WO2016057120A1

WO2016057120A1 - Spacer for wind turbine rotor blade

Info

Publication number: WO2016057120A1
Application number: PCT/US2015/045600
Authority: WO
Inventors: Richard Von Berg; Douglas N. DELINE
Original assignee: Richard Von Berg; Deline Douglas N
Priority date: 2014-10-11
Filing date: 2015-08-18
Publication date: 2016-04-14
Also published as: WO2016057110A1; WO2016057107A1

Abstract

A wind turbine includes a rotor having a hub and at least one blade adapted for attachment to said hub by means of a spacer, said spacer being adapted for attachment by means of it's distal terminus to the base of a wind turbine blade such that the alignment axis of the blade is disposed at an aft acute angle relative to the alignment axis of the spacer or tapering in cross-sectional size at least over a portion of the distance from proximal terminus to distal terminus.

Description

Spacer For Wind Turbine Rotor Blade

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority from United States Provisional application 62/122,091, filed October 11, 2014.

DESCRIPTION

BACKGROUND OF THE INVENTION

[0001] This invention relates to spacers for use with blades of wind turbine rotors, especially wind turbines of the front-runner or forward facing type, and to blades incorporating such spacers, the resulting rotors and to wind turbines utilizing such spacers, blades and/ or rotors. Desirably, the spacer is tapered or formed from an aluminum alloy, and may include pitch control means in it's distal terminus for adjusting the pitch or angle of attack of the working portion of the blade. Previously, the use of aluminum alloys in wind turbine blades has been thought to be impractical due to concerns about stress fracturing.

[0002] It is previously known in the art to provide a spacer that may be interposed between a wind turbine hub and a conventional blade to extend the diameter of the rotor thereby providing increased power production. In FR 2863318 the spacer or extender provides an acute angle terminus for mounting the blade so that the axis of the blade does not intersect the rotational axis of the wind turbine. The angle is inclined in the plane of rotation of the rotor. In WO 2003060319, the spacer is fixed to the rotor hub by means of a first flange and comprises a second flange for fixing the rotor blade thereto at an acute angle that opens away from the tower to provide increased clearance between the blade and tower under wind loads. Cylindrical extenders for wind turbine blades including telescopic versions and those including pitch angle control mechanism are disclosed in WO2013/121054, DE- 4428731, WO2013/097847, US2009/208337, and US2012/141,267.

[0003] While prior art designs have achieved improved performance due to increase in rotor swept area and corresponding increased torque under wind conditions due to movement of the center of pressure radially outward from the center of rotation of the wind turbine, even further improvement in wind turbine design is desired by the industry. In particular, it would be desirable to provide a blade spacer for use in wind turbines that achieves improved performance and/or reduced cost.

BRIEF DESCRIPTION OF THE INVENTION

[0004] Accordingly, in one aspect the present invention provides a blade spacer adapted for use on a wind turbine, said spacer being substantially torsionally rigid and adapted for attachment by it's proximal terminus to a wind turbine hub and further adapted for attachment to the base of a wind turbine blade by means of it's distal terminus. Desirably the alignment axis of the blade is disposed at an aft acute angle relative to the alignment axis of the spacer or the spacer tapers in cross-sectional size at least over a portion of the distance from proximal terminus to distai terminus. Further desirably, the spacer contains a pitch control mechanism located in the distal terminus for adjusting the angle of attack of the blade. As used herein the term "spacer" refers to the innermost section of a blade combination that is incapable of generating substantial amounts of lift or torque under operating conditions. Preferred spacers for use in combination with wind turbine blades herein do not possess a surface in the shape of an airfoil, excepting for purposes of drag reduction. Highly desirably they are incapable of generating more than 2 percent of total torque for the blade and spacer combination, more preferably, no more than 1 percent of total torque of the blade and spacer combination. By the term "substantially rigid" is meant that no deformation or delamination results from torque forces and bending moments encountered during operation according to design specifications and deflection, if any, is inconsequential under the same conditions.

[0005] In addition, the present invention provides a rotor for a wind turbine having a hub and at least one blade spacer according to the present design.

[0006] Finally, the present invention provides a wind turbine that includes a rotor having a hub and at least one blade spacer according to the present design.

[0007] By the use of the presently invented blade spacers, forces experienced by the pitch control mechanism are substantially reduced because only the blade and not the additional mass of the spacer needs to be rotated, in addition, spacers according to the present invention may be designed purely for strength and not airfoil shaped. This allows for the use of cheaper materials of construction, such as cast or rolled steel or aluminum alloys, and the manufacture of larger effective blade lengths (counting spacer and blade) which may be separately transported within current safety parameters, with little compromise of performance while obtaining improved operational longevity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is an illustrative drawing of an airfoil shape.

[0009] FIG. 2 is a drawing of an exemplary configuration of wind turbine employing a spacer of the present invention.

[0010] FIGs. 3a , 3b and 3c are side view drawings of exemplary spacers of the present invention suitable for use in the wind turbine configuration represented in FIG. 2.

[0011] FIG. 4 is a partial front view of a rotor comprising one embodiment of blade configuration according to the present invention.

[0012] FIG. 5 is a frontal view of an embodiment of spacer and blade combination of the present invention having non-radial alignment of the blade.

[0013] FIG. 6 is a drawing of a preferred blade airfoil shape for use in a rotor according to the present invention.

[0014] FIG. 7 is a cross section drawing of one embodiment of blade for use in a rotor according to the present invention. [0015] FIG. 8 is a partial front view of a rotor comprising one embodiment of blade configuration according to the present invention.

[0016] FIG. 9 is a top partial sectional view of a blade for use according to the invention comprising multiple segments.

[0017] FIG. 10 is a frontal view of a blade end for use in a further configuration of the present invention having improved aerodynamic properties.

[0018] FIG. 11 is an oblique side view of a blade end fitted with a fin in a further alternate embodiment of the present invention having improved aerodynamic properties.

