EP3341568B1 - Turbine blade with groove in crown base - Google Patents

Description

The invention relates to a turbine blade for use in a gas turbine with a blade root and an airfoil, a cooling air opening being present in the crown base of the airfoil.

Turbine blades for use in a gas turbine are known in various embodiments, these generally having at least one blade root for fastening in the respective turbine stage as well as an airfoil adjoining the blade root. The blade is aerodynamically shaped here, the specific shape initially being irrelevant for the embodiment according to the invention. Here, the blade is initially formed by a blade wall which extends from the blade root to a free end. As a rule, the free end of the blade is closed there by means of a crown base.

State of the art

Because of the high temperatures that occur in a gas turbine, the turbine blade continues to be cooled in a known manner by means of cooling air. Cooling air ducts run through the inside of the turbine blade. Here, both embodiments are known, for example from EP 2 196 625 A1 , in which the cooling air is returned to the blade root, and also cooling air openings are arranged in the blade wall and in the crown bottom, through which the cooling air can escape. The latter show for example GB 2 061 400 , US 2002/119045 A1 and US 2005/281671 A1 . Further known embodiments for a turbine blade with cooling channels are disclosed in the publications EP 1 557 553 A1 as well as the EP 2 863 013 A1 . For the targeted determination of the cooling air flow through the cooling air openings which are generally present in large numbers on the blade blade, these cooling air openings are distributed in a correspondingly suitable manner and usually as round ones Drilling carried out. In addition, designs are also known in which the cooling air openings open in a funnel shape.

Although an advantageous cooling of the airfoil can already be brought about with the known embodiments, the problem arises, however, that zones of different temperatures arise as a result of the airfoil cooling and thus local thermal stresses arise. These show up in a special way in the crown base, due to the high outside temperatures and the lower inside temperatures in the blade due to the cooling air.

Description of the invention

The object of the present invention is therefore to reduce thermal stresses due to differing temperature distributions in the airfoil.

The object set is achieved by an embodiment according to the invention according to the teaching of claim 1.

Advantageous embodiments are the subject of the subclaims.

A turbine blade of the generic type is initially used for a turbine of a gas turbine. Here, the turbine blade has a blade root and an airfoil adjoining the blade root. The blade is aerodynamically curved, so that the turbine blade can be used to effectively generate a rotation in the rotor of the gas turbine. The blade is initially formed by a blade wall which extends from the blade root in the direction of a free end. The blade wall comprises a pressure-side wall section and a suction-side wall section, both of which extend from a leading edge (usually rounded) of the blade to a rear edge (usually tapering to a point) of the blade. At the free end of the blade a crown bottom is arranged, which the The blade essentially shoots at the free end. With regard to the specific arrangement of the crown bottom at the free end of the blade, it is initially irrelevant whether the crown bottom is arranged directly at the end of the blade wall and at the same time forms the free end of the blade or whether the crown bottom is positioned set back from the outer free end of the blade.

The blade wall with the two wall sections, the crown base and the blade flow form a cavity which encloses at least a first and a second flow chamber. In this regard, it is irrelevant whether further flow chambers are formed in the interior of the airfoil. At least the first flow chamber is separated from the second flow chamber by a first partition. Both the first and second flow chambers and the first partition wall likewise extend from the blade root in the direction of the free end of the blade. At the end of the first partition wall facing the crown bottom there is a free opening which forms a connection between the first and second flow chambers so that the cooling air coming from the second flow chamber can flow through the opening into the first flow chamber. In this case, it is initially irrelevant whether the opening extends over the entire width of the partition and thus limits it towards the top or has a smaller width than the partition and thus a piece of the partition remains on one and / or the other side.

Furthermore, the generic turbine blade has at least one cooling air opening in the crown base which opens into the first and / or second flow chamber and through which cooling air can consequently escape from the interior of the turbine blade to the free end. The cooling air opening is arranged at a distance from the wall sections, the exact position initially being irrelevant. The object is now achieved according to the invention in that instead of a further distribution of cooling air openings over the surface of the crown base, at least one cooling air opening is designed as a relief groove, which is arranged above the first opening.

