LEADING EDGE PROTECTION OF A WIND TURBINE BLADE

Abstract

The invention relates to a leading edge protection cover for a wind turbine blade. The protection cover comprises first and second longitudinally extending edges, and outer and inner arcuate surfaces extending there between. The inner arcuate surface is shaped to be attached to an outer surface portion of the wind turbine blade such as to cover at least a part of the leading edge of the blade, and with the first longitudinally extending edge being attached to a suction side of the wind turbine blade. The protection cover further comprises a number of vortex generating members positioned on the outer arcuate surface of the protection cover along at least a part of the first longitudinally extending edge. The proposed protection cover results in an increased protection of the wind turbine blade against impacting particles and improved fluid properties over the surface of the wind turbine blade. The invention further relates to a method of preparing a wind turbine blade with a leading edge protection cover, comprising the steps of moulding a leading edge protection cover comprising a number of vortex generating members and attaching the leading edge protection cover to an outer surface portion of the wind turbine blade.

Claims

1. A leading edge protection cover for attachment to a wind turbine blade, the wind turbine blade extending longitudinally between a root end and a tip end of the blade, and extending transversely between a trailing edge and a leading edge, wherein the protection cover comprises first and second longitudinally extending edges, and outer and inner arcuate surfaces extending there between, and the inner arcuate surface is shaped to be attached, in use, to an outer surface portion of the wind turbine blade comprising at least a part of the leading edge with the first longitudinally extending edge being attachable to a suction side of the wind turbine blade, and the protection cover is configured to be statically fixed to the wind turbine blade, wherein the protection cover further comprises a number of vortex generating members positioned on the outer arcuate surface of the protection cover along at least a part of the first longitudinally extending edge and the vortex generating members are formed integrally with the protection cover; and the vortex generating members are positioned on the outer arcuate surface of the protection cover such that they project away from the outer surface portion of the wind turbine blade when the protection cover is attached to the blade.

2. The leading edge protection cover according to claim 1, wherein the vortex generating members comprise a body of a tetrahedron-like shape protruding from the outer arcuate surface of the protection cover.

3. The leading edge protection cover according to claim 2, wherein the tetrahedron-like shaped body comprises a pressure surface, a suction surface and a back surface, wherein the back surface faces towards the first longitudinally extending edge and the pressure surface faces towards the tip end or the root end of the blade when the protection cover is attached on the blade.

4. The leading edge protection cover according to claim 3, wherein the pressure surface is curved inwardly.

5. The leading edge protection cover according to claim 3, wherein the back surface extends substantially perpendicularly from the outer arcuate surface.

6. The leading edge protection cover according to claim 3, wherein the pressure surface extends substantially perpendicularly from the outer arcuate surface.

7. The leading edge protection cover according to claim 1, wherein the vortex generating members comprise a body of increasing height from the outer arcuate surface in a direction from the leading edge towards the first longitudinally extending edge.

8. The leading edge protection cover according to claim 1, wherein the vortex generating members protrude a maximum height from the outer arcuate surface in the range of 0.2-0.7% of a chord length of the wind turbine blade and/or in the range of 2-10 mm.

9. The leading edge protection cover according to claim 1, wherein the protective cover comprising the number of vortex generating members is moulded of a flexible plastic material such as a polyurethane or epoxy.

10. The leading edge protection cover according to claim 1, wherein the vortex generating members are positioned with a distance between the vortex generating member and the first longitudinally extending edge, the distance being in the range of 2-30 mm such as in the range of 7-15 mm.

11. A wind turbine blade extending a length between a root end and a tip end of the blade, and extending a width between a trailing edge and a leading edge, the wind turbine blade comprising an outer surface portion comprising at least a part of the leading edge, wherein the wind turbine further comprises a leading edge protection cover according to claim 1 attached to the outer surface portion of the wind turbine blade and with the first longitudinally extending edge being attached to a suction side of the wind turbine blade.

12. The wind turbine blade according to claim 11, wherein the protection cover is attached to the outer surface portion of the blade by an adhesive.

