FR3146165A1 - HEAT EXCHANGE SYSTEM FOR AN AIRCRAFT TURBOMACHINE - Google Patents

Abstract

Heat exchange system (20), in particular for an aircraft turbomachine (1), this system comprising: - two annular walls which extend around each other and around the same axis (X), and which define between them a flow path (V2) for a gas flow (F2), - a first annular heat exchange device (21) which is carried by one of said walls (22), and which is located in the flow path (V2), this first device (21) occupying at most 75%, or even 50%, of a height (H) of the flow path (V2), and - a second annular heat exchange device (30) which is carried by the other of said walls (23), and which is located in the flow path (V2), this second device (30) occupying at most 75%, or even 50%, of a height (H') of the flow path (V2). Figure for abstract: Figure 8

Description

HEAT EXCHANGE SYSTEM FOR AN AIRCRAFT TURBOMACHINE Field of invention

The present invention relates to the general field of cooling, and its application in particular in the field of aeronautics. It relates in particular to a heat exchange system, in particular for a turbomachine, in particular an aircraft.

Technical background

A turbomachine, particularly an aircraft turbomachine, comprises various components and/or equipment that must be lubricated and/or cooled, such as rolling bearings and gears. The heat released by these components, which can be very significant depending on the power of the component and/or equipment, is transported by a fluid and evacuated to cold sources available in the aircraft.

It is known to equip the turbomachine with one or more heat exchange systems to carry out the heat exchange between the fluid (typically oil) and the cold source (air, fuel, etc.). There are even different types of heat exchange systems which are for example fuel/oil heat exchangers generally known by the English acronym FCOC for " Fuel Cooled Oil Cooler " and air/oil heat exchangers known by the English acronym ACOC for " Air-Cooled Oil Cooler ".

FCOC heat exchangers have a dual function of heating the fuel before combustion in the combustion chamber of the turbomachine and cooling the oil heated by the heat dissipation of the turbomachine. However, FCOC heat exchangers are not sufficient to absorb all the heat dissipation because the fuel temperature is limited in view of safety constraints.

Additional cooling is achieved by ACOC heat exchangers, particularly those of the surface type and known by the acronym SACOC. Surface heat exchangers are generally arranged in the secondary vein of the turbomachine and use the secondary air flow to cool the oil circulating in the turbomachine. These heat exchangers are in the form of a metal surface part allowing the oil to pass through machined channels. The secondary air flow is guided along a heat exchange matrix carried by this surface part and which have the role of increasing the contact surface with the secondary air flow and extracting calories. However, SACOC heat exchangers have the disadvantage of creating additional pressure losses in the secondary vein concerned since they disrupt the air flow, which impacts the performance of the turbomachine as well as the specific fuel consumption.

The Applicant has already proposed a solution to this problem in documents FR-A1-3 096 409 and FR-A1-3 096 444.

In addition, the cooling requirements of the lubricating fluid are increasing due to the increase in rotation speeds and powers involved to meet specification trends on turbomachines.

Indeed, ACOC exchangers are increasingly in demand in the future generation of engines due to the significant increase in heat dissipation, mainly due to:

- to the engines of the future which are larger, which increases the need for lubrication and cooling by oil,

- the presence of a speed reducer in new engine architectures, this reducer transmitting very high mechanical power and needing to be lubricated and cooled by oil, and

- the addition of electrical machines on board an engine for hybridization, these machines needing to be lubricated and cooled by oil.

The engine may have several oil circuits, each with a defined function, for example a first circuit for cooling the oil dedicated to lubricating and cooling the engine, a second for lubricating and cooling the engine reducer, a third for cooling the machines, etc. The oil temperature and flow rate must be controlled according to the corresponding circuit. For example, the oil used to lubricate and cool the electrical machines has a different temperature range than that for engine cooling. Thus, the ACOC is preferably divided into several exchangers, each exchanger being dedicated to a given oil circuit. These different exchangers are generally distributed around the longitudinal axis of the engine

The growing need for cooling has a direct impact on the dimensions of the ACOCs. It is therefore necessary to expect to have large exchangers to be able to evacuate the calories from the oil. In order to evacuate the oil calories, the ACOCs could occupy all the available space in a vein, and thus extend all around the vein and over the entire height or radial dimension of the vein, in order to have the air flow necessary to evacuate the calories at the dimensioning point generally occurring during the take-off phase in the case of an extremely hot day.

