SLING TO REDUCE STRESS IN A TURBINE BLADE NOSE

Abstract

SHIMMER FOR REDUCING STRESS IN A TURBINE BLADE NOOT One aspect of the invention relates to a shimmer (1) for mounting on a blade foot (21) of a turbine wheel, the shimmer (1) comprising a base (17), and first and second lateral arms (12d) connected to each other by the base (17), each lateral arm (12c, 12d) comprising: a longitudinal edge (16c, 16d) and a bulbous portion (121c, 121d) comprising: a lower part (120c, 120d) extending outwards from the base (17) and a contact part (122c, 122d) extending from the lower portion (17) to its longitudinal edge (16c, 16d) and to the other lateral arm (122d, 122c), the contact portion (122c) of the first lateral branch (12c) has a minimum longitudinal length (d) less than the minimum longitudinal length (e) of the base (17). Figure to be published with the abbreviation: Figure 3

Description

Title of the invention: FOIL FOR REDUCING STRESS IN A TURBINE BLADE FOOT NECK TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of foils for turbine blades.

[0002] The present invention relates to a foil for a moving blade of a turbomachine, as well as an assembly comprising a moving blade whose root is provided with said foil. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Conventionally, an axial turbine of a turbomachine consists of a succession of axial stages (along the axis of circulation of the gas flows) arranged one behind the other. Each stage comprises a bladed moving wheel forming the rotor and a bladed distributor forming the stator. The moving wheel is rotated opposite the corresponding distributor.

[0004] The moving wheel is conventionally made up of an annular disc centered on the axis of rotation of the wheel, comprising cells and a plurality of moving blades each comprising an attachment member called hereinafter a blade root in a housing in the form of a dedicated cell.

[0005] In the contact zones between the root of each moving blade and the cell of the disc housing this root, several types of constraints are exerted.

[0006] We encounter in particular "fretting", that is to say contact wear, which is the consequence of the repetitive friction of one part on another, the resulting friction forces being able to cause damage to the material by different fatigue processes. This phenomenon is particularly sensitive in the case of contact between two parts, for example metal or CMC.

[0007] These areas are therefore subject to a significant tendency towards damage to the material, as well as to wear of the blade root surfaces which are the areas in contact with the wall of the cell, or even deformation of these contact areas.

[0008] In addition, the level of local stresses is very high due to the coefficient of friction at the interface between the contacting walls of the blade root and the cell, formed by a metal / metal contact. In the following, this interface is called the blade root bearing surface and the cell bearing surface.

[0009] To solve these problems, we are seeking in particular to strengthen the wear resistance of the surfaces in contact and to reduce the coefficient of friction.

[0010] To do this, generally a protective part is used which can be a consumable, formed of one or more metal foils fitting the foot of the blade along the entire longitudinal length of the bulb of the blade root.

[0011] With this type of solution, we manage to reduce the coefficient of friction and we can change the foil instead of an entire blade.

[0012] For example, document EP2042689A1 proposes using an assembly with a metal foil between a blade root and a disc.

[0013] On turbine blades, foils are placed between the blade roots and the disc cells to prevent wear of these parts. These guarantee the mechanical integrity of the parts with which they are in contact.

[0014] During operation of the turbine, with the centrifugal force, all the forces pass through these contact surfaces on the blade root. The current thickness of the foils is generally 0.08 mm.

[0015] In certain situations, stress peaks have been observed in localized areas of a blade root neck which can lead to a reduction in the life of the blade root.

[0016] [Fig. 1] represents a lower part of a turbomachine wheel blade 2.

[0017] The blade 2 comprises an aerodynamic blade 23, a small part of which is visible in [Fig.l], which extends radially from a platform 29, the blade 2 further comprises a stilt 28, the platform 29 connecting Péchasse 28 to the aerodynamic blade 23. The blade further comprises a root 21 comprising a bulb 211 intended to be inserted into an annular disc of the wheel and a neck 212 extending from the bulb 211 towards Péchasse 28. The neck 212 comprises a restricted portion which extends from the bulb 211, comprising a smaller section compared to that of bulb 211. The neck 212 comprises in this example at its upstream and downstream ends, a connecting portion 2118a, 2128b, extending towards Péchasse 28. The wheel of tubomachine comprises an annular disc centered on the longitudinal axis comprising grooves each receiving the bulb of corresponding shape.

