Turbomachine rotor blade, turbomachine rotor disc, turbomachine rotor, and gas turbine engine with different root and slot contact face angles

Abstract

A turbomachine rotor blade has a firtree shaped root, to be secured in a rotor disc rotatable around a rotor axis. In a plane perpendicular to the rotor axis, the root has a first, second, and third root lobe with a first, second, and third root contact face. Each of the first, second, and third root contact face is angled relative to a radial root bottom axis with a first, second, and third root angle, respectively. The first root angle is smaller than the second and the second root angle is substantially equal to the third. A turbomachine rotor disc has a firtree shaped slot having a first, second, and third slot angle, the first slot angle being smaller than the second and the second slot angle being substantially equal to the third. A gas turbine engine has the turbomachine rotor herein.

Claims

1. A turbomachine rotor blade comprising: a firtree shaped root, arranged to be secured in a turbomachine rotor disc, the rotor disc being rotatable around a rotor axis, wherein in a plane perpendicular to the rotor axis the root comprises a root bottom and a root side; the root side comprises a plurality of root lobes, each of the root lobes comprises a root contact face, arranged to be in physical contact with a slot contact face of the rotor disc; the plurality of root lobes comprises a first root lobe with a first root contact face, a second root lobe with a second root contact face and a third root lobe with a third root contact face, the first root lobe being closer to the root bottom than the second root lobe and the second root lobe being closer to the root bottom than the third root lobe; the first root contact face is angled relative to a radial root bottom axis with a first root angle, the radial root bottom axis being defined by a line through the rotor axis and the root bottom; the second root contact face is angled relative to the radial root bottom axis with a second root angle; and the third root contact face is angled relative to the radial root bottom axis with a third root angle; wherein any one or more of the first root angle or the second root angle or the third root angle is in the range 1 to 15 of any of the other root angles; and wherein the first root angle is greater than the second root angle and greater than the third root angle, effective to increase stress in the first root lobe relative to the second root lobe and third root lobe, so that in the event of a failure of the first root lobe, the second root lobe and third root lobe are capable of carrying a total loading.

2. The turbomachine rotor blade according to claim 1, wherein any one or more of the first root angle or the second root angle or the third root angle is in the range 1 to 5 of any of the other root angles.

3. The turbomachine rotor blade according to claim 1, wherein the second root angle is substantially equal to the third root angle.

4. The turbomachine rotor blade according to claim 1, wherein the first root angle is 2 greater than the second root angle or third root angle.

5. The turbomachine rotor blade according to claim 1, wherein the first root angle is 2 greater than the second root angle and the second root angle is equal to the third root angle.

6. The turbomachine rotor blade according to claim 1, wherein the root comprises a further root side, the further root side comprising a plurality of further root lobes, and the root side and the further root side being circumferentially opposite to each other.

7. The turbomachine rotor blade according to claim 6, wherein the plurality of root lobes comprises a first root shape and the plurality of further root lobes comprises a second root shape, the first root shape being a copy, flipped at the radial root bottom axis, of the second root shape.

8. The turbomachine rotor blade according to claim 1, wherein each of the root lobes has a maximum root distance to the radial root bottom axis, the root distance being defined by the length of a root line segment between a surface section of a root lobe and an axis section of the radial root bottom axis, the root line segment being perpendicular to the radial root bottom axis; and wherein the maximum root distance of the first root lobe is smaller than the maximum root distance of the second root lobe and/or the maximum root distance of the second root lobe is smaller than the maximum root distance of the third root lobe.

9. The turbomachine rotor blade according to claim 1, wherein the turbomachine rotor blade is part of a gas turbine engine, part of a turbine section of the gas turbine engine and/or part of a compressor section of the gas turbine engine.

10. A turbomachine rotor comprising the turbomachine rotor blade according to claim 1, and the turbomachine rotor disc comprising: a firtree shaped slot, the rotor disc being rotatable around the rotor axis; wherein in the plane perpendicular to the rotor axis the slot comprises a slot bottom and a slot side; the slot side comprises a plurality of slot lobes, each of the slot lobes comprises the slot contact face, arranged to be in physical contact with the root contact face of the turbomachine rotor blade; the plurality of slot lobes comprises a first slot lobe with a first slot contact face, a second slot lobe with a second slot contact face and a third slot lobe with a third slot contact face, the first slot lobe being closer to the slot bottom than the second slot lobe and the second slot lobe being closer to the slot bottom than the third slot lobe; the first slot contact face is angled relative to a radial slot bottom axis with a first slot angle, the radial slot bottom axis being defined by a line through the rotor axis and the slot bottom; the second slot contact face is angled relative to the radial slot bottom axis with a second slot angle; and the third slot contact face is angled relative to the radial slot bottom axis with a third slot angle; characterised in that any one or more of the first slot angle or the second slot angle or the third slot angle is in the range 1 to 15 of any of the other slot angles.

