U.S. patent application number 13/511266 was filed with the patent office on 2012-09-20 for turbine stage in a turbine engine.
This patent application is currently assigned to SNECMA. Invention is credited to Emmanuel Berche, Vincent Philippot.
Application Number | 20120237342 13/511266 |
Document ID | / |
Family ID | 42331016 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120237342 |
Kind Code |
A1 |
Berche; Emmanuel ; et
al. |
September 20, 2012 |
TURBINE STAGE IN A TURBINE ENGINE
Abstract
A turbine stage for a turbine engine includes a bladed wheel
rotatable inside a sectorized ring of composite material carried by
a casing. Each ring sector has a downstream circumferential rim
held to bear radially against an annular tab that is engaged
radially in an annular groove of the downstream circumferential rim
of the ring with axial clearance, when cold, that is designed to be
reduced to zero in operation when hot, and to enable the annular
tab of the casing to be clamped axially in leaktight manner in the
annular groove of the ring sector.
Inventors: |
Berche; Emmanuel; (Moissy
Cramayel Cedex, FR) ; Philippot; Vincent; (Moissy
Cramayel Cedex, FR) |
Assignee: |
SNECMA
Paris
FR
|
Family ID: |
42331016 |
Appl. No.: |
13/511266 |
Filed: |
December 14, 2010 |
PCT Filed: |
December 14, 2010 |
PCT NO: |
PCT/FR2010/052721 |
371 Date: |
May 22, 2012 |
Current U.S.
Class: |
415/174.1 |
Current CPC
Class: |
F05D 2230/642 20130101;
F05D 2240/55 20130101; F01D 11/005 20130101; F05D 2300/603
20130101; Y02T 50/672 20130101; Y02T 50/60 20130101; F01D 11/08
20130101; F05D 2300/10 20130101; F01D 25/246 20130101; F05D 2240/11
20130101 |
Class at
Publication: |
415/174.1 |
International
Class: |
F01D 11/00 20060101
F01D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2009 |
FR |
09/06162 |
Claims
1-6. (canceled)
7. A turbine stage for a turbine engine, the stage comprising: a
bladed wheel rotatable inside a sectorized ring made of composite
material and carried by a casing, each ring sector having a
downstream circumferential rim held to bear radially against an
annular tab of the casing by a C-section fastener, wherein the
annular tab of the casing is engaged radially in an annular groove
in the downstream circumferential rim of the ring with axial
clearance, when cold, that is designed to be reduced to zero in
operation, when hot, and to enable leaktight axial clamping of the
annular tab of the casing in the annular groove of the ring
sector.
8. The turbine stage according to claim 7, wherein the annular tab
of the casing has upstream and downstream radial faces for bearing
when hot against radial flanks of the groove.
9. The turbine stage according to claim 7, wherein the axial
clearance when cold is of the order of one-tenth of a
millimeter.
10. The turbine stage according to claim 7, wherein an annular
sealing ring is housed in an annular groove in the face of the
annular tab that is pressed against the bottom wall of the annular
groove in the ring sector.
11. The turbine stage according to claim 7, wherein the composite
material is of the ceramic matrix type and the casing is made of a
metal material.
12. A turbine engine such as an airplane turboprop or turbojet,
wherein the engine includes the turbine stage according to claim 7.
Description
[0001] The present invention relates to a turbine stage in a
turbine engine such as a turboprop or a turbojet.
[0002] A turbine engine essentially comprises, going from upstream
to downstream: a compressor, a combustion chamber, and a turbine,
the compressor feeds the combustion chamber with air under
pressure, and the turbine receives the hot gas coming from the
combustion chamber in order to extract energy therefrom.
[0003] Conventionally, a low pressure turbine stage comprises a
nozzle constituted by an annular row of stationary vanes extending
radially between two annular platforms, namely an inner platform
and an outer platform, and a rotor wheel mounted downstream from
the nozzle inside a sectorized ring carried by a casing surrounding
the turbine stage.
