VARIABLE PITCH ROTOR BLADE FOR AN AIRCRAFT TURBOMACHINE

Abstract

Variable-pitch rotor blade (30) for an aircraft turbomachine, comprising: - a blade (32) comprising a lower surface (32a) and an upper surface (32b), as well as a leading edge (32c) and a trailing edge (32d), the trailing edge (32d) of the blade (32) comprising serrations (35) formed by alternating teeth (35a) and hollows (35b), - a platform (32) connected to one end of the blade (32) and defining a blade setting axis (A), the blade (32) comprising: - a first body (36) made of metallic or composite material defining the leading edge (32a) of the blade (32), and - a second body (38) made of elastically deformable material defining at least a portion of the trailing edge (32d) of the blade (32) and comprising at least a portion of the serrations (35), the second body (38) being fixed to the first body (36). Figure for abstract: Figure 4

Description

Title of the invention: VARIABLE-PITCH ROTOR BLADE FOR AN AIRCRAFT TURBOMACHINE Technical field of the invention

[0001] The present invention relates to a variable-pitch rotor blade for an aircraft turbomachine. Technical approval plan

[0002] The state of the art includes in particular document FR-A1-3 073 017.

[0003] An aircraft turbomachine conventionally comprises a gas generator which drives at least one propeller. The gas generator comprises at least one compressor, a combustion chamber and at least one turbine. The rotor or one of the rotors of the gas generator is connected to the rotor of the propeller for its rotational drive.

[0004] A propeller can be shrouded. This is the case for a fan in a turbomachine of the turbojet or turbofan type, for example.

[0005] A propeller can be unducted. This is the case for a turboprop, for example.

[0006] A propeller comprises a hub and an annular row of blades which are mounted all around the hub. The blades can be fixed and therefore have a fixed angular position around their axes of elongation.

[0007] In the context of the present invention, the blades are on the contrary variable pitch, that is to say they are capable of being moved in rotation around axes called pitch axes, which generally extend along the axes of elongation of the blades. The pitch axes may be radial axes relative to the axis of rotation of the propeller.

[0008] A variable-pitch rotor blade conventionally comprises a blade having a lower surface and an upper surface, as well as a leading edge and a trailing edge, and a platform connected to one end of the blade and defining the pitch axis of the blade. The platform is generally mounted in an orifice in the hub and centered and guided in rotation in this orifice around the pitch axis.

[0009] It is known to produce such blades from metallic, ceramic or composite material. A well-known composite material for a variable-pitch rotor blade comprises a body based on woven carbon fibers which is embedded in a polymer matrix based on epoxy, for example. The leading edge of the blade can be reinforced by a bonded metal shield.

[0010] The evolution of the performance of turbomachines tends towards the increase of their dilution ratio, which is mainly achieved by the increase of the diameter of the propellers and therefore of the length and mass of their blades.

[0011] In addition, a so-called slow and high bypass ratio propeller comprises a reduced number of blades whose chord is increased to improve the propulsive efficiency of the turbomachine.

[0012] In the case of a shrouded propeller, the nacelle surrounding the propeller includes an internal acoustic treatment which makes it possible to reduce noise emissions outside the turbomachine.

[0013] In the case of an unducted propeller, other solutions must be found for reducing propulsive noise. This is particularly the case for the turbomachine illustrated in [Fig.l]. This turbomachine 10 comprises a propeller 12 upstream, which comprises variable-pitch rotor blades 14, and a rectifier 16 downstream, which comprises stator blades 18 also with variable pitch.

[0014] To remedy the problem of noise emission, a noise reduction technology already known on fans and inspired in particular by the wings of nocturnal birds of prey consists of arranging serrations 20 on the trailing edges of the rotor blades 14 or on the leading edges of the stator blades 18 (figures 2 and 3).

[0015] Serrations 20 of a leading or trailing edge are formed by alternating teeth 20a and hollows 20b along this edge. The serrations can cause variations in the chord of the blade as a function of the radial height, with variable thicknesses and a very thin trailing or leading edge.

[0016] The teeth 20a are defined so as to reduce noise in the average emission spectrum without unduly worsening other frequencies at other engine speeds.

