angle a2 with the axis A. The first angle a1 is strictly positive and the second angle a2 is negative or zero, the first angle a1 and the second angle a2 each being taken in a plane transverse to the cells.

[0053] The 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 may 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 may have a frustoconical shape, one generatrix of which corresponds to the turbine axis, where appropriate to the longitudinal axis, the abradable element 30 widening towards the downstream.

[0054] The abradable element 30 has low resistance to friction and wear, so that when the abradable element 30 comes into contact, during operation of the turbomachine, with another element of the turbine, the abradable element 30 is damaged without damaging the other element.

[0055] The abradable element 30 may 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 vane 10 of the distributor or the casing 100, and is located opposite a corresponding mobile element 20, 26 of the turbine. As illustrated by way of non-limiting example in [Fig.2], the leakage flow Ffl, 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 lip 40 which is carried by the movable element 20, 26. Thus, the leakage flow Ffl, Ff2 is directed by the cells, the abradable element 30 imparting a direction to the flow.

[0056] The abradable element 30 comprises a plurality of cells. In particular, the element abradable element 30 may comprise a base 31, or plate, and a honeycomb structure 32 formed by the plurality of cells and comprising the upstream part 33 and the downstream part 34 of the abradable element 30.

[0057] 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 honeycomb structure 32, serving as a support for the honeycomb structure 32.

[0058] 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 mobile element 20, 26 opposite which the abradable element 30 is arranged. The cellular structure 23 may be formed by a plurality of cells juxtaposed in a continuous network according to a pattern of the abradable element 30. The cellular structure 32 is adapted to be in contact with the leakage flow Ffl, Ff2 circulating in the primary vein. The honeycomb structure 32 can be arranged in a radially internal position relative to the base 31, outside and facing a mobile element 20, 26. The honeycomb structure 32 is adapted to come into contact with the mobile element 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 mobile 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.

[0059] In a first variant embodiment, all the cells in the upstream part 33 have a greater longitudinal extension dimension which extends along the first axis XL. All the cells of the upstream part 33 are thus aligned with each other and inclined along the first angle al.

[0060] In a second embodiment, only a portion of the cells in the upstream portion 33 has a larger longitudinal extension dimension which extends along the first axis XL. Only a portion of the cells in the upstream portion 33 are thus aligned with each other and inclined at the first angle a1. The other cells in the upstream portion 33 have larger dimensions extending along one or more axes different from the first axis X1 and forming one or more angles different from the first angle a1 with the axis A. A majority of the cells in the upstream portion 33 may have a larger longitudinal extension dimension which extends along the first axis XL.

[0061] In a third embodiment, all the cells in the downstream part 34 have a greater longitudinal extension dimension which extends along the second axis X2. All the cells of the downstream part 34 are thus aligned with each other and inclined along the second angle a2.

[0062] In a fourth embodiment, only a portion of the cells in the downstream portion 34 has a larger longitudinal extension dimension which extends along the second axis X2. Only a portion of the cells in the downstream portion 34 are thus aligned with each other and inclined at the second angle a2. The other cells in the downstream portion 34 have larger dimensions extending along one or more axes different from the second axis X2 and forming one or more angles different from the second angle a2 with the axis A. A majority of the cells in the downstream portion 34 may have a larger longitudinal extension dimension which extends along the second axis X2.

[0063] The first embodiment variant is compatible with the third embodiment variant and the fourth embodiment variant. The second embodiment variant is compatible with the third embodiment variant and the fourth embodiment variant.

[0064] The first angle al formed between the first axis XI of the cells of the upstream part 33 and the axis A is different and may have a sign opposite to the second angle a2 formed between the second axis X2 of the cells of the downstream part 34 and the axis A. In other words, the cells of the abradable element 30 are arranged according to an irregular abradable element pattern 30, the pattern of the abradable element 30 having an axial evolution. The leakage flow Ffl, 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 [Fig.3a], in [Fig.3b], and in [Fig.4b].Thus, the leakage flow Ffl, Ff2 can be diverted by the abradable element 30 so as in particular to reduce the reinjection of the leakage flow Ffl, Ff2 into the primary flow Fp downstream of the abradable element 30, thus improving the efficiency of the turbomachine. The leakage flow Ffl, Ff2 can thus be straightened by the abradable element 30 in the downstream part 34 so as to bring its gyration back 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 at several different angles a1, a2 makes it possible to control the gyration of the leakage flow Ffl, Ff2 at the level of the abradable element 30, in order to reduce a difference in orientation between the leakage flow Ffl, Ff2 and the rest of the primary flow Fp flowing along the blades 10, 20 of the moving wheel and the distributor of the turbine, this primary flow Fp being illustrated by way of non-limiting example in [Fig.4a]. The abradable element 30 thus makes it possible to reduce the losses generated by the presence. first and second radial clearances between the moving elements 20, 26 and the fixed elements 10, 100 of the turbine. The efficiency of the turbomachine is thus improved.

