Aramid fiber fabric to protect a shovel against impacts

Description

FIELD OF THE INVENTION

[0001] The invention relates generally to the field of turbomachines, and more particularly to that of the fan blades of these turbomachines and their manufacturing method.

[0002] The invention applies more particularly to fan blades made of composite or metallic material, and whose leading edge comprises a metallic structural shield. TECHNOLOGICAL BACKGROUND

[0003] A fan blade of a turbomachine has an aerodynamic surface, a leading edge, a trailing edge and intrados and extrados sidewalls which connect the leading edge to the trailing edge.

[0004] Turbomachine blades, and particularly fan blades, are subject to significant mechanical and thermal stresses and must meet strict weight and size requirements. It has therefore been proposed to use blades made from a composite material comprising a fiber reinforcement densified by a polymer matrix, which are lighter than metal blades with equivalent propulsive characteristics and which have satisfactory heat resistance.

[0005] During certification and engine life, fan blades are subject to bird ingestion. The mechanical behavior of fan blades is therefore optimized during the blade design phase to comply with certification rules.

[0006] It is known, as mentioned in documents US 2018 / 0010614 A1, US 2016 / 0201480 A1 and US 2016 / 0201607 A1, to produce a turbomachine fan blade made of composite material and whose leading edge is equipped with a metal structural shield. In US 2018 / 0010614 A1 a piece of fabric comprising aramid fibers is added and fixed to a wall of the blade so that the piece of fabric extends in the extension of the structural shield.

[0007] In US 2016 / 0201480 A1 a piece of fabric comprising aramid fibers is added and fixed to the intrados wall of the blade so that the piece of fabric is away from the extension of an intrados fin of the shield.

[0008] It is known to equip the fan blades of a turbomachine, made of composite materials, with a metal structural shield extending over the entire height of the blade and beyond its leading edge, as mentioned in documents EP 3045260 A1, US 2016 / 0201480 A1 and EP1908919, and comprising fins configured to bear against the lower and upper surfaces of the blade. Such a shield in fact makes it possible to protect the blade made of composite material during an impact of a foreign body on the fan, such as for example a bird, hail or stones. In particular, the metal shield protects the leading edge of the blade by avoiding risks of delamination, fiber breakage or damage by fiber / matrix decohesion.This shield also contributes to the rigidity of the blade, which is necessary in particular for frequency and deflection aspects on impact, as well as for the aerodynamics of the blade, by allowing a thinning of the leading edge.

[0009] The shield then follows the shape of the leading edge of the blade and extends towards the trailing edge so as to follow the profile of the lower and upper surfaces of the blade, between the root and the tip of the blade. As is known, the shield can be a metal part, particularly made of titanium, and is generally produced by milling, for example from a block of material.

[0010] Upon impact with a given object, particularly a bird, the object slides significantly on the intrados. Conventionally, the length of the shield fins, and in particular the intrados fin, is therefore adjusted so that said fins properly cover the part of the blade likely to be impacted by objects (taking into account the size, weight, etc. of the objects likely to impact a fan blade). However, on turbomachines whose fan has a reduced rotational speed and number of blades, the impact of the object takes place over a longer chord length than in the case of fans whose rotational speed and number of blades are high. In particular, the axial length of the fan blade to be protected from impacts increases when the rotational speed of the fan and the number of fan blades decrease.

[0011] In order to protect the composite material blade, it would therefore be necessary to significantly increase the axial length of the shield's intrados fin (up to half the blade chord). However, such an increase is not desirable or not feasible due to issues of mass, manufacturing complexity, etc. SUMMARY OF THE INVENTION

[0012] An objective of the invention is therefore to propose a solution making it possible to protect a blade for a rotating part, and more particularly for a fan, made from a composite material in the event of ingestion, without penalizing the mass of the rotating part or its aerodynamics.

