Supporting structure for a gas turbine engine

Abstract

A supporting structure for a gas turbine engine comprises an inner ring, an outer ring, and a plurality of circumferentially spaced, load carrying radial elements connecting the inner and outer rings, said radial elements being configured to transfer loads between the inner ring and the outer ring, wherein a gas channel for a primary axial gas flow is defined between the inner and outer rings, wherein the supporting structure has an inlet side for primary gas flow entrance and an outlet side for primary gas outflow, wherein the radial elements have an airfoil shape with a leading edge directed towards the inlet side, a trailing edge directed towards the outlet side, and two opposite sides connecting the leading edge and the trailing edge, and wherein at least a first of said radial elements is connected to an adjacent part of the supporting structure via a weld joint that extends across the leading edge and circumferentially at least partly around the first radial element.

Claims

1. A supporting structure for a gas turbine engine, comprising: an inner ring; an outer ring; a plurality of circumferentially spaced, load carrying radial elements connecting the inner and outer rings, said radial elements being configured to transfer loads between the inner ring and the outer ring; and a gas channel for a primary axial gas flow defined between the inner and outer rings, wherein the supporting structure has an inlet side for primary gas flow entrance and an outlet side for primary gas outflow; wherein the radial elements have an airfoil shape with a leading edge directed towards the inlet side, a trailing edge directed towards the outlet side, and two opposite sides connecting the leading edge and the trailing edge; at least a first of said radial elements is connected to an adjacent part of the supporting structure via a weld joint that extends across the leading edge and circumferentially at least partly around the first radial element; the first radial element is provided with a region of reduced stiffness in a vicinity of the leading edge; and the first radial element is hollow and comprises a wall structure forming the leading edge and the two opposite sides, wherein a wall thickness of the wall structure is greater along the weld joint than in at least parts of the region of reduced stiffness.

2. The supporting structure of claim 1, wherein the supporting structure has a lower stiffness in the region of reduced stiffness than in a region along the weld joint.

3. The supporting structure of claim 1, wherein the region of reduced stiffness has an elongated shape and extends along the leading edge.

4. The supporting structure of claim 1, wherein the region of reduced stiffness comprises a plurality of sub-regions with reduced wall thickness, wherein said sub-regions are distributed along the region of reduced stiffness.

5. The supporting structure of claim 1, wherein all transitions between larger and thinner wall thickness as well as corners in the region of reduced thickness are rounded and smooth.

6. The supporting structure of claim 1, wherein a distance along the leading edge between an end point of the region of reduced stiffness and a center line of the weld joint is at least two times the wall thickness at the weld line or at least 5 millimeters.

7. The supporting structure of claim 1, wherein the thickness of the wall structure is substantially uniform except in the region of reduced stiffness, wherein the thickness outside of the region of reduced stiffness is in a range of 1-3 millimeters, and wherein the wall thickness in parts of the region of reduced stiffness with reduced thickness is at least twenty percent lower than the thickness outside of the region of reduced stiffness.

8. The supporting structure of claim 1, wherein the adjacent part of the supporting structure that is connected to the first radial element via the weld joint forms a radial extension of the first radial element, wherein the weld joint is located between the inner ring and the outer ring.

9. The supporting structure of claim 8, wherein the weld joint is located substantially closer to one of the rings than the other one of the rings.

10. The supporting structure of claim 1, further comprising an annular load transfer structure arranged inside of the inner ring for transferring loads between said elements, and a bearing structure for a turbine shaft positioned centrally in the supporting structure.

11. A gas turbine engine, comprising a supporting structure, the supporting structure comprising: an inner ring; an outer ring; a plurality of circumferentially spaced, load carrying radial elements connecting the inner and outer rings, said radial elements being configured to transfer loads between the inner ring and the outer ring; and a gas channel for a primary axial gas flow defined between the inner and outer rings, wherein the supporting structure has an inlet side for primary gas flow entrance and an outlet side for primary gas outflow; wherein the radial elements have an airfoil shape with a leading edge directed towards the inlet side, a trailing edge directed towards the outlet side, and two opposite sides connecting the leading edge and the trailing edge; at least a first of said radial elements is connected to an adjacent part of the supporting structure via a weld joint that extends across the leading edge and circumferentially at least partly around the first radial element; and the first radial element is provided with a region of reduced stiffness in a vicinity of the leading edge; and the first radial element is hollow and comprises a wall structure forming the leading edge and the two opposite sides, wherein a wall thickness of the wall structure is greater along the weld joint than in at least parts of the region of reduced stiffness.

