A wind turbine blade with reinforcements to prevent leading edge bending

Abstract

A wind turbine blade having a blade shell comprising a lead edge and a trailing edge and at least one girder, the wind turbine blade comprising at least one longitudinal reinforcing member mounted on the inner surface of the leading or trailing edge, and extending longitudinally at least part of the length of the wind turbine blade between its root and tip, and / or at least one angled reinforcing member connected at one end to the girder or to a junction between an end of the girder and the blade shell, and extending towards the leading or trailing edge and being fixed to said leading edge or trailing edge or to one or more of the longitudinally arranged members.

Description

[0001] A Wind Turbine Blade with Reinforcements to Prevent Leading Edge Bending

[0002] Typically, a wind turbine blade has an aerodynamic blade shell shape and at least one girder, such as a beam or a spar. The girder can be a single girder, but often two girders are used. The two girders together with the parts of the blade shell extending between the two girders form a so-called box profile. The top and bottom of the box profile are often referred to as the caps or the spar caps. Some types of blades are designed with a spar in the form of a box profile which is manufactured separately and bonded in between prefabricated surface blade shells. The aerodynamic shell is typically made of a laminate of fibre reinforced plastics, fibreglass and / or other materials. Typically, the aerodynamic shell is made from two blade shell parts that are assembled to form the blade shell by adhesive bond lines.

[0003] Wind turbine blades with one or more girders are well-known. A conventional girder has a longitudinal extension in the longitudinal direction of the blade and a transverse extension substantially perpendicular to the profile chord of the blade. The one or more conventional girders primarily strengthen the blade along the longitudinal extension of the blade. A girder may also be referred to as a web or a shear web. The conventional girder or web may be constituted by any type of elongate constructional member capable of taking up loads, such as a beam or a spar, e.g., shaped as an l-profile or a C-profile, preferably made from fibre reinforced plastics or other suitable material. Typically, conventional girders extend along substantially the entire length of the blade.

[0004] Under normal operating conditions, the wind turbine blade is subjected to loads at an angle to the flap-wise direction. It is common to resolve this load on the blade into its components in the flap-wise and edge-wise direction. The blade is further subject to torsional loads which are mainly aerodynamic-, gravity- and inertia- induced loads. These loads can subject the blade to harmonic motions or oscillations substantially at one or more of the blades’ eigenfrequencies.

[0005] When a blade is subjected to edge-wise loading combined with flap-wise loading combined with torsional loading the cross section of the blade is deforming. The deformation can lead to buckling of the blade shell leading edge area and this reduces the ultimate strength of the blade because the blade shell is often load carrying. Furthermore, the deformations also compromise the aerodynamic efficiency of the blade since the designed shape of the blade profile is no longer maintained. The edge-wise loading combined with flap-wise loading combined with torsional loading can further cause the leading edge of the blade to deform in a post buckling pattern. The blade material in the trailing edge is then subject to tension and the leading edge to compression. Since the leading edge may be relatively thin, it cannot withstand substantial compression forces before it bends out of its neutral plane. When this happens, some of the load on the leading edge is transferred to and distributed through part of the blade shell further away from the leading edge, until equilibrium of the forces is established. Although this deformation may not immediately lead to blade failure, it decreases the safety margin for the general failure load of the blade.

[0006] Thus, there is a need for a wind turbine blade in which out of plane deformations of the leading edge is prevented or reduced and wherein the blade structure is strengthened without significantly increasing the overall weight of the blade. It is yet an object of the present invention to provide a wind turbine blade with increased overall strength.

[0007] It is yet another object of the present invention to provide a wind turbine blade with increased resistance to fatigue load induced failures.

[0008] It is yet another object of the present invention to provide a wind turbine blade with increased torsional stiffness.

[0009] It is yet another object of the present invention to provide a wind turbine blade with increased resistance to buckling or local bending of the leading edge.

[0010] It is yet another object of the present invention to provide a wind turbine blade with improved resistance against deformations of the blade profile. It is also an object of the present invention to provide a reinforced blade profile for a wind turbine blade.

