Three-flow axial turbine comprising diverging heat exchanger in third flow

Abstract

The invention discloses an axial turbine, in particular a three-flow axial turbine comprising a diverging heat exchanger in the third flow. The invention relates to an axial turbine comprising: a first separation nozzle capable of separating an incoming air flow into a radially inner air flow and a radially outer air flow, referred to as a secondary flow; a second separation nozzle capable of separating the radially inner air flow into a main flow and a third flow, the third flow being located in a third flow passage radially outward of the main flow; and an air / oil type heat exchanger disposed in the third flow passage and including a heat exchange surface that exchanges heat with air and an oil passage extending in the third flow passage; and a structural arm extending radially through the third flow passage. The axial turbine is characterized in that each structural arm comprises, in the third flow channel, a cross-section having a downstream portion having a width decreasing toward the downstream, the heat exchanger being adjacent to the downstream portion of the structural arm.

Description

[0001] This application is a divisional application of the PCT application entering the Chinese national phase with an application date of November 30, 2022, application number CN202280087052.X (international application number PCT / EP2022 / 083801), and invention name “Three-flow axial turbine including a gradually expanding heat exchanger in the third flow”. Technical Field

[0002] The present invention relates to the field of turbomachines, more particularly to three-flow turbomachines.The present invention relates to an arrangement of a heat exchanger intended to cool the oil of a turbomachine. Background Art

[0003] In turbomachines (turbojets), it is often necessary to cool the oil in the lubrication circuit. For this purpose, it is known to arrange one or more heat exchangers in the secondary flow (ie downstream of the fan).

[0004] However, the placement of a heat exchanger at the secondary circuit impairs the performance and overall efficiency of the turbine. In fact, the thrust generated by the fan is partially slowed down by the bulky exchanger. In addition, aerodynamic disturbances may occur in the secondary flow, causing vibrations and noise pollution.

[0005] The published patent document EP 3 674 531 A1 discloses an air-oil type heat exchanger arranged in the channel of the secondary flow. This heat exchanger generates significant disturbances in the secondary flow channel. In fact, the speed of the air traveling in this channel is so high that the aerodynamic or thrust losses can be ignored.

[0006] Published patent document US 2021 / 0108597 A1 discloses a turbine including a heat exchanger positioned in a fan channel.

[0007] The prior art therefore presents drawbacks associated with performance losses, with the added constraint of being associated with the fragility of the exchanger. In fact, the heat exchanger cannot be arranged directly upstream of the turbine to avoid disturbing the thrust of the turbine, in particular due to the risk of collision with foreign bodies that may enter the turbine. Summary of the invention

[0008] Technical issues

[0009] The present invention aims to solve the shortcomings of the design / manufacture of prior art turbines. In particular, the present invention aims to propose a solution that enables effective cooling in confined spaces while reducing the impact on the efficiency of the turbine.

[0010] Technical Solution

[0011] The present invention relates to an axial turbine, which includes: a first separation nozzle, which is capable of dividing an incoming air flow into a radially inner air flow and a radially outer air flow, the radially outer air flow being referred to as a secondary flow; a second separation nozzle, which is capable of dividing the radially inner air flow into a mainstream and a third flow, the third flow being located in a third flow channel radially outside the mainstream; and an air / oil type heat exchanger, which is arranged in the third flow channel and includes a heat exchange surface for heat exchange with air and an oil passage, the oil passage extending in the third flow channel; and a structural arm, which extends radially through the third flow channel; wherein each structural arm includes a cross-section having a downstream portion in the third flow channel, the downstream portion having a width that decreases toward the downstream, and the heat exchanger is adjacent to the downstream portion of the structural arm.

[0012] According to an advantageous embodiment of the invention, a heat exchange surface is adjacent to the downstream portion of the structural arm, said heat exchange surface having a diverging circumferential profile conforming to the downstream portion of the structural arm.

[0013] According to an advantageous embodiment of the invention, the circumferential profile diverging from the heat exchanging surface is formed by side profiles directly adjacent to the structural arms, said side profiles each comprising an inclined side profile with respect to the axial direction.

[0014] According to an advantageous embodiment of the invention, the axial turbine comprises a stator arranged in the passage of the third flow and upstream of each structural arm.

[0015] According to an advantageous embodiment of the invention, each structural arm is arranged axially between the low-pressure compressor and the high-pressure compressor.

[0016] According to an advantageous embodiment of the invention, each structural arm comprises an upstream portion comprising a leading edge, the heat exchanger being arranged downstream of said leading edge.

[0017] According to an advantageous embodiment of the invention, the downstream portion of each structural arm comprises a trailing edge, the heat exchanger being arranged between the leading edge and said trailing edge.

[0018] According to an advantageous embodiment of the invention, the heat exchanger is arranged at the maximum width of the structural arm.

[0019] According to an advantageous embodiment of the invention, the axial turbine comprises an inner casing arranged between the primary flow and the tertiary flow, said inner casing comprising a "VBV" duct having an outlet at the third flow channel, said outlet being arranged downstream of the heat exchanger.

