Perforated turbine bucket tip cover

Abstract

An airfoil with a tip cover surface treatment for reducing leakage flows, minimizing tip vortex size and penetration into main flow that will improve turbine efficiency. The surface treatment for the airfoil tip covers includes a series of concave shapes, such as grooves or holes. These grooves and holes will cause the leakage flow into separate flow paths within the cavities and generate more resistance to leakage flows through the airfoil tip clearance, thereby reducing the leakage mass flow and weakening tip vortex and its interaction with turbine main flows. The material removed from the tip cover provides the additional benefit of reducing the weight of the tip cover, thereby enhancing blade reliability.

1 . A blade for a turbine engine including a root, a tip, a leading edge, a trailing edge, and opposed pressure and suction sidewalls extending generally along a radial axis within an inner casing of the turbine engine, the blade comprising:
 a tip cover extending between a tip-cover pressure sidewall and a tip-cover suction sidewall;   a top surface on the tip cover extending between the tip-cover pressure sidewall and the tip-cover suction sidewall and adapted to permit the blade to rotate with a limited clearance to a shroud of a casing of the turbine engine;   a thickness of the tip cover extending from the top surface to a tip of the blade;   a plurality of depressions over essentially the full top surface of the tip cover, the plurality of depressions extending into the thickness of the tip cover and adapted to restrict leakage flow between the tip cover and the shroud of the casing of the turbine engine.   
     
     
         2 . The blade according to  claim 1 , the plurality of depressions comprising:
 a plurality of grooves extending into the thickness of the tip cover.   
     
     
         3 . The blade according to  claim 2 , wherein the plurality of grooves extend parallel to each other between a first interlocking end of the tip cover and a second interlocking end of the tip cover. 
     
     
         4 . The blade according to  claim 3 , wherein the plurality of grooves include a U-shaped cross-section. 
     
     
         5 . The blade according to  claim 4 , wherein the U-shaped cross-section includes vertical walls roughly normal to the top surface of the tip cover and a bottom surface roughly parallel to the top surface of the tip cover. 
     
     
         6 . The blade according to  claim 5 , wherein when the blade is rotating at a full operating speed the plurality of grooves at the first interlocking end of the tip cover are aligned with the plurality of grooves of the second interlocking end of a tip cover on an adjacent blade and the plurality of grooves at the second interlocking end of the tip cover are aligned with the plurality of grooves of the first interlocking end of a tip cover on an adjacent blade. 
     
     
         7 . The blade according to  claim 2 , further comprising at least one seal tooth on the top surface of the tip cover, the at least one seal tooth disposed generally parallel with the plurality of grooves on the top surface and the at least one seal tooth extending between a first interlocking end of the tip cover and a second interlocking end of the tip cover. 
     
     
         8 . The blade according to  claim 1 , wherein the plurality of depressions comprise a plurality of holes in the top surface of the tip cover extending into the thickness of the tip cover, the plurality of holes being aligned in a plurality of rows extending between the opposite interlocking ends of the tip cover and a plurality of columns extending between the pressure side and the suction side of the tip cover. 
     
     
         9 . The blade according to  claim 8 , wherein the holes of adjacent columns may be staggered relative to the holes of the adjacent rows of holes. 
     
     
         10 . The blade according to  claim 8  wherein when the blade is rotating at a full operating speed, the rows of holes at the first interlocking end of the tip cover are aligned with the rows of holes of the second interlocking end of a tip cover on an adjacent blade and the rows of holes at the second interlocking end of the tip cover are aligned with the rows of holes of the first interlocking end of a tip cover on an adjacent blade. 
     
     
         11 . The blade according to  claim 2 , further comprising:
 at least one seal tooth on the top surface of the tip cover, the at least one seal tooth situated generally parallel with the rows of holes on the top surface and the at least one seal tooth extending between a first interlocking end of the tip cover and a second interlocking end of the tip cover.   
     
     
         12 . The blade according to  claim 1 , wherein the turbine engine is a gas turbine. 
     
     
         13 . The blade according to  claim 1 , wherein the turbine engine is a steam turbine. 
     
     
         14 . A method for fabricating a blade for a turbine engine, the method comprising:
 providing a blade including a tip cover with a top surface extending between a tip-cover pressure sidewall and a tip-cover suction sidewall, a first interlocking end at a trailing edge of the rotor blade and a second interlocking end at a leading edge of the rotor blade, and a thickness of the tip cover extending radially from the top surface of the tip cover to the rotor blade; and   removing a portion of the thickness of the tip cover forming a plurality of depressions over essentially the full top surface of the tip cover, the plurality of depressions being adapted to adapted to restrict leakage flow between the tip cover and the shroud of the casing of the turbine engine.   
     
     
         15 . The method for fabricating a blade according to  claim 14 , the step of removing a portion of the thickness of the top cover comprising:
 forming a plurality of grooves extending parallel to each other between a first interlocking end of the tip cover and a second interlocking end of the tip cover.   
     
     
         16 . The method for fabricating a blade according to  claim 15 , the step of forming a plurality of grooves comprising:
 forming grooves on the tip covers of adjacent blades so when the blades are rotating at a full operating speed, the grooves at the first interlocking end of the tip cover for each blade are aligned with the grooves of the second interlocking end of a tip cover on an adjacent blade and the grooves at the second interlocking end of the tip cover are aligned with the grooves of the first interlocking end of a tip cover on an adjacent blade.   
     
     
         17 . The method for fabricating a blade according to  claim 15 , further comprising:
 forming at least one seal tooth on the top surface of the tip cover, the seal tooth situated generally parallel with the grooves on the top surface and the seal tooth extending between a first interlocking end of the tip cover and a second interlocking end of the tip cover.   
     
     
         18 . The method for fabricating a blade according to  claim 17 , the step of removing a portion of the thickness of the top cover comprising:
 forming a plurality of holes in the top surface of the tip cover extending into the thickness of the tip cover; and   arranging the holes in a plurality of rows extending between the opposite interlocking ends of the tip cover and a plurality of columns extending between the pressure side and the suction side of the tip cover.   
     
     
         19 . The method for fabricating a blade according to  claim 14 , the step of arranging the closed-end holes comprising:
 staggering the holes of adjacent columns of holes relative to the holes of the adjacent rows of holes.   
     
     
         20 . The method for fabricating a blade according to  claim 14 , further comprising:
 forming at least one seal tooth on the top surface of the tip cover, the seal tooth situated generally parallel with the rows of holes on the top surface and the seal tooth extending between a first interlocking end of the tip cover and a second interlocking end of the tip cover.