Combustion chamber of a gas turbine engine with an upstream fairing for separating the gas stream, annular wall forming a cap of the upstream fairing of the chamber, and gas turbine engine with the chamber

The present invention is concerned with an annular combustion chamber of a gas turbine engine with an external annular wall and an internal annular wall, including an upstream fairing for separating the gas stream at the inlet of the chamber into a combustion stream and a bypass stream which bypasses the inlet of the chamber, the fairing including an annular wall forming a cap, which includes a downstream portion for fastening to a wall of the chamber and an upstream portion forming an edge of the flow cross section for the combustion stream, wherein the upstream portion is continued into at least one additional downstream portion for fastening to the wall of the chamber.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

The invention relates to a combustion chamber of a gas turbine engine with an upstream fairing for separating the gas stream, to an annular wall forming a cap of the upstream fairing of the chamber, and to a gas turbine engine with the chamber.

A turbojet comprises, from upstream to downstream in the direction of gas flow, a fan, one or more compressor stages, a combustion chamber, one or more turbine stages and a gas exhaust nozzle. The terms “external” and “internal” are intended to mean radially external and internal with respect to the axis of the turbojet. The terms “outer” and “inner” are intended to mean the outer side and the inner side of the combustion chamber.

With reference toFIG. 1, which represents a combustion chamber1of the prior art, the combustion chamber1is generally annular around the axis of the turbojet. It comprises, in its upstream portion, a chamber end section2with injection systems supplied with fuel by injectors3connected to a supply line4. The injection systems are distributed along the chamber end section2. The gas of the primary stream emerges upstream of the chamber1via a diffuser5, from which the gas stream is separated into a stream6passing into the combustion chamber1to allow combustion of the fuel injected by the injector3, referred to as combustion stream6, into an external bypass stream7which externally bypasses the inlet of the chamber1, and into an internal bypass stream8which internally bypasses the inlet of the chamber1. The streams7,8which bypass the inlet of the chamber are used for cooling the chamber1, in particular.

The primary gas stream is separated at a fairing9. This fairing9comprises two parts, called an external cap10and an internal cap11. The external cap10takes the form of an annular metal sheet domed toward the upstream side, fastened to the combustion chamber1at an outer downstream surface portion15, and the inner upstream edge12of which forms a fold in the downstream direction, thus forming an aerodynamic surface for separation into an external bypass stream7and a combustion stream6. Likewise, the internal cap11takes the form of an annular metal sheet domed toward the upstream side, fastened to the combustion chamber1at an outer downstream surface portion16, and the inner upstream edge13of which forms a fold in the downstream direction, forming an aerodynamic surface for separating the internal bypass stream8and the combustion stream6.

The external10and internal11caps are fastened on the outer side of the external31and internal32wall, respectively, of the combustion chamber1, at their outer downstream surface portion15,16, respectively, by bolts14. The external10and internal11caps are therefore mounted in cantilever fashion on the combustion chamber1.

The combustion chamber is subjected to vibrational stresses, particularly as a result of the combustion and the engine speed. The caps10,11are therefore subjected to these vibrations, in particular the external cap10. The caps10,11are also subjected to other dynamic excitation frequencies, in particular certain harmonic frequencies of the rotational speed of the rotating elements of the turbojet. The caps10,11, mounted in cantilever fashion, may have resonance modes close to the aforementioned frequencies and are therefore subjected to high mechanical dynamic stresses. The caps10,11are consequently exposed to the risks of breaking or cracking.

Various solutions to this problem have been proposed.

A first solution involves providing an annular damping ring, housed in the fold12,13of the caps10,11(or only in the fold of the external cap which is most subjected to the vibrational stresses); the fold12,13is to this end wrapped around the ring so as to hold it in place. The friction caused by the presence of the ring provides an effect of damping and therefore of shifting the frequencies of the resonance modes of the caps10,11, which enables them to be distanced from the vibrational frequencies to which the caps10,11are subjected. However, such a device has the disadvantage of low mechanical strength. There is a risk of the ring loosening, or even breaking (on account of the vibrations to which it is subjected), which diminishes or cancels out its effectiveness.