However, the fact that the ACOC exchangers occupy the entire radial height of the vein prevents the flow passing through the exchanger from being controlled with the solution described in documents FR-A1-3 096 409 and FR-A1-3 096 444.

As a result, all the air flow passes through the ACOCs and consequently, each of the ACOCs operates with non-optimal aerothermal performances. This results in a high pressure drop on the air side and leads to inefficient exchangers.

The objective of the present invention is to propose an improvement to existing technologies making it possible to optimize the efficiency of heat exchanges while avoiding pressure losses and disrupting the gas flow as little as possible.

The invention thus proposes a heat exchange system, in particular for an aircraft turbomachine, this system comprising:

- two annular walls, respectively external and internal, which extend around each other and around the same axis, and which are configured to define between them a flow vein for a gas flow,

- a first annular heat exchange device which extends around the axis and is carried by one of said walls, and which is located in the vein, this first device occupying at most 75% of a height of the vein, this height being measured in the radial direction in a zone of the vein in which this first device is located,

characterized in that it further comprises:

- a second annular heat exchange device which extends around the axis and is carried by the other of said walls, and which is located in the vein, this second device occupying at most 75% of a height of the vein, this height being measured in the radial direction in a zone of the vein in which this second device is located.

The present invention thus proposes to combine at least two annular heat exchange devices in the same annular flow vein of a gas flow. Each of the walls of the system carries a device which extends only in a part of the height or radial dimension of the vein, which makes it possible to limit the impact of this device on the flow of the gas flow by limiting the pressure losses.

The heat exchange system may include one or more of the following features, considered independently of each other or in combination with each other:

- the devices are spaced axially from each other in the vein;

- the devices overlap each other axially in the vein;

- the system comprises a third annular heat exchange device, preferably, which extends around the axis and is located in the vein;

- the third device is located at a radial distance from said walls and occupies at most 50% of a height of the vein, this height being measured in a radial direction in a zone of the vein in which this third device is located;

- the third device is located axially between the first and second devices;

- the first and third devices overlap each other axially in the vein, and/or the third and second devices overlap each other axially in the vein;

- the third device extends between said walls and is connected to these walls, for example by fixing arms;

- the devices are of the air-oil type and comprise an oil circuit and a heat exchange matrix located in the vein and configured to be swept by said gas flow; in the present application, a heat exchange matrix may comprise fins and/or plates and/or tubes. A matrix may be stepped and comprise for example a stack of several layers, each of the layers comprising fins, or at least one plate or at least one tube. The fins are intended to be swept by a gas flow, and the plates or tubes are crossed for example by an oil circuit or comprise such an oil circuit;

- the heat exchange matrix of each of the first and second devices is covered by an annular cover which comprises a first end located upstream of the heat exchange matrix relative to the flow of the gas flow, and which has a divergent shape with respect to this gas flow, and a second end located downstream of the heat exchange matrix relative to the flow of the gas flow, and which has a convergent shape with respect to this gas flow;

- the heat exchange matrices of the first and second devices are axially spaced from each other, and the second end of the cover of one of the first and second devices axially overlaps the first end of the cover of the other of the first and second devices;

- the heat exchange matrix of the third device is sandwiched between two annular covers which are independent and at a distance from the covers of the first and second devices;

- the heat exchange matrix of the third device is sandwiched between two annular covers, a first cover which is connected to the cover or forms the cover of the first device, and a second cover which is connected to the cover or forms the cover of the second device;

- each of the devices occupies at least 10% of the aforementioned height of the vein;

