COOLED BLADE FOR A GAS TURBINE

Info

Publication number: 20120070308
Type: Application
Filed: Sep 16, 2011
Publication Date: Mar 22, 2012
Applicant: ALSTOM Technology Ltd. (Baden)
Inventors: Shailendra Naik (Gebenstorf), Gaurav Pathak (Ennetbaden)
Application Number: 13/234,592

Abstract

A cooled blade for a gas turbine includes an airfoil section which extends in the radial direction of the turbine or in the longitudinal direction of the blade between a platform and a blade tip which is provided with a cap. The airfoil section is bounded transversely with respect to the longitudinal direction by a leading edge and a trailing edge and has a pressure face and a suction face. Cooling channels extend in a radial direction between the platform and the blade tip in an interior of the airfoil section. The cooling channels can be acted upon by a cooling air flow from the platform. The blade tip is cooled by first cooling holes for convection cooling provided on the pressure face of the blade, and second cooling holes for film cooling provided on the suction side of the blade, through the cap of the blade, in the blade tip from the cooling channels, and distributed over the blade width.

Description

Description

RELATED APPLICATIONS

This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2010/053286, which was filed as an International Application on Mar. 25, 2010, designating the U.S., and which claims priority to European Application 09155437.8 filed in Europe on Mar. 18, 2009. The entire contents of these applications are hereby incorporated by reference in their entireties.

FIELD

The present disclosure relates to the field of gas turbine technology, and relates to a cooled blade for a gas turbine.

BACKGROUND INFORMATION

The efficiency of gas turbines can depend on the temperature of hot gas that expands in turbine when performing work. In order to be able to raise the efficiency, the components (stator blades, rotor blades, heat accumulating segments, etc), should not only be produced from heat resistant materials but should also be cooled as effectively as possible during operation. Known methods for blade cooling can be used alternatively or together. One method is to pass a cooling medium, for example, compressed cooling air, from the gas turbine compressor, through an interior of the blades in cooling channels, and to allow it to emerge into a hot gas channel through cooling holes arranged in a distributed manner. The cooling channels can pass through the interior of the blade more than once in a serpentine shape. See, for example, WO A1 2005/068783). The heat transfer between the cooling medium and walls of the blade can be improved by using suitable elements (turbulators) to produce additional turbulence in the cooling medium flow, or by using impingement cooling. In another method, the cooling medium can emerge from the interior of the blade such that a film of cooling medium is formed on the blade surface, and protects the blade (film cooling).

It is desirable to cool the blade tip. The blade tip is furthest away from the blade root, through which the cooling air is supplied. Attention should therefore be paid to its cooling. Furthermore, cooling that is as uniform as possible should be achieved in all operating states, and the consumption of cooling medium should be restricted to what is appropriate, in order to avoid disadvantageously influencing the efficiency of the machine.

DE A1 199 44 923 discloses a comparatively complex solution for cooling the blade tip.

SUMMARY

A blade for a gas turbine is disclosed, including an airfoil section extending in a radial direction of the turbine or in a longitudinal direction of the blade between a platform and a blade tip, the blade tip being provided with a cap, the airfoil section being bounded transversely with respect to the longitudinal direction by a leading edge and a trailing edge and having a pressure face and a suction face; cooling channels extending substantially in a radial direction between the platform and the blade tip in an interior of the airfoil section, through which cooling channels a cooling medium flows, first cooling holes for convection cooling provided on the pressure face of the blade; second cooling holes for film cooling provided on the suction face of the blade, the first and second cooling holes being arranged in an area of the blade tip and operatively connected to the cooling channels and distributed over the blade width, the cooling medium being passed to an exterior of the area of the cap and/or through the cap of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawings. The drawings show only those elements which are essential for immediate understanding exemplary embodiments of the disclosure. The same elements are provided with the same reference symbols in the various figures, in which:

FIG. 1 shows a cross-sectional profile through an airfoil section of a blade, according to an exemplary embodiment of the disclosure;

FIG. 2a shows an arrangement of cooling holes in a blade tip according to an exemplary embodiment of the disclosure;

