U.S. patent application number 12/200160 was filed with the patent office on 2010-03-04 for airfoil insert.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. Invention is credited to William Abdel-Messeh, Matthew A. Devore, Eleanor D. Kaufman, Raymond Surace.
Application Number | 20100054915 12/200160 |
Document ID | / |
Family ID | 41203644 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100054915 |
Kind Code |
A1 |
Devore; Matthew A. ; et
al. |
March 4, 2010 |
AIRFOIL INSERT
Abstract
An airfoil insert comprises an insert wall, a contact element
and a flow director. The insert wall defines an interior extending
inside the insert wall from a first end to second end, and an
exterior extending outside the insert wall from the first end to
the second end. The contact element is formed on the exterior of
the insert wall. The flow director is formed on the insert wall at
a boundary between the interior and the exterior. The flow director
increases a heat transfer coefficient of convective flow along the
insert wall by directing the convective flow to the exterior of the
insert wall.
Inventors: |
Devore; Matthew A.;
(Manchester, CT) ; Kaufman; Eleanor D.; (Cromwell,
CT) ; Surace; Raymond; (Newington, CT) ;
Abdel-Messeh; William; (Middletown, CT) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
41203644 |
Appl. No.: |
12/200160 |
Filed: |
August 28, 2008 |
Current U.S.
Class: |
415/116 ;
415/208.1; 416/96A |
Current CPC
Class: |
F01D 5/189 20130101;
F05D 2260/202 20130101; Y02T 50/67 20130101; Y02T 50/676 20130101;
Y02T 50/60 20130101 |
Class at
Publication: |
415/116 ;
415/208.1; 416/96.A |
International
Class: |
F04D 29/58 20060101
F04D029/58; F01D 25/12 20060101 F01D025/12; F01D 5/18 20060101
F01D005/18 |
Claims
1. An airfoil insert comprising: an insert wall defining an
interior extending inside the insert wall from a first end to a
second end, and an exterior extending outside the insert wall from
the first end to the second end; a contact element formed on the
exterior of the insert wall; and a flow director formed on the
insert wall at a boundary between the interior and the exterior,
wherein the flow director increases a heat transfer coefficient of
convective flow along the insert wall by directing the convective
flow to the exterior of the insert wall.
2. The insert of claim 1, wherein the contact element comprises a
collar for spacing the insert wall from an internal cooling passage
of an airfoil.
3. The insert of claim 1, wherein the flow director comprises
convection flow apertures for directing the convective flow to the
exterior of the insert wall.
4. The insert of claim 3, wherein the contact element comprises
tabs for spacing the insert wall from an internal cooling passage
of an airfoil.
5. The insert of claim 4, wherein the tabs define the convection
flow apertures therebetween.
6. The insert of claim 3, wherein the flow director comprises an
inlet for conducting flow to the interior of the insert wall.
7. The insert of claim 6, wherein the convection flow apertures are
formed in the insert wall.
8. The insert of claim 6, further comprising an outlet formed in
the second end of the insert wall, for conducting flow from the
interior of the insert wall to a downstream cooling load.
9. The insert of claim 1, wherein the flow director comprise a stop
for stopping flow through the interior of the insert wall.
10. The insert of claim 1, further comprising a flame spray coating
on the insert wall for attaching the insert along an internal
cooling passage of an airfoil.
11. The insert of claim 1, wherein the insert wall has a closed
cross-sectional geometry.
12. The insert of claim 1, wherein the insert wall has an open
cross-sectional geometry formed by a unitary U-shaped or C-shaped
structure.
13. The insert of claim 1, wherein the insert wall has an open
cross-sectional geometry formed by two panels.
14. An airfoil comprising: an airfoil section comprising a leading
edge, a trailing edge, pressure and suction surfaces defined
between the leading edge and the trailing edge, and an inner
surface defining an internal cooling passage; and an insert
comprising an insert wall and a flow director for restricting
convective flow to a region between the insert wall and the inner
surface of the airfoil section.
15. The airfoil of claim 14, wherein the flow director increases a
Reynolds number of the convective flow.
16. The airfoil of claim 14, wherein the flow director increases a
Mach number of the convective flow.
17. The airfoil of claim 14, further comprising augmentors formed
along the internal cooling passage to augment convective heat
transfer along the inner surface of the airfoil section.
