COOLED TURBINE BLADE TIP SHROUD WITH FILM/PURGE HOLES

Abstract

A cooled turbine blade shroud with purge holes located proximate regions of the tip shroud cooling cavity that experience cooling air flow recirculation or stagnation. The purge holes may be oriented radially from the cooling cavity to a surface, such as the outer top surface and/or inner/bottom surface, of the tip shroud, and may provide improved heat transfer and consequent cooling and enhanced tip shroud life.

Description

TECHNICAL FIELD

The subject matter disclosed herein relates generally to gas turbine engines, and, more specifically, to a gas turbine engine rotor blade having improved tip cooling, and more specifically to a turbine blade having a cooled tip shroud.

BACKGROUND OF THE INVENTION

A gas turbine engine includes one or more turbine blade rows, or stages, each row or stage having buckets or blades which project radially outwardly into the hot combustion gas path of the turbine, and disposed downstream of the combustor, which stages extract energy from the combustion gases generated by the combustor. Disposed radially outwardly of the rotor blade tips may be a stator shroud which is spaced from the blade tips to provide a relatively small clearance between the blade tips and shroud for reducing leakage of the combustion gases over the blade tips during operation. Each of the rotor blades includes conventionally known pressure and suction sides which are preferentially aerodynamically contoured for extracting as much energy as possible from the combustion gases flowing over the rotor blades. The pressure and suction sides extend to the blade tip and are disposed as close as possible to the stator shroud for maximizing the amount of energy extracted from the combustion gases. The clearance gap, however, between the blade tips and the stator shroud must nevertheless be adequate to minimize the occurrence of blade tip rubs during operation, which may damage the blade tips.

The efficiency of the turbine assembly is limited in part by “spillover:” the escape of hot combustion gases through the clearance gap between the turbine blade and the wall of the turbine assembly, which is commonly referred to as the turbine shroud. To reduce spillover, it is a common practice in the art to provide a tip shroud on the end of the airfoil opposite the end attached to the rotating shaft. The tip shroud includes a shelf and, optionally, one or more blade teeth that reduces spillover by decreasing the size of the clearance gap and interrupting the hot gas path around the end of the turbine blade.

Tip shrouds are subject to creep damage due to the combination of high temperature and centrifugally induced bending stresses. The creep is usually manifested by the formation of “dog ears” along unsupported edges of the shelf formed by the tip shroud. “Dog ears” as used herein, means the folding or degrading of the metal edges of the shelf formed by the tip shroud. Because it has been generally found that reinforcing the shelf simply transfers the stress from tip shroud to the root of the airfoil, the approach to reducing creep in this region of the turbine blade has been to “scallop” i.e., remove unsupported portions of the shelf. Scalloping, however, leads to increased hot gas path leakage past the turbine blade. If the tip shroud and shelf could be adequately cooled, the need to scallop the shelf could be substantially reduced. Consequently spillover would also be reduced and turbine efficiency could be improved.

One approach to cooling the tip shroud involves providing in the shroud tip an internal cooling cavity defining primary cooling flow passages through which cooling air flows and exits proximate the tip shroud edges (i.e. slashface). Inherent in such internal cooling cavities, however, are regions which are susceptible to flow recirculation or stagnation, which can cause localized hot spots in that region of the tip shroud.

BRIEF DESCRIPTION OF THE INVENTION

These and other features of the present disclosure will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the drawings and the appended claims.

According to one embodiment of the disclosure, there is provided a turbine blade comprising a blade attachment portion; a radially extended turbine airfoil integral with the blade attachment portion, the turbine airfoil comprising one or more internal cooling passages; a tip shroud affixed to a top portion of the airfoil, the tip shroud comprising an internal cooling cavity in communication with the one or more internal cooling passages, the internal cooling cavity comprising at least one high velocity region and at least one low velocity region, the regions configured to pass cooling air therethrough; at least one exit port in communication with the internal cooling cavity configured to exhaust spent cooling air from the at least one high velocity region; and at least one purge hole in communication with the internal cooling cavity configured to exhaust spent cooling air from the at least one low velocity region.

