WO2012040320A2

WO2012040320A2 - Wind turbine with multi-stage blades

Info

Publication number: WO2012040320A2
Application number: PCT/US2011/052540
Authority: WO
Inventors: Ph.D Imad Mahawili
Original assignee: E-Net, Llc
Priority date: 2010-09-21
Filing date: 2011-09-21
Publication date: 2012-03-29
Also published as: WO2012040320A3

Abstract

A wind turbine includes a first set of wind turbine blades mounted for rotation about an axis of rotation, and a second set of wind turbine blades mounted for rotation about the axis of rotation with the first set of blades. Each blade of the first set of wind turbine blades includes a blade surface formed by at least two blade portions. Further, each blade of the second set of blades includes a blade surface area that is formed by at least one blade portion, which has a different blade surface area configuration than the surface area of the blades of the first set of blades.

Description

WIND TURBINE WITH MULTI-STAGE BLADES

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a wind turbine and, more particularly, to a wind turbine with a multi-staged blade assembly that exhibits faster reaction time to a wind speed change and, further, a reduced time to rise to a given voltage.

[0002] As described in the referenced application, conventional wind turbines typically start to operate when the wind speed is at or above 8 mph. This is due in part to the weight of the turbine blades, but also in part to the friction in the gears between the turbine blade shaft and the generator. Therefore, the current wind turbines do not typically harness energy from wind speeds of less than 8 mph. Because wind speed below 8 mph represent a significant component of the overall wind speed spectrum in the U.S., and elsewhere in the world, current wind turbines overlook a significant potential source of energy. Further, as a result, the time the wind turbine takes to respond to a change in wind speed and the time the wind turbine takes to reach a given output are significant, which impact the efficiency of the wind turbine.

SUMMARY OF THE INVENTION

[0003] Accordingly, the present invention provides a wind turbine that provides groups or sets of multi-stage wind turbine blades to reduce the reaction time of the wind turbine blade assembly to a change in wind speed so that the wind turbine can reach a desired output, e.g. an optimized output for a given wind speed or wind speed profile, is faster than prior wind.

[0004] According to one form of the invention, a wind turbine includes a first set of wind turbine blades mounted for rotation about an axis of rotation and a second set of wind turbine blades mounted for rotation about the axis of rotation with the first set of blades. Each blade of the first set of wind turbine blades includes a blade surface area formed by at least two discrete blade portions. Each blade of the second set of blades includes a blade surface area that is formed by at least one blade portion, and which has a smaller blade surface area than the surface area of the blades of the first set of blades.

[0005] In one aspect, each blade of the second set of wind turbine blades has a stepped blade surface area formed by at least two blade portions. [0006] In another aspect, each of the wind turbine blades has a blade root end and a blade distal or tip end. The blade root ends of the second set of wind turbine blades are at or radially outward of the blade root ends of the first set of wind turbine blades.

[0007] In further aspects, the blade tip ends of the first sets of blades are aligned along a circumference, with the blade tip ends of the second set of blades being generally aligned along the same circumference.

[0008] In a further aspect, the wind turbine also includes a plurality of spokes, which support the first and second sets of wind turbine blades.

[0009] In yet another aspect, the width of each blade of the first set of blades has a stepped profile with one edge of each of the respective blades being supported along one spoke and forming a linear edge, and the opposed edge of each blade forming the stepped profile.

[0010] According to yet another aspect, each blade of the first set of blades is formed from a plurality of blade segments joined together.

[0011] In another form of the invention, a wind turbine includes a first set of wind turbine blades mounted for rotation about an axis of rotation and a second set of wind turbine blades, with each of the blades of the first set of wind turbine blades having a wind blade surface, at least first and second blade segments defining said wind blade surface, and a variable wind attack angle, and each blade segment having a blade root end and a blade tip end. The wind blade surfaces of the first set of blades extend radially inward relative to the second set of wind turbine blades. And, the variable wind attack angle of the blades of the first set of blades varies from a first value at the blade tip end of a first segment to a second value at the blade root end of the first segment to a third value greater or less than the second value at the blade tip end of the second segment.

[0012] In one aspect, each blade includes at least first and second blade segments, each segment having a tip end width and a root end width, the root end widths of each segment being less than the tip end widths of the immediately adjacent segment.

[0013] In yet other aspect, the wind turbine also includes a rim, which supports spokes and a plurality of magnets.

[0014] In yet other aspects, each of the wind turbine blades comprises a web, formed, for example, from a fabric or a polymeric material, which forms at least a portion of each wind blade surface. [0015] According to yet another form of the invention, a wind turbine includes a first set of wind turbine blades mounted for rotation about a rotational axis and a second set of wind turbine blades supported for rotation with the first set of wind turbine blades about the rotational axis. Each of the blades is formed from at least two blade segments, with each blade segment having a blade tip end and a blade root end and a varying attack angle, which decreases from its respective blade root end to its respective blade tip end.

