CONFLUENCE STRUCTURE OF A PRIMARY FLOW AND A SECONDARY FLOW IN A BYPASS GAS TURBINE

Abstract

The invention relates to a confluence structure of an aircraft bypass turbine engine which comprises a confluence plate (13) with a downstream end (16) supported by a portion (20) that is movable in the direction of the axis (X) by a control mechanism (26 to 32) which can optionally be adjusted in flight. A mobile portion (22) of a sleeve (18) delimiting the secondary stream (10) on the outside, and an inner projection (25) of the outer casing (11) can also slide axially in certain embodiments. This provides a wide range of options for modifying the gas dilution and operating conditions of the engine.

Description

[0001] Description

[0002] Title: CONFLUENCE STRUCTURE OF A PRIMARY VEIN AND A VEIN

[0003] SECONDARY IN A DUAL-FLOW TURBOMACHINE

[0004] The subject of the invention is a confluence structure of a primary flow and a secondary flow, in a dual-flow turbomachine.

[0005] Finding an optimal thermodynamic cycle is a constant challenge for turbomachinery, particularly aircraft engines, and the solution varies depending on the flight regime. Traditionally, turbomachine design seeks to achieve a compromise between the requirements of different flight regimes. It is also important to emphasize that the inevitable margins of uncertainty between theoretical and actual operating conditions can further deviate the actual performance from optimal performance for each flight regime.

[0006] In the specific case of turbofan engines with a confluence of primary and secondary streams downstream of the flow, a parameter influencing the cycle characteristics is the engine's bypass ratio, which can be defined as the ratio of the secondary flow rate to the primary flow rate downstream of the low-pressure compressor. This ratio depends, in particular, on the conditions of the confluence of the two streams downstream of the low-pressure turbine, and especially on their cross-sections at this point. This cross-section governs the local gas pressures of the two streams and affects the air intake flow rates at the stream inlets. The confluence occurs at the trailing edge (downstream end) of a circular flange, called the confluence plate, which separates the primary stream from the secondary stream downstream of the low-pressure turbine, and the streams join immediately afterward.The dilution rate therefore depends on the shape of this confluence plate and its position relative to other concentric ferrules, which define the sections of the veins at the point of confluence.

[0007] The object of the invention is to be able to adjust the turbomachine's bypass ratio as needed, possibly during flight. The fundamental means used is the ability to vary the position of the end of the confluence plate in the axial direction of the turbomachine, by means of an adjustment mechanism for a portion of the confluence plate that is made movable relative to the other components of the surrounding structure.

[0008] US documents 4072008 A, FR 2399547 Al and FR 2296769 Al describe various arrangements where the dilution rate or pressure at the confluence of two turbomachine lines can be adjusted by changing the confluence conditions, for example the opening section of one of the lines.

[0009] In general form, the invention thus relates to a confluence structure of a primary and a secondary flow, surrounding the primary flow of an aircraft engine, a confluence plate separating the primary and secondary flows and having a shape of revolution and a downstream end (according to a direction of gas flow in the primary and secondary flows in an axial direction of the engine), the secondary flow 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 relative to a complementary part, fixed relative to the outer casing, of said confluence plate, the movable part comprising the downstream end, the primary flow and the secondary flow joining only downstream of said downstream end.

[0010] By moving the end of the confluence plate, the sections of at least one of the veins can be modified in a chosen way, in an environment where the other walls that delimit them can have variable radii, and in particular be conical.

[0011] A more complex embodiment of the invention involves the existence of another part of revolution, called a liner, surrounded by the casing and defining an annular outer channel with it. In this channel flows an external gas stream, diverted from the secondary flow and protecting the outer casing from the hot gases downstream of the confluence. This liner extends, in particular, downstream of the downstream end of the confluence plate and has a nozzle (an upstream end, according to the direction of gas flow).In conventional designs, when present, it is a single unit fixed relative to the outer casing; however, according to the invention, it can also be provided with an extension, referred to here as a ferrule, comprising a portion fixed within the outer casing and a portion movable on the fixed portion, similarly to that provided for the confluence head: the movable portion comprises the upstream end and slides in an adjustable manner in the axial direction relative to the fixed portion of said ferrule. This arrangement will allow the inlet geometry of the annular external channel and the proportion of the secondary vein flow that enters it, and especially the complementary portion that contributes to the dilution of gases from the primary vein, to be varied according to the configuration of the surrounding structure.

[0012] This effect is particularly noticeable if the casing includes a radially inward protrusion in the secondary vein, and the movable part of the ferrule is movable in positions where the upstream end is upstream of the protrusion, and in positions where the upstream end is downstream of the protrusion, since the inlet section of the annular external channel then varies very strongly.

[0013] In a preferred embodiment, allowing easy control of the movement of the confluence plate or the moving part of the ferrule, at least one of these moving parts is moved by adjusting devices extending outside the outer casing: these devices can then be controlled by mechanisms external to the turbomachine, which are relatively easy to design and arrange.

[0014] Such adjustment devices may consist of pivoting pins, radially supported on the outer casing, fitted with cams bearing on edges of the confluence plate or the ferrule.

[0015] 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 there by ball joints.

[0016] This arrangement ensures good isostaticity of the mounting of the relevant fixed parts, maintaining their concentricity to the turbomachine axis while allowing free expansion through the sliding of the ball joints within the sleeves. Furthermore, the ball joints on the spindles minimize leakage where they pass through the ferrules.

[0017] The concentricity of the moving part relative to the fixed part, for at least one of the confluence plate and the ferrule, can easily be maintained by springs compressed between the fixed and moving parts in the radial direction, but allowing them to slide, or by mechanisms including, for example, rollers, or lubricated surfaces. Fine adjustment over a long centering distance between the two fixed and moving parts may nevertheless suffice, possibly with the addition of a solid lubricant, such as a coating.

[0018] In a particularly preferred embodiment, because it allows an easy transition 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 the ferrule) is connected to the corresponding moving part by at least one curved plate comprising an end tangent to the fixed part, an end tangent to the moving part, and an intermediate curved 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 moving part, being divided into angular sectors by axially oriented slots.

[0019] According to a common practical design, at least one of the moving parts of the confluence plate and the moving part of the shell is traversed by radial extension elements of the structure, with oblong bores that can be covered by seals. Such radial elements may include afterburner fuel supply rods.

[0020] The various aspects, characteristics and advantages of the invention will now be described in more detail by means of the following figures, which illustrate some preferred embodiments, given purely for illustrative purposes:

[0021] Fig. 1 is a general view of a double-flow turbomachine;

[0022] Fig. 2 is an enlargement of the confluence zone;

[0023] Fig. 3 illustrates the structural characteristics of the invention in the confluence zone

[0024] Fig. 4 is another view, in perspective, of the confluence zone;

[0025] Fig. 5 represents a connection between a fixed part and a moving part of the structure; Fig. 6 represents a centering means between a fixed part and a moving part;

[0026] Fig. 7 represents a first state of the device;

[0027] Fig. 8 a second state;

[0028] Fig. 9 a third state;

[0029] Fig. 10 illustrates another, more general embodiment of the invention.

[0030] Figures 1 and 2 depict a turbojet engine that conventionally comprises a rotor 1, rotating around a central axis X, and a stator 2 arranged around the rotor 1. The rotor 1 and the stator 2 share the blades of a low-pressure compressor 3, a high-pressure compressor 4, a high-pressure turbine 5, and a low-pressure turbine 6, which are arranged successively along the X-axis. The space between the rotor 1 and the stator 2 is occupied by a flow 8, a single flow upstream, which divides into a concentric primary flow 9 and secondary flow 10 downstream of the low-pressure compressor 3. The single flow 8 and the secondary flow 10 are enclosed by an outer casing 11. The primary flow 9 and the secondary flow 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 gas flow relative to the central axis 1 - is a confluence plate 13.The high-pressure compressor blades 4 and turbines 5 and 6 are present in the primary duct 9, as well as a combustion chamber 14. And the turbojet may include a fan 15 upstream of the low-pressure compressor 3, whose blades extend into the unit portion 8 of the duct.

[0031] Figure 2 shows that the confluence plate 13 is the only structure separating the streams 9 and 10 downstream, and therefore also serves to delimit them. Streams 9 and 10 join downstream of a downstream end, or trailing edge 16, of the confluence plate 13. The primary stream 9 is further delimited at its radially inner edge by a cone 17 of the rotor 1, which narrows downstream; the secondary stream 10 is delimited at its radially outer edge by the outer casing 11, referred to here as the diffusion casing; another internal part of revolution in the outer casing 11, called sleeve 56, extends however in front of the section of the secondary vein 10 downstream of a spout 50 (upstream end): it delimits an external annular channel or channel under sleeve 51, which intercepts a portion of the flow of the secondary vein 10 and removes it from the confluence and dilution of the gases of the primary vein 9.The air passing through the channel under the sleeve 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 ratio and the thrust of the turbomachine then depend in particular on the ratio of the cross-sections of the primary stream 9 and the secondary stream 10 at the point of 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, and between the confluence plate 13 and the sleeve 56 on the other, which determine the gas pressures in the streams and the flow rate passing through the channel under the sleeve 51.

[0032] The more particularly original features of the invention will now be described with reference to Figures 3 and 4. The confluence plate 13 consists of a fixed portion 19 and a movable portion 20, which slides relative to the fixed portion 19 in the direction of the X-axis, extends it downstream, and includes the trailing edge 16. Both the fixed portion 19 and the movable portion 20 of the confluence plate 13 are continuous sheets. The movable portion 20 is at least partially cylindrical. More precisely, it is cylindrical where it covers the fixed portion 19 by sliding over 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 in a similar way, with a fixed part 21 and a movable part 22, sliding relative to the previous one in the direction of the X axis, but which extends it upstream and includes the beak 50. When this arrangement of the movable part of the ferrule 18 is adopted, the outer casing 11 advantageously carries a step 25 on its inner face, slightly upstream of the trailing edge 16, and which corresponds to a slight constriction of the cross-section of the secondary vein 10.

[0033] Pins 26 and 27 allow the movable part 20 of the confluence plate 13, and the movable part 22 of the ferrule 18, to be moved respectively relative to the corresponding fixed parts 19 and 21. These pins 26 and 27 pass through the outer casing 11 and each includes an outer end 28, bearing on a boss 29 of the outer casing 11, a ball joint 30 projecting around them at the point where the pins 26 and 27 pass through the fixed parts 19 and 21, and a cam 31 at their inner end, which bears 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 allows the edges 32 and 33, and therefore the moving parts 20 and 22, to be pushed back in the axial direction when the pins 26 and 27 are rotated.The control mechanism for the pins 26 and 27 is not shown in detail, but it is not critical to the implementation of the invention and may consist of known devices with a control ring surrounding the outer casing 11 and connecting rods, each of which is articulated 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 the pins 26 and 27 pivot. Such mechanisms are common in the art for the similar application of modifying the angular position of certain fixed blade stages having pivots through the outer casing. Other mechanisms could also be proposed: cable-driven, rack and pinion-driven, or actuator-driven, for example.It is preferable to be able to control the mechanisms in flight to adjust the confluence conditions at any time, but the invention could also include mechanisms adjustable only on the ground. Alternatively, assemblies of fixed pins, carrying the ball joints 30, and pins rotating within the former and carrying the cams 31 could be used.

[0034] The pins 26 and 27 are arranged around the turbojet in two circular groups. They help maintain the concentricity of the fixed parts 19 and 21 with the engine axis. They also allow for thermal expansion, thanks to the sliding provided by the adjustment of the ball joints 30 in 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 areas with significant clearances that form annular housings 34 and 35, which accommodate the ends of the pins 26 and 27, the cams 31, and the rims 32 and 33. The housings 34 and 35 are bordered by corrugated portions connecting the fixed parts 19 and 21 to the moving parts 20 and 22.These portions include, for the confluence plate 13, an outer portion 36 belonging to the fixed part 19, through which the pins 26 pass and which ends downstream on a cylindrical end 37 fitted around the movable part 20 with little play; and an inner portion 38 fixed to the fixed part 19 at an upstream end and whose 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 plate 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 includes an outer portion 41 corrugated, through which the pins 27 pass and which terminates upstream on a cylindrical end 42, fitted 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 abrupt variation of slope, to preserve good quality of flow in the primary vein 9 (for the inner portion 38), the secondary vein 10 (for the outer portion 36 and the inner portion 43), or the channel under the liner 51 (for the outer portion 41).

[0035] Radial structural elements can extend through the confluence plate 13 or the ferrule 18. This is the case here with flame-holding arms 44, which pass through the ferrule 18, and afterburner rods 45, which pass through the confluence plate 13. If these flame-holding arms 44 or rods 45 must 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 allow it to slide. These oblong holes 46 or 47 can be covered by sliding or deformable seals to cover their opening and prevent leaks.

[0036] The concentricity of the moving parts 20 or 22 within the fixed parts 19 or 21 can be ensured by springs such as arched bridges 48 (Figure 6), having ends 49 fixed to one of the parts and a curved central portion 55 bearing against 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 with little clearance from them, their central portions 55 then sliding on the moving parts 20 and 22, which are cylindrical at this point. Concentricity could also be ensured by rollers, solid lubricant coatings, or wear-resistant layers.

[0037] The annular step 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 bores 54 also cut through the outer casing 11 and extending in the direction of the X axis. This arrangement allows for greater variation of the opening section and the ease of access to the channel under the sleeve 51 than with the movable portion 22 of the ferrule 18 alone.