[0011] It is therefore an object of the present invention to provide a wind turbine blade with improved resistance against deformations of the blade shell.

[0012] It is another object of the present invention to provide a wind turbine blade with reduced weight and reduced costs.

[0013] It is also an object of the present invention to provide a wind turbine blade with improved leading edge structural reliability.

[0014] It is a further object of the present invention to provide a wind turbine blade capable of working under severe aerodynamic loads and to optimise the aerodynamic efficiency, e.g. energy output of the blade.

[0015] It is further an object of the present invention to provide alternatives to the prior art.

[0016] It is the ultimate object of the present invention to provide a system and a method to generate cost-efficient clean energy and help decrease carbon dioxide emissions, decarbonize human and industrial activities, fight against climate change, and make a more sustainable world.

[0017] In a broad aspect the invention provides a reinforced blade for a wind turbine, the blade having at least one angled reinforcing member and / or at least one longitudinal oblong reinforcing member in the blade in order to prevent or reduce local deformation of the leading edge of the wind turbine blade.

[0018] In a first aspect the invention provides a wind turbine blade having a blade shell comprising a leading edge and a trailing edge and at least one girder, the wind turbine blade comprising at least one longitudinal reinforcing member mounted on the inner surface of the leading or trailing edge, and extending longitudinally at least part of the length of the wind turbine blade between its root and tip, and / or at least one angled reinforcing member connected at one end to the girder, or to a junction between an end of the girder and the blade shell, and extending towards the leading or trailing edge and being fixed to said leading edge or trailing edge or to one or more of the longitudinally arranged members.

[0019] The connection to the girder serves to prevent the blade shell leading edge from local bending. During operation the blade bends in its entire length or in a major part of its entire length depending on the bending mode shape. This bending is not as critical as local bending meaning that only a minor part of the blade shell leading edge bends locally resulting in a smaller local radius of curvature than when the blade bends in its entire length or in a mode shape.

[0020] The wind turbine blade may be utilized in a vertical axis wind turbine, such as a Darrieus wind turbine, a wind star turbine, etc., or preferably in a horizontal axis wind turbine, such as common modern wind turbines usually three-bladed, sometimes two-bladed or even one-bladed (and counterbalanced).

[0021] The blade shell of the wind turbine blade may preferably, but not exclusively, comprise a composite or laminated material. The material may preferably, but not exclusively, comprise fibreglass and / or carbon fibres and / or other durable and flexible or stiff materials typically with a high strength / weight ratio. This may further comprise at least in part light weight metals or alloys. The blade shell may typically be a solid laminate and / or sandwich- construction.

[0022] Preferably, at least one of the angled reinforcing members extends in a direction that is substantially perpendicular to the longitudinal extension of the blade. In the case of a curved blade in which the longitudinal extension of the blade forms a non-linear curve in space, the angled reinforcing member may extend in a direction that is substantially perpendicular to the longitudinal extension of the blade in the vicinity of the angled reinforcing member in question. The longitudinal reinforcing member may be formed in a T-shape, H-shape, I- shape or other shape.

[0023] Preferably, the angled reinforcing member has a straight shape. If the shape of the angled reinforcing member is not straight, the shape of the angled reinforcing member could be straightened when subjected to stretching forces leading to movement of its end points and obviously, this is not desired.

[0024] The angled reinforcing member or members secure and keep the shape of the leading edge substantially unchanged when the aerodynamic profile is loaded by forces in the edge-wise and flap-wise and torsional direction. This in turn causes the overall strength of the aerodynamic profile to increase significantly since the resistance against buckling is also increased.

[0025] An angled reinforcing member according to the present invention also improves the peeling strength of the adhesive bond lines. One of the at least one angled reinforcing member may form an angle with another angled reinforcing member.