[0019] FIG. 12 is a frontal view of the blade end of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

[0020] As used herein the term "airfoil" refers to a closed curve, such as closed curve 100 depicted in FIG. 1, which represents the cross-sectional shape of an elongated surface (blade) designed to produce lift when in contact with moving air. Each airfoil shape likewise is elongated and the line connecting both extremities along the major dimension is referred to as the "chord". The median points between two respective points of the airfoil closed curve (measured perpendicularly to the chord line) taken together form a curved segment called the "median line" with terminal points that are the same as the terminal points of the chord. The working portion of a wind turbine blade comprises a series of such airfoil shaped cross-sections extending from the base to the tip or outer end of the blade, the set of midpoints of the median lines thereof defining it's structural axis which is a line for a fiat blade or a curve for a twisted or bent blade. As used herein the term "alignment axis" of the blade refers to a line defined by the innermost and outermost median line mid-points of the blade measured at full deflection under maximum operating conditions, the length of the blade being the distance between the innermost and outermost median line mid-points. The outer surface of the working blade is defined by the collection of curves from adjacent airfoil shaped cross-sections, the set of respective median lines of each airfoil shaped cross-section dividing said outer surface into two minor surfaces, a "high pressure" surface and a "low pressure" surface. Because airfoil shapes are often depicted with the chord arranged horizontally and the direction of wind proceeding relatively from left to right, the high pressure surface is often referred to as the "lower surface" and the low pressure surface is referred to as the "upper surface" regardless of the actual orientation of the working blade surfaces when in use.

[0021] When air moves over the surface of an airfoil-shaped body aerodynamic forces are produced. The component of this force perpendicular to the wind direction is called "lift". The component parallel to the direction of wind motion is called "drag". The component of lift experienced by the wind turbine blade in a direction that is perpendicular to the rotational axis of the turbine is referred to as "thrust", and causes rotation of the wind turbine rotor which may be converted into useful work, especially generation of electrical energy. As wind moves past the blades with enough speed to generate sufficient lift to overcome inertial and drag forces, the rotor system rotates and the wind turbine converts the wind energy into electrical or mechanical energy for performing useful work. The skilled artisan will appreciate that closed curve 100 is merely one illustrative embodiment of a suitable airfoil shape for use in the present invention and not intended as a limitation thereon.

[0022] Referring to FIG. 2, a forward-running wind turbine 101 in some configurations comprises a nacelle 102 housing a generator and associated gearbox or alternative power transfer mechanism (not shown in FIG. 2). Nacelle 102 is mounted atop a tail tower 104, only a portion of which is shown in F!G. 2. Wind turbine 101 also comprises a rotor 106 that includes one or more combination blades 108 (shown in partial view) and attached to a rotating hub 110 having rotational axis S. Most often, axis S is tilted up from horizontal from about 3 to 10 degrees, to lessen the effect of any bow wave emanating from the tower and to obtain more evenly balanced wind currents from top to bottom of the rotor's swept area since wind speeds close to ground level are often attenuated due to ground effect. The direction of rotation of rotating hub 110 is indicated by arc D which is usually clockwise viewed from the front. Although wind turbine 101 illustrated in FIG. 2 includes three combination blades 108, there are no specific limits on the number of rotor blades required by the present invention. The innermost portion of each combination blade, identified as 114, comprises the spacer of the present invention. The outermost segment of combination blade 108 is identified as blade 116 and comprises a suitable airfoil shape designed to produce thrust that causes rotation of rotor 106. ideally, blade 116 is a conventional wind turbine blade which is used or reused in combination with the present spacer to retrofit existing wind turbines in conformance with the present invention.

[0023] Nacelle 102, containing the rotor system, typically pivots about the vertical tower 104 to take advantage of wind from any direction. The pivoting about this vertical-axis is known as yaw or yaw response and the vertical-axis is commonly referred to as the yaw-axis.

Effective yaw control of upwind horizontal axis wind turbines is highly desirable in order to position the rotor system properly relative to the mean wind direction. When a rotor system is not properly positioned with reference to the mean wind direction, the efficiency of the rotor system is significantly reduced. When an angle of separation develops between the mean wind direction and the axis of rotor rotation, the power output of the rotor system, and therefore of the turbine, decreases.

[0024] Various undepicted components of wind turbine 101 are housed in nacelle 102 and hub 110 atop tower 104. Examples include a generator, drive train, bearings, braking system, yaw control mechanism, wind speed sensors, and so forth. In some configurations, one or more sensors and controllers comprise a control system used for overall system monitoring and control including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring, electrical wave form modification and energy storage. Alternatively, distributed or centralized control architectures are used in some configurations. Hub 110 and combination blades 108 together comprise wind turbine rotor 106. Rotation of rotor 106 causes a generator to produce electrical power, generally through a power transfer mechanism such as a gear box. Desirably, main bearings are provided both in front of and behind hub 110 to support the entire rotor weight while in operation. Support for the forward bearing may be provided by a fixed quill (not depicted) supported from the main structural base of nacelle 102 and projecting through the center of hub 110 as is known in the art. A pitch controller, desirably located within the distal terminus of spacer 114, is employed to change the angle of attack, or pitch, of each individual blade 116.

