GB2628854A

GB2628854A - HEX strut arrangement

Info

Publication number: GB2628854A
Application number: GB2305202.0A
Authority: GB
Inventors: Rikemanson Dennis; Samuelsson Rickard
Original assignee: GKN Aerospace Sweden AB
Current assignee: GKN Aerospace Sweden AB
Priority date: 2023-04-06
Filing date: 2023-04-06
Publication date: 2024-10-09
Also published as: GB202305202D0; WO2024208524A1

Abstract

A casing structure (20,fig.7) for a gas turbine engine comprising inner (28,fig.7) and outer (27,fig.7) annuli defining a radial space therebetween. The structure has a plurality of struts (22a,22b etc.,fig.3) extending radially between the inner and outer annuli and defining a plurality of annular circumferentially extending airflow passages (23,fig.3). The airflow passages are defined circumferentially between two opposing strut side surfaces and radially between the inner surfer of the outer annulus and outer surface of the inner annulus. The inner surface of the outer annulus and/or outer surface of the inner annulus comprises a recess (33,fig.8b) arranged in use to receive a portion of a heat exchanger (29,fig.7). One or both side surfaces of the struts may comprise a recess 42 arranged in use to receive a portion of the heat exchanger. A strut for a casing structure and a gas turbine engine are also claimed.

Description

HEX Strut Arrangement

Background

The present invention is concerned with a heat exchanger arrangement for use in a gas turbine engine and in particular, but not exclusively, a heat exchanger arrangement for use in an outer flow path of a gas turbine engine.

Heat exchangers are used for a variety of heating and cooling purposes in gas turbine engines and in particular gas turbine engines use in aircraft. For example, heat exchangers are used to provide cooling to oil for numerous bearings operating within the engine. An oil circuit can also be used to lubricate and cool a reduction gearbox to reduce the fan speed compared to the turbine driving the fan in some arrangements. Heat exchangers are also used for cabin temperature control amongst other things.

Typically, the high speed cool air flow in the outer flow path of an engine can be conveniently used as a source of cold air. Conventional heat exchanger integration involves locating the heat exchanger matrix within the airflow at a suitable location. Heat exchange can take place using a suitable heat exchange fluid passing through the heat exchanger conduits as cold air passed through the air duct, through the heat exchanger and to an outlet of the engine.

Conventional arrangements of heat exchangers provide a convenient way to achieve heating or cooling for an engine. However, the heat exchangers used in outer flow paths may be positioned around the struts which connect the inner and outer annuli of the structure (the inner and outer annuli defining the outer air flow channel). 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 as well as containing services (such as oil piping and fuel piping) from the outer annulus to the inner annulus of the engine.

The variety and complexity of strut requirements for a given engine place significant limitations on the way conventional heat exchangers can be integrated into a gas turbine engine. Furthermore, the relative thermal expansion of the structure comprising the struts and annuli versus the thermal expansion of the heat exchangers themselves causes further complications in integrating a heat exchanger into the outer air channel in an efficient manner.

These problems result in a number of design compromises that need to be made with conventional arrangements when seeking to achieve efficient operation of heat exchangers in such a structure.

However, the inventors have devised an alternative configuration of heat exchanger integration which allows for the optimisation of struts whilst simultaneously optimising the performance of a heat exchanger for a given engine configuration.

Summary of the Invention

Aspects of inventions described herein are set out in the accompanying claims.

Viewed from a first aspect there is provided a casing structure for a gas turbine engine, the casing structure comprising an inner annulus and an opposing outer annulus defining a radial space therebetween, a plurality of struts spaced around the structure and extending radially between the inner annulus and outer annulus, each strut intersecting with the inner and outer annulus, the inner and outer annulus and plurality of struts defining a plurality of annular circumferentially extending airflow passages, wherein each airflow passage is defined circumferentially between two opposing strut side surfaces and radially between the inner surface of the outer annulus and the 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 the body of a heat exchanger.

The effect of the recess or in-step is to provide a larger cross-sectional area than the inlet area to the airflow passage such than when a heat exchanger is located into the passageway it can be larger in cross-section than the airflow inlet. This, in turn, causes (a) a significant portion of the incoming airflow to the passage to flow directly into the heat exchanger and (b) prevents airflow leakage around the sides of the heat exchanger casing.

One or both side surfaces of a strut may also advantageously comprise a recess arranged in use to receive a portion of the body of a heat exchanger.

