Abstract:
The present disclosure provides an aircraft nacelle including: an outer aerodynamic wall having an upstream air intake lip; an inner aerodynamic wall, the air intake lip connecting the two outer and inner aerodynamic skins; a front wall arranged downstream of the air intake lip and connecting the two outer and inner aerodynamic skins; and a network for the circulation of a first fluid for cooling a second fluid. The network includes two air/oil-type heat exchangers, one air/air type heat exchanger, an air scoop to collect air from the outside of the nacelle, an orifice to collect cold air, and an outlet orifice to discharge air.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/FR2014/050520, filed on Mar. 7, 2014, which claims the benefit of FR 13/52069, filed on Mar. 7, 2013. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a nacelle for a turbojet engine equipped with a cooling system for the engine oil. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    An aircraft is driven by one or several propulsion units each comprising a turbojet engine housed in a tubular nacelle. Each propulsion unit is fastened to the aircraft by a mast which is generally located under or above a wing or at the fuselage. 
         [0005]    By upstream, it is referred to everything that lies before the considered point or element, in the direction of the air flow in a turbojet engine, and by downstream, it is referred to everything that lies after the considered point or element, in the direction of the air flow in a turbojet engine. 
         [0006]    A nacelle generally has a structure comprising an air inlet upstream of the engine, a mid-section intended to surround a fan or the compressors of the turbojet engine and its casing, a downstream section able to integrate thrust reversal means and intended to surround the gas turbine of the turbojet engine, and is generally terminated by an ejection nozzle the outlet of which is located downstream of the turbojet engine. 
         [0007]    Conventionally, the space that it is comprised between the nacelle and the turbojet engine is called the secondary duct. 
         [0008]    In general, the turbojet engine comprises a set of blades (the compressor, and possibly a fan or an unshrouded propeller) which are driven in rotation by a gas turbine via a set of mechanical transmission means. 
         [0009]    A lubricant distribution system is provided in order to provide good lubrication of these transmission means and any other accessory such as the electric generators, and to cool them. 
         [0010]    As a consequence, the lubricant must also be cooled by a heat exchanger. 
         [0011]    To this end, a first known method consists of cooling the lubricant by conveying it through an air/oil heat exchanger which uses air that is collected in a secondary duct (so-called the cold stream) of the nacelle or in either one of the compressor stages. 
         [0012]    Collecting and conveying air through this heat exchanger disturbs the air flow stream and results in a loss of thrust of the engine, which is not desired. 
         [0013]    In particular, it has been assessed that, in the case of a geared turbofan engine, this may represent losses that are equivalent to 1% of the total fuel consumption. 
         [0014]    Another solution has appeared with the nacelle deicing systems. 
         [0015]    In fact, during flight and depending on the conditions of temperature and humidity, ice may form on the nacelle, in particular at the outer surface of the air inlet lip which equips the air inlet section. 
         [0016]    The presence of ice or frost modifies the aerodynamic properties of the air inlet and disturbs the delivery of air toward the fan. In addition, the formation of frost on the air inlet of the nacelle and the ingestion of ice by the engine in the case where the ice blocks are detached may damage the engine or the wings, and pose a risk to the safety of the flight. 
         [0017]    Another solution for defrosting the outer surface of the nacelle consists in preventing ice from forming on this outer surface by maintaining the considered surface at a sufficient temperature. 
         [0018]    Thus, the lubricant heat may be used to reheat the outer surfaces of the nacelle, and consequently, the lubricant is cooled and ready to be used again in the lubrication circuit. 
         [0019]    In particular, the documents U.S. Pat. No. 4,782,658 and EP1479889 describe the implementation of such defrosting systems which use the heat of the engine lubricant. 
         [0020]    More specifically, the document U.S. Pat. No. 4,782,658 describes a defrosting system which uses external air that is collected by an air scoop and reheated through an air/oil heat exchanger in order to serve for defrosting. Such a system allows for a better control of the exchanged heat flows, but the presence of air scoops at the outer surface of the nacelle results in a loss of the aerodynamic performances. 
