Field of Invention

The present invention relates to the field of vertical wind turbines. In particular, the present invention relates to a wind turbine with improved efficiency. More particularly, the present invention relates to a wind turbine having inner and outer blades for directing wind flow towards each other.

Background of Invention

Traditional wind turbines are well known for exploiting energy by converting one form of energy (wind energy) to another (electricity). Turbine blades are mounted on a tower in order to harness the wind energy above the ground surface. The wind spins the blades, which, in turn, cause an attached generator to rotate. The generator then converts that moving energy of the wind into electricity via electromagnetic induction.

The two main types of wind turbines are horizontal axis and vertical axis wind turbines, depending on whether the turbine blades rotate about the horizontal or vertical axis.

The main rotor shaft and electrical generator are situated at the top of a tower^f the horizontal axis wind turbine, and^mus be pointed into the wind. Small turbines are pointed by a wind vane, whereas large turbines typically use a wind sensor and a servo motor. Most horizontal axis turbines also have a gearbox, which converts the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.

Vertical-axis wind turbines have the main rotor shaft oriented vertically. Some advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is advantageous particularly at locations where the wind direction is highly variable. With a vertical axis wind turbine, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance.

Referring to Fig. 1 showing a schematic top view of a prior art vertical axis wind turbine (1), one drawback associated with prior art vertical turbines is that the turbine is essentially divided into two sections when rotating (5) about a vertical axis (2) - a first section (3) on one side of the vertical axis (2), that rotates in the direction (3a) of the wind flow indicated by arrows (6), and a second section (4) on the other side of the vertical axis (2), that rotates in the opposite direction (4a) of (i.e. towards) the wind flow (6). As such, only the half of the turbine that faces the wind is utilized to turn the turbine blades (7), whereas the other half provides resistance to the rotating turbine blades (7).

There exist several prior art turbines that appear to relate to the drawback mentioned above, as described in the following patent documents, however none provide a suitable solution to the problem described herein.

Patent documents that relate to the present invention include: WO

2007/129049 _^ GB 1911X7005, JP 2008150963, US 5,380,149, US 4,115,027,

SE 468,445, FR 2,541,732, US 3,938,907 DE 3,126,749, US 7,329,965, JP 2001132617, US 4,061,926.

It is therefore an object of the present invention to provide a vertical axis wind turbine that overcomes the drawbacks associated with the conventional vertical wind turbines including those mentioned herein above. It is an additional object of the present invention to provide a vertical axis wind turbine that utilizes a larger percentage of air flow than prior art vertical wind turbines.

Additional objects and advantages of the present invention are described in detail herein below.

Summary of Invention

The present invention relates to a vertical axis wind turbine comprised of an array of outer blades and an array of inner blades. The arrays of blades are rotatable concentrically about a central vertical axis, whereby the force created by a wind directed at the turbine causes the outer blades to rotate in a first direction and the inner blades to rotate in a second direction, opposite that of the first direction. The wind turbine of the present invention is characterized in that the outer blades comprise at least a radially inward facing surface for directing wind toward the inner blades, and the inner blades comprise at least a radially outward facing surface for directing wind toward the outer blades.

Brief Description of the Figures

In the drawings:

- Fig. 1 shows a schematic top view of a prior art vertical wind turbine;

- Fig. 2 shows a schematic top view of a first embodiment of the vertical wind turbine of the present invention;

- Fig. 3 shows an enlarged view of a single outer blade and a single inner blade of the turbine of the present invention;

- Fig. 4 shows an enlarged view of the second section of the turbine of the present invention; 1 000538

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- Figs. 5a-d show four alternative designs of an outer blade of the present invention;

- Fig. 6 shows an enlarged view of a portion of the first section of the turbine of the present invention;

- Figs. 7a-c show alternative embodiments of the inner blades, in addition to the configuration shown in Fig. 6;

- Fig. 8 shows an enlarged view of a single outer blade and a single inner blade of the turbine of the present invention, similar to that of Fig. 3;

- Fig. 9 shows an alternative aspect of a the turbine of the present invention, with a curved rotating panel for guiding wind flow; and,

- Fig. 10 shows a schematic side view of the turbine of the present invention.

