WO2021214726A1

WO2021214726A1 - Wind turbine blade with reinforcing structure

Info

Publication number: WO2021214726A1
Application number: PCT/IB2021/053371
Authority: WO
Inventors: Anil Kumar SAHOO; Utsa Majumder; Mohamed Shaik Sahul HAMEED; Sathiyagopi MADURAI
Original assignee: Lm Wind Power Blades (India) Pvt. Ltd.
Priority date: 2020-04-24
Filing date: 2021-04-23
Publication date: 2021-10-28
Also published as: GB202008692D0

Abstract

The present invention relates to a wind turbine blade (10) comprising an elongate reinforcing structure (62). The reinforcing structure (62) comprises a plurality of strips (63, 64, 65) of fibre-reinforced polymer arranged into adjacent stacks (66) of strips, and at least one alignment member (68). The latter comprises a plurality of alternating horizontal segments (70) and vertical segments (72), wherein a vertical segment of the alignment member is arranged between adjacent stacks of strips, and wherein a horizontal segment of the alignment member is arranged on top of or below each stack of strips.

Description

WIND TURBINE BLADE WITH REINFORCING STRUCTURE

Field of the Invention

The present invention relates to a wind turbine blade comprises an elongate reinforcing structure and to a method of producing said wind turbine blade.

Background of the Invention

Wind power provides a clean and environmentally friendly source of energy. Wind turbines usually comprise a tower, generator, gearbox, nacelle, and one or more rotor blades. The wind turbine blades capture kinetic energy of wind using known airfoil principles. Modern wind turbines may have rotor blades that exceed 90 meters in length.

Wind turbine blades are usually manufactured by forming two shell parts or shell halves from layers of woven fabric or fibre and resin. Spar caps or main laminates are placed or integrated in the shell halves and may be combined with shear webs or spar beams to form structural support members. Spar caps or main laminates may be joined to, or integrated within, the inside of the suction and pressure halves of the shell.

As the size of wind turbine blades increases, various challenges arise from such blades being subject to increased forces during operation, requiring improved reinforcing structures. The manufacturing of large reinforcing structures, such as spar caps or spar beams, is likewise challenging, in particular when pultruded, carbon fiber-reinforced spar caps are used as the reinforcing members. Carbon fibres are typically lighter than glass fibres by volume, and have improved tensile and compressive strength. However, laminate defects, such as voids, wrinkles or misaligned fibers, may have disadvantageous effects on mechanical properties. Carbon pultrusion lay-up thus often results in slight overlap and/or misplacement of carbon pultrusion layers. Such defects and misalignments are often only identified after resin infusion.

WO 2001/088372 A1 discloses a spar cap for a wind turbine blade, which comprises a composite beam having multiple stacked preform layers of elongate and rigid unidirectional strength elements or rods, wherein each preform layer includes at least one fibre textile structure to which the strength elements or rods are joined to retain the strength elements or rods in a single layer. The fiber textile structure includes an interlocking textile fiber weave and a fabric made by stitching. The fibre textile structure extends across the transverse width of the preform layer and interfaces with individual strength elements or rods so that the fiber weave retains the elements or rods in a single preform layer.

EP 3174704 A1 relates to a method of making an elongate reinforcing structure for a wind turbine blade. The elongate reinforcing structure comprises a plurality of strips of fibre-reinforced polymer arranged into a stack structure, and at least one adjacent pair of the plurality of strips including an infusion promoting layer, wherein the infusion promoting layer is a fabric comprising a plurality of twisted yarns. The use of twisted yarn fabric helps in controlling the speed of infusion through the blade. The infusion promoting layer may be a glass-fibre fabric and may be interleaved between each pair of the plurality of strips in order to have the same influence on infusion speed throughout the stack structure. Furthermore, a partitioning layer is provided in between two stack structures, wherein overlapping edges of the infusion promoting layer are in contact with the partitioning layer.

While these prior art solutions may provide satisfactory resin infusion pathways, they suffer from the disadvantage of using complicated interlocking or partitioning structures, which require costly manufacturing and tedious arrangement within stacked structures. In addition, due to the fact that various materials and layers are combined, these arrangements are prone to undesired displacement during resin infusion, thus creating misalignments and defects in the finished stacked structure.

