U.S. patent application number 10/345225 was filed with the patent office on 2003-07-24 for moving blade for a high pressure turbine, the blade having a trailing edge of improved thermal behavior.
This patent application is currently assigned to SNECMA MOTEURS. Invention is credited to Boury, Jacques, Judet, Maurice, Tabardin, Jacky.
Application Number | 20030138322 10/345225 |
Document ID | / |
Family ID | 8871382 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030138322 |
Kind Code |
A1 |
Boury, Jacques ; et
al. |
July 24, 2003 |
Moving blade for a high pressure turbine, the blade having a
trailing edge of improved thermal behavior
Abstract
A moving blade for a high pressure turbine of a turbomachine,
the blade having at least one cooling circuit comprising at least
one cavity extending radially between a tip and a base of the
blade, at least one air admission opening at a radial end of the
cavity(ies) to feed the cooling circuit(s) with cooing air, and a
plurality of slots opening out into the cavity(ies) and opening out
into the concave side of the blade between the base and the tip of
the blade in a manner that is substantially perpendicular to a
longitudinal axis of the blade, a connection zone being provided
between a slot closest to the base of the blade and a top surface
of a platform defining an inside wall for a stream of combustion
gas flowing through the high pressure turbine, and the moving blade
further comprising an additional cooling air exhaust slot opening
out into said cavity and opening out into said connection zone in
line with the trailing edge.
Inventors: |
Boury, Jacques; (Saint Ouen
en Brie, FR) ; Judet, Maurice; (Dammarie Les Lys,
FR) ; Tabardin, Jacky; (Villiers Le Bel, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SNECMA MOTEURS
PARIS
FR
|
Family ID: |
8871382 |
Appl. No.: |
10/345225 |
Filed: |
January 16, 2003 |
Current U.S.
Class: |
416/97R |
Current CPC
Class: |
F01D 5/186 20130101;
F05B 2240/801 20130101; F01D 5/187 20130101; F05D 2240/81
20130101 |
Class at
Publication: |
416/97.00R |
International
Class: |
F01D 005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2002 |
FR |
02 00802 |
Claims
What is claimed is:
1/ A moving blade for a high pressure turbine of a turbomachine,
the blade having at least one cooling circuit comprising at least
one cavity extending radially between a tip and a base of the
blade, at least one air admission opening at a radial end of the
cavity(ies) to feed the cooling circuit(s) with cooing air, and a
plurality of slots opening out into the cavity(ies) and opening out
into the concave side of the blade between the base and the tip of
the blade in a manner that is substantially perpendicular to a
longitudinal axis of the blade, a connection zone being provided
between a slot closest to the base of the blade and a top surface
of a platform defining an inside wall for a stream of combustion
gas flowing through the high pressure turbine, the blade further
comprising an additional cooling air exhaust slot opening out into
said cavity and opening out into said connection zone in line with
the trailing edge.
2/ A blade according to claim 1, wherein said additional slot
presents a shape taken from the following group of shapes: oblong;
rectangular; triangular; and an upside-down T-shape.
3/ A blade according to claim 2, wherein said additional slot
presents an outlet section which is different from the section of
its feed channel.
4/ A blade according to claim 1, wherein said additional slot is
obtained directly by casting.
5/ A blade according to claim 1, wherein a longitudinal bottom end
of the additional slot is disposed immediately above said top
surface of the platform.
6/ A high pressure turbine of a turbomachine, the turbine including
a plurality of moving blades according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the general field of moving
blades for a high pressure turbine in a turbomachine, and more
particularly it relates to slots for exhausting cooling air from
the moving blades of a high pressure turbine.
[0002] In conventional manner, a turbomachine has a combustion
chamber in which air and fuel are mixed together prior to being
burned therein. The gas that results from this combustion flows
downstream in the combustion chamber and then feeds a high pressure
turbine. The high pressure turbine has one or more rows of moving
blades that are circumferentially spaced apart all around the rotor
of the turbine. The moving blades of the high pressure turbine are
thus subjected to the very high temperatures of the combustion
gases. These temperatures reach values that are well above those
that can be withstood without damage by the blades which are in
contact with said gases, and as a result their lifetime is
limited.
[0003] In order to solve this problem, it is known that such blades
can be provided with internal cooling circuits seeking to lower
their temperature. By means of such circuits, cooling air, which is
generally introduced into the blade via its base, passes through
the blade following a path formed by cavities that are made inside
the blade, and is then ejected via slots that open out into the
surface of the blade in its trailing edge, as in European
application EP 0 945 594, or in its concave side, as in U.S. Pat.
