COMPRESSOR SHAFT FOR AN AIRCRAFT TURBOMACHINE

Abstract

Compressor shaft (11) for a turbomachine, the shaft (11) being in one piece, annular, and comprising a body (38) and a flange (39), the flange (39) having an internal end (42) which is connected to the body (38); characterized in that the body (38) is divided into an upstream portion (44) and a downstream portion (45) longitudinally separated from each other, the inner end (42) of the collar (39) being connected to the upstream and downstream portions (44, 45) of the body (38) via a fork (46), the fork (46) comprising an upstream arm (47) connecting the inner end (42) of the collar (39) and a downstream end (48) of the upstream portion (44) of the body (38), and a downstream arm (49) connecting the inner end (42) of the collar (39) and an upstream end (50) of the downstream portion (45) of the body (38), such that the upstream and downstream arms (47, 49) internally form an open recess (51). Figure for the abstract: 2

Description

Title of the invention: COMPRESSOR SHAFT FOR AN AIRCRAFT TURBOMACHINE Technical field of the invention

[0001] The present invention relates to a compressor shaft for an aircraft turbomachine, as well as to an aircraft turbomachine comprising such a compressor shaft. Technical background

[0002] A so-called “Open Fan” turbomachine comprises an unducted mobile fan which is driven in rotation by a power turbine (or low pressure turbine), and an unducted fixed rectifier which is configured to straighten at least part of the air flow generated by the unducted fan.

[0003] Such a high bypass ratio turbomachine has the advantage of having excellent efficiency, with in particular a reduction in fuel consumption and carbon dioxide emissions.

[0004] Conventionally, the power turbine is associated with a gas generator which comprises at least one compressor, a combustion chamber and at least one expansion turbine (or high pressure turbine). More precisely, the power turbine is rotated by the gases leaving the expansion turbine.

[0005] To optimize the performance of the “Open Fan” turbomachine, it is known to install a ducted mobile fan and a low-pressure compressor (more commonly called a “booster”) in the air inlet which feeds the gas generator. Such a ducted fan is commonly called a “Mid-Fan”.

[0006] Such a ducted fan can be rotated together with the rotor of the low-pressure compressor via a compressor shaft, this compressor shaft being rotated by the power turbine.

[0007] To achieve this, engine manufacturers have considered jointly clamping the shrouded fan and the rotor of the low-pressure compressor to a flange on the compressor shaft. Such a flanged shaft is traditionally made of a single piece and obtained, for example, by turning.

[0008] However, the first results obtained by calculation show that according to the first solution hypotheses the compressor shaft has a stiffness that is too low compared to that predefined in the specifications, which takes into account in particular the vibratory behavior of the turbomachine. Too low a stiffness here leads to excessive stress on the bearings used to guide the compressor shaft.

[0009] To further stiffen the compressor shaft, and in particular its collar, a solution could be to increase its thickness. Such a solution allows a slight gain in stiffness but significantly increases the mass of the compressor shaft, and consequently the fuel consumption of the turbomachine, which is not desirable.

[0010] The objective of the present invention is therefore to propose a solution making it possible to increase the stiffness of the compressor shaft to meet the requirements of the specifications while minimizing the increase in its mass. Summary of the invention

[0011] The invention thus proposes a compressor shaft for an aircraft turbomachine, the shaft being in one piece and annular around a longitudinal axis X, the shaft comprising a body extending longitudinally and a collar extending substantially radially with reference to the axis X, the collar having an outer end which carries a flange and an inner end which is connected to the body, the flange being intended to be secured to a ducted fan and to a rotor of a low-pressure compressor; characterized in that the body is divided into an upstream portion and a downstream portion longitudinally spaced from each other, the inner end of the collar being connected to the upstream and downstream portions of the body via a fork, the fork comprising an upstream arm connecting the inner end of the collar and a downstream end of the upstream portion of the body, and a downstream arm connecting the inner end of the collar and an upstream end of the downstream portion of the body, so that the upstream and downstream arms internally form an open recess.

