Heat exchanger support plate arrangement

Abstract

A housing structure for a gas turbine engine includes a plurality of struts defining a plurality of annular circumferentially extending airflow flow passages, and wherein a strut side surface includes a recess.

Description

TECHNICAL FIELD

[0001] The present invention relates to a heat exchanger arrangement for a gas turbine engine, and in particular, but not exclusively, to a heat exchanger arrangement for the outer flow path of a gas turbine engine. BACKGROUND

[0002] Heat exchangers are used in gas turbine engines, and in particular in gas turbine engines for aircraft, for various heating and cooling purposes. For example, heat exchangers are used to provide cooling for the lubricating oil of numerous bearings operating within the engine. In certain arrangements, an oil circuit can also be used to lubricate and cool a reduction gearbox used to reduce the rotational speed of a fan (compared to the turbine driving the fan). Heat exchangers are also used for temperature control of the passenger cabin, etc.

[0003] Generally, the high speed cooling air flow in the outer flow path of the engine can conveniently be used as a source of cold air. Conventional heat exchanger integration involves arranging a heat exchanger matrix in the air flow at a suitable location. Heat exchange can be achieved by flowing a suitable heat exchange fluid through the heat exchanger ducts, while the cold air flows through the air ducts, passes through the heat exchanger and reaches the outlet of the engine.

[0004] Conventional arrangements of heat exchangers provide a convenient way of achieving heating or cooling of the engine. However, heat exchangers used in the outer flow path can be positioned around struts connecting the inner and outer annuli of the structure (which define the outer air flow passage). The struts are in the form of a plurality of radially extending supports. The struts are arranged at specific locations around the structure and are designed to accommodate engine loads and to house service lines (such as oil ducts and fuel ducts) from the outer annulus to the inner annulus of the engine.

[0005] The variety and complexity of strut requirements for a given engine greatly limit the way in which conventional heat exchangers can be integrated into a gas turbine engine. Furthermore, the relative thermal expansion of the structure comprising the struts and annuli, compared to the thermal expansion of the heat exchanger itself, causes further complexity in integrating the heat exchanger in the outer air passage in an efficient manner. These issues result in the need for many design compromises to conventional arrangements when seeking to achieve efficient operation of the heat exchanger in such a structure.

[0006] However, the present inventors have conceived an alternative configuration of heat exchanger integration which allows for optimisation of the struts, while optimising the performance of the heat exchanger for a given engine configuration. SUMMARY

[0007] Various aspects of the invention described herein are set out in the appended claims.

[0008] Viewed from a first aspect, there is provided a casing structure for a gas turbine engine, the casing structure comprising: an inner ring and an opposed outer ring, defining a radial space therebetween; a plurality of struts spaced around the structure and extending radially between the inner and outer rings, each strut intersecting the inner and outer rings, the inner ring, the outer ring and the plurality of struts defining a plurality of annular, circumferentially extending air flow channels, wherein each air flow channel is defined circumferentially between two opposed strut side surfaces and radially between an inner surface of the outer ring and an outer surface of the inner ring, and wherein one or both of the inner surface of the outer ring and / or the outer surface of the inner ring comprises a recess arranged in use to receive a portion of a main body of a heat exchanger.

[0009] The recess or indentation serves to provide a larger cross-sectional area than the inlet area of the air flow channel, such that when the heat exchanger is positioned into the passageway, its cross-section can be larger than the air flow inlet. This in turn results in (a) a greater proportion of the incoming air flow to the channel flowing directly into the heat exchanger; and (b) preventing air flow around the sides of the heat exchanger casing from leaking.

[0010] One or both side surfaces of the struts can also advantageously comprise a recess arranged in use to receive a portion of a main body of a heat exchanger.

[0011] According to this arrangement, each strut within the casing structure has side surfaces which extend along the casing in the direction of the air flow, which are concave or "indented" in relation to the leading edge geometry. The recess or indentation serves to provide a larger cross-sectional area than the inlet area of the air flow channel, such that when the heat exchanger is positioned into the passageway, its cross-section can be larger than the air flow inlet. This in turn results in (a) a greater proportion of the incoming air flow to the channel flowing directly into the heat exchanger; and (b) preventing air flow around the sides of the heat exchanger casing from leaking.

[0012] From a thermodynamic perspective, this improves the operation and efficiency of the heat exchanger.

[0013] Advantageously, this represents one embodiment of the casing described herein which uses struts. As described above, one or both side surfaces of the struts can comprise a recess arranged in use to receive a portion of a main body of a heat exchanger. This means that the side surfaces can be adapted to allow some air flow to leak, and others not.

[0014] The inventors have determined that by providing struts with improved profiles downstream of the leading edge, a range of design options are provided in terms of heat exchange location, air flow and performance. Furthermore, the structural performance of the struts can also be optimised in conjunction with the required air flow characteristics.

