Patent Publication Number: US-2022213809-A1

Title: Heatshield for a gas turbine engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2020/064027 filed 20 May 2020, and claims the benefit thereof. The International Application claims the benefit of United Kingdom Application No. GB 1907545.6 filed 29 May 2019. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a heatshield that may be used in a gas turbine engine and in particular a stiffening and flow-control feature to improve longevity of the heatshield. 
     BACKGROUND OF INVENTION 
     A heatshield can be found in several locations in a gas turbine engine and in particular the heatshield can be located radially outwardly of an annular array of turbine blades. The heatshield is usually a circumferential segment of an array of heatshields which are held in position by a carrier structure. The heatshield forms part of a gas-path which channels combustion gases through the turbine and drives turbine rotor blades in a conventional manner. These heatshields have a hot side, which is exposed to the hot working gases of the turbine, and a cold side facing radially outwardly, and which is often cooled with cooling air. It is important that there is a minimal gap between the tip of the blade and the heatshield to minimise over tip leakage and therefore minimise efficiency losses. 
     Conventionally, long ribs are provided on the cold side to stiffen the heatshield. The long ribs are integral or unitary with the cold side and form cooling channels. An impingement plate is brazed on the cold side and covers the long ribs. Cooling air is distributed along the cooling channels. 
     However, these heatshields incur high thermal gradients between their hot side and their cold side. Such thermal gradients create loading in the heatshield that causes material fatigue and distortion of the heatshields in operation. Distortion of the heatshield may lead to rubbing of the heatshield surface against rotating blade causing damage of both parts and subsequent turbine performance degradation. Stiffening features are necessary on the heatshield&#39;s cold side to resolve service life and distortion problems. 
     At the same time, the heatshield requires even distribution of the cooling air across the inlets of the heatshield cooling holes. Special design features are usually needed to achieve that, because cooling air supply from the carrier is typically very localized. Such cooling localisation can also incur localised thermal gradients. 
     Thus, it remains an objective to provide an improved heatshield which reduces distortion, reduces temperature gradients, reduces absolute temperatures and minimises the use of cooling air. 
     SUMMARY OF INVENTION 
     To address the problems of known coating systems there is provided a heatshield for a gas turbine engine, the heatshield comprising a main body having a leading edge, a trailing edge, lateral edges, a first surface and a second surface, the first surface being exposed to a hot working gas in use passing through the gas turbine engine, a leading hook and a trailing hook each extending between the lateral edges, the leading hook and the trailing hook extending from the second surface, characterised by a stiffening structure extending from the leading hook to the trailing hook and free from direct contact or attachment to the second surface. 
     The stiffening structure may be arranged in the general form of at least one X when looking towards the second surface. 
     The stiffening structure may comprise four arms. Two arms may attach to the leading hook. Two arms may attach to the trailing hook. The fours arms may meet at an intersection. 
     The stiffening structure may comprise an extended portion. The extended portion may extend between any one or more of the pairs of arms, arm  104 A and arm  104 B, arm  104 B and arm  104 C, arm  104 C and arm  104 D and arm  104 A and arm  104 D. In use, the extended portion may block the jet of coolant from impinging on second surface and/or at least one inlet defined in the second surface. 
     The heatshield may comprise a centre-line and perpendicular to the centre-line a line. An angle α is defined from an arm  104 C to the line and an angle β is defined from the arm  104 C to another arm  104 D, both arms  104 C,  104 D attached to the same leading or trailing hook. The ratio of angles may be angle α/angle β≥2. 
     The stiffening structure may comprise one or more of the cross-sectional profiles: an I-beam, a T-beam, a box-beam or a rectangle. 
     The stiffening structure may be a beam arrangement. The beam arrangement comprising at least one beam, the at least one beam having at least one web and at least one flange. 
     The extended portion may be formed by an extension of the flange, advantageously the radially outer flange. 
     The stiffening structure may be a lattice structure. 
     The lattice structure may be an array of X-shaped elements, each X-shaped element having the arms. 