18. The airfoil of claim 17, wherein the augmentors comprise at
least one of trip strips, turbulators, pins, dimples, warts and
pedestals.
19. The airfoil of claim 14, further comprising a plurality of
ribs, pin-fins or other stand-off features of various cross
section, formed along the internal cooling passage for spacing the
insert wall from the inner surface of the airfoil section.
20. The airfoil of claim 14, further comprising a contact element
formed on an exterior of the insert wall for spacing the insert
wall from the inner surface of the airfoil section.
21. The airfoil of claim 14, wherein the flow director comprises a
convection flow aperture for directing convective flow to the
region between the insert wall and the inner surface of the
airfoil.
22. The airfoil of claim 21, wherein the flow director further
comprises an inlet for conducting flow into an interior of the
insert wall.
23. The airfoil of claim 22, wherein the convection flow aperture
is formed in the insert wall.
24. The airfoil of claim 22, further comprising an outlet for
conducting flow from the interior of the insert wall to a
downstream cooling load.
25. The airfoil of claim 14, wherein the flow director further
comprises a flow stop for stopping flow through an interior of the
insert wall.
26. The airfoil of claim 14, wherein the insert wall has a
substantially closed cross-sectional geometry.
27. The airfoil of claim 14, wherein the insert wall has a
substantially open cross-sectional geometry and forms a seal
against the internal cooling passage.
28. The airfoil of claim 14, further comprising a platform for
attaching the airfoil to a stationary component of a turbine.
29. The airfoil of claim 14, further comprising a root for
attaching the airfoil to a rotating component of a turbine.
30. A method for cooling an airfoil, the method comprising:
positioning an insert along an internal surface of the airfoil;
spacing the insert from the internal surface; and restricting
convective flow along the insert to a region between the insert and
the internal surface, such that a Reynolds number of the convective
flow is increased.
31. The method of claim 30, further comprising directing
non-convective flow into an interior of the insert.
32. The method of claim 31, further comprising converting the
non-convective flow to the convective flow.
33. The method of claim 31, further comprising conducting the
non-convective flow to a downstream cooling load.
34. The method of claim 30, further comprising forming augmentors
on the internal surface of the airfoil to augment the convective
cooling.
35. The method of claim 30, further comprising attaching the insert
to the airfoil such that the insert functions as a cast-in wall.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter of this application relates generally to
gas turbine engines, and specifically to cooling techniques for the
airfoil sections of turbine blades and vanes. In particular, the
invention concerns an insert for convective cooling the interior
surfaces of turbine airfoils exposed to high-temperature working
fluid flow.
[0002] Gas turbine engines are built around a power core comprising
a compressor, a combustor and a turbine, which are arranged in flow
series with a forward (upstream) inlet and an aft (downstream)
exhaust. The compressor compresses air from the inlet, which is
mixed with fuel in the combustor and ignited to produce hot
combustion gases. The hot combustion gases drive the turbine
section, and are exhausted with the downstream flow.
[0003] The turbine drives the compressor via a shaft or a series of
coaxially nested shaft spools, each driven at different pressures
and speeds. The spools employ a number of stages comprised of
alternating rotor blades and stator vanes. The vanes and blades
typically have airfoil cross sections, in order to facilitate
compression of the incoming air and extraction of rotational energy
in the turbine.
[0004] In addition to its use as an oxidant, compressor air is also
utilized to cool downstream engine components, particular turbine
and exhaust parts exposed to hot gas flow. Depending upon
application, compressed air is also utilized for environmental
control, pneumatics and other accessory functions.
[0005] Energy not used to drive the compressor and provide cooling
or accessory functions is available for external use. In
ground-based industrial gas turbines, for example, power is
typically provided in the form of rotational energy, which is used
to drive an electrical generator or other mechanical load. In
aviation applications, on the other hand, reactive thrust is
generated directly from the exhaust.
[0006] In turbofan engines, one of the spools also drives a forward
fan or ducted propeller, producing additional thrust from bypass
flow directed around the engine core. Turbofans are either directly
driven by the low-pressure turbine spool, or employ a reduction
gearbox to slow the fan, reducing noise and increasing
efficiency.
[0007] The majority of commercial aircraft employ high-bypass
turbofan engines, which generate most of their thrust from bypass
flow. Supersonic jets and other high-performance aircraft typically
employ low-bypass turbofans, which rely primarily on reactive
thrust from the exhaust. Low-bypass turbofans are louder and less
fuel efficient, but provide greater response and specific thrust.
