Abstract:
An air ejection device comprises an aerodynamic profile provided with a slot and an ejection nozzle. The device comprises a flexible tongue fixed flush with the aerodynamic profile in such a way as to obstruct the slot, the tongue being able to lift under the effect of a pressure differential between the air situated in the ejection nozzle and the outside air. The tongue makes it possible for the slot made in the profile to be obstructed during phases of flight during which the ejection of the air is unnecessary, and prevents external air from entering the slot. The flow of air over the aerodynamic profile is unaffected, and there is no increase in drag. Because the tongue lifts as a result of a pressure differential, it does not require any control mechanism to lift it.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to French Patent Application No. 1362160, filed Dec. 5, 2013, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Embodiments described herein relate generally to an aerodynamic profile provided with an air ejection device. More particularly, embodiments described herein relate to a pylon supporting a propulsion unit for an aircraft comprising such an aerodynamic profile and to an aircraft comprising such a pylon. 
     BACKGROUND 
     During the course of its motion, any aerodynamic profile of a vehicle is exposed to the wake of other profiles of this vehicle, or to phenomena that disturb its boundary layer of air. Aircraft in which the propulsion unit is situated on a pylon are particularly affected because, whatever its design, the pylon generates a wake. This is notably caused by the fact that the thickness of the boundary layer of the profile of the pylon increases in the downstream direction of the profile. Thus, a “velocity shortfall” (or “velocity deficit”) embodied by a difference between the velocity of the free flow of the air and the local velocity of the air in the downstream zone of the profile occurs at the trailing edge of the pylon. The zone exhibiting this velocity shortfall is also the site of a “mass flow rate shortfall” (or “mass flow rate deficit”) regarding the air. As a result, the air has a tendency to be pulled into the velocity shortfall zone, thus causing turbulence. 
     The discontinuity in the velocities and the turbulence in the wake cause, amongst other things, an increase in the noise generated by the fans of the turbine of the propulsion unit, which may detract from passenger comfort and cause environmental disturbances when the fans pass through the wake of the pylon. This is referred to as a “masking” effect. 
     There is therefore a need to limit this “masking” effect that gives rise to a variation in pressure in the wake of the pylon. In the specific case of pylons supporting propulsion units, there is a need to eliminate the air flow deficit and therefore to reduce the velocity deficit over the surface thereof. 
     One of the solutions to this is to blow air from a high-pressure source near the trailing edge of the profile in order to eliminate the air flow deficit and therefore reduce the velocity deficit. To this end, document U.S. Pat. No. 4,917,336 describes an air ejection device comprising an ejection nozzle delivering air, in which device the air escapes through slots made on the suction face and the pressure face of a pylon supporting an aircraft propulsion unit. This solution has the disadvantage of not allowing the openings made in the pylon to be obstructed. A permanent opening on the aerodynamic profile of the pylon at the trailing edge thereof constitutes a break in the aerodynamic profile. Such a break generates disturbances in the air flow and therefore increases the induced drag during phases of flight for which the ejection of air is not needed. Furthermore, with no obturation of the opening, air has a tendency to enter the opening, further disturbing the flow. 
     In order to solve this problem, document FR 2971765 proposes a similar ejection device further comprising two gratings comprising holes through which air is ejected. The gratings can move relative to one another, allowing the holes to be partially or fully obstructed as the situation dictates, for example as the incidence of the pylon varies. Such a device is, however, complicated to use because it requires a system controlling the opening and closing of the gratings. It is difficult to achieve in terms of manufacturing tolerances and is also not very robust. 
     SUMMARY 
     The embodiments described herein overcome at least one of the disadvantages of the prior art by proposing an air ejection device comprising a profile provided with a first opening and an ejection nozzle opening into the first opening. The ejection device comprises a flexible tongue fixed in the continuity of the profile in such a way as to obstruct the opening, the flexible tongue being able to lift under the effect of a pressure differential between the air situated in the ejection nozzle and the outside air. The tongue allows the opening made in the profile to be obstructed during motion (phases of flight in the case of an aircraft aerodynamic profile) for which the ejection of air is unnecessary. In this way, outside air is prevented from entering it. The flow of air over the surface of the profile is therefore unaltered, making it possible to avoid an increase in induced drag. In particular, the tongue may be fixed flush with the aerodynamic profile to extend in the continuity of the profile. The latter therefore exhibits no discontinuity or roughness likely to disturb the flow of the air. 
     The fact that the tongue is flexible and able to lift under the effect of a simple pressure differential between the air situated inside the ejection nozzle and the outside air offers the advantage that there is no need to provide any mechanism for opening it. 
     According to one advantageous feature, the air ejection device comprises a blowing box (a pressurized chamber), the ejection nozzle constituting a narrowing of the blowing box, the narrowing being curved in such a way that the air contained in the blowing box is ejected through the opening tangential to the profile. 
     In one particular embodiment, the blowing box further comprises stiffeners extending in a plane perpendicular to the longitudinal direction of the opening. 
     In another particular embodiment, the blowing box comprises a baffle plate (a plate that homogenizes the air) situated at the inlet to the ejection nozzle arranged in the box in such a way that the air entering the ejection nozzle passes through said baffle plate. 
     In another particular embodiment, the blowing box, the ejection nozzle, and the baffle plate situated at the inlet of the injection nozzle are produced as a single piece. 
     In one particular embodiment, the opening is a slot made over the entire length of the profile. 
     In yet another particular embodiment, the cross section of the ejection nozzle in a plane perpendicular to a longitudinal direction of the opening is in the shape of a comma. 
     In one particular embodiment, the ejection device comprises, in the region of the opening, stiffeners uniformly distributed along the length of the profile. 
     In a further particular embodiment, the flexible tongue is made up of several parts of different rigidities along the length of the profile. 
     Other embodiments relate to a pylon supporting a propulsion unit for an aircraft comprising an air ejection device and finally to an aircraft comprising such a device. 
     Other objects, features, and advantages will become apparent from the following detailed description, given by way of nonlimiting example and made with reference to the attached drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description is merely exemplary in nature and is not intended to limit the embodiments or the application and uses of the embodiments. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the embodiments or the following detailed description. 
         FIG. 1  is a schematic perspective view of an airplane propelled by two contra-rotating propeller engines mounted downstream of the wings of the airplane; 
         FIG. 2  is a schematic perspective view of a detail of  FIG. 1 , comprising the zone subjected to the disturbances caused by a pylon supporting one of the engines; 
         FIG. 3  is across sectional view of the aerodynamic profile of the pylon of  FIG. 2 , also illustrating the viscous boundary layer on its surface and the air velocity profile downstream of the velocity profile; 
         FIG. 4  is a schematic perspective view of part of a pylon intended to support a propulsion unit for an aircraft provided with an aerodynamic profile according to an embodiment; 
         FIG. 5  is a schematic perspective view of a detail of a detail shown in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of part of an aerodynamic profile according to one embodiment; 
         FIG. 7A  is a schematic perspective view of an air ejection device provided with a baffle plate situated at the inlet to the ejection nozzle according to an embodiment; 
         FIG. 7B  is a schematic perspective view of an air ejection device provided with a baffle plate situated at the inlet to the ejection nozzle according to a further embodiment; and 
         FIG. 8  is a schematic perspective view of an aerodynamic profile provided with an air ejection device according to a third still further embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an airplane fuselage  1  comprising a propulsion system  2 , an engine contained in a nacelle  4 , and propellers  6 , in accordance with the prior art. It is also conceivable to have just one propeller per propulsion system. This nacelle  4  is supported by and connected to the fuselage  1  by a pylon  8 . The term pylon here refers to an aerodynamic fairing surrounding the structure supporting the propulsion system and any devices that may be connected thereto. Such devices have not been depicted. As explained hereinabove, during flight, the pylon  8  causes disturbances and turbulence in its wake  10  as illustrated in  FIG. 2 .  FIG. 3  illustrates the fact that the thickness of the boundary layer  12  increases progressively in the downstream direction of the profile of the pylon  8 , leading to the velocity profile  14 . 
     The velocity profile  14  of the trailing edge  16  of the pylon  8  has a velocity shortfall (or deficit) V d  in the zone  18  situated downstream of the pylon  8 . This velocity shortfall V d  corresponds to the difference between the free flow velocity V 0  and the local velocity V in the example considered in  FIG. 3 . 
     The zone  18  exhibiting this velocity shortfall V d  also exhibits a mass flow rate shortfall which has the effect of pulling air into it along a path indicated schematically by the arrow  17 . 
     The ejection device  19  illustrated in  FIGS. 4-8  makes it possible to alleviate this velocity shortfall (deficit). In what follows, the profile of the ejection device is incorporated into that of an aircraft pylon but it may be mounted on other surfaces of the aircraft. The terms pylon, pylon profile, or ejection device profile will therefore be used interchangeably. In this particular instance, it is an aerodynamic profile.  FIG. 4  illustrates a pylon  20  extending along an axis X and comprising a primary structure  22  provided with a blowing box (i.e. a pressurized chamber)  24  supplied with air by a blowing pipe  26  (feed pipe). The blowing box  24  is situated in the trailing edge  28  of the pylon  20 . In  FIG. 4 , by way of example, blowing box  24  is situated more than half way along the chord of the pylon  20  (in fact, it is preferably situated over 75% of the way along the chord of the pylon  20 ), the chord extending along the axis Z. Air from the blowing pipe  26  comes, for example, from the aircraft engine. This is therefore pressurized air bled off by an air bleed system that has not been depicted but which is known in the prior art. 
     It will be noted that in the embodiment depicted in  FIG. 5 , the blowing pipe  26  stops at the inlet  29  of the blowing box  24 . The inlet  29  is made in a lateral rib  30  of the blowing box  24  of the trailing edge of the pylon  20  and is dimensioned so as to allow the volume  31  of the blowing box  24  to be supplied with air. The volume  31  of the blowing box  24  extends from a front rib  32   a  of the pylon  20  (furthest from the trailing edge  28 ), as far as a rear rib  32   b  (closest to the trailing edge  28 ). Thus, this volume  31  includes an intermediate rib  32   c  of the pylon  20 . The blowing pipe  26  may extend beyond the rear spar  30  into the blowing box  24 . In such a case, the blowing pipe  26  passes through the rear spar  30  and extends over all or part of the length of the pylon  20 , i.e. along the axis X. The blowing pipe  26  may be regularly pierced in order to allow air to escape into the blowing box  24 . The advantage connected with this alternative is that the air inside the volume  31  of the blowing box  24  is more uniform. 
     Once it has left the blowing pipe  26 , the air spreads out in the blowing box  24  as was seen earlier and escapes via the ejection zone  34 . The ejection zone  34  forms part of the volume  31  of the blowing box  24  and is situated near the front rib  32   a . In other words, the ejection zone  34  is distant from the trailing edge  28  of the pylon  20 . Ejection zone  34  it comprises an opening  36  made in the external surface of the aerodynamic profile of the pylon  20  as is particularly visible in  FIG. 6 . In this particular instance, the opening  36  is a slot extending over the entire length of the profile of the pylon  20 , along the axis X. Indeed it is preferable, in the case of a profile built into a pylon supporting a propulsion unit with propellers, for the opening  36  to extend over a maximum length along the axis X so as to blow air over the entire propeller blade or even beyond. The opening  36  may, however, also extend over just part of the length of the profile of the pylon  20 . In what follows, and nonlimitingly, the opening  36  will be referred to as a slot. The slot  36  is made in the suction face  38  of the pylon  20 . However, it is also conceivable to make such a slot  36  in the pressure face of the aerodynamic profile of the pylon  20  or even in both the suction face and the pressure face of the aerodynamic profile of the pylon  20 . In what follows, and in a nonlimiting manner, reference will be made to the embodiment depicted with a slot  36  made in the suction face  38  of the profile of the pylon  20 . 
