Re-use and modulated cooling from tip clearance control system for gas turbine engine

A control system for a gas turbine engine comprises a case structure, a clearance control ring mounted for movement relative to the case structure, an outer air seal mounted to the clearance control ring and facing a first engine component, and a control and valve assembly that receives flow from a flow input source. The control and valve assembly is configured to direct flow into a first cavity positioned radially between the case structure and the outer air seal, and wherein the control and valve assembly is configured to direct flow into a second cavity positioned downstream of the first cavity to interact with a second engine component. A method of controlling flow between a compressor section and turbine section is also disclosed.

BACKGROUND OF THE INVENTION

Gas turbine engines typically include a fan delivering air into a compressor. The air is compressed in the compressor and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine blades, driving them to rotate. Turbine rotors, in turn, drive the compressor and fan rotors. The efficiency of the engine is impacted by ensuring that the products of combustion pass in as high a percentage as possible across the turbine blades. Leakage around the blades reduces efficiency. Thus, a blade outer air seal (BOAS) is provided radially outward of the blades to prevent leakage.

The BOAS is spaced from a radially outer part of the blade by a tip clearance. The BOAS is traditionally associated with a carrier element that is mounted to a case structure. Since the blades, the BOAS, and the structure that support the BOAS are different sizes and/or are formed of different materials, they respond to temperature changes in different manners. As these structures expand at different rates in response to temperature changes, the tip clearance may be reduced and the blade may rub on the BOAS, or the tip clearance may increase reducing efficiency, both of which are undesirable.

Clearance control systems are used to control the tip clearance under different operational conditions. Traditional clearance control systems utilize valves and manifolds to direct fan air to specific engine case locations. The cooling air thermally shrinks the engine case at these locations to improve tip clearance and thus fuel burn. However, these manifolds and valves are large, heavy, and expensive. These systems can also be slow to respond and provide limited clearance improvement. By further reducing tip clearances increasing engine efficiency demands can be met.

SUMMARY OF THE INVENTION

In a featured embodiment, a control system for a gas turbine engine comprises a case structure, a clearance control ring mounted for movement relative to the case structure, an outer air seal mounted to the clearance control ring and facing a first engine component, and a control and valve assembly that receives flow from a flow input source. The control and valve assembly is configured to direct flow into a first cavity positioned radially between the case structure and the outer air seal, and wherein the control and valve assembly is configured to direct flow into a second cavity positioned downstream of the first cavity to interact with a second engine component.

In another embodiment according to the previous embodiment, the control and valve assembly controls a temperature of flow supplied to the first cavity to control movement of the clearance control ring to allow the outer air seal to move in a desired direction to maintain a desired clearance between the outer air seal and the first engine component.

In another embodiment according to any of the previous embodiments, the control and valve assembly directs flow into the second cavity in combination with directing flow into the first cavity, or directs flow into the second cavity independently of directing flow into the first cavity.

In another embodiment according to any of the previous embodiments, the first engine component comprises a first rotating blade and the second engine component comprises a vane. The second cavity is positioned radially between the vane and the case structure.

In another embodiment according to any of the previous embodiments, an intermediate cavity is positioned axially between the first and second cavities. The intermediate cavity is in fluid communication with the first cavity such that flow from the first cavity is directed through the intermediate cavity and into a first inlet to the second cavity.

In another embodiment according to any of the previous embodiments, the second cavity includes a second inlet that is fluidly connected to the control and valve assembly such that flow from the first and second inlets are mixed together in the second cavity.

In another embodiment according to any of the previous embodiments, flow from the second cavity is directed to at least one passage within the vane.

In another embodiment according to any of the previous embodiments, flow exits the passage from the vane and enters a radially inner cavity between the first rotating blade and a second rotating blade that is downstream from the vane, and wherein flow from the radially inner cavity is directed through an opening in a rotating structure and toward the second rotating blade.

In another embodiment according to any of the previous embodiments, flow from the second cavity is directed to a downstream cavity to interact with a second outer air seal and/or a third engine component.

In another featured embodiment, a control system for a gas turbine engine comprises a turbine case structure, a clearance control ring mounted for movement relative to the turbine case structure, an outer air seal mounted to the clearance control ring, and a control and valve assembly that receives flow from a flow input source. The control and valve assembly is configured to direct flow into a first cavity positioned radially between the turbine case structure and the outer air seal. The control and valve assembly controls a temperature of flow supplied to the first cavity to control movement of the clearance control ring to allow the outer air seal to move in a desired direction to maintain a desired clearance between the outer air seal and a first turbine blade, and wherein the control and valve assembly is configured to direct flow into a second cavity positioned downstream of the first cavity to interact with a second turbine component. The control and valve assembly directs flow into the second cavity in combination with directing flow into the first cavity, or directs flow into the second cavity independently of directing flow into the first cavity.

