Abstract:
A wind turbine includes a tower supporting a drive train with a rotor, at least one hollow blade extending radially from the rotor; a drain hole arranged in a tip portion of the blade; a baffle, arranged inside the blade and inboard of the drain hole, for impeding a flow of particulate matter to the drain hole; a flexible drain conduit arranged inside the blade for connecting to the drain hole; and a non-flexible drain conduit arranged inside the blade for connecting to the flexible drain conduit, the non-flexible conduit having a plurality of openings for receiving fluid from inside the blade.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The subject matter described here generally relates to fluid reaction surfaces with specific blade structures that are apertured or permeable, and, more particularly, to clog-resistant drains for wind turbines blades. 
         [0003]    2. Related Art 
         [0004]    A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If that mechanical energy is used directly by 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 further transformed into electrical energy, then the turbine may be referred to as a wind generator or wind power plant. 
         [0005]    All wind turbines use one or more airfoils in the form of a “blade” to generate lift and capture momentum from moving air that is them imparted to a rotor. Each blade is typically secured at its “root” end, and then “spans” radially “outboard” to a free, “tip” end. 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. 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 a chord line is simply referred to as the “chord.” 
         [0006]    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  1  includes a tower  2  supporting a drive train  4  with a rotor  6  that is covered by a protective enclosure referred to as a “nacelle.” The blades  8  are arranged at one end of the rotor  6  outside the nacelle for driving a gearbox  10  and electrical generator  12  at the other end of the drive train  4  inside the nacelle. 
         [0007]    Wind turbine blades are typically hollow in order to reduce their weight. Consequently, water vapor will sometimes condense inside the blade where it can wreak havoc on the balance of the rotor, freeze and crack the blade structure, cause steam explosions when rapidly heated by lightning strikes, or simply flow down the blade and into the nacelle. Wind turbine blades are therefore typically provided with a drain hole at their tip. However, since the relatively high tip speeds of modern turbines can cause air moving over the tip opening to vibrate or whistle, these blade tip drain openings are typically limited to about six millimeters in diameter. At that small size, any extraneous material left inside the blade after manufacturing, or that comes loose during normal operation, can easily clog the drain hole, especially when propelled by centrifugal force along the length of the span. 
         [0008]    Various approaches have been suggested for draining liquids from turbine blades. For example, an English-language abstract of European Patent Publication No. 1,607,623 describes a rotor blade for a wind turbine with one or more drainage apertures having a diameter of five millimeters and a net, gauze, or felt in the hollow space adjacent to each aperture. U.S. Patent Publication No. 2007/0086897 discloses a wind turbine blade with an eight to fifteen millimeter wide bore located in the root area and within five centimeters of an enclosure member for strengthening the root and enclosing the blade. U.S. Pat. No. 6,979,179 discloses a wind turbine blade in which a drain passage is formed of a longitudinal bore in a lightening receptor, where the longitudinal bore communicates with the inner cavity of the blade through openings in the lightening receptor. 
         [0009]    However, these and other related wind turbine blade drainage techniques can suffer from various drawbacks. For example, the net or gauze can become clogged with fine sediment, grease, or resin particles that are flushed from inside the blade. Any relatively large bores in the blade, especially near the root, require additional strengthening with corresponding additional material and weight. Similarly, the metallic materials that are required for lightening receptors can be relatively heavy and sometimes difficult to properly align and fit with the drain hole through the surface of the blade. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    These and other drawbacks of such conventional approaches are addressed here by providing, in various configurations, a hollow blade for a wind turbine including a flexible drain conduit arranged inside the blade for connecting to a drain hole through a surface of the blade. Also provided is a hollow blade for a wind turbine, including a a drain hole through a surface of the blade; and a baffle, arranged inside the blade and inboard of the drain hole, for impeding a flow of particulate matter to the drain hole. In another configuration, the subject matter disclosed here relates to a wind turbine, including a tower supporting a drive train with a rotor; at least one hollow blade extending radially from the rotor; a drain hole arranged in a tip portion of the blade; and a baffle, arranged inside the blade and inboard of the drain hole, for impeding a flow of particulate matter to the drain hole. The wind turbine may also include a flexible drain conduit arranged inside the blade for connecting to the drain hole; and a non-flexible drain conduit arranged inside the blade for connecting to the flexible drain conduit where the non-flexible conduit has a plurality of openings for receiving fluid from inside the blade. 
     
    
     
       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 illustration of a conventional wind turbine. 
           [0013]      FIG. 2  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0014]      FIG. 3  is a schematic cross-sectional view taken along section line III-IV in  FIG. 2 . 
           [0015]      FIG. 4  is an alternate schematic cross-sectional view taken along section line III-IV in  FIG. 2 . 
           [0016]      FIG. 5  is a schematic cross-sectional illustration of a tip of a Wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0017]      FIG. 6  is a schematic cross-sectional view taken along section line VI-VI in  FIG. 5 . 
