GB2119022A - Gas turbine engine nozzle - Google Patents

Abstract

The nozzle comprises a duct 17(c), a plurality of movable flaps 38,43 for varying the geometry of the nozzle, one or more openings 59 and a pair of rotatably mounted mutually confronting doors 61. The doors 61 are mounted so that, in a first position, they obturate the openings 59 and mutually confronting surfaces 67 of the doors define therebetween part of the gas flow path through the nozzle, and the doors 61 are movable to a second position, upstream of the first position,where they uncover the openings 59, define, at their upstream ends 68, a reduced area throat for the gas flow path through the nozzle. The reduced pressure downstream of the throat induces ambient air through the openings 59 into the gas flow path through the nozzle. (Fig.2, not shown). In this way the infrared emission of the gas plume exiting from the nozzle is suppressed by the cool air. <IMAGE>

Description

SPECIFICATION Turbomachine nozzle This invention relates to nozzles for gas tu rbine aero-engines and is particularly concerned with variable geometry nozzles and the suppression ofthe infra red radiation emitted by the hot exhaust plume of such engines.

Modern combataircraft require the flexibility of being able to fly at subsonic or supersonic speeds and to perform a variety of roles. In some roles it is necessary to augmentthe basic thrust produced by the engine in the "dry" mode by burning additional fuel downstream of the engine's turbines, utilizing the unburntoxygenintheexhaustgasestosupport combustion. This mode is known as reheat or after-burning. During reheat it is necessary to increase the area of the nozzle to accommodate the increased volume of gases so as notto impair the efficient functioning ofthe engine.In other roles such as supersonic cruise, it is desirable to varythe geometry ofthe exhaust nozzle ofthe enginefrom a convergent geometryfor subsonic speed to a configuration having an increased area throat (compared to that required during the "dry" mode or at subsonic cruise) formed between a convergent and divergent part of the nozzle-often referred to as a con-di nozzle.

There are times during the flight envelope of an aircraft when reheat is not required and when the prime requisite is to reduce the infra red emission of the exhaust plume and thereby reduce or avoid detection by heat seeking missiles directed towards the aircraft.

These missiles usually detectthe infra red radiation ofthe hot exhaust gas plume and once the plume is located home in on the hot parts of the engine to destroy the aircraft.

There is a need for a nozzle design that not only caters for dry and reheat modes of operation, but also enables one selectively to reducetheinfra-red emission ofthe engine.

An objectofthe present invention isto provide a variable geometry nozzle which is capable of use both in the dry and reheat modes of operation and also capable of reducing the infra red emission of the hot exhaust gas plume.

The invention as claimed enables one to vary the geometry of the nozzletocopewith dry and reheat modes of operation by moving the flaps and enables one to reduce the infra red emission by opening additional air inlets which admit ambient airto cool and shield the hot exhaust plume.

The nozzle of the present invention may be installed on a fixed jet pipe or on a vectorablejet pipe.

Furthermore, the nozzle ofthe present invention may be installed on the vectorablefront nozzles of an engine such as the Rolls-Royce Limited Pegasus engine which discharge cold or reheated by-pass air.

The invention will now be described, by way of an example, with reference to the accompanying drawings in which: Figure 1 illustrates schematically a gas turbine aero-engine incorporating three vectorable nozzles.

For convenience only one ofthe nozzles is shown constructed in accordance with the present invention.

Figure 2 illustrates in more detail a sectional elevation of part ofthe rear nozzle ofthe engine shown in Figure 1, Figure 3 shows in greater detail part ofthe set offirst flaps of the nozzle of Figure 2, Figure 4 shows in greater detail the ejector nozzle constructed in accordance with the present invention, and, Figure 5 shows a modification to the clamshell doors of the nozzle shown in Figure 4, Referring to Figure 1 there is shown schematically a gasturbine aero engine 10 ofthe by-pass type. The engine comprises in flow series, an axial flow low pressure compressor 11, an axial flow high pressure compressor 12, a combustion chamber 13, a high pressureturbine 14which drivesthe H.P. compressor 12, a low pressure turbine 15which drives the L.P.

compressor 11, and a jet pipe 16 terminating in a vectorablevariable area nozzle 17.

