Variable height fin heat exchanger and corresponding turbomachine

Abstract

The invention relates to a heat exchanger (1) for a turbomachine, having a longitudinal axis (X), for performing an exchange of heat between a first fluid (2) and a second fluid (3), the heat exchanger comprising two panels (25, 26) and a plurality of fins (29) extending between the panels, the fins being arranged in a plurality of rows along the longitudinal axis and being arranged in a staggered manner, each row of fins being parallel and connected to one another, the heat exchanger being annular and centered on the longitudinal axis X. The panels extend radially between an inner cylindrical surface (34a) and an outer cylindrical surface (34b) of the heat exchanger, the fins having a first and second exchange surface which are defined in planes substantially perpendicular to the radial axis and intended to be swept by the first fluid along the longitudinal axis, the fins of each row further having a height, measured between the panels, that increases radially between the inner and outer cylindrical surfaces.

Description

[0001] DESCRIPTION

[0002] TITLE: VARIABLE HEIGHT FIN HEAT EXCHANGER AND CORRESPONDING TURBOMACHINE

[0003] Field of invention

[0004] The present invention relates to the general field of aeronautics. It relates in particular to a heat exchanger for a turbomachine, in particular an aircraft.

[0005] Technical background

[0006] An aircraft turbomachine and an aircraft comprise various components and / or equipment that must be lubricated and / or cooled for their proper operation or fluids that must be cooled for the proper operation of the turbomachine. These components and / or equipment and / or fluids may be rotor guidance means in the turbomachine, electrical and / or electronic components for electrical systems of the aircraft turbomachine, hot exhaust gases from the turbomachine intended to be introduced upstream of the combustion chamber, or even systems for conditioning the interior spaces of the aircraft. The heat released by these components, equipment and / or fluids, which may be very significant, is removed by heat exchange in the turbomachine and / or the aircraft.

[0007] Heat exchange is achieved using one or more heat exchangers installed in the turbomachine or aircraft and for various applications. Depending on the applications, the heat exchangers generally use a cold source that can be ambient air, air from the secondary stream of the turbomachine, etc. and a hot source that can be the fuel of the turbomachine, oil, air (bleed air) taken from the low-pressure or high-pressure compressor of the turbomachine, or air from the primary stream of the turbomachine.

[0008] Heat exchangers can be of the tube, fin, plate and fin type, etc. Plate and fin heat exchangers, and in particular those with offset strip fins, are used in turbomachines due to their low mass. These heat exchangers comprise rows of fins parallel to each other and fins that are arranged in a staggered pattern or with offset strip fins. The heat exchanger can be configured in several stages. Generally, a first fluid, for example, hot exhaust gases, and a second fluid, for example, an air flow circulating in the turbomachine, pass through the heat exchanger. An example of a plate and fin heat exchanger is described in patent document FR3077630.

[0009] The prior art also includes the following documents, US-A-3818984, US-A- 2792200, US-A1 -2021 / 0180886, US-B2-10866030, US-A1 -2016 / 0054071, US-A1 - 2021 / 0222963, US-A1 -2012 / 0216543, FR-A1 -3097257, US-A-2429508, and US-B2- 8601791.

[0010] This type of heat exchanger presents difficulties in integration into the turbomachine due to the number of stages it comprises and the fact that the turbomachine includes restricted spaces.

[0011] Annular heat exchangers have been developed that facilitate integration into the turbomachine but have other types of fin configuration. The arrangement of the fins in these annular heat exchangers presents a significant pressure drop, in particular due to a significant form drag. It is difficult to increase the number of fins significantly to improve the performance of the turbomachine. Furthermore, the difference in temperatures of the fluids circulating in the heat exchanger of this type implies differences in the circulation speed of the fluids. These speed differences are accentuated by the difference in hydraulic diameter and the hydraulic resistances that increase with the radius of the heat exchanger (in cylindrical coordinate). This leads to a heterogeneity in the distribution of flows or fluids in the heat exchanger which can degrade the hydraulic / aeraulic performances.

