Partially turbulated trailing edge cooling passages for gas...

Details Partially turbulated trailing edge cooling passages for gas... Partially turbulated trailing edge cooling passages for gas...

1999-05-14

2001-02-20

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

With passage in blade, vane, shaft or rotary distributor...

C415S178000, C416S09700R

Reexamination Certificate

active

06190120

ABSTRACT:

TECHNICAL FIELD
The present invention relates to gas turbine nozzles having cooling passages for flowing a thermal medium from a cavity within the nozzle vane through the passages into the hot gas path for cooling the trailing edge and particularly relates to trailing edge cooling passages having turbulators and cooling passage inlets arranged to enhance temperature distribution, minimize thermal stresses and trailing edge cracks and reduce the magnitude of required bleed air.
BACKGROUND OF THE INVENTION
Trailing edges of nozzle vanes in gas turbines often contain cooling passages for cooling the trailing edges. Typically, cooling air is provided in a cavity in the vane and passes through a plurality of passages spaced from one another along the length of the trailing edge of the vane and exits into the hot gas path. The cooling air cools the metal of the trailing edge surrounding the passages and along outer surfaces of the trailing edge. Conventionally, thermal barrier coatings are provided along the side walls of the trailing edge and about the trailing edge tip. However, notwithstanding efforts to uniformly apply the thermal barrier coating to the side walls and tip of the trailing edge, the coating oftentimes breaks off from the tip during handling or spalls off the tip during operation. Thus, cooling the tip of the trailing edge is of particular concern and therefore requires heat transfer enhancement for effective cooling.
Turbulators have also been employed in the passages for cooling the trailing edges of nozzles. The turbulators interrupt the cooling air flow, creating turbulence and cause enhanced cooling effect. Turbulators are conventionally located along the entire length of the cooling passages. This therefore results in enhanced cooling of the surrounding metal and trailing edge surfaces throughout the length of the trailing edge passages. The material of these regions, however, are protected, to a large extent, by the thermal barrier coating along the sides of the trailing edge. Consequently, the region requiring cooling enhancement, i.e., the tip of the trailing edge, is effectively cooled, while those regions which are protected by the thermal barrier coating and do not require cooling enhancement are nonetheless provided with enhanced cooling effects by the turbulators. This causes a wide-ranging temperature distribution laterally along the trailing edge, with consequent thermal mismatches resulting in high stresses in the metal of the trailing edge.
Further, it will be appreciated that air for cooling the trailing edge of nozzle vanes typically comprises compressor discharge air. To the extent air is bled from the compressor for cooling purposes, the turbine has diminished efficiency. Accordingly, the problem at hand is to provide enhanced cooling effect in the regions requiring enhanced cooling, while eliminating enhanced cooling for those regions of the trailing edge which do not require enhanced cooling, while simultaneously limiting required cooling bleed air from the compressor discharge.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a gas turbine nozzle vane having trailing edge cooling passages for receiving a thermal medium, preferably air, for cooling the trailing edge and which vane employs partially-turbulated trailing edge cooling passages. By providing cooling air passages only partially turbulated, a temperature distribution across the trailing edge is achieved with minimized thermal gradients and consequent reduced stresses, while affording enhanced cooling along the tip of the trailing edge with minimal compressor bleed discharge air. To accomplish the foregoing, a nozzle vane trailing edge is provided having a plurality of cooling passages spaced one from the other along the length of the trailing edge and lying in communication with a cavity within the vane. Cooling air flows from the cavity through the cooling passages into the hot gas stream. The passages, however, are only partially turbulated and then only in regions where enhanced heat transfer is required. Thus, the aft portions of the trailing edge passages adjacent the tip, i.e., adjacent the outlet of the cooling air flowing into the hot gas stream, are turbulated, while the majority of the passages forwardly of the turbulated passage portions are not turbulated. Preferably, those forward passage portions have smooth bores. Consequently, the temperature distribution in the metal regions surrounding the non-turbulated passage portions minimizes the thermal gradients and reduces stresses, while the turbulated aft passage portions afford enhanced cooling effects in the region along the trailing edge tip where the thermal barrier coating has worn or spalled off during operation.
Further, bleed compressor discharge air is minimized for flow through the cooling passages by limiting the size of the entry slots into the passages. Thus, each entry slot adjacent the forward end of the passages has a reduced cross-section, limiting the air flow into the passage. In this manner, reduced compressor bleed discharge air is required thereby affording improved turbine efficiency.
In a preferred embodiment according to the present invention, there is provided cooling apparatus for a turbine comprising a turbine vane having a trailing edge terminating in an aft tip and a cavity forward of the trailing edge for receiving a thermal medium, the trailing edge including a plurality of discrete passages spaced one from another along the length of the trailing edge, the passages lying in communication at one end with the cavity for receiving the thermal medium from the cavity for flow therethrough to apertures along the tip of the trailing edge and turbulators disposed in the passages along aft portions thereof with portions of the passages forwardly of the aft portions and forming the majority of the lengths of the passages being without turbulators, each turbulator forming an abutment surface in the aft passage portion for creating turbulence in the thermal medium passing through the aft passage portions thereby cooling the trailing edge and minimizing thermal gradients and stresses therealong.
In a further preferred embodiment according to the present invention, there is provided cooling apparatus for a turbine comprising a turbine vane having a trailing edge terminating in an aft tip and a cavity forward of the trailing edge for receiving a thermal medium, the trailing edge including a plurality of discrete passages spaced one from another along the length of the trailing edge, the passages lying in communication at one end with the cavity for receiving the thermal medium from the cavity for flow therethrough to apertures along the tip of the trailing edge and turbulators disposed in the passages forming abutment surfaces for creating turbulence in the thermal medium passing through the passage portions thereby cooling the trailing edge and forward portions of the passages having reduced flow inlet apertures adjacent junctions of the cavity and passages for limiting the flow of thermal medium into the passages.


REFERENCES:
patent: 3528751 (1970-09-01), Quinones et al.
patent: 5931638 (1999-08-01), Krause et al.
patent: 6004100 (1999-12-01), Przirembel et al.

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