U.S. patent application number 10/121613 was filed with the patent office on 2003-01-30 for turbine blade tip cooling construction.
Invention is credited to Downs, James P., Narcus, Andrew R..
Application Number | 20030021684 10/121613 |
Document ID | / |
Family ID | 26819647 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030021684 |
Kind Code |
A1 |
Downs, James P. ; et
al. |
January 30, 2003 |
Turbine blade tip cooling construction
Abstract
A gas turbine blade (1) with a tip squealer (7) comprises
cooling passages (12, 13) that provide cooling fluid for the
cooling of the tip squealer (7). A first portion of the cooling
passages (12) extends from an internal hollow space (11) through an
end cap to a tip pocket. A second portion (13) of the cooling
passage extends from the end cap in part through the rails (8) of
the tip squealer (7) to the tip crown (9). The second portion (13)
is partially bounded by the rail (8) and partially open to the tip
pocket (14). The cooling passages according to the invention
provide an improved cooling of the tip squealer and have the
advantage that cooling fluid can cool the tip squealer (7) even in
the event of clogging of the second portions (13) of the
passages.
Inventors: |
Downs, James P.; (Jupiter,
FL) ; Narcus, Andrew R.; (Loxahatchee, FL) |
Correspondence
Address: |
Robert S. Swecker
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
26819647 |
Appl. No.: |
10/121613 |
Filed: |
April 15, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60307176 |
Jul 24, 2001 |
|
|
|
Current U.S.
Class: |
416/92 ; 416/224;
416/97R |
Current CPC
Class: |
F01D 5/145 20130101;
F01D 5/20 20130101 |
Class at
Publication: |
416/92 ;
416/97.00R; 416/224 |
International
Class: |
F01D 005/18 |
Claims
1. Gas turbine blade (1) comprising a pressure sidewall (2) and
suction sidewall (3) extending from a leading edge (4) to a
trailing edge (5) and from a root (6) to a tip with a tip having an
end cap (10) and a tip squealer (7) with rails (8) that extend
radially from the end cap (10) to a tip crown (9) and along the
suction sidewall (3) and pressure sidewall (2) and surrounding a
tip pocket (14), and furthermore comprising an internal hollow
space (11) between the inner surfaces of the pressure and suction
sidewall (2,3), through which a cooling fluid can flow and cooling
passages for directing the cooling fluid to the tip squealer (7)
characterized in that the cooling passages have a first portion
(12) leading from the internal hollow space (11) through the end
cap (10) to the tip pocket (14) and a second portion that extends
in part through the rails (8) to the tip crown (9) of the tip
squealer (7), where the second portion (13) is in one part bounded
by a sidewall (15) in the rail and in another open to the tip
pocket (14).
2. Gas turbine blade (1) according to claim 1 characterized in that
the first and second portion (12, 13) of the cooling passages
extend radially from the internal hollow space (11) within the
blade to the tip crown (9).
3. Gas turbine blade (1) according to claim 1 characterized in that
the longitudinal axis of the first and second portion (12, 13) of
the cooling passages is oriented at an angle (.theta.) with respect
to the radial direction either in the plane perpendicular to the
blade sidewalls (2,3) or at an angle (.phi.) with respect to the
radial direction in the plane of the blade sidewalls (2, 3) or at a
compound angle with respect to the radial direction in each of
these planes.
4. Gas turbine blade (1) according to claim 3 characterized in that
the angle of orientation (.theta.) of the longitudinal axis of the
first and second portion (12, 13) of the cooling passages in the
plane perpendicular to the blade sidewalls (2,3) is in the range
from 0 to 45.degree..
5. Gas turbine blade (1) according to claim 3 characterized in that
the angle of orientation (.phi.) of the longitudinal axis of the
first and second portion (12, 13) of the cooling passages in the
plane of the blade sidewalls (2,3) is in the range from 0 to
60.degree.
