WO2019035800A1

WO2019035800A1 - Turbine blades

Info

Publication number: WO2019035800A1
Application number: PCT/US2017/046686
Authority: WO
Inventors: Taylor HYNDS; Ali Akturk; Jose L. Rodriguez; David Monk; Krishan Mohan
Original assignee: Siemens Aktiengesellschaft
Priority date: 2017-08-14
Filing date: 2017-08-14
Publication date: 2019-02-21

Abstract

A blade tip (30) for a turbine blade (1) includes a tip cap (32) disposed over an airfoil outer wall (12) and at least one squealer tip wall (34, 36) extending radially outward of the tip cap (32) and extending along a chord-wise direction of the airfoil (10). The at least one squealer tip wall (34, 36) includes laterally opposed first (34a, 36a) and second (34b, 36b) side faces. In relation to a radial axis (40), the first (34a, 36a) and second (34b, 36b) side faces of the at least one squealer tip wall (34, 36) are oriented at respective angles which vary independently along the chord-wise direction. Thereby, the chord-wise variation of a first angle (α34, α36) between the first side face (34a, 36a) and the radial axis (40) is different from the chord-wise variation of a second angle (β34, β36) between the second side face (34b, 36b) and the radial axis (40).

Description

TURBINE BLADES

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] In a turbomachine, such as a gas turbine engine, air is pressurized in a compressor section and then mixed with fuel and burned in a combustor section to generate hot combustion gases. The hot combustion gases are expanded within a turbine section of the engine where energy is extracted to power the compressor section and to produce useful work, such as turning a generator to produce electricity. The hot combustion gases travel through a series of turbine stages within the turbine section. A turbine stage may include a row of stationary airfoils, i.e., vanes, followed by a row of rotating airfoils, i.e., turbine blades, where the turbine blades extract energy from the hot combustion gases for providing output power.

[0003] Typically, a turbine blade is formed from a root at one end, and an elongated portion forming an airfoil that extends outwardly from a platform coupled to the root. The airfoil comprises a tip at a radially outward end, 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.

SUMMARY [0004] Briefly, aspects of the present invention provide a turbine blade with an improved squealer tip design.

[0005] According to a first embodiment of the invention, a turbine blade is provided. The turbine blade 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 blade further comprises a blade tip at a first radial end and a root at a second radial end opposite the first radial end for supporting the blade and for coupling the blade to a disc. The blade tip comprises a tip cap disposed over the outer wall of the airfoil, and at least one squealer tip wall extending radially outward of the tip cap and extending along a chord-wise direction of the airfoil. The at least one squealer tip wall comprises laterally opposed first and second side faces. In relation to a radial axis, the first and second side faces of the at least one squealer tip wall are oriented at respective angles which vary independently along the chord-wise direction, such that the chord-wise variation of a first angle between the first side face and the radial axis is different from the chord-wise variation of a second angle between the second side face and the radial axis.

[0006] According to a second embodiment of the invention, a turbine blade is provided. The turbine blade 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 blade further comprises a blade tip at a first radial end and a root at a second radial end opposite the first radial end for supporting the blade and for coupling the blade to a disc. The blade tip comprises a tip cap disposed over the outer wall of the airfoil and a pair of squealer tip walls extending radially outward of tip cap and extending along a chord-wise direction of the airfoil. The pair of squealer tip walls includes a pressure side squealer tip wall and a suction side squealer tip wall, wherein a tip cavity is located between the pressure side squealer tip wall and the suction side squealer tip wall. Each squealer tip wall comprises an inner side face facing the tip cavity and an outer side face laterally opposite to the inner side face. For each squealer tip wall, the inner side face and the outer side face are oriented at respective angles in relation to a radial axis which vary independently along the chord-wise direction, such that the chord-wise variation of an inner angle between the inner side face and the radial axis is different from the chord-wise variation of an outer angle between the outer side face and the radial axis.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0010] FIG. 3 is a perspective view of a portion of a turbine blade with a squealer tip according to one embodiment of the present invention; [0011] FIG. 4, FIG. 5 and FIG. 6 are schematic cross-sectional views along the sections IV-IV, V-V and VI- VI respectively of FIG. 3, illustrating a chord -wise variation of inclination of the inner and outer side faces of the squealer tip walls of the squealer tip; and

[0012] FIG. 7 is a schematic view of an alternate embodiment of the present invention involving stepped squealer geometry.

