Abstract:
A rotor structure is provided for a wind turbine and includes a central hub from which a plurality of blades radially extends. The blades have distal free ends that are surrounded by and coupled to a circumferentially arranged hood for rotation therewith. As such, with the rotor mounted to a generator of the wind turbine, when air flows caused by winds get into wind facing surfaces of the blades, the air flows are accelerated by either a divergent configuration, a convergent configuration, or a convergent-divergent configuration of the hood to remarkably enhance the performance of wind power generation and reduce the overall size of the rotor of the wind turbine.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to wind power generation techniques, and particularly to a rotor for application in wind turbines. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    Recently, with the increased price fluctuation of fossil fuels, a crisis of energy rises. Scientists of all the countries of the world are seeking for energy substitutes (green energy), such as solar energy, wind energy, tidal energy, and even bio-energy, in order to meet the needs of energy consumption of human beings by generation of electrical power with theses sustainable energy provided by the Nature and to achieve the goal of carbon reduction and energy saving. Taking wind energy as an example, the development of the wind energy based power generation has started since the first wind turbine built up by Danish meteorologist Poul La Cour in the 19th century. The wind energy is a non-exhaustible, non-polluting, and self-generated energy and has a wide distribution over the whole world so that it can be various local needs of power supply, reduces power loss due to long distance transmission, and lowers down the costs of power supplying. 
         [0003]    Wind power generation uses wind energy to drive the rotation of a rotor for conversion the wind energy into electrical power. Thus, aerodynamic performance (such as shape and number of blades) is critical to the output efficiency of the wind power generation. There are lots of inventions related to the wind power generation, such as U.S. Pat. No. 7,094,018 B2, Taiwan Utility Model Publication No. M279736, Design No. D119380, and U.S. Pat. No. 4,075,500. 
         [0004]    As shown in  FIG. 1  of the attached drawings, a conventional rotor  1  comprises a central hub  11  from which a plurality of blades  12  radially extends. The rotor illustrated in the drawing is of a type having nine blades  12 . The central hub  11  is coupled to a drive shaft of a generator  2 . However, as shown in  FIG. 2 , when this type of known rotor  1  is put in operation, air flows caused by winds to move through the rotor  1  are broken by ends of the blades  12 , leading to generation of noise and turbulences. The turbulences may cause expansion of the air flows, decelerating the air flow and thus reducing the rotational speed of the rotor  1  and eventually affecting the performance of wind power generation. 
       SUMMARY OF THE INVENTION 
       [0005]    Thus, an objective of the present invention is to provide a rotor structure of a wind turbine, which increases the speed of the air flow passing the rotor so as to improve performance of power generation. 
         [0006]    Another objective of the present invention is to provide a rotor structure of a wind turbine that reduces noise. 
         [0007]    A further objective of the present invention is to provide a rotor structure of a wind turbine that offers greater flexibility of design. 
         [0008]    A rotor structure of a wind turbine in accordance with the present invention comprises a central hub and a plurality of blades radially extending from the central hub. A hood is circumferentially set around and connected to distal free ends of the blades so that each blade is coupled to the hood to rotate therewith. When the rotor is mounted to a wind turbine for operation, with winds causing air flows entering the rotor, the hood is also caused to rotate and the air flows effect acceleration to thereby improve performance of wind power generation. When the distal ends of the blades rotate with the hood, due to the existence of the hood, noise caused by breaking air flows may not occur. Further, the central hub of the rotor may be provided with a concentrically arranged connection ring to offer flexible increase of the number of blades between the central hub and the hood so as to increase the rotational torque of the rotor and also provide the effect of accelerating the rotation of the rotor. Comparison between the rotor of the present invention and the conventional rotor that is done by coupling theses rotors to generators that are of identical performance of power generation reveals that the size and the area of wind facing surface of the rotor of the present invention are far less than those of the conventional rotors. Thus, the present invention also offers the advantage of reducing the size of rotor. 
         [0009]    The foregoing objective and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. 
         [0010]    Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a conventional rotor. 
           [0012]      FIG. 2  is a cross-sectional view illustrating the operation of the conventional rotor. 
           [0013]      FIG. 3  is a perspective view of a rotor in accordance with an embodiment of the present invention. 
           [0014]      FIG. 4  is a cross-sectional view of the rotor of the embodiment of the present invention. 
           [0015]      FIG. 5  is a cross-sectional view showing another type of the rotor of the embodiment of the present invention. 
           [0016]      FIG. 6  schematically illustrates the principle of the flow of liquid. 
           [0017]      FIG. 7  is a perspective view of a rotor in accordance with another embodiment of the present invention. 
           [0018]      FIG. 8  is a cross-sectional view of the rotor of said another embodiment of the present invention. 
           [0019]      FIG. 9  is a cross-sectional view showing another type of the rotor of said another embodiment of the present invention. 
           [0020]      FIG. 10  is a perspective view of a rotor in accordance with a further embodiment of the present invention. 
           [0021]      FIG. 11  is a cross-sectional view of the rotor of said further embodiment of the present invention. 
           [0022]      FIG. 12  is a cross-sectional view showing another type of the rotor of said further embodiment of the present invention. 
           [0023]      FIG. 13  is a perspective view of a rotor in accordance with yet a further embodiment of the present invention. 
           [0024]      FIG. 14  is a cross-sectional view of the rotor of said further embodiment of the present invention. 
           [0025]      FIG. 15  shows torque-rotational speed curves for various rotors. 
           [0026]      FIG. 16  shows performance-rotational speed curves for various rotors. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
         [0028]    With reference to  FIGS. 3-6 , a rotor constructed in accordance with the present invention generally designated with reference numeral  3  comprises a central hub  31  from which a plurality of blades  32  radially extends. The blades  32  have distal free ends that are surrounded by and coupled to a circumferentially arranged horn-like hood  33 . The hood  33  has a first circumferential edge portion  331  and a second circumferential edge portion  332  and an extension section  333  formed and extending between the first circumferential edge portion  331  and the second circumferential edge portion  332 . The first circumferential edge portion  331  has a diameter that is smaller than a diameter of the second circumferential edge portion  332  so that the extension section  333  of the hood  33  exhibits a divergent configuration. The distal end of each blade  32  is connected to an inner surface of the first circumferential edge portion  331  and each blade  32  has a wind facing surface that is in a direction opposite to the extension section  333  of the hood  33 . Further, the extension section  333  of the hood  33  can be of an outward-deflected curved configuration (as shown in  FIGS. 3 and 4 ) or a straight configuration that inclines outward (as shown in  FIG. 5 ). 
         [0029]    The central hub  31  of the rotor  3  is fit to a drive shaft of a generator  4 , and when winds cause air flows to enter through the wind facing surfaces of the blade  32 , making the blade  32  rotating, the power generated by the generator  4  can be calculated with the following equation: 
         [0000]    
       