     The ejection zone  34  and the elements of the ejection device  19  located there will now be described in greater detail with reference to  FIG. 6  which is a view of the YZ plane perpendicular to the axis X. 
     The ejection device  19  comprises an ejection nozzle  42  the end of which  44  (end directed toward the outside of the profile  20 ) opens into the slot  36 . This end  44  is more particularly directed opposite the trailing edge  28  of the pylon  20  so that the air leaving it is directed toward the trailing edge  28  of the pylon  20 . The end  44  of the ejection nozzle  42  is delimited by a reinforcing rib  46  that extends over all or part of the length of the pylon  20 , on the one hand, and on the other hand, by the suction face  38  of the pylon  20 . The reinforcing rib  46  is situated as an additional thickness in relation to the suction face  38  of the pylon  20  so that the air remains in contact with the suction face  38  of the pylon  20  as it is ejected and is directed toward the trailing edge  28 . 
     It will be noted that the slot  36  and the reinforcing rib  46  here extend over the entire length of the pylon  20 . The ejection device  19  further comprises a flexible tongue  48  flush with the suction face  38 , so as to obstruct the slot  36 . Here it is fixed to the reinforcing rib  46 . 
     Thus, when no flow of air from the blowing box  24  is ejected by the ejection nozzle  42 , the slot  36  is obstructed. This makes possible the prevention of the boundary layer of air flowing over the suction face  38  from rushing into the slot  36 . Furthermore, because the flexible tongue  48  is fixed flush to the suction face  38 , it ensures the continuity of the profile of the suction face  38  on either side of the slot  36 . In other words, because of the presence of the flexible tongue  48 , the suction face  38  is continuous and smooth from the trailing edge  28  as far as the reinforcing rib  46 . The flow of air over the suction face  38  is therefore not disturbed by the presence of the slot  36  because the flexible tongue  48  does not form any roughness on the surface of the suction face  38 . 
     In a further embodiment, the flexible tongue  48  may be made up of several parts of different rigidities along the pylon  20  (along the axis X). That makes it possible, depending on the flexibility of each of the parts, to vary the dimensions of the slot  36  along the pylon  20  and therefore the air flow rate blown onto the blades of the propeller of the propulsion system  2 . It is thus possible to blow more air over the tip of a blade than over the base of the blade. The flexible tongue  48  is also able to lift under the effect of a pressure differential between the air situated inside the ejection nozzle  42  and the outside air. 
     The flexible tongue  48  is preferably made of aluminum, of a composite material such as a carbon fiber reinforced plastic (CFRP in which plastic is reinforced with films of carbon), or an elastomeric material. Thus, the flexible tongue  48  lifts only when air is being ejected, or in other words, only when necessary. 
     The flexible tongue  48  is, for example, fixed to the reinforcing rib  46  using fasteners  49  uniformly distributed along the length of the pylon  20 . 
     For example, the fasteners  49  may be fixed with a countersunk head of diameter 3.2 mm. Alternatively, in an embodiment that has not been depicted, the flexible tongue  48  may be fixed to the reinforcing rib  46  by bonding or welding. 
     The inside of the blowing box  24  in conjunction with the ejection nozzle  42  will now be described. The ejection nozzle  42  constitutes a narrowing of the blowing box  24 . 