13. The wind turbine blade according to claim 11, wherein the protection cover is attached to the outer surface portion of the blade by attachment means such as screws, bolts and/or rivets placed between the vortex generating means and the first longitudinally extending edge.

14. The wind turbine blade according to claim 13, wherein the leading edge protection cover has a stiffness in the range of 500 MPamm to 250 GPamm, preferably the leading edge protection cover has a stiffness in the range of 1 GPamm to 100 GPamm.

15. A method of preparing a wind turbine blade with a leading edge protection cover, the wind turbine blade extending a length between a root end and a tip end of the blade, and extending a width between a trailing edge and a leading edge, the wind turbine blade comprising an outer surface portion comprising at least a part of the leading edge, the method comprising: moulding a leading edge protection cover comprising a number of vortex generating members and according to claim 1, attaching the leading edge protection cover to the outer surface portion of the wind turbine blade such as to cover the part of the leading edge and such that the vortex generating members are positioned on a suction side of the wind turbine blade.

16. The method of preparing a wind turbine blade according to claim 15, wherein the leading edge protection cover is moulded in a mould comprising a number of recesses for the moulding of the vortex generating members.

17. The method of preparing a wind turbine blade according to claim 15, wherein the method steps form part of a manufacture of the wind turbine blade.

18. The method of preparing a wind turbine blade according to claim 15, wherein the method step of attaching the leading edge protection cover is performed as post processing during repair or maintenance of the wind turbine blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following different embodiments of the invention will be described with reference to the drawings, wherein:

[0037] FIG. 1 shows a wind turbine blade comprising a leading edge protection cover,

[0038] FIGS. 2A and B show a wind turbine blade comprising a leading edge protection cover in a partially perspective view and the leading edge area comprising a leading edge protection cover according to an embodiment of the invention in an enlargement,

[0039] FIGS. 3A-C illustrate the wind flow around a wind turbine blade profile without and with a protection cover, and with a protection cover according to an embodiment of the invention, respectively,

[0040] FIGS. 4A-E illustrate different shapes of vortex generation members to be positioned on a protection cover according to different embodiments of the invention,

[0041] FIG. 5 illustrates the positioning of a vortex generating member on a protection cover as seen in a perspective and cross-sectional view, and FIGS. 6A-D illustrate different shapes of a part of a vortex generation member as seen in a top view.

DETAILED DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a wind turbine blade 110 extending a length 201 between a root end 202 and a tip end 203 of the blade, and extending a width between a trailing edge 205 and a leading edge 206 as indicated by the arrow 204. An outer surface portion 210 of the wind turbine blade covers a part of the leading edge 206 and is provided with a leading edge protection cover 100 according to the invention.

[0043] FIG. 2A illustrates a part of the wind turbine blade 101 as seen in a cross-sectional view corresponding to the indicated profile 300 in FIG. 1 in a mid-blade position 211 and the outer part of the blade towards the tip 203 in a perspective view. The foremost area around the leading edge 206 is seen in an enlargement in FIG. 2B. An outer or exterior surface portion 210 of the blade covers and extends across the leading edge 206 of the blade. In FIG. 2A the arrows 207 indicate the flow paths around the wind turbine blade under normal wind turbine operation below rated power. The wind turbine blade 110 comprises a leading edge protection cover 100 attached to the surface portion 210 thereby covering at least a part of the leading edge of the blade.

[0044] The leading edge protection cover 100 comprises a first 221 and a second 222 longitudinally extending edge, and an outer 223 and an inner 224 arcuate surface extending there between. The thickness 208 of the cover is the distance between the outer 223 and inner 224 arcuate surfaces orthogonal to the inner 224 arcuate surface. The thickness 208 is typically substantially constant (i.e. having a thickness variation of less than 20%) for the whole protection cover. In some embodiments the protection cover has a maximum thickness in a part of the cover between 221 and 222 that is more than 20% higher than a minimum thickness of the protection cover as described elsewhere. The first longitudinally extending edge 221 is attached to a suction side of the wind turbine blade. The protection cover 100 further comprises a number of vortex generating members 250 positioned on the outer arcuate surface 223 of the protection cover and along at least a part of the first longitudinally extending edge 221 and thereby on the suction side of the wind turbine blade. The vortex generating members 250 are positioned upstream from the first longitudinally extending edge 221 of the protection cover and thereby upstream of the step or discontinuity, 230 between the protection cover and the blade surface. The vortex generating members 250 may additionally be positioned along at least a part of the second longitudinally extending edge 222 on the pressure side of the wind turbine blade as indicated in FIG. 2B.

[0045] FIGS. 3A-C illustrate how a leading edge protection cover 100 affects the flow around a wind turbine blade profile 300, and the advantageous functioning of the vortex generating members on the protection cover. In FIG. 3A is shown the typical laminar flow 310 around a wind turbine blade profile 300. In FIG. 3B is illustrated how the attachment of a traditional protection cover 100 creates stepped surfaces or a discontinuity 230 on both the suction side and the pressure side causing the boundary layer to separate 311 and a loss of lift. In FIG. 3C is illustrated the effect of a protection cover 100 according to the invention and comprising a vortex generating member 250 positioned upstream from the edge of the cover. The vortex generator 250 on the protection cover creates turbulence in the flow causing mixing in the air flow thereby stabilizing the boundary layer along the suction surface. In this way the vortex generating member 250 effectively hides the geometric discontinuity between the protection cover 100 and the blade surface increasing the lift.

[0046] FIGS. 4A-E illustrate different preferred shapes of vortex generation members 250 to be positioned on the protection cover 100. Here, the vortex generating members 250 comprise a body 400 of a tetrahedron-like shape protruding from the outer arcuate surface 223 of the protection cover 100. The tetrahedron-like shaped bodies 400 here all comprise a pressure surface 401, a suction surface 402 and a back surface 403. The surfaces are oriented such that the back surface 403 faces towards the first longitudinally extending edge 221. The vortex generating members 250 in FIG. 4 are thus seen in a perspective view from the back toward the leading edge and against the general direction of the wind inflow as indicated by the arrow 410 for the member in FIG. 4D. The pressure surface 401 faces towards the tip end 203 of the blade. The body 400 of the vortex generating members 250 has a height as measured from the outer arcuate surface which increases in the direction from the leading edge 206 towards the first longitudinally extending edge 221, i.e. in the general direction of the wind flow, 410. The maximum height 430 of one of the vortex generating members 250 is indicated in FIG. 4E. The maximum height 430 is preferably in the range of 0.2-0.7% of a chord length of the wind turbine blade and/or in the range of 2-10 mm.

[0047] The angling 420 of the pressure surface 401 relative to the general direction of the wind inflow 410 is illustrated in FIG. 5 and for some different pressure surface shapes in FIGS. 6A-D as seen in a top view.

[0048] The criteria for angling and for the shape of the pressure surface 401 and/or suction surface 402 of the body of the vortex generating member 250 are generally that the pressure surface 401 is angled and shaped to obtain favourable flow properties. The shape and angling of this surface therefore in general follow the same design rules as for traditional fin-like type vortex generators. Furthermore, the suction side 402 is shaped and angled to obtain a body volume and enough material volume to achieve the desired stiffness of the vortex generating member.

[0049] The angle 420 between the pressure surface 401 and the general direction of the wind flow 410 is typically around 5-20 degrees. In its simplest form, the pressure surface may be a flat surface as illustrated in FIG. 6A. In the embodiments shown in FIG. 6B and C, the pressure surfaces 401 curve at least partly inward guiding the airflow accordingly. Alternatively, as shown in FIG. 6D, the pressure surface 401 may curve or bulge outwardly towards the incoming air, i.e. form a convex shape. In this way the shape of the vortex generating members can be tuned to obtain the desired altering of the flow along the surface of the blade which enables the hiding of the geometric discontinuity between the protection cover 100 and the blade surface. The protection cover is preferably moulded in a relatively soft and flexible material such as a soft polyurethane to withstand and follow the deformations of the wind turbine blade. By the proposed tetrahedron-like shapes of the vortex generating members, these can be formed integrally with the protection cover and preferably of the same material and still have the necessary stiffness to cause the vortex generation and mixing of the airflow.

[0050] While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.