[0025] Referring to FIG. 3a, in its simplest embodiment, the present invention comprises a spacer 114a having proximal terminus 201a adapted for attachment to the rotor hub and a distal terminus 202a adapted for attachment to the base of blade 116 (not shown) thereby forming combination blade 108. A is the alignment axis of the spacer defined as a longitudinal line connecting the geometrical centers, CI and C2, of the proximal and distal terminal surfaces. The length of spacer 114 is the distance between respective geometrical centers of the outer faces of proximal terminus 201a and distal terminus 202a. Although flanges are depicted in F!G. 3a for attachment to the rotor hub and blade 116 using, for example, bolts or other attachment means, it is to be understood that any suitable method of attaching both termini, such as interlocking clasps; a socket and corresponding fitment; stud bolts bonded, molded, or otherwise inserted into either the hub, spacer or blade base; or other suitable mechanism may be employed for joining the respective portions of the rotor. In US-B-7,517,194 and US-B-8,231,351, suitable attachment methods for joining blade segments or joining blade segments to rotor hubs, which may be used herein to join spacers and blades, are disclosed. Spacer 114 may be attached to the hub by means of proximal terminus 201a such that the alignment axis of the spacer is oriented either orthagonaily to the axis or rotation of the rotor or preferably at a slight forward angle (forward cone angle), preferably from zero to 5 degrees, as is known in the art. Aft cone angle may be imparted to the combination of spacer 114a and blade 116 by the fact that the mounting surface of the base of blade 116 is not perpendicular to the alignment axis of the blade, or by the use of an angled adapter or union to join the spacer and blade, thereby imparting a slight aft cone angle between the alignment axis of the blade and alignment axis A. However, while some or all of said reverse alignment angle may be due to orientation of the mounting fittings of blade 116, in a preferred embodiment, at least some, and more preferably, most, if not all, of the reverse angle alignment is the result of orientation of the attachment face on the spacer end at a non-orthogonal angle to alignment axis A. Highly preferably, the aft cone angle at the distal terminus of the spacer is due, at least in part, to off-axis alignment between the structural axis of the innermost one percent length of blade 116 and alignment axis A.

[0026] FIG. 3b discloses an alternative embodiment of spacer 114b which tapers in cross- sectional size from proximal terminus 201b to distal terminus 202b. Tapering reduces the total mass of the spacer and is highly desirable for this reason. As one example, a spacer having circular cross-sectional shape may have a diameter at the proximal terminus of about 5 m while the diameter at the distal terminus may be about 4 m. The proximal and distal termini in general are shaped so that their faces conform in size and shape to the corresponding attachment surface, that is, either the corresponding hub or blade face, in general, all joints or surface transitions are chamfered, rounded, filleted, beveled or fairings are placed over any protruding or receding sections of various rotor components to improve aerodynamic performance. [0027] in some configurations of the present invention utilizing a tapered spacer, blade 116 may be aligned on axis or with a slight forward or aft cone angle, within the limitations of providing adequate tower clearance, especially where aft cone angle in a forward running turbine is employed. Cone angles (the measure of departure of the blade from alignment axis of the spacer) are from 0 to 5 degrees, preferably from 1 to 3 degrees aft of the alignment axis. The skilled artisan will appreciate that the total length of combination blade 108, of spacer 114, and blade 116 as well as the height of the tower and the angle by which the wind turbine's rotational axis S is tilted up from horizontal will affect the blade's aft cone angle, in as much as adequate clearance between blade tip and tower must be maintained.

[0028] FIG. 3c discloses a suitable spacer 114c adapted for use in another embodiment of the invention, comprising proximal terminus 201c and distal terminus 202c, the face of which is not perpendicular to alignment axis A. Upon attachment of a conventional blade 116 (not depicted) the alignment axis of the blade is oriented at an aft acute angle relative to alignment axis A. in a highly preferred embodiment, the alignment axis of the blade is disposed at an aft acute angle relative to a plane that is norma! to the axis of rotation of the hub, preferably at an aft angle of 1 to 4 degrees. Desirably the amount of aft cone angle in the working blade is sufficient to provide improved aerodynamic performance, especially increased stability under adverse wind conditions as well as improved productivity. The latter benefit is believed to be due to several factors, including improved wind flow through the central opening in the rotor (thereby maintaining wind speeds over the blade) and less adverse effect from pressure waves (bow wave) associated with the tower. In addition, the skilled artisan will appreciate that the requisite distal terminal surface oriented with aft cone angle for mounting of the wind turbine blade may also result from use of an adapter or coupling employed in combination with an otherwise straight spacer to provide the identical structure as depicted in FIG. 3c.

[0029] Referring to FIG. 4, the respective lengths of spacer 114 and blade 116 (measured along their respective axes) are selected so as to produce a desired increase in torque due to increased blade swept area compared to the swept area obtained without use of a spacer. Desirably, the spacer length g, is a minimum of at least 5 percent of g', the length of blade 116 along alignment axis A', more preferably 10 percent, and most preferably 20 percent. Further desirably, the spacer maximum length is 60 percent of g', more preferably 50 percent, and most preferably 40 percent. Suitable blade lengths for use herein are from 20 m to 200 m, preferably from 30 m to 100 m. One specific application may employ a rotor diameter of about 110 m, and have a total swept area of 10,000 m² or more. The cross sectional size of spacer 114 near distal terminus 202 may be smaller than the cross-sectional size of blade 116 near it's base, causing a discontinuation of the airfoil shape 206 where the leading edge of blade 116 joins spacer 114. That is, when viewed in profile, the leading edge of the blade, or at least the innermost portion thereof, describes a line or curve that, if continued in the direction of the spacer, does not intersect the spacer's forward edge. This desirably acts as a vortex generator, leading to improved aerodynamic response of the combination blade as changing wind conditions or gust induced air-stream separation is more likely to initiate at the base of blade 116 rather than further outward and is less likely to induce vibration and flutter in the blade combination. All outside and inside corners where blade 116 joins spacer 114 may be chamfered, rounded, beveled, filleted, or fitted with a fairing or fairings without losing the foregoing advantageous property of the invention. Desirably, spacer 114 is tapered and hollow. The skilled artisan will appreciate that the portion of blade 116 identified as 206 may also be a separable adapter, union or connector which in combination with spacer 114 and blade 116 imparts aft cone angle to the spacer and blade combination. That is, the invention also comprises a combination comprising a spacer, an adapter, and a blade, said spacer being substantially rigid and adapted for attachment by it's proximal terminus to the hub of the wind turbine and further adapted for attachment by means of it's distal terminus to the base of a wind turbine blade by means of said adapter such that the alignment axis of the blade is disposed at an aft acute angle relative to the alignment axis of the spacer. In this embodiment, the adapter is substantially rigid or highly rigid, formed from a similar material of construction as the spacer or blade, especially metal such as steel or aluminum alloy, and fitted with flanges, studs, clasps or other attachment means for joining together the spacer and blade into a unitary structure. In this embodiment, adapter 206 need not be smaller in cross-sectional size than the cross-sectional size of blade 116 near it's base.

