US20150184518A1

US20150184518A1 - Turbine airfoil cooling system with nonlinear trailing edge exit slots

Info

Publication number: US20150184518A1
Application number: US14/140,593
Authority: US
Inventors: Ching-Pang Lee
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2013-12-26
Filing date: 2013-12-26
Publication date: 2015-07-02
Also published as: WO2015116325A3; WO2015116325A2

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.

Description

FIELD OF THE INVENTION

This invention is directed generally to turbine airfoils, and more particularly to trailing edge cooling systems in hollow turbine airfoils

BACKGROUND

Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures As a result, turbine blades must be made of materials capable of withstanding such high temperatures In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine blades are formed from a root portion having a platform at one end and an elongated portion forming a blade that extends outwardly from the platform coupled to the root portion The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge The inner aspects of most turbine blades typically contain an intricate maze of cooling channels forming a cooling system The cooling channels in a blade receive air from the compressor of the turbine engine and pass the air through the blade. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade.
Typically, the trailing edge of turbine airfoils develop hot spots Trailing edges are thus often designed to be thin and include cooling channels that exhaust cooling fluids from the pressure side of the trailing edge. Often times, the trailing edge exhaust channels are formed via machining, which adds expense to the manufacturing process. Thus, a need exists for a more cost effective cooling system capable of providing sufficient cooling to trailing edge of turbine airfoils.

SUMMARY OF THE INVENTION

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.
The turbine airfoil may be formed from 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 The cooling system may include 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 The trailing edge exit slot may have a nonlinear longitudinal axis with a plurality of turns In particular, the trailing edge exit slot may include 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 that 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 slot on an opposite side from the first side A lateral distance between the first and second linear line may be 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. The first side of the trailing edge exit slot may be formed from at least two ridges and at least two valleys and the second side of the at least one trailing edge exit slot may be formed from at least one ridge and at least two valleys. The ridge on the second side may be aligned with a valley on the first side positioned between two ridges.
In at least one embodiment, the trailing edge exit slot extending from the central trailing edge cooling channel to the trailing edge may be 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. The trailing edge rib may include a pointed leading edge formed by two linear edges that intersect at a tip of the trailing edge rib. The tip of the trailing edge rib may be rounded. A downstream end of the trailing edge rib may be aligned with the trailing edge of the turbine airfoil The trailing edge exit slot may include a tapered mouth such that an opening of the mouth is wider than a width of the trailing edge exit slot at the intersection between the trailing edge exit slot and the mouth. A ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots may be between about 2•3 and about 2:5. In another embodiment, a ratio of width of trailing edge exit slot to width of trailing edge rib separating adjacent trailing edge slots may be about 2:3.2.
An advantage of this invention is that 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.
Another advantage of this invention is that the design provides sufficient mechanical support while providing sufficient flow metering with quality heat transfer capability
Yet another advantage of this invention is that the mechanically supportive trailing edge exit slots may be form with investment casting rather than machining holes which saves costs
These and other embodiments are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention.

FIG. 1 is a perspective view of a turbine airfoil having features according to the instant invention

FIG. 2 is a side view of a pressure side of the turbine airfoil

FIG. 3 is a side view of a suction side of the turbine airfoil.

FIG. 4 is a fillet view of the turbine airfoil of FIG. 1 taken along section line 4-4.

FIG. 5 is a side view of a ceramic core used to form the cooling system within the turbine airfoil.

FIG. 6 is a perspective view of a wax die containing the ceramic core and a blade wax pattern.