[0018] The greatest mechanical stresses are therefore located in the neck 212 because it has a smaller section or a smaller thickness compared to the bulb 211 of the root 21 and Péchasse 28, and because of the centrifugal force which is applied to the rotating blade 2. The centrifugal forces are transmitted to the bulb 211 by the geometry of the root of the blade 2, in particular, by the walls of Péchasse 28. The radial stresses experienced by the root 21 are in particular located at the level of the connecting portions 2128a, 2128b at the upstream and downstream ends of the neck 212 and are amplified by the edge effects of these connecting portions 2128a, 2128b at the upstream and downstream ends. This impacts the mechanical strength of the root, at the level of the neck in particular, and limits the service life of the blades. Such degradation could lead to cracks with debris, or even breakage of the blade causing damage to the turbomachine.

[0019] Also known in document FR3090032 is a turbomachine blade including a local thickening of the Péchasse walls and in particular around the connecting portion of the neck where they connect to reduce stress concentrations in the bulb. The life of the blade is then improved.

[0020] However, this solution is not always possible for reasons of size and weight gain; in fact, the design of certain blades has been optimized in order to reduce the weight as much as possible. As a result, the size of the blade necks (length / width) has been reduced in order to limit the weight while ensuring acceptable mechanical strength. In addition, this solution requires a change in the design of the blade and therefore does not solve the problem on blades already produced or in production.

[0021] The neck constraints can be greater on certain blades, which greatly limits any flexibility in margin of error during the manufacture of the blade. In other words, the slightest non-conformity in production (reduction in the neck length or width) creates a risk of non-acceptability from a mechanical point of view and therefore an increased risk of rejecting the parts.

[0022] There is therefore a need to reduce in a simple, economical and effective manner the stress concentrations in the root of the blade, in particular at the neck. Summary of the invention

[0023] The invention provides a solution to at least one of the problems mentioned above, by allowing a foil to modify the path of the forces in the neck during operation and to better distribute the stresses in the neck and to reduce the local maxima and thus avoid stress concentrations.

[0024] A first aspect of the invention relates to a foil intended to be mounted on a blade root of a moving wheel of a turbomachine rotor and the foil comprising a base, and a first lateral branch and a second lateral branch connected to each other by the base, each lateral branch comprising: • a longitudinal edge • a bulb portion having a convex external surface extending from the base towards the longitudinal edge, the bulb portion comprising: • a lower part extending from the base and moving outwards and • a contact part extending from the lower portion towards its longitudinal edge and towards the other lateral branch,

[0025] characterized in that at least the contact portion of the first lateral branch comprises a minimum longitudinal length less than the minimum longitudinal length of the base.

[0026] Thus, the invention makes it possible to have a foil comprising a contact portion intended to come over a portion of the length of the bearing surface of a blade root, thus making it possible to reduce the contact length of the active flanks (bearing surfaces) of the blade with the disk by means of the foil. This reduction allows a modification of the path of the forces in the root, in particular in the neck of the root in operation, and thus reduces the stresses in at least one connecting portion at an upstream and / or downstream end of the intrados and / or extrados side of the neck, and therefore reduces the local stress maxima. Very surprisingly, reducing the length of the contact portion of the foil therefore allows a more homogeneous distribution effect of the stresses in the root.

[0027] In addition to the characteristics which have just been mentioned in the preceding paragraph, the foil according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations:

[0028] According to one embodiment, the foil comprises first and second lateral edges extending over one end of the base and lateral branches forming the opposite longitudinal ends of the foil, each contact portion comprising at its longitudinal ends a contact edge portion of the lateral edge delimiting the contact portion, and in that each contact edge portion of the contact portion of the first lateral branch is equidistant from a plane passing perpendicularly and in the middle of the base and the first and second lateral branches and is closer to this plane than a lower edge portion of each lateral edge delimiting the lower portion of the first lateral branch.

