Patent Application
20100196150
The present invention relates to wind turbines used to convert wind energy into mechanical energy, more specifically to wind turbines that uses the phenomenon of boundary layer on a surface to extract the wind energy.
Wind as a source of energy is a concept that has been promoted from ancient time. According to historical sources, there is evidence which shows that windmills were in use in Babylon and in China as early as 2000 B.C.
Wind is used as a source of energy for driving horizontal axis and vertical axis windmills. Horizontal axis windmills have been used extensively to drive electrical generators, however they suffer from several disadvantages, including the need for an even horizontal air inflow, danger to birds and air traffic, obscuring the landscape with banks of rotating windmills, and in the case of large diameter horizontal axis propellers, supersonic speeds at the tips of the rotors.
Vertical axis wind turbines (VAWT) have been provided in the prior art with a central rotor surrounded by stationary devices that serve to redirect and compress air flow toward the rotor blades.
Compared to VAWT where its exposure remains constant regardless of the wind direction, the horizontal axis windmill must turn to face the wind direction, which is considered a disadvantage as there are additional moving parts involved in the construction.
An example of vertical axis wind turbine is shown in U.S. Pat. No. 5,391,926 to Staley et al. that uses double curved stator blades to direct wind current to the rotor assembly and to increase structure stability of the thin stator blades.
U.S. Pat. No. 6,015,258 to Taylor discloses another wind turbine that includes a ring of stator blades of an airfoil shape to reduce impedance of air directed towards the central rotor assembly.
Further, U.S. Patent Application Publication No. 2002/0047276 A1 (ELDER) discloses an outer ring of planar stator blades to direct flow of wind into a central rotor assembly.
Canadian Patent No. 1,126,656 (SHARAK) discloses a vertical axis turbine with stator blades that redirect the air to the rotor blades by straight extending vertical air guide panels that intermittently surround the rotor unit and direct air currents to the rotor unit for rotation by the wind. The air guide panels are closed at the top and bottom by horizontally extending guide panels that are canted in complementary directions. The upper panel is tilted downwardly as it progresses inwardly and the lower panel is tilted upwardly on its inward extent to thereby increase the velocity and pressure of the wind as it is directed to the rotor unit.
Another Canadian Patent Application No. 2,349,443 (TETRAULT) discloses a new concept of vertical axis wind turbine comprising an air intake module, which redirects the airflow vertically to a series of rings with parabolic evacuations. One of the major drawbacks of that design is the fact that the air intake module needs to face the wind, so it requires a yaw mechanism to orient it into the wind. Moreover, the whole design forces the airflow to change its direction from horizontal to vertical into a sort of internal enclosure from where the air is evacuated by changing again its direction from vertical to horizontal. The numerous and drastic changes in airflow directions entail a power loss in the airflow and a reduction of the turbine efficiency, as the energy of the wind is transformed into rotation of the turbine only at the last airflow direction change.
A disadvantage of all the horizontal and vertical axis windmills of the prior art relates to their inability to use remaining energy left in the airflow after hitting the windmill blades. Ideally, the airflow exiting a blade will be reused again and again to a certain extent. Unfortunately, in most cases the prior art enables the capture of only a fraction, the first impulse, of the wind power.
A prior art that uses the fluids' properties to transform efficiently a linear fluid movement into a rotational mechanical movement is the turbine described in U.S. Pat. No. 1,061,142 accorded to Nikola Tesla in 1913. The Tesla turbine used a plurality of rotating disks enclosed inside a volute casing and the rotation of the turbine was due to a viscous high-pressured fluid, oil in Tesla experiments, directed tangentially to the disks. Unfortunately this previous art is not suited to capture wind energy for several reasons such as the air viscosity is too low, the normal wind speed is too low and the whole design with a casing enclosure and only one access opening is impractical for wind turbines.
The International Patent Application No. PCT/CA2006/000278, attributed to the applicant, and published under No. WO2006089425A1 discloses a wind turbine including a stator assembly having a plurality of stator blades for tangentially redirecting wind into a rotor assembly having a plurality of vertical rotor blades disposed circumferentially on a plurality of disks stacked one on top of each other. The extraction of the wind energy using the boundary layer effect, via stacked disks, proves to be very efficient over the portion of the air flow that enters between the rotor's disks. However, one of the drawbacks of that design is the fact that the stator assembly, as designed with the stator blades redirecting the wind tangentially into the rotor, creates around the rotor a natural enclosure that prevents the air flow to enter or exit easily, hence creating a region of high pressure in front of the turbine forcing the majority of the air flow to diverge from its path onto the turbine, which ultimately reduces the wind turbine's total efficiency.
There is therefore a need for a boundary layer stacked disk design that does not need any stator assembly, allowing the airflow to enter and exit freely into and from the rotor assembly.
It is a preferred object of the present invention to provide a vertical axis wind turbine boundary layer stacked disk design where the air flow is imparted tangentially to the disks without any need for stator assembly.
It is a further preferred object of the invention to provide a turbine assembly that is structurally reinforced.