         
           
             P 
             = 
             
               
                 1 
                 2 
               
                
               ρ 
                
               
                   
               
                
               
                 AV 
                 3 
               
             
           
         
       
     
         [0000]    where P is the power generated, ρ indicates air density, A represents a cross-sectional area of the rotor, and V is the speed of the air flow. It is apparent from the equation that since the air density can be considered fixed and is regarded as a constant, to change the power generated, a feasible way is to change the cross-sectional area of the rotor, or to change the speed of air flow, between which changing the speed of the airflow is of more remarkable results. 
         [0030]    Also referring to  FIG. 6 , a circular opening  51  is formed in a bottom of a container  5  that is full of liquid. The circular opening  51  has a cross-sectional area of A 1  and the speed of the liquid flow in the circular opening  51  is V 1 . By adding a horn-like hood  52  that diverges outwards under the circular opening  51 , with the cross-sectional area of the horn-like hood  52  being A 2  and the speed that the liquid flows outward being V 2 , in accordance with fluid dynamics, A 1 V 1 =A 2 V 2 , it is evident that when the liquid flows through the outward-divergent horn-like hood  52 , expansion of the liquid is induced (namely, A 2 &gt;A 1 ). Although the speed of outward flow V 2  is reduced (namely V 1  being greater than V 2 ), yet acceleration of the liquid results when the liquid enters the hood  52 . Based on the same principle, the hood  52  in accordance with the present invention is designed on the basis of the effect of expansion to accelerate the speed of air flow and thus improve the performance of power generation. For example, increasing the flow speed to 1.1 times make an increase of power generated by 1.1 3  times, namely 0.133 times of power generated. 
         [0031]    On the other hand, the power generation performance is conventionally increased by increasing area, which makes the original size increased to 1.33 times to provide the same power generation performance. This makes the conventional techniques facing problems associated with machining precision in the manufacturing thereof, as well as drawbacks associated with wastes in the respects of manufacturing and material costs. In addition, in use, due to the increase of the size of the rotor  3 , additional limitation is imposed to the installation thereof, making it difficult to get popular. Taking a generator  4  having the same power generation capacity as an example, since the speed of the incoming air flow in the present invention can be made higher, when compared to the conventional rotor  1  (see  FIG. 1 ) having a fixed air flow speed, the present invention allows a reduction of the cross-sectional area (in other words, reducing the overall size). Further, when the hood  33  is put in rotation, since no breaking of air flow occurs, the noise induced by the operation thereof can be reduced. 
         [0032]    As shown in  FIGS. 7-9 , in another embodiment, the distal ends of the blades  62  that are mounted to the central hub  61  of the rotor  6  are similarly surrounded by and coupled to a horn-like hood  63  and the hood  63  has a first circumferential edge portion  631  and a second circumferential edge portion  632  with an extension section  633  similarly formed and extending between the first circumferential edge portion  631  and the second circumferential edge portion  632 . The first circumferential edge portion  631  has a diameter that is greater than that of the second circumferential edge portion  632  so that the extension section  633  exhibits a convergent configuration. The distal end of each blade  62  is connected to an inner surface of the second circumferential edge portion  632  and each blade  62  has a wind facing surface that is in the same direction as the extension section of the hood  63 . Further, the extension section  633  of the hood  63  is of an outward-deflected curved configuration (as shown in  FIGS. 7 and 8 ) or a straight configuration that inclines outward (as shown in  FIG. 9 ). 
         [0033]    As shown in  FIGS. 8 and 9 , when winds cause air flows to enter through the wind facing side of the rotor  6 , the air flows first contact the convergent configuration of the curved or straight hood  63  (namely the side corresponding to the first circumferential edge portion  631 ), making the air flows moving toward the side corresponding to the second circumferential edge portion  632  and thus concentrated centrally with increased flow speed, whereby the force that acts on and drives the blades is increased and the power generation performance is improved. 
