WO2013026127A1

WO2013026127A1 - Cross-wind-axis wind-turbine rotor vane

Info

Publication number: WO2013026127A1
Application number: PCT/CA2011/000960
Authority: WO
Inventors: Diego CASTANON SEOANE
Original assignee: Castanon Seoane Diego
Priority date: 2011-08-22
Filing date: 2011-08-22
Publication date: 2013-02-28

Abstract

Each vane on a cross-wind turbine rotor is airfoil-shaped in cross section orthogonal to the axis of rotation of the rotor. Each vane has a radially outermost surface, which is radially outermost relative to the axis of rotation, and an opposite radially innermost surface. The radially innermost surface includes aerodynamic surface features chosen from the group comprising: (a) dimples, so as to increase surface area drag of each vane during the downwind leg and so as to decrease drag of each vane during the upwind leg, (b) scales so as capture a backwind over the vane to increase surface area drag during the downwind leg of each vane, (c) micro-lines across each vane in a direction substantially perpendicular to the longitudinal axis of each vane.

Description

CROSS-WIND-AXIS WIND-TURBINE ROTOR VANE

Field of the Invention

This invention relates to the field of cross-wind-axis wind turbines which have a cross-wind-axis rotor on which are mounted a radially spaced apart array of vertical vanes around the outer circumference of the rotor for converting wind to energy into rotational mechanical work and in particular to an improved vane which increases drag during the vanes downwind leg of its rotational cycle around the axis of rotation of the rotor and which decreases drag during the upwind lift-producing leg of the rotational cycle of the vane.

Background of the Invention

In the prior art, applicant is aware of United States Patent No. 4,180,367 which issued to Drees on December 25, 1979 for a Self-Starting Wind to Mill Energy Conversion System. Drees discloses a wind turbine apparatus having a plurality of wind response of elements which are pivotally mounted on a rotor which produces rotary motion and which are arranged to provide a drag force in response to the wind when the rotor speed is below a predetermined level so as to produce a starting force to initiate and maintain rotary motion of the rotor. When the speed of the rotor exceeds the predetermined level the positions of the wind responsive elements are such that a lift force is provided to increase the speed of the rotor. Applicant is also aware of United States Patent No. 5, 193,978 which issued March

16, 1993 to Gutierrez for an Articulated Blade with Automatic Pitch and Camber Control. Gutierrez teaches an articulated blade whose forward vane section is directly pitched by relative fluid flow upon it and whose rear deflector section deflects the flow upon it. A control arm is disclosed which through a parallelogram linkage maintains the deflector in parallel orientation with it thus cambering the blade when the blade pitches.

Applicant is also aware of United States Patent No. 5,518,367 which issued on May 21, 1996, to Verastegui for a Cross-Wind-Axis Wind Turbine. Verastegui discloses a cross-wind- axis rotor having multiple orientatable blades around its periphery mounted parallel to the rotor axis where each blade is interconnected with an orientatable stabilizer mounted on the same rotor radial line as the blade, at a smaller radius, so that during rotation the blade and the stabilizer are able to pivot simultaneously and essentially parallel to each other. The opposing pitching moments created by the lift forces over the blade and stabilizer equilibrate each other.

In the prior art application is also aware of United States Patent No. 6,960,062 which issued November 1 , 2005, to Blank et. al. for a Frost-Resistant Windmill for use in Urban Environment. Blank et. al. disclose carrying a plurality of blades on a windmill frame so as to define a serpentine internal air pathway for the introduction of warm air from an external source to prevent freezing when used during winter months.

Applicant is also aware of United States Patent Application by Grabau, Publication No. US 2009/0285691, published November 19, 2009, for a Blade for a Wind Turbine Rotor. Grabau discloses a blade for use on a wind turbine rotor having a substantially horizontal rotor shaft. On the blade a surface zone with a plurality of indentations and/or projections is provided in at least the root area. The indentations and/or projections are formed and dimensioned to improve the wind flow across the surface of the blade. In the Grabau patent application, Figures 3 a and 3b of Grabau show the air flow over a smooth sphere and over a sphere having indentations on the surface respectively.