It is a further preferred object of the invention to provide a turbine assembly that is simply constructed of inexpensive light material.
It is a further preferred object of the present invention to provide a vertical axis wind turbine based on the Coanda effect in fluids which translates into an efficient wind turbine.
According to the present invention, there is provided a wind turbine comprising a rotor assembly having a plurality of stacked disks for rotation about an axis, at least one set of the stacked disks having disks being closely spaced from each other for creating a boundary layer effect on surfaces of the disks that contributes in rotating the disks, each disk having a plurality of rotor blades disposed on an outer circumference thereof, each rotor having at least one surface extending tangentially from the outer circumference of each disk so as to redirect the airflow tangentially to a peripheral surface of each disk, each disk defining at least one opening thereon for redirecting the wind axially through each of the disks.
Preferably, a wind turbine according to the present invention is able to operate in very broad wind conditions, such as velocities up to 130 mph (200 Km/h), and frequently changing wind directions. The device provides a reliable and effective means for directing air currents into the rotor assembly, which is attached directly to a vertical shaft.
In general terms, the invention involves various embodiments of a vertical-axis wind turbine. Preferably, the rotor blades are designed with an airfoil profile and disposed tangentially to the disks. The rotor blades are disposed around the circumference of the disks as such that, regardless of the wind direction, the air inflow will be redirected tangentially to the disks' surfaces to impart a higher rotational velocity and greater torque upon the turbine shaft. In a preferred embodiment, the rotor blades are angled from the vertical direction and form a helical shape to allow smooth transitions of the blades over the incoming airflow.
The turbine may be equipped with any number of disks; however a preferred embodiment has at least 50 disks.
In a preferred embodiment, the turbine is designed with an airflow augmenter stator assembly where the stator blades impart the airflow directly into the rotor assembly. The significant size difference between the inflow and the outflow openings of the air channels created by the stator blades create a natural compression and a substantial air speed increase that achieve higher efficiency even in low wind. The disposition of the stator blades also prevents the disruption of rotation by shielding the rotors from winds counter-directional to their rotation which may occur as the wind shifts. The stator assembly may be equipped with any number of stator blades; however a preferred embodiment has between six and twelve stator blades.
Preferably, the wind turbine acts to convert wind currents into mechanical energy used to directly act upon a water pump, or to drive an electrical generator for use as an alternate power source.
The invention as well as its numerous advantages will be better understood by reading of the following non-restrictive description of preferred embodiments made in reference to the appending drawings.
The airfoil shape of the rotor blades 2 and their tangential disposition to the disk circumference redirect the airflow tangentially to the surface of disk. The length of the blade 2 and the number of the blades on the circumference of the disk are in a close relationship, as such that the gap between the tip of a blade 5 and the tail 6 of the next blade prevents any airflow to travel in a counter-rotating direction between the disks 1.
The illustrated rotor blades orientation is counter clockwise. It will be understood of course that the orientation of the rotor blades 2 may be reversed to drive the turbine in a clockwise direction if desired.
A vertical shaft 12 passes through the center of each disk 1. The rotor assembly is preferably manufactured from a corrosion resistant light material, such as reinforced fiberglass composite, to rotate very easily even in slow wind.
The airflow hits with its first impulse the airfoil blades 2 and then enters in the space between two disks 10 of the rotor assembly 11. The airflow creates a laminar region on the surface of each disk 1 that extends up to 0.03 inch (0.762 mm) thick. Doubling that for the two disks and considering a transition layer, the distance between two disks is best set to be less than 0.1 inches (2.54 mm). However, the turbine rotates in the wind even with wider disk distances. Due to the Coanda effect, the airflow adheres to the disks surface adding rotational velocity to the rotor assembly 11 via the viscous pressure effect. Then, the air passes through the openings 4 of the disks 1 and creates a vortex that contributes to increase the rotation of the turbine and as a consequence its efficiency. The air currents and vortices are able to escape from said enclosure through the openings 4 of the disks 1.
As persons skilled in the art will understand, a majority of the disks may be closely spaced apart, while some of the disks may be separated by larger distances. However, the efficiency of the rotor assembly may be diminished with such configuration.
Alternatively, the top and bottom surfaces of the stator assembly may be hemispheres or elliptical surfaces.
The rotor disks are preferably made from a light non-corrosive material, preferably a light polymer. The stator structure is preferably made from a more resistant non-corrosive material, such as a stronger type of polymer. The whole vertical axis turbine may be made from inexpensive plastic material to create a cost effective alternate power source.
Although the above description relates to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.
A model of the wind turbine was simulated via specialized CFD tool and then a prototype was built as proof of concept. The prototype included a stator assembly. The prototype has one (1) meter in height and 0.70 meter in diameter and develops 600 Watts in a wind of 14 m/s.
Without limiting the possibilities of alternate embodiments, there is described below some of such functional equivalents of the boundary layer vertical axis turbine.
In alternate embodiments of the turbine:
Although preferred embodiments of the present invention have been described in detail herein and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the present invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA2007/001200 | 7/9/2007 | WO | 00 | 1/8/2010 |