[0026] The angle may range from 10° to 50°. Preferably, the at least one angled reinforcing member extends substantially in a 45-degree angle to the profile chord of the blade in a cross-section of the blade. Two or more angled reinforcing members may be positioned in spaced relationship along at least a part of the longitudinal extension of the blade in such a way that neighbouring angled reinforcing members are mounted with different angles in relation to the profile chord of the blade.

[0027] The maximum distance between two angled reinforcing members may be based on specific requirements, such as, but not limited to, a need for a particularly strong wind turbine blade design, e.g. when the wind turbine is intended to be subjected to repeatedly severe weather conditions, such as when erected offshore at open sea or onshore in a mountain area. The angled reinforcing members may be positioned in certain sections of the blade only, possibly without any predetermined or calculated maximum distance. Particularly, but not exclusively, the angled reinforcing members may be located at positions wherein a substantial deformation of the leading edge is expected or established.

[0028] The angled reinforcing member may be constituted by any type of angled constructional member capable of taking up loads. The angled reinforcing member may comprise one or more elements selected from the group consisting of a rod, a plate, and a tube, capable of resisting both compression forces and tensional forces. Since, the angled reinforcing member need not necessarily be capable of resisting compression forces, the angled reinforcing member may further comprise one or more elements selected from the group consisting of a wire, a rope, a thread, a fibre, and a web of fabric. The elements may have any suitable cross-section, for example a substantially round or polygonal cross-section, such as substantially rectangular, triangular, circular, oval, elliptical, etc, but is preferably circular or oval.

[0029] The longitudinal reinforcing member may be pultruded or otherwise formed.

[0030] The elongate reinforcing member is preferably connected to a junction between the girder and the blade shell.

[0031] Preferably, a plurality of longitudinal members and / or elongate longitudinal reinforcing members are provided.

[0032] The angled reinforcing members may form an angle with the longitudinal extension of the blade in the vicinity of the angled reinforcing member in question preferably ranging from 70° to 110°, more preferably from 80° to 100°, and even more preferred from 85° to 95°.

[0033] One or all of the angled reinforcing members may form an angle between 10 and 80 degrees, preferably between 30 and 60 degrees and more preferably between 40 and 50 degrees to the profile chord of the blade. The profile chord of the blade is an imaginary surface that contains the leading edge and the trailing edge of the blade and extends therebetween.

[0034] Preferably, at least elongate reinforcing member is connected between a girder and a respective longitudinal member so as to form a rigid reinforcement structure comprising the elongate member comprising the girder, the elongate reinforcing member and the longitudinal reinforcing member.

[0035] Preferably the angled member or members are provided at an angle to the profile chord line of the blade section. This angle is preferably between 10 and 80 degrees, preferably between 30 and 60 degrees and most preferably between 40 and 50 degrees to this profile chord line.

[0036] The elongate reinforcing member may be provided to the upper part, lower part or centre of the blade shell at the leading edge.

[0037] The longitudinal reinforcing member may be provided on a flat back portion of the trailing edge of the wind turbine blade.

[0038] The at least one angled reinforcing member comprises a plurality of angled pultruded reinforcing members positioned in spaced relationship along the longitudinal extension of the blade.

[0039] At least one of the at least one angled reinforcing member extends in a direction that forms an angle with relation to a longitudinal extension of the blade ranging from 70 degrees to 110 degrees, preferably from 80 degrees to 100 degrees, more preferred from 85 degrees to 95 degrees and most preferred from 89 degrees to 91 degrees.

[0040] At least one angled reinforcing member may comprise a plurality of angled reinforcing members positioned in spaced relationship along the longitudinal extension of the blade with a mutual distance that is less than 2xD, wherein D is the distance between the first and second end of one of the plurality of angled pultruded reinforcing members. A distance between them less than 2xD represents a conservative design or an extra strong design or an extra robust design.

[0041] At least one angled reinforcing member may form an angle with another one of the at least one angled reinforcing member and preferably this angle ranges from 10 degrees to 50 degrees. This is to further increase the buckling stability of the Leading edge or trailing edge structure.

