Heatshield for a gas turbine engine

A heatshield for a gas turbine engine includes 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. The main body having an array of cooling channels for conveying a coolant flow, where each cooling channel of the array of cooling channels having a surface. At least one cooling channel of the array of cooling channels includes at least one flow disturbing feature extending from the surface and into the cooling channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2020/064026 filed 20 May 2020, and claims the benefit thereof. The International Application claims the benefit of United Kingdom Application No. GB 1907544.9 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 advantageously a heatshield having a cooling arrangement to improve temperature capability and longevity.

BACKGROUND OF INVENTION

A heatshield can be found in several locations in a gas turbine engine, for example, 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 that 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, 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.

US2017/0138211 A1 discloses a ring segment of a gas turbine engine and having a main body with upstanding forward and rearward hooks. The hooks attach the ring segment to a carrier structure that is radially outwardly located with respect to the rotational axis of the gas turbine engine. The ring segment comprises a cooling arrangement including an impingement plate and an array of cooling channels. The impingement plate is located radially outwardly of the main body and directs jets of air against a cold side of the main body. The array of cooling channels is formed within the main body and is supplied with the used impingement cooling air via an opening on the cold side and a gallery channel formed centrally and extending axially within the main body. The cooling channels extend circumferentially away from the gallery channel. Thus, the cooling channels extend in their longest dimension in a direction parallel to the rotation of rotor blades.

US 2013/108419 (A1) discloses a ring segment for a gas turbine engine which includes a panel or main body and a cooling system. The cooling system is provided within the panel and includes a cooling fluid supply trench having an open top portion and extending radially inwardly from a central recessed portion of the panel. The cooling system further includes a plurality of cooling fluid passages extending from the cooling fluid supply trench to a leading edge and/or a trailing edge of the panel. The cooling fluid passages receive cooling fluid from the cooling fluid supply trench, wherein the cooling fluid provides convective cooling to the panel as it passes through the cooling fluid passages.

EP3167164B1 discloses a turbomachine component comprising at least one part built in parts from a curved or planar panel, particularly a sheet metal, the part comprising a plurality of cooling channels via which a cooling fluid, particularly air, is guidable, wherein at least one of the plurality of cooling channels has a continuously tapered section.

However, these heatshields or ring segments can incur high thermal gradients not only between their hot side and their cold side but also between leading edge and trailing edge as well as between lateral edges. 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's hot surface against rotating blades causing damage of both parts and subsequent turbine performance degradation.

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 known problems 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. The main body having an array of cooling channels for conveying a coolant flow, where each cooling channel of the array of cooling channels having a surface. At least one cooling channel of the array of cooling channels comprising at least one flow disturbing feature extending from the surface and into the cooling channel.

The at least one flow disturbing feature may be a pin. The pin extending from one part of the surface to another part of the surface may be such that its sides are free of contact with the surface of the cooling channel.

The or another at least one flow disturbing feature may be a part-pin. The part-pin may be attached along its length to another side of the cooling channel.

The or another at least one flow disturbing feature may comprise a second part-pin. The part-pin and the second part pin may be arranged opposite one another across the channel.

The at least one cooling channel may comprise an array of pin(s) and part-pin(s) and/or second/part pin(s) along at least a part of a length of the cooling channel. Advantageously the pin(s) and part-pin(s) and/or second/part pin(s) may be arranged in an alternating pattern with one another.

The flow disturbing feature may have a cross-sectional shape of a polygon. Advantageously the cross-sectional shape may be a quadrilateral or a parallelogram. The cross-sectional shape may have a diagonal line and the diagonal line being in-line with the longitudinal extent of the cooling channel.

The flow disturbing feature may have a plurality of side faces, wherein the angle between any two neighbouring side faces is ≥45°.

The cooling channel or cooling channels may comprise a restrictor. The restrictor forming the smallest cross-sectional area within the cooling channel.

The array of cooling channels may comprise a leading array of cooling channels and a trailing array of cooling channels. Each of the leading array of cooling channels and trailing array of cooling channels may comprise parallel, especially straight cooling channels which each extend in a direction generally perpendicular to the respective leading edge and trailing edge. The cooling channels of the trailing array of cooling channels may be longer than the cooling channels of leading array of cooling channels.