FIG. 2b shows in detail some of the film cooling holes at the suction side of the blade according to FIG. 2a;

FIG. 3a shows part of a longitudinal section through the blade of FIG. 2a, wherein the film cooling holes at a pressure side of the blade are in the form of simple cylindrical bores;

FIG. 3b shows part of a longitudinal section through the blade of FIG. 2a, wherein the film cooling holes at the pressure side of the blade exit section of a 2D or 3D fan-shaped form;

FIG. 3c shows an inclination of the film cooling holes at the suction side of the blade according to FIG. 2a;

FIGS. 4a, 4b show different longitudinal sections of the first film cooling holes outside a trailing edge at the pressure side of the blade in FIG. 2a;

FIG. 4c shows a boundary of an exit of the first film cooling holes according to FIG. 4a, 4b;

FIGS. 5a, 5c show different longitudinal sections of the first film cooling holes at the trailing edge at the pressure side of the blade in FIG. 2a; and

FIG. 5b shows a boundary of the exit of the first film cooling holes according to FIGS. 5a, 5c.

DETAILED DESCRIPTION

The disclosure provides a cooled blade for a gas turbine which, for example, provides cooling in the area of the blade tip.

In an exemplary embodiment according to the disclosure, first cooling holes for convection cooling are provided on a pressure face of the blade, and second cooling holes for film cooling are provided on a suction face of the blade, through a cap of the blade, in a blade tip from cooling channels, and distributed over a blade width. The combination of convection cooling on the pressure face and film cooling on the suction face of the blade tip can result in particularly effective and stable cooling without this having any disadvantageous influence on the efficiency.

According to an exemplary embodiment of the disclosure, the first and second cooling holes include at least sections in the form of cylindrical bores with a predetermined first diameter.

The first cooling holes can be in the form of long cylindrical bores which run obliquely upwards and include a first angle of between, for example, 25° and 35° (for example, substantially 30°±10%), with an outer surface of the blade.

According to an exemplary embodiment of the disclosure, the first cooling holes open into an environment of the blade with a fan-shaped section of the bore.

According to an exemplary embodiment of the disclosure, those of the first cooling holes arranged outside the trailing edge of the blade open into the environment of the blade with a 3D symmetric fan-shaped section of the bore, whereby the 3D symmetric fan-shaped section has a first aperture angle having a range of 10° to 50°, for example, about 24°, and a second aperture angle perpendicular to the first aperture angle, the second aperture angle having a range of 5° to 25°, and for example, substantially 12°.

According to an exemplary embodiment of the disclosure, those of the first cooling holes arranged outside the trailing edge of the blade include a second angle of between 15° and 45°, for example, of substantially 30°, with the outer surface of the blade.

According to an exemplary embodiment of the disclosure, those of the first cooling holes arranged at the trailing edge of the blade open into the environment of the blade with a 2D symmetric fan-shaped section of the bore, whereby the 2D symmetric fan-shaped section has a third aperture angle having a range of, for example, 10° to 40°, and for example, substantially 20° (e.g., ±10%)

According to an exemplary embodiment of the disclosure, those of the first cooling holes arranged at the trailing edge of the blade include a third angle of between, for example, 5° and 45°, for example, substantially 30°, with the outer surface of the blade.

According to an exemplary embodiment of the disclosure, those of the first cooling holes arranged at the trailing edge of the blade have a bore of a predetermined first length, which is subdivided into the 2D symmetric fan-shaped section and a cylindrical section of a predetermined second length, whereby the ratio of the second length and the first length is in the range of, for example, 0.2 to 0.7 (for example, substantially 0.5).

According to an exemplary embodiment of the disclosure, the first cooling holes are arranged along the pressure face in a row with a predetermined first periodicity, and the ratio between the first periodicity and the first diameter is in the range of, for example, 3 to 8 (for example, substantially 6).

According to an exemplary embodiment of the disclosure, the second cooling holes pass through the cap of the blade in a radial direction, whereby the second cooling holes can be in the form of long cylindrical bores which run obliquely upwards and include an angle of, for example, 0° to 45° (for example, substantially 30°), with the longitudinal axis of the blade.

