VORTEX WAKE ATTENUATION DEVICE

Abstract

A device is provided for attenuating the vortex wake created in the zone behind an aircraft, the aircraft having at least one wing and an afterbody having a strong upward asymmetrical reduction of section of the rear fuselage. The device is positioned downstream of the wing of the aircraft symmetrically relative to the longitudinal plane of the aircraft. The device includes vortex-generating aerodynamic appendages capable of being deployed between a folded-down position in which the aerodynamic appendages are folded down substantially in the direction of the fuselage, capable of switching from a folded-down position in which they are folded down substantially in the direction of the fuselage, and a deployed position calculated to generate vortex structures having an intensity and a trajectory which modify the local pressure field in order to interact with the vortex wake to attenuate it and separate the upsweep vortices from the longitudinal plane of the aircraft.

Claims

1. A device for attenuating the vortex wake created in the zone behind an aircraft, the aircraft having at least one wing and an afterbody having a strong upward asymmetrical reduction of section of the rear fuselage, the device being positioned downstream of the wing of the aircraft symmetrically relative to the longitudinal plane of the aircraft, the comprising: at least two vortex-generating aerodynamic appendages capable of being deployed between a folded-down position in which the aerodynamic appendages are folded down substantially in the direction of the fuselage, and a deployed position, the deployed position being calculated to generate vortex structures having an intensity and a trajectory which modify the local pressure field in order to interact with the vortex wake to attenuate it and separate the upsweep vortices from the longitudinal plane of symmetry of the aircraft.

2. The device as claimed in claim 1, wherein each aerodynamic appendage in deployed position is oriented according to a predetermined angle of incidence , defined relative to the local flow lines of the flow arriving on the aerodynamic appendage.

3. The device as claimed in claim 2, wherein the angle of incidence ranges between 20 and +30.

4. The device as claimed in claim 2, comprising hydraulic or electrical or electrohydraulic or electromechanical means making it possible to vary the angle of incidence a of the aerodynamic appendages in deployed position.

5. The device as claimed in claim 1, comprising hydraulic or electrical or electrohydraulic or electromechanical means making it possible to switch the aerodynamic appendages from one position to another position.

6. The device as claimed in claim 1, wherein the aerodynamic appendages are of substantially delta wing form, having two substantially right-angled edges (b, h) of which one constituting the base b is placed adjacent to the surface of the aircraft and of which the other constituting the height h is at right angles to the surface of the aircraft when the appendage is in fully deployed position.

7. The device as claimed in claim 6, wherein the ratio b/h between the base and the height of the two edges of the aerodynamic appendage is of the order of two.

8. The device as claimed in claim 6 or 7, wherein the height h of an aerodynamic appendage lies within a range from approximately 50% to 120% of a predefined thickness 6 of the boundary layer.

9. The device as claimed in claim 1, wherein the aerodynamic appendages are produced in a material similar to that of the fuselage of the aircraft.

10. The device as claimed in claim 1, also comprising means for controlling the deployment of said at least two aerodynamic appendages and the orientation of each of said at least two appendages.

11. An aircraft having an afterbody having a strong upward asymmetrical reduction of section of the rear fuselage comprising at least one device as claimed in claim 1.

12. The aircraft as claimed in claim 11, comprising at least one side door and at least one device positioned in the vicinity and upstream of the side door.

13. The aircraft as claimed in claim 11, wherein said at least one device comprises a first aerodynamic appendage positioned at approximately of the height of the fuselage and a second aerodynamic appendage positioned at approximately of the height of the fuselage.

14. The aircraft having an afterbody having a strong upward asymmetrical reduction of section of the rear fuselage and comprising at least one door and/or rear ramp for air-dropping by door and/or rear ramp, the aircraft comprising at least one device as claimed in claim 1, said at least one device being positioned on the rear fuselage along the afterbody, on each side of the aircraft along the door and/or the rear ramp, on the fixed part of the fuselage, in an azimuthal position slightly upstream of the separating line of the flow.

