Cooled blade for a gas turbine, method for producing such a blade, and gas turbine having such a blade

A blade for a gas turbine includes an airfoil extending in radial direction of the turbine or longitudinal direction of the blade, respectively, between a platform and a blade tip. The airfoil is bordered across the airfoil by a leading edge and a trailing edge and has a suction side and a pressure side. At the trailing edge a first cooling passage runs parallel to the trailing edge from the platform to the blade tip in the interior of the airfoil. The cooling passage is supplied with a cooling air flow from the platform side, and from which cooling air is discharged through a plurality of cooling holes arranged all over the blade. For such a blade the cooling is optimized by providing a first cooling passage, the passage area of which is tapered in radial direction by between 35% and 59%.

FIELD

The present disclosure relates to the field of gas turbines, such as a cooled blade for a gas turbine and a method for producing such a blade.

BACKGROUND INFORMATION

The efficiency of gas turbines can depend substantially on the temperature of hot gas that expands in a turbine while performing work. In order to increase efficiency, components (guide vanes, moving blades, heat accumulating segments etc.) exposed to the hot gas can be produced from heat resistant materials and can be cooled as effectively as possible during operation. Different methods have been developed in relation to the cooling of blades, and these can be used alternatively or cumulatively.

One known method includes conducting a coolant, such as pressurized cooling air from the compressor of the gas turbine, in cooling ducts through an interior of the blades. This coolant is allowed to enter into the cooling duct through cooling bores arranged in a distributed fashion. The cooling ducts can be repeatedly reversed in the interior of the blade in a serpentine fashion. See, for example, WO A1 2005/068783. The heat transfer between the coolant and walls of the blade can be improved in this case by additional turbulence generated in the coolant flow by suitable cooling elements, for example turbulators, or impingement cooling. However, complementary methods can permit the coolant to emerge from the interior of the blade such that there is formed on the blade surface a film of coolant, known as film cooling, that provides the blades additional protection against thermal loads.

Particular attention can be paid to the cooling of a narrow trailing edge of the blade. It can be advantageous for the efficiency of the turbine if the trailing edge can be designed to be as thin as possible. The trailing edge should be adequately cooled. Moreover, it can be advantageous to have cooling that is uniform in all operating states. It can be advantageous that the use of coolant be restricted to what is required in order not to exert a disadvantageous influence on the efficiency of the machine.

SUMMARY

A blade for a gas turbine is disclosed, including a platform, a blade tip, a leading edge, a trailing edge, and an airfoil extending between the platform and the blade tip, the airfoil being bounded in at least one direction by the leading edge and the trailing edge and having a suction side and a pressure side, wherein in a region of the trailing edge and in a direction running parallel to the trailing edge from the platform up to the blade tip, in an interior of the airfoil, there is a first cooling duct for feeding a coolant flow from the platform and from which coolant is guided to an outside of the airfoil via a multiplicity of holes arranged distributed on the blade, wherein a cross section of the first cooling duct tapers toward the blade tip, the taper being between 35% and 59%.

A method for producing a blade for a gas turbine, including forming a blade which includes a platform, a blade tip, a leading edge, a trailing edge, and an airfoil extending between the platform and the blade tip, the airfoil being bounded in at least one direction by the leading edge and the trailing edge and having a suction side and a pressure side, wherein in a region of the trailing edge and in a direction running parallel to the trailing edge from the platform up to the blade tip in an interior of the airfoil, there is a first cooling duct for feeding a coolant flow from the platform and from which coolant is guided to an outside of the airfoil via a multiplicity of holes arranged distributed on the blade, and wherein a cross section of the first cooling duct tapers toward the blade tip, the taper being between 35% and 59%, and forming the holes on the blade from outside into the blade as cooling bores with specified geometric tolerance by at least one of EDM (Electro-Discharge Machining) or laser drilling.

DETAILED DESCRIPTION

The disclosure relates to a cooled blade for a gas turbine which is distinguished by improved cooling, and a method for producing it. It can be advantageous that in a region of a trailing edge of a blade, and running parallel to the trailing edge from a platform up to a blade tip in an interior of an airfoil, there is a first cooling duct to which a coolant flow is supplied from the platform and from which coolant is guided to an outside via a multiplicity of holes distributed on the blade. The cross section of the first cooling duct tapers toward the blade tip, the taper being between, for example, 35% and 59%. For example, the taper of the blade can be approximately 42% (e.g., ±10%).

In an exemplary embodiment of the disclosure, a cross-sectional area of the first cooling duct has a height in a circumferential direction of the turbine, and a width in an axial direction of the turbine. The height/width side ratio diminishes toward the blade tip. The height/width side ratio diminishes toward the blade tip at, for example, 5% to 14%; for example, the height/width side ratio diminishes toward the blade tip by approximately 9%.

The holes arranged distributed on the blade can be designed as elongated cooling bores that can be produced with low geometric tolerance, for example, by EDM (Electro-Discharge Machining) or laser drilling.

