Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-03-17
2001-02-06
Lopez, F. Daniel (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
06183199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cooled wall having cooling-air bores, in particular film-cooling bores.
2. Discussion of Background
To increase the output and the efficiency, increasingly higher turbine inlet temperatures are being used in modern gas-turbine plants. In order to protect the turbine blades from the increased hot-gas temperatures, they must be intensively cooled. At correspondingly high inlet temperatures, purely convective cooling is no longer sufficient. The film-cooling method is therefore often used. In this case, the turbine blades are protected from the hot gas by a cooling film. To this end, openings, for example bores, through which the cooling air is blown out, are made in the blades.
In order to achieve as high a cooling effect as possible, the cooling air which is blown out must be deflected as rapidly as possible and flow in a protective manner along the profile surface. In order to also protect the zones lying between the bores, rapid lateral spreading of the cooling air is also necessary. This may be achieved by the cooling-air bores having a diffuser, which on account of the lateral widening permits a wider area of the surface to be covered. To further improve the mixing behavior, geometrical diffuser forms in which the bore is widened not only laterally but also on the downstream side of the bore are used. The blow-out rates in the case of these geometrical diffuser forms are small, so that there is little risk of the cooling air passing through the flow boundary layer. The cooling efficiency can therefore be increased considerably compared with a cylindrical bore.
Publication U.S. Pat. No. 4,197,443 discloses a spark-erosion electrode with which holes which widen in the lateral and longitudinal directions can be made in airfoils.
Publication EP-B-228 338 describes a cooled wall having a cooling-medium passage which has a dosing section and a diffuser section. The diffuser section contains a plane surface in the downstream and upstream directions respectively. Two side surfaces diverge from one another toward the cooling-medium outlet.
Experience shows that malfunctions repeatedly occur during the operation of a gas turbine, and these malfunctions may lead to parts of the machine becoming detached, being transported through the turbine and causing damage in the process. The regions having considerable flow deflection are most affected by the impact of foreign bodies. The foreign bodies generally have a higher specific density than the hot gas flowing through the machine. Consequently, the foreign bodies are deflected to a less pronounced degree at these locations and strike a wall. Typical impact locations are found, for instance, in the region of the leading edge on the suction side of turbine blades. If the foreign bodies strike those locations of the blade at which cooling bores are made, there is the risk in the case of the hitherto known geometrical diffuser forms that the hole cross section will be reduced or even completely closed. As a result, the cooling effect is greatly reduced. With the tight design limits normal nowadays, this may lead to the maximum permissible material temperatures being exceeded, which drastically reduces the service life of the blade.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel cooled wall which is provided with an arrangement of cooling bores which have improved stability and reliability with considerable cooling effectiveness. This object is achieved by the cooled wall of independent claim
1
. Further advantageous and expedient refinements follow from the dependent claims, the description and the drawings.
A cooled wall of the generic type comprises an outer surface, which is exposed to a hot-gas flow, which flows along the outer surface in the downstream direction, an inner surface, preferably for forming part of a cooling-medium chamber for receiving preferably pressurized cooling medium, and at least one film-cooling hole within the wall, which film-cooling hole has a diffuser section and an outlet at the outer surface. In this case, the axis of the film-cooling hole is directed in such a way that a cooling-medium flow from the outlet is directed in such a way that it has a velocity component in the downstream direction of the hot gas. The diffuser section has a first internal surface at a distance from a second internal surface, the first and second internal surfaces intersecting the outer surface of the wall. At the same time, the intersection edge between the first internal surface and the outer surface forms an upstream edge of the outlet, and the intersection edge between the second internal surface and the outer surface forms a downstream edge of the outlet. Furthermore, the diffuser section has side surfaces, which face one another, connect the first and second internal surfaces and diverge from one another toward the outlet of the diffuser section. According to the invention, the first internal surface of the diffuser section is designed in such a way that it is rounded toward the axis of the film-cooling hole.
FIGS.
2
(
a
), (
b
) show a known geometrical diffuser form having a lateral widened portion, and FIGS.
3
(
a
), (
b
) show a known geometrical diffuser form having an additional downstream widened portion of the film-cooling hole. It has now been found that such cooling bores are especially susceptible to the impact of foreign bodies at the upstream outlet edge (reference numeral W). The wall is very thin there and is easily pressed downward by the impact of foreign bodies. The cross section of the cooling bore is thereby reduced; in the extreme case, the bore is even completely closed.
The rigidity of the edge is markedly increased by the first internal surface of the diffuser section being rounded off according to the invention toward the axis of the cooling bore, since the forces which are produced during the impact of a foreign body are laterally deflected into a zone of greater wall thickness.
The stability of such a film-cooling hole according to the invention is lower than that of a cylindrical hole but is markedly higher than that of conventional non-circular holes. On the other hand, the cooling characteristics are clearly superior to those of cylindrical holes; they are virtually not reduced compared with the conventional geometrical diffuser forms (FIGS.
2
and
3
).
The first internal surface of the diffuser section is preferably rounded in an elliptical manner, particularly preferably in a circular manner. The specification of the curve shape relates here to a section of the hole having a plane parallel to the outer surface. In particular, in the case of circular or elliptical rounding of the internal surface, the intersection edge between the internal surface and the outer surface will thus itself be circular or elliptical. The radius of curvature may vary along the axis of the film-cooling hole and then merges continuously from the curvature at the inlet of the diffuser section to the curvature at the outer surface.
Parabolic or hyperbolic rounding-off or the configuration of the rounding-off of the internal surface with the use of two or more compound curves is also expedient.
The first internal surface is preferably designed in such a way that it merges in a smooth curve into the side surfaces. The second internal surface is advantageously essentially plane and likewise merges advantageously in a smooth curve into the side surfaces.
The first and second internal surfaces advantageously diverge from one another toward the outlet of the diffuser section at an angle of less than 30°, preferably at an angle of between 5° and 20°. Furthermore, it is advantageous if at least one of the side surfaces diverges from the axis of the film-cooling hole at an angle of greater than 5°, preferably greater than 10°. In an especially advantageous manner, both side surfaces diverge from the axis at such an angle. The axis of each film-cooling hole advantageously encloses with the outer surface an a
Beeck Alexander
Bonhoff Bernhard
Wilfert Gunter
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Lopez F. Daniel
Nguyen Ninh
LandOfFree
Cooling-air bore does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cooling-air bore, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cooling-air bore will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2570079