[0042] All angled reinforcing members and / or all longitudinal reinforcing members may be situated at the inner one third of the wind turbine blade, or at the middle one third of the wind turbine blade or at the outermost one third of the wind turbine blade.

[0043] At least one of the at least one angled reinforcing members may be a flexible wire with high tensional strength without a capability of resisting compression forces.

[0044] In a further aspect the invention provides a method of retrofitting a wind turbine blade to reinforce it, comprising mounting at least one longitudinal reinforcing member to the inner surface of the wind turbine blade at the leading edge and / or trailing edge, and / or mounting at least angled reinforcing member between the leading edge and / or the trailing edge at one end, and to a girder of the wind turbine blade at the other end, or to a junction between an end of the girder and the blade shell

[0045] Preferably each angled reinforcing member is connected to a junction between the girder and the blade shell.

[0046] In a yet further aspect, there is provided a method of forming a wind turbine blade, comprising affixing at least one longitudinal reinforcing member to an inner surface of a blade shell at the leading edge or trailing edge of the blade shell and / or affixing at least one angled reinforcing member between the leading edge or trailing edge at one end, and to a girder, or a junction between an end of the girder and the blade shell, at the other end. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0047] Figure 1 shows a wind turbine blade with a longitudinal reinforcing member;

[0048] Figure 2 shows a wind turbine with a plurality of angled reinforcing members;

[0049] Figure 3 and 4 show alternative embodiments of wind turbine blades with angled reinforcing members;

[0050] Figure 5 shows a wind turbine blade with connected longitudinal and angled reinforcing members;

[0051] Figure 6 shows an alternative view of a wind turbine blade with a longitudinal member;

[0052] Figure 7 to 11 show alternative designs in which reinforcing members are connected to a trailing edge;

[0053] Figure 12 shows an expanded view of part of Figure 11 ;

[0054] Figure 13 shows a design in which members are provided which are attached to the trailing and leading edges;

[0055] Figure 14 shows a design in which a V shaped angled element or member is provided,

[0056] Figure 15 shows an alternative design, and:

[0057] Figure 16 shows a plot of Out of Panel bending against length.

[0058] Referring to Figure 1 , a wind turbine blade 1 comprising an outer blade shell 2 which itself forms an aerodynamic profile shown generally as 3 is provided. Typically, the turbine blade will be 40m long or more and the invention is particularly useful in blades of this length to reduce deformation. It may be even more useful in longer blades, eg of blade length 60m or more or 80m or more. However, it may be used in shorter blades.

[0059] At least one longitudinal girder (otherwise known as a shear web) is provided, in this case, two of these are provided but only one is labelled; this being the one closest to the leading edge 6. The blade also, of course, has a trailing edge 11 opposite the leading edge.

[0060] In the example shown in Figure 1 , a longitudinally arranged reinforcing member 4 is located on the inner surface of the blade shell 2 at the leading edge 6. In this example, the longitudinal member is T-shaped. This is provided longitudinally within the inner surface of the blade and extends a certain amount of the distance between the root and the tip. It may, for example, be positioned on the first third, the second third or the third third of the wind turbine blade in the longitudinal direction.

[0061] It is affixed to the inner surface of the wind turbine blade by any suitable means. It may be connected by glue or adhesive, or physically fixed by pin, blot, screw or any other suitable means. As shown, it is provided in the upper part of the blade shell leading edge. However, it could alternatively of course be positioned in the centre or at the lower part of the leading edge. More than one such longitudinally disposed reinforcing member may be provided.

[0062] The T-shape cross-section is a very useful one since this provides a relatively larger resistance towards local bending. Thus, when the longitudinally arranged reinforcing member 7 is glued or otherwise affixed on the inner surface of the blade shell leading edge, the blade shell leading edge will also experience a larger resistance towards local bending.

[0063] In other embodiments, shown below, the longitudinal member is provided at the trailing edge rather than the leading edge and the same effect applies in some embodiments. Reinforcing members (longitudinal and / or angled ones) may be provided at both the leading and trailing edges.