According to such as arrangement each strut within the casing structure has side surfaces extending in an airflow direction along the casing which are recessed or 'stepped-in' with respect to the leading edge geometry. The effect of the recess or in-step is to provide a larger cross-sectional area than the inlet area to the airflow passage such than when a heat exchanger is located into the passageway it can be larger in cross-section than the airflow inlet. This, in turn, causes (a) a significant portion of the incoming airflow to the passage to flow directly into the heat exchanger and (b) prevents airflow leakage around the sides of the heat exchanger casing.

Thermodynamically this enhances the operation and efficiency of the heat exchanger.

Advantageously, this represents one embodiment of a casing using a strut described herein.

As set out above, one or both side surfaces of a strut may comprise a recess arranged in use to receive a portion of the body of a heat exchanger. This means that side surfaces may be adapted to allow for some airflow leakage whilst others do not.

It has been established by the inventors that by providing a strut with a modified profile downstream of the leading edge a range of design options are provided in terms of heat exchange location, airflow and performance. Furthermore, the structural performance of the strut may additionally be optimised in combination with the desired airflow characteristics.

As well as the side surfaces of the struts, as discussed above, one or both of the inner surface of the outer annulus and/or the outer surface of the inner annulus may also comprise a recess arranged in use to receive a portion of the body of a heat exchanger. Thus, the perimeter of the heat exchanger may be optionally provided with controlled airflow leakage on one or more faces.

Each strut may comprise an upstream edge proximate to an inlet of a respective airflow passage. The upstream edge of the respective strut may advantageously comprise an aerodynamic profile such as a smooth curved profile to split incoming air and direct it into the passage. The aerodynamic profile may extend in an airflow direction and intersect with an upstream end of a 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 the point at which the heat exchanger may be positioned i.e. close to or in abutment with the inside of the recess and aerodynamic profile.

The inner annulus and outer annulus may also each comprise an upstream leading edge proximate to an inlet of a respective airflow passage. Each upstream leading edge may comprise a similar aerodynamic profile extending in an airflow direction and also intersecting with an upstream end of a recess in the respective inner or outer surface of an annulus. In effect the recesses in the struts and the inner and outer annulus create a cross-section to receive the heat exchanger behind i.e. downstream of the inlet to the passage.

Advantageously, the cross-sectional area of the inlet to an airflow passage measured at the intersection of an aerodynamic profile and recess may be less than the cross-sectional area of the airflow passage measured at a position downstream of the intersection of an aerodynamic profile and recess. In effect, the inlet is smaller in cross-section than the space in which the main body of the heat exchanger is located which allows the airflow to be optionally direction substantially into the heat exchanger rather than round the sides of the casing. The term optionally is used because the recess may be selected to position the heat exchanger in specific locations (as described further below).

Advantageously one or both side surfaces of the strut may comprise one or more ribs or protrusions extending from the surface towards the airflow passage i.e. extending from the side surfaces in a generally perpendicular direction. The ribs may serve multiple purposes. For example the ribs may be selected to provide increase stiffness and strength to the strut. They may also be selected to provide support for the heat exchanger located in the passage. Still further they may acts as guide surfaces against which the heat exchanger casing may slide when the heat exchanger is position into the passage.

A plurality of ribs may be located at discrete predetermined positions along the strut in an airflow direction. This provides the advantages described above at various positions along the length and depth of the strut.

One or more ribs may extend along the surface of the strut in a generally radial direction with respect to the annulus surfaces. Thus ribs may be arranged in a radial direction between the inner and out annulus and/or in an airflow direction along the strut surface. The distribution, side and depth of the ribs can be selected according to the design requirements for the passage and the strut as part of the entire casing.

The ribs may be arranged in used to contact an outer surface of a heat exchanger casing to provide the support discussion above.

A fairing or cover may optionally be connected to the ends of the ribs i.e. the passage/heat exchanger facing ends of the ribs, so as to define a surface on one or both sides of a strut. Such an outer surface may be smooth by virtue of the fairing surface whilst the surface of the strut may not then require machining to any degree of surface finish i.e. aerodynamic surface finish.

Advantageously the ribs on one side of a strut side surface may be asymmetrical with respect to ribs on an opposing side surface of a respective strut. Thus, each side of the strut may have different ribs and associated properties. Similarly the central thickness of the strut between the leading and trailing edge defined by the recess may have different thicknesses on each side of the strut. Thus, significant design flexibility is provided by such as strut arrangement.

The inner annulus and outer annulus may also each comprise a downstream trailing edge proximate to an outlet of a respective airflow passage, wherein each downstream trailing edge may comprise an aerodynamic profile extending in an airflow direction. Thus, the trailing edge may be adapted so as to minimise any detrimental aerodynamic effects as air leaves the passage.