[0017] The angular setting of the blades implies variable acoustics of the blades depending on the engine speed and the orientation of the blades.

[0018] It has been found that, in most engine speeds, the serrations make it possible to reduce the noise emitted. However, a significant increase in the noise emitted has also been observed when the blades are set in reverse or thrust reversal mode. In the case of a rotor blade, the serrations of the trailing edge are oriented upstream in reverse mode, which greatly disrupts the aerodynamic flow. The serrations are then counterproductive.

[0019] The thrust reversal phase is a phase which, on the contrary, should be as quiet as possible because it generally takes place in a nearby urban environment.

[0020] Another disadvantage of the prior art is related to the fact that the serrations cannot be manufactured with the same material as the woven or ceramic blades because the serrations are too thin, and they would be too fragile and in particular brittle.

[0021] For metal blades, the problem comes from the risk of tearing of the serrations as well as the complexity of producing these serrations which leads to significant rejects due to geometric defects.

[0022] The present invention provides a solution to at least some of the problems of the prior art, which is simple, effective and economical. Summary of the invention

[0023] The invention relates to a variable-pitch rotor blade for an aircraft turbomachine, this blade comprising:

[0024] - a blade comprising a lower surface and an upper surface, as well as a leading edge and a trailing edge, the trailing edge of the blade having serrations formed by alternating teeth and hollows along this trailing edge,

[0025] - a platform connected to one end of the blade and defining a setting axis of dawn,

[0026] characterized in that the blade comprises:

[0027] - a first body made of metallic or composite material defining the leading edge of the blade, and

[0028] - a second body made of elastically deformable material defining at least one part of the trailing edge of the blade and comprising at least part of the serrations, the second body being fixed to the first body.

[0029] The invention thus proposes to produce the rotor blade blade from two distinct materials. The first body of the blade is made of metallic or composite material and comprises the leading edge of the blade. The second body of the blade is made of elastically deformable material such as elastomer. This second body defines at least a portion of the trailing edge and comprises all or part of the serrations. It is therefore understood that these serrations are made of elastic material and are capable of deforming elastically during operation. The deformations of the serrations depend on the engine speed. The serrations are therefore likely to adopt different positions and / or shapes depending on the engine speed.

[0030] The invention makes it possible, for example, to integrate variability in the geometry and radial position of the teeth as a function of the engine speed as well as the aerodynamic pressure forces exerted by the air flow in operation. Since a rotor blade tends to untwist in a centrifuge, it is also more advantageous to have a deformable material so as not to interfere with the internal forces in the blade and its own operation.

[0031] The second body is fixed to the first body, for example by gluing, as is the case with a protective shield of the prior art.

[0032] The blade 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 second body defines the entire trailing edge of the blade and includes all the serrations; - the second body extends over the entire longitudinal extent of the blade along the pitch axis; - at least some of the teeth include internal cavities; the cavities allow the dynamic behavior of the teeth to be modified in operation; - at least some of the internal cavities are empty; - at least some of the internal cavities contain weights; - teeth located on the platform side include cavities with weights, and teeth located on the side opposite the platform comprise empty cavities, the teeth comprising cavities with weights being able to be separated from the teeth comprising empty cavities by teeth without internal cavities, i.e. solid teeth. - the trailing edge of the blade is a double trailing edge which comprises two separate trailing edge walls located next to each other, each of these trailing edge walls comprising serrations formed by alternating teeth and hollows along this trailing edge; the double trailing edge makes it possible to reduce the noise emitted in an optimal manner, whatever the engine speed; - at least some of the teeth of one of the trailing edge walls are in contact with at least some of the teeth of the other of the trailing edge walls; - at least some of the teeth of one of the trailing edge walls are spaced from at least some of the teeth of the other of the trailing edge walls; - at least some of the teeth of one of the trailing edge walls are elastically deformable independently of the teeth of the other of the trailing edge walls; - the second body defines a downstream part of the intrados and the extrados of the blade; - the second body has a general U or V shape in cross section; - the second body is glued to the first body; - the second body is made of elastomer.