[0016] In one aspect, each of the blade segments has an asymmetrical cross section.

[0017] In a further aspect, the wind turbine further includes an annular rim, which supports the wind turbine blades.

[0018] In further aspects, the rim supports a plurality of magnets, and the turbine further includes a conductive coil, which is sufficiently close to at least one of the magnets such that rotary motion of the rim and magnets induces current flow in the coil.

[0019] Accordingly, the wind turbine of the present invention provides a wind turbine with staged wind blade surface areas to reduce the reaction time of the turbine blade assembly and, therefore, reduce the rise time of the wind turbine to reach a given output.

[0020] These and other objects, advantages, purposes, and features of the invention will become more apparent from the study of the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is an elevational view of the wind turbine of the present invention

incorporating multi-stage blades;

[0022] FIG. 2 is an enlarged view of the blades; and

[0023] FIG. 3 is a side elevation view of one embodiment of the wind turbine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring to FIG. 1, the numeral 10 generally designates one embodiment of the wind turbine of the present invention. Wind turbine 10 includes a wind turbine wheel assembly 12 supported on a base 14. Base 14 may be similar to any of the bases of the wind turbines (e.g. wind turbine 610) described in the above-referenced co-pending applications, including Ser. No. 12/714,913, entitled WIND TURBINE (Attorney Docket WIN04 P-103A). As will be more fully described below, wind turbine 10 includes two sets of turbine blades, which increase the energy extraction efficiency over prior blades and, further, decreases the turbine response time (or stated alternately speeds up the response time) to a change in the wind speed as compared to current blade designs. Additionally, the cut-in wind speed may also be reduced. Consequently, the rise time (the time for the wind turbine to reach a given output) is decreased, which increases the efficiency of the wind turbine.

[0025] Referring again to FIG. 1, wind turbine wheel assembly 12 includes two sets of wind turbine blades 16 and 18 mounted to spokes 23 of wheel 20. As described in the co-pending applications and as shown in FIG. 3, magnets 24 are mounted to the rim 22 of wheel 20, which extend into a plurality of stator assemblies 30 that are arranged around the perimeter of rim 22 to thereby generate electrical flow when wheel assembly 12 rotates about its rotational axis 12a. The spokes provide support for the blades and support for the rim and magnets. However, the weight of the magnets is not bourne by the blades so that the overall weight of the blades can be reduced, which can reduce the inertia of the wind turbine and hence increase its responsiveness, especially at low wind speeds. For further details of wheel 20 and its rim 22 and spokes 23, reference is made to the wind turbines described in the above incorporated co-pending patent applications.

[0026] As best seen in FIG. 2, the first set of wind turbine blades 16 have a longer radial extent than the second set of wind turbine blades 18, with each of their blade tip ends being generally aligned along a circumference at or adjacent the inner circumference of rim 22, but with the blade root ends of the first set of wind turbine (16) blades being radially inward of the blade root ends of the second set of wind turbine blades (18). Therefore, blades 16 provide wind blade surface areas that extend radially inward of the second set of blades.

[0027] In addition, each blade of the first set and second of blades 16, 18 includes at least two discrete regions or segments 16a, 16b, 18a, 18b with each segment (16a, 16b, 18a, 18b) having a blade tip end and a blade root end. Each segment 16a, 16b, 18a, 18b optionally has a varying attack angle starting at its blade tip end, which increases along its length to its blade root end. For example, each segment may be similar to blades 1226 described in U.S. co-pending application Ser. No. 12/714,913, filed March 1, 2010, entitled WIND TURBINE (Attorney Docket No. WIN04 P-103A) with an attack angle at their blade tip end that ranges from 0 degrees to 10 degrees and an attack angle at their blade root end, for example, in a range of 40 degrees to 50 degrees. In this manner, optionally, the blade root end of each segment may have a smaller attack angle than the attack angle of the blade tip end of the adjacent blade segment. [0028] Further, the width of each segment varies along its length so that each segment has a generally trapezoidal- shape with a greater width at its blade tip end than its blade root end. In addition, the blade root end of each outermost segment (e.g. 16a, 18a) of each blade has a smaller width than the blade tip end of the adjacent blade segment (e.g. 16b, 18b) so that the blade has a stepped blade profile along its wind edge attack edge.

