Untitled record

Description

Title of the invention: VARIABLE SECTION FAN NOZZLE FOR TURBOFAN

FIXED GEOMETRY BASKET

[0001] The present invention relates to the field of aircraft gas turbine engines, in particular for a ducted turbofan, i.e. comprising a nacelle. A double-flow ducted turbofan can be defined generally as a gas turbomachine, driving at least one ducted fan of a fan module.

The air entering the engine is divided into two streams: a so-called "hot" stream entering the turbomachine, and a so-called "cold" stream passing through the fairing, also called the nacelle. The ratio between the volume of the cold and hot streams defines what is commonly called the "bypass ratio" of the engine.

[0002] The new generations of high bypass ratio turbofans also include a mechanical speed reducer connected coaxially between the turbomachine output shaft and the fan shaft. Typically, the speed reducer, or reducer, is used to transform the so-called fast rotation speed of the turbomachine shaft into a slower rotation speed for the shaft driving the fan, thus optimizing the rotation speed of the turbomachine while maintaining a suitable fan rotation speed. This also increases propulsion efficiency and reduces the engine noise level.

[0003] In order to further improve the propulsive efficiency of high bypass turbofans, it is possible to use a low pressure ratio fan, having an "FPR" (Fan Pressure Ratio in English) of less than 1.4 or even less. The FPR expresses the ratio between the pressure upstream and downstream of the fan. It is known to those skilled in the art that such low FPR fans significantly improve propulsive efficiency and therefore enable more fuel-efficient engines.

The fan allowing the lowest FPR is the so-called open rotor fan, i.e. an unducted fan, but the latter is however difficult to integrate on a commercial aircraft due to a larger fan diameter than a ducted fan and the non-containment of the fan blades which can pose safety and certification problems.

[0004] At equivalent thrust, the ducted fan allows a smaller fan diameter than the open rotor, but generally requires a higher FPR, such as for example an FPR greater than 1.5, to maintain a sufficient operational safety margin.

Indeed, for complex reasons known to those skilled in the art, a ducted fan does not have the same operating characteristics during cruise and takeoff, with, in particular, very different speed and atmospheric pressure conditions. Since the engine can only be optimized for a single flight phase, generally the cruise phase, the ducted fan may be subject to malfunctions during takeoff if its FPR is too low.

[0005] Solutions have been proposed in the prior art to attempt to have a low FPR fan while maintaining a sufficient operational safety margin. The variable pitch fan makes it possible to circumvent this problem by adjusting the propeller pitch to the flight conditions. However, this technology is mechanically delicate and can pose undesired reliability problems.

Another technology known to those skilled in the art is the variable area fan nozzle, also known as a "VAFN". The principle of the VAFN is to vary the area, or surface, of the cold flow outlet by means of a variable geometry device allowing more or less air to pass through.

This device thus makes it possible to adjust the pressure inside the fairing according to the flight conditions and makes it possible to resolve the safety margin problem encountered with a low FPR fan.

[0006] The VAFN systems imagined in the prior art, such as for example in publications US 10156205 B2 or US 10174716 B2, are however not optimal because they are generally positioned on the periphery of the fairing, at its downstream end in the direction of flow of the streams. In addition to the technical complexity and excess weight caused by a fairing incorporating such a VAFN, the very sensitive aerodynamics of the fairing are significantly degraded by the integration of said system, which is very detrimental to the propulsive efficiency of the engine.

[0007] Furthermore, it is known to those skilled in the art that a pair of counter-rotating fans, i.e. a fan composed of two fans rotating in opposite directions to one another, allows on the one hand greater propulsion efficiency than a single fan rotating in one direction, and is on the other hand less sensitive to said malfunctions during takeoff.

Due to the current strong trend of research for an aircraft engine with very high propulsive efficiency, it would be advantageous to be able to use such a low FPR fan, single fan or counter-rotating doublet, without degrading the aerodynamic performance of the nacelle.

Statement of the invention

[0008] Since the energy performance and reliability of commercial aircraft engines are in constant need of improvement, the objective of the invention is to propose a variable ejection surface fan nozzle VAFN device solving the aforementioned problems of the prior art.

