Patent Publication Number: US-2010119374-A1

Title: Wind turbine &amp; wind turbine blade

Description:
FIELD OF THE INVENTION 
     The present invention relates to wind powered turbines and, in particular to a wind turbine blade and a wind turbine using the blades. 
     The invention has been developed primarily for use in 2 kW to 10 kW horizontal axis wind turbine electricity generators and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use. 
     BACKGROUND ART 
     Horizontal axis wind turbines are well known, the windmill being a most exemplary example. The principle of operation of a windmill has been expanded from pumping water or grinding to the generation of electricity. In use, at least a pair of turbine blades are mounted symmetrically about a rotating turbine hub. In response to an incident wind, the hub is caused to rotate. The hub is connected either directly or indirectly to an electrical generator shaft (rotor) such that rotation of the shaft generates an electrical output from the generator. 
     Wind turbine blade design is commonly based on blade element theory (BET), whether by manufacturers of large or small turbine blades. In the blade element theory, a turbine blade is longitudinally divided into a number of elements and each element is assumed to behave as an aerofoil section at the same velocity and angle of attack. 
     Once this is done, the lift and drag coefficients for the aerofoil can then be used to determine the torque acting on each element. The sum of the torque on all of the blade elements provides a total torque from which a total power output is derived. Reference is made to the “Wind Energy Handbook”, Burton et al (John Wiley &amp; Sons) 2001, the disclosure of which is incorporated herein in its entirety by cross-reference. An extensive description of blade element theory is provided by Burton et al. and it will be understood that this teaches the determination of the power output and optimisation of the blade shape for maximising the generated power in given wind conditions. 
     Most large wind turbine (for example 20 kW+) blades have a circular or substantially circular blade root to allow the most secure connection to the wind turbine hub. The blade section gradually transforms to the circular or substantially circular root shape as the blade length decreases and the hub approaches. Unfortunately, such blade designs and arrangements cause an overly significant decrease in starting performance when used on relatively small turbine blades. 
     Genesis of the Invention 
     It is the genesis of the invention to provide a wind turbine that optimises both the starting characteristics of the turbine and the power extracted therefrom at a nominal speed, or to provide a useful alternative. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a wind turbine blade configured to be mounted to a wind turbine hub configured to be mounted for rotation in a hub plane of rotation so as to generate electricity, the blade extending lengthwise between a hub mounting root end and a blade tip end, and extending a blade width between a leading edge and trailing edge, such that when mounted to the hub the blade is twisted at the root end by an angle of between 19° to 21° relative to the plane of rotation of the hub and wherein the blade is twisted at a tip end to rotate in a plane parallel to the plane of rotation of the hub to within ±1°. 
     According to a second aspect of the present invention there is provided a wind turbine including a turbine hub configured to be rotatably mounted for rotation in a hub plane of rotation so as to inductively generate electricity, and two or more wind turbine blades each according to the first aspect of the invention and being mounted symmetrically about the hub. 
     According to a third aspect of the invention there is provided a wind turbine blade configured to be mounted to a wind turbine hub configured to be mounted for rotation in a hub plane of rotation so as to generate electricity, the blade extending lengthwise between a hub mounting root end and a blade tip end, and extending a blade width between a leading edge and trailing edge, such that when mounted to the hub the blade is twisted by an angle of between −1° to 25° about a blade longitudinal axis extending lengthwise along the blade relative to the plane of rotation of the hub and wherein the blade tip end is configured to rotate in a plane parallel to the plane of rotation of the hub to within ±1°. 
