Abstract:
An axial flow wind turbine having forwardly swept blades with an annular ring interconnecting the blade tips. A rearwardly directed rake profile is also provided together with unequal blade spacing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Wind turbines are available in the prior art with rearwardly swept blades and with blades having forward and rearward rake profiles and such turbines have been satisfactory in general. However, none of the prior art designs has been completely satisfactory in all respects. 
         [0002]    It is the general object of the present invention to provide an improved wind turbine design incorporating a number of features, which in the aggregate result in a significant improvement in noise reduction and in overall performance. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with present invention and in fulfillment of the foregoing general object, an axial flow turbine is provided with a hub, which is mounted for rotation about an axis, and which supports a plurality of narrow radially elongated wind responsive blades in circumaxially spaced driving relationship thereabout. The blades have root portions connected with and supported by the hub and remote tip portions spaced radially outwardly from their root portions. Their cross sectional configurations are such that wind impinging thereon results in a substantial aggregate torque rotating the blades and hub in one direction. A forward sweep of each blade in a radial plane is provided by displacing the tip of each blade forwardly and this may be provided by a forwardly inclined angular arrangement of blades with linear centerlines or, preferably, by employing blades with centerlines which curve gradually forwardly with either constant or non-uniform rates of curvature. A means adding mass at the tips of the blades increases centrifugal forces generated during rotation and urges the blades in a direction opposite the direction of rotation and rearwardly to oppose forces generated by wind engaging the blades. Preferably, the means adding weight takes the form of an annular ring interconnecting the blade tips. 
         [0004]    Further, the angle of blades with linear centerlines or the rate of curvature of the centerlines is such that movement of the blades is insignificant at operating speeds of the turbine. 
         [0005]    Another feature of the invention resides in the provision of blades having rake profiles which are displaced rearwardly in axial planes and in a downwind direction. Here again, blades with straight or curved centerlines may be employed, as well as blades with partially curved centerlines. 
         [0006]    Finally, a still further feature of the invention resides in the provision of blades with unequal circumaxial spacing for reduction in noise generation. The blades may be unequally spaced at their root connections with the hub, or in the alternative, root connections may be equal with tip spacing unequal due to variation in blade centerlines. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  is a schematic front view of a turbine with forwardly swept blades in accordance with the invention, 
           [0008]      FIG. 2  is a schematic side view of a turbine illustrating blades with a rearward linear rake, 
           [0009]      FIG. 3  is a schematic view of a turbine having blades with a gradually curved rearward rake, 
           [0010]      FIG. 4  is a schematic view of a turbine with blades which have an outer portion with a rearward rake, and 
           [0011]      FIG. 5  is a schematic front view of a turbine with unequal blade spacing. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0012]    Referring particularly to  FIG. 1 , a turbine is indicated generally therein at  10  with a hub  12 , a plurality of circumaxially spaced blades, five (5) shown, at  14 ,  14  and an annular ring  16  interconnecting the blade tips. The blades are narrow, radially outwardly elongated and configured to respond to wind pressure and provide a torque in one direction. Each blade has a root portion connected with and supported by the hub  12  and a remote tip portion connected with the ring  16 . The blade tips are displaced forwardly as a result of centerlines  18 ,  18 , which curve gradually forwardly from their root portions to their tip portions to provide a forward blade sweep. Alternatively, the blades may have linear centerlines angularly arranged to provide a forward sweep. Preferably, the blades have arcuate centerlines as shown with constant angles of curvature selected to cooperate with centrifugal force to provide insignificant blade movement at operating speeds. As shown, the blades  14 ,  14  have tip displacements of approximately nine degrees, although tip displacements in the range one tenth of one degree to twenty degrees are contemplated. 
         [0013]    The annular tip ring  16  interconnecting the blade tips, in addition to enhancing the generation of centrifugal force, tends to minimize vortices adjacent the blade tips and as a result noise generation is reduced and turbine performance enhanced. Twisting of the long narrow blades about their centerlines is also reduced by the ring  16 . 
         [0014]    Turbine  10   a,  best illustrated in  FIG. 2 , has a hub  12   a,  blades  14   a,    14   a  and an end ring  16   a.  As will be obvious from an inspection of the drawing, the blades  14   a,    14   a  have a rake profile with their tip portions displaced rearwardly, or downwind, in relation to their root potions. The blades have linear centerlines  18   a,    18   a  in  FIG. 2  but gradually curved centerlines as at  18   b,    18   b  in  FIG. 3  are contemplated as well as blades having only portions  20 , 20  near their tips curved rearwardly as in  FIG. 4 . 
         [0015]    Irrespective of the precise configuration, the displacement of each blade tip portion relative to its root portion should fall in the range of one degree to fifteen degrees and, preferably, the displacement should be approximately five degrees. 
         [0016]    In  FIG. 5  turbine  10   b  has a hub  12   b,  blades  14   b,    14   b,  and an end ring  16   b.  The blades  14   b,    14   b  may have any of the configurations described above but the circumaxial spacing thereof must be unequal in accordance with another aspect of the present invention. As shown, the blades  14   b,    14   b  have gradually curving centerlines  18   b,    18   b  in a forward sweep configuration as described above and their tip portions are unequally spaced circumaxially, spacing progressing from seventy degrees to seventy four degrees for the five blades shown. The root spacing is equal in  FIG. 5  but the tip spacing unequal, but it will be obvious that unequal spacing may be provided at both root and tip portions of the blades. Substantial reduction in noise generation is achieved with the configuration shown. 
         [0017]    From the foregoing it will be apparent that each of the features of the invention has merit either in noise reduction or in improvement in performance. In the aggregate, substantial overall improvements in both noise reduction and in performance are achieved.