Systems and Methods for Providing a Flow of Purge Air and an Adjustable Flow of Cooling Air in a Gas Turbine Application

Abstract

Embodiments of the disclosure include systems and methods for providing a flow of purge air and an adjustable flow of cooling air to a wheel space cavity or a stator cavity. According to one embodiment, there is disclosed a turbine assembly. The turbine assembly may include a rotor assembly, a stator assembly positioned adjacent to the rotor assembly, and a wheel space cavity formed between the rotor assembly and the stator assembly. At least one fixed purge air orifice may be associated with the stator assembly. The fixed purge air orifice may be configured to provide a flow of purge air to the wheel space cavity. Moreover, at least one adjustable cooling air orifice may be associated with the stator assembly. The at least one adjustable cooling air orifice may be configured to provide a flow of cooling air to the wheel space cavity.

Description

FIELD OF THE DISCLOSURE

Embodiments of the disclosure relate generally to gas turbine engines and more particularly to systems and methods for providing a flow of purge air and an adjustable flow of cooling air to a wheel space cavity and/or a stator cavity.

BACKGROUND OF THE DISCLOSURE

Gas turbine engines are widely used in industrial and commercial operations. A typical gas turbine engine includes a compressor at the front, one or more combustors around the middle, and a turbine at the rear. The compressor imparts kinetic energy to the working fluid (e.g., air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows to the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine where they expand to produce work. Consequently, the turbine is exposed to very high temperatures due to the combustion gases. As a result, the various turbine components (such as the shroud assemblies, rotor assemblies, wheel space cavities, and the like) typically need to be cooled and/or supplied purge air. Accordingly, there is a need to provide improved turbine cooling systems and methods.

BRIEF DESCRIPTION OF THE DISCLOSURE

Some or all of the above needs and/or problems may be addressed by certain embodiments of the disclosure. According to one embodiment, there is disclosed a turbine assembly. The turbine assembly may include a rotor assembly, a stator assembly positioned adjacent to the rotor assembly, and a wheel space cavity formed between the rotor assembly and the stator assembly. At least one fixed purge air orifice may be associated with the stator assembly. The fixed purge air orifice may be configured to provide a flow of purge air to the wheel space cavity. Moreover, at least one adjustable cooling air orifice may be associated with the stator assembly. The at least one adjustable cooling air orifice may be configured to provide a flow of cooling air to the wheel space cavity.

According to another embodiment, there is disclosed a turbine assembly. The turbine assembly may include a rotor assembly, a stator assembly positioned adjacent to the rotor assembly, and a wheel space cavity formed between the rotor assembly and the stator assembly. At least one purge air circuit may be associated with the stator assembly. The purge air circuit may be configured to provide a flow of purge air to the wheel space cavity. Moreover, at least one cooling air circuit may be associated with the stator assembly. The cooling air circuit may be configured to provide a flow of cooling air to the wheel space cavity.

According to another embodiment, there is disclosed a method for providing a flow of purge air and a flow of cooling air to a cavity in a gas turbine assembly. The method may include providing the flow purge air to the cavity by way of at least one fixed purge air orifice. Moreover, the method may include varying the flow of cooling air to the cavity by way of at least one adjustable cooling air orifice. In some instances, the cavity may include a wheel space cavity and/or a stator cavity.

According to another embodiment, there is disclosed a system for providing an adjustable flow of cooling air from a stator cavity to a wheel space cavity of a turbine assembly. The system may include at least one cooling air passage configured to provide the adjustable flow of cooling air to the wheel space cavity from the stator cavity. The system may also include a flow control device associated with the at least one cooling air passage. The flow control device may include a valve configured to control the adjustable flow of cooling air within the at least one cooling air passage. Moreover, the flow control device may include a temperature dependent actuator positioned at least partially within the wheel space cavity and in mechanical communication with the valve. The temperature dependent actuator may be configured to open and close the valve.

Other embodiments, aspects, and features of the invention will become apparent to those skilled in the art from the following detailed description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale.

FIG. 1 is an example schematic view of a gas turbine engine, according to an embodiment of the disclosure.

