FIXED INTERNAL STRUCTURE FOR AIRCRAFT COMPRISING A HONEYCOMB STRUCTURE, A THERMO-ACOUSTIC EXCHANGER, THERMAL INSULATION AND FIXING MEANS

Abstract

INTERNAL FIXED STRUCTURE FOR AIRCRAFT COMPRISING A HONEYCOMB STRUCTURE, A THERMO-ACOUSTIC EXCHANGER, THERMAL INSULATION AND FIXING MEANS The invention relates to an internal fixed structure (300) for an aircraft nacelle, said external fixed structure (300) comprising a honeycomb structure (302) with a first face covered with a resistive sheet (302a) and a second face covered with a base skin (302b), a thermo-acoustic exchanger (304) opposite the resistive sheet (302a) and thermal insulation (308) opposite the base skin (302b). The internal fixed structure (300) also includes a plurality of fastening means (306a), each securing the thermal insulation (308) and the heat exchanger (304) to the honeycomb structure (302). With this arrangement, the fastening means are shared, and it is no longer necessary to dismantle the thermal insulation to remove the heat exchanger. Fig. 4

Description

Title of the invention: FIXED INTERNAL STRUCTURE FOR AN AIRCRAFT COMPRISING A HONEYCOMB STRUCTURE, A THERMO-ACOUSTIC EXCHANGER, THERMAL INSULATION AND FIXING MEANS Technical field

[0001] The present invention relates to an internal fixed structure for an aircraft wherein said internal fixed structure comprises a honeycomb structure, a thermoacoustic exchanger, a thermal insulator and fastening means which ensure the attachment of the thermoacoustic exchanger and the thermal insulator to the honeycomb structure, a propulsion assembly comprising such an internal fixed structure and an aircraft comprising at least one such propulsion assembly. PREVIOUS STATE OF THE ART

[0002] Figure 2 is a side and cross-sectional view of a propulsion unit 200 for an aircraft. The propulsion unit 200 comprises a turbojet engine 202 and a nacelle 204 arranged around the turbojet engine 202. The turbojet engine 202 comprises a core 207 and a fan 206 mounted at the front of the core 207. Outside air enters the propulsion unit 200 through an air inlet 208 delimited by the front of the nacelle 204.

[0003] After passing through the blower 206, the air splits into a primary flow which passes through the core 207 comprising among other things a combustion system, and into a secondary flow which circulates between the core 207 and the nacelle 204 in a secondary channel 210 provided for this purpose.

[0004] The nacelle 204 comprises an external fixed structure 211 (or OFS for "Outer Fixed Structure" in Anglo-Saxon terminology) and an internal fixed structure 212 (or IFS for "Inner Fixed Structure" in Anglo-Saxon terminology) which are concentric and delimit between them the secondary vein 210. The internal fixed structure 212 is around the nucleus 207.

[0005] Figs. 9 to 11 show an internal fixed structure 900 of the prior art.

[0006] Conventionally, the internal fixed structure 900 comprises a honeycomb structure 902 has two faces between which are alveoli. The first face is covered by a resistive sheet 902a, which is perforated to allow the sound waves to be attenuated to pass to the alveoli. The first face is oriented towards the secondary vein 210. The second face is covered by a backing skin 902b, which seals the alveoli. The second face is oriented towards the core 207.

[0007] The internal fixed structure 900 also includes a thermal insulator 904 which is fixed on the side of the core 207 to the honeycomb structure 902 using first fixing means 906.

[0008] The internal fixed structure 900 also includes a thermo-acoustic exchanger 908 which has a plate 908a which extends over the entire surface of the thermo-acoustic exchanger 908 and channels 908b which extend under a central part of the plate 908a.

[0009] The 908b channels constitute the active part of the thermo-acoustic exchanger 908 in which a heat transfer fluid circulates.

[0010] The plate 908a allows among other things the fixing of the thermo-acoustic exchanger 908 to the honeycomb structure 902 on the side of the secondary vein 210 by means of second fixing means 910a-b.

[0011] Due to the thermal expansions undergone by the elements constituting the internal fixed structure 900, there is a second fixing means 910a of a first type which ensures a fixing without play and second fixing means 910b of a second type which ensure a fixing with play.

