Airfoil for turbine vane or turbine blade of an axial gas turbine

Abstract

The present invention relates to an airfoil (AF), comprising - a suction and a pressure side wall (SW, PW), both walls (SW, PW) extending, from a leading edge (LE) to a trailing edge (TE) and from an inner end (IE) to an outer end (OE), - a first feed plenum (FP1) for a coolant, - at least two cooling circuits (CC1 - CC5), which are located in the suction and / or pressure side wall and which are in flow connection with a first feed plenum, - wherein each cooling circuit comprises a number of channel sections (CS), and an outlet region (OR1-OR5), in which the most downstream arranged channel sections of the respective cooling circuit open out into one the suction and / or pressure side wall of the airfoil, wherein in an overlapping region (PR) of the airfoil, in which the channel sections of different cooling circuits overlaps, the channel sections of the different cooling circuits are arranged alternatingly in a regular pattern.

Description

DescriptionTITLEAirfoil for turbine vane or turbine blade of an axial gas turbineTECHNICAL FIELD

[0001] The present invention relates to an airfoil for a turbine vane or a turbine blade of an axial gas turbine.

[0002] In gas turbines the airfoils of turbine blades and vanes play a critical role in converting the energy of a hot working gas into mechanical work. The reliability and efficiency of the gas turbine depends highly on the reliability and efficiency of the turbine blades and vanes utilized in their turbine section.

[0003] Over recent decades, and even today, gas turbine inlet temperatures haven been and are still increasing to achieve higher gas turbine efficiencies. Therefore, there has been and continues to be a constant need to improve the cooling efficiency, such, that the turbine blades and vanes are able to withstand the hot temperatures of the working gas as long as possible. The state of the art comprises already are a large variety of cooling concepts which addresses both requirements. One example is disclosed in US 7,717,675 B1 , which shows a so- called near-wall cooling of a turbine blade airfoil. According to this publication, several supply channels feed a number of mainly chordwise extending cooling networks located in the suction and pressure side walls of the blade. Further, the leading edge of the airfoil is cooled with the aid of several shower head cooling rows. Further, from EP 2 472 062 B1 it is known to have straight chordwise cooling channels extending from the leading edge to trailing edge of the airfoil. The same discloses US 2022 / 0333490 A1 for cooling the trailing edge of a turbine blade.

[0004] As the trend for higher turbine inlet temperatures and longer lifetimes of turbine blades and vanes is still unbroken, new solutions are needed that enables even higher turbine temperatures and / or longer lifetimes of these parts and especially, of their airfoils. Furthermore, the airfoils have to be capable to be continuously operated with limited operational risk when a foreign object damage (FOD) occurs.SUMMARY OF INVENTION

[0005] Based on this, the objective of the present invention is to provide an airfoil for a turbine vane or a turbine blade of a gas turbine having improved properties in terms of coolant consumption, durability, lifetime and / or FOD capability.

[0006] The solution is an airfoil in accordance with the features of claim 1 . In detail the inventive airfoil for a turbine vane or turbine blade of a gas turbine, comprises- a suction side wall and a pressure side wall for guiding a hot working gas of the gas turbine, both side walls extending, when the airfoil is utilized in a gas turbine, in a chord direction from a leading edge to a trailing edge and in radial direction of said gas turbine from an inner end of the airfoil to an outer end of the airfoil,- for a coolant at least one feed plenum extending in radial direction,- in the suction side wall and / or the pressure side wall at least two cooling circuits, each of which is in flow connection with the at least one feed plenum, wherein each cooling circuit comprises a number of channel sections extending in chord direction, and an outlet region, in which channel sections of the respective cooling circuit open out into one the suction side wall or the pressure side wall of the airfoil, wherein the outlet regions of the different cooling circuits are with respect to the chord direction of the airfoil separated from each other, and wherein in an overlapping region of the airfoil, in which the channel sections of different cooling circuits overlaps, the channel sections of the different cooling circuits arearranged alternatingly, preferably in a regular pattern, facilitated to cool the overlapping region of the airfoil simultaneously.One advantage of this cooling scheme for an airfoil is the very efficient utilization of coolant while achieving a sufficient cooling of an airfoil, even if the airfoil is utilized in a first stage of a turbine section of a stationary heavy-duty gas turbine. This reduction of coolant volume can be used either to increase the gas turbine efficiency and / or the increase the working gas temperature. By having the coolant exit region also significant downstream of the leading edge, i.e., at a larger chordwise distance to the leading edge, the available pressure ratio for the coolant is increased which allows for an optimized distribution of coolant along the chord.

