Exhaust casing of a turbomachine with improved aerodynamics

A turbomachine exhaust casing extending about an axis including a hub extending about the axis; an external ferrule; arms which extend between the hub and the external ferrule, attachment yokes radially projecting toward the outside of the external ferrule; pockets hollowed into the external ferrule and wherein the yokes are arranged, the pockets extending in a hollow radially projecting toward the inside of the external ferrule; a ring portion which extends radially under the pockets and forms a duct wall by delimiting with the hub a portion of a gas flow duct.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a turbomachine casing, particularly a turbomachine exhaust casing.

Description of Related Art

The exhaust casing is a structural part of a turbomachine usually disposed at the outlet of a turbine, upstream of the exhaust nozzle with respect to the direction of flow of the gases in the turbomachine.

As illustrated inFIG.1, a turbomachine conventionally comprises from upstream to downstream, in the direction of flow of the gases (illustrated by the arrow G inFIG.1), at least one compressor (not shown), a combustion chamber (not shown) and at least one turbine12. Downstream of the turbine12is disposed the exhaust casing10which comprises an internal hub14and an external annular ferrule16which is attached to the hub14via structural arms20and which is disposed about an axis A of revolution which is the longitudinal axis of the turbomachine.

The ferrule16and the hub14together define a portion of an annular duct18for the flow of the combustion gases leaving the turbine12.

The ferrule16and the hub14are rigidly linked to one another by the arms20, which are structural, and mainly radial with respect to the axis A. The arms20can be inclined with respect to radial planes passing through the axis A.

The casing10includes flanges22a-22dfor coupling with the turbine upstream and the exhaust nozzle downstream. These attachment flanges are located at the longitudinal ends upstream and downstream of the casing10. In the example shown inFIG.1, the ferrule16comprises an annular flange22a,22bat each of its upstream and downstream longitudinal ends. The upstream flange22ais attached to a downstream end of a casing of the turbine12and the downstream flange22bis attached to an upstream end of an exhaust nozzle24.

As can be seen inFIG.2andFIG.3(on the left) in order to attach the exhaust casing10to a support of the turbomachine, such as a pylon, it is known to make provision for named attachment points, yokes5, radially projecting toward the outside of the external ferrule16, the lugs of which extend radially and which have bores for receiving a shaft (not shown) used for the attachment of rods (not shown) on the pylon.

In a known manner, these yokes undergo heavy loads which makes it necessary to reinforce them. For reasons of mechanical withstand, the center of the yokes must be positioned radially at the level of the external ferrule16. As a consequence, provision is made for pockets6. However, these pockets extend in a hollow radially projecting toward the inside of the duct18. Thus, the pockets impede the aerodynamics of the duct18with the consequence of losses of aerodynamic load and therefore losses regarding the performance of the turbomachine.

BRIEF SUMMARY OF THE INVENTION

The invention proposes to palliate at least one of these drawbacks.

For this purpose, the invention proposes, according to a first aspect, a turbomachine exhaust casing extending about an axis and comprising a hub extending about the axis; an external ferrule; arms which extend between the hub and the external ferrule; attachment yokes radially projecting toward the outside of the external ferrule; pockets hollowed into the external ferrule and wherein the yokes are arranged, the pockets extending in a hollow radially projecting toward the inside of the external ferrule; a ring portion which extends radially under the pockets and forms a duct wall by delimiting with the hub a portion of a gas flow duct.

The invention, according to the first aspect, is advantageously completed by the following features, taken alone or in any one of their technically possible combinations:the ring portion has a first radius with respect to the axis;the ring portion comprises a plate provided with openings each surrounding one arm;the ring portion comprises a first and a second plate, the first and second plates together delimiting openings each intended to surround one arm.the plates are attached together, by means of clips, rivets or by swaging.the first plate is disposed upstream of the second plate.

The invention proposes, according to a second aspect, a turbomachine assembly comprising, from upstream to downstream, in the direction of flow of the gas stream in the turbomachine;a turbine comprising a turbine casing comprising a downstream attachment flange;an exhaust casing, according to the first aspect of the invention, said exhaust casing comprising an upstream attachment flange, the turbine casing being attached to the exhaust casing between the downstream flange of the turbine casing and the upstream flange of the exhaust casing;a nozzle comprising an upstream flange, the nozzle being attached to the exhaust casing between the upstream flange of the nozzle and the downstream flange of the exhaust casing.

The invention according to the second aspect is advantageously completed by the following features, taken alone or in any one of their technically possible combinations:the ring portion is attached, upstream by clamping between the upstream flange of the exhaust casing and the downstream flange of the turbine casing, or by riveting to the external ferrule of the exhaust casing.the ring portion is attached, downstream, by clamping between the downstream flange of the exhaust casing and the upstream flange of the nozzle, or by riveting to the external ferrule of the exhaust casing.

Finally, the invention proposes according to a third aspect a turbomachine comprising an exhaust casing according to the first aspect of the invention.

The advantages of the invention are several.

The pockets no longer extend in projection into the flow duct of the gas stream. The performance of the turbomachine is therefore improved.

Furthermore, as the pockets are no longer in contact with the gas stream, the temperature of them is reduced, which leads to better mechanical strength. It is also possible to make provision for pockets, the thickness of which is reduced with respect to the usual configuration.

Thus, the casing can be reinforced at the level of the yokes via the pockets without it affecting the aerodynamics of the duct.

On all the figures similar elements bear identical reference numbers.

DETAILED DESCRIPTION OF THE INVENTION

FIG.3, on the right, illustrates a schematic front view of a turbomachine exhaust casing according to an embodiment.

Such an exhaust casing comprises a hub240extending about a longitudinal center axis of the turbomachine and a structural external ferrule26. Arms20, which are structural, extend from the hub240toward the external ferrule26. Projecting yokes are disposed on the structural external ferrule and allow the attachment of the casing, particularly to a pylon. The yokes are disposed, in particular radially above structural arms20. InFIG.3, on the right, these yokes are four in number without this being limiting. It will specifically be understood that the number of yokes depends on the method of attachment of the exhaust casing10to the pylon.

As already discussed, pockets27are disposed under the structural external ferrule26and below each yoke25. More precisely, the pockets27are disposed on the internal surface of the external ferrule26below each yoke25.

In order to remove the drawbacks due to the pockets, presented above, a non-structural ring portion40,50is disposed below the pockets27and defines with the hub240a flow duct28of the gas stream in the turbomachine.

The stream flow duct is therefore no longer formed by the hub and the external ferrule but by this ring portion and the internal hub as regards the area at the level of the yokes and the pockets.

As a consequence, the external ferrule no longer has a constant radius over its entire circumference, but has an area located radially above the ring portion40,50, at the level of the yokes, which has a radius R2greater than the rest of the ferrule of radius R1. It is precisely below this portion that the ring portion40,50is disposed. The duct28meanwhile has a constant radius R1over its entire circumference.

To a certain extent, the center of the yokes has been off-centered with respect to the configuration of the prior art, and the stream flow duct (circular) has been reshaped by means of the ring portion40,50. This is visible on the left and right parts ofFIG.3disposed side by side. Hence, the pockets are radially disposed above the stream circulation duct and are no longer disposed in the duct.

The ring portion40,50therefore makes it possible to reshape the duct.

Furthermore, the ring portion40,50prevents the gases circulating in the duct to come and flow onto the hollows formed by the pockets.

As in the prior art, the pockets are disposed about structural arms radially disposed below yokes and it is therefore necessary to make provision for an adapted geometry for the non-structural ring portion40,50. In particular, the assembly of the ring portion40,50can be carried out in several ways.

FIG.4illustrates a ring portion40used to reshape the duct according to a first variant. According to this first variant, the ring portion is composed of a plate41wherein openings42are formed to allow the structural arms to pass through.

FIG.5illustrates a ring portion50used to reshape the duct according to a second variant. According to this variant, the ring portion is composed of two plates51,52: a first plate and a second plate, the first plate comprising first portions of openings53which cooperate with second portions of openings of the second plate such as to form openings for receiving the arms that surround the arms. Still according to this variant, the plates51,52are mutually attached by several types of attachment: clips, clamps formed by swaging, riveting etc.

The openings42or53are of an appropriate geometry for the geometry of the structural arms.

The ring portion40,50makes it possible to ensure that the gas stream flow duct is annular. To avoid leaks of the gas stream, the ring portion can be attached in an airtight manner on the one hand to the turbine12and on the other hand to the nozzle24.

Upstream of the exhaust casing10, the turbine comprises a turbine casing comprising a downstream attachment flange12aand the exhaust casing comprises an upstream attachment flange22a. In this case, the turbine casing is attached to the exhaust casing by way of a coupling between the downstream flange of the turbine casing and the upstream flange of the exhaust casing.

Upstream, provision can be made for attaching the ring portion40,50to the turbine by way of the flanges12a,22a, preferably by clamping between the upstream annular flange of the exhaust casing and the downstream flange of the turbine casing. Alternatively, the ring portion is attached to the external ferrule26by riveting.

Downstream of the exhaust casing, the nozzle comprises an upstream flange24band the exhaust casing comprises a downstream flange22b, in this case, the nozzle24is attached to the exhaust casing10by way of a coupling between the upstream flange of the nozzle and the downstream flange of the exhaust casing.

Preferably, the ring portion is attached downstream by clamping between the downstream annular flange of the exhaust casing and the upstream flange of the nozzle. Alternatively, the ring portion is attached to the external ferrule26by riveting.

It is of course possible to make provision for an attachment upstream of the ring portion by clamping and downstream by riveting and vice versa.

Whatever the method of attachment, the only restriction is that the downstream and upstream coupling of the ring portion with on the one hand the turbine12and on the other hand the nozzle be airtight.