PRIORITY NOTICE

(0001] T he present application makes no claim of priority to any other related filed patent applications.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

[0002] T he present application makes no reference to any other related filed patent applications.

STATEMENT REGARDING FEDERAL SPONSORSHIP

[0003] No part of this invention was a result of any federally sponsored research.

TECHNICAL FIELD OF THE INVENTION

[0004] T he present invention relates in general to vertical wind turbine blades, and, more specifically, to a Darrieus Vertical Axis Wind Turbine (DVAWT) blade comprising a convex top surface and a convex bottom surface combined with a flat section to increase airfoil efficiency.

COPYRIGHT AND TRADEMARK NOTICE

[0005] A portion of the disclosure of this patent application may contain material that is subject to copyright protection. The owner has no objection to the facsimile reproduction by anyone of the l patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyrights whatsoever.

[0006] Certain marks referenced herein may be common law or registered trademarks of third parties affiliated or unaffiliated with the applicant or the assignee. Use of these marks is by way of example and should not be construed as descriptive or to limit the scope of this invention to material associated only with such marks.

BACKGROUND OF THE INVENTION

[0007] Renewable Energy is that electrical energy collected from renewable resources such as sunlight, wind, water, or geothermal heat. With the advance of technology, more efficient methods of collecting such renewable energy have become commonly available to consumers and commonplace in the environment. One such common method of renewable energy collection comes in the form of wind turbines, which convert the kinetic energy of wind into electrical energy. Wind turbines are generally divided into vertical axis types and horizontal axis types, depending primarily on the orientation of the axis about which the various blades rotate.

[0008] It is known to have a Vertical Axis Wind Turbine (VAWT) where the main rotor shaft is set transverse to the wind and where the main components of the turbine are located within its base. Further, VAWTs need not be pointed into the wind, removing the need for wind-sensing and orientation mechanisms. Such designs, though, suffer from balance issues resulting in torque variations and large bending moments on the blades. One such design is known as a Darrieus Vertical Axis Wind Turbine (DVAWT) and is fully disclosed in US Patent 1835018.

[0009] The DVAWT generally comprises a plurality of curved airfoil blades arranged symmetrically around a vertical rotating shaft. Because of the particular blade design and orientation each surface of each blade faces into the wind depending on its position in the horizontal 360° travel arc, and the total profile of the blade contributes significantly to the overall efficiency of the turbine system. Commonly used blade profiles are not optimized for efficient use in DVAWT applications as the theory underlying their design is based on outmoded principles.

[0010] There is a need in the art for a DVAWT blade designed using modem principles to provide increased efficiency to the overall system. Such a blade design may comprise a convex top surface and a different convex bottom surface combined with a planar section to increase efficiency. Such a design may further reduce the visual and audible disturbances generated by the system as a result of such increased efficiency.

[0011] It is to these ends that the present invention has been developed.

BRIEF SUMMARY OF THE INVENTION

[0012] To minimize the limitations in the prior art, and to minimize other limitations that will be apparent upon reading and understanding the present specification, the present invention describes a Darrieus Vertical Axis Wind Turbine (DVAWT) blade comprising a convex top surface and a partially convex bottom surface combined with a flat section to increase airfoil efficiency.

[0013] It is an objective of the present invention to provide a DVAWT blade of increased efficiency without increasing the production cost of such a blade so as to improve acceptance and use of such blade designs.

[0014] It is another objective of the present invention to provide a DVAWT blade generating reduced visual disturbances so as to improve the acceptability of onshore wind turbines near population centers.

[0015] It is another objective of the present invention to provide a DVAWT blade generating reduced audible disturbances so as to improve the acceptability of onshore wind turbines near population centers. [0016] It is another objective of the present invention to provide a DVAWT blade of increased long-term reliability so as to reduce overall costs of operation and maintenance of the turbine system.