[0008] The arrangement of the channel section of the different cooling circuits in the overlapping region can be regular and / or non-regular. One understanding of a regular pattern is, that along span the sequence of channel sections of the different cooling circuits is each time the same. Hence, another understanding of a regular pattern is the density of channel sections in a respective range of the airfoil span, is constant. E.g., as at the outer end (or inner end) of the airfoil the thermal load from the hot working gas might be higher than at midspan of the airfoil, the density of channel sections next the outer end is constant, but higher as well than the density of channel sections at midspan. This kind of a regular pattern allows a balanced distribution of the locally required cooling capabilities onto the affected cooling circuits. Nonetheless, a regular pattern might be understood as well as an identical radial distance between the channel sections of different cooling circuits.Overall, the invention allows the increase in cooling efficiency through using the coolant flow in the multiple regions along the airfoil chord direction. First, in the leading edge region where high temperature differences occurs and where coolant pressures are necessary to comply with Foreign Object Damage Criteria and where to maintain the low-pressure differences between the coolant feed and the pressure of the hot working gas at the stagnation point. Second, the heatup of the coolant while cooling the leading edge does not fully consume coolant cooling capabilities and therefore, the coolant can be used further downstream of the leading edge to convectively cool other chord areas of the airfoil. This leads to further heat up of the coolant and in turn to a higher cooling efficiency and finally, to an increase of the gas turbine efficiency, equipped with turbine vanes or blades comprising such an airfoil.

[0010] For the sake of clarity, it is mentioned that the terms “radial direction”, “axial direction”, and “circumferential direction” are in reference to the machine axis of the gas turbine, when the airfoil is assembled therein. The “cord direction” is usually a combination of the axial and circumferential direction and depends on a predetermined cross-section of the airfoil and its blade angle. The span direction of the airfoil is identical to the radial direction.

[0011] The terms “upstream” and “downstream” both refer either to the main flow direction of the hot working gas. This is the case when these terms are linked to the surfaces of the side walls or to the airfoil as a whole. Or these terms are referring to the flow direction of the coolant. This is the case when they are linked to the channel sections or cooling circuits.

[0012] The term “overlapping” has to be understood such that in the considered chord region on different span heights cooling channels of different cooling circuits are arranged. I.e. , in this region the cooling channels of different cooling circuits are arranged in different distances to the inner end of the airfoil.

[0013] According to a first preferred embodiment the feed plenum is arranged in a leading edge region of the airfoil. The feed plenum extends in radial direction between the inner and outer end of the airfoil. This enables an effective and efficient cooling of the airfoil region subjected during operation to the highest thermal load. Furthermore, the most upstream arranged channel sections of the different cooling circuits has a channel inlet, wherein the most, preferably all of them are arranged in respect to the chord direction, i.e., chordwise in the same region. Preferably the affected channel inlets are arranged in respect to the chord in the region of the leading edge and most preferably opposite to the leadingedge of the airfoil. This enables in the thermally higher loaded chord regions of the airfoil a higher density of cooling channels of more cooling circuits and in thermally lower loaded chord regions of the airfoil a lower density of cooling channels belonging to lesser cooling circuits,

[0014] In a very preferred embodiment, the most upstream arranged channel section of the respective channel sections are L-shaped when viewed in crosssection of the airfoil, with a first sub-section starting from the first feed plenum, a turning section underneath a stagnation area of the leading edge and a second sub-section extending along the respective side wall in chord direction. This geometric structure of the most upstream channel sections of the respective cooling circuit leads due to flow direction change to thin boundary layers in the coolant flow and consequential to a heat transfer enhancement. The utilization of the heat transfer enhancement in the leading edge, which during operation is thermally loaded most, is most beneficial.