In another embodiment according to the previous embodiment, the second cavity is positioned radially between the case structure and a turbine vane that is downstream of the first turbine blade, and including an intermediate cavity positioned axially between the first and second cavities, the intermediate cavity being in fluid communication with the first cavity such that flow from the first cavity is directed through the intermediate cavity and into a first inlet to the second cavity.

In another embodiment according to any of the previous embodiments, the second cavity includes a second inlet that is fluidly connected to the control and valve assembly such that flow from the first and second inlets are mixed together in the second cavity.

In another embodiment according to any of the previous embodiments, flow from the second cavity is directed into at least one passage within the turbine vane.

In another embodiment according to any of the previous embodiments, flow exits the passage from the turbine vane and enters a radially inner cavity between the first turbine blade and a second turbine blade that is downstream from the turbine vane, and wherein flow from the radially inner cavity is directed through an opening in a rotating structure and toward the second turbine blade.

In another embodiment according to any of the previous embodiments, flow from the second cavity is directed to a third cavity downstream of the second cavity to interact with a second outer air seal and/or a low pressure turbine component.

In another featured embodiment, a method of controlling flow between a compressor section and turbine section in a gas turbine engine comprises mounting a clearance control ring for movement relative to a turbine case structure, mounting an outer air seal to the clearance control ring to face a first turbine blade, directing flow from a flow input source into a first cavity positioned radially between the turbine case structure and the outer air seal, controlling a temperature of flow supplied to the first cavity to control movement of the clearance control ring to allow the outer air seal to move in a desired direction to maintain a desired clearance between the outer air seal and the first turbine blade, and directing flow into a second cavity positioned downstream of the first cavity to interact with a second turbine component.

In another embodiment according to the previous embodiment, a control and valve assembly directs flow into the second cavity in combination with directing flow into the first cavity, or directs flow into the second cavity independently of directing flow into the first cavity.

In another embodiment according to any of the previous embodiments, an intermediate cavity is positioned axially between the first and second cavities, an including fluidly connecting the intermediate cavity with the first cavity such that flow from the first cavity is directed through the intermediate cavity and into a first inlet to the second cavity, and providing the second cavity with a second inlet that is fluidly connected to the control and valve assembly such that flow from the first and second inlets are mixed together in the second cavity.

In another embodiment according to any of the previous embodiments, flow is directed from the second cavity into at least one passage within a turbine vane that is downstream of the first turbine blade.

In another embodiment according to any of the previous embodiments, flow is directed from the second cavity into a third cavity downstream of the second cavity to interact with a second outer air seal and/or a low pressure turbine component.

The foregoing features and elements may be combined in any combination without exclusivity, unless expressly indicated otherwise.

DETAILED DESCRIPTION

FIGS. 2A-2Bshow an outer air seal assembly60spaced by a clearance gap G from a radially outer tip of a rotating blade62. In one example, the blade62is a component of the turbine section28as shown inFIG. 1. However, the outer air seal assembly60may be used in other engine configurations and/or locations, for example in the compressor sections. The outer air seal assembly60includes an outer air seal body64that is mounted to a clearance control ring66. An internal cavity68is formed between a case structure70and the outer air seal assembly60. A support structure72is associated with the case structure70to provide support for the outer air seal assembly60.

In an active clearance control system, air impinges on the turbine case when activated to cool and shrink the case diameter. This in turn reduces the diameter of the segmented blade outer air seal assembly. The seal body in this application is in segments to prevent thermal fighting between the seal and the turbine case to which the seal ultimately mounts to and which is a full hoop. The turbine case that comprises the full hoop structure is what controls the position of the blade outer air seal. Due to the mass of the turbine case and the thermal environment within which the turbine case operates, the turbine case is slow to respond thermally as the engine power level is increased. The turbine rotor diameter, however, will increase rapidly as the rotational speed and temperature of the engine increases. For this reason, extra clearance must be added between the tip of the blade and the blade outer air seal assembly to prevent rubbing contact between these two structures. However, this extra clearance can adversely affect engine performance.

In one example, the clearance control ring66is positioned adjacent the support structure72but is not directly tied to the case structure70or support structure72. In one example configuration, the clearance control ring66includes a first mount feature74and the seal body64includes a second mount feature76that cooperates with the first mount feature74such that the clearance control ring66can move within the internal cavity68independently of the support structure72and case structure70in response to changes in temperature. In one example, the clearance control ring66is a full hoop ring made from a material with a high thermal expansion coefficient, for example. This new configuration with the clearance control ring66reacts much faster than prior active control systems due to the reduced thermal mass and due to being exposed to air from the engine gaspath in contrast to prior systems where the heavy turbine case was exposed to the engine core compartment temperatures.

An injection source78injects or delivers cooling fluid flow, for example, air flow, into the internal cavity68to control a temperature of the clearance control ring66to allow the outer air seal body64to move in a desired direction to maintain a desired clearance between the outer air seal body64and a tip of the blade62, i.e. to control the size of the clearance gap G. In one example, the injection source78comprises a tube or conduit78athat receives air flow from a flow input source such as the compressor section24(FIG. 1) of the gas turbine engine, for example. Other flow input sources, such as bypass flow, for example, could also be used. As shown inFIG. 2A, a control80is configured to deliver the compressor air at a first temperature T1into the internal cavity68and against the clearance control ring66to allow the outer air seal body64to move in a first direction to maintain a desired clearance during a first operating condition, and is configured to deliver compressor air at a second temperature T2into the internal cavity68and against the outer air seal body64to allow the outer air seal body64to move in a second direction to maintain a desired clearance during a second operating condition. In one example, the first operating condition comprises a take-off or high load event, and the second operating condition comprises a descending event.

In these example operating conditions, the second temperature T2is less than the first temperature T1. In this example, the compressor air at the second temperature T2can comprise cooled cooling air from the compressor exit while the air at the first temperature can comprise uncooled compressor exit air. The control80comprises a microprocessor and/or control unit that is programmed to deliver air flow at the first T1or second T2temperature as needed dependent upon the engine operating condition. The control C can further include valves V, flow conduits, and/or heat exchangers as needed to deliver the compressor air at the desired temperature. The control80delivers higher temperature air T1into the cavity68when the clearance control ring66is to increase in diameter and delivers lower temperature air T2into the cavity68when the clearance control ring66is to decrease in diameter. It should be understood that while two different temperatures are discussed as examples, the system is infinitely variable and the system can deliver fluid at any desired temperature.

The case structure70includes an opening82(FIG. 3) to receive the conduit78awhich directs compressor air into the cavity68. The support structure72includes a first radial wall portion84extending radially inward from the case structure70and a second radial wall portion86axially spaced from the first radial portion84to define the internal cavity68. The opening82is positioned axially between the first84and second86radial portions. The case structure70includes trenches or grooves88adjacent to each of the first84and second86radial wall portions.

The seal body64includes a seal support portion90and a ring mount portion92. The grooves88receive the seal support portion90to seat the outer air seal assembly60relative to the case structure70. These comprise tight radial fits to the case structure70at the grooves88. The clearance control ring66is radially moveable relative to the first84and second86radial wall portions in response to temperature changes via the connection interface to the ring mount portion92. A main seal portion94extends from the ring mount portion92to face the blade62.

The first74and second76mount portions are shown in greater detail inFIG. 2B. One of the first74and second76mount features comprises a slot98and another of the first74and second76mount features comprises an extension100that is received within the slot98to couple the outer air seal body64and clearance control ring66together. In the example shown, the clearance control ring66includes the slot98and the seal body64includes the extension100; however, the reverse configuration could also be used. In one example, the slot98and the extension100comprise a key-shape, with each of the slot98and extension100having a first portion98a,100aextending in a radial direction and a second portion98b,100bextending in an axial direction. This type of configuration provides a floating connection interface that fully supports and properly locates the seal64while still controlling the seal64to move radially inwardly and outwardly as needed.

As shown inFIGS. 4A-4B, when the clearance control ring66is in a first temperature, the ring has a first diameter D1. When the control80delivers lower temperature air T2(FIG. 4B) to the cavity68, the clearance control ring66contracts to a second diameter D2that is less than the first diameter D1. This allows the seal body64to move radially inwardly toward the blade62. When the control80delivers higher temperature air T1(FIG. 4C) to the cavity68, the clearance control ring66expands to a third diameter D3that is greater than the first diameter D1. This allows the seal body64to move radially outwardly away from the blade62. Thermal growth rate TGis calculated as TG=RαΔT where R is the radius of the ring, ΔT is the difference between the initial and final temperatures, and a is a thermal coefficient of expansion determined based on the material of the ring.

In one example, the control ring66optionally includes one or more through holes96(see dashed lines inFIG. 2Bthat direct air through the body of the control ring66.

In one example, the outer air seal body64comprises a segmented ring and the clearance control ring66comprises a full hoop ring. The segmented ring includes a plurality of body segments that are circumferentially arranged to form the annular outer air seal assembly60as known. In one example, the full hoop ring comprises a radial spline104similar to that shown inFIG. 5. In the subject clearance control system, the radial spline may include additional splines or a reduced number of splines than that which is shown inFIG. 5.

