GB2058932A - Gas turbine engine propulsion nozzle - Google Patents

Abstract

The engine has a variable area primary nozzle comprising flaps 12a pivotally mounted at 19, and an axially movable ejector sleeve 14 which terminates in an assembly of flaps 32a pivotally mounted at 34 on the sleeve to permit area variation. The flaps 32a of the ejector nozzle have limited freedom of movement on each side of the stop member 46, to enable them to find their own best position according to flight conditions, operating loads being derived from differences between engine pressures and ambient pressure. <IMAGE>

Description

SPECIFICATION Variable area ejector nozzle This invention is concerned with a gas turbine engine having a variable area nozzle.

It is known that the provision of a variable area thrust nozzle, on a jet engine which powers an aircraft, whilst giving the capability of catering for widely varying gas velocities also creates an undesirable base area, i.e. an area immediately adjacent the nozzle outlet plane, which is of relatively low pressure.

Such a situation creates base drag.

Attempts have been made to minimise the base area by extending the structure which surrounds the nozzle, in a downstream direction and forming the extension into further flaps which are movable inwardly to occupy some of the base area which is created, when the flaps of the primary nozzle move inwards to reduce the nozzle outlet area. Such arrangement is disclosed in British patent specification 951,130. However, it is not entirely satisfactory because, although base area is filled the postions of the flaps of the translating sleeve shown in the patent specification are controlled via a mechanical connection between them and the primary flaps of the engine nozzle. In consequence, the sleeve flaps are not bound to adopt a best position having regard to airflows and/or altitude, though the primary flaps may be in a best position for doing their particular job.

It is an object of the present invention to obviate the need for mechanical connection between the respective flaps, in order to position both sets of flaps to extract optimum performance from the gas turbine engine.

According to the present invention a gas turbine engine includes a primary exhaust nozzle comprising a first ring of hinged flaps, the downstream ends of which cooperate to form a variable area exhaust gas nozzle, said primary exhaust nozzle being surrounded by a translating sleeve the downstream end of which comprises a further ring of hinged flaps, the inner surfaces of which cooperate to provide a gas expansion control surface, said further ring of flaps being movable about their hinges with respect to the first ring of flaps, only by and in accordance with pressure differences which exist between the gases within the gas turbine engine and ambient atmosphere.

Damping means may be provided to reduce fluttering of said further flaps under rapidly fluctuating pressure differentials.

Preferably the translating sleeve and its associated further flaps form an ejector nozzle.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a gas turbine engine, including a variable area nozzle in accordance with an embodiment of the invention.

Figures 2 and 3 are an enlarged cross sectional view of the nozzle of Fig. 1 axially of the gas turbine engine, Figure 4 is an enlarges pictorial part view of the nozzle of the gas turbine engine in Fig. 1, Figure 5 is a cross sectional part view of an alternative embodiment of the invention, Figure 6 is a pictorial view of a further flap construction.

Figure 7 is a cross sectional view corresponding to Fig. 3, but of an alternative embodiment of the invention.

In Fig. 1 a gas turbine engine 10 terminates in a variable area thrust nozzle 1 2.

Thrust nozzle 1 2 is surrounded by a sleeve 14 which terminates in 9 variable area gas outlet 16.

Sleeve 14 is translatable in upstream/ downstream directions and in the present example, the translation is achieved by rams 18, through screwjacks or other convenient means may be employed.

The jet pipe 20 of gas turbine engine 10 contains reheat equipment 22.

Referring now to Fig. 2 the variable nozzle 1 2 is formed by a ring of master flaps 1 2a each connected by a hinge 1 9 at its upstream end to the downstream end of jet pipe 20, in known manner.

Each pair of adjacent master flaps 1 2a is underlapped by a slave flap 126(Fig. 4) and each individual master flap 1 2a carries a track 22 on its outer surface.

Sleeve 14 has a number of inverted channels 24 on and protruding beyond, its downstream end, the number being equal to the number of master flaps 1 2a on nozzle 1 2.

A roller 26 is rotatably fixed in each channel 24, adjacent its downstream end and each roller 26 engages a respective flap track 22.

Each roller 26 supports a further, smaller roller 28 such that a lip 30 on track 22 is held between them. The arrangement prevents the flaps 1 2a dropping inwards when no gas loads are acting on them.

During operation of the gas turbine engine, movement of sleeve 1 4 in a downstream direction allows flaps 1 2a to adopt the position shown in Fig. 3, thus increasing the outlet area of nozzle 1 2.

Sleeve 1 4 has a variable area downstream end 32 comprising a ring of further flaps 32a.

Flaps 32a are connected by respective hinges 34 to the downstream end of a cylindrical portion 14a. Each flap 21 a is provided with cut-outs 32b (Figs. 4 and 5) so that they fit closely round respective channels 24, when in the position shown in Fig. 2. However, flaps 32a have no mechanism with which to bring about pivoting with respect to the cylindrical portion 14a. Instead they operate as follows.

During cruise of an aircraft (not shown) powered by an engine 10, the flaps 1 2a of primary nozzle 12, will be set in the position shown in Fig. 2, by appropriate positioning of sleeve 14. Exhaust gases thus flow out of the nozzle in the manner indicated by arrows 40.

Ambient air flows over the outer surface of sleeve 1 4 and leaves the downstream ends of flaps 32a in the manner indicated by arrows 42. The two flows generate a base area 'A' the pressure in which is low relative to ambient and engine pressures, drag is thus created.

