RUNNING SHELL FOR A TURBINE OF A TURBINE DRIVE UNIT WITH AN INCLINATION AND PROJECTS FOR RADIALLY HOLDING THE SHELL

Description

TECHNICAL FIELD

[0001] The invention relates to the field of movable turbine blades for turbomachinery, preferably for aircraft turbomachinery. More particularly, it relates to the means used to ensure the radial retention of the blades relative to the turbine disk, in order to prevent certain blades from moving excessively towards the wheel axis when stopped and under the effect of gravity.

[0002] The invention applies to any type of turbomachine, such as for example a turbojet or a turboprop. STATE OF PRIOR ART

[0003] In an aircraft turbomachine, the turbine wheels are generally made using a disc, around the periphery of which turbine blades are mounted. The gas flow path is radially delimited inwards by platforms provided on the blades, near their roots.

[0004] The blades have already been the subject of numerous developments, and an example of design is known for example from document FR 2 954 797 A1.

[0005] In operation, each moving blade is radially held in place by its foot, which is housed in a groove on the periphery of the turbine disk. To achieve this, the foot is typically equipped with two circumferentially opposed bearing surfaces, each bearing against two teeth on the peripheral part of the disk that define the groove receiving the foot. Thanks to these bearing surfaces, resulting from centrifugal force, each blade is initially held radially by its foot, preventing it from moving radially outwards from the turbine disk.

[0006] When the turbomachine is not running, i.e., when the rotor is stopped, the movable blades in the upper part of the blade ring can fall under the effect of gravity, meaning they move towards the rotor axis. Without a means to stop this inward radial movement, the root of each affected blade can come to rest against the bottom of the groove on the periphery of the disc. If this radial movement of the blade is excessive, it can become problematic because it may lead to circumferential misalignment of the blade tips, potentially resulting in a detrimental overlap of these tips when the turbomachine is next started up.

[0007] To avoid this risk, it is known to provide two walls arranged on either side of the blade's stilt, along its axial direction. Each wall originates from the platform and extends radially inwards until it is very close to the teeth of the peripheral part of the disc.

[0008] While these retaining walls are satisfactory in that they limit the radial displacement of certain blades when the turbomachine is stopped, they nevertheless significantly increase the overall mass of the blade. Moving wheels of aircraft turbomachine turbines comprising a turbine disk and a plurality of blades are also known from FR 3 092 612 A1 and US 2016 / 146016 A1. SUMMARY OF THE INVENTION

[0009] To address at least partially the aforementioned drawback, the invention first relates to a moving turbine wheel for a turbomachine, according to the characteristics of claim 1.

[0010] With the solution proposed by the present invention, the radial retention of the blade, towards the inside, is advantageously achieved using simple protrusions fitted to the strut. These protrusions remain simple to manufacture, reliable, and help to limit the overall mass of the blade compared to the wall-based solutions known in the prior art.

[0011] Furthermore, the mass reduction achieved by incorporating the protrusions, combined with the removal of all or part of the blade walls, leads to a reduction in the mechanical stresses exerted on the blade root during operation. This also allows for a more compact design of the blade root, as well as that of the teeth on the peripheral part of the turbine disk.

[0012] The invention preferably includes at least one of the following optional features, taken individually or in combination.

[0013] Preferably, each radial retaining protrusion of the blade has a shape that narrows as it moves circumferentially away from the stilt, for example, a general triangular shape. Other shapes are nevertheless conceivable, such as a ridge shape, without departing from the scope of the invention.

[0014] Preferably, each radial retaining protrusion of the blade extends over all or part of the axial length of the stilt.

[0015] Preferably, each of the first and second cavities is also delimited in part, along an axial direction of the blade, by a first and a second connecting wall, the blade also comprising an upstream beak as well as a downstream beak, both separated from the platform along the direction of the height, the first connecting wall connecting the upstream beak to an upstream axial end of the platform, and the second wall connecting the downstream beak to a downstream axial end of the platform, each radial retaining protrusion of the blade being arranged radially between the upstream and downstream beaks, and the blade foot.