12. The gas turbine engine of claim 11, arranged for propulsion of an aircraft.

13. A method for manufacturing a supporting structure that comprises an inner ring; an outer ring; a plurality of circumferentially spaced, load carrying radial elements connecting the inner and outer rings, said radial elements being configured to transfer loads between the inner ring and the outer ring; and a gas channel for a primary axial gas flow defined between the inner and outer rings, wherein the supporting structure has an inlet side for primary gas flow entrance and an outlet side for primary gas outflow; wherein the radial elements have an airfoil shape with a leading edge directed towards the inlet side, a trailing edge directed towards the outlet side, and two opposite sides connecting the leading edge and the trailing edge; at least a first of said radial elements is connected to an adjacent part of the supporting structure via a weld joint that extends across the leading edge and circumferentially at least partly around the first radial element; the first radial element is provided with a region of reduced stiffness in a vicinity of the leading edge; and wherein the first radial element comprises a wall structure forming the leading edge and the two opposite sides, wherein a wall thickness of the wall structure is greater along the weld joint than in at least parts of the region of reduced stiffness; the method comprising: providing a substantially flat wall structure, forming the region of reduced stiffness in the substantially flat wall structure, and forming the substantially flat wall structure into at least an inlet side portion of the first radial element comprising the leading edge and at least a portion of each of the two opposite sides.

14. The method of claim 13, characterized in that it comprises the steps of forming the two opposite sides and connecting them along the trailing edge.

15. The method of claim 13, wherein at least one of the two opposite sides form part of the substantially flat wall structure.

16. The method of claim 13, wherein at least one of the two opposite sides comprises at least one remaining portion, wherein the method further comprises connecting the inlet side portion of the first radial element to the corresponding at least one remaining portion of the at least one opposite side.

17. The method of claim 13, wherein the step of forming the region of reduced stiffness comprises the step of forming one or several sub-regions with reduced a wall thickness.

18. The method of claim 13, further comprising connecting the first of said radial elements to an adjacent part of the supporting structure by welding such as to form said weld joint.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In the description given below reference is made to the following figure, in which:

(2) FIG. 1 shows, in a schematic overview, an example of an axial flow aircraft gas turbine engine provided with a supporting structure,

(3) FIG. 2 shows, in a perspective front view, an embodiment of a supporting structure,

(4) FIG. 3 shows a detail of the embodiment according to FIG. 2,

(5) FIG. 4 shows another view of the detail shown in FIG. 3,

(6) FIG. 5 shows still another view of the detail shown in FIG. 3,

(7) FIG. 6 shows a variant of the detail shown in FIG. 3,

(8) FIG. 7 shows another view of the detail shown in FIG. 6, and

(9) FIG. 8 shows still another view of the detail shown in FIG. 6.

DESCRIPTION OF EXAMPLE EMBODIMENTS

(10) FIG. 1 shows, in a schematic overview, an axial flow aircraft gas turbine engine 1 provided with supporting structures 27, 37. In general, the gas turbine engine 1 shown in FIG. 1 is of conventional construction and comprises, in axial flow series, an air intake 3, a low pressure compressor 4, a high pressure compressor 5, combustion equipment 6, a high pressure turbine 7, a low pressure turbine 8 and an exhaust outlet 9. During operation, the high pressure compressor 5 is driven by the high pressure turbine 7 via a first hollow shaft, the high pressure (HP) turbine shaft 10. Similarly, the low pressure compressor 4 is driven by the low pressure turbine 8 via a second hollow shaft, the low pressure (LP) turbine shaft 11, which is coaxially disposed within the first turbine shaft 10. A common axis 2 is also shown.

(11) The gas turbine engine 1 operates, in general, in a conventional manner whereby air drawn in through the air intake 3 is compressed by the low pressure compressor 4 before passing into the high pressure compressor 5 where it is further compressed. The compressed air then flows into the combustion equipment 6 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through the high and low pressure turbines 7, 8 before being exhausted to the atmosphere through the exhaust outlet 9.

(12) The engine 1 comprises a rear supporting structure 27 and a front supporting structure 37 for supporting the drive shafts and for mounting the engine to an aircraft.

(13) The following description is provided with reference to the rear supporting structure 27. Such a supporting structure is commonly referred to as Turbine Rear Frame (TRF), Turbine Exhaust Case or Tail Bearing Housing.

(14) Generally, rear support structures in jet engines support one or two shafts by means of roller and/or ball bearings, i.e. only radial load is transmitted through the structure (axial load only at shaft fwd bearing). The load is transmitted through an inner support structure (support cone) to an inner hub connected to an outer structure (shroud) by means of radial elements. In order to reduce aerodynamic drag and to straighten the outlet angle of the main gas flow leaving the low pressure turbine, these elements are usually covered with an airfoil structure or made integral to the structure. Integrated airfoils or vanes are sometimes denoted “struts”. In the example described below the term structural vanes is used. Structural vanes are capable of supporting both aerodynamic loads as well as a combination of structural and thermally induced loads. Most of the modern jet engines utilize such vanes in ring-vane-ring components, such as the rear supporting structure 27.

