A WIND TURBINE BLADE AND A METHOD FOR MANUFACTURING A WIND TURBINE BLADE

Abstract

A wind turbine blade (108) providing enhanced shear distortion resistance comprises a root end (118) and a tip end (116), a leading edge (112) and a trailing edge (114), and a suction side shell (122) and a pressure side shell (124) between which there is provided first and second shear webs (150, 152, 166, 168, 170, 172). The first and second shear webs (150, 152, 166, 168, 170, 172) are arranged in V-configuration in a chordwise cross section of the blade, whereby at least one of the first and second shear webs (150, 152, 166, 168, 170, 172) is non-orthogonal to the chord line (115), and the first and second shear webs are non-parallel. A method of manufacturing the wind turbine blade includes the step of providing respective upper and lower mould halves (200, 202) for the blade interconnecting the first and second shear webs (150, 152, 166, 168, 170, 172) by an elastic structure (190) biasing the shear webs towards one another before closing the mould.

Claims

1. A wind turbine blade comprising: a root end and a tip end a leading edge and a trailing edge, wherein the leading edge and the trailing edge extend in a lengthwise direction of the blade from the root end of the blade towards the tip end; a suction side shell and a pressure side shell; at least one airfoil defined by the suction side shell and the pressure side shell, the airfoil having a chord line interconnecting the leading edge and the trailing edge in a chordwise direction of the blade; at least a first and a second shear web, each of which interconnects the suction side shell and the pressure side shell; wherein, in a chordwise cross section of the blade: the first and second shear webs are arranged at a mutual distance in the chordwise direction of the blade; at least one of the first and second shear webs is non-orthogonal to the chord line in said chordwise cross section; and the first and second shear webs are non-parallel.

2. The wind turbine blade according to claim 1, wherein the first and second shear webs are arranged in a V-configuration when seen in the chordwise cross section of the blade.

3. The wind turbine blade according to claim 1, further comprising spar structures at the suction side and pressure side shells; wherein the first and second shear webs attach to the suction side and pressure side shells at the spar structures at respective attachment points; and a first chordwise distance between attachment points of the first and second shear webs at the suction side shell is different from a second chordwise distance between attachments points of the first and second shear webs at the pressure side shell.

4. The wind turbine blade according to claim 3, wherein: a chordwise length of the spar structure at the suction side shell is greater than a chordwise length of the spar structure at the pressure side shell; or a chordwise length of the spar structure at the pressure side shell is greater than a chordwise length of the spar structure at the suction side shell.

5. The wind turbine blade according to claim 3, wherein: said spar structures comprise two separated first spar caps at the suction side shell and two second separated spar caps at the pressure side shell; and the first and second shear webs attach to respective ones of the first spar caps at the suction side shell and to respective ones of the second spar caps at the pressure side shell.

6. The wind turbine blade according to claim 3, wherein: said spar structures comprise two separated first spar caps at one of the suction side and pressure side shells and a single second spar cap at the other one of the suction and pressure side shells; and the first and second shear webs attach to respective ones of the first spar caps at one of the shells and to the single second spar cap at the other shell.

7. The wind turbine according to claim 3, wherein said spar structures comprise: two separated first caps at one of the suction side and pressure side shells; two separated second caps at the other one of the suction side and pressure side shells; wherein at least one of the two separated first and second spar caps has a chordwise length substantially equal to half a chordwise length of at least another one of the two separated first and second spar caps.

8. The wind turbine blade according to claim 6, wherein a combined chordwise length of the two separated first spar caps is substantially equal to a chordwise length of the single second spar cap.

9. The wind turbine blade according to claim 6, wherein said single spar cap is at the pressure side shell.

10. The wind turbine blade according to claim 1, wherein the first and second shear webs are at a first mutual distance in the vicinity of the suction side shell and at a second mutual distance in the vicinity of the pressure side shell, wherein the first mutual distance is larger than the second mutual distance.

11. The wind turbine blade according to claim 1, further comprising a third shear web which: when seen in the chordwise cross section of the blade is arranged at a chordwise position closer to the trailing edge than the first and second shear webs; and which extends orthogonally to the chord line.