FIG. 2 is an example schematic cross-sectional view of a system for providing a flow of purge air and an adjustable flow of cooling air to a wheel space cavity, according to an embodiment of the disclosure.

FIG. 3 is an example schematic cross-sectional view of a system for providing a flow of purge air and an adjustable flow of cooling air to a wheel space cavity, according to an embodiment of the disclosure.

FIG. 4 is an example schematic cross-sectional view of a system for providing an adjustable flow of cooling air to a wheel space cavity, according to an embodiment of the disclosure.

FIG. 5 is an example schematic cross-sectional view of a system for providing an adjustable flow of cooling air to a wheel space cavity, according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Illustrative embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. The disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout.

Illustrative embodiments are directed to, among other things, systems and methods for providing a flow of purge air and an adjustable flow of cooling air to a wheel space cavity and/or a stator cavity. That is, the systems and methods described herein provide a means to modulate cooling airflow extracted from the compressor and provided to the wheel space cavity and/or the stator cavity. The cooling airflow may be modulated by way of an adjustable cooling air orifice and/or an adjustable cooling air circuit.

In certain embodiments, a turbine assembly may include a rotor assembly, a stator assembly positioned adjacent to the rotor assembly, and a wheel space cavity formed between the rotor assembly and the stator assembly. At least one fixed purge air orifice and at least one adjustable cooling air orifice may be associated with the stator assembly. The fixed purge air orifice may be configured to provide a flow of purge air to the wheel space cavity, and the adjustable cooling air orifice may be configured to provide an adjustable flow of cooling air to the wheel space cavity. In this manner, the flow of purge air may purge the wheel space cavity, and the adjustable flow of cooling air may cool the rotor assembly.

In some instances, a flow control device may be associated with the adjustable cooling air orifice. For example, the flow control device may be configured to vary the flow of cooling air to the wheel space cavity by varying the size of the adjustable cooling air orifice. In other instances, the flow control device may include a value associated with the adjustable cooling air orifice or a cooling air circuit in communication with the wheel space cavity.

In certain embodiments, the stator assembly may include a stator cavity defined by a stator wall. In some instances, the fixed purge air orifice and the adjustable cooling air orifice may be positioned in the stator wall. In other instances, the stator cavity may be in communication with a flow of compressor extraction air. In this manner, the flow of compressor extraction air may at least partially form a portion of the flow of purge air and the flow of cooling air. That is, the flow of compressor extraction air may enter the stator cavity, wherein a portion of the flow of compressor extraction may pass through the fixed purge air orifice in the stator wall and into the wheel space cavity, and a portion of the flow of compressor extraction may pass through the adjustable cooling air orifice in the stator wall and into the wheel space cavity. The flow of purge air may purge the wheel space cavity, and the flow of cooling air may cool the rotor assembly.

In some instances, the flow control device may be positioned within the stator cavity. In other instances, the flow control device may be positioned eternal to the gas turbine engine. In certain embodiments, a temperature sensor and/or actuator may be in communication with the flow device or valve and may be associated with the wheel space cavity and/or stator assembly. For example, the temperature sensor and/or actuator may be in communication with the flow device or valve and may be mounted to the stator wall and at least partially protrude into the wheel space cavity. The temperature sensor and/or actuator may be configured to manipulate the flow device or valve. In other embodiments, an inter-stage seal may be positioned between the rotor assembly and the stator assembly.

In certain embodiments, the turbine assembly may include at least one purge air circuit and at least one cooling air circuit associated with the stator assembly. In some instances, a flow control device may be associated with the cooling air circuit. That is, the flow control device may be configured to vary the flow of cooling air to the wheel space cavity. For example, the flow control device may include a valve in communication with the cooling air circuit. In this manner, the cooling air circuit may include a flow circuit that directs a flow of compressor extraction air through a tube or pipe which connects to the wheel space cavity. The valve may modulate the cooling flow to the wheel space cavity by responding to the wheel space and/or rotor assembly temperature as measured by one or more monitoring instruments, such as the temperature sensor.

In certain embodiments, the systems and methods described herein may be configured to provide the cooling and purge flow to a stator cavity. That is, in some instances, a fixed amount of purge air flow may be provided from one stator cavity to another, and an additional amount of modulated cooling flow may also be provided between stator cavities.

