Nacelle outlet duct for an aircraft turbojet engine comprising a straightening device for improving performance during the reverse thrust phase

Abstract

An outlet duct (4) for a nacelle (2) of a turbofan engine, the nacelle (2) extending circumferentially about a longitudinal axis (X), the outlet duct (4) comprising a straightening device (9), the straightening device including a plurality of flaps (90) projecting circumferentially, each flap being rotatable about a rotation axis (X9) and forming a converging angle in a radial plane relative to the longitudinal axis, in a closed position, each flap (90) extends along the rotation axis (X9) in an aerodynamic extension of the trailing edge to improve performance during the thrust phase, in a deployed position (D), each flap (90) extends in a deployment plane formed by rotating through a deployment angle (α) about the rotation axis (X9) relative to the closed position, thereby improving performance during the reverse thrust phase (P2).

Description

Technical Field

[0001] The present invention relates to the field of aircraft turbojet engines, and more particularly to a nacelle outlet duct for an aircraft turbojet engine, the turbojet engine including a straightening device for improving the performance during the reverse thrust phase. Background Art

[0002] It is known that an aircraft includes one or more turbojet engines configured to propel the aircraft during the thrust phase by accelerating the air flow (referred to as the internal air flow) flowing from upstream to downstream in each turbojet engine. Hereinafter, the terms "upstream" and "downstream" are defined relative to the flow direction of the internal air flow during the thrust phase.

[0003] It is known that, referring to Figure 1 , which shows an aircraft bypass turbojet engine (also called a turbofan engine) 100 extending along a longitudinal axis X, which includes a fan 500 that rotates about the longitudinal axis X and is configured to accelerate the internal air flow F-INT during the thrust phase P1 of the turbojet engine 100. The turbojet engine 100 further includes a radially inner main flow path 600 and a radially outer secondary flow path 700 located downstream of the fan 500, and the main flow path 600 and the secondary flow path 700 are separated by a housing 800. The housing 800 is configured to guide a first portion (referred to as the main air flow F1) of the internal air flow F-INT in the main flow path 600 for fuel combustion, and to guide a second portion (referred to as the secondary air flow F2) of the internal air flow F-INT in the secondary flow path 700 to generate the thrust of the turbojet engine 100. Hereinafter, the terms "inner" and "outer" are defined relative to the radial direction of the longitudinal axis X.

[0004] It is known that, still referring to Figure 1 , which shows an aircraft propulsion assembly 900 including a turbojet engine 100 and a nacelle 200. The nacelle 200 circumferentially extends around the longitudinal axis of the turbojet engine 100 radially outside the fan 500 and defines the secondary flow path 700. The nacelle 200 is provided with an inlet duct 300 at its upstream end and an outlet duct 400 at its downstream end. The inlet duct 300 is provided with an upstream inner wall 310 facing the longitudinal axis X and an upstream outer wall 320 opposite to the upstream inner wall 310. The upstream inner wall 310 and the upstream outer wall 320 are connected together at the upstream by an inlet duct lip 330 including a leading edge to form an upstream annular cavity 340. The inlet duct 300 has an aerodynamic circular profile, so that the upstream air flow F can be separated into an internal air flow F-INT guided by the upstream inner wall 310 and an external air flow F-EXT guided by the upstream outer wall 320.

[0005] Still referring to Figure 1, similar to the intake duct 300, the exhaust duct 400 of the nacelle 200 has a downstream inner wall 410 facing the longitudinal axis X and a downstream outer wall 420 opposite to the downstream inner wall 410. The downstream inner wall 410 and the downstream outer wall 420 are connected together at the downstream by a trailing edge 430. The exhaust duct 400 has a downstream-tapering profile so as to be able to guide the secondary air flow F2 from the secondary flow path 700 to the outside of the turbofan engine 100.

[0006] In order to reduce the braking distance of the aircraft, especially during landing, it is known to integrate a reverse thrust system in the nacelle 200 so as to be able to change the direction of the secondary air flow F2 at the discharge port, thereby achieving reverse thrust.

[0007] It is known that the reverse thrust phase can be achieved by the opening of a hatch and / or a grid in the secondary flow path 700 located downstream of the fan 500 so as to redirect the secondary air flow to the outside of the turbofan engine 100 in a radial manner relative to the longitudinal axis X or in an upstream direction. For a turbofan engine 100 with a high bypass ratio (i.e., the ratio of the mass of the secondary air flow F2 to the mass of the main air flow F1 is greater than 16), the nacelle 200 has a large diameter, and it is not ideal to integrate a reverse thrust system with a hatch and / or a grid thereon, because this will significantly affect the mass, volume and drag of the turbofan engine 100.

[0008] Another solution for reducing the braking distance of the aircraft is to provide a variable pitch fan (VPF) 500. The fan 500 includes blades, and the tilt angle of the blades is controlled to be able to reverse the flow direction of the secondary air flow F2 in the secondary flow path 700, thereby achieving deceleration of the aircraft, especially during landing.

[0009] Reference Figure 2 , during the reverse thrust phase P2, the reverse air flow F-INV drawn from the external air flow F-EXT enters at the position of the trailing edge 430 of the exhaust duct 400 of the nacelle 200 and flows from downstream to upstream in the secondary flow path 700, that is, opposite to Figure 1 the secondary air flow F2 therein. The reverse air flow F-INV from the secondary flow path 700 then passes through the fan 500 and is guided by the upstream inner wall 310 of the intake duct 300 upstream. The reverse air flow F-INV is opposite to the upstream air flow F, especially opposite to the upstream air flow F in the radial outer part, thereby achieving braking. In some cases and during the thrust phase P1, the internal air flow F-INT from the upstream air flow F flows from upstream to downstream in the nacelle 200 in the radial inner part in a direction opposite to the reverse air flow F-INV to provide the main air flow F1. The main air flow F1 can also be provided by a part of the reverse air flow F-INV bypassing the housing 800.

[0010] In practice, as Figure 2 andFigure 3 As shown, the blades of the fan 500 drive a reverse airflow F-INV at the location of the intake duct 300 according to a torsional movement V along the longitudinal axis X. This torsional movement V can be transmitted to the external airflow F-EXT that is guided by the upstream outer wall 320 of the intake duct 300 and flows from upstream to downstream along the nacelle 200. The external airflow F-EXT is then extracted at the location of the outlet duct 400 of the nacelle 200 to form the reverse airflow F-INV. The reverse airflow F-INV entering the secondary flow path 700 thus also includes a portion V' of the torsional movement transmitted by the external airflow F-EXT, and this solution is not optimal due to the reduction in reverse thrust performance.

[0011] In addition, still referring to Figure 2 and Figure 3 , the outlet duct 400 has a conical profile with aerodynamic characteristics during the thrust phase P1, and a recirculation zone R is generated at the location of the outlet duct 400 in the secondary flow path 700 during the reverse thrust phase P2. More precisely, the external airflow F-EXT from upstream detaches from the downstream outer wall 420 and bypasses the trailing edge 430 to enter the outlet duct 400 and form the reverse airflow F-INV. Such a recirculation zone R reduces the amount of the reverse airflow F-INV that can enter the outlet duct 400, thereby reducing the reverse thrust performance.

