Abstract:
A method of assembling a rotor assembly is provided. The method includes coupling a first turbine bucket to a rotor disk wherein the first turbine bucket includes a first tip shroud including a first surface, providing a second turbine bucket that includes a second tip shroud including a second surface, and coupling the second turbine bucket to the rotor disk such that the second turbine bucket is circumferentially adjacent to the first turbine bucket and such that during operation of the rotor assembly the first tip shroud contacts the second tip shroud along the first and second surfaces to enable at least one of a portion of radial loading induced to the first tip shroud to be transferred to the second tip shroud and a portion of radial loading induced to the second tip shroud to be transferred to the first tip shroud.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to turbine rotor assemblies and more particularly to methods and apparatus for relieving stress at a tip shroud of rotating airfoils used with turbine rotor assemblies. 
         [0002]    At least some known turbine rotor assemblies include a plurality of rotor blades or buckets (hereinafter, the term “bucket” shall be used to refer generically to a turbine bucket or an aircraft engine blade) that extend from a root to a tip shroud. Generally, tip shrouds facilitate improving the performance of the turbine rotor assembly. During operation, tip shrouds are subject to high thermal and mechanical loading which induce stresses into the tip shrouds which must be addressed to maintain the useful life of the blade. 
         [0003]    To facilitate reducing stresses induced to tip shrouds, at least some known bucket tip shrouds are scalloped such that selected portions of the tip shroud are removed. For example, it is known to remove portions of the tip shroud along the leading edge and/or trailing edge of the tip shroud during a scalloping process. Although the scalloped areas facilitate reducing mechanical loading, and thus stresses, induced to the tip shrouds, scalloping the tip shrouds may adversely affect the performance of the engine. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one aspect, a method of assembling a rotor assembly is provided. The method includes coupling a first turbine bucket to a rotor disk wherein the first turbine bucket includes a first tip shroud including a first surface, providing a second turbine bucket that includes a second tip shroud including a second surface, and coupling the second turbine bucket to the rotor disk such that the second turbine bucket is circumferentially adjacent to the first turbine bucket and such that during operation of the rotor assembly the first tip shroud contacts the second tip shroud along the first and second surfaces to enable at least one of a portion of radial loading induced to the first tip shroud to be transferred to the second tip shroud and a portion of radial loading induced to the second tip shroud to be transferred to the first tip shroud. 
         [0005]    In a further aspect, a rotor assembly is provided. The rotor assembly includes a first turbine bucket including a first tip shroud extending from a radially outer end of the first turbine bucket. The first tip shroud includes a first surface. The rotor assembly also includes a second turbine bucket including a second tip shroud extending from a radially outer end of the second turbine bucket. The second tip shroud is positioned circumferentially adjacent to the first tip shroud. The second tip shroud includes a second surface configured to transfer at least one of a portion of radial loading induced to the second tip shroud to the first tip shroud and a portion of radial loading induced to the first tip shroud to the second tip shroud. 
         [0006]    In a further aspect, a turbine bucket assembly is provided. The turbine bucket assembly includes a turbine bucket and a tip shroud extending from a radially outer end of the turbine bucket. The tip shroud includes a leading edge and an opposing trailing edge such that a first circumferential side and an opposing second circumferential side each extend between the leading edge and the trailing edge. The tip shroud further includes at least one tip rail extending between the first and second circumferential side. The turbine bucket assembly also includes a first surface and a second surface each extending along a portion of at least one of the first circumferential side, the at least one tip rail, the leading edge, and the trailing edge. The first and second surfaces are configured to enable radial load transfer from the first tip shroud to an adjacent second tip shroud. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of an exemplary bucket that may be used with an axial flow turbine; 
           [0008]      FIG. 2  is a perspective view of a portion of a pair of the buckets shown in  FIG. 1  and coupled in position within a turbine rotor assembly; 
           [0009]      FIG. 3  is a perspective top view of an exemplary bucket tip shroud shown in  FIG. 2 ; and 
           [0010]      FIG. 4  is a perspective bottom view of the bucket tip shroud shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    As used herein, an element or step recited in the singular and proceeded with the word “a,” “an,” or “one” (and especially, “at least one”) should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” (or to “other embodiments”) of the present invention are not intended to be interpreted as excluding either the existence of additional embodiments that also incorporate the recited features or of excluding other features described in conjunction with the present invention. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. 
