Note: Descriptions are shown in the official language in which they were submitted.
_ CA 02208801 1997-06-24
A BLEED APPARATUS FOR A GAS TURBINE ENGINE
The present invention relates to bleed apparatus for gas
turbine engines, particularly, but not exclusively, to bleed
apparatus for industrial gas turbine engines.
In industrial gas turbine engines which comprise in flow
series a low pressure compressor, a core engine and a low
pressure turbine directly connected to an electrical
generator it is a requirement that the low pressure turbine
rotate at the same speed from zero to full power. This
requirement has made it necessary to provide a bleed
apparatus between the low pressure compressor and the core
engine in order to bleed a large amount of air from the gas
turbine engine during zero power and at power levels below a
predetermined level.
It is known to provide bleed apparatus between a low
pressure compressor and a core engine to bleed air from the
gas turbine engine during power levels below a predetermined
level. These bleed apparatus comprise a plurality of
circumferentially spaced bleed apertures, each one of which
has a bleed valve means to pivot between a first position in
which the bleed apertures are closed and a second position in
which the bleed apertures are fully open. Each bleed valve
means is actuated by a respective bell crank, or lever, and
the bell cranks, or levers, are operated by a unison ring
which is mounted coaxially of the engine on a support ring.
The bell cranks are pivotally mounted on the support ring.
However, this arrangement may suffer from the problem of~one
bleed valve means, or actuating means, seizing and disabling
the entire system. Additionally deflections of the unison
ring may necessitate the use of bearings between the support
ring and the unison ring. There may be a requirement for
springs between the unison ring and the bleed valve means to
ensure that all bleed valve means close after one bleed valve
means closes to guarantee uniform closure of all the bleed
valve means.
Accordingly the present invention seeks to provide a
bleed apparatus for a gas turbine engine which overcomes the
above mentioned problems.
CA 02208801 2005-03-08
2
Accordingly the present invention provides a gas turbine
engine comprising in flow series a low pressure compressor, a
core engine, and a low pressure turbine, the low pressure
turbine being arranged to drive the low pressure compressor,
the core engine comprising in flow series at least one
compressor, combustion means and at least one turbine, the at
least one turbine being arranged to drive the at least one
compressor,
a duct connecting the outlet of the low pressure compressor
and the inlet of the at least one compressor of the core engine,
the duct being defined by a casing,
a bleed apparatus for bleeding air from the duct, the bleed
apparatus comprising a plurality of circumferentially spaced
bleed apertures extending through the casing, a plurality of
bleed valve means arranged to selectively move between a first
position in which the bleed apertures are closed and a second
position in which the bleed apertures are fully open to allow a
bleed flow from the low pressure compressor, and a plurality of
independent actuating means, each independent actuating means is
arranged to independently actuate one of the plurality of bleed
valve means, the actuating means being arranged to actuate the
plurality of bleed valve means in unison, the independent
actuating means comprising ram means.
Preferably the core engine comprises in flow series an
intermediate pressure compressor, a high pressure compressor,
combustion means, a high pressure turbine and an intermediate
pressure turbine, the intermediate pressure turbine being
arranged to drive the intermediate pressure compressor, the high
pressure turbine being arranged to drive the high pressure
compressor.
The low pressure turbine may be arranged to drive a load.
Preferably the load is an electrical generator, a pump or a
drive shaft.
Preferably each actuator means comprises a piston and
cylinder. Preferably there are means to supplied fluid to the
cylinders to move the pistons. Preferably there are means to
supply fluid is a supply of hydraulic fluid.
Preferably the cylinders are mounted on a support ring, the
support ring is mounted coaxially on the gas turbine engine.
CA 02208801 2005-03-08
3
Preferably the bleed valve means are pivotally mounted onto
the casing. Preferably each piston is pivotally connected to
the respective bleed valve means.
Preferably each bleed aperture has a first side wall and a
second side wall extending radially outwardly from the casing at
the circumferentially spaced sides of each bleed aperture, each
bleed valve means being pivotally mounted by a pivot extending
between the respective first side wall and second side wall.
Preferably the first and second side walls extend the full axial
length of the bleed aperture and extend a predetermined distance
radially outwardly from the casing whereby the first and second
walls prevent the bleed flow flowing circumferentially from the
bleed aperture until the bleed valve means have opened a
predetermined amount to provide a continuously increasing bleed
area as the bleed valve means move towards the second position.
Preferably each bleed valve means comprises a first member
and a second member, the first member is pivotally mounted onto
the casing, the first member is arranged to carry the second
member, the second member has an inner surface, the casing has
an inner surface and an outer surface, the first member is
arranged to abut the outer surface of the casing in the first
position, the second member is arranged to fit in the bleed
aperture and the inner surface thereof is arranged to lie flush
with inner surface of the casing when in the first position.
