Cooling air injection housing for a turbomachine turbine

Description

DOMAINE DE L'INVENTION

[0001] The invention relates to the field of ventilation of a turbomachine turbine, in particular the ventilation of a high-pressure turbine of a twin-spool turbomachine, such as an aircraft turbojet.

[0002] More specifically, the invention relates to an air injection casing for cooling the rotor disc of a turbine, in particular a high-pressure turbine, of a turbomachine. ETAT DE LA TECHNIQUE

[0003] A twin-spool turbomachine includes in particular a high-pressure turbine, which is positioned at the outlet of a combustion chamber to recover energy from the combustion gas flow and thus drive rotation of a high-pressure compressor, arranged upstream of said combustion chamber and supplying the latter with pressurized air (see figure 1 attached).

[0004] In the remainder of the description and the claims, the terms "upstream" and "downstream" are to be taken into consideration in relation to the direction of air flow inside the high-pressure turbine, as well as inside the cooling air injection casing according to the invention.

[0005] Typically, and as can be seen on the figure 1 attached which illustrates the state of the art, a high-pressure turbine A comprises a rotor disc B, arranged at the outlet of the combustion chamber C and on which are mounted turbine blades D, driven in rotation by the flow of gas ejected by this combustion chamber.

[0006] Due to the high temperatures reached by the combustion gases, the rotor disc B, and the turbine blades D that it carries, are subjected to significant thermal stresses that can cause expansion. To limit the negative impact of these thermal stresses on the service life of the turbine blades, the latter are equipped with internal cooling circuits that include ducts traversed by ventilation air taken from the bottom of the combustion chamber.

[0007] This ventilation air is generally brought into an annular cavity by ventilation air injectors E distributed circumferentially around the longitudinal axis of the turbomachine. The injectors E extend below the combustion chamber and are connected to an annular bypass space F, this annular space making it possible to convey ventilation air from the bottom of the compressor to the turbine of the turbomachine.

[0008] The ventilation air, leaving the injectors E, enters an annular cavity F located upstream of the rotor disc B, passing through orifices G formed in a sealing flange H arranged upstream of the rotor disc. The cavity F communicates with the internal cooling circuits arranged inside the turbine blades.

[0009] Reference may be made to publications FR 2,841,591 and FR 2,937,371 which describe examples of such high-pressure turbine architecture.

[0010] Two aerodynamic parameters generally drive the shape of an injector: the flow of air taken which is calibrated by the section at the neck of an injector, and the tangential speed at the outlet of the injector (or more generally the entrainment coefficient K) of the air which is involved in the relative total temperature, which is globally the total temperature seen by the rotors.

[0011] Thus, the relative total temperature T r,t,1 is expressed as follows: T r , t , 1 = T t , 1 + 1 − 2 K ⋅ Ω rotor ⋅ r 2 2 C p , avec K = V θ , air V θ , rotor = V θ , 1 Ω rotor ⋅ r Or T t,1 denotes the absolute total temperature in Kelvin K Ω rotor denotes the rotor rotation speed in rad / sr denotes the radius relative to the motor axis in m C p denotes the specific heat capacity at constant pressure (J / Kg / K) V θ ,air denotes the tangential speed of the air at the radius r considered in m / s V θ ,rotor = Ω rotor * r denotes the tangential speed of the rotor at the radius r considered in m / s.

[0012] The higher the ratio of tangential air velocity to entrainment coefficient K, the higher the relative total temperature T r,t,1 decreases.

[0013] Generally, the injectors are axial (i.e. the air circulates substantially parallel to an axis of rotation of the turbomachine) and consist of either a crown of independent holes inclined at a fixed angle, or a row of static blades, resulting in a significant mass of the assembly.

[0014] This architecture has the advantage of drawing low power from the rotor and not causing too much temperature increase in the turbine.

[0015] However, this architecture needs to be improved to better control the seals located near the injector and guarantee good control of the air flow, as well as good distribution of ventilation.

[0016] Already known from documents FR 3101 670 and US 2020 / 0240279 are cooling air injection casings provided with air injection channels, but the latter do not extend in an axial plane but on the contrary in a plane perpendicular to the longitudinal axis of the casing. Also known from document WO 2019 / 180365 is a bearing support comprising an angled duct but which does not have undulations as in the present invention and which serves only for supplying oil to the bearing. EXPOSE DE L'INVENTION

[0017] An aim of the invention is to improve the following aspects: Improved airflow in the injectors to maximize airflow at the injector necks without introducing pressure drop, while reducing the risk of air separation, thus resulting in improved robustness of the device regardless of the turbine operating point, Reduced leakage rates through sealing devices placed near the injectors, due to the injector outlet being placed at a smaller radius than the injector inlet Significant reduction in the mass of the air injection casing compared to conventional air injection casings (by at least 50%).

