Variable stator vane assemblies and variable stator vanes thereof having a locally swept leading edge and methods for minimizing endwall leakage therewith

Abstract

Variable stator vane assemblies and stator vanes thereof having a local swept leading edge are provided. The variable stator vane comprises an airfoil disposed between spaced apart inner and outer buttons centered about a rotational axis. The inner and outer buttons each having a button forward edge portion and the airfoil including leading and trailing edges, pressure and suction sides, and a root and a tip. The leading edge, at least a portion of which extends forward of the buttons, includes a local aft sweep at the tip, thereby forming a locally swept tip of the leading edge thereat. The button forward edge portion of the outer button is substantially vertically aligned with the locally swept tip of the leading edge. Methods are also provided for minimizing endwall leakage in the variable stator vane assembly using the same.

What is claimed is: 
     
         1 . A variable stator vane comprising:
 an airfoil disposed between spaced apart inner and outer buttons centered about a rotational axis, the inner and outer buttons each having a button forward edge portion and the airfoil including leading and trailing edges, pressure and suction sides, and a root and a tip; and   wherein:   the leading edge, at least a portion of which extends forward of the buttons, includes a local aft sweep at the tip, thereby forming a locally swept tip of the leading edge thereat; and   the button forward edge portion of the outer button is substantially vertically aligned with the locally swept tip of the leading edge.   
     
     
         2 . The variable stator vane of  claim 1 , wherein the leading edge of the airfoil includes the local aft sweep at the tip of the airfoil in a shroud region of the compressor. 
     
     
         3 . The variable stator vane of  claim 1 , wherein the button forward edge portion of the outer button substantially covers the leading edge of the airfoil at the tip. 
     
     
         4 . The variable stator vane of  claim 1 , wherein a sweep offset of the local aft sweep is 15° or greater. 
     
     
         5 . The variable stator vane of  claim 1 , wherein the button forward edge portion of the inner button is spaced apart from the leading edge at the root. 
     
     
         6 . The variable stator vane of  claim 1 , wherein the local aft sweep at the tip extends from 75 up to 100% of the blade span to minimize leading edge endwall gaps at the tip. 
     
     
         7 . A variable stator vane assembly comprising:
 an inner and an outer button spaced apart and centered about a rotational axis, each of the inner and outer buttons having an edge circumscribed about the rotational axis at a button radius, the edge comprising a button forward edge portion and a button aft edge portion;   at least one annular row of variable stator vanes, each variable stator vane in the at least one annular row comprising:
 an airfoil disposed between the spaced apart inner and outer buttons, the airfoil including leading and trailing edges, pressure and suction sides, and a root and a tip; and 
 wherein the leading edge of the airfoil, at least a portion of which extends forward of the buttons, includes a local aft sweep at the tip, thereby forming a locally swept tip of the leading edge, and the button forward edge portion of the outer button is substantially vertically aligned with the locally swept tip of the leading edge. 
   
     
     
         8 . The variable stator vane assembly of  claim 7 , wherein, for each variable stator vane in the at least one annular row, the leading edge of the airfoil includes the local aft sweep at the tip of the airfoil in a shroud region of the compressor. 
     
     
         9 . The variable stator vane assembly of  claim 8 , wherein, for each variable stator vane in the at least one annular row, the button forward edge portions of the outer button substantially covers the leading edge of the airfoil at the tip. 
     
     
         10 . The variable stator vane assembly of  claim 7 , wherein, for each variable stator vane in the at least one annular row, the local aft sweep at the tip extends from 75 up to 100% of the blade span. 
     
     
         11 . The variable stator vane assembly of  claim 7 , wherein, for each variable stator vane in the at least one annular row, a sweep offset of the local aft sweep is 15° or greater. 
     
     
         12 . A method for minimizing endwall leakage in a variable stator vane assembly, the method comprising:
 providing a variable stator vane for the variable stator vane assembly having spaced apart inner and outer buttons centered about a rotational axis, the variable stator vane comprising an airfoil including leading and trailing edges, pressure and suction sides, and a root and a tip, the leading edge, at least a portion thereof which extends forward of the buttons, including a local aft sweep at the tip with a sweep offset of 15° or greater, thereby forming a locally swept tip of the leading edge to minimize leading edge endwall gaps at the tip; and   disposing the variable stator vane between the spaced apart inner and outer buttons, the inner and outer buttons each having a button forward edge portion, the variable stator vane being disposed such that the button forward edge portion of the outer button is substantially vertically aligned with the locally swept leading edge at the tip.   
     
     
         13 . The method of  claim 12 , wherein the step of providing the variable stator vane comprises providing the leading edge of the airfoil with the local aft sweep at the tip of the airfoil in a shroud region of the compressor. 
     
     
         14 . The method of  claim 12 , wherein providing the variable stator vane for the variable stator vane assembly further comprises providing the local aft sweep at the tip from 75 up to 100% of the blade span to minimize the leading edge endwall gaps at the tip.