A wind turbine blade including a root end structure having a pultruded element with a transition section

Abstract

The present invention relates to a root end structure, a wind turbine blade including such a root end structure, and a method of manufacturing such a wind turbine blade. The root end structure includes a plurality of fastening members distributed along the root end of the blade component, wherein a first plurality of pultruded elements are arranged between the fastening members, and a second pultruded element is further arranged at the blade engagement end adjacent to the outermost fastening member. Each first pultruded element has a relatively facing second side, and each relatively facing second side faces the first side of an adjacent fastening member. The second pultruded element has one second side facing the outermost fastening member and another second side facing the blade engagement interface. The second pultruded element includes a transition portion that forms a smooth transition for an inner layer to further extend along the die edge surface.

Description

Technical Field

[0001] The present invention relates to a root end structure comprising a plurality of fastening members and a plurality of pultruded elements arranged between each fastening member, wherein the fastening members and the pultruded elements are sandwiched between an inner layer and an outer layer of a fibrous material.

[0002] The present invention also relates to a wind turbine blade comprising such a root end structure, and a method of manufacturing such a wind turbine blade. Background Art

[0003] The root end of a wind turbine blade is manufactured by laying a plurality of layers of fibrous material in a mold to form an outer skin. A plurality of fastening elements are then positioned relative to the mold and the fibrous layers, wherein each fastening element is connected to a root end plate which holds it in place during manufacture. Thereafter, a plurality of retaining members are positioned between each fastening member. Additional layers of fibrous material are laid over the fastening members and the retaining members to form an inner skin. The structure is then enclosed by a bag material and resin is introduced using vacuum infusion. The resin is finally cured to form a first wind turbine blade component. A second wind turbine blade component is manufactured in a similar manner, and the two wind turbine blade components are then attached together.

[0004] Movement of the inner or outer skin may occur during vacuum infusion, which can result in longitudinal misalignment between the retaining members and the outer skin. This in turn can result in wrinkles in the transition skin region at the ends of the retaining elements, which will have an adverse effect on the structural performance of the root end.

[0005] US2015 / 0233160A1 discloses such a root end configuration in which bushings and butterfly wedge elements are arranged between the inner and outer skins. Various cross-sectional shapes of the bushings are disclosed. Each wedge element has a local inner surface and a local outer surface and relatively facing local side surfaces, wherein the local side surfaces have a profile corresponding to the profile of the local side surfaces of the bushing. This forms a tight fit and thereby prevents any relative movement between the bushing and the wedge element.

[0006] US2013 / 0111752A1 discloses a root end configuration that includes a plurality of bushings uniformly distributed along a semi-circular shaped root end structure, wherein rovings are disposed between each of the bushings. Each roving element extends partially along the length of the bushing and contacts the opposing facing side surfaces of adjacent bushings. The inner surface of each bushing is in direct contact with an inner layer of fiber material that extends along the inner surface of the root end structure. Additionally, the outer surface of each bushing is in direct contact with an outer layer of fiber material that extends along the outer surface of the root end structure. The outer layer of fiber material extends along the molding surface and further along the mold edge surface. The inner layer of fiber material extends along the inner surface and the free facing side surface of the uppermost bushing and further along the mold edge surface. The uppermost bushing contacts the adjacent roving elements only at opposing side surfaces. Thus, the uppermost bushing forms a transition contact surface for laying an inner skin layer above the mold edge.

[0007] US2013 / 0285284A1 discloses a root end configuration that includes a plurality of root end portions, each root end portion including bushings spaced apart by spacer elements. The spacer elements have a butterfly portion that extends along the length of the bushing and a wider wedge portion that extends beyond the bushing in the longitudinal direction. The spacer elements have opposing facing local side surfaces that contact the corresponding local side surfaces of adjacent bushings. The bushings have an outer diameter that is greater than the local thickness of the spacer elements, wherein the local side surfaces of each spacer element have a curved profile such that it conforms to the curved profile of the bushing and thus forms a tight fit. This prevents any relative movement between the bushing and the spacer element.

[0008] EP 3121441A1 discloses a root end structure that includes bushings embedded in pultruded elements, wherein the embedded bushings are disposed between pultruded wedge elements. The outermost wedge element is disposed at a blade joint edge at a blade joint edge. The embedded bushings and the wedge elements each have a square cross-sectional profile with a constant thickness.

[0009] Object of the Invention

[0010] An object of the present invention is to provide a root end structure, a wind turbine blade, and a method of manufacturing such a wind turbine blade that overcomes the above problems.

[0011] Another object of the present invention is to provide a root end structure, a wind turbine blade, and a method of manufacturing such a wind turbine blade that reduces the risk of forming wrinkles at the blade joint interface.

[0012] Another object of the present invention is to provide a root end structure, a wind turbine blade, and a method of manufacturing such a wind turbine blade that allows for improved laying of fiber material. Summary of the Invention

[0013] An object of the present invention is achieved by a root end structure of a wind turbine blade, the root end structure extending from the blade root into the root end portion of the blade shell, the blade shell being formed by at least one blade component having an inner surface, an outer surface and at least one blade joint edge, the root end structure including a plurality of fastening members distributed circumferentially along the root end of the at least one blade component, each fastening member having a first inner surface, a first outer surface and opposite facing first side surfaces extending in a longitudinal direction, wherein a second pultruded element is arranged between the outermost fastening member and the blade joint edge of the at least one blade component, and optionally, a first pultruded element is arranged between at least a pair of fastening members, each of the first pultruded element and the second pultruded element having a second inner surface, a second outer surface and opposite facing second side surfaces extending further in the longitudinal direction, the root end structure further including a plurality of outer layers of fiber material extending along the outer surface and a plurality of inner layers of fiber material extending along the inner surface, wherein the second pultruded element forms a transition portion extending from one second side surface towards the other second side surface, wherein a local thickness of the transition portion gradually decreases towards the blade joint edge and / or the other second side surface.

[0014] By providing a smooth transition of the inner layer above the outermost pultruded element, this provides an improved root end structure, reducing the risk of forming wrinkles at the blade joint end. This also increases the structural load transfer at the blade joint interface.