[0020] According to an advantageous embodiment of the invention, the exchanger extends circumferentially between two structural arms, such that said heat exchanger is in direct contact with each of said two structural arms.

[0021] According to an advantageous embodiment of the invention, heat exchange surfaces extend radially and are distributed angularly in the third flow channel, said heat exchange surfaces being adjacent to a downstream portion of the structural arm and having an inclination with respect to the axial direction in order to conform to said downstream portion.

[0022] According to an advantageous embodiment of the invention, the heat exchange surface comprises an oil passage extending fluidly between an inner wall and an outer wall of the third flow channel.

[0023] According to an advantageous embodiment of the invention, the inner wall and the outer wall of the third flow channel are formed integrally with the exchange surface.

[0024] According to an advantageous embodiment of the invention, the number of heat exchange surfaces per unit area adjacent to the side profiles is at least 20% greater than the number of heat exchange surfaces per unit area situated in the central part of the exchanger.

[0025] According to an advantageous embodiment of the invention, the number of heat exchange surfaces per unit area increases with the circumferential enlargement of the cross section of the heat exchange surfaces.

[0026] According to an advantageous embodiment of the invention, the number of heat exchange surfaces per unit area adjacent to the downstream portion increases gradually with the inclination of the inclined side profile.

[0027] Advantages of the invention

[0028] The invention is particularly advantageous in that, in particular due to the expansion of the exchanger in the direction of flow of the air, air of sufficient cold velocity can be circulated in the heat exchanger, thus ensuring cooling efficiency. In fact, good cooling efficiency enables the use of less bulky and therefore smaller, lighter and less expensive exchangers.

[0029] Furthermore, the positioning of the exchanger at the third flow channel makes it possible to reduce the risk of hampering the efficiency of the engine, which results in energy efficiency and optimized thrust, which advantageously makes it possible to reduce carbonaceous gas emissions.

[0030] Design Description

[0031] The invention is particularly advantageous in that, due to the progressive expansion of the exchanger in the direction of flow of the air, cold low-velocity air can circulate in the heat exchanger, thereby ensuring cooling efficiency. In fact, good cooling efficiency enables the use of less bulky and therefore smaller, lighter and less expensive exchangers.

[0032] Furthermore, the positioning of the exchanger at the third flow channel makes it possible to avoid hampering the efficiency of the engine, which results in energy efficiency and optimized thrust, which advantageously makes it possible to reduce carbon dioxide emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a longitudinal sectional view of a turbine including a heat exchanger according to a first embodiment of the present invention;

[0034] Figure 2 yes Figure 1 Detailed view of the turbine heat exchanger;

[0035] Figure 3 is a front view of a third flow passage including a heat exchanger according to the first embodiment;

[0036] Figure 4 Schematically shows the oil circuits on an angular sector in a heat exchanger according to a first embodiment;

[0037] Figure 5 is a perspective longitudinal sectional view of a heat exchanger of a turbine according to a second embodiment;

[0038] Figure 6 shows a cross-sectional view from above of an exchanger in a third flow channel according to a second embodiment;

[0039] Figure 7 shows a partial top view of a heat exchanger according to a third embodiment;

[0040] Figure 8 The evolution of the density of the heat exchange surface in the axial direction and in the circumferential direction is shown. DETAILED DESCRIPTION

[0041] In the following description, the terms "inner" and "outer" refer to the positioning relative to the longitudinal rotation axis of the turbine. The axial direction corresponds to the direction along the longitudinal rotation axis of the turbine. The radial direction is perpendicular to the longitudinal axis. Upstream and downstream refer to the flow direction of the flow in the turbine.

[0042] The drawings show the elements schematically and not to scale. In particular, some dimensions are exaggerated to facilitate reading of the drawings.

[0043] Figure 1 A turbomachine 2 according to a first embodiment is shown. A propeller 4 fixed to a hub 6 rotates about a longitudinal axis 8 .

[0044] The turbine 2 moves in an air flow F, the movement of which relative to the turbine 2 is caused by the rotation of the propeller 4 and by the advancement of the aircraft on which the turbine 2 is mounted.

[0045] The air flow F is separated into a radially inner air flow F′ and a radially outer air flow F2 (referred to as a secondary flow F2 ) by the first separation nozzle 10 . The propeller 4 may be arranged upstream or downstream of the first separation nozzle 10 .

[0046] The radially inner air flow F′ passes through a movable wheel 12 which directs it towards a second separation nozzle 14 capable of dividing it into a primary flow F1 and a tertiary flow F3 , which is different from the secondary flow F2 .

[0047] The first separating nozzle 10 comprises an inner wall which forms a first outer guide wall 11 for the radially inner air flow F′, said first outer guide wall 11 forming a convex profile seen from said radially inner air flow F′.

[0048] The second separation nozzle 14 comprises an outer wall forming a second outer guide wall 13 for the radially inner air flow F′ that has passed through the movable wheel 12 , said second outer guide wall 13 forming a convex profile seen from the third flow F3 .

