Cooled Airfoil

Abstract

A transpiration-cooled turbine blade has a porous wall and may have an internal strut extending spanwise of the blade and carrying cooling air into the blade. A honeycomb material with the cells extending generally from face-to-face of the blade is bonded to the interior of the blade wall and to the strut, if present. If there is no strut, the honeycomb extends from face-to-face, and has air supply passages cut through the honeycomb extending spanwise of the blade.

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. 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 blades 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 blade and is discharged from multifarious pores in the outer surface of the blade. The term "blade" 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 blade.

Considering a turbine blade, the amount of heat transfer to the blade varies over the area of the blade wall. Also, external pressures vary, being generally low on the convex surface of the blade 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 blade. The pressure of the cooling fluid supplied to the blade must, of course, be greater than the maximum pressure outside the blade 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 blade 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 blade to balloon the airfoil and there may be gas bending loads and buffeting forces on the blade from the motive gas, and possibly other forces which tend to deflect the walls of the blade or other flow-deflecting element.

My invention is directed to improvements in porous walled blades 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 blade is an airfoil having walls formed of a laminated porous metal sheet of the type described in U.S. Pat. No. 3,584,972 of Meginnis and Bratkovich.

The blade walls define a hollow interior which is filled with material which distributes fluid to the blade walls, and strengthens and stiffens the blade. Two forms are disclosed, in one of which honeycomb material extends from face to face of the blade between the inner surfaces of the walls, thus connecting the faces together and providing a reinforcement within the blade. Spanwise extending passages cut through the honeycomb material distribute the cooling fluid spanwise of the blade, and it flows from these passages through the cells of the honeycomb material to the blade wall. In this structure the honeycomb serves to stiffen the blade against bending loads, as well as other deflections or ballooning.

In a further form of the invention, a greater degree of stiffness is obtained by the use of a hollow strut of relatively heavy section compared to the blade walls. In this case, the strut provides the spanwise extending cooling air passages and delivers the air to a layer of honeycomb between the strut and the blade wall.

Of course, various structures embodying the principles of the invention may be derived from these preferred embodiments, described in detail in this specification.

The principal objects of my invention are to provide transpiration-cooled turbine blades and vanes and other analogous airfoil devices of improved strength and rigidity, which may be readily fabricated, and which have superior structure for distribution of the cooling air to various areas of the wall of the airfoil.

The nature of my invention and its advantages will be more clearly apparent 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 elevation view of a turbine blade.

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 considerably enlarged view of a fragment of FIG. 2.

FIG. 4 is a fragmentary sectional view taken on a curved surface indicated generally by the line 4--4 in FIG. 3.

FIG. 5 is a sectional view, taken on a plane similar to that of FIG. 2, of a second form of blade structure.

FIG. 1 illustrates what may be regarded as a typical turbine blade except for structure not shown in FIG. 1. The blade 6 includes a fluid-directing airfoil 7 and a base 8 by which it is mounted on a turbine rotor. The base is an integral cast structure comprising a platform 10, a stalk 11, and a root 12. The airfoil 7 is a formed structure of sheet metal of controlled porosity for diffusion of cooling air through the walls of the blade for transpiration cooling. While various types of porous material may be employed in the blade wall, the preferred material is that described and claimed in the Bratkovich et al., patent referred to above. The airfoil may be bicast or otherwise secured to the base 8. The airfoil 7 may have any suitable shape but, as illustrated more clearly in FIG. 2, is of cambered airfoil cross section having a convex or low-pressure face 14 and a concave or high-pressure face 15, these extending from a rounded leading edge 16 to a sharp-trailing edge 18.

Cooling air may be admitted to the interior of the airfoil 7 through an opening 19 in the blade base and the free end or tip of the blade is closed by a cap 20 or other suitable closure. The air introduced into the blade escapes through numerous small pores 22 distributed over the surface of the airfoil.

The blade structure illustrated in FIGS. 1, 2, and 3 includes a hollow strut 23, which may be a cast structure, and which may be cast integral with the blade base 8 or be otherwise secured to it. Strut 23 may be the means to fix the blade wall to the blade base, or part of such means. Strut 23 is of such contour as generally to parallel the interior of the blade wall but be spaced a substantial distance from it. It includes a number of cross walls 24 in the preferred structure, these defining with the outer wall of the strut a number of spanwise extending cooling air passages 26. A layer of honeycomb material 27 defined by walls extending across the gap from the strut 23 to the interior of the airfoil wall 7 is bonded both to the wall and to the strut by any suitable process, preferably diffusion bonding, although some such process as brazing might be employed.

As shown more clearly in FIG. 4, the honeycomb material defines a number of polyhedral cells 28, preferably hexagonal, terminating at the airfoil wall and at the strut. Numerous apertures 30 are provided in the wall of strut 23 to distribute the cooling air from the passages 26 into the cells of the honeycomb. The size and spacing of these apertures should be such as to meter the cooling fluid to the respective areas of the blade as needed for proper cooling, providing sufficient differential pressure between the interior and the exterior of the blade for this purpose. The apertures 30 may communicate with various ones of the cells 28 but need not connect directly to all of the cells, since they are interconnected as seems desirable through pores 31 in the walls of the honeycomb. Thus air may flow through apertures 30 and pores 31 to the interior of wall 7. The nature of this distribution of air is indicated by the flow arrows on FIGS. 3 and 4. In FIG. 3, the airfoil or wall 7 is indicated as a porous structure by numerous pores 32 through the wall. These are, in a sense, schematic since the wall 7 may not have pores specifically as illustrated in the FIG. 3. In many cases it is desirable to obtain a preferred wall thickness by laminating layers of metal. However, for the present purpose, the wall 7 as illustrated may be considered as a representation of a porous wall of whatever structure is suitable for the purpose. Several types of porous sheet material are presently available commercially.

