Wind turbine blade with elongated fastening members in the root region thereof

Abstract

A wind turbine blade for a wind turbine is a shell structure of a fiber-reinforced composite and comprises a root region and an airfoil region. The root region has a ring-shaped cross section and comprises a plurality of elongated bushings 7 with an inner thread 22 and embedded interspaced in the fiber-reinforced polymer so as to substantially follow the circumference of the root region and allow access from the outside to the inner threads. Each fastening member 7 is provided with a notch 60 in the periphery 11 thereof. A rod-shaped locking element 61 passes through the notch 60 in engagement therewith. The locking element 61 is fixedly and tightly fitting arranged in a through-going circular bore 65 extending through the wall of the root region.

Claims

1. A wind turbine blade for a wind turbine rotor comprising a hub from which the wind turbine blade extends when mounted to the hub, the wind turbine blade including a shell structure of a fibre-reinforced composite material comprising fibres embedded in a polymer matrix, the wind turbine blade extending in longitudinal direction and having a profiled contour including a pressure side and a suction side as well as a leading edge and a trailing edge, said edges defining a chord plane therebetween, when seen in the longitudinal direction the profiled contour comprising a root region with a root end face, an airfoil region and optionally a transition region between the root region and the airfoil region, the root region having a ring-shaped cross section with an outer surface and an inner surface, the root region comprising a plurality of elongated fastening members provided with fastening means, wherein the elongated fastening members are embedded mutually spaced apart in the fibre-reinforced polymer matrix so as to substantially follow a circumference of the root region and allow access from outside of the blade to the fastening means used for mounting the blade to the hub, the fastening members comprising an outer surface, a first end arranged at the root end face and a second end opposite the first end thereof, characterised in that at least a number of the elongated fastening members are provided with at least one notch in the periphery thereof, said notch having a notch wall, a first notch end and an opposite second notch end, and that a rod-shaped locking element passes through said notch so as to at least substantially engage at least a portion of the notch wall and so that a first portion of the rod-shaped locking element extends beyond the first notch end and a second portion of the rod-shaped locking element extends beyond the second notch end, the rod-shaped locking element being fixedly arranged in a circular bore having an axis and extending at least partly through the shell structure of the root region from the inner or outer surface of the shell structure.

2. A wind turbine blade according to claim 1, wherein the notch wall is partly cylindrical with a cylinder axis being coaxial with the axis of the bore.

3. A wind turbine blade according to claim 1, wherein the rod-shaped locking element has a circular cross section corresponding at least substantially to that of the bore.

4. A wind turbine blade according to claim 1, wherein the bore is a through-going bore.

5. A wind turbine blade according to claim 1, wherein the axis of the bore extends substantially in radial direction relative to the root region.

6. A wind turbine blade according to claim 1, wherein the notch is placed at distance from the first end of the elongated fastening members, said distance being 50-95% or 60-95% or 70-95% of the length of the elongated fastening members.

7. A wind turbine blade according to claim 1, wherein the fastening members are provided with two notches, a first notch and a second notch, said notches being arranged substantially opposite each other.

8. A wind turbine blade according to claim 1, wherein the notches of adjacent fastening members are arranged so as to face each other and the bore and the rod-shaped locking element are provided in such a way between the adjacent fastening members that the rod-shaped locking element engages the notch wall of both notches.

9. A wind turbine blade according to claim 1, wherein the notches of all of the fastening members are arranged at the same distance from the first end of the elongated fastening members.

10. A wind turbine blade according to claim 1, wherein the fastening members are bushings and the fastening means is a thread in a bore of the bushing.

11. A wind turbine blade according to claim 10, wherein the at least one notch is provided so as to intersect the bore of the bushing.

12. A wind turbine blade according to claim 1, wherein the fastening members and the rod-shaped locking elements are made of metal.

13. A wind turbine blade according to claim 1, wherein metal fibres are firmly fixed to the fastening members so as to extend therefrom and are embedded in the polymer matrix of the fibre-reinforced composite material of the root region.

14. Method of producing a wind turbine blade according to claim 1, wherein the elongated fastening members are provided with at least one notch before being embedded in the fibre-reinforced composite material of the root region, and wherein the bore is drilled through the composite material of the root region from the inner or outer surface of the shell structure such that it passes through the notch and at least substantially reveals the notch surface and subsequently thereto the rod-shaped locking element is fixedly arranged in the bore.

15. Method of producing a wind turbine blade according to claim 1, wherein the elongated fastening members are embedded in the fibre-reinforced composite material of the root region and wherein the bore is drilled through the composite material of the root region from the inner or outer surface of the shell structure such that it intersects the periphery of the elongated fastening member and thereby provides the notch surface, and subsequently thereto the rod-shaped locking element is fixedly arranged in the bore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in greater detail below with reference to the drawings, in which

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 is a diagrammatic perspective view of a wind turbine blade according to the invention,

(4) FIG. 3 is a perspective, longitudinal, sectional view of a portion of a root region of an embodiment of a wind turbine blade according to the invention,

(5) FIG. 4 shows a portion of the root region shown in FIG. 3,

(6) FIG. 5 is a perspective view of a separate pre-formed insert arranged next to an elongated fastening member in form of a bushing,

(7) FIG. 6 shows an embodiment of an elongated fastening member in form of a bushing including two notches,

(8) FIG. 7 shows the bushing shown in FIG. 6, a rod-shaped locking element engaging each of the notches.

DETAILED DESCRIPTION OF THE INVENTION

(9) FIG. 1 illustrates a conventional, modern upwind turbine 24 according to the so-called Danish concept with a tower 36, a nacelle 25 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 23 and three blades 2 extending radially from the hub 23, each having a blade root 31 nearest the hub, and a blade tip 32 furthest from the hub 23.

(10) As evident seen from FIG. 2, the blade 2 comprises a root region 26 with a root end face 29 closest to the hub, an airfoil region 27 furthest away from the hub, and a transition area 28 between the root region 26 and the airfoil region 27. The airfoil region 27 has an ideal or almost ideal blade shape, whereas the root region 26 has a substantially circular cross section, which reduces storm loads and makes it easier and safer to mount the blade 2 to the hub 23. Preferably, the diameter of the blade root 31 is constant along the entire root region 26. The transition region 28 has a shape gradually changing from the circular shape of the root region 26 to the airfoil profile of an airfoil region 27. The width of the transition region 28 increases substantially linearly with increasing distance from the hub 23.

(11) The blade is often made of two blades halves assembled by being glued or bolted together substantially along a chord plane 35 of the blade. The blade 2 comprises a leading edge 34 facing the rotational direction of the blade 2 when the blade 2 is mounted on the hub 23 and a trailing edge 33 facing in the opposite direction of the leading edge 34. The chord plane 35 extends between the leading edge 34 and the trailing edge 33 of the blade 2. It should be noted that the chord plane does not necessarily run straight over its entire extent, since the blade may be twisted and/or curved, thus providing a chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub. Due to the circular cross section, the root region 26 does not contribute to the production of the wind turbine and, in fact, it lowers the production slightly due to the wind resistance.

(12) As seen in FIGS. 3 and 4, the blade including the root region 26 is formed as a shell structure. The shell structure of the root region 26 is ring-shaped and comprises an outer surface 3 formed by an outer layer 5 of a fibre-reinforced polymer matrix advantageously of glass fibres and/or carbon fibres and a resin, such as epoxy, polyester or vinylester, and an oppositely arranged inner surface 4 formed by an inner layer 6 being made of the same material as the outer layer 5. Elongated fastening members 7 with fastening means 22 are placed between the layers 5, 6. Advantageously, the elongated fastening members 7 are bushings having a circular cross section and comprise a central bore 12 with an inner thread 22 as fastening means. The bushing 7 comprises an outer periphery 11, a first end 9 and an oppositely arranged second end 10. The first end 9 of the bushing 7 is placed at the root end face 29 of the root region. The bushings 7 are arranged mutually spaced apart so as to substantially follow the circumference of the root region and allow access from the outside to the fastening means 22, i.e. the threads used for mounting the blade to the hub. Further and as shown in FIG. 4, metal fibres 13, such as steel fibres, may be firmly fixed to the bushings 7, especially to the second end 10 thereof, so as to provide an increased retention of the bushings 7 in the fibre-reinforced composite material of the root region.

(13) Intermediate retaining means comprising metal fibres 13 is arranged in each region between adjacent interspaced lateral surface portion of the fastening members 7, i.e. in the present example the bushings. Further, in the present embodiment the intermediate retaining means are formed of separately manufactured inserts 39. As it appears from FIG. 5, the inserts 39 comprise a first insert part 40 and a second insert part 41. The first insert part 40 essentially corresponds to the region between the lateral surface portions of adjacent bushings 7 and is provided with opposite lateral faces 42, 43 formed complimentary to the lateral surface portions of the adjacent bushings 7. The inserts 39 substantially extend up next to the adjacent bushings when seen in circumferential direction. Further, the first insert part 40 extends from the first end of the bushings 7 and beyond the second end thereof, as clearly seen in FIG. 5. The second insert part 41 is a wedge-shaped tapering extension of the first insert part 40. As seen in radial direction of the root region, the first insert part 40 has an extent substantially corresponding to that of the bushings.

(14) The pre-formed insert 39 comprises a number of first layers 16 comprising metal fibres 13 and intermediate second layers 37 comprising a second fibre material 38 differing from the metal fibres, as shown in FIG. 5.

(15) As seen in FIG. 3 a wedge-shaped element 17 is arranged behind each bushing 7 when seen in longitudinal direction of the blade. A first end 18 of the element 17 is arranged in abutment with the second end of the bushing 7, and a second end 19 of the element 17 is tapered. The wedge-shaped elements 17 are made of balsawood or a hard polymer foam or a similar material. In a longitudinal sectional view, the bushing 7 and the abutting wedge-shaped element 17 have a shape corresponding to the shape of the inserts 39 so that the wall thickness of the root region decreases gradually in the longitudinal direction of the blade.

(16) As seen especially in FIG. 3, through-going bores 65 are drilled through the wall of the root region from the inner surface 4 to the outer surface 3 thereof. The bores 65 are arranged in line with a notch 60, 60 provided in the outer periphery 11 of the bushings 7.

(17) As shown in FIGS. 6-7, a first notch 60 may be arranged diametrically opposite a second notch 60. Each notch has a part-cylindrical notch surface 67 having a first end 68 and a second end 69. Further, as it appears from FIGS. 6 and 7, the notches 60, 60 are arranged adjacent the second end of the bushings 7. As shown the bushings 7 may have a corrugated outer surface.

(18) A rod-shaped locking element 61 is fixedly arranged and tightly fitting in the bore 65. A central portion of the surface of the rod-shaped locking element 61 engages the notch surface 67 of the notch 60, 60 so that a first end 62 of the rod-shaped locking element 61 extends beyond the first end 68 of the notch and a second end 63 of the rod-shaped locking element 61 extends beyond a second 69 of the notch, as seen in FIG. 7.

(19) The rod-shaped locking elements 61 have a cylindrical shape and extend coaxially with the bores 65 in which they are received and such that the end faces thereof are substantially flush with the inner surface 4 and the outer surface 3, respectively, of the root region 26.

(20) During manufacture of the blade the bushings 7 are placed in a mould and embedded in the polymer matrix of the fibre-reinforced composite material. The fibre material may comprise any type of fibres, such as glass fibres, carbon fibres and metal fibres. The polymer matrix may comprise a resin, such as polyester, epoxy or vinylester.

(21) The circular bores 65 are drilled through the fibre-reinforced composite material. By this drilling process the notches 60, 60 may be formed in the bushings 7. Alternatively, the notches 60, 60 may be formed in the bushings 7 before the bushings are placed in the mould, whereby the bores 65 are only formed in the fibre-reinforced composite material and not in the material of the bushings 7.

(22) Finally, a rod-shaped locking element 61 is fixedly arranged tightly fitting in each bore 65. Each bore 65 is arranged such that the axis thereof is substantially perpendicular to the longitudinal axis of the bushings 7 and so that the axis of the bore 65 extends substantially radial relative to the root region 26.

(23) With respect to FIG. 5 it should be noted that it discloses the position of the bushings 7 in relation to the pre-made inserts 39 during manufacture of the wind turbine blade, why a bore passing through the notch 60 and the insert 39 is not shown. The through-going bore 65 is drilled after the manufacture of the wind turbine blade and the rod-shaped locking element 61 is subsequently arranged in the formed bore 65.

(24) It should be noted that neither fibre-reinforced composite material nor bores 65 drilled therein are shown in FIGS. 6 and 7, as these figures serve to illustrate the bushings 7, the notches 60, 60 provided therein, and the rod-shaped locking elements 61 engaging the notch surfaces 67 of the notches 60, 60.

(25) Further, as seen in FIGS. 3-4 the notches 60, 60 of all of the elongated fastening members 7 and consequently also the bores 65 may be arranged at the same distance from the root end face 29, i.e. that the notches of the bushings 7 are also placed at the same distance from the first end 9 of the bushings 7.

(26) Advantageously, the bushings 7 and the rod-shaped locking elements 61 are made of a metal, such as iron or steel.

LIST OF REFERENCE NUMERALS

(27) 2 Wind turbine blade 3 Outer surface of root 4 Inner surface of root 5 Outer layer 6 Inner layer 7 Elongated fastening member (bushing) 9 First end of fastening member 10 Second end of fastening member 11 Outer periphery of fastening member 12 Central bore 13 Metal fibres 16 First layer comprising metal fibres 17 Wedge-shaped element 18 First end of element 19 Second end of element 22 Fastening means (inner threads) 23 Hub 24 Wind turbine 25 Nacelle 26 Root region 27 Airfoil region 28 Transition region 29 Root end face 31 Blade root 32 Blade tip 33 Trailing edge 34 Leading edge 35 Chord plane 36 Tower 37 Second layers 38 Second fibre material 39 Insert 40 First insert part 41 Second insert part 42 Lateral face of insert 43 Lateral face of insert 60 First notch 60 Second notch 61 Rod-shaped locking element 62 First end of rod-shaped locking element 63 Second end of rod-shaped locking element 65 Bore 66 Opening into bore 67 Notch surface 68 First end of notch surface 69 Second end of notch surface