[0029] Thus, the contact part is as much shorter on one side as on the other side compared to the base. This makes it possible to have this effect of distributing the stresses more homogeneously on the downstream and upstream sides on a lateral longitudinal face of the foot of the blade partially covered by this contact part of the foil which is shorter longitudinally on each side than the lateral longitudinal face.

[0030] According to one example, the foil is symmetrical with respect to this plane. This makes it possible to have this effect of distributing the stresses more homogeneously on the intrados and extrados sides of the blade root and thus to arrange the foil in one direction or the other on the blade root.

[0031] According to one embodiment, in which each contact edge portion delimiting the contact portion of the first lateral branch comprises a concave portion extending from the lower edge portion. This makes it possible to increase the mechanical resistance of the foil, in particular against folding at the contact portion relative to the lower portion.

[0032] According to an example of this embodiment, the lower edge portion of each edge lateral each extends in the same plane as a part of the edge delimiting the base of the foil. The two planes are in particular parallel to each other.

[0033] According to one embodiment, the ratio of the minimum longitudinal length of the contact portion to the minimum longitudinal length of the base is between 0.55 and 0.8.

[0034] This makes it possible to reduce the contact surface between the disc and the active flank of the blade by 20% to 45% by means of the foil compared to a foil covering all of the active flanks. This reduction makes it possible to sufficiently reduce the level of maximum stresses at the throat. Indeed, a reduction in the contact surface of 45% allows a reduction in the maximum stresses at the throat of the order of 20% and a reduction in the contact surface of 20% allows a reduction in the maximum stresses at the throat of the order of 10%.

[0035] According to one example, the ratio of the minimum longitudinal length of the contact portion of each lateral branch to the minimum length of the base is 0.6. Such a ratio allows a 40% reduction in the surface area covered by the foil on the side covered by this first lateral branch and, in the case of two identical lateral branches, a reduction of 10% to 20% in the level of maximum stresses at the neck on the intrados and extrados sides.

[0036] According to one embodiment, the thickness of the foil is between 0.09 mm and 0.1 mm. This makes it possible to increase the thickness of the foil compared to a 0.08 mm foil to compensate for the loss of length of the contact portion of the foil.

[0037] According to one embodiment, the second lateral branch is identical to the first lateral branch.

[0038] According to one embodiment, each longitudinal edge is rectilinear and in that the longitudinal length of the longitudinal edge is less than the minimum length of the base.

[0039] According to one embodiment, each lateral branch further comprises a flat portion extending between the contact part of the bulb and the longitudinal edge.

[0040] According to an example of this previous embodiment, the planar portion comprises a longitudinal length less than the longitudinal length of the base.

[0041] According to an example of this embodiment, the contact portion comprises a minimum longitudinal length equal to the planar longitudinal length.

[0042] According to one embodiment, the contact portion comprises a minimum longitudinal length less than the minimum longitudinal length of the lower portion of the bulb portion.

[0043] According to one embodiment, the foil material is a cobalt-based alloy, in particular HS25 (DMD0415).

[0044] According to one embodiment, the foil comprises a tongue extending along longitudinally from the base, the tab intended to be folded against a radial face of the blade root, the lateral edge comprising a portion forming the outline of the tab. The tab makes it possible to retain the foil axially. According to one example, the foil comprises a tab on each side of the base, or two tabs for axially retaining the foil around the blade root in both directions.

[0045] A second aspect of the invention relates to an assembly comprising: • a blade of a wheel movable about an axis of rotation, comprising: a. an internal platform, b. an aerodynamic blade extending radially from the internal platform, c. a stilt extending radially from the inner platform opposite the aerodynamic blade, d. a blade root extending radially from this internal stilt opposite the platform, the blade root comprising: • a first radial face and a second radial face longitudinally opposite the first radial face, • a first and a second lateral longitudinal face each joining each radial face, • a bulb comprising: • a base surface, extending between the first radial face and the second radial face and between the first and second lateral longitudinal faces, • a flank on each lateral longitudinal face, comprising a span, • a neck extending from the bulb to Péchasse, • a foil according to the first aspect of the invention with or without the various characteristics described above, characterized in that the base of the foil covers the base surface of the foot of the blade and in that the contact portion of the first and second lateral branches of the foil is in contact with the bearing surface of the flank of the first and second longitudinal faces respectively, the contact portion of the foil having a minimum longitudinal length less than the longitudinal length of the flank.

[0046] Thus, the invention makes it possible to reduce the stresses in at least one end of the neck of the blade root. BRIEF DESCRIPTION OF THE FIGURES

[0047] The figures are presented for information purposes only and in no way limit the invention.

[0048] [Fig.l] is a partial view of one face of a turbine blade.

[0049] [Fig.2] is a perspective and partial view of an example of a moving wheel which comprises a disc and blades extending from the periphery of the turbine blade disc.

[0050] [Fig.3] is a side view of an assembly according to the invention comprising a foil according to the invention mounted on the turbine blade.

[0051] [Fig.4] is a perspective view of the assembly according to the invention.

[0052] [Fig.5] is a view of the other lateral side of the assembly according to the invention.

[0053] [Fig.6a] schematically represents by arrows the path of the forces on a bearing surface of the flank on the intrados side of the blade root without foil or with a foil of the prior art.

[0054] [Fig.6b] schematically represents by arrows the path of the forces on a carried by the flank on the intrados side of the foot of the blade with a foil according to the example of this first embodiment.

[0055] [Fig.7a] schematically represents a simulation of the constraints on the neck of a foot of the dawn without foil or with a foil of the prior art during an airplane takeoff.

[0056] [Fig.7b] schematically represents constraints on the neck of a blade root with a foil according to the example of this first embodiment. DETAILED DESCRIPTION

[0057] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0058] The invention relates to a foil for a root of a moving turbine blade, as well as to an assembly for a moving turbine wheel comprising a moving blade having its root inserted into such a foil.

[0059] A first aspect of the invention relates to a foil 1 shown in FIGS. 3, 4 and 5 mounted on a foot 21 of a blade 2 of a mobile wheel 8 of a turbomachine and a second aspect of the invention relates to an assembly comprising the foil 1 and the blade 2.

[0060] [Fig. 2] shows a perspective and partial view of an example of a movable wheel 8 which comprises a disc 7 and blades 2 extending from the periphery of the disc. The annular disc 7 centered on a longitudinal axis comprises a washer 70 (or a plurality of arms forming spokes), fixed to a shaft comprising an axis of rotation, and a crown 71 comprising a plurality of teeth and notches 72 on the periphery of the disc 7. The blades 2 each comprise a root 21 mounted in a corresponding notch 72 and are thus distributed circumferentially regularly, around the disc 70 of the movable wheel. Each notch 72 comprises a surface in alveolus shape allowing the blade 2 to be held against centrifugal force.

[0061] The blades 2 each further comprise a stilt 28 which extends radially from the root 21, an internal platform 29 which extends radially from the Péchasse 28 opposite the root 21 and an aerodynamic blade 23 which extends radially outwards from the internal platform 29 opposite the Péchasse 28.

[0062] The wheel further comprises a foil 1 (not visible in this [Fig.2], but visible in the following figures 3 to 5) according to one aspect of the invention per blade. Each foil 1 is mounted around the foot 21 of one of the blades 2. The foil 1 has a shape complementary to the foot 21. Figures 3, 4, 5, partially represent an example of an assembly according to an embodiment of the invention, comprising a blade 2 of the moving wheel 8 and the foil 1 mounted on the foot 21 of the blade 2, only Péchasse 28 and the foot 21 surrounded by the foil 1 is visible. The root 21 comprises a first lateral longitudinal face 24c corresponding to the intrados face of the blade 2 and a second lateral longitudinal face 24d corresponding to the extrados face of the blade 2. [Fig. 3] is a view of the first lateral longitudinal face 24c, [Fig. 4] is a perspective view of the assembly seen in perspective from the side of the first lateral longitudinal face 24c and [Fig.5] is a view of the second lateral longitudinal face 24d. .

