AEROFOIL WITH ONE OR MORE PEDESTALS HAVING DIMPLED SURFACE FOR COOLING

Abstract

 An aerofoil for a gas turbine engine is presented. The aerofoil has a pressure side wall and a suction side wall that join each other at a leading edge and a trailing edge. The pressure side wall has a pressure side outer surface and a pressure side inner surface. The suction side wall has a suction side outer surface and a suction side inner surface. The pressure side inner surface and the suction side inner surface are opposing surfaces. Within the aerofoil, a cooling passage is arranged between the pressure side inner surface and the suction side inner surface. A plurality of pedestals extending longitudinally between the pressure side inner surface and the suction side inner surface are arranged within the cooling passage. The plurality of pedestals includes one or more pedestal having dimpled surface.

Description

[0001] The present invention relates to turbomachine components having an aerofoil, such as a vane or a blade, and more particularly to turbomachine components having aerofoils that include pedestals for cooling of the aerofoil of the turbomachine component in gas turbine engines.

[0002] To effectively use cooling air for cooling of gas turbine components is a constant challenge and an important area of interest in gas turbine engine designs. For example, for cooling different parts of a turbomachine component having an aerofoil, such as a vane or a blade, conventional design uses various ways including film cooling and circulation of cooling fluid through cooling passages arranged within the aerofoil of the turbomachine components. Usually to enhance cooling, besides optional other functions such as increasing mechanical strength of the aerofoil, pedestals are arranged in the cooling passages within the aerofoil in flow path of the cooling fluid. The pedestals are attached to a pressure side and/or a suction side of the aerofoil and conduct heat from the pressure side and/or the suction side into the flow path of the cooling fluid. The cooling fluid flowing over and in contact with surfaces of the pedestals cools the pedestal and as a result the pressure side and/or the suction side are cooled which therefore results in overall cooling of the aerofoil and thus of the turbomachine component having the aerofoil. However, present pedestals designs may be improved to enhance further cooling of the pedestals resulting from flow of the cooling fluid over and in contact with surfaces of the pedestals.

[0003] Thus the object of the present disclosure is to provide a pedestal design wherein cooling of the pedestal arranged within the aerofoil is improved.

[0004] The above objects are achieved by an aerofoil for a gas turbine engine according to claim 1, a turbine blade according to claim 12 and a turbine vane according to claim 13 of the present technique. Advantageous embodiments of the present technique are provided in dependent claims.

[0005] In a first aspect of the present technique, an aerofoil for a gas turbine engine is presented. The aerofoil has a pressure side wall and a suction side wall. The pressure side and the suction side walls extend in a radial direction. The pressure side wall and the suction side wall join each other at a leading edge and a trailing edge. The pressure side wall has a pressure side outer surface and a pressure side inner surface. The suction side wall has a suction side outer surface and a suction side inner surface. The pressure side inner surface and the suction side inner surface are opposing surfaces. Within the aerofoil, a cooling passage is arranged between the pressure side inner surface and the suction side inner surface. A plurality of pedestals extending longitudinally between the pressure side inner surface and the suction side inner surface are arranged within the cooling passage. The plurality of pedestals includes one or more pedestal having dimpled surface. The dimpled surface of the pedestals provides a different aerodynamic characteristic to the pedestals as compared to a pedestal without a dimpled surface, i.e. the point at which the cooling air flow contacting the pedestal surface breaks away from the pedestal surface, i.e. the separation point, is further downstream at the pedestal surface for the dimpled pedestal surface as compared to a pedestal surface without dimples for example a pedestal having a smooth surface. As a result, for a pedestal with dimpled surface the cooling air flowing around the pedestals remains in contact with the pedestal surface for a longer time and over a greater area of the pedestal surface as compared to a pedestal surface without dimples, and thus the cooling efficiency due to cooling air flowing over and in contact with the pedestal with dimpled surface is greater as compared to cooling efficiency due to cooling air flowing in contact with a pedestal without dimpled surface. Furthermore as a result of flow of cooling air over and in contact with the dimpled surface more turbulence is introduced in the cooling air as compared to turbulence, if any, introduced in cooling air as a result of flow of cooling air over a smooth surfaced pedestal, thus overall turbulence of the cooling air within the cooling passage is greater and thus better heat exchange is performed by the cooling air from the structures lining and in the cooling passage for example, the pressure side inner surface, the suction side inner surface, the pedestals, and so on and so forth.

