US2568726A

US2568726A - Air-cooled turbine blade

Info

Publication number: US2568726A
Application number: US108402A
Authority: US
Inventors: Franz Anselm
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-08-03
Filing date: 1949-08-03
Publication date: 1951-09-25
Anticipated expiration: 1968-09-25

Description

Sept. 25, 1951 A. FRANZ 2,568,726

AIR COOLED TURBINE BLADE Filed Aug. 5, 1949 MAY?"- Patented Sept. 25, 1951 UNITED STATES PATENT OFFICE 2.56832 4 p Ant-coonisn TURBINE BLADE Anselm Franz, Wood City, Dayton, Ohio. Application August 3, 1949, SerialNo. 108,402

' 7 Claims. .(01. 253-3915 (Granted under the act of March 3, 1883, as

1 The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the shell sections independently of the core and independently of each other.

A further object of the invention is to provide an air cooled turbine blade having a hollow blade shell made in overlapping sections to simplify the manufacture thereof and wherein the overlapping sections are individually and independently secured to a central core member spaced inwardly from the hollow blade shell.

A further object of the invention to to provide an air cooled turbine blade including a central core member rigidly secured to the turbine wheel and an outer blade shell housing said core member and uniformly spaced therefrom with the blade shell being secured to the central core member.

Another object of the invention is to provide an air cooled turbine blade including a central core member enclosed by a blade shell and characterized by a sectional shell construction to minimize internal stresses due to heating and cooling.

The above and other objects of the invention will become apparent upon reading the'following detailed description in conjunction with the ac companying drawing, in which:

Fig. 1 is a cross sectional view of portions of a turbine wheel and an associated'bearin'g.

Fig. 2 is a longitudinal cross section taken through the present turbine bladestructure.

Fig. 3 is a partial 1 cross section showing the means for attachingthe outer sheet metal blade member to the central core member.

Fig. 4 is an enlarged perspective view of a, portion of the turbine blade with part, of the sheet metal blade membercut away to show the attaching meanstherefor. 1

f Air cooled turbine'xblades have been proposed and used in the pastiinlorderto maintain Iower .blade temp'eratures'. the present invention such a blade-v is provided and includes a blade amended April 30, 19285370 0. o. 757) stiffening or strengthening core to which the outer contour-forming blade member is secured. The securing is accomplished in such a way as to permit expansion and contraction of the outer blade member during heating and cooling thereof. The outer-blade member is preferably although not necessarily of two-piece construction with each piece individually secured to the blade strengthening core, but not rigidly connected to each other. The details of the structure as well as some of the advantages inherent therein will beset out below. v

In Fig. 1 there is shown a portion of a turbine wheel I secured to a flanged main shaft 2 by means of bolts 3. The shaft 2 is rotatably mounted in bearings, one of which is indicated at 4. The bearing 4 is supported by an outwardly extending flange 5 having a plurality of air flow holes 6 therethrough whereby cooling air from a compressor may reach one side of the turbine wheel I. The turbine wheel may form one element of a turbo-jet engine as used on modern aircraft and the turbine-driven air compressor will provide a source of high pressure coolingair for passage rearwardly to the forward side of the turbine wheel I. A more complete illustration of sucha turbo-jet engine maybe found on page 393 of Gas Turbine Construction (1947) by R. Tom Sawyer. Secured to the forward face of the turbine wheel I in spaced relation thereto is a manifold plate I, which follows the general contour of the wheel and is spaced or separated therefrom by spacers 8. Secured to the bearing flange 5 is an annular flange member 9 which carries a labyrinth seal l0 extending into closely adjacent relation to the annular flange II on the manifold plate 1. The flat rings forming the seal l0 do not actually rub on the flange l I but by providing a series of annular chambers reduce the pressure drop across the sealto a small fraction of the total pressure, so that air loss through the seal is very small.

The turbine blade as shown in Fig. 1 includes a central metallic core member 12 having a dovetail connection 13 at'its root end in the wheel I. After the root dovetailhas been slid transversely into the dovetail recess, a dovetail block I4 is forced in to lock the blade root in place. For further security a sheet metal block retaining ring 15 is welded or otherwise secured to the -wheel rim to 'preventremoval of the dovetail blocks distributed around the wheel. Fastened to the core member in a manner to be more fully described below are 'the blade shell sections l6 and ll spaced from the core member and having escapee adjacent interfltting marginal portions which fit snugly together but which are not directly fastened to each other. The outermost section II has a closed outer end and each section has an open ormlotted trailing edge portion, as indicated at IE, to allow escape of blade cooling air and subsequent discharge thereof with the engine exhaust gases. At the forward side of the wheel rim there is provided an air flow recess [9 for each blade. Between the recesses are projecttions to which the rim portion 1 of the manifold plate I is secured, as by welding. Each of these projections is recessedto receive the inner edge of a closure ring 20 extending into closely adjacent relation to each blade section 16. Since the inner end of section I6 is outwardly of the wheel periphery, an air flow passage is provided to permit air flow through recess [9 and thence out through the blade and passing therethrough in a crosswises direction to issue from the slot l8. Since the cooling air is heated up very considerably in passing through the blade its expansion will cause a reaction effect to give a thrust on the blade and some gain in turbine power over a solid blade or over an air cooled blade in which the air flows from the blade tip in a radially outward direction. The use of a sectional blade shell in which the individual sections are attached to the core member has the advantage of permitting unequal expansion of the shell and core without setting up distorting stresses in the thin shell. The reason for the unequal expansion is that the shell is exposed to very hot gases flowing from the combustion chambers of the engine, while the core member is kept relatively cool by the cooling air passing between the shell and core.

