Patent Description:
Various factors exert pressures on aircraft engine manufacturers to continually improve their designs. Design improvements take many factors into consideration, such as weight, structural optimization, durability, production costs, etc. Accordingly, while known turbine exhaust cases were satisfactory to a certain extent, there remained room for improvement.

<CIT> discloses a turbine exhaust case assembly.

<CIT> discloses a fabricated ITD-strut and a vane ring for a gas turbine engine.

According to an aspect of the present invention, there is provided a turbine exhaust case (TEC) in accordance with claim <NUM>.

Optionally, and in accordance with any of the above, the strut wall extension has a horseshoe cross-sectional shape.

Optionally, and in accordance with any of the above, the strut wall extension extends chordwise up to <NUM>% of a total chord length of the airfoil body.

Optionally, and in accordance with any of the above, the annular exhaust gas path has a radial height (D), and wherein a combined length (A) of the stiffener ring and the strut wall extension in a chordwise direction is greater than or equal to half the radial height (D).

Optionally, and in accordance with any of the above, the stiffener ring has a length (B), and wherein (B) is equal to about one-third of (A).

Optionally, and in accordance with any of the above, the stiffener ring has a radial height (C), and wherein (C) is greater than or equal to two-thirds of (B).

Optionally, and in accordance with any of the above, the stiffener ring (<NUM>) is monolithically casted with the strut wall extension (<NUM>) of each of the plurality of circumferentially spaced-apart struts (<NUM>).

Optionally, and in accordance with any of the above, a first fillet is provided between the airfoil body and the radially outer surface of the inner case, and wherein a second fillet is provided between the strut wall extension and the radially inner surface of the inner case, the second fillet being inverted relative to the first fillet.

<FIG> illustrates an aircraft engine of a type preferably provided for use in subsonic flight, and generally comprising in serial flow communication an air inlet <NUM>, a compressor <NUM> for pressurizing the air from the air inlet <NUM>, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, a turbine <NUM> for extracting energy from the combustion gases, and a turbine exhaust case (TEC) <NUM> through which the combustion gases exit the engine <NUM>. The turbine <NUM> includes a low pressure (LP) turbine 14a (also known as a power turbine) drivingly connected to an input end of a reduction gearbox (RGB) <NUM>. The RGB <NUM> has an output end drivingly connected to an output shaft <NUM> configured to drive a rotatable load (not shown). For instance, the rotatable load can take the form of a propeller or a rotor, such as a helicopter main rotor. The engine <NUM> has an engine centerline <NUM>. According to the illustrated embodiment, the compressor and the turbine rotors are mounted in-line for rotation about the engine centerline <NUM>.

According to the embodiment shown in <FIG>, the TEC <NUM> terminates the core gas path <NUM> of the engine. The TEC <NUM> is disposed immediately downstream of the last stage of the low pressure turbine 14a for receiving hot gases therefrom and exhausting the hot gases to the atmosphere. The TEC <NUM> comprises an outer case <NUM> having a radially inner surface 22a facing the centerline <NUM> and forming a radially outer delimitation (i.e. outer gas path wall) of an annular exhaust gas path 20a of the core gas path <NUM>, an inner case <NUM> having a radially outer surface facing away from the centerline <NUM> and forming a radially inner delimitation (i.e. inner gas path wall) of the annular exhaust gas path 20a of the core gas path <NUM>, and a plurality of turbine exhaust struts <NUM> (e.g. <NUM> struts in the embodiment shown in <FIG>) extending generally radially across the annular exhaust gas path 20a. As shown in <FIG>, the struts <NUM> are circumferentially interspaced from one another. The outer and inner cases <NUM>, <NUM> are provided in the form of outer and inner structural rings concentrically mounted about the engine centerline <NUM>. According to some embodiments, the outer case <NUM> may be bolted or otherwise suitably mounted to the downstream end of the turbine case via a flange connection. For instance, as exemplified in <FIG>, <FIG>, the outer case <NUM> can have an outer flange 22b bolted to a corresponding flange at the downstream end of the turbine case. The struts <NUM> structurally connect the inner case <NUM> to the outer case <NUM>. According to the embodiment illustrated in <FIG>, the inner case <NUM> is configured to support a bearing <NUM> of the LP spool via a hairpin connection <NUM> or the like. The struts <NUM> provide a load path for transferring loads from the inner case <NUM> (and thus the bearing <NUM>) to the outer case <NUM>. According to some embodiments, the outer case <NUM>, the inner case <NUM> and the struts <NUM> are of unitary construction. For instance, the outer case <NUM>, the inner case <NUM> and the struts <NUM> can be integrally formed as a monolithic component. According to one aspect, the TEC <NUM> is unitary cast component.