[0033] The invention further relates to a turbomachine for an aircraft, comprising a rotor equipped with blades such as described above. Brief description of the figures

[0034] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

[0035] [Fig-1] [Fig.l] is a schematic perspective view of a turbomachine with unducted propeller and an unducted stator, the propeller and stator having variable pitch blades;

[0036] [Fig.2] [Fig.2] is a schematic view of a rotor or propeller blade with pitch variable;

[0037] [Fig.3] [Fig.3] is a schematic view of a stator or rectifier blade with variable timing;

[0038] [Fig.4] [Fig.4] is a schematic view of a variable pitch rotor blade, according to one embodiment of the invention;

[0039] [Fig.5] [Fig.5] is a sectional view along line VV of [Fig.4];

[0040] [Fig.6] [Fig.6] is a sectional view along line VI-VI of [Fig.4];

[0041] [Fig.7] [Fig.7] is a schematic view of the second body of a stator blade with variable timing, according to an alternative embodiment of the invention;

[0042] [Fig.8] [Fig.8] is a sectional view along line VIII-VIII of [Fig.4];

[0043] [Fig.9] [Fig.9] is a sectional view along line IX-IX of [Fig.4];

[0044] [Fig. 10] [Fig. 10] is a sectional view similar to those of Figures 5-6 and 8-9, and which shows another alternative embodiment of the invention;

[0045] [Fig. 11] [Fig. 10] is a sectional view similar to those of Figures 5-6 and 8-9, and which shows the alternative embodiment of [Fig. 10];

[0046] [Fig.l2a-12b] Figures 12a and 12b are schematic perspective views of the stator blade of figures 10 and 11 and show a position of the serrations of this blade, by default or at rest;

[0047] [Fig.l3a-13b] Figures 13a and 13b are schematic perspective views of the stator blade of figures 10 and 11 and show a position of the serrations of this blade, at take-off;

[0048] [Fig.l4a-14b] Figures 14a and 14b are schematic perspective views of the stator blade of figures 10 and 11 and show a position of the serrations of this blade, in cruise;

[0049] [Fig.l5a-15b] Figures 15a and 15b are schematic perspective views of the stator blade of figures 10 and 11 and show a position of the serrations of this blade, in thrust reversal mode. Detailed description of the invention

[0050] Figures 1 to 3 have been described in the above.

[0051] The invention relates to a variable-pitch rotor blade for an aircraft turbomachine, which may be the turbomachine of [Fig.l] or another turbomachine.

[0052] [Fig.4] illustrates a first embodiment of a rotor blade 30 according to the invention. This is a variable-pitch rotor blade 30 for an aircraft turbomachine, which comprises:

[0053] - a blade 32 comprising a lower surface 32a and an upper surface 32b, as well as an edge 32c leading edge and a 32d trailing edge, and

[0054] - a platform 34 connected to one end of the blade 32 and defining an axis A of dawn setting 30.

[0055] The trailing edge 32d of the blade 32 comprises serrations 35 formed by an alternation of teeth 35a and hollows 35b along this trailing edge.

[0056] The particularity of the dawn 30 is that its blade 32 comprises:

[0057] - a first body 36 made of metallic or composite material defining the edge attack 32c of blade 32, and

[0058] - a second body 38 made of elastically deformable material defining at least a portion of the trailing edge 32d of the blade 32 and comprising at least a portion of the serrations 35, the second body 38 being fixed to the first body 36.

[0059] As seen in the drawing, the platform 34 may be made of the first material. The first body 36 and the platform 34 may be made monolithically.

[0060] In the example shown, the second body 38 defines the entire trailing edge 32d of the blade 32 and comprises all of the serrations 35.

[0061] The second body 38 can extend over the entire longitudinal extent of the blade 32 along the pitch axis A.

[0062] In the embodiment shown in Figures 4 to 6, the teeth 35a are solid. It can be seen that these teeth 35a can have different shapes and / or dimensions, all the teeth 35a being able to be different.