[0006] In an embodiment of the aerofoil, the one or more pedestal having dimpled surface includes at least one pedestal joining the pressure side inner surface and the suction side inner surface i.e. the pedestal is connected on one of its end with the pressure side inner surface and on its other end with the suction side inner surface and longitudinally extends all the way from the pressure side inner surface to the suction side inner surface. Thus the pedestal acts as a thermal bridge between the pressure side inner surface and the suction side inner surface and thereby between the pressure side wall and the suction side wall. Furthermore, as a result of extending the entire way between the pressure side inner surface and the suction side inner surface, the pedestal with dimpled surface has a larger surface area compared to a similarly placed pedestal that does not extend the entire way between the pressure side inner surface and the suction side inner surface, and larger surface area results in more number of dimples and more contact with the cooling air and thus better cooling.

[0007] In another embodiment of the aerofoil, the one or more pedestal having dimpled surface includes at least one pedestal extending from the pressure side inner surface towards the suction side inner surface. The pedestal extending from the pressure side inner surface towards the suction side inner surface is non-contiguous with the suction side inner surface i.e. the pedestal does not extend the entire way between the pressure side inner surface and the suction side inner surface. The pedestal aids in cooling of the pressure side inner surface and thereby in cooling of the pressure side wall. In a related embodiment, the at least one pedestal extending from the pressure side inner surface towards the suction side inner surface and non-contiguous with the suction side inner surface includes a top surface with dimples, for example the top surface with dimples is spherical cap shaped. The dimpled top surface ensures that cooling air contacts the top surface for a longer time and over a greater area of the pedestal top surface and thus facilitating the cooling of the top surface and thereby of the pedestal extending from the pressure side inner surface towards the suction side inner surface and non-contiguous with the suction side inner surface.

[0008] In another embodiment of the aerofoil, the one or more pedestal having dimpled surface includes at least one pedestal extending from the suction side inner surface towards the pressure side inner surface. The pedestal extending from the suction side inner surface towards the pressure side inner surface is non-contiguous with the pressure side inner surface i.e. the pedestal does not extend the entire way between the suction side inner surface and the pressure side inner surface. The pedestal aids in cooling of the suction side inner surface and thereby in cooling of the suction side wall. In a related embodiment, the at least one pedestal extending from the suction side inner surface towards the pressure side inner surface and non-contiguous with the pressure side inner surface includes a top surface with dimples, for example the top surface with dimples is spherical cap shaped. The dimpled top surface ensures that cooling air contacts the top surface for a longer time and over a greater area of the pedestal top surface and thus facilitating the cooling of the top surface and thereby of the pedestal extending from the suction side inner surface towards the pressure side inner surface and non-contiguous with the pressure side inner surface.

[0009] In another embodiment of the aerofoil, the one or more pedestal having dimpled surface is positioned in a trailing edge section of the aerofoil. Thus enhancing the cooling of the trailing edge section. Furthermore, the cooling passage arranged within the aerofoil generally exits towards the trailing edge through holes or slits at the trailing edge and thus pedestals positioned in the trailing edge section of the aerofoil ensure that pressure drop in the cooling air flowing across the pedestals is reduced, due to the dimpled surface, hence the pressure in the cooling air exiting the trailing edge holes or slots is high. Reducing pressure drop is beneficial for working of the turbine engines in various ways for example if the pressure drop is smaller additional cooling features can be used so more effective cooling schemes can be implemented.

[0010] In another embodiment of the aerofoil, the one or more pedestal having dimpled surface have elliptical cross-sections, for example a circular cross-section. This provides an implementation for a shape of the pedestal with the dimpled surface.

[0011] In a second aspect of the present technique a turbine blade for a gas turbine engine is presented. The turbine blade includes an aerofoil according to the first aspect of the present technique as described hereinabove. Thus the turbine blade has the aerofoil with the pedestal having dimpled surface and thus cooling of the turbine blade is aided by the pedestal having dimpled surface.

[0012] In a third aspect of the present technique a turbine vane for a gas turbine engine is presented. The turbine vane includes an aerofoil according to the first aspect of the present technique as described hereinabove. Thus the turbine vane has the aerofoil with the pedestal having dimpled surface and thus cooling of the turbine vane is aided by the pedestal having dimpled surface.