15. The aircraft as claimed in claim 14, wherein said at least one device is composed of a plurality of aerodynamic appendages substantially aligned in a longitudinal direction of the fuselage.

16. The aircraft as claimed in claim 15, wherein the aerodynamic appendages are regularly spaced.

17. A method for attenuating the vortex wake created by an aircraft having an afterbody having a strong upward asymmetrical reduction of section of the rear fuselage, the aircraft comprising a vortex wake attenuation device as claimed in claim 1, the method comprising the steps of: deploying and orienting said at least two aerodynamic appendages of the device according to an angle of incidence having a predefined initial value; measuring the pressure in a zone of the aircraft representative of the presence of vortex structures; and adjusting the angle of incidence of the aerodynamic appendages as a function of the measured pressure.

18. The method as claimed in claim 17, wherein the step of adjustment of the angle of incidence consists in locking the appendages according to the incidence for which the measured pressure is maximized.

19. The method as claimed in claim 17, wherein the step of measuring the pressure consists in measuring the pressure on the upper surface of said appendages, and the step of adjustment of the angle of incidence comprises the steps of: varying the angle of incidence of the appendages; measuring the pressure on the upper surface for a given position of the aerodynamic appendages; and locking the appendages according to the incidence for which the measured pressure is minimized.

20. A computer program product, said computer program comprising code instructions making it possible to perform the steps of the method as claimed in claim 17, when said program is run on a computer.

21. An information storage means, removable or not, partially or totally readable by a computer or a microprocessor comprising code instructions of a computer program for the execution of each of the steps of the method as claimed in claim 17.

Description

DESCRIPTION OF THE FIGURES

[0050] Different aspects and advantages of the invention will become apparent in support of the description of a preferred, but non-limiting, mode of implementation of the invention, with reference to the figures below:

[0051] FIG. 1 schematically shows a transport airplane on which a device of the invention has been installed;

[0052] FIG. 2a shows an aerodynamic appendage according to the invention in retracted position;

[0053] FIG. 2b illustrates different forms of aerodynamic appendages according to the invention;

[0054] FIG. 3 shows an aerodynamic appendage according to the invention in deployed position;

[0055] FIGS. 4a and 4b show two embodiments of the device of the invention according to a first variant implementation upstream of a side door;

[0056] FIG. 5 shows an embodiment of the device of the invention according to a variant implementation for a rear air-dropping door;

[0057] FIG. 6 shows a sequence of steps making it possible to adjust the incidence of the appendages of the device of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0058] In general terms, the principle of the invention consists in controlling the generation of vortex sheets by the placement of series of aerodynamic appendages called vortex generators (VGs) at chosen locations on the fuselage of the aircraft, in zones of the fuselage downstream of the wing, symmetrically relative to the longitudinal plane of symmetry of the airplane. The positioning of the aerodynamic appendages is defined so as to ensure both an optimal efficiency for the reduction of the intensity of the upsweep vortices, and the modification of the trajectory thereof in the near wake of the airplane, by separating them, for example, from the longitudinal plane of symmetry of the airplane, while guaranteeing a deployment of these appendages outside of the potential zones of interaction with the air-dropped personnel or equipment.

[0059] Preferentially, the positioning of the appendages is situated in the upstream zone where the upsweep vortices originate. By producing a series of vortex structures upstream of the zone where the air flow naturally separates from the rear fuselage of the airplane and produces upsweep vortices, the air flow is initially re energized, then delaying its separation at the upsweep zone, then delaying its consecutive winding into upsweep vortices. The vortex structures or sheets deliberately produced by the series of aerodynamic appendages interact with the natural upsweep vortices. This interaction produces an intense shearing, responsible for the production of small-scale turbulences, which makes it possible to more rapidly dissipate the upsweep vortices and the vortex structures produced by the appendages and makes it possible to augment the diffusion of the vortices thereof through an increase of their radius, a strong reduction of their intensity and of their speed of rotation.

[0060] Moreover, the generation by the aerodynamic appendages of the different vortex structures induces a local modification of the pressure field which affects the trajectory of the upsweep vortices. These vortices are then offset substantially from the plane of symmetry of the airplane, and therefore from the zone of operability for air-dropping missions, thus making the operations safer.

[0061] FIG. 1 schematically illustrates a transport airplane (100) on which a device according to the invention can be installed. Such a type of aircraft has an afterbody (106) having a strong upward asymmetrical reduction of section of the fuselage (110). This zone with strong upward asymmetrical reduction of section of the fuselage is called upsweep zone. As detailed later with reference to FIGS. 4 and 5, aerodynamic appendages can be arranged in zones of the fuselage downstream of the wing (108), at the side doors (102) and/or the rear door (104) symmetrically relative to the longitudinal plane of symmetry of the aircraft. The person skilled in the art understands that, for reasons of simplification, FIG. 1 illustrates a side view of the airplane, but the latter can have another symmetrical side door where aerodynamic appendages can also be installed. Likewise, the rear appendages are positioned symmetrically on either side of the fuselage. Preferentially without constituting a limitation, the aerodynamic appendages are produced in a material similar to that of which the fuselage of the aircraft is composed or in any material compatible with the rules of airplane design art, capable of withstanding the mechanical stresses induced by the airflows, by guaranteeing the rigidity of the device.

[0062] Advantageously, the aerodynamic appendages can be deployed on demand. In a first retracted position, the appendages are folded down substantially in the direction of the fuselage. They can be brought into a second deployed positon, where they are deployed substantially vertically relative to the surface of the fuselage. In an initial flight phase, the appendages are preferably in folded-down position, then deployed for the duration of the air-dropping operations. The appendages can be retracted once again after the end of the air-drop, thus making it possible to control the fuel consumption or the noise emitted throughout the duration of the flight.

[0063] FIG. 2a illustrates an aerodynamic appendage (200) in retracted mode positioned on the fuselage (106) of an airplane. In this mode, the appendages are embedded in the surface of the fuselage, not forming an obstacle to the existing flow, as illustrated by the local air flow flux lines (210) in FIG. 2a. In a preferential embodiment, the aerodynamic appendages (200) are of delta wing form, having two substantially right-angled edges (b, h) of which one, the base b, is placed adjacent to the surface of the aircraft and of which the other, the height h, is substantially at right angles to the surface of the aircraft when the appendage is in fully deployed position. This edge of height h can have a smaller angle than that at right angles to the surface of the aircraft when the appendage is not fully deployed.

[0064] The person skilled in the art will be able to adapt, without adversely affecting the efficiency thereof, the form and the dimensions of these appendages as a function of the existing constraints for their incorporation on each type of airplane. As variants, a few forms of aerodynamic appendages suited to the vortex attenuation device of the invention are illustrated in FIG. 2b.

[0065] FIG. 3 shows an aerodynamic appendage VG (200) in deployed position on the fuselage (106) of an airplane, according to one embodiment. The deployment of an aerodynamic appendage forms an obstacle to the local flux lines of the airflow (210) and, behind a deployed aerodynamic appendage, vortex structures (212) are created, the intensity and the trajectory of which are controlled by the form, the positioning on the fuselage, the degree of deployment and the alignment in incidence of the aerodynamic appendages.

[0066] By taking the delta wing form shown in FIG. 2a, the aerodynamic appendage (200) preferentially has a ratio b/h of the order of 2 between its base b (202) and its height h (204).

[0067] Advantageously, the thickness of the aerodynamic appendages VGs is not critical for the efficiency of the device of the invention, and it can be set according to the dimensioning rules associated with the mechanical strength of these appendages subject to wind, in conditions of flight relating to the deployment thereof.