[0012] The exchanger is generally sized to have an optimal convection thermal resistance ratio. The optimal thermal resistance ratio depends on the nature of the two fluids, temperatures / pressures / flow rates and the permitted pressure drop for each of the fluids. This can be close to 1 if the fluids are of the same nature with relatively similar temperature / pressure / flow rate conditions and similar target pressure drops.

[0013] There is a need to address some or all of the above drawbacks.

[0014] Summary of the invention The objective of the present invention is to provide a heat exchanger allowing better optimization of aerothermal and aerodynamic performances while reducing pressure losses and avoiding significant impact on mass.

[0015] We achieve this objective in accordance with the invention by means of a heat exchanger for a turbomachine, in particular an aircraft turbomachine, with a longitudinal axis, the heat exchanger being intended to carry out a heat exchange between a first fluid and a second fluid, the heat exchanger comprising at least a first panel, a second panel and a plurality of fins extending between the first and second panels, the fins being arranged in several rows along the longitudinal axis and being arranged in a staggered manner, each row of fins being parallel to each other and connected to each other, the heat exchanger being annular and centered on the longitudinal axis X, the first panel and the second panel extending radially between an internal cylindrical surface and an external cylindrical surface of the heat exchanger,the fins having a first and second exchange surface which are defined in planes substantially perpendicular to the radial axis of the heat exchanger and intended to be swept by the first along the longitudinal axis, and in that the fins of each row have a height which is on the one hand, measured between the first and second panels and which on the other hand, increases radially, between the internal cylindrical surface and the external cylindrical surface.,

[0016] Thus, this solution makes it possible to achieve the aforementioned objective. In particular, by adapting the dimensions and characteristics of the exchange surfaces on the first fluid according to the distance from the central axis of the exchanger, the thermal performance of the heat exchanger is significantly improved. With this configuration, the heat exchanger offers a relatively homogeneous and improved distribution of the first fluid. Increasing the height of the fins in fact leads to a variation in the hydraulic diameter and the coefficients of the exchange surfaces. There will be less resistance to the flow of the first fluid at the fins with a greater height. Furthermore, the geometric variations of the exchange surfaces make it possible to maintain a constant apparent permeability of the heat exchanger.

[0017] The heat exchanger also comprises one or more of the following features, taken alone or in combination: - the longitudinal pitch defining a distance between a trailing edge of a first fin of the plurality of fins and a leading edge of an adjacent second fin and successively of the plurality of fins, is constant.

[0018] - the fins are spaced radially with a transverse spacing which is constant.

[0019] - the fins are radially spaced at a transverse spacing, the transverse spacing decreasing from the inner cylindrical surface to the outer cylindrical surface.

[0020] - each fin has a length along the longitudinal axis which is constant.

[0021] - each fin has a length along the longitudinal axis which varies from upstream to downstream.

[0022] - the first panel, the second panel and the fins between the first and second panels form a stage and in that the heat exchanger comprises several stages, the stages being spaced apart by passages intended for the circulation of the second fluid, the passages opening onto an upstream surface and onto a downstream surface.

[0023] - the first panel, the second panel and the fins between the first and second panels form a stage and in that the heat exchanger comprises several stages which are arranged around the longitudinal axis, the stages being spaced apart by passages intended for the circulation of the second fluid, the passages opening onto the internal cylindrical surface and onto the external cylindrical surface.

[0024] - the heat exchanger is made in one piece.

[0025] - the fins are connected alternately by top walls and base walls, the top walls and the base walls being connected respectively to the first and second panels.

[0026] - the heat exchanger comprises an inlet defined in an upstream surface in which the first fluid and / or the second fluid enter(s) the heat exchanger and an outlet defined in an opposite downstream surface along the longitudinal axis through which the first fluid and / or the second fluid is(are) discharged from the heat exchanger.

[0027] - the heat exchanger comprises an inlet defined in the inner cylindrical surface through which the second fluid enters the heat exchanger and an outlet defined in the outer cylindrical surface through which the second fluid discharges from the heat exchanger.

[0028] - the increase in fin height is linear.