[0049] The third flow F3 enters the third flow channel 16 located radially outside the main flow F1 . The third flow F3 passes through a heat exchanger 18 arranged in the third flow channel 16 .

[0050] exist Figure 1 As can be seen in FIG. 1 , the turbine 2 is shown symmetrically about the longitudinal axis 8 . In fact, the third flow channel 16 is annular around the longitudinal axis 8 and is circumferentially continuous over 360°. For this reason, the third flow F3 is a flow that passes through the third flow channel 16 annularly.

[0051] In this configuration, the third flow F3 extends substantially in the axial direction and is located radially between the primary flow F1 and the secondary flow F2.

[0052] The third flow F3 extends in the third flow channel 16 from the radially inner air flow F′ downstream of the moving wheel 12 and, after passing through the heat exchanger 18 , to the secondary flow F2 .

[0053] The turbine 2 also comprises a stator (not shown) arranged upstream of the heat exchanger 18 at the third flow channel 16. Advantageously, the stator makes it possible to straighten the third flow before it passes through the heat exchanger 18, so as to minimize aerodynamic disturbances of the third flow F3 that may be caused by the moving wheels 12, which makes it possible to optimize the heat exchange between the air and the oil.

[0054] The stator corresponds to a row of stator vanes arranged in the third flow channel downstream of the separation nozzle 14. Alternatively, the stator may be arranged upstream of the separation nozzle 14 and downstream of the movable wheel 12.

[0055] The heat exchanger 18 extends radially and axially in an upstream section 20 of the third flow channel 16 , the upstream section having a longitudinal cross section that diverges in the flow direction of the third flow F3 .

[0056] The heat exchanger 18 may axially overlap the high-pressure compressor 15 and the low-pressure compressor 17 (referred to as a "booster" 17), and the heat exchanger 18 may also be axially positioned above the low-pressure compressor 17. Preferably, the heat exchanger 18 is axially arranged between the low-pressure compressor 17 and the high-pressure compressor 15.

[0057] A “Variable Bleed Valve” (VBV) duct 19 having an outlet passing through the inner wall of the third flow channel 16 and arranged axially downstream of the heat exchanger 18 makes it possible to ensure a drainage function by returning a portion of the main flow F1 to the third flow F3, in particular when the flow rate of the main flow F1 becomes too low, which makes it possible to discharge, for example, any ice particles from the main flow F1 to avoid clogging of the high-pressure compressor 15.

[0058] Advantageously, the outlet of the “VBV” duct 19 is arranged downstream of the heat exchanger 18 so as to protect the heat exchanger from possible risks of blockage.

[0059] The heat exchanger 18 may extend continuously over 360° around the longitudinal axis 8 of the turbine 2 in the upstream section 20 of the channel 16. Preferably, the heat exchanger 18 extends discontinuously over 360° around the longitudinal axis 8 by being divided into a plurality of angular sectors, and each angular sector may ensure a heat exchange function between air and oil, which may differ from one sector to another. Examples of different heat exchange functions will be given later in this specification.

[0060] The third flow F3 passes through the heat exchanger 18 occupying the upstream section 20 of the passage 16 at a speed of Mach number comprised between 0.1 and 0.6, typically 0.3. Advantageously, the divergence of the upstream section 20 of the passage 16 makes it possible to help decelerate the air by reducing its speed.

[0061] The third flow channel 16 also comprises a downstream section 22 having a longitudinal section converging along the third flow F3. Advantageously, this enables the third flow F3 to be accelerated at its exit from the heat exchanger 18, thereby joining the secondary flow F2 to contribute to the thrust of the aircraft.

[0062] The heat exchanger 18 is of the “Air-Cooled Oil Cooler (ACOC)” type and comprises an oil passage extending in the third flow channel, in particular between the upper and lower walls of the heat exchanger 18 in radial and axial directions.

[0063] Indeed, the heat exchanger 18 of the present invention differs from a surface air-oil exchanger (SACOC) in that the oil is retained in the lower and upper walls and does not pass radially through the exchanger.

[0064] Advantageously, the "ACOC" heat exchanger 18 enables cooling of the oil, preferably by air, thereby exchanging heat between air and oil. In practice, the temperature of the oil can reach operating temperatures up to 180°C and flow rates up to 30,000 l / h.

[0065] In this respect, the exchanger 18 can ensure cooling of the oil used in the various components of the aircraft, in particular the engine, the gearbox, the engine generator and any electronic components requiring cooling.

[0066] A single heat exchanger 18 can combine the cooling of multiple functions or oil circuits of the turbine, and the different circuits can be arranged in thermal contact or thermal isolation depending on the different parameters related to the need for oil cooling (i.e. inlet temperature, flow rate, required outlet temperature or air conditions). The exchanger 18 and in particular the oil passages of the exchanger can withstand low oil temperatures of up to -54°C.

[0067] Figure 2 yes Figure 1 Detailed view of the heat exchanger 18 .

[0068] Reference Figure 2 , the heat exchanger 18 is of the air / oil type and has a heat exchange surface 26 in contact with the oil passage 24 for exchanging heat with the air.

