OPTIMIZED DISCHARGE CONDITIONER GRID AND OPTIMIZED DISCHARGE VALVE

Description

Domaine Technique

[0001] The invention relates to the field of noise from aircraft propulsion systems, and more particularly to noise from discharge valves used on aircraft propulsion systems. Technique antérieure

[0002] In most configurations, aircraft propulsion systems, such as turbofans, turboprops, or open rotors, are constructed like the turbojet engine, a sectional view of which in a longitudinal plane of the turbojet engine is illustrated in figure 1 .

[0003] The turbojet engine 1 comprises a nacelle 2, an intermediate casing 3 and an inner casing 4. The nacelle 2 and the two casings 3 and 4 are coaxial and define a turbojet axial direction D AT and a turbojet radial direction D RT. The nacelle 2 defines at a first end an inlet channel 5 for a fluid flow and at a second end, opposite the first end, an exhaust channel 6 for a fluid flow. The intermediate casing 3 and the inner casing 4 delimit between them a primary fluid flow vein 7. The nacelle 2 and the intermediate casing 3 delimit between them a secondary fluid flow vein 8. The primary vein 7 and the secondary vein 8 are arranged in a turbojet axial direction D AT between the inlet channel 5 and the exhaust channel 6.

[0004] The turbojet 1 further comprises a fan 9 configured to deliver an air flow F as fluid flow, the air flow F being divided at the outlet of the fan into a primary flow Fp circulating in the primary vein 7 and into a secondary flow Fs circulating in the secondary vein 8.

[0005] The secondary vein 8 comprises a rectifier ring 10, and the primary vein 7 comprises a low pressure compression stage 11, a high pressure compression stage 12, a combustion chamber 13, a high pressure turbine 14 and a low pressure turbine 15.

[0006] Aircraft propulsion systems generally include discharge valves 16 such as, for example, valves known in English as “Variable Bleed Valves” (VBV), “Transient Bleed Valves” (TBV) or “Handling Bleed Valves” (HBV). These valves 16 have the function of regulating the operation of the turbojets 2, by adjusting the air flow at the inlet and / or outlet of the high-pressure compressor 12, to increase the pumping margin, at low speed, or during acceleration or deceleration phases. The flow thus taken is evacuated through a conduit 17, then reintroduced into the secondary vein 8 conveying the secondary flow Fs, or further downstream into the primary flow Fp, depending on the strategy employed.

[0007] In the case where the air flow is reintroduced downstream of the primary vein 7 carrying the primary flow Fp as illustrated in the figure 1 (common case for the regulation of transient regimes), a common practice for optimizing the system consists of partially obstructing the duct by a multi-perforated grid or a diaphragm. The interest of this optimization is to generate a pressure drop allowing the thermodynamic conditioning of the flow to be adapted to the fluid medium in which it will be reintroduced, within controlled mass and size constraints. The case where the grid is positioned in the duct is called a duct configuration.

[0008] In the case illustrated on the figure 2 , where the air flow is reintroduced into the secondary vein 8 carrying the secondary flow Fs, or in the case where the air flow is reintroduced into the ambient environment (common case for the regulation of low speeds), the duct 17 of the discharge system is shorter and is, conventionally, without a diaphragm. This being the case, it is common to position a grid at the downstream end of this duct 17, in order to reduce the aero-acoustic phenomena generated by the ejection of gas at high speed. The case where the grid is positioned at the end of the duct is called the free configuration.

[0009] In both cases illustrated on the figures 1 et 2 , significant acoustic radiation results from the interaction between the perforated grid and the flow passing through it. This noise, which can reach a high level on the scale of effective perceived noise in decibels, known in English by the abbreviation EPNdB for "Effective perceived noise in decibels", contributes to aircraft noise, during regime transitions and at low regimes.

[0010] Document WO 2015 / 110748 discloses a strategy for reintroducing the sampled charge, as well as the use of a micro-perforated diaphragm to minimize the acoustic penalties associated with supersonic phenomena generated downstream of this diaphragm. An acoustic treatment grid according to the prior art is also disclosed in document US2018 / 100440A1.

