TURBINE ENGINE SEPARATE FLOW MIXER

Abstract

The invention relates to a turbine engine separate flow mixer centered on a longitudinal axis, comprising an exhaust housing, a shroud directly connected to the exhaust housing and intended to mix the flows originating in the turbine engine, said shroud comprising a metal sheet formed by a succession of first and second longitudinal strips distributed circumferentially around the longitudinal axis of the mixer by circumferentially placing the second strips on either side of the first strips, the first and second strips being configured to form the shroud when at rest and grooves in the shroud when operating, the grooves being defined by an alternation of internal lobes and of external lobes.

Claims

1. A turbine engine separate flow mixer centered on a longitudinal axis, comprising an exhaust housing, a shroud directly connected to the exhaust housing and intended to mix the flows originating in the turbine engine, wherein said shroud comprises a metal sheet formed by a succession of first and second longitudinal strips distributed circumferentially around the longitudinal axis of the mixer by circumferentially placing the second strips on either side of the first strips, the first and second strips being configured to form the shroud when at rest and grooves in the shroud when operating, the grooves being defined by an alternation of internal lobes and of external lobes.

2. The mixer according to claim 1, wherein the first and second strips of the shroud have different thicknesses.

3. The mixer according to claim 1, wherein the first and second strips of the shroud are made of different materials.

4. The mixer according to claim 1, wherein the shroud is connected to an external shroud of the exhaust housing by brazing.

5. The mixer according to claim 1, wherein the shroud is connected to an external shroud of the exhaust housing by welding.

6. The mixer according to claim 1, wherein it is configured to obtain, when operating, a temperature difference of more than 100° C. between the first and second strips.

7. The mixer according to claim 1, wherein it is configured to obtain, when operating, a temperature difference of more than 200° C. between the first and second strips.

8. The mixer according to claim 1, wherein the first and second strips of the shroud are made of an aluminum-based material.

9. The mixer according to claim 1, wherein the exhaust housing comprises an annular hub centered on the longitudinal axis and a plurality of arms connecting the hub to the external shroud, each arm of the exhaust housing having a leading edge and a trailing edge, the trailing edge being axially aligned with a junction between the first and second strips of the shroud.

10. A turbine engine comprising a separate flow nozzle which is equipped with a mixer according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a schematic perspective view of a turbine engine separate flow mixer according to the invention in a so-called “cold” configuration.

[0017] FIG. 2 shows the mixer of FIG. 1 in a so-called “hot” configuration.

DESCRIPTION OF THE EMBODIMENTS

[0018] The invention applies to any turbine engine nozzle equipped with a separate flow mixer like that shown by FIG. 1. In known fashion, the mixer 2 of a nozzle comprises in particular a shroud 4 which is centered on a longitudinal axis X-X of the separate flow mixer which is connected to an exhaust housing 6 of the turbine engine.

[0019] When hot, this shroud 4 appears in the form of a sinusoidal portion having internal lobes alternating with external lobes, these lobes being distributed over the entire circumference of the exhaust housing.

[0020] The internal lobes form grooves (or chutes) radially guiding the cold flow (or secondary flow) of the fan to the channel in which passes the hot flow (or primary flow) originating in the combustion chamber, and the external lobs for other chutes radially guiding the hot flow to the channel in which the cold flow passes. Thus, at the outlet of the mixer, the flow mix by shear in a direction which is essentially radial.

[0021] The exhaust housing 6 is typically placed behind the low-pressure turbine of the turbine engine and ensures the inner and outer continuity of the stream, allowing separating the hot flow originating in the combustion chamber from the cold flow originating in the fan.

[0022] More precisely, the exhaust housing 6 comprises an annular shaped hub 8 which is centered on the longitudinal axis X-X, an external shroud 10 coaxial with the hub 8 with a diameter greater than the latter, and a plurality of arms 12 connecting the hub 8 to the external shroud 10.

[0023] The annular space 14 formed between the hub 8 and the external shroud 10 delimits the flow channel of the primary flow (or hot flow) at the outlet of the low-pressure turbine of the turbine engine.

[0024] The exhaust housing 6 also comprises several devises 16 protruding radially outward with respect to the external shroud 10 in order to form attachment points for fastening the exhaust housing to a pylon fastened to the wing of the airplane.

[0025] The arms 12 of the exhaust housing, which here for example are 18 in number, are regularly distributed around the longitudinal axis X-X of the mixer.

[0026] According to the invention, the shroud 4 of the mixer is formed by an identical single metal sheet which is directly connected to the external shroud 10 of the exhaust housing.

[0027] Preferably, the shroud 4 of the mixer is connected to the external shroud 10 of the exhaust housing of the nozzle by brazing or by welding. In particular, this connection is accomplished without having to utilize flanges and other attachment systems (such as screw/nut systems).

