Joining method for wind turbine blade shells

Abstract

A method of manufacturing a wind turbine blade is described, the blade being formed from at least a pair of blade shells being joined together. For at least a portion of the wind turbine blade, the blade shells are joined by an overlamination applied between the edges of the blade shells, thereby substantially reducing or eliminating the need for a structural adhesive to join the blade shells, particularly in the area of the leading edge of the blade or the root region of the blade trailing edge. The overlamination can be formed from the same material as the blade shells themselves, thereby minimising the possibility of structural faults or cracks due to differences in materials or stiffness levels at the interface between the blade shells.

Claims

1. A method of manufacturing at least a portion of a wind turbine blade, wherein the method comprises the steps of: providing a pressure side blade shell part having a first edge; providing a suction side blade shell part having a second edge, wherein the first and second edges extend along a spanwise direction of the wind turbine blade; and joining said pressure side blade shell part to said suction side blade shell part along at least a portion of said first edge and said second edge to form a joined leading edge of a closed blade shell, wherein said joining consists of providing an overlamination extending between said first edge and said second edge, such that said joining is performed without a structural adhesive, and wherein said overlamination is applied to external surfaces of said first edge and said second edge, said first and second edges of said pressure side and suction side blade shell parts, respectively, being joined to one another solely by the overlamination along at least a common portion thereof, the closed blade shell comprising the pressure side and suction side blade shell parts, the first edge of the pressure side blade shell part and the second edge of the suction side blade shell part abutting each other at an interface.

2. The method of claim 1, wherein said pressure side and suction side blade shell parts are arranged wherein a recess is defined at the interface between said first edge and said second edge, and wherein said overlamination is received at least partly within said recess.

3. The method of manufacturing at least a portion of a wind turbine blade as in claim 1, wherein the pressure side blade shell part has a first tapered section along at least a portion of an edge of said pressure side blade shell part, the suction side blade shell part has a second tapered section along at least a portion of an edge of said suction side blade shell part, said step of joining said pressure side blade shell part to said suction side blade shell part comprising: bringing together said pressure side and suction side shell parts such that said first tapered section abuts said second tapered section to form a recess channel located along a boundary between the edges of said pressure side and suction side blade shell parts; and applying the overlamination in said recess channel to join said pressure side and suction side blade shell parts.

4. The method of claim 3, wherein said overlamination is arranged to substantially fill said recess channel.

5. The method of claim 3, wherein said first and second tapered sections are located along the leading edges of respective said pressure side and suction side blade shell parts.

6. The method of claim 3, wherein said first and second tapered sections are located along the respective trailing edges of said pressure side and suction side blade shell parts.

7. The method of claim 6, wherein said first and second tapered sections are located along the respective trailing edges of said pressure side and suction side blade shell parts adjacent the root end of said pressure side and suction side blade shell parts.

8. The method of claim 3, wherein the overlamination is formed from the same material as said pressure side and suction side blade shell parts.

9. The method of claim 3, wherein said step of applying the overlamination laminate comprises: positioning at least one layer of fibre material along at least a portion of said first edge and said second edge of said pressure side and suction side blade shell parts; infusing said at least one layer of fibre material with a resin; and curing said resin to bond said pressure side and suction side blade shell parts.

10. The method of claim 9, wherein the at least one layer of fibre material is positioned in the recess channel.

11. A wind turbine blade comprising: a pressure side blade shell part; and a suction side blade shell part, wherein for at least a portion of a boundary between said pressure side and suction side blade shell parts, said pressure side and suction side blade shell parts are joined by an overlamination to form a joined leading edge of a closed blade shell, without the use of a structural adhesive, wherein joining of the pressure side and suction side blade shell parts consists of the overlamination, and wherein said overlamination is applied to external surfaces of said pressure side and suction side blade shell parts, said pressure side and suction side blade shell parts being joined to one another solely by the overlamination along at least a common portion thereof, the closed blade shell comprising the pressure side and suction side blade shell parts, the pressure side blade shell part and the suction side blade shell part abutting each other at an interface.

12. The wind turbine blade of claim 11, wherein the pressure side blade shell part has a first tapered section along at least a portion of an edge of said pressure side blade shell part, and the suction side blade shell part has a second tapered section along at least a portion of an edge of said suction side blade shell part, wherein said pressure side and suction side blade shell parts are arranged such that said first tapered section abuts said second tapered section to form a recess channel located along a boundary between the edges of said pressure side and suction side blade shell parts, wherein the respective edges of the pressure side and suction side blade shell parts extend along a spanwise direction of the wind turbine blade, and wherein the overlamination is located in said recess channel, said overlamination joining said pressure side and suction side blade shell parts.

