Patent Grant
8047765
The subject matter disclosed herein relates to actuators and, more particularly, to devices, methods and systems for thermally activated displacement.
Various systems and devices may include components that are configured to be displaced during operation. Examples of such devices include combustion engines and elevators. In one example, gas turbines such as those used in power generation or aviation utilize a turbine “shroud” disposed in a turbine shell. The shroud provides for a reduced clearance between the tips of buckets disposed on the turbine rotor and the shroud in comparison to a clearance between the bucket tips and the turbine shell, to enhance efficiency by reducing unwanted “leakage” of hot gas over tips of the buckets. Current shroud systems employ solely segmented shrouds connected to the turbine shell and held together by, for example, turbine shell hooks. The clearance between the bucket tips and the shroud is simply driven by the thermal time constant behavior between the turbine shell and rotor/buckets. Cold-built clearances set during assembly, can be set high enough to mitigate rubbing, but tends to increase steady state operating clearances, reducing engine efficiency and output.
Other clearance control or displacement systems employ mechanical, electrical and/or electromechanical actuators, which can suffer degradation in harsh environments such as those found in gas turbines and engines.
Accordingly, there is a need for improved systems and methods for controlling displacement of devices, such as clearances between bucket tips and shrouds in a gas turbine during transient and/or steady state operation of the turbine.
An actuating device, constructed in accordance with exemplary embodiments of the invention includes: at least one first elongated member having a first coefficient of thermal expansion (CTE); and at least one second elongated member having a second CTE different from the first CTE, the second elongated member being nested within the first elongated member, the device being configured to displace a portion of the device a selected distance along a major axis of the device based on a relationship between the first CTE and the second CTE in response to a change in temperature.
Other exemplary embodiments of the invention include a method of displacing a portion of an actuating device. The method includes: securing a first end of the actuating device at a fixed position, the actuating device including at least one first elongated member having a first coefficient of thermal expansion (CTE) and at least one second elongated member having a second CTE different from the first CTE, the second elongated member being nested within the first elongated member; applying a thermal source to the device to change a temperature of the device; and displacing a second end of the device a selected distance along a major axis of the device in response to the change in temperature, the selected distance being based on a relationship between the first CTE and the second CTE.
Further exemplary embodiments of the invention include a system for adjusting a clearance in a gas turbine including a turbine rotor and a plurality of buckets. The system includes: a shroud assembly including at least one shroud segment, the at least one shroud segment being disposed in an interior of a turbine shell; and an actuating device extending through at least a portion of the turbine shell and having a first end in a fixed position relative to the turbine shell, the actuating device including: at least one first elongated member having a first coefficient of thermal expansion (CTE); and at least one second elongated member having a second CTE different from the first CTE, the second elongated member being nested within the first elongated member, the device being configured to displace a second end of the device a selected distance along a major axis of the device based on a relationship between the first CTE and the second CTE in response to a change in temperature.
Additional features and advantages are realized through the techniques of exemplary embodiments of the invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features thereof, refer to the description and to the drawings.
There is provided a device, system and method for thermally actuated displacement. The system includes a thermally actuating device included in a gas turbine system for adjusting a displacement of a component thereof, such as a clearance between bucket tips and one or more shrouds. Although the actuating device is described in the context of the gas turbine system, the device may be utilized in any system that would benefit from displacement of components by thermal actuation.
The actuating device includes at least one first elongated member having a first coefficient of thermal expansion (“CTE”) and at least one second elongated member having a second CTE different from the first CTE. The second elongated member is nested within the first elongated member, and the device is configured to extend a selected distance along a major axis of the device based on a relationship between the first CTE and the second CTE in response to a change in temperature. The elongated member is described herein as a generally cylindrical rod, tube or combination thereof, but may be any suitable shape. A method is provided that includes thermally activating the elongated member to cause a displacement of an end of the member.
Referring to
Referring to
In use, a thermal source, such as an electric current, an electric heater and/or a gas such as air or steam is applied to change the temperature of the device 18. The device 18 has a first end 52 and a second end 54.
In one embodiment, the first end 52 is secured relative to a body such as the turbine shell 12. The first end 52 is secured by any suitable mechanism, such as a bayonet attachment or a threaded attachment. A change in temperature will cause the second end 54 to displace a distance “δ” along the major axis 50.