[0015] As mentioned above, in addition to the side surfaces of the struts, one or both of the inner surface of the outer ring member and / or the outer surface of the inner ring member can also comprise a recess arranged in use to receive a portion of the body of the heat exchanger. Thus, the periphery of the heat exchanger can optionally be provided with a controlled air flow leak on one or more faces.

[0016] Each strut can comprise an upstream edge proximate the inlet of the respective air flow channel. The upstream edge of the respective strut can advantageously comprise an aerodynamic profile, for example a smoothly curved profile, to separate and direct incoming air into the channel. The aerodynamic profile can extend in the direction of air flow and meet the upstream end of the respective recess in the strut. Thus, a step is formed at the point where the downstream limit of the aerodynamic profile meets the point at which the recess begins. This advantageously provides a point at which the heat exchanger can be located, i.e. proximate or abutting the inner side of the recess and the aerodynamic profile.

[0017] The inner and outer ring members can also each comprise an upstream leading edge proximate the inlet of the respective air flow channel. Each upstream leading edge can comprise a similar aerodynamic profile extending in the direction of air flow which also meets the upstream end of the recess in the respective inner or outer surface of the ring member. In effect, the struts and the recesses in the inner and outer ring members form a cross-section to receive the heat exchanger behind (i.e. downstream of) the inlet of the channel.

[0018] Advantageously, the cross-sectional area of the inlet of the air flow channel measured at the intersection of the aerodynamic profile and the recess can be less than the cross-sectional area of the air flow channel measured at a position downstream of the intersection of the aerodynamic profile and the recess. In effect, the cross-section of the inlet is smaller than the space in which the main body of the heat exchanger resides, which allows the air flow to be selectively substantially drawn into the heat exchanger rather than bypassing the side of the housing. The term "selectively" is used because the recess can be selected to locate the heat exchanger in a particular position (as described further below).

[0019] Advantageously, one or both side surfaces of the strut can include one or more ribs or protrusions extending from the surface towards the air flow passage (i.e. extending in a generally perpendicular direction from the side surface). The ribs can serve a variety of purposes. For example, the ribs can be selected to increase the stiffness and strength of the strut. They can also be selected to provide support for heat exchangers positioned in the flow passage. Furthermore, they can also act as a guide surface against which the housing of a heat exchanger can slide when the heat exchanger is positioned into the flow passage.

[0020] A plurality of ribs can be positioned at discrete predetermined locations along the strut in the direction of air flow. This provides the above-mentioned advantages at various locations along the length and depth of the strut.

[0021] One or more ribs can extend in a generally radial direction relative to the surface of the ring member along the surface of the strut. Thus, the ribs can be arranged in a radial direction between the inner and outer ring members and / or in the direction of air flow along the surface of the strut. The distribution, side and depth of these ribs can be selected according to the design requirements of the flow passage and strut as part of the overall housing.

[0022] The ribs can be arranged in use to contact the outer surface of a heat exchanger housing to provide the above-mentioned support effect.

[0023] A fairing or cover can optionally be connected to the end of the ribs, i.e. the end of the ribs facing the passage / heat exchanger, to define a surface on one or both sides of the strut. Such an outer surface can be smooth due to the fairing surface, whereas the surface of the strut can not need to be machined to any degree of surface finish, i.e. aerodynamic surface finish.

[0024] Advantageously, the ribs on one side of the side surface of the strut can be asymmetric relative to the ribs on the opposite side surface of the respective strut. Thus, each side of the strut can have different ribs and associated characteristics. Similarly, the central thickness of the strut defined by the recess between the leading edge and the trailing edge can have different thicknesses on each side of the strut. Thus, significant design flexibility is provided by such a strut arrangement.

[0025] The inner and outer ring members can also each include a downstream trailing edge proximate the outlet of the respective air flow passage, wherein each downstream trailing edge can include an aerodynamic profile extending in the direction of air flow. Thus, the trailing edge can be tailored to minimise any adverse aerodynamic effects as air exits the flow passage.

[0026] A portion of the trailing edge proximate the outlet can also advantageously be selectively removable to allow the heat exchanger to be positioned in the air flow stream passage. Indeed, by providing the trailing edge of the strut and, optionally, all or a portion of the trailing edge of the inner and outer rings, the heat exchanger can be conveniently positioned from the rear of the housing structure into a recess formed in the stream passage. This allows for maintenance and repair while maintaining the integrity of the aerodynamic profile of the leading edge.

[0027] Viewed from another aspect, there is provided a strut for a housing structure of a gas turbine engine, the strut being arranged in use to extend between an inner ring and an opposed outer ring of the housing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion therebetween, wherein the intermediate portion is in the form of a recess on one or both sides of the strut such that the strut is narrower in cross section at the intermediate portion than at the upstream leading edge.

[0028] As mentioned above, the leading edge can comprise an aerodynamic profile extending in the direction of the air flow which intersects the upstream end of the respective recess in the side of the strut. As mentioned above, each strut can be provided with a recess on each side.