It is therefore an object of the present invention to provide a wind turbine blade with a reinforcing structure having improved stability.

It is another object of the present invention to provide a reinforcing structure for a wind turbine blade which is easily manufactured, handled and assembled.

It is another object of the present invention to provide a reinforcing structure for a wind turbine blade which is cost-effective, and which avoids the above-discussed misalignments and defects.

Summary of the invention It has been found that one or more of the aforementioned objects can be obtained by a wind turbine blade having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, wherein the wind turbine blade comprises an elongate reinforcing structure, the reinforcing structure comprising a plurality of strips of fibre-reinforced polymer arranged into adjacent stacks of strips, and at least one alignment member comprising a plurality of alternating horizontal segments and vertical segments, wherein a vertical segment of the alignment member is arranged between adjacent stacks of strips, and wherein a horizontal segment of the alignment member is arranged on top of or below each stack of strips.

It was found that this solution greatly reduces undesired overlap and/or misplacement of the plurality of strips of the fibre-reinforced polymer, in particular if carbon pultrusion layers are used. Thus, the arrangement of the present invention is advantageous in maintaining the required tolerances and positions of the strips along the length of the stacks.

The reinforcing structure will typically be a spar cap. In some embodiments, the reinforcing structure comprises a box spar. In other embodiments, the reinforcing structure comprises a spar beam. It is preferred that the reinforcing structure extends along the blade in a spanwise direction. Typically, the reinforcing structure will extend over 60-95% of the blade length.

The wind turbine blade is usually manufactured from two shell halves, a pressure side shell half and a suction side shell half. Preferably, both shell halves comprise an elongate reinforcing structure, such as a spar cap, according to the present invention.

The plurality of strips will typically extend in a spanwise direction of the blade. Thus each strip has preferably a length corresponding to 60-95% of the blade length. It is particularly, preferred that each strip comprises a pultruded carbon fibre material. According to a preferred embodiment, the fibre-reinforced polymer comprises pultruded carbon fibres. In some embodiments, each strip contains a carbon fibre material. In other embodiments, each strip contains a glass fibre material. In other embodiments, each strip contains a glass fibre material and a carbon fibre material. In some embodiments, the strips may not contain any polymer when laying up the strips in the mould. In this embodiments, a polymer resin is typically infused into strips following the lay-up. Each stack of strips may comprise 2-30, such as 3-20 strips successively arranged on top of each other. Thus, each stack will usually extend in a spanwise direction of the blade. Typically, two or more, or three or more stacks of strips are arranged next to each other, adjacent to each other in a substantially chordwise direction. In a preferred embodiment, the strips are substantially flat. It is preferred that each strip within the stack of strips is a pultruded plank having a generally rectangular cross section. Preferably, each pultruded plank has a cross-sectional width of at least 20 mm, preferably at least 50 mm, and a cross-sectional thickness of at least 1 mm, preferably at least 2 mm. In a preferred embodiment, each pultruded plank has a cross-sectional width of 20-500 mm, and a cross-sectional thickness of 1 -10 mm.

The length of the strip, preferably pultruded plank, is typically between 50 and 150 meters, preferably between 50 and 100 meters, more preferably between 70 and 100 meters. The height/thickness of the strip, preferably pultruded plank, is preferably between 2 and 10 millimeters, preferably between 3 and 7 millimeters, most preferably between 4 and 6 millimeters. The width of the strip, preferably pultruded plank, is preferably between 20 and 300 millimeters, most preferably between 80 and 150 millimeters. In a preferred embodiment, each strip comprises a pultrusion fibre material comprising a plurality of tows of fibre material, such as carbon fibre material. Thus, each strip may comprise 50-300 tows of fibre material, preferably 25-180 tows of fibre material. The tows will usually extend in the length direction of the strip, i.e. substantially parallel to its longitudinal axis, or parallel to the spanwise direction when arranged in the blade shell.