6. Gas turbine blade (1) according to one of the foregoing claims 1
through 3 characterized in that the first portion of the cooling
passages (12) has a cylindrical shape leading from the internal
hollow space (11) between the inner surfaces of the suction and
pressure sidewall (2, 3) through the end cap (10) to the tip pocket
(14) and the second portion of the cooling passage has the shape of
a partial cylinder within the rails (8) of the tip squealer
(7).
7. Gas turbine blade (1) according to one of the foregoing claims 1
through 3 characterized in that the first and second portions of
the cooling passages (12, 13) have an elongated or oval shape in
the direction along the rails (8) of the tip squealer (7).
8. Gas turbine blade (1) according to one of the foregoing claims 1
through 3 characterized in that the cooling passages have parallel
extending sidewalls over a first part (12') of the first portion
(12) within the tip cap (10) and a diffused shape over a second
part of its first portion (12) within the tip cap (10) and over its
second portion or extension (13).
9. Gas turbine blade (1) according to claim 8 characterized in that
the diffused shape of the cooling passages is defined by angles
(.alpha.,.beta.) between the passage sidewalls and the longitudinal
axis of the cooling passages that are in the range from 5 to
10.degree..
Description
FIELD OF INVENTION
[0001] This invention pertains to gas turbine blades and in
particular to a cooling construction for their tip portion.
BACKGROUND ART
[0002] Gas turbine components are exposed to the very high
temperatures of the gas flow driving the turbine. In order to
maintain the metal temperatures of the components within acceptable
limits for structural integrity and longevity they are actively
cooled by means of a cooling fluid. Typically, cooling air bled
from the compressor of the gas turbine is used as a cooling
fluid.
[0003] The gas turbine blades, which operate directly downstream of
the combustion process, pose a particular technical challenge for
cooling. Especially the edges and tips of these blades are
difficult to cool as access for cooling is restricted. The tip
region is often subjected to the highest heat loads as the hottest
gases, which flow through the center of the hot gas flow path, are
pulled to the tip by secondary flows generated on the pressure side
of the airfoil. These secondary flows are usually driven by leakage
of hot gas from the concave or high-pressure side of the airfoil to
the convex or low-pressure side of the airfoil through the tip gap.
The tip gap is the clearance gap between the blade tip and
stationary heat shield and serves to prevent interference between
the rotating blade tips and stationary heat shields.
[0004] Gas turbine blades typically incorporate a so-called tip
squealer, which consists of a recessed pocket at the blade tip
surrounded by a raised wall, or rails, which extend along the tip
of the pressure side and suction side of the airfoil and radially
outward to the tip crown. The squealer provides a dual orifice at
the tip gap that increases the resistance against hot gas flow
across the tip. It also provides rub tolerance in the event that
the tip clearance is diminished during turbine operation and the
blade tip rubs against the stationary heat shield. The tip squealer
further increases the challenge of cooling the tip because access
to the rails of the squealer is restricted.
[0005] A cooling construction for the tip of a gas turbine blade is
disclosed in U.S. Pat. No. 5,183,385. It comprises several cooling
holes, which extend from a cooling passage within the blade through
the end cap of the blade tip portion to the tip pocket. The exit
ports of the cooling holes are positioned adjacent to the inner
wall of the tip squealer that is adjacent to the inner wall of the
rail. The cooling hole comprises two sections, of which the first
section has a cylindrical shape and the second section is diffused
forming a rectangular trapezoid. In this type of cooling
construction there is a potential that the cooling flow detaches
from the surface of the squealer rail such that the cooling
effectiveness in the region of the rails is much reduced.
[0006] A further cooling construction for the tip portion of a gas
turbine blade is disclosed in U.S. Pat. No. 5,660,523. It comprises
several cooling holes leading from internal cooling passages of the
blade through the rails to the outer surface, or crown, of the tip
squealer rails. The outer surface of the rails has a groove, which
contains the exit ports of the cooling holes. The cooling
construction provides more direct cooling of the rails of the
squealer. However, as the exit ports are located at the outermost
surface of the rails, there is a high risk that the cooling holes
get plugged by material rubbed off the heat shield or blade itself
in the event of contact between the blade and the stationary
components near it. The groove on the outer surface provides
protection against such plugging to a certain degree. However, a
robust tip cooling configuration would require such rub tolerance
all the way to the bottom of the tip pocket.
