Turbine blade and turbine with improved sealing

Abstract

The disclosure pertains to a turbine with a gas turbine blade and a rotor heat shield for separating a space region through which hot working medium flows from a space region inside a rotor arrangement of the turbine. The rotor heat shield includes a platform which forms an axial heat shield section and which is arranged substantially parallel to the surface of a rotor and a radial heat shield section at the upstream end of the axial heat shield section, which is extending in a direction away from the surface of the axial heat shield section towards the hot gas. Further the turbine comprises a blade rear cavity which is delimited by the downstream end of the platform and/or the downstream end of the blade foot, the radial heat shield section. The disclosure further refers to a gas turbine blade and a rotor heat shield designed for such a turbine.

Claims

1. A gas turbine blade comprising: a blade platform having a trailing edge side, a pressure side, a suction side, and a leading edge side; an airfoil connected to the blade platform, and a first groove formed in the trailing edge side of the platform, wherein the first groove extends between the pressure side and the suction side, and wherein the first groove extends in an axial direction below a root of a trailing edge of the airfoil, the first groove configured so that the trailing edge side of the blade platform is not rigidly connected to a foot of a blade, a trailing edge side seal groove formed in the trailing edge side of the blade platform closer to a platform surface of the blade platform facing the airfoil than the first groove, wherein the trailing edge side seal groove extends between the pressure side and the suction side, and wherein a depth of the trailing edge side seal groove in axial direction is smaller than a depth of the first groove; a main seal above the first groove; and a rear seal positioned adjacent the first groove below the trailing edge side seal groove, the rear seal extending radially from the main seal to the foot of the blade to control leakage from the blade to a heat shield cavity of a heat shield downstream of the blade; an upper seal above the first groove, a portion of the upper seal positioned in the trailing edge side seal groove of the blade platform; and a lower seal below the first groove that extends between the foot and the heat shield to separate a blade rear cavity from the heat shield cavity.

2. The gas turbine blade according to claim 1, wherein the first groove has an axial depth that enters into a line of stress created by a blade load.

3. The gas turbine blade according to claim 1, wherein the trailing edge side seal groove is configured to hold a strip seal.

4. The gas turbine blade according to claim 1, wherein the blade comprises a seal groove extending to the trailing edge of the blade platform on the pressure side of the blade platform and/or on the suction side of the blade platform for receiving the main seal above the first groove.

5. The gas turbine blade according to claim 1, wherein the blade comprises a seal groove on the pressure side of the platform and/or on the suction side of the platform for receiving the rear seal extending radially inwardly below the first groove.

6. A gas turbine rotor heat shield for separating a space region through which hot working medium flows from a space region inside a rotor arrangement of a gas turbine through which coolant flows, comprising: a platform which forms an axial heat shield section and which is arranged substantially parallel to a surface of a rotor, wherein the rotor heat shield includes a radial heat shield section arranged at one end of an axial heat shield section, the radial heat shield section extending radially in a direction away from a surface of the axial heat shield section towards a hot gas side of the heat shield; a first end of the radial heat shield section being adjacent an upper seal extending between the rotor heat shield and a blade platform; a second end of the radial heat shield section being adjacent the axial heat shield section; a blade rear cavity being defined between the radial heat shield section, the upper seal, and the blade platform such that a heat shield cavity of the rotor heat shield and the blade rear cavity are independently suppliable with coolant; and a lower seal that separates the heat shield cavity from the blade rear cavity below the upper seal.

7. The gas turbine rotor heat shield according to claim 6, wherein the radial heat shield section is extending at an angle of more than 30° in a direction away from the surface of the axial heat shield section towards the hot gas side.

8. The gas turbine rotor heat shield according to claim 6, wherein the radial heat shield section comprises a kink to bridge a gap between the blade platform and the rotor heat shield for holding the upper seal.