According to another embodiment of the disclosure, there is provided a method of cooling a turbine blade shroud tip comprising providing a turbine blade comprising a radially extended turbine airfoil comprising one or more internal cooling passages; providing a tip shroud affixed to a top portion of the airfoil, the tip shroud comprising an internal cooling cavity in communication with the one or more internal cooling passages, the internal cooling cavity comprising at least one high velocity region and at least one low velocity region; passing cooling air through the one or more internal cooling passages and the internal cooling cavity; exhausting spent cooling air through at least one exit port in communication with the at least one high velocity region; and exhausting spent cooling air through at least one purge hole in communication with the at least one low velocity region.

According to another embodiment of the invention, there is provided a tip shroud configured for being disposed at the tip portion of an airfoil, comprising an internal cooling cavity, the internal cooling cavity comprising a plurality of high flow velocity regions and a plurality of low flow velocity regions, the regions configured to pass cooling air therethrough; at least one exit port in communication with each high flow velocity region configured to exhaust spent cooling air therefrom to a side edge of the tip shroud; and at least one purge hole in communication with each low flow velocity region configured to exhaust spent cooling air therefrom to a top or bottom surface of the tip shroud.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an embodiment of the disclosure.

FIG. 2 is an isometric plan view of a portion of a tip shroud of the disclosure.

FIG. 3 is an isometric plan view of a portion of a tip shroud of the disclosure.

FIG. 4 is a cross sectional view of the embodiment of FIG. 1 taken along lines E-E.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring now to FIGS. 1 and 4, there is illustrated a turbine blade or airfoil, 10, with an associated radially outer tip shroud 12. The airfoil 10 may have an inboard, or pressure side face 11, and an outboard, or suction side face 13. The airfoil 10 may further include a first set of internal, radially extending cooling channels generally designated as 14 along and proximate the leading edge 16 of the airfoil 10. Similarly, a second set of internal radially extending cooling channels generally designated 18 may be arranged along and proximate the airfoil trailing edge 20. Both sets of cooling channels 14, 18 may extend radially outwardly into the tip shroud 12 and, specifically, pass cooling air represented by the arrows D to a common, relatively large but shallow chamber, plenum, or internal tip shroud cavity 22, which may serve as an internal cooling chamber for the tip shroud 12.

As illustrated in FIGS. 1, 2 and 4, the internal tip shroud cavity 22 may comprise a central plenum 23 flowably connected to a number of interconnected primary cooling cavities 24 by a number of connecting passages 26. As illustrated, the interconnected primary cooling cavities 24 may comprise a substantially serpentine configuration, and may comprise one set of interconnected primary cooling cavities 24 disposed outwardly relative to the inboard face 11 of the airfoil 10, and another set of interconnected primary cooling cavities 24 disposed outwardly relative to the outboard face 13 of the airfoil 10.

The internal tip shroud cavity 22 may be of conventional design, for example, as illustrated and described in Brittingham, et al., U.S. Publication No. US2008/0170946A1. The internal tip shroud cavity 22 may extend across the tip shroud 12 substantially from front to back and side to side, within the plane of the tip shroud 12. As illustrated in FIG. 2, the tip shroud cavity 22 may be supported in the spaces 17 by one or more ribs (not shown), represented by the bold boundary line 19. These ribs may be of conventional design, and may, in addition to defining the interconnected primary cooling cavities 24, assist in supporting the bottom and top sides of the tip shroud 12. Such structural support may be critical to tip shroud life, as the tip shroud 12 may be heavily stressed due to rotational forces and thermal stresses.

The internal tip shroud cavity 22 may be created in the tip shroud 12 by a ceramic core and formed during the investment casting process. This core may be held in place by one or more tabs extending out the edges 28 of the tip shroud 12. Spent cooling air may exit into the hot gas path from the interconnected primary cooling cavities through exit channels 30 that lead to exit holes 32 in the tip shroud edges or slash face 28.

As further illustrated in FIG. 2, the internal tip shroud cavity 22 may include high flow velocity regions 25, the boundaries of which, in exemplary fashion, are represented by the dotted boundary line 27. The internal tip shroud cavity 22 may further include low flow velocity regions 34, the boundaries of which, in exemplary fashion, are represented by the dotted boundary line 35 in FIGS. 2 and 4. As illustrated In FIG. 2, the low flow velocity regions 34 may be elongated and/or may include a narrower end region 42 that may transition to a relatively wider opposing end region 44, although other configurations for both the high flow velocity regions 25 and low flow velocity regions 34 are possible depending upon tip shroud cavity geometry.