[0013] The above mentioned attributes and other features and advantages of the present technique and the manner of attaining them will become more apparent and the present technique itself will be better understood by reference to the following description of embodiments of the present technique taken in conjunction with the accompanying drawings, wherein:

FIG 1

shows part of a turbine engine in a sectional view and in which an exemplary embodiment of an aerofoil of the present technique is incorporated;

FIG 2

schematically illustrates a perspective view of an exemplary embodiment of a turbomachine component, for example a turbine blade, in which an exemplary embodiment of the aerofoil of the present technique is incorporated;

FIG 3

schematically illustrates a top perspective view of an exemplary embodiment of the turbomachine component, i.e. the turbine blade, in which an exemplary embodiment of the aerofoil of the present technique is incorporated;

FIG 4

schematically illustrates a top perspective view of a part of the exemplary embodiment of the turbomachine component of FIG 3;

FIG 5

schematically illustrates a perspective view of an exemplary embodiment of a pedestal having dimpled surface according to the present technique;

FIG 6

schematically illustrates different exemplary embodiments of the pedestal having dimpled surface according to the present technique;

FIG 7

schematically illustrates different exemplary embodiments of the pedestal having dimpled surface and having top surfaces with dimples;

FIG 8

schematically illustrates position of the pedestals having dimpled surface in the aerofoil;

FIG 9

schematically illustrates flow of cooling air over a surface of a conventionally known pedestal i.e. a pedestal without dimpled surface; and

FIG 10

schematically illustrates flow of cooling air over a dimpled surface of the pedestal of the present technique; in accordance with aspects of the present technique.

[0014] Hereinafter, above-mentioned and other features of the present technique are described in details. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details.

[0015] 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 or compressor section 14, a combustor section 16 and a turbine section 18 which are generally arranged in flow series and generally about and in the direction of a rotational axis 20. 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 to the compressor section 14.

[0016] 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 extending along a longitudinal axis 35 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 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.

[0017] 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 combustor 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.

[0018] 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 44 are provided and turn the flow of working gas onto the turbine blades 38.

[0019] The combustion gas 34 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, 44 serve to optimise the angle of the combustion or working gas 34 on the turbine blades 38.

[0020] The turbine section 18 drives the compressor section 14. The compressor section 14 comprises an axial series of vane stages 46 and rotor blade stages 48. The rotor blade stages 48 comprise a rotor disc supporting an annular array of blades. The compressor section 14 also comprises a casing 50 that surrounds the rotor stages and supports the vane stages 48. The guide vane stages include an annular array of radially extending vanes that are mounted to the casing 50. The vanes are provided to present gas flow at an optimal angle for the blades at a given engine operational point. Some of the guide vane stages have variable vanes, where the angle of the vanes, about their own longitudinal axis, can be adjusted for angle according to air flow characteristics that can occur at different engine operations conditions.

[0021] The casing 50 defines a radially outer surface 52 of the passage 56 of the compressor 14. A radially inner surface 54 of the passage 56 is at least partly defined by a rotor drum 53 of the rotor which is partly defined by the annular array of blades 48.

[0022] The present technique 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 technique is equally applicable to two or three shaft engines and which can be used for industrial, aero or marine applications. Furthermore, the cannular combustor section arrangement 16 is also used for exemplary purposes and it should be appreciated that the present technique is equally applicable to annular type and can type combustion chambers.

[0023] The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow 34 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, unless otherwise stated.

[0024] FIG 2 schematically illustrates a turbomachine component 1 having an aerofoil 5 depicting a portion of an inside of the turbomachine component 1. Examples of the turbomachine component 1 are the turbine blade 38 or the vane 40 of FIG 1. FIG 3 schematically illustrates a top perspective view of the aerofoil 5 of the turbomachine component 1, hereinafter also referred to as the blade 1. It may be noted that the present technique has been explained in details with respect to an embodiment of a turbine blade such as the turbine blade 38, however, it must be appreciated that the present technique is equally applicable and implemented similarly with respect to a turbine vane, such as the guiding vane 40, 44 or any other turbomachine component having an aerofoil and where the aerofoil is being cooled by a cooling channel or a cooling cavity or a cooling passage through which a cooling fluid flows or can flow in order to cool the aerofoil in which the cooling channel or the cooling cavity or the cooling passage is arranged. FIG 4 represents detailed view of a region A of FIG 3.