Low-bypass turbofans are also commonly configured for afterburning,
in which additional fuel is injected into in an augmentor assembly
downstream of the turbine, where it is ignited to provide
additional thrust.
[0008] The main goals in gas turbine engine design are efficiency,
performance and reliability. Efficiency and performance both favor
high combustion temperatures, which increase the engine's
thermodynamic efficiency, specific thrust, and maximum power
output. Unfortunately, high combustion temperatures also increase
thermal and mechanical loads, particularly on turbine airfoils
downstream of the combustor. This reduces service life and
reliability, and increases operational costs associated with
maintenance and repairs.
[0009] There is thus a need for enhanced turbine airfoil cooling
techniques. In particular, there is a need for techniques that not
only improve cooling efficiency, reducing the required cooling
fluid mass flow rate and resulting energy losses, but also improve
cooling efficacy, reducing thermal stresses, extending service life
and increasing reliability.
BRIEF SUMMARY OF THE INVENTION
[0010] This disclosure concerns an airfoil insert for convective
cooling and a method of cooling using the insert. The insert
comprises an insert wall, a contact element and a flow director.
The insert wall defines an interior region extending inside the
insert from a first end to a generally opposed second end, and an
exterior region extending along the outside of the insert from the
first end to the second end.
[0011] The contact element is formed on the exterior of the insert
wall between the first end and the second end, for attaching the
insert to an airfoil and for spacing the insert wall from the
internal airfoil surfaces. The flow director is formed on the
insert wall at a boundary between the exterior and interior, and
increases the heat transfer coefficient of convective flow along
the insert by directing the convective flow to the exterior region,
between the insert wall and the surface of the cooling passage.
[0012] The method comprises positioning the insert along an
internal surface of an airfoil, spacing the insert from the
internal surface, and restricting convective flow along the insert
to a region between the insert and the inner surface. This
increases the Reynolds number of the convective flow, which in turn
increases the heat transfer coefficient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional schematic of an airfoil insert
and airfoil.
[0014] FIG. 2A is a top schematic view of an airfoil section and
insert, in embodiment with a collar and an inlet for internal
flow.
[0015] FIG. 2B is a top schematic view of an airfoil section and
insert, in an embodiment with spacing tabs and an upstream flow
stop.
[0016] FIG. 3A is a top schematic view of an airfoil section and
insert, in an embodiment with spacing ribs and an upstream flow
stop.
[0017] FIG. 3B is top schematic view of an airfoil section and
insert, in an embodiment with spacing ribs and multiple inlets for
internal flow.
[0018] FIG. 4A is a perspective view of an airfoil insert with
indirect convective flow apertures and a downstream outlet.
[0019] FIG. 4B is a perspective view of an airfoil insert with
supplemental convective flow apertures and a downstream flow
stop.
[0020] FIG. 5A is a top schematic view of a U-shaped
(open-geometry) insert and airfoil section.
[0021] FIG. 5B is a perspective view of the insert in FIG. 5A.
[0022] FIG. 6A is a top schematic view of a two-panel
(open-geometry) insert and airfoil section.
[0023] FIG. 6B is a perspective view of the insert in FIG. 6A.
DETAILED DESCRIPTION
[0024] FIG. 1 is a cross-sectional schematic of insert 10 for
airfoil 20. Insert 10 comprises insert wall 11 with first end 12,
second end 13 and contact element 14 for attaching insert 10 to
airfoil 20 and for positioning insert wall 11 within airfoil
section 21. Insert 10 increases the heat transfer coefficient of
convective flow by directing the convective flow around insert wall
11, away from internal region 15 and into external region 16,
between insert wall 11 and airfoil section 21.
[0025] Airfoil 20 comprises airfoil section 21, inner platform 22
and outer platform 23. Airfoil section 21 extends axially between
leading edge 24 and trailing edge 25, and radially between
platforms 22 and 23. Internal cooling passages 26A, 26B, 26C and
26D are defined along internal surfaces 27 of airfoil section 21.
Augmentors such as trip strips 28 and pedestals 29 are formed along
internal surfaces 27 of passages 26A, 26B and 26C, in order to
increase turbulence and improve internal cooling. Film cooling
holes 30A, 30B and 30C provide cooling fluid to external surfaces
of airfoil section 21 that are exposed to hot working fluid
flow.
