WIND TURBINE BLADE

Abstract

According to the present invention there is provided a wind turbine blade extending in a spanwise direction between a root and a tip, and in a chordwise direction between a leading edge and a trailing edge. The wind turbine blade has a spar cap comprising a plurality of strips of fibrous composite material. Each strip extends in the spanwise direction between a first end and a second end to define a length of the strip, and each strip has a width and a thickness, the width being less than the length, and the thickness being less than the width. Each strip has upper and lower major surfaces defined by the length and width dimensions. Each strip has side surfaces defined by the length and thickness dimensions. The plurality of strips includes a first strip and a second strip. The first strip has a tapered end portion in which the thickness of the first strip decreases towards the first end of the first strip. The tapered end portion defines a tapered end face inclined with respect to the upper and lower major surfaces of the first strip. The first and second strips are bonded together such that the first end of the first strip meets the upper or lower major surface of the second strip to define an interface between the first and second strips. The spar cap further comprises a patch arranged across the interface. The patch comprises a stack of fibrous plies.

Claims

1. A wind turbine blade extending in a spanwise direction between a root and a tip, and in a chordwise direction between a leading edge and a trailing edge, the wind turbine blade having a spar cap comprising a plurality of strips of fibrous composite material, each strip extending in the spanwise direction between a first end and a second end to define a length of the strip, each strip having a width and a thickness, the width being less than the length, and the thickness being less than the width, each strip having upper and lower major surfaces defined by the length and width dimensions, and side surfaces defined by the length and thickness dimensions; the plurality of strips including a first strip and a second strip, the first strip having a tapered end portion in which the thickness of the first strip decreases towards the first end of the first strip, the tapered end portion defining a tapered end face inclined with respect to the upper and lower major surfaces of the first strip; the first and second strips being bonded together such that the first end of the first strip meets the upper or lower major surface of the second strip to define an interface between the first and second strips; wherein the spar cap further comprises a patch arranged across the interface, the patch comprising a stack of fibrous plies.

2. The wind turbine blade of claim 1, wherein the patch plies comprise fibres extending in the spanwise direction and/or multi-axial fibres.

3. The wind turbine blade of claim 1, wherein the patch is a preform in which the patch plies are connected together prior to the patch being arranged across the interface.

4. The wind turbine blade of claim 1, wherein the patch plies are staggered in the spanwise direction.

5. The wind turbine blade of claim 1, wherein edges of adjacent patch plies are staggered in the chordwise direction.

6. The wind turbine blade of claim 1, wherein the patch plies are all substantially the same shape and size.

7. The wind turbine blade of claim 1, wherein the patch plies are shaped as trapeziums.

8. The wind turbine blade of claim 1, wherein a width of the patch in the chordwise direction is greater than the width of the first and second strips.

9. The wind turbine blade of claim 1, wherein a length of the patch in the spanwise direction is significantly less than the length of the first or second strips.

10. The wind turbine blade of claim 1, wherein the thickness of the patch plies is significantly less than the thickness of the first and second strips.

11. The wind turbine blade of claim 1, wherein a first part of the patch is arranged on the upper major surface of the first strip and a second part of the patch is arranged on the upper major surface of the second strip, or wherein a first part of the patch is arranged on the lower major surface of the first strip and a second part of the patch is arranged on the lower major surface of the second strip.

12. The wind turbine blade of claim 1, wherein the second strip has a tapered end portion in which the thickness of the second strip decreases towards an end of the second strip, the tapered end portion defining a tapered end face inclined with respect to the upper and lower major surfaces of the second strip.

13. The wind turbine blade of claim 12, wherein the tapered end face of the first strip is bonded to the tapered end face of the second strip to form a scarf joint between the two strips.

14. The wind turbine blade of claim 1, wherein the first and second strips are stacked on top of one another.

15. The wind turbine blade of claim 14, wherein a first part of the patch is arranged on the tapered end face of the first strip and a second part of the patch is arranged on the upper or lower major surface of the second strip.

16. The wind turbine blade of claim 1, further comprising one or more glass-fibre layers extending over the first and second strips and over the patch, the glass-fibre layer(s) completely covering the first and second strips and the patch.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Examples of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

[0032] FIG. 1a is a schematic plan view of a wind turbine blade;

[0033] FIG. 1b is a schematic cross-sectional view of a portion of a spar cap of the wind turbine blade comprising a plurality of strips;

[0034] FIG. 1c is a detail view of a tapered end portion of a spar cap strip;

[0035] FIG. 2a is schematic exploded view of another example of a wind turbine blade;

[0036] FIG. 2b is a schematic cross-sectional view of a scarf joint between a first and second strip of the spar cap; and

[0037] FIG. 2c is a schematic detail view of the scarf joint shown in FIG. 2b;

[0038] FIG. 3 is a schematic plan view of a patch arranged across an interface between first and second strips of the spar cap.

DETAILED DESCRIPTION

[0039] FIG. 1a is a schematic plan view of a wind turbine blade 10. The wind turbine blade 10 extends in a spanwise direction(S) between a blade root 12 and a blade tip 14, and in a chordwise direction (C) between a leading edge 16 and a trailing edge 18. The wind turbine blade 10 includes a spar cap 20 configured to take up and transfer bending loads experienced by the blade 10 in use.