[0025] In the blade 1, the aerofoil 5 extends from a platform 6 in a radial direction. The platform 6 extends circumferentially. Also from the platform 6 emanates a root 8 or a fixing part 8. The root 8 or the fixing part 8 may be used to attach the blade 1 to the turbine disc 36 (shown in FIG 1). The root 8 and the platform 6 together form a base in the blade 1. It may be noted that in some other embodiments of the turbomachine component 1, the root 8 may not be present and the base is then formed only of the platform 6 which may be an integrally fabricated part of a larger structure (not shown) such as a stator disc in the turbine section 16 of the engine 10, as shown in FIG 1.

[0026] The aerofoil 5 includes a suction side wall 60, also called suction side 60, and a pressure side wall 70, also called pressure side 70. The side walls 60 and 70 meet at a trailing edge 92 on one end and a leading edge 91 on another end. The aerofoil 5 has a tip end 93 and a platform end 94. The aerofoil 5 may be connected to a shroud (not shown) or an outer platform (not shown) at the tip end 93 of the aerofoil 5. The suction side wall 60 has a suction side outer surface 61 i.e. the surface of the suction side wall 60 that forms the outside of the aerofoil 5 and that is positioned in the hot gas path when the aerofoil 5 is arranged in the gas turbine engine 10. The suction side wall 60 has a suction side inner surface 62, opposite face of the suction side wall 60 as compared to the suction side outer surface 61. The suction side inner surface 62 is the surface of the suction side wall 60 that is at the inside of the aerofoil 5 and that is not positioned in the hot gas path when the aerofoil 5 is arranged in the gas turbine engine 10. Similarly, the pressure side wall 70 has a pressure side outer surface 71 i.e. the surface of the pressure side wall 70 that forms the outside of the aerofoil 5 and that is positioned in the hot gas path when the aerofoil 5 is arranged in the gas turbine engine 10. The pressure side wall 70 has a pressure side inner surface 72, opposite face of the pressure side wall 70 as compared to the pressure side outer surface 71. The pressure side inner surface 72 is the surface of the pressure side wall 70 that is at the inside of the aerofoil 5 and that is not positioned in the hot gas path when the aerofoil 5 is arranged in the gas turbine engine 10. The suction side inner surface 62 and the pressure side inner surface 72 are opposing surfaces. The side walls 60 and 70 of the aerofoil 5 act as boundary for an aerofoil cavity or volume enclosed by the side walls 60 and 70.

[0027] As shown in FIG 2, within the aerofoil 5, i.e. within the volume enclosed by the side walls 60 and 70, a cooling passage 9 is arranged, more particularly between the suction side inner surface 62 and the pressure side inner surface 72. The cooling passage 9 defines a flow path for a cooling fluid such as cooling air for purpose of cooling the aerofoil 5. An exemplary embodiment of the cooling passage 9 and a direction of flow of cooling air represented by arrows marked with reference numeral 7 have been schematically depicted in FIG 2. It may be noted that dimensions, arrangement, design etc of the cooling passage 9 and pattern of flow 7 of the cooling air or fluid within the cooling passage 9 may be different depending on different blade/vane designs. It may also be noted that the cooling passage 9 may be formed of one or more parts, for example smaller cooling passages or channels that define different flow paths for the cooling fluid and that are not fluidly connected. The cooling passage 9 or its constituting passages or channels may exit the aerofoil 5 through one or more exits that are usually arranged at the leading edge 91 and/or the trailing edge 92, for example trailing edge slits 95 in FIG 2. Generally cooling fluid enters the cooling passage 9 through the base of the blade 1.

[0028] As depicted in FIG 3, and in detailed view in FIG 4, in combination with FIG 2, in the aerofoil 5, a plurality of pedestals 80 are arranged within the cooling passage 9. The pedestals 80 extend longitudinally between the suction side inner surface 62 and the pressure side inner surface 72 as shown in details in FIG 4. FIG 5 presents an exemplary embodiment of one such pedestal 80 according to the present technique and that has been removed from the aerofoil 5. The pedestal 80 generally has an extended body, i.e. extending along an axis 85, and two ends 86, 87. Both the ends 86 and 87 may be attached to the inner surfaces 62, 67 for example one end 86 may be attached to the suction side inner surface 62 whereas the other side 87 may be attached to the pressure side inner surface 72; or one of the two ends 86 and 87 may be attached to the inner surface 62 or 67 for example one end 86 may be attached to the suction side inner surface 62 whereas the other side 87 may be free standing i.e. not attached to the pressure side inner surface 72 or the other end 87 may be attached to the pressure side inner surface 72 whereas the one side 86 may be free standing i.e. not attached to the suction side inner surface 62. It may be noted that attached includes formed as integral part, for example by casting, wherein the pedestal 80 and the inner surfaces 62,72 are formed together as one part and then the phrase 'attached to' as used hereinabove means joint with or formed with.