According to the invention, two embodiments come into consideration for implementation, a single relief groove being used in a first embodiment according to the invention. In a second embodiment according to the invention, on the other hand, it is provided that at least two relief grooves are used, which are to be arranged offset next to one another above the first opening.

Here, the one relief groove or the relief grooves together have at least one minimum length which corresponds to half the width of the partition. By introducing a relief groove with a minimum length of at least half the width of the partition wall, thermally induced material expansion in the upper area of the crown base in the area of the relief groove is made possible without the high thermal stresses that otherwise occur due to the temperature differences.

The width of the partition wall is measured in this case at the end of the partition wall under the crown base (if the first opening does not extend over the entire width) or adjacent to the first opening (if the first opening extends over the entire width) as the distance between the pressure-side wall section and the suction-side wall section.

The length of the relief groove can be determined in two ways. On the one hand, the immediate length can be measured from one end of the relief groove to the other end of the relief groove, regardless of its shape, ie the length of a straight connecting line of the two ends of the respective relief groove. However, this must be taken into account for the effectiveness of the reduction of thermally induced stresses the shape of the relief groove in relation to the position of the partition. Therefore, on the other hand, the effective minimum length of the individual relief groove or of the relief grooves together is measured in a direction transverse to the first partition. In other words, in this case the minimum length corresponds to a perpendicular to the partition wall, which on surfaces parallel to the first partition wall through the respective end of the individual relief groove or the common relief grooves. In the case of a single relief groove oriented essentially perpendicular to the first partition wall, the immediate length thus corresponds to the minimum length. If two or more relief grooves are present, this consideration applies with regard to the effective minimum length when considering the two or more relief grooves together, measured in a direction transverse to the first partition.

An essential factor for the development of the thermal stresses is the presence of the partition wall, which has a lower temperature and therefore lower thermal expansion due to the cooling air, while the outside of the crown base, on the other hand, is subject to greater material expansion due to the high temperatures prevailing in the gas turbine. Furthermore, in order to effectively reduce the thermally induced stresses, it is therefore necessary for the individual relief groove to extend on both sides beyond the first opening and thus beyond the first partition wall located below. If two or more relief grooves are considered together, they must extend beyond the first partition on both sides, analogous to the design with a single relief groove.

With at least two relief grooves, these must overlap in such a way that there is an interruption in the crown base in the connection from the pressure-side wall section to the suction-side wall section in the area of the first partition wall, above the first opening. The two or more relief grooves are the same as when using one to arrange individual relief grooves in such a way that they extend beyond the opening on both sides when viewed together. Furthermore, each of the at least two relief grooves must extend at least as far as the breakthrough.

Regardless of the first or second embodiment, however, it is irrelevant whether there are additional groove-like cooling air openings in the crown base in addition to the individual relief groove or the relief grooves under consideration.

Furthermore, there are at least a second partition and a third flow chamber. The second partition wall also adjoins the second flow chamber and is located opposite the first partition wall in connection with the pressure-side wall section and the suction-side wall section. A second free opening is also located above the second partition. Adjacent to the second partition, opposite the second flow chamber, there is a third flow chamber, with cooling air being able to flow through the second opening from the third flow chamber to the second flow chamber.

In this case, the third flow chamber advantageously adjoins an inflow-side edge of the airfoil or a front edge which, opposite to the rear edge, connects the pressure-side wall section with the suction-side wall section.

The size of the second opening is initially insignificant, this advantageously being at least twice the size of the first opening. In other words, the free cross section of the first opening is a maximum of 0.5 times the free cross section of the second opening. However, it is particularly advantageous if the second opening is at least five times the size of the first opening. Both the second opening and the width of the second partition wall can have a narrow width Advantageously, the second opening extends over the width of the second partition wall and insofar limits it upwards on the side facing the crown base.

