Abstract:
A blade of a wind turbine is provided having an improved spar cap. The spar cap includes at least one trench extending in a substantially span-wise direction in at least a portion of the spar cap. At least one shear web is connected to the spar cap. At least a portion of the shear web is positioned within the trench of the spar cap.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter described here generally relates to wind turbine blades, and, more particularly, to wind turbine blades having improved spar caps. 
         [0002]    A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator, wind turbine or wind power plant. 
         [0003]    Wind turbines are typically categorized according to the vertical or horizontal axis about which the blades rotate. One so-called horizontal-axis wind generator is schematically illustrated in  FIG. 1 . This particular configuration for a wind turbine  2  includes a tower  4  supporting a nacelle  6  enclosing a drive train  8 . The blades  10  are arranged on a hub to form a “rotor” at one end of the drive train  8  outside of the nacelle  6 . The rotating blades  10  drive a gearbox  12  connected to an electrical generator  14  at the other end of the drive train  8  arranged inside the nacelle  6  along with a control system  16  that receives input from an anemometer  18 . 
         [0004]    The blades  10  generate lift and capture momentum from moving air that is then imparted to a rotor as the blades spin in the “rotor plane.” Each blade is typically secured at its “root” end, and then “spans” radially “outboard” to a free, “tip” end. The distance from the tip to the root, at the opposite end of the blade, is called the “span.” The front, or “leading edge,” of the blade connects the forward-most points of the blade that first contact the air. The rear, or “trailing edge,” of the blade is where airflow that has been separated by the leading edge rejoins after passing over the suction and pressure surfaces of the blade. 
         [0005]    A “chord line” connects the leading and trailing edges of the blade in the direction of the typical airflow across the blade. The length of the chord line is simply called “the chord.” Since many blades  10  change their chord over the span, the chord length is referred to as the “root chord,” near the root, and the “tip chord,” near the tip of the blade. The chord lines are arranged in the “chord planes” that extend through the streamlines on the corresponding pressure and suction surfaces of the blade. Multiple “shear web planes” are arranged perpendicular to the to the chord plane. 
         [0006]    As illustrated in  FIG. 2 , the blades  10  for such wind turbines  2  are typically fabricated by building up two or more skin or “shell” portions  20  from layers of woven fabric and resin. Spar caps  22  are placed in the shell portions  20  and are combined with shear webs  24  to form a structural support member. The shear webs  24  and spar caps  22  extend at least partially spanwise along the inside of the blade  10  and are typically configured as I-shaped members. For example, the spar caps  22  may be joined to the inside of the suction and pressure surfaces of the shell  20  or they may form part of the shell. In some blades, an additional trailing edge shear web  26  may also be incorporated into the blade. 
         [0007]    The top and bottom spar caps  22  together with the shear web  24  form the main fore-aft structural member of the wind turbine blade  10 .  FIG. 3  illustrates a partial view of one known spar cap and shear web. The spar cap  22  can be made from an assemblage of layers of unidirectional (UD) glass fiber tapes. Thinner root and tip sections have fewer layers of the UD glass fiber tapes. The cross-sections at any section along the length of the spar cap is typically rectangular. Some known manufacturing methods use foam wedges  32  to bridge the gap at sections where the skin foam  34  thickness is less than the spar cap thickness. This is needed to avoid abrupt changes in the surface of the subsequent layers of glass fiber and resin. If the wedges  32  were not used, then a wrinkle or crack could appear in the subsequently applied layers. Typically, the shear web  24  is joined to the spar caps  22  using a bonding material  36 , such as an adhesive. The fabrication of each of these constituent parts is in itself an involved and labor-intensive process comprised of laying out fabric, glass fibers, and foam, followed by or with intervening resin application steps. In addition, the thickness of the shear web  24 , in the span-wise direction, should be thick enough to provide enough surface area to securely bond with adhesive  36 . As a result, the shear web  24  is often much thicker, and heavier, than needed for structural purposes. This is a disadvantage from a weight perspective. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    According to an aspect of the present invention, a blade of a wind turbine is provided having an improved spar cap. The spar cap includes at least one trench extending in a substantially span-wise direction in at least a portion of the spar cap. At least one shear web is connected to the spar cap. At least a portion of the shear web is positioned within the trench of the spar cap. 
         [0009]    According to another aspect of the present invention, a blade of a wind turbine is provided having an improved spar cap. The spar cap includes at least one trench extending in a substantially span-wise direction in at least a portion of the spar cap. 
         [0010]    According to yet another aspect of the present invention, a blade of a wind turbine is provided. The blade includes at least one spar cap having at least one trench. The trench extends in a substantially span-wise direction in at least a portion of the spar cap. The spar cap has a first surface that extends from the trench towards a side of the spar cap. At least one shear web is connected to the spar cap. Skin foam is disposed next to the spar cap and has a predetermined height. At least a portion of the shear web is positioned within the trench and at least a portion of the first surface is tapered or contoured towards the skin foam so that at least a portion of the first surface is at substantially the same height as the skin foam. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Various aspects of this technology will now be described with reference to the following figures (“FIGS.”), which are not necessarily drawn to scale, but use the same reference numerals to designate corresponding parts throughout each of the several views. 
