SYSTEM AND METHOD FOR IMPROVING EFFICIENCY OF TURBINE AIRFOILS

Abstract

Double blade airfoils and related systems are disclosed. The double blade design may efficiently use a minimal amount of material yet achieve exceptional aerodynamic efficiencies well above the previously understood theoretical maximum. The disclosed designs may operate at lower wind speeds than those known in the art. Furthermore, the balance of forces generated by the disclosed designs may also reduce the stress felt by the airfoils and rotor, enhancing the longevity of the system.

Claims

1. A wind turbine comprising: an airfoil connected to a rotor on the wind turbine comprising: a lower profile and an upper profile; wherein the lower profile and the upper profile have different shapes, wherein an inner surface of the lower profile and an inner surface of the upper profile are separated by a gap, the airfoil being configured to rotate about an axis upon an impact of a wind flow on the blade; wherein for each profile the inner surface leading side is configured to reduce the velocity of incoming wind and create a high pressure area along the inner surface; and wherein a mid-blade force is generated by the high pressure area and the mid-blade force includes components in the direction of the airfoil's rotation and opposite the direction of the wind flow.

2. The wind turbine of claim 1, wherein the size of the gap varies along longitudinal axis of the airfoil.

3. The wind turbine of claim 1, wherein the airfoil is helically shaped along its longitudinal axis.

4. The wind turbine of claim 3, wherein the relative orientation of the upper profile and the lower profile retain does not substantially vary along the airfoil longitudinal axis.

5. The wind turbine of claim 1, wherein the size of at least one of the upper profile or lower profile decreases with distance from the rotor along the longitudinal axis.

6. The wind turbine of claim 1, wherein the size of both the upper profile and lower profile decrease with distance from the rotor along the longitudinal axis.

7. The wind turbine of claim 1, wherein each profile contains at least 5 aerodynamically distinct surfaces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Features and advantages of the methods and apparatus of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings in which:

[0029] FIG. 1 illustrates the general components found in a wind turbine.

[0030] FIG. 2 illustrates a cross section of the profile surfaces of an embodiment.

[0031] FIG. 3 illustrates, according to one embodiment, the forces generated by the varying pressures created as air flows along the surface of the profiles.

[0032] FIG. 4 illustrates a side view of one embodiment.

[0033] While the invention is described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word may is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words include, including, and includes mean including, but not limited to.

DETAILED DESCRIPTION OF EMBODIMENTS

[0034] This specification includes references to one embodiment or an embodiment. The appearances of the phrases in one embodiment or in an embodiment do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.

[0035] In the context of this patent, the term coupled means either a direct connection or an indirect connection (e.g., one or more intervening connections) between one or more objects or components. The phrase directly connected means a direct connection between objects or components such that the objects or components are connected directly to each other so that the objects or components operate in a point of use manner.

[0036] The lift coefficient (C.sub.L) is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a complete foil-bearing body such as a fixed-wing aircraft. C.sub.L is a function of the angle of the body to the flow, its Reynold number and its Mach number. It is well known in the art that regular blade profiles have a C.sub.L of 1.4 to 1.6. By comparison, the C.sub.L of the disclosed double blade profile is approximately 3.2. In other words, the torque generated by the double blade profile is double that of existing profiles. Further, the efficiency of the disclosed double blade profile is approximately 79%, which exceeds the Betz limit of 59.3%.

[0037] Compared with existing profiles, the disclosed double blade profile produces twice the power for a given rotor diameter, operates efficiently with lower minimum wind velocity, and extended mechanical life due to reduced strain on the rotor.

[0038] The particular arrangement of rising and falling pressures zones, which are created on the profile surfaces based on their unique shapes, bring about the high efficiency and power of the overall design. The compressive force between the zones of high and low pressure is always on the attack side of the profile, which is a characteristic that has not been observed in any design known to the art.

[0039] On the existing blades, when a vertical lifting force develops, a dragging force is also observed. In the disclosed embodiments, the lift force and drag force are on the attack sides of the wing design. This orientation naturally increases the torque that the blades exert.

[0040] The calculated net momentum ratio of the disclosed embodiments is around 0.79, which, as noted above, handedly exceeds the Betz theoretical upper limit for a profile design. Another interesting aspect of the disclosed embodiments is that, despite using two blades in place of one, the overall material quantity and fabrication cost are not substantially increased when compared to a standard blade design. This is a major practical advantage, as the disclosed embodiments are cost competitive with existing designs even before accounting for the greatly enhanced efficiency and other operating characteristics.