         [0012]      FIG. 1  is a perspective view of a turbine bucket  100  that may be used with an axial flow turbine. In an exemplary embodiment, each bucket  100  includes an airfoil  42  and an integrally-formed dovetail  43  used for mounting airfoil  42  to a rotor disk (not shown). 
         [0013]    Airfoil  42  includes a first sidewall  44  and a second sidewall  46 . First sidewall  44  is concave and defines a pressure side of airfoil  42 , and second sidewall  46  is convex and defines a suction side of airfoil  42 . Sidewalls  44  and  46  are connected at a leading edge  48  and at an axially-spaced trailing edge  50  of airfoil  42  that is downstream from leading edge  48 . 
         [0014]    First and second sidewalls  44  and  46 , respectively, extend longitudinally or radially outward to span from a blade root  52  positioned adjacent dovetail  43 . In the exemplary embodiment, airfoil  42  and blade root  52  are fabricated as a unitary component. In an alternative embodiment, airfoil  42  and root  52  are not fabricated as a unitary piece. In the exemplary embodiment, bucket  100  includes a tip shroud  212 . Bucket  100  is coupled to a rotor shaft and extends radially outward from the rotor shaft. In an alternative embodiment, bucket  100  may be coupled to a rotor shaft by other devices configured to couple a bucket to a rotor shaft, such as, a blisk. 
         [0015]      FIG. 2  is a perspective view of a portion of a pair of circumferentially-adjacent buckets  100  and  101  coupled in position within a turbine rotor assembly.  FIG. 3  is a perspective top view of tip shroud  212 .  FIG. 4  is a perspective bottom view of tip shroud  212 . 
         [0016]    Specifically, in the exemplary embodiment, buckets  100  and  101  are substantially identical and each includes tip shroud  212 . For simplicity, a first bucket is identified as bucket  100  and a second bucket is identified as bucket  101 . Bucket  100  includes a first tip shroud  212  and bucket  101  includes a second tip shroud  214 . As described in more detail below, tip shroud  212  is sized and oriented at the time of manufacture to cooperate and mate against a portion of tip shroud  214 . Moreover, as described in more detail below, in the exemplary embodiment, a portion of first tip shroud  212  is configured to support a radial load from second tip shroud  214  that is circumferentially adjacent to first tip shroud  212 . 
         [0017]    As shown in  FIG. 2 , each tip shroud  212  and  214  includes a first sidewall  234  and an opposite circumferentially-spaced second sidewall  238  that are connected together via a leading edge side  240  and an opposite trailing edge side  242 . In the exemplary embodiment, neither leading edge side  240  nor trailing edge side  242  are scalloped. Leading and trailing edge sides  240  and  242  each extend circumferentially between first and second sidewalls  234  and  238 , respectively. In the exemplary embodiment, each tip shroud  212  and  214  includes a pair of tip rails  241  and  243 . In an alternative embodiment, each tip shroud  212  and  214  includes one tip rail. 
         [0018]    As shown in  FIG. 3 , in the exemplary embodiment, first sidewall  234  is formed with an overhang portion  250  that is defined along a portion of first sidewall  234 . Specifically, in the exemplary embodiment, overhang portion  250  extends from leading edge side  240  towards trailing edge side  242 . As shown in  FIG. 4 , in the exemplary embodiment, overhang portion  250  extends a distance D 1  from leading edge side  240  towards trailing edge side  242 . First sidewall  234  is also formed with a notch  252 . Specifically, in the exemplary embodiment, notch  252  is defined by a first end  254  and a second end  255  that are connected together at an apex  253 . In the exemplary embodiment, notch  252  is a Z-notch that extends continuously from first end  254  to second end  255 . As such, in the exemplary embodiment, overhang portion  250  extends from leading edge side  240  to notch first end  254 . 
         [0019]    Overhang portion  250  is formed by a recess  257  that extends a width W 1  from first sidewall  234  towards second sidewall  238  and along a radially inner surface  251 . In the exemplary embodiment, a radially outer surface  245  is offset a distance (not shown) outboard from radially outer surface  244  of leading edge  240 . Overhang portion radially inner surface  251  forms a mating surface that enables circumferentially-adjacent tip shrouds  212  and  214  to abut each other, as described in more detail below. 
