Abstract:
A wind turbine is provided with turbine blades mounted for axial rotation about an axis. The blades are surrounded by a shroud to define an axial air passage. A conical ring is attached to the shroud and includes vanes for directing the airflow. Plates are attached to the shroud at a position radially outward from the shroud forming an air passage between the shroud and the plates. The plates have gaps between the adjacent plates so that air exiting the downstream opening of the shroud and air moving through the axial air passage between the shroud and the plates are mixed and a portion of the mixed air exits through the gaps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Continuation-in-Part of a pending U.S. patent application Ser. No. 13/094,952, filed Apr. 27, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to wind turbines. More particularly, the present invention relates to high efficiency wind turbines for extracting energy from the wind. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wind energy has been used for centuries for a variety of useful purposes including grinding grain and pumping water. Recently, there has been extensive research and development worldwide in technology to use wind to generate electricity. Generating electricity from wind power does not result in the emission of carbon dioxide, hydrocarbons, carbon monoxide, particulates or other harmful compounds. Wind energy is, therefore, an attractive alternative to at least a portion of the power generated by burning fossil fuels in conventional power plants. The use of wind energy also reduces the need for coal mining which can be hazardous to miners and harmful to the environment. 
         [0004]    There has been a continuing need and desire for improvements in wind driven power generators, including the desire to overcome the shortcomings of conventional power generators while also providing a generator which is efficient and physically compact. This increasingly competitive source of energy is steadily providing a growing share of worldwide electricity. Significant numbers of these wind turbines have been located in particular areas with high average wind speeds to form wind farms with considerable generating capability. Wind turbines have also been used to generate electricity in off-grid applications such as remote sites. 
         [0005]    Traditional wind turbines are typically mounted on tall towers. The towers are often placed in open fields or along a ridgeline. In,addition to accessing higher wind speeds, the height of traditional wind turbines reduces or avoids risk to people, livestock, and wildlife that may be on or near the ground. But towers are expensive to build and, at least in some cases, their height may be objectionable, for example, for obstructing a view. Property owners in the vicinity of these wind turbines also have been known to object to the noise caused by the large rotating blades. Many of these traditional wind turbines have blades over 40 meters long, meaning the diameter of the rotor is over 80 meters, mounted on towers 80 meters tall. Land for the wind farm has to be purchased or leased, and transmission line easements have to be obtained from the wind farm to the existing transmission power grid. As a result, the development time is long and costs are very high. Because of these restrictions, many new wind farms cannot be built for several years. 
         [0006]    Thus, because of the problems associated with such traditional wind farms, much current research has been devoted to smaller wind turbines. While it is possible to create turbines with a wide range of blade lengths, much recent development has been devoted to turbines with smaller blade lengths than those found in traditional wind turbines. These smaller turbines can be mounted on the roofs of buildings or on poles, which are only a fraction of the height of traditional wind turbine towers. However, typical small wind driven turbines are relatively inefficient, often only converting a small fraction of the wind&#39;s kinetic energy into usable electrical power. When these smaller wind turbines have the blades mounted within a housing, or shroud, the designs allow for greater power extraction out of the wind, compared to prior art open designs. Examples of such wind turbines are found in U.S. Pat. Nos. 7,218,011, 4,204,799, 4,075,500, 6,655,907 and 6,887,031, the disclosures of which are hereby incorporated by reference herein. These smaller scale wind turbines may be mounted on lower poles, such as at a height of 10 meters, or may be mounted on the top of buildings. Thus, the smaller turbines are less expensive to build, and create less of an impact on the environment compared to the traditional larger turbines. A small scale wind turbine is needed which is highly efficient and which retains the other advantages of wind power generation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    A wind turbine is provided for extracting energy out of an