Gas turbine engine active clearance control system using inlet particle separator

A turbine section for a gas turbine engine includes blade outer air seals and stator vanes that provide a core flow path. A turbine case supports blade outer air seals and stator vanes. An annular cavity is provided between an interior surface of the turbine case and the blade outer air seals and the stator vanes. A hole extends through the turbine case from an exterior surface to the interior surface. The annular cavity extends axially to an exit. A manifold circumscribes the exterior surface of the turbine case and provides an annular space therebetween. The annular space is in fluid communication with the exit of the annular cavity via the hole.

BACKGROUND

This disclosure relates to turbomachinery, and more particularly, the disclosure relates to an active clearance control system for a gas turbine engine.

Gas turbine engines include a compressor that compresses air, a combustor that ignites the compressed air and a turbine across which the compressed air is expanded. The expansion of the combustion products drives the turbine to rotate, which in turn drives rotation of the compressor.

In order to increase efficiency, a clearance between the tips of the blades in the compressor, turbine and power turbine across the outer diameter of the flowpath is kept sufficiently small. This ensures that a minimum amount of air passes between the tips and the outer diameter. Some engines include a blade outer air seal (BOAS) supported by case structure to further reduce tip clearance.

The clearance between the BOAS and the blade tips is sensitive to the temperature of the gas path at different engine conditions. If the BOAS support structure heats up at a faster rate than the rotating blades, the tip clearance could increase and cause a drop in efficiency. Conversely, if the blades heat up at a faster rate than the BOAS support structure, the blades can undesirably rub against the BOAS. As a result, it is difficult to accommodate a consistent tip clearance during different power settings in the engine.

Active clearance control (ACC) systems have been developed to selectively direct cooling fluid at the case structure to more closely control the clearance between the BOAS and blade tips. A simpler, more effective ACC system is needed.

Inlet particle separators are used at an inlet of some gas turbine engines that are exposed to a large amount of dust and debris. The inlet particle separator is used to separate out the debris from the core flowpath. Separated debris-laden air is expelled directly out through exhaust.

SUMMARY

In one exemplary embodiment, a turbine section for a gas turbine engine includes blade outer air seals and stator vanes that provide a core flow path. A turbine case supports blade outer air seals and stator vanes. An annular cavity is provided between an interior surface of the turbine case and the blade outer air seals and the stator vanes. A hole extends through the turbine case from an exterior surface to the interior surface. The annular cavity extends axially to an exit. A manifold circumscribes the exterior surface of the turbine case and provides an annular space therebetween. The annular space is in fluid communication with the exit of the annular cavity via the hole.

In a further embodiment of any of the above, the turbine case includes hooks that support the vanes and the blade outer air seals.

In a further embodiment of any of the above, at least one set of the hooks includes axially extending apertures configured to communicate air along the annular cavity from the hole to the exit.

In a further embodiment of any of the above, the holes are axially aligned with a last stator stage.

In a further embodiment of any of the above, the turbine section includes up to four rotor stages. The last stator stage is immediately axially upstream from a last rotor stage.

In a further embodiment of any of the above, seal structure is provided between the blade outer air seals and the turbine case and stator vanes. The seal structure encloses the annular space and separates the annular cavity from the core flow path.

In a further embodiment of any of the above, the turbine case includes forward and aft flanges. The manifold extends axially from and engages the forward and aft flanges.

In a further embodiment of any of the above, the manifold includes an annular plate that has holes in fluid communication with the annular cavity.

In a further embodiment of any of the above, the annular plate encloses an open end of an undulation in the manifold.

In a further embodiment of any of the above, an inlet tube is in fluid communication with the undulation and is axially aligned with the plate.

In another exemplary embodiment, an active clearance control system for a gas turbine engine includes an inlet which includes an inlet particle separator configured to separate debris from inlet air entering the inlet. Blade outer air seals and stator vanes provide a core flow path. A turbine case supports blade outer air seals and stator vanes. An annular cavity is provided between an interior surface of the turbine case and the blade outer air seals and the stator vanes. A hole extends through the turbine case from an exterior surface to the interior surface. The annular cavity extends axially to an exit. An exhaust case is secured to the turbine case. A manifold circumscribes the exterior surface of the turbine case and provides an annular space therebetween in fluid communication with the inlet particle separator. The annular space is in fluid communication with the exit of the annular cavity via the hole. The exit is in fluid communication with the exhaust case.

In a further embodiment of any of the above, the turbine case includes hooks that support the vanes and the blade outer air seals. At least one set of the hooks includes axially extending apertures configured to communicate air along the annular cavity from the hole to the exit. Seal structure is provided between the blade outer air seals and the turbine case and stator vanes. The seal structure encloses the annular space and separates the annular cavity from the core flow path.

In a further embodiment of any of the above, the holes are axially aligned with a last stator stage. The turbine section includes four rotor stages. The last stator stage is immediately axially upstream from the fourth rotor stage.

In a further embodiment of any of the above, the turbine case includes forward and aft flanges. The manifold extends axially from and engaging the forward and aft flanges.

In a further embodiment of any of the above, the manifold includes an annular plate having holes in fluid communication with the annular cavity. The annular plate encloses an open end of an undulation in the manifold and comprises an inlet tube in fluid communication with the undulation and is axially aligned with the plate. The inlet tube is configured to receive debris-laden air from the inlet particle separator.

In a further embodiment of any of the above, the exhaust case at least partially blocks the exit. The exhaust case includes outlets in fluid communication with the exit.

In a further embodiment of any of the above, the inlet particle separator includes a blower configured to be rotationally driven by the gas turbine engine.

In another exemplary embodiment, a method of actively controlling clearance between a blade outer air seal and a rotor blade. The method includes supplying debris-laden air from an inlet particle separator to a manifold of an active clearance control system. The debris-laden air passes from the manifold through a turbine case and into an annular space between the turbine case and blade outer air seals. The debris-laden air expels from the annular space to an engine exhaust.

In a further embodiment of any of the above, the method includes the step of generating the debris-laden air with a blower rotationally driven within the inlet particle separator.

In a further embodiment of any of the above, the expelling step includes passing the debris-laden air into the core flow downstream from a power turbine.

The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1schematically illustrates a gas turbine engine20. In this example, the engine20is a turboshaft engine, such as for a helicopter. The engine20includes an inlet duct22supplying inlet air to a core engine including a compressor section24, a combustor section26, and a turbine section28.

The compressor section24is an axial compressor and includes a plurality of circumferentially-spaced blades. Similarly, the turbine section28includes circumferentially-spaced turbine blades. The compressor section24and the turbine section28are mounted on a main shaft29for rotation about an engine central longitudinal axis A relative to an engine static structure32via several bearing systems (not shown).

During operation, the compressor section24draws air through the inlet duct22. Although gas turbine engines ingest some amount of dust, such engines are typically not designed for highly dusty environments. Engines such as the engine20are subject to operating in highly dusty environments during takeoff and landing. In this example, the inlet duct22has an opening radially relative to the central longitudinal axis A. The compressor section24compresses the air, and the compressed air is then mixed with fuel and burned in the combustor section26to form a high pressure, hot gas stream. The hot gas stream is expanded in the turbine section28, which may include first and second turbine42,44. The first turbine42rotationally drives the compressor section24via a main shaft29. The second turbine44, which is a power turbine in the example embodiment, rotationally drives a power shaft30, gearbox36, and output shaft34. The output shaft34rotationally drives the helicopter rotor blades39used to generate lift for the helicopter. The hot gas stream is expelled through an exhaust38.

The engine20also includes a seal system in the turbine section28around the blades. Such a seal system may be referred to as a blade outer air seal (BOAS)74shown inFIG. 3. The seal system serves to provide a minimum clearance around the tips of the blades, to limit the amount of air that escapes around the tips.

Referring toFIG. 2, an example inlet particle separator (IPS)50is schematically shown. The IPS50, which is fed by the inlet duct22(FIG. 1), includes an inlet56receiving inlet air for the engine20. The inlet56includes a ramp58creating a tortuous flow path for the inlet air that will be used for the core engine.

A blower52is coupled to the shaft29with a coupler54that selectively rotationally affixes the blower52to the shaft29. In this manner, the blower52may be driven when desired, and rotationally idled when undesired. However, it should be understood that the IPS50may use a blower that is constantly driven with the core engine. When the blower52is rotationally driven, the debris-laden air64is directed to an exhaust outlet62, which is routed to the exhaust38. Clean air is provided to a core outlet60, which provides a core flow66to the compressor section24of the core engine.

The second, or power, turbine44is shown in more detail inFIG. 3. The power turbine44includes a turbine case68, which is part of the engine static structure32, that has hooks70provided at an inner surface used to support stator vanes72and blade outer air seals (BOAS)74. The BOAS74seal with respect to the tips of rotor blades76that are axially interleaved between the stator vanes72. As will be appreciated, the BOAS74may be an arc segment, a full ring, a split ring that is mounted around the blades76, or an integration into an engine casing.

Seal structure78is provided between the stator vanes72, BOAS74and turbine case68. The seal structure78separates the annular space80from the core flow path.

An active clearance control (ACC) system79is used to selectively cool the turbine case68. The ACC system79controls the running tip clearance of the blades76by varying the amount of cooling air on the turbine case68. The ACC system79includes a manifold82that circumscribes an exterior surface of the turbine case68. The debris-laden air64from the exhaust outlet62of the IPS50may be selectively supplied to the manifold82through a valve81, particularly if the blower52is continually driven during engine operation. The valve81is selectively controlled by a controller83to maintain a desired clearance between the case structure46and the blades76to target a specific tip clearance value at a given power turbine speed. The controller83may receive inputs from various temperature sensors or other sensing elements (not shown).

The manifold82extends axially between and seals against forward and aft flanges84,86. An inlet tube88is fluidly connected to the manifold82to supply the fluid with debris-laden air64to the annular cavity90provided between the manifold82and the exterior surface of the turbine case68.

The manifold82may be constructed from multiple pieces of sheet metal secured to one another in the example embodiment. In the example, the manifold82includes an annular plate85having holes87in fluid communication with the annular cavity90. The annular plate85encloses an open end of an undulation in the manifold82. The inlet tube88is in fluid communication with the undulation and is axially aligned with the plate85. The manifold82is fed by the debris-laden air64from the IPS50when the blower52is driven and/or the valve81is opened. The debris-laden air64cools the turbine case68.

Circumferentially arranged holes92are provided in the turbine case68and extend from the interior surface to the exterior surface. In the example illustrated, the holes92are axially aligned with the last stator stage, which is arranged immediately upstream of the last rotor stage, in the example, the fourth rotor stage. Fewer or more than four rotor stages may be used. First and second axially extending apertures94,96are provided in axially spaced apart hooks70to provide a flowpath in the annular cavity90from the holes92to an exit97radially beneath the aft flange86.

An exhaust case100is secured to the aft flange86. The exhaust case100at least partially covers the exit97. Outlets98are provided in the exhaust case100to fluidly connect the exit97to the core flow66entering the exhaust38.

In operation, the debris-laden air64is generated with the blower52rotationally driven within the inlet particle separator50. The debris-laden air64from the IPS50is supplied to the manifold82. The debris-laden air64is then passed from the manifold82through the turbine case68and into the annular space80between the turbine case68and blade outer air seals74. The debris-laden air64is expelled from the annular space80to the engine exhaust into the core flow66downstream from a power turbine44. In this manner, the IPS is used to both separate debris and provide active clearance control.

Since the pressure and temperature of the debris-laden air64in the IPS50is close to ambient, the air needs to exit into the core flow66since there is not enough pressure gradient to have an impingement style ACC system. The ACC system79fed by the IPS50does not have a negative impact on the engine cycle since the IPS blower52is operating along with the engine. The IPS50dumps the air and solid particles through the engine exhaust38. The IPS50uses centrifugal force to remove the solid particles like sand, rocks and other debris from the air which enters the core engine. It may not be desirable to use the IPS50air for BOAS clearance control during takeoff, since the IPS air may be too debris-laden.