Abstract:
A method enables a stator assembly for a turbine engine to be assembled. The method comprises forming a recess within a portion of each base, and coupling the stator vanes within the turbine engine in a circumferentially-spaced arrangement such that the recessed portion of each base facilitates reducing excitation responses of each of the plurality of stator vanes during engine operation.

Description:
BACKGROUND OF THE INVENTION 
     This application relates generally to turbine engines and, more particularly, to methods and apparatus for controlling contact within turbine engine stator assemblies. 
     At least some known rotor assemblies include at least one row of circumferentially-spaced rotor blades. Each row of rotor blades is positioned between a pair of axially-spaced rows of circumferentially-spaced stator vanes or blades. At least some known stator vanes are fabricated with a base and an integrally-formed airfoil that extends radially outward from the base. Each base is configured to couple the stator vanes within the engine such that the stator vanes extend radially through a flow path defined within the rotor assembly. 
     Within at least some known stator assemblies, the base of each stator vanes is substantially wedge-shaped or square based such that a radially outer surface of the base may have an arcuate length that is longer than a corresponding length of a radially inner surface of the base. The wedge shape facilitates coupling the stator vanes circumferentially within the stator assembly. However, within such stator vanes the geometry of the base also makes control of contact between adjacent stator vanes, known as circumferential contact, and between each stator vanes and the casing, known as axial contact, difficult to accurately predict. As a result, during rotor operation excitation responses generated by such stator vanes often do not match predicted experimental frequencies. Over time, the increased excitation responses may result in shortening the useful life of the stator vanes. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a method for assembling a stator assembly for a turbine engine is provided. The method comprises forming a recess within a portion of each base, and coupling the stator vanes within the turbine engine in a circumferentially-spaced arrangement such that the recessed portion of each base facilitates reducing excitation responses of each of the plurality of stator vanes during engine operation. 
     In another aspect, a stator vane for a turbine engine is provided. The stator vane includes a base and an airfoil. The base is configured to couple the stator vane within the turbine engine. The airfoil extends radially outward from the base. The base includes a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side, wherein at least a portion of the base is recessed to facilitate reducing excitation responses of the vane during engine operation. 
     In a further aspect, a rotor assembly including a rotor shaft and a plurality of stator vanes circumferentially-spaced around the rotor shaft is provided. Each stator vane includes a base and an integrally-formed airfoil extending radially outward from the base. Each base includes a pair of circumferentially-spaced sides coupled together by an upstream side and a downstream side, wherein at least a portion of each base is recessed to facilitate reducing excitation responses of each of the plurality of stator vanes during rotor operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic illustration of an exemplary gas turbine engine; 
         FIG. 2  is an enlarged perspective view of an exemplary stator vane that may be used with the gas turbine engine shown in  FIG. 1 ; 
         FIG. 3  is a front view of a pair of the stator vanes shown in  FIG. 2  and illustrates a relative circumferential orientation of adjacent stator vanes as positioned when assembled within an engine, such as the gas turbine engine shown in  FIG. 1 ; and 
         FIG. 4  is a cross-sectional view of the pair of stator vanes shown in  FIG. 3  and taken along line  4 - 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine  10  coupled to an electric generator  16 . In the exemplary embodiment, gas turbine system  10  includes a compressor  12 , a turbine  14 , and generator  16  arranged in a single monolithic rotor or shaft  18 . In an alternative embodiment, shaft  18  is segmented into a plurality of shaft segments, wherein each shaft segment is coupled to an adjacent shaft segment to form shaft  18 . Compressor  12  supplies compressed air to a combustor  20  wherein the air is mixed with fuel  22  supplied thereto. In one embodiment, engine  10  is a 6C gas turbine engine commercially available from General Electric Company, Greenville, S.C. 
     In operation, air flows through compressor  12  and compressed air is supplied to combustor  20 . Combustion gases  28  from combustor  20  propels turbines  14 . Turbine  14  rotates shaft  18 , compressor  12 , and electric generator  16  about a longitudinal axis  30 . 
       FIG. 2  is an enlarged perspective view of an exemplary stator vane  40  that may be used with gas turbine engine  10  (shown in  FIG. 1 ). More specifically, in the exemplary embodiment, stator vane  40  is coupled within a compressor, such as compressor  12  (shown in  FIG. 1 ).  FIG. 3  is a front view of a pair of stator vanes  40  and illustrates a relative circumferential orientation of adjacent stator vanes  40  when assembled within a stator assembly, used with a rotor assembly such as gas turbine engine  10  (shown in  FIG. 1 ).  FIG. 4  is a cross-sectional view of the pair of stator vanes  40  and taken along line  4 - 4  (shown in  FIG. 3 ). In the exemplary embodiment, each stator vane  40  has been modified to include the features described herein. 
