Prime-mover dynamo plants – Electric control – Fluid-current motors
Reexamination Certificate
2001-02-12
2002-10-15
Waks, Joseph (Department: 2834)
Prime-mover dynamo plants
Electric control
Fluid-current motors
C415S004200
Reexamination Certificate
active
06465899
ABSTRACT:
The present invention relates to an omni-directional wind turbine and more particularly to a vertical-axis turbine with expanded capability of converting wind power to electrical power.
BACKGROUND OF THE INVENTION
The ever increasing global demand for electricity and the effect the generation of such has on the ecosystem, in concert with the lack of natural resources to keep up with growing demand, has provided new impetus to look toward the development of alternative and renewable energy sources.
Vertical-axis wind machines are well known in the art, as shown in U.S. Pat. No. 5,664,418—Walters and the patents cited therein, and have been the subject of numerous innovative proposals. Such wind machines have the inherent advantages of stability due to gyroscopic action of the rotor, simplicity of design due to the avoidance of yaw mechanisms and blade controls, and strength of construction. However, the fact that the sails of the rotor are exposed to the force of the wind during only one-half of each cycle and then must be shielded from the wind to prevent creation of back pressure during the remaining half of each cycle has been a major problem. A variety of structural changes have been proposed in an effort to avoid or minimize formation of back pressure on the sails during their return sweep, for instance: the segmented sails of Wilhelm—U.S. Pat. No. 5,004,878, the louvered sails of Darvishian—U.S. Pat. No. 4,015,911 and the reversal of a portion of the air stream of Baughman—U.S. Pat. No. 4,350,900. But these, and similar, efforts have not been successful in overcoming the problems associated with the prior known vertical-axis wind machines. As a consequence, vertical-axis machines have not been commercially attractive and have not achieved substantial acceptance in competition with the horizontal-axis windmills.
The windmill construction which has been most commonly utilized for the generation of electricity is a plural-bladed propeller positioned vertically for rotation about a horizontal axis. This type of construction has been widely used because, when positioned into the wind, the entire surface of each blade of the propeller is exposed to the full force of the moving air. The commercial windmill industry has developed around the horizontal-axis construction and the aerodynamic principles and knowledge discovered in connection with atmospheric flight. Accordingly, it has become common practice to design such machines for the atmospheric/wind conditions of specific locations by varying the number and/or dimensions of the blades employed. The fewer the propeller blades, the more efficient the machines become at high wind speeds but the less efficient they are at lower wind speeds.
Because the blades of horizontal-axis windmills are coupled indirectly to an electric generator which is effective only at a constant design speed, and because the blades themselves become unsafe at high speeds, the horizontal-axis windmills have been capable of utilizing only a small percentage of the theoretically-available power in the wind. The multi-blade windmills have high starting torque at low wind speeds, harvesting up to 30% of the kinetic energy from the wind but become very inefficient at high wind speeds. The Dutch 4-blade machines, for instance, utilize only about 16% of the winds' kinetic energy. The most common and efficient windmills today are of the two and three blade types designed for high tip speed operation. These machines harvest roughly 42% of the theoretical 59.2% kinetic energy from the wind. Such windmills operate within a narrow window or range of wind velocities defined by a cut-in wind speed of 3-5 mps (meters/sec.) and a cut-out wind speed of about 25 mps. To maintain a near constant level of torque to drive the generator has required either: complex controls, in the case of pitch control, or intricate blade designs, in the case of stall control, both of which are expensive to build and maintain. In addition, such wind machines require yaw mechanisms with motors, gearboxes, cable twist counters, etc. to keep the machine yawed against the wind. These requirements have combined to make the horizontal-axis windmills economically unattractive except in areas where alternative forms of electricity generation are not readily available.
Today's windmill designs also have other drawbacks. They have problems with gyroscopic vibration when the machine veers with changing wind direction. They are vulnerable to high bending moments at the base or root of the blades as each blade passes by or into the wind-shade of the supporting mast as well as when being braked during tempest conditions. These bending moments lead to frequent blade replacements and high maintenance costs. Because of their massive structures, these machines, of necessity, are remotely located miles from the area of power usage, thus necessitating construction of expensive power grids to transport the energy produced to the point of consumption, (generally large cities). Consequently, an approximate eight to ten percent of the power generated never reaches its destination due to line and transformer losses. Lastly, because of opposition from environmentalists with regard to the esthetics in natural settings as well as prohibition from municipal regulating authorities due to safety hazards associated with these large-prop machines in populated areas, many areas which would be ideal for generating wind energy, such as atop large buildings, are simply off-limits due to opposing design constraints.
SUMMARY OF THE INVENTION
The present invention avoids the shortcomings of the prior known wind turbines by provision of a vertical-axis wind turbine which can be safely and efficiently operated over an expanded range of wind velocities.
The above object is realized by providing a vertical-axis wind turbine which includes a rotor/stator combination with provision for maximizing energy production by means of increasing wind velocity and pressure as well as eliminating back pressure. The rotor is connected in driving relation with a plurality of electrical generators which are capable of producing harmonic-free alternating or direct current and means for activating said generators in series or in parallel in accordance with a predetermined program.
The stator section of the present invention is constructed with upper and lower annular, conical sails joined by a series of arcuate deflection blades which circumscribe the turbine's rotor at a predetermined angle. Since the kinetic energy of wind varies as a cube function, or third power, of its speed, the stator has been designed to utilize the law of conservation of angular momentum; effectively increasing the wind speed and kinetic energy at the rotor. Wind entering the vortical section of the stator is directed, concentrated and compressed to a higher velocity and energy level as it is focused cyclonically toward the airfoil blades of the rotor via the narrowing channels of the stator. As a result, at slow wind speeds the wind energy is increased and the envelope of operation of the turbine is widened, while at high wind speeds the flow across the stator blades will stall and create back pressure to be self limiting. The rotor blades feed upon this intensified wind energy, providing it with a much higher power output than can otherwise be obtained using a standard prio-art turbine per a given wind speed. Wind moving around the periphery of the stator will induce an area of significant low pressure on the concave side of all obstructive or wind-shade stator blades as a result of the venturi effect. This venturi (vacuum) not only eliminates back pressure on the return side of the rotor, but adds considerably to the overall torque. As the expended air exits the turbine it loses velocity as well as kinetic energy while it diffuses outwardly through the expanding vortical channels on the antipodal side of the stator so it merges smoothly with the air moving circumferentially around the turbine and moves smoothly and rapidly away.
The stator section of the turb
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