Abstract:
A tip shrouded blade includes an airfoil rotatable about an axial centerline. Also included is a tip shroud connected at a radially outer tip of the airfoil, wherein the tip shroud includes at least one portion angled about a tangential axis defined by the radially outer tip of the airfoil.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to turbine systems, and more particularly to tip shrouds. 
         [0002]    Gas turbine buckets or blades are airfoil-shaped components designed to convert thermal and kinetic energy of flow gases into mechanical rotation of the rotor. Turbine performance may be enhanced by providing a seal at the tip of the airfoil to block the flow of air over the tip of the airfoil which would otherwise bypass the airfoil and thus not perform any work on the rotor. Thus, such tip seals reduce the gap between the bucket and the surrounding stationary casing. 
         [0003]    Typically a tip shroud is provided to the tip of the airfoil and adjacent turbine buckets are aligned in a cold assembly condition. However, during hot operating conditions, the tip shrouds tend to have some degree of misalignment. Radial misalignment between two adjacent shrouds will cause obstruction in a main flow path, leading to inefficiency and possibly disengagement. Tangential misalignment will lead to a leakage area for air that therefore does not perform work on the rotor. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a tip shrouded blade includes an airfoil rotatable about an axial centerline. Also included is a tip shroud connected at a radially outer tip of the airfoil, wherein the tip shroud includes at least one portion angled about a tangential axis defined by the radially outer tip of the airfoil. 
         [0005]    According to another aspect of the invention, a tip shrouded blade includes an airfoil extending away from and rotatable about an axial centerline. Also included is a tip shroud provided at a tip of the airfoil, wherein the tip shroud is tilted about a tangential axis and twisted about a radial axis. 
         [0006]    According to yet another aspect of the invention, a turbine system having at least one row of circumferentially aligned tip shrouded blades includes a first turbine bucket having a first airfoil. Also included is a first tip shroud provided at an outer tip of the first airfoil, wherein the first tip shroud is angled about a tangential axis defined by the outer tip of the first airfoil. Further included is a second turbine bucket having a second airfoil disposed adjacent to the first airfoil. Yet further included is a second tip shroud provided at an outer tip of the second airfoil, wherein the second tip shroud is angled to correspond to the first tip shroud during a steady state operation of the turbine system. 
         [0007]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a perspective view of a turbine bucket; 
           [0010]      FIG. 2  is a top plan view of a first tip shroud and an adjacent second tip shroud; 
           [0011]      FIG. 3  is a side elevational view of a rear portion of the first tip shroud and a front portion of the second tip shroud; and 
           [0012]      FIG. 4  is a rear elevational view of the rear portion of the first tip shroud and the front portion of the second tip shroud. 
       
    
    
       [0013]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIGS. 1 and 2 , a gas turbine bucket  10  is illustrated and includes an airfoil  12 . The airfoil  12  intercepts a flow of gases that are generated by, and delivered from, upstream components within a turbine system, such as a compressor and combustor (each not illustrated). The airfoil  12  functions as a windmill vane to convert the energy of the flow of gases into tangential motion, which in turn rotates a rotor to which the gas turbine bucket  10  is attached. Proximate an outer tip  14  of the airfoil  12  is disposed a tip shroud  16 . The tip shroud  16  includes a seal rail  18  that extends generally along the outer tip  14  of the airfoil  12 , and therefore along the tip shroud  16 . 
         [0015]    The turbine system includes a plurality of rows of circumferentially aligned turbine buckets  10 . The seal rail  18  extends circumferentially around at least one of the plurality of rows, beyond the airfoil  12  sufficiently to relatively match up with seal rails  18  provided at the outer tip  14  of adjacent airfoils  12 , thereby blocking flow from bypassing the row so that airflow must be directed to the length of the airfoil  12 , ensuring more efficient rotation of the rotor. 
         [0016]    The airfoil  12  rotates in a direction  20  about an axial centerline  22  of the turbine system. A tangential axis  24  and an axial axis  26  at the outer tip  14  of the airfoil  12  are formed relative to the direction  20  of rotation of the outer tip  14 . The axial axis  26  extends in the axial direction of the turbine system and is parallel to the axial centerline  22 . Additionally, a radial axis  27  extends in a longitudinal direction of the airfoil  12 , and specifically an axis extending radially outward from the axial centerline  22  toward the tip shroud  16 . 