In one example, the first elongated members 46 have a CTE that is greater than the CTE of the second elongated member 48. An increase in temperature will accordingly cause the second end 54 to displace a distance δ away from the first end 52. This displacement occurs in a telescoping fashion, as each of the first elongated members 46 expand along the major axis 50 by a greater amount than the expansion of the second elongated member 48, which causes the second end 54 to displace farther than it would if a single elongated member 46 were used.
In another example, the first elongated members 46 have a CTE that is less than the CTE of the second elongated member 48. An increase in temperature will accordingly cause the second end 54 to displace a distance δ toward the first end 52, i.e., cause the device 18 to retract. This displacement occurs as the second elongated member 48 expands along the major axis 50 by a greater amount than the first elongated members 46. This retraction effect is also amplified relative to a single elongated member 46.
The first and second elongated members 46, 48 are made from any suitable thermally conductive material having a desired CTE. Examples of such materials include Cr—Mo—V steel, Niobium-strengthened superalloys such as Inconel® 909, stainless steel such as 310SS, and high strength iron-based superalloys such as A286. Although the embodiments described herein describe the first and second elongated members 46, 48 as being in the form of solid or hollow cylindrical members, the first and second elongated members 46, 48 may take any suitable shape.
Referring to
The actuating device 18 forms gas flow paths or cavities 36, allowing air, gas or other materials having selected temperatures to surround the structures of the actuating device 18 to cause the actuating device 18 to expand or retract. Each of the elongated members 46, 48 may also include holes or perforations therethrough to facilitate exposure of the actuating device to the air, gas or other material.
Referring to
Referring to
In one example, the body 20 is a turbine shell and the movable member 22 is a turbine shroud separated from a turbine blade or bucket 44, although this embodiment is not limited thereto. Controlling the temperature of the actuating device 18, such as by exposing the elongated members 46, 48 to air having a selected temperature, to control a clearance “C” between the shroud 22 and the bucket 44.
Referring to
Referring again to
In one embodiment, the actuating device 18 includes various gas flow paths formed within the actuating device 18. In one embodiment, the gas flow paths are formed by the first and second elongated members 46, 48 and/or by additional conduits formed through selected portions of the elongated members 46, 48. In one example, the hollow exterior member 60 is solid, and the second elongated member 48 includes one or more holes or perforations therethrough.
In another example, the first end 52 is hollow and forms a conduit connecting to the flow paths formed between the hollow exterior member 60 and the second elongated member 48. Optionally, one or more perforations or holes are included in the second elongated member 48 to allow gas to flow between the hollow exterior member 60 and the interior member 56. In another example, the second end 54 is hollow and forms a gas flow conduit therethrough.
In other embodiments, additional exterior members 60 are included to further amplify the displacement effect. Each of the additional exterior members 60 are connected to an additional second elongated member 48 in a concentric fashion.
As indicated above, utilizing different CTE materials for the first and second elongated members 46, 48 results in an amplifying effect on the displacement δ. This amplifying effect results from the fact that the CTE difference, as well as the connections between the first and second elongated members 46, 48 result in the members 46, 48 expanding in opposite directions along the major axis 50.
The relationship between displacement δ and the difference in CTE can be represented by the following equations:
where “α1” is the coefficient of thermal expansion (CTE) of the first elongated member 46, “α2” is the CTE of the second elongated member 48, “L” is the length of the active parts of the actuating device 18 along the major axis 50, and “ΔT” is the change in temperature of the actuating device 18. In this embodiment, the active parts are the first and second elongated members 46, 48. In one embodiment, the active parts include any number of elongated members 46, 48.
It follows from this equation that the following relationships between CTE difference and displacement δ exist:
The relationship between displacement δ and the difference in CTE can be further generalized for any number “n” of first elongated members:
It follows from this equation that the following relationships between CTE difference and displacement δ exist:
Thus, the amplification of the displacement is achievable by increasing the number of first elongated members 46, which in this embodiment are hollow tubes but may take any desired form. For example, for n=5 and α1=(2)*α2, the displacement would be:
Thus, for 5 tubes with a difference in CTE of a factor of 2, the displacement amplification of the active parts of the actuating device 18 would be (3*α1*L*ΔT).