[0017] These and other advantages and features of the present invention are described herein with specificity so as to make the present invention understandable to one of ordinary skill in the art, both with respect to how to practice the present invention and how to make the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018] Elements in the figures have not necessarily been drawn to scale in order to enhance their clarity and improve understanding of these various elements and embodiments of the invention. Furthermore, elements that are known to be common and well understood to those in the industry are not depicted in order to provide a clear view of the various embodiments of the invention.

[0019] FIG. 1 schematically presents an overview of a theoretical model upon which previous DVAWT blades have been designed.

[0020] FIG. 2 illustrates theoretical airflow vectors over a DVAWT blade.

[0021] FIG. 3 illustrates expected airflow from the theory over a DVAWT blade.

[0022] FIG. 4 illustrates airflow modeled over a DVAWT blade.

[0023] FIG. 5 illustrates airflow modeled over a NACA 63-415 airfoil.

[0024] FIG. 6 illustrates airflow modeled over a NACA 63-415 airfoil.

[0025] FIG. 7 illustrates a preferred embodiment of a DVAWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0026] FIG. 8 illustrates four general positions of a DVAWT blade in the horizontal 360° travel arc, relative to wind direction. [0027] FIG. 9 illustrates some major characteristics of a preferred embodiment of a DV AWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0028] FIG. 10 illustrates where the torque and drag are generated by a preferred embodiment of a DVAWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0029] FIG. 11 illustrates the lift, torque, and drag vectors generated by a preferred embodiment of a DVAWT blade.

[0030] FIG. 13 illustrates an asymmetrical nose design of a DVAWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0031] FIG. 14 illustrates an asymmetrical nose design of a DVAWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0032] FIG. 15 illustrates an asymmetrical nose design of a DVAWT blade comprising a convex top surface and a partially convex bottom surface combined with a flat planar section.

[0033] FIG. 20 illustrates an air pressure model around a blade without a deflector.

[0034] FIG. 21 illustrates an air pressure model around a blade with an appropriate deflector.

[0035] FIG. 22 illustrates a deflector shape based on an air pressure model.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Certain terminology is used in the following description for reference only and is not limiting. The words“front,”“rear,”“anterior,”“posterior,”� ��lateral,”“medial,”“upper,”“lower,” “outer,”“inner,” and“interior” refer to directions toward and away from, respectively, the geometric center of the invention, and designated parts thereof, in accordance with the present disclosure. The words“lift,”“drag,” and“torque” refer to forces generated by and acting upon Vertical Axis Wind Turbine (VAWT) blades, and designated parts thereof, in accordance with the present disclosure. Unless specifically set forth herein, the terms“a,”“an,” and“the” are not limited to one element, but instead should be read as meaning“at least one.” The terminology includes the words noted above, derivatives thereof, and words of similar import.

[0037] The present invention is related to the production of electricity by wind turbines, and allows a more efficient production of electricity in Darrieus Vertical Axis Wind Turbine (DVAWT) applications. The blade profile is one of the most important aspects of a DVAWT system, though the prevailing techniques for blade design are based on outmoded theories of airfoil. The DVAWT blade disclosed herein will provide improved airflow efficiency and reduce visual and audible disturbance caused by the wind turbine system.

[0038] FIG. 1 schematically presents an overview of a theoretical model upon which previous DVAWT blades have been designed. Such models produce energy-generating torque by the turbine as a result of different angles of the lift vector forces. According to the prevailing theory the analysis of the force on the blade of FIG. 2 should correspond to the airflow of FIG. 3, which is not the case.

[0039] FIG. 4 shows what happens in reality in addition to what is shown in FIGS. 2 and 3. A blade designed under the vector theory cannot result in an optimal design as it does not consider a real image of the airflow situation.

[0040] FIGS . 5 and 6 show a NAC A blade number 63-415 that is often mentioned as a good design for DVAWTs. The detail view of FIG. 6 shows clearly the restriction of the airflow due to the pointy nose of the blade, and the resulting vorticity below the blade. The efficiency of this blade is nearly half of the present design, as demonstrated in computer simulations and field tests.

