Cooled shroud

A shroud includes a panel having leading and trailing edges and inner and outer surfaces extending therebetween. A cooling passage extends through the panel from adjacent the leading edge to an intermediate location and is generally parallel to the inner and outer surfaces. The cooling passage has an inlet for receiving cooling air from adjacent the panel outer surface, a plurality of spaced apart turbulators disposed adjacent to the panel inner surface, and an outlet disposed at the leading edge for discharging the cooling air from the passage.

The present invention relates generally to gas turbine engines, and, more 
specifically, to shrouds and flowpath components therein requiring 
cooling. 
BACKGROUND OF THE INVENTION 
A gas turbine engine includes a combustor which generates hot combustion 
gases which flow downstream therefrom and through a turbine nozzle which 
suitably directs the flow into a row of turbine blades which extract 
energy therefrom. The turbine nozzle includes a plurality of 
circumferentially spaced apart stator vanes mounted radially between 
radially inner and outer bands which confine the combustion gas flow. 
Disposed radially outwardly of the turbine blades are a plurality of 
circumferentially adjacent shrouds which also confine the combustion gas 
flow. 
Both the nozzle bands and the turbine shrouds are typically cooled by 
channeling thereto cooling air which is bled from the compressor of the 
engine. 
Turbine shrouds typically have forward and aft hooks extending radially 
outwardly therefrom for conventionally mounting the shrouds to stationary 
components of the engine. In one exemplary design, the leading edge of the 
shroud extends axially upstream from the leading edge of the turbine 
blades and effects a relatively large overhang as measured between the 
shroud leading edge and the forward hook from which it is supported. The 
turbine shrouds are typically cooled by providing bleed air from the 
compressor into the shroud between the forward and aft hooks thereof 
through a suitable impingement baffle which directs the cooling air in 
impingement against the radially outer surface of the shroud. The shroud 
typically includes a plurality of rows of inclined film cooling holes 
which extend through the shrouds, with inlets disposed between forward and 
aft hooks and outlets at the leading edge overhang. As the overhang 
lengths increases, the lengths of the film cooling holes also increases 
which decreases the effectiveness of cooling the overhang since the 
cooling air increase in temperature at it travels through the relatively 
long, thin cooling holes. Improved cooling configurations are desired for 
turbine shrouds having particularly large overhangs. 
SUMMARY OF THE INVENTION 
A shroud includes a panel having leading and trailing edges and inner and 
outer surfaces extending therebetween. A cooling passage extends through 
the panel from adjacent the leading edge to an intermediate location and 
is generally parallel to the inner and outer surfaces. The cooling passage 
has an inlet for receiving cooling air from adjacent the panel outer 
surface, a plurality of spaced apart turbulators disposed adjacent to the 
panel inner surface, and an outlet disposed at the leading edge for 
discharging the cooling air from the passage.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Illustrated schematically in FIG. 1 is an exemplary high pressure turbine 
10 of an aircraft gas turbine engine. The turbine 10 includes a plurality 
of circumferentially spaced apart, radially extending turbine blades 12 
fixedly joined to an annular rotor disk 14 about an axial centerline axis 
16. Disposed upstream from the turbine blades 12 is a conventional high 
pressure turbine nozzle 18 including radially inner and outer bands 18a,b 
and a plurality of circumferentially spaced apart stator vanes 18c 
extending radially therebetween. The turbine nozzle receives hot 
combustion gas 20 from a conventional combustor (not shown), with the 
combustion gas 20 being directed downstream between the blades 12 which 
extract energy therefrom. 
To confine the combustion gas 20 from flowing freely over the radially 
outer tips of the blades 12, a plurality of circumferentially adjoining 
shrouds 22 are conventionally supported from an outer casing 24 by hangers 
26. 
Each of the shrouds 22 is an arcuate segment which collectively provide a 
360.degree. flowpath boundary around the blade tips. In accordance with 
one embodiment of the present invention as illustrated in FIG. 1, each 
shroud 22 includes an arcuate plate or panel 28 having a leading edge 28a 
for first receiving the combustion gas 20, and a trailing edge 28b at an 
opposite end thereof from which the combustion gas 20 flows downstream 
therefrom. Each of the panels 28 further includes a radially inner surface 
28c extending axially between the leading and trailing edges 28a,b which 
defines the flowpath boundary of the combustion gas 20. The panel 28 also 
includes a radially outer surface 28d extending between the leading and 
trailing edges 28a,b which is spaced radially outwardly from the inner 
surface 28c for providing a suitably thick panel 28. 