[0029] Likewise, the strut can additionally be provided with a fairing or cover connected to the end of the rib to define a surface on one or both sides of the strut. Furthermore, the rib on one side of the side surface of the strut can be asymmetrical to the rib on the opposite side surface of the respective strut in terms of location or extension from the surface of the strut.

[0030] Viewed from another aspect, there is provided a strut for a housing structure of a gas turbine engine, the strut being arranged in use to extend between an inner ring and an opposed outer ring of the housing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion therebetween, wherein the intermediate portion is in the form of a recess on one or both sides of the strut such that the strut is narrower in cross section at the intermediate portion than at the upstream leading edge.

[0031] Thus, a novel strut is provided for a housing structure and associated gas turbine engine, wherein the strut can be tailored for structural properties and is capable of receiving and supporting a heat exchanger against an inner surface. As described herein, the option to tailor the cross section of each strut asymmetrically allows for a variety of design requirements to be met.

[0032] Viewed from a further aspect, there is provided a casing structure for a gas turbine engine, the casing structure comprising: an inner ring and an opposed outer ring, defining a radial space therebetween; a plurality of struts spaced around the structure and extending radially between the inner and outer rings, each strut intersecting the inner and outer rings, the inner ring, the outer ring and the plurality of struts defining a plurality of annular, circumferentially extending air flow channels, wherein each air flow channel is defined circumferentially between two opposed strut side surfaces and radially between an inner surface of the outer ring and an outer surface of the inner ring, and wherein one or both side surfaces of a strut comprises a recess arranged in use to receive a portion of a main body of a heat exchanger.

[0033] Viewed from a further aspect, there is provided a gas turbine engine comprising a casing structure as described herein, and a gas turbine engine comprising one or more struts as described herein. BRIEF DESCRIPTION OF DRAWINGS

[0034] Other aspects, features, and advantages of the application described herein will become apparent from the following description, taken in conjunction with the accompanying drawings, which, by way of illustration, show example embodiments of the application.

[0035] Figure 1 A schematic diagram showing the basic components of a gas turbine engine is shown;

[0036] Figure 2 An alternative gas turbine engine configuration is shown, illustrating where the application described herein can be used;

[0037] Figure 3 is a schematic diagram showing a radial flow passage and a circumferential flow passage in which a heat exchanger can be placed;

[0038] Figure 4A and Figure 4B A schematic diagram of a conventional strut is shown, showing the internal cavity;

[0039] Figure 5A and Figure 5B An end view from a forward or upstream position of the generally cylindrical body 20 is shown;

[0040] Figure 6 A schematic diagram of the prior strut and heat exchanger arrangement as described with reference to Figure 5A and Figure 5B is shown;

[0041] Figure 7 An end view from a forward or upstream position of the generally cylindrical body 20 according to the application described herein is shown;

[0042] Figure 8A andFigure 8B is a cross-sectional view along Figure 7 A-A' in Figure 1 ;

[0043] Figure 9 is a corresponding cross-sectional view showing the air flow into the heat exchanger; Figure 8B

[0044] Figure 10 shows one arrangement of heat exchangers;

[0045] Figure 11A and Figure 11B shows a comparison of a conventional strut with one embodiment of a strut provided by the present invention;

[0046] Figure 12 schematically shows two adjacent heat exchangers and associated struts;

[0047] Figures 13A to 13D shows a conventional heat exchanger arrangement between adjacent struts Figure 13A and three different configurations of recesses, heat exchangers and ribs;

[0048] Figure 14 shows an upstream or front step or recess according to the invention described herein;

[0049] Figures 15A to 15D shows other alternative arrangements of heat exchangers and struts;

[0050] Figure 16A and Figure 16B shows another arrangement which combines conventional heat exchanger integration with improved integration according to the concepts described herein, Figure 16B improved on both sides but the rib structure extends only towards one of the heat exchangers;

[0051] Figures 17A to 17D shows possible other arrangements of struts according to the invention described herein.

[0052] Any reference in this specification to prior art documents is not to be regarded as an admission that such prior art is widely known, or forms part of the common general knowledge in the field. The use of "including", "comprising" and variations thereof in this specification is not to be construed as implying any exclusivity of the features so covered. In other words, use of these terms is not intended to exclude from the scope of the application any subject matter that would otherwise be included if the term were omitted. The application is further described with reference to the following examples. It will be appreciated that the application claimed is not intended to be limited in any way by these examples. It will also be appreciated that the application encompasses not only the individual embodiments described herein, but also combinations of the embodiments described herein.

[0053] ​The various embodiments described herein are provided only to aid in understanding and teaching the claimed features. These embodiments are provided as representative examples of embodiments only and are not exhaustive and / or exclusive. It should be understood that the advantages, embodiments, examples, functions, features, structures and / or other aspects described herein should not be considered as limitations on the scope of the invention as defined by the claims, or limitations on the equivalents of the claims, and other embodiments and modifications may be utilized without departing from the spirit and scope of the claimed invention. In addition to those specifically described herein, various embodiments of the invention may suitably include suitable combinations of the disclosed elements, components, features, parts, steps, devices, etc., and may consist of, or substantially consist of, suitable combinations of the disclosed elements, components, features, parts, steps, devices, etc. Furthermore, this disclosure may include other inventions not currently claimed but which may be claimed in the future.