13. The wind turbine blade of claim 11, wherein said overlamination is formed from the same material as said pressure side and suction side blade shell parts.

14. The wind turbine blade of claim 11, wherein the wind turbine blade comprises a recess channel extending along at least a portion of the leading edge of said wind turbine blade, wherein the overlamination a laminate is located in the leading edge recess channel and joins said pressure side and suction side blade shell parts along said at least a portion of the leading edge of said wind turbine blade.

15. The wind turbine blade of claim 14, wherein the recess channel extends along an entirety of the leading edge of said wind turbine blade.

16. The wind turbine blade of claim 11, wherein the wind turbine blade comprises a recess channel extending along at least a portion of the trailing edge of the wind turbine blade, wherein the overlamination located in the trailing edge recess channel joins said pressure side and suction side blade shell parts along said at least a portion of the trailing edge of said wind turbine blade.

17. The wind turbine blade of claim 16, wherein the overlamination laminate joins said pressure side and suction side blade shell parts in the root region of the wind turbine blade.

18. A wind turbine comprising at least one wind turbine blade as claimed in claim 11.

19. A method of manufacturing at least a portion of a wind turbine blade, wherein the method comprises the steps of: providing a pressure side blade shell part having a first edge; providing a suction side blade shell part having a second edge, wherein the first and second edges extend along a spanwise direction of the wind turbine blade; and joining said pressure side blade shell part to said suction side blade shell part along at least a portion of said first edge and said second edge to form a joined leading edge of a closed blade shell, wherein the joining consists of providing an overlamination extending between said first edge and said second edge, such that said joining is performed without a structural adhesive, and wherein said overlamination is applied to external surfaces of said first edge and said second edge, said first and second edges of said pressure side and suction side blade shell parts, respectively, being joined to one another solely by the overlamination along at least a common portion thereof, the closed blade shell consisting of the pressure side and suction side blade shell parts and the overlamination.

Description

DESCRIPTION OF THE INVENTION

(1) An embodiment of the invention will now be described, by way of example only, 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 a schematic view of an airfoil profile of the blade of FIG. 2;

(5) FIG. 4 shows a schematic view of the wind turbine blade of FIG. 2, seen from above and from the side;

(6) FIG. 5 illustrates an enlarged cross-sectional view of a leading edge adhesive bond for a prior art wind turbine blade; and

(7) FIG. 6 illustrates an enlarged cross-sectional view of a bond for a wind turbine blade according to the invention, along a wind turbine blade leading edge.

(8) It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings.

(9) FIG. 1 illustrates a conventional modern upwind wind turbine 2 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.

(10) FIG. 2 shows a schematic view of a wind turbine blade 10. 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.

(11) 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 is typically constant along the entire root area 30. The transition region 32 has a transitional profile 42 gradually changing from the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increasing distance r from the hub.

(12) The airfoil region 34 has an airfoil profile 50 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.

(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. 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.

(15) 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.

(16) FIG. 4 shows some other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 2, 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. 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.

(17) The wind turbine blade 10 generally comprises a shell made of fibre-reinforced polymer, and is typically made as a pressure side or upwind shell part 24 and a suction side or downwind shell part 26 that are attached together along bond lines 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of 30 or 40 metres in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading.

(18) With reference to bond lines 28, an enlarged view of a leading edge bond line according to an aspect of the invention is illustrated in FIG. 6. In this embodiment, the leading edges of the blade shells 24,26 are joined using an overlamination, which eliminates the need for a structural adhesive 100 between the blade shells 24,26.

(19) In this case, it will be understood that the bond line 28 refers to the general area of an overlamination joining the upwind and downwind shells 24,26.

(20) In FIG. 6, the pressure side or upwind shell part 24 and the suction side or downwind shell part 26 meet at the leading edge 18 of the blade 10, in the area of a bond line 28. The shells 24,26 comprise layers or fibre material 70 suspended in a cured resin, which may be applied around portions of a core material 72, e.g. balsa wood, foam, etc. The bodies of the shells 24,26 are tapered in thickness towards the leading edge 18 ends of the shells 24,26, at least along a portion of the leading edge 18.