- each of the devices comprises a single heat exchanger, or is sectorized and comprises two or more heat exchangers distributed around the axis;

-- each of the devices is of the ACOC or SACOC type;

-- the or each hood comprises end parts, respectively upstream and downstream, which respectively form a divergent and a convergent part;

-- each divergent and each convergent has a truncated or rounded shape; the rounded shape improves the aerodynamics of the flow bypassing the device, which reduces the pressure losses due to the installation of this assembly. These shapes can be obtained by additive manufacturing for example;

-- the first heat exchange device is of the surface type, and/or the second heat exchange device is of the surface type, and/or the third heat exchange device is of the surface type;

-- the or each heat exchange device is of the SACOC or ACOC type;

-- the or each cover is at a distance from the walls of the vein so that part of the gas flow flowing in the vein can bypass or bypass the or each heat exchange device;

-- the first device occupies at most 50% of the height of the vein,

-- the second device occupies at most 50% of a height of the vein. The invention further relates to a turbomachine or an electronic device comprising at least one heat exchange system as mentioned above. The present invention can indeed be used for cooling an electronic device.

Brief description of the figures

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly on reading the detailed explanatory description which follows, of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which:

There is a half schematic view in axial section of an example of a turbomachine to which the invention applies;

There is a very schematic cross-sectional view of a heat exchange system;

There is a very schematic view in axial section of the system of the ;

There is another very schematic view of a system similar to that of the ;

There is a schematic perspective and partial view of a heat exchange device;

Figures 6a and 6b are highly schematic cross-sectional views of heat exchange systems each comprising a sectorized heat exchange device;

There is a very schematic view in axial section of the system of figure 6a;

There is a very schematic view in axial section of a heat exchange system according to a first embodiment of the invention;

There is a very schematic view in axial section of a heat exchange system according to a second embodiment of the invention;

There is a very schematic view in axial section of a heat exchange system according to a third embodiment of the invention;

There is a very schematic view in axial section of a heat exchange system according to a fourth embodiment of the invention;

There is a very schematic view in axial section of a heat exchange system according to a fifth embodiment of the invention;

There is a very schematic view in axial section of a heat exchange system according to a sixth embodiment of the invention;

there is a very schematic view in axial section of a heat exchange system according to a seventh embodiment of the invention.

Detailed description of the invention

There shows an axial sectional view of a turbomachine with longitudinal axis X to which the invention applies. The turbomachine shown is a dual-flow turbomachine 1 intended to be mounted on an aircraft. Of course, the invention is not limited to this type of turbomachine.

This dual-flow turbomachine 1 generally comprises a gas generator 2 upstream of which a blower or blower module 3 is mounted.

In the present invention, the terms “upstream” and “downstream” are defined in relation to the circulation of gases in the turbomachine 1 and here along the longitudinal axis X.

The gas generator 2 comprises a gas compressor assembly (here comprising a low pressure compressor 4a and a high pressure compressor 4b), a combustion chamber 5 and a turbine assembly (here comprising a high pressure turbine 6a and a low pressure turbine 6b).

Typically, the turbomachine 1 comprises a low pressure shaft 7 which connects the low pressure compressor 4a and the low pressure turbine 6a to form a low pressure body, and a high pressure shaft 8 which connects the high pressure compressor 4b and the high pressure turbine 6b to form a high pressure body.

The low-pressure shaft 7, centered on the longitudinal axis X, here drives a fan shaft 9 by means of a speed reducer 10. Rotating guide bearings 15 also make it possible to guide the low-pressure shaft 7 in rotation relative to a fixed structure or stator of the turbomachine. The high-pressure shaft 8 is also guided in rotation by guide bearings (not shown).

The blower 3 is shrouded by a blower casing 11 carried by a nacelle 12 and generates a primary air flow F1 which circulates through the gas generator 2 in a primary vein V1, and a secondary air flow F2 which circulates in a secondary vein V2 around the gas generator 2.