         [0034]    As shown in  FIGS. 10-12 , in a further embodiment, the distal ends of the blades  72  that are mounted to the central hub  71  of the rotor  7  are provided with a horn-like hood  73 . Two opposite side portions of the hood  73  respectively comprises a first circumferential edge portion  731  and a second circumferential edge portion  732 , both being convergent, with an extension section  733  similarly formed and extending therebetween. Each blade  72  is connected to the inner surface of the extension section  733  and each blade  72  has a wind facing surface that is in a direction toward the first circumferential edge portion  731 . The portion of the hood  73  from the first circumferential edge portion  731  to the extension section  733  is of an inward-deflected curved configuration (see  FIG. 11 ) or a straight configuration that inclines inward (see  FIG. 12 ) and the portion of the hood  73  from the extension section  733  to the second circumferential edge portion  732  is of an outward-deflected curved configuration (see  FIG. 11 ) or a straight configuration that inclines outward (see  FIG. 12 ). The first circumferential edge portion  731  has a diameter that is smaller than that of the second circumferential edge portion  732 . 
         [0035]    As shown in  FIGS. 13 and 14 , when winds cause air flows to enter through the wind facing side of the rotor  7 , the air flows first contact the curved or straight convergent configuration of the first circumferential edge portion  731 , making the air flows concentrated centrally to realize a first stage of acceleration. Further, since the portion from the extension section  733  to the second circumferential edge portion  732  shows a divergent configuration, based on the effect of flow expansion discussed previously, a second stage of acceleration is induced. With the two stages of acceleration, the air flows applies a speed to the rotation of the drive the blades  72  that are arranged in the extension section  733 , thereby increasing the force driving the blades  72  and more brilliantly improving the performance of power generation. 
         [0036]    As shown in  FIGS. 13 and 14 , the present inventor makes a further improvement to the construction of the blades  82  of the rotor  8 , wherein the central hub  81  of the rotor  8  is provided, at an outer side thereof, with at least one concentrically arranged connection ring  83  and a plurality of blades  82  connects between the connection ring  83  and the central hub  81 , while another plurality of blades  82  connects between the connection ring  83  and the hood  84 . The number of the blades  82  that connect between the connection ring  83  and the central hub  81  is less than that of the blades  82  connecting between the connection ring  83  and the hood  84 . The blades  82  between the connection ring  83  and the hood  84  are used to increase the rotational torque of rotor  8  without affecting incoming air flow rate (or also referred to as thickness) so as to increase the rotational speed of the rotor  8  and improve power generation performance. Further, the configuration of the hood  84  can be any one of the hoods  33 ,  63 ,  73  illustrated in  FIGS. 3-12 , such as the divergent hood  33 , the convenient hood  63  or the convergent-divergent hood  73 , and the hood  84  is connected to the outer set of the blades  82  to also effect increase of air flow speed and improvement of power generation performance. 
         [0037]    Also referring to  FIGS. 15 and 16 , the present inventor has taken records of the operations of the conventional rotor, the divergent rotor, and the multi-stage-blade rotor and comparison is made for the torque-rotational speed relationship and the performance-rotational speed relationship to evidence the difference between the present invention and the conventional techniques and the improved performance realized by the present invention. 
         [0038]    As shown in  FIG. 15 , L 1  indicates the torque-rotational speed curve of the conventional rotor, L 2  is the torque-rotational speed curve of the divergent rotor, and L 3  is the torque-rotational speed curve of the multi-stage-blade rotor, for there is a corresponding relationship between the torque and the angular momentum that drives the rotation of the rotor. When the rotational speed is zero (0), the torque generated is referred to as the brake torque (the higher the better). Comparison of theses curves indicates that the curve having a peak showing up earliest is Curve L 3  (the earlier the better), and then sequentially Curve L 2  and Curve L 1 . It can be seen that the peak torque value of the present invention appears in a lower rotational speed and thus, a good angular momentum can be obtained early at a low rotational speed, resulting in excellent power generation performance. 
         [0039]    Further, as shown in  FIG. 16 , L 4  indicates a performance-rotational speed curve of the conventional rotor, L 5  is the performance-rotational speed curve of the divergent rotor, and L 6  is the performance-rotational speed curve of the multi-stage-blade rotor. The performance (CP) is calculated with the following equation: 
         [0000]    
       