[0030] In preferred embodiments of the present invention, spacers 114 are highly rigid with respect to both torsional and bending forces, desirably having an elastic limit that is at least three times, preferably at least four times, the maximum stress expected under operational conditions (design limit). Suitable materials of construction include glass fiber, carbon fiber, polyaramide fiber, or other high strength fiber or fabric reinforced resins and laminates comprising the same, as well as metals, especially aluminum, titanium or steel alloys that are rolled and/or welded, cast, forged, or otherwise formed. Because the latter materials are more durable than laminates or fiber reinforced resinous materials, their use allows the present spacer, which is releaseably attached to blade 116, to be used with multiple replacement blades. Worn or damaged blades 116 may simply be replaced at reduced cost and inconvenience than is the case with the use of single piece blades. Construction, transportation and field mounting are also simplified due to reduced size and weight of the portion of the blade that needs to be replaced. The use of such metals as the materials of construction also allows the diameter or thickness of the spacer to be substantially reduced, or at least the longitudinally outer most portions thereof tapered, thereby reducing overall weight of the rotor and providing less aerodynamic drag. Although the cross-sectional shape of spacers 114 is unlimited and specifically may include an airfoil shape, for simplicity of construction and ease of assembly, spacer 114 desirably has a cross-sectional shape that is incapable of generation of substantial amounts of wind generated torque or power. That is, the cross-sectional shape of spacer 114 is desirably circular, oval, tear-drop or ellipsoidal shaped. Furthermore, said diameter or major axis, at least at or near the outer terminal portion thereof, is desirably less than the diameter or major cross-sectional axis length of the innermost terminal portion of blade 116, not counting any mounting or fastening apparatus or fairings. Most desirably, spacer 114 has a circular cross-sectional shape and tapers in diameter from proximal terminus to distal terminus.

[0031] It will also be observed that configurations of the present invention wherein the spacer possesses the foregoing shape and size produce a beneficial decrease in parasitic drag in the inner rotor area along with improved aerodynamic performance of the blade due to coupling of the thrust generating outer regions of the blade with an inner "donut" hole of relatively undisturbed air flow over the spacer. This results in movement of the center of pressure radially outward along the blade thereby maximizing torque and power generation. This mitigates at least to some degree the loss of contribution to thrust from the inner most portion of the rotor due to the presence of the spacer. This loss is generally insignificant because the distance from the axis of rotation at which the wind force is applied is rather small. Highly desirably, spacer 114 is tapered, that is, it has a generally gradually decreasing diameter or cross-sectional major and minor axis measurements over a majority of the distance from the inner to the outer ends thereof (not counting any larger sized distal terminus and corresponding adjoining radii). Because the working length of combination blade 108 is longer than blade 116 alone, rotors according to the present invention are capable of increased torque and power generation. Because spacers according to the present invention may be designed purely for strength and not airfoil shaped, cheaper materials of construction, such as steel or aluminum may be employed for their manufacture. Suitable aluminum alloys for use especially include high strength alloys such as 6000 or 7000 series alloys (International Alloy Designation System), and scandium containing alloys. Combination blades are attainable having larger effective blade lengths, the components of which are more durable and easily transported than single piece units, with little compromise of performance or even improved performance.

[0032] As previously mentioned, pitch controllers are desirably located in the distal terminus of the spacer 114. In as much as only the outer or working blade section is to be rotated by the pitch controller and the pitch axis and blade axis are more closely aligned, smaller and lighter pitch control mechanisms may be employed and a wider range of pitch control and faster pitch response times are attainable. With regard to construction and operation of pitch control mechanisms, regardless of location herein, any suitable design may be employed, including electromechanical or hydraulically actuated mechanisms as well as associated blade bearings including roller bearings or hydrostatic plain bearings. Examples of suitable pitch control mechanisms and systems for use herein include those disclosed in US- B's 8,430,632, 8,172,531, 8,096,762, 8,070,446 and 7,750,493.

[0033] Configurations of the present invention can be applied to an existing wind turbine by replacing conventional blades with blade configurations of the present invention.

Furthermore, use of spacers having reduced cross-sectional diameter, at least in the outer regions thereof according to the present invention results in improved aerodynamic performance of the resulting rotor.

[0034] it is to be understood that in addition to any forward or aft alignment with respect to the mounting position of spacer 114 and blade 116, inclination of the spacer and blade with respect to the direction of rotor rotation, that is within a plane that is normal to the axis of rotation of the rotor, is also permitted. Desirably, the distal terminus of the blade spacer is adapted such that the alignment axis of the outboard section is disposed at an acute receding angle with respect to the direction of rotation of the rotor about its rotational axis. Referring to F!G. 5, in this embodiment of the invention, spacer 114 of blade 108 is attached to hub 110 such that the spacer alignment axis A, is aligned with the hub in a leading angle, f, with respect to radial line R, a line intersecting S and located in a plane that is normal to S. Accordingly, axis A is disposed either axially (not depicted) or in a forward inclination with respect to the direction of rotation. The distal terminus of spacer 114 is adapted such that the alignment axis A' of blade 116 is oriented backward with respect to the direction of rotation D of the wind turbine thereby defining an angle f with respect to radial line R. In such design, reduced stress at the blade base and improved stability of the rotor is achieved. In addition, if a pitch control mechanism is present in the distal terminus of spacer 114, it should be oriented such that the pitch control axis diverges with respect to the alignment axis A of the spacer and conforms rather with the alignment axis A' of the blade.

