Wind turbine blades

Abstract

A reinforcing structure for a wind turbine blade is in the form of an elongate stack of layers of pultruded fibrous composite strips supported within a U-shaped channel. The length of each layer is slightly different to create a taper at the ends of the stack; the centre of the stack has five layers, and each end has a single layer. The ends of each layer are chamfered, and the stack is coated with a thin flexible pultruded fibrous composite strip extending the full length of the stack. The reinforcing structure extends along a curved path within the outer shell of the blade. The regions of the outer shell of the blade on either side of the reinforcing structure are filled with structural foam, and the reinforcing structure and the foam are both sandwiched between an inner skin and an outer skin.

Claims

1. A wind turbine blade of generally hollow construction and formed from first and second opposing half-shells; each opposing half-shell comprising an inner skin and an outer skin and first and second elongate reinforcing structures being located between the inner and outer skins; each elongate reinforcing structure extending along a lengthwise direction of the wind turbine blade and comprising a stack of layers; each stack of layers having a thickness which extends in a direction substantially perpendicular to a surface of the wind turbine blade and a width that is perpendicular to the lengthwise direction of the wind turbine blade and perpendicular to the thickness of the stack, and each layer comprising at least one pre-cured pultruded fibrous composite strip; each opposing half-shell further comprising core material disposed between the inner and outer skins and extending: (a) between the first and second elongate reinforcing structures; (b) from the first elongate reinforcing structure towards a leading edge of the wind turbine blade; and (c) from the second elongate reinforcing structure towards a trailing edge of the wind turbine blade; a first elongate web extending between the first elongate reinforcing structure in the first and second opposing half-shells; and a second elongate web extending between the second elongate reinforcing structure in the first and second opposing half-shells.

2. The wind turbine blade as claimed in claim 1, wherein the first and second elongate reinforcing structures and the core material define abutment edges which are substantially perpendicular to the surface of the wind turbine blade.

3. The wind turbine blade as claimed in claim 1, further comprising, within each opposing half-shell, a pre-cured mesh located between the outer skin and at least one of the first or second elongate reinforcing structures.

4. The wind turbine blade as claimed in claim 3, wherein the or each pre-cured mesh is formed from glass weave and pre-cured resin.

5. The wind turbine blade as claimed in claim 1, further comprising, within each opposing half-shell, a pre-cured mesh located between the inner skin and at least one of the first or second elongate reinforcing structures.

6. The wind turbine blade as claimed in claim 1, further comprising, within at least one of the first or second opposing half-shells, a pre-cured mesh located between the outer skin and a region of abutment of one of the first or second elongate reinforcing structures and the core material.

7. The wind turbine blade as claimed in claim 1, further comprising, within at least one of the first or second opposing half-shells, a pre-cured mesh located between the inner skin and a region of abutment of one of the first or second elongate reinforcing structures and the core material.

8. The wind turbine blade as claimed in claim 1, wherein each layer comprises a single pultruded fibrous composite strip extending across a full width of the layer.

9. The wind turbine blade as claimed in claim 1, wherein each layer comprises a plurality of pultruded fibrous composite strips.

10. The wind turbine blade as claimed in claim 9, wherein the plurality of pultruded fibrous composite strips comprises a parallel configuration of strips within each layer.

11. The wind turbine blade as claimed in claim 10, wherein longitudinal edges of the plurality of pultruded fibrous composite strips within each layer of the stack are aligned with edges of the plurality of pultruded fibrous composite strips of other layers that form the stack of layers.

12. The wind turbine blade as claimed in claim 10, wherein longitudinal inner edges of the plurality of pultruded fibrous composite strips within each layer of the stack are staggered with respect to inner longitudinal edges of another one of the plurality of pultruded fibrous composite strips within the or each adjacent layer.

13. The wind turbine blade as claimed in claim 9, wherein the plurality of pultruded fibrous composite strips comprises a plurality of strips arranged end to end.

14. The wind turbine blade as claimed in claim 1, wherein the stack further comprises a covering layer extending a full length of the stack.

15. The wind turbine blade as claimed in claim 14, wherein a thickness of the covering layer is substantially less than a thickness of the layers within the stack.

