GB2489475A

GB2489475A - Variable geometry duct

Info

Publication number: GB2489475A
Application number: GB201105328A
Authority: GB
Inventors: Donato Bitondo
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-03-30
Filing date: 2011-03-30
Publication date: 2012-10-03
Also published as: GB201105328D0

Abstract

A duct 10 for a gas turbine engine 2 comprises a duct wall 16, 18 having a geometry which is variable between a first condition in which the duct wall defines a first flow path, and a second condition in which the duct wall defines a second flow path. The duct has an opening 26 in the duct wall and the second flow path is diverted with respect to the first flow path such that debris entrained in flow along the duct is directed through the opening. The duct wall may comprise a deformable portion 20 which is deformed to vary the geometry of the duct between the first condition and the second condition. The deformed portion may deflect debris entrained in the flow along the duct and through the opening. The deformable portion may be resilient. The deformable portion may be expandable. The deformable portion may be inflatable. A second deformable portion 30 may oppose the first deformable portion and the duct may further comprise a panel 32 which is slidable over the duct wall to vary the geometry of the duct.

Description

I

VARIABLE GEOMETRY DUCT

This invention relates to a variable geometry duct and particularly, although not exclusively, relates to a variable geometry inlet duct for a gas turbine engine.

Gas turbine engines are commonly used on aircraft as propulsion systems.

For example, gas turbine engines are suspended beneath wings of aeroplanes to provide propulsion for the aircraft in high-altitude flight as well as during take-off and landing. In addition, the engines are often used to propel the aircraft during taxiing manoeuvres on the ground.

It is known that during take-off, landing and taxiing debris such as dust, stones or litter on the ground is picked up and ingested by the gas turbine engine. The debris damages the internal components of the gas turbine engine such as the compressor stator vanes and rotor blades. This can cause immediate failure of the components or else reduce their operational life.

It is known to provide screens made from wire mesh at the front of the gas turbine engine to prevent ingestion of debris. However, wire mesh screens create a large amount of drag which is detrimental to the performance of the aircraft.

US4702071 and US3616616 disclose deflectors which are positioned forward of a compressor in the intake duct of the engine. Each deflector deflects inflowing debris radially outwardly through flow passages extending from an outer wall of the intake duct. Although these deflectors reduce the amount of debris entering a compressor, they increase the aerodynamic losses through the engine, for example by causing flow separation within the duct which also increase engine noise. Consequently, they are unsuitable for use in aircraft which operate for prolonged periods at high-altitude flight where aerodynamic efficiency is paramount.

US3302396 discloses a jet engine in which diaphragms are inflated in the intake to close the intake. A hatch in the side of the engine is opened to provide an auxiliary intake through the side of the engine through which air is drawn.

The auxiliary intake is provided with a screen to prevent ingestion of debris. A problem with this arrangement is that debris would accumulate on the diaphragms and so be subsequently ingested by the engine when the diaphragms are deflated. Furthermore, a screen is still required to prevent ingestion of debris through the auxiliary intake.

US51 23240 discloses a scoop which can be positioned within a flow path to collect debris travelling along the intake duct. The scoop can be retracted in high power conditions.

According to a first aspect of the present invention there is provided a duct comprising a duct wall having a geometry which is variable between a first condition in which the duct wall defines a first flow path, and a second condition in which the duct wall defines a second flow path, wherein the duct has an opening in the duct wall and the second flow path is diverted with respect to the first flow path such that debris entrained in flow along the duct is directed through the opening.

The duct wall may comprise a deformable portion which is deformed to vary the geometry of the duct between the first condition and the second condition.

The deformable portion may be disposed facing the opening such that, when deformed, the deformable portion deflects debris entrained in flow along the duct through the opening.

The deformable portion may be resilient. The deformable portion may be expandable.

The deformable portion may be inflatable and may be expanded by inflating the deformable portion.

The deformable portion may be adapted such that, when inflated, the deformable portion assumes a predefined shape.

The deformable portion may be adapted to expand non-uniformly.

The deformable portion may comprise a panel having a non-uniform thickness such that the panel expands non-uniformly.

The duct may further comprise pressure regulation means for regulating the pressure within the deformable portion.

The pressure regulation means may comprise valves which maintain the deformable portion in an inflated state, wherein the valves are biased open.

The duct may further comprise a second deformable portion which opposes the deformable portion and is disposed upstream of the deformable portion with respect to the general flow direction through the duct.

The duct may comprise a panel which is slidable over the duct wall to vary the geometry of the duct wall between the first condition and the second condition.

The duct wall may further comprise a concave portion which is concealed by the panel in the first condition, the panel being slidable over the duct wall to reveal the concave portion in the second condition thereby varying the geometry oftheductwall.

The concave portion may be adjacent to the opening in the duct wall and situated upstream of the opening with respect to the general flow direction through the duct.

The duct may be an annular intake duct for a compressor, comprising a radially inner duct wall and a radially outer duct wall. The opening may be provided in the radially outer duct wall.

The radially inner duct wall may be defined by a static plug located coaxially with the longitudinal axis of the engine. The static plug may be

inflatable.

According to a second aspect of the present invention there is provided a turbine engine comprising a duct in accordance with the first aspect of the invention.

According to a third aspect of the present invention there is provided a duct comprising a duct wall having a geometry which is variable between a first condition in which the duct wall defines a first flow path, and a second condition in which the duct wall defines a second flow path, wherein the duct has an opening in the duct wall and the second flow path is diverted with respect to the first flow path such that debris entrained in flow along the duct is directed through the opening, the duct wall comprises a deformable portion which is deformed to vary the geometry of the duct between the first condition and the second condition, the duct comprises a second deformable portion which opposes the deformable portion and is disposed upstream of the deformable portion with respect to the general flow direction through the duct, the duct comprises a panel which is slidable over the duct wall to vary the geometry of the duct wall between the first condition and the second condition, the duct wall comprise a concave portion which is concealed by the panel in the first condition, the panel is slidable over the duct wall to reveal the concave portion in the second condition thereby varying the geometry of the duct wall.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-Figure 1 is a schematic representation of an intake duct for a gas turbine engine in section; Figure 2 is a schematic representation of the intake duct shown in Figure 1 in a first condition; and Figure 3 is a schematic representation of the intake duct shown in Figure 1 in a second condition.

Figure 1 shows a front part of an axial flow gas turbine engine 2 in the region of a compressor 4. The gas turbine engine 2 comprises an annular fairing 6 which is arranged coaxially with a nose cone, or plug 8. The plug 8 and the fairing 6 are connected together and are both static (i.e. non-rotating).

The fairing 6 and the plug 8 define an annular intake duct 10 which extends between an inlet 12 and an intake 14 of the compressor 2. The fairing 6 defines a radially outer wall 16 of the intake duct 10 and the plug 8 defines a radially inner wall 18 of the intake duct 10.

The general flow direction along the duct is from the inlet 12 towards the compressor intake 14.

The plug 8 comprises a plug wall 20 which defines with the inner wall 18 of the intake duct 10 a cavity within the plug 8. The plug wall 20 is made from a resilient material, such as rubber or a similar elastomer, and so can be expanded into the intake duct 10 by increasing the air pressure within the plug 8. The plug wall 20 has a non-uniform thickness which varies in the direction from the front of the plug 8 towards the compressor intake 14. In the embodiment shown, the plug wall 20 has a forward portion 22 and a rearward portion 24. The rearward portion 24 is thicker than the forward portion 22. The plug 8 has a first deflated condition in which the diameter of the plug 8 increases continuously from the inlet 12 to the compressor intake 14.

The outer wall 16 has an opening 26 situated adjacent the compressor intake 14. In the embodiment shown, the opening 26 is in a portion of the outer wall 16 which curves inwardly towards the compressor intake 14. The opening 26 is disposed radially outwardly of the compressor intake 14 and is substantially perpendicular to the general flow direction.

The outer wall 16 comprises a concave portion 28 adjacent the opening 26.

The concave portion 28 is formed by a circumferential recess in the outer wall 16 of the intake duct 10. The concave portion 28 extends from the opening 26 towards the inlet 12. The concave portion 16 is substantially rigid.

The outer wall 16 further comprises a flexible band 30 made of a resilient material such as rubber or a similar elastomer disposed between the concave portion 28 and the nose of the fairing 6. The flexible band 30 is sealed against the remainder of the outer wall 16 and so provides a flexible panel which is inflatable from within the fairing 6. For example, the flexible band 30 may comprise a diaphragm sealed against adjacent portions of the outer wall 16 or a tubular bladder disposed within a recess in the fairing 6. The flexible band 30 has a first condition in which the flexible band 30 is deflated such that the radially inner surface of the flexible band 30 extends in a circumferential plane that lies parallel with the engine axis. The flexible band 30 has a non-uniform thickness, which varies in the axial direction. In the embodiment shown, the flexible band is thinnest in the mid-portion axially between the forward and rearward circumferentially extending edges of the flexible band 30.