In another exemplary embodiment of the disclosure, first cooling bores can be arranged distributed along the trailing edge. Second cooling bores can be arranged distributed on the blade tip, and the first and second cooling bores open into the exterior on a pressure side of the blade or have been introduced into the blade from the pressure side.

The inlets of the first cooling bores can be arranged substantively on a centerline of the first cooling duct.

The first cooling bores can have a cylindrical shape in that the ratio of a length to diameter of the first cooling bores can be between, for example, 20 and 35. The spacing of neighboring first cooling bores in a radial direction can be, for example, 2 to 5 times, for example, 3.5 times their diameter. The first cooling bores can enclose with the horizontal an angle of, for example, 20°-40°; for example, approximately 30°. The angle of the first cooling bores to the surface of the blade can be between, for example, 8° and 15°; for example, approximately 10°.

In accordance with an exemplary embodiment of the disclosure, at the transition between the platform and airfoil, the first cooling bores can be aligned with the centerline of the airfoil such that the coolant air is ejected centrally through these cooling bores at the intersection point between the centerline and the profile of the trailing edge.

In an exemplary embodiment the first cooling bores can merge uniformly at the blade tip into the second cooling bores. The second cooling bores can have a cylindrical shape. The ratio of length to diameter of the second cooling bores can be between, for example, 4 and 15. The spacing of neighboring second cooling bores can be, for example, 4 to 6 times; for example, 5 times their diameter. The angle of the second cooling bores to the surface of the blade can be between, for example, 25° and 35°; for example, approximately 30°.

In an exemplary embodiment for the cooling of the blades, third and fourth cooling bores can run through the platform, and the third cooling bores open into an exterior on a suction side of the blade, and the fourth cooling bores open into the exterior on the pressure side of the blade.

The fourth cooling bores can have a cylindrical shape and enclose different angles with the edge of the platform. The spacing of neighboring fourth cooling bores on the outside of the platform can be, for example, 5 to 8 times; for example, approximately 6 times their diameter. The ratio of length to diameter of the fourth cooling bores can be between, for example, 25 and 35. A proportion of the fourth cooling bores exit from the first cooling channel on its side facing the pressure side of the blade.

The third cooling bores can have a cylindrical shape and enclose different angles with the edge of the platform. The spacing on neighboring third cooling bores on the outside of the platform can be, for example, 6 to 8 times; for example, approximately 6.5 times their diameter. The ratio of length to diameter of the third cooling bores can be between, for example, 30 and 45. The third cooling bores can emerge from the first cooling duct on its side facing the suction side of the blade.

In order to generate and/or reinforce a turbulent cooling air flow, obliquely positioned ribs can be arranged in the first cooling duct. In the region of the platform, the first cooling duct can be connected via a bend to a parallel running second cooling duct. An outwardly guiding particle hole of relatively large diameter can be provided in the blade tip at the end of the first cooling duct.

In an exemplary embodiment of a method for producing the blade, holes arranged distributed on the blade are introduced from outside into the blade in the form of cooling bores with low geometric tolerance by, for example, EDM (Electro-Discharge Machining) or laser drilling.

The disclosure can be applied advantageously in a gas turbine having a multiplicity of moving blades fitted on a rotor and of guide vanes fitted in the housing surrounding the rotor. This can be done by using blades according to the disclosure as moving blades and/or guide blades.

FIG. 1shows a perspective, simplified illustration of a cooled gas turbine blade in accordance with an exemplary embodiment of the disclosure. The blade10, which can be a moving blade rotating with the rotor about the machine axis, or a guide blade mounted in stationary fashion on the housing, includes an airfoil11that extends in a longitudinal direction of the blade or in a radial direction of the gas turbine and terminates at the free end in a blade tip14. Adjoining the other end of the airfoil11is a platform12that bounds the hot gas duct and below which there is integrally formed a blade root13for mounting the blade10in a groove, provided for the purpose, in the rotor. The airfoil is bounded in the direction transverse to the longitudinal axis, that is to say in the flow direction of the hot gas of the turbine, upstream by a leading edge15, and downstream by a trailing edge16. The airfoil11has a cross sectional profile of a wing, the convexly curved side being the suction side17and the concavely curved side being the pressure side18.

In an interior a number of cooling ducts are provided that run parallel in the longitudinal direction, and are connected in a serpentine fashion. The figures show only a last cooling duct25, arranged in the region of a trailing edge16, and a portion of a cooling duct26arranged upstream thereof (FIG. 2). The two cooling ducts25and26can be interconnected by a bend28conforming to the flow (FIG. 2). In order to cool the blade10, there can be applied to the cooling ducts25,26a cooling air flow21that (as indicated by a dashed and dotted arrow inFIG. 1) can be guided up from below through the blade root13and the platform12from a plenum with compressed air of the gas turbine.