[0069] The exchange surfaces 26 have a longitudinal section that diverges along the third flow F3, i.e. the radial height that separates the two exchange surfaces 26 downstream of the exchanger is greater than the radial height that separates the two exchange surfaces upstream of the exchanger. Furthermore, the exchange surfaces 26 have a cross section that increases along the third flow F3. Preferably, the heat exchanger 18 is a single piece obtained by additive manufacturing, and more preferably by laser fusion on a bed of aluminum powder. The exchange surfaces 26 are preferably formed by thin plates, and advantageously, each plate defines two exchange surfaces 26.

[0070] The oil passages 24 are arranged side by side, and the number of the oil passages is between 1 and 50, preferably between 5 and 30, and more preferably between 10 and 25. Alternatively, the oil passages 24 may be merged together to form only one conduit.

[0071] Advantageously, the divergent heat exchanger 18 is dimensioned so as to reduce the air velocity by approximately 25%, the third flow F3 for example changing from a velocity of Mach 0.33 to a velocity of approximately Mach 0.2 at the outlet of the exchanger 18 .

[0072] In order to promote heat exchange between the oil passages 24 and the exchange surface 26, 60% of the cumulative length of the oil passages 24 extends in a longitudinal plane distributed at an angle around the longitudinal axis 8, and preferably 80% of the cumulative length extends in the longitudinal plane. Advantageously, the oil passages 24 extending in the longitudinal plane are parallel to the direction of the air flow.

[0073] To this end, the remaining 20% ​​of the length of the oil passage 24 corresponds to a transition 28 from one longitudinal plane to another to enable the oil to travel circumferentially through the heat exchanger 18. The upstream section 20 of the third flow channel 16 comprises an outer shell 30 and an inner shell 32. The upstream section 20 also comprises an outer intermediate shell 31 and an inner intermediate shell 33, each of which is in one piece with the exchanger 18.

[0074] Advantageously, the oil passages 24 and / or the exchange surfaces 26 are formed integrally with the outer intermediate casing 31 and with the inner intermediate casing 33 of the exchanger 18 .

[0075] The outer housing 30 is an integral part of the outer intermediate housing 31 , while the inner housing 32 is an integral part of the inner intermediate housing 33 .

[0076] In this respect, the outer casing 30 comprises a fixing flange 34 at the upstream end and / or at the downstream end. Preferably, the outer casing 30 comprises two fixing flanges 34 arranged at the upstream end and at the downstream end of the exchanger 18.

[0077] Similarly, the outer intermediate casing 31 of the exchanger 18 comprises at least one fixing flange 36 at its upstream end and / or at its downstream end. To this end, each fixing flange 34 is configured to be attached to a flange fixing bracket 36 belonging to the exchanger 18. Preferably, the fixing flanges 34, 36 are circumferentially continuous around the longitudinal axis 8.

[0078] The assembly direction of the exchanger 18 in the turbine is preferably from downstream to upstream, i.e. in the opposite direction to the third flow F3. In this configuration, the fixing of the exchanger 18 to the outer casing 30 can be ensured by a threaded engagement. In this configuration, the exchanger 18 is an integral part of the third flow channel 16 and thus ensures the aerodynamic continuity of the third flow F3 within the channel 16.

[0079] The fixing of the exchanger 18 to the inner casing 32 can be achieved by a rigid connection between a fixing flange belonging to the inner casing 32 and another fixing flange belonging to the exchanger 18 (specifically, to the angular sectors 38 of the exchanger 18 ).

[0080] In fact, the angular sector 38 is an integral part of the exchanger 18 and comprises an oil inlet passage 40 enabling the oil to be distributed in the oil passage 24. In this configuration, the fixing is preferably achieved by a threaded engagement between two flanges (not shown) which may be arranged circumferentially around the longitudinal axis 8.

[0081] The exchanger 18 comprises, over the entire extent of the exchanger along the third flow F3, a material-free portion 42 forming a bypass 42, usually called air bypass 42, also called "Foreign Object Debris (FOD)" bypass. In fact, the main function of the air bypass is to enable the debris contained in the air flow to pass through the turbine. The debris or "FOD" may be, for example, birds, hail, hailstones or any other object that could clog or damage the exchanger.

[0082] In this regard, the exchanger 18 includes a bypass 42 to enable debris to pass through the channel 16 without blocking the passage of the third flow F3 through the exchanger 18 or damaging the exchanger.

[0083] In parallel with the air bypass 42 , a protection grid may be arranged on the front surface of the exchanger 18 in order to further protect the oil passages 24 and the exchange surfaces 26 without hampering their heat exchange capabilities.

[0084] Reference Figure 1 and Figure 2 , an air bypass 42 is adjacent to the outer casing 30 of the upstream section 22 of the third flow channel 16. The air bypass 42 is delimited radially to the outside by the outer intermediate casing 31 and more precisely by an upper surface 44 of the outer intermediate casing 31 belonging to the exchanger 18, said upper surface 44 being adjacent to the first outer guide wall 11 belonging to the outer casing 30.

