WO2007095022A2

WO2007095022A2 - Improved wind turbine rotor

Info

Publication number: WO2007095022A2
Application number: PCT/US2007/003223
Authority: WO
Inventors: Michael Serpa
Original assignee: Michael Serpa
Priority date: 2006-02-10
Filing date: 2007-02-05
Publication date: 2007-08-23
Also published as: US20070189899A1; WO2007095022A3

Abstract

A wind turbine rotor, the rotor blades of which are shaped generally to resemble the sail of an Oceanic sprit rig sailboat (a traditional sailing craft with a sail plan having unusual and significant aerodynamic properties). The rotor blades might be movably mounted to maximize use of apparent wind. An alternative embodiment includes a contra-rotating rotor of similar design.

Description

IMPROVED WIND TURBINE ROTOR

Field of the Invention

[0001] This invention relates to the rotors of wind-driven turbines.

More specifically, it concerns rotors for those wind turbines that can produce electrical power when linked to a generator.

Background of the Invention

[0002] Since long ago, humans have tried to harness the kinetic energy in wind and put it to useful purposes. Numerous successful attempts at this have produced valuable labor saving devices.

[0003] In modern times, the most sophisticated arrangements for harnessing wind power have resulted in electricity-producing wind turbines. This field of development is increasingly important. As concern about global petroleum supplies and prices continues to grow, and environmental problems associated with the burning of fossil fuels in general yield another set of worries, the promise of renewable and pJanet-friendly energy sources is immeasurably attractive.

[0004] Traditional wind turbines derive their power input by converting some of the wind's energy into a torque, or turning force, acting on a rotor. Rotor blades deflect the wind in a given direction and this causes the rotor to rotate. Electrical power is produced when the turning force is transferred to a generator. The amount of energy that the wind transfers to the rotor depends upon the density of the air, the rotor area, and the wind speed.

[0005] A successful and popular present-day wind turbine design is the three-bladed tower. In this model, a housing, or nacelle, sits atop a tall support tower. Attached to the front of the nacelle is a large three-bladed rotor (similar to an airplane propeller — except with the camber on back of the blades instead of the front). Housed within the nacelle are typically a gearbox and a generator. A nosecone covers the center of the rotor. Added features, such as variable pitch rotor blades, are sometimes included.

[0006] To keep the rotor perpendicular to the wind, a yaw mechanism is employed. This can be a simple mechanical pivot or it can be a sophisticated motorized setup. (If the rotor is not perpendicular to the wind, the wind turbine will be much less effective and "yaw error" is said to be present.)

[0007] The three-bladed rotor type of wind turbine can be costly to construct. Because taller turbines produce more power than shorter ones, large support towers must be built to derive the maximum benefit. In addition, due to the design of the propeller-like rotor, the rotor blades must be built with enough strength to handle the stress loads they must endure in high winds, especially at the point where the three blades are joined inside the nosecone.

[0008] In this "horizontal axis" design (wherein the rotor rotates around a horizontal axis), the blades of the rotors face constant wind energy when wind is present. It is possible, nevertheless, that an airplane propeller, though good for propelling an aircraft through the sky, is not the best design for a rotor intended to extract energy from wind. There are also numerous "vertical axis" wind turbine rotor designs that can be somewhat less efficient because some of the rotor blades are shielded from the wind by the other rotor blades at certain points in the rotation cycle. On the other hand, these vertical axis turbines are well-suited to be installed in locations where a horizontal axis design would be inappropriate. Furthermore, vertical axis turbines typically do not have yaw error problems because their rotors are not oriented perpendicular to the wind direction.

[0009] All of these designs have merit and contribute significantly to the green energy revolution. Yet there remains room for improvement. The problem with most existing horizontal axis prior art wind turbines is that the camber of the rotor blades at some point detracts from the rotor's productive output. At lower speeds the camber (on the back — or downwind — side of the rotor blades) generates "lift" and helps the rotor's performance. This beneficial effect continues as the apparent wind produced from the rotational movement increases. Yet in very strong winds the camber increases the tendency of the rotor blades to flex in a direction away from the wind, often necessitating that the wind turbine be shut down for reasons of safety. (This is especially true in the case of upwind turbine designs, where there is a danger that the rotor blades can strike the support tower.) The ensuing anomaly is that the strongest winds — which hold the most kinetic energy — cannot be fully exploited to produce electrical power.