[0054] In this application, the phrase "constructed for..." is used to indicate that the elements of the device have a configuration capable of performing the defined operation. In this context, "configuration" refers to the interconnection arrangement or manner of the hardware or software. "Constructed for..." does not imply that the device elements need to be replaced in any way to provide the defined operation. Detailed Implementation

[0055] Figure 1 A cross-section of a gas turbine engine 1 is shown, which integrates an external airflow passage that can accommodate a heat exchanger arranged with a support plate according to the description herein.

[0056] Those skilled in the art will understand the main components of a gas turbine engine and its operation. In short, engine 1 includes an air inlet 2 that allows air to flow into the engine and to a fan 3 located at the upstream end of the engine. All components are housed within an engine nacelle 4.

[0057] The engine shown in the figure is a turbofan engine, including a bypass passage 19 downstream of the fan and a central engine core housing a compressor, a combustion chamber, and a turbine. The engine core is formed by a first low-pressure compressor 5 and a second high-pressure compressor 6. This multi-stage compressor arrangement raises air from ambient pressure and temperature to high temperature and pressure. The compressed air is then delivered to the combustion chamber 7, where fuel is injected and combustion occurs. It should be understood that this arrangement is only one example of how an engine can be arranged. In other examples, the engine may have, for example, a geared fan or an open fan.

[0058] Combustion gases exit the rear of the combustion chamber 7 and first impinge on the high pressure turbine 10 before exiting the rear of the engine through the core nozzle 11, then impinging on the second low pressure turbine 12. Thrust from the engine is generated by two air streams: a first air stream from the fan nozzle 8 (receiving thrust from the fan) and a second air stream from the exhaust of the core nozzle 11.

[0059] It will be appreciated that the air flow in the engine 1 is from left to right through Figure 1 the flow (from front to rear). Thus, Figure 1 the rightward direction in Figure 1 corresponds to a downstream direction of the engine 1, while the leftward direction in

[0060] corresponds to an upstream direction of the engine.

[0061] A transition duct 14 is arranged to receive air from the low pressure compressor 5 and pass it radially inwards to supply the high pressure compressor 6.

[0062] As shown, both compressors are coaxial with the central (rotational) axis of the turbine. The outer radius of the low pressure compressor 5 (measured from the central axis of the compressor) is greater than the outer radius of the high pressure compressor 6.

[0063] This requires that the duct or passage passing air between the two compressors is generally S-shaped in order to pass the compressed air towards the central axis of the turbine and into the high pressure turbine 6.

[0064] As shown in Figure 1 an extraction duct 15 is provided which provides an openable flow passage to allow air to selectively flow from the transition duct 14 into a cavity 16 (which in some embodiments can be referred to as a plenum or fire zone compartment). The cavity 16 can be arranged downstream of the low pressure compressor 5. In particular, the cavity 16 can be arranged radially outward of the core and the extraction flow passage is generally downstream of the low pressure compressor 5 and receives air released from the main flow path. In effect, the cavity 16 acts as a collection chamber or reservoir for air released from the main flow path.

[0065] The cavity is enclosed on the downstream side by a fire wall 17 (which can also be referred to as a downstream wall). The fire wall 17 provides a boundary between fire zones of the engine 1 to prevent the leakage of flammable fluids between different sections of the engine 1. To allow extraction air to escape from the cavity 16 into a bypass passage 19, a duct 18 is provided through the fire wall 17. The duct 18 can provide a flow passage through the fire wall 17 at a radially extreme point of the fire wall 17, such that the duct 18 can be considered to provide a flow passage over or beyond the fire wall.

[0066] As Figure 1 shown, the bleed duct 15, the cavity 16 and the duct 18 provide a flow path for the transfer of bleed air between the core flow path and the bypass passage 19. In other embodiments, bleed air can alternatively or additionally be transferred from the core flow path to another flow path within the gas turbine engine 1, such as an intermediate flow path of the low pressure core flow path, which is further radially from the axis of the engine 1 than the core flow path.

[0067] The bypass passage 19 conveniently provides a location of high velocity, low temperature air flow which can be conveniently used in conjunction with a heat exchanger to control the temperature of engine components.

[0068] As shown, a radial strut S is positioned within the bypass passage and upstream (in the direction of air flow) of the point at which hot gases are released into the bypass passage. As described herein, a heat exchanger can be integrated between adjacent struts S using an unconventional strut design in accordance with the application described herein.

[0069] Figure 2 An alternative engine configuration is shown, illustrating a location at which the application described herein can be used. The engine shown is an open fan engine, but similarly incorporates an external air flow passage 73. The box L shows a possible location for a heat exchanger and strut arrangement in accordance with the application described herein.

