Abstract:
A turbine shroud mounting apparatus includes: (a) a shroud hanger having an arcuate body and including an arcuate first hook which protrudes radially inward and extends axially forward from the body, so as to define a first slot in cooperation with the body; (b) an anti-rotation element disposed within the first slot, the anti-rotation element being integrally formed with the shroud hanger; and (c) an arcuate shroud segment including an arcuate first mounting flange which protrudes radially outward and extends axially aft, the first mounting flange having a receptacle formed therein, where the first mounting flange is received in the first slot and the anti-rotation member is received in the receptacle.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
       [0001]    The U.S. Government may have certain rights in this invention pursuant to contract number N00019-04-C-0093 awarded by the Department of the Navy. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to gas turbine engines and more particularly to methods for mounting components in the turbine sections of such engines. 
         [0003]    A gas turbine engine includes a turbomachinery core having a high pressure compressor, combustor, and a high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary gas flow. The high pressure turbine includes one or more rotors which extract energy from the primary gas flow. Each rotor comprises an annular array of blades or buckets carried by a rotating disk. The flowpath through the rotor is defined in part by annular shrouds encircling the blades or buckets. 
         [0004]    Conventional turbine shrouds are supported by segmented hangers which are in turn mounted to the engine&#39;s casing. Shrouds and shroud hangers require an anti-rotation feature to hold the shroud and hanger circumferentially in place. The majority of prior art shrouds utilize a pin press fitted into a hole in a hook of the shroud hanger. The pin interfaces with a notch on the shroud. The pin installation process requires tight tolerances and extra assembly processes that could include an additional braze operation. The pin has also been known to cause maintenance problems. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    These and other shortcomings of the prior art are addressed by the present invention, which provides a turbine shroud hanger which incorporates an integral anti-rotation element. 
         [0006]    According to one aspect of the invention, a turbine shroud mounting apparatus includes: (a) a shroud hanger having an arcuate body and including an arcuate first hook which protrudes radially inward and extends axially forward from the body, so as to define a first slot in cooperation with the body; (b) an anti-rotation element disposed within the first slot, the anti-rotation element being integrally formed with the shroud hanger; and (c) an arcuate shroud segment including an arcuate first mounting flange which protrudes radially outward and extends axially aft, the first mounting flange having a receptacle formed therein, where the first mounting flange is received in the first slot and the anti-rotation member is received in the receptacle. 
         [0007]    According to another aspect of the invention, a turbine shroud apparatus for a gas turbine engine includes: (a) a shroud hanger mounted to a casing of the engine, the shroud hanger having an arcuate body and including an arcuate aft hook which protrudes radially inward and extends axially forward from the body, so as to define a first slot in cooperation with the body; (b) an anti-rotation element disposed within the first slot, the anti-rotation element being integrally formed with the shroud hanger; and (c) an arcuate shroud segment including an arcuate first mounting flange which protrudes radially outward and extends axially aft, the first mounting flange having a receptacle formed therein, where the first mounting flange is received in the first slot and the anti-rotation member is received in the receptacle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0009]      FIG. 1  is a schematic cross-sectional view of a high pressure turbine of a gas turbine engine, incorporating a shroud apparatus constructed in accordance with an aspect of the present invention; 
           [0010]      FIG. 2  is a perspective view of a turbine shroud hanger shown in  FIG. 1 ; 
           [0011]      FIG. 3  is a perspective view of a turbine shroud shown in  FIG. 1 ; and 
           [0012]      FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts a portion of a high pressure turbine, which is part of a gas turbine engine of a known type. The function of the high pressure turbine is to extract energy from high-temperature, pressurized combustion gases from an upstream combustor  10  and to convert the energy to mechanical work. The high pressure turbine drives an upstream compressor (not shown) through a shaft so as to supply pressurized air to the combustor  10 . 
         [0014]    In the illustrated example, the engine is a turbofan engine and a low pressure turbine would be located downstream of the high pressure turbine  10  and coupled to a shaft driving a fan and optionally a low-pressure compressor or “booster”. However, the principles described herein are equally applicable to turboprop, turbojet, and turboshaft engines, as well as turbine engines used for other vehicles or in stationary applications. 
         [0015]    The high pressure turbine includes a nozzle  12  which comprises an array of circumferentially spaced airfoil-shaped hollow vanes  14  that are supported between an arcuate, segmented outer band  16  and an arcuate, segmented inner band  18 . The vanes  14 , outer band  16  and inner band  18  are arranged into a plurality of circumferentially adjoining nozzle segments that collectively form a complete 360° assembly. The outer and inner bands  16  and  18  define the outer and inner radial flowpath boundaries, respectively, for the hot gas stream flowing through the nozzle  12 . The vanes  14  are configured so as to optimally direct the combustion gases to a rotor  20 . 