[0013] For this, the invention proposes a blade of a rotating part of a turbomachine, in particular of a fan for a turbomachine, comprising: a leading edge and a lower surface wall, a structural shield, said shield being attached and fixed to the leading edge of the blade and comprising an upper surface fin fixed to the lower surface wall, a piece of fabric comprising aramid fibers, said piece of fabric being attached and fixed to the lower surface wall of the blade so that the piece of fabric extends in the extension of the lower surface fin of the shield without covering said lower surface fin, and an erosion protection film, said erosion protection film being attached and fixed to the lower surface wall of the blade so as to extend in the extension of the piece of fabric without covering said piece of fabric.

[0014] Some preferred but non-limiting features of the above-described blade are the following, taken individually or in combination: the piece of fabric comprises a two-dimensional fabric the piece of fabric is partially covered by the intrados fin of the shield the piece of fabric is in the field of the intrados fin of the shield, without covering by the shield an aerodynamic surface of the blade has a main direction of extension, defining a longitudinal axis of the blade which is substantially radial to an axis of revolution of the rotating part, and a height corresponding to a distance between a lower limit of the aerodynamic surface and a tip of the blade, the piece of fabric covering the aerodynamic surface over only part of said height the aerodynamic surface comprises a surface portion at the intrados wall which is devoid of a piece of fabric,said surface portion being adjacent to the lower limit of the aerodynamic surface the piece of fabric covers at most 70% of the height of the blade in the areas of the blade which comprise a piece of fabric, an axial length of the assembly formed by the shield and the piece of fabric is between 20% and 50% of an axial length of the blade, where the axial length of the assembly and the axial length of the blade correspond to a curvilinear length in a direction parallel to the axis of revolution of the rotating part the blade is made of a composite material comprising a fibrous reinforcement densified by a polymer matrix, the fibrous reinforcement can be formed from a fibrous preform obtained by three-dimensional weaving with evolving thickness.

[0015] According to a second aspect, the invention also provides a fan for a turbomachine comprising at least one blade as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other characteristics, aims and advantages of the present invention will appear more clearly on reading the detailed description which follows, and with regard to the appended drawings given as non-limiting examples and in which: There figure 1 is a side view of a blade having a structural shield in accordance with the prior art. The figure 2 is a side view of an example of a blade comprising a structural shield according to the invention, in the case where the piece of fabric and the intrados fin of the shield are in field. The figure 3 is a side view of an example of a blade comprising a structural shield according to the invention, in the case where the piece of fabric is partially covered by the intrados fin of the shield. DETAILED DESCRIPTION OF AN EMBODIMENT

[0017] In the following, the invention will be described more particularly in the case of a fan blade. It will be understood, however, that the invention applies mutatis mutandis to the blades of any rotating part of the turbomachine.

[0018] In a manner known per se, a fan blade 1 according to the invention comprises an aerodynamic surface 2 having a main direction extending along a longitudinal axis X between a blade root 1 and a blade tip 1. The blade 1 has a leading edge 4, a trailing edge 5, a pressure side wall 6 and an extrados wall 7. The leading edge 4 is configured to extend opposite the flow of gases entering the turbomachine. It corresponds to the front part of an aerodynamic profile which faces the air flow and which divides the air flow into an intrados flow and an extrados flow. The trailing edge 5 corresponds to the rear part of the aerodynamic profile, where the intrados and extrados flows meet.

[0019] Only the intrados wall 6 is shown on the figures 2 And 3 .

[0020] The aerodynamic surface 2 of the blade 1 has a main direction of extension, defining the longitudinal axis X of the blade 1 which is substantially radial to an axis of revolution Y of the fan. The aerodynamic surface 2 also has a height h corresponding to a distance between a lower limit 3 of the aerodynamic surface 2 and a head of the blade 1, at the intersection of the leading edge 4 and the lower limit 3.

[0021] The blade 1 can be made from a composite material comprising a fibrous reinforcement densified by a polymer matrix.

[0022] The fiber reinforcement can be formed from a fiber preform obtained by three-dimensional weaving with evolving thickness. It can notably include carbon, glass, aramid and / or ceramic fibers. The matrix is ​​typically a polymer matrix, for example epoxy, bismaleimide or polyimide.