Detailed Description of the Preferred Embodiments

A first embodiment of the vertical axis wind turbine of the present invention is shown schematically in a top view in Fig. 2, and designated generally by reference numeral (10). Turbine (10) comprises a shaft (12) disposed along the vertical central axis of turbine (10). An array of outer blades (20) and an array of inner blades (30) concentrically rotate about the central axis as a result of a force applied to blades (20), (30). The force is provided by a fluid,

The curvature of outer and inner blades (20), (30) is designed such that the force created by the wind (6) causes outer blades (20) to rotate in a first direction (22) and inner blades (30) to rotate in a second direction (32), wherein first and second directions (22), (32) are opposite that of each other.

Thus, in a first section (14) of turbine (10), situated on a first side of shaft (12), outer blades (20) rotate in the direction of the wind flow (6). In a second 11 000538

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section (16) of turbine (10), situated on a second side of shaft (12), inner blades (30) rotate in the direction opposite that of the wind flow (6).

Fig. 3 shows an enlarged view of a single outer blade (20) and a single inner blade (30) of the turbine of the present invention. Outer blade (20) comprises a lead face (24) and a trailing face (26). Similarly, inner blade (30a) comprises a lead face (34) and a trailing face (36). According to the preferred embodiment, the surface of lead face (24) of outer blade (20) comprises a radially inward facing portion (25a) having a curvature designed to direct (or, guide) the wind flow toward trailing face (36) of inner blade (30), as indicated by arrow (8) in Fig. 4, showing an enlarged view of second section (16) of the turbine.

Thus, the mechanical efficiency of the turbine of the present invention is improved by the design of the outer blades, whereby the outer blades assist in causing the rotation of the inner blades by directing the wind thereto.

Alternative embodiments of the outer blades, in addition to the configuration shown in Figs. 2-4, are shown in Figs. 5a-d. Fig. 5a shows a multi-blade design (20b) comprising three semi-circular blades (20b'), (20b"), (20b'"), similar to the single semi-circular curvature shown in Figs. 2-4. The three blades (20b i2Qh"), 2flh'") are joined to each other such that the convex portion of each blade forms a portion of the lead face (24a) of the multi-blade design. The trailing face (26a) of the multi-blade design (20b) comprises the concave portion of each blade. Trailing face (26a) is designed to "catch" the wind directed thereat, as described herein above. When wind is directed at the turbine from the opposite direction, wind flowing over lead face (24a) is directed towards the inner blades (not shown in the figure) by the radially inward facing portion, as indicated by arrow (8). Fig. 5b shows an alternative design of outer blade (20b) comprising a lead face (24b) having an elongated radially inward facing portion (28b) and a radially outward facing portion (29a). Trailing face (26b) is designed to "catch" the wind directed thereat, as described herein above. When wind is directed at the turbine from the opposite direction, wind flowing over lead face (24b) is directed towards the inner blades (not shown in the figure) by the radially inward facing portion, as indicated by arrow (8).

Fig. 5c shows an alternative design of outer blade (20c) comprising a lead face (24c) having an elongated radially inward facing portion (28c) and a radially outward facing portion (29b) having a spiral curvature. Trailing face (26c) is designed to "catch" the wind directed thereat, as described herein above. When wind is directed at the turbine from the opposite direction, wind flowing over lead face (24c) is directed towards the inner blades (not shown in the figure) by the radially inward facing portion, as indicated by arrow (8).

Fig. 5d shows a further alternative design of outer blade (20d) comprising a semi-circular lead face (24d) similar to that of the first embodiment of the present invention, wherein the radially inward facing portion (28d) is elongated. Trailing face (26d) is designed to "catch" the wind directed thereat, as described herein above. When wind is directed at the turbine from the opposite direction _^ wind flowing over lead face (24b) is directed towards the inner blades (not shown in the figure) by the radially inward facing portion, as indicated by arrow (8).