11. The turbomachine rotor according to claim 10, wherein the physical contact between the first root contact face and the first slot contact face and/or between the second root contact face and the second slot contact face and/or between the third root contact face and the third slot contact face is established during operation of the turbomachine rotor.

12. A gas turbine engine, comprising a turbomachine rotor according to claim 10.

13. A turbomachine rotor disc comprising: a firtree shaped slot, the rotor disc being rotatable around a rotor axis; wherein in a plane perpendicular to the rotor axis the slot comprises a slot bottom and a slot side; the slot side comprises a plurality of slot lobes, each of the slot lobes comprises a slot contact face, arranged to be in physical contact with a root contact face of a turbomachine rotor blade; the plurality of slot lobes comprises a first slot lobe with a first slot contact face, a second slot lobe with a second slot contact face and a third slot lobe with a third slot contact face, the first slot lobe being closer to the slot bottom than the second slot lobe and the second slot lobe being closer to the slot bottom than the third slot lobe; the first slot contact face is angled relative to a radial slot bottom axis with a first slot angle, the radial slot bottom axis being defined by a line through the rotor axis and the slot bottom; the second slot contact face is angled relative to the radial slot bottom axis with a second slot angle; and the third slot contact face is angled relative to the radial slot bottom axis with a third slot angle; characterised in that any one or more of the first slot angle or the second slot angle or the third slot angle is in the range 1 to 15 of any of the other slot angles; and wherein the first slot angle is greater than the second slot angle and greater than the third slot angle.

14. The turbomachine rotor disc according to claim 13, wherein any one or more of the first slot angle or the second slot angle or the third slot angle is in the range 1 to 5 of any of the other slot angles.

15. The turbomachine rotor disc according to claim 13, wherein the first slot angle is greater than the second slot angle and the second slot angle is substantially equal to the third slot angle.

16. The turbomachine rotor disc according to claim 13, wherein the first slot angle is 2 greater than the second slot angle or third slot angle.

17. The turbomachine rotor disc according to claim 13, wherein the first slot angle is 2 greater than the second slot angle and the second slot angle is equal to the third slot angle.

18. The turbomachine rotor disc according to claim 13, wherein the slot comprises a further slot side, the further slot side comprising a plurality of further slot lobes, and the slot side and the further slot side being circumferentially opposite to each other.

19. The turbomachine rotor disc according to claim 18, wherein the plurality of slot lobes comprises a first slot shape and the plurality of further slot lobes comprises a second slot shape; the first slot shape being a copy, flipped at the radial slot bottom axis, of the second slot shape.

20. The turbomachine rotor disc according to claim 13, wherein each of the slot lobes has a maximum slot distance to the radial slot bottom axis, the slot distance being defined by the length of a slot line segment between a surface section of a slot lobe and an axis section of the radial slot bottom axis, the slot line segment being perpendicular to the radial slot bottom axis; and wherein the maximum slot distance of the first slot lobe is smaller than the maximum slot distance of the second slot lobe and/or the maximum slot distance of the second slot lobe is smaller than the maximum slot distance of the third slot lobe.

21. The turbomachine rotor disc according to claim 13, wherein the turbomachine rotor disc is part of a gas turbine engine, part of a turbine section of the gas turbine engine and/or part of a compressor section of the gas turbine engine.

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. 1: shows part of prior art rotor discs in a perspective view;

(3) FIG. 2: illustrates a prior art blade in a perspective view;

(4) FIG. 3: shows parts of a firtree shaped root and a firtree shaped slot focussing on contact face angles relative to a radial root and slot bottom axis, respectively, in a cross-sectional view;

(5) FIG. 4: shows parts of a firtree shaped root and a firtree shaped slot focussing on root and slot distances, respectively, in a cross-sectional view.

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

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring to FIG. 1, parts of two prior art rotor discs, a rotor disc 11 and a further rotor disc 11, are shown in a perspective view. At a radially outer region of the disc 11 a plurality of slots 12 are shown. Each firtree shaped slot is designed such that a firtree shaped root (not shown) fits into it.

