Mount arrangement

Abstract

A turbine rear structure for a gas turbine engine. The turbine rear structure comprises an outer shroud and an inner hub, wherein a gas flow path is defined between the shroud and the hub. The turbine rear structure further comprises a plurality of struts extending radially between the shroud and the hub, each strut intersecting with the shroud at a first end and the hub at an opposing end and at least two primary engine mounts on an outer radial side of the shroud configured to mount the turbine rear structure in an aircraft. The primary engine mounts are arranged circumferentially in between adjacent struts. The turbine rear structure further comprises a catcher mounting lug between the primary engine mounting lugs, wherein the catcher mounting lug is radially aligned with one of the plurality of struts.

Description

MOUNT ARRANGEMENTFIELD AND BACKGROUND

[0001] The present invention is concerned with an improved turbine rear structure for a gas turbine engine.

[0002] Existing gas turbine components experience high levels of pylon drag due to their length. This increases aircraft fuel consumption. Furthermore, gas turbine components, such as a turbine rear structure (TRS), are subjected to extreme temperature differentials during operation. For example, a TRS may be elevated from ambient temperature conditions to temperatures in excess of 700 degrees C during operation. Aircraft engines are particularly prone to high temperatures during taxi to or from a run-way when airflow can be low and ambient air temperature high. These temperature differentials can create thermally induced stresses in the engine components such as the shroud casing. The problem is compounded over time by the cyclical effect of loading which can dramatically reduce fatigue life. There is a desire therefore to improve the fatigue life of the engine and specifically the TRS.

[0003] Still further, pressure loss can often be seen in turbine casings due to engine mount recesses in the TRS. There is a desire to reduce these pressure losses.

[0004] The present inventors have established a new and counterintuitive approach to TRS design and in particular an arrangement which reduces the turbine rear structure total length. This therefore improves the aerodynamic performance of the TRS and reduces the specific fuel consumption. The approach taken by the inventors further increases the fatigue life of the engine and reduces pressure loss in the engine mount.

[0005] Although the invention is primarily concerned with a turbine rear structure it will be recognised that the arrangement may equally be applied to other static casing components in a gas turbine engine, generator or a compressor. For example, the invention can be used in any load bearing structure with aerofoils.

[0006] The operation of a gas turbine engine is well known to a person skilled in the art who will also be familiar with the arrangement of a conventional TRS which comprises an inner circumferential casing portion (a hub portion) and an outer circumferential casing portion (a shroud portion).

[0007] A plurality of radially extending struts extend between the inner hub and the outer shroud and provide structural support between the two portions. The struts are mechanically coupled to the hub at a radially inward end (measured from a central rotational axis of the engine) and to the shroud at a radially outward end (again measured from the central rotationalaxis of the engine). The TRS comprises a mount sector with a plurality of mounting lugs to mount the casing to the aircraft through attachment to a pylon.

[0008] An invention described herein is therefore concerned with optimising the TRS and its attachment to the pylon and reducing the overall length of the engine.SUMMARY

[0009] Particular aspects and embodiments are set out in the appended claims.

[0010] Viewed from a first aspect, there is provided a turbine rear structure (TRS) for a gas turbine engine. The turbine rear structure comprises an outer shroud and an inner hub, wherein a gas flow path is defined between the shroud and the hub. The turbine rear structure further comprises a plurality of struts extending radially between the shroud and the hub, each strut intersecting with the shroud at a first end and the hub at an opposing end and at least two primary engine mounting lugs on an outer radial side of the shroud configured to mount the turbine rear structure in an aircraft. The primary engine mounting lugs are arranged circumferentially in between adjacent struts. The turbine rear structure further comprises a catcher mounting lug between the primary engine mounting lugs, wherein the catcher mounting lug is radially aligned with one of the plurality of struts.

[0011] The primary engine mounting lugs may be used to mount the turbine rear structure to an aircraft pylon. The wording ‘circumferentially in between adjacent struts’ is intended to mean that when the TRS is viewed in cross section along its axis, the primary engine mounting lugs, rather than being radially aligned with a strut, are located between two adjacent struts. The term ‘radially aligned’ is intended to mean that the catcher mounting lug is on the same radial line as one of the struts. Specifically, when viewed in cross section, the catcher mounting lug extends outside the shroud of the turbine rear structure in line with one of the struts.