DETAILED DESCRIPTION

[0013] In the following detailed description of the preferred embodiment, 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.

[0014] Referring to the drawings wherein identical reference characters denote the same elements throughout the various views, FIG. 1 illustrates a turbine blade 1. The blade 1 includes a generally hollow airfoil 10 that extends radially outwardly from a blade platform 6 and into a stream of a hot gas path fluid. A root 8 extends radially inward from the platform 6 and may comprise, for example, a conventional fir-tree shape for coupling the blade 1 to a rotor disc (not shown). 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, defining a camber line 29. The airfoil 10 extends from the root 8 at a radially inner end to a tip 30 at a radially outer 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 may comprise at least one internal cavity 28 defined between an inner surface 14a of the pressure sidewall 14 and an inner surface 16a 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 8. Within the internal cavity 28, the coolant may flow in a generally radial direction, absorbing heat from the inner surfaces 14a, 16a of the pressure and suction sidewalls 14, 16, before being discharged via external orifices 17, 19, 37, 38 into the hot gas path.

[0015] Particularly in high pressure turbine stages, the tip 30 may be formed as a so-called "squealer tip". Referring jointly to FIG. 1-2, the blade tip 30 may be formed of a tip cap 32 disposed over the outer wall 12 at the radially outer end of the outer wall 12, and at least one squealer tip wall extending radially outward from the tip cap 32. In the shown configuration, a pair of squealer tip walls 34, 36 are provided, including a pressure side squealer tip wall 34 and a suction side squealer tip wall 36. The pressure and suction side squealer tip walls 34 and 36 may extend substantially or entirely along the perimeter of the tip cap 32 to define a tip cavity 35 between an inner surface 34a of the pressure side squealer tip wall 34 and an inner surface 36a of the suction side squealer tip wall 36. An outer surface 34b of the pressure side squealer tip wall 34 may be aligned with an outer surface 14b of the pressure sidewall 14, while an outer surface 36b of the suction side squealer tip wall 36 may be aligned with an outer surface 16b of the suction sidewall 16. The blade tip 30 may additionally include a plurality of cooling holes 37, 38 that fluidically connect the internal cavity 28 with an external surface of the blade tip 30 exposed to the hot gas path fluid. In the shown example, the cooling holes 37 are formed through the pressure side squealer tip wall 34 while the cooling holes 38 are formed through the tip cap 32 opening into the tip cavity 35. Additionally or alternately, cooling holes may be provided at other locations at the blade tip 30. [0016] In operation, pressure differences between the pressure side and the suction side of the turbine blade 1 may drive a leakage flow F_L from the pressure side to the suction side through the clearance between the rotating blade tip 30 and the surrounding stationary turbine component (not shown). The leakage flow F_L may lead to a reduction in efficiency of the turbine rotor. There are two primary causes of such an efficiency loss: first, the tip leakage flow F_L exerts no work on the blade, thus reducing the power generated; second, the tip leakage flow F_L may mix with the main flow F_M of the gas path fluid (which is generally along an axial direction) as it exits the clearance gap, rolling up into a vortical structure V (see FIG. 2). The vortical structure V, referred to as tip leakage vortex, results in a pressure loss and a further reduction in rotor efficiency. Configuring the tip of the blade as a squealer with one or more squealer tip walls 34, 36 may mitigate some of the issues related to tip leakage flow. Typically, the squealer tip walls 34, 36 have a rectangular cross-section, as shown in FIG. 2, wherein the laterally opposed side faces of the squealer tip walls are essentially parallel to each other. Embodiments of the present invention are aimed at further improving tip leakage losses by providing a novel squealer geometry incorporating squealer tip walls with variably inclined inner and outer side faces.

