WO2007006619A1

WO2007006619A1 - Film-cooled component, in particular a turbine blade and method for manufacturing a turbine blade

Info

Publication number: WO2007006619A1
Application number: PCT/EP2006/063178
Authority: WO
Inventors: Stefan Baldauf
Original assignee: Siemens Aktiengesellschaft
Priority date: 2005-07-12
Filing date: 2006-06-14
Publication date: 2007-01-18

Abstract

In a cool blade (1) of a gas turbine, a number of air-cooling channels (14) are provided, wherein each air-cooling channel (14) in its air outlet region (18) is designed with shaped hole geometry such that the free flow cross section of the respective air-cooling channel (14) increases in the flow direction of a cooling medium, wherein the cross-sectional area in said outlet region (18) comprises at least one first section (20) with a curved outer boundary (26) and at least one second section (24) with a number of linear outer boundaries (26) .

Description

FILM-COOLED COMPONENT, IN PARTICULAR A TURBINE BLADE AND METHOD FOR MANUFACTURING A TURBINE BLADE

The present invention relates to a cooled component of a technical system, in particular to a cooled blade of a tur^¬ bine. Furthermore, it relates to a method for manufacturing such a turbine blade and to an erosion stamp to be used in this method.

In highly efficient turbines such as high-temperature gas turbines, cooled turbine blades are used in order to allow for sufficiently high life times event in the relatively hos^¬ tile environment. In typical applications, air-cooled turbine blades may be used. These air-cooled turbine blades comprise a body in which a number of air-cooling channels are pro^¬ vided. During operation of the gas turbine, cooling air is passed through these air-cooling channels, and at an outlet opening of the channel is discharged into the gas flow of the working fluid streaming in the gas turbine. Due to the pres^¬ sure conditions and the like in the turbine body, the cooling air discharged from the air-cooling channels typically is guided along the outer contour of the body of the turbine blade for a while, providing for additional film cooling of the blade surface in the neighboring, downstream area.

For optimization of turbine blades of this air-cooled type, two goals contradicting each other are followed: On the one hand side, for a sufficient cooling performance a high den^¬ sity of cooling air channels in the body of the turbine blade and a high density of outlet holes of these channels on the surface of the turbine blade providing for a high area of film cooling is desirable. On the other hand side, structural stability, in particular in view of the high mechanical stress the turbine blade is exposed to, requires a relatively low density of air-cooling channels. In order to optimize the blade design in view of both of these goals, some or all of the air-cooling channels may be configured with shaped holes on their outlet side.

In this design, the respective air-cooling channel in its air outlet region has a tapered design with a cross section wid^¬ ening in flow direction of the cooling air. By this design, the relative surface area of the blade body that is covered by the outlet openings of the cooling air channels may be kept relatively high whereas in the bulk of the blade body the volume fraction of the air-cooling channels may be kept comparatively low. In addition, due to the tapered shape of the cooling air channels in their outlet regions, the outlet speed of the cooling air exiting the channels may be reduced, which favors smooth transition of the cooling air into forming a cooling film along the outer contour of the blade body.

In US patent No. 6,036,436, a turbine blade is disclosed in which shaped holes in the outlet regions of the air-cooling channels of the mentioned type are used. These shaped holes in the outlet region of the respective air-cooling channel have a circular cross section that continuously widens in flow direction of the cooling air until the outlet opening is reached. Shaped holes of this type may be manufactured by us- ing laser systems that widen the outlet regions of the pre- implemented air-cooling channels in the desired way. In al^¬ ternative methods for manufacturing gas turbine blades of this type, erosion procedures such as spark erosion may be used. In these concepts, an erosion stamp comprising a main body, which in its tip region is shaped in a contour corre^¬ sponding to the desired shape of the outlet region of the re^¬ spective air-cooling channel, may be used. This erosion stamp is immersed into the outlet regions of the pre-manufactured air-cooling channels and there due to the erosion process ablates the material until the desired shape for the outlet region is achieved. An object of the present invention is to provide a cooled component of a technical system, in particular a blade of a turbine, with a number of air-cooling channels that in their outlet regions are designed in a shaped hole geometry that allows for a particularly smooth and efficient transition of the cooling air from the air-cooling channels into a flow of the working fluid in the gas turbine and a particularly effi^¬ cient film cooling of a surface area of the turbine blade. It is another object of the invention to provide an erosion stamp that may be used for manufacturing an appropriate ge^¬ ometry of the shaped holes of the cooled component. It is still another object of the invention to provide a method for manufacturing the cooled component, in particular by using this erosion stamp.

According to the present invention, with regard to the cooled component this object is achieved by providing a particularly shaped hole geometry for the outlet regions of the air-cool^¬ ing channels under consideration. According to the invention, this geometry of the shaped holes is chosen in a configura^¬ tion that generates and influences vortices and turbulences at the outlet openings of the air-cooling channels such that a smooth outflow of the cooling air from each channel and a subsequent guided flow of the cooling air along the outer surface of the cooled component is favored, thus enhancing the effectiveness of film cooling. In order to achieve these effects of turbulences, the respective cooling air channel in its outlet region has a cross section that is a combination of a rounded, curved part and a polygonal part. Therefore, the outlet region comprises one first section with a curved outer boundary between two first end points and one second section between to second end points enclosing a number of linear outer boundaries, each first end point of the curved outer boundary lies on one of the second end points of the linear outer boundaries.