[0023] Blade 1 is then formed by molding using a vacuum resin injection process of the RTM (Resin Transfer Molding) type, or VARRTM (Vacuum Resin Transfer Molding).

[0024] The blade 1 further comprises a structural shield 10 which is attached and fixed to its leading edge 4.

[0025] The shield 10 is a single-piece part comprising a substantially V-shaped section having a base configured to extend in the extension of the leading edge 4 of the blade 1, as well as a lower surface fin 11 and an upper surface fin configured to fit respectively the lower surface 6 and upper surface 7 walls of the blade 1. The fins may have a tapered or thinned profile in the direction of the trailing edge 5 of the blade 1.

[0026] The shield 10 extends over the entire height of the aerodynamic surface 2 of the blade 1. Conventionally, when the blade 1 is integrated into a fan, the radially internal portion of the flow vein is delimited by an inter-blade platform (represented by hatched lines on the figures 2 And 3 ). The aerodynamic surface 2 of the blade 1 then corresponds to the surface of the blade 1 extending between the head of the blade 1 and the inter-blade platforms placed on either side of its root. Furthermore, the lower limit 3 of the aerodynamic surface 2 of the blade 1 corresponds to the intersection between the blade 1 and the inter-blade platform.

[0027] As illustrated in the figure 2 , the shield 10 matches the shape of the leading edge 4 of the blade of the vane 1 which it extends to form a new leading edge 12, called leading edge 12 of the shield 10. The shield 10 therefore forms the aerodynamic profile of the vane 1 at the level of the leading edge 4.

[0028] The shield 10 of the blade 1 is generally metallic, for example titanium, in order to provide a high capacity for absorbing energy due to possible impacts.

[0029] The shield 10 and the blade 1 are produced separately. The shield 10 is then attached to the leading edge 4 of the blade 1 and fixed thereto by gluing, for example using a cyano-acrylic or epoxy adhesive. For this purpose, the shield 10 has an internal profile adapted to match the rounded shape of the leading edge 4 of the blade 1, with or without contact with said leading edge 4. If necessary, the intrados 6 and extrados 7 walls of the blade 1 may be grooved in order to facilitate the assembly of the shield 10.

[0030] In order to protect the fan blade 1 without penalizing its mass or its aerodynamics, a piece of fabric 20 comprising aramid fibers is added and fixed to its intrados wall 6, so that the piece of fabric 20 extends in the extension of the intrados fin 11 of the shield 10 without covering said fin. In this way, during an impact with an object, the latter slides on the piece of fabric 20 without damaging the wall of the blade 1 on which the piece of fabric 20 is fixed.

[0031] Preferably, the piece of fabric 20 is fixed to the intrados wall 6 only. The Applicant has in fact noticed that the extrados wall 7 was less subject to impact, so that the protection provided by the shield 10 was sufficient to prevent it from being damaged in the event of an impact.

[0032] The piece of fabric 20 comprises aramid fibers coated with polymer resin. In this way, the piece of fabric 20 makes it possible to improve the mechanical behavior of the blade 1 in the event of an impact. Indeed, the absorption energy of the aramid fibers on the one hand and of their interface with the polymer resin on the other hand is greater than that of the composite material of the blade 1. Furthermore, the piece of fabric 20 makes it possible to propagate the damage to the wall of the blade 1 over a larger area than the impact surface.

[0033] The piece of fabric 20 therefore acts as additional protection for the composite material of the blade 1, in addition to or even as a local and partial replacement for the shield 10, without penalizing the mass of the blade 1. The mass of the piece of fabric 20 is in fact very low given the use of aramid fibers. The mass of the blade 1 thus obtained is therefore significantly lower than if the shield 10 had been extended so as to cover the same surface as that occupied by the piece of fabric 20. Furthermore, the use of such a piece of fabric 20 has no impact on the behavior of the blade 1 in operation or its aerodynamic shape and therefore does not require it to be resized.

[0034] Advantageously, the aramid fibers also provide protection against erosion. However, conventionally, such protection is obtained by applying an anti-erosion film 30 over the entire surface of the blade 1. Typically, the anti-erosion film 30 may comprise polyurethane.

[0035] Consequently, according to the invention, the areas of the blade 1 to which the piece of fabric 20 is applied are devoid of anti-erosion film 30. The anti-erosion film 30 and the piece of fabric 20 are then in field, that is to say that they extend in the extension of one another without overlapping but without leaving a space devoid of both anti-erosion film 30 and piece of fabric 20. Thus, the entire surface of the blade 1 is covered either by the anti-erosion film 30 or by the piece of fabric 20.

[0036] The piece of fabric 20 may in particular comprise a two-dimensional fabric. The strands of the two-dimensional fabric piece then have a low count (i.e. a number of fibers in each strand, for example, equal to 8K, corresponding to 8000 fibers per strand, and if possible lower than this value, possibly being at the value of 3K for 3000 fibers per strand), which makes it possible to limit the undulations on the surface of the piece of fabric 20. Advantageously, the area of ​​the blade 1 to which the piece of fabric 20 made of aramid fibers is applied then has fewer undulations than the rest of the blade 1, which is devoid of aramid fiber fabric before application of the anti-erosion film 30.

[0037] Aramid fibers may include, among others, poly(p-phenyleneterephthalamide) (PPD-T - known under the brand name Kevlar) fibers.

[0038] The piece of fabric 20 can be applied either so as to be in the field of the intrados fin 11 of the shield 10 ( figure 2 ), without covering by the shield 10, or in such a way as to be partially covered by the intrados fin 11 of the shield 10 ( figure 3 ).

[0039] For this, the piece of fabric 20 can be applied against the fiber preform intended to form the blade 1 in the injection mold, before injection of the matrix. Alternatively, the piece of fabric 20 can be fixed on the blade 1 after injection of the matrix, for example by gluing.

[0040] In one embodiment, the piece of fabric 20 covers the aerodynamic surface 2 over only part of its height h. Preferably, the aerodynamic surface 2 comprises a surface portion at the intrados wall 6 which is devoid of a piece of fabric 20. For example, in the case of a fan blade 1 having a reduced rotation speed, the surface portion devoid of a piece of fabric 20 is adjacent to the lower limit 3 of the aerodynamic surface 2. Indeed, the Applicant has noticed that the impacts of objects, and in particular birds, do not damage the blade 1 beyond the shield 10 in this portion of the blade 1.

[0041] Typically, the piece of fabric 20 covers at most 70% of the height of the aerodynamic surface 2, without covering the lower portion of the aerodynamic surface 2 (as illustrated by way of example in the figures 2 And 3 ).

[0042] The shape and dimensions of the piece of fabric 20 can be determined based on the following parameters, taken individually or in combination: the rotation speed of the fan, the number of blades 1 of the fan, the inter-blade spacing 1, the three-dimensional shape of the blade 1.

[0043] Especially, the lower the fan rotation speed, the lower the number of fan blades 1, and / or the greater the inter-blade spacing 1, the larger the surface area of ​​the assembly formed by the intrados fin 11 and the piece of fabric 20 must be.

[0044] Preferably, the shape and dimensions of the piece of fabric 20 are determined based on these four parameters taken in combination.

[0045] For example, for a fan blade 1 having a reduced rotation speed and number of blades 1, at any point of the height h of the aerodynamic surface 2 provided with a piece of fabric 20, the axial length l2 of the assembly formed by the intrados fin 11 and the piece of fabric 20 is between 20% and 50% of the axial length l1 of dawn 1.

[0046] By axial length l2 of the assembly formed by the intrados fin 11 and the piece of fabric 20, we will understand here the curvilinear length of said assembly between the leading edge 4 of the shield 10 and a downstream edge 21 of the piece of fabric 20, in a direction parallel to the axis of revolution Y of the fan. The downstream edge 21 of the piece of fabric 20 corresponds here to the edge of the piece of fabric 20 which is closest to the trailing edge 5 of the blade 1, as opposed to the upstream edge 22 which is closest to the leading edge 4 of the blade 1.

[0047] By axial length l1 of the blade 1, we will understand here the curvilinear length of the intrados wall 6 between the leading edge 4 and the trailing edge 5 of the blade 1, in a direction parallel to the axis of rotation of the fan.

[0048] Of course, the axial length l2 of the assembly formed by the shield 10 and the piece of fabric 20 and the axial length l1 of blade 1 vary between the lower limit 3 of the aerodynamic surface 2 of blade 1 and the tip of blade 1.

[0049] The size and shape of the piece of fabric 20 and the intrados fin 11 can also be optimized. In particular, the shield 10 represents a significant mass in comparison with the piece of fabric 20, but gives the fan blade 1 a necessary rigidity, in particular for the frequency and deflection aspects upon impact. It is therefore necessary to retain the intrados fin 11, despite the attachment of the piece of fabric 20. Its size and shape can, however, be adapted in order to reduce the mass of the fan blade 1.

[0050] Finally, the piece of fabric 20 may extend continuously along the aerodynamic surface 2. Alternatively, the piece of fabric 20 may be discontinuous and comprise several portions of disjointed piece of fabric 20.

Claims

1. A blade (1) for a rotating part of a turbomachine, in particular of a fan for a turbomachine, comprising: - a leading edge (4) and a suction wall (6), and - a structural shield (10), said shield (10) being attached and fixed to the leading edge (4) of the blade (1) and comprising a suction fin (11) fixed to the suction wall (6), a piece of fabric (20) comprising aramid fibres, said piece of fabric (20) being attached and fixed to the suction wall (6) of the blade (1) so that the piece of fabric (20) extends in the extension of the suction fin (11) of the shield (10) without covering said suction fin (11), and - an erosion protection film (30), said erosion protection film (30) being attached and fixed to the suction wall (6) of the blade (1) so as to extend in the extension of the piece of fabric (20) without covering said piece of fabric (20).

2. The blade (1) as claimed in claim 1, wherein the piece of fabric (20) comprises a two-dimensional fabric.

3. The blade (1) as claimed in one of claims 1 or 2, wherein the piece of fabric (20) is partially covered by the suction fin (11) of the shield (10).

4. The blade (1) as claimed in one of claims 1 or 2, wherein the piece of fabric (20) adjoins the suction surface (11) of the shield (10), without overlapping by the shield (10).

5. The blade (1) as claimed in one of claims 1 to 4, wherein an aerodynamic surface (2) of the blade (1) has a main direction of extension, defining a longitudinal axis (X) of the blade (1) which is substantially radial to an axis of revolution (Y) of the rotating part, and a height (h) corresponding to a distance between a lower limit (3) of the aerodynamic surface (2) and a tip of the blade (1), the piece of fabric (20) covering the aerodynamic surface (2) over only a part of said height (h).

6. The blade (1) as claimed in claim 5, wherein the aerodynamic surface (2) has a surface portion at the suction wall (6) which is free of piece of fabric (20), said surface portion being adjacent to the lower limit (3) of the aerodynamic surface (2).

7. The blade (1) as claimed in one of claims 5 or 6, wherein the piece of fabric (20) covers not more than 70% of the height (h) of the blade (1).

8. The blade (1) as claimed in one of claims 1 to 7, wherein, in the areas of the blade (1) which comprise a piece of fabric (20), an axial length (l2) of the assembly formed by the shield (10) and the piece of fabric (20) is between 20% and 50% of an axial length (l1) of the blade (1), where the axial length (l2) of the assembly and the axial length (l1) of the blade (1) correspond to a curvilinear length in a direction parallel to the axis of revolution (Y) of the rotating part.

9. The blade (1) as claimed in one of claims 1 to 8, wherein the erosion protection film (30) comprises polyurethane.

10. The blade (1) as claimed in one of claims 1 to 9, said blade (1) being made of a composite material comprising a fibrous reinforcement densified by a polymer matrix, the fibrous reinforcement can be formed from a fibrous preform obtained by three-dimensional weaving with evolving thickness.

11. A fan for a turbomachine, characterized in that it comprises at least one blade (1) as claimed in one of claims 1 to 10.