GB2156004A - Thrust modulation device for a gas turbine engine - Google Patents

Abstract

An exhaust duct thrust modulation device includes a converging/diverging nozzle, a plurality of reverse flow cascade vanes 30 in a frame 28, and a plurality of blocker flaps 32 each pivotally connected to the nozzle 24. The frame is connected at its aft end to the nozzle and is slideably connected at its forward end to the exhaust duct 16. The nozzle and frame are thereby axially translatable with respect to the engine so that in a forward stowed position, substantially all of the engine exhaust flow stream passes through the exit area and in an aft deployed position the blocker flaps cooperate with the cascades to direct a portion of the flow stream through the cascade vanes. The nozzle may be variable and the converging section 40a,b of the nozzle cooperates with the blocker flap to increase the flow stream through the cascade vanes when the reverser is deployed. <IMAGE>

Description

SPECIFICATION Thrust modulation device This invention relates generally to gas turbine engine exhaust systems and, more particularly, to variable area exhaust nozzles and thrust reversers for use therein.

BACKGROUND OF THE INVENTION The exhaust nozzle of a gas turbine engine provides thrust for propulsion by imparting a high velocity to exhaust gases. This thrust is substantially opposite to the direction of the gas flow stream exiting the nozzle. In order to provide maximum thrust, a converging/diverging (CD) nozzle may be advantageously employed. The CD nozzle has a cross-sectional area that decreases in a downstream direction to a position of minimum area, called the throat, and then increases to the downstream end of the nozzle. The primary converging section of the nozzle is designed to accelerate the flow subsonically until it reaches the throat, at which point it reaches a sonic velocity. The secondary diverging section subsequently allows controlled expansion of the flow stream to a supersonic velocity.

Improved performance can be achieved through the use of a variable geometry exhaust nozzle to modulate thrust. A variable geometry nozzle permits the size of the throat area to be changed in response to changes in engine power setting and flight conditions such as air speed and altitude. Typically, the variable area nozzle is opened during augmented takeoff and closed at an appropriate altitude in order to obtain necessary cruise thrust.

A typical variable geometry nozzle includes a number of annularly positioned flaps and seals. Each flap has a converging member and diverging member. Seals are located to cover the spaces between adjacent flaps. Flaps and seals collectively define the converging and diverging sections of the nozzle.

Another feature of some exhaust systems is a thrust reverser which further modulates thrust. A thrust reverser is a means to reverse the direction of flow of the jet stream so as to produce a reverse thrust. Many different kinds of reversers are known, but most use the basic principle of blocking the aft flow stream and diverting it laterally and forwardly. One type of reverser uses cascade vanes located upstream of the exhaust nozzle in the exhaust duct with various means to block the aft flow stream and uncover the cascades.

While such reversers have been used successfully, they present several problems. First, openings must be provided in the exhaust duct liner, casing, and outer fairing with cover doors and actuating means for such doors.

These openings and associated mechanisms add to the weight and complexity of the exhaust system. In addition, the blocking mechanism used in conjunction with the cascades tends to be heavy due to the relatively large flow stream area required to be blocked.

In addition to the weight penalties of such exhaust systems, efficiency losses tend to be high due to the increased gas leakage path around the cascade cover doors. A further problem relates to reingestion of exhaust gases and reverse gas efflux impingement on the aircraft. The reingestion problem is caused by the reverse gas being sucked into the front of the engine. Aircraft impingement of such gases is due to the forward position of the reversed flow cascades relative to the airframe.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a new and improved thrust modulation device.

It is another object of the present invention to provide a lighter weight thrust reverser than was heretofore known.

It is yet another object of the present invention to provide a thrust reverser for a gas turbine engine which reduces the leakage path for the aft flow stream when the engine is in a forward thrust mode.

It is a further object of the present invention to provide a variable area converging/diverging nozzle wherein a primary flap of the nozzle provides a blocking function when in reverse mode.

It is yet a further object of the present invention to provide a reverser for a gas turbine engine which minimizes reingestion of reverse gas efflux.

It is still another object of the present invention to provide a variable area exhaust nozzle that allows full nozzle area modulation throughout all phases of forward and reverse thrust.

It is still a further object of the present invention to provide a thrust modulation device with redundant means for stowing a thrust reverser.

These and other objects of the invention, together with the features and advantages thereof, will become apparent from the following detailed specification.

SUMMARY OF THE INVENTION One form of the present invention comprises a thrust modulation device attachable to the downstream end of an exhaust duct of a gas turbine engine. The device includes a converging/diverging exhaust nozzle, a plurality of reverse flow cascade vanes, and a plurality of blocker flaps. The nozzle defines a flow stream exit area. The cascade vanes are contained within a frame with a forward and aft end. The aft end of the frame is connected to the nozzle and the forward end of the frame is slideably connectable to the exhaust duct. Each blocker flap is pivotally connected to the nozzle at a first location. The nozzle and frame are axially translatable with respect to the exhaust duct so that in a forward stowed position substantially all of the engine exhaust flow stream passes through the exit area.In an aft deployed position, the flaps cooperate with the cascade vanes to direct a portion of the flow stream through the cascade vanes.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic of a gas turbine engine with thrust modulation device according to one form of the present invention.

FIGURE 2 is a view of the thrust modulation device of Figure 1 taken along line 2-2 in Figure 1.

FIGURE 3 is a view of a reverser and blocker flap in a fully deployed position taken along line 3-3 in Figure 2.

FIGURE 3a is a view of the reverser and blocker flap of Figure 3 in a stowed position.

FIGURE 4 is a view of a reverser and variable area nozzle in a fully deployed position taken a!ong line 4-4 in Figure 2.

FIGURE 4a is a view of the reverser and variable area nozzle of Figure 4 in a stowed position.

FIGURE 5 is a view of the reverser cascade vanes from the direction of line 5 in Figure 3.

FIGURE 6 is a view showing greater detail of cascade vane rotation means.

DETAILED DESCRIPTION OF THE INVEN TION Figure 1 shows a gas turbine engine 1 2 with gas generator 14 and exhaust duct 1 6.

Attached to the downstream end 18 of exhaust duct 1 6 is thrust modulation device 20 according to one form of the present invention. Thrust modulation device 20 comprises exhaust nozzle 22 defining a flow stream exit area 24. Hot gases from gas generator 14 form flow stream 26 which is directed downstream by exhaust duct 1 6 and through exit area 24. Nozzle 22 is configured to impart a relatively high velocity to flow stream 26 to provide increased thrust to engine 1 2.

Thrust modulation device 20 further comprises a frame 28 containing a plurality of reverse flow cascade vanes 30 and a plurality of blocker flaps 32. As will be discussed more fully hereinafter, nozzle 22 and frame 28 are axially translatable with respect to exhaust duct 1 6 so that in a forward stowed position substantially all of the engine exhaust flow stream 26 passes through exit area 24. In an aft deployed position, as shown in Figure 1, blocker flaps 32 cooperate with cascade vanes 30 to direct a portion of flow stream 26 through cascade vanes 30.

Figures 2, 3, and 4 show thrust modulation device 20 in greater detail. Figure 4 shows one set of exhaust flaps 34 of exhaust nozzle 22. Figure 3 shows one set of exhaust seals 36 for exhaust nozzle 22. It should be clear to a person skilled in the art that a variable area converging/diverging exhaust nozzle comprises a plurality of exhaust flaps and seals.

Such flaps 34 and seals 36 overlap, as shown in Figure 2, thereby preventing leakage of exhaust gases therebetween during the different stages of engine operation. In the embodiment shown, exhaust seals 36 are concentrically located with respect to exhaust flaps 34 and are slideably connected thereto by retaining means 38.

Exhaust nozzle 22 is converging/diverging.

Thus, nozzle 22 comprises a primary converging section, a secondary diverging section, and an outer section. Primary converging section includes primary flap 40a, shown in Figure 4, and primary seal 40b, shown in Figure 3. Secondary diverging section includes secondary flap 42a, shown in Figure 4, and secondary seal 42b, shown in Figure 3.

Outer section includes outer flap 44a, shown in Figure 4, and outer seal 44b, shown in Figure 3. The term "section" as used herein will refer to both corresponding flap and seal.

As best shown in Figure 4, exhaust nozzle 22 includes a four-bar linkage which comprises primary flap 40a, secondary flap 42a, compression link 46, and aft frame member 48. These four members are joined at pivot points 50a, 50b, 50c, and 50d.

Exit area 24 of exhaust nozzle 22 may be varied by nozzle actuator 52. As shown in Figure 4a, nozzle actuator 52 is fixedly attached at a first end 54 to exhaust duct 1 6 and is in slideable contact at a second end 56 with exhaust nozzle 22. Second end 56 includes annular actuation ring 57 which follows cam surface 58. Flow stream 26 provides a first force 60 on nozzle 22 for increasing exit area 24. Nozzle actuator 52 provides a second force for reducing exit area 24.

Thus, as second end 56 of nozzle actuator 52 expands axially aft translating ring 57 from position 64a to position 64b, nozzle 22 pivots outwardly about point 50d. Secondary flap 42a is articulated outwardly by the action of compression link 46 to increase exit area 24.

Similarly, as second end 56 of actuator 52 is drawn axially forward, second force 62 on cam surface 58 acts to decrease exit area 24.

Thrust modulation device 20 also includes frame 28 containing a plurality of reverse flow cascade vanes 30. As shown in Figures 4 and 5, frame 28 includes forward end or frame member 66, aft end or frame member 48, and a plurality of axially directed stringers 68 joining ends 66 and 48. In the embodiment shown, ends 66 and 48 may take the form of 360 rings. Aft end 48 is connected to nozzle 22 at pivot points 50c and 50d. Forward end 66 is slideably connectable to exhaust duct 1 6 by bearing means 70. As shown in Figure 5, adjacent stringers 68 together with forward and aft rings or ends 66 and 48 define a frame section 72. It will be clear that a number of such frame sections 72 may be coaxially formed with respect to exhaust nozzle 22.Depending upon the particular engine and aircraft needs, at least one of the frame sections 72 will contain openings with a plurality of reverse flow cascade vanes. However, it may not be necessary to have vanes in all of the sections thus formed.

Thrust modulation device 20 further includes a plurality of blocker flaps 32, as shown in Figures 3 and 3a. Each flap 32 is pivotally connected to nozzle 22 at a first location 74. Blocker flap 32, shown in forward thrust mode in Figure 3a, is stowed in recess 76 of secondary seal 42b. It may be possible in an alternative configuration to have blocker flaps 32 contained in secondary flap 42a.

Blocker flaps 32 are progressively deployed into exit area 24 in response to the axially aft translation of nozzle 22. This is achieved by blocker deployment mechanism 78 which includes first link 80, second link 82, third link 84, and fourth link 86. First link 80 is pivotally connected at one end to blocker flap 32 and at its opposite end to one end of link 82.

Link 82 is pivotally connected at its other end to secondary seal 42b. Link 84 is pivotally connected at one end to end 85 of second link 82 and pivotally connected at its other end 88 to fourth link 86. End 88 is constrained to slide within track 90 on aft frame member 48. End 92 of fourth link 86 is similarly constrained to slide within track 94 which is connected to exhaust duct 1 6.

In order to allow exit area 24 to vary, as shown in Figure 4a, without deployment of blocker flaps 32, certain geometric similarities between seals 36 and flaps 34 may be necessary. For a given exit area, the axial and radial location of point 50b must coincide with end 85. Similarly, the axial and radial locations of point 50c and end 88 as well as point 50a and location 74 must coincide.

Thrust modulation device 20 also includes reverser actuator 96 with a first end 98 being fixedly attached to exhaust duct 1 6 and a second end 100 being connected to aft frame member 48 of frame 28. Reverser actuator 96 is effective for axially translating nozzle 22 and frame 28 with respect to exhaust duct 1 6. In a forward stowed position, shown in Figure 3a, substantially all of the engine exhaust flow stream passes through exit area 24. In an aft deployed position, shown in Figure 3, blocker flaps 32 cooperate with cascade vanes 30 to direct a portion 27 of flow stream 26 through said cascade vanes.

A feature of the present invention is the location of the exhaust duct liner 1 24 relative to cascade vanes 30 and frame 28. In prior art thrust reversers, the liner must be interrupted at the reverser. As shown in Figures 4 and 4a, liner 1 24 is uninterrupted to its aftmost end 1 26 at which point nozzle 22 separates from exhaust duct 1 6.

In operation, as reverser actuator 96 axially translates nozzle 22 and frame 28 in an aftward direction, blocker deployment mechanism 78 initially translates aftwardly in fixed relation to nozzle 22 with end 92 of fourth link 86 being drawn axially aft along track 94. When nozzle 22 is partially translated, fourth link end 92 will contact stop 102 of track 94. Further translation of nozzle 22 will draw end 88 of third link 84 axially forward relative to track 90 thereby moving second link 82 and first link 80 so as to deploy blocker flap 32 into the flow stream 26. It will be clear to a person skilled in the art that in order to vary the rate at which blocker flap 32 is deployed, it will be necessary to change the length of tracks 90 and 94 and the lengths of links 80, 82, and 86.

Figure 3a shows cascade vanes 30 in frame 28 in a generally radial or thrust spoil position. Thus, as nozzle 22 translates aft, but before blocker flaps 32 are deployed, a portion of flow stream 26 may escape radially thereby modulating or reducing the amount of forward thrust. When nozzle 22 reaches a partially deployed position wherein blocker flap 32 starts being deployed into exit area 24, rotation means 104, shown in Figure 6, progressively rotate vanes 30 forward in response to the axially aft translation of nozzle 22.Rotation means 104 comprises a unison bar 106 pivotally connected to a point near the radially outer end 1 30 of each cascade vane 30, a connection link 107 pivotally connected at opposite ends to unison bar 106 and pull link 108, respectively, a pull link 108 pivotally connected at one end to connection link 107, and a collar 110 connected to link 108 through which fourth link 86 may slide. A stop 11 2 on link 86 is adapted to contact collar 110 at a predetermined point of the axially aft translation of nozzle 22. By pivotally connecting the radially inner ends 1 32 of each vane 30 to stringer 68, pull link 108 will rotate vanes 30 forward.

As best seen in Figure 3, the deployment of blocker flaps 32 decrease flow stream 26 through exit area 24. As blocker flaps 32 are progressively deployed, the converging section of nozzle 22 provides a blocking function thereby cooperating with blocker flaps 32 to increase the flow of exhaust gases through cascade vanes 30. The converging section thereby serves the dual function of increasing the velocity of flow stream 26 when in forward thrust mode and blocking the exhaust flow when in reverse mode.

The flow area of converging/diverging nozzle 22 may be varied by nozzle actuator 52.

The range of motion of nozzle 22 by stroking nozzle actuator 52 is shown in Figure 4a. In order to translate nozzle 22 for deployment of blocker flaps 32 and opening of cascade vanes 30, reverser actuator 96 must be stroked. It should be clear, however, that nozzle actuator 52 must be stroked at the same rate as reverser actuator 96 in order for thrust modulation device 20 to properly operate. If it is desired to change exit area 24 as nozzle 22 is being translated, a differential motion between nozzle actuator 52 and reverser actuator 96 is required.

In order to have nozzle actuator 52 and reverser actuator 96 stroke at the same rate, it is necessary to have synchronizing means.

Such means will keep the second end 114 of reverser actuator 96 fixed with respect to second end 56 of nozzle actuator 52. Thus, nozzle 22 and frame 28 may be axially translated without varying the area of nozzle 22.

One type of synchronizing means which may be used includes a motion transducer affixed to reverser actuator 96 with an electrical feedback signal to nozzle actuator 52.

Another feature of the present invention includes redundancy for returning nozzle 22 to a forward stowed position in the event of a failure of reverser actuator 96. Such redundancy is shown in Figure 4 by limiting means 11 6 for limiting the axially forward translation of nozzle actuator 52 relative to nozzle 22 and frame 28. Limiting means 11 6 may include a physical stop attached to aft frame member 48. In the event that reverser actuator 96 should fail when nozzle 22 is deployed, nozzle actuator 52 and limiting means 116 are cooperatively effective for translating nozzle 22 and frame 28 into the forward stowed position.

A further feature of the present invention is means for limiting the axially aft translation of nozzle actuator 52. Such means include a jam nut 1 20 on the shaft of actuator 52 and a physical stop 1 22 attached to aft frame member 48. In the event that nozzle actuator 52 receives an inadvertent signal to overstroke beyond position 64b, nut 1 20 will contact stop 1 22 thereby preventing such overstroke.

The invention having been thus described, numerous modifications may be undertaken which are still within the scope of the present invention. For example, the number, size, and placement of frame section 72 containing cascade vanes 30 may be appropriately located so as to reduce aircraft impingement of the reverse gas efflux. In addition, further control of thrust modulation may be achieved by providing separate actuation means in the form of covered doors or actuated louvers for cascade vanes 30. In this manner, by actuating only selected sections of cascade vanes 30, greater modulation of thrust or even some degree of thrust vectoring is possible. The actuation means in such alternative embodiments would be operable independently of the axial translation.

It will be clear to those skilled in the art that the present invention is not limited to the specific embodiments described and illustrated herein. Rather, it applies equally to thrust modulation devices with fixed area nozzles. Furthermore, the mechanical linkages shown described herein are exemplary only and numerous alternative mechanical linkages are possible.

It will be understood that the dimensions and proportional and structural relationships shown in the drawings are by way of example, and these illustrations are not to be taken as the actual dimensions or proportional structural relationships used in the thrust modulation device of the present invention.

Numerous modifications, variations, and full and partial equivalents can be undertaken without departing from the invention as limited only by the spirit and scope of the appended claims.

Claims (11)

1. A thrust modulation device attachable to the downstream end of an exhaust duct of a gas turbine engine comprising: a converging/diverging exhaust nozzle defining a flow stream exit area; a frame with forward and aft ends, containing a plurality of reverse flow cascade vanes, said aft end being connected to said nozzle and said forward end being slideably connectable to said exhaust duct; and a plurality of blocker flaps, each flap being pivotally connected to said nozzle at a first location; wherein said nozzle and frame are axially translatable with respect to said exhaust duct so that in a forward stowed position substantially all of the engine exhaust flow stream passes through said exit area and in an aft deployed position said flaps cooperate with said cascade vanes to direct a portion of said flow stream through said cascade vanes.

2. A device, as recited in claim 1, wherein said frame aft end is pivotally connected to said nozzle and said exit area of said nozzle is variable.

3. A device, as recited in claim 2, further comprising: a nozzle actuator for varying the area of said nozzle, said nozzle actuator having first and second ends and being fixedly attached at said first end to said exhaust duct and in slideable contact at said second end with said nozzle; wherein said flow stream provides a first force on said nozzle for increasing said area and said actuator provides a second force on said nozzle for reducing said area.

4. A device, as recited in claim 1, further comprising: linkage means for progressively deploying said blocker flaps into said flow stream in response to the axially aft translation of said nozzle, thereby decreasing said flow stream through said exit area.

5. A device, as recited in claim 1, further comprising: rotation means for progressively rotating said vanes forward in response to the axially aft translation of said nozzle.

6. A device, as recited in claim 4, wherein said nozzle includes: a primary converging section; and a secondary diverging section pivotally joined to said primary section substantially at said first location; wherein said converging section cooperates with said blocker flaps to increase the flow of said exhaust gases through said cascade vanes as said blocker flaps are progressively deployed.

7. A thrust modulation device attachable to the downstream end of an exhaust duct of a gas turbine engine comprising: a frame including a forward ring, aft ring, and a plurality of axially directed stringers joining said rings, wherein two adjacent stringers and forward and aft rings define a frame section, and wherein at least one of said sections contains a plurality of reverse flow cascade vanes; a converging/diverging exhaust nozzle defining a flow stream exit area; and a plurality of blocker flaps, each flap being pivotally connected to said nozzle; wherein said forward ring is slideably connectable to said exhaust duct and said aft ring is connected to said nozzle so that said nozzle and frame are axially translatable with respect to said engine; wherein substantially all of the engine exhaust gas passes through said exit area when said nozzle and frame are in a forward stowed position, ana said flaps cooperate with said cascade vanes to direct a portion of said flow stream through said cascade vanes when said nozzle and frame are in an aft deployed position.

8. A device, as recited in claim 7, further comprising: cascade actuation means for opening or closing said cascade vanes in at least one of said sections, wherein said means are operable independently of said axial translation thereby providing thrust vectoring.

9. A thrust modulation device attachable to the downstream end of an exhaust duct of a gas turbine engine comprising: an exhaust nozzle with a flow stream exit area; a frame with forward and aft ends, containing a plurality of reverse flow cascade vanes, said aft end connected to said nozzle and said forward end slideably connected to said exhaust duct; a plurality of blocker flaps, each flap being pivotally connected to said nozzle at a first location; a reverser actuator with first and second ends, said first end being fixedly attached to said exhaust duct and said second end being connected to said frame;; wherein said reverser actuator is effective for axially translating said nozzle and frame with respect to said exhaust duct, so that in a forward stowed position substantially all of the engine exhaust flow stream passes through said exit area and in an aft deployed position said flaps cooperate with said cascade vanes to direct a portion of said flow stream through said cascade vanes; and a nozzle actuator with first and second ends for varying the area of said nozzle, said nozzle actuator being fixedly attached at said first end to said exhaust duct and in slideable contact at said second end with said nozzle; wherein said flow stream provides a first force on said nozzle for increasing said area and said nozzle actuator provides a second force on said nozzle for reducing said area.

10. A device, as recited in claim 9, further comprising: synchronizing means for keeping said second end of said reverser actuator fixed with respect to said second end of said nozzle actuator so that said nozzle and frame may be axially translated without varying the area of said nozzle.

11. A device, as recited in claim 9, further comprising: limiting means for limiting the axially forward translation of said nozzle actuator means relative to said nozzle and frame; whereby said nozzle actuator and limiting means are cooperatively effective for translating said nozzle and frame into said forward stowed position.

1 2. A thrust modulation device substantially as hereinbefore described with reference to and as illustrated in the drawings.