Cooled Airfoil

Abstract

A transpiration-cooled turbine vane has a porous wall and an internal strut with a slidable dovetail connection to the wall to reinforce the wall. The dovetails may be directly on the wall or on a fluid distributing plate bonded to the wall. This fluid distributing plate, if present, or the strut provides for metering flow of cooling air to some areas of the wall.

Description

The invention herein described was made in the course of work under a contract or subcontract thereunder with the Department of Defense."

This patent application was filed under the provisions of 35 U.S. P Code Section 118 by General Motors Corporation, a corporation of Delaware, which asserts ownership of the application by virtue of a contract of employment of the inventor with General Motors Corporation.

DESCRIPTION

My invention relates to improvements in hollow fluid directing members for high temperature turbomachines, such as vanes and blades for gas turbines. It is particularly directed to improving the cooling and providing adequate stiffening in vanes in which the wall is a thin laminate of porous material or is of other material of a porous nature so that the blade may be cooled by transpiration cooling; that is, by air or other cooling fluid which flows through the walls of the vane and is discharged from multifarious pores in the outer surface of the vane. The term "vane" will be used here to refer to vanes and blades and other analogous structures. My invention may apply to any such which require cooling and which need to be strengthened or internally reinforced and to have the distribution of cooling fluid controlled, although the preferred embodiment is in a turbine nozzle vane.

Considering a turbine vane, the amount of heat transfer to the vane varies over the area of the vane wall. Also, external pressures vary, being generally low on the convex surface of the vane relative to the concave or high-pressure face. Economy of cooling fluid and even cooling of the surface may be improved by arrangements to control or meter the flow of fluid to the lower pressure surfaces of the vane. The pressure of the cooling fluid supplied to the vane must, of course, be greater than the maximum pressure outside the vane for cooling fluid to flow through the entire surface. Thus, it may be desirable to throttle or meter the flow to some parts of the vane so as to reduce the pressure and prevent undue and wasteful discharge of cooling fluid through the areas exposed to lower pressure. Also, there is a tendency for the pressure within the vane to balloon the airfoil and there may be gas bending loads and buffeting forces on the vane from the motive gas, and possibly other forces which tend to deflect the walls of the vane or other flow-deflecting element.

My invention is directed to improvements in porous walled vanes such as to strengthen the wall and to improve the distribution of cooling fluid to the wall. In the preferred embodiments of the invention, the vane is an airfoil having walls formed of a laminated porous metal sheet of the type described in U.S. Pat. application of Meginnis and Bratkovich, Ser. No. 526,207 for Laminated Porous Metal, filed Feb. 9, 1966, of common ownership with this application. A stiffening strut is provided in the vane and coupled to one or both faces of the vane by dovetail connections which allow relative expansion of the vane wall and strut. The strut may provide cooling air manifolds on its outer surface which are supplied with cooling air metered through passages from an air supply passage within the strut. Alternatively, a sheet having cooling air manifolds and passages to meter fluid may be bonded to the inside of one face of the vane such as the low-pressure face and this sheet in turn may have a dovetail connection to a stiffening strut extending spanwise of the vane. By virtue of such arrangements, the strength of the vane is enhanced and the evenness of cooling is improved.

The nature of my invention and its advantages will be clear to those skilled in the art from the succeeding detailed description of the preferred embodiments of the invention and the accompanying drawings.

FIG. 1 is an elevation view of a turbine vane.

FIG. 2 is a cross section of the same taken on the plane indicated by the line 2--2 in FIG. 1.

FIG. 3 is a partial sectional view of the vane taken on the spanwise extending plane indicated by the line 3--3 in FIG. 2.

FIG. 4 is a partial sectional view taken on the spanwise extending plane indicated by the line 4--4 in FIG. 2.

FIG. 5 is a sectional view, taken on the same plane as FIG. 2, illustrating a second form of vane structure.

FIG. 6 is a partial sectional view of the same taken on the plane indicated by the line 6--6 in FIG. 5.

Referring first to FIGS. 1 and 2, a flow directing member such as the turbine vane 10 comprises an airfoil 11 which is connected to platforms or shroud segments 12 and 14 at each end of the span of the vane. The details of the platforms 12 and 14 are immaterial to this invention. Referring to FIG. 2, the airfoil 11 is a chambered airfoil with a leading edge at 15 and a trailing edge at 16, having a concave or high-pressure face 18 or wall and a convex or low-pressure face or wall 19. The wall of the vane is a folded and formed laminated metal sheet comprising an outer layer 20, an intermediate layer 21, and an inner layer 22. An arrangement of perforations through the layers and spacing bosses on the surface of the layers provides a structure of controlled porosity. The layers 20, 2, and 22 are suitably bonded together to form a unitary porous sheet and, after folding and forming, the two faces of the blade are fixed together by welding or otherwise at the trailing edge 16. The structure of the vane so far described may, so far as my invention is concerned, be of the type described in U.S. Pat. application Ser. No. 691,834 of Emmerson for Turbine Cooling, filed Dec. 19, 1967, of common ownership with this application.

Referring to FIG. 3, it will be seen that the blade wall has holes 24 through the outer layer 20, holes 25 through the intermediate layer 21, and holes 26 through the inner layer 22. The holes in adjacent layers are out of register and, in connection with bosses on the surfaces of the layers which partly space the layers, the laminated metallic sheet provides a path for conduction of cooling air from the inner surface to the outer surface of the blade wall in such manner that the cooling air pervades the fabric of the blade wall. While this structure preferably is such as that disclosed in greater detail in the Bratkovich et al. application, other porous materials such as those sold under the trademarks Rigimesh and Porolloy could be employed in the outer walls.