It is understood that the curvature designs of the outer blades of the present invention are not limited to those shown in the figures herein, and additional alternative designs of outer blades are within the scope of the present invention. An enlarged view of a portion of the first section (14) of the turbine of the present invention is shown in Fig. 6. According to the preferred embodiment, the surface of lead face (34) of inner blades (30) comprises a radially outward facing portion (35a) having a curvature designed to direct (or, guide) the wind flow toward trailing face (26) of outer blade (20n), as indicated by arrow (9).

Thus, the mechanical efficiency of the turbine of the present invention is further improved by the design of the inner blades, whereby the inner blades assist in causing the rotation of the outer blades by directing the wind thereto.

Alternative embodiments of the inner blades, in addition to the configuration shown in Fig. 6 and described herein, are shown in Figs. 7a-c. Fig. 7a shows three inner blades (30a), wherein each blade comprises at least a semicircular curvature. Arrow (32) indicates the rotational direction of inner blades (30a), and arrow (9) indicates the wind flow directed towards inner blades (30a). The radially outward facing portion (34a) of inner blade (30a) direct the wind flow (9) toward the trailing face of the outer blades (not shown), as described in detail herein above. The trailing face (36a) is designed to "catch" the wind directed thereat from the outer blades, as described herein above.

Fig. 7b shows an inner blade (30b) having a radially outward facing curvature similar to that shown in Fig. 7a, and a radially inward facing portion (34b) having the curvature of a spiral. Arrow (32) indicates the rotational direction of inner blades (30b), and arrow (9) indicates the wind flow directed towards inner blades (30b). The radially outward facing portion (34b) of inner blade (30b) direct the wind flow (9) toward trailing face of outer blade (not shown), as described herein above. The trailing face (36b) is designed to "catch" the wind directed thereat from the outer blades, as described herein above.

Fig. 7c shows three inner blades (30c), each having a curvature similar to that shown in Fig. 7a, wherein blades (30c) are joined to each other, forming an essentially continuous radially inward facing inner blade. Arrow (32) indicates the rotational direction of inner blades (30c), and arrow (9a) indicates the wind flow directed towards inner blades (30c) from the surroundings. The radially outward facing portion (34c) of inner blade (30c) direct the wind flow (9) toward trailing face of outer blade (not shown), as described herein above. The trailing face (36c) is designed to "catch" the wind directed thereat from the outer blades, as described herein above.

Fig. 8 shows an enlarged view of a single outer blade (20) and a single inner blade (30) of the turbine of the present invention, similar to that shown in Fig. 3. In order for outer blade (20) to direct the maximum amount of wind towards the inner blade (30), the angle (a) of inward facing portion (25a) of outer blade (20) is preferably between 0° and 90° with respect to the central axis of the turbine, and more preferably between 20° and 60°, as shown. Correspondingly, in order for inner blade (30) to direct the maximum amount of wind towards the outer blade (20), the angle (o) of outward facing portion (34) of inner blade (30) is preferably between 0° and 90° with respect to the central axis of the turbine, and more preferably between 20° and 60°, as shown.

According to an alternative aspect of the first embodiment as shown in Fig. 9, turbine (10') comprises a curved rotating panel (40) made of a rigid or resilient material, which is positioned along a portion of the circumference circumscribing inner blades (30). Panel (40) serves as an additional or alternative guide for directing the wind toward outer blades (20), as indicated by arrow (9). Panel (40) is shown in the figure circumscribing the entire first section (14) of turbine (10'), however it is understood that panel (40) may alternatively circumscribe only a portion of first section (14).

Panel (40) is preferably pivotably joined to and freely rotatable about the central shaft (12) situated along the central vertical axis. Panel (40) is fixedly joined to a wind vane (not shown in the figures) such that panel (40) remains positioned within the first section of the turbine.

