Patent Application
20140119937
The present disclosure relates in general to rotor blades for wind turbines, and more particularly to a tensioned fabric rotor blade and methods for assembling such rotor blades for wind turbines.
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 modern wind turbine typically includes a tower, generator, gearbox, nacelle, and 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 construction of a modern rotor blade generally includes skin or shell components, span-wise extending spar caps, and one or more shear webs. The shell components, typically manufactured from layers of fiber composite and a lightweight core material, form the exterior aerodynamic foil shape of the rotor blade. The spar caps provide increased rotor blade strength by integrating one or more structural elements running along the span of the rotor blade on both interior sides of the rotor blade. Shear webs are structural beam-like components running essentially perpendicular between the top and bottom spar caps and extending across the interior portion of the rotor blade between the outer skins.
The size, shape, and weight of rotor blades are factors that contribute to energy efficiencies of wind turbines. An increase in rotor blade size increases the energy production of a wind turbine, while a decrease in weight furthers the efficiency of a wind turbine. Furthermore, as rotor blade sizes grow, extra attention needs to be given to the structural integrity of the rotor blades. Presently, large commercial wind turbines in existence and in development are capable of generating from about 1.5 to about 12.5 megawatts of power. These larger wind turbines may have rotor blade assemblies larger than 90 meters in diameter. Additionally, advances in rotor blade shape encourage the manufacture of a forward swept-shaped rotor blade having a general arcuate contour from the base to the tip of the blade, providing improved aerodynamics. Accordingly, efforts to increase rotor blade size, decrease rotor blade weight, and increase rotor blade strength, while also improving rotor blade aerodynamics, aid in the continuing growth of wind turbine technology and the adoption of wind energy as an alternative energy source.
As the size of wind turbines increases, particularly the size of the rotor blades, so do the respective costs of manufacturing, transporting, and assembly of the wind turbines. The economic benefits of increased wind turbine sizes must be weighed against these factors. For example, to improve stiffness/weight ratio, the current blade architecture demands higher stiffness materials (e.g., carbon) to be used in critical load bearing components, such as the spar caps, which significantly increases the overall cost of wind energy production. As blades get wider and longer, transportation limitations, in both maximum chord width and blade length, start to pose restrictions on blade design. Conventional blade manufacturing processes generally require high upfront equipment costs in molds and associated labor costs, particularly for the shell components.
One known strategy for reducing the costs of pre-forming, transporting, and erecting wind turbines having rotor blades of increasing sizes is to manufacture the rotor blades in blade sections. Each blade section may include a portion of the span-wise extending spar caps and shear webs, or each blade section may be assembled onto large spar caps that extend the full span of the rotor blade. After the individual blade sections are transported to the erection destination, the blade sections are assembled. However, manufacture of current blade sections is difficult. For example, current manufacturing and assembly techniques have encountered problems with bonding line control, edge contour control, reparability of the various blade sections, weight reduction, and the handling of larger components, such as span-wise extending spar caps.
Thus, an improved rotor blade and method for assembling such a rotor blade for a wind turbine would be desired in the art.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one embodiment, a rotor blade for a wind turbine is disclosed. The blade includes an internal support structure extending span-wise from a blade root to a blade tip. This internal support structure includes a plurality of fixed, spaced apart ribs extending in a generally chord-wise direction. The ribs have a generally aerodynamic blade contour. A plurality of chord-wise oriented fabric strips are affixed to the ribs in a tensioned state, wherein the fabric strips define an aerodynamic outer skin of the rotor blade.
In various embodiments, the internal support structure may include any manner of span-wise extending reinforcement or support elements interconnecting the ribs to add structural rigidity and support to the rotor blade. For example, in one embodiment, the span-wise extending support elements may include a plurality of strip members circumferentially spaced around the aerodynamic contour of ribs. The strip members may be directly connected to each other within the rotor blade, for example by a truss, brace, or other support member. In an alternate embodiment, the strips members may be spaced around the circumference of the ribs and not connected to each other.
In still a further embodiment, the internal support structure may include comprises a shear web interconnecting opposite spar caps, with the ribs fixed to the spar caps. Additional span-wise support elements may also be included in this embodiment, with the ribs also connected to these additional elements.
In certain embodiments, the support structure may also include a leading edge member and a trailing edge member (e.g., protective or structural cap members) interconnecting the ribs along the respective leading and trailing edge of the rotor blade.
In yet another embodiment, the support structure may be defined by a truss structure having chord-wise elements connected to span-wise elements so as to define a generally closed-cell skeleton frame structure, with the chord-wise elements defining the ribs. The tensioned fabric is connected to the ribs, and may also be connected to the span-wise elements.
