Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
2002-12-20
2004-12-28
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...
Reexamination Certificate
active
06835046
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to a turbine blade through which cooling fluid flows.
BACKGROUND OF THE INVENTION
A turbine blade, through which cooling fluid flows, has internal flow ducts, which are separated from one another by internal walls. The working fluid flows around the turbine blade. The turbine blade can be a gas turbine blade. The working fluid is then gas. The turbine blade is inclined relative to the approaching working fluid, so that a force component in the peripheral direction of the turbine occurs in the usual manner. The efflux direction of the working fluid is, therefore, essentially that direction along the turbine blade in which the working fluid flows around the latter.
The type mentioned is a turbine blade in the rear region of a turbine. In this location, the working fluid has already expanded and cooled to such an extent that only slightly cooled turbine blades are employed. Thus, only a small flow of cooling fluid through the turbine is provided. Because of the small flow, a meander structure of flow ducts for the cooling fluid does not function satisfactorily in the case of slightly cooled turbine blades. Because of the slow flow velocity of the cooling fluid, the latter would have an excessive cooling effect in the initial region of a meandering flow duct and would be too strongly heated in the final region, in consequence, the cooling effect would be inadequate in that region; in the case of the turbine blades mentioned, the flow velocity of the cooling fluid can also be too low with respect to the centrifugal forces occurring due to the rotation of the turbine.
The cooling fluid therefore only flows in a simple manner along the radial extent of the turbine blade. In the case of simple flow—i.e. in the case of flow ducts with practically no reversal locations relative to the radial direction of the cooling fluid flow—the problems mentioned above do not occur. For this purpose, turbine blades are known which have radial holes or straight radial ducts extending from a radially inner blade root to outlet flow openings located further radially outward—outlet flow openings introduced into the rubbing edge. The resulting cooling fluid flow then has the desired local—at each location of the flow duct—radial flow components which are expediently directed, predominantly to exclusively, radially outward.
Because of the technically determined minimum dimensions of both the cast core and the wall thickness, the flow, and therefore also the cooling effect, is strongly inhomogeneous in such turbine blades. As an example, the region of a trailing edge, which has to become narrower in the efflux direction, can as a rule no longer have a radial flow duct passing through it because of the minimum dimensions mentioned, determined by the manufacturing process. The result is overheating of the overhanging trailing edge. In addition, there are limitations—in particular due to the minimum dimensions mentioned above—to the geometry of the usually large turbine blades in the rear region of the turbine.
SUMMARY OF THE INVENTION
An object of an embodiment of the present invention is to provide a turbine blade which, despite a small cooling fluid flow, is matched in terms of its geometry to the technical requirements for slightly cooled turbine blades and nevertheless permits substantially homogeneous cooling, in particular in the edge zones.
An embodiment of the invention offers the advantage that it permits a homogeneous cooling of the turbine blade, in particular in the region of the edges. The region of the trailing edge duct, in which the aerodynamic requirements demand narrowing of the turbine blade, for example, is particularly problematic in this connection.
The advantage mentioned may be achieved by one or more trailing edge ducts being present whose cooling fluid flow have local transverse flow components at predetermined locations, outlet flow openings being introduced into a trailing edge of the turbine blade for these trailing edge ducts. The use of the trailing edge as the region for the outlet flow of the cooling fluid opens a large variety of design possibilities, which were not previously accessible, for slightly cooled turbine blades.
As an example, the trailing edge ducts can—at least in part—conduct their cooling fluid away via the outlet flow openings which are introduced into the trailing edge. By this, more free space is also created for the ducts located—viewed in the efflux direction—before the trailing edge ducts. Outlet flow openings, particularly on the rubbing edge, admission to which had previously been through the trailing edge ducts, can now be used for conducting away cooling fluid from flow ducts located in front of the trailing edge ducts.
A trebly useful effect is achieved: by this it is, namely, possible for the first time to effectively and homogeneously cool the trailing edge of a turbine blade according to an embodiment of the invention and to have, at the same time, a thin trailing edge (with respect to improved aerodynamics). In addition, a natural efflux of the cooling fluid is achieved for the trailing edge ducts and this also permits the front flow ducts located in front of the trailing edge ducts to be matched, in their geometry and particularly in their efflux behavior, to the technical requirements.
Thus, for example, front flow ducts can provide admission to more outlet flow length along the rubbing edge than was previously the case. Because the trailing edge ducts are, on the one hand, displaced further in the efflux direction toward the trailing edge and, on the other, are deflected due to their bent shape, the front flow ducts located in front of them can fill the resulting free space. Due to the local transverse flow components of the trailing edge ducts, the front flow ducts can likewise be bent in such a way that they also have local transverse flow components. This provides a different space utilization within the cooling volume of the turbine blade, with better utilization of the cooling air.
By this, even turbine blades in the rear region of the turbine—i.e. turbine blades with little cooling—can, for the first time, be embodied with minimum to disappearing limitations with respect to the geometry. It is, for example, an adequately known requirement (for strength reasons and casting reasons) that the turbine blade should become narrower away from the blade root in the radial direction. Because the outlet flow openings of the trailing edge are used, the other flow ducts, in particular the front and central flow ducts, can be extended in this direction in terms of their extent parallel to the efflux direction and, therefore, can compensate for the decrease in thickness in the radial direction by spreading parallel to the efflux direction and utilizing a plurality of the outlet flow openings in the rubbing edge by use of a flow duct. By this, a practically constant internal cross section of the flow ducts can be achieved, at the best possible efficiency of the turbine, in association with a slender profile. This is only possible by use of an embodiment of the invention because the additional space is only made possible by the outlet flow openings now freed on the rubbing edge and by the curved shape of the flow ducts. In addition, a profile shape imposed to optimize the aerodynamics (edge zone effect) is possible—in contrast to drilled blades—with a cooling possibility for the trailing edge, in contrast to previous geometries.
The flow ducts can be shaped in such a way that transverse flow components are present in the efflux direction and opposite to it. Exclusively or predominantly transverse flow components in the efflux direction are, however, preferred. The transverse flow components effect a flow through the trailing edge, which was not previously present. Due to the utilization of the transverse flow components mentioned, furthermore, the cooling fluid is automatically conducted to the outlet flow openings in the trailing edge.
Preference is given to a trailing edge duct and/or a front fl
Strassberger Michael
Tiemann Peter
Edgar Richard A.
Harness & Dickey & Pierce P.L.C.
Look Edward K.
Siemens Aktiengesellschaft
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