Referring jointly to <FIG>, it can be appreciated that the exemplified struts <NUM> have an airfoil profile to serve as vanes for guiding the incoming flow of hot gases through the exhaust gas path 20a. According to the illustrated example, each of the struts <NUM> has an airfoil body with a hollow core <NUM>, the airfoil body having opposed pressure and suction side walls <NUM>, <NUM> extending chordwise from a leading edge <NUM> to a trailing edge <NUM> and spanwise from a radially inner end <NUM> to a radially outer end <NUM>. As shown in <FIG>, the hollow core <NUM> of the struts <NUM> may provide an internal passageway for service lines L and the like.

In certain engine running conditions, high thermal gradients may developed across the struts <NUM>. This is particularly true during transient engine cycles due to the flow swirl angle. In such instances, the delta temperature (ΔT) between the pressure and suction side walls <NUM>, <NUM> of the struts <NUM> may result in relatively high bending stresses in the pressure and suction side walls <NUM>, <NUM>. Such bending stresses may create high stress concentration at the junction of the struts <NUM> with the inner case <NUM>. According to some embodiments, this undesirable stress can be relieved and/or at least partly moved out from the strut-inner case junctions by extending at least a portion of the strut wall to a radially inner side of the inner case <NUM>, thereby allowing the struts <NUM> to be connected/joined to the inner case <NUM> on both the radially outer and the radially inner surfaces 24a, 24b of the inner case <NUM>.

As shown in <FIG>, the inner end <NUM> of each strut <NUM> may have a strut extension wall <NUM> extending radially through the inner case <NUM> to a location radially inward thereof. The strut wall extension <NUM> has a leading edge component or segment 50a extending in a spanwise direction in continuity to the leading edge of the airfoil body of the strut <NUM>, a suction side extension component or segment 50b extending in a spanwise direction in continuity to the strut suction side wall <NUM> and a pressure side extension component or segment 50c extending in a spanwise direction in continuity to the strut pressure side wall <NUM>. The suction side extension segment 50b and the pressure side extension segment 50c extend in a chordwise direction from the leading edge extension segment 50a towards the trailing edge <NUM> of the strut <NUM>. According to the illustrated embodiment and as best shown in <FIG> and <FIG>, the suction and pressure side extension segments 50b, 50c of the strut wall extension <NUM> extend chordwise along only a portion of the chord length of the strut <NUM> and confer to the strut wall extension a horseshoe cross-sectional shape. According to one aspect, the strut wall extension <NUM> can start at the leading edge <NUM> of the strut <NUM> and follow the airfoil contour up to about <NUM>% of the strut chord (i.e. the strut wall extension <NUM> terminates in a mid-chord region of the airfoil body). However, it is understood that depending on the level of stress concentration and the location thereof, the chord dimension of the strut wall extension <NUM> may vary. For instance, the strut wall extension <NUM> could extend from the leading edge <NUM> to the trailing edge <NUM>. However, this would increase the weight of the TEC <NUM>. According to another variant, the strut wall extension <NUM> could extend chordwise from the leading edge <NUM> to a location less than half of the strut chord. For instance, the strut wall extension <NUM> could extend along only the first <NUM>% of the strut chord starting from the strut leading edge <NUM>. The skilled reader will understand that various chordwise dimensioning are possible depending on the loading condition of the struts <NUM>.

As can be appreciated from <FIG>, the strut wall extension <NUM> merges with a stiffener ring <NUM> projecting from the radially inner surface 24b of the inner case <NUM>. The stiffener ring <NUM> extends along a full circumference of the inner case <NUM> and structurally interconnect the individual struts <NUM> via their respective strut wall extensions <NUM>. The stiffener ring <NUM> is axially disposed to span the leading edge <NUM> at the inner end <NUM> of the struts <NUM>. The stiffener ring also extends axially forwardly relative to the leading edge <NUM>. According to one aspect, the stiffener ring <NUM> and the strut wall extension <NUM> are integrally formed as a monolithic structure. According to another aspect, the whole TEC <NUM> (including the strut wall extension <NUM> of the struts <NUM> and the stiffener ring <NUM> on the inner case <NUM>) is casted as a unitary component.

Referring more particularly to <FIG>, it can be appreciated that the stiffener ring <NUM> merges with the leading edge segment 50a of each strut wall extension <NUM>. According to the illustrated exemplary strut reinforcing structure, the combined length (A) of the stiffener ring <NUM> and the strut wall extension <NUM> in the chordwise direction is greater than or equal to half the radial height (D) of the annular exhaust gas path 20a. Still according to the embodiment shown in <FIG>, the stiffener ring <NUM> has an axial length (B) equal to about one-third of the combined length (A). According to another aspect, the radial height (C) of the stiffener ring <NUM> is greater than or equal to two-thirds of (B). The radial height (C) corresponds to the radial distance by which the stiffener ring (<NUM>) and the strut wall extension <NUM> extend from the radially inner surface 24b of the inner case <NUM>.

