Valve for an aircraft turbine engine

Abstract

The invention relates to a valve (100) for an aircraft turbine engine, comprising a seat (111) defining an air inlet (113), a shutter (120) movable relative to the seat (111) between a closed position, in which the shutter (120) at least partially closes the air inlet (113), and an open position in which the shutter (120) closes the air inlet (113) less than in the closed position, a frame (112) fixed relative to the seat (111), the frame (112) defining a housing (114) and a recovery chamber (116) in communication with each other, and a plug (140) located in the housing (114), the plug (140) being meltable and configured to, in the solid state, maintain the shutter (120) in a first position among the closed position and the open position, and in the molten state, flow into the recovery chamber (116).

Description

Valve for aircraft turbomachine Technical field

[0001] This disclosure relates to the field of aircraft turbomachines, and more particularly to a valve for an aircraft turbomachine. Such a valve can be used to regulate ventilation in the turbomachine. Prior art

[0002] In aircraft turbomachines, secondary air circuits are sometimes used to ensure the necessary ventilation flows in certain regions of the turbomachine. Some of these secondary air circuits may only be necessary in the event of a malfunction and not during nominal operation of the turbomachine. Conversely, they may be useful during nominal operation but must be shut off in the event of a malfunction.

[0003] In this context, the Applicant has developed an improved ventilation device for an aircraft turbomachine module which is the subject of patent application FR 3 095 831 A1. This device comprises a closing flap retained by a fusible locking means.

[0004] This device provides complete satisfaction in its function of regulating the secondary air circuits. However, when the locking means melts, it is evacuated into the turbomachine, which is not desirable for several reasons.

[0005] The invention aims to remedy at least in part these drawbacks. Statement of the invention

[0006] For this purpose, the present disclosure relates to a valve for an aircraft turbomachine, comprising a seat defining an air inlet, a shutter movable relative to the seat between a shutter position, in which the shutter at least partially closes the air inlet, and an open position in which the shutter closes the air inlet less than in the position shutter, a frame fixed relative to the seat, the frame defining a housing and a recovery chamber in communication with each other, and a plug located in the housing, the plug being fusible and configured to, in the solid state, maintain the shutter in a first position among the shutter position and the open position, and in the molten state, flow towards the recovery chamber.

[0007] When the plug melts, it flows at least partially into the collection chamber. In doing so, the plug frees up space in the housing and is no longer able to hold the shutter in the first position, allowing the shutter to move into the second position.

[0008] Thus, when the temperature increases near the plug, the shutter can automatically move to the second position, either the open position so that the valve provides additional cooling air, or on the contrary the closed position so that the valve prevents the supply of oxygen to a fire, for example.

[0009] Due to the fact that the valve includes a frame defining a housing and a recovery chamber, the melted plug is recovered and does not get lost in unwanted parts of the turbomachine, which increases the reliability of the turbomachine.

[0010] In the closed position, the shutter can partially or completely block the air inlet. In the open position, the shutter can be set back from the seat, so as to block the air inlet less.

[0011] In addition to the characteristics just mentioned, the proposed method may have one or more of the following characteristics, considered in isolation or in technically possible combinations: - a partition separates the recovery chamber from the air inlet; - the housing protrudes towards the opposite side of the air inlet; - a wall of the chassis is locally refined at the level of the housing; - the valve further comprises an elastic element configured to return the shutter to a second position among the shutter position and the open position; - the housing is defined between the frame and the shutter; - in the second position, the shutter is housed at least partially in the housing; - in the second position, one face of the shutter opposite the air inlet is pressed against the frame; - the shutter is movable in translation between the shutter position and the open position; - the shutter is mounted between the frame and the seat; - the frame and / or the seat define an air outlet, and in the open position, the air outlet communicates with the air inlet.

[0012] The present disclosure also relates to an aircraft turbine, comprising a valve as previously described.

[0013] The aircraft turbine may comprise an annular hot air flow duct and a sub-duct cavity coaxial with said duct, the valve being provided on a ventilation device opening into the sub-duct cavity. Furthermore, the housing may open into the sub-duct cavity. Brief description of the drawings

[0014] Other characteristics and advantages of the subject of the present disclosure will emerge from the following description of embodiments, given as non-limiting examples, with reference to the appended figures.

[0015] Figure 1 is a schematic longitudinal sectional view of a turbomachine.

[0016] Figure 2 is a schematic view in longitudinal and partial section of a low pressure turbine of the turbomachine of Figure 1.

[0017] Figure 3 is a longitudinal sectional view of a valve according to a first embodiment, in the closed position.

[0018] Figure 4 is a front view of the valve seat according to the first embodiment, in direction IV-IV of Figure 3.

[0019] Figure 5 is a longitudinal sectional view of the valve according to the first embodiment, in the open position.

[0020] Figure 6 is a longitudinal sectional view of a valve according to a second embodiment, in the closed position.

[0021] Figure 7 is a longitudinal half-sectional view of a valve according to a third embodiment, in the closed position. Detailed description

[0022] A first embodiment of the present disclosure will be presented with reference to Figures 1 to 5.

[0023] The terms "upstream" and "downstream" are subsequently defined in relation to the direction of gas flow through the turbomachine, indicated by arrow G in Figures 1 and 2.

[0024] Figure 1 illustrates a double-flow turbomachine 1 comprising in a known manner from upstream to downstream successively at least one fan 10, an engine part successively comprising at least one low-pressure compressor stage 20, high-pressure compressor stage 30, a combustion chamber 40, at least one high-pressure turbine stage 50 and low-pressure turbine stage 60. In the engine part, the gases flow along an annular hot air flow vein 5, in which the blades of the compressors and turbines extend.

[0025] Rotors, rotating around the main axis X of the turbomachine 1 and able to be coupled together by different transmission and gear systems, correspond to these different elements.

[0026] In a manner known per se, a fraction of air is taken from the high-pressure compressor 30 and is conveyed via a cooling air circulation duct 32 in order to cool hotter zones of the turbomachine 1, in particular the high-pressure turbine 50 and the low-pressure turbine 60.

[0027] Figure 2 is an enlargement of an area of ​​the turbomachine 1, illustrating in a simplified manner the upstream part of the low pressure turbine 60, the high pressure turbine 50 not being shown.

[0028] The low-pressure turbine 60 illustrated here comprises a plurality of turbine stages 61, 62. A first stage 61 and the stages 62 located downstream thereof respectively comprise a set of fixed distributors 70 and 65. Each stage 61, 62 further comprises a movable disc 63 on which is mounted a set of blades 64 driven in rotation by the movable disc 63. The first stage 61 of the low-pressure turbine 60 comprises at least one movable blade 64, as well as at least one hollow distributor 70, in which cooling air circulates. In the example illustrated in FIG. 2, the distributor 70 forms a single piece with a casing 66 of the turbine and is hollow to allow cooling air to pass through. from the cooling duct 32. This cooling air exits via an injection device 80 associated with the distributor 70, comprising a plurality of injectors. The following stages 62, located downstream of the low-pressure turbine 60, each comprise at least one movable blade 64 and a distributor 65 in the form of a fixed blade. The movable disc 63 is integral in rotation with a low-pressure shaft 102 extending along the axis XX, while each distributor 65 is connected to the casing 66. Each turbine stage 61, 62 further comprises a turbine ring 67 located opposite the movable blades 64, and which is integral with the casing 66.

[0029] The turbomachine 1 comprises a cooling device for conveying the fraction of air taken from the high-pressure compressor 30 to at least one stage of the low-pressure turbine 60. In the present embodiment, the fraction of cooling air taken is distributed at an upstream stage of the low-pressure turbine 60. The low-pressure turbine 60 is thus cooled. However, the invention is not limited to this embodiment, the fraction of air taken can also be distributed to other stages of the low-pressure turbine 60 and / or to the high-pressure turbine 50.

[0030] In the embodiment illustrated in Figure 2, the fraction of air taken from the high-pressure compressor 30 flows into the cooling duct 32, then into the hollow distributor 70. The direction of circulation of the fraction of air through the hollow distributor 70 is illustrated by the arrows 71. The fraction of air is then injected via the injection device 80 into a cavity under the vein 68, coaxial with the hot air flow vein 5. The distributed air makes it possible in particular to cool the disks 63 of the turbines, as illustrated by the arrows 75.

