Wind turbine blade with improved fibre transition

Abstract

A wind turbine blade having a transition between two reinforcement fiber types is described. A gradual transition is provided by a combined double-tapered thickness section with a first type of reinforcement fibers sandwiched between a second type of reinforcement fibers or vice versa. The double-tapering is provided during layup and the reinforcement material is impregnated with a polymer resin and then cured or hardened so that the two types of reinforcement fibers are embedded in a common polymer matrix.

Claims

1. A wind turbine blade (10) having a longitudinal direction between a root end and a tip end, wherein the wind turbine blade (10) comprises at least a wind turbine blade component made of fibrous composite material and comprising a first type of reinforcement fibres having a first elastic modulus, and a second type of reinforcement fibres having a second elastic modulus, wherein the wind turbine blade component comprises a thickness between a first surface (172) and a second surface (182), wherein a proportion between the first type of reinforcement fibres and the second type of reinforcement fibres gradually changes in a first direction of the wind turbine blade so that an effective elastic modulus of the wind turbine blade component gradually changes in said first direction, wherein said gradual change in the first direction is provided by: a first thickness section, where the first type of reinforcement fibres along a first common boundary (175) between the first type of reinforcement fibres and the second type of reinforcement fibres are tapered towards the first surface (172) of the wind turbine blade component in the first direction, and the second type of reinforcement fibres are tapered towards the second surface (182) of the wind turbine blade component in a direction opposite the first direction, and a second thickness section, where the first type of reinforcement fibres along a second common boundary (185) between the first type of reinforcement fibres and the second type of reinforcement fibres are tapered towards the second surface (182) of the wind turbine component in the first direction, and the second type of reinforcement fibres are tapered towards the first surface (172) of the wind turbine component in a direction opposite the first direction, and wherein the first type of reinforcement fibres and the second type of reinforcement fibres are embedded in a common polymer matrix.

2. The wind turbine blade according to claim 1, wherein the first direction is the longitudinal direction of the blade.

3. The wind turbine blade according to claim 1, wherein the first thickness section and the second thickness section are layered on top of each other and have a common surface boundary (186) between the first surface (172) and the second surface (182) of the wind turbine blade component.

4. The wind turbine blade according to claim 3, wherein taper sections of the first thickness section and the second thickness coincide at the common surface boundary.

5. The wind turbine blade according to claim 1, where the first thickness section and/or the second thickness section comprises a stepped tapering between layers comprising the first type of reinforcement fibres and the second type of reinforcement fibres.

6. The wind turbine blade according to claim 1, where the first thickness section and/or the second thickness section comprises a continuous tapering between layers comprising the first type of reinforcement fibres and the second type of reinforcement fibres.

7. The wind turbine blade according to claim 1, wherein the wind turbine component is a load carrying structure.

8. The wind turbine blade according to claim 7, wherein the load carrying structure is selected from the group consisting of a spar and a spar cap.

9. The wind turbine blade according to claim 1, wherein the first type of reinforcement fibres are glass fibres.

10. The wind turbine blade according to claim 1, wherein the second type of reinforcement fibres are carbon fibres or a hybrid of carbon fibres and glass fibres.

11. The wind turbine blade according to claim 1, wherein the wind turbine blade further comprises a gradual transition comprising a taper section between the first type of reinforcement fibres and a third type of reinforcement fibres embedded in an additional polymer matrix, different from the common polymer matrix.

12. The wind turbine blade according to claim 11, wherein the third type of reinforcement are glass fibres.

13. The wind turbine blade according to claim 11, wherein the additional polymer matrix is a hardened or cured polyester.

14. The wind turbine blade according to claim 1, wherein the common polymer matrix is a hardened or cured vinylester or epoxy.

