U.S. patent application number 10/387528 was filed with the patent office on 2003-08-14 for gas turbine engine and a rotor for a gas turbine engine.
This patent application is currently assigned to Rolls-Royce plc. Invention is credited to Jones, Alan R..
Application Number | 20030152457 10/387528 |
Document ID | / |
Family ID | 10850455 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030152457 |
Kind Code |
A1 |
Jones, Alan R. |
August 14, 2003 |
Gas turbine engine and a rotor for a gas turbine engine
Abstract
A rotor (38) for a gas turbine engine (10) has a low emissivity
surface finish, or high emissivity surface finish (44), on at least
a portion of its surface (42) to reduce temperature differentials
between an upper portion and a lower portion of the rotor (38).
This reduces bowing of the rotor (38) to allow the gas turbine
engine (10) to be started without harmful vibrations of the rotor
(38).
Inventors: |
Jones, Alan R.; (Derby,
GB) |
Correspondence
Address: |
Manelli, Denison & Selter
Suite 700
2000 M Street N.W.
Washington
DC
20036
US
|
Assignee: |
Rolls-Royce plc
|
Family ID: |
10850455 |
Appl. No.: |
10/387528 |
Filed: |
March 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10387528 |
Mar 14, 2003 |
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09531960 |
Mar 21, 2000 |
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6575699 |
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Current U.S.
Class: |
415/199.5 |
Current CPC
Class: |
F01D 19/00 20130101;
F01D 11/18 20130101; F05D 2260/85 20130101; F01D 5/26 20130101;
F05D 2300/504 20130101; F05D 2300/611 20130101; F05D 2300/142
20130101; F05D 2230/90 20130101; F02C 7/26 20130101; F05D 2300/141
20130101; F04D 29/321 20130101; F05D 2300/224 20130101; F04D 29/584
20130101; F01D 5/288 20130101 |
Class at
Publication: |
415/199.5 |
International
Class: |
F01D 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 1999 |
GB |
9907045.0 |
Claims
I claim:
1. A gas turbine engine comprising at least one rotor and at least
one casing arranged coaxially around the at least one rotor, the
rotor having an upper portion, a lower portion and a surface, the
at least one casing having a surface, at least one of the at least
one rotor or the at least one casing having a surface finish on at
least a portion of its surface to reduce temperature differentials
between the upper portion and the lower portion of the at least one
rotor, the surface finish being selected from the group comprising
a low emissivity surface finish and a high emissivity surface
finish.
2. A gas turbine engine as claimed in claim 1 wherein the gas
turbine engine comprises a low pressure rotor, a high pressure
rotor and at least one casing, the high pressure rotor being
arranged coaxially around the low pressure rotor and the at least
one casing being arranged coaxially around the high pressure rotor,
the high pressure rotor having a radially inner surface and a
radially outer surface, the low pressure rotor having a radially
inner surface and a radially outer surface.
3. A gas turbine engine as claimed in claim 2 wherein the surface
is the radially inner surface of the high pressure rotor, the
surface finish is arranged on substantially the whole of the
radially inner surface of the high pressure rotor and the surface
finish is a high emissivity surface finish.
4. A gas turbine engine as claimed in claim 3 wherein the surface
is the radially inner surface of the low pressure rotor, the
surface finish is arranged on substantially the whole of the
radially inner surface of the low pressure rotor and the surface
finish is a high emissivity surface finish.
5. A gas turbine engine as claimed in claim 3 wherein the surface
is the radially outer surface of the low pressure rotor, the
surface finish is arranged on substantially the whole of the
radially outer surface of the low pressure rotor and the surface
finish is a high emissivity surface finish.
6. A gas turbine engine as claimed in claim 2 wherein a low
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the high pressure rotor and a low
emissivity surface finish is arranged on a portion of the radially
inner surface of the high pressure rotor.
7. A gas turbine engine as claimed in claim 2 wherein a high
emissivity surface finish is arranged on at least a portion of the
radially inner surface of the high pressure rotor, a high
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the high pressure rotor, a low emissivity
surface finish is arranged on at least a portion of the radially
outer surface of the high pressure rotor and a low emissivity
surface finish is arranged on at least a portion of the radially
inner surface of the high pressure rotor.
8. A gas turbine engine as claimed in claim 2 wherein the surface
is the downstream surface of the high pressure rotor, the surface
finish is arranged on at least a portion of the downstream surface
of the high pressure rotor and the surface finish is a high
emissivity surface finish.
9. A gas turbine engine as claimed in claim 8 wherein the high
emissivity surface finish is arranged on substantially all of the
downstream surface of the high pressure rotor.