[0029] As best seen in FIG. 2, the first set of wind turbine blades may include a third blade portion or segment 16c, which similarly has a greater width at its blade tip end than the width of the blade root end of the adjacent, in this case intermediate blade segment 16b. Further, its angle of attack at its blade tip end may be greater than that of the blade root end of the adjacent, intermediate blade segment. Therefore, first and second sets of blades 16, 18 may form a plurality of discrete wind surface areas that have different geometries (e.g. attack angle, surface area, and surface topology) to drive the wind turbine wheel assembly over different or overlapping wind speeds to form a multi-stage blade wind turbine. Consequently, the multistage blades may increase the range of wind speeds over which the wind turbine can extract energy. It should be understood that the number or segments may be increased or decreased as desired and further their shape, size and material may be varied to harvest energy from different wind speeds and wind from different directions so that if the wind shifts or slows down the wind turbine can still operate and still extract energy. However, for ease of manufacturer and to reduce costs, it may be beneficial to assembly each blade from multiples of similar blade segments.

[0030] While described as having a varying attack angle along their lengths, each segment 16a- 16c, 18a and 18b may be planar so that the angle of attack does not vary along its length or some segments may be planar and others have a varying attack angle. Further, in some applications the angle of attack may be reduced at the step between the adjacent blade segments. For example, the angle of attack at the blade root end of segment 16a may be greater than the angle of attack of the blade tip end of segment 16b. Again, by changing the geometric characteristics of the blades or blade surface areas, the range and responsiveness of the wind turbine can be adjusted.

[0031] Similar to the blades described in the referenced applications, blades 16, 18 include a web or membrane that may be formed from a metal, a moldable material, such as a polymer, including a plastic, or a fabric, such as a nylon or Kevlar^®. Further, the blades may be formed from a single sheet or panel of material or each segment may be formed from a panel or sheet of material, with the segments then joined, as noted below. Further, when made of a polymer or a fabric sheet, the blades may be formed from a translucent or transparent polymer. The thickness of the web may be varied, for example, in a range of a few mils to several hundred mils or more. For further details of optional blade material and construction, reference is made to the blades described in the co-pending application Ser. No. 12/714,913 (Attorney Docket No. WIN04 P- 103A). With this or other similar constructions, the weight of the blades can be varied, for example reduced, which again can adjust the responsiveness of the wind turbine weights and lower inertia to overcome, the wind turbine can be more responsive at lower wind speeds.

[0032] As best seen in FIG. 2, blades 16, 18 are each mounted to spokes 23, for example, by ties or clips 16d, 18d. The clips or ties can be made of an elastic or spring material so that the blade can deflect, for example deflect parallel to the wind at high wind speeds. This can act as an automatic safety limit for the wind turbine rotation. Further, as noted each blade may be molded or formed as a unitary blade comprised of the two or more segments described above or may be formed from discrete segments that are secured together by fasteners (16e, 18e) or welds or the like. Additionally, the web thickness of each segment may be uniform or be varied and, further, may be varied from the adjacent segment. Alternately, the blades have a defined hinge (as described in the reference application) or instead bend under the pressure of the wind (when the wind exceeds a preselected value) due to its cross-section properties. The location of where the blade bends may be controlled, at least to some extent, by varying the thickness of the web. The change in thickness may be gradual, or the blade may have an abrupt change in thickness. Therefore, the blade may bend or simply deflect when the wind pressure exceeds a desired maximum wind pressure. Further, the magnitude of deflection or bending will increase as the pressure increases. Again the result is a self-adjusting or dynamic blade. In this latter application, the blades are optionally made out of a material that has sufficient elastic or has sufficient spring properties, so the blade will return to its pre-bent shape.

[0033] As noted above, the roots of blades may be narrower than the tips of the blades. Additionally as noted the blades may be curved so that the blade angle of attack is varied along its length to accommodate efficient aerodynamic energy conversion to mechanical rotation of the wheel. For example, in the illustrated embodiment, the attack angle of blade segments may decrease along their lengths from their blade root end (where the wheel experiences the slowest radial velocity) to their blade tip end (where the wheel experiences the maximum radial velocity) to thereby form asymmetrical blade segments similar to the blades (e.g. blades 26) disclosed in the referenced co-pending applications. In a similar manner to the referenced blades, blades 16 and 18 and/or their blade segments may have very steep attack angle, for example in a range of 40° to 50° or in a range of 42° to 48° or approximately 45° at their root ends. While the attack angle at the tip ends of each segment can range from 0° to 10° or from 2° to 5°, or be

approximately 3°. This increases the lift co-efficient and minimizes the drag forces along the blade length at various wind speeds. This parameter can be achieved by the asymmetrical shape of the blade, which is concave on its leeward side and convex on its windward side. Given that the blade may be formed from a thin web or membrane (as described in reference in the copending application) the blade segment's asymmetry can be formed by twisting the blade segment' s root end relative to its tip end during its formation or may be formed during mounting of the blade. Therefore, as it will be understood, the windward facing side of each blade may be configured so that it is not perpendicular to the incoming wind. Further, as noted above, the blade may fold or bend when the wind speed exceeds a predetermined magnitude, which thereby reduces the solidity of the turbine blade but may return to its previous solidity when the wind speed reduces below the predetermined or preselected value.