As stated by Grabau: FIG. 3a [in the Grabau patent application] shows a laminar airflow past a sphere, FIG. 3b [in the Grabau patent application] shows a turbulent airflow past a sphere with dimples. With laminar airflow, the separation behind the sphere is comparatively large. Therefore, there is a great pressure drop behind the sphere, and thus the differential pressure between the front and the rear of the sphere is correspondingly large. The differential pressure causes a force to act on the rear of the sphere. With turbulent air flow, the separation behind the sphere is considerably smaller, and thus the differential pressure between the front and the rear of the sphere is considerably smaller, and therefore the force acting towards the rear of the sphere is also smaller. The reason why e.g. golf balls have a surface with indentations or so-called dimples is based on the desire to alter the critical Reynolds number of the ball, which is the Reynolds number, where the flow changes from laminar to turbulent flow. For a smooth surface as shown in FIG. 3B, the critical Reynolds number is much higher than the average Reynolds number which a golf ball achieves when moving through the air. For a golf ball having a sandblasted surface the decrease in wind resistance at the critical Reynolds number is larger than for a golf ball with dimples. But the wind resistance increases with increasing Reynolds number. However, a golf ball with dimples has a low critical Reynolds number and the resistance is substantially constant for Reynolds numbers higher than the critical Reynolds number. In other words, the indentations ensure a decrease of the critical Reynolds number, which results in the flow becoming turbulent at lower wind velocities than with a smooth sphere. This makes the air flow "stick" to the surface of the golf ball for a longer period, which results in a decrease in wind resistance. The idea behind the surface is to use this known effect to reduce the wind resistance particularly in those parts of the wind turbine blade, where the blade does not possess an ideal airfoil profile, according to the principles known from golf balls.

Grabau further states that the root area of his blade and the transition area may be provided with a plurality of indentations and/or projections, stating that the indentations or dimples may be both concave or convex, i.e., projections. Grabau states that the airfoil area of the blade is not provided with indentations but rather that the root area is provided with indentations along its entire longitudal direction and the indentations are preferably arranged all the way around the circular root area. The transition area adjacent the root area also has indentations along its longitudal direction. Grabau further states that it is most important that the area of the transition area situated closest to the root area is provided with indentations since this point of the cross sectional profile shows the greatest deviation from the ideal air foil profile. Grabau also shows in his Figure 5 that, instead of dimples being provided all the way around the root area, that it maybe sufficient to provide oppositely disposed first and second zone segments having dimples. Similarly, as shown by Grabau in his Figure 6, the transition area may also have two different zone segments having indentations on oppositely disposed sides of the transition area when viewed in cross section. Again, Grabau states that, as in the root area, the indentations are preferably arranged all the way around the transition area or at least from the area where the thickness of the profile is greatest to the trailing edge of the blade. Grabau states that although the indentations may be circular concave indentations corresponding to dimples on a golf ball, they may also be triangular, rectangular, hexagonal or any other polygonal shape as, for example, a hexagonal shape to reduce the wind resistance further compared to circular indentations. Summary of the Invention

In one aspect, the present invention maybe characterized as including a plurality of unique blades or vanes (collectively herein referred to as vanes) for mounting on a rotor for a cross-wind-axis wind turbine having a cross-wind axis of rotation, wherein the rotor includes a hub mounted for rotation about the axis of rotation, a plurality of radially extending arms mounted to the hub and extending radially outwardly relative to the axis of rotation in a radially spaced apart array about the axis of rotation. The plurality of elongate cross-wind vanes are mounted to the arms so that the vanes rotate the rotor about the axis of rotation under the influence of a cross- wind crossing relative to the axis of rotation, and wherein each vane rotates about the axis of rotation sequentially and cyclically through an upwind leg wherein said each vane rotates into the direction of the cross-wind, and a downwind leg wherein each vane rotates downstream in the direction of the cross-wind. In one embodiment each vane is airfoil-shaped in cross section orthogonal to the axis of rotation. Each vane has a radially outermost surface, which is radially outermost relative to the axis of rotation, and an opposite radially innermost surface. The radially outermost surface looks outward from the rotor. The radially innermost surface looks inward into the rotor. The radially outermost surface includes aerodynamic surface features chosen from the group comprising: (a) dimples, so as to increase surface area drag of each vane during the downwind leg and so as to decrease drag of each vane during the upwind leg, (b) scales so as capture a backwind over the vane to increase surface area drag during the downwind leg of each vane, (c) micro-lines across each vane in a direction substantially perpendicular to the longitudinal axis of each vane.