[0026] In the particular embodiment of FIG. 1, airfoil 20 is a
stationary turbine vane for use in a turbojet or turbofan engine.
In this embodiment, airfoil 20 is typically attached to a turbine
case or flow duct at inner platform 22 and outer platform 23, using
mechanical coupling structures such as hooks or by forming
platforms 23 as part of a case or shroud assembly. In other
embodiments, airfoil 20 is configured for use in an industrial gas
turbine engine, and platforms 22, 23 are modified accordingly.
[0027] Alternatively, airfoil 20 is formed as a rotating blade. In
these embodiments, airfoil section 21 is typically formed into a
tip at outer platform 23, and inner platform 22 accommodates a root
structure or other means of attachment to a rotating shaft. In
further embodiments, airfoil 20 is provided with additional
structures for improved working fluid flow control, including, but
not limited to, platform seals, knife edge seals, tip caps and
squealer tips.
[0028] Airfoil 20 is exposed to a generally axial flow of
combustion gas F, which flows across airfoil section 21 from
leading edge 24 to trailing edge 25. Flow F has a radially inner
flow margin at inner platform 22, and a radially outer flow margin
at outer platform 23, or, in blade embodiments, at the blade
tip.
[0029] To protect airfoil 20 from wear and tear due to the working
fluid flow, its various components are manufactured from durable,
heat-resistant materials such as high-temperature alloys and
superalloys. Typically, surfaces that are directly exposed to hot
gas are also coated with a protective coating such as a ceramic
thermal barrier coating (TBC), an aluminide coating, a metal oxide
coating, a metal alloy coating, a superalloy coating, or a
combination thereof.
[0030] Airfoil 20 is manufactured as a hollow structure with
internal cooling passages 26A, 26B, 26C and 26D. The cooling
passages are defined along internal surfaces 27, forming channels
or conduits for cooling fluid flow through airfoil section 21. In
turbofan embodiments, the cooling fluid is usually provided from a
compressed air source such as compressor bleed air. In ground-based
industrial gas turbine embodiments, other fluids such as steam are
also used.
[0031] The flow of cooling fluid depends upon the particular
configuration of airfoil 20. In the embodiment of FIG. 1, for
example, cooling flow C is radially inward through leading edge
cooling passage 26A (in the direction from outer platform 23 toward
inner platform 22), and exits cooling passage 26A in downstream
cooling flow direction D. In serpentine passages 26B, 26C and 26D,
cooling fluid flow C alternates back and forth between radially
inward and radially outward directions, with regions of substantial
axial and rearward flow in between.
[0032] As shown in FIG. 1, trip strips (or turbulators) 28 are
provided to improve cooling along internal passage 26A, and
pedestals (or pins) 29 are provided to improve cooling along
internal passages 26B and 26C. In other embodiments, a combination
of trip strips 28, pedestals 29 and other cooling augmentation
structures such as dimples or warts are provided along any or all
of internal cooling passages 26A, 26B, 26C and 26D, including
passages occupied by insert 10.
[0033] Airfoil 20 also employs external cooling, in which
additional cooling fluid is directed from cold internal surface(s)
27 to the hot (outer) surfaces of airfoil section 21. The cooling
fluid is directed through a combination of film cooling hole
structures, including, but not limited to, "showerhead" openings
30A in cooling passage 26A along leading edge 24, film cooling
holes 30B in passage 26D, and film cooling slots 30C along trailing
edge 25.
[0034] Like airfoil 20, insert 10 is manufactured from a durable,
heat-resistant material such as a metal alloy or superalloy. In
typical embodiments, insert 10 is not provided with a TBC coating
because insert wall 11 is not directly exposed to hot combustion
gas flow. In other embodiments, an anti-oxidant coating or other
protective coating is applied. In further embodiments, insert 10 is
provided with a flame spray coating or other coating for forming a
fluid seal, a contact surface, a coupling or a mechanical
attachment between insert wall 11 and airfoil section 21.
[0035] As shown in FIG. 1, insert 10 is positioned along cooling
passage 26A in a downstream cooling flow direction, such that first
end 12 is an upstream end and second end 13 is a downstream end. In
other configurations the flow is reversed, or insert 10 is inserted
from inner platform 22 rather than outer platform 23, such that the
upstream and downstream ends are interchanged.