In a preferred embodiment, the second section may be shaped in a rectangular shape. In another preferred embodiment, in which, if both second end points of the linear outer boundaries are connected by a fictitious linear line, the boundaries and the fictitious line draw an isosceles trapezoid. A symmetrical shape of the film cooling opening leads to a stream of cooling air having vortexes which are kidney-shaped in cross section. It has been found, that this kind of vortexes improves the cooling effect .

In another preferred embodiment, in which an intersection line, resulting from the surface of the second section intersected with a cross section, is curved. Up to know usually this surface was flat and not arched in a concave way. Due to this configuration the film cooling effect of cooling air could be further increased.

In another preferred embodiment, the cooling air channels in their main direction of extension are tilted with respect to the outer surface of the main body of the cooled component. Due to the tilted arrangement, the cooling air discharged from the air-cooling channels already tends to continue streaming along the outer downstream surface of the component, thus providing for efficient film cooling. In order to enhance this effect even further, the rounded, curved part of the cross section in the shaped hole geometry is provided in the "inner region", thus smoothening the crossover from the exiting cooling air into the cooling film along the outer surface of the body.

With respect to the erosion stamp, the object identified above according to the invention is achieved by defining a shape for the erosion stamp that matches the desired shape of the outlet region of the respective cooling air channel. Ac- cordingly, the erosion stamp comprises a main body extending along an extension direction, wherein in a tip region the cross-sectional area of this main body comprises at least one first section with a curved outer boundary and at least one second section with a number of linear outer boundaries.

This erosion stamp according to the invention preferably is used in a method for manufacturing a turbine blade.

The invention is shown in the figures.

FIG 1 is a perspective view of an air-cooled stationary blade of a gas turbine,

FIG 2 is a plan-sectional view of an air-cooled stationary blade of a gas turbine,

FIG 3 is an enlarged view of a shaped hole in an outlet region of an air-cooling channel in a view along the flow direction of the cooling air, FIG 4,5,6,7 shows enlarged views from different positions on to the outlet-region of an air-cooling channel,

FIG 8 is a perspective view of an erosion stamp, and

FIG 9 is a schematic perspective view of the flow behavior of the cooling air exiting from the air-cooling channel.

As shown in a perspective view of a cooled stationary blade 1 of a gas turbine according to FIG 1, an outside shroud 2 and an inside shroud 4 each have a cooling air inlet hole 6, and a main body 8 forming the blade structure extends between the two shrouds 2, 4. On the surface of the body 8 ranging from the blade leading edge to the blade trailing edge, holes for shower head cooling, film cooling, and pin fin cooling are formed. Also, the two shrouds 2, 4 are formed with shroud cooling holes 10. As may be seen from FIG 2 in a cross-sectional view, the body 8 forming the blade shape comprises a number of air-cooling channels 14 through which cooling air may be guided. Each cooling channel 14 extends along a direction of extension in flow direction of the cooling medium, i. e. the cooling air, as indicated by the arrows 16. As seen from FIG 2, the extension direction of each air-cooling channel 14 is tilted with respect to the outer surface of the body 8. As a conse^¬ quence, cooling air exiting from the cooling channels 14 when entering the hot gas stream in the turbine interior is encouraged to bend towards the outer surface of the body 8 and to flow along the curved outer surface of the body 8 for a while. As a consequence, a film of cooling air is established in the outlet area of each cooling channel 14, providing for efficient film cooling in this section of the body 8.

According to the invention, the outlet regions 18 of the air- cooling channels 14 with respect to their geometric design are shaped such that the formation of the cooling film in the neighboring surface area is improved and the transition of the cooling air from the respective air-cooling channel 14 and into the gas stream in the turbine is smoothened. In or^¬ der to achieve this, each air-cooling channel 14 in its air outlet region 18 is designed in a shaped hole geometry such that the free flow cross section of the respective air-cool^¬ ing channel 14 increases in flow direction of the cooling medium. This tapered design of the respective air-cooling channel 14 in its outlet region 18 may be seen in FIG 3, 4.

In order to increase the efficiency of the formation of the cooling film, in the tapered region in the air outlet region 18, the respective air-cooling channel 14 has a cross-sec^¬ tional area that in its outer shape is a combination of a curved, rounded region and a polygonal region with a number of linear outer boundaries. As may be seen from FIG 6, this results in a cross-sectional area in the outlet region 18 that comprises at least one first section 20 with a curved outer boundary 22 between two first end points 50, 52 and a second section 24 with a number of linear outer boundaries 26 between to second end points 54, 56. Each of the first end points 50, 52 lies (or overlap) one of the second end points 54, 56. The cross section of the air-cooling channel 14 along line 28 is shown in FIG 7. There, the first section 20 and the second section 24 together with their respective outer boundaries 22, 26 is clearly visible. The first section 20 has at this location a concave curved surface 23, and not, as know from state of the art, a flat one.