15. A method of manufacturing a wind turbine blade component of a wind turbine blade having a longitudinal direction between a root end and a tip end, wherein the wind turbine blade component comprises a thickness between a first surface and a second surface, the method comprising the steps of: a) building up a first thickness section by: i) arranging a number of first fibre layers comprising reinforcement fibres of a first type, and ii) arranging a number of second fibre layers comprising reinforcement fibres of a second type, wherein the first layers and second layers are arranged so that the first fibre layers along a first common boundary are tapered towards the first surface of the wind turbine blade component in a first direction, and the second fibre layers are tapered towards the second surface of the wind turbine blade component in a direction opposite the first direction, and b) building up a second thickness section by: i) arranging a number of additional first fibre layers comprising reinforcement fibres of the first type, and ii) arranging a number of additional second fibre layers comprising reinforcement fibres of the second type, wherein the additional first fibre layers and the additional second fibre layers are arranged so that the additional first fibre layers along a second common boundary are tapered towards the second surface of the wind turbine blade component in the first direction, and the additional second fibre layers are tapered towards the first surface of the wind turbine blade component in a direction opposite the first direction, and c) supplying a common polymer resin to the first thickness section and second thickness section, and d) curing or hardening the common polymer resin so as to embed the reinforcement fibres of the first type and the reinforcement fibres of the second type in a common polymer matrix.

16. The method according to claim 15, wherein the first fibre layers and the second fibre layers of the first thickness section collectively comprise a plurality of fibre layers, wherein the first common boundary is formed by boundaries between the first fibre layers and the second fibre layers, the boundaries being mutually shifted in the first direction of the wind turbine blade, and wherein ends of the plurality of fibre layers at the common boundary are tapered.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Embodiments of the invention are described below, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows a schematic view of a wind turbine blade according to the invention,

(4) FIG. 3 shows the layup of fibre material for forming a cured blade element,

(5) FIG. 4 shows the layup of fibre material for forming an integrated reinforced section on the cured blade element of FIG. 3,

(6) FIG. 5 shows a cross section of the cured blade element and integrated reinforced section,

(7) FIG. 6 shows a schematic view of a blade shell part comprising the cured blade element and integrated reinforced section,

(8) FIG. 7 shows a schematic view of a the fibre layup of a first thickness section of a blade component,

(9) FIG. 8 shows a schematic view of a the fibre layup of a second thickness section of a blade component, and

(10) FIGS. 9a-d show different variations of embodiments according to the invention.

(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 farthest 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 farthest 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) The blade is typically made from a pressure side shell part 36 and a suction side shell part 38 that are glued to each other along bond lines at the leading edge 18 and the trailing edge of the blade 20.

(17) In the following, the invention is explained with respect to the manufacture of the pressure side shell part 36 or suction side shell part 38.

(18) FIGS. 3 and 4 illustrate the layup process involved in manufacturing a blade shell part of a wind turbine blade and show a part of a longitudinal cross-section of a blade mould. The process involves the steps of laying up a primary fibre material in a mould 50. The primary fibre material comprises a number of outer skin layers 52, which form an outer part of the blade shell part. The outer skin layers 52 may for instance be made of biaxially oriented glass fibres. A plurality of reinforcement layers 54, preferably made of glass fibres, are arranged on top of the outer skin layers 52. The reinforcement layers 54 are preferably made of unidirectionally arranged glass fibres extending substantially in the longitudinal direction of the blade shell part in order to provide stiffness in the spanwise direction of the finished blade. The ends of the plurality of reinforcement layers are preferably tapered and arranged so as to form a taper section 56. A number of inner skin layers 58 are arranged on top of the reinforcement layers. The inner skin layers may also be made of biaxially oriented glass fibres. The inner skin layers 58 may as shown in FIG. 3 be laid over the ends of the reinforcement layers 54 so that the inner skin layers make up part of the taper section 56.

(19) Subsequently a number of resin inlets (not shown) and vacuum outlets (not shown) are arranged on top of the primary fibre material, and finally a vacuum bag (not shown) is arranged on top. Then the primary fibre material is infused with a primary resin, advantageously a polyester resin, via a VARTM process, and the resin is cured in order to form a cured blade element 60. In the shown embodiment, the outer skin layers 56 form part of the aerodynamic shell of the finished wind turbine blade, whereas the fibre reinforcement layers 54 form part of a root laminate of the wind turbine blade.

