Abstract:
A heat exchange and noise reduction panel the panel for an aircraft comprising: an external surface intended to be swept by an airflow and from which fins extend along a first and a second main predetermined direction; cavities forming Helmholtz resonators, linked to the first ends of channels for the passage of air, the second ends of which communicate with said airflow, such that said channels form necks, referred to as Helmholtz resonators, extending substantially along the first direction; and at least one oil flow chamber extending between said external surface and said at least one cavity, and intended to discharge the thermal energy carried by the oil, characterized in that wherein said channels are formed, at least in part, inside said fins.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a heat exchange and noise reduction panel for a turbine engine, in particular of an aircraft. 
       PRIOR ART 
       [0002]    A turbine engine, such as a bypass turbojet engine, conventionally comprises an air inlet having a fan, the air flow at the output of which is divided into an air flow that enters the engine and forms a hot flow, or primary flow, and an air flow that flows around the engine and forms a cold flow, or secondary flow. 
         [0003]    The engine typically comprises, from upstream to downstream, in the direction of gas flow, at least one compressor, a combustion chamber, at least one turbine, and an exhaust nozzle in which the combustion gases leaving the turbine and forming the primary flow are mixed with the secondary flow. 
         [0004]    The fan of the turbine engine is surrounded by a fan housing which is integrated in the nacelle of the turbine engine. It is known to line the inner surface of said housing with acoustic panels in order to limit the propagation of the noise generated by the fan. 
         [0005]    The housing may also be provided with surface air cooled oil coolers (SACOC). A heat exchanger of this kind comprises an outer surface which is intended for being swept over by the secondary air flow and on which fins are located, and at least one oil circulation chamber extending below the outer surface. The outer surface is intended to discharge thermal energy generated by the oil. Depending on the design of the engine, the amount of thermal energy from the oil which has to be dissipated may be a very significant amount, it being possible for the oil to reach temperatures of approximately 160° C. 
         [0006]    Some turbine engines have nacelles that have a relatively short longitudinal dimension. Therefore, there is little space for installing equipment and in particular heat exchangers and acoustic panels used to attenuate the noise from the fan. 
         [0007]    The size and integration of equipment therefore become significant issues, particularly with regard to the installation of heat exchangers and acoustic panels in the flow path of the secondary flow. 
         [0008]    U.S. Pat. No. 8,544,531 already proposes that the functions of the air/oil exchanger and the functions of acoustic treatment be integrated in the same piece of equipment so that there is no longer any competition between the two requirements in a single installation space. 
         [0009]    The present invention proposes an improvement to this technology, which makes it possible in particular to optimise the design and arrangement of the functions of air/oil heat exchange and the functions of acoustic treatment in a single installation space. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention proposes a heat exchange and noise reduction panel for a turbine engine, in particular of an aircraft, the panel comprising:
       an outer surface which is intended for being swept over by an air flow and from which fins extend in a first predetermined main direction and a second predetermined main direction, which directions are preferably substantially perpendicular,   recesses which form Helmholtz resonators and are connected to first ends of air-passage channels, second ends of which communicate with said air flow, such that said channels form necks of said Helmholtz resonators that extend substantially in the first direction of the fins,   at least one oil circulation chamber which extends between said outer surface and said at least one recess and is intended for discharging thermal energy generated by the oil,
 
the stack consisting of said outer surface, said at least one recess and said at least one chamber extending substantially in the first predetermined direction, characterised in that said channels are formed at least in part inside said fins.
       
 
         [0014]    In the present application, a Helmholtz resonator is understood to mean an acoustic system comprising a generally small neck which is connected to a larger recess capable of resonating. The neck ensures that the sound waves to be attenuated and the recess are in communication. Once the system has been optimised, the neck provides for visco-thermal dissipation (quick and alternating movements of the sound waves, through the necks, that dissipate sound energy by friction). Frequency tuning, i.e. optimisation allowing these maximum speeds for frequencies to be attenuated to be reached, is performed primarily by the volume in the resonant recesses, i.e. the dimensions thereof and in particular the height thereof. It should be noted that, owing to the thermal environment, the local temperatures may be taken into account in order to properly optimise the system. 
         [0015]    The invention thus proposes that the aforementioned functions of the air/oil heat exchanger and the aforementioned functions of acoustic treatment be combined in the same piece of equipment in the form of a panel. Furthermore, for a given tuned frequency, the invention makes it possible to reduce the size of the air recesses of the resonators as a result of channels which are significantly longer. In terms of acoustics, in order to optimise the operation of the system at a given frequency, making the necks (channels) of the resonators longer makes it possible to increase the mass of moving air and thus compensate for the low volume of the resonant recesses. Moreover, the reduction in the volume of the resonant recesses has a positive impact on the equipment. Indeed, it would be possible to either reduce the overall size of the equipment or increase the volume of the oil chamber in order to thus reduce the loss of pressure generated by the channels in the oil chamber. 
         [0016]    The panel according to the invention may comprise one or more of the following features, taken in isolation or in combination with one another:
       the fins are substantially normal or inclined with respect to the outer surface,   said channels open onto walls of the fins to form openings for bleeding air from said air flow,   a plurality of channels pass through each fin,   the channels have a substantially rectangular, circular or elliptical cross section,   the panel has a curved general shape and is designed to form a sector of an annular heat exchange and noise reduction casing, for example for a turbine engine nacelle,   the channels have a constant cross section or a general shape which is flared towards said recesses,   at least some of said recesses communicate with one another, and   said first direction is substantially perpendicular to said outer surface or inclined with respect to said outer surface.       
 