The secondary air flow F2 is ejected by a secondary nozzle 13 terminating the nacelle while the primary air flow F1 is ejected outside the turbomachine 1 via an ejection nozzle 14 located downstream of the gas generator 2.

In the remainder of the description, the fan casing 11 and the nacelle 12 are considered as one and the same part.

The guide bearings 15 and the speed reducer 10 in this example configuration of the turbomachine 1 must be lubricated and/or cooled to ensure the performance of the turbomachine 1. The power generated by them is dissipated in a fluid coming from a fluid supply source installed in the turbomachine 1 and which makes it possible to lubricate and/or cool various components and/or equipment of the turbomachine 1. Of course, other equipment of the turbomachine 1 generates a lot of heat which must be extracted from its environment.

For this purpose, the turbomachine 1 comprises a heat exchange system 20 which makes it possible to cool the fluid intended to lubricate and/or cool these components and/or equipment. In the present example, the fluid is an oil and the cold source intended to cool the oil is a gas flow circulating in the turbomachine, in particular the secondary air flow F2.

In the context of the present invention, a heat exchange system 20 is understood to mean a system comprising:

- two annular walls, respectively external and internal, which extend around each other and around the same axis, and which are configured to define between them a flow vein for a gas flow, and

- at least one annular heat exchange device located in this vein.

In the case of the for example, the heat exchange system 20 of the turbomachine 1 comprises an external wall 22 formed by the fan casing 11 and/or the nacelle 12, an internal wall 23 formed by a casing of the gas generator 2, and a heat exchange device 21 which is here carried by the external wall 22 and located in the vein V2.

The heat exchange device 21 is for example of the surface type (for example of the SACOC type) and preferably of the air/oil type.

The device 21 comprises an oil circuit and a heat exchange matrix located in the vein V2 and configured to be swept by said gas flow F2. As mentioned above, the heat exchange matrix may comprise fins and/or plates and/or tubes. A matrix may be stepped and comprise, for example, a stack of several layers, each of the layers comprising fins, or at least one plate or at least one tube. The fins are intended to be swept by a gas flow, and the plates or tubes are traversed, for example, by an oil circuit or comprise such an oil circuit.

Figures 2 and 3 schematically show a heat exchange system 20 of this type. It can be seen that the heat exchange device 21 of this system 20 is annular and extends continuously over 360° around the X axis.

It is also noted that it occupies only part of the height H of the vein V2. The device 21 has a height h or radial dimension which represents only part of the height H or radial dimension of the vein V2. These heights H, h are measured in the radial direction with respect to the axis X, in a zone of the vein V2 in which this device 21 is located. The height H of the vein V2 is likely to change along the axis X.

One of the problems observed in a device 21 of this type is the disturbances and pressure losses generated in the gas flow F2, which has the effect of increasing the specific and fuel consumption of the turbomachine 1. Hence the interest in optimizing the aerothermal performance of this system 20.

In the aforementioned documents, the Applicant proposed a solution to optimize the integration of this type of device 21 in a vein, which is illustrated in . The idea is to slow down the speed of the gas flow passing through the device 21. Indeed, the gas flow passing through the device 21 is very turbulent. Slowing down the flow speed of the air flow at the inlet of the device 21 makes it possible to optimize its aerothermal performance and thus to minimize the pressure drop for a given heat dissipation. The flow passing through the device 21 can be controlled by associating with the device 21 a divergent 24 at the inlet and a convergent 25. The divergent 24 upstream of the device 21 is configured so as to compress and slow down the gas flow entering the device 21, and the convergent 25 arranged downstream of the device 21 is configured so as to accelerate and expand the gas flow leaving the device. At the inlet of the device 21, the slowdown factor is inversely proportional to the ratio of the heights h/h0, h being the aforementioned height and h0 being the height at the inlet of the divergent 24. Note that the more the flow is slowed, the more the pressure loss generated by the device 21 decreases. At the outlet of the device 21, the acceleration factor is inversely proportional to the ratio of the heights h/h3, h3 being the height at the outlet of the convergent 25.

