U.S. patent number 3,698,834 [Application Number 04/879,110] was granted by the patent office on 1972-10-17 for transpiration cooling.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to George B. Meginnis.
United States Patent |
3,698,834 |
Meginnis |
October 17, 1972 |
TRANSPIRATION COOLING
Abstract
An airfoil such as a vane or blade intended to be cooled by
transpiration of air from the interior to the exterior of the blade
has an outer layer in which pores for the cooling air are defined
by pits extending in from the outer and inner faces of the layer
and intersecting at the bottoms of the pits, the pits being offset
to provide a hole from which flow tends to proceed at an acute
angle to the face. To decrease the angle between the discharge of
gas and the surface of the airfoil, a control sheet underlying the
outer layer has holes to supply air to the pits in the inner
surface of the outer layer which are offset with respect to the
pits. In one form the outer layer is composed of two laminations
each having holes entirely through the laminations which are then
bonded together with the holes offset to provide the general type
of structure defined by the offset intersecting pits in a single
sheet or lamination.
Inventors: |
Meginnis; George B.
(Indianapolis, IN) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25373451 |
Appl.
No.: |
04/879,110 |
Filed: |
November 24, 1969 |
Current U.S.
Class: |
416/96R;
416/231R |
Current CPC
Class: |
F01D
5/184 (20130101) |
Current International
Class: |
F01D
5/18 (20060101); F01d 005/18 () |
Field of
Search: |
;416/90,96,97,229,231 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Powell, Jr.; Everette A.
Claims
I claim:
1. A wall structure adapted to have a gas flow over the exterior
surface of the wall in a particular direction and having a porous
wall for transpiration cooling of the structure by a cooling gas
discharged from the inner side of the wall through pores in the
wall to the exterior thereof characterized by an outside layer
having an array of pores extending through the said layer; each
pore being defined by two intersecting pits extending into the
exterior and interior faces of the layer, respectively, each pit
only partially overlapping the other, the pit extending into the
interior face being offset upstream, with reference to the
direction of flow over the surface, with respect to the pit
extending into the exterior face, the opening defined by the
intersection between the said pits being substantially entirely in
the bottom of each pit and having an axis directed at an angle of
less than 30.degree. to the normal to the faces of the layer.
2. A wall structure adapted to have a gas flow over the exterior
surface of the wall in a particular direction and having a porous
wall for transpiration cooling of the structure by a cooling gas
discharged from the inner side of the wall through pores in the
wall to the exterior thereof characterized by an outside layer
having an array of pores extending through the said layer; the
outside layer comprising two laminae abutting and bonded together,
an outer and an inner lamina; each pore being defined by two
intersecting pits extending through the outer and inner laminae,
respectively, each pit only partially overlapping the other, the
pit extending through the inner lamina being offset upstream, with
reference to the direction of flow over the surface, with respect
to the pit extending through the outer lamina, the opening defined
by the intersection between the said pits being in the bottom of
each pit and having an axis directed substantially normal to the
faces of the layer.
3. A hollow airfoil adapted to have a gas flow over the exterior
surface of the airfoil in a particular direction and having a
porous wall for transpiration cooling of the airfoil by a cooling
gas discharged from the interior of the wall through pores in the
wall to the exterior thereof characterized by an outside layer
having an array of pores extending through the said layer; each
pore being defined by two intersecting pits extending into the
exterior and interior faces of the layer, respectively, each pit
only partially overlapping the other, the pit extending into the
interior face being offset upstream, with reference to the
direction of flow over the surface, with respect to the pit
extending into the exterior face, the opening defined by the
intersection between the said pits being substantially entirely in
the bottom of each pit and having an axis directed at an angle of
less than 30.degree. to the normal to the faces of the layer.