     In other words, the air contained in the volume  31  ( FIG. 4 ) of the blowing box  24  passes continuously from the blowing box  24  to the ejection nozzle  42 . The cross-sectional area of the ejection nozzle  42  in the plane YZ perpendicular to the longitudinal direction of the pylon  20  is smaller than the cross-sectional area of the rest of the blowing box  24  in this same plane YZ. The ejection nozzle  42  also has a curved shape so that the air contained in the blowing box  24  is ejected via its end  44  such that it is tangential to the suction face  38  of the pylon. 
     More specifically, the cross section of the ejection nozzle  42  in a plane (YZ) perpendicular to the longitudinal direction (in the direction of the axis X) of the slot  36  is in the shape of a comma, the curved end  44  of which is directed toward the trailing edge  28  of the pylon. The widened other end of the ejection nozzle  42  opens into the blowing box  24 . 
     Such a configuration takes into account the aerodynamic conditions that allow air to be ejected tangentially to the surface of the aerodynamic profile (in this instance the profile of the pylon  20 ). In particular, the curved shape of the end  44  means that the air has to make an “about turn” before being ejected. 
     Furthermore, the curved shape of the end  44  makes it possible to achieve an assembly made up of a blowing box  24  and of an ejection nozzle  42  which is compact. That notably means that such an assembly can be situated as close as possible to the rear spar  30  of the pylon  20 . This has the advantage that the position of the rear spar  30  of the primary structure  22  of the pylon can be set as far back as possible, thus making it possible to maximize the chord of the pylon  20  and therefore improve the mechanical integrity thereof. 
     The comma-shape of the ejection nozzle  42  also allows the aerodynamic conditions to be optimized further by ensuring that the air is ejected at a tangent to the surface of the aerodynamic profile of the pylon  20 . 
       FIGS. 7 and 8  illustrate two distinct embodiments of the complementary elements of the blowing box  24 . In a preferred embodiment illustrated in  FIG. 7 , the blowing box  24  comprises a first part  24   a  extending from the curved shape of the ejection nozzle  42 , and widening as far as a second part  24   b . The second part  24   b  in the plane YZ has a cross section of substantially rectangular shape. It thus comprises a flat surface  24   e  comprising a baffle plate (plate for homogenizing the air)  50 , or a separating filter, situated at the inlet to the ejection nozzle  42 . The flat surface  24   e  is connected on the one hand to the first part  24   a  through a lower joining surface  24   c  that is perpendicular to the flat surface  24   e , and is connected on the other hand to the first part  24   a  via an upper joining surface  24   d  that is slightly oblique with respect to the lower joining surface  24   c . The flat surface  24   e , and, therefore, the baffle plate  50 , are positioned in the blowing box  24  substantially perpendicular to the suction face  38 , or in other words in a plane substantially parallel to the plane XY. 
     In the path of the air arriving from the blowing pipe  26 , the baffle plate  50  is positioned upstream in the blowing box  24  with respect to the ejection nozzle  42 . Thus, air from the blowing pipe  26  advantageously passes through the baffle plate  50  to be homogenized before it expands in the volume  31  of the blowing box  24 . In other words, the baffle plate  50  constitutes the inlet to the blowing box  24 , via which inlet air from the blowing pipe  26  arrives. 
       FIGS. 7A and 7B  illustrate two options for the baffle plate  50 , comprising holes of different shapes and cross sections. Thus, the baffle plate  50  of  FIG. 7A  comprises rectangular holes extending along the entire length of the filter. In  FIG. 7B , the baffle plate  50  comprises holes of circular shape, uniformly distributed in a number of rows, in this instance seven rows, along the entire length and the entire width of the plate. It goes without saying that the size, number, layout and shape of the holes may vary in order best to suit the required ejection conditions i.e. the pressure and flow rate that are desired in the ejection nozzle  42 . Thus, for preference, the holes are dimensioned in such a way as to obtain a homogeneous flow. 