Advantageously, with the exception of the micro-lines which may be on both the radially innermost and outermost surfaces, the aerodynamic surface features including the dimples and scales are substantially only on the radially outermost surface. The aerodynamic surface features may be only dimples, or may be only scales, or may only be micro-lines or some combination of these. The scales may be hinged at one end thereof to the radially outermost surface of the vane. The dimples and scales aerodynamic surface features may substantially completely cover the radially outermost surface. The micro-lines features may substantially completely cover both the radially innermost and outermost surfaces. Brief Description of the Drawings

Figure 1 , is in perspective view, one embodiment of a cross-wind-axis wind turbine rotor incorporating a plurality of radially spaced apart vanes aligned parallel to the rotor hub. Figure 2a and 2b are, in perspective view, a rotor vane incorporating arrays of dimples across, respectively, substantially the vane's entire lift-generating and non-lift generating surfaces, and wherein the trailing edge of the vane is serrated. Figure 3a is, in partially cut-away perspective view, the radially outermost surface of a vane showing the plurality of dimples and a scalloped trailing edge.

Figure 3b is, in perspective view, the radially innermost surface of the vane of Figure 3 a.

Figure 4a is, in perspective view, the radially outermost surface of a vane having a plurality of scales mounted thereto.

Figure 4b is, in partially cut away enlarged view, one end of the vane of Figure 4a.

Figure 5a is, in perspective view, the radially outermost surface of a vane having a plurality of flaps mounted thereon.

Figure 5b is, in plan view, the radially outermost surface of the vane of Figure 5a.

Figure 5c is, in end elevation view, the end of the vane of Figure 5a.

Figure 6a is a perspective view illustrating a vane having micro-line striations formed across the radially innermost and radially outermost surfaces of the vane in a direction perpendicular to the longitudinal axis of the vane.

Figure 6b is a sectional view along line 6b-6b in Figure 6a.

Figure 7a is an alternative embodiment of a wind turbine including helically spiraling vanes in the form of spiraled airfoil strips having dimples on the outer surfaces of the strips, and where the strips are spaced radially outwardly of the rotor hub.

Figure 7b is a further alternative embodiment of a wind turbine according to a further aspect of the present invention incorporating linear vanes having dimples on their outer surfaces. Figure 7c is a further alternative embodiment of a wind turbine according to yet a further aspect of the present invention incorporating bowed vanes having dimples on their outer surfaces. Figure 7d is a further alternative embodiment of a wind turbine according to a further aspect of the present invention incorporating a helically spiraling vane having dimples on its upper surface, where the vane which extends contiguously radially outwardly of the rotor hub.

