Gas turbine engine rapid response clearance control system with variable volume turbine case

An active clearance control system of a gas turbine engine includes a radially adjustable blade outer air seal system movable between a radially contracted Blade Outer Air Seal (BOAS) position that defines a first air volume and a radially expanded Blade Outer Air Seal (BOAS) position that defines a second air volume, the second air volume different than the first air volume. An accumulator system accommodate a difference in air volume between the first air volume and the second air volume.

BACKGROUND

The present disclosure relates to a gas turbine engine and, more particularly, to a blade tip rapid response active clearance control (RRACC) system therefor.

Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor to pressurize an airflow, a combustor to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine to extract energy from the resultant combustion gases. The compressor and turbine sections include rotatable blade and stationary vane arrays. Within an engine case structure, the radial outermost tips of each blade array are positioned in close proximity to a shroud assembly. Blade Outer Air Seals (BOAS) supported by the shroud assembly are located adjacent to the blade tips such that a radial tip clearance is defined therebetween.

When in operation, the thermal environment in the engine varies and may cause thermal expansion and contraction such that the radial tip clearance varies. The radial tip clearance is typically designed so that the blade tips do not rub against the Blade Outer Air Seal (BOAS) under high power operations when the blade disk and blades expand as a result of thermal expansion and centrifugal loads. When engine power is reduced, the radial tip clearance increases. To facilitate engine performance, it is operationally advantageous to maintain a close radial tip clearance through the various engine operational conditions.

SUMMARY

An active clearance control system of a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes a radially adjustable blade outer air seal system movable between a radially contracted Blade Outer Air Seal position that defines a first air volume and a radially expanded Blade Outer Air Seal position that defines a second air volume, the second air volume different than the first air volume and an accumulator system that accommodate a difference in air volume between the first air volume and the second air volume.

A further embodiment of the present disclosure includes, wherein the accumulator system is operable to maintain a constant volume between a multiple of air seal segments of the radially adjustable blade outer air seal system and an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system is passively operable.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system includes a piston.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the piston is biased.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the piston is movable to maintain a constant volume between a multiple of air seal segments of the radially adjustable blade outer air seal system and an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the piston is momentarily displaced from a home position to maintain a constant volume between a multiple of air seal segments of the radially adjustable blade outer air seal system and an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a biasing member to return the piston to the home position.

A further embodiment of any of the foregoing embodiments of the present disclosure includes an orifice in the piston to control a return of the piston to the home position.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system includes a pneumatic cylinder located internal to an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system includes a pneumatic cylinder located external to an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system includes a pneumatic cylinder located external to an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the accumulator system includes a pneumatic cylinder that is at least partially annular.

A method of active blade tip clearance control for a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure includes maintaining a constant volume between a multiple of air seal segments of a radially adjustable blade outer air seal system and an engine case structure.

A further embodiment of any of the foregoing embodiments of the present disclosure includes maintaining the constant volume with an accumulator system.

A further embodiment of any of the foregoing embodiments of the present disclosure includes maintaining the constant volume with by moving a piston within a pneumatic cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes momentarily displacing the piston within the pneumatic cylinder then returning the piston to a home position.

A further embodiment of any of the foregoing embodiments of the present disclosure includes returning the piston to the home position with a biasing member.

A further embodiment of any of the foregoing embodiments of the present disclosure includes locating the accumulator system within an engine case structure.

DETAILED DESCRIPTION

FIG. 1schematically illustrates a gas turbine engine20. The gas turbine engine20is disclosed herein as a two-spool low-bypass augmented turbofan that generally incorporates a fan section22, a compressor section24, a combustor section26, a turbine section28, an augmenter section30, an exhaust duct section32, and a nozzle system34along a central longitudinal engine axis A. Although depicted as an augmented low bypass turbofan in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are applicable to other gas turbine engines including non-augmented engines, geared architecture engines, direct drive turbofans, turbojet, turboshaft, multi-stream variable cycle adaptive engines and other engine architectures. Variable cycle gas turbine engines power aircraft over a range of operating conditions and essentially alters a bypass ratio during flight to achieve countervailing objectives such as high specific thrust for high-energy maneuvers yet optimizes fuel efficiency for cruise and loiter operational modes.

An engine case structure36defines a generally annular secondary airflow path40around a core airflow path42. Various case structures and modules may define the engine case structure36that essentially defines an exoskeleton to support the rotational hardware.

Air that enters the fan section22is divided between a core airflow through the core airflow path42and a secondary airflow through a secondary airflow path40. The core airflow passes through the combustor section26, the turbine section28, then the augmentor section30where fuel may be selectively injected and burned to generate additional thrust through the nozzle system34. It should be appreciated that additional airflow streams such as third stream airflow typical of variable cycle engine architectures may additionally be sourced from the fan section22.

The secondary airflow may be utilized for a multiple of purposes to include, for example, cooling and pressurization. The secondary airflow as defined herein may be any airflow different from the core airflow. The secondary airflow may ultimately be at least partially injected into the core airflow path42adjacent to the exhaust duct section32and the nozzle system34.

The exhaust duct section32may be circular in cross-section as typical of an axisymmetric augmented low bypass turbofan or may be non-axisymmetric in cross-section to include, but not be limited to, a serpentine shape to block direct view to the turbine section28. In addition to the various cross-sections and the various longitudinal shapes, the exhaust duct section32may terminate in a Convergent/Divergent (C/D) nozzle system, a non-axisymmetric two-dimensional (2D) C/D vectorable nozzle system, a flattened slot nozzle of high aspect ratio or other nozzle arrangement.

With reference toFIG. 2, a blade tip rapid response active clearance control (RRACC) system58includes a radially adjustable Blade Outer Air Seal System (BOAS)60that operates to control blade tip clearances inside for example, the turbine section28, however, other sections such as the compressor section24may also benefit herefrom. The radially adjustable Blade Outer Air Seal System (BOAS)60may be arranged around each or particular stages within the gas turbine engine20. That is, each rotor stage may have an associated radially adjustable Blade Outer Air Seal System (BOAS)60of the blade tip rapid response active clearance control system58.

Each radially adjustable Blade Outer Air Seal System (BOAS)60is subdivided into a multiple of circumferential segments62, each with a respective air seal segment64and a puller68(illustrated schematically). In one disclosed non-limiting embodiment, each circumferential segment62may extend circumferentially for about nine (9) degrees. It should be appreciated that any number of circumferential segments62and various other components may alternatively or additionally be provided.

Each of the multiple of air seal segments64is at least partially supported by a generally fixed full-hoop thermal control ring70. That is, the full-hoop thermal control ring70is mounted to, or forms a portion of, the engine case structure36to thermally expand and contract and at least partially control blade tip clearances in a passive manner. It should be appreciated that various static structures may additionally or alternatively be provided to at least partially support the multiple of air seal segments64yet permit relative radial movement therebetween.

Each air seal segment64may be manufactured of an abradable material to accommodate potential interaction with the rotating blade tips28T within the turbine section28and includes numerous cooling air passages64P to permit secondary airflow therethrough.

A radially extending forward hook72and an aft hook74of each air seal segment64respectively cooperates with a forward hook76and an aft hook78of the full-hoop thermal control ring70. The forward hook76and the aft hook78of the full-hoop thermal control ring70may be segmented (FIG. 3) or otherwise configured for assembly of the respective air seal segment64thereto. The forward hook72may extend axially aft and the aft hook74may extend axially forward (shown); vice-versa or both may extend axially forward or aft within the engine to engage the reciprocally directed forward hook76and aft hook78of the full-hoop thermal control ring70.

With continued reference toFIG. 2, each air seal segment64is radially positioned between an extended radially contracted Blade Outer Air Seal (BOAS) position (FIG. 4) and a retracted radially expanded Blade Outer Air Seal (BOAS) position (FIG. 5) with respect to the full-hoop thermal control ring70by the puller68. The puller68need only “pull” each associated air seal segment64as a differential pressure from the core airflow biases the air seal segment64toward the extended radially contracted Blade Outer Air Seal (BOAS) position (FIG. 4). For example, the differential pressure may exert an about 1000 pound force (4448 newtons) inward force on each air seal segment64.

The puller68from each associated air seal segment64may extend from, or be a portion of, an actuator86(illustrated schematically) that operates in response to a control88(illustrated schematically) to adjust the radially adjustable Blade Outer Air Seal (BOAS) system60between the extended radially contracted Blade Outer Air Seal (BOAS) position (FIG. 4) and the retracted radially expanded Blade Outer Air Seal (BOAS) position (FIG. 5). It should be appreciated that various other control components such as sensors, actuators and other subsystems may be utilized herewith.

The actuator86may include a mechanical, electrical and/or pneumatic drive that operates to move the respective air seal segment64along an axis W so as to contract and expand the radially adjustable Blade Outer Air Seal System (BOAS)60. That is, the actuator86provides the motive force to pull the puller68.

The control88generally includes a control module that executes radial tip clearance control logic to thereby control the radial tip clearance relative the rotating blade tips. The control module typically includes a processor, a memory, and an interface. The processor may be any type of known microprocessor having desired performance characteristics. The memory may be any computer readable medium which stores data and control algorithms such as logic as described herein. The interface facilitates communication with other components such as a thermocouple, and the actuator86. In one non-limiting embodiment, the control module may be a portion of a flight control computer, a portion of a Full Authority Digital Engine Control (FADEC), a stand-alone unit or other system.

When the radially adjustable Blade Outer Air Seal System (BOAS)60is pulled from the radially expanded Blade Outer Air Seal (BOAS) position (FIG. 3) to the radially contracted Blade Outer Air Seal (BOAS) position (FIG. 4) an increased pressure loading is formed on the back side of the multiple of air seal segments64which operates against the actuator86. In other words, an increased pressure occurs between the multiple of air seal segments64and the engine case structure36.

With reference toFIG. 6, to accommodate the increased pressure, an accumulator system100is in communication with an air volume102in the generally annular space between the multiple of air seal segments64and the engine case structure36. The air volume102may be of a particular stage or multiple stages within the gas turbine engine20.

In one disclosed non-liming embodiment, the accumulator system100may be a pneumatic cylinder102with a movable piston104which is moved to accommodate the air volume102when the radially adjustable Blade Outer Air Seal System (BOAS)60is pulled from the radially expanded Blade Outer Air Seal (BOAS) position (FIG. 7) to the radially contracted Blade Outer Air Seal (BOAS) position (FIG. 7). That is, the piston104is passively operable.

The pneumatic cylinder102may be located internal (FIG. 8) or external (FIG. 9) with respect to the engine case structure36. Further, in one disclosed non-limiting embodiment, the pneumatic cylinder may be annular (FIG. 10) to facilitate packaging within the engine case structure36(FIG. 6).

As the radially adjustable Blade Outer Air Seal System (BOAS)60is actuated, the piston104is moved to maintain a constant volume between the multiple of air seal segments64and the engine case structure36. In one disclosed non-limiting embodiment, the piston104is a momentarily displacement piston that includes a bias member106such as a spring and one or more orifice108therethrough (FIG. 8). The piston104is only displaced momentarily and returns to a home position by the bias member106. The movement of the piston104is controlled by the orifice108which allows the air to bleed from one side of the piston104to another. The accumulator system100may be more efficient than dampening each of the multiple of air seal segments64individually.

With reference toFIG. 9, a backside of the piston104vents to atmosphere through an orifice108′ in the engine case structure36when the system actuated. That is, the piston104is controlled by the orifice108′ which allows the air on the bias member106side to vent directly through the engine case structure36.

The reduced air pressure load on the radially adjustable Blade Outer Air Seal System (BOAS)60provided by the accumulator system100facilitates the use of a relatively smaller actuator86.