         [0025]    The present invention also relates to a turbine engine, in particular of an aircraft, characterised in that said engine comprises at least one panel as described above. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0026]    The invention will be better understood and other details, features and advantages of the invention will become apparent upon reading the following description given by way of non-limiting example and with reference to the accompanying drawings, in which: 
           [0027]      FIG. 1  is a very schematic perspective view of a heat exchange and noise reduction panel according to the invention, 
           [0028]      FIG. 2  is a perspective cross section along line II-II in  FIG. 1 , 
           [0029]      FIG. 3  is cross section along line III-III in  FIG. 1 , 
           [0030]      FIG. 4  is a cross section along line IV-IV in  FIG. 1 , 
           [0031]      FIG. 5  is a plan view of the panel from  FIG. 1 , 
           [0032]      FIGS. 6 to 9  are views similar to that of  FIG. 4 , showing other variants of the invention, and 
           [0033]      FIGS. 10 and 11  are views similar to that of  FIG. 5 , showing further variants of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Reference is first made to  FIGS. 1 to 5  which show an embodiment of a heat exchange and noise reduction panel 10 according to the invention for a turbine engine of an aircraft. 
         [0035]    In the following description, terms such as “below”, “under”, “on”, “above”, “upper”, “lower”, etc. are to be understood relative to the orientation of the figures. Similarly, dimensions are given on the basis of this orientation of the figures. Therefore, “height” refers to a dimension extending vertically or from the bottom to the top (or vice versa), and “thickness”, “length” and “width”, or even “distance”, are to be understood to mean dimensions measured in a substantially horizontal plane. 
         [0036]    The panel  10  essentially comprises three portions or superposed layers, namely:
       an outer portion  12  intended to be exposed to a cooling air flow, such as a secondary air flow of the turbine engine,   an intermediate portion  14  having a chamber  16  for circulating oil to be cooled, and   an inner portion  18  having air recesses  20 .       
 