     The extended portion may not be connected to either of the leading hook or the trailing hook. 
     A gas turbine engine may comprise the heatshield as described above and a carrier. The carrier may be positioned radially outwardly of the heatshield and comprise corresponding engagement features to engage the leading hook and the trailing hook and at least one aperture for directing a coolant therethrough and towards the heatshield, the at least one aperture having a centre-line. The centre-line may intersect the stiffening structure such that the coolant at least partly impinges on the stiffening structure. 
     The centre-line may intersect the stiffening structure such that the coolant at least partly impinges on the extended portion. 
     The heatshield may be one of an annular array of heatshields and the carrier may be annular. The carrier may comprise an annular array of apertures. The centre-line of each aperture may be radially aligned with one of the heatshields and in particular the centre-line of each aperture may be radially aligned with one of the stiffening structures such that in use coolant impinges on the heatshield and in particular impinges on the stiffening structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The abovementioned attributes and other features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein 
         FIG. 1  shows part of a turbine engine in a sectional view and in which the present heatshield is incorporated, 
         FIG. 2  is a perspective view of the present heatshield looking radially inwardly and circumferentially with respect to the rotational axis of the turbine engine, a first embodiment of a stiffening structure can be seen on the radially outer side of the heatshield, 
         FIG. 3  is a section A-A of the present heatshield and a carrier for holding the heatshield, 
         FIG. 4  is a view looking radially inwardly at an alternative embodiment of the heatshield and showing a second alternative stiffening structure, 
         FIG. 5  is a view looking radially inwardly at an alternative embodiment of the heatshield and showing a third alternative stiffening structure, 
         FIG. 6  is a first embodiment of a cross-section B-B through an arm of the stiffening structure of the present heatshield, 
         FIG. 7  is a second embodiment of the cross-section B-B through an arm of the stiffening structure of the present heatshield, 
         FIG. 8  is a third embodiment of the cross-section B-B through an arm of the stiffening structure of the present heatshield, 
         FIG. 9  is a view looking radially inwardly at an alternative embodiment of the heatshield and showing a fourth alternative stiffening structure, and 
         FIG. 10  is a cross-section C-C through the fourth alternative of the heatshield in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows an example of a gas turbine engine  10  in a sectional view. The gas turbine engine  10  comprises, in flow series, an inlet  12 , a compressor section  14 , a combustor section  16  and a turbine section  18  which are generally arranged in flow series and generally about and along the direction of a longitudinal or rotational axis  20  in an axial turbine. The gas turbine engine  10  further comprises a shaft  22  which is rotatable about the rotational axis  20  and which extends longitudinally through the gas turbine engine  10 . The shaft  22  drivingly connects the turbine section  18  and the compressor section  14 . 
     In operation of the gas turbine engine  10 , air  24 , which is taken in through the air inlet  12  is compressed by the compressor section  14  and delivered to the combustion section or burner section  16 . The burner section  16  comprises a burner plenum  26 , one or more combustion chambers  28  and at least one burner  30  fixed to each combustion chamber  28 . The combustion chambers  28  and the burners  30  are located inside the burner plenum  26 . The compressed air passing through the compressor  14  enters a diffuser  32  and is discharged from the diffuser  32  into the burner plenum  26  from where a portion of the air enters the burner  30  and is mixed with a gaseous and/or liquid fuel. The air/fuel mixture is then burned and the combustion gas  34  or working gas from the combustion is channelled through the combustion chamber  28  to the turbine section  18  via a transition duct  17 . 
     This exemplary gas turbine engine  10  has a cannular combustor section arrangement  16 , which is constituted by an annular array of combustor cans  19  each having the burner  30  and the combustion chamber  28 , the transition duct  17  has a generally circular inlet that interfaces with the combustion chamber  28  and an outlet in the form of an annular segment. An annular array of transition duct outlets form an annulus for channelling the combustion gases to the turbine  18 . In other examples, the combustor section  16  may be an annular combustor as known in the art. 