10. A gas turbine engine as claimed in claim 2, wherein the surface
is the downstream surface of the low pressure rotor, the surface
finish is arranged on at least a portion of the downstream surface
of the low pressure rotor and the surface finish is a high
emissivity surface finish.
11. A gas turbine engine as claimed in claim 10 wherein the high
emissivity surface finish is arranged on substantially all of the
downstream surface of the low pressure rotor.
12. A gas turbine engine as claimed in claim 2 wherein the high
pressure rotor comprises a high pressure compressor and a high
pressure turbine and the low pressure rotor comprises a low
pressure compressor and a low pressure turbine.
13. A gas turbine engine as claimed in claim 12 wherein the high
pressure turbine comprises at least one turbine disc and the low
pressure turbine comprises at least one turbine disc and each
turbine disc has an upstream surface and a downstream surface.
14. A gas turbine engine as claimed in claim 13 wherein a high
emissivity surface finish is arranged on the upstream surface of
each turbine disc on the high pressure rotor and the downstream
surface of each turbine disc on the high pressure rotor.
15. A gas turbine engine as claimed in claim 13 wherein the high
emissivity surface finish is arranged on the upstream surface of
each turbine disc on the low pressure rotor and the downstream
surface of each turbine disc on the low pressure rotor.
16. A gas turbine engine as claimed in claim 12 wherein the at
least one casing is arranged around the high pressure turbine and
the low pressure turbine, the surface is a radially outer surface
of the at least one casing, at least a portion of the at least one
casing having a high emissivity surface finish on its radially
outer surface to increase the rate of radiation of heat from at
least one of the turbines.
17. A gas turbine engine as claimed in claim 1 wherein the surface
is a radially outer surface of the at least one casing, the surface
finish is arranged on at least a portion of the radially outer
surface of the at least one casing, the surface finish is a high
emissivity surface finish.
18. A gas turbine engine as claimed in claim 17 wherein the at
least one casing has a radially inner surface, at least a portion
of the at least one casing having a high emissivity surface finish
or a low emissivity finish on its inner surface.
19. A gas turbine engine as claimed in claim 1 wherein the high
emissivity surface finish is selected from the group comprising a
coating applied to the surface of the at least one rotor or the at
least one casing and a coating formed on the surface of the at
least one rotor or the at least one casing.
20. A gas turbine engine as claimed in claim 19 wherein the coating
is selected from the group comprising a high emissivity metal
oxide, a metal oxide formed on the at least one rotor or the at
least one casing due to oxidation of the at least one rotor or the
at least one casing, carbon, black paint and other suitable colour
paint.
21. A gas turbine engine as claimed in claim 1 wherein the low
emissivity surface finish is selected from the group comprising a
polished portion of the surface of the at least one rotor, a
machined portion of the surface of the at least one rotor and the
at least one casing or a coating applied to the surface of the at
least one rotor or the at least one casing.
22. A gas turbine engine as claimed in claim 21 wherein the coating
is selected from the group comprising a polished metal coating, a
polished silver coating, a polished gold coating, and a low
emissivity metal oxide.
23. A rotor for a gas turbine engine having an upper portion, a
lower portion and a surface, the surface having a surface finish on
at least a portion of its surface to reduce temperature
differentials between the upper portion and the lower portion of
the rotor, the surface finish being selected from the group
comprising a low emissivity surface finish and a high emissivity
surface finish.
24. A rotor for a gas turbine engine as claimed in claim 23 wherein
the surface is a radially inner surface of the rotor, a high
emissivity surface finish is arranged on at least a portion of the
radially inner surface of the rotor.
25. A rotor for a gas turbine engine as claimed in claim 24 wherein
the high emissivity surface finish is arranged on substantially the
whole of the radially inner surface of the rotor.
26. A rotor for a gas turbine engine as claimed in claim 23 wherein
the surface is a radially outer surface of the rotor, a high
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the rotor.
27. A rotor for a gas turbine engine as claimed in claim 26 wherein
the high emissivity surface finish is arranged on substantially the
whole of the radially outer surface of the rotor.
28. A rotor for a gas turbine engine as claimed in claim 23 wherein
the surface is a radially outer surface of the rotor, a low
emissivity surface is arranged on at least a portion of the
radially outer surface of the rotor.
29. A rotor for a gas turbine engine as claimed in claim 28 wherein
the low emissivity surface finish is arranged on substantially the
whole of the radially outer surface of the rotor.
30. A rotor for a gas turbine engine as claimed in claim 23 wherein
the rotor has a radially inner surface and a radially outer
surface, a high emissivity surface finish is arranged on at least a
portion of the radially inner surface of the rotor, a high
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the rotor, a low emissivity surface
finish is arranged on at least a portion of the radially outer
surface of the rotor and a low emissivity surface finish is
arranged on at least a portion of the radially inner surface of the
rotor.
