Optimized interlayer for a spar cap for a wind turbine blade

Abstract

An interlayer sheet for a spar cap is provided. The interlayer sheet includes a first fibre layer having a first plurality of fibres with a first upper fibre surface and a first lower fibre surface, and a second fibre layer having comprising a second plurality of fibres with a second upper fibre surface and a second lower fibre surface. The first fibre layer is arranged on top of the second fibre layer, such that the first lower fibre surface is in contact with the second upper fibre surface. The first fibre layer is of a different characteristic than the second fibre layer. A number of the interlayer sheets may be arranged between a plurality of pre-cured fibre-reinforced elements to make a spar cap for a wind turbine blade.

Claims

1. A spar cap (10) for a wind turbine blade (1000), comprising: a plurality of pre-cured fibre-reinforced elements, including a first pre-cured fibre-reinforced element and a second pre-cured fibre-reinforced element; and a plurality of interlayer sheets (20) arranged between the plurality of pre-cured fibre-reinforced elements, wherein each of the interlayer sheets (20) comprises: a first fibre layer (30) comprising a first plurality of fibres, having a first upper fibre surface (31) and a first lower fibre surface (32); a second fibre layer (40) comprising a second plurality of fibres, having a second upper fibre surface (41) and a second lower fibre surface (42); a third fibre layer (50) comprising a third plurality of fibres, having a third upper fibre surface (51) and a third lower fibre surface (52), wherein the first fibre layer (30) is arranged on top of the second fibre layer (40), such that the first lower fibre surface (32) is in contact with the second upper fibre surface (41), and wherein the first fibre layer is of a different characteristic than the second fibre layer, wherein the first and second fibre layers (30, 40) are arranged on top of the third fibre layer (50), such that the second lower fibre surface (42) is in contact with the third upper fibre surface (51) and such that the second fibre layer (40) is sandwiched between the first and third fibre layers (30, 50), and wherein the first fibre layer (30) and the third fibre layer (50) are polyester veils and the second fibre layer (40) is a bidirectional glass-fibre fabric.

2. The spar cap (10) according to claim 1, wherein the different characteristic is fibre type and/or fibre density and/or fibre ratio.

3. The spar cap (10) according to claim 1, wherein the first fibre layer (30) and/or the third fibre layer (50) comprises randomly oriented fibres.

4. The spar cap (10) according to claim 1, wherein the fibres in the first fibre layer (30) and/or the second fibre layer (40) and/or the third fibre layer (50) are maintained relative to each other by a binding agent or are stitched together by a thread.

5. The spar cap (10) according to claim 1, wherein the plurality of pre-cured fibre-reinforced elements and the plurality of interlayer sheets (20) are embedded in a first cured resin and wherein the spar cap (10) extends in a length direction between a first end and a second end of the spar cap, wherein the spar cap has a width direction between a first side and a second side of the spar cap, and wherein the spar cap has a thickness direction between a lower surface and an upper surface of the spar cap.

6. The spar cap (10) according to claim 1, wherein each of the plurality of pre-cured fibre-reinforced elements is a pultruded carbon plank.

7. The spar cap (10) according to claim 1, wherein each of the plurality of pre-cured fibre-reinforced elements has a length in a longitudinal direction, a width in a width direction, and a height in a height direction, wherein the length is longer than the width and the width is longer than the height, wherein each of the plurality of pre-cured fibre-reinforced elements has a lower surface and an upper surface extending in the longitudinal direction and the width direction, and wherein the first pre-cured fibre-reinforced element and the second pre-cured fibre-reinforced element are arranged such that the lower surface of the first pre-cured fibre-reinforced element is facing the upper surface of the second pre-cured fibre-reinforced element and an interlayer sheet (20) of the interlayer sheets (20) is arranged between the lower surface of the first element and the upper surface of the second element.

8. A wind turbine blade (1000) comprising the spar cap (10) according to claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) 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.

