IMPROVED FAN DISC FOR A TURBOMACH

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the general field of aeronautical turbomachines, and more precisely to the field of fan discs of an aeronautical turbomachine, an assembly comprising the fan platforms and the disc, and a fan comprising this assembly. STATE OF PRIOR ART

[0002] In a turbomachine, the fan blade platforms must perform several functions. From an aerodynamic point of view, the primary function of these platforms is to define the airflow path. In addition, they must also be able to withstand significant forces while deforming as little as possible and remaining attached to the disc that carries them.

[0003] In order to satisfy these different requirements, certain configurations have been proposed in which the platforms have a first part making it possible to define the air flow path and to ensure the retention of the platform when the engine is rotating, and a second part making it possible to limit the deformations of the first part under the effects of centrifugal forces and to maintain the platform in position when the engine is stopped.

[0004] In existing solutions, the platform can take the form of a box with a two-dimensional vein wall retained downstream by a drum and upstream by a shell, the upstream retention by the shell being carried out above the tooth of the fan disc (a flange of the shell blocking the platform axially and radially upstream).

[0005] Such upstream retention carried out above the tooth of the disc with a ferrule has the disadvantage of imposing a high hub ratio, the hub ratio being the ratio of the radius taken between the axis of rotation and the point of the leading edge of the blade flush with the surface of the platform, to the radius taken between the axis of rotation and the point of the outermost leading edge. Furthermore, this upstream retention is likely to generate over-stresses on the tooth and in the cell of the disc, at the connection between the ferrule and the disc. RU 87 212 U1, FR 3 048 448 A1 and US 2011 / 0176925 A1 disclose other examples of upstream retention of a fan disc.

[0006] In order to optimize the performance of the fan, and more generally of the turbomachine, it is desirable to have an assembly of a fan blade platform attached to a fan disc which has the lowest possible hub ratio, while limiting the stresses at the level of the tooth and the disc cavity. PRESENTATION OF THE INVENTION

[0007] One embodiment relates to an assembly as defined in claim 1, comprising a disc adapted to support platforms and blades of a fan, and comprising: an outer surface having a succession of grooves for receiving the fan blades and teeth interposed between the grooves for supporting the fan platforms, an upstream face of the disc, and an annular axial projection disposed radially around an axis of the disc on the upstream face of the disc, and 11 a plurality of radial projections disposed radially around the axis and extending from an upstream face of the annular axial projection towards the center of the disc, and being fixed to a fan platform retention flange, the projections being offset radially towards the inside of the disc relative to the grooves of the disc, and being disposed circumferentially between two consecutive teeth of the disc, the number of radial projections being equal to half the number of grooves of the disc.

[0008] By "upstream face" we mean upstream in relation to the direction of air flow, when the disc is placed in a blower.

[0009] By "axial projection" we mean axial along the direction of air flow, or along the axis of rotation of the disc, when the disc is placed in a blower.

[0010] By "radially offset" we mean offset towards the inside of the disc, that is to say towards the axis of rotation of the disc.

[0011] The radial projections being offset radially inwardly of the disc relative to the grooves of the disc, and arranged circumferentially between two teeth of the disc, when the projections are fixed on a platform retention flange, the fixing zone located on the projections is thus offset radially and circumferentially relative to the teeth of the disc. This has the advantage of limiting the stresses at the disc tooth, when an external element, in the case of the present invention the platform retention flange, is fixed on the disc.

[0012] Furthermore, this fixing zone being radially offset relative to the teeth of the disc, this has the advantage of freeing up space at the upstream axial end of the disc tooth, allowing for example the disc tooth to be machined. Such machining can make it possible to modify the shape of the upstream axial end of a platform supported by said tooth, compared to known platforms, and thus to modify the air flow path when the platform is arranged in a fan. It is thus possible to reduce the hub ratio in order to improve the performance of the fan, and therefore of the turbomachine in which the fan is mounted.