[0029] - the length of each fin is defined linearly and the length of the fin is determined using the parameter X r = , where s is the transverse spacing between the s(^max) fins of the same row and as a function of the radial position of the fin in cylindrical coordinates, Rmin being the minimum radius of the heat exchanger defined by the internal cylindrical surface, Rmax being the maximum radius of the heat exchanger defined by the external cylindrical surface.

[0030] The invention also relates to a turbomachine comprising a heat exchanger having any one of the aforementioned characteristics, the first and second panels being arranged regularly around the longitudinal axis, the fins being arranged between the first and second panels.

[0031] The invention further relates to an aircraft comprising a turbomachine as mentioned above.

[0032] The invention also relates to a method for manufacturing a heat exchanger as mentioned above, the method comprising a step of producing the heat exchanger by additive manufacturing by selective fusion on powder beds.

[0033] Brief description of the figures

[0034] 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:

[0035] Figure 1 is a perspective view of a heat exchanger comprising plates and fins according to the invention;

[0036] Figure 2 is an axial sectional view of an example of a turbomachine to which the invention applies;

[0037] Figure 3 is a schematic and front view of a stage of a heat exchanger according to the invention;

[0038] Figure 4 is a perspective view of an exemplary fin arrangement of a heat exchanger according to the invention;

[0039] Figure 5 is a radial sectional view of an embodiment of the heat exchanger according to the invention;

[0040] Figure 6 is a radial sectional view of another embodiment of the heat exchanger according to the invention; and,

[0041] Figure 7 is a front view of an example of a heat exchanger according to the invention.

[0042] Detailed description of the invention Figure 1 represents a heat exchanger 1 which allows a transfer of thermal energy between a first fluid 2 and a second fluid 3. The heat exchanger 1 is intended to be mounted in an aircraft turbomachine 4. Of course, the heat exchanger 1 can be installed in any system where a transfer of thermal energy is necessary.

[0043] In Figure 2 is shown, in an axial sectional view, a double-flow turbomachine 4 with longitudinal axis X to which the invention can be applied. Of course, other types of turbomachine are envisaged.

[0044] The dual-flow turbomachine 4 generally comprises a gas generator or gas turbine engine 5 upstream of which is mounted a fan or fan module 6. In the present invention, the terms “upstream” and “downstream” are defined in relation to the circulation of gases in the turbomachine and here along the longitudinal axis X and with reference to Figure 2 from left to right.

[0045] The fan 6 comprises blades 7 which are shrouded by a fan casing 8. The fan casing 8 carries a nacelle 9. The latter is annular, centered on the longitudinal axis X and connected to the aircraft.

[0046] In a known and non-limiting manner, the gas generator 5 comprises, from upstream to downstream, a low-pressure compressor 10a, a high-pressure compressor 10b, an annular combustion chamber 11, a high-pressure turbine 12a and a low-pressure turbine 12b. Conventionally, the turbomachine 1 comprises a low-pressure shaft 13 which connects the low-pressure compressor 10a and the low-pressure turbine 12a to form a low-pressure body and a high-pressure shaft 14 which connects the high-pressure compressor 10b and the high-pressure turbine 13a to form a high-pressure body.

[0047] The low pressure shaft 13, centered on the longitudinal axis, here drives a fan shaft 15. A speed reducer 16 can be interposed, as here, between the fan shaft 15 and the low pressure shaft 13. Advantageously, rotating guide bearings 17 also make it possible to guide the low pressure shaft 13, the high pressure shaft 14 and the fan shaft 15 in rotation relative to a fixed structure of the turbomachine.

[0048] The guide bearings 17 and the speed reducer 16 in this example configuration of the turbomachine 1 must be lubricated and / or cooled to ensure the performance of the turbomachine. The power generated by these is dissipated in a fluid coming from a fluid supply source installed in the turbomachine and which makes it possible to lubricate and / or cool various components and / or equipment of the turbomachine. Other equipment of the turbomachine or of the aircraft such as electrical machines, generators, batteries, an accessory box, electronic / electrical systems, systems for cooling the interior spaces of the aircraft, or even the exhaust gases may have significant thermal energy to transfer.

