Blade for a gas turbine

Abstract

Blade (20) for a gas turbine, which blade (20) comprises a blade airfoil (11) extending in a longitudinal direction, - which extends transversely to the longitudinal direction between a leading edge (15) and a trailing edge (16) and has a pressure side (13) and a suction side (14), and - at one end it merges into a platform (12) lying transversely to the longitudinal direction, - wherein a slot-shaped coolant outlet (18) extending along the trailing edge (16) is provided on the trailing edge (16), through which a coolant supplied via the interior (17) of the blade (20) is expelled, - wherein the coolant outlet (18) is formed between a pressure-side wall (13') of the blade (11) and a suction-side wall (14') of the blade (11), - wherein the transition from the blade (11) to the platform (12) at the trailing edge (16) has a transition thickness profile (21), the thickness (D) of which increases disproportionately with increasing approach to the underside (12') of the platform (12), - that the pressure-side wall (13') has a curved transition edge profile (23) in the transition from the blade (11) to the platform (12), and - wherein the coolant outlet (18) is extended (19) into the platform (12) to reduce the temperature in the region of the transition from the blade (11) to the platform (12), characterized by that the transition thickness profile (21) has a substantially exponential shape, that the transition from the blade (11) to the platform (12) has an approximately elliptical transition edge profile (22) which resembles an upside-down Eiffel Tower, that the trailing edge (16) at the transition from the blade (11) to the platform (12) is projected to the edge (12'') of the platform (12), and that the wall thickness of the pressure-side wall (13') in the region of the transition from the blade (11) to the platform (12) is approximately equal to the wall thickness in the remaining region of the blade (11).

Description

Technical area

[0001] The present invention relates to the field of gas turbines. It concerns a blade for a gas turbine according to the preamble of claim 1. State of the art

[0002] The demand for increased efficiency of gas turbines means that the thickness of the trailing edges of the blades used in gas turbines must be continually reduced. This results in a blade geometry as shown in Fig. 1 is shown in cross-section as an example: The blade 10 of the Fig. 1 extends in the manner of a wing profile transversely to its longitudinal direction between a rounded leading edge 15 and a comparatively tapered trailing edge 16. The blade 10 has a (concave) pressure side 13 and a (convex) suction side 14 with corresponding walls 13' and 14'. A gaseous coolant or cooling medium is supplied to the hollow interior 17 and expelled into the environment, among other things, through a coolant outlet formed on the trailing edge 16. A particularly tapered, slim trailing edge 16 is achieved in that the coolant outlet 18 is arranged entirely on the pressure side 13 of the blade 10, and the two walls 13' and 14' in the region of the trailing edge 16 are particularly thin.

[0003] If, as shown in the perspective view of the Fig. 2, the blade 11 merges at the end of its longitudinal extension into a platform 12 lying transversely to the longitudinal direction and is delimited by this platform 12, the transition of the blade 11 to this platform 12 in the region of the trailing edge 16 represents a typical factor limiting the service life of a gas turbine component because it is subjected to a superposition of high thermal stress, caused by the thermomechanical mismatch between platform 12 and blade 11, and mechanical stress peaks, caused by the loading of the blades by the gas flow. Reducing the thickness of the trailing edge 16 causes an increase in stress in this critical area, so that measures must be considered when designing the blade in order to achieve and ensure a sufficiently long service life.

[0004] US Pat. No. 6,328,531 discloses a gas turbine blade that attempts to mitigate some of these disadvantages. For example, the immediate transition area from the blade to the platform has a transition thickness profile whose thickness increases disproportionately with increasing approach to the platform and is perceived as a rounded fillet. Furthermore, the slot-shaped coolant outlet is drawn down to slightly below the platform's surface for more intensive cooling, forming a trough-like depression that flattens at the trailing edge of the blade between the pressure and suction sides and finally merges into the platform's surface. According to this document, these combined measures are intended to reduce the high thermally induced stresses in this critical blade area.