According to an exemplary embodiment of the disclosure, the second cooling holes are arranged along the suction face in a row with a predetermined second periodicity, and the ratio between the second periodicity and the first diameter is in the range of, for example, 3 to 8 (for example, substantially 6).

According to an exemplary embodiment of the disclosure, the first cooling holes exit into the environment of the blade at a predetermined height below the upper end of the blade tip, and the ratio between the height and the first diameter is in a range between, for example, 5 and 10 (for example, substantially 6.5).

According to an exemplary embodiment of the disclosure, there are dust holes arranged along the cap between the leading edge and trailing edge, and the dust holes have a second diameter, such that the ratio between the second diameter and the first diameter is between, for example, 1.2 and 4.5.

According to an exemplary embodiment of the disclosure, the cap of the blade is bounded at the edge on its upper face by a circumferential blade crown, and the second cooling holes open into the outside area within the blade crown.

The blade can have a blade crown at the blade tip, which is bounded by a circumferential rail having a predetermined thickness. The width between the opposing rails varies with the distance along the chord line, such that, for example: t/W is between 0.05 and 0.15 for κ/κ0 between 0 and 0.3, and t/W is between 0.15 and 0.3 for κ/κ0 larger than 0.3 and up to 1.0, κ0 being the overall chord line length.

With relation to the blade tip geometry, the following exemplary ratios are preferable in exemplary embodiments:

D/W32 0.1 to 0.3 for κ/κ0 0 to 0.3;

D/W=0.1 to 0.8 for κ/κ0 >0 to 1.0;

whereas D means the depth of the tip crown and W means the width, according FIG. 3a.

The disclosure relates to a cooled gas turbine blade which can be suitable for implementation of the disclosure. The blade (10 in FIGS. 1, 2), which is a rotor blade, has an airfoil section (12 in FIG. 2), which extends in the radial direction of the turbine and extends in the radial direction between a platform (not shown), which bounds the hot gas channel, and a blade tip (11 in FIG. 2). In this case, it should be noted that the following statements are not restricted exclusively to a rotor blade, and they can also relate to a stator blade, to an appropriate extent. The airfoil section 12 has a leading edge 15 and a trailing edge 16 (FIG. 1), and has a (concave) pressure face 17 and a (convex) suction face 18 in the form of an airfoil profile. A blade root (not shown) is formed underneath the platform, and is used to mount the blade 10 in a groove provided for this purpose in the rotor (or, in the case of a stator blade, in the housing surrounding the rotor).

Cooling channels 19a, 19b, 19c and 20 (FIG. 1) are provided through which cooling air flows run in a radial direction in an interior of the airfoil section 12. The cooling air enters the blade 10 as a cooling air flow through appropriate cooling air inlets (not shown) in the blade root. The cooling channels 19a, 19b and 19c are connected to one another by a serpentine-like channel structure. The cooling air flowing through the cooling channels 19a, 19b and 19c cools the blade 10 from the inside and emerges to the outside at different points through cooling holes or cooling openings. The cooling channel 20 can be used to cool the leading edge 15. In order to improve the internal cooling, turbulators (not shown) in the form of obliquely positioned ribs can be provided in the cooling channels 19a, b, c and 20 and lead to swirling of the cooling air, and therefore to an improvement in the heat transfer.

As shown in the exemplary embodiment in FIG. 2a, first, comparatively long first cooling holes 25 for convection cooling are provided, distributed over the blade width, from the cooling channels 19 and 19a, 19b, 19c in the blade tip 11, passing to the outside on the pressure face 17 of the blade 10. Second cooling holes 27 are passed to the outside through the cap 33 of the blade 10, for film cooling on the suction face 18 of the blade 10. A desirable cooling effect can be achieved by the combination of convection cooling on the pressure face 17 and film cooling on the suction face 18 of the blade.