There illustrates in perspective a part of a heat exchange device 21. It shows the heat exchange matrix 26 which is intercalated or sandwiched between a cover 27 and the wall 22, 23 which carries this device 21. The convergent 25 and the divergent 24 can be formed by ends of the cover 26, as in the example shown.

In the and the other figures, arrows are used to schematically represent the oil circuit 28.

Figures 6a and 6b schematically show alternative embodiments of heat exchange systems 20.

In the case of Figure 6a, the system 20 comprises an annular heat exchange device 21 which is sectorized and comprises two sectors each having an angular extent of approximately 180°.

In the case of Figure 6b, the system 20 comprises an annular heat exchange device 21 which is sectorized and comprises four sectors each having an angular extent of approximately 90°.

Furthermore, in these figures 6a-6b, the heat exchange device 21 extends over the entire height H of the vein and is connected to the two walls 22, 23. The height h of the device 21 is then equal to the height H of the vein ( ).

The present invention provides an improvement to this technology and provides several embodiments which are illustrated in Figures 8 and following.

One of the particularities of the invention is based on the fact that the heat exchange system comprises at least two separate annular heat exchange devices and that each of these devices occupies at most 75%, or even 50%, of the height of the vein in which they are implanted.

In the first embodiment of the invention shown in , the heat exchange system 20 comprises:

- two annular walls, respectively external 22 and internal 23, which extend around each other and around the same axis X, and which are configured to define between them a flow vein V2 of a gas flow, such as a secondary flow F2,

- a first annular heat exchange device 21 which extends around the axis X and is carried by one of said walls, here the external wall 22, and which is located in the vein V2, this first device 21 occupying at most 75%, or even 50%, of a height H of the vein V2, this height H being measured in the radial direction in a zone of the vein V2 in which this first device 21 is located, and

- a second annular heat exchange device 30 which extends around the axis X and is carried by the other of said walls, here the internal wall 23, and which is located in the vein V2, this second device 30 occupying at most 75%, or even 50%, of a height H' of the vein V2, this height H' being measured in the radial direction in a zone of the vein in which this second device is located.

We note at the that the devices 21, 30 are spaced axially from each other in the vein V2. They are spaced from each other by an axial distance denoted L. The device 21 located on the external wall 22 is located upstream of the device 30 located on the internal wall 23.

These devices 21, 30 are preferably of the air-oil type and for example surface type and each comprise an oil circuit 28 and a heat exchange matrix 26 located in the vein V2 and configured to be swept by the gas flow F2, as mentioned above.

The heat exchange matrix 26 of each of the devices 21, 30 are covered by an annular cover 27 which comprises a first end 27a located upstream of the heat exchange matrix 26 relative to the flow of the gas flow F2, and which has a divergent shape with respect to this gas flow F2, and a second end 27b located downstream of the heat exchange matrix 26 relative to the flow of the gas flow F2, and which has a convergent shape with respect to this gas flow F2.

In the example shown, the ends 27a, 27b each have a truncated cone shape.

Each of the devices 21, 30 may comprise a single heat exchanger, or be sectorized and comprise two or more heat exchangers distributed around the X axis, as discussed above.

In the example shown, the first device 21 located on the left in the drawing is an upstream device which occupies a height h in the vein of between 20 and 50% of the height H. The second device 30 located on the right in the drawing is a downstream device which occupies a height h’ in the vein of between 20 and 50% of the height H’.

The height difference H-h can be equal to the height difference H’-h’ or different from this height difference. Furthermore, h’ can be greater or less than h.

It is understood that an external peripheral part of the air flow F2 (for example 5 to 30% of the flow rate) flowing in the vein will enter the device 21 while the remainder will bypass the device 21. Among this remainder, an internal peripheral part will enter the device 30 (for example 5 to 30% of the flow rate) while the remaining middle part of the flow will bypass this device 30.