[0012] By positioning the mounting lugs between adjacent struts rather than on top of the struts, the engine mount load is shared between two adjacent vanes. Specifically, the offset between the center of action and the center of the lug pin creates a moment force. The lugs and adjacent material must accommodate the force. By positioning the lug centre between the struts, the moment force is divided in two directions and shared between the adjacent struts. This means the struts can be made thinner as they are sharing the load. This therefore means the weight of the engine primary mount sectors is reduced. Mechanical equilibrium is achieved by reacting the load in the two adjacent vanes.

[0013] Furthermore, when mounting lugs are located on top of struts, the mounting lugs must be recessed into the flow path to avoid a local moment being formed. As the primary mounts in the present invention are located between struts, they are not recessed into the flow path. The length of the component is driven by the amount the mounts are recessed into the path, also known as the bump length. Specifically, where the mounting lug is recessed to a greater extent, the length of the component must be increased in order to avoid flow turbulence. By removing these mount recesses, the length of the turbine rear structure andtherefore the engine can be reduced. A shorter engine enables less pylon drag and better aircraft fuel consumption.

[0014] The outer shroud and the inner hub may be generally cylindrical. In another example, the inner hub may be generally cylindrical and the outer shroud may be polygonal when viewed in the axial direction. In this configuration, the outer shroud comprises a plurality of vertices, wherein each strut meets the shroud at a vertex of the plurality of vertices. The polygonal configuration increases the stiffness of the outer shroud.

[0015] The catcher mounting lug may be located at top dead centre of the casing when the casing is installed in an aircraft. In some examples, the catcher mounting lug may comprise an oversized lug hole, a web shaped link hole or a swing link comprising an attached lug pin for attachment to the pylon. This mounting lug may be for redundancy purposes in case one of the primary mounting lugs fails. The catcher mounting lug may be located on top of a strut. This mounting lug is not reacting any moment since the applied load is in the radial direction only. The catcher mounting lug may be recessed into the flow path of the turbine rear structure to reduce the radial distance between the engine and the pylon i.e. increase the distance between the wing and the ground. The size of this recess is reduced compared to conventional turbine rear structures. This is because this mount acts as a redundancy mount meaning the requirements are less stringent than for the primary mounts. The pressure loss in the TRS may be reduced by eliminating the recesses on the primary mounting lugs and by minimizing the catcher mount recess at top dead centre of the TRS.

[0016] By reducing the length of the mount recess and by increasing the strut count (which reduce the length of the struts for the same redirecting work on the airflow), the length of the turbine rear structure and therefore the engine can be reduced. This reduces the overall weight of the TRS. A shorter engine also enables less pylon drag and better aircraft fuel consumption. Furthermore, due to the smaller catcher mount recess, the distance between the aircraft pylon and engine centre axis is minimised. A smaller distance is preferred to prevent the engine hanging down too far which would reduce ground clearance. Therefore, by using a smaller catcher mounting lug at a constant pylon clearance, the wing to engine centreline distance is reduced.

[0017] The two primary engine mounting lugs may be located at an angle of + / -45 degrees from top dead centre of the casing when the casing is installed in an aircraft. This angle is chosen to ensure that interference with the nacelle is prevented (which would be caused by a much larger angle) whilst minimising stress (which is achieved by keeping a wide stance between the two active mounting lugs). A wider stance also reduces reacting forces. Furthermore, it is desirable to not have the lugs positioned too widely as this would lead to anincreased pylon width which would reduce aircraft performance. In other examples, the two primary engine mounting lugs may be located more or less than 45 degrees from top dead centre. For example, the primary engine mounting lugs 5a may be located at + / -40 to 50 degrees from top dead centre.

[0018] The struts may be evenly distributed around a circumference of the turbine rear structure. Specifically, the struts may have an equal pitch. This prevents ovalisation of the TRS. In other examples, the struts may be unevenly distributed around a circumference of the turbine rear structure, i.e. have a variable pitch between them. Specifically, there may be more struts arranged in the upper half the casing than the lower half. By doing this, the strut count can be increased adjacent the mounting lugs to provide an improved interface between the nacelle and the primary engine mounting lugs without increasing the overall weight of the TRS as fewer struts are used in the lower half. Furthermore, by reducing the number of struts at the bottom of the TRS, the number of parts can be reduced.

[0019] The struts proximal to the primary engine mounting lugs may be spaced circumferentially closer together than the struts distal from the primary engine mounting lugs. Specifically, the struts which are near (for example directly below) the lugs may be closer together than those on the other circumferential side of the turbine rear structure from the lugs.

[0020] The struts may perpendicularly intersect both the hub and the shroud. This configuration can be easily and efficiently manufactured.