airflow. The wind turbine includes a plurality of turbine blades mounted for rotation about a longitudinal axis. For example, the blades could be mounted to a rotating hub. In some embodiments, the turbine could have between 3 and 20 blades. Preferably, the blades have a length which will extend almost all the way to the shroud which surrounds the blades. The shroud, preferably constructed from steel or aluminum, surrounds the turbine blades. The shroud could be cylindrical, conical, square or other suitable shapes. The shroud has an upstream opening and a downstream opening. A plurality of plates are attached to the shroud and can be spaced radially outward from the shroud or can be mounted on the surface of the shroud. The plates are constructed from any suitable material such as steel, aluminum, or other materials known to those of skill in the art. The plates could be attached at various positions along the axis of the shroud, such as near the upstream opening, near the downstream opening, or at a midpoint between the two. The plates are spaced around the circumference of the shroud and project beyond the downstream opening of the shroud. The plates could be planar or arcuate, and could have a constant width, or a width which varies along the longitudinal direction. The plates could have a curvature generally corresponding to,the shroud. The plurality of plates form a second discontinuous shroud. The shroud and the plurality of plates form a second axial air passage between them. Because the plates form a discontinuous shroud, there are gaps between adjacent plates such that air exiting the downstream opening of the shroud and air moving through the axial air passage between the shroud and plates is mixed and a portion of the mixed air exits through the gaps. The ratio of the total area of the plates to the total area of the gaps is between 8:1 and 1:1, and is preferably 3:1. The plates can be tiled away from the axis of rotation of the blades from 0 degrees to 40 degrees. The plates allow for the wind turbine to turn about its mount so that the axis of rotation is aligned with the wind direction. The gaps in the plates cannot be so large as to prevent this alignment. 
         [0008]    The wind turbine can also include a ring mounted near the downstream opening of the plates and spaced radially outward from the plates to create a third axial air passage between the ring and the plates. 
         [0009]    To further improve the efficiency of the turbine, a conical ring can be attached in the upstream opening of the shroud. The conical ring is preferably made from steel, aluminum or other suitable material. The conical ring has an upstream edge defining an upstream area, and a downstream edge defining a downstream area. The length of the conical ring may vary depending on the size of the shroud to which it is attached. The upstream area is larger than the downstream area. The degree of taper of the conical ring from the upstream edge to the downstream edge and the thickness of the conical ring may vary, but the conical ring should be designed such that it does not introduce turbulence into the airflow. The conical ring causes increased airflow through the turbine by capturing more air and directing it through the turbine. The diameter of turbine blades defines a swept area. The downstream area of the conical ring is larger than the swept area of the blades. The conical ring includes a plurality of vanes between the upstream area and the downstream area. The vanes are generally perpendicular to the swept area of the blades. The vanes reduce turbulence in the airflow and increase the energy transferred from the airflow to the turbine blades. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    Embodiments and applications of the invention are illustrated by the attached non-limiting drawings. The attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. 
           [0011]      FIG. 1  is a front elevation view of the a conical shroud and turbine blades in accordance with one embodiment of the present invention; 
           [0012]      FIG. 2  is a side view of the shroud and turbine blades of  FIG. 1 ; 
           [0013]      FIG. 3  is a perspective view of the shroud and turbine blades of  FIG. 1 ; 
           [0014]      FIG. 4  is a front view of the shroud, turbine blades and plates in accordance with one embodiment of the present invention; 
           [0015]      FIG. 5  is a side view of the shroud, turbine blades and plates of  FIG. 4 ; 
           [0016]      FIG. 6  is a perspective view of the shroud, turbine blades and plates of  FIG. 3 ; 
           [0017]      FIG. 7  is a front elevation view of the a cylindrical shroud and turbine blades in accordance with another embodiment of the present invention; 
           [0018]      FIG. 8  is a side view of the shroud and turbine blades of  FIG. 7 ; 
           [0019]      FIG. 9  is a perspective view of the shroud and turbine blades of  FIG. 7 ; 