           [0012]      FIG. 1  is a schematic side illustration of a conventional wind turbine. 
           [0013]      FIG. 2  is a partial, perspective illustration of the conventional wind turbine blade in  FIG. 1 . 
           [0014]      FIG. 3  is a partial, cross-sectional illustration of a spar cap and a shear web of the conventional wind turbine blade in  FIG. 1 . 
           [0015]      FIG. 4  is a partial, cross-sectional illustration of a spar cap and a shear web, according to aspects of the present invention. 
           [0016]      FIG. 5  is a partial, cross-sectional illustration of a spar cap, according to aspects of the present invention. 
           [0017]      FIG. 6  is a partial, cross-sectional illustration of a spar cap and a shear web, according to aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 4  is a partial, cross-sectional illustration of an improved spar cap according to aspects of the present invention. The spar cap  422  has a contoured or tapered upper surface  424  and a trench  426 . The trench  426  can extend fully or partially along the length (i.e., span-wise direction) of the spar cap. The shear web  430  fits into the trench  426  and is secured by adhesive  440 . For example, the shear web  430  may include a low-density material such as foam or balsa wood. The outer shell of the shear web  430  may be formed from one or more layers of resin impregnated fiber reinforcements, such as glass, carbon, aramid (e.g., Kevtar®, a registered trademark of E. I. du Pont de Nemours and Company), and/or any combination thereof. For example, the outer shell of the shear web  430  may be formed from 45 degree biaxial structural fabric. However other materials and configurations may also be used. The spar cap  422  may be joined to the inside of shell  20  or it may form part of the shell. The sides of the spar cap can be sized to substantially match the dimension or thickness of the skin foam  34 . 
         [0019]    The spar cap  422  can incorporate tapered surfaces in areas where the mating skin foam  34  is thinner. This tapered surface  424  eliminates the use of foam wedges  32  (see  FIG. 3 ) and greatly reduces the labor required during the manufacture of blades  10 . The tapered surface  424  can begin at the skin foam edge and extend partially or all the way to trench  426 . 
         [0020]      FIG. 5  illustrates a cross-sectional illustration of a spar cap  522  having a contoured edge  524 , according to aspects of the present invention. In this embodiment, the spar cap  522  thickness is gradually reduced from the thickest (middle) section to the thinnest edge near the skin foam (not shown) following a curved contour. The trench  526  can be positioned near the middle of the spar cap and sized to accept a shear web  430 . In addition to the shape as illustrated, any suitable curved or compound curved profile could be used. However, other curvature configurations may also be used, including, but not limited to any portion or combination of various types algebraic curves, caustic curves, cissoids, conchoids, conic sections, elliptic curves, hyperbolic curves, general plane curves, implicit curves, inverse curves, involutes and evolutes, pedal curves, polar curves, pursuit curves, radial curves, roulettes, strophoids, rational, transcendental, fractal, continuous, discontinuous, and/or piecewise curves. Other curvatures may also be used including semicircular, hyperbolic. The tapered or contoured edges may be blended into rectangular sections where the spar cap is thinner (e.g., towards the root or the tip section of the blade). 
         [0021]      FIG. 6  is a partial, cross-sectional illustration of an improved spar cap according to another aspect of the present invention. The spar cap  622  includes two trenches  626  which accept two shear webs  630 . It is to be understood that the spar cap  622  could include more than two trenches  626  and more than two shear webs  630  if desired. The use of multiple shear webs can provide the advantages of a stiffer spar beam having increased resistance to torsional loads on the blade  10 . 
         [0022]    The technology disclosed here offers various advantages over conventional approaches. One advantage of the present invention is that the spar cap may be made with fewer strands of unidirectional composite tape in the tapered region than used in the broader base or central region. This reduces material cost as less unidirectional composite tape and molding resin is required. Additional cost savings can be obtained by the elimination of blending foam wedges  32 , reduced labor for installation, and elimination of resin needed to bond these components, in areas where the spar cap is thicker than the skin foam  34 . A further advantage is the increased structural robustness of the shear web/spar cap joint provided by the increased surface area for bonding due to the incorporation of a trench. This ability to achieve increased bonding area, while still being able to optimize/reduce the shear web thickness helps meet Germanischer Lloyd (GL) certification requirements for minimum bonding area. Germanischer Lloyd is a leading certification body in the wind-energy sector, offering project and type certifications, also in other fields of renewable-energy, for manufacturers of wind turbines and components. 
         [0023]    It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here to provide a clear understanding of various aspects of this technology. One of ordinary skill will be able to alter many of these embodiments without substantially departing from scope of protection defined solely by the proper construction of the following claims.