[0015] Further preferred, each of the most downstream arranged channel sections of the resp. cooling circuit open outs into the suction side wall resp. pressure side wall with an outlet, and wherein for at least one cooling circuit, preferable for each cooling circuit, in the proximity of its outlets an exit plenum is arranged, which interconnects the most downstream arranged channel sections of the respective cooling circuit, and which extends in radial direction between the inner end and outer end of the airfoil.

[0016] Advantageously, for at least one cooling circuit, preferable for each cooling circuit an intermediate plenum is arranged which interconnects the channel sections of the resp. cooling circuit, wherein the intermediate plenum extends in radial direction between the inner end and outer end of the airfoil.

[0017] The utilization of exit and / or intermediate plenums facilitate different flow distributions and allows to improve the cooling efficiency further. Besides this, the use of plenums enables the adjustment of coolant flows as well as even coolant flow distribution along span. However, the invention also includes the possibility of not using plenums without redistributing the flow in a plenum.

[0018] Another advantage of using exit and / or intermediate plenums appears when a single or multiple channel sections are defect, e.g., when at least partially or completely blocked by dust and / or other particles carried with the coolant, or when a channel section is uncovered due to a foreign object damage. In these cases, further downstream arranged channel sections remain active as other parallel channel sections, which are connected by the exit and / or intermediate plenums, acts as bypasses for the defect channel section. This increases the reliability of the airfoil in case of defects and prolongs its lifetime. In a very preferred embodiment, some of the channel sections of one cooling circuit of the at least two cooling circuits are arranged between a) a surface of the pressure side wall or suction side wall and b) the exit or intermediate plenum of another circuit of the at least two cooling circuits. This enables an adapted cooling of different regions of the airfoil fitting to the local thermal load. With that, a more uniform thermal temperature distribution can be achieved along the chord direction of the airfoil, which increases the lifetime of the airfoil.

[0020] In one preferred embodiment the respective cooling circuit the number of channel sections located upstream of the intermediate plenum, or the exit plenum and the number of channel sections located downstream of the same plenum are different. This enables an adapted cooling of different chord regions of the airfoil fitting to the local thermal load. With that, a more uniform thermal temperature distribution can be achieved along the chord direction of the airfoil, which increases the lifetime of the airfoil. This allows a high degree of flexibility in the cooling schemes in order to cool the airfoil efficiently and effectively.

[0021] In another advantageous embodiment, the outlet regions of the at least two cooling circuits are located on the same side wall or on different side walls of the airfoil.

[0022] Further preferred, some of the channel sections are located with a distance to the surface of the resp. side wall being designated to not cool the resp. side wall, i.e., which distance is larger than the distance between those channel sections designated to cool the resp. side wall and the surface of that side wall.In the same manner, some channel sections or subsections can extend through a stiffening rib of the airfoil, which connects the suction side wall and the pressure side wall. These features enable the provisioning of less heated coolant to locations of the airfoil which are on larger distances from the feed plenum than the most upstream channel sections of the at least one cooling circuits.

[0023] In a very preferred embodiment of the invention the at least two cooling circuits comprises three, four or five cooling circuits and wherein each of the channel sections are assigned to one of the said three, four or five cooling circuits and / or wherein the at least one feed plenum comprises a second feed plenum. With that, the inventive cooling scheme can be applied multiple times in the same airfoil on different regions for multiplying its benefits of the reduction of coolant consumption and the increase of cooling efficiency.Preferably, when seen in cross section, each outlet region has a cord length of no longer than 20% of the axial chord of the airfoil and / or wherein the chord distance between two adjacent outlet regions is at least 30 % of the axial chord in case of two cooling circuits or at least 20 % of the axial chord in case of three cooling circuits or at least 15 % of the axial chord in case of four or five cooling circuits.

[0025] Of course, the channel sections are arranged in the suction side wall and / or the pressure side wall in a near-wall cooling configuration and / or the outlet is embodied as a film cooling hole. The utilization of the invention is not limited to its application only on the pressure side of the airfoil.

[0026] As the inventive cooling scheme comprises lots of channel sections usually with a diameter in the size between 0,3 - 3,0 mm in the overlapping regions of the airfoil, the preferred manufacturing method is an additive manufacturing process, especially by laser powder-bed fusion, which leads to monolithic airfoil design, i.e. , the modular design known from the prior art with increases assembly efforts can be avoided.

[0027] A turbine blade or turbine vane comprising an airfoil according to one of the preceding claims.