[0013] In some embodiments, the radial projections are tabs machined on the upstream face of the disc and folded toward the center of the disc.

[0014] The tabs may have a main face perpendicular to the axis of the disc, and a thickness, along the axis of the disc, small compared to the dimensions of the main face. The shape of these radial projections has the advantage of being simple to produce.

[0015] In some embodiments, one face of the radial projections has an axis hole parallel to the axis of the disc.

[0016] The hole can be made on the main face of the tab. It allows an external element to be fixed to the disc, for example a retention flange or a ferrule, using a screw or a bolt, for example.

[0017] In some embodiments, in a view of the upstream face of the disc along the axis of the disc, the center of the orifice of each radial projection is arranged on a straight line passing through the center of the disc and the bottom of a groove in the disc, the bottom of a groove being the point of the groove, according to this view, located at an equal distance from the two teeth between which it is located.

[0018] In other words, the center of the orifice of each radial projection is radially aligned with the bottom of a groove. The end of the disc teeth is the seat of significant mechanical stresses when the disc is arranged in a fan. This arrangement thus makes it possible to optimize the circumferential distance, in a view of the upstream face of the disc along the axis of the disc, of the center of the orifice of each projection relative to the two teeth, where the mechanical stresses are significant, between which it is located. The attachment of a ferrule on the radial projections can therefore be carried out in an area less mechanically stressed than if the projections were aligned with the teeth. The distribution of stresses within the disc, when it is arranged in a fan, is thus optimized, and the existence of local over-stresses can thus be limited or avoided.

[0019] In some embodiments, a radius of the disc being a segment between the center of the disc and the bottom of a groove, a distance between the center of the disc and the center of the orifice of the radial projection is less than 95% of the radius of the disc, preferably less than 90%, more preferably less than 80%.

[0020] Moving the center of the radial projection hole closer to the center of the disc allows the attachment point between a ferrule and the disc to be moved away from more mechanically stressed areas when the disc is placed in a blower.

[0021] In some embodiments, the radial projections are arranged on the upstream face of the disc at regular intervals along the circumference of the disc. This allows for uniform distribution of mechanical stresses on the upstream face of the disc, when a ferrule is attached thereto.

[0022] According to the claimed invention, the number of radial projections is equal to half the number of grooves of the disc.

[0023] Preferably, the radial projections are distributed at regular intervals so as to be radially aligned with the bottom of every other groove. Consequently, half as many connections are required between the disc and a ferrule, when a ferrule is fixed to the disc, as if a radial projection were provided for each groove. This makes it possible to reduce the number of assembly steps and the number of connection parts required. Assembly time and cost can thus be limited.

[0024] The assembly comprises at least one platform, and at least one upstream retention flange for providing axial and radial retention of the upstream axial end of the platform, wherein the upstream retention flange is fixed to the axial projections of the upstream face of the disc.

[0025] When the retention flange is fixed on the disc, the interface between the flange and the disc, corresponding to the area of ​​attachment of the flange on a radial projection of the disc, is offset radially towards the inside of the disc, relative to a groove of the disc, and is interposed circumferentially between two teeth of the disc, unlike known systems in which this interface is located at the level of the disc tooth. This offset makes it possible to limit the stresses at the upstream axial end of the teeth. In addition, the offset of this interface makes it possible to free up space at the upstream axial end of the disc tooth, offering more possibilities for machining the tooth and therefore for modifying the shape of the platform and thus, reducing the hub ratio.

[0026] In some embodiments, the upstream retention flange is a ferrule.