         [0021]    As for the document EP1479889 it describes, a system for defrosting an air inlet structure of a nacelle of a turbojet engine which uses an air/oil heat exchanger in a closed circuit, the reheated internal air of the air inlet structure being driven in forced convection by a blower. 
         [0022]    It is worth noting that the air inlet structure is hollow and it forms a closed chamber intended for conveying the defrosting air which is reheated by the heat exchanger disposed inside this chamber. 
         [0023]    Thus, the heat energy that is available for defrosting depends on the temperature of the lubricant. 
         [0024]    Furthermore, the exchange surface of the air inlet structure is stationary and limited, and the energy that is actually dissipated depends mainly on the heat that is required for defrosting, and hence, it is dependent on the external conditions. 
         [0025]    It follows that the lubricant cooling, as well as the temperature at which the air inlet is maintained, are difficult to control. 
         [0026]    There is another solution wherein a heat exchanger and ducts for circulating a fluid to be reheated are associated so as to form several loops for recirculating the fluid to be reheated through the heat exchanger, and in such a manner that an area intended for circulating the fluid to be reheated is in contact with an outer wall so as to allow a conductive heat exchange with the external air of the nacelle. The circulation of the fluid to be reheated is achieved by forced circulation. 
         [0027]    It has been observed that systems such as those described before cause pressure drops in the secondary duct due to the presence of the heat exchanger, and cause engine thrust losses when an air collection is performed in the secondary duct where these losses considerably affect the consumption (they represent about 0.5% of the total consumption). Furthermore, such systems have a poor efficiency when the turbojet engine idles and/or rotates at low speed (for example, when the aircraft is on the ground, during the taxiing phase) in the case where cooling the engine oil requires collecting air from the outside of the nacelle. 
       SUMMARY 
       [0028]    The present disclosure provides a nacelle for an aircraft comprising: an outer aerodynamic skin comprising an upstream air inlet lip, an inner aerodynamic skin, the air inlet lip connecting upstream the two outer and inner aerodynamic skins, a front partition wall located immediately downstream of the lip and connecting the two outer and inner aerodynamic skins, a circulation network for a first fluid intended for cooling a second fluid comprising at least two air/oil type heat exchangers and at least one air/air type heat exchanger, characterized in that the circulation network ( 1 ) comprises at least one dynamic air scoop ( 112 ) for collecting air from the outside of the nacelle ( 100 ), at least one orifice ( 121 ) for collecting cold air from a fan ( 130 ) and at least one outlet orifice ( 113 ) for discharging air out of the nacelle ( 100 ). 
         [0029]    The air inlet lip may or may not be integrated into the outer aerodynamic skin of the aircraft nacelle. 
         [0030]    According to other features of the present disclosure, the nacelle includes one or several of the following features, considered separately or according to any possible combination:
       the air/air type heat exchanger is located, with regard to the path of the first fluid, between the two air/oil type heat exchangers;   the air/air type heat exchanger is a surface heat exchanger which has an exchange surface;   the exchange surface is produced from the outer aerodynamic skin of the nacelle;   the air/air type heat exchanger comprises an intermediate wall pierced by a plurality of orifices;   the air/air type heat exchanger has a confined space, comprising an inlet and an outlet for the first fluid, enclosed by walls including the exchange surface and a peripheral wall ;   the confined space is located in the air inlet lip;   the nacelle comprises at least one controlled means for collecting hot air coming from a compressor of the aircraft so as to allow supplying the air inlet lip with hot air;   the nacelle comprises at least one high-pressure injector which is controlled so as to inject hot air coming from the controlled hot air collection means in the air inlet lip;   the outer aerodynamic skin comprises at least one outlet orifice for discharging the reheated first fluid out of the nacelle after having flowed through the network.       
 
         [0040]    This solution improves the cooling of the second fluid while reducing the pressure drops in the nacelle. In some cases, it also defrosts the air inlet lip. In fact, the pressure that is collected on the outside, at high speed, is sufficient for supplying the two air/oil type heat exchangers in series, the air/air type heat exchanger lowers the temperature at the inlet of the second heat exchanger in which the air penetrates. At low speed, the pressure that is collected from the fan only allows supplying one of the two heat exchangers, therefore, these are supplied in parallel. In comparison with a solution that is known by those skilled in the art where the two heat exchangers always operate in parallel, even when the aircraft is flying at high speed, the proposed solution allows dividing by two the flow rate of the collected air, and therefore, dividing by two the losses that are related to the cooling of the engine oil. 
