Patent Description:
The present disclosure relates generally to wind turbines, and more particularly to a scarf connection for a rotor blade of a wind turbine.

Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having a rotatable hub with one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

The rotor blades generally include a suction side shell and a pressure side shell typically formed using molding processes that are bonded together at bond lines along the leading and trailing edges of the blade. Further, the pressure and suction shells are relatively lightweight and have structural properties (e.g., stiffness, buckling resistance and strength) which are not configured to withstand the bending moments and other loads exerted on the rotor blade during operation. Thus, to increase the stiffness, buckling resistance and strength of the rotor blade, the body shell is typically reinforced using one or more structural components (e.g. opposing spar caps with a shear web configured therebetween) that engage the inner pressure and suction side surfaces of the shell halves. The spar caps and/or shear web may be constructed of various materials, including but not limited to glass fiber laminate composites and/or carbon fiber laminate composites.

When designing the internal structural components of the rotor blades, the optimum material with regard to strength, weight, E-modulus and cost etc. is often not the same as the rest of the components in the rotor blade. For example, in the spar caps, the preferred material for the majority of the component may be a glass fiber reinforced composite due to low cost and limited mechanical requirements. In contrast, the preferred material for the other portions of the component may be carbon fiber reinforced composite due to the higher stiffness and lower weight. The physical properties (e.g. stiffness and thermal expansion) of such materials, however, are very different. Therefore, it can be difficult to join such parts effectively. Document <CIT> discloses a wind turbine blade with an improved fibre transition. A scarf connection between two blade elements is provided by laying up a primary fibre material which comprises a number of outer skin layers, a number of tapered reinforcement layers and a number of inner skin layers which are laid over the ends of the tapered reinforcement layers. Subsequently to curing the first blade element of the primary fibre material, a secondary fibre material which comprises a number of reinforcement layers and a number of inner skin layers is laid over the cured first blade element. Document <CIT> discloses a method of joining blade sections using thermoplastics. A thermoplastic material is arranged at each of two joint ends which form a scarf joint. The joint ends are welded together via thermoplastic welding.

Accordingly, the present disclosure is directed to an improved scarf connection for wind turbine rotor blades.

In one aspect, the present disclosure is directed to a rotor blade for a wind turbine. The rotor blade includes at least one blade segment defining an airfoil surface and an internal support structure. The internal support structure is formed, at least in part, of a first portion constructed of a first composite material and a second portion constructed of a different, second composite material, the second composite material arranged in a plurality of layers. The first and second portions are connected together via a scarf joint. Each of the plurality of layers of the second composite material includes an end that terminates at the scarf joint. The scarf joint includes a different, third composite material arranged between the first and second composite materials. The third composite material includes a plurality of segments, each of which is arranged so as to completely wrap the ends of the plurality of layers of the second composite material.

In an embodiment, the second portion of the internal support structure may be constructed, at least in part, of a plurality of pultruded plates. In such embodiments, the plurality of pultruded plates may be formed of the second composite material.

In an embodiment, the third composite material may also include a plurality of layers. As such, in certain embodiments, one or more of the plurality of layers of the third composite material may extend between one or more of the pultruded plates.

In another embodiment, each of the plurality of segments of the third composite material may be spaced apart from each of the plurality of layers of the third composite material. In further embodiments, each of the plurality of layers of the third composite material may terminate before respective ends of the pultruded plates of the second composite material.

In additional embodiments, each of the plurality of segments of the third composite material may include at least one of a C-shape, a V-shape, a U-shape, or an L-shape that wraps at least partially around one of the ends of the plurality of layers of the second composite material.

In particular embodiments, each of the plurality of segments of the third composite material may include the L-shape. In such embodiments, adjacent L-shaped segments may be secured together in an opposing direction so as to wrap around the ends of adjacent layers of the plurality of layers of the second composite material.

In an embodiment, adjacent segments of the plurality of segments of the third composite material may contact each other.

In several embodiments, the first, second, and third composite materials may be a thermoset resin or a thermoplastic resin. In an embodiment, at least one of the first composite material, the second composite material, and/or the third composite material may be reinforced with one or more fiber materials. In such embodiments, the fiber material(s) may include glass fibers, carbon fibers, polymer fibers, wood fibers, bamboo fibers, ceramic fibers, nanofibers, metal fibers, and/or combinations thereof. In another embodiment, third composite material may be a composite veil material, a biax composite material, or a chopped strand mat.