(2) FIG. 1 is a schematic diagram illustrating a wind turbine,

(3) FIG. 2 is a schematic diagram illustrating a wind turbine blade and a spar cap structure arranged within the wind turbine blade,

(4) FIG. 3 is a schematic diagram illustrating the simplest embodiment of an interlayer sheet according to the present invention,

(5) FIG. 4 is a schematic diagram illustrating a preferred embodiment of an interlayer sheet according to the present invention,

(6) FIG. 5 is a schematic diagram illustrating two embodiments of a spar cap according to the present invention, and

(7) FIG. 6 is a schematic diagram illustrating an embodiment of an interlayer sheet comprising a plurality of carbon fibres extending through the interlayer.

DETAILED DESCRIPTION

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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.

(14) FIG. 2B is a schematic diagram illustrating a cross-sectional view of an exemplary wind turbine blade 1000 showing a cross-sectional view of the airfoil region of the wind turbine blade 1000 as illustrated by the line. 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.

(15) FIG. 3 shows different views of an embodiment of an interlayer sheet according to the present invention. FIG. 3A is a schematic diagram illustrating a three-dimensional view of an embodiment of an interlayer sheet 20 for a spar cap 10 according to the present invention. FIG. 3B shows a cross-sectional view A-A of the interlayer sheet 20 of FIG. 3A, and FIG. 3C shows an exploded view of FIG. 3B.

(16) The interlayer sheet 20 of the embodiment shown in FIG. 3 comprises a first fibre layer 30 and a second fibre layer 40.

(17) The first fibre layer 30 comprises a first plurality of fibres, and the second fibre layer 40 comprises a second plurality of fibres.

(18) Importantly, the first fibre layer has a different characteristic than the second fibre layer. For example, the first plurality of fibres is a different type of fibres than the second plurality of fibres. Alternatively or additionally, fibre ratio and/or density of the first fibre layer may be different than fibre ratio and/or density of the second fibre layer. In that way, each fibre layer in the interlayer sheet 20 has different properties. Particularly, it is desired that at least one fibre layer increases the fracture toughness of the spar cap to a desired level, whereas at least one layer increases the structural integrity of the spar cap to a desired level. Any fibre material which can achieve the above effects may be used within the scope of the present invention. For example, the first plurality of fibres may comprise or essentially consist of polymeric filaments, such as polyester filaments, preferably thermoplastic polyester filaments, or polypropylene filaments or polyethylene filaments. A fibre layer comprising such fibres would increase the fracture toughness and promote resin infusion. The second plurality of fibres may comprise or essentially consist of glass fibres or carbon fibres. A fibre layer comprising such fibres provides structural integrity.

(19) As can be seen in FIG. 3C, the first fibre layer 30 has a first upper fibre surface 31 and a first lower fibre surface 32. In the same way, the second fibre layer 40 has a second upper fibre surface 41 and a second lower fibre surface 42.

(20) In FIGS. 3A and 3B, the first fibre layer 30 is arranged on top of the second fibre layer 40, such that the first lower fibre surface 32 is in contact with the second upper fibre surface 41.

(21) The interlayer sheet in FIGS. 3A-3C is illustrated as a substantially square sheet for illustrative purposes. However, the interlayer sheet may also have other shapes and is preferably substantially rectangular.

(22) FIG. 4 shows different views of another embodiment of an interlayer sheet according to the present invention. FIG. 4A is a schematic diagram illustrating a three-dimensional view of an embodiment of an interlayer sheet 20 for a spar cap 10 according to the present invention. FIG. 4B shows a cross-sectional view B-B of the interlayer sheet 20 of FIG. 4A, and FIG. 4C shows an exploded view of FIG. 4B.

(23) The interlayer sheet 20 in the embodiment shown in FIG. 4 comprises a first fibre layer 30, a second fibre layer 40 and a third fibre layer 50.

(24) As can be seen in FIG. 4C, the first fibre layer 30 has a first upper fibre surface 31 and a first lower fibre surface 32. In the same way, the second fibre layer 40 has a second upper fibre surface 41 and a second lower fibre surface 42, and the third fibre layer 50 has a third upper fibre surface 51 and a third lower fibre surface 52.