         [0041]    The solution reduces the total consumption of the aircraft by approximately from 0.25% to 0.4% in comparison with a cooling performed only by collection in the secondary duct. In the cases where it allows defrosting the air inlet lip, it then allows reducing the temperature of the air inlet lip, thereby reducing the recurrent issues of fatigue, and by the upstream area of the outer aerodynamic skin, the temperature of said area not exceeding the maximum temperature of the oil of a turbine engine, which is typically in the range of 180° C., thus allowing to realize a front partition wall of the air inlet lip in aluminum rather than titanium. 
         [0042]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0043]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0044]      FIG. 1  is a schematic view of a first circulation network for the first fluid according to a first form of the present disclosure; 
           [0045]      FIG. 2  is a schematic view of the first network detailing the circulation of the first fluid throughout the network in the case where the aircraft is flying at high speed; 
           [0046]      FIG. 3  is a schematic view of the first network detailing the circulation of the first fluid throughout the network in the case where the aircraft is flying at low speed; 
           [0047]      FIG. 4  is a schematic view of a second circulation network for the first fluid according to a second form of the present disclosure; 
           [0048]      FIG. 5  is a partial perspective view of an air inlet lip of an aircraft nacelle in which the second network is installed; 
           [0049]      FIG. 6  is a schematic view of the second network detailing the circulation of the first fluid throughout the network in the case where the aircraft is flying at high speed; 
           [0050]      FIG. 7  is a schematic view of the second network detailing the flow of the first fluid throughout the network in the case where the aircraft is flying at low speed; 
           [0051]      FIG. 8  is a schematic view of the second network detailing a circulation of the first fluid throughout the network when the defrosting mode of the air inlet lip is activated; 
           [0052]      FIG. 9  is a schematic view of a third circulation network for the first fluid according to a third form of the present disclosure; 
           [0053]      FIG. 10  is a schematic view of the air inlet lip equipped with a fourth circulation network for the first fluid according to a fourth form of the present disclosure; 
           [0054]      FIG. 11  is a schematic view of the fourth circulation network for the first fluid according to the fourth form of the present disclosure; 
           [0055]      FIG. 12  is a schematic view of the fourth network detailing the circulation of the first fluid throughout the network in the case where the aircraft is flying at high speed; 
           [0056]      FIG. 13  is a schematic view of the fourth network detailing a circulation of the first fluid throughout the network in the case where the aircraft is flying at low speed; 
           [0057]      FIG. 14  is a schematic view of the fourth network detailing a circulation of the first fluid throughout the network when the defrosting mode of the air inlet lip is activated; and 
           [0058]      FIG. 15  is a schematic view of the fourth network detailing the operation of the network in the event of a failure of one or more of the elements intended for controlling the circulation of the first fluid throughout the network. 
       
    
    
       [0059]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0060]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0061]    In forms that are described below, the first fluid is substantially constituted by air, and the second fluid is substantially constituted by engine oil chosen from among those that are commonly used in the aeronautical field. Nonetheless, the first fluid and the second fluid may be constituted substantially by any other materials that may be used together in the aeronautical field. 
         [0062]    For the sake of simplicity, in all forms that are described below, the ducts that connect the different elements of the different air circulation networks  1  are called “duct  19 ”. 
         [0063]    In all forms that are described below, it is meant by “flowing throughout the network”, flowing through all or part of a network  1 , by “controlled valve”, it is intended a valve which acts as a gate valve, whether power-actuated or not, by “dynamic air scoop”, it is intended an air scoop, preferably equipped with at least one control valve. 
         [0064]    Referring to  FIG. 1 , there is described the structure of the first air circulation network  1  according to the first form of the present disclosure. 
         [0065]    The first network  1  is comprised in an aircraft nacelle  100 . 