         [0017]    During operation of the turbine system, such as steady-state operation, the turbine buckets  10  and the tip shrouds  16  are subjected to significant forces and thermal stresses that result in asymmetric deflections of the tip shrouds  16 . Such asymmetric deflections of the tip shrouds  16  cause misalignment between adjacent tip shrouds  16 , resulting in inefficiency and/or stress imbalance which can lead to material creep. 
         [0018]    Referring now to  FIG. 3 , the tip shroud  16  is assembled in a cold, non-operating condition, such that it is configured to be tilted about the axial axis  26 . The tip shroud  16  includes a front region  28  and a rear region  30 , with respect to the direction  20  of rotation of the airfoil  12 . The direction and magnitude of tilt of the tip shroud  16  is determined by the application of use and is set based on experimentation and analysis showing the magnitude and direction of deflection occurring under various operating conditions. In the illustrated example, the tip shroud  16  is tilted forwardly in a cold, non-operating condition, such that the front region  28  is closer to the rotor or axial centerline  22  of the turbine system than the rear region  30 , however, this forward tilting is merely for illustrative purposes and it should be appreciated that rearward tilting is contemplated. During operation of the turbine bucket  10 , such as steady-state operation, for example, the tip shroud  16  rotates due to the previously described forces and thermal loads imposed thereon. Such pre-tilting and rotation of the tip shroud  16  reduces the degree of misalignment of adjacent tip shrouds  16  during operation. Pre-tilting results in advantageous alignment of adjacent tip shrouds  16 . 
         [0019]    Referring to  FIG. 4 , in addition to tilting about the axial axis  26 , the tip shroud  16  is assembled in a cold, non-operating condition, such that it is configured to be tilted about the tangential axis  24 . The tip shroud  16  includes an upstream region  32  and a downstream region  34 . As is the case with any tilt about the axial axis  26 , the direction and magnitude of tilt of the tip shroud  16  about the tangential axis  24  is determined by the application of use. In the illustrated example, the tip shroud  16  is tilted in an upstream direction, such that the upstream region  32  is closer to the rotor or axial centerline  22  of the turbine system than the downstream region  34 , however, this upstream tilting is merely for illustrative purposes and it should be appreciated that downstream tilting is contemplated. Similar to the effect of tilting about the axial axis  26 , tilting about the tangential axis  24  reduces the degree of misalignment between components. Additionally, the tip shroud  16  is pre-twisted about the radial axis  27 , such that desirable orientation of the tip shroud  16  occurs during operation of the turbine bucket  10 . The degree of angling (e.g., tilting, twisting, etc.) may vary based on the application, however, it is contemplated that such angles will range between +/−10 degrees in either direction of rotation about a respective axis, and more typically between +/−5 degrees in either direction of rotation. 
         [0020]    The tip shroud  16  may take on various configurations and features, including a recess  40  proximate the rear region  30  of the tip shroud  16  that is configured to allow a protrusion  42  from the front region  28  of an adjacent tip shroud  16  to optionally be disposed therein. Such an arrangement permits the rotational movement of the tip shrouds  16  relative to one another during operation of the turbine bucket  10 . 
         [0021]    As described above, it is advantageous to pre-tilt or pre-twist the tip shroud  16  to account for deformations that occur during operation of the turbine bucket  10 , particularly about multiple axes, such as the axial axis  26 , the radial axis  27  and the tangential axis  24 . Alternatively, it is contemplated that only one pre-tilting or pre-twisting may be imposed and is determined by the application of use, and additionally more than two axes may be rotated about. The tip shroud  16  merely need be rotated about some axis that is offset in any direction from that of the axial centerline  22 . This refers to axes of rotation that are shifted radially, tangentially, or axially from the axial centerline  22 . The tip shroud  16  is configured such that it may deflect into a relatively planar member during steady-state operation and oriented within a plane tangential to the outer tip  14  of the airfoil  12 . 
         [0022]    Irrespective of the precise tip shroud  16  configuration, it should be appreciated that several advantages are attained by such an assembly. Steady-state alignment of the seal rails  18  occurs when the tip shroud  16  is an operating position upon rotation of the airfoil at a predetermined speed. Alignment of the seal rails  18  leads to lower overall flow path leakage, such as through a honeycomb-shaped casing surface located radially outward of the seal rail  18 . Additionally, stress states in the tip section of the airfoil  12  are balanced and the potential for disengagement is reduced. These and other advantages are achieved by the tip shroud  16  disclosed herein. 
         [0023]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.