Preferably a seal is located between the first member and
the second member, the second member has a periphery, the seal
extends around the periphery of the second member such that the
seal abuts the outer surface of the casing around the respective
bleed aperture in the first position. Preferably the seal is P
shaped in cross-section. Preferably the seal comprises rubber
enclosed in a fabric.
Preferably the outer surface of the casing has chamfered
edges around the respective bleed aperture.
Preferably the bleed valve means have upstream ends, the
bleed valve means are pivotally mounted to the casing at their
upstream ends.
CA 02208801 2005-03-08
4
The present invention also provides a gas turbine engine
comprising in flow series a low pressure compressor, a core
engine, and a low pressure turbine, the low pressure turbine
being arranged to drive the low pressure compressor,
the core engine comprising in flow series at least one
compressor, combustion means and at least one turbine, the at
least one turbine being arranged to drive the at least one
compressor,
a duct connecting the outlet of the low pressure compressor
and the inlet of the at least one compressor of the core engine,
the duct being defined by a casing,
a bleed apparatus for bleeding air from the duct, the bleed
apparatus comprising a plurality of circumferentially spaced
bleed apertures extending through the casing, a plurality of
bleed valve means arranged to selectively move between a first
position in which the bleed apertures are fully open to allow a
bleed flow from the low pressure compressor,
actuating means to actuate the bleed valve means in unison,
each bleed aperture has a first side wall and a second side
wall extending radially outwardly from the casing at the
circumferentially spaced sides of each bleed aperture, the first
and second side walls extend the full axial length of the bleed
apertures and extend a predetermined distance radially outwardly
from the casing whereby the first and second walls prevent the
bleed flow flowing circumferentially from the bleed aperture
until the bleed valve means have opened a predetermined amount
to provide a continuously increasing bleed area as the bleed
valve means move towards the second position.
Preferably there is a plurality of independent actuating
means, each independent actuating means is arranged to
independently actuate one of the plurality of bleed valve means,
the actuating means being arranged to actuate the plurality of
bleed valve means in unison, the independent actuating means
comprising ram means.
CA 02208801 1997-06-24
Preferably each bleed valve means is pivotally mounted
by a pivot extending between the respective first side wall
and second side wall.
The present invention will be more fully described by
5 way of example with reference to the accompanying drawings,
in which:
Figure 1 is a partially cut away view of an industrial
gas turbine engine showing a bleed apparatus according to t~:e
present invention.
Figure 2 is an enlarged view in the direction of arrow A
in figure 1 showing the bleed apparatus.
Figure 3 is a further enlarged view of one of the bleed
valve means and independent actuating means shown in figure
2.
Figure 4 is a cross-sectional view on line B-B of figure
3, and
Figure 5 is a cross-sectional view on line C-C of figure
3.
An industrial gas turbine engine 10, shown in figure 1,
comprises in axial flow series an inlet 12, a low pressure
compressor 14, an inter compressor duct 16, an intermediate
pressure compressor 18, a high pressure compressor 20,
combustion means 22, a high pressure turbine 24, an
intermediate pressure turbine 26, a low pressure turbine 28
and an exhaust 30. The high pressure turbine 24 is arranged
to drive the high pressure compressor 20 via a shaft (not
shown), the intermediate pressure turbine 26 is arranged to
drive the intermediate pressure compressor 18 via a shaft
(not shown) and the low pressure turbine 28 is arranged to
drive the low pressure compressor 14 via a shaft (not shown).
Also the low pressure turbine 28 is arranged to drive an
electrical generator 32 via a shaft 31. However, the low
pressure turbine 28 may be arranged to provide drive for
other purposes, for example a pump or a drive shaft of a ship
etc. The intermediate pressure compressor 18, the high
pressure compressor 20, the combustion means 22, the high
pressure turbine 24, and the intermediate pressure turbine 26
form a core engine. The operation of the gas turbine engine
10 is quite conventional, and will not be discussed further.
CA 02208801 2005-03-08
6
However, as stated above because the low pressure turbine
28 drives the electrical generator 32 it is a requirement that
the low pressure turbine 28, low pressure compressor 14 and
shaft 31 rotate at the same speed throughout the full power
range of the gas turbine engine 10. This makes it necessary to
provide a bleed apparatus 34 in the inter compressor duct 16 to
bleed air from between the low pressure compressor 14 and the
intermediate pressure compressor 18 below predetermined power
levels. For example for a 50MW industrial gas turbine engine
this would necessitate bleeding of air at power levels below
about 40MW, and at certain condition up to 50% of the air
leaving the low pressure compressor 14 may be bleed air.