[0040] The spar cap 20 comprises a plurality of strips 22 of fibrous composite material as shown more clearly in the cross-sectional view of FIG. 1b and the detail view of FIG. 1c. Each spar cap strip 22 extends in the spanwise direction(S) between a first end 24 and a second end 26 to define a length, i.e. a spanwise length, of the strip 22. Each strip 22 also has a width, i.e. a chordwise width, and a thickness, where the thickness is orthogonal to both the length and width of the strip. The width of each strip 22 is less than the length of the strip 22, and the thickness of each strip 22 is less than the width of the strip 22. Each strip 22 has an upper and lower major surface 28, 30 defined by the length and width dimensions, and, whilst not shown in the cross-sectional views, each strip 22 also has side surfaces defined by the length and thickness dimensions.

[0041] Referring still to FIGS. 1b and 1c, the spar cap 20 comprises a first strip 22a and a second strip 22b which are bonded together. In some examples, the first and second strips 22a, 22b may be stacked on top of one another. To form a spar cap 20 with a tapering thickness, the strips 22 in the stack may be staggered in the spanwise direction(S). In order to minimise stress concentrations and gradually transfer loads between the adjacent strips 22, the first strip 22a has a tapered end portion 32a in which the thickness of the first strip 22a decreases towards the first end 24a of the first strip 22a. The tapered end portion 32a defines a tapered end face 34a that is inclined, i.e. angled, with respect to the upper and lower major surfaces 28a, 30a of the first strip 22a. The first end 24a of the first strip 22a meets a major surface of the second strip 22b, in this example the upper major surface 28b, to define an interface 36 between the first and second strips 22a, 22b.

[0042] With reference now to FIG. 2a, another example of a wind turbine blade 10 is shown in a schematic exploded view. FIG. 2b shows a cross-sectional view of a portion of the spar cap 20 of the blade 10, and FIG. 2c shows a detail view of a portion of the spar cap 20. Equivalent features to those previously described with reference to FIGS. 1a to 1c will not be repeated here for conciseness. However, as shown in FIGS. 2a, in some examples the blade 10 may be a modular wind turbine blade comprising blade modules 38a, 38b which are connected together at a joint 40. Preferably, the joint 40 may be formed between spar cap strips 22a, 22b associated with each blade module 38a, 38b.

[0043] Whereas the first and second spar cap strips 22a, 22b are arranged on top of one another in a stack in the example of FIGS. 1a to 1c, in some examples, the first and second strips 22a, 22b may be bonded together in the same layer of a stack. For example, with reference more particularly to FIG. 2b, the second strip 22b, to which the first strip 22a is bonded, may also have a tapered end portion 32b. As such, the thickness of the second strip 22b may decrease towards an end 24b of the second strip 22b. The tapered end portion 32b of the second strip 22b may therefore define a tapered end face 34b that is inclined with respect to the upper and lower major surfaces 28b, 30b of the second strip 22b. Accordingly, in some examples the tapered end face 34a of the first strip 22a may be bonded to the tapered end face 34b of the second strip 22b to form a scarf joint 42 between the two strips 22a, 22b. The first end 24a of the first strip 22a again meets a major surface 28b or 30b of the second strip 22b, in this example the lower major surface 30b, to define an interface 36 between the first and second strips 22a, 22b.

[0044] It will be appreciated that the schematic accompanying figures are not drawn to scale. The tapered end portion 32a, 32b of the first and/or second spar cap strip 22a, 22b may taper at a rate of approximately 1:100, i.e. 1 cm in thickness for every 100 cm in spanwise distance. In order to illustrate the examples more clearly, the tapered end portions 32a, 32b are shown with a steeper taper. However, it will be appreciated that in practice, the thin tapered ends 32a, 32b configured for advantageous load transfer, may be susceptible to peel loads in use as described by way of background.

[0045] As such, the spar cap 20 further comprises a patch 44 arranged across the interface 36 between the first and second strips 22a, 22b, as shown in FIGS. 1b, 1c and 2b for example. The patch 44 provides strength to the interface 36 and helps to resist peel loads that act to separate the first and second strips 22a, 22b in use. The patch 44 additionally helps to resist shear loads at the interface 36. The patch 44 comprises a stack of fibrous plies 46, such as glass fibre plies, and will now be described in more detail with reference to FIG. 3.

[0046] The patch 44 shown in the schematic plan view of FIG. 3 may be arranged across an interface 36 between first and second staggered strips 22a, 22b in a stack, as shown in FIG. 1b for example, or the patch 44 may be arranged across an interface 36 between first and second strips 22a, 22b that form a scarf joint 42, as shown in FIG. 2b for example. As such, the following description of the patch 44, interface 36, and strips 22a, 22b applies equally to each of the previously described examples.

[0047] The fibrous plies 46 in the patch 44 may be referred to herein as patch plies 46. The patch plies 46 may comprise fibres extending in the spanwise direction(S) and/or multi-axial fibres. In preferred examples, one or more of the patch plies 46 may comprise spanwise extending unidirectional fibres to increase the strength of the patch 44 to resist bending loads in use, and to thereby also help resist peel loads and shear loads that act to separate the ends 32a, 32b of the strips 22a, 22b.

[0048] In some examples, as shown in FIG. 1c, a first part 44a of the patch 44 may be arranged on the tapered end face 34a of the first strip 22a and a second part 44b of the patch 44 may be arranged on the upper or lower major surface 28b, 30b of the second strip 22b. Alternatively, and as shown in FIG. 2b for example, a first part 44a of the patch 44 may be arranged on the upper or lower major surface 28a, 30a of the first strip 22a, and a second part 44b of the patch 44 may be arranged similarly on the upper or lower major surface 28b, 30b of the second strip 22b. As such, in each example the patch 44 spans the interface 36 between the first and second strips 22a, 22b. Accordingly the patch 44 provides a secondary load path for transferring loads between the first and second strips 22a, 22b of the spar cap 20.

[0049] As shown in FIGS. 1b and 2b as well as FIG. 3, the patch plies 46 may be staggered in the spanwise direction(S) in preferred examples. As most clearly shown in the cross-sectional views of FIGS. 1b and 2b, staggering the plies 46 in the spanwise direction(S) results in a patch 44 having a tapered thickness. As such, the patch 44 may be configured to receive loads gradually from one of the strips 22, and subsequently transfer the loads gradually from the patch 44 to the other strip 22, thereby reducing the risk of stress concentrations and faults near the interface 36. In some examples, as shown most clearly in FIG. 3, edges 48 of adjacent patch plies 46 may be staggered in the chordwise direction (C) to similarly distribute loads and reduce stress concentrations in the patch 44.

[0050] Referring still to FIGS. 1b and 2b, the thickness of each patch ply 46 is preferably significantly less than the thickness of the first and second strips 22a, 22b. As such, the patch plies 46 are preferably configured to only take up a small proportion of the loads transferred between the first and second strips 22a, 22b, with the thicker spar cap strips 22a, 22b being configured to take up and transfer a majority of the load. As such, the patch 44 is preferably configured to provide a secondary load path, whilst the main load path for transferring loads remains between the first and second spar cap strips 22a, 22b.

[0051] Further the patch 44 is preferably configured with a spanwise length significantly less than the length of the first or second strips 22a, 22b. Such a configuration simplifies arrangement of the patch 44 across the interface 36. In some examples, the patch 44 may be a preform in which the patch plies 46 are connected together prior to the patch 44 being arranged across the interface 36. Again, such a configuration further facilitates a simple arrangement of the patch 44 across the interface 36 between the first and second spar cap strips 22a, 22b, and may help to ensure the patch plies 46 are accurately aligned relative to one another.

[0052] With reference again to FIG. 3, a chordwise width of the patch 44 may be greater than the chordwise width of the first and second strips 22a, 22b. This helps to ensure that peel loads are resisted across the full width of the interface 36, thereby providing a robust connection between the first and second spar cap strips 22a, 22b.

[0053] The patch plies 46 may be substantially the same shape and size. In some examples, as shown in FIG. 3, the patch plies 46 may be shaped as trapeziums to help distribute loads in the patch 44 and avoid stress concentrations. Whilst not shown in the accompanying figures, in some examples the blade 10 may comprise one or more glass-fibre layers extending over the first and second strips 22a, 22b and over the patch 44. For example, the glass-fibre layer, or layers, may completely cover the first and second strips 22a, 22b and the patch 44. Staggering the patch plies 46 in the spanwise direction(S), and/or staggering edges 48 of adjacent patch plies 46 in the chordwise direction (C) is particularly beneficial in such examples. The staggered patch plies 46 form a patch 44 having a tapering thickness, i.e. a thickness that changes incrementally, which helps to ensure that additional layers extending over the first and second strips 22a, 22b and over the patch 44, do not experience a sudden step change in thickness, thereby avoiding kinks and/or stress concentrations in the additional layer(s).

[0054] Further, it will be appreciated that the above description and accompanying figures are provided merely as an example of the present invention. Many alternatives to the specific examples described above are therefore possible without departing from the scope of the invention as defined in the appended claims.

[0055] For example, it will be appreciated that whilst the description of a scarf joint 42 formed between the first and second strips 22a, 22b has been provided above in the context of a joint 40 between two blade modules 38a, 38b, in some examples a wind turbine blade 10 may comprise a scarf joint 42 between first and second strips 22a, 22b of the spar cap 20 without the scarf joint 42 necessarily being part of a joint 40 between two blade modules 38a, 38b. For example, the spar cap 20 may comprise a scarf joint 42 between two shorter spar cap strips 22a, 22b that are bonded together at a scarf joint 42 to form a spar cap 20 having the requisite length.

[0056] It will be appreciated that the description provided above serves to demonstrate a plurality of possible examples of the present invention. Features described in relation to any of the examples above may be readily combined with any other features described with reference to different examples without departing from the scope of the invention as defined in the appended claims.