[0010] Vertical axis wind turbine rotors cannot benefit at all from apparent wind. It might therefore be the case that another type of foil would provide a better starting point for wind turbine rotor design. A better design would be one that: (i) maximizes apparent wind benefits; and (ii) can operate safely and effectively in strong winds.

[0011] Comparing prior art wind turbines to sailboats is helpful because sailboats accomplish both of these objectives. Consider first the apparent wind effect. When sailing off the wind, as on a broad reach or run, a sailboat can sail no faster than the true wind speed. In theory it can absorb a substantial portion of the energy from the wind it is in contact with, but the sailboat still cannot exceed the true wind speed when sailing downwind (assuming no effect from water currents, waves, etc.). The sail is simply being pushed by the wind, similar to the way that the wind pushes the rotors of prior art turbines.

[0012] When, however, sailing on a beam reach—the fastest point of sail — the vessel benefits both from the true wind speed and from the apparent wind generated by the forward motion of the boat. The apparent wind is added to the true wind to create a stronger diving force. The sails capture this driving force and generate lift. Even when on a close reach the sailboat realizes this advantage. [0013] The physics behind a sailboat's ability to sail against the wind is probably best explained by the concept of "attached flow" (whereby the airflow over the leeward side of the sail attaches to the sail and pulls it along to avoid leaving a vacuum). But regardless of the explanation for the principle, it might be that sailboats — due to the considerable extent to which they benefit from apparent wind- provide, a more proper starting point for wind turbine rotor design.

[0014] And this approach appears even more appealing when including the issue of strong winds as sailboats can operate safely and effectively in such conditions because the size and shape of their sails can be controlled.

[0015] Therefore, wind turbine rotors having rotor blades modeled after sailboats offer a solution, with the sail plan of one particular type of sailboat having the greatest potential to significantly advance wind turbine technology. The present invention provides such an advancement; It is intended to yield an extremely efficient turbine rotor capable of operating safely in a variety of wind conditions while incorporating a simple construction, low production cost, a low maintenance cost, and sound structural integrity."

Summary

[0016] The present invention comprises a horizontal axis wind-driven turbine rotor which can be situated atop a tower or other suitable support structure. The innovation it offers results from the unique shape of the rotor's blades.

[0017] The blades are shaped to resemble generally the sail of a traditional sailing craft which is believed to have been developed by Pacific Islanders many years ago. The native Pacific proa (a canoe-like boat) employed an exceptionally well-performing sail and sail support structure called the "Oceanic sprit rig", sometimes also referred to as the "Oceanic lateen rig" or the "crab claw rig" (presumably as a result of the sail's resemblance to a crab's claw). These three terms will be used interchangeably herein.

[0018] The Oceanic lateen rig's sail possesses some unusual properties and has been shown to be astonishingly effective at harnessing the wind's energy to propel a sailing craft over water. This is especially true when the boat is sailing on a beam reach. [0019] While the issue is the subject of debate, it is believed by some that the sail of the crab claw rig develops lift under very different aerodynamic principles than those of other sailing rigs, especially as compared to the popular "Bermudan" rig which is used on most sailboats made today. The Oceanic sprit rig has been shown to be aerodynamically superior to the Bermudan rig in many respects. [For a general discussion of the crab claw rig's benefits and the science behind it, see Sail Performance; Techniques to Maximize Sail Power, revised edition, by CA. Marchaj (International Marine/McGraw-Hill 2003) pages 152 to 176]

[0020] The present invention exploits the remarkable aerodynamic properties of the Oceanic lateen rig and applies them to wind turbine technology to provide an alternative wind turbine rotor design. The crab claw rig's sail provides a model for the rotor blades of this new rotor. It supplements the prior art, thereby contributing to the overall effort to produce electricity from wind power.

Brief Description of the Drawings

[0021] Fig. 1 is a perspective view of an Oceanic sprit rig.

[0022] Fig. 2 is a plan view of a sail from an Oceanic lateen rig.

[0023] Fig. 3 is a plan view of a variation of the Oceanic lateen rig's sail.

[0024] Fig. 4 is a plan view of another variation of the Oceanic lateen rig's sail.

[0025] Fig. 5 is a perspective view of a de-powered Oceanic lateen rig sail.

[0026 Fig. 6 is a front view of a preferred embodiment.