In another aspect, the present disclosure is directed to a method of joining first and second structures of a rotor blade of a wind turbine. The method includes arranging the first structure with the second structure at a scarf joint. The first structure is constructed of a first composite material. The second structure is constructed of a different, second composite material. The second structure also includes a plurality of layers, each of which includes an end that terminates at the scarf joint. The method also includes arranging a plurality of segments of a different, third composite material between the first and second composite materials at the scarf joint so as to completely wrap the ends of the plurality of layers of the second composite material with the plurality of segments of the third composite material. Further, the method includes infusing the scarf joint so as to join the first and second structures together. It should be understood that the method may further include any of the additional features and/or steps as described herein.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present invention. In the illustrated embodiment, the wind turbine <NUM> is a horizontal-axis wind turbine. In addition, as shown, the wind turbine <NUM> may include a tower <NUM> that extends from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, a generator <NUM> positioned within the nacelle <NUM>, a gearbox <NUM> coupled to the generator <NUM>, and a rotor <NUM> that is rotationally coupled to the gearbox <NUM> with a rotor shaft <NUM>. Further, as shown, the rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outward from the rotatable hub <NUM>. As shown, the rotor blade <NUM> includes a blade tip <NUM> and a blade root <NUM>.

Referring now to <FIG>, a plan view of one of the rotor blades <NUM> of <FIG> is illustrated. As shown, the rotor blade <NUM> may include a first blade segment <NUM> and a second blade segment <NUM>. Further, as shown, the first blade segment <NUM> and the second blade segment <NUM> may each extend in opposite directions from a chord-wise joint <NUM>. In addition, as shown, each of the blade segments <NUM>, <NUM> may include at least one shell member defining an airfoil surface. The first blade segment <NUM> and the second blade segment <NUM> are connected by at least an internal support structure <NUM> extending into both blade segments <NUM>, <NUM> to facilitate joining of the blade segments <NUM>, <NUM>. The arrow <NUM> shows that the segmented rotor blade <NUM> in the illustrated example includes two blade segments <NUM>, <NUM> and that these blade segments <NUM>, <NUM> are joined by inserting the internal support structure <NUM> into the second blade segment <NUM>. In addition, as shown, the second blade segment includes multiple spar structures <NUM> (also referred to herein as spar caps) that extend lengthwise for connecting with a blade root section <NUM> of the rotor blade <NUM> and with the first blade segment <NUM>. In addition, as shown, the first blade segment <NUM> may also include one or more scarf joints <NUM> at an interface of one or more pultrusions (e.g. pultruded components or plates) and a composite structure as discussed in more detail with respect to <FIG>.

Referring now to <FIG>, a perspective view of a section of the first blade segment <NUM> according to the present disclosure is illustrated. As shown, the first blade segment <NUM> includes a beam structure <NUM> that forms a portion of the internal support structure <NUM> and extends lengthwise for structurally connecting with the second blade segment <NUM>. Further, as shown, the beam structure <NUM> forms a part of the first blade segment <NUM> having an extension protruding from a spar section <NUM>, thereby forming an extending spar section. The beam structure <NUM> includes a shear web <NUM> connected with a suction side spar cap <NUM> and a pressure side spar cap <NUM>. As such, the scarf joints <NUM> described herein may be part of the beam structure <NUM>.

Moreover, as shown, the first blade segment <NUM> may include one or more first pin joints towards a first end <NUM> of the beam structure <NUM>. In one embodiment, the pin joint may include a pin that is in a tight interference fit with a bushing. More specifically, as shown, the pin j oint(s) may include one pin joint tube <NUM> located on the beam structure <NUM>. Thus, as shown, the pin joint tube <NUM> may be oriented in a span-wise direction. Further, the first blade segment <NUM> may also include a pin joint slot <NUM> located on the beam structure <NUM> proximate to the chord-wise joint <NUM>. Moreover, as shown, the pin joint slot <NUM> may be oriented in a chord-wise direction. In one example, there may be a bushing within the pin joint slot <NUM> arranged in a tight interference fit with a pin joint tube or pin (shown as pin <NUM> in <FIG>). Further, the first blade segment <NUM> may include multiple second pin joint tubes <NUM>, <NUM> located at the chord-wise joint <NUM>. Thus, as shown, the second pin joint tubes <NUM>, <NUM> may include a leading edge pin joint tube <NUM> and a trailing edge pin joint tube <NUM>. Further, each of the second pin joint tubes <NUM>, <NUM> may be oriented in a span-wise direction. In addition, as shown, each of the second pin joint tubes <NUM>, <NUM> may include multiple flanges <NUM>, <NUM>, respectively, that are configured to distribute compression loads at the chord-wise joint <NUM>.