         [0020]    First sidewall  234  is also formed with an undercut portion  260  that extends along a portion of first sidewall  234 . Specifically, in the exemplary embodiment, undercut portion  260  extends from trailing edge side  242  towards leading edge side  240 . More specifically, in the exemplary embodiment, undercut portion  260  extends a distance D 3  from trailing edge side  242  to apex  253 . In an alternative embodiment, undercut portion  260  extends from trailing edge side  242  to a projection  261  is positioned adjacent notch second end  255 . In the exemplary embodiment, distance D 3  is approximately equal to distance D 1 . In an alternative embodiment, distance D 3  is different than distance D 1 . 
         [0021]    Undercut portion  260  is defined by a recessed area  263  that extends a width W 2  from first sidewall  234  towards second sidewall  238  and along a radially outer surface  264 . Undercut portion radially outer surface  264  forms a mating surface that enables circumferentially adjacent tip shrouds  212  and  214  to abut each other, as described in more detail below. 
         [0022]    Second sidewall  238  includes an undercut portion  270 , a projection  271 , a notch  272 , and an overhang portion  274 . In the exemplary embodiment, undercut portion  270 , notch  272 , and overhang portion  274  are formed similarly to undercut portion  260 , notch  252 , and overhang portion  250  in that each is sized, shaped, and oriented to mate against a respective circumferentially-adjacent overhang portion  250 , notch  252 , and undercut portion  260 . More specifically, in the exemplary embodiment, undercut portion  270  extends from leading edge side  240  towards trailing edge side  242 . Specifically, undercut portion  270  extends a distance D 5  from leading edge side  240  towards trailing edge side  242 . Specifically, undercut portion  270  extends from leading edge side  240  to an apex  279 . Alternatively, undercut portion  270  extends from leading edge side  240  to projection  271 . In the exemplary embodiment, distance D 5  is substantially equal to distance D 3  of undercut portion  260 . In an alternative embodiment, distance D 5  is different than undercut portion distance D 3 . Second sidewall  238  is also formed with a notch  272  that is defined by a first end  276  and a second end  278  that are connected together at apex  279 . In the exemplary embodiment, notch  272  is a Z-notch extending continuously from first end  276  to second end  278 . As such, in the exemplary embodiment, undercut portion  270  extends from leading edge side  240  to projection  271  near notch second end  278 . 
         [0023]    Undercut portion  270  is defined by a recessed area  273  that extends a width W 3  from second sidewall  238  towards first sidewall  234  and along shroud a radially outer surface  280 . Undercut portion radially outer surface  280  forms a mating surface that enables circumferentially adjacent tip shrouds  212  and  214  to abut each other, as described in more detail below. 
         [0024]    Additionally, second sidewall  238  is formed with overhang portion  274  that extends along a portion of second sidewall  238 . Overhang portion  274  extends from trailing edge side  242  towards leading edge side  240 . In the exemplary embodiment, overhang portion  274  extends a distance D 6  from trailing edge side  242  towards leading edge side  240 . In the exemplary embodiment, distance D 6  is substantially equal to distance D 1  of overhang portion  250 . In an alternative embodiment, D 6  is different than overhang portion distance D 1 . Specifically, overhang portion  274  extends from trailing edge side  242  to first end  276  of notch  272 . Overhang portion  274  is formed by a recess  282  that extends a width W 4  from second sidewall  238  towards first sidewall  234  and along a shroud radially inner surface  284 . Overhang portion radially inner surface  284  forms a mating surface that enables circumferentially-adjacent tip shrouds to abut each other, as described in more detail below. 
