BLADE FOR A GAS TURBINE
A blade for a gas turbine includes an airfoil extending in a longitudinal direction and extending transversely to the longitudinal direction between a leading edge and a trailing edge. The airfoil has a pressure side, a suction side, and a slot-like cooling medium outlet extending along the trailing edge. The cooling medium outlet is configured to discharge cooling medium supplied from an inner space of the blade. A platform extends transversely to the longitudinal direction. An end of the airfoil merges into an underside of the platform and has a transition from the airfoil to the platform at the trailing edge of the airfoil that increases in thickness in a direction toward the underside of the platform. The cooling medium outlet extends into the platform so as to reduce an operating temperature in a region of the transition from the blade airfoil to the platform.
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This application claims priority to International Patent Application No. PCT/EP2009/062213, filed Sep. 21, 2009, which claims priority from Swiss Patent Application No. 01548/08, filed Sep. 30, 2008, each of which are incorporated by reference herein in their entirety. The International Application was published as WO2010/037659 on Apr. 8, 2010.
FIELDThe present invention relates to the field of gas turbines, and particularly relates to a blade for a gas turbine.
BACKGROUNDThe requirements for increasing the efficiency of gas turbines leads to the thickness at the trailing edges of the blade airfoils of the blades which are fitted in the gas turbines having to be continuously reduced. This results in a geometry of the blade as is exemplarily shown in cross section in
If, as is shown in the perspective view of
An aspect of the present invention is to further develop a blade for a gas turbine so that despite a low thickness at the trailing edge of the blade airfoil a satisfactory service life is achieved.
In an embodiment, the present invention provides a blade for a gas turbine including an airfoil extending in a longitudinal direction and extending transversely to the longitudinal direction between a leading edge and a trailing edge. The airfoil has a pressure side, a suction side, and a slot-like cooling medium outlet extending along the trailing edge. The cooling medium outlet is configured to discharge cooling medium supplied from an inner space of the blade. A platform extends transversely to the longitudinal direction. An end of the airfoil merges into an underside of the platform and has a transition from the airfoil to the platform at the trailing edge of the airfoil that increases in thickness in a direction toward the underside of the platform. The cooling medium outlet extends into the platform so as to reduce an operating temperature in a region of the transition from the blade airfoil to the platform.
Exemplary embodiments of the present invention are described in more detail below, with reference to the drawings. Some non-essential elements of the invention have been omitted. Like elements are provided with the same designations in the different figures. In the drawings:
In an embodiment, the present invention provides a transition from the blade airfoil to the platform at the trailing edge that has a transition thickness profile in which the thickness increases above average the closer it gets to the underside of the platform, and that the cooling medium outlet is extended right into the platform for reducing the temperature in the region of the transition from the blade airfoil to the platform. As a result of increasing the thickness of the trailing edge towards the platform the mechanical stress in the transition region is reliably reduced. Extending the cooling medium outlet right into the platform leads to improved cooling there so that thermally induced stresses are also significantly reduced.
In one embodiment, the transition thickness profile has an essentially exponential shape which resembles an inverted, very slender, truncated pyramid or an inverted virtual pyramid. As a result of this an especially “smooth” transition between trailing edge and platform is achieved.
In another embodiment, the transition from the blade airfoil to the platform has an approximately elliptical transition border profile which also reduces stresses.
Furthermore, it is advantageous if according to another development the trailing edge at the transition from the blade airfoil to the platform is extended up to the edge of the platform.
In an other embodiment, the cooling medium outlet is formed between a pressure-side wall of the blade airfoil and a suction-side wall of the blade airfoil, and in that the pressure-side wall has a curvilinear transition edge profile in the transition from the blade airfoil to the platform in such a way that the wall thickness of the pressure-side wall in the region of the transition from the blade airfoil to the platform is approximately equal to the wall thickness in the remaining region of the blade airfoil.