It is to be noted that the pin joint tube <NUM> located at the first end of the beam structure <NUM> may be separated span-wise with the multiple second pin joint tubes <NUM>, <NUM> located at the chord-wise joint <NUM> by an optimal distance D. This optimal distance D may be such that the chord-wise joint <NUM> is able to withstand substantial bending moments caused due to shear loads acting on the chord-wise joint <NUM>. In another embodiment, each of the pin joints connecting the first and second blade segments <NUM>, <NUM> may include an interference-fit steel bushed joint.

Referring now to <FIG>, a perspective view of a section of the second blade segment <NUM> at the chord-wise joint <NUM> according to the present disclosure is illustrated. As shown, the second blade segment <NUM> includes a receiving section <NUM> extending lengthwise within the second blade segment <NUM> for receiving the beam structure <NUM> of the first blade segment <NUM>. The receiving section <NUM> includes the spar structures <NUM> that extend lengthwise for connecting with the beam structure <NUM> of the first blade segment <NUM>. As shown, the second blade segment <NUM> may further include pin joint slots <NUM>, <NUM> for receiving pin joint tubes <NUM>, <NUM> (shown in <FIG>) of the first blade segment <NUM> and forming tight interference fittings. In one example, each of the multiple pin joint slots <NUM>, <NUM> may include multiple flanges <NUM>, <NUM>, respectively, that are configured to distribute compression loads at the chord-wise joint <NUM>.

Referring now to <FIG>, an assembly <NUM> of the rotor blade <NUM> having the first blade segment <NUM> joined with the second blade segment <NUM> according to the present disclosure is illustrated. As shown, the assembly <NUM> illustrates multiple supporting structures beneath outer shell members of the rotor blade <NUM> having the first blade segment <NUM> joined with the second blade segment <NUM>. Further, as shown, the receiving section <NUM> includes the multiple spar structures <NUM> extending lengthwise and supports the beam structure <NUM>. The receiving section <NUM> also includes a rectangular fastening element <NUM> that connects with the pin joint tube <NUM> of the beam structure <NUM> in the span-wise direction. Further, the first and the second blade segments <NUM>, <NUM> may also include chord-wise members <NUM>, <NUM> respectively at the chord-wise joint <NUM>. Further, as shown, the chord-wise members <NUM>, <NUM> may include leading edge pin openings <NUM> and trailing edge pin openings <NUM> that allows pin joint connections between the first and second blade segments <NUM>, <NUM>. For example, as shown, the chord-wise members <NUM>, <NUM> are connected by pin joint tubes <NUM> and <NUM> that are in tight interference fit with bushings located in the leading edge pin openings <NUM> and the trailing edge pin openings <NUM>. In another embodiment, each of the spar structures <NUM>, the rectangular fastening element <NUM>, and the chord-wise members <NUM>, <NUM> may be constructed of glass reinforced fibers. In this example, the assembly <NUM> may also include multiple lightening receptor cables <NUM> that are embedded between the multiple pin joint tubes or pins <NUM>, <NUM> and the bushing connections attached to the chord-wise members <NUM>, <NUM>.

Referring now to <FIG>, an exploded perspective view of the multiple supporting structures of the assembly <NUM> towards the receiving section <NUM> of the rotor blade <NUM> is illustrated. As shown, a pair of spar structures <NUM> is configured to receive the beam structure <NUM> and includes pin joint slots <NUM>, <NUM> that are aligned with the pin joint slot <NUM> of the beam structure <NUM> through which a pin joint tube or pin <NUM> may be inserted. Further, the pin <NUM> is configured to remain in a tight interference fit within the aligning pin joint slots <NUM>, <NUM>, <NUM> such that spar structures <NUM> and the beam structure <NUM> are joined together by during assembling. Further, <FIG> also illustrates the rectangular fastening element <NUM> that includes a pin joint slot <NUM> configured for receiving the pin joint tube <NUM> of the beam structure <NUM>. As such, the pin joint tube <NUM> is configured to form a tight interference fit bolted joint. Further, the pair of spar structures <NUM> may be joined together at one end <NUM> using any suitable adhesive material or an elastomeric seal.

Referring to <FIG>, detailed plan views of one embodiment of the connection between one or more pultruded parts <NUM> and an adjacent composite structure of the first blade segment <NUM> of the rotor blade <NUM> of <FIG> are illustrated. As shown, the connection is a scarf joint <NUM>. Further, as shown particularly in <FIG>, the first blade segment <NUM> may include at least two scarf joints <NUM>. In addition, as shown, a first portion <NUM> or end of the first blade segment <NUM> (e.g. the portion of the beam structure <NUM> adjacent to the pin joint tube <NUM> of the receiving end <NUM>) may be constructed of a first composite material <NUM>, whereas a second portion <NUM> of the first blade segment <NUM> may be constructed of a different, second composite material <NUM>. Thus, as shown, the scarf joint <NUM> may further include a different, third composite material <NUM> arranged between the first and second composite materials <NUM>, <NUM>.

More specifically, as shown in the illustrated embodiment, the second portion <NUM> of the first blade segment <NUM> may be constructed, at least in part, of a plurality of layers <NUM> formed of the second composite material <NUM>. For example, in one embodiment, the plurality of layers <NUM> may be a plurality of pultruded plates. Thus, as shown, each of the pultruded plates <NUM> may be formed of the second composite material <NUM>. In addition, as shown, each of the layers <NUM> may have an end <NUM> that terminates at the scarf joint <NUM>. Further, as shown, the third composite material <NUM> may include a plurality of segments <NUM>. More specifically, as shown, each of the segments <NUM> may be arranged so as to completely wrap the ends <NUM> of the layers <NUM> of the second composite material <NUM>. Thus, as shown, in an embodiment, adjacent segments <NUM> of the third composite material <NUM> may contact each other.

Still referring to <FIG>, the third composite material <NUM> may also include a plurality of layers <NUM> arranged between each of the pultruded plates <NUM>. In such embodiments, as shown, one or more of the layers <NUM> of the third composite material <NUM> may extend between one or more of the pultruded plates <NUM>. Further, in an embodiment, as shown, each of the plurality of layers <NUM> of the third composite material <NUM> may terminate before respective ends <NUM> of the pultruded plates <NUM> of the second composite material <NUM>.

Thus, as shown particularly in <FIG>, each of the plurality of segments <NUM> of the third composite material <NUM> may be spaced apart from each of the layers <NUM> of the third composite material <NUM> such that there is a gap <NUM> therebetween.

In addition, each of the segments <NUM> of the third composite material <NUM> may have any suitable shape, including but limited to, a C-shape, a V-shape, a U-shape, or an L-shape that wraps at least partially around one of the ends <NUM> of the layers <NUM> of the second composite material <NUM>. For example, as shown in <FIG>, the segments <NUM> have a C-shape. In another embodiment, as shown in <FIG>, the segments <NUM> have a V-shape. Thus, in an embodiment, by providing such shapes of the third composite material <NUM> at the ends <NUM> of pultruded plates <NUM>, the pultruded plates <NUM> are completely covered, without requiring the interleaving layers <NUM> of the third composite material <NUM> to extend past the ends <NUM> of the pultruded plates <NUM>. This results in better resin infusion between the pultruded plates <NUM> and therefore increases joint strength. It should also be understood that the composite material forming the segments <NUM> may be the same as the interleaving layer material. However, it should also be understood that the composite material forming the segments <NUM> may be a different material than the interleaving layer material.

In alternative embodiments, the segments <NUM> of the third composite material <NUM> may be provided in a split fashion. For example, as shown in <FIG>, the segments <NUM> of the third composite material <NUM> may include the L-shape. In such embodiments, as shown, adjacent L-shaped segments <NUM> may be secured together (e.g. via adhesive, resin, tape, etc.) in an opposing direction so as to wrap around the ends <NUM> of adjacent layers <NUM> of the second composite material <NUM>. More specifically, in one embodiment, in order to provide the third composite material <NUM> at the ends <NUM> in a split fashion, two interleaving L-shaped fabrics can be joined with adhesive and then can be peeled at the ends to join one piece of the third composite material <NUM> with another at the ends. In such embodiments, care should be taken that the thickness of the interleaving composite material <NUM> and the combined thickness of the two joined segments <NUM> in between the pultruded plates <NUM> are equal. Such an embodiment assists in maintaining uniform thickness between the interleaving composite material <NUM> and two joined segments <NUM> that are in between the pultruded plates <NUM>.

Thus, as shown, the pultruded plates <NUM> are completely covered at their ends <NUM> by the joined segments <NUM>, while the interleaving composite material <NUM> does not extend past the pultruded plates <NUM>. This results in better resin infusion between pultrusions and/or increases joint strength.