         [0016]    The rotor  20  includes a array of airfoil-shaped turbine blades  22  extending outwardly from a disk  24  that rotates about the centerline axis of the engine. A shroud comprising a plurality of arcuate shroud segments  26  is arranged so as to closely surround the turbine blades  22  and thereby define the outer radial flowpath boundary for the hot gas stream flowing through the rotor  20 . 
         [0017]    The shroud segments  26  are carried by arcuate shroud hangers  28 , which are in turn mounted to an annular casing  30 . Each shroud hanger  28  includes an arcuate body  32  with opposed inner and outer faces, and forward and aft ends. It is noted that the terms “forward” and “aft” and other similar directional indications are relative and are used herein solely for reference. An arcuate seal lip  34  extends from the forward end and contacts a leaf seal  36  of a known type carried by the outer band  16  of the upstream turbine nozzle  12 . An arcuate forward flange  38  with an “L”-shaped cross-section extends radially outward from the forward end of the shroud hanger  28  and engages a slot in the casing  30 . An arcuate aft flange  40  with an “L”-shaped cross-section extends radially outward from the aft end of the shroud hanger  28  and engages another slot in the casing  30 . An arcuate forward hook  42  disposed at the forward end of the shroud hanger  28  protrudes radially inward and extends axially forward. It defines a forward slot  44  in cooperation with the body  32 . An arcuate aft hook  46  disposed at the aft end of the shroud hanger  28  protrudes radially inward and extends axially forward. It defines an aft slot  48  in cooperation with the body  32 . 
         [0018]    As best seen in  FIG. 2 , the shroud hanger  28  incorporates a fixed anti-rotation element  50  disposed in the aft slot  48 , spanning the distance between the body  32  and the aft hook  46 . So long as it is securely fixed in place, the anti-rotation element  50  may be an integral part of the shroud segment  28  or it may be fabricated separately and then securely attached to the shroud hanger  28 , for example by welding or brazing. If desired, it could be incorporated in the forward slot  44  instead. In the illustrated example the anti-rotation element  50  is an axially-elongated tab with a radiused forward end. However, any shape which is effective to resist tangential motion of the shroud segment  26  when engaged with a mating feature of the shroud segment  26  may be used. As used herein the term “tangential” refers to motion in or out of the page in  FIG. 1 . 
         [0019]    The shroud hangers  28  may be constructed from a material such as a known cobalt, nickel, or steel-based superalloy which has acceptable strength at the elevated temperatures of operation in a gas turbine engine. Various superalloys are commercially available under trade names such as INCONEL, HASTELLOY, and RENE. The shroud hangers  28  may be formed from castings which are then machined to final dimensions. The aft hooks  46  of the shroud hangers  28  may be formed by machining with an EDM electrode (not shown). EDM is a known process in which an electrode is fed into the workpiece while an electrical potential is applied between the electrode and workpiece. Spark discharge across the gap between workpiece and electrode causes erosion of the workpiece. The anti-rotation element  50  described above may be created by removing a notch or other negative feature of equal shape and size from an EDM electrode used to machine prior art shroud hangers. Once the material has been removed from the electrode, the EDM process is identical to the original hook machining process. 
         [0020]    Referring back to  FIG. 1 , each shroud segment  26  includes an arcuate forward mounting flange  52  disposed at the forward end of the shroud segment  26  which protrudes radially outward and extends axially aft. An arcuate aft mounting flange  54  disposed at the aft end of the shroud segment  26  protrudes radially outward and extends axially aft. As shown in  FIG. 3 , the shroud segment  26  incorporates a receptacle  56  disposed in the aft mounting flange  54  which has a shape complementary to the anti-rotation element  50 . In the illustrated example the receptacle  56  is an axially-elongated notch having parallel sidewalls and a radiused forward end. However, any shape which is effective to resist tangential motion of the shroud segment  26  when engaged with a mating feature of the shroud hanger  28  may be used. The receptacle  56  may be formed in the aft mounting flange  42  using an EDM process as described above. 
         [0021]    The shroud segments  26  are assembled to the shroud hangers  28  by engaging the forward mounting flanges  40  with the forward hooks  44  and the aft mounting flanges  42  with the aft hooks  46 . The shroud segments  26  are then slid aft so that the receptacles  56  engage the anti-rotation elements  52 .  FIG. 4  shows the two components in the assembled condition. No further assembly or manufacturing operations are required to provide positive anti-rotation between the shroud segment  26  and the shroud hanger  28 . 
         [0022]    As compared to a conventional design, the shroud mounting apparatus described herein eliminates extra machining steps, provides for simplified assembly, and reduces part count. The principles described herein may easily be implemented for any turbine shroud that uses an EDM procedure to machine its support hooks. 
         [0023]    The foregoing has described a shroud mounting apparatus. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. In particular, the principles of the present invention may be extended to other types of turbine hardware, in particular any assembly of two or more static elements which must be restrained against relative rotation. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.