[0035] Desirably, the angles of forward inclination f, as above defined, may range between 0 degrees and 10 degrees, preferably from 0 degrees to 8 degrees, more preferably from 0 to 7 degrees, and highly desirably from 0 to 5 degrees. Desirable ranges for backward orientation f are from 1 to 12 degrees, more desirably from 2 to 10 degrees, and most desirably from 2 to 8 degrees. In a most preferred embodiment, a plane containing radial line R and rotational axis S (not depicted in F!G. 5) intersects alignment axis A' at or near the center of mass of combination blade 108, preferably no more than 5 percent of total blade length from the center of mass of the blade.

[0036] Blade 116 comprises the working airfoil of combination blade 108. in FIG.6 one suitable airfoil shape is depicted for a sample cross-section of blade 116 showing the upper or low pressure surface and bottom or high pressure surface of the airfoil. Desirably, highly asymmetrical airfoil designs are avoided, especially an airfoil design having negative camber in the trailing half of the blade, due to the large amount of drag created during usage and large shift in center of lift under varying wind conditions. Depicted is a modestly asymmetrical airfoil design such as a NACA 4412, or a Grant X series airfoil shape, or Grant X- 8 through Grant X-10, (c.f., Charles Hampson Grant, Model Airplane Design and Theory of Flight, Jay Publishing Corporation, New York, 1942, pg. 27). Characteristics include a chord length X, that is the distance between front and rear chord starting points, half chord point f, half chord length, X_f, point of maximum chord diameter d, and length at maximum chord diameter, X_<j. The shape of the airfoil joining upper and lower surfaces at the front leading edge is a partial circle having radius r_N. Desirably, the ratio of r_N/d is from 1/5 to 1/20, most preferably from 1/6 to 1/10. Highly desirably in order to reduce the incidence of insect strikes and resulting buildup on the leading edge of the blade (which leads to reduced aerodynamic efficiency and increased drag of the blade) r_N is relatively small, ideally from 10 to 50 mm, more preferably from 12 to 30 mm. in one embodiment of the invention blade 116 has a substantially constant chord length and airfoil shape, a substantially straight taper, or a combination of such shapes over at least the inner most 85 percent of blade length, preferably at least the inner most 90 percent of blade length. Further desirably the leading edge of the outer blade section substantially conforms to a straight line and the blade is twisted such that the outer most blade leading edge has a reduced angle of attack with respect to the effective wind direction.

[0037] in addition, desirable airfoil designs include those having a center of lift close to the structural center of the blade, more desirably between X_<j and X_f. By close, is meant that the center of lift under working conditions is desirably within 10 percent of total chord length from the center of the chord. Further desirably, the blade is designed and constructed of materials selected to provide a center of mass that is forward of the structural or geometric center of the blade as well as forward of the midpoint of the chord as well as the midpoint of the median line. One method of insuring that the center of mass of the blade conforms to the foregoing requirement is to include materials of construction having greater density such as steel, brass or iron components in the forward portions of the blade or to use designs containing more massive construction components in the forward portions of the blade. Most generally, the blade includes a box beam or other structural member to carry loads the axis of which is centered along the structural axis of the blade or at least parallel thereto.

[0038] FIG. 7 shows a cross-section of a suitable laminated blade 116 for use according to the invention having internal structural components 130 forming a box beam and outer surface skin 131 forming the lower and upper surfaces of the blade, the laminated structure forming a single mass. Suitable materials of construction include, without limitation, glass fiber, carbon fiber, polyaramide fiber, or other high strength fiber or fabric reinforced thermosetting resins, especially epoxy resins. The method of construction is controlled such that the center of mass of the resulting structure is located at a point forward of the center point of the chord, without addition of metal rods or beams in the front interior portion of the blade. However, in a desirable embodiment of the invention, additional mass may be included in the forward half of blade 116 by the inclusion of a metal rod or shaft 132. Highly desirably, this metal rod is steel or brass and is located in an extreme forward portion of the blade, especially adjacent to the leading edge of blade 116, or within 10 percent of the total chord distance from the leading edge, most preferably within 5 percent of the total chord length from the leading edge of blade 116. Alternatively, multiple rods or shafts may be included in the blade design, and if extending longitudinally end to end within the blade, are desirably joined into a single structure, such as by welding or brazing adjoining ends, to increase blade rigidity. Desirably rod or shaft 132 is long enough or multiple rods are joined together to extend for at least the outer 40 percent, preferably 50 percent, and most preferably 70 percent of the length of blade 116. Due to the concentration of mass in the present blade design in the stated forward position with respect to the structural axis of the blade, greater stability is provided, leading to increased resistance to vibration and oscillating forces and improved longevity of the present blade design.

[0039] Referring to FIG. 8 there is depicted in partial front view an embodiment of a wind turbine rotor according to the invention having combination blades 108, comprising spacer 114 joined to blade 116 by means of flanges 202c and 202c'. Blade 116 is slightly tapered over all or a portion thereof, and terminates with a relatively highly tapered outer end, 220 having length g", starting at a point 223 on the leading edge of the blade. Highly desirably, the relatively highly tapered section 220 is only tapered on the leading edge of the blade. That is, the width or chord length of blade 116 decreases, preferably linearly, from front to back proceeding longitudinally outward over the remaining length g' of the blade with the trailing edge remaining substantially in line with the trailing edge of the remainder of the blade. The length of relatively highly tapered section 220, that is, g", is desirably from 5 to 12 percent of g', the length of blade segment 116, more desirably from 6 to 10 percent. In one desirable configuration, the width of tapered outer end 220 at its outer extremity is from 75 percent to 50 percent of its initial width. [0040] The presence of tapering on the outer extreme end of the blade is desirable due to formation of a discontinuity in the leading edge a point 223 which causes vortices to be shed outward, especially at high angles of attack, resulting in a reduction in blade pulsation, oscillation, or vibration generation and improved aerodynamic performance. Additionally, ice build-up is more readily shed from the blade by the presence of an angled leading edge after point 223.

