DEVICE FOR COOLING A TDRBOMACHIKE TURBINE CASING
Background of the invention and description of the
prior art
The present invention relates to a device for cooling a
turbine casing of a turboinachine, particularly an
aviation turbojet engine or turboprop.
A turbine of this type comprises several stages each
including a distributor formed of an annular row of
fixed vanes borne by the casing of the turbine and an
impeller mounted to rotate downstream of the nozzle
assembly in a cylindrical shroud formed by ring sectors
fixeo circumferentially on casing hooks of the turbine
via C-shaped or D-shaped fasteners,
The vanes of the first-stage or upstream-stage nozzle
assemoly are exposed to high temperatures and comprise
internal cavities for the flow of cooling air bled off
upstreair from the turbomachine compressor and carried
by ducts to a volume formed in the casing around the
turbine upstream nozzle assembly. Cylindrical
ccnnecting tubes are mounted in the volume and each
connect the volume to an internal cavity of a vane of
the upstream nozzle assembly. The cooling air leaves
this cavity at the radially internal end of the vane,
the trailing edge of which may also comprise orifices
opening into the cavity sc that the cooling air can
leave.
The hooks that secure the ring sectors, and especially
these located directly downstream of the vanes of the
upstrearn-stage nozzle assembly are shielded fronv the
heat by an annular sealing plate which is mounted
between the ring sectors and the external ends of the
vanes o± the nozzle assembly in order to restrict the
passage of gas from the airstreain radially outward into
an annular space that houses the casing hooks.
However, sealing is imperfect and leaks of hot gases
from the turbine airstreain may cause the temperature of
the casing hooks to rise and cause cracking or
fissuring liable to destroy the hooks.
Furthermore, it would not be possible to fit the
turbine with an additional cooling circuit leading cool
air bled off upstream of the coinbust.ion chamber onto
these suspension hooks because of the complexity,
limitation on space and costs involved.
of the Invention
It is a particular object of the invention to respond
to this problem simply, effectively and economically.
To this end, the invention proposes a device for
ccoling a tarbine casing in a turbomachine particularly
in an aviation turbojet engine or turboprop, this
turbine comprising several stages each including a
nozzle assembly ferried of an annular row of fixed vanes
borne by the casing of the turbine and an impeller
mounted to rotate inside the casing in a cylindrical
shroud formed of ring sectors fixed circumferentially
to the casing, and a cooling circuit for cooling the
vanes of the nozzle assembly of the upstream stage,
comprising ducts for carrying cooling air into cavities
formed in the vanes of the nozzle assembly, and means
of carrying air to casing upstream hooks for suspending
the ring sectors surrounding the impeller of the
upstream stage, these air-carrying means connecting the
internal cavities of the vanes of the nozzle assembly
of the upstream stage to the annular space in which the
upstream hooks lie, wherein: the internal cavities of
the vanes are closed, at their radially external ends,
by plates attached to the nozzle assembly; and the
air-carrying means comprise drillings fornned in these
plates and drillings formed in an external annular rim
of the nozzle asseinbly which extends radially between
the radially external walls of the vane cooling
cav.ties and the upstream hooks for suspending the ring
sectors.
The air bled from the cavities of the vanes of the
casing upstream stage nozzle asseinbly is carried into
the annular space housing the casing upstream hooks and
allows their temperature to be brought down, something
which results in an appreciable reduction in the risk
of cracking or fissuring of the hooks without the need
to add ducts carrying cool air to the turbine casing.
This air also makes it possible to keep the annular
space in which the hooks are housed at a pressure
higher than that of the combustion gases passing
through the turbine, and this itself opposes the
ingress of these gases into the annalar apace housing
the hooks,
The airflow bled off for cooling the upstream, hooks
represents a small fraction of the total airflow used
for cooling the vanes of the nozzle assembly, and so
has very little influence on the cooling of the vanes
of the nozzle asseinbly of the upstream stage and on the
output of the turbomachine.
According to another characteristic of the invention,
the means for carrying air to the upstream casing hooks
are distributed over the periphery of the nozzle
assembly and are formed in each fixed vane.