16. The wind turbine blade as claimed in claim 1, wherein the at least one pre-cured pultruded fibrous composite strip is formed from at least one of the following: carbon fibres; glass fibres; aramid fibres; and natural fibres.

17. The wind turbine blade as claimed in claim 1, further comprising an elongate support element for supporting the stack of layers.

18. The wind turbine blade as claimed in claim 17, wherein the elongate support element comprises a channel of generally U-shaped cross section, and wherein the stack of layers is supported within the channel.

19. The wind turbine blade as claimed in claim 17, wherein the elongate support element is formed from a glass-reinforced plastics (GRP) material.

20. The wind turbine blade as claimed in claim 1, wherein the first and second elongate webs are formed from a resilient material.

21. The wind turbine blade as claimed in claim 1 and comprising at least one elongate channel of generally U-shaped cross section in which an elongate reinforcing structure may be supported.

22. The wind turbine blade as claimed in claim 1, wherein the inner and outer skins extend substantially uninterrupted across the core material and the first and second elongate reinforcing structures.

23. The wind turbine blade as claimed in claim 1, wherein each of the first and second elongate webs includes a flange at each end to engage with the inner skin of the wind turbine blade.

24. The wind turbine blade as claimed in claim 23, wherein each flange has a width that is less than a width of the first and second elongate reinforcing structures of each opposing half-shell.

25. The wind turbine blade as claimed in claim 1, wherein each of the first and second elongate webs has an “I”-shaped or “C”-shaped cross-section.

26. The wind turbine blade as claimed in claim 1, wherein the first elongate reinforcing structure of the first and second opposing half-shells is located at a region of maximum distance between the first and second opposing half-shells.

27. The wind turbine blade as claimed in claim 1, wherein the second elongate reinforcing structure for each opposing half-shell is located closer to the trailing edge compared to the first elongate reinforcing structure for each opposing half-shell.

28. A method of manufacturing a wind turbine blade of generally hollow construction and comprising first and second half-shells; disposing, in each of a first and second elongated half-mould, one or more fibre cloths for respective outer skins; locating, in each of the first and second elongated half-moulds, first and second elongate reinforcing structures on the one or more fibre cloths for the outer skins so as to extend along the lengthwise direction of the first and second elongated half-moulds; each elongate reinforcing structure comprising a stack of layers, each stack having a thickness which extends in a direction substantially perpendicular to a surface of a corresponding one of the first and second elongated half-mould; each layer extending across a width of a corresponding stack, the width being perpendicular to the lengthwise direction of the corresponding one of the first and second elongated half-mould and perpendicular to the thickness of the stack, and each layer comprising at least one pre-cured pultruded fibrous composite strip; disposing within each of the first and second elongated half-mould core material on the one or more fiber cloths for the outer skin so as to extend: (a) between the first and second elongate reinforcing structures; (b) from the first elongate reinforcing structure towards a leading edge of the first and second elongated half-mould; and (c) from the second elongate reinforcing structure towards a trailing edge of the first and second elongated half-mould; disposing, in each of the first and second elongated half-mould, on upper surfaces of the first and second elongate reinforcing structures and the core material, one or more fibre cloths for respective inner skins; supplying resin into the first and second elongated half-moulds; subsequently curing the resin so as to form the first and second half-shells; subsequently disposing a first elongate web and a second elongate web in one of the first and second elongated half-moulds such that the first elongate web extends between the first elongate reinforcing structure in the first and second opposing half-shells and the second elongate web extends between the second elongate reinforcing structure in the first and second opposing half-shells; and pivoting the first half-mould into a position above the second half-mould such that the first elongate web extends between the first elongate reinforcing structure in the first half-mould and the first elongate reinforcing structure in the second half-mould, and the second elongate web extends between the second elongate reinforcing structure in the first half-mould and the second elongate reinforcing structure in the second half-mould.

29. The method as claimed in claim 28, further comprising locating, within at least one of the first and second elongated half-moulds, a pre-cured mesh between the outer skin and a region of abutment of one of the first or second elongate reinforcing structures and the core material.

30. The method as claimed in claim 28, further comprising locating, within at least one of the first and second elongated half-moulds, a pre-cured mesh between the inner skin and a region of abutment of one of the first or second elongate reinforcing structures and the core material.