Typically, a resin will be infused in the stack of strips containing a fibre material, such as a carbon fibre material, to form the fibre-reinforced polymer of the reinforcing structure. This can, for example, be done using vacuum-assisted resin transfer moulding. In other embodiments, a prepreg material can be used for the strips, which contains a fibre material pre-impregnated with a resin system, such as an epoxy resin. The alignment member comprises a plurality of alternating horizontal segments and vertical segments. Advantageously, a horizontal segment adjoins a vertical segment, which in turn adjoins the next horizontal segment, and so on. Typically, the alignment member comprises a plurality of alternating horizontal segments and vertical segments as seen in a substantially chordwise direction. It is preferred that the alignment member is oriented in a substantially chordwise direction, i.e. having its largest dimension oriented substantially chordwise, whereas the spanwise extent is less than the chordwise extent of the alignment member. Preferably, the chordwise extent is at least two times the spanwise extent of the alignment member.

A vertical segment of the alignment member is arranged between adjacent stacks of strips. The space between adjacent stacks, is preferably less than 0.5 mm, such as less than 0.3 mm, as seen in a substantially chordwise direction. Thus, each vertical segment of the alignment member extends in a substantially flapwise direction, being either disposed between two adjacent stacks or adjacent to the last or first stack, as seen in the chordwise direction.

The horizontal segments of the alignment member are preferably arranged below the respective stacks of strips. It is preferred that the alignment member extends along the entire reinforcing structure as seen in a chordwise direction. It is also preferred that the alignment member only extends along part of the reinforcing structure as seen in a spanwise direction. It has been found that a satisfactory alignment can be achieved by providing for example two alignment members at each end of the reinforcing structure as seen in a spanwise direction.

In a preferred embodiment, each reinforcing structure comprises two alignment members positioned at opposing ends of the reinforcing structure. In a preferred embodiment, the alignment member is manufactured using a pre-designed mould or 3D printing/additive manufacturing. In some embodiments, the alignment member is made of a polymer material.

The elongate reinforcing structure will typically extend in a substantially spanwise direction. As used herein, the term vertical segment refers to a segment that extends in a substantially flapwise direction. Also, as used herein, the term horizontal segment refers to a segment that extends in a substantially chordwise direction. In a preferred embodiment, the alignment member comprises at least three horizontal segments and at least two vertical segments. In some embodiment, the alignment member comprises at least three horizontal segments and at least three vertical segments. In a preferred embodiment, the alignment member comprises more vertical segments than horizontal segments, preferably one more vertical segment than horizontal segments. In some embodiments, the alignment member comprises at least three horizontal segments and at least four vertical segments.

In a preferred embodiment, the alignment member is a folded fabric. This has been found to result in a particularly simple, yet efficient way to provide the alignment member. The fabric could be e.g. a veil fabric, such as a veil mat. The fabric preferably has a thickness of not more than 1 mm, preferably not more than 0.5 mm. The fabric may comprise a series of substantially 90° folds and substantially 180° folds. For example, the unfolded fabric may constitute the plane in which the horizontal segments of the folded fabric lie, wherein the adjacent vertical segment is obtainable by providing a substantially 90° fold, i.e. to provide at least part of a vertical segment extending in a substantially flapwise direction, followed by a 180° fold and another 90° to revert to the next adjacent horizontal segment, and so on. Thus, when using a folded fabric as the alignment member, each horizontal segment may comprise a single layer of fabric, whereas one or more of the vertical segments may comprise a double layer of fabric. The double layer in one or more of the vertical segments is provided by the 180° fold for returning to the horizontal segment.

In a preferred embodiment, the folded fabric comprises a veil cloth or a veil mat, preferably a pre-impregnated veil cloth or veil mat. As used herein, a veil mat or veil cloth preferably comprises plies of continuous strand fibers that are looped randomly throughout the material. A veil mat or veil cloth may also comprise a binding agent to hold the veil together. Taken alone, veil mats or veil cloths are usually not intended for structural use.

In a preferred embodiment, the alignment member is a pre-infused or pre-impregnated folded fabric. Thus, a substantially hardened folded fabric, such as a hardened folded veil cloth or veil mat may be provided as alignment member.