[0028] Other embodiments, features, and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the invention.BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG 1 is a cross-section through an airfoil in accordance with a first exemplary embodiment of the invention,

[0030] FIG 2 is schematic perspective view onto the airfoil according to the first embodiment,

[0031] FIG 3 is a schematic cross-section through an airfoil in accordance with a second exemplary embodiment of the invention, and

[0032] FIG 4 shows the detail X of FIG 3.DESCRIPTION OF EMBODIMENTS

[0033] FIG 1 shows schematically a cross-section through an airfoil AF in accordance with a first exemplary embodiment of the invention. The plane of the cross-section plane is arranged perpendicular to a radial direction RD (FIG 2). With that, FIG 1 shows as the outer contour of the airfoil AF a profile, which represents the surface of the airfoil AF as well. The surface is during operation in contact with the hot working gas of the gas turbine.

[0034] Like conventional airfoils of prior known turbine blades or turbine vanes of gas turbines, the airfoil comprises a suction side wall SW and a pressure side wall PW, which are merging into one another at a leading edge LE and at a trailing edge TE of the airfoil AF, whereas the terms leading and trailing refers to the flow direction of the hot gas working of the gas turbine.Perpendicular to this, in radial direction, the airfoil AF and with that, the suction side wall SW and the pressure side wall PW, the leading edge LE and the trailing edge as well extent with a span from an inner end IE to an outer end OE. When the airfoil AF is part of a turbine blade (not shown), at the inner end IE usually a platform is arranged. In the same manner, when the airfoil AF is part of a turbine vane (not shown as well), usually at the inner end IE and at the outer end OE comprises a platform. Those platforms are also known as shrouds. A chord direction CD extends from the leading edge LE to the trailing edge TE and is arranged in the plane of the cross-section.

[0036] Next, the invention will be explained in more detail with reference to FIG1 and FIG 2. In or directly adjacent to the leading edge LE a first feed plenum FP1 is arranged, which can be supplied with a coolant, e.g., compressor air, in a conventional manner. In accordance with the first exemplary embodiment of the invention, the airfoil AF comprises four - a first, a second, a third and a fourth - cooling circuits CC1 , CC2, CC3, CC4, although the fundamental idea of the invention can be realized with just two cooling circuits. Each of them comprises a number of channel sections CS. The cooling circuits CC1 , CC2, CC3, CC4 are located on the pressure side of the airfoil AF and with that, in the pressure side wall PW, as a near-wall cooling configuration. The channel sections CS in general extend in chord direction CD.

[0037] Although channel section CS of the different cooling circuits are shown in all figures as lines with distinctive styles, it has to be understood that the lines shall represent conventional cooling channels or passages in the airfoil AF with preferably circular, elliptical or rectangular shapes. A typical diameter of the cooling channels is in the range between 0,3 and 3,00 mm, depending on the size of the airfoil and the local cooling requirements. Rectangular shapes offer larger surfaces and larger cross sections.

[0038] The most upstream arranged channel sections CSU of the four cooling circuits CC1-CC4 are connected with the first feed plenum FP1. Their channel inlets Cl are preferably all arranged in the same chord region and in accordancewith the shown exemplary embodiment next to the leading edge LE. Downstream of the channel inlet the most upstream arranged channel sections CSU extend in the pressure side wall directly underneath the surface of the airfoil along the chord. In such a case and during operation, the coolant flowing through these sections are effectively cooling respective side wall sections.

[0039] Contrary to this, sub-sections NCC of the channel sections CS of the third and fourth cooling circuits CC3, CC4 are arranged on a larger distance to the surface than channel sections CS of the first and second cooling circuits CC1 , CC2. Those sub-sections are designated to not cool the side walls effectively. Their objective is to forward already heated up coolant, without or with lowest possible heating, to chord regions where said coolant can still be utilized to cool the side wall.Each of a most downstream arranged channel sections CSD of the four cooling circuits CC1-CC4 ends in an outlet OT, which is arranged in the surface of the airfoil AF. Preferably, the outlets OT can be embodied as a conventional film cooling hole. The outlets OT of the different cooling circuits CC1-CC4 are distributed along the chord direction CD, cf. FIG 2.