Turning now to the drawings, FIG. 1 depicts an example schematic view of a gas turbine engine 100 as may be used herein. The gas turbine engine 100 may include a gas turbine having a compressor 102. The compressor 102 may compress an incoming flow of air 104. The compressor 102 may deliver the compressed flow of air 104 to a combustor 106. The combustor 106 may mix the compressed flow of air 104 with a pressurized flow of fuel 108 and ignite the mixture to create a flow of combustion gases 110. Although only a single combustor 106 is shown, the gas turbine engine may include any number of combustors 106. The flow of combustion gases 110 may be delivered to a turbine 112. The flow of combustion gases 110 may drive the turbine 112 so as to produce mechanical work. The mechanical work produced in the turbine 112 may drive the compressor 102 via a shaft 114 and an external load 116, such as an electrical generator or the like.

The gas turbine engine may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine may be any one of a number of different gas turbine engines offered by General Electric Company of Schenectady, N.Y., including, but not limited to, those such as a 7 or a 9 series heavy duty gas turbine engine and the like. The gas turbine engine may have different configurations and may use other types of components. The gas turbine engine may be an aeroderivative gas turbine, an industrial gas turbine, or a reciprocating engine. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together.

In certain embodiments, as schematically depicted in FIG. 2, the turbine 112 of FIG. 1 may include a rotor assembly 118 and a stator assembly 120. The stator assembly 120 may be positioned adjacent to the rotor assembly 118. A wheel space cavity 122 may be formed between the rotor assembly 118 and the stator assembly 120. In some instances, an inter-stage seal 121 may be positioned between the rotor assembly 118 and the stator assembly 120.

The stator assembly 120 may include a stator wall 124. That stator wall 124 may define a stator cavity 126 therein. The stator cavity 126 may be in communication with a flow of compressor extraction air 128. That is, the flow of compressor extraction air 128 may at least partially fill the stator cavity 126.

In some instances, a fixed purge air orifice 130 and an adjustable cooling air orifice 132 may be positioned in the stator wall 124. The fixed purge air orifice 130 may be configured to provide a flow of purge air 134 to the wheel space cavity 122, and the adjustable cooling air orifice 132 may be configured to provide an adjustable flow of cooling air 136 to the wheel space cavity 122. For example, the flow of compressor extraction air 128 may enter the stator cavity 126, wherein a first portion 134 of the flow of compressor extraction 128 may pass through the fixed purge air orifice 130 and a second portion 136 may pass through the adjustable cooling air orifice 132. The flow of purge air 134 may purge the wheel space cavity 122, and the adjustable flow of cooling air 136 may cool the rotor assembly 118.

In some instances, a flow control device 138 may be positioned within the stator cavity 126. The flow control device 138 may also be associated with the adjustable cooling air orifice 132. For example, the flow control device 138 may be configured to vary the flow of cooling air 136 to the wheel space cavity 122. In one example, the flow control device 138 may vary the flow of cooling air 136 to the wheel space cavity 122 by varying the size of the adjustable cooling air orifice 132. In other instances, the flow control device 138 may include a valve-type mechanism or actuator associated with the adjustable cooling air orifice 132 for varying the flow of cooling air 136 to the wheel space cavity 122. For example, in certain embodiments, a temperature sensor 140 may be associated with the wheel space cavity 122 and/or the stator assembly 120. The temperature sensor 140 may be part of the flow control device 138 or a separate component. In some instances, the temperature sensor 140 and/or actuator may be in communication with the flow control device 138 and may be mounted to the stator wall 124 and at least partially protrude into the wheel space cavity 122. Depending on the temperature of the wheel space cavity 122, the stator assembly 120, and/or the rotor assembly 118 (as determined by the temperature sensor 140) the flow control device 138 may increase or decrease the flow of cooling air 136 entering the wheel space cavity 122 via the adjustable cooling air orifice 132 by way of a temperature dependent actuator or the like. However, in certain embodiments, regardless of the temperature of the wheel space cavity 122, the fixed purge air orifice 130 may provide a constant metered flow of purge air 134 to the wheel space cavity 122.