A portion of the trailing edge proximate to the outlet may also advantageously be selectively removable to allow a heat exchanger to be positioned into an airflow passage. In effect by providing a trailing edge of the struts and optionally all or a portion of the trailing edges of the inner and outer annulus a heat exchanger can be conveniently located into the recess formed in the passage from the rear of the casing structure. This allows for maintenance and repair whilst maintaining the integrity of the leading edge aerodynamic profile.

Viewed from another aspect there is provided a strut for a casing structure for a gas turbine engine, the strut being arranged in use to extend between an inner annulus and an opposing outer annulus of the casing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion extending 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 the upstream leading edge.

As described above the leading edge may comprise an aerodynamic profile extending in an airflow direction and intersecting with an upstream end of a respective recess in the side of the strut. Each strut may, as described above, have recesses on each side.

Again the strut may additionally be provided with a fairing or cover connected to the ends of the ribs to define a surface on one or both sides of a strut. Furthermore, ribs on one side of a strut side surface may be asymmetrical with ribs on an opposing side surface of a respective strut in respect of position or extension from the strut surface.

Viewed from yet another aspect there is provided a strut for a casing structure for a gas turbine engine, the strut being arranged in use to extend between an inner annulus and an opposing outer annulus of the casing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion extending therebetween, wherein the intermediate portion is narrower in cross-section than the upstream leading edge at a point where the leading edge and recess intersect and is asymmetrical with respect to a centre line extending from the centre line of the leading edge and the centre line of the trailing edge.

Thus, a novel strut is provided for a casing structure and an associated gas turbine engine in which a strut may be adapted for structural properties as well as being able to receive and support a heat exchanged against an inner surface. The option to asymmetrically adapt each strut cross-sections allows for various design requirements to be met as described herein.

Viewed from another aspect there is provided a casing structure for a gas turbine engine, the casing structure comprising an inner annulus and an opposing outer annulus defining a radial space therebetween, a plurality of struts spaced around the structure and extending radially between the inner annulus and outer annulus, each strut intersecting with the inner and outer annulus, the inner and outer annulus and plurality of struts defining a plurality of annular circumferentially extending airflow passages, wherein each airflow passage is defined circumferentially between two opposing strut side surfaces and radially between the inner surface of the outer annulus and the outer surface of the inner annulus, and wherein one or both side surfaces of a strut comprises a recess arranged in use to receive a portion of the body of a heat exchanger.

Viewed from still further aspects there is provided a gas turbine engine comprising a casing structure as described herein and a gas turbine engine comprising one or more strut as described herein.

Figures Further aspects, features, and advantages of the inventions described herein will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which: Figure 1 shows a schematic of the fundamental components of a gas turbine engine; Figure 2 shows an alternative engine configuration illustrating the location at which an invention described herein may be used; Figure 3 is a schematic illustrating the radial and circumferential passages into which heat exchangers may be positioned; Figures 4A and 4B shows a schematic of a conventional strut illustrating the internal cavity; Figures 5A and 5B show an end view from a fore or upstream position of a cylindrical body 20; Figure 6 shows a schematic of an existing strut and heat exchanger arrangement as described with reference to figures 5A and 5B; Figure 7 shows an end view from a fore or upstream position of a generally cylindrical body according to an invention described herein; Figures 8A and 8B are cross-section views through A-A' in figure 7; Figure 9 is a cross-section corresponding to figure 8B illustrating the airflow into the heat exchanger; Figure 10 illustrates one arrangement of heat exchanger; Figure 11A and 11B illustrate a comparison of a conventional strut and one embodiment of a strut the present invention provides; Figure 12 illustrates schematically two adjacent heat exchanger and associated struts; Figures 13A to 13D illustrate a conventional heat exchanger arrangement between adjacent struts (figure 13A) and three difference configurations of recess, heat exchanger and rib; Figure 14 illustrates the upstream or fore step or recess according to an invention described 30 herein; Figures 15A to 15D show further alternative arrangements of heat exchanger and strut; Figures 16A and 16B shows yet another arrangement which combines a conventional heat exchanger integration in one passageway with a modified integration as per the concepts described herein, Figure 16 B is modified on both sides but having rib a structure extending towards only one of the heat exchangers; and Figure 17A to 17D show still further arrangements which are possible according to a strut arrangement described herein.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. 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". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

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.