[0065] Finally, the first strictly positive angle al makes it possible to maximize the tangential speed of the leakage flow Ffl, Ff2 upstream of the abradable element, and the second negative or zero angle a2 makes it possible to maximize the tangential speed of the leakage flow Ffl, Ff2 downstream of the abradable element 30. Thus, the shear losses of the leakage flow Ffl, Ff2 with the rest of the primary flow Fp flowing in the turbine are reduced. Indeed, in particular when the turbine axis corresponds to the longitudinal axis, the first axis XI of the cells of the upstream part 33 is directed according to a first strictly positive inclination relative to the axis A and to 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 al, which corresponds to the first inclination, is configured to reduce a difference in tangential speed between the leakage flow Ffl, Ff2 at the level of its collection in the primary flow Fp upstream of the abradable element 30, and the remainder of the primary flow Fp. The strictly positive first angle al thus makes it possible to limit the pressure losses at the level of the separation between the leakage flow Ffl, Ff2 and the remainder 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 X2 of the cells of the downstream part 34 is directed according to a second zero or negative inclination relative to the axis A and to the circumferential direction. In particular, when the second angle a2 is zero, the second axis X2 is parallel to the axis A and to the circumferential direction.The second angle a2, which corresponds to the second inclination, is configured to reduce a difference in tangential speed between the leakage flow Ffl, Ff2 at its reinjection into the primary flow Fp, and the remainder of the primary flow Fp. The second negative or zero angle al thus makes it possible, by straightening the leakage flow Ffl, Ff2 before its reinjection into the remainder of the primary flow Fp, to limit the disturbance of the flow in the primary vein due to the reintroduction of the leakage flow Ffl, Ff2, and therefore to limit the pressure losses at the reintroduction of the leakage flow Ffl, Ff2 into the remainder of the primary flow Fp downstream of the abradable element 30 and the mobile element 20, 26. In particular, a shearing effect of the flows, in particular in the tangential direction, is thus avoided. The efficiency of the turbomachine is thus improved.

[0066] In a first embodiment, illustrated by way of non-limiting example in [Fig. 3a] and in [Fig. 3b], the abradable element 30 is arranged so as to partially cover an internal face of the casing 100, the abradable element 30 being arranged opposite a blade 20 of the moving wheel, more particularly opposite 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 leakage flow Ffl by reducing the value of the first clearance.

[0067] The turbine may comprise a single abradable element 30 according to the first embodiment. The single abradable element 30 may extend substantially over an entire circumference of the inner face of the casing 100, so as to be arranged opposite all of the blades 20 of the moving wheel, or alternatively may cover only a portion of the circumference of the inner face of the casing 100, so as to be arranged opposite 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 may be associated with a corresponding blade 20 of the moving wheel, and be arranged 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.

[0068] In a second embodiment, illustrated by way of non-limiting example in [Fig. 5], the abradable element 30 is arranged so as to cover the internal end of the foot of the distributor opposite the ferrule 26 of the moving wheel and opposite a blade 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 leakage flow Ff2 by reducing the value of the second clearance.

[0069] 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 a single blade 10 of the distributor and opposite the shroud 26. Alternatively, the turbine may comprise several abradable elements 30 according to the second embodiment. For example, an abradable element 30 may be associated with a corresponding blade 10 of the distributor, several abradable elements 30 being arranged on the foot of the distributor at several blades 10 of the distributor. The number of abradable elements 30 may be less than or equal to the number of blades 10 of the distributor.