[0017] FIG. 3-6 illustrate an exemplary embodiment of the present invention. For the sake of simplicity, in relation to the configuration shown in FIG. 1-2, similar or equivalent elements are designated by like reference characters in FIG. 3-6. As shown, the exemplary blade tip 30 comprises a tip cap 32 disposed over the outer wall 12, and at least one squealer tip wall, in this case, a pair of squealer tip walls 34, 36 which are configured as winglets. The tips walls or winglets 34, 36 include a pressure side squealer tip wall or winglet 34 and a suction side squealer tip wall or winglet 36, each extending radially outward of the tip cap 32 and extending along a chord-wise direction of the airfoil 10. A tip cavity 35 is located between the pressure side squealer tip wall 34 and the suction side squealer tip wall 36. [0018] As shown in FIG. 4-6, the pressure side squealer tip wall or winglet 34 comprises an inner side face 34a facing the tip cavity 35 and an outer side face 34b laterally opposite to the inner side face 34a, the lateral direction being defined from the pressure side to the suction side. The inner side face 34a and the outer side face 34b are oriented at respective angles in relation to a radial axis 40, which vary independently along the chord-wise direction. The cross-sectional views in FIG. 4-6 are taken at different chord-wise locations. As seen therein, the chord-wise variation of an inner angle a₃₄ between the inner side face 34a and the radial axis 40 is different from the chord-wise variation of an outer angle β₃₄ between the outer side face 34b and the radial axis 40. Consequently, the angle between the inner and outer side faces 34a, 34b varies in the chord-wise direction.

[0019] In addition to or alternate to the above, a chord-wise variation of the inclination of the side faces may be provided for the suction side squealer tip wall 36. As shown in FIG. 4-6, the suction side squealer tip wall or winglet 36 comprises an inner side face 36a facing the tip cavity 35 and an outer side face 36b laterally opposite to the inner side face 36a. The inner side face 36a and the outer side face 36b are oriented at respective angles in relation to a radial axis 40, which vary independently along the chord-wise direction. As seen from the cross-sectional views of FIG. 4-6, the chord-wise variation of an inner angle a₃₆ between the inner side face 36a and the radial axis 40 is different from the chord- wise variation of an outer angle β₃₆ between the outer side face 36b and the radial axis 40. Consequently, the angle between the inner and outer side faces 36a, 36b varies in the chord- wise direction.

