AIRCRAFT WITH REDUCED DRAG THROUGH INTERACTION BETWEEN MARGINAL VORTICLES

Abstract

AIRCRAFT WITH REDUCED DRAG BY INTERACTION BETWEEN MARGINAL VORTICULATIONS The invention relates to an aircraft (2) comprising a fuselage (4); two nacelles (8) arranged on either side of the fuselage (4) and forming an auxiliary wing with positive lift, comprising two ends (8.3, 8.4) determining a span of said auxiliary wing; a secondary wing (10) extending on either side of the fuselage (4), at the rear of the auxiliary wing, with negative lift and comprising two ends (10.3, 10.4) determining a span of said secondary wing; in which the wingspans of the auxiliary and secondary wings are dimensioned so that under flight conditions, marginal vortices (Γ) produced at the two ends (8.3, 8.4) of the auxiliary wing interact with opposite marginal vortices (Γ') produced at the two ends (10.3, 10.4) of the secondary wing (10) so as to reduce the net intensity of said marginal vortices after interaction. (Figure to be published with the abstract: Figure 1).

Description

Title of the invention: AIRCRAFT WITH REDUCED DRAG THROUGH INTERACTION BETWEEN MARGINAL VORTICULATIONS Technical field

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

[0002] The lift of an aircraft wing induces aerodynamic drag through the formation of vortices. Indeed, the 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 the wake of the wing. Also, the pressure difference between the upper and lower surfaces of the wing causes marginal vortices at each of the two ends of the wing. These vortices form an induced drag in that it consumes energy from the aerodynamic phenomena linked to the lift of the wing. It should be noted that a wing, like any other element in contact with the air flow, also causes friction drag linked to the viscosity of the air in the boundary layer.

[0003] It is generally sought to reduce the drag of a wing, in particular the induced drag, that is to say that linked to the lift of the wing.

[0004] Published patent document WO 2021 / 074516 A1 proposes an aircraft architecture with a generally elongated fuselage, a lifting wing consisting of two wings arranged on either side of the fuselage, and two lifting nacelles arranged directly aft of the two wings, so as to be directly in the wake of the two wings. Each of the nacelles forms an air inlet fairing, with an upper wall, a lower wall and two side walls, and houses several propulsion engines in the fairing. The upper and lower walls form an auxiliary lifting wing. The air inlet edge of the lower wall is arranged directly downstream of the trailing edge of the corresponding wing, so as to take advantage of the wing's wake.More specifically, the nacelles are positioned relative to the wings so that the boundary layer of the upper surface of the wings passes under the lower wall, the lower wall in question then being swept by the wake of the wing. The wake of the nacelles is thus reduced. The wake of the stabilizers remains unchanged. Statement of the invention

[0005] The invention aims to overcome at least one drawback of the aforementioned state of the art. More specifically, the invention aims to reduce the induced drag of an aircraft, especially stabilizer drag.

[0006] The subject of the invention is an airplane comprising a fuselage elongated along a longitudinal axis; two nacelles arranged on either side of the fuselage and forming an auxiliary wing with positive lift, comprising two ends determining a span of said auxiliary wing; a secondary wing extending on either side of the fuselage, at the rear of the auxiliary wing, being with negative lift and comprising two ends determining a span of said secondary wing; remarkable in that the spans of the auxiliary and secondary wings are dimensioned so that in flight conditions, marginal vortices produced at the two ends of the auxiliary wing interact with opposite marginal vortices produced at the two ends of the secondary wing so as to reduce the net intensity of said marginal vortices after interaction.

[0007] By negative lift of a wing, it is meant that the wing is capable of generating, in flight conditions, a force perpendicular to the mean plane of the wing, directed downwards. Similarly, by positive lift of a wing, it is meant that the wing is capable of generating, in flight conditions, a force perpendicular to the mean plane of the wing, directed upwards.

[0008] According to an advantageous embodiment of the invention, the reduction in the net intensity of the marginal vortices after interaction is at least 10%, preferably at least 30%, more preferably at least 50%.

[0009] According to an advantageous embodiment of the invention, the span of the auxiliary wing and the span of the secondary wing are identical or different from each other by less than 15%.

[0010] According to an advantageous embodiment of the invention, the aircraft further comprises a main wing extending on either side of the fuselage, at the front of the two nacelles, said main wing having positive lift.

[0011] According to an advantageous embodiment of the invention, each of the two nacelles comprises an upper wall and a lower wall, said upper and lower walls forming the auxiliary wing, said lower walls each comprising an air inlet edge aligned longitudinally with the corresponding trailing edge of the main wing.