FIG. 3 schematically depicts a system 300 for providing a flow of purge air 322 and an adjustable flow of cooling air 324 to a wheel space cavity 306. For example, the system 300 may include a stator assembly 302 positioned adjacent to a rotor assembly 304. The wheel space cavity 306 may be formed between the rotor assembly 304 and the stator assembly 302. In some instances, an inter-stage seal 307 may be positioned between the rotor assembly 304 and the stator assembly 302.

The stator assembly 302 may include at least one purge air circuit 308 and at least one cooling air circuit 310. Both the purge air circuit 308 and the cooling air circuit 310 may be in communication with the wheel space cavity 306 and a flow of compressor extrusion air 312. In some instances, a flow control device 314 may be associated with the cooling air circuit 310. That is, the flow control device 314 may be configured to vary the flow of cooling air to the wheel space cavity 306. For example, the flow control device 314 may include a valve 316 in communication with the cooling air circuit 310. In this manner, the cooling air circuit 310 may include a flow circuit that directs a flow of compressor extraction air 312 through a tube or pipe to the wheel space cavity 306. The valve 316 may modulate the cooling flow to the wheel space cavity 306 by responding to the wheel space, stator assembly, and/or rotor assembly temperature as measured by one or more monitoring instruments, such as a temperature sensor 320 in communication with the valve 316. In some instances, the temperature sensor 320 and/or an actuator may be in communication with the valve 316 and may be mounted to the stator wall and at least partially protrude into the wheel space cavity 306. In some instances, the valve 316 may be disposed external to the gas turbine engine.

As described above, the purging orifices (e.g., holes) and/or circuits are fixed and sized to provide the required purge flow to meet purge requirements in the wheel space cavity. The rotor cooling airflow provided by the adjustable cooling air orifice and/or cooling air circuit may be modulated and can therefore be optimized to ambient conditions. For example, during cold ambient conditions, less cooling airflow is required to maintain the wheel space cavity temperature; in this case, the flow device may restrict or stop the cooling airflow. During hot ambient conditions, more cooling airflow may be required to maintain the wheel space cavity temperature under the design limit; under these conditions, the flow device may allow more cooling airflow. Accordingly, the flow device used to control rotor cooling air may respond directly to the wheel space cavity temperature and adjust the flow of cooling air as required to maintain rotor temperature within design limits. Having a variable flow area, and therefore the ability to vary the effective flow area of the cooling circuit, provides the additional benefit of optimizing and improving back flow margin.

Any number of fixed and/or variable holes and/or circuits may be used herein. The fixed and/or variable holes and/or circuits may be any size, shape, and/or configuration. Moreover, the variable flow holes and/or circuits do not necessarily have to operate in unison. That is, some may open and some may close. In addition, the variable flow holes and/or circuits may be adjusted in response to any parameter, such as, but not limited to, temperature, power output, ambient conditions, cost, etc.

FIGS. 4 and 5 schematically depict an example cross-sectional view of a system 400 for providing an adjustable flow of cooling air to a wheel space cavity 406. For example, the system 400 may include a stator assembly 402 positioned adjacent to a rotor assembly 404. The stator assembly 402 may include a stator wall 405 that defines a stator cavity 407. The wheel space cavity 406 may be formed between the rotor assembly 404 and the stator assembly 402. In some instances, an inter-stage seal 408 may be positioned between the rotor assembly 404 and the stator assembly 402.

In certain embodiments, the system 400 may be configured to sense, control, and/or modulate the temperature within wheel space cavity 406 by increasing or decreasing an adjustable flow of cooling air 412 to the wheel space cavity 406. For example, the system 400 may include at least one cooling air passage 410 configured to provide the adjustable flow of cooling air 412 to the wheel space cavity 406 from the stator cavity 407. The cooling air passage 410 may include any opening or passage between the stator cavity 407 and the wheel space cavity 406. The adjustable flow of cooling air 412 provided to the wheel space cavity 406 by the cooling air passage 410 may be controlled by a flow control device 414. In this manner, the flow control device 414 may be associated with the cooling air passage 410, but not necessarily positioned within the cooling air passage 410, so as to modulate the adjustable flow of cooling air 412 provided to the wheel space cavity 406 by the cooling air passage 410. In some instances, portions of the flow control device 414 may be mounted to the stator wall 405.