The main body has a dimension L that is perpendicular to the leading edge and the trailing edge and the cooling channels of the trailing array of cooling channels may extend 55-70% of L, advantageously 60% of L, and the cooling channels of the leading array of cooling channels may extend 30-45% of L, advantageously 40% of L.

Each cooling channel of the leading array of cooling channels may have an outlet in the leading edge of the main body. Each cooling channel of the trailing array of cooling channels may have an outlet in the trailing edge of the main body.

Each cooling channel of the leading array of cooling channels may have an inlet formed in the second surface. Each cooling channel of the trailing array of cooling channels may have an inlet formed in the second surface. Advantageously, each cooling channel may have an inlet formed in the second surface.

The cooling passage(s) located closest to the lateral edge(s) of the main body may have a plurality of outlets defined in the lateral edge such that in use coolant passes out of the cooling channel, through the cooling passage and is exhausted at the lateral edge through the outlet. Where each cooling channel has an inlet formed in the second surface, the inlet of the cooling passage(s) located closest to the lateral edge(s) of the main body being larger than the inlets of the other cooling channels.

The at least one cooling channel may have a cross-sectional shape that is polygonal, advantageously quadrilateral. Advantageously, all cooling channels have a cross-sectional shape that is polygonal, advantageously quadrilateral. Advantageously, all cooling channels have a cross-sectional shape that is rectangular, triangular or trapezoidal.

Further, to address the known problems there is also 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. The main body having an array of cooling channels for conveying a coolant flow. At least one cooling channel has a cross-sectional shape that is polygonal, advantageously quadrilateral. Advantageously, all the cooling channels have a cross-sectional shape that is polygonal, advantageously quadrilateral. Advantageously, all cooling channels have a cross-sectional shape that is rectangular, triangular or trapezoidal.

Yet further, to address the known problems 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. The main body having an array of cooling channels for conveying a coolant flow, where each cooling channel of the array of cooling channels having and a surface. The array of cooling channels comprising a leading array of cooling channels and a trailing array of cooling channels. Each of the leading array of cooling channels and trailing array of cooling channels comprising parallel, especially straight cooling channels which each extend in a direction generally perpendicular to the respective leading edge and trailing edge. The cooling channels of the trailing array of cooling channels being longer than the cooling channels of leading array of cooling channels.

The main body has a dimension L that is perpendicular to the leading edge and the trailing edge and the cooling channels of the trailing array of cooling channels may extend 55-70% of L, advantageously 60% of L, and the cooling channels of leading array of cooling channels may extend 30-45% of L, advantageously 40% of L.

DETAILED DESCRIPTION OF INVENTION

FIG.1shows an example of a gas turbine engine10in a sectional view. The gas turbine engine10comprises, in flow series, an inlet12, a compressor section14, a combustor section16and a turbine section18which are generally arranged in flow series and generally about and along the direction of a longitudinal or rotational axis20. The gas turbine engine10further comprises a shaft22which is rotatable about the rotational axis20and which extends longitudinally through the gas turbine engine10. The shaft22drivingly connects the turbine section18and the compressor section14.

In operation of the gas turbine engine10, air24, which is taken in through the air inlet12is compressed by the compressor section14and delivered to the combustion section or burner section16. The burner section16comprises a burner plenum26, one or more combustion chambers28and at least one burner30fixed to each combustion chamber28. The combustion chambers28and the burners30are located inside the burner plenum26. The compressed air passing through the compressor14enters a diffuser32and is discharged from the diffuser32into the burner plenum26from where a portion of the air enters the burner30and is mixed with a gaseous and/or liquid fuel. The air/fuel mixture is then burned and the combustion gas34or working gas from the combustion is channeled through the combustion chamber28to the turbine section18via a transition duct17.