In a preferred embodiment, the alignment member comprises a non-woven folded fabric, preferably a non-woven fabric comprising fibres with random orientation. In a preferred embodiment, the horizontal segments of the alignment member are arranged below each stack of strips, e.g. a first horizontal segment is arranged below the first stack of strips followed chordwise by a vertical segment that extends in a substantially flapwise direction, followed by a second horizontal segment arranged below the second stack of strips, and so on.

In some embodiments, the alignment member comprises, or consists of, a glass fibre fabric. In other embodiments, the alignment member comprises, or consists of, a carbon fibre fabric.

In a preferred embodiment, the horizontal segments lie in the substantially same plane. It is preferred that the horizontal segments lie in a plane extending in a chordwise and in a spanwise direction, preferably directly underneath the stacks of strips.

In a preferred embodiment, the vertical segments lie in substantially parallel planes. It is preferred that the planes in which the vertical segments lie extend in a spanwise and in a flapwise direction. It is also preferred that each vertical segment laterally abuts at least one stack of strips. Usually, the vertical segments will be oriented substantially perpendicularly to the horizontal segments of the alignment member.

In a preferred embodiment, the alignment member is substantially rack-shaped. Thus, the alignment member may take the form of a rack-shaped folded fabric, preferably a rack-shaped veil fabric.

In a preferred embodiment, the strips comprise pultruded strips, preferably pultruded strips comprising carbon fibres. In some embodiments, the elongate reinforcing structure is a spar structure, such as a spar cap, a spar beam or a box spar.

It is preferred that the thickness of the alignment member is between 0.1 and 0.5 mm, such as between 0.1 and 0.4 mm. When a fabric is used as alignment member, at any given point, the thickness of the alignment member may correspond to one times (horizontal segment) or two times (vertical segment) of the thickness of the fabric. In other embodiments, an additional fabric can be used running parallel to the horizontal segments, such that the horizontal segments have a thickness of two times of the thickness of the fabric as well. In some embodiments, the alignment member is not an infusion promoting layer.

In a preferred embodiment, the chordwise extent of the alignment member is between 1 and 10 meters. It is preferred that the alignment member extends along the entire chordwise dimension of the elongate reinforcing structure.

In one embodiment, an infusion promoting layer is interleaved between the strips of each stack.

In a preferred embodiment, the elongate reinforcing structure extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure has a tip end, closest to the tip end of the blade, and a root end, closest to the root end of the blade, wherein a first alignment member is arranged at the tip end of the elongate reinforcing structure, and a second alignment member is arranged at the root end of the elongate reinforcing structure. Thus, the blade of the present invention may comprise at least two alignment members. In some embodiments, the first and second alignment members may extend 0.1-2 meters from the respective root end or tip end of the elongate reinforcing structure, as seen in a spanwise direction.

In a preferred embodiment, the elongate reinforcing structure extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure has a tip end, closest to the tip end of the blade, a root end, closest to the root end of the blade, and a spanwise midpoint having an equal distance from each of the tip end and the root end of the elongate reinforcing structure, wherein a single alignment member is arranged at the spanwise midpoint of the elongate reinforcing structure. In some embodiments, the single alignment member may extend 0.1-2 meters in a spanwise direction.

In a preferred embodiment, the elongate reinforcing structure extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure comprises a spanwise extending front edge, which is closest to the leading edge of the blade, and a spanwise extending rear edge, which is closest to the trailing edge of the blade, wherein one of the vertical segments of the alignment member is arranged adjacent to the front edge of the elongate reinforcing structure, and wherein one of the vertical segments of the alignment member is arranged adjacent to the rear edge of the elongate reinforcing structure. It is preferred that the two respective vertical segments of the alignment member abut the respective rear or front edge of the elongate reinforcing structure.

In a preferred embodiment, the vertical segments of the alignment member extend over the thickness of each stack. Typically, the thickness of each stack is defined by the sum of the individual thicknesses of the strips within a given stack.

In a preferred embodiment, the alignment member has a spanwise extent of not more than 1 meter, preferably not more than 50 cm, such as 15-100 mm, preferably 15-25 mm.