31. A wind turbine blade of generally hollow construction and formed from first and second opposing half-shells; each opposing half-shell comprising an inner skin and an outer skin and first and second elongate reinforcing structures being located between the inner and outer skins; each elongate reinforcing structure extending along a lengthwise direction of the wind turbine blade and comprising a stack of layers, each elongate reinforcing structure having a thickness which extends in a direction substantially perpendicular to a surface of the wind turbine blade and a width that is perpendicular to the lengthwise direction of the wind turbine blade and perpendicular to the thickness of the elongate reinforcing structure, and each layer comprising at least one pre-cured pultruded fibrous composite strip; each opposing half-shell further comprising core material disposed between the inner and outer skins and extending: (a) between the first and second elongate reinforcing structures; (b) from the first elongate reinforcing structure towards a leading edge of the wind turbine blade; and (c) from the second elongate reinforcing structure towards a trailing edge of the wind turbine blade; and the wind turbine blade further comprising an elongate web extending between at least one of the reinforcing structures in the first opposing half-shell and at least one of the reinforcing structures in the second opposing half-shell; wherein each elongate reinforcing structure has an upper surface and a lower surface which are planar in a chordwise direction of the wind turbine blade.

32. The wind turbine blade as claimed in claim 31, wherein each elongate reinforcing structure has an oblong rectangle-shaped cross-section.

33. The wind turbine blade as claimed in claim 31, wherein the layers of each stack have different lengths in the lengthwise direction such that the thickness of each elongate reinforcing structure is tapered towards at least one longitudinal end.

34. The wind turbine blade as claimed in claim 33, wherein the thickness of each elongate reinforcing structure is thickest at a central region thereof.

35. The wind turbine blade as claimed in claim 31, wherein longitudinal ends of each elongate reinforcing structure are chamfered.

36. The wind turbine blade as claimed in claim 35, wherein each elongate reinforcing structure has a constant width along a length of the reinforcing structure between the longitudinal ends.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the present invention may more readily be understood, preferred embodiments thereof will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates the main structural components of a wind turbine;

(3) FIG. 2 is a schematic illustration of the inner surface of one half of the outer shell of a wind turbine blade incorporating reinforcing structures in accordance with a preferred embodiment of the present invention;

(4) FIGS. 3(a) and 3(b) are cross-sectional sketches of arrangements of reinforcing structures within a half-shell of a wind turbine blade;

(5) FIGS. 4(a) to 4(e) are schematic longitudinal cross-sectional views of a wind turbine blade incorporating the reinforcing structures shown in FIG. 2;

(6) FIG. 5 illustrates a lateral cross-sectional view of part of one of the reinforcing structures illustrated in FIG. 2;

(7) FIGS. 6(a) to 6(c) illustrate longitudinal sections of three different embodiments of reinforcing structures in accordance with the present invention;

(8) FIGS. 7(a) and 7(b) are two schematic representations of an X-section web, in accordance with a preferred embodiment, at different positions along the length of a wind turbine blade;

(9) FIG. 8 is a longitudinal cross-sectional view of a reinforcing structure mounted within a mould during the manufacture of a wind turbine blade in accordance with a preferred embodiment;

(10) FIGS. 9(a) and 9(b) illustrate a method of manufacturing a wind turbine blade in accordance with a preferred embodiment of the present invention;

(11) FIGS. 10(a) to 10(f) illustrate alternative forms of web, in accordance with further embodiments, shown at different positions along the length of a wind turbine blade;

(12) FIGS. 11(a) and 11(b) illustrate further alternative forms of web, in accordance with embodiments of the present invention;

(13) FIG. 12 is a flowchart illustrating steps in the manufacture of a wind turbine blade in accordance with a preferred embodiment of the present invention;

(14) FIG. 13 illustrates an alternative method in the manufacture of a wind turbine in accordance with an embodiment of the present invention;

(15) FIG. 14 is a flowchart illustrating the steps in the method shown in FIG. 12; and

(16) FIGS. 15(a) to 15(c) illustrate a preferred embodiment in which meshes are provided in each half-shell of the wind turbine blade.