In the present application, the words "configured to..." are used to mean that an element of an apparatus has a configuration able to carry out the defined operation. In this context, a "configuration" means an arrangement or manner of interconnection of hardware or software.

"Configured to" does not imply that the apparatus element needs to be changed in any way in order to provide the defined operation.

Detailed Description

Figure 1 shows a cross-section of a gas turbine engine 1 incorporating an outer airflow 5 passageway which may accommodate a heat exchanger according to a strut arrangements described herein.

The skilled person will understand the principal components of a gas turbine engine and their operation. In summary, the engine 1 comprises an air intake 2 which permits air to flow into the engine to the fan 3 located at the upstream end of the engine. All of the components are housed within the engine nacelle 4.

The engine shown is a turbo fan engine and comprises a bypass channel 19 downstream of the fan and a central engine core which contains the compressors, combustors and turbines. The core of the engine is formed of a first low pressure compressor 5 and a second high pressure compressor 6. This multi-stage compressor arrangement takes air from ambient pressure and temperature to high temperature and pressure. Compressed air is then communicated to the combustion chamber 7 where fuel is injected and combustion occurs. It will be appreciated that this arrangement is only one example of how the engine could be arranged. In other examples, the engine may have a geared fan or open fan, for example.

The combustion gases are expelled from the rear of the combustion chamber 7 and impinge first on a high pressure turbine 10 and then on a second low pressure turbine 12 before leaving the rear of the engine through the core nozzle 11. Thrust from the engine is created by two gas flows: a first from the fan nozzle 8 (receiving thrust from the fan) and secondly from the exhaust gases from the core nozzle 11.

It will be appreciated that the gas flow in the engine 1 progress from left to right across Figure 1 (fore to aft). Accordingly, a rightwards direction in Figure 1 can be referred as a downstream direction of the engine 1 with a leftwards direction in Figure 1 corresponding to an upstream direction of the engine.

A transition duct 14 is arranged to receive air from the low pressure compressor 5 and communicate it radially inwards to be supplied to the high pressure compressor 6.

As shown, both compressors are coaxial with the central (rotational) axis of the turbine. The low pressure compressor 5 has a larger outer radius (measured from the central axis of the compressor) than the outer radius of the high pressure compressor 6.

This requires that the duct or channel communicating air between the two compressors is a generally S shaped to communicate the compressed air towards the central axis of the turbine and into the high pressure turbine 6.

It is desirable to be able to release or bleed some air within the transition duct out of the engine.

This may be used to control the volume of air being passed to the high pressure compressor and prevent a compressor stall, for example.

As shown in Figure 1, a bleed duct 15 is provided which provides an openable passage allowing air to selectively flow from the transition duct 14 into a cavity 16 (which may in some implantations be referred to as a plenum or fire zone compartment). The cavity 16 may be arranged downstream of the low pressure compressor 5. Specifically the cavity 16 may be arranged radially outside of the core and the bleed passage is usually located downstream of the low pressure compressor 5 and receives air that is released from the main flow path. In effect the cavity 16 acts as a collecting chamber or reservoir for air released from the main flow path.

The cavity is enclosed on a downstream side by a firewall 17 (which may also be referred to as a downstream wall). The firewall 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 the bleed air to escape from the cavity 16 into the bypass channel 19, a duct 18 is provided through the firewall 17.The duct 18 may provide a passage through the firewall 17 at a radially extreme point of the firewall 17 such that the duct 18 may be considered to provide the passage above or beyond the firewall.

As shown in Figure 1, the bleed duct 15, the cavity 16 and the duct 18 provide a flow path to communicate bleed air between the core flow path and the bypass channel 19. In other implementations, the bleed air may instead or additionally be communicated from the core flow path to another flow path within the gas turbine engine 1 such as intermediate flow path of a low pressure core flow path situated radially further from the axis of the engine 1 than the core flow path.

The bypass channel 19 conveniently provides a location with high speed, low temperature airflow which can conveniently be used in combination with a heat exchanger to control engine component temperatures.

As shown a radial strut S is located within the bypass channel and is located upstream (in an airflow direction) of the point at which the hot gases discussed above are released into the bypass channel. As described herein it is between adjacent struts S that a heat exchanger can be integrated according to an invention described herein using an unconventional strut design.

Figure 2 shows an alternative engine configuration illustrating the location at which an invention described herein may be used. The engine illustrated is a open-fan engine but similarly incorporates an outer airflow channel 73. Box L illustrates a possible location of heat exchanger and strut arrangement according to the inventions described herein.