     The turbine section  18  comprises a number of blade carrying discs  36  attached to the shaft  22 . In the present example, two discs  36  each carry an annular array of turbine blades  38 . However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes  40 , which are fixed to a stator  42  of the gas turbine engine  10 , are disposed between the stages of annular arrays of turbine blades  38 . Between the exit of the combustion chamber  28  and the leading turbine blades  38  inlet guiding vanes  40  are provided and turn the flow of working gas onto the turbine blades  38 . 
     The combustion gas from the combustion chamber  28  enters the turbine section  18  and drives the turbine blades  38  which in turn rotate the shaft  22 . The guiding vanes  40  serve to optimise the angle of the combustion or working gas on the turbine blades  38 . 
     The stator  42  of the turbine section  18  further comprises a carrier  58  and an annular array of heatshields  60  mounted to the carrier  58  and partly defining a working gas path through the turbine section. The heatshields  60  are mounted radially outwardly of the rotor blades  38 . In other gas turbine engines, the heatshields  60  may be mounted between annular arrays of rotor blades  38  and/or may be mounted on the radially inner casing  56 . 
     The present invention is described with reference to the above exemplary turbine engine having a single shaft or spool connecting a single, multi-stage compressor and a single, one or more stage turbine. However, it should be appreciated that the present invention is equally applicable to two or three shaft engines and which can be used for industrial, aero or marine applications. 
     The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow through the engine unless otherwise stated. The terms forward and rearward refer to the general flow of gas through the engine. The terms axial, radial and circumferential are made with reference to the rotational axis  20  of the engine. 
     The term ‘heatshield’ is used to denote not only a heatshield  60  as described herein, refers to a circumferential segment or a blade outer air seal (BOAS) or a shroud of a turbine system  18  of the gas turbine engine  10 . 
     The present heatshield  60  will now be described with reference to  FIGS. 2 to 10 . Features of any one or more embodiment(s) may be combined with other embodiments as will be apparent to the skilled reader. 
     Referring to  FIGS. 2 to 3 , the heatshield  60  is a circumferential segment of an annular array of circumferential segments  60  that form part of the gas washed outer surface of the gas path through the turbine section  18 . The heatshield  60  is located radially outwardly of rotating blades  38  and where located axially adjacent the rotating blades, forms a tip gap therebetween. 
     The heatshield  60  has a main body  61 , a leading edge  62 , a trailing edge  64  and, when viewed looking axially downstream, to the left and to the right lateral edges  66 ,  67  respectively. When installed in a gas turbine engine immediately and circumferentially adjacent heatshields  60  may abut or be in close proximity to one another such that one left lateral edge  66  is facing one right lateral edge  67  and a gap may exist therebetween. The gap is sealed by a seal strip that is located in corresponding grooves in each lateral edge or surface of immediately adjacent heatshields as known in the art. The heatshield  60  has a first surface or gas washed surface  70 , which is also a radially inner surface and that partly defines the radially outer gas washed surface of the gas path in the turbine section  18 . The gas washed surface  70  may also be referred to as the hot side, that being subject to the hot working gases flowing through the gas path. The heatshield  60  has a second surface or cold side surface  72  which is a radially outer surface relative to the hot gas flow and is supplied with coolant usually in the form of compressor air, but other sources of coolant can be used. 
     The heatshield  60  is mounted to the carrier  58  by a front hook or hanger  74  and a rear hook or hanger  76 . The front hook  74  and the rear hook  76  engage with corresponding features  75  and  77  respectively of the carrier  58 . Other or additional securing means for securing the heatshield to the carrier  58  or other supporting structure may be provided as known in the art. 
     The heatshield  60  has a centre-line  21  which when viewed radially inwardly towards the rotational axis  20  of the gas turbine  10  is parallel to the rotational axis  20 . The heatshield  60  is generally symmetrical about its centre-line  21 . The heatshield  60  is generally arcuate when viewed along centre-line  21  and its curvature is that of part of the circumferential surface of the array of heatshields  60  that forms the gas washed surface of the turbine section  18 . 