For an explanation of the preferred blade shell attaching means and a more detailed showing of the blade construction, reference is made to Figs. 2, 3 and 4. Slight difierences in the blade shell and arrangement over that shown in Fig. 1 will also be noted, particularly in Fig. 2. The wheel has secured thereto the core member l2 in a manner similar to that previously described. The manifold plate 1 is secured at'its outer edge to a series of projections separating air flow channels or passages IS in the rim of the wheel I. Mounted over the core 12 are

shell sections

26 and 21, which overlap at 26. The inner shell section 26 includes

extensions

29 and 30 extending inwardly over the manifold plate I and the opposite side of the wheel I but not attached rigidly thereto. Outwardly of the extension 29 'the interior of shell 26 may include a gusset flange 3| abutting the leading edge of core l2. The flange 3| is pierced to allow free outward flow of cooling air. Outwardly of the extension 30 the shell section 26 is open along the trailing edge to permit egress of cooling air, as at 32. Similarly the outer shell section 21 is open along the trailing edge, as at 33, and is closed at the outer free end as at 34. Across the inside wall of each" shell section about midway of the length thereof is secured an attaching strip 35 having a series of shell attached bight portions 36 and a series of core attached bight portions 31. The portions 36 may be welded to the shell, a strip 35 being used on both sides of the blade. A series of fingers or tongues 38 are secured on each side of the core l2 to hook over the bight portions 31 when the shell sections are slid down over the core l2, the shell section 26 being installed first and then the shell section 21 being installed over the core and over the outer end of shell section 26. To accomplish this assembly operation the respective shell sections may be sprung open tovlet the attaching strip 35 pass the tongues 38. Then the shell sections are closed again to the relative shape as shown in Fig. 4, after which the shell sections are pushed outwardly until the tongues slide over the bight portions 31. Finally retaining screws 39 are inserted through apertures in the opposite face sides of the shell sections and threaded into the bosses 40 extending from the opposite faces of core l2. It is further noted that the outer shell section 21 which includes the closed end portion 34, is installed in the manner described before the end cover plate 34 is welded or in some manner secured onto the outer end of shell section 21. During operation of a turbinewheelequippedwlth the blades as herein described, the centrifugal force tends to throw the blade shells radially outwardly. This force is resisted by engagement of the attaching strips with the upstanding portions of core I 2 adjacent to or under the tongues 38 (see Fig. 3). When the turbine wheel is at rest the screws 39 prevent any shifting of the shell sections away from the normal installed position as shown in the drawing, and at all times these screws perform their positioning and securing function independently of the attaching strips 35 and retaining tongues 38. Instead of the oppositely directed screws 39, it is within the scope of the invention to use a single rivet member extending through the shell walls and interveing core material in place of each pair of opposite screws. Furthermore it is pointed out that the shell around the blade may be made up of one or more sections, depending on the length of blade and other design factors. The outstanding feature of the multiple section shell is that each section may expand and contract without affecting other shell sections and also in a manner independently of the core member centered therewithin. The shell sections are attached to the core both by attaching strips 35 and screws 39 but the tongue retaining means for the strips plus the resiliency of the strips will allow the shell sections to expand and contract lengthwise and crosswise of the blade just as though they were attached only by the centrally located screws 39. It is also seen that the telescopic arrangement of the shell sections, as at 28, permits, relative movement therebetween at the marginal overlapping portions. Thus each separate shell section, which is heated to a high temperature because of the combustion gases passing thereover, may act as a free body to be expanded and contracted without regard to expansion or contraction of other parts of the turbine blade.

Another source of unbalance and unequal stresses in air cooled turbine blades is the temperature variation from the inside surface to the outside surface of the blade shell. However in the present shell construction the shell section or sections contribute little to the overall blade strength and may be made of thin metal accordingly. A suggested thickness range for the shell material in aircraft gas turbines is 0.01 to 0.05 of an inch. The result which flows from the use of thin-walled shell sections is a more uniform temperature in the walls thereof and less tendency to internal stressing and warping of the shell walls. Also smaller quantities of scarce steel alloys capable of resisting high temperatures will be required in making these thin blade shells. The core l2 being maintained at lower temperatures than the shell, theselection and production of a suitable alloy therefor presents little dimculty.

The cooling air diverted from the air compressor of the engine in limited quantities finally flows into the manifold formed by cover plate I spaced from wheel I and flow of the air outwardly to the turbine blades is promoted by the static pressure of the air as well as by the centrifugal forces set up by the rotation of wheel I at high speeds. This same centrifugal force is of assistance in causing portions of the cooling air to flow out to the ends of the blade shells before issuing from the open edges'33 of the sectional blade shells. The cooling air not only cools the shelland core of the blade but also passes the attaching strips 35 to carry away heat conducted thereto.