DETAILED DESCRIPTION OF THE DRAWINGS

(17) Throughout the following description of the preferred embodiments of the present invention, and in the drawings, the same reference numerals are used to indicate the same, or corresponding, structural features.

(18) Referring to FIG. 2, one half 8 of the outer shell of a wind turbine blade is formed with three elongate reinforcing structures 9, 10, 11, to be described in greater detail below. Two of the reinforcing structures 9, 10 extend substantially along the full length of the turbine blade from the root section 12 to the blade tip 13. The root section 12 of the blade is formed with threaded metallic inserts 14 for receiving bolts by which the blade is attached to the central hub of the wind turbine, as described above with reference to FIG. 1.

(19) The third reinforcing structure 11 extends only part-way along the blade from the root section 12 and is also laterally displaced from the other two reinforcing structures 9, 10 towards the trailing edge 15 of the blade and away from the leading edge 16 of the blade.

(20) The two reinforcing structures 9, 10 form the spar caps of the wind turbine blade and the third reinforcing structure 11 acts as a stiffener for the trailing edge 15.

(21) The ends of the three reinforcing structures 9, 10, 11 within the root section 12 of the blade are encased in a glass-reinforced plastics (GRP) material for added strength and stability, as are the distal ends of the two reinforcing structures 9, 10 which extend to the blade tip 13.

(22) The remaining portions of the outer shell are filled with structural foam 17, and the reinforcing structures 9, 10, 11 and the structural foam 17 are all formed within an outer skin and an inner skin to be described in greater detail below.

(23) The structural foam 17 is a lightweight core material, and it will be appreciated that other core materials can be used, such as wood, particularly balsa wood, and honeycomb.

(24) The complete turbine blade is formed from the upper half 8 of the outer shell shown in FIG. 2, together with a corresponding lower half and two internal webs.

(25) FIG. 3(a) illustrates a cross-sectional view of a conventional arrangement in which each half-shell 8′ comprises an inner skin 18′ and an outer skin 19′ between which only a single reinforcing structure 9′ is provided. The regions between the inner skin 18′ and the outer skin 19′ to each side of the reinforcing structure 9′ are filled with structural foam 17′. As can be seen from the drawing, there is a significant curvature across the width of the half-shell 8′. Since the reinforcing structure 9′ is formed with a substantially rectangular cross-section, it follows that that substantial voids 20′ are formed between the outer skin 19′ and the central region of the reinforcing structure 9′, and between the inner skin 18′ and the end regions of the reinforcing structure 9′. During the moulding stage, to be described in detail below, resin is introduced into these voids 20′, which is undesirable in a composite structure, since this increases both the weight and the cost of the blade, and could also give rise to structural problems.

(26) FIG. 3(b) is a cross-sectional view of a preferred embodiment of the present invention in which each half-shell 8 is provided with at least two reinforcing structures 9, 10 provided between the inner skin 18 and the outer skin 19. As can be seen, the volume of the resulting voids 20 which are formed between the outer skin 19 and the central region of the reinforcing structure 9, and between the inner skin 18 and the end regions of the reinforcing structure 9 is substantially less than that of the voids 20′ which occur when only a single reinforcing structure 9′ is provided. As a result, the amount of resin required to fill the voids 20 during the moulding process is substantially less.

(27) In addition, by using two reinforcing structures in each half shell, as shown FIG. 3(b), as opposed to the single reinforcing structure shown in FIG. 3(a), the overall widths of the reinforcing structures are located more closely to the outer skin 19 of the wind turbine blade. This is advantageous for structural reasons, since it provides a higher second moment of inertia such that the wind turbine blade has a greater resistance to bending.

(28) FIGS. 4(a) to 4(e) are cross-sectional representations of the complete turbine blade at different positions along the length of the blade. FIG. 4(a) represents the blade near the blade tip 13, from which it can be seen that only the first two reinforcing structures 9, 10 are present at this position along length of the upper half of the outer shell shown in FIG. 2. The lower half 21 of the outer shell is also provided with three reinforcing structures 22, 23, 24, again only two of which 22, 23 are present at this position.

