AIRCRAFT WITH REDUCED DRAGGING BY REDUCING THE INTENSITY OF MARGINAL VORBILLS

Abstract

AIRCRAFT WITH REDUCED DRAG BY REDUCING THE INTENSITY OF EDGE VORTES The present invention relates to a propulsion unit (10) for a fixed-wing aircraft (2), the propulsion unit comprising a nacelle (12) housing at least two non-coaxial fans, said nacelle comprising an upper wall, a lower wall, and two side walls connecting the upper and lower walls, each wall having an upstream edge and a downstream edge, the walls together defining a generally oblong or rectangular fairing, notable in that the nacelle comprises at least one fin arranged near a corner of the fairing, the fin extending internally into the fairing from one of the walls and being closer to the downstream edge than to the upstream edge of the wall from which it extends. The invention also relates to an aircraft notable in that it comprises propulsion units according to the invention.(Figure to be published with the abbreviation: Figure 1).

Description

Title of the invention: AIRCRAFT WITH REDUCED DRAG BY REDUCING THE INTENSITY OF VORBILLONS MARGINALS technical field

[0001] The invention relates to the field of aircraft, more particularly to aircraft comprising a generally elongated fuselage and a wing consisting of two wings arranged on either side of the fuselage. Previous art

[0002] The lift of an aircraft wing induces aerodynamic drag through the formation of vortices. Indeed, lift results from a difference in speed between the upper and lower surfaces of the wing, causing, in addition to a pressure difference, a rotational circulation around the wing forming vortices in its wake.

[0003] Also, the pressure difference between the upper and lower surfaces of the wing causes wingtip vortices at each of the two wingtips. These vortices create induced drag because they consume energy from the aerodynamic phenomena related to the wing's lift. It should be noted that a wing, like any other element in contact with the airflow, also causes friction drag related to the viscosity of the air at the boundary layer.

[0004] It is generally sought to reduce the drag of a wing, in particular the induced drag, that is to say that related to the lift of the wing.

[0005] Published patent document WO 2021 / 074516 A1 proposes an aircraft architecture with an elongated fuselage, a lifting wing consisting of two wings arranged on either side of the fuselage, and two lifting nacelles positioned directly behind the two wings, so as to be directly in the wake of the two wings. Each of the nacelles forms an air intake fairing, with an upper wall, a lower wall, and two side walls, and houses several propulsion engines within the fairing. The upper and lower walls form an auxiliary lifting wing. The air intake edge of the lower wall is positioned directly downstream of the trailing edge of the corresponding wing, so as to take advantage of the wing's wake.

[0006] This design aims to reduce aerodynamic drag and increase the aircraft's lift. Similar to the aircraft's wings, the nacelle's lifting surfaces can generate induced vortices, particularly at the lateral ends of the lifting walls (lower and upper). Therefore, there is room for improvement to further reduce aerodynamic drag and ensure a reduction in fuel consumption. Description of the invention

[0007] The present invention aims to provide a propulsion system for an aircraft that benefits from the advantages of the prior art in terms of low drag and increased lift and aims to significantly reduce or even eliminate the creation of marginal vortices inside the nacelle while maintaining sufficient thrust for the aircraft to efficiently perform all its flight phases.

[0008] The invention relates to a propulsion unit for a fixed-wing aircraft, the propulsion unit comprising a nacelle housing at least two non-coaxial fans, said nacelle comprising an upper wall, a lower wall, and two side walls ensuring the connection between the upper and lower walls, each of the walls having an upstream edge and a downstream edge, the walls together defining a fairing generally oblong or rectangular, remarkable in that the nacelle comprises at least one fin arranged in the vicinity of a corner of the fairing, the fin extending internally into the fairing from one of its walls and being closer to the downstream edge than to the upstream edge of the wall from which it extends.

[0009] The nacelle profile is not substantially circular but rather oblong or rectangular, the nacelle housing at least two non-coaxial blowers. The upper and lower walls of the nacelle are load-bearing.

[0010] To this end, the aircraft nacelle has, at the corners of at least one of its two lateral ends, wingtip vortices caused by the lift of the nacelle. When the nacelle is oblong, that is to say when the side walls are curved rather than straight, the term "corner" refers to a lateral end area of ​​the nacelle.