         
           
             CP 
             = 
             
               
                 τ 
                 · 
                 ω 
               
               
                 
                   1 
                   2 
                 
                  
                 ρ 
                  
                 
                     
                 
                  
                 
                   AV 
                   3 
                 
               
             
           
         
       
     
         [0000]    where τ indicates torque, ω is angular speed, P is power, ρ is air density, A is cross-sectional area of rotor, and V is speed of air flow. 
         [0040]    In accordance with the above equation, the performance curve of each rotor can be calculated. The maximum performance of the conventional rotor for conversion of wind power into mechanical power is 0.593, which is set by Betz limit and the performance can be calculated by multiplying it with a power coefficient. As shown in the drawing, the performance provided by the present invention is higher than that of the conventional techniques. In other words, using the present invention to generate power has a higher performance. 
         [0041]    To conclude, the present invention offers the following advantages: 
         [0042]    (1) As shown in  FIGS. 3-6 , the divergent hood  33  of the present invention applies the effect of air flow expansion to increase the air flow speed at the wind facing surfaces of the blades  32  to thereby improve the performance of power generation. 
         [0043]    (2) As shown in  FIGS. 7-9 , the convergent hood  63  of the present invention centrally concentrates the air flows so as to increase the air flow speed at the wind facing surface of the blades  62  to thereby improve the performance of power generation. 
         [0044]    (3) As shown in  FIGS. 10-12 , the convergent-divergent hood  73  of the present invention may centrally concentrate the air flows to provide a first stage acceleration and further applies the effect of expansion to provide a second stage of acceleration whereby dual effect of acceleration is realized to increase the force driving the blades  72  and thus effectively improve the performance of power generation. 
         [0045]    (4) Further, as shown in  FIGS. 3-12 , the various configurations of the hoods  33 ,  63 ,  73  offered by the present invention is rotated in synchronization with the blades  32 ,  62 ,  72  so that breaking air flow does not occur and the noise induced in the operation can be reduced. 
         [0046]    (5) As shown in  FIGS. 13 and 14 , the multi-stage-blade rotor  8  of the present invention comprises at least one internally set connection ring  83  and blades  82  are respectively between the connection ring  83  and the hood  84  and between the connection ring  83  and the central hub  81 , whereby without affecting incoming flow rate, the rotational torque of the rotor  1  can be increased to effect acceleration of the rotation of the rotor  1 , which also leads to improvement of the performance of power generation. Thus, as compared to the known techniques, the present invention is useful in meeting various needs for different applications and offers flexibility in design practice. 
         [0047]    While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.