[0009] To do this, the invention relates, in its most general sense, to a VAFN device for varying the ejection surface of a nozzle of a cold flow circulating in the annular air stream formed by the outer walls of said VAFN device, and the inner wall of the fairing with non-variable geometry, of a double-flow turbofan, with a longitudinal axis of rotation X;

Said VAFN device, generally annular in shape with an axis of revolution X, is arranged close to the fan, downstream of the latter, encircling the upstream part of the turbofan turbomachine.

[0010] Said VAFN device is generally made up of a cylindrical wall, with an axis of revolution X, configured to be attached to a fixed casing of the turbofan; of a shaped wall, with an axis of revolution X, coaxial and radially smaller than said cylindrical wall; and of at least one linear cylinder or actuator, configured to be attached at one end to said casing, and at the other end to said shaped wall;

and is characterized in that said variation of said ejection surface is obtained by the longitudinal translation, along the X axis, of said shaped wall of the VAFN device, relative to said fixed inner wall of the turbofan fairing. Said shaped wall, with axis of revolution X and extending along X, is generally formed of a short cylindrical wall, extended by a conical wall narrowing from said short cylindrical wall towards the outer casing of the turbomachine of the turbofan.

[0011] In the present embodiment of the invention, said cylindrical wall diametrically centers said short cylindrical wall of the shaped wall to ensure longitudinal guidance in translation along the X axis, and said shaped wall is driven in longitudinal translation along X, by at least one linear jack or any other device allowing such translation. Said at least one linear actuator may, for example, be a linear actuator of the electric or hydraulic type well known to those skilled in the art.

Furthermore, in a non-limiting variant of the embodiment of the invention, said at least one linear cylinder can provide both longitudinal guidance and translation along the X axis of said shaped wall.

[0012] When the at least one cylinder is in the retracted position with a rod length reduced to a length L1, said conical wall of the shaped wall is distant from said fixed inner wall of the fairing, thus allowing a large ejection surface, of value B1, corresponding to the maximum opening of said nozzle.

Conversely, when the at least one cylinder is in the extended position with a rod length increased to a length L2, greater than said length L1, said conical wall of the shaped wall is then brought closer to said fixed inner wall of the fairing, thus restricting the ejection surface to a value B2, smaller than Bl, corresponding to the minimum opening of said cold flow ejection nozzle.

[0013] In a non-limiting example of embodiment of the present invention, said shaped wall is formed by a plurality of shaped plates fitting together, for example, by a set of tenon-mortises arranged on their edges and/or by screwing or any other means allowing the assembly of said shaped plates together.

[0014] The present invention further relates to an aircraft turbofan characterized in that it comprises at least one device as described above.

[0015] The invention will be better understood, and other characteristics, details, aims, and advantages thereof will appear more clearly during the detailed explanatory description which follows, of an embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the appended schematic drawings. DESCRIPTION OF THE FIGURES

[0016] In these drawings:

- [Fig.l] is a general view in half longitudinal section of an example of a double-flow turbofan architecture with a reduced counter-rotating fan incorporating the device according to the invention

- [Fig.2] is a general view in half longitudinal section of a second example of a double-flow turbofan architecture with a single fan incorporating the device according to the invention

- [Fig.3] is a front detail view according to figures (1) or (2), following a first position Bl of the VAFN device, corresponding to the maximum opening of the ejection surface of the nozzle

- [Fig.4] is a front detail view according to figures (1) or (2), following a second position B2 of the VAFN device, corresponding to the minimum opening of the ejection surface of the nozzle

- [Fig.5] is an isometric detail view according to figure (3) of an exemplary embodiment of the invention

- [Fig.6] is an isometric detail view according to figure (4) of an exemplary embodiment of the invention

- [Fig.7] is an exploded isometric view of the VAFN device according to figures (5) and (6) [0017] In [Fig.l] is shown a non-limiting example of a double-flow, shrouded turbofan (10), incorporating a reduced counter-rotating fan, comprising from upstream to downstream, in the direction of flow of the flows (A; B), a reducer (5) driving the fans S and S', and a turbomachine (2) comprising, a low-pressure compressor (2a), a high-pressure compressor (2b), a combustion chamber (2c), a high-pressure turbine (2d), a low-pressure turbine (2e) and an exhaust nozzle (2f). The high-pressure compressor (2b) and the high-pressure turbine (2d) are connected by a high-pressure shaft (3). The low-pressure compressor (2a) and the low-pressure turbine (2e) are connected by a low-pressure shaft (4).

[0018] The reducer (5) is positioned in the upstream part of the turbofan (10) and is attached to a casing (8) which can be likened to an element of the stator of the turbofan (10). The low pressure shaft (4) of the turbomachine (2) drives the reducer (5) in rotation.

[0019] [Fig. 2] represents a second non-limiting example of a double-flow, shrouded turbofan (10), incorporating a single-fan fan S, not reduced, directly driven in rotation by the low-pressure shaft (4) of the turbomachine (2). The axes of the high-pressure shaft (3), of the low-pressure shaft (4) and of the fan S;S' are substantially coincident with the axis of rotation X of the turbofan (10). Said casing (8) is attached to a fairing (11) of the turbofan (10) by means of a plurality of profiled spokes (9).

[0020] As illustrated in Figures 1 to 4,

The air flow sucked in by the fan S;S' is, at its downstream end, divided into two flows A and B. An air flow A entering the turbomachine (2) and an air flow B, called "cold flow" circulating in the air stream formed by the outer wall (2g) of the turbomachine (2) on the one hand and the inner wall (11a), fixed, of the fairing (11).

[0021] In order to vary the ejection surface of the nozzle at the outlet of the cold flow B at the downstream end of the fairing (11), that is to say to vary the ejection surface (12) of said air stream, without modifying the geometry of the fairing (11);

a VAFN device (6) according to the invention makes it possible to increase to a value B1 or reduce to a value B2, said ejection surface (12), thus allowing a more or less narrow passage of the cold flow B, between said VAFN device (6) and said fixed inner wall (11a), with axis of revolution X, of the fairing (11).

[0022] The VAFN device (6) is generally made up of a shaped wall (20), with an axis of revolution X, here called a “nozzle”, generally formed by a short cylindrical wall (20a), extended by a conical wall (20b), with an axis X; and a cylindrical wall (7), with an axis of revolution X, encircling the turbomachine (2) and attached to the fixed casing (8), guiding said nozzle (20) longitudinally in translation, said short cylindrical wall (20a) being diametrically centered and sliding along the axis X, inside said cylindrical wall (7).

[0023] The nozzle (20) is further driven in longitudinal translation along X, by at least one linear cylinder (25) or any other device allowing said translation of the nozzle (20). The at least one cylinder (25) may for example be an electric or hydraulic linear type actuator well known to those skilled in the art.

[0024] In a variant of the invention not shown, said cylindrical wall (7) does not guide in translation said cylindrical wall (20a) of the nozzle (20), and said at least one linear cylinder (25) ensures both longitudinal guidance and translation along the X axis of said nozzle (20).

[0025] As shown in Figures 3 and 5,

The at least one jack (25), attached at one end to the fixed frame corresponding to the stator of the turbomachine (2), and attached at the other end to the nozzle (20), is in the retracted position, with a rod length reduced to a length Ll, moving the conical wall (20b) of the nozzle (20) away from the inner wall (11a) of the fairing (11), thus opening said nozzle, increasing the ejection surface (12) to a value Bl.

In the reverse position, as shown in figures (4) and (6), the at least one cylinder (25) is in the extended position, with a rod length increased to a length L2, greater than the length L1, bringing the conical wall (20b) of the nozzle (20) closer to the inner wall (11a) of the fairing (11), thus closing said nozzle, reducing the ejection surface (12) to a value B2.

[0026] The translation of the nozzle (20) along the X axis allows a variation of the ejection surface (12), without modification of the geometry of the fairing (11), thus making it possible to regulate the pressure in the air stream of the cold flow B, without degrading the aerodynamic performance of said fairing (11).

[0027] Referring to Figures 5 to 7,

In a non-limiting example of embodiment, the nozzle (20) is formed from a plurality of shaped plates (21) fitting together to form said nozzle (20).

Said plates (21) can for example be made in casting, in stamped metal plates, or even molded in composite materials, and have, for example, tenon-mortise assemblies (21a; 21b) and/or assembly screws on their adjacent edges, in order to hold each other together once assembled together.

Said short cylindrical wall (20a) of the nozzle (20) is diametrically adjusted so as to be centered on a sliding surface (7a) of the cylindrical wall (7).

A plurality of jacks (25), for example identical in number to the plurality of plates (21), can, for example, be attached to said plates (21) at the end of their movable rod (25a), via a hole made in the shaped plate (21) and a fixing nut.