12. The wind turbine blade according to claim 1, wherein the first and second shear webs are arranged in a V-configuration at a lengthwise position between 5% and 50% of the length of the blade when measured from the root towards the tip.

13. The wind turbine blade according to claim 12, wherein any one of the shear webs is orthogonal to the chord line at lengthwise positions above 50% of the length of the blade when measured from the root towards the tip.

14. The wind turbine blade according to claim 1, wherein the first and second shear webs are arranged in a V-configuration at lengthwise positions within the blade, at which the thickness-to-chord ratio of the airfoil is at least 30%.

15. The wind turbine blade according to claim 1, wherein the trailing edge is truncated in said chordwise cross section of the blade.

16. The wind turbine blade according to claim 1, wherein said at least one of the first and second shear webs which is non-orthogonal to the chord line defines an angle of between 50 and 80 with respect to the chord line.

17. A method for manufacturing a wind turbine blade according to claim 1, comprising: providing the suction side shell and the pressure side shell in respective mould halves; bonding the first and second shear webs to one of the suction and pressure side shells, whereby respective ends of the shear webs opposite to ends bonded to said one of the shells remain unattached to the other one of the suction and pressure side shells; applying an adhesive to said opposite ends of the shear webs and/or to attachment regions for the shear webs at an inner surface of said other one of the shells; and subsequently: closing the mould to engage the inner surface of said other one of the shells with said opposite ends of the first and second shear webs.

18. The method according to claim 17, comprising further comprising, prior to the step of closing the mould: interconnecting the first and second shear webs by an elastic structure biasing the shear webs towards one another, and optionally interconnecting the first and second shear webs by a rigid distance piece, wherein the elastic structure and the optional rigid distance piece remain attached to the first and second shear webs during the step of closing the mould.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments of the invention will now be further described by reference to the accompanying drawings, in which:

[0062] FIG. 1 generally illustrates a horizontal-axis wind turbine including three blades according to the present invention;

[0063] FIG. 2 generally illustrates a wind turbine blade according to the present invention;

[0064] FIG. 3 illustrates a prior art configuration of a chordwise cross section of a wind turbine blade;

[0065] FIG. 4 illustrates a first embodiment of a wind turbine blade according to the present invention seen in a chordwise cross section through the blade;

[0066] FIG. 5 illustrates a second embodiment of a wind turbine blade according to the present invention seen in a chordwise cross section through the blade;

[0067] FIG. 6 illustrates a manufacturing stage of the blade according to the embodiment of FIG. 4;

[0068] FIG. 7 is a flowchart including steps of a method of manufacture according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0069] FIGS. 1 and 2 generally illustrate a horizontal-axis wind turbine 100 including three blades 108 according to the present invention (FIG. 1) and a blade 108 (FIG. 2). The blades 108 constitute a rotor of the wind turbine connected to a main shaft at a hub 110. The wind turbine 100 includes a tower 102 and a nacelle 104 at the upper end of the tower. Each blade 108 has a root end 118, a tip end 116, a leading edge 112 and a trailing edge 114. The blade has a total length l from the root 118 to the tip 116. At any position between the root 118 and the tip 116, the chord length c is defined as the shortest straight line distance between the leading edge 112 and the trailing edge 114. As shown in FIG. 2, the chord length may vary along the length of the blade to take into account the fact that the aerodynamics vary along the length of the blade. Likewise the blade may be twisted along its length. The aerodynamic profile of the blade in a chordwise cross sectional view may vary along the length of the blade. At the root 118, the profile is typically circular, and near the root the blade undergoes a transition into an aerodynamic profile. At its root 118 the blade may be mounted to a pitch-regulating device for controlling the pitch of the blade, i.e. its rotation around a longitudinal axis extending in the lengthwise direction of the blade.