FIG. 7 is a detailed view of the trailing edge exit slots on the ceramic core taken a detail line 7-7 in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-7, a cooling system 10 for a turbine airfoil 12 of a turbine engine having a trailing edge cooling channel 16 formed from a central trailing edge cooling channel 18 and at least one trailing edge exit slot 20 with a nonlinear longitudinal axis 22 is disclosed As shown in FIGS. 4, 5 and 7, the trailing edge exit slot 20 may be defined by ribs 24 having wavy side edges 26 that form a jagged edge. As such, the nonlinear longitudinal axis 22 of the trailing edge exit slot 20 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 20 may be formed using a ceramic core 106 and investment casting
In at least one embodiment, as shown in FIGS. 1 and 4, the turbine airfoil 12 may be formed from a generally elongated, hollow airfoil 30 formed by an outer wall 32 and having a leading edge 34, a trailing edge 36, a tip section 38 at a first end 40, a root 42 coupled to the airfoil 30 at an end 44 generally opposite the first end 40 for supporting the airfoil 30 and for coupling the airfoil 12 to a disc, and a cooling system 10 formed from at least one cavity 46 in the elongated, hollow airfoil 30 positioned in internal aspects of the generally elongated, hollow airfoil 30 The cooling system 10 may have any appropriate configuration In at least one embodiment, as shown in FIG. 4, the cooling system 10 may include a leading edge cooling channel 48 including a spanwise extending impingement rib 50 having a plurality of impingement orifices 52 A plurality of film cooling orifices 53 may extend through the leading edge 34 forming a showerhead, as shown in FIG. 1. The cooling system 10 may include a serpentine cooling channel 54 positioned within a midchord region 56, as shown in FIGS. 4 and 5. In at least one embodiment, the serpentine cooling channel 54 may be a triple pass serpentine cooling channel
The leading edge cooling channel 48 or the serpentine cooling channel 54, or both, may include one or more turbulators 58 that may extend from an inner surface of the suction side 60 or the pressure side 62, or both The turbulators 58 may be positioned nonlinear and nonorthogonal to the flow of cooling fluids through the cooling system 10 In at least one embodiment, the turbulators 58 may be positioned at about 45 degrees relative to a direction of flow 64 of cooling fluids through the cooling system 10. A plurality of film cooling orifices 53 may extend through the pressure and suction sides 62, 60 to exhaust cooling fluids from the serpentine cooling channel 54
The cooling system 10 may include one or more trailing edge cooling channels 16 positioned within the generally elongated, hollow airfoil 30 and proximate to the trailing edge 36 The trailing edge cooling channel 16 may include one or more impingement ribs 66 extending spanwise within the channel 16 In at least one embodiment, the trailing edge cooling channel 16 may include three impingement ribs 66.
The trailing edge cooling channel 16, as shown in FIG. 7, may also include a central trailing edge cooling channel 18 extending spanwise within the generally elongated, hollow airfoil 30 and one or more trailing edge exit slots 20 extending from the central trailing edge cooling channel 18 to the trailing edge 36. The trailing edge exit slot 20 may have a nonlinear longitudinal axis 22 whereby a first linear line 68 may extend between a first ridge 70 and a second ridge 72 on a first side 74 of the trailing edge exit slot 20 that is separated laterally from a second linear line 76 extending between a first ridge 78 and a second ridge 80 on a second side 82 of the trailing edge exit slot 20 on an opposite side from the first side 74 A lateral distance between the first and second linear line 68, 76 more than one half of a distance from the first ridge 70 on the first linear side 74 and a valley 86 opposite the first ridge 78 on the second side 82. The first side 74 of the trailing edge exit slot 20 may be formed from at least two ridges 70, 72 and at least two valleys 86 and the second side 82 of the at least one trailing edge exit slot 20 may be formed from at least one ridge 78 and at least two valleys 86. The at least one ridge 78 on the second side 82 may be aligned with a valley 86 on the first side 74 positioned between two ridges 70, 72.
In at least one embodiment, the trailing edge exit slot 20 extending from the central trailing edge cooling channel 18 to the trailing edge 36 may be formed from a plurality of trailing edge exit slots 20 extending from the central trailing edge cooling channel 18 to the trailing edge 36. Adjacent trailing edge exit slots 20 may be separated from each other by a trailing edge rib 24 extend from the suction side 60 to the pressure side 62. The trailing edge rib 24 may include a pointed leading edge 90 formed by at two linear edges 92, 94 that intersect at a tip 96 of the trailing edge rib 24. In at least one embodiment, the tip 96 of the trailing edge rib 24 may be rounded A downstream end 98 of the trailing edge rib 24 may be aligned with the trailing edge 36 of the turbine airfoil 12. The trailing edge exit slot 20 may include a tapered mouth 100 such that an opening 102 of the mouth 100 is wider than a width of the trailing edge exit slot 20 at the intersection 104 between the tapered edge exit slot 20 and the mouth. A ratio of width of trailing edge exit slot 20 to width of trailing edge rib 24 separating adjacent trailing edge slots 20 may be between about 2•3 and about 2•5 In another embodiment, the ratio of width of trailing edge exit slot 20 to width of trailing edge rib 24 separating adjacent trailing edge slots 20 may be about 2•3 2. In yet another embodiment, the ratio of width of trailing edge exit slot 20 to width of trailing edge rib 24 separating adjacent trailing edge exit slots 20 may be about 2:3 17 In at least one embodiment, the trailing edge exit slot 20 may have a width extending from the suction side to the pressure side between about 0.5 millimeter and about 1.5 millimeters, a slot height between about 1 millimeter and about 3 millimeters and a pitch between about 4 millimeters and about 6 millimeters. In yet another embodiment, the trailing edge exit slot 20 may have a width extending from the suction side to the pressure side of about 1 millimeter, a slot height of about 2 millimeter, and a pitch of about 5.17 millimeters.
The turbine airfoil 12 may be formed via a method of investment casting whereby a die 110, as shown in FIG. 6, is formed in the shape of the turbine blade 12 and is filled with wax to form the turbine blade shape. The cooling system 10 within the turbine airfoil 12 may be formed via a ceramic core 106 that is configured in the shape of the cooling system 10 and inserted into the die forming the turbine blade 12. In particular, the cooling system may be formed by first forming a ceramic core 106 in the shape of at least one trailing edge cooling channel 16 positioned within the generally elongated, hollow airfoil 30 and proximate to the trailing edge 36, wherein the at least one trailing edge cooling channel 16 comprises a central trailing edge cooling channel 18 extending spanwise within the generally elongated, hollow airfoil 30 and at least one trailing edge exit slot 20 extending from the central trailing edge cooling channel 18 to the trailing edge 36, wherein the trailing edge exit slot 20 has a nonlinear longitudinal axis 22 whereby the first linear line 68 extending between the first ridge 70 and a second ridge 72 on the first side 74 of the trailing edge exit slot 20 is separated laterally from the second linear line 76 extending between the first ridge 78 and the second ridge 80 on the second side 82 of the trailing edge slot 20 on the opposite side from the first side 74. The ceramic core 106 may be positioned within a wax die 110 formed in the shape of the turbine blade 12 The wax die 110 may be filled with wax to form a wax blade 108 in the form of the generally elongated, hollow airfoil 30. The wax blade 108 may be coated with a ceramic material to form an external shell. After removing the wax pattern, the external shell and the internal core form a hollow casting mold. The hollow mold may then be cast with a material, such as, but not limited to, an alloy such as CM247LC-CC, to form the turbine blade 12. The ceramic core 106 may be dissolved in a solution to remove the ceramic core 106 to form the cooling system 10 and related components. The turbine airfoil 12 may be coated with a thermal barrier coating (TBC), and the film cooling holes 53 may be machined into the turbine airfoil 12.
During use, cooling fluids may flow into the cooling system 10 from a cooling fluid supply source. At least a portion of the cooling fluids may flow into the leading edge cooling channel 48 and the serpentine cooling channel 54 in the midchord region 56. A portion of the cooling fluid flowing into the serpentine cooling channel 54 in the midchord region 56 may flow into the trailing edge cooling channel 18 The cooling fluid flowing into the trailing edge cooling channel 18 may flow through one or more impingement rib 66 and into one or more trailing edge exit slots 20. The fluid flowing through the trailing edge exit slots 20 follows a nonlinear longitudinal axis 22 Such nonlinear path within the trailing edge exit slot 20 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 foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.

Claims

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:

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.