U.S. patent application number 10/428219 was filed with the patent office on 2004-11-04 for high pressure turbine elastic clearance control system and method.
This patent application is currently assigned to General Electric Company. Invention is credited to Albers, Robert J., Boyle, Marcia, Ruiz, Rafael.
Application Number | 20040219011 10/428219 |
Document ID | / |
Family ID | 32990469 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219011 |
Kind Code |
A1 |
Albers, Robert J. ; et
al. |
November 4, 2004 |
High pressure turbine elastic clearance control system and
method
Abstract
A system and method for achieving clearance control for a
high-pressure turbine by means of casing mechanical deflection. An
active clearance control system is provided to act on a blade that
rotates near a shroud. The shroud is attached to a case at a shroud
supporting location, or shroud hanger. A clearance is required
between a tip of the blade and the shroud. The blade tip and shroud
are surrounded with an elastic case. This case can deflect radially
in response not only to thermal expansion, but also to a difference
in pressures acting on the inner and outer diameters of the
case.
Inventors: |
Albers, Robert J.; (Park
Hills, KY) ; Ruiz, Rafael; (Mason, OH) ;
Boyle, Marcia; (Lebanon, OH) |
Correspondence
Address: |
Barbara Joan Haushalter
Law Office
228 Bent Pines Court
Bellefontaine
OH
43311
US
|
Assignee: |
General Electric Company
|
Family ID: |
32990469 |
Appl. No.: |
10/428219 |
Filed: |
May 2, 2003 |
Current U.S.
Class: |
415/174.2 |
Current CPC
Class: |
F01D 11/18 20130101;
F01D 11/16 20130101; F01D 25/246 20130101 |
Class at
Publication: |
415/174.2 |
International
Class: |
F01D 005/00 |
Claims
What is claimed is:
1. A method of controlling clearance in a gas turbine engine,
comprising the steps of: providing an active clearance control
system acting on at least one blade that rotates near at least one
shroud, the at least one shroud having an associated shroud hanger,
wherein a clearance is required between a tip of the at least one
blade and the at least one shroud; and surrounding the blade tip
and shroud with an elastic case, wherein the case can deflect
radially in response to thermal expansion and a difference in
pressures acting on inner and outer diameters of the case.
2. A method as claimed in claim 1 further comprising the step of
attaching a band to the case outer diameter to account for blade
tip loss during operation.
3. A method as claimed in claim 2 wherein the step of attaching a
band further comprises the step of attaching a band of high
temperature alloy or coating.
4. A method as claimed in claim 1 wherein the step of providing an
active clearance control system further comprises the step of
providing a single stage active clearance control system.
5. A method as claimed in claim 1 wherein the step of providing an
active clearance control system further comprises the step of
providing a dual stage active clearance control system.
6. A method as claimed in claim 1 wherein the step of surrounding
the blade tip and shroud with an elastic case further comprises the
step of providing an elastic case having elastic deflection during
engine operation.
7. A system for controlling clearance in a gas turbine engine,
comprising: an active clearance control system to act on at least
one blade that rotates near at least one shroud, the at least one
shroud having an associated shroud hanger, wherein a clearance is
required between a tip of the at least one blade and the at least
one shroud; and an elastic case to surround the blade tip and
shroud, wherein the case can deflect radially in response to a
difference in pressures acting on inner and outer diameters of the
case.
8. A system as claimed in claim 7 further comprising a band
attached to the case outer diameter to account for blade tip loss
during operation.
9. A system as claimed in claim 8 wherein the step band comprises a
band of high temperature alloy or coating.
10. A system as claimed in claim 7 wherein the active clearance
control system comprises a single stage active clearance control
system.
11. A system as claimed in claim 7 wherein the active clearance
control system comprises a dual stage active clearance control
system.
12. A system as claimed in claim 7 wherein the elastic case
comprises an elastic case having elastic deflection during engine
operation.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the active clearance
control system of a high-pressure turbine and, more particularly,
to casing mechanical deflection for the high-pressure turbine.