The first and second cooling holes 25 and 27, respectively, can have the form of cylindrical bores in a simple embodiment (FIG. 3a) and can be introduced into the blade 10 by appropriate drilling methods (for example, EDM, laser drilling). The first cooling holes 25 can be in the form of holes or bores which run obliquely upwards, in order to achieve the necessary hole length. They can include an exemplary first angle α1 of between 25° and 35° (for example, substantially 30°), with the outer surface 17 of the blade 10.

In an exemplary embodiment, the first and second cooling holes (25a,b in FIG. 2 and FIG. 3b) can include only sections in the form of cylindrical bores with a predetermined first diameter d. They therefore can open into the environment of the blade 10 with a fan-shaped section (29, 30 in FIGS. 4a-c, 5a+b) of the bore.

There can be two different kinds 25a (see FIGS. 4a) and 25b (see FIG. 5a) of first cooling holes provided at the pressure side (17) of the blade 10. Those of the first cooling holes arranged outside the trailing edge 16 of the blade 10, for example, first cooling holes 25a, can open into the environment of the blade 10 with a 3D (3-dimensional) symmetric fan-shaped section 29 of the bore, which is shown in FIGS. 4a, 4b and 4c. The 3D symmetric fan-shaped section 29 can have, for example: a first aperture angle 2φ1 (FIG. 4b) having an exemplary range of 10° to 50° (for example, substantially)24°, and a second aperture angle φ2 (FIG. 4a) perpendicular to the first aperture angle 2φ1. The second aperture angle φ2 can have an exemplary range of 5° to 25° (for example, substantially 12°). Furthermore, these first cooling holes 25a arranged outside the trailing edge 16 of the blade 10 can include a second angle α2 of between, for example, 15° and 45° (for example, substantially 30°), with the outer surface 17 of the blade 10 (FIG. 4a).

Those of the first cooling holes 25b arranged at the trailing edge 16 of the blade 10 can open into the environment of the blade 10 with a 2D (2-dimensional) symmetric fan-shaped section 30 of the bore (FIGS. 5a, 5b and 5c). The 2D symmetric fan-shaped section 30 can have a third aperture angle 293 (FIG. 5a), which has an exemplary range of 10° to 40° (for example, substantially 20°). These first cooling holes 25b arranged at the trailing edge 16 of the blade 10 include a third angle α3 (FIG. 5c) of between, for example, 5° and 45° (for example, substantially 30°), with the outer surface 17 of the blade 10.

As can be seen in FIG. 5a, those of the first cooling holes 25b arranged at the trailing edge 16 of the blade 10 have a bore of a predetermined overall length L. This overall length L is subdivided into the aforementioned 2D symmetric fan-shaped section 30 and a cylindrical section of a second length L₁. The ratio L₁/L of both lengths lies in the exemplary range of 0.2 to 0.7 (for example, substantially 0.5).

FIG. 2a shows, that the first cooling holes 25a and 25b are arranged along the pressure face 17 in a row with a (first) periodicity P₁. It is desirable to choose a certain ratio P₁/d between this periodicity P₁and the diameter d (see FIG. 3a) of the cooling hole bores. This ratio is chosen to be in the exemplary range of 3 to 8 (for example, substantially 6).

Accordingly, the second cooling holes 27 are arranged along the suction face 18 in a row with a (second) periodicity P₂. Again, the ratio P₂/d₁between the second periodicity P₂and the diameter d lies in the exemplary range of 5 to 8 (for example, substantially 6).

In the exemplary embodiment illustrated in FIG. 3, the blade 10 is closed at the blade tip 11 at the top by a flat cap 33, which is surrounded on the upper face by a circumferential rail-like blade crown 32. As can be seen in FIGS. 3a and 3b, the second cooling holes 27 pass through the cap 33 of the blade 10 in a radial direction. They are in the form of long cylindrical bores which run obliquely upwards and include an exemplary angle γ of 0° to 45° (for example, substantially 30°), with the longitudinal axis of the blade 10 (FIG. 3c).

The first cooling holes 25 open into the outside area underneath the cap 33 of the blade 10. They exit into the environment of the blade 10 at a predetermined height H below the upper end of the blade tip 11 (FIG. 3a). The ratio H/d between the height H and the diameter d is in an exemplary range between 5 and 10 (for example, substantially 6.5).