     According to another aspect of the invention there is provided a wind turbine blade configured to be mounted to a wind turbine hub configured to be mounted for rotation in a hub plane of rotation so as to generate electricity, the blade extending lengthwise between a hub mounting root end and a blade tip end, and extending a blade width between a leading edge and trailing edge, such that when mounted to the hub the blade is twisted at the root end by an angle of between 19° to 21° relative to the plane of rotation of the hub wherein the turbine blade is twisted by an angle of between −1° to 25° about a blade longitudinal axis extending lengthwise along the blade. 
     It can therefore be seen that there is provided a wind turbine blade and a horizontal axis wind turbine employing the blades  1  which each advantageously optimise the starting characteristics of a 2 kW to 10 kW horizontal axis wind turbine generator and also optimise the power extracted from the horizontal axis wind turbine generator at a nominal operating rotations speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic top view of a wind turbine blade according to the preferred embodiment; 
         FIG. 2  is a schematic side view of the blade of  FIG. 1 ; 
         FIG. 3  is an end view of the blade of  FIG. 1 ; 
         FIG. 4  is a top view of the blade of  FIG. 1  as mounted to one part of a wind turbine hub; 
         FIG. 5  is a side view of the blade and hub of  FIG. 4 ; 
         FIG. 6  is an end view of the blade and hub of  FIG. 4 ; 
         FIG. 7  is a schematic top view of a pair of blades of  FIG. 1  mounted to a wind turbine hub; 
         FIG. 8  is a schematic side view of the blades of  FIG. 7 ; 
         FIG. 9  is an end view of the blades of  FIG. 7 ; 
         FIG. 10  is a schematic perspective view of a horizontal axis wind turbine having the blades shown in  FIG. 7  mounted thereto; 
         FIG. 11  is a graph of the chord length as a function of blade length for the blade of  FIG. 1 ; and 
         FIG. 12  is a graph of the blade twist as a function of blade length for the blade of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings generally, it will be appreciated that like reference numerals refer to like components. 
     Referring to  FIGS. 1 to 3  generally, there is shown various views of a wind turbine blade  1  according to the preferred embodiment of the invention. The blade  1  is configured to be mounted to a horizontal axis wind turbine hub  2  as shown in  FIGS. 4 to 9 . The hub  2  is configured to be rotatably mounted for rotation in a hub plane of rotation to a horizontal axis of a wind turbine generator  3 , as shown in  FIG. 10 . 
     Rotation of the hub  2  causes rotation of a 2 kW to 10 kW horizontal axis wind turbine generator  11  which causes an inductive electricity generator rotor (not illustrated) to rotate to thereby inductively generate electricity. An inductive electrical generator  11  is disposed in the horizontal axis wind turbine housing  3  (or nacelle) best shown in  FIG. 10 . 
     A pair of turbine blades  1  are symmetrically disposed about the hub  2 . The blades  2  are disposed about the hub with a 180° angular spacing and are therefore equi-spaced about the hub axis of rotation. Each wind turbine blade  1  extends lengthwise between a hub mounting root end  4  and a blade tip end  5 . Each wind turbine blade also extends a blade width between a blade leading edge  6  and a blade trailing edge  7 . 
     When mounted to the hub  2 , each wind turbine blade is twisted at the root end  4  by an angle of between 19° to 21° relative to the plane of rotation of the hub  2 . 
     Each turbine blade  1  is configured such that each blade tip end  5  may be twisted to rotated in a plane of rotation of the hub to within ±1°. In the embodiment shown, each blade tip end  5  is configured to rotate in a plane parallel to the plane of rotation of the hub  2  to within 0.5°. 
     The chord length of each turbine blade  1  varies along the blade length as shown in  FIGS. 1 and 2 .  FIG. 11  is a graph of the chord length of each wind turbine blade as a function of the blade length. The data forming the graph of  FIG. 11  is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Radius (mm) 
                 Chord (mm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 300.83 
                 250.00 
               