Detailed Description of Embodiments of the Invention

As set out in the United States Patent No. 5,518,367 which issued to Verastegui on May 21, 1996, which is incorporated herein by reference in its entirety, cross-wind-axis wind turbines are known in the prior art and have varying degrees of efficiency. The present specification is directed to improvements in the wind turbine art to thereby increase the efficiency of cross-wind-axis wind turbines by the introduction of an asymmetric aerodynamic mechanism on each vane for either increasing the drag in the downstream leg of the rotation cycle of each such vane of the wind turbine rotor or decreasing the drag of each such vane in the upstream leg of the rotation cycle, or both as better described below. As described in the prior art, in a cross-wind-axis wind turbine, energy may be extracted from a flow of air through the turbine no matter which direction the wind is coming from. Cross- wind- axis wind turbines have a low inertial start up. No matter which direction the wind is coming from, and during a shifting wind, at all times a downstream-most vane, presuming a plurality of radially spaced apart vertically aligned vanes which are aligned generally parallel to the vertical axis of rotation, will rotate on the turbine rotor through positions where the air flow, that is the relative wind, may be smooth to generate lift, or may be stalled, or may be back-winded etc. For example, the vane enters into an upstream leg of its rotation from a blade-stalled position wherein flow over the leading edge of the vane separates over the radially outermost surface of the vane. The vane then passes through a lift-generating phase wherein the air flow over the radially innermost surface of the vane generates lift proportionally to the relative wind i.e. proportionally to the sum of the wind speed approaching the turbine and the rotational speed of the vane itself. The vane then passes into a further stalled position as the vane approaches and passes through the upstream-most position in the rotation cycle. In the upstream-most position, the vane is stalled by flow separation across the radially innermost surface of the vane, and lift drops due to the reduction in velocity of the incoming relative wind component felt by the vane. During the downstream leg of the cycle, the relative wind felt by the vane drops below the rotation speed of the vane due to the backwind felt by the vane. The backwind is the incoming wind flow through the wind turbine which impacts from the rear (the trailing edge) of the vane as the vane rotates in a downstream direction. The vane feels a backwind flowing over it in the downstream direction due to the incoming wind velocity exceeding the rotational speed of the vane as the vane translates in the downstream direction along the downstream leg. Applicant believes that minimal if any aerodynamic lift is generated due to the backwind over the vane. Applicant has determined that increasing the drag acting on the vane due to the backwind flow over the vane during the downstream leg of the rotation cycle increases the efficiency of the turbine. The effect maybe achieved by increasing the effective surface area of the vane impacted by the backwind. This may be done for example in the manner of a sail boat extending its sails to catch the wind as the boat sails directly downwind, so that the wind merely pushes against the sails thereby driving the boat in the downwind direction. Similarly, applicant has determined that the use of a plurality of hinged scales or flaps or scoops or the like (herein collectively referred to as scales or fish scales) which are hinged or pivotally mounted or flexibly mounted (herein collectively referred to as being hinged) to the radially outermost surface of the vane at the edge or ends of the scales closest to the leading edge of the vane allow the scales to lie flush against the radially outermost surface of the vane while the vane is rotating through its upstream leg of the rotation cycle, and allow the scales to hinge outwardly from the vane as the scales are caught by the backwind during the downstream leg of the rotation cycle. Once the scales pivot outwardly during the downstream leg, they each act as small "sails" so that the backwind felt by the vane pushes on the deployed scales. The plurality of scales provide much increased surface area to catch the backwind thereby imparting the energy from the backwind into the vane and assisting in energy conversion from the backwind into rotational energy of the rotor which of course may then be converted to useful work. Another means of increasing the drag of a vane during the downwind leg of its rotation cycle is to otherwise increase the effective surface area of the radially outermost surface without the use of hinged or flexible scales or by the use of surface protuberances. In one embodiment the radially outermost surface of the vane may be the lift generating surface of an airfoil, that is, which corresponds to the top surface of a conventional aircraft wing, although this is not intended to be limiting as the radially outermost surface may in some cases be the "bottom" of the airfoil, (i.e. the surface which in a wing does not normally generate lift). One means for increasing the effective surface area of the vane is the use of dimples or otherwise shaped depressions or concavities (collectively referred to herein as dimples) on only the radially outermost surface of the vane. The dimples may be of various sizes and depths. Keeping in mind that the relative wind felt by a vane during the downstream leg of the vane' s rotation cycle is a relatively low velocity backwind, and thus for a significant part of the downstream leg creates what applicant postulates to be a laminar flow over the radially outermost surface and its dimples, applicant believes that this laminar flow remains attached to the surface via its corresponding laminar boundary layer which interacts with the dimples to increase surface drag caused by the backwind flow over the radially innermost surface of the vane. Interestingly, applicant has determined that the use of additional dimples on the radially outermost surface of the vane according to experimental test data measured by applicant appears to indicate that some efficiency is lost when measuring the overall rotation cycle efficiency of the turbine. As mentioned above, one way of increasing the turbine efficiency is to decrease the drag of the vane during its upstream leg of its rotation cycle. The use of the dimples on the radially outermost surface of the vane which as describes above assists the turbine efficiency by increasing the surface drag during the downstream leg of the rotation cycle, also beneficially decreases the drag during the upstream leg of the rotation cycle. Applicant postulates that due to the relatively higher relative wind flowing over the radially outermost surface of the vane during its upstream leg, the dimples act in the manner of the dimples found on a golf ball such as described in the Verastegui reference above, which are intended to decrease the drag. Thus, although applicant does not wish to be bound by any particular theory of operation, applicants experiments have born out that the use of dimples on only the radially outer surface of the vane increase the efficiency of the turbine by, as applicant postulates, decreasing the drag of a particular vane during its upstream leg, and by increasing the drag of the vane during its downstream leg as it rotates about the axis of rotation of the turbine rotor. Another surface feature found to increase the efficiency of the turbine rotor is the use of micro- depth striated lines (hereinafter also referred to as micro-lines) over the surface of at least the radially outermost surface of the vane, or over both the radially inner and outer surfaces of the vane, where the micro-lines have for example a resolution of about 35 thousands of an inch, although this is not meant to be limiting, and are aligned substantially perpendicular to the longitudinal axis L. As seen in Figure 1 , longitudinal axis L for linear vanes is the long axis of the vane and is the axis which is substantially parallel to axis of rotation A of the rotor. In embodiments where the vanes are curved, spiraled, bowed, etc (i.e. which are non-linear), the micro-lines may extend perpendicular to the vanes corresponding curved, spiraled or bowed long axis running along the length of the vane.