SUMMARY OF INVENTION
[0007] It is the object of the invention to provide a cooling
construction for the tip squealer of a gas turbine blade that
provides improved cooling of the rails or walls of the tip squealer
as well as improved protection from plugging of the cooling holes
by rubbed-off material.
[0008] According to the invention a gas turbine blade comprises a
pressure sidewall and suction sidewall extending from a root to a
tip and from a leading edge to a trailing edge. The tip of the
blade comprises a tip squealer with rails or raised walls extending
radially from an end cap of the blade to a tip crown and along the
radial outer end of the suction and pressure sidewalls of the
blade. The rails furthermore surround a tip pocket. Between the
inner surfaces of the pressure and suction sidewalls of the blade a
hollow space is arranged, through which a cooling fluid can flow
and cool the blade from within.
[0009] Cooling passages providing cooling fluid to the tip squealer
have a first portion that leads from the internal space through the
end cap to the tip pocket and a second portion that extends in part
through the rails of the tip squealer to the tip crown. The second
portion of the cooling passages is in one part bounded by a
sidewall in the rail and is in another part open to the tip
pocket.
[0010] By a cooling construction according to the invention the
cooling fluid flow is bounded in one part, which provides a more
predictable air flow compared to the cooling construction disclosed
in U.S. Pat. No. 5,183,385. The high velocity jet exiting the
cooling passages directly influences the heat transfer on the
bounding wall. In particular, the cooling fluid can flow unimpeded
through the cooling passage to the outer surface or tip crown of
the squealer rail. Even in the event of rubbed-off material present
due to a contact between the tip squealer and the stationary
components cooling fluid can reach the tip crown unimpeded and cool
the tip squealer effectively.
[0011] The cooling of the squealer pocket by means of the cooling
construction according to the invention occurs by convection as
well as by film cooling. The convective heat transfer between the
ejected cooling flow and the surfaces of the squealer is greater
the larger the surface of the rails. Hence, the convective heat
transfer between the cooling flow and the surfaces with the slots
according to the invention is increased over the heat transfer
between a cooling flow and a rail with a flat surface.
[0012] Film cooling is accomplished by reducing the driving
temperatures of the hot gases. The mere presence of the ejected
cooling flow will dilute the hot gases to some degree. The film
cooling effect is also increased if the cooling flow is kept close
to the rail wall. This is accomplished with the help of the slots
in the rail for the ejected flow.
[0013] In a first particular embodiment of the invention the
cooling passages extend radially from the internal hollow space for
the cooling fluid within the blade to the tip crown. The passages
then extend in parallel to the pressure and suction sidewalls and
the radially extending rails.
[0014] In a further particular embodiment of the invention the
cooling passages extend at an angle with respect to the radial
direction either in the plane perpendicular to the blade walls or
in the plane of the blade sidewalls and rails or at a compound
angle in both of these planes. The cooling passages extending at an
angle in the plane of the blade sidewalls and rails can be oriented
either toward the leading edge or toward the trailing edge of the
turbine blade.
[0015] Cooling passages with such orientations have a longer path
to the tip crown and the wetted surface or effective area for
convective cooling is enlarged compared to the embodiment with
radially extending cooling passages.
[0016] In a further particular embodiment the first portion of the
cooling passages has a cylindrical shape beginning from the
internal hollow space between the inner surfaces of the suction and
pressure sidewall through the end cap of the blade to the tip
pocket. The second portion of the cooling passage has the shape of
a partial cylinder extending through the rails.
[0017] In a further particular embodiment of the invention the
first and second portion of the cooling passages are shaped or
elongated in the direction along the crown of the tip squealer.
[0018] This elongated or oval shape provides a further increase of
the wetted surface exposed to the cooling fluid.