As shown in <FIG>, an outer fillet 56a is provided at the juncture of the airfoil body of the strut <NUM> and the radially outer surface 24a of the inner case <NUM>. The outer fillet 56a extends around the leading edge and along the pressure and suction side walls <NUM>, <NUM> and around the trailing edge <NUM>. The geometry of the outer fillet 56a can vary all around the periphery of the airfoil body from the leading edge <NUM> to the trailing edge <NUM>. For instance, as shown in <FIG>, the outer fillet at the leading edge <NUM> of the strut <NUM> has a different radius than that of the outer fillet at the trailing edge <NUM> of the strut <NUM>. Also, at a given peripheral location around the airfoil body, the outer fillet 56a can be a compounded fillet having a variable radius between the outer surface 24a of the inner case <NUM> and the airfoil body of the strut <NUM>.

An inner fillet 56b is provided at the juncture of the strut wall extension <NUM> and the stiffener ring <NUM> with the radially inner surface 24b of the inner case <NUM>. The inner fillet <NUM> extends around the leading edge extension segment 50a and along the suction and pressure side extension segments 50b, 50c. The inner fillet 56b is inverted relative to the outer fillet 56a. This provides for a reversed dual fillet arrangement between the inner end <NUM> of the strut <NUM> and the inner case. So connecting/joining the struts <NUM> on both the inner and outer sides of the inner case <NUM> allows minimizing strut deformation due to thermal variations.

The combination of the strut wall extensions <NUM> with the stiffener ring <NUM> on the radially inner side of the inner case <NUM> allows distributing the loads outside the struts <NUM>, thereby relieving stress from the struts <NUM>. For instance, the strut wall extensions <NUM> and the stiffener ring <NUM> can cooperate to remove tensile stress in the strut leading edge <NUM> when there is a high delta temperature between the struts <NUM> and cases <NUM>, <NUM> of the TEC <NUM>. According to another aspect, the strut wall extensions <NUM> and the stiffener ring <NUM> eliminate the need for a heavy structural inner case, thereby providing weight savings.

According to one aspect of the technology, there is provided a TEC having a strut wall structure extending through an inner gaspath wall such as to form a strut continuity across the inner gaspath wall building a reversed cast fillet on the radially inner side of the inner gaspath wall. By so connecting the strut on both radial sides of the gaspath wall, the strut can be reinforced and, thus, be less subject to deformation due to thermal variations.

Claim 1:
A turbine exhaust case (<NUM>) comprising:
an outer case (<NUM>) extending around a central axis (<NUM>);
an inner case (<NUM>) concentrically disposed inside the outer case (<NUM>), the inner case (<NUM>) having a radially outer surface (24a) facing away from the central axis (<NUM>) and a radially inner surface (24b) facing towards the central axis (<NUM>);
an annular exhaust gas path (20a) radially between the outer case (<NUM>) and the inner case (<NUM>); and
a plurality of circumferentially spaced-apart struts (<NUM>) extending across the annular exhaust gas path (20a) and structurally connecting the inner case (<NUM>) to the outer case (<NUM>), at least one of the plurality of circumferentially spaced-apart struts (<NUM>) having an airfoil body with a hollow core (<NUM>), the airfoil body having opposed pressure and suction sides (<NUM>, <NUM>) extending chordwise from a leading edge (<NUM>) to a trailing edge (<NUM>) and spanwise from a radially inner end (<NUM>) to a radially outer end (<NUM>), wherein the radially inner end (<NUM>) of the airfoil body has a strut wall extension (<NUM>) that extends through the inner case (<NUM>) to a location radially inward of the inner case (<NUM>) relative to the central axis (<NUM>), the radially inner end (<NUM>) of the airfoil body connected to the inner case (<NUM>) on both the radially inner surface (24b) and the radially outer surface (24a) of the inner case (<NUM>),
wherein the inner case (<NUM>) has a stiffener ring (<NUM>) projecting radially inwardly from the radially inner surface (24b), and the strut wall extension (<NUM>) projects radially inwardly through the inner case (<NUM>) for connection with the stiffener ring (<NUM>) on the radially inner surface (24b) of the inner case (<NUM>),
characterised in that:
the strut wall extension (<NUM>) has a pressure side extension segment (50c) and a suction side extension segment (50b) extending in a spanwise direction in continuity to the pressure side (<NUM>) and suction side (<NUM>) of the airfoil body of the strut (<NUM>), the pressure side extension segment (50c) and the suction side extension segment (50b) projecting in a chordwise direction from a leading edge extension segment (50a), the leading edge extension segment (50a) monolithically merging with the stiffener ring (<NUM>).