[0012] The incorporation of a fork to connect the collar to the body not only makes it possible to meet the requirements of the specifications in terms of stiffness (radial stiffness and rotational stiffness) but also to limit the impact in terms of mass.

[0013] The tree according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another: - the thickness of the upstream arm is greater than the thickness of the downstream arm; - the thickness of the upstream arm varies increasingly from the downstream end of the upstream portion of the body to the internal end of the collar; - the flange is located axially upstream of the fork; - the collar extends in the extension of the downstream arm; - the downstream arm flares from downstream to upstream from the upstream end of the downstream portion of the body to the internal end of the collar; - the collar flares from downstream to upstream from its internal end to its external end; - the upstream arm flares from upstream to downstream from the downstream end of the portion upstream of the body to the internal end of the collar; - the internal and external faces of the upstream arm form between them an acute angle A, the acute angle A being defined in a half-section whose cutting plane is longitudinal and passes through the X axis, the acute angle A preferably being between 5° and 15°; - the internal face of the upstream arm and the internal face of the downstream arm are connected by a fillet, the fillet preferably having a radius R between 10 mm and 30 mm.

[0014] The present invention also relates to an aircraft turbomachine comprising: - a gas generator which is powered by an air inlet; - a power turbine which is independent of the gas generator; - a low pressure compressor comprising a rotor which is driven in rotation by the power turbine; - an unducted fan which is mobile in rotation and which is driven in rotation by the power turbine; - an unshrouded rectifier which is fixed in rotation; - a ducted fan which is placed in the air inlet, the ducted fan being rotatable and driven in rotation by the power turbine; the ducted fan and the rotor of the low pressure compressor being jointly driven in rotation by the power turbine via a compressor shaft as described previously.

[0015] The turbomachine according to the invention may comprise one or more of the characteristics, taken in isolation from one another or in combination with one another: - the shrouded blower comprises a flange, the rotor of the low pressure compressor comprising a drum which comprises a flange, the shrouded blower flange, the compressor shaft flange and the drum flange being secured to each other via an annular row of bolts; - the unducted fan is rotated by the power turbine via a speed reducer; - the upstream end of the upstream portion of the compressor shaft is rotationally connected to an input element of the speed reducer, the unducted fan being rotationally connected to an output element of the speed reducer; - the unducted fan comprises an annular row of variable-pitch blades and the unducted rectifier comprises an annular row of variable-pitch guide vanes. Brief description of the figures

[0016] The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given to by way of non-limiting example and with reference to the appended drawings in which:

[0017] [Fig.l] [Fig.l] is a schematic view in longitudinal half-section of an aircraft turbomachine according to the invention;

[0018] [Fig.2] [Fig.2] is a detail view of [Fig.l] which illustrates the connection between the shaft compressor, the low pressure compressor rotor and the ducted fan;

[0019] [Fig.3] [Fig.3] is a perspective view of the compressor shaft shown in the figures 1 and 2;

[0020] [Fig.4] [Fig.4] is a detail view of the compressor shaft at the fork. Detailed description of the invention

[0021] In [Fig.l] is shown a turbomachine 1 for an aircraft 2, such as an airplane.

[0022] The turbomachine 1 comprises: - a gas generator 3 which is supplied by an air inlet 4; - a power turbine 5 (or low pressure turbine) which is independent of the gas generator 3; - a low pressure compressor 6 (more commonly called a “booster”) comprising a rotor 7 which is driven in rotation by the power turbine 5; - an unducted fan 8 which is rotatable and which is driven in rotation by the power turbine 5; - an unshrouded rectifier 9 which is fixed in rotation; - a ducted fan 10 which is placed in the air inlet 4, the ducted fan 10 being movable in rotation and driven in rotation by the power turbine 5.

[0023] The ducted fan 10 and the rotor 7 of the low-pressure compressor 6 are jointly driven in rotation by the power turbine 5 via a compressor shaft 11 according to the invention.

[0024] The term “unducted” associated with the fan 8 means that the blades 21 of the fan 8 are not surrounded at their free end by a fairing.

[0025] Furthermore, the term “unshrouded” associated with the rectifier 9 means that the guide vanes 27 of the rectifier 9 are not surrounded at their free end by a shroud.