[0041] The present invention discloses novel aspects for the design of a DVAWT blade. The disclosure focuses on the shape of the blade and the shape of the nose. [0042] The design requirements for the shape of a DVAWT blade is unlike any other blade as it operates differently at each position of the blade around the central axis. The operating characteristics must be considered in 360 positions around the blade’s circular travel arc. The total efficiency of the turbine is the summation of all the torque and drag at each position.

[0043] The efficiency of a wind blade depends on many factors that act together as a whole. FIG.

7 shows a blade that has all the required characteristics of its shape, though it is not the only design possible. Many variations can meet the requirement of the imiovations and disclosures herein.

[0044] FIG. 8 shows four general positions of the blades of a DVAWT that face the wind, which is represented by arrows. In position 1, the blade is directly in the front of the wind, which is where the blade produces maximum torque, so the torque optimization is prioritized in this region. In position 2, the blade runs in the same direction as the wind. Some drag exists around this position, but this is the less important area. There is still significant torque produced in position 3, but less so than in position 1. In position 4 the blade runs directly against the wind, and is where the drag must be minimized.

[0045] In order to produce maximum torque in position 1 it is mandatory that the shape of the blade is not symmetrical. Referring back to FIG. 4, it is known that the air flow over the top surface of the blade differs from the bottom surface of the blade.

[0046] The best way to enhance torque, drag and lift on a blade is to study the pressure all around it. FIG. 9 shows the most important pressure variation on a good embodiment of a DVAWT blade. There is three main zone of pressure but the most important was near the nose of the blade. The pressures show in FIG. 9 are related to position 1 , when the torque is maximum, the numbers shows are for understanding as they vary greatly with wind speed. The zone 9 as an important over pressure beside ambient, this push on the blade and generate the drag. Conversely, zone 10 as an important under-pressure beside ambient. This pull on the blade and generate the torque. The rest of the blade as relatively ambient pressure if the design of the end minimizes turbulences and vorticities.

[0047] Still on FIG. 9, when the blade is in position 4, both zone 9 & 10 as over-pressure and the drag is maximum. To minimize this, the nose of the blade must be at the center of the overall height of the blade and as small as possible, which is well known in the industry.

[0048] FIG. 10 shows some important claims of the present disclosure. To reduce the drag in the position 1 of the blade, the attack angle 6 of the top face near the nose of the blade must be smaller then the attach angle 7 of the bottom face near the nose of the blade. In the shown embodiment, the top angle 6 is of 34 degrees and the bottom angle is of 41 degrees for a difference of 7 degrees. Several variations of this disclosure is possible in regards of the objectives of the design of the blade. The top angle 6 may be between 30 and 40 degrees, the bottom angle 7 may be between 35 and 45 degrees but the difference between both angles must be between 5 and 10 degrees.

[0049] Still on FIG. 10, the shape of the blade must minimize the turbulence and vortices at the end of the blade. Making the end of the blade long and pointy is common design that apply in a good embodiment of a DVAWT, this apply in our design, but it is not a disclosure. To improve the smoothness of the airflow on the top of the blade, the convex shape must be long and stay positive. To enhance this, the end point of the blade 8 must be bellow the center line of the blade. In the design shown, the end point 8 is lower from the centerline of 9% of the overall height. Base on the overall length and other parts of the blade and the target wind speed of the turbine, this optimal height variation may be from 5 to 15%.

[0050] Still on FIG. 10, in position 1 of the travel of the blade, the airflow at the bottom of the shape is very low. To avoid the production of vorticities bellow and at the end of the blade, the face 5 must be as flat as possible. In the prefer embodiment, the length of this flat section is 75% of the overall length of the blade. For other needs of the turbine design, this flat bottom part of the blade can be from 60 to 80% of the length of the blade.