           [0018]      FIG. 7  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0019]      FIG. 8  is a schematic cross-sectional view taken along section line VIII-VIII in  FIG. 7 . 
           [0020]      FIG. 9  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0021]      FIG. 10  is a schematic cross-sectional view taken along section line X-X in  FIG. 9 . 
           [0022]      FIG. 11  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0023]      FIG. 12  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0024]      FIG. 13  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0025]      FIG. 14  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0026]      FIG. 15  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0027]      FIG. 16  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0028]      FIG. 17  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0029]      FIG. 18  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
           [0030]      FIG. 19  is a schematic cross-sectional illustration of a tip of a wind turbine blade for use with the wind turbine shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]      FIGS. 2-19  are schematic cross-sectional illustrations of various configurations for a tip portion of a wind turbine blade  20  for use with the wind turbine  1  shown in  FIG. 1 . For example, the blade  8  shown in  FIG. 1  may be modified to include any of the features of the various configurations of the blades  20  illustrated in  FIGS. 2-19 , and/or combinations of those features. 
         [0032]    In  FIG. 2 , the wind turbine blade  20  is provided with a drain hole  22  for draining fluids that may accumulate inside the blade. A flexible drain conduit (or drain line)  24  is arranged inside the turbine blade  20  and connected to the drain hole  22  at one end. The flexibility of the drain conduit  24  allows it to be easily positioned and/or attached inside the blade  20 . For example, the flexible drain conduit may be loosely coiled near the tip of the blade  20  and/or secured to an internal surface of the blade  20  by various techniques including fastening, laminating and/or adhesive bonding. The drain hole  24  may also be provided with a coupling, spigot, nozzle, or other feature (not shown) for receiving an end of the flexible drain conduit  24 . Alternatively, the (butt) end of the flexible drain conduit  24  may be welded, glued, or otherwise adhered to the perimeter of the drain hole  22  inside the blade  20 . 
         [0033]    In the configuration shown in  FIG. 2 , the flexible drain conduit  24  includes one or more openings  26  for receiving fluid from inside the blade  20 . These openings help to prevent particulate material from accumulating inside the flexible drain conduit  24  and/or otherwise clogging the fluid flow path through the drain hole  22 . Therefore, and internal dimension at each of the openings  26  is typically smaller than an internal dimension of the conduit. However, the openings  26  in the drain conduit  24  may be formed in a variety of sizes, configurations, and shapes including round, square, diamond-shaped, quadrilateral, slot-shaped, elliptical, octagonal, and/or a variety of other shapes. If one of the openings  26  becomes clogged by particulate matter, then the remaining openings  26  will continue to allow fluid flow through the drain hole  24 . 
         [0034]    The shape of the flexible drain conduit  24  may also be arranged in various configurations. For example,  FIGS. 3 and 4  are alternate schematic cross-sectional views taken along section line III-IV in  FIG. 2  showing rectangular and tubular cross-sections of the flexible drain conduit  24 , respectively. However, the flexible drain conduit  24  may also be provided in a variety of other shapes and the size of the conduit  24  may change along its length. For example, the flexible conduit  24  may be larger at its free end. The free end of the flexible drain conduit  24  may also be closed, as illustrated in  FIG. 3 , open, or partially open as illustrated in  FIG. 4 . In the tubular flexible drain conduit configuration of  FIG. 4 , the free end of the tubular (or any other shape) flexible drain conduit  24  is provided with one or more openings  26  which may have other shapes, sizes, or configurations. As in  FIG. 2 , the round openings  26  in the end of the tubular flexible drain conduit  24  shown in  FIG. 4  are also smaller than the outer diameter of the tubular flexible drain conduit  24  shown in  FIG. 4 . 
         [0035]    Turning to  FIG. 5 , the turbine blade  20  may also be further provided with a non-flexible conduit  28  for connecting to the flexible drain conduit  24 . For example, the non-flexible conduit  28  may be formed from fiberglass, polyvinyl chloride, wood, metal, or other relatively rigid material. In  FIG. 5 , the non-flexible conduit  28  includes one or more openings  26  for receiving fluid from inside the blade  20 . The flexible drain conduit  24  may also be provided with openings (not shown in  FIG. 5 ). These openings also help to prevent particulate material from accumulating inside the non-flexible drain conduit  28 , flexible drain conduit  24 , and/or otherwise obstructing the fluid flow path through the drain hole  22 . In this configuration, and the flexible drain conduit  24  is particularly useful for connecting the end of the non-flexible conduit  28  with the drain hole  22 . The flexibility of the drain conduit  24  thus accommodates for any errors in the position or alignment of the non-flexible drain conduit  28  and improves the manufacturability of the blade  20 . 