[0070] In operation flapwise loads, mainly conferred by aerodynamic loads, and edgewise loads, mainly conferred by gravity, generate transverse shear forces as generally indicated by arrows 142 and 144 in FIG. 3 which shows a chordwise cross-sectional view through a prior art wind turbine blade. The blade has a suction side 120 and a pressure side 124 defined by a suction side shell 122 and a pressure side shell 126, respectively. As illustrated, the shells 122 and 126 are joined at the leading and trailing edges 112 and 114. Internally within the blade, the suction side shell 122 and the pressure side shell 126 are interconnected by shear webs 128 and 130 extending in a thickness direction of the blade, i.e. transverse to the chordwise direction. At the attachment zones of the shear webs 128 and 130 to the shells 122 and 126, the shells are provided with spar caps 134 and 136. The transverse shear forces 142 and 144 occur in consequence of intrinsic asymmetries of the blade geometry and its mass distribution. The transverse shear forces confer bending moments in the chordwise cross sectional plane illustrated in FIG. 3, whereby the spar caps 134 and 138 and/or the shear webs 128 and 130 may be distorted. These effects are generally referred to herein as shear distortion.

[0071] In order to mitigate shear distortion, the present invention provides a wind turbine blade according to the accompanying claims. In one embodiment as illustrated in FIG. 4, the blade comprises, in a cross-sectional view, first and second shear webs 150, 152 arranged in a V configuration. The blade has a chord length c. The shortest straight line distance between the leading edge 112 and the trailing edge 114 is generally referred to as the chord length. The chord line 115 is defined as the straight line defining the chord length.

[0072] As shown in FIG. 4, the trailing edge 114 may be truncated, i.e. it the airfoil section does not form a sharp point at the trailing edge, but instead the airfoil has a flatback trailing edge. The chord length c is taken from the middle point of the flatback trailing edge.

[0073] Whereas in the prior art example of FIG. 3, the shear webs 128 and 130 are perpendicular to the chord line and hence parallel, according to the present invention, as illustrated in the embodiment of FIG. 4, at least one of the first and second shear webs 150, 152 is non-orthogonal to the chord line 115, resulting in a V configuration of the shear webs. In the exemplary embodiment of FIG. 4, both the first and second shear webs 150, 152 are non-orthogonal to the chord line 115. The first shear web 150 leans towards the leading edge 112 and forms an acute angle with respect to the chord line 115 as well as an opposite obtuse angle . The second shear web 152 leans towards the trailing edge 114 and forms an acute angle with respect to the chord line 115, the angle being thus opposite to the angle ox of the first shear web 150. The obtuse angle of the second shear web 152 with respect to the chord line 115 is denoted in FIG. 4.

[0074] The first and second shear webs 150 and 152 attach to a common first spar cap 162 embedded in the pressure side shell 126 and to respective second spar caps 156 and 158 embedded in the suction side shell 122. In other embodiments, separate first spar caps for the first and second shear webs 150, 152 are provided in place of the first common spar cap 162. In yet other embodiments, a common spar cap at the suction side shell 122 may be provided in place of the second spar caps 156 and 158.

[0075] As indicated, the combined chordwise lengths of the second spar caps 156 and 158 are substantially equal to the chordwise length of the first common spar cap 162. The first common spar cap 162 may conveniently comprise two spar caps of a standard width arranged next to one another in the chordwise direction of the pressure side shell 126, whereas each of the second spar caps 156 and 158 may comprise one such spar cap of a standard width. The use of spar caps, such as pultruded elements, of standard widths contributes to keeping manufacturing costs at a minimum. In the present context, the notion of chordwise lengths of the spar caps is to be understood as the length of the spar cap parallel to a tangent to the shell, in which the spar cap is comprised. Thus, the chordwise lengths of the spar caps may be larger than their projected lengths x and 2x onto the chord line indicated in FIG. 4.

[0076] A third shear web 154 is provided towards the trailing edge 114 of the blade, with the third shear web 154 attaching to the shells 122 and 126 at respective spar caps 160 and 164. In the exemplary embodiment shown in FIG. 4, the third shear web 154 is perpendicular to the chord line 115.

[0077] As shown, the embodiment of FIG. 4 includes respective spar structures a and b at the suction side shell 122 and the pressure side shell 126. At the suction side shell 122 the spar structure a comprises the spar caps 156 and 158 as two separated spar caps. At the pressure side shell 126 the spar structure b comprises a single spar cap 162. The spar cap 162 may comprise elements of a standard width, such as pultruded elements, identical to those comprised in the spar caps 156 and 158. Thus, at spar cap 162 two such elements may be arranged next to one another, resulting in the length of spar cap 162 being twice the length of each one of the respective spar caps 156 and 158.