[0011] Among the noise sources identified during the passage of the flow through the grid, two noises are particularly annoying: the mixing noise generated as its name indicates by the mixing of the flow in the jets generated by the grid, and the shock noise which can appear when the flow becomes supersonic at the exit of the grid. Exposé de l'invention

[0012] The invention aims to propose an improved grid making it possible to optimize the mixing downstream of the grid and thus to minimize the intensity of the aero-acoustic phenomena generated by this type of discharge system and more particularly to reduce the mixing noise and the impact noise, while ensuring a perforated surface making it possible to ensure the operability of the air system.

[0013] In an object of the invention according to claim 1, there is provided an acoustic treatment grid intended to be mounted inside or at the outlet of a conduit of a discharge valve of a turbomachine of an aircraft intended to convey a gas flow (F), the grid comprising a perforated plate and circular orifices passing through the perforated plate in a first direction, the orifices having a diameter and a geometric center.

[0014] According to a general characteristic of the invention, each orifice (230) is separated from an adjacent orifice by a space whose length (e) is equal to the product of the diameter (D) of said orifice (230) with a spacing coefficient whose value is between 1.1 and 6.

[0015] The grid according to the invention makes it possible to optimize the spatial distribution of the perforations on the surface of the grid, and thus to limit the interaction of the jets coming from each perforation of the grid, which promotes rapid dissipation of the turbulent structures generated downstream of the grid-flow system, and thus makes it possible to minimize low-frequency noise, while ensuring the operability of the discharge valve.

[0016] The acoustic radiation is in fact mainly governed by the expansion of the flow through the grid, and is therefore strongly linked to the geometry of the grid. Adjusting the spacing of the plate orifices according to the diameters of the orifices makes it possible to significantly shift the acoustic radiation towards high frequencies and thus to partially remove it from the audible range.

[0017] Furthermore, since high-frequency radiation is easier to reduce using porous materials, for example, the acoustic absorption of acoustic radiation is made easier.

[0018] The range chosen for the spacing coefficient ensures a good compromise between the shift of the radiation towards high frequencies and the various compactness constraints linked to the application.

[0019] According to a first aspect of the acoustic treatment grid, the diameter of the holes in the perforated plate is preferably between 0.5 mm and 20 mm. Such a range of diameters for the holes in the perforated plate makes it possible to maximize the shift of the acoustic radiation towards high frequencies. According to a second aspect of the acoustic treatment grid, the perforated plate preferably has a thickness in the first direction of between 1 mm and 20 mm.

[0020] The range chosen for the thickness of the perforated plate makes it possible to withstand the forces exerted and the temperatures prevailing in the turbomachine in which the discharge valve comprising such a discharge grid is mounted.

[0021] According to a characteristic of the invention, the perforated plate comprises, with respect to the gas flow intended to pass through the perforated plate, an upstream face intended to receive the gas flow and a downstream face, opposite the upstream face, from which the gas flow is intended to escape, the grid further comprising a layer of porous material arranged on said downstream face of the perforated plate.

[0022] The use of a porous material on the downstream face of the grid makes it possible to attenuate the phenomena of acoustic resonance in the outlet duct, and thus to reduce the longitudinal modes which are established.

[0023] According to a fourth aspect of the acoustic treatment grid, the layer of porous material arranged on said downstream face of the perforated plate has a thickness in the first direction preferably between a first thickness equal to half the diameter of an orifice around which the layer of porous material is arranged and a second thickness equal to twenty times the greatest length of the perforated plate measured in a plane orthogonal to the first direction.

[0024] Thus, if the perforated plate has a disc shape, its thickness is preferably less than twenty times the diameter of the perforated plate.

[0025] According to a fifth aspect of the acoustic treatment grid, the perforated plate can include between 2 and 500 holes.

[0026] According to a sixth aspect of the acoustic treatment grid, the holes can be distributed evenly on the perforated plate.

[0027] According to a seventh aspect of the acoustic treatment grid, the perforated plate may comprise at least one first orifice with a first diameter and at least one second orifice with a second diameter distinct from the first diameter.

[0028] In another object of the invention, there is provided a discharge valve for an aircraft turbojet according to claim 8 comprising a duct intended to convey a gas flow mainly in a first direction from at least one inlet of the duct to at least one outlet of the duct, and at least one acoustic treatment grid as defined above mounted inside the duct or on an outlet of the duct. The first direction of the acoustic treatment grid coincides with the first direction of the discharge valve.