[0070] Figure 3 is a schematic view showing a radial flow passage and a circumferential flow passage in which a heat exchanger can be positioned. As Figure 3 shown, a generally cylindrical body 20 includes an outer ring 21 and an inner ring 22, i.e. two generally cylindrical and coaxial rings. A plurality of radially extending struts 22a, 22b, 22c, etc. are spaced around the body 20 and extend between the inner and outer rings. The cylindrical body can also be formed of scallops which are each welded together. The inner and outer cylindrical coaxial rings can be constructed of separate sectors and segments which are manufactured together, assembled together using fasteners, or a combination of the two.

[0071] The two opposite side surfaces of adjacent struts together with the inner surface of the outer ring and the outer surface of the inner ring define a plurality of air flow passages 23 which extend through the body 20 and allow air to flow from upstream US to downstream DS as shown by the arrows.

[0072] Each passage 23 is in the general form of a truncated segment of a circle. In accordance with the application described herein, each passage can conveniently be provided with a heat exchanger 25 which is positioned within the passage and as Figure 3As indicated by the arrows in the diagram. Each of these pathways, or subset thereof, may be equipped with a heat exchanger having a shape that is substantially complementary to the pathway profile.

[0073] Reference Figure 4A and Figure 4B Describe the support plate.

[0074] Figure 4A A schematic diagram of a conventional support plate is shown. A single support plate is shown, but it should be understood that the support plate is positioned around the circumference of the cylindrical body 20. The support plates serve multiple purposes, including providing structural support for the engine core. They also provide a path through the hollow cavity within the support plate to allow service piping to pass through and enter the engine core. Figure 4B yes Figure 4A The top view of the support plate shows the internal cavity in a typical support plate, indicated by dashed lines. Each support plate is designed to include an internal cavity for servicing piping or controlling weight.

[0075] Figure 5A and Figure 5B An end view is shown, taken from the front or upstream position of the cylindrical body 20. Figure 5A and Figure 5B The diagram shows a conventional arrangement, in which the heat exchanger 25 is positioned at the above reference point. Figure 3 In the described pathways, as schematically shown, each heat exchanger is positioned to provide clearance around the outer periphery of the heat exchanger (a) between the inner surfaces of the heat exchanger housing and the inner surfaces of the circumferentially opposed support plates, and (b) between the radially opposed inner and outer annular surfaces.

[0076] Circumferential clearance Figure 5B The diagram is shown schematically. It will be clear that the clearance has been exaggerated for ease of understanding.

[0077] like Figure 5B The diagram shows the corner of the passage and the positioned heat exchanger. A radial clearance is also defined, as further shown. r and circumferential clearance c. Depending on the specific construction, these clearances may be located on each of the four end faces of the heat exchanger, or on a subset of these end faces.

[0078] Gaps r and cArise from a variety of factors, including manufacturing limitations that produce large tolerance chains, and thermal expansion considerations between the body 20 and the heat exchanger 25. During operation of the engine, the body 20 will expand at a different rate than the heat exchanger, and the expansion of the heat exchanger can fluctuate as the heat exchanger is activated and deactivated. This results in potentially complex loading scenarios, depending on the relative thermal expansion of the components. This is controlled with appropriate clearances.

[0079] Figure 6 A schematic view of an existing strut and heat exchanger arrangement as described above with reference to Figure 5A and Figure 5B is shown. The view is looking generally radially inward at a pair of adjacent heat exchangers and associated struts, including an intermediate strut located between the adjacent heat exchangers. The clearances described above are shown. These clearances advantageously allow for positioning of the heat exchangers, and also allow for accommodation of different thermal characteristics. However, these clearances do allow cooling air to bypass the heat exchanger bodies as shown by arrows 26A-26D. In fact, the leakage of cooling air around the heat exchangers reduces the potential performance of the heat exchangers in terms of heat transfer. The greater the leakage, the more the efficiency is reduced.

[0080] As described above, the inventors have established an alternative integration or embodiment of heat exchangers and struts. Reference will be made to Figures 7 to 16B to describe these.

[0081] In particular, it is beneficial to place heat exchangers between struts to maximize the air flow through the heat exchangers as described herein. The novel strut design described herein improves the amount of air flow through the heat exchangers while reducing the need for difficult to manufacture cavities within the struts. Different strut widths, whether at the strut periphery or service lines at the back of the strut, can result in different strut stiffness and weight for a given strut. The arrangement described herein also allows for machining of adjacent surfaces, which results in better positioning of the aerodynamic control surfaces, enabling a significant improvement in overall engine performance.

[0082] The open ended rib structure allows for a design that is not sensitive to wall thickness variations, and enables machining of areas to reduce overall tolerance build-up by 75-80%. The inlet and outlet areas are typically machined to improve flow conditions. However, due to accessibility issues and geometry complexity, extensive machining within the air flow passage is generally avoided. Single-sided machining (opposite side from casting) also creates unfavorable thickness variations on the large faceplate surface.