[0027] Fig. 7 is a front view of an alternative preferred embodiment with contra-rotating rotors.

Detailed Description of the Preferred Embodiments and their Operation

[0028] The basic design of the Oceanic sprit rig and its unique sail is displayed in Fig. 1. A sail 20 of the Oceanic lateen has an arrowhead-like profile with a deeper camber— or curve to the sail — at or near a trailing edge 21. The camber gradually diminishes towards the tip, designated by arrow "A", where it may disappear entirely. The sail 20 has leading edges 22 forming the other two sides of the arrowhead, and the leading edges 22 lie generally in the same plane. Also, the sail 20 is more or less symmetrical along its longitudinal axis.

[0029] When sailing upwind or on a beam reach, the tip is closer than the trailing edge 21 to the direction the wind is coming from. That is, the tip is in general nearer to the front of the boat than is the trailing edge 21. Also, like other types of sails, the concave side of the sail 20 always faces the wind. That is, the windward side of the sail 20 is concave and the leeward side is convex.

[0030] For a sailboat, the sail of crab claw rig is typically made of a cloth material, like most other sails. As a result, the leading edges 22 must be affixed to rigid spars, or "sprits" (not shown). For purposes of the preferred embodiments of the present invention, however, the crab-claw-sail-like-rotor-blades can be manufactured from a rigid or semi-rigid material of sufficient strength and durability. This might be the most beneficial construction for many applications.

[0031] For certain embodiments, though, a pliant fabric material

(supported by one or more spars of some sort) might be an appropriate construction.

[0032] In Figs. 2, 3, and 4 are shown plan views of three variations of the Oceanic lateen rig sail, all of which are suitable rotor blade designs for the wind turbine rotor of the present invention. In Fig. 2 the leading edges 22 are slightly curved, the trailing edge 21 is curved, and the tip (marked by arrow "A") is pointed. In Fig. 3, the leading edges 22 have a greater curvature and the tip (marked by arrow "A") is rounded. Also in Fig. 3, the trailing edge 21 is straight. In Fig. 4, the sail has a "delta wing" shape with straight leading edges 22, a pointed tip (marked by arrow "A"), and a straight trailing edge 21.

[0033] Any combination of these features are appropriate for the preferred embodiments of the present invention (i.e., straight leading edges/rounded tip, or curved leading edges/pointed tip; curved trailing edges, straight trailing edges, or some mixing of the two). Specific operating conditions, though, might dictate a preferred combination. What is important is that the blades for the rotor of the present invention have an arrowhead-like profile with maximum camber at or near the trailing edge (corresponding to the trailing edge of a crab claw rig's sail) and camber decreasing towards the tip of the rotor blade (which corresponds to the tip of the sail of the crab claw rig), where the camber can disappear entirely. Also, the leading edges (corresponding to the leading edges of the crab claw rig's sail) of the rotor blades preferably lie in the same plane.

[0034] When sailing in strong winds, sailboats sometimes can be

"overpowered" if they have too much sail area exposed to the wind or have sails trimmed too tight for the conditions. This situation is usually remedied by easing lines to spill wind from the sail (or sails) and, in extreme situations, by reducing total sail area. On an Oceanic sprit rigged-craft, the sail is "de-powered" by permitting the rigid spars at the leading edges to move closer together, thus increasing the camber of the sail along more or less a centerline (the centerline extending from the tip of the sail to the trailing edge 21). The dramatic increase in the camber of the sail resulting from this action apparently disrupts the attached flow on the leeward side of the sail and moderates the lifting power of the sail.

[0035] This is illustrated in Fig. 5. The leading edges 22 of the sail 20 have moved towards one another, resulting in increased camber which will de-power the rig. Indicative of the de-powering is the dramatic curvature of the trailing edge 21. In Fig. 5, the concave side of the sail 20 is indicated by arrow "B".

[0036] If a rotor blade of the rotor in this disclosure is capable of flexing, or folding, along more or less a centerline, it could mimic the de-powering of an Oceanic lateen rig's sail and thus de-power the wind turbine rotor. This would be a valuable safety feature for handling extreme winds.