[0026] Furthermore, the term “faired” associated with the fan 10 means that the blades 32 of the fan 10 are surrounded at their free end by a fairing (here a nacelle 28).

[0027] Finally, the term “independent” associated with the power turbine 5 means that the power turbine 5 is not linked in rotation with the gas generator 3.

[0028] The turbomachine 1 is defined along a longitudinal axis X which corresponds in particular to the axis of rotation of the unducted fan 8, of the ducted fan 10, and rotors 7 of compressors 6, 12 and turbines 5, 14.

[0029] According to the embodiment illustrated in [Fig. 1], the low pressure compressor 6, the gas generator 3 and the power turbine 5 are arranged downstream of the unducted and ducted fans 8, 10. Furthermore, the low pressure compressor 6 is arranged upstream of the gas generator 3 and the power turbine 5 is arranged downstream of the gas generator 3.

[0030] The gas generator 3 is supplied with air by the air inlet 4 which opens between the unducted fan 8 and the rectifier 9. Conventionally, the gas generator 3 comprises in particular at least one high-pressure compressor 12, a combustion chamber 13 and at least one expansion turbine 14 (or high-pressure turbine). The rotors of the high-pressure compressor 12 and of the expansion turbine 14 are linked in rotation by one or more transmission shafts 15.

[0031] The rotor 7 of the low pressure compressor 6 and the ducted fan 10 are jointly driven in rotation by the power turbine 5 via the compressor shaft 11 and a turbine shaft 16.

[0032] More precisely, as illustrated in [Fig.l], the low pressure compressor 6 here comprises two axial compression stages. The low pressure compressor 6 comprises a rotor 7 comprising a drum 17 on which two annular rows of blades 18 are attached. The drum 17 comprises a flange 19 which is secured to the compressor shaft 11.

[0033] The high pressure compressor 12 here comprises five axial compression stages.

[0034] The combustion chamber 13 is supplied with compressed air via the high-pressure compressor 12, and with fuel via several injectors. The air / fuel mixture is burned under the action of several ignition devices. The exhaust gases from the combustion chamber 13 are expanded in the expansion turbine 14 and then in the power turbine 5.

[0035] The expansion turbine 14 here comprises two axial expansion stages.

[0036] The power turbine 5 here comprises four axial expansion stages. The power turbine power 5 is driven in rotation by the exhaust gases leaving the expansion turbine 14, the exhaust gases then being evacuated via a nozzle 20.

[0037] The embodiment illustrated in [Fig.l] is in no way limiting. The compressors 6, 12 and the turbines 5, 14 could, for example, comprise a different number of stages. Generally speaking, a compressor may comprise one or more axial and / or centrifugal compression stages. A turbine may comprise one or more axial and / or centripetal expansion stages.

[0038] As illustrated in [Fig.l], the unducted fan 8 is rotatable about the axis X. The unducted fan 8 comprises an annular row of variable-pitch blades 21, each blade 21 being pitched about an axis of rotation Y1 which is sen possibly perpendicular to the X axis. The unducted fan 8 comprises a system 22 for adjusting the pitch of the blades 21, this adjustment system 22 being able to be common to all the blades 21 or specific to each of the blades 21.

[0039] According to an exemplary embodiment, the adjustment system 22 comprises an actuator common to all the blades 21 and a mechanism specific to each of the blades 21, this mechanism making it possible to transform the movement initiated by the actuator into a rotational movement of the corresponding blade 21.

[0040] The unducted fan 8 is driven in rotation by the power turbine 5 via a speed reducer 23. The speed reducer 23 makes it possible to reduce the rotation speed of the unducted fan 8 relative to that of the power turbine 5, while increasing its torque.

[0041] More precisely, the compressor shaft 11 is rotationally connected to an input element 24 of the speed reducer 23 and the unducted fan 8 is rotationally connected to an output element 25 of the speed reducer 23.

[0042] Advantageously, the speed reducer 23 is a gear train reducer, and preferably an epicyclic train reducer. An epicyclic train reducer has the advantage of having a high reduction ratio while being compact.

