Patent Description:
In turbofan engines, hot gases exhausted from the engine core mix with cooler bypass air flowing through an annular bypass duct surrounding the engine core. The turbine exhaust gasses from the engine core and the bypass airstream from the bypass duct are mixed together, before expulsion through a single nozzle. In order to perform the mixing function, mixers have been coupled to the downstream end of a shroud of the turbine exhaust case (TEC).

Typically, such TEC include a radially inner center body or inner hub to which a mixer may be connected through struts. The large temperature gradients to which TEC and mixers are exposed can cause their respective components to undergo significant thermal cycling (thermal expansion and shrinkage). Interconnected components of the TEC and mixers may undergo thermal expansion and/or shrinkage differentials, as a result of their respective interaction with hot exhaust gases and/or cold air. Thermal cycling differential between components may cause thermal stress and/or limit the lifespan of such components. Additionally, components within existing TEC mixers may be difficult to access for installation or repair purposes.

<CIT> discloses a prior art TEC mixer assembly for an aircraft engine as set forth in the preamble of claim <NUM>.

<CIT> discloses prior art flow mixer stiffener ring springs.

<CIT> discloses a prior art gas turbine engine exhaust mixer.

<CIT> discloses a prior art annular fairing structure for the rear frame housing of a gas turbine engine.

From one aspect, there is provided a turbine exhaust case (TEC) mixer assembly for an aircraft engine as recited in claim <NUM>.

<FIG> illustrates an exemplary turbofan aeroengine <NUM> (also referred to herein as an "aircraft engine") which includes a nacelle <NUM>, a core casing <NUM>, a low pressure spool assembly seen generally at <NUM> which includes a fan assembly <NUM>, a low pressure compressor assembly <NUM> and a low pressure turbine assembly <NUM>, and a high pressure spool assembly seen generally at <NUM> which includes a high pressure compressor assembly <NUM> and a high pressure turbine assembly <NUM>. The core casing <NUM> surrounds the low and high pressure spool assemblies <NUM> and <NUM> in order to define a main gas path (not numbered) therethrough. In the main gas path there is provided a combustion chamber <NUM> in which a combustion process produces combustion gases to power the high and low turbine pressure assemblies <NUM> and <NUM>. A turbine exhaust case (TEC) <NUM> is provided at a downstream end of the core casing <NUM> and a mixer <NUM> is coupled to a downstream end of the TEC <NUM> for mixing hot exhaust gases discharged from the high and low pressure turbine assemblies <NUM>, <NUM>, with a bypass airstream driven by the fan assembly <NUM> through an annular bypass duct <NUM> which is defined radially between the nacelle <NUM> and the core casing <NUM>.

Referring to <FIG>, the TEC <NUM> and the mixer <NUM> define a common central axis X which in the embodiment shown superposes a central rotation axis of the aeroengine <NUM>. The mixer <NUM> may have in at least some embodiments an annular wavy configuration around the central axis X which may axially extend between an upstream end and a downstream end of the mixer <NUM>. The mixer <NUM> may include inner and outer circumferential flow surfaces extending between the upstream and downstream ends of the mixer <NUM>. The inner and outer flow surfaces may be in a circumferentially wavy or twisted annular configuration to thereby form a plurality of lobes 29A (see <FIG>) of the mixer <NUM>. The lobes 29A may be axially extending or axially straight and may define a plurality of alternating crests and valleys, as described in <CIT>.

The TEC <NUM> has a center body <NUM> in an exhaust section, or downstream end, of the aeroengine <NUM>. The center body <NUM> includes an annular hub <NUM> (or simply "hub <NUM>"). The hub <NUM> encloses a center body cavity <NUM> (or simply "cavity <NUM>"). The center body cavity <NUM> is surrounded at least partially (or entirely) by the hub <NUM>. In the depicted embodiment, the center body <NUM> has a generally conical shape. The hub <NUM> may be referred to as an exhaust cone in some embodiments. The TEC <NUM> may include an annular shroud 28A (or simply "shroud 28A"). The annular mixer <NUM> (or simply "mixer <NUM>") may be coupled to a downstream end of the shroud 28A. The mixer <NUM> could be considered a part of the shroud 28A in some cases. In the depicted embodiment, the shroud 28A and the mixer <NUM> surround the hub <NUM> to form an annular exhaust gas duct <NUM> disposed radially therebetween.