(8) FIG. 2 shows a prior art blade 20, comprising an aerofoil 21, a platform 22 and a root 23. It should be repeated that the drawings are not to scale: In particular, the aerofoil 21 may be substantially larger in other exemplary embodiments. The root 23 comprises a root bottom 24, a first root lobe 25, a second root lobe 26 and a third root lobe 27. Each root lobe 25, 26, 27 comprises a contact face on its surface section. The first root 25 comprises a first root contact face 251, the second root 26 comprises a second root contact face 261 and the third root 27 comprises a third root contact face 271.

(9) FIG. 3 depicts parts of a root 23 and a slot 12. This time, a cross-sectional view in a plane perpendicular to the rotor axis 31 is shown. The root 23 comprises a root bottom 36 and exhibits a radial root bottom axis 32, intersecting the rotor axis 31 and the root bottom 36. The root 23 comprises a first root contact face 33 with a first root angle 331 of approximately 45, a second root contact face 34 with a second root angle 341 of approximately 55 and a third root contact face 35 with a third root angle 351 of approximately 55, too. The given root angles 331, 341, 351 are exemplarily and apply only to the depicted exemplary embodiment.

(10) The slot 12 comprises a first slot contact face 33 with a first slot angle 331 of approximately 45, a second slot contact face 34 with a second slot angle 341 of approximately 55 and a third slot contact face 35 with a third slot angle 351 of approximately 55. In the exemplary embodiment of FIG. 3, the root 23 and the slot 12 comprise the same root angles 331, 341, 351 and slot angles 331, 341, 351, respectively. This fact as well as the given slot angles 331, 341, 351 are exemplarily and apply only to the depicted exemplary embodiment.

(11) In another exemplary embodiment, the root 23 comprises a first root contact face 33 with a first root angle 331 of approximately 43, a second root contact face 34 with a second root angle 341 of approximately 45 and a third root contact face 35 with a third root angle 351 of approximately 45, too. Similarly, the slot 12 comprises a first slot contact face 33 with a first slot angle 331 of approximately 43, a second slot contact face 34 with a second slot angle 341 of approximately 45 and a third slot contact face 35 with a third slot angle 351 of approximately 45. In this exemplary embodiment, the root 23 and the slot 12 comprise the same root angles 331, 341, 351 and slot angles 331, 341, 351, respectively. This fact as well as the given slot angles 331, 341, 351 are exemplary and apply only to the depicted exemplary embodiment.

(12) As it can be seen, the first contact face angle 331, 331 is smaller than the second contact face angle 341, 341 and the second contact face angle 341, 341 is substantially equal to the third contact face angle 351, 351.

(13) Finally, FIG. 4 shows, in a cross-sectional view, parts of a firtree shaped root 23 and a firtree shaped slot 12 focussing on root and slot distances, respectively. The root 23 comprises a root bottom 36 and a first root lobe 41. The first root lobe 41 comprises a portion of the root 23 which is defined by a first area surrounded from the surface section in-between the root bottom 36 and a first local root distance minimum 414, a line segment limited by 413 and 414, and a first projected root lobe line segment, determined by a line segment limited by 36 and 413. Analogously, a second root lobe 43 comprises a portion of the root 23 which is defined by a second area surrounded from the surface section in-between the first local root distance minimum 414 and a second local root distance minimum 434, a line segment limited by 433 and 434, and a second projected root lobe line segment, determined by a line segment limited by 413 and 433. Analogously again, a third root lobe 45 comprises a portion of the root 23 which is defined by a third area surrounded from the surface section in-between the second local root distance minimum 434 and a third local root distance minimum 454, a line segment limited by 453 and 454, and a third projected root lobe line segment, determined by a line segment limited by 433 and 453.

(14) FIG. 4 also illustrates the slot distances. The slot 12 comprises a slot bottom 37 and a first slot lobe 42. The first slot lobe 42 comprises a portion of the slot 12 which is defined by a first area surrounded from the surface section in-between the slot bottom 37 and a first local slot distance minimum 422, a line segment limited by 421 and 422, and a first projected slot lobe line segment, determined by a line segment limited by 37 and 422. Analogously, a second slot lobe 44 comprises a portion of the slot 12 which is defined by a second area surrounded from the surface section in-between the first local slot distance minimum 422 and a second local slot distance minimum 442, a line segment limited by 441 and 442, and a second projected slot lobe line segment, determined by a line segment limited by 421 and 441. Analogously again, a third slot lobe 46 comprises a portion of the slot 12 which is defined by a third area surrounded from the surface section in-between the second local slot distance minimum 442 and a third local slot distance minimum 462, a line segment limited by 461 and 462, and a third projected slot lobe line segment, determined by a line segment limited by 441 and 461.