           [0020]      FIG. 10  is a front view of the shroud, turbine blades and plates in accordance with another embodiment of the present invention; 
           [0021]      FIG. 11  is a side view of the shroud, turbine blades and plates of  FIG. 10 ; 
           [0022]      FIG. 12  is a perspective view of the shroud, turbine blades and plates of  FIG. 10 ; 
           [0023]      FIG. 13  is a perspective view of another embodiment of the present invention; 
           [0024]      FIG. 14  is a perspective view of another embodiment of the present invention; 
           [0025]      FIG. 15  is a perspective view of another embodiment of the present invention; 
           [0026]      FIG. 16  is a perspective view of a conical ring of the present invention; 
           [0027]      FIG. 17  is a front elevation view of the conical ring of  FIG. 16 ; 
           [0028]      FIG. 18  is a perspective view of another embodiment of a conical ring of the present invention; 
           [0029]      FIG. 19  is a front elevation view of the conical ring of  FIG. 18 ; 
           [0030]      FIG. 20  is a perspective view of another embodiment of the present invention; and 
           [0031]      FIG. 21  is a perspective view of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention. Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  FIGS. 1 through 21  show the various embodiments of the invention. As best seen in  FIGS. 1 through 3 , the present invention includes a wind turbine  10  with a plurality of blades  12  arranged around a hub  14 . The blades  12  are capable of rotation about the longitudinal axis  16 . Surrounding the blades  12  is a shroud  20 . The shroud  20  is shown as conical in shape, but may be any one of many suitable shapes. The conical shroud  20  includes an upstream opening  22  and a downstream opening  24 . A post  26  is provided to mount the wind turbine  10  to a structure or above the ground. The conical shroud  20  has fins  28  which assist in aligning the longitudinal axis  16  with the direction of the wind  18 . 
         [0033]    Turning to  FIGS. 4 through 6 , plates  30  are mounted above the conical shroud  20 . The plates  30  have gaps  32  between them. The plates  30  are mounted on a mounting structure  34  such that they are mounted to the surface of the conical shroud  20 . The plates  30  project past the downstream opening  24  ( FIG. 2 ) of the conical shroud  20 . As air moves through the upstream opening  22  of the conical shroud, past the blades  12 , it exits through the downstream opening  24  of the conical shroud  20 . The function of blades  12  is accentuated by the downwind shroud  20  which serves to reduce pressure which increases the velocity of the air downwind of blades  12 . A portion of the air exits through the gap  32 . This configuration reduces the downstream air pressure and increases the efficiency of the wind turbine  10 . 
         [0034]    Optionally, an additional ring  40  is provided to create yet another moving airstream in the passage  42  between the plates  30  and the ring  40 . This air stream further reduces the pressure at the downstream opening  24  ( FIG. 2 ) of the conical shroud  20 . 
         [0035]    As shown in  FIGS. 7 through 12 , a cylindrical shroud  120  is shown, in place of the conical shroud  20  ( FIG. 3 ). The cylindrical shroud  120  has fins  128  which assist in aligning the longitudinal axis  16  with the direction of the wind  118 . The plates  130  are shown as arcuate instead of the planar plates  30  of  FIG. 6 . It will be understood by those of skill in the art that various configurations of the plates  30  and  130  can be used with the different embodiments of the invention disclosed herein. Turning to  FIGS. 10-12 , plates  130  are mounted above the cylindrical shroud  120 . The plates  130  have fins  128  which assist in aligning the longitudinal axis  16  with the direction of the wind  118 . The plates  130  have gaps  132  between them. The plates  130  are mounted on a mounting structure  134  such that they are raised off the surface of the cylindrical shroud  120 . The plates  130  project past the downstream opening  124  of the cylindrical shroud  120 . As air moves through the upstream opening  122  of the shroud, past the blades  12 , it exits through the downstream opening  124  of the cylindrical shroud  120 . Air also moves in the passage  136  underneath the plates  130 . The air moving through the passage  136  mixes with the air exiting the downstream opening  124  ( FIG. 9 ) of the shroud  120 . A portion of that air exits through the gap  132 . This configuration reduces the downstream air pressure and increases the efficiency of the wind turbine  10 . 
         [0036]    Optionally, an additional ring  140  is provided to create yet another moving airstream in the gap  142  between the plates  130  and the ring  140 . This third air stream further reduces the pressure at the downstream opening  124  of the cylindrical shroud  120 . 