[0016] Preferably, the blade also includes a first and a second stiffening wall extending respectively from the upstream and downstream spurs towards the blade foot, the first and second stiffening walls also each contributing to delimiting the first and second cavities, and each radial retaining protrusion of the blade is arranged radially between the stiffening walls and the blade foot.

[0017] Preferably, in a first configuration of radial retention of the blade by its foot, radially inwards with respect to the turbine disk, each thrust surface defines a clearance with the radially outer surface of its associated disk tooth, the clearance being for example between 0.10 and 0.15 mm.

[0018] Preferably, in a second configuration of radial retention of the blade by the protrusions, radially outwards with respect to the turbine disk, each thrust surface defines, with the radially outward surface of its associated disk tooth, a contact area extending over a circumferential length for example greater than or equal to 1 mm.

[0019] The invention also relates to a turbomachine turbine comprising at least one rotating wheel as described above, the turbine preferably being a low pressure turbine, but alternatively being a high pressure turbine.

[0020] Finally, the invention relates to an aircraft turbomachine comprising at least one such turbine, the turbomachine preferably being a twin-spool, twin-body turbojet.

[0021] Other advantages and features of the invention will appear in the detailed, non-limiting description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] This description will be made with reference to the attached drawings, among which are; [ Fig. 1 ] represents a schematic axial cross-sectional view of a turbofan engine according to the invention; [ Fig. 2 ] represents a perspective view of a moving turbine blade of the turbojet engine shown on the figure 1 , and taking the form of a preferred embodiment of the invention; [ Fig. 3 ] represents a partial and enlarged perspective view of the dawn shown in the previous figure; [ Fig. 4 ] represents a front view of part of a turbine wheel, including blades such as the one shown on the figures 2 And 3 ; Fig. 5 ] is an even more enlarged front view of part of the wheel shown on the figure 4, with one of the wheel's blades shown in an initial radial retention configuration by its foot; and [ Fig. 6 ] is a front view similar to that of the figure 5 , with the same blade represented in a second radial retention configuration by the protrusions equipping the stilt of this blade. DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0023] With reference first and foremost to the figure 1 Figure 1 represents an aircraft turbomachine according to a preferred embodiment of the invention. This is a twin-spool, turbofan engine. However, it could be a turbomachine of another type, for example a turboprop, without departing from the scope of the invention.

[0024] The turbomachine 1 has a longitudinal axis 2 around which its various components extend. It comprises, from upstream to downstream along a main direction 5 of gas flow through this turbomachine, a blower 3, a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 11, a high-pressure turbine 7 and a low-pressure turbine 8.

[0025] Conventionally, after passing through the blower, the air splits into a central primary flow 12a and a secondary flow 12b that surrounds the primary flow. The primary flow 12a flows into a main gas circulation channel 14a, passing through the compressors 4, 6, the combustion chamber 11, and the turbines 7, 8. The secondary flow 12b flows into a secondary channel 14b, radially delimited outwards by an engine casing, surrounded by a nacelle 9.

[0026] THE figures 2 And 3represent a movable blade 20 according to a preferred embodiment of the invention, this blade 20 being intended to equip a movable wheel of any of the turbines 7 and 8, and in particular the low pressure turbine 8. The movable wheel is, in a conventional manner, centered on the axis 2.

[0027] The elements of the blade 20 will be presented in the order in which they appear successively according to the direction of the height 22 of this blade, from bottom to top, or from inside to outside since this direction of the height 22 also corresponds to the radial direction of the blade and of the moving turbine wheel in which this blade is intended to be integrated.

[0028] Typically, the blade 20 comprises a blade foot 24, a strut 26, a platform 28, a blade 30 constituting the aerodynamic part of the blade, and possibly a head structure 31 comprising another platform.

