Cooled cooling air system for a gas turbine engine

A gas turbine engine includes a compressor section, a combustor fluidly connected to the compressor section via a primary flowpath and a turbine section fluidly connected to the combustor via the primary flowpath. Also included is a cascading cooling system having a first inlet connected to a first compressor bleed, a second inlet connected to a second compressor bleed downstream of the first compressor bleed, and a third inlet connected to a third compressor bleed downstream of the second compressor bleed. The cascading cooling system includes at least one heat exchanger configured to incrementally generate cooling air for at least one of an aft compressor stage and a foremost turbine stage relative to fluid flow through the turbine section.

TECHNICAL FIELD

The present disclosure relates generally to gas turbine engines, and more specifically to a cooled cooling air system for a gas turbine engine.

BACKGROUND

Gas turbine engines, such as those utilized on commercial and military aircraft, include a compressor section that draws in air, a combustor section that mixes the compressed air with a fuel, and ignites the mixture, and a turbine section across which the results of the combustion are expanded. The expansion across the turbine section drives the turbine section to rotate, which in turn drives rotation of the compressor.

In some example engines, this configuration results in excess heat at the aft stages of the compressor section and in the turbine section. In order to prevent the excess heat from damaging engine components, or reducing the lifecycle of engine components, portions of the compressor section and the turbine section are actively cooled using cooled cooling air.

SUMMARY OF THE INVENTION

In one exemplary embodiment a gas turbine engine includes a compressor section, a combustor fluidly connected to the compressor section via a primary flowpath, a turbine section fluidly connected to the combustor via the primary flowpath, and a cascading cooling system having a first inlet connected to a first compressor bleed, a second inlet connected to a second compressor bleed downstream of the first compressor bleed, and a third inlet connected to a third compressor bleed downstream of the second compressor bleed. The cascading cooling system includes at least one heat exchanger configured to incrementally generate cooling air for at least one of an aft compressor stage and a foremost turbine stage relative to fluid flow through the turbine section.

In another exemplary embodiment of the above described gas turbine engine, the third compressor bleed is at an outlet of the compressor section.

In another exemplary embodiment of any of the above described gas turbine engines, the at least one heat exchanger includes a first heat exchanger, a second heat exchanger in series with the first heat exchanger, and a third heat exchanger in series with the second heat exchanger.

In another exemplary embodiment of any of the above described gas turbine engines, a heat sink input of the second heat exchanger is a cooled flow output of the first heat exchanger and originates at the first inlet, and wherein a heat sink input of the third heat exchanger is a cooled flow output of the second heat exchanger and originates at the second inlet.

In another exemplary embodiment of any of the above described gas turbine engines, a cooled flow output of the third heat exchanger is provided to an aft most compressor stage as a cooled cooling flow and originates at the third inlet.

In another exemplary embodiment of any of the above described gas turbine engines, the at least one heat exchanger includes a parallel heat exchanger having at least a first heat sink input, a first cooled flow input and a second cooled flow input, and wherein fluid passing through the first cooled flow input is simultaneously cooled by the first heat sink input and cools the second cooled flow input.

In another exemplary embodiment of any of the above described gas turbine engines, the at least one heat exchanger further includes a third cooled flow input, and fluid passing through the second cooled flow input is simultaneously cooled by the first cooled flow input and cools the third cooled flow input.

In another exemplary embodiment of any of the above described gas turbine engines, the third cooled flow input is returned to an aft most compressor stage as a cooled cooling flow.

In another exemplary embodiment of any of the above described gas turbine engines, further includes an auxiliary compressor system having an auxiliary turbine connected to an auxiliary compressor such that rotation of the auxiliary turbine drives rotation of the auxiliary compressor, and wherein an input of the auxiliary turbine is connected to a heat sink outlet of a third heat exchanger such that cooling air originating at the second compressor bleed is compressed in the auxiliary compressor.

In another exemplary embodiment of any of the above described gas turbine engines, an output of the auxiliary compressor system is provided to a foremost stage of the turbine section as cooled cooling air.

In another exemplary embodiment of any of the above described gas turbine engines, an input of the auxiliary turbine is at least one of an output heat sink air of a second heat exchanger, and an output heat sink air of a fourth heat exchanger, and wherein an output of the auxiliary turbine is returned to a compressor section inlet.

In another exemplary embodiment of any of the above described gas turbine engines, the input of the auxiliary turbine is a combination of a heat sink output of the second heat exchanger, and a heat sink output of the fourth heat exchanger, and wherein the combination is controlled by a modulation valve.

In another exemplary embodiment of any of the above described gas turbine engines, fluid flow through the auxiliary turbine is at least partially controlled by a modulation valve downstream of an auxiliary turbine outlet, and wherein fluid flow to the inlet of the auxiliary compressor is at least partially controlled by a modulation valve connecting the heat sink outlet of the third heat exchanger to a second or later stage of the turbine section.

In another exemplary embodiment of any of the above described gas turbine engines, each of the modulation valves is controlled by at least one controller.

In another exemplary embodiment of any of the above described gas turbine engines, the gas turbine engine is a geared turbofan engine.

In another exemplary embodiment of any of the above described gas turbine engines, the gas turbine engine is a multiple bypass flow engine.

An exemplary method for generating cooled cooling air in a gas turbine engine includes providing air from a plurality of compressor bleeds as inputs to a cascading heat exchanger, incrementally cooling air received via the inputs such that a first of the inputs is a heat sink for a second of the inputs, and the second of the inputs is a heat sink for a third of the inputs, and actively cooling at least one of an aft most compressor stage and a fore most turbine stage using cooled cooling air output from the cascading heat exchanger.

In a further example of the above described exemplary method for generating cooled cooling air in a gas turbine engine, incrementally cooling air received via the inputs includes cooling the air using a plurality of serially arranged heat exchangers, each of the serially arranged heat exchangers increasing a pressure of cooled output air relative to a serially previous heat exchanger.

In a further example of any of the above described exemplary methods for generating cooled cooling air in a gas turbine engine, incrementally cooling air received via the inputs includes cooling the air using at least one parallel heat exchanger configured such that air from at least one of the inputs simultaneously cools an adjacent air flow and is cooled by another adjacent airflow.

In one exemplary embodiment a gas turbine engine includes a compressor section, a combustor fluidly connected to the compressor section via a primary flowpath, a turbine section fluidly connected to the combustor via the primary flowpath, and a cascading cooling system having a plurality of inlets, each of the inlets connected to one of a plurality of compressor bleeds. The cascading cooling system includes at least one heat exchanger configured to incrementally generate a cooled cooling air across a plurality of stages, each of the stages having approximately the same pressure differential as each other of the stages.

DETAILED DESCRIPTION OF AN EMBODIMENT

With regards to engines for military applications, there has recently been provision of multiple bypass flow engines. An example multiple bypass flow engine is shown schematically inFIG. 2. A first stage fan180delivers air into an outer housing181. The outer housing181defines an outer bypass duct182outwardly of an inner housing183. The outer bypass duct182is alternatively referred to as a “third stream”, and air from the outer bypass duct182is referred to as third stream air. A second stage fan184delivers air downstream of the first stage fan180into an inner bypass duct186. The inner bypass duct186is defined between an inner periphery of the inner housing183and an outer periphery of a core housing187. Core housing187defines a radially inner extent of inner bypass duct186. Controls196and198are shown schematically. In one example, the controls are nozzles which control the flow of air through the bypass flow ducts182and186.

The first stage fan180delivers air inwardly of outer housing181and inwardly of inner housing183. A second stage fan184delivers air inwardly of inner housing183, but does not deliver air inwardly of the outer housing181.

A core engine inlet188receives air downstream of the second stage fan184. That air passes into a compressor190, a combustor192and a turbine194. It should be understood that the compressor190may include multiple rotors and the turbine194may also comprise multiple rotors. The turbine rotors drive the compressor190and the fan stages180and184.

In some examples, the aft stages of the compressor section24,190and the turbine section28,194of a given engine20are actively cooled using cooled cooling air sourced at one or more compressor bleeds. The cooling air bleed from the compressor section24,190is cooled in a heat exchanger using air from the bypass flowpath B as a heat sink, in the example ofFIG. 1, or using air from the third stream182, in the example ofFIG. 2. A fraction of air is bled from the compressor section24,190diffuser and cooled in a heat exchanger and is returned to the compressor section24,190and/or the turbine section28,194.

When the air is fully cooled in a single step, the pressure differential between the cold side of the heat exchanger (the bypass flow path B or the third stream182) and the compressor bleed can be excessively high. Further, the magnitude of cooling required in a single cooling step incurs a large thermal gradient across the heat exchanger. The high pressure differential and large thermal gradients places high stresses on the heat exchanger in the cooling step. The high stresses in turn, reduce the life cycle of the heat exchanger, require the heat exchanger to be excessively large and heavy to accommodate the higher stresses, or both.

In order to minimize the weight requirements and the thermal stresses on the heat exchanger, an example gas turbine engine200, schematically illustrated inFIG. 3, utilizes a cascaded heat exchanger configuration to provide cooled cooling air to the segments of the engine200being actively cooled. The example gas turbine engine200includes a compressor section210having multiple stages212, a combustor section220, and a turbine section230having multiple stages232.

A mid compressor bleed240withdraws a first bleed air241from a compressor flowpath between compressor stages212at approximately midway through the compressor section210. The first bleed air241is provided to a first heat exchanger250. Also provided to the heat exchanger250is cold air260from the bypass flowpath (in the case of a geared turbofan engine) or the third stream (in the case of a multiple bypass flow engine). The cold air260is used as a heat sink in the first heat exchanger250to cool the first bleed air241.

A second compressor bleed242, aft of the mid compressor bleed240, withdraws a second bleed air243from between compressor stages212. The second bleed air243is provided to a second heat exchanger251. Also provided to the second heat exchanger251is the cooled air output of the first heat exchanger250. The cooled air output of the first heat exchanger250is the first bleed air241. The first bleed air241acts as a heat sink for the second bleed air243in the second heat exchanger251.

A third compressor bleed244is positioned at an aft end of the compressor section210. The third compressor bleed244removes a third bleed air245from the compressor flowpath, and provides the third bleed air245to a third heat exchanger252. Also provided to the third heat exchanger252is the cooled air output of the second heat exchanger251. The cooled air output of the second heat exchanger251is the second bleed air243. The second bleed air243acts as a heat sink for the third bleed air245in the third heat exchanger252. Once cooled in the third heat exchanger, the third bleed air is returned to the aftmost stage212of the compressor section210and actively cools the aftmost stage212. Because the third bleed air245is pulled from a third compressor bleed244at the aftmost stage, the pressure difference between the third bleed air245and the compressor flowpath at the point where the third bleed air245is returned to the compressor flowpath is minimal.

The heat sink air from the second heat exchanger251is provided to a fourth heat exchanger253. As with the first heat exchanger250, the fourth heat exchanger253is provided cold air260from the bypass flowpath (in the case of a geared turbofan engine) or the third stream (in the case of a multiple bypass flow engine). The cold air260cools the heat sink air from the second heat exchanger251.

The heat sink air in the first heat exchanger250and the fourth heat exchanger253is drawn from the same source. As a result, in some configurations, the first heat exchanger250and the fourth heat exchanger253can be combined into a single heat exchanger254. The output heat sink air from both the first heat exchanger250and the fourth heat exchanger253, or the combined heat exchanger254, is returned to the bypass flowpath or the third stream.

Also included within the gas turbine engine200is an auxiliary compressor system270. The auxiliary compressor system270includes an auxiliary turbine272and an auxiliary compressor274. The cooled air output of the fourth heat exchanger253(the first bleed air241) is provided to the turbine272, and expanded across the auxiliary turbine272. The expansion across the turbine drives rotation of the auxiliary compressor274. The auxiliary compressor274, in turn, receives and compresses at least a portion of the second bleed air243after the second bleed air243has been utilized as a heat sink in the third heat exchanger252.

An auxiliary compressor output276is provided as cooled cooling air to the first turbine stage232. In some example cooling systems, a portion of the second bleed air243is provided to a second or later stage232of the turbine section230and provides active cooling. The portion is removed from the second bleed air243prior to the second bleed air243being provided to the auxiliary compressor274at a branch278. A valve280controls the amount of air removed from the second bleed air243prior to being provided to the auxiliary compressor274. The valve280is connected to and controlled by an engine controller282, or any other similar control device.

In some examples, the flow of first bleed air241through the auxiliary turbine272is controlled via a second valve284. The second valve284is also controlled via the engine controller282. Expanded air273is output from the auxiliary turbine272and returned to an inlet of the compressor section210, where it is ingested and recompressed through the compressor section210.

In some examples, the gas turbine engine200can further include an auxiliary generator290. An exemplary gas turbine engine200with the additional inclusion of an auxiliary generator290is illustrated inFIG. 4. The auxiliary generator290is connected to the auxiliary compressor274, and is driven to rotate by the rotation of the auxiliary compressor274. The rotation of the auxiliary generator290generates electrical power according to known electricity generation principles. The auxiliary generator290can be connected to aircraft electrical systems and provide electrical power to onboard electronic systems.

With continued reference toFIGS. 3 and 4, the pressure differential between the first bleed air241and the heat sink air of the first heat exchanger250is relatively small. The heat sink configuration is cascaded upward in pressure, while maintaining approximately the same relatively small pressure differential, such that the cooled air in each heat exchanger250,251,252,253is cooled by a heat sink air with a relatively small pressure differential. In some examples, the pressure differential in each heat exchanger250,251,252,253is approximately the same. This upward cascade in cooling and pressure is referred to as a cascaded cooled cooling air system.

With continued reference toFIGS. 3 and 4,FIG. 5illustrates an alternate heat exchanger250arrangement for providing cascaded cooled cooling air to cool an aft stage of a compressor310and at least a first stage of a turbine330. As with the example ofFIGS. 3 and 4, the example gas turbine engine300ofFIG. 5includes a compressor section310having multiple stages312, a combustor section320, and a turbine section330having multiple stages332. In place of the first, second, third and fourth heat exchangers250,251,252,253ofFIGS. 3 and 4, the example gas turbine engine ofFIG. 5utilizes a single parallel heat exchanger350. The parallel heat exchanger350utilizes parallel flows, where a single flow acts as a heat sink to one adjacent flow and is actively cooled by another adjacent flow.

As with the examples ofFIGS. 3 and 4, the example ofFIG. 5utilizes a first compressor bleed340at an approximate mid-point in the compressor310, a second compressor bleed341aft of the first compressor bleed340, and a third compressor bleed aft of the second compressor bleed341. The cooled cooling air for each area in the example ofFIG. 5is generated in the same manner as described above with regards to the examples ofFIGS. 3 and 4. Similarly, an auxiliary compressor system370is connected to the outputs of the parallel heat exchanger350in the example ofFIG. 5.

The heating and cooling flows through the parallel heat exchanger350are cooled via identical heat sinks as the sequential heat exchangers250,251,252,253described above with regards toFIGS. 3 and 4, and provide for the same heating and cooling generation. One of skill in the art, having the benefit of this disclosure, will understand that any number of sequential heat exchangers can be combined into at least one parallel heat exchanger, provided the required heat duties sustain a positive temperature gradient between each adjacent pair of fluids. Further, the number of sequential heat exchangers and parallel heat exchangers to be used in a given example can be determined based on the available volume, weight limitations, and cooling requirements of any given engine.

With continued reference toFIGS. 3 and 4,FIG. 6illustrates another example configuration of a cascaded heat exchanger configuration for generating cooled cooling air in a gas turbine engine400. The example ofFIG. 5utilizes a first compressor bleed440at an approximate mid-point in the compressor410, a second compressor bleed441aft of the first compressor bleed440, and a third compressor bleed442aft of the second compressor bleed441. As with the examples ofFIGS. 3 and 4, a first heat exchanger450and a fourth heat exchanger453utilize air from the bypass duct or the third stream as a heat sink. The first heat exchanger450receives air from the first compressor bleed440and cools the air using the heat sink air.

The cooled first bleed air441is provided as a heat sink in a parallel heat exchanger451. The parallel heat exchanger451receives the second bleed air443and the third bleed air444. The second bleed air443is simultaneously cooled by the first bleed air441and cools the third bleed air444. Each of the outputs of the parallel heat exchanger451is provided to an auxiliary compressor system470. The remainder of the features and connections are substantially similar to the features illustrated inFIGS. 3 and 4and described above.

With continued reference toFIGS. 3 and 4,FIG. 7illustrates a modification that can be applied to the gas turbine engine200in an example gas turbine engine600. The heat exchangers650,651,652,653are arranged in the same sequential cascading manner as in the example ofFIG. 3. In addition to the heat sink flows, and cooled air flows ofFIGS. 3 and 4, the example ofFIG. 7includes multiple diverter valves691,692. The diverter valves691,692enable an increased power extraction from the auxiliary turbine672. The fourth heat exchanger653can be partially or wholly bypassed such that an inlet temperature of the auxiliary turbine672is higher. Higher inlet temperatures increase the power output from the auxiliary turbine utilized to drive the auxiliary compressor674and an attached generator690.

Further, the second diverter valve691shunts auxiliary turbine discharge from the auxiliary turbine672to the fan bypass stream (in the case of an engine according toFIG. 1) or the third stream (in the case of an engine according toFIG. 2). The fan bypass stream or the third stream is at a lower pressure than the inlet to the core compressor. The expansion across the auxiliary turbine672is increased to expand the cooled air to match the inlet pressure of the bypass flow or the third duct flow, allowing the auxiliary turbine to extract more work from the cooled air.

With reference toFIGS. 3-7, the illustrated heat exchangers and cooled cooling air systems can be located in any physical location within a gas turbine engine, subject to design restraints. By way of example, each of the heat exchangers and the auxiliary compressor system can be positioned in a core cowling that surrounds the compressor, combustor, and turbine sections of the gas turbine engine. In alternative examples, the heat exchangers, auxiliary compressor system, generator, or any other elements, can be disposed in any other location within the gas turbine engine.