[0027] The present disclosure also relates to a turbomachine fan comprising an assembly according to any one of the embodiments described in the present disclosure, and a plurality of blades mounted in the grooves of the disc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which: there figure 1 is a schematic sectional view of a turbomachine according to the invention, the figure 2 is a schematic view along direction II of the fan of the figure 1 , There figure 3 is a perspective view of a disc according to the invention, The figure 4 is a longitudinal sectional view of an assembly comprising a retention flange, a platform and a disc according to the invention. DETAILED DESCRIPTION OF EXAMPLES OF IMPLEMENTATION

[0029] In this presentation, the term “longitudinal” and its derivatives are defined in relation to the main direction of the platform considered; the terms “radial”, “internal”, “external” and their derivatives are defined in relation to the axis of the disk, corresponding to the main axis of the turbomachine; finally, the terms “upstream” and “downstream” are defined in relation to the direction of flow of the fluid passing through the turbomachine. Also, unless otherwise indicated, the same reference signs in different figures designate the same characteristics.

[0030] There figure 1 shows a schematic view in longitudinal section of a double-flow turbojet 1 centered on the axis A according to the invention. It comprises, from upstream to downstream: a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6, and a low-pressure turbine 7.

[0031] There figure 2 shows a schematic view of blower 2 of the figure 1 according to direction II. The fan 2 comprises a fan disc 40 in which a plurality of grooves 42 are formed at its outer periphery. These grooves 42 are rectilinear and extend axially from upstream to downstream along the entire length of the disc 40. They are furthermore regularly distributed all around the axis A of the disc 40. In this way, each groove 42 defines with its neighbor a tooth 44 which also extends axially from upstream to downstream along the entire length of the disc 40. Equivalently, a groove 42 is delimited between two neighboring teeth 44.

[0032] The fan 2 further comprises a plurality of blades 20 of curvilinear profile (only four blades 20 have been shown on the figure 2 ). Each blade 20 has a root 20a which is mounted in a respective groove 42 of the fan disc 40. For this purpose, the root 20a of a blade 20 may have a fir tree or dovetail shape adapted to the geometry of the grooves 42.

[0033] Finally, the fan 2 comprises a plurality of attached platforms 30, each platform 30 being mounted in the interval between two neighboring fan blades 20, in the vicinity of the roots 20a thereof, in order to delimit, on the inner side, an annular air inlet vein into the fan 2, the vein being delimited on the outer side by a fan casing.

[0034] THE figures 1 et 2 also show an internal radius RI and an external radius RE. The internal radius RI corresponds to the radius taken between the axis of rotation A and the point of the leading edge of a blade 20 flush with the surface of a platform 30. The external radius RE corresponds to the radius taken between the axis of rotation A and the most external point of the leading edge of a blade 20. These two radii RI, RE are those used in the calculation of the hub ratio RI / RE. Reducing the internal radius RI makes it possible to reduce this hub ratio. In other words, reducing the hub ratio, by acting in particular on the internal radius RI, amounts to bringing the air intake aerodynamic vein as close as possible to the fan disc.

[0035] There figure 3shows a perspective view of a fan disc comprising an external surface 40a and an upstream face 40b. The external surface 40a has a succession of grooves 42 in which a fan blade 20 root 20a can be housed, and teeth 44 interposed between the grooves 42, capable of supporting the fan platforms 30. Each tooth 44 may comprise a main tooth surface 44a, and a beveled surface 44b at its upstream axial end.

[0036] Furthermore, the disc 40 comprises, on its upstream face 40b, a plurality of radial projections 46, having a tongue shape and being arranged circumferentially, at regular intervals, around the axis A. These projections can be produced for example by machining on the upstream face 40b of the disc, for example on the pin of the disc. The number of radial projections 46 is equal to half the number of grooves 42, each projection 46 being radially aligned with the corresponding groove 42. In other words, each projection 46 is interposed circumferentially between two teeth 44 of the disc 40. In addition, each radial projection 46 is offset radially towards the inside of the disc, that is to say towards the axis A, relative to the corresponding groove 42.

