GB2279703A

GB2279703A - Variable Area Outlet

Info

Publication number: GB2279703A
Application number: GB9313664A
Authority: GB
Inventors: Robert Charles Tonks
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1993-07-02
Filing date: 1993-07-02
Publication date: 1995-01-11
Anticipated expiration: 2013-07-02
Also published as: GB9313664D0; US5476224A; GB2279703B

Abstract

A variable area exit for a fluid flow duct having a generally rectangular outlet includes a pair of rotatable flaps 42, 44 which extend between opposing sidewalls of the duct. Each of the flaps are provided with a profiled cam track 50 which cooperates with a cam roller 54 mounted on an axially moveable shroud ring 56. The shroud ring is coaxially disposed about the duct axis such that translation of the shroud causes the flaps to rotate and the duct exit area to alter. <IMAGE>

Description

VARIABLE AREA OUTLET 2279703 This invention concerns a variable area

outlet for a fluid flow duct and in particular a variable area nozzle outlet for a gas turbine engine.

Modern gas turbine engines often utilise variable area nozzles as a means of optimising engine performance at off-design conditions.

Although known prior art variable area nozzles have proved effective in achieving the degree of area variation required, they have done so at the expense of increased weight and complexity. This is of particular concern in the field of vertical and short take-off and landing (V/STOL) aircraft engine applications which utilise rotatable nozzles to direct engine thrust. With such nozzles the mechanism for varying the area of the outlet must be simple to operate, capable of being operated independently of the mechanism for rotating the nozzle, and above all lightweight in construction so as not to impose unacceptable loads on the mechanism for supporting and rotating the nozzle.

An objective of the present invention is, therefore, to provide a lightweight variable area outlet, and in particular a variable outlet suitable for a rotatable nozzle in a V/STOL powerplant application.

According to the invention there is provided a variable area outlet for a fluid flow duct, comprising a pair of opposed elements which extend in spaced apart relation between opposing sides of the duct at the downstream end thereof, and a moveable shroud ring coaxially disposed about the duct axis, each of the elements being mounted 2 for rotation relative to the duct about an axis orthogonal to the duct axis and comprising cam means which cooperate with the shroud ring such that translation of the shroud ring causes each of the elements to rotate and thereby alter the exit area of the duct.

The invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows a rotatable nozzle having a variable area outlet according to a first general embodiment of the invention, Figure 2 shows in plan view a rotatable nozzle of the type shown in Figure 1 having a variable area outlet according to a second embodiment of the invention, Figure 3 shows a sectional view, in the direction of arrows I-I, of the rotatable nozzle shown in Figure 2, and Figure 4 shows the nozzle of the present invention in the same sectional view as Figure 3 but with the nozzle in a second configuration.

Referring to Figure 1 there is shown a gas turbine engine exhaust section 10 for a V/STOL powerplant application. The engine includes a main axial discharge nozzle 12 for directing engine gases rearwards during forward flight, and a pair of side mounted rotatable lift nozzles 14 for vectoring engine gases during periods of vertical and transitional flight. Nozzles 14 are each mounted in bearings 16 for rotation about an axis 18 orthogonal to the main engine axis 20. A diverter valve 22 of a generally well known type is further provided for selectively directing the engine gases exclusively to either the side mounted lift nozzles 14 or the axial thrust nozzle 12.

Referring now to Figures 2 to 4, nozzle 14 comprises a part toroidal wall 26 which defines a gas flow duct 28 having a generally rectangular downstream section 30, and a variable area convergent outlet 32 which also has a generally rectangular section. The nozzle outlet 32 comprises a pair of parallel sidewalls 34,36 which extend downstream from opposing sides 38,40 of the duct to define lateral flow boundaries, and a pair of rotatable flap elements 42,44 which extend spanwise in spaced apart relation between sidewalls 34,36 to define top and bottom flow boundaries. Elements 42,44 are mounted for rotation at the downstream end of duct 28 about respective spanwise axes 46,48 which are disposed orthogonally to the duct axis 58. Preferably elements 42,44 are U-shaped so that they sealingly engage the sidewalls 34,36 of duct 28 over a increased area.

As shown each of the elements 42,44 is provided with a profiled cam trackway 50 extending from its outer surface 52. The respective trackways 50 are each engaged by a roller element 54 which defines a corresponding cam follower means. The cam roller elements 54 are each mounted to an axially moveable shroud ring 56 which is coaxially disposed about duct axis 58. The shroud ring 56 is itself supported by a pair of actuators 60 which are attached to opposing sides of the duct. The actuators are arranged so as to translate the shroud ring backwards and forwards in the direction of arrows A and B along duct axis 58.

It is to be appreciated that in this arrangement the shroud ring 56 restrains the elements 42,44 in position about their respective axes 46, 48 such that, in use, the gas loads acting on the elements are reacted by the shroud ring 56 and not actuators 60. This enables actuators of relatively lightweight construction to be used.

In operation the maximum nozzle exit area is obtained by translating the shroud ring to the position shown in Figure 3. This causes the cam rollers 54 to translate along the respective cam tracks 50 such that the elements 42,44 rotate to the positions shown.

To obtain a nozzle of minimum exit area shroud ring 56 is translated rearwards by energisation of actuators 60 to the position shown in Figure 4. This causes elements 42,44 to rotate about their respective axes 46,48 to define a minimum nozzle exit area.

Clearly the dimensions of the nozzle exit area can be varied progressively between the maximum and minimum configurations shown simply by positioning the shroud ring in some intermediate position.

Although this invention has been described with reference to a side mounted rotatable nozzle for a gas turbine engine it is to be appreciated that it is not restricted to such an application. Indeed it is equally applicable to nozzles such as the main axial thrust nozzle described above.

It is to be appreciated also that the invention is not restricted to gas turbine engine applications, but is applicable to any type of fluid flow duct requiring a simple variable area exit means.

Claims

A variable area outlet for a fluid flow duct, comprising a pair of opposed elements which extend in spaced apart relation between opposing sides of the duct at the downstream end thereof, and a moveable shroud ring coaxially disposed about the duct axis, each of the elements being mounted for rotation relative to the duct about an axis orthogonal to the duct axis and comprising cam means which cooperate with the shroud ring such that translation of the shroud ring causes each of the elements to rotate and thereby alter the exit area of the duct.
2 A variable area outlet as claimed in claim 1 wherein the elements and opposing sides of the duct collectively define a generally rectangular flow passage.
3 A variable area outlet as claimed in claim 2 wherein the elements are generally U-shaped.
A variable area outlet as claimed in any preceding claim wherein the elements are each rotatably mounted towards the downstream end of the duct.
A variable area outlet as claimed in any preceding claim wherein the elements define a convergent nozzle section.
6 A variable area outlet as claimed in any preceding claim wherein the outlet forms the discharge nozzle of a gas turbine engine.
A variable area outlet as claimed in claim 6 wherein the nozzle is mounted for rotation about an axis orthogonal to the main engine axis.
8 A variable area outlet as hereinbefore described with reference to and as shown in the accompanying drawings.