To compensate for thermal deformations to avoid inadmissibly high thermal stresses, it is also advantageous if the individual relief groove or the two or more relief grooves are located essentially centrally between the suction-side wall section and the pressure-side wall section in the crown base. The exact position, on the other hand, is irrelevant if a thermally induced expansion of the upper side of the crown base is possible on both sides due to the relief groove or relief grooves.

It is also advantageous if the individual relief groove or, in an alternative embodiment, the two or more relief grooves are located essentially in the center of the partition. Since, in particular, the first partition is responsible for the thermal stresses in the crown base, it is correspondingly advantageous to arrange the relief groove or the relief grooves in the center of this first partition. If the length of the relief groove is extended beyond the required dimension, it is of secondary importance whether the extension is only on one side from the partition.

The specific alignment of the relief groove or the several relief grooves is initially irrelevant, provided that a corresponding thermal expansion of the crown base on the outward-facing side is possible due to the presence of the relief groove. However, when using a single relief groove, it is particularly advantageous if the relief groove extends essentially transversely to the first partition. A rectilinear right-angled alignment is not necessary here, but it is sufficient if the relief groove runs in accordance with the course of the pressure-side wall section and the suction-side wall section. In this respect, for example, are angular deviations from 15 ° from an orientation perpendicular to the partition wall is irrelevant.

Furthermore, when arranging at least two relief grooves connected to the opening, it is advantageous if these are each arranged at an angle with respect to a perpendicular to the partition wall. An arrangement that is essentially parallel to one another and offset in the longitudinal direction of the relief grooves is thus promoted. Nevertheless, the angular deviation from an alignment perpendicular to the partition should, if possible, not be more than 45 °, particularly advantageously not more than 30 °.

The effectiveness of the relief groove is improved in a particularly advantageous manner if the individual relief groove has an effective minimum length corresponding to the width of the partition, i.e. the minimum length corresponds to at least 1 times the width of the first partition.

Since the web between the relief grooves in the crown base causes a certain stiffening, it is advantageous in this second embodiment if each of the relief grooves has a length of at least 0.3 times the width of the first partition. The length of the respective relief grooves is particularly advantageously at least 0.5 times the width of the first partition.

It is also advantageous if the minimum length of the at least two relief grooves together corresponds to at least 0.7 times the width of the first partition. In this second embodiment, it is particularly advantageous if the relief grooves together have a minimum length of at least 1 times, preferably 1.2 times the width of the first partition.

Furthermore, it is advantageous if the first opening is used primarily to relieve the crown base and then to guide the cooling air. It is particularly advantageous if the height of the first opening, measured from the inwardly facing underside of the crown base to the greatest distance of the first opening to the crown base, corresponds to a maximum of twice the thickness of the crown base.

In any case, to enable the thermally induced expansions in the crown base, it is particularly advantageous if the height (as stated above) of the first opening corresponds to at least 0.5 times the thickness of the crown base.

A cooling air flow through the relief groove or the relief grooves with at the same time a - in particular multiple - deflected flow within the airfoil through the first and second flow chambers is favored if the first opening is advantageously chosen not to be excessively large. Therefore, the first opening advantageously has a free cross section (area size of the first opening viewed in a plane of the first partition) which is a maximum of 0.8 times the smallest free cross section (viewed in an area parallel to the top of the crown base) individual relief groove in the first embodiment or the at least two relief grooves together in the second embodiment.

In this case, however, the free cross section of the first opening should advantageously correspond to at least 0.2 times the free cross section of the relief groove or the relief grooves.

The course of the relief groove or the relief grooves is initially irrelevant, a straight course being selected in the simplest way. Alternatively, it is also possible that the side surface of the relief groove or grooves facing the pressure-side wall section has or have an arcuate course corresponding to the curvature of the pressure-side wall section. Analogously, it is possible for the side surface of the relief groove or relief grooves facing the suction-side wall section to form one has or have arcuate course corresponding to the curvature of the suction-side wall section. In this respect, the relief groove follows the course of the pressure-side or suction-side wall section.

