Abstract:
The invention relates to an air intake for an aircraft nacelle that comprises a shroud ( 19 ) that can be mounted on the fan casing ( 15 ) of a turbojet engine ( 1 ). The shroud ( 19 ) is sized so as to define a circumferential gap (J) relative to the casing ( 15 ). Punctual linking means ( 27, 33 ) between the shroud ( 19 ) and the casing ( 15 ) are discretely distributed at the periphery of said shroud ( 19 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns in particular an air intake for aircraft nacelle. 
       BACKGROUND 
       [0002]    An airplane is propelled by one or several propulsion assemblies each comprising a turbojet engine housed in a tubular nacelle. Each propulsion assembly is attached to the plane by a mast generally situated under a wing or at the fuselage. 
         [0003]    A nacelle generally comprises a structure including an air intake upstream from the engine, a middle section designed to surround a fan of the turbojet engine, a downstream section housing thrust reverser means and designed to surround the combustion chamber of the turbojet engine, and generally ends with a jet nozzle whereof the outlet is situated downstream from the turbojet engine. 
         [0004]    The air intake comprises, on one hand, an intake lip adapted to allow optimal collection towards the turbojet engine of the air necessary to supply the fan and internal compressors of the turbojet engine, and on the other hand, a downstream structure on which the lip is attached and designed to suitably channel the air towards the vanes of the fan. The assembly is attached upstream from a fan casing. 
         [0005]    The inner face of the downstream air intake structure is formed by a tubular member frequently called “shroud”, generally having an acoustic function (structure formed by a honeycomb assembly of panels). 
         [0006]    The connection of this shroud with the fan casing is done by a flange with an L-shaped section, comprising on one hand a portion of tubular shape fixed on the shroud, and on the other hand a return of annular shape fastened on the fan casing: documents FR2847304 and FR2869360 show such examples of fastening. 
         [0007]    In case of deformation or rupture of vane of the fan (commonly referred to as “FBO” for “Fan Blade Out”), the turbojet engine causes very significant vibrations and/or shocks that reverberate on the entire nacelle, and in particular on the air intake. 
         [0008]    The latter, which has a significant overhang relative to the rest of the nacelle, is vulnerable to such vibrations/shocks, which can cause local deformations or even the ruin of this air intake. 
       BRIEF SUMMARY 
       [0009]    The present invention aims in particular to provide means making it possible to limit this risk of deformation or ruin of the air intake in case of deformation or rupture of the vane of the fan of the turbojet engine. 
         [0010]    This aim of the invention is achieved with an air intake for aircraft nacelle comprising a shroud capable of being mounted on the fan casing of a turbojet engine, said shroud being dimensioned to define a circumferential gap relative to said casing, and punctual linking means of said shroud to said casing being discretely distributed at the periphery of said shroud. 
         [0011]    This discrete linking of the shroud to the air intake with the fan casing allows elastic and/or plastic movements of the shroud relative to the fan casing in case of vibrations or shocks created in particular by a loss of vane: these relative movements make it possible to absorb part of the energy associated with these vibrations or these shocks, and thereby to reduce the impact of these vibrations or shocks on the air intake assembly. 
         [0012]    In this way, it is possible to considerably reduce the risk of deformation or ruin of this air intake. 
         [0013]    According to other optional features of this air intake: 
         [0014]    said linking means comprise a plurality of support beams fastened equidistantly on said shroud, and lugs mounted articulated on these support beams and capable of being fastened on said casing; 
         [0015]    said lugs are adapted to be mounted on a flange integrated to said casing; 
         [0016]    said lugs are adapted to be mounted directly on the outer face of said casing; 
         [0017]    said linking means comprise a plurality of support beams fastened equidistantly on said shroud and adapted to be mounted directly on a flange integrated to said fan casing; 
         [0018]    said linking means comprise a plurality of orifices formed on the downstream edge of said shroud, capable of being passed through by fastening means mounted on the upstream edge of said casing; 
         [0019]    said shroud includes an annular groove in which said orifices lead; 
         [0020]    said shroud comprises an annular recess in which said orifices lead, a cover flap being provided to close said recess; 
         [0021]    said linking means comprise a plurality of lugs distributed on the outer face of said shroud, capable of engaging with fastening means mounted on the upstream edge of said casing; 
         [0022]    said shroud is an acoustic shroud: such a shroud makes it possible to absorb part of the energy from the sound waves emitted by the fan and the turbojet engine; 
         [0023]    said shroud is adapted to extend in part under the upstream edge of said casing: this arrangement makes it possible to bring the acoustic shroud closer to the sound emission zones of the fan and the turbojet engine, and to thereby improve the sound attenuation. 