[0012] To increase the amount of the reverse airflow F-INV that can enter the outlet duct 400, from the patent application FR2120172A1, more precisely from Figure 11 and Figure 12 the fifth embodiment shown, a nacelle is known that includes a flap protruding from the trailing edge of the outlet duct. This flap rotates between a closed position suitable for the thrust phase and a deployed position suitable for the reverse thrust phase along a tangential axis orthogonal to the nacelle radius. More precisely, in the closed position, the flap extends along the axis of the nacelle in the extension of the outlet duct, while in the deployed position, the flap extends in a radial direction towards the outside of the nacelle. The reverse airflow F-INV with the torsional movement V can enter the turbofan engine 1.

[0013] Incidentally, from the same patent application, more precisely, from Figures 1 to 3In the first embodiment shown, a nacelle is known, which nacelle includes a reverse thrust system mounted in a central peripheral opening of the nacelle formed downstream of the fan. The reverse thrust system includes flaps that are pivotally mounted on the periphery of the opening by a pivot parallel to the nacelle axis, and the flaps are fixed upstream and downstream of the opening. The flaps rotate between a closed position suitable for the thrust phase and a deployed position suitable for the reverse thrust phase. In the closed position, the flaps overlap each other to close the opening in the nacelle wall, and in the deployed position, the flaps extend substantially radially relative to the axis of the nacelle. However, this reverse thrust system is not suitable for a turbofan engine 100 with a high bypass ratio because it will significantly affect the mass, volume, and drag of the turbofan engine 100.

[0014] Incidentally, a reverse thrust mechanism is known from patent application US3040524A, which is rotatably mounted on the casing of a turbofan engine so as to extend into, in the operating state:

[0015] · Figure 1 the exhaust duct of the nacelle in the embodiment shown, or

[0016] · Figure 3 and Figure 4 the opening of the nacelle in the embodiment shown. This patent application does not relate to a nacelle, let alone an exhaust duct. SUMMARY OF THE INVENTION

[0017] An object of the present invention is an exhaust duct for a nacelle of an aircraft bypass turbofan engine, such that the performance of the turbofan engine can be improved during the reverse thrust phase without degrading the performance during the thrust phase.

[0018] The present invention relates to an exhaust duct for a nacelle of an aircraft bypass turbofan engine, the turbofan engine extending along a longitudinal axis and including a radially inner main flow path and a radially outer secondary flow path, the secondary air flowing from upstream to downstream in the secondary flow path during the thrust phase and the reverse air flowing from downstream to upstream in the secondary flow path during the reverse thrust phase, the nacelle extending circumferentially around the longitudinal axis of the turbofan engine and forming the exhaust duct at its downstream end, the exhaust duct including a downstream inner wall and a downstream outer wall, the downstream inner wall facing the longitudinal axis and being configured to define the outside of the secondary flow path to guide the secondary air and the reverse air, the downstream outer wall being opposite to the downstream inner wall and being configured to guide the external air flowing from upstream to downstream, and the downstream inner wall and the downstream outer wall being connected together at the downstream by a trailing edge.

[0019] The remarkable feature of the present invention is that the outlet duct includes a straightening device, the straightening device including a plurality of flaps mounted on the trailing edge and protruding downstream, each flap rotating about a rotation axis so as to form a convergence angle between 0° and 45° with respect to the longitudinal axis in the radial plane, each flap rotating between a closed position and at least one deployed position:

[0020] - In the closed position, each flap extends along the rotation axis in the aerodynamic extension of the trailing edge to improve the performance during the thrust phase;

[0021] - In the deployed position, each flap extends in a deployment plane formed by rotating through a deployment angle about the rotation axis relative to the closed position, the deployment angle being greater than 20°, so as to straighten the reverse airflow entering the outlet duct, thereby improving the performance during the reverse thrust phase.

[0022] With the present invention, during the reverse thrust phase, the external airflow is extracted at the position of the outlet duct of the nacelle to form the reverse airflow. In the deployed position, the external airflow flows between the flaps, which enables the airflow to be straightened before entering the secondary flow path. The torsional movement of the reverse airflow is generated by the blades of the fan at the position of the inlet duct and transmitted to the external airflow, and part of the torsional movement of the reverse airflow is thus changed at the position of the flaps, thereby preventing the reverse airflow with torsional movement from entering the secondary flow path. Therefore, the performance during the reverse thrust phase is improved, thereby not only achieving efficient braking, but also preventing suction and improving the maneuverability of the aircraft under adverse weather conditions.

[0023] In addition, in the deployed position, the recirculation in the secondary flow path at the position of the outlet duct is reduced, which is also beneficial to the reverse thrust phase. In addition, in the deployed position, the diameter of the outlet duct increases, which enables an increase in the flow velocity of the reverse airflow entering the secondary flow path. Finally, in the closed position, the flaps extend into the extension of the outlet duct, which enables the secondary airflow to be guided outwards along the aerodynamic profile, thereby maintaining the performance during the thrust phase.

[0024] Preferably, the convergence angle is less than 20°, preferably less than 15°, so as to maintain the performance during the thrust phase and enable the reverse airflow entering the secondary flow path to be substantially longitudinal during the reverse thrust phase, so as to maximize it.

[0025] According to a preferred aspect of the present invention, the straightening device includes at least 10 flaps, preferably at least 30 flaps. Such a number of flaps is large enough to enable the efficient change of the torsional movement of the reverse airflow at multiple points circumferentially of the outlet duct. Preferably, the number of flaps is less than 50 in order to control them and ensure that they have sufficient dimensions to guarantee their robustness in the face of external air turbulence and shocks and vibrations associated with the aviation environment.

[0026] According to another preferred aspect of the present invention, the deployment angle is between 30° and 135°, preferably between 40° and 90°. Preferably, the optimal deployment angle varies between 40° and 90°, depending on the engine speed, the direction of rotation of the engine, and the amount of reverse airflow desired to enter the secondary flow path. Such a deployment angle advantageously enables the efficient change of the torsional movement of the reverse airflow and ensures that it enters the secondary flow path substantially along the longitudinal profile.

[0027] According to one aspect of the present invention, in the closed position, each flap converges circumferentially along a longitudinal axis extending from upstream to downstream. Compared with the closed position, such flaps have a larger cross-sectional area of the outlet duct in the deployed position, which increases the flow rate of the reverse airflow entering the outlet duct.

[0028] According to a preferred aspect of the present invention, each flap includes an inner wall extending in an extension of the inner wall of the outlet duct to guide the internal airflow and an outer wall extending in the downstream outer wall of the outlet duct to guide the external airflow in the closed position, and the inner wall and the outer wall are connected by a top that forms a rear end in the closed position. Advantageously, each flap forms a conical profile extending in the continuation of the outlet duct in the closed position, enabling the performance in the thrust phase to be maintained. Furthermore, in the reverse thrust phase, the downstream inner walls and downstream outer walls of two opposite flaps define a flow channel for the external airflow before it enters the secondary flow path. Such a flow channel advantageously promotes the reverse airflow to flow substantially in the longitudinal direction in the secondary flow path.

[0029] According to a first aspect of the present invention, in the closed position, the flaps are adjacent to each other to jointly form a ring extending circumferentially along the longitudinal axis. Advantageously, in the closed position, the straightening device adopts the outlet duct in the prior art and thus maintains the performance in the thrust phase. In the reverse thrust phase, the straightening device enables the overall change of the torsional movement of the reverse airflow over the entire circumference of the outlet duct.

[0030] Preferably, the flaps are evenly distributed on the trailing edge to uniformly change the torsional movement of the reverse airflow over the entire circumference of the outlet duct.

[0031] According to one aspect of the present invention, the width of the flap is defined as the arc length in its closed position, and the flaps overlap each other in the closed position, preferably partially overlap, and preferably the overlapping surface is less than 25% of its width. Advantageously, such overlapping ensures the sealing of the straightening device during the thrust phase (i.e., when the flap is in the closed state).

[0032] According to a second aspect of the present invention, the straightening device includes at least one spline fixed to the trailing edge and protruding downstream, and the spline and the flap are adjacent to each other in the closed position to jointly form a ring extending circumferentially along the longitudinal axis. Preferably, the straightening device includes a plurality of splines fixed to the trailing edge and protruding downstream, and the splines and the flap are adjacent to each other in the closed position to jointly form a ring extending circumferentially along the longitudinal axis. Advantageously, in the closed position, the straightening device is the same as the exhaust pipe of the prior art and thus maintains the performance during the thrust phase. During the reverse thrust phase, each spline enhances the mechanical strength of the straightening device. Such a straightening device also enables the targeted change of the torsional movement of the reverse airflow on the circumference of the exhaust pipe.

[0033] Preferably, at least one spline is arranged circumferentially between two flaps to ensure the optimal mechanical strength of the straightening device.

[0034] According to one aspect, in the closed position, at least one flap radially abuts against the spline, preferably the abutting surface is less than 25% of its width, and the width is defined as the arc length of the flap in the closed position. Advantageously, the spline enables both the increase of the robustness of the straightening device and serves as the abutting portion of the flap in the closed position. In other words, the spline enables the sealing of the straightening device during the thrust phase while preventing the flap from opening in an untimely manner.

[0035] According to a preferred aspect, the straightening device includes flaps and splines alternately installed on the trailing edge in the circumferential direction to uniformly change the torsional movement of the reverse airflow on the entire circumference of the exhaust pipe by a robust straightening device.

[0036] According to another preferred aspect, the flaps are installed on one or more given parts of the circumference of the trailing edge so as to specifically change the torsional movement of the reverse airflow at the positions of the one or more given parts. Such a straightening device can thus eliminate specified local recirculation zones. Preferably, the splines are installed on complementary parts on which the flaps are installed so that the straightening device forms an aerodynamic longitudinal ring of axis X during the thrust phase.

[0037] According to one aspect, the spline extends at the corner of the circumference of the trailing edge while forming an angle less than 360°, preferably less than 30°.

[0038] According to one aspect of the present invention, the straightening device includes at least one driving member for driving the flap to rotate. Preferably, the straightening device includes a single driving member configured to simultaneously drive a plurality of flaps to rotate. Advantageously, the driving member enables the flap to be rotated in a simple and practical manner. Using a single driving member further enables the flaps to be simultaneously rotated at the same deployment angle, which is advantageous for the thrust phase and the reverse thrust phase. In addition, such a single driving member is beneficial for shortening the transition time between the thrust phase and the reverse thrust phase.

[0039] Preferably, the straightening device includes a pivot shaft on which the flap is mounted and is installed along the rotation axis in the secondary flow path. Each pivot shaft is connected to the driving member upstream and extends cantilevered downstream. This pivot shaft enables the flap to be easily rotated while having a minimum volume. Preferably, the diameter of the pivot shaft is greater than 10 mm to support the flap and the turbulence of the external air as well as the vibrations and impacts related to the aviation environment.

[0040] According to one aspect of the present invention, each flap rotates about a rotation axis located at the center of the flap. In other words, each flap is mounted on a pivot shaft that is centered relative to the width of the flap. Advantageously, the driving member provides a minimum force when transitioning from the thrust phase to the reverse thrust phase, and vice versa.

[0041] According to an alternative aspect of the present invention, the width of each flap is defined as the arc length of the flap in the closed position, and each flap rotates about an eccentric rotation axis relative to the flap width.

[0042] According to another alternative aspect of the present invention, each flap includes a flap extension portion and a flap reduction portion divided by the eccentric rotation axis. Each flap extension portion is adapted to overlap in the closed position. Preferably, the flap extension portion of each flap can overlap with the flap reduction portion of an adjacent flap. Advantageously, this enables the sealing of the straightening device during the thrust phase to be ensured. In fact, the secondary air flowing in the secondary flow path exerts a greater radially outward pressure on each flap extension portion, which generates a radially inward pressure on each flap reduction portion. The flap extension portion that tends to unfold is thus held by the flap reduction portion that overlaps it. In addition, this flap has the advantage that it can advantageously fold down from the unfolded position to the closed position by using the secondary air flow without the help of the driving member, and more accurately using the radially outward force exerted by it.

[0043] The present invention also relates to a nacelle for a bypass turbofan engine of an aircraft, the turbofan engine extending along a longitudinal axis and including a radially inner main flow path and a radially outer secondary flow path, a secondary air flow flowing from upstream to downstream in the secondary flow path during a thrust phase, and a reverse air flow flowing from downstream to upstream in the secondary flow path during a reverse thrust phase, the nacelle circumferentially extending around the longitudinal axis of the turbofan engine and forming an outlet duct as described above at its downstream end.

[0044] The present invention also relates to an aircraft propulsion assembly including a bypass turbofan engine of an aircraft, the turbofan engine extending along a longitudinal axis and including a radially inner main flow path and a radially outer secondary flow path, wherein a secondary air flow flows from upstream to downstream in the secondary flow path during a thrust phase, and a reverse air flow flows from downstream to upstream in the secondary flow path during a reverse thrust phase, the propulsion assembly including the nacelle as described above mounted on the turbofan engine.

[0045] Preferably, the turbofan engine includes a reverse thrust device, preferably a fan including variable pitch blades. More preferably, the turbofan engine has a bypass ratio greater than 16, i.e., the nacelle has a large diameter. Advantageously, such a turbofan engine is efficient during a reverse thrust phase because all of the reverse air flow entering the outlet duct is efficiently straightened. In the case of a large diameter nacelle, reverse thrust cannot be efficiently performed through hatches and / or grid openings formed in the secondary flow path, but rather a variable pitch fan is required, which does not affect the weight of the turbofan engine. The straightening device is adapted for a fan including variable pitch blades because the flaps are configured to change the torsional movement generated by the fan.

[0046] The present invention also relates to an aircraft including at least one propulsion assembly as described above.

[0047] The present invention also relates to a method of using an aircraft propulsion assembly as described above, wherein at least one flap is in a closed position during a thrust phase of the turbofan engine, the method including at least one step of rotating the flap from the closed position to an open position during a reverse thrust phase of the turbofan engine.

[0048] The present invention particularly relates to a method of using an aircraft propulsion assembly as described above, wherein a pitch angle of blades of a fan of the turbofan engine is adapted for a thrust phase and at least one flap is in a closed position, the method including a step of changing the pitch angle of the blades of the fan to adapt to a reverse thrust phase of the turbofan engine and at least one step of rotating the flap from the closed position to an open position.

[0049] Preferably, the pitch angle of the blades of the fan of the turbofan engine is adapted to the reverse thrust phase and at least one flap is in the deployed position. The method includes the step of reversely changing the pitch angle of the blades of the fan to adapt the turbofan engine to the thrust phase and at least one step of reversely rotating the flap from the deployed position to the closed position.

[0050] Advantageously, this method makes it possible to adjust the profile of the exhaust duct according to whether the aircraft turbofan engine is in the thrust phase or in the reverse thrust phase, so that the profile of the exhaust duct is aerodynamic for each phase. In addition, by simple rotation, the switching between the closed position and the deployed position and from the deployed position to the closed position can be achieved in a simple, practical and rapid manner.

[0051] Preferably, the rotation step is achieved by a drive member. Preferably, in the case of a flap having a central axis of rotation, the reverse rotation step is achieved by a drive member. Preferably, in the case of a flap having an eccentric axis of rotation, due to the secondary air flow, more precisely due to the radially outward pressure it exerts, the reverse rotation step of the flap is automatically achieved.

[0052] Preferably, all flaps are rotated in the rotation step and / or the reverse rotation step, preferably simultaneously, and preferably at the same deployment angle. Description of the Drawings

[0053] The present invention can be better understood by reading the following description given by way of example only and by referring to the accompanying drawings given by way of non-limiting examples, in which the same reference numerals are used to refer to similar objects, where:

[0054] Figure 1 is a longitudinal schematic view of an aircraft propulsion assembly of a bypass turbofan engine of the prior art in the thrust phase;

[0055] Figure 2 is Figure 1 a longitudinal schematic view of the aircraft propulsion assembly of the bypass turbofan engine in the reverse thrust phase;

[0056] Figure 3 is Figure 2 a longitudinal half-sectional schematic view of the nacelle of the aircraft propulsion assembly;

[0057] Figure 4 is a longitudinal schematic view of an aircraft propulsion assembly of a bypass turbofan engine according to an embodiment of the present invention in the thrust phase;

[0058] Figure 5 is Figure 4 a longitudinal schematic view of the aircraft propulsion assembly of the bypass turbofan engine in the reverse thrust phase;

[0059] Figure 6 is Figure 5 a longitudinal half-sectional schematic view of the nacelle of the propulsion assembly;

[0060] Figure 7 and Figure 8 are perspective schematic views of the nacelle of an embodiment of the present invention in the thrust phase and the reverse thrust phase, respectively;

[0061] Figure 9 and Figure 10 are perspective schematic views of the flaps of the nacelle of an embodiment of the present invention in the thrust phase and the reverse thrust phase, respectively;

[0062] Figure 11 and Figure 12 are cross-sectional schematic views of the flaps of the nacelles of two embodiments of the present invention;

[0063] Figure 13 and Figure 14 are perspective schematic views of the flaps of the nacelle of an alternative embodiment of the present invention in the thrust phase and the reverse thrust phase, respectively;

[0064] Figure 15 is a cross-sectional schematic view of the flap of the nacelle of an alternative embodiment of the present invention.

[0065] It should be noted that the drawings illustrate the present invention in detail to implement the present invention, and if necessary, the drawings can clearly better define the present invention. Detailed Description of the Invention

[0066] Referring to Figure 4 and as previously described, it shows the aircraft propulsion assembly E, which includes a bypass turbofan engine 1 that extends along the longitudinal axis X and is configured to be able to propel the aircraft in the thrust phase P1 by accelerating the airflow (referred to as the internal airflow F-INT) flowing from upstream to downstream in each turbofan engine. Hereinafter, the terms "upstream" and "downstream" are defined relative to the flow direction of the internal airflow F-INT in the thrust phase P1. The turbofan engine 1 includes a fan 5 that rotates around the longitudinal axis X and is configured to accelerate the internal airflow F-INT in the thrust phase P1 of the turbofan engine 1. The turbofan engine 1 further includes a radially inner main flow path 6 and a radially outer secondary flow path 7 located downstream of the fan 5, and the main flow path 6 and the secondary flow path 7 are separated by a housing 8. The housing 8 is configured to guide a first portion (referred to as the main airflow F1) of the internal airflow F-INT in the main flow path 6 for fuel combustion and to guide a second portion (referred to as the secondary airflow F2) of the internal airflow F-INT in the secondary flow path 7 to generate the thrust of the turbofan engine 1. Hereinafter, the terms "inner" and "outer" are defined in the radial direction relative to the longitudinal axis X.

[0067] The turbojet engine 1 hereinafter has a high bypass ratio, i.e., the ratio of the mass of the secondary flow F2 to the mass of the primary flow F1 is greater than 16, and the fan 5 is a variable pitch fan (VPF). As Figure 5 shown, such a fan 5 is configured such that it is possible to decelerate the aircraft during the reverse thrust phase P2, especially during landing. To this end, the fan 5 includes blades, the inclination of which is controlled such that it is possible to reverse the flow direction of the secondary flow F2 in the secondary flow path 7. During the reverse thrust phase P2, the reverse flow F-INV flows from downstream to upstream in the secondary flow path 7, i.e., opposite to Figure 4 the secondary flow F2 in

[0068] Reference Figure 4 and Figure 5 , the aircraft propulsion assembly E further includes a nacelle 2, which circumferentially extends radially outside the fan 5 around the longitudinal axis X and defines the secondary flow path 7. The nacelle 2 is provided with an intake duct 3 at its upstream end and an exhaust duct 4 at its downstream end. The intake duct 3 includes an upstream inner wall 31 facing the longitudinal axis X and an upstream outer wall 32 opposite to the upstream inner wall 31, and the upstream inner wall 31 and the upstream outer wall 32 are connected together at the upstream by an intake duct lip 33 including a leading edge to form an upstream annular cavity 34.

[0069] As Figure 4 shown, during the thrust phase P1 of the turbojet engine 1, the intake duct 3 has an aerodynamic circular profile such that it can separate the upstream airflow F into an internal airflow F-INT guided by the upstream inner wall 31 and an external airflow F-EXT guided by the upstream outer wall 32. During the reverse thrust phase P2 of the turbojet engine 1, as Figure 6 shown, the upstream inner wall 31 of the intake duct 3 guides the reverse flow F-INV that sequentially passes through the secondary flow path 7 and the fan 5 to flow upstream such that it is opposite to the upstream airflow F, especially opposite to the upstream airflow radially outside, thereby achieving braking. In some cases, such as during the thrust phase P1, the internal airflow F-INT from the upstream airflow F flows from upstream to downstream radially outside in the nacelle 200 and in a direction opposite to the reverse flow F-INV to supply the primary flow F1. The primary flow F1 can also be supplied by a part of the reverse flow F-INV that bypasses the casing 800. At the position of the intake duct 3, the reverse flow F-INV guided by the upstream inner wall 31 has a torsional motion V along the longitudinal axis, and this torsional motion V is generated by the blades of the fan 5. This torsional motion V can be transmitted to the external airflow F-EXT, which is guided by the upstream outer wall 32 of the intake duct 3 and flows from upstream to downstream along the nacelle 2.

[0070] The present invention more particularly relates to the outlet duct 4 of the nacelle 2, which, like the inlet duct 3, refers to Figure 4 and Figure 5 , the outlet duct 4 comprising a downstream inner wall 41 facing the longitudinal axis X and a downstream outer wall 42 opposite the downstream inner wall 41, the downstream inner wall 41 and the downstream outer wall 42 being connected together at the downstream by a trailing edge 43.

[0071] According to the invention, referring to Figure 6 , Figure 7 and Figure 8 , the outlet duct 4 further comprises a straightening device 9, the straightening device 9 comprising a plurality of flaps 90 mounted circumferentially on the trailing edge 43 and protruding downstream. Each flap 90 rotates between two positions about a rotation axis X9, the rotation axis X9 forming a convergence angle β between 0° and 45° in a radial plane relative to the longitudinal axis. The two positions of each flap 90 are:

[0072] - Figure 4 and Figure 7 the closed position F shown in, in which each flap 90 extends along the rotation axis X9 in an aerodynamic extension of the trailing edge 43; and

[0073] - Figure 5 , Figure 6 and Figure 8 the deployed position D shown in, in which each flap 90 extends in a deployed plane formed by rotating the deployment angle α about the rotation axis X9 relative to the closed position F, the deployment angle α being greater than 20°.

[0074] In order to drive the flaps 90 to rotate from the closed position F to the deployed position D and from the deployed position D to the closed position F, the straightening device 9 further comprises one or more drive members 97 and a pivot 98 on which the flaps 90 are mounted (see Figure 9 and Figure 10 ). As will be described in detail below, the pivot 98 is connected to the pivot member 97 and extends cantilevered downstream.

[0075] In certain embodiments of the invention, the straightening device 9 further comprises one or more splines fixedly mounted on the trailing edge 43 located between the flaps 90. In the example described below with reference to Figures 4 to 12 , the straightening device 9 only comprises the flaps 90. The straightening device 9 including splines located between the flaps 90 will be presented later with reference to Figures 13 to 15 .

[0076] Thanks to the present invention, the outlet duct 4 has a profile that is suitable and efficient both in the thrust phase P1 (by placing the flaps 90 in the closed position F) and in the reverse thrust phase P2 (by placing the flaps 90 in the deployed position D).

[0077] Actually, during reverse thrust phase P2, with reference to Figure 6 , the reverse airflow F-INV flowing in the secondary flow path 7 extracted from the external airflow F-EXT enters at the position of the exhaust pipe 4. More precisely, the external airflow F-EXT flowing along the nacelle 2 from upstream to downstream is guided by the downstream outer wall 43 of the exhaust pipe 4 and then crosses the straightening device 9 to form the reverse airflow F-INV entering the secondary flow path 7. Advantageously, the torsional movement V of the external airflow F-EXT is changed on the path of the straightening device 9, so that the reverse airflow F-INV entering the exhaust pipe 4 can be straightened. This straightened reverse airflow F-INV improves the performance of the reverse thrust phase P2. Therefore, the reverse airflow F-INV flows in a manner opposite to the internal airflow F-INT, which not only achieves optimal braking, but also protects the engine from the pumping phenomenon and promotes the maneuverability of the aircraft under adverse weather conditions.

[0078] In addition, the straightening device 9 can prevent the formation of a recirculation zone R as shown in the prior art at the position of the exhaust pipe in the secondary flow path. Figure 3 Actually, the external airflow F-EXT crosses the straightening device 9 while flowing between the flaps 90, instead of bypassing the trailing edge 43 as in the prior art. Therefore, the straightening device 9 prevents the external airflow F-EXT from detaching from the downstream outer wall 420 behind the recirculation zone R of the exhaust pipe.

[0079] During Figure 7 and Figure 8 In the example of, during thrust phase P1, the straightening device 9 extends in an aerodynamic extension of the trailing edge 43 of the exhaust pipe 4, that is, it is generally annular along the longitudinal axis X. Advantageously, the secondary airflow F2 in the secondary flow path 7 is aerodynamically guided to the outside of the turbojet engine 1. Preferably and as Figure 6 shown, the straightening device 9 forms a converging ring from upstream to downstream. Therefore, compared with the closed position F, the cross-sectional area of the exhaust pipe 4 in the deployed position D increases, thereby increasing the flow rate of the reverse airflow F-INV in the secondary flow path 7.

[0080] In practice, as Figure 6 shown, the converging angle β is preferably less than 20°, preferably less than 15°, in order to maintain the performance during thrust phase P1 and facilitate the entry of the reverse airflow F-INV substantially longitudinally during the reverse thrust phase P2. Also in practice, the deployment angle α is preferably between 30° and 135° by itself, preferably between 40° and 90°. The optimal deployment angle α is selected within this range according to the engine speed, the rotation direction of the engine, and the amount of reverse airflow F-INV desired to enter the secondary flow path 7.

[0081] The structural and functional characteristics of the straightening device 9 are described more precisely below.

[0082] In Figure 7 and Figure 8 example, the straightening device 9 includes about thirty flaps 90 which are circumferentially mounted on the trailing edge 43. Advantageously, such a number of flaps 90 enables the efficient modification of the torsional movement V of the external air flow F-EXT, i.e., in each position of the flaps 90. A channel is formed between two adjacent flaps 90 in the deployed position D to direct the external air flow F-EXT, thus efficiently straightening the reverse air flow F-INV. It goes without saying that such a number of flaps 90 is suitable for the exhaust pipe 4 with a large diameter, i.e., for the exhaust pipe of the turbojet engine 1 with a bypass ratio greater than 16, and it can be suitable for the exhaust pipe 4 with a smaller diameter. Preferably, the number of flaps 90 is greater than 20, preferably greater than 30, to efficiently straighten the reverse air flow F-INV. Also preferably, the number of flaps 90 is less than 50 to reduce the volume, cost and on-board mass.

[0083] Still referring to Figure 7 and Figure 8 example, the flaps 90 are evenly distributed on the circumference of the trailing edge 43 of the exhaust pipe 4 so as to obtain a reverse air flow F-INV that is straightened in a uniform manner in each radial position of the secondary flow channel 7. However, it goes without saying that the flaps 90 can be mounted closer together in one or more parts of the circumference of the trailing edge 43 where the torsional movement V is stronger. Conversely, the flaps 90 can be mounted farther apart in one or more parts of the circumference of the trailing edge 43 where the torsional movement V is less strong.

