Windmill blade

Abstract

To improve the durability of a windmill blade against buckling.SOLUTION: A windmill blade includes a spar cap essentially comprising a plurality of substantially elongated, plate-shaped composite materials aligned in a width direction and a height direction of the windmill blade. In a cross section perpendicular to a longitudinal direction of the spar cap, at least one pair of composite materials adjacent to each other in the width direction are adjacent via an engagement structure which is formed such that an engagement projection formed at an end of one of the composite materials in the width direction engages with an engagement projection formed at an end of the other composite material in the width direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a wind turbine blade used in wind turbines for wind power generation and the like. [Background technology]

[0002] From the perspective of carbon neutrality, wind power generation, which does not emit greenhouse gases when generating electricity, is attracting attention. Generally, the longer the wind turbine blades are, the more electricity can be generated. However, when wind turbine blades are made longer, the area exposed to the wind increases, which causes greater bending deformation in the wind turbine blades. As bending deformation increases, greater stress is generated at the base of the wind turbine blades, so greater durability is required.

[0003] To address this issue, Non-Patent Document 1 studies ways to improve the durability of wind turbine blades by using carbon fiber reinforced resin, which has excellent mechanical properties, for 117m blades. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Definition of the IEA Wind 15MW Offshore Reference Wind Turbine(2020) Summary of the Invention [Problem to be solved by the invention]

[0005] The spar cap disclosed in Non-Patent Document 1 may be highly durable against compressive and tensile forces due to bending deformation of wind turbine blades by using carbon fiber reinforced resin. However, no measures have been taken to address the problem of cracks occurring in the spar cap inside the wind turbine blade and their progression leading to buckling.

[0006] An object of the present invention is to improve the durability of wind turbine blades against buckling. [Means for solving the problem]

[0007] The present invention for solving the above problems is as follows. 1. A wind turbine blade having a spar cap essentially made of a plurality of substantially long plate-shaped composite materials arranged in the width direction and height direction of the wind turbine blade, In a cross section perpendicular to the longitudinal direction of the spar cap, at least one pair of composite materials adjacent to each other in the width direction are adjacent via an interlocking structure configured so that an interlocking protrusion formed on an end portion in the width direction of one composite material interlocks with an interlocking protrusion formed on an end portion in the width direction of the other composite material. 2. A wind turbine blade as described in 1, wherein the set of composite materials consists of two composite materials each having a mating convex portion formed at one end in the width direction and a mating concave portion formed at the other end in the width direction. 3. The wind turbine blade according to 1 or 2, wherein all of the composite materials constituting the spar cap are adjacent to each other via the interlocking structure. 4. A wind turbine blade as described in 1 or 2, wherein the mating convex portion has a shape in which its height decreases toward the tip, and the mating concave portion has a shape in which its height decreases toward the back, corresponding to the mating convex portion. 5. A wind turbine blade as described in 4, wherein the mating convex portion has a shape in which its height decreases at a constant inclination angle toward the tip, and the mating concave portion has a shape in which its height decreases at a constant inclination angle toward the back, corresponding to the mating convex portion. 6. The wind turbine blade according to 5, wherein the tilt angle is greater than 0° and not more than 5°. 7. The wind turbine blade according to 1 or 2, wherein in a cross section perpendicular to the longitudinal direction, the mating convex portion and the mating concave portion of the composite material are both approximately rectangular. 8. The wind turbine blade according to 1 or 2, wherein in a cross section perpendicular to the longitudinal direction, the mating convex portion and the mating concave portion of the composite material are both approximately triangular in shape. 9. A wind turbine blade according to 1 or 2, wherein in the spar cap, the composite material is arranged symmetrically with respect to the center line in the cross section. 10. A wind turbine blade according to 1 or 2, wherein the composite material is a pultrusion molded product of carbon fiber reinforced resin. 11. A wind turbine for wind power generation, comprising the wind turbine blade according to any one of 1 to 10.

