U.S. patent application number 11/397560 was filed with the patent office on 2007-10-11 for gas turbine compressor casing flowpath rings.
This patent application is currently assigned to General Electric Company. Invention is credited to Lynn C. Gagne, Raymond H. Goetze, David Martin Johnson, Jeff Moree, Nicholas P. Poccia.
Application Number | 20070237629 11/397560 |
Document ID | / |
Family ID | 38050207 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070237629 |
Kind Code |
A1 |
Moree; Jeff ; et
al. |
October 11, 2007 |
Gas turbine compressor casing flowpath rings
Abstract
A flowpath ring is securable in a machined groove of a gas
turbine compressor stator casing. The ring includes a connector
section engageable with and shaped corresponding to the machined
groove. A flowpath section is disposed radially inward relative to
the connector section and includes a clearance surface disposed
facing a turbine rotor blade. The flowpath section defines a blade
flowpath when secured in the turbine stator casing machined groove.
The use of flowpath rings facilitates flowpath repair if rotor
blade tip rubs occur. Additionally, the rings enable better
matching of transient thermal responses between the compressor
rotor and compressor casings.
Inventors: |
Moree; Jeff; (Greer, SC)
; Poccia; Nicholas P.; (Gansevoort, NY) ; Gagne;
Lynn C.; (Simpsonville, SC) ; Goetze; Raymond H.;
(Greenville, SC) ; Johnson; David Martin;
(Simpsonville, SC) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
38050207 |
Appl. No.: |
11/397560 |
Filed: |
April 5, 2006 |
Current U.S.
Class: |
415/173.1 |
Current CPC
Class: |
F01D 9/04 20130101; F05D
2240/11 20130101 |
Class at
Publication: |
415/173.1 |
International
Class: |
F01D 11/08 20060101
F01D011/08 |
Claims
1. A flowpath ring securable in a machined groove of a compressor
stator casing, the flowpath ring comprising: a connector section
engageable with the machined groove, the connector section being
shaped corresponding to the machined groove; and a flowpath section
disposed radially inward relative to the connector section, the
flowpath section including a clearance surface disposed facing a
compressor rotor blade and defining a blade flowpath when secured
in the compressor stator casing machined groove.
2. A flowpath ring according to claim 1, wherein the flowpath ring
comprises a plurality of segments.
3. A flowpath ring according to claim 1, wherein the ring is
attachable in the compressor stator casing machined groove between
adjacent stator airfoils.
4. A flowpath ring according to claim 1, further comprising an
abradable coating on the clearance surface.
5. A flowpath ring according to claim 4, further comprising a
groove in the clearance surface, the abradable coating being
disposed in the groove.
6. A flowpath ring according to claim 1, further comprising at
least one air gap insulator disposed on a casing side surface of
the flowpath ring.
7. A flowpath ring according to claim 6, wherein the air gap
insulator comprises a groove formed in the casing side surface.
8. A flowpath ring according to claim 6, wherein the air gap
insulator further comprises a seal interposable between the casing
side surface of the flowpath ring and the casing.
9. A flowpath ring according to claim 1, comprising a substantially
T-shaped cross-section, wherein the connector section defines a
stem of the T-shape, and wherein the flowpath section defines a
cross of the T-shape.
10. A compressor comprising: a stator casing having airfoil grooves
each supporting a plurality of stator airfoils; a rotor supporting
a plurality of rotor blades for rotation relative to the stator
casing; and a plurality of flowpath rings secured in respective
ring grooves in the stator casing, wherein each of the flowpath
rings comprises: a connector section engaged with the ring groove,
the connector section being shaped corresponding to the ring
groove, and a flowpath section disposed radially inward relative to
the connector section, the flowpath section including a clearance
surface disposed facing the rotor blades and defining a blade
flowpath.
11. A compressor according to claim 10, wherein each of the
flowpath rings comprises a plurality of segments.
12. A compressor according to claim 10, wherein the ring grooves
are formed between adjacent ones of the airfoil grooves.
13. A compressor according to claim 10, wherein each of the
flowpath rings further comprises an abradable coating on the
clearance surface.
14. A compressor according to claim 10, wherein each of the
flowpath rings further comprises at least one air gap insulator
disposed on a casing side surface thereof.
15. A compressor according to claim 14, wherein the air gap
insulator comprises a groove formed in the casing side surface.
16. A compressor according to claim 14, wherein the air gap
insulator further comprises a seal interposable between the casing
side surface of the flowpath ring and the casing.