The trailing edge16, the platform12and the blade tip14of the blade can be penetrated by a multiplicity of long cooling bores19,20,22and23through which cooling air moves outward out of the cooling ducts25,26, and in the process cools the regions of the blade10which are flowed through. The cooling bores19,20,22and23can be produced, for example, by EDM (Electro-Discharge Machining; spark erosion) and/or laser drilling, it thereby being possible to effect narrow geometric tolerances in the bores.

All the cooling bores22and23of the airfoil11and of the blade tip14can open outward on the pressure side18of the blade10. The cooling bores19and20and20a, brunning through the platform12can open into the exterior on the suction side17of the blade (cooling bores19) or on the pressure side18of the blade (cooling bores20and20a, b). All the cooling bores of the cooling channels25(cooling bores19,20a,22,23) and26(cooling bores20b) can emerge in the interior of the blade10.

In order to permit the cooling air guided in the cooling ducts25,26to emerge at predetermined rates through all the cooling bores19,20,22,23on the trailing edge16, the blade tip14and the platform12, the cooling duct25at the trailing edge can be dimensional with regard to flow cross section and side ratio (H/W inFIG. 2a). This can ensure that the cooling air pressure in the cooling duct25assumes and maintains a predetermined value in all operating states of the machine. In particular, the dependence of the flow cross sections and side ratios in the cooling ducts25on the blade height (spatial coordinates in blade longitudinal direction) is arranged. The flow cross section of the cooling duct25can taper conically toward the blade tip14, by, for example, 35% to 59%; for example, approximately 42%. The ratio H/W of duct height H in a circumferential direction and duct width W in an axial direction (seeFIG. 2a) can diminish toward the blade tip14by, for example, 5% to 40%; for example, by approximately 9%.

The first cooling bores22of the blade10can be introduced into the airfoil11from the pressure side18. They open in the interior of the blade10into the cooling duct25, specifically such that their holes can lie directly on the centerline (dashed and dotted line30inFIG. 2) of the cooling duct cross section.

The first cooling bores22can be aligned in this case such that they enclose an angle between, for example, 20° and 40°; for example, approximately 30° with the horizontal. The angle between the first cooling bores22and the surface of the airfoil11can be between, for example, 8° and 15°; for example, approximately 10°. The spacing between neighboring first cooling bores22in a radial direction can correspond to 2 to 5 times, for example, approximately 3.5 times the bore diameter. The ratio of the length of the first cooling bores22to the diameter can vary along the blade heights in the region between20and35. The first cooling bores22can all have a cylindrical shape.

At the transition between the platform12and the airfoil (at the lower end of the cooling duct25at the transition to the bend28), the first cooling bores22there can be aligned along or substantially along the chord line29of the airfoil11(dashed and dotted line inFIG. 1) such that the cooling air can be ejected centrally through these first cooling bores22at the intersection point between the chord line29and the profile of the trailing edge16.

The first cooling bores22can merge uniformly into shorter second cooling bores23on the blade tip14. The second cooling bores23can have a cylindrical shape. The ratio of length to diameter of the second cooling bores23can be between, for example, 4 and 15. The spacing of neighboring second cooling bores23can be, for example, 4 to 6 times; for example, 5 times their diameter. The angle of the second cooling bores23to the surface of the blade10can be between, for example, 25° and 35°, for example; approximately 30°.

As described above, third and fourth cooling bores19and20,20a, brun through the platform12, the third cooling bores19open into the exterior on the suction side17of the blade10, and the fourth cooling bores20,20a, bopen into the exterior on the pressure side18of the blade10. The fourth cooling bores20,20a, balso have a cylindrical shape. They enclose various angles with the edge of the platform12(spreading). The spacing on neighboring fourth cooling bores20;20a, bon the outside of the platform12is, for example, 5 to 8 times; for example, approximately 6 times their diameter. The ratio of length to diameter of the fourth cooling bores20,20a, bis between, for example,25and35. A proportion (20a) of the fourth cooling bores can exit from the first cooling channel25on its side facing the pressure side18of the blade10. Another portion (20b) can exit from the second cooling duct26at its side facing the pressure side18of the blade10.

The third cooling bores19can also have a cylindrical shape and enclose different angles with the edge of the platform12. The spacing of neighboring third cooling bores19on the outside of the platform12is, for example, 6 to 8 times; for example, approximately 6.5 times their diameter. A ratio of length to diameter of the third cooling bores19lies between, for example,30and45. The third cooling bores19can exit from the first cooling duct25at its side facing the suction side17of the blade10.

In order to generate and/or reinforce a turbulent cooling air flow, obliquely positioned ribs27can be arranged in the first cooling duct25. It is possible to provide in the blade tip14, at the end of the first cooling duct25, a dust hole24of larger diameter that leads outward and is known per se, for example, from EP A2 1 882 817 and can contribute to preventing accumulation of dust in the cooling duct25.

LIST OF REFERENCE NUMERALS