[0015] The fastening members (such as bushings) are held in a fixed longitudinal position relative to the outer layer forming the outer skin. This can be achieved by temporarily mounting the bushings to a root end plate positioned at the root end. The root end plate can be directly mounted or fixed to the blade mold or held in place relative to the blade mold by a holding structure.

[0016] The holding members (such as pultruded elements) are clamped between an inner skin and an outer skin respectively defining the inner surface and the outer surface of the blade shell. The inner skin can be formed by a plurality of inner layers of fiber material. The outer skin can be formed by a plurality of outer layers of the same fiber material or different fiber materials. The fiber material can include fibers made of glass, carbon, aramid or any combination thereof. Each skin can include two, three, four or more individual layers.

[0017] Each bushing has a local first inner side facing the inner skin and a local first outer side facing the outer skin. Each bushing also has a relatively facing local first side extending between the local inner and outer sides. Similarly, each pultruded element has a local second inner side facing the inner skin and a local second outer side facing the outer skin. Each pultruded element also has a relatively facing local second side extending between the local inner and outer sides. The bushing and the pultruded element each have a local thickness measured between the inner and outer sides and a local width measured between the two first or second sides.

[0018] The pultruded element (i.e., the first pultruded element) can be arranged between each pair of adjacent bushings. Another pultruded element (i.e., the second pultruded element) is arranged at one or both blade joint edges of the blade component, where the second pultruded element is positioned adjacent to the outermost bushing facing the blade joint edge. This allows all bushings to be clamped between the respective pultruded elements. Alternatively, the bushing can be embedded in an integrated element (e.g., the first pultruded element), and thus the second pultruded element can be positioned adjacent to the outermost integrated element (e.g., the first pultruded element). Alternatively, the first pultruded element can be omitted and replaced by another spacer structure.

[0019] During the laying process, the inner skin can extend over the second pultruded element and further along the die edge surface of the blade die. After the blade component is molded, for example, before or after resin curing, the inner skin and the outer skin can be trimmed off to form the respective blade joint edges.

[0020] According to one embodiment, the transition portion forms a transition contact surface contacting the inner layer, wherein the transition contact surface forms at least a part of the second inner surface.

[0021] The first pultruded element may have recesses formed in the two local second sides, wherein each recess is configured to receive the local first side of an adjacent bushing. The recesses can extend partially or fully along the local second side. The recesses can have a second side surface that forms a surface profile corresponding to the surface profile formed by the first side surface of the bushing. Alternatively, the first and second side surfaces can have different surface profiles.

[0022] The second pultruded element may have similar recesses formed in the local second side facing the outermost fastening member. The opposite local second side can form an adjacent blade joint edge together with the inner layer. The maximum width that the second pultruded element can have is equal to or less than the maximum width of the first pultruded element. For example, the maximum width of the second pultruded element can be between 25% and 75% of the maximum width of the first pultruded element, for example, between 40% and 60%, for example 50%. However, other widths can also be used.

[0023] The second pultrusion includes a transition portion that extends from the blade engagement edge towards the outermost fastening member. The transition portion has a transition contact surface that is shaped to form a smooth transition of the inner layer. The transition portion has a local thickness that gradually decreases from a maximum thickness towards a minimum thickness.

[0024] According to one embodiment, the transition contact surface also forms at least a part of the second side surface of the one side.

[0025] The transition portion may extend along a part of the width of the second pultrusion element. Thus, a first non-transition portion may be arranged adjacent to the transition portion and extend along the remaining part of the width of the second pultrusion element. The first non-transition portion may have a uniform local thickness, for example corresponding to the above-mentioned maximum thickness. The transition portion and the first non-transition portion may together define the inner side of the second pultrusion element.

[0026] The transition portion may extend along a part of the thickness of the second pultrusion element. Thus, a second non-transition portion may be arranged adjacent to the transition portion and extend along the remaining part of the thickness of the second pultrusion element. The second non-transition portion may have a local width corresponding to the maximum width of the second pultrusion element or a variable local width. The transition portion and the second non-transition portion may together define the outermost second side of the second pultrusion element. This forms a relatively short transition between the inner side and the second side.

[0027] Alternatively, the transition portion may extend along the entire width and / or the entire thickness of the second pultrusion element. Thus, the transition contact surface may define the entire inner side and / or the outermost second side of the second pultrusion element. Thereby, the width of the second pultrusion element may gradually decrease or vary over the entire thickness, and vice versa. This forms a longer and smoother transition between the inner side and the second side.

[0028] Preferably, the transition portion extends along 10% to 100% of the inner side and / or the second side, for example, between 25% and 75%, for example 50%. Since the second pultrusion element does not form any sharp transition contact surface, this enhances the overhang of the inner layer above the blade mold edge.

[0029] According to one embodiment, the second pultrusion element terminates at an inner point in the thickness direction, where the outermost fastening member extends beyond the inner point of the second pultrusion element in the thickness direction.

[0030] The recesses of the first pultrusion element may extend along the entire second side and thus intersect the local inner and outer sides. Each recess may alternatively extend along a part of the second side and thus intersect the planar side surface located on the opposite side of the recess. The respective corners of the first pultrusion element may be rounded to form a smooth transition between the respective surfaces.

[0031] Similarly, the recess of the second pultruded element can extend along the entire second side and thus intersect the inner and outer sides. Alternatively, the recess can extend along a portion of the second side and thus intersect the planar side surface located on the opposite side of the recess. The respective corners of the second pultruded element can be rounded to form a smooth transition between the respective surfaces.

[0032] The first pultruded element and the second pultruded element can have the same maximum thickness and thus extend equally along the outermost bushing. Alternatively, the second pultruded element can have a reduced thickness compared to the thickness of the first pultruded element. Thus, the second pultruded element can extend partially along the outermost bushing in the thickness direction.

[0033] Thus, the transition contact surface or the inner surface can intersect the second side surface of the recess. This intersection point can thus define an inner point at which the second pultruded element can be terminated. This allows for increased contact of the inner layer with the outermost bushing.

[0034] According to one embodiment, the transition portion has a planar surface profile arranged at an angle with respect to the local outer surface of the second pultruded element.