[0029] As shown in FIG 3 and 4, the aerofoil 5 may include a plurality of the pedestals 80. According to the present technique, the plurality of pedestals 80 includes one or more pedestal 80 that have dimpled surface 84 as shown in FIG 5. The pedestal 80 having the dimpled surface 84 may have an elliptical cross-section, for example a circular cross section. An example of a shape of the pedestal 80 may be a rod shape.

[0030] FIG 9 and 10 depict an advantage in cooling provided due to the pedestal 80 having dimpled surface 84 in comparison to a conventionally known pedestal 78 having a surface that is not dimpled surface 84 for example a pedestal 78 having a smooth surface. As shown in FIG 9, when the flow 7 of cooling fluid for example cooling air encounters the pedestal 78, the cooling air is forced to flow over the smooth surface of the pedestal 78. The cooling air starts to flow in contact with the surface of the pedestal 78 from point or region wherefrom the cooling air comes in contact with the surface of the pedestal 78, however as is known conventionally, due to curvature of the surface of the pedestal 78, the flow 7 of the cooling air separates from the surface of the pedestal 78 at a point 79, also referred generally to as separation point or flow separation point, after flowing for some duration in contact with the surface of the pedestal 78. As shown in FIG 10, when the flow 7 of the cooling air encounters the pedestal 80, the cooling air is forced to flow over the dimpled surface 84 of the pedestal 80 from point or region wherefrom the cooling air comes in contact with the dimpled surface 84 of the pedestal 80, and although due to curvature of the dimpled surface 84 of the pedestal 80, the flow 7 of the cooling air eventually separates from the dimpled surface 84 of the pedestal 80, due to the dimpled surface 84 the separation point 79 on the dimpled surface 84 is further downstream, with respect to flow direction 7 of the cooling air wherefrom the cooling air comes in contact with the dimpled surface 84 of the pedestal 80.

[0031] The movement of position of the separation point 79 on the dimpled surface 84 of the pedestal 80, in comparison with position of the separation point 79 on the surface of the pedestal 78, results from the dimpled surface 84 and is present even when the pedestals 78 and 80 are same in all other respects besides the dimples on the surface of the pedestal 80 and absence of dimples on the surface of the pedestal 78. This shift of the position of the separation point 79 on the dimpled surface 84 of the pedestal 80 results in greater contact time between the cooling air and the dimpled surface 84 and greater contact area of the dimpled surface 84 with the cooling air before the occurrence of the flow separation at the separation point 79.

[0032] FIG 6 presents various exemplary embodiments of the aerofoil 5 differing in the arrangement of the pedestals 80.

[0033] In an embodiment of the aerofoil 5, as depicted in FIG 6, the one or more pedestal 80 having dimpled surface 84 includes at least one pedestal 81 that joins or is attached with or is formed with the pressure side inner surface 72 and the suction side inner surface 62 i.e. the pedestal 81 is physically in contact with the pressure side inner surface 72 as well as the suction side inner surface 62 and extends the entire way between the pressure side inner surface 72 as well as the suction side inner surface 62.

[0034] In another embodiment of the aerofoil 5, as depicted in FIG 6, the one or more pedestal 80 having dimpled surface 84 includes at least one pedestal 82 extending from the suction side inner surface 62 towards the pressure side inner surface 72. The pedestal 82 extends towards the pressure side inner surface 72 but is non-contiguous with the pressure side inner surface 72 i.e. the pedestal 82 does not extend the entire way between the suction side inner surface 62 and the pressure side inner surface 72. Similarly, in another embodiment of the aerofoil 5, as depicted in FIG 6, the one or more pedestal 80 having dimpled surface 84 includes at least one pedestal 83 extending from the pressure side inner surface 72 towards the suction side inner surface 62. The pedestal 83 extends towards the suction side inner surface 62 but is non-contiguous with the suction side inner surface 62 i.e. the pedestal 83 does not extend the entire way between the pressure side inner surface 72 and the suction side inner surface 62.

[0035] FIG 7 presents further exemplary embodiments of the aerofoil 5 and the pedestals 80 that are related to embodiments of the pedestals 82 and 83 of the plurality of pedestals 80. In an embodiment of the pedestal 82, the pedestal 82 includes a top surface 88 with dimples, for example the top surface 88 with dimples is spherical cap shaped as shown in FIG 7. Similarly, in an embodiment of the pedestal 83, the pedestal 83 includes a top surface 89 with dimples, for example the top surface 89 with dimples is spherical cap shaped as shown in FIG 7.