[0012] According to an advantageous embodiment of the invention, the air inlet edge of the lower wall of each of the two nacelles is located at a distance from the corresponding trailing edge of the main wing which is between 0.02 and 0.2 times an average aerodynamic chord length of the main wing over the span of the auxiliary wing.

[0013] According to an advantageous embodiment of the invention, each of the two nacelles comprises at least one propulsion motor arranged between the upper wall and the lower wall of said nacelle.

[0014] According to an advantageous embodiment of the invention, the main wing and the at least one propulsion engine are dimensioned so that in flight conditions and in nominal regime of said at least one propulsion engine, additional marginal vortices, adjacent to the marginal vortices at the two ends of the auxiliary wing, are produced and interact with the opposite marginal vortices produced at the two ends of the secondary wing so as to reduce the net intensity of said marginal vortices after interaction.

[0015] According to an advantageous embodiment of the invention, the additional marginal vortices are produced at the trailing edge of the main wing, between each of the ends of the auxiliary wing and the corresponding end of the main wing.

[0016] According to an advantageous embodiment of the invention, the span of the auxiliary wing is less than the span of the secondary wing.

[0017] The measures of the invention are advantageous in that they reduce the induced drag of the aircraft. They essentially consist of dimensioning the wings, in this case the auxiliary wing and the secondary wing, so that their respective marginal vortices interact destructively, that is to say in such a way as to reduce their net intensity after interaction. This makes it possible to reduce the drag induced by the positive and negative lift of the auxiliary and secondary wings, respectively, and also to reduce the turbulence caused by the flight of the aircraft, potentially disturbing for aircraft using the same air corridors. Brief description of the drawings

[0018] [Fig.l] is a top view of an aircraft according to the invention;

[0019] [Fig.2] is a perspective view of the aircraft of [Fig.l];

[0020] [Fig.3] is a top view of an aircraft variant according to the invention;

[0021] [Fig.4] is a top view of an aircraft according to the state of the art, illustrating the vortex system associated with the lift of the wing, of an aircraft according to the invention, further illustrating the vortex system associated with the lift of the nacelles, and of the same aircraft further illustrating the vortex system associated with the lift of the main wing due to the coupling with the propulsion engines of the nacelles. Detailed description

[0022] In the description which follows, the notions of relative positioning expressed in particular by the terms "rear" and "front" are to be understood in the longitudinal direction and in the normal direction of advance of the aircraft. Also, the notions of orientation expressed in particular by the terms "vertical", "horizontal" are to be understood when the aircraft is in normal flight position, that is to say with its longitudinal axis and its wings generally horizontal.

[0023] [Fig.l] is a top view of an aircraft according to the invention.

[0024] The aircraft 2 essentially comprises a fuselage 4 extending in a longitudinal direction, a main wing 6 formed by two wings extending on either side of the fuselage 4, two nacelles 8 arranged on either side of the fuselage 4, behind the main wing 6, and a secondary wing 10 formed by two stabilizers extending on either side of the fuselage 4, behind the main wing 6 and the two nacelles 8. The secondary wing 10 has negative lift, meaning that it is capable of generating, in flight conditions, a force perpendicular to the mean plane of the secondary wing, directed downwards.

[0025] The two nacelles 8 each form a fairing generally elongated in a transverse direction and housing one or more propulsion engines. This fairing has the particularity of forming an auxiliary wing with positive lift. This auxiliary wing is formed essentially by upper and lower walls forming a wing profile capable of generating positive lift. Each of the nacelles is advantageously arranged close to the trailing edge 6.2 of the main wing 6, so as to take advantage of the wake of the main wing 6 in question.

[0026] The two nacelles 8 have a span which is identical or at least close to the span of the secondary wing 10, so that the marginal vortices formed by the positive lift of the auxiliary wing of the nacelles oppose the marginal vortices formed by the negative lift of the secondary wing 10.

[0027] When the aircraft is in flight, the airflow along the nacelles 8 causes air circulation around each nacelle. This air circulation is, along the upper wall of the nacelle, namely the extrados, from the leading edge 8.1 towards the trailing edge 8.2 of the nacelle, and along the lower face of the nacelle, namely the intrados, from the trailing edge 8.2 towards the leading edge 8.1. Indeed, the profile of the nacelle is such that the flow along the extrados is accelerated relative to the flow along the intrados. This difference in speed causes a pressure difference, namely a depression on the extrados and an overpressure on the intrados, causing the lift of the auxiliary wing. This difference in flow speed between the extrados and the intrados causes a vortex system which manifests itself at each of the two ends 8.3 and 8.4 of the nacelles by a marginal vortex r (capital Greek letter gamma).Each of these two marginal vortices has an axis of rotation generally parallel to the longitudinal axis of the aircraft, passing through the corresponding end 8.3 or 8.4 of the nacelle 8. These two marginal vortices are counter-rotating in that they have opposite directions of rotation. The marginal vortex r produced at the left end 8.3 of the nacelles 8 rotates, seen from the rear of the aircraft, in a clockwise direction while the marginal vortex T produced at the right end 8.4. of the nacelles 8 rotates, seen from the rear of the aircraft, in an anti-clockwise direction. These directions of rotation are the result of the lift of the auxiliary wing of the nacelles 8. Indeed, the positive pressure difference between the intrados (lower wall) and the extrados (upper wall) dictates these two opposite directions of rotation. This phenomenon is in itself well known to those skilled in the art.

[0028] Similar to what is described above, the secondary wing 10 formed by the stabilizers causes, when the aircraft is in flight, a circulation of air around each stabilizer. This circulation of air is however in a direction opposite to that around the nacelles 8 due to the "offset" or negative lift nature of the secondary wing 10. This means that the extrados, that is to say the face along which the air flow is accelerated, is on the lower face of the secondary wing and, similarly, the intrados, that is to say the face along which the air flow is decelerated, is on the upper face of the secondary wing. The airflow along the lower face is therefore faster than the flow along the upper face, leading to circulation, along the upper face, from the trailing edge 10.2 to the leading edge 10.1, and along the lower face, from the leading edge 10.1 towards the trailing edge 10.2. Similar to the auxiliary wing of the nacelles 8, this difference in flow speed between the upper and lower surfaces causes a vortex system which manifests itself at each of the two ends 10.3 and 10.4 of the nacelles by a marginal vortex T' (Greek letter gamma capital prime). These two marginal vortices are counter-rotating for the same reasons as for the auxiliary wing of the nacelles 8. The directions of rotation of these marginal vortices T' are however opposite to those of the corresponding marginal vortices T, so that the interaction of these marginal vortices T and T' causes their cancellation, or at least a significant reduction in their intensity. This interaction takes place thanks to the correspondence between the spans of the auxiliary and secondary wings.For this interaction to take place, it is in fact necessary for the marginal vortices T and T' on each side of the fuselage 4, rotating in opposite directions, to meet.

[0029] The cancellation or significant reduction of the marginal vortices T' of the secondary wing 10 by the marginal vortices T of the auxiliary wing of the nacelles 8 is advantageous in that it reduces the induced drag of the aircraft 2. These marginal vortices in fact involve air movement speeds and thus quantities of movement whose power is drawn from the lift of the corresponding wings. It is therefore particularly advantageous, from an energy point of view, to reduce these marginal vortices as much as possible.

[0030] [Fig. 2] is a perspective view, from a viewpoint located in front of and above the aircraft 2, of the main wing 6, the nacelles 8 and the secondary wing 10, illustrating the marginal vortices F and P described above.

[0031] In [Fig. 2] the construction of the nacelles 8 can be seen, namely their fairings with the end walls 8.3 and 8.4, and the upper 8.5 and lower 8.6 walls. In this case, each nacelle fairing 8 houses four propulsion engines, it being understood that this number can be different, namely larger or smaller. It can also be seen that each of the lower walls 8.6 is aligned with the main wing 6. More precisely, the nacelles are positioned so that the boundary layer of the upper surface of the main wing 6 passes under the lower walls 8.6, the lower walls then being swept by the wake of the main wing 6. This means that the propulsion engines housed in the nacelles 8 are located above the wake of the main wing 6, thus ensuring maximum thrust.

[0032] Still in [Fig.2], it can be observed that the axes of rotation of the marginal vortices T and T', on each side of the fuselage 4, are not perfectly aligned. Perfect alignment can be difficult to achieve and moreover can depend on the flight conditions, essentially the speed of the aircraft and its attitude. Also, the marginal vortices T and P have a certain diameter, so that a certain offset between their axes of rotation allows at least partial destructive interaction of said marginal vortices.

[0033] [Fig. 3] is a top view of an aircraft variant of [Fig. 1], according to the invention, illustrating a partial cancellation of the marginal vortices T and P.