By testing of various vane air foil shapes and surface textures, applicant has determined that further efficiency may be gained by the use of the micro lines in closely spaced parallel array perpendicular to the long axis L of the vane, and/or by varying the shape of the trailing edge of the vane from a linear trailing edge, to for example, a scalloped - shaped or serrated trailing edge.

Thus as seen in the figures wherein like reference numerals denote corresponding parts in each view, cross-wind-axis wind turbine rotor 10 includes a hub 12 mounted for rotation about axis of rotation A, wherein hub 12 and axis A are aligned generally perpendicularly to a cross-axis wind such as for example arriving in direction B so as to impinge upon elongate cross-wind vanes 14 mounted to hub 12 by radially extending arms 16. Vanes 14 may be mounted to arms 16 by various conventional mounting means such as shown illustrated, for example by means of welding, bolting or being clamped within supporting brackets. It is understood that although hub 12 is illustrated as being mounted vertically, hub 12 may be mounted at other orientations so long as an incoming wind will generally be directed perpendicularly across axis A, and that wind direction B may be from any compass orientation about axis A. In a preferred embodiment, each of vanes 14 is an airfoil shape when viewed in cross section orthogonally to both axis A and to longitudinal axis L, for example the cross section shown at end 14a in Figure 2. Vane 14 has a leading edge 14b and an opposite trailing edge 14c. Extending between leading edge 14b and 14c is a radially outermost surface 14d and an opposite radially innermost surface 14e. Radially outermost surface 14d and radially innermost surface 14e are outermost and innermost relative to a radius "r" extending perpendicularly radially outwardly from axis A. Radially outermost surface 14d may be the lift generating surface of an airfoil as illustrated (i.e. the top of the airfoil in the sense of an aircraft wing), or may be the opposite non-lift- generating surface (i.e. the bottom of the wing of an aircraft). As stated above, vanes 14 may be mounted to arms 16 by conventional means such as for example by means of welding, clamping, adhesive or mechanical fasteners in embodiments where the vanes are rigidly affixed to the arms or other supporting structures extending from hub 12. In other embodiments such as seen in Figures 7a, 7c and 7d, vanes 14 may be spiral ed, bowed or otherwise curvilinear, or helically spiraled instead of merely being linear relative to axis A as seen in Figure 7b. Vanes 14 may also be pivotally mounted (not shown) for very limited pivoting movement relative to arms 16 or other supporting structures supporting the vanes on the hub. Applicant postulates that efficiencies may be gained by utilizing the vane surface structures described herein, for example, by employing an outermost surface 14d which is substantially completely covered, or at least substantially covered in a spaced apart array of dimples 18, where advantageously dimples 18 are only found on outermost surface 14d and not substantially on innermost surface 14e.

Another surface feature found to increase the efficiency of the turbine rotor is the use of parallel closely spaced micro-lines or striations 26, as seen in Figures 6a and 6b, over the surface of both vane surfaces 14d, 14e, or over at least the radially outer surface 14d of the vane 14. The micro- lines 26 may have a very minimal depth and may be formed with a resolution or a spacing of for example 35 thousands of an inch. Micro-lines 26 are aligned substantially perpendicular to the longitudinal axis L of vane 14, or substantially perpendicular to the long axis of the vane running the length of the vane in embodiments where the vane is curved, bowed, spiraled, etc.