[0035] The transition contact surface can have a planar surface profile, where the planar surface can be placed at a predetermined angle with respect to the outer side surface of the second pultruded element.

[0036] The planar surface can extend perpendicular to the outer side surface, for example. In this configuration, the planar surface can extend from the outer side to the aforementioned inner point. In this configuration, the inner side can be defined by an inner edge extending along the inner point in the longitudinal direction.

[0037] Alternatively, the planar surface can extend at an inclined angle with respect to the outer side surface, the angle being, for example, between 30° and 90°, preferably between 45° and 60°. However, other angles can be used.

[0038] According to one embodiment, the transition portion has a curved surface profile, preferably a circular or elliptical arc profile with a predetermined radius.

[0039] The transition contact surface can alternatively have a curved profile with a predetermined curvature. The curved profile can be, for example, a circular arc profile with a predetermined radius. This forms a smooth transition above the second pultruded element, such that any sharp bends or transitions in the inner layer are avoided.

[0040] The curved profile can be, for example, an elliptical arc profile with a predetermined radius. The radius can be defined by a maximum radius measured along the major axis and a minimum radius measured along the minor axis. This also forms a smooth transition above the second pultruded element, such that any sharp bends or transitions in the inner layer are avoided.

[0041] According to one embodiment, the transition portion extends partially or entirely along the length of the second pultruded element.

[0042] The first pultruded element and the second pultruded element may have a total length corresponding to the length of the bushing. Alternatively, the first pultruded element and the second pultruded element may have a first portion (where the local length of the first portion corresponds to the length of the bushing) and a second portion (the second portion extending beyond the bushing towards the end). The second portion may have a local length corresponding to the length of the spacer element placed at the end of the bushing. The second portions of the first pultruded element and the second pultruded element, as well as the spacer element, may have the same longitudinal profile, such as a tapered profile, to form a smooth transition between the root end region and the rest of the blade shell. In this configuration, the first pultruded element and the second pultruded element may have a uniform width along the total length.

[0043] Alternatively, the spacer element may be omitted, and the second portion of the second pultruded element and the subsequent first pultruded element may extend into the space to fill the space. In this configuration, the two pultruded elements may have a first width along the first portion and a second width along the second portion. This reduces the total number of items required to form the root end structure.

[0044] According to one embodiment, the second pultruded element includes a first sub - part and at least one second sub - part arranged relative to the first sub - part, wherein the first sub - part and the at least one second sub - part extend in the longitudinal direction.

[0045] The first pultruded element and / or the second pultruded element may be formed as a single continuous element extending in the length direction. This reduces the total number of items required to manufacture the root end structure and allows for a simplified laying process.

[0046] The first pultruded element may also be formed by a plurality of sub - parts extending in the length direction, wherein the sub - parts are arranged relative to each other to form a substantially butterfly - shaped cross - sectional profile in the width direction. This allows for an alternative laying process.

[0047] Alternatively or additionally, the second pultruded element may also be formed by a plurality of sub - parts arranged relative to each other. The sub - parts together may form a substantially semi - butterfly - shaped cross - sectional profile in the width direction. For example, the second pultruded element may include at least two sub - parts arranged symmetrically relative to each other. The sub - parts may be arranged back - to - back or face - to - face to form a semi - butterfly - shaped cross - sectional profile.

[0048] For example, the first sub-component may extend in the thickness direction and have a substantially rectangular cross-sectional profile in the width direction. A set of second sub-components may be arranged relative to the first sub-component and project outwardly from a side surface of the first sub-component. The second sub-components may each have a substantially triangular cross-sectional profile. The second sub-components may be located respectively at a local inner side and a local outer side. The first sub-component and the second sub-components together form a semi-butterfly cross-sectional profile.

[0049] For example, the first sub-component may extend in the width direction and have a substantially parallelogram cross-sectional profile in the width direction. The second sub-component may project outwardly from a side surface of the first sub-component and extend in the thickness direction. The second sub-component may have a substantially rectangular cross-sectional profile in the width direction. The third sub-component may project outwardly from a side surface of the second sub-component and extend in the width direction. The third sub-component may have a substantially triangular cross-sectional profile in the width direction. The three sub-components together form a semi-butterfly cross-sectional profile.

[0050] The transition portion may form part of one of the above sub-components, for example, the first sub-component. This allows the transition portion to be integrally formed by the above sub-components. Alternatively, the transition portion may be formed as a separate sub-component arranged relative to the other sub-components.

[0051] An object of the present invention is also achieved by a wind turbine blade that extends in a longitudinal direction from a blade root to a tip and further extends in a chord direction from a leading edge to a trailing edge. The wind turbine blade includes a blade shell formed by at least two blade components, each blade component having an inner surface and an outer surface, wherein the at least two blade components are connected in the longitudinal direction along at least one blade joint interface, and each blade joint interface is defined by a first blade joint edge of one blade component and a second blade joint edge of another blade component, characterized in that the at least two blade components include a root end structure configured as described above.

[0052] This provides a wind turbine blade having an improved root end structure as described above. The above root end structure reduces the risk of forming wrinkles at the respective blade joint ends. The transition portion of the second pultruded element provides an improved laying of the inner layer, which in turn allows for better structural load transfer.

[0053] A wind turbine blade is formed of at least two blade components, each blade component defining a pressure side and a suction side of the blade shell. The blade shell of each blade component has an inner surface defined by an inner layer and an outer surface defined by an outer layer. The two blade components are joined together at blade joining interfaces located at the trailing edge and the leading edge, respectively. Each joining interface includes a first blade joining edge of one blade component and a second blade joining edge of the other blade component. The blade components can also be joined together via shear webs or box beams located between the trailing edge and the leading edge.