[0037] Each radial projection 46 may comprise a fixing orifice 46a on its upstream face 46b, allowing a fixing means 49 to be inserted, for example a screw or a bolt. The fixing of an upstream retention flange 50, for example a ferrule, may thus be carried out at a radial projection 46, for example by inserting the fixing means 49 through a flange orifice 52 and the fixing orifice 46a of the projection, the fixing means 49 then being fixed, for example by a bolt, to the radial projection 46. The retention flange 50 being fixed to the disc 40, an upper surface 54 of the flange 50 then makes it possible to ensure the radial retention of a retention surface 32 located at the upstream axial end of the platform 30.

[0038] The attachment zone between the disc 40 and the retention flange 50 being located at the level of the radial projections 46, therefore closer to the center of the disc, this makes it possible to limit the stresses exerted during operation of the fan at the level of sensitive surfaces such as the upstream axial end of the teeth 44. Furthermore, this interface between the disc 40 and the retention flange 50 being offset radially relative to the grooves of the disc, in comparison with known structures, the overhangs 44c, usually allowing the attachment of the shell to the upstream end of the teeth of the disc, can be eliminated. This makes it possible to free up space at the upstream axial end of the teeth 44 of the disc.It is furthermore possible to modify more freely the upstream axial end of the teeth 44, and therefore the upstream axial end of the platform 30, for example by providing an inclined wall 34 on the upstream end of the platform 30, the inclined wall 34 coming into contact with the beveled surface 44b of the tooth 44. It is thus possible to reduce the hub ratio in order to optimize the performance of the fan, and therefore of the turbomachine in which the fan is mounted.

[0039] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

1. An assembly comprising a disc (40) configured to support blades (20) of a fan (2), at least one platform (30) supported by the disc (40), and at least one upstream retaining flange (50) to ensure the axial and radial retention of the upstream axial end of the platform (30), the disc (40) including: - an external surface (40a) having a succession of grooves (42) for receiving the fan blades (20) and teeth (44) interposed between the grooves (42) to support the fan platforms (30), - an upstream face (40b) of the disc, and - an annular axial protrusion disposed radially around an axis (A) of the disc (40) on the upstream face (40b) of the disc (40), characterized in that the disc further includes a plurality of radial protrusions (46) disposed radially around the axis (A) and extending from an upstream face of the annular axial protrusion towards the center of the disc (40), and being fastened to the fan platform retaining flange (50), the radial protrusions (46) being offset radially toward the interior of the disc (40) relative to the grooves (42) of the disc (40), and being disposed circumferentially between two successive teeth (44) of the disc (40), the number of radial protrusions being equal to half the number of grooves (42) of the disc (40).

2. The assembly according to claim 1, wherein the radial protrusions (46) are tabs machined on the upstream face (40b) of the disc and folded toward the center of the disc.

3. The assembly according to claim 1 or 2, wherein one face of the radial protrusions includes an opening with an axis parallel to the axis (A) of the disc.

4. The assembly according to claim 3, wherein, in an upstream side view of the disc along the axis (A) of the disc, the center of the opening of each radial protrusion is disposed on a straight line passing through the center of the disc and the bottom of a groove of the disc, the bottom of a groove being the point in the groove, in this view, situated at equal distance from the two teeth between which it is located.

5. The assembly according to claim 4, wherein, a radius of the disc being a segment between the center of the disc and the bottom of a groove, a distance between the center of the disc and the center of the opening of the radial protrusion is less than 95% of the radius of the disc, preferably less than 90%, more preferably less than 80%.

6. The assembly according to any one of claims 1 to 5, wherein the radial protrusions (46) are disposed on the upstream face (40b) of the disc at regular intervals along the circumference of the disc (40).

7. The assembly according to any one of claims 1 to 6, wherein the upstream retaining flange (50) is a shroud fastened to each axial protrusion (42) by means of a bolt.

8. A turbomachine fan (2) comprising an assembly according to any one of claims 1 to 7, and a plurality of blades (20) mounted in the grooves (42) of the disc (40).