DOUBLE-WALL GEOMETRY

Abstract

There is disclosed wall cooling system 50 having a double-wall geometry. A first wall 55 and a second wall 60 extend over a plan area with the second wall spaced from the first wall by a gap. The first wall 55 has multiple upstanding members 65 spanning the gap and contacting the second wall 60 such that the first and second walls are mechanically and thermally connected. The first wall 55 is shaped so as to provide a two-dimensional array of crests 85 and recesses 90. The crests 85 are spaced from the second wall 60. The first wall 55 has a plurality of through-holes 70 for flow of coolant through the first wall and into the gap. The cooling system 50 is suitable for use in a gas turbine engine 10, for example in the turbine 17, 19.

Claims

1. A wall cooling system comprising a double-wall geometry having: a first wall extending over a plan area; and a second wall extending over the plan area and spaced from the first wall by a gap, the first wall comprising a plurality of upstanding members spanning the gap and contacting the second wall such that the first and second walls are mechanically and thermally connected, the first wall shaped so as to provide a two-dimensional array of crests and recesses, wherein the crests are spaced from the second wall, and the first wall comprising a plurality of through-holes for flow of coolant through the first wall and into the gap.

2. The cooling system according to claim 1, wherein each of the plurality of through-holes is provided through a crest of the first wall.

3. The cooling system according to claim 1, wherein the crests each comprise a discrete apex, spaced from each adjacent crest of the array by a recess.

4. The cooling system according to claim 1, wherein each crest is surrounded on all sides in the plan area by a recess.

5. The cooling system according to claim 1, wherein the first wall is undulating in form to provide the two-dimensional array of crests and recesses.

6. The cooling system according to claim 5, wherein the first wall is undulating in at least two directions so as to define the two-dimensional array of crests and recesses.

7. The cooling system according to claim 1, the plurality of upstanding members being positioned in the recesses of the two-dimensional array.

8. The double-wall geometry according to claim 7, the plurality of upstanding members being positioned in the recesses of the two-dimensional array in-between two adjacent crests of the first wall.

9. The cooling system according to claim 1, wherein the second wall is planar in form such that the two-dimensional array of crests and recesses causes variation in the gap between the first and second walls over the plan area.

10. The cooling system according to claim 1, wherein the plurality of upstanding members comprises a plurality of helical upstanding members.

11. The cooling system according to claim 10, wherein the first wall comprises an interspersed array of straight upstanding members and helical upstanding members.

12. The cooling system according to claim 1, wherein the second wall comprises an array of apertures over the plan area.

13. The cooling system according to claim 12, wherein the apertures are angled through the second wall relative to a surface normal of the second wall.

14. The cooling system according to claim 1, wherein the height of the crests is greater than a quarter of the height of the upstanding members and/or the gap in an adjacent recess.

15. The cooling system according to claim 1, wherein the height of the crests is approximately half the height of the upstanding members and/or the gap in an adjacent recess.

16. A combustion engine comprising the cooling system of claim 1, wherein the second wall is arranged to be exposed to heat and/or combustion products generated by the combustion engine in use.

17. The combustion engine according to claim 16, comprising a turbine arranged to be driven by the combustion products and the cooling system comprises a double-wall geometry of a blade and/or a vane of the turbine.

18. A sub-assembly of a gas turbine engine comprising the cooling system of claim 1.

19. The sub-assembly of claim 18, comprising a combustor or turbine sub-assembly.

20. A gas turbine engine 10 for an aircraft comprising: an engine core 11 comprising a turbine 19, a compressor 14, and a core shaft 26 connecting the turbine to the compressor; a fan 23 located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox 30 that receives an input from the core shaft 26 and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, wherein the turbine 19 comprises a cooling system according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

[0050] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0051] FIG. 1 is a sectional side view of a gas turbine engine;

[0052] FIG. 2 is a close-up sectional side view of an upstream portion of a gas turbine engine;

[0053] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0054] FIG. 4 is a partially cut-away perspective view of a double-wall geometry according to a first embodiment of the disclosure;

[0055] FIG. 5 is a cross-section of the double-wall geometry of FIG. 4;

[0056] FIG. 6 is a partially cut-away plan view of the double-wall geometry of FIGS. 4 and 5;

[0057] FIG. 7 is a partially cut-away perspective view of a double-wall geometry according to a second embodiment of the disclosure;

[0058] FIG. 8 is a cross-section of the double-wall geometry of FIG. 7; and

[0059] FIG. 9 is a graph comparing the efficiency of the double-wall geometry according to the example of the present disclosure shown in FIG. 4 and a conventional double-wall geometry.

