Air-fire seal and assembly comprising such a seal

Abstract

An air-fire seal designed to be attached to a first tubular member of a turbomachine, such as a bleed duct, and to rest against a second member of the turbomachine, such as an intermediate casing hub, includes an attachment base having an annular shape around a reference axis (Y); a first annular fire-stop lip extending from the attachment base over a first length (L1); and a second annular air-sealing lip extending from the attachment base over a second length (L2) lower than the first length and facing the first lip.

Claims

1. An assembly comprising: a first tubular member of a turbomachine provided with a flange; a second member of the turbomachine comprising a first contact surface and a second contact surface, and an air-fire seal configured to be attached to the first tubular member, and to rest against the second member of the turbomachine, the air-fire seal including an attachment base having an annular shape around a reference axis, the attachment base being attached to the flange; a first annular fire-stop lip extending from the attachment base over a first length and resting against the first contact surface; and a second annular air-sealing lip extending from the attachment base over a second length lower than the first length and facing the first annular fire-stop lip, the second annular air-sealing lip resting against the second contact surface.

2. The assembly according to claim 1, wherein the first tubular member is a bleed duct of the turbomachine and the second member is an intermediate casing hub of the turbomachine.

3. The assembly according to claim 1, wherein the first contact surface of the second member is perpendicular to the reference axis and wherein the second contact surface of the second member is parallel to the reference axis.

4. The assembly according to claim 1, wherein the first fire-stop lip is located radially outermost relative to the reference axis and the second air-sealing lip is located radially innermost relative to the reference axis.

5. The assembly according to claim 1, wherein the first fire-stop lip and the second air-sealing lip are tilted outwardly by an angle between 5° and 7° relative to the reference axis.

6. The assembly according to claim 1, wherein the air-fire seal comprises a third annular fire-stop lip extending from the attachment base over a third length lower than the first length and radially disposed between the first fire-stop lip and the second air-sealing lip.

7. The assembly according to claim 1, wherein the first fire-stop lip comprises plies of ceramic fibres embedded in an elastomeric material.

8. The assembly according to claim 7, wherein the elastomeric material is silicone.

9. The assembly according to claim 7, wherein the number of plies of ceramic fibres in the first fire-stop lip is between 1 and 3.

10. The assembly according to claim 1, wherein the first fire-stop lip comprises a metal reinforcement embedded in an elastomeric material.

11. The assembly according to claim 10, wherein the elastomeric material is silicone.

12. The assembly according to claim 1, wherein the second air-sealing lip is coated with an antifriction fabric.

13. A turbomachine comprising an assembly according to claim 1.

14. The turbomachine according to claim 13, wherein the turbomachine is a two-spool turbofan engine.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further characteristics and advantages of the invention will clearly appear from the description thereof given below, by way of indicating and in no way limiting purposes, in reference to the appended figures, in which:

(2) FIG. 1, previously described, is a partial axial cross-section view of an intermediate casing hub according to prior art;

(3) FIG. 2 is an axial cross-section view of an air-fire seal according to a preferential embodiment of the invention;

(4) FIG. 3 illustrates a first exemplary embodiment of the air-fire seal according to the invention; and

(5) FIG. 4 illustrates a second exemplary embodiment of the air-fire seal according to the invention.

(6) For more clarity, identical or similar elements are marked by identical reference signs throughout the figures.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

(7) FIG. 2 shows an axial cross-section view of an air-fire seal 30 according to a preferential embodiment of the invention. The seal 30 is housed between a first member 31 of a turbomachine, such as a two-spool turbofan engine, and a second member 32 of the turbomachine. It is designed to ensure air and fire sealing between a first enclosure 33a and a second enclosure 33b disposed on either side of the seal 30 and delimited, at least partly, by the first and second members 31-32. In the example represented in FIG. 2, the first enclosure 33a is a zone of the turbofan engine with a fire risk and the second enclosure 33b is likely to be crossed by an air flow.

(8) The first member 31, which is tubular shaped, occupies a port 34 of corresponding shaped provided in a first wall 321 of the second member 32. This port 34 being of dimensions slightly higher than the external dimensions of the first tubular member 31, there is a clearance 35 between the first and second members 31-32. The seal 30 is located in the immediate proximity of this clearance 35.

(9) The seal 30 is advantageously symmetrical around a reference axis Y, which is the same as the symmetry axis of the first tubular member 31. It comprises a Y-axis annular attachment base 300 and at least two annular lips 301-302, coaxial with the attachment base 300. Both lips 301-302 extend facing each other from the attachment base 300 toward the second member 32.