[0008] In this specification, the longitudinal direction of the spar cap (hereinafter simply referred to as the "longitudinal direction") is the direction of a line connecting the center of gravity in a cross section near the part fixed to the hub and the part (blade tip) farthest from the part fixed to the hub, and corresponds to the direction of the z axis in FIG. 2. The width direction of the spar cap (hereinafter simply referred to as the "width direction") is the direction connecting the leading edge and trailing edge in a cross section perpendicular to the longitudinal direction, and corresponds to the direction of the y axis in FIG. 2. The height direction of the spar cap (hereinafter simply referred to as the "height direction") is the direction perpendicular to the width direction in a cross section perpendicular to the longitudinal direction, and corresponds to the direction of the x axis in FIG. 2. [Effects of the Invention]

[0009] According to the present invention, it is possible to improve the durability against buckling of wind turbine blades for wind power generation. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an overall view of a wind turbine for wind power generation. [Figure 2] FIG. 1 is a perspective view showing a wind turbine blade 1, including a cross section taken along a plane perpendicular to the longitudinal direction of the wind turbine blade. [Figure 3] FIG. 2 is a cross-sectional view of the spar cap and the share web when the wind turbine blade 1 is cut in a plane perpendicular to the longitudinal direction of the wind turbine blade. [Figure 4] FIG. 10 is a diagram showing deformation when pressure simulating wind is applied to a wind turbine blade. [Figure 5]1 is a cross-sectional view of a spar cap and a composite material that constitutes the spar cap when a wind turbine blade according to an embodiment of the present invention is cut along a plane perpendicular to the longitudinal direction of the spar cap. FIG. [Figure 6] FIG. 10 is a cross-sectional view of another embodiment of the spar cap and the composite material that constitutes the spar cap, when the wind turbine blade of the present invention is cut along a plane perpendicular to the longitudinal direction of the spar cap. [Figure 7] 1 is a simulation procedure of an embodiment. [Figure 8] <step1>FIG. 1 is a diagram schematically illustrating an overview of an overall analysis. [Figure 9] <step2>FIG. 1 is a diagram schematically illustrating an outline of a detailed analysis. [Figure 10] 10 is a graph showing the results of a simulation comparing the buckling strength when the cross-sectional shape of the composite material is changed. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the description of the specific embodiments shown in the drawings can also be understood as a description of the present invention as a general concept.

[0012] FIG. 1 shows an overall view of a wind turbine for wind power generation. As shown in FIGS. 1A and 1B, a typical wind turbine for wind power generation is composed of wind turbine blades 1, a tower 2, a nacelle 3, and a hub 4. The wind turbine blades 1 are attached to the hub 4, and rotate due to wind force. This rotation is transmitted to a power transmission shaft in the nacelle 3 via the hub 4, driving a generator in the nacelle 3. The wind turbine blades 1 may be pre-bent at the tip end in a direction away from the tower 2 to make them less likely to collide with the tower 2. In the present invention, the wind turbine blades 1 may also be pre-bent. Such a wind turbine for wind power generation, equipped with the wind turbine blades of the present invention described below, is one aspect of the present invention.

[0013] Figure 2 is a perspective view of a typical wind turbine blade 1, including a cross section taken perpendicular to the longitudinal direction. Because wind turbine blades are required to be lightweight and have high mechanical properties, a structure is adopted in which beam materials are placed inside a hollow structure made of skin material that forms the outer shape of the blade. In Figure 2, wind turbine blade 1 has skin material 11 that becomes the pressure side and contraction side when it receives wind, spar caps 12 that are placed in contact with the pressure side and contraction side skin material 11 or as part of skin material 11 at the part where the blade cross-sectional thickness is greatest, and share webs 13 that act as beam materials and connect the spar caps together.

[0014] Figure 3 is a schematic diagram showing a typical wind turbine blade, and is an enlarged schematic diagram showing a cross section (xy plane) perpendicular to the longitudinal direction at the joint 14 between the spar cap and the share web in Figure 2. As shown in Figure 3, the spar cap 12 is generally formed by arranging a plurality of substantially long plate-shaped composite materials 15 along the longitudinal direction in the width and height directions (i.e., the y and x directions in the figure), and bonding these composite materials 15 together with resin 16. Note that, as shown in Figure 3, the composite material 15 generally has a rectangular cross section, i.e., the width direction ends are straight.