[0060] Like reference numerals are used for corresponding features throughout the Figures.

DETAILED DESCRIPTION

[0061] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0062] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0063] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0064] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0065] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed disclosure. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0066] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0067] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0068] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0069] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0070] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0071] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0072] The following disclosure concerns a wall cooling system and structure for components and sub-assemblies located in a hot region of the engine, such as the combustor 16, high-pressure turbine 17 or low-pressure turbine 19. Whilst the cooling structure is described in that context herein, it is to be noted that the structure could find application in other engine, flow-machine and/or heat exchanger applications where there is a need for a high rate of heat transfer away from a wall. The cooling structure is particularly suitable for components operating at a temperature greater than the melting point of their material make-up.

[0073] The disclosure concerns a double-wall, effusion type (e.g. quasi-transpiration) cooling system.

[0074] FIG. 4 illustrates a double-wall geometry 50 according to a first embodiment of the present disclosure. In this example, the double-wall geometry 50 is comprised in a rotor blade for use in the high-pressure turbine 17 or low-pressure turbine 19, for example. However, the double-wall geometry 50 could equally apply to the turbine stators/vanes or the wall structure of the rotor hub or the static turbine casing.

[0075] The double-wall geometry 50 comprises an inner wall 55 and an outer wall 60. The inner wall 55 and outer wall 60 extend in generally parallel directions, i.e.

[0076] such that the outer wall 60 overlies the inner wall 55. The outer wall 60 is shown as being generally planar in this example but could be arched or curved in other examples such that the inner and outer walls follow a parallel path.

[0077] Whilst the inner wall 55 is parallel with the outer wall 60 in a general sense, i.e. such that the inner wall 55 follows the same gross path as the outer wall 60, the inner wall 55 is itself profiled. The inner wall 55 has a repeating, undulating profile.

[0078] The inner wall 55 is profiled in both the longitudinal direction, x, and the transverse direction, y, to form crenulations 75, e.g. crests. Some of the crests formed by the crenulations 75 comprise impingement holes 70.

[0079] The inner wall 55 comprises an array of pedestals 65 extending from its inner surface to the outer wall 60. The pedestals 65 hold the inner 55 and outer 60 walls at a fixed spacing such that a gap exists therebetween. The gap beneath the outer wall defines a void between the inner and outer walls extending over the area of the walls.

[0080] It will be appreciated that he outer wall 60 has opposing surfaces, an inner surface of which faces the inner wall 55, and an outer surface of which faces an exterior of the structure 50

[0081] In this example, the outer wall 60 comprises an array of apertures 80 extending between its inner and outer surfaces, as will be described in further details below. The apertures are generally evenly spaced over the area of the outer wall 60. However in other examples, the apertures 80 could be omitted such that the outer surface is generally continuous, i.e. devoid of openings or discontinuities.

[0082] The crenulations 75 of the inner wall 55 define a two-dimensional array of crests 85 and a network of recesses 90 across the surface of the inner wall 55 (explained in more detail with reference to FIG. 6 further on). For the sake of simplifying the following description, the crests 85 and recesses 90 will be defined based on the viewpoint of FIG. 4, i.e. the crests 85 are defined as the highest points of the crenulations 75 in relation to the outer wall 60 and the recesses 90 are defined as the lowest points of the crenulations 75 in relation to the outer wall 60. That is, the crests 85 are defined as the points of inner wall 55 which are nearest to the outer wall 60 and the recesses 90 are defined as the points of inner wall 55 that are furthest from the outer wall 60. The crenulations 75 are of an amplitude such that the crests 85 do not extend to the outer wall 60.

