Turbomachine assembly alleviating stresses at turbine discs

Abstract

A turbine arrangement is provided, particularly a gas turbine arrangement, having at least one rotor blade and a turbine disc, the rotor blade having a root portion, the turbine disc having at least one slot in which the root portion of the rotor blade is secured. The slot has a plurality of opposite pairs of slot lobes and a plurality of opposite pairs of slot fillets, and a slot bottom of the slot. The slot bottom is arranged to have a first convex surface section. Furthermore the root portion of the rotor blade has a root bottom with a first concave surface section corresponding to the first convex surface section of the slot bottom. Additionally, the first convex surface section is pierced by an outlet of a cooling duct through the turbine disc.

Claims

1. A turbine arrangement, comprising at least one rotor blade and a turbine disc, the rotor blade comprising a root portion, the turbine disc comprising at least one slot in which the root portion of the rotor blade is secured, the slot comprising a plurality of opposite pairs of slot lobes, a plurality of opposite pairs of slot fillets, and a slot bottom of the slot, wherein the slot bottom comprises a first convex surface section, wherein the root portion of the rotor blade comprises a root bottom comprising a first concave surface section corresponding to the first convex surface section of the slot bottom, and wherein the first convex surface section is pierced by an outlet of a cooling duct through the turbine disc.

2. The turbine arrangement according to claim 1, wherein the first convex surface section of the slot bottom merges into a first and a second concave surface sections of the slot, each of the first and second concave surface sections of the slot being adjacent to the first convex surface section and further forming a surface of a lower slot fillet of the plurality of opposite pairs of slot fillets.

3. The turbine arrangement according to claim 2, wherein the first and/or the second concave surface sections of the slot merges into a first planar surface section defining a mating surface with a corresponding second planar surface section of the rotor blade, the first planar surface section and the second planar surface section being in physical contact during operation of the turbine arrangement.

4. The turbine arrangement according to claim 2, wherein the outlet of the cooling duct additionally pierces the first and the second concave surface sections of the slot.

5. The turbine arrangement according to claim 1, further comprising a rim formed in the slot bottom by the outlet of the cooling duct having substantially a saddle-like shape.

6. The turbine arrangement according to claim 1, wherein the root portion comprises at least one inlet opposite to the outlet of the cooling duct of the turbine disc such that cooling fluid can be guided from the outlet via the inlet to a hollow interior of the rotor blade during operation of the turbine arrangement.

7. The turbine arrangement according to claim 6, wherein the root portion of the rotor blade comprises a cavity in the root bottom, a bottom of the cavity defining at least a first one and a second one of the at least one inlet.

8. A gas turbine comprising a turbine arrangement, wherein the turbine arrangement is arranged according to claim 1.

9. The turbine arrangement according to claim 1, wherein the cooling duct provides a passage through the turbine disc from a side face of the turbine disc or from an annular cavity within the turbine disc or from an annular cavity formed by a side face of the turbine disc and adjacent components.

10. The turbine arrangement according to claim 1, wherein the turbine arrangement is a gas turbine arrangement.

11. A turbine disc comprising: at least one slot in which a root portion of a rotor blade can be secured, the slot comprising, a plurality of opposite pairs of slot lobes, a plurality of opposite pairs of slot fillets, and a slot bottom of the slot, wherein the slot bottom comprises a first convex surface section, wherein the first convex surface section is pierced by an outlet of a cooling duct through the turbine disc.

12. The turbine disc of claim 11, wherein the first convex surface section of the slot bottom merges into a first and a second concave surface sections, each of the first and second concave surface sections being adjacent to the first convex surface section and further forming a surface of a lower slot fillet of the plurality of opposite pairs of slot fillets.

13. The turbine disc of claim 12, wherein the first and/or the second concave surface sections of the slot merges into a first planar surface section defining a mating surface with a corresponding second planar surface section of a rotor blade, the first planar surface section configured to be in physical contact with the second planar surface section during operation of a turbine arrangement comprising the turbine disc.

14. The turbine disc of claim 12, wherein the outlet of the cooling duct additionally pierces the first and the second concave surface sections.

15. The turbine disc of claim 11, further comprising a rim formed in the slot bottom by the outlet of the cooling duct having substantially a saddle-like shape.

16. The turbine disc of claim 11, wherein the cooling duct provides a passage through the turbine disc from a side face of the turbine disc or from an annular cavity within the turbine disc or from an annular cavity formed by a side face of the turbine disc and adjacent components.