Flaps 1 2a are trapped between rollers 26 and the gas loads and therefore, cannot move to occupy any part of the base and so reduce its magnitude. Flaps 32a however, are free to move under the load exerted on their external surfaces by static pressures developed in the ambient airflow. In consequence, flaps 32a move inwards about hinges 34 and so occupy and reduce the magnitude of the base area 'A', and therefore the base drag effect.

Flaps 32a must not pivot inwardly to the extend that their outer profile becomes abruptly malaligned with the profile of the cylindrical portion 1 4a for if they did, ambient air flow would break away from the sleeve and create a further base area on the flaps outer surface. A stop member is therefore provided, in the form of a bar 46 which is annular in shape and is supported at the downstream ends of each inverted channel 24. On pivoting of flaps 32a inwardly, they eventually engage the stop and are held there by pressure differential across them.

When reheat equipment 22 (Fig. 1) is operated, sleeve 14 with flaps 32a is translated in a downstream direction. Primary flaps 1 2a open to increase the nozzle area and in so doing, become more nearly aligned with flaps 32a as shown in Fig. 3. In such circumstances, reheated exhaust gases will exert a greater pressure on the inner surfaces of flaps 32a than will ambient air. Flaps 32a therefore move outwards. However, it is important that the flaps should not move to the extent that they provide no control over the expansion of the exhaust gases after they have left the primary nozzle 1 2. Should this occur, forward thrust which is available for extraction via the static pressure generated across flaps 32a, is lost. Therefore bar 46 is arranged to act as a stop against excessive outward movement of flaps 32a as shown in Fig. 3.In consequence, flaps 32 will adopt any position from that shown in chain dotted lines, to that shown in full lines, dependant upon the pressure differential across them.

Flaps 32a may have a damping mechanism attached in the event that rapid fluctuation occurs in the pressure differentials across them. Such a mechanism would act to damp out flutter and could comprise e.g. a piston and cylinder assembly 50, indicated generally in Fig. 5. Either side of the piston could be connected to receive some engine pressure which would be related to and compensate for, effects generated by any altitude at which an aircraft (not shown) powered by engine 10, would fly.

Alternatively, the further flaps 32a would be resiliently biased i.e. by springs or the like, to minimise flutter.

Referring now to Fig. 6, further flaps 32a are each provided with an extension piece 52 on one side, which is a sliding, sealing fit in the immediately adjacent flap 32a, thus obviating the need for slave flaps.

A further advantage would accrue, if the sleeve 14 is adapted so as to provide an ejectors nozzle. Ambient air would be drawn between the sleeve 1 4 and jet pipe 20, to be ejected into the base area 32, thereby providing a flow of cooling air for the jet pipe and also serving to partially fill the base area.

Referring now to Fig. 7, the differences between the static pressure exerted on the outer and inner surfaces of flaps 32a may be great. The hot exhaust gases rapidly expand against the inner surfaces of the flaps thereby applying larger forces in a radially outward direction, than are applied radially inwardly. It may be necessary therefore, for each flap outer surfaces to have a larger area than the inner surfaces. For example, the outer surface of each flap 32a may be 'A' units long and the inner surface 'B' units long, whilst both surfaces were of similar width. The actual values of 'A' and 'B' would be decided by test and calculation.

Fig. 7 further depicts an arrangement wherein the inner flap portion 32c is a separate entity and is connected adjacent its downstream end, to the downstream end of the outer flap portion 32d via a slot and pin assembly 50. The upstream end of inner flap portion 32c is connected to a bracket 52 in common with roller 26, and via a hinge 54.

The arrangement enables relative movement between inner flap portions 32c and outer flap portions 32d in directions radially and axially of sleeve 14 and further enables inner flap portion 32cto move through a greater angle about pivot axis 54, for a given angular movement of outer flap portion 32d. It follows that the change in boat tail angle is reduced to a minimum, whilst the respective inner and out flap portions 32c, 32dare finding their best positions, having regard to the pressure differentials across them.

Claims (8)

1. A gas turbine engine including a primary exhaust nozzle comprising a first ring of hinged flaps, the downstream ends of which cooperate to form a variable area exhaust gas nozzle, a translatable sleeve surrounding said nozzle and the downstream end of which comprises a further ring of hinged flaps, the inner surfaces of which cooperate to form a gas expansion control surface, said further ring of flaps being movable about their hinges with respect to the first ring of flaps, only by and in accordance with, pressure differences which exist between the gases within the gas turbine engine and ambient atmosphere.

2. A gas turbine engine as claimed in claim 1 wherein said translatable sleeve comprises an ejector nozzle.

3. A gas turbine engine as claimed in claim 1 or claim 2 including damping means for damping fluttering in said further flaps.

4. A gas turbine engine as claimed in claim 3 wherein said damping means comprises means operable by engine pressures and includes a piston and cylinder assembly for each flap, wherein a said piston is connected to its respective further flap so as to apply a load thereto to counter fluttering of said respective flap, said load being derived from said engine pressures.

5. A gas turbine engine as claimed in claim 3 wherein said damping means comprises resilient means.

6. A gas turbine engine substantially as described in this specification with reference to Figs. 1 to 6 of the drawings.

7. A gas turbine engine as claimed in any of claims 1 to 5 wherein each said further flap comprises inner and outer portions of which the outer portion has its upstream end hinged to said sleeve and its downstream end formed to the downstream end of the inner flap portion such as to permit relative radial and axial movement between them, the upstream end of the inner flap portion being hinged to a further portion of said sleeve.

8. A gas turbine engine substantially as described in this specification, with reference to Fig. 7 of the drawings.