Rapid response clearance control system with spring assist for gas turbine engine

An active clearance control system of a gas turbine engine includes an actuation cylinder, a puller engaged with an air seal segment and damped with respect to the actuation cylinder, and a full-hoop thermal control ring that at least partially supports the air seal segment. The puller may move the air seal segment between an extended radially contracted BOAS position and a retracted radially expanded BOAS position.

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 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

A drive link for an active clearance control system of a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes a puller damped with respect to an actuation cylinder.

A further embodiment of the present disclosure includes, wherein the puller is damped with respect to the actuation cylinder by a spring.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a stop within the actuation cylinder to limit relative movement of the puller.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the puller includes a plate configured to engage a forward hook and an aft hook of an air seal segment.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a rod affixed to the plate.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a rod affixed to the plate, the rod extends into the actuation cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a radial flange that extends from the rod, the radial flange engaged with the spring.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the radial flange is engageable with the stop.

An active clearance control system of a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes a puller mounted to the actuation cylinder to move an air seal segment between an extended radially contracted BOAS position and a retracted radially expanded BOAS position, said puller damped with respect to an actuation cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes an actuator mounted to the actuation to move the puller in response to a control.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the puller is damped with respect to the actuation cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the puller is damped with a spring with respect to said actuation cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes a stop to limit compression of the spring.

A method of active blade tip clearance control for a gas turbine engine, according to one disclosed non-limiting embodiment of the present disclosure includes engaging a puller with an air seal segment; and damping the puller with respect to an actuation cylinder.

A further embodiment of any of the foregoing embodiments of the present disclosure includes at least partially supporting the air seal segment with a full-hoop thermal control ring.

A further embodiment of any of the foregoing embodiments of the present disclosure includes engaging a plate of the puller with the forward hook and the aft hook of each of the multiple of air seal segments.

A further embodiment of any of the foregoing embodiments of the present disclosure includes damping the puller with respect to the actuation cylinder with a spring.

A further embodiment of any of the foregoing embodiments of the present disclosure includes limiting compression of the spring.

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 static structure36defines a generally annular secondary airflow path40around a core airflow path42. Various case static structures and modules may define the engine case static structure36which 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 system60that 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 system60may 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 system60of the blade tip rapid response active clearance control system58.

Each radially adjustable blade outer air seal system60is subdivided into a multiple of circumferential segments62, each with a respective air seal segment64and a drive link66with a puller68(also shown inFIG. 3). 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 segments62may be and 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 static 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 section28. Each air seal segment64also 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 corresponding 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, the forward hook76and the aft hook78also interact with the puller68which permits the respective air seal segment64to be radially positioned between an extended radially contracted BOAS position (FIG. 4) and a retracted radially expanded 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 BOAS position (FIG. 4). For example, the differential pressure may exert an about 1000 pounds (454 Kilograms) inward force on each air seal segment64.

The puller68generally includes a plate80and a rod82. The plate80may be X-shaped or otherwise configured to engage the forward hook72and the aft hook74of the respective air seal segment64(FIG. 3). It should be appreciated that other configurations may alternatively be provided. The rod82is rigidly mounted to the plate80, e.g., fastened, bolted, welded, brazed, etc. such that movement of the rod82moves the plate80which then radially positions the respective air seal segment64.

The puller68provides actuation of the respective air seal segment64yet permits the effective use of legacy cooling schemes. That is, the plate80is engageable with the respective air seal segment64but because the plate80is not rigidly mounted directly to the retractable air seal segment64, the puller80has minimal—if any—effect upon the numerous cooling air passages64P. The plate80interfaces with the respective air seal segment64and also reduces the radial tolerance stack to permits the puller68to support at least a portion of a radial load when the respective air seal segment64are in the circumferentially contracted position (FIG. 4).

Each drive link66may extend through an engine case84to an actuator86(illustrated schematically) that operates in response to a control88(illustrated schematically). The actuator86may include a mechanical, electrical and/or pneumatic drive that operates to move the drive link66along a drive link axis W so as to contract and expand the radially adjustable blade outer air seal system60. It should be appreciated that various other control components such as sensors, actuators and other subsystems may be utilized herewith.

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.

In operation, the blade tip rapid response active clearance control system58may utilize, for example, an actuator86that provides about 1200-1400 pounds (544-635 kilograms) of force to provide a radial displacement capability for the array of air seal segments64of about 0.040″ (40 thousandths; 1 mm) in one disclosed non-limiting embodiment. The radial displacement may, at least partially, be a function of the engine core size and the dynamic conditions of the particular engine architecture.

With reference toFIG. 6, the drive link66generally includes the puller68an actuation cylinder90, a spring92and a stop94. The rod82of the puller68includes a flanged end96within the actuation cylinder90that is biased by the spring92with respect to the stop94.

The actuation cylinder90may be a portion of, or extend from the actuator86(illustrated schematically). The actuation cylinder90is thereby movable along the drive link axis W so as to contract and expand the radially adjustable blade outer air seal system60between the extended radially contracted BOAS position (FIG. 6) and a retracted radially expanded BOAS position (FIG. 7) to contract and expand the radially adjustable blade outer air seal system60. That is, the actuation cylinder90of the drive link66is actively actuated and the puller68is partially isolated thereform to provide a predefined damped movement thereto at the extended radially contracted BOAS position (FIG. 6) and the retracted radially expanded BOAS position (FIG. 7).

The rod82extends through an aperture98in an end section100of the actuation cylinder90along axis W. The spring92interacts with the flanged end96to bias the puller68outward with respect to the engine case84toward the retracted radially expanded BOAS position (FIG. 6). That is, the spring92provides a bias force towards the retracted radially expanded BOAS position (FIG. 7).

The stop94prevents the spring92from being crushed during retraction of the actuation cylinder90(FIG. 8) toward the retracted radially expanded BOAS position (FIG. 7). That is, a “hard stop” is provided when the full force of the BOAS load is being applied by the actuator86(FIG. 8) that may be on the order of about 1200-1400 pounds (544-635 kilograms) of force. This is particularly beneficial when an on-off type blade tip rapid response active clearance control (RRACC) system58is utilized.

The drive link66of the rapid response active clearance control system58provides thermal and aerodynamic isolation from the respective air seal segment64; and allows radial growth due to thermal expansion, yet maintains tension when de-activated that reduces an impact load when retracting. The drive link66provides mechanical attachment that accommodates radial grown due to thermal expansion yet, when de-activated, minimizes rattle and vibration.