[0049] The heat exchanger 1 is described below in more detail in the context of its installation in a turbomachine and in this example makes it possible to cool the first fluid 2 by the second fluid 3. In the present example, the first fluid 2 comprises the gases leaving the compressor(s) and the second fluid 3 comprises the exhaust gases from the turbomachine 4 at an ejection nozzle 18. The exhaust gases make it possible to heat, for example, the gas leaving the compressor(s) before passing through the combustion chamber 11. Indeed, the heat of the exhaust gases is generally lost.

[0050] Alternatively, the first fluid 2 is a secondary flow generated by the blower and the second fluid 3 is a secondary flow passing through the gas generator.

[0051] Advantageously, but not limitingly, the primary flow circulates in a primary vein 19 which is delimited radially by an internal wall 20a of an annular inter-vein casing 20 and an external wall 21a of an internal casing 21. The secondary flow circulates in a secondary vein 22 which is delimited radially by at least one internal wall 8a of the fan casing 8 and a wall 20b of the inter-vein casing 20 surrounding the gas generator.

[0052] The term "radially" or "radial" is defined with respect to a radial axis Z which extends from the longitudinal axis L of the turbomachine 1 and which is perpendicular to it.

[0053] The heat exchanger 1 can be arranged in the primary vein 19 or alternatively in the secondary vein 22. According to yet another alternative, the heat exchanger can be arranged at the level of the ejection nozzle 18. Advantageously, the heat exchanger can be arranged upstream of the combustion chamber or downstream of the combustion chamber.

[0054] With reference to Figure 3, the heat exchanger 1 comprises a primary exchange surface 23 and a secondary exchange surface 24. The primary exchange surface 23 comprises two panels (or plates) respectively called a first panel

[0055] 25 and a second panel 26.

[0056] The heat exchanger 1 also comprises a plurality of fins 29 which extend between the first panel 25 and the second panel 26. The fins 29 form the secondary exchange surface 24. The fins 29 extend transversely to the first and second panels 25, 26. Advantageously, the fins 29 form channels 30 in which the first fluid 2 circulates. The first fluid 2 is intended to pass through / sweep the fins 29 and to flow between the first and second panels 25, 26.

[0057] Figure 4 shows in perspective the fins 29 of the heat exchanger 1 without the panels 25, 26. Each fin 29 has a generally flat shape and extends in a first direction D1.

[0058] The fins 29 each have a leading edge 29a and a trailing edge 29b of the first fluid 2. The leading edges 29a and trailing edges 29b are opposite each other along the first direction D1. The leading edges 29a and trailing edges 29b longitudinally delimit the fins 29. The leading edge 29a is the edge by which the first fluid 2 first comes into contact with the fin 29. The trailing edge 29b is the edge with which the first fluid 2 is last in contact with the fin 29. The leading edges 29a and trailing edges 29b extend generally along the second direction D2. Each fin 29 also comprises a first exchange surface 29c and a second exchange surface 29d which are connected to each other by the leading edges 29a and trailing edges 29b. In the example shown, the first and second exchange surfaces 29c, 29d are opposite in a third direction D3.The third direction D3 is perpendicular to the first and second directions D2, D3.

[0059] Advantageously, each fin 29 has in this example a generally rectangular shape. According to yet another alternative, the fins 29 have a trapezoidal shape or any other shape or can still be inclined relative to the plane D1, D2 in the example of figure 4.

[0060] We use the term "direction" to describe the heat exchanger in particular. In the installation situation, the first direction D1 is parallel to the longitudinal axis X of the turbomachine 1. The fins 29 are arranged in several rows R1, R2, Rn following the first direction D1. Each row of fins comprises several fins 29. The rows of fins 29 are parallel to each other. In the present case, the rows R1, R2, Rn of fins 29 are parallel to the third direction D3.

[0061] As illustrated in Figure 4, the fins 29 are also arranged in a staggered pattern. More specifically, the fins 29 are offset along the third direction D3. Advantageously, the fins 29 of every other row are located in the same plane parallel to the plane D1, D2. This arrangement makes it possible to improve the heat exchange by interruption and regular reformation of the thermal boundary layer on the surface of the fins 29. The thermal boundary layer is interrupted at the trailing edge of each fin 29 and reforms at the leading edge of each fin 29.