In another aspect, the present invention relates to a method of manufacturing a wind turbine blade having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, the method comprising the steps of: arranging a plurality of blade components in a blade mould, and assembling an elongate reinforcing structure in the blade mould relative to the plurality of blade components, the reinforcing structure comprising a plurality of strips of fibre material arranged into adjacent stacks of strips, and at least one alignment member comprising alternating horizontal segments and vertical segments, wherein a vertical segment of the alignment member is arranged between adjacent stacks of strips, and wherein a horizontal segment of the alignment member is arranged on top of or below each stack of strips, infusing resin into the stacks of strips to form a fibre-reinforced polymer.

All features and embodiments discussed above with respect to the wind turbine blade of the present invention likewise apply to the method of the present invention and vice versa.

In a preferred embodiment, the method of the present invention further comprises a step of, prior to assembling the elongate reinforcing structure in the blade mould, folding a fabric, such as a veil fabric or veil mat, and optionally hardening the folded fabric, e.g. by resin infusion, for providing the alignment member comprising the alternating horizontal segments and vertical segments. The folding step may preferably comprise providing a series of alternating 90° folds and 180° fold to provide the alternating horizontal segments and vertical segments of the alignment member. Thus, when using a folded fabric as the alignment member, each horizontal segment may comprise a single layer of fabric, whereas one or more of the vertical segments may comprise a double layer of fabric. The double layer in one or more of the vertical segments is provided by the 180° fold for returning to the horizontal segment.

The unfolded fabric may have a substantially flat of planar rectangular shape, wherein the folds are provided perpendicular to the length extension of the fabric. The fabric preferably has a thickness of not more than 1 mm, preferably not more than 0.5 mm. In a preferred embodiment, the folded fabric comprises a veil cloth or a veil mat, preferably a pre-impregnated veil cloth or veil mat. As used herein, a veil mat or veil cloth preferably comprises plies of continuous strand fibers that are looped randomly throughout the material. A veil mat or veil cloth may also comprise a binding agent to hold the veil together.

In a preferred embodiment, the alignment member is a pre-infused or pre-impregnated folded fabric. Thus, a substantially hardened folded fabric, such as a hardened folded veil cloth or veil mat may be provided as alignment member. In a preferred embodiment, the alignment member comprises a non-woven folded fabric, preferably a non-woven fabric comprising fibres with random orientation.

Usually, the blade will comprise a pressure side shell half and the suction side shell half which are manufactured over the entire length of the wind turbine blade, i.e. over their entire final length. The pressure side shell half and the suction side shell half will typically be adhered or bonded to each other near the leading edge and near the trailing edge. Each shell half may comprise longitudinally/spanwise extending load carrying structures, such as one or more main laminates or spar caps, preferably comprising reinforcement fibres such as glass fibres, carbon fibres, aramid fibres, metallic fibres, such as steel fibres, or plant fibres, or mixtures thereof.

The shell halves will typically be produced by infusing a fibre lay-up of fibre material with a resin such as epoxy, polyester or vinyl ester.

Usually, the pressure side shell half and the suction side shell half are manufactured using a blade mould. Each of the shell halves may comprise spar caps or main laminates provided along the respective pressure and suction side shell members as reinforcing structures. The spar caps or main laminates may be affixed to the inner faces of the shell halves.

The spar structure is preferably a longitudinally extending load carrying structure, preferably comprising a beam or spar box for connecting and stabilizing the shell halves. The spar structure may be adapted to carry a substantial part of the load on the blade.

In some embodiments, the reinforcing structure is arranged within the pressure side shell half. In other embodiments, the reinforcing structure is arranged within the suction side shell half.

In a preferred embodiment, the alignment member is a folded fabric that is pre-infused and hardened prior to its arrangement in the blade mould.

In a preferred embodiment, the strips of fibre material are pultruded strips, preferably pultruded strips comprising carbon fibres

According to another aspect, the present invention relates to a wind turbine blade obtainable by the method according to any of the preceding claims.

In a preferred embodiment, the pressure side shell half and the suction side shell half of the blade are manufactured in respective mould halves, preferably by vacuum assisted resin transfer moulding. According to some embodiments, the pressure side shell half and the suction side shell half each have a longitudinal extent L of 50-90 m, preferably 60-80 m. In a preferred embodiment, the pressure side shell half and the suction side shell half each comprise one or more layers of carbon fibres.