[0029] According to a first aspect of the discharge valve, the conduit may comprise at least one wall provided with an acoustic treatment means and located downstream of the discharge grid relative to the direction of flow of the gas flow intended to be conveyed in the conduit.

[0030] The application of an acoustic treatment means to one or more walls of the duct makes it possible to reduce the high-frequency acoustic radiation generated by the expansion of the gas flow through the grid.

[0031] According to a second aspect of the discharge valve, the acoustic treatment means of said at least one wall may comprise a layer of porous material and / or an acoustic treatment panel.

[0032] The acoustic treatment panel may be a panel comprising a honeycomb structure. The acoustic treatment means may be optimized according to the size of the holes to act on the range of frequencies radiated by said grid.

[0033] According to a third aspect of the relief valve, the shortest distance between the acoustic treatment means and the grid is less than or equal to a length equal to forty times the greatest length of the duct section, the duct section extending orthogonally to the first direction.

[0034] According to a fourth aspect of the discharge valve, the length in the first direction of the acoustic treatment means is preferably between a first length equal to half the greatest length of the section of the conduit and a second length equal to fifty times the greatest length of the section of the conduit, the section of the conduit extending orthogonally to the first direction.

[0035] According to a fifth aspect of the discharge valve, the thickness of the acoustic treatment means in a direction orthogonal to the first direction is preferably between a first thickness equal to half the diameter of an orifice of the perforated plate and a second thickness equal to twenty times the greatest length of the section of the conduit, the section of the conduit extending orthogonal to the first direction.

[0036] According to a sixth aspect of the relief valve, the conduit may comprise at least one section whose diameter varies along the first direction.

[0037] According to a seventh aspect of the relief valve, the conduit may comprise at least one section whose geometric shape of the section of the conduit varies, the section of the conduit extending orthogonally to the first direction.

[0038] According to an eighth aspect of the discharge valve, the conduit may comprise at least two outlets, at least one bifurcation, at least a first section extending between the inlet of the conduit and a bifurcation, a second section extending between a bifurcation and a first outlet, a third section extending between a bifurcation and a second outlet, at least one of said at least one grid being mounted in one of the first, second or third sections, or on one of the first or second outlets.

[0039] The use of a duct with a variable cross-section and / or a non-circular geometric shape and / or bifurcations makes it possible to minimize any areas of recirculation or detachment of the ducts (source of additional noise) and to adapt the system to the space available on the engine architecture. According to a ninth aspect of the discharge valve, said at least one grid and / or said at least one acoustic treatment means may be made of ceramic material.

[0040] The advantage of using a ceramic material is to reduce the weight of the grille while ensuring the part's resistance in the engine environment (high temperatures, etc.). In addition, acoustic treatments made from ceramic matrix composite (CMC) material have good high-temperature properties.

[0041] In another object of the invention, there is provided a turbojet according to claim 18 comprising a nacelle, an intermediate casing and a coaxial inner casing, and a discharge valve as defined above, the intermediate casing and the inner casing delimiting between them a primary fluid flow vein, the nacelle and the intermediate casing delimiting between them a secondary fluid flow vein, and the discharge valve being mounted between the primary vein and the secondary vein and configured to take a portion of the air from the primary vein and deliver it into the secondary vein.

[0042] In another object of the invention, there is provided a turbojet according to claim 19 comprising a nacelle, an intermediate casing and a coaxial inner casing, and a discharge valve as defined above, the intermediate casing and the inner casing delimiting between them a primary fluid flow vein in which a combustion chamber is mounted, the nacelle and the intermediate casing delimiting between them a secondary fluid flow vein, and the discharge valve being configured to take a portion of the air in the primary vein upstream of the combustion chamber and deliver it into the primary vein downstream of the combustion chamber. Brève description des dessins