No. 4,601,638. More precisely, these cooling air exhaust slots are
generally distributed between the base and the tip of the blade in
a manner that is substantially perpendicular to the longitudinal
axis of the blade.
[0004] It is also known that high pressure turbine blades fitted
with cooling circuits are made by molding. The locations of the
cooling circuit slots are conventionally occupied by cores disposed
parallel to one another inside the mold before the metal is cast.
In order to avoid weakening the core during casting, the cooling
air exhaust slot closest to the base of the blade is generally made
of dimensions that are greater than the dimensions of the other
slots, as shown in FIG. 3 of the above-mentioned US patent.
[0005] Unfortunately, in practice, the connection zone situated
between the slot and the platform supporting the blade is very
poorly cooled, particularly since the air exhausted via the slot
tends to be deflected towards the tip of the blade because of the
large dimensions of the slot and because of the centrifugal force
generated by the blade rotating. This gives rise to large
temperature gradients in the trailing edge which, by conduction,
give rise to cracking in the vicinity of the connection zone, which
cracking is particularly harmful for the lifetime of the blade.
OBJECT AND SUMMARY OF THE INVENTION
[0006] The present invention thus seeks to mitigate that drawback
by proposing a moving blade for a high pressure turbine that
presents a novel shape that avoids cracking. The invention also
seeks to avoid degrading the general mechanical strength of the
blade, which is a part that is subjected to very high levels of
mechanical stress. Finally, the invention also seeks to provide a
high pressure turbine for a turbomachine, which turbine is equipped
with such moving blades having improved thermal behavior.
[0007] To this end, the invention provides a moving blade for a
high pressure turbine of a turbomachine, the blade having at least
one cooling circuit comprising at least one cavity extending
radially between a tip and a base of the blade, at least one air
admission opening at a radial end of the cavity(ies) to feed the
cooling circuit(s) with cooing air, and a plurality of slots
opening out into the cavity(ies) and opening out into the concave
side of the blade between the base and the tip of the blade in a
manner that is substantially perpendicular to a longitudinal axis
of the blade, a connection zone being provided between a slot
closest to the base of the blade and a top surface of a platform
defining an inside wall for a stream of combustion gas flowing
through the high pressure turbine, the blade further comprising an
additional cooling air exhaust slot opening out into said cavity
and opening out into said connection zone in line with the trailing
edge.
[0008] As a result, the cooling air exhausted via said additional
slot is guided to the vicinity of the trailing edge over the entire
surface of the connection zone so as to avoid cracks appearing
therein. This particular shape for the blade base makes it possible
to lower the local temperature in said zone by about 10% while
conserving the aerodynamic performance obtained by having exhaust
slots in the concave side. Under such circumstances, it is no
longer necessary for the closest slot of the blade to present
dimensions that are greater than those of the other slots since it
is now the additional slot which is subjected to the pressure
effects due to casting the metal. In addition, because the closest
slot has been returned to normal dimensions, the problem posed by
cooling air being deflected by centrifugal force is eliminated and
the resulting losses in terms of flow rate are therefore reduced.
Finally, the ability of the blade to withstand the various
mechanical stresses to which it is subjected is not degraded by
this special shape.
[0009] The additional slot is preferably of a shape taken from the
following group of shapes: oblong; rectangular; triangular; and an
upside-down T-shape; and it is obtained directly by casting.
[0010] In addition, this additional slot may present an outlet
section that is different from the section of its feed channel.
[0011] Advantageously, a bottom longitudinal end of the additional
slot is disposed immediately above said top surface of the
platform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Other characteristics and advantages of the present
invention appear from the following description given with
reference to the accompanying drawings which show an embodiment
having no limiting character. In the figures:
[0013] FIG. 1 is a perspective view of a moving blade of the
invention for a high pressure turbine;
[0014] FIG. 2 is a fragmentary view on a larger scale than FIG. 1
showing a first embodiment of the additional slot for exhausting
cooling air that is provided in the connection zone between the
base of the blade and the platform;
[0015] FIGS. 2A and 2B are end views of the trailing edge in the
vicinity of the connection zone with the platform for two variant
embodiments of the additional cooling air exhaust slot;
[0016] FIG. 2C is a section view on plane AA of FIG. 2A;
[0017] FIG. 3 is a fragmentary view on a larger scale than FIG. 1
showing a second embodiment of the additional slot for exhausting
cooling air; and
[0018] FIG. 4 is a view of the base of a blade and the connection
zone between said base and the platform in a prior art blade.