This exemplary gas turbine engine10has a cannular combustor section arrangement16, which is constituted by an annular array of combustor cans19each having the burner30and the combustion chamber28. The transition duct17has a generally circular inlet that interfaces with the combustion chamber28and an outlet in the form of an annular segment. An annular array of transition duct outlets form an annulus for channeling the combustion gases to the turbine18. In other examples, the combustor section16may be an annular combustor as known in the art.

The turbine section18comprises a number of blade carrying discs36attached to the shaft22. In the present example, two discs36each carry an annular array of turbine blades38. However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes40, which are fixed to a stator42of the gas turbine engine10, are disposed between the stages of annular arrays of turbine blades38. Between the exit of the combustion chamber28and the leading turbine blades38inlet guiding vanes40are provided and turn the flow of working gas onto the turbine blades38.

The combustion gas from the combustion chamber28enters the turbine section18and drives the turbine blades38which in turn rotate the shaft22. The guiding vanes40serve to optimise the angle of the combustion or working gas on the turbine blades38.

The stator42of the turbine section18further comprises a carrier44and an annular array of heatshields60mounted to the carrier44and partly defining a working gas path through the turbine section. The heatshields60are mounted radially outwardly of the rotor blades38. In other gas turbine engines, the heatshields60may be mounted between annular arrays of rotor blades38and/or may be mounted on the radially inner casing.

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 axis20of the engine.

The term ‘heatshield’ is used to denote not only a heatshield60as described herein, but also refers to a circumferential segment or a blade outer air seal (BOAS) or a shroud of a turbine system18of the gas turbine engine10.

The present heatshield60will now be described with reference toFIGS.2to8.

Referring toFIGS.2to6, the heatshield60is a circumferential segment of an annular array of circumferential segments that form part of the gas washed outer surface of the gas path through the turbine section18. The heatshield60is located radially outwardly of rotating blades38and forms a tip gap therebetween.

The heatshield60has a main body61, a leading edge62, a trailing edge64and, when viewed looking axially downstream, to the left and to the right lateral edges66,67respectively. When installed in a gas turbine engine immediately and circumferentially adjacent heatshields60may abut or be in close proximity to one another such that one left lateral edge66is facing one right lateral edge67and a gap may exist therebetween. The heatshield60has a first surface or gas washed surface70, which is also a radially inner surface and that partly defines the radially outer gas washed surface of the gas path in the turbine section18. The gas washed surface70may also be referred to as the hot side, that being subject to the hot working gases flowing through the gas path. The heatshield60has a second surface or cold side or surface72which is a radially outer surface relative to the hot gas flow.

The heatshield60is mounted to the casing58by a front hook or hanger74and a rear hook or hanger76. The front hook74and the rear hook76engage with corresponding features on the carrier44. Other or additional securing means for securing the heatshield to the carrier44or other supporting structure may be provided as known in the art.

The heatshield60has a centre-line21which when viewed radially inwardly towards the rotational axis20of the gas turbine10is parallel to the rotational axis20. The heatshield60is generally symmetrical about its centre-line21. The heatshield60is generally arcuate when viewed along centre-line21and its curvature is that of part of the circumferential surface of the array of heatshields60that forms the gas washed surface of the turbine section18.

The main body61has an array of cooling channels78for conveying a coolant flow80, which is supplied to the cold side72of the heatshield60via the carrier44. The array of cooling channels78comprises a leading array of cooling channels82and a trailing array of cooling channels84. Each of the leading array of cooling channels82and trailing array of cooling channels84comprises parallel, straight cooling channels86which each extend in a direction generally perpendicular to the respective leading edge62and trailing edge64.

Each cooling channel86of leading array of cooling channels82has an outlet88in the leading edge62and each cooling channel86of the trailing array of cooling channels84has an outlet90in the trailing edge64of the main body61. Each cooling channel86has an inlet92,94formed in the second surface72. In this embodiment, there is no gallery feeding multiple cooling channels86. In addition, the cooling passages68located closest to the lateral edges66,67of the main body61each have a plurality of outlets96defined in the respective lateral edge66,67. As can be seen inFIG.3the outlets96are short lateral cooling passages that extend from the cooling channel68to the lateral edge of the heatshield. Although not shown, the outlets96are located radially inwardly of a seal strip that seals between immediately adjacent heatshields and is usually located in a groove in the lateral edge or surface. At least a part of the cooling passages68located closest to the lateral edges66,67is located radially inwardly of the seal strip.