(15) FIG. 2 shows a perspective front view of an inlet side of an embodiment of the rear supporting structure 27. This structure 27 comprises an inner annular member or ring 20 in the form of an inner housing or hub for receiving the second turbine drive shaft 11 and an outer annular member or ring 21, wherein the two annular members 20, 21 are concentrically arranged around the common axis 2. The supporting structure 27 further comprises a plurality of circumferentially spaced elements, structural vanes 22, that extend in a radial direction and connect the inner and outer annular members 20, 21. The vanes 22 define gas flow passages for a primary axial gas flow between the rings 20, 21 and, in the example shown, each radial element 22 has an airfoil shape in cross section and is structurally integrated in the supporting structure 27. FIG. 2 shows a gas inlet side for primary gas flow entrance to the component 27. Accordingly, an outlet side for primary gas outflow is formed on the backside of the structure 27. FIG. 2 further indicates a first element/vane 22a provided with a region of reduced stiffness 10 as will be described further below.

(16) An annular load transfer structure 23 is positioned internally of the inner ring 20 for transferring loads between the elements 22 and a bearing structure 24 for the turbine shaft 11 which is positioned centrally in the component 27. The exemplified supporting structure 27 further comprises engine mounts 19 for fastening of the gas turbine engine 1 to an aircraft. The radial elements 22 are thus load carrying components and are configured to transfer loads between the inner ring 20 and the outer ring 21.

(17) The radial elements 22 have an airfoil shape with a leading edge 221 directed towards the inlet side, a trailing edge 222 directed towards the outlet side, and two opposite sides 223, 224 connecting the leading edge 221 and the trailing edge 222 (see FIG. 4). The locus of points midway between the two opposite sides 223, 224 forms a mean camber line of each radial element 22.

(18) The supporting structure 27 will now be described with reference to FIGS. 3-5. Several radial elements 22 are in this example provided with a similar region of reduced stiffness 10 but this region is only indicated for the first element 22a and the description below therefore focus on the first element 22a.

(19) The first radial element 22a is connected to an adjacent part 30 of the supporting structure 27 via a weld joint 50 that extends across the leading edge 221 and circumferentially around the first radial element 22a. The weld joint 50 is indicated by a weld line positioned in the center of the joint. The adjacent part 30 forms a radial extension of the first radial element 22a and the weld joint 50 is thus located between the inner ring 20 and the outer ring 21, substantially closer to the inner ring 20. As can be seen in FIG. 4 the weld joint extends around the first element 22a in a path some, roughly constant, distance from the inner ring 20.

(20) The adjacent part 30 is connected to the inner ring 20. In this example the adjacent part 30 forms part of an inner, casted part that includes both the inner ring and a number of similar adjacent parts 30 forming extensions and connection points for all radial elements 22. A similar design may be arranged at the other end of the radial elements 22 in the vicinity of the outer ring 21, including for instance an outer weld joint that connects the elements 22 to an additional adjacent part and further to the outer ring 21 and that extends in a similar way as the weld joint 50.

(21) As shown in FIGS. 3-5 the first radial element 22a comprises a wall structure that forms the leading edge 221 and the two opposite sides 223, 224. The element 22a is thus a hollow component. The sides 223, 224 are joined together at the outlet side of the structure 27 as to form the trailing edge 222.

(22) The thickness of the wall structure is greater along the weld joint 50 than in the region of reduced stiffness 10. In this example the thickness of the wall structure is substantially uniform all over the element 22a except in the region of reduced stiffness, where the wall thickness has been reduced. This can clearly be seen in FIG. 5 where a cross section taken substantially parallel to the weld line 50 shows that the wall thickness is less in the region of reduced stiffness 10. In this example the general thickness of the wall structure is 2 mm (millimeters), whereas the thickness in the region of reduced stiffness 10 is 1 mm.

(23) As shown in FIGS. 2-5, the region of reduced stiffness 10 is arranged in the vicinity of the leading edge 221 and has an elongated shape and extends along the leading edge 221 in a radial direction between the inner and outer rings 20, 21.

(24) A main effect of reducing the wall thickness in the vicinity of the leading edge 221 is that the supporting structure 27, or more exact the first element 22a, achieves a lower radial stiffness in this region 10 than in another region along the weld joint 50. As described above, this leads to a reduced stress in the weld joint 50 and in particular in the part of the weld joint 50 crossing the leading edge 221.