(10) Preferably, the attachment base 300 rests against a flange 310 of the first tubular member 31 and extends in a radial direction, that is perpendicular to the reference axis Y. The attachment base 300 can be bonded to the flange 310 prior to assembling the first and second members 31-32, for example by means of a silicone elastomer cross-linking at room temperature, or RTV (for “Room Temperature Vulcanising”).

(11) The first lip 301, disposed in this example radially outermost with respect to the reference axis Y, is a stop-fire type lip, that is it is designed to resist a fire that would take place in the first enclosure 33a and to stop the advance of this fire to the second enclosure 33b, at least temporarily. The first lip 301 is dimensioned to rest against the first wall 321 of the second member 32. The first lip 301 thus protects other parts of the seal 30 from fire, in particular the second lip 302. The first wall 321 of the second member 32 is preferably oriented perpendicular to the reference axis Y.

(12) The second lip 302, disposed radially innermost relative to the reference axis Y, is an air-sealing lip. Its role is to maintain the second enclosure 33b under pressure by preventing the air flow from penetrating in the first enclosure 33a and from feeding the fire contained in this zone. The second lip 302 is of a length L2 lower than the length L1 of the first lip 301, so as not to contact the first wall 321, which would increase the mounting force of the first member 31 (equipped with the seal 30) with the second member 32. By way of example, the length L1 of the first lip 301 is about 9 mm and the length L2 of the second lip 302 is about 8 mm.

(13) To ensure air-sealing, the second lip 302 rests against a second wall 322 of the second member 32, preferably oriented parallel to the reference axis Y. By way of example, this second wall 322 consists of an (Y-axis) annular rib set back relative to the port 34 and projecting from the first wall 321 towards the flange 310 of the first member 31.

(14) Because it is substantially shorter than the first lip 301, the second lip 302 is free to slide along the second wall 322. This enables it not to be impacted by dimensional variations in the housing in view of axial manufacturing tolerances and compensate for possible axial movements between the first and second members 31-32 when the turbofan engine is operated.

(15) By virtue of these arrangements, the second air-sealing lip 302 is radially rather than axially stressed. The stresses are low because they are essentially due to air pressure in the second enclosure 33b, and not upon mounting the first and second members 31-32. The deformation rate of the second lip 302 is thus low in comparison with the sealing solutions of prior art, which minimising damage or premature aging risks.

(16) Advantageously, the second air-sealing lip 302 is tilted outwardly by an angle α between 5° and 7° relative to the reference axis Y and extends over its entire length in parallel to the first fire-stop lip 301. Further, as is represented in FIG. 2, the free end of the first lip 301, projecting from the second lip 302, can be further outwardly tilted, for example by an angle β between 7° and 16° (still with respect to the reference axis Y). These tilts facilitate the mounting of the first and second members 31-32 and ensure a better air-fire sealing.

(17) The seal 30 comprises, in this preferential embodiment of FIG. 2, a third fire-stop lip 303 disposed radially between the first lip 301 and the second lip 302. The length of this third lip 303 is lower than the length L1 of the first lip 301, for example equal to the length L2 of the second lip 302. The third lip 303 thus constitutes a further fire barrier, which will slowdown fire propagation after the first lip 301 has failed, by forming a chicane with the second wall 322 of the second member 32. Since it is not supposed to rest on either wall of the second member 32, this third lip 303 does not increase the mounting force. The third lip 303 preferably extends in parallel to the first lip 301. In other words, it is tilted outwardly by the angle α.

(18) The seal 30 can be built in different ways. In a first exemplary embodiment represented in FIG. 3, the seal 30 comprises ceramic fibres 40 embedded in a matrix 41 of a self-extinguishable silicone elastomer. The ceramic fibres 40 are preferably in the form of a fabric, as that marketed by the “3M” Company under the reference “Nextel™312”. Such fibres are known to provide a large fire resistance but have a significant stiffness, which can increase the compression force of the seal upon mounting (the first lip 301 being more or less compressed as a function in particular of the dimensions of the members 31-32). The attachment base 300, the first fire-stop lip 301 and the third fire-stop lip 303, which all are likely to be exposed to fire, advantageously have a number of plies of ceramic fibres between 1 and 3. This range offers an excellent compromise between fire performance and mounting force. The second air-sealing lip 302 advantageously has a lower number of plies of ceramic fibres 40, for example a single ply, in order to provide it with further flexibility.

(19) In a second exemplary embodiment, the seal 30 comprises a metal reinforcement 42 embedded in the matrix 41 of self-extinguishable silicone elastomer. The metal reinforcement 42, for example of steel, Hastelloy® or titanium, makes an efficient fire barrier. It extends preferentially in the attachment base 300, the first fire-stop lip 301 (except for its free end, such that this can bend in contact with the second member 32) and the third fire-stop lip 303. The second air-sealing lip 302 is preferentially free of metal reinforcement to accommodate more readily to movements and vibrations of the members 31-32.

(20) In each of these exemplary embodiments, the second air-sealing lip 302 can be coated with an antifriction fabric 43 at its contact surface, in order to more readily slide on the second wall 322 of the second member 32. The antifriction fabric 43 is also resistant to high temperatures (up to 1100° C. in case of fire) and antistatic (in order not to create sparks). The antifriction fabric 43 is for example that marketed by the “DuPont” Company under “Nomex®”.

(21) The seal 30 of FIGS. 2 to 4 can be used in different places of a turbomachine. A preferred application of the seal 30 relates to the bleed ducts of a two-spool turbofan engine. These ducts are for redirecting part of the primary flow to the secondary flow space. The bleed ducts can in particular be of the same type as that described in connection with FIG. 1. In reference to this figure, each duct comprises a first end opening into an intermediate space 23 of the intermediate casing hub 10 and a second end opening into the secondary flow space 21. The intermediate space 23 of the hub 10, in fluid communication with the primary flow space 18 through a bleed valve 20, is delimited by the inner 12 and outer 13 annular shells on the one hand and by the upstream 14 and downstream 15 transverse flanges on the other hand. Each bleed duct extends through the inter-stream zone or “core zone” ZC of the turbofan engine, which is known to be a zone with fire risk.

(22) The seal 30 can thus be mounted around a bleed duct and cooperate with the downstream transverse flange 15 of the intermediate casing hub. In other words, in this application, the first tubular member 31 of FIG. 2 corresponds to the bleed duct, the second member 32 corresponds to the intermediate casing hub, and more particularly to its downstream transverse flange, the first enclosure 33a corresponds to the core zone ZC of the turbofan engine and the second enclosure 33b corresponds to the hub intermediate space.

(23) The seal 30 has the advantage, because of its design, not to significantly impact the geometries of the bleed duct and of the intermediate casing hub. Indeed, a deep change in these geometries could increase the mass and manufacturing costs of the intermediate casing. The use of the seal 30 only requires a repositioning of the existing flange of the bleed duct and a provision of the surface of the downstream transverse flange on which the sealing second lip rests. The length of this contact surface (in the axial direction of FIG. 3) is at least 5 mm.

(24) In some two-spool turbofan engines, such as that partially represented in FIG. 1, the bleed ducts are pieces belonging to the intermediate casing hub. They are attached at their second end to the outer shell of the hub.

(25) In other turbofan engines, the bleed ducts belong to an extension of the intermediate casing, commonly called “kit engine”. This extension of the intermediate casing conventionally comprises several shell sectors which reform the secondary flow space and structural connecting arms enabling (electrical, mechanical, hydraulic) ancillary pieces of equipment to pass between the nacelle and the different components of the turbofan engine (core zone in particular). The bleed ducts are then premounted on the shell sectors and then mounted by hand without specific tooling in the intermediate casing. The seal 30 is particularly adapted to this last type of turbofan engine, because it is designed to minimise the mounting force, as has been previously described.

(26) Many variants and modifications of the seal according to the invention will appear to those skilled in the art. For example, in some places of the turbomachine, the location of the first and second enclosures 33a-33b can be reversed, that is the first enclosure 33a is travelled by an air flow and the second enclosure 33b has a fire risk. The positions of the first fire-stop lip 301 and the second air-sealing lip 302 will be also reversed. In other words, the first fire-stop lip 301 will be located radially innermost and the air-sealing second lip 302 will be located radially outermost. Finally, the lips 301-302 could be tilted (i.e. rotated) by the angle α in the other direction, that is inwardly.

(27) Eventually, the composition of the seal 30 is not limited to the examples of materials described previously in connection with FIGS. 3 and 4. All or part of the ceramic fibres can in particular be replaced by glass fibres and elastomeric materials other than silicone can be used.