Patent Application
20100007092
The present application relates generally to any type of turbine and more particularly relates to systems and methods for sealing the gap between a turbine bucket dovetail and a turbine rotor via a labyrinth seal.
Gas turbines generally include a turbine rotor (wheel) with a number of circumferentially spaced buckets (blades). The buckets generally may include an airfoil, a platform, a shank, a dovetail, and other elements. The dovetail of each bucket is positioned within the turbine rotor and secured therein. The airfoils project into the hot gas path so as to convert the kinetic energy of the gas into rotational mechanical energy. A number of cooling medium passages may extend radially through the bucket to direct an inward and/or an outward flow of the cooling medium therethrough.
Leaks may develop in the coolant supply circuit based upon a gap between the tabs of the dovetails and the surface of the rotor due to increases in thermal and/or centrifugal loads. Air losses from the bucket supply circuit into the wheel space may be significant with respect to blade cooling medium flow requirements. Moreover, the air may be extracted from later compressor stages such that the penalty on energy output and overall efficiency may be significant during engine operation.
Efforts have been made to limit this leak. For example, one method involves depositing aluminum on a dovetail tab so as to fill the gap at least partially. Specifically, a 360-degree ring may be pressed against the forward side of the dovetail face. Although this design seals well and is durable, the design cannot be easily disassembled and replaced in the field. Rather, these rings may only be disassembled when the entire rotor is disassembled.
There is thus a desire for improved dovetail tab sealing systems and methods. Such systems and methods should adequately prevent leakage therethrough so as to increase overall system efficiency while being installable and/or repairable in the field.
The present application thus provides a labyrinth seal for a gap between a dovetail tab and a rotor. The labyrinth seal may include a first leg positioned about a high-pressure side of the dovetail tab, a second leg positioned about a low-pressure side of the dovetail tab, and a labyrinth chamber positioned between the first leg and the second leg. High-pressure fluid passing through the gap about the first leg expands within the labyrinth chamber so as to limit an amount of the high-pressure fluid that passes beyond the second leg.
The present application further provides a method of sealing a gap between a dovetail tab of a bucket and a rotor of a turbine. The method may include the steps of machining the dovetail tab to create a labyrinth chamber, operating the turbine, forcing high-pressure fluid into the gap, and expanding the high-pressure fluid within the labyrinth chamber so as to limit an amount of the high-pressure fluid passes beyond the labyrinth chamber.
The present application further provides a labyrinth seal for a gap between a dovetail tab and a rotor. The labyrinth seal may include a first leg positioned about a high pressure side of the dovetail tab, a second leg positioned about a low pressure side of the dovetail tab, and a labyrinth chamber positioned about a perimeter of the dovetail tab between the first leg and the second leg. High-pressure air passing through the gap about the first leg of the dovetail tab expands within the labyrinth chamber so as to limit an amount of the high-pressure air that passes beyond the second leg so as to limit an effective clearance of the gap about the second leg.
These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
As is known, the bucket 10 may include an airfoil 30, a platform 40, a shank 50, a dovetail 60, and other elements. It will be appreciated that the bucket 10 is one of a number of circumferentially spaced buckets 10 secured to and about the rotor 20 of the turbine. The bucket 10 of
As described above, the rotor 20 may have a number of slots 25 for receiving the dovetails 60 of the buckets 10. Likewise, the airfoils 30 of the buckets 10 project into the hot gas stream so as to enable the kinetic energy of the stream to be converted into mechanical energy through the rotation of the rotor 20. The dovetail 60 may include a first tang or tab 70 and a second tab 80 extending therefrom. Similar designs may be used herein. A gap 90 may be formed between the ends of the tabs 70, 80 of the dovetail 60 and the rotor 20. A high pressure cooling flow may escape via the gap 90 unless a sealing system of some type is employed.
The labyrinth chamber 110 may define a first leg 120 and any number of subsequent second legs 130. The legs 120, 130 extend towards the gap 90 between the bucket 10 and the rotor 20. The first leg 120 may be positioned adjacent to a high-pressure side 140 of the dovetail 60. The high-pressure side 140 may provide the bucket cooling supply air. The second leg 130 may be positioned about a low-pressure side 150, i.e., the wheel space. The legs 120, 130 may have sharp corners or edges, but slightly rounded edges may be used.
In use, the high-pressure air or other fluids from the high-pressure side 140 about the first leg 120 of the dovetail 60 extends into the gap 90. The high velocity flow expands within the labyrinth chamber 110 so as to create vortices that impede the flow therethrough. Coolant loss through the gap 90 about the second leg 130 thus may be significantly reduced. The labyrinth chamber 110 and the legs 120, 130 thus form a labyrinth so as to reduce the airflow therethrough. Other configurations also may be used herein so as to deflect and/or reduce the airflow.
The labyrinth seal 100 also may be used about the second tab 80 or otherwise as may be desired. Moreover, adding the labyrinth seal 100 drops the effective clearance of the gap 90 from, for example, about ten (10) millimeters or more to about 8.6 millimeters. These clearance levels approach those of the known aluminum strips but without the addition of this further material. The reduction of the effective clearance and hence the reduction in cooling flow loss thus improves overall system efficiency. The labyrinth seal 100 also may be used with other sealing systems and methods.
The present application thus provides a non-contact, labyrinth seal 100 that is integrally formed about the turbine dovetail 60 for the gap 90 between the dovetail 60 and the rotor 20. The labyrinth seal 100 created by the legs 120, 130 and the gap 90 provides a non-contact flow sealing or control system by forcing the leakage flows from the high pressure side 140 into the labyrinth chamber 110 where the leakage flows produce a vortex or vortex-like fluid motion that reduces fluid leakages as compared to a similar gap that does not include the legs and the labyrinth chamber.
It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
