Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1998-09-14
2001-07-17
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
Reexamination Certificate
active
06261053
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a segment arrangement for platforms, in particular in a gas turbine, along the surface of which a hot-gas stream flows, having segments arranged next to one another and in each case separated from one another by a gap, the hot-gas stream, in at least one section of the gap, having a velocity component perpendicular to the direction of the gap from a first segment to a second segment.
BACKGROUND OF THE INVENTION
In order to achieve a maximum turbine output, it is advantageous to work at the highest possible gas temperatures. In modern gas turbines, the temperatures are so high that many components have to be cooled, since otherwise the temperature of the components which is permissible for maximum durability would be exceeded. A suitable design and/or cooling of critical components is therefore of crucial importance in modern gas turbines. The cooling problem of platforms occurs to an increased extent in annular combustion chambers, since the latter produce a very uniform temperature profile at the entry to the turbine. This means that the platform of the blade has to bear almost the average hot-gas temperature. To achieve the lowest possible NOx emissions, virtually the entire proportion of the combustion air is delivered through the burners themselves in modern combustion chambers; the proportion of the cooling air for the film cooling of the combustion chamber is therefore reduced. This likewise leads to a more uniform temperature profile at the turbine entry and thus to increased thermal loading.
Critical components in turbines are, inter alia, heat shields, combustion-chamber segments and combustion-chamber plates, moving and guide blades, inner and outer shroud bands of the moving and guide blades, and also moving- and guide-blade platforms.
In particular at the sides of segments (platforms) arranged next to one another, experience shows that increased thermal loading often occurs. If, for instance, the segments of a platform are coated with a heat-insulating coating, peeling of the coating is often found. This results in a weak point, at which oxides rapidly form, and these oxides in turn encourage the peeling of the coating. Large uncoated metal surfaces can thus be subjected to the hot-gas stream in a short time.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to design the components which are critical with regard to high temperatures, in particular components composed of segments, in such a way that the thermal loading of these components is effectively reduced with the simplest possible means.
This object is achieved according to the invention in a first aspect in that that edge of each segment which is subjected to the hot-gas stream is set back from the impinging hot-gas stream.
The hot-gas stream flows along the surface of the segments, which are arranged next to one another and are in each case separated from one another by a gap. It can now be found that the boundary layer separates at the gap located between the platforms arranged next to one another. The boundary layer then forms again at that side edge of the downstream platform which is acted upon by the hot-gas stream. Very high heat transfer and thus increased thermal loading of the exposed material therefore occur at this point due to the very thin boundary layer. If there are protruding steps at the gap due to production tolerances, the material of these steps is subjected to especially high thermal loading by the impinging hot-gas stream. Furthermore, hot gas can be deflected into the gap by the edges and in particular by projecting steps. This may lead to a reduced service life and also often to damage to the components adjoining the gap.
A remedy is provided here by that edge of each segment which is acted upon by the hot-gas stream being set back according to the invention by bevelling or rounding off the edge. In this case, the edge need not be bevelled or rounded off over its entire length, since the direction of the hot-gas stream on the segment can change. A precondition for the applicability of the invention, however, is that the hot-gas stream, in at least one section of the gap between the segments, has a velocity component perpendicular to the direction of the gap and thus points from a first to a second segment. In this section, that edge of the second segment which faces the gap is acted upon by the hot-gas stream and is therefore rounded off or bevelled in the first aspect of the invention.
In the case just described, the hot gas flows over the gap, which separates two segments, from the surface of the first segment to the surface of the second segment. In this case, the main component of the velocity of the hot-gas stream is mostly directed from the front side to the rear side of the segments, that is, along the gap. In addition to this flow across the segments, the hot-gas stream has a velocity component perpendicular or at right angles to the gap. Only this perpendicular velocity component leads to the segment edges being acted upon by the hot-gas stream. In many applications, the hot-gas stream on the second segment changes its direction, for instance owing to the fact that a guide device or an airfoil part is put on each segment. In this case, the velocity component along the gap is largely retained; the velocity component perpendicular to the gap merely reverses. The result of this is that there is then a second section downstream of the first section in which the hot-gas stream flows from the first to the second segment, in which second section the hot-gas stream flows from the second segment over the gap to the surface of the first segment. In this second section, that edge of the first segment which faces the gap is then advantageously rounded off or bevelled, since in this section this edge is acted upon by the hot-gas stream.
In a transition region between the first and the second section, the hot-gas stream will flow essentially parallel to the direction of the gap. It is now advantageous if the bevels or rounded-off portions of the first and second sections respectively are gradually reduced to zero in this transition region.
The segment arrangements described here generally involve a multiplicity of segments which are arranged next to one another, so that in each case two segments are separated from one another by a gap. The segment arrangement as a unit may form, for example, a closed ring or it may be arranged on the inside or outside on the circumference of a cylinder. As a rule, the segments are identical, except for any end pieces, so that it always suffices in the present invention to describe a single segment. If a first and a second segment are referred to in the present invention, this relates to two segments which are selected as an example and lie on the two sides of a gap. This serves to illustrate the direction of the gas flow and does not mean that the invention is restricted to only two segments. The gap between two segments may vary statistically due to production tolerances, and in the extreme case may even be omitted at individual segments as a result.
Within the scope of the first aspect of the present invention, the edges are bevelled at an angle &agr; of between 1 and 60 degrees, preferably between 20 and 40 degrees, and in particular preferably less than about 30 degrees. If the bevel extends over a length L perpendicular to the gap, the depth T of the bevel is related to the length L and the angle &agr; via tan &agr;=T/L. In general, the maximum depth is predetermined, for instance by a recess in the interior of the segments, in which recess a sealing strip, for example, is located. It has been found that, with this selection of the angle, a depth of less than the maximum depth and a corresponding length of the bevel, the risk of separation of the boundary layer at the gap is markedly reduced.
It is also advantageous for the stability of the boundary layer if the transition points between the bevelled region and the inside of the gap, and/or between the bevelled region and the
Anderson Gordon
Ferber Jörgen
Hall Kenneth
Hock Michael
Tarada Fathi
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Ryznic John E.
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