     When assembled within the stator assembly, each stator vane  40  is coupled to an engine casing (not shown) that extends circumferentially around a rotor shaft, such as shaft  18  (shown in  FIG. 1 ). As is known in the art, when fully assembled, each circumferential row of stator vanes  40  is located axially between adjacent rows of rotor blades (not shown). More specifically, stator vanes  40  are oriented to channel a fluid flow through the stator assembly in such a manner as to facilitate enhancing engine performance. In the exemplary embodiment, circumferentially adjacent stator vanes  40  are identical and each extends radially across a flow path defined within the rotor and stator assemblies. Moreover, each stator vane  40  includes an airfoil  60  that extends radially outward from, and in the exemplary embodiment, is formed integrally with, a base or platform  62 . 
     Each airfoil  60  includes a first sidewall  70  and a second sidewall  72 . First sidewall  70  is convex and defines a suction side of airfoil  60 , and second sidewall  72  is concave and defines a pressure side of airfoil  60 . Sidewalls  70  and  72  are joined together at a leading edge  74  and at an axially-spaced trailing edge  76  of airfoil  60 . More specifically, airfoil trailing edge  76  is spaced chord-wise and downstream from airfoil leading edge  74 . First and second sidewalls  70  and  72 , respectively, extend longitudinally or radially outward in span from its root positioned adjacent base  62  to an airfoil tip  80 . 
     Base  62  facilitates securing stator vanes  40  to the casing. In the exemplary embodiment, base  62  is known as a “square-faced” base and includes a pair of circumferentially-spaced sides  90  and  91  that are connected together by an upstream face  92  and a downstream face  94 . Alternatively, base  62  could include an arcuate surface. In the exemplary embodiment, sides  90  and  91  are identical and are substantially parallel to each other. In an alternative embodiment sides  90  and  91  are not parallel. Moreover, in the exemplary embodiment, upstream face  92  and downstream face  94  are substantially parallel to each other. 
     A pair of integrally-formed hangers  100  and  102  extend from each respective face  92  and  94 . Hangers  100  and  102 , as is known in the art, engage the casing to facilitate securing stator vane  40  within the stator assembly. In the exemplary embodiment, each hanger  100  and  102  extends outwardly from each respective face  92  and  94  adjacent a radially outer surface  104  of base  62 . 
     To facilitate controlling contact between circumferentially-adjacent stator vanes  40  during rotor operation, in the exemplary embodiment, at least one of circumferential sides  90  and  91  includes a recessed or scalloped portion  110  that extends partially between radially outer surface  104  and a radially inner surface  112  of base  62 . Recessed portion  110  is sized and oriented to facilitate controlling an amount of contact between adjacent stator vanes  40  during rotor operation. More specifically, in the exemplary embodiment, recessed portion  110  extends from radially outer surface  104  towards radially inner surface  112  such that a hinge  116  is created adjacent radially inner surface  112 . Accordingly, when adjacent stator vanes are coupled within the stator assembly, a gap  118  is defined between adjacent stator vanes  40  and contact between the stator vanes is limited being only along hinge  116 . As a result, line contact between adjacent stators  40  is driven along the rotor assembly flow path. Alternatively, line contact may be anywhere between hinge  116  and side  91 . 
     In addition, to facilitate controlling contact between each respective stator vane  40  and the engine casing during rotor operation, in the exemplary embodiment, upstream face  92  includes a recessed portion  120  that extends across face  92  between sides  90  and  91 . Recessed portion  120  is sized and oriented to facilitate controlling an amount of contact between stator vane  40 , along face  92 , and the engine casing. More specifically, in the exemplary embodiment, recessed portion  120  extends from hanger  100  to a hinge  117 . As a result, line contact between each stator vane  40  and the engine casing is controlled. Alternatively, line contact may be anywhere along portion  120 . 
     The combination of recessed portions  120  and  110  facilitates controlling stator-to-stator contact and stator-to-casing contact. The enhanced control of the contact facilitates each stator base  62  being defined more accurately such that the stator vanes natural frequencies can be optimized more accurately to match predicted expermimental frequencies. Moreover, excitation responses induced within each stator vane  40  are facilitated to be reduced, thus resulting in fewer component failures and extending a useful life of the stator vanes. 
     The above-described stator vanes provide a cost-effective and reliable method for optimizing performance of a rotor assembly. More specifically, each stator vane includes recessed portions that facilitate controlling circumferential and axial contact with each stator vane such that excitation responses induced within each stator vane during engine operation are facilitated to be reduced. As a result, the redefined base geometry facilitates extending a useful life of the stator assembly and improving the operating efficiency of the gas turbine engine in a cost-effective and reliable manner. 
     Exemplary embodiments of stator vanes and stator assemblies are described above in detail. The stator vanes are not limited to the specific embodiments described herein, but rather, components of each stator vane may be utilized independently and separately from other components described herein. For example, each stator vane recessed portion can also be defined in, or used in combination with, other stator vanes or with other stator or rotor assemblies, and is not limited to practice with only stator vane  40  as described herein. Rather, the present invention can be implemented and utilized in connection with many other vane, stator, and rotor configurations. 
     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.