[0041] As shown in FIG. 1, a wind turbine consists of a one or more airfoils 100 attached to a rotor 101. The airfoils 100 rotate around the rotor 101. When wind passes over the airfoils, a lifting force is created in the direction of rotation for the overall wind turbine assembly. A drag force is also generated in the direction of the wind. The portion of the profile that first feels the oncoming wind is the leading edge while the opposite end is the trailing edge.

[0042] FIG. 2 shows a cross section of one of the embodiments. As can be seen from the cross section, two profiles with different shapes are paired together in a double blade airfoil that synergistically combines the forces developed by each profile. The cross section is viewed from the tip of the profile looking towards the rotor, i.e., from the tip of the blades looking towards the middle of the wind turbine. The arrows around 212 indicate the direction of the wind hitting the profile.

[0043] For ease of explication, various surfaces of the two profiles are denoted 201, 202, 203, 204, 205, 206, 207, 208, 209, and 210. Starting with the top profile (note that the concept of top and bottom are purely for illustrative clarityas the blades of the turbine rotate the absolute orientation of the profiles changes depending on view point), wind 212 is split in to two at surface 201 and flows along surfaces 203 and 202. In the same way, on the bottom profile wind 212 splits along surface 206 and flows along surfaces 207 and 208. According to the hump shape of these four surfaces, the flow speed increases at various rates and pressure decreases at various rates. Air expands along surfaces 204 to 205 and 209 to 210 between two profiles. These surfaces create volumetric expansion in the middle of the two profiles. The air speed of the wind decreases in this expanded region, with a corresponding increase in pressure. This high pressure creates a force towards the low pressure areas elsewhere along the surfaces of the profiles. This pressure force component is in the direction of rotation of the blade and opposite the direction of wind drag.

[0044] FIG. 3 shows representative force vectors generated by the pressures described with respect to FIG. 2. As can be seen, the velocity and direction of the pressure force moving the blade is different from standard blades designs. The pressure differentials generated on the profile surfaces are much larger than in standard designs, and the corresponding pressure force and velocity are also increased relative to standard designs. Furthermore, the generated pressure forces are aligned and positioned to positively impact the lifting and pushing forces experienced by the blades. The net result is an increase in performance, torque, and force while improving reliability via reduced mechanical strain on the blades and rotor.

[0045] As shown in FIG. 4, as one moves along the chord of the blade, the exact shape of the profile varies the optimized angle of attack at each point along the blade and the previously described aerodynamic effects. As noted elsewhere, this is due to the fact that the blades are rotating in a circle around an axis and that the outer tip of the blades move more rapidly through the air than the inner portion. At a conceptual level, the variations in profile shape can be thought of as twisting the profile along the blade's major axis, though the exact angle and variation in shape is calculated for each point along the blade, accounting for the speed of the wind as well as the rotating blade. This twisting of the profile helps ensure that the pressure formed on the front and back surfaces of the blade profile balances the pressure occurring in the middle of the profile. As a result of this, the breaking risk of the blade decreases.

[0046] Additionally, the cross section of each profile is superimposed on this view as 401 through 404. In some embodiments, the profile tapers as one moves from the rotor, illustrated by cross sections 401 and 402, at the A-A section, to the tip, illustrated by cross sections 403 and 404, at the B-B section. This change helps optimize the distribution of pressure along, preventing, e.g., an excessively large torque at the tip of the blade from shattering the blade. Additionally, as noted above, in some embodiments the profiles twists around the major axis of the blades. In certain embodiments, this twisting is combined with the tapered shape to further optimize the forces on the blades.

[0047] As used herein, the terms or is intended to cover a non-exclusive inclusion. That is, or includes both meanings of both or and and/or.

[0048] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0049] As used herein, airfoil means a body designed to provide a desired aerodynamic force when in motion relative to the surrounding fluid. Fluids may be gaseous or liquid.

[0050] As used herein, blade refers to an airfoil.

[0051] As used herein, turbine refers to a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. Fluids may be gaseous or liquid.

[0052] As used herein, profile refers to the contour or form of a body, especially in a cross section.

[0053] As used herein, rotor refers to the rotating assembly in a turbine, especially a wind turbine.

[0054] The flowchart and block diagrams in the drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods and program products, according to various embodiments of the present invention.

[0055] While this specification contains many specifics, these should not be construed as limitations on the scope of the invention or of what can be claimed, but rather as descriptions of features specific to particular implementations of the invention. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable sub combination. Moreover, although features can be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination can be directed to a sub combination or variation of a sub combination.

[0056] Similarly, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0057] Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Methods may be implemented manually, in software, in hardware, or a combination thereof. The order of any method may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

[0058] Furthermore, the recitation of any element is expressly intended not to invoke 35 U.S.C. 112, paragraph (f) interpretation for that element unless the language means for or step for is specifically recited.