[0062] Advantageously, each fin 29 is located at a distance from the adjacent fin 29 along the first direction D1 and at a determined longitudinal pitch PI. More precisely, the pitch PI defines the distance between the trailing edge 29b of a first fin and the leading edge 29a of a second adjacent fin and successively. Each row of fins is also at a distance from each other along this longitudinal pitch PI. Advantageously, the longitudinal pitch PI is constant.

[0063] According to another advantageous characteristic, the fins 29 of the same row are spaced apart transversely (along the third direction D3). A transverse spacing s is thus provided between each fin 29 transversely. More precisely, the transverse spacing s defines the distance between a first exchange surface 29 of a first fin 29 and a second exchange surface 29d of a second fin.

[0064] Advantageously, but not limitatively, the fins 29 of each row are connected to each other alternately by a top wall 31 and by a base wall 32. The top walls 31 and the base walls 32 have a generally planar shape and are opposite in the second direction D2. The top walls 31 and the base walls 32 extend in the first direction D1. Similarly, the fins 29 of the adjacent rows in the first longitudinal direction are connected to each other by means of the top walls 31. These top walls 31 and base walls 32 have a leading edge 33a connected to the leading edges 29a of the fins 29 and a trailing edge 33b connected to the trailing edges 29b of the fins 29. The fins 29 are fixed to the first and second panels 25, 26. Advantageously, the fixing is carried out by means of the top walls 31 and the base walls 32.Fixing can be done by welding or brazing.

[0065] The heat exchanger 1 may be presented in the form of one stage or several stages. In Figure 2 a single stage is shown. A stage is defined by the fins 29 and by the first and second panels 25, 26. In this way, the first fluid 2 circulates through the fins 29, in the channels 30 and between the two panels 25, 26 while the second fluid 3 circulates above the first panel 25 and below the second panel 26. In the case of a heat exchanger 1 with several stages, the stages would be spaced by passages in which the second fluid is intended to circulate. Each passage would be formed between two adjacent panels 25, 26 of different stages.

[0066] With reference to Figures 1 and 5, the heat exchanger 1 is annular (360°) or in the shape of an angular sector. Advantageously, the heat exchanger 1 is centered on the first longitudinal direction D1. In the installation situation, the first direction D1 is centered on the longitudinal axis X. The annular shape of the heat exchanger 1 allows better integration thereof and a reduction in the size in the turbomachine 4.

[0067] Advantageously, the annular heat exchanger 1 has an internal cylindrical surface 34a defining an internal radius Ri and an external cylindrical surface 34b defining an external radius Re. The heat exchanger 1 also has an upstream surface 35 (or front surface) and a downstream surface 36 which are opposite along the longitudinal axis (first direction). The upstream surface 35 and the downstream surface 36 are connected by the internal and external cylindrical surfaces 34a, 34b.

[0068] The heat exchanger 1 comprises an inlet E through which the first fluid 2 enters the heat exchanger 1. The inlet E is defined at the upstream surface 35. The heat exchanger 1 also comprises an outlet S through which the first fluid 2 escapes from the heat exchanger 1. The outlet S is defined at the downstream surface 36. In other words, the first fluid 2 circulates axially, from upstream to downstream, and along the longitudinal axis.

[0069] Advantageously, the heat exchanger 1 comprises another inlet and another outlet through which the second fluid 3 enters the heat exchanger. The second fluid 3 can circulate in the heat exchanger 1 axially (along the longitudinal axis) or radially (along the radial axis).

[0070] The fins are configured to improve the aerothermal and aerodynamic performance of the annular heat exchanger.

[0071] The fins 29 have a height H which varies linearly along the radial axis of the heat exchanger. Advantageously, the height H of each fin is measured between the first panel 25 and the second panel 26.