[0078] FIG. 5 illustrates a second embodiment of a blade according to the invention, comprising, in addition to first and second shear webs 166 and 168 arranged in a V configuration, two further shear webs 170 and 172, likewise arranged in a V configuration. As illustrated, the shear webs 166, 168, 170 and 172 form a W configuration and attach to the suction side shell 122 at common spar caps 176 and 178 and to the pressure side shell 126 at spar caps 182, 184 and 186. Like in the embodiment of FIG. 4, a third shear web 174 extending orthogonally to the chord line 115 is provided in addition to the V- and W-configured shear webs 166, 168, 170 and 172.

[0079] In the embodiment shown in FIGS. 4 and 5 all of the shear webs 150, 152, 166, 168, 170, 172 and 174 are essentially I-shaped and extend along an essentially straight line between the suction side and pressure side shells 126 and 122 without intersecting one another.

[0080] The embodiments of the blade according to the invention illustrated in FIGS. 4 and 5 may be manufactured according to the method according to the second aspect of the invention. An embodiment of the method will hereinafter be described by reference to FIGS. 6 and 7.

[0081] As shown in FIG. 6, at a manufacturing stage of the blade 108 according to the invention, the suction side shell 122 and pressure side shell 126 are provided in respective halves of a mould which may be mutually hinged at the position of the leading edge 112. The suction side shell 122 and the pressure side shell may be manufactured by a manufacturing step known per se, in which reinforcement fibres are laid up, impregnated with a resin and cured. The fibres and resin may be provided as prepregs, or alternatively non-impregnated dry fibres may be laid up and infused with a resin.

[0082] Prior to closing the mould by rotating the pressure side mould half, i.e. the upper mould half as indicated by an arcuate arrow in FIG. 6, the first and second shear webs 150, 152, as well as the optional third shear web 154, are bonded, e.g. by an adhesive, to the suction side shell, i.e. the lower shell, at attachment points at the respective spar caps 156, 158 and 160. The first and second shear webs 150, 152 are interconnected by an elastic structure 190, such as a rubber band, as well as by a rigid distance piece 192. The elastic structure 190 contributes to ensuring that the first and second shear webs 150, 152 do not drift away from one another under the action of gravity and/or under the action of pressure imparted by the upper mould half for the pressure side shell 126 when the mould is closed. The rigid distance piece 192 contributes to ensuring that the first and second shear webs keep their intended distance.

[0083] Also prior to closing the mould, adhesive is applied at the leading and trailing edges 112, 114 along the length of the blade, as well as at upper surfaces 150a, 152a and 154a of the shear webs 150, 152, 154. Alternatively or additionally to providing adhesive at the upper surfaces 150a, 152a, 154a of the shear webs, adhesive may be applied at attachment zones of the spar caps 162 and 164. After application of adhesive for bonding the suction side shell 124 and the pressure side shell 126 together the mould is closed for bonding the shells together.

[0084] FIG. 7 is a flowchart including steps of a method of manufacture according to the invention. At step 300, fibres for the blade shells are laid up in two half shell moulds. Next, at step 302, a resin is infused and cured at step 304 to form the suction side and pressure side shells. If the fibres are provided in the form of prepregs, the step of infusing a resin is omitted. At step 306 the shear webs are laid up by providing a fibrous material embedded in a resin which is cured. Step 306 may occur at any stage before step 308, i.e. before any one of steps 300, 302 and 304, or at the same time as any one of steps 300, 302 and 304.

[0085] At step 308 the shear webs are arranged in an inversed V configuration and bonded to the lower half shell as exemplified above by reference to the embodiment of FIG. 6. At step 310 the elastic structure and rigid distance piece are provided to interconnect the shear webs. Step 310 may alternatively occur prior to step 308 in order to minimize the amount of work to be carried out to the shear webs once arranged in the lower half mould. At step 312, adhesive is applied to the leading and trailing edges along their length as well as to the upper surface of the shear webs. Subsequently, the mould is closed.

[0086] Once the adhesive has cured, the mould is opened, and the blade is removed from the mould.