A TURBINE ENGINE STATOR WHEEL AND A TURBINE OR A
COMPRESSOR INCLUDING SUCH A STATOR WHEEL
Background of the invention
The invention relates to a stator wheel for a
turbine engine, in particular an aviation gas turbine
engine on an industrial turbine, where such a stator
wheel forms a turbine nozzle or a compressor diffuser.
Improving the performance of turbine engines and
reducing their polluting emissions leads to ever-higher
operating temperatures being envisaged.
For the elements in the hot portions of turbine
engines, proposals have thus been made to use ceramic
matrix composite (CMC) materials. Such materials present
remarkable thermostructural properties, i.e. mechanical
properties that make them suitable for constituting
structural elements combined with the ability to conserve
these mechanical properties at high temperatures.
Furthermore, CMC materials are of much lower density
than the metal materials conventionally used for making
the elements in the hot portions of turbine engines.
Thus, documents WO 2010/061140, WO 2010/116066, and
WO 2011/080443 describe making turbine engine blades with
integral inner and outer platforms. The use of CMC
material specifically for turbine nozzles has also been
proposed, in particular in document WO 2010/146288.
Traditional metal turbine nozzles are usually built
by assembling together a limited number of sectors
obtained by casting, each sector having quite a large
number of vanes. The complex shape of such sectors makes
them difficult to obtain as a single piece of CMC
material. In order to obtain a turbine nozzle made of
CMC material, it has therefore been necessary to envisage
assembling together a relatively large number of
individual elements, or vanes, each vane having only a
small number of airfoils, and possibly only one airfoil.
This leads to a problem of making an assembly of nozzle
vanes simply and economically while achieving
satisfactory sealing, in particular for the purpose of
avoiding leaks between the gas flow passage through the
turbine and the outside of the nozzle.
A similar problem arises with making turbine engine
compressor diffusers, either using CMC materials in the
downstream compressor stages that are exposed to higher
temperatures, or else using organic matrix composite
(OMC) materials, at least in the upstream compressor
stages.
Object and summary of the invention
An object of the invention is to provide a solution
to this problem, and for this purpose the invention
proposes a turbine engine stator wheel comprising a
plurality of vanes made of composite material, each vane
comprising an inner platform, an outer platform
presenting attachment tabs on the outside, and at least
one airfoil extending between the inner and outer
platforms and secured thereto, the vane and the outer
platform together with the attachment tab forming a
single piece of composite material,
the stator wheel comprising a metal assembly ring in
which the attachment tabs of the vanes are engaged, the
metal ring supporting all of the vanes, extending
continuously along the outer platforms of a plurality of
adjacent vanes, and forming a distinct assembly part
between the vanes and a casing.
The metal assembly ring thus serves both to
integrate the vanes of the stator wheel and also to
provide sealing by extending along the outer platforms of
the vanes.
Preferably, the metal ring is made of sheet metal
and can thus present capacity for deformation suitable
for compensating for differential dimensional variations
of thermal origin.
Advantageously, the metal ring presents
frustoconical bearing surfaces contributing to holding
the vanes radially and axially while also making it
possible to accommodate differential dimensional
variations more easily.
In an embodiment, the metal ring has a section that
is substantially R-shaped and outwardly open, having a
web portion and flanges terminating in end portions
forming hooks for attaching to a casing, and
frustoconical bearing surfaces in contact with the
attachment tabs of the vanes are situated on the outside
faces of the flanges of the ring.
Advantageously, the outer platform of each vane
presents a rib projecting outwards and coming into radial
abutment against a surface portion of the metal ring,
thus contributing to opposing tilting of the vane. The
rib also performs a stiffener function. It may extend
the airfoil of the vane when the vane has only one
airfoil.
Preferably, the metal ring comprises a single piece
and presents a vane insertion window. Under such
circumstances, the stator wheel may further include at
least one latch for blocking in position a vane mounted
at the level of the insertion window.
In order to further improve sealing, sealing wafers
may be arranged on the outer faces of the outer platforms
of the vanes, each wafer covering at least part of a
junction between the outer platforms of two adjacent
vanes.
The invention also provides a turbine or a
compressor for a turbine engine and including at least
one stator wheel as defined above.
Advantageously, when the turbine engine further
comprises a rotor wheel adjacent to the stator wheel and
comprising blades provided at their ends with wipers
facing an abradable material supported by a ring, an
additional metal ring is mounted between the abradable
support ring and the outer platforms of the vanes of the
stator wheel, bearing thereagainst.