[0036] Insert wall 11 defines internal region 15, extending along
the inside (interior) of insert 10 between first end 12 and second
end 13, and external region 16, extending along the outside
(exterior) of insert 10 between first end 12 and second end 13.
External region 16 also extends along cooling passage 26A, between
insert wall 11 and internal surface 27 of airfoil section 21.
[0037] In some embodiments, insert wall 11 has a closed-tube
geometry in which interior 15 and exterior 16 are defined along a
substantially complete cross-sectional perimeter (see, e.g., FIGS.
2A-4B). Alternatively, insert wall 11 has a U-shaped, C-shaped,
two-panel or other open-tube geometry, in which interior region 15
is bounded on at least one side by internal surfaces 27 (that is,
the inner or interior surfaces of the cooling passages inside
airfoil section 21; see, e.g., FIGS. 5A-6B).
[0038] The particular form of contact element 14 varies. In the
closed-geometry embodiment of FIG. 1, for example, contact element
14 comprises a collar formed onto the upstream end of insert wall
11, for attaching insert 10 to airfoil 20 and for spacing insert
wall 11 from internal surfaces 27 of cooling passage 26A. Insert 10
also provides convective flow apertures (see below) that direct
convective flow along exterior region 16, and an inlet to maintain
a positive overpressure for non-convective flow through internal
region 15, in order to generate downstream cooling fluid flow D at
second end 13.
[0039] Insert 10 increases the heat transfer coefficient within
airfoil 20 by directing flow around insert wall 11, excluding
convective flow from internal region 15 and restricting it to
external region 16. Essentially, the heat transfer coefficient
varies with the Reynolds number, which describes the ratio of
inertial to viscous forces (inertial and viscous effects) in the
flow. When convective flow is restricted to external region 16, the
flow area is reduced and the impedance rises. The convective flow
becomes less laminar and more turbulent, increasing the Reynolds
number. This enhances flow interactions along internal surfaces 27
of cooling passage 26A, allowing greater thermal transfer from
airfoil section 21.
[0040] In some embodiments, convective flow is also described in
terms of Mach number. In these embodiments, insert 10 produces Mach
acceleration in the convective flow, increasing the heat transfer
coefficient by generating greater turbulence and other flow
interactions in the region between insert wall 11 and internal
airfoil surfaces 27.
[0041] Increasing the heat transfer coefficient enhances convective
cooling within airfoil section 21. In particular, insert 10 lowers
operating temperatures and thermal gradients, reducing thermal
stresses and increasing service life. Insert 10 also reduces the
cooling flow required to achieve these benefits, improving cooling
efficiency and reserving capacity for additional downstream cooling
loads.
[0042] FIG. 2A is a top schematic view of airfoil section 21 and
insert 10, located in midbody cooling channel 26B (shown in hidden
lines). In this embodiment, insert 10 comprises contact element 14
with collar 31 and inlet 32 for directing flow to the interior of
insert wall 11.
[0043] Airfoil section 21 extends axially between leading edge 24
and trailing edge 25, along pressure or concave side 33 (the upper
surface in FIG. 2A) and suction or convex side 34 (the lower
surface). Internal cooling passages 26A-26D are defined along
internal airfoil surfaces 27, and extend in a generally radial
sense along airfoil section 21 (that is, into the plane of the
figure).
[0044] As shown in FIG. 2A, leading edge cooling passage 26A and
first midbody cooling passage 26B exhibit open-ended designs, and
each is configured to accept particular embodiments of insert 10
(see, e.g., FIG. 2B, below). Second midbody cooling passage 26C and
trailing edge cooling body 26D exhibit closed-end geometries (shown
in dashed or hidden lines), and are not configured for insert 10.
In alternate embodiments, different combinations of cooling
passages 26A, 26B, 26C and 26D have open-ended designs, and any of
the passages can be configured to accept an embodiment of insert
10.
[0045] In this particular embodiment, Insert 10 is located in first
midbody cooling passage 26B. Collar 31 provides means for
positioning insert 10 within cooling passage 26B, such that collar
31 extends outside of cooling passage 26B and insert wall 11 is
spaced within cooling passage 26B. Internal surface 27 defines the
outside edge of cooling passage 26B, which is located between the
outside edge of insert 11 (inside the cooling passage) and the
outside edge of collar 31 (outside the cooling passage).
