Fluid reaction surfaces (i.e. – impellers) – Method of operation
Reexamination Certificate
1999-03-22
2001-08-14
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Method of operation
C416S064000, C416S079000, C416S083000, C416S066000, C416S068000, C416S081000, C416S082000
Reexamination Certificate
active
06273680
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention comprises improvements to the methods and apparatus disclosed in my earlier U.S. Pat. No. 4,184,805 (January 1980) and U.S. Pat. No. 4,347,036 (August 1982) and, in general, is useful in Oscillating Cascade Power Systems (OCPS).
1. Field of the Invention
The present invention relates to techniques and apparatus for using the kinetic energy of a moving fluid stream and more particularly a cascade of aero- or hydro-foils oscillating in such a stream. These will produce useful work, e.g. generate electricity, by removing energy from the stream or produce propulsion by adding externally supplied energy to create a negative drag.
2. Description of the Prior Art
The continuing search for alternative sources of energy has caused a renewal of interest in utilizing the essentially inexhaustible kinetic energy of moving fluids such as wind, stream, river and ocean currents. These are derivative solar energy sources in that they are driven by solar heating. The windmill is a simple example of a device capable of harnessing such energy but is of limited utility because of the large centrifugal forces produced by large rotating blades, the dependence of the operating frequency on wind speed and the need for large areas of production, i.e. the circle made by the rotating blades, to produce sufficient power from naturally occurring wind flows.
One alternative to the windmill is disclosed in U.S. Pat. No. 4,024,409 to Peter R. Payne. This patent discloses a device including a wire which is oscillated by the shedding of vortices therefrom which oscillations are then converted into useful work. Like the aeolian harp, the Tacoma Narrows bridge and a street sign flapping in a gust of wind, this type of movement is induced when vortices are shed from a blunt body at a frequency in resonance with the natural frequency of the object. The patent also discloses the use of a single blade oscillated in response to wind conditions. However, as the windmill, the amount of energy which can be harnessed is limited. Furthermore, such oscillations are due to the Karman vortex street phenomena rather than the aeroelastic phenomenon of flutter.
U.S. Pat. No. 3,995,972 discloses a device including a stack of rigidly interconnected aerofoils positioned in a wind stream. By sequentially varying the angle of attack of the aerofoils, uniform oscillatory motion is produced for reciprocating a rod which then in turn drives an output device. The disadvantage of this system, like the windmill, is that there is no way to compensate for variations in wind speed to assure a substantially constant power output at a substantially uniform frequency.
Some work has also been done on the production of negative drag in the case of a single oscillating aerofoil, see I. E. Garrick,
Propulsion of a Flapping and Oscillating Airfoil,
NACA Rep. No. 567, May 1936.
It has long been known that a great amount of energy is available when an aerofoil is subjected to the phenomenon of aeroelastic flutter. While this phenomenon also applies to hydrofoils at sufficiently high water speeds, this was not observed in nature. Furthermore, studies of this phenomenon have been directed solely to preventing its occurrence because if left uncontrolled, it would lead to the eventual destruction of the aerofoil. My U.S. Pat. Nos. 4,347,036 and 4,184,805 addressed the useful application of this phenomenon for energy production and propulsion; these are extended here.
SUMMARY OF THE INVENTION
The present invention extends those disclosed in my earlier patents to improve their efficiency and applicability in naturally occurring fluid streams. It avoids the disadvantages of prior art by means of a novel method and apparatus for efficiently harnessing large amounts of the available energy from a moving fluid stream with a cascade of foils positioned therein. Except when specifically referring to a particular fluid, the term “aerofoil” as used below will include the concept of a hydrofoil as well with appropriately modified language, e.g. hydrosystem for aerosystem, etc. The term “aerofoil” is used in place of the more usual “airfoil” to emphasize this connection and to emphasize the use of such foils in energy generation rather than lift for aircraft.
Another aspect of the invention is the application of this novel method to a hydroenvironment. While flutter is not generally observed at naturally occurring water speeds, if the inertia of the system is increased by the use of flywheels attached to the generators or in between the hydrofoils and the generator system, flutter has been experimentally verified for hydrosystems.
According to one aspect of the invention, there is provided a novel method for converting the kinetic energy of an air flow into useful work by positioning a cascade of thin aerofoils in a moving stream to define an aerodynamic system. The aerofoils are at zero angle of attack when undisturbed and each aerofoil has two degrees of freedom with adjacent aerofoils moveable out of phase. The system is then adjusted until the speed of the fluid stream is a critical velocity for the system sufficient to induce flutter oscillations. The aerofoils are then disturbed and the resultant oscillations of the aerofoils are utilized to produce useful work. Variations in the fluid speed are detected and the system controlled to maintain critical velocity and steady state oscillations.
According to another aspect of the invention, there is provided apparatus for converting the kinetic energy of a fluid stream to useful work comprising a support structure open at opposite ends to permit fluid flow therethrough with a plurality of thin aerofoils and means for mounting these aerofoils within the support structure in a cascade and at zero angle of attack when undisturbed. In addition, the aerofoils are provided with at least two degrees of freedom with adjacent aerofoils moveable out of phase with each other. The support structure consists of a frame with barriers below and/or above and to the sides to channel flow through the structure, thereby increasing its speed and thus the efficiency of the system. The apparatus further includes means for utilizing the oscillatory movement of the aerofoils to produce useful work.
The aerofoils are preferably arranged in two subsystems of alternating foils, the aerofoils of each subsystem being interconnected to oscillate in phase. The subsystems may be interconnected to move 180 degrees out of phase or may be interconnected solely with oppositely acting mechanical oscillators which maintain and enhance the flutter oscillations and also provide the initial disturbance of the aerofoils within the fluid stream.
A control system may also be provided to maintain the flutter oscillations when the velocity of the fluid varies.
According to a further aspect of the invention, there is provided a method for converting the kinetic energy of the fluid stream into useful work by positioning a device including a pair of parallel plates and a thin aerofoil equally spaced from each plate and having at least two degrees of freedom within the fluid stream. The plates are positioned parallel to the free stream and the aerofoil is at zero angle of attack when undisturbed to define an aerodynamic system. The system is then adjusted until the velocity of the fluid is sufficient to induce flutter oscillations, the aerofoil is disturbed and the resultant oscillations are utilized to produce useful work.
According to a still further aspect of the invention, there is provided apparatus for converting the kinetic energy of a fluid stream into useful work comprising a support structure open at opposite ends to permit fluid flow therethrough and including a plurality of equally spaced flat plates extending parallel to the direction of fluid flow, a plurality of aerofoils within the support structure in a cascade with each aerofoil having at least two degrees of freedom and being equally spaced between adjacent flat plates at zero angle of attack when undisturbed, means interconnecting the aerofoils to osc
Holt William H.
Verdier Christopher
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