The L.P. compressor 11 supplies compressed airto the H.P. compressor 12 and to a plenum chamber 18 which forms part of the by-pass duct 19 and which terminates in two vectorable nozzles 20. The nozzles 20 are mounted in bearings 25 for rotation through an angle of approximately 1100 about an axis 21.

Additional combustion equipment 22 is provided in the plenum chamber 18 so that additional fuel can be burnt in the air stream ejected through the nozzles 20 to increasethe thrust. Too enable the engine to run efficiently the nozzles 17 and 20 are provided with variable-area, variable-geometry outlets and are constructed in accordance with the present invention.

For convenience the invention will be more particularly described with reference to nozzle 17 but it is to be understood that the mechanism forvarying the area and geometry is similarforall the nozzles 17 and 20, and may also be used with nozzles forfixed jet pipes.

The nozzle 17 is of the type in which a scarfed rotatable duct 17(a) is mounted in bearings 23 on the downstram end ofthejet pipe 16, and a second scarfed duct 17(b) is mounted in bearings 24 for rotation in the opposite direction to that of duct 17(a).

The bearing 24 is, in turn, rotatable bodily on trunnions 26 which extend transverse to the axis of duct 17(b). This type of nozzle is described in more detail in co-pending U.S. Patent Application No.

376,388 entitled Vectorable Nozzl es fo r Tu rbo- machines naming Gary Frank Szuminski and Thomas John Jones as the inventors. In operation the bearing 24 is rotated about the axis of the trunnions 26 by means of a screwjack (shown schematically by the numeral 50) which pushes on the brackets that support the bearing 24 in thetrunnions 26. As the bearing 24 is swung aboutthe axis ofthe trunnions 26 the ducts 17(a) and 17(b) are rotated in opposite directions by means of a motor 51 and sprockets 52, 53, chain drives 54,55 and flexible drive shaft 56 as explained in the above-mentioned U.S. patentapplication.

The nozzle 17 has at its downstream end a duct 17(c) which is carried by the fixed race ofthe bearing. It is this duct 17(c)that is provided with the mechanism for varying the geometry and area of the outlet of the nozzle 17 in accordance with the present invention, as shown in Figures 2 and 3.

Referring to Figures 2 and 3, the mechanism for varying the geometry and area of the outlet nozzle comprises an annular member 28which is translat- able axially and on which is carried three sets of flaps aswill be described below. The member28 is mounted to slide axially insidethe downstream end duct 17(c) and the member 28 comprises an annular hollow box structure which has face 29 extending in a direction transvereto the axis 30 of the duct 17(c).

Pressurised gas flowing through duct 17(c) acts on face 29 to urge the member 28 rearwards.

The member 28 slides inside the bore of the duct 17(c) and a heat shield liner 31 is provided to protect the duct 17(c) and the member 28from the hot gases flowing through the noule when the reheat combus tor32inthejetpipe is ignited.

The member 28 is supported on axially extending tubes 33 which carry an annular cam-ring assembly 34.

Located in at least some ofthe tubes 33 is a lead screw 35 of a screwjackwhich engages a nut 36 (of the recirculating ball type) fixed to the member 28.

Rotation ofthe lead screws 35 by a motor drive through gearboxes pushes and pulls Is the member 28 to-andfro in the axial direction.

The cam ring assembly 34 comprisestwo polygonal frameworks of tubes 34(a) interconnected by which a plurality of cams 37 facing inwards (only one of which is shown). The cams 37 are equispaced around the axis 30.

A set of first primary flaps 38 is pivotally attached to the member 28. Each first primaryflap 38 is povitally attached at its upstream end to the downstream inner circumferential end ofthe member 28 and has a web 39 projecting from its outerfacing side. The web 39 carries a cam follower 40, in the form of a roller, that engages one ofthe cams 37to define and vary the attitude oftheflap 38 relativeto member28 as member 28 is moved in axial directions.