[0085] The air bypass 42 is delimited radially inwardly by a surface 45 belonging to a wall radially delimiting the heat exchange surface 26 , said wall having a constant radial height.

[0086] The air bypass 42 extends radially over a height corresponding to a maximum of 20% of the total radial height of the upstream section 22 of the third flow channel 16. Preferably, the air bypass 42 extends radially to a maximum of 15% of the corresponding total radial height of the diverging longitudinal section of the channel 16.

[0087] The air bypass 42 has a constant radial height along the third flow F3 over the entire extent of the exchanger 18. In fact, the height of the air bypass 42 remains constant and does not vary in any way as a function of the flow of the air, since it is not desirable to vary the velocity of the air, only to make the debris pass through the air bypass 42. Advantageously, this makes it possible to limit the pressure loss difference between the air bypass 42 and the rest of the exchanger 18.

[0088] However, the radial height of the air bypass 42 may vary to compensate for possible pressure losses that may be caused by aerodynamic disturbances downstream of the exchanger. In this regard, the air bypass 42 may have a converging and / or diverging longitudinal cross-section.

[0089] Figure 3 yes Figure 1 A front view (ie in the direction of air flow) of the third flow channel 16 of the turbine including the exchanger 18 is shown.

[0090] Reference Figure 3 , the exchangers 18 are distributed at an angle in the third flow channel 16 , and in fact, it can be considered that the multiple exchangers 18 in the channel 16 represent a single exchanger 18 .

[0091] The exchanger 18 comprises a plurality of angular sectors 38 , each comprising an oil inlet 48 situated on the second outer guiding wall 13 of the radial inner air flow, referred to as the inner wall 13 , situated at the angular end of said sector 38 .

[0092] The angular sector 38 also comprises oil outlets 50 on the inner wall 13 at opposite angular ends, one end opposite the other with respect to a radial axis (not shown) situated in the middle of the angular sector.

[0093] The oil inlet 48 or the oil outlet 50 is integrally formed in the inner wall 13. Preferably, the oil inlet 48 and the oil outlet 50 are integrally formed in the inner wall 13.

[0094] Figure 4 Shows Figure 1 Simplified cross-sectional view of the exchanger 18 of the turbine of FIG. 1 , wherein the air bypass 42 is located radially adjacent to the outer casing. Figure 4 , the exchange surface 26 is not shown.

[0095] The angular sector 38 comprises an oil distribution portion 52 extending in the circumferential direction of the inner wall 13 and an oil collection portion 54 also extending in the circumferential direction of the inner wall 13 .

[0096] A plurality of angular sectors 38 may comprise a single distribution portion 52 and a single oil collecting portion 54. In such a configuration, the single distribution portion may be connected, for example, to a plurality of cooling circuits of an axial turbomachine.

[0097] The oil distribution portion 52 includes the oil inlet 48, and the oil collection portion includes the oil outlet 50. In this regard, the oil passage 24 fluidly extends between the corresponding oil inlet 48 and the corresponding oil outlet 50 into the third flow channel.

[0098] The oil outlet passage 55 is disposed between the oil passage 24 and the oil collecting portion 54 , and a court-circuit passage may connect the oil inlet passage 40 to the oil outlet passage 55 .

[0099] Reference Figure 2 , the angular sector 38 comprises a bypass passage 56 of said sector 38 (also called oil bypass 56 ) which is integrally formed in the inner wall 13 and extends fluidically along the inner wall 13 between the oil inlet 48 and the oil outlet 50 . The exchanger 18 may comprise a plurality of oil bypasses 56 .

[0100] Advantageously, the oil bypass 56 ensures cold operation of the exchanger 18 , in particular at temperatures of about −40° C., in fact, cold oil has a high viscosity which is not suitable for oil entering the exchanger 18 , so the oil enters the oil bypass 56 until the oil reaches a suitable viscosity.

[0101] In this regard, another circuit, known as a defrost circuit (not shown), can be arranged near or in contact with the oil bypass 56 and also in contact with the oil passage 24 , which defrost circuit can ensure heating of the oil comprised in the exchanger 18 .

[0102] The oil bypass 56 comprises a normally closed valve 58 which can be opened if the pressure difference between the oil inlet 48 and the oil outlet 50 is greater than or equal to a limit value. The valve 58 can also be opened when the viscosity of the oil is too high compared to a previously specified threshold value.

[0103] The oil inlet 48 is located on the terminal downstream portion of the exchanger 18, while the oil outlet 50 is located on the upstream portion of the exchanger 18. However, the opposite may be achieved or substituted. Both the inlet 48 and the outlet 50 may be located on the downstream portion or the upstream portion.

[0104] exist Figure 4 As can be seen in the figure, the oil inlet 48 is located at the angular end of the angular sector 38 and at the oil inlet passage 40, and the oil outlet 50 and the oil outlet passage 55 are located in the opposite angular end of the angular sector 38. Advantageously, the oil passage 24 extending from the oil inlet 48 towards the oil outlet 50 extends circumferentially over the entire circumferential extent of the heat exchanger 18, thereby making it possible to maximize the heat exchange area between the tertiary flow and the oil.