[0011] The fact that at least one fin is arranged in the vicinity of the corner means that said fin is preferably arranged at no more than 30% of a distance separating a first corner from a second corner. Indeed, the nacelle fairing comprises at least one lateral end, an upper corner formed by the upper wall and the lateral wall of the nacelle, and a second corner formed by the lower wall and said lateral wall.

[0012] Preferably, at least one fin extends perpendicularly to the wall (lateral and / or upper and / or lower) from which said fin extends.

[0013] At least one fin near the corner allows to generate an opposing vortex so as to create a vortex interaction with the marginal vortex initially created in the corner of the nacelle, thus allowing to decrease the net intensity of the marginal vortices and therefore of the induced drag generated by the nacelle.

[0014] Advantageously, the fins do not generate additional airflow. For this reason, the reduction in induced drag of the nacelle is achieved without a change in lift, which helps to preserve it.

[0015] According to an advantageous embodiment of the invention, at least one fin extends from a lateral wall and comprises an extrados facing the upper wall and an intrados facing the lower wall.

[0016] According to an advantageous embodiment of the invention, at least one fin extends from the lower wall or from the upper wall and comprises an intrados and an extrados, said extrados facing the nearest lateral wall.

[0017] The two side walls define the total extent of the nacelle. Preferably, at least one fin is arranged adjacent to one of the two side walls.

[0018] According to an advantageous embodiment of the invention, from upstream to downstream, at least one fin gradually protrudes from the fairing up to a maximum length before tapering downstream.

[0019] Advantageously, the progressive shape of at least one fin facilitates the guidance of the airflow encountering the fin. This also further smooths the upstream to downstream vortex interaction in order to further reduce potential aerodynamic disturbances due to vortex interaction, which can present a risk of thrust loss.

[0020] According to an advantageous embodiment of the invention, at least one fin has a length corresponding to approximately 10% of the distance between the upstream and downstream edges of the wall from which it extends. A longer fin is not essential because it would have no effect on the vortices and would therefore add unnecessary mass and friction drag to the aircraft.

[0021] According to an advantageous embodiment of the invention, at least one fin has a maximum width of between 5 and 10% of the distance between the side walls. Similarly, an excessively wide fin is not essential.

[0022] According to an advantageous embodiment of the invention, at least one fin is disposed in a downstream portion of the nacelle extending over less than 30% of the distance between the upstream edge and the downstream edge of the wall from which it extends.

[0023] It is preferable that the length of at least one fin corresponds to at least 10% and at most 30% of the distance separating the upstream edge from the downstream edge of the wall from which said fin extends.

[0024] According to an advantageous embodiment of the invention, the side walls each comprise two fins, in the vicinity of their respective corners with the lower and upper walls.

[0025] In this configuration, at least one fin comprises an upper fin extending in the vicinity of the upper corner and whose extrados is opposite the upper wall, at least one fin further comprising a lower fin extending in the vicinity of the lower corner and whose intrados is opposite the lower wall.

[0026] According to an advantageous embodiment of the invention, the two respective fins of a given side wall are separated from each other by a distance corresponding to at least 70% of a total height of the fairing.

[0027] Advantageously, the proximity of the upper fin to the lower fin allows the creation of two opposing vortices (contrarotating to the marginal vortices) in close proximity to each other, thus partially eliminating the energy transmitted to the external flow at the level of the nacelle wake, which makes it possible to effectively reduce the local intensity of the marginal vortex and the induced drag.

[0028] According to an advantageous embodiment of the invention, at least one fin comprises two substantially parallel fins extending respectively from the upper wall and the lower wall and arranged in the vicinity of two respective corners with the same lateral wall.

[0029] According to an advantageous embodiment of the invention, the propulsion unit comprises a vertical wall connecting the upper wall to the lower wall and substantially parallel to the side walls, and at least one intermediate fin arranged in the vicinity of a corner between the vertical wall and one of the upper or lower walls.

[0030] The invention also relates to a fixed-wing aircraft comprising a fuselage, two wings and two propulsion units arranged respectively on either side of the fuselage, downstream and at a distance from the wings, said propulsion units forming an auxiliary wing with positive lift, comprising two ends determining a wingspan of said auxiliary wing, remarkable in that the propulsion units conform to one of the embodiments mentioned above, the fins being dimensioned so that in flight conditions, marginal vortices produced at the two ends of the auxiliary wing interact with opposing vortices produced at the fins so as to reduce the vortex drag of the nacelle after interaction.

[0031] According to an advantageous embodiment of the invention, the reduction in the nacelle's vortex drag is at least 5%, and preferably at least 50%. More preferably, the reduction in the nacelle's vortex drag is 10%. It is understood that this reduction is comparable to the vortex drag generated by a nacelle without fins.

[0032] According to an advantageous embodiment of the invention, each fin extends axially in a direction that is substantially parallel to the direction assumed by the airflow in the fairing of the propulsion unit.

[0033] In general, the invention makes it possible to reduce the marginal vortices of the nacelle and thereby reduce the induced drag of the nacelle. This results in savings. fuel. At the same time, the aircraft's wake turbulence is reduced, which benefits the flow of air traffic around the runway.

[0034] The invention is adaptable to existing aircraft because it does not require modification of a standard wing or fuselage. Brief description of the drawings

[0035] [Fig-1] represents an aircraft according to the invention;

[0036] [Fig.2] represents an isometric view of a gondola according to a first method of publication of the invention;

[0037] [Fig.3] schematically illustrates vortex interactions in a fairing of the gondola of the [Fig.2];

[0038] [Fig.4] represents an enlarged view of a lateral side of a gondola according to a second method of implementing the invention;

[0039] [Fig.5] schematically illustrates a vortex interaction in the fairing of the gondola of the [Fig.4]. Detailed description

[0040] The figures represent the elements schematically. Some dimensions may be exaggerated to facilitate reading the drawings.

[0041] Upstream and downstream are understood in the direction of airflow. The longitudinal direction is the direction of the aircraft's longest dimension, i.e., parallel to the fuselage (corresponding to the X-axis of [Fig. 1]). The transverse direction (Y-axis of [Fig. 1]) is perpendicular to the fuselage and horizontal when the aircraft is on the ground.

[0042] It is understood that particular embodiments of the invention are drawn but that the figures do not in any way limit the scope of protection which is only dictated by the claims.

[0043] Also, each element of each figure can be combined with each other element of each other figure according to all technically possible combinations.

[0044] Fig. 1 shows an aircraft 2. This consists of a fuselage 4 and two wings 6, fixed relative to the fuselage 4. The wings are equipped with flaps 8.

[0045] On either side of the fuselage 4 and downstream of the wings 6 are located two propulsion units 10. By "propulsion unit" is meant a module capable of generating thrust necessary for the flight of the aircraft 2.

[0046] The propulsion unit 10 comprises a nacelle 12 which can be mechanically connected to the fuselage 4 and / or the wing 6 by means of connecting links. An arm extending substantially transversely from the fuselage 4 can, for example, connect the nacelle 12 to the fuselage 4 on the downstream side of the nacelle 12.

[0047] The nacelle 12 comprises a plurality of blowers. These can be driven rotated by their respective turbines. Each fan can be part of a self-contained unit (like a turbojet with a compressor, combustion chamber, and turbines). Alternatively, the turbines driving the fans can be powered by a pressurized gas produced elsewhere in the aircraft: for example, a single compressor for several fans can supply the nacelle turbines with pressurized gas. In another variant, the fans are driven by an electric motor.

[0048] The aircraft 2 comprises several fixed wings generating lift, such as a tail assembly 3, the wings 6 and the nacelle 12. For this purpose, these elements create wingtip vortices 3', 6' and 12', respectively at the tips of said fixed wings, these tips being away from the fuselage 4.

[0049] Thus, the two nacelles 12 on either side of the fuselage 4 are considered to form an auxiliary wing. The present invention aims to limit the drag associated with the wingtip vortices 12' at the lateral extremities of the auxiliary wing. This reduction will be detailed in this description.

[0050] Fig.2 shows on its right side an isometric view of a downstream portion 12.2 of the nacelle 12 of Fig.1.

[0051] With reference to the right-hand side of [Fig. 2], the nacelle 12 is laterally bounded on both sides by a side wall 17, at the bottom by a lower wall 16, and at the top by an upper wall 14. The lower, upper, and side walls form a fairing 14, 16, 17 that defines a passage for an airflow. Vertical walls 20 connecting the lower wall 16 to the upper wall 14 subdivide the nacelle into several compartments. Each compartment internally defines an air passage housing a blower 18.

[0052] Each of the walls 14, 16, 17 comprises an upstream edge (14.3, 16.3, 17.3) and a downstream edge (14.2, 16.2, 17.2), respectively.

[0053] At the downstream portion 12.2 of the nacelle 12, an intermediate wall 22 can be arranged, the latter preferably extending over a total span of the nacelle 12 (along the transverse axis Y). The intermediate wall 22 is preferably arranged at approximately half the height of the fairing.

[0054] The left-hand side of [Fig. 2] is an enlarged view of a lateral side of the nacelle 2 according to a first embodiment. This is the lateral side outside the fuselage of the aircraft of [Fig. 1], and particularly the starboard side of the aircraft. An upper fin 24 and a lower fin 26 are visible, the two fins 24, 26 extending preferably perpendicularly to the lateral wall 17. Thus, in this example, "at least one fin" of the invention consists of the two fins 24, 26.

[0055] In this configuration, the upper fin 24 is close to the upper wall 14, and particularly close to an upper corner 14.1 formed between said upper wall 14 and the side wall. In parallel, the lower fin 26 is close to a lower corner 16.1 formed between the lower wall 16 and the side wall 17.

[0056] By "close", we mean at a distance from the corner corresponding to less than 10% of the height H of the fairing 14, 16, 17.

[0057] However, in an alternative to the first embodiment (not illustrated), "at least one fin" comprises only one fin, namely the upper fin 24 or the lower fin 26.

[0058] The fins 24, 26 are arranged closer to the downstream edge 17.2 of the side wall 17 (approximately at the same level as the downstream portion 12.2 of the nacelle 12) than to the upstream edge 17.3 of said wall 17.

[0059] According to the first embodiment illustrated in [Fig.2], from the upstream part 12.3 of the nacelle 12 towards the downstream portion 12.2, each fin 24, 26 gradually protrudes internally from the fairing up to a maximum length 1 before tapering towards the downstream portion 12.2.

[0060] Preferably, the length 1 corresponds to approximately 10% of the distance L between the upstream edge 17.3 and the downstream edge 17.2 of the side wall 17. Here, the term "approximately" denotes a margin of ±5% of the nominal value. However, the length 1 may be up to 30% of said distance.

[0061] Each fin 24, 26 has a maximum width w between 5 and 10% of the distance D between the side walls 17. For this purpose, the maximum width w corresponds to 5% and up to 10% of the total span of the nacelle 12.

[0062] Preferably, the two fins 24, 26 are parallel and arranged symmetrically in the nacelle 12, possibly symmetrically on either side of the intermediate wall 22. In this configuration, the upper fin 24 comprises an extrados 24.1 facing the upper wall 14 and an intrados 24.2 facing the intermediate wall 22. The lower fin 26 comprises an extrados 26.1 facing the intermediate wall 22 and an intrados 26.2 facing the lower wall 16.

[0063] Preferably, the two fins 24, 26 are spaced apart by a distance corresponding to at least 70% of the total height of the fairing. The distance between the two fins 24, 26 can be up to 90% of the height of the fairing.

[0064] In addition to or as an alternative to the fins 24, 26, one or more fins may extend from the vertical wall 20, in order to ensure internal vortex cancellation, for example, by canceling any vortex that may be generated in the vicinity of a corner 20.1 formed by the lateral wall 20 and the upper wall 14.

[0065] In addition to the fins 24 and 26, two other fins may be provided at the two other corners of the fairing. These may be symmetrical with respect to a median (vertical) plane of the nacelle with fins 24, 26.

[0066] Fig. 3 schematically illustrates the vortex interactions in the fairing of nacelle 12 of Fig. 2.

[0067] At the right of the upper corner 14.1 of the nacelle, a first internal marginal vortex 14' can be observed, the latter being generated by the lift of the nacelle 12 and more precisely of the upper wall 14. Similarly, at the right of the lower corner 16.1 of the nacelle, a second internal marginal vortex 16' is due to the lift of the lower wall 16.

[0068] It should be noted that the marginal vortex 12' of [Fig. 1] can result from the combination of the two internal marginal vortices 14' and 16'.