[0043] An epicyclic gear reducer comprises at least one reduction stage comprising a sun (or planetary), a crown, satellites and a planet carrier. An epicyclic gear reducer can be configured in different ways.

[0044] According to a first configuration, the solar is the input element 24 of the reducer 23, the crown is the output element 25 of the reducer 23, and the planet carrier is fixed or immobile. In other words, the solar is linked in rotation with the compressor shaft 11, and the crown is linked in rotation with the unducted fan 8.

[0045] According to a second configuration, the solar is the input element 24 of the reducer 23, the crown is fixed or immobile, and the planet carrier is the output element 25 of the reducer 23. In other words, the solar is linked in rotation with the compressor shaft 11, and the planet carrier is linked in rotation with the unducted fan 8.

[0046] The two configurations explained above are in no way limiting, other configurations are obviously conceivable depending in particular on the desired reduction ratio.

[0047] Similarly, the gear train reducer 23 may comprise one or more reduction stages.

[0048] The unducted blower 8 internally defines an enclosure 26 in which the gear train reducer 23 is housed and lubricated here.

[0049] When the turbomachine 1 is in “propulsor” mode, the unducted fan 8 generates an air flow F which flows from upstream to downstream around the outer fairings of the streamlined body of the turbomachine 1, so as to generate the majority of the thrust. which will propel or move aircraft 2 forward. Turbomachine 1 can also operate in “reverser” mode, so as to brake aircraft 2 when it lands.

[0050] By convention in the present application, the terms “upstream” and “downstream” are defined relative to the direction of circulation of the air flow F, when the turbomachine 1 is in “propulsor” mode.

[0051] As illustrated in [Fig.l], the unducted rectifier 9 is fixed in rotation about the axis X and is configured to straighten at least a portion of the air flow F generated by the unducted fan 8. The rectifier 9 is arranged here directly downstream of the unducted fan 8. The rectifier 9 comprises an annular row of guide vanes 27 (or stator vanes or OGV vanes for “Outlet Guide Vane”), the guide vanes 27 being arranged regularly around the nacelle 28.

[0052] The guide vanes 27 are variable-pitch, each guide vane 27 being pitched around an axis of rotation Y2 which is substantially perpendicular to the axis X.

[0053] The rectifier 9 comprises a system 29 for adjusting the timing of the guide vanes 27, this adjustment system 29 being able to be common to all the guide vanes 27 or specific to each of the guide vanes 27. The adjustment system(s) 29 are located in an interior compartment 30 of the nacelle 28.

[0054] According to an exemplary embodiment, the adjustment system 29 comprises an actuator common to all the guide vanes 27 and a mechanism specific to each of the guide vanes 27, this mechanism making it possible to transform the movement initiated by the actuator into a rotational movement of the corresponding guide vane 27.

[0055] As illustrated in [Fig.l], the ducted fan 10 is placed in the air inlet 4 and is surrounded by a nacelle 28. The ducted fan 10 is commonly called a “Mid-Fan”.

[0056] The ducted fan 10 is rotatable about the axis X. The ducted fan 10 comprises a disk 31 carrying an annular row of blades 32 with fixed pitch. The blades 32 can be attached to the disk 31 or be in one piece with the disk 31 to form a single-piece bladed disk.

[0057] The ducted fan 10 is driven in rotation by the power turbine 5 via the compressor shaft 11. More precisely, the disc 31 comprises a flange 33 which is secured to the compressor shaft 11.

[0058] The air flow generated by the ducted fan 10 is divided, by a separation nozzle 34 of a fixed structure 35 of the turbomachine 1, into a primary air flow fl which enters a primary vein 36 intended to supply the gas generator 3, and into a secondary air flow f2 which flows around the low-pressure compressor 6 and the gas generator 3 in a secondary vein 37. The secondary air flow f2 contributes in a minor way to the thrust provided by the turbomachine 1.

[0059] In the remainder of the description, we will focus more particularly on the compressor shaft 11 hereinafter referred to as “shaft” 11.

[0060] In the same way as the turbomachine 1, the compressor shaft 11 is defined along the longitudinal axis X.