[0083] The inner wall 55 is shaped so as to define a two-dimensional array of discrete crests 85 over the area of the wall. In this example, the crests 85 are arranged in straight lines, i.e. in rows and columns, although in other examples the crests could form a different two-dimensional pattern. Each crest 85 has a plurality of adjacent/neighbouring crests. In the ordered grid-like arrangement shown, each crest has four neighbouring crests, although other arrangements with differing numbers of neighbouring crests could be devised.

[0084] The inner wall may be described as being generally egg-box or egg-tray shaped.

[0085] The whole inner wall 55 is profiled in the manner described herein such that the inverse of the array of crests 85 and recesses 90 is visible within the underside of the inner wall 55.

[0086] Impingement holes 70 are defined in alternating crests 85 when viewed along the longitudinal axis x or transverse axis y of the array of crests 85 formed by the crenulations 75. When viewed along the diagonal axis y, alternate diagonals of the array of crests 85 comprise impingement holes 70 (best illustrated by FIG. 6). This provides a uniform/even distribution of impingement holes 70. Different patterns of impingement holes 70 could be provided, or else all crests 85 could have an impingement hole. The optimal arrangement of holes 70 can be determined for each cooling application.

[0087] In each recess 90 of the crenulations 75, there is provided a pedestal 65 protruding therefrom. There is therefore a pedestal 65 provided between any two crests 85 when viewed from any of the longitudinal, transverse and diagonal axes x, y, z (best illustrated by FIG. 6). These pedestals 65 are of a height such that they extend and make mechanical and thermal connection with the outer wall 60 so as to mechanically and thermally connect the inner and outer walls 55, 60.

[0088] The array of pedestals 65 extending from the recesses 90 of the inner surface of the inner wall 55 are formed as cuboidal pedestals of various dimensions and aligned in various orientations. Different shapes of pedestals are possible. Each of the pedestals 65 extends the full height from the inner surface of the inner wall 55 to the inner surface of the outer wall 60 to provide the predetermined gap/spacing between the inner and outer walls 55, 60.

[0089] The apertures 80 in the outer wall 60 are formed in a regular array. The separation between apertures 80, the number of apertures 80 in the array, and the arrangement of apertures 80 in the array is dependent on the cooling application in question. The separation between apertures 80 may be designed based on the number and spacing of the impingement holes 70 present in the array of crenulations 75. The apertures 80 are laterally offset from the impingement holes 70, i.e. such that they are not directly above the impingement holes.

[0090] FIG. 5 illustrates a side view of the double-wall geometry 50 of FIG. 4 when viewed from the transverse direction y. From this view, it can be seen that the crenulations 75 are shaped so as to from raised crests 85 and lowered recesses 90 relative to the plane of the inner wall 55. Each crest 85 is flanked, or fully surrounded, by a recess 90.

[0091] The apertures 80 in the outer wall 60 are angled relative to the longitudinal axis x at an angle of approximately 30 degrees. That is, the central axes of the apertures 80 in the outer wall 60 are angled relative to the outer wall 60 at an angle of approximately 30 degrees. The apertures 80 are angled such that the point at which the central axes of the apertures 80 meet the inner surface of the outer wall 60 (i.e. the opening in the inner wall) is roughly aligned with the crests 85 that do not contain the impingement holes 70. The apertures can be at any desired angle and may be fan shaped, cylindrical or otherwise shaped to suit specific requirements.

[0092] The diameter of the impingement holes D.sub.i is of the order of 1 mm but could vary from approximately 0.1 to 2.5 mm.

[0093] The height of the pedestals z.sub.1 is approximately five times the diameter of the impingement holes D.sub.i, i.e. approximately 5 mm in this example. However the height could vary between one and ten times the diameter D.sub.i in other examples, e.g. between 0.1 and 25 mm.

[0094] It can be seen that the height of the pedestals z.sub.1 is equal to the separation distance between the inner wall 55 and the outer wall 60, i.e. the pedestals 65 extend between the inner wall 55 and the outer wall 60. The amplitude of the crenulations z.sub.2 is approximately half the height of the pedestals z.sub.1, i.e. approximately 2.5 mm. It will therefore be appreciated that that the amplitude of the crenulations z.sub.2 is equal to half the separation distance between the inner wall 55 and the outer wall 60, i.e. the crenulations 75 do not extend to the outer wall 60.