(25) In FIGS. 4A and 4B, the first fibre layer 30 is arranged on top of the second fibre layer 40, such that the first lower fibre surface 32 is in contact with the second upper fibre surface 41. Furthermore, the first and second fibre layers 30, 40 are arranged on top of the third fibre layer 50, such that the second lower fibre surface 42 is in contact with the third upper fibre surface 51 and such that the second fibre layer 40 is sandwiched between the first and third fibre layers 30, 50. The interlayer sheet in FIG. 4 is illustrated as a substantially square for illustrative purposes. However, the interlayer sheet may also have other shapes and is preferably substantially rectangular.

(26) The first fibre layer 30 comprises a first plurality of fibres, and the second fibre layer 40 comprises a second plurality of fibres, and the third fibre layer 50 comprises a third plurality of fibres.

(27) Importantly, the first fibre layer has a different characteristic than the second fibre layer e.g the first plurality of fibres is a different type of fibres than the second plurality of fibres. In that way, each fibre layer in the interlayer sheet 20 has different properties. Particularly, it is desired that at least one fibre layer increases the fracture toughness of the spar cap to a desired level, whereas at least one layer increases the structural integrity of the spar cap to a desired level. Any fibre material which can achieve the above effects may be used within the scope of the present invention. For example, the first plurality of fibres may comprise or essentially consist of polymeric filaments, such as polyester filaments, preferably thermoplastic polyester filaments, or polypropylene filaments or polyethylene filaments. A fibre layer comprising such fibres increases the fracture toughness and promote resin infusion. The second plurality of fibres may comprise or essentially consist of glass fibres or carbon fibres. A fibre layer comprising such fibres provides structural integrity. The third plurality of fibres may be of the same or a different type than the first fibre layer. Preferably, the third layer comprises or essentially consists of polymeric filaments, such as polyester filaments, preferably thermoplastic polyester filaments, or polypropylene filaments or polyethylene filaments, like the first fibre layer 30. Since the interlayer sheet 20 is configured to be arranged in a spar cap between a first and a second pre-cured fibre-reinforced element 60, 70, such an interlayer sheet 20 promotes resin infusion in areas between the interlayer sheet 20 and the pre-cured fibre-reinforced elements 60, 70, further ensuring adhesion between the fibre-reinforced elements 60, 70 and the interlayer sheet 20. In a preferred embodiment, the first fibre layer and the third fibre layer are polyester veils, and the second fibre layer is a bidirectional glass-fibre fabric.

(28) FIG. 5 shows two different embodiments of a spar cap for a wind turbine blade according to the present invention.

(29) FIG. 5A is a schematic diagram showing a cross-sectional view of a spar cap according to the simplest embodiments of the present invention. FIG. 5B shows an exploded view of the spar cap of FIG. 5A.

(30) The spar cap illustrated in FIGS. 5A and 5B comprises a first pre-cured fibre-reinforced element 60 and a second pre-cured fibre-reinforced element 70. Furthermore, the spar cap 10 comprises an interlayer sheet 20 with a first and a second fibre layer 20, 30 arranged between the first and second pre-cured fibre-reinforced elements 60, 70. The interlayer sheet 20 is a sheet as described in relation to FIG. 3. However, it may also be an interlayer sheet 20 as described in relation to FIG. 4, or another interlayer sheet within the scope of the present invention.

(31) The first and second pre-cured fibre-reinforced elements 60, 70 each have a length in a longitudinal direction, a width in a width direction, and a height in a height direction. The length is larger than the width, and the width is larger than the height.

(32) Furthermore, the first and second pre-cured fibre-reinforced elements 60, 70 each have a lower surface 62, 72 and an upper surface 61, 71 extending in the longitudinal direction and the width direction. FIGS. 5A and 5B are cross-sectional views showing the width and height of the spar cap 10, but not the length.