(29) A resilient elongate web 25 made from a layer of balsa wood or lightweight foam sandwiched between two outer layers of GRP and having a generally X-shaped longitudinal cross section is provided within the outer shall and serves to transfer the shear forces which act on the turbine blade in use. One of the two diagonal arms of the X-shape extends between a first pair of the reinforcing structures 9, 23, and the other diagonal arm extends between a second pair of the reinforcing structures 10, 22.

(30) In FIG. 4(b), which represents a position along the length of the turbine blade between that of FIG. 4(a) and the central section, the end-portions of the two remaining reinforcing structures 11, 24 can be seen.

(31) FIG. 4(c) represents the central section of the turbine blade, from which it can be seen that a further resilient elongate web 26 having a generally Z-shaped longitudinal cross section is provided which extends between the two reinforcing structures 11, 24 at the trailing edge 15 of the blade. The two outer limbs of the Z-shape act as flanges for connecting the Z-shaped web 26 to the two associated reinforcing structures 11, 24.

(32) Referring to FIG. 4(d), which is a detail of the cross-sectional view of FIG. 4(c), the reinforcing structure 22 is sandwiched between the inner skin 18 and the outer skin 19, and the remaining parts of the outer shell are formed from a layer of structural foam 17, also sandwiched between the inner and outer skins 18, 19. The skins are made from GRP.

(33) The reinforcing structure 22 is in the form of a stack 27 of layers of pultruded fibrous composite strips supported within a U-shaped channel 28, which in turn is supported on an elongate wedge 29 such that the base of the channel 28 is at an acute angle to the outer skin 19 of the shell. The channel 28 includes material which acts as a lightning conductor in use. In other embodiments, the U-shaped channel 28 and the wedge 29 may be omitted.

(34) The end of the arm of the X-shaped web 25 is provided with a flange 30 for directing the shear force applied across the full width of the reinforcing structure 22 to the X-shaped web 25.

(35) It will be appreciated that the enlarged view shown in FIG. 4(d) applies equally to each of the six reinforcing structures 9, 10, 11, 22, 23, 24.

(36) FIG. 4(e) illustrates a cross-sectional view of the blade between the central section represented in FIG. 4(c) and the root section 12, and it can be seen that the reinforcing structures 9, 10, 11, 22, 23, 24 within each half-shell are closer together than at the central section of the blade, reflecting the curvature of the reinforcing structures.

(37) In FIGS. 4(a) to 4(e) it can be seen that the reinforcing structures 9, 10, 22 and 23 are spar caps which, together with the shear webs 25, form the main structural spar of the wind turbine blade. The reinforcing structures 11 and 24 at the trailing edge stiffen the wind turbine blade in the region of the trailing edge to provide stability against buckling and, together with the web 26, form a trailing edge spar.

(38) Each of the stacks 27 of the reinforcing structures 9, 10, 11, 22, 23, 24 is tapered longitudinally at both ends. This is achieved by a reduction in the number of layers of pultruded fibrous strips from five at the central section to only a single layer at each end. This feature is indicated in the drawings, wherein, in FIGS. 4(a) and 4(e), the respective stacks 27 of the reinforcing structures 9, 10, 22, 23, 24 have only a single layer, whereas the stacks 27 within the central section illustrated in FIG. 4(c) have five layers. Equally, in FIG. 4(b), the stacks 27 of the reinforcing structures 9, 10, 22, 23 at the ends of the X-shaped web 25 have five layers, whereas the stacks 27 of the reinforcing structures 11, 24 at the ends of the Z-shaped web 26 have only a single layer.

(39) This feature enables the reinforcing structures 9, 10, 11, 22, 23, 24 to adopt a profile consistent with the thickness profile of the outer shell of the blade.

(40) This is further illustrated in the side cross-sectional view of FIG. 5, which shows how the thickness of the stack 27 of five layers 31 is tapered towards both the root end 12 and the distal end 32. It should be emphasised that the drawing is merely illustrative of the tapered arrangement: in practice, the tapering may be distributed throughout a large part of the length of the reinforcing structure.

