Stator heat shield for a gas turbine, gas turbine with such a stator heat shield and method of cooling a stator heat shield

Abstract

A stator heat shield for a gas turbine having a hot gas flow path, is disclosed. The stator heat shield includes a first surface configured to face the hot gas flow path of the gas turbine; a second surface opposite to the first surface; cooling channels for directing cooling fluid from the second surface towards the first surface; and cavities arranged at the first surface for receiving the cooling fluid from at least a part of the cooling channels; wherein at least a part of the cavities each have at least two corresponding cooling channels open thereto, the at least two corresponding cooling channels being inclined towards each other. In use, a vortex is created in the cavity.

Claims

1. A stator heat shield for a gas turbine having a hot gas flow path, the stator heat shield comprising: a first surface configured to face a hot gas flow path of a gas turbine; a second surface opposite to the first surface; cooling channels for directing cooling fluid from the second surface towards the first surface; and cavities arranged at the first surface for receiving the cooling fluid from at least a part of the cooling channels; wherein each cavity has at least two corresponding cooling channels open thereto, said at least two corresponding cooling channels being inclined towards each other, wherein said at least two corresponding cooling channels each have a central axis, and said central axes of said at least two corresponding cooling channels are offset relative to each other so that the central axes of said at least two corresponding cooling channels do not intersect in a respective cavity.

2. The stator heat shield according to claim 1, wherein said at least two corresponding cooling channels each comprise: an inlet to receive cooling fluid at the second surface and an outlet to discharge a jet of cooling fluid into a respective cavity, wherein said at least two corresponding cooling channels are arranged so that the jets of the cooling fluid discharged from said at least two corresponding cooling channels interact, providing thereby swirling of cooling fluid in the cavity.

3. The stator heat shield according to claim 2, wherein the cavities are configured so as to promote the swirling of the cooling fluid in the cavities.

4. The stator heat shield according to claim 1, wherein the cavities expand towards the first surface.

5. The stator heat shield according to claim 1, wherein the cavities are substantially hemispherical.

6. The stator heat shield according to claim 1, wherein the cavities are oval as viewed from the first surface.

7. The stator heat shield according to claim 1, wherein said at least two corresponding cooling channels are inclined to the first surface of the stator heat shield at an angle between 20 and 40.

8. The stator heat shield according to claim 1, wherein said at least two corresponding cooling channels are inclined to the first surface of the stator heat shield at an angle between 25 and 35.

9. The stator heat shield according to claim 1, wherein said at least two corresponding cooling channels are inclined to the first surface of the stator heat shield at an angle of 30.

10. The stator heat shield according to claim 1, wherein said at least two cooling channels of at least one cavity intersect with cooling channels of other cavities to arrange intersections of two respective cooling channels, wherein the cooling channels are in fluid communication in the intersections.

11. The stator heat shield according to claim 10, wherein the cooling channels each have a central axis, and the central axes of said two respectively intersecting cooling channels are offset relative to each other so as not to be arranged in one common plane.

12. The stator heat shield according to claim 1, wherein said at least two corresponding cooling channels associated with a respective cavity comprise: two cooling channels inclined towards each other.

13. The stator heat shield according to claim 12, wherein the cooling channels each have a central axis, the central axes of said two cooling channels being offset relative to each other so that the central axes of said two cooling channels do not intersect in a respective cavity.

14. The stator heat shield according to claim 12, wherein one of said two cooling channels of one cavity intersects with one of the two cooling channels of a neighboring cavity to arrange a first intersection, wherein the cooling channels intersecting in the first intersection are in fluid communication.

15. The stator heat shield according to claim 14, wherein the first intersection is located substantially between said one cavity and said neighboring cavity, as viewed as a projection onto the first surface.

16. The stator heat shield according to claim 14, wherein said one of said two corresponding cooling channels of said one cavity intersect also with one of the two cooling channels of at least one cavity next to said neighboring cavity to arrange at least a second intersection, wherein the cooling channels intersecting in said at least second intersection are in fluid communication.

