US2896907A - Air-cooled blade - Google Patents

Description

July 28, 1959 J. c. FRECHE AIR-COOLEDM BLADE Filed Sept. 28. 1955 x. I I P7117515 FIG. 3

I INV ENT OR JOHN a. FREGHE ATTORNEYS United States Patent UnitedStates; of America-as represented by the Secretary of the Navy Application September 28, 1955, Serial No. 537,313

1 Claim. (Cl. 25339.1'5)

(Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used byor for the Government of the United: States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to air-cooled blades for turbines, compressors, blowers and the like where light Weight is an important consideration.

Turbine blades are commonly made of an impermeable metal shell attached to a heavy metal base as by welding or brazing. This shell must be sufiicient-ly strong not only to support its own mass at the high turbine rotor speeds but also, in many cases, to support internal fins or tubes inserted to facilitate heat transfer. Alternately, a light blade shell may be used by inside the shell is inserted a massive supporting strut which is integral With blade base. The strut and base, thus, form a solid block of metal having approximately the same mass as a standard uncooled turbine blade. In either type of blade, as above described, the manufacturing processes are complex and the relatively high weight of the blade results in large wheel rim loading and heavy rotors.

A primary object of this invention is to provide a blade for turbines and the like which is light in weight permitting important reductions in rim loading and overall rotor weight.

Another object is to provide a turbine blade which may be entirely fabricated by simple techniques from stampings, castings or formed parts.

An additional object is to provide a light-Weight blade which lends itself readily to efficient air cooling.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a perspective view of a turbine blade with the outer shell partly broken away to show the rib construction;

Fig. 2 is a detail view showing the blades attached to the turbine rotor;

Fig. 3 is a detail view of a blade rib and also showing the rib relationship to the blade shell, base shell and spacer plate; and

Fig. 4 is a side elevation of the blade with the airfoil shell broken away taken along lines 4-4 of Fig. 1.

For ease of description, the blade has been illustrated and will be described as applied to a turbine. In Fig. 2, the rotor of the turbine is indicated, with blade units 11 attached thereto. The rotor is formed with a series of radial air ducts 12 which communicate with the pressurized air supply system (not shown). Each of these ducts terminates at the rotor periphery in a transverse blade attachment groove 13 having sigmoid walls, thus providing the groove cavity with a lateral constriction 14 placed at about one-half the groove depth which c0- operates with the lib plates 30 to secure the blades in the grooves.

The blade unit 11 is formed of four elements, the shell ice 20, the-ribs 21- for-supporting the shell, the spacerplates 22 for spacingthe-ribs,-- and the base plate 23'; The air foil shell 20'is shaped' 'tom'eetthe aero'dynamic requirementsfor' eflective' turbine use witha rounded'leading edge 24 and'a th'inner tr'ailin'gedgathe edges being joined by con'cavo- convex side plates 26 and 27, giving the required camber.

Supporting the shell- 20 are a plurality of flat strips forming parallel ribs 21-. The'faces 19 of ribs-21 extend across theblade-depth and arespaced-fro'm'eachother to'form' coolant'ducts, the depth of the faces of each rib being-equal to'the blade depth atthepoint of rib location and consequently differing-in depthfrom each other. The base of each n'b terminates -in -arib' plate 30, which'con form's in'= edge outline to*' that ofjthe rotor groove 1 3; so' that 'each' plate 30 and rib 2 1 may be moved into mat ing engagement with groove 13. These rib plates 30 are separated from each other by suitable rectangular spacer plates 22, preferably placed at the inner ends of the rib plates 30, as shown in Figs. 1 and 4 and uniformly apertured, as at 40, to permit air flow from rotor ducts 12. To bind the shell and ribs together and to prevent coolant leakage, the base plate 23 is applied to the base of the airfoil shell 20. This base plate is shaped to overlie closely the upper edges 18 of the rib attachment plates 30 and has an aperture 16 conforming in contour to the external surface of the airfoil shell 20. The base plate 23 is provided with an upstanding flange 17 around the aperture 16 which engages the lower external surface of the airfoil shell to prevent the coolant from escaping from the blade interior. The leading and trailing edges of the base plate are down-turned at 41 to engage a portion of the corresponding edges 18 of the rib plates 30 as shown in Figs. 2 and 3. As shown in Fig. 2, the edges 18 project beyond the outer periphery of the rotor when the plates 30 are engaged in the grooves 13 with the edges 41 of the base plates engaging the peripheral surface of the rotor thereby preventing coolant leakage between the plates 30 and the rotor.

In the final assembled form of the blade, the various component parts are permanently fixed together, as by welding or brazing, to form a rigid blade unit entirely free of weight concentration in the base and yet possessing ample strength for high speed use. The rib spacing, also, permits free access of cooling air from rotor ducts 12 to all parts of the blade interior, insuring adequate shell cooling. Particular attention is directed to the fact that apertures 40 are of equal dimensions and hence, the amount of coolant entering each rib duct is the same. However since the depth of ribs 21 varies with the contour of airfoil shell 20, being lesser at the leading and trailing edges of the blade where the heat effects are greatest, the rib ducts at these edges are of reduced crosssection. As a result, the velocity of coolant is greatest at the leading and trailing edges of the blade and, hence, the cooling action is most eflicient at these points of the blade structure. In addition, the elements of the blade are such as to lend themselves readily to stamping, casting or forming procedures permitting rapid assembly-line production of the blades.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

A rotor for turbines and the like comprising a rotor having a rim with circumferentially spaced grooves ex tending across the periphery of said rim, said grooves having side walls curved reversely inward and radially extending air ducts formed in the rotor and connected with the grooves to supply coolant thereto, and a lightweight blade mounted radially on the rdmifim, said blade comprising a plurality of flat strips forming ribs, said ribs being positioned in parallel face-to-face relationship and spaced apart substantially along the chord of the blade, the depth of the faces of said ribs-progressively increas: ing from the end ribs to the intermediate ribs, a thin, concave-convex, impermeable aircraft foil shell enclosing and attached to the side edges of said ribs, the shell and rib faces cooperating to form coolant channels, the channels at the leading and trailing edges of said blade having transverse areas reduced over those of intermediate chan; nels whereby the velocity of coolant in said channels will be a maximum at the leading and trailing edges, the bottom of each rib terminating in a rib plate, the rib plates having a shape complementary to the curved walls of said spaced grooves and cooperating with said grooves to secure the blade to the rotor rim, the upper edges of said rib plates projecting beyond the surface of the rotor rim when the blade is secured thereto, thin, flat spacer plates positioned between said rib plates whereby said ribs are in equally-spaced relationship, said spacer plates being uniformly apertured to permit equal coolant flow in each channel, and a base plate overlying the upper edges of said rib plates, said base plate having an aperture with a narrow, upstanding flange conforming in contour to the external surface of said shell, saidbase plate being permanently secured to said upper edges of said rib plates and said flange being permanently secured to the base of said shell, said base plate further having turn-down edges which engage the surface of the rotor rim whereby, the coolant is prevented from escaping from said ducts and from said channels.

References Cited in the file of this patent UNITED STATES PATENTS 2,656,146 Sollinger Oct. 20, 1953 FOREIGN PATENTS 860,438 Germany Dec. 22, 1952

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