         [0037]    Turning to  FIG. 13 , a shroud  220  has curved plates  230  attached thereto. Fins  228  are between the curved plates  230 . Between the plates  230  are also gaps  232  near the downstream end  224  of the shroud  220 . Between the shroud  220  and the curved plates  230  are passages  236 . These passages  236  are isolated from one another and from gaps  232 . As air moves through the upstream opening  222  of the shroud  220 , past the blades  12 , it exits through the downstream opening  224  of the cylindrical shroud  220 . Air also moves in the passage  236  underneath the plates  230 . The air moving through the passage  236  mixes with the air exiting the downstream opening  224  of the shroud  220 . A portion of that air exits through the gap  232 . This configuration reduces the downstream air pressure and increases the efficiency of the wind turbine  10 . 
         [0038]      FIG. 14  shows another embodiment of the invention. A shroud  320  has plates  330  attached to the surface  321  of the shroud  320 . Fins  328  are between the plates  330 . Optionally, a ring  340  is provided to create a moving airstream through gap  342  downwind of the opening  324 . This airstream reduces the pressure at the downstream opening  324  of the shroud  320 . Between the plates  330  are gaps  332  near the downstream end  324  of the shroud  320 . As air moves through the upstream opening  322  of the shroud  320 , past the blades  12 , it exits through the downstream opening  324  of the cylindrical shroud  320 . A portion of that air exits through gaps  332 , reducing the pressure at the downstream opening  324 . 
         [0039]      FIG. 15  shows another embodiment of the invention. A shroud  420  has fins  428  spaced about the circumference. The fins  428 , as described above, assist in aligning the shroud  420  with the airflow. Plates  430  are mounted on the shroud  420 . Gaps  432  are provided between the plates  430  to allow a portion of the airflow exiting past the blades  12  and the downstream opening  424  to exit through the gaps  432  reducing the pressure at the downstream opening  424 . 
         [0040]    Another embodiment of the invention is shown in  FIGS. 16-21 . In  FIGS. 16 and 17 , a conical ring  60  is shown with radial vanes  62  extending from a hub  64 . The conical ring  60  captures airflow within the area defined by its upstream edge  66  and concentrates that airflow as it passes through the area defined by the downstream edge  68 . As shown in  FIG. 20 , a shroud  520  surrounds the blades  12 . The conical ring  60  is attached to the shroud  520  by means known in the art such as screws, bolts, rivets, welding or other means. Fins  528  are between the curved plates  530 . Between the plates  530  are also gaps  532  near the downstream end  524  of the shroud  520 . Between the shroud  520  and the curved plates  530  are passages  536 . These passages  536  are isolated from one another and from gaps  532 . Air moves through the shroud  520 , past the blades  12 , and it exits through the downstream opening  524  of the shroud  520 . 
         [0041]      FIGS. 18 and 19  show another embodiment. The conical ring  160  has radial vanes  162  surrounding a hub  164 . Circumferential vanes  170  are also provided. The conical ring  160  captures airflow within the area defined by its upstream edge  166  and concentrates that airflow as it passes through the area defined by the downstream edge  168 . 
         [0042]      FIG. 21  shows the ring  60  attached to a shroud  620 . The conical ring  160  is attached to the shroud  620  by means known in the art such as screws, bolts, rivets, welding or other means. The blades  12  have a swept area which is inside of the edge  168 . The vanes  162  make the air less turbulent and provide for more efficient transfer of energy from the air to the blades  12 . As with other embodiments, a shroud  620  surrounds the blades  12 . Fins  628  are between the curved plates  630 . Between the plates  630  are also gaps  632  near the downstream end  624  of the shroud  620 . Between the shroud  620  and the curved plates  630  are passages  636 . These passages  636  are isolated from one another and from gaps  632 . Air moves through the shroud  620 , past the blades  12 , and it exits through the downstream opening  624  of the shroud  620 . 
         [0043]    The term “airflow” is used throughout this application to denote a fluid flow. Although the primary intent of invention is for the extraction of energy from wind, the principles and innovations may apply equally to the flow of other fluids such as flowing water. It is to be understood that the exemplary embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by one skilled in the art without departing from the scope of the invention.