         [0036]      FIGS. 6-8  illustrate various techniques for securing the non-flexible conduit  28  to an internal surface of the blade  20 . However, similar techniques may also be used for securing the flexible drain conduit  24  inside the blade  20 . 
         [0037]      FIG. 6  is a schematic cross-sectional view taken along section line VI-VI in  FIG. 5  while  FIG. 8  is a schematic cross-sectional view taken along section line VI-VII in  FIG. 7 . In  FIG. 6 , the rectangular non-flexible conduit  28  is adhered to an internal surface of the blade  20  by an adhesive  30 . For example, in the adhesive  30  may include a resin which is used to impregnate the fiberglass, carbon fiber, or other material of the body of the blade  20 . In  FIG. 8 , the non-flexible conduit  28  is secured to the internal surface of the blade  20  by straps  32 . The straps  32  may be fastened, adhered, bonded, or otherwise secured to the internal surface all of the played  20  by a variety of techniques. For example, be straps  32  may be strips of fiberglass, carbon fiber, or other material which are resin-impregnated and bonded to the internal surface of the blade  20 . 
         [0038]      FIGS. 9 and 10  illustrate another embodiment of a hollow blade  20  for a wind turbine  1  in which the non-flexible conduit  28  is integrally-formed into an internal surface of the blade  20 .  FIG. 10  is a cross-section taken along section line X-X in  FIG. 9 , and illustrates a pocket space  34  formed by the non-flexible conduit  28  over the internal surface all of the blade  20 . For example, where the blade  20  is formed through a resin impregnated fiberglass transfer molding process, the non-flexible conduit  28  may be formed from a resin-impregnated fiberglass layer which is spaced from the internal surface of the blade. Once the top surface of the non-flexible conduit is formed and hardened, then openings  26  may be drilled or otherwise machined in the exterior surface of the non-flexible conduit  28 . The flexible conduit  24  then aids in aligning and connecting the non-flexible conduit  28  with the drain hole  22 . The flexible conduit  24  may also be replaced and/or supplemented with an extension of the non-flexible conduit  26  or a separate non-flexible conduit leading to the drain hole  22 . 
         [0039]    In addition to the flexible and non-flexible drain conduits  24  and  28  discussed above, the blade  28  may also be provided with a baffle, arranged inside the blade and inboard of the drain hole  22 , for in restricting the flow of particular matter to the drain hole. For example, various wind turbine blade baffle configurations are illustrated in  FIGS. 11-18 . However, other baffle configurations may also be implemented. 
         [0040]    For example, as illustrated in  FIG. 11 , the baffle  36  may include one or more first flow deflectors  38  extending from a leading edge of the blade  20  and/or one or more second flow deflectors  40  extending from the opposite, trailing edge of the blade  20 . In  FIG. 11 , each of the flow deflectors  38  and  40  extends from one edge substantially across the entire chord, except for a flow space at one end. In  FIG. 12 , some of the first and second flow deflectors are shorter than those illustrated in  FIG. 11 , and there are third flow deflectors  42  spaced from the leading and the trailing edge of the blade  20 . In  FIG. 13 , the first and second flow deflectors  38  and  40  are angled inboard from their respective leading and trailing edges, while the third float deflector  42  extends substantially along a chord which is substantially perpendicular to the leading and trailing edges of the blade  20 . However, others of the flow deflectors  38 - 42  may also be aligned with the chord or angled in the inboard and/or outboard directions. 
         [0041]    In  FIG. 14 , the end portions of the first flow deflector  38  and the second flow deflector  40  are curved inboard toward a third flow deflector  42  which also extends substantially along a chord that is perpendicular to the leading and trailing edges. In  FIGS. 15 and 16 , the ends of these third flow deflector  42  have been curved toward a tip of the blade so that a convex portion of the third flow deflector  42  is oriented toward the inboard direction on blade  20 . In  FIG. 16 , the first and second flow deflector  38  and  40  have been curved toward a root of the blade  20 , so that a convex portion of the flow deflectors  38  and  40  is oriented toward a tip portion of the blade. In  FIG. 17 , the radius of curvature for each of the first, second, and third flow deflectors  38 ,  40 , and  42  has been increased and the third flow deflector  42  has been oriented with a convex portion facing the inboard direction of the blade  20 . In  FIG. 18 , each of the flow deflectors  42  is provided with a generally cylindrical shape. However, a variety of other shapes may also be used including triangular, rectangular, pentagonal, et cetera. 
         [0042]      FIG. 19  illustrates another embodiment of a wind turbine blade  20  which includes the baffle  36  configuration illustrated in  FIG. 11  and the flexible conduit  24  and nonflexible drain conduit  28  configuration illustrated in  FIG. 7 . Combinations of other baffle and/or conduit configurations, including ones not explicitly shown in these Figures, are also within the scope of this disclosure. 
         [0043]    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. These embodiments may be modified without substantially departing from scope of protection defined solely by the proper construction of the following claims.