[0054] An object of the present invention is further achieved by a method of manufacturing a wind turbine blade, the method comprising the steps of:

[0055] - laying a plurality of outer layers of fiber material along a blade mold surface,

[0056] - providing a plurality of fastening members configured to mount the wind turbine blade to a rotor hub interface or a pitch bearing unit,

[0057] - positioning the fastening members at a root end of the wind turbine blade relative to the outer layer (44),

[0058] - positioning a second pultrusion element between the outermost fastening member and a blade joining edge of at least one blade component, and optionally positioning a first pultrusion element between at least one pair of fastening members,

[0059] - further laying a plurality of inner layers of fiber material along the first and second pultrusion elements and the fastening members to form a root end structure,

[0060] - at least enclosing the root end structure via a vacuum bag material,

[0061] - introducing a resin into the fiber material,

[0062] - curing the resin to form a cured blade component,

[0063] wherein the inner layer extends above a transition contact surface of the second pultrusion element during laying and further extends along a mold edge surface.

[0064] This provides a manufacturing method that allows for improved laying of the inner layer. The above root end structure enhances the overhang of the inner layer above the mold blade edge by providing a smooth transition contact surface above the second pultrusion element. This eliminates any sharp corners and thus reduces the risk of forming wrinkles at the blade joining interface.

[0065] A wind turbine blade can be manufactured by laying a plurality of outer layers along a blade mold surface, wherein these outer layers further extend along a mold edge surface.

[0066] The fastening members (such as bushings) can then be positioned relative to these outer layers in any suitable manner during laying and held in place relative to the root end. The retaining members (such as pultruded elements) can then be positioned between the respective bushings and also optionally at the blade joint ends. This positioning of the pultruded elements and / or bushings can be done before moving the entire structure into place relative to the root end of the outer layer.

[0067] After that, a plurality of inner layers are laid along the local inner surfaces of the bushings and / or pultruded elements, where these inner layers extend above the outermost bushing or pultruded element and further along the mold edge surface.

[0068] Then the vacuum bag material is placed over the root end structure and resin is introduced, for example using any type of VARTM system. The resin is cured to form the cured blade part. This process is repeated for other blade parts.

[0069] According to one embodiment, the inner layer further extends above a part of the outermost fastening member.

[0070] During the laying process, if the second pultruded element has a reduced thickness compared to the outermost bushing, the inner layer can extend above the surface portion of the outermost bushing. This allows the outermost bushing to be located closer to the blade joint edge. This surface portion can be formed as part of a wider transition surface for the inner layer.

[0071] According to one embodiment, at least the excess fiber material of the inner layer is trimmed in a post-laying step or a post-molding step.

[0072] The excess lengths of the inner layer and the outer layer can be trimmed at or near the blade joint edge before joining the two blade parts. This can be done after completing the laying process or during the post-molding process. The inner layer and the outer layer can be trimmed by means of any suitable type of cutting tool or machine.

[0073] Then, the two blade parts can be joined together at the blade joint interface to form a wind turbine blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The present invention will be described in detail below with reference to the embodiments shown in the drawings, where

[0075] Figure 1 a wind turbine is shown,

[0076] Figure 2 an exemplary embodiment of a wind turbine blade is shown,

[0077] Figure 3 an exemplary embodiment of a root end structure is shown,

[0078] Figure 4 shows a cross-sectional view of a first embodiment of a root end structure placed in a blade mold,

[0079] Figure 5 shows a cross-sectional view of a second embodiment of a root end structure placed in a blade mold,

[0080] Figure 6 shows a third embodiment of a second pultrusion element,

[0081] Figure 7 a-c show three views of a fourth embodiment of a second pultrusion element,

[0082] Figure 8 shows a fifth embodiment of a second pultrusion element,

[0083] Figure 9 a-b show two views of a sixth embodiment of a second pultrusion element,

[0084] Figure 10 shows a side view of a fastening member,

[0085] Figure 11 shows a side view of a first embodiment of a first pultrusion element,

[0086] Figure 12 shows a side view of a second embodiment of a first pultrusion element,

[0087] Figure 13 a-c show three views of a root end structure including a third embodiment of a first pultrusion element,

[0088] Figure 14 shows a root end structure including a fourth embodiment of a first pultrusion element,

[0089] Figure 15 a-b show two views of a root end structure including a fifth embodiment of a first pultrusion element,

[0090] Figure 16 a-b show a sixth embodiment of a first pultrusion element,

[0091] Figure 17 a-b show two views of a root end structure including a seventh embodiment of a first pultrusion element,

[0092] Figure 18 a-b show two views of another alternative embodiment of a first pultrusion element,

[0093] Figure 19 shows a longitudinal view of the root end structure, where there is misalignment between the outer layer and the first pultrusion element,

[0094] Figure 20 shows a longitudinal view of a root end structure, where a first pultruded element conforms to the shape of the outer layer, and

[0095] Figure 21 shows a transverse view of the root end structure, where the first pultruded element is arranged between a pair of adjacent fastening members.

[0096] List of references

[0097] 1. Wind turbine

[0098] 2. Wind turbine tower

[0099] 3. Nacelle

[0100] 4. Hub

[0101] 5. Wind turbine blade

[0102] 6. Pitch bearing

[0103] 7. Blade root

[0104] 8. Tip

[0105] 9. Leading edge

[0106] 10. Trailing edge

[0107] 11. Blade shell

[0108] 12. Pressure side

[0109] 13. Suction side

[0110] 14. Blade root portion

[0111] 15. Aerodynamic blade portion

[0112] 16. Transition portion

[0113] 17. Wind turbine blade length

[0114] 18. Wind turbine blade chord length

[0115] 19. Root end structure

[0116] 20a. First blade joint edge

[0117] 20b. Second blade joint edge

[0118] 21. Inner surface

[0119] 22. Outer surface

[0120] 23. Fastening member, bushing

[0121] 23a. Outermost fastening member, bushing

[0122] 24. Blade mold

[0123] 25. Blade mold surface

[0124] 26. Mold edge surface

[0125] 27. First pultrusion element, holding member

[0126] 27a - b. First part and second part

[0127] 28. Second pultrusion element, holding member

[0128] 28a - c. First, second and third sub - parts

[0129] 29. Inner layer

[0130] 30. Wrinkle

[0131] 31. Transition part

[0132] 32. Transition contact surface

[0133] 33a - b. Local second side

[0134] 34. Local inner side

[0135] 35. Local outer side

[0136] 36. Recess

[0137] 37. Inner point

[0138] 38. Second side surface

[0139] 39. Local inner side

[0140] 40. Local outer side

[0141] 41a - b. Local first side

[0142] 42. Outer layer

[0143] 43. Gap

[0144] 44. First side surface

[0145] 45. Contact area

[0146] 46. First sub - part

[0147] 47. Second sub - part

[0148] 48. Wrinkle

[0149] 49. Spacer element

[0150] The listed reference numerals are shown in the above-mentioned drawings, where not all reference numerals are shown on the same drawing for illustrative purposes. Identical components or locations seen in the drawings will be numbered with the same reference numeral in different drawings. Detailed Description