31. A rotor for a gas turbine engine as claimed in claim 23 wherein
the surface is a downstream surface of the rotor a high emissivity
surface finish is arranged on at least a portion of the downstream
surface of the rotor.
32. A rotor for a gas turbine engine as claimed in claim 31 wherein
the high emissivity surface finish is arranged on substantially all
of the downstream surface of the rotor.
33. A rotor for a gas turbine engine as claimed in claim 23 wherein
the rotor is selected from the group comprising a high pressure
rotor, an intermediate pressure rotor and a low pressure rotor.
34. A rotor for a gas turbine engine as claimed in claims 23 to 37
wherein the high emissivity surface finish is selected from the
group comprising a coating applied to the surface of the rotor and
a coating formed on the surface of the rotor.
35. A rotor for a gas turbine engine as claimed in claim 34 wherein
the coating is selected from the group comprising a high emissivity
metal oxide, a metal oxide formed on the rotor due to oxidation of
the rotor, carbon, black paint and other suitable colour paint.
36. A rotor for a gas turbine engine as claimed in claim 23 wherein
the low emissivity surface finish is selected from the group
comprising a polished portion of the surface of the rotor, a
machined portion of the surface of the rotor and a coating applied
to the surface of the rotor.
37. A rotor for a gas turbine engine as claimed in claim 36 wherein
the coating is selected from the group comprising a polished metal
coating, a polished silver coating, a polished gold coating, and a
low emissivity metal oxide.
Description
[0001] The present invention relates to gas turbine engines,
particularly aero gas turbine engines.
[0002] One problem with gas turbine engines is the thermal
distortion which occurs when a gas turbine engine is shut down
after use. The residual heat in the various components of the gas
turbine engine causes convection currents to be set up which cause
the upper portion of the gas turbine engine to retain their heat
for longer than the lower portion of the gas turbine engine. This
produces a temperature differential which in turn causes
differential thermal expansion.
[0003] The effect of the differential thermal expansion is to cause
at least the rotors, particularly the high pressure rotor, to bow
upwardly. The amount of rotor bow is time dependent. For a given
heat content within the gas turbine engine, the maximum rotor bow
will occur some time after shut down, when the convective heat
transfer has had time to act, but before the gas turbine engine has
cooled down. The magnitude of the temperature differential between
the upper portion and the lower portion of the gas turbine engine
and the magnitude of the rotor bow depends on the heat content of
the gas turbine engine, so that when the gas turbine engine has
cooled down the temperature differential and rotor bow
disappear.
[0004] The distortion, or bowing, of the rotor in itself is not
harmful to the gas turbine engine. However, if it is desired to
restart the gas turbine engine while the rotor of the gas turbine
engine is distorted, or bowed, due to the differential thermal
expansion the displacement of the centre of mass of the distorted
rotor from the centre of rotation may create problems.
[0005] The first problem is large, damaging vibrations of the rotor
and possibly rubbing of the rotor with the surrounding stator when
the rotor passes through its first critical speed because the rotor
of the gas turbine engine is distorted, or bowed, due to the
differential thermal expansion. It is normal practice to arrange
for the first critical speed of the rotor to be less than the idle
speed. The rotor typically comprises two portions which are
connected by a spigotted, bolted, joint. As the rotor cools down
the spigotted, bolted, joint may become loose due to the
differential thermal expansion and hence the vibrations of the
rotor may produce wear at the spigotted, bolted, joints. The worn
spigotted, bolted, joints exacerbate the vibrational response of
the gas turbine engine rotor to rotor bowing.
[0006] The second problem is additional stresses are produced in
the rotor when the rotor reaches high speed operation after start
up if the rotor of the gas turbine engine is distorted, or bowed,
due to the differential thermal expansion. The gas turbine engine
may be started from a cooling condition and accelerated to idle
speed and then to high speed before the rotor has warmed through to
a uniform temperature circumferentially around the rotor. This is
because of the high thermal inertia of the rotor discs and drums.
The effect of the rotor bow is to superimpose an extra stress onto
the high stress levels in the rotor, thus some circumferential
parts of the rotor will have an additional tensile stress and some
circumferential parts will have an additional compressive stress.
The result is that the expected service life of a rotor that is
frequently started in a bowed condition is less than that of a
rotor that is never started in a bowed condition.
[0007] UK patent application GB2117842A discloses the use of ducts
and blowers to circulate warmer gas from the upper portion of the
gas turbine engine to the lower portion of the gas turbine engine
or circulate cooler gas from the lower portion of the gas turbine
engine to the upper portion of the gas turbine engine. This
requires the provision of ducts and blowers to the gas turbine
engine which adds weight and cost to the gas turbine engine.
