Rotary kinetic fluid motors or pumps – With means for controlling casing or flow guiding means in... – Natural fluid current force responsive
Reexamination Certificate
2002-06-24
2004-02-10
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With means for controlling casing or flow guiding means in...
Natural fluid current force responsive
C415S004400, C415S907000, C416S140000
Reexamination Certificate
active
06688842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to wind turbines and the like, and more particular to a vertical axis wind turbine that utilizes the kinetic energy of moving air to provide rotational energy useable for generating electric power and/or other useful purposes.
2. Description of Related Art
Wind turbines usually take the form of horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs). By virtue of their vertical axes of rotation, VAWTs do not require alignment with the windstream. In addition, drive train components can be located at ground level instead of being mounted higher above ground at HAWT rotor level. For those and other reasons, VAWTs attract attention . . . especially for commercial electric power generating purposes.
VAWTs include drag-based designs and lift-based designs. U.S. Pat. No. 226,357 issued Apr. 6, 1880 to Saccone, for example, describes an early, drag-based, vertical axis, windmill design. Designed over twenty years before the Wright brothers' flight, the windmill uses flat “fans” mounted pivotally on a support structure in order to catch the wind and cause the support structure to rotate. As the fans orbit the vertical axis, they pivot between a downwind orientation, in which each presents a broad profile in order to catch the wind, and an upwind orientation in which each presents a narrower profile for less drag. The windmill was designed without the benefit of aerodynamic design and performance theory. Operation is jerky, rough, and slow as the fans are continually pulled out of position by centrifugal force. The fans provide drive only intermittently during a somewhat small portion of each rotation. Upright bars at the outermost ends of the fans are highly disruptive to airflow. The system cannot achieve rotor speeds faster than wind speed.
U.S. Pat. No. 2,038,467 issued some fifty-six years later on Apr. 21, 1936 to Zonoski describes another vertical axis, drag-based, windmill design utilizing flat “vanes” on a rotatable frame. The two-phase vanes are better balanced. As they orbit the vertical axis, they pivot about 170 degrees, or so, between a high-drag downwind orientation and a low-drag upwind orientation. Although the windmill shows potential for drag rotation over 180 degrees of each revolution, wind shadow and vane interference reduces overall effectiveness, and relative wind reduces the draft phase to less than 180 degrees. U.S. Pat. Nos. 4,408,956; 4,474,529; and U.S. Pat. No. Des. 300,932 show other drag-based designs.
U.S. Pat. No. 4,383,801 issued May 17, 1983 to Pryor shows a lift-based VAWT. It includes vertically aligned airfoils mounted pivotally on a rotatable support. As the airfoils drive the support, they orbit the vertical axis. Meanwhile, a wind-vane-controlled pitch adjustment continually orients the airfoils relative to the wind direction. The machine detects wind direction by means of a vane and positions the controlling pitch flange accordingly. The mechanism is somewhat complicated, and positioning of the airfoils (angle of attack) is optimized only in the directly upwind and directly leeward positions, using crosswind lift force in both cases. In addition,
FIGS. 8 through 11
in the patent illustrate somewhat complex mechanisms for manipulating the airfoil shapes. The airfoils are underutilized during most of each rotation. The additional control appears to be an attempt to improve the efficiency of the machine. In a class of VAWTs called cycloturbines, the pitch of the airfoils is controlled to create crosswind lift, but they must run at rotor speeds in excess of wind speed to be effective. They also frequently have difficulty self-starting.
Thus, the prior art has progressed to the use of airfoils in lift-based VAWT designs. More efficient conversion of wind energy is still desirable, however, along with better VAWT mechanical attributes. So a need exists for a better VAWT . . . preferably a lift-based VAWT incorporating benefits of modern aerodynamic design and performance theory.
SUMMARY OF THE INVENTION
It is an object of this invention to overcome the forgoing and other disadvantages of prior art wind turbines. This object is achieved by providing a VAWT (referred to herein as a vertical axis wind engine) having “free flying” airfoils that self position according to the local dynamic conditions to which they are subjected, thus creating a condition of equilibrium under which a highly efficient means of wind energy extraction may be established. More particularly, the vertical axis wind engine includes a rotor mounted on a support structure for rotation about a vertical axis. At least one airfoil mounted pivotally on the rotor (preferably more than one) causes the rotor to rotate under influence of the wind. The airfoil is mounted on the rotor so that it is free to pivot between preset first and second limits of pivotal movement (e.g., set by stop mechanisms). That arrangement enables the airfoil to align according to the wind as it orbits the vertical axis, thereby achieving better conversion of wind energy to useable rotational energy by combining lift and drag characteristics at low speeds and shifting to lift-only characteristics at rotor speeds approaching or exceeding local wind speed.
The dynamic phase lag effect of the free flying airfoils creates a “virtual stop.” Recall the Law of Conservation of Angular Momentum and consider its influence in combination with airfoil responsiveness to the instantaneous force of the true relative wind (TRW) acting on an airfoil. The result is that the airfoil resists rotational changes along its pivotal axis and shifts out of phase relative to its rotor position. That is what the stops do also. The stops cannot be completely eliminated, however, because they are required during start-up, operation at low speed, heavy load conditions, turbulence, and wind direction shifts requiring reorientation and stabilization of the system. The stops are important in getting the system up to equilibrium speed.
To paraphrase some of the more precise language appearing in the claims and introduce the nomenclature used, a vertical axis wind engine constructed according to the invention includes a support structure, a rotor mounted rotatably on the support structure for rotation about a vertical axis, and at least one airfoil mounted on the rotor for causing the rotor to rotate about the vertical axis in response to wind passing the wind engine. The airfoil has vertically extending leading and trailing edges, an angle-of-attack axis extending horizontally through the leading and trailing edges, and a pivotal axis extending vertically intermediate the leading and trailing edges. The airfoil is mounted on the rotor for pivotal movement about the pivotal axis and the rotor includes means for limiting pivotal movement of the airfoil to first and second limits of pivotal movement.
According to a major aspect of the invention, the airfoil is mounted on the rotor so that the airfoil is free to pivot about the pivotal axis intermediate the first and second limits of pivotal movement as the rotor rotates about the vertical axis. That arrangement enables the airfoil to align the angle-of-attack axis continually according to the wind as it orbits the vertical axis. Preferably, the wind engine has more than one airfoil and the rotor includes first and second stops for each airfoil that limit pivotal movement to a radially aligned first limit and a tangentially aligned second limit. According to another aspect of the invention, multiple wind engines are stacked. Yet another aspect provides an exponentially shaped structure surrounding the vertical axis that funnels wind toward the rotor.
In terms of its many advantageous design features, the wind engine of the invention is a vertical axis wind engine with one or more self-positioning airfoils that achieve better conversion of wind energy to useable rotational energy by optimizing the lift and drag characteristics within the appropriate rotor speed ranges. The design uses no cams,
Hanson Loyal McKinley
Look Edward K.
McCoy Kimya N
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