         [0040]    The portions  12  and  14  form a SACOC surface heat exchanger and the portions  12 ,  14  and  18  form an acoustic panel having Helmholtz resonators. 
         [0041]    The outer portion  12  comprises an outer surface  22  which is intended to be swept over by the air flow  24  and on which fins  26  are located. The fins  26  extend from the surface  24  in a first main direction, in this case the vertical direction, and in a second main direction, in this case the horizontal direction. The first direction and the second direction are substantially perpendicular. The horizontal direction perpendicular to the first direction and the second direction is defined as being the third direction. Air flows between the fins  26  that are intended in particular for increasing the surface area of the surfaces for exchanging heat with the air. In the example shown, the fins  26  are preferably rectilinear, parallel and independent, i.e. they are not interconnected. Other arrangements are however conceivable, as will be explained below. In the example shown, the outer surface  22  is shown having a shape which is substantially square or rectangular in the area or surface denoted A. Although the surface  22  is shown in the drawings as being planar, said surface could also have a curved shape, in particular if the panel  10  is curved so as to make it easier to mount in an annular housing of the turbine engine, for example. A panel  10  which has a curved general shape is designed to form a sector of an annular heat exchange and noise reduction casing, for example for a turbine engine nacelle. 
         [0042]    The fins  26  extend over substantially the entire length or longitudinal direction of the surface  22  in the second, horizontal direction. The number of fins is defined in a known manner, depending in particular on the exchange conditions to be met. 
         [0043]    The oil circulation chamber  16  extends below the outer surface  22  over substantially the entire extent thereof. Said chamber is connected to an oil inlet and an oil outlet, which are not shown in the drawings. The flow direction and the flow orientation of the oil in the chamber may be the same as that/those of the air on the surface  22  (arrow  28 ) or may be different therefrom. 
         [0044]    The air recesses  20  in the third portion  18  are located below the oil chamber  16 . Said recesses are preferably regularly distributed and substantially identical. Said recesses extend side by side in the same plane which is substantially parallel to the surface  22 . Said recesses  20  are connected to lower longitudinal ends of air-passage channels  30 , the upper longitudinal ends of which form openings  32  for communicating with the sound source to be attenuated. The assembly formed by the channels  30  and the recesses  20  forms Helmholtz resonators, the channels forming necks and the recesses forming resonant recesses of the resonators. At least some of the recesses  20  can communicate with one another, as is shown in  FIGS. 7 and 8 . 
         [0045]    The invention proposes a panel having a reduced size owing to at least a portion of the channels  30  being formed inside the fins  26 . As can be seen in the example shown, the channels  30  are oriented in a substantially rectilinear and vertical manner and comprise lower portions which extend into the oil chamber  16  and upper portions which extend into the fins  26 . Moreover, in the particular case shown, the upper ends of the channels  30  open onto walls of the fins, in particular on the tops or upper free ends of the fins  26  and form the aforementioned communication openings  32 . In  FIG. 2 , a plurality of channels  30  pass through each fin  26 . 
         [0046]    The channels  30  are preferably distributed in a matrix. Therefore, the channels  30  are distributed in lines and columns in the oil chamber  26 . In the example shown, each fin  26  comprises a row of openings  32 . 
         [0047]    The panel  10  according to the invention can have the following dimensions, which are optimised for attenuating the acoustic frequencies of a turbine engine, namely frequencies of between 400 and 2,000 Hz, to the greatest extent possible:
       the fins  26  have a thickness e (i.e. a dimension in the third direction) of between 0.5 and 2 mm and are spaced apart from one another by a distance a (in the third direction) of between 1 and 5 mm,   the oil chamber  16  has a height c (in the first, vertical direction) of between 1 and 10 mm,   the channels  30  have an average diameter d of between 1 and 2 mm,   the recesses  20  have a height f (in the first, vertical direction) of between 5 and 150 mm, and   the perforation level a of said outer surface is between 5% and 10%. This perforation level is equal to the ratio of the cumulative cross section of the openings  32  (n.π.(d/2) 2 , n being the number of openings  32  or channels  30 ) to the area A of the surface of the resonators, which is considered to be substantially equal to that of the outer surface  22 . The difference between the surface area of the outer surface and that of the resonators may be negligible. The resonators are separated by walls that reduce the surface area thereof relative to that of the outer surface. At first approximation, however, the two surface areas are equal.       
 
         [0053]    “Average diameter” is understood to mean the diameter of a channel when said channel is cylindrical, the average of the diameters of a channel when said channel has a non-constant circular cross section and when said channel is flared or frustoconical, for example, and the diameter of a circular cross section that is equivalent to the cross section of the channel when said channel is not circular and is for example rectangular. 
         [0054]    The tuned frequency of a Helmholtz resonator can be estimated using the following formula: 
         [0000]    
       
         
           
             
               Tuned 
                
               
                   
               
                
               frequency 
             
             = 
             
               
                 C 
                 
                   2 
                    
                   π 
                 
               
                
               
                 
                   S 
                   
                     Vl 
                     ′ 
                   
                 
               
             
           
         
       
       
         
           where 
         
       
       
         
           
             
               
                 
                   C 
                    
                   
                     : 
                   
                 
               
               
                 
                   speed 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   the 
                    
                   
                       
                   
                    
                   sound 
                 
               
               
                 
                   ( 
                   
                     m 
                      
                     
                       / 
                     
                      
                     s 
                   
                   ) 
                 
               
             
             
               
                 
                   S 
                    
                   
                     : 
                   
                 
               
               
                 
                   cross 
                    
                   
                       
                   
                    
                   section 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   the 
                    
                   
                       
                   
                    
                   neck 
                 
               
               
                 
                   ( 
                   
                     m 
                     2 
                   
                   ) 
                 
               
             
             
               
                 
                   V 
                    
                   
                     : 
                   
                 
               
               
                 
                   volume 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   the 
                    
                   
                       
                   
                    
                   resonator 
                 
               
               
                 
                   ( 
                   
                     m 
                     3 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     l 
                     ′ 
                   
                    
                   
                     : 
                   
                 
               
               
                 
                   corrected 
                    
                   
                       
                   
                    
                   neck 
                    
                   
                       