The ribs may be variously configured in accordance with aspects of the invention. For example, in one embodiment the ribs formed from multiple components that are attached to the span-wise extending support elements to define a generally closed loop structure once assembled.
In an alternate embodiment, the ribs are individually formed closed loop elements that are subsequently fixed to the span-wise extending support elements. For example, the ribs may be separately formed in a filament winding process and subsequently fixed to the span-wise extending support elements. In an alternate embodiment, the ribs may be wound directly onto the span-wise extending support elements.
In particular embodiments, the fabric strips have a span-wise width so as to span between and attach to at least adjacent ones of the ribs. The opposed chord-wise edges of adjacent fabric strips may abut or overlap along a common rib.
The fabric strips may, in certain embodiments, have a chord-wise length such that opposite transverse edges of the fabric strips are joined together along a common one of the span-wise extending support elements, for example along a common spar cap, leading edge member, or trailing edge member.
It should be appreciated that any combination of finishing steps may be applied to the fabric strips to enhance the aerodynamic shape and performance of the rotor blade, including reinforcing the seams between adjacent strips, or coating the strips with a resin or other material to provide and essentially seamless outer surface.
The present invention also encompasses various method embodiments for making a rotor blade for a wind turbine, as described above. An exemplary method may include forming a span-wise internal support structure, such as any conventional shear web/spar cap, truss, or grid assembly. A plurality of aerodynamically-shaped ribs are configured on the internal support structure, with the ribs spaced apart span-wise along the internal support structure and extending in a generally chord-wise direction. Additional span-wise extending reinforcement or support elements may be added. A plurality of chord-wise oriented fabric strips are then wound under tension over the ribs. The fabric strips are tensioned over the rib structure to define an aerodynamic outer skin of the rotor blade. The fabric strips may also be tensioned in the chord-wise and span-wise direction.
The ribs may be formed by attaching multiple components to the spar caps of the internal support structure. In a particular method embodiment, the ribs are closed-loop elements formed in a filament winding process. For example, the ribs may be wound directly onto the internal support structure in one embodiment, or may be separately wound and subsequently joined to the internal support structure.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Referring to
The rotor blade 16 according to the present disclosure may include a plurality of individual fabric sections 40 between the blade tip 32 and the blade root 34. Each of fabric sections 40 may be uniquely configured so that the plurality of sections 40 define a complete rotor blade 16 having a designed aerodynamic profile, length, and other desired characteristics. For example, each of the fabric sections 40 may have an aerodynamic profile that corresponds to the aerodynamic profile of adjacent section 40. Thus, the aerodynamic profiles of the fabric sections 40 may form a continuous aerodynamic profile of the rotor blade 16.
The rotor blade 16 may, in exemplary embodiments, be curved. Curving of the rotor blade 16 may entail bending the rotor blade 16 in a generally flapwise direction and/or in a generally edgewise direction. The flapwise direction may generally be construed as the direction (or the opposite direction) in which the aerodynamic lift acts on the rotor blade 16. The edgewise direction is generally perpendicular to the flapwise direction. Flapwise curvature of the rotor blade 16 is also known as pre-bend, while edgewise curvature is also known as sweep. Thus, a curved rotor blade 16 may be pre-bent and/or swept. Curving may enable the rotor blade 16 to better withstand flapwise and edgewise loads during operation of the wind turbine 10, and may further provide clearance for the rotor blade 16 from the tower 12 during operation of the wind turbine 10.
The rotor blade 16 may further define a chord 42 and a span 44 extending in chord-wise and span-wise directions, respectively. As shown, the chord 42 may vary throughout the span 44 of the rotor blade 16.
The configuration of the internal support structure 50 may vary widely within the scope and spirit of the invention. For example, in the embodiments of
In an alternative embodiment illustrated for example in
In various embodiments, the internal support structure includes a plurality of span-wise extending support elements that interconnect the ribs 62 and add overall structural support and rigidity to the internal support structure 50. For example, in the embodiment of
In the embodiment of
In the embodiment of
The various components of the internal support structure 50 (e.g., ribs 62, truss structure 53, span-wise strip or spar members 51, and so forth) may be formed from any suitable structural material, including metals (e.g., steel, aluminum, titanium, and their alloys or combinations thereof) or composites (e.g., GFRP, CFRP, natural composites, and sandwich composites (manufactured by hand lay-up or other methods). The materials may include a combination of metals and composites (including natural composites such as wood, and the like).