     The main body  61  has an array of cooling channels  78  for conveying a coolant flow  80 , which is supplied to the cold side  72  of the heatshield  60  via the carrier  58 . The array of cooling channels  78  comprises a leading array  82  of cooling channels and a trailing array  84  of cooling channels. Each of the leading array  82  of cooling channels and trailing array  84  of cooling channels comprises parallel cooling channels  86  which each extend in a direction generally perpendicular to the respective leading edge  62  and trailing edge  64 . Other arrangements of cooling schemes and concepts may be used in conjunction with the presently described heatshield  60 . 
     Each cooling channel  86  of leading array of cooling channels  82  has an outlet  88  in the leading edge  62  and each cooling channel  86  of the trailing array of cooling channels  84  has an outlet  90  in the trailing edge  64  of the main body  61 . Each cooling channel  86  has an inlet  92  formed in the second surface  72 . Nonetheless, other forms, arrangements and positioning of inlet(s) can be used for the cooling channels such as those fed from a gallery or common feed. 
     In use, pressurised coolant  80 , usually air bled from the compressor, is supplied via the carrier  58  to the cold side  72  of the heatshield  60 . The coolant  80  enters the cooling channels  86  through the inlets  92 , passes along the cooling channels  86  and is exhausted through the outlets  88 ,  90  at the leading, trailing and the lateral edges (not shown) respectively. Exhausting the coolant  80  at the edges of the heatshield  60  helps to prevent hot gas ingestion to the gaps surrounding the heatshield  60 . Exhausting the coolant  80  at the edges of the heatshield also helps to prevent hotspots at and near to the edges of the heatshield  60 . Further, any temperature gradient is minimised across the entire main body  61  of the heatshield  60 . 
     Even though the cooling scheme attempts to minimise temperature gradients and absolute temperatures of the heatshield  60 , the heatshield  60  can distort due to thermal loads and cause the blade tips to rub and/or increase gap sizes around the heatshield into which hot gases can escape the gas path. Conventionally, heatshields are stiffened by means of long ribs attached to, integrally or monolithically formed on the cold side surface  72  however, this arrangement has limited effect. 
     For the present heatshield  60 , there is a stiffening structure  100  provided that extends from the leading hook  74  to the trailing hook  76  and which is free from contact or attachment to the second surface  72 . In this way the stiffening structure does not deflect or distort when the main body  61  and hence second surface  72  is deformed. The stiffening structure  100  does not attach to the second surface or the main body  61  directly. The stiffening structure  100  is spaced apart from the second surface  72  and forms a gap  102  therebetween. 
     In an embodiment shown in  FIGS. 2 and 3 , the stiffening structure  100  is arranged in the general form of an X (or an X-shaped element) when looking towards the second surface  72  from a radially outward position. The dotted lines further indicate a generally regular X-shaped arrangement of the stiffening structure  100 . The stiffening structure  100  has four arms generally referenced  104 , with leading arms  104 A,  104 B located toward the leading edge  62  of the heatshield  60  and attached to the leading hook  74  and trailing arms  104 C,  104 D located towards the trailing edge  64  of the heatshield  60  and attached to the trailing hook  76 . 
       FIG. 4  is a view looking radially inwardly at an alternative embodiment of the heatshield  60  and showing a second alternative stiffening structure  100 . In this embodiment, there are two beam arrangements  101  (or X-shaped elements) forming the stiffening structure  100  and which are similar to that described with reference to  FIG. 3  except that the optional extended portion  130  that shields the inlets  92  from the direct impingement of coolant  80  spans between the arm  104 A of one beam arrangement  101 A and the arm  104 B of beam arrangement  100 B. 
       FIG. 5  is a view looking radially inwardly at an alternative embodiment of the heatshield  60  and showing a third alternative stiffening structure  100 . In this example, the stiffening structure  100  is similar to that shown and described with reference to  FIGS. 3 and 4  except that there are two additional ‘central’ arms  104 E and  104 F. Arm  104 E attaches to the forward hook  74  and arm  104 F attaches to the rearward hook  76 . Advantageously and as shown the two arms  104 E and  104 F are arranged in line with the centre line  21  of the heatshield  60 . Indeed, the remaining arms  104 A and  104 B are symmetrical about centre line  21  as to arms  104 C and  104 D are also symmetrical about centre line  21 . 