Referring to
Referring to
In one embodiment, the system 70 includes a computer 71 coupled to an actuator 72, which is in turn coupled to the actuating device 18 for providing thermal energy to the actuating device 18. A clearance measurement sensor 74 is also coupled to the computer 71 so that the computer 71 can control the actuating device to achieve or maintain a desired clearance. In one embodiment, the actuator 72 includes a heating mechanism such as the electric heater 36 and/or a relay or other switch connected to an electrical power source. In another embodiment, the actuator 72 includes a valve connected to a source of air, gas and/or steam. Exemplary components of the computer 71 include, without limitation, at least one processor, storage, memory, input devices, output devices and the like. As these components are known to those skilled in the art, these are not depicted in any detail herein.
Generally, some of the teachings herein are reduced to instructions that are stored on machine-readable media. The instructions are implemented by the computer 81 and provide operators with desired output.
In the first stage 81, the first end 52 of the actuating device is secured at a fixed position. For example, the actuating device 18 is secured to the protrusion 34 and/or the turbine shell 12.
In the second stage 82, a thermal source such as the electric heater 36, steam, air and gas is applied to the actuating device 18 to cause displacement of the second end 54. In one embodiment, a thermal source in the form of heated air or gas is introduced to the exterior of the actuating device 18, to interior cavities formed between the first and second elongated members 46, 48, and/or to various conduits formed in the actuating device 18. In one embodiment, a thermal source is applied to the actuating device 18 via the protrusion 34 and/or the inlet 38, to extend or retract the inner shroud 26.
In the third stage 83, in response to the change in temperature as a result of application of the thermal source, the second end 54 of the actuating device 18 is displaced a selected distance along the major axis 50. As discussed above, the selected displacement distance is based on a relationship between the first CTE and the second CTE. In one example, the second end 54 is connected to the inner shroud 26, and application of the thermal source to the actuating device 18 causes corresponding movement of the inner shroud relative to the bucket tips.
In one embodiment, the actuating device 18 is maintained at a selected temperature, such as by applying air from the interior of the turbine shell 12 through the inlet 38, and the actuating device 18 is retracted by applying heat to the protrusion 34 and causing the protrusion 34 to expand and thereby retract the actuating device 18. For example, during transient operation, the electric heater 36 is turned on at the time of maximum pinch between the bucket tip and the inner shroud 26 to expand the protrusion 34 and cause the actuating device 18 to retract.
Although the systems and methods described herein are provided in conjunction with gas turbines, any other suitable type of turbine may be used. For example, the systems and methods described herein may be used with a steam turbine or turbine including both gas and steam generation.
The devices, systems and methods described herein provide numerous advantages over prior art systems. For example, the devices, systems and methods provide the technical effect of allowing active control of the clearance between the bucket tip and the shroud, which will allow a user to run the turbine engine at tighter clearances than prior art systems. These devices, systems and method are a simple and inexpensive means of moving the shrouds independently to control clearances and to account for manufacturing differences.
The devices, systems and methods described herein allow for placement of the actuating device inside the gas turbine and the use of air or other thermal source at a specified temperature to cause the actuator to move. There are no holes to the outside of the turbine that would need to be sealed and there are no parts that have temperature limitations typical of prior art electrical and/or mechanical solutions.
The devices, systems and methods described herein are more reliable, can be used in harsher environments, and require shorter assembly lengths than prior art systems. All of these result in lower costs due to the inherent reliability of the system. Furthermore, the devices, systems and methods herein provide an actuator that can be designed to cause either positive or negative displacement of an end with application of a positive temperature change.
The capabilities of the embodiments disclosed herein can be implemented in software, firmware, hardware or some combination thereof As one example, one or more aspects of the embodiments disclosed can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has embodied therein, for instance, computer readable program code means for providing and facilitating the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately. Additionally, at least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform the capabilities of the disclosed embodiments can be provided.
In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of exemplary embodiments of the invention if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
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| Number | Date | Country | |
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| 20100054912 A1 | Mar 2010 | US |