[0068] The height h of an aerodynamic appendage is preferably determined relative to the thickness of the local boundary layer at the zone of installation, and set at a few tens of percentage of this thickness. It is well known to the person skilled in the art that the boundary layer is defined as the zone of interface between a body and a surrounding fluid in a relative movement between the two, and as being the zone where the rate of flow is slowed down by the wall. It begins at the surface contact where the rate of flow is practically nil and extends through a distance where the rate of flow is substantially equal to that of the free flow, a distance giving the thickness of the boundary layer.

[0069] According to variant implementations, the height h of an aerodynamic appendage VG can range from approximately 50% to 120% of the thickness of the boundary layer.

[0070] Although not illustrated, the deployment of an appendage is done by common place means making it possible to ensure the robustness of the mechanism, by using, for example, hydraulic or electrohydraulic cylinders, of a type similar to those implemented for example for the deployment of lateral deflectors embedded on airplanes such as an Airbus A400M or a Boeing C17, but having a dimensioning and a power suited to the alar surface of each of the appendages, which is much less than that of the lateral deflectors.

[0071] Preferentially, for maintenance reasons, but also for minimization of the cables and pipes connecting to the hydraulic and electrical utilities (cables, etc.) for supplying the devices, the aerodynamic appendages VGs are installed in zones of the fuselage downstream of the wing where the hydraulic and/or electrical utilities necessary to the deployment of the appendages are easily accessible, the whole also allowing for a weight saving.

[0072] The deployed appendages can be raised to an opening of approximately 90 relative to the local surface of the fuselage.

[0073] Advantageously, the appendages can be oriented. The incidence a relative to the local flow lines of the airflow, initially defined at a nominal value associated with a given mission, can be adjustable for each appendage. The angle of incidence can be adjusted via a hydraulic, electrical, electrohydraulic or even electromechanical rotation device (not illustrated) about the axis of the cylinder used for the deployment of the appendage, and controlled on demand by the onboard personnel, from a control interface, or automatically by a logic controller operating in closed loop mode as represented subsequently with reference to FIG. 6.

[0074] The exact positioning and the alignment in incidence of each of the appendages can be refined as a function of the local flux lines of the flow, as a function of the type of airplane concerned in mission configuration. It should be noted that the local flux lines are determined previously during the development of the airplane, through digital simulations, wind tunnel tests or in-flight tests.

[0075] Advantageously, the range of variation of the local incidence can lie between =20 and =+30 according to the zone of installation and the mission targeted.

[0076] FIGS. 4a and 4b show two embodiments of the device of the invention that are particularly suited to paratrooper air-dropping through the side door. In this configuration, designated in the present description as TwinVG configuration, the device is composed of a pair of aerodynamic appendages (402, 404) positioned on the fuselage (106), upstream of the side door (102), for each side door of the airplane. The coupling created between the two aerodynamic appendages, through their geometry and their positioning, produces controlled vortex sheets which interact with the upsweep vortexes to attenuate the intensity thereof and modify the trajectory thereof.

[0077] Preferentially as illustrated in FIG. 4a, the two vortex-generating appendages (VGs) are positioned at approximately of the height of the fuselage for the first appendage (402) and at approximately of the height of the fuselage for the second appendage (404), on each side of the fuselage symmetrically. However, as illustrated in FIG. 4b, the vertical positioning can be slightly adapted according to the installation constraints depending on the type of airplane, without penalizing the efficiency of the device.

[0078] In one embodiment, the vertical spacing between the two aerodynamic appendages of one pair is calculated to be of the order of two times the height h of the appendage VG. However, variants with a reasonable tolerance margin are applicable to this value.

[0079] The aerodynamic appendages are, in a preferential embodiment, installed at a distance d.sub.PT from the side door, a distance defined as being of the order of 1 to 5 times the height h of the appendages.