One aspect of the heatshield60that is not symmetrical is that each of the plurality of outlets96defined in lateral edge66is off-set, in the axial direction or along the edges66,67, from the other plurality of outlets96defined in lateral edge67. For two immediately adjacent heatshields the lateral edge66of one heatshield opposes the lateral edge67of the other heatshield60. The outlets96in lateral edge66are formed such that the jets of coolant issuing therefrom impinge on the surface of lateral edge67and not on the outlets96of the lateral edge67. Similarly, the outlets96in lateral edge67are formed such that the jets of coolant impinge on the surface of lateral edge66and not on the outlets96of the lateral edge66. Thus, for any one heatshield60, the outlets and short lateral cooling passages that extend from the cooling channel68located closest to each of the lateral edges66,67are not quite symmetrical about the centre line21. This off-set arrangement of outlets96ensures very good sealing between adjacent heatshields and provides very good cooling of the lateral edges66,67.

In use, pressurised coolant80, usually air bled from the compressor, is supplied via the carrier44to the cold side72of the heatshield60. The coolant80enters the cooling passage68through the inlets92,94, passes along the cooling channels68and is exhausted through the outlets88,90,96at the leading, trailing and the lateral edges62,64,66,67respectively as coolant sub-flows80A,80B and80C respectively. Exhausting the coolant80at the edges of the heatshield helps to prevent hot working gases entering the gaps surrounding the heatshield60. Exhausting the coolant80at the edges of the heatshield60also helps to prevent hotspots at and near to the edges62,64,66,67of the heatshield60. Further, any temperature gradient is minimised across the entire main body61of the heatshield60.

The cooling passages68located closest to the lateral edges66,67of the main body61have larger inlets94than the inlets92of the other cooling channels68in order to have a greater coolant flow than the other cooling channels68and adequately feed the outlets96to the lateral edges66,67as well as their outlets88,90in the leading and trailing edges62,64respectively. In this exemplary embodiment, the cooling passages68located closest to the lateral edges66,67have the same cross-sectional shape and area as the other cooling channels68; however, it is possible for the cooling passages68located closest to the lateral edges66,67to have a greater cross-sectional area and/or shape to allow a greater amount of coolant to flow into their inlet and through the cooling channel so that their lateral outlets96and outlets88,90at the leading and trailing edges62,64are adequately supplied with coolant.

To further reduce the temperature gradient and absolute temperature of the main body61, the cooling channels68of the trailing array of cooling channels84are longer, in the axial direction20,21, than the cooling channels68of leading array of cooling channels82. The pressure and temperature of the working gas at the leading edge62is higher than at the trailing edge64and the lengths of the trailing array of cooling channels84and of the leading array of cooling channels82are such that adequate coolant is passed through the leading array of cooling channels82as well as the trailing array of cooling channels84. In other words the lengths of the trailing array of cooling channels84and leading array of cooling channels82are such that the pressure losses along the respective cooling channels are balanced against the pressure outside their outlets such that there is a positive pressure of coolant in the cooling channels to provide an adequate flow of coolant through each cooling channel for its cooling demand. The main body61has a dimension L that is perpendicular to the leading edge62(i.e. axial length) and the trailing edge64and the cooling channels68of the trailing array of cooling channels84extend 55-70% of L and in the embodiment shown 60% of L. The cooling channels68of leading array of cooling channels82extend 30-45% of L and in the embodiment shown 40% L. Note that these relative dimensions are considered from a central point or line93between the inlets92of trailing array of cooling channels84and the inlets92of the leading array of cooling channels82.

