Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-11-29
2001-08-21
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S19300A, C416S095000, C415S115000, C415S116000
Reexamination Certificate
active
06276897
ABSTRACT:
TECHNICAL FIELD
The invention relates to arrangements and methods for cooling components in turbomachines, in particular in gas turbines.
PRIOR ART
The efficiencies normal nowadays in turbomachines, in particular in gas turbines, require very high process temperatures. In particular in the region of the combustion chamber and the turbine inlet of the gas turbine, the temperatures are often markedly above the maximum admissible material temperatures of the components of the gas turbine. In order to avoid damage to the components as a result of excess temperature, it is therefore often necessary to cool these components. As a rule, in gas tubines, fluid, usually air, is extracted for this purpose from the compressor and fed to the components to be cooled. In this case, the fluid extracted from the compressor has a markedly lower temperature than the hot fluid flowing through the combustion chamber or the turbine. In one method of cooling components by means of a cooling fluid, so-called film cooling, the cooling fluid is blown out of cooling holes onto the component surface and thus into the flow of the hot fluid. On account of the displacement effect of the cooling fluid, a separating layer in the form of a fluid film forms between the hot fluid and the component. Consequently, the heat is no longer transferred directly from the hot fluid into the component. In this case, the separating layer is not only formed from the blown-out cooling fluid, but rather, in particular due to vortex systems, hot fluid is also admixed to and intermixed with the separating layer. This in turn leads to an increase in the average temperature of the fluid of the separating layer, as a result of which the cooling effect ultimately deteriorates.
Furthermore, in particular at component gaps, it is often conventional practice to seal off these component gaps from the hot fluid flowing over the component gap by means of a cooling fluid continuously flowing out of the component gap. In this case, the components adjacent to the component gap are cooled at the same time. In a turbomachine, component gaps occur, for example, between stationary and rotating components. Likewise, however, component gaps are also provided in order to take into account thermally induced changes in length, occurring during operation, of the components. The latter is usually the case, for example, between the combustion chamber and the turbine inlet guide wheel.
Both in the case of the film cooling described and in the case of the sealing of a component gap by means of a cooling-fluid flow flowing out of the component gap, a reliable mode of operation is only ensured with an adequate pressure difference between the cooling fluid and the hot fluid. Since, on the one hand, the cooling fluid in turbomachines is usually extracted from the compressor, but, on the other hand, only small pressure losses in the flow of the hot fluid occur in the combustion chamber, there are often only very small pressure differences between the cooling fluid and the hot fluid, in particular in the turbine inlet region. Furthermore, if an increase in the static pressure occurs locally, for example in front of the stators of the turbine inlet guide wheel, the pressure difference of the cooling fluid relative to the hot fluid is no longer sufficient in order to ensure that the component gap is completely sealed off from the hot fluid or also that a closed cooling-fluid film is formed on the surface of the component. Consequently, a local penetration of hot fluid into the component gap or into the cooling-fluid film occurs. As a result, local overheating of the adjacent components may occur. In U.S. Pat. No. 4,739,621, for the purpose of cooling the regions of the turbine inlet guide blades, special cooling-fluid feeds having elongated cross sections are arranged directly upstream of the turbine inlet guide blades. However, the design is exceptionally elaborate on account of the large number of parts and the complicated geometry.
In Patent EP 0 615 055, it is proposed to design the cooling holes upstream of the turbine inlet guide blades of a gas turbine in the regions in front of the guide blades with a larger cross section. In this case, the centers of the cooling holes are arranged at equal distances from one another. As a result of the design of the cooling holes with different cross sections, a larger cooling-fluid mass flow discharges from the cooling holes into the flow of the hot fluid in each case in the regions in front of the turbine inlet guide wheels, as a result of which a uniform cooling effect can be achieved at the periphery of the turbine inlet guide wheel. The very complicated and thus expensive production of the cooling holes having different cross sections may be mentioned as a disadvantage. In addition, the variation in the cross sections results in a deterioration in the cooling effectiveness at a cross section of the cooling holes which differs from a fluidically optimum cross section.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide an arrangement and a method in order to efficiently and reliably cool one or more components of a turbomachine even in the case of a local variation in the static pressure of the hot fluid.
This object is achieved according to the invention owing to the fact that, for the purpose of feeding a cooling fluid, cooling holes which have cross sections identical to one another and are arranged at different distances from one another are arranged in the component. In this case, the hot fluid flows over the component. A local increase in the static pressure results, for example, as a consequence of a local retention of the flow in front of the blades of the turbomachine. The arrangement of cooling holes having cross sections identical to one another can be realized in a simple and cost-effective manner from the point of view of production. In this case, the cross sections of the holes are advantageously to be selected in such a way that maximum cooling effectiveness is achieved with the lowest possible losses. Furthermore, it has been found that, by varying the distance between the cooling holes, the locally introduced cooling-fluid mass flow can be advantageously adapted to the local requirement. It has been found that very efficient and reliable cooling of the component is made possible by the arrangement according to the invention. For technical reasons related to the cooling, the smallest possible cross sections or diameters of the cooling holes are desired as a rule. In this way, the cooling effectiveness can be optimized on the one hand and, in addition, the cooling-air consumption can be limited on the other hand. Normally, however, on account of the operating conditions, a minimum cross section or diameter of the cooling holes is required, so that the cooling holes also do not become obstructed on account of dirt or particles contained in the cooling air. It has been found that a considerable advantage of the invention lies in the fact that, by the clever distribution of the cooling holes having identical cross sections and/or diameters optimized from the point of view of cooling, markedly improved cooling of the components with greater cooling effectiveness of the cooling fluid is achieved.
Of course, the design of the cooling holes with identical cross sections and/or identical diameters relates to identical cross sections and/or identical diameters of the cooling holes within the conventional manufacturing or production tolerances. Likewise, other comparable statements with regard to geometrical dimensions are always to be evaluated from the point of view of conventional manufacturing or production tolerances.
The distances between the cooling holes are advantageously selected and the cooling holes advantageously arranged in such a way that they are at smaller distances from one another in a region of increased static pressure of the fluid flow than in the region of lower static pressure of the fluid flow. Such an arrangement of the cooling holes thus results in a greater
ABB Alstom Power ( Schweiz) AG
Burns Doane Swecker & Mathis L.L.P.
Verdier Christopher
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