[0046] Collar 31 also provides means for attaching insert 10 to
airfoil section 21, for example by welding or brazing, by thermal
or friction fitting, or by forming a mechanical attachment via a
flame spray coating or other material applied to insert wall 11 or
to internal surface 27 of cooling passage 26B. In some embodiments,
the attachment features are constructed such that insert 10 is
removable for adjustment and repair. In other embodiments, insert
10 is permanently attached to airfoil 21. In these embodiments,
insert 10 also functions as a cast-in wall within cooling passage
26B, without requiring the same complex manufacturing steps.
[0047] In the particular embodiment of FIG. 2A, collar 31 is formed
on the exterior of insert 10 at the upstream end (or first end) of
insert wall 11, and extends beyond the cross-sectional area of
cooling passage 26B. In other embodiments, collar 31 is formed
within the cross-sectional area of cooling passage 26B, and is
located anywhere between the first and second ends of insert 10. In
further embodiments, a number of collars 31 or other spacing and
attachment means are provided at various locations along insert
wall 11.
[0048] Inlet 32 is typically formed by stamping, drilling, cutting
or machining an opening or orifice on the upstream end of insert
wall 11. Inlet 32 defines a boundary between the interior and
exterior of insert wall 11, and directs flow through this boundary
into insert 10. The internal flow is provided with a positive
overpressure, as compared to the exterior flow, and is utilized for
downstream cooling functions. In some embodiments, for example, the
internal flow is converted to convective flow via a number of
indirect (downstream) apertures in insert wall 11, and in other
embodiments the internal flow conducted through an outlet to a
downstream cooling load (see FIGS. 4A and 4B).
[0049] FIG. 2B is top schematic view of airfoil section 21 and
insert 10, located in leading edge cooling channel 26A. In this
embodiment, insert 10 comprises contact element 14 with spacing
tabs 35 and flow stop 36, for directing flow to the exterior of
insert wall 11 via direct-flow convection apertures 37.
[0050] Spacing tabs 35 comprise spacing and contact or coupling
members formed onto the exterior of insert wall 11 via techniques
such as stamping, welding, brazing, milling, molding, cutting and
machining, as described above for collar 31 of FIG. 2A. Similarly,
spacing tabs 35 provide means to position insert 10 within cooling
channel 26A, spacing insert wall 11 from internal surfaces 27 of
airfoil section 21, and means for attaching insert 10 to airfoil
section 21, within cooling passage 26A.
[0051] In some embodiments, spacing tabs (or fingers) 35 extend
within the cross-sectional area of cooling passage 26A, and are
provided anywhere along the length of insert 10 between the
upstream and downstream ends of insert wall 11. Alternatively,
spacing tabs 35 are provided at the first (upstream) end of insert
wall 11, and sometimes extend beyond the cross-sectional area of
cooling passage 26A, as described above for collar 31 of FIG.
2A.
[0052] Direct-flow convection apertures 37 are sometimes co-formed
with contact element 14, for example by defining the apertures
between tabs 35. Apertures 37 direct cooling fluid flow around
insert 10, into the convective flow region between insert wall 11
and internal surface(s) 27 of airfoil section 21.
[0053] In some embodiments, spacing tabs 35 are adjustable by
bending, twisting, turning or similar mechanical manipulation, in
order to change the spacing between insert wall 11 and cooling
passage 26A, or to change the dimensions of apertures 37. This
allows the convective flow rate and heat transfer coefficient to be
adjusted to suit the particular cooling needs of airfoil section
21.
[0054] FIG. 3A is top schematic view of airfoil section 21 and
insert 10, located in leading edge cooling channel 26A. In this
embodiment insert 10 contacts the interior airfoil surface along
spacing ribs 38, and flow stop 36 directs flow to the exterior of
insert wall 11 via direct-flow convection apertures 37.
[0055] Spacing ribs 38 comprise spacing and attachment members
formed by casting, welding, brazing, milling, molding, cutting or
machining internal cooling passage 26A. Spacing ribs 38 provide
means for spacing insert wall 11 from internal surface(s) 27 of
cooling passage 26A, and for attaching airfoil section 21 to insert
10 along contact element 14.
