Blade/disk dovetail backcut for blade/disk stress reduction (9FA, stage 1)

Abstract

A turbine blade that may include an airfoil and a blade dovetail, the blade dovetail being shaped corresponding to a dovetail slot in a turbine disk. The blade dovetail may include a dovetail backcut sized and positioned according to blade geometry to maximize a balance between stress reduction on the disk, stress reduction on the blade, a useful life of the turbine blade, and maintaining or improving the aeromechanical behavior of the turbine blade. A start point of the dovetail backcut, which defines a length of the dovetail backcut along a dovetail axis, may be determined relative to a datum line positioned a fixed distance from a forward face of the blade dovetail along a centerline of the dovetail axis. The start point of the dovetail backcut may be at least approximately 1.539 inches in an aft direction from the datum line.

1 . A method for reducing stress on at least one of a turbine disk and a turbine blade, wherein a plurality of turbine blades are attachable to the disk, and wherein each of the turbine blades includes a blade dovetail engageable in a correspondingly-shaped dovetail slot in the disk, the method comprising:
 (a) determining a start point for a dovetail backcut relative to a datum line, the start point defining a length of the dovetail backcut along a dovetail axis;   (b) determining a cut angle for the dovetail backcut; and   (c) removing material from at least one of the blade dovetail or the disk dovetail slot according to the start point and the cut angle to form the dovetail backcut;   wherein the start point and the cut angle are optimized according to blade and disk geometry to maximize a balance between stress reduction on the disk, stress reduction on the blade, a useful life of the turbine blades, and maintaining or improving the aeromechanical behavior of the turbine blade;   wherein the datum line is positioned a fixed distance from a forward face of the blade dovetail along a centerline of the dovetail axis, and wherein step (a) is practiced such that the start point of the dovetail backcut is at least approximately 1.539 inches in an aft direction from the datum line.   
   
   
       2 . The method of  claim 1 , wherein each of the turbine blades is configured to operate within a first stage of a 9FA turbine. 
   
   
       3 . The method according to  claim 1 , wherein step (b) is practiced such that the cut angle is a maximum of about 3°. 
   
   
       4 . The method according to  claim 1 , wherein step (b) is practiced such that the cut angle is about 0.7°. 
   
   
       5 . The method according to  claim 1 , wherein the fixed distance from the forward face of the blade dovetail for the datum line is approximately 2.964 inches. 
   
   
       6 . The method according to  claim 3 , wherein optimizing of the start point and the cut angle is practiced by executing finite element analyses on the blade and disk geometry. 
   
   
       7 . The method according to  claim 1 , wherein step (b) is practiced by determining multiple cut angles to define the dovetail backcut with a non-planar surface. 
   
   
       8 . The method according to  claim 1 , wherein step (c) is practiced by removing material from the blade dovetail. 
   
   
       9 . The method according to  claim 1 , wherein step (c) is practiced by removing material from the disk dovetail slot. 
   
   
       10 . The method according to  claim 1 , wherein step (c) is practiced by removing material from the blade dovetail and from the disk dovetail slot. 
   
   
       11 . The method according to  claim 10 , wherein step (c) is further practiced such that a resulting angle based on the material removed from the blade dovetail and the disk dovetail slot does not exceed the cut angle. 
   
   
       12 . A turbine blade comprising an airfoil and a blade dovetail, the blade dovetail being shaped corresponding to a dovetail slot in a turbine disk;
 wherein the blade dovetail includes a dovetail backcut sized and positioned according to blade geometry to maximize a balance between stress reduction on the disk, stress reduction on the blade, a useful life of the turbine blade, and maintaining or improving the aeromechanical behavior of the turbine blade;   wherein a start point of the dovetail backcut, which defines a length of the dovetail backcut along a dovetail axis, is determined relative to a datum line positioned a fixed distance from a forward face of the blade dovetail along a centerline of the dovetail axis; and   wherein the start point of the dovetail backcut is at least approximately 1.539 inches in an aft direction from the datum line.   
   
   
       13 . The turbine blade according to  claim 12 , wherein each of the turbine blades is configured to operate within a first stage of a 9FA turbine. 
   
   
       14 . The turbine blade according to  claim 12 , wherein a cut angle of the dovetail backcut is a maximum of about 3′. 
   
   
       15 . The turbine blade according to  claim 12 , wherein a cut angle of the dovetail backcut is about 0.7°. 
   
   
       16 . A turbine blade according to  claim 12 , wherein the fixed distance from the forward face of the blade dovetail for the datum line is approximately 2.964 inches. 
   
   
       17 . A turbine blade according to  claim 12 , wherein the dovetail backcut has a non-planar surface. 
   
   
       18 . A turbine blade comprising an airfoil and a blade dovetail, the blade dovetail being shaped corresponding to a dovetail slot in a turbine disk;
 wherein each of the turbine blades is configured to operate within a first stage of a 9FA turbine and the blade dovetail includes a dovetail backcut;   wherein a start point of the dovetail backcut, which defines a length of the dovetail backcut along a dovetail axis, is determined relative to a datum line positioned a fixed distance from a forward face of the blade dovetail along a centerline of the dovetail axis;   wherein the start point of the dovetail backcut is at least approximately 1.539 inches in an aft direction from the datum line; and   wherein a cut angle of the dovetail backcut is a maximum of about 3°.   
   
   
       19 . A turbine blade according to  claim 17 , wherein a cut angle of the dovetail backcut is about 0.7°. 
   
   
       20 . A turbine blade according to  claim 17 , wherein the fixed distance from the forward face of the blade dovetail for the datum line is approximately 2.964 inches.