EP1978305B1 - Shielding for the bottom of a combustion chamber - Google Patents

Description

The invention relates to an annular fairing intended to cover the annular chamber bottom of a turbomachine combustion chamber. It is intended for any type of turbomachine, terrestrial or aeronautical, and more particularly to aircraft turbojets.

Conventional turbojet combustion chambers comprise an inner wall, an outer wall and an annular chamber bottom disposed between said walls, in the upstream region of the chamber. This chamber bottom supports injection heads that spray the fuel into the combustion chamber.

These conventional combustion chambers also include an annular fairing intended, on the one hand, to cover upstream (ie at the front) said chamber bottom and said injection heads to protect them from possible shocks (that can produce ingestion of a bird or an ice block in the turbojet engine) and, on the other hand, to ensure an aerodynamic bypass of the bottom of the chamber with low losses.

In the present application, upstream and downstream are defined with respect to the normal flow direction of the gases (from upstream to downstream) through the turbomachine, and the adjectives inside and outside are used with reference to a radial direction, that is to say a direction perpendicular to the axis of rotation X of the rotor of the turbomachine. Thus, the inner part of an element is closer to the X axis than the outer part of the same element.

Some known fairings are composed of two separate and concentric annular pieces, commonly called "caps", which extend on the inner periphery and the outer periphery of the chamber bottom. These inner and outer "caps" are fixed on the combustion chamber and separated by an annular space which allows access to the injection heads and through which pass the fuel injectors connected to the injection heads. A "cap" fairing is described, for example, in the document EP 1265031 A1 .

Other so-called monobloc fairings are also known, formed of a single annular piece. The two "caps" of the fairing are then connected by bars defining between them openings through which pass the fuel injectors. In half-section in an axial plane comprising the axis of rotation X, the fairing has a shape substantially semicircular. Being more rigid, this type of fairing is more resistant to vibratory stress than the aforementioned "cap" fairings. A one-piece fairing is described, for example, in the document US 6148600 .

The fairings are usually bolted because a bolted joint offers a lot more latitude in terms of maintenance than a welded joint.

To mount a fairing on a chamber bottom, the inner and outer edges of the fairing are fixed with bolts regularly distributed around the periphery of the chamber bottom. During this step, a rather large tightening must be applied to catch the mounting clearance, inherent to the assembly and manufacturing tolerances, which has the disadvantage of losing the fairing ring shape, the inner and / or outer edges of the fairing forming deformation lobes between the pairs of bolts, which gives these edges a shape called "daisy". These lobes show gaps between the assembled parts, causing air leaks and pressure drops. Moreover, mechanically, taking into account said mounting clearances, the rigidity of the assembly leads either to a tightening torque that is too great for the holding of the screw and / or the fairing, or to the lack of the necessary contact to pass by friction the service efforts passing through the bolted connections.

To significantly reduce these disadvantages, a known solution is to make slots in the edges of the fairing, between the bolts, to provide a little more flexibility when setting up the fairing and thus improve the effective clamping parts. However, this solution has other drawbacks: in operation, the slots generate air leaks that are aerodynamically detrimental and they may be generating crack initiation primers.

Annular fairings are also known divided into several adjacent sectors whose side edges are edge-to-edge, described for example in the document EP-0 488 557 . Due to edge-to-edge mounting, the inner and / or outer edges of the fairing can form deformation lobes between the pairs of bolts.

The invention aims to provide a fairing without the aforementioned drawbacks.

This object is achieved thanks to an annular fairing intended to cover the annular chamber bottom of a turbomachine combustion chamber, this fairing having openings to allow the passage of fuel injectors supported by the chamber bottom, this fairing being divided into several adjacent sectors, each fairing area presenting inner and outer fixing edges which can be fixed on either side of said chamber bottom, characterized in that the fairing sectors have lateral edges such that the lateral edges of two adjacent sectors overlap.

The shroud of the invention is fixed sector by sector on the upstream edges of the outer and inner walls of the combustion chamber, which avoids the formation of the aforementioned deformation lobes and to ensure good contact between the fixing edges of each sector and these walls. In addition, it becomes unnecessary to make slots in these fixing edges and avoids the disadvantages associated with the presence of these slots.