Each of the shrouds 22 includes a conventional forward hook 30 extending 
radially outwardly from the panel 28 at a suitable distance from the 
leading edge 28a for defining a cantilevered overhang 28e. A conventional 
aft hook 32 extends radially outwardly from the panel 28 adjacent to the 
trailing edge 28b. The forward and aft hooks 30, 32 are conventionally 
configured as L-shaped hooks which are complementary to the hangar 26 for 
supporting the shroud 22 radially above the turbine blade 12. 
Fixedly joined to the hangers 26 is a conventional perforated impingement 
baffle 34 which extends between the forward and aft hooks 30, 32 and above 
the panel outer surface 28d, and is conventionally provided with cooling 
air 36 which is bled from a compressor (not shown) of the gas turbine 
engine. The cooling air 36 is directed in impingement against the panel 
outer surface 28d for effecting impingement cooling thereof for the region 
of the panel 28 between the forward and aft hooks 30, 32. 
Since the panel 28 includes a relatively large overhang 28e extending 
upstream from both the forward hook 30 and the turbine blades 22, 
effective cooling thereof is required in order to obtain useful life 
thereof with minimal expenditure of the cooling air 36. In accordance with 
one embodiment of the present invention, the panel 28 includes a cooling 
manifold or passage 38 extending therein from an intermediate location of 
the panel 28 between the leading and trailing edges 28a,b, and in 
particular between the forward and aft hooks 30, 32, to the leading edge 
28a which includes the overhang 28e to be cooled. 
As shown in more particularity in FIG. 2, the cooling passage 38 is 
disposed generally parallel to the panel inner and outer surfaces 28c,d 
and includes a circumferentially elongate inlet 40 disposed at the 
intermediate location between the forward and aft hooks 30, 32 for 
receiving the cooling air 36 from adjacent the panel outer surface 28, 
with most of the cooling air 36 being used firstly for impingement cooling 
the panel outer surface 28d prior to entering the cooling passage inlet 
40. Disposed inside the cooling passage 38 are a plurality of axially 
spaced apart elongate turbulators 42 which are disposed adjacent to the 
panel inner surface 28c and are formed integrally with the radially inner 
side of the cooling passage 38. The cooling passage 38 includes an outlet 
44 disposed at the leading edge 28a for discharging the cooling air 36 
from the cooling passage 38 and along the panel inner surface 28c. The 
cooling passage outlet 44 preferably comprises one or more rows of film 
cooling holes, with two rows being illustrated for example. 
The turbulators 42 as shown in FIGS. 2 and 3 are conventional, 
circumferentially elongate ribs having a suitable height and pitch or 
spacing for enhancing the heat transfer between the cooling air 36 within 
the passage 38 and the panel 28 itself. The turbulators 42 may take any 
conventional form as desired. As illustrated in FIG. 2, the cooling 
passage 38 provides enhanced cooling of the leading edge region of the 
panel 28, and particularly at the overhang 28e, since it is a relatively 
large passage within the panel itself, and therefore decreases the 
thickness of the panel portion above and below the passage 38 itself as 
compared to the thickness of the panel 28 downstream therefrom. 
Accordingly, less mass of the panel 28 in the overhang 28e region is 
subject to being heated which decreases the initial need for the cooling 
thereof. Furthermore, instead of having relatively long film cooling holes 
extending through the relatively long overhang 28e, relatively short film 
cooling holes 44 can be provided solely adjacent to the panel leading edge 
28a for effecting cooling therefrom. 
As shown in FIGS. 2 and 3, a plurality of laterally or circumferentially 
spaced apart impingement holes 46 are disposed between the outlets 44 and 
the turbulators 42 in the cooling passage 38 for dividing the cooling 
passage 38 into an inlet plenum 38a extending aft to the passage inlet 40, 
and an outlet plenum 38b extending forward to the leading edge 28a. The 
impingement holes 46 are spaced rearwardly from the leading edge 28a to 
impinge the cooling air against the inside surface of the leading edge 28a 
for impingement cooling thereof prior to being discharged from the passage 
outlet 44. In this way, the initial cooling air 36 channeled to the 
shrouds 22 is used firstly for impingement cooling of the panel outer 
surface 28d and then flows through the passage inlet 40 for convection 
cooling of the panel 28 through the cooling passage 38, with the 
turbulators 42 providing enhanced heat transfer. The cooling air 36 is 
ejected through the impingement holes 46 for providing impingement cooling 
of the panel leading edge 28a and then flows through the plurality of film 
cooling outlet holes 44 for cooling the panel 28 adjacent thereto and then 
establishing a film of cooling air which flows aft from the leading edge 
28 along the panel inner surface 28c for providing film cooling. 
