Patent Application
20210317816
The present disclosure relates to fluid turbines. Classifications might include “F03D3/0427, Wind motors with rotation axis substantially perpendicular to the air flow entering the rotor having stationary wind-guiding means, e.g. with shrouds or channels with augmenting action, i.e. the guiding means intercepting an area greater than the effective rotor area;” “G08G5/0095, Aspects of air-traffic control not provided for in the other subgroups of this main group;” and “F03D7/02—Controlling wind motors the wind motors having rotation axis substantially parallel to the air flow entering the rotor.”
In general, vertical-axis fluid turbines comprise arrays of vertical rotor blades arranged evenly about a central, vertical axis and coupled to an electrical generation machine. A Savonius turbine is commonly referred to as a drag-driven turbine. In this type of wind turbine, Some of the stream volume encounters a rotor blade on the downwind side of the vertical axis and some of the stream volume encounters a blade on the upwind side. The rotor blade shape reduces drag as the rotor moves against the wind on the upwind side of the rotor. When moving with the wind on the downwind side of the rotor, the shape of the rotor increases drag.
A datum plane is an imaginary surface from which measurements or locations are measured. Some examples of this embodiment refer to a non-planar surface as a datum surface. A datum sphere is an imaginary spherical surface connoting a measurement or location of objects in space that lie on the surface of a sphere.
Fluid turbines generate electricity from a fluid stream. One skilled in the art understands that air is a fluid and water is also a fluid. The aerodynamic principles that govern a wind turbine may function as hydrodynamic principles in a water turbine. In this disclosure example terms such as “wind” “fluid” and “stream” may be used interchangeably.
Generally, a fluid turbine captures energy from a fluid stream. As fluid flows from the upstream side of the rotor to the downstream side, the average axial fluid velocity remains constant as the flow passes through the rotor. Energy is extracted at the rotor, resulting in a pressure drop on the downstream side. The fluid directly downstream of the rotor is at sub-atmospheric pressure due to the energy extraction. The fluid directly upstream of the rotor is at greater-than-atmospheric pressure. The high pressure upstream of the rotor deflects some of the upstream air around the rotor, diverting a portion of the fluid stream around the open rotor as if by an impediment. As the fluid stream is diverted around the open rotor, it expands. This is referred to as flow expansion at the rotor.
According to Betz's Law, a maximum 59% of the total energy in a column of wind may be extracted by an open-rotor turbine. As a wind turbine extracts energy from a column of wind, the wind in the wake of the rotor plane slows down, creating relatively lower air pressure and lower energy flow in the wake. The low-pressure, low-energy air impedes the column of wind in its approach. As a result, some of the wind flows around the rotor blades. This is known as bypass flow. Bypass flow contains energy that cannot be captured by the turbine. The more energy extracted by a wind turbine, the more impediment is encountered. This, in general, is the reason only 59% of wind energy can be captured.
A fluid-turbine power coefficient is the power generated divided by the ideal power available by extracting all the wind's kinetic energy approaching the rotor area. It is commonly known that rotor wake affects rotor intake. A volume of fluid encounters a rotor as an impediment in part because a portion of the fluid flowing around the rotor expands in the wake of the rotor in a form referred to as stream volume.
Bypass flow passes over the outer surface of the stream volume. The amount of energy extracted from the stream volume creates slower-moving flow in the rotor wake, impeding flow through the rotor. This impediment increases the volume of the rotor wake. As more power is extracted at a rotor, the rotor stream volume will expand and more fluid flow will bypass the rotor. If a significant amount of energy is extracted, most of the fluid flow will bypass the rotor and the rotor can effectively stop extracting energy, a condition known as rotor stall. Thus maximum power is achieved from the two opposing effects: that of increased power extraction resulting in relatively lower flow rates, and that of reduced power extraction resulting in relatively higher flow rates. Greater efficiency can be achieved by increasing the speed of a rotor wake. Wake-flow velocity may be increased by injecting higher velocity fluid streams into the wake flow, thus allowing for increased power extraction at the rotor and providing a relatively greater coefficient of power.
In an example embodiment, a Savonius-type vertical-axis wind turbine has a plurality of revolute blades arranged on its vertical axis. The blades' outer surfaces form a substantially spherical shape. Each of the revolute rotor blades captures air flow like any vertical turbine: perpendicular to the axis of rotation. The rotor blades are concave on their inner side and convex on their outer side, and arcuate at top and bottom surfaces, together forming a substantially spherical shape or datum sphere. This shape enables increased drag on the concave, inner side and reduced drag on the convex, outer side. The shape of the blades enables airflow through the center of the array, which is open. The ratio of open space in the center of the turbine to that of the rotor blades is between 1:5 and 1:7. A flow path through the substantially spherically shaped turbine blades increases in volume as it approaches the center of the sphere and decreases as it exits the sphere. Air flowing through a concave side of a first blade, through the open center and out along the concave surface of a second blade is also flowing through the spherical form and is therefore compressed at the exit as the flow path decreases in size.
A portion of the stream volume encounters a rotor blade on the downwind side of the vertical axis, and a portion of the stream volume encounters a rotor blade on the transverse, upwind side of the vertical axis. On the downwind side of the vertical axis, the convex side of each rotor blade faces upwind. An open center on the vertical axis allows some wind to flow through the turbine. The exhaust wind, having encountered the concave side of a rotor blade at a position referred to as θ=0°, continues through the center of the turbine and flows through a downwind blade, which is also referred to as a blade at position θ=90°, increasing the rotational velocity of the blade about the turbine vertical axis. Some of the wind that flows through an upwind rotor blade, otherwise referred to as a blade at θ=270°, flows through the center of the turbine and continues out through the concave side of a blade at position θ=270°, and out into the wake of the turbine, thus reducing the pressure on the back side of the upwind rotor blade. Injection of relatively higher speed air behind a rotor, minimizes wake pressure, reinforces the motion and reduces the pressure differential between the ambient flow and the wake.
The blades' substantially spherical shape causes air to flow into each subsequent blade portion by directing the flow toward the hollow center of the blade array and into the concave portion of the adjacent blade, which is in a downwind position. The spherical shape formed by the edges of each blade also serve to compress the exiting flow. This flow increases in velocity as it is compressed. The increased velocity allows more mass flow into the turbine, and helps dissipate the wake flow as it exits the turbine. Quicker wake-dissipation results in faster down-stream air recovery to ambient pressure. A reduced wake allows the turbines to be arranged more closely together in columns in a turbine field, improving efficiency.
In some embodiments, ultraviolet coloration of the rotor blades deters wildlife from approaching. Rotor blades are made of a composite-fiber-reinforced polymer with an ultraviolet reflective dye or laminated by an ultraviolet polymer film. The ultraviolet reflective surface appears fluorescent to birds but not to humans.
In
The rotor blades 110 are connected to a shaft 117 that turns a generator 115. A housing 119 is located proximal to the rotor blades 110 and houses electronic controls. The apparatus is mounted on a base 123. The overall shape of the blades when assembled is that of a sphere. In an example embodiment, rotor blades are constructed of a fiber-reinforced polymer combined with a dye that appears fluorescent to birds and as monochromatic to humans.
The illustration in
While example embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63009866 | Apr 2020 | US |