In further embodiments, the first, second, and third composite materials <NUM>, <NUM>, <NUM> may include a thermoset resin or a thermoplastic resin. The thermoplastic materials as described herein may generally encompass a plastic material or polymer that is reversible in nature. For example, thermoplastic materials typically become pliable or moldable when heated to a certain temperature and returns to a more rigid state upon cooling. Further, thermoplastic materials may include amorphous thermoplastic materials and/or semi-crystalline thermoplastic materials. For example, some amorphous thermoplastic materials may generally include, but are not limited to, styrenes, vinyls, cellulosics, polyesters, acrylics, polysulphones, and/or imides. More specifically, exemplary amorphous thermoplastic materials may include polystyrene, acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), glycolised polyethylene terephthalate (PET-G), polycarbonate, polyvinyl acetate, amorphous polyamide, polyvinyl chlorides (PVC), polyvinylidene chloride, polyurethane, or any other suitable amorphous thermoplastic material. In addition, exemplary semi-crystalline thermoplastic materials may generally include, but are not limited to polyolefins, polyamides, fluropolymer, ethyl-methyl acrylate, polyesters, polycarbonates, and/or acetals. More specifically, exemplary semi-crystalline thermoplastic materials may include polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polypropylene, polyphenyl sulfide, polyethylene, polyamide (nylon), polyetherketone, or any other suitable semi-crystalline thermoplastic material.

Further, the thermoset materials as described herein may generally encompass a plastic material or polymer that is non-reversible in nature. For example, thermoset materials, once cured, cannot be easily remolded or returned to a liquid state. As such, after initial forming, thermoset materials are generally resistant to heat, corrosion, and/or creep. Example thermoset materials may generally include, but are not limited to, some polyesters, some polyurethanes, esters, epoxies, or any other suitable thermoset material.

In addition, the first, second, and/or third material <NUM>, <NUM>, <NUM> may be reinforced with one or more fiber materials. In such embodiments, the fiber material(s) may include glass fibers, carbon fibers, polymer fibers, wood fibers, bamboo fibers, ceramic fibers, nanofibers, metal fibers, or combinations thereof. In addition, the direction or orientation of the fibers may include quasi-isotropic, multiaxial, unidirectional, biaxial, triaxial, or any other another suitable direction and/or combinations thereof. Thus, in certain embodiments, the third composite material <NUM> may include, for example, a composite veil material, a biax composite material, or a chopped strand mat.

Referring now to <FIG>, a flow chart <NUM> of a method <NUM> of joining first and second structures (such as first and second portions of the beam structure <NUM>) of a rotor blade of a wind turbine according to the present disclosure is illustrated. In general, the method <NUM> will be described herein with reference to the wind turbine <NUM> and the rotor blade <NUM> shown in <FIG>. However, it should be appreciated that the disclosed method <NUM> may be implemented with rotor blades having any other suitable configurations. In addition, although <FIG> depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and/or adapted in various ways without deviating from the scope of the present disclosure.

As shown at (<NUM>), the method <NUM> may include arranging the first structure with the second structure at a scarf joint. The first structure is constructed of a first composite material. The second structure is constructed of a different, second composite material. The second structure also includes a plurality of layers, each of which includes an end that terminates at the scarf joint. As shown at (<NUM>), the method <NUM> may include arranging a plurality of segments of a different, third composite material between the first and second composite materials at the scarf joint so as to completely wrap the ends of the plurality of layers of the second composite material with the plurality of segments of the third composite material. As shown at (<NUM>), the method <NUM> may include infusing the scarf joint so as to join the first and second structures together.

The skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art.

Claim 1:
A rotor blade for a wind turbine, comprising:
at least one blade segment (<NUM>, <NUM>) defining an airfoil surface and comprising an internal support structure (<NUM>),
wherein the internal support structure is formed, at least in part, of a first portion (<NUM>) constructed of a first composite material (<NUM>) and a second portion (<NUM>) constructed of a different, second composite material (<NUM>), the second composite material arranged in a plurality of layers (<NUM>), the first and second portions connected together via a scarf joint (<NUM>), each of the plurality of layers of the second composite material comprising an end (<NUM>) that terminates at the scarf j oint, the scarf joint comprising a different, third composite material (<NUM>) arranged between the first and second composite materials, the third composite material comprising a plurality of segments (<NUM>), characterized in that the plurality of segments are arranged so as to completely wrap the ends of the plurality of layers of the second composite material.