[0008] UK patent application GB2117450A discloses the use of a
particular mounting arrangement for the compressor casing and
heaters to differentially heat the mounting to displace the casing
to compensate for the distortion of the rotor. This requires the
provision of the particular mounting and heaters which adds weight
and cost to the gas turbine engine and does not solve the problem
of vibration of the rotor.
[0009] Accordingly the present invention seeks to provide a novel
component for a gas turbine engine which overcomes the above
mentioned problems.
[0010] Accordingly the present invention provides a gas turbine
engine comprising at least one rotor and at least one casing
arranged coaxially around the at least one rotor, at least one of
the at least one rotor or the at least one casing having a low
emissivity surface finish, or high emissivity surface finish, on at
least a portion of its surface to reduce temperature differentials
between an upper portion and a lower portion of the at least one
rotor.
[0011] Preferably the gas turbine engine comprises a low pressure
rotor and a high pressure rotor arranged coaxially around the low
pressure rotor and at least one casing arranged coaxially around
the high pressure rotor, at least one of the high pressure rotor,
the low pressure rotor or the at least one casing having a low
emissivity surface finish, or high emissivity surface finish, on at
least a portion of its surface to reduce temperature differentials
between an upper portion and a lower portion of at least one of the
low pressure rotor and the high pressure rotor.
[0012] The high emissivity surface finish may be arranged on
substantially the whole of the radially inner surface of the high
pressure rotor. The high emissivity surface finish may be arranged
on substantially the whole of the radially inner surface of the low
pressure rotor. The high emissivity surface finish may be arranged
on substantially the whole of the radially outer surface of the low
pressure rotor.
[0013] A low emissivity surface finish may be arranged on at least
a portion of the radially outer surface of the high pressure rotor
and a low emissivity surface finish is arranged on a portion of the
radially inner surface of the high pressure rotor.
[0014] A high emissivity surface finish may be arranged on at least
a portion of the radially inner surface of the high pressure rotor,
a high emissivity surface finish is arranged on at least a portion
of the radially outer surface of the high pressure rotor, a low
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the high pressure rotor and a low
emissivity surface finish is arranged on at least a portion of the
radially inner surface of the high pressure rotor.
[0015] The high emissivity surface finish may be arranged on at
least a portion of the downstream surface of the high pressure
rotor. The high emissivity surface finish may be arranged on
substantially all of the downstream surface of the high pressure
rotor.
[0016] The high emissivity surface finish may be arranged on at
least a portion of the downstream surface of the low pressure
rotor. The high emissivity surface finish may be arranged on
substantially all of the downstream surface of the low pressure
rotor.
[0017] The high pressure rotor may comprise a high pressure
compressor and a high pressure turbine and the low pressure rotor
comprises a low pressure compressor and a low pressure turbine.
[0018] The high pressure turbine may comprise at least one turbine
disc and the low pressure turbine comprises at least one turbine
disc.
[0019] The high emissivity surface finish may be arranged on the
upstream surface of each turbine disc on the high pressure rotor
and the downstream surface of each turbine disc on the high
pressure rotor.
[0020] The high emissivity surface finish may be arranged on the
upstream surface of each turbine disc on the low pressure rotor and
the downstream surface of each turbine disc on the low pressure
rotor.
[0021] The at least one casing may be arranged around the high
pressure turbine and the low pressure turbine, at least a portion
of the at least one casing having a high emissivity surface finish
on its outer surface to increase the rate of radiation of heat from
at least one of the turbines.
[0022] At least a portion of the at least one casing may have a
high emissivity surface finish on its outer surface. At least a
portion of the at least one casing may have a high emissivity
surface finish or a low emissivity surface finish on its inner
surface.
[0023] The high emissivity surface finish may comprise a coating
applied to, or formed on, the surface of the at least one rotor or
the at least one casing. The coating may comprise a high emissivity
metal oxide, a metal oxide formed on the at least one rotor or the
at least one casing due to oxidation of the at least one rotor or
the at least one casing, carbon, black paint or other suitable
colour paint.
[0024] The low emissivity surface finish may comprise a polished or
machined portion of the surface of the at least one rotor or the at
least one casing, or a coating applied to the surface of the at
least one rotor or the at least one casing. The coating may
comprise a polished metal coating, a polished silver coating, a
polished gold coating, or a low emissivity metal oxide.
[0025] The at least one rotor may be rotatably mounted on the
casing by a support structure, the support structure carrying a
bearing chamber having a bearing.
[0026] The surface of the bearing chamber having a low emissivity
surface finish. The upstream and downstream surfaces of the support
structure having a high emissivity surface finish.
[0027] The present invention also provides a rotor for a gas
turbine engine having a low emissivity surface finish, or high
emissivity surface finish, on at least a portion of its surface to
reduce temperature differentials between an upper portion and a
lower portion of the rotor.
[0028] A high emissivity surface finish may be arranged on at least
a portion of the radially inner surface of the rotor. The high
emissivity surface finish may be arranged on substantially the
whole of the radially inner surface of the rotor. A high emissivity
surface finish may be arranged on at least a portion of the
radially outer surface of the rotor. The high emissivity surface
finish may be arranged on substantially the whole of the radially
outer surface of the rotor.
[0029] A low emissivity surface may be arranged on at least a
portion of the radially outer surface of the rotor. The low
emissivity surface finish may be arranged on substantially the
whole of the radially outer surface of the rotor.
[0030] A high emissivity surface finish may be arranged on at least
a portion of the radially inner surface of the rotor, a high
emissivity surface finish is arranged on at least a portion of the
radially outer surface of the rotor, a low emissivity surface
finish is arranged on at least a portion of the radially outer
surface of the rotor and a low emissivity surface finish is
arranged on at least a portion of the radially inner surface of the
rotor.
[0031] A high emissivity surface finish may be arranged on at least
a portion of the downstream surface of the rotor. The high
emissivity surface finish may be arranged on substantially all of
the downstream surface of the rotor.
[0032] The rotor may be a high pressure rotor, an intermediate
pressure rotor or a low pressure rotor.
[0033] The high emissivity surface finish may comprise a coating
applied to, or formed on, the surface of the rotor. The coating may
comprise a high emissivity metal oxide, a metal oxide formed on the
rotor due to oxidation of the rotor, carbon, black paint or other
suitable colour paint.
[0034] The low emissivity surface finish may comprise a polished or
other machined portion of the surface of the rotor or a coating
applied to the surface of the rotor. The coating may comprise a
polished metal coating, a polished silver coating, a polished gold
coating, or a low emissivity metal oxide.
[0035] The present invention will be more fully described by way of
example with reference to the accompanying drawings in which:
[0036] FIG. 1 shows a gas turbine engine having a rotor according
to the present invention.
[0037] FIG. 2 is an enlarged cross-sectional view through the gas
turbine engine in FIG. 1 showing rotors according to the present
invention.
[0038] FIG. 3 is an enlarged cross-sectional view through the gas
turbine engine in FIG. 1 showing alternative rotors according to
the present invention.
[0039] FIG. 4 is an enlarged cross-sectional view through the gas
turbine engine in FIG. 1 showing further rotors according to the
present invention.
[0040] FIG. 5 is an enlarged cross-sectional view through the gas
turbine engine in FIG. 1 showing further rotors according to the
present invention.
[0041] FIG. 6 is a graph showing magnitude of rotor bow against
time after gas turbine engine shut down.
[0042] FIG. 7 is a graph showing temperature difference between
upper and lower portions of a rotor against time after isolation
from heat source for high emissivity coated and uncoated
rotors.
[0043] A turbofan gas turbine engine 10, as shown in FIG. 1,
comprises an intake 12, a fan section 14, a compressor section 16,
a combustion section 18, a turbine section 20 and an outlet 22. The
fan section 14 has a fan outlet 24. The compressor section 16
comprises an upstream, low pressure or booster, compressor 26 and a
downstream, high pressure, compressor 28. The turbine section 20
comprises an upstream, high pressure, turbine 30 and a downstream,
low pressure, turbine 32. The fan section 14 and the low pressure
compressor 26 are driven by the low pressure turbine 32 via a shaft
36. The high pressure compressor 28 is driven by the high pressure
turbine 32 via a shaft 34. The shaft 36 is coaxially arranged
within shaft 34. The fan section 14, low pressure compressor 26,
shaft 36 and low pressure turbine 32 form a low pressure rotor 40.
The high pressure compressor 28, shaft 34 and high pressure turbine
30 form a high pressure rotor 38.
[0044] One arrangement of the high pressure rotor 38 and low
pressure rotor 40 to reduce rotor bowing during shut down of the
gas turbine engine 10 is shown in FIG. 2. The whole of the radially
inner surface 42 of the high pressure rotor 38 is provided with a
high emissivity surface finish 44. A portion 48 of the radially
outer surface 46 of the low pressure rotor 40 is provided with a
high emissivity surface finish 50, preferably the whole of the
radially outer surface 46 of the low pressure rotor 40 is provided
with a high emissivity surface finish 50. The radially inner
surface of the low pressure rotor 40 is provided with a high
emissivity surface finish 50, preferably the whole of the radially
inner surface of the low pressure rotor 40 is provided with a high
emissivity surface finish 50. The portion 48 of the radially outer
surface 46 of the low pressure rotor 40 is aligned axially with and
coaxially within the high pressure rotor 38 and the portion 48 is
on the low pressure shaft 36. The inner surface 42 of the high
pressure rotor 38 includes those surfaces actually facing in a
radially inward direction and may include those surfaces facing in
an axially upstream direction or an axially downstream direction on
the individual discs making up the high pressure rotor.
[0045] A high emissivity surface finish absorbs more radiation than
a low emissivity surface finish at a given level of incident
radiated heat and a high emissivity surface finish emits more
radiation than a low emissivity surface finish at a given
temperature.
[0046] The high emissivity surface finish 44 on the high pressure
rotor 38 and the high emissivity surface finish 50 on the low
pressure rotor 40 increases the emissivity of these surfaces and
this increases radiation heat transfer from the hotter upper
portion 52 of the high pressure rotor 38 to the cooler lower
portion 54 of the high pressure rotor 38 and from the hotter upper
portion 56 of the low pressure rotor 40 to the cooler lower portion
58 of the low pressure rotor 40. This reduces, or minimises, the
temperature difference between the upper portion 52 of the high
pressure rotor 38 and the lower portion 54 of the high pressure
rotor 38 and reduces, or minimises, the temperature difference
between the upper portion 56 of the low pressure rotor 40 and the
lower portion 58 of the low pressure rotor 40. The reduction in
temperature difference will reduce the differential thermal
expansion, the bowing, of the high pressure rotor 38 and the low
pressure rotor 40 and will therefore reduce the amount of vibration
of the high pressure rotor 38 and low pressure rotor 40, at their
respective critical speeds, if the gas turbine engine 10 is
restarted while the gas turbine engine 10 is cooling down.
[0047] Another advantage is that the high emissivity surface
finishes 44 and 50 improve the service life of the rotor because a
more uniform temperature is produced circumferentially around the
high pressure rotor 38 and low pressure rotor 50. Hence the thermal
expansion differences circumferentially around the rotor are
reduced and hence the strains produced in the rotor, at high speeds
if the gas turbine engine 10 is restarted and run up to high speeds
while the gas turbine engine 10 is cooling down, are reduced.
[0048] Another arrangement of the high pressure rotor 38 to reduce
rotor bowing during shut down of the gas turbine engine 10 is shown
in FIG. 3. Portions 62 and 64 of the radially inner surface 42 of
the high pressure rotor 38 and portions 66 of the radially outer
surface 60 of the high pressure rotor 38 are provided with a low
emissivity surface finish 68. A portion 72 of the radially inner
surface 70 of the surrounding combustion section 18 is provided
with a low emissivity surface finish 74. The portion 72 of the
radially inner surface 70 of the combustion section 18 is aligned
axially with and coaxially around the high pressure shaft 34 of the
high pressure rotor 38.
[0049] The low emissivity surface finish 68 on the portions 62, 64
and 66 of the high pressure rotor 38 and the low emissivity surface
finish 74 on the portion 72 of the radially inner surface 70 of the
combustion section 18 decreases the emissivity of these surfaces
and reduces radiation heat transfer axially from the hotter turbine
section 20 to the cooler lower compressor section 16 of the gas
turbine engine 10. This reduces, or minimises, the amount of heat
transferred from the turbine section 20 to the compressor section
16 and therefore reduces, or minimises, the ability of the
convection currents to create the temperature difference between
the upper portion 52 of the high pressure rotor 38 and the lower
portion 54 of the high pressure rotor 38. The temperature
difference produced between the upper portion 52 of the high
pressure rotor 38 and the lower portion 54 of the high pressure
rotor 38 is reduced. The reduction in temperature difference will
reduce the differential thermal expansion, the bowing, of the high
pressure rotor 38 and the low pressure rotor 40 and will therefore
reduce the amount of vibration of the high pressure rotor 38 and
low pressure rotor 40 if the gas turbine engine 10 is restarted
while the gas turbine engine 10 is cooling down.
[0050] A further arrangement of the high pressure rotor 38 to
counteract the effects of rotor bowing during shut down of the gas
turbine engine 10 is shown in FIG. 4. A spigotted, bolted, joint 80
for fastening two portions 82 and 84 of the high pressure rotor 38
is shown. The first portion 82, which comprises the spigot, of the
high pressure rotor 38, has a radially outer surface portion 86 and
a radially inner surface portion 88 provided with a high emissivity
surface finish 90 and a radially inner surface portion 92 provided
with a low emissivity surface finish 94. The second portion 84 of
the high pressure rotor 38 has a radially outer surface portion 96
which has a low emissivity surface finish 98 and a radially inner
surface portion 100 which has a high emissivity surface finish 102.
The radially outer surface 104 of the low pressure shaft 36 has a
high emissivity surface finish 106 and the radially inner surface
108 of the combustion section 18 has a low emissivity surface
finish 110.
[0051] The high emissivity surface finish 102 on the radially inner
surface portion 100 of the second portion 84 of the high pressure
rotor 38 loses heat by radiation to the shaft 36 more quickly than
the low emissivity surface finish 94 on the radially inner surface
portion 92 of the first portion 82 of the high pressure rotor 38.
The high emissivity surface finish 90 on the radially outer surface
portion 86 of the first portion 82 of the high pressure rotor 38
absorbs more heat by radiation from the radially inner surface of
the combustion section 18 than the low emissivity surface finish 98
of the radially outer surface portion 96 of the second portion 84
of the high pressure rotor 38 absorbs by radiation from the
radially inner surface of the combustion section 18. This results
in the spigot on the first portion 82 cooling at a lower rate than
the second portion 84 and thus the spigot interference is
maintained. The low emissivity surface finish 110 on the radially
inner surface 108 of the combustion section 18 minimises radiation
heat transfer from the combustion section 18 to the high pressure
rotor 38. The high emissivity surface finish 106 on the radially
outer surface 104 of the low pressure shaft 36 maximises radiation
heat transfer from the high pressure rotor 38 to the low pressure
shaft 36. The low emissivity surface finish 94 on the radially
inner surface portion 92 of the first portion 82 of the high
pressure rotor 38 minimises axial radiation heat transfer. The high
emissivity surface finish 90 on the radially inner surface portion
88 of the first portion 82 of the high pressure rotor 38 maximises
radiation heat transfer from the upper portion of the high pressure
rotor 38 to the lower portion of the high pressure rotor 38.
[0052] This arrangement maintains the interference fit of the
spigotted, bolted, joint 80 as the high pressure rotor 38 cools
down and reduces wear of the spigotted, bolted, joint 80 due to
vibration of the high pressure rotor 38 if the gas turbine engine
10 is restarted while the gas turbine engine 10 is cooling down.
This arrangement therefore reduces the rate of increase in
sensitivity of the spigotted, bolted, joint 80 to rotor 38 bowing
over the service life of the gas turbine engine 10.
[0053] Alternatively, the inner surface portion 92 of the high
pressure rotor 38 may be provided with a high emissivity surface
finish rather than a low emissivity surface finish.
[0054] In a further embodiment of the invention, as shown in FIG.
5, a high emissivity surface finish 44 is provided on the
downstream surface of the high pressure turbine disc of the high
pressure turbine 30 and a high emissivity surface finish 50 is
provided on the upstream surface of the low pressure turbine disc
of the low pressure turbine 32 and on the outer and inner surfaces
of the shaft 36 downstream of the high pressure turbine 30.
Additionally the upstream and downstream surfaces of a support
structure 112 for the bearing chamber 114 for the high pressure
rotor 38 are provided with a high emissivity surface finish 116 and
the bearing chamber 114 is provided with a low emissivity surface
finish 118. The upstream and downstream surfaces of a support
structure 120 for the bearing chamber 122 for the low pressure
rotor 40 are provided with a high emissivity surface finish 124 and
the bearing chamber 122 is provided with a low emissivity surface
finish 126.
[0055] In operation the high emissivity surface finish 44 on the
downstream surface of the high pressure turbine 30 of the high
pressure rotor 38 increases the rate of transfer of heat by
radiation from the high pressure turbine 30 to the support
structure 112. The high emissivity surface finish 116 on the
upstream surface of the support structure 112 increases the amount
of heat absorbed by the support structure 112 and the high
emissivity surface finish 116 on the downstream surface of the
support structure 112 increases the rate of transfer of heat by
radiation to the low pressure turbine 32.
[0056] The high emissivity surface finish 50 on the upstream
surface of the low pressure turbine 32 increases the amount of heat
absorbed by the low pressure turbine 32 and the high emissivity
surface finish 50 on the downstream surface of the low pressure
turbine 32 of the low pressure rotor 40 increases the rate of
transfer of heat by radiation to the support structure 120. The
high emissivity surface finish 124 on the upstream surface of the
support structure 120 increases the amount of heat absorbed by the
support structure 120 and the high emissivity surface finish 124 on
the downstream surface of the support structure 120 increases the
rate of transfer of heat by radiation, conduction and convection to
the outside of the gas turbine engine 10.
[0057] When the gas turbine engine 10 is shut down the quantity of
heat in the turbines 30 and 32 is fixed. This arrangement reduces,
or minimises, the amount of heat transferred in an axially upstream
direction from the turbine section 20 to the compressor section 16
and therefore reduces, or minimises, the ability of the convection
currents to create the temperature difference between the upper
portion 52 of the high pressure rotor 38 and the lower portion 54
of the high pressure rotor 38. This arrangement achieves this
result by increasing the amount of heat transferred in an axially
downstream direction from the turbine section 20 through the
exhaust.
[0058] The low emissivity surface finish 126 on the bearing chamber
122 minimises the amount of heat transferred by radiation from the
turbines 30 and 32 to the bearing chamber 122 while the engine is
cooling down.
[0059] Also the outer surface of the turbine casing 130 is provided
with a high emissivity surface finish 132, the inner and outer
surfaces of the turbine casing cooling duct 134 are provided with a
high emissivity surface finish 136 and the inner and outer surfaces
of the core casing 138 are provided with a high emissivity surface
finish 140. In some instances a number of axially spaced hollow
annular turbine casing cooling ducts are provided around the
turbine casing 130, instead of the single turbine casing cooing
duct 134, these are provided with a high emissivity surface finish
132 on their outer surfaces. The inner surface of the fan casing
may also be provided with a high emissivity surface.
[0060] In operation the high emissivity surface finish 132 on the
turbine casing 130 increases the rate of transfer of heat by
radiation to the turbine casing cooling duct 134. The high
emissivity surface finish 136 on the turbine casing cooling duct
134 increases the rate of transfer of heat by radiation to the core
casing 138 and the high emissivity surface finish on the core
casing 138 increases the rate of heat transfer by radiation,
conduction and convection to the air around the core casing
138.
[0061] The temperatures of components surrounding the turbine
casing 130 may vary and this may result in circumferential and
axial variations in the rate of cooling of the turbine casing 130.
This may result in distortions of the turbine casing 130, due to
differential thermal strains, resulting in a non-circular turbine
casing 130 and a bowed static structure.
[0062] The surface finishes on the turbine casing 130, turbine
casing cooling duct 134 and the core casing 138 may be varied
locally to compensate for these circumferential and/or axial
variations in the temperature of components surrounding the turbine
casing 130. These variations in the surface finish may be locally
higher emissivity surface finish or locally lower emissivity
surface finish to vary the rate of radiation heat transfer from the
turbine casing 130, cooling duct 134 and core casing 138.
[0063] The high emissivity surface finish may comprise a coating
applied to, or formed on, the surface of the rotor, casing or
bearing support. The high emissivity surface finish coating may be
a metal oxide, a metal oxide formed on the surface of the material
of the rotor, carbon, black or other suitable colour paint or other
suitable coating.
[0064] The low emissivity surface finish may comprise a polished or
machined portion of the surface of the rotor or a coating applied
to the surface of the rotor, bearing chamber or casing. The low
emissivity surface finish coating may be a polished metal coating,
for example a polished silver coating, a polished gold coating, a
polished chromium coating, a polished nickel coating, or a low
emissivity metal oxide or other suitable coating. The machined
portion of the surface of the rotor may be a turned, milled, ground
or finish produced by other suitable machining process.
[0065] The magnitude of rotor bow against time after gas turbine
engine shut down for a conventional two shaft gas turbine engine is
shown in FIG. 6 for a gas turbine engine shut down when very hot
and for a gas turbine engine shut down after cooling at low power.
Line A shows the magnitude of rotor bow increasing to a peak some
time after the gas turbine engine has been shut down before
gradually decreasing to zero for a gas turbine engine shut down
when very hot. Line B shows the magnitude of rotor bow increasing
to a peak some time after the gas turbine engine has been shut down
before gradually decreasing to zero for a gas turbine engine shut
down after cooling at low power. It is seen that the cooling of the
gas turbine engine by running at low power reduces the maximum
magnitude of bowing of the rotor, possibly to just below the
magnitude at which bowing of the rotor becomes critical and
produces damaging vibrations.
[0066] The temperature difference between the upper portion and
lower portion of a rotor test rig against time after isolation from
heat source for a high emissivity coated rotor and an uncoated
rotor are shown in FIG. 7. Lines C and D show the temperature
difference between the upper portion and lower portion for a rotor
having a high emissivity coating on its radially inner surface and
lines E and F show the temperature difference between the upper
portion and lower portion for an uncoated conventional rotor. It is
seen that the temperature difference for the rotor with a high
emissivity coating on its inner surface is about 30% lower than the
uncoated rotor.
[0067] Although the invention has been described with reference to
a gas turbine engine comprising two shafts it may equally well be
used in a gas turbine engine comprising a single shaft or three or
more shafts. In the case if a three shaft gas turbine engine the
high or low emissivity surface finish may be applied to an
intermediate pressure shaft arranged coaxially around the low
pressure shaft and coaxially within the high pressure shaft.
[0068] It may also be possible to provide an intermediate
emissivity surface finish to portions of the rotors or casings.
* * * * *