[0061] The shaft 11 is a single piece and annular (or of revolution) around the longitudinal axis X. The shaft 11 comprises a body 38 extending longitudinally and a collar 39 (or a collar) extending substantially radially with reference to the axis X. The collar 39 has an external end 40 which carries a flange 41 and an internal end 42 which is connected to the body 38. The flange 41 is secured to the ducted fan 10 and to the rotor 7 of the low-pressure compressor 6.

[0062] According to the invention, the body 38 of the shaft 11 is divided into an upstream portion 44 and a downstream portion 45 longitudinally spaced apart from each other. The inner end 42 of the collar 39 is connected to the upstream and downstream portions 44, 45 of the body 38 via a fork 46 (or a fork). The fork 46 comprises an upstream arm 47 which connects the inner end 42 of the collar 39 and a downstream end 48 of the upstream portion 44 of the body 38, and a downstream arm 49 which connects the inner end 42 of the collar 39 and an upstream end 50 of the downstream portion 45 of the body 38, so that the upstream and downstream arms 47, 49 internally form a recess 51 open on the side of the axis X.

[0063] The incorporation of a fork to connect the collar to the body not only makes it possible to meet the requirements of the specifications in terms of stiffness (radial stiffness and rotational stiffness) but also to limit the impact in terms of mass.

[0064] Advantageously, the thickness E1 of the upstream arm 47 is greater than the thickness E2 of the downstream arm 49. Indeed, with regard to the stiffness of the shaft, engine manufacturers have highlighted that the contribution of the upstream arm 47 is greater than that of the downstream arm 49.

[0065] Advantageously, the thickness E1 of the upstream arm 47 varies in an increasing manner from the downstream end 48 of the upstream portion 44 of the body 38 to the internal end 42 of the collar 39. Such a dimensioning is favorable to increasing the stiffness of the shaft.

[0066] The flange 41 carried by the collar 39 can be located axially upstream of the fork 46 so that the collar is, from downstream to upstream, inclined radially opposite the axis X.

[0067] The collar 39 can extend in the extension of the downstream arm 49.

[0068] The downstream arm 49 can flare from downstream to upstream from the upstream end 50 of the downstream portion 45 of the body 38 to the internal end 42 of the collar 39.

[0069] The collar 39 can flare from downstream to upstream from its internal end 42 to its external end 40.

[0070] The upstream arm 47 can flare from upstream to downstream from the downstream end 48 of the upstream portion 44 of the body 38 to the internal end 42 of the collar 39.

[0071] Advantageously, as illustrated in [Fig.4], the internal and external faces 52, 53 of the upstream arm 47 form between them an acute angle A, the acute angle A being defined in a half-section whose section plane is longitudinal and passes through the axis X, the acute angle A preferably being between 5° and 15°. Such a dimensioning is favorable to increasing the stiffness of the shaft.

[0072] Advantageously, the internal face 52 of the upstream arm 47 and the internal face 54 of the downstream arm 49 are connected by a fillet 55, the fillet 55 preferably having a radius R of between 10 mm and 30 mm. Such a dimensioning is favorable to increasing the stiffness of the shaft and allows the application of paint.

[0073] Advantageously, the maximum radial dimension D of the recess 51 is greater than the respective maximum radial dimensions D1, D2 of the upstream and downstream portions 44, 45. Such dimensioning makes it possible to optimize the stiffness / mass ratio of the shaft.

[0074] The dimensions D1 and D2 may be representative of the order of magnitude of radii associated with internal bearing radii provided to cooperate with internal bearing rings supporting the shaft 11 in rotation relative to its environment in the turbomachine.

[0075] As illustrated in Figures 1 and 2, the flange 33 of the ducted fan 10, the flange 41 of the shaft 11 and the flange 19 of the drum 17 are secured to each other via an annular row of bolts 56 around the axis X.

[0076] Each bolt 56 comprises a screw 57 and a nut 65, the shank of the screw 57 passing simultaneously through a through hole 58 formed in the flange 41 of the shaft 11, a through hole 59 formed in the flange 19 of the drum 17 and a through hole 60 formed in the flange 33 of the ducted fan 10.

