Abstract:
A nacelle for a propulsion unit includes at least one scoop opening to the external air, and a canal supplying external air from the scoop to two ducts which separate downstream of the canal, forming a dividing lip, and at least one exchanger to cool a stream of fluid entering the exchanger. The exchanger is arranged in the region of and in contact with the separation lip. The external air circulates from the scoop towards the two ducts making it possible to cool the stream of fluid entering the exchanger.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a nacelle for a propulsion unit, said nacelle comprising an exchanger configured for cooling a fluid flow. 
       PRESENTATION OF THE PRIOR ART 
       [0002]    Installing an air/air exchanger of the SACAC type (surface air cooled air cooler) in a turbine engine for cooling an air flow, drawn for example at a pressurized air bleed outlet of a compressor, is known. In the case of a compressor with several compressor stages, such a bleed outlet can be provided to communicate with the air under pressure of the last stage or of a preceding stage. 
         [0003]    As illustrated in  FIG. 1 , the exchanger  52  receives a stream of hot air  51  (with a temperature typically above 200° C.) coming from an air bleed outlet of a high-pressure compressor  50 . At it leaves the heat exchanger  52 , the air flow  53  is cooled and has a temperature less than 200° C. 
         [0004]    In the case of turbofans, the exchanger is positioned on the secondary stream, so as to cool the air flow entering the heat exchanger using the air of the secondary stream. 
         [0005]    In the case of turboprops, the equivalent of the secondary stream is the air that passes around the nacelle and is accelerated by the propellers. The exchanger must therefore be positioned outside the nacelle. However, this solution causes interferences with the flow around the nacelle, which increases drag. This solution is therefore not satisfactory. 
       PRESENTATION OF THE INVENTION 
       [0006]    So as to correct these disadvantages, the invention proposes a nacelle for a propulsion unit comprising at least one scoop opening to the exterior air, a channel feeding with exterior air, from the scoop, two ducts which separate downstream of the channel forming a separator nose, characterized in that it comprises at least one exchanger configured to cool a fluid flow entering the exchanger, said exchanger being positioned at and in contact with the separator nose, the exterior air circulating from the scoop to the two ducts allowing cooling of the fluid flow entering the exchanger. 
         [0007]    The invention is advantageously completed by the following characteristics, taken alone or in any one of their technically possible combinations:
       the exchanger comprises a frame and a plurality of fins positioned on one or more faces of the frame;   the exchanger is attached to at least one of the ducts by at least one plate;   the ducts have a wall made of composite material and the plate is made of metal;   the frame has a tapered profile at its leading edge;   the fluid flow entering the exchanger is an air flow bled at an outlet of a compressor of the turbine engine;       
 
         [0013]    The invention also relates to a turboprop comprising a nacelle as described and a turbine engine. In one embodiment, an air inlet of the exchanger is connected to an outlet of a compressor of the turbine engine, so as to cool the air flow bled at this outlet of the compressor. 
         [0014]    The invention also relates to a method for mounting an exchanger receiving a fluid flow to be cooled, in a turbine engine comprising a nacelle wherein is provided at least one scoop opening to the exterior air, a channel feeding with exterior air, from the scoop, two ducts which separate forming a separator nose, characterized in that it comprises the steps of forming an opening in the separator nose, introducing the exchanger through the opening, and positioning it at the separator nose so that the exchanger separates the two ducts. The method can further comprise the step of attaching the exchanger to one of the ducts through a plate. 
         [0015]    The invention has numerous advantages. 
         [0016]    The invention makes it possible to cool a fluid flow through an exchanger simply and effectively. 
         [0017]    In particular, it makes it possible to re-use a flow of cold air circulating in the ducts of the propulsion unit so as to cool the fluid flow entering the exchanger. 
         [0018]    In addition, the invention makes it possible both to resolve the icing problem which can occur in certain areas of the propulsion unit, in particular on the separator noses of the ducts, and to cool a flow of hot fluid passing through an exchanger of the propulsion unit. 
         [0019]    The invention thus allows dispensing with the installation of many ducts which would be necessary for eliminating icing and cooling the fluid flow entering the exchanger. 
     
    
     