[0063] The foot 21 further comprises a first radial face 23a (upstream) visible in particular in [Fig.4] and a second radial face 23b (downstream) longitudinally opposite the first radial face 23a. The radial faces 23a, 23b, each join the first lateral longitudinal face 24c and the second lateral longitudinal face 24d.

[0064] The foot 21 further comprises a base surface covered by a base 17 of the foil 1. The base surface extends between the first and second lateral longitudinal faces 24c, 24d and each radial face 23a, 23b.

[0065] The foot 21 comprises a bulb 211 comprising the base surface, and on each lateral longitudinal face 24c, 24d, a flank 2110c, 2110d extending from the base surface. The foot 21 further comprises a neck 212 extending from the bulb 211 to Péchasse 28. The neck 212 has a maximum thickness (measured along one of the radial faces 23a, 23b parallel to the base surface) smaller than the maximum thickness of the bulb 211. The neck 212 has a portion extending from the bulb 211 of constant thickness. The neck 212 comprises in this example at its upstream and downstream ends, a connecting portion 2118a, 2128b, extending towards Péchasse 28.

[0066] Each flank 2110c, 2110d comprises a bearing surface. A bearing surface is understood to mean the surface of the flank on which the forces are exerted to retain the blade when the rotor rotates. The bearing surface is therefore the surface compressing a surface of the foil (hereinafter called the contact part) against the cell, the bearing surface is therefore the surface in contact with the honeycomb-shaped surface of the notch in the absence of foil 1. Foil 1 mounted on blade 2 protects the bearing surfaces of blade 2.

[0067] The foil 1 therefore further comprises the base 17, a first lateral branch 12c and a second lateral branch 12d each surrounding respectively the first and second lateral longitudinal faces 24c, 24d of the foot 21. The two lateral branches 12c, 12d are connected to each other via the base 17. The parts, portions, surfaces, edges of the first lateral branch 12c include a reference with the letter “c” and those of the second lateral branch 12d include a reference with the letter “d”.

[0068] The foil 1 comprises a first lateral edge 15a and a second lateral edge 15b each extending over one end of the base 17 and one end of the lateral branches 12c, 12d, thus forming the opposite longitudinal ends of the foil 1. The parts of the first lateral edge 15a comprise a reference with the letter "a" and those of the second lateral edge 15b comprise a reference with the letter "b".

[0069] The foil 1 comprises a tongue 18a, 18b extending longitudinally from the base 17 on each side of the base 17, each tongue 17 is folded and in contact against a radial face 23a, 23b of the foot 21. Each lateral edge 15a, 15b thus comprises a portion forming the outline of the tongue 18a, 18b.

[0070] The foil 1 comprises in this example on each lateral branch 12c, 12d, a flat portion 18c, 18d located at one end of the corresponding lateral branch 12c, 12d opposite the base 17. The flat portions 18c, 18d surround the portion of constant thickness of the neck 212, in particular, as explained below, in this example the flat portions 18c, 18d partially surround the portion of constant thickness of the neck 212.

[0071] The foil 1 also comprises at the end of each of its lateral branches 12c, 12d, a longitudinal edge 16c, 16d extending longitudinally along the flat portion 18c, 18d and connecting the two lateral edges 15a, 15b. Each flat portion 18c, 18d therefore extends in this example along a part of a lateral longitudinal flat surface of the portion of constant thickness of the neck 212.