[0105] Figure 5 FIG. 1 shows a partial perspective view of an exchanger 118 according to a second embodiment of the present invention. It should be noted that the perspective view of the exchanger 118 should have a curved profile, however, for ease of understanding, Figure 5 It has been greatly simplified.

[0106] In fact, the first embodiment consists in positioning the air bypass 42 adjacent to the outer casing 30. The second embodiment consists essentially in positioning the air bypass 142 with the same geometric configuration as the previously described air bypass 42. In this respect, the exchange surface 26 as well as the oil passages and all the other elements forming the exchanger 118 are identical to the exchanger 18.

[0107] The air bypass 142 is configured adjacent the inner housing 32 , which involves structural adjustments that will be fully described later in this specification.

[0108] Reference Figure 5 , an air bypass 142 is adjacent to the inner casing (not shown) of the upstream section of the third flow channel. The air bypass 142 is delimited radially inwardly by the inner intermediate casing 33, more precisely by the lower surface 46 of the inner intermediate casing belonging to the exchanger 118, which is adjacent to the inner casing and in particular to the inner wall 13 shown in the previous figures.

[0109] In this configuration, the lower surface 46 forms a continuation of the third flow channel with the inner wall 13 , so we can consider that the air bypass 142 is radially delimited toward the inside by the inner wall 13 .

[0110] The air bypass 142 is delimited radially towards the outside by a surface 47 belonging to a wall radially delimiting the heat exchange surface 26 , said wall having a constant radial height.

[0111] The arrangement of the different elements of the axial turbine can be determined according to the general arrangement (more precisely, according to the radial position of the tip of one of the blades of the movable wheel relative to the heat exchanger 18, 118) and in combination with the Figure 1 The embodiment of the present invention is selected based on the geometry of the second outer guide wall 13 shown.

[0112] In fact, the position of the tips of the blades of the moving wheel and the change in the geometry of the walls of the third flow channel result in a change in the trajectory of the "FOD" fragments.

[0113] Advantageously, the exchanger 18 , 118 can be manufactured and adapted according to the architecture of the turbomachine in which it will be installed, anticipating the radial portion of the passage 16 comprising the greatest risk of collision with debris so that the air bypass 42 , 142 is arranged at this radial portion.

[0114] Figure 6 A cross-sectional view from above is shown of an exchanger 118 according to a second embodiment located in a third flow channel.

[0115] The turbine comprises a structural arm 60 adjacent to an angular sector and extending radially in the third flow channel at the junction between said angular sectors of the exchanger 118 .

[0116] Each angular sector of the exchanger 118 extends circumferentially between two structural arms 60 , so that in the event that the exchanger 118 is divided angularly in the third flow channel, said division can be ensured by the structural arms 60 .

[0117] The structural arm 60 is arranged axially downstream of the stator in the third flow channel and preferably between the low-pressure compressor and the high-pressure compressor.

[0118] Each structural arm 60 comprises an upstream portion including a leading edge, downstream of which the exchanger 118 is arranged. Advantageously, this arrangement makes it possible to further minimize the aerodynamic disturbances of the third flow F3 that may be caused by the moving wheels.

[0119] The width of the cross section of the structural arm 60 decreases over the downstream half of said cross section, thereby forming a converging downstream portion 62 of the structural arm 60 .

[0120] The downstream portion 62 of each structural arm 60 comprises a trailing edge upstream of which the exchanger 118 is arranged. Preferably, the exchanger 118 is arranged between the leading edge and said trailing edge.

[0121] Advantageously, this makes it possible to improve the rigidity of the assembly of the exchanger 118 in the turbine and to better control the pressure losses and aerodynamic disturbances. Furthermore, the leading edge of the structural arm 60 makes it possible to promote convective heat exchanges between the oil and the third flow F3 .

[0122] The exchanger 118 extends circumferentially between the two structural arms so that it is in direct contact with at least one of the two structural arms, and preferably with each of the two structural arms 60. In this configuration, the heat exchange surface 26 is adjacent to the downstream portion 62 of the structural arm 60.

[0123] In fact, Figure 6 As can be seen in FIG, the exchanger 118 is adjacent to the downstream portion 62 of the structural arm 60 in the axial direction and in the circumferential direction. Thus, the exchanger 118 is in direct circumferential contact (glued) with the downstream portion 62, while axially overlapping at least 80% of the total axial extent of said downstream portion 62. Here, the term "adjacent" means that the exchanger 118 is in contact with at least 80% of the downstream portion 62.

[0124] Preferably, the heat exchange surface 26 has a diverging circumferential profile conforming to the downstream portion 62 of the structural arm 60. Advantageously, this makes it possible to limit pressure losses and to increase the efficiency of the heat exchange between the third flow and the oil inside the exchanger 118.

[0125] The circumferential profile diverging from the heat exchange surface 26 is formed by side profiles 64 which are directly adjacent to the structural arm 60 and which each comprise a downstream portion 62. In this respect, each downstream portion 62 comprises at least one inclined side profile 65 which is inclined relative to the axial direction and which extends over at least 5% of the corresponding side profile 64.