This additional metal ring contributes to improving
sealing. It may be made of sheet metal. The additional
5 metal ring is preferably a single piece.
Brief description of the drawings
The invention can be better understood on reading
the following description given by way of non-limiting
10 indication and with reference to the accompanying
drawings, in which:
Figure 1 is a fragmentary section view of a low
pressure turbine of a turbine engine incorporating a
nozzle in an embodiment of the invention;
15 Figure 2 is a perspective view of a vane of the
Figure 1 turbine nozzle;
Figure 3 is a fragmentary perspective view of a
metal assembly ring of the Figure 1 nozzle;
Figure 4 is a perspective view of a latch used for
20 assembling the Figure 1 nozzle;
Figures 5 to 11 are fragmentary views in section
and/or in perspective showing successive steps in
assembling the Figure 1 turbine nozzle; and
Figure 12 is a fragmentary view in perspective and
25 partially cut away showing a variant embodiment of a
turbine nozzle of the invention.
Detailed description of embodiments
A multistage low pressure turbine of a turbine
30 engine as shown in part in Figure 1 comprises a plurality
of stator wheels forming nozzles 10 that alternate with
rotors 30 and that are mounted in a turbine casing 40.
Each rotor 30 comprises a plurality of blades 32
each having an inner platform 34, an outer platform 36,
35 and an airfoil 38 extending between the platforms 34 and
36. Under the platform 34, the blade is extended by a
root that is engaged in a housing in a disk 33. On the
outside, the outer platform 36 supports wipers 37 facing
an abradable material 41 carried by a sectorized ring 42.
The blades 32 may be conventional metal blades or
they may be blades made of CMC material, e.g. obtained as
5 described in the above-mentioned documents
WO 2010/061140, WO 2010/116066, or FR 2 953 885.
In accordance with the invention, at least one of
the nozzles, e.g. the nozzle 10 in Figure 1, is made up
of a plurality of nozzle vanes 12 of CMC material that
10 are assembled together with the help of an assembly ring
20.
In the example shown (Figures 1 and 2), each vane 12
is a single-airfoil vane with an inner platform 14, an
outer platform 16, and one airfoil 18 extending between
15 the platforms 14 and 16 and secured thereto.
The outer faces of the platforms 14, 34 and the
inner faces of the platforms 16, 36 define the gas-flow
passage 50 through the turbine.
On their inner faces, the inner platforms 14 of the
20 vanes 12 present ribs 141, 142 for mounting a ring 15
supporting abradable material 151 facing wipers 35
carried by the disk 33. The ring of abradable material
may, for example, be constituted by a strip of honeycomb
material that is rolled up and positioned between the
25 ribs 141 and142.
The wipers 35 co-operate with the abradable material
151 to provide sealing on the inside, while the wipers 37
co-operate with the abradable material 41 to provide
sealing at the tips of the blades 32.
30 On the outside, each outer platform 16 of a vane 12
presents attachment tabs 162, 164 that project outwards
respectively on the upstream and downstream sides. The
terms "upstream" and "downstream" are used in the present
description relative to the flow direction of gas along
35 the passage 50. The upstream attachment tab 162 has an
end portion 162a that is folded downstream so as to
present a frustoconical internal bearing surface portion
162b. The downstream attachment tab 164 has an end
portion 164a that is folded upstream so as to present a
frustoconical internal bearing surface 164b.
Also on the outside, each outer platform 16 of a
5 vane 12 presents a rib 166 that extends in the
longitudinal (axial) direction of the platform 16 and
that constitutes a stiffener for the platform. The rib
166 may be formed by an extension of the airfoil 18.
Each vane 12 is made as a single piece of CMC
10 material. For this purpose, it is possible to use a
method as described in document WO 2010/146288 or in
document WO 2011/080443, the content of those documents
being incorporated herein by way of reference. Briefly,
a fiber blank is made by multilayer or three-dimensional
15 weaving using yarns made of ceramic fibers, e.g. silicon
carbide (Sic) fibers or carbon fibers. The fiber blank
is shaped so as to obtain a fiber preform having a shape
close to that of the vane to be made. The preform is
consolidated in its shape, e.g. by being impregnated with
20 a carbon or ceramic precursor resin, followed by curing
and then pyrolyzing the resin, with the preform being
held in tooling. The consolidated preform as extracted
from the tooling is densified by a ceramic matrix, e.g.
by chemical vapor infiltration (CVI). By way of example,
25 the matrix may be made of Sic or it may be a self-healing
matrix having matrix phases made of boron carbide B,C or
of a tertiary Si-B-C system. The preparation of such
self-healing matrices is described in particular in
documents US 5 246 756 and US 5 965 266.
30 The vanes 12 are assembled to form the axisymmetric
turbine nozzle 10 with the help of an annular assembly
ring 20 (Figures 1, 3). The ring 20 is advantageously
made of metal sheet. The material constituting the ring
20 is a metal suitable for withstanding the temperatures
35 that are encountered in service, e.g. a metal or metal
alloy as commonly used in low pressure (LP) turbine
enclosures such as an alloy based mainly on nickel and
chromium and known under the name Inconel@ or Waspaloy@.
In the example shown, the ring 20 has a crosssection
that is R-shaped and open towards the outside.
5 It comprises a web portion 26 extended upstream and
downstream by respective upstream and downstream flanges
22, 24 that are of substantially S-shaped section. On
their outer faces, the flanges 22 and 24 present surface
portions in their respective middle portions 222, 242,
10 which surface portions form frustoconical bearing
surfaces 222a, 242a. On their outer faces, the flanges
22, 24 also present frustoconical surface portions in
their respective middle portions 222, 242 that form
bearing surfaces 222b, 242b. The flanges 22, 24 are
15 terminated by end portions that are folded respectively
upstream and downstream to form upstream and downstream
hooks given respective references 224, 244 for the
purpose of assembly in the turbine casing 40.
The ring 20 is preferably in the form of a single-
20 piece annulus and it presents an opening or window 21
through which the attachment tabs 162, 164 of the vanes
12 can be inserted. The width of the window 21 is thus
equal to or slightly greater than the dimension of the
attachment tabs 162, 164 in the circumferential
25 direction. In the example shown, the window 21 is formed
by a gap extending between a first end 212 situated
substantially at the connection between the middle
portion 222 and the hook 224, and a second end 214
situated substantially at the connection between the web
30 26 and the middle portion 242. The way the vanes 12 are
assembled together by the ring 20 is described below with
reference to Figures 4 to 11.
A first step consists in inserting locking means in
the ring 20 for use, after the last vane 12 has been put
35 into place in the insertion window 21, to hold that vane
in position.
In the example shown, the locking means comprise two
latches 26,, 26, as shown in Figure 4. The latches 26,,
26, are made of a metal material that is similar and
preferably identical to the material of the ring 20.
5 The latches 26,, 26, present respective similar latch
bodies 262,, 262, in the form of annular sectors. In the
vicinity of one of its circumferential ends 263,, the
latch body 262, is extended at its tip by a locking lug
264,. In similar manner, in the vicinity of one of its
10 circumferential ends 261,, the latch body 262, is extended
at its tip by a locking lug 264,. On its opposite
circumferential faces, the latch body 262, presents
surface portions forming frustoconical bearing surfaces
266,, 268,. Likewise, on its opposite circumferential
15 faces, the latch body 262, presents surface portions
forming frustoconical bearing surfaces 266,, 268,.
The latch bodies 262,, 262, are of dimensions and
profiles that are suitable for being engaged in the ring
20 by passing through the window 21 in order to be
20 inserted in the portion of the ring 20 that is situated
between the web 26 and the middle portions of the flanges
22, 24, and so as to be capable of taking up a position
in which the frustoconical bearing surfaces 266, and 266,
are in contact with the frustoconical bearing surface
25 222af the frustoconical bearing surfaces 268, and 268, are
in contact with the frustoconical bearing surface 242af
and the locking lugs 264,, 264, bear against the outer
face of the upstream hook 224. Figure 5 shows the latch
26, engaged in the window 21 of the ring 20. Figure 6
30 shows the latches 26,, 26, put into place in the ring 20
on either side of the window 21, their end faces 263,,
261, associated with the locking lugs 264,, 264, facing
each other.