[0004] Each ring sector carries a sealing lining on an inside face
that co-operates with the outer peripheries of the blades of the
rotor wheel, and it includes on an outside face means for fastening
to the casing, which means are formed by upstream and downstream
circumferential rims. The upstream circumferential rim is engaged
axially in an annular groove carried by an upstream annular tab of
the casing, and the downstream circumferential rim is clamped
radially against a downstream annular tab of the casing by a
C-section fastener member engaged axially from downstream onto the
downstream circumferential rim and the downstream annular tab.
[0005] An annular cavity is defined between the ring and the casing
and it extends from upstream to downstream between annular tabs of
the casing. The upstream annular tab includes orifices feeding the
cavity with air taken from a compression stage of the turbine
engine.
[0006] Introducing cooling air into a cavity in register with the
turbine ring serves to avoid greatly enlarging the clearance at the
tips of the blades, i.e. between the radially outer ends of the
blades and the sealing lining, in order to minimize the amount of
air that passes under pressure outside the zone that is swept by
the blades, thereby avoiding penalizing the performance of the
turbine.
[0007] It is known to make ring sectors out of ceramic matrix
composite material in order to take advantage of the good
mechanical properties of such material at high temperatures, even
though the casing is itself generally made of a metal material. The
ring is therefore more rigid than the casing and it possesses a
coefficient of thermal expansion that is smaller than that of the
metal casing, thus leading to differences of expansion between the
ring and the casing.
[0008] In patent application FR 09/51446, the Applicant proposes
blocking the ring axially against the downstream annular tab by
radially engaging complementary shapes provided on the ring and on
the annular tab, an annular sealing ring being mounted in an
annular groove in a face of the annular tab facing the downstream
circumferential rim of the ring and pressed against said rim.
[0009] Nevertheless, in operation, each ring sector expands and
deforms, taking up a curved shape that is concave in the
circumferential direction, with its concave side facing outwards
(negative camber phenomenon). Thus, radial spaces are observed to
form between the downstream annular tab of the casing and the
downstream circumferential rims of the ring sectors.
[0010] These radial spaces are such that the annular sealing ring
becomes incapable of providing sealing between the downstream
circumferential rim and the annular tab of the casing, so leaks of
cooling air occur between the downstream circumferential rims of
the ring sectors and the downstream annular tab of the casing.
[0011] In other embodiments where the ring is not made of composite
material, the downstream fastening between the downstream
circumferential rim of the ring and the downstream annular tab of
the casing is sealed by axially prestressing the downstream annular
tab against a radial face of the downstream circumferential rim
that is opposite to the fastener member.
[0012] Nevertheless, such assembly with axial prestress when cold
cannot be envisaged when the ring is made of composite material
because of its high stiffness and its small thermal expansion.
[0013] A particular object of the invention is to provide a
solution to these problems that is simple, inexpensive, and
effective, and that makes it possible to avoid the drawbacks of the
prior art.
[0014] To this end, the invention provides a turbine stage for a
turbine engine, the stage comprising a bladed wheel rotatable
inside a sectorized ring made of composite material and carried by
a casing, each ring sector having a downstream circumferential rim
held to bear radially against an annular tab of the casing by a
C-shaped fastener, the stage being characterized in that the
annular tab of the casing is engaged radially in an annular groove
in the downstream circumferential rim of the ring with axial
clearance, when cold, that is designed to be reduced to zero in
operation, when hot, and to enable leaktight axial clamping of the
annular tab of the casing in the annular groove of the ring
sector.
[0015] According to the invention, the downstream circumferential
rim of the ring is sealed in operation by axial clamping of the
upstream and downstream ends of the downstream annular tab of the
casing in the annular groove as a result of the greater expansion
of the casing compared with the composite ring. The concave
curvature of the ring and of its downstream circumferential rim is
thus compensated by the axial clamping of the annular tab, thereby
guaranteeing sealing of the downstream fastening of the ring.
[0016] Advantageously, the annular tab of the casing has upstream
and downstream radial faces for bearing when hot against radial
flanks of the groove. In operation, the radial faces of the annular
tab and the radial flanks of the groove conserve their radial
shape, thereby ensuring annular contact between the radial faces of
the ring and the radial flanks of the groove.
