METHOD AND MOULD FOR MANUFACTURING PREFORMS FOR A WIND TURBINE ROTOR BLADE

Abstract

The present invention relates to a method of manufacturing a preform for a wind turbine blade and to a preform mould. The method involves providing a plurality of support elements (70), each support element (70) comprising a planar member (72), arranging a plurality of strips (88) on the top surface (78) of the planar member (72) of each support element (70), wherein the strips (88) are arranged in juxtaposition. Subsequently, a fibre material and a binding agent may be laid on at least part of the strips (88) for forming the preform.

Claims

1. A method of manufacturing a preform for a wind turbine blade, said method comprising the steps of providing a plurality of support elements (70), each support element (70) comprising a planar member (72) having a front surface (74) and an opposing back surface (76), a top surface (78) and an opposing bottom surface (80), and two opposing lateral surfaces (82, 84), arranging a plurality of strips (88) on the top surface (78) of the planar member (72) of each support element (70), wherein the strips (88) are arranged in juxtaposition, laying a fibre material, and optionally a binding agent, on at least part of the strips (88) for forming the preform.

2. A method according to claim 1, wherein the support element (70) comprises one or more tabs (92) extending substantially perpendicularly from the top surface (78) of the planar member (72) for supporting the strips (88).

3. A method according to claim 1, wherein the top surface (78) of the planar member (72) is curved.

4. A method according to claim 3, wherein the curvature of the top surface (78) of the planar member (72) corresponds to a cross sectional profile of a wind turbine blade half or a part thereof.

5. A method according to claim 3, wherein the curvature of the top surface (78) of the planar member (72) of one support element (70) is different from the curvature of the top surface (78) of the planar member (72) of another support element (70).

6. A method according to claim 1, wherein the plurality of support elements (70) are arranged substantially in parallel to each other.

7. A method according to claim 1, wherein the strips (88) are arranged in juxtaposition with a predefined gap between adjacent strips (88).

8. A method according to claim 7, wherein the gap between adjacent strips (88) is between 1 and 25 mm wide.

9. A method according to claim 1, wherein each strip (88) has a width W of between 0.04 and 5 m and wherein each strip has a length L of between 15 and 50 m.

10. A method according to claim 1, wherein the strips (88) are attached to the support elements (70) by one or more blind fasteners or spot weldings.

11. A method according to claim 1, wherein the planar member (72) of the support element (70) has a thickness of less than 3 cm.

12. A method according to claim 1, wherein adjacent strips (88) are interconnected along their longitudinal edges

13. A method according to claim 1, wherein the method further comprises the step of heating the fibre material and the binding agent to a temperature of between 40 and 200 C. to form a plurality of preforms

14. A preform mould for manufacturing a preform for a wind turbine blade, the preform mould comprising a plurality of support elements (70), each support element (70) comprising a planar member (72) having a front surface (74) and an opposing back surface (76), a top surface (78) and an opposing bottom surface (80), and two opposing lateral surfaces (82, 84), a plurality of strips (88) arranged in juxtaposition on the top surface (78) of the planar member (72) of each support element (70).

15. A method of manufacturing a wind turbine blade part, the method comprising: manufacturing one or more preforms (98) according to the method of claim 1, arranging the preforms (98) in a blade mould cavity (97), optionally together with additional material (94), infusing resin to the blade mould cavity (97), curing or hardening the resin in order to form the blade part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0071] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0072] FIG. 1 shows a wind turbine,

[0073] FIG. 2 shows a schematic view of a wind turbine blade,

[0074] FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

[0075] FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

[0076] FIG. 5 is a perspective drawing of an arrangement of support elements for a preform mould according to the present invention,

[0077] FIG. 6 is a perspective drawing of a preform mould according to the present invention,

[0078] FIG. 7 is a perspective drawing of another embodiment of a preform mould according to the present invention,

[0079] FIG. 8 is a perspective drawing illustrating an arrangement of support elements for a preform mould according to another embodiment of the present invention,

[0080] FIG. 9 is a perspective drawing of a support element according to an embodiment of the present invention, and

[0081] FIG. 10 is a perspective drawing of a blade mould for lay up of preforms according to the present invention.

DETAILED DESCRIPTION

[0082] FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called Danish concept with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8.

[0083] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

[0084] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

[0085] A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

[0086] It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0087] FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention. FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during usei.e. during rotation of the rotornormally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0088] Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

[0089] FIG. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 3, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=L.sub.w, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius r.sub.o and a minimum inner curvature radius r.sub.h which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as y, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

[0090] FIG. 5 is a perspective view of an arrangement of support elements for a preform mould for manufacturing a wind turbine blade according to the present invention. The arrangement of FIG. 5 comprises four support elements 70a-d, each support element comprising a planar member 72 having a front surface 74 and an opposing back surface 76, a curved top surface 78 and an opposing bottom surface 80, and two opposing lateral surfaces 82, 84 (shown for support element 70a). The top surface 78 of each support element is curved, corresponding to a cross sectional profile of a wind turbine blade half or a part thereof. In the embodiment shown in FIG. 5, the support elements 70a-d are arranged substantially parallel to each other and are interconnected by two lateral rails 86a, 86b.

[0091] As seen in FIG. 6, a preform mould 90 according to the present invention can be obtained by arranging a plurality of strips 88a-e, in juxtaposition, on the top surface 78 of the support elements 70a-d. A fibre material and a binding agent can be laid on at least part of the strips to form the preform, usually after a heating step. FIG. 6 also indicates the length L and width W of the strips 88.

[0092] In the embodiment of FIG. 6, the strips 88a-e are arranged in juxtaposition with a predefined gap between adjacent strips. The distance between adjacent strips may be between 1 and 25 mm. By contrast, FIG. 7 illustrates an embodiment in which the strips 88a-f are placed edge-to-edge with substantially no gap between adjacent strips.

[0093] FIG. 8 illustrates another arrangement of support elements for a preform mould according to the present invention. Here, the support elements 70a-d differ in terms of the curvature of their respective top surfaces 78a-d. This allows for manufacturing of preforms with complex geometries. According to the method of the present invention, preform moulds of different shapes and curvatures can be easily manufactured and adapted to specific requirement.

[0094] FIG. 9 is a perspective drawing of one embodiment of a support element 70 according to the present invention. The support element 70 comprises a planar member 72 and several tabs 92a-f extending substantially perpendicularly from its top surface 78 for supporting the strips. The tabs 92a-f effectively increase the surface area of the top surface 78 to provide further support and stability to the preform mould.

[0095] As illustrated in FIG. 10, the manufactured preforms 98a, 98b, 98c can be laid up in a blade mould 96 to form part of a wind turbine blade, such as the root laminate. It is particularly preferred that the preforms manufactured according to the present invention are used for a blade section starting from the root end of the blade, such as the root region. The preforms 98a, 98b, 98c are arranged in the blade mould cavity 97, usually together with additional fibre material 94. Then, resin is infused to the blade mould cavity 97, which is subsequently cured or hardened in order to form the blade part, such as a blade half.

[0096] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.

LIST OF REFERENCE NUMERALS

[0097] 2 wind turbine [0098] 4 tower [0099] 6 nacelle [0100] 8 hub [0101] 10 blade [0102] 14 blade tip [0103] 16 blade root [0104] 18 leading edge [0105] 20 trailing edge [0106] 22 pitch axis [0107] 30 root region [0108] 32 transition region [0109] 34 airfoil region [0110] 40 shoulder/position of maximum chord [0111] 50 airfoil profile [0112] 52 pressure side [0113] 54 suction side [0114] 56 leading edge [0115] 58 trailing edge [0116] 60 chord [0117] 62 camber line/median line [0118] 70 support element [0119] 72 planar member [0120] 74 front surface [0121] 76 back surface [0122] 78 top surface [0123] 80 bottom surface [0124] 82 lateral surface [0125] 84 lateral surface [0126] 86 rail [0127] 88 strip [0128] 90 preform mould [0129] 92 tab [0130] 94 fibre material [0131] 96 blade mould [0132] 97 blade mould cavity [0133] 98 preform [0134] c chord length [0135] d.sub.t position of maximum thickness [0136] d.sub.f position of maximum camber [0137] d.sub.p position of maximum pressure side camber [0138] f camber [0139] L blade length [0140] r local radius, radial distance from blade root [0141] t thickness [0142] y prebend