DETAILED DESCRIPTION OF AN EMBODIMENT
[0019] FIG. 1 is a perspective view of a moving blade 10 in
accordance with the present invention, e.g. for a high pressure
turbine in a turbomachine. This blade has a longitudinal axis X-X
and it is fixed to a rotor disk (not shown) of the high pressure
turbine by means of a root 12 that is generally in the shape of a
fir-tree. It typically comprises a base 14A, a tip 14B, a concave
wall 16A, a convex wall 16B, a leading edge 18, and a trailing edge
20. The root 12 joins the base 14A of the blade at a platform 22
defining an inside wall for the stream of combustion gas flowing
through the high pressure turbine.
[0020] Such a blade is subjected to the very high temperatures of
the combustion gases and it therefore needs to be cooled. For this
purpose, and in known manner, the moving blade 10 has at least one
internal cooling circuit made up, for example, of at least one
cavity 24 extending radially between the base 14A and the tip 14B
of the blade. This cavity is fed with cooling air via one of its
radial ends by means of an air admission opening (not shown). This
air admission opening is generally provided in the root 12 of the
blade. A plurality of slots 26 are also provided that open out both
into the cavity 24 and, in the example shown, into the concave side
16A of the blade so as to exhaust the cooling air flowing in the
cavity. This disposition of the exhaust slot directly through the
concave wall 16A of the blade is preferable to a disposition in the
trailing edge (which requires the blade to be of greater
thickness), because of the improved aerodynamic performance that it
makes possible. The cooling air exhaust slots 26 are typically
distributed between the base 14A and the tip 14B of the blade in a
manner that is substantially perpendicular to the longitudinal axis
X-X of the blade. More particularly, the slot 28 closest to the
base 14A of the blade 10 is formed immediately above a connection
zone 30 between the base 14A of the blade and a top surface 22A of
the platform 22 beside the stream of flowing combustion gases.
[0021] The perspective view of FIG. 2 and FIGS. 2A to 2C show more
clearly the shape of the trailing edge 20 of the blade in said
connection zone and including the slot 28 that is closest to the
base 14A of the blade 10.
[0022] In accordance with the invention, an additional slot is
provided that opens out into the cavity 24 and also into said
connection zone in line with the trailing edge 20. This additional
slot 32 makes it possible to provide cooling by convection of this
portion of the connection zone, and by conduction of the slot that
is closest to the base of the blade and also of the portion of the
platform that is situated as an extension of the trailing edge.
Thus, by making temperature more uniform in this vicinity, it is
possible to eliminate all hot spots and thus to improve the thermal
behavior of the blade. The cooling air exhausted through this
additional slot covers all of the surface of the connection zone in
the vicinity of the trailing edge and it lowers local temperature
by about 10%, doing this without modifying the aerodynamic behavior
that is achieved by using exhaust slots in the concave side. Thus,
any risk of cracking in the vicinity of this connection zone
between the base of the blade and the platform disappears and the
lifetime of the blade is lengthened. Under such circumstances, it
is no longer necessary for the slot 28 closest to the base of the
blade to present dimensions greater than those of the other slots
26, as illustrated by the prior art of FIG. 4, and because it can
be of normal dimensions, the problem posed by cooling air being
deflected in the vicinity of this slot due to centrifugal force is
eliminated as are losses in terms of the resulting flow rate.
[0023] The additional slot may be of various shapes that are
determined as a function of desired mechanical and thermal
dimensioning criteria. Similarly, the feed channel and the outlet
orifice can have sections that are different. Thus, FIG. 2 shows an
additional slot presenting a feed channel and an outlet orifice
that are elongate in shape, advantageously being oblong (it is also
possible to envisage using a rectangular section). In FIG. 2A, the
outlet section is still oblong, but the internal feed channel is
substantially triangular, i.e. it flares on either side of the
outlet hole so as to provide better cooling of the connection zone
while also delivering a well-calibrated outlet flow rate. Depending
on the thermal stresses and the mechanical forces to which the
blade is subjected, this flare of varying angle may be
asymmetrical, and can thus be directed towards one side only, as
shown in FIG. 2B.
[0024] A variant embodiment of the additional slot in which the
feed channel is of an upside-down T-shape that coincides with the
shape of the outlet orifice 34 is also shown in FIG. 3.
[0025] This slot is advantageously obtained directly by casting
simultaneously with the blade itself (as opposed to being machined
subsequently) and it passes through the blade as far as the cavity
24 while remaining constantly immediately above the level of the
top surface of the platform (i.e. its longitudinal bottom end 32A
or 34A is above said top surface 22A). As a result, it is this
additional slot which is subjected to the effects of the casting
pressure of the metal and it is not the slot 28 closest to the base
of the blade that is subjected thereto as in the prior art, so any
risk of the blade being weakened because of machining is
avoided.
* * * * *