Figure 3 is a schematic illustrating the radial and circumferential passages into which heat exchangers may be positioned. As shown in figure 3, the generally cylindrical body 20 comprises an outer annulus 21 and an inner annular 22 i.e. two generally cylindrical and coaxial rings. A plurality of radially extending struts 22a, 22b, 22c etc. are space around the body 20 and extend between the inner and outer annulus. The cylindrical body may also be formed of sectors each welded together. The inner and outer cylindrical coaxial rings may consist of separate sectors and segments fabricated together alternatively assembled together using fastener, or a combination thereof The two opposing side surfaces of adjacent strut together with the inner surface of the outer annulus and the outer surface of the inner annulus define a plurality of airflow passageways 23 which extend through the body 20 and allow air to flow from an upstream US to a DS as indicated by the arrows.

Each of the passageways 23 is in the general form of a truncated segment of a circle.

According to an invention described herein each of the passageways may be conveniently provided with a heat exchanger 25 which is located within a passageway and shown by the arrow in figure 3. Each or a subset of the passageways may be provided with such a heat exchanger which itself has a generally complementary shape to the passageway profile.

The struts will be described with reference to figures 4A and 4B.

Figure 4A shows a schematic of a conventional strut. A single strut is shown but it will be recognised that the struts are located at positions around the circumference of the cylindrical body 20. The struts serve a number of purposes including structural support for the engine core. They also provide a path, through a hollow cavity within the strut for services to pass into the core of the engine. Figure 4B is a plan view of the strut in figure 4A illustrating by dotted line an internal cavity in a conventional strut. Each strut is designed to accommodate an internal cavity for services or weight control.

Figures 5A and 5B show an end view from a fore or upstream position of a cylindrical body 20. In figure 5A and 5B a conventional arrangement is shown in which heat exchangers 25 are located in each of the passageways described above with reference to figure 3. As illustrated schematically, the heat exchangers are each located so as to provide a clearance around the periphery of the heat exchanger between (a) the heat exchanger outer casing of body and the inner surfaces of the circumferentially opposing strut inner surfaces and (b) the radially opposing inner annulus and outer annulus surfaces.

The circumferential clearances are illustrated schematically in Figure 5B. It will be appreciated the clearances are exaggerated for each of understanding.

As shown in figure 5B a corner of a passageway and located heat exchanger is shown. As also shown a radial clearance Ar is defined and a circumferential clearance Ac is defined. These clearances may be on each of the 4 faces of the heat exchanger or on a sub-set of the faces depending on the particular configuration.

The clearances Ar and Ac are caused by a number of factors including manufacturing limitations creating 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 to the heat exchanger which may fluctuate in expansion as it is activated and deactivated. This results in potential complex loading scenarios depending on the relative thermal expansion of the components. This is controlled by means of a suitable clearance.

Figure 6 shows a schematic of an existing strut and heat exchanger arrangement as described above with reference to figures 5A and 5B. The view is looking generally radially inwards at a pair of adjacent heat exchangers and associated struts including an intermediate strut positioned between the adjacent heat exchangers. The clearance described above is illustrated. The clearances advantageously allow for the location of the heat exchangers and also allow for the differential thermal characteristics to be accommodated. However, the clearance does allow for cooling air to pass around the heat exchanger body as illustrated by arrows 26A to 26D. In effect the leakage of cooling air around the heat exchangers reduces the potential performance of the heat exchanger in terms of heat transfer. The greater the leakage, the greater the reduction in efficiency.

As described above the inventors has established an alternative integration or implementation of heat exchanger and strut. These will be described with reference to figures 7 to 16B.

Specifically, as described herein there are benefits in placing heat exchangers between struts to maximize the air going through the heat exchangers. A novel strut design described herein improves the amount of airflow going through the heat exchanger while reducing the need of hard to produce internal cavities within struts. Services, either within the strut perimeter or aft of the strut may lead to different strut widths which influences the ultimate stiffness and weight of a given strut. The arrangements described herein also allows for machining of adjacent surfaces which generates better positioning of aerodynamic control surfaces which can significantly improve overall engine performance.

Open ended rib structure allow for design insensitive to wall thickness variations and enable machining of area to reduce overall tolerance stack-up by 75-80%. Inlet and exit areas are often machined to improve flow conditions. However, extensive machining in the airflow channel is mainly avoided due to accessibility issues and geometry complexity. One sided machining (opposite side as cast) will also create unfavourable thickness variations over large panel surfaces.