         [0066]    The nacelle  100  comprises an outer aerodynamic skin  110  comprising an upstream air inlet lip  111  and an inner aerodynamic skin  120 . The air inlet lip  111  connects the two outer  110  and inner  120  aerodynamic skins upstream. 
         [0067]    The first air circulation network  1 , intended for cooling the engine oil, comprises two air/oil heat exchangers (respectively,  2  and  3 ), and one air/air heat exchanger  4 . The first network  1  comprises check valves which only allow the circulation of air in one direction (respectively,  5 ,  6  and  7 ), controlled valves (respectively,  8  and  9 ), and the duct  19 . The valves  5 ,  6 ,  7 ,  8  and  9  serve to control the air circulation in the first network  1 . 
         [0068]    The air/air heat exchanger  4  is a surface heat exchanger which has an exchange surface  10  integrated into the outer aerodynamic skin  110  of the nacelle  100 . The air/air heat exchanger  4  also comprises a confined space  11 , comprising an air inlet  12  and an air outlet  13  for the first fluid, enclosed by the exchange surface  10  and a peripheral wall  14 . The air/air heat exchanger  4  also comprises an intermediate wall  15  which divides the confined space  11  into two volumes so that its midplane is substantially parallel to the midplane of the exchange surface  10 , and that one of the volumes, so-called the upper volume  16 , is delimited by the exchange surface  10 , the peripheral wall  14  and the intermediate wall  15 , whereas the other volume, so-called the lower volume  17 , is delimited by the peripheral wall  14  and the intermediate wall  15 . The intermediate wall  15  is pierced by a plurality of orifices  18 . The lower volume  17  is in communication with the air inlet  12 , and the upper volume  16  is in communication with the air outlet  13 . 
         [0069]    The air/air heat exchanger  4  may also only comprise one exchange surface  10  in the contact of which there is a duct  19  of the first circuit  1  in order to cool the air that is flowing in the first network  1  and coming out of the air/oil heat exchanger  2  so that the air is cooled when penetrating in the air/oil heat exchanger  3 . 
         [0070]    The outer aerodynamic skin  110  of the nacelle comprises a dynamic air scoop  112  for collecting air from the outside of the nacelle, in addition to an outlet orifice  113  for discharging the reheated air out of the nacelle  100  after having flowed throughout the first network  1 . 
         [0071]    The inner aerodynamic skin  120  comprises an orifice  121  for collecting cold air that comes from a fan  130  of the aircraft by means of a controlled valve  8  of the first network  1 , so-called the fan-side collection orifice  121 . 
         [0072]    Referring to  FIG. 2 , there is described the operation of the first network  1  in the case where the aircraft is flying at high speed. 
         [0073]    The controlled valves  8  and  9 , as well as the check valve  6 , are closed. 
         [0074]    Air penetrates in the duct  19  of the first network  1  through the dynamic air scoop  112  of the outer aerodynamic skin  110 . The air that is collected by the dynamic air scoop  112  comes from the outside of the nacelle  100 , therefore, it is cold. 
         [0075]    Then, the air passes through the check valve  5  of the first network  1 , the duct  19 , the air/oil heat exchanger  2  where it retrieves the oil heat, and then, it then penetrates in the air/air heat exchanger  4  through the air inlet  12 . 
         [0076]    In the air/air heat exchanger  4 , the air flows from the air inlet  12  in the lower volume  17  and passes across the intermediate wall  15  through the orifices  18  before reaching the upper volume  16 . While flowing in the upper volume  16 , the air enters into contact with the exchange surface  10  which consists of a heat exchange surface providing heat exchange by impact or by simple circulation of the fluids. At this stage, the air outside of the nacelle  100  is cold and thereby cools the exchange surface  10 , which in turn, cools the air in the upper volume  16 . 
         [0077]    Afterwards, the cooled air that flows in the upper volume  16  penetrates in the duct  19 , this time through the air outlet  13 , and it passes successively through the check valve  7 , the air/oil heat exchanger  3  where it retrieves the oil heat, and then, it is discharged out of the nacelle  100  through the outlet orifice  113  of the nacelle  100 . 
         [0078]    Referring to  FIG. 3 , there is described the operation of the first network  1  in the case where the aircraft is flying at low speed. 