[0041] Also depicted in FIG. 8 is a protective surface cover or coating 140 applied or bonded to some or all of the leading edge of blade 116, for example sheet metal such as copper, brass, tin, stainless steel, or steel. Desirably, the cover or coating is applied to at least the outermost 10 to 20, more preferably 10 to 50 percent of the blade length. The coating may also comprise a durable, non-metallic hard surface such as ceramic or other impact resistant material. The purpose of the protective surface cover or coating is to protect the blade leading edge from impact with hail or other hard objects as well as to increase the mass located forward of the structural center of the blade. Suitably, the leading edge surface for a distance from 1 to 10 percent of total distance to the trailing edge above and below the blade center line is covered by the protective surface coating. As an aid in the dissipation of electrical charge and prevention of lightning strikes, the leading edge surface covering, if conductive, may also be grounded, through connection to a suitable grounding point (not illustrated). The skilled artisan will appreciate that the spacer of the invention must itself be conductive and grounded or include therein a conductor connected to ground for completion of the grounding circuit with surface cover 140 in this embodiment of the invention. The presence of tapering on the outer extreme end of the blade is desirable in order to cause vortices to be shed outward from the end of the blade, especially at high angles of attack, resulting in a reduction in blade pulsation, oscillation, or vibration generation and improved aerodynamic performance. Additionally, ice build-up is more readily shed by the presence of an angled leading edge after point 223. The point identified as 224 marks an inflection point on the high pressure surface of the blade where an optional sloping end cap begins.

[0042] In FIG. 9 there is depicted a blade comprising multiple sections 116a, 116b and 116c, each comprising a protective coating 140a, 140b and 140c respectively, on the surface of the leading edge of one or more blade segments. The leading edge of each segment describes substantially a straight line however, each succeeding section proceeding outward toward the blade tip progressively narrows due, at least partially, to slight angling of the leading edge. The difference in angle of the leading edge between two representative segments is indicated by q, the amount by which two adjacent blade segments differ in outer blade width. The skilled artisan will appreciate that the amount by which adjacent blade segments differ in width may or may not remain constant and the numbers of such segments per blade is not limited, but is preferably a number from 3 to 10. Each segment length likewise is variable and the portion of the blade in which such segmented construction occurs is desirably at least the outer most length of the blade, most preferably at least the outermost 25 percent, more preferably the outermost 50 percent, and most preferably the outermost 75 percent of blade length. Because each segment's leading edge is substantially linear, sheet metal may be readily shaped to conform to the leading edge, with the entire blade thereby approximating a curved leading edge over the course of its length. Preferred metals for use in this embodiment of the invention include aluminum, steel, galvanized steel, brass or titanium. A desirable benefit of employing such a segmented, leading edge comprising a protective coating or cladding, besides imparting impact and abrasion resistance to the blade's leading edge, is that the multiple discontinuations in leading edge angle between segments provide desirable vortex generation along the blade length, thereby improving blade aerodynamic properties.

[0043] Referring to F!G. 10, in some embodiments of the invention, the distal portion of blade 116, regardless of the presence of tapering along the blade length, terminates in a sloped end piece or cap 222 starting on the high pressure side of the blade at previously identified point 224 on the blade surface and in a plane perpendicular to the alignment axis A' and terminating on the low pressure side of the blade. The angle at which the sloped end piece 222 is inclined with respect to axis A' is indicated by angle t. Desirably, t is an angle from 30 to 60 degrees, more preferably from 40 to 50 degrees, and most desirably 45 degrees. The purpose of slopping the end of blade 116 by means of end cap 222 is to allow gradual recombination of high and low pressure air streams and also to cause the ensuing vortex to be directed outside the radius of the spinning rotor. This greatly reduces flutter, vibration and noise generation by the spinning turbine rotor. Most desirably, the point 224 is located at approximately 85 to 99 percent of the distance of g' starting at the base of blade 116, most desirably from 87 to 98 percent of the distance g'. The skilled artisan will appreciate that blade end 222 need not form a fiat surface as depicted, but may also be a rounded or curved surface, without departing from the scope of the invention.

[0044] Referring to FIGs. 11 (end view) and 12 (frontal view), in additional embodiments of the invention, blade end 222 comprises a fin 225 which, with respect to its point of attachment to blade 116, projects both outward (above) and behind the trailing portion of blade 116 on the low pressure side thereof and terminates in an apex 226 located outward and behind the trailing edge of blade segment 116. Desirably, fin 225 extends above the upper surface of blade 116 for a distance that is from 10 to 50 percent of the blade thickness measured at point 224, and extends behind the trailing edge of blade 116 for a distance that is from 2 to 10 percent of the blade chord length measured at point 224. !n operation, fin 225 causes the vortex formed upon recombination of high and low pressure air masses on opposite sides of blade segment 116 to be directed further outside and behind the blade than is obtainable with only a sloped blade end, to thereby further reduce pulsation, oscillation, or vibration generation by the rotor blade. Highly desirably, fin 225 is also conductive and is grounded by means of a conductor 227 which is connected through the blade and spacer to a suitable grounding source and connected to fin 225 by an electrically conductive connector 229. Due to rotation of the turbine rotor, conductor 227 may ultimately require connection to ground via a commutator or other rotating electrical connection (not depicted) within the turbine hub in order to form a suitable connection to fin 225. An additional advantage of inclusion of electrical conductor 227 in the location depicted, forward of the structural axis of the blade, is to provide additional mass in the forward portion of the blade as previously discussed. Ideally, conductor 227 is securely attached within the interior of blade 116 within 20 percent, preferably within 15 percent of total chord length from the leading edge of the blade. Alternatively, the entire blade segment 116 may be formed of conductive materials such as aluminum or steel and suitably attached to conductive fin 225 and a grounding source to thereby effectively ground fin 225. Suitable materials of construction of conductive fin 225 include metal, especially steel, brass or aluminum, as well as electrical conductive laminated materials such as the previously mentioned metal mesh reinforced laminated materials. The thickness of fin 225 may vary within wide tolerances, but generally is from about 2 to 20 mm in maximum thickness. Although depicted as a flat plate with squared off edges, the skilled artisan will appreciate that fin 225 may be rounded or curved on its edges, sides and surfaces as well as embossed, engraved, grooved, or otherwise shaped if desired.