The second end points 54, 56 of the linear outer boundaries 26 are arranged such, that, if they are connected by a fictitious linear line 58, the boundaries 26 and the fictitious line 58 draw an isosceles trapezoid.

Due to the tilted positioning of the cooling air channels 14 in the body 8, this configuration results in a shape of the outlet opening 25 that is shown in FIG 5.

The first section 20 of the cross-sectional area of the cool^¬ ing air channel 14 in its outlet region 18 is intended to provide for extra flow space of the cooling air in the re^¬ spective air-cooling channel 14 in order to allow for local additional expansion of the cooling medium and in order to facilitate the bend-over from the flowing cooling air within the air-cooling channel 14 when mixing into the hot gas flow. Accordingly, the first section 20 with the curved outer boundary 22 is positioned downstream of the cooling air channel 14, at the inner flank of the curved flow path of the cooling medium in the outlet region 18. The second section 24 with its basically rectangular cross-sectional shape with its center is aligned with the main body of the cooling air channel 14 as may be seen from FIG 6.

The shaped hole in the outlet region 18 of the respective cooling air channel 14 is manufactured by spark erosion. In this method, an erosion stamp 30 is used, the shape of which is shown in FIG 8. The erosion stamp 30 comprises a main body 32 that extends along an extension direction as shown by arrow 34. In a tip region 36, the main body 32 has a cross sec^¬ tion that continuously decreases in said extension direction. In this tip region 36, the cross-sectional area of the main body 32 comprises at least one first section with a curved outer surface 31 and at least one second section with a number of linear outer boundaries. In the configuration as shown in FIG 8, this is achieved by a base plate 38 with more or less rectangular cross section, that in the tip region 36 is wedge-shaped, and an added part cylinder 40 that in the tip region 36 is tapered in accordance with the wedged shape of base plate 38. Together, the base plate 38 and the part cylinder 40 form the main body 32.

In FIG 9, the resulting gas flows and turbulences when using the geometry as pointed out above are shown. As can be seen from FIG 9, the main body 8 has a surface directly exposed to the flow of hot gas in the turbine as represented by the ar^¬ row 40. From the outlet 25, cooling air is discharged from the air-cooling channels 14 in the interior of the main body 8 into the hot gas stream. Mixing of the flow of cooling air and the hot gas stream in the turbine generate turbulences that are indicated in FIG 9 by showing arrows 42 representa^¬ tive for flow paths. The increase in the cross section of the cooling air channel 14 in its outlet region 18 in flow direc^¬ tion of the cooling air provides additional turbulences 44 at the lower edges 46 of the outlet opening which reduce the inward flow of hot gas into the outlet area and increase the film cooling efficiency. These helpful and desired turbu- lences 44 are increased and strengthened by the curved shape of the air-cooling channel 14 in the tapered outlet region

Claims

1. Cooled component of a technical system, comprising a body (8) in which a number of air-cooling channels (14) are provided, wherein each air-cooling channel (14) in its air outlet region (18) is designed in a shaped hole geometry such that the free flow cross section of the respective air-cooling channel (14) increases in flow direction of a cooling medium, wherein the cross-sectional area in said outlet region (18) comprises one first section (20) with a curved outer boundary (22) between two first end points (50, 52) and one second section (24) with a number of linear outer boundaries (26) between to second end points (54, 56), each first end point (50, 52) of the curved outer boundary (22) lies on one of the second end points (54, 56) of the linear outer boundaries (26) .

2. Component according to claim 1, in which said second section (24) has rectangular shape.

3. Component according to claim 2, in which if the second end points (54, 56) of the linear outer boundaries (26) are connected by a fictitious linear line (58), the boundaries (26) and the fictitious line (58) draw an isosceles trapezoid.

4. Component according to claim 1, 2 or 3, in which an intersection line (23) , resulting from the surface of the second section intersected with a cross section, is curved.

5. Component according to one of the claims 1 through 4, in which a central point of said second section (24) is aligned with a central line of the respective cooling channel (14) .

6. Component according to one of the claims 1 through 5, in which each cooling channel (14) in its main region extends along an extension direction, said extension direction being tilted with respect to an outer surface of said body (8, 32) .

7. Blade (1) of a turbine, said blade (1) being configured as a cooled component according to either one of the claims 1 through 6.

8. Erosion stamp (30) for producing a component according to one of the claims 1 to 7, comprising a main body (8, 32) ex^¬ tending along an extension direction, said main body (8, 32) in a tip region (36) having a cross section continuously de- creasing in said extension direction, wherein the cross-sectional area of said main body (8, 32) in said tip region (36) comprises at least one first section (20) with a curved outer surface (31) and at least one second section (24) with a number of linear outer boundaries (26) .

9. Method for manufacturing a turbine blade (1), in which an erosion stamp (30) according to claim 8 is used to shape an outlet region (18) in a number of cooling air channels (14) provided in a turbine blade body.