[0012] Each first fastening means 906 includes an insert 906a which has a rod which is inserted and fixed in the honeycomb structure 902 and a stud which extends through the thermal insulation 904. Each first fastening means 906 also includes a clip 906b which has a collar and a shaft which is fitted onto the stud of the insert 906a through the thermal insulation 904 and the collar bears against the thermal insulation 904.

[0013] Each second fastening means 910a-b includes a screw 912a-b whose head is supported against the plate 908a and whose threaded shank passes through the honeycomb structure 902 through a hole provided for this purpose in a resin 917. Each second fastening means 910a-b also includes a nut 914a-b which screws onto the threaded shank and sandwiches the thermo-acoustic exchanger 908 and the honeycomb structure 902.

[0014] Each second fixing means 910a-b also includes a column 916a-b which is positioned around the threaded rod between the plate 908a and the resistive sheet 902a.

[0015] For the second fixing means 910a of the first type, the inner diameter of the column 916a and the diameter of the hole through the honeycomb structure 902 are adjusted to the diameter of the threaded rod.

[0016] For the second fixing means 910a of the second type, the inner diameter of the column 916b and the diameter of the hole through the honeycomb structure 902 are greater than the diameter of the threaded rod to allow free thermal expansion.

[0017] Although such an arrangement is satisfactory, it requires several types of fastening means to fix the thermal insulation 904 and the thermo-acoustic exchanger 908. In addition, it is necessary to dismantle the thermal insulation 904 in order to remove the thermo-acoustic exchanger 908, hence a loss of time. Description of the invention

[0018] An object of the present invention is thus to propose an internal fixed structure for an aircraft, said internal fixed structure comprising a honeycomb structure, a thermo-acoustic exchanger, a thermal insulator and fixing means which are common for fixing the thermo-acoustic exchanger and the thermal insulator to the honeycomb structure.

[0019] To this end, an internal fixed structure is proposed for a nacelle of an aircraft propulsion system, said external fixed structure comprising:

[0020] - a honeycomb structure having two faces between which extend cells, where the first face is covered by a perforated resistive sheet and the second face is covered by a backing skin that seals the cells,

[0021] - a thermo-acoustic exchanger arranged opposite the resistive sheet, and including a plate, and

[0022] - a thermal insulator placed opposite the base skin,

[0023] the internal fixed structure being characterized in that it comprises a plurality of fastening means (306a-b) and in that each fastening means ensures the fastening of the thermal insulation (308) to the honeycomb structure and the fastening of the thermo-acoustic exchanger (304) to the honeycomb structure.

[0024] With such an arrangement, the means of fixing are common and it is no longer necessary to dismantle the thermal insulation to remove the thermo-acoustic exchanger.

[0025] Advantageously, the internal fixed structure comprises a fastening means of a first type ensuring a play-free fastening and a plurality of fastening means of a second type ensuring a play-free fastening.

[0026] Advantageously, each fastening means comprises:

[0027] - an insert housed and fixed in the honeycomb structure and which is traversed by a a threaded bore that opens on one side through the resistive foil and on the other side through the base skin,

[0028] - a first screw which is screwed into a first end of the tapped bore and whose threaded rod passes successively through the plate and the resistive foil, and whose head rests against an outer face of the plate,

[0029] - a second screw that screws into a second end of the tapped bore and whose threaded rod passes through the bottom skin, and

[0030] - a fastening system that secures the thermal insulation to the head of the second screw.

[0031] Advantageously, the fixing means of the first type comprises a column which is positioned around the threaded rod between the plate and the resistive sheet, and where the inner diameter of the column is adjusted to the diameter of the threaded rod of the first screw.

[0032] According to a particular embodiment, the fixing means of the second type comprises a column which is positioned around the threaded rod between the plate and the resistive sheet, and where the inner diameter of the column is greater than the diameter of the threaded rod of the first screw.

[0033] According to a particular embodiment, the hole through which the first screw passes through the plate takes the form of an oblong hole, the fixing means of the second type comprises a column which is positioned around the threaded rod between the plate and the resistive sheet, and where the inner diameter of the column is adjusted to the diameter of the threaded rod of the first screw and the column has an upper pad bearing against the plate and a lower pad bearing against the resistive sheet.

[0034] Advantageously, the faces of the pads which are in contact with the plate and the resistive sheet are covered with a sliding coating.

[0035] According to a particular embodiment, the fastening system is a blind nut which is screwed onto the head of the second screw by passing through the thermal insulation and which has a collar which is in contact with an outer face of the thermal insulation.

[0036] According to a particular embodiment, the fastening system is a clip which clips onto the head of the second screw by passing through the thermal insulation and which has a collar which is in contact with an outer face of the thermal insulation.

[0037] According to a particular embodiment, the fastening system is the head of the second screw against which an outer face of the thermal insulation rests.

[0038] The invention also proposes a propulsion assembly for an aircraft, said propulsion assembly comprising a turbojet engine with a core, a nacelle arranged around the turbojet engine and wherein the nacelle comprises an external fixed structure and an internal fixed structure according to one of the preceding variants around the core, wherein the two fixed structures delimit between them a secondary flow, wherein the bottom skin is oriented towards the core and wherein the resistive sheet and the thermo-acoustic exchanger are oriented towards the secondary flow.

[0039] The invention also proposes an aircraft comprising a propulsion assembly according to the previous variant. Brief description of the drawings

[0040] The features of the invention mentioned above, as well as others, appear will become clearer upon reading the following description of an example implementation, said description being made in relation to the attached drawings, among which:

[0041] [Fig. 1] is a side view of an aircraft according to the invention,

[0042] [Fig.2] is a schematic cross-sectional and side-view representation of an assembly propulsive,

[0043] [Fig.3] is a top view of an internal fixed structure according to the invention,

[0044] [Fig.4] is a cross-sectional view along line IV-IV of [Fig.3] of a system of fastening of a first type,

[0045] [Fig.5] is a cross-sectional view along line VV of [Fig.3] of a fastening system of a second type,

[0046] [Fig.6] is a view similar to [Fig.5] for an alternative embodiment of the invention,

[0047] [Fig.7] is a perspective view of a column implemented in the embodiment variant of [Fig.6],

[0048] [Fig.8] is a view similar to [Fig.4] for an alternative embodiment of the invention,

[0049] [Fig.9] is a perspective and cross-sectional view of a first prior art fastening method,

[0050] [Fig. 10] is a cross-sectional view of a fastening system of a first type of the prior art, and

[0051] [Fig. 11] is a cross-sectional view of a second type of prior art fastening system.

[0052] DETAILED STATEMENT OF IMPROVEMENTS

[0053] [Fig.1] shows an aircraft 100 which includes a propulsion unit 200 fixed under a wing 104 by means of a mast 106. The propulsion unit 200 takes the same form as that shown in [Fig.2] and the difference between the propulsion unit according to the invention and the propulsion unit of the prior art lies in the structure of the internal fixed structure.

[0054] The propulsion assembly 200 comprises a turbojet engine 202, a nacelle 204 arranged around the turbojet engine 202. The turbojet engine 202 comprises a core 207 and a fan 206 mounted at the front of the core 207. Outside air enters the propulsion assembly 200 through an air inlet 208 delimited by the front of the nacelle 204.

[0055] After passing through the blower 206, the air splits into a primary flow which passes through the core 207 comprising among other things a combustion system, and into a secondary flow which circulates between the core 207 and the nacelle 204 in a secondary channel 210 provided for this purpose.

[0056] The nacelle 204 comprises an external fixed structure 211 (or OFS for "Outer Fixed Structure" in Anglo-Saxon terminology) and an internal fixed structure 212 (or IFS (for "Inner Fixed Structure" in Anglo-Saxon terminology) which are concentric and delimit between them the secondary vein 210. The internal fixed structure 212 is around the nucleus 207.

[0057] In the following description, terms relating to a position are taken with reference to an aircraft 100 in its normal flight position, i.e., as shown in [Fig. 1], and the positions "forward" and "aft" are taken with respect to the front and rear of the propulsion assembly 200 and of the aircraft 100 with respect to the direction of forward movement of the aircraft 100 when the turbojet engine 202 is operating. Arrow F represents the direction of forward movement of the aircraft 100 in flight.

[0058] In the following description, and by convention, X is called the longitudinal direction of the turbojet 202 which is parallel to the longitudinal axis of said turbojet, Y is called the transverse direction which is horizontal when the aircraft 100 is on the ground, and Z is called the vertical direction which is vertical when the aircraft 100 is on the ground, these three directions X, Y and Z being orthogonal to each other.

[0059] Figure 3 shows an internal fixed structure 300 according to the invention, comprising a honeycomb structure 302 and a thermo-acoustic exchanger 304, which includes a plate 304a extending over the entire surface of the thermo-acoustic exchanger 304 and channels 304b extending under a central portion of the plate 304a. The channels 304b constitute the active part of the thermo-acoustic exchanger 304, and the plate 304a allows, among other things, the thermo-acoustic exchanger 304 to be attached to the honeycomb structure 302 on the side of the secondary vein 210 by means of fastening means 306a-b. The 304b channels extend here parallel to the longitudinal direction X and a heat transfer fluid such as oil for example circulates in the 304b channels.

[0060] Due to the thermal expansion undergone by the elements constituting the internal fixed structure 300, there is a first type of fastening means 306a that ensures a play-free fixing, thus providing a reference point for the assembly, and a plurality of second type of fastening means 306b that ensure a fixing with play parallel to the longitudinal direction. In the embodiment of the invention presented here, the first type of fastening means 306a is located in the middle and at the front of the thermo-acoustic exchanger 304, and the second type of fastening means 306b are distributed around the plate 304a and between the channels 304b.

[0061] Figs. 4 and 5 show cross-sections of the internal fixed structure 300 with the fixing means 306a of the first type for [Fig.4] and the fixing means 306b of the second type for [Fig.5].

[0062] The honeycomb structure 302 has two faces between which cells extend. The first face is covered by a resistive sheet 302a which is perforated to allow the sound waves to be attenuated to pass to the cells. The first face and the Resistive sheet 302a is oriented towards the secondary vein 210. The second face is covered by a base skin 302b which seals the alveoli. The second face and the base skin 302b are oriented towards the nucleus 207.

[0063] The thermo-acoustic exchanger 304 is arranged opposite the resistive sheet 302a and is oriented towards the secondary vein 210.

[0064] The internal fixed structure 300 also includes a thermal insulator 308 which is disposed opposite the bottom skin 302b on the side of the core 207 and which is fixed to the honeycomb structure 302 by the fixing means 306a-b.

[0065] Thus, the internal fixed structure comprises a plurality of fastening means 306a-b and each fastening means 306a-b simultaneously secures the thermal insulation 308 to the honeycomb structure 302 and the thermoacoustic exchanger 304 to the honeycomb structure 302. In addition, it is not necessary to remove the thermal insulation 308 in order to remove the thermoacoustic exchanger 304, thus saving time.

[0066] Fig. 4 shows an embodiment of the first type of fastening means 306a.

[0067] The fastening means 306a comprises an insert 401, in particular metallic, which is housed and fixed in the honeycomb structure 302, in particular here between the resistive sheet 302a and the base skin 302b, and it is embedded here in a resin 403 to ensure its fixation.

[0068] The insert 401 has a through-tapped bore 405 which opens on one side at through the resistive foil 302a and on the other side through the base skin 302b.

[0069] The fixing means 306a includes a first screw 402 which is screwed into a first end of the tapped bore 405 and whose threaded stem passes successively through the plate 304a and the resistive sheet 302a, and whose head is in contact with the outer face of the plate 304a, i.e. the face oriented towards the secondary vein 210.

[0070] The fastening means 306a also includes a column 406 which is positioned around the threaded rod between the plate 304a and the resistive foil 302a. The inner diameter of the column 406 is adjusted to the diameter of the threaded rod of the first screw 402.

[0071] The fastening means 306a includes a second screw 408 which is screwed into a second end of the tapped bore 405 and whose threaded shank passes through the bottom skin 302b.

[0072] The fastening means 306a also includes a fastening system 410 which secures the thermal insulation 308 to the head of the second screw 408. The fastening system 410 is, for example, a cap nut which is screwed onto the head of the second screw 408 by passing through the thermal insulation 308 and which has a flange 412 which bears against the outer face of the thermal insulation 308, i.e. the one oriented towards the core 207. The fastening system 410 is for example a clip which takes the same shape as the blind nut described above and which clips onto the head of the second screw 408.

[0073] In the embodiment of the invention in [Fig.4], the second screw 408 has a collar 414 attached to the threaded rod and which is in contact with the bottom skin 302b.

[0074] In the embodiment of the invention, the tapped bore 405 has two different diameters, but it is possible to have the same diameter. Furthermore, to allow the two screws 402 and 408 to be tightened, the two threads of the tapped bore 405 are in opposite directions.

[0075] Fig. 5 shows an embodiment of the 306b fastening means of the second type.

[0076] The fixing means 306b includes an insert 501, in particular metallic, which is housed and fixed in the honeycomb structure 302, in particular here between the resistive sheet 302a and the base skin 302b, and it is embedded here in a resin 503 to ensure its fixing.

[0077] The insert 501 has a through-tapped bore 505 which opens on one side at through the resistive foil 302a and on the other side through the base skin 302b.

[0078] The fixing means 306b includes a first screw 502 which is screwed into a first end of the tapped bore 505 and whose threaded stem passes successively through the plate 304a and the resistive sheet 302a, and whose head is in contact with the outer face of the plate 304a, i.e. the face oriented towards the secondary vein 210.

[0079] The fastening means 306b also includes a column 506 which is positioned around the threaded rod between the plate 304a and the resistive sheet 302a. The inner diameter of the column 506 is greater than the diameter of the threaded rod of the first screw 502 to limit the stresses in case of thermal expansion if the plate 304a and the column 506 move.

[0080] The fastening means 306b includes a second screw 508 which is screwed into a second end of the tapped bore 505 and whose threaded shank passes through the bottom skin 302b.

[0081] The fastening means 306b also includes a fastening system 510 that secures the thermal insulation 308 to the head of the second screw 508. The fastening system 510 is, for example, a cap nut that screws onto the head of the second screw 508 by passing through the thermal insulation 308 and has a flange 512 that bears against the outer face of the thermal insulation 308, i.e., the face oriented towards the core 207. The fastening system 510 is, for example, a clip that has the same shape as the cap nut described above and that clips onto the head of the second screw 508.

[0082] In the embodiment of the invention in [Fig.5], the second screw 508 has a collar 514 attached to the threaded rod and which is in contact with the bottom skin 302b.

[0083] In the embodiment of the invention, the tapped bore 505 has a single diameter, but it is possible to have two different diameters. Furthermore, to allow the two screws 502 and 508 to be tightened, the two threads of the tapped bore 505 are in opposite directions.

[0084] In the embodiments of the invention shown in Figs. 5 and 6, the columns 406 and 506 are independent components, but to limit losses during disassembly, the columns 406 and 506 can be one piece with the resistive sheet 302a.

[0085] Figure 6 shows a particular embodiment of the fastening means 306b of the second type which ensures better thermal expansion of the thermoacoustic exchanger 304 when needed and more particularly of the plate 304a.

[0086] In this embodiment, the hole 602 through which the first screw 502 passes through the plate 304a takes the form of an oblong hole whose major axis is parallel to the longitudinal direction X.

[0087] The column 606 is always positioned around the threaded rod of the first screw 502 between the plate 304a and the resistive sheet 302a and the inner diameter of the column 606 is adjusted to the diameter of the threaded rod of the first screw 502.

[0088] Figure 7 shows the column 606 which also includes two pads 606a-b which are perpendicular to the axis of the column 606 and therefore of the first screw 502.

[0089] There is an upper pad 606a which comes to rest against the plate 304a and more particularly against an inner face of the plate 304a.

[0090] There is a lower pad 606b which bears against the resistive sheet 302a and more particularly against an outer face of the resistive sheet 302a, that is to say the face oriented towards the secondary vein 210.

[0091] Thus, in the event of thermal expansion of the plate 304a, it will move by sliding on the upper pad 606a without being constrained by the first screw 502 due to the presence of the oblong hole 602.

[0092] To limit stress and wear on the parts when there is movement, the faces of the pads 606a-b which are in contact with the plate 304a and the resistive sheet 302a are covered with a sliding coating such as a Teflon fabric.

[0093] Figure 9 shows a variant that can be implemented for the fastening means. 306a of the first type and each fastening means 306b of the second type. In this variant, the second screw 808 does not have a collar and the fastening system 810 is formed directly by the head of the second screw 808 against which the face The exterior of the thermal insulation 308 rests directly against it. In this variant, the footprint on the side of the core 207 is thus reduced and it is not necessary to create a gap with the thermal insulation 308, thus improving the flow lines.

Claims

Demands

1. Internal fixed structure (300) for a nacelle (204) of a propulsion unit (200) of an aircraft (100), said internal fixed structure (300) comprising: - a honeycomb structure (302) having two faces between which cells extend, the first face being covered by a perforated resistive sheet (302a) and the second face being covered by a base skin (302b) closing the cells, the resistive sheet (302a) being oriented towards a secondary channel (210) delimited by the internal fixed structure (300), - a thermo-acoustic heat exchanger (304) disposed opposite the resistive sheet (302a), and comprising a plate (304a) and channels (304b) through which a heat transfer fluid circulates and which extend under a central portion of the plate (304a), where the thermo-acoustic exchanger (304) is intended to be oriented towards the secondary vein (210), and - a thermal insulator (308) disposed opposite the bottom skin (302b),the internal fixed structure (300) being characterized in that it comprises a plurality of fastening means (306a-b) and in that each fastening means (306a-b) ensures the fastening of the thermal insulation (308) to the honeycomb structure (302) and the fastening of the thermoacoustic exchanger (304) to the honeycomb structure (302).

2. Internal fixed structure (300) according to claim 1, characterized in that it comprises a fastening means (306a) of a first type ensuring a play-free fastening and a plurality of fastening means (306b) of a second type ensuring a play-free fastening.

3. Internal fixed structure (300) according to claim 2, characterized in that each fastening means (306a-b) comprises: - an insert (401, 501) housed and fixed in the honeycomb structure (302), and through which passes a threaded bore (405, 505) which opens on one side through the resistive sheet (302a) and on the other side through the base skin (302b), - a first screw (402, 502) which is screwed into a first end of the threaded bore (405, 505) and whose threaded shank passes successively through the plate (304a) and the resistive sheet (302a), and whose head bears against an outer face of the plate (304a), - a second screw (408, 508) which is screwed into a second end of the tapped bore (405, 505) and whose threaded rod passes through the bottom skin (302b), and - a hooking system (410, 510) which ensures the fixing of the thermal insulation (308) to the head of the second screw (408, 508).

4. Internal fixed structure (300) according to claim 3, characterized in that the fixing means (306a) of the first type comprises a co-ring (406) which is positioned around the threaded rod between the plate (304a) and the resistive sheet (302a), and where the inner diameter of the co-ring (406) is adjusted to the diameter of the threaded rod of the first screw (402).

5. Internal fixed structure (300) according to claim 3, characterized in that the fixing means (306b) of the second type comprises a co-ring (506) which is positioned around the threaded rod between the plate (304a) and the resistive sheet (302a), and where the inner diameter of the co-ring (506) is greater than the diameter of the threaded rod of the first screw (402).

6. Internal fixed structure (300) according to claim 3, characterized in that the hole (602) through which the first screw (502) passes through the plate (304a) takes the form of an oblong hole, in that the fixing means (306b) of the second type comprises a column (606) which is positioned around the threaded rod between the plate (304a) and the resistive sheet (302a), and where the inner diameter of the column (606) is adjusted to the diameter of the threaded rod of the first screw (502) and in that the column (606) has an upper pad (606a) bearing against the plate (304a) and a lower pad (606b) bearing against the resistive sheet (302a).

7. Internal fixed structure (300) according to claim 6, characterized in that the faces of the pads (606a-b) which are in contact with the plate (304a) and the resistive foil (302a) are covered with a sliding coating.

8. Internal fixed structure (300) according to any one of claims 3 to 7, characterized in that the fastening system (410, 510) is a blind nut which screws onto the head of the second screw (408, 508) by passing through the thermal insulation (308) and which has a collar (412, 512) which is in contact with an outer face of the thermal insulation (308).

9. Internal fixed structure (300) according to any one of claims 3 to 7, characterized in that the fastening system (410, 510) is a clip that clips onto the head of the second screw (408, 508) by passing through the thermal insulation (308) and which has a collar (412, 512) which is in contact with an outer face of the thermal insulation (308).

10. Internal fixed structure (300) according to any one of claims 3 to 7, characterized in that the fastening system (810) is the head of the second screw (808) against which an outer face of the thermal insulation (308) rests.

11. Propulsion assembly (200) of an aircraft (100), said propulsion assembly (200) comprising a turbojet (202) with a core (207), a nacelle (204) disposed around the turbojet (202) and wherein the nacelle (204) comprises an external fixed structure (211) and an internal fixed structure (212, 300) according to any one of the preceding claims around the core (207), wherein the two fixed structures delimit between them a secondary stream (210), wherein the bottom skin (302b) is oriented towards the core (207) and wherein the resistive sheet (302a) and the thermo-acoustic exchanger (304) are oriented towards the secondary stream (210).

12. Aircraft (10) comprising a propulsion assembly (200) according to the preceding claim.

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