[0020] Thus, as illustrated in FIG. 4-6, across different sectional planes (parallel to the radial axis) spaced along the chord-wise direction, the angle between the inner side face 34a, 36a and the respective outer side face 34b, 36b of the pressure side squealer tip wall 34 and/or the suction side squealer tip wall 36 varies. The underlying idea of the illustrated embodiments is to address the above-described problems associated with tip leakage flow by providing for an independent chord-wise variation of the inclination angles on the inner side face and outer side face of one or more of the squealer tip walls 34, 36. The present inventors have recognized that by increasing the tip inclination in areas of high leakage flow, the flow is redirected away the blade, creating a blockage in the tip region which reduces the mass of leakage flow. The inventors also recognized, however, that it is not necessary or effective to maintain this inclination over the entire extent of the squealer tip. Accordingly, introducing a chord-wise variation in the tip shape along with independent variation in the inner and outer side face inclination angles allows for a more efficient blade tip design. [0021] In a further variant, as illustrated in FIG. 7, the blade tip 30 may be provided with a step feature adjoining the tip cavity 35. As shown, the step feature may include a radially outward step 64, 66 located respectively at either or both of the pressure side edge 44 and the suction side edge 46 of the tip cap 32. In this case, the winglets, respectively the pressure side squealer tip wall 34 and the suction side squealer tip wall 36 may be disposed on the steps 64, 66, extending radially outward of the tip cap 32. The steps 64, 66 may extend chord-wise direction along a portion or the entire chord-wise extent of the winglets 34, 36. In this embodiment, analogous to the previously described embodiment, in relation to a radial axis 40, the first 34a, 36a and second 34b, 36b side faces of the winglets 34, 36 are oriented at respective angles which vary independently along the chord-wise direction. Thereby, the chord-wise variation of a first angle a₃₄, a₃₆ between the first side face 34a, 36a and the radial axis 40 is different from the chord-wise variation of a second angle β₃₄, β₃₆ between the second side face 34b, 36b and the radial axis 40. Advantageously, the steps 64, 66 may be provided with film cooling channels (not shown). [0022] The chord-wise variation of the tip shape may result in a chord-wise variation of the thickness t₃₄, t₃₆ of the squealer tip walls 34, 36 at the radial ends thereof, as shown in FIG. 4-6 and FIG. 7. In an exemplary embodiment, a larger angle of inclination/ squealer tip wall thickness may be provided in regions where a high tip leakage flow has been identified. In the depicted examples, the chord-wise varying inclination of the inner and outer side faces is provided along the entire axial length (from the leading edge to the trailing edge) of both the pressure side squealer tip wall 34 and the suction side squealer tip wall. In alternate embodiments, such a variable inclination of the inner and outer side faces may be provided only for a designated portion extending partially along the axial length of one or both of the squealer tip walls 34, 36. In one embodiment, the inner angles a₃₄, ₃₆ and the outer β₃ , β₃₆ may independently vary from about - 45 degrees to about + 75 degrees along the chord- wise direction. In the context of this specification, an inclination of any squealer tip wall side face 34a-b. 36a-b away from the tip cavity 35 (outward in a direction away from the blade) is referenced as a positive angle, while an inclination toward the tip cavity 35 (inward toward the camber line) is referenced as a negative angle. The precise geometry of the squealer tip walls 34, 36, including the inclination angles, and/or chord-wise/axial extent of the variation may be determined based on a number of factors, including for example, size of the tip gap, inlet flow conditions (e.g., Mach number), size of the airfoil, among others. An optimized tip shape reduces leakage mass flow over the tip surface, which, in turn, reduces pressure loss and strength of the tip leakage vortex, thus increasing rotor efficiency. [0023] Although the illustrated embodiments depict a blade tip 30 with two squealer tip walls, namely a pressure side squealer tip wall 34 and a suction side squealer tip wall 36 having chord-wise variably inclined side faces, aspects of the present invention may apply to a squealer tip design with only one squealer tip wall. In one example, only a pressure side squealer tip wall 34 may be provided in accordance with embodiments of the present invention, while suction side squealer tip wall 36 may be omitted, and optionally, replaced at least partially by other tip leakage control features.

[0024] Furthermore, although not shown, the blade tip 30 may also comprise cooling holes or channels provided in one or both of the squealer tip walls 34, 36, which are in fluid communication with an internal cooling system within the airfoil. The illustrated blade tip shaping may make efficient use of the cooling flow by controlling the trajectory of the tip leakage flow. Simultaneous optimization of the tip shape and the cooling hole/channel location may thus make use of the change of tip flow trajectory to cool the blade tip, allowing reduced cooling flow, improved engine efficiency and increased component lifetime.