[0041] The arrangement of channel sections CS as displayed in FIG 1 is multiple times present on different span levels of the airfoil AF. The stacking of these arrangements is schematically shown in FIG 2, wherein therebetween other arrangements with less channel sections are arranged as well. Hence, the outlets OT of the same cooling circuit CC1-CC4 are arranged in spanwise extending rows. The size of a region in chord direction, in which the outlets OT of the same cooling circuit are arranged, is relatively short. This region, also mentioned herein as outlet region OR, has preferably a size of at most 20% of the chord length of the airfoil AF. Depending on the number of cooling circuits, the distances in chord direction between the outlet regions is at least 15%, or 20% or 30% of the total chord. With that, channel sections belong to the same cooling circuit, when their outlet OT is in the same outlet region.(8(M 2] Alternatively, channel sections belong to the same cooling circuit when they are connected by either exit plenums EP1-EP4 and / or intermediate plenums IP2- IP4. The cooling circuit CC1 comprises just the exit plenum EP1 , whereas the cooling circuits CC2, CC3 and CC4 each comprises both, one exit plenum EP2, EP3, EP4 and one intermediate plenum IP2, IP3, IP4. More intermediate plenums per cooling circuit are possible. In figures 1 , 3 and 4 the exit plenums EP1-EP5 and the intermediate plenums IP2-IP4 are shown as filled circles and in FIG 2 as bold lines extending in spanwise direction between inner end IE and outer end OE. In this case each cooling circuit is separated from the other ones.

[0043] As exemplarily and only schematically shown in FIG 2 as well, sub-sections of the most upstream channel sections CSU of all four cooling circuits CC1 , CC2, CC3, CC4 overlaps in an overlapping region PR, wherein in accordance with the invention they are arranged in an alternating, preferably regular pattern along span direction. The feed plenum is not shown in FIG. 2.It is to mention that FIG. 1 does not reflect that in the overlapping region PR the subsections of all most upstream channel sections CSU of the four cooling circuits are arranged with the same distance towards the pressure side surface, such, that they all contribute - to at least a similar extent - to cool this wall region.Between the outlet region OR1 and outlet region OR2 another overlapping region exists, as well between outlet region OR2 and outlet region OR3, but each time with a stepwise reduced density of channel sections. The pattern in the different overlapping regions OP can differ as well and with that, the density of channel sections CS which cools the side wall can be different in different chord regions: In an intermediate regions IR2, arranged between outlet regions OR1 and OR2, the density of channel sections, which are designated to cool the side wall, is lower than in the overlapping region PR. The same is valid for other intermediate regions IR3 and IR4, wherein the intermediate regions IR2, IR3 and IR4 comprises the same density of channel sections between their intermediate plenums IP2, IP3, IP4 and their exit plenums EP2, EP3, EP4, which are designated to cool the side wall. It is worth noting that in the most downstreamlocated intermediate region, in this example in IR4, no overlapping of different cooling circuits resp. of the cooling channels takes place.[80-F] In the area of the one exit plenum the channel sections of other cooling circuits can be arranged not in the interior of the airfoil, as mentioned above, but close to the surface as well. This is exemplarily shown on position QW, where the most upstream located channel section CSU of the second cooling circuit CC2 is between the exit plenum EP of the first cooling circuit CC1 and the surface of the pressure side wall PW.As shown in FIG 2, the number of channel sections counted along the span upstream of the exit plenum plenum is different to the number of the channel sections of the same cooling circuits located downstream of the respective plenum.

[0047] The cooling of the suction side wall SW and / or remaining regions, e.g., the trailing edge TE can be performed in a conventional manner, e.g., as shown in the prior art.

[0048] Turning to a second exemplary embodiment of the invention, FIG 3 shows schematically a cross-section through another airfoil AF. Features being identical to the first exemplary embodiment are not described again. In the following only the differences to the first exemplary embodiment are described in detail.

[0049] In contrast to the first exemplary embodiment the second exemplary embodiment comprises a second feed plenum FP2 in mid chord region between leading edge LE and trailing edge TE. This second feed plenum FP2 is linked to the fourth cooling circuit CC4 and replaces - only for the fourth cooling circuit CC4 - the feed plenum FP1. Another difference is that no cooling circuit comprises an intermediate plenum.

