Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1999-08-11
2001-05-01
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
Reexamination Certificate
active
06224328
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to German Patent Application No. 198 39592.2 filed Aug. 31, 1998 the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a turbomachine, in particular a compressor of a gas turbine.
2. Discussion of Background
In turbomachines with high thermal loading, in particular in the case of compressor stages of modern gas turbines, the rotor shaft is to be regarded as a particularly endangered component. As a consequence of the extreme temperature loadings, the life of conventionally used materials falls drastically so that additional measures have to be taken in order to deal with this problem.
A first approach to a solution consists in providing so-called heat shields which prevent direct contact between the heated flow medium and the rotor shaft and, by this means, should keep the heating within limits considered to be permissible. A disadvantageous feature is then the increase in the manufacturing costs and complexity of the turbomachine due to the additional components.
A further approach to a solution consists in manufacturing the rotor shaft from a material with improved high temperature behavior. Although such materials are available, problems arise in practical use due to a differing thermal expansion behavior as compared with the materials of adjacent components, in addition to increased material costs. Transient procedures in particular, such as, for example, the starting of the machine, introduce enormous difficulties due to the different time-dependent thermal expansion behavior.
Finally, it is also known to cool rotor shafts, made from conventional materials, by means of a central coolant hole which passes through the rotor shaft. Such a solution, however, is extremely cost-intensive and, in addition, not very effective.
SUMMARY OF THE INVENTION
The invention attempts to avoid the disadvantages described. Accordingly, one object of the invention is to provide a novel turbomachine, of the type mentioned at the beginning, which permits the rotor shaft to be cooled locally with a high level of effectiveness so that the life expectation of the rotor shaft is not appreciably impaired even in the case of extremely high thermal loading.
This is achieved, in accordance with the invention, by individual or all guide vanes being configured as cooled vanes which are fed from a cooling air supply. The cooled vanes are configured in such a way that air guidance ducts pass through them in the essentially radial direction and that they have outlet openings, which are directed onto the rotor shaft, in the region of the vane tips.
The advantages of the invention are of a manifold nature and relate to both technical design simplifications and aerothermodynamic aspects.
One of the main advantages of the invention may be seen in the fact that an optimum cooling effect can be achieved by directly subjecting the rotor shaft to cooling air. Even a relatively small quantity of cooling air is sufficient to hold the rotor shaft locally at a low temperature level. This last-named effect can be utilized in various ways.
It is, on the one hand, possible to use conventional, low-cost materials for the production of the rotor shaft even if a higher pressure ratio than previously is realized.
It is possible to dispense completely with heat shields even in thermally severely loaded high-pressure compressor stages because the rotor shaft can be cooled locally in a targeted manner.
Because of the high cooling effectiveness, it can be sufficient to design only individual guide vanes of a guide vane row as cooled vanes. In the normal case, however, all the rotor blades of a blading row are cooled because, in this way, it is possible to subject the rotor shaft to cooling air in an optimally even manner.
On the other hand, the life of the blading is increased because of the low temperature level effected by the cooling air. This affects not only the cooled vanes through which cooling air passes but also the downstream uncooled blading rows.
The compressor outlet temperature is also lowered overall so that the aerothermodynamic efficiency of the compressor is improved.
The cooling air emerging at the vane tips also effects an improvement to the fluid mechanics properties. Thus, on the one hand, kinetic energy is locally supplied to the boundary layer by the cooling airflow and has a positive influence on it. Given an appropriate design and arrangement of the outlet openings, on the other hand, the emerging cooling airflow prevents flow around the guide vanes in the gap between the vane tips and rotor shaft. Leakage losses in this region can therefore be avoided almost completely.
Because of the improvement to these aerothermodynamic relationships, the compressor also exhibits an improved operating behavior which is reflected by the surge line being clearly lifted.
The vibration behavior of the blading can be varied within wide limits by variation in the design parameters of the air guidance ducts, such as the number, dimensioning or location provided. This makes it possible to tune, within limits, the natural frequency and flutter characteristics in such a way that critical vibration conditions no longer occur.
The provision of the air guidance ducts at the guide vanes may, as a rule, be considered to be simple and inexpensive to configure because cooled vanes have to be provided, in particular, in the thermally highly-loaded rear stages of compressors and these guide vanes are not as a rule twisted or are only slightly twisted. The air guidance ducts can therefore usually be configured as simple holes which pass through the particular guide vane entirely radially or which branch off in an axial direction from a central air guidance duct.
The cooling device according to the invention has, in addition, the advantage that it can be very easily and precisely actuated. The cooling air can be extracted directly from upstream or downstream compressor stages but still requires preparation so that it can be fed in at a higher pressure and a lower temperature than those corresponding to the local condition parameters of the main flow. If a cooling airflow from a higher compressor stage is taken as cooling air, the cooling airflow must be cooled. If, on the other hand, the cooling airflow is taken from a lower compressor stage, this cooling airflow must first be further compressed externally and subsequently cooled.
The cooling concept according to the invention can be also applied with particular advantage in the case of guide vane rows with a shroud. The shroud permits the cooling film to be made even more uniform in the peripheral direction because the emerging partial cooling airflows are not immediately intercepted and entrained by the main flow.
Further preferred embodiments of the invention are directed toward simultaneously using the cooling air to influence the gap width between the guide vane tips and the rotor shaft. For this purpose, the cooled vanes are supported so that they can be displaced in the radial direction and are displaced from their initial position, against the action of return springs, by the pressure of the cooling air. This makes it possible to substantially raise the compressor efficiency and, in particular, the surge line. This effect is clearly marked in the case of modern high-pressure compressor stages because, in this case, large gap widths have to be provided, for safety reasons associated with the sluggish response behavior, in order to reliably prevent the vane tips from running into the rotor shaft.
The return springs represent a safety measure in case the cooling air supply should be interrupted. The cooled vanes return directly to their initial position and, in this way, increase the gap between the vane tips and the rotor so that, even when a severe radial expansion takes place for thermal reasons, the rotor cannot come into contact with the vane tips.
In accordance with an application of this concept which is particularly simp
Fitzsimons Conor
Kappis Wolfgang
Weigand Bernhard
Wettstein Hans
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Look Edward K.
McAleenan James M
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