     All three embodiments of the stiffening structure  100  may be designed to accommodate and combat deformation of the heatshield  60 . The key feature of the stiffening structure  100  is that it is not in direct contact with the second surface  72  and therefore not only does it remain relatively cool having no direct thermally conductive route (only via the hooks  74 ,  76 ), but it is also not subject to thermal distortion of the main body  61  and second surface  72  directly. 
       FIG. 6  is a section B-B, shown in  FIG. 2 , through an arm  104  of the stiffening structure  100 . In section the arm  104  has the general shape of an I-beam  142  having two flanges  106 ,  108  and a web  110 . The sizing of the I-beam  142  and sectional dimensions of the flanges  106 ,  108  and web  110  is well known in the art for accommodating loads to provide a required stiffness and limit deflections of the heatshield  60 . 
       FIG. 7  is an alternative embodiment of section B-B, shown in  FIG. 2 , through the arm  104  of the stiffening structure  100 . In section the arm  104  has the general shape of a box-beam  144  having, structurally-speaking, two flanges  116 ,  118  and two web  120 ,  122 . The sizing of the box-beam  144  and sectional dimensions of the flanges  106 ,  108  and web  110  is well known in the art for accommodating loads to provide a required stiffness and limit deflections of the heatshield  60 . 
       FIG. 8  is an alternative embodiment of section B-B, shown in  FIG. 2 , through the arm  104  of the stiffening structure  100 . In section the arm  104  has the general shape of a T-beam  146  having, structurally-speaking, one flange  147  and one web  148 . The sizing of the T-beam  146  and sectional dimensions of the flange  147  and web  148  is well known in the art for accommodating loads to provide a required stiffness and limit deflections of the heatshield  60 . 
     Referring back to  FIG. 2 , a line  124  is defined in the circumferential direction and which is perpendicular to the centre line  21  of the heatshield  60 . An angle a is defined between a centre-line  126  of an arm  104  and the line  124 ; and an angle β is defined between two arms  104 . Where the heatshield  60  is manufactured by a 3D-printing process and based, from one lateral edge to the other lateral edge, the ratio of angles should be angle β/angle α≥2. One reason for this ratio is to ensure that there is a minimum angle of any feature that is 45° without being supported during the manufacturing process. Angle of features less than 45° requires supporting to give the necessary build quality and in this case an undesirable further machining process would be required to remove the supporting feature. 
     The centre-lines  126  of the arms  104  intersect at a point  128 . Point  128  is mid-way between the two hooks  74 ,  76 , but can be located within the middle third of the distance between the two hooks  74 ,  76 . Point  128  is located on the centre line  21  of the heatshield  60 . Indeed, the four arms  104  meet at an intersection  129  and within which is the point  128 . 
     Referring to  FIG. 3 , the carrier  58  is generally annular and carries the annular array of heatshields  60  that surrounds the rotor stage as previously mentioned. The carrier  58  comprises an annular gallery or chamber  79  which is supplied with coolant  80 . The carrier  58  has an aperture  81 , one of an array of apertures  81  arranged about the carrier  58 ; each aperture  81  feeds a portion of the coolant  80  to one heatshield  60  of the array of heatshields  60  and each aperture  81  is arranged centrally with respect to the centre-line  21  of a respective heatshield  60 . 