(15) FIG. 4 furthermore illustrates an exemplary embodiment of the invention with increasing maximum root and slot distances. As can be seen in FIG. 4, the maximum root distance of the first root lobe 41, which is determined by the length of the line segment limited by 411 and 412, is smaller than the maximum root distance of the second root lobe 43, which is determined by the length of the line segment limited by 431 and 432, which in turn is smaller than the maximum root distance of the third root lobe 45, which is determined by the length of the line segment limited by 451 and 452. Analogously, the maximum slot distance of the first slot lobe 42, which is determined by the length of the line segment limited by 423 and 424, is smaller than the maximum slot distance of the second slot lobe 44, which is determined by the length of the line segment limited by 443 and 444, which in turn is smaller than the maximum slot distance of the third slot lobe 46, which is determined by the length of the line segment limited by 463 and 464.

(16) The exemplary embodiments of FIG. 3 and FIG. 4 show contact face angles 331, 331, 341, 341, 351, 351, which particularly are advantageous with respect of the distribution of stress and mechanical load across the root and the slot surfaces.

(17) From a blade root and disc slot design having nominal equal contact face or bearing flank angles to the present invention having a first flank angle 331, 33 smaller rather than the second flank angle 341, 341 and third flank angle 35, 35 means that the first contact face 33, 33 incurs reduced loading and therefore reduced contact stress and reduced bending stress in the first root lobe 25. Consequently, the loading on the second contact face 34, 34 and the third contact face 35, 35 increases and therefore increases contact stress and increased bending stress in the second and third root lobes 26, 27.

(18) In reducing a flank contact angle (331, 331) the associated lobe becomes less stiff (more flexible) by virtue of a reduced cross-sectional area and hence the lobe has less capacity to resist bending from the contact force applied.

(19) This increased flexibility reduces the amount of loading on the flank contact face and consequently there is a redistribution of the total load carried by the root 23 between all lobes with the second and third lobes seeing a relative increase in loading.

(20) It should be appreciated that the loads experienced by the contact faces 33, 33, 34, 34, 35, 35 and the distribution of the total load between contact faces can arise and be influenced by a number of factors which can include the centrifugal loading from the mass of the blade, aerodynamic loading of the blade, thermal strains, radial growth of the disc and hence geometric changes of the disc post/slot.

(21) Tolerances and tolerance build-ups can also cause each lobe's contact faces to experience different loads from nominal design loads. Additionally, distribution of load on the contact faces of each of the lobes may be further influenced by the geometry and therefore flexural behaviour of the root and slot geometries and of the individual lobes themselves. Thus for a rotor disc slot and blade root design having nominally equal contact flank angles the distribution of loads during operation can be significantly different from one another and can be detrimental to the longevity of the root or disc post/slot.

(22) In one case, a blade root and disc slot design having nominal equal contact face or flank angles and where the loading on the first contact face 33, 33 is greater than on the second and third faces, reducing the contact face angle of the first root and slot lobes relative to the second and third contact faces increases flexibility of the first lobe and therefore reduces load on the first lobe. This reduces the amount of load on the contact face and therefore reduces its bedding stress and bending stress in the first lobe 25. The advantageous result is a more beneficial distribution of the total load on the each of the first, second and third contact faces. Of course, where the contact area of root flank and slot flank is different between first, second and third contact flanks then more equal bedding stress or pressure is achievable. This reduction of stress on the first contact face 33, 33 and in first lobe 25 can increase the service life of the blade and/or disc.

(23) In another case, it may be desirable to increase the loading or contact stress and/or bending stress in the first lobe 25. In this case, such an increase is desirable so that there is a redundant failure condition for the root 23. Here the second and third contact faces 34, 34 and 35, 35 are relatively less loaded or have a reduced load from a nominal equally loaded or stressed contact face design. Thus in the event of a failure the second and third contact faces 34, 34 and 35, 35 and their lobes 26, 27 are capable of carrying the total loading at least until the next service interval for example.

(24) It should be noted that the quoted angles are nominal angles and that these angles are subject to tolerances. The contact faces of the root and slot can be referred to as flank faces.

(25) The same objective and advantages for the root may be applied to the disc post(s) that define the disc slots along with the same principles for reducing or increasing one or more the slot contact face angles relative to any other.