The means of carrying air comprise drillings formed in
the plates attached to the radially external ends of
the vanes for hermetically closing off the vane cooling
cavities of the nozzle asseinbly of the upstream stage,
and drillings formed in the external annular rim of the
nozzle assembly which extends radially between the
radially external walls of the vane cooling cavities
and the upstream hooks for suspending the ring sectors.
The drillings may be formed by electro-discharge
machining and have a diameter of between about 0.1 and
5 nun.
In one embodiment of the invention, the drillings
formed in the external annular rim of the nozzle
assembly extend obliquely with respect to this rim and
with respect to the axis of rotation.
These drillings may at their downstream ends open
directly into the annular space in which the casing
upstream hooks lie.
As an alternative, the drillings are formed at the
internal periphery of the external annular rim and at
their downstream ends open into an annular passage
formed between the external annular rim of the nozzle
assembly and an annular deflector attached and fixed to
a downstream end part of the nozzle assembly.
The crillings may in this case be formed in the
external rim of the nozzle assembly in the immediate
vicinity of an external wall of revolution of the
noz2.1e assenbly, thus making it possible to avoid
creating a thermal gradient in the external rim of the
nozzle assembly as such a gradient would result in
differential thermal expansion of this rim across its
radial spread and in significant stresses in the vanes
of the nozzle assembly,
The annular deflector is for example engaged and fixed
in an external annular groove of the nozzle assembly
and bears axial ly on the upstream ends of the ring
sectors in order to limit the passage of gas from the
turbine airstream radially outward into the annular
passage that houses the casing hooks.
The annular deflector is advantageously split into
sectors and made up of several parts assembled end to
end via sealing strips.
In yet another alternative, the drillings formed in the
external annular rim of the nozzle assembly are more or
less perpendicular to this rim and are supplied wiuh
coo],ing air via slots formed in regions where this rim
catches on the casing of the turbine.
The present invention also relates to a turbine for a
uurbcmachine such as an aviation turbojet engine or
turboprop and which comprises a cooling device as
described hereinabove.
The present invention also relates to a turbomachine
turbine upstream nozzle assembly comprising an annular
row of vanes which are connected at their radially
internal ends to an internal wall of revolution and at
-heir radially external ends to an external wall of
revolution, the vanes comprising internal cavities for
the flow of cooling air and the external wall
comprising an external annular rim at its downstream
end whJ ch rim is formed with means for catching on a
casing of the turbomachine, wherein: the internal
cavities of the vanes are closed, at their radially
external ends, by plates attached co the external wall
of the nozzle assembly; and these plates and the
annular rim of the nozzle assembly comprise drillings
for the passage of cooling air.
The drillings may be formed at the internal periphery
of the annular rim. They may also be formed, obliquely
or perpendicularly with respect to the annular rim.
An annular deflector may also be fixed to the external
wall of revolution of the nozzle assembly downstream, of
i'cs annular rim.
Brief description of the drawings
The invention will be better understood and other
characteristics, details and advantages thereof will
become more clearly apparent ' from reading the
description which follows, given by way of nonlimiting
example with reference to the attached drawings in
figure 1 is a schematic part-view in axial section
of a turbomachine equipped with the device according to
the invention;
figure 2 is a view on a larger scale of part of
figure 1 and depicts the nozzle assembly of the
upstream stage of the turbine;
figure 2a is an enlarged view of detail I2 of
figure 2;
figure 3 is a schematic part-view in perspective
of thu nozzle assembly of the upstream stage of the
turbine, viewed in side view and from the upstream end;
figure 4 is a view corresponding to figure 2 and
depicts an alternative form of embodiment of the device
according to the invention;
figure 4a is an enlarged view of detail IA of
figure 4;
figure 5 is a schematic part-view in axial section
of another alternative form cf embodiment of the device
according to the invention;
figures 6 and 7 are schematic part-views in
perspective of the external annular rim of the nozzle
assembly of figure 5.