[0019] In a further particular embodiment of the invention the
first portion of the cooling passages has parallel extending
sidewalls over a first part of their length and a diffused shape
over a second part of their length. The first part having a
cylindrical or elongated shape serves as a metering section
streamlining the cooling fluid. The second portion of the cooling
passage has sidewalls that diffuse at an angle with respect to the
longitudinal axis of the passage. This allows a reduction of the
cooling fluid flow velocity as it flows along the rails and a
spreading of the flow over a larger surface, which increases the
film cooling effectiveness. Also, in this case, a larger area is
available for convective heat transfer.
BRIEF DESCRIPTION OF THE FIGURES
[0020] FIG. 1 shows a perspective view of a gas turbine blade with
a tip squealer and cooling passages at the tip portion according to
the invention.
[0021] FIG. 2 shows a cross-section of the blade of FIG. 1 along
the line II-II and the cooling passages extending radially through
the end cap and through the rails up to the tip crowns.
[0022] FIG. 3 shows in a further cross-sectional view of a gas
turbine blade a variant of cooling passages that extend at an angle
with respect to the radial direction and in the plane perpendicular
to the blade walls.
[0023] FIG. 4 shows a perspective view of a gas turbine blade with
a further variant of the cooling passages according to the
invention that extend at an angle with respect to the radial
direction and in the plane of the blade walls and rails.
[0024] FIG. 5 shows a perspective view of a gas turbine blade with
cooling passages with an elongated shape.
[0025] FIG. 6a shows a cross-sectional view of a gas turbine blade
with cooling passages having diffused sidewalls over a portion of
their length and
[0026] FIG. 6b shows a further cross-section of the same cooling
passages along the line B-B.
DETAILED DESCRIPTION OF THE INVENTION
[0027] FIG. 1 shows a gas turbine blade 1 according to the
invention comprising a pressure sidewall 2 and a suction sidewall
3, which extend from the blade's leading edge 4 to its trailing
edge 5 and from a root section 6 to a tip with a tip squealer 7.
The tip squealer 7 comprises a rail 8 that extends radially away
from the pressure and suction sidewalls 2 and 3 ending at the tip
crown 9. The tip squealer 7 furthermore comprises a tip pocket that
is bounded by the tip cap or end cap and on the sides by the rails
8.
[0028] Between the pressure and suction sidewall 2 and 3 the blade
comprises a hollow space 11 indicated by the broken lines. The
hollow space comprises for example several passages for a cooling
fluid to flow through and convectively cool the blade to a
temperature at which the blade's material takes no damage. From the
internal space 11 several cooling passages 12 lead radially outward
toward the tip cap to the tip pocket. The same passages 12 each
have an extension 13 through the rails 8 and to the tip crown 9.
The passage extensions 13 are bounded on one side by a sidewall in
the rail 8. On their other side they are partially open to the tip
pocket. The cooling passages shown in FIG. 1 are a first variant of
the invention. The passages extend radially outward and have a
straightforward cylindrical shape in their first portion and the
shape of a partial cylinder in their second portion or extension
13. The cooling fluid, typically air bled from a compressor, flows
from the hollow space 11 through the passages 12 to the tip pocket
while cooling the tip cap from within. From the tip pocket it
follows the passage extension 13 to the tip crown 9 cooling the
rails by convection and film cooling.
[0029] In the event of an accidental or intentional contact of the
blade with stationary components of the gas turbine material can
rub off and smear the material of the radially outmost portions of
the tip squealer. The extensions 13 of the cooling passages can
then be filled with material. However, in such a case the cooling
fluid can still reach the tip crown unimpeded by flowing around the
rubbed off material.
[0030] The cross-sectional view in FIG. 2 shows a first variant of
the cooling passages according to the invention. They comprise a
first portion 12 leading from the hollow space 11 between the
pressure and suction sidewall 2 and 3 through the tip cap 10 to the
tip pocket 14. From there the cooling passages extend through the
rail 8 to the tip crown 9 in a second portion or extension 13 with
a sidewall 15 in the rail 8 and being partially open to the tip
pocket 14.