As shown in FIG. 2, the cooling passage 38 extends upstream from its inlet 
40 between the forward and aft hooks 30, 32 to channel the cooling air 36 
to the panel overhang 28e for providing enhanced cooling therefrom, with 
the cooling air 36 being discharged from the film cooling outlets 44 in an 
aft, downstream direction. As shown in FIG. 3, the cooling passage 38 
preferably extends almost the entire circumferential or lateral extend of 
each of the shrouds 22 for providing effective cooling of the entire 
circumferential extent of the overhang 28e. 
More specifically, each of the panels 28 preferably includes a plurality of 
substantially identical cooling passages 38, with adjacent ones of which 
having an elongate first rib 48a or second rib 48b extending axially 
between the impingement holes 46 and the passage inlets 40 to effect a 
flow barrier between adjacent inlet plenums 38a. In the exemplary 
embodiment illustrated in FIG. 3, the second rib 48b is a structural 
stiffening rib disposed along the center of the panel 28 parallel to the 
centerline axis 16 and extends from the leading edge 28a to adjacent the 
trailing edge 28b for stiffening the entire panel 28 in an axial 
direction. A pair of the first ribs 48a are disposed on respective sides 
of the second rib 48b for effective or creating four of the cooling 
passages 38 disposed in parallel flow for separately channeling the 
cooling air 36 from respective ones of the four inlets 40 thereof to 
respective film cooling outlet holes 44 thereof. Each of the several ribs 
48a,b provide both structural stiffening of the panel 28 as well as 
separating the adjacent cooling passages 38. The aft hook 32, as well as 
the forward hook 30, which extends radially outwardly above the cooling 
passages 38, also provide stiffening of the panel 28 in the 
circumferential direction. 
As shown in FIG. 3, the first ribs 48a end or terminate at the impingement 
holes 46, and adjacent outlet plenums 38b are disposed together in flow 
communication. However, the center second rib 48b extends completely to 
the leading edge 28a to provide a flow barrier between adjacent outlet 
plenums 38b for effecting independent channeling of the cooling air 36 
through adjacent cooling passages 38. Since the flow of the cooling air 36 
through the several cooling passages 38 is controlled by the differential 
pressure between the inlet 40 and the outlets 44, circumferential 
variation in the pressure at either the inlet 40 or the outlet 44 will 
promote circumferential crossflow through the cooling passages 38 but for 
the ribs 48a,b located therein for providing effective barriers to such 
crossflow. 
The turbine nozzle 18 is shown in FIG. 3 adjacent to the leading edge 28a 
of one of the shrouds 22. Since the turbine nozzle 18 includes a plurality 
of circumferentially spaced apart stator vanes 18c, the pressure of the 
combustion gas 20 flowing therefrom varies in the circumferential 
direction. Accordingly, it is desirable to locate the trailing edge 18d of 
each stator vane 18c in circumferential alignment with the center, second 
rib 48b of the corresponding shroud 22. In this exemplary embodiment, 
there is a one-to-one correspondence between the number of stator vanes 
18c and the number of shrouds 22, with each vane 18c being preferentially 
aligned with the center of each panel 28. Since the center rib 48b 
completely blocks the adjacent two cooling passages 38, circumferential 
crossflow through the adjacent outlet plenums 38b is prevented. In this 
way, the density and flowrate through the film cooling outlet holes 44 for 
the separate cooling passages 38 on both sides of the center rib 48b may 
be independently varied for better matching the circumferentially varying 
pressure distribution of the combustion gas 20 from the turbine nozzle 18 
for providing more effective cooling of the panel overhang region 28e. 
Accordingly, the improved shrouds 22 are effective for providing enhanced 
cooling of relatively long panel overhangs 28e near the leading edges 28a 
thereof. Furthermore, the invention may be practiced for overhangs at the 
trailing edges 28b as well. The invention may also be practiced wherever 
beneficial including analogous overhangs in the nozzle bands 18a,b for 
example. 
While there have been described herein what are considered to be preferred 
and exemplary embodiments of the present invention, other modifications of 
the invention shall be apparent to those skilled in the art from the 
teachings herein, and it is, therefore, desired to be secured in the 
appended claims all such modifications as fall within the true spirit and 
scope of the invention. 
Accordingly, what is desired to be secured by Letters Patent of the United 
States is the invention as defined and differentiated in the following 
claims: