Abstract:
A bypass turbine engine includes a precooler having an annular cross-sectional shape about the axis of a pod and arranged inside the rear part of an inner shroud in contact with a cold fluid exiting a fan duct.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bypass turbine engine provided with a precooler. 
     BACKGROUND OF THE INVENTION 
     It is known that, on board an aircraft, it is necessary to have hot air available to perform certain functions, such as air conditioning in the cockpit and the passenger cabin or for deicing certain parts of the aircraft. 
     It is also known that this hot air is taken from the turbine engines of the aircraft and has to be cooled significantly before it can be used. To do this, a heat exchanger is provided, this generally being known as a precooler, in which the hot air bled from the central generator of the turbojet engine is cooled by cold air bled from the fan duct, that is to say from the cold stream of the turbine engine, thus disrupting the correct operation of this engine. What is more, said precooler is generally housed in said fan duct, and this adds aerodynamic disturbances to the disruption caused by the tapping-off of cold air. 
     What is more, the cold air bled from the cold stream of the turbine engine and used to cool the hot stream bled from the central generator gives rise to a current of heated cold air, which has to be discharged to the outside of the turbine engine, thus increasing the drag of the aircraft. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to remedy the disadvantages of the prior art. 
     To these ends, according to the invention, the bypass turbine engine for an aircraft comprising:
         a hollow nacelle of longitudinal axis provided, at the front, with an air inlet and, at the rear, with an air outlet;   a central hot-stream generator, positioned axially in said nacelle;   a fan positioned axially in said nacelle forward of said central generator and able to generate the cold stream for said turbine engine;   an outer fairing borne internally by said nacelle and an inner fairing surrounding said central generator, said outer and inner fairings between them delimiting a fan duct of annular cross section for said cold stream; and   a precooler comprising an inlet for a current of hot air bled from said central generator and an outlet for a current of hot air cooled using said cold stream,
 
is notable in that said precooler is positioned inside at least a portion of said rear part of the inner fairing around said longitudinal axis and in thermal contact with said rear part of the inner fairing so as to be cooled by said cold stream blown onto said rear part of the inner fairing.
       

     Thus, by virtue of the present invention it is possible to avoid aerodynamic disturbances in the fan duct attributable to the precooler because the precooler is now housed in the rear part of said inner fairing. In addition, the disadvantages attributable to tapping air from the cold stream and discharging the heated cold air are avoided because said precooler can, without tapping or discharging, make direct use of the cold stream exiting the fan duct and which is blown onto said rear part of the inner fairing. 
     Thus the problems of the prior art are solved. 
     As a preference, in order to obtain a satisfactory area for heat exchange between the hot air flowing through said precooler and the cold stream blown thereonto, provision is made for said precooler to have a shape of annular cross section and extends over the entire internal periphery of said rear part of the inner fairing. 
     It is known that, in certain turbine engines, said inner fairing and said central generator between them delimit an intermediate chamber of annular cross section surrounding said central generator, said intermediate chamber being used to circulate a current of cold air able to regulate the temperature of said central generator. In this case, the embodiment of the present invention is particularly advantageous because said precooler is then positioned on the same side as said intermediate chamber. 
     In a preferred embodiment of the present invention, said inner fairing is, at least in its rear part, double walled, that is to say comprises an inner wall and an outer wall which are separated from one another by a space in the form of an annular gap, and said precooler is positioned in said space. 
     To these ends, said precooler may comprise:
         a distribution pipe, connected to said inlet for the current of hot air and able to distribute said hot air to at least approximately the entire length (parallel to the longitudinal axis of the nacelle) of said annular space; and   a collection pipe connected to said outlet for the current of cooled hot air and able to collect said cooled hot air over at least approximately the entire length of said annular space.       

     As a preference, between said distribution pipe and said collection pipe (which pipes are positioned at the internal periphery of the rear part of the inner fairing in a way that is optimized for the cooling of the hot air), said precooler comprises a plurality of curved ducts for guiding the hot air, said ducts being transverse to the longitudinal axis of the nacelle and distributed over the length of said annular space. 
     Such ducts may advantageously be formed by a framework that reinforces the inner fairing, secured to said inner and outer walls thereof. 
     Advantageously, in order to provide even finer and easier regulation of the temperature of the cooled hot air, a duct is provided, preferably equipped with a controllable valve, mounted in parallel with said precooler and connecting its hot air inlet to its cooled hot air outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the attached drawing will make it easy to understand how the invention may be embodied. In these figures identical references denote elements that are similar. 
         FIG. 1  illustrates, in schematic axial section, a known bypass turbine engine. 
         FIGS. 2 and 3  illustrate, in views similar to  FIG. 1 , two alternative forms of the turbine engine according to the present invention. 
         FIG. 4  illustrates, in schematic longitudinal half section, the inner fairing surrounding the hot stream of the engines of  FIGS. 2 and 3 . 
         FIGS. 5 and 6  illustrate, on a larger scale, the structure of the fairing of  FIG. 4 . 
         FIG. 7  is an external view in perspective from the rear depicting said inner fairing. 
         FIG. 8  is an external view from the front of said inner fairing. 
         FIGS. 9 and 10  are partial cross sections on IX-IX and X-X of  FIG. 7 , respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The bypass turbine engine shown by each of  FIGS. 1 ,  2  and  3 , comprises a hollow nacelle  1  of longitudinal axis L-L provided, at the front, with an air inlet  2 , and, at the rear, with an air outlet  3 . Said hollow nacelle  1  internally bears a fairing  4 , preferably at least partially coated with acoustic attenuation coatings  5  intended to reduce the internal noise of said turbine engine. 
     Positioned inside the hollow nacelle  1  are:
         a central hot stream generator  6  comprising, in the known way, low-pressure and high-pressure compressors, a combustion chamber and low-pressure and high-pressure turbines, and generating the axial hot stream  7  of said turbine engine;   a fan  8  positioned axially in front of said central generator  6  and generating the annular cold stream  9  of said turbine engine; and   an inner fairing  10  surrounding said central generator  6  and forming, between itself and the casing  11  of this generator, an intermediate chamber  12  of annular cross section surrounding said generator, the rear part  10 R of said fairing forming the outer wall of the jet pipe  16  for said hot stream  7 .       