According to some embodiments, the method further comprises a step of arranging one or more shear webs in at least one of the shell halves, usually at the location of the reinforcing structure. Each shear web may comprise a web body, a first web foot flange at a first end of the web body, and a second web foot flange at a second end of the web body. In some embodiments, the shear webs are substantially l-shaped. Alternatively, the shear webs may be substantially C-shaped.

In another aspect, the present invention relates to a wind turbine blade having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, wherein the wind turbine blade comprises an elongate reinforcing structure, the reinforcing structure comprising a plurality of strips of fibre-reinforced polymer arranged into adjacent stacks of strips, and at least one alignment member comprising a folded fabric, the folded fabric comprising a base and a series of spaced projections each extending at a substantially right angle from the base, wherein a projection of the folded fabric is arranged between each adjacent stacks of strips, and wherein the base of the fabric is arranged on top of or below the stacks of strips.

The unfolded fabric may have a substantially flat of planar rectangular shape, wherein the folds are provided perpendicular to the length extension of the fabric. The fabric preferably has a thickness of not more than 1 mm, preferably not more than 0.5 mm. In a preferred embodiment, the folded fabric comprises a veil cloth or a veil mat, preferably a pre-impregnated veil cloth or veil mat. The fabric may also comprise a binding agent to hold the fabric together. In a preferred embodiment, the alignment member comprises a pre-infused or pre-impregnated folded fabric. Thus, a substantially hardened folded fabric, such as a hardened folded veil cloth or veil mat may be provided as alignment member. In a preferred embodiment, the alignment member comprises a non-woven folded fabric, preferably a non-woven fabric comprising fibres with random orientation.

The features and embodiments described above for one aspect of the present invention may likewise be combined with one or more of the other aspects of the present invention.

As used herein, the term “spanwise” is used to describe the orientation of a measurement or element along the blade from its root end to its tip end. In some embodiments, spanwise is the direction along the longitudinal axis and longitudinal extent of the wind turbine blade.

Description of the Invention

The invention is explained in detail below with reference to an embodiment shown in the drawings, in which Fig. 1 shows a wind turbine,

Fig. 2 shows a schematic view of a wind turbine blade,

Fig. 3 shows a schematic view of a cross-section of a wind turbine blade,

Fig. 4 is a schematic side view of a reinforcing structure according to the prior art and according to the present invention, respectively,

Fig. 5 is a perspective view of an alignment member according to the present invention, which is being folded into its final configuration, and

Fig. 6 is a perspective view of an alignment member according to the present invention,

Fig. 7 is a perspective view of a partially completed reinforcing structure according to the present invention,

Fig. 8 is a cross sectional view taken along the line A-A’ in Fig. 7, and

Fig. 9 is a schematic to view of the wind turbine blade according to the present invention.

Detailed Description

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.

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 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. 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.

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. Fig. 2 also illustrates the longitudinal extent L, length or longitudinal axis of the blade.

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.

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.

Fig. 3 shows a schematic view of a cross section of the blade along the line l-l shown in Fig. 2. As previously mentioned, the blade 10 comprises a pressure side shell part 36 and a suction side shell part 38. The pressure side shell part 36 comprises a spar cap 41 , also called a main laminate, which constitutes a load bearing part of the pressure side shell part 36. The spar cap 41 comprises a plurality of fibre layers 42 mainly comprising unidirectional fibres aligned along the longitudinal direction of the blade in order to provide stiffness to the blade. The suction side shell part 38 also comprises a spar cap 45 comprising a plurality of fibre layers 46. The pressure side shell part 36 may also comprise a sandwich core material 43 typically made of balsawood or foamed polymer and sandwiched between a number of fibre-reinforced skin layers. The sandwich core material 43 is used to provide stiffness to the shell in order to ensure that the shell substantially maintains its aerodynamic profile during rotation of the blade. Similarly, the suction side shell part 38 may also comprise a sandwich core material 47.

