Claims:1. A wind turbine blade, comprising:
a body having a root, a first airfoil section and a transition section disposed between the root and the first airfoil section, wherein at least one of the transition section and first airfoil section comprises a plurality of airfoils and wherein each airfoil of the plurality of airfoils comprises a chord line and a pressure side defined by a positive curvature at all locations across the chord line.
2. The wind turbine blade of claim 1, wherein up to 40% of a total length of the wind turbine blade as measured from the root comprises the plurality of airfoils.
3. The wind turbine blade of claim 1, wherein at least one of the plurality of airfoils is symmetrical about the chord line.
4. The wind turbine blade of claim 1, wherein at least one of the plurality of airfoils is asymmetrical about the chord line.
5. The wind turbine blade of claim 4, wherein the at least one of the plurality of airfoils comprises a positive camber proximate a leading edge of up to about 4%.
6. The wind turbine blade of claim 4, wherein the at least one of the plurality of airfoils comprises a negative camber proximate a trailing edge of about -1% to about -4%.
7. The wind turbine blade of claim 1, wherein each airfoil of the plurality of airfoils comprises a suction side disposed opposite the pressure side, wherein the suction side is defined by a positive curvature at all locations across the chord line.
8. The wind turbine blade of claim 1, wherein each airfoil of the plurality of airfoils comprises a thickness to chord ratio of about 40 to about 80%.
9. A wind turbine blade, comprising:
a body having a root, a tip and a span coupling the root to the tip;
a plurality of airfoils disposed within the body, wherein each airfoil of the plurality of airfoils comprises:
a leading edge;
a trailing edge;
a chord line extending from the leading edge to the trailing edge; and
a pressure side; and
a suction side disposed opposite the pressure side, wherein pressure side and the suction side are convex at all locations across the chord line.
10. The wind turbine blade of claim 9, wherein up to 40% of a total length of the wind turbine blade as measured from the root comprises the plurality of airfoils.
11. The wind turbine blade of claim 9, wherein at least one of the plurality of airfoils is symmetrical about the chord line.
12. The wind turbine blade of claim 9, wherein at least one of the plurality of airfoils is asymmetrical about the chord line.
13. The wind turbine blade of claim 12, wherein the at least one of the plurality of airfoils comprises a positive camber proximate a leading edge of up to about 4%.
14. The wind turbine blade of claim 12, wherein the at least one of the plurality of airfoils comprises a negative camber proximate a trailing edge of about -1% to about -4%.
15. The wind turbine blade of claim 9, wherein each airfoil of the plurality of airfoils comprises a suction side disposed opposite the pressure side, wherein the suction side is defined by a positive curvature at all locations across the chord line.
16. The wind turbine blade of claim 9, wherein each airfoil of the plurality of airfoils comprises a thickness to chord ratio of about 40 to about 80%.
, Description:BACKGROUND
[0001] The subject matter disclosed herein relates to wind turbine blades. Specifically, the subject matter relates to positive curvature airfoils for wind turbine blades.
[0002] Conventional wind turbines typically include a blade pitch mechanism that requires a circular connection to allow coupling the wind turbine blade to the hub of the wind turbine rotor. As such, each blade of the rotor has a circular end (“root”) to facilitate such coupling. Between the circular end and first airfoil section of the blade is a section (“transition section”) that provides a geometric transition between the circular shape of the root and the first airfoil section. To achieve a requisite amount of lift and reduction in stall, the airfoils of this transition section and/or first airfoil section are aft-loaded by providing a strong pressure side curvature variation. Such an “S”-shaped pressure side increases the pressure difference at the aft portion of the airfoil, thereby increasing lift. However, the inventors have observed that such airfoil designs are prone to buckle under edge and flap wise compression loads and, therefore, require additional material to increase the strength against compression loads. This additional material undesirably increases the weight of the rotor which leads to increase in weight of other sub systems.
[0003] Therefore, the inventors have provided an improved airfoil for wind turbine blades.