         [0024]    The present invention also concerns an assembly comprising an air intake including a shroud according to the preceding and a turbojet engine including a fan casing on which said shroud is mounted. 
         [0025]    According to optional features of that assembly: 
         [0026]    the upstream edge of said casing includes a flange on which said lugs are fastened; 
         [0027]    the upstream edge of said casing includes orifices receiving said fastening means; 
         [0028]    the inner face of said casing includes a step defining the gap between said shroud and the casing; 
         [0029]    said step has a ramp; 
         [0030]    said casing has a tubular tab closing the recess formed in said shroud; 
         [0031]    the upstream edge of said casing is configured to define a gap with said shroud upstream and downstream from said lugs. 
         [0032]    The present invention also concerns a propulsion assembly for aircraft comprising an assembly according to the preceding. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Other features and advantages of the present invention will appear in light of the following description, and upon examination of the appended figures, in which: 
           [0034]      FIG. 1  is a partial diagrammatic view in axial cross-section of a propulsion assembly according to the invention, in which one can see in particular the acoustic shroud of the air intake and the turbojet engine; 
           [0035]      FIG. 2  is a detail view of the cooperation zone of the shroud of the air intake with the fan casing of the turbojet engine, corresponding to zone II illustrated in  FIG. 1 , 
           [0036]      FIGS. 3 and 4  are views of an alternative embodiment to that shown in  FIG. 1 , and 
           [0037]      FIGS. 5 to 8  illustrate four alternatives of another embodiment according to the invention. 
       
    
    
       [0038]    In all of these figures, identical or similar numerical references designate identical or similar members or sets of members. 
       DETAILED DESCRIPTION 
       [0039]    In the following, the terms “upstream” and “downstream” must be understood in relation to the direction of circulation of the air and gases in the propulsion assembly, and correspond in this case to the left and right, respectively, of the figures. 
         [0040]    In reference now to  FIG. 1 , we have diagrammatically illustrated an aircraft turbojet engine, including, in its upstream portion, a fan  3  provided with vanes  5 , and in its downstream portion the engine  7  strictly speaking, comprising as known in itself its compression  9 , combustion  11  and propulsion  13  stages. 
         [0041]    Around the fan  3  and the compression stage  9 , is a fan casing  15 , defining a cold air stream  17  with the engine  1 . 
         [0042]    Upstream from this casing  15 , and situated in the extension thereof, is a tubular member  19 , frequently designated by “shroud”, which is part of the nacelle designed to surround the turbojet engine  1 . 
         [0043]    More precisely, this shroud  19  constitutes the inner face of the air intake of the nacelle, as was indicated in the preamble of this description. 
         [0044]    In all of the figures of this invention, this shroud  19  is illustrated in the form of a structure having acoustic absorption properties, such as a honeycomb structure: indeed, such a structure is generally used to reduce the energy of the sound waves emitted by the turbojet engine  1  and the fan  3 . 
         [0045]    One will, however, bear in mind that the present invention is in no way limited to a shroud  19  having such acoustic properties. 
         [0046]    One will also note that, in all of the figures of the present invention, we have illustrated a fan casing  15  extending to the debris exhaust cone  21 , but this invention is in no way limited to that particular case (as a reminder, the cone  21 , defined by an angle α relative to the feet of the vanes  5 , corresponds to the zone in which one considers that debris coming from a vane rupture can be ejected and strike the casing  15 ). 
         [0047]    In the embodiment illustrated in  FIGS. 1 and 2 , one can see that the upstream edge of the casing  15  defines an annular housing  23  situated in the zone of the exhaust cone  21 , and receiving the downstream edge of the casing  15 . 
         [0048]    At this housing  23 , is an essentially annular flange  25 , integrated into the outer face of the shroud  19 . 
         [0049]    A plurality of support beams  27 , essentially L-shaped, are fastened on the outer face of the shroud  19 . 
         [0050]    These support beams extend to the flange  25 , and include, at their downstream end, an articulated lug  29  fastened (for example by screwing) to the flange  25 . 
         [0051]    These support beams  27  are preferably distributed equidistantly on the circumference of the shroud  19 , and the geometry of the assembly is determined such that there is a slight gap J between the outer face of the shroud  19  and the inner face of the upstream edge of the casing  15 . 
         [0052]    The alternative of  FIG. 3  differs from the preceding in that the support beam  27  is practically laying down along the outer face of the casing  15 , and in that this support beam is directly connected to said casing via a fitting  31 . 
         [0053]    Other than the gap J similar to that of  FIG. 2 , a gap J′ is formed between the support beam  27  of the outer face of the casing  15 . 