[0063] The sections of Figures 5 and 6 show that the second body 38 may have a general U or V shape in cross section. The second body 38 may thus comprise two longitudinal wings 38a, 38b connected together by a middle part 38c. The middle part 38c is the part which comprises the teeth 35a and the hollows 35b. The wings 38a, 38b are respectively applied on each side of the blade 32 to define at least a part of the intrados 32a and the extrados 32b, or to extend in the extension thereof.

[0064] The second body 38 can thus define a downstream part of the intrados 32a and the extrados 32b of the blade 32.

[0065] The fixing of the second body 38 on the first body 36 can be carried out by gluing the wings 38a, 38b and the middle part 38c on the body 36. Ideally, the first body 36 has a shape complementary to that of the second body 38 and matches the internal shape of this second body 38. The glue can form a thin film between the first and second bodies 36, 38.

[0066] The second body 38 is preferably made of elastomer.

[0067] Figures 7 to 9 illustrate an alternative embodiment of the invention which differs from the previous embodiment in that at least some of the teeth 35a comprise internal cavities 40.

[0068] At least some of the internal cavities 40 are empty, as illustrated in [Fig.8].

[0069] At least some of the internal cavities 40 contain weights 42, i.e. say elements which have a predetermined mass ([Fig.9]).

[0070] The weights make it possible to improve the behavior and in particular the deformation capacity of the teeth 35a when they are subjected to a centrifugal force.

[0071] In the example shown, teeth 35a located on the side of the platform 32 comprise cavities 40 with weights 42, and teeth 35a located on the side opposite the platform 32 comprise empty cavities 40.

[0072] The teeth 35a comprising cavities 40 with weights 42 can be separated from the teeth 35a comprising empty cavities 40 by teeth 35a devoid of internal cavities 40, i.e. solid teeth 35a ([Fig.7]).

[0073] Alternatively, the reverse would be possible, the teeth 35a with weights 42 would be located opposite the platform 32, and the hollow teeth 35a would be located on the side of the platform 32.

[0074] Figures 10 and following illustrate another variant embodiment of the invention which differs from the first embodiment in that the trailing edge 32d of the blade 32 is a “double” trailing edge which comprises two separate trailing edge walls 44a, 44b located next to each other.

[0075] Each of these trailing edge walls 44a, 44b comprises serrations 35 formed by an alternation of teeth 35a and hollows 35b along this trailing edge.

[0076] At least some of the teeth 35a of one of the trailing edge walls 44a may be in contact with at least some of the teeth 35a of the other of the trailing edge walls 44b, as illustrated in [Fig. 10]. This position may be adopted at rest or by default for some or all of the teeth 35a.

[0077] At least some of the teeth 35a of one of the trailing edge walls 44a may be spaced apart from at least some of the teeth 35a of the other of the trailing edge walls 44b, as illustrated in [Fig.l 1]. This position may be adopted at rest or by default for some or all of the teeth 35a. It may further be adopted during operation of the turbomachine, for an engine speed for several engine speeds. In particular, the spacing between the walls 44a, 44b may vary as a function of the engine speed to optimize the reduction of the noise emitted.

[0078] Preferably, at least 70% or even at least 80% of the teeth 35a are contiguous in the rest position as in [Fig. 10].

[0079] At least some of the teeth 35a of one of the trailing edge walls 44a are elastically deformable independently of the teeth 35a of the other of the trailing edge walls 44b.

[0080] Figures 12a and following show the behavior of the serrations 35 as a function of the speed of the turbomachine equipped with rotor blades according to Figures 10 and 11, that is to say with two trailing edge walls 44a, 44b with serrations 35.

[0081] In figures 12a and 12b, the turbomachine is at rest or almost (for example the aircraft equipped with this turbomachine can be rolling or taxiing), and we see that the teeth 35a of the trailing edge walls 44a, 44b are for the most part touching.

[0082] In Figures 13a and 13b, the turbomachine takes off. It can be seen that teeth 35a of the trailing edge walls 44a, 44b move away from each other. The centrifugal forces are very high and the teeth also tend to lengthen and extend radially outwards relative to the axis of rotation of the propeller.