[0151] Figure 1 A modern wind turbine 1 is shown, which includes a wind turbine tower 2, a nacelle 3 arranged on top of the wind turbine tower 2, and a rotor defining a rotor plane. The nacelle 3 is connected to the wind turbine tower 2 via a yaw bearing unit, for example. The rotor includes a hub 4 and a plurality of wind turbine blades 5. Three wind turbine blades are shown here, but the number of blades can be larger or smaller. The hub 4 is connected to a drivetrain located in the wind turbine 1 via a rotating shaft.

[0152] The hub 4 includes a mounting interface for each wind turbine blade 5. A pitch bearing unit 6 is optionally connected to this mounting interface and further connected to the blade root of the wind turbine blade 5.

[0153] Figure 2 A schematic view of a wind turbine blade 5 is shown, which extends from a blade root 7 to a tip 8 in a longitudinal direction. The wind turbine blade 5 further extends from a leading edge 9 to a trailing edge 10 in a chordwise direction. The wind turbine blade 5 includes a blade shell 11 having two relatively facing side surfaces that respectively define a pressure side 12 and a suction side 13. The blade shell 11 also defines a root portion 14, an aerodynamic portion 15, and a transition portion 16 between the root portion 14 and the aerodynamic portion 15.

[0154] The root portion 14 has a substantially circular or elliptical cross-section (indicated by the dashed line). The root portion 14, together with a load-bearing structure (not shown), is configured to add structural strength to the wind turbine blade 5 and transfer dynamic loads to the hub 4. The load-bearing structure extends between the pressure side 12 and the suction side 13 and further extends in the longitudinal direction.

[0155] The aerodynamic blade portion 15 has a cross-section with an aerodynamic shape designed to generate lift (indicated by the dashed line). The cross-sectional profile of the blade shell 11 gradually changes from a circular or elliptical profile to an aerodynamic profile in the transition portion 16.

[0156] The wind turbine blade 5 has a longitudinal length 17 of at least 35 m, preferably at least 50 m. The wind turbine blade 5 further has a chord length 18 as a function of the length 17, wherein the maximum chord length is found between the aerodynamic section 15 and the transition section 16. The wind turbine blade 5 also has a blade thickness as a function of the chord length 18, wherein the blade thickness is measured between the pressure side 12 and the suction side 13.

[0157] Figure 3 An exemplary embodiment of a root end structure 19 formed by two blade parts is shown, wherein one blade part includes two first blade joining edges 20a, and the other blade part includes two second blade joining edges 20b. The blade joining edges 20a, 20b extend in the longitudinal direction, and when joined together, the first blade joining edge 20a and the second blade joining edge 20b form a leading edge joining interface and a further trailing edge interface.

[0158] The blade shell 11 of the root end structure 19 forms an inner surface 21 and an outer surface 22. A plurality of fastening members 23 are distributed along the root end 7 in a first circumferential direction. A plurality of retaining members (shown in FIGS. 4 and Figure 5 are arranged relative to each fastening member 23, wherein the fastening member 23 and the retaining members are clamped between a plurality of inner layers (shown in Figures 19 - 20 and a plurality of outer layers (shown in Figures 19 - 20 ).

[0159] FIG. 4 shows a cross-sectional view of the root end structure 19 placed in a blade mold 24. The blade mold 24 has a blade mold surface 25 (which has a predetermined surface profile) and a mold edge surface 26.

[0160] The outer layer (shown in Figures 19 - 20 extends along the mold edge surface 26 and further along the blade mold surface 25 during laying, but is removed in FIGS. 4 and Figure 5 for illustrative purposes. The outer layer forms the outer skin of the blade shell 11 defining the outer surface 22.

[0161] The fastening member 23 is formed here as a bushing, and each bushing is arranged between a pair of adjacent retaining members. The retaining members are formed here as pultruded elements. A first pultruded element 27 is arranged between a pair of adjacent bushings 23, and the outermost bushing 23a is arranged between the first pultruded element 27 and the second pultruded element 28.

[0162] The first pultruded element 27 can be formed as a single continuous element or from a plurality of sub-parts. Two symmetrical sub-parts are shown here, which are arranged back-to-back as indicated by the dashed lines. The first pultruded element 27 has a butterfly-shaped cross-sectional profile in the width direction.

[0163] The second pultruded element 28 has a semi - butterfly cross - sectional profile in the width direction. The second pultruded element 28 is arranged at the first and / or second blade engagement edges 20a, 20b. FIG. 4 shows a prior art embodiment of the second pultruded element 28, where a sharp transition is formed between the second side surface (see Figure 6 ) and the second inner surface (see Figure 6 ). Due to this sharp transition, wrinkles 30 are formed in the inner layer 29 at the blade engagement edges 20a, 20b.

[0164] During laying, the inner layer 29 extends along the local inner side of the first pultruded element 27 (shown in Figure 6 and Figure 16 ), above the second pultruded element 28 and further along the die edge surface 25. After curing, the excess material of the inner layer 29 and the outer layer is trimmed. The inner layer 29 forms the inner skin of the blade shell 11 that defines the inner surface 21.

[0165] Figure 5 FIG. shows a cross - sectional view of the root end structure 19 still placed in the blade mold 24, where the root end structure 19 includes a first embodiment of the second pultruded element 28'.

[0166] Here, the second pultruded element 28' includes a transition portion 31 that forms a transition contact surface 32 for contacting the inner layer 29. The local thickness of this transition portion 31 gradually decreases towards the second side surface (see Figure 6 ) facing the blade engagement edges 20a, 20b. The local width of the transition portion 31 further gradually decreases towards the second inner side (shown in Figure 6 ). The transition contact surface 32 forms a smooth transition of the inner layer 29, thereby reducing the risk of wrinkles 30.