               
                   
                 452.50 
                 250.00 
               
               
                   
                 604.17 
                 250.00 
               
               
                   
                 755.83 
                 250.00 
               
               
                   
                 907.50 
                 229.66 
               
               
                   
                 1059.17 
                 207.31 
               
               
                   
                 1210.83 
                 185.17 
               
               
                   
                 1362.50 
                 163.84 
               
               
                   
                 1514.17 
                 143.91 
               
               
                   
                 1665.83 
                 125.99 
               
               
                   
                 1817.50 
                 110.67 
               
               
                   
                 1969.17 
                 98.55 
               
               
                   
                 2120.83 
                 90.23 
               
               
                   
                 2272.50 
                 86.31 
               
               
                   
                 2424.17 
                 86.31 
               
               
                   
                 2500.00 
                 86.31 
               
               
                   
                   
               
            
           
         
       
     
     It can be seen that the chord length of each turbine blade  1  is substantially constant at the blade root end  4  and the chord length is also substantially constant at the blade tip end  5 . In this preferred embodiment, the chord length of each turbine blade  1  is constant over approximately the first 33% of the length of the turbine blade  1  from the blade root end  4  towards the blade tip end  5 . The chord length of each turbine blade is also substantially constant over approximately 6% of the length of the turbine blade  1  from the blade tip end  5  toward the blade root end  4 . 
     In the preferred embodiment of the blade  1  shown in  FIGS. 1 to 9 , each blade length from the blade root end  4  to the blade tip end  5  is 2.5 meters. The maximum chord length, as shown in  FIG. 11 , is 250 mm at the blade root end  4  and about 90 mm at the tip end  5  of each blade  1 . Although not clearly shown, the hub mounting root end  4  of each blade  1  is substantially rectangular in cross-section. 
     As best shown in  FIG. 10 , each blade  1  when mounted to the wind turbine hub  2  and horizontal axis wind turbine generator  11  is configured such that each blade leading edge  6  forms a substantially straight line from the hub mounting end  4  to the blade tip end  5 . Further, each blade leading edge  6  is configured to be disposed upwind relative to the trailing edge  7  in an “up-wind” wind turbine where the blades  1  are faced directly into the wind. Although not illustrated, it will be appreciated that the horizontal axis wind turbine generator  11  can be a “down-wind” type wind turbine in which the blades face away from the wind and are partly shadowed by the horizontal axis wind turbine generator  11  and/or its support post. 
     Each wind turbine blade  1  is twisted along a blade longitudinal axis extending lengthwise along the blade  1  by an angle of between −1° and 21° relative to the plane of rotation of the hub  2 . In the preferred embodiment shown, each wind turbine blade  1  is twisted at the blade root end  4  by an angle of 20° with respect to the plane of rotation of the hub  2 . Each wind turbine blade  1  is twisted at the blade tip  5  end by an angle of between −0.5° to 0° relative to the plane of rotation of the hub. 
       FIG. 12  shows the blade twist relative to the plane of rotation of the blades  1  when  25 , mounted to the hub  2  and the horizontal axis wind turbine generator  11 , shown in  FIG. 10  for example. The data forming the graph of  FIG. 11  is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Radius (mm) 
                 Twist (°) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 300.83 
                 24.73 
               
               
                   
                 452.50 
                 23.40 
               
               
                   
                 604.17 
                 20.95 
               
               
                   
                 755.83 
                 17.84 
               
               
                   
                 907.50 
                 14.44 
               
               
                   
                 1059.17 
                 11.07 
               
               
                   
                 1210.83 
                 7.97 
               
               
                   
                 1362.50 
                 5.33 
               
               
                   
                 1514.17 
                 3.25 
               
               
                   
                 1665.83 
                 1.76 
               
               
                   
                 1817.50 
                 0.83 
               
               
                   
                 1969.17 
                 0.36 
               
               
                   
                 2120.83 
                 0.18 
               
               
                   
                 2272.50 
                 0.05 
               
               
                   
                 2424.17 
                 −0.10 
               
               
                   
                 2500.00 
                 −0.16 
               
               
                   
                   
               
            
           
         
       
     
     In the preferred embodiment, each wind turbine blade  1  is preferably moulded from fibreglass, however, any preferred wind turbine blade construction techniques can be employed. Likewise, it will be appreciated that the blade length can be any preferred and that any preferred inductive electrical generator or horizontal axis wind turbine generator can be used. It will be appreciated that active or passive yaw control of the turbine generator  11  can be employed as desired, as can any preferred gearbox mechanism with any preferred gearbox ratio, or the hub  2  may be directly rotatably mounted to the horizontal axis wind turbine generator if desired. 
     It can therefore be seen that the wind turbine blade  1 , and the horizontal axis wind turbine  11  employing the blades  1 , advantageously optimise the starting characteristics of a 2 kW to 10 kW horizontal axis wind turbine generator  11 . The horizontal axis wind turbine generator  11  also advantageously optimises the power extracted from the horizontal axis wind turbine generator  11  at a nominal operating rotations speed. 
     The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.