BRIEF DESCRIPTION
[0004] Embodiments of a wind turbine blade are provided herein. In some embodiments, a wind turbine blade may include a body having a root, a first airfoil section and a transition section disposed between the root and the first airfoil section, wherein at least one of the transition section and first airfoil section comprises a plurality of airfoils and wherein each airfoil of the plurality of airfoils comprises a chord line and a pressure side defined by a positive curvature at all locations across the chord line.
[0005] In some embodiments, a wind turbine blade may include a body having a root, a tip and a span coupling the root to the tip; a plurality of airfoils disposed within the body, wherein each airfoil of the plurality of airfoils comprises: a leading edge; a trailing edge; a chord line extending from the leading edge to the trailing edge; and a pressure side; and a suction side disposed opposite the pressure side, wherein pressure side and the suction side are convex at all locations across the chord line.
DRAWINGS
[0006] Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention and are therefore not to be considered limiting in scope, for the invention may admit to other equally effective embodiments.
[0007] FIG. 1 depicts a conventional wind turbine blade.
[0008] FIG. 2 depicts a conventional airfoil suitable for use in the wind turbine blade shown in FIG. 1.
[0009] FIG. 3 depicts an airfoil in accordance with some embodiments of the present invention.
[0010] FIG. 4 depicts an airfoil in accordance with some embodiments of the present invention.
[0011] To facilitate understanding, identical reference numbers have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
DETAILED DESCRIPTION
[0012] Embodiments of an airfoil suitable for use with wind turbine blades are disclosed herein. In at least some embodiments, the inventive wind turbine blade may comprise a plurality of airfoils having a positive curvature that provides an increase in strength and stiffness of the airfoil, thereby making the airfoil less susceptible to buckling as compared to conventionally utilized airfoils having strong pressure side curvature variation.
[0013] Referring to FIG. 1, a conventional wind turbine blade 100 may generally include a body 102 having a leading edge 112, trailing edge 114, tip 106 and root 104.
[0014] In some embodiments, the wind turbine blade 100 may include a plurality of sections across the span (length) of the wind turbine blade 100. For example, in some embodiments, the wind turbine blade 100 may include a root section 118, transition section 110, airfoil section 108 and tip section 124. In such embodiments, the airfoil section 108 may be further divided into a plurality of smaller airfoil sections, for example, such as the first airfoil section 126 shown in the figure. Each of the sections may be of any length sufficient to facilitate desired functioning of the wind turbine blade 100. For example, in some embodiments, the root section 118 may be about 0 to about 10 %, the transition section 110 may be about 10 to about 20 %, the air foil section 108 may be about 20 to about 95 % and the tip section 124 may be about 95 to about 100 % of a total length of the wind turbine blade 100.
[0015] The root 104 is generally circular in shape and is configured to facilitate coupling of the wind turbine blade 100 to a blade pitch mechanism and hub of a rotor. The transition section 110 provides a geometric transition from the circular shape of the root 104 to the first airfoil section 126.
[0016] In some embodiments, the wind turbine blade 100 comprises a plurality of airfoils (five airfoils 116 shown) disposed throughout the wind turbine blade 100. The plurality of airfoils 116 generally defines a shape of the wind turbine blade 100 to provide lift and facilitate rotation of the wind turbine blade 100. Although only a limited number of airfoils are shown in the figure, it is to be understood that the wind turbine blade 100 may include any number of airfoils suitable to facilitate a desired performance of the wind turbine blade 100.
[0017] Referring to FIG. 2, each airfoil 200 generally comprises a body 216 having a rounded leading edge 208 and trailing edge 210, pressure side 202 and suction side 206. The trailing edge may having a pointed or sharp terminal end (shown at 210) or, alternatively, may be blunt or “flat back” (shown in phantom at 204). In some embodiments, one or more structural supports 212 or frames 214 may be utilized to provide strength or stiffness to the airfoil 200.