[0072] According to the embodiment of Figure 5, the first fluid flows in a direction normal to the plane of Figure 5. The lines which are arranged in the circumferential direction around the longitudinal axis and which define heights H1, H2, etc. represent trailing or leading edges or the thickness of the fin between the first and second exchange surfaces 29c, 29d along the radial section. The height H of the fins 29 increases linearly from the internal cylindrical surface 34a to the external cylindrical surface 34b. The height of the fins varies transversely to the flow of the first fluid. The fins 2 of the same row R1, R2, Rn along the radial axis have a height H1, H2, H3, H4, H5 which is different. The first and second exchange surfaces 29c, 29d of the fins 29 are defined in a plane which is perpendicular or substantially perpendicular (+ / - 5°) to the radial axis.

[0073] In this example, the fins of the same row which extends along the longitudinal axis have an identical height. In particular, the fins 29 which are closer to the longitudinal axis have a height H1 which is the minimum and the fins which are furthest from the longitudinal axis have a height Hn which is the maximum.

[0074] The hydraulic diameter of the heat exchanger is larger at the outer cylindrical surface 34b. The first fluid can flow easily and with less resistance at the fins close to the outer cylindrical surface 34b compared to the first fluid entering the heat exchanger at the fins close to the inner cylindrical surface 34a. The flow rate is lower close to the inner cylindrical surface. With the variation in height, the heat exchange is also improved and pressure losses are avoided.

[0075] As can be seen in Figure 5, the transverse spacing s between the fins 29 along the radial axis is constant. The first fluid 3 is oriented in the axis normal to the plane of Figure 5. In other words, the first fluid 2 circulates along the longitudinal axis. The spacing s is for example between 5 and 100 mm. With a constant transverse spacing s, the heat exchanger is more “permeable” near the internal cylindrical surface 34a, which implies that the first fluid will tend to “pass” rather than through the internal cylindrical surface 34a and have a higher speed.

[0076] Advantageously, the fins 29 each have a predetermined length L which is constant. The length L of each fin is measured (along the first direction D1 (longitudinal axis) and) between the leading edge 29a and the trailing edge 29b. The length L of each fin 29 is for example between 0.5 mm and 150 mm. Advantageously, the length L of the fins can vary linearly.

[0077] According to the embodiment of Figure 6, the height H of the fins 29 and the transverse spacing s between the fins of the same row vary. Here, the transverse spacing s1, s2, s3, s4, s5, s6 between each fin 29 along the radial axis decreases or diminishes from the internal cylindrical surface 34a to the external cylindrical surface 34b. The variation of the spacing s is advantageously continuous. The spacing s increases here with the radius of the heat exchanger (i.e. along the radial axis).

[0078] The height H increases linearly from the inner cylindrical surface 34a to the outer cylindrical surface 34b. The fins 29 which are close to the longitudinal axis have the same height H1. The fins of each row and which are furthest from the longitudinal axis also have the same height H5. As the height of the fins increases, the permeability of the heat exchanger also increases. The velocity of the first fluid 2 is greater, particularly near the outer cylindrical surface 34b.

[0079] Advantageously, the transverse spacing s close to the longitudinal axis is between 5 mm and 100 mm and the transverse spacing s between the fins furthest from the longitudinal axis is between 5 mm and 50 mm. Varying the transverse spacing s allows compensation and adjustment of the permeability that has increased due to varying the fin heights. The transverse spacings decrease with the radius of the heat exchanger. The distribution of the second fluid is more homogeneous.

[0080] In this example of Figure 6, the length L of the fins is constant but can also vary linearly. The longitudinal pitch PI between each fin 29 is constant. The longitudinal pitch can be between 0.5 mm and 50 mm.

[0081] Figure 7 schematically represents, in radial section, a heat exchanger 1 mounted in the turbomachine. The heat exchanger 1 is annular and centered on the longitudinal axis X. The heat exchanger 1 has several stages which are arranged around the longitudinal axis X. The pattern formed by the fins 29 between two panels 25, 26 is non-uniform. The first and second panels 25, 26 each extend radially relative to the longitudinal axis X. The first and second exchange surfaces 29, 29d of each row of fins 29 are defined in planes perpendicular to the radial axis. The exchange surfaces 29c, 29d are swept by the first fluid along the longitudinal axis. The channels 30 formed by the fins 29 open onto the upstream surface 35 and onto the downstream surface 36.

