GB1605428A

GB1605428A - Flow control systems for variable cycle gas turbine engines

Info

Publication number: GB1605428A
Application number: GB2938375A
Authority: GB
Inventors: Harald Alan Scarce; Roy Simmons
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1975-07-12
Filing date: 1975-07-12
Publication date: 2003-03-12
Anticipated expiration: 1991-07-12

Description

(54) FLOW CONTROL SYSTEMS FOR VARIABLE CYCLE GAS TURBINE ENGINES (71) We, ROLLS-ROYCE LIMITED a British Company of 65 Buckingham Gate, London SW 1 E 6AT formerly Rolls-Royce (1971) Limited a British Company of Norfolk House, St. James's Square, London, SW 1 Y 4JR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The present invention relates to variable cycle gas turbine engines and to flow control system therefore which enable the change-over from one cycle to another to be made.

According to the present invention a variable cycle gas turbine engine comprises compressor means having an upstream part with an outlet duct, a downstream part with an inlet passage, an auxiliary inlet duct and an auxiliary outlet passage, the auxiliary outlet passage having an annular part which surrounds the upstream part of the coiiipi-essor, and a flow control systeiii for providing two cycles of operation of the engine, wherein said flow contro I system includes a change-over valve having at least one circumferential array of pivotable flaps and means for pivoting the flaps from a first position, which provides a first one of said cycles of operation and wherein the delivery of the upstream part of the compressor means is directed into the downstream part thereof, to a second position, which provides the second one of the said cycles of operation and wherein the valve directs the delivery of the upstream part of the compressor through an angle of at least 90 into the auxiliary outlet passage and directs flow from the auxiliary inlet duct into the downstream part of the compressor means.

The invention is particularly concerned with a variable cycleV/STOL engine which supplies compressed air, and/or combustion products to forward and rearward directionally-variable nozzles, either on the engine itself or on an airframe in which the engine is mounted, and said forward nozzles are disposed upstream of the valve means to receive flow from the auxiliary outlet passage.

One form of change-over valve for use ill a variable cycle engine of the present invention comprises inner and

outer casings defining a substantially annular passageway communicating between the upstream and 9 C, C. downstream parts of the compressor means, axially spaced circumferential rows of apertures in one of said casings communicating respectively with the auxiliary inlet duct and the auxiliary outlet passage, and flap means which are pivotable to selectively cover and uncover said apertures and to block said annular passageway depending on the cycle of operation required from the engine.

The flap means may comprise a row of circumferentially spaced flaps extending axially of the casing to cover both of the axially spaced rows of apertures, each flap being pivotable about a transverse axis between its axial ends to uncover both rows of apertures and block the passageway simultaneously.

Alternatively, there may be a separate row of flaps for covering each row of apertures and further flaps or vanes ZD for blocking the flow between the outlet duct of the upstream part of the compressor and the inlet passage of the downstream part of the compressor.

Examples of the invention will now be more particularly described with reference to the accompanying drawings in which :- Fig. 1 is a diagrammatic part-sectional elevation of a variable cycle engine of the present invention,

Fig. 2 is a detailed section of parts of the compressors and valve means of the engine of Fig. 1, t z : l Fig. 3 is a pictorial view of the valve casing, Fig. 4 is an enlarged side elevation of that part of the flap which blocks the flow through the valve, Fig. 5 is an enlarged plan view of the part of the valve shown in Fig. 4, Fig. 6 is a pictorial sectional view on the axial end of one of the flaps, Fig. 7 is an enlarged view of the actuating linkage and overcentre mechanism, and Fig. 8 is a sectional elevation of an alternative valve arrangement.

Referring to the drawings, in Fig. 1 there is shown a dual-cycle vectored thrust engine mounted in an aircraft. t C, The top of the figure is sectioned to show the engine inside the fuselage. zn The engine comprises a first compressor I mounted in a duct and arranged to receive air from a pair of intakes z : l on the side of the aircraft fuselage.