It should be noted that the terms "upstream" and "downstream" used herein and hereinafter refer to the direction of a gas flow passing through the main gas path of the engine. It should also be noted that the terms "axial", "radial" and "circumferential" are used with respect to the central axis X. Although the TEC <NUM> and the mixer <NUM> are described as separate components, the mixer <NUM> may be considered as part of the TEC <NUM>, or stated differently, the assembly of the TEC <NUM> and the mixer <NUM> may be referred to as a TEC and mixer (or "TEC mixer") assembly for convenience.

Referring to <FIG>, according to an embodiment, the hub <NUM> has at least two separate hub sections 31A, 31B removably coupled to each other. The hub sections 31A, 31B define an outer periphery <NUM> of the center body <NUM>. As shown, the sections 31A, 31B are axially disposed along the central axis X relative to each other. The hub sections 31A, 31B may be referred to as axial sections of the hub <NUM> because of their relative axial position.

As shown at least in <FIG>, the hub sections 31A, 31B define walls of the exhaust gas duct <NUM>. Such walls or wall portions of the exhaust gas duct <NUM>, which may also be referred to as wall portions of the hub <NUM> may be in direct contact with the exhaust gas flow within the exhaust gas duct <NUM>. In the depicted embodiment, these hub sections 31A, 31B define the outer periphery <NUM> of the center body <NUM>. The hub sections 31A, 31B (or wall portions of the hub <NUM>) may respectively define an upstream end portion and a downstream end portion of the center body <NUM>. In other words, the hub sections 31A, 31B or wall portions of the hub <NUM> may form at least part of an external "envelope" of the center body <NUM>. The hub <NUM> may have more than two axial sections, even though only the two sections 31A, 31B adjacent to each other are identified herein by reference numbers.

The hub sections 31A, 31B are coupled to each other. The hub sections 31A, 31B have respective axial end segments 31E. As shown, the axial end segment 31E of the hub section bearing the reference 31A and the axial end segment of the hub section bearing the reference 31B engage each other at a coupling interface <NUM>. In the depicted embodiment, the coupling interface <NUM> is defined along opposing surfaces of those axial end segments 31E, with such surfaces extending circumferentially about the central axis X. The axial end segments 31E are removably coupled to each other at such coupling interface <NUM> radially inward from the outer periphery <NUM> of the center body <NUM> via a fixing arrangement.

Referring to <FIG>, in an embodiment, the fixing arrangement includes a plurality of fasteners <NUM> to removably couple the hub sections 31A, 31B. The fasteners <NUM> may be circumferentially spaced about the outer periphery <NUM> of the center body <NUM>, about the central axis X, whether equally spaced or not. The fasteners <NUM> may be clips, rivets, bolts, screws, in at least some embodiments. Other fixing arrangement may include, for instance, a single fastener, such as a ring (e.g. clamp ring, lock ring, etc.).

In the depicted embodiment, the fasteners <NUM> extend through the axial end segments 31E of the hub sections 31A, 31B. As shown, each of the fasteners <NUM> has a fastener longitudinal axis Y which extend in a direction parallel to the central axis X. In other embodiments, the fasteners <NUM> may have their respective fastener longitudinal axes Y at a relative angle with the central axis (e.g. acute angle, such as ± <NUM> degrees, or even less, such as ± <NUM> degrees).

A plurality of struts <NUM> are circumferentially spaced about the central axis X. The struts <NUM> extend radially across the annular exhaust gas duct <NUM> and interconnect the mixer <NUM> and the hub <NUM> of the TEC <NUM>. In at least some embodiments, the struts <NUM> are respectively coupled to at least some of the plurality of the lobes 29A of the mixer <NUM>. There may be a second group of struts, as shown at 40A extending radially across the annular exhaust gas duct <NUM> and interconnecting the mixer <NUM>, or the shroud 28A at the downstream end of the core casing <NUM> to which the mixer <NUM> may be coupled, and the hub <NUM>. As shown in <FIG>, such second group of struts 40A are upstream of the struts <NUM>. Such struts <NUM>, 40A may be referring to as deswirling struts and may have a cambered profile so as to deswirl the swirling flow of exhaust gases and mix the exhaust gases with the bypass air stream, as described in <CIT>.