With regard to the use of the cooling air emerging from the relief groove and taking into account the cooling air flow from the second flow chamber to the first flow chamber that prevails in the airfoil, it is also advantageous if the relief groove is inclined. For this purpose, it is advantageous if the end of the relief groove pointing away from the blade root, d. H. the end of the relief groove facing the outside, closer to the pressure-side wall section than the end of the relief groove facing the blade root, d. H. the end of the relief groove adjacent to the opening is located.

Furthermore, to limit the flow in the relief groove and taking into account the manufacturing possibilities, one relief groove or at least one of the two or more relief grooves widens starting from a smallest free cross section to one end or to both ends of the respective relief groove . In this respect, the flow out of the first flow chamber is limited by the smallest free cross section, the widening of the relief groove simplifying its production.

The relief groove according to the invention is used in a particularly advantageous manner in a partition wall in which the first flow chamber is arranged on an edge or rear edge of the airfoil on the outflow side. The rear edge adjoining the first flow chamber connects the pressure-side wall section with the suction-side wall section. In this regard, it is unimportant whether there are elements for flow guidance and / or stiffening of the airfoil in the first flow chamber facing the edge on the outflow side.

In a particularly advantageous manner, the cooling air flowing through the turbine blade is guided essentially through the second opening, but only to a small extent through the first opening. For this purpose, the first opening has a free cross section of at most 0.1 times the free cross section of the second opening.

When using a first partition and a second partition to subdivide the cavity present in the airfoil into a first flow chamber, a second flow chamber and a third flow chamber, it is particularly advantageous if the first flow chamber and the first partition are on the side facing the downstream edge and the the third flow chamber and the second partition wall is arranged on the side of the airfoil facing the edge on the inflow side.

Furthermore, it is advantageous if there is also a free third opening at the end of the first partition facing the blade root, so that the cooling air from the third flow chamber via the second opening into the second flow chamber and partly via the first opening and mostly via the third opening can flow into the first flow chamber.

Various options are available with regard to the arrangement of the crown base on the bucket wall. In a first and simple embodiment, the crown base is located exactly at the end of the blade wall and thus forms the end of the blade. On the other hand, however, it is advantageous if the crown base is set back with respect to the end of the blade wall, and in this respect, at least in sections, the pressure-side wall section and / or the suction-side wall section protrudes beyond the crown base. In another alternative, it is also possible to place the crown bottom at the end of the To arrange the blade wall, but to provide further ribs or webs or the like above the crown base. Furthermore, a coating is advantageously applied to the crown base. Here, on the one hand, it can be provided that a coating is applied before the relief groove is produced. On the other hand, it is advantageous if a coating is applied to the crown base provided with the relief groove. The second variant offers the particular advantage that the coating can be applied at least partially to the outside ends of the side surfaces of the relief groove, whereby its gap width is reduced. Thus, the cooling air flow through the relief groove can be reduced, the desired

Sufficient expansion space is retained.

Brief description of the figures

In the following figures, an exemplary turbine blade with exemplary sketched relief grooves is shown.

Show it:

FIG 1

a turbine blade for an example of the invention;

FIG 2

a section through the airfoil centrally between the pressure-side and the suction-side wall section;

FIG 3

a plan view of the airfoil with a first embodiment of a relief groove;

FIG 4

a top view of the airfoil with an alternative arrangement of relief grooves;

FIG 5

a section through the airfoil parallel to the first partition wall with an inclined relief groove;

FIG 6

a cut analog FIG 5 with a widening relief groove.