         [0079]    In this case, the air is collected in the fan  130  of the nacelle  100 , therefore, it is also cold. The check valves  5  and  7  are closed. 
         [0080]    Air penetrates through the fan-side collection orifice  121  of the inner aerodynamic skin  120  of the duct  19  of the first network  1 , and passes through the electric or pneumatic controlled valve  8 . At this stage, the duct  19  is split in order to divide the air flow into two portions, a first portion of the air that has passed through the controlled valve is directed toward the air/oil heat exchanger  2 , whereas a second portion is directed toward the air/oil heat exchanger  3 . 
         [0081]    Before reaching the air/oil heat exchanger  2 , the first air portion passes through a check valve  6 , once the air has penetrated in the air/oil heat exchanger  2 , it is directed toward the outlet orifice  113  of the outer aerodynamic skin  110  after passing through the controlled valve  9 . 
         [0082]    The second air portion penetrates directly in the air/oil heat exchanger  3 , and then, it is directed toward the outlet orifice  113 . 
         [0083]    Referring to  FIG. 4 , there is described the structure of the second air circulation network  1  according to the second form of the present disclosure. 
         [0084]    In this form, the air inlet lip  111  acts as an air/air heat exchanger  4 . 
         [0085]    The second network  1  comprises five controlled valves  8 ,  9 ,  20 ,  21  and  22 ; three check valves  5 ,  6  and  23 ; two air/oil heat exchangers  2  and  3 ; one air/air heat exchanger  4 . 
         [0086]    The nacelle  100  comprises a means for collecting hot air coming from a compressor of the aircraft, so-called the compressor-side collection orifice  122 , so as to allow supplying the air inlet lip  111  with hot air. The compressor-side collection orifice  122  is connected to the controlled valve  21  which is, in turn, directly connected to the air/air heat exchanger  4  via the orifice  13 . 
         [0087]    The air/air heat exchanger  4  comprises three air inlet and outlet orifices. One air outlet orifice  24  is directly connected to the outlet orifice  113  of the nacelle  100  via the controlled valve  22 . Another orifice is the orifice  13  which is connected, on the one hand, to the air/oil heat exchanger  3  thereby severing as an air outlet, and on the other hand, to the compressor-side collection orifice  122  via the controlled valve  21  thereby serving as an inlet for the hot air that comes from the compressor (not represented). The third orifice is the air inlet  12  for the air that comes from the air/oil heat exchanger  2 . 
         [0088]    The air/air heat exchanger  4  operates substantially in the same manner as the heat exchanger described in the previous form (the first network  1 ). 
         [0089]    Referring to  FIG. 5 , there is described the air inlet lip  111  of the nacelle  100  in which the second air circulation network  1  is installed. 
         [0090]    The air inlet lip  111  acts as an air/air heat exchanger  4 . The air penetrates thereto through the orifice  13  or through the air inlet  12  and it is discharged through the outlet orifice  24  or through the orifice  13  according to the mode of operation of the second network  1 . 
         [0091]    Referring to  FIG. 6 , there is described the operation of the second network  1  in the case where the aircraft is flying at high speed. 
         [0092]    The controlled valves  8 ,  9 ,  21  and  22 , as well as the check valve  6 , are closed. 
         [0093]    The air penetrates in the duct  19  through the dynamic air scoop  112 ; coming from the outside of the nacelle  100 , the air is thus cold. 
         [0094]    Afterwards, the air passes successively through the check valve  5 , the air/oil heat exchanger  2  where it is reheated by the engine oil heat, the check valve  23 , the air inlet  12 , the air/air heat exchanger  4  where it is cooled, the orifice  13 , the controlled valve  20 , the air/oil heat exchanger  3  where it is reheated by the engine oil heat, and the outlet orifice  113  of the outer aerodynamic skin  110  of the nacelle  100 . 
         [0095]    Referring to  FIG. 7 , there is described the operation of the second network  1  in the case where the aircraft is flying at low speed. 
         [0096]    The controlled valves  9 ,  20  and  21 , as well as the check valve  5 , are closed. 