The device 30 is thus crossed by a flow of air taken from it that is different from that of the device 21. Indeed, one of the advantages of installing the two devices on either side of the walls of the vein makes it possible not to use the same flow of air at the outlet of the first to carry out the exchange in the second, since the air at the outlet of the first is heated by oil and therefore has a low cooling potential. Thus the air at the inlet of each device has the same temperature which is that at the inlet of the vein (to the nearest degree Kelvin).

Alternatively, L could be zero, or negative in the case of axial overlap of the devices 21, 30.

The second embodiment illustrated in the differs from the first embodiment in particular in that the device 21 located on the external wall 22 is located downstream of the device 30 located on the internal wall 23.

The devices 21, 30 are spaced axially from each other by a distance which is noted L0 and which can be close to zero or even equal to zero (and therefore zero), that is to say that the devices 21, 30 can be arranged directly one behind the other in the vein V2.

Furthermore, the ends 27a, 27b of the covers 28 here have curved shapes and no longer truncated cones.

It is understood that an internal peripheral part of the air flow F2 flowing in the vein will enter the device 30 while the remainder will bypass the device 30. Among this remainder, an external peripheral part will enter the device 21 while the remaining middle part of the flow will bypass this device 21.

Alternatively, L0 could be positive and non-zero, or negative in the case of axial overlap of the devices 21, 30.

The third embodiment illustrated in the differs from the second embodiment in particular in that the devices 21, 30 are even closer axially to each other and even overlap each other in the axial direction.

The heat exchange matrices 26 of the devices 21, 30 are axially spaced from each other. The cover 27 of the device 30 has its downstream end 27b which axially overlaps the upstream end 27a of the cover 27 of the device 21.

The operation of this embodiment is similar to that of the .

The overlap allows for a more gradual variation in the flow section for the flow bypassing the two devices, thus avoiding a significant variation in the flow section bypassing the devices as it passes through the area where these two devices are located.

The fourth embodiment illustrated in the differs from the second embodiment in particular in that the device 30 is sectorized and comprises two or more heat exchangers distributed around the X axis. This principle is explained in the above and illustrated in Figures 6a and 6b for example.

Device 21 could also be sectorized.

The operation of this embodiment is similar to that of the .

The embodiments of figures 12 and following differ from the previous embodiments in particular by the fact that they comprise a third annular heat exchange device 40 which extends around the axis X and is located in the vein V2.

In the fifth embodiment of the , devices 21 and 30 are similar to those of the . The third device 40 is located at a radial distance from the walls 22, 23 and occupies at most 75%, or even 50%, of a height H'' of the vein V2, this height H'' being measured in the radial direction in a zone of the vein V2 in which this third device 40 is located.

The third device 40 is located axially between the first and second devices 21, 30.

The first and third devices 21, 40 may be axially spaced from each other, may be located directly behind each other, or may overlap each other axially in the vein.

Similarly, the third and second devices 40, 30 may be axially spaced from each other, may be located directly behind each other, or may overlap each other axially in the vein.

The third device 40 comprises a heat exchange matrix 41 which is sandwiched between two annular covers, respectively internal 42 and external 43.

In the example shown, the covers 42, 43 are independent and at a distance from the covers 27 of the first and second devices 21, 30.

Like the covers 27 of the devices 21, 30, the covers 42, 43 of the device 40 can be curved or alternatively truncated cone-shaped.

The height difference H-h can be equal to the height difference H’-h’ and can still be equal to the height difference H’’-h’’, as schematically illustrated in the drawing.

It is understood that an external peripheral part of the air flow F2 flowing in the vein will enter the device 21 while the remainder will bypass the device 21. Among this remainder, a middle part will enter the device 40 while the peripheral parts of the flow will bypass this device 40. The internal peripheral part of this remainder will partly enter the device 30 and the remainder will bypass it to join the external peripheral part of the flow which has bypassed the device 40.

In the sixth embodiment of the , devices 21 and 30 are similar to those of the . The third device 40 extends between the walls 22, 23 and is connected to these walls 22, 23.