The flaps 38 comprise a hollow structure with spaced walls which are made from a carbon-carbon material such as Pyrocarb (Registered US Trade Mark) material as manufactured by Hitco of USA). Pyrocarb materials comprise a carbon matrix in which is embedded a woven cloth ofcarbon fibres. The material is projected from oxidation either by overcoating itwith a non-oxidising protective layer or by impregnating silicon into it and converting the silicon to silicon carbide.

A second primary flap 43 is pivotal Iy attached at its upstream end ofthe downstream end of each first primary flap 38. Each flap 43 is a hollow structure of spaced carbon-carbon walls similar to flaps 38, and each flap 43 is provided with a lug 42 partway along its length.

Theflaps 38 are spaced apart circumferentially and each ofthe gaps between the flaps 38 is closed off by thin seal plate 41 (see Figure 3 which is a section through the hinge between flaps 38 and the member 28). The seal plates 41 are located on the inward-facing side oftheflaps 38 and are constrained from falling inwards by means of rollers 46that engage the outside surface of the flaps 43. The seal plates 41 accommodate different positions of the flaps 38 by sliding circumferentially.

A plurality of struts44are pivotally attached at one oftheirendsto a downstream outer circumference of the member 28. Each ofthe struts 44 is pivotally connected at its outer end to the tug 42 of one of the second flaps 38.

Here again, the second flaps 43 are spaced circumferential ly and the gaps between them are closed-off by thin carbon-carbon seal plates 45 that are pivotally attached attheirupstream end to the downstream end ofthe seal plates 41. The seal plates 45 are located on the inward-facing side of the flaps 43 and are constrained from falling inwards by rollers 46 which are mounted on flanges that projectthrough the gaps between flaps 43 to engagethe outer surface ofthe flaps 43. The seal plates 45 allowthe flaps 43 to assume different positions where they define a convergent part ofthe nozzleto where they define a divergent part ofthe nozzle by sliding relative to the flaps 43. The seal plates 45 do not have lugs 42 and no struts 44 are connected to the seal plates 45.

A set ofthird flaps 47 made of a carbon fibre reinforced polymide material are provided on the member28. Each of thethird flaps 47 is pivotally attached at their upstream end to the downstream end ofthe member 28, and are pivotallyattached attheir downstream ends to the downstream end of one of the second flaps 38. The pivot 45 at the upstream end ofthethird flaps 47 locates in an elongated hole 46 in the member 28.

Theflaps47 overlap each otherto accommodate the different positions ofthe flaps 47.

In operation ofthe nozzle with the member 28 in the fully rearwards position shown in solid lines in Figure 2, the flaps 38 define a convergent part ofthe nozzle and theflaps 43 define a parallel of slightly divergent part of the nozzle with the throat area ofthe nozzle (in a radial plane ofthe pivotal connections between the flaps 38 and 43) at a minimum dimension. This configuration would be used for a subsonic dry maximum thrust mode of operation such as for take-off, or subsonic accelerations.

By pulling the member 28forwardsthe cam followers 40 move along the cams 37 and the flaps 38 define a parallel or slightly convergent part the nozzle (as shown with dotted lines) a maximum area throat, and flaps 43 define a divergent part of the nozzle with a maximum area exit atthe downstream ends of flaps 43. This configuration would be used for maximumthrustwith reheat or P.C.B. mode of operation.

As flaps 38 and 43 take up different positions the seal plates 41 and 45 slideto fill up the gaps between the respective flaps 38 and 43. AIso,theflaps 37 are moved to alter the boat-tail angle and thereby reduce base drag.

The gas loads on the flaps 38 and 43 and seal plates 41 and 45 aretransmitted backto thee member 28 and exert a netforce forwards (i.e. towards the jet pipe 16) on the member 28. Accordingly, by exposing the front face of the member 28to the pressurised gases flowing through the duct 17(c) the gases exert a rearward force on the member28thatpartlycoun- terbalancestheforward loads exerted on the member 28. This in turn reduces the forces required to move the member 28 in axial directions. The area of the front face 29 ofthe member can be chosen to achieve the optimum rearwards force on the member 28.