[0064] The longitudinally arranged reinforcing member may be made in a moulding process, a pultruding process or otherwise. Typically, it may be made of a composite material. This may be a plastics material.

[0065] The connections on the inner surface of the blade profile may in principle be positioned anywhere on the inner surface but it should be observed that the chosen positioning is suitable for the angled reinforcing member to be able to provide a reasonable and useful reinforcing effect to the adhesive bond line in question. The connections may comprise any suitable kind of joint such as welded, glued, melted, fused or other simple mechanical connections. The angled reinforcing member itself may comprise the connections or it may comprise additional connections or connection parts adapted to engage or cooperate with the connections on the inner surface of the blade shell and the girder.

[0066] The connections may be releasable connections that may comprise any suitable kind of joint, such as a snap-fit, press-fit, groove-and-tongue connection or other simple mechanical connection.

[0067] Figure 2 shows a similar internal structure of a wind turbine with a plurality (in this case three) of angled reinforcing members 5. The first ends of these are connected to the inner shell at the leading edge (or indeed at the trailing edge) and this embodiment may be connected by adhesive for example. The members are angularly disposed and are connected at their opposite ends to the girder 10. As shown, they are most preferably connected at the junction 12 between the girder and the inner surface of the blade shell (leading or trailing edge) and may be connected in such a way that they contact both. This may be done by being adhesively connected to both. In this way, they provide additional reinforcement in combination with the girder 10 and the internal edge blade at end 5.

[0068] The angled reinforcing members secure and keep the shape of the leading edge substantially unchanged when the aerodynamic profile is loaded by forces in the edge-wise and flap-wise and torsional direction. This in turn causes the overall strength of the aerodynamic profile to increase significantly since the resistance against buckling is also increased.

[0069] In preferred embodiments, as described below, both a longitudinal enforcing member 7 (or a plurality of these) and one or more angularly disposed reinforcing elements are provided and these may be connected together or separately provided.

[0070] Figure 3 shows an example showing an angular reinforced blade extending from a top part of the leading edge 6 to a junction between the leading edge 6 and girder 10 towards the bottom of the leading edge.

[0071] Figure 4 shows an alternative example in which the member 5 extends from a lower section of the leading edge towards a junction between girder 10 and leading edge 6 at its top end.

[0072] Figure 5 shows an example in which both a longitudinal reinforcing member 4 and angled reinforcing member 5 are provided and which these are connected to each other. The figure shows a T-shaped longitudinal member 4 positioned towards the top of the leading edge and an angled reinforcing elongate member 5 extending the inner most end 4a of the longitudinal member towards a junction between the girder and the blade shell. The members may be connected together by adhesive, or otherwise, for example.

[0073] Of course, in practise, the longitudinal member extends a distance towards the end of the wind turbine blade (ie into the figure) and a plurality of angled reinforcing members are connected thereto, as shown in Figure 2.

[0074] The angled members may be of rods, tubes, wire or otherwise. Typically, a plurality of these are provided, generally in parallel although they may be at angles to each other and they may be at a fixed constant distance from each other or the distance of one angled reinforcing member from another may vary along the length of the wind turbine blade. Where they are tubes they will preferably be hollow tubes and may have a circular cross-section,

[0075] Figure 6 shows an example in which a longitudinal element 4 is provided generally at the midpoint of the leading edge and a plurality of angled reinforcing members extend from these at spaced intervals towards a junction between girder 10 and the leading edge part and the blade shell 2.

[0076] Figures 3 to 5 and other figures have a wind turbine blade having flat back 12 at the trailing edge. The reinforcing members of the present invention may be positioned at the trailing edge, instead of, or in addition to, at the leading edge.

[0077] Figure 7 shows an embodiment in which the longitudinal member 4 is provided at an interior surface of the flat back 12 leading edge.

[0078] Similarly, Figure 8 shows an example in which an angled reinforcing member is mounted between a flat back 12 and a second girder 14 which is spaced from the first girder 10. Again, it would be most preferably mounted at the junction between the girder 14 and the blade shell 2, in order to provide the best reinforcement structure.