In the example shown, the third device 40 is located upstream of the devices 21, 30.

This third device 40 comprises a heat exchange matrix 41 which is directly connected to the walls 22, 23. The third device 40 therefore has a height h’’ equal to the height H’’ of the vein V2.

It is understood that the entire air flow F2 enters the device 40. Then an internal peripheral part of the flow will enter the device 30 while the rest will bypass the device 30. Among this remainder, an external peripheral part will enter the device 21 while the rest will bypass this device 21.

This is a hybrid (series/parallel) installation configuration, with the third device 40 installed in series with the other two devices 21, 30, which in turn are installed in parallel.

In the seventh embodiment of the , devices 21 and 30 are similar to those of the . The third device 40 is located axially between the first and second devices 21, 30.

It is also noted that the third device 40 is located radially between the first and second devices 21, 30.

The third device 40 comprises a heat exchange matrix 41 which is sandwiched between two annular covers, the internal cover of the device 40 being formed by the upstream end 27a of the cover 27 of the device 30, and the external cover of the device 40 being formed by the downstream end 27b of the cover 27 of the device 30.

It is thus understood that the entire height of the vein is occupied by the devices 21, 30, 40 to the extent that there is no part of the gas flow F2 which can bypass the devices, the entire gas flow thus participating in the exchange of calories with the oil of the circuit 28.

It is understood that an external peripheral part of the air flow F2 flowing in the vein will enter the device 21 while the remainder will bypass the device 21. A middle part of this remainder will enter the device 40 and an internal peripheral part of this remainder will enter the device 30 so that the entire air flow is used to participate in the exchange of calories with the devices.

• Amélioration des performances aérothermiques des dispositifs : le concept proposé permet d’optimiser l’écoulement d’un point de vue aérothermique dans chaque dispositif. En effet, le système d’échange de chaleur n’occupe pas forcément toute la hauteur radiale disponible, ce qui rend possible d’installer un dispositif divergent/convergent en amont/aval pour mieux gérer l’écoulement dans chacun des échangeurs, sans obstruer la veine, et ainsi de réaliser un ralentissement important du flux traversant chaque dispositif. Cela permet d’optimiser les performances aérothermiques de chaque dispositif, de réduire les pertes de charges côté air, et d’avoir des dispositifs plus efficaces.
• Le fait d’installer les dispositifs de part et d’autre des parois de la veine permet de prélever de l’air à la même température en entrée de ces deux dispositifs, qui est approximativement la même que celle en entrée veine. Cela évite de réutiliser le même flux d’air réchauffé en sortie du premier échangeur pour refroidir l’huile dans le deuxième échangeur, et ainsi d’augmenter les performances aérothermiques des deux dispositifs.
• Le décalage axial entre les deux dispositifs permet de désencombrer la veine dans la direction radiale.

The invention brings several advantages including:

• Improving the aerothermal performance of the devices: the proposed concept makes it possible to optimize the flow from an aerothermal point of view in each device. Indeed, the heat exchange system does not necessarily occupy all the available radial height, which makes it possible to install a divergent/convergent device upstream/downstream to better manage the flow in each of the exchangers, without obstructing the vein, and thus to achieve a significant slowdown of the flow passing through each device. This makes it possible to optimize the aerothermal performance of each device, to reduce the pressure losses on the air side, and to have more efficient devices.
• Installing the devices on either side of the vein walls allows air to be taken at the same temperature at the inlet of these two devices, which is approximately the same as that at the vein inlet. This avoids reusing the same flow of heated air at the outlet of the first exchanger to cool the oil in the second exchanger, and thus increasing the aerothermal performances of the two devices.
• The axial offset between the two devices allows the vein to be cleared in the radial direction.