[0021] In other examples, the struts may intersect both the hub and the shroud at an angle. In other words, the struts may be slanted in the flow path between the shroud and the hub.

[0022] By using slanted struts, reaction forces are redirected from a radial to a circumferential direction. This improves the fatigue life of the struts by reducing thermally driven stresses in the outer diameter casing. When in use, the struts expand due to the increase in temperature. The expansion of the struts is similar to the inner diameter casing but greater than the expansion of the outer diameter casing due to the temperature mismatch. As a result of this, the vanes try to ‘punch’ through the outer diameter casing. This canincrease the dimensions and weight of hub, struts and outer diameter casing. With a slanted strut, the inner diameter hub is caused to rotate due to the temperature mismatch instead of the strut ‘punching’ through the outer diameter casing. This therefore prevents the same aerodynamic drawbacks. However, the rotation introduces a bending moment at the root of the blade which creates local stresses. The angle of the struts is therefore optimised to prevent punching in the outer casing whilst limiting local stresses at the hub.

[0023] Furthermore, due to the redirection of the load into the circumferential direction, the thickness of the struts can be reduced which leads to a reduction in weight of the component which in turn increases the fuel efficiency of the engine.

[0024] The angle between a radial direction of the turbine exhaust casing and the slanted struts may be between about 20 and about 35 degrees. Specifically the angle may be about 30 degrees. In other examples, the angle may be less than this. It can be seen that by arranging the struts at about 30 degrees, the punch load is reduced by about half.

[0025] The struts may be straight. Specifically, whether or not the struts are angled with respect to the shroud and hub, they extend in a straight line between the two.

[0026] The struts may be curved. Specifically, whether or not the struts are angled with respect to the shroud and hub, they have a curved profile when the turbine rear structure is viewed in the axial direction. A radius of curvature of the struts may be between about 45 and about 60% of a radius of the outer shroud. The ratio of the radius of the inner hub to outer shroud may be about 50 to 65%. The exact ratio is dependent on the size of the engines; it is smaller for medium thrust engines (15 000 lb) and higher for large engines (70000 lb). The diameter of the outer shroud is between about 1 metre and about 2 metres. In other examples it may be smaller or larger than this.

[0027] In some examples, the TRS may have between ten and eighteen struts. For example, the TRS may have twelve or sixteen struts. In some examples, fewer struts are preferred in order to reduce weight of the TRS and allow for service tubes accommodation. However, if too few struts are used, the flow will be insufficiently redirected to the axial direction. Furthermore, by having more vanes, the TRS component length may be reduced.

[0028] Specifically, the strut count can be varied based on the application and the desired interface between the nacelle and the primary engine mounting lugs. The positioning of the primary engine mounting lugs can be varied based on the application and the desired parameters by increasing the strut count or by introducing a variable pitch between the struts.

[0029] The turbine rear structure may be formed of four sectors: a catcher engine mount sector, two primary mount sectors and a lower part of the component or bottom sector.

[0030] In other examples, the TRS may be formed of one or two sectors. The number of sectors may be chosen based on the manufacturing method.

[0031] When multiple sectors are used, these may be joined together by axially extending weld lines. By using multiple sectors joined together by axial weld lines, theproducibility of the part is improved. For example, an axial weld is used to attach the primary engine mount sectors with the catcher engine mount sector.

[0032] The inner radial side of the shroud may be recessed into the gas flow path at the intersection between the catcher mounting lug and the shroud. As discussed above, the recess may be smaller than in conventional TRSs. This reduces the distance between the aircraft pylon and engine centre of axis. For example, in a conventional TRS, the inner radial side of the shroud may protrude into the flowpath up to about 18% of the channel height. In the present invention, this may be reduced to about 12% of the channel height due to the use of the catcher mount. The distance to the pylon is then reduced in the order of 10 mm. Thus the component is shorter and therefore lighter.

[0033] The inner radial side of the shroud may not be recessed into the gas flow path at the intersection between the primary engine mounting lugs and the shroud. This is because the mounting lug is located between adjacent struts. As discussed above, by removing the recess between of the primary mounting lugs, the length of the TRS can be reduced. Furthermore, the aerodynamic capability of the TRS is optimised as a result of optimised pressure loss and separation. As the primary engine mounting lugs no longer require recesses into the flow path, the distance between the strut and the low pressure turbine can be reduced resulting in a shorter engine. Furthermore, upstream forcing, which is dictated by the distance between the strut and the low pressure turbine, is reduced.

