Abstract:
A diffuser-augmented wind-turbine assembly in which the diffuser has a cylindrical central section rotatably supporting a rotor drum which in turn supports turbine blades without requiring a central support shaft. Wind energy drives the turbine blades and rotor drum, which in turn drive a generator of electrical power.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 60/466,124 filed Apr. 16, 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     Wind turbines are in widespread use for the generation of electrical energy. In a typical form, a multi-blade turbine is rotatably mounted on a support such as a pole or tower to be driven by surface winds, the turbine in turn driving an electrical generator coupled, for example, to electrical utility lines. The turbine can be rotated about a vertical axis of the pole or tower to compensate for shifts in wind direction. 
     The use of diffusers with wind turbines is also known, the objective being to increase the efficiency of converting wind energy to electrical energy. Such known diffusers are typically mounted on the support tower, and a shaft-mounted turbine rotates within the diffuser. Such an arrangement is disclosed in U.S. Pat. No. 4,075,500, which, for brevity, is incorporated herein by reference. 
     The improvement of this invention relates to integration of the turbine blades with a surrounding hollow cylindrical-shell rotor drum, the drum in turn being rotatably supported within a central part of the surrounding diffuser. A central hub and supporting shaft for the turbine blades is eliminated, and blade stiffness is significantly increased. The blades and rotor drum can be cast, or injection molded in a single manufacturing step. 
     SUMMARY OF THE INVENTION 
     A diffuser-augmented wind turbine for generating electrical power, and having a diffuser outer-housing shell with a cylindrical portion rotatably supporting a rotor drum having an inner surface rigidly supporting a plurality of turbine blades, the rotor drum being in driving engagement with a rotatable electrical generator. The device can also be operated in reverse as a wind-generating fan by supplying electrical energy to the generator to act as a motor. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pole-mounted wind-turbine assembly according to the invention; 
         FIG. 2  is a front view of a blade and rotor-drum assembly; 
         FIG. 3  is a sectional side elevation of the turbine assembly; 
         FIG. 4  is an exploded perspective view of the turbine assembly shown in  FIG. 3 ; 
         FIG. 5  is a view similar to  FIG. 3 , but showing a side-mounted belt-driven electrical generator; and 
         FIG. 6  is a perspective view of an embodiment using inlet guide vanes. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a diffuser-augmented wind-turbine assembly  10  according to the invention, and rotatably mounted on a conventional support pole  11  so it can be moved by a fin  12  to compensate for shifting wind directions. The assembly has an outer diffuser shell  15 , within which can be seen a blade and rotor-drum assembly  16  as described in greater detail below. 
       FIG. 2  shows assembly  16  in greater detail, and as having an outer cylindrical rotor drum  18 , with turbine blades  19  extending radially therein, and preferably integrally formed with the rotor drum. The assembly can be cast or of welded construction if made of metal (e.g., aluminum), or integrally injected molded if made from a composite material strengthened by glass, carbon, or similar reinforcing fibers. Though six blades are shown, the number of blades can be selected by the designer. Multiple blades, such as five or six, are preferred as they improve turbine efficiency, as well as increasing the rigidity of assembly  16 . 
     Turbine-blade strength and stiffness is significantly increased by the fixed support of the blades on the drum. The assembly is stable and balanced, and can be safely operated at high wind speeds encountered in storm conditions. For smaller wind-turbine assemblies which typically operate at high rotation speeds, centrifugal force compressively loads the blades, making them less prone to fatigue failure. 
       FIG. 3  is a sectional side elevation of one embodiment of assembly  10 , and shows assembly  16  as rotatably mounted within diffuser shell  15 . The diffuser shell is preferably molded from a strong composite material, and has an outwardly divergent section  21  which merges with outwardly stepped ring-shaped inner and outer cylindrical support sections  22  and  23 . An end portion  24  of the diffuser shell is separately formed, and is rigidly secured to a more forward part of the diffuser shell after the blade and rotor drum is fitted therein. The outlet end of the diffuser shell may be made more divergent to optimize aerodynamic conditions. 
     A pair of spaced-apart ring-shaped bearings  26  have outer races secured to the inner surface of support section  22 , and inner races secured to the outer surface of the rotor drum, thereby rotatably mounting assembly  16  within the diffuser shell. The absence of any clearance between the blade tips and the rotor drum (which forms a cylindrical part of the diffuser) is another feature eliminating tip losses, and producing high turbine efficiency. Magnetic bearings can also be used to augment bearings  26  for lower friction at high rotational speeds 
     The embodiment shown in  FIG. 3 , and the exploded view of  FIG. 4 , positions the components of an electrical generator assembly  28  cylindrically around the rotor drum. These components include a cylindrical assembly  29  of permanent magnets secured to the outer surface of the rotor drum to rotate therewith. Slightly outwardly spaced from the magnet assembly is a cylindrical assembly  30  of stator coils secured to a support ring  31  which is in turn rigidly secured to the inner surface of support section  23 . 
       FIG. 5  shows an alternative embodiment using a conventional drum-shaped electrical generator  33  secured at one side of support section  23 . Generator  33  is driven by a flexible timing belt  34  engaged with a toothed wheel on the generator, and extending around a cylindrically toothed section of the rotor drum. 
       FIG. 6  shows another alternative embodiment using an assembly  35  of stator vanes or inlet guide vanes secured within the inner end of outwardly divergent section  21  of the diffuser shell. The use of such vanes is a known technique enabling use of fixed-pitch turbine blades, but with the advantages of more complex variable-pitch blades. The diffuser shell can also be lined with a sound-absorbing material for noise reduction during turbine operation. 
     Other applications on the wind-turbine assembly include “reverse” operation as a wind-generating fan, by applying electrical energy to the generator which then acts as a motor to rotate the blades. Another application involves adding blades to the outside of the rotor drum which is appropriately sealed to act as a wind-driven water pump, air compressor, or fan. 
     There has been described a wind-turbine assembly featuring a diffuser-supported assembly of turbine blades. The described designs are useful in both small and large wind turbines, are economical to manufacture, and operate at high efficiency.