[0029] The blade foot 24 has an external shape known as "fir tree" or "bulb," allowing it to be inserted into a corresponding blade housing groove in a turbine disc designed to support the moving blades. The strut 26 typically has a small thickness along a circumferential direction 32 of the blade and runner, while the platform 28 also extends on either side of the strut 26 along this same circumferential direction 32.

[0030] More specifically, the platform 28 can extend circumferentially beyond the intrados 34 and extrados 36 of the blade 30, and can also extend beyond a leading edge 38 and a trailing edge 40 of the blade, along an axial direction 42 of the blade and the wheel into which this blade is intended to be integrated.

[0031] With its outer surface 29a, called the first surface from which the blade 30 extends in the direction 22, the platform 28 radially delimits inwards the main gas circulation channel 14a.

[0032] With its inner surface 29b, called the second surface opposite to the first surface 29a along the direction 22, and from which the stilt 26 extends in this same direction substantially in line with the blade 30, the platform 28 radially delimits outwards a first cavity 33a and a second cavity 33b, arranged on either side of the stilt 26 along the direction 32.

[0033] The platform 28 comprises an upstream axial end 35a and a downstream axial end 35b. A first connecting wall 37a extends from the upstream axial end 35a of the platform, radially inwards and parallel or substantially parallel to directions 22 and 32, to an upstream spoiler 40a projecting axially upstream. Similarly, a second connecting wall 37b extends from the downstream axial end 35b of the platform, radially inwards and parallel or substantially parallel to directions 22 and 32, to an upstream spoiler 40b projecting axially downstream.

[0034] The first connecting wall 37a partially delimits, axially upstream, each of the two cavities 33a, 33b planned under the platform 28. Similarly, the second connecting wall 37b also partially delimits, axially downstream, each of these two cavities 33a, 33b.

[0035] The spoilers 40a, 40b are thus radially offset inwards relative to the platform 28, being closer to the foot 24. A connecting radius is preferably provided at the junction between each spoiler 40a, 40b and its associated connecting wall 37a, 37b, and the same is true between each of these walls 37a, 37b and the platform 28.

[0036] From the upstream spur 40a, a first stiffening wall 42a can be provided, extending radially inwards and parallel or substantially parallel to directions 22 and 32, over a limited height. The inner edge of this first stiffening wall 42a is located at a considerable radial distance from the foot 24, and therefore only axially covers a radially outer portion of the stilt 26.

[0037] Similarly, from the downstream spoiler 40b, a second stiffening wall 42b can be provided extending radially inwards and parallel or substantially parallel to the directions 22, 32, also over a limited height.

[0038] The stiffening walls 42a, 42b, also called "walls", can be located respectively in the radial extensions of the connecting walls 37a, 37b, or be slightly offset axially from them, as shown in the figures 2 And 3 .

[0039] The first stiffening wall 42a partially delimits, axially upstream, each of the two cavities 33a, 33b provided under the platform 28, just as the second stiffening wall 42b also partially delimits, axially downstream, each of these two cavities 33a, 33b.

[0040] The first cavity 33a remains circumferentially open in the direction opposite to the stilt 26, while it also remains radially open in the direction opposite to the platform 28. In the circumferential direction 32, the first cavity 33a thus opens at the level of a first circumferential opening 44a referenced on the figure 3 This first opening 44a is delimited by a first junction zone 46a with the second cavity 33b of a blade directly adjacent to the wheel, as is known to those skilled in the art. The first junction zone 46a is located at a lower circumferential end of the blade and has a general inverted U shape, open radially inwards.

[0041] One of the distinctive features of the invention lies in the absence of the first and second stiffening walls 42a, 42b under the spoilers, or in the fact that they are retained but at a low height, so as to considerably reduce their mass. In the exposed part of the strut 26, not axially covered by the elements 37a, 42a, 37b, 42b, another distinctive feature of the invention is that on each of its two sides along the circumferential direction 32, this strut 26 is provided with a radial retaining protrusion 50 for the blade.