The following step of constructing the nozzle
35 consists in engaging the vanes 12 in succession in the
ring 20. As shown in section in Figures 7 and 8, each
vane 12 is engaged by inserting the upstream hooking tab
162 into the window 21 and then titling so as to cause
the vane to slide along the ring 20. The shapes of the
outer platforms 16 of the vanes 12 and of the ring 20 are
arranged so that putting a vane 12 in position causes the
5 frustoconical bearing surfaces 162b and 222b to press
mutually against each other, and also causes the
frustoconical bearing surfaces 164b and 242b to press
mutually against each other, while the stiffener rib 166
comes into abutment against the rib 26 of the ring 20
10 (Figure 1). The frustoconical bearing surfaces 222b and
242b of the ring 20 contribute to holding the vane 12
radially and axially. The rib 166 and the web of the
ring 20 advantageously present substantially plane
contact surfaces, with the radial bearing of the rib 166
15 against the web 26 opposing tilting of the vane 12.
In order to assemble the last vane 12 in the
insertion window 21, this vane is provided with a capsule
19 for reconstructing the ring 20 in the portion
corresponding to the window 21 (Figure 9). The capsule
20 19 is made of metal material, preferably material
identical to that of the ring 20.
After the last vane has been put into place, the
latches 26, and 26, are moved towards each other as shown
in Figure 10. The locking lugs 264,, 264, are then close
25 to each other at the window 21, thereby preventing the
latches from tilting, such that the last vane is blocked
in its position, as shown in section in Figure 11.
The nozzle as constituted in this way is put into
place in the turbine casing by means of the hooks 224,
30 244 in a manner similar to a conventional metal nozzle.
The function of the ring 20 is not only to enable
the vanes 12 to be mounted and assembled together but
also to limit outward leakage from the passage 50 in the
nozzle, with no particular sealing means being provided
35 in this example between the touching outer platforms of
adjacent vanes 12.
Upstream from the nozzle 10, the sectors of the ring
42 supporting the abradable material 41 may be held by
overhangs 168 formed at the upstream ends of the outer
platforms 16 of the vanes 12. Nevertheless, it is
preferable for the sectors of the ring 42 to be held by
an annular ring 60 (Figure I), e.g. made in the form of
sheet metal. The ring 60 may be made of a metal that is
similar or identical to that of the ring 20.
The ring 60 is preferably in the form of a complete
annulus. In the example shown, it presents a portion 62
of channel-section for attaching to the turbine casing.
The portion 62 is extended inwards by a portion 64 of
substantially C-shaped channel section forming a hook for
holding the sectors of the ring 42, it being understood
that both of the portions 62 and 64 are open upstream.
On its downstream side, the ring 60 bears axially
against the upstream faces of the upstream attachment
tabs 162 of the vanes 12 via the web of the channelsection
portion 62 and/or via the portion 64. The
overhangs 168 can hold the portion 64 radially by bearing
thereon.
In addition to supporting the sectors of the ring
42, the ring 60 contributes to improving sealing on the
outside of the passage 50.
An additional improvement in sealing can be achieved
by placing sealing wafers 170 on the outside faces of the
outer platforms 16 of the vanes 12, as shown in
Figure 12. By way of example, the wafers 170 are in the
form of pieces of metal sheet of channel-section with
flanges bearing against the inside portions of the
attachment tabs 162, 164. The wafers 170 are made of a
metal material similar and preferably identical to that
of the ring 20. Each wafer covers the junction between
two outer platforms 16, e.g. extending between the
stiffener ribs 166 of two adjacent vanes. The wafers 170
are put into place progressively as the vanes 12 are
being assembled.
11
It should be observed that the facts of making the
ring 20 out of metal sheet so that it has a certain
capacity for deformation, and of the mutual bearing
between the ring 20 and the vanes 12 taking place via
surfaces that are frustoconical make it possible to
accommodate differential expansion between the CMC
material of the vanes 12 and the metal material of the
ring 20, particularly since the bearing surfaces are
situated on the outside of the platforms 16, and are thus
not directly exposed to the stream flowing in the passage
50.
The description above relates to making a turbine
nozzle using single-airfoil vanes. Naturally, the
invention can also be implemented with vanes having more
than one airfoil extending between a single inner
platform and a single outer platform, e.g. vanes having
two airfoils or three airfoils.
In addition, it is possible to envisage making the
assembly ring 20 out of a plurality of sectors, e.g. two,
three, or four sectors, each sector covering a plurality
of adjacent vanes. It is then possible to simplify
assembling vanes in the ring sectors since there is no
need for an insertion window, a closure capsule, or
locking latches, with the complete nozzle being assembled
on being mounted in the turbine casing. Sealing wafers
are then advantageously arranged between adjacent metal
ring sectors. In similar manner, the ring 60, if any,
may also be made using a plurality of sectors.