Description of the preferred embodiments
In figure 1, the reference 10 denotes a turbine of a
turbomachine consisting of a high-pressure module 12
arranged at the outlet of a combustion chamber 14 and
of a low-pressure module 16 situated downstream of the
high-pressure module 12 and comprising four stages each
including a nozzle assembly 18 formed of an annular row
of fixed vanes 12 borne by an external casing 22 of the
turbine and an impeller 24 downstream of the nozzle
assembly 18.
The impellers 24 comprise disks 26 assembled ax^ally
with one another by annular flanges 28 and bearing
radial vanes 30, The impellers 24 are connected to a
turbine shaft (not depicted) by means of a drive cone
32 fixed to annular flanges 28 of the disks 26.
Each -impeller 24 is surrounded externally, with a small
clearance, by a cylindrical shroud formed of ring
sectors 34 fixed circumferentially to the casing 22 of
the; turbine by means of C-shaped or U-shaped locking
pieces as will be described in greater detail
hereinafter.
The nozzle assemblies 18 comprise internal and external
walls cf revolution 36 and 38, respectively, which
between there delimit the air stream for the flow of the
gases through the turbine and between which the vanes
20 extend radially.
The external wall 38 of the no?.zle assembly 18 of the
upstream stage best visible in figure 2 comprises
upstream 40 and downstream 42 radially external annular
rims including axial annular lugs 44 directed in the
upstream direction and intended to be engaged in
corresponding axial annular grooves 45 in the casing 22
of the turbine.
The vanes 20 of this nozzle assembly 18 comprise
internal cavities 46 for the circulation of cooling air
originating from a supply volume 48 (as depicted by the
arrows 43 i radially external to the wall 38 of the
nozzle assembly, this air being partially removed in
the airflow of gases of the turbine through orifices 50
formed near the trailing edge of the vanes 20 and
opening into their internal cavities 46 (arrows 51) and
partially removed into a volume 52 radially internal to
the wall 36 of the nozzle assembly (arrows 53} . The
~oo3irig air is bled off upstream from a compressor of
the turbomachine and carried to the supply volume by
ducts which have not been depicted.
The vane cavities 46 are connected to the external 48
and _nternal 52 volumes by cylindrical tubes 54 and 55
respectively. Each tube 54 for the passage of air
between the external volume 48 and the cavity 46 of a
vane has one end engaged airtightly in a bushing 56
fixed into an orifice formed in the wall 38 of the
nozzle assembly between the external annular rims 40,
42 and opening into the internal cavity 46 of a vane.
The other of its ends is engaged airtightly in a
bushing 57 fixed in an orifice formed in the casing 22
cf the turbine. The tubes 55 for the passage of air
between the cavities 46 of the vanes and the internal
volume 52 have their ends engaged airtightly in
orifices 58, 59 in the wall 36 of the nozzle assembly
and of an annular rim of a casing 60 of the volume 52,
respectively.
The cavity 46 of each vane of the nozzle assembly 18
comprises an opening formed in the external wall 38 of
the nozzle assembly near the orifice in which the
bushing 56 is fixed. A plate 64 is attached and fixed
to the wall 38 as can be seen in figure 3 in order to
hermetically close off the vane cavity 46.
The ring sectors 34 situated directly downstream of the
nozzle assembly 18 of the upstream stage (figures 2 and
2a) each comprise, at their upstream ends, a
circumferential hook 70 in the form of a portion of a
cylinder which is pressed against a corresponding
circumferential hook 72 in the form of a portion of a
cylinder belonging to the casing 22 and is held in
place by a C-shaped or U-shaped fastener 74 engaged via
the upstream side over the circumferential hooks 70 and
72.
The fasteners 74 and the hooks 70, 72 are housed in an
annular space 76 which extends around the ring sectors
34 between the casing and the nozzle assembly 18, the
fasteners "M bearing at their upstream ends against a
downstream face of the downstream annular rim 42 of the
external wall 38 of the nozzle assembly.
Ihe fasteners 74 and the circuraferentia 1 hooks 70 and
72 ot the ring sectors 34 and of. the casing 22 are
shielded from the heat by an annular sealing sheet; 78
which is mounted between the ring sectors 34 and the
downstream face of the annular rim 42 of the nozzle
assembly in order to restrict the passage of gas from
the turbine airflow radially outward into the annular
space 76 that houses the casing hooks 72.