[0034] It is indeed possible to observe a shift, in this case horizontal, between the axes of rotation of the marginal vortices T and P. It is understood that this shift can be vertical, or a combination of horizontal shift and vertical shift. It is observed that, on each side of the fuselage 4, the marginal vortex after interaction y, downstream of the secondary wing 10 and the interaction between the marginal vortices T and P, has an intensity which is lower than that of each of the marginal vortices T and T'. In this case the marginal vortex after interaction y is of the same direction of rotation as the corresponding marginal vortex T, because the latter is of greater intensity than the marginal vortex P. In other words, the marginal vortex P generated by the secondary wing 10 is essentially cancelled by the marginal vortex T generated by the auxiliary wing of the nacelles 8, the latter then being reduced.Partial cancellation can therefore be due to a difference in intensity, a shift in the axes of rotation, or a combination of the two.

[0035] [Fig. 4] is a top view of an aircraft according to the state of the art, illustrating the vortex system associated with the lift of the wing, of an aircraft according to the invention, illustrating, in addition, the vortex system associated with the lift of the nacelles, and of the same aircraft illustrating, in addition, the vortex system associated with the lift of the main wing due to the coupling with the propulsion engines of the nacelles.

[0036] On the left of [Fig. 4], the vortex system of the main wing 106 of an aircraft 102 according to the state of the art is illustrated. It can be seen that it extends transversely along the wings on either side of the fuselage 104 to end at the ends of the wings and form two marginal vortices.

[0037] In the center of [Fig. 4], illustrating an airplane according to the invention, one can observe, in addition to the vortex system of the main wing 6, the vortex system of the auxiliary wing of the nacelles 8. This vortex system is similar to that of the main wing, with the difference that it ends at the ends of the nacelles having a wingspan substantially smaller than that of the main wing 6. As illustrated in [Fig. 1], the marginal vortices of the vortex system of the auxiliary wing of the nacelles 8 pass through the ends of the secondary wing 10. This configuration of the vortex systems corresponds to the absence of influence of the propulsion engines housed in the nacelles 8, for example when the power of these engines is reduced or zero (i.e. in freewheel mode).

[0038] To the right of [Fig.4], an additional vortex system can be observed on the main wing 6, generated by the propulsion of the propulsion engines, i.e. when they are under load. In this situation, the propulsion engines, due to the air displacement that they generate, form above the upper surface of the main wing 6 an air flow with speeds higher than those of the flow linked to the speed of movement of the aircraft. This air flow creates this additional vortex system increasing the lift of the main wing 6, at least limited to an extent of said wing corresponding essentially to the span of the nacelles 8. This additional vortex system produces additional marginal vortices separating from the main wing 6 near the ends of the nacelles 8, however at a distance towards the outside of these ends.The directions of rotation of these marginal vortices are those of a lifting wing, that is to say identical to those of the vortex systems of the main wing 6 and of the auxiliary wing of the nacelles 8, and therefore opposite to those of the vortex system of the secondary wing 10. This means that when the propulsion engines are under load, as opposed to flight conditions where the aircraft is gliding, there is a generation of additional marginal vortices likely to be shifted outwards relative to the marginal vortices of the vortex system of the auxiliary wing of the nacelles 8. Depending on this shift, these marginal vortices will be less likely to cancel or reduce the marginal vortices of the vortex system of the secondary wing 10.

[0039] It is thus possible to provide for a dimensioning of the wingspans of the auxiliary and secondary wings, taking into account the additional vortex system due to the coupling between the main wing and the propulsion engines, so as to obtain an optimal reduction of the marginal vortices of the vortex system of the secondary wing for the different flight conditions. For example, the wingspan of the auxiliary wing may be less than that of the secondary wing, while being close to it, so as to reduce the drag of the secondary wing when the propulsion engines are at low or zero load and to further reduce, or even cancel, the drag of the secondary wing when the propulsion engines are at nominal load, by the effect of the marginal vortices of the additional vortex system resulting from the aero-propulsive coupling between the propulsion engines and the main wing.

[0040] It should be noted that for the generation of the additional vortex system to take place, it is necessary to have an aerodynamic coupling between the propulsion engines and the main wing. In other words, the airflow generated by the propulsion engines must be active along the upper surface of the main wing. The distance between the nacelles 8 and the main wing 6 must then be reduced. Advantageously, the air inlet edge of the lower wall of each of the two nacelles is located at a distance from the corresponding trailing edge of the main wing which is between 0.02 and 0.2 times an average aerodynamic chord length of the main wing over the span of the auxiliary wing.