Figure 7 shows an end view from a fore or upstream position of a cylindrical body 20 according to an invention described herein. As shown the body 20 comprises an outer annulus surface 27 and an inner annulus surface 28. Heat exchangers 29 are positioned in each of the passageways 30 located circumferentially around the body 20.

Importantly, as shown in a comparison of figure 7 and figure 5B any clearances or spaces around the perimeter of the heat exchanger casing cannot be seen from the fore of the engine due to the recess or step. In effect cooling air flowing towards the body 20 shown in figure 7 almost exclusively passed into the heat exchangers 29.

Figures 8A and 8B are cross-section views through A-A' in figure 7 for a conventional heat exchanger integration (figure 8A) and a heat exchanger integration according to an invention described herein (figure 8B).

Figure 8A shows a conventional arrangement. As will be appreciated from the teaching herein the clearance around the heat exchanger body allow for thermal expansion but come at a noticeable cost to efficiency owing to the gap losses as illustrated by arrows 31.

Figure 8B shows the arrangement according to the alternative integration of the invention described herein. As shown in Figure 8B the inner and outer annulus surfaces 32A, 32B each incorporate a step or recess 33 downstream of the inlet 34 to the passageway.

Advantageously, the axial gap 35 is relatively small and generally smaller than the downstream gap 36. The clearance 36 is convenient for mounting the heat exchanger and also for maintenance/removal/replacement of the heat exchanger. The gap 35 may be any suitable size according to the heat exchanger and strut combination.

Figure 9 is a cross-section corresponding to figure 8B illustrating the airflow into the heat exchanger 37. As shown the leakage around the heat exchanger is minimised by the circumferential and radial extension of the heat exchanger into the recesses or steps provided in the struts and inner and out annular surfaces. It will be recognised that all 4 surrounding surfaces may comprise the step and recess or a subset may be selected as discussed below.

In effect, when viewed in an airflow direction from a fore (front) viewpoint the cross-sectional area of the heat exchanger is larger than the cross-sectional area defined by the passageway inlet. Thus, maximum airflow is direction into the heat exchanger.

Figure 10 illustrates one arrangement of heat exchanger. As shown the heat exchange profile is curved to correspond to the shape of the passageway.

Figure 11A and 11B illustrate a comparison of a conventional strut and one embodiment of a strut the present invention provides. Figure 11A shows a conventional strut between two adjacent heat exchangers. As shown by arrows 38 the air leakage occurs through the thermal expansion clearances as well as manufacturing tolerances and clearances needed for installation and removal procedures.

Figure 11B illustrates the adapted strut side surfaces or walls which incorporate the leading for upstream step 39. As described above the step 39 allows the heat exchanger to be recessed into the strut to cause the airflow 40 to be directed into the heat exchanger matrix 41.

The recess 42 into the side walls of the strut allow the heat exchanger to extend circumferentially (and radially in the case of a recess in the inner and/or outer annulus). Not only does it allow for a larger heat exchanger but it also means that because the airflow can be reduced significantly around the heat exchanger casing (as shown in figure 11A by arrows 38) the outer side surfaces of the struts may not need an aerodynamic or smooth surface.

This provides a number of advantages including a lack of machining to provide a smooth surface.

Importantly it also allows the cross-section of profile of the strut to be fundamentally changed. As illustrated in figure 11B, because the surface no longer has any aero-requirements ribs can be applied to increase rigidity and stiffness and to locate the heat exchanger. The ribs 43 are shown in figure 11B. The ribs can be configured to optimise rigidity, bending strength and weight. It will be recognised that complex rib geometries may be provided on the outer surfaces of the struts.

It will be recognised that the rib concept may equally (either alternatively or additionally) be applied to the inner surface of the outer annulus and/or the outer surface of the inner annulus.

Figure 11B as illustrates a possible additional feature of a selectively removable trailing or aft edge TE to the strut. Providing for a removable trailing edge or surface allows the heat exchanger body or casing to be conveniently located into the passageway between adjacent struts from the aft of the body 20.

Figure 12 illustrates schematically two adjacent heat exchanger and associated struts.

Figures 13A to 13D illustrate a conventional heat exchanger arrangement between adjacent struts (figure 13A) and three difference configurations of recess, heat exchanger and rib.

Specifically: Figure 13A illustrates a conventional heat exchanger integration with normal clearance incorporated between the strut and heat exchanger; -Figure 13B illustrates a single strut and pair of heat exchangers with a large recess or step; Figure 13C illustrates a single strut and a pair of heat exchangers with a large rib and small heat exchanger recess. The ribbed side may maximise strut rigidity.