Referring to
The edges 68 of adjacent fabric strips 66 may be attached to the outer surface 64 of the ribs 62 in a direct abutting relationship, as depicted in
Referring to
In other embodiments, a mechanical fastener may be used to attached the edges 70 to the trailing edge of the blade in a tensioned state. Any type of fastener that is capable of grasping or otherwise attaching to the edges 70 of the fabric strips 66, maintaining the strips 66 in a tensioned state, and fixing the edges 70 to the blade structure along the trailing edge may be used in this regard.
As depicted by the arrows in
As depicted in the various embodiments, it should be appreciated that the fabric strips 66 may be attached in the spaces between the various structural support members, or affixed over the structural members, or a combination thereof
As can be particularly seen in
In an alternate embodiment depicted in
The blades 16 are not limited by any particular type of fabric for the fabric strips 66. A relatively low cost, light-weight architecture fabric may be desirable in certain embodiments. The fabric may be a woven or non-woven material, including film materials. The fabric material may be a single layer or formed from multiple layers, such as multi-axial fabrics. The fabric material may be resin impregnated and eventually cured to provide a relatively stiff outer skin to the blade 16. Certain types of architecture fabrics that may be used for the present invention include PTFE-coated fiberglass or PVC-coated polyester fabrics. ETFE film may also be suitable in certain environments.
Any manner of finishing process or product may be applied to the fabric strips 66 to provide a relatively smooth aerodynamic surface for the pressure 22 and suction 24 sides of the blade. For example, most architectural PVC polyesters have a top coating applied to their exterior surface to improve the appearance and extend the life of the material. Typically, this top coat may be acrylic, polyvinylidene fluoride (PVDF), a PVDF top coat, or a polyvinyl fluoride (PVF) film layer that is laminated to the PVC fabric during manufacture. As mentioned, the fabric strips 66 may be impregnated with a resin, or coated with a resin after application to the ribs 62. Reinforcing tapes may be applied over the seams between adjacent fabric strips 66.
As mentioned, the ribs 62 may be formed in a filament winding process. In a particular filament winding process as depicted in
Once a sufficient length of the continuous filaments are wound onto the formers 73 such that the ribs 62 have the desired degree of thickness, rigidity, and stability, the process is terminated and the ribs are cured. The resin may be sufficient for adhering the ribs 68 directly onto the spar caps 56 in the curing process. However, additional adhesives or bonding material may also be utilized to insure a stable joint between the ribs 62 and spar caps 56. Once the ribs 62 are cured, the formers 74, 76 may be removed, leaving the closed-loop individual ribs 62 wound directly onto the support structure 50.
It should be readily appreciated that the ribs 62 may be individually wound onto the support structure 50 in a winding process wherein a filament supply 88 is moved from one former 73 to the next former 73 in a serial operation. In other words, it is not a necessity that all of the formers 73 are wound with the filament supplies 88 in a simultaneous operation.
It should be appreciated that the filament winding process may be controlled such that the filaments 88 are applied with a relatively high tension, resulting in ribs 62 having a higher rigidity and strength. The orientation of the filaments 88 may also be controlled so that successive layers are plied or oriented differently from the previous layer. Any suitable carbon or glass fiber, or other types of fibers, may be used to form the ribs 62.
In the embodiment depicted in
It should thus be appreciated from the above discussion that the present invention also encompasses various method embodiments for making a rotor blade 16 for a wind turbine 10, wherein the method includes forming a span-wise internal support structure 50. A plurality of ribs 62 are configured on the support structure 50, with the ribs 62 spaced span-wise along the internal support structure 50 with each rib 62 extending in a generally chord-wise direction. The ribs 62 have a generally aerodynamic outer surface and define the overall aerodynamic profile of the blades 16. The method includes wrapping a plurality of chord-wise oriented fabric strips over the ribs and tensioning the fabric strips in at least a chord-wise direction to define the aerodynamic outer skin of the rotor blade.
The method may include forming each of the ribs 62 as an individually formed closed-loop element fixed to the spar caps 56. For example, the ribs 62 may be formed in a filament winding process wherein the ribs are wound directly onto the spar caps 56, as discussed above with respect to
The various method embodiments may include tensioning the fabric strips in a span-wise and chord-wise direction over the ribs 62 prior to final fastening of the fabric strips 66 to the ribs. The fabric strips may be fixed to adjacent ribs in one method embodiment, or span at least three of the ribs or more in an alternate embodiment.
In a particular method embodiment, the chord-wise edges 68 of the fabric strips 66 may be attached to a respective rib in an abutting relationship. In an alternate embodiment, the edges 68 may be spaced apart on the ribs 62.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
