WO2018063353A1

WO2018063353A1 - Turbine blade and squealer tip

Info

Publication number: WO2018063353A1
Application number: PCT/US2016/054862
Authority: WO
Inventors: Ching-Pang Lee; Gm Salam Azad; Ozgur Bozkurt; Alan A. THRIFT; Todd JOBIN
Original assignee: Siemens Aktiengesellschaft
Priority date: 2016-09-30
Filing date: 2016-09-30
Publication date: 2018-04-05

Abstract

A squealer tip (30) for a turbine blade (1) includes a tip cap (32) disposed over an airfoil outer wall (12), a pressure side tip wall (34) extending radially from the tip cap (32) and aligned with an outer surface (14a) of an airfoil pressure sidewall (14), and a suction side tip wall (36) extending radially from the tip cap (32) and aligned with an outer surface (16a) of an airfoil suction sidewall (16). The tip cap (32), the pressure side tip wall (34) and the suction side tip wall (36) define a tip cavity (35). Contiguous surfaces (34b, 32b, 36b) of the pressure side tip wall (34), the tip cap (32), and the suction side tip wall (36) form a continuous, concave surface defining the tip cavity (35).

Description

TURBINE BLADE AND SQUEALER TIP

BACKGROUND

1. Field

[0001] The present invention relates to turbine blades for gas turbine engines, and in particular to turbine blade tips.

2. Description of the Related Art

[0002] 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.

[0003] Typically, 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. The tip features are often referred to as squealer tips and are frequently incorporated onto the tips of blades to help reduce pressure losses between turbine stages. These features are designed to minimize the leakage between the blade tip and the ring segment. The tip cap, the pressure side tip wall and the suction side tip wall define a tip cavity. Contiguous surfaces of the tip cap, the pressure side tip wall and the suction side tip wall for a continuous, concave surface defining the tip cavity. SUMMARY

[0004] Briefly, aspects of the present invention provide a turbine blade having a squealer with a continuously curved tip cavity.

[0005] According to a first aspect of the invention, a turbine blade is provided, which comprises an airfoil comprising an outer wall formed by a pressure sidewall and a suction sidewall joined at a leading edge and at a trailing edge. The airfoil further comprises a squealer tip at a first radial end and a root at a second radial end generally opposite the first radial end for supporting the blade and for coupling the blade to a disc, and at least one internal cavity forming an internal cooling system. The squealer tip comprises a tip cap disposed over the outer wall, a pressure side tip wall extending radially from the tip cap and being aligned with an outer surface of the pressure sidewall, and a suction side tip wall extending radially from the tip cap and being aligned with an outer surface of the suction sidewall. The tip cap, the pressure side tip wall and the suction side tip wall define a tip cavity. Contiguous surfaces of the pressure side tip wall, the tip cap, and the suction side tip wall form a continuous, concave surface defining the tip cavity.

[0006] According to a second aspect of the invention, a squealer tip is provided for a turbine blade. The squealer tip comprises a tip cap configured to be disposed over a radially outer end of an airfoil outer wall. The squealer tip further comprises a pressure side tip wall and a suction side tip wall. The pressure side tip wall extends radially from the tip cap and is configured to be aligned with an outer surface of an airfoil pressure sidewall. The suction side tip wall extends radially from the tip cap and is configured to be aligned with an outer surface of an airfoil suction sidewall. The tip cap, the pressure side tip wall and the suction side tip wall define a tip cavity. Contiguous surfaces of the pressure side tip wall, the tip cap, and the suction side tip wall form a continuous, concave surface defining the tip cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention. [0008] FIG. 1 is a perspective view of a turbine blade with a squealer tip;

[0009] FIG. 2 is a schematic cross-sectional view along the section II-II of FIG. 1 ;

[0010] FIG. 3 is an enlarged perspective view of a squealer tip of a turbine blade according to a first embodiment of the present invention; [0011] FIG. 4 is a schematic cross-sectional view along the section IV-IV of FIG.

3;

[0012] FIG. 5 is a schematic cross-sectional view of a squealer tip according to a second embodiment of the present invention; and

[0013] FIG. 6 is a schematic cross-sectional view of a squealer tip according to a third embodiment of the present invention.