Once the flow has been used to control movement of the control ring66, the subject invention provides a control system200that uses supplemental flow alone or in combination with flow from the BOAS cavity68to cool downstream engine components such as a high pressure turbine vane, blade outer air seal, second stage turbine blade, etc. As shown inFIG. 2A, the control system200includes a first control80and first valve202that are configured to deliver compressor flow from compressor section24into the internal cavity68of a first outer air seal assembly60. The control80and valve202cooperate to deliver flow at a desired temperature into the cavity68to control movement of the control ring66to maintain a desired tip clearance as discussed above. In one example, flow of various temperatures T1, T2can be mixed via the control80and valve202to provide the desired temperature.

The control system200further includes a second control204and a second valve206that cooperate to deliver supplemental flow from the compressor section24to a plenum208(FIG. 3) that is downstream of the cavity68of the first outer air seal assembly60. A conduit210connects the second control80and second valve206to the compressor section24and another conduit212directs flow from the second valve206to an injection member214that directs flow into the plenum208via an opening216in the case structure70.

In one example, flow directed through opening216is mixed in the plenum208with flow that was used to control temperature of the clearance control ring66of the first outer air seal assembly60. As shown inFIG. 2A, a hole218is formed within the radial wall portion86of the case support structure72. The hole218is in fluid communication with cavity68and directs flow from cavity68into a downstream/intermediate cavity220that is between first blade outer air seal94and second stage vane114as shown inFIG. 3. Flow through the hole218can vary in relation to movement of the clearance control ring66.FIG. 7shows an example where the clearance control ring66covers approximately half of the hole218. As the clearance control ring66is subjected to higher temperature levels, the clearance control ring66moves radially outwardly to cover a greater portion of the hole218. As the clearance control ring66is subjected to cooling temperatures, the clearance control ring66moves radially inwardly to open a greater area of the hole218.

The second stage vane114has a first vane arm222and a second vane arm224that are on opposing sides of a vane platform226, and which the connect the vane114to the case70. The plenum208is formed between the case70, the platform226, and the first222and second224vane arms. A hole228is formed in the first vane arm222. The hole228receives flow from intermediate cavity220and directs flow into the plenum208to be mixed with flow entering the plenum208through hole216.

In one example configuration shown inFIG. 6, the outer air seal assembly60is positioned within the turbine section28downstream of the compressor section24. The turbine section28includes a plurality of turbine stages with the first outer air seal assembly60being positioned between a vane110of a first turbine stage112and the vane114of second turbine stage116. As discussed above, the plenum208is located radially outwardly of the vane114.

In one example, the flow from the plenum208can be directed through a hole230in the platform226to cool the vane114. Flow can then exit the vane114via hole232into cavity234. Cavity234is positioned between the blade62of the first turbine stage112and a blade236of the second turbine stage116. In one example, the flow exits hole232via a turbine on-board injector238that is mounted to the vane114and which swirls flow in a direction of the rotating cavity234. The flow can then be directed from the cavity234through a hole240formed in a cover plate242associated with blade236to cool the blade236as indicated at244.

In another example shown inFIG. 3, flow can exit plenum208via an opening250formed in the second vane arm224. Flow exiting this opening250enters a mixing cavity252. Flow can then exit mixing cavity252to cool a second blade outer air seal assembly254spaced from a tip of blade236(FIG. 6). Flow can also optionally be directed from mixing cavity252, through hole256, and then toward the low pressure turbine46.

As such, subject invention provides a control system200that can be used to direct flow from the compressor section24to various other engine components in an efficient manner. The control system200utilizes controllers and valves to control flow to outer air seal assemblies, blades, vanes, etc. that are associated with the high and low pressure turbines. The subject invention further provides a high pressure turbine internal ring comprising a clearance control ring66connected to an outer air seal body64, where the control ring66is made from a material with a high thermal expansion coefficient. The control ring66is configured to be mounted to the air seal body64in an isolated manner such that the connecting mass is much lower than that of a turbine case structure70. The control ring66is free floating on a radial spline such that the control ring's movement is not restricted. When the system is activated, cooled cooling air from the compressor, which is approximately 50-400 degrees Fahrenheit cooler than the air surrounding the control ring, is pumped into the internal cavity68and channeled around or through the control ring66to rapidly reduce the ring temperature and diameter as needed. In the same manner, during specified operating conditions, the control directs uncooled compressor exit air to rapidly increase the temperature of the control ring and diameter as needed.

The rapid response of the system allows for overall tighter high pressure turbine clearances to be set which yields an improved thrust specific fuel consumption (TSFC). In one simulated example, the TSFC increases as much as 0.4% with the use of the subject control ring66. The subject system is also lighter and less expensive than traditional systems, which use large pipes, valves, and complex manifolds. The subject system uses small diameter plumbing and valves without the complex manifold. The subject system also allows both heated and cooled air to be channeled through the control ring66to increase and decrease the diameter of the ring as needed.