[0041] The aerodynamic phenomena described above are presented in a schematic and simplified manner, for the purpose of clarity of presentation of the invention. It is understood that in reality these phenomena are more complex and are in particular subject to disturbances by other phenomena not mentioned and of lesser importance. They are also subject to variations depending on the flight conditions, namely depending on the speed of movement of the aircraft relative to the ambient air and the power supplied by the propulsion engines. In the absence of specific mention, the flight conditions are flight conditions in nominal regime.

[0042] Generally, the reduction in the total intensity of the marginal vortices may have different levels. It may be at least 10%, preferably at least 20%, more preferably at least 30%, more preferably still at least 50%, more preferably still at least 70%, more preferably still at least 80%.

[0043] For this purpose, the span of the auxiliary wing and the span of the secondary wing are identical or different from each other by less than 15%, preferably by less than 10%, more preferably still by less than 5%. The span of the auxiliary wing may be less than the span of the secondary wing. Alternatively, the span of the auxiliary wing may be greater than the span of the secondary wing.

[0044] It should be noted that the ends of the wings, commonly referred to as wingtips, can have complex shapes that can have several possible points for measuring the span. For this purpose, and with reference to the complexity of the aerodynamic phenomena as mentioned above, it is appropriate to define the spans of the auxiliary and secondary wings by reference to the destructive interactions between the marginal vortices, which are, themselves, easily detectable and measurable.

Claims

Claims

1. Aircraft (2) comprising: - a fuselage (4) elongated along a longitudinal axis; - two nacelles (8) arranged on either side of the fuselage (4) and forming an auxiliary wing with positive lift, comprising two ends (8.3, 8.4) determining a span of said auxiliary wing; - a secondary wing (10) extending on either side of the fuselage (4), at the rear of the auxiliary wing, being with negative lift and comprising two ends (10.3, 10.4) determining a span of said secondary wing; - a main wing (6) extending on either side of the fuselage (4), at the front of the two nacelles (8), said main wing being with positive lift; in which the wingspans of the auxiliary and secondary wings are sized so that in flight conditions, marginal vortices (F) produced at both ends (8.3, 8.4) of the auxiliary wing interact with opposite marginal vortices (F') produced at the two ends (10.3, 10.4) of the secondary wing (10) so as to reduce the net intensity of said marginal vortices after interaction (y); characterized in that each of the two nacelles (8) comprises an upper wall (8.5) and a lower wall (8.6), said upper (8.5) and lower (8.6) walls forming the auxiliary wing, said lower walls (8.6) each comprising an air inlet edge (8.1) longitudinally aligned with the corresponding trailing edge (6.2) of the main wing (6).

2. Aircraft (2) according to claim 1, wherein the reduction in the total intensity of the marginal vortices (F, F') is at least 10%, preferably at least 30%, more preferably at least 50%.

3. Aircraft (2) according to one of claims 1 and 2, in which the span of the auxiliary wing and the span of the secondary wing (10) are identical or different from each other by less than 15%.

4. Aircraft (2) according to one of claims 1 to 3, in which the air inlet edge (8.1) of the lower wall (8.6) of each of the two nacelles (8) is located at a distance from the corresponding trailing edge (6.2) of the main wing (6) which is between 0.02 and 0.2 times an average aerodynamic chord length of the main wing (6) over the span of the auxiliary wing.

5. Aircraft (2) according to one of claims 1 to 4, in which each of the two nacelles (8) comprises at least one propulsion engine arranged between the upper wall (8.5) and the lower wall (8.6) of said nacelle.

6. Aircraft (2) according to claim 5, wherein the main wing (6) and the at least one propulsion engine are dimensioned so that in flight conditions and in nominal regime of said at least one propulsion engine, additional marginal vortices, adjacent to the marginal vortices (F) at the two ends (8.3, 8.4) of the auxiliary wing, are produced and interact with the opposite marginal vortices (F') produced at the two ends (10.3, 10.4) of the secondary wing (10) so as to reduce the net intensity of said marginal vortices after interaction (y).

7. Aircraft (2) according to claim 6, wherein the additional marginal vortices are produced at the trailing edge (6.2) of the main wing (6), between each of the ends (8.3, 8.4) of the auxiliary wing and the corresponding end of the main wing (6).

8. Aircraft (2) according to one of claims 1 to 7, in which the span of the auxiliary wing is less than the span of the secondary wing (10).

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