[0042] Each of the two protrusions 50 includes a thrust surface 52 oriented radially inwards, and intended to cooperate with a radially external surface of one of the two disc teeth defining the groove in which the foot 24 of the blade concerned is housed, as will be described later.

[0043] In this preferred embodiment, each radial retaining protrusion 50 of the blade has a shape that narrows as it moves circumferentially away from the stilt 26, adopting a generally triangular or beaded shape. Each protrusion 50 is preferably formed in one piece with the stilt, extending over a limited circumferential length, strictly less than that of the aforementioned elements 37a, 37b, 40a, 40b, 42a, 42b, and, for example, identical or similar to the circumferential length of the longest part of the foot 24 along direction 32. It also extends over an axial length corresponding, for example, to the entire axial length of the stilt 26, as shown in the figures 2 And 3Alternatively, each outgrowth 50 could extend only over part of the axial length of the stilt 26, for example by being formed by axially spaced segments from each other.

[0044] Each radial retaining protrusion 50 is arranged radially between, on the one hand, the radially inner edges of the stiffening walls 42a, 42b, and on the other hand, the upper part of the blade foot 24, while remaining at a radial distance from each of these elements 42a, 42b, 24. In addition, each radial retaining protrusion 50 extends axially between the stiffening walls 42a, 42b, therefore also between the spoilers 40a, 40b.

[0045] There figure 4 shows part of a turbine wheel 60, comprising a disc 62 centered on the axis 2 and equipped with a peripheral part 64 having axial grooves 66 for housing the blades 20. The axial grooves 66 follow one another in the circumferential direction 32.

[0046] The wheel 60 also includes a crown of blades 20 of design of the type described above, with the foot 24 of each blade being housed in one of the grooves 66 of the peripheral part 64 of the disc.

[0047] On the figure 5 , the blade 20 is represented in a first radial retention configuration by its foot 24, this configuration being observed in operation when the centrifugal force causes the blade foot 24 to press radially against an inner surface 72 of teeth 70. These teeth 70 are those which form the peripheral part 64 of the disk, extending radially outwards and defining between them, according to the direction 32, the grooves 66 for housing the blade feet.

[0048] Thus, the blade root 24 is equipped with two circumferentially opposed bearing surfaces 74, which, in operation, bear against the two surfaces 72 of two directly consecutive teeth along the direction 32, and which define between them the axial groove 66 receiving this root. Thanks to these bearing surfaces resulting from the centrifugal force, each blade is in the first radial retention configuration by its root 24, preventing it from escaping radially outwards relative to the turbine disk 62. The blade 20 is designed so that in this first radial retention configuration, a small radial clearance 76 remains between the abutment surface 52 of each protrusion 50 and the radially outer surface 78 of its associated disk tooth 70 against which it faces. This clearance 76 is preferably between 0.10 and 0.15 mm.

[0049] On the figure 6The blade 20 is represented in a second radial retention configuration by its protrusions 50. This second configuration is observed when the turbomachine is not in operation, i.e., when it is stopped, and the blades 20 of the upper part of the blade ring can fall under the effect of gravity and move closer to the wheel axis. This movement is limited to the consumption of the radial clearance 76, described with reference to the figure 5 Once this clearance 76 is consumed and the protrusions 50 make contact with the two teeth 70, each thrust surface 52 defines, with the radially outer surface 78 of its associated disc tooth 70, a contact area / interface extending over a circumferential length 80 greater than or equal to 1 mm. This also causes the bearing surfaces 74 of the blade root 24 to shift radially from the inner surfaces 72 of the teeth 70, leaving a small clearance 82 between them.

[0050] Of course, various modifications can be made by a person skilled in the art to the invention just described, only by way of non-limiting examples, and the scope of which is defined by the attached claims.