[0005] US Patent No. 3,885,609 describes a gas turbine blade with improved cooling in the trailing edge region. This improved cooling is achieved by a special design of the cooling air duct within the blade and by discharging a first portion of the cooling air into the hot gas duct on the intake side in the trailing edge region, while a second portion of the cooling air exits the hot gas duct on the pressure side.

[0006] DE 698 14 341 T2 describes a gas turbine blade in which the wall thickness of the gas turbine blade is specifically increased in certain areas to reduce thermally induced stresses.

[0007] DE 60 2004 003 331 T2 describes a gas turbine blade in which a cooling air slot arranged adjacent to the blade root is designed in such a way that the formation of cracks is prevented and the cooling of the connection area between the blade and the blade root is ensured. Description of the invention

[0008] The invention is based on the object of further developing a blade of the type mentioned at the outset for a gas turbine, starting from the aforementioned prior art, in such a way that a sufficient service life is achieved despite a small thickness at the trailing edge of the blade.

[0009] The problem is solved by the totality of the features of claim 1. It is essential for the invention that the transition from the blade to the platform at the trailing edge has a transition thickness profile in a manner known per se, in which the thickness increases disproportionately as the underside of the platform approaches, and that the coolant outlet is extended into the platform to reduce the temperature in the region of the transition from the blade to the platform. By expanding the thickness of the trailing edge towards the platform, the mechanical stress in the transition region is reliably reduced. The extension of the coolant outlet into the platform leads to improved cooling there, so that thermally induced stresses are also significantly reduced.

[0010] Furthermore, the transition thickness profile has a substantially exponential shape, resembling an upside-down Eiffel Tower. This creates a particularly smooth transition between the trailing edge and the platform.

[0011] In addition, the transition from the blade to the platform has an approximately elliptical transition edge profile, which also reduces stresses, and the trailing edge at the transition from the blade to the platform is advanced to the edge of the platform.

[0012] The invention is further characterized in that the coolant outlet is formed between a pressure-side wall of the blade and a suction-side wall of the blade, and in that the pressure-side wall has a curved transition edge profile in the transition from the blade to the platform, such that the wall thickness of the pressure-side wall in the region of the transition from the blade to the platform is approximately equal to the wall thickness in the remaining region of the blade. Brief explanation of the figures

[0013] The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawings. All elements not essential for a direct understanding of the invention have been omitted. Identical elements are provided with the same reference numerals in the various figures. Fig. 1 is a highly simplified cross-section through an exemplary gas turbine blade with a narrow trailing edge and a coolant outlet arranged on the pressure side at the trailing edge, as is suitable for the application of the invention; Fig. 2 for a shovel according to Fig. 1 the previously used abrupt transition between blade and platform; and Fig. 3 the low-stress transition between the blade and the platform according to an embodiment of the invention. Ways to implement the invention

[0014] In Fig. 3 shows a blade 20 for a gas turbine with a low-stress transition between the blade airfoil 11 and the platform 12 according to an exemplary embodiment of the invention. The blade 20 of the exemplary embodiment comprises a blade airfoil 11 extending in a longitudinal direction, which extends transversely to the longitudinal direction between a leading edge 15 and a trailing edge 16 in the manner of a wing and has a pressure side 13 and a suction side 14. At the upper (or lower) end, the blade airfoil 11 merges into a platform 12 lying transversely to the longitudinal direction, which projects laterally beyond the blade cross-section. At the trailing edge 16 of the blade airfoil 11, a slot-shaped coolant outlet 18 is provided, extending along the trailing edge 16, through which coolant, e.g., cooling air, supplied via the (hollow) interior 17 of the blade 20 is expelled. The trailing edge 16 is very narrow with its thin walls 13' and 14'.To reduce thermal stresses at the transition between the narrow trailing edge 16 and the massive platform 12, the transition has a transition thickness profile 21, in which the thickness D increases disproportionately with increasing approach to the underside 12' of the platform 12. At the same time, the coolant outlet 18 is extended into the platform 12 (extension 19) to reduce the local temperature in the area of the transition from the blade 11 to the platform 12.