In addition, with the known fairings (as explained above) a part of the tightening force of the bolts was used to deform the fairing which was rigid. The sectors of the fairing of the invention being more flexible, one can either reduce the clamping force, or get a better contact between the assembled parts for the same clamping force.

Such overlap avoids air leakage between two adjacent sectors.

Moreover, a better damping of the vibrations with the sectorized fairing of the invention is obtained than with the monolithic or "cap" fairings known until now, because each sector of the fairing has a proper dynamic behavior and the friction between sectors. adjacent ones promote said damping. Diameter modes specific to the annular parts which are likely to resonate with the harmonics of the engine speed are also avoided.

The inner and outer fixing edges of each sector are respectively fixed to the inner and outer walls of the combustion chamber. According to a particular embodiment of the invention, each of said fixing edges is fixed in N fixing points, with N greater than or equal to 2, and at least N-1 of said fixing points are each made by means of a fastener (especially a bolt) passed through an oblong hole.

Said N-1 oblong holes extend in the circumferential direction of the fairing, and these holes allow said fastening elements to move circumferentially during assembly, this displacement being due to the radial approach of the fairing on the diameters of each wall and on the outside and inside diameters of the bottom of the combustion chamber. This allows a better contact, thus a more effective clamping in the assembly, and avoids the creation of constraints in the sectors.

According to another particular embodiment of the invention, the inner and outer fixing edges of each sector are each fixed in a single point of attachment, this fixing point being located outside the zone of overlapping sectors.

With a single point of attachment per fixing edge, it avoids the problems related to the difference in expansion between the assembled parts, in the case where the difference in expansion is important during operation of the turbomachine. In addition, said fixing points being generally made by means of a fastening element, in particular a bolt, passed through a hole drilled in the sector, by reducing the number of fixing points to the maximum, the number of elements is reduced. fasteners (bolts) used and a gain in mass is achieved. It also reduces the number of holes to drill and therefore the manufacturing cost of each sector. In addition, since the side edges of two adjacent sectors overlap, a sector helps to maintain in position the adjacent sector that it overlaps. Finally, as described below, the fixing of the sectors on the outer and inner walls and on the chamber bottom remains a simple operation.

• La figure 1 représente, schématiquement, un exemple de chambre de combustion selon l'invention, dans son environnement à l'intérieur d'un turboréacteur d'avion, en demi-coupe axiale dans un plan axial comprenant l'axe de rotation X du turboréacteur. Le fond de cette chambre est recouvert par un carénage.
• La figure 2 représente en perspective la région amont de la chambre de combustion de la figure 1, recouverte par deux secteurs adjacents d'un exemple de carénage selon l'invention.
• La figure 3 représente en perspective un des secteurs de carénage de la figure 2.
• La figure 4 représente en perspective les deux secteurs de carénage de la figure 2.
• La figure 5 est une vue analogue à celle de la figure 4, représentant deux secteurs adjacents d'un autre exemple de carénage selon l'invention.
• La figure 6 représente en perspective plusieurs secteurs adjacents d'un autre exemple de carénage selon l'invention.

The invention and its advantages will be well understood from reading the detailed description of the invention which follows. This description refers to the plates of annexed figures in which:

• The figure 1 represents, schematically, an example of a combustion chamber according to the invention, in its environment inside an aircraft turbojet engine, in axial half-section in an axial plane comprising the axis of rotation X of the turbojet engine. The bottom of this room is covered by a fairing.
• The figure 2 represents in perspective the upstream region of the combustion chamber of the figure 1 covered by two adjacent sectors of an example of fairing according to the invention.
• The figure 3 represents in perspective one of the fairing areas of the figure 2 .
• The figure 4 represents in perspective the two fairing areas of the figure 2 .
• The figure 5 is a view similar to that of the figure 4 , representing two adjacent sectors of another example of fairing according to the invention.
• The figure 6 represents in perspective several adjacent sectors of another example of fairing according to the invention.

The figure 1 represents an example of a turbojet, in half-section along a section plane containing the axis of rotation X of the rotor of the turbojet engine. The turbojet comprises a centrifugal high pressure compressor (not shown) and, downstream thereof, a diffuser 4 opening into a space 5, delimited by an outer casing 6 and a concentric inner casing 7, and occupied by a combustion chamber. annular 8 supported by the casings 6 and 7.

Although the figure 1 relates to a turbojet engine with centrifugal compressor, the invention is not limited to this type of turbomachine.

The combustion chamber 8 comprises an inner wall 2, an outer wall 3 and an annular chamber bottom 11 disposed between said walls, in the upstream region of said chamber. This chamber bottom 11 has fixing flanges, inside 11a and outside 11b, folded upstream with respect to the main wall of the chamber bottom 11.

The chamber bottom 11 carries injection heads 12 in connection with a fuel supply system 13, via fuel injectors 14 passing through the space 5. These elements represented on the figure 1 have not been included in the other figures.

The combustion chamber 8 is equipped with an annular shroud 10. This shroud 10 covers the chamber bottom 11 to protect it, and has openings 16 to allow the passage of said injectors 14. The section of the shroud 10 in the plane of the figure 1 , has a substantially semicircular shape. Thus, the fairing 10 has good rigidity and therefore a better dynamic behavior than the known "cap" fairings. It also presents an adequate aerodynamic bypass.

In addition, according to the invention, the fairing 10 is divided into several adjacent sectors denoted 100, 100 '(see Figures 2 to 5 ) or 200, 200 ', 200 "(see figure 6 ). In the example, these adjacent sectors are all identical, which allows them to be mass-produced.

Of course, the number of sectors can vary. Thus, in the case of a combustion chamber 8 with eighteen fuel injectors 14, equipped with a shroud 10 having an opening 16 for each injector 14, ie eighteen openings 16, it is possible, for example, to divide the fairing in eighteen sectors, each sector having a single opening 16, or divide the fairing into nine, six, or even three sectors, each sector then having respectively two, three or six openings 16. Of course, the greater the number of sectors is weak, the assembly of fairing 10 is fast, but less areas are flexible. Conversely, the more the number of sectors is important, the more these sectors are flexible and the easier it is to get a good contact between the fixing edge of these sectors and the outer walls 3 and inner 2, but the assembly of the fairing It takes time. In addition, the greater the number of sectors, the better the vibration damping.

In general, each fairing sector has at least one opening allowing the passage of at least one fuel injector. The Figures 2 to 5 represent exemplary embodiments where each sector 100, 100 'has a single opening 16 for the passage of a fuel injector 14. The figure 6 represents an exemplary embodiment where each sector 200, 200 ', 200 "has three openings 16, each opening allowing the passage of a fuel injector 14. According to other exemplary embodiments, not shown, each fairing sector has a or several openings, each opening being sufficiently circumferentially extended to allow the passage of several fuel injectors.

With reference to Figures 2 to 5 each sector 100 covers, upstream, the chamber bottom 11 and includes inner fixing edges 100a and outer 100b fixed to the inner fixing flange 11a and outer 11b of the chamber bottom 11 and to the upstream edges 2a and 3b of the inner walls 2 and outer 3, at different attachment points. More specifically, the outer binding edge 100b (or inner 100a) of the fairing sector, the upstream edge 3b (or 2a) of the outer wall 3 (or inner 2), and the outer fixing flange 11b (or inner 11a). from the bottom of the room 11 are superimposed from the outside to the inside of the combustion chamber 8, and are traversed by holes coinciding with each other and through which have passed bolts 15. These bolts 15 maintain said edges 100a, 100b, 3a, 3b and flanges 11a, 11b, assembled together and are distributed in two concentric circles around the axis X.

Adjacent sectors 100 and 100 'of Figures 2 to 5 each have two side edges 101, 102 and 101 ', 102' and when these sectors are joined, the side edge 101 of the sector 100 overlaps the side edge 102 'of the adjacent sector 100'. Thus, there is no circumferential space between the assembled sectors, which limits or even avoid air leakage between these sectors.

More particularly, in the embodiments of the figures, each sector 100 comprises on its lateral edge 101 a lip 105 connected to the rest of the sector by a riser 107. It is this lip 105 which covers the lateral edge 102 'of the adjacent sector. 100 ', when the sectors 100 and 100' are assembled (see figures 2 , 4 and 5 ). The riser 107 can also serve as a stop for the lateral edge 102 'of the sector 100' and thus facilitate the establishment of the sectors relative to each other.

In the exemplary embodiment of Figures 2 to 4 , the inner fixing edges 100a and outer 100b of each sector 100 are each fixed at two fixing points. These two attachment points are respectively located at the side edges 101 and 102 of the sector 100. More specifically, these two attachment points are made by means of a bolt 15 passed through a hole 108 or 109 crossing the edge. concerned. At least one of said holes is oblong, its largest dimension being oriented in the circumferential direction of the shroud 10. This oblong hole 108 allows a distance or a relative approximation of the bolts 15, such spacing / approximation can be caused during assembly of the sector 100 on the walls 2 and 3 or, in operation, by the difference in expansion between the walls 2 and 3 and / or the bottom 11 of the chamber 8 and the sector 100. This avoids the occurrence of stresses in the sector 100 .

In the example of Figures 2 to 4 two circular holes 109 are respectively formed in the fixing edges 100a and 100b, on the side of the lateral edge 102, while two oblong holes 108 are respectively arranged in the fixing edges 100a and 100b, on the side of the lateral edge 101. More precisely, the two oblong holes 108 pass through the lip 105.

The figure 5 is a view similar to that of the figure 4 representing two adjacent sectors 100, 100 'of another example of a fairing according to the invention. The fairing areas 100, 100 'of the figure 5 differ from those of the figure 4 only with regard to their fixing points at the bottom of the chamber. Indeed, in the example of figure 5 , the inner fixing edges 100a and outer 100b of each sector 100 are each fixed at a single point of attachment. This fixing point is made with a bolt 15, passed through a hole 111 which passes through the fastening edge 100a or 100b of the sector. This makes it possible to limit as much as possible the number of bolts 15 and holes 111, and thus to minimize the mass and the manufacturing cost of the sector 100.

Advantageously, said attachment point is situated outside the zone of overlap of the sectors 100, but is positioned in the vicinity of this zone. In this way, a part of the clamping forces of the bolt 15 is used so that the side edge 101 of the sector 100 exerts pressure on the side edge 102 'of the adjacent sector 100' and maintains the sector 100 'in position.

The assembly of the fairing 10 of the figure 5 can be achieved as follows: first, the sector 100 is fixed on the chamber bottom 11, without completely tightening the bolts 15 through the openings 111, then the side edge 102 'of the adjacent sector 100' is passed under the lip 105. Then, the second sector 100 'is fixed without completely tightening the bolts 15 passing through the openings 111', so as to be able to pass under the lip 105 'of the sector 100' the lateral edge of another adjacent sector, not shown, And so on. Once all sectors are in place, bolts 15 are fully used.

Note that due to the overlap of the sectors, the first sector 100 when partially fixed (i.e. by incomplete clamping of the bolt 15) maintains the second sector 100 'while it is not yet bolted to the chamber bottom. This facilitates the assembly of the fairing areas.

Claims (7)

1. An annular fairing (10) for covering the annular chamber end wall (11) of a turbomachine combustion chamber (9) and having openings (16) for letting through fuel injectors (14) which are supported by the chamber end wall, this fairing being subdivided into several adjacent sectors (100, 100' ; 200, 200', 200"), each fairing sector (100) having inner (100a) and outer (100b) fastener edges capable of being fastened on either side of said chamber end wall (11), characterized in that said sectors have side edges such that the side edges (101, 102') of two adjacent sectors (100, 100') overlap.
2. The fairing according to claim 1, wherein each sector (100) comprises, on one of its side edges (101), a lip (105) connected to the remainder of the sector by a riser (107), this lip being intended to overlap the side edge (102') of the adjacent sector (100').
3. The fairing according to claim 1 or 2, wherein the inner (100a) and outer (100b) fastener edges of each sector (100) are each fastened at N fastening points, with N greater than or equal to 2, and wherein at least N-1 of said fastening points are each produced by means of a fastener element (15) passed through an oblong hole (108).
4. The fairing according to claim 1 or 2, wherein the inner (100a) and outer (100b) fastener edges of each sector (100) are each fastened at a single fastening point, this fastening point being located outside the sector overlapping area.
5. The fairing according to any of claims 1 to 4, wherein each fairing sector (100) has at least one opening (16) for letting through at least one fuel injector (14).
6. A combustion chamber (8) comprising an inner wall (2), an outer wall (3), and in the upstream region of said chamber, an annular chamber end wall (11) positioned between said walls, this chamber end wall being covered with a fairing (10) according to any of claims 1 to 5.
7. A turbomachine comprising a combustion chamber (8) according to claim 6.

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