The intake duct 10 further comprises a panel in the form of a cylindrical shell 32 aligned coaxially with the engine axis. The inner diameter of the shell 32 is such that the inner surface of the shell 32 is substantially coaxial, and aligned, with the inner surface of the flexible band 30 when the flexible band 30 is in the deflated condition. The shell 32 is shown in Figure 1 partially concealing the concave portion 28. The shell 32 is mounted with respect to the fairing 6 50 that it can slide, or translate, forward and rearward in order to conceal and expose respectively the concave portion 28. A recess 34 is provided in the fairing 6 for receiving the shell 32 as it is moved in a rearward direction away from the concave portion 28.

An air supply is connected to the plug 8 and the fairing 6 for supplying pressurised air to the flexible band 30 and the cavity within the plug 8. Individual pressure regulation devices are provided for the flexible band 30 and the plug 8.

The air may, for example, be bleed air from the compressor 4.

The plug 8 and the flexible band 30 are provided with respective vent valves (not shown). The vent valves are biased open such that, in the event of failure of the valve control systems, the valves open to deflate the plug 8 and the flexible band 30.

In use, the intake duct 10 is operated between a first condition, shown in Figure 2, corresponding to high-altitude flight, and a second condition, shown in Figure 3, corresponding to low-altitude flight or ground manoeuvres.

In the first condition, shown in figure 2, the plug 8 and the flexible band 30 are deflated and the shell 32 is disposed over the concave portion 28 to conceal the concave portion 28. In the first condition, the inner surfaces of the shell 32 and the flexible band 30 form a continuous surface of the outer wall 16 of the intake duct 10 which is parallel with the engine axis. The plug waIl 20 diverges continuously from the nose of the plug 8 towards the compressor intake 14 such that the inner and outer waIls 16, 18 of the duct 10 converge towards the compressor intake 14.

In the first condition, the intake duct 10 defines a first flow path in which air flowing through the duct 10 towards the compressor intake 14 is generally straight and unobstructed. Aerodynamic losses through the duct are therefore relatively small. Although debris entrained by the flow along the duct would be more likely to enter the compressor intake, this is acceptable at high-altitude flight where debris which is likely to damage the inner components of the engine is less prevalent.

When an aircraft on which the engine is mounted is about to enter low-altitude flight, for example on approach to landing, or when the aircraft is readying on the ground for take-off, pressurised air is supplied to the region of the fairing 6 behind the flexible band 30 and to the plug 8 to inflate the flexible band 30 and the plug 8. The vent valves are closed during inflation and remain closed to keep the flexible band 30 and plug 8 inflated. The shell 32 is displaced rearward into the recess 34 to reveal, or expose, the concave portion 28 of the outer wall 16.

For a particular inflation pressure, the amount of expansion of the flexible band 30 and the plug 8 is dependent on the thickness of the flexible band 30 or the plug wall 20. Consequently, the variation in the panel/wall thickness causes the flexible band 30 and the plug wall 20 to expand non-uniformly.

The thicker rearward portion 24 of the plug wall 20 expands less than the forward portion 22. The plug wall 20 therefore assumes a bulbous shape in which the forward portion 22 diverges and the rearward portion 24 converges towards the compressor intake 14. The divergence of the forward portion 22 is greater in the inflated second condition than in the deflated first condition.

Similarly, the central thinner portion of the flexible band 30 expands more radially inwardly than the regions adjacent the forward and rearward circumferentially extending edges of the flexible band 30. The flexible band 30 therefore assumes a curved shaped having a substantially plateaued mid portion.

It will be appreciated that the thickness variation of the plug wall 20 or the flexible band 30 can be defined to produce a predefined complex contoured shape when inflated which provides the optimal flow characteristics along the duct 10.

As shown in Figure 3, the plug wall 20, flexible band 30 and concave portion 28 define a bend 36 in the intake duct 10 such that the intake duct 10 defines a second flow path which is diverted from the first flow path (Figure 2) and so directs flow along the duct 10 radially outwardly and then radially inwardly before passing through the compressor intake 14. Debris entrained by the flow is deflected radially outwardly by the forward portion 22 of the plug wall 20 towards the concave portion 28 and the opening 26. The momentum of the debris causes it to flow close to the concave portion 28 as the air flows around the bend 36. Debris therefore passes directly through the opening 26 or else accumulates along the concave portion 28 which then guides the debris through the opening 26. The momentum of the debris is sufficient to carry the debris through the opening 26 rather than being re-entrained by the flow through the compressor intake 14. Once debris has passed through the opening 26 it is discharged from the engine 2.

As shown in Figure 3, the flexible band 30 opposes the plug wall 20 and the flexible band 30 is disposed generally upstream of the plug wall 20 with respect to the general flow direction through the intake duct 10. The flexible band 30 is also disposed upstream of the concave portion 28 with respect to the general flow direction through the intake duct 10. The concave portion 28 and plug wall 20 are generally arranged such that the maximum diameter of the concave portion 28 is substantially aligned with the maximum diameter of the plug wall 20 when the plug wall 20 is in the second condition.

The vent valves are opened to return the intake duct 10 to the first condition.

Means may be provided for closing the opening 26 when in the first condition to prevent air from being discharged through the opening 26.

The components described with respect to the embodiment shown in Figure 1, for example the plug 8, flexible band 30 and concave portion 28 with the shell 32 can be incorporated independently. For example, it is envisaged that an embodiment may comprise the plug 8 without the flexible band 30 or the concave portion 28 and the shell 32.

In a variant of the embodiment shown in Figure 1, the rigid concave portion 28 and the shell 32 are substituted by a further flexible band similar to the flexible band 30 shown in Figure 1. The additional flexible band can be deformed into a concave shape by applying a vacuum within the fairing 6 in the region of the flexible band, or by suitable actuators.

Claims

CLAIMS1. A duct comprising a duct wall having a geometry which is variable between a first condition in which the duct wall defines a first flow path, and a second condition in which the duct wall defines a second flow path, wherein the duct has an opening in the duct wall and the second flow path is diverted with respect to the first flow path such that debris entrained in flow along the duct is directed though the opening.
2. A duct as claimed in claim 1, wherein the duct wall comprises a deformable portion which is deformed to vary the geometry of the duct between the first condition and the second condition.
3. A duct as claimed in claim 2, wherein the deformable portion is disposed facing the opening such that, when deformed, the deformable portion deflects debris entrained in flow along the duct through the opening.
4. A duct as claimed in any one of the preceding claims, wherein the deformable portion is resilient.
5. A duct as claimed in any one of the preceding claims, wherein the deformable portion is expandable.
6. A duct as claimed in claim 5, wherein the deformable portion is inflatable and is expanded by inflating the deformable portion.
7. A duct as claimed in claim 6, wherein the deformable portion is adapted such that, when inflated, the deformable portion assumes a predefined shape.
8. A duct as claimed in claim 7, wherein the deformable portion is adapted to expand non-uniformly.
9. A duct as claimed in claim 8, wherein the deformable portion comprises a panel having a non-uniform thickness such that the panel expands non-uniformly.
10. A duct as claimed in any one of claims 6 to 9, wherein the duct further comprises pressure regulation means for regulating the pressure within the deformable portion.
11. A duct as claimed in claim 10, wherein the pressure regulation means comprises valves which maintain the deformable portion in an inflated state, wherein the valves are biased open.
12. A duct as claimed in any one of claims 2 to 11, wherein the duct further comprises a second deformable portion which opposes the deformable portion and is disposed upstream of the deformable portion with respect to the general flow direction through the duct.
13. A duct as claimed in any one of the preceding claims, wherein the duct comprises a panel which is slidable over the duct wall to vary the geometry of the duct wall between the first condition and the second condition.
14. A duct as claimed in claim 13, wherein the duct wall further comprises a concave portion which is concealed by the panel in the first condition, the panel being slidable over the duct wall to reveal the concave portion in the second condition thereby varying the geometry of the duct wall.
15. A duct as claimed in claim 14, wherein the concave portion is adjacent to the opening in the duct wall and situated upstream of the opening with respect to the general flow direction through the duct.
16. A duct as claimed in any one of the preceding claims, in which the duct is an annular intake duct for a compressor, comprising a radially inner duct wall and a radially outer duct wall.
17. A duct as claimed in claim 16, wherein the opening is provided in the radially outer duct wall.
18. A duct as claimed in claim 16 or 17, wherein the radially inner duct wall is defined by a static plug located coaxially with the longitudinal axis of the engine.
19. A duct as claimed in claim 18, wherein the static plug is inflatable,
20. A duct as claimed in claim 1, wherein the duct wall comprises a deformable portion which is deformed to vary the geometry of the duct between the first condition and the second condition, the duct comprises a second deformable portion which opposes the deformable portion and is disposed upstream of the deformable portion with respect to the general flow direction through the duct, the duct comprises a panel which is slidable over the duct wall to vary the geometry of the duct wall between the first condition and the second condition, the duct wall comprise a concave portion which is concealed by the panel in the first condition, the panel is slidable over the duct wall to reveal the concave portion in the second condition thereby varying the geometry of the duct wall.
21. A duct substantially as herein before described with reference to and as shown in the accompanying drawings.
22. A gas turbine engine having a duct as claimed in any of claims I to 21.