It is believed that cooling air flows through the internal tip shroud cavity 22 at a higher velocity in high flow velocity regions 25, than through low flow velocity regions 34, in part because such high flow velocity regions 25 may exhaust spent cooling air along primary flow paths through the relatively large exit holes 32 in the shroud edges 28, as represented by the arrows A. Indeed, it is believed that the low flow velocity regions 34, because of the tortuous and/or constricted flow path and/or lack of proximal exit holes, experience cooling air flow recirculation and/or stagnation, which may lead to hot spots and premature tip shroud failure. The relatively low air flow through the low flow velocity regions 34 may further be the result of flow moving past what is sometimes referred to as a “bluff” body, for example, the supporting ribs previously described, which may separate the moving air and create a wake recirculation zone, similar to what occurs when air moves over a large blunt obstruction like a vehicle and then separates behind the rear face of the object.

According to the present disclosure, there may be provided one or more purge holes 36 positioned in the low flow velocity regions 34 of the tip shroud 12. The purge holes 36 may be circular, and may be drilled from the outer top surface 38 and/or interior or bottom surface 41 of the tip shroud 12. As illustrated in FIG. 3, the purge holes 36 may include side walls 39 that may be cylindrical, and oriented radially from the internal tip shroud cavity 22 outwardly, as illustrated by the directional arrows B. Other orientations, such as angled or flared purge holes 36 that may be oriented to direct the spent cooling air in the direction of flow of the combustion gas stream (i.e. film cooling), are also possible.

The number and diameter of the purge holes 36 may depend on the design requirements and manufacturing process capability. For example, as illustrated in FIG. 2, the purge holes 36 may be oriented substantially linearly along the low flow velocity region 34. In the embodiment illustrated, the purge holes 36 may be substantially the same size and substantially equally spaced along a line P that may substantially bisect the width of the low flow velocity region 34. Such an orientation may place the purge holes 36 in the vicinity of the low flow velocity region 34 that is the greatest distance from the outer boundaries 40 of adjacent high flow velocity regions 25, where the flow velocity of cooling air may be lowest and stagnation highest absent such purge holes 36. Other orientations are possible, including, for example, a matrix of purge holes, particularly for larger areas of low flow velocity, and/or purge holes that follow a substantially curvilinear path, for low flow velocity areas that are substantially curvilinear.

The purge holes 36 may, as illustrated in FIGS. 1-3 be substantially the same size and/or substantially equally spaced. Other configurations are of course possible, including purge holes that increase in size and/or number, or decrease in relative spacing, from relatively narrower regions 42 of the low flow velocity region 34 to the relatively wider region 44 of the low flow velocity region 34. Although the purge holes 36 are shown as circular, other configurations, such as elliptical, oval, square, conical, etc., may be employed.

Incorporating purge holes 36 in the low flow velocity regions 34 of the tip shroud 12 may provide for exit of cooling air from the outer top surface 38 and/or bottom surface 41 of the tip shroud 12, also represented by solid line arrows B and dotted line arrows C, respectively, in FIG. 3. This, in turn, may lead to reducing or eliminating stagnation of cooling air in the low flow velocity regions 34, and may increase cooling air velocity through such regions, with resultant increase in the local heat transfer coefficient due to flow acceleration around the entrance 37 of the purge holes 36, and therefore increased cooling of the tip shroud 12 proximate such regions. This improved heat transfer, in turn, may reduce localized metal temperatures of the tip shroud 12, thereby enhancing part durability.

Furthermore, the incorporation of purge holes 36 may result in exiting film flow of spent cooling air, which may in turn, cause a reduction in external film temperature proximate the outer top surface 38 and/or bottom surface 41 of the tip shroud, which may also enhance part durability.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided below, unless specifically indicated. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/ or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/ or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any, and all, combinations of one or more of the associated listed items. As used herein, the phrases “coupled to” and “coupled with” as used in the specification and the claims contemplates direct or indirect coupling.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person of ordinary skill in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The steps recited in the accompanying method claims need not be taken in the recited order, where other orders of conducting the steps to achieve the desired result would be readily apparent to those of ordinary skill in the art. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A turbine blade comprising:

a blade attachment portion;

a radially extended turbine airfoil integral with said blade attachment portion, said turbine airfoil comprising one or more internal cooling passages;

a tip shroud proximate a top portion of said turbine airfoil, said tip shroud comprising an internal cooling cavity in communication with said one or more internal cooling passages, said internal cooling cavity comprising at least one high velocity region and at least one low velocity region, said at least one high velocity region and at least one low velocity region configured to pass cooling air therethrough;

at least one exit port in communication with said internal cooling cavity configured to exhaust spent cooling air from said at least one high velocity region; and

at least one purge hole in communication with said internal cooling cavity configured to exhaust spent cooling air from said at least one low velocity region.