     The coolant  80  forms a jet of coolant that would otherwise impinge on the second surface  72  of the main body  61 . This impinging jet of coolant  80  would cause a cold region and increase the temperature gradient across the main body  61 . In addition, the inlets  92  are located radially inwardly of the aperture  81  or in other embodiments the inlets  92  may be located in-line with the jet of coolant  80  passing through the aperture  81 . This jet of coolant  80  would otherwise impinge on the second surface  72  and some of the inlets  92  and cause an increase in the dynamic pressure of coolant entering these affected inlets  92 . Therefore, some of the inlets  92  and their respective cooling channels  86  would otherwise have a greater mass flow of coolant therethrough compared to those inlets  92  and cooling channels  86  that are not impinged upon. This would otherwise cause irregular cooling of the main body  61  and potentially increase the temperature gradient thereacross and limit the longevity of the heatshield  60  or potentially cause the heatshield to distort with the previously mentioned disadvantages. 
     Therefore, to prevent the jet of coolant  80  that passes through the aperture  81  impinging on the second surface  72  and/or the inlets  92 , the radially outer web  104  of the stiffening structure  100  has an extended portion  130  that extends between leading arms  104 A,  104 B. The extended portion  130  is located radially inwardly of the aperture  81  and is sized to cover at least the inlets  92  from the jet of coolant  80 . In other words, there is no clear line-of sight between any part of the aperture  81  and the relevant inlets  92  in a direction of the jet of coolant  80 . ‘Relevant’ inlets  92  meaning those inlets  92  that would otherwise be impinged upon were it not for the provision of the extended portion  130 .  FIG. 2  shows a dashed circular line  81 P which is a projection of the aperture  81  onto the stiffening structure  100 . In this example, the projection is along a centre-line  132  of the aperture  81  which is aligned with a radial line with respect to the centre-line  20  of the gas turbine engine  10  (see  FIG. 3 ); however, the projection can be in the direction of the coolant  80  passing through the aperture  81 . The aperture  81  may be arranged at an angle away from a radial line and therefore the centre-line  132  and direction of the jet of coolant  80  would also be angled away from the radial line. This angle may be in the circumferential direction and/or the axial direction. 
     It should be understood, for the reasons given above, extended portion  130  may extend between any one or more of the pairs of arms: arm  104 A and arm  104 B, arm  104 B and arm  104 C, arm  104 C and arm  104 D and arm  104 A and arm  104 D in order to block the jet of coolant  80  from impinging on the inlets  92  and/or second surface  72 . 
     The arms  104  are provided with a radiused intersection or blend radius  134 ,  136 ,  138  where they join each other and/or the hooks  74 ,  76 . Blend radius  134  is formed on an obtuse angle with the hooks  74 ,  76 ; blend radius  136  is formed on an acute angle with the hooks  74 ,  76 ; and the blend radius  138  is formed between any one or more of the pairs of arms: arm  104 A and arm  104 B, arm  104 B and arm  104 C, arm  104 C and arm  104 D and arm  104 A and arm  104 D. Specifically, in the  FIG. 4  embodiment it is the webs  104 ,  108  that comprise the blend radius  134 ,  136 ,  138 . In the  FIG. 5  embodiment, the box-beam&#39;s two flanges  116 ,  118  and two webs  120 ,  122  will all comprise blend radii  134 ,  136 ,  138 . The purpose of the radius is to reduce stress concentration at joints. 
     The stiffening structure  100  defines an aperture  140  between the front hook  74 , the arms  104 A and  104 B and the extended portion  130  of the radially outer web  104  (or  120 ). The aperture  140  is shaped by virtue of the blend radii  136  and the extended portion  130  being of minimum size to deflect the jet of coolant  80 . The aperture  140  allows coolant through to the second surface  72  so that the pressure of the coolant over the second surface  72  is as even as possible. Put another way, the overall area of the stiffening structure  100 , when looking radially inwardly, is minimised and in consideration of a function of the structural stiffness/distortion requirements of the heatshield  60 , deflection of the jet of coolant  80  via the extended portion  130  and the desire to evenly distribute the coolant  80 . 
     By virtue of the jet of coolant  80  impinging on the stiffening structure  100  rather than the second surface  72  and/or inlets  92  an even distribution of pressure is present above the second surface  72  and therefore there is an even distribution of coolant into the inlets  92  and their respective cooling channels  86 . Thus, in this way the temperature gradient is minimised across the main body  61  and stress/strains associated with temperature are minimised. 
