Turbine airfoil cooling system with nonlinear trailing edge exit slots

Abstract

A cooling system for a turbine airfoil of a turbine engine having a trailing edge cooling channel formed from a central trailing edge cooling channel and at least one trailing edge exit slot with a nonlinear longitudinal axis is disclosed. The trailing edge exit slot may be defined by ribs having wavy side edges that form a jagged edge As such, the nonlinear longitudinal axis of the trailing edge exit slot reduces the effective flow area, generates impingement and turbulence to increase heat transfer and provides sufficient mechanical strength for better casting yield without overflowing for better performance The nonlinear trailing edge exit slot may be formed using a ceramic core and investment casting.

I claim: 
     
         1 . A turbine airfoil, comprising:
 a generally elongated, hollow airfoil formed by an outer wall and having a leading edge, a trailing edge, a tip section at a first end, a root coupled to the airfoil at an end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc, and a cooling system formed from at least one cavity in the elongated, hollow airfoil positioned in internal aspects of the generally elongated, hollow airfoil;   at least one trailing edge cooling channel positioned within the generally elongated, hollow airfoil and proximate to the trailing edge, wherein the at least one trailing edge cooling channel comprises a central trailing edge cooling channel extending spanwise within the generally elongated, hollow airfoil and at least one trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge; and   wherein the at least one trailing edge exit slot has a nonlinear longitudinal axis whereby a first linear line extending between a first ridge and a second ridge on a first side of the at least one trailing edge exit slot is separated laterally from a second linear line extending between a first ridge and a second ridge on a second side of the at least one trailing edge exit slot on an opposite side from the first side   
     
     
         2 . The turbine airfoil of  claim 1 , wherein a lateral distance between the first and second linear lines is more than one half of a distance from a first ridge on the first linear side and a valley opposite the first ridge on the second side. 
     
     
         3 . The turbine airfoil of  claim 1 , wherein the first side of the at least one trailing edge exit slot is formed from at least two ridges and at least two valleys and the second side of the at least one trailing edge exit slot is formed from at least one ridge and at least two valleys. 
     
     
         4 . The turbine airfoil of  claim 3 , wherein the at least one ridge on the second side is aligned with a valley on the first side positioned between two ridges. 
     
     
         5 . The turbine airfoil of  claim 1 , wherein the at least one trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge is formed from a plurality of trailing edge exit slots extending from the central trailing edge cooling channel to the trailing edge, wherein adjacent trailing edge exit slots are separated from each other by a trailing edge rib extend from the suction side to the pressure side. 
     
     
         6 . The turbine airfoil of  claim 5 , wherein the trailing edge rib includes a pointed leading edge formed by two linear edges that intersect at a tip of the trailing edge rib. 
     
     
         7 . The turbine airfoil of  claim 6 , wherein the tip of the trailing edge rib is rounded. 
     
     
         8 . The turbine airfoil of  claim 6 , wherein a downstream end of the trailing edge rib is aligned with the trailing edge of the turbine airfoil. 
     
     
         9 . The turbine airfoil of  claim 1 , wherein the at least one trailing edge exit slot includes a tapered mouth such that an opening of the mouth is wider than a width of the at least one trailing edge exit slot at an intersection between the trailing edge exit slot and the mouth. 
     
     
         10 . The turbine airfoil of  claim 1 , wherein a ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots is between about 2:3 and about 2•5. 
     
     
         11 . The turbine airfoil of  claim 10 , wherein the ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots is about 2:3.2. 
     
     
         12 . A turbine airfoil, comprising:
 a generally elongated, hollow airfoil formed by an outer wall and having a leading edge, a trailing edge, a tip section at a first end, a root coupled to the airfoil at an end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc, and a cooling system formed from at least one cavity in the elongated, hollow airfoil positioned in internal aspects of the generally elongated, hollow airfoil;   at least one trailing edge cooling channel positioned within the generally elongated, hollow airfoil and proximate to the trailing edge, wherein the at least one trailing edge cooling channel comprises a central trailing edge cooling channel extending spanwise within the generally elongated, hollow airfoil and at least one trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge;   wherein the at least one trailing edge exit slot has a nonlinear longitudinal axis whereby a first linear line extending between a first ridge and a second ridge on a first side of the at least one trailing edge exit slot is separated laterally from a second linear line extending between a first ridge and a second ridge on a second side of the at least one trailing edge exit slot on an opposite side from the first side;   wherein the first side of the at least one trailing edge exit slot is formed from at least two ridges and at least two valleys and the second side of the at least one trailing edge exit slot is formed from at least one ridge and at least two valleys;   wherein the at least one ridge on the second side is aligned with a valley on the first side positioned between two ridges;   wherein the at least one trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge is formed from a plurality of trailing edge exit slots extending from the central trailing edge cooling channel to the trailing edge, wherein adjacent trailing edge exit slots are separated from each other by a trailing edge rib extend from the suction side to the pressure side; and   wherein the at least one trailing edge exit slot includes a tapered mouth such that an opening of the mouth is wider than a width of the at least one trailing edge exit slot at an intersection between the trailing edge exit slot and the mouth.   
     
     
         13 . The turbine airfoil of  claim 12 , wherein a lateral distance between the first and second linear lines is more than one half of a distance from a first ridge on the first linear side and a valley opposite the first ridge on the second side. 
     
     
         14 . The turbine airfoil of  claim 12 , wherein the trailing edge rib includes a pointed leading edge formed by two linear edges that intersect at a tip of the trailing edge rib. 
     
     
         15 . The turbine airfoil of  claim 14 , wherein the tip of the trailing edge rib is rounded 
     
     
         16 . The turbine airfoil of  claim 12 , wherein a downstream end of the trailing edge rib is aligned with the trailing edge of the turbine airfoil. 
     
     
         17 . The turbine airfoil of  claim 12 , wherein a ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots is between about 2•3 and about 2:5. 
     
     
         18 . The turbine airfoil of  claim 17 , wherein the ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots is about 2:3.2. 
     
     
         19 . A method of forming a turbine airfoil, comprising:
 forming ceramic core a cooling system for a turbine airfoil, wherein the cooling system is formed at least one trailing edge cooling channel positioned within the generally elongated, hollow airfoil and proximate to the trailing edge, wherein the at least one trailing edge cooling channel comprises a central trailing edge cooling channel extending spanwise within the generally elongated, hollow airfoil and at least one trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge, wherein the at least one trailing edge exit slot has a nonlinear longitudinal axis whereby a first linear line extending between a first ridge and a second ridge on a first side of the at least one trailing edge exit slot is separated laterally from a second linear line extending between a first ridge and a second ridge on a second side of the at least one trailing edge exit slot on an opposite side from the first side;   positioning the ceramic core within a wax die;   filling the wax die with wax to form a wax blade having a form of the generally elongated, hollow airfoil;   coating the wax blade with ceramic material to form an external shell;   removing the wax to form a hollow casting mold;   casting the generally elongated, hollow airfoil including by pouring an alloy into the external shell, wherein the generally elongated, hollow airfoil is formed by an outer wall and having a leading edge, a trailing edge, a tip section at a first end, a root coupled to the airfoil at an end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc, and a cooling system formed from at least one cavity in the elongated, hollow airfoil positioned in internal aspects of the generally elongated, hollow airfoil; and   removing the ceramic core to form the at least one trailing edge cooling channel, the central trailing edge cooling channel, and the at least one trailing edge exit slot.