[0082] The length L of the fins 29 also extends axially. Between each stage is formed the passage 37 intended for the circulation of the second fluid. Each passage 37 extends between a radially internal end 37a and a radially external end 37b.

[0083] Advantageously, the radially inner end 37a of the passages 37 opens into the inner cylindrical surface 34a. The radially outer end 37b opens into the outer cylindrical surface 34b.

[0084] According to another advantageous characteristic, the passages 37 open into the upstream surface 35 which can form an inlet for the second fluid 3. The passages 37 also open into the downstream surface which can form an outlet for the second fluid 3.

[0085] The height H of the fins 29 increases along the radial axis (i.e. from the central axis of the heat exchanger 1 to the position furthest from the center). The transverse spacing s is constant in Figure 7.

[0086] The length of each fin 29 can be defined linearly. The variation in length can be a function of the mean radial coordinate of the fin and be defined by a parameter Δ r = where s is the transverse spacing between the fins 29 and in function of the radial position of the fin in cylindrical coordinates. A cylindrical coordinate system allows a given point in a space to be located in a known manner using an azimuthal angle, a height, and a radius relative to a principal axis (here the longitudinal axis).

[0087] For example, the parameter X r can be between 1.2 and 1.8.

[0088] Alternatively, but not limited to, the fins are wavy and staggered.

[0089] Advantageously, in the case where the transverse spacing s decreases as the fin height H increases, this makes it possible to have a relatively constant hydraulic diameter over the entire upstream, frontal surface of the heat exchanger for the first fluid 2 considered: with s the transverse spacing between two fins consecutive along the radial axis, H the fin height and D H 0 the average reference hydraulic diameter.

[0090] The first fluid 2 circulates along the longitudinal axis. The first fluid 2 advantageously enters the heat exchanger at the upstream, front surface 35 and leaves it at the downstream surface 36. Similarly, the second fluid 3 circulates along the longitudinal axis and / or along the radial axis.

[0091] Advantageously, the fins 29, the first panels 25 and the second panels 26 are formed from a single piece (made from a single piece or monobloc). Advantageously, these are obtained by an additive manufacturing process and in particular selective fusion on powder beds known by the English acronym SLM for "Selective Laser Melting". This process is particularly suitable for producing the annular heat exchanger in a single piece. In particular, the process makes it possible to obtain complex shapes and parts with good strength and mechanical characteristics. The principle of SLM additive manufacturing is based on the fusion of thin two-dimensional (2D) layers of powder, for example metallic, plastic, or ceramic, using a high-power laser.

[0092] In the context of this additive manufacturing process, the heat exchanger is devoid of top walls and base walls. The process in fact allows a direct connection of the fins and the first and second panels 25, 26. Thus, additive manufacturing and the absence of these walls allow a weight saving. Additive manufacturing is carried out from an SLM installation which generally comprises a feed tank containing a powder and a manufacturing support on which the part to be manufactured is produced, in this case the heat exchanger 1. The installation also comprises a sweeping element making it possible to transfer a quantity of the powder from the feed tank onto the manufacturing support which is mounted movably following a vertical translation Z.The installation also includes a laser beam generation element for melting the powder intended to produce the part and means for directing the laser beam towards the support, such as mirrors. A recycling tank allows the recycling of unused or unmelted powder.

[0093] The process involves manufacturing the part by superimposing layers of powder from the feed tank and transferring them to the manufacturing support. These layers of powder are then melted one after the other using the laser beam moving over the surface of each layer. The powder temperature is raised to a temperature higher than the melting temperature of the powder via the laser beam. The melted layers solidify gradually and form a single block.

[0094] Advantageously, the different layers intended to form the heat exchanger are superimposed along a manufacturing axis which is parallel to the first direction D1.