[0031] The cooling air injected by the injection device 80 also allows the hot air present in the low-pressure turbine 60 to be purged, thus ensuring the cooling thereof. More precisely, the cooling air, taken from the high-pressure compressor and conveyed to the under-vein cavity 68, constitutes a pressure barrier, or purge, preventing the hot air coming from the combustion chamber and flowing in the main air circulation vein 5 of the turbines, that is to say in the primary air circulation vein of the turbomachine 1, from penetrating into the under-vein cavity 68. The purge of the hot air from the low-pressure turbine 60 is here symbolized by the arrow 76. The risks of overheating of the disks 63 of the turbines are thus limited. In particular, by preventing the air from the vein 5 from entering the sub-vein cavity 68, this sub-vein cavity 68 is less hot than the vein 5, and the disks 63 of the turbine can therefore withstand higher centrifugal forces and be sized for lower limit stresses.

[0032] In a known manner, one or more cooling air circulation ducts 32 each take a fraction of cooling air from an air flow circulating in the high-pressure compressor 30, and convey the fraction of air taken to at least one stage of the low-pressure turbine 60.

[0033] A malfunction of the cooling of the turbine 60 can have several causes. One cause of the cooling malfunction can be the malfunction of a duct 32, for example the accidental rupture or blocking of one of the air circulation ducts 32. Another cause of this malfunction can result from excessive wear or rupture of one or more seals, or dynamic seals of the low-pressure turbine 60. A malfunction of the cooling of the turbine 60 results, for example, from a failure of a labyrinth seal 69 ensuring the pressure isolation of the under-vein cavity 68 of the low-pressure turbine 60.

[0034] The injection device 80 comprises a plurality of first injectors 81, and at least one, preferably several valves 100, distributed on a wall P of the distributor 70 around the axis X. The presence of the first injectors 81 is optional, the injection device 80 being able to comprise only valves 100. In order to simplify the description of this embodiment, a single first injector 81 and a single valve 100 are shown in FIG. 2. Furthermore, although the embodiment is described with reference to the low-pressure turbine 60, one or more valves 100 could also be provided at other locations of the turbomachine 1, such as the high-pressure turbine 50.

[0035] In any event, the valve 100 is provided on a ventilation device, here the injection device 80, opening into the sub-vein cavity 68.

[0036] The first injector 81 is an orifice made in the wall P of the distributor 70, allowing continuous injection, that is to say in a continues when the turbomachine is in operation, a first flow of cooling air into the cavity under the vein 68. This first flow makes it possible to ensure cooling, more precisely the purge 76 and the maintenance of the temperature of the low pressure turbine 60 under nominal operating conditions thereof, that is to say in the absence of one of the malfunctions mentioned above. The dimensions of the orifice are determined so that the first flow is for example between 270 and 310 g / s. In certain applications where the temperatures involved are lower, such cooling by a first flow is not necessary under nominal operating conditions. In this case, only the valves 100 are necessary.

[0037] As illustrated in Figure 3, in the first embodiment, the valve 100 comprises a fixed part 110 and a shutter 120. The fixed part 110 comprises a seat 111 and a frame 112 fixed relative to the seat 111. The seat 111 defines an air inlet 113, for example in fluid communication with the conduit 32.

[0038] The seat 111 may have a cylindrical shape with axis A, a major part of which is arranged on one side of the wall P opposite the under-vein cavity 68. However, one end 111a of the seat 111 may be inserted into an orifice in the wall P and protrude inside the under-vein cavity 68. It will be noted that the seat 111 may be fixed to the wall P, for example by welding or brazing, typically at its end 111a. Furthermore, the end 111a may be threaded.

[0039] According to one example, a portion of the frame 112, comprising a thread, is then screwed onto the end 111a. The screw thread may be self-locking. The frame 112 is arranged on the other side of the wall P than the seat 111, that is to say in the cavity under the vein 68. The chassis 112 thus has a general disc shape, seen from the front. The assembly of the seat 111 and the chassis 112 forms an internal cavity I.

[0040] The chassis 112 comprises at least one air outlet 112a, preferably a plurality of air outlets 112a (two are visible in FIG. 3) distributed circumferentially around the axis A on a lateral face of the chassis. 112, putting the internal cavity I of the valve 100 into fluid communication with the under-vein cavity 68.

[0041] Furthermore, the frame 112 defines a housing 114 and a recovery chamber 116, in fluid communication with each other. The housing 114 may project from the frame 112 in a direction opposite to the air inlet 113, i.e. in this case towards the under-vein cavity 68. The housing 114 therefore opens into the under-vein cavity 68. As a result, the housing 114, which receives the plug 140 described later, is more sensitive to the temperature in the under-vein cavity 68. In addition, the housing 114 is not excessively cooled by any leaks from the air inlet 113.

[0042] Further, as illustrated, the wall of the frame 112 may be locally thinned at the housing 114. This facilitates thermal conduction at the housing 114 and also helps make the housing 114 more sensitive to the temperature in the under-vein cavity 68.

[0043] The recovery chamber 116 is in fluid communication with the housing 114 but isolated on the one hand from the air inlet 113, on the other hand from the air outlets 112a. In this embodiment, the recovery chamber 116 is a part of the internal cavity I which is located between the shutter 120 and the frame 112. A wall 117, here annular, projects from the frame 112 in the direction of the air inlet 113, the wall 117 forming a partition to separate the recovery chamber 116 from the air inlet 113 and, in this case, from the air outlet 112a.

[0044] The shutter 120 is movable relative to the seat 111. The shutter 120 may be arranged at least partly in the internal cavity I, between the seat 111 and the frame 112. More specifically, the shutter 120 comprises a closing member 121 arranged entirely in the internal cavity I, and a guide rod 122 extending from a downstream face of the closing member 121 and arranged partly in the housing 114, at least in the open position which will be described later. In this embodiment, the shutter 120 thus has the shape of a piston capable of moving by translation along the axis A.

[0045] Thus, more generally, the housing 114 is defined between the chassis 112 and shutter 120.

[0046] Furthermore, the shutter 120 may comprise a guide 124. In this case, the guide 124 projects from the closing member 121 towards the frame 112. The guide 124 may provide a guiding role for the shutter 120, here by cooperating with the wall 117 so as to form a slide. In this case, the guide 124 is substantially coaxial with the wall 117. The clearance between the wall 117 and the guide 124 makes it possible to take into account the differential expansion of the shutter 120 and the frame 112, without hindering their relative movement. Furthermore, the guide 124 can define, in cooperation with the wall 117, a partition of the recovery chamber 116, in this case by an overlap between the wall 117 and the guide 124 in the direction of the axis A.

[0047] In the closed position shown in Figure 3, the shutter 120 at least partially closes the air inlet 113. In this case, the shutter 120 is positioned along the axis A so that the closing member 121 is in contact with a wall of the seat 111. Thus, the cooling air entering through the air inlet 113 upstream of the closing member 121, that is to say to the left of the closing member 121 in Figure 3, cannot access the part of the internal cavity I located downstream of the closing member 121, and consequently the air outlets 112a.

[0048] The shutter 120 is held in this closed position (corresponding to a first position in this embodiment) by a plug 140 located in the housing 114. In the solid state, the plug 140 forms a spacer between the shutter 120, for example the guide rod 122, and the chassis 112 so as to prevent any movement of the shutter 120 towards the chassis 112.

[0049] The plug 140 is made of a fusible material, in particular fusible at certain operating temperatures or malfunction of the low pressure turbine 60. The plug 140 may be made of a eutectic material.

[0050] The plug 140 may have an annular shape, for example a hollow cylinder, to facilitate its fusion.

[0051] The seat 111 further comprises an upstream wall 130, fixed by welding or brazing, for example, to an internal wall of the seat 111. The upstream wall 130 is here a washer, a front view of which along the axis A is shown in FIG. 4. The washer comprises a contour 135 fixed to the internal wall of the seat 111, and a central part 133, typically circular, connected to the contour 135 by at least one arm 132, here two. Between the contour 135, the arms 132 and the central part 133, one or more openings 131 are formed defining the air inlet 113. The openings 131 in fact allow the passage of the fraction 71 of the cooling air circulating in the hollow distributor 70, up to the interior of the internal cavity I of the valve 100, in the portion of said internal cavity I located upstream of the shutter 120.

[0052] An elastic element 150 such as a return spring may be arranged in the internal cavity I to return the shutter 120 to a second position, namely here an open position. In this example, the elastic element 150 is positioned upstream of the closure member 121 and mounted in compression between the central portion 133 of the upstream wall 130 and the upstream face of the closure member 121. For this purpose, the central portion 133 of the upstream wall 130 preferably comprises a circular groove 134, configured to receive one end of the elastic element 150 in order to hold the latter.

[0053] It is thus understood that the plug 140 is sufficiently incompressible to resist the force exerted by the elastic element 150 on the shutter 120, as well as the force exerted by the pressure of the cooling air upstream of said shutter 120. In nominal operating conditions, the shutter 120 is thus held in the closed position by the plug 140 in the solid state.

[0054] In the event of a rise in temperature in the under-vein cavity 68 due to an anomaly, the plug 140 melts at least partially. The molten portion of the plug 140 then flows towards the recovery chamber 116, for example through one or more grooves 123 provided in the shutter 120, in this case in the guide rod 122. This flow may be facilitated by the fact that in the use configuration, the retention chamber 116 is located lower than the housing 114, so that the molten plug can flow by gravity from the housing 114 to the retention chamber 116.

[0055] The plug 140, which has therefore partially or totally disappeared from the housing 114, therefore frees up a space that can be taken by the shutter 120, and particularly the guide rod 112, for example under the effect of the force exerted by the elastic element 150 and / or the air pressure at the air inlet 113. The shutter 120 then moves in translation along the axis A towards the chassis 112, which allows it to move into a second position, in this case an open position shown in FIG. 5, and to be maintained in this position.

[0056] Thus, in this second position, as shown in Figure 5, the shutter 120 is housed at least partly in the housing 114.

[0057] In this open position, the closing member 121 is no longer in sealed contact with the seat 111, such that the upstream and downstream parts of the internal cavity I are in communication. Consequently, the cooling air initially present upstream of the closing member 121 can flow to the air outlets 112a, and thus be injected into the under-vein cavity 68. In other words, in the open position, the shutter 120 closes the air inlet 113 less than in the closed position, and moreover, the air outlets 112a communicate with the air inlet 113.

[0058] The second position may be such that a face of the shutter 120 opposite the air inlet 113 is pressed against the frame. This prevents air from entering downstream of the shutter and risking pushing the shutter 120 towards the air inlet 113. The shutter 120 therefore remains reliably in the second position.

[0059] Thus, when one of the malfunctions mentioned above occurs, the temperature within the under-vein cavity 68 increases and reaches values ​​higher than the temperatures representative of nominal operation. When the temperature within the under-vein cavity 68 reaches a threshold value for melting the plug 140, the valve 100 opens. An additional cooling air flow rate, for example between 80 and 90 g / s, can then be injected into the under-vein cavity 68 via the valve 100, in addition to the first flow rate injected by the first injector 81.

[0060] The sum of the first and second flow rates is greater than the flow rate ranges representative of nominal operation, and makes it possible to cover cases of malfunctions, characterized by an increase in the temperature in the turbine. Thus, it is possible to increase the cooling of the discs 63, before these elements are damaged by an excessive increase in temperature. In particular, the injection of the additional cooling air flow makes it possible to increase the purge flow rate 76, and thus to prevent the hot air from the vein from penetrating into the sub-vein cavity 68.

[0061] Upon return to nominal operating conditions, it is possible to reuse the valve 100, in particular by unscrewing the frame 112 and removing the shutter 120. The melted plug 140a can be removed from the recovery chamber 116 and a new plug 140 can be placed in the housing 114. Then, the shutter 120 can be placed back in the closing position by compressing the elastic element 150.

[0062] Figures 6 and 7 show the valve in other embodiments. In these figures, elements corresponding to or identical to those of the first embodiment will receive the same reference sign and will not be described again.

[0063] The valve 100 according to the second embodiment, illustrated in FIG. 6, is similar to that of the first embodiment. Instead of a helical spring, the elastic element 150 is here formed by a leaf spring.

[0064] Furthermore, the housing 114 and the recovery chamber 116 communicate via a gutter 118 provided in the frame 112. Thus, the guide rod 122 may be devoid of the grooves 123 mentioned previously. The gutter 118 may open onto a lower wall of the housing 114, as illustrated.

[0065] Furthermore, instead of the annular wall 117 described for the first embodiment, the frame of the valve 100 according to the second embodiment comprises an insert 117a. The insert 117a, housed in the remainder of the frame 112, defines a passage for the guide rod 122. The guide rod 122 engages in said passage regardless of the position of the shutter 120. This allows the housing 114 to be sized independently of the guide rod 122, because the housing 114 no longer has the guiding role that it had in the first embodiment.

[0066] Furthermore, the insert 117a forms a partition separating the recovery chamber 116 from the air inlet 113. In this embodiment, the recovery chamber is formed between the frame 112 and the insert 117a, for example by a recess in the lower part of the insert 117a.

[0067] Thus, the presence of a guide 124 like that of the first embodiment is not useful. Therefore, the respective shapes of the shutter 120 and the insert 117a of the chassis are such that in the second position, the shutter 120 is pressed against the chassis 112, here against the insert 117a.

[0068] Figure 6 shows that the air outlets 112a can be provided in the form of transverse ducts, here radial, opening onto the internal cavity I.

[0069] The valve 100 according to the third embodiment, illustrated in FIG. 7, is similar to that of the second embodiment. As shown previously, it does not include an elastic element 150, only the air pressure from the air inlet 113 being used to move the shutter 120 to the open position. Therefore, the upstream wall 130 described previously can also be omitted.

[0070] In order to maximize the force exerted by the air coming from the air inlet 113 on the shutter 120, the upstream face of the shutter may comprise a central portion 121a transverse to the direction of injection of the air by the air inlet 113. Around it, the portions of the closing member 121 configured to come into contact with the seat 111 may retain corresponding shapes, for example, in this case, substantially conical.

[0071] In addition to the air outlet 112a, there is the presence of one or more vents 112b, provided on the frame 112 downstream of the air outlet 112a, in order to balance the pressures between the internal cavity I and the under-vein cavity 68. When the shutter 120 moves into the open position, this vent 112b can be closed by the shutter 120, for example a part of the shutter similar to the guide 124 previously described, in order to prevent air from entering downstream of the shutter 120 through this vent 112b and risking pushing the shutter 120 towards the air inlet 113.

[0072] Although the present description refers to specific exemplary embodiments, modifications may be made to these examples without departing from the general scope of the invention. For example, as mentioned previously, the first position and the second position of the shutter may be interchanged. Typically, a shutter may be held in the open position by the solid-state stopper, for example by providing windows in a central portion of the shutter for the passage of air, and in the closed position, said windows could be closed following movement of the shutter.

[0073] More generally, individual features of the various embodiments illustrated or mentioned may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

CLAIMS

1. Valve (100) for an aircraft turbomachine, comprising a seat (111) defining an air inlet (113), a shutter (120) movable relative to the seat (111) between a shutter position, in which the shutter (120) at least partially closes the air inlet (113), and an open position in which the shutter (120) closes the air inlet (113) less than in the shutter position, a frame (112) fixed relative to the seat (111), the frame (112) defining a housing (114) and a recovery chamber (116) in communication with each other, and a plug (140) located in the housing (114), the plug (140) being fusible and configured to, in the solid state, maintain the shutter (120) in a first position among the closed position and the open position, and in the molten state, flow towards the recovery chamber (116).

2. Valve according to claim 1, in which a partition separates the recovery chamber (116) from the air inlet (113).

3. A valve according to claim 1 or 2, wherein the housing (114) projects away from the air inlet (113).

4. A valve according to any one of claims 1 to 3, wherein a wall of the frame (112) is locally tapered at the housing (114).

5. A valve according to any one of claims 1 to 4, wherein the housing (114) is defined between the frame (112) and the shutter (120).

6. Valve according to any one of claims 1 to 5, in which, in the second position, the shutter (120) is housed at least partly in the housing (114).

7. Valve according to any one of claims 1 to 6, in which, in the second position, a face of the shutter (120) opposite the air inlet (113) is pressed against the frame (112).

8. Valve according to any one of claims 1 to 7, in which the shutter (120) is movable in translation between the closing position and the opening position, and / or the shutter (120) is mounted between the frame (112) and the seat (111).

9. Valve according to any one of claims 1 to 8, wherein the frame (112) and / or the seat (111) define an air outlet (112a), and in the open position, the air outlet (112a) communicates with the air inlet (113).

10. Aircraft turbine (60), comprising a valve (100) according to any one of claims 1 to 10, optionally wherein the turbine comprises an annular hot air flow duct (5) and a sub-duct cavity (68) coaxial with said duct, the valve (100) being provided on a ventilation device opening into the sub-duct cavity (68), the housing (114) opening into the sub-duct cavity (68).

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