[0002] The active clearance control system (ACC) of a high-pressure
turbine (HPT) has two basic functions. The first is to maintain
tight blade-shroud clearances during transient operation, to
minimize exhaust gas temperature (EGT). The second is to close the
tip clearances during steady-state operation to increase turbine
efficiency and reduce fuel burn.
[0003] For both types of designs, i.e., single and dual stage, the
case will shrink or grow, depending on the air-cooling temperature
and the effect on the temperature of the case. Changing the case
temperature will result in a clearance change. The thermal part of
the clearance system is a slow response deflection approximately
30-60 seconds.
[0004] State of the art active clearance control systems account
for disk elastic deflection and blade thermal growth from idle
conditions to take off by having a large clearance at idle. Such a
system requires a large change in temperature at steady state
conditions to reduce clearance to a minimum level. However, the
desired case temperature change can be beyond system capabilities.
In addition, it is difficult for the state of the art system to
respond in time to overcome any rotor elastic stretch due to an
instantaneous acceleration or re-acceleration (reburst) resulting
in airfoil to shroud contact or rub.
[0005] It would be desirable to provide an improved active
clearance control system and method for a high-pressure turbine
that overcomes problems in the existing art.
BRIEF DESCRIPTION OF THE INVENTION
[0006] A system and method are proposed wherein casing elastic
deflection is used to improve active clearance control of a
high-pressure turbine.
[0007] Accordingly, the present invention provides a system and
method for achieving clearance control for a high-pressure turbine
by means of casing mechanical deflection. An active clearance
control system is provided to act on a blade that rotates near a
shroud. The shroud is attached to a case at a shroud supporting
location, or shroud hanger. A clearance is required between a tip
of the blade and the shroud. The blade tip and shroud are
surrounded with an elastic case. This case can deflect radially in
response not only to thermal expansion, but also to a difference in
pressures acting on the inner and outer diameters of the case.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic illustration of a single stage active
clearance control system of the type that may employ the casing
mechanical deflection technique of the present invention;
[0009] FIG. 2 is a schematic illustration of a dual stage active
clearance control system of the type that may employ the casing
mechanical deflection technique of the present invention;
[0010] FIG. 3 illustrates the thin case active clearance control
according to the present invention;
[0011] FIG. 4 is a diagram that shows the relation between pressure
and rotor speed for idle to cruise conditions;
[0012] FIG. 5 is a diagram comparing the radial deflection of the
rotor and stator for a state of the art system and for the system
applying the present invention; and
[0013] FIG. 6 illustrates an alternative embodiment of the thin
case active clearance control according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Modern gas turbine engine control systems typically require
an active clearance control system for maintaining blade-shroud
clearances and tip clearances during operation. For a single and
dual stage HPT, illustrated in FIGS. 1 and 2, respectively, the
appropriate clearance 18 between the blade 14 and the shroud 16 is
achieved by controlling the case 10 temperature. For a single stage
high-pressure turbine type, the case is heated and cooled by air
coming from compressor mid stage 12 and discharge pressure source.
Moreover, for a dual stage high-pressure turbine type, the first
stage turbine case is controlled by compressor discharge pressure
air. The second stage is controlled by compressor inter-stage bleed
air. At appropriate times, the case is cooled by fan air in order
to reduce case ring 25 temperatures.
[0015] In FIGS. 1 and 2, the blade 14 and blade tip rotate as a
result of the hot air flowing through the turbine. The shroud 16 is
a piece of metal that defines the distances, or clearances, between
the blade 14 tip and the shroud 16 itself. The purpose of the
active clearance control system is to minimize clearance 18. The
larger the clearance, the less efficient the turbine will be. The
shroud 16 is attached to the case of the ACC by a hanger 22. Case
growth causes the shroud 16 to move radially. In the existing art,
the case 10 grows only by thermal expansion. With the present
invention, the case will deflect due to thermal expansion and
pressure acting on the outer and inner diameter of the case.