[0028] Still according to the invention, the shroud 4 of the mixer comprises a succession of first and second longitudinal strips 4a, 4b which are distributed circumferentially around the longitudinal axis X-X of the mixer, each of these first and second longitudinal strips 4a, 4b being aligned longitudinally with one of the arms 12 of the exhaust casing 6.

[0029] More precisely, the distribution is accomplished at the outlet by alternating the second strips 4b, having a first temperature T.sub.1 when hot, with first strips 4a having a second temperature T.sub.2 when hot which is greater than the first temperature T.sub.1. In other words, the second strips 4b are positioned circumferentially on either side of the first strips 4a.

[0030] The first and second strips 4a, 4b, are configured to form the shroud 4 of the mixer when at rest and to form grooves (or chutes) in the shroud when operating. More precisely, in operation, the first strips 4a are configured to form by dilation when hot the external lobes of the mixer, while the second strips 4b are configured to form, by dilation when hot, the internal lobes of said mixer.

[0031] The lobes which are thus formed preferably have an elongated shape.

[0032] FIG. 2 thus shows the mixer according to the invention, and more particularly its shroud 4, when it is “in the hot state,” i.e. when the turbine engine is operating at cruise speed.

[0033] In this figure, it is easy to see that the heating of the shroud 4 of the mixer induces a more or less great radial thermal dilation of it depending on the longitudinal strip 4a, 4b which composes it, this dilation giving a daisy shape to the mixer shroud. In other words, a circumferential gradient is imposed depending on the position of the first and second longitudinal strips 4a, 4b of the shroud 4 of the mixer.

[0034] By a thermomechanical calculation taking into account the hot temperature of the external shroud of the exhaust housing and the respective thermal dilation coefficients C.sub.t1 and C.sub.t2 of the first and second longitudinal strips of the mixer shroud, it is thus possible to create, in the hot state, an alternation of the external lobes 18a corresponding to the first longitudinal strips 4a and internal lobes 18b corresponding to the second longitudinal strips 4b.

[0035] For example, the shape of the external 18a and internal 18b lobes obtained in FIG. 1 was obtained by applying a thermal gradient of 200° C. to the mixer shroud (namely T.sub.1=400° C. of the longitudinal strips 4b and T.sub.2=600° C. for the longitudinal strips 4a) and for a uniform temperature of the exhaust housing equal to 600° C.

[0036] For the same material constituting the mixer shroud, there exists a thermal dilation coefficient curve as a function of the temperature. Thus, the mixer shroud initially has the same thermal dilation coefficient. On the other hand, when hot, the presence and the shape of the arms 12 of the exhaust housing 6 will have the effect of dilating the shroud to a more or less great degree, a dilation which manifests itself by a movement of the shroud given by the formula:

[0037] Movement (in mm)=radius of the shroud (in mm)×alpha (T)×(T-20° C.) with: alpha (T) =thermal dilation coefficient at temperature T and T=temperature

[0038] The parameter alpha(T) therefore varies with the temperature and forms, when hot, the longitudinal strips of the shroud with a different thermal dilation coefficient.

[0039] It will be noted that the number of external lobes 18a is equal to the number of first longitudinal strips 4a (18 here) and that the number of internal lobes 18b is equal to the number of second longitudinal strips 4b (18 here).

[0040] Thus, to obtain the specified stream when hot, (i.e. the number and the shape of the external and internal lobes of the mixer), it is necessary to know the number of arms 12 of the exhaust housing 6, as well as the tangential temperature gradient. In fact, the exhaust housing imposes thermal differences downstream when on the pressure side and on the suction side of each of its arms. The parts situated downstream of the exhaust housing therefore undergo a tangential thermal gradient due to the presence of the arms of the exhaust housing.

[0041] As previously indicated, the first and second strips 4a, 4b of the shroud 4 of the mixer must each be aligned longitudinally with one of the arms 12 of the exhaust housing 6, and the number of arms corresponds to the number of external lobes and of internal lobes of the mixer.

[0042] Likewise, the shape of the arms 12 of the exhaust housing influences the means by which the mixer shroud 4 will deform when hot: the more convex the profile of the arm is, the greater the temperature gradient is, and will easily form the arms by deformation when hot.

[0043] In order to obtain different thermal dilations in the first and second strips 4a, 4b based on the same metal sheet, it is possible to adjust the thickness of the sheet for each strip: the first strips 4a can have a smaller thickness than the second strips 4b in order to confer upon them a flexibility for thermal dilation greater than that of the second strips 4b.

[0044] Of course, other arrangements can be made to confer different thermal dilations for the longitudinal strips of the mixer shroud.

[0045] In addition, if the tangential thermal gradient due to the presence of the arms of the exhaust housing is low, it is necessary to take a metal with a high thermal dilation coefficient to produce the mixer shroud 4. Conversely, if the tangential thermal gradient due to the presence of the arms is high, it will be necessary to limit the thermal dilation coefficient of the sheet metal forming the mixer shroud.