US3695778A

US3695778A - Turbine blade

Info

Publication number: US3695778A
Application number: US73658A
Authority: US
Inventors: John E M Taylor
Original assignee: TRW Inc
Current assignee: Ex-Cell-O Corp
Priority date: 1970-09-18
Filing date: 1970-09-18
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A lightweight turbine blade having a metallic center body and root section with hollowed areas through the center body. The center body is covered by a composite skin interfitted with the center body adjacent the edges of the blade to provide a smooth surface. The edges of the blade are formed by portions of the center body. The skin is attached to the body by diffusion bonding, adhesives, or other means and the hollowed areas may be filled with plastic foam or other low density material, or may be left hollow.

Description

United States Patent [1 1 3,695,778 Taylor Oct. 3, 1972 [54] TURBINE BLADE 2,015,332 9/1935 Baumann ..416/233 X 2,293,801 8/1942 Caldwell ..416/233 [72] invent Tayh" Pepper 2,929,755 3/1960 Porter ..416/229 x 2,991,973 7/1961 Cole et al. ..416/92 [73] Assignee: TRW Inc., Cleveland, Ohio 3,240,468 3/ 1966 Watts et al ..416/231 X [22] Filed: Sept 1970 Primary Examiner-Everette A. Powell, Jr. 211 App] 73, 53 Att0rneyl-lill, Sherman, Meroni, Gross & Simpson Related us. Application Data [57 ABSTRACT [62] Division of Ser. No. 764,207, O t, 1, 1968, A lightweight turbine blade having a metallic center abandoned.

US. Cl. ..416/92, 416/96, 416/233,

body and root section with hollowed areas through the center body. The center body is covered by a composite skin interfitted with the center body adjacent 416,241 the edges of the blade to provide a smooth surface. [511 rm. Cl ..F01d 5/18 ff fgggq g 533 3 3331 gfg o o y y l u- [58] Field of Search ..416/233, 226, 229, 230, 232, Sion bonding adhesives, or other means and the 416/241 97 lowed areas may be filled with plastic foam or other 56 R f C ed low density material, or may be left hollow. e erences it 12 Claims, 7 Drawing Figures UNITED STATES PATENTS .l t t,

2,006,339 7/1935 Baumann ..416/233 X 1 g r E-" 1( [L J- I.'

\ I I \l r I 42' {5 43/ PATENTEBucI 3 I972 SHEET 2 OF 2 TURBINE BLADE This case is a divisional application of John E. M. Taylor application for patent entitled TURBINE BLADE, Ser. No. 764,207, filed Oct. 1, 1968, now abandoned.

BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to turbine blades and more particularly to a lightweight turbine blade having a hollowed center body.

2. Prior Art In recent years increasingly greater emphasis has been placed on designs for turbine blades such as compressor airfoils which insure increased efficiency while providing lighter weight and lower production cost. Such turbine blades operate at extremely high speeds and varying temperatures. The operational requirements are such that the blades should be light in weight and yet strong enough to function against the air resistance and the dynamic loading created during operation of the turbine.

Pure composite blades may reduce weight while providing a fairly strong structure. However, such blades do not sufficiently resist erosion at the leading and trailing edges of the airfoil, nor do they have sufficient impact strength and edge sharpness for digesting foreign material which may be sucked into the turbine area. Additionally, pure composite blades create a problem in attaching the blade through a root area. A further disadvantage found in the prior art turbines arises from the fact that in a solid turbine blade the center of mass is spaced an appreciable distance from the root attachment, thereby adversely affecting the blades ability to reduce vibrational flutter and resultant fatigue.

SUMMARY OF THE INVENTION This invention provides a composite turbine blade having a metallic core structure or center body which has hollowed-out areas or slots therethrough. The slots reduce the weight of the center body and place its center of mass closer to the root area of the blade.

The front and back faces of the center body are then covered by a composite skin. The skin may be adhered to the center body by any suitable means such as adhesives or diffusion bonding.

A composite skin is defined as a skin made of high modulus fine filaments, fibers, or foils embedded in or laminated to a lower modulus matrix material, which holds the high modulus material in place. The resulting combination, or composite, structure can have strength, rigidity, toughness, and damping properties which far exceeds these properties in the individual constituents.

The skin is fitted into the center body adjacent the leading and trailing edges thereof such that those edges are formed of the center body metal thereby providing sufficient impact strength and sharpness. In one embodiment, the hollowed areas or slots are longitudinal, running substantially the length of the blade area and are transversely spaced apart a short distance.

In another embodiment, the hollowed or slotted areas comprise a plurality of longitudinal slots spaced from each other both transversely and longitudinally with longitudinal drainage holes connecting the ho]- lowed areas. This embodiment provides for a substantially solid cross section blade in the areas of greatest stress while at the same time providing for blade weight reduction. The drainage passages prevent buildup of water in the hollowed areas and provide equalization of internal pressure.

In order to provide additional skin support on very highly loaded airfoils, the hollow areas may be filled with a material such as a foamed plastic, or a lower cost composite material, or the skin material. The fill material supplies a bottom support forthe composite skin while at the same time, because of its low mass-tovolume ratio, allows sufficient weight reduction. In order to further reduce weight, the root section may also be partially hollowed. The root section may be joined to the center body by any metal joining method or may be formed as a part thereof.

It is therefore an object of this invention to provide a reduced weight turbine blade.

It is a further object of this invention to provide a low weight turbine blade having hollowed areas covered by a skin.

It is yet another and more specific object of this invention to provide a turbine blade having a center body with hollowed out areas covered by a composite skin.

It is yet another and more specific object of this invention to provide a turbine blade having a center body with hollowed out areas, the hollow areas being covered by a composite skin forming portions of the front and back surfaces of the blade, the skin being fitted to the center body adjacent the leading and trailing edges whereby those edges are formed from the center body material.

Other and further objects of this invention will be apparent to those skilled in this art from the following detailed description of the annexed sheets of drawings which, by way of a preferred embodiment of the invention, illustrate one example of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a center body and root section of a turbine blade according to this invention.

FIG. 2 is a plan view similar to FIG. 1 illustrating the center body with the composite skin attached and underlying portions shown by broken lines.

FIG. 3 is a cross-sectional view of the turbine blade of FIG. 2 taken along the lines IIIIII.

FIG. 4 is a fragmentary sectional view similar to FIG. 3 illustrating a modified form of the invention.

FIG. 5 is a top plan view of another modified form of the turbine blade of this invention with underlying portions illustrated by broken lines.

FIG. 6 is a cross-sectional view taken along the lines VI-VI of FIG. 5.

FIG. 7 is a top plan view of yet another modified form of the turbine blade of this invention with underlying portions illustrated by broken lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a center body or core structure 10 for a turbine blade. The blade comprises a blade area 11 and a root structure 12. The blade area 11 projects from the root structure 12 and is integral therewith. The blade area 11 may be tapered, curved and twisted in a manner known to the art. The center body can be either machined, forged or cast from materials such as titanium, aluminum, stainless steel, super alloys or other appropriate airfoils metals, or a composite material, which may require different properties from the skin material.

In order to reduce the weight of the center body 10, a reduced thickness area 13 may be provided in the central portion of the blade area 1 l. The reduced thickness portion 13 is provided on both the front and back sides of the blade area 11 and provides thereby a greater thickness peripheral portion 14 around the blade 11. The reduced thickness portion 13 has curved comers as at 15 to prevent local stress concentration. A plurality of longitudinal slots 16 are provided in the reduced thickness portion 13. The slots are usually tapered. The slots 16 extend through the body of the center structure 10 and lie somewhat parallel to the longitudinal axis of the center body. The slots 16 are spaced transversely of the blade and as shown in FIG. I, extend longitudinally for most of the blade 11. The slots may be varied in width and spaced to achieve load carrying capability. The areas between adjacent slots 16 form longitudinal ribs 17.

The provision of the slots 16 reduces the weight of the center body 10 and moves its center of mass closer to the root structure 12. The longitudinal ribs 17 provide strengthening supports for the blade area 11, and help give the skin its aerodynamic contour. In order to further reduce the mass of the center body 10, bores 18 may be introduced into the root section 12 thereby removing metal from the root section and decreasing its weight. The slots 16 may be introduced in the center body 10 by any acceptable method such as punching, E.D.M., E.C.M., chemical milling, leaching, or the like.

After preparation of the center body 10 and provision of the slots 17 and bores 18, a composite skin is applied to the center body as shown in FIGS. 2 and 3. The composite skin consists of a matrix material reinforced with a high strength filament or foil. Matrix materials such as epoxy resins, polymides, polybenzimidazoles or the like may be used. In addition metallic and ceramic matrix materials may be used. The filament material may be carbon based such as the material known as Thornell 50 marketed by the Union Carbide Corporation or boron, borsic, beryllium, titanium, aluminum or the like materials for the lower temperature regions of the gas turbine. Tungsten, molybdenum, and super alloys may be preferred for high temperature regions.