In a further embodiment, trailing edge 14c may be non-linear, for example, may be serrated as illustrated in figure 2 or may be scalloped as seen in Figures 3a and 3b. In the further embodiment of Figures 4a and 4b, instead of the use of dimples 18 on radially outermost surface 14d, scales 22 are mounted on outermost surface 14d. Scales 22 are either hinged or otherwise pivotally mounted or may, if scales 22 are flexible, be rigidly mounted at the leading edges 22a of scales 22. As depicted, scales 22 maybe mounted in overlapping rows in a manner offish scales. In the view of Figure 4b, vane 14 is on its upwind leg so as to advance into the on-coming wind arriving in direction B. Scales 22 are thus laying flush on top of one another, flush against outermost surface 14d. When on its downwind leg, a backwind such as in direction D overtaking vane 14 as vane 14 is rotating downwind, the backwind gets under scales 22 so that scales 22 deploy outwardly from outermost surface 14d, for example, so that each scale 22 deploys outwardly in direction E about its leading edge 22a.

In the alternative embodiment of Figures 5a-5c, scales 22 are replaced with flaps 24. As stated above, as used herein, reference to scales is intended to collectively refer to flaps, scales, scoops or the like which hinge or pivot or flex between a deployed position and retracted position flush on the outer surface. Flaps 24 are hinged or pivotally mounted about their leading edges 24a for rotation outwardly of outermost surface 14d in direction F so as to capture a backwind during the downwind leg of rotation of vane 14 about axis A.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A rotor for a cross-wind axis wind turbine having a cross-wind axis of rotation, the rotor comprising:

A hub mounted for rotation about said axis of rotation, a plurality of radially extending arms mounted to the hub end extending radially outwardly relative to said axis of rotation in a radially spaced apart array about said axis of rotation, a plurality of elongate cross-wind vanes mounted to said arms so that said vanes rotate said rotor under the influence of a cross-wind relative to said axis of rotation and wherein each vane in said plurality of elongate cross-wind vanes rotates about said axis of rotation sequentially and cyclically through an upwind leg wherein said each vane rotates into the direction of said cross-wind, and a downwind leg wherein said each vane rotates downwind in said direction of said cross-wind, and wherein said each vane is airfoil-shaped in cross section orthogonal to said axis of rotation and has a radially outermost surface, which is radially outermost relative to said axis of rotation, and an opposite radially innermost surface for generating lift during said upwind leg, and wherein said radially outermost surface includes aerodynamic surface features chosen from the group comprising:

(a) dimples, so as to increase surface area drag of said each vane during said downwind leg and so as to decrease drag of said each vane during said upwind leg,

(b) scales so as to increase surface area drag during said downwind leg of said each vane.

(c) micro-line striations aligned substantially perpendicularly to said axis of rotation.

2. The rotor of claim 1 wherein said aerodynamic surface features are substantially only on said radially outermost surface.

3. The rotor of claim 2 wherein said aerodynamic surface features are only said dimples.

4. The rotor of claim 2 wherein said aerodynamic surface features are only said scales.

5. The rotor of claim 1 wherein said scales are hinged at one end thereof to said radially outermost surface.

6. The rotor of claim 1 wherein said aerodynamic surface features substantially completely cover only said radially outermost surface.

7. The rotor of claim 6 wherein said vanes are helically spiral ed about said axis of rotation.

8. The rotor of claim 6 wherein said vanes are bowed outwardly relative to said axis of rotation.

9. The rotor of claim 6 wherein said vanes are substantially linear.

10. The rotor of claim 6 wherein said each vane has a leading edge and an opposite trailing edge, and wherein said trailing edge is curvilinear.

11. The rotor of claim 10 wherein said trailing edge is scalloped.

12. The rotor of claim 6 wherein said each vane has a leading edge and an opposite trailing edge, and wherein said trailing edge is serrated.

13. The rotor of claim 1 wherein said micro-lines have a resolution of substantially 35 thousands of an inch.

14. The rotor of claim 1 wherein said micro lines cover both said radially innermost and radially outermost surfaces.

15. The rotor of claim 1 wherein said radially outermost surface is shaped as an airfoil lift- generating surface to generate lift during said upwind leg.