US3065955A

US3065955A - Rotor blade and shroud assembly

Info

Publication number: US3065955A
Application number: US783487A
Authority: US
Inventors: Harlin Floyd
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-12-29
Filing date: 1958-12-29
Publication date: 1962-11-27
Anticipated expiration: 1979-11-27

Description

Nov. 27, 1962 F. HARLTIN 3,065,955

' ROTOR BLADE AND SHROUD ASSEMBLY Filed Dec. 29, 1958 INVENTOR. FZ 0V0 #461 M/ United States Patent 3,065,955 ROTOR BLADE AND SHROUD ASSEMBLY Floyd Harlin, Cincinnati, Ohio, assignor to General Electric Company, a corporation or New York Filed Dec. 29, 1958, Ser. No. 783,487 1 Claim. (Cl. 253-7 7) This invention relates to gas turbine type engines and more particularly to rotor blade and shroud assemblies for axial flow compressors and the like for gas turbine type engines.

One of the problems inherent in the use of axial flow compressors is the subjection of rotor blades to flexural and torsional vibrational stresses. Various arrangements have been provided in the prior art which attempt to solve this problem. For example, some of the prior art provides shrouds surrounding rotor blade tips for the purpose of minimizing vibrational stresses. Other solutions include disclosures wherein blade tips are slotted to receive tongues depending from the cylindrical shroud members. However, one of the prime requirements in modern high speed gas turbine design is a light-weight structure capable of eflicicnt operation at high rotational speeds. The prior art of which I am aware has failed to provide a structure that is light-weight and capable of minimizing vibrational stresses. By the use of my invention, lightweight shrouding may be employed having great strength and capable of minimizing vibrational stresses. While I discuss the invention in connection with compressors, it will be obvious that it is also applicable to turbines and the term compressor is merely used for illustration.

Accordingly, it is an object of this invention to provide an improved compressor rotor blade and shroud assembly which has a high strength-to-weight ratio and is capable of use at high rotational speeds.

Another object of this invention is to provide an improved rotor blade and shroud assembly capable of minimizing the fiexural and torsional vibrational stresses present in the lightweight rotor blades.

A third object of this invention is to provide an improved rotor blade and shroud assembly having means to minimize bending stresses resulting from high centrifugal loads acting upon the shroud.

A further object of this invention is to provide an improved rotor blade and shroud assembly having means to minimize aerodynamic gaps and provide a smooth flow path.

These and other objects and advantages of this invention will become more apparent as the following description proceeds.

Briefly stated, in accordance with one embodiment of my invention, I provide a compressor rotor blade shroud composed of a plurality of arcuate segments which are secured to the tips of rotor blades and, when assembled, form a substantially annular shroud. Each shroud segment has a plurality of outwardly extending, circumferential ribs which provide strength, minimize bending stresses, and provide openings positioned to receive blade securing means. A plurality of radial slots are located in each shroud segment and these slots receive outwardly extending tangs on the blade tips. These tangs have openings which align with the openings in the outwardly extending ribs, and which are positioned to receive a pin or similar means to secure the shroud to the blade tips. The shroud structure is located within grooves formed within the stator casing, and the shroud has substantially axially extending overhanging projections which cooperate with the stator casing to form a smooth flow path.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, it is believed that the invention will be better understood from the following "ice description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a plan view of a portion of a shroud segment;

FIG. 2 is a cross-sectional view taken on line 2-2 of FIG. 1 showing the shroud and blade assembly; and,

FIG. 3 is a perspective view of a portion of a rotor blade showing the tang arrangement.

Referring to FIGS. 1 and 2, a light-weight compressor rotor blade and shroud assembly has been illustrated. In this arrangement, only one stage of rotor blades has been shown for the purpose of simplicity and clarity. However, it will be understood that the following description relating to this stage is equally applicable to each stage of blades used. The shroud and blade assembly includes a plurality of arcuate segmental shroud members, one of which is shown at 1 transversely and peripherally spanning the ends of the blades, and a plurality of light-weight'r'otor blades, one of which is shown at 2, which are mounted within a stator casing 3.

