Patent Application
20110070083
1. Field
Embodiments of the present invention relate to the field of wind turbines and fluid turbines for converting one form of energy (for example, an airflow energy) into another form of energy.
2. Description of the Related Art
Wind power is capable of being converted to mechanical energy by using wind turbines. Average wind speeds in most parts of the world, however, are insufficient to make efficient use of existing wind turbine technology. Conventional wind turbines, with long blades capable of spinning at speeds of 200 miles per hour, are also a serious hazard to birds.
With increased demand for cleaner sources of energy, such as wind-powered turbines, it is desirable to provide an efficient wind turbine capable of delivering reasonable amounts of power in average wind speed environments. It is also desirable to have a wind turbine that is less dangerous to native bird populations.
Embodiments of the present invention address these problems through a wind turbine body design that directs the airflow in such a manner so as to significantly increase its velocity before it reaches the blades. This, combined with numerous short blades, allows these embodiments to harness significant amounts of wind energy (which in turn can lead to significant amounts of electric power) even in average wind speed environments (and with significantly less risk to native bird populations).
As illustrated in
Various configurations are provided, including single or multiple bodies, stationary or floating, where some or all of the body rotates in response to an airflow directed at the body. Fixed body portions may also be used for advertising, while rotating portions may, for example, have synchronized lights. The body can be any size. The embodiments of the present invention can also be applied to media other than wind, such as fluids, streams, etc.
In an exemplary embodiment according to the present invention, a wind turbine body is disclosed. The wind turbine body includes a curved body and a plurality of blades. The curved body includes a front portion, a rear portion, and a middle portion between the front portion and the rear portion. The curved body is configured such that at least the middle portion rotates about an axis of rotation. A diameter of the curved body gradually increases from the front portion to the middle portion, and gradually decreases from the middle portion to the rear portion. The blades are attached to and around the middle portion about the axis of rotation. The blades are configured to convert an airflow energy into rotational motion energy of the middle portion.
The curved body may be sphere shaped.
The curved body may be torpedo shaped.
The curved body may be teardrop shaped.
The curved body may be inflatable.
The curved body may be configured to be filled with lighter-than-air gas and the middle portion may be configured to rotate while floating.
The curved body may be configured to attach to a pole.
The wind turbine body may further include an axle along the axis of rotation.
The axle may be configured to attach to a supporting frame.
The wind turbine body may further include the supporting frame.
The supporting frame may be configured to attach to a pole.
Each of the blades may have a height in a radial direction of the axis of rotation that is substantially equal to a thickness of a laminar layer at the middle portion.
Each of the blades may have a shape of an airfoil.
According to another exemplary embodiment of the present invention, a wind turbine is disclosed. The wind turbine includes a wind turbine body and a fin. The wind turbine body includes a curved body and a plurality of blades. The curved body includes a front portion, a rear portion, and a middle portion between the front portion and the rear portion. The curved body is configured such that at least the middle portion rotates about an axis of rotation. A diameter of the curved body gradually increases from the front portion to the middle portion, and gradually decreases from the middle portion to the rear portion. The blades are attached to and around the middle portion about the axis of rotation, and configured to convert an airflow energy into rotational motion energy of the middle portion. The fin is at the rear portion and configured to steer the wind turbine about a steering axis so that the front portion faces the airflow.
The curved body may be teardrop shaped.
The curved body may be configured to be filled with lighter-than-air gas and the middle portion may be configured to rotate while floating.
The curved body may be configured to attach to a pole along the steering axis.
The wind turbine may further include an axle located along the axis of rotation.
The axle may be configured to attach to a supporting frame.
The wind turbine may further include the supporting frame.
The supporting frame may be configured to attach to a pole along the steering axis.
Each of the blades may have a height in a radial direction of the axis of rotation that is substantially equal to a thickness of a laminar layer at the middle portion.
Each of the blades may have a shape of an airfoil.