[0015] In this specification, the term "composite material" refers to a plastic in which a reinforcing fiber layer is impregnated with a matrix resin and cured. Examples of reinforcing fibers constituting the reinforcing fiber layer include inorganic fibers such as carbon fiber and glass fiber, and organic fibers such as Kevlar® fiber, polyethylene fiber, and polyamide fiber. From the viewpoint of high strength and high rigidity, carbon fiber is particularly preferred as the reinforcing fiber. The matrix resin contained in the composite material is not particularly limited, and examples include thermosetting resins such as epoxy resins, unsaturated polyester resins, and vinyl ester resins, as well as thermoplastic resins such as polyamide resins, polyolefin resins, polyester resins, polyphenylene sulfide resins, ABS resins, polycarbonate resins, polyacetal resins, and polybutylene terephthalate resins. Vinyl ester resins are particularly preferred because they offer an excellent balance between moldability and mechanical properties, while epoxy resins are preferred because they also have excellent mechanical properties and adhesion to carbon fibers. The composite material in the present invention is typically a pultrusion molded product of fiber reinforced resin, and most preferably a pultrusion molded product of carbon fiber reinforced resin.

[0016] Examples of resin 16 that can be used to bond composite materials together include thermosetting resins such as epoxy resin, unsaturated polyester resin, vinyl ester resin, and phenolic resin, thermoplastic resins such as acrylic resin, polycarbonate resin, polyethylene resin, polypropylene resin, polyamide resin, polyolefin resin, dicyclopentadiene resin, polyurethane resin, polybutylene terephthalate resin, polyacetal resin, and ABS resin, and modified resins made by alloying these resins.

[0017] 4A and 4B are conceptual diagrams illustrating how cracks develop in the spar cap 12 when it is bent by wind. As shown in FIG. 4A, a crack 19A extending in the longitudinal direction initiates near the base of the wind turbine blade 1, where large stresses are generated by the longitudinal bending deformation of the spar cap 12, and propagates longitudinally toward the tip of the wind turbine blade. Furthermore, as shown in FIG. 4B, bending deformation in the width direction occurs in the plane perpendicular to the longitudinal direction. Bending deformation in the width direction refers to a bending deformation in the spar cap 12 such that the area near the joint with the share web 13 is displaced toward the contraction side and the area near the center is displaced toward the pressure side, i.e., the spar cap 12 is curved so as to be convex toward the pressure side. This causes a crack 19B to propagate in the height direction (x direction in the figure) of the spar cap 12. In other words, in the spar cap of a wind turbine blade, a crack generally initiates near the base of the pressure side of the wind turbine blade and propagates in the longitudinal and height directions.

[0018] 5 is a schematic diagram showing one embodiment of a wind turbine blade of the present invention, and is an enlarged schematic diagram showing a cross section (xy plane) perpendicular to the longitudinal direction at a joint 14 between a spar cap 12 and a share web 13. In the following explanation, the definitions of the longitudinal direction, width direction, and height direction of the composite material will follow those of the spar cap.

[0019] In this embodiment, focusing on a pair of composite materials 201 and 202 adjacent to each other in the width direction, the composite material 201 has a convex rib (a rib continuing in the longitudinal direction) having a generally rectangular cross section formed at its left end in the width direction so as to protrude from the center, and the composite material 202 has a concave rib (a groove continuing in the longitudinal direction) having a generally rectangular cross section formed at its right end in the width direction so as to gouge out the center and correspond to the convex rib of the adjacent composite material 201. The convex rib of the composite material 201 is inserted into the concave rib of the composite material 202, and the gap between the two is filled with resin 16, thereby bonding the composite materials. That is, the composite materials 201 and 202 are adjacent to each other via an engagement structure configured so that the convex rib (engagement convex portion) formed at the left end of the composite material 201 and the concave rib (engagement concave portion) formed at the right end of the composite material 202 are engaged with each other. This structure suppresses the propagation of cracks that occur in the height direction of the spar cap due to bending deformation in the width direction, and ultimately suppresses buckling of the blade.