[0050] The next difference is that on the suction side wall SW as well two cooling circuits CC3, CC5 are arranged, creating another overlapping region OP directly downstream of the leading edge LE. A further difference is that the third cooling circuit CC3 comprises a channel section with three sub-sections CSS1 , CSS2and CSS3. A first sub-section CSS1 is located in the suction side wall SWfor cooling the respective region, and not on the pressure side anymore. A second sub-section CSS2 acts a transfer channel for guiding the coolant from the suction side to the pressure side of the airfoil and a third sub-section CSS3 acts again as a cooling passage in mid chord region of the pressure side wall PW, before it merges into the exit plenum EP of the third cooling circuit CC3. With that, the most upstream channel section of the third cooling circuit CC3 comprises the three sub-sections CCS1 - CSS3. The second sub-section CSS2 is located in a stiffening rib SR, which connects the suction side wall SW and the pressure side wall PW and which separates the two feed plenums FP1 , FP2 from another.

[0051] The detail X of FIG 3 is repeatedly shown in a larger scale in FIG 4, for clearly showing two features. At first, the structure of the most upstream located channels sections CSU comprising a first sub-section FL and a second subsection SL, and therebetween a turning section. Each of the most upstream located channels sections CSU and therefore each of the first sub-section FL has at the feed plenum FP1 a channel inlet Cl. These channel inlets are arranged again in the same chordwise region, i.e. , in cross section as shown in FIG 3 and 4, as the leading edge LE of the airfoil AF. In detail, the channel inlets Cl are located in the internal surface which renders the feed plenum FP1 so that they are located opposite of the leading edge The first sub-section FL is rather short and extents perpendicular into the wall of the leading edge LE. The turning section acts similar like an impingement channel section with increased heat transfer capability. Hence, the shown structure is very beneficial when applied in the area with the highest thermal load, i.e., in the leading edge. With that, a shower head cooling of the leading edge can be avoided, which contributes to coolant savings as well. With that, the four most upstream channel sections CSU are L-shaped, when seen in cross section.

[0052] At second, in the area of the exit plenum EP1 the channel sections of the second cooling circuit CC2 is between the exit plenum EP1 of the first cooling circuit CC1 and the surface of the pressure side wall PW. In this case the most downstream located channel section CSD of the first cooling circuit CC1 and themost upstream located channel section CSU of the second cooling circuit CC2 do not merge into one another, they are spanwise arranged with an offset.

Claims

Claims1 . An airfoil (AF) for a turbine vane or turbine blade of a gas turbine, comprising:- a suction side wall (SW) and a pressure side wall (PW) for guiding a hot working gas of the gas turbine, both side walls (SW, PW) extending, when the airfoil (AF) is utilized in a gas turbine, in chord direction (CD) of said gas turbine from a leading edge (LE) to a trailing edge (TE) and in radial direction (RD) of said gas turbine from an inner end (IE) of the airfoil to an outer end (OE) of the airfoil,- at least one feed plenum (FP1 , FP2) for a coolant (CM) extending in radial direction (RD) ,- in the suction side wall (SW) and / or the pressure side wall (PW) at least two cooling circuits (CC1 - CC5) and which are in flow connection with a first feed plenum (FP1 ) of the at least one feed plenum (FP1 , FP2),- wherein each cooling circuit (CC1 - CC5) comprises a number of channel sections (CS) extending in chord direction (CD), and an outlet region (OR1 - OR5), in which the most downstream arranged channel sections (CS) of the respective cooling circuit (CC1 - CC5) open out into one the suction side wall (SW) or the pressure side wall (PW) of the airfoil (AF), wherein the outlet regions (OR1 -OR5) of the different cooling circuits (CC1 - CC5) are with respect to the chord direction (CD) of the airfoil (AF) separated from each other, wherein in an overlapping region (PR) of the airfoil (AF), in which the channel sections (CS) of different cooling circuits (CC1 - CC5) overlaps, the channel sections (CS) of the different cooling circuits (CC1 - CC5) are arranged alternatingly, preferably in a regular pattern, facilitated to cool this overlapping region of the airfoil simultaneously.