The filament or foil reinforced matrix sheets may be laid up in alternate layers with the filaments in various layers at an angle to the filaments in succeeding layers to give bi-directional stiffness and strength.

A plurality of prepared sheets are then bonded together and cured to form the skin 20.

The skin 20 may have either a constant thickness or a tapered variable thickness. The thickness may be on the order of 0.030 inches to 0.150 inch, the thickness being determined on the basis of various considerations including intended turbine blade use and its size.

The skin 20 is attached to the blade area 11 of the center body 10 so that it covers the reduced thickness portion 13. The skin 20 may be attached to the center body 10 by adhesive bonding, diffusion bonding, or any other suitable bonding means. The skins 20 may be made oversized to overlap the edge areas of the reduced thickness portion 13. The overlap can then be machined to provide a smooth surface transition from the skin to the peripheral area 14 of the centerbody. In this manner, air will flow over the turbine blade without encountering any interruptions of the surface.

The skins for both the front and back of the airfoil may be bonded to the center body 10 separately or simultaneously in a suitably shaped die under pressure. The bonding can be cured at a modest temperature such as 350 degrees over a period of time such as 20 minutes in those applications using low temperature resins. Difiusion bonding of high temperature skins may require up to 2 hours at 2, 1 00 F.

FIG. 3 is a cross section of the completed turbine blade illustrated in FIG. 2 and shows internal fillets 21 formed along the four longitudinal junctions between the side walls of the slots 16 and the inside surface of the top and bottom skins 20. The fillets 21 are formed by reason of the application of a controlled excess amount of adhesive and their formation is controlled by selection of the bonding pressure. The formation of the fillets aids in providing an internal support for the skins adjacent the ribs 17. The dimensions illustrated in FIG. 3, relating to the amount of adhesive present in an airfoil turbine blade have been exaggerated for purposes of clarity.

The leading and trailing

edges

23 and 24 of the turbine blade are formed by the peripheral portion 14 of the center body 10. FIG. 3 illustrates two embodiments of skin-to-periphery mating which provide a smooth juncture between the skin 20 and the periphery 14 of the core body. In both embodiments, the periphery 14 is tapered to provide a sharp, longitudinal edge 26 at both the, leading and trailing edges. This reduces air friction at the edges while at the same time providing a sufficient sharpness to allow the blade to cut up or digest foreign matter such as birds, etc., which may find its way into the compressor. Because the leading and trailing edges are formed from the peripheral portion 14 of the center body 10 which is of solid metal such as titanium or metallic composite, the strength necessary to digest the foreign matter is present to a greater extent than in a single composition blade of material having less impact resistance.

One embodiment of the skin-to-peripheral portion mating is illustrated in connection with the edge 24. In this embodiment, the peripheral portion 14 has the same thickness as the otherwise reduced thickness" portion 13 presenting opposed planar faces 27 and 28 which extend transversely outwardly from the outside slot 29 for a short distance and which thereafter taper to form the pointed edge 26. The skins 20 are bonded to the faces 27 and 28 and thereafter machined to a smooth mating with the peripheral portion 14 transversely spaced from the slot 29.

Another embodiment is illustrated in connection with the edge 23 adjacent the slot 30 on the side remote from the slot 29. This embodiment utilizes the reduced thickness portion 13 in the center body 10. The reduced thickness portion 13 provides a ledge 31 adjacent the peripheral portion 14. The skins 20 are fitted into the ledges and have a thickness equal to the depth of the ledge, thereby providing a smooth mating surface between the peripheral portion 14 and the skin 20.

When initially applied, the skins may have a thickness greater than the depth of the ledge and may thereafter be machined to provide a smooth transition from the metallic peripheral portion 14 to the composite skin in order to assure a smooth face on the turbine blade.

As shown in FIG. 4, in those instances where the turbine blade is to be subjected to extremely high loads, the slots 16 may be filled with a low weight-to-volume material such as a foamed plastic 33. The plastic 33 provides additional support for the skins 20 in the area of the slots 16. Because the weight of the foam plastic which fills the slots is less than the weight of the metal removed to form the slots, the advantageous weight reduction of the blade is retained.