DETAILED DESCRIPTION

[0014] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

[0015] Referring to the drawings wherein identical reference characters denote the same elements throughout the various views, FIG. 1 illustrates an exemplary turbine blade 1. The turbine blade 1 includes a conventional dovetail 2, which may have any suitable form including tangs that engage with complementary tangs of a dovetail slot in a rotor disc (not shown) for radially retaining the blade 1 to the rotor disc as it rotates during operation of the turbine engine. A blade shank 4 extends radially outwardly from the dovetail 2 and terminates in a platform 6 that projects laterally outwardly from and surrounds the shank 4. A generally hollow airfoil 10 extends radially outwardly from the platform 6 and into a stream of a hot gas path fluid. The airfoil 10 comprises an outer wall 12 which is formed of a generally concave pressure sidewall 14 and a generally convex suction sidewall 16 joined together at a leading edge 18 and at a trailing edge 20. The airfoil 10 extends from a root 26 at a radially inner first end to a tip 30 at a radially outer second end, and may take any configuration suitable for extracting energy from the hot gas stream and causing rotation of the rotor disc. As shown in FIG. 2, the interior of the hollow airfoil 10 comprises at least one internal cavity 28 defined between an inner surface 14b of the pressure sidewall 14 and an inner surface 16b of the suction sidewall 16, to form an internal cooling system for the turbine blade 1. The internal cooling system may receive a coolant, such as air diverted from a compressor section (not shown), which may enter the internal cavity 28 via coolant supply passages typically provided in the blade root 26. Within the internal cavity 28, the coolant may flow in a generally radial direction, absorbing heat from the inner surfaces 14b, 16b of the outer wall 12, before being discharged via external orifices 17, 19, 37, 38 into the hot gas path.

[0016] Particularly in high pressure turbine stages, the tip 30 may be formed as a so-called "squealer tip". Referring jointly to FIGs. 1 -2, the squealer tip 30 may be formed of a tip cap 32, a pressure side tip wall 34 and a suction side tip wall 36. The tip cap 32 is disposed over the outer wall 12 at the radially outer end of the outer wall 12. The pressure and suction side tip walls 34 and 36 extend radially outwardly from the tip cap 32 and may extend partially or entirely along the perimeter of the tip cap 32 to define a tip cavity 35 over a radially outboard surface 32b of the tip cap 32, between an inner surface 34b of the pressure side tip wall 34 and an inner surface 36b of the suction side tip wall 36. An outer surface 34a of the pressure side tip wall 34 may be aligned flush with an outer surface 14a of the pressure sidewall 14, while an outer surface 36a of the suction side tip wall 36 may be aligned flush with an outer surface 16a of the suction sidewall 16.

[0017] The squealer tip 30 may further include a plurality of cooling holes 37, 38 that fluidically connect the internal cavity 28 with an external surface of the squealer tip 30 exposed to the hot gas path fluid. In the shown example, the cooling holes 37 are formed through the pressure side tip wall 34 and are arranged in an array along at least a portion of the perimeter of the pressure side tip wall 34 from the leading edge 18 to the trailing edge 20. The cooling holes 38 are formed through the tip cap 32 and open into the tip cavity 35. The cooling holes 38 are arranged in an array generally parallel to and in close proximity to the suction side tip wall 36, i.e., offset toward the suction side tip wall 36 in relation to an airfoil centerline 29 extending centrally between the pressure and suction sidewalls 14 and 16.