(41) Two further features of the preferred embodiment enhance the smoothness of the tapering so as reduce the impact of stresses which would arise with discontinuities in the surface profile of the stack 27. First, each layer 31 is chamfered at both ends so as to remove the square-cut ends which are formed during the cutting of the pultruded strips which form the layers 31. Secondly, the stack 27 is covered with a top layer 33 formed from an additional pultruded fibrous composite strip having a lesser thickness than that of the underlying layers 31. Since the top layer 33 is thinner than the other layers 31, it is also more flexible and therefore able to bend around the angled chamfered ends of the stack 27 within the tapered end regions to form a relatively smooth upper surface.

(42) Each layer 31 within the stack has a thickness of approximately 4 mm, and the thickness of the top layer is approximately 1 mm.

(43) FIGS. 6(a) to 6(c) are longitudinal cross-sectional views showing three different arrangements of pultruded fibrous composite strips, or pultrusion strips 34 within the five layers 31. In FIG. 6(a), each layer 31 has only a single pultrusion strip 34 within each layer. In FIG. 6(b), each layer 31 is formed from a parallel arrangement of three pultrusion strips 34 of equal width laid together side by side. In FIG. 6(c), each layer 31 has either three or four pultrusion strips 34 in a parallel side-by-side arrangement, but containing pultrusion strips 34 of two different widths.

(44) In the preferred embodiments, each of the pultrusion strips 34 within the above three arrangements extends the full length of the respective layer 31, although it may be beneficial in some embodiments for at least some of the layers 31 to include shorter strips 34 which are arranged end to end.

(45) FIGS. 7(a) and 7(b) illustrate in greater detail the central section and root section 12 respectively of the wind turbine blade showing the X-shaped resilient web 25. The reinforcing structures are not shown in the drawings, for the sake of clarity. The web is formed in two generally V-shaped halves 25a, 25b, and the lower ends of each half 25a, 25b as viewed in the drawings is attached to the lower half of the outer shell by means of a layer of adhesive (not shown), and the two halves 25a, 25b of the web 25 are joined together by bolts 36.

(46) FIG. 8 is a longitudinal cross-sectional view illustrating in greater detail the region of the outer shell which includes a reinforcing structure 22 within a lower half-mould 37. During manufacture, the outer skin 19, in the form of a dry fibre cloth, or a plurality of superposed and/or overlapping dry fibre cloths, is first placed on the surface of the half-mould 37, and elongate wedges 29 are then positioned on the outer skin 19 along the curvilinear regions where the reinforcing structures 9, 10, 11, 22, 23, 24 are to be positioned. The inner skin, described further below, is also formed by a dry fibre cloth, or a plurality of superposed and/or overlapping dry fibre cloths. The dry cloths are, once positioned in the half-moulds with other components as described below, impregnated with resin supplied into the half-moulds, e.g., in an infusion process, such as the one described below. It should be pointed out that as an alternative, also mentioned below, the inner and outer skin could be provided from prepreg (pre-impregnated fibre) cloths, where the resin is supplied into the half-moulds together with the fibre material of the cloths.

(47) The reinforcing structures are positioned along respective upper surfaces of the wedges 29. This can be achieved by firstly positioning the U-shaped channel 28 of each reinforcing structure along the upper surface of the wedge 29 and then introducing the stack 27 of pultruded layers of fibrous composite strips into the channel 28, or alternatively forming the entire reinforcing structure outside the half-mould 37 and then placing it along the upper surface of the wedge 29. In either case, the reinforcing structure can be lowered into position on the wedge 29 or slid into position along the surface of the wedge 29.

(48) The orientation of the upper surfaces of the wedges 29 is varied along their length in dependence on the curvature of the linear regions so as to retain the reinforcing structures in the desired positions.

(49) A layer of structural foam 17 is then introduced into the half-mould 37 to fill the regions between the reinforcing structures 9, 10, 11, 22, 23, 24. The inner skin 18, in the form of a dry fibre cloth, or a plurality of superposed and/or overlapping dry fibre cloths, is then placed on the upper surfaces of the reinforcing structures and the structural foam 17 and the components covered with an airtight bag to form an evacuation chamber which is subsequently evacuated and resin introduced, as described in greater detail below.

(50) The components within the lower half-mould 37 are then heated and the resin thereby cured so as to form the lower outer half-shell of the blade.