[0072] Each of the lateral branches 12c, 12d comprises a bulb portion 121c, 121d having a convex external surface extending from the base 17 towards the longitudinal edge 16c, 16d. The bulb portion 121c, 121d thus surrounds the bulb 211 of the foot 21. Each bulb portion 121c, 121d comprises a lower part 120c, 120d extending from the base 17 away towards the outside relative to the base 17. Each bulb portion 121c, 121d further comprises a contact part 122c, 122d extending from the bulb portion 121c, 121d towards its longitudinal edge 16c, 16d and towards the other lateral branch 122d, 122c. In this example, each contact part 122c, 122d extends from the bulb portion 121c, 121d to the flat portion 18c, 18d.

[0073] Thus each contact portion 122c, 122d is in contact with the bearing surface of the flank 2110c, 2110d of the bulb 211 of the foot 21. Each contact portion 122c, 122d covers less than 90% of the length of the corresponding flank 2110c, 2110d of the bulb 211 of the foot 21, in this case in this example it covers approximately 77% of the length of the corresponding flank unlike the foils of the prior art which covers more than 95%. The span of the flank 2110c, 2110d is therefore dependent on the surface of the contact part 122c, 122d of the foil 1. Here, the span of the flank 2110c, 2110d is therefore reduced in longitudinal length by 33% compared to the root 21 of blade 2 without this foil 1.

[0074] When the assembly is mounted in a notch 72 of the disc 7, each contact part 122c, 122d is therefore sandwiched between the surface of the flank 2110c, 2110d of the bulb 211 of the foot 21 and the surface of the cell of the notch 72 of the disc 7.

[0075] The contact portion 122c of the first lateral branch 12c comprises a minimum longitudinal length d less than the minimum longitudinal length e of the base 17 (the two minimum lengths d and e are visible in [Fig.3]).

[0076] By minimum longitudinal length is meant the smallest possible longitudinal length measurement.

[0077] In this example, the two side branches 12c and 12d are identical. For simplicity, only the first side branch 122c is explained below, but since the second side branch 122d is identical, the references of the second side branch 122d are mentioned.

[0078] Thus, the contact portion 122c, 122d of the foil 1 has a longitudinal length less than the longitudinal length of the flank 2110c, 2110d.

[0079] The contact portion 122c, 122d therefore comprises at its longitudinal ends a contact edge portion 152ac, 152ad, 152bc, 152bd of the lateral edge 15a, 15b. The minimum length d of each contact portion 122c, 122d can therefore be measured between their two contact edge portions 152ac, 152bc, and 152ad 152bd.

[0080] Thus, a portion of each flank 2110c, 2110d is not covered by the foil 1.

[0081] In particular in this embodiment, each contact edge portion 152ac, 152bc, and 152ad 152bd is spaced by the same distance x from the radial face 23a and 23b of the foot. Of course, the distance between a contact edge portion 152ac, 152bc of the first lateral edge 15c may be different from the distance between the contact edge portion 152ad 152bd of the second lateral edge 15d. The difference between the minimum length d of the contact portion 122c, 122d and the minimum length e of the base 17 is equal to the two distances x, here in this case twice the distance x.

[0082] Each lateral edge 15a, 15b further comprises a lower edge portion 150ac, 150bc delimiting the lower portion 120c of the first lateral branch 12c. In this case, in this example of this embodiment, the distance between these two edge portions low 150ac, 150bc, delimiting the lower part 120c of the first lateral branch 12c is equal to the length e. In this example, as the two lateral branches 12c and 12d are identical, each lateral edge 15a, 15b further comprises a low edge part 150ad, 150bd delimiting the lower part 120d of the second lateral branch 12d. Here the minimum longitudinal length e of the base 17 is similar but less (approximately 99%) than the length of the foot 21 due to the fold of the tabs 18a, 18b.

[0083] Each contact edge portion 152ac, 152bc delimiting the contact portion 122c of the first lateral branch 12c comprises a concave portion extending from the lower edge 150ac, 150bc.

[0084] In this example, each longitudinal edge 16c, 16d is rectilinear and in that the longitudinal length of the longitudinal edge is less than the minimum length (e) of the base 17. Each planar portion 18c, 18d in this example therefore also comprises a longitudinal length less than the minimum longitudinal length of the base 17.