The thickness of the vane outer wall is exaggerated in all the sectional views and the size of the pores or holes in the wall is exaggerated in FIGS. 3, 4, and 6 accordingly. The form of vane shown in FIGS. 2, 3, and 4 embodies a plate 28 which in practice preferably is segmented into a number of square or rectangular elements or segments by spanwise and chordwise cuts to minimize thermal stresses, this plate being contoured to fit the inner surface of the wall 19 and being bonded thereto by diffusion bonding or other suitable means. Narrow gaps between segments of the plate 28 are indicated at 29 in FIG. 2. Plate 28 defines air manifolds 30 distributed over the surface of the wall 19. These manifolds are in communication with the interior surface of plate 28 through passages indicated at 34, the passages being at varying points along the span of the blade and, therefore, some of them not being visible in FIG. 2. These ports communicate with spanwise extending recesses 35 in the inner surface of plate 28 or with a spanwise extending passage 36 within the vane. Cooling air under pressure is supplied to the interior of the vane from either or both ends thereof by means which are immaterial to the present invention. There are many disclosures of arrangements for supplying air to the shrouds of turbine nozzles and to the roots of turbine blades.

Adjacent the trailing edge of the vane the plate 28 is provided with a number of ridges 38 which define between them channels for passage of cooling air to the trailing edge portion of the vane. The various passages 34 and 38 are calibrated to pass the desired amount of cooling air to the particular areas of the vane with which they communicate. Plate 28 of itself tends, to some extent, to stiffen the vane, particularly the wall 19. However, additional stiffening is provided by a strut 39 extending spanwise of the vane which is dimensioned to abut the plate 28 and the inner surface of the opposite wall 18. Strut 39 is formed with spanwise-extending dovetail slots 40 within which are slidably mounted dovetail tenons 42 extending from the segments of the plate 28. The strut 39 may have a spanwise extending recess 43 in its face adjacent the wall 18 and have ridges 44 and 46 on the remainder of the surface engaging the wall 18 so as to define passages between the ridges for flow of cooling air to a chamber 47 at the leading edge of the blade and to the passage 36. The strut 39 may have passages through its wall to supply air to the recesses 35 if it is not desired to supply them from the end of the vane.

As will be seen, the cooling air entering at the end of the vane is distributed over the entire high-pressure surface more or less directly and at substantially constant maximum pressure and is distributed to various areas of the convex or low-pressure surface through the metering passages 34 and the manifolds 30. Because of the slidability of the dovetail connection between the plate 28 and the strut 39, the wall of the vane may expand relatively to the strut with changes in temperature.

FIG. 5 illustrates a different structure of the vane in which the strut performs the function of an air-distributing member for the entire surface of the blade and the plate 28 is omitted. The walls 18 and 19 may be as previously described. A number of spanwise-extending tenons 48 are diffusion bonded or otherwise fixed to the interior of both walls of the vane. These engage in spanwise extending dovetail slots 50 in the strut 51. Strut 51 is hollow and defines a spanwise extending cooling air duct 52. Its outer surface defines localized cooling air manifolds 30 similar to those in the plate 28 previously described. It also defines cooling air manifolds 54 which communicate with the chamber 47 at the leading edge of the blade vane and manifolds 55 which communicate with the trailing edge portion of the blade. These manifolds are supplied from the cooling air duct 52 through passages such as 56 and 57 which may be dimensioned to meter the air to provide the desired pressure of air at the vane interior surface.

It will be seen that both forms of the invention provide a structure in which the wall of the vane, with or without the air distributing plate, may readily be slipped onto the internal strut which stiffens the vane wall and in which means are provided for distributing the cooling air as required to the various areas of the vane. pg,8

The detailed description of preferred embodiments of my invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

Claims

I claim:

1. A hollow flow-directing member comprising, in combination, a wall of controlled porosity adapted for transpiration cooling effected by fluid flowing outward through the wall, the member being of airfoil cross section with a high-pressure face and a low-pressure face, means providing localized cooling fluid manifolds communicating with diverse areas of the inner surface of the wall and defining metering passages for supply of cooling fluid to said manifolds, internal strut means adapted to support the wall against deflection, and means defining a dovetail connection between the wall and the strut means slidable spanwise of the airfoil.

2. A member as recited in claim 1 in which the means providing the cooling fluid manifolds is segmented.

3. A member as recited in claim 1 in which cooling fluid manifolds are provided on the strut means.

4. A hollow flow-directing member comprising, in combination, a wall of controlled porosity adapted for transpiration cooling effected by fluid flowing outward through the wall, the member being of airfoil cross section with a high pressure face and a low-pressure face, a fluid distributing and metering plate bonded to the inner surface of the low-pressure face, and an internal strut adapted to support the wall against deflection, the strut and plate having a dovetail interconnection slidable spanwise of the member to interlock the plate and strut.

5. A member as recited in claim 4 in which the strut bears against the high-pressure face of the member.

6. A member as recited in claim 4 in which the said plate is segmented.

7. A hollow flow-directing member comprising, in combination, a wall of controlled porosity adapted for transpiration cooling effected by fluid flowing outward through the wall, the member being of airfoil cross section with a high-pressure face and a low-pressure face, a plural number of dovetail ribs extending spanwise of the member bonded to the inner surface of the wall, and an internal strut adapted to support the wall against deflection having dovetail slots receiving the dovetail ribs, the strut being hollow to serve as a supply conduit for cooling fluid and defining passages from the interior of the strut to distribute and meter flow to diverse areas of the wall.

8. A member as recited in claim 7 in which the said ribs are provided on the interior of both faces of the member.