The casing hooks 72 are, in service, subjected to high
temperatures which may cause cracking or fissuring
liaole to destroy them.
The invention provides a simple solution to this
problem by virtue of means for carrying cooling air to
these hooks.
In a first embodiment of the invention as depicted in
figures 2 and 3, these means comprise drillings 80
forned in the plates 64 of each vane and drillings 82
formed obliquely in the downstream external rim 42 of
the external wall 38 of the nozzle assembly to connect
the internal cavities 46 of the vanes to the annular
space 76 housing the hooks 70, 72, the drillings 80 and
82 being uniformly distributed about the axis of ~he
turbine.
In the example depicted, each plate 64 comprises, more
or less in the middle, a cylindrical drilling 80
(figure 3) directed more or less: radially with respect
to the axis of the turbine and opening at one end Into
the cavity 46 of the corresponding vane and at its
other end into an annular passage 79 situated radially
outside the wall 38 of the nozzle assembly and bounded
axially by the external annular rims 40, 42 of the
nozzle assembly. As an alternative, just some of the
plates may nave drillings 80 or the plates may comprise
two drillings 80 or more. The drillings could equally
be inclined with respect ~o the axis of the turbine
and, for example, directed downstream and outward.
The drillings 82 formed in the external annular rim 42
cf the nozzle assembly 18 are oblique with respect to
the axis of the turbine and directed downstream and
outward. At their upstream end they open into the
annular passage 79 and at their downstream ends they
open onto an internal cylindrical face of the fasteners
74 fitted over the hooks 70, 72.
A small fraction of the airflow circulating through the
cavities 46 of the vanes of the nozzle assembly 16
enters the annular passage 79 through the drillings 80
in the plates 64, then enters the annular space 75
housing the hooks 70, 72 through the drillings 82 in
the annular rim 42 of the nozzle assembly as depicted
by the arrows 84. The hooks 72 are thus cooled
sufficiently to eliminate the risk of cracking or
fissur:.ng of the hooks.
This supply of air also makes it poasible to keep the
annuiar space 16 housing the hooks at a pressure higher
than that of the hot gases flowing through the turbine,
thus opposing the passage of these gases between the
ring sectors 34 and the annular rim 42 of the nozzle
assembly 18 at the annular sealing sheet 78.
The number of drillings 80 formed in the plates 64 in
the example depicted is greater; than the number of
drillings 82 formed in the annular rim 42 of the nozzle
assembly 18. The number of drillings 80 is, for
example, about 96, and the number of drillings 82 is,
for example, about 72. :
As an alternative, the number of drillings 80 formed in
the plates 64 may be equal to or lower than the number
of drillings 82 formed in the annular rim 42 of the
nozzle assembly 18.
In the alternative form of embodiment of the invention
depicLed in figures 4 and 4a, the! drillings BO formed
:n the plates 64 of t.he nozzle assembly are identical
to those described with reference to figures 2, 2a and
3 and the annular passage 79 is connected to the
annular space 76 housing the hooks by way of axial
orillings 90 formed in the external annular rim 42 of
the nozzle assembly and of axial slots 92 formed in the
annular lugs 44 of this external rim 42. The drillings
90 and the slots 92 are uniformly distributed about the
axis of the turbine.
Tne drillings 90 formed in the external annular rim 42
of ~he nozzle assembly 18 are more or less parallel to
the axis of the turbine and perpendicular to the rim 42
and at their upstream ends open onto an upstream face
of the annular rim 42 which face lies radially on the
outside of the annular catching lug 44 and at their
downstream ends they open onto the downstream face of
the annular rim 42 ia the annular space 76 housing the
hooks 70, 72.
The slots 92 are formed in internal 94 and external 96
cylindrical surfaces of the annular lug engaged in the
annular groove 45 of the casing 22.