The spar cap 41 of the pressure side shell part 36 and the spar cap 45 of the suction side shell part 38 are connected via a first shear web 50 and a second shear web 55. The shear webs 50, 55 are in the shown embodiment shaped as substantially l-shaped webs. The first shear web 50 comprises a shear web body and two web foot flanges. The shear web body comprises a sandwich core material 51 , such as balsawood or foamed polymer, covered by a number of skin layers 52 made of a number of fibre layers. The blade shells 36, 38 may comprise further fibre-reinforcement at the leading edge and the trailing edge. Typically, the shell parts 36, 38 are bonded to each other via glue flanges.

Fig. 4 is a schematic side view of a reinforcing structure according to the prior art and according to the present invention, respectively. As seen in Fig. 4a, a prior art reinforcing structure 62 surface from misalignments within and between adjacent stacks 66a, 66b, comprising strips 63a-c, 64a-c of fibre-reinforced polymer. This problem is addressed by the present invention which has been found to result in greatly improved properties of the reinforcing structure 62, which virtually no misalignments or related structural defects of the stacks 66a, 66b of strips 63a-d, 64a-d of fibre-reinforced polymer. As illustrated in Figs. 5 and 6, the alignment member 68 of the present invention may comprise a folded fabric, such as a folded fabric comprising a veil cloth or a veil mat, preferably a pre-impregnated veil cloth or veil mat. The alignment member 68 comprising a plurality of alternating horizontal segments 70a-d, which together may form a base, and vertical segments 72a-c, which may also be termed projections herein. In the illustrated embodiment, the folded fabric 68 is substantially rack-shaped. The fabric 68 may comprises a series of substantially 90° folds and substantially 180° folds, as shown in Fig. 5. Starting from horizontal segment 70a, the adjacent vertical segment 72a is obtained by providing a substantially 90° fold, for providing part of vertical segment 72a extending in a substantially flapwise direction, followed by a 180° fold and another 90° to revert to the next horizontal segment 70b, and so on. In this embodiment, each horizontal segment comprises a single layer of fabric, whereas each vertical segment comprises a double layer of fabric.

Fig. 7 is a perspective view illustrating the arrangement of a plurality of strips 63a, 64a, 65a on two alignments members 68a and 68b. This figure only illustrates the arrangements of the initial strip of each stack, whereas the cross section of Fig. 8 illustrates the completed stacks 66a-c of the strips 63a-c, 64a-c, 65a-c. A vertical segment 72a-c of the alignment member 68a is arranged between adjacent stacks 66a- c of strips 63a-c, 64a-c, 65a-c. A horizontal segment 70a-c of the alignment member is arranged on top of or below each stack 66a-c of strips. As seen in Figs. 5, 6 and 8, the horizontal segments 70 lie in the substantially same plane. The thickness T of the alignment member is illustrated in Fig. 8 in between the two arrows.

As seen in Figs. 7-9, the elongate reinforcing structure 62 extends in a substantially spanwise direction of the blade. The elongate reinforcing structure 62 has a tip end 74, closest to the tip end of the blade, and a root end 76, closest to the root end of the blade, wherein a first alignment member 68b is arranged at the tip end 74 of the elongate reinforcing structure 62, and a second alignment member 68a is arranged at the root end 76 of the elongate reinforcing structure 62. The elongate reinforcing structure also comprises a spanwise extending front edge 78, which is closest to the leading edge of the blade, and a spanwise extending rear edge 80, which is closest to the trailing edge of the blade, wherein one of the vertical segments 72d of the alignment member is arranged adjacent to the front edge 78 of the elongate reinforcing structure 62, and wherein one of the vertical segments 72a of the alignment member is arranged adjacent to the rear edge 80 of the elongate reinforcing structure.

The invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the present invention.