17. A rotor blade for a turbine, comprising: at least one rotor blade, the rotor blade comprising a root portion, the root portion of the rotor blade being arranged such that it can be secured to a turbine disc comprising at least one slot in which the root portion of the rotor blade can be secured, the root portion comprising a plurality of opposite pairs of root lobes, a plurality of opposite pairs of root fillets, and a root bottom of the root portion, wherein the root portion of the rotor blade comprises a root bottom comprising a first concave surface section, and wherein the first concave surface section provides an inlet for guiding cooling fluid.

18. The rotor blade for a turbine of claim 17, wherein the root portion comprises at least one inlet opposite to an outlet of a cooling duct of a turbine disc such that cooling fluid can be guided from the outlet via the inlet to a hollow interior of the rotor blade during operation of a turbine arrangement, and wherein the root portion of the rotor blade comprises a cavity in the root bottom, a bottom of the cavity defining at least a first one and a second one of the at least one inlet.

19. The rotor blade for a turbine of claim 17, further comprising: the first concave surface section merges into a first and a second convex surface section, each of the first and second convex surface sections being adjacent to the first concave surface section and further forming a surface of the root bottom.

20. The rotor blade for a turbine of claim 19, wherein the inlet for guiding cooling fluid pierces the first and second convex surface sections.

21. A rotor blade for a turbine, characterized by a root bottom comprising a concave surface section; wherein the root bottom is further characterized by first and second convex surface sections on respective opposed sides of the concave surface section; further characterized by an inlet of a cooling duct of the rotor blade piercing the concave surface section and the first and second convex surface sections; and further characterized by the inlet of the cooling duct extending past an area of most radial depth of the respective first and second convex surface sections.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

(2) FIG. 1A shows schematically a prior art rotor blade in perspective, and FIG. 1B shows the same blade in cross-section. FIG. 1C shows a section of a prior art rotor disc;

(3) FIG. 2: illustrates in a perspective way a section of a rotor disc;

(4) FIG. 3: shows in a side view a turbine arrangement comprising a section of a rotor disc and a blade root of a rotor blade. FIG. 4 shows a side view of an alternative turbine arrangement wherein a cavity in the blade root bottom defines first and second cooling fluid inlets.

(5) The illustration in the drawing is schematical. It is noted that for similar or identical elements in different figures, the same reference signs will be used.

(6) Some of the features and especially the advantages will be explained for an assembled gas turbine, but obviously the features can be applied also to the single components of the gas turbine but may show the advantages only once assembled and during operation. But when explained by means of a gas turbine during operation none of the details should be limited to a gas turbine while in operation. In general embodiments of the invention may be applied to other types of machines that provide a rotational movement about an axis of rotation and at which rotating parts need to be connected to a carrier element this executing a rotational movement about the axis, so that centrifugal forces effect the rotating parts. Particularly this technology may be applied to gas turbines engines or steam turbines engines. In regards of gas turbine engines, embodiment of the invention may be applied to rotor blades within a turbine section and/or within a compressor section.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIGS. 1A and 1B show a blade design that is known from the prior art and that will slightly be modified according to aspects of the invention, which is then later shown in FIG. 3. FIG. 1C shows a prior art rotor disc design, which is updated according to aspects of the invention as shown in FIGS. 2 and 3.

(8) FIG. 1A shows a rotor blade 2 of a gas turbine engine in a perspective view. FIG. 1B shows the same rotor blade 2 in a cross sectional view, the cross section being located in a plane defined by an axial direction A—parallel to an axis of rotation of the engine—and a radial direction R—perpendicular to the axis of rotation. The rotor blade 2 is made up of an aerofoil section 10, a platform 12, and a blade root portion 1. The blade root portion 1 engages with a correspondingly shaped slot in a rotor disc. The blade root portion 1 is configured as “fir tree” shape, this being often preferred because of its excellent resistance against the centrifugal forces exerted upon the rotor blade when the rotor disc is rotated at high speed. In use, the rotor blade 2 is subjected to considerable stresses, due to the very high temperature of the working fluid flowing over the surface of the aerofoil section 10. In order to lengthen the life of the blade, the blade is often cooled by passing a cooling fluid through cooling ducts provided inside the blade. FIG. 1B shows two separate such ducts 18 and 20, which are separated by a partition piece 22. Duct 18 is defined by the inside walls of the aerofoil section and a partition piece 22. Duct 20 covers the remainder of the interior of the aerofoil section 10 and defines a hollow interior of the rotor blade 2.