A second solution involves providing an integrated fairing9, which will thus be termed a covering. The external10and internal11caps are then formed in a single piece, with connection tabs between them at their inner upstream edges12,13. Such a device has two disadvantages. First, given the connecting tabs between the caps10,11, the flow cross section for the combustion stream6is reduced; now it is an established fact that this cross section must be as large as possible so as to promote the flow of this stream in order to achieve better combustion efficiency. Second, it is appropriate for the cutouts between the tabs to be formed by laser cutting, these cutouts having to have the equivalent of the folds12,13around their contour. Producing such an integrated covering is very difficult and therefore expensive.

SUMMARY OF THE INVENTION

The invention aims to overcome these disadvantages and to provide a fairing sufficiently withstanding the vibrational stresses, complying with the aerodynamic criteria of stream separation and at the same time having a maximum cross section for the flow of the combustion stream6, and being able to be produced simply and at low cost.

To this end, the invention relates to an annular combustion chamber of a gas turbine engine with an external annular wall and an internal annular wall, comprising an upstream fairing for separating the gas stream at the inlet of the chamber into a combustion stream and a bypass stream which bypasses the inlet of the chamber, the fairing comprising an annular wall forming a cap, which comprises a downstream portion for fastening to a wall of the chamber and an upstream portion forming an edge of the flow cross section for the combustion stream, wherein the upstream portion is continued into at least one additional downstream portion for fastening to the wall of the chamber.

By virtue of the invention, the cap-forming annular wall, which is fastened not only at its downstream fastening portion but also at the additional downstream fastening portion integral with its upstream portion, is stiffened, which increases the frequency of its resonance modes, which do not intersect with the vibration frequencies to which the flange is subjected. The cantilever effect is attenuated. Moreover, such a cap is mechanically solid, which avoids the disadvantages associated with the presence of a ring, while it allows the fairing for separating the air stream upstream of the chamber to be formed as an external cap and an internal cap, thereby providing an optimum flow cross section for the combustion stream.

Preferably, the downstream fastening portion of the cap is fastened on the outer side of the wall of the chamber and the additional downstream fastening portion of the cap is fastened on the inner side of the wall of the chamber.

Advantageously in this case, with the combustion chamber comprising a chamber end section, the additional downstream fastening portion is fastened to a flange of the chamber end section, which flange is fastened to the wall of the chamber on its inner side.

Preferably again, the downstream fastening portion of the cap, the combustion chamber and the additional downstream fastening portion of the cap are fastened by fastening bolts.

Advantageously in this case, the flange of the chamber end section is also fastened by the fastening bolts.

According to a first embodiment, the additional downstream fastening portion comprises a downstream wall with a downstream portion for fastening to the wall of the chamber.

In a particular embodiment, this downstream wall has cutouts.

According to a second embodiment, the additional downstream fastening portion comprises fastening tabs, extending from the upstream edge, comprising a downstream portion for fastening to the wall of the chamber.

According to a third embodiment, the additional downstream fastening portion comprises reinforcing tabs connected by a downstream rim which supports tabs for fastening to the wall of the chamber.

The invention also relates to an annular wall forming a cap of the upstream fairing of the combustion chamber presented above.

The invention further relates to a gas turbine engine comprising the combustion chamber presented above.

Preferably, the annular wall forming the external cap of the upstream fairing of the combustion chamber is the one according to the invention, because it is this wall which is most subjected to the vibrational stresses. The invention also applies to the internal cap.

The invention is here described in relation to a turbojet, but it goes without saying that it applies to any gas turbine engine comprising a combustion chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the three embodiments of the fairing9described hereinafter, only the annular wall forming the external cap of the fairing9of the combustion chamber is in accordance with the invention, the annular wall forming the internal cap being in accordance with the caps of the prior art, since it is the external cap which is most subjected to the vibrational stresses. It goes without saying that provision can also be made for the internal cap to be in accordance with the invention by simply transposing the characteristics of the external cap to the internal cap.

In the description which follows, the elements of the turbojet which are similar will be denoted by the same references as inFIG. 1. In particular, for the sake of simplification, the upstream fairing9of the combustion chamber1, comprising an external cap and an internal cap, is always denoted by the reference “9”. The same applies to the internal cap11, which is similar to the internal cap11ofFIG. 1, and to elements which are common to the various embodiments of the external caps.

With reference toFIGS. 2 to 7, and according to the three embodiments described here, the external cap20,20′,20″ takes the form of a shaped metal sheet of constant thickness (it is thus less expensive and simpler to manufacture). This sheet may be made of any suitable material, for example the same material as the walls of the combustion chamber, in this instance a nickel- or cobalt-based alloy.

The external cap20,20′,20″ comprises an upstream annular wall21for separating the primary gas stream into a combustion steam6and a bypass stream7, an external bypass stream here, which bypasses the inlet of the combustion chamber1. This upstream wall21has a surface similar to that of the caps of the prior art, shaped to allow good separation of the primary gas stream.

On its downstream and outer side, the upstream wall21comprises a downstream portion22for fastening to the external wall31of the combustion chamber1, on its outer side here. This downstream portion22is in this case planar and obtained by folding the sheet metal on the downstream side, in the same way as in the prior art. It comprises holes23for the insertion of a bolt (not shown) so that it can be fastened to the external wall31of the combustion chamber1, which comprises corresponding holes33for the insertion of the fastening bolts.

On its upstream and inner side, the upstream wall21of the external cap20,20′,20″ comprises an upstream portion24folded in the downstream direction, termed upstream edge24, forming an edge of the flow cross section for the combustion stream6, in this instance the external edge of this cross section. This downstream portion24is continued, on the downstream side, into an additional portion25for fastening to a wall of the combustion chamber1, in this instance the external wall31, which will be referred to as the additional downstream fastening portion25.

In the first embodiment ofFIGS. 2 and 3, the additional downstream fastening portion25comprises a downstream annular wall26which extends downstream from the upstream wall21. This downstream wall26extends from the upstream edge24, fixedly with the latter, in this instance in a single piece therewith. More precisely, from the upstream edge24folded in the downstream direction there extends a planar portion27and then a second, outwardly folded edge28, from which the downstream wall26extends outwardly and in the downstream direction, downstream of the upstream wall21. This downstream wall26comprises a planar downstream fastening portion29folded in the downstream direction, which is in this case parallel to the downstream fastening portion22of the cap20fixed to the upstream wall21and situated on the inside with respect to this upstream wall. The downstream fastening portion29of the downstream wall26comprises holes30for the insertion of a bolt (not shown) so that it can be fastened to the external wall31of the combustion chamber1, each hole being coaxial with a corresponding hole23of the downstream fastening portion22of the upstream wall21.

With reference toFIG. 3, the downstream fastening portion29of the downstream wall26is fastened to the external wall31of the combustion chamber1, on its inner side. More precisely, it is fastened to a flange34of the chamber end section2, on its inner side, which flange is itself fastened directly to the inner surface of the external wall31of the combustion chamber1. This flange34comprises corresponding holes35for the insertion of the fastening bolts. Each fastening bolt passes through from the outside to the inside and therefore plays a part in fastening the downstream fastening portion22of the upstream wall21of the cap20, the external wall31of the combustion chamber1, the flange34of the chamber end section2, and the downstream fastening portion29of the downstream wall26of the cap20.

The external cap20is intended to be fastened here, on the one hand, on the outer side of the external wall31of the combustion chamber1, as regards the downstream fastening portion22of the upstream wall21, and, on the other hand, on the inner side of the external wall31of the combustion chamber1, as regards the downstream fastening portion29of the downstream wall26. It goes without saying that any other arrangement can be contemplated in which the external cap20is fastened to the external wall31of the chamber1, on the one hand, at the downstream fastening portion22of its upstream wall21, and, on the other hand, at its additional downstream fastening portion25continuing its upstream edge24. It is in particular not necessary for the fastening of these parts also to participate in the fastening of the flange34of the chamber end section2. Fastening is performed here by means of bolts, but any other fastening method may be contemplated, for example by welding, riveting, etc.