The embodiments of the invention herein shown and described are to be regarded as illustrative only and it is to be understood that the invention is susceptible of variations, modifications and changes within the scope of the appended claims.

I claim:

1. In a gas turbine power plant including -'a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at the root end {of the blade to a turbine wheel in radially extenf'ding relation, a metallic blade shell surrounding said core member in spaced relation and including a plurality of telescopicshell sections of similar size and shape, positioning and securing means engaging each shell section and said core member at opposite sides of said blade'construction and at points directly opposite each other, and means to conduct limited quantities of said high pressure air into the space between said core member and said blade shell.

2. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at the root end of the blade to a turbine wheel in radially extending relation, a metallic blade shell surrounding said core member in spaced relation and including a plurality of telescopic shell sections of similar size and shape open along the trailing edge thereof, means for closing the outer end of the shell section remote from the root end of the blade, positioning and securing means engaging each shell section and said core member at opposite sides of said blade construction and at points directly opposite each other, and means to conduct limited quantities of said high pressure air into the space between said core member and said. blade shell.

3. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at the root end of the blade to a turbine wheel in radially extending relation, a metallic blade shell surrounding said core member in spaced relation and including a plurality of telescopic shell sections of similar size and shape, each shell section having an attaching strip secured on the opposite inside surfaces thereof and extending across the respective sections, laterally oflset bight portions on each attaching stripsituated close to the outer surface 6 Y engage between said bight portions and the inner surfaces of said shell sections, abutmentmeans adjacent to said tongues for engagement by portions of said strip to prevent said shell sections from being thrown 011' said core member under centrifugal forces set up during rapid rotation of said turbine wheel, and means to conduct limited quantities of said high pressure air into the space between'said core member and said blade shell.

4. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at the root end of the blade to a turbine wheel in radially extending relation, a metallic blade shell surrounding said core member in spaced relation and having a typical-blade shape on the outer surface thereof, an attaching strip of sheet metal extending across said shell on the inside surface thereof and rigidly secured to said surface, laterally oflset bight portions on said attaching strip situated close to the outer surface of said core member, tongues rigidly secured to the outer surface of said core member and spaced so as to engage between said bight portions and the innor surface of said shell, at least one positioning and securing means engage both said shell and said core member to prevent disengagement of said tongues and bight portions, and means to conduct limited quantities of said high pressure air into the space between said core memher and said blade shell.

5. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at the root end of the blade to a turbine wheel in radially extending relation, a metallic blade shell surrounding said core member in spaced relation and having a typical blade shape on the outer surface thereof, an attaching strip of sheet metal extending across said shell on the inside surface thereof and rigidly secured to said surface, laterally offset bight portions on said attaching strip situated close to'the outer surface of said core member, tongues rigidly secured to the outer surface of said core member, extending toward the root end of said core member and spaced so as to engage between said bight portions and the inner surface of said shell, the material of said core member adjacent to said tongues providing abutment means for portions of said strip to prevent said blade shell from 'being thrown off said core member under centrifugal forces set up during rapid rotation of said turbine wheel, and means to conduct limited quantities of said high pressure air into the space between said core member and said blade shell.

6. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a solid metallic core member adapted for rigid attachment to a turbine wheel or other structural member at one end of said core member, a metallic blade shell surrounding said core member in spaced relation 5 and including a plurality of shell sections each of said core member, tongues rigidly secured to the outer surfaces of said coremem-ber atthe opposite side faces, each extending toward the.

extending around said blade and engaging adjacent sections end-to-end, a plurality of spaced fastening elements extending between saidcore member and each of said shell sections and said fastening elementshaving enough flexibility to permit thermal expansion and contraction of said shell sections independently of said core memroot end of said core member and spaced so as to ber, and means to conduct limited quantities of assume said high pressure air into the spaces between said core member and said blade shell sections.

7. In a gas turbine power plant including a source of high pressure air, a turbine blade construction comprising a metallic core member adapted for rigid attachment at one end to a turbine wheel or other structural member, a metallic blade shell surrounding said core member in spaced relation and having a typical blade shape on the outer surface thereof, attaching strips of sheet metal extending across said shell on opposite sides of the inside surface thereof and rigidly secured to said inside surface, laterally offset bight portions on said attaching strips situated close to the outer surface of said core member, tongues rigidly secured to the outer surface of said core member, extending toward one end of said core member and spaced so as to engage between said bight portions and both side faces of said shell, and means to con duct limited quantities of said high pressure air into the space between said core member and said blade shell.

ANSELM FRANZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date.

1,368,751 Rateau Feb. 15, 1921 1,966,104 Noack July 10, 1934 2,236,426 Faber Mar. 25, 1941 2,440,069 Bloomberg Apr. 20, 1948 FOREIGN PATENTS Number Country Date 346,599 Germany Jan. 5, 1922 602,530 Great Britain May 28, 1948