In order to control the adjustable flow of cooling air 412 provided to the wheel space cavity 406 by the cooling air passage 410, the flow control device 414 may include a valve 418 that is configured to open and close, thereby increasing or decreasing the adjustable flow of cooling air 412 provided to the wheel space cavity 406 by the cooling air passage 410. For example, as depicted in FIG. 4, the valve 418 is in the closed position, thereby preventing and/or limiting the adjustable flow of cooling air 412 from entering the wheel space cavity 406. Conversely, as depicted in FIG. 5, the valve 418 is in the open position, thereby enabling the adjustable flow of cooling air 412 to enter the wheel space cavity 406.

In certain embodiments, a temperature dependent actuator 420 may be in mechanical communication with the valve 418. The temperature dependent actuator 420 may be configured to open and close the valve 418. For example, the temperature dependent actuator 420 may be positioned at least partially within the wheel space cavity 406 so as to be at least partially exposed to the wheel space cavity 406. In this manner, the temperature dependent actuator 420 may sense and/or react to the temperature within the wheel space cavity 406. In response, the temperature dependent actuator 420 may open or close the valve 418 to regulate the temperature within the wheel space cavity 406.

In certain embodiments, the temperature dependent actuator 420 may include an actuator housing 422. In some instances, the actuator housing 422 may be positioned at least partially within the wheel space cavity 406 and/or at least partially within the stator cavity 407. That is, the actuator housing 422 may be at least partially exposed to the wheel space cavity 406. In addition, a temperature dependent element 424 may be positioned within the actuator housing 422. The temperature dependent element 424 may be configured to expand or contract in response to a temperature of the wheel space cavity 406. For example, as the temperature dependent element 424 expands, it may push a rod 426 (or other mechanical linkage) attached to the valve 418, thereby opening the valve 418 and allowing the adjustable flow of cooling air 412 to enter the wheel space cavity 406 by way of the cooling air passage 410. Conversely, as the temperature dependent element 424 contracts, it may pull the rod 426 (or other mechanical linkage) attached to the valve 418, thereby closing the valve 418 and preventing or limiting the adjustable flow of cooling air 412 from enter the wheel space cavity 406 by way of the cooling air passage 410.

In some instances, the valve 418 may include a valve body 428 and a valve disc 430. For example, the valve body 428 may include an opening 432 to the stator cavity 407, and the valve disc 430 may be configured to open and close the opening 432. That is, the valve disc 430 may be configured to open or close in response to the temperature dependent actuator 420 expanding or contracting. In this manner, the position of the valve disc 430 about the opening 432 may determine the adjustable flow of cooling air 412 that is provided to the wheel space cavity 406 by the cooling air passage 410.

In certain embodiments, the cooling air passage 410 may be positioned upstream of the temperature dependent actuator 420 so as to deliver the adjustable flow of cooling air 412 upstream of the temperature dependent actuator 420. That is, the fluid flow 436 within the wheel space 406 may be radially outward. In certain embodiments, the flow control device 420 may not be directly mounted to the cooling air passage 410.

Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments.

Claims

1. A turbine assembly, comprising:

a rotor assembly;

a stator assembly positioned adjacent to the rotor assembly;

a wheel space cavity formed between the rotor assembly and the stator assembly;

at least one fixed purge air orifice associated with the stator assembly; and

at least one adjustable cooling air orifice associated with the stator assembly, wherein the at least one fixed purge air orifice is configured to provide a flow of purge air to the wheel space cavity, and wherein the at least one adjustable cooling air orifice is configured to provide an adjustable flow of cooling air to the wheel space cavity.

2. The assembly of claim 1, further comprising a flow control device associated with the at least one adjustable cooling air orifice, wherein the flow control device is configured to vary the flow of cooling air to the wheel space cavity by varying the size of the at least one adjustable cooling air orifice.

3. The assembly of claim 2, wherein the stator assembly comprises:

a stator wall; and

a stator cavity defined by the stator wall, wherein the stator cavity is in communication with a flow of compressor extraction air.