[0070] 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 opposite at least one blade 20 of the moving wheel, and / or at least one abradable element 30 can be arranged so as to cover the internal end of the foot of the distributor opposite the ferrule 26. First angle and second angle

[0071] The first angle al may be between 40° and 75°, for example may be equal to 50°, 60° or 70°. Such a first angle al makes it possible to further reduce the difference in orientation and tangential speed between the leakage flow Ffl, Ff2 and the remainder of the primary flow Fp at the level of the sampling of the leakage flow Ffl, Ff2 from the primary flow Fp. Thus, the pressure losses at the level of the separation of the leakage flow Ffl, Ff2 from the remainder of the primary flow Fp are still limited, which makes it possible to further improve the efficiency of the turbomachine.

[0072] The second angle a2 may be between 0° and -30°, for example may be equal to -10° or -20°, and / or may be strictly negative. Such a second angle a2 makes it possible to further reduce the difference in orientation and tangential speed between the leakage flow Ffl, Ff2 and the remainder of the primary flow Fp at the level of the reinjection of the leakage flow Ffl, Ff2 into the primary flow Fp. Thus, the pressure losses at the level of the reinjection of the leakage flow Ffl, Ff2 into the remainder of the primary flow Fp are still limited, which makes it possible to further improve the efficiency of the turbomachine.

[0073] An absolute value of the first angle a1 may be strictly greater than an absolute value of the second angle a2. In other words, the first angle is greater than the second angle, the cells of the upstream portion 33 being more inclined relative to the axis A than the cells of the downstream portion 34. The cells of the upstream portion 33 thus impart a greater tangential speed to the leakage flow Ffl, Ff2 than the cells of the downstream portion 34. The tangential speed of the leakage flow Ffl, Ff2 circulating in the cells of the abradable element 30 is thus further increased, which allows less bypassing of the mobile element 20, 26 by the leakage flow Ffl, Ff2. The shear losses of the leakage flow Ffl, Ff2 with the rest of the primary flow Fp flowing in the turbine are thus further reduced, which makes it possible to further improve the efficiency of the turbomachine.

[0074] Geometry of the cells and the upstream and downstream parts

[0075] 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, so as to form a continuous abradable element 30.

[0076] One or more walls of the cell may extend in the direction of greatest longitudinal extension dimension of the cell. Thus, one or more walls of the cells in the upstream portion 33 are oriented along the first angle a1 with the axis A. Similarly, one or more walls of the cells in the downstream portion 34 are oriented along the second angle a2 with the axis A.

[0077] The cells in the upstream part 33 may have a geometry and / or dimensions that are substantially equivalent, or alternatively different, to those of the cells in the downstream part 34.

[0078] The cells may have any shape suitable for forming 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 rhombus, a hexagon, an ellipse.

[0079] Where appropriate, the shape of the cell may be flattened, or elongated, to give the cell a direction of greater longitudinal extension dimension, for example example oriented along the first axis XI or the second axis X2. For example, the cell may have the shape of an irregular hexagon comprising two sides of greater longitudinal extension dimension oriented along the first axis XI or the second axis X2.

[0080] When the cell has a diamond shape, the first angle a1 of a cell of the upstream part 33, respectively the second angle a2 of a cell of the downstream part 34, may 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 may be identical to each other, and all the diamonds of the cells of the downstream part 34 may be identical to each other and be different from the diamonds of the cells of the upstream part 33 due at least to the fact that the second angle a2 is different from the first angle a1.

[0081] Each cell has a cell surface area which corresponds to a surface area of ​​the hollow cell delimited by the cell wall. The plurality of cells of the upstream portion 33 and the plurality of cells of the downstream portion 34 may each define a friction surface configured to extend opposite a movable element 20, 26 of the turbine, in particular opposite a sealing lip 40 of the turbine, said sealing lip 40 being for example arranged on the movable element 20, 26 opposite 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 portion 33 and the friction surface of the plurality of cells of the downstream portion 34.The friction surface of the abradable element 30 may correspond substantially to the sum of the surface areas 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 surface areas 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 surface areas of each cell of the downstream part 34.

[0082] The friction surface of the plurality of cells of the upstream part 33 may 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 downstream part 34. More particularly, the axial dimension of the friction surface of the plurality of cells of the upstream part 33 may 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 may 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 leakage flow Ffl, Ff2 and the rest of the primary flow Fp at the level of the sampling and reintroduction of the leakage flow Ffl, Ff2, and thus to further improve the efficiency of the turbomachine.

[0083] The abradable element 30 may have a parallelepiped shape, or even a plate shape, 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 may 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 length direction and to the depth direction. 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 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 radial direction.