         [0097]    The air penetrates in the duct  19  through the fan-side collection orifice  121 . The air comes from the fan, therefore, it is cold. Afterwards, the air passes through the controlled valve  8 . 
         [0098]    At this stage, the duct  19  is split in order to divide the air flow into two portions, a first portion of the air having passed through the controlled valve  8  is directed toward the air/oil heat exchanger  2 , whereas a second portion is directed toward the air/oil heat exchanger  3 . 
         [0099]    Before reaching the air/oil heat exchanger  2 , the first air portion passes through the check valve  6 , once the air has penetrated in the air/oil heat exchanger  2 , it is reheated, and then, it passes through the check valve  23 , penetrates in the air/air heat exchanger  4  through the air inlet  12 , and immediately afterwards, it is evacuated through the outlet orifice  24  toward the outlet orifice  113  of the outer aerodynamic skin  110  through the controlled valve  22 . 
         [0100]    The second air portion penetrates directly in the air/oil heat exchanger  3 , it is reheated inside, and then, it is evacuated through the outlet orifice  113 . 
         [0101]    Referring to  FIG. 8 , there is described the operation of the second network  1  when the defrosting mode of the air inlet lip  111  of the nacelle  100  is activated. 
         [0102]    The controlled valve  20 , as well as the check valves  5  and  23 , are closed. 
         [0103]    The air penetrates in the duct  19  through the fan-side collection orifice  121 . The air comes from the fan, therefore, it is cold. Afterwards, the air passes through the controlled valve  8 . 
         [0104]    At this stage, the duct  19  is split in order to divide the air flow into two portions, a first portion of the air having passed through the controlled valve  8  is then directed toward the air/oil heat exchanger  2 , whereas a second portion is directed toward the air/oil heat exchanger  3 . 
         [0105]    Before reaching the air/oil heat exchanger  2 , the first air portion passes through a check valve  6 , once the air has penetrated in the air/oil heat exchanger  2 , it is reheated, and then, it is evacuated toward the outlet orifice  113  through the controlled valve  9 . 
         [0106]    The second air portion penetrates directly in the air/oil heat exchanger  3 , it is reheated inside, and then, it is evacuated through the outlet orifice  113 . 
         [0107]    Thus, by passing through the air/oil heat exchangers  2  and  3 , the engine oil is cooled. 
         [0108]    Meanwhile, air penetrates in the duct  19  of the second network  1  through the compressor-side collection orifice  122 . Coming from the compressor, the air is thus hot and at high pressure. This air then passes through the controlled valve  21 , to then be directed directly toward the orifice  13  and be injected at high pressure in the air inlet lip  111  which acts as an air/air heat exchanger  4 . The air thus injected at high pressure performs several revolutions along the circumference of the air inlet lip  111  in order to defrost the entire air inlet lip  111 , and then, it is evacuated toward the outlet orifice  113  through the controlled valve  22 . 
         [0109]    Referring to  FIG. 9 , there is described the third air circulation network  1  according to the third form of the present disclosure. 
         [0110]    The third network  1  has the same structure as the second network ( FIGS. 4 ,  5 ,  6 ,  8 ) in which have been added a second air/air heat exchanger  25  as well as an additional check valve  26 . 
         [0111]    Referring to  FIG. 10 , there is described an air inlet lip  111  of an outer aerodynamic skin  110  of a nacelle  100  in which an air/air heat exchanger  4  is installed. 
         [0112]    The air/air heat exchanger  4  of  FIG. 10  is realized on the same principle as the heat exchanger of  FIG. 1 . In fact, it comprises the exchange surface  10  and the peripheral wall  14 , wherein the front partition wall of the air inlet lip  111  delimiting a confined space  11 , the intermediate wall  15  divides this confined space into two portions, the upper volume  16  and the lower volume  17 , the intermediate wall  15  is pierced by a plurality of orifices  18 . The lower volume  17  is in communication with the air inlet  12 , and the upper volume  16  is in communication with the air outlet  13 . 
         [0113]    The air/air heat exchanger  4  is different from the heat exchanger of  FIG. 1  in that it comprises a collector  31  which serves for retrieving the air that is comprised in the upper volume  16  of the air/air heat exchanger  4 , which is then directed toward the outlet orifice  113  of the nacelle  100 . 