(9) In order to supply cooling fluid to the ducts 18 and 20, in the example shown two fluid inlets 26, 28 of the rotor blade 2 are provided. Cooling-fluid flow is then from outside the blade 2 through the inlets 26, 28 and into the ducts 18, 20, as shown in FIG. 1B. The fluid leaves the blade through holes provided in the leading and trailing edges of the aerofoil section, as shown by the arrows 30, 32, respectively.

(10) In order to supply cooling fluid to the inlet 28 in FIG. 1B, a cooling duct is provided in the rotor disc, which carries cooling fluid from outside the disc to the slot, from where it flows into the inlet 28. An example of such an arrangement is given in FIG. 1C. This example shows the fir-tree shaped disc slot 40, the cooling duct 42 in the rotor disc 5, an outlet 44 at the radially outer end of the duct 42, and an inlet 46 for the cooling duct in an end-face of the rotor disc 5. In FIG. 1C the rotor blade is not inserted in the disc slot 40. Also shown is the bottom portion 48 of the slot.

(11) In operation—with installed rotor blades—cooling fluid passes through a system of cavities and ducts up to inlet 46 of the cooling duct 42 arranged within the rotor disc 5. The fluid then enters the inlet 46, passes through the cooling duct 42 and leaves the rotor disc 5 at the outlet 44, where it finally enters a cooling passage of the rotor blade 2—as indicated by inlet 28 in FIG. 1B.

(12) In FIG. 2 a perspective view of a segment of a rotor disc 5 is shown, which shows an embodiment of the inventive idea. As before in FIG. 1C, the rotor blade 2 is not shown in this figure. Merely the empty slot 40 is shown, that will later be used to slide in a blade root—root portion 1—of a rotor blade 2. Obviously the rotor disc 5 provides a plurality of these slots 40, but only one is shown for the following explanation. The figure shows the section of the rotor disc 5 such that a part of an axial side face of the rotor disc 5 is shown and furthermore a part of a substantially cylindrical surface of the rotor disc 5 expanding in the axial direction A and a circumferential direction—the latter being perpendicular to the axial direction A and the radial direction R at a specific point—, which is cut by a slots 40.

(13) In the figure within the turbine disc 5 one slot 40 is present in which a root portion of a corresponding rotor blade can be secured. The slot 40 comprises a plurality of opposite pairs of slot lobes 100 projecting into the slot 40 and a plurality of opposite pairs of slot fillets 101. “Opposite” means that the slot 40 is substantially mirror symmetrical and that the slot lobes 100 and the slot fillets 101 come in symmetrical pairs. The slot 40 further comprises a slot bottom 105 defining that radial end of the slot 40 that is closest to the axis of rotation or which has the longest distance to the hot gas path or the blade aerofoil. The slot bottom 105 comprises a first convex surface section 102. This means that there is a radial elevation in the slot bottom 105. Not shown in this figure but later in FIG. 3, the slot bottom 105 is arranged such that its first convex surface section 102 corresponds to a first concave surface section (reference sign 51 in FIG. 3) of a root portion or a rotor blade to be inserted in the slot 40.

(14) In FIG. 2 furthermore a cooling duct 42 is indicated by dotted lines and an outlet 44 of the cooling duct that is present in the slot bottom 105. In a first embodiment, as shown in FIG. 2, the outlet 44 will be closer to one of the side faces of the rotor disc 5. In an alternative embodiment—not shown—the outlet 44 will have the same axial distance to both side faces of the rotor disc 5.

(15) The cooling duct 42 may be cylindrical with a circular cross section or with an elliptical or oval cross section. As the cooling duct 42 pierces or penetrates the slot bottom 105 a rim 49 is present on the surface of the slot bottom 105 defining the outlet 44 of the cooling duct 42 (as an intersection of the cooling duct 42 and the surface of the slot bottom 105). The rim 49 will have a saddle-like shape due to the first convex surface section 102.

(16) Preferably the outlet 44 stretches in a direction perpendicular to the axial and radial direction—in circumferential direction—such that the cooling duct 42 pierces the first convex surface section 102 and two concave surface sections—reference signs 103 and 104 in FIG. 3—which are adjacent to the convex surface section 102 in both circumferential directions.

(17) This design is specifically advantageous as—during operation of the gas turbine engine—the base of the disc slot form is profiled in order to minimise the encroachment of hoop stresses around the periphery of the cooling hole and thus minimise the peak stress. This is realised by effectively undercutting the form so as to disassociate the position of peak stress around the cooling hole from the main hoop stress field.