At least the struts <NUM> are coupled to the hub <NUM> at respective strut-hub interfaces <NUM>. As shown in <FIG>, the struts <NUM> (here only one strut shown due to the cross-section, but it should be understood that a circumferential array of such struts <NUM> are present) are coupled to one of the hub sections 31A, 31B, and the struts 40A are coupled to the other one of the hub sections 31A, 31B. The coupling of the hub sections 31A, 31B is upstream of the struts <NUM>. As shown, the coupling of the hub sections 31A, 31B is located axially between the struts <NUM> and the struts 40A along the outer periphery <NUM> of the center body <NUM>. In embodiments where the struts <NUM> may be angled in an axial direction, the coupling of the hub sections 31A, 31B may be upstream of at least the strut-hub interface <NUM>. Separation of the hub sections 31A, 31B at such location may provide greater accessibility to the strut-hub interfaces <NUM>, for access, repair, maintenance, or quality control purposes. The struts <NUM> and the hub <NUM> may be welded at the strut-hub interfaces <NUM>. Other fixing may be contemplated, such as rivets, bolts, co-molding, etc. In embodiments where the struts <NUM> are welded to an outer surface of the hub <NUM> at respective strut-hub interfaces <NUM>, removably coupling the hub sections 31A, 31B may provide greater accessibility during the assembly of the TEC <NUM>, for welding and/or quality control of the welds (or other coupling) at the strut-hub interfaces <NUM>, for instance.

The struts 40A may also be coupled to the hub <NUM> in a similar manner as the struts <NUM> and hub <NUM> at the strut-hub interfaces <NUM>. In at least some embodiments, the struts <NUM> are respectively coupled to at least some of the plurality of the lobes 29A of the mixer <NUM>. Coupling may be by welding, rivets, bolts, co-molding, etc. The struts 40A may be coupled to the mixer <NUM> or annular shroud 28A of the downstream end of the core casing <NUM> (<FIG>) to which the mixer <NUM> may be coupled in a similar manner.

During operation of the aeroengine <NUM>, the TEC mixer assembly undergoes thermal cycling, which may be due at least to the interaction of the hot exhaust gases coming out through the exhaust gas duct <NUM> and the bypass airstream coming out through the annular bypass duct <NUM>. Such thermal cycling may occur at a different rate depending on the components and placement of such components relative to such hot exhaust gases and bypass airstream. More specifically, there may be a thermal expansion/shrinkage differential between the mixer <NUM> and the hub <NUM>, which are coupled to each other by the struts <NUM>. It may be desired to compensate for such thermal expansion/shrinkage differential between the hub <NUM> and the mixer <NUM> interconnected at least by the struts <NUM>.

The TEC <NUM> includes an axial spring <NUM> deformable to allow thermal contraction and/or expansion of the hub <NUM> at least in an axial direction. The axial spring <NUM> forms a thermal joint between the hub sections 31A, 31B, in that it is capable of absorbing thermal expansion differentials, in at least the axial direction, between the axial sections 31A, 31B of the hub <NUM>. The axial spring <NUM> is axially offset from the struts <NUM> on the outer periphery <NUM> of the center body <NUM>. The axial spring <NUM> is located upstream of the struts <NUM>, at least at their strut-hub interfaces <NUM>, which extend between the hub <NUM> and the outer lobes 29A of the mixer <NUM>. In at least some cases, the lobes 29A may be radially deformable, for instance due to their thickness and/or the curved shape of the lobes. As such, the lobes 29A of the mixer <NUM> may take up at least part of the thermal expansion differential in a radial direction.

The axial spring <NUM> is defined by the respective axial end segments 31E of the hub sections 31A, 31B. In an embodiment, at a portion of the axial end segments 31E of the hub sections 31A, 31B, the axial spring <NUM> defines a gap <NUM> or recess in the outer periphery <NUM> of the center body <NUM>. The gap <NUM> is defined between a first part and a second part of the axial spring <NUM>, which may be portions of the respective axial end segments 31E of the hub section 31A, 31B. The gap <NUM> extends at least partially peripherally (peripherally and/or circumferentially) about the outer periphery <NUM> of the center body <NUM>. In one embodiment, the gap <NUM> may extend uninterrupted about the full perimeter and/or circumference of the outer periphery <NUM>. In another embodiment, however, the gap <NUM> may be circumferentially interrupted, in that it may include a number of circumferentially spaced apart gaps which collectively define the gap <NUM>. In the embodiment shown, the gap <NUM> has a generally U-shape when viewed in a cross-sectional plane containing the central axis X, as that of <FIG>. The gap <NUM> may also have a different shape, such as a V, Y or U shape, or a combination of these gap shapes. The end segments 31E define opposing (in the axial direction) walls of the gap <NUM>. The end segments 31E define respective bends 31F angled radially inwardly and respective radially inwardly extending flanges <NUM> from the bends 31F. During thermal cycling, the gap <NUM> may expand or contract axially (in an orientation of the central axis X). The bends 31F may deform to allow the gap <NUM> to expand or retract axially. The bends 31F each form a bend angle α, β. At least one, if not both, of such angles α, β may be greater than <NUM> degrees in a non-deformed state in at least some embodiments, such as shown in <FIG>. This may facilitate the manufacturing of the end segments 31E. Such bend angle(s) α, β may be between <NUM> and <NUM> degrees in at least some embodiments. The gap <NUM> has an axial dimension or width <NUM> which may be measured as a distance between the axial end segments 31E (walls of the gap <NUM>) along the outer periphery <NUM> of the centre body <NUM> (as shown in <FIG>), and which may vary while the end segments 31E deform under thermal load.

As shown, the width <NUM> of the gap <NUM> reduces in a radially inward direction, to the point where the end segments 31E define the coupling interface <NUM> radially inward from the gap <NUM>. The bends 31F may deform to allow the gap <NUM> to expand or contract axially, as discussed above. In the depicted embodiment, both bend angles α, β are greater than <NUM> degrees in a non-deformed state. In the depicted embodiment, the flange <NUM> of one of the end segments 31E (see left side in <FIG>) defines a rounded concave corner <NUM> in the wall of the gap <NUM> before the coupling interface <NUM> begins at an end of the flange <NUM>. The coupling interface <NUM> may be sized so as to minimize the length of the flange <NUM>. For instance, the coupling interface <NUM> may be sized along the plane PP, described in more detail below, so as to provide just enough clearance for a tool to engage the fasteners <NUM> during assembly, without or with limited interference between the tool and the hub section(s) 31A, 31B.

The shape, bend angles α, β, material type and wall thickness of the end segments 31E may influence the axial spring rate K of the axial spring <NUM>, for instance. In at least some embodiments, the axial end segments 31E have respective bending stiffnesses K1, K2, which may be measured by applying and monitoring a force on the axial end segments 31E in a direction parallel to the central axis X. The stiffness K (or spring rate) of the axial spring <NUM> may correspond to (K1*K2)/(K1+K2).

As discussed above, the end segments 31E are coupled to each other at the coupling interface <NUM> via a fixing arrangement, which is in the embodiment shown a plurality of fasteners <NUM>. The coupling interface <NUM> is radially inward relative to the gap <NUM>. The coupling interface <NUM> extends in a plane PP intersecting with the central axis X. In the depicted embodiment, the plane PP in which the coupling interface <NUM> extends is normal to the central axis X, although it may be otherwise transverse thereto in other embodiments. In the depicted embodiment, the plane PP intersects with the gap <NUM>. The coupling interface <NUM> is flat, at least where the fasteners <NUM> are located. The coupling interface <NUM> may not be entirely flat, such that part of the coupling interface <NUM> may not extend within the plane PP in some embodiments. For instance, the coupling interface <NUM> could be defined at least in part by curved surfaces, or flat surfaces not entirely extending in one plane such as the plane PP. The coupling interface <NUM> may vary in dimension(s), e.g. radial dimension, about the central axis X. For instance, the coupling interface <NUM> may have a reduced or varying dimensions between adjacent fasteners <NUM>.

As shown, the fasteners <NUM> intersect with the plane PP and/or the coupling interface <NUM>. The fasteners <NUM> extend through the end segments 31E of the hub sections 31A, 31B at the coupling interface <NUM>. In the depicted embodiment, the fasteners <NUM> are enclosed within the center body cavity <NUM>. That is, the fasteners <NUM> are surrounded, or within, the center body cavity <NUM>. The fasteners <NUM>, as shown, are not accessible through the gap <NUM> (or more generally not accessible from the exhaust gas duct <NUM> radially thereabove). Such configuration for the fixing arrangement may permit the fasteners <NUM>, such as bolts shown herein, to be efficiently/readily accessible from the center body cavity <NUM>. As can be seen, with the fasteners <NUM> being bolts (or other similar types of fasteners) and extending through the end segments 31E of the hub sections 31A, 31B, their head ends and tip ends are both accessible from within the center body cavity <NUM>. During assembly of the hub sections 31A, 31B, a person (and/or assembly tool) may access the coupling interface <NUM> from within the center body cavity <NUM> to assemble the hub sections 31A, 31B from within the center body cavity <NUM>. This configuration may allow more convenient installation and removal of one hub section 31A from the other hub section 31B. In such configuration, the gap <NUM> is free of fasteners <NUM>. The absence of fasteners <NUM> (or parts thereof) from within the gap <NUM> may allow a gap design with a reduced axial dimension or width <NUM> of the gap <NUM>, which may limit the aerodynamic impact of the gap <NUM> on the exhaust gas flow within the exhaust gas duct <NUM>.

Referring to <FIG>, a variant of the TEC <NUM> with an axial spring <NUM> as presented in <FIG> is shown. Similar features will not be explained again, for conciseness. It should be understood from the readings of the preceding paragraphs that what was described with respect to <FIG> also generally apply to what is shown in <FIG>. In the depicted embodiment, the end segments 31E and the coupling interface <NUM> is radially inward from the outer periphery <NUM> of the center body <NUM>. At least the bend angle α of the end segment 31E of the hub section 31A is greater than <NUM> degrees (see <FIG>). In the depicted embodiment, the plane PP in which the coupling interface <NUM> is defined is normal to the central axis X. However, such plane PP does not intersect with the gap <NUM>, as the plane PP coincides with one of the walls of the gap <NUM> (see <FIG>, the wall on the left side in the illustration). In such variant of the TEC with axial spring <NUM>, the gap <NUM> may have an even more limited width <NUM> as that of the configuration shown in <FIG>. In the depicted embodiment, the flange <NUM> on one of the end segments 31E (e.g. left side of the illustration of Fig. <NUM>) extends from the bend 31F radially straight down to the coupling interface <NUM> (radially inwardly towards the central axis X), without additional bending other than the bend 31F, such as the concave corner <NUM> in <FIG>, before the coupling interface <NUM>. The gap <NUM> has a generally V-shape when viewed in a cross-sectional plane containing the central axis X, as that of <FIG>. The flange <NUM> which extends from the bend 31F having the angle α on the opposite end segment 31E (right side of the illustration of <FIG>) defines an additional bend 31J where the coupling interface <NUM> begins. This is also shown in <FIG>. In a variant of that shown in <FIG>, in <FIG>, the flanges <NUM> of both end segments 31E include such an additional bend 31J to generally widen the gap <NUM> relative to the configuration shown in <FIG>. Also shown in the embodiment of <FIG>, both end segments 31E have a rounded concave corner <NUM> in the wall of the gap <NUM>, between the bends 31F and the additional bend 31J.

Claim 1:
A turbine exhaust case (TEC) mixer assembly for an aircraft engine (<NUM>), comprising:
a center body (<NUM>) extending along a central axis (X) of the TEC mixer assembly, the center body (<NUM>) including a hub (<NUM>), the hub (<NUM>) at least partially enclosing a center body cavity (<NUM>) and having a first wall portion (31A) and a second wall portion (31B) axially spaced apart from the first wall portion (31A), the first wall portion (31A) and the second wall portion (31B) together defining an outer periphery (<NUM>) of the center body (<NUM>), the first wall portion (31A) and the second wall portion (31B) each having a respective axial end segment (31E), the axial end segment (31E) of the first wall portion (31A) and the axial end segment (31E) of the second wall portion (31B) removably coupled to each other radially inwardly from the outer periphery (<NUM>) of the center body (<NUM>) via a fixing arrangement including at least one fastener (<NUM>), the at least one fastener (<NUM>) enclosed within the center body cavity (<NUM>);
an axial spring (<NUM>) including a gap (<NUM>) axially defined between portions of the respective axial end segments (31E) of the first wall portion (31A) and the second wall portion (31B), the gap (<NUM>) defined at the outer periphery (<NUM>) of the center body (<NUM>); and
a mixer (<NUM>) extending peripherally about the center body (<NUM>) and spaced radially outward from the hub (<NUM>) by a plurality of struts (<NUM>) extending between the hub (<NUM>) and the mixer (<NUM>), the plurality of struts (<NUM>) axially offset from the gap (<NUM>) at a strut-hub interface (<NUM>),
characterised in that
the fixing arrangement includes a plurality of fasteners (<NUM>) including the at least one fastener (<NUM>), the plurality of fasteners (<NUM>) being circumferentially spaced about the outer periphery (<NUM>) of the center body (<NUM>), the plurality of fasteners (<NUM>) extending through the axial end segment (31E) of the first wall portion (31A) and the axial end segment (31E) of the second wall portion (31B).