[0020] Furthermore, in this embodiment, a recessed streak similar to that at the right end of composite material 202 is formed at the right end of composite material 201, and a protruding streak similar to that at the left end of composite material 201 is formed at the left end of composite material 202, so that composite material 201 and composite material 202 have the same cross-sectional shape. That is, a set of composite materials made up of composite material 201 and composite material 202 consists of two composite materials having the same cross-sectional shape, with a mating protrusion formed at one end in the width direction (the left end in FIG. 5) and a mating recess formed at the other end in the width direction (the right end in FIG. 5). By using composite materials with such the same cross-sectional shape, it is possible to arrange a large number of composite materials adjacent to each other via the mating structure, using composite materials produced using a common molding die.

[0021] In the present invention, the pair of composite materials adjacent in the width direction via the interlocking structure may exist as at least a part of the composite materials constituting the spar cap, but it is preferable that such a pair exists at least in the central portion in the width direction, particularly in the central portion on the pressure side, where cracks are more likely to occur. However, if such a pair exists only in the central portion in the width direction, there is a possibility that the starting point of cracks will move to a location in the spar cap where no such pair exists. Therefore, it is preferable that 50% or more of the composite materials constituting the spar cap are adjacent in the width direction via the interlocking structure, and it is more preferable that all of the composite materials constituting the spar cap are adjacent in the width direction via the interlocking structure.

[0022] 6A is a schematic diagram showing another embodiment of the wind turbine blade of the present invention, showing an enlarged cross section (xy plane) perpendicular to the longitudinal direction at the joint between the spar cap and the share web. In this embodiment, focusing on a pair of composite materials 211 and 212 adjacent to each other in the width direction, composite material 211 has a step at its left end in the width direction that continues in the longitudinal direction so that its upper half protrudes (its lower half is missing), and composite material 212 has a step at its right end in the width direction that continues in the longitudinal direction so that its lower half protrudes (its upper half is missing). Composite materials 211 and 212 are bonded together by having the steps mesh with each other and filling the gap between them with resin 16. In other words, the protruding upper half of the step at the left end of composite material 211 can be seen as a mating convex portion, and the missing upper half at the right end of composite material 212 can be seen as a mating concave portion, and this pair of composite materials are adjacent in the width direction via a mating structure configured so that the mating convex portion of composite material 211 and the mating concave portion of composite material 212 can fit together.

[0023] Furthermore, in this embodiment, a step similar to that at the right end of composite material 212 is formed at the right end of composite material 211, and a step similar to that at the left end of composite material 211 is formed at the left end of composite material 212, so that composite material 211 and composite material 212 have the same cross-sectional shape. A composite material having such a step that is continuous in the longitudinal direction at its widthwise end can be molded more easily than the composite material having the ridges or grooves used in the embodiment shown in Figure 5 above. Therefore, a large number of composite materials can be arranged adjacent to each other via an interlocking structure at lower cost.

[0024] In this embodiment, if the missing lower half of the step of composite material 211 is viewed as a mating recess and the protruding upper half of the step of composite material 212 is viewed as a mating convex portion, then this pair of composite materials can also be said to be adjacent via a mating structure configured so that the mating recess of composite material 211 and the mating convex portion of composite material 212 fit together. 5, composite material 201 has longitudinally continuous cutouts with rectangular cross sections formed at two locations, one above the other, on the left end in the width direction, and composite material 202 has longitudinally continuous ribs with rectangular cross sections formed at two locations, one above the other, on the right end in the width direction, that correspond to the cutouts of composite material 201. In other words, composite materials 201 and 202 can be considered to be adjacent to each other via an interlocking structure configured so that an interlocking protrusion formed at the left end of composite material 202 interlocks with an interlocking recess formed at the right end of composite material 201. As such, the terms "interlocking protrusion" and "interlocking recess" used in this specification are concepts that arise from the relationship between the shapes of the two composite materials of interest, and it will be readily apparent to those skilled in the art that the positions of the interlocking protrusions and interlocking recesses cannot always be absolutely determined when only one composite material is viewed.