(20) In a second step, the fibre material that makes up part of the load carrying structure, e.g. a spar cap, is laid up on the cured blade element 60 as shown in FIG. 4. The second step involves laying up a secondary fibre material on top of at least a portion of the cured blade element 60. The secondary fibre material comprises a number of fibre reinforcement layers 62. The fibre reinforcement layers 62 may advantageously be made of unidirectionally arranged carbon fibres or hybrid mats comprising glass fibres and carbon fibres. Finally a number of additional inner skin layers 64 are arranged on top of the fibre reinforcement layers 62. Subsequently a number of resin inlets (not shown) and vacuum outlets (not shown) are arranged on top of the secondary fibre material, and finally a vacuum bag (not shown) is arranged on top. Then the secondary fibre material is infused with a secondary resin, advantageously a vinylester resin, via a VARTM process, and the resin is cured in order to form an integrated reinforced section 70 on the cured blade element 60. The integrated reinforced section may advantageously make part of the spar, spar cap, or main laminate of the finished wind turbine blade. The secondary resin has a higher strength level than said primary resin.

(21) The ends of the fibre reinforcement layers 62 of the secondary fibre material are also tapered so that a gradual transition is obtained between the reinforcement fibres of the primary fibre material and the reinforcement fibres of the secondary fibre material. Further, a gradual transition is obtained between the primary resin and the secondary resin with higher strength level.

(22) The cured blade element 60 may as shown in FIG. 4 remain in the mould 50 during the second step. However, according to an advantageous embodiment, the cured blade element 60 is removed from said mould 50 and transferred to a secondary support, e.g. a support cradle, where the second step is carried out.

(23) FIG. 5 shows a transverse cross section through the mould in a part of the airfoil region of the finished blade and FIG. 6 shows a perspective view of a blade shell part, which is made up of the cured blade element 60, which comprises an aerodynamic shell part and a root laminate, and the integrated reinforced section 70, which forms a spar cap or main laminate of the blade shell part. It is seen that the cured blade element 60 may also comprise a number of sandwich core material 66 arranged on lateral sides of the integrated reinforced section 70.

(24) It is further seen that a recess may be formed in the cured blade element 60, and that the secondary fibre material may be arranged in said recess. This method provides an advantage over prior art methods, since the less critical step of forming the aerodynamic shell and the more critical part of forming the load carrying structure may be separated. By forming a recess in the aerodynamic shell, the secondary fibre material may more easily be arranged without the fibre layers wrinkling and forming mechanically weak areas. Further, as previously mentioned, the two steps may be performed at different work stations, which means that the two steps can be carried in sequence and the throughput be increased, since it is possible to work on two different blade shell parts simultaneously.

(25) While the two-step manufacturing method provides an advantage over prior art manufacturing methods, it has been found that the scarf joint like transition between the glass fibres and carbon fibres or carbon-glass hybrid may in some circumstances not provide a sufficient strength. Therefore, although not shown in the figures, an over-lamination or local thickening is usually necessary. Further, it is not necessarily advantageous to have a transition between both fibre types and resin types in the same taper section.

(26) Accordingly, the invention also provides a method of manufacturing a wind turbine blade component, in particular a spar cap or main laminate, of a wind turbine blade. The fibre layup process involved in the manufacturing method is illustrated in FIGS. 7 and 8.

(27) The wind turbine blade has a longitudinal direction between a root end and a tip end of the wind turbine blade. As before a spar cap 170 is formed by arranging secondary fibre material in a recess of a cured blade element 160. The method involves a first step shown in FIG. 7 of building up a first thickness section 171 by arranging a number of first fibre layers 173 comprising first type reinforcement fibres, preferably glass fibres, and arranging a number of second fibre layers 174 comprising a second type reinforcement fibres, preferably carbon-glass hybrid mats or carbon fibres. The first fibre layers 173 and the second fibre layers 174 have tapered ends and are arranged so that the first fibre layers 173 along a first common boundary or taper section 175 are tapered towards the first surface 172 of the wind turbine blade component in the longitudinal direction of the blade, and the second fibre layers 174 are tapered towards the second surface 182 of the wind turbine blade component 170 in a direction opposite the longitudinal direction.