Although the description relates to a ring having a
section that is substantially R-shaped, other shapes
could be envisaged, providing the ring presents
frustoconical portions enabling the vanes to be held
radially and axially and portions enabling the ring to be
attached to the turbine casing.
The above detailed description relates to a turbine
engine stator wheel forming a turbine nozzle. The
invention is equally applicable to a turbine engine
stator wheel forming a compressor diffuser. The
compressor diffuser then comprises a plurality of vanes,
each having an inner platform, an outer platform
presenting attachment tabs on the outside, and at least
5 one airfoil extending between the inner and outer
platforms, the vane with the outer platform and the
attachment tabs forming a single piece of composite
material. The compressor diffuser vanes are assembled
together and supported by means of a metal assembly ring
10 that extends continuously along the outer platforms of a
plurality of adjacent vanes and that forms a distinct
assembly part between the vanes and a compressor casing,
the vanes being assembled together by means of a metal
ring in the manner described above for a stator wheel
15 forming a turbine nozzle.
In the upstream stage(s) of the compressor where the
temperatures encountered in service are the lowest in the
compressor, the composite material of the compressor
diffuser vanes may be an organic matrix composite (OMC)
20 material having reinforcing fibers, e.g. carbon, glass,
aramid, or ceramic fibers densified by a polymer matrix,
e.g. an epoxy, bismaleimide, or polyimide matrix. In the
downstream stage(s) of the compressor, the composite
material of the compressor diffuser vanes may be a CMC
25 material.

CLAIMS
1. A turbine engine stator wheel comprising:
a plurality of vanes each comprising an inner
platform, an outer platform presenting attachment tabs on
the outside, and at least one airfoil extending between
the inner and outer platforms, the vane and the outer
platform together with the attachment tab forming a
single piece of composite material; and
a metal assembly ring in which the attachment tabs
of the vanes are engaged, the metal ring supporting all
of the vanes, extending continuously along the outer
platforms of a plurality of adjacent vanes, and forming a
distinct assembly part between the vanes and a casing.
2. A stator wheel according to claim 1, wherein the metal
ring is made of sheet metal.
3. A stator wheel according to claim 1 or claim 2,
wherein the metal ring presents frustoconical bearing
surfaces contributing to holding the vanes radially and
axially.
4. A stator wheel according to any one of claims 1 to 3,
wherein the metal ring has a section that is
substantially R-shaped and outwardly open, having a web
portion and flanges terminating in end portions forming
hooks for attaching to a casing, and frustoconical
bearing surfaces in contact with the attachment tabs of
the vanes are situated on the outside faces of the
flanges of the ring.
5. A stator wheel according to any one of claims 1 to 4
wherein the outer platform of each vane presents a rib
projecting outwards and coming into radial abutment
against a surface portion of the metal ring.
I 6. A stator wheel according to any one of claims 1 to 5,
I wherein the metal ring comprises a single piece and
presents a vane insertion window.
5 7. A stator wheel according to claim 6, further including
at least one latch for blocking in position a vane
mounted at the level of the insertion window.
8. A stator wheel according to any one of claims 1 to 7 ,
1Q wherein sealing wafers are arranged on the outer faces of
the outer p.l- atforms of the vanes, each wafer covering at
least part of a junction between the outer platforms of
two adj acent vanes.
15 9. A turbine engine turbine including at least one stator . wheel forming a turbine nozzle according to any one of
claims 1 to 8, wherein the composite material is a
ceramic matrix composite material.
I
20 10. A turbine engine compres'sor including at least one
stator wheel forming a compressor diffuser according to
any one of claims 1 to 8, wherein the composite material
is a composite material having a matrix that is ceramic
or organic.
25
- . 11: A turbine or a compressor according to claim 9 or
claim 10, having a rotor wheel adjacent to the nozzle or
diffuser and comprising blades' provided at their ends
with wipers facing an abradable material supported by a
30 ring, wherein an additional metal ring is mounted between
the abradable support ring and the outer platforms of the
vanes of the nozzle or the diffuser, bearing
thereagainst.
- - -- . -. - - -- - - - - - - - -
Dated this 2nd day of January, 2014 1 B H A SRIVASTAVA]
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]