[0025] Furthermore, in the present invention, the mating convex portion may have a shape in which its height decreases toward the tip of the convex portion, and the mating concave portion may have a shape in which its height decreases toward the bottom of the concave portion. This shape can alleviate stress concentration that occurs at the corners of the tip of the mating convex portion, thereby preventing the composite material from breaking. In particular, it is preferable that the mating convex portion and mating concave portion have a shape in which their height decreases at a certain angle in the width direction (hereinafter referred to as the "inclination angle"). However, if the inclination angle is too large, the crack suppression effect may not be sufficient, so it is more preferable that the inclination angle be greater than 0° and less than or equal to 5°.

[0026] 6B is a schematic diagram showing another embodiment of the wind turbine blade of the present invention, showing an enlarged cross section (xy plane) perpendicular to the longitudinal direction at the joint between the spar cap and the share web. In this embodiment, focusing on a pair of composite materials 221 and 222 adjacent to each other in the width direction, the left end of composite material 221 in the width direction forms a wedge-shaped portion with a generally triangular cross section whose height decreases toward the tip. In contrast, the right end of composite material 222 in the width direction forms a recessed portion with a generally triangular cross section whose height decreases toward the back, corresponding to the wedge-shaped portion of composite material 221. The wedge-shaped portion of composite material 221 is inserted into the recessed portion of composite material 222, and the two composite materials are bonded together by filling the gap between them with resin 16. That is, composite material 221 and composite material 222 are adjacent in the width direction via an interlocking structure configured to interlock a wedge-shaped portion (interlocking protrusion) formed at the left end of composite material 221 with a recessed portion (interlocking recess) formed at the right end of composite material 222. In addition to the above-mentioned effects, this structure makes it difficult for initial cracks to occur because the direction of crack propagation in the height direction is oblique. Furthermore, because crack propagation can be suppressed at the apex of the wedge-shaped portion, buckling of the blade is suppressed.

[0027] As described above, in this embodiment as well, if the upper and lower missing portions in the cross section of the wedge-shaped portion of composite material 221 are viewed as fitting recesses, and the upper and lower protruding portions in the cross section of the recessed portion of composite material 222 are viewed as fitting protrusions, then it can be said that this pair of composite materials are adjacent via a fitting structure configured so that the fitting recess of composite material 231 fits into the fitting protrusion of composite material 222. Furthermore, no matter which way it is viewed, this embodiment can be said to be an example in which the height of the fitting protrusion decreases toward the tip of the protrusion, and the height of the fitting recess decreases toward the bottom of the recess.

[0028] In the wind turbine blade of the present invention, the composite materials constituting the spar cap are preferably arranged symmetrically with respect to the center line in the width direction of the cross section perpendicular to the longitudinal direction of the spar cap. By arranging them symmetrically, it is expected that the deformation behavior of the spar cap in the width direction will not change peculiarly, and height-wise cracks caused by bending deformation in the width direction will be more effectively suppressed. [Example]

[0029] (Evaluation method) Figure 7 shows the procedure for deriving the buckling load caused by the occurrence and propagation of cracks in the spar cap when the wind hits the surface of a wind turbine blade. First, in Step 1, an overall analysis is performed, using the wind pressure as input information to derive the amount of deformation over the entire length of the wind turbine blade. Next, in Step 2, a detailed analysis is performed, using the deformation derived in Step 1 as input information for only a portion of the wind turbine blade to analyze the amount of crack propagation and buckling occurrence.

[0030] The overall analysis of Step 1 was evaluated as shown in Figure 8. Figure 8A is a schematic diagram showing a distributed load of 5778 Pa, simulating wind (indicated by the arrow in the figure), being applied to the surface of the wind turbine blade, and evaluates the amount of displacement in the x direction of each part of the spar cap when the root end of the wind turbine blade is completely restrained all around. Figure 8B shows an arbitrary cross section in the xy plane.

[0031] The Step 2 detailed analysis was evaluated as shown in Figure 9. In Figure 9A, the region from the root end of the wind turbine blade to 7,500 m in the longitudinal direction was extracted, and forced displacement was applied to the longitudinal end based on the deformation amount derived from the Step 1 overall analysis to evaluate the progression of cracks and the occurrence of buckling.

[0032] Figure 9B is an arbitrary cross section in the XY plane, and assumes that multiple, approximately long, plate-shaped composite materials are arranged in the width and height directions along the longitudinal direction, and that the composite materials are bonded together with resin. The generation and propagation of cracks occurring between the composites and buckling of the spar cap are taken into consideration.

[0033] Assuming a configuration in which the shape of the drawn material in level 3 was changed as shown in Table 1, simulations were performed for a total of three levels in the cross section perpendicular to the longitudinal direction of the spar cap: level 1, which does not have a mating convex portion; level 2, which has a mating convex portion in the height direction; and level 3, which has a mating convex portion in the width direction.

[0034] As a result of the simulation, as shown in Figure 10, it was shown that the buckling strength of the spar cap (level 3) of the embodiment shown in Figure 5, in which a mating protrusion is formed at the widthwise end, is greater than that of levels 1 and 2.

[0035] [Table 1] [Explanation of symbols]

[0036] 1. Windmill blades 2. Tower 3 Nacelle 4 Hub 11 Skin material 12 Super Cap 13 Share Web 14 Spar cap and share web joint 15 General composite material with straight edges in the width direction 16 Resin 19A Longitudinal crack 19B Crack extending in the vertical direction 201, 202 Composite material having convex and concave stripes at the widthwise ends 211, 212 Composite material having steps at the widthwise ends 221, 222 Composite material having a wedge-shaped portion and a recessed portion at the widthwise end

Claims

1. A wind turbine blade including a spar cap essentially made of a plurality of substantially long plate-shaped composite materials arranged in the width direction and height direction of the wind turbine blade, In a cross section perpendicular to the longitudinal direction of the spar cap, at least one pair of composite materials adjacent to each other in the width direction are adjacent via an interlocking structure configured so that an interlocking protrusion formed on an end portion in the width direction of one composite material interlocks with an interlocking protrusion formed on an end portion in the width direction of the other composite material.

2. 2. The wind turbine blade according to claim 1, wherein the set of composite materials comprises two composite materials each having a fitting convex portion formed at one end in a width direction and a fitting concave portion formed at the other end in the width direction.

3. The wind turbine blade according to claim 1 or 2, wherein all of the composite materials constituting the spar cap are adjacent to each other via the fitting structure.

4. 3. The wind turbine blade according to claim 1, wherein the fitting protrusion has a shape whose height decreases toward a tip, and the fitting recess has a shape whose height decreases toward a depth corresponding to the fitting protrusion.

5. 5. The wind turbine blade according to claim 4, wherein the fitting convex portion has a shape whose height decreases at a constant inclination angle toward the tip, and the fitting concave portion has a shape whose height decreases at a constant inclination angle toward the back, corresponding to the fitting convex portion.

6. The wind turbine blade according to claim 5, wherein the tilt angle is greater than 0° and not greater than 5°.

7. The wind turbine blade according to claim 1 or 2, wherein the fitting protrusion and the fitting recess of the composite material are both substantially rectangular in a cross section perpendicular to the longitudinal direction.

8. The wind turbine blade according to claim 1 or 2, wherein the mating protrusion and the mating recess of the composite material are both substantially triangular in a cross section perpendicular to the longitudinal direction.

9. The wind turbine blade according to claim 1 or 2, wherein in the spar cap, the composite materials are arranged symmetrically with respect to a center line in the cross section.

10. 3. The wind turbine blade according to claim 1, wherein the composite material is a pultrusion molded product of carbon fiber reinforced resin.

11. A wind turbine for wind power generation, comprising the wind turbine blade according to claim 1 or 2.

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