[0018] In FIGs. 1 and 2, the stream-wise or axial hot gas flow is schematically depicted as FA, while the pitch-wise hot gas flow in a direction from the pressure sidewall 14 to the suction sidewall 16 is schematically depicted as FX. The pitch- wise flow FX may also be referred to as leakage flow between the squealer tip 30 and a surrounding stationary shroud 41. The present inventors have recognized that the leakage flow FX passing over the pressure side tip wall 34 and the suction side tip wall 36 may cause circulation vortices VI , V2 at the corners of the tip cavity 35, as shown in FIG. 2. The formation of the vortices VI , V2 result in losses in total pressure leading to a drop in turbine efficiency. Embodiments of the present invention illustrated hereinafter address at least the above mentioned technical problem by providing a squealer tip incorporating a continuously curved tip cavity. [0019] FIGs. 3 and 4 illustrate a first exemplary embodiment of the present invention. As shown therein, an inventive squealer tip 30 includes a tip cap 32 disposed over the airfoil outer wall 12. The squealer tip 30 further includes a pressure side tip wall 34 extending radially from the tip cap 32 and aligned with an outer surface 14a of the pressure sidewall 14, and a suction side tip wall 36 extending radially from the tip cap 32 and aligned with an outer surface 16a of the suction sidewall 16. The tip cap 32 comprises a radially inner surface 32a facing the internal cavity 28 of the airfoil and a radially outer surface 32b facing the tip cavity 35. The pressure side tip wall 34 comprises a laterally outer surface 34a and a laterally inner surface 34b. In this embodiment, the laterally outer surface 34a is aligned flush the outer surface 14a of the pressure sidewall 14, while the laterally inner surface 34b faces the tip cavity 35. Likewise, the suction side tip wall 36 comprises a laterally outer surface 36a, which, in this example, is aligned flush with the outer surface 16a of the suction sidewall 16, and a laterally inner surface 36b facing the tip cavity 35. The tip cap 32, the pressure side tip wall 34 and the suction side tip wall 36 define a tip cavity 35. In particular, as per the exemplary embodiment, contiguous surfaces 34b, 32b, 36b respectively of the pressure side tip wall 34, the tip cap 32, and the suction side tip wall 36 form a continuous, concave surface defining the tip cavity 35. A continuously curved tip cavity, as illustrated herein, minimizes the formation of vortices in the leakage flow FX between the squealer tip 30 and the stationary ring segment 41, due to the smooth transition between the contiguous surfaces 34b, 32b, 36b that define the tip cavity 35, thereby minimizing pressure losses and providing improved turbine efficiency.

[0020] As shown in FIGs. 3 and 4, the pressure side tip wall 34 and the suction side tip wall 36 have respective outboard surfaces 34c, 36c that face radially outward. At least one or preferably both of the pressure side tip wall 34 and the suction side tip wall 36 may be flared radially outwardly, as shown in FIG. 4. In the illustrated embodiment, the radially outboard surface 34c of the pressure side tip wall 34 overhangs laterally over the pressure sidewall 14, while the radially outboard surface 36c of the suction side tip wall 36 overhangs laterally over the suction sidewall 16. The laterally outer surfaces 34a, 36a of the pressure and suction side tip walls 34, 36 may be configured to have a concave shape. In alternate embodiments, one or more of the surfaces 34a, 36a may be configured to be straight or planar. In such a case, the respective planar surface 34a, 36a may be parallel to or inclined with respect to the radial direction R. The flared configuration of the pressure and suction side tip walls 34, 36 provides an effective restriction of the radially outward flow of the hot combustion gases, thereby reducing over-tip leakage and increasing turbine efficiency. The flare may be provided for the entire chord-wise extent of the pressure and suction side tip walls 34, 36 or a portion thereof. The geometry of the flare, for example, the width W of the overhang, may be constant or variable in the chord-wise direction. The chord-wise extent and geometry of the flare on the pressure and suction side tip walls 34, 36 may vary, for example, depending upon the specific turbine blade design and combustion gas flow field over the airfoil tip.

[0021] Referring to FIGs. 3 and 4, the squealer tip 30 may further comprise a plurality of tip cooling holes 38 formed through the tip cap 32 between the pressure side tip wall 34 and the suction side tip wall 36. The tip cooling holes 38 may be fluidically connected to the internal cooling system in the internal cavity 28 of the airfoil. In particular, the tip cooling holes 38 may comprise an array of holes 38 arranged proximate to the suction side tip wall 36. In the present example, the squealer tip further comprises a plurality of film cooling holes 37 formed on the pressure side tip wall 34. The film cooling 37 may also be fluidically connected to the internal cooling system in the internal cavity 28 of the airfoil.

[0022] Several variants of the inventive concept may be conceived. For example, a second embodiment of the present invention is shown in FIG. 5. In contrast to the configuration of FIG. 4, in this case, only one of the tip walls, in this case, the suction side tip wall 36 may be flared radially outwardly. That is to say, the radially outboard surface 36c of the suction side tip wall 36 overhangs laterally over the suction sidewall 16, while such an overhang is not provided in case of the pressure side tip wall 34. As shown, in this case, the laterally outer surface 36a of the suction side tip wall 36 is inclined at an angle with respect to the radial direction R, while the laterally outer surface 34a of the pressure side tip wall 34 is aligned parallel to the radial direction. A third embodiment of the present invention is illustrated in FIG. 6. As per this configuration, in contrast to FIG. 4, each of the pressure side tip wall 34 and the suction side tip wall 36 may be symmetrically flared. That is, each of radially outboard surfaces 34c, 36c overhangs laterally outwardly from the pressure sidewall 14 and the suction sidewall 16 respectively, and further overhangs laterally inwardly over the tip cavity 35. In each case, contiguous surfaces 34b, 32b, 36b of the pressure side tip wall 34, the tip cap 32, and the suction side tip wall 36 form a concave surface to define a continuously curved tip cavity 35. [0023] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.