[0034] The turbine rear structure may have an axial length of 200-400 mm.

[0035] The circumferential wall thickness of the mount struts is typically 4.0 mm and can typically be reduced to 2.0-3.0 mm. Furthermore, the circumferential width of the struts can be reduced due to reduced moment on the struts from primary engine mounting lugs.

[0036] According to a second aspect, there is provided a method of manufacturing a turbine rear structure according to any preceding claim wherein the TRS is manufactured from: a) A one piece casting; b) A shroud-strut-hub casting with welded interface flanges; c) A weld fabrication wherein the struts comprise a sheet, cast or printed material; d) A weld fabrication from sectors formed of a printed, cast or wrought material; or e) A weld fabrication wherein the struts are T shaped and are welded with circumferential panels in sheet material with interface flanges.

[0037] The welding may be laser, plasma, electron beaom or fusion welding. The weld method depends on joined material thickness and also depends on participating tolerances inparts manufacture. High precision thick materials tend to focus on EB or plasma welding. Panel, cast and thin material is better suited for laser or fusion welding. The weld shrinkage is lesser for the first methods but laser welding is considered more versatile spanning more options in both thickness and shrinkage.

[0038] The combination of the two Primary Mounts being located in between struts and the Catcher Mount being located on top of the TRS Top Dead Center strut enables an assembly with one single strut sector at the TRS T op Dead Center with Catcher Mount welded to two double sectors with Primary Mounts. The welds are located at the panels in between the engine mounts. The size of the welded together parts is limited to two strut sectors. Limitation of part size is important for enabling manufacturing of the parts with Additive Manufacturing, Castings or fabricated forgings. The panels are joined to the strut with shrouds that on the Engine Mount Sectors include Engine Mounts. The panels are joined to the forward and aft flanges by means of circumferential welds.

[0039] When the TRS is manufactured from shroud-strut-hub castings, a pluraility of ‘H- sectors’ may be formed. These may then be welded together and inner and outer diameter rings may be welded at the shroud and hub respectively.

[0040] Other aspects will also become apparent upon review of the present disclosure, in particular upon review of the Brief Description of the Drawings, Detailed Description and Claims sections.BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Examples of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0042] Figure 1 shows an isometric view of a turbine rear structure for a gas turbine engine according to the invention;

[0043] Figure 2 shows an engine mount for connecting to primary engine mounting lug pairs and a catcher mounting lug pair or a turbine rear structure.

[0044] Figure 3 shows a cross-sectional view of part of the turbine rear structure according to the invention;

[0045] Figures 4A to 4F show cross-sectional views of different configurations of the turbine rear structure according to the invention;

[0046] Figure 5 shows a cross sectional view of a strut of the turbine rear structure viewed in a circumferential direction.

[0047] While the disclosure is susceptible to various modifications and alternative forms, specific example approaches are shown by way of example in the drawings and are herein described in detail. It should be understood however that the drawings and detailed description attached hereto are not intended to limit the disclosure to the particular form disclosed but rather the disclosure is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention.

[0048] As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”.

[0049] It will be recognised that the features of the above-described examples of the disclosure can conveniently and interchangeably be used in any suitable combination. It will also be recognised that the invention covers not only individual embodiments but also combinations of the embodiments that have been discussed herein.DETAILED DESCRIPTION

[0050] The present invention is concerned with an improved turbine rear structure for a gas turbine engine.

[0051] Figure 1 shows an isometric view of a turbine rear structure 1 (TRS) for a gas turbine engine according to the invention. The TRS 1 comprises an outer generally cylindrical shroud 2 and an inner generally cylindrical hub 3, wherein a gas flow path 7 is defined between the shroud 2 and the hub 3. A plurality of struts 4 extend radially between the shroud 2 and the hub 3, each strut 4 intersecting with the shroud 2 at a first end and the hub at an opposing end.

[0052] The TRS 1 further comprises at least two primary engine mounting lug pairs 5a on an outer radial side of the shroud 2 configured to mount the turbine rear structure 1 in an aircraft. The primary engine mounting lug pairs 5a are arranged circumferentially in between adjacent struts 4. This is best seen from figure 3. The TRS 1 further comprises a catcher mounting lug pair 5b located at top dead centre of the casing when the casing is installed in an aircraft. The catcher mounting lug pair 5b is radially aligned with a strut 4. The catcher mounting lug pair 5b may function as a redundant mounting lug pair in that it only carries load if one of the active primary engine mounting lug pairs 5a fail.