[0017] According to another characteristic of the invention, the
above-mentioned axial clearance when cold is of the order of
one-tenth of a millimeter.
[0018] It is also possible to provide an annular sealing ring
housed in an annular groove in the face of the annular tab that is
pressed against the bottom wall of the annular groove of the ring
sector.
[0019] Advantageously, the composite material is of the ceramic
matrix type and the casing is made of a metal material.
[0020] The invention also provides a turbine engine such as an
airplane turboprop or turbojet, the engine including a high
pressure turbine stage of the above-described type.
[0021] The invention can be better understood and other details,
advantages, and characteristics of the invention appear on reading
the following description made by way of non-limiting example and
with reference to the accompanying drawings, in which:
[0022] FIG. 1 is a fragmentary diagrammatic view in axial section
of a prior art turbine stage;
[0023] FIG. 2 is a diagrammatic view in cross-section on section
plane A-A shown in FIG. 1;
[0024] FIG. 3 is a fragmentary diagrammatic view in axial section
of a turbine stage of the invention while cold, the section plane
not passing through a fastener member; and
[0025] FIG. 4 is a fragmentary diagrammatic view in axial section
of a turbine stage of the invention while hot, on a section plane
that contains a fastener member.
[0026] Reference is made initially to FIG. 1 which shows a portion
of a turbine stage 10 in a turbine engine that includes a nozzle
stage having a plurality of stationary vanes arranged upstream from
a rotary wheel carrying a plurality of blades and rotatable inside
a ring 12 carried by an outer casing 14.
[0027] The ring 12 is made up of a plurality of substantially
cylindrical ring sectors that are circularly juxtaposed, end to
end. Each ring sector comprises a cylindrical portion 16 carrying
on its inside face a sealing lining 18 of abradable material that
cooperates with the outer peripheries of the blades of the rotor
wheel. Each ring sector includes two annular tabs, namely an
upstream tab 18 and a downstream tab 20 for attaching to the casing
14. The outer end of the upstream annular tab 18 has a
circumferential rim 22 extending upstream and engaged axially in an
annular groove 24 facing downstream and formed in a radial annular
tab 26 of the casing. The outer end of the downstream annular tab
20 of the ring has a circumferential rim 28 facing downstream and
clamped radially against a cylindrical portion 30 of an annular tab
32 of the casing 14 by means of a C-section fastener member 32
engaged axially on the downstream circumferential rim 28 and on the
cylindrical portion 30 of the downstream annular tab 32 of the
casing 14.
[0028] Each downstream circumferential rim 20 of a ring sector
includes at least one notch in radial alignment with a notch in the
cylindrical portion 30 of the downstream annular tab 32 of the
casing 14 and of width that is sufficient to enable the fastener
member 32 to be engaged axially therein and to enable the ring 12
to be fastened on the casing 14.
[0029] An annular cavity 34 is defined between the sectorized ring
12 and the casing 14 being defined upstream by the upstream annular
tabs 18, 26 of the ring 12 and of the casing 14, respectively, and
downstream by the downstream annular tabs 20, 32 of the ring 12 and
of the casing 14, respectively.
[0030] The upstream annular tab 26 of the casing 14 has orifices 36
for passing cooling air coming from a space surrounding the
combustion chamber, i.e. air that flows between the outer casing of
the combustion chamber and the outer wall of the combustion
chamber, which wall forms a body of revolution. In order to avoid
cooling air leaking between the cylindrical portion 30 of the
downstream annular tab 32 of the casing 14 and the downstream
circumferential rim 20 of the ring 12, an annular sealing ring 38
is mounted in an annular groove 40 of the inside face of the
cylindrical portion 30. This sealing ring 38 is compressed radially
in the annular groove 40 and against the downstream circumferential
rim 28 of the ring 12. The inside face of the cylindrical portion
30 includes a rib 42 engaged radially in an annular recess in the
downstream circumferential rim 28 of the ring 12 in order to
prevent the ring 12 from moving axially relative to the casing
14.