The second cooling holes 27 are arranged on the opposite face and pass through the cap 33 of the blade 10 in the radial direction, opening into the outside area within the blade crown 32.

Also within the blade crown 32 dust holes 26 are provided and arranged along the cap 33 between the leading edge 15 and trailing edge 16 (FIG. 2). These dust holes 26, which are used to remove dust particles from the interior cooling channels, each have a diameter d1, such that the ratio d1/d between the diameter d1 and the bore diameter d (see FIG. 3a) is between, for example, 1.2 and 4.5.

As has already been said, the blade 10 is provided with a blade crown 32 at the blade tip 11, which blade crown 32 is bounded by a circumferential rail having a predetermined thickness t (FIG. 3a). The width W between the opposing rails varies with the distance K along the chord line (FIG. 2), such that, for example: t/W is between 0.05 and 0.15 for κ/κ₀between 0 and 0.3, and that /W is between 0.15 and 0.3 for κ/κ₀larger than 0.3 and up to 1.0, KO being the overall chord line length. Additionally, relating the blade tip geometry, the following ratios can be desirable for exemplary embodiments: D/W=0.1 to 0.3 for κ/κ₀0 to 0.3 and D/W=0.1 to 0.8 for κ/κ₀>0 to 1.0, whereas D means the depth of the tip crown and W means the width, according FIG. 3a.

In addition to the described cooling, the surfaces of the pressure face 17 and suction face 18 as well as the upper face of the cap 33 can be provided with a thermal protection layer (Thermal Barrier Coating TBC) 28.

Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

LIST OF REFERENCE SYMBOLS

10 Blade (gas turbine)

11 Blade tip

12 Airfoil section

15 Leading edge

16 Trailing edge

17 Pressure face

19 Suction face

19a,b,c Cooling channel

20 Cooling channel

21,22 Bend

23,24 Cooling hole

25,25a,25b,27 Cooling hole

26 Dust hole, particle openings

28 Thermal protective layer (Thermal Barrier Coating TBC)

29 3D fan-shaped section

30 2D fan-shaped section

32 Blade crown

33 Cap

α₁,α₂,α₃angle

γ angle

φ1,φ2 angle (aperture)

P1, P2 Periodicity

d,d1 Diameter

H Height

W Width

D Depth of the tip crown

t Thickness

κ Distance (along chord line)

κ0 Chord line length

Claims

1. A blade for a gas turbine, comprising:

an airfoil section extending in a radial direction of the turbine or in a longitudinal direction of the blade between a platform and a blade tip, the blade tip being provided with a cap, the airfoil section being bounded transversely with respect to the longitudinal direction by a leading edge and a trailing edge and having a pressure face and a suction face;

cooling channels extending substantially in a radial direction between the platform and the blade tip in an interior of the airfoil section, for receiving a cooling medium flow,

first cooling holes for convection cooling provided on the pressure face of the blade; and

second cooling holes for film cooling provided on the suction face of the blade, the first and second cooling holes being arranged in an area of the blade tip and operatively connected to the cooling channels and distributed over the blade width, the cooling medium being passed to an exterior of the area of the cap and/or through the cap of the blade.

2. The blade as claimed in claim 1, wherein the first and second cooling holes comprise:

at least a section formed as a cylindrical bore with a predetermined first diameter.

3. The blade as claimed in claim 2, wherein the first cooling holes are formed as long cylindrical bores which run obliquely upwards and include a first angle (α1) of between 25° and 35° with an outer surface of the blade.

4. The blade as claimed in claim 2, wherein the first cooling holes open into an environment of the blade with a fan-shaped section of the bore.

5. The blade as claimed in claim 4, wherein first cooling holes arranged outside the trailing edge of the blade open into the environment of the blade with a 3D symmetric fan-shaped section of the bore, whereby the 3D symmetric fan-shaped section has a first aperture angle (2φ1) having a range of 10° to 50°, and a second aperture angle (φ2) perpendicular to the first aperture angle (2φ1), a second aperture angle (φ2) having a range of 5° to 25°.