(18) FIG. 3 shows a side view from axial direction of the turbine disc 5 as shown in FIG. 2. Furthermore FIG. 3 depicts a configuration in which rotor blade 2 is already inserted in the disc slot 40, as it would be during operation of the gas turbine engine. The reference signs are identical to the previous figures so that not all parts need to be discussed in full detail. All previously said still applies for the configuration of FIG. 3.

(19) According to FIG. 3, a rotor blade 2 with its root section 1 is inserted into a slot 40 of the disc 5. The disc 5 provides a cooling duct 42 that is directed and ends at the slot bottom 105 of the slot 40.

(20) The root portion 1 of the rotor blade 2 corresponds to the shape of the slot 40 such that root fillets match slot lobes 100 and root lobes match slot fillets 101. In between a slot lobe 100 and a slot fillet 101 there is a substantially flat surface, a first planar surface section 106 which is provided as a bearing surface for a corresponding second planar surface section 52 or flank of the blade root 1, both surfaces being in physical and bearing contact during operation of the turbine arrangement.

(21) Within the blade root 1, a blade root cooling duct 53 is indicated by dotted lines. An inlet of the blade root cooling duct 53 is aligned with the cooling duct 42 through the rotor disc 5 so that the cooling fluid will be guided into the interior of the rotor blade 2.

(22) In FIG. 3 the specific shape of the lowest root lobe or the lowest slot fillet become apparent. The lowest root lobe is substantially cylindrical formed by a first concave surface section 103 following a first planar surface section 106 and a second concave surface section 104 following a further one of a first planar surface section 106. The first concave surface section 103 and the second concave surface section 104 do not meet at the root bottom 50. The first concave surface section 103 merges into a first convex surface section 102 and the second concave surface section 104 also merges into the first convex surface section 102 from a second side. The first convex surface section 102 will be located right in the center of the lowest lobe, i.e. at the axis of symmetry of the slot 40.

(23) Compared to its circumferential stretch the first convex surface section 102 has a mirror elevation in radial direction. The circumferential stretch may be in a ratio of 10:1 compared to the radial elevation.

(24) Within the turbine disc 5, the cooling duct 42 is present. Its circumferential stretch is indicated by a double arrow and fully extends the circumferential width of the first convex surface section 102. Preferably, and as indicated in the figure, the circumferential stretch is extending into the region of the first concave surface section 103 and also is extending into the region of the second concave surface section 104. Particularly it will extend just up to an area of most radial depth of the slot 40 within the first concave surface section 103 and up to an area of most radial depth of the slot 40 within the second concave surface section 104.

(25) Alternatively—as it is shown in the figure—the first convex surface section 102 even extends past the area of most radial depth of the slot 40 within the first concave surface section 103 and extends past the area of most radial depth of the slot 40 within the second concave surface section 104. In this configuration the expanse of the first convex surface section 102 is substantially the complete slot bottom 105 in circumferential direction (wherein the circumferential direction corresponds to a horizontal direction in FIG. 3).

(26) The arrangement, as previously introduced for the disc slot 40 affects also the configuration of the blade root 1, such as the blade root bottom 50 follows the shape of the disc slot bottom 105. That means that starting on one circumferential side, a lowest flank provides a second planar surface section 52, merging into a convex surface section (opposite to the first concave surface section 103), which again merges into first concave surface section 51 of the blade root 1. Further continuing, this first concave surface section 51 then merges into a further convex surface section (opposite to the second concave surface section 104) and then merges into a further second planar surface section located on the opposite circumferential side.

(27) Corresponding to the cooling duct 42 and its outlet 44 (which is not indicated explicitly in FIG. 3), the blade root cooling duct 53 has the same size inlet 28 (which is not indicated explicitly in FIG. 3) as the outlet 44. The blade root cooling duct 53 may be a straight passage to the aerofoil section. The blade root cooling duct 53 may also narrow its width, as indicated in FIG. 3.

(28) The previously discussed turbine arrangement may particularly be applied to a high power stage of a turbine section within a gas turbine engine.

(29) Embodiments as introduced before may have a substantial benefit in regards of the lifetime of rotor discs. Stresses can be avoided that could result in cracks. Monitoring cycles can be stretched.

(30) It has to be noted that that it may be advantageous if exactly three pairs of lobes and three pairs of fillets may be present on the blade root and in the slot, as shown in FIG. 3. Possibly other configurations may also be possible.