The cooling effectiveness of the cooling arrangement of the present heatshield is greatly enhanced by at least one, but advantageously all, cooling channels68of the array of cooling channels78comprising at least one flow disturbing feature100. The cooling channel(s) has a cross-sectional shape that is a quadrilateral, in this example rectangular, has a surface104over which the coolant flows. In this exemplary embodiment the surface104is formed of a radially inner surface108, radially outer surface106and lateral surfaces105,107. In this embodiment, there are a number of flow disturbing features100namely pins102and part-pins110and which generally extend from the surface104and into the cooling channel68.

The pins102extend from the surface108to the surface106such that its sides112are free of contact with the surface104of the cooling channel68. In other words, the pins102are only attached to the surface104at its ends114,116. The pin(s)102is located equidistant from the lateral surfaces105,107within the cooling channel68, although in other embodiments the pins102may be off-set and nearer one lateral surface105,107than the other lateral surface107,105. The pins102have a cross-sectional shape of a diamond, but other polygonal shapes are possible such as quadrilaterals or parallelograms. The pin has a diagonal line120, defined between two opposing edges that are defined by its sides112, which is in-line with the longitudinal axis118of the cooling channel68.

Another flow disturbing feature100is a part-pin110which has a similar cross-sectional shape as one half of the pin102when divided by a plane that is perpendicular to view ofFIG.4and defined by the diagonal line120. The part-pin is110is shown in dashed lines onFIG.5and is attached along its length to another side107of the cooling channel68such that there are two side surfaces and one edge extending from the surface104. The (first) part-pin110is also attached to the cooling channel68via its ends to surface106and surface108. As shown inFIG.4andFIG.5this flow disturbing feature100comprises a second part-pin110arranged on the opposite surface105to the first part-pin110and across the cooling channel68.

The total and minimum flow area of the cooling channel68at a cross-section through the pin102is approximately equal to the minimum flow area of the cooling channel68between the opposing part-pins110.

Referring toFIG.3, each cooling channel68comprising an array of flow disturbing features100has a number of pins102and opposing (first and second) part-pins110along at least a part of a length of the cooling channel68. The array of flow disturbing features100is formed by an alternating pattern of one pair of opposing (first and second) part-pins110and then one pin102or vice-versa.

It should be appreciated that other arrangements of the pair of opposing (first and second) part-pins110and pins102are possible and the first and second part-pins110do not need to be aligned across the cooling channel and instead may be off-set. Indeed, it is possible to have various cooling arrangements with no pins and only part-pins110or no part-pins110and only pins102. Where there are no part-pins, each pin102of an array of pins102may be positioned off-set from the centre-line118of the cooling channel68. Where there are no pins102, the part-pins110may be attached along their length to only one surface e.g. surface108, or more than one surface e.g. surfaces105,106,107,108and each consecutive part-pin110may be attached to any of the surfaces105,106,107,108. Further, the pins102are shown extending from surface108to surface106, but may extend between surface105to surface107. Similarly, the part-pins110are shown extending from surface108to surface106, but may extend between surface105to surface107.

In theFIG.4example of the present heatshield each cooling channel68further comprises a restrictor130. The restrictor130forms the smallest cross-sectional area within the cooling channel68and controls the quantity of coolant passing through the cooling channels68. The flow restrictor130is essentially the same cross-sectional shape and general configuration as an opposing pair of part-pins110except that the restrictor130is larger and as mentioned before forms a flow cross-sectional area of the cooling channel68that is smaller than the flow areas around the pin102and through the opposing pair of part-pins110. The restrictor130is positioned downstream of the pins102and part-pins110with respect to the coolant flowing along the cooling channel68from the inlet92,94to the outlet88. The restrictor130is located very close to the outlet88.

In other embodiments of the present heatshield60, and to balance heat transfer or the cooling effect across the heatshield60, not all cooling channels68have a restrictor130or the restrictor130may be sized differently; that is the flow area of the restrictor130may be tuned for one or a number of the cooling flow channels68. For example, the leading array of cooling channels82may have no restrictor130or a restrictor with a greater flow area than the trailing array of cooling channels84, thereby preferentially supplying coolant to the leading array of cooling channels82. In another example, either or both the leading array of cooling channels82and trailing array of cooling channels84may have a number of cooling channels nearest the lateral edges66,67with no restrictor130or a restrictor with a greater flow area than the cooling channels68nearer the centre-line21; thus, preferentially cooling the lateral edge regions of the heatshield60.