     Referring now to  FIG. 9  and  FIG. 10 ;  FIG. 9  is a view looking radially inwardly at an alternative embodiment of the heatshield  60  and showing a fourth alternative stiffening structure  100  and  FIG. 10  is a cross-section C-C through the fourth alternative. In this embodiment the stiffening structure  100  is a lattice arrangement  150 . The lattice arrangement  150  is a plate  152  having a thickness  154  which in this embodiment is approximately a constant thickness. Essentially, the lattice arrangement  150  is the plate  152  having an array of apertures  155  having a number of differently sized apertures  156 ,  158 ,  160  to suit the structural stiffening requirements or more accurately the remaining structure provides the required stiffness and structural performance to the heatshield. The lattice arrangement  150  shown in  FIG. 9  is one example and is particularly suited to this heatshield  60 ; however, there are a multitude of different arrangements that are possible for this and other heatshield applications and stress-strain calculations are well known the skilled person in designing any particular arrangement to primarily stiffen the hooks  74 ,  76  whilst keeping the stiffening structure  100  free from direct contact with the second surface  72 . 
     The lattice arrangement  150  has a frame  162  defining the periphery of the stiffening structure  100  and alternatively the lattice arrangement  100  may not have a frame  162 . 
     The lattice arrangement  150  may have a regular arrangement of diamond-shaped apertures  156  with triangular-shaped apertures  158  against the edges or frame of the lattice arrangement. In this case the remaining material may form straight ‘strips’ of material in a conventional criss-cross pattern or array of X-shaped elements having arms. This array of X-shaped arms (these arms are analogous to the fours arms  104 A,  104 B,  104 C,  104 D meeting at an intersection  129 ), except that some arms of one X-shaped element are continuous with some of the arms of the next X-shaped element either in the direction from the leading hoot  74  to trailing hook  76  and/or from one lateral edge  66  to the other lateral edge  67 . In section, these arms are generally rectangular  151  in shape as shown in  FIG. 10 . 
     The lattice arrangement  150  is connected to the leading hook  74  and trailing hook  76  along their circumferential lengths and performs the same structural benefits as previously described. The apertures  156 ,  158 ,  160  may be located and/or sized to also provide a shield, i.e. extended portion  130  shown in dashed lines, for the impingement of the cooling flow  80  as previously described. 
     The shape of the stiffening structure  100  is such that good quality manufacturing is possible, particularly considering an advantageous method is  3 D-printing or additive-manufacturing. In this way, the stiffening structure  100  is formed integrally or is monolithic with the hooks  74 ,  76  and indeed the entire heatshield is monolithic, being built from a layer-by-layer continuous process. Thus ‘printability’ is a significant consideration in the design of the heatshield and the stiffening structure in particular. Nonetheless, one key feature is that the stiffening structure is detached from the main body  61  and/or second surface  72  of the additively-manufactured heatshield. 
     The present heatshield  60  is advantageous because it has increased stiffness to prevent distortion and is better sealed around its edges  62 ,  64 ,  66 ,  67  than previous designs; the addition of the stiffening structure  100  spanning directly between hooks  74  and  76  means that it is surrounded by coolant and does not directly pick up heat from the main body  61  and is therefore inherently stiffer than previous designs; the extended portion  130  improves even distribution of coolant into the inlets and cooling channels in the main body to provide a more evenly cooled main body  61  with associated benefits mentioned hereinbefore. 
     All these factors contribute to an increased life and/or temperature capability of the heatshield  60 . Temperature capability meaning that the hot working gases can be at a higher temperature than before because of the improved heat management of the present heatshield compared to previous and conventional designs. 
     The presently described heatshield  60  is particularly suited to manufacture by an additive manufacturing process such as direct laser deposition, laser sintering, select laser melting or other 3D printing techniques. Specifically, the direction of formation of the heatshield  60  is, layer-by-layer, from one lateral edge towards the other and specifically in the direction of the line  124  in  FIG. 2 . 
     All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.