[0085] According to another example not shown, the two or one of the two flat portions 18c, 18d could have a longitudinal length identical to that of the base 17, thus forming a notch on each side at the level of each contact edge portion 152ac, 152bc of the contact portions 122c, 122d. In this example, each contact edge portion 152ac, 152bc may be concave or rectilinear.

[0086] Thus in this example, each contact edge part 152ac, 152bc and 152ad, 152bd, of the contact part 122c and respectively 122d, of the first lateral branch 12c and respectively of the second lateral branch 12d, is equidistant from a plane P visible in [Fig.3], crossing perpendicularly and in the middle of the base 17 and of the first and second lateral branches 12c, 12d and is closer to this plane P than the lower edge part 150ac, 150bc of each lateral edge 15a, 15b.

[0087] [Fig.6a] schematically represents by arrows the path of the forces on the bearing surface 211 le of the sidewall on the intrados side (first lateral longitudinal face 24c) when it is in direct contact with the cell or protected by a foil of the prior art. The bearing surface is schematically represented by a rectangle referenced 211 le. It can thus be seen that a part of the stresses go into the connecting portions 2118a, 2128b at the upstream and downstream ends of the neck 212. [Fig.6b] also represents by arrows the path of the forces on the bearing surface 211 le of the sidewall 2110c on the intrados side (first lateral longitudinal face 24c) but when it is in contact between a contact part 122c of the foil 1 according to this embodiment comprising a longitudinal length d less than that of the longitudinal length of the foot 21.It can thus be seen that there are fewer arrows and therefore fewer constraints going into the connecting portions 2118a, 2128b at the upstream and downstream ends of the neck 212.

[0088] In this example, the ratio of the minimum longitudinal length d of the contact portion 122c, 122d of each lateral branch 12c, 12d to the minimum length e of the base 17 is 0.6. In other words, the surface area of ​​the contact portion 122c, 122d and therefore also that of the span of each flank 2110c, 2110d has been reduced by 40%, but it could be reduced between 20% and 45%.

[0089] The foil 1 comprises a thickness of between 0.09 mm and 0.1 mm and is in a cobalt-based alloy, in particular HS25 (DMD0415), the increase in the thickness of the foil compared to a foil of standard thickness makes it possible to compensate for the loss of length of the contact portion 122c, 122d of the foil 1 compared to a foil of 0.08 mm comprising a contact portion over the entire longitudinal length of the tooth 21.

[0090] [Fig.7a] schematically represents a simulation of the stresses on the neck 212 of a foot 21 of the blade 2 at the time of takeoff of the aircraft, without foil or with a foil of the prior art.

[0091] [Fig.7b] schematically represents a simulation of the stresses on the neck 212 of a foot 21 of the blade 2 at the time of takeoff of the aircraft, with the foil 1 according to this example of this embodiment, that is to say with a 40% reduction in the contact part 122c, 122d.

[0092] Figures 7a and 7b comprise two simulation images, the first image on the left represents the simulation of the stresses on the first longitudinal face 24c, i.e. intrados side, and the second image on the right represents the simulation of the stresses on the second longitudinal face 24d, i.e. extrados side.

[0093] Thus, a reduction of 10 to 20% of the stresses can be seen on the zones having the maximum stresses at the level of the connecting portions 2118a, 2128b at the level of the upstream and downstream ends of the neck 212.

[0094] Thus, thanks to the foil 1, it is possible to increase the life of the blades.

Claims

Claims

1. Foil (1) intended to be mounted on a foot (21) of a blade (2) of a mobile wheel (8) of a turbomachine, the foil (1) comprising a base (17), and a first lateral branch (12c) and a second lateral branch (12d) connected to each other by the base (17), each lateral branch (12c, 12d) comprising: - a longitudinal edge (16c, 16d) and - a bulb portion (121c, 121d) having a convex external surface extending from the base (17) towards the longitudinal edge (16c, 16d), the bulb portion (121c, 121d) comprising: • a lower part (120c, 120d) extending from the base (17) away towards the outside and • a contact portion (122c, 122d) extending from the lower portion (17) towards its longitudinal edge (16c, 16d) and towards the other lateral branch (122d, 122c), - characterized in that at least the contact portion (122c) of the first lateral branch (12c) comprises a minimum longitudinal length (d) less than the minimum longitudinal length (e) of the base (17) such that the ratio of the minimum longitudinal length (d) of the contact portion (122c) to the minimum longitudinal length (e) of the base (17) is between 0.55 and 0.

8.

2. Foil (1) according to the preceding claim, comprising first and second lateral edges (15a, 15b) extending over one end of the base (17) and lateral branches (12c, 12d) forming the opposite longitudinal ends of the foil (1), each contact portion (122c, 122d) comprising at its longitudinal ends a contact edge portion (152ac, 152ad, 152bc, 152bd) of the lateral edge (15a, 15b) delimiting the contact portion (122c, 122d), and in that each contact edge portion (152ac, 152bc) of the contact portion (122c) of the first lateral branch (12c) is equidistant from a plane (p) passing perpendicularly and in the middle of the base (17) and the first and second lateral branches (12c, 12d) and is closer to this plane P than a lower edge part (150ac, 150bc) of each lateral edge (15a, 15b) delimiting the lower part (120c) of the first side branch (12c).

3. Foil (1, 1') according to the preceding claim, wherein each contact edge portion (152ac, 152bc) delimiting the contact portion (122c) of the first lateral branch (12c) comprises a concave portion extending from the lower edge (150ac, 150bc).

4. Foil (1, 1') according to one of the preceding claims, in which the thickness of the foil is between 0.09mm and 0.1mm.

5. Foil (1, 1') according to one of the preceding claims, in which the second lateral branch (12d) is identical to the first lateral branch (12c).

6. Foil (1, 1') according to one of the preceding claims, in which each longitudinal edge (16c, 16d) is rectilinear and in that the longitudinal length of the longitudinal edge (16c) of the first lateral branch (12c) is less than the minimum length (e) of the base (17).

7. Foil (1, 1') according to one of the preceding claims, in which the material of the foil is a cobalt-based alloy, in particular HS25 (DMD0415).

8. Foil (1, 1') according to one of the preceding claims, comprising a tongue (18a, 18b) extending longitudinally from the base (17), the tongue (18a, 18b) being intended to be folded against a radial face of the blade root, the lateral edge (15a, 15b) comprising a portion forming the outline of the tongue (18a, 18b).

9. Assembly comprising: - a blade (2) of a wheel movable about an axis of rotation, comprising: • an internal platform (29) • an aerodynamic blade (23) extending radially from the internal platform (29), • a stilt (28) extending radially from the internal platform (29) opposite the aerodynamic blade (23), • a blade (2) root (21) extending radially from this internal stilt (28) opposite the platform (29), the blade (2) root (21) comprising:

1. a first radial face (23a) and a second radial face (23b) opposite longitudinally dinal to the first radial face (23a), 2. a first and a second lateral longitudinal face (24c, 24d) each joining each radial face (23a, 23b) 3. a base surface extending between each lateral longitudinal face (24c, 24d) and each radial face (23a, 23b), 4. a bulb (211) comprising: a. a base surface, extending between the first radial face (23a) and the second radial face (23b) and between the first and second lateral longitudinal faces (24c), b. a flank (2110c, 2110d) on each lateral longitudinal face (24c, 24d), comprising a bearing surface, 5. a neck (212) extending from the bulb (211) to Péchasse (28), a foil (1) according to one of the preceding claims, characterized in that the base (17) of the foil (1) covers the base surface of the root (21) of the blade (2) and in that the contact portion (122c, 122d) of the first and second lateral branches (12c, 12d) of the foil (1) is in contact with the bearing surface of the flank (2110c) of the first and second longitudinal faces (24c, 24d) respectively, the contact portion (122c, 122d) of the foil having a minimum longitudinal length (d) less than the longitudinal length of the flank (2110c, 2110d).

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