[0126] The average inclination of the inclined side profile 65 depends on the axial extent of the inclined side profile relative to the side profile 64 and may vary between 5° and 60°.

[0127] Preferably, the inclination of the inclined side profile 65 relative to the side profile 64 is approximately 30°, said inclination preferably extending over 30% of the axial length of the structural arm 60 .

[0128] The oil passage 24 may partially or completely follow the inclination of the inclined side profile 65 of the structural arm 60 .

[0129] It should be noted that the arrangement of the oil inlet and of the oil outlet in the angular sectors of the exchanger 118 depends on the embodiment of the invention.

[0130] In fact, Figure 6 A second embodiment is shown in which the air bypass 42 is delimited radially inwardly by the inner casing. In this respect, for each angular sector of the exchanger 118, the oil inlet passage 40 and the oil outlet 55 are located in the axial projection 61 of the greater width cross section of the structural arm 60 at the downstream half 62.

[0131] The axial projection 61 is referred to as the terminal downstream portion 61 in which the oil inlet passage 40 and the oil outlet 55 are arranged. This further enables the oil inlet to be moved circumferentially away from the oil outlet to maximize the circulation of oil in the exchanger 118 in the third flow channel.

[0132] Preferably, the exchanger is arranged axially at the maximum width of the structural arm 60 , which advantageously makes it possible to facilitate the assembly of said exchanger, which is done from downstream to upstream.

[0133] Preferably, the oil inlet and / or the oil outlet are positioned at a distance from the downstream edge 63 of the exchanger 118 that is less than 20% of the total axial extent of the exchanger, more preferably less than 5% of the total extent of the exchanger.

[0134] exist Figure 6As can be seen in FIG. 1 , the oil inlet at the oil inlet passage 40 and the oil outlet at the oil outlet passage 55 are circumferentially aligned. The distances of the oil inlet and the oil outlet from the downstream edge 63 are each between 5% and 20% of the total axial extent of the exchanger 118 .

[0135] The air bypass 142 is circumferentially defined by the side portion 43, which can conform to the side profile 64. Figure 6 In the embodiment shown in FIG. 6 , the side portion 43 does not conform to the inclined side profile 65 .

[0136] The oil inlet passage 40 and the oil outlet passage 55 extend radially and laterally to the air bypass 142 , being spaced apart from each other by a distance greater than the circumferential width of the air bypass 142 , ie between the two side portions 43 .

[0137] Preferably, the oil inlet passage 40 is spaced apart from the oil outlet passage 55 by a distance at most 20% greater than the circumferential width of the air bypass 142 , and more preferably, by a distance at most 5% greater than the circumferential width of the air bypass 142 .

[0138] It should be noted that Figure 6 The arrangement of the oil inlet passage 40 and the oil outlet passage 55 shown in FIG. 5 can be applied to the exchanger 18 according to the first embodiment.

[0139] Figure 7 A partial top view of an exchanger 18 or 118 is shown, which shows a third embodiment of the invention, in which the exchanger 18, 118 presents an evolution (called density evolution) of the number of exchange surfaces 26 per unit area of ​​the exchanger located in the adjacent part 66 adjacent to the structural arm 60 relative to the number of exchange surfaces 26 per unit area located in the central part 68.

[0140] The adjacent portion 66 can be considered as a boundary layer of the exchanger, the evolution of density being in the circumferential direction and being at least 20%, preferably 50%.

[0141] Thus, the exchanger 18 , 118 has 50% more exchange surfaces 26 in the adjacent portion 66 than in the central portion 68 .

[0142] Advantageously, the density evolution in the circumferential direction enables the air to be decelerated and thus promotes heat exchange between oil and air as it flows towards the downstream portion 62. The reduction in pressure losses and the resulting resistance at the level of the flow of the third flow F3 also provides another advantage of the invention.

[0143] Figure 8The evolution of the density of the exchange surface 26 in the axial direction and in the circumferential direction is shown.

[0144] The cross section of the exchange surface 26 of the exchanger has a pattern preferably in the form of a hexagon, however, in order to illustrate the evolution in a simplified manner, Figure 7 and Figure 8 A rectangular pattern is shown in FIG.

[0145] Reference Figure 7 and Figure 8 , the number of exchange surfaces 26 per unit area increases in adjacent portions 66 as the cross section at the third flow F3 increases in the circumferential direction.

[0146] In fact, the flow of the third flow F3 gradually diverges in the circumferential direction so as to follow the inclined side profile 65 of the downstream portion 62 of each structural arm 60 .

[0147] To this end, the number of exchange surfaces 26 per unit surface is increased according to one or more sectors 67 , 69 , increasing by at least 20%, preferably by 50%, between each sector of adjacent portions 66 .

[0148] By following the divergence of the third flow channel in longitudinal section, an evolution of the density of the exchange surface in radial direction is also possible, which enables the same advantages as the evolution of the density in axial and circumferential directions.