Downstream of, and in flow series with, the first compressor are a change-over valve 2, a second compressor 3, combustion equipment 4, a high pressure (HP) turbine 5, a low pressure (LP) turbine 6 and a pair of vectorable propulsion nozzles 7.

The flow of air through the compressor means is governed by a flow control system which includes the changeover valve 2 and the various flaps and doors as described below.

On the fuselage of the aircraft, which is represented by line 10, are a series of doors 11 which close off auxiliary inlets 12 which lead directly to the valve 2. The inlets merge together into a single annular duct 13, (Fig. 2) at the valve face and duct 13 constitutes theauxiliary inlet duct. The doors I 1 may be ofthe"blow-in"type which automatically open inwards when the pressure in the duct 13 is reduced below a certain level, or may be selectively operable by a suitable mechanical, pneumatic or hydraulic device under the control of a pilot's lever.

Also on the fuselage 10 is a plenum chamber 15 which is fed with air from thevalve2 and on which are supported a pair of vectorable nozzles 16. The plenum chamber is fed from the valve through an auxiliary outlet passage

17.

Referring now to Figs. 2 and 3, the valve has a first annular inlet 20 which communicates with an outlet duct 22 leading from the downstream end ofthe first compressor, and a second annular inlet 24 which communicates with the auxiliary annular inlet duct 13. The valve also has a first annular outlet 26 at the downstream end of the valve, which communicates with an annular inlet passage 28 leading to the second compressor, and a second annular outlet 30 which communicates with the auxiliary outlet passage 17.

The change-over valve itself comprises a plurality of flaps 32 in an annular passageway 33. The flaps are circumferentially spaced apart and are pivoted about a transverse axis tangential to the outer wall of the passageway, which axis passes through the flap at a point 34 near the m id-length ofthe flap. A total of nine flaps is provided but clearly the number is a matter of design expediency. Each flap is of such size as to be able to completely close apertures 36 and 38 in the outer wall of the passageway in one mode of operation, referred to as the closed position, and to be able to block the flow through the passageway 33 in the other mode of operation referred to as the open position.

The inner and outer walls together with the side walls of the passageway 33 are formed integrally as one casting as can be seen from Fig. 3. The apertures 36 and 38 are rectangular in shape and aperture 38 which receives ambient air from the auxiliary intake passage is greater in area than the aperture 36 which communicates with

the auxiliary outlet duct. The casting has flanges 40 and 42 at each end forthe attachment of the ducting form ing C, ZD the various inlet and outlet passages and ducts described, and has an integral flange 44 to which the flaps 32 are z : l pivoted.

Since a part 31 of each of the flaps 32 has to close the passageway 33 in the open position of the flaps, the sides of those parts of the flaps must seal against the side walls of the passageway in this position (which is shown in the full lines of Fig. 2). Therefore, because of the angle of the flaps in this position the part 31 of each flap is madetrapeziodal in shape and is provided with a seal along its side edges to make sealing contact at all radii with the radial side-walls. Seals are also provided on the axial ends of the flaps to seal the apertures 36 and 3 8 when the valve is in the closed position.

In order thatthe trapeziodal parts 3] of the flaps can close the apertures 38 they are provided with closure plates 40 (Figs. 4 and 5) which are spring loaded by springs 42 to lie over the surface of the flaps at the sides of the parts dz and are pivotably mounted by pivots 44 on the flaps. The closure plates are sized to form seals with the sides of the apertures 38 when the valve is in the closed position but pivot outwardly to rest on the surfaces of the side walls of the passageway when the valve is in the open position. Figure 4 shows one of the closure plates 40 on a flap in both the closed and open positions of the valve in thetop and bottom views of the drawing respectively. Sealing surfaces 46 and 48 are provided where the closure plates contact the edge of the flap part 31 and a shoulder at the radially outer extremities of the side walls. Figure 5 shows the shapes of the flaps and the closure plates and the position ofthe hinges and Figure 6 shows seals 50 and 52 at the axial ends ofthe flap parts 31 for sealing againstthe outer wall ofthe passageway in the closed position and for sealing againstthe inner wall of the passageway in the open position respectively.