In order'to accomplish the dual functions of strengthening the rotor assembly while maintaining a high strengthto-weight ratio, and also of providing for the joining of the blades and the arcuate'shroud members, the shroud members are formed to provide a base member and to include a plurality of spaced circumferential ribs extending outwardly therefrom. In the preferred embodiment of my invention, three ribs 4, 5 and 6 have been employed. The ribs have a plurality of aligned openings 7. A plurality of tang receiving radial slots 8 and 9 are formed in the shroud members 1 between the spaced outwardly extending ribs. The use of outwardly extending ribs provides a shroud of relatively light weight, yet having high strength characteristics. In carrying out my invention in practice, I have found the following dimen sions of the shroud structure to be satisfactory; as for example, when used with a shroud segment of 45 degrees in arc and having a base of .05 inch or less in thickness on a blade of 1.5 inches chord, the ribs are .05 to .0 8 inch thick and .25 inch high. It will, of course, be understood that these dimensions are given by way of example only and that the dimensions will have to be varied in accordance with the many variables encountered in different gas turbine designs.

A compressor rotor blade 2 having a working fluid face 10 and outwardly extending tangs 11 and 12 is shown in FIG. 3. The tangs have openings 13 positioned to align with the openings 7 in the shroud ribs. Upon assembly, the blade tangs 11 and 12 are inserted through radial slots 8 and 9 and between

ribs

4 and 5, and 5 and 6, respectively. A locking pin 14 is inserted in aligned

openings

7 and 13 to secure the shroud transversely .and peripherally spanning the ends of the light-weight rotor blades.

In FIG. 2 the stator casing is shown provided with first and second outwardly directed but inwardly facing internal circumferential stepped shallow and deep grooves 15 and 16 respectively, which are positioned to receive the blade and shroud assembly with 15 being wider than 16. The arcuate, segmental shroud members 1 are provided with substantially axially extending, upstream and downstream projections 17 and 18. The projections are entirely received within and span radially inner groove 15 .and thereby establish a smooth flow path through the casing. The projections also form substantially annular members, the outer surfaces of which are positioned in close proximity to the substantially cylindrical inner surfaces of groove 15, thus providing a radial seal to minimize the leakage of fluid between the shroud and the casing. Circumferential groove 16 is positioned to receive the outwardly extending ribs 4, 5 and 6, and tangs 11 and 12.

Thus it may be seen that a plurality of blade tips are securely tied together by means of compressor rotor shrouds. In addition to reducing fiexural and torsional vibrational stresses in the light-weight rotor blades, the shroud further serves to provide a smooth flow path and to provide a radial seal between the shroud and the casing.

It is obvious that I have provided a simple, light-weight shroud assembly capable of being used in modern high speed applications. The ribs 4, 5 and 6, in addition to providing receiving means for the blade locking pins, also serve to minimize bending stresses imposed by high centrifugal loads acting upon the shroud between blade tips. Further, the ribbed structure provides for a high strength-to-weight ratio not heretofore possible when using known prior art structures. Additionally, the substantially axial shroud projections serve the dual functions of insuring a smooth fiow path and providing a radial seal.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A shrouded rotor assembly comprising:

(a) a plurality of blades mounted on said rotor,

(12) a segmental arcuate shroud member transversely and peripherally spanning the ends of said blades and secured thereto,

(c) a stator casing enclosing said blades,

(d) a circumferential groove in said casing having a deep central portion and a shallow portion wider than the deep portion extending axially from each side of said deep portion and terminating at the inner surface of said casing,

(e) a radially protruding circumferential portion on said shroud extending into said deep central portion of said groove, and

(f) one axial projection on each side of said circumferential portion extending into respective parts of the shallow portion of said groove to form a smooth flow path through the casing and a radial seal between said shroud and said casing.

References Cited in the file of this patent UNITED STATES PATENTS 764,451 Geisenhonor July 5, 1904 903,167 Boyd Nov. 10, 1908 906,400 Ferranti Dec. 8, 1908 980,562 Rice Jan. 3, 1911 1,158,755 Weaver Nov. 2, 1915 1,371,328 Schneider Mar. 15, 1921 1,457,404 Snyder June 5, 19.23 1,876,067 Lorenzen Sept. 6, 1932 1,998,951 Downer Apr. 23, 1935 2,518,660 Browne Aug. 15, 1960 2,959,893 Rankin Nov. 8, 1960 FOREIGN PATENTS 342,900 Germany Oct. 26, 1921