[0083] Figure 7An end view from the front or upstream position of the cylindrical body 20 is shown in accordance with the invention described herein. As shown, the body 20 includes an outer ring surface 27 and an inner ring surface 28. Heat exchangers 29 are positioned in each of the passages 30 positioned circumferentially around the body 20.

[0084] Importantly, as Figure 7 and Figure 5B illustrate by comparison, due to the recess or step, there is no gap or space around the perimeter of the heat exchanger housing visible from the front of the engine. In fact, Figure 7 the cooling air flowing into the body 20 shown in

[0085] Figure 8A and Figure 8B are cross-sectional views taken through A-A' in Figure 7 illustrating a conventional heat exchanger integration Figure 8A and a heat exchanger integration in accordance with the invention described herein Figure 8B .

[0086] Figure 8A A conventional arrangement is shown. As can be appreciated from the teachings herein, the gap around the body of the heat exchanger allows for thermal expansion, but results in a significant efficiency cost due to the gap loss as illustrated by arrows 31.

[0087] Figure 8B An alternative integrated arrangement in accordance with the invention described herein is shown. As Figure 8B illustrates, the inner ring surface 32A and the surface of the outer ring 32B are each provided with a step or recess 33 downstream of the inlet 34 of the passage.

[0088] Advantageously, the axial gap 35 is relatively small, and typically less than the downstream gap 36. The gap 36 facilitates installation of the heat exchanger, and also facilitates maintenance / disassembly / replacement of the heat exchanger. The gap 35 can be provided in any suitable size depending on the combination of heat exchanger and stay plate.

[0089] Figure 9 is a cross-section corresponding to Figure 8B illustrating the flow of air into the heat exchanger 37. As shown, by extending the heat exchanger circumferentially and radially into the recesses or steps provided in the stay plate and inner and outer ring surfaces, leakage around the heat exchanger is minimized. It will be appreciated that all 4 of the surrounding surfaces can include steps and recesses, or as described below, a subset can be selected.

[0090] In fact, the cross-sectional area of the heat exchanger is larger than the cross-sectional area defined by the passage inlet when viewed from the front (face-on) perspective in the direction of air flow. Thus, the maximum air flow is directed into the heat exchanger.

[0091] Figure 10 An arrangement of heat exchangers is shown. As shown, the heat exchanger profile is curved to correspond to the shape of the passage.

[0092] Figure 11A And Figure 11B A comparison of a conventional strut with one embodiment of a strut provided by the present invention is shown. Figure 11A A conventional strut between two adjacent heat exchangers is shown. Air leakage occurs through the thermal expansion clearance as well as the manufacturing tolerances and clearances required for the installation and removal procedures, as indicated by arrow 38.

[0093] Figure 11B An adjusted strut side surface or wall is shown, which incorporates a leading portion for the upstream step 39. As noted above, the step 39 allows the heat exchanger to recess into the strut, such that the air flow 40 is directed to the heat exchanger base 41.

[0094] The recess 42 in the side wall of the strut allows the heat exchanger to extend circumferentially (and radially in the case of recesses in the inner and / or outer rings). This not only allows for a larger heat exchanger, but also means that the outer side surface of the strut can not require an aerodynamically smooth surface. This provides a number of advantages, including not requiring machining to provide a smooth surface. Figure 11A As indicated by arrow 38 in the middle, air flow around the heat exchanger housing can be significantly reduced, as a result of which the outer side surface of the strut can not require an aerodynamically smooth surface. This provides a number of advantages, including not requiring machining to provide a smooth surface.

[0095] Importantly, this also allows the cross-section of the profile of the strut to be fundamentally changed. As shown in Figure 11B Since the surface no longer has any aerodynamic requirements, ribs can be provided to increase stiffness and rigidity, and to locate the heat exchanger. Ribs 43 are shown in Figure 11B These ribs can be configured to optimise stiffness, bending strength and weight. It will be appreciated that complex rib geometries can be provided on the outer surface of the strut.

[0096] It will be appreciated that the concept of ribs can equally (alternatively or additionally) be applied to the inner surface of the outer ring and / or the outer surface of the inner ring.

[0097] Figure 11B A possible additional feature of the selectable removal tail or trailing edge TE of the strut is shown. The provision of a removable tail edge or surface allows the body or housing of the heat exchanger to be conveniently located in the passage between adjacent struts from the rear of the body 20.

[0098] Figure 12 Two adjacent heat exchangers and associated struts are shown schematically.

[0099] Figures 13A to 13D A conventional heat exchanger arrangement between adjacent struts is shown Figure 13A along with three different configurations of recess, heat exchanger and rib.

[0100] In detail: Figure 13A A conventional heat exchanger integration is shown, with normal clearance integrated between the struts and heat exchangers; Figure 13B A strut and pair of heat exchangers are shown with a large recess or step; Figure 13C A strut and pair of heat exchangers are shown with a large rib and a small heat exchanger recess. The ribbed side can maximise strut stiffness; Figure 13D An asymmetric arrangement of heat exchangers with symmetric ribs is shown.