[0080] FIG. 5 illustrates an embodiment of the device of the invention that is particularly suited for air-dropping through the door and/or rear ramp (104). In this configuration, designated in the present description as VGramp configuration, the device is composed of a plurality of aerodynamically appendages (502-1 to 502-n) positioned ramp-fashion along a longitudinal direction of the fuselage (106) and evenly spaced apart from one another. In a preferential embodiment, the distance d.sub.VG between two aerodynamic appendages VGs is chosen to be equal to approximately two times the height h of the appendage. However, variants with a reasonable tolerance margin are applicable to this value.

[0081] The plurality of aerodynamic appendages VGs is situated all along the upsweep zone, symmetrically on either side of the fuselage, alongside the door and/or rear ramp, on the fixed part of the fuselage, in an azimuthal position on the fuselage, slightly upstream of the flow separating line. The separating line and the local flux lines in the zone of installation of the ramps of aerodynamic appendages have been previously determined during the development of the airplane, through digital simulations, wind tunnel tests or in-flight tests.

[0082] Advantageously, with each appendage being deployable on demand, the alignment in incidence a of each appendage can be adapted relative to the local flux lines. Preferentially, the adjustable of the angle of incidence is situated between =20 and =+30 , the value depending on the zone of installation and on the air-dropping mission targeted.

[0083] Advantageously, the adaptive alignment in incidence of each of the appendages can be managed by software means in the form of an algorithm taking into account real-time pressure measurements, on points distributed in the rear cone zone of the fuselage (112), and distributed symmetrically on either side of the plane of symmetry of the airplane.

[0084] The method (600) of alignment of the incidence is described in FIG. 6. The method begins (602) with the activation of the deployment of an aerodynamic appendage VG and its alignment in incidence according to an initial reference value (602). The initial incidence value is a value predefined before the air-dropping operations and dependent on the air-dropping mission and on the type of aircraft.

[0085] Then, the method makes it possible (604) to recover pressure values measured in real time in the rear cone zone of the fuselage (112). The person skilled in the art understands that the pressure measurements can be performed by known components of pressure sensor type. It should be noted that the method is described to allow the alignment in incidence of a single aerodynamic appendage but it is applicable for all or some of the appendages implemented. Moreover, the alignment can have one and the same value for all of the appendages or be set at different values.

[0086] In a next step, the method seeks to maximize the pressure measured in the rear cone zone of the fuselage (112), at the end of the upsweep zone, by varying the alignment in incidence of the different appendages (606). The method enters into a process of convergence (608) which makes it possible to vary the incidence of the appendage VG to reach the maximized pressure value. When a local maximum of pressure is obtained by varying the alignment and incidence of the different VGs, the alignment in incidence is considered optimal and the appendage VG is kept on this alignment (610).

[0087] In one embodiment, the step of convergence (608) to the optimal alignment of each of the appendages consists in varying the incidence about the reference alignment value, within a range of variation predefined during an initial calibration obtained by simulations, in a wind tunnel or during certification tests.

[0088] In an alternative mode, the step of measurement of the pressure (606) consists in measuring the pressure on the upper surface of each of the appendages VGs and the step of convergence (608) consists in varying the incidence to minimize the upper surface pressure of the appendage, and block the appendage in the orientation according to the incidence giving the minimized pressure value.

[0089] Advantageously, the capacity to robustly adapt the alignment in incidence of the different aerodynamic appendages guarantees the device of the invention a maximum efficiency despite possible variations of the air-dropping conditions, such as the speed of the airplane, the wind imbalance relative to the airplane, the greater or lesser opening of the ramp and of the rear door, for example, or of the mission conditions, which would require air-dropping speeds given as a function of the aircraft, of the flight altitude, of the type of air-dropped equipment (tonnage, air-dropping rate, etc.), but also of the chance conditions associated with the weather, the theatre of operation not necessarily secured (air drop not necessarily possible in the axis of the prevailing wind), etc.

[0090] The person skilled in the art will appreciate that variations can be made to the implementation described preferentially, while maintaining the principles of the invention.