4. A hollow airfoil adapted to have a gas flow over the exterior
surface of the airfoil in a particular direction and having a
porous wall for transpiration cooling of the airfoil by a cooling
gas discharged from the interior of the wall through pores in the
wall to the exterior thereof characterized by an outside layer
having an array of pores extending through the said layer; each
pore being defined by two intersecting pits extending into the
exterior and interior faces of the layer, respectively, each pit
only partially overlapping the other, the pit extending into the
interior face being offset upstream, with reference to the
direction of flow over the surface, with respect to the pit
extending into the exterior face, the opening defined by the
intersection between the said pits being in the bottom of each pit
and having an axis directed substantially normal to the faces of
the layer; the said outside layer comprising an outer lamina and an
inner lamina, the said pits being within the respective laminae and
overlapping at the interface between the laminae.
5. A structure adapted to have a gas flow over the exterior surface
of the structure in a particular direction and having a porous
exterior portion for transpiration cooling of the structure by a
cooling gas discharged from the inner side of the structure through
pores in the structure to the exterior thereof characterized by an
array of pores extending through the exterior portion configured to
direct the gas at an acute angle to the surface of the structure in
a direction downstream relative to flow over the surface in normal
operation, the said exterior portion comprising a discharge layer
defining the exterior surface of the structure and a control layer
immediately adjacent to and bonded to the discharge layer, the
discharge layer having pores defined by intersecting pits extending
into the layer from the opposite faces of the layer, each pit only
partially overlapping the other, mutually offset in the direction
of the said gas flow with the pit in the outer face downstream, and
having an intersection at the bottoms of the pits, and the control
layer defining a feed hole for each pore offset from the said
intersection feeding into the pit in the adjacent face of the
discharge layer so as to direct the flow into the pore toward the
said intersection.
6. A structure as recited in claim 5 in which the discharge layer
comprises an outer lamina defining the pits extending from the
exterior face and an inner lamina defining the pits extending from
the interior face of the layer.
7. A structure adapted to have a gas flow over the exterior surface
of the structure in a particular direction and having a porous
exterior portion for transpiration cooling of the structure by a
cooling gas discharged from the inner side of the structure through
pores in the structure to the exterior thereof characterized by an
array of pores extending through the exterior portion configured to
direct the gas at an acute angle to the surface of the structure in
a direction downstream relative to flow over the surface in normal
operation, the said exterior portion comprising a discharge layer
defining the exterior surface of the structure and a control layer
immediately adjacent to and bonded to the discharge layer, the
discharge layer having pores defined by intersecting pits extending
into the layer from the opposite faces of the layer, each pit only
partially overlapping the other, mutually offset in the direction
of the said gas flow with the pit in the outer face downstream, and
having an intersection at the bottoms of the pits, and the control
layer defining a feed hole for each pore offset from the said
intersection feeding into the pit in the adjacent face of the
discharge layer so as to direct the flow into the pore toward the
said intersection, the feed hole being directed normal to the
surface of the control layer so as to direct the cooling gas
against the bottom of the pit in the inner face of the discharge
layer for deflection by the surface bounding the pit in a direction
toward the said intersection.
8. A structure adapted to have a gas flow over the exterior surface
of the structure in a particular direction and having a porous
exterior portion for transpiration cooling of the structure by a
cooling gas discharged from the inner side of the structure through
pores in the structure to the exterior thereof characterized by an
array of pores extending through the exterior portion configured to
direct the gas at an acute angle to the surface of the structure in
a direction downstream relative to flow over the surface in normal
operation, the said exterior portion comprising a discharge layer
defining the exterior surface of the structure and a control layer
immediately adjacent to and bonded to the discharge layer, the
discharge layer having pores defined by intersecting pits extending
into the layer from the opposite faces of the layer, each pit only
partially overlapping the other, mutually offset in the direction
of the said gas flow with the pit in the outer face downstream, and
having an intersection at the bottoms of the pits, and the control
layer defining a feed hole for each pore offset from the said
intersection feeding into the pit in the adjacent face of the
discharge layer so as to direct the flow into the pore toward the
said intersection, the feed hole being defined by a passage
extending parallel to the surface of the said layers having a
supply entrance to the said passage offset from the pit in the
inner face of the discharge layer so as to direct the cooling gas
into the said pore generally parallel to the surface of the said
layers.