Clearly, at intermediate positions between those shown in solid and dotted lines in Figure 2various combinations of convergence and divergence with different throat areas can be obtained.

Referring to Figure 4 that duct 17(c) is provided with forwardly directed openings 59 spaced around its circumference. An axiallytranslatable hollow cylin- drical cover door 60 is provided to obturate the outer extremity of all the openings 59. A pair of frustohemispherical hollow clamshell doors 61 which picot about a transverse axis 62 of the duct 17(c), is provided upstream of the flaps 38 to close off the inner extremities ofthe openings 59 when the doors 61 are in a stowed position (shown in dotted lines).

When in the stowed position, the confronting surfaces 67 ofthe doors 61 definetherebetween part ofthe gas flow path through the nozzle 17. A motor 66 is provided to rotate the doors 61 in a forwards direction aboutthe axis 62 from the stowed position to a second position (ejector position) upstream ofthe openings 59. By moving the doors 61 to the ejector position, they uncover the openings 59 and simul taneouslythe front edges 68 of the doors form a dam that defines a reduced area throat for the gas flow through the nozzle immediately upstream ofthe openings 59. The confronting surfaces 67 ofthe doors also define a divergent part of a primary nozzle immediately downstream ofthis reduced area throat.

The resulting depression caused by the flow of gases downstream ofthethroat induces ambientairto flow into the nozzle through the openings 59to cool and shield the hot gas plume emitted by the nozzle.

When the doors 61 are deployed in the ejector position the member 28 is moved rearwardsto move the flaps 38 and thereby to increase the area of the throat of the secondary nozzle formed by the flaps 38 and 45 to cope with the increased airflow due to the ambient air induced to flow through the openings 59.

It will be seen that with the doors stowed, the effective nozzle for the engine is that defined by the flaps 38 but when the doors are in the ejector position the nozzle controlling thethermodynamic cycle oftheengine is thatformed by the doors 61.

The cover door 60 is supported concentrically relative to the bearing 24 by means of eightcircum- ferentially spaced pinion gears 63 which engage racks 64 on the inside circumference ofthe cover door 60.

The gears 63 are driven by means of a motor 65 which drives all the gears 63 via gearboxes and drive shafts (not shown) so that they rotate in unison to move the door60 axiallyto open and close the outer extremities ofthe openings 59.

The drivetothe gears 63 is synchronised with the drive to the clamshell doors 61 so that the door 60 is moved to open the openings 59 only when the clamshell doors 61 are moved to the ejector position.

In addition the drive to the mechanism that moves the member axially to vary the geometry ofthe nozzle is synchronised so thatwhen the clamshell doors 61 are moved to the ejector position the flaps 3 & re moved to increase the throat area defined by the flaps 38.

It cannot be stressed too strongly, that although the nozzle described above has been described in connection with a vectorable nozzle, the present invention is eminently suitable for use at the downstream end of a fixed jet pipe.

Referring to Figure 5, the throat area defined bythe up stream edges 68 ofthe doors 61 can be supplemented or modified to enhance ambient ejector air flow and mixing potential by providing openings 69 in each of the doors 61, the openings 69 are covered by shutters 70 on the inward facing face 67 of each door 61. These shutters are constructed to blow open when the doors 61 are in the ejector position and are held closed in the stowed position by the pressure ofthe gases acting on the shutters 70. Alternatively, the shutters 70 could be opened or closed by mechanical means.

From Figure 4 it will be seen that by reversing the motor 66 the doors 61 can be rotated in a downstream direction to a third position where they uncover the openings 59 and co-operate with the flaps 38 (when they are positioned in a convergent position).