[0077] The flange 19 of the drum 17 is arranged axially between the flange 33 of the ducted fan 10 and the flange 41 of the shaft 11.

[0078] The flange 19 of the drum 17 comprises an external rim 61 which projects from an upstream face of the flange 19, this external rim 61 makes it easier to position the flange 33 of the ducted fan 10. In addition, the flange 19 of the drum 17 comprises an internal rim 62 which projects from a downstream face of the flange 19, this internal rim 62 makes it easier to position the flange 41 of the shaft.

[0079] The three bolted flanges 19, 33, 41 are located upstream of the fork 46 of the shaft 11.

[0080] As illustrated in the figures, the collar 39 flares from downstream to upstream from its internal end 42 to its external end 40. The collar 39 extends in the extension of the downstream arm 49.

[0081] As illustrated in Figures 2 and 4, the upstream and downstream arms 47, 49 of the fork 46 are asymmetrical with respect to a median transverse plane of the fork 46. The upstream and downstream arms 47, 49 form between them an internal angle which is substantially equal to 90°, this internal angle being defined in a half-section whose section plane is longitudinal and passes through the X axis. The thickness E1 of the upstream arm 47 is greater than the thickness E2 of the downstream arm 49. The upstream arm 47 here has a thickness E1 at its base of 14.5 mm and the downstream arm 49 has a constant thickness E2 of 12 mm.

[0082] More precisely, as illustrated in [Fig.4], the upstream arm 47 widens from upstream to downstream from the downstream end 48 of the upstream portion 44 of the body 38 to the internal end 42 of the collar 39. The thickness E1 of the upstream arm 47 varies in an increasing manner from the downstream end 48 of the upstream portion 44 of the body 38 to the internal end 42 of the collar 39.The internal and external faces 52, 53 of the upstream arm 47 form between them an acute angle A, the acute angle A being defined in a half-section whose cutting plane is longitudinal and passes through the axis X. The acute angle A is here approximately 10°.

[0083] As illustrated in [Fig.4], the downstream arm 49 flares from downstream to upstream from the upstream end 50 of the downstream portion 45 of the body 38 to the internal end 42 of the collar 39. The thickness E2 of the downstream arm 49 is constant from the upstream end 50 of the downstream portion 45 of the body 38 to the internal end 42 of the collar 39.

[0084] As illustrated in [Fig.4], the internal face 52 of the upstream arm 47 and the internal face 54 of the downstream arm 49 are connected by a fillet 55. The fillet 55 here has a radius R of 20 mm.

[0085] The fillet 55 is defined by a center C which is marked in [Fig.4] by a cross. The radial dimension Dr between the center C and the internal point P of the downstream end 48 of the upstream portion 44 (or of the upstream end 50 of the downstream portion 45) is 14 mm.

[0086] The upstream and downstream portions 44, 45 of the shaft 11 may each comprise one or more bearing surfaces on which rolling bearings are attached for guiding the shaft 11.

[0087] The upstream end 63 of the upstream portion 44 and the downstream end 64 of the downstream portion 45 may each comprise connecting means (such as grooves) intended to cooperate with complementary connecting means.

[0088] As illustrated in [Fig.l], the upstream end 63 of the upstream portion 44 is rotationally connected directly to an input element 24 of the speed reducer 23 and the downstream end 64 of the downstream portion 45 is rotationally connected directly to the turbine shaft 16.

[0089] The shaft 11 is for example manufactured by turning.