[0031] The radial face at each circumferential end of each ring
sector includes three slots 44, 46, 48, each of which houses a
sealing strip. A first slot 44 is formed in the cylindrical portion
16 of the ring 12 and extends over substantially the entire length
of the ring 12, being parallel to the longitudinal axis of the ring
12. The other two slots 46 and 48 are oblique, each being formed in
a respective one of the upstream and downstream annular tabs 18 and
20 of the ring. The radially inner ends of the two oblique slots 46
and 48 open out into a middle portion of the longitudinal slot 44,
and their radial ends open out into the outside faces of the
upstream and downstream circumferential rims 22 and 28
respectively. Each sealing strip is inserted half in a slot 44, 46,
48 of one sector with the other half in a corresponding facing slot
that is formed in a radial face of an adjacent ring sector.
[0032] Nevertheless, as explained above, each sector of the
composite ring deforms under the effect of temperature and adopts a
concave curved shape with its concave side facing outwards (FIG.
2). The casing 14 is also subjected to deformation and has
circumferential undulations. As a result, because of the
differential expansions between the ring 12 made of composite
material and the casing 14, a radial space R forms between each
circumferential rim 28 and the cylindrical portion 30 of a
downstream tab 32 of the casing 14, thereby leading to leaks of
ventilation air from the annular cavity 34 towards the gas flow
passage through the turbine.
[0033] The invention serves to remedy this problem and those
mentioned above by forming an annular groove 50 in the outside
cylindrical face of the downstream circumferential rim 52 of the
ring 54, which groove receives radially the downstream cylindrical
portion 55 of the downstream annular tab 56 of the casing 14 with
axial clearance j, when cold, that is designed to be reduced to
zero in operation as a result of the greater expansion of the
casing 14 and of its downstream annular tab 56 compared with the
expansion of the ring 54 made of composite material (FIG. 3).
[0034] The annular groove 50 has two radial annular flanks, an
upstream flank 58 and a downstream flank 60. The downstream
cylindrical portion 55 of the downstream annular tab 56 of the
casing 14 has two radial faces, an upstream face 62 and a
downstream face 64. When hot, in operation, the radial faces 62 and
64 of the downstream annular tab 56 of the casing 14 come to bear
against the radial flanks 58 and 60 of the groove 50 as a result of
the differential expansion between the composite ring 54 and the
casing 14, thereby ensuring that the annular tab 56 is clamped
axially in the groove 50 and establishes sealing against the
ventilation air flowing in the cavity 34. This axial clamping also
serves to hold the ring 54 axially relative to the casing 14.
[0035] The depth of the groove 50 is selected in such a manner as
to be greater than the maximum radial difference R in operation
between the inside face 66 of the downstream cylindrical portion 55
of the downstream tab 56 of the casing 14 and the bottom wall 68 of
the groove 50, so as to ensure continuous leakproof axial clamping
when hot and so as to avoid any axial separation of the ring 54
relative to the casing 14.
[0036] A ring sector is assembled by inserting the upstream
circumferential rim 22 of the ring 54 in the annular groove of the
upstream tab 18 of the casing 14, and then tilting the downstream
end of the ring outwards so that the cylindrical portion 55 bears
against the bottom wall of the groove 50. The axial clearance j,
when cold, serves to make it easier to tilt the ring 54 outwards
against the casing 14.
[0037] An annular sealing ring 38 is housed in an annular groove 40
of the face 66 of the downstream annular tab 56 of the casing that
presses against the bottom wall 68 of the groove 50.
[0038] In a manner similar to the prior art, each downstream
circumferential rim 52 of a ring sector includes a notch in radial
alignment with a notch in the cylindrical portion of the downstream
annular tab of the casing to enable the C-section fastener member
32 to be mounted axially.
[0039] The inter-sector sealing means are similar to those of the
prior art. Nevertheless, it should be observed that in the
invention the sloping slot in the downstream annular tab 64 of the
ring 54 opens out into the groove 50 in register with the sealing
ring 38.
[0040] In one particular embodiment of the invention, the axial
clearance, when cold, is of the order of 0.1 millimeters.
[0041] The ring 54 may be made of a ceramic matrix composite
material that withstands well the high temperatures of the kind
that exist in a high pressure turbine, and the casing 14 is made of
a metal material such as Inco or steel.
* * * * *