[0038] Figures 7, 8, and 9 illustrate the possible configurations of the device. The movable parts 20 and 22 and the step 25 can all be moved independently, and the device may even consist of only the movable part 20 fitted to the confluence plate 13. By moving this movable part 20 around the cone 17, it is possible to vary the cross-section of the primary vein 9 at the point of confluence. Furthermore, by moving the movable part 22 of the ferrule 18 and possibly the step 25, it is possible to position the movable part 22 in front of the step 25 or away from it, thereby either hindering or facilitating the passage of air into the channel under the sleeve 51 and thus varying the airflow of the secondary vein 10, which contributes to dilution upon reaching the confluence, even though the movable parts 20 and 22 are both cylindrical.

[0039] But the movement of the mobile part 22 of the ferrule 18 acts mainly on the confluence, independently of the channel under the liner 51, by modifying the position of the trailing edge 16 in relation to the curved inner portion 43 of the mobile part 22 of the ferrule 18, that is to say the exit section of the secondary vein 10 at the confluence when the curved part 43 slides around the trailing edge 16.

[0040] It is therefore possible to adjust the cross-sections of the primary 9 and secondary 10 ports at the confluence, and of the channel under the liner 51 at its inlet, thus influencing the gas pressures at the confluence, the flow rate of the secondary 10 port at the confluence, and the gas temperature. This implies that the engine thrust—which depends primarily on the gas temperature—and fuel consumption—which depends heavily on the extraction rate, i.e., the pressure ratio of the ports—can be regulated. The invention does not require afterburning. The step 25 is optional, and the liner 56 can be completely fixed, or even omitted, by accepting a lesser degree of benefit from the invention.

[0041] Figure 7 illustrates a state where the movable portion 20 of the confluence plate 13, the movable portion 22 of the ferrule 18, and the step 25 are pushed downstream. The curved inner portion 43 is downstream of the trailing edge 16, and the liner channel 51 is moderately open. The cross-sections of the primary vein 9 and secondary vein 10 are large at the confluence, and the flow through the liner channel 51 is moderate.

[0042] Figure 8 differs from Figure 7 in that the movable portion 22 of the ferrule 18 is pushed upstream. This allows for much stronger occlusion of the channel under the liner 51, which increases the flow of the secondary vein 10 that contributes to dilution. Furthermore, the curved portion is then upstream of the trailing edge 16, which reduces the cross-section of the secondary vein 10.

[0043] Figure 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 step 25 upstream, which reduces the cross-section of the primary vein 9 and opens the channel under the liner 51 as much as possible, thus reducing the flow of the secondary vein 10 which participates in 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 dilution.

[0044] Intermediate states can also be considered.

[0045] Figure 10 illustrates another important embodiment of the invention, in accordance with previous remarks: the afterburner pencils 45, the flame-catching arms 44, the sleeve 56 and the step 25 are absent, as are the means for controlling the 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. Dilution control is achieved solely by the pins 26, to modify the cross-section of the primary stream 9 at the confluence, the cross-section of the secondary stream 10 being unchanged with a cylindrical outer casing 19.The advantageous features of the invention, set out in connection with the preceding figures, are found in this embodiment of the invention, which is also of at least as great importance as the previous one since it corresponds to the more general and more frequent situation where after combustion is not required.

Claims

Demands 1. Confluence structure of a primary and a secondary flow, surrounding the primary flow, of an aircraft engine, a confluence plate (13) separating the primary flow (9) and the secondary flow (10) and having a shape of revolution and a downstream end (16), according to a direction of gas flow in the primary and secondary flows in an axial direction (X) of the engine, the secondary flow 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) relative to a complementary part (19), fixed relative to the outer casing, of said confluence plate, the movable part (20) comprising the downstream end (16), the primary flow (9) and the secondary flow (10) joining only downstream of said downstream end (16).

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

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

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 sheet and of the movable part (22) of the ferrule is moved by adjustment devices (26, 27) extending out of the outer casing.

5. Confluence structure according to claim 4, characterized in that the adjustment devices are pivoting pins (26, 27) bearing radially on the outer casing and provided with cams (31) bearing on rims (32) of the moving 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 sheet and of the fixed part (21) of the ferrule, being centered therein 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 ferrule, 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 abrupt change of slope.

9. Confluence structure according to claims 2 and 8, characterized in that a said curved portion (43) belongs to the ferrule (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 sheet (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 spring 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 sheet and of the movable part of the ferrule is traversed by radial extension elements (44, 45) of the structure, through oblong bores (46, 47) covered with sealing gaskets.

14. Confluence structure according to claim 13, characterized in that said elements comprise afterburner fuel supply pencils (45) or flame-catching arms (44).

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

16. Dual-flow turbomachine equipped with the confluence structure according to any one of the preceding claims.