                   
                    
                   length 
                 
               
               
                 
                   
                     
                       ( 
                       m 
                       ) 
                     
                      
                     
                         
                     
                      
                     or 
                      
                     
                         
                     
                      
                     
                       l 
                       ′ 
                     
                   
                   = 
                   
                     l 
                     + 
                     δ 
                   
                 
               
             
           
         
       
       
         
           where 
         
       
       
         
           
             
               
                 
                   l 
                    
                   
                     : 
                   
                 
               
               
                 
                   geometrical 
                    
                   
                       
                   
                    
                   neck 
                    
                   
                       
                   
                    
                   length 
                 
               
               
                 
                   ( 
                   m 
                   ) 
                 
               
             
             
               
                 
                   δ 
                    
                   
                     : 
                   
                 
               
               
                 
                   neck 
                    
                   
                       
                   
                    
                   correction 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                     
                 
               
               
                 
                   { 
                   
                     
                       
                         
                           δ 
                           = 
                           
                             1.7 
                              
                             
                                 
                             
                              
                             
                               r 
                                
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     0.7 
                                      
                                     
                                       σ 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           for 
                            
                           
                               
                           
                            
                           juxtaposed 
                            
                           
                               
                           
                            
                           resonators 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   r 
                    
                   
                     : 
                   
                 
               
               
                 
                   radius 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   an 
                    
                   
                       
                   
                    
                   opening 
                 
               
               
                 
                   ( 
                   m 
                   ) 
                 
               
             
             
               
                 
                   σ 
                    
                   
                     : 
                   
                 
               
               
                 
                   perforation 
                    
                   
                       
                   
                    
                   level 
                 
               
               
                 
                     
                 
               
             
           
         
       
     
         [0055]    In this formula, the cross section of the neck S is the aforementioned cross section of an opening  32 , the volume of the resonator V is the volume of one recess  20 , and the length of the neck I or I′ substantially equates to the sum of the thickness c of the oil chamber  16  and the height b of the fins  26 . 
         [0056]    Advantageously:
       the fins  26  have a height b (in the first, vertical direction) of between  10  and  25  mm, and   openings  32  in the same row are spaced apart from one another by a distance g (in the second direction) of between  1 . 57  and  31 . 42  mm. The spacing between the openings of two adjacent rows equates to the spacing a (in the third direction) between two adjacent fins  26 .       
 
         [0059]    The channels  30  have longitudinal axes which are substantially perpendicular to said outer surface  22  or inclined with respect to said outer surface  22 . Said channels have a cylindrical longitudinal general shape having a constant or parallelepiped cross section in the example shown in  FIGS. 1 to 5 . Said channels could have a different shape and be for example frustoconical or flared towards the recesses  20 , as shown in  FIG. 6 . The channels  30 ′ in  FIG. 6  have an inlet cross section, i.e. a cross section measured at the opening  32  by which the channel  30  opens onto the surface  22 , that is smaller than the opposed cross section, referred to as the outlet cross section. The channels  30  have a substantially rectangular, circular or elliptical cross section. This makes it possible in particular to limit the reduction in the width of the frequency band of attenuation generated by the length of the channels  30 ′, i.e. by the height of the oil chamber  16 . 
         [0060]    Moreover, as shown in  FIGS. 7 and 8 , air passages  40  could be provided between the resonant recesses  20  in order to optimise heat exchange therebetween, but to the detriment of acoustic performance. This option also makes it possible to overcome problems relating to the expansion of the partitions which define the recesses  20 . These air passages can be located in the region of the upper ends of the recesses ( FIG. 7 ) or in the region of the lower ends thereof ( FIG. 8 ). 
         [0061]      FIGS. 8 to 10  show other arrangement variants, the performance of which is slightly less satisfactory by comparison with that of rectilinear, parallel and independent fins. In the variant in  FIG. 8 , the fins are no longer independent of one another but are instead interconnected in pairs. The upper end of each fin  26 ′ is connected to the upper end of an adjacent fin  26 ′ by a bridge of material  42 . In the variant in  FIG. 9 , the fins  26 ″ are rectilinear but not strictly parallel. In the variant in  FIG. 10 , the fins  26 ″ have an undulating (not rectilinear) general shape and are largely parallel in the second extension direction. 
         [0062]    The invention offers a solution to the real need for finding a means for integrating the functions of the air/oil exchanger and the functions of acoustic treatment in the same piece of equipment so that there is no longer any competition between the two requirements in a single installation space. 
         [0063]    Although the invention relates in particular to an aircraft turbine engine in the above description, it also relates to any kind of turbine engine.