Conveniently, the heatshield60may be designed for all versions of a particular gas turbine and the restrictor130alone can be simply modified to tailor the amount of coolant through each of the cooling channels68dependent on the version of the engine. Different versions of the gas turbine, e.g. different power outputs, mean that the working gas temperature and/or pressure may be different so in a high output gas turbine the restrictor130is removed or its flow area increased in some or all the cooling channels. Furthermore, modifications of the restrictor130only may be easily made for and during engine development testing.

In use, the coolant80enters the cooling passages68through the inlets92,94, passes along the cooling channels68and is exhausted through the outlets88,90,96at the leading, trailing and the lateral edges62,64,66,67respectively as coolant sub-flows80A,80B and80C respectively. As the coolant80passes along the cooling passages68the flow disturbing feature(s)100creates disturbances or vortices in the coolant flow. These vortices not only mix the coolant within the cooling passages68and prevent lamina flow over the surfaces104. Lamina flow or boundary layers can cause the hottest coolant to remain against the surface104along the cooling passage68and diminish the cooling effect the further downstream the coolant flows. In other words, allowing boundary layers or lamina flow can cause a severe and detrimental temperature gradient in the coolant across the cooling passage. By introducing the flow disturbing feature(s)100the coolant is mixed and therefore the cooling effect significantly improved compared to a smooth undisturbed passage. In addition, the flow disturbing feature(s)100increase the surface area of the cooling passage68increasing heat transfer from the heatshield60to the coolant. Yet further, the coolant also impinges on the flow disturbing feature100and subsequently the vortices impinge on the surfaces enhancing heat transfer.

In another aspect of the present heatshield60, the cooling channels68have a cross-sectional shape that is rectangular although other polygonal and advantageously quadrilateral shapes are possible.FIG.6shows the outlets88,90are rectangular although the corners may have small radii. This rectangular cross-sectional shape allows a greater cross-sectional area of the cooling passages than conventional circular cross-section. This configuration means that there is less material for a given thickness and/or length of the main body61of the heatshield60than conventional designs having circular cross-sectional cooling passages i.e. the main body61has thinner walls132,134than conventionally and so can be cooled more effectively. Other particularly useful cross-sectional shapes of the cooling channels68are triangular and trapezoidal and are shown inFIG.7andFIG.8respectively. In each case one cooling channel68A is next to another cooling channel68B that is inverted. This arrangement ensures that there is a planar wall69between each cooling channel68A,68B and that has a minimum thickness. Therefore, there is a higher ratio of cooling channel to surface area of wall in the views shown inFIGS.6,7and8than conventional designs.

It is particularly advantageous that the most lateral cooling channel can be located very close to the lateral edge of the main body61to combat potential oxidation problems associated with particularly high metal temperatures that would otherwise be found. It is particularly advantageous that the outlets96and lateral-most cooling channels are formed radially inwardly of the seal strip in the lateral edges. The surface area of the cooling channels68is also increased from the conventionally drilled circular cross-section passages.

The conventional circular cross-sectional cooling holes are formed by conventional processes such a machine drilling, electric discharge machining and laser boring, other processes may be apparent. The present heatshield is formed by an additive manufacturing process such as direct laser deposition, selective laser melting, and other 3D printing techniques, material jetting, material extrusion or powder bed fusion. The additive manufacturing process allows manufacturing of a monolithic heat shield comprising the aforementioned cooling channels to be formed in their rectangular cross-section shape which is not possible by the convention fabrication methods. Similarly, the flow disturbing features are also possible, whereas the conventional machining techniques allow only smooth and circular cross-sectional shaped cooling channels.

In the additive manufacturing process, it is preferable that all corners or angles136between connected sides of the heatshield or elements of the heatshield and particularly the flow disturbing features100have an angle ≥45°. It has been found that features having geometry having an external angle less than 45° requires additional supporting structure during manufacture and which then requires removal. This is not possible for the flow disturbing features100which are inside the cooling channels.