Presentation of the invention

The FIG 1 shows an example of a turbine blade 01 with a blade root 02 and an airfoil 03 adjoining the blade root. The embodiment of the blade root 02 is irrelevant for the present invention and in this respect will not be discussed in more detail in this respect. The blade 03 comprises first of all the blade wall 04, which in this exemplary embodiment is formed by a pressure-side wall section 05 (in the drawing plane at the front) and a suction-side wall section 06 (in the drawing plane at the rear), which 05, 06 extend from a leading edge to extend to a trailing edge. Here, the blade wall 04 encloses a cavity, which in turn is formed by flow chambers 11, 12, 13. At the free end of the blade 03 is the crown base 07, which 07 in this exemplary embodiment is set back slightly in relation to the end of the blade 03. Within the airfoil 03, the cavity is converted into a first flow chamber 11 between the trailing edge and the first partition 08 and a second flow chamber 12 between the first partition 08 and the second partition 09 and into a third flow chamber by a first partition element 08 and a second partition element 09 13 divided between the second partition wall 09 and the front edge. The relief groove 21 in the crown base 07 can be seen to some extent on the upper side.

The FIG 2 shows now schematically a section through the blade 03 in a view cut centrally between the pressure-side wall section 05 and the suction-side wall section 06. First of all, the blade wall 04 with the leading edge and the trailing edge can be seen. At the top is the crown base 07, which 07 is set back slightly with respect to the end of the blade wall 04. Inside the airfoil 03 are the first partition 08 and the second partition 09, which 08, 09 form the cavity divide inside the airfoil 04 into the first flow chamber 11, the second flow chamber 12 and the third flow chamber 13. In this exemplary example it is provided that a cooling air flow flows from the third flow chamber 13 into the second flow chamber 12 and subsequently into the first flow chamber 11. The cooling air can escape via cooling air bores 18 arranged on the rear edge in the blade wall 04. To realize the transition of the cooling air from the first flow chamber 11 to the second flow chamber 12, there is a second free opening 15 between the second partition wall 09 and the crown base 07.

To reduce the thermal stresses in the crown base 07 according to the invention, a first free opening 14 is also arranged in the first partition 15 at the end facing the crown base 07. Furthermore, there is at least one relief groove 21 in the crown base 07. This 21 extends centrally over the opening 14 and thus enables thermal expansion of the top of the crown base 07 while at the same time holding the pressure-side wall section 05 with the suction-side wall section 06 by the first partition 08.

The FIG 3 now shows a top view of the blade 03, initially again showing the blade wall 04 with the pressure-side wall section 05 and the suction-side wall section 06. Inside the blade 03 below the crown bottom 07 are the first partition 08 and the second partition 09. Above the first partition 08 is the relief groove 21 arranged in the center of the crown bottom 07. In this embodiment, this 21 has a length L, measured transversely to Partition wall, which L corresponds approximately to the width B of the partition wall.

In the following FIG 4 is in a further embodiment analogous to FIG 3 a plan view of the airfoil 03 is outlined. In contrast to the previous embodiment Instead of a single relief groove 21, three relief grooves 22a, 22b and 22c running parallel and offset to one another are now used in the crown base 07. These 22, 22b2, 22c here also extend over the first partition wall 08 and are arranged in the middle of the first partition wall 08. The length L of the three relief grooves 22a, 22b and 22c considered together, measured across the first partition 08, is slightly greater than the width B of the first partition 08.

In the following FIG 5 the relief groove 21 is sketched as an example in a section parallel to the partition wall 08. In contrast to a straight-line embodiment of the relief groove 21 that is possible perpendicular to the crown base 07, the relief groove 21 is placed at an angle in this exemplary embodiment. The top, outward-facing end of the relief groove 21 is located approximately centrally in the crown base 07 between the pressure-side wall section 05 and the suction-side wall section 06. On the side of the opening 14 above the first partition 08, however, the relief groove 21 is closer to the suction-side wall section .