9. A structure as defined in claim 8 in which the discharge layer
is a single lamina.
10. A structure as recited in claim 8 in which the discharge layer
comprises two laminae bonded together.
11. A hollow airfoil adapted to have a gas flow over the exterior
surface of the airfoil in a particular direction and having a
porous exterior portion for transpiration cooling of the airfoil by
a cooling gas discharged from the interior of the airfoil through
pores in the airfoil to the exterior thereof characterized by an
array of pores extending through the exterior portion configured to
direct the gas at an acute angle to the surface of the airfoil in a
direction downstream relative to flow over the surface in normal
operation, the exterior portion comprising a discharge layer
defining the exterior surface of the airfoil and a control layer
immediately adjacent to and bonded to the discharge layer, the
discharge layer having pores defined by intersecting pits extending
into the layer from the opposite faces of the layer, each pit only
partially overlapping the other, mutually offset in the direction
of the said gas flow with the pit in the outer face downstream, and
having an intersection at the bottoms of the pits, and the control
layer defining a feed hole for each pore offset from the said
intersection feeding into the pit in the adjacent face of the
discharge layer so as to direct the flow into the pore toward the
said intersection.
Description
The invention herein described was made in the course of work under
a contract or subcontract thereunder with the Department of
Defense.
DESCRIPTION
My invention relates to improvements in turbine vanes and blades
and other such devices which are protected from high temperature
gas by discharge of a cooling gas through numerous pores
distributed over the surface of the vane or the like. This mode of
cooling is referred to as transpiration cooling.
My invention is particularly adapted to transpiration cooled vanes
and blades of the general sort described in prior patent
applications, of common ownership with this application, as
follows: Bratkovich and Meginnis, Ser. No. 526,207 for Laminated
Porous Metal, filed Feb. 9, 1966 U.S. Pat. No. 3,584,972; Emmerson,
Ser. No. 691,834 for Turbine Cooling, filed Dec. 19, 1967; Helms,
Ser. No. 707,556 for Turbine Blade, filed Feb. 23, 1968; and
Meginnis, Ser. No. 742,900 for Turbine Blade, filed July 5, 1968
U.S. Pat. No. 3,619,082.
These applications describe turbine vanes or blades having
laminated walls, the outermost layer of which has pores which are
machined in the surface of the layer by a process such as
photoetching to provide numerous outlets for cooling air or other
gas from the interior of the vanes or blades. Vanes, blades, or
other structures to be protected from hot gas by transpiration
cooling will be referred to hereafter in this specification as
"vanes" for conciseness.
It has been found that the discharge of the cooling air from the
surface of the vane has some adverse effect upon the efficiency of
the turbine or other aerodynamic machine. This appears to be due to
some interference between the cooling air coming out substantially
perpendicularly from the vane surface and the motive fluid or other
gas flowing substantially tangentially to the surface.
I have conceived a modification of the configuration of the
passages from which the cooling air is discharged adjacent the
outer surface of the vane such that this interference may be
substantially reduced and the efficiency of the turbomachinery
correspondingly enhanced.
In the preferred embodiments of my invention, this is accomplished
by offsetting the pores in the vane facing or outer layer and the
adjacent layer or layers so that the gas discharged from the pores
is directed largely downstream with respect to the motive fluid
flow past the vane.
The principal objects of my invention are to improve the efficiency
and temperature tolerance of high temperature turbomachinery; to
improve the efficiency of transpiration cooled vanes, blades, and
other elements of engines; and to provide a simple and effective
means for discharging transpiration cooling air from a vane in a
direction largely conforming to the flow past the vane rather than
directly transverse to such flow.
The nature of my invention and its advantages will be clear to
those skilled in the art from the succeeding detailed description
of preferred embodiments of the invention and the accompanying
drawings thereof.
FIG. 1 is an axonometric view of a hollow laminated porous
airfoil.
FIG. 2 is a partial sectional view of the same taken on the plane
indicated by the line 2--2 in FIG. 1.