17. A compressor according to claim 10, wherein each of the
flowpath rings comprises a substantially T-shaped cross-section,
wherein the connector section defines a stem of the T-shape, and
wherein the flowpath section defines a cross of the T-shape.
18. A compressor according to claim 10, wherein each of the
flowpath rings is shaped to match transient thermal responses
between the rotor and the stator casing.
19. A method of assembling a stator casing, the method comprising:
machining a plurality of airfoil grooves each for supporting a
plurality of stator airfoils; machining a plurality of ring grooves
interposed between adjacent ones of the airfoil grooves; and
securing a plurality of the flowpath rings of claim 1 in respective
ones of the ring grooves.
20. A method of restoring original performance and compressor surge
margin or modifying performance and compressor surge margin in the
compressor of claim 10, the method comprising removing damaged ones
of the flowpath rings, and inserting replacement rings.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to compressor rotors and
stator casings and, more particularly, to rings set in dedicated
grooves in the stator casing that define the outer flowpath and
that can be easily replaced in the event of rotor airfoil tip
rubbing.
[0002] With reference to FIG. 1, showing a cross-sectional view of
a typical gas turbine, gas turbines attain optimum performance when
the clearance 22 between rotating blades 20 and the casing 12 is
maintained at an optimal distance, which is generally very small,
e.g., 40-80 mils at steady state temperatures. This clearance must
be made large enough, however, to account for part stack up
tolerance, mechanical and thermal growth differences between the
casing 12 and the rotating airfoil 20.
[0003] A common occurrence in gas turbine compressors is rotor
blades rubbing on compressor casings for various reasons. Rubbing
can be caused by a number of conditions such as improper alignment
between the rotor 18 and the casing, casing joint slippage at the
horizontal and vertical flanges, or transient thermal response
differences between the casing 12 and rotating parts. The end
result is airfoil 20 tip loss and/or casing flowpath wear. These
conditions lead to a loss of compressor performance and surge
margin. If rubs are severe enough, the casing and rotating airfoils
have to be replaced. Typically, this will result in loss of service
of the gas turbine for an extended period of time.
[0004] With continued reference to FIG. 1, current industrial gas
turbine compressor casings are built with circumferential slots 14
machined into the casing for stationary airfoils 16. Between the
slots, the casing 12 is machined to a cylindrical or conical shape
and forms the outer flowpath for the rotating blades 20. With
current designs, the casing thickness is the main design variable
that can be changed in an effort to thermally match the
displacements of the casing 12 and rotor 18.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In an exemplary embodiment of the invention, a flowpath ring
is securable in a machined groove of a compressor stator casing.
The flowpath ring includes a connector section engageable with the
machined groove where the connector section is shaped corresponding
to the machined groove. A flowpath section is disposed radially
inward relative to the connector section and includes a clearance
surface disposed facing a compressor rotor blade and defining a
blade flowpath when secured in the compressor stator casing
machined groove.
[0006] In an another exemplary embodiment of the invention, a gas
turbine compressor includes a stator casing having airfoil grooves
each supporting a plurality of stator airfoils. A rotor supports a
plurality of rotor blades for rotation relative to the stator
casing. A plurality of the noted flowpath rings are secured in
respective ring grooves in the stator casing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a typical gas turbine
compressor;
[0008] FIG. 2 shows the machined stator casing including ring
grooves between the stator grooves;
[0009] FIG. 3 shows flowpath rings secured in the stator ring
grooves;
[0010] FIG. 4 illustrates the flowpath rings including air gap
insulators; and
[0011] FIG. 5 shows the flowpath ring including seals to minimize
back side leakage.
DETAILED DESCRIPTION OF THE INVENTION
[0012] It would be desirable to facilitate repairs in rotor
flowpaths due to rotor airfoil tip rubbing. In this manner, optimum
clearances can be restored while recovering performance and surge
margin. Also, clearances can be made tighter in order to increase
performance and surge margin.
[0013] By utilizing easily replaceable rings installed in the
casing where the rotor blades may rub the casing, flowpath repairs
can be effected rapidly and efficiently. Additionally, replaceable
rings (or flowpath rings) can reduce the rate of heat transfer into
the casing, thereby changing the transient and steady state
matching of the rotor and casing thermal growth. This allows for a
passive clearance controlling design feature that permits tighter
clearances between the rotor blades and the casing, adding to
overall engine performance and surge margins.
[0014] With reference to FIGS. 1-3, a gas turbine includes a stator
casing 12 having a plurality of airfoil grooves 14 machined therein
as is conventional. The airfoil grooves 14 are formed generally
continuously in the inside circumference of the stator casing 12.