         [0054]      FIG. 4  illustrates another possible geometry of the support beam  27 , in this case directly linked to the flange  25 , while keeping the gaps J and J′ similar to those of  FIG. 3 . 
         [0055]    In the embodiment of  FIG. 5 , the shroud  19  is linked to the inner face of the upstream edge of the casing  15  via a plurality of fastening means  33  of the screw-nut type. 
         [0056]    More precisely, these fastening means  33  pass through orifices formed in the upstream edge of the casing  15  and in the downstream edge of the shroud  19 . 
         [0057]    The orifices formed in the downstream edge of the shroud  19  open into an annular groove  35  formed in the downstream edge of the shroud  19 . 
         [0058]    When this shroud  19  is a honeycomb acoustic shroud, the annular groove  35  can be defined by a compact zone (called monolithic) of the honeycomb structure. 
         [0059]    It will be noted that this alternative assumes that all of the nuts  37  are fastened in the groove  35  before the placement of the associated screws  39 , the groove  35  in fact no longer being accessible once the shroud  19  has been placed inside the housing  23  defined in the upstream edge of the fan casing. 
         [0060]    It will also be noted that, for reasons of structural resistance, it may be useful to provide an annular return  41  on the end of the upstream edge of the casing  15 . 
         [0061]    It will also be noted that, as in the preceding embodiment, a gap J is formed between the outer face of the shroud  19  and the inner face of the upstream edge of the casing  15 , such a gap being able to be obtained using a step  43  provided on the inner face of the upstream portion of the fan casing  15 . 
         [0062]    In the alternative illustrated in  FIG. 6 , the downstream edge of the shroud  19  no longer defines an annular groove as in the preceding alternative, but a simple annular recess  45 , i.e. an open zone opposite the axis A of the turbojet engine. 
         [0063]    This open annular zone allows the placement of nuts  37  and screws  39  after the shroud  19  has been inserted inside the housing  23 , an essentially tubular cover flap  47  then being attached on the inner face of the shroud  19  is fastened using appropriate means  49  so as to close the recess  45  and thus allow the aerodynamic continuity between the shroud  19  and the fan casing  15 . 
         [0064]    It will be noted that, in this alternative as in the previous ones, a step  43  forms a gap J between the outer face of the shroud  19  and the inner face of the fan casing  15 . 
         [0065]    In the alternative illustrated in  FIG. 7 , the annular recess  45  of the shroud  19  is closed by a tubular tab  50  integral with the fan casing  15 : in this alternative as in that of  FIG. 5 , one must provide for fastening the nuts  37  on the acoustic shroud  19  before inserting the latter inside the fan casing  15 . 
         [0066]    It will be noted that one can advantageously provide that the step  43  has a ramp shape, as illustrated in  FIG. 7 , making it possible to facilitate the insertion of the shroud  19  inside the fan casing  15 . 
         [0067]    In the alternative illustrated in  FIG. 8 , lugs  51  are fastened on the outer face of the acoustic shroud  19 , preferably equidistantly on the circumference of said shroud. 
         [0068]    Other than the first housing  23 , the upstream edge of the fan casing  15  has a geometry defining a second housing  53  allowing the positioning of the lugs  51 . 
         [0069]    Screws  39  pass through the upstream edge of the fan casing  15 , and engage with these lugs  51 . 
         [0070]    Here again the geometry of the assembly is defined so as to allow a gap J downstream from the lugs  51  and a gap J″ upstream from said lugs. 
         [0071]    As will have been understood in light of the preceding description, the common point to all of the embodiments and alternatives explained above lies in the fact that the shroud  19  is linked to the fan casing  15  by punctual means, i.e. by means distributed discretely at the circumference of these elements. 
         [0072]    The geometry of the assembly is studied such that there is a gap between the shroud  19  and the fan casing  15 . 
         [0073]    Owing to all of these features, in case of deformation or rupture of one or several of the vanes  5  of the fan  3 , causing vibrations or shocks of the turbojet engine  1 , the shroud  19  can move elastically or plastically relative to the fan casing  15 , thereby causing a dissipation of the energy transmitted by the turbojet engine  1  and making it possible to avoid the ruin of the air intake and of the nacelle. 
         [0074]    It will be noted in particular that, in the case of the alternatives illustrated in  FIGS. 5 and 8 , it is in particular the elasticity of the shroud  19  itself (in particular when this is an acoustic shroud) that allows the energy dissipation. 
         [0075]    Of course, the present invention is in no way limited to the embodiments and alternatives described and illustrated, provided as examples.