         [0114]    Referring to  FIG. 11 , there is described the structure of the fourth air circulation network  1  which equips the air inlet lip  111 . 
         [0115]    The fourth network  1  comprises three controlled valves  8 ,  21  and  28 , three check valves  5 ,  6  and  30 , one two-position valve  27 , two air/oil heat exchangers  2  and  3 , and two air/air heat exchangers  4  and  29 . 
         [0116]    The nacelle  100  comprises the compressor-side collection orifice  122 , connected to the controlled valve  21  which, in turn, is connected to the air inlet  12  of the air/air heat exchanger  4 , the fan-side collection orifice  121 , connected to the controlled valve  8 , the dynamic air scoop  112  and the outlet orifice  113 . 
         [0117]    Since the collector  31  is comprised in the air/air heat exchanger, it is not represented here. However, it leads to the air outlet  13  which, in turn, leads to the outlet orifice  113  of the nacelle. 
         [0118]    The two-position valve  27  allows directing the air flow that comes from the air/oil heat exchangers  2  and  3 , alternately toward two different directions, the first leading directly to the outlet orifice  113  of the nacelle  100 , the other leading directly to the air/air heat exchanger  4 . 
         [0119]    The air/air heat exchanger  29  may be installed in the nacelle  100  in the same manner as detailed in  FIG. 1 . 
         [0120]    Referring to  FIG. 12 , there is described the operation of the fourth network  1  in the case where the aircraft is flying at high speed. 
         [0121]    The controlled valves  8 ,  21  and  28  are closed, the check valve  6  is closed, and the two-position valve  27  directs the air flow directly toward the outlet orifice  113 . 
         [0122]    The air penetrates in the fourth network  1  through the dynamic air scoop  112  of the nacelle  100 , and then, it passes successively through the check valve  5 , the air/oil heat exchanger  2  where it is reheated, the air/air heat exchanger  29  where it is cooled, the check valve  30 , the air/oil heat exchanger  3  where it is reheated, and then, it is directed directly toward the outlet orifice  113  through the two-position valve  27  which is positioned for this purpose. 
         [0123]    Thus, by passing through the air/oil heat exchangers  2  and  3 , the engine oil is cooled. 
         [0124]    This operation of the fourth network  1  with regard to the circulation of air within it is substantially similar to that of the first network as detailed in  FIG. 2 . 
         [0125]    Referring to  FIG. 13 , there is described the operation of the fourth network  1  in the case where the aircraft is flying at low speed. 
         [0126]    In this case, the controlled valve  21  is closed, the check valves  5  and  30  are closed, and the two-position valve  27  directs the air flow directly toward the outlet orifice  113 . 
         [0127]    The air penetrates in the duct  19  through the fan-side collection orifice  121 , coming from the fan, the air is therefore cold. Then, the air passes through the controlled valve  8 . 
         [0128]    At this stage, the duct  19  is split in order to divide the air flow into two portions, a first portion of the air having passed through the controlled valve  8  is directed toward the air/oil heat exchanger  2 , whereas a second portion is directed toward the air/oil heat exchanger  3 . 
         [0129]    Before reaching the air/oil heat exchanger  2 , the first air portion passes through the check valve  6 , once the air has penetrated in the air/oil heat exchanger  2 , it is reheated, and then, it passes through the controlled valve  28 , and immediately afterwards, it is evacuated toward the outlet orifice  113  via the two-position valve  27 . 
         [0130]    The second air portion penetrates directly in the air/oil heat exchanger  3 , it is reheated inside, and then, it is evacuated through the outlet orifice  113  via the two-position valve  27 . 
         [0131]    Thus, by passing through the air/oil heat exchangers  2  and  3 , the engine oil is cooled. 
         [0132]    Referring to  FIG. 14 , there is described the operation of the fourth circuit  1  when the defrosting mode of the air inlet lip  111  of the nacelle  100  is activated. 
         [0133]    The check valves  5  and  30  are closed, the two-position valve  27  directs the air flow directly toward the air/air heat exchanger  4 . 