In yet another exemplary embodiment according to the present invention, a wind turbine is disclosed. The wind turbine includes a plurality of wind turbine bodies, an interconnecting frame for connecting the wind turbine bodies, and a fin. The wind turbine bodies are for converting an airflow into rotational motion. Each of the wind turbine bodies includes a curved body and a plurality of blades. The curved body includes a front portion, a rear portion, and a middle portion between the front portion and the rear portion. The curved body is configured such that at least the middle portion rotates about an axis of rotation. The diameter of the curved body gradually increases from the front portion to the middle portion, and gradually decreases from the middle portion to the rear portion. The blades are attached to and around the middle portion about the axis of rotation. The blades are configured to convert the airflow into rotational motion of the middle portion. The fin is configured to steer the wind turbine about a steering axis so that the front portion of each of the wind turbine bodies faces the airflow.
The fin may be located on the interconnecting frame.
The wind turbine bodies may be all of a same shape and size.
The shape may be a teardrop.
The curved body of each of the wind turbine bodies may be configured to be filled with lighter-than-air gas and the middle portion of each of the wind turbine bodies may be configured to rotate while floating.
The frame may be configured to attach to a pole along the steering axis.
Each of the wind turbine bodies may further include an axle along its respective axis of rotation.
The axle of each of the wind turbine bodies may be attached to the interconnecting frame.
Each of the blades may have a height in a radial direction of its respective axis of rotation that is substantially equal to a thickness of a laminar layer of its respective curved body at the middle portion.
Each of the blades may have a shape of an airfoil.
The accompanying drawings illustrate embodiments of the present invention, and together with the description, serve to explain the principles of the embodiments of the present invention.
The illustrative embodiments that follow are only exemplary applications of the present invention and not intended to limit the scope of the invention. In the drawings, like reference numerals denote like structures throughout.
Wind power is capable of being converted to mechanical energy by using wind turbines. This mechanical energy can then be converted to other forms of energy (for example, heat exchange, gravity, generator, pump, and the like). While wind power may offer an attractive source of clean energy, average wind speeds and existing wind turbine technology limit its applicability. According to a study by Cristina Archer and Mark Jacobson from Stanford University “Evaluation of Global Wind Power,” the global average 10 meter altitude wind speed over land is 3.28 m/s (meters per second), while the 80 meter altitude (typical for 77 m diameter conventional wind turbines) wind speed over land is only slightly better, namely 4.54 m/s. Neither of these speeds is sufficient for efficient use of conventional wind turbines.
Referring to
For illustration purposes, curve 1310 is also depicted in curve 1330 at 1.5 times the average wind speed and in curve 1340 at 2 times the average wind speed. Comparing these faster wind speed curves to the coefficient curve 1320, it can be seen that in order for conventional wind turbines to operate as efficiently as they are capable, wind speeds more like 1.5 or 2 times the average wind speed are necessary.
An efficient conventional three-blade wind turbine extracts less than one-half of the kinetic energy at the optimal wind speed. However, during the spinning process, the blade tips can shed vortex and create swirl wakes, causing energy loss. Most of the torque generated from conventional wind turbines comes from the tip areas of the blades, which can attain speeds as high as 200 miles per hour (on a side note, these large, high speed blades can be lethal to birds that stray in their path). That is why conventional blades are so long, in order to generate as much torque as possible. Meanwhile, the shaft end of the blade next to the center hub travels very little compared to the blade tip. Thus, the shaft end contributes very little in the way of torque.
To harness more power using a conventional three-blade wind turbine, it is necessary to either install it at a higher altitude to catch faster wind speed or extend the wind turbine blades (that is, make them longer) to capture a larger wind area. Extending the blades, however, may easily cause breakdown of the blades due to increased centrifugal force and stress on the blades. It may also require more wind speed to operate since longer blades are likely to be heavier and harder to rotate.
In addition to the limitations of the regular turbine structure itself, having access to the useful wind speed is another challenge. It is generally acknowledged that at least a wind speed of five meters per second, or about eleven miles per hour, is required in order to make energy recovery economically feasible using a conventional wind turbine. In vast urban areas, where energy is needed most, it is not feasible to do so due to the low wind speed.
It is well known that captured power=torque×RPM, and torque=force(lift)×radius. Further, lift can be expressed as
lift=coefficient of lift×0.5×air density×blade surface area×(air velocity)2×number of blades
Increasing torque and/or RPM will enhance the ability of capturing more power. Embodiments of the present invention address areas of both increasing wind speed (RPM) and increasing torque.