Claims

1. A turbine blade (1 ) comprising:

an airfoil (10) comprising an outer wall (12) formed by a pressure sidewall (14) and a suction sidewall (16) joined at a leading edge (18) and at a trailing edge (20), the airfoil (10) further comprising a squealer tip (30) at a first radial end and a root (26) at a second radial end generally opposite the first radial end for supporting the blade (1) and for coupling the blade (1 ) to a disc, and at least one internal cavity (28) forming an internal cooling system;

wherein the squealer tip (30) comprises:

a tip cap (32) disposed over the outer wall (12),

a pressure side tip wall (34) extending radially from the tip cap (32) and being aligned with an outer surface (14a) of the pressure sidewall (14),

a suction side tip wall (36) extending radially from the tip cap (32) and being aligned with an outer surface (16a) of the suction sidewall (16),

wherein the tip cap (32), the pressure side tip wall (34) and the suction side tip wall (36) define a tip cavity (35), and

wherein contiguous surfaces (34b, 32b, 36b) of the pressure side tip wall (34), the tip cap (32), and the suction side tip wall (36) form a continuous, concave surface defining the tip cavity (35).

2. The turbine blade (1) according to claim 1 , wherein at least one of the pressure side tip wall (34) and the suction side tip wall (36) is flared radially outwardly.

3. The turbine blade (1) according to claim 2, wherein a respective radially outboard surface (34c, 36c) of the flared pressure side tip wall (34) or the flared suction side tip wall (36) overhangs laterally outwardly from a respective one of the pressure sidewall (14) and the suction sidewall (16).

4. The turbine blade (1) according to any of claims 2 and 3, wherein only the suction side tip wall (36) is flared radially outwardly.

5. The turbine blade (1) according to any of claims 2 and 3, wherein both the pressure side tip wall (34) and the suction side tip wall (36) are flared radially outwardly.

6. The turbine blade (1) according to claim 2, wherein a radially outboard surface (34c, 36c) of the flared pressure side tip wall (34) or the flared suction side tip wall (36) overhangs laterally outwardly from a respective one of the pressure sidewall (14) and the suction sidewall (16), and further overhangs laterally inwardly over the tip cavity (35)

7. The turbine blade (1) according to claim 1, wherein the pressure side tip wall (34) has a first laterally outer surface (34a) disposed flush with the outer surface (14a) of the pressure sidewall (14) and the suction side tip wall (36) has a second laterally outer surface (36a) disposed flush with the outer surface (16a) of the suction sidewall (16).

8. The turbine blade (1) according to claim 7, wherein at least one of the first (34a) and second (36a) laterally outer surfaces is concave.

9. The turbine blade (1) according to claim 7, wherein at least one of the first (34a) and second (36a) laterally outer surfaces is planar.

10. The turbine blade (1) according to claim 9, wherein said at least one of the first (34a) and second (36a) laterally outer surfaces is parallel to a radial direction.

11. The turbine blade (1) according to claim 9, wherein said at least one of the first (34a) and second (36a) laterally outer surfaces is inclined to a radial direction.

12. The turbine blade (1) according to claim 1, further comprising a plurality of tip cooling holes (38) formed through the tip cap (32) between the pressure side tip wall (34) and the suction side tip wall (36), the tip cooling holes (38) being fluidically connected to the internal cavity (28).

13. The turbine blade (1) according to claim 12, wherein the tip cooling holes (38) are positioned proximate to the suction side tip wall (36).

14. The turbine blade (1) according to claim 1 , further comprising a plurality of film cooling holes (37) formed on the pressure side tip wall (34), the film cooling (37) being fluidically connected to the internal cavity (28)

15. A squealer tip (30) for a turbine blade (1), comprising:

a tip cap (32) configured to be disposed over a radially outer end of an airfoil outer wall (12),

a pressure side tip wall (34) extending radially from the tip cap (32) and configured to be aligned with an outer surface (14a) of an airfoil pressure sidewall (14),

a suction side tip wall (36) extending radially from the tip cap (32) and configured to be aligned with an outer surface (16a) of an airfoil suction sidewall (16),