[0034] Accordingly, the present invention provides a wind turbine that provides groups or sets of multi-stage wind turbine blades to reduce the reaction time of the wind turbine blade assembly to a change in wind speed so that the wind turbine can reach a desired output, e.g. an optimized output for a given wind speed or wind speed profile, is faster than prior wind turbines. Further, the cut-in wind speed for the turbine is significantly lower than conventional turbines, which may be as low as 0.3 mph, and the range of wind speeds in which the turbine may be operated can be increased by allowing the turbine to reduce the wind pressure when the wind speeds exceeds a preselected maximum wind speed. In addition, as described in the co-pending application, a micro-processor based control system may be provided to control the direction of the turbine blade assembly to reduce the stress on the wind turbine or to optimize the direction of the turbine blade assembly so that the angle of receipt of the wind can be maintained at, for example 120°, relative to the face of the turbine blade assembly.

[0035] While several forms of the invention have been shown and described, other forms will now be apparent to those skilled in the art. For example, wind turbine 10 may incorporate the wind deflectors or concentrators and/or control systems described in the reference cop- pending applications. It should be understood that the embodiments shown in the drawings and described above are merely for illustrative purposes, and are not intended to limit the scope of the invention which is defined by the claims which follow as interpreted under the principles of patent law including the doctrine of equivalents.

Claims

What is claimed is:

1. A wind turbine comprising:

a first set of wind turbine blades mounted for rotation about an axis of rotation; a second set of wind turbine blades mounted for rotation about the axis of rotation with the first set of blades;

each blade of the first set of wind turbine blades including a surface area with at least two blade portions; and

each blade of the second set of blades including a blade surface area that is formed by at least one blade portion, which has a different blade surface area configuration than the surface area of the blades of the first set of blades.

2. The wind turbine according to claim 1, wherein each blade of the second set of wind turbine blades has a stepped profile formed by said at least two blade portions.

3. The wind turbine according to any previous claim, wherein each of the wind turbine blades has a blade root end and a blade distal or tip end, the blade root ends of the second set of wind turbine blades being at or radially outward of the blade root ends of the first set of wind turbine blades.

4. The wind turbine according to any previous claim, wherein the blade tip ends of the first sets of blades are aligned along a circumference, with the blade tip ends of the second set of blades being generally aligned along the same circumference.

5. The wind turbine according to any previous claim, the wind turbine also includes a plurality of spokes, which support the first and second sets of wind turbine blades.

6. The wind turbine according to any previous claim, wherein one edge of each of the first set of blades is supported along one spoke and forms a linear edge, and the opposed edge of each blade forming the stepped profile.

7. The wind turbine according to any previous, wherein each blade of the first set of blades is formed from a plurality of blade segments joined together.

8. A wind turbine comprising:

a first set of wind turbine blades mounted for rotation about an axis of rotation; a second set of wind turbine blades;

each of the blades of the first set of wind turbine blades having a wind blade surface, at least first and second blade segments defining said wind blade surface, and a variable wind attack angle;

each blade segment having a blade root end and a blade tip end; and

the variable wind attack angle of the first set of blades varying from a first value at the blade tip end of the first segment of the blade to a second value at the blade root end of the first segment to a third value greater or less than the second value at the blade tip end of the second segment.

9. The wind turbine according to claim 8, wherein each of said second set of blades blade includes at least first and second blade segments, each of said blade segments having a tip end width and a root end width, the root end widths of each segment being less than the tip end widths of the immediately adjacent blade segment.

10. The wind turbine according to any one of claims 8 and 9, wherein the wind turbine also includes a rim, which supports the spokes and a plurality of magnets.

11. The wind turbine according to any previous claim, wherein each of the wind turbine blades comprises a web, formed, for example, from a fabric or a polymeric material, which forms at least a portion of each wind blade surface.

12. A wind turbine comprising:

a first set of wind turbine blades mounted for rotation about a rotational axis;

a second set of wind turbine blades supported for rotation with the first set of wind turbine blades about the rotational axis; each of the blades being formed from at least two blade segments, with each blade segment having a blade tip end and a blade root end and a varying attack angle, which varies from its respective blade root end to its respective blade tip end.

13. The wind turbine according to any previous claim, wherein each of the blade segments has an asymmetrical cross section.

14. The wind turbine according to any previous claim, wherein the wind turbine further includes an annular rim, which supports the wind turbine blades.

15. The wind turbine according to claim 14, wherein the rim supports a plurality of magnets, and the turbine further includes a conductive coil, which is sufficiently close to at least one of the magnets such that rotary motion of the rim and magnets induces current flow in the coil.