[0084] 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 portion 33 of the abradable element 30 may be substantially equal to the width of the downstream portion 34 of the abradable element 30. Thus, the difference between the friction surface of the plurality of cells of the upstream portion 33 and the friction surface of the plurality of cells of the downstream portion 34 corresponds to a difference in length between the upstream portion 33 and the downstream portion 34. Thus, the upstream portion 33 may have a length greater, or even strictly greater, than a length of the downstream portion 34, for example between 1 and 5 times greater than the length of the downstream portion 34, for example between 2 and 3 times greater than the length of the downstream portion 34. length of the downstream part 34. [Fig.3a] and [Fig.3b] 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.

[0085] 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.

[0086] 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 at 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 having an inclination strictly between 0° and 90° to the axis A, a curved line, etc.

[0087] The junction 35 between the upstream portion 33 and the downstream portion 34 may be located closer to the trailing edge than to the leading edge of the blade 10, 20 of the movable element 20, 26 opposite which the abradable element 30 is arranged. More particularly, as illustrated by way of non-limiting examples in [Fig. 3a] and in [Fig. 3b], the junction 35 between the upstream portion 33 and the downstream portion 34 may be located substantially at the trailing edge of said blade 10, 20, that is to say in a substantially identical position along the turbine axis, the junction 35 being external relative to the blade 10, 20.

[0088] When the abradable element 30 is mounted on the casing 100 opposite at least one blade 20 of the moving wheel, the junction 35 between the upstream part 33 and the downstream part 34 may extend closer to the trailing edge than to 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 opposite which the abradable element 30 extends.

[0089] When the abradable element 30 is mounted on the foot of the distributor opposite the shroud 26 of the moving wheel and opposite at least one blade 10 of the distributor, the junction 35 between the upstream part 33 and the downstream part 34 may 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 30 extends.

[0090] In a second exemplary embodiment, the upstream part 33 and the downstream part 34 are separated by at least one intermediate part having cells of which a direction of greatest longitudinal extension dimension is oriented along one or more axes different from the first axis XI and the second axis X2.

[0091] For example, an intermediate portion located, for example arranged contiguously, between the upstream portion 33 and the downstream portion 34 may comprise a plurality of cells. All or part of the cells in the intermediate portion have a larger longitudinal extension dimension which extends along a third axis forming a third angle with the axis A, the third angle being strictly between the first angle a1 and the second angle a2. Such an intermediate portion allows a more gradual evolution of the tangential speed of the leakage flow Ffl, Ff2 circulating through the cells of the abradable element 30. Several intermediate portions may 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 between the first angle a1 and the second angle a2. The intermediate parts are arranged from the upstream part 33 to the downstream part 34 in decreasing order of the angles of the intermediate part axes, so that the angles formed between the cells and the axis A decrease progressively from upstream to downstream of the abradable element 30. Such several intermediate parts allow an even more gradual evolution of the tangential speed of the leakage flow Ffl, Ff2 circulating through the cells of the abradable element 30.

[0092] Alternatively, the cells of the intermediate portion of the abradable element 30 may have a larger longitudinal extension dimension 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 portion of the abradable element 30, in particular from the first angle a1 at the upstream end to the second angle a2 at the downstream end. Such an intermediate portion comprising cells having a progressive change in angle allows an even more gradual evolution of the tangential speed of the leakage flow Ffl, Ff2 circulating through the cells of the abradable element 30. Sealing gasket (lip + abradable)

[0093] The turbine may further comprise a sealing lip 40 arranged on a movable element 20, 26 opposite 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 rotating movable element 20, 26 and the fixed element 10, 100 located opposite the seal. During operation of the turbomachine, the sealing lip 40 has a rotation speed 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 leakage flow Ffl, Ff2 bypassing the movable element 20, 26, and thus to further improve the efficiency of the turbomachine. The sealing lip 40 may be formed in one piece with the movable element 20, 26, or be attached and fixed to the movable element 20, 26.During operation of the turbomachine, in particular when differential thermal or mechanical expansions 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 engages the abradable element 30 without itself being worn by the contact. For example, a sealing lip 40 may be arranged on the head of a blade 20 of the moving wheel opposite the casing 100. Alternatively or in . furthermore, a sealing lip 40 can be arranged on the ferrule 26 of the moving wheel, opposite at least one vane 10 of the distributor.