[0167] Figure 6 FIG. shows a second embodiment of the second pultruded element 28', where the transition portion 31' extends along the entire width of the second pultruded element 28'. The local thickness gradually decreases from one second side 33a to the opposite second side 33b.

[0168] Here, the transition portion 31' extends along the entire local inner side 34 of the second pultruded element 28' and partially along the local second side 33b. The transition port 31' can extend completely along both the local inner side 34 and the local second side 33b. The transition port 31' can also extend partially along both the local inner side 34 and the local second side 33b, as indicated in Figure 5 .

[0169] The second pultruded element 28' also has a local outer side 35 facing the outer layer.

[0170] Recesses 36 are formed in a partial second side 33a of the second pultruded element 28 and in two partial second sides 33a, 33b of the first pultruded element 27. The recesses 36 are configured to partially receive the outermost bushing 23a, as indicated in FIG. 4. The recesses 36 may extend partially along the partial second side 33a, as Figure 6 indicated, or alternatively may extend along the entire partial second side 33a.

[0171] Figure 7 a - c show three views of a third embodiment of the second pultruded element 28”, where the profiles of the second pultruded elements 28', 28” terminate at the partial inner side 34 or at an inner point 37 forming an inner edge.

[0172] In Figure 7 a, the transition contact surface 32' has a planar surface profile extending perpendicularly from the partial outer side 35. The transition contact surface 32' intersects the second side surface 38 of the partial second side 33a, thereby forming a reduced recess 36' for receiving the outermost bushing 23a. The recess 36 may have a semi - circular shaped profile, while the recess 36' may have a circular segment shaped profile. The inner layer 29 may thus contact a part of the outer surface of the outermost bushing 23a (dashed line), as indicated in 7a.

[0173] In Figure 7 b, the transition contact surface 32” has a curved profile extending from the partial outer side 35 to the inner point 37. In Figure 7 c, the transition contact surface 32' has a planar surface profile extending at an inclined angle with respect to the partial outer side 35.

[0174] Figure 8 A fourth embodiment of the second pultruded element 28”' is shown, which includes a plurality of sub - parts that together form a substantially semi - butterfly cross - sectional profile in the width direction. The first sub - part 28a extends in the thickness direction, and a set of second sub - parts 28b projects from the side surface of the first sub - part 28a. Here, the second sub - parts 28b are arranged at both the partial inner and outer sides 34, 35.

[0175] The individual sub - parts 28a, 28b together form a recess 36 for partially receiving the outermost bushing 23a.

[0176] Figure 9 a - b show two views of a fifth embodiment of the second pultruded element 28”', where the transition part 31” is integrally formed by one of the sub - parts 28a - c.

[0177] In Figure 9In a, the first sub-component 28a' has a substantially rectangular profile in the width direction, where the transition portion 31” faces the local inner side 34. The second sub-component 28b has a substantially triangular profile in the width direction.

[0178] In Figure 9 In b, the first sub-component 28a” extends in the width direction and has a profile in the shape of a substantially parallelogram. Here, the transition portion 31” forms one end of the first sub-component 28a”. The second sub-component 28b' extends in the thickness direction and has a substantially rectangular profile in the width direction. Additionally, the third sub-component 28c projects from the side surface of the second sub-component 28b and has a substantially triangular profile in the width direction.

[0179] Figure 10 A side view of the fastening members 23, 23a having a predetermined length measured between the local root end 7' and the opposite end is shown. Here, the fastening members 23, 23a have a uniform cross-sectional profile in the length direction. However, the cross-sectional profile can alternatively vary or gradually decrease along the length. As indicated in FIGS. 4-5, the fastening members 23, 23a have a circular cross-sectional profile. However, the fastening members 23, 23a can have another suitable cross-sectional profile, such as an elliptical or polygonal profile. The fastening members 23, 23a thus have a uniform or variable outer diameter or thickness along their length.

[0180] The fastening members 23, 23a have a local inner side 39, a local outer side 40, and two relatively facing local first sides, as Figure 13 indicated in b-c. Here, only one local first side 41a is shown.

[0181] The outer surface of the fastening members 23, 23a is optionally wrapped in a fiber material, as indicated by the dashed line, where the wrapped fiber material extends along at least a portion of the length of the fastening members 23, 23a.

[0182] Figures 11 - 12 A side view of the first and second embodiments of the first pultruded element 27 including a first portion 27a and a second portion 27b is shown. The first portion 27a extends from the local root end 7” towards the opposite end, while the second portion 27b extends from the first portion 27a to the opposite end.

[0183] The first portion 27a has a uniform thickness along its local length, as Figures 11 - 12 indicated. The local length of the first portion 27a substantially corresponds to the length of the fastening members 23, 23a, as Figures 19 - 20 indicated.

[0184] The second part 27b has a tapered profile that extends beyond the fastening members 23, 23a, where the local thickness gradually decreases from a maximum thickness to a minimum thickness. As Figure 11 indicated, the first part 27a and the second part 27b can form a continuous local outer side 35, where the second part 27b gradually decreases from the inner side 34 to the local outer side 35. As Figure 11 indicated, the second part 27b can form an inclined local inner and outer sides 34, 35, where the second part 27b gradually decreases towards the local center line.

[0185] The second pultruded element 28 has a configuration similar to that of the Figures 11 - 12 first pultruded element 27 shown.

[0186] Figure 13 a - c show three views of the root end structure 19' of the third embodiment including the first pultruded element 27'. Figure 13 b - c show a simplified view of a first pultruded element 27', where the local first sides 41a, 41b of a pair of adjacent bushings 23 extend into the local second sides 33a, 33b of the first pultruded bushing 27'.

[0187] The first pultruded element 27' has a thickness greater than the outer diameter of the fastening member 23. The inner layer 29 extends along the local inner side 34, and the outer layer 42 extends along the local outer side 35 of the first pultruded element 27'.

[0188] The local second sides 33a, 33b of a pair of adjacent first pultruded elements 27' can be in contact with each other, as Figure 13 indicated in a, or spaced apart, as Figure 14 indicated.

