This application is the US National Stage of International Application No. PCT/EP2021/063617 filed 21 May 2021, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 10 2020 207 646.4 filed 22 Jun. 2020. All of the applications are incorporated by reference herein in their entirety.
The invention relates to a turbine blade for a gas turbine with a blade root and an aerodynamically curved blade leaf, arranged above the blade root, wherein the blade leaf has a pressure-side blade wall and a suction-side blade wall which extend together from a leading edge, onto which a working medium can flow, of the blade leaf to a trailing edge of the blade leaf, wherein a plurality of cooling-air outlet openings are formed on the pressure-side blade wall which, starting from the trailing edge, each extend upstream relative to the direction of flow of a working medium which flows around the blade leaf and through which cooling air routed through the inside of the blade leaf can issue, wherein at least one of the cooling-air outlet openings has an essentially rectangular or trapezoidal shape with rounded corners which preferably widens out in the direction in which the cooling air issues. The invention moreover relates to a method for machining such a turbine blade.
Turbine blades of the type mentioned at the beginning are known from the prior art in different embodiments. During operation, they are exposed to high thermal stresses, as a result of which their blade leaves are cooled in order to increase their lifetime. For this purpose, cooling air is introduced through the blade root into the blade leaf and issues essentially axially into the flow duct of the working medium through the cooling-air outlet openings provided on the pressure-side blade wall in the region of the trailing edge. The cooling-air outlet openings have an essentially trapezoidal and/or rectangular shape which widens out in the direction in which the cooling air issues and are often also referred to as cutback openings. There is a problem, on the one hand, that geometrical stresses are induced in the blade leaf by the provision of such cooling-air outlet openings and, on the other hand, that the cooling caused by the cooling air is not uniform in the region of the cooling-air outlet openings, which entails thermally induced stresses. These geometrical and thermal stresses can limit the lifetime of the turbine blades and mean that turbine blades often have to be replaced as part of maintenance work. Attempts to overcome the negative effects of the stresses by reinforcing the blade leaf in the region of the cooling-air outlet openings have proved to be unsuccessful. As a result, either a greater degree of risk has been accepted or the period for which the turbine blades are used has been restricted.
Starting from this prior art, an object of the present invention is to provide an improved turbine blade of the type mentioned at the beginning.
In order to achieve this object, the present invention provides a turbine blade for a gas turbine with a blade root and an aerodynamically curved blade leaf arranged above the blade root, wherein the blade leaf has a pressure-side blade wall and a suction-side blade wall which extend together from a leading edge, onto which a working medium can flow, of the blade leaf to a trailing edge of the blade leaf, wherein a plurality of cooling-air outlet openings are formed on the pressure-side blade wall which, starting from the trailing edge, each extend upstream relative to the direction of flow of a working medium which flows around the blade leaf and through which cooling air routed through the inside of the blade leaf can issue, wherein at least one of the cooling-air outlet openings has an essentially rectangular or trapezoidal shape with rounded corners which preferably widens out in the direction in which the cooling air issues, characterized in that at least the lower corner, facing the leading edge, of this at least one cooling-air outlet opening forms a relief notch which projects outward from the rectangular shape and has a rounded notch base. It has been established during the development of turbine blades that the high stresses in the region of the cooling-air outlet openings are primarily thermally caused geometrically only to a small extent. Against this background, the geometry of at least the most highly stressed cooling-air outlet opening has been redesigned such that a relief notch with a rounded notch base has been added in the lower corner facing the leading edge. Even though this relief notch significantly reduces the rigidity of the turbine blade in the region of the corresponding cooling-air outlet opening, it assists the thermal expansion of the blade leaf, as a result of which the stresses within the turbine blade as a whole are significantly reduced, which entails an appreciable increase in the lifetime. It was also possible to verify this positive effect by 3D finite element analysis.
According to a variant of the present invention, the relief notch continues the line of a lower edge of the cooling outlet opening, wherein the notch base arranged above the lower edge of the cooling outlet opening faces in the direction of the leading edge of the blade leaf. In this variant, the blade leaf can be produced in the region of the cooling-air outlet opening in the casting process with no undercut, which is desirable in principle.
According to a further variant of the present invention, the relief notch extends, starting from the lower edge of the cooling outlet opening, obliquely downward at an obtuse angle, wherein the notch base arranged below the lower edge of the cooling outlet opening faces in the direction of the blade root. This variant is advantageous in terms of stress. However, it cannot be manufactured in the casting process without disruptive undercuts.
The relief notch preferably widens out, starting from its notch base, in the manner of a chalice, as a result of which particularly good thermal expansibility of the blade leaf is obtained in the region of the cooling-air outlet opening.
The at least one cooling-air outlet opening is advantageously the lowest cooling-air outlet opening because it is there that the highest thermal stresses occur.
The present invention moreover provides a method for machining a turbine blade with a blade root and an aerodynamically curved blade leaf, wherein the blade leaf has a pressure-side blade wall and a suction-side blade wall which extend together from a leading edge, onto which a working medium can flow, of the blade leaf to a trailing edge of the blade leaf, wherein a plurality of cooling-air outlet openings are formed on the pressure-side blade wall which, starting from the trailing edge, each extend upstream relative to the direction of a working medium which flows around the blade leaf and through which cooling air routed through the inside of the blade leaf can issue, and wherein one of the cooling-air outlet openings has an essentially rectangular or trapezoidal shape with rounded corners, characterized in that a relief notch which projects outward from the rectangular shape and has a rounded notch base is formed in at least the lower corner, facing the leading edge, of this at least one cooling-air outlet opening in order to produce a turbine blade according to the invention.
Further features and advantages of the present invention will become clear with the aid of the following description embodiments with reference to the attached drawings, in which:
The same reference numerals refer below to similar components or component regions.
The turbine blade 1 shown in
It should be noted that it is of course also alternatively possible to manufacture the turbine blade 1 shown in
The turbine blade 1 illustrated in
The relief notch 11 shown in
Although the invention has been illustrated and described in detail by the preferred exemplary embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by a person skilled in the art without going beyond the protective scope of the invention. In particular, further cooling-air outlet openings 9 and/or a cooling-air outlet opening 9 other than the lowest one can also be provided with a relief notch 11.
Number | Date | Country | Kind |
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10 2020 207 646.4 | Jun 2020 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/063617 | 5/21/2021 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2021/259569 | 12/30/2021 | WO | A |
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Entry |
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PCT International Search Report and Written Opinion of International Searching Authority dated Sep. 9, 2021 corresponding to PCT International Application No. PCT/EP20211063617 filed May 21, 2022. |
Number | Date | Country | |
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20230220778 A1 | Jul 2023 | US |