WO2016148691A1

WO2016148691A1 - Shrouded turbine airfoil with knife edge seal

Info

Publication number: WO2016148691A1
Application number: PCT/US2015/020851
Authority: WO
Inventors: Rachael M. JONES; Thomas W. Zagar; Sankar Nellian
Original assignee: Siemens Aktiengesellschaft; Siemens Energy, Inc.
Priority date: 2015-03-17
Filing date: 2015-03-17
Publication date: 2016-09-22

Abstract

A shrouded turbine airfoil (10) with a tapered knife edge seal (12) for weight reduction at the turbine airfoil tip (14) and for enhanced contact is disclosed. The shrouded turbine airfoil (10) may include one or more shrouds (16) attached to a tip (14) of the airfoil (10). The shroud (16) may be formed from a shroud body (18) attached to the tip (14) of the airfoil (10) and a knife edge seal (12) extending radially outward from a radially outer end of the shroud body (18). In at least one embodiment, the shroud body (18) may be narrower in width at a midpoint (20) of the shroud body (18) than circumferential ends (22, 24) of the shroud body (18). The knife edge seal (12) may be generally circumferentially symmetric, thereby forming an efficient seal when installed in a turbine engine.

Description

SHROUDED TURBINE AIRFOIL WITH KNIFE EDGE SEAL

FIELD OF THE INVENTION

This invention is directed generally to turbine airfoils, and more particularly to knife edge seals on shrouded 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.

A turbine blade is formed from a root portion at one end and an elongated portion forming a blade that extends outwardly from a platform coupled to the root portion at an opposite end of the turbine blade. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The tip of a turbine blade often has a tip feature to reduce the size of the gap between ring segments and blades in the gas path of the turbine to prevent tip flow leakage, which reduces the amount of torque generated by the turbine blades. Some turbine blades include outer shrouds attached to the tips. There is an established need to reduce weight in the turbine blade tip while also maintaining appropriate contact between the shrouds of the blade.

SUMMARY OF THE INVENTION

A shrouded turbine airfoil with a knife edge seal with reduced mass for weight reduction at the turbine airfoil tip and for enhanced contact is disclosed. The shrouded turbine airfoil may include one or more shrouds attached to a tip of the airfoil. The shroud may be formed from a shroud body attached to the tip of the airfoil and a knife edge seal extending radially outward from a radially outer end of the shroud body. In at least one embodiment, the shroud body may be narrower in width at a midpoint of the shroud body than circumferential ends of the shroud body. The knife edge seal may be generally circumferentially symmetric, thereby forming an efficient seal when installed in a turbine engine.

In at least one embodiment, the turbine airfoil may be formed from a generally elongated airfoil having a leading edge, a trailing edge, a pressure side, a suction side on a side opposite to the pressure side, a tip at a first end, a root coupled to the airfoil at a second end generally opposite the first end for supporting the airfoil and for coupling the airfoil to a disc. The turbine airfoil may include one or more outer shrouds coupled to the tip of the generally elongated airfoil. The outer shroud may extend in a direction generally from the pressure side toward the suction side and extends circumferentially in a turbine engine. The outer shroud may be formed from an outer shroud body and one more knife edge seals. The outer shroud body at a midpoint of the outer shroud body may have a thickness in an axial direction that is less than a thickness of the outer shroud body at a first end of the outer shroud body. In at least one embodiment, the thickness of the outer shroud body at a midpoint of the outer shroud body may be between a minimum thickness at the top of the knife edge seal and 99% of the thickness of the outer shroud body at a first end of the outer shroud body.

In at least one embodiment, a forward side of the outer shroud body may have a midpoint that is closer to an aft side than first or second ends of the forward side. In at least one embodiment, a forward side of the outer shroud body may be defined via a single radius. In another embodiment, the forward side of the outer shroud body may be defined via a plurality of radii. The forward side of the outer shroud body may also be defined via at least two linear sections.

In at least one embodiment, the aft side of the outer shroud body may have a midpoint that is closer to the forward side than first or second ends of the aft side. In at least one embodiment, an aft side of the outer shroud body may be defined via a single radius. In another embodiment, the aft side of the outer shroud body may be defined via a plurality of radii. The aft side of the outer shroud body may also be defined via at least two linear sections.

In at least one embodiment, the knife edge seal may have a thickness in an axial direction that is less than the thickness of the outer shroud body in the axial direction at the midpoint. The knife edge seal may be circumferentially symmetric or have another appropriate configuration.

An advantage of the reduced mass of the shroud body yields a weight reduction at the turbine airfoil tip.

Another advantage of the reduced mass of the shroud body is that the knife edge seal experiences enhanced contact.

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.

Figure 1 is a perspective view of a turbine airfoil with an outer shroud.

Figure 2 is a detail view of the outer shroud at the tip of the airfoil shown in Figure 1 .

Figure 3 is a cross-sectional view of the outer shroud at the tip of the airfoil taken at section line 3-3 in Figure 1 .

Figure 4 is a top view of the outer shroud at the tip of the airfoil of Figure 1 .

Figure 5 is a top view of the outer shroud of Figure 1 .

Figure 6 is a top view of an alternative embodiment of the outer shroud of Figure

1 .

Figure 7 is a top view of another alternative embodiment of the outer shroud of Figure 1 . DETAILED DESCRIPTION OF THE INVENTION

As shown in Figures 1 -7, a shrouded turbine airfoil 10 with a knife edge seal 12 with reduced mass for weight reduction at the turbine airfoil tip 14 and for enhanced contact is disclosed. The shrouded turbine airfoil 10 may include one or more shrouds 16 attached to a tip 14 of the airfoil 10. The shroud 16 may be formed from a shroud body 18 attached to the tip 14 of the airfoil 10 and a knife edge seal 12 extending radially outward from a radially outer end 20 of the shroud body 18. In at least one embodiment, the shroud body 18 may be narrower in width at a midpoint 20 of the shroud body 18 than circumferential ends 22, 24 of the shroud body 18. The knife edge seal 12 may be generally circumferentially symmetric, thereby forming an efficient seal when installed in a turbine engine.

In at least one embodiment, as shown in Figures 1 and 2, the turbine airfoil 10 may be formed from a generally elongated airfoil 28 having a leading edge 30, a trailing edge 32, a pressure side 34, a suction side 36 on a side opposite to the pressure side 34, a tip 14 at a first end 38, a root 39 coupled to the airfoil 28 at a second end 40 generally opposite the first end 38 for supporting the airfoil 28 and for coupling the airfoil 28 to a disc. The turbine airfoil 10 may include one or more outer shrouds 16 coupled to the tip 14 of the generally elongated airfoil 28. The outer shroud 16 may extend in a direction generally from the pressure side 34 toward the suction side 36 such as circumferentially 42 in a turbine engine. The length of the outer shroud 16 in the circumferential direction 42 may vary based upon the requirements of the blade count in that particular row of blades.

The outer shroud 16 may be formed from an outer shroud body 18 and one or more knife edge seals 12, as shown in Figures 1 -7. As shown in Figures 4-7, the outer shroud body 18 at a midpoint 20 of the outer shroud body 18 may have a thickness in an axial direction 44 that is less than a thickness of the outer shroud body 18 at a first end 22 of the outer shroud body 18. With such a configuration, the amount of material needed to form the outer shroud 16 is reduced, thereby reducing the weight of the airfoil 10 at the airfoil tip 14. The thickness of the outer shroud body 18 at a midpoint 20 of the outer shroud body 18 may be between a minimum thickness at the top of the knife edge seal 12 and 99% of the thickness of the outer shroud body 18 at a first end 22 of the outer shroud body 18. In at least one embodiment, a forward side 46 of the outer shroud body 18 may have a midpoint 20 that is closer to an aft side 48 than first or second ends 22, 24 of the forward side 46. In at least one embodiment, the forward side 46 of the outer shroud body 18 may have any configuration that enables the midpoint 20 to be closer to the aft side 48 than first or second ends 22, 24 of the forward side 46. For instance, as shown in Figure 5, the forward side 46 of the outer shroud body 18 may be defined via a single radius 50. In other embodiments, as shown in Figure 6, the forward side 46 of the outer shroud body 18 may be defined via a plurality of radii 50. Still yet, as shown in Figure 7, the forward side 46 of the outer shroud body 18 may be defined via at least two linear sections 52, 54.

Similarly, an aft side 48 of the outer shroud body 18 may have a midpoint 20 that is closer to the forward side 46 than first or second ends 38, 40 of the aft side 48. For example, as shown in Figure 5, the aft side 48 of the outer shroud body 18 may be defined via a single radius 50. In other embodiments, as shown in Figure 6, the aft side 48 of the outer shroud body 18 may be defined via a plurality of radii 50. Still yet, as shown in Figure 7, the aft side 48 of the outer shroud body 18 may be defined via at least two linear sections 52, 54.

The knife edge seal 12 may be attached to the outer shroud body 18 or, in other embodiments, integrally formed with the outer shroud body 18. In at least one embodiment, while the outer shroud body 18 may be configured with a reduced thickness at the midpoint 20 of the outer shroud body 18, the knife edge seal 12 may be circumferentially symmetric. As such, the knife edge seal 12 may have a generally constant thickness in the axial direction 44 when measured at any point between the first and second circumferential ends 22, 24. The knife edge seal 12 may also be configured such that the knife edge seal 12 has a thickness in the axial direction 44 that is less than the thickness of the outer shroud body 18 in the axial direction 44 at the midpoint 20. The knife edge seal 12 may be formed from an conventional material or heretofore yet developed material capable of preforming the functions of the knife edge seal 12.

In at least one embodiment, as shown in Figures 5-7, an outer surface 56 forming a first circumferential end 22 of the outer shroud body 18 may be nonparallel and nonlinear with an outer surface 58 forming the forward side 46 of the outer shroud 16. The outer surface 56 forming the first circumferential end 22 of the outer shroud body 18 may be aligned with an adjacent outer surface forming a circumferential end of an outer shroud on an adjacent airfoil tip. The orientation of the outer surface 56 forming a first circumferential end 22 of the outer shroud 16 may be any appropriate orientation. A second circumferential end 24 of the outer shroud body 18 positioned on an opposite end of the outer shroud body 18 from the first circumferential end 22 may be configured similarly to the first circumferential end 22. The first and second circumferential ends 22, 24 may or may not be aligned with each other.

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

CLAIMS I claim:

1 . A turbine airfoil (10), characterized in that:

a generally elongated airfoil (28) having a leading edge (30), a trailing edge (32), a pressure side (34), a suction side (36) on a side opposite to the pressure side (34), a tip (14) at a first end (38), a root (39) coupled to the airfoil (28) at a second end (40) generally opposite the first end (38) for supporting the airfoil (28) and for coupling the airfoil (28) to a disc;

at least one outer shroud (16) coupled to the tip (14) of the generally elongated airfoil (28);

wherein the at least one outer shroud (16) extends in a direction generally from the pressure side (34) toward the suction side (36) and extends circumferentially in a turbine engine;

wherein the at least one outer shroud (16) is formed from an outer shroud body (18) and at least one knife edge seal (12); and

wherein the outer shroud body (18) at a midpoint (20) of the outer shroud body (18) has a thickness in an axial direction that is less than a thickness of the outer shroud body (18) at a first end (38) of the outer shroud body (18).

2. The turbine airfoil (10) of claim 1 , characterized in that the thickness of the outer shroud body (18) at the midpoint (20) of the outer shroud body (18) is between a minimum thickness at the top of the knife edge seal (12) and 99% of the thickness of the outer shroud body (18) at a first end (38) of the outer shroud body (18).

3. The turbine airfoil (10) of claim 1 , characterized in that a forward side (46) of the outer shroud body (18) is defined via a single radius (50).

4. The turbine airfoil (10) of claim 1 , characterized in that a forward side (46) of the outer shroud body (18) is defined via a plurality of radii (50).

5. The turbine airfoil (10) of claim 1 , characterized in that a forward side (46) of the outer shroud body (18) is defined via at least two linear sections (52, 54).

6. The turbine airfoil (10) of claim 1 , characterized in that an aft side (48) of the outer shroud body (18) is defined via a single radius (50).

7. The turbine airfoil (10) of claim 1 , characterized in that an aft side (48) of the outer shroud body (18) is defined via a plurality of radii (50).

8. The turbine airfoil (10) of claim 1 , characterized in that an aft side (48) of the outer shroud body (18) is defined via at least two linear sections (52, 54).

9. The turbine airfoil (10) of claim 1 , characterized in that the at least one knife edge seal (12) is circumferentially symmetric.

10. The turbine airfoil (10) of claim 1 , characterized in that the at least one knife edge seal (12) has a thickness in an axial direction (44) that is less than the thickness of the outer shroud body (18) in the axial direction (44) at the midpoint (20).