[0056] As shown in FIG. 3A, one spacing rib 38 is provided along
cooling passage 26A opposite pressure surface 33 of airfoil section
21, and another rib 38 is provided opposite suction surface 34. In
alternate embodiments, one, two, three or more ribs 38 are located
opposite any of pressure surface 33, suction surface 34, leading
edge surface 24 or trailing edge surface 25. In further
embodiments, pin-fins and other stand-off features are utilized
instead of fibs, where these features have various different
cross-sectional geometries.
[0057] Flow stop 36 comprises a plug, wall, baffle, flow block or
other structure formed across insert wall 11, using any of the
mechanical fabrication techniques described above. As shown in FIG.
3A, stop 36 is an upstream flow stop, formed onto the upstream end
of insert wall 11 at the boundary between the internal and external
regions of insert 10. In other embodiments, flow stop 36 is a
downstream stop, formed onto the downstream end of insert 10, or an
intermediate stop, formed anywhere along insert wall 11 (see, e.g.,
FIGS. 6A and 6B).
[0058] Flow stop 36 blocks flow to the interior of insert wall 11,
stopping the internal flow through insert 10. Convective flow is
directed through apertures 37 to the exterior of insert 10, to the
convective region along cooling passage 26A, between insert wall 11
and internal surfaces 27 of airfoil section 21.
[0059] FIG. 3B is a top schematic view of airfoil section 21 and
insert 10, located in leading edge cooling channel 26A. Insert 10
contacts the inner airfoil surface along ribs 38, as shown in FIG.
3A, above, and directs convective flow through apertures 37. In
this embodiment, however, insert 10 also provides internal flow via
multiple inlets 32.
[0060] FIGS. 2A, 2B, 3A and 3B illustrate a range of representative
embodiments in which the various contact, coupling, attachment,
spacing and flow direction elements take on a variety of different
forms. The numbers, sizes and shapes of individual collar, inlet,
aperture, tab, inlet, stop and rib elements also vary, in order to
generate a desired ratio of convective (exterior) and
non-convective (internal) flow, and to regulate these flows in a
desired manner around the exterior and interior of insert wall 11.
In some embodiments, individual flow direction elements are also
adjustable by rotating, sliding, bending or other mechanical
manipulation, in order to provide additional flow regulation. In
these embodiments, some flow direction structures operate as valves
or provide analogous variable-area component functions.
[0061] FIGS. 4A and 4B are perspective views of airfoil insert 10
with indirect-flow convection apertures 41. In these embodiments,
insert 10 comprises contact element 14 with collar 31 and inlet 32
for directing cooling flow C to the interior of insert wall 11, and
indirect convection apertures 41 for converting the interior flow
to convective flow c along the exterior of insert wall 11.
[0062] Indirect convective flow apertures 41 are formed into insert
wall 11 downstream of inlet 32, using one or more of the mechanical
techniques described above. In contrast to direct-flow apertures,
however, which direct convective flow around insert wall 11,
indirect-flow apertures 41 generate flow through insert wall 11,
converting the internal (non-convective) flow inside insert 10 to
an external (convective) flow on the outside of insert 10.
[0063] The number, sizes, shapes and locations of indirect-flow
apertures 41 vary, depending upon the desired convective flow rate
along insert wall 11. In the embodiment of FIG. 4A, for example, a
number of substantially rectangular apertures 41 are formed in an
upstream region of insert wall 11, proximate first end 12. In FIG.
4B, supplemental convective flow apertures 41 are also formed
between first (upstream) end 12 and second (downstream) end 13. In
further embodiments, apertures 41 are formed with circular, oval,
triangular, slotted or other geometries, in order to provide
desired rates of convective flow for a range of different airfoil
and cooling passage geometries.
[0064] Convective flow apertures 41 are distinguished from
impingement holes and related structures, which direct relatively
high-pressure flow away from insert wall 11 in order to impinge on
interior airfoil surfaces. In contrast, insert 10 maintains a
relatively low overpressure, so that the flow through apertures 41
is generated with a generally parallel sense along the exterior of
insert wall 11. This produces a substantially convective flow,
rather than an impingement flow. Similarly, direct flow apertures
37 (above) generate convective flow that is directed along insert
wall 11, rather than impingement jets that are directed away from
insert wall 11 and toward interior surfaces of the airfoil.