[0018] To this end, the invention relates to a casing for injecting cooling air into a bladed rotor disc of a turbine, in particular a high-pressure turbine, of a turbomachine, the casing extending around a longitudinal axis and being traversed by at least one channel forming an air injector, the channel comprising an inlet mouth and an outlet mouth.

[0019] According to the invention, the channel comprises a primary section which extends in an axial plane from the inlet mouth to a bend and a secondary section which extends from this bend to the outlet mouth, the secondary section having a progressive variation in its orientation according to a tangential component between the section of the bend and the outlet section of the outlet mouth, the channel has a reduction in section between the inlet section of the inlet mouth and the section of a neck, and the channel has at least one undulation in its primary section, so that the outlet mouth is located closer to the longitudinal axis than the inlet mouth.

[0020] Thanks to these characteristics of the invention, and in particular thanks to the combination of the reduction in section between the inlet mouth and the neck, its orientation according to a tangential component and the fact that the outlet mouth is located at a lower radial level than the inlet mouth, a synergy is obtained in improving the cooling. Indeed, the reduction in section and the tangential orientation increases the tangential velocity component of the injected air and the fact that the outlet mouth is closer to the longitudinal axis makes it possible to inject the air at a location where the tangential velocity of the high-pressure turbine is lower.

[0021] Furthermore, the corrugation helps to limit pressure losses in the channel and prevents the air from slowing down inside it.

[0022] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination:said at least one undulation of the channel comprises, from upstream to downstream relative to the direction of circulation of the air in the channel, a first curved part whose concavity is oriented towards the longitudinal axis then a second curved part whose convexity is oriented towards the longitudinal axis; the outlet mouth of the channel has an outlet section which extends tangentially and in a plane perpendicular to the longitudinal axis; the elbow is oriented so that the air flow leaving the outlet mouth circulates tangentially in the same direction as the direction of rotation of the rotor disk intended to be cooled; the ratio between the inlet section of the inlet mouth and the section of the throat is greater than or equal to 2, preferably is between 2 and 10; the evolution of the section of the channel between the inlet mouth and the throat is strictly monotonically decreasing;the casing comprises an annular outer wall flared from upstream to downstream, a radially inner wall extending downstream from said outer wall and supporting a radially inner sealing device, a radially outer wall extending from said outer wall, and an end wall joining the respective downstream ends of the radially inner wall and the radially outer wall, this end wall extending in a plane perpendicular to the longitudinal axis, the flared annular outer wall, the radially inner wall, the radially outer wall and the end wall together define an annular inner cavity, the channel is arranged at least partly in this inner cavity and the outlet mouth of the channel is formed in the end wall; the inlet mouth is formed in the flared annular outer wall and is rectangular in shape;the inlet mouth of the channel comprises a tube of circular section, which projects axially and upstream from said flared annular outer wall; the casing comprises an annular wall which extends axially downstream from said radially outer wall and which supports a radially external sealing device; said end wall comprises at least one dust removal hole; the outlet mouth is rectangular in shape.;

[0023] The invention also relates to a high-pressure turbine of a turbomachine comprising at least one bladed rotor disc provided with a hub. According to the invention, this turbine comprises a cooling air injection casing as mentioned above and the casing is arranged upstream of the rotor disc so that these outlet openings are located opposite the hub.

[0024] The invention also relates to a turbomachine comprising at least one cooling air injection casing as mentioned above.

[0025] The invention also relates to a method for manufacturing a cooling air injection casing as mentioned above in which said cooling air injection casing is produced by additive manufacturing. DESCRIPTION DES FIGURES