9. A turbine comprising: a blade comprising: a blade platform having a trailing edge side, a pressure side, a suction side, and a leading edge side; an airfoil connected to the blade platform, and a first groove formed in the trailing edge side of the blade platform, wherein the first groove extends between the pressure side and the suction side and wherein the first groove extends in an axial direction below a trailing edge of the airfoil, and a rotor heat shield for separating a space region through which hot working medium flows from a space region inside a rotor arrangement of the turbine, wherein the rotor heat shield comprises an axial heat shield section which is arranged substantially parallel to a surface of a rotor of the rotor arrangement, wherein the rotor heat shield comprises a radial heat shield section at an upstream end of the axial heat shield section, the radial heat shield section extending in a direction away from a surface of the axial heat shield section towards a hot gas side of the rotor heat shield such that a blade rear cavity is defined between the radial heat shield section and at least one of the blade platform and a foot of the blade; a main seal above the first groove and above the blade rear cavity; a rear seal positioned adjacent the first groove, the rear seal extending radially from the main seal toward the foot of the blade to control leakage from the blade to a heat shield cavity of the rotor heat shield downstream of the blade; and a lower seal arranged between the radial heat shield section and the rear seal below the blade rear cavity for separating the blade rear cavity from the heat shield cavity.

10. The turbine according to claim 9, wherein the blade comprises a trailing edge side seal groove formed in the trailing edge side of the blade platform closer to a platform surface facing the airfoil than the first groove, wherein the trailing edge side seal groove extends between the pressure side and the suction side, and wherein the depth of the trailing edge side seal groove in axial direction is smaller than the depth of the first groove.

11. The turbine according to claim 10, wherein the turbine comprises an upper seal arranged between the trailing edge side seal groove and the radial heat shield section.

12. The turbine according to claim 9, wherein the blade comprises a seal groove for receiving the rear seal on the pressure side of the blade platform and/or on the suction side of the blade platform, the rear seal extending radially inwardly below the first groove for sealing a space formed between adjacent blades of one turbine row at a downstream end towards the blade rear cavity.

13. A turbine comprising: a blade comprising: a blade platform having a trailing edge side, a pressure side, a suction side, and a leading edge side; an airfoil connected to the blade platform, and a first groove formed in the trailing edge side of the blade platform, wherein the first groove extends between the pressure side and the suction side and wherein the first groove extends in an axial direction below a trailing edge of the airfoil, and a rotor heat shield for separating a space region through which hot working medium flows from a space region inside a rotor arrangement of the turbine, wherein the rotor heat shield comprises an axial heat shield section which is arranged substantially parallel to a surface of a rotor of the rotor arrangement, wherein the rotor heat shield comprises a radial heat shield section at an upstream end of the axial heat shield section, the radial heat shield section extending in a direction away from a surface of the axial heat shield section towards a hot gas side of the rotor heat shield such that a blade rear cavity is defined between the radial heat shield section and at least one of the blade platform and a foot of the blade; a main seal above the first groove and above the blade rear cavity; and a rear seal positioned adjacent the first groove, the rear seal extending radially from the main seal toward the foot of the blade to control leakage from the blade to a heat shield cavity of the rotor heat shield downstream of the blade; and a lower seal below the first groove that extends between the foot of the blade and the heat shield to separate the blade rear cavity from the heat shield cavity.

14. The turbine of claim 13, wherein the radial heat shield section comprises a kink to bridge a gap between the blade platform and the rotor heat shield for holding an upper seal positioned above the first groove, the radial heat shield, and the lower seal between the blade platform and the rotor heat shield.

15. The turbine of claim 13, comprising: an upper seal above the lower seal, the first groove, and the blade rear cavity, the upper seal extending from the blade platform to the rotor heat shield.

16. The turbine of claim 13, wherein the lower seal is configured so that coolant is independently suppliable to the heat shield cavity and the blade rear cavity.