Claims

Claims

1. Compressor shaft (11) for a turbomachine (1) of an aircraft (2), the shaft (11) being in one piece and annular about a longitudinal axis (X), the shaft (11) comprising a body (38) extending longitudinally and a collar (39) extending substantially radially with reference to the axis (X), the collar (39) having an outer end (40) which carries a flange (41) and an inner end (42) which is connected to the body (38), the flange (41) being intended to be secured to a ducted fan (10) and to a rotor (7) of a low-pressure compressor (6);characterized in that the body (38) is divided into an upstream portion (44) and a downstream portion (45) longitudinally spaced from each other, the inner end (42) of the collar (39) being connected to the upstream and downstream portions (44, 45) of the body (38) via a fork (46), the fork (46) comprising an upstream arm (47) connecting the inner end (42) of the collar (39) and a downstream end (48) of the upstream portion (44) of the body (38), and a downstream arm (49) connecting the inner end (42) of the collar (39) and an upstream end (50) of the downstream portion (45) of the body (38), so that the upstream and downstream arms (47, 49) internally form an open recess (51).;

2. Shaft (11) according to claim 1, characterized in that the thickness (El) of the upstream arm (47) is greater than the thickness (E2) of the downstream arm (49).

3. Shaft (11) according to one of the preceding claims, characterized in that the thickness (El) of the upstream arm (47) varies increasingly from the downstream end (48) of the upstream portion (44) of the body (38) to the internal end (42) of the collar (39).

4. Shaft (11) according to one of the preceding claims, characterized in that the flange (41) is located axially upstream of the fork (46).

5. Shaft (11) according to one of the preceding claims, characterized in that the collar (39) extends in the extension of the downstream arm (49).

6. Shaft (11) according to one of the preceding claims, characterized in that the downstream arm (49) flares from downstream to upstream from the upstream end (50) of the downstream portion (45) of the body (38) to the internal end (42) of the collar (39).

7. Shaft (11) according to one of the preceding claims, characterized in that the collar (39) flares from downstream to upstream from its internal end (42) to its external end (40).

8. Shaft (11) according to one of the preceding claims, characterized in that the upstream arm (47) flares from upstream to downstream from the downstream end (48) of the upstream portion (44) of the body (38) to the internal end (42) of the collar (39).

9. Shaft (11) according to one of the preceding claims, characterized in that the internal and external faces (52, 53) of the upstream arm (47) form between them an acute angle (A), the acute angle (A) being defined in a half-section whose cutting plane is longitudinal and passes through the axis (X), the acute angle (A) preferably being between 5° and 15°.

10. Shaft (11) according to one of the preceding claims, characterized in that the internal face (52) of the upstream arm (47) and the internal face (54) of the downstream arm (49) are connected by a fillet (55), the fillet (55) preferably having a radius (R) of between 10 mm and 30 mm.

11. Turbomachine (1) of aircraft (2) comprising: - a gas generator (3) which is supplied by an air inlet (4); - a power turbine (5) which is independent of the gas generator (3); - a low pressure compressor (6) comprising a rotor (7) which is driven in rotation by the power turbine (5); - an unducted fan (8) which is mobile in rotation and which is driven in rotation by the power turbine (5); - an unducted rectifier (9) which is fixed in rotation; - a ducted fan (10) which is placed in the air inlet (4), the ducted fan (10) being mobile in rotation and driven in rotation by the power turbine (5); the ducted fan (10) and the rotor (7) of the low pressure compressor (6) being jointly driven in rotation by the power turbine (5) via a compressor shaft (11) according to one of the preceding claims.

12. Turbomachine (1) according to the preceding claim, characterized in that the ducted fan (10) comprises a flange (33), the rotor (7) of the low pressure compressor (6) comprising a drum (17) which comprises a flange (19), the flange (33) of the ducted fan (10), the flange (41) of the compressor shaft (11) and the flange (19) of the drum (17) being secured to each other via an annular row of bolts (56).

13. Turbomachine (1) according to one of claims 11 or 12, characterized in that the unducted fan (8) is driven in rotation by the power turbine (5) via a speed reducer (23).

14. Turbomachine (1) according to the preceding claim, characterized in that the upstream end (63) of the upstream portion (44) of the compressor shaft (11) is linked in rotation with an input element (24) of the speed reducer (23), the unducted fan (8) being linked in rotation with an output element (25) of the speed reducer (23).

15. Turbomachine (1) according to one of claims 11 to 14, characterized in that the unducted fan (8) comprises an annular row of variable-pitch blades (21) and the unducted rectifier (9) comprises an annular row of variable-pitch guide vanes (27).

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