The bleed apparatus 34, as shown more clearly in figures 2
to 5, comprises a plurality of, for example eighteen, equi-
circumferentially spaced apertures 38 in a casing 36 which
defines the outer surface of the inter compressor duct 16. The
inter compressor duct 16 connects the outlet of the low pressure
compressor 14 and the inlet of the intermediate pressure
compressor 18. There are a plurality of bleed valve means,
bleed doors 40, one for each bleed aperture 38. The bleed doors
40 have an upstream end 41 and a downstream end 43 and axially
extending side edges 45 and 47. The bleed doors 40 are
pivotally mounted at their upstream ends 41 to the casing 36 by
a pivot 42. Each bleed door 40 is provided with its own
independent actuator 44, 46 and each actuator comprises a
cylinder 44 and a piston 46. The cylinders 44 are supplied with
fluid, either hydraulic fluid or pneumatic fluid, to move the
pistons 46 to vary the position of the bleed doors 40. Each
actuator 44, 46 is arranged centrally and substantially
perpendicularly to the respective bleed door 40 to ensure
uniform sealing of the bleed doors 40 around the bleed apertures
38.
Each bleed door 40 comprises a first member 48 and a second
member 50, as show more clearly in figures 4 and 5. The first
member 48 is pivotally mounted onto the casing 36 by the pivot
42 and the first member 48 is arranged to carry the second
member 50 by means of four threaded studs 52 extending from the
second member 50 which pass through
CA 02208801 1997-06-24
7
corresponding apertures 54 in the first member 48 and by four
nuts 55 which are threaded onto the studs 52. The second
member 50 has a contoured inner surface 51 to match the inner
surface of the casing 36. The outer surface of the second
member 50 and the inner surface of the first member 48 are
substantially planar.
Each bleed door 40 has a pair of circumferentially
spaced lugs 56 and 58 which extend outwardly from the first
member 48 and the corresponding piston 46 is attached to the
lugs 56 and 58 by a pivot arrangement in which a bolt 60
passes through coaxial apertures in the lugs 56 and 58 and
also through an aperture in the end of the piston 46 and a
nut 62 is located on the threaded end of the bolt 60. The
piston 46 is free to slide axially along the bolt 60 to some
extent to avoid binding and to reduce side loads on the
actuator 44,46.
Each bleed door 40 has a hinge 64 which fits around the
pivot 42 and which is secured to the first member 48 by
threaded studs 66 which extend outwardly from the first
member 48 and pass through apertures in the hinge 64 and nuts
67 which are threaded onto the studs 66. The hinge 64 is U-
shaped and flexes in operation to allow the bleed door 40 to
seat properly around the bleed aperture 38 to prevent
leakage.
Each first member 48 is designed such that it has axial
and circumferential dimensions greater than those of the
corresponding bleed aperture 38 such that the periphery of
the first member 48 will abut the outer surface of the casing
36 around the bleed aperture 38. Each second member 50 is
designed such that it has axial and circumferential
dimensions slightly smaller than those of the corresponding
bleed aperture 38 such that the second member 50 will fit in
the bleed aperture 38.
Each bleed door 40 is provided with a seal 68 which is
located between the first member 48 and the second member 50.
The seal 68 extends beyond the periphery of the second member
50 but under the periphery of the first member 48. The seal
68 is secured to the first member 48 by four retainers (not
CA 02208801 2005-03-08
g
shown) and twelve screws (not shown) and nuts 69,70. The seal
68 is P shaped in cross-section and comprises rubber enclosed in
a fabric, for example rubber enclosed in nylon fabric. It may
also be necessary to provide silicone sealant to seal any small
leaks.
Each bleed aperture 38 has circumferentially spaced side
edges 37 and 39 and all the edges of each bleed aperture are
chamfered at the outer surface of the casing 36. Each bleed
aperture 38 has a first side wall 72 and a second side wall 74
extending radially outwardly from the casing 36 and spaced
circumferentially from its axially extending side edges 37 and
39. Each bleed door 40 is pivotally mounted by the pivot 42
which extends between the respective first side wall 72 and the
second side wall 74. The first and second side walls 72 and 74
are secured to the casing by bolts 76 and 78 respectively.
The cylinder 44 of each actuator 44, 46 is mounted onto a
support ring 80 by means of brackets 82 and 84 which are secured
to the support ring by bolts 86 and 88 respectively. Each
cylinder 44 is rotably mounted on the respective brackets 82 and
84 by support pins 87 and 89 which locate in bushes 91 and 93 in
the brackets 82 and 84 to allow the cylinder to pivot slightly
as the piston 46 moves in the cylinder 44.
Each cylinder 44 defines a first chamber 98 and a second
chamber 100 at opposite sides of the respective piston 46. The
first chamber 98 of each actuator 44, 46 is supplied with fluid
by a manifold 90 and one of a plurality of pipes 94 and fluid is
bled from the chamber 100 of each actuator 44, 46 by a manifold
92 and one of a plurality of pipes 96. A servo valve (not
shown) varies the pressure difference between the fluid in the
manifolds 90 and 92 to move the pistons 46 in unison in the
cylinders 44 so as to vary the position of the bleed doors 40 in
unison.