2. The turbine blade of claim 1 wherein said at least one exit port exits through a shroud edge of said tip shroud.

3. The turbine blade of claim 1 wherein said at least one purge hole exits through an outer top surface and/or bottom surface of said tip shroud.

4. The turbine blade of claim 1 comprising a plurality of said at least one low velocity regions and at least one of said at least one purge hole in communication with each said at least one low velocity region and an outer top surface and/or inner surface of said tip shroud.

5. The turbine blade of claim 4 comprising a plurality of said at least one high velocity regions and at least one said at least one exit port in communication with each said at least one high velocity region.

6. The turbine blade of claim 5 wherein each said purge hole exits through an outer top portion and/or bottom portion of said tip shroud and each said at least one exit port exits through a shroud edge of said tip shroud.

7. A method comprising:

providing a turbine blade comprising a radially extended turbine airfoil comprising one or more internal cooling passages;

providing a tip shroud affixed to a top portion of said airfoil, said tip shroud comprising an internal cooling cavity in communication with said one or more internal cooling passages, said internal cooling cavity comprising at least one high velocity region and at least one low velocity region, both said at least one high velocity region and at least one low velocity region configured to pass cooling air therethrough;

passing cooling air through said one or more internal cooling passages and said internal cooling cavity;

exhausting spent cooling air through at least one exit port in communication with said at least one high velocity region; and

exhausting spent cooling air through at least one purge hole in communication with said at least one low velocity region.

8. The method of claim 7 wherein exhausting spent cooling air through said at least one exit port further comprises exhausting said spent cooling air through an exit of said at least one exit port on a shroud edge of said tip shroud.

9. The method of claim 7 wherein exhausting spent cooling air through said at least one purge hole further comprises exhausting said spent cooling air through an exit of said at least one purge hole on an outer top surface and/or inner surface of said tip shroud.

10. The method of claim 7 further comprising providing a plurality of said at least one low velocity regions and further providing at least one said purge hole in communication with each said at least one low velocity region and an outer top surface and/or inner surface of said tip shroud.

11. The method of claim 10 further comprising providing a plurality of said at least one high velocity regions and at least one of said at least one exit port in communication with each said at least one high velocity region.

12. The method of claim 11 further comprising exhausting spent cooling air from an exit of each said at least one purge hole through a top portion and/or bottom portion of said tip shroud and exhausting said cooling air from an exit of each said at least one exit port through a shroud edge of said tip shroud.

13. A tip shroud configured for being disposed at a tip portion of an airfoil, comprising an internal cooling cavity, said internal cooling cavity comprising a plurality of high flow velocity regions and a plurality of low flow velocity regions, each of said plurality of low flow velocity regions configured to pass cooling air therethrough; at least one exit port in communication with each said at least one of the plurality of high flow velocity regions configured to exhaust spent cooling air therefrom to a side edge of said tip shroud; and at least one purge hole in communication with each said at least one low flow velocity region configured to exhaust spent cooling air therefrom to an outer top surface and/or bottom surface of said tip shroud.

14. The tip shroud of claim 13 wherein at least one of said plurality of low flow velocity regions is substantially elongated, and comprises a plurality of said at least one purge hole disposed therealong.

15. The tip shroud of claim 14 wherein said at least one purge hole are disposed substantially linearly along said plurality of low flow velocity regions.

16. The tip shroud of claim 15 wherein said at least one purge hole is disposed substantially along a line substantially bisecting a width of said plurality of low flow velocity regions.

17. The tip shroud of claim 13 wherein at least one of said plurality of low flow velocity regions comprises a narrow end transitioning to a wider opposing end.

18. The tip shroud of claim 17 comprising a plurality of said at least one purge hole wherein said at least one purge hole increase in size from said narrow end to said wider opposing end.

19. The tip shroud of claim 17 wherein said at least one purge hole decreases in relative spacing from said narrow end to said wider opposing end.

20. The tip shroud of claim 13 wherein at least one of said plurality of low flow velocity regions includes a plurality of said at least one purge hole disposed in a matrix configuration.