Embedding element for a wind turbine blade

Abstract

The present invention relates to an embedding element (76) for embedment in a shell structure of a wind turbine rotor blade (10), the element having a wedge-shaped part (85). The embedding element (76) comprises a fibre material and a binding agent, wherein the fibre material is at least partially joined together by means of the binding agent. The inventive element provides improved structural flexibility and elasticity resulting in less wrinkle formation during blade manufacturing. In other aspects, the invention relates to a method of manufacturing the embedding element (76), to a method of manufacturing a wind turbine rotor blade (10) using the embedding element (76), and to a wind turbine blade (10) obtainable by said method.

Claims

1. A root end assembly for a wind turbine rotor blade (10) comprising a plurality of embedding elements (76) embedded together with a plurality of bushings in a root region of a blade shell structure in between an outer shell part and an inner shell part, wherein each of the embedding elements is placed between a corresponding pair of adjacent bushings, such that alternating ones of the embedding elements and the bushings are arranged about a circumference of a cross-section of the root region, each of the embedding elements (76) being elongated and having a first end portion (77) and a second end portion (79), the first end portion (77) and the second end portion (79) having a uniform width, wherein the width extends perpendicular to a longitudinal axis of the embedding element (76), wherein each of the embedding elements (76) comprises a wedge-shaped part (85) which tapers in a direction towards the second end portion (79), each of the embedding elements (76) comprising a fibre material and a binding agent, wherein the fibre material is at least partially joined together by means of the binding agent, and wherein the binding agent is present in an amount of 0.1-15 wt % relative to the weight of the fibre material, the fibre material consisting of glass fibres, carbon fibres or a combination of glass and carbon fibres, the binding agent comprising a thermoplastic binding agent, wherein each of the embedding elements (76) is separately formed through a pultrusion process comprising pulling a pultrusion string formed from the fibre material and the binding agent, and cutting the pultrusion string to form the embedding element (76), and wherein each of the embedding elements (76) consists essentially of the fibre material and the binding agent, wherein the root end assembly is formed by placing each of the embedding elements between the corresponding pair of adjacent bushings, such that the alternating ones of the embedding elements and the bushings are arranged about the circumference of the cross-section of the root region, a resin material being subsequently infused between the outer shell part and the inner shell part for fixing the embedding elements and the bushings within the blade shell structure, and wherein the embedding element (76) has an elastic modulus of between 0.01 and 110 GPa.

2. The root end assembly for a wind turbine rotor blade according to claim 1, wherein the binding agent is present in an amount of 0.5-5 wt % relative to the weight of the fibre material.

3. The root end assembly for a wind turbine rotor blade according to claim 2, wherein the binding agent is present in an amount of 0.5-2.5 wt % relative to the weight of the fibre material.

4. The root end assembly for a wind turbine rotor blade according to claim 1, wherein the melting point of the binding agent is between 40° C. and 220° C.

5. The root end assembly for a wind turbine rotor blade according to claim 4, wherein the melting point of the binding agent is between 40° C. and 160° C.

6. The root end assembly for a wind turbine rotor blade according to claim 1, wherein the binding agent comprises a polyester.

7. The root end assembly for a wind turbine rotor blade according to claim 6, wherein the polyester is a bisphenolic polyester.

8. The root end assembly for a wind turbine rotor blade according to claim 1, wherein between its two end portions the embedding element (76) is provided with a first longitudinal lateral face (86) extending concavely in a cross-sectional view perpendicular to the longitudinal axis of the embedding element (76) and provided with a second longitudinal lateral face (87) facing opposite the first lateral face (86) and extending concavely in a cross-sectional view perpendicular to the longitudinal axis of the embedding element (76).

9. The root end assembly for a wind turbine rotor blade according to claim 1, wherein the embedding element (76) has an elastic modulus of between 0.01 and 45 GPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

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

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows a schematic view of a wind turbine blade,

(4) FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

(5) FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

(6) FIG. 5 shows a perspective, longitudinal, sectional view of a portion of a root region of a wind turbine blade according to the invention,

(7) FIG. 6 shows a perspective view of a cylindrical bushing arranged next to an embedding element,

(8) FIG. 7 shows a cross-sectional view of one embodiment of a wind turbine blade according to the invention,

(9) FIG. 8 is a schematic view of a pultrusion system for manufacturing an embedding element according to the present invention, and

(10) FIG. 9 is a perspective view of a preform for manufacturing an embedding element according to the present invention.

DETAILED DESCRIPTION

(11) FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The rotor has a radius denoted R.

(12) FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

(13) The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

(14) A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

(15) It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the 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.

(16) FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention.

(17) FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use—i.e. during rotation of the rotor—normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

(18) Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

(19) FIG. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 3, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=L.sub.w, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius r.sub.o and a minimum inner curvature radius r.sub.i, which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Δy, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

(20) As seen in FIG. 5, the blade comprising the root region is formed as a shell structure. The shell structure is typically ring-shaped and comprises an outer part 64 formed by a fibre-reinforced polymer matrix, typically made of glass fibres and/or carbon fibres and a resin, such as epoxy, polyester or vinyl ester. The shell structure also comprises an oppositely arranged inner part 66 being made of the same material as the outer part. Elongated bushings 68 are placed between the parts 64, 66.

(21) As seen in FIG. 7, the bushings 68 have a circular cross section and comprise a central bore 70 with an inner thread as fastening means. Now referring to FIG. 6, the bushing 68 comprises a first end 71, an oppositely arranged second end 72 and a lateral face 74 with circular cross section in between the ends 71, 72. The first end 71 of the bushing 68 is placed at the root end face of the root region. The bushings 68 are arranged mutually spaced apart so as to substantially follow the circumference of the root region and allow access from the outside to the bushings, i.e. the threads used for mounting the blade to the hub.

(22) As seen in FIG. 5, the bushings 68 may be further connected to a wedge-shaped extension 78 arranged behind each bushing 68 as seen in the longitudinal direction of the blade. A first end 80 of the extension 78 is arranged in abutment with the second end of the bushing 68, and a second end 82 of the extension 78 is tapered. The wedge-shaped extensions 78 may be made of balsawood or a hard polymer foam or another similar material. An intermediate embedding element 76 is arranged in between adjacent bushings 68.

(23) A more detailed view of the embedding element 76 is shown in FIG. 6. The embedding element 76 comprises a first part 84 and a second part 85, as well as a first end portion 77 and a second end portion 79. The first part 84 essentially corresponds to the region between the lateral surface 74 of adjacent bushings 78. The first part 84 is provided with opposite longitudinal lateral faces 86, 87 formed complementary to the surface 74 of adjacent bushings. As seen in FIG. 7, the first and second lateral faces 86, 87 extend concavely in a cross-sectional view perpendicular to the longitudinal axis of the embedding element. The embedding element 76 substantially extends up next to the adjacent bushings when seen in circumferential direction.

(24) Furthermore, the first part 84 of the embedding element 76 may extend from the first end 71 of the bushing 68 and beyond the second end 72 thereof. The second part 85 of the embedding element 76 is a wedge-shaped tapering extension of the first element part 84, which tapers in the direction towards the second end portion 79. The first part 84 may have an extent substantially corresponding to that of the bushings 68.

(25) FIG. 8 schematically illustrates a method for manufacturing an embedding element of the present invention comprising a pultrusion process. A number of bands or rovings of fibre material 90 are drawn from a shelf 89 into a receiving and heating station 91. A binding agent is fed from a reservoir 92 into the receiving and heating station 91 to provide contact with the fibre material 90, wherein the binding agent is present in an amount of 0.5-10 wt % relative to the weight of the fibre material. The resulting material is passed through a nozzle 93 from which a pultrusion string 94 extends, said string having a cross section corresponding to that of the preform 97 shown in FIG. 9. Alternatively, the binder could be added to the glass material prior to this process by the glass supplier.

(26) The pultrusion string 94 is extracted from the nozzle by means of a pulling station 95. On the other side of the pulling station 95 a knife 96 cuts the pultrusion string 94, whereby a preform 97 is obtained. As shown in FIG. 9 the resulting preform 97 is then cut along a plane, as indicated by the dashed line, which is inclined relative to the longitudinal axis of the preform, to provide two symmetrical embedding elements 76, 76′, each comprising a wedge-shaped part.

(27) The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.

LIST OF REFERENCE NUMERALS

(28) 2 wind turbine 4 tower 6 nacelle 8 hub 10 blade 14 blade tip 16 blade root 18 leading edge 20 trailing edge 22 pitch axis 30 root region 32 transition region 34 airfoil region 40 shoulder/position of maximum chord 50 airfoil profile 52 pressure side 54 suction side 56 leading edge 58 trailing edge 60 chord 62 camber line/median line 64 outer part of shell 66 inner part of shell 68 bushing 70 central bore 71 first end of bushing 72 second end of bushing 74 lateral face of bushing 76 embedding element 77 first end portion of embedding element 78 wedge-shaped extension of bushing 79 second end portion of embedding element 80 first end of extension of bushing 82 second end of extension of bushing 84 first part of embedding element 85 second part of embedding element 86 longitudinal lateral face of embedding element 87 longitudinal lateral face of embedding element 88 pultrusion system 89 shelf 90 bands of fibre material 91 receiving and heating station 92 agent reservoir 93 nozzle 94 pultrusion string 95 pulling station 96 knife 97 preform c chord length d.sub.t position of maximum thickness d.sub.f position of maximum camber d.sub.p position of maximum pressure side camber f camber L blade length r local radius, radial distance from blade root t thickness Δy prebend