FIG. 3 is a transverse sectional view of the same taken on the
plane indicated by the line 3--3 in FIG. 1.
FIG. 4 is a greatly enlarged fragmentary sectional view
illustrating one form of the invention.
FIG. 5 is a similar view illustrating a second form of the
invention.
FIG. 6 is a similar view illustrating a third form of the
invention.
Referring first to FIG. 1, this illustrates a hollow tubular member
6 which may be a turbine vane airfoil or the airfoil portion of a
turbine blade or might represent some other structure in a high
temperature machine such as a turbine. The airfoil 6 has a formed
outer wall 7 perforated by numerous small closely spaced pores 8.
This structure as so far described may be similar to those
described in the above-mentioned patent applications. Referring
also to FIGS. 2 and 3, the vane airfoil illustrated has a leading
edge at 10, a trailing edge at 11, a convex face 12, and a concave
face 14, although, of course, the structure might have other
configurations than the specific one described. The vane defines an
interior chamber 15 to which air for cooling may be supplied by any
suitable structure.
As illustrated in FIGS. 2, 3, and 4, the vane wall is defined by
four layers or laminae, these being respectively, from the outside
of the blade to the inside, an outside or discharge layer 16, a
control layer 18, a layer 19, and an innermost layer 20. The
thickness of these layers may be considered as exaggerated for
clarity, depending upon the overall size of the airfoil. Generally
as described in the above-mentioned patent applications, each of
these layers is formed with holes through the layers and with
elevations on the surface which serve to provide spaces between the
layers for conduction of the cooling gas, all the layers being
bonded together so that a structure of overall controlled porosity
is provided with a multiplicity of paths for flow of the cooling
air from the interior of the vane to the large number of
distributed pores 8 on the surface.
The general nature of such a structure may be apprehended from
consideration of FIG. 4 in which the cooling air may flow through a
hole 22 in layer 20 into a space 23 from which it flows through a
hole 24 offset from hole 22 into a space 26 between layers 19 and
18 from which it flows through pores which have been developed in
accordance with the present invention in layers 18 and 16, flowing
out at the outlets 8 as indicated in FIGS. 3 and 4. So far as the
present invention is concerned, sheets or layers 19 and 20 serve
only as means to support the outer layers 16 and 18 and to
distribute the cooling air to them and, so far as the present
invention is concerned, their presence is nonessential.
Referring now to FIG. 4 for a detailed description of one
embodiment of the invention, it will be understood that the gas
flow past the air foil is in the direction indicated by the legend
FLOW and arrow in FIGS. 4, 5, and 6. In order to give a sense of
scale to the discussion of the succeeding figures, it may be
mentioned that the sheets 16, 18, 19 and 20 in FIG. 4, in the
preferred embodiment of the invention, are about 0.010 inch thick
and are diffusion bonded together to provide a blade wall having a
thickness of about 0.040 inch. The surface relief and the holes
through the layers are provided by a chemical machining process
such as photoetching in the preferred mode of manufacture of the
blade wall.
For each pore 8 the layer 16 has etched into its exterior surface a
pit 27 and into its interior surface a pit 28, these each extending
slightly more than half way through the thickness of the sheet and
intersecting to define a passage 30 for the cooling air to flow to
the exterior of the vane. In the form illustrated in FIG. 4, the
overlap between the two pores is something like one-third of their
total width providing a more or less elliptical passage 30 about
0.006 to 0.008 of an inch in minor diameter. Air is supplied to
each pit 28 from a feed hole or groove 31 in the outer surface of
layer 18 which in turn is supplied by a hole 32 extending from the
inner surface of this layer in register with a part of the space
26. Hole 32 connects to the feed hole 31 at a point substantially
offset from pit 28. It will also be noted that the feed hole 31
terminates at 34 so that, in general the portion of pit 28 which
underlies the passage 30 is cut off from the direct supply of air;
or, to put it otherwise, the discharge from the hole 31 into pit 28
is offset from the center of pit 28 in the same direction that pit
28 is offset from pit 27. This fact tends to increase the angle of
discharge of the cooling air with respect to the direction normal
to the surface. Also, since the cooling air must flow substantially
parallel to the inner surface of layer 16 to reach the point of
discharge into pit 28, it arrives at this point with a velocity
substantially parallel to the surface of the sheet and is then
deflected slightly outwardly, generally as indicated by the arrow
35 in FIG. 4. It will be understood that the mode of supply of air
to each of the pores 8 may be the same. It has been found that the
arrangement illustrated in FIG. 4 results in a lower angle between
the direction of flow of the gas and the surface of the sheet than
a construction in which the direction of flow is determined
primarily by the configuration of the offset pits in sheet 16 only.