[0189] A plurality of gaps 43 are formed between the first side surface 44 of the bushing 23 and the second side surface 38 of the first pultruded element 27'. Here, a first gap 43' and a second gap 43' are formed on opposite sides of the bushing 23. The first gap 43' and the second gap 43' extend in the longitudinal direction and further extend along the second circumferential direction defined by the second side surface 38.

[0190] Here, the second side surface 38 has an elliptical arc profile, while the first side surface 44 has a circular profile. The second side surface 38 and the adjacent local side surface can form a sharp transition, as Figure 13 indicated in b, or form a smooth transition, as Figure 13 indicated in c.

[0191] The elliptical arc profile of the second side surface 38 forms a profile with a predetermined height h 2 and width w 2a part of the inscribed contour, as Figure 13 illustrated in b. In addition, the circular contour of the first side surface 44 forms a part of the circumscribed contour having a predetermined height h 1 and width w 1 also as illustrated in Figure 13 b.

[0192] Here, the first pultruded element 27' contacts the adjacent bushing 23 at the contact area 45 formed on the second side surface 38, as Figure 13 indicated in b-c. The first gap 43' and the second gap 43' have a radial distance that varies along the second side surface 38, as Figure 13 indicated in a-c. This allows for the adaptive positioning of the first pultruded element 27' in the longitudinal direction.

[0193] Figure 14 The root end structure 19” of the fourth embodiment including the first pultruded element 27” is shown, where the first pultruded element 27” has a local thickness less than the outer diameter of the bushing 23. The inner layer 29 and the outer layer 42 contact both the local inner side 35 of the first pultruded element and the local inner side 43 of the bushing 23 here.

[0194] Figure 15 a-b show two views of the root end structure 19”' of the fifth embodiment including the first pultruded element 27”'. Figure 15 b shows a simplified view of a first pultruded element 27”', where a pair of adjacent bushings 23 partially extend into the recess 36 formed in the first pultruded bushing 27”'.

[0195] Here, a central gap 43” is formed between the first side surface 38 and the second side surface 44, where the radial distance varies along the first circumferential direction. A first contact area 45' and a second contact area 45” are also formed between the first side surface 38 and the second side surface 44, where the bushing 23 contacts the pultruded element 27”' at these first and second contact areas 45”. This allows for the adaptive positioning of the first pultruded element 27”' in the width direction.

[0196] Here, the second side surface 38 has an alternative elliptical arc-shaped contour, while the first side surface 44 has a circular contour.

[0197] Figure 16 a-b show the sixth embodiment of the first pultruded element 27””, where the second side surface of the recess 36 includes a planar surface portion 38' arranged between two curved surface portions 38”. The curved surface portions 38” can be shaped as circular arc segments, as Figure 16 indicated in a. The inner arc segment has a first radius r 1, and the outer arc segment has a second radius r 2 . The first radius r 1 and the second radius r 2 have the same or different values.

[0198] The curved surface portion 38" can also be formed into an elliptical or super-elliptical arc segment, as Figure 16 indicated in b. The two elliptical arc segments have the same or different major and minor radii.

[0199] The planar surface portion 38' serves as a contact area for contacting the bushing 23. Unlike Figure 15 and 17 the embodiments of, a gap 43 can be formed while maintaining the minimum width in the width direction between the recesses 36, as indicated by the dashed line in Figure 16 a.

[0200] Figure 17 a - b show three views of the root end structure 19"" of the seventh embodiment including the first pultruded element 27""", where a continuous gap 43"" is formed between the first side surface 38 and the second side surface 44.

[0201] The gap 43"" has a uniform radial distance along the second side surface 38, as Figure 17 indicated in b. The second side surface 38 can have a circular arc profile with equal height h w and width w w , and the first side surface 44 can further have a circular profile with equal height h b and width w b , as Figure 17 indicated in b. The first side surface 38 and the second side surface 44 can also have an elliptical arc profile, as Figure 17 indicated in c. The first side surface 38 and the second side surface 44 have a common center point, but different radii. This increases the flexibility of the adaptive positioning of the first pultruded element 27""".

[0202] Here, since the first pultruded element 27"" can move relative to the bushing in both the thickness direction and the width direction, the bushing 23 is not firmly and closely in contact with the first pultruded element 27"".

[0203] Figure 18 a - b show another alternative embodiment of the first pultruded element 27. Here, the first pultruded element 27 is formed by a plurality of sub-parts arranged relative to each other.

[0204] A first sub-component 46 having a rectangular cross-sectional profile in the width direction is arranged between a pair of adjacent bushes 23. A first set of second sub-components 47 is arranged at the local inner side 34, and a second set of second sub-components 47 is arranged at the local outer side 35. The individual second sub-components 47 of each set are positioned on the opposite facing sides of the first sub-component 46.

[0205] In a conventional root end design, as Figure 18 indicated in a, all of the first sub-components 46 and the second sub-components 47 contact the bushes 23 to prevent any relative movement. The first sub-component 46 and the second sub-components 47 together form an inscribed circular profile having equal height and width.

[0206] In the present invention, as Figure 18 indicated in b, only the first sub-component 46 contacts the bushes 23, while the second sub-components 47' are spaced apart from the bushes 23 to form a gap 43. The first sub-component 46 and the second sub-components 47' together form an inscribed substantially elliptical profile having a height h” greater than its width w”. Here, the bushes 23 form a circumscribed circular profile having equal values of height h' and width w'. This also allows for the adaptive positioning of the first pultrusion element 27 in the longitudinal direction.

[0207] Figure 19 A longitudinal view of the root end structure 19 is shown, in which there is a misalignment in the longitudinal direction between the outer layer 42 and the first pultrusion element 27. This misalignment results in the formation of wrinkles 48 in the transition region between the inner layer 29 and the outer layer 42.

[0208] This misalignment can occur when evacuating the root end structure 19 during the vacuum-assisted resin infusion process.

[0209] Figure 20 A longitudinal view of the root end structure 19 is shown, in which the first pultrusion element 27 conforms to the shape of the outer layer 42. This is achieved by providing one or more gaps 43 between the first side surface 38 and the second side surface 44. The gap 43 in turn enables the first pultrusion element 27 to move relative to the bushes 23 (indicated by the arrow) during the vacuum-assisted resin infusion. Thus, during the vacuum-assisted resin infusion, the first pultrusion element 27 is allowed to passively adapt its longitudinal position relative to the outer layer 42.

[0210] Figure 21 A transverse view of the root end structure 19 is shown, in which the first pultrusion element 27 is arranged between a pair of adjacent bushes 23.

[0211] Here, the first pultrusion element 27 is prevented from moving relative to the bushes 23 and the spacer element 49 in the width plane (indicated by the arrow) while being able to move relative to the bushes 23 in the thickness plane, as Figure 20Indicated in

[0212] The spacer element 49 is positioned relative to the bushing 23 and further extends in the longitudinal direction. The spacer element 49 has a length substantially corresponding to the local length of the second part 27b of the first pultruded element 27. The spacer element 49 has a tapered profile corresponding to the tapered profile of the second part 27b in the longitudinal direction. The gap 43 extends optionally along the length of the bushing 23 and further along at least a part of the length of the spacer element 49.

[0213] The above embodiments can be combined in any combination without departing from the present invention.

Claims

1. Root end structure (19) of a wind turbine blade (5), said root end structure (19) extending from the blade root (7) into the root end portion (14) of the blade shell (11), said blade shell (11) being formed by at least one blade component having an inner surface (21), an outer surface (22) and at least one blade joining edge, said root end structure (19) comprising a plurality of fastening members distributed circumferentially along the root end of said at least one blade component, each fastening member having a first inner surface (39), a first outer surface (40) and opposite facing first side surfaces (41a, 41b) extending in a longitudinal direction, wherein a second pultruded element is arranged between the outermost fastening member and the blade joining edge (20a, 20b) of said at least one blade component, said second pultruded element having a second inner surface (34), a second outer surface (35) and opposite facing second side surfaces (33a, 33b) further extending in said longitudinal direction, said root end structure (19) further comprising a plurality of outer layers (44) of fiber material extending along said outer surface (22) and a plurality of inner layers (29) of fiber material extending along said inner surface (21), characterized in that, said second pultruded element forms a transition portion (31) extending from one second side surface (33b) towards the other second side surface (33a), wherein the local thickness of said transition portion (31) gradually decreases towards the blade joining edge (20a, 20b) and / or said other second side surface (33a), thereby providing a smooth transition of the inner layer above the outermost pultruded element.

2. The root end structure according to claim 1, characterized in that, said transition portion (31) forms a transition contact surface (32) contacting said inner layer (29), wherein said transition contact surface (32) forms at least a part of said second inner surface (34).

3. The root end structure according to claim 2, characterized in that, said transition contact surface (32) also forms at least a part of said one second side surface (33b).

4. The root end structure according to any one of claims 1 to 3, characterized in that, said second pultruded element terminates at an inner point (37) in the thickness direction, wherein said outermost fastening member extends beyond said inner point (37) of said second pultruded element in the thickness direction.

5. The root end structure according to any one of claims 1 to 3, characterized in that, said transition portion (31) has a planar surface profile arranged at an angle with respect to the second outer surface (35) of said second pultruded element.

6. The root end structure according to any one of claims 1 to 3, characterized in that, said transition portion (31) has a curved surface profile.

7. The root end structure according to any one of claims 1 to 3, characterized in that, said transition portion (31) extends partially or entirely along the length of said second pultruded element.

8. The root end structure according to any one of claims 1 to 3, characterized in that, The second pultruded element includes a first sub-part (28a) and at least one second sub-part (28b) arranged relative to the first sub-part (28a), wherein the first sub-part (28a) and the at least one second sub-part (28b) extend in the longitudinal direction.

9. The root end structure according to claim 1, wherein, a first pultruded element (27) is arranged between at least a pair of fastening members, the first pultruded element (27) having a second inner surface (34), a second outer surface (35) and relatively facing second side surfaces (33a, 33b) further extending in the longitudinal direction.

10. The root end structure according to claim 6, wherein, the transition portion (31) has a circular or elliptical arc-shaped profile, the circular or elliptical arc-shaped profile having a predetermined radius.

11. A wind turbine blade, the wind turbine blade (5) extending in a longitudinal direction from a blade root (7) to a tip (8) and further extending in a chordwise direction from a leading edge (9) to a trailing edge (10), the wind turbine blade (5) including a blade shell (11) formed by at least two blade components, each of the blade components having an inner surface (21) and an outer surface (22), wherein the at least two blade components are connected along at least one blade joint interface in the longitudinal direction, each blade joint interface being defined by a first joint edge (20a) of one blade component and a second joint edge (20b) of another blade component, wherein, the at least two blade components include a root end structure (19) configured according to any one of claims 1 to 10.

12. A method of manufacturing a wind turbine blade according to claim 11, comprising the steps of: - laying a plurality of outer layers (44) of fiber material along a blade mold surface (26), - providing a plurality of fastening members configured to mount the wind turbine blade (5) to a rotor hub interface or a pitch bearing unit, - positioning the fastening members at the root end of the wind turbine blade (5) relative to the outer layer (44), - positioning a second pultruded element between the outermost fastening member and the blade joint edges (20a, 20b) of the at least one blade component, - further laying a plurality of inner layers (29) of fiber material along the second pultruded element and the fastening members to form a root end structure (19), - at least enclosing the root end structure (19) via a vacuum bag material, - introducing resin into the fiber material, - curing the resin to form a cured blade component, wherein the inner layer (29) extends above the transition contact surface (32) of the second pultruded element and further extends along a mold edge surface (25) during the laying.

13. The method according to claim 12, wherein, the inner layer (29) further extends above a part of the outermost fastening member.

14. The method according to claim 12 or 13, wherein, At least the excess fiber material of the inner layer (29) is trimmed in a post-laying step or a post-molding step.

15. The method according to claim 12, wherein, a first pultrusion element (27) is positioned between at least a pair of fastening members, and inner layers (29) of a plurality of fiber materials are laid along the first and second pultrusion elements and the fastening members to form a root end structure (19).

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