[0101] All strut configurations with a ribbed side allow minimal surface machining for control of strut width. This facilitates simplified machining.

[0102] Different heat exchanger sectors can be designed differently, as they can provide cooling for different engine functions. This can result in different recess requirements on each side of the strut.

[0103] The strut arrangements described herein allow a single strut to be configured to accommodate different heat exchanger bodies or casings on each side of the strut.

[0104] Different heat exchangers can operate at different maximum temperatures, and require different thermal growth space. The struts described herein allow this design option.

[0105] From the examples shown Figures 13B to 13D it can be seen that the arrangements described herein have great versatility in terms of strut stiffness and heat exchanger location.

[0106] Figure 13C and Figure 13D The examples shown also show the optional concept of the outlet section of the strut extending downstream of the heat exchanger, with or without a step. Figure 13D There is no outlet step to facilitate outlet air flow.

[0107] Figure 14A front or upstream step or recess according to the invention described herein is shown. To accommodate thermal expansion of the heat exchanger and strut shell, according to the arrangement described herein, leakage can be controlled by controlling the size, clearance and depth of the step or recess at the upstream end of the strut and heat exchanger.

[0108] As shown, the tangential gap 44 (extending from the leading edge and intersection of the recess with the strut recess) can be predetermined to accommodate thermal expansion of the mid-section of the strut and the required structural properties. It can also be configured to build a negative step in the heat exchanger. Likewise, the front / rear gap 45 can be predetermined and selected to be smaller than gap 36 or 44 to control the leakage flow. It should be appreciated that the arrangement described herein allows for maximum flexibility in design.

[0109] If the gap 36 is larger, then using a smaller gap 45 will slow the air flow. Lower flow velocity will result in lower losses as the flow passes through the ribs shown in the various embodiments. Thus, controlling the gap 45 to a smaller value will reduce the need for a fine and smooth surface on the strut side and outside of the heat exchanger.

[0110] Figures 15A to 15D Further alternative arrangements of the heat exchanger and strut are shown. In particular as shown, in various arrangements, multiple or single heat exchangers can be used; for example, one pass can not contain a heat exchanger. Alternatively or in addition, one sector or flow channel 23 can contain two or more smaller heat exchangers. These heat exchangers can be arranged side-by-side or in series along the flow direction.

[0111] A smooth or uniform surface or "fairing" F can then be applied to cover the ribs to avoid any adverse aerodynamic effects. The fairing can be welded or coupled to the ribs in any suitable manner. As shown, various combinations of ribs and fairings can be used. Again, it should be appreciated that the strut concept described herein is extremely versatile in design.

[0112] Providing panels on the sides can create a cavity, thereby protecting service lines that extend through the strut from any debris or sand that could otherwise erode sensitive service lines such as oil lines or electrical wires.

[0113] Figure 16A And Figure 16B Yet another arrangement is shown that integrates a conventional heat exchanger in one pass with an improved integration according to the concept described herein (see Figure 16A ). Figure 16B Another hybrid arrangement is shown with a ribbed surface on one side of the strut and a conventional heat exchanger on the opposite side with a recess.

[0114] Advantageously, if different heat exchanger types are used, and for one heat exchanger, the air flow can be tailored for that particular heat exchanger. For example, air can be allowed to leak around one heat exchanger, but be forced to flow through an adjacent heat exchanger without leaking.

[0115] Figures 17A to 17D Further arrangements of struts, heat exchangers and optional fairings according to the invention described herein are shown. These arrangements will be described below. Each configuration provides design flexibility to accommodate different heat exchangers, different desired air flows, and additionally different structural properties of the struts.

[0116] Figure 17A An arrangement is shown in which there are multiple ribs extending from a recessed portion of the strut, a pair of side fairings for attachment to the strut, and a pair of opposing heat exchangers.

[0117] Figure 17B An arrangement is shown in which a pair of recessed heat exchangers are combined with side fairings. As shown, the fairings can be coupled to the ribs or spaced apart from the ribs.

[0118] Figure 17C An arrangement is shown in which there are asymmetric ribs, a pair of fairings, and asymmetrically arranged heat exchangers. Here, air flow is allowed to leak on one side, but not on the other.

[0119] Finally, Figure 17D Ribs are shown with associated fairings and a pair of heat exchangers, each having air flow leakage between the heat exchanger housing and the associated fairing.

[0120] Thus, the struts as described herein allow for meeting the structural and thermodynamic requirements of the heat exchangers by optimizing the profile of each side of the strut. According to the invention described herein, specific heat transfer can be achieved in adjacent air flow channels of the housing.