[0053] The two primary engine mounting lug pairs 5a are located at an angle of about + / -45 degrees from top dead centre of the casing when the casing is installed in an aircraft.

[0054] The turbine rear structure is formed of four sectors: a top mount sector 8a, two primary mount sectors 8b and a lower part or bottom sector 8c. The sectors are joined together by axially extending weld lines.

[0055] Figure 2 shows an engine mount 6 for connecting to the primary engine mounting lug pairs 5a and the catcher mounting lug 5b. The engine mount 6 is then connected to a pylon of the aircraft (not shown). The engine mount 6 comprises a fixed link 9 for connecting to one of the two primary engine mounting lug pairs 5a and a swing link 10 for connecting to the other of the two primary engine mounting lug pairs 5a. The fixed link 9 is a boomerang shaped link which is configured to be attached to the aircraft pylon by three pins. The catcher mounting lug pair 5b is inactive until malfunction of either of the fixed link or swing link. The links use a spherical bearing so there is no axial load, the engine can expand axially.

[0056] The fixed link 9 results in two perpendicular forces, and the swing link 10 transfers loads in link direction only. The offset between the center of action and the center of the lugpin creates a moment force which is taken up by the lugs and adjacent material. By positioning the lug centre between the struts, the moment force is divided in two locations.

[0057] Figure 3 shows an axial cross-sectional view of part of the TRS 1 according to the invention. From this figure, the position of one of the primary engine mounting lugs 5a can be seen located between two adjacent struts 4. This figure also shows the catcher mounting lug 5b aligned with a strut 4 at top dead centre of the TRS 1. The location of the nacelle 13 of the aircraft is also shown in this figure. The positioning of the lugs 5a are chosen to avoid interference with the nacelle 13.

[0058] As can be seen from this figure, the inner radial side of the shroud 2 is recessed into the gas flow path 7 at the catcher mounting lug 5b but is not recessed into the gas flow path at the intersection between the primary engine mounting lugs 5a and the shroud 2.

[0059] Figures 4A to 4F show schematic cross-sectional views of different configurations of the turbine rear structure according to the invention.

[0060] Figure 4A shows a TRS 1 with sixteen struts 4 evenly distributed around its circumference. The struts 4 are arranged such that they are perpendicular with the shroud 2 and the hub 3. Although sixteen struts 4 are shown in figure 3A, more or fewer than this may be used.

[0061] Figure 4B shows a TRS 1 with twelve struts 4 unevenly distributed around its circumference. The struts 4 are more closely spaced at the top of the TRS 1. The struts 4 are arranged such that they are perpendicular with the shroud 2 and the hub 3. The manufacturing involves joining sectors by panels in a selectable alloy. The panels are joined to the strut with shrouds that on the Engine Mount Sectors include Engine Mounts. The panels are joined to the forward and aft flanges by means of circumferential welds.

[0062] Figure 4C shows a TRS 1 with twelve struts 4 unevenly distributed around its circumference. The struts 4 are more closely spaced at the top of the TRS 1. The struts 4 intersect both the hub 3 and the shroud 2 at an angle. The angle between a radius of the TRS and the struts is between 20 to 40 degrees. In other examples, slanted struts 4 may be used with the struts 4 evenly distributed about the TRS 1 circumference. Although twelve struts 4 are shown in figures 3B and 3C, more or fewer than this may be used.

[0063] As can be seen from figures 4A to 4C, the shroud may be formed of a plurality of panels 12. The panels 12 are located between the stuts 4. The panels may be formed from sheets and welded to the struts.

[0064] Figures 4D and 4E show the same configurations as in figures 4A and 4C respectively but wherein the outer shroud is polygonal. In this configuration, the outer shroud comprises a plurality of vertices, wherein each strut meets the shroud at a vertex of the plurality of vertices.

[0065] Figure 4F shows a TRS 1 with eleven struts 4 distributed around its circumference. The struts 4 are slanted as in figure 3C in that they intersect both the hub 3 and the shroud 2 at an angle. For example, the angle between a radius of the TRS and the struts is between 20 to 40 degrees. Additionally, the struts are curved when viewed in an axial direction of the TRS. The radius of curvature of the struts may be between about 45 and about 60% of a radius of the outer shroud.

[0066] Figure 5 shows a cross sectional view of one of the struts 4 extending between the hub 3 and the shroud 2 and its position with respect to a low pressure turbine blade 11. Due to the primary engine mounting lug pairs not being recessed into the gas flow path as in a conventional turbine rear structure, the distance B between the strut and the LPT last blade can be made shorter resulting in a shorter engine. Furthermore, due to the reduced recesses or bumps in the flow path, the upstream forcing is reduced.