17. The turbine of claim 13, wherein the hot gas side of the rotor heat shield is a side of the rotor heat shield that is closest to the space region through which the hot working medium flows.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying drawings. Referring to the drawings:

(2) FIG. 1 shows a top view of a row or turbine blades;

(3) FIG. 2 shows a cut out of a turbine with a side view of a turbine blade and a section of the rotor holding the blade and the heat shield as well as a section of a vane facing the heat shield.

(4) FIG. 3 shows a cut out of a turbine with a side view of a turbine blade and a section of the rotor holding the blade as well as a section of a heat shield and a rear blade cavity.

(5) FIG. 4 shows a cut out of a turbine with a side view of a turbine blade and a section of the rotor holding the blade as well as a section of a heat shield, a rear blade cavity and a rear seal.

(6) FIG. 5 shows a cut out of a turbine with an additional lower seal.

DETAILED DESCRIPTION

(7) FIG. 1 shows a top view of a section of a row or turbine blades. Each blade 1 comprises an airfoil 3 attached to a platform 2. The airfoil has a leading edge, a trailing edge, a concave pressure side and a convex suction side. The corresponding sides of the platform are the leading edge side 9, the trailing edge side 10, the pressure side 29, and the suction side 30. A foot 4 of the blade 1 is below the platform for fixation of the blade to a rotor. In this Figure only the rear end of the foot 4 is visible.

(8) In the example of FIG. 1 the pressure side 29 and the suction side 30 of the platforms 2 of adjacent blades 1 are straight parallel lines, respectively surfaces along the extension of the platform 2 from the leading edge side 9 towards the trailing edge side 10. However, at the trailing edge side 10 of the platform 2 the platform of one blade is extended into the direction of a neighboring blade. The corresponding neighboring blade has a gap to allow an overlapping of the trailing edges of the platform 2 and of the foot 4 below (not shown) to form a so called ship lap. All standard blades 31 have a shiplap 28. Only one closing blade 32 does not have a shiplap 28, which can lead to additional leakages.

(9) FIG. 2 shows a cut out of a turbine with a side view of a turbine blade 1 and a section of the rotor 6 holding the blade as well as a section of a heat shield 7. Above the heat shield 7 and downstream of the blade 2 a turbine vane 34 (only partly shown) is arranged. To reduce leakages in the gap between the heat shield 7 and an inner platform of the vane a honeycomb 35 can be attached to the vane 34 facing the heat shield 7.

(10) The blade 1 comprises an airfoil 3 attached to a platform 2 and a foot 4. Part of the foot 4 can be designed as a fir tree 5 for fixation of the blade in the rotor. Coolant is supplied via a coolant feed 8 to the blade 1. Part of the coolant is supplied to the blade 1 as blade coolant 26 and part of the coolant is feed as cavity coolant 27 to a heat shield cavity 25 downstream of the blade. The flow of the cavity coolant 27 can be controlled by a throttle lug 24. Uncontrolled loss of coolant 8 to the heat shield cavity and in the region downstream of the platform 2 above the heat shield 7 is limited by the shiplap 28. Loss of coolant to the hot gas flow path above the platform 2 is limited by a main seal 17, which is sealing the gap between the platforms 2 of adjacent blades 1. Uncontrolled coolant flow at the upstream end of the blade can be limited by a lock plate interposed between the front ends of the feet 4 of adjacent blades 1 which extend from the rotor 6 to the inner side of the platform 2.

(11) Loss of cavity coolant 27 is limited by axial platform seals 21 which are sealing the gap between the axial heat shield sections 14 of adjacent heat shields 7.

(12) FIG. 3 shows a first embodiment of the disclosure with a side view of a turbine blade and a section of the rotor holding the blade as well as a section of a heat shield. FIG. 3 is based on FIG. 2 but the cut out vane section is omitted for simplification. The blade of FIG. 3 does not have a ship lab.