[0016] The present invention proposes a system and method for
improving an existing high-pressure turbine active clearance
control system by modifying the turbine case, as illustrated in
FIG. 3. In accordance with the present invention, the elastic case
24 will be a continuous 360-degree shell flexible enough to deflect
radially due to the difference between the pressures P.sub.low
acting on the outer diameter of the case 24 and P.sub.high acting
on the inner diameter of the case 24. The case 24 flexibility will
be achieved by making the case average thickness in the locations
supporting the hangers thin, so that the casing elastic deflection
is increased from the prior art design. Although the specific
thickness can vary, in the prior art the thickness of the casing at
the location where the shroud supports are attached to the casing
will be substantially thicker than that proposed by the present
invention, with the prior art configuration therefore having
negligible casing deflection. In a preferred embodiment of the
present invention, the thickness will be thinner than the current
design by eliminating the case rings 25, typically, by way of
example only, on the order of approximately 0.1 inches to 0.2
inches, or otherwise significantly thinner than the 1 to 2 inch
thickness of existing casings. It will be obvious to those skilled
in the art, however, that the thickness can vary beyond the
thickness of a preferred embodiment, still being thinner than the
existing art provides for, without departing from the scope of the
invention. As with existing systems, the shrouds 16 will be
attached to the case 24 by shroud hangers 22. The shroud and the
case will be made of a high temperature alloy.
[0017] With the application of the present invention, the blade 14
to shroud 16 clearance 18 will change when the case 24 deflects
radially due to pressure. The blade tip to shroud clearance will
depend on the magnitude of the pressure acting on the case. The
pressure acting on the case depends on the engine operating
condition. Referring now to FIG. 4 the relationship between
pressure and speed is shown. The present invention takes advantage
of this pressure and speed, resulting in the illustration of FIG.
5. In FIG. 4, the pressure is at a minimum when the engine is at
idle conditions, in region 26. It will reach a maximum during high
power at low altitude, in region 28. At cruise conditions, in
region 30, when the engine is at high altitudes, the pressure will
decrease (.about.30% change) while the speed remains almost
constant (.about.10% change). According to this relationship
between pressure and speed, illustrated in FIG. 4, the clearance
will increase when the engine goes from idle to take off
conditions. This pressure to speed relationship will allow the
system to compensate for some disk elastic stretch and blade
thermal expansion without the necessity of having large clearance
at idle. Moreover, at high altitudes the pressure acting on the
case will decrease, causing the case to shrink while the rotor
speed change is small, thus maintaining high elastic stretch. This
will result in smaller clearance at cruise relative to clearances
required by current state of the art systems.
[0018] The present invention takes advantage of the relationship
between pressure and speed. FIG. 5 illustrates the stator and rotor
deflection when the elastic case of the present invention is
applied to a single or dual stage high pressure turbine. The
elasticity of the case is indicated by dotted line 32 in FIG. 5.
The prior art stator response is shown by line 34, indicating the
thermal expansion. The rotor response for both the invention and
the prior art is shown by line 36, indicating disk elastic stretch
and blade thermal expansion during periods of idle, acceleration
and cruise. The present invention will provide a protection against
airfoil to shroud contact due to instantaneous acceleration
(reburst). The pressure will increase at nearly the same rate as
the rotor speed during an instantaneous acceleration allowing the
case to deflect to avoid airfoil to shroud contact (rubs).
[0019] Referring now to FIG. 6, an alternative embodiment for the
thin case active clearance control can be applied by modifying the
case elastic deflection to account for airfoil tip loss over
operation time. The alternative embodiment comprises a band 38
attached to the case outer diameter. The band is preferably
comprised of any suitable high temperature alloy or coating. The
band thickness will be sized depending on the amount of airfoil
material loss. The band will cause the case elastic deflection to
be less by the same amount of airfoil material loss.
[0020] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation to the teachings of the invention
without departing from the essential scope thereof. Therefore, it
is intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *