OPTIMIZED SPAR CAP STRUCTURE FOR A WIND TURBINE BLADE

Abstract

The present invention relates to a spar cap for a wind turbine blade comprising a plurality of pre-cured fibre-reinforced elements and a plurality of interlayers. The plurality of pre-cured fibre-reinforced elements include a first pre-cured fibre-reinforced element and a second pre-cured fibre-reinforced element and the plurality of interlayers include a first interlayer comprising a first plurality of fibres embedded in a first cured resin. The first interlayer is being arranged between the first pre-cured fibre-reinforced element and the second pre-cured fibre-reinforced element. The first plurality of fibres have a first elastic modulus, the first cured resin has a second elastic modulus, the first and/or second pre-cured fibre-reinforced elements have a third elastic modulus, and the first interlayer has a fourth elastic modulus. The ratio between the first elastic modulus and the second elastic modulus is between 1:4 and 4:1 and/or the ratio between the third elastic modulus and the fourth elastic modulus is between 1:4 and 4:1.

Claims

1. Spar cap (10) for a wind turbine blade comprising: a plurality of pre-cured fibre-reinforced elements, including a first pre-cured fibre-reinforced element (30) and a second pre-cured fibre-reinforced element (40); a plurality of interlayers, including a first interlayer (20) comprising a first plurality of fibres embedded in a first cured resin and being arranged between the first pre-cured fibre-reinforced element (30) and the second pre-cured fibre-reinforced element (40); wherein the first plurality of fibres (20) have a first elastic modulus, the first cured resin has a second elastic modulus, the first and/or second pre-cured fibre-reinforced elements (40) have a third elastic modulus, and the first interlayer (20) has a fourth elastic modulus; wherein the ratio between the first elastic modulus and the second elastic modulus is between 1:4 and 4:1 and/or the ratio between the third elastic modulus and the fourth elastic modulus is between 1:4 and 4:1.

2. Spar cap (10) according to claim 1, wherein the ratio between the first elastic modulus and the second elastic modulus is between 1:3 and 3:1, preferably between 1:2 and 2:1, more preferably between 1:1.5 and 1.5:1, such as 1:1 and/or the ratio between the third elastic modulus and the fourth elastic modulus is between 1:3 and 3:1, preferably between 1:2 and 2:1, more preferably between 1:1.5 and 1.5:1, such as 1:1.

3. Spar cap (10) according to claim 1, wherein the first and/or second and/or third and/or fourth elastic modulus is less than 10 GPa, such as less than 8 GPa, such as less than 7 GPa, such as less than 6 GPa, preferably less than 5 GPa.

4. Spar cap (10) according to claim 1, wherein the second elastic modulus is between 1-5 GPa, such as between 1.5-4.5 GPa, such as between 2-4 GPa.

5. Spar cap (10) according to claim 1, wherein the first elastic modulus is equal to or differs from the second elastic modulus with less than 5 GPa, such as with less than 2 GPa, preferably with less than 1 GPa, such as with less than 0.5 GPa, such as with less than 0.3 GPa, such as with less than 0.2 GPa, such as with less than 0.1 GPa, such as with less than 0.05 GPa, such as with less than 0.025 GPa.

6. Spar cap (10) according to claim 1, wherein the third elastic modulus is equal to or differs from the fourth elastic modulus with less than 5 GPa, such as with less than 2 GPa, preferably with less than 1 GPa, such as with less than 0.5 GPa, such as with less than 0.3 GPa, such as with less than 0.2 GPa, such as with less than 0.1 GPa, such as with less than 0.05 GPa, such as with less than 0.025 GPa.

7. Spar cap (10) according to claim 1, wherein the first cured resin comprises epoxy resin or polyester resin or vinyl ester resin.

8. An interlayer sheet (20) according to claim 1, wherein the first interlayer is a fibre sheet comprising one or more layers, wherein each layer is selected from a group consisting of: a unidirectional fabric, a bidirectional fabric or a tridirectional fabric, a veil comprising randomly oriented fibres and a net comprising woven fibres.

9. An interlayer sheet (20) according to claim 1, wherein the fibres in the first fibre layer (30) and/or the second fibre layer (40) and/or third fibre layer (50) are maintained relative to each other and/or the other fibre layers by a binding agent or are stitched together by a thread.

10. Spar cap (10) according to claim 1, wherein the first plurality of fibres are polymeric fibres, preferably polyester fibres.

11. Spar cap (10) according to claim 1, wherein the interlayer (20) is a polyester veil or a polyester mesh.

12. Spar cap (10) according to claim 1, wherein the plurality of pre-cured fibre-reinforced elements are pultruded elements, such as carbon pultrusion planks comprising carbon fibres and a second cured resin.

13. Spar cap (10) according to claim 1, wherein the first cured resin and the second cured resin is the same type or a different type of resin.

14. Wind turbine blade (1000) comprising a blade shell with a spar cap (10) according to claim 1 integrally formed with or attached to the blade shell.

15. Wind turbine blade (1000) according to claim 14 comprising a first spar cap (10a) integrally formed with or attached to an pressure side (2400) of the blade, a second spar cap (10b) integrally formed with or attached to a suction side (2600) of the blade (1000), and one or more shear webs (4200) connected between first spar cap (10a) and the second spar cap (10b).

16. Method of manufacturing spar cap (10) according to claim 1, comprising the steps of: a) providing a plurality of pre-cured fibre-reinforced elements including a first pre-cured fibre-reinforced element (30) and a second pre-cured fibre-reinforced element (40); b) providing a plurality of interlayers, including a first interlayer (20) comprising a first plurality of fibres; c) arranging the first interlayer (20) in between the first pre-cured fibre-reinforced element (30) and the second pre-cured fibre-reinforced element (40) such that the pre-cured fibre-reinforced elements (30,40) are separated by the first interlayer (20); d) infusing a first resin between the plurality pre-cured fibre-reinforced elements and the plurality of interlayers; e) curing the resin in order to form the spar cap (10); wherein the first plurality of fibres (20) have a first elastic modulus, the first cured resin has a second elastic modulus, the first and/or second pre-cured fibre-reinforced elements (40) have a third elastic modulus, and the first interlayer (20) has a fourth elastic modulus; wherein the ratio between the first elastic modulus and the second elastic modulus is between 1:4 and 4:1 and/or the ratio between the third elastic modulus and the fourth elastic modulus is between 1:4 and 4:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0077] Embodiments of the disclosure will be described in more detail in the following with regard to the accompanying figures. The figures show one way of implementing the present disclosure and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0078] FIG. 1 is a schematic diagram illustrating a wind turbine,

[0079] FIG. 2 is a schematic diagram illustrating a wind turbine blade and a spar cap structure arranged within the wind turbine blade,

[0080] and

[0081] FIG. 3 is a schematic diagram illustrating a cross-sectional view of a spar cap comprising an interlayer arranged between pre-cured fibre-reinforced elements.

DETAILED DESCRIPTION

[0082] Various exemplary embodiments and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

[0083] FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called “Danish concept” with a tower 400, a nacelle 600 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 800 and three blades 1000 extending radially from the hub 800, each having a blade root 1600 nearest the hub and a blade tip 1400 furthest from the hub 800.

[0084] FIG. 2A shows a schematic view of a first embodiment of a wind turbine blade 1000. The wind turbine blade 1000 has the shape of a conventional wind turbine blade and comprises a root region 3000 closest to the hub, a profiled or an airfoil region 3400 furthest away from the hub and a transition region 3200 between the root region 3000 and the airfoil region 3400. The blade 1000 comprises a leading edge 1800 facing the direction of rotation of the blade 1000, when the blade is mounted on the hub, and a trailing edge 2000 facing the opposite direction of the leading edge 1800.

[0085] The airfoil region 3400 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 3000 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 1000 to the hub. The diameter (or the chord) of the root region 3000 may be constant along the entire root area 3000. The transition region 3200 has a transitional profile gradually changing from the circular or elliptical shape of the root region 3000 to the airfoil profile of the airfoil region 3400. The chord length of the transition region 3200 typically increases with increasing distance r from the hub. The airfoil region 3400 has an airfoil profile with a chord extending between the leading edge 1800 and the trailing edge 2000 of the blade 1000. The width of the chord decreases with increasing distance r from the hub.

[0086] A shoulder 4000 of the blade 1000 is defined as the position, where the blade 1000 has its largest chord length. The shoulder 4000 is typically provided at the boundary between the transition region 3200 and the airfoil region 3400.

[0087] 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.

[0088] FIG. 2B is a schematic diagram illustrating a cross sectional view of an exemplary wind turbine blade 1000, e.g. a cross-sectional view of the airfoil region of the wind turbine blade 1000. The wind turbine blade 1000 comprises a leading edge 1800, a trailing edge 2000, a pressure side 2400, a suction side 2600, a first spar cap 10a, and a second spar cap 10b. The wind turbine blade 1000 comprises a chord line 3800 between the leading edge 1800 and the trailing edge 2000. The wind turbine blade 1000 comprises shear webs 4200, such as a leading edge shear web and a trailing edge shear web. The shear webs 4200 could alternatively be a spar box with spar sides, such as a trailing edge spar side and a leading edge spar side. The spar caps 10a, 10b may comprise carbon fibres, while the rest of the shell parts 2400, 2600 may comprise glass fibres.

[0089] FIG. 3A is a schematic diagram illustrating a cross sectional view of an interlayer 20 arranged between a first and a second pre-cured fibre-reinforced element 30, 40, such as a first pultruded carbon fibre element and a second pultruded carbon fibre element. The interlayer and pre-cured fibre-reinforced elements each have a length in a longitudinal direction, a width in a width direction, and a thickness in a thickness direction. The length is longer than the width and the width is larger than the thickness. In FIG. 3A, the width and thickness of the interlayer and pre-cured fibre-reinforced elements can be seen, but not in the length. The first and second pre-cured fibre-reinforced elements 30, 40 and the interlayer 20 may form part of a spar cap 10 arranged in a wind turbine blade, such as the spar caps 10a, 10b of the wind turbine blade 1000 as illustrated in FIG. 2.

[0090] FIG. 3B is a schematic diagram illustrating an exploded view of the interlayer 20 arranged between the first and second pre-cured fibre reinforced elements 30, 40. The interlayer 20, in the illustrated example, is an interlayer sheet having an upper interlayer surface 21 and a lower interlayer surface 22. In the same way, the first pre-cured fibre-reinforced element 30 has a first upper surface 31 and a first lower surface 32 and the second pre-cured fibre-reinforced element 40 has a second upper surface 41 and a second lower surface 42.

[0091] The first pre-cured fibre-reinforced element 30 and the second pre-cured fibre-reinforced element 40 are arranged such that the first lower surface 32 of the first pre-cured fibre-reinforced element 50 is facing the second upper surface 41 of the second pre-cured fibre-reinforced element 40. The interlayer 20 is arranged between the lower surface 32 of the first pre-cured fibre-reinforced element 30 and the upper surface 41 of the second pre-cured fibre-reinforced element 40, e.g. such that the upper interlayer surface 21 is in contact with the first lower surface 32 and the lower interlayer surface 22 is in contact with the second upper surface 41.

[0092] FIG. 3C is a schematic diagram illustrating a cross-sectional view of a fibre reinforced composite material, e.g. spar cap 10 or part of a spar cap, comprising a plurality of pre-cured fibre-reinforced elements, such as pultruded carbon fibre elements, including a first pre-cured fibre-reinforced element 30 and a second pre-cured fibre-reinforced element 40. The plurality of pre-cured fibre-reinforced elements 30, 40 are arranged in an array with three rows of pre-cured fibre-reinforced elements arranged adjacent to each other. Each row comprise three pre-cured fibre-reinforced elements arranged adjacent to each other. The rows are separated by an interlayer 20. It is of course clear that the spar cap 10 may comprise other number of layers and juxtaposed pre-cured fibre-reinforced elements.

[0093] The fibre-reinforced composite material may form part of a spar cap arranged in a wind turbine blade 1000, such as the spar caps 10a, 10b of the wind turbine blade 1000 as illustrated in FIG. 2. Although not specifically illustrated, interlayers may also be provided between adjacent elements in the width direction, to facilitate resin flow between elements also in this direction.

LIST OF REFERENCE NUMERALS

[0094] 200 wind turbine [0095] 400 tower [0096] 600 nacelle [0097] 800 hub [0098] 1000 blade [0099] 1400 blade tip [0100] 1600 blade root [0101] 1800 leading edge [0102] 2000 trailing edge [0103] 2200 pitch axis [0104] 2400 pressure side [0105] 2600 suction side [0106] 3000 root region [0107] 3200 transition region [0108] 3400 airfoil region [0109] 4000 shoulder/position of maximum chord [0110] 4200 shear web [0111] 10 spar cap [0112] 10a first spar cap [0113] 10b second spar cap [0114] 20 interlayer [0115] 21 upper interlayer surface [0116] 22 lower interlayer surface [0117] 30 first pre-cured fibre-reinforced element [0118] 31 first upper surface [0119] 32 first lower surface [0120] 40 second pre-cured fibre-reinforced element [0121] 41 second upper surface [0122] 42 second lower surface