4. The assembly of claim 3, wherein the at least one fixed purge air orifice is positioned in the stator wall.

5. The assembly of claim 3, wherein the at least one adjustable cooling air orifice is positioned in the stator wall.

6. The assembly of claim 3, wherein the flow control device is positioned within the stator cavity.

7. The assembly of claim 3, wherein the flow of compressor extraction air forms at least a portion of the flow of purge air and the flow of cooling air.

8. The assembly of claim 1, further comprising a temperature sensor associated with the wheel space cavity and in communication with the at least one adjustable cooling air orifice.

9. The assembly of claim 1, further comprising an inter-stage seal positioned between the rotor assembly and the stator assembly.

10. A turbine assembly, comprising:

a rotor assembly;

a stator assembly positioned adjacent to the rotor assembly;

a wheel space cavity formed between the rotor assembly and the stator assembly;

at least one purge air circuit associated with the stator assembly; and

at least one cooling air circuit associated with the stator assembly, wherein the at least one purge air circuit is configured to provide a flow of purge air to the wheel space cavity, and wherein the at least one cooling air circuit is configured to provide an adjustable flow of cooling air to the wheel space cavity.

11. The assembly of claim 10, further comprising a flow control device associated with the at least one cooling air circuit, wherein the flow control device is configured to vary the flow of cooling air to the wheel space cavity.

12. The assembly of claim 11, wherein the flow control device comprises a valve in communication with the at least one cooling air circuit.

13. The assembly of claim 10, wherein the stator assembly comprises:

a stator wall; and

a stator cavity defined by the stator wall, wherein the stator cavity is in communication with a flow of compressor extraction air.

14. The assembly of claim 13, wherein the at least one purge air circuit comprises an orifice positioned in the stator wall.

15. The assembly of claim 14, wherein the orifice is fixed

16. The assembly of claim 13, wherein the at least one cooling air circuit comprises an adjustable orifice positioned in the stator wall.

17. The assembly of claim 10, further comprising a temperature sensor associated with the wheel space cavity and in communication with the at least one cooling air circuit.

18. The assembly of claim 10, further comprising an inter-stage seal positioned between the rotor assembly and the stator assembly.

19. A method for providing a flow of purge air and a flow of cooling air to a cavity in a gas turbine assembly, comprising:

providing the flow purge air to the cavity by way of at least one fixed purge air orifice; and

varying the flow of cooling air to the cavity by way of at least one adjustable cooling air orifice, wherein the cavity comprises a wheel space cavity or a stator cavity.

20. The method of claim 19, further comprising varying the size of the at least one adjustable cooling air orifice with a flow control device.

21. A system for providing an adjustable flow of cooling air from a stator cavity to a wheel space cavity of a turbine assembly, the system comprising:

at least one cooling air passage configured to provide the adjustable flow of cooling air to the wheel space cavity from the stator cavity; and

a flow control device associated with the at least one cooling air passage, the flow control device comprising: a valve configured to control the adjustable flow of cooling air within the at least one cooling air passage; and a temperature dependent actuator positioned at least partially within the wheel space cavity and in mechanical communication with the valve, wherein the temperature dependent actuator is configured to open and close the valve.

22. The system of claim 21, wherein the temperature dependent actuator comprises:

an actuator housing positioned at least partially within the wheel space cavity; and

a temperature dependent element positioned within the actuator housing, wherein the temperature dependent element is configured to expand or contract in response to a temperature of the wheel space cavity to open and close the valve.

23. The system of claim 21, wherein the valve comprises:

a valve body in fluid communication with the at least one cooling air passage; and

a valve disc configured to open and close in response to the temperature dependent actuator to modulate the adjustable flow of cooling air provided to the wheel space cavity by the at least one cooling air passage.

24. The system of claim 21, wherein the at least one cooling air passage is positioned upstream of the temperature dependent actuator so as to deliver the adjustable flow of cooling air upstream of the temperature dependent actuator.

25. The system of claim 21, further comprising at least one fixed purge air orifice in communication with the wheel space cavity, wherein the at least one fixed purge air orifice is configured to provide a constant flow of purge air to the wheel space cavity.