FIG. 5 illustrates an embodiment which provides a midspan support metal base in the airfoil blade. The metallic center body 35 has two reduced thickness portions 36 and 37 which are longitudinally spaced apart thereby providing a solid span 38 therebetween. The midspan support base 38 is composed of the solid center body structure. The reduced thickness portions 36 and 37 contain longitudinal slots 39 transversely spaced apart by ribs 40 as in previous embodiments. The reduced thickness portions 36, 37 are covered by composite skins 41 of the type above described. The skins are applied in the same manner as in previous embodiments and are interfitted with peripheral areas 42 surrounding the reduced thickness portions 36 and 37 to produce smooth top and bottom surfaces on the blade. The provision of the solid metal mid-span support base 38 aids in reducing vibrational flutter and fatigue in large blades. The mid span support bars 42 are attached to the mid span support base 38 to aid in stiffening the blade. Either metal or composite materials may be used. Referring to FIG. 6, longitudinal connecting channels 43 may extend through the mid-span support 38 connecting the slots in one reduced thickness portion to the slots in the other reduced thickness portion. Additional channels 44 may extend through the peripheral portion 42 in the end of the blade remote from the root structure 12 and communicate with the exterior of the blade. The combination of the

channels

43 and 44 provides a drainage path to prevent accumulation of moisture in the slots at 39 as well as to equalize air pressure between the interior and exterior of the hollow blade.

FIG. 5 also illustrates a secondary set of channels or bores 61 which connect the slots 39 through the root section 12 to the base thereof. The optional provision of such slots allows for a heated or cooled air foil which can be provided by connecting the bores 61 to a heating or cooling fluid such as air which will then pass through the air foil and out the tip channels 44. Thus cooling fluid can be passed through high temperature blades or de-icing fluid through low temperature blades. It is to be understood that this method of producing a heated or cooled air foil may be used with any of the embodiments illustrated.

FIG. 7 illustrates another embodiment which provides transverse span support in high stress areas. The metallic center body 50 has a single reduced thickness portion 51 comprising the majority of the central portion of the blade 52 leaving a peripheral portion 53 therearound on both the front and back surfaces of the blade..A plurality of hollowed slots 54 are provided through the metallic center body in the reduced thickness portion 51. As illustrated, the slots 54 are arranged in longitudinal and transverse columns spaced apart both longitudinally and transversely of the blade, thereby providing both longitudinal ribs 55 and transverse ribs 56. The slots are dimensioned to provide the transverse ribs 56 in the areas of high stress thereby creating a plurality of mid-span supports each equivalent to the support 38 in FIGS. 5 and 6. As in previous embodiments, the slots 54 are joined throughconnecting channels 57 while other connecting channels 58 connect the slots to the atmosphere through the tip of the blade. After formation of the slots and channels, skins 59 equivalent to the composite skins described above are affixed to the center body 50 in the reduced thickness area 51. The skins are interfitted with the peripheral area 53 to provide a smooth blade surface over both the front and back sides.

Although each of the embodiments has been illustrated as having rounded corner slots, it is to be understood that the slots can have different configurations and can be placed in different arrangements so as to provide the desired stress resistant configuration of ribs. Further, although those embodiments which have been illustrated as having connecting channels between the slots have also been illustrated as having connecting channels extending to the exterior of the blade, it is to be understood that the connecting channels are optional and may be provided in different arrangements.

It can therefore be seen from the above that my invention provides a lightweight turbine blade having metallic center body and root sections, which may be formed from the same monolithic piece of material, and which has hollowed-out portions in the blade area, thereby reducing the weight of the blade. The hollowed-out areas are covered on the front and back of the blade by composite skins which are adhered to the metallic center body in such a manner as to provide a smooth surface.

Although I have herein set forth my invention with respect to certain specific principles and details thereof, it will be understood that these may be varied without departing from the spirit and scope of the invention as set forth in the hereunto appended claims.

I claim as my invention:

1. A turbine blade comprising: a metal center body structure shaped to define a turbine blade, said structure having a reduced thickness portion, a peripheral portion of said structure extending around the said reduced thickness portion, leading and trailing edges on said blade, portions of said peripheral portion providing said edges, slots extending through said reduced thickness portion from a front side thereof to a back side thereof, ribs separating said slots, the ends of said ribs integral with the said metal center body structure, the thickness of said ribs corresponding with the thickness of the reduced thickness portion whereby the said ribs have a thickness which is never greater than the thickness of the said reduced thickness portion, composite skins covering said slots and said reduced thickness portion, said skins adhered to said front and back sides, said skins mating with said peripheral portion to produce smooth surfaces on said structure from said leading edge to said trailing edge, a plurality of said slots spaced apart transversely and longitudinally defining longitudinal and transverse ribs therebetween, the ends of said ribs integral with the said peripheral portion, and a single skin covering each of said front and back sides.