- Figure 13D illustrates an asymmetrical arrangement of heat exchanger with asymmetrical ribs.

All strut configurations with ribbed sides allow for minimal surface machining to control the strut width. This advantageously simplifies machining.

Different heat exchanger sectors may be designed differently as they may provide cooling to different engine functions. This may give a different need of a recess on each side of one strut.

The strut arrangement described herein allows a single strut to be configured to accommodate a different heat exchanger body or casing on each side of the strut.

Different heat exchangers may operate at different max temperatures and need different space for thermal growth. The strut described herein allows for this design option.

It will be appreciated from the examples shown in figures 13B to 13D that the arrangement described herein allows for great versatility in strut rigidity and heat exchanger location.

The examples shown in 13C and 13D also illustrate an optional concept of the exit part of a strut extending downstream of the heat exchanger with or without step. Figure 13D has no exit step facilitating exit air flow.

Figure 14 illustrates the upstream or fore step or recess according to an invention described herein. In order to accommodate thermal expansion of the heat exchanger and strut/casing the leakage according to the arrangement described herein may be controlled by controlling the size, clearance and depth of the step or recess at the up-stream end of the strut and heat exchanger.

As illustrated the tangential gap 44 (extending from the intersection of leading edge and recess and the strut recess) may be predetermined to accommodate thermal expansion and the desired structural properties of the intermediate portion of the strut. It may also be set to create a negative step into the heat exchanger. Similarly the fore/aft gap 45 may be predetermined and selected so as to be smaller than the gap 36 or 44 to control leakage flow.

It will be recognised that the arrangement described herein allows for maximum flexibility in design.

The use of a smaller gap 45 will cause the airflow to slow down if the gap 36 is larger. Lower flow velocities will generate lower losses when flowing pass the ribs shown in each embodiment. Hence controlling gap 45 to a small value will reduce the need of fine and smooth surfaces of the strut sides and exterior of the heat exchanger.

Figures 15A to 15D show further alternative arrangements of heat exchanger and strut.

Specially as shown in the varying arrangements multiple or single heat exchangers may be used; for example one passageway may not contain a heat exchanger. Alternatively, or additionally, one sector or passage 23 may contain two or more smaller heat exchangers. These may be positioned side by side or in series in the flow direction.

A smooth or uniform surface or 'fairing' F may then be applied to cover the ribs so as to avoid any detrimental aerodynamic effects. This may be welded or coupled to the ribs in any suitable manner. As shown, various combinations of ribs and fairings may be used. Again it will be recognised that the strut concept described herein provides for significant versatility in design.

Having panels on the sides may create cavities allowing for services going through the strut protected from any debris or sand that can cause erosion on sensitive services, like oil tubes or electrical wires.

Figures 16A and 16B shows yet another arrangement which combines a conventional heat exchanger integration in one passageway with a modified integration as per the concepts described herein (see figure 16A). Figure 16B shows a further hybrid arrangement with a ribbed surface on one side of the strut and a conventional heat exchanger on the opposing side with a recess.

Advantageously if different heat exchanger types are used and one heat exchanger the airflow can be adapted for the specific heat exchanger. For example air may be permitted to leak around one heat exchanger but be caused to flow through an adjacent heat exchanger with no leakage.

Figures 17A to 17D show still further arrangements of strut, heat exchanger and optional fairings according to the invention described herein. These are described below. Each configuration provides for design flexibility to accommodate different heat exchangers, different desired airflows and furthermore different structural properties of the strut.

Figure 17A illustrates an arrangement with multiple ribs extending from the recessed portion of the strut, a pair of side fairings for attachment to the struts and a pair of opposing heat exchangers.

Figure 17B illustrates an arrangement with a pair of recess heat exchangers in combination with side fairings. As shown the fairings may be coupled to the ribs or spaced therefrom.

Figure 17C illustrates an arrangement with asymmetrical ribs, a pair of fairings and asymmetrically positions heat exchangers. Here, airflow leakage is permitted on one side but not or limited to the other.

Finally, Figure 17D illustrates ribs with associated fairings and a pair of heat exchangers, each having airflow leakage between the heat exchange casing and an associated fairing.

Thus, a strut as described herein allows both structural requirements and thermodynamic requirements of a heat exchanger to be accommodated through optimising the profile of each side of a strut. Specific heat transfers can be achieved in adjacent airflow passages in a casing according to an invention described herein.