Claims

1. A turbine rotor wheel (60) of an aircraft turbomachine, comprising a turbine disc (62) including a peripheral portion (64) provided with grooves (66) for housing blades which are succeeding each other in a circumferential direction (32) of the wheel, said wheel also comprising a plurality of blades (20), the root (24) of each blade being housed in one of the grooves (66) of the peripheral portion (64) of the disc, each blade comprising successively, in a radial direction (22) of height of the blade relative to the axis (2), a blade root (24), a stilt (26), a platform (28), as well as a vane (30), the blade root being intended to be housed in a blade housing groove (66) provided on a peripheral portion (64) of a turbine disc (62) of the rotor wheel, said housing groove (66) being defined between two disc teeth (70) which are directly consecutive in a circumferential direction (32) about the axis (2), the platform (28) comprising a first surface (29a) as well as a second surface (29b) which is opposite to the first surface in the radial direction (22), the first surface (29a), from which the vane (30) extends, being intended to delimit a gas flow path (14a), and the second surface (29b), from which the stilt (26) extends, partially delimiting a first (33a) and a second cavity (33b) arranged on either side of the stilt (26) in the circumferential direction (32), characterised in that on each of the two sides thereof, in the circumferential direction (32), the stilt (26) is provided with a protrusion (50) for radially retaining the blade, each protrusion (50) comprising a stop surface (52) which is radially inwardly directed and intended to cooperate with a radially outer surface (78) of a disc tooth (70) defining a groove in which the root (24) of the concerned blade is housed.

2. The turbine rotor wheel according to claim 1, characterised in that each protrusion (50) for radially retaining the blade has a shape which narrows by being circumferentially spaced from the stilt (26), for example a general triangular shape.

3. The turbine rotor wheel according to claim 1 or 2, characterised in that each protrusion (50) for radially retaining the blade extends over all or part of the axial length of the stilt (26).

4. The turbine rotor wheel according to any one of the preceding claims, characterised in that each of the first and second cavities (33a, 33b) is also partially delimited, in an axial direction (42) of the blade, by first (37a) and second (37b) connecting walls, the blade also comprising an upstream spoiler (40a) as well as a downstream spoiler (40b), both separated from the platform (28) in the radial direction (22), the first connecting wall (37a) connecting the upstream spoiler (40a) to an upstream axial end (35a) of the platform, and the second wall (37b) connecting the downstream spoiler (40b) to a downstream axial end (35b) of the platform, each protrusion (50) for radially retaining the blade being arranged radially between the upstream and downstream spoilers (40a, 40b), and the blade root (24).

5. The turbine rotor wheel according to claim 4, characterised in that it further comprises first (42a) and second (42b) stiffening walls extending respectively from the upstream spoiler (40a) and the downstream spoiler (40b), in the direction of the blade root (24), the first and second stiffening walls (42a, 42b) also each participating in delimiting the first and second cavities (33a, 33b), and in that each protrusion (50) for radially retaining the blade is arranged radially between the stiffening walls (42a, 42b) and the blade root (24).

6. The turbine rotor wheel according to any one of the preceding claims, characterised in that in a first configuration of radial retention of the blade by the root (24) thereof, radially inwardly relative to the turbine disc (62), each stop surface (52) defines a clearance (76) with the radially outer surface (78) of the associated disc tooth (70) thereof.

7. The turbine rotor wheel according to any one of the preceding claims, characterised in that in a second configuration of radial retention of the blade by the protrusions (50), radially outwardly relative to the turbine disc (62), each stop surface (52) defines, with the radially outer surface (78) of the associated disk tooth (70) thereof, a contact area extending over a circumferential length (80).

8. A turbomachine turbine (8) comprising at least one rotor wheel (60) according to any one of the preceding claims, the turbine preferably being a low-pressure turbine.

9. An aircraft turbomachine (1) comprising at least one turbine (8) according to claim 8, the turbomachine preferably being a bypass turbojet engine.