[0037] A preferred embodiment of the present invention is depicted in

Fig. 6 (the side depicted being that which will face the wind). A wind turbine rotor 23 consists of struts or spokes 24 extending from a central hub 25. Rotor blades 26 are situated at the end of each of the struts or spokes 24 opposite the central hub 25. The rotor blades 26 are shaped generally like the sail of a crab claw rig. The rotor blades 26 are also oriented such that their tips are pointed somewhat towards the direction of rotation for the wind turbine rotor 23 (this direction of rotation is indicated in Fig. 6 as arrow "C"; i.e., counter-clockwise). Also, the concave side of the rotor blades (corresponding to the concave side of the Oceanic sprit rig sail) substantially face the wind.

[0038] Because the lift generated by a Oceanic lateen rig's sail comes from the leeward — or convex — side of the sail, the rotor blades 26 are preferably mounted to the struts or spokes 24 by their concave sides only so as to ensure that the leeward side of each of the rotors blades 26 remains unobstructed. This will result in the cleanest air flow over the convex leeward surfaces.

[0039] [NOTE: the size of the rotor blades 26 relative to the struts or spokes 24 and the wind turbine rotor 23 may vary from the depiction of Fig. 6. The rotor blades 26 can be larger or smaller, depending upon the particular adaptation.]

[0040] Any number or combination of struts or spokes 24 can be included. For example, multiple struts or spokes 24 can support each of the rotor blades 26. To provide a stronger structure, the struts or spokes 24 can be connected to one another by suitable means. Alternatively, a rim (not shown) can encircle the struts or spokes 24 and the rotor blades 26 can be attached to the rim for added structural integrity.

[0041] Returning to Fig. 6 each of the rotor blades 26 have two leading edges 27, and each of the rotor blades 26 is set such that one of their leading edges 27 is closer than the other to the central hub 25.

[0042] In operation, as the wind turbine rotor 23 starts to rotate it will begin to generate apparent wind which will increase the driving force (i.e., lift) produced by the rotor blades 26.

[0043] As for a still other embodiment, the struts or spokes 24 can be eliminated entirely and the rotor blades 26 can be affixed directly to the central hub 25.

[0044] In addition, the rotor blades 26 can be movably mounted such that, as the rotational speed of the wind turbine rotor 23 increases, the rotor blades 26 will themselves turn so that their tips face even closer to the direction of the apparent wind. This would permit the rotor blades 26 to benefit to the fullest extent from the apparent wind for achieving maximum lift.

[0045] In Fig. 6 the wind turbine rotor 23 has three evenly-spaced rotor blades 26 arranged to substantially balance forces when operating. But the number of rotor blades 26 can vary for different applications. Embodiments of the present invention may have any number, even or odd, of rotor blades 26 as deemed appropriate. Experimentation will yield insight as to the arrangement providing superior performance for a given situation. There might even be an application where only one rotor blade is appropriate, though the best designs attempt to balance forces to ensure safety and stability in high wind situations. [0046] Furthermore, the rotor of the present invention may also include rotor blades of other designs in combination with the Oceanic-sprit-rig-sail- shaped-rotors.

[0047] A significant advantage offered by the Fig. 6 embodiment is that the turning force is generated as far as possible from the central hub 25. The turning force the rotor blades 26 generate therefore benefits from leverage. This results in greater usable torque at the central hub 25 for producing electrical power if the present invention is coupled to a generator.

[0048] As for other embodiments, the wind turbine rotor of the present invention can have a lattice-like structure consisting of multiple struts or spokes. The advantage of the lattice construction being that the overall strength of the wind turbine rotor can be increased by buttressing high stress load areas. The "airplane propeller" rotor blade cannot increase thickness at the high stress point near the central hub because to do so would decrease the aerodynamic efficiency of the rotor blade. But the wind turbine rotor of the preferred embodiments can work with struts or spokes with reinforcing support at high stress areas.

[0049] The lattice construction can even take the form of a crisscrossing spokes "bicycle wheel-like" arrangement, resulting in a light and strong structure.

[0050] Another advantage of the lattice construction is that a second wind turbine rotor of the present invention can be housed within the lattice-like structure of a larger one. The two wind turbine rotors could then work in combination to generate electricity. For example, one of the wind turbine rotors could rotate in a clockwise direction and the second wind turbine rotor could be arranged to rotate in the opposite direction. If one of the wind turbine rotors is connected to the rotor of an electrical generator, and the second of the wind turbine rotors is connected to the stator of the same generator, then the relative motion of the generator's rotor relative to its stator would increase. This would maximize the electricity-generating capacity.