Actuation of the flaps is effected by means of at least two circumferential1y spaced actuating rods 54 which in turn are operated by any known suitable hydraulic, pneumatic, electrical or mechanical device, for example an air motor driven screw jack, and the actuating links are connected to the flaps through overcentre mechanisms 56. Figure 7 shows the actuating system and overcentre mechanism in greater detail. Each overcentre mechanism comprises triangular plates 60 pivoted by a fixed pivot 62 at one corner to the auxiliary inlet ducting, and pivotally connected to the actuating rod 54 via a link 55, and to a link 64 on the flap part 31 by pivots 66 and 68 and 69 respectively.

In the closed position of the flap the I ink 64 is substantially vertical, the triangular plates 60 are in the broken line position shown and the actuating rod 54 is fully extended. Due to the different areas of the flap exposed to compressor delivery air in the passageway on opposite sides ofthe pivot34, the flap is pressure biassed into the closed position and wil1 remain in that position in the event of failure of the actuating system. The pressure z : l balancing also reduces actuator loads when the flap is moved between its positions.

To move the flap to its open position, the actuator rod is retracted and the triangular plates 60 rotate anticlockwise about pivot 62 to the full tine position. The movement of the plates is arranged to be such that the

reaction line from the flap to the plates passes overcentre and the gas pressure on the flap thus tends to maintain the flap in the open position should the actuation system fail with the flaps in this position.

It can be seen therefore that the above described flow control system provides the engine with two cycles of operation. In the first, with the valve in the closed position, air compressed by the first compressor I is passed directly into the second compressor 3 to provide a high pressure supply to the combustion equipment 4 and turbines 5,6. The exhaust from the turbines passes out of the rear nozzles 7 in a high speed rearwardly directed jet giving an aircraft in which the engine is mounted a supersonic capability. The auxiliary inlets 12 and the front vectorable nozzles 16 may be closed to reduce drag during this cycle of operation. In the second cycle of operation the valve is set in the open position and air compressed by the first compressor 1 is directed through the apertures 3 6 by the valve and into the front vectorable nozzles 16. At the same time the second compressor

3 draws air in through the auxiliary inlets 12 via the auxiliary inlet duct 13, and this air passes through the t y combustion equipment 4 and turbines 5, 6, to produce a low velocity jet. The low velocity jet from the rear

nozzles 7 combined with the low velocity coidjet from the front nozzles 16 produces a higher mass flow at lower velocity which produces sufficient thrust for take-off and low speed flight with reduced noise.

A further embodiment wh ich is a modification to the above-described valve is shown in Fig. 8, those parts wh ich are common to both embodiments being given the same reference numerals. The flow control valve comprises at each of several stations around the compressor two hinged flaps 70, 7] and a pivoting flap or vane 72. The apertures 3 8, 36 in the outer wall of the passageway 33 leading respectively to the auxiliary inlet duct 13 and the auxiliary outlet passage 17, are closed or opened by movement ofthe flaps, and the flow through the passageway 33 is closed simultaneously with the opening of apertures 38, 36 by turning the vanes 72.

The two flaps 70, 71 are actuated by actuating rods 54 as described in relation to the embodiments of Figs. 1 to 6. In this case however, the operation of the two rows of flaps must be synchronised and the rod 54 acts on a first ring 74 which is connected to all of the first row of flaps 70 by links 75, and the first ring is connected by means of a push-rod 76 to a second ring 73 which connects with each flap 71 in the second row by means of links 77.

The vanes 72 are operated by an actuator 78 which, simultaneously with the actuation of rods 54 produces rotation of a ring 80 which is attached by pivoting links 82 to the radially inner ends of the vanes.

In operation with the flaps 70, 71 in the open position as shown, the vanes 72 block the flow through the passageway 33 so that air compressed by the first compressor 1 is directed by flaps 71 to the auxiliary outlet passage 17 through which it is conveyed to forward vectorable nozzles upstream of the valve. The second

compressor 3 draws air in from the auxiliary inlet duct 13, only part ofwhich is shown, the remainder form ing part of the aircraft fuselage. This cycle of operation produces the high mass flow at lower pressures and temperatures, as explained above, for take-off and operation near airfields.

In the second cycle, the flaps 70 and 71 block the apertures 38, 36 in the outer wall of the passageway 33, and the vanes 72 are pivoted to allow air compressed by the first compressor I to pass to the second compressor 3, to provide a high velocity gas efflux from the rearvectorable nozzles for supersonic operation of the aircraft.

In this closed position the rod 54 is arranged to have moved sufficiently that the rings 73 and 74 have passed the centres of the flaps and the links 75 and 77 go just beyond the vertical position. By this means the gas

pressures on the flaps are passed through the links 75 and 77 into the rings which carry the loads in hoop tension.

Seals 80 are provided for sealing the apertures when the flaps are in the closed position.

Claims

WHAT WE CLAIM IS : 1. A variable cycle gas turbine engine comprising compressor means having an upstream part with an outlet duct, a downstream part with an inlet passage, an auxiliary inlet duct and an auxiliary outlet passage, the auxiliary outlet passage having an annular part which surrounds the upstream part of the compressor, and a flow control system for providing two cycles of operation of the engine, wherein said flow control system includes a changeover valve having at least one circumferential array of pivotable flaps and means for pivoting the flaps from a

first position, which provides a first one of said cycles of operation and wherein the delivery of the upstream part of the compressor means is directed into the downstream part thereof, to a second position, which provides the second one of the said cycles of operation and wherein the valve directs the delivery of the upstream part ofthe compressor through an angle of at least 90'into the auxiliary outlet passage and directs flow from the auxiliary inlet duct into the downstream part of the compressor means.
2. A variable cycle gas turbine engine as claimed in clai m I and in which the change-over valve comprises inner and outer casings defining a substantially annular passageway communicating between the upstream and downstream parts ofthe compressor means, axially spaced circumferentially rows of apertures in one of said

casings communicating respectively with the auxiliary inlet duct and the auxiliary outlet passage, and flaps which

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are pivotable to selectively cover and uncover said apertures and to block said annular passageway depending on the cycle of operation required from the engine.
3. A variable cycle gas turbine engine as claimed in claim 2 and in which a single circumferential row of flaps is used which extend axially of the casing to cover both of the axially spaced rows of apertures, each flap being tn pivotable about a transverse axis between its axial ends to uncover both rows of apertures and to block the passageway simultaneously.
4. A variable cycle gas turbine engine as claimed in claim 3 and in which the flaps are provided with pivoting z : l closure plates adapted to seal on the radial side-walls of the annular passageway when the flaps are in the closed position.
5. A variable cycle gas turbine engine as claimed in claim 2 and in which a separate row of flaps is provided for covering each row of apertures, and vanes are provided for blocking the annular passageway, actuating means being provided for simultaneously moving all of the flaps and vanes to control the flows through the compressor means according to the cycle of operation of the engine.
6. A variable cycle gas turbine engine as claimed in claim I and in which the auxiliary outlet passage is adapted to communicate with a pair of directionally variable nozzles disposed upstream of the valve on an airframe in which the engine is adapted to be mounted.
7. A variable cycle gas turbine engine as claimed in claim 1 wh ich includes a pair of directionally variable nozzles disposed upstream of the valve and with which the auxiliary outlet passage communicates.
8. A variable cycle gas turbine engine substantially as hereinbefore described with reference to Figures 1 to 7

or Figure 8 of the accompanying drawings. t : l