17. The stator heat shield according to claim 14, wherein the cooling channels each have a central axis, and the central axes of the cooling channels intersecting in a respective intersection are offset relative to each other so as not to be arranged in one common plane.

18. The stator heat shield according to claim 17, the central axes of the cooling channels intersecting in a respective intersection are half-diameter offset relative to each other.

19. The stator heat shield according to claim 12, wherein the cooling channels each have a central axis, and the central axes of said two cooling channels converge in a respective cavity, as viewed in a plane perpendicular to the first surface of the stator heat shield.

20. The stator heat shield according to claim 1, wherein the cavities are arranged in rows extending in the longitudinal direction of the stator heat shield, as viewed from the first surface.

21. The stator heat shield according to claim 20, wherein the rows of the cavities are staggered.

22. The stator heat shield according to claim 1, wherein the cooling channels are provided as convective cylindrical through channels or tubes.

23. The stator heat shield according to claim 1, wherein the stator heat shield is a cast, machined, brazed or selective laser melted component.

24. A gas turbine, comprising: at least one stator heat shield according to claim 1.

25. The gas turbine according to claim 24, wherein the cooling fluid is cooling air.

26. A method of cooling a stator heat shield, the stator heat shield having a first surface configured to face a hot gas flow path of a gas turbine, a second surface opposite to the first surface, cooling channels for directing cooling fluid from the second surface towards the first surface, and cavities arranged at the first surface for receiving the cooling fluid from at least a part of the cooling channel, wherein at least a part of each cavity has at least two corresponding cooling channels open thereto, said at least two corresponding cooling channels being inclined towards each other; wherein the method comprises: causing cooling air to flow through the cooling channels and injecting cooling gas flow of two cooling channels into one cavity, the two cooling channels being offset such that a vortex is created in the cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross-sectional view of a segment of the stator heat shield according to the present invention, with a combination of intersecting cooling channels and retaining discharge cavities, and flow arrangement;

(2) FIG. 2 shows an isometric view of the stator heat shield from FIG. 1;

(3) FIG. 3 shows a view from the first surface (hot has exposed surface) of the stator heat shield according to the invention with a staggered arrangement of the retaining discharge cavities;

(4) FIG. 4 shows a cross-sectional view of the stator heat shield according to the present invention, with a combination of intersecting cooling channels and retaining discharge cavities, arranged in respect to a blade of the rotor of the gas turbine.

PREFERRED EMBODIMENT OF THE INVENTION

(5) Referring to FIG. 1, a stator heat shield 1 for a gas turbine, particularly of first stage, comprises a first surface 2 adapted to be exposed to hot gases flowing through the gas turbine during the operation of the gas turbine, that is, to face a hot gas flow path of the gas turbine. Further, the stator heat shield 1 comprises a second surface 3 opposite to the first surface 2. The second face faces away from the hot gas flow path and is connected to a cooling fluid supply. During the operation of the gas turbine, the second surface 3 is exposed to cooling fluid 4. To direct the cooling fluid 4 from the second surface 3 towards the first surface 2, the stator heat shield 1 has through cooling channels 5, 5. Each of the cooling channels 5, 5 has a feeding inlet to receive the cooling fluid 4 and an outlet to discharge a cooling fluid jet. Cavities 6 are provided on the first surface 2, which have a special profile with an expansion towards the first surface 2 washed by hot gas. The cavities are open to the hot gas flow path. Each cavity 6 has two cooling channels 5, 5 open thereto. The two cooling channels 5, 5 are inclined towards each other and arranged so as to provide a circulation 7 of the cooling fluid in the cavity 6. The cooling channels 5, 5 may be inclined to the surface of the SHS at optimal 30.

(6) The cavities 6 are profiled so as to allow a circulation 7 of the cooling fluid in the cavities 6. Due the circulation 7, the cooling fluid may be retained in the cavities 6 before it is sucked out of the retaining cavity 6 mixing with hot gas and reducing downstream exposure temperature at the SHS and the tip region of a passing blade. This arrangement allows external cooling of the SHS and, at the same time, mitigation of the impact of rubbing event, preventing thereby discharge holes from closure.