[0051] One example of this contra-rotating embodiment is displayed in

Fig. 7, shown as it will face the wind. A first rotor 30 has a lattice construction support structure as previously described. The lattice support structure includes a circular rim 31 for added strength. The first rotor 30 also has four rotor blades 32. A second four-bladed wind turbine rotor 33 sits nestled within the lattice construction support structure of the first rotor 30. In operation, the first rotor 30, as depicted here, would rotate counter-clockwise and the second four-bladed wind turbine rotor 33 would rotate clockwise.

[0052] Alternatively, the second four-bladed wind turbine rotor 33 can simply be mounted in front of or behind the first rotor 30, while still employing the contra-rotating element. Also, the number of rotors blades for each or the rotors can vary, and rotor blades of other designs can be included.

[0053] Other alterations to the preferred embodiments are possible.

For example, a wind turbine with a rotor design of the present invention might be made foldable such that it can be transported to a variety of locations. Also, many different sizes of rotors are possible. A smaller rotor might be set up atop the roof of an electrically-powered automobile to recharge the vehicle's batteries when it is parked, while larger rotors could be made for permanent wind turbines that provide electricity for homes or offices. Furthermore, sensors can be employed to help optimize rotor blade angle relative to the apparent wind.

[0054] Although the description above contains several specificities, these should not be construed as limits on the scope of the present invention. The details given are intended merely to provide illustrations of some of the presently preferred embodiments. It is to be therefore understood that many changes and modifications by one of ordinary skill in the art are considered to be within the scope of the invention. Thus, the full scope should be determined by the appended claims and their legal equivalents, rather than by examples given.

Claims

I claim:

1 ) A wind turbine rotor;

the wind turbine rotor having at least one rotor blade shaped to resemble generally the sail of an Oceanic sprit rig.

2) The wind turbine rotor of claim 1 , wherein the at least one rotor blade shaped to resemble generally the sail of an Oceanic sprit rig is manufactured from a rigid or semi-rigid material, or from a pliant fabric material.

3) The wind turbine rotor of claim 1 , wherein the at least one rotor blade shaped to resemble generally the sail of an Oceanic sprit rig is movably mounted to the wind turbine rotor.

4) The wind turbine rotor of claim 1 , wherein the at least one rotor blade shaped to resemble generally the sail of an Oceanic sprit rig is attached to a strut or spoke opposite a central hub.

5) The wind turbine rotor of claim 1 , in combination with a second, contra-rotating, rotor.

6) The wind turbine rotor of claim 1 , wherein the at least one rotor blade shaped to resemble generally the sail of an Oceanic sprit rig is capable of flexing or folding to increase camber.

7) A wind turbine rotor;

the wind turbine rotor having one or more rotor blades;

at least one of the one or more rotor blades resembling generally the sail of an

Oceanic lateen rig. 8) The wind turbine rotor of claim 7, wherein the one or more rotor blades is/are manufactured from a rigid or semi-rigid material, or from a pliant fabric material.

9) The wind turbine rotor of claim 7, wherein the one or more rotor blades is/are movably mounted to the wind turbine rotor.

10) The wind turbine rotor of claim 7, wherein the one or more rotor blades is/are attached to struts or spokes opposite a central hub.

11) The wind turbine rotor of claim 7, in combination with a second rotor that rotates in the opposite direction.

12) The wind turbine rotor of claim 7, wherein at least one of the one or more rotor blades is capable of flexing or folding for de-powering.

13) A wind turbine rotor;

the wind turbine rotor having rotor blades;

some or all of the rotor blades resembling generally the sail of a crab claw rig.

14) The wind turbine rotor of claim 13, wherein the rotor blades are arranged to substantially balance forces when operating in wind.

15) The wind turbine rotor of claim 13, wherein one or more of the rotor blades is/are manufacture from a rigid or semi-rigid material.

16) The wind turbine rotor of claim 13, wherein one or more of the rotor blades is/are movably mounted to the wind turbine rotor. 17) The wind turbine rotor of claim 13, arranged in combination with a second, contra-rotating, rotor;

the second, contra-rotating, rotor having one or more rotor blades resembling generally the sail of a crab claw rig.

18) The wind turbine rotor of claim 13, wherein one or more of the rotor blades is/are capable of flexing or folding along more or less a centerline for de-powering.