Based on Bernoulli's Principle, air flowing over a curved object travels faster than air flowing over a straight surface. The disclosed wind turbine in exemplary embodiments is built with a body having a curved shape, such as teardrop, sphere, or torpedo, to force oncoming wind to go around the body about an axis of rotation. See, for example, axle 6 in
In addition, in some embodiments, a relatively fixed (i.e., does not rotate about the axis of rotation) rear (tail) fin (or vane) is employed to steer the wind turbine, keeping the front pointed to face the wind. In other embodiments, the shape of the body or the location of a steering axis (e.g., at or in front of the center of gravity) may be sufficient to keep the front pointed to face the wind. For instance, in other configurations, the fin may not provide any benefit due to the body's streamline shape. That is, the body may turn to face the wind by itself in order to encounter the least turbulence, and not need any assistance from a tail fin.
The middle portion of the wind turbine body is between a front portion and a rear portion, with at least the middle portion (and the blades) configured to rotate, to generate as much torque as possible. See, for example,
To effect efficient wind turbine rotation, a set of blades is placed around the teardrop body where the accelerated laminar flow is located (which, for purposes of this disclosure, will be referred to as the “middle portion” of the body). Unlike a conventional three-blade wind turbine, there may be considerably more blades in embodiments of the present invention (to contact as much of the laminar flow as possible), and they may be considerably shorter (in the radial direction), as the laminar flow is the main source of power and only extends a short distance from the body. See, for example, the exemplary wind turbine 100 in
Unlike the conventional wind turbine, the disclosed wind turbine in exemplary embodiments forces oncoming airflow to contour along its curved (for example, teardrop) shaped body. The streamlined air in direct contact with the teardrop body forms a thin layer of laminar flow surrounding its body, and travels at accelerated speed according to Bernoulli' Principle. Its trailing tail reduces air drag, making the wind turbine more stable under higher wind speed. See, for example,
Other techniques can also be used to reduce drag, which can lead to more efficient operation of exemplary wind turbine embodiments of the present invention. For instance, in some embodiments, airfoil-shaped blades are used to generate “lift” and reduce drag. In other embodiments, the wind turbine body is dimpled (like, for example, a golf ball), which is also a known technique for reducing drag. The dimpling, for instance, can be applied to any curved portion of the body's shape, such as the front or the back of the wind turbine body.
The teardrop body shape of wind turbine 100 forces the oncoming air (in cross section 30, the leading airflow) to flow around the body 1, starting at a front portion 1a (which faces the wind), then increasing velocity as the body expands to a middle portion 1b, which is configured to rotate and is where the airflow contacts the blades 2 of the wind turbine 100. The laminar layer around body 1 speeds up at the blade 2 area, where air pressure is the lowest, and expands after passing the middle portion 1b while traveling towards the rear portion 1c, thus normalizing air pressure to ambient level based on Bernoulli's Principle. In this way, air turbulence and air drag around the rear portion 1c is reduced or minimized. Trailing fin 3 steers the body 1 to point in the correct orientation to face the wind.
It should be noted that other methods or devices can be used to direct the wind turbine to face the wind (i.e., not just the tail fin). For example, in another embodiment, a motor is used to direct the wind turbine, with a wind sensor to control the motor. In another exemplary embodiment, the wind turbine body is positioned on a steering axis that is forward of the body's center of gravity, thus favoring the lighter (front) portion to face an oncoming wind. In still another embodiment, no automatic method or device is provided to compensate for changing wind directions. That is, the wind turbine faces the same direction until manually adjusted to face another direction. This can be useful, for example, in areas where the winds tend to come from one direction, or when manual adjustment is sufficient for the intended purpose. Further embodiments of the present invention may face oncoming wind automatically (without a tail fin) in order to find the lowest drag position. For example, a body shape with a more tapered trailing portion than leading portion will tend to face the wind when pivoting on a steering axis located at the center of gravity of the body, even in the absence of a tail fin.