The slots 92 on the external cylindrical surface 96 at
their downstream ends open in the vicinity of the
upstream ends of the drillings 90 and at their upstream
ends open into the bottom of the groove 45, and the
slots on the internal cylindrical surface 94 at their
upstream ends open into the bottom of the groove 45 and
at their downstream ends open into the annular passage
79.
In the exanple depicted, each drilling 90 as associated
with two slots 92 farmed in the internal 94 and
external 96 cylindrical surfaces of the annular lug 44,
respectively, which may or may not lie in the same
radial plane as the drilling 90.
The air in the annular passage 79 originating from the
internal, cavities 46 of the vanes is carried into the
annular space 76 housing the hooks by the slots S2 on
t.ie internal then external surfaces of the annular lug
44 of the external rim 42 of the nozzle assembly, then
by the drillings 90 in the external rim 42, as depicted
by the arrows 98.
As an alternative, it is possible for the slots 92 not
to be parallel to the axis of the turbine. These slots
92 could also be formed on the cylindrical surfaces of
the groove 45 against which the cylindrical surfaces
94, 96 of t:ie annular lug 44 rest, these slots opening
into the annular passage 79 and in the vicinity of the
drillings 90 as describea previously.
In the alternative form depicted in figures 5 to 1, the
drillings 100 of the external angular rim 42 of the
nozzle assembly 18 are not formed in the central or
radially external part of the rim 42 but are formed in
the immediate vicinity of the external wall 38 of the
nozzle assembly and extend more or leas parallel to
this wall.
The drillings 100 at their upstream ends open into the
annular passage 79 and at the downstream ends open into
a second annular passage 102 running transversely with
respect, to the axis of the turbines and ccmmunicating at
its external periphery with the annular space 76 that
houses the hooks 72.
Che anr.ular passage 102 surrounds;the external wall 38
of the nozzle assembly and is axially bounded by the
rim 42 of the nozzle assembly and by a deflector 104
attached and fixed to the external wall 38 of the
nozzle assembly, downstream of the 'external rim 42.
In the example depicted, the drillings 100 at their
downstream ends open into an annular groove 106 opening
outward and formed in the external wall 38 of the
nozzle assembly, downstream of the rim 42, and also
comprising a radial wall 108 to which a radially
internal end part of che deflector 104 is pressed and
fixed by brazing or welding.
The deflector 104 is axially preloaded through the
pressing of its radially external end part against the
annular sealing sheet 78 mounted on the upstream ends
of the ring sectors 34, so as to limit the passage of
gas from the turbine airflow radially outward into the
annular space 76 housing the hooks 70, 72.
As an alternative, the deflector 104 can bare axially
directly on the downstream ends of the ring sectors 34.
Air from the first annular passage 79 enters che second
anr.ular passage 102 through the drillings 100 and is
then carried into the annular space 76 housing the
hooks as depicted by the arrows 119.
In the example depicted in figure 6 the number of
drillings 100 is greater than the number of drillings
60 formed in the plates 64 (figure 3). The number of
drillings 100 lies for example between 360 and 504.
The deflector 104 is preferably split into sectors and
formed of a plurality of parts 112 assembled end to end
by means of sealing strips.
In the example depicted in figure':*?, -he parts 112 are
associated at each of their encis I with means 114 into
which a sealing strip can fit (although this is not
depicted), each strip being engaged at one end in the
means 114 of one part 112 and at aiji opposite end in the
means 112 of an adjacent part 114.
The fasteners 74 and the hooks 70 on the ring sectors
34 may also comprise drillings 116 and 118 for the
passage of air in order to cool the hooks 72 of the
casing 22 (figure 5}.
The drillings 80, 82, 90, 10G, 116 and 118 have a
diameter ranging between about 0.1 and 5 mm and may be
formed by electro-discharge machining or by any other
appropriate technique.
The embodiment of figures 5 to 1 makes it possible to
avcid the creation of a cherroal gradient in the
external annular rim 42 of the nozzle assembly,
something which would result in differential thermal
expansion of this rim across its radial spread and in
stresses in the vanes of the nozzle assembly 18. The
high number of drillings IOC allows the temperature
over the internal periphery of the rim 42 to be evened
out and allows this temperature to be lowered
considerably.