In operation at high power, for example at power levels
greater than 40MW for a 50MW gas turbine engine, the servo valve
sets the pressure difference between the fluid in the manifolds
90 and 92 such that the pistons 46 move in the
CA 02208801 1997-06-24
9
cylinders 44 so as to push the bleed doors 40 to a first
position in which the bleed apertures 38 are closed by the
bleed doors 40 to prevent a bleed flow from the low pressure
compressor 14. At zero power and idle the servo valve sets
the pressure difference between the fluid in the manifolds 90
and 92 such that the pistons 46 move in the cylinders 44 so
as to pull the bleed doors 40 to the second position in which
the bleed apertures 38 are fully open to allow maximum, in
this example 500, bleed flow from the low pressure compressor
14. At low power, for example at power levels less than 40MW
for a 50MW gas turbine engine and greater than zero power,
the servo valve sets the pressure difference between the
fluid in the manifolds 90 and 92 such that the pistons 46
move in the cylinders 44 so as to pull the bleed doors 40 to
a position between the first position and the second position
such that the bleed apertures 38 are partially open by the
bleed doors 40 to allow a bleed flow between zero and 50%
from the low pressure compressor 14.
The first member 48 is arranged such that its periphery
abuts the outer surface of the casing 36 around the bleed
aperture 38 when the bleed door 40 is in the first position.
The second member 50 is arranged to fit in the bleed aperture
38 and the inner surface 51 is arranged to lie flush with the
inner surface of the casing 36 when the bleed door 40 is in
the first position. The seal 68 is arranged to abut the
outer surface of the casing 36 around the respective bleed
aperture 38, in particular on the chamfered edges of the
bleed apertures 38, when the bleed door 40 is in the first
position.
The first and second side walls 72 and 74 extend the
full axial length of each bleed aperture 38 and extend a
predetermined distance radially outwardly from the casing 36
whereby the first and second walls 72 and 74 prevent the
bleed air flowing circumferentially from the bleed aperture
38 until the bleed doors 40 have opened a predetermined
amount to provide a continuously increasing bleed area as the
bleed doors 40 move from the first position towards the
second position. When the bleed doors 40 have opened beyond
the predetermined amount the bleed air is able to flow
CA 02208801 1997-06-24
circumferentially from the bleed apertures 38. The
circumferential dimension of each first member 48 is
substantially the same but only slightly smaller than the
circumferential dimension between the corresponding first and
5 second side walls 72 and 74 to minimise leakage of bleed air
therebetween while the bleed door 40 moves from the first
position to the predetermined position.
The periphery of the second member 50 of the bleed doors
40 are tapered and are given a radius to provide a smooth
l0 transition for the air as it passes over the closed bleed
doors 40. The tapered periphery of the second member 50 of
the bleed doors 40 also provides cavities for the P seals to
deform into when the bleed doors 40 are closed to minimise
damage to the P seals.
I5 The servo valve is operated by an engine management
system which schedules the amount of bower reaui rPr3 from rt,A
gas turbine engine 10.
The advantages of this arrangement are that the direct
piston force on the bleed door 40 ensures proper sealing of
the bleed aperture 38 by the bleed door 40, in particular the
P cross-section seal 68 seats properly on the chamfered edges
of the bleed aperture 38. Also the use of the piston and
cylinder actuators and fluid provides a uniform force on each
of the bleed doors 40 to ensure that all the bleed doors 40
close together. Additionally if one of the bleed doors 40 or
actuator 44,46 seizes the remaining bleed doors 40 will
operate to open or close the remaining bleed doors 40. If
there is a loss of fluid then all the bleed doors 40 will
open to provide a failsafe feature. The side walls 72 and 74
provide a gradual increase in flow area as the bleed doors 40
are opened.
The first and second members 48 and 50 of the bleed
doors 40 are preferably made from materials with low density
so as to decrease the response time of the bleed doors 40,
i . a . the time for the bleed doors 40 to open or close . For
example the second member 50 is cast from aluminium and the
first member is cast from stainless steel.
Although the description has referred to a core engine
comprising an intermediate pressure compressor, a high
CA 02208801 1997-06-24
pressure compressor, combustor means, a high pressure turbine
and an intermediate pressure turbine it is possible for the
core engine to comprise a high pressure compressor, combustor
means, and a high pressure turbine. Although the descriptior_
has referred to actuators comprising a cylinder and piston
arrangement supplied with hydraulic or pneumatic fluid, which
are fluid driven rams, it is possible to use other types of
ram arrangements for example electrically driven rams.