         [0134]    The air penetrates in the duct  19  through the fan-side collection orifice  121 , the air is therefore cold. Then, it passes through the controlled valve  8 . 
         [0135]    At this stage, the duct  19  is split in order to divide the air flow into two portions, a first portion of the air that has passed through the controlled valve  8  is directed toward the air/oil heat exchanger  2 , whereas a second portion is directed toward the air/oil heat exchanger  3 . 
         [0136]    Before reaching the air/oil heat exchanger  2 , the first air portion passes through the check valve  6 , once the air has penetrated in the air/oil heat exchanger  2 , it is reheated, and then, it passes through the controlled valve  28 , and immediately afterwards, it is directed via the two-position valve  27  toward the air/air heat exchanger  4 . 
         [0137]    The second air portion penetrates directly in the air/oil heat exchanger  3 , it is reheated inside, and then, is directed toward the air/air heat exchanger  4  via the two-position valve  27 . 
         [0138]    Thus, by passing through the air/oil heat exchangers  2  and  3 , the engine oil is cooled. 
         [0139]    Meanwhile, air penetrates in the duct  19  of the fourth network  1  through the compressor-side collection orifice  122 , coming from the compressor, therefore, it is hot and at high pressure. This air is then passed through the controlled valve  21 , and then, is directed directly toward the air inlet  12 . 
         [0140]    At this stage, the air that comes from the compressor and the air that comes from the air/oil heat exchangers  2  and  3  meet in the duct  19 , the new air flow that is formed then reaches the air inlet  12 . Then, the air is injected at high pressure in the air inlet lip  111  which acts as an air/air heat exchanger  4 . The air that is injected at high pressure then performs several revolutions along the circumference of the air inlet lip  111  in order to defrost the entire air inlet lip  111 , and then, it is evacuated toward the outlet orifice  113  through the collector  31  and then the air outlet  13 . 
         [0141]    Referring to  FIG. 15 , there is described the operation of the fourth network  1  in the event of a failure of one valve or more. 
         [0142]    In this case, the controlled valves  8 ,  21  and  28  are forced to open, and the two-position valve  27  is forced to direct the air flow that passes therethrough directly toward the outlet orifice  113  of the nacelle  100 . The check valve  6  is open whereas the check valves  5  and  30  are closed. 
         [0143]    In this case, the air flow that comes from the fan through the fan-side collection orifice  121  follows the same path as detailed in the description of  FIG. 13 , whereas the air flow coming from the compressor through the compressor-side collection orifice  122  follows the same path as that detailed in the description of  FIG. 14 . 
         [0144]    It is also possible to consider a fourth network  1  wherein the compressor-side collection orifice has been removed. This type of network is implemented when the air that has flowed through the air/oil heat exchangers  2  and  3  has reached a temperature that is sufficient for defrosting the air inlet lip  111 , which also acts as an air/air heat exchanger  4 . 
         [0145]    In all the aforementioned forms, the outlet orifice  113  may be placed at the inner aerodynamic skin  120  of the nacelle  100 . 
         [0146]    In the forms where the air/air heat exchanger  4  is installed in the air inlet lip  111 , the air that is introduced in the air/air heat exchanger  4  performs at least one revolution along the circumference of the air inlet lip  111  in order to defrost the entire air inlet lip  111  before being evacuated from the air/air heat exchanger  4 . 
         [0147]    The aforementioned forms allow significantly reducing the total consumption of the aircraft by approximately from 0.25% to 0.4% in comparison with a cooling performed only by collection in the secondary duct. In the cases where they allow defrosting the air inlet lip, they then allow reducing the temperature of the air inlet lip, thereby reducing the recurrent issues of fatigue, and of the upstream area of the outer aerodynamic skin, the temperature of said area not exceeding the maximum temperature of the turbine engine oil, which is typically in the range of 180° C., allowing to realize the front partition wall of the air inlet in aluminum rather than titanium. 
         [0148]    Although the present disclosure has been described through particular form examples, it goes without saying that it is not limited thereto and that it encompasses all technical equivalents of the described means, as well as their combinations, should these fall within the scope of the present disclosure.