     Still according to the embodiment illustrated in  FIGS. 7A and 7B , the blowing box  24  further comprises internal stiffeners  52  extending in a plane perpendicular to the longitudinal direction of the slot  36  (the direction X), namely in a transverse plane of the blowing box  24 . In this instance, the internal stiffeners  52  run in planes parallel to the plane YZ or even perpendicular to the axis X. The function of the internal stiffeners  52  is to reinforce the blowing box  24  structurally and thus prevent excessive deformation of the end  44  of the ejection nozzle  42  and therefore of the slot  36  when the latter experiences loadings during flight. This is because any alteration to the shape of the end  44  may prove detrimental to the required constancy of the flow of air to be ejected. The reinforcement provided by the internal stiffeners  52  allows this to be avoided. The internal stiffeners  52  are preferably uniformly distributed over the length of the blowing box  24 . In one embodiment, the internal stiffeners  52  are, for example, made of aluminum having a thickness of about 2 mm thick, and are arranged every 150 mm. The number of internal stiffeners  52  may naturally vary according to the loadings experienced by the end  44 . 
     The presence of at least one internal stiffener  52  is positioned inside the blowing box  24  offers the advantage of reinforcing the end  44  of the ejection nozzle  42  without altering the external surface of the pylon  20 . This means that the flow of air over the aerodynamic profile thereof is undisturbed. It is to be noted that the gap (separation) between each of the internal stiffeners  52  is dependent on a number of factors. Thus, for a given manufacturing tolerance on the slot  36 , the more rigid the material used (for example if use is made of titanium rather than aluminum) or the thicker the internal stiffeners  52 , the greater the possibility of increasing the gap between the internal stiffeners  52 . Conversely, for a given material and thickness of internal stiffener  52 , the tighter the manufacturing tolerance on the slot  36  will be the smaller the gap between two successive internal stiffeners  52  will have to be. 
     For preference, the blowing box  24 , the ejection nozzle  42 , and the baffle plate  50  are produced as a single piece. Such a piece may preferably be manufactured by three-dimensional printing (“additive layer manufacturing”) or by casting. For preference, the material chosen may be titanium or aluminum, which provides a good compromise between mechanical strength and reduction of on-board mass. This method of manufacture ensures better flow of air through the blowing box  24  and the slot  36  and better homogenization of this air flow notably thanks to the fact that defects in the shape of the component are limited. Furthermore, it allows easier positioning of the internal stiffeners  52 , which is more difficult to achieve using machining methods. There is therefore no need to place external stiffeners on the aerodynamic surface of the pylon  20 , thus further limiting disturbances of the boundary layer of air thereof during flight still further. 
     In one alternative embodiment illustrated in  FIG. 8 , which is better suited to manufacture by conventional machining, a blowing box  124  is limited to a bottom base  126  and a top base  128  which are separated by an empty space through which the air diffuses. In this embodiment, the blowing pipe (not depicted) passes through the pylon  20  along the entire length (along the axis X) thereof. The top base  128  comprises an ejection device  119  similar to that of the ejection device  19  is the previous embodiment, apart from the fact that the reinforcing rib  146  comprises external stiffeners  147  uniformly distributed along the slot  36 . These external stiffeners  147  perform the role of the internal stiffeners  52 , namely they reinforce the end  44  of the ejection nozzle  42  to prevent it and the slot  36  from deforming during flight. The bottom base  126  comprises a baffle plate  150  that performs the same role as in the previous embodiment; namely it is positioned in such a way that air from the blowing pipe (not depicted in this figure) passes through it before being diffused in the blowing box  124 . This solution is an alternative that is more economical because it does not rely on three-dimensional printing technology. 
     In an alternative embodiment connected to the previous one, the baffle plate is incorporated into the ejection nozzle. In this case, the blowing pipe stops at the inlet to the blowing box. One advantage to this is that the mass of the air ejection device is reduced. 
     Of course, other embodiments are possible. It will be noted that the air ejection device works whatever the shape of the blowing box, or even without there being a blowing box. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the embodiment in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the embodiment as set forth in the appended claims and their legal equivalents.