2. The blade of claim 1 wherein connecting channels extend through some of said ribs communicating some of said slots to other of said slots.

3. The blade of claim 2 wherein second connecting channels extend through portions of the said peripheral portion communicating some of said slots to the atmosphere exterior of the said turbine blade.

4. A turbine blade comprising: a metal center body structure shaped to define a turbine blade, said structure having a reduced thickness portion, a peripheral portion of said structure extending around the said reduced thickness portion, leading and trailing edges on said blade, portions of said peripheral portion providing said edges, slots extending through said reduced thickness portion from a front side thereof to a back side thereof, ribs separating said slots, the ends of said ribs integral with the said metal center body structure, the thickness of said ribs corresponding with the thickness of the reduced thickness portion whereby the said ribs have a thickness which is never greater than the thickness of the said reduced thickness portion, composite skins covering said slots and said reduced thickness portion, said skins adhered to said front and back sides, said skins mating with said peripheral portion to produce smooth surfaces on said structure from said leading edge to said trailing edge, a plurality of said reduced thickness portions each having slots extending therethrough from a front side thereof to a back side thereof, said reduced thickness portions spaced apart by a portion having a thickness greater than the reduced thickness portions, a plurality of said composite skins, one of said skins covering each of said front and back sides of each of said reduced thickness portions, and said skins mating with said peripheral portions and said greater thickness portion along the sides of the said reduced thickness portions to produce smooth surfaces on said structure from said leading edge to said trailing edge.

5. The blade of claim 4 wherein the said slots are arranged to define longitudinal ribs therebetween and the said ribs are integral at both ends thereof with portions of the said center body.

6. The blade of claim 5 wherein the said slots are arranged to define longitudinal and transverse ribs therebetween, said ribs integral at both ends thereof with portions of the said structure.

7. The blade of claim 4 wherein connecting channels communicate some of said slots in one of said reduced thickness portions to some of said slots in another of said reduced thickness portions.

8. The blade of claim 7 wherein second connecting channels communicate some of said slots in one of said reduced thickness portions to the atmosphere exterior of the blade.

9. A turbine blade comprising: a metal center body structure shaped to define a turbine blade, leading and trailing edges on said blade, said edges formed by said structure, slots extending through said structure intermediate the said edges, center body material ribs having their ends integral with the s id structure separating a acent slots, sai ribs spaced rom one another, composite skins covering said slots terminating in spaced relation from the said edges, said skins adhered to front and back sides of the said structure, said skins and structure dimensioned to mate in a smooth transition adjacent the said edges to provide smooth surfaces on the front and back faces of the said blade, a plurality of said slots spaced apart transversely and longitudinally defining longitudinal and transverse ribs therebetween, the ends of said ribs integral with the said structure, and single skins covering each of the said front and back sides.

10. The blade of claim 9 wherein connecting channels extend through some of said ribs communicating some of said slots to other of said slots.

11. The blade of claim 10 wherein second connecting channels extend through the portions of the said structure communicating some of said slots to the atmosphere exterior of the said blade.

12. A turbine blade comprising: a root section, a blade section integral with said root section having a leading and a trailing edge, said blade section having a plurality of slots extending therethrough from a front surface to a back surface of said blade section, said slots spaced apart by ribs integral with the blade section material, composite skins overlying said apertures, said composite skins adhered to the said blade section, said composite skins interfitting with the said blade section adjacent the peripheral areas thereof to provide smooth front and back surfaces for said blade section, portions of said blade section spaced from said skins defining said edges, connecting channels connecting at least some of said slots through the tip of said blade section to the atmosphere exterior of said blade and secondary connecting channels connecting at least some of said slots through the root section of said blade to define passageways through the said blade comprising said secondary channels, said slot, and said first channels for passage of fluid through the said turbine blade to control the temperature thereof.

Claims

9. A turbine blade comprising: a metal center body structure shaped to define a turbine blade, leading and trailing edges on said blade, said edges formed by said structure, slots extending through said structure intermediate the said edges, center body material ribs having their ends integral with the said structure separating adjacent slots, said ribs spaced from one another, composite skins covering said slots terminating in spaced relation from the said edges, said skins adhered to front and back sides of the said structure, said skins and structure dimensioned to mate in a smooth transition adjacent the said edges to provide smooth surfaces on the front and back faces of the said blade, a plurality of said slots spaced apart transversely and longitudinally defining longitudinal and transverse ribs therebetween, the ends of said ribs integral with the said structure, and single skins covering each of the said front and back sides.