[0084] The following describes a single flap 90, and this description is valid for each flap 90 of the straightening device 9. Preferably, all the flaps 90 are identical to ensure the uniform straightening of the reverse air flow F-INV. However, it goes without saying that, especially in the case where there is one or more radial parts with non-uniform torsional movement V on the circumference of the trailing edge 43, a plurality of flaps 90 can have different shapes and sizes.

[0085] Referring to Figure 9 and Figure 10 , the flap 90 in the closed position F is provided with an inner wall 91 and an outer wall 92 which extend respectively in the extensions of the downstream inner wall 41 and the downstream outer wall 42 of the exhaust pipe 4. The inner wall 91 and the outer wall 92 are connected at the downstream by a top 93, at the upstream by a base 94 and laterally by a side 96.

[0086] Still referring to Figure 9 and Figure 10, the inner wall 91 and the outer wall 92 have an inwardly curved shape such that the outer diameter of the straightening device 9 at the upstream position of the base 94 is greater than its outer diameter at the downstream position of the top 93. This curved shape gives the outlet pipe 4 an aerodynamic profile during the thrust phase P1. In fact, the inner wall 91 and the outer wall 92 respectively guide the internal air flow F-INT and the external air flow F-EXT while preventing detachment. This curved shape also helps to extract the external air flow F-EXT to form a reverse air flow F-INV during the reverse thrust phase P2. In fact, this curved shape, in conjunction with the deployment angle α of the flap 90, defines an aerodynamic flow channel for the external air flow F-EXT, which improves the straightening effect.

[0087] Still referring to Figure 9 and Figure 10 , the radial thickness of the top 93 is less than the radial thickness of the base 94, such that the straightening device 9 has a downstream-tapering profile, reproducing the tapered profile of the outlet pipe in the prior art. In other words, at the closed position F, the top 93 forms a rear end corresponding to the trailing edge of the outlet pipe in the prior art. Advantageously, the performance during the thrust phase P1 is maintained.

[0088] Still referring to Figure 9 and Figure 10 , the flap 90 has a length l greater than 20 cm, which length l is defined as the longitudinal distance separating the base 94 from the top 93, such that during the reverse thrust phase P2, all of the external air flow F-EXT configured to form the reverse air flow F-INV crosses the straightening device 9. The length l of the flap 90 is further preferably less than 50 cm to ensure its robustness and durability. In fact, this range of the length l reduces the forces exerted on the flap 90 protruding from the trailing edge 43 by the turbulence of the surrounding air and the vibrations and shocks associated with the aviation environment.

[0089] Still referring to Figure 9 and Figure 10 , the flap 90 has a width L, which width L is defined as the circumferential distance separating the lateral edges 96 in the closed position F, and this width L is at least equal to the ratio of the circumference of the straightening device 9 to the number of flaps 90 of the straightening device 9. Preferably, the width L of the flap 90 is greater than this ratio such that the flaps 90 overlap each other in the closed position F. That is to say, the inner wall 91 of the flap 90 abuts against the outer wall 92 of the adjacent flap 90.

[0090] In this example, all the flaps 90 have the same length l and the same width L to achieve uniform straightening of the reverse air flow F-INV, but it goes without saying that multiple flaps may have different lengths l and / or widths L, especially in order to achieve a set straightening of one or more corners on the circumference of the trailing edge 43.

[0091] Advantageously, when the flap 90 is in the closed position F, the overlapping of the flap 90 ensures the sealing of the straightening device 9. The overlapping of the flap 90 also advantageously promotes the rotation of the flap 90 from the closed position F to the deployed position D and from the deployed position D to the closed position F while being driven mutually. In fact, the deployment of one flap 90 drives the deployment of the adjacent flap 90, and so on. Preferably, the overlapping is partial, preferably about less than 25% of the width L of the flap 90, so as to reduce the on-board mass of the straightening device 9.

[0092] In Figure 11 the example of, in order to avoid local radial over-thickness related to the overlapping, the flap 90 includes a lateral edge 96 with a reduced radial thickness. The lateral edges 96 of adjacent flaps 90 thus advantageously cooperate by complementary shape so as to obtain a substantially constant radial thickness at the periphery. The outer wall 92 and the inner wall 91 of the flap 90 thus extend respectively at the continuations of the outer wall 92 and the inner wall 91 of the adjacent flaps 90. Advantageously, such a lateral edge 96 with reduced thickness makes the outlet pipe 4 have a more aerodynamic profile.

[0093] Also preferably, the flap 90 is made of composite material so as to obtain particularly high mechanical strength while having a small on-board mass, especially in the face of shocks and vibrations related to the aviation environment, which is beneficial for its cantilever support.

[0094] The drive member 97 and the pivot 98, which are associated with each flap 90 and are configured to together effect the rotation of the flap 90 from the closed position F to the deployed position D and from the deployed position D to the closed position F, will be described more precisely hereinafter.

[0095] Reference Figures 9 to 11 And as previously mentioned, each flap 90 is fixedly mounted on the pivot 98 along the rotation axis X9 of the corresponding flap 90. The pivot 98 is connected to the drive member 97, and the pivot 98 is configured to rotate through the deployment angle α about the rotation axis X9 to drive the drive member 97, thereby rotating the flap 90 from the closed state F to the deployed position D or from the deployed position D to the closed position F.

[0096] Preferably, the outlet duct 4 includes an abutment device configured to limit the deployment angle between a closed position F and a deployed position D. As an example, the pivot 98 preferably includes a projection configured to limit the rotation of the flap 90 when abutting against the drive member 97. Thus, during the transition from the closed position F to the deployed position D, each pivot 98 includes a first projection that forms an abutment at the maximum deployed position D. Similarly, during the transition from the deployed position D to the closed position F, each pivot 98 includes a second projection that forms an abutment at the closed position F. It goes without saying that, in addition to the projections that abut at the deployed position D and the closed position F, the angular deployment can also be limited in other ways.

[0097] More precisely, the pivot 98 extends cantilever-like downstream from the trailing edge 43 of the outlet duct 4, which enables the associated flap 90 to be easily displaced and have a small volume. Preferably, the pivot 98 is in the form of a rod to have sufficient mechanical strength and a low airborne mass. For the same reason, the pivot 98 is preferably made of steel.

[0098] Reference Figures 9 to 11 , each drive member 97 is mounted in the outlet duct 4 so as not to interfere with the flow of the external air flow F-EXT and the reverse air flow F-INV and to reduce the volume. According to one aspect of the invention, each flap 90 is connected to a pivot 98 connected to the drive member 97 so that each flap 90 can rotate independently according to a specific deployment angle α. Preferably and as Figure 9 and Figure 10 shown, the drive members 97 are connected together so as to rotate the flaps 90 from the closed position F to the deployed position D and to rotate the flaps 90 from the deployed position D to the closed position F simultaneously in a simple and practical manner. According to another preferred aspect of the invention, the pivot 98 is connected to a single drive member 97, which is, as an example, a wheel coaxial with the longitudinal axis X. Advantageously, such a wheel enables all the flaps 90 to be displaced simultaneously at the same deployment angle α by a simple rotation. Such a wheel thus enables the entry of the reverse air flow F-INV to be uniformly changed in the circumferential direction of the trailing edge 43.

[0099] Optionally, in order to improve the non-uniform entry of the reverse air flow F-INV in the circumferential direction of the trailing edge 43, such as to eliminate local recirculation zones, a single drive member 97, such as a wheel, connected to pivots 98 of different sizes is employed. Advantageously, such a wheel enables all the flaps 90 to be displaced simultaneously along the deployment angle α specific to the pivot 98 by a simple rotation.

[0100] In Figures 9 to 11 the example, the flap 90 is also mounted at the center of each pivot 98 so as to minimize the rotational force provided by the drive member 97.

[0101] In an example showing an alternative embodiment of the present invention Figure 12 the flap 90 is mounted along an eccentric axis of rotation X9' relative to the width L of the flap 90. The eccentric axis of rotation X9' of each flap 90 thus defines a flap reduction portion 90B and a flap extension portion 90A. Advantageously, it is possible to ensure the sealing of the straightening device 9 during the thrust phase P1. In fact, the secondary air flow F2 flowing in the secondary flow path 7 exerts a greater radially outward pressure E1 on each flap extension portion 90A, which in turn generates a radially inward pressure E2 on each flap reduction portion 90B. Based on the sum of the forces applied to each pivot 98, the flap extension portion 90A that tends to unfold is thus held by the flap reduction portion 90B that overlaps it. Advantageously, since the lateral edge 96 has a reduced radial thickness, the flap extension portion 90A is configured to be overlapped by the flap reduction portion 90B in the closed position F. Thus, by wisely using the secondary air flow F2, the flap 90 can be rotated from the deployed position D to the closed position E without a drive member 97. Otherwise, in the event of a failure of the drive member 97, the flap 90 is naturally displaced to the closed position F by the flow of the internal air flow F-INT. Thus, even in case of failure, the best performance can be maintained.

[0102] According to Figures 13 to 15 another embodiment of the present invention shown, the straightening device 9 is described below. The straightening device 9 further includes one or more splines 99 fixedly mounted on the trailing edge 43 between the flaps 90 in addition to the flaps 90. Each spline 99 cooperates with the flap 90 to form a ring circumferentially extending around the longitudinal axis X. In other words, the spline 99 extends in the same manner as the flap 90 in the closed position F.

[0103] According to the first configuration, the straightening device 9 includes alternately arranged flaps 90 and splines 99. The purpose of the splines 99 is to increase the mechanical strength of the straightening device 9 against vibrations and shocks related to the aviation environment. Preferably, as Figure 15 shown, the flap 90 is configured to abut against the spline 99 in the closed position F, more precisely against the radial abutment portion E3. Thus, the spline 99 also helps to ensure the sealing of the straightening device 9 in the closed position F and to prevent the flap 90 from unfolding in an untimely manner. In Figure 15 the example, the abutment is achieved by the spline 99 overlapping the flap 90. This overlap is similar to the overlap shown in Figure 11 and Figure 12 shown and described above. Similarly, for Figure 11 and Figure 12 as Figure 15 shown, the flap 90 is configured to rotate along the central axis of rotation X9 to obtain the minimum rotational force, or to rotate along the eccentric axis of rotation X9', so that it is possible to wisely use the secondary air flow E2 to automatically rotate the flap 90 in the closed position F.

[0104] According to the second configuration, the straightening device 9 includes flaps 90 mounted on one or more corners circumferentially of the trailing edge 43. One or more splines 99 are mounted on one or more complementary corners. This configuration enables targeted straightening of the reverse airflow F-INV at the position of the flaps 90, thus avoiding the local recirculation zone in the example. In this configuration, by forming a ring coaxial with the longitudinal axis X with the flaps 90, the splines 99 serve to maintain the aerodynamic profile of the outlet duct 4 during the thrust phase P1.

[0105] Preferably, the splines 99 have a shape and size similar to those of the flaps 90 as described above. Specifically, the splines 99 include a rear end similar to that of the flaps 90 and a similar length. However, it goes without saying that the splines can have different shapes and / or sizes, especially their width, depending on the desired straightening of the reverse airflow F-INV and the necessary mechanical strength.

[0106] A method for using the outlet duct 4 of an aircraft propulsion assembly E is described below, the outlet duct 4 including the straightening device 9 as described above, i.e., including flaps 90 and optionally one or more fixed splines 99. By default, the aircraft turbojet engine is initially in the thrust phase P1 and the flaps 90 of the straightening device 9 are in the closed position F. In other words, the top 93 of the flaps 90 forms the trailing end of the outlet duct 4.

[0107] In the reverse thrust phase P2, the pitch angle of the blades of the fan 5 is changed so as to reverse the direction of the secondary airflow F2 flowing in the secondary flow path 7 in the reverse airflow F-INV, thereby promoting deceleration of the aircraft. According to the invention, similar to changing the pitch angle of the blades of the fan 5, the flaps 90 are rotated by driving one or more drive members 97 at a deployment angle α greater than 20°, such as by rotating a wheel connected to all the flaps 90. The rotation of a single wheel advantageously enables the flaps 90 to be rotated in a simple, rapid and synchronous manner and at the same deployment angle α. The flaps 90 that initially extend in the extension of the trailing edge 43 of the outlet duct 4 in the closed position F then define a flow channel for the external airflow F-EXT in the deployment position D.

[0108] In the deployment position D, the flaps 90 straighten the torsional movement of the external airflow F-EXT, thus improving the entry of the reverse airflow F-INV into the secondary flow path 7 and enhancing the performance of the reverse thrust phase P2. The flaps 90 further prevent the formation of a recirculation of the external airflow F-EXT downstream of the outlet duct 4. When the straightening device has converging flaps 90 extending from upstream to downstream and no splines 99, the flaps 90 in the deployment position D further increase the diameter of the outlet duct 4, which increases the flow velocity of the incoming reverse airflow F-INV. In fact, due to the convergence of the flaps 90, the diameter of the outlet duct 4 is defined between the trailing edges 43, rather than between the tops 93 of the flaps 90.

[0109] In the new thrust phase P1, the pitch angle of the blades of the fan 5 is changed again to re-establish the secondary air flow F2 flowing from upstream to downstream. According to the present invention, similar to changing the pitch angle of the blades of the fan 5, the flap 90 is reversely rotated from the deployed position D to the closed position F at the same deployment angle α. The flap 90 then optionally forms the rear end of the outlet duct 4 together with the spline 99 and enables the performance to be maintained in the thrust phase P1 with an aerodynamic profile.

[0110] According to an embodiment of the present invention, the step of rotating the flap 90 from the closed position F to the deployed position D and the reverse rotation step of rotating it from the deployed position D to the closed position F are achieved by one or more drive members 97. According to another embodiment of the present invention, the reverse rotation step is automatically achieved by the flap 90, advantageously by the secondary air flow F2, and more precisely by the radial force generated by the secondary air flow F2 on the flap 90 to fold it back.