[0079] Figure 9 shows a similar arrangement but in which the reinforcing member 5 extends angularly upwards from the flat back (instead of downwards as in Figure 8) towards an uppermost junction between girder 14 and blade shell 2.

[0080] Figure 10 shows an embodiment in which reinforcing members are provided at the trailing edge a number of angled elongate reinforcing member 5 may be provided spaced apart from each other, typically parallel to one another.

[0081] Instead of a flat back, a sharp trailing edge may be provided. Figure 11 shows an example in which a longitudinal member 4 and an angled reinforcing member 5 are provided at the trailing edge and connected to each other.

[0082] Thus, the longitudinal member 4 is connected to the inside surface of the flat back 12, typically at its midpoint, and one end of the angled reinforcing member 5 is connected to the edge of the T-part of the member 4. The other end of member 5 is attached to the junction between girder 14 and the blade shell 2.

[0083] Figure 12 shows an exploded view of the left hand part of Figure 8 showing in more detail the elongate member 4 and the angled reinforcing member 5 which are connected together to form a single reinforcing structure.

[0084] Figure 13 shows an embodiment in which members are connected at both the leading and trailing edges. Thus, in addition to reinforcing members at the leading or trailing edge a further set of members may also be provided at the other one of the leading or trailing edges. Thus, in Figure 13 a further longitudinally arranged reinforcing member 4b is provided at the leading edge and a further set of angled reinforcing members 5c, as shown. The longitudinally arranged reinforcing member 4b is generally at the midpoint of the leading edge, but it may be provided at the top or bottom part, or more than one of these may be provided on the leading edge. Alternatively, or addition, more than one may also be provided on the trailing edge. In addition, more than one sets of parallel angled reinforcing members 5, 5a, 5b and 5c may also be provided as extending from different locations on the leading and / or trailing edges.

[0085] Figure 14 shows a similar arrangement in which the angled reinforcing member is attached to the inner end of the longitudinal reinforcing member 4 and to the bottom part of the wind turbine blade which there are two sets of angled reinforcing members 5a and 5b, one of which extends generally downwardly from the longitudinally extending member 4 to the junction between girder 14 and the blade shell 2 and the other of which extends from the same part of the longitudinal member 4 generally upwardly towards the upper junction between the girder 14 and blade shell 2. Thus, a generally V-shaped reinforcement structure is obtained formed by longitudinal member 4, the angled bars 5a and 5b and the girder 14. This improves the rigidity and resists deformation further. Instead of being V-shaped it may alternatively be U-shaped.

[0086] Where such a V-shaped configuration is made it may be formed of a single V- shape structure or of two separate structures as shown. Again, the angled bars will be provided as separate cubes, rods, wires etc spaced longitudinally along at least part of a length of wind turbine blade.

[0087] Figure 15 shows an embodiment in which adjacent reinforcing members 5d and 5e are at different angles in the longitudinal direction. One at 30 degrees and the other at 50 degrees. Other angles may be used. By using different angles, or angles different from 0 degrees relative to the longitudinal direction a structure is achieved which is similar to a truss or a lattice structure and thereby transfer parts of the edgewise loads to this structure. The advantages may be savings in edgewise structural materials in the blade shells and / or new means to optimize the blade structure.

[0088] Note that the reinforcing members will typically be pultruded. However, they may also be produced by other processes such as pull-winding, filament-winding, or extrusion.

[0089] In some embodiments, at least some of the reinforcing members, particularly the longitudinal reinforcing member or members, may form a part of the wind turbine blade’s lighting protection system. They may need to be formed of a conductive material for this.

[0090] Of course, it is possible to use the present invention to retrofit existing blades. That is an existing wind turbine blade may be retrofitted with the various reinforcing member, even after they are out in the field. The reinforcing members may be provided at any desired position of the blade, for example at the centre of the blade longitudinally in the first third or so of the blade longitudinally or in the last third of the blade longitudinally from the tip to the roots. There may be two or more longitudinal reinforcing members and three or more of the other reinforcing members, although numbers may differ from this.