An importantfeatureofthe present invention is that the clamshell doors 61 are provided atthe throat of the nozzle. That is to say that the doors 61 co-operate with the flaps 38 when they are deployed to form a convergent duct as would bethe case when the engine is operated inthe "dry" subsonic mode. The driveto the gears 63 is synchronised with the drive to the clamshell doors 61 so thatthe door 60 is moved to open the openings 59 when the clamshell doors 61 are moved to the reversed thrust position. In addition the drive to the mechanism that movesthe member 28 axially to vary the geometry of the nozzle is synchro- nised so thatthe clamshell doors 61 can be moved to the reverse thrust position only when the flaps 38 are in the convergent position (that is when the member 28 is pushed rearwards to its fullest extent and the engine is operating in the "dry" subsonic mode).

By locating the clamshell doors 61 atthe region of the throat ofthe nozzle and by using the flaps 38 to assist in forming part ofthe deflecting surface during thrust reverse mode, the clamshell doors 61 can be made with smaller and, therefore, are lighter and much easierto deploy. This is particularly important when a thrust reverser is required on a nozzle that can be vectored.

Claims (11)

1. An exhaust nozzle for a gas turbine aero-engine comprising a duct, a plurality of movable flaps for varying the geometry of the nozzle, one or more forwardly and outwardly directed openings located upstream of the flaps, and a pair of mutually confronting doors each of which is mounted for rotationaboutan axis extending transverseto the length of the duct, wherein the doors are located relative to the duct and the openings so that, in a first position, they obturate the openings and mutually confronting surfaces of the doors define therebetween part of the gas flow path through the nozzle, the doors being movable to a second position, upstream ofthefirstposition, where they uncoverthe openings, define, at their upstream ends, a reduced area throat for the gas flow path through the nozzle, and also define a divergent part of the gas flow path im mediately downstream of the said th roatthereby to reduce the preSsure downstream ofthe throat to induce ambient airthrough the openings into the gas flow path through the nozzle, and means are provided for moving the flapsto accommodate the increased gas flow through the nozzle when the said openings are uncovered.

2. A nozzle according to Claim 1 wherein the doors are movable to a third position, downstream of the first position, where the doors uncover the said openings and co-operate with the flaps, when the flaps are in a convergent position, so that the flaps, together with the doors, provide deflecting surfaces that redirect the flow of gases outthrough said openings.

3. A nozzle according to Claim 1 or Claim 2 wherein a second door means is provided to obturate an outer extremity ofthe or each opening.

4. A nozzle according to Claim 1 or Claim 2 wherein the means for moving the flaps comprises a translatable member movable in a direction extending along the length ofthe duct and theflaps are pivotally mounted attheir upstream end to the member.

5. A nozzle according to Claim 4wherein the translatable member is mounted to slide on axially extendingsupports and the supports carry an annular frameworkthatdefinesa plurality of axially extending cam surfaces spaced around the axis ofthe annular framework.

6. A nozzle according to Claim 5wherein the cam surfaces face inwards and each flap is provided, on its outer facing side, with the cam follower that cooperates with one of the surfaces.

7. A nozzle according to Claim 4wherein the flaps comprise an axisymmetric array offirstflaps and there is furtheer provided an axisymmetric array of second flaps each of which is pivotally mounted at its upstream end to the downstream end of the first flaps, and constraining means are provided for constraining the second flaps to assume a divergent position relative to the duct in at least one position of the second flaps.

8. A nozzle according to Claim 7 wherein the constraining means comprises a plurality of struts each of which is pivotally attached at one end to the axiallytranslating member and is pivotally attached at its other end to one ofthe second flaps.

9. Anozzle according to Claim 6wherein an axisymmetric array ofthird flaps are provided, each of the third flaps being pivotally connected at their downstream end to the downstream end of a second flap and being mounted at its upstream end on the said axially translating member.

10. A nonle according to Claim 7 wherein the axiallytranslatable member is a right circular cylindrical annular structure and thefirstflaps are pivotally mounted on aninnercircumferenceoftheannular member, andthethird flaps are pivotally mounted on an outer circumference ofthe annular member.

11. A nozzle according to Claim 1 or Claim 2 wherein the doors have openings in them which are covered by shutters which are opened when the doors are in the second position and are held closed when the doors are in thefirst and third positions.