[0036] FIG 8 schematically depicts another exemplary embodiment of the aerofoil 5 wherein the one or more pedestal 80 having dimpled surface 84, for example including the pedestals 81, 82 and 83, is positioned in a trailing edge section 99 of the aerofoil 5. The trailing edge section 99 may be understood as an a region of the aerofoil 5 starting at the trailing edge 92 and extending up to a length 98 along a chord 96 of the aerofoil 5. The length 98 is less than 50 percent of a chord length 97 of the chord 96 of the aerofoil 5, and more particularly, the length 98 is less than 25 percent of the chord length 97 of the chord 96 of the aerofoil 5, or the length 98 is less than 10 percent of the chord length 97 of the chord 96 of the aerofoil 5. When the pedestals 80 are located in the trailing edge section 99 with dimensions of less than 25 percent and less that 10 percent, progressively more turbulence is introduced in the cooling air as a result of flow of cooling air over the dimpled surface and thus overall turbulence of the cooling air within the cooling passage is increased and thus overall pressure of the cooling air at the trailing edge section 99 before flow exit through slits 95 is higher than when the cooling air flows through similarly positioned pedestals without the dimpled surface 84.

[0037] While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Claims

1. An aerofoil (5) for a gas turbine engine (10), the aerofoil (5) comprising:

- a pressure side wall (70) and a suction side wall (60) joined at a leading edge (91) and a trailing edge (92), the pressure side wall (70) having a pressure side outer surface (71) and a pressure side inner surface (72), and the suction side wall (60) having a suction side outer surface (61) and a suction side inner surface (62); wherein the pressure side inner surface (72) and the suction side inner surface (62) are opposing surfaces;

- a cooling passage (9) arranged between the pressure side inner surface (72) and the suction side inner surface (62); and

- a plurality of pedestals (80) arranged within the cooling passage (9) and extending longitudinally between the pressure side inner surface (72) and the suction side inner surface (62), wherein the plurality of pedestals (80) comprises one or more pedestal (80) having dimpled surface (84).

2. The aerofoil (5) according to claim 1, wherein the one or more pedestal (80) having dimpled surface (84) comprises at least one pedestal (81) joining the pressure side inner surface (72) and the suction side inner surface (62).

3. The aerofoil (5) according to claim 1 or 2, wherein the one or more pedestal (80) having dimpled surface (84) comprises at least one pedestal (83) extending from the pressure side inner surface (72) towards the suction side inner surface (62) and non-contiguous with the suction side inner surface (62).

4. The aerofoil (5) according to claim 3, wherein the at least one pedestal (83) extending from the pressure side inner surface (72) towards the suction side inner surface (62) and non-contiguous with the suction side inner surface (62) comprises a top surface (89) with dimples.

5. The aerofoil (5) according to claim 4, wherein the top surface (89) with dimples is spherical cap shaped.

6. The aerofoil (5) according to any of claims 1 to 5, wherein the one or more pedestal (80) having dimpled surface (84) comprises at least one pedestal (82) extending from the suction side inner surface (62) towards the pressure side inner surface (72) and non-contiguous with the pressure side inner surface (72).

7. The aerofoil (5) according to claim 6, wherein the at least one pedestal (82) extending from the suction side inner surface (62) towards the pressure side inner surface (72) and non-contiguous with the pressure side inner surface (72) comprises a top surface (88) with dimples.

8. The aerofoil (5) according to claim 7, wherein the top surface (88) with dimples is spherical cap shaped.

9. The aerofoil (5) according to any of claims 1 to 8, wherein the one or more pedestal (80) having dimpled surface (84) is positioned in a trailing edge section (99) of the aerofoil (5).

10. The aerofoil (5) according to any of claims 1 to 9, wherein the one or more pedestal (80) having dimpled surface (84) have elliptical cross-sections.

11. The aerofoil (5) according to claim 10, wherein the elliptical cross-sections are circular cross-sections.

12. A turbine blade (38) for a gas turbine engine (10), wherein the turbine blade (38) comprises an aerofoil (5) according to any of claims 1 to 11.

13. A turbine vane (40,44) for a gas turbine engine (10), wherein the turbine vane (40,44) comprises an aerofoil (5) according to any of claims 1 to 11.

Drawing