(25) All transitions between larger and thinner wall thickness as well as the corners in areas with reduced thickness are rounded and smooth.

(26) The distance along the leading edge 221 between an end point of the region of reduced stiffness 10 and the center line of the weld joint 50 is at least two times the wall thickness at the weld line or at least 5 mm (0.2 inch). This distance forms a security distance and its position is indicated with the letter D in FIG. 4 (and in FIG. 7). The distance D is thus the minimum radial distance between the center of the weld line 50 and the closest area with reduced wall thickness.

(27) FIGS. 6-8 show another variant of the design of the region of reduced stiffness 10. The first element is now denoted 22b. The main difference from what is described above regarding element 22a is that the region of reduced stiffness 10 comprises a plurality of sub-regions 10a with reduced wall thickness. These sub-regions 10a are distributed along the leading edge 221 as to form the elongated region of reduced stiffness 10. In this example there are five sub-regions 10a. The number and distribution pattern of the sub-regions 10a can be varied.

(28) In the example shown in FIGS. 6-8 the general thickness of the wall structure is 2 mm, whereas the thickness in each of the sub-regions 10a with reduced thickness (and stiffness) is 1.5 mm.

(29) FIGS. 6-8 also show a further weld joint/line 40 that extends approximately in parallel to the leading edges 221, and approximately perpendicular to the weld joint 50, at a distance from the leading edge 221 along the side wall 224. This side weld joint 40 is not related to the region of reduced stiffness 10 in the same way as the weld joint 50 but is a result of an example of a method for producing the element 22b as will be described below. The method of production of the elements 22 is not strictly connected to the design of the region of reduced stiffness 10 which means that the weld line 40 instead could have been shown in FIGS. 3-5. Further, the weld line 40 could have been indicated in the other side wall 223 instead, or in both sides 223, 224.

(30) A method for manufacturing a supporting structure 27 having a wall structure radial element 22 as described above can comprise the following steps: providing a substantially flat wall structure, forming the region of reduced stiffness 10 in the substantially flat wall structure by forming one or several sub-regions 10a with reduced wall thickness, e.g. by milling, forming the substantially flat wall structure, at least an inlet side portion of the first radial element 22a, 22b comprising the leading edge 221 and at least a portion of each of the two opposite sides 223, 224, and forming the two opposite sides 223, 224 and connecting them by welding along the trailing edge 222.

(31) In the example shown in FIGS. 3-5 both the entire opposite sides 223, 224 form part of the substantially flat wall structure. Both sides are thus formed by shaping/bending the flat wall structure.

(32) In the example shown in FIGS. 6-8, the entire side wall 223 forms part of the flat wall structure but only a forward part of the other side wall 224 forms part of the flat wall structure. These parts form the inlet side portion of the first radial element 22a, 22b comprising the leading edge 221 and at least a portion of each of the two opposite sides 223, 224. Thus, the side wall 224 comprises a remaining portion, and this remaining portion is welded to the forward part along the weld line 40. Thus, in this case the method comprises the step of connecting the inlet side portion of the first radial element 22a, 22b to the corresponding remaining portion of the at least one opposite side 224.

(33) The method preferably also includes the step of connecting the first of said radial elements 22a, 22b to an adjacent part of the supporting structure 27 by welding such as to form said weld joint 50.

(34) A general intention with respect to the subject matter disclosed herein is thus to introduce features in the leading edge zone of a structural fabricated vane such that there is a stress relief in the weld connecting vane to hub or to shroud aiming to increase life in these welds. The more inclination of the vane (the angle between engine axial direction and aero flow direction) the more load will, in a ring-strut-ring configuration, be transferred through the leading edge zone of the vane when subjected to thermal loads, hence a leading edge stress relief feature is more beneficial to the weld life for such designs.

(35) The term radial elements should be interpreted such that the elements extend between an inner ring and an outer ring in a direction that is generally radial (with reference to an axial flow gas turbine engine). The radial elements may be inclined to the true radial direction.

(36) The supporting structure 27 is produced by welding at least two parts together, wherein at least the first radial element 22a, 22b has a weld joint 50 that extends circumferentially around the first radial element 22a, 22b along the opposite sides 223, 224 and across the leading edge 221.

(37) The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims. For instance, the supporting structure provided with the region(s) of reduced stiffness does not necessarily have to be positioned downstream of the combustion equipment as exemplified above. Further, more than one supporting structure can comprise such regions. Further, the supporting structure can be applied to other types of gas turbine engines than the one exemplified in FIG. 1. The design of the region of reduced stiffness may vary among the radial elements of the same supporting structure.