(33) The first pre-cured fibre-reinforced element 60 and the second pre-cured fibre-reinforced element 70 are arranged such that the lower surface of the first pre-cured fibre-reinforced element 62 is facing the upper surface of the second pre-cured fibre-reinforced element 71, and the interlayer sheet 20 is sandwiched between the lower surface of the first pre-cured fibre-reinforced element and the upper surface of the second pre-cured fibre-reinforced element.

(34) For an interlayer sheet 20, as described in relation to FIG. 3, comprising a first fibre layer 30 and a second fibre layer 40, either the first or second fibre layer 30, 40 may be in contact with the first fibre-reinforced element 60 and either the first or second fibre layer may be in contact with the second fibre-reinforced element 70. For an interlayer sheet 20, as described in relation to FIG. 4, comprising a first fibre layer 30, a second fibre layer 40 and a third fibre layer 50, either the first or third fibre layer 30, 40 may be in contact with the first fibre-reinforced element 60, and either the first or second fibre layer may be in contact with the second fibre-reinforced element 70.

(35) Preferably, the plurality of pre-cured fibre-reinforced elements 60, 70 and the plurality of interlayer sheets 20 are embedded in a first cured resin to form the finished spar cap. This may be done in an offline pre-form mould or directly in a blade mould.

(36) FIG. 5C shows a cross-sectional view of a spar cap according to another embodiment according to the present invention.

(37) The spar cap illustrated in FIG. 5C comprises an array of pre-cured fibre-reinforced elements 60, 70 including a plurality of spar cap layers arranged on top of each other. Each spar cap layer comprises a row of pre-cured fibre-reinforced elements between a first and a second side of the spar cap (along the width), preferably each extending between the first and second ends of the spar cap (not visible in FIG. 5).

(38) The pre-cured fibre-reinforced elements 60, 70 are arranged adjacent to each other in each spar cap layer. Preferably, the pre-cured fibre-reinforced elements of each spar cap layer are separated from the pre-cured fibre-reinforced elements of a second spar cap layer by at least one interlayer sheet according to the present invention 20. In some embodiments, more than one interlayer sheet may separate the first and second spar cap layers.

(39) 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.

(40) Preferably, each of the plurality of pre-cured fibre-reinforced elements 60, 70 is a pultruded carbon plank.

(41) The spar cap illustrated in FIG. 5C 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.

(42) In some embodiments, as illustrated in FIG. 6, the interlayer sheet 20 comprise a plurality of carbon fibres 23 forming part of an upper interlayer surface 21 as well as an lower interlayer surface 22. Thus, the plurality of carbon fibres 23 extend through the interlayer sheet 20. In FIG. 6 the number of fibre layers in the interlayer sheet 20 are not illustrated. However, the carbon fibres 23 extend through all fibre layers present in the interlayer sheet 20, including the first fibre layer and the second fibre layer and optionally also further fibre layers such as a third fibre layer. In this way, electrical conductivity through the interlayer may be obtained, which facilitates electron flow between elements, such as pultruded elements, when sandwiched therebetween.

LIST OF REFERENCE NUMERALS

(43) 10 spar cap 10a first spar cap 10b second spar cap 20 interlayer sheet 21 upper interlayer surface 22 lower interlayer surface 23 carbon fibres extending through interlayer sheet 30 first fibre layer 31 first upper fibre surface 32 first lower fibre surface 40 second fibre layer 41 second upper fibre surface 42 second lower fibre surface 50 third fibre layer 51 third upper fibre surface 52 third lower fibre surface 60 first pre-cured fibre-reinforced element 61 first upper surface 62 first lower surface 70 second pre-cured fibre-reinforced element 71 second upper surface 72 second lower surface 200 wind turbine 400 tower 600 nacelle 800 hub 1000 blade 1400 blade tip 1600 blade root 1800 leading edge 2000 trailing edge 2200 pitch axis 2400 pressure side 2600 suction side 3000 root region 3200 transition region 3400 airfoil region 3800 chord line 4000 shoulder/position of maximum chord 4200 shear web