(28) Then as shown in FIG. 8, a second thickness section 181 is built up by arranging a number of additional first fibre layers 183 comprising the first type reinforcement fibres, and arranging a number of additional second fibre layers 184 comprising the second type reinforcement fibres. The additional first fibre layers 183 and the additional second fibre layers 184 have tapered ends and are arranged so that the first fibre layers 183 and second additional fibre layers 184 are arranged so that the additional first fibre layers 183 along a second common boundary or second taper section 185 are tapered towards the second surface 182 of the wind turbine blade component 170 in the longitudinal direction, and the additional second fibre layers 184 are tapered towards the first surface 172 of the wind turbine blade component 170 in a direction opposite the longitudinal direction. The first thickness section 171 and the second thickness section are stacked along a common boundary 186. Further, a number of inner skin layers 164 may be arranged on top of the layers comprising first type reinforcement fibres and second type reinforcement fibres.

(29) Subsequently a number of resin inlets (not shown) and vacuum outlets (not shown) are arranged on top of the secondary fibre material, and finally a vacuum bag (not shown) is arranged on top. Then the secondary fibre material comprising the first thickness section 171 and second thickness section 181 is infused with a secondary resin, advantageously a vinylester resin, via a VARTM process, and the resin is cured in order to form the wind turbine blade component 170, which has the first type reinforcement fibres and the second type reinforcement fibres embedded in a common polymer matrix.

(30) Accordingly, it is seen that the gradual transition is provided by a combined double-tapered thickness section 171, 181 with first type reinforcement fibres sandwiched between second type reinforcement fibres or vice versa. Although this increases the complexity of the fibre layup procedure, this embodiment provides a stronger stiffness transition of the wind turbine component between the two fibre types, and further the transition may be shorter than prior art wind turbine components having a single taper section. Further, it is clear that the double-tapering is provided during layup and that the reinforcement material is impregnated with a polymer resin and then cured or hardened so that the two types of reinforcement fibres are embedded in a common polymer matrix.

(31) As before, the first fibre layers and second fibre layers advantageously comprise unidirectionally arranged fibres so as to provide stiffness in the spanwise/longitudinal direction of the blade. The inner skin layers may comprise biaxially oriented glass fibres.

(32) While the shown embodiment has been shown with a double tapered lap like joint with two types of fibres embedded in a common matrix, a strong transition may also be achieved by a double lap joint like transition between the two types of fibres.

(33) Overall, it is seen that the invention provides a wind turbine blade component which has three different types of fibre-resin zones. The first zone may comprise glass fibres embedded in a polyester resin, the second zone comprise glass fibres embedded in a vinylester resin, and the third zone comprise glass-carbon hybrid fibre material or carbon fibres embedded in the vinylester resin.

(34) While the preferred embodiment is shown in FIGS. 7 and 8, it is recognised that the above three part transition may be achieved in various ways utilising the afore-mentioned two-step manufacturing method according to the invention. The transitions may for instance be achieved by two single taper sections as shown in FIGS. 9a and 9b, where FIG. 9a shows a short transition, and FIG. 9b shows a long transition. The preferred embodiment with two tapered thickness sections may also be provided with a short transition as shown in FIG. 9c or a long transition as shown in FIG. 9d.

(35) The various taper sections may advantageously be tapered with a 1:5-1:50 thickness-to-length ratio, advantageously around 1:20.

(36) The invention has been described with reference to advantageous embodiments. However, the scope of the invention is not limited to the illustrated embodiments, and alterations and modifications can be carried out without deviating from the scope of the invention.

LIST OF REFERENCE NUMERALS

(37) 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 36 pressure side shell 38 suction side shell 40 shoulder 50 mould 52 outer skin layers 54 reinforcement layers 56 taper section 58 inner skin layers 60, 160 cured blade element 62 reinforcement layers 64, 164 inner skin layers 66 sandwich core material 70, 170 integrated reinforced section/spar cap/main laminate 171 first thickness section 172 first surface 173 first fibre layers comprising first type reinforcement fibres 174 second fibre layers comprising second type reinforcement fibres 175 first common boundary/first common taper section 181 first thickness section 182 second surface 183 additional first fibre layers comprising first type reinforcement fibres 184 additional second fibre layers comprising second type reinforcement fibres 185 second common boundary/second common taper section 186 common surface boundary