[0094] The seal formed by the sealing lip 40 and abradable element 30 pair may be a labyrinth seal. The seal may comprise one or more sealing lips 40 spaced apart from each other along the turbine axis. Each sealing lip 40 extends from the movable element 20, 26 to the abradable element 30 mounted on the fixed element 10, 100, i.e. from the inside to the outside of the turbomachine. The abradable element 30 is arranged opposite the sealing lips 40 of the seal.

[0095] When the sealing lip 40 is arranged on the head of a blade 20 of the moving wheel, the sealing lip 40 may be arranged on a platform 50 attached and fixed to the head of the blade 20 of the moving 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.

[0096] The junction 35 between the upstream portion 33 and the downstream portion 34 of the abradable element 30 may extend between two sealing lips 40, in particular between an upstream lip and a downstream lip arranged downstream of the upstream lip. Thus, the tangential velocity of the leakage flow Ffl, Ff2 at the sealing lips 40 is maximized, which makes it possible to further reduce the shear losses of the leakage flow Ffl, Ff2 with the rest of the primary flow Fp flowing in the turbine. More particularly, the leakage flow Ffl, Ff2 is deflected by the upstream lip, so that it has a strong rotating component after passing the upstream lip. The abradable element 30 then straightens the leakage flow Ffl, Ff2 to reduce its gyration, or even change its direction to facilitate its reintroduction into the rest of the primary flow Fp once the leakage flow Ffl, Ff2 has passed the downstream lip. Production of cells

[0097] The cells, in particular the cellular 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 a1, a2 can be easily manufactured, including at the junction 35 between the upstream part 33 and the downstream part 34.

[0098] 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 a honeycomb structure 32.

[0099] The abradable element 30 may be coated with a particular surface treatment, for example NiCrAlY or ceramic (for example ZrO2 type).

[0100] The solution described above is not limited to the described embodiment examples, and can be used in other locations of the turbomachine comprising a movable element rotating around the longitudinal axis and a fixed element.

[0101] Other embodiments may be envisaged and a person skilled in the art may readily modify the embodiments or examples set forth above or envisage others while remaining within the scope of the application.

Claims

Claims

1. 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 portion (33) and a downstream portion (34) each comprising a plurality of cells, the upstream to 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 portion (33) having a greater longitudinal extension dimension which extends along a first axis (XI) forming a first angle (al) with the axis (A), all or part of the cells in the downstream portion (34) having a greater longitudinal extension dimension which extends along a second axis (X2) forming a second angle (a2) with the axis (A),in which the first angle (al) is strictly positive and the second angle (a2) is negative or zero, the first angle (al) and the second angle (a2) each being taken in a plane transverse to the alveoli.,

2. Abradable element (30) according to claim 1, wherein the first angle (al) is between 40° and 75°.

3. Abradable element (30) according to claim 1 or 2, in which the second angle (a2) is between 0° and -30°

4. 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 rhombus, an ellipse.

5. 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 friction surface configured 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) according to an axial dimension greater than the friction surface of the plurality of cells of the downstream part (34).

6. Abradable element (30) according to claim 5, wherein 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).

7. An abradable element (30) according to any one of claims 1 to 6, wherein the upstream portion (33) and the downstream portion (34) are arranged contiguously without overlapping along the axis (A), and wherein a junction (35) between the upstream portion (33) and the downstream portion (34) forms a line oriented substantially perpendicular to the axis (A).

8. Turbine, in particular a low-pressure turbine, for a turbomachine, comprising: - a movable wheel comprising a shroud (26) integral in rotation with a crown formed by a plurality of radial blades (20) distributed around a disc (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 movable 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) opposite at least one blade (20) of the moving wheel, and / or on the foot of the distributor opposite the ferrule (26) of the moving wheel.

9. A turbine according to claim 8, wherein the upstream portion (33) and the downstream portion (34) of the abradable element (30) are arranged contiguously without overlapping along the axis (A), a junction (35) between the upstream portion (33) and the downstream portion (34) forming a line oriented substantially perpendicular to the axis (A), wherein when the abradable element (30) is mounted on the casing (100) opposite a blade (20) of the moving wheel, the junction (35) between the upstream portion (33) and the downstream portion (34) extends closer to a trailing edge than to a leading edge of the blade (20) of the moving wheel, and wherein when the abradable element (30) is mounted on a blade (10) of the distributor opposite 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.

10. A turbomachine comprising a turbine according to claim 9.

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