In the specific case in question, the downstream wall26has cutouts36distributed along its circumference so as to reduce its mass. However, the downstream wall26may also be solid. In this case, the rigidity and mechanical strength of the external cap20are increased, while in the event of a foreign body being ingested and striking the upstream wall21and causing a fracture there, the downstream wall26can act as a safety wall.

By virtue of the additional downstream fastening portion25of the external cap20, fastened to the external wall31of the chamber1, the rigidity of the external cap20is increased, which involves shifting the frequency values of its resonance modes, which are thus distanced from the vibrational frequencies to which the external cap20is subjected. The external cap20is therefore subjected to smaller vibrational forces and moreover has greater overall strength. Its dynamic response is greater. The cantilever effects are attenuated. The aerodynamic function of separating the primary gas stream is also preserved, since the surface encountered by this stream—the upstream surface of the upstream wall21—is the same as for the external caps20of the prior art. The fairing9is, moreover, formed by two caps20,11, which allows an optimum flow cross section for the combustion stream6.

In the second embodiment ofFIGS. 4 and 5, the additional downstream fastening portion25comprises a plurality of fastening tabs37, also forming reinforcements, which extend from the upstream edge24of the external cap20′, fixedly with the latter, in this instance in a single piece therewith. More precisely, from the upstream edge24folded in the downstream direction there extends a planar portion27and then a second edge28folded symmetrically to the upstream edge24, from which the tabs37extend outwardly and in the downstream direction, downstream of the upstream wall21of the external cap20′.

The tabs37are uniformly angularly distributed along the circumference of the second edge28, or downstream inner edge28, in line with the holes23in the downstream fastening portion22of the external cap20′ fixed to its upstream wall21. Each fastening tab37comprises a planar downstream fastening portion38folded in the upstream direction, which in this case is parallel to the downstream fastening portion22of the upstream wall21of the cap20′ and situated on the inside with respect to this upstream wall. The downstream fastening wall38of each fastening tab37comprises a hole39for the insertion of a bolt (not shown) so that the tab37can be fastened to the external wall31of the combustion chamber1, this hole being coaxial with a corresponding hole23in the downstream fastening portion22of the upstream wall21.

With reference toFIG. 5, the fastening tabs37are fastened, at their downstream fastening portion38, to the external wall31of the combustion chamber1, on its inner side. More precisely, they are fastened to the flange34of the chamber end section2, on its inner side, which flange is itself fastened directly to the inner surface of the external wall31of the combustion chamber1. This flange34comprises corresponding holes35for the insertion of the fastening bolts. Each fastening bolt passes through from the outside to the inside and therefore plays a part in fastening the downstream fastening portion22of the upstream wall21of the cap20′, the external wall31of the combustion chamber1, the flange34of the chamber end section2, and the downstream fastening portion38of the fastening tabs37of the cap20′.

The external cap20′ is intended to be fastened here, on the one hand, on the outer side of the external wall31of the combustion chamber1, as regards the downstream fastening portion22of the upstream wall21, and, on the other hand, on the inner side of the external wall31of the combustion chamber1, as regards the downstream fastening portion38of the fastening tabs37. It goes without saying that any other arrangement can be contemplated in which the external cap20′ is fastened to the external wall31of the chamber1, on the one hand, at the downstream fastening portion22of its upstream wall21, and, on the other hand, at its additional downstream fastening portion25continuing its upstream edge24. It is in particular not necessary for the fastening of these parts also to participate in the fastening of the flange34of the chamber end section2. Fastening is performed here by means of bolts, but any other fastening method can be contemplated, for example by welding, riveting, etc.

Again, by virtue of the additional downstream fastening portion25of the external cap20′, fastened to the external wall31of the chamber1, the rigidity of the external cap20′ is increased and the cap20′ is less subjected to the vibrational stresses. Moreover, it has greater strength and its dynamic response is greater. The cantilever effects are attenuated. The aerodynamic function of separating the primary gas stream is also preserved, with an optimum flow cross section for the combustion stream6. It will be noted that the discrete distribution of the fastening tabs37makes it possible for the external cap201to be fitted more simply by comparison with the first embodiment in which the downstream fastening portion29is continuous. However, the rigidity of the additional downstream fastening portion25is less than in the first embodiment.

In the third embodiment ofFIGS. 6 and 7, the additional downstream fastening portion25comprises a plurality of tabs40, forming reinforcements, which extend from the upstream edge24of the external cap20″, fixedly with the latter, in this instance in a single piece therewith, these tabs being interconnected at their downstream outer end by an annular rim41bearing a plurality of fastening tabs42, or scallops, extending in the upstream direction. More precisely, from the upstream edge24folded in the downstream direction there extends a planar portion27and then a second edge28folded symmetrically to the upstream edge24, from which the tabs40extend outwardly and in the downstream direction, downstream of the upstream wall21of the external cap20″. At their downstream end, the tabs40bear, and are connected by, an annular rim41folded in the upstream direction. This annular rim41bears the plurality of fastening tabs42, which are planar and extend in the upstream direction, these tabs in this case being parallel to the downstream fastening portion22of the upstream wall21of the cap20″ and being situated on the inside with respect to this portion.

The reinforcing tabs40are uniformly angularly distributed along the circumference of the second edge28. Each fastening tab42is situated angularly between two reinforcing tabs40, in this instance equidistantly from these reinforcing tabs40, and is situated in line with a hole23in the downstream fastening portion22of the upstream wall21. Each fastening tab42comprises a hole43for the insertion of a bolt (not shown) so that the tab42can be fastened to the external wall31of the combustion chamber1, this hole being coaxial with a corresponding hole23in the downstream fastening portion22of the upstream wall21.

With reference toFIG. 7, the fastening tabs42are fastened to the external wall31of the combustion chamber1, on its inner side. More precisely, they are fastened to the flange34of the chamber end section2, on its inner side, which flange is itself fastened directly to the inner surface of the external wall31of the combustion chamber1. This flange34comprises corresponding holes35for the insertion of the fastening bolts. Each fastening bolt passes through from the outside to the inside and therefore plays a part in fastening the downstream fastening portion22of the upstream wall21of the cap20″, the external wall31of the combustion chamber1, the flange34of the chamber end section2, and the fastening tabs42of the cap20″.

The external cap20″ is intended to be fastened here, on the one hand, on the outer side of the external wall31of the combustion chamber1, as regards the downstream fastening portion22of the upstream wall21, and, on the other hand, on the inner side of the external wall31of the combustion chamber1, as regards the fastening tabs42. It goes without saying that any other arrangement may be contemplated in which the external cap20″ is fastened to the external wall31of the chamber1, on the one hand, at the downstream fastening portion22of its upstream wall21, and, on the other hand, at its additional downstream fastening portion25continuing its upstream edge24. It is in particular not necessary for the fastening of these parts also to participate in the fastening of the flange34of the chamber end section2. Fastening is performed here by means of bolts, but any other fastening method can be contemplated, for example by welding, riveting, etc.

Again, by virtue of the additional downstream fastening portion25of the external cap20″, fastened to the external wall31of the chamber1, the rigidity of the external cap20″ is increased and the cap20″ is less subjected to the vibrational stresses. Moreover, it has greater strength and its dynamic response is greater. The cantilever effects are attenuated. The aerodynamic function of separating the primary gas stream is also preserved, with an optimum flow cross section for the combustion stream6.

It will be noted that this third embodiment is, as it were, intermediate between the first two embodiments, with fastening provided by discretely distributed tabs42, which facilitates fitting of the cap20″, but with a more rigid structure than in the case of the second embodiment on account of the rim41connecting the reinforcing tabs40. The alternating angular arrangement of the reinforcing tabs40and the fastening tabs42affords better distribution of the forces.

It is possible to envision other embodiments in which the external cap comprises a downstream portion22, fixed to its upstream wall21, for fastening to the external wall31of the combustion chamber1, and an additional downstream fastening portion25, fixedly continuing the upstream edge24of its upstream wall21, for fastening to this same external wall31.