The deflectors 104 allow the air used to cool the rim
42 to be recovered for cooling the casing hooks 72. A
slight increase in the cooling air flow rate
compensates for the fact that the air is warmed &
iittle by cooling the annular rim 42, without
detracting from engine performance.

CLAIMS
1. A device for cooling a turbine casing in a
turboraachine particularly in an aviation turbojet
engine or turboprop, this turbine comprising several
stages each including a nozzle assembly formed of ar.
annular row of fixed vanes borne by the casing of the
turbine and an impeller mounted to rotate inside the
casing in a cylindrical shroud formed of ring sectors
fixed circumferentially to the casing, and a cooling
circuit for cooling the vanes of the nozzle assembly of
the upstream stage, comprising ducts for carrying
cooling air into cavities formed in the vanes of the
nozzle assembly, and means of carrying air to casing
upstream hocks for suspending ; the ring sectors
surrounding the impeller of the upstream stage, these
air-carrying means connecting the internal cavities of
the vanes cf the nozzle assembly of the upstream stage
to the annular space in which the upstream hooks lie,
wherein: the internal cavities of the vanes are closed,
at their radially external ends, by plates attached to
the nozzle assembly; and the air-carrying means
comprise drillings formed in these plates and drillings
formed in an external annular rim of the nozzle
assembly which extends radially between the radially
external walls of the vane cooling cavities and the
upstream hooks for suspending the ring sectors.
2. The device as claimed in claim 1, wherein the
means for carrying air to the upstream casing hooks are
distributed over the periphery of the nozzle assembly
and are formed in each fixed vane.
3. The device as claimed in claim 1 or 2, wherein the
drillings are formed by electro-discharge machining.
4. The device as claimed in one of claims 1 to 3,
wherein the drillings termed in the external annular
rim of the nozzle assembly extend obliquely with
respect to this rim and with respect to the axis of
rot ation.
5. The device as claimed in claim 4, wherein the
drillings at their downstream ends open directly into
the annular space in which the upstream hooks lie.
6. The device as claimed in one of claims 1 to 4,
wherein the drillings are fonined at the internal
periphery of the external annular rim and at their
downstream ends open into an annular passage formed
between the external annular rim of the nozzle assembly
and an annular deflector attached and fixed to a
downstream end part of the nozzle assembiy.
7 . The device as claimed in claim 6, wherein the
annular deflector is engaged and fixed in an external
annular groove of the nozzle assembly and bears axially
on the upstream ends of the ring sectors,
8. The device as claimed in claim 6 or 7, wherein the
annular deflector is split into sectors and made up of
several parts assembled end to end via sealing strips.
9. The device as claimed in one of claims 1 to 3,
wherein the drillings formed in the external annular
rim of the nozzle assembly are more or less
perpendicular to this rim and are supplied with cooling
air vis sloes formed in regions where this rira catches
on the casing of rhe turbine.
10. A turbine for a turbamachane such as an aviation
turbojet, engine or turboprop and which comprises s
cooling device as claimed in one of the preceding
claims.
11. A turbcrna chine turbine upstream nozzle assembly
comprising an annular row of vanes which are connected
at their radially internal ends to an internal wall cf
revolution and at their radially! external ends ~o an
external wall of revolution, the vanes comprising
i nternal cavities for the flow of cooling air and the
external wall, comprising an external annular rim at its
downstream end which rim is formed with means for
catching on a casing of the turbomachine, wherein: the
internal cavities of the vanes are closed, at their i
radially external ends, by plates attached to the
external wall of the nozzle assembly; and these plates
and -he annular rim of the nozzle assembly comprise
drillings for the passage of cooliring air.
12. The nozzle assembly as claimed in claim 11,
wherein the drillings are forced at the internal
periphery of the annular rim.
13. The nozzle assembly as claimed in claim 11 or 12,
wherein the drillings are formed obliquely or
perpendicularly with respect to the annular rim.
14. The nozzle assembly as claimed in claim 11 or 12,
wherein an annular deflector is fixed to the external
wall of revolution downstream of the annular rim.