[0043] [ Fig. 1 ] There figure 1 , already described, presents a sectional view in a longitudinal plane of a turbojet according to the state of the art with a wastegate with reinjection into the primary flow. Fig. 2 ] There figure 2 , already described, presents a sectional view in a longitudinal plane of a turbojet according to the state of the art with a wastegate with reinjection into the primary flow. Fig. 3 ] There figures 3 schematically shows a sectional view of a discharge valve provided with an acoustic treatment grid according to a first embodiment of the discharge valve. Fig. 4 ] There figure 4 presents a front view of the acoustic treatment grille of the figure 3 . [ Fig. 5 ] There figure 5 schematically shows a sectional view of a relief valve according to a second embodiment of the relief valve. Fig. 6 ] There figure 6 shows a front view of a perforated plate of the acoustic treatment grid according to a third embodiment of the acoustic treatment grid. Fig. 7 ] There figure 7 shows a front view of a perforated plate of the acoustic treatment grid according to a fourth embodiment of the acoustic treatment grid. Fig. 8 ] There figure 8 shows a front view of a perforated plate of the acoustic treatment grid according to a fifth embodiment of the acoustic treatment grid. Fig.9 ] There figure 9 shows a front view of a perforated plate of the acoustic treatment grid according to a sixth embodiment of the acoustic treatment grid. Fig.10 ] There figure 10 shows a front view of a perforated plate of the acoustic treatment grid according to a seventh embodiment of the acoustic treatment grid. Fig.11 ] There figure 11 shows a front view of a perforated plate of the acoustic treatment grid according to an eighth embodiment of the acoustic treatment grid. Fig.12 ] There figure 12 schematically shows a view of a relief valve according to a third embodiment of the invention of the relief valve. Fig.13 ] There figure 13 schematically shows a view of a relief valve according to a fourth embodiment of the relief valve. Description des modes de réalisation

[0044] On the figure 3 schematically illustrated is a sectional view of a discharge valve 20 provided with an acoustic treatment grid 22 according to one embodiment of the invention.

[0045] The discharge valve 20 for an aircraft turbojet engine according to the first embodiment of the invention comprises a cylindrical conduit 21 with a circular base of a first diameter De and intended to convey a gas flow F, and a grid 22 comprising a perforated plate 23 also cylindrical and comprising orifices 230.

[0046] The conduit 21 defines an axial direction DA parallel to the cylindrical axis of symmetry of the conduit 21 and a radial direction DR orthogonal to the axial direction DA. The sectional view of the discharge valve 20 of the figure 3 is made in a plane comprising the axial direction DA and the radial direction DR.

[0047] The perforated plate 23 comprises an upstream face 232 receiving the gas flow F and a downstream face 234 opposite the upstream face 232 through which the gas flow F escapes after passing through the perforated plate 23.

[0048] The conduit 21 is only partially obstructed by the grid 22 in the sense that the flow F can flow through the orifices 230 of the perforated plate 23 forming the grid 22, and only through these orifices 23.

[0049] The perforated plate 23 of the grid 22 may be made of a metallic material or a ceramic matrix material or another material resistant to thermal conditions, in particular when the discharge valve 20 is in operation.

[0050] The grid 22 may be mounted at an outlet end of the conduit 21 or inside the conduit 21 as indicated by the dotted portion of the conduit 21.

[0051] In addition, as indicated on the figure 3 , the grid 22 further comprises a layer of porous material 24 arranged on the downstream face 234 without covering the orifices 230. The plate 23 and the layer of porous material 24 thus form channels from the orifices 230 of the perforated plate 23.

[0052] The perforated plate 23 comprises a thickness h of between 1 mm and 20 mm, and the layer of porous material 24 comprises a thickness he.

[0053] On the figure 4 a front view of the perforated plate 23 of the figure 3 according to a first embodiment. The perforated plate 23 extends in a radial plane comprising the radial direction DR and orthogonal to the axial direction DA.

[0054] In one variant, the perforated plate 23 may be curved in the axial direction DA. In another variant, the plate 23 may be arranged inside the duct so as to form an angle of between 0 and 10° with a plane orthogonal to the axial direction DA, the orifices 230 extending in the axial direction DA, which makes it possible to slightly extend the length of the channel formed by the orifice 230 with a reduced thickness h of the plate 23.

[0055] As illustrated in the figure 4 , the perforated plate 23 comprises, in this example, 37 orifices 230 each having the shape of a circle with a second diameter D between 0.5 mm and 20 mm and a geometric center C.