In some embodiments, the turbine of the present invention comprises significantly fewer outer blades than inner blades, depending on the length and curvature of the blades. For instance, the turbine of the present invention preferably comprises 2-10, or more preferably 3-8 outer blades, and preferably 36-40 inner blades. The outer blades situated at the second section of the turbine at least partially obstruct the wind directed towards the turbine from contacting the inner blades. Thus, the presence of few outer blades reduces the obstruction of the wind. The presence of many inner blades, comprising a suitable design as described herein above, provides a continuous obstruction of the wind at the first section of the turbine for directing the wind towards the outer blades.

Alternatively, in embodiments of h& present invention comprising ^he panel, as described herein above, few inner blades may be present, such that inner and outer blades are similar in number, for instance, wherein each of the inner and outer array of blades comprises between 3-8 blades. In this embodiment, the panel provides the continuous obstruction of the wind at the first section of the turbine for directing the wind towards the outer blades.

A side view of turbine (10) is shown schematically in Fig. 10. Inner blades (30) are affixed to central shaft (12) situated along the central vertical axis of turbine (10), and outer blades (20) are rotatable about shaft (12) via bearings (11). Shaft (12) is rotatingly mounted on frame (18) via bearings (15).

In a preferred embodiment, inner blades (30) are enclosed by a cover (44a) at the upper longitudinal end (38a) and a cover (44b) at the lower longitudinal end (38b), thereby preventing the wind from escaping turbine (10) from the two ends (38a), (38b), while simultaneously directing the wind outward toward the outer blades (20).

Alternator (50) is positioned beneath turbine blades (20), (30), wherein the rotor (52) is affixed to the lower end of the frame (21) of outer turbine blades (20), and the stator (54) is affixed to shaft (13). Hence, when turbine (10) is acted upon by an outside (wind) force, outer turbine blades (20) rotate rotor (52) in a first direction and inner turbine blades (30) rotate stator (54) in a second, opposing direction, thereby increasing the relative rotational speed of rotor (52) and stator (54).

Optionally, alternator (50) is coupled with one or more gears (not shown) for providing a mechanical advantage and to change the rotational speeds of rotor (52) and stator (54). A counterweight (not shown) is additionally provided for balancing the additional weight provided by the gears.

Example:

The efficiency of a prototype of the turbine of the present invention was tested and measured, and shown to result in utilization of 100% of the wind that came in contact with turbine blades.

Three prototype turbines where manufactured. The first turbine was the dual turbine of the present invention. The second turbine comprised only the outer turbine blades of the present invention. The third turbine comprised only the inner turbine blades of the present invention.

The outer diameter of the turbines comprising the outer turbine blades was measured to be 20cm wide, and the length of the outer turbine blades was measured to be 40cm. The outer diameter of the inner turbine blades was measured to be 10.5cm, and the length of the inner turbine blades was measured to be 38cm.

The second and third turbines were placed on their side (i.e. lengthwise) in a wind tunnel and measurements where taken at four different wind speeds.

The revolutions per minute were first measured for the second and third turbines, and the moment force per revolution was measured in grams by attaching a weight to the respective turbine blades. The relationship between the rotational speed and the moment per rotation were determined.

Table 1 below shows the measurements taken and the relationship between the measurements of the second and third turbine.

Table 1 P T/IL2011/000538

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Results:

The inner turbine blades rotate at a relatively high rpm, and low force. When the speed increases, the ratio between rpm and force increases.

The outer turbine blades rotate at a relatively low rpm, and a large force. When the speed increases, the ratio decreases.

Next, the first turbine was placed in a wind tunnel and measurements were taken at the same four different wind speeds as for the second and third turbines.

The revolutions per minute where measured for the inner and outer turbine blades individually.

Table 2 below shows the measurements taken for the inner and outer turbine blades of the first turbine.

Table 2 Results:

When the inner and outer blades work together in a single turbine, they act as a counterbalance to each other. Thus, the rotational speed of each array of blades tend to become similar. As a result of this, the total speed of the outer turbine increases, and the total output of the turbine increases.

It is understood that the above description of the embodiments of the present invention are for illustrative purposes only, and is not meant to be exhaustive or to limit the invention to the precise form or forms disclosed, as many modifications and variations are possible. Such modifications and variations are intended to be included within the scope of the present invention as defined by the accompanying claims.