Claims (15)

Heat exchange system (20), in particular for an aircraft turbomachine (1), this system comprising:
- two annular walls, respectively external (22) and internal (23), which extend around each other and around the same axis (X), and which are configured to define between them a flow vein (V2) of a gas flow (F2),
- a first annular heat exchange device (21) which extends around the axis (X) and is carried by one of said walls (22), and which is located in the vein (V2), this first device (21) occupying at most 75% of a height (H) of the vein (V2), this height (H) being measured in the radial direction in a zone of the vein (V2) in which this first device (21) is located,
characterized in that it further comprises:
- a second annular heat exchange device (30) which extends around the axis (X) and is carried by the other of said walls (23), and which is located in the vein (V2), this second device (30) occupying at most 75% of a height (H') of the vein (V2), this height (H') being measured in the radial direction in a zone of the vein (V2) in which this second device (30) is located. Heat exchange system (20) according to claim 1, characterized in that the devices (21, 30) are axially spaced from each other in the vein (V2). Heat exchange system (20) according to claim 1, characterized in that the devices (20) overlap each other axially in the vein (V2). Heat exchange system (20) according to one of the preceding claims, characterized in that it comprises a third annular heat exchange device (40), preferably of the surface type, which extends around the axis (X) and is located in the vein (V2). Heat exchange system (20) according to claim 4, characterized in that the third device (40) is located at a radial distance from said walls (22, 23) and occupies at most 50% of a height (H'') of the vein (V2), this height (H'') being measured in the radial direction in a zone of the vein (V2) in which this third device (40) is located. Heat exchange system (20) according to claim 5, characterized in that the third device (40) is located axially between the first and second devices (21, 30), the first and third devices (21, 40) overlapping each other axially in the vein (V2), and/or the third and second devices (40, 30) overlapping each other axially in the vein (V2). Heat exchange system (20) according to claim 4, characterized in that the third device (40) extends between said walls (22, 23) and is connected to these walls. Heat exchange system (20) according to any one of claims 1 to 7, characterized in that the devices (21, 30, 40) are of the air-oil type and comprise an oil circuit (28) and a heat exchange matrix (26, 41) located in the vein (V2) and configured to be swept by said gas flow (F2). Heat exchange system (20) according to claim 8, characterized in that the heat exchange matrix (26) of each of the first and second devices (21, 30) are covered by an annular cover (27) which comprises a first end (27a) located upstream of the heat exchange matrix (26) relative to the flow of the gas flow, and which has a divergent shape with respect to this gas flow (F2), and a second end (27b) located downstream of the heat exchange matrix (26) relative to the flow of the gas flow, and which has a convergent shape with respect to this gas flow (F2). A heat exchange system (20) according to claim 9, when claim 8 is dependent on claim 3, characterized in that the heat exchange matrices (26) of the first and second devices (21, 30) are axially spaced from each other, and the second end (27b) of the cover (27) of one of the first and second devices (21, 30) axially overlaps the first end (27a) of the cover (27) of the other of the first and second devices (21, 30). Heat exchange system (20) according to claim 9, when claim 8 is dependent on claim 5 or 6, characterized in that the heat exchange matrix (41) of the third device (40) is sandwiched between two annular covers (42, 43) which are independent and spaced from the covers (27) of the first and second devices (21, 30). Heat exchange system (20) according to claim 9, when claim 8 is dependent on claim 5 or 6, characterized in that the heat exchange matrix (41) of the third device (40) is sandwiched between two annular covers, a first cover which is connected to the cover or forms the cover (27) of the first device (21), and a second cover of which is connected to the cover or forms the cover (27) of the second device (30). Heat exchange system (20) according to any one of claims 1 to 12, characterized in that each of the devices (21, 30, 40) occupies at least 10% of the aforementioned height (H, H’, H’’) of the vein (V2). Heat exchange system (20) according to any one of claims 1 to 13, characterized in that each of the devices (21, 30, 40) comprises a single heat exchanger, or is sectorized and comprises two or more heat exchangers distributed around the axis (X). Turbomachine (1) or electronic device comprising at least one heat exchange system (20) according to any one of claims 1 to 14.