[0149] Advantageously, the arrangement of the heat exchanger and in particular the divergent third flow channel according to the invention makes it possible to supply the exchanger with sufficiently cold and slow air, so as to ensure both the cooling efficiency of the oil and the limitation of the aerodynamic losses associated with the presence of the exchanger, thus increasing the thrust of the aircraft while contributing to the reduction of CO2 emissions.

[0150] It should be noted that the invention is not limited to the examples depicted in the drawings. The teachings of the invention may be particularly applicable to another type of turbomachine.

[0151] Each technical feature of each of the examples shown is applicable to the other examples. In particular, the evolution of the density of the heat exchange surface can be applied in three directions to exchangers in which the air bypass is radially adjacent to the outer casing or the inner casing.

Claims

1. An axial turbine (2), comprising: - a first separation nozzle (10) capable of separating an incoming air flow (F) into a radially inner air flow (F') and a radially outer air flow (F2), the latter being referred to as a secondary flow (F2); a second separation nozzle (14) capable of separating the radially inner air flow (F') into a main flow (F1) and a third flow (F3), the third flow (F3) being located in a third flow channel (16) radially outside the main flow (F1); as well as an air / oil type heat exchanger (18, 118) arranged in the third flow channel (16) and comprising a heat exchange surface (26) for exchanging heat with air and an oil passage (24) extending into the third flow channel (16); as well as - a structural arm (60) extending radially through the third flow channel (16); Characterized in that each structural arm (60) includes a cross-section having a downstream portion (62) in the third flow channel (16), the downstream portion having a width that decreases toward the downstream, the heat exchanger (18, 118) being adjacent to the downstream portion (62) of the structural arm (60), and the heat exchanger (18, 118) extending circumferentially between the two structural arms (60), so that the heat exchanger (18, 118) is in direct contact with at least one of the two structural arms (60).

2. The axial turbine (2) according to claim 1, characterized in that The heat exchange surface (26) is adjacent to a downstream portion (62) of the structural arm (60), the heat exchange surface (26) having a diverging circumferential profile conforming to the downstream portion (62) of the structural arm (60).

3. The axial turbine (2) according to claim 2, characterized in that A circumferential profile diverging from the heat exchange surface (26) is formed by side profiles (64) directly adjacent to the structural arms (60), the side profiles (64) each comprising an inclined side profile (65) relative to the axial direction.

4. The axial turbine (2) according to any one of claims 1 to 3, characterized in that The axial turbine (2) comprises a stator arranged in the passage (16) of the third flow and upstream of each structural arm (60).

5. The axial turbine (2) according to any one of claims 1 to 4, characterized in that Each structural arm (60) is arranged axially between the low-pressure compressor (17) and the high-pressure compressor (15).

6. The axial turbine (2) according to any one of claims 1 to 5, characterized in that Each structural arm (60) comprises an upstream portion including a leading edge, the heat exchanger (18, 118) being arranged downstream of the leading edge.

7. The axial turbine (2) according to any one of claims 1 to 6, characterized in that The downstream portion (62) of each structural arm (60) comprises a trailing edge, the heat exchanger (18, 118) being arranged between the leading edge and the trailing edge.

8. An axial turbine (2) according to any one of claims 1 to 7, characterized in that The heat exchanger (18, 118) is arranged at the maximum width of the structural arm (60).

9. The axial turbine (2) according to any one of claims 1 to 8, characterized in that The axial turbine (2) comprises an inner casing (32) arranged between the primary flow (F1) and the tertiary flow (F3), the inner casing (32) comprising a "VBV" duct (19) having an outlet at the third flow channel (16), the outlet being arranged downstream of the heat exchanger (18, 118).

10. An axial turbomachine (2) according to any one of claims 1 to 9, characterized in that The heat exchanger (18, 118) extends circumferentially between the two structural arms (60) such that the heat exchanger (18, 118) is in direct contact with each of the two structural arms (60).

11. An axial turbine (2) according to any one of claims 1 to 11, characterized in that The heat exchange surface (26) extends radially and angularly in the third flow channel (16), is adjacent to a downstream portion (62) of the structural arm and has an inclination relative to the axial direction to conform to the downstream portion (62).

12. Axial turbine (2) according to claim 11, characterized in that The heat exchange surface (26) includes an oil passage (24) extending fluidly between an inner wall (13) and an outer wall (11) of the third flow channel (16).

13. The axial turbine (2) according to claim 12, characterized in that The inner wall (13) and the outer wall (11) of the third flow channel (16) are integrally formed with the exchange surface (26).

14. The axial turbine (2) according to any one of claims 1 to 13, characterized in that The number of heat exchange surfaces (26) adjacent to the side profile (64) per unit area is at least 20% greater than the number of heat exchange surfaces (26) per unit area located in the central portion (68) of the exchanger (18, 118).

15. The axial turbine (2) according to any one of claims 1 to 14, characterized in that The number of heat exchange surfaces (26) per unit area increases with the circumferential increase of the cross section of the heat exchange surface (26).

16. Axial turbine (2) according to claim 15, characterized in that The number of heat exchange surfaces (26) adjacent to the downstream portion (62) per unit area gradually increases with the inclination of the inclined side profile (65).

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