[0083] In Figures 14a and 14b, the turbomachine is in cruising mode. It can be seen that some of the teeth 35a are touching and others are spaced apart. The teeth 35a are less subject to centrifugal forces but the atmospheric pressure applied to the blades is greater. Thermal pressure could also have an impact on the deformation of the teeth.

[0084] Finally, in figures 15a and 15b, the turbomachine is in thrust reversal mode, and it can be seen that the teeth 35a of the trailing edge walls 44a, 44b are very far apart from each other.

[0085] It can thus be seen that the teeth 35a of the serrations 35a adopt different positions depending on the engine speed. These positions are advantageously designed to attenuate noise. It is therefore understood that, whatever the engine speed, the serrations 35 can attenuate the noise generated during operation, including in thrust reversal mode.

Claims

Claims

1. Variable-pitch rotor blade (30) for an aircraft turbomachine, this blade (30) comprising: - a blade (32) comprising a lower surface (32a) and an upper surface (32b), as well as a leading edge (32c) and a trailing edge (32d), the trailing edge (32d) of the blade (32) comprising serrations (35) formed by an alternation of teeth (35a) and hollows (35b) along this trailing edge, - a platform (32) connected to one end of the blade (32) and defining a blade setting axis (A), characterized in that the blade (32) comprises: - a first body (36) made of metallic or composite material defining the leading edge (32a) of the blade (32), and - a second body (38) made of elastically deformable material defining at least a portion of the trailing edge (32d) of the blade (32) and comprising at least part of the serrations (35), the second body (38) being fixed to the first body (36).

2. A blade (30) according to claim 1, wherein the second body (38) defines the entire trailing edge (32d) of the blade (32) and includes all of the serrations (35).

3. A blade (30) according to claim 1 or 2, wherein the second body (38) extends over the entire longitudinal extent of the blade (32) along the pitch axis (A).

4. A blade (30) according to one of claims 1 to 3, wherein at least some of the teeth (35a) comprise internal cavities (40).

5. A blade (30) according to claim 4, wherein at least some of the internal cavities (40) are empty.

6. A blade (30) according to claim 4 or 5, wherein at least some of the internal cavities (40) contain weights (42).

7. A blade (30) according to any one of claims 5 and 6, wherein teeth (35a) located on the side of the platform (34) comprise cavities (40) with weights (42), and teeth (35a) located on the side opposite the platform (34) comprise empty cavities (40), the teeth (35a) comprising cavities (40) with weights (42) being separable from the teeth (35a) comprising cavities (40) empty by teeth (35a) devoid of internal cavities, i.e. full teeth.

8. Blade (30) according to one of claims 1 to 7, in which the trailing edge (32d) of the blade (32) is a double trailing edge which comprises two distinct trailing edge walls (44a, 44b) located next to each other, each of these trailing edge walls (44a, 44b) comprising serrations (35) formed by an alternation of teeth (35a) and hollows (35b).

9. A blade (30) according to claim 8, wherein at least some of the teeth (35) of one of the trailing edge walls (44a, 44b) are in contact with at least some of the teeth (35a) of the other of the trailing edge walls (44a, 44b).

10. A blade (30) according to claim 8, wherein at least some of the teeth (35a) of one of the trailing edge walls (44a, 44b) are spaced from at least some of the teeth (35a) of the other of the trailing edge walls (44a, 44b).

11. A blade (30) according to one of claims 8 to 10, wherein at least some of the teeth (35a) of one of the trailing edge walls (44a, 44b) are elastically deformable independently of the teeth (35a) of the other of the trailing edge walls (44a, 44b).

12. Blade (30) according to one of claims 1 to 11, in which the second body (38) defines a downstream part of the intrados (32a) and the extrados (32b) of the blade (32).

13. Blade (30) according to one of claims 1 to 12, in which the second body (38) has a general U or V shape in cross section.

14. A blade (30) according to one of claims 1 to 13, wherein the second body (38) is bonded to the first body (36).

15. Blade (30) according to one of claims 1 to 14, in which the second body (38) is made of elastomer.

16. Turbomachine for an aircraft, comprising a rotor equipped with blades (30) according to one of claims 1 to 15.

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