The airfoil grooves 14 each support a plurality of stator airfoils
16 as is also conventional.
[0015] A rotor 18 supports a plurality of rotor blades 20 for
rotation relative to the stator casing 12. As noted, gas turbines
attain optimum performance when the clearance, designated by
reference numeral 22, between rotating airfoils and the stator
casing 12 is maintained at an optimal distance, which is generally
very small (e.g., 40-80 mils at steady state temperature). A common
occurrence during the operation of a gas turbine compressor is
rubbing or contact between tips of the rotor blades 20 and the
stator casing 12. The end result is rotor tip loss and/or casing
flowpath wear, which can lead to a loss of compressor performance
and surge margin. Moreover, if rubs are severe enough, the stator
casing 12 and rotor blades 20 may require replacement, resulting in
loss of service of the turbine for an extended period of time.
[0016] With reference to FIG. 2, the stator casing 12 is machined
with additional grooves 24 preferably interposed between adjacent
ones of the airfoil grooves 14. The machining process for forming
the ring grooves 24 is very similar to the conventional process
conducted in machining the stator airfoil grooves 14, and details
of the manufacturing/machining process will not be described.
[0017] A plurality of flowpath rings 26 (FIG. 3) are secured in
respective ring grooves 24 in the stator casing 12. The flowpath
rings 26 include a connector section 28 shaped corresponding to the
machined groove 24 and a flowpath section 30 disposed radially
inward relative to the casing 12 (i.e., toward the rotor 18). The
flowpath section 30 includes a clearance surface 32 disposed facing
the turbine rotor blades 20 and defining a blade flowpath when the
flowpath rings 26 are secured in the stator casing 12. Preferably,
the flowpath rings 26 are each formed of a plurality of ring
segments to minimize binding in the groove 24.
[0018] The flowpath rings 26 can be used to optimize tip clearance
by using an abradable coating 34 formed on the clearance surface 32
of the flowpath rings 26. Preferably, the clearance surface 32
includes a groove 36 or the like in which the abradable coating 34
is disposed. Examples of abradable coatings that can be used for
this application are aluminium silicon alloy/polymer composite,
nickel/graphite composite, aluminium bronze/polymer composites. By
using the abradable coating 34, the rotor blades 20 can serve to
carve/cut the coating during the clearance pinch-point to attain an
optimal steady state running clearance.
[0019] With reference to FIG. 4, the flowpath rings 26 may
additionally include at least one air gap insulator 38 formed on a
casing side surface as shown. The air gap insulators 38 are
preferably machined as a groove in the casing side surface. An
optimum air gap on the casing side of the flowpath rings 26 can
serve to insulate the casing 12 from the rapid transient response
of the flowpath temperature. The air gap insulators 38 control heat
transfer between the flowpath rings 26 and the casing 12 to thereby
control the rate of heating or cooling of the casing 12 in response
to temperature changes in the flowpath. Increases to the air gap
insulator 38 thickness and decreases in the surface area of the
points of contact will reduce the rate of heat transfer and thus
reduce the casing thermal responsiveness. These are the primary
design variables which may be used to match the casing response to
the rotor 18 response.
[0020] Moreover, in order to further minimize flowpath gas leakage
behind the rings 26, a seal 40 (FIG. 5) may be interposed between
the casing side surface of the rings 26 and the stator casing 12.
As shown in FIG. 5, an additional groove or notch 42 may be formed
in the casing side surface of the ring flowpath section 30 to
accommodate the seal 40. Preferably, the seal 40 is formed of a
metallic wire/rope or other suitable material.
[0021] Since the flowpath rings are replaceable, flowpath repairs
due to rotor blade tip rubbing can be quickly facilitated in a
reliable and cost effective manner. Thus, even on units with heavy
rubbing, original performance and compressor surge margin can be
restored. Moreover, the cycle time and associated cost to replace
the flowpath rings is considerably less than to replace casings.
Additionally, the flowpath rings 26 allow for a better thermal
match between rotors and compressor casings, allowing a designer to
better match the thermal responses and thereby run with tighter
clearances. As noted, the compressor casing flowpath rings can be
coated with an abradable material to allow closer clearances and an
improvement in compressor performance. As would be appreciated by
those of ordinary skill in the art, the flowpath rings can be
installed in new units as a performance enhancement feature,
particularly if combined with abradable coatings. Since the
flowpath ring grooves can be machined into a stator casing in the
same manner as stator slots with similar tolerance control, the
flowpath rings can be accommodated with minimal cost and cycle
impact on the casing.
[0022] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be
limited to the disclosed embodiments, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *