Reversible exhaust structure

Abstract

The present invention relates to an air flow arrangement for a gas turbine engine in which air can be selectively directed into and out of a bypass passage of the engine and into a duct connecting the air to a compressor of the gas turbine engine.

Description

Technical Field

[0001] The present invention relates to an improved gas turbine arrangement. In particular, but not exclusively, the present invention relates to an alternative exhaust configuration for use in conjunction with a low pressure compressor (LPC) and / or a high pressure compressor (HPC) of a gas turbine engine. Background Art

[0002] A typical gas turbine engine includes a pair of compressors, a first upstream low-pressure compressor and a second downstream high-pressure compressor. The pair of compressors compresses the air entering the engine in two stages and then the compressed gas enters the combustion chamber where fuel is introduced and the mixture is ignited. The operation of a gas turbine engine is well known to those skilled in the art and will not be described in detail.

[0003] The compressor is usually optimized for flight conditions, that is, when the aircraft is at cruising speed and altitude. Under cruising conditions, sufficient air is drawn into the first low-pressure compressor and compressed to a first pressure. The air is then connected to the second high-pressure compressor through a transition duct between the two compressors before being introduced into the combustor.

[0004] When the aircraft is not in flight, such as when taxiing for takeoff, very different airflow conditions exist within the engine. For example, with the engine running at low speed (such as taxiing), the air demand on the compressor will be much lower than when cruising.

[0005] In this case, a compressor stall may occur. This occurs when there is a discrepancy between the air being introduced into the compressor and the air the compressor can compress at a given speed. Stalling can result in a temporary loss of power or, in extreme cases, engine damage.

[0006] To prevent compressor stall at low speeds, modern gas turbine engines are provided with a flow path that allows air to be diverted from the compressor to prevent a stall condition. This air is called compressor bleed air.

[0007] Different engine manufacturers have used a variety of methods to divert air away from the compressor.

[0008] In one example, holes are provided on the inside of the duct that directs air to the compressor. These holes form air passages that allow air to flow out of the duct to the engine bypass passage (a passage around the core in a gas turbine engine). For example, a butterfly valve can be used to automatically control the exhaust (also known in the art as "process exhaust level").

[0009] In another example of an existing system, a flap or door may be provided which may also be opened in the same manner to release air to the bypass passage.

[0010] In yet another example, the "scoop" may extend into the conduit through a suitable valve which, when opened, collects air from the conduit and communicates it again with the bypass passage.

[0011] Each of these existing devices has proven to be very effective in purging air from the compressor ducts and preventing the compressor from stalling.

[0012] Sometimes it is also necessary for the airflow to flow in the opposite direction, that is, intake instead of exhaust. This is a special case of engines with variable pitch fans, where suction may be required, for example, during braking when an aircraft is landing. This is also called "reverse thrust". In conventional devices, there are mechanical flaps that direct the bypass airflow outwards, which acts as an air brake.

[0013] The inventors have identified an alternative manner in which exhaust may be accomplished and which provides additional advantages over those provided by existing exhaust systems in gas turbine engines. Summary of the invention

[0014] Aspects of the invention are set out in the following sections.

[0015] From the first aspect of the invention described herein, there is provided an exhaust / intake device for a gas turbine engine, the gas turbine engine comprising a bypass passage and an engine core, the engine core comprising: a duct, which is arranged in use to guide air to a compressor, and an airflow passage, which passes through the core and extends from the bypass passage toward the duct, the device further comprising a first exhaust port, which is arranged in use to fluidly connect the duct and the airflow passage, and is constructed to connect air from the duct to the bypass passage; and a second intake port, which is arranged in use to fluidly connect the duct and the airflow passage, and is constructed to connect air from the bypass passage to the duct.

[0016] The invention described herein provides a novel exhaust and intake configuration that provides extremely versatile control of the air in the compressor (transition) duct. Specifically, the arrangement allows accurate control and optimization of the amount of air delivered to the compressor for all landing and flight conditions.

[0017] The device also prevents the reverse flow of air and combustion products from the burner through the compressor and ducting toward the front of the engine.

[0018] According to the invention described herein, it is possible to selectively allow air to be released from a transition duct into a bypass passage or allow air from a bypass passage to communicate into a transition duct. This control can be achieved by reciprocating movement of a body containing one or more passages when the engine is running.

[0019] The first exhaust port and the second intake port may be one of a plurality of ports arranged circumferentially relative to the core of the engine. This may allow airflow from around the engine or from a specific location within the engine. Depending on the engine operating conditions, one or more ports may be required.

[0020] The first exhaust port and the second exhaust port may advantageously be integrally formed in a single circumferentially extending body or in a pair of circumferentially extending bodies arranged to abut each other (i.e., placed immediately adjacent to each other or suitably close together) in use. For example, the body or each body may be in the form of a ring or annulus having a flow passage extending from a surface of the ring facing the central axis of the ring and outwardly toward a surface radially displaced from the axis. In practice, the flow passage is formed to pass generally radially outwardly through the ring or annulus. There may be a single body or a pair of bodies placed back to back. For example, they may be mirror images of each other.

[0021] For example, the or each body comprises an inner surface which, in use, faces the core of the engine and an outwardly facing surface which, in use, faces the bypass passage of the engine, wherein ports extend from the inner surface to the outer surface. This allows selective control of air between passages in the core of the engine towards or from the bypass passage of the engine.

[0022] The first exhaust port and the second intake port are one or more discrete ports arranged circumferentially with respect to the engine core.

[0023] Advantageously, the body can be moved relative to the engine core to open or close exhaust ports or intake ports. Exhaust is intended to refer to the release of air from a duct or transition duct within the gas turbine engine core to a bypass duct or similar duct. Intake is intended to refer to the opposite situation, i.e. allowing air to flow from a bypass duct to and into a duct or transition duct of the gas turbine engine upstream of one or more compressors.

[0024] The body can be moved along the axis of the engine to cause selective opening and closing of the ports described herein. For example, axial movement in a first direction can cause the ports to open, allowing air to flow radially outward through the ports. Conversely, axial movement in an opposite second direction can cause the ports to open, allowing air to flow radially inward through the ports.

[0025] Axial movement may be achieved in any suitable manner and by a range of power sources. For example, axial movement may be caused by one or more linear actuators arranged to move the body in a first direction and an opposite second direction.

[0026] Advantageously, the port can be moved between the following locations:

[0027] (A) a first position allowing exhaust gas to flow radially outward from the transition duct to the bypass passage;

[0028] (B) a second position in which air cannot flow into or out of the transition duct; and

[0029] (C) A third position allows intake air to flow radially inward from the bypass duct to the transition duct.

[0030] Thus, full control of air entering and exiting the transition duct can be achieved, including not allowing air to exit from the bypass passage or enter the transition duct to reach the position of the bypass passage. For example, the port can be selectively moved to an intermediate position between the first position and the second position and an intermediate position between the second position and the third position.

[0031] The ports extending from the core to the bypass passage may be of any suitable aerodynamic shape or profile (cross-section) which permits efficient flow of air therethrough. For example, one or all of the first exhaust ports may be provided with a curved profile curving radially outwards so that the downstream end of the port directs air in a radially outward direction relative to the axis of the engine in use.

[0032] Similarly, one or all of the second inlet ports may be provided with a curved profile that curves radially inwardly so that the downstream end of the port, in use, directs air into a transition duct having a flow component along the axis of the transition duct.

[0033] From another aspect of the invention described herein, there is provided an auxiliary air supply arrangement for a compressor of a gas turbine engine, the gas turbine engine comprising a bypass passage and an engine core, the engine core comprising a duct arranged to connect air to the compressor, wherein one or more air flow passages are provided and configured to selectively operate in a first mode to supply air from the bypass passage to the duct, or in a second mode to supply air from the duct to the bypass passage.

[0034] As described herein, the device may advantageously be selectively controlled to operate in a first mode of operation or a second mode of operation and optionally in a position that does not allow air to flow into or out of the duct.

[0035] Viewed from a further aspect of the invention described herein, there is provided an air bypass arrangement for a gas turbine engine, the arrangement comprising a mobile body arranged about a central axis of rotation of the gas turbine engine and arranged, in use, to reciprocate along a portion of said axis, the body comprising:

[0036] at least one first upstream airflow passage extending radially outwardly from a portion of the body proximate the axis and away from the axis to allow airflow away from the axis, and

[0037] At least one second downstream airflow passage extends radially inwardly from a portion of the body radially disposed from the axis and toward the axis to allow airflow to flow toward the axis.

[0038] As described herein, circumferentially positioned bodies may be provided within the core of an engine that may selectively allow air to exit a transition duct from the engine (e.g., into a bypass passage) or to enter a transition duct from outside the engine (e.g., from a bypass passage).

[0039] To allow air to flow efficiently through the device without causing harmful pressure differentials within an engine or the like, the inlet to the first upstream passage may be located upstream of the outlet of the first upstream passage as measured in the direction of airflow along the engine.

[0040] Similarly and for the same reasons, the inlet to the second downstream passage may be upstream of the outlet of the second downstream passage as measured along the engine in the direction of airflow.

[0041] Therefore, as described above, the first upstream passage is arranged in use to allow air to flow from the transition duct of the gas turbine engine to the bypass duct of the gas turbine engine, and the second downstream passage is arranged in use to allow air to flow from the bypass duct of the gas turbine engine to the transition duct of the gas turbine engine.

[0042] The device can advantageously allow the air flow to be selected by moving the body in the axial direction toward the front of the engine or the rear of the engine. Specifically, the reciprocating movement of the body along the axis of the gas turbine engine selectively or

[0043] (A) opening the first upstream passage to allow airflow and closing the second downstream passage; or

[0044] (B) Opening the second downstream channel to allow airflow and closing the first upstream channel.

[0045] Viewed from another aspect, there is provided a gas turbine engine comprising an apparatus as described herein, and an aircraft comprising one or more gas turbine engines as described herein.

[0046] From a further aspect, there is provided a method of selectively controlling air flow into a compressor of a gas turbine engine using the apparatus described herein, wherein in use the air is selectively caused to flow in the following manner:

[0047] (A) From a passage communicating air to the compressor to a bypass passage; or

[0048] (B) From the bypass passage to the passage that connects air to the compressor.

[0049] In such an arrangement, automatic control of airflow may be provided to the aircraft, for example in response to a stall determination.

[0050] Viewed from another aspect, there is provided a method of making an airflow device for a transition duct as described herein.

[0051] In summary, the present invention provides an exhaust / intake arrangement for a gas turbine engine, the gas turbine engine comprising a bypass passage and an engine core, the engine core comprising: a transition duct, the transition duct being arranged in use to guide air toward one or more compressors; and an airflow passage extending from the bypass passage through the core and toward the transition duct, the arrangement further comprising a first exhaust port, the first exhaust port being arranged in use to fluidically connect the transition duct and the airflow passage, and being configured to communicate air from the transition duct to the bypass passage; and a second air intake port, the second air intake port being arranged in use to fluidically connect the transition duct and the airflow passage, and being configured to communicate air from the bypass passage to the transition duct, wherein the first exhaust port and the second air intake port are integrally formed in a single circumferentially extending body, or in a pair of circumferentially extending bodies arranged to be adjacent to each other in use, wherein the single circumferentially extending body or the pair of circumferentially extending bodies are both in the form of rings.

[0052] The present invention also provides a gas turbine engine, which comprises the device as described above.

[0053] The invention also provides an aircraft comprising one or more gas turbine engines as described above.

[0054] The present invention also provides a method of selectively controlling air flow into a compressor of a gas turbine engine as described above, wherein in use the air is selectively caused to flow in the following manner:

[0055] (A) From a transition duct connecting air to the compressor to a bypass duct; or

[0056] (B) A transition duct flowing from the bypass passage to communicate air to the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0058] Figure 1 shows a cross section of a gas turbine engine incorporating an air flow arrangement according to the invention described herein;

[0059] Figure 2A schematic diagram showing a conventional exhaust arrangement for a gas turbine engine;

[0060] Figure 3 shows a schematic diagram of a multi-directional airflow device according to the invention described herein;

[0061] Figure 4 Shows Figure 3 A schematic diagram of the device shown in FIG. 1 in an exhaust mode of operation; and

[0062] Figure 5 Shows Figure 3 Schematic diagram of the device shown in FIG. 1 in the intake operating mode.

[0063] While the present teachings are susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and described in detail herein. However, it should be understood that the drawings and their detailed description are not intended to limit the scope to the particular forms disclosed, but on the contrary, the scope is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention.

[0064] The words "include", "comprising" and similar words used in this specification should not be interpreted in an exclusive or exhaustive sense. In other words, they mean "including but not limited to".

[0065] It will be appreciated that the features of the aspects of the invention described herein may be used conveniently and interchangeably in any suitable combination.It will also be appreciated that the invention encompasses not only individual embodiments but also combinations of embodiments that have been discussed herein. DETAILED DESCRIPTION

[0066] Figure 1 A cross section of a gas turbine engine 1 is shown, which may incorporate an exhaust configuration according to the invention, as described in detail below.

[0067] Those skilled in the art will understand the main components of a gas turbine engine and its operation. In summary, the engine 1 comprises an air intake 2 which allows air to flow into the engine and reach a fan 3 located at the upstream end of the engine. All components are housed in a nacelle 4.

[0068] The engine comprises a bypass passage downstream of the fan and a central engine core comprising a compressor, a combustor and a turbine. The engine core is formed by a first low pressure compressor (LPC) 5 and a second high pressure compressor (HPC) 6. This multi-stage compressor arrangement brings air from ambient pressure and temperature to high temperature and pressure. The compressed air is then communicated to a combustion chamber 7 where fuel is injected and combustion occurs.

[0069] The combustion gases are exhausted from the rear of the combustion chamber 7, first hitting the high pressure turbine 9, then the second low pressure turbine 10, before leaving the rear of the engine through the core nozzle 11. The thrust from the engine is generated by two air flows: the first from the bypass passage 8 (receiving thrust from the fan), and the second from the exhaust gas from the core nozzle 11.

[0070] The invention relates to the air flow in a transition duct 12 between a first low-pressure compressor 5 and a second high-pressure compressor 6. The transition duct 12 is an annular passage which extends around the core and which communicates the air between the two compressors.

[0071] Figure 2 A conventional exhaust system is illustrated. In practice, a portion of the wall of the transition duct is opened to allow air to escape to the outside instead of being directed to the second high-pressure compressor. As mentioned above, this can be done in a variety of ways, and different engine manufacturers have adopted different solutions to release air from the transition duct.

[0072] exist Figure 2 In the embodiment of the invention, a simple butterfly valve 13 is located near the wall of the duct 12 and allows selective opening and closing. The valve is connected to an airflow passage 14 which extends through a portion of the core to a bypass passage 8 where air can escape. Thus, in the event that the compressor only requires a small amount of air, any excess air can be released or vented into the bypass passage, thereby preventing the compressor from stalling. As also mentioned above, this arrangement is very effective in preventing the compressor from stalling.

[0073] When the butterfly valve 13 is open, a portion of the air flows along the path indicated by the first arrow 15. When the butterfly valve 13 is closed, all the air flows along the transition duct indicated by the second arrow 16 to the high pressure compressor (not shown). Figure 2 ).

[0074] Reverse thrust essentially involves redirecting the airflow, which is usually directed out the back of the engine, radially outwards or fully or partially backwards, i.e. in the opposite direction of the normal airflow. This significantly reduces the thrust produced by the engine and allows the aircraft to be stopped more quickly. This can be achieved, for example, by opening panels on the outside of the bypass duct to allow air to flow radially outwards instead of in a backward direction.

[0075] For conventional engines, reverse thrust refers to the axial flow through the bypass duct (outside the engine core) in the direction of aircraft movement. This is a particular problem for aircraft with fan blades with adjustable angles. In such engines, the fan can be used as a thrust reverser instead of using movable panels. Then there may be a situation where the flow in the bypass duct slows down or even reverses compared to the core flow, resulting in the engine being inoperable. Then, intake air may be needed instead of exhaust air.

[0076] In this case, it is necessary to increase the airflow into the compressor rather than exhausting air from the compressor. In fact, in these cases, it is desirable to draw additional air from the bypass passage into the duct and thereby into the compressor.

[0077] Figures 3 to 5 An exemplary embodiment of the invention described herein is illustrated wherein a multi-directional exhaust / intake configuration is provided.

[0078] Figure 3 A schematic diagram of the air control device of the present invention is shown.

[0079] The device comprises a cylindrical body 17 extending around the outer surface of the transition duct 12. The body defines two passages for the air flow as follows.

[0080] The first passage is the first exhaust port 19, which connects the transition duct 12 to the airflow passage 14 when in use. In this operating mode, a normal exhaust path is provided to prevent compressor stall as described above. As shown, the contour or shape of the first exhaust port 19 enables air to flow smoothly from the transition duct to the bypass passage 8.

[0081] The second passage is a second intake port 20 which, when in use, connects the bypass passage 8 to the transition duct, but has an opposite profile or shape. When connected to the airflow passage 14, the bypass passage air is drawn into the transition duct and communicated to the high pressure compressor ( Figure 3 not shown).

[0082] Due to the pressure, when the blades of the variable pitch fan are turned to reverse the airflow in the bypass channel (to brake the aircraft), airflow into the high pressure compressor is required, and this is achieved by using a reversible bleed. In this case, due to the pressure difference, air will flow into the compressor.

[0083] The body is arranged to be axially moved relative to the engine using a suitable actuator such as a linear actuator or an actuator (or similar device) that axially moves (pushes or pulls) the ring into or out of position, as shown by the arrow representing the axial direction 21. The body can thereby be moved between a first maximum position in which the exhaust path is fully open to a second maximum position in which the intake path is fully open.

[0084] Advantageously, the body can be moved to any position therebetween, depending on the amount of airflow required and the important direction of airflow, i.e., the direction of airflow into and out of the transition duct. Similarly, the body can be positioned in a closed position (e.g., Figure 3 ), in which the air is not connected to the duct or bypass passage in or out. This may be an example used in a normal flight operating mode.

[0085] Thus, stalling of the compressor may be prevented and additionally any reverse flow through the compressor may be avoided.

[0086] As mentioned above and also Figure 3 As shown, an intermediate position is also provided in which the transition duct 12 is sealed relative to the gas flow channel 14. The port 22 in the outer wall of the transition duct is sealed by the central portion 23 of the body 17.

[0087] The curvature of the port may be selected according to the different amounts of gas that must be conveyed into and out of the engine.

[0088] The device may be formed from a single continuous ring or alternatively a plurality of discrete portions forming ports distributed around the circumference of the core.

[0089] Figure 4 and Figure 5 The air control device is illustrated in two modes of operation.

[0090] Figure 4 The arrangement is shown in exhaust mode, where the body has been moved in a rearward direction (along the engine axis). This aligns the exhaust port with the airflow passage 14. As shown, the second intake port 20 has been moved away from the port 22, thereby allowing air communication from the duct towards the bypass passage.

[0091] Figure 5 The arrangement is shown in either exhaust or intake mode. The body has been moved in the opposite direction, towards the front of the engine to align the second intake port 20 with both the air flow passage 14 and the port 22. This thereby allows air to flow from the bypass passage into the duct.

[0092] In use, the aircraft control system can select not only the amount of air communicated through the transition duct, but also the direction, ie from or to the bypass passage. Alternatively, automatic control can be provided and the air control device can be controlled to optimize the airflow within the compressor.

[0093] The circumferential (or segmented) body can be moved in a simple linear manner using linear actuation as described above. The movement can be controlled by the ridges and the channels in which the ridges are located to control the movement.

[0094] In another arrangement, the passage may be generally S-shaped or serpentine so as to release the air into a bypass passage or duct as a flow more in line with the corresponding air flow.

[0095] In practice, the air exhausted into the bypass passage may be released into the bypass passage to have a flow direction that generally corresponds to the flow direction of the air in the bypass passage. Similarly, the air exhausted into the transition duct may be released into the transition duct to have a flow direction that generally corresponds to the flow direction in the transition duct.

Claims

1. An exhaust / intake arrangement for a gas turbine engine (1), the gas turbine engine comprising a bypass passage and an engine core, the engine core comprising: a transition duct (12) arranged, in use, to direct air towards one or more compressors; and an airflow passage (14) extending from the bypass passage through the core and toward the transition duct, the device further comprising a first exhaust port (19) arranged to fluidly connect the transition duct and the airflow passage in use and configured to communicate air from the transition duct to the bypass passage; and a second intake port (20), which is arranged to fluidically connect the transition duct and the air flow channel in use and is configured to communicate air from the bypass channel to the transition duct, wherein the first exhaust port and the second intake port are integrally formed in a single circumferentially extending body, or are formed in a pair of circumferentially extending bodies arranged to be adjacent to each other in use, wherein the single circumferentially extending body or the pair of circumferentially extending bodies are both in the form of a ring.

2. The device according to claim 1, wherein: The first exhaust port and the second intake port are one of a plurality of ports arranged circumferentially relative to the core of the engine.

3. The device according to claim 1, wherein: The single circumferentially extending body or the pair of circumferentially extending bodies each comprises an inner surface which faces a core of the engine when in use, and an outwardly facing surface which faces a bypass passage of the engine when in use, wherein the first exhaust port and the second intake port extend from the inner surface to the outwardly facing surface.

4. The device according to any one of claims 1 to 3, wherein: A body including the first exhaust port and the second intake port is movable relative to an engine core to open or close the first exhaust port or the second intake port.

5. The device according to claim 4, wherein: The body is movable in an axial direction (21) relative to the axis of the engine.

6. The device according to claim 5, wherein: Axial movement in a first direction causes the first exhaust port to open, allowing air to flow radially outward through the first exhaust port, and axial movement in an opposite second direction causes the second intake port to open, allowing air to flow radially inward through the second intake port.

7. The device according to claim 6, wherein: The axial movement is caused by one or more linear actuators arranged to move the body in a first direction and an opposite second direction.

8. The device according to any one of claims 1 to 3, wherein: The first exhaust port and the second intake port are movable between the following positions: (A) a first position allowing exhaust gas to flow radially outward from the transition duct to the bypass passage; (B) a second position in which air cannot flow out of the transition duct and air cannot flow into the transition duct; and (C) A third position allows intake air to flow radially inward from the bypass duct to the transition duct.

9. The device according to claim 8, wherein: The first exhaust port and the second intake port are selectively movable to an intermediate position between the first position and the second position and to an intermediate position between the second position and the third position.

10. The device according to any one of claims 1 to 3, wherein: One or all of the first exhaust ports may be provided with a curved profile curving radially outwardly such that a downstream end of the first exhaust port directs air in a radially outward direction relative to the axis of the engine in use.

11. The device according to any one of claims 1 to 3, wherein: One or all of the second inlet ports are provided with a curved profile curving radially inwardly such that a downstream end of the second inlet port, in use, directs air into the transition duct having a flow component along an axis of the transition duct.

12. A gas turbine engine comprising a device according to any one of claims 1-11.

13. An aircraft comprising one or more gas turbine engines according to claim 12.

14. A method of selectively controlling air flow into a compressor of a gas turbine engine according to claim 12, wherein: In use, the air is selectively made to flow in the following ways: (A) From a transition duct connecting air to the compressor to a bypass duct; or (B) A transition duct flowing from the bypass passage to communicate air to the compressor.

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