Claims

CLAIMS1. A casing structure for a gas turbine engine, the casing structure comprising an inner annulus and an opposing outer annulus defining a radial space therebetween, a plurality of struts spaced around the structure and extending radially between the inner annulus and outer annulus, each strut intersecting with the inner and outer annulus, the inner and outer annulus and plurality of struts defining a plurality of annular circumferentially extending airflow passages, wherein each airflow passage is defined circumferentially between two opposing strut side surfaces and radially between the inner surface of the outer annulus and the 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 the body of a heat exchanger.
2. A casing structure as claimed in claim 1, wherein one or both side surfaces of a strut comprises a recess arranged in use to receive a portion of the body of a heat exchanger.
3. A casing structure as claimed in claim 2, wherein each strut comprises an upstream edge proximate to an inlet of a respective airflow passage, and wherein the upstream edge of a respective strut comprises an aerodynamic profile extending in an airflow direction and intersecting with an upstream end of a respective recess in the strut.
4. A casing structure as claimed in claim 1, wherein the inner annulus and outer annulus each comprise an upstream leading edge proximate to an inlet of a respective airflow passage, and wherein each upstream leading edge comprises an aerodynamic profile extending in an airflow direction and intersecting with an upstream end of a recess in the respective inner or outer surface of an annulus.
5. A casing structure as claimed 3 or 4, wherein the cross-sectional area of the inlet to an airflow passage measured at the intersection of an aerodynamic profile and recess is less than the cross-sectional area of the airflow passage measured at a position downstream of the intersection of an aerodynamic profile and recess.
6. A casing structure as claimed in any preceding claim wherein one or both side surfaces of a strut comprises one or more ribs extending from the surface towards the airflow passage.
7. A casing structure as claimed in claim 6, wherein a plurality of ribs are located at discrete positions along the strut in an airflow direction.
8. A casing structure as claimed in claim 6 or 7 wherein one or more ribs extend along the surface of the strut in a generally radial direction with respect to the annulus surfaces.
9. A casing structure as claimed in any of claims 6 to 8 wherein the ribs are arrange in used to contact an outer surface of a heat exchanger casing.
10. A casing structure as claimed in of claims 6 to 9 wherein a fairing or cover is connected to the ends of the ribs to define a surface on one or both sides of a strut.
11. A casing structure as claimed in any of claims 6 to 10, wherein ribs on one side of a strut side surface are asymmetrical with ribs on an opposing side surface of a respective strut.
12. A casing structure as claimed in claim 4, wherein the inner annulus and outer annulus each comprise a downstream trailing edge proximate to an outlet of a respective airflow passage, and wherein each downstream trailing edge comprises an aerodynamic profile extending in an airflow direction.
13. A casing structure as claimed in claim 12, wherein a portion of the trailing edge proximate to the outlet is selectively removable to allow a heat exchanger to be positioned into an airflow passage.
14. A strut for a casing structure for a gas turbine engine, the strut being arranged in use to extend between an inner annulus and an opposing outer annulus of the casing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion extending 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 the upstream leading edge.
15. A strut as claimed in claim 14, wherein the leading edge comprise an aerodynamic profile extending in an airflow direction and intersecting with an upstream end of a respective recess in the side of the strut.
16. A strut as claimed in claim 14 or 15, wherein one or both side surfaces of a strut comprise one or more ribs extending generally perpendicularly from the surface.
17. A strut as claimed in claim 16, wherein a plurality of ribs are located at discrete positions along the strut in an airflow direction.
18. A strut as claimed in claim 16 or 17 wherein one or more ribs extend along the surface of the strut in direction generally parallel to the leading edge.
19. A strut as claimed in any of claims 16 to 18 further comprising a fairing or cover connected to the ends of the ribs to define a surface on one or both sides of a strut.
20. A strut as claimed in any of claims 16 to 19, wherein ribs on one side of a strut side surface are asymmetrical with ribs on an opposing side surface of a respective strut in respect of position or extension from the strut surface.
21. A strut for a casing structure for a gas turbine engine, the strut being arranged in use to extend between an inner annulus and an opposing outer annulus of the casing, wherein the strut comprises an upstream leading edge, a downstream trailing edge and an intermediate portion extending therebetween, wherein the intermediate portion is narrower in cross-section than the upstream leading edge at a point where the leading edge and recess intersect and is asymmetrical with respect to a centre line extending from the centre line of the leading edge and the centre line of the trailing edge.
22. A gas turbine engine comprising a casing structure as claimed in any of claims 1 to 13.
23. A gas turbine engine comprising one or more strut as claimed in any of claims 14 to 21.