[0025] Thus, in contrast to the known type of squealer tips having rectangular geometry of the squealer tip walls, the illustrated embodiments of the squealer tip may be adapted to redirect leakage flow and mitigate leakage losses, as well as enhance the heat transfer performance for a given engine application. [0026] 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),

a blade tip (30) at a first radial end and a root (8) at a second radial end opposite the first radial end for supporting the blade (1) and for coupling the blade (1) to a disc,

wherein the blade tip (30) comprises:

a tip cap (32) disposed over the outer wall (12) of the airfoil (10), and at least one squealer tip wall (34, 36) extending radially outward of the tip cap (32) and extending along a chord-wise direction of the airfoil (10), the at least one squealer tip wall (34, 36) comprising laterally opposed first (34a, 36a) and second (34b, 36b) side faces,

wherein in relation to a radial axis (40), the first (34a, 36a) and second

(34b, 36b) side faces of the at least one squealer tip wall (34, 36) are oriented at respective angles which vary independently along the chord-wise direction, such that the chord-wise variation of a first angle (α₃₄, a₃₆) between the first side face (34a, 36a) and the radial axis (40) is different from the chord-wise variation of a second angle (β₃₄, β₃₆) between the second side face (34b, 36b) and the radial axis (40).

2. The turbine blade (1) according to claim 1, wherein the first (a₃₄, a₃₆) and second angles (β₃₄, β₃₆) independently vary from about - 45 degrees to about + 75 degrees along the chord-wise direction.

3. The turbine blade (1) according to claim 1, wherein the chord -wise variation of the first (a₃₄, a₃₆) and second angles (β₃₄, β₃₆) is provided for a designated portion extending at least for a partial axial length of the turbine blade (1).

4. The turbine blade (1) according to claim 3, wherein the chord -wise variation of the first (a₃₄, a₃₆) and second angles (β₃₄, β₃₆) extends for the entire axial length of the turbine blade (1).

5. The turbine blade (1) according to claim 1, wherein a thickness (t₃₄, t₃₆) of the at least one squealer tip wall (34, 36) at a radial end of said squealer tip wall (34, 36) varies in the chord-wise direction.

6. A turbine blade (1) comprising:

wherein the blade tip (30) comprises:

a tip cap (32) disposed over the outer wall (12) of the airfoil (10), and a pair of squealer tip walls (34, 36) extending radially outward of the tip cap (32) and extending along a chord-wise direction of the airfoil (10), the pair of squealer tip walls including a pressure side squealer tip wall (34) and a suction side squealer tip wall (36), wherein a tip cavity (35) is located between the pressure side squealer tip wall (34) and the suction side squealer tip wall (36),

wherein each squealer tip wall (34, 36) comprises an inner side face (34a, 36a) facing the tip cavity (35) and an outer side face (34b, 36b) laterally opposite to the inner side face (34a, 36a),

wherein, for each squealer tip wall (34, 36), the inner side face (34a, 36a) and the outer side face (34b, 36b) are oriented at respective angles in relation to a radial axis (40) which vary independently along the chord-wise direction, such that the chord-wise variation of an inner angle (α₃₄, a₃₆) between the inner side face (34a, 36a) and the radial axis (40) is different from the chord -wise variation of an outer angle(p₃₄, β₃₆) between the outer side face (34b, 36b) and the radial axis (40).

7. The turbine blade (1) according to claim 6, wherein the inner (a₃₄, a₃₆) and outer (β₃₄, β₃₆) angles independently vary from about - 45 degrees to about + 75 degrees along the chord-wise direction.

8. The turbine blade (1) according to claim 6, wherein the chord -wise variation of the inner (a₃₄, a₃₆) and outer (β₃₄, β₃₆) angles is provided for a designated portion extending at least for a partial axial length of the turbine blade (1).

9. The turbine blade (1) according to claim 8, wherein the chord-wise variation of the inner (a₃₄, a₃₆) and outer (β₃₄, β₃₆) angles extends for the entire axial length of the turbine blade.

10. The turbine blade according to claim 6, wherein a thickness (t₃₄, t₃₆) of the pressure side squealer tip wall (34) and/or the suction side squealer tip wall (36) at a radial end thereof varies in the chord-wise direction.