[0015] The transition thickness profile 21 has a substantially exponential shape and thus resembles an upside-down Eiffel Tower. Particularly advantageous with regard to stress distribution is the fact that the transition from the blade 11 to the platform 12 has an approximately elliptical transition edge profile 22. While in the conventional blade according to Fig. 2 the trailing edge 16 of the blade 11 ends within the platform 12 and does not extend to the edge of the platform 12, in the embodiment of the Fig. 3 the trailing edge 16 at the transition from the blade 11 to the platform 12 is pulled forward to the edge 12'' of the platform 12.

[0016] As in Fig. 3, the coolant outlet 18 is delimited by the pressure-side wall 13' and the suction-side wall 14' of the blade 11. The pressure-side wall 13' has a curved transition edge profile 23 in the transition from the blade 11 to the platform 12, such that the wall thickness of the pressure-side wall 13' in the region of the transition from the blade 11 to the platform 12 is approximately equal to the wall thickness in the remaining region of the blade 11.

[0017] Overall, the invention achieves a significant improvement in the service life at the transition between the blade trailing edge and the platform of a gas turbine blade through the following measures: (1) The extension of the coolant outlet (cooling slot) into the platform to reduce the metal temperature in the critical area by introducing coolant, whereby convective cooling of the walls on both sides takes place. (2) Relocation of the blade trailing edge to the edge of the platform to reduce stress and make the blade design independent of deviations in the radial position of the casting core. (3) Introduction of an “Eiffel Tower” type transition thickness profile by increasing the size and introducing a special elliptical contour of the fillet at the transition between the blade and the platform in the trailing edge area. (4) Introduction of a specially curved transition edge profile to the pressure side of the blade at the fillet at the transition between the blade face and the platform in the trailing edge area in order to achieve a wall thickness in the transition area that corresponds to the wall thickness of the blade, thereby reducing stress and metal temperature and increasing the service life at the transition. List of reference symbols 10, 20 blades (gas turbine) 11 Blade 12 Platform 12' bottom (platform) 12'' edge (platform) 13 Printed page 13' wall (pressure side) 14 Suction side 14' wall (suction side) 15 leading edge 16 trailing edge 17 Interior 18 Coolant outlet (slot-shaped) 19 Extension (coolant outlet) 21 Transition thickness profile 22 Transition edge profile 23 Transition edge profile D Thickness (transition thickness profile)

Claims

[1] Blade (20) for a gas turbine, which blade (20) comprises a blade (11) extending in a longitudinal direction, - which extends transversely to the longitudinal direction between a front edge (15) and a rear edge (16) and has a pressure side (13) and a suction side (14), and - at one end it merges into a platform (12) lying transversely to the longitudinal direction, - wherein a slot-shaped coolant outlet (18) extending along the trailing edge (16) is provided on the trailing edge (16), through which a coolant supplied via the interior (17) of the blade (20) is expelled, - wherein the coolant outlet (18) is formed between a pressure-side wall (13') of the blade (11) and a suction-side wall (14') of the blade (11), - wherein the transition from the blade (11) to the platform (12) at the trailing edge (16) has a transition thickness profile (21) whose thickness (D) increases disproportionately with increasing approach to the underside (12') of the platform (12), - that the pressure-side wall (13') has a curved transition edge profile (23) in the transition from the blade (11) to the platform (12), and - wherein the coolant outlet (18) is extended (19) into the platform (12) to reduce the temperature in the region of the transition from the blade (11) to the platform (12), characterized by , that the transition thickness profile (21) has a substantially exponential shape, that the transition from the blade (11) to the platform (12) has an approximately elliptical transition edge profile (22) which resembles an upside-down Eiffel Tower, that the trailing edge (16) at the transition from the blade (11) to the platform (12) is projected to the edge (12'') of the platform (12), and that the wall thickness of the pressure-side wall (13') in the region of the transition from the blade (11) to the platform (12) is approximately equal to the wall thickness in the remaining region of the blade (11).

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