In FIG 6 a further exemplary embodiment for a relief groove 23 is sketched, the representation being analogous FIG 5 is executed. In this exemplary embodiment, the relief groove 23 has a smallest cross section in the middle between the two ends of the relief groove, from which the relief groove 23 widens in both directions, ie inwards and outwards. On the one hand, this enables the cooling air to be limited and, on the other hand, it simplifies the manufacture of the relief groove 23.

Claims (9)

1. Turbine blade (01) for a gas turbine,
   having a blade root (02) and having an aerodynamically curved blade airfoil (03), which (03) has a blade wall (04) and has a crown base (07) which is arranged at the free end of the blade airfoil (03), wherein the blade wall (04) comprises a pressure-side and a suction-side wall section (05, 06) and encloses at least one first and one second flow chamber (11,12), between which (11,12) a first separating wall (08), which connects the wall sections (05, 06), is arranged, wherein the first separating wall (08) has, at the end pointing toward the crown base (07), a through-passage (14) for connecting the first flow chamber to the second flow chamber (11,12), and wherein at least one cooling-air opening is present in the crown base (07),
   the cooling-air opening being formed as a single relief groove (21,23), or being formed by at least two relief grooves (22a,22b,22c) which are arranged next to one another in an offset manner, the individual or combined minimum length (L) of which (21,22a,22b,22c,23) corresponds to at least 0.5 times the width (B) of the first separating wall (08) and which (21,22a,22b,22c,23), on both sides, extends/extend individually or in combination to beyond the through-passage (14), characterized
   in that a second separating wall (09) is arranged adjacent to the second flow chamber (12) and a third flow chamber (13) is arranged opposite the first flow chamber (11), and
   in that a second through-passage (15) is present between the second separating wall (09) and the crown base (07), which (15) has at least 2 times, in particular at least 5 times or in particular at least 10 times, the free cross section of the first through-passage (14).
2. Turbine blade (01) according to Claim 1,
   characterized
   in that the relief groove (21,23) or the relief grooves (22a,22b,22c) in combination is/are arranged centrally between the wall sections (05, 06) and/or centrally with respect to the first separating wall (08).
3. Turbine blade (01) according to Claim 1 or 2,
   characterized
   in that the relief groove (21,23) or the relief grooves (22a,22b,22c) in combination has/have at least a minimum length (L), measured transversely to the separating wall (08), corresponding to the width (B) of the separating wall (08), wherein in particular the relief grooves (22a,22b,22c) each have a length of at least 0.3 times the width (B) of the first separating wall (08).
4. Turbine blade (01) according to one of Claims 1 to 3,
   characterized
   in that the height of the first through-passage (14) perpendicular to the crown base (07) corresponds to at least 0.5 times and/or at most 2 times the thickness of the crown base (07) .
5. Turbine blade (01) according to one of Claims 1 to 4,
   characterized
   in that the free cross section of the first through-passage (14) is at least 0.2 times and/or at most 0.8 times the minimum free cross section of the relief groove (21,23) or of the relief grooves (22a,22b,22c) in combination.
6. Turbine blade (01) according to one of Claims 1 to 5,
   characterized
   in that those side surfaces of the relief groove (21,23) or of the relief grooves (22a,22b,22c) which face the wall sections (05, 06) have a rectilinear profile, or an arcuate profile corresponding to the curvature of the respective wall section (05, 06).
7. Turbine blade (01) according to one of Claims 1 to 6,
   characterized
   in that the first flow chamber (11) is arranged adjacent to an outflow-side edge of the blade airfoil (03).
8. Turbine blade (01) according to one of Claims 1 to 7,
   characterized
   in that the first separating wall (14) is arranged facing the outflow-side edge, and the second separating wall (15) is arranged facing the inflow-side edge, of the blade airfoil (03) .
9. Turbine blade (01) according to one of Claims 1 to 8,
   characterized
   in that the pressure-side and/or the suction-side wall section (05, 06), in particular the blade wall (04), projects beyond the crown base (07) at least in sections.

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