[0045] The purpose of providing a grounded fin is to enhance dissipation of static electricity from the blade surface through a corona discharge from the tips of the blades, thereby reducing the incidence of damage to the blades of the invention due to lightning strikes. When employed in combination with a metallic covering for impact protection of the leading edge of the blade which also serves as at least a portion of the electrical grounding circuitry, an additional desirable benefit to the present design is achieved, since an internal conductor or wiring is not required to be included within the blade itself or a smaller sized grounding conductor may be employed. It will again be appreciated by the skilled artisan, that the spacer of the invention must itself be conductive and grounded or include therein a conductor connected to ground for completion of the grounding circuit with fin 225 in this embodiment of the invention. Preferably, the spacer is electrically conductive and serves partially or wholly as a lightening strike ground conductor or a static discharge ground conductor.

[0046] The skilled artisan will appreciate that the working blade section of the present wind turbine blades, or at least the outermost regions thereof, may include a lengthwise twist to better match the airfoil to the apparent wind angle. This ideally allows the outermost regions of the blade to maintain thrust under reduced wind speeds or varying wind conditions thereby avoiding vibration or flutter inducing conditions. All of the previously disclosed modifications to blade design including longitudinal and cross-sectional tapering and fin placement also contribute to the foregoing improved aerodynamic properties.

[0047] Example 1

[0048] A wind turbine having a rotor equipped with three blades is provided having a design rating of 8 Mw. The blades are comprised of spacers of circular cross-section 24 m long, with proximal diameter 3.7 m, distal diameter 2.0 m, disposed at a 2 degree forward alignment angle (forward cone angle). The axis of rotation is tilted up approximately 5 degrees. The working blades are 56 m long. Blade tip clearance in front of the base is approximately 10 m, and blade loading is 122 kg/m².

[0049] Although described in several embodiments, preferred, more preferred, most preferred, desired, more desired, most desired embodiments, and other alternative language, it is intended that various combinations of the presently described embodiments and portions thereof may all be employed in a single design without departing from the scope of the present invention; that such combinations are intended to be fully enabled by the present description; and that minor variations in design, form or application of the presently disclosed embodiments are included in the present inventive concept. In particular, the following specifically disclosed embodiments of the invention are provided as enablement for the attached claims.

Embodiments

1. A blade spacer adapted for use on a wind turbine, said spacer being substantially rigid and adapted for attachment by it's proximal terminus to a wind turbine hub and further adapted for attachment by means of it's distal terminus to the base of a wind turbine blade, said spacer further tapering in cross-sectional size at least over a portion of the distance from proximal terminus to distal terminus.

2. A blade spacer adapted for use on a wind turbine, said spacer being substantially rigid, constructed primarily of metal, and adapted for attachment by it's proximal terminus to a wind turbine hub and further adapted for attachment by means of it's distal terminus to the base of a wind turbine blade, said spacer further containing a pitch control mechanism located in the distal terminus thereof for adjusting the angle of attack of the blade.

3. A blade spacer according to embodiment 1 further comprising a pitch control mechanism located in the distal terminus thereof for adjusting the angle of attack of the blade.

4. A blade spacer according to embodiment 3 which is constructed primarily from metal.

5. A blade spacer according to embodiment 1 wherein the spacer cross-section over at least a majority of its length is approximately circular shaped.

6. A combination comprising a blade spacer and a blade for use in a wind turbine, wherein the blade spacer corresponds to embodiment 1.

7. A combination comprising a blade spacer and a blade for use in a wind turbine, wherein the blade spacer corresponds to embodiment 2.

8. A combination comprising a blade spacer and a blade for use in a wind turbine, wherein the blade spacer corresponds to embodiment 3.

9. A combination comprising a blade spacer and a blade for use in a wind turbine, wherein the blade spacer corresponds to embodiment 4.

10. A combination according to embodiment 6 wherein the spacer length is from 5 to 60 percent of the blade length.

11. A combination according to embodiment 6 wherein the blade has an airfoil cross sectional shape and the chord length thereof is constant or the blade is straight tapered over a majority of the blade length and the leading edge thereof substantially conforms to a straight line.

12. A combination according to embodiment 6 wherein some or all of the leading edge of the blade is covered with a protective surface cover or coating.

13. A combination according to embodiment 12 wherein the protective surface cover is sheet metal. 14. A combination according to embodiment 13 wherein the protective surface is grounded by means of an electrically conductive spacer or a conductor passing within the spacer.

15. A combination according to embodiment 6 wherein the outer section of the blade has an airfoil cross sectional shape and the chord length decreases from front to back over the outer 5 to 12 percent of the length of said section with the trailing edge remaining substantially in line with the trailing edge of the remainder of the blade.

16. A combination according to embodiment 6 wherein the blade terminates in a sloped end starting on the high pressure side of the blade and terminating on the low pressure side of the blade.

17. A combination according to embodiment 16 wherein the sloped end comprises a fin which, with respect to its point of attachment to the blade, projects both outward and behind the trailing portion of the blade on the low pressure side thereof and terminates in an apex located outward and behind the trailing edge of blade section.