[0056] The thickness he of the layer of porous material 24 is between half a second diameter D of orifice 230 and twenty times the first diameter De of the conduit 21, which corresponds to the diameter of the perforated plate 23 when the grid is mounted inside the conduit 21.

[0057] Each orifice 230 is separated from the other adjacent orifices by a length e of between 1.1 times and 6 times the second diameter D of the orifice. By adjacent orifices is meant two orifices having no other orifices between them. The length e separating the two orifices is measured from the center of the first orifice to the center of the second orifice.

[0058] On the figure 5 a sectional view of a discharge valve 20 according to a second embodiment of the invention is illustrated.

[0059] The second embodiment differs from the first embodiment illustrated in the figure 3 in that the duct 21 comprises a portion of duct 210 located downstream of the grid 22 relative to the direction of the gas flow F, this portion of duct 210 being provided with an acoustic treatment panel 25. In a variant, the acoustic treatment panel could be replaced by a layer of porous material.

[0060] The acoustic treatment panel 25 comprises a core having a honeycomb structure forming resonant sound absorption cavities. The cavities are tuned over a range of frequencies to be treated.

[0061] The acoustic treatment panel 25 extends along the wall of the duct portion 210, that is to say in the axial direction DA, over a length Lm between an upstream end 251 and a downstream end 252 relative to the direction of the gas flow F. The length Lm is between a first length equal to half the first diameter De of the duct 21 and a second length equal to fifty times the first diameter De of the duct 21.

[0062] The upstream end 251 of the acoustic treatment panel 25 is separated from the grid 22 by a length Sm in the axial direction DA less than or equal to forty times the first diameter De of the duct 21.

[0063] The acoustic treatment panel 25 further comprises a thickness hm in the radial direction DR between a first thickness equal to half the second diameter D of an orifice 230 of the perforated plate 23 and a second thickness equal to twenty times the first diameter De of the duct 21.

[0064] On the figure 6 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to a third embodiment of the acoustic treatment grid is shown.

[0065] In this third embodiment, the perforated plate 23 comprises 22 orifices 230 distributed over a single half 231 of the disc formed by the perforated plate 23.

[0066] On the figure 7 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to a fourth embodiment of the acoustic treatment grid is shown.

[0067] In this fourth embodiment, the perforated plate 23 comprises 30 orifices 230 distributed over a crown 233 formed between the outer perimeter of the circular perforated plate 23 and an internal circle Ci of smaller diameter than that of the outer perimeter.

[0068] On the figure 8 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to a fifth embodiment of the acoustic treatment grid is shown.

[0069] In this fifth embodiment, the perforated plate 23 comprises 32 orifices 230 distributed over the perforated surface to form first zones 235 without orifices and second zones 236 provided with orifices 230.

[0070] On the figure 9 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to a sixth embodiment of the acoustic treatment grid is shown.

[0071] In this sixth embodiment, the perforated plate 23 comprises 36 orifices 230 distributed over the entire surface of the perforated plate 23 like the first embodiment illustrated in the figure 4 . The sixth embodiment differs from the first embodiment illustrated in the figure 4 in that the orifices 230 comprise orifices of different diameters, the diameter of the orifices 230 increasing from a first end 237 of the circular perforated plate 23 to a second end 238 of the circular perforated plate 23.

[0072] On the figure 10 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to a seventh embodiment of the acoustic treatment grid is shown.

[0073] The seventh embodiment differs from the sixth embodiment illustrated in the figure 9 in that the diameter of the orifices 230 increases away from the center of the circular perforated plate 23.

[0074] On the figure 11 a front view of a perforated plate 23 of the acoustic treatment grid 22 according to an eighth embodiment of the acoustic treatment grid is shown.

[0075] The eighth embodiment differs from the sixth embodiment illustrated in the figure 9 in that the diameter of the orifices 230 increases as it approaches the center of the circular perforated plate 23.

[0076] On the figure 12 schematically illustrated is a view of a relief valve according to a third embodiment of the relief valve.

[0077] In the third embodiment of the discharge valve 20, the conduit 21 comprises a single inlet 211, a first outlet 212, a second outlet 213, a bifurcation 214, a first section 215 extending between the inlet 211 of the conduit 21 and the bifurcation 214, a second section 216 extending between the bifurcation 214 and the first outlet 212, and a third section 217 extending between the bifurcation 214 and the second outlet 213.

[0078] In the third embodiment, the discharge valve 20 comprises a grid 22 mounted in the first section 215, as well as a first acoustic treatment panel 25a mounted on the first section 215, between the grid 22 and the bifurcation 214, and a second acoustic treatment panel 25b mounted on the third section 217 between the bifurcation 214 and the second outlet 213.

[0079] The first acoustic treatment panel 25a extends over a first length Lm1 of the first section 215 and is separated from the grid 22 by a first space of length Sm1, and the second acoustic treatment panel 25b extends over a second length Lm2 of the third section 217 and is separated from the grid 22 by a second space of length Sm2.

[0080] On the figure 13 schematically illustrated is a view of a relief valve according to a fourth embodiment of the relief valve.

[0081] The fourth embodiment of the relief valve 20 differs from the third embodiment illustrated in the figure 12in that it comprises two grilles 22a and 22b and two acoustic treatment panels 25a and 25b, the first grille 22a and the first acoustic treatment panel being mounted on the second section 216 of the duct 21 and the second grille 22b and the second acoustic treatment panel being mounted on the third section 217 of the duct 21.

[0082] The first acoustic treatment panel 25a extends over a first length Lm1 of the second section 216 and is separated from the first grid 22a by a first space of length Sm1, and the second acoustic treatment panel 25b extends over a second length Lm2 of the third section 217 and is separated from the second grid 22b by a second space of length Sm2.

[0083] The grid and the discharge valve according to the invention make it possible to optimize the mixing downstream of the grid and thus to minimize the intensity of the aero-acoustic phenomena generated by this type of discharge system and more particularly to reduce the mixing noise and the impact noise, while ensuring a perforated surface making it possible to ensure the operability of the air system.

Claims

1. An acoustic treatment grid (22) intended to be mounted inside or at the outlet of a duct (21) of a bleed valve (20) of a turbomachine (1) of an aircraft intended to convey a gas flow (F), the grid (22) comprising a perforated plate (23) and circular holes (230) traversing the perforated plate (23) along a first direction (DA), the holes (230) having a diameter (D) and a geometrical center (C), the perforated plate (23) comprising, with respect to the gas flow (F) intended to traverse the perforated plate (23), an upstream face (232) intended to receive the gas flow (F) and a downstream face (234), opposite the upstream face (232), from which the gas flow (F) is intended to escape, the grid (22) being characterized in that each hole (230) is separated from an adjacent orifice by a space, the length (e) of which is equal to the product of the diameter (D) of said hole (230) and a spacing coefficient of a value between 1.1 and 6 to minimize low-frequency noise, while ensuring the operability of the bleed valve (20), the length (e) separating two holes (230) being measured between the geometrical centers (C) of the two holes (230), and the grid (22) further comprising a layer of porous material (24) disposed on said downstream face (234) of the perforated plate (23) without covering the holes (230), the plate (23) and the layer of porous material (24) forming channels.

2. The grid (22) as claimed in claim 1, wherein the diameter (D) of the orifices (230) of the perforated plate (23) is preferably between 0.5 mm and 20 mm.

3. The grid (22) as claimed in one of claims 1 or 2, wherein the perforated plate (23) has a thickness (h) along the first direction (DA) between 1 mm and 20 mm.

4. The grid (22) as claimed in one of claims 1 to 3, wherein the layer of porous material (24) disposed on said downstream face (234) of the perforated plate (23) includes a thickness (he) along the first direction (DA) between a first thickness equal to half the diameter (D) of a hole (230) around which the layer of porous material (24) is disposed and a second thickness equal to twenty times the greatest length of the perforated plate (23) measured in a plane orthogonal to the first direction (DA).

5. The grid (22) as claimed in one of claims 1 to 4, wherein the perforated plate (23) comprises between 2 and 500 holes (230).

6. The grid (22) as claimed in one of claims 1 to 5, wherein the holes (230) are uniformly distributed over the perforated plate (23).

7. The grid (22) as claimed in one of claims 1 to 6, wherein the perforated plate (23) comprises at least a first orifice with a first diameter and at least a second orifice with a second diameter separate from the first diameter.

8. A bleed valve (20) for an aircraft turbojet engine (1) comprising a duct (21) intended to convey a gas flow (F) mainly along a first direction (DA) from at least one inlet (211) of the duct (21) to at least one outlet (212, 213) of the duct (21), and at least one grid (22) as claimed in one of claims 1 to 7 mounted inside the duct (21) or on an outlet (212, 213) of the duct (21).

9. The bleed valve (20) as claimed in claim 8, wherein the duct (21) comprises at least one wall equipped with an acoustic treatment means (25) and located downstream of the bleed grid (22) with respect to the direction of flow of the gas flow (F) intended to be conveyed through the duct (21).

10. The bleed valve (20) as claimed in claim 9, wherein the acoustic treatment means (25) of said at least one wall comprises a layer of porous material and / or an acoustic treatment panel.

11. The bleed valve (20) as claimed in one of claims 9 or 10, wherein the shortest distance (Sm) between the acoustic treatment means (25) and the grid (22) is less than or equal to a length equal to forty times the greatest length of the section of the duct (21), the section of the duct extending orthogonally to the first direction (DA).

12. The bleed valve (20) as claimed in one of claims 9 to 11, wherein the length (Lm) along the first direction (DA) of the acoustic treatment means (25) is between a first length equal to half the greatest length of the section of the duct (21) and a second length equal to fifty times the greatest length of the section of the duct (21), the section of the duct extending orthogonally to the first direction (DA).

13. The bleed valve (20) as claimed in one of claims 9 to 12, wherein the thickness (hm) along a direction (DR) orthogonal to the first direction (DA) of the acoustic treatment means (25) is between a first thickness equal to half the diameter of an orifice (D) of the perforated plate (23) and a second thickness equal to twenty times the greatest length of the section of the duct (21), the section of the duct extending orthogonally to the first direction (DA).

14. The bleed valve (20) as claimed in one of claims 8 to 13, wherein the duct (21) comprises at least one segment, the diameter of which varies along the first direction (DA).

15. The bleed valve (20) as claimed in one of claims 8 to 14, wherein the duct (21) comprises at least one segment (215, 216, 217) in which the geometrical shape of the section of the duct (21) varies, the section of the duct extending orthogonally to the first direction (DA).

16. The bleed valve (20) as claimed in one of claims 8 to 15, wherein the conduit (21) comprises at least two outlets (212, 213), at least a fork (214), at least a first segment (215) extending between the inlet (211) of the duct (21) and a fork (214), a second segment (216) extending between a fork (214) and a first outlet (212), a third segment (217) extending between a fork (214) and a second outlet (213), at least one of said at least one grid (22) being mounted in one of the first, second or third segment (215, 216, 217), or on one of the first or second outlets (212, 213).

17. The bleed valve (20) as claimed in one of claims 8 to 16, wherein said at least one grid (22) and / or said at least one acoustic treatment means (25) are made of ceramic material.

18. A turbojet engine (1) comprising a nacelle (2), an intermediate casing (3) and an inner casing (4), coaxial, and a bleed valve (20) as claimed in one of claims 8 to 17, the intermediate casing (3) and the inner casing (4) together delimiting a primary fluid flow path (7), the nacelle (2) and the intermediate casing (3) together delimiting a secondary fluid flow path (8), and the bleed valve (20) being mounted between the primary flow path (7) and the secondary flow path (8) and configured to draw a portion of the air from the primary flow path (7) and deliver it into the secondary air path (8).

19. A turbojet engine (1) comprising a nacelle (2), an intermediate casing (3) and an inner casing (4), coaxial, and a bleed valve (20) as claimed in one of claims 8 to 17, the intermediate casing (3) and the inner casing (4) together delimiting a primary fluid flow path (7) in which is mounted a combustion chamber (13) , the nacelle (2) and the intermediate casing (3) together delimiting a secondary fluid flow path (8), and the bleed valve (20) being configured to draw a portion of the air from the primary flow path (7) upstream of the combustion chamber (13) and deliver it into the primary flow path (7) downstream of the combustion chamber (13).