     The inner fairing  10  and the fairing  4 , external to it, between them form a fan duct  13  of annular cross section surrounding the central generator  6  and through which the cold stream  9  flows. 
     Formed between the inner fairing  10  and the central generator  6  are, at the front, an annular air intake slot  14 , and, at the rear, an annular air discharge slot  15 . Thus, the intermediate chamber  12  can be swept by a current of cold air f bled from the cold stream  9  at the front slot  14  and discharged at the boundary between said hot stream  7  and said cold stream  9  at the rear slot  15 , this current of cold air f being used to regulate the temperature of the central generator  6 . 
     Furthermore, in the usual way, the nacelle  1  is supported by a wing  17  of the aircraft (this wing is depicted in part) via a suspension pylon  18 . 
     In the known turbine engine illustrated in  FIG. 1 , a precooler  19  is provided, this being positioned in the upper part of the fan duct  13  in the cold stream  9 . This precooler  19  is fed with a current of hot air  20 , from the central generator  6 , via a duct  21  on which there is a hot air regulating valve  22 . The cooled hot air  23  generated by the precooler  19  is dispatched to the user equipment (not depicted) via a duct  24  which passes through the suspension pylon  18  and which may be fitted with a regulating valve  25 . 
     Thus, in this known layout, some of the cold stream is bled off by the precooler  19  to cool the current of hot air  20  and to generate the cooled hot air current  23  and this also results in said precooler forming a current of heated cold air (not depicted) corresponding to said bled-off portion of the cold stream. This current of heated cold air is discharged to the outside, in any known way not depicted in  FIG. 1 , and generally causes an increase in drag. 
     It will be readily understood therefore that the presence of the precooler  19  in the fan duct  13 , the bleeding-off of some of the cold stream  9  and the discharging of the heated cold air are detrimental to the performance of the known engine illustrated in  FIG. 1 . 
     In the nacelle  1 . 1 , according to the present invention and depicted in  FIG. 2 , we find all of the elements  2  to  18  and  20  to  25  described with reference to  FIG. 1 . In this nacelle  1 . 1 , the precooler  19  has been eliminated and replaced by the precooler  30  which has an inlet  31  connected to the duct  21  supplying the hot air current  20  and an outlet  32  connected to the duct  24  carrying the cooled hot air  23 . 
     The precooler  30  has an annular cross section and is positioned inside said rear part  10 R of the inner fairing  10 , on the same side as the intermediate chamber  12  and extends over the entire internal periphery of said rear part. It is coaxial with the axis L-L and is in thermal contact with said rear part  10 R. Because this rear part is in contact with the cold stream  9  exiting the fan duct  13 , said precooler  30  is itself cooled by the cold stream  9  without in any way having to bleed off some of the air or having to discharge cooled hot air. 
       FIG. 3 , which shows all the elements of  FIG. 2 , additionally shows the existence, in the nacelle  1 . 2  according to the invention of a bypass duct  33  mounted in parallel with the precooler  30 , connecting its inlet  31  and its outlet  32  and provided with a valve  34 . Thus, if necessary, hot air can be routed directly from the inlet  31  to the outlet  32 , thereby bypassing the precooler  30 . 
     The exemplary embodiment of the precooler  30  which is illustrated by  FIGS. 4 to 10  is structurally incorporated into said rear part  10 R of the inner fairing  10 . 
     As can be seen in  FIGS. 4 to 6 , said rear part  10 R comprises an inner wall  35  and an outer wall  36  which are parallel and spaced apart from one another by a space  37  in the form of an annular gap. Positioned in this space is a framework  38  ( FIG. 5 ) or  39  ( FIG. 6 ) secured to said inner and outer walls  35  and  36  and delimiting curved ducts  40  which subdivide the space  37 . The ducts  40  are transverse to the axis L-L of the nacelle and are distributed along said rear part  10 R. 
     Furthermore, said precooler  30  comprises (see  FIG. 7 ):
         a distribution pipe  41  connected to the hot air inlet  31  and able to distribute said hot air (see arrows  42 ) within said space  37  (and therefore into the ducts  40 ) along the entire rear part  10 R and transversely thereto; and   a collection pipe  43  connected to the cooled hot air outlet  32  and able to collect said air (see arrows  44 ) passing through said space  37  through the ducts  40 , along the length of the rear part  10 R.       

     As illustrated in  FIGS. 7 to 10 , the cross section of the pipes  41  and  43  decreases from the front rearward, while the reverse is true of the distribution orifices  45  and the collection orifices  46  with which they are respectively provided.