[0069] Partial vortex cancellation takes place in the fairing thanks to the opposing vortices 24' and 26' generated respectively by the fins 24, 26. In this configuration, the first internal marginal vortex 14' can be canceled by the first opposing vortex 24', and similarly, the second internal marginal vortex 16' can be canceled by the second opposing vortex 26'.

[0070] It should be noted that the two fins 24, 26 create, in addition to the opposing vortices 24', 26', a vorticity layer 28 along the lateral wall 17, this vorticity corresponds to a downward deviation of the airflow between the upper fin 24 and the lower fin 26. Indeed, the vorticity layer 28 induces a flow having an induced velocity V resulting from the downward circulation of said vorticity 28 from the upper fin 24.

[0071] In this configuration, the vorticity layer 28 produces an airflow equal in quantity and opposite in direction of rotation to that of the corner vortices 24' and 26'. Thus, the presence of the fins 24, 26 cancels out the vortices without hindering the lift of the nacelle. The reduction of the induced drag of the nacelle is therefore achieved without impairing its lift.

[0072] Fig. 4 represents an enlarged view of a lateral side of a gondola according to a second embodiment of the invention.

[0073] In this case, at least one fin is formed of an upper fin 24 and a lower fin 26. As in the previous case, a single fin may also suffice.

[0074] The two fins 24, 26 are preferably identical to the fins 24, 26 according to the first embodiment but their arrangements in the fairing of the nacelle are different.

[0075] The two fins 24, 26 are here substantially parallel and aligned, extending respectively from the upper wall 14 and from the lower wall 16. The fins 24, 26 are however this time again arranged in the vicinity of the two respective corners 14.1 and 16.1 with the lateral wall 17.

[0076] The two fins 24, 26 extend preferentially perpendicularly to the edges downstream of the upper wall 14 and the lower wall 16. The upper fin 24 is close to the upper corner 14.1 and the lower fin 26 is close to the lower corner 16.1. Preferably, the downstream edge of each of the two walls 14 and 16 is formed of a pivoting flap thus allowing adjustment of the air outlet section of the nacelle.

[0077] Advantageously, this allows for management of the outgoing flow which makes it possible to further reduce the marginal vortex at the exit of the nacelle.

[0078] Preferably, the two fins 24, 26 are parallel and arranged symmetrically in the nacelle 12 with respect to the intermediate wall 22. Alternatively, and as described in [Fig.5], the fins 24, 26 may be antisymmetric with respect to the intermediate wall 22.

[0079] Indeed, on [Fig.5], the extrados 24.1 of the upper fin 24 faces the adjacent vertical wall (vertical wall 20 of [Fig.4]) and the intrados 24.2 faces the lateral wall 17. At the same time, the extrados 26.1 of the lower fin 26 faces the intermediate wall 22 and the intrados 26.2 faces the lower wall 16.

[0080] Advantageously this arrangement and orientation of the fins 24, 26 allows the opposing vortices 24' and 26' to be generated in order to ensure vortex cancellation with the two internal marginal vortices 14' and 16'.

[0081] The invention is not limited to the two embodiments described. Indeed, the two embodiments are combinable. To this end, the nacelle 12 of [Fig. 1] can comprise both at least one fin extending from the side wall according to the first embodiment, and at least one fin extending from the lower wall and / or the upper wall according to the second embodiment of the invention.

[0082] The combination of the two embodiments of the invention may correspond to a nacelle having four fins, two extending from the side wall, and two others extending from the upper and lower walls. Alternatively or in addition, the nacelle may include fins at its four corners: upper and lower corners, laterally inside (i.e., near the fuselage) or outside.

[0083] In this regard, the dimensions (1, w) as well as the thicknesses of the fins of the invention can vary with respect to each other in order to ensure effective and targeted vortex cancellation according to the intensity of the marginal vortex to be canceled.

[0084] In addition, intermediate fins can be added to the vertical walls of the nacelle in order to ensure vortex cancellation in all corners inside the nacelle.

[0085] The reduction in the total intensity of the vortex drag is at least 5%, and preferably at least 50%, and may even be a total cancellation of the marginal vortices at the ends of the nacelle.