(51) The inner skin 18 and the outer skin 19 are formed in this embodiment from a layer of biax glass cloth, although multiple layers may alternatively be used. As mentioned above, it would also be possible to omit the U-shaped channel 28 and the elongate wedges 29 so that the stack 27 is formed and located directly on the outer skin 19. It would also be possible to position the structural foam 17 on the outer skin 19 and then subsequently to introduce the stack 28 into the mould 37.

(52) An upper half-mould with an outer shell is then positioned above the lower half-mould 37 mould so as to form the complete outer shell of the blade.

(53) FIG. 9(a) illustrates the overall structure of the components of the lower half of the outer shell when in the lower mould-half 37. Referring to FIG. 9(b), after the inner skin 18 has been placed over the surface of the reinforcing structures 22, 23 and the upper surface of the structural foam 17, an air-tight sealing layer (i.e., a vacuum bag) 38 is attached to the mould so as form an evacuation chamber encapsulating all of the components, and the chamber is then evacuated using a vacuum pump 39. With the pump 39 still energised, a supply of liquid resin 40 is connected to the chamber so as to infuse both the components and the interstitial spaces therebetween. A corresponding infusion process is applied to the components of the upper half of the outer shell. The pump 39 continues to operate during a subsequent moulding operation in which the mould is heated so as to cure the resin, although during the curing process the extent of de-pressurisation may be lowered.

(54) The X-shaped web 25 and the Z-shaped web 26 are then attached by means of adhesive to the inner skin 18 immediately above the reinforcing structures 22, 23, 24 in the lower half-mould 37, and the upper free ends of the webs 25, 26 are coated with respective layers of adhesive.

(55) The upper half-mould is then pivoted into position above the lower half-mould 37, and the two half-moulds connected together. This causes the reinforcing structures 9, 10, 11 within the upper half-mould to adhere to the upper free ends of the webs 25, 26. The resilient nature of the webs 25, 26 give rise to a biasing force of the webs 25, 26 against the upper reinforcing structures 9, 10, 11 so as to ensure good adhesion. The leading edge of the blade is formed along leading edges of the respective half-moulds, and trailing edge of the blade is formed along trailing edges of the respective half-moulds.

(56) The mould is then opened, and the finished turbine blade lifted from the mould.

(57) FIGS. 10(a) to 10(f) are cross-sectional illustrations of alternative embodiments of wind turbine blades in which each of the webs 41, 42, 43 is of I-shaped cross section, which, in combination with the associated reinforcing structures, results in an I-beam construction. Since each of the webs is provided with a flange 30 at each end, these could alternatively be considered as C-section webs, where the arms of the C-shape constitute the flanges 30.

(58) In FIGS. 10(a) to 10(c), there are only four reinforcing structures 9, 10, 22, 23. FIG. 10(a) represents a cross sectional view near the blade tip, FIG. 10(b) a sectional view mid-way along the blade, and FIG. 10(c) a sectional view near the root end, where it can be seen that the thickness of the reinforcing structure 9, 10, 22, 23 is tapered. As can be seen from the drawings, the reinforcing structures within each half-shell are closer together near the tip of the blade.

(59) In FIGS. 10(d) to 10(f), there are six reinforcing structures 9, 10, 11, 22, 23, 24, and a respective I-shaped web 41, 42, 43 linking each pair of opposed structures 9, 19; 10, 23; and 11, 24. FIG. 10(d) represents a cross sectional view near the blade tip, FIG. 10(e) a sectional view mid-way along the blade, and FIG. 10(f) a sectional view near the root end, where again it can be seen that the thickness of the reinforcing structure 9, 10, 22, 23 is tapered.

(60) FIGS. 11(a) and 11(b) illustrate two further forms of web. In FIG. 11(a), the web 44 has an X-shaped cross section in which the two diagonals are bent at the intersection 45, so that the upper limbs diverge at an angle α which is greater than the angle β between the lower two limbs. An advantage of this arrangement is that the upper wide angle gives rise to additional flexibility when the two half-moulds are closed, while the lower limbs serve merely to bridge the gap between the two shells. In FIG. 11(b), the lower two limbs have been combined into a single limb, resulting in a web 46 of Y-shaped cross section. Such a web can replace the X-shaped and/or Z-shaped webs described above.

(61) Referring to FIG. 12, the method described above can be summarised as comprising a step 47 of providing the support surface within the lower half-mould 37, a step 48 of introducing reinforcing structures 9 into the lower half-mould 37 and a step 49 of sliding the reinforcing structures 9 along the surface of the wedge 29 into the respective desired positions.

(62) FIG. 13 illustrates an alternative method, in which the pultruded strips 34 are placed in a separate mould, provided as a U-shaped channel 28, outside of the main half-mould 50, together with a matrix (resin or adhesive) which is pre-cured so that the stack 27 is formed in the separate mould 28. The pre-cured cured stack 27 is then placed in the main half-mould 50 for an infusion resin process together with the other structural elements.

(63) Referring to FIG. 14, this method can be summarised as comprising the following steps: (a) forming a stack of fibrous layers 51; (b) pre-curing the stack of fibrous layers in a first mould 52; (c) introducing the pre-cured stack into a second mould 53; and (d) integrating the stack and the other structural elements together in the second mould 54. In some embodiments, the stack can be partially cured in the first mould and then fully cured in the second mould. In other embodiments the stack can be fully cured in the first mould and integrated as such with the other structural elements in the second mould wherein some of other structural elements are cured.

(64) FIGS. 15(a) to 15(c) illustrate schematically a further preferred embodiment, which may be combined with any of the embodiments described above. For the sake of enhanced clarity, the elements are not drawn to scale. In each half-shell 8 there are provided inner and outer pre-cured meshes 55, 56 formed from glass weave and pre-cured resin, and these are positioned between the respective inner and outer skins 18, 19 and the underlying reinforcing structures 9, 10. The meshes 55, 56 extend over the regions where the underlying reinforcing structures 9, 10 abut the core material 17. In the region of the blade tip 13, the two reinforcing structures 9, 10 are closely separated, as illustrated in the cross-sectional view of FIG. 15(a) taken along the line A-A′ of FIG. 15(c). In this case, each of the inner and outer meshes 55, 56 extends across both of the underlying reinforcing structures 9, 10, so as to cover all of the four transition regions between the reinforcing structure 9, 10 and the core material 17. However, in the region of the root section 12 of the blade, the two reinforcing structures 9, 10 are further apart, as illustrated in the cross-sectional view of FIG. 15(b) taken along the line B-B′ of FIG. 15(c). In this case, each of the inner and outer meshes 55, 56 extends across only a respective one of the underlying reinforcing structures 9, 10, so as to cover only the two transition regions between the respective reinforcing structure, e.g., 9 and the adjacent core material 17.

(65) The function of the inner and outer meshes 55, 56 is to prevent the inner and outer skins 17, 18 from wrinkling due to: (a) gaps between the underlying reinforcing structures 9, 10 and the adjacent core material 17; and (b) any slight differences between the thickness of the underlying reinforcing structures 9, 10 and the thickness of the core material 17.

(66) FIG. 15(c) is a plan view of this arrangement, from which it can be seen that the meshes 55, 56 form an approximate V-shape. The outlines of the reinforcing structures 9, 10 sandwiched between the inner and outer meshes 55, 56 are illustrated in the drawing by the dashed line. The side edges of the inner and outer meshes 55, 56 extend about 20 mm over the underlying core material. It would also be possible to provide a single pre-cured mesh 55 located under the reinforcing structures 9, 10 and the core material 17. However, in practice, it is beneficial for the layup, i.e., the inner and outer layers 17, 18, the reinforcing structures 9, 10 and the foam 17, to be symmetrical about a mid-point plane of the layup.

(67) It will be appreciated that numerous variations to the above embodiments may be made without departing from the scope of the present invention which is defined solely by the following claims. For example, although in the preferred embodiment there are six reinforcing structures and both an X-shaped web and a Z-shaped web, alternative embodiments may comprise only four reinforcing structures and a single X-shaped web.

(68) In a further example, as opposed to using the resin infusion method of manufacturing the blade described above with reference to FIG. 9(b), fibres which are pre-impregnated with resin (i.e., “pre-preg” fibres) may be used for the inner and outer skins, in which case it would not be necessary to infuse resin into the shell construction. In this arrangement, adhesive film layers can be provided between the individual layers in the stack so that they adhere together when the structure is cured.