[0031] A vortex will typically form in the tip pocket 14 as a
result of the flow driven through the tip cap 10. The vortex flow
is in the same direction as the ejected cooling flow on the
pressure side rail 2 and opposed to the ejected cooling flow on the
suction side rail 3. On the pressure rail 2 the vortex flow acts to
hold the ejected flow in the slot formed in the rail, which
benefits the film cooling in that region. On the suction side rail
3 the opposed flow of the vortex will tend to pull the cooling jet
off the rail wall. However, the presence of the slots 13 helps to
retain that flow along the rail wall, which again benefits the film
cooling of the rail.
[0032] FIG. 3 shows a second variant of the cooling passages
according to the invention. They are shown in a similar
cross-section as in FIG. 2. The longitudinal axis 16 of the
passages extend from the hollow space 11 at an angle .theta. with
respect to the inner surface of the pressure or suction sidewall 2
and 3 of the blade and in a plane perpendicular to the blade
sidewalls. Again, the first portion 12 of the passages has a
cylindrical shape while the second portion 13 has a partial
cylindrical shape. The angle .theta. is for example 5-15.degree.
and preferably optimized for specific applications to maximize
cooling within established criteria for manufacturing.
[0033] FIG. 4 shows a further variant of the cooling passages 12,
13 according to the invention. Their longitudinal axes 16 are
oriented at an angle .phi. with respect to the radial direction and
in the plane of the rail 8. This orientation yields a greater
surface over which the cooling fluid can cool the tip squealer. In
this example, the passages are oriented toward the trailing
edge.
[0034] The angle .phi. between the radial direction and the
longitudinal axis of the passages is preferably about
45.degree..
[0035] Furthermore, the longitudinal axis of the cooling passages
can also be oriented at a compound angle with respect to the radial
direction where this compound angle is in the plane perpendicular
to the plane of angle .theta. as well as in the plane angle
.phi..
[0036] FIG. 5 shows another variant of the cooling passages. In
this example, the cooling passages are oriented radially outward.
They have an elongated shape in the direction along the rail. In
this variant the surface over which the cooling fluid can cool the
tip squealer is yet enlarged compared to the variants in FIGS. 3 or
4.
[0037] FIGS. 6a and b show a further variant of the passages
according to the invention. FIG. 6a shows a similar cross-section
of the blade as in FIGS. 2 and 3. FIG. 6b shows a cross-section
along line B-B. The passages for the cooling fluid are
cylindrically shaped over a first part 12' within the tip cap 10
and have a diffused shape over a second part extending from the
first part to the tip crown. The sidewalls of the diffused part
extend at an angle .alpha. with respect to the longitudinal axis of
the cooling passages and in the plane perpendicular to the rail 8.
The sidewalls are diffused at a further angle .beta. in the plane
tangent to the rail according to FIG. 6b. The angles .alpha. and
.beta. are each preferably in the range from 5 to 10.degree..
[0038] In further variants of the invention the features described
in the figures may be combined.
Terms Used in the Figures
[0039] 1 gas turbine blade
[0040] 2 pressure sidewall
[0041] 3 suction sidewall
[0042] 4 leading edge
[0043] 5 trailing edge
[0044] 6 root portion
[0045] 7 tip portion, tip squealer
[0046] 8 rail
[0047] 9 tip crown
[0048] 10 end cap or tip cap
[0049] 11 hollow space within blade
[0050] 12 first portion of cooling passage
[0051] 12' first part of first portion, metering section
[0052] 13 second, partially bounded, partially open portion of
cooling passage
[0053] 14 tip pocket
[0054] 15 sidewall of second portion of cooling passage
[0055] 16 longitudinal axis of cooling passage
[0056] .alpha. angle of diffusion of sidewall with respect to
longitudinal axis in direction of blade sidewall
[0057] .beta. angle of diffusion of sidewall with respect to
longitudinal axis in direction along rail
[0058] .theta. angle of orientation of longitudinal axis with
respect to radial direction in plane perpendicular to rails 8
[0059] .phi. angle of orientation of longitudinal axis with respect
to radial direction in plane of rail 8.
* * * * *