Patent Application
20240200460
The present invention relates to a foil for a turbomachine rotor blade. It also relates to an assembly for rotor including such a foil mounted to a blade root and to a turbomachine equipped with at least one such assembly.
The invention finds applications in the field of aeronautics and, in particular, in the field of turbomachine rotors to increase the service life of said rotors.
It is known in aeronautics that a rotor blade 10 (“aube” in French language), one example of which is represented in
During operation of the rotor, contact between the blade roots, for example made of titanium aluminide, and the disc, generally made of a nickel-based alloy, leads to premature wear of the blade roots. But significant wear of the blade roots can cause the heels of the rotating blades to overlap or even disengage from each other and thus generate a loss of contact between the heels and/or the start of a crack in the contact zone of the blade root, leading subsequently to the breakage of the blade root with a potential release of the blade into the turbomachine stream.
In order to limit wear of the blade roots and the disc cavities, it is known to place a contact piece, called a foil and referenced 30, at the contact interfaces, commonly referred to as seats, between the blade roots and the disc cavities. The foil 30, integral with the blade root 20 and in contact with the disc, takes up most of the energy dissipated by friction in the contact between said blade root and the disc, thereby limiting wear on the blade root.
As can be seen in
In order to prevent the foil 30 from disengaging from the root 20, the base 31 of the foil comprises radial tabs 33, 34 bearing against the upstream 23 and downstream 24 faces of the root 20 of the blade. The radial tabs 33, 34 are strips cut out at the end of the base 31 and radially folded along the upstream and downstream faces 23, 24 of the root 20. These radial tabs 33, 34 extend over a greater or lesser width, between the lateral legs 32 of the foil, and form stops which make it possible to block relative axial movements between the root 20 and the foil 30.
However, despite the presence of these radial tabs, turbomachine maintenance operators have noticed that the foils tend to move axially, which damages the radial tabs and even sever them. As a result of their radial folding during the manufacturing phase and/or their unfolding during the assembly phase, the radial tabs are weakened and the friction generated by the repeated axial displacement of the foils has the effect of severing them. Once the radial tabs are broken, the foils can become partially or even totally disengaged from the blade roots, requiring the rotor to be removed for repair. Removing and repairing the rotor involves significant repair costs (parts and labour) and downtime for the turbomachine.
There is therefore a real need for a foil that is more robust and more resistant to friction.
In response to the problems discussed above concerning robustness and friction resistance of foils, the applicant provides a foil for a rotating blade, equipped with an oblique tab configured to be inserted into an housing in the lower face of the blade root.
According to a first aspect, the invention relates to a foil for a rotating blade of a turbomachine, configured to be mounted to a root of said rotating blade and comprising blocking means for prohibiting at least some of the relative movements between the blade root and said foil. This foil is characterised in that the blocking means include at least one oblique tab, partially cut out of a lower surface of the foil and forming, with respect to said lower surface of the foil, a protrusion in a tilted plane able to be inserted into a housing formed in a lower face of the blade root.
This foil includes an overall U-shaped section formed by two lateral legs connected through a lower surface, the lower surface covering a lower face of the blade root, the lateral legs each covering at least part of two lateral flanks of the blade root.
The oblique tab of the foil according to the invention has the advantage, on the one hand, of being folded only once during manufacture or assembly of the foil, which prevents it from becoming brittle. This oblique tab has the further advantage of being substantially parallel to the direction of forces and therefore of being able to withstand these forces during the relative movements between the blade root and the foil, which ensures it has a longer service life. It also has the advantage of not hindering operation of the blade because it is implemented on the lower face of the blade root, which is a non-functional face of said blade root.
The use of a foil according to the invention in a turbomachine makes it possible to limit the number of engine removals, to reduce the number of parts to be changed during an engine removal and, therefore, to reduce maintenance costs of the turbomachine. It also makes it possible to increase service life of turbomachines and improve flight safety.
In the present application, the terms “lower”, “upper” and “outer” are interpreted with reference to the position of a part or surface in relation to the axis of rotation of the turbomachine, a lower surface being closer to the axis of rotation than an external or outer surface. The term “lateral” is interpreted as “which is located on the sides of a part which extends radially” along an axis perpendicular to the axis of rotation XX. The term “axial” is to be interpreted as “along the direction of the axis of rotation” and the term “radial” as “along a direction perpendicular to the axis of rotation” or “along the direction of a radius of the blade rim”. The terms “upstream” and “downstream” will be interpreted with reference to the flow direction of the air stream in the turbomachine.
Further to the characteristics just discussed in the preceding paragraph, the foil according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or according to any technically possible combinations:
A second aspect of the invention relates to an assembly for a turbomachine rotor, including a rotating blade configured so as to be rotatably rotating about an axis of rotation and comprising a vane radially extending between a blade heel and a blade root, said blade root comprising a lower face extending in a plane parallel to the axis of rotation. The assembly is characterised in that it includes a foil as defined above and mounted at least partially around the blade root, the lower face of the blade root including a recess forming a housing for the oblique tab of the foil.
According to some embodiments, the blade root is configured so as to be mounted in an alveolus of a disc of the turbomachine and the assembly is characterised in that a height between the lower surface of the foil and the free edge of the oblique tab furthest from said lower surface is greater than a clearance between the lower face of the blade root and a bottom of the alveolus of the disc.
According to some embodiments, the recess of the blade root includes an oblique upper wall forming a tilted plane substantially parallel to the tilted plane formed by the oblique tab.
A third aspect of the invention relates to a turbomachine, characterised in
that it includes at least one rotor assembly as defined above.
Further advantages and characteristics of the invention will become apparent upon reading the following description, illustrated by the figures in which:
An exemplary embodiment of a foil for a rotating blade, configured to be more robust and more resistant to friction than conventional foils, is described in detail below, with reference to the appended drawings. This example illustrates the characteristics and advantages of the invention. However, it is reminded that the invention is not limited to this example.
In the figures, identical elements are marked by identical references. For reasons of legibility of the figures, the size scales between the elements represented are not respected.
One example of a foil in accordance with the invention, mounted around a rotating blade root, is represented in perspective view in part A of
This foil, referenced 300, is designed to be mounted around a blade root 20, especially at the contact interfaces between said blade root 20 and a cavity 45 of a rotor disc, adapted to receive this blade root. Indeed, as a reminder, each blade root 20 of the rotating blade 10 is engaged in a cavity 45 formed in the outer periphery of the disc 40 and held radially in said cavity by shape cooperation between the blade root 20 and the cavity 45. Generally, the blade root 20 is dovetail-shaped and the cavity 45 of the disc is alveolus-shaped. The blade root 20 of the rotating blade 10 comprises a lower face 21, two lateral flanks 22, an upstream face 23 and a downstream face 24.
Upon rotating the rotor disc 40, the rotating blades 10 are subjected to centrifugal forces and, under the effect of these centrifugal forces, the lateral flanks 22 forming the contact interfaces of the blade roots 20 come into stop against the contact interfaces of the disc cavities 45. A foil 300 is positioned around each rotating blade root, between the contact interface of the blade root and the contact interface of the corresponding cavity of the disc, so as to limit wear of said blade roots.
Like most foils, the foil 300 according to the invention includes an overall U-shaped section formed by two lateral legs 302 connected through a lower surface 301. The lower surface 301 of the foil, or base of the foil, covers the lower face 21 of the blade root 20. The lateral legs 302 each cover at least part of the two lateral sides 22 of the blade root 20.
The foil according to the invention may also comprise radial tabs 303, 304, produced by cutting the lower surface 301 and radially folding along the upstream 23 and downstream 24 faces of the blade root 20. Each of the radial tabs 303, 304 is cut out at one of the free ends of the lower surface 301, that is on one of the sides of the lower surface 301 extending between the two lateral legs 302 of the foil, with a predefined shape, for example rectangular or square, with reduced dimensions compared with the dimensions of the upstream and downstream faces of the blade root. During manufacture of the foil 300 or during assembly of said foil on the blade root 20, each radial tab 303, 304 is folded and bent radially along the upstream face 23 or the downstream face 24 of the blade root so as to form, with the lower surface 301, a substantially right angle. These radial tabs 303, 304 thus form axial stops for limiting relative axial movements between the root 20 and the foil 300.
The foil 300 according to the invention includes one or more oblique tabs 305. This/these oblique tab(s) 305 may be made in addition to the radial tabs 303, 304 to overcome the problem of wear of said radial tabs. If the oblique tab(s) 305 are more resistant than the radial tabs (for example with a different choice of material or a treatment applied to the material), then they can be made instead of said radial tabs. In the remainder of the description, consideration will be given to the alternative in which the oblique tab(s) form a blocking means additional to that formed by the radial tabs.
In examples A and B of
The oblique tab 305 is a leaf or lamella partially cut out in the lower surface 301 of the foil and having a contour, a part of which forms a free edge and another part of which forms a non-free edge, attached to said lower surface. The term “free edge” refers to an edge which is detached from the lower surface of the foil, as opposed to the non-free edge which is connected or attached to said lower surface. This leaf or lamella is placed in an oblique position with respect to the lower surface 301 of the foil, that is it extends along a tilted plane, in a position forming an angle that is neither right nor flat with said lower surface 301. The angle formed by the tilted tab 305, with respect to the lower surface 301, may be, for example, between 10° and 25°. Whatever its tilt angle, the oblique tab 305 forms a protrusion in a tilted plane with respect to the lower surface of the foil, this protrusion being designed to be inserted into the blade root, as explained below.
The tilted plane formed by the oblique tab 305 preferably extends in the positive direction of the axis X, that is in the direction of the air flow, from upstream to downstream, this direction being favourable to the placement of the foil on the blade root. Of course, the oblique tab 305 can extend in different directions insofar as the oblique tab blocks the relative movement of the blade root with respect to the foil whatever the direction of said oblique tab.
The oblique tab 305 may, for example, be substantially square or rectangular in shape with three free sides 305a, 305b, 305c, that is sides entirely cut out and therefore not attached to the lower surface 301, and one non-free side 305d, i.e. a side at least partly attached to the lower surface 301.
The oblique tab 305 is designed to be housed in a recess 25 of the blade root 20. This recess 25 having a shape and dimensions adapted to those of the oblique tab 305 so as to form a housing able to receive said tab. As represented in
The recess 25 may include an oblique upper wall 25a, or ceiling, that is tilted at a slope more or less similar to that of the oblique tab 305. In other words, the oblique ceiling of the recess 25 forms a tilted plane, which may be parallel to the tilted plane formed by the oblique tab 305. In the example of
According to some embodiments, and in order to ensure completely stable positioning of the foil, the distance or height H between the lower surface 301 of the foil and the free end 305b of the oblique tab, in the recess 25, is greater than the distance or clearance J between the lower face 21 of the blade root and the bottom 41 of the alveolus of the disc 40. The free end 305b is the free edge of the oblique tab 305 which is furthest from the lower surface 301 of the foil.
In some embodiments, such as that shown in
In some embodiments, the oblique tab 305 is folded prior to insertion into the recess 25 of the blade root. In particular, after having been cut out of the lower surface 301 of the foil 300, the tab 305 can be made oblique by a folding operation, before mounting the foil to the blade root. During assembly, the oblique tab 305 is able to be inserted, by elasticity, into the recess 25 of the blade root. The foil 300 has some flexibility, especially due to the choice of material (titanium aluminide, for example) and also its thinness (0.08 mm or 0.16 mm, for example). This flexibility allows not only the shaping of the foil around the blade root, but also positioning of the oblique tab 305 in the recess 25 of the blade root. In this way, the oblique tab is folded only once, either when the foil is mounted to the blade root or when the two side legs 302 are drawn. Due to its flexibility, the oblique tab 305 has some spring effect which allows it, when mounted to the blade root, to unfold slightly and, once in the recess 25 of the blade root, to unfold by spring effect.
In some embodiments, the tab 305 may be folded, by human or mechanical action, after the foil 300 has been mounted to the blade root. In these embodiments, it may be advantageous for the top wall 25a of the recess to be tilted as this tilt may serve as a stop for the oblique tab during the operation of folding said tab.
In the embodiments described previously, the oblique tab 305 may have a planar cross-section, as represented in the examples of
In other embodiments, the oblique tab 305 may have a curved or convex profile, as represented in the examples of
Although described through a number of examples, alternatives and embodiments, the foil for a rotating blade according to the invention comprises various alternatives, modifications and improvements which will be obvious to the person skilled in the art, it being understood that these alternatives, modifications and improvements are within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2103391 | Apr 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2022/050524 | 3/22/2022 | WO |
