Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-08-23
2001-08-14
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S09600A, C415S115000
Reexamination Certificate
active
06273682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to air-cooled airfoils of turbomachinery. More particularly, this invention is directed to a gas turbine engine airfoil equipped with a cooling passage near its trailing edge, in which the cooling passage is configured to preferentially cool the pressure wall of the airfoil for the purpose of reducing a thermal gradient between the pressure and suction walls of the airfoil.
BACKGROUND OF THE INVENTION
Higher operating temperatures for gas turbine engines are continuously sought in order to increase their efficiency. However, as operating temperatures increase, the high temperature properties of the engine components must correspondingly increase. While significant advances have been achieved through formulation of iron, nickel and cobalt-base superalloys, the high temperature properties of such alloys are often insufficient to withstand long exposures to operating temperatures within the turbine, combustor and augmentor sections of some high-performance gas turbine engines. As a result, internal cooling of components such as turbine blades (buckets) and nozzles (vanes) is generally necessary, and is often employed in combination with a thermal barrier coating (TBC) system that thermally protects their exterior surfaces. Effective internal cooling of turbine blades and nozzles often requires a complex cooling scheme in which bleed air is forced through serpentine passages within the airfoil and then discharged through carefully configured cooling holes at the airfoil trailing edge, and frequently also film cooling holes at the airfoil leading edge and/or cooling holes at the blade tip.
The performance of a turbine airfoil is directly related to the ability to provide a generally uniform surface temperature with a limited amount of cooling air. To promote convective cooling of the airfoil interior, it is conventional to cast turbulators, such as ribs or other surface features, in the interior surfaces that define the cooling passages. With film cooling holes, the size, shape and placement of the turbulators determine the amount and distribution of air flow through the airfoil cooling circuit and across the external surfaces of the airfoil downstream of the film cooling holes, and as such can be effective in significantly reducing the service temperature of the airfoil. Turbulators are typically employed throughout the interior cooling passages of an airfoil in order to promote cooling. To maximize heat transfer efficiency, turbulators are often formed on the interior surfaces of the airfoil sidewalls, often termed the pressure and suction walls, the former of which has a generally concave exterior profile while the latter has a generally convex exterior profile.
While cooling circuits, cooling holes and turbulators have been developed that significantly increase the maximum operating temperatures sustainable by turbomachinery airfoils, further improvements would be desirable in order to further extend airfoil life and increase engine efficiency.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an air-cooled airfoil whose surfaces adjacent the airfoil trailing edge are not equally cooled in order to compensate for operating conditions in which unequal heat loads are imposed on the pressure and suction sidewalls near the trailing edge. The invention is generally based on the determination that the external heat loads imposed by the hot combustion gases on the exterior airfoil surfaces vary from location to location, and that a significantly hotter wall temperature can occur on the pressure wall as compared to the suction wall near the trailing edge of a turbomachine airfoil. The result is a large thermal gradient at the trailing edge that can significantly promote thermal stresses, leading to cracks in the pressure wall near the trailing edge.
To compensate for this heat load imbalance, the airfoil of this invention is formed to have a cooling passage defined by interior surfaces of the pressure and suction walls at the airfoil trailing edge, with the interior surface of the suction wall being substantially smooth and uninterrupted. In contrast, the opposing interior surface of the pressure wall is formed to include surface features that project into the cooling passage to cause preferential convective cooling of the pressure wall as compared to the suction wall when air flows through the cooling passage. As a result, the present invention is able to achieve more uniform airfoil wall temperatures at the trailing edge by intentionally promoting heat transfer from the pressure wall over the suction wall.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
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General Electric Company
Hess Andrew C.
Look Edward K.
Woo Richard
Young Rodney M.
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