[0026] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: [ Fig. 1 ] there figure 1 is an axial sectional view of a part of a state-of-the-art turbomachine equipped with a rotor cooling circuit. Fig. 2 ] there figure 2 is an axial sectional view of a turbomachine according to the invention. Fig. 3 ] there figure 3 is a perspective view of an angular portion of the annular cooling air injector casing according to the invention. Fig. 4 ] there figure 4 is a partial perspective and axial sectional view of one of the injectors of the casing according to the invention. Fig. 5 ] there figure 5 is a sectional and top view of one of the injectors of the casing according to the invention. Fig. 6 ] there figure 6 is a perspective view of an angular portion of the annular cooling air injector casing according to the invention, representing a first embodiment of the inlet mouth of the injectors. Fig. 7 ] there figure 7 is a perspective view of an angular portion of the annular cooling air injector casing according to the invention, representing a second embodiment of the inlet mouth of the injectors. Fig. 8 ] there figure 8 is a perspective view of an angular portion of the casing according to the invention, the casing being cut along an axial section plane. Fig. 9 ] there figure 9 is a detail view of a portion of the casing. Fig. 10 ] there figure 10 is a view showing a part of the casing according to the invention and the supports which are used for its manufacture by additive manufacturing. Fig. 11 ] there figure 11 is a detail view showing part of the casing and one of the supports of the figure 10 . [ Fig. 12 ] there figure 12 is a perspective view of an angular portion of the annular cooling air injector casing according to the invention and of an angular portion of a rotor disc to be cooled. DESCRIPTION DETAILLEE DE L'INVENTION

[0027] The invention applies to a turbomachine turbine, in particular to a high-pressure turbine of a twin-spool turbomachine, such as an aircraft turbojet. Such a turbomachine is shown in the figure 2 .

[0028] In this figure, it can be seen that the turbomachine 1 extends around a longitudinal axis X-X'. This turbomachine 1 comprises from left to right, that is to say from upstream to downstream with reference to the gas flow which flows therein during operation: a fan 10, a low pressure compressor 11, a high pressure compressor 12, a combustion chamber 13, a high pressure turbine 14 and a low pressure turbine 15.

[0029] The high-pressure turbine 14 comprises at least one rotor disc 140 having a hub 141 and a plurality of blades 142 fixed to the periphery of this hub.

[0030] The rotor disc 140 is centered on the X-X' axis.

[0031] In the remainder of the description and claims, the term "axial" designates the direction along the axis XX' and the term "radial" designates a direction perpendicular to the axis X-X'.

[0032] A possible embodiment of the cooling air injection casing 2 according to the invention will now be described. It has a shape of revolution, with an axis X-X'.

[0033] The casing 2 is crossed by at least one channel 20 which forms an air injector, preferably by several channels 20.

[0034] Each channel 20 has an inlet mouth 201 and an outlet mouth 202. The inlet mouth 201 makes it possible to take part of the air located under the combustion chamber to cool the rotor.

[0035] As it appears better on the figures 5 And 8 , each channel 20 successively comprises from upstream to downstream a primary section 203 then a secondary section 207.

[0036] The primary section 203 extends from the inlet mouth 201 to an elbow 206 in an axial plane P, this plane P including the longitudinal axis X-X'.

[0037] The secondary section 207 extends from this elbow 206 to the outlet mouth 202.

[0038] The secondary section 207 has a progressive variation in its orientation according to a tangential component Z between the section Φ206 of the elbow 206 and the outlet section Φ202 of the outlet mouth 202. By “progressive variation in orientation”, we mean a variation in the orientation of a vector normal to the center of a section of the channel 20 and having as its origin the center of said section.

[0039] Preferably, the outlet section Φ202 of the outlet mouth 202 of each channel 20 extends tangentially in a plane P1 perpendicular to the longitudinal axis X-X'. In addition, the elbow 206 is advantageously oriented so that the air flow leaving the outlet mouth 202 circulates tangentially in the same direction as the direction of rotation of the rotor disk facing it.

[0040] As seen on the figure 8 , the outlet mouth 202 is located closer to the longitudinal axis XX' than the inlet mouth 201. In other words, the radius R1 between the point of the inlet mouth 201 located most radially inside is greater than the radius R2 of the point of the outlet mouth 202 located most radially inside. The air taken is thus brought to a smaller radius R2 thereby increasing the air entrainment coefficient, which allows a larger surface area of the rotor to be cooled and which also allows better compression of the air in the rotor cooling circuit.

[0041] Each channel 20 has a reduction in section between the inlet section Φ201 of the inlet mouth 201 and the section Φ204 of a neck 204. The neck 204 thus corresponds to the point of the channel 20 which has the smallest cross-section.

[0042] Preferably, the ratio between the inlet section Φ201 of the inlet mouth 201 and the section Φ204 of the neck 204 is greater than or equal to 2. More preferably, this ratio is between 2 and 10.

[0043] Furthermore, the evolution of the section of the channel 20 between the inlet mouth 201 and the neck 204 is preferably strictly monotonically decreasing.

[0044] This reduction in section makes it possible to increase the air speed in the channel

[0045] As can be seen on the figure 5 , advantageously, the elbow 206 is upstream of the neck 204.

[0046] Furthermore, each channel 20 has at least one corrugation 205 in the primary section 203. This corrugation 205 extends in the axial plane P.

[0047] By "undulation" is meant the fact of having two successive curved portions of respective opposite orientations. Thus, the channel 20 comprises from upstream to downstream, that is to say from the right to the left of the figure 8 , successively a first curved part 205a whose concavity is oriented towards the longitudinal axis XX' then a second curved part 205b whose convexity is oriented towards the longitudinal axis (X-X').

[0048] The 205 corrugation limits pressure losses in the channel and prevents a reduction in the speed of the air circulating there.

[0049] Advantageously, the casing 2 comprises at least seven channels 20 forming injectors in order to minimize aerodynamic heterogeneities in the rotor cooling circuit.

[0050] The casing 2 can have different shapes, a particular embodiment of which will now be described.

[0051] As it appears better on the figure 3 , the casing 2 comprises an annular outer wall 31, flared from upstream to downstream, a radially inner wall 32, a radially outer wall 33, an end wall 34 and an axial wall 36. These different walls are annular and centered on the axis X-X'.

[0052] The annular outer wall 31 has the function of separating the cavity located under the combustion chamber and the cavities intended to cool the high pressure rotor.

[0053] The radially inner wall 32 extends downstream from the outer wall 31. More specifically, this wall 32 comprises a first part 321, which extends in an axial direction from the inner face 310 of the annular outer wall 31, a second part 322, which is inclined from the downstream end of the first part 321 downstream and towards a point located closer to the longitudinal axis XX' than the first part 321 and finally a third part 323, which extends in an axial direction and downstream from said second part 322.

[0054] As it appears better on the figure 8 , the radially inner part of the channel 20 substantially matches the shape of the radially inner wall 32.

[0055] The radially outer wall 33 extends downstream from the outer wall 31. More specifically, this wall 33 comprises a first portion 331, which extends in an axial direction from the inner face 310 of the annular outer wall 31, a second portion 332, which is inclined from the downstream end of the first portion 331 upstream and towards a point located closer to the longitudinal axis XX' than is the first portion 331, a third portion 333 which is inclined from the second portion 332 downstream and towards a point located even closer to the longitudinal axis XX' than is the second portion 332 and finally a fourth portion 334, which extends in an axial direction and downstream from the third portion 333.

[0056] The radially outer wall 33 has the function of separating the mixing cavity located at the outlet of the injectors into two smaller cavities, in order to maintain the high speed of the air at the outlet of the injectors (channels 20) and therefore an acceptable cooling efficiency of the high pressure rotor.

[0057] The end wall 34 joins the respective downstream ends of the radially inner wall 32 and the radially outer wall 33, more precisely the respective downstream ends of the third part 323 and the fourth part 334. This end wall 34 extends in a plane P1 perpendicular to the longitudinal axis X-X'.

[0058] The flared annular outer wall 31, the radially inner wall 32, the radially outer wall 33 and the end wall 34 together define an annular inner cavity 35.

[0059] The axial wall 36 extends axially downstream from the downstream end of the first part 331 of the radially outer wall 33 in the extension thereof.

[0060] Preferably, the radially inner wall 32 and more precisely its third part 323 supports a radially inner sealing device 4. This sealing device 4 is fixed on the radially inner face 3230 of the third part 323.

[0061] Also preferably, the axial wall 36 supports a radially external sealing device 5. This sealing device 5 is fixed on the radially internal face 360 of the axial wall 36.

[0062] Preferably, the radially outer wall 33 is provided with an annular rib 335 which extends axially from the second part 332 and which makes it possible to axially wedge the radially external sealing device 5.

[0063] The main function of the sealing device 4 is to limit the leakage flow coming from the outlet of the high-pressure compressor and going towards the cavities of the high-pressure turbine. The device 5 makes it possible to calibrate the flow coming from the injector and the device 4 in order to be able to sufficiently seal and cool the cavity located between the high-pressure distributor and the rotor disc of the high-pressure turbine.

[0064] The different channels 20 are formed inside the cavity 35.

[0065] As it appears better on the figures 6 et 7 , the inlet mouth 201 of each channel 20 opens through the annular outer wall 31.

[0066] According to a first embodiment shown in the figure 6 , this inlet mouth 201 has a rectangular shape.

[0067] According to a second embodiment shown in the figure 7 , this inlet mouth comprises a tube 201a, which extends axially and projects upstream from the flared outer wall 31. Thus, in the case where the turbine incorporates a sub-assembly obstructing one or more injectors, known under the English terminology of " variable cooling » or a mechanical subassembly taking air to cool it in a heat exchanger then returning it to the injectors, known by the English terminology of « cooled cooling », tube 201a is better suited because it allows the tubes associated with the aforementioned subassemblies to be inserted.

[0068] The outlet mouth 202 of each channel 20 opens through the end wall 34. Preferably, this outlet mouth 202 is rectangular in shape.

[0069] According to the invention, this cooling air injection casing 2 can be manufactured by an additive manufacturing method. This method will now be described in more detail in connection with the figures 10 et 11 .

[0070] When manufactured by additive manufacturing, this casing 2 has the advantage of being a single piece (i.e. monobloc).

[0071] Such an additive manufacturing process can, for example, be a laser powder bed fusion process or an electron gun fusion process.

[0072] These methods consist of depositing successive layers of the powder of the material constituting the casing to be manufactured, here a metallic powder, on a horizontal manufacturing plate 6 and of fusing each layer of powder with the previous one, according to the diagram of the structure of the casing 2 to be obtained, by an energy input, namely by a laser beam or an electron gun.

[0073] The printing direction of the part is represented by arrow F1.

[0074] Printing is carried out starting from the downstream end of casing 2 (located at the bottom on the figure 10 ), in order to minimize the number of printing supports required and the risk of deformation of excessively inclined walls.

[0075] Two supports are required for manufacturing.

[0076] A first support 61 makes it possible to support the end wall 34 and the walls 32 and 33. This support 61 has projecting elements 610 (as many as there are channels 20 to be formed). Each projecting element 610 of substantially triangular section makes it possible to support the most inclined wall of the channel 20, located between the neck 204 and the outlet mouth 202.

[0077] A second support 62 supports the annular rib 335 which is horizontal relative to the plate 6 during manufacturing.

[0078] It will be noted that when the casing 2 is manufactured by an additive manufacturing process, the parts 322, 332 and 333 of the walls 32, respectively 33 are inclined at an angle which does not exceed 40° relative to the vertical, in order to be able to be manufactured without support.

[0079] Once additive manufacturing is complete, all that is required is machining to remove supports 61 and 62 from the resulting casing 2.

[0080] Finally, it will be noted that a dust removal hole 340, formed in the end wall 34 and opening into the cavity 35, allows the metal powder remaining in this cavity to be evacuated and allows this same cavity to be pressurized during use of the casing 2. The number of holes 340 is identical to the number of channels 20.

[0081] Finally, the functional surfaces, i.e. the internal faces of the channels 20 forming injectors and the surfaces which will be in contact with other parts are polished.

[0082] The casing 2 is then positioned opposite the rotor disc 140, as shown in the figure 12 . This positioning is carried out so that the radially internal sealing device 4 (visible only on the figure 3 ) and which is fixed on the third part 323 of the wall 32 either opposite the radially internal sealing tabs 143 of the disc 140 and that the radially external sealing device 5 (visible only on the figure 3 ) and which is fixed on the axial wall 36 either opposite the radially external sealing tabs 144 of the disc 140.

[0083] The invention has many advantages.

[0084] The reduction in the cross-section and the inclination of the channels 20 forming the air injectors makes it possible to obtain a tangential velocity at the outlet mouth 202 that is higher than with the conventional injectors currently used (set of blades). A higher tangential velocity results in a lower relative total temperature of the cooling air and therefore better cooling of the rotor discs.

[0085] This casing also results in a reduction in leaks through sealing devices 4 and 5.

[0086] In fact, the leakage section through the devices 4 and 5 is defined as follows: S = 2 * R * j where R is the radius of the sealing device 4 or 5 relative to the motor axis and j the clearance between the stator and the top of the sealing device lips.

[0087] The leakage flow rate Q is: Q = ρ*V*S where ρ is the density, V the air velocity through the sealing device.

[0088] As the outlet of the channels is located at a smaller radius (compared to straight or constant radius injectors relative to the engine axis), devices 4 and 5 are also located at a smaller R, so S decreases and therefore the leakage flow rate Q also decreases.

[0089] Finally, the mass of the entire casing is reduced by more than 50% compared to conventional injector casings.

Claims

1. A casing (2) for injecting cooling air into a bladed rotor disc of a turbine, in particular a high-pressure turbine of a turbomachine, the casing extending around a longitudinal axis (X-X') and being traversed by at least one channel (20) forming an air injector, the channel (20) comprising an inlet mouth (201) and an outlet mouth (202), characterized in that the channel (20) comprises a primary section (203) which extends in an axial plane (P) from the inlet mouth (201) to a bend (206) and a secondary section (207) which extends from this bend (206) to the outlet mouth (202), the secondary section (207) having a progressive variation of its orientation according to a tangential component (Z) between the section (Φ206) of the bend (206) and the outlet section (Φ202) of the outlet mouth (202), in that the channel (20) has a reduction in cross-section between the inlet cross-section (Φ201) of the inlet mouth (201) and the cross-section (Φ204) of a neck (204), and in that the channel (20) has at least one undulation (205) in its primary section (203), so that the outlet mouth (202) is located closer to the longitudinal axis (X-X') than the inlet mouth (201).

2. The casing (2) according to claim 1, characterized in that said at least one corrugation (205) of the channel (20) comprises, from upstream to downstream with respect to the direction of air flow in the channel (20), a first curved portion (205a) whose concavity is oriented towards the longitudinal axis (X-X') and then a second curved portion (205b) whose convexity is oriented towards the longitudinal axis (X-X').

3. The casing (2) according to claim 1 or 2, characterized in that the outlet mouth (202) of the channel (20) has an outlet section (Φ202) which extends tangentially and in a plane (P1) perpendicular to the longitudinal axis (X-X').

4. The casing (2) according to claim 3, characterized in that the elbow (206) is oriented so that the air flow exiting from the outlet mouth (202) flows tangentially in the same direction as the direction of rotation of the rotor disc to be cooled.

5. The casing (2) according to any one of the preceding claims, characterized in that the ratio between the inlet cross-section (Φ201) of the inlet mouth (201) and the cross-section (Φ204) of the neck (204) is greater than or equal to 2, preferably between 2 and 10.

6. The casing (2) according to any one of the preceding claims, characterized in that the evolution of the cross-section of the channel (20) between the inlet mouth (201) and the neck (204) is strictly monotonically decreasing.

7. The casing (2) according to any one of the preceding claims, characterized in that it comprises: - an annular outer wall (31) flared from upstream to downstream, - a radially inner wall (32) extending downstream from said outer wall (31) and supporting a radially inner sealing device (4), - a radially outer wall (33) extending from said outer wall (31), and - an end wall (34) which joins the respective downstream ends of the radially inner wall (32) and the radially outer wall (33), this end wall (34) extending in a plane (P1) perpendicular to the longitudinal axis (X-X'), in that the flared annular outer wall (31), the radially inner wall (32), the radially outer wall (33) and the end wall (34) together delimit an annular inner cavity (35), in that the channel (20) is arranged at least partly in this inner cavity (35), and in that the outlet mouth (202) of the channel (20) is formed in the end wall (34).

8. The casing (2) according to claim 7, characterized in that the inlet mouth (201) is formed in the flared annular outer wall (31) and is rectangular in shape.

9. The casing (2) according to claim 7, characterized in that the inlet mouth (201) of the channel (20) comprises a tube (201a) of circular cross-section, which projects axially and upstream from said flared annular outer wall (31).

10. The casing (2) according to one of claims 7 to 9, characterized in that it comprises an annular wall (36) which extends axially downstream from said radially outer wall (33) and which supports a radially outer sealing device (5).

11. The casing (2) according to one of claims 7 to 10, characterized in that said end wall (34) comprises at least one dust removal hole (340).

12. The casing (2) according to any of the preceding claims, characterized in that the outlet mouth (202) is rectangular in shape.

13. A high-pressure turbine (14) for a turbomachine (1) comprising at least one bladed rotor disc (140) fitted with a hub (141), characterized in that it comprises a cooling air injection casing (2) according to any one of the preceding claims and in that the casing (2) is arranged upstream of the rotor disc (140) so that its outlet mouths (202) are located opposite the hub (141).

14. A turbomachine (1) characterized in that it comprises at least one cooling air injection casing (2) according to any one of claims 1 to 12.

15. A method of manufacturing a cooling air injection casing (2) according to any one of claims 1 to 12, wherein said cooling air injection casing (2) is produced by additive manufacturing.