The shape and orientation of the fin 3 also causes the body 1 to redirect itself about a steering axis (see, for example, pole 7, working in conjunction with bearings 5b and frame 4) to a change in the direction of the airflow so that the front portion 1a continues to face the airflow. For example, a flat diamond-shaped vertical plate 3 depicted in
In addition, in order to harvest more energy from the surrounding laminar layer, multiple blades with extra width may be installed (see, for example,
With embodiments of the present invention, however, the streamlined shape body directs and concentrates the wind force to the tip area of multiple blades. Thus, extra torque is generated in embodiments of the present invention when compared to conventional wind turbines. See, for example,
The building material of the parts of the wind turbine (for example, the body, the blades, and the tail fin) may vary based on a user's needs (such as weight, cost, or efficiency). For instance, they can be metal, fabric, plastic, Styrofoam, wood, carbon fiber, fiberglass, etc. The body can be inflatable, for example, to keep costs down, and it helps build pressure to better define and maintain the desired shape. Inflatable bodies can also be filled with lighter-than-air gas (for example, helium) to reduce weight or make them float in air.
The body can be any size. Smaller sizes can be easier to build and maintain the desired shape, but do not catch as much wind as larger sizes. While, for the same body shape, the amount of wind cross-section grows as the square of the linear dimension (for example, diameter), the size of the body grows as the cube of the linear dimension. Thus, while larger bodies may be more efficient to operate (since they capture more wind energy), they may become impractical to build at some point because of considerations like weight and structural integrity. Inflatable bodies may be capable of larger sizes than non-inflatable bodies because of such considerations.
The blades can be any sturdy material (for instance, airplane-like material) configured to turn the body in one direction (for example, an airfoil). Their length is relatively short as the laminar layer (from which the wind turbine obtains most of the wind energy) does not extend far from the body, so additional length would only serve to slow down the wind turbine (i.e., generate less torque). For example, in an embodiment, the blade length may be one quarter of the body diameter. In another embodiment, the blade length may be less than one quarter of the body diameter. In yet another embodiment, the blade length may be equal to or substantially equal to a thickness of the laminar layer of the body at its middle portion.
The curvature of the blades should be consistent (in, for example, an airfoil shape), which can help to provide “lift” to spin the body, reduce air drag, minimize turbulence, and not disturb the laminar layer. According to body designs of exemplary embodiments of the present invention, numerous blades (see, for example, exemplary wind turbines depicted in
The disclosed wind turbine in exemplary embodiments may be constructed in a variety of curved shapes, such as a teardrop shape (
Referring now to
The blades 2 have a generally curved (and possibly airfoil) shape, angled similarly with respect to the axis of rotation (to work together in rotating the wind turbine 100) when attached to the middle portion 1b to convert wind energy into rotational energy. Their number, lengths (protrusion from the body 1), widths (contact along the body 1), and angles (i.e., how oblique they are from the axis of rotation) can vary from one wind turbine to another, depending on factors such as the body shape and size, blade material composition, intended deployment location, etc. For instance, in some embodiments, the length of the blades is substantially that of the thickness of the laminar flow surrounding the body during normal operation.
Referring to
Some of the wind not converted into rotational energy by the blades 2 travels around the body 1 to the rear portion 1c and encounters the tail fin 3, whose shape, relatively fixed location (compared to the body 1), and symmetry about the axis of rotation help direct the front portion of the wind turbine 100 about a steering axis (for example, along the direction of pole 7 in
Supporting frame 4 connects to the axle 6 to support the body 1, while the pole 7 supports the frame 4 off the ground and, in combination with bearings 5b (or other suitable rotation methods or devices of the pole 7 and/or the frame 4), allows the wind turbine 100 to rotate freely about the steering axis to face the wind. Bearings 5a (or other suitable methods or devices) allow the axle 6 to rotate freely about the axis of rotation.
The described wind turbine may rotate as a whole or partially (including at least the middle portion), as shown in different embodiments in
In the wind turbine 100′ of
In the wind turbine 100″ of
In the wind turbine 100′″ of
To harvest more wind energy, the wind turbine may employ multiple bodies, as shown in
In the wind turbine 200′ of
Unlike conventional wind turbines, the disclosed wind turbines according to embodiments of the present invention can be compact, lightweight, and cost effective in conditions unsuitable for conventional wind turbines. In addition, these wind turbines can require less maintenance than conventional wind turbines.
In other embodiments of the present invention (see, for example,
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims, and equivalents thereof.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/244,039, entitled “Streamlined Wind Turbine Optimized for Laminar Layer,” filed on Sep. 19, 2009, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61244039 | Sep 2009 | US |