[0095] In other examples, the amplitude of the crenulations z.sub.2 could vary between one tenth and nine tenths of the maximum spacing between the walls or the height of the pedestals (i.e. 0.1-0.9 z.sub.1).

[0096] FIG. 6 illustrates a partially cut-away plan view of the double-wall geometry 50 of FIG. 4. It can be seen from this view that each crest 85 of the crenulations 75 is completely surrounded by a network of recesses 90 as a result of the inner wall 55 being crenulated in both the longitudinal direction x and the transverse direction y.

[0097] Each crest 85 has a levelled surface, or land, at its peak. A generally rectangular or square end of the crest is shown. The surrounding recess network therefore comprises four recesses 90 surrounding the perimeter of each crest 85. The crest could be circular or differently shaped as required.

[0098] The array of crests 85 comprises a regular array in which the crests 85 are distributed in rows in the longitudinal direction x and columns in the transverse direction y. Pedestals 65 are positioned in the recesses 90 between any two crests 85 such that each crest is surrounded by eight pedestals 65. In the example shown, a pedestal is located part-way along each edge of a crest, as well as at each corner of the crest.

[0099] Each crest may have a total of eight neighbouring crests in the array, i.e. with a pedestal interposed in the recess between a crest and its neighbours.

[0100] The embodiments shown and described herein have generally attempted to maximise impingement cooling effects and form channels for the coolant flow. However those geometries can be altered according to the general principles described herein as may be required for specific operational requirements. The openings 80a of the apertures 80 on the outer surface of the wall 60 are elliptically shaped in this example. This may be the same as the openings of the apertures 80 in the internal surface of the wall 60. Alternatively the internal surface openings could be smaller and/or circular in shape to create an aperture that varies in profile between inlet and outlet.

[0101] FIG. 7 illustrates a double-wall geometry 100 according to a second embodiment of the present disclosure, and FIG. 8 illustrates a side view of the double-wall geometry 100 of FIG. 7 when viewed from the transverse direction, y.

[0102] The double-wall geometry 100 of the second embodiment differs from the double-wall geometry 50 of the first embodiment only in that it further comprises helical pedestals 105 (i.e. pedestals that take a coiled or wound form, rather than the straight pedestals 50 that have substantially constant cross-sectional profile).

[0103] As with the first embodiment, the coiled pedestals 105 are provided in the recesses 90 of crenulations 75. These coiled pedestals 105 are of a height such that they extend and make mechanical and thermal connection with the outer wall 60 so as to mechanically and thermally connect the inner and outer walls 55, 60.

[0104] The coiled pedestals 105 are provided in a first portion of the recesses 90. The double-wall geometry 100 additionally comprises pedestals 65 provided in a second portion of the recesses 90. The first and second portions overlap to provide an interspersed array of coiled pedestals 105 and pedestals 65 extending from the inner surface of the inner wall 55 to the inner surface of the outer wall 60 to provide a mechanical and thermal connection between the inner and outer walls 55, 60.

[0105] In use, coolant is fed under pressure to the underside of the inner wall 55, i.e. the side that faces away from the outer wall 60. A cavity may be maintained under elevated pressure for constant supply of coolant to the whole area of the underside of the inner wall 55. In this regard, the relevant component may be hollow, e.g. in the case of a turbine blade or vane.

[0106] Coolant is injected under pressure into the double-wall geometry 50, 100 through the impingement holes 70 in the crests 85 of the inner wall 55. The resultant high velocity jet of coolant flow impinges on the opposing surface of the hotter outer wall 60 causing heat loss from the outer wall 60. Coolant flows laterally though the void towards an outlet, thereby flowing over pedestals and other crenulations 75. This promotes turbulent, cooling flow over those parts also. Thus the conductive pedestals 65 can conduct heat from the external wall 60 along the pedestals to the internal wall 55, all of which components can experience cooling by the coolant flow through the double-wall geometry.

[0107] In the examples of FIGS. 4 to 8, the outlet openings are provided by apertures 80. In other examples it may be possible to vent coolant from the edges of the structure.

[0108] Coolant leaves the double-wall geometries 50, 100 via the apertures 80, which creates a thin protective film of cold fluid over the external surface of the outer wall 60, further reducing the temperature of the outer wall. The array of apertures 80 can provide a generally uniform layer of coolant over the external surface to envelope it from the hotter external environment. This can be used to maintain the external surface at a temperature significantly below the external environment in which it is located.

[0109] The crenulated/undulating wall 55, as well as offering a good area for convective cooling, can also offer improved thermo-mechanical properties for dissipating thermal stress due to differences in temperature between the inner and outer wall and/or over the area of the double wall geometry.

[0110] Some of the features and embodiments described herein may provide one or more of the following advantages: [0111] An aerothermal benefit as a result of a larger coolant wetted surface area; [0112] A reduction in the magnitude of the thermal gradient between the inner and outer walls; [0113] A reduction in thermal stresses of the double-wall geometry, particularly when under load; [0114] An increase in the overall mechanical compliance of the double-wall geometry, particularly when under load; [0115] An increase in the component/system lifetime; [0116] An increased turbulent flow mixing within the double-wall geometry; [0117] The ability to channel the direction of coolant flow; [0118] An increased heat transfer effect; [0119] An added convective cooling effect within the outer wall; [0120] An increased conductive cooling effect; [0121] A reduction in the coolant flow volume required to achieve a predetermined design life of the rotor blade.

[0122] The double-wall geometries 50, 100 may be manufactured using a casting process, via bonding of multiple parts, via laser sintering, or any combination of these methods. Alternatively, it will be appreciated that the double-wall geometries 50, 100 may be formed by any suitable method provided the resultant parts can withstand high temperatures and/or high pressures.

[0123] Although each of the above embodiments has been described in relation to the inner wall 55 being crenulated, it will be appreciated that the inner wall 55 may be castellated, concertinaed, corrugated, convoluted, folded, bent, wrinkled, rumpled, ridged, grooved or otherwise structurally altered to form crests and recesses as described herein.

[0124] Although the present disclosure has been described above in relation to the double-wall geometry 90 comprising both coiled pedestals 95 and pedestals 65, it is foreseen that the double-wall geometry may comprise only the coiled pedestals 95. It is also foreseen that the coiled pedestals 95 may be springs and/or helical pedestals.

[0125] Although the pedestals of both embodiments have been described in relation to cuboidal pedestals 65, it will be appreciated that the pedestals may be of any shape, or any combination of shapes, for example triangular prisms, pentagonal prisms or hexagonal prisms.

[0126] Although the diameter of the impingement holes D.sub.i has been described above as being of the order of 1 mm, it will be appreciated that the diameter of the impingement holes may be between 0.1 mm and 2.5 mm, between 0.3 mm and 2 mm, or between 0.5 mm and 1.5 mm.

[0127] Although the height of the pedestals z.sub.1 has been described above as being between 1 times and 10 times the diameter of the impingement holes, that height may more-specifically be between 3 times and 8 times the diameter of the impingement holes, or between 4 times and 6 times diameter of the impingement holes.

[0128] Although the amplitude of the crenulations z.sub.2 has been described above as being between 0.1 times and 0.9 times the height of the pedestals, the amplitude of the crenulations may more-specifically be between 0.3 times and 0.7 times the height of the pedestals, or between 0.4 times and 0.6 times the height of the pedestals.

[0129] Although the diameter of the apertures D.sub.f has been described above as being between 0.1 mm and 2.5 mm, the diameter may more-specifically be between 0.3 mm and 2 mm, or between 0.5 mm and 1.5 mm. The diameter of the apertures D.sub.f may or may not be set such that it is equal to the diameter of the impingement holes D.sub.i.

[0130] Although the present disclosure has been described in relation to a double-wall geometry, it will also be appreciated that a system having more than two walls is anticipated. In such a system, crenulations 75, pedestals 65 and impingement holes 70 may be present on every wall, or on selected walls.

[0131] It will also be understood that the double-wall geometry described herein is suitable for any components having a wall intended to be exposed to an extreme temperature environment, such as a temperature greater than the melting point of the material make-up of said wall. For example, the double-wall geometry could be implemented in other regions of a gas turbine engine, such as the nozzle guide vanes, the stator vanes, the turbine vanes, in combustor cooling, or the like. Alternatively, the double-wall geometry may be implemented in other heat exchange fields outside of gas turbine engines.