[0065] In the embodiment of FIG. 4A, outlet 42 is formed in
downstream end 13 of insert wall 11 via techniques similar to those
described above for inlet 32. Outlet 42 converts the internal flow
to downstream flow D, which supplies a downstream cooling load such
as a serpentine cooling passage, a platform or shroud cooling
system, or another airfoil. In contrast to designs that commingle
the convective and downstream flows, insert wall 11 also provides a
shielded cooling flow conduit that isolates the interior
(non-convective) flow from the exterior (convective) flow. This
allows insert 10 to generate downstream flow D at lower
temperatures than non-shielded designs, further improving cooling
efficiency.
[0066] Alternatively, insert 10 is provided with downstream flow
stop 36, as shown in FIG. 4B. In this embodiment, flow stop 36
stops flow through the interior of insert 10, and directs
additional convective flow along the exterior of insert wall
11.
[0067] The cross-sectional profile of insert 10 is configurable to
control heat pick up and absorption, to augment heat transfer, and
to limit pressure losses along the internal cooling passage, while
maintaining a positive overpressure within insert wall 11. Thus
insert 10 and insert wall 11 take on a variety of shapes and
forms.
[0068] In FIG. 2A, for example, insert 10 exhibits a relatively
regular oval or oblate geometry, which does not necessarily conform
to the surface of the cooling passage. In FIGS. 4A and 4B, insert
wall 11 exhibits a taper, such that the cross section decreases
between upstream end 12 and downstream end 13. Alternatively,
insert wall 11 conforms to the interior of the cooling passage, as
shown in FIGS. 3A and 3B. In these embodiments, insert 10 sometimes
accommodates bends or angles along the cooling passage, as shown in
FIG. 1, so that the spacing between insert wall 11 and the internal
airfoil surfaces is closely controlled. This allows insert 10 to
perform the functions of a secondary or cast-in wall, but with
significantly less manufacturing complexity and cost than other
designs. Insert 10 is also configurable to be removable for
maintenance and repair, while cast-in walls are typically permanent
structures.
[0069] In each of the above embodiments, insert 10 exhibits a
generally closed geometry in which insert wall 11 has a generally
tubular or annular cross section, which forms a substantially
complete perimeter boundary between the interior (non-convective)
and exterior (convective) regions. In other embodiments, insert
wall 11 exhibits an open configuration, in which the boundary
extends to at least one interior surface of the airfoil. FIGS. 5A
and 5B are a top schematic view and a perspective view,
respectively, of U-shaped (open-geometry) insert 10 for airfoil
section 21. In this embodiment, insert wall 11 comprises a unitary
structure with a substantially open U-shaped or C-shaped cross
section. As shown in FIG. 5A, insert 10 is spaced from internal
surfaces 27 via ribs 38. In this embodiment, contact elements are
formed along the extent of insert wall 11, where it contacts ribs
38, and insert 10 contacts airfoil section 21 at seals 51.
[0070] The overpressure within insert wall 11 is maintained via
seals 5l along internal surface 27 of cooling passage 26A, which
complete the boundary between the interior (non-convective) and
exterior (convective) flow regions of insert 10. The seals
typically extend from first end 12 to second end 13 of insert wall
11 (see FIG. 5B).
[0071] Flow stop 36 works in cooperation with seals 51 to direct
flow from feed 52 through apertures 37, but restricts convective
flow to internal surfaces 27 of cooling passage 26A opposite
leading edge 24, pressure side 33 and suction side 34. This
increases cooling efficiency by reducing flow along the interior
wall between cooling passages 26A and 26B, where there is no
exposure to hot working fluid.
[0072] FIGS. 6A and 6B are a top schematic view and a perspective
view, respectively, of two-panel (open-geometry) insert 10 for
airfoil section 21. In this embodiment, insert wall 11 comprises a
two-panel structure with a substantially open cross section.
[0073] As shown in FIG. 6A, insert 10 contacts airfoil section 21
along four seals 51, which extend along insert wall 11 from first
end 12 to second end 13 (see FIG. 6B). Convective flow from feed 52
is directed along midbody cooling channel 26B through apertures 37,
and restricted to internal airfoil surfaces 27 opposite pressure
side 33 and suction side 34. This reduces flow along the interior
walls between channel 26B and cooling passages 26A and 26C, where
there is no exposure to working fluid flow.
[0074] The present invention has been described with reference to
preferred embodiments. The terminology used is for the purposes of
description, not limitation, and workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *