The subject of the invention is a confluence structure of a primary stream and a secondary stream, in a dual-flow turbomachine.

The search for an optimum thermodynamic cycle is a constant problem for turbomachines, in particular aircraft engines, and the solution of which varies according to the flight regime considered. It is traditionally sought to achieve a compromise between the requirements of the different flight regimes when designing the turbomachine. It should also be emphasized that the inevitable margins of uncertainty between the theoretical conditions and the real operating conditions of the machine can further distance, for each flight regime, the actual operation from the optimal operation.

In the particular case of dual-flow engines comprising a confluence of the primary and secondary streams downstream of the flow, a parameter intervening in the characteristics of the cycle is the rate of dilution of the engine, which can be defined as the ratio flow rate of the secondary flow on the flow rate of the primary flow downstream of the low pressure compressor; however, this rate depends in particular on the conditions of the confluence of the two veins downstream of the low pressure turbine, and in particular on their sections at this location, which governs the local pressures of the gases of the two streams and affects the admission flow rates of air at the entrance to the veins. The confluence takes place at a trailing edge (downstream end) of a circular shell, called the confluence plate, which separates the primary vein from the secondary vein downstream of the low pressure turbine, and the veins join just after. The dilution rate therefore depends on the shape of this confluence plate and its position relative to other concentric shells, which define the sections of the veins at the location of the confluence.

The object of the invention is to be able to adjust the bypass ratio of the turbomachine as required, possibly during flight. The fundamental means used is the possibility of varying the position of the end of the confluence plate in the axial direction of the turbomachine, by means of a mechanism for adjusting a

part of the confluence plate which is made mobile with respect to the other constituents of the surrounding structure.

The documents US 4072008 A, FR 2399547 Al and FR 2296769 Al describe various arrangements where the dilution rate or the pressure at the confluence of two streams of a turbomachine can be adjusted by modifying the confluence conditions, for example the section of opening of one of the veins.

In a general form, the invention thus relates to a confluence structure of a primary stream and a secondary stream, surrounding the primary stream of an aircraft engine, a confluence plate separating the primary stream and the secondary stream and having a shape of revolution and a downstream end (according to a direction of gas flow in the primary stream and the secondary stream in an axial direction of the engine), the secondary stream being limited externally in a radial direction of the engine by an outer casing, characterized in that the confluence plate has a movable part, sliding in an adjustable manner in the axial direction with respect to a complementary part, fixed with respect to the outer casing, of the said confluence plate, the movable part comprising the downstream end,the primary vein and the secondary vein joining only downstream of said downstream end.

By moving the end of the confluence plate, the sections of at least one of the veins can be modified in a chosen manner, in an environment where the other walls which delimit them can have variable radii, and in particular be conical.

A more complex design of the invention involves the existence of another part of revolution, called a jacket surrounded by the casing by delimiting an annular external channel with it, in which circulates an external flow of gas withdrawn from the secondary stream and protecting the outer hot gas casing downstream of the confluence. This jacket extends in particular downstream from the downstream end of the confluence plate and has a beak (an upstream end, according to said gas flow direction). It is unitary and fixed relative to the outer casing in the usual designs, when it exists; but it can also be provided, according to the invention, with an extension, called here shell, comprising a part fixed in the outer casing and a movable part on the fixed part, analogously to what is provided at the confluence head: the movable part comprises the upstream end, and slides in an adjustable manner in the axial direction with respect to the fixed part of said shroud. This arrangement will make it possible to vary, according to the configuration of the surrounding structure, the inlet geometry of the annular external channel and the part of the flow of the secondary vein which enters it, and especially the complementary part, which participates in the dilution. gases from the primary stream.

This effect is particularly noticeable if the casing includes a projecting projection radially inwards in the secondary stream, and the mobile part of the shroud is mobile in positions where the upstream end is upstream of the projection, and in positions where the upstream end is downstream of the jump, since the inlet section of the annular outer channel then varies very greatly.

In a preferred embodiment, allowing easy controls of the movement of the confluence plate or of the movable part of the ferrule, at least one of these movable parts is moved by adjusting devices extending outside the outer casing : these devices can then be controlled by mechanisms external to the turbomachine, relatively easy to design and to arrange.

Such adjustment devices may consist of pivoting pins, bearing radially on the outer casing, provided with cams resting on the edges of the confluence plate or of the ferrule.

If necessary, the pivoting pins can pass through sleeves of at least one of the fixed part of the confluence plate and the fixed part of the ferrule, being fitted therein by ball joints.

Such an arrangement guarantees good isostaticity of the assembly of the fixed parts concerned, by making it possible to maintain their concentricity with the axis of the turbomachine, but also to expand freely by the sliding of the ball joints in the sleeves. And ball joints on the pins help minimize leakage where they pass through ferrules.

The concentricity of the movable part with respect to the fixed part, for at least one of the confluence plate and the shell, can for its part easily be maintained by springs compressed between the fixed part and the movable part in the radial direction, but allowing their sliding, or by mechanisms comprising for example rollers, rollers, or lubricated surfaces. A fine adjustment on a long centering, between the two fixed and mobile parts can nevertheless suffice, with possibly the addition of a solid lubricant, a coating for example.

In a particularly preferred embodiment, since it allows an easy transition and without loss of flow efficiency between the different positions of the moving parts, the fixed part (of at least one of the confluence plate and of the shell) is connected to the corresponding movable part by at least one curved sheet comprising an end tangent to the fixed part, an end tangent to the movable part, and a curved intermediate part tangent to each of the ends; the intermediate part and at least one of the ends, which is sliding either on the fixed part or on the movable part, being divided into angular sectors by slots in the axial direction.

According to an important construction in practice, at least one of the movable part of the confluence plate and of the movable part of the shroud is crossed by radial extension elements of the structure, at oblong holes which can be covered by seals sealing. Such radial members may include afterburner fuel rods.

The various aspects, characteristics and advantages of the invention will now be described in more detail by means of the following figures, which illustrate certain preferred embodiments thereof, given purely by way of illustration:

Fig. 1 is a general view of a turbofan engine;

Fig. 2 is an enlargement of the confluence zone;

Fig. 3 illustrates the structural features of the invention in the confluence zone

Fig. 4 is another view, in perspective, of the confluence zone;

Fig. 5 shows a connection between a fixed part and a mobile part of the structure;

Fig. 6 represents a centering means between a fixed part and a mobile part;

Fig. 7 represents a first state of the device;

Fig. 8 a second state;

Fig. 9 a third state;

Fig. 10 illustrates another, more general embodiment of the invention.

FIGS. 1 and 2 represent a turbojet which conventionally comprises a rotor 1, rotating around a central axis X, and a stator 2 disposed around rotor 1. Rotor 1 and stator 2 share the blades of a low compressor pressure 3, a high pressure compressor 4, a high pressure turbine 5 and a low pressure turbine 6 which follow one another along the axis X. The space between the rotor 1 and the stator 2 is occupied by a vein 8, unitary upstream, and which is divided into a primary vein 9 and a secondary vein 10 concentric downstream of the low pressure compressor 3. The unitary part 8 of the vein and the secondary vein 10 are surrounded by a outer casing 11. The primary stream 9 and the secondary stream 10 are separated from each other by an intermediate casing 12,the downstream part of which - in this description, "upstream" and "downstream" refer to the direction of flow of the gases with respect to the central axis 1 - is a confluence plate 13. The blades of the high pressure compressor 4 and of the turbines 5 and 6 are present in the primary stream 9, as well as a combustion chamber 14. And the turbojet engine can comprise a fan 15 upstream of the low pressure compressor 3, the blades of which extend in the unitary portion 8 of the vein.And the turbojet engine can comprise a fan 15 upstream of the low pressure compressor 3, the blades of which extend in the unitary portion 8 of the stream.And the turbojet engine can comprise a fan 15 upstream of the low pressure compressor 3, the blades of which extend in the unitary portion 8 of the stream.

Figure 2 shows that the confluence plate 13 is the only structure separating the veins 9 and 10 downstream, and that it therefore also serves to delimit them. The veins 9 and 10 join downstream of a downstream end, or trailing edge 16 of the confluence plate 13. The primary vein 9 is further delimited at its radially inner edge by a cone 17 of the rotor 1, tapering downstream; the secondary stream 10 is delimited at its radially outer edge by the outer casing 11, here called the diffusion casing; another part of revolution inside the outer casing 11, called sleeve 56, however extends in front of the section of the secondary stream 10 downstream of a spout 50

(upstream end): it delimits an annular outer channel or channel under jacket 51, which intercepts a portion of flow from the secondary stream 10 and subtracts it from the confluence and dilution of the gases from the primary stream 9. The air passing through the under-jacket channel 51 serves to protect the outer casing 11 from the heat of the combustion gases downstream of the confluence. The nozzle 50 extends here, upstream of the trailing edge 16. The dilution rate and the thrust of the turbomachine then depend in particular on the ratio of the sections of the primary stream 9 and of the secondary stream 10 at the location of the confluence, which is a function of the differences in radii A and B between the cone 17 and the confluence plate 13 on the one hand, the confluence plate 13 and the jacket 56 on the other hand,

The more particularly original arrangements of the invention will now be described in connection with FIGS. 3 and 4. The confluence plate 13 consists of a fixed part 19 and a movable part 20, sliding with respect to the fixed part 19 in direction of the X axis, and which extends it downstream and includes the trailing edge 16. The fixed part 19 and the movable part 20 of the confluence plate 13 are both continuous plates. The mobile part 20 is at least partially cylindrical. It is more precisely cylindrical at the places where it covers the fixed part 19 can be covered by sliding on it; it may have a different shape, conical for example, further downstream, in the portions adjacent to the trailing edge 16. The sleeve 56 is extended upstream by a ferrule 18 constructed of

Pins 26 and 27 make it possible to respectively move the movable part 20 of the confluence plate 13, and the movable part 22 of the ferrule 18, relative to the corresponding fixed parts 19 and 21. These pins 26 and 27 pass through the outer casing 11 and each comprise an outer end 28, resting on a boss 29 of the outer casing 11, a ball joint 30 projecting around them at the place where the pins 26 and 27 pass through the parts fixed 19 and 21, and a cam 31 at their inner end, which rests on circular edges 32 or 33 of the moving parts 20 and 22. The cams 31 are circular and eccentric with respect to the axis of the pins 26 and 27 , which makes it possible to push the flanges 32 and 33, and therefore the movable parts 20 and 22, in the axial direction when the pins 26 and 27 are turned. The control mechanism of pins 26 and 27 is not shown in detail, but it is not critical for the implementation of the invention and can consist of known control ring devices surrounding the outer casing 11 and connecting rods, each of which is hinged to the control ring and to a respective pin 26 or 27: by rotating the ring around the outer casing 11 by a motor, the inclination of the connecting rods in the angular direction of the outer casing 11 varies, and pins 26 and 27 rotate. Such mechanisms are common in the art for the resembling application of modifying the angular pitch of certain fixed vane stages provided with pivots passing through the outer casing. Other mechanisms could also be proposed: cable, rack and pinion, with an actuator for example. It will be preferred to be able to control the mechanisms in flight in order to adjust the confluence conditions at any time, but the invention would also encompass mechanisms that can be adjusted only on the ground. As a variant, one could use assemblies of fixed spindles, carrying ball joints 30, and spindles rotating in the previous ones and carrying cams 31.

Pins 26 and 27 are distributed around the turbojet engine in two circular groups. They contribute to maintaining the concentricity of the fixed parts 19 and 21 with the axis of the motor. However, they allow their thermal expansion, thanks to the sliding offered by the adjustment of the ball joints 30 in the sleeves 52 radiating from the fixed parts 19 and 21. The fixed parts 19 and 21 and the moving parts 20 and 22 have overlapping regions with large clearances which constitute annular housings 34 and 35, where the ends of the pins 26 and 27, the cams 31 and the edges 32 and 33 are housed. The housings 34 and 35 are limited by corrugated connecting portions of the fixed parts 19 and 21 to the moving parts 20 and 22. These portions comprise, for the confluence plate 13,

cylindrical and fitted around the mobile part 20 with little play; and an inner portion 38 fixed to the fixed part 19 at an upstream end and of which a downstream end 39 is cylindrical and slides on the movable part 20 upstream of the pins 26; this inner portion 38 may consist, as shown in Figure 5, of a sheet provided with longitudinal slots 40 which divide it into petals, at the downstream end 39 and the intermediate curved region at the ends, giving it sufficient flexibility so that it rubs without significant effort on the movable part 20 and maintains a good seal of the primary vein 9 at the connection between the fixed and movable parts 19 and 20. The fixed part 21 of the ferrule 18 also comprises an outer portion 41 corrugated, crossed by the pins 27 and ending upstream on a cylindrical end 42, adjusted with little play around the movable part 23; and an inner portion 43 is shaped on the movable part 22. These portions 36, 38, 41 and 43 therefore generally comprise two cylindrical ends, and a corrugated or curved region connecting the ends without sudden variation in slope, to preserve good quality of the flow in the primary vein 9 (for the interior portion 38), the secondary vein 10 (for the exterior portion 36 and the interior portion 43), or the channel under the jacket 51 (for the exterior portion 41).

Radial structural elements can extend through the confluence plate 13 or the shroud 18. This is the case here with flame holder arms 44, which cross the shroud 18, and post-combustion rods 45 which cross the confluence plate 13. If these flame holder arms 44 or these rods 45 have to pass through the movable part 20 or 22, the latter is provided with oblong holes 46 or 47 extending in the axial direction X to enable it to slide. These oblong holes 46 or 47 can be covered by sliding or deformable seals to cover their opening and not tolerate leaks.

The concentricity of the moving parts 20 or 22 in the fixed parts 19 or 21 can be ensured by springs such as bridges 48 (FIG. 6) of arcuate shape, having ends 49 fixed to one of the parts and a middle portion 55 curved resting on the other part. Such bridges 48 can be mounted in particular at the ends 37 and 42 of the fixed parts 19 and 21, tangent to the moving parts 20 and 22 and spaced from them with little play, their middle portions 55 then sliding on the moving parts 20 and 22 , cylindrical at this location. Concentricity could also be ensured by rollers or rollers, coatings of solid lubricant or anti-wear layers.

The annular projection 25 can itself be slidably mounted in the outer casing 11, by providing it with pins 53 passing through the outer casing 11, which will allow them to be gripped by a control mechanism, and movable in oblong holes 54 also dug through the outer casing 11 and extending in the direction of the axis X. This arrangement makes it possible to vary more greatly the opening section and the ease of access to the channel under the jacket mobile 22 alone of the ferrule 18.

The other figures 7, 8 and 9 illustrate the steps that the device can take. The mobile parts 20 and 22 and the projection 25 can all be moved independently, and the device can also comprise only the mobile part 20 fitted to the confluence plate 13. By moving this mobile part 20 around the cone 17, it is possible to vary the section of the primary vein 9 at the point of confluence. And by moving the mobile part 22 of the ferrule 18 and possibly the projection 25, it is possible to place the mobile part 22 in front of the projection 25 or to move it away from it, so as to hinder or on the contrary favor the passage of the air in the channel under the jacket 51 and therefore to vary the air flow of the secondary vein 10 which participates in the dilution by reaching confluence,

But the movement of the movable part 22 of the ferrule 18 acts above all on the confluence, independently of the channel under the jacket 51, by modifying the position of the trailing edge 16 with respect to the curved inner portion 43 of the movable part 22 of the ferrule. 18, i.e. the outlet section of the secondary vein 10 at the confluence when the curved part 43 slides around the trailing edge 16.

It is therefore possible to act on the sections of the primary 9 and secondary 10 veins at the confluence, and of the channel under the jacket 51 at its entrance, therefore on the gas pressures at the confluence, the flow rate of the secondary vein 10 at the confluence, and the gas temperature. This implies that we can adjust the thrust of the engine - which depends above all on the temperature of the gases - and the fuel consumption - which depends a lot on the rate of extraction, that is to say on the pressure ratio of the veins. The invention does not imply that post-combustion is present. The projection 25 is optional, and the sleeve 56 can be completely fixed, or even absent, agreeing to benefit from the advantages of the invention to a lesser degree.

FIG. 7 thus illustrates a state where the movable part 20 of the confluence plate 13, the movable part 22 of the ferrule 18 and the projection 25 are pushed downstream. The curved inner portion 43 is downstream of the trailing edge 16, and the undersleeve channel 51 is moderately open. The sections of the primary 9 and secondary 10 veins are significant at the confluence, and the flow passing through the channel under the jacket 51 is moderate.

Figure 8 differs from Figure 7 in that the movable part 22 of the ferrule 18 is pushed upstream. This makes it possible to obstruct the channel under the jacket 51 much more strongly, which increases the flow rate of the secondary vein 10 which participates in the dilution. And the curved part is then upstream of the trailing edge 16, which reduces the section of the secondary vein 10.

FIG. 9 illustrates a state where the mobile part 20 of the confluence plate 13 is pushed upstream, and the mobile part 22 of the ferrule 18 is pushed downstream, and the projection 25 upstream, this which reduces the section of the primary stream 9 and opens the channel under the jacket 51 as much as possible, thus reducing the flow rate of the secondary stream 10 which contributes to the dilution, the curved inner portion 43 then being downstream of the trailing edge 16 The states of Figures 8 and 9 are therefore opposite states of the dilution.

Intermediate states can also be considered.

Figure 10 illustrates another important embodiment of the invention, in accordance with previous remarks: the post-combustion rods 45, the flame holder arms 44, the sleeve 56 and the projection 25 are absent, as well as the control means position of the latter and of the movable part 22 of the ferrule 18. The rest of the device is unchanged, except that the outer casing 11 is smooth and continuous downstream of the pins 26 and that the confluence plate 13 is devoid of the oblong holes 47. The control of the dilution is done only by the pins 26, to modify the section of the primary vein 9 at the confluence, the section of the secondary vein 10 being unchanged with an outer casing 19 cylindrical. The advantageous characteristics of the invention, exposed with regard to the preceding figures,

WE CLAIMS

1. Confluence structure of a primary vein and a secondary vein, surrounding the primary vein, of an aircraft engine, a confluence plate (13) separating the primary vein (9) and the secondary vein (10 ) and having a shape of revolution and a downstream end (16), according to a direction of gas flow in the primary stream and the secondary stream in an axial direction (X) of the engine, the secondary stream being limited externally, in a radial direction of the engine, by an outer casing (11), characterized in that the confluence plate (13) has a movable part (20), sliding in an adjustable manner in the axial direction (X) with respect to a part complementary (19), fixed relative to the outer casing, of said confluence plate, the movable part (20) comprising the downstream end (16),the primary vein (9) and the secondary vein (10) joining only downstream of said downstream end (16).

2. confluence structure according to claim 1, wherein a ferrule (18) is mounted in the outer casing (11) by delimiting an annular outer channel (51) therewith, the ferrule extending in particular downstream of the end downstream (16) of the confluence plate (13) and having an upstream end (50), according to the said direction of gas flow, characterized in that the shroud (18) has a movable part (22), comprising the upstream end sliding in an adjustable manner in the axial direction with respect to a complementary part (21), fixed with respect to the outer casing, of the said ferrule (18).

3. confluence structure according to claim 2, characterized in that the outer casing (11) comprises a projection (25) projecting radially inwards into the secondary vein (10), and the movable part of the shell is movable in positions where the upstream end (50) is upstream of the jump, and in positions where the upstream end (50) is downstream of the jump.

4. confluence structure according to any one of claims 1 to 3, characterized in that at least one of the movable part (20) of the confluence plate and the movable part (22) of the shell is moved by adjusters (26, 27) extending out of the outer casing.

5. confluence structure according to claim 4, characterized in that the adjustment devices are pins (26, 27) pivoting in radial support on the outer casing and provided with cams (31) resting on flanges (32) movable parts (20, 22).

6. confluence structure according to claim 5, characterized in that the pivoting pins pass through sleeves (52) of at least one of the fixed part (19) of the confluence plate and of the fixed part (21) of the ferrule, being centered there by ball joints (30) projecting around the pins.

7. confluence structure according to any one of claims 1 to 6, characterized in that the movable part is connected to the fixed part, for at least one of the confluence plate and the shell, by springs ( 48) compressed in the radial direction.

8. Confluence structure according to any one of claims 1 to 7, characterized in that at least one of the fixed and movable parts comprises a curved portion of radius variation without sudden variation in slope.

9. confluence structure according to claims 2 and 8, characterized in that a said curved portion (43) belongs to the shell (18), and the downstream end (16) is movable in front of the curved part and surrounded by the curved part.

10. confluence structure according to claim 9, characterized in that the curved portion (43) belongs to the movable part (22) of the ferrule (18).

11. confluence structure according to claim 8, characterized in that a said curved portion connects the fixed part (19) to the movable part (20) of the confluence plate (13), is integral with one of said parts and connects to the other of said parts by a cylindrical portion sliding on said other part, the curved portion and the cylindrical portion being divided into angular sectors by slots extending in the direction of the axis (X).

12. Confluence structure according to claim 3, characterized in that the projection is movable in the outer casing (11) in the direction of the axis (X), thanks to an adjustment mechanism (53, 54) comprising pins (53) passing through the outer casing and sliding in slots (54) also passing through the outer casing.

13. Confluence structure according to any one of claims 2 to 12, characterized in that at least one of the movable part (20, 22) of the confluence plate and of the movable part of the shell is crossed by elements (44, 45) of radial extension of the structure, through oblong holes (46, 47) covered with seals.

14. Confluence structure according to claim 13, characterized in that said elements comprise post-combustion fuel supply rods (45) or flame holder arms (44).

15. Confluence structure according to any one of the preceding claims, characterized in that the movable part (20) of the confluence plate is continuous and cylindrical at least at one overlapping portion of the complementary part (19).

16. Turbofan engine equipped with the confluence structure according to any one of the preceding claims.