Claims

Demands

1. Propulsion unit (10) for fixed-wing aircraft (2), the propulsion unit (10) comprising a nacelle (12) housing at least two non-coaxial fans (18), said nacelle (12) comprising an upper wall (14), a lower wall (16), and two side walls (17) providing the connection between the upper (14) and lower (16) walls, each of the walls (14, 16) having an upstream edge (14.3, 16.3) and a downstream edge (14.2, 16.2), the walls together defining a fairing (14, 16, 17) generally oblong or rectangular, characterized in that the nacelle (12) comprises at least one fin (24, 26) arranged in the vicinity of a corner (14.1, 16.1, 20).1) of the fairing (14, 16, 17), the fin (24, 26) extending internally into the fairing (14, 16, 17) from one of its walls (14, 16, 17) and being closer to the downstream edge than to the upstream edge of the wall (14, 16, 17) from which it extends, and in that the lateral walls (17) each comprise two fins (24, 26), in the vicinity of their respective corners (14.1, 16.1) with the lower (16) and upper (14) walls, said two fins (24, 26) respective to a given lateral wall (17) are separated from each other by a distance corresponding to at least 70% of a total height (H) of the fairing (14, 16, 17).

2. Propulsion unit (10) according to claim 1, characterized in that at least one fin (24, 26) extending from the side wall (17) comprises an extrados (24.1, 26.1) facing the upper wall (14) and an intrados facing the lower wall (16).

3. Propulsion unit (10) according to claim 1 or 2, characterized in that at least one fin (24, 26) extends from the lower wall (16) or from the upper wall (14) and comprises an intrados (24.2, 26.2) and an extrados (24.1, 26.1), said extrados (24.1, 26.1) facing the nearest lateral wall (17, 20).

4. Propulsion unit (10) according to any one of claims 1 to 3, characterized in that from upstream (12.3) to downstream (12.2), at least one fin (24, 26) gradually protrudes from the fairing (14, 16, 17) up to a maximum length (1) before tapering downstream (12.2).

5. Propulsion unit (10) according to any one of claims 1 to 4, characterized in that at least one fin (24, 26) is of a length (1) corresponding to approximately 10% of the distance (L) between the upstream edge (14.3, 16.3, 17.3) and the downstream edge (14.2, 16.2, 17.2) of the wall (14, 16, 17) from which it extends.

6. Propulsion unit (10) according to any one of claims 1 to 5, characterized in that at least one fin (24, 26) has a maximum width (w) between 5 and 10% of the distance (D) between the side walls (17).

7. Propulsion unit (10) according to any one of claims 1 to 6, characterized in that at least one fin (24, 26) is disposed in a downstream portion (12.3) of the nacelle extending over less than 30% of the distance (L) between the upstream edge (14.3, 16.3, 17.3) and the downstream edge (14.2, 16.2, 17.2) of the wall (14, 16, 17) from which it extends.

8. Propulsion unit (10) according to any one of claims 1 to 7, characterized in that at least one fin (24, 26) comprises two substantially parallel fins (24, 26) extending respectively from the upper wall (14) and the lower wall (16) and arranged in the vicinity of two respective corners (14.1, 16.1) with the same side wall (17).

9. Propulsion unit (10) according to any one of claims 1 to 8, characterized in that it comprises a vertical wall (20) connecting the upper wall (14) to the lower wall (16) and substantially parallel to the side walls (17), and at least one intermediate fin arranged in the vicinity of a corner (20.1) between the vertical wall (20) and one of the upper (14) or lower (16) walls.

10. Fixed-wing aircraft (2) comprising a fuselage (4), two wings (6) and two propulsion units (10) disposed respectively on either side of the fuselage (4), downstream and at a distance from the wings (6), said propulsion units (10) forming a positive-lift auxiliary wing, comprising two ends determining a wingspan of said auxiliary wing, characterized in that the propulsion units (10) conform to any one of claims 1 to 9, the winglets (24, 26) being dimensioned so that under flight conditions, wingtip vortices (12') produced at the two ends of the auxiliary wing interact with opposing vortices (24', 26') produced at the winglets (24, 26) so as to reduce the vortex drag of the nacelle (12) after interaction.

11. Aircraft (2) according to claim 10, characterized in that the reduction of the vortex drag of the nacelle (12) is at least 5%, and preferably at least 50%.

12. Aircraft (2) according to any one of claims 10 and 11, characterized in that each winglet (24, 26) extends axially in a direction that is substantially parallel to the direction assumed by the airflow in the propulsion unit fairing (10).

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