List of reference numerals

4 tower

6 nacelle

8 hub

10 blades 14 blade tip

16 blade root

18 leading edge

20 trailing edge 30 root region

32 transition region

34 airfoil region

36 pressure side shell part

38 suction side shell part 40 shoulder

41 spar cap

42 fibre layers

43 sandwich core material

45 spar cap 46 fibre layers

47 sandwich core material

50 first shear web

51 core member

52 skin layers 55 second shear web

56 sandwich core material of second shear web

57 skin layers of second shear web

60 filler ropes

62 reinforcing structure 63 strip

64 strip

65 strip

66 stack

68 alignment member 70 horizontal segment

72 vertical segment

74 tip end of reinforcing structure

76 root end of reinforcing structure

78 front edge of reinforcing structure 80 rear edge of reinforcing structure

L length r distance from hub

R rotor radius

T thickness of alignment member

Claims

1 . A wind turbine blade (10) having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, wherein the wind turbine blade comprises an elongate reinforcing structure (62), the reinforcing structure (62) comprising a plurality of strips (63, 64, 65) of fibre-reinforced polymer arranged into adjacent stacks (66) of strips, and at least one alignment member (68) comprising a plurality of alternating horizontal segments (70) and vertical segments (72), wherein a vertical segment of the alignment member is arranged between adjacent stacks of strips, and wherein a horizontal segment of the alignment member is arranged on top of or below each stack of strips.

2. A wind turbine blade according to claim 1 , wherein the alignment member comprises at least three horizontal segments and at least four vertical segments.

3. A wind turbine blade according to claims 1 or 2, wherein the alignment member comprises a folded fabric.

4. A wind turbine blade according to claim 3, wherein the folded fabric comprises a veil cloth or a veil mat, preferably a pre-impregnated veil cloth or veil mat.

5. A wind turbine blade according to claims 3 or 4, wherein the alignment member comprises a non-woven folded fabric, preferably a non-woven fabric comprising fibres with random orientation.

6. A wind turbine blade according to any one of the preceding claims, wherein the horizontal segments lie in the substantially same plane.

7. A wind turbine blade according to any one of the preceding claims, wherein the alignment member is substantially rack-shaped.

8. A wind turbine blade according to any one of the preceding claims, wherein the elongate reinforcing structure (62) is a spar structure, such as a spar cap, a spar beam or a box spar.

9. A wind turbine blade according to any one of the preceding claims, wherein the thickness of the alignment member is between 0.1 and 0.5 mm.

10. A wind turbine blade according to any one of the preceding claims, wherein the elongate reinforcing structure (62) extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure (62) has a tip end, closest to the tip end of the blade, and a root end, closest to the root end of the blade, wherein a first alignment member is arranged at the tip end of the elongate reinforcing structure (62), and a second alignment member is arranged at the root end of the elongate reinforcing structure (62).

11. A wind turbine blade according to any one of the preceding claims, wherein the elongate reinforcing structure (62) extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure (62) has a tip end, closest to the tip end of the blade, a root end, closest to the root end of the blade, and a spanwise midpoint having an equal distance from each of the tip end and the root end of the elongate reinforcing structure (62), wherein a single alignment member is arranged at the spanwise midpoint of the elongate reinforcing structure (62).

12. A wind turbine blade according to any one of the preceding claims, wherein the elongate reinforcing structure (62) extends in a substantially spanwise direction of the blade, wherein the elongate reinforcing structure (62) comprises a spanwise extending front edge, which is closest to the leading edge of the blade, and a spanwise extending rear edge, which is closest to the trailing edge of the blade, wherein one of the vertical segments of the alignment member is arranged adjacent to the front edge of the elongate reinforcing structure (62), and wherein one of the vertical segments of the alignment member is arranged adjacent to the rear edge of the elongate reinforcing structure (62).

13. A wind turbine blade according to any one of the preceding claims, wherein the alignment member has a spanwise extent of not more than 1 meter, preferably not more than 50 cm.

14. A method of manufacturing a wind turbine blade having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, the method comprising the steps of: arranging a plurality of blade components in a blade mould, and assembling an elongate reinforcing structure (62) in the blade mould relative to the plurality of blade components, the reinforcing structure (62) comprising a plurality of strips of fibre material arranged into adjacent stacks of strips, and at least one alignment member comprising alternating horizontal segments and vertical segments, wherein a vertical segment of the alignment member is arranged between adjacent stacks of strips, and wherein a horizontal segment of the alignment member is arranged on top of or below each stack of strips, infusing resin into the stacks of strips to form a fibre-reinforced polymer.

15. A method according to claim 14, wherein the alignment member is a folded fabric that is pre-infused and hardened prior to its arrangement in the blade mould.