2. The airfoil (AF) according to claim 1 , wherein a first feed plenum (FP1 ) is arranged in a leading edge region of the airfoil (AF) and which extends in radial direction (RD) between the inner (IE) and outer end (OE) of the airfoil (AF)3. The airfoil (AF) according to claim 1 or 2, wherein each of the most upstream arranged channel sections (CSU) of the different cooling circuits has a channel inlet (Cl), wherein the most, preferably all of them are arranged with respect to the chord direction in the same region and preferably of in the region the leading edge (LE) and most preferably opposite to the leading edge (LE) of the airfoil (AF).

4. The airfoil (AF) according to claim 1 or 3, wherein the most upstream arranged channel sections (CSU) of the respective channel section are - in cross-section of the airfoil - L-shaped, with a first subsection (FL) starting from the first feed plenum (FP1), a turning section underneath a stagnation area of the leading edge and a second sub-section (SL) extending along the respective side wall (PW, SW).

5. The airfoil (AF) according to one of the preceding claims, wherein each of the most downstream arranged channel sections (CS, CSD) of the resp. cooling circuit (CC1 - CC5) open outs into the suction side wall (SW) resp. pressure side wall (PW) with an outlet (OT), and wherein for at least one cooling circuit (CC1 - CC5), preferable for each cooling circuit (CC1 - CC5), in the proximity of the outlets (OT) an exit plenum (EP) is arranged, which interconnects the most downstream arranged channel sections (CSD) of the respective cooling circuit (CC1 - CC5), and which extends in radial direction between the inner end (IE) and outer end (OE) of the airfoil (AF).

6. The airfoil (AF) according to claim 5, wherein some of channel sections (CS) of one cooling circuit (CC1 - CC5) of the at least two cooling circuits (CC1 - CC5) are arranged between a surface (SE) of the respective side wall (SW, PW) and the exit plenum (EP) of another circuit (CC2, CC1 ) of the at least two cooling circuits (CC1 - CC5).

7. The airfoil (AF) according to one of the preceding claims, wherein for at least one of the cooling circuits (CC1-CC5) an intermediate plenum (IP2-IP5) is provided, which interconnects the channel sections (CS) of the resp. cooling circuit (CC1-CC5), and which extends in radial direction (RD) between the inner end (IE) and outer end (OE) of the airfoil (AF).

8. The airfoil (AF) according to claim 5, 6 or 7, wherein the number of channel sections (CS) located upstream of the intermediate plenum (IP) or exit plenum (EP) and the number of channel sections (CS) located downstream of the same plenum (IP, EP) are different.

9. The airfoil (AF) according to one of the preceding claims, wherein the outlet regions (0R1-0R5) of the at least two cooling circuits (CC1- CC5) are located in the same side wall (SW, PW) and / or in different side walls (SW, PW).

10. The airfoil (AF) according to one of the preceding claims, wherein some (NCC, CCS2) of the channel sections (CS) or subsections are located with a distance to the surface (SE) of the resp. side wall (SW, PW) and designated to not cool the resp. side wall (SW, PW), i.e. , their distance is larger than the distance between those channel sections designated to cool the resp. side wall and the surface of that side wall.11 . The airfoil (AF) according to one of the preceding claims, wherein the at least two cooling circuits comprises three, four or five cooling circuits (CC1-CC5) each comprising a number of channel sections (CS) and / or wherein the at least one feed plenum (FP1 , FP2) comprises a second feed plenum (FP2).

12. The airfoil (AF) according to one of the preceding claims, wherein each outlet region (0R1-0R5) has a cord length of no longer than 20% of the axial chord of the airfoil (AF) and / or wherein the chord distance between two adjacent outlet regions (OR1-OR5) is at least 30 % of the axial chord in case of two cooling circuits (CC1 - CC5) or at least 20 % of the axial chord in case of three cooling circuits or at least 15 % of the axial chord in case of four or more cooling circuits.

13. The airfoil (AF) according to one of the preceding claims, wherein the channel sections (CS) are arranged in the suction side wall (SW) and / or the pressure side wall (PW) in a near-wall cooling configuration and / or the outlet (OT) is embodied as a film cooling hole (FCH).

14. The airfoil (AF) according to one of the preceding claims, wherein the airfoil (AF) is monolithic and / or manufactured by an additive manufacturing process, especially by laser powder-bed fusion.