[0067] A method of manufacturing a turbine rear structure according to the present invention will now be described. The TRS is manufactured as a welded sectorized fabrication of struts, casings (hub and shroud) and flanges. The welded parts are manufactured from sheets and forgings or castings.

[0068] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

CLAIMS:

1. A turbine rear structure, the turbine rear structure comprising: an outer shroud; an inner hub, wherein a gas flow path is defined between the shroud and the hub; a plurality of struts extending radially between the shroud and the hub, each strut intersecting with the shroud at a first end and the hub at an opposing end; at least two primary engine mounting lugs on an outer radial side of the shroud configured to mount the turbine rear structure in an aircraft, wherein the primary engine mounting lugs are arranged circumferentially in between adjacent struts; a catcher mounting lug between the primary engine mounting lugs, wherein the catcher mounting lug is radially aligned with one of the plurality of struts.

2. A turbine rear structure as claimed in claim 1 , wherein the outer shroud and the inner hub are generally cylindrical.

3. A turbine rear structure as claimed in claim 1 , wherein the inner hub is generally cylindrical and wherein the outer shroud is polygonal when viewed in the axial direction, wherein the outer shroud comprises a plurality of vertices, wherein each strut meets the shroud at a vertex of the plurality of vertices.

4. A turbine rear structure as claimed in any of claims 1 to 3, wherein the catcher mounting lug is located at top dead centre of the casing when the casing is installed in an aircraft.

5. A turbine rear structure as claimed in any of claims 1 to 4, wherein the two engine mounting lugs are located at an angle of + / - about 45 degrees from top dead centre of the casing when the casing is installed in an aircraft.

6. A turbine rear structure as claimed in any preceding claim, wherein the struts are evenly distributed around a circumference of the turbine rear structure.

7. A turbine rear structure as claimed in any of claims 1 to 5, wherein the struts are unevenly distributed around a circumference of the turbine rear structure.

8. A turbine rear structure as claimed in claim 7, wherein the struts proximal to the primary engine mounting lugs are spaced circumferentially closer together than the struts distal from the primary engine mounting lugs.

9. A turbine rear structure as claimed in any preceding claim, wherein the struts perpendicularly intersect both the hub and the shroud.

10. A turbine rear structure as claimed in any preceding claim, wherein the struts intersect both the hub and the shroud at an angle.

11. A turbine rear structure as claimed in any preceding claim, wherein the angle between a radial direction of the turbine exhuaust casing and the struts is about 30 to about 35 degrees.

12. A turbine rear structure as claimed in any preceding claim, wherein the struts are straight.

13. A turbine rear structure as claimed in any of claims 1 to 11 , wherein the struts are curved.

14. A turbine rear structure as claimed in claim 13, wherein a radius of curvature of the struts is between about 45 and about 60% of a radius of the outer shroud.

15. A turbine rear structure as claimed in any preceding claim, wherein the plurality of struts comprises between ten and eighteen struts.

16. A turbine rear structure as claimed in any preceding claim, wherein the turbine rear structure is formed of four sectors: a top catcher mount sector, two primary mount sectors and a lower part or bottom sector.

17. A turbine rear structure as claimed in claim 16, wherein the sectors are joined together by axially extending weld lines.

18. A turbine rear structure as claimed in any preceding claim, wherein the inner radial side of the shroud is recessed into the gas flow path at the intersection between the catcher mounting lug and the shroud.

19. A turbine rear structure as claimed in any of claims 1 to 17, wherein the inner radial side of the shroud is not recessed into the gas flow path at the intersection between the primary engine mounting lugs and the shroud.

20. A turbine rear structure as claimed in any preceding claim having an axial length of200-400 mm.

21. A turbine rear structure as claimed in any preceding claim, wherein the circumferential thickness of the struts is between about 2 mm and about 3 mm.

22. A method of manufacturing a turbine rear structure according to any preceding claim, wherein the TRS is manufactured from: a) A one piece casting; b) A shroud-strut-hub casting with welded interface flanges; c) A weld fabrication wherein the struts comprise a sheet, cast or printed material; d) A weld fabrication from sectors formed of a printed, cast or wrought material; or e) A weld fabrication wherein the struts are T shaped and are welded with circumferential panels in sheet material with interface flanges.

23. The method of claim 22, wherein the welding is laser, plasma, electron beam or fusion welding.

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