Claims

CLAIMS 1 . Heat exchanger (1) for a turbomachine (4), in particular an aircraft turbomachine, with a longitudinal axis (X), the heat exchanger (1), annular and centered on the longitudinal axis, being intended to carry out a heat exchange between a first fluid (2) and a second fluid (3), the heat exchanger (1) comprising at least a first panel (25), a second panel (26) and a plurality of fins (29) extending between the first and second panels (25, 26), the first panel (25) and the second panel (26) extending radially between an internal cylindrical surface (34a) and an external cylindrical surface (34b) of the heat exchanger (1), the fins (29) having a first and second exchange surface (29c, 29d) which are defined in planes substantially perpendicular to the radial axis of the heat exchanger and intended to be swept by the first fluid (2) following the longitudinal axis, the fins (29) of each row (R1, R2,Rn) having a height (H) which is on the one hand, measured between the first and second panels (25, 26) and which on the other hand, increases radially, between the internal cylindrical surface (34a) and the external cylindrical surface (34b), characterized in that the fins (29) are arranged in several rows (R1, R2, Rn) along the longitudinal axis and are arranged in a staggered manner, each row (R1, R2, Rn) of fins (29) being parallel to each other and connected to each other and in that the longitudinal pitch (PI) defining a distance between a trailing edge (29b) of a first fin of the plurality of fins and a leading edge (29a) of a second adjacent fin and successively of the plurality of fins, is constant., 2. Heat exchanger (1) according to claim 1, characterized in that the fins (29) are spaced radially by a transverse spacing (s) which is constant.

3. Heat exchanger (1) according to claim 1, characterized in that the fins (29) are radially spaced by a transverse spacing (s), the transverse spacing (s) decreasing from the internal cylindrical surface (34a) towards the external cylindrical surface (34b).

4. Heat exchanger (1) according to one of the preceding claims, characterized in that each fin (29) has a length (L) along the longitudinal axis which is constant.

5. Heat exchanger (1) according to one of claims 1 to 3, characterized in that each fin (29) has a length (L) along the longitudinal axis which varies from upstream to downstream.

6. Heat exchanger (1) according to any one of the preceding claims, characterized in that the first panel (25), the second panel (26) and the fins (29) between the first and second panels (23, 24) form a stage and in that the heat exchanger (1) comprises several stages, the stages being spaced apart by passages (37) intended for the circulation of the second fluid (3), the passages (37) opening onto an upstream surface (35) and onto a downstream surface (37).

7. Heat exchanger (1) according to any one of the preceding claims, characterized in that it is made in a single piece.

8. Heat exchanger (1) according to any one of claims 1 to 6, characterized in that the fins (29) are connected alternately by top walls (31) and base walls (32), the top walls (31) and the base walls (32) being connected respectively to the first and second panels (25, 26).

9. Heat exchanger (1) according to any one of claims 1 to 8, characterized in that it comprises an inlet defined in an upstream surface (35) in which the first fluid and / or the second fluid enter(s) the heat exchanger (1) and an outlet defined in an opposite downstream surface along the longitudinal axis (X) through which the first fluid and / or the second fluid is(are) discharged from the heat exchanger (1).

10. Heat exchanger (1) according to any one of claims 1 to 9, characterized in that it comprises an inlet defined in the internal cylindrical surface (34a) through which the second fluid enters the heat exchanger (1) and an outlet defined in the external cylindrical surface (34b) through which the second fluid is discharged from the heat exchanger (1).

11. Heat exchanger (1) according to any one of claims 5 to 10, characterized in that the length (L) of the fins (29) is defined linearly and s(R • is determined using the parameter À r = , where s is the transverse spacing (s) s(^max) between the fins (29) of the same row and as a function of the radial position of the fin (29) in cylindrical coordinates, Rmin being a minimum radius of the heat exchanger (1) defined by the internal cylindrical surface (34a) and Rmax being a maximum radius of the heat exchanger (1) defined by the external cylindrical surface (34b).

12. A turbomachine with a longitudinal axis X comprising a heat exchanger according to any one of the preceding claims, the first and second panels (25, 26) are arranged regularly around the longitudinal axis (X), the fins (29) being arranged between the first and second panels (25, 26).

13. A method of manufacturing a heat exchanger according to any one of claims 1 to 11, characterized in that the method comprises a step of producing the heat exchanger (1) by additive manufacturing by selective fusion on powder beds.

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