(21) The shells 24,26 may be integrally formed with such a tapering of the leading edge 18 ends of the shells 24,26, e.g. through the use of suitably-shaped blade shell moulds (not shown) having shell profile surfaces, and/or mould inserts, incorporating a leading edge tapering profile. Additionally or alternatively, the tapering of the leading edge 18 ends of the shells 24,26 may be fully or partially formed through a post-moulding process, e.g. a cutting, grinding or polishing of the leading edge 18 ends of the shells 24,26 after said shells 24,26 have been removed from a blade shell mould (not shown).

(22) Once the shells 24,26 are provided with tapered ends, the shells 24,26 are brought together and closed to form a wind turbine blade 10, such that the leading edge end of the upwind shell 24 abuts the leading edge end of the downwind shell 26, without the presence of a structural adhesive between the shell ends. Accordingly, the tapered leading edge 18 ends of the shells 24,26 come together to form a recess channel 74 along a portion of the leading edge 18 of the blade 10.

(23) An overlamination 76 is applied in the recess channel 74, the overlamination 76 extending between the tapered portions of the upwind and downwind shells 24,26 and acting to join the shell leading edges together. In the embodiment of FIG. 6, the overlamination 76 is selected such that the overlamination 76 substantially fills the recess channel 74 and is flush with the adjacent surfaces of the wind turbine blade shells 24,26, thereby preserving the aerodynamic profile of the leading edge 18 of the blade 10.

(24) The overlamination 76 preferably comprises a plurality of layers of fibre material applied to the leading edge 18 of the blade 10, the layers of fibre material provided in a resin which bonds the layers of fibre material together, while also bonding to the tapered portions of the upwind and downwind shells 24,26.

(25) The overlamination 76 may be provided in the form of separate layers which are subsequently infused with a resin, and/or the overlamination 76 may be provided as a bundle or a stack of layers may be applied as a pre-preg, which may be at least partially infused with an uncured resin, where the pre-preg may be infused with additional resin to bond the overlamination 76 to shells 24,26, wherein the resin is subsequently cured.

(26) Preferably, the overlamination 76 is formed from the same material as the body of the wind turbine blade shells 24,26, e.g. as a glass- and/or carbon-fibre material infused with a suitable resin, e.g. polyester, vinyl ester, epoxy, etc.

(27) The overlamination 76 allows for the blade shells 24,26 to be joined without the use of a relatively heavy and expensive structural adhesive. Furthermore, as the overlamination 76 may be formed from the same material as the body of the blade shells 24,26, accordingly the fault resistance of the leading edge join between the shells 24,26 is increased, as the differences in stiffness levels and other material properties between the shells and the joining material are substantially eliminated.

(28) Preferably, the overlamination 76 can be used in joins between substantially circular-profile portions of the airfoil profile of the wind turbine blade 10, e.g. along the leading edge 18 of the blade 10, and/or along the trailing edge 20 near the root and 16 of the blade 10. It will be understood that the joining method of the invention may be combined with other joining techniques in other areas of the blade, e.g. using structural adhesive between the blade shells.

(29) The step of infusing the overlamination 76 may comprise applying a resin to the surface of a fibre material applied in the recess channel 74, e.g. using a roller application, vacuum infusion, etc. Alternatively, the step of applying a laminate may comprise positioning a precast laminate piece in said recess channel 74, and attaching the laminate piece in said recess channel with a cured resin.

(30) The embodiment of FIG. 6 shows the leading edge 18 ends of the blade shells 24,26 ending in a tapered section. It will be understood that the tapering of the blade shells 24,26 at the leading edge 18 may comprise a full or partial tapering of the thickness of the blade shell body at said ends. In one aspect, the tapering may extend through the body of the blade shells 24,26 to a single layer of fibre material. Additionally or alternatively, the leading edge 18 ends of the shells 24,26 may comprise a stepped tapering or a partial tapering through the thickness of the shell body.

(31) Preferably, the tapering is performed to have a substantially constant cross-section along a portion of the longitudinal length of the blade shells 24,26. Additionally or alternatively, the tapering may be performed in a serrated or zig-zag manner along the longitudinal direction of the blade shells 24,26. Additionally or alternatively, the tapering may be performed in a undulating or wave-like manner along the longitudinal direction of the blade shells 24,26.

(32) The use of a overlamination to join blade shell components allows for the manufacture of a wind turbine blade having reduced use of structural adhesive.

(33) Additionally, the use of overlaminations formed from substantially the same material as the body of the blade shell components themselves results in reduced risk of structural faults along the bond line between components, due to substantially identical stiffness levels and material properties between the shell components and the joining material.

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