       PRESENTATION OF THE FIGURES 
         [0020]    Other features and advantages of the invention will be revealed by the description that follows, which is purely illustrative and not limiting, and must be read with reference to the appended drawings wherein: 
           [0021]      FIG. 1  is a representation of the operation of an air/air exchanger in a turbine engine; 
           [0022]      FIG. 2  is a representation of a propulsion unit according to the invention, in side view; 
           [0023]      FIG. 3  is a representation of a propulsion unit according to the invention, in top view; 
           [0024]      FIG. 4  is a representation of the positioning of the exchanger at the separator nose of the two ducts; 
           [0025]      FIG. 5  is a representation of the exchanger; 
           [0026]      FIG. 6  is a representation of  FIG. 4  in side view; 
           [0027]      FIG. 7  is a representation of  FIG. 4  in top view; 
           [0028]      FIG. 8  is a representation of the attachment of the exchanger to a duct through a plate; 
           [0029]      FIG. 9  is a representation of an embodiment of a method for mounting an exchanger. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Shown in  FIGS. 2 and 3  is a propulsion assembly  1  of an aircraft. In these figures, the propulsion assembly  1  is a turboprop. 
         [0031]    The propulsion assembly  1  comprises a turbine engine and a nacelle  11  in which is provided at least one scoop  2  opening to the exterior air. During displacement of the aircraft, the exterior air penetrates into the nacelle  11  through the scoop  2 . Generally, the scoop  2  is placed at  12  o&#39;clock (azimuth angle). 
         [0032]    A channel  3  is connected to the scoop  2  and is fed with exterior air. This channel  3  feeds two ducts  13 ,  14  in the nacelle  11 , which separate to form a separator nose  8 . The two ducts  13 ,  14  each constitute a distinct extension of the channel  3 . As illustrated, the two ducts  13 ,  14  separate downstream of the channel  3  (the upstream-downstream direction being defined by the direction of flow of the exterior air in and around the nacelle  11 ). 
         [0033]    The separator nose  8  is at the junction between the channel  3  and the inlet of the two ducts  13 ,  14 . It delimits the separation between the inlets of the two ducts  13 ,  14 . This separator nose  8  can be flat or protruding. 
         [0034]    After the separator nose  8 , the ducts  13 ,  14  are separated by a slot  30  and are therefore quite distinct. 
         [0035]    The ducts  13 ,  14  are for example respectively a duct which feeds cold air to equipment  31  (which is for example the “air cooled oil cooler” which cools the oil of the “variable frequency generator”) and a duct which feeds cold air to equipment  32  (which is for example the “pre-cooler” or upstream cooler). 
         [0036]    The nacelle  11  further comprises at least one exchanger  7  configured to cool a fluid flow  12  entering said exchanger  7 . 
         [0037]    This is for example an air flow bled from a pressurized air bleed outlet of a compressor of the turbine engine of the propulsion unit. In this case, an air inlet of the exchanger is connected to the bleed outlet of the compressor of the turbine engine, so as to cool the air flow bled from the compressor. 
         [0038]    Once cooled, the air flow can in particular be sent to equipment which controls pneumatic valves. 
         [0039]    This can be any fluid which it is desired to cool (lubrication oil, heat transport fluid, etc.). 
         [0040]    The exchanger  7  is positioned at the separator nose  8 . Consequently, the exterior air entering the scoop  2 , and passing through the channel  3 , then the two ducts  13 ,  14  flows around the exchanger  7 . As illustrated, the exchanger  7  is in contact with said separator nose  8 . 
         [0041]    The fluid flow  12  entering the exchanger  7  is cooled by the circulation of exterior air flowing around the exchanger  7 . 
         [0042]    This judicious configuration makes it possible to re-use existing ducts  13 ,  14  so as to cool the fluid flow entering the exchanger  7 . It is therefore not necessary to re-create a new circulation of cold air so as to cool the fluid flow  12  entering the exchanger  7 . 
         [0043]    The structure of the exchanger  7  is cooled on its two faces by the air circulating toward the duct  13  and the air circulating toward the duct  14 . Thanks to this installation, the space required by the exchanger  7  is reduced. 
         [0044]    Moreover, the separator nose  8  is generally subject to the formation of ice. Thanks to the sound positioning of the exchanger  7  at the separator nose  8 , icing is eliminated, and it is not necessary to install additional devices so as to combat the formation of ice, such as de-icing ducts. 
         [0045]    In one embodiment, the exchanger  7  comprises a frame  16  and a plurality of fins  18  positioned on one or more faces of the frame  16 . One or more channels  23  bring the fluid flow  12  to be cooled into the frame  16 . The fluid flow  12  leaves the frame  16 , by the same side or by another side, via at least one other channel  24 , with a lower temperature. 
         [0046]    The fins  18  make it possible to channel and to guide the exterior air around the frame  16  of the exchanger  7 , which improves thermal exchanges and therefore the effectiveness of cooling. Advantageously, the fins  18  are positioned on either side of the frame  16 . They extend parallel to one another, and are parallel to the flow direction of the exterior air. 
         [0047]    In one embodiment, the frame  16  has a tapered profile in its leading edge  21 . This configuration makes it possible to improve the flow of exterior air around the frame  16 . 
         [0048]    According to another embodiment, the turbine engine is a turboprop. 
         [0049]    The attachment of the exchanger  7  can for example be accomplished through at least one plate  19 . The plate  19  is, on the one hand, attached to one of the ducts  13 ,  14  and on the other hand to the exchanger  7 . The attachment is for example achieved via screws  35 . 
         [0050]    Generally, the ducts  13 ,  14  have a wall made of composite material. The frame  16 , for its part, is made of metal. So as to connect the frame  16  to at least one of the ducts, the plate  19  can be made of metal. 
         [0051]    With reference to  FIG. 9 , a method for mounting the exchanger  7  in the nacelle  11  of the propulsion unit  1  is described. 
         [0052]    The method comprises step S 1  of forming an opening in the separator nose  8  separating the two ducts  13 ,  14 . 
         [0053]    The section and the dimensions of the opening are selected so as to correspond to the section and the dimensions of the exchanger  7 . For example, the opening has a rectangular section, the area whereof allows the exchanger  7  with the fins  18  to pass. 
         [0054]    In step S 2 , the exchanger  7  is introduced through the opening and is positioned (step S 3 ) at the separator nose  8  so that the exchanger  7  separates the two ducts  13 ,  14 . The exchanger  7  then plays the role of a separator nose between the two ducts  13 ,  14 . 
         [0055]    Finally, the frame  16  of the exchanger  7  is attached to at least one of the ducts  13 ,  14  through at least one plate  19 .