Because of the narrowness of the trailing edge portion of the blade, the strut terminates considerably ahead of the trailing edge but the strut may be provided with air discharge apertures 34 at the trailing edge communicating with the honeycomb adjacent the trailing edge which may have openings through the honeycomb wall, generally as illustrated in FIG. 4, to conduct the fluid toward the trailing edge of the blade. AS will be seen, with the blade wall rigidly fixed to the struts through the honeycomb material, the overall blade is extremely stiff and resistant to ballooning or tinpanning, as well as rigid to resist bending because of the beam loads due to the pressure of motive fluid on the blade. Also, the honeycomb material provides a very suitable path for conduction of cooling air from the strut to the porous surface of the blade with a minimum of obstruction of the interior of the blade wall. Only the narrow edges of the metal strips which define the honeycomb are in abutting relation to the wall.

FIG. 5 illustrates a different structure, which is in some respects simpler, and in which the strut such as 23 of FIG. 2 is omitted. In the structure of FIG. 5, the blade base and airfoil may be as previously described and are given the same reference numerals. In this case, however, the blade wall 7 is reinforced by honeycomb material extending from face to face of the blade and bonded to the interior of the wall at both faces of the blade by diffusion bonding or otherwise. In this structure, a number of cells 37 are defined by walls indicated at 38, these walls defining a honeycomb structure generally as indicated in FIG. 4, although the cells may be of larger cross section. A number of spanwise extending passages 40 are machined in the honeycomb material, cutting through the walls of the cells to distribute fluid from the blade base throughout the length of the airfoil. These passages communicate directly with many of the cells 37, which in turn direct the fluid to the interior of the wall 7 through which it flows for transpiration cooling. Moreover, apertures 42, as indicated at various points, may be provided through the walls of the cells to distribute fluid into various cells which do not otherwise communicate with the spanwise extending passages 40. Since each spanwise extending passage distributes fluid to a particular portion of the chordwise extent of the blade, the cooling fluid may be metered either by the size of the passage, by the entrance to the passage, or otherwise so that the quantity of fluid is appropriate to the requirements of the particular chordwise portion of the blade. In this case, however, the pressure will be the same on both faces of the blade. This may be a disadvantage, as it will require that the porosity of the low-pressure surface be less than that of the high-pressure surface of the blade wall. On the other hand, the structure of FIG. 5 is lighter and simpler than that of FIG. 2, and may have ample strength for many applications.

It will be apparent to those skilled in the art that the structures described provide for reinforcement of the blade as a beam and also for reinforcement of the sheet metal faces of the blade and for efficient metering and distribution of cooling air to the blade wall.

The detailed description of preferred embodiments 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.

Claims

I claim:

1. A fluid-directing airfoil member for use in hot environments comprising, in combination, an outer skin defining the airfoil contour, the outer skin being of a porous material adapted for transpiration cooling by flow of coolant outwardly through the skin; an open-cell honeycomb structural material lining the outer skin and bonded to the outer skin, with the cells of the honeycomb open to the skin and extending inwardly from the skin to define cooling fluid passages from the interior of the airfoil element to the inner surface of the skin and providing a structural reinforcement for the skin resisting displacement of the skin; and means for conducting a cooling fluid through the interior of the airfoil member into the honeycomb material for flow through the said passages and skin.

2. A member as defined in claim 1 in which the last-recited means includes a rigid hollow strut extending spanwise of the blade bonded to the honeycomb material.

3. A member as defined in claim 1 in which the last-recited means is formed by passages extending spanwise of the blade cutting through the cell walls of the honeycomb material.

4. A member as defined in claim 1 in which the last-recited means includes means defining at least one passage extending spanwise of the blade and includes apertures through the cell walls of the honeycomb material for distribution of the cooling fluid from cell to cell.

5. A member as defined in claim 1 in which the last-recited means includes metering restrictions adapted to proportion the flow of cooling fluid to various areas of the outer skin in accordance with external pressure and cooling requirements at such various areas.

6. A hollow flow-directing airfoil 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 layer bonded to the inner surface of the wall at both faces, and an internal strut adapted to support the wall against deflection and to supply a cooling fluid to the wall, the internal strut being a hollow structure extending spanwise of the airfoil and defining at least one cooling fluid passage extending spanwise of the airfoil, the said layer being bonded to the strut and being composed of a honeycomb material with cells extending from the strut to the interior surface of the wall, and fluid distributing apertures in the strut connecting the said duct to the said layer.

7. A member as defined in claim 6 including also apertures between some of the honeycomb material cells for further distribution of the fluid.

8. A fluid-directing airfoil member for use in hot environments comprising, in combination, an outer skin defining the airfoil contour, the outer skin being of a porous material adapted for transpiration cooling; the skin defining an airfoil with a leading edge, a trailing edge, and high- and low-pressure faces extending from the leading edge to the trailing edge and enclosing the interior of the blade; a reinforcing and fluid-distributing structure within the airfoil comprising a structural honeycomb extending between, and bonded to the interior of, the inside of the skin of the faces, the honeycomb having open cells extending from face to face of the blade; passages within the honeycomb material extending spanwise of the airfoil being defined by voids in the honeycomb material, the passages communicating with the cells of the honeycomb material, so that a cooling fluid may be supplied through the passages and thence through the cells of the honeycomb to the interior of the outer skin.

9. A member as defined in claim 8 including also apertures between some of the honeycomb material cells for further distribution of the fluid.