[0018] The inventors have observed that the portion of the wind turbine blade proximate the root (e.g., root section and/or transition section and/or first airfoil section) airfoil typically requires a comparatively higher amount of lift to facilitate higher torque generation from the wind turbine rotor. Conventionally, to increase lift from an airfoil section, the camber of the airfoils are increased. However, the increased camber leads to a sharper stall and higher loads. As such, in conventional designs, to achieve a soft stall, the airfoils are aft-loaded by providing a strong pressure side curvature variation. The resultant “S” shaped pressure side (i.e., such as shown at 202 of FIG. 2) increases the pressure difference at the aft portion of the airfoil and, therefore, provides an increase in lift. However, such airfoils are susceptible to buckling under compressive loads. To reduce instances of buckling, the airfoil may require additional or more robust materials. Such materials increase the overall weight of the airfoil and wind turbine blade, thereby reducing efficiency and increasing stress on supporting systems.
[0019] As such, in some embodiments, the airfoil 300 comprises a body 302 having a positive curvature (e.g., convex shape) on both the pressure 304 and suction side 306 of the body 302 at all locations across the chord 308, such as shown in FIG. 3. The inventors have observed that the convex shape of the positive curvature airfoil (e.g., airfoil 300) increases the strength and stiffness of the airfoil, thereby making the airfoil less susceptible to buckling as compared to conventionally utilized airfoils having strong pressure side curvature variation (e.g., airfoil 200 of FIG. 2). Moreover, the inventors have further observed that the positive curvature airfoil provides the aforementioned increase in buckling strength without requiring the excess materials typically needed to provide such strength, thereby reducing weight and reducing manufacturing cost as compared to conventionally utilized airfoils.
[0020] Referring to FIG. 4, the airfoil 300 may have any dimensions suitable to allow the airfoil 300 to be utilized in a wind turbine blade. As shown in the figure, the x/c values represent locations on the chord line 408 in relation to the leading edge 418 and the y/c values represent heights from the chord line 408 to points on either the suction side 412 or pressure side 414 of the airfoil 300.
[0021] In some embodiments, the airfoil 300 may have a thickness to chord ratio (t/c) of about 40 to about 60 %, or in some embodiments, about 35%. In addition, the airfoil 300 may be symmetrical (e.g., shown at 402) or be asymmetrical, having a larger upper camber (e.g., shown at 404) or a larger lower camber (e.g., 406). In embodiments where the airfoil is asymmetric, the positive camber near the leading edge may be up to about 4 %, or in some embodiments about 1%, or in some embodiments about 2%, or in some embodiments about 4%, the negative camber near the trailing edge may be about -1% to about -4 %, or in some embodiments about -2%, or in some embodiments about -3%, or in some embodiments about -4%. In some embodiments, the trailing edge 410 may having a pointed or sharp terminal end (shown at 410) or, alternatively, may be blunt or “flat back” (shown in phantom at 416).
[0022] The airfoil 300 as described herein may be utilized at any location(s) along a wind turbine blade (e. g, wind turbine blade 100 described above). For example, the inventive airfoil 300 may be any or all of the plurality of airfoils 116 discussed above with respect to FIG. 1. In some embodiments, the airfoil 300 may be utilized selectively in one or more portions of the wind turbine blade, for example, in the transition section (e.g., transition section 110 shown in FIG. 1), one or more of the first airfoil sections (e.g., the first airfoil section 126) or the like. In addition, the airfoil maybe utilized, for example, up to about 40%, or in some embodiments, about 30% of the span of the wind turbine blade, as measured from the root.
[0023] Thus, an improved airfoil for use in a wind turbine blade has been provided herein. In at least some embodiments, the inventive airfoil advantageously comprises a convex shape that provides an increase in buckling strength while requiring less materials, thereby reducing weight and manufacturing cost as compared to conventionally utilized airfoils.
[0024] Ranges disclosed herein are inclusive and combinable (e.g., ranges of “about 0 psi to about 25,000 psi”, is inclusive of the endpoints and all intermediate values of the ranges of “about 0 psi to about 25,000 psi,” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the state value and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the colorant(s) includes one or more colorants). Reference throughout the specification to “one embodiment”, “some embodiments”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
[0025] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.