[0091] Additional reinforcing members may be used with the angled reinforcing members to provide a lattice structure.

[0092] The wind turbine blades may be typically made of a material such as carbon fibre, although there may be of other materials. In some embodiments, the angled angled reinforcing members may have a “chicken foot” like shape in order to reduce the load impact from the reinforcing member to the blade shell and / or reduce stresses in the bonding adhesive.

[0093] In some embodiments, the longitudinal reinforcing member or members are prefabricated and bonded via a resin via a vacuum infusion process. In effect, this means it can be made in the same process and as part of the same process as the blade shell itself.

[0094] In some embodiments the blade shell may include additional reinforced areas in the vicinity of the angled reinforcing members for example or in other positions, in order to reduce the load impact from these members on the blade shell.

[0095] The elements of both the angled reinforcing member and the longitudinal reinforcing member may be applied individually or may be applied as a number of individual elements together forming a "thicker" element. Particularly, the element may comprise fibres of very high stiffness and strength such as, glass fibres, carbon fibres, aramid fibres, polyethylene fibres, PBO fibres (polypheylene benzobisoxqazole), etc.

[0096] The angled reinforcing members and the longitudinally arranged reinforcing members may be made of any suitable material. Fibre reinforced plastic is presently preferred for rods, plates and tubes. The angled reinforcing members may also be made of wood, such as bamboo, birch, plywood, etc.

[0097] The angled reinforcing member and the longitudinally arranged reinforcing member may also be made of steel, light metal alloys, etc.

[0098] The angled reinforcing members and the longitudinally arranged reinforcing members may also be made of material based on plant fibres with high cellulose content, such as bast fibres, such as flax, jute, etc. These fibres may be used as reinforcement in a composite material, such as a reinforced plastic, or may be used in the form of wires or rods. The angled reinforcing member may also be made of a combination of the above-mentioned materials.

[0099] The angled reinforcing member is required to have a high tensional strength only, i.e. , preferably, the angled reinforcing member need not necessarily carry other loads so that the angled reinforcing member may be thin whereby its weight and cost are kept at a minimum. The thickness of the angled reinforcing member is preferably less than 10 times the maximum thickness of the blade shell, more preferred less than 5 times the maximum thickness of the blade shell, still more preferred less than 2 times the maximum thickness of the blade shell, most preferred less than the maximum thickness of the blade shell.

[0100] Note that any feature shown in any example or drawing may be used in any other example or embodiment interchangeably.

[0101] Figure 16 shows a plot of bending strain for a flatback trailing edge, illustrating out of plane (OOP) panel bending with length for different configurations. The dotted line shows a ‘clean’ blade without reinforcements, The dot-dashed line shows a blade with the T shape profile elongate member and the solid line shows a blade with the additional reinforcing members. A significant reduction is show with the T profile and almost complete elimination of bending is seen when further applying the reinforcing members. The effect will be similar at lower loads as well.

Claims

Claims1 . A wind turbine blade having a blade shell comprising a lead edge and a trailing edge and at least one girder, the wind turbine blade comprising at least one longitudinal reinforcing member mounted on the inner surface of the leading or trailing edge, and extending longitudinally at least part of the length of the wind turbine blade between its root and tip, and / or at least one angled reinforcing member connected at one end to the girder or to a junction between an end of the girder and the blade shell, and extending towards the leading or trailing edge and being fixed to said leading edge or trailing edge or to one or more of the longitudinally arranged members.

2. A wind turbine blade as claimed in claim 1 comprising at least one longitudinally extending member and one or a plurality of angled reinforcing members.

3. A wind turbine blade claimed in claim 1 or claim 2 wherein the angled reinforcing members are connected between the girder and at least one longitudinally extending member.

4. A wind turbine blade as claimed in any preceding claim wherein the longitudinally extending member has a T-shape.

5. A wind turbine blade as claimed in any preceding claim wherein the angled reinforcing members extend at an angle to the profile chord of the blade between the girder and a respective leading or trailing edge.