Claims

1. A casing structure for a gas turbine engine, the casing structure comprising: an inner annulus and an opposing outer annulus, the inner annulus and the outer annulus defining a radial space therebetween; a plurality of struts spaced about the structure and extending radially between the inner annulus and the outer annulus, each strut intersecting the inner annulus and the outer annulus, the inner annulus, the outer annulus and the plurality of struts collectively defining a plurality of annular, circumferentially extending air flow channels, wherein each air flow channel is defined circumferentially between two opposing strut side surfaces and radially between an inner surface of the outer annulus and an outer surface of the inner annulus, and wherein one or both of the inner surface of the outer annulus and / or the outer surface of the inner annulus comprises a recess arranged in use to receive a portion of a body of a heat exchanger.

2. The housing structure of claim 1, wherein, One or both side surfaces of a strut comprises a recess arranged in use to receive a portion of a body of a heat exchanger.

3. The housing structure of claim 2, wherein, Each strut comprises an upstream edge proximate an inlet of a respective air flow channel, and wherein the upstream edge of a respective strut comprises an aerodynamic profile extending in the direction of air flow, the aerodynamic profile intersecting an upstream end of a respective recess in the strut.

4. The housing structure of claim 1, wherein, The inner annulus and the outer annulus each comprise an upstream leading edge proximate an inlet of a respective air flow channel, and wherein each upstream leading edge comprises an aerodynamic profile extending in the direction of air flow, the aerodynamic profile intersecting an upstream end of a recess in the respective inner or outer surface of the annulus.

5. The housing structure of claim 3 or 4, wherein, A cross-sectional area of an inlet of an air flow channel measured at an intersection of an aerodynamic profile and a recess is less than a cross-sectional area of the air flow channel measured at a location downstream of the intersection of the aerodynamic profile and the recess.

6. The housing structure of any preceding claim, wherein, One or both side surfaces of a strut comprises one or more ribs extending from the surface towards the air flow channel.

7. The housing structure of claim 6, wherein, The plurality of ribs are positioned in the direction of air flow at discrete locations along the strut.

8. The housing structure of claim 6 or 7, wherein, One or more ribs extend in a generally radial direction relative to the surface of the annulus along the surface of the strut.

9. The housing structure of any one of claims 6-8, wherein, The ribs are arranged in use to contact an outer surface of a heat exchanger housing.

10. The housing structure of any one of claims 6 to 9, wherein, A fairing or cap is connected to an end of the ribs to define a surface on one or both sides of a strut.

11. The housing structure of any one of claims 6 to 10, wherein, Ribs on one side of a strut side surface are asymmetrical to ribs on the opposite side surface of a respective strut.

12. The housing structure of claim 4, wherein, The inner annulus and the outer annulus each comprise a downstream trailing edge proximate an outlet of a respective air flow channel, and wherein each downstream trailing edge comprises an aerodynamic profile extending in the direction of air flow.

13. The housing structure of claim 12, wherein, A portion of the trailing edge proximate the outlet can be selectively removed to allow positioning of a heat exchanger into an air flow channel.

14. A strut panel for a casing structure of a gas turbine engine, the strut panel being arranged in use to extend between an inner ring and an opposed outer ring of the casing, wherein, The strut plate includes an upstream leading edge, a downstream trailing edge, and a middle portion extending between the upstream leading edge and the downstream trailing edge, wherein the middle portion is in the form of a recess on one or both sides of the strut plate such that a cross-section of the strut plate at the middle portion is narrower than a cross-section at the upstream leading edge.

15. The stay according to claim 14, wherein, The leading edge includes an aerodynamic profile extending in the direction of air flow that intersects an upstream end of the respective recess in the side of the strut plate.

16. The stay according to claim 14 or 15, wherein One or both side surfaces of the strut plate include one or more ribs extending generally perpendicularly from the surface.

17. The stay according to claim 16, wherein, The plurality of ribs are positioned at discrete locations along the strut plate in the direction of air flow.

18. The stay according to claim 16 or 17, wherein, One or more ribs extend along the surface of the strut plate in a direction that is generally parallel to the leading edge.

19. The strut plate of any one of claims 16 to 18, further comprising a fairing or cover connected to an end of the rib to define a surface on one or both sides of the strut plate.

20. The splint of any one of claims 16 to 19, wherein, The ribs on one side of a strut plate side surface are asymmetrical to the ribs on the opposite side surface of the respective strut plate in terms of location or extension from the strut plate surface.

21. A strut panel for a casing structure of a gas turbine engine, the strut panel being arranged in use to extend between an inner ring and an opposed outer ring of the casing, wherein, The strut plate includes an upstream leading edge, a downstream trailing edge, and a middle portion extending between the upstream leading edge and the downstream trailing edge, wherein a cross-section of the middle portion is narrower than a cross-section of the upstream leading edge at a point where the leading edge intersects the recess, and is asymmetrical with respect to a centerline extending from a centerline of the leading edge and a centerline of the trailing edge.

22. A gas turbine engine comprising a casing structure according to any one of claims 1 to 13.

23. A gas turbine engine comprising one or more strut plates according to any one of claims 14 to 21.

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