Also, it has been found easier to control accurately the magnitude
and general configuration of the pores 8 where the passage such as
30 is determined primarily by an intersection between the bottoms
of the pits rather than by an intersection between the side walls
of pits as in a copending application of Thomas H. Mayeda Ser. No.
879,094 for Cooled Airfoil filed Nov. 24, 1969.
FIG. 5 illustrates a modification of the structure of FIG. 4, the
basic difference being that the outside or discharge layer
corresponding to layer 16 in FIG. 4 is, in the structure of FIG. 5,
a layer made up of two laminae 36 and 38 bonded together in proper
registry and bonded to the layer 18. In this case, the pores 40
corresponding to pores 8 of FIG. 4 are defined by a first pore
section 42 in the lamina 36 and a second pore section 43 in the
lamina 38, these being offset so that the overall effect is a pore
inclined to the direction normal to the surface of the airfoil, the
discharge passage 44 being defined by the area of overlap between
these two pore sections. As illustrated, the pores are etched in
from both faces of the laminae, but this is not necessary.
The arrangement for supplying cooling air to the pore section 43
through holes 32 and feed hole 31 remains as previously described.
The point of the structure of FIG. 5 as compared to that of FIG. 4
is that it is easier to control the pores and particularly control
precise overlap between them if the pores are made in two similar
sheets which are then bonded together with the proper shift in
registry of these pores to provide a structure as illustrated in
FIG. 5. The area of the passage 44 is not as sensitive to minor
variations in the speed or duration of the etching operation as the
passage 30 in FIG. 4.
FIG. 6 illustrates a somewhat different approach to the provision
of the air discharge pores and feed holes. In this form, there is a
discharge layer 46 defining the exterior surface of the cooled body
and a control layer 47. There may, if desired, be additional layers
such as layers 19 and 20 illustrated in the other figures. The pore
48 through layer 46 comprises an outer pit 50 and an inner pit 51,
these, as illustrated, being offset by an amount about one-half the
width of the pits so that the overlap is about half the diameter of
each pit. As before, the pits extend slightly more than half way
through the layer 46 which may be, for example, 0.010 inch thick
and their intersection defines passage 52 corresponding to passages
30 and 44 previously described. In the structure of FIG. 6, there
is a difference in the arrangement of the feed hole which is
indicated at 54. As previously, the feed hole is offset so as in
general to be beyond or principally beyond the periphery of the pit
50. However, it does not have the extension parallel to the surface
of the sheet but is simply a small hole going directly through the
layer 47. In this form of the structure, the impingement of the
cooling air against the bottom surface 55 of the pit 51 is depended
upon to divert the air to a direction roughly parallel to the
surface of the layer 46 as indicated by the arrow 56. The result is
a discharge of the air generally in the path indicated by the two
parallel lines 58.
It has been found by experiment that very low discharge angles of
the cooling air with respect to the outer surface of the airfoil
may be obtained with the structure described herein. Angles as low
as 10.degree. are quite feasible. This improves the adherence of
the transpiration cooling air to the outer surface of the airfoil
and minimizes any interference with the flow of the exterior of hot
gas over the surface of the airfoil.
The detailed description of the preferred embodiment of the
invention for the purpose of explaining the principles thereof is
not to be considered as limiting or restricting the invention, as
many modifications may be made by the exercise of skill in the
art.
* * * * *