6. A wind turbine blade as claimed in any preceding claim comprising a plurality of angled reinforcing members which are spaced apart and mounted between the girder, or a junction between the girder and the blade shell, and a longitudinally extending member.

7. A wind turbine blade as claimed in claim 6 wherein the angle of an angled reinforcing member relative to the longitudinal extension of the blade is between 70 and 110 degrees, preferably 80 degrees to 100 degrees, more preferably 85 degrees to 95 degrees and most preferably between 89 degrees and 91 degrees.

8. A wind turbine blade as claimed in claim 6 or claim 7 wherein at least one of the angled reinforcing members forms an angle between 10 and 80 degrees, preferably between 30 and 60 degrees and most preferably between 40 and 50 degrees to the profile cord line of the blade section at that part of the blade.

9. A wind turbine blade as claimed in any preceding claim wherein at least two angled reinforcing members are spaced apart longitudinally along the blade with a distance between them that is less than 2 x D where the D is the distance between the first and second of the one of the angled reinforcement members.

10. A wind turbine blade as claimed in any preceding claim wherein at least two angled reinforcing members have an angle between each other and are not parallel.11 . A wind turbine blade as claimed in claim 10 wherein the angle is between 10 degrees and 50 degrees.

12. A wind turbine blade as claimed in any preceding claim wherein all of the longitudinally reinforcing members and. are situated at the inner one third, the middle one third or at the outer one third of the wind turbine blade.

13. A wind turbine blade as claimed in any preceding claim wherein at least one angled reinforcing member is a flexible wire.

14. A wind turbine blade as claimed in any preceding claim wherein at least one angled reinforcing member is a tube.

15. A wind turbine blade as claimed in claim 15 wherein the tube is a hollow tube.

16. A wind turbine blade as claimed in any preceding claim wherein at least two angled members converge at the girder, or towards the leading edge or trailing edge, to form a V-shaped reinforcing structure.

17. A wind turbine blade as claimed in any preceding claim comprising at least two longitudinal reinforcing members or at least three longitudinal reinforcing members.

18. A wind turbine blade as claimed in any preceding claim wherein all angled reinforcing members and / or longitudinally reinforcing members are situated at the inner one third of the wind turbine blade, or at the middle one third of the wind turbine blade or at the outer most one third of the wind turbine blade.

19. A wind turbine blade as claimed in any preceding claim wherein the reinforcing members are connected by glue or adhesive.

20. A wind turbine blade as claimed in any preceding claim wherein the angled reinforcing blades are connected to a junction between the girder and the blade shell.21 .A method of retrofitting a wind turbine blade to reinforce it, comprising mounting at least one longitudinal reinforcing member to the inner surface of the wind turbine blade at the leading edge and / or trailing edge, and / or mounting at least angled reinforcing member between the leading edge and / or the trailing edge at one end, and to a girder of the wind turbine blade, or a junction between a girder and the blade shell of the wind turbine blade, at the other end.

22. A method as claimed in claim 21 wherein each angled reinforcing member is connected to a junction between the girder and the blade shell.

23. A method of forming a wind turbine blade, comprising affixing at least one longitudinal reinforcing member to an inner surface of a blade shell at the leading edge or trailing edge of the blade shell and / or affixing at least one angled reinforcingP 127084 wo member between the leading edge or trailing edge at one end and to a girder, or a junction between a girder and the blade shell of the wind turbine blade, at the other end..

24. A method as claimed in claim 23 wherein the angled reinforcing member is connected to an end of the inner section between the girder and the blade shell.

25. A wind turbine blade, or a method, as claimed in any preceding claim wherein each longitudinal reinforcing member is prefabricated and bonded by resin by a vacuum infusion process to be formed in the same process as blade shell.

26. A method or apparatus as claimed in any preceding claim wherein at least one angled reinforcing member has a chicken foot like shape at at least one end.

Images