[0111] In summary, the outlet duct 4 of the present invention has a profile suitable for each thrust phase P1 and reverse thrust phase P2, an aerodynamic shape that tapers downstream in the thrust phase P1, and a flow channel for the external air flow F-EXT in the reverse thrust phase P2. By changing the torsional motion V of the external air flow F-EXT carried upstream by the fan 5 and by improving the access to the direction and flow rate of the reverse air flow F-INV in the secondary flow path 7, the outlet duct 4 significantly improves the performance in the reverse thrust phase P2. Due to the lapping of the edge 96 and the eccentric rotation axis X9', the sealing of the flap 90 in the closed position F is further ensured. All the pivots 98 driven by a single wheel further enable the flap 90 to be rotated in a fast, simple, practical and synchronous manner while reducing the volume and on-board mass, thus enabling adaptation to rapid or repeated phase changes. The fixed spline 99 further enhances the mechanical strength of the straightening device, thus enabling targeted straightening in the specified recirculation zone and serving as an abutment for the flap 90.

[0112] Preferably, in order to form the outlet duct 4 according to the present invention, the length of the outlet duct of the prior art is reduced to provide the flap 90. The longitudinal volume of the outlet duct 4 advantageously remains unchanged.

Claims

1. An outlet duct (4) for a nacelle (2) of a bypass turbofan engine (1), the turbofan engine (1) extending along a longitudinal axis (X) and including a radially inner main flow path (6) and a radially outer secondary flow path (7), a secondary air flow (F2) flowing downstream from upstream in the radially outer secondary flow path (7) during a thrust phase (P1), and a reverse air flow (F-INV) flowing upstream from downstream in the radially outer secondary flow path (7) during a reverse thrust phase (P2), the nacelle (2) extending circumferentially around the longitudinal axis (X) of the turbofan engine (1) and forming the outlet duct (4) at its downstream end, the outlet duct (4) including a downstream inner wall (41) and a downstream outer wall (42), the downstream inner wall (41) facing the longitudinal axis (X) and being configured to define the outside of the secondary flow path (7) to guide the secondary air flow (F2) and the reverse air flow (F-INV), the downstream outer wall (42) being opposite to the downstream inner wall (41) and being configured to guide an external air flow (F-EXT) flowing downstream from upstream, and the downstream inner wall (41) and the downstream outer wall (42) being connected together at a downstream trailing edge (43). Characterized in that the outlet duct includes a straightening device (9), the straightening device (9) including a plurality of flaps (90) mounted on the trailing edge (43) and protruding downstream, each flap (90) rotating about a rotation axis (X9, X9') and forming a convergence angle (β) between 0° and 45° in a radial plane relative to the longitudinal axis (X), each flap (90) rotating between a closed position (F) and at least one deployed position (D): - In the closed position (F), each flap (90) extends along the rotation axis (X9, X9') in the aerodynamic extension of the trailing edge (43) to improve the performance during the thrust phase (P1); - In the deployed position (D), each flap (90) extends in a deployment plane formed by rotating a deployment angle (α) about the rotation axis (X9, X9') relative to the closed position (F), the deployment angle (α) being greater than 20°, to straighten the reverse air flow (F-INV) entering the outlet duct (4), thereby improving the performance during the reverse thrust phase (P2).

2. The outlet duct (4) according to claim 1, Characterized in that in the closed position (F), the flaps (90) converge circumferentially along the longitudinal axis (X) extending from upstream to downstream.

3. The outlet duct (4) according to claim 1, Characterized in that in the closed position (F), the flaps (90) are adjacent to each other to jointly form a ring extending circumferentially along the longitudinal axis (X).

4. The outlet duct (4) according to claim 1, Characterized in that the width (L) of the flap (90) is defined as the arc length of the flap in the closed position (F), and the flaps (90) overlap in the closed position (F).

5. The outlet duct (4) according to claim 4, Characterized in that When each flap (90) is in the closed position (F), the overlapping portion is less than 25% of its width (L).

6. The outlet duct (4) according to claim 1, characterized in that the straightening device (9) includes at least one spline (99) fixed to the trailing edge (43) and protruding downstream, and the spline (99) and the flap (90) are adjacent to each other when in the closed position (F) to jointly form a ring extending circumferentially along the longitudinal axis (X).

7. The outlet duct (4) according to claim 6, characterized in that in the closed position (F), at least one flap (90) radially abuts against a spline (99).

8. The outlet duct (4) according to claim 7, characterized in that the abutting surface where at least one flap (90) radially abuts against a spline (99) is less than 25% of its width (L), and the width is defined as the arc length of the flap in the closed position (F).

9. The outlet duct (4) according to claim 1, characterized in that the straightening device (9) includes at least one driving member (97) for driving the flap (90) to rotate.

10. The outlet duct (4) according to claim 9, characterized in that the straightening device (9) includes at least one single driving member (97) for simultaneously driving a plurality of flaps (90) to rotate.

11. The outlet duct (4) according to claim 1, characterized in that each flap (90) rotates about a rotation axis (X9) located at the center of the flap (90).

12. The outlet duct (4) according to claim 1, characterized in that the width (L) of each flap (90) is defined as the arc length of the flap in the closed position (F), and each flap (90) rotates about an eccentric rotation axis (X9') relative to the flap width (L).

13. The outlet duct (4) according to claim 12, characterized in that each flap (90) includes a flap extension portion (90A) and a flap reduction portion (90B) divided by the eccentric rotation axis (X9'), and the flap extension portion (90A) is adapted to overlap in the closed position (F).

14. A nacelle (2) for a bypass turbofan engine (1), the turbofan engine (1) extending along a longitudinal axis (X) and including a radially inner main flow path (6) and a radially outer secondary flow path (7), a secondary air flow (F2) flowing from upstream to downstream in the radially outer secondary flow path (7) during a thrust phase (P1), and a reverse air flow (F-INV) flowing from downstream to upstream in the radially outer secondary flow path (7) during a reverse thrust phase (P2), characterized in that the nacelle (2) extends circumferentially around the longitudinal axis (X) of the turbofan engine (1) and forms an outlet duct (4) as described in any one of claims 1 to 13 at its downstream end.

15. An aircraft propulsion assembly (E) comprising a bypass turbojet engine (1), said turbojet engine (1) extending along a longitudinal axis (X) and comprising a radially inner main flow path (6) and a radially outer secondary flow path (7), a secondary air flow (F2) flowing from upstream to downstream in the radially outer secondary flow path (7) during a thrust phase (P1), and a reverse air flow (F-INV) flowing from downstream to upstream in the radially outer secondary flow path (7) during a reverse thrust phase (P2). Characterized in that the propulsion assembly (E) comprises a nacelle (2) as claimed in claim 14 mounted on the turbojet engine (1).

16. An aircraft propulsion assembly (E) comprising a bypass turbojet engine (1) as claimed in claim 15 Characterized in that the propulsion assembly (E) comprises a reverse thrust device.

17. A method for using an aircraft propulsion assembly (E) as claimed in claim 15 or 16 Characterized in that at least one flap (90) is in a closed position (F) during the thrust phase (P1) of the turbojet engine (1), and the method comprises at least one step of rotating the flap (90) from the closed position (F) to at least one deployed position (D) during the reverse thrust phase (P2) of the turbojet engine (1).

Images