(7) Additionally, the cooling channels 5, 5 extending through the body of the stator heat shield 1 define an internal convective cooling system of the SHS. Therefore, the cooling channels 5, 5 may be provided as convective channels or tubes.

(8) To increase the internal cooling effect, the inclined cooling channels 5, 5 of one cavity 6 intersect with the inclined cooling channels 5, 5 of the other cavities 6 to arrange intersections 8, 8. In this preferred embodiment, one 5 of the two cooling channels 5, 5 associated with one cavity 6 intersects with one 5 of the two cooling channels 5, 5 of a neighboring cavity 6 to arrange a first intersection 8. The first intersection 8 is located substantially between said one cavity 6 and said neighboring cavity 6, as a projection onto the first surface 2. Said one 5 of the two cooling channels 5, 5 associated with one cavity 6 may intersect also with one 5 of the two though channels 5, 5 of at least one cavity next to said neighboring cavity to arrange at least a second intersection 8. Each intersection 8, 8 includes two intersecting cooling channels 5, 5.

(9) Referring now to FIG. 2, it can be seen that the central axes of the two cooling channels 5, 5 open into the same cavity 6 are offset, preferably half-diameter offset, relative to each other to arrange swirling interaction between the discharged jets of the cooling fluid and thereby a more stable circulation 7.

(10) Further, as can be seen in FIG. 2, the cooling channel 5 of one cavity 6 and the cooling channel 5 of another cavity 6 intersect with each other so that their axes are offset, preferably half-diameter offset, relative to each other so as not to be arranged in one common plane. The intersecting cooling channels 5, 5 are in fluid communication in the intersections 8, 8. In application to cooling effect of the cooling channels, the intersection and offset of the though channels 5, 5 allows achievement of high heat transfer enhancement rates with moderate pressure losses.

(11) Referring now to FIG. 3, the cavities 6 are arranged in rows extending in the longitudinal direction of the stator heat shield 1. The rows of the cavities 6 are staggered to arrange a homogeneous external cooling network. The offset of the central axes of the intersecting cooling channels 5, 5 can be also seen in FIG. 3, too.

(12) FIG. 4 shows an example of implementation of the stator heat shield. In this example, the stator heat shield is facing the rotor. A plurality of the cavities are arranged on the side of the stator heat shield which is facing the hot gas flow side. Two cooling channels extend from the cooling air supply side to the hot gas flow path side of the stator heat shield and open into the cavities.

(13) It is clear that varying the inclination angles of the cooling channels, the offset values of the cooling channels, the number of intersections, and the profile of the cavity allows achievement of a better circulation of the cooling fluid in the cavities, a better interaction of the cooling fluid in the intersections and thereby a better cooling effects.

(14) It should be understood that the description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. Variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

(15) Summarizing, the main aspects of the present invention distinguishing it from other schemes are the following: the use of internal cooling system built on the basis of highly efficient intersecting convective channels with preferably two intersections to achieve high and uniform cooling heat transfer rates; the use of angled discharge jets with half-pitch shift (half-diameter offset) and profiled retaining cavities allows a stable circulation of cooling air which is discharged into the cavities for external cooling; the use of retaining cavities expanding towards hot gas washed surface provides mitigation of rubbing event and allows minimization of radial tip clearance with a target to increase turbine performance; the use of air discharge to flowpath allows reduction of hot gas to coolant mixture temperature and improvement of thermal boundary conditions in blade tip region (to improve lifetime and/or reduce coolant consumption) and reduction of aerodynamic tip clearance losses; the given cooling scheme of the SHS allows a very local optimization of cooling heat transfer rates (by varying the size of convective channels and offset value) in relation to external factors such as axial pressure distribution and hot gas wakes with a target to reach maximum uniformity of resulting metal temperatures and stresses in all locations and remove of all critical zones and provide maximum lifetime and/or coolant savings.