Aerodynamic Shroud and Method

Abstract

A leading edge of a wind-turbine blade has a carefully designed predetermined shape. After operation of the blade, erosion damages that shape and the blade needs repair. Repair is difficult to carry out in the field or, for offshore turbines, at sea. A shroud (8) for repairing a damaged leading edge of a wind-turbine blade (2) is rigid and has a shape matching the predetermined shape of the leading edge. Advantageously the shroud has a multi-layered structure in which a base layer (10) of the shroud comprises a rigid material.

Claims

1. A shroud for repairing a leading edge of a wind-turbine blade, the leading edge having a predetermined shape, the shroud being rigid and having a shape matching the predetermined shape of the leading edge.

2. A shroud according to claim 1, having a U-shaped cross section that, in use, fits over the leading edge of the wind-turbine blade.

3. A shroud, according to claim 1, in which in use a central portion of the shroud is adjacent to the leading edge of the wind-turbine blade, and side portions of the shroud are at an angle of more than 60 to a plane tangential to the central portion.

4. A shroud according to claim 1, in which side portions of the shroud end at tapered trailing edges of the shroud.

5. A shroud according to claim 1, having a multi-layered structure in which a base layer of the shroud comprises a rigid material.

6. A shroud according to claim 5, in which the rigid material comprises a fibre-reinforced composite.

7. A shroud according to claim 1, having a multi-layered structure in which an outer layer of the shroud comprises an impact-absorbing material.

8. A method for repairing or protecting a leading edge of wind-turbine blade by securing over the leading edge a shroud as defined in claim 1.

9. A method according to claim 8, comprising securing the shroud with an adhesive.

10. A method for making a shroud for repairing a leading edge of a wind-turbine blade, comprising moulding at least a first portion of the shroud using a mould having the same shape as the leading edge of the wind-turbine blade.

11. A method according to claim 10, in which the portion of the shroud formed using the mould is a rigid support layer of the shroud.

12. A method according to claim 11, in which the support layer comprises a fibrous material reinforced with a curable resin, and the resin is cured in the mould to form a rigid shroud matching the shape of the leading edge of the wind-turbine blade.

13. A method according to claim 11, in which the support layer is a base layer which, in use, is adjacent to the leading edge of the wind-turbine blade.

14. A method according to claim 10, comprising the step of applying a further portion of the shroud after the moulding of the first portion of the shroud.

15. A method according to claim 14, in which the further portion is an outer layer forming, in use, a replacement leading edge of the wind-turbine blade.

16-19. (canceled)

Description

DESCRIPTION OF SPECIFIC EMBODIMENTS

[0030] Specific embodiments of the invention will now be described by way of illustrative and enabling example only, with reference to the accompanying drawings, in which:

[0031] FIG. 1 is an image of an eroded wind-turbine blade;

[0032] FIG. 2 is a schematic cross-section of a shroud according to a first embodiment of the invention in position on a wind-turbine blade leading edge;

[0033] FIG. 3 is a perspective view of a shroud embodying the invention in position on a mould, which has been used to form the shroud; and

[0034] FIGS. 4 and 5 are perspective views of the exterior and interior surfaces of the shroud of FIG. 3.

[0035] FIG. 1 is an image of a wind-turbine blade 20 showing erosion of the leading edge 22 after a period of service. As can clearly be seen, the erosion has changed the shape of the leading edge, which may lead to a significant reduction of aerodynamic efficiency.

[0036] FIG. 2 shows a schematic transverse section of a wind-turbine blade 2, showing the leading edge 4 and a portion of the blade behind the leading edge.

[0037] In the same way as shown in FIG. 1 the blade has been in use for a period of time and erosion has damaged the leading edge, causing loss of material 6 and damaging the aerodynamic profile of the blade.

[0038] A shroud 8 embodying the invention has been used to repair the leading edge. The shroud has a U-shaped cross-section and is formed with a multi-layered structure. A base layer 10 of the shroud is adjacent to the blade surface and comprises a rigid, fibre-reinforced material. The base layer is typically formed of more than one individual layer of a thermosetting or thermoformed composite material. Suitable materials are glass-fibre or carbon-fibre or Kevlar-fibre reinforced with a two-component epoxy or other curable resin, or a thermoplastic matrix. The matrix may be toughened by the addition of a particulate reinforcement, such as rubberised or nano-particle constituents.

[0039] An outer layer, or top layer, 12 of the shroud comprises a paint or coating or other film, such as a polyurethane, epoxy-urethane, or siloxane materials.

[0040] The trailing edges of the shroud, spaced from the leading edge, are tapered 14 to allow airflow passing over the shroud, in use, to flow onto the blade surface, in order to optimise aerodynamic performance.

[0041] The shroud is glued to the blade using a single or two-part glue 16. The glue preferably has a setting time which is long enough to allow application of the shroud to the blade in the field. Suitable glues, or adhesives may be two-part epoxy adhesives, two-part methyl acrylate, two-part polyurethane, or a glue film.

[0042] The shape of the rigid shroud matches the shape of the blade, at and on either side of its leading edge.

[0043] It should be noted that in the schematic cross-section of FIG. 1, the thickness of the shroud has been exaggerated significantly in order to illustrate its layered structure. In practice, the depth of the shroud, from its leading edge to its tapering rear edges, is more than about 80 mm or 100 mm or 125 mm and less than about 250 mm or 200 mm or 150 mm. At the leading edge, the thickness of the base layer is about 1 mm and the thickness of the outer layer about 0.5 mm. The total thickness reduces towards the tapered trailing edges. For repairing a typical wind-turbine blade, the shroud may be between 5 m and 7 m long, for installation on the portion of the blade near the tip of the blade.

[0044] It is preferable that the shroud extends sufficiently far behind the leading edge of the blade, around the sides of the blade, so that airflow over the shroud flows smoothly onto and over the trailing edge of the blade. Thus, for example, where a central portion of the shroud is positioned over a leading edge of a blade, the trailing edges of the shroud are preferably at an angle of more than 50, or more than 60 or 70 or 80, to a plane tangential to the central portion.

[0045] FIG. 3 is three-quarter view of a shroud 8 in position on a mould 24 which has been used to make the shroud.

[0046] FIGS. 4 and 5 are a three-quarter views of the front side and the underside of a shroud 8, showing the shape of the rigid shroud and the base layer 10 and the outer layer 12.

[0047] FIGS. 3 to 5 show a shroud which, for the purposes of illustration, is much shorter in length than would be used to repair a longer portion of a blade. The shroud in the figures is about 50 cm long. A full-length shroud may be 5 m to 7 m long as described above.

[0048] To a fabricate a shroud as illustrated in FIGS. 2 to 5, layers of a suitable composite material, such as glass/epoxy prepreg (pre-impregnated sheet), carbon/epoxy prepreg or Kevlar/epoxy prepreg are placed over a male mould 24 having a shape identical to an unused wind-turbine blade of the type intended for repair. A vacuum may be applied between the male mould and a corresponding female mould placed over the prepreg as the matrix of the composite material is cured. The shaped composite material may then be removed from the mould and the outer layer added by painting or other coating technique. The tapered rear edges of the shroud are preferably formed during the moulding and coating processes.