6. The blade as claimed in claim 5, wherein first cooling holes arranged outside the trailing edge of the blade include a second angle (α2) of between 15° and 45°, with the outer surface of the blade.

7. The blade as claimed in claim 4, wherein first cooling holes arranged at the trailing edge of the blade open into the environment of the blade with a 2D symmetric fan-shaped section of the bore, whereby the 2D symmetric fan-shaped section has a third aperture angle (2φ3) having a range of 10° to 40°.

8. The blade as claimed in claim 7, wherein first cooling holes arranged at the trailing edge of the blade include a third angle (α3) of between 5° and 45°, with the outer surface of the blade.

9. The blade as claimed in claim 7, wherein first cooling holes arranged at the trailing edge of the blade have a bore of a predetermined first length, which is subdivided into the 2D symmetric fan-shaped section and a cylindrical section of a predetermined second length, whereby a ratio of the second length and the first length is in the range of 0.2 to 0.7.

10. The blade as claimed in claim 3, wherein the first cooling holes are arranged along the pressure face in a row with a predetermined first periodicity, and a ratio between the first periodicity and the first diameter is in the range of 3 to 8.

11. The blade as claimed in claim 2, wherein the second cooling holes pass through the cap of the blade in a radial direction.

12. The blade as claimed in claim 11, wherein the second cooling holes are formed as long cylindrical bores which run obliquely upwards and include an angle (γ) of 0° to 45° with the longitudinal axis of the blade.

13. The blade as claimed in claim 11, wherein the second cooling holes are arranged along the suction face in a row with a predetermined second periodicity, and a ratio between the second periodicity and the first diameter is in the range of 3 to 8.

14. The blade as claimed in claim 3, wherein the first cooling holes exit into the environment of the blade at a predetermined height below an upper end of the blade tip, and a ratio between the height and the first diameter is in a range between 5 and 10.

15. The blade as claimed in claim 2, comprising:

dust holes arranged along the cap between the leading edge and trailing edge, the dust holes having a second diameter, such that a ratio between the second diameter and the first diameter is between 1.2 and 4.5.

16. The blade as claimed in claim 11, wherein the cap of the blade is bounded at an edge on its upper face by a circumferential blade crown, and the second cooling holes open into an outside area within the blade crown.

17. The blade as claimed in claim 1, wherein the blade has a blade crown at the blade tip, which is bounded by a circumferential rail having a predetermined thickness, whereby a width between opposing rails varies with a distance along the chord line, such that t/W is between 0.05 and 0.15 for κ/κ0 between 0 and 0.3, that t/W is between 0.15 and 0.3 for κ/κ0 larger than 0.3 and up to 1.0, κ0 being the overall chord line length.

18. The blade as claimed in claim 1, wherein the blade has a ratio D/W between 0.1 and 0.3 for κ/κ0 between 0 and 0.3, and the ratio D/W is between 0.3 and 0.8 for κ/κ larger 0.3 and up to 1.0.

19. The blade as claimed in claim 3, wherein the first angle (α1) is substantially 30°.

20. The blade as claimed in claim 5, wherein the first aperture angle (2φ1) is substantially 24° and the second aperture angle (φ2), is substantially 12°.

21. The blade as claimed in claim 6, wherein the second angle (α2) is substantially 30°.

22. The blade as claimed in claim 7, wherein the third aperture angle (2φ3) is substantially 20°.

23. The blade as claimed in claim 8, wherein the third angle (α3) is substantially 30°.

24. The blade as claimed in claim 9, wherein the ratio of the second length and the first length is substantially 0.5.

25. The blade as claimed in claim 10, wherein the ratio between the first periodicity and the first diameter is substantially 6.

26. The blade as claimed in claim 12, wherein the angle (γ) is substantially 30°.

27. The blade as claimed in claim 13, wherein the ratio between the second periodicity and the first diameter is substantially 6.

28. The blade as claimed in claim 14, wherein the ratio between the height and the first diameter is substantially 6.5.