         [0025]    In the exemplary embodiment, first sidewall  234  is designed to mate against second sidewall  238  such that a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 . Specifically, overhang portion  250  is designed to mate against undercut portion  270 , and overhang portion  274  is designed to mate against undercut portion  260 . In the exemplary embodiment, overhang portions  250  and  274  are designed to ensure overlap with undercut portions  270  and  260 , respectively. It should be noted that the orientation and configurations of tip shrouds  212  and  214  is the exemplary embodiment. For example, in an alternative embodiment, neither tip shroud  212  nor tip shroud  214  is formed with overhang portions  250  and  274  or with undercut portions  260  and  270 . In an alternative embodiment, tip shroud first sidewall  234  is formed with a first surface that is positionable relative to tip shroud second sidewall  238  to enable the first surface and second surface to contact during operation of the rotor assembly such that a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 . In another alternative embodiment, for example, at least one of tip shroud  212  and/or tip shroud  214  includes, but is not limited to including, circumferential pins, tabs, and/or any other suitable mechanisms that enables a portion of radial loading induced to tip shroud  212  to be translated to tip shroud  214 . 
         [0026]    In an alternative embodiment, leading edge  240  includes overhang portion  250  and undercut portion  260 , and/or trailing edge  242  includes overhang portion  274  and undercut portion  270  wherein a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 . In a further alternative embodiment, tip rail  241  includes overhang portion  250  and undercut portion  260 , and/or tip rail  243  includes overhang portion  274  and undercut portion  270  wherein a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 . 
         [0027]    During assembly, in the exemplary embodiment, buckets  100  and  101  are positioned circumferentially adjacent one another such that tip shrouds  212  and  214  are positioned circumferentially adjacent to each other. More specifically, when aligned, the leading edge side  240  of tip shroud  212  is substantially circumferentially aligned with the leading edge side  240  of tip shroud  214 . As such, first sidewall  234  of tip shroud  212  is positioned circumferentially adjacent second sidewall  238  of tip shroud  214 . More specifically, in the exemplary embodiment, when tip shrouds  212  and  214  are adjacent to each other, radially inner surface  251  of overhang portion  250  is aligned with radially outer surface  280  of undercut portion  270 , projection  271  is aligned with the walls within notch  252 , and apex  279  receives projection  261 . Furthermore, radially outer surface  264  of recessed area  263  of undercut portion  260  is aligned with radially inner surface  284  of recess  282  of overhang portion  274 . Positioning undercut portions  260  and  270  and overhang portions  250  and  274  in a mating relationship with one another facilitates increasing the useful life of tip shrouds  212  and  214 , and thus prevents the inclusion of scallops and/or other weakening cut away portions of tip shrouds  212  and  214 . Prior to thermal expansion of buckets  100  and  101 , first sidewall  234  of tip shroud  212  is aligned with adjacent second sidewall  238  of tip shroud  214 . Tip shrouds  212  and  21   4  are positioned to contact one another during operation of the turbine. 
         [0028]    During operation of a turbine, air flows along tip shrouds  212  and  214  and from leading edge  240  towards trailing edge side  242 . As tip shrouds  212  and  214  thermally and mechanically expand, overhang portions  250  and  274  facilitate resisting radially outward movement of undercut portions  260  and  270  such that stresses induced to tip shrouds  212  and  214  during turbine operation are reduced. During operation, the combination of overhang portions  250  and  274 , and undercut portions  260  and  270 , transmit tip shroud centrifugal loading into each corresponding bucket  100  and  101 . Specifically, in the exemplary embodiment, a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 , or a portion of radial loading induced to tip shroud  214  is transferred to tip shroud  212 . Moreover, in the exemplary embodiment, a portion of radial loading induced to tip shroud  212  is transferred to tip shroud  214 , and a portion of radial loading induced to tip shroud  214  is simultaneously transferred to tip shroud  212 . The enhanced radial retention enables a manufacturer to prevent from having to scallop the leading and/or trailing edges of the tip shroud. Additionally, the radial retention facilitates preventing a fillet (not shown) located between the airfoil and tip shroud from being solely responsible for carrying the load of the tip shroud. By reducing and lowering stresses in tip shroud  212  and  214 , the useful life of the tip shrouds is facilitated to be increased. 
         [0029]    The above-described invention provides an overlapping tip shroud assembly that facilitates reducing stresses induced within the tip shroud. Reducing stresses within the tip shroud facilitates increasing the useful life of the tip shroud white maintaining engine performance. 
         [0030]    An exemplary embodiment of a turbine rotor assembly is described above in detail. The assembly illustrated is not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. 
         [0031]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.