[0051] FIG. 11 shows that pressure is a force perpendicular to the surface. On each point the force vector can be split into its parallel and perpendicular components relative to the turbine axis. The vector parallel to the axis generates a pull or a lift on its point while the perpendicular vector generates the torque or the drag. The summation of all forces on the blade gives the total torque and lift forces.

[0052] FIGS. 9 and 11 show that the end part of the blade has very little impact on the forces applied on the blade, all pressure being relatively equal to ambient. In the front of the blade, two over-pressure zones are shown where air pushes on the blade and creates lift and drag. In the same area three under-pressure zones are shown where the air pulls the blade to generate the torque and enhances the lift force.

[0053] FIG. 11 shows more details on the torque component of the blade. The length of the vectors has been drawn in proportion of the force they apply on the surface. The maximum over-pressure, identified as 13, is in this case, as example, about 1,000 Pascals above the ambient pressure. The attack angle gives a small drag and a strong lift to the blade. On the opposite side, the under-pressure zone, identified as 11, is about 2,000 Pascal’s below the ambient pressure. The inflexion point between over- and under-pressure is over the nose of the blade. This means that the force, identified as 12, on the nose on the blade is pure torque. As the very small section around the nose produces most of the torque on the blade, the optimization of this area is mandatory.

[0054] FIG. 13 shows that the nose design must be asymmetrical. The inflection points from over- pressure 12 to under-pressure 13 is slightly above the tip of the nose, which is at the center of the blade which is marked with the dotted straight line. The shape of the surface of the blade in the torque zone must be optimized between a flat nose that will maximize torque in position 1, but induce turbulence when the blade is upwind in position 4, and a symmetric or pointy nose that will reduce the torque. The zone 14 shown in FIG. 13 is thus the most important part of the blade of a DVAWT.

[0055] FIG. 14 shows that the radius 15 above the nose of the blade must be at least two times smaller than the radius 16, the one below the nose of the blade. In most designs, a 2 to 1 factor is optimal, but some alternative configurations for high wind blades may have proportions between 1.5 to 3 for 1.

[0056] FIG. 15 shows that a variation of the nose configuration may include an almost flat small section 17 in an appropriate angle, to enhance the size of the best torque zone. As mentioned above, this flat section cannot be parallel to the axis of the turbine; a 10 to 20 degree offset is mandatory.

[0057] DVAWT blades, especially short ones, have a significant weakness at their ends. FIGS. 9 and 11 show huge pressure difference between each side in the front of the blade.

[0058] FIG. 20 shows a front view of the blade 25 in operation. On one side there is a high over- pressure zone beside an ambient one, and on the other side an even higher under -pressure zone. Thus, there is a strong airflow 27 at the ends of the blade that generates both 1) turbulences that produce noise and drag, and 2) a loss of pressure 26 on both sides near the top and bottom that reduce the efficiency of the blade.

[0059] Most DVAWT on the market have no deflector at the end of their blades, and those that do have some that are too small and mostly used as closing. FIG. 21 shows the same front view as FIG. 20, but with a flat deflector 28 that reduces to close to nothing the air flow lost on the top of the blade. In one embodiment a deflector may be added that is wide enough to make sure that the pressure differences in and out of the blade operation field are minimize. The size 29 of the deflector can be calculated with appropriate computer simulations. The aerodynamic noise of the blade in full speed operation is then reduced to close to nothing. [0060] The size and shape of the deflectors are not fixed measurements surrounding the blade all around. As shown in FIG. 22, the size of the deflector 28 is in relation with maximum and minimum pressures acceptable to avoid energy loss and turbulences. This means the deflector is relatively wide at the front of the blade, and close to nothing at the end side. The pressure measurement around the blade must be done at all the positions around the rotation of the turbine. In one embodiment a preferred pressure reduction will be to 500 Pa, but specific applications, like urban wind turbines, may require larger deflectors that will reduce pressure variation to 250 or 300 Pa. Conversely, large offshore wind turbines may require less noise protection and a 1000 Pa deflector may be acceptable for efficiency purpose.

[0061] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.