In
The transition thickness profile 21 has an essentially exponential shape and as a result resembles an inverted rampant pyramid. It is especially favorable in this case with regard to the stress distribution if the transition from the blade airfoil 11 to the platform 12 has an approximately elliptical transition border profile 22. While in the case of the conventional blade according to
As is to be seen in
In all, an appreciable improvement of the service life at the transition between the blade-airfoil trailing edge and the platform of a gas turbine blade is achieved by the invention as a result of the following measures:
-
- (1) Extending the cooling medium outlet (cooling slot) into the platform in order to reduce the metal temperature in the critical region by feeding cooling medium, wherein convective cooling of the walls on both sides takes place.
- (2) Relocating the blade-airfoil trailing edge to the boundary of the platform in order to lower stress and to make the design of the blade independent of deviations in the radial position of the cast core.
- (3) Introducing a transition thickness profile of a rampant pyramid type by increasing the height and introducing a special elliptical contour of the fillet at the transition between blade airfoil and platform in the region of the trailing edge.
- (4) Introducing a specially curvilinear transition edge profile towards the pressure side of the blade airfoil on the fillet at the transition between blade airfoil and platform in the region of the trailing edge in order to achieve a wall thickness in the transition region which corresponds to the wall thickness of the blade airfoil, as a result of which stress and metal temperature is reduced and service life at the transition is increased.
10, 20 Blade (gas turbine)
11 Blade airfoil
12 Platform
-
- 12′ Underside (platform)
12″ Edge (platform)
13 Pressure side
13′ Wall (pressure side)
14 Suction side
14′ Wall (suction side)
15 Leading edge
16 Trailing edge
17 Inner space
18 Cooling medium outlet (slot-like)
19 Extension (cooling medium outlet)
21 Transition thickness profile
22 Transition border profile
23 Transition edge profile
D Thickness (transition thickness profile)
Claims
1. A blade for a gas turbine, the blade comprising:
- an airfoil extending in a longitudinal direction and extending transversely to the longitudinal direction between a leading edge and a trailing edge, the airfoil having a pressure side, a suction side, and a slot-like cooling medium outlet extending along the trailing edge, the outlet configured to discharge cooling medium supplied from an inner space of the blade;
- a platform extending transversely to the longitudinal direction, a first end of the airfoil merging into an underside of the platform and having a transition from the airfoil to the platform at the trailing edge of the airfoil that increases in thickness in a direction toward the underside of the platform, and
- wherein the cooling medium outlet extends into the platform so as to reduce an operating temperature in a region of the transition from the blade airfoil to the platform.
2. The blade as recited in claim 1, wherein the transition from the blade airfoil to the platform has a thickness profile having a substantially exponential shape corresponding to at least one of an inverted rampant pyramid, an inverted truncated pyramid, and an inverted virtual pyramid.
3. The blade as recited in claim 1, wherein the transition from the blade airfoil to the platform has an approximately elliptical profile.
4. The blade as recited in claim 1, wherein the transition from the blade airfoil to the platform extends to an edge of the platform.
5. The blade as recited in claim 2, wherein the transition from the blade airfoil to the platform extends to an edge of the platform.
6. The blade as recited in claim 3, wherein the transition from the blade airfoil to the platform extends to an edge of the platform.
7. The blade as recited in claim 1, wherein the cooling medium outlet is formed between a pressure-side wall of the blade airfoil and a suction-side wall of the blade airfoil, and wherein the transition from the blade airfoil to the platform along the pressure-side wall has a curvilinear edge profile such that a wall thickness of the pressure-side wall in a region of the transition is approximately equal to a wall thickness in a remaining region of the blade airfoil.
8. The blade as recited in claim 7, wherein the transition from the blade airfoil to the platform extends to an edge of the platform.
Type: Application
Filed: Mar 30, 2011
Publication Date: Sep 29, 2011
Applicant: ALSTOM TECHNOLOGY LTD (Baden)
Inventors: Christoph Nagler (Zurich), Erich Kreiselmaier (Stetten), Jose McFeat Anguisola (Lauchringen), Sergei Riazantsev (Nussbaumen)
Application Number: 13/075,234
International Classification: F01D 5/18 (20060101);