(13) To reduce stresses in the trailing edge of the airfoil 3 a first groove 11 is “cut out” of the trailing edge side 10 of the platform 2, respectively out of the trailing edge side 10 of the foot 4. The groove is extending in radial direction from a position above the fir tree 5 to the platform 2. In axial direction the groove is extending from the trailing edge side 10 of the platform 2 up to a location upstream of the trailing edge of the airfoil 3. Consequently the trailing edge side 10 of the platform 2 is not rigidly connected to the foot 4 and therefore more flexible. Thus differences in thermal extension lead to lower stresses in the airfoil trailing edge.

(14) The heat shield of FIG. 3 is based on the heat shield of FIG. 2. It additionally comprises a radial heat shield section 15, which, starting from outer surface of the axial heat shield section 14 at the upstream end of the axial heat shield section 14, extends radially outwards.

(15) To protect the rear end of the platform 2 and the foot 4 of the blade 1 a blade rear cavity 16 is arranged downstream of the blade 1. It is enclosed towards the downstream side by the radial heat shield section 15 of the heat shield 7. To control the leakage towards the hot gas side (radially outwards) an upper seal 19 can be arranged between the trailing edge side 10 of the platform 2 and the outer end of the radial heat shield section 15. A trailing edge side seal groove 12 can be formed in the platform 2 adjacent the main seal 17. The trailing edge side seal groove 12 can be formed in the trailing edge side of blade platform closer to platform surface of the platform 2 facing the airfoil 3 than the first groove 11.

(16) As shown in this embodiment the radial heat shield section 15 can have a kink at its radially outer end in upstream direction parallel to and in line with the heat shield 7 of the blade 1. This kink bridges the gap between heat shield 7 and the trailing edge side 10 of the platform 2. Further, it can serve to better hold the upper seal 19.

(17) FIG. 4 shows a further refinement based on FIG. 3. In addition to the example shown in FIG. 3 this example comprises a rear seal 33, which is arranged at the downstream end of the foot 4. The rear seal 33 extends from the main seal 17 below the platform radially inwardly towards the fir tree 5 to control the leakage from the blade to the heat shield cavity 25 and in particular to the blade rear cavity 16.

(18) FIG. 5 shows another example based on FIG. 4 In this example the blade rear cavity 16 is separated from the heat shield cavity 25 by a lower seal 22 which extends between the foot 4 and the heat shield 7. In this example it extends between the axial heat shield section 14 and the blade foot 4, however it can also extend between the radial heat shield section 15 and the blade foot 4.

(19) Typically the design pressure of the heat shield cavity 25 and the blade rear cavity 16 are practically identical or very close to each other, e.g. they differ by less than 10% or even less than 5% in total pressure. The two cavities have independent coolant supply. For such a design the lower seal 22 serves mainly as a safety in case one of the other seals sealing the blade rear cavity 16 fails.

(20) All the explained advantages are not limited just to the specified combinations but can also be used in other combinations or alone without departing from the scope of the disclosure. Other possibilities are optionally conceivable, for example additional coolant feeds can be directed from the rotor 6 directly to the heat shield cavity 25 or from the blade 1 to the blade rear cavity. Additional or alternative coolant feeds from an upstream or downstream end can be foreseen without passing the coolant through the rotor, e.g. through the looking blade area.

(21) To avoid high local stresses due to centrifugal forces during operation the first groove 11 can also have a smaller depth than shown in the FIGURES such that it does not extend into the line of stress caused by the blade load. Such a first groove 11 can also serve the purpose of reducing thermal stresses.

(22) The arrangement of the blade rear cavity radially outside of the heat shield cavity leads to a fail-save design. If one of the seals towards the hot gas side, i.e. the radial heat shield seal 20 or the upper seal 19 fails, the pressure difference across the remaining seals, i.e. rear seal 33 and lower seal 22 will increase and sufficient coolant flow will enter the blade rear cavity to purge it and thereby avoid hot gas ingestion.