18. A combination according to embodiment 17 wherein the fin is conductive and is grounded.

19. A combination according to embodiment 18 wherein the fin is grounded by means of an electrically conductive spacer or a conductor passing within the spacer.

20. A wind turbine comprising a combination spacer and blade according to embodiment 6.

21. A rotor for use on a wind turbine comprising a central hub capable of rotation about an axis having at least one combination blade spacer and blade according to embodiment 6 attached thereto.

22. A rotor for use on a wind turbine comprising a central hub capable of rotation about an axis having at least one combination blade spacer and blade according to embodiment 7 attached thereto.

23. A rotor for use on a wind turbine comprising a central hub capable of rotation about an axis having at least one combination blade spacer and blade according to embodiment 8 attached thereto.

24. A rotor according to embodiment 21 wherein the distal terminus of the spacer is adapted such that the alignment axis of the outboard blade section is disposed at an acute receding angle with respect to the direction of rotation of the rotor about its rotational axis.

25. A rotor according to embodiment 22 wherein the distal terminus of the spacer is adapted such that the alignment axis of the outboard blade section is disposed at an acute receding angle with respect to the direction of rotation of the rotor about its rotational axis.

26. A rotor according to embodiment 23 wherein the distal terminus of the spacer is adapted such that the alignment axis of the outboard blade section is disposed at an acute receding angle with respect to the direction of rotation of the rotor about its rotational axis. 27. A rotor according to embodiment 24 wherein the receding angle is from 1 to 12 degrees.

28. A rotor according to embodiment 25 wherein the receding angle is from 1 to 12 degrees.

29. A rotor according to embodiment 25 wherein the receding angle is from 1 to 12 degrees.

30. A rotor in accordance with embodiment 24 wherein a plane containing a radial line intersecting the axis of rotation and the rotational axis intersects the alignment axis of the blade at or near the center of mass of the combination blade.

31. A rotor in accordance with embodiment 25 wherein a plane containing a radial line intersecting the axis of rotation and the rotational axis intersects the alignment axis of the blade at or near the center of mass of the combination blade.

32. A rotor in accordance with embodiment 26 wherein a plane containing a radial line intersecting the axis of rotation and the rotational axis intersects the alignment axis of the blade at or near the center of mass of the combination blade.

33 A rotor in accordance with embodiment 26 wherein the pitch control mechanism is oriented such that the pitch control axis diverges with respect to the alignment axis of the spacer.

Claims

CLAIMS:

1. A blade spacer for use on a wind turbine, said spacer being substantially rigid and adapted for attachment by it's proximal terminus to the hub of the wind turbine and further adapted for attachment by means of it's distal terminus to the base of a wind turbine blade such that the alignment axis of the blade is disposed at an aft acute angle relative to the alignment axis of the spacer.

2. A blade spacer for use on a wind turbine, said spacer being substantially rigid and adapted for attachment by it's proximal terminus to a wind turbine hub and further adapted for attachment by means of it's distal terminus to the base of a wind turbine blade, said spacer further tapering in cross-sectional size at least over a portion of the distance from proximal terminus to distal terminus.

3. The blade spacer of claim 1 wherein the alignment axis of the blade is disposed at an aft acute angle relative to a plane that is normal to the axis of rotation of the hub.

4. A blade spacer according to claim 1 further comprising a pitch control mechanism located in the distal terminus thereof for adjusting the angle of attack of the blade.

5. A blade spacer according to claim 2 further comprising a pitch control mechanism located in the distal terminus thereof for adjusting the angle of attack of the blade.

6. A blade spacer according to claim 3 further comprising a pitch control mechanism located in the distal terminus thereof for adjusting the angle of attack of the blade.

7. A blade spacer according to claim 4 wherein the pitch control mechanism is oriented such that the pitch control axis diverges with respect to the alignment axis of the spacer.

8. A blade spacer according to claim 5 wherein the pitch control mechanism is oriented such that the pitch control axis diverges with respect to the alignment axis of the spacer.

9. A blade spacer according to claim 6 wherein the pitch control mechanism is oriented such that the pitch control axis diverges with respect to the alignment axis of the spacer.

10. A combination comprising a blade spacer and a blade for use in a wind turbine, wherein the blade spacer corresponds to claim 1.

11. A combination according to claim 10 wherein the spacer length is from 5 to 60 percent of the blade length.

12. A combination according to claim 10 wherein the blade has an airfoil cross sectional shape and the chord length thereof is constant or the blade is straight tapered over a majority of the blade length and the leading edge thereof substantially conforms to a straight line.

13. A combination according to claim 10 wherein some or all of the leading edge of the blade is covered with a protective surface comprising sheet metal.

14. A combination according to claim 13 wherein the protective surface is grounded by means of an electrically conductive spacer or a conductor passing within the spacer.

15. A combination according to claim 10 wherein the outer section of the blade has an airfoil cross sectional shape and the chord length decreases from front to back over the outer 5 to 12 percent of the length of said section with the trailing edge remaining substantially in line with the trailing edge of the remainder of the blade.

16. A combination according to claim 10 wherein the blade terminates in a sloped end starting on the high pressure side of the blade and terminating on the low pressure side of the blade.

17. A combination according to claim 16 wherein the sloped end comprises a fin which, with respect to its point of attachment to the blade, projects both outward and behind the trailing portion of the blade on the low pressure side thereof and terminates in an apex located outward and behind the trailing edge of blade section.

18. A combination according to claim 17 wherein the